Identification of Pollutants from
Chlorination and Related Unit Processes
               Alan S. Goldfarb
               William W. Duff
               Elbert C. Herrick
            Michael P. McLaughlin

                 Project Advisor
                   John King
               EPA/ORD/OEET

                 Project Officer
                David R. Watkins
           EPA/ORD/IERL-Cincinnati
                 February 1980
                  Grant No.: RS05620-OI
                   Project No.: 13810
                    Depu:W.S6
               The MITRE Corporation
                   Metrek Division
               1820 Dolley Madison Boulevard
                 McLean, Virginia 22102


                MITRE Technical Report
                    MTR-80W27

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                              ABSTRACT
     The manufacture of sixteen chemicals by chlorination and related
unit processes was studied as part of an assessment of the feasibil-
ity of identifying generic process contaminants from.unit processes.
Process descriptions with flow diagrams are presented for the manu-
facture of each of the compounds.  The chemistry of the processes is
described to illustrate how the products and contaminants might be
formed.  The effect of process operating conditions on the formation
of contaminants is also discussed.
                                  iii

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                          TABLE OF CONTENTS

                                                                 Page

LIST OF ILLUSTRATIONS                                            ^i

LIST OF TABLES                                                   viii

EXECUTIVE SUMMARY                                                  ix

1.0  INTRODUCTION                                                  ^

2.0  DESCRIPTION OF THE MANUFACTURE OF SELECTED PRODUCTS BY        7
     CHLORINATION AND RELATED UNIT PROCESSES

2.1  Manufacture of Chloromethanes (Dow Process for Chlorina-      7
     tion of Methane)
2.2  Manufacture of Chloromethanes (Hydrochlorination)             14
2.3  Manufacture of Carbon Tetrachloride and Perchloroethylene     19
2.4  Manufacture of Vinyl Chloride Monomer (VCM) and Ethylene      24
     Dichloride (EDC) , (The "Balanced" Process)

     2.4.1  Stauffer Balanced Process for the Manufacture of       25
            Vinyl Chloride Monomer (VCM) and .Ethylene Dichlor-
            ide (EDC)

2.5  Manufacture of Chlorophenols                                  31
2.6  Manufacture of Allyl Chloride (Shell Process)                 36
2.7 ^HatftifScT^^oirffio'Ha- and Dichlorobenzenes                     40
3.0  IDENTIFICATION OF CONTAMINANTS FORMED IN CHLORINATION AND    45
     RELATED UNIT PROCESSES

3.1  Direct Chlorination                                          45

     3.1.1  Chlorination of Methane                               46
     3.1.2  Chlorination of Mixed Hydrocarbons and Chloro-        48
            hydrocarbons
     3.1.3  High Temperature Propylene Chlorination               50
     3.1.4  .Ethylene Chlorination                                 55
     3.1.5  Chlorobenzenes                                        55
     3.1.6  Chlorophenols                                         59

3.2  Hydrochlorination of Methanol                                65
3.3  Oxychlorination                                              66
3.4  Dehydrochlorination (Pyrolysis) of Ethylene Dichloride       68

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                     TABLE  OF  CONTENTS  (CONTINUED)

                                                                  Page
4.0  COMPARISON  OF  CONTAMINANTS  AND WASTE'DISCHARGES  FOR         71
x     CHLORINATION PROCESSES

4.1  Comparison  of  Chlorination  Processes with  Respect  to         71
     Process  Stream Contaminants
4.2  Pollutant Discharges  from Chlorination  Processes             31

     4.2.1  Emissions  to the Atmosphere                           81
     4.2.2  Wastewater Discharges                                 82
     4.2.3  Liquid  Organic Wastes                                 S3
     4.2.4  Solid Waste and Sludges                               S3
     4.2.5  Other Wastes                                          84

5.0  CONCLUSIONS                                                 85

5.1  Direct Chlorination and Dehydrochlorination                  85

     5.1.1  Free Radical Reactions Including Dehydrochlorin-      85
            ation
     5.1.2  Electrophilic  Aromatic Substitution Reactions         87
     5.1.3  Addition Reactions to a Double Bond                  88

5.2  Hydrochlorination                                           89

5.3  Oxychlorination                                             89

6.0  REFERENCES                                                   91
                                  vi

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                            ERRATA SHEET


           Identification of Pollutants from Chlorination
                     and Related Unit Processes
                                   Correction


                                   In title of Figure 2.1, correct
                                   Mehylene Chloride to Methylene
                                   Chloride.

35                                 On fourth line from the top, correct
                                   opthochlorophenol to orthochlorophenol.

91                                 In References, correct Dylewaki,
                                   S.W.  to Dylewski,  S.W.

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                        LIST OF ILLUSTRATIONS
Figure Number                                                    Pagi

 2.1        Dow Process For the Chlorination of Methane to         9
            Methyl Chloride, Methylene Chloride, Chloroform
            and Carbon Tetrachloride

 2.2        Process for the Manufacture of Chloromethanes by      15
            Hydrochlorination of Methanol to Methyl Chloride
            followed by Chlorination of Methyl Chloride

 2.3        Scientific Design Process for Manufacture of          21
            Perchloroethylene and Carbon Tetrachloride by
            Chlorination of Propane

 2.4        Stauffer Balanced Process for the Manufacture of      27
            Vinyl Chloride Monomer and Ethylene Dichloride
            by Direct Chlorination and Oxychlorination of
            Ethylene to Ethylene Dichloride followed by
            Thermal Dehydrochlorination to Vinyl Chloride

 2.5        Chlorination Process for Manufacture of               32
            Chlorophenols

 2.6        Chlorination Process for the Manufacture of           37
            Allyl Chloride from Propylene

 2.7        Manufacture of Mono- and Dichlorobenzene by           41
            Chlorination of Benzene
                                 vii

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                           LIST OF TABLES
Table Number                                                     Page
  I         Pollutants fron Chlorination and Related Unit        xvii
            Processes

 II         List of Chemicals and Processes Included in this        4
            Study

III         Composition of Commercial-Grade and Purified-Grade     64
            Pentachlorophenol (PCP)

 IV         Generic Listing of Substances Present in Chlorina-     72
            tion Process Streams

  V         Priority Pollutants From Chlorination Processes        74
                               viii

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                           EXECUTIVE  SUMMARY




     The U.S. Environmental  Protection Agency is required by law  to




regulate toxic  and  hazardous chemicals in  products and waste




discharges  from manufacturing operations.  The current approach to




regulating  the  chemical  industry is  to identify and control pollutant




discharges  from the manufacture of individual products by specific




processes.  A problem with this approach is  that there are thousands




of chemical products in  commerce, and developing individual regula-




tions  for  the wastes generated by each of  the manufacturing opera-




tions  is a  time consuming  and costly task.




     Most  of the  product-specific processes  widely used in the organ-




ic chemical industry today consist of "unit  processes" where the




fundamental reactions in synthesis are carried out, e.g., amination




by ammonolysis, chlorination, etc.   Since  the by—products and con-




taminants  produced  during  the manufacture  of a chemical are related




to the chemistry  of the  process, it  seems  reasonable to expect that




different  substances manufactured by the same unit process would




produce similar by-products  and contaminants.  Thus by characterizing




the by-products and contaminants for a unit  process, the by—products




and contaminants  of all  products manufactured by that unit process




would  be characterized without studying each individual manufacturing




process.  This  approach  has  the potential  for reducing the time and




cost associated with developing regulations, since it may not be




necessary to study  individual product/processes.  It may also be
                                 ix

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possible to write regulations for a unit process rather than for

individual product/processes, thus reducing the number of regula-

tions.

     In a previous study, MITRE identified 39 unit processes used in

the manufacture of 263 commercial organic chemicals.  Following this,

a study was made to characterize the by-products, contaminants, and

pollutant discharges from the unit process amination by ammonolysis,

and to determine whether similarities in those characteristics exist

between the manufacturing processes for different products of the

amination reaction.

     This is the third report in the series.  It Is an examination of

processes used to manufacture chlorinated hydrocarbons.   The chemical

manufacturing processes included in this study are as follows:

     •  Four chloromethanes by direct chlorination of methane

     e  Perchloroethylene and carbon tetrachloride by high tem-
        perature chlorination of mixed hydrocarbons

     •  Allyl chloride by high temperature chlorination of
        propylene

     •  Ethylene dichloride by direct chlorination of ethylene

     •  Mono- and dichlorobenzene by direct chlorination of benzene

     •  Five chlorophenols by direct chlorination of phenol

     •  Methyl chloride by hydrochlorination of methanol

     •  Ethylene dichloride by oxychlorination

     •  Vinyl chloride by dehydrochlorination

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The reaction  chemistry and  operating  conditions  for  each  process were




examined and  the  by-products  and  contaminants  likely to be  present in




the process streams  were  determined on  the  basis of  the known reac-




tion chemistry and information  available  in the  literature.




     The manufacturing processes  studied  use four unit processes:




direct chlorination, hydrochlorination, oxychlorination and dehydro-




chlorihation.  It wa^ found that  the  unit process of direct chlorina-




tion consists of  three distinct subgroups with regard to  the types of




by-products and/or contaminants present in  the process and waste




streams.   These subgroups are based on the  type  of reaction.  They




are as follows:




     •  Free  radical reaction




     •  Electrophilic aromatic  substitution reaction




     •  Addition  reaction to  a double bond




The high temperature, uncatalyzed dehydrochlorinatioa unit process




fits in the free  radical  subgroup of  the  direct  chlorination unit




process.   Base catalyzed  dehydrochlorination was not covered in this




study.  The unit  processes  of hydrochlorination  and  oxychlorination




each have  characteristic  by-product and process  stream contaminants.




They do not fit into any  of the above subgroups.




     The chloromethanes, perchloroethylene  and carbon tetrachloride,




allyl chloride, and vinyl chloride are formed by free radical reac-




tions.  Free radical reactions are characterized by  an initiation




reaction in which a free radical  is formed; by propagation reactions
                                 xi

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in which" a  free  radical  reacts with a molecule'to form a new compound




and a new free radical;  and by a termination step where tw> free




radicals combine to  form a new molecule.  Through the termination




reaction, a wide variety of chlorinated and unchlorinated hydrocar-




bons may be generated.   The probability of generating a particular




molecule decreases with  the size of the molecule and the level of




chlorination.  Other factors such as long residence time, high




temperatures, and high chlorine to hydrocarbon mole ratio tend to




increase by-product  formation.  Pyrolytic temperatures tend to result




in the  fragmentation of  larger molecules and the formation of unsat-




urated  compounds.  The main by-product of free radical chlorination




is hydrogen chloride.  One molecule of hydrogen chloride is formed




for each atom of chlorine substituted on the hydrocarbon molecule.




Waste products from  free radical reactions include an inert gas purge




stream  from hydrogen chloride recovery operations; a spent caustic




and/or  wastewater from process stream washing and neutralization




steps;  spent sulfuric acid waste from process stream drying opera-




tions;  and a distillation column residue of high molecular weight




polychlorlnated  compounds.  An intermittent wastewater stream may




be produced as a  result  of the necessity to occasionally dispose of




off-grade and/or unsaleable hydrochloric acid generated by the pro-




cess.    The unsaleable hydrochloric acid is often neutralized with




lime,  limestone, oyster  shells or clam shells, and discharged as




wastewater.  The wastewater may contain salts of metals such as iron,
                                 xii

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aluminum, copper  and  lead, "which are  impurities in  the lime, lime-




stone, oyster shells, and clam shells. The caustic  wash may contain




products of hydrolysis of chlorohydrocarbons.  A carbonaceous build-




up may be periodically removed from the reactor and distillation




equipment and disposed of.




     Chlorobenzenes and chlorophenols are representative of compounds




produced by ring  chlorination of aromatic compounds.  Ring chlorina-




tion of an aromatic compound is an electrophilic aromatic substitu-




tion reaction in  which a chlorine atom is substituted for a hydrogen




atom on the ring.  The reaction is catalyzed by a Lewis acid (e.g.,




ferric chloride,  aluminum chloride).  All the hydrogen atoms on the




aromatic ring may be  replaced by chlorine.  The extent to which




polychlorinated aromatic compounds are formed depends on the reac-




tion temperature, molar ratio of aromatic hydrocarbon to chlorine,




the catalyst used, and the reaction temperature.  For each atom of




chlorine substituted  on the ring, a molecule of hydrogen, chloride is




formed.




     The nature of side reactions that occur during ring chlorination




is also influenced by the substituent groups on the aromatic feed-




stock.  Chlorinated phenols tend to form chlorinated benzo-p-dioxins,




chlorinated dibenzofurans, chlorophenoxy chlorophenols, and chloro-




diphenyl ethers.




     Waste streams from the ring chlorination of aromatic compounds




usually include an inert gas purge stream from the hydrogen chloride
                                xiii

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recovery operation, a wastewater  from a caustic wash or acid neutral-
ization operation, and a distillation column residue.  The caustic
wash may contain products of  the  hydrolysis of the chlorinated aro-
matic (e.g., chlorinated phenols  from washing crude chlorobenzene
from a chlorobenzene reactor).  The wash water may also contain
catalyst salts.  The distillation column residue will contain poly-
chlorinated aromatic compounds and other reaction side products as
well as catalyst residue not  previously removed.  Carbonaceous accu-
mulations  in reactors and distillation equipment may also be periodi-
cally disposed of.  An intermittent wastewater stream containing
metal salts may also be produced  as a result of the need to occasion-
ally dispose of off-specification and/or unsaleable hydrochloric
acid.
     The direct chlorination  of ethylene is an example of an addition
reaction.  In the addition reaction two chlorine atoms are added to
an olefin  compound at the double  bond to form a saturated chloro-
hydrocarbon.  The reaction is catalyzed by a Lewis acid under rela-
tively mild conditions forming no by-products.  By-products will form
if conditions are favorable to free radical reaction of the olefin,
e.g., high temperature.  Thus, control of reaction conditions is
essential  to minimizing by-product formation.
     The main waste discharge from this process is a spent caustic
solution which will contain hydrocarbons, chlorohydrocarbons,
hydrolysis products of the chlorohydrocarbons, and spent catalyst
residues.
                                 xiv

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     The  reaction  of methanol with hydrogen chloride  to form methyl


chloride  is an example of a hydrochlorination reaction.  The reaction


is catalyzed by a  Lewis acid in  a fixed bed, and involves substitut-


ing a chloride atom for the hydroxyl group on the alcohol, forming


water as  a by-product.  The by-product water, and spent caustic from


process stream washing and neutralization operations, constitute the


waste generated in the process.  The waste will contain feedstock


materials and product, hydrolysis products of the chlorohydrocarbon,


and some  catalyst  residue.  The  catalyst in this process does not


require continuous renewal.  It  may, however, require periodic


replacement.


     Ethylene dichloride is an example of a compound that may be


produced  in an oxychlorination process.  The process involves the


reaction  of ethylene with oxygen and hydrogen chloride in the pres-


ence of a copper catalyst.  The  details of the reaction mechanism


have not  been completely determined.  Side reactions occur that pro-

                       \
duce various saturated and unsaturated derivatives of the feedstock,


including smaller  molecules by fragmentation.  Oxygenated compounds


are also  formed (e.g., chloral,  acetaldehyde, carbon dioxide, and


carbon monoxide).


     Waste discharges include an inert gas purge stream, a spent


caustic waste, and a distillation column residue.  The volume of the


inert gas purge stream can be reduced by using pure oxygen instead of


air as the source  of oxygen for  the process.
                                 xv

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     Table I is a listing of generic pollutants generated by the unit



processes described in chis report.
                                 xvi

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                                                              TABLE :

                                      POLLUTAKTS FSOH C8LOUMAIIOS AND RELATED CKIT PROCESSES
   Unit Proeeaa
                           Subtroup
                        Examplea Of
                       Products Mad*
                         by Process
                                                                     Wastes Cenerstad
                                                        Contaminants In
                                                             Maate
Chlorineclan
                         free Radical
                         Ruction
                   AUjri Chloride
                   Chlonmethanas
                   ?erchloroethylaae
                         Electrophllic
                         aromatic
                         substitution
                         i*ac don
                   Chloropbenols
                   Chlorobenxeoes
Debydrochlorinacion


EvdrochlortnacIon






Oxyehlorlnacioa
                         Addition
                         raaccion
FTM Radical
raactloo
                   EtbjrlaiM dlchlorlda
Vtayi chlorlda
     ir
                   M.chyl chlerld*
                                            Ethylan* dlchlorloa
                        In«rt ga« purg*
                                                                    Spaat cauaclc
                        Spent sulfurlc
                        add

                        Dlatlllatloa colian
                        raaldua

                        Inart (
                                                                    Spent eaoatlc
                                                                    DlaClllatloa calu
                                                                    naldua
Spant cauatlc



Similar CO fzM radical


Uatar

Spant cauatlc




Inart gaaaa



Spant cauatlc
                                                                    Distillation colu
                                                                    raaldua
                         Hydrogen chlorlda* low oolecular
                         valght, hydrocarbona and chloro-
                         hydncarbona, chlorine      •

                         Saturated and imaaturatad hydro-
                         carbon*, chlorobydrocarboaa,
                         aroaatlc hydroearbona.  pbaaola.
                         orbonyl tulflde, MCbanel,
                        I formic acid

                         Hydrocarbons aad chlorohydrocarbona
                         High oolacular ualght and poly-
                         chlorlnatad hydrocarbons

                         Aromatic hydrocarbona, chlarlae,
                         hydrogen chlorlda.  volatlla
                         cmlorlnatad aromatic cempoimda

                         Inorganic salts, aromatic hydro-
                         carbons, phenola
 ?alycU.orinacad aromatic
 catalyst raaldua, products of
 reaction of substltuent groups
 on feedatock compound

 Ethylane dlcnlorlde, catalyst
 residuea, hydrolysis products of
 •thylana dlchlorlda

direct chlorinatlon vajle process
                                                                   HethaneO.. hydrogen chloride

                                                                   Hathanol, sodium chloride, mecnyl
                                                                   chlorine and hydrolysis products
                                                                   of methyl chlorlda. catalyst
                                                                   residues

                                                                   Law —»' — •'— weight hydrocarbons
                                                                   and chlorohydrocarbons, hydrogen
                                                                   chloride, carbon
                                                                    Hydrocarbona, chlomhydrocarbana,
                                                                    aldehydes, chlorinated aldehydes,
                                                                    hydrolysis products of chlorinated
                                                                    hydrocarbons

                                                                    Polychlorlnacad hydrocarbona
                                                           XVII

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1.0  INTRODUCTION




     The U.S. Environmental Protection Agency  (EPA) is required under




recently enacted federal statutes to regulate  toxic or hazardous chem-




icals in both products and waste discharges from chemical manufactur-




ing operations.  These statutes include the Toxic Substances Control




Act of 19/6  (PL 94-469); Clean Air Act as amended in 1977 (PL 95-05);




Clean Water  Act of  1977 (PL 95-217); and the Resource Conservation and




Recovery Act of 1976  (PL 94-580).




     Regulation of  the organic chemical industry is complex because of




the large number of products and their many different end uses.  In




1976, the U.S. Tariff Commission reported over 7000 different organic




compounds in commercial production which were estimated to total 289




billion pounds.




     The current approach to regulating the chemical industry is to




identify and control pollutant discharges from the manufacture of




individual products by specific processes.  However, most of the




product-specific processes widely used in the chemical industry today




consist of "unit processes," where the fundamental chemical reactions




in organic synthesis are carried out (e.g., nitration, amination by




ammonclysis, etc.).  The unit processes are the basic building blocks




of chemical  manufacturing, and for most commercial applications of a




given unit process, the physical and organic chemistry tend to be




similar or the same.  Therefore, it would appear that through




systematic examination of the process chemistries associated with

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the unit processes, one could identify the air emissions, water pol-

lutants, and hazardous wastes, as well as the potentials for product

contamination that are likely to be associated with the manufacture

of chemicals by a particular unit process.  This approach has the

potential to reduce the time and cost of the development of regula-

tions,, since it may not be necessary to study each chemical manufac-

turing operation separately in order to determine the nature of the

pollutants that are emitted.  Also, it may be possible to write a

single regulation that covers the manufacture of many chemicals.

     As a first step in exploring the feasibility of the "unit pro-

cess approach," MITRE published a "Catalog of Organic Chemical In-
                                            •v
dustry Unit Processes" (Ilerrick and King, 1979b), which identifies

all of the unit processes used to manufacture 263 commercial organic

chemicals.  Twenty-three major unit processes and 16 minor unit pro-

cesses were identified.  Following this, a report was written identi-

fying pollutants generated by one of the 39 unit processes—amination

by ammonolysis (Herrick and King, 1979a) .

       This is the third report in the series.  It presents an ex-

amination of processes used to manufacture chlorinated hydrocarbons.

Chlorination and related unit processes were selected for study

because they are used in the manufacture of the largest number of

product/processes on the U.S. Environmental Protection Agency's list

of 200 chemical products that are scheduled for regulation in 1981

under the Water Pollution Control Act, and also because 60 of the

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compounds on the Agency's list of 129 priority  pollutants are

chlorinated hydrocarbons.

     The manufacturing processes for the production of 17 chlorinated

hydrocarbon compounds selected by the EPA for this study are examined.

Some of the processes produce more than one compound, and some com-

pounds are produced by more than one manufacturing process.  The

specific unit processes are direct chlorination, hydrochlorination,

oxychlorination and dehydrochlorination.  The purpose of this study is

to determine whether generic process stream contaminants can be

identified for each of these unit processes.

       This report includes the following:

       •  A description of seven manufacturing processes
          that produce one or more of 17 chlorinated hydro-
          carbons (see Table II)

       •  A discussion of the chemistry associated with the
          manufacturing processes that illustrate the generation
          of byproducts and contaminants

       •  A list of priority pollutants produced in the manu-
          facturing processes

       •  A list of generic categories of substances produced in the
          manufacturing processes

       •  A categorization of chlorination processes into
          groups having common characteristics with respect
          to process contaminants and waste products.
*Priority pollutant is the name given by the EPA to toxic
 pollutants, for which the Clean Water Act of 1977 requires that
 effluent limitations, in terms of best available technology, be
 established.

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                                     TABLE II

              LIST OF CHEMICALS AND PROCESSES INCLUDED IN THIS STUDY
    UNIT PROCESS

Direct Chlorination
Hydrochlorination


Oxychlorination




Dehydrochlorination
      CHEMICAL NAME

Methyl Chloride
Methylene Chloride
Chloroform
Carbon Tetrachloride
                         Perchloroethylene
                         and Carbon Tetrachloride

                         Ethylene Dichloride
                         Monochlo ro ben sen e
                         p-dichlorobenzene'
                         o-dichlorobenzene
                         p-chlorophenol
                         o-chlorophenol
                         2,4 dichlorophenol
                         2,4,6 trichlorop'nenol
                         2,3,4,6 tetrachlorophenol
                         pentachlorophenol

                         Allyl Chloride
Methyl Chloride
Ethylene Dichloride
Vinyl Chloride Monomer
  MANUFACTURING PROCESS
Chlorination of Methane
(Dow Process)


Chlorination of mixed
hydrocarbons

Direct Chlorination of
Ethylene in Stauffer
Balanced Process for
Manufacture of Vinyl
Chloride Monomer
                                 Chlorination of benzene
                                 Chlorination of phenol
High Temperature Chlori-
nation of Propylene
(Shell Process)

Hydrochlorination of
Methanol

Qxychlorination of ethylene
in Stauffer Balanced Process
for Manufacture of Vinyl
Chloride Monomer

Dehydrochlorination of
ethylene dichloride in
Stauffer Balanced Process
for Manufacture of Vinyl
Chloride Monomer

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     In discussing by-product and contaminant generation, a process




was considered as an entity independent of other unit processes that




are commonly associated with it in industrial operations.  In a multi-




ple process operation, each process will produce the by-products and •




wastes identified in this report as characteristic of that process.




However, the wastes and by-products from one process may be mixed with




wastes from another process in the plant and lose their identity.




Some wastes or by-products may be used as a raw material in another




process.  Examples of such situations are vinyl chloride production




and chloromethane production.  In the case of vinyl chloride produc-




tion, half of the precursor compound—ethylene dichloride—is made by




direct chlorination, and half is made by oxychlorination, using hydro-




gen chloride generated from the dehydrochlorination of the ethylene




dichloride to make the vinyl chloride.  Distillation column bottoms




from vinyl chloride purification are recycled to the ethylene dichlor-




ide purification section to recover unreacted ethylene dichloride.




The distillation column wastes generated by the dehydrochlorination




process are thus mixed with the wastes from ethylene dichloride




manufacture.

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2.0  DESCRIPTION OF THE MANUFACTURE OF SELECTED PRODUCTS BY
     CHLORINATION AND RELATED UNIT PROCESSES

     In this section, flow diagrams and process descriptions are pre-

sented for the manufacture of 17 chlorinated compounds.  Some

processes produce several compounds (e.g., the Dow process for

chlorination of methane produces four chloromethanes [Section 2.1]).

Also, some compounds may be produced by two or more processes (e.g.,

methyl chloride is produced by the chlorination of methane [Sectipn

2.1] and by the hydrochlorination of methanol [Section 2.2]).

2.1  Manufacture of Chloromethanes (Dow Process for the Chlorination
     of Methane)

     The flow diagram of the Dow process for the chlorination of

methane is given in Figure 2.1 (Hirschkind, 1949).  Methane is

purified by removal of higher molecular weight hydrocarbons, such as

ethane and propane, and other impurities, such as nitrogen, using two

absorption columns in series (not shown).  The purified methane,

toge'ther with recycled methane, is passed into gas phase chlorinators

of either the photochemical or thermal type.  The methane reacts with

chlorine to form the three chloromethanes—methyl chloride, methylene

chloride, and some chloroform--and hydrogen chloride.  The product

distribution is controlled by reaction rates and the feed methane-to-

chlorine ratio.  The product gas stream from the reactor (which

contains, in addition to the chlorinated products, excess methane,

hydrochloric acid and a small amount of chlorine), is passed through

a film cooler into an absorption column.  In the absorption column,

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                                         ua3Cl, CH2C12,  CHCli
                                              HO., C12
                       Hoe H20
                                                                    CH3C1, CH2Cl-2, CHC13
                                                                              HC1
•essor
Recycle CH*
Purified CH4
C12

I
i
Gas
Phase
Reactor
j
1
Film Coo
 CH3C1
 CH2C12
 CBC13
 HC1
 H20
Alkali
             Condensers

                       T
                 Compressor I   J
98Z H2S04
                                   CH3C1

                                   CHCJ..J
                              Pressurized Distilling Column

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                   FIGURE 2.1
DOW PROCESS FOR THE CHLORINATION OF METHAI
 METHYL CHLORIDE (CH,CI). MEHYLENE CHLORIDE
 CHLOROFORM (CHCIj), AND CARBON TETRACHLOF

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the chlorinated .hydrocarbons are separated from the methane, chlor-

ine, and hydrogen chloride by absorption into a mixture of carbon

tetrachloride and chloroform.  The methane, chlorine, and hydrogen


chloride leave the absorber as a gas stream, which is termed major

gas, and pass through an absorption system for recovery of hydrogen

chloride and methane.  The liquid mixture from the absorber is fed to

a stripping column where absorbed methyl chloride, methylene chlor-

ide, chloroform, chlorine, and hydrogen chloride are stripped off as

a gas stream, termed minor gas.  The minor gas is processed to

recover the hydrogen chloride and the chlorinated products.  The

stripped liquid, consisting mainly of chloroform, is split into two
                                                              »
streams, one of which is recycled to the absorption column.  The

remainder is chlorinated in a liquid phase chlorination reactor.

     The commercial success of the Dow process depends on the separa-

tion of hydrochloric acid from the several chlorinated products and


the fractionation of the chlorinated hydrocarbons from each other.

Separation of the hydrochloric acid from the chlorinated hydrocarbon

stream in the presence of excess methane and chlorine is accomplished


by using a unique absorption system in which full strength hydro-

chloric acid (31.6 percent) is recovered.  The process proceeds as


follows:

     The minor gas stream from the top of the stripping column (con-

taining methyl chloride, raethylene chloride, chloroform, hydrogen

chloride and chlorine), is passed through an adiabatic hydrochloric
                                  11

-------
acid absorption column fed with hot water.  The chlorinated hydro-




carbons, saturated with water vapor, and containing small.quantities




of hydrochloric acid and chlorine, are removed from the top of the




column.  Hot, 15 percent acid solution flows from the bottom of the




column through a film cooler into the top of a second water-cooled




absorption column.  This second column is also fed with the major gas




stream from the chlorohydrocarbon absorber which contains the bulk of




the hydrogen chloride.  Commercial 20° Baume hydrochloric acid is




obtained from the bottom of the second hydrochloric acid absorption




column.




     Overhead from the second column (consisting of methane satu-




rated with water vapor and some hydrogen chloride), is passed through




a neutralizing column.  The methane from this column is passed




through a sulfuric acid drying column and sent to a compressor to be




recycled to the gas phase reactor.




     The overhead stream from the top of the first hydrochloric acid




absorber (consisting of methyl chloride, methylene chloride, and




chloroform contaminated with hydrochloric acid and some chlorine), is




also passed through a neutralizing column and a sulfuric acid drying




column.  The stream is then compressed and charged to a pressure dis-




tillation column, where methyl chloride is separated as a side stream




product from methylene chloride and chloroform.




     The methylene chloride—chloroform mixture (bottoms) from the




distillation column—is charged to a second distillation column,







                                 12

-------
 which operates at a, lower pressure and separates most of the methyl-


 ene  chloride from the chloroform as a sidestream product.  The


 chlorinated hydrocarbons from the bottom of the methylene chloride


 column,  together with the bottoms from the chlorohydrocarbons


 stripping column, are fed to a liquid phase chlorination reactor.


 Here the remaining methylene chloride reacts with chlorine to form


 chloroform, some carbon tetrachloride and hydrogen chloride.  The


 chlocoform-carbon tetrachloride mixture flows from the reactor into a


 storage  tank.  The hydrogen chloride gas may be scrubbed with water


 and  disposed of or recovered as hydrochloric acid.


      The chloroform-carbon tetrachloride mixture from the storage


 tank is  fed into a topping column where unreacted methylene chloride


 is taken off as overhead and recycled through the liquid phase


 chlorinator.  The bottoms from the topping column are fed to the


 chloroform refining column where U.S.P. grade chloroform is obtained


 as a sidestream product by distillation.


      The bottoms from the chloroform distilling column, are fed to  a
                                   \

.second liquid phase chlorination reactor in which carbon tetra-


 chloride and hydrogen chloride are produced in a continuous process.


 The  liquid product from the reactor is fed to the carbon tetra-


 chloride refining column, where a refined grade of carbon tetra-


 chloride is obtained as a sidestream product by distillation.  The


 hydrogen chloride from the reactor may be scrubbed with water and


 disposed of or recovered as hydrochloric acid.  The bottoms from the



                                  13

-------
carbon teCrachloride column (heavy ends) are sent to waste treatment.




The sidestream chlorinated products from each of the distillation




columns are neutralized with caustic prior to storage and sale.




2.2  Manufacture of Chloromethanes (Hydrochlorination)




     In the United States the main process for producing chloro-




metha'nes is a dual process involving the hydrochlorination of metha-




nol to methyl chloride, followed by the subsequent direct chlorina-




tion of all or a portion of the methyl chloride to methylene chloride




and chloroform.  The hydrogen chloride produced in the direct chlor-




ination of methyl chloride is used to hydrochlorinate the methanol.




As of May 1977, about 90 percent of methyl chloride capacity, about




75 percent of methylene chloride capacity, and about 77 percent of




chloroform capacity in the United States were based on the combina-




tion of these processes (Hobbs and Stuewe, 1978).  Some carbon




tetrachloride is formed as a by-product in the chlorination of methyl




chloride, but it is generally not directly purified into product by




Uuited States producers.  The unpurified carbon tetrachloride may




either be sold as is or used in-house as feed for carbon




tetrachloride-perchloroethylene producing facilities (Section 3.3).




     A typical vapor phase, continuous-process for the manufacture of




chloromethanes from methanol is shown in Figure 2.2 (Hobbs and




Stuewe, 1978).  Vaporized methanol and hydrogen chloride are fed in




equimolar proportions at 180 to 200°C to the hydrochlorination
                                 14

-------
HC1
                                    CH3OH
                                    CH3C1
       Methanol Storage
            Recycle HC1
                       Stripper
                   Dilute HC1
                                           Catalyst
                 H20 CH3C1


                     —»
                                                                           H2S°4
                                         CH3OH
                                         CH3C1
   Methanol
Hydrochlorination
   Reactor
                                                                          CH3C1
                                                                 Drying
                                                                 Tower
                                                            Quench Tower
C12
  CH3C1


Lgp

 •&•
          Methyl Chloride
        Chlorination Reactor
                      Hydrogen Chloride
                         Stripper
                                            Methylene Chloride
                                            Distillation Column
                                                                    Surge Tank
                              Methylene Chlor
                                 Storage

-------
                       Methyl Chloride
                          Storage
Chloroform Distillation
      Column
 Carbon Tetrachloride
1 And Heavies (To Further
       Processing)
                    FIGURE 2.2.
 PROCESS FOR MANUFACTURE OF CHLOROMETHANE'
HYDROCHLORINATION OF METHANOLTO METHYL CHLC
   FOLLOWED BY CHLORINATION OF METHYL CHLORIC
                                                                             15

-------
reactor.  The reactor is packed with a catalyst, such as alumina gel,




cuprous or zinc chloride on activated carbon or pumice, or phosphoric




acid on activated carbon.  Reactor temperatures may vary between 280




and 350°C depending on the catalyst used.  Yields of up to 95 per-




cent, tiased on tnethanol, are commonly obtained.




     The exit gases from the reactor enter a quench tower where unre-




acted hydrogen chloride and methanol are removed by water scrubbing.




The scrubbing water solution from the quench tower is sent to a




stripper, where methyl chloride and methanol are removed overhead for




recycle to the hydrochlorination reactor.  The bottoms from the




stripper consist of dilute hydrochloric acid which may. be used in-




house or sent to wastewater treatment.




     Methyl chloride and water, comprising the overhead from the




quench tower, are fed to a drying tower where the water is removed by




concentrated sulfuric acid.  The dilute sulfuric acid from the bottom




of the drying tower is sold or reprocessed on site.




     A portion of the dried methyl chloride (overhead from the drying




tower) is compressed, cooled, and liquified for storage as product.




The remainder of the 'dried methyl chloride is fed to a chlorination




reactor.  In the reactor, methyl chloride and chlorine react exother-




mically to form methylene chloride, chloroform, hydrogen chloride,




and a small amount of carbon tetrachloride.  The product stream




leaves the reactor as a gas and is cooled and condensed.
                                 17

-------
     The condensed crude product is sent to a stripper where hydrogen




chloride is removed as overhead and recycled to the raethanol hydro-




chlorination reactor.  The amounts of the individual chloromethanes




produced determine whether sufficient by-product hydrogen chloride is




available to operate the hydrochlorination reactor, or if make-up




hydrogen chloride must be added.




     The bottoms from the stripper, consisting of a mixture of methy-




lene chloride, chloroform, and carbon tetracHloride, are transferred




to an intermediate storage tank from which they are fed to a distil-




lation reaction for separation into chloromethane products.   In the




first distillation column, methylene chloride is recovered as an




overhead product and fed to a day tank, where an inhibitor such as




phenol is added to inhibit decomposition.  The stabilized product is




then sent to methylene chloride storage and loading.




     The bottoms from the methylene chloride distillation column are




sent to the chloroform distillation column.  The chloroform, which is




recovered as an overhead product from this column, is sent to a day




tank where an inhibitor such as ethyl alcohol is added to inhibit




decomposition.  The stabilized chloroform is then sent on to chloro-




form storage and loading.  The bottoms from the chloroform distilla-




tion column consist of crude carbon tetrachloride containing heavier




chlorocarbons.  The bottoms may be stored for subsequent feed to a




carbon tetrachloride—perchloroethylene process, or may be sold.
                                 13

-------
2.3  Manufacture of Carbon Tetrachloride and Perchloroethylene




     Perchloroethylene (tetrachloroethylene, 1,1,2,2-tetrachloroethy-




lene) and carbon tetrachloride are produced by the chlorination of




mixed hydrocarbons and chlorinated hydrocarbons at pyrolytic or near




pyrolytic temperatures.  Chlorination at such temperatures is some-




times referred to as chlorinolysis since it involves a simultaneous




breakdown of the hydrocarbons and chlorination of the molecular frag-




ments.  Another common name for the reaction is "perchlorination-."




Feedstocks used include methane, ethane, propane, butane, their




partly chlorinated derivatives, and mixed chlorohydrocarbon streams




from other chlorination processes.




     The flow diagram of the Scientific Design process for the man-




ufacture of perchloroethylene and carbon tetrachloride by chlorina-




tion of propane is given in Figure 2.3 (Miller, 1966).  The process




can be generalized to use other hydrocarbons such as propylene,




1,2-dichloropropane, or mixtures of hydrocarbons.  Chlorine, propane




and recycled chlorocarbon vapors are fed in the gaseous state to a




chlorination furnace which maintains a temperature of 500-650°C with-




out external heating.  The effluent gas from the furnace is quenched




wich 21-36 percent aqueous hydrochloric acid.  The use of hydrochlo-




ric acid of more than 19 percent concentration is claimed as the key




factor for minimizing side reactions during the quench (Miller,




1966).
                                  19

-------
Chlorinacion Furnace
                                                             Partial Condenser
                                                                             Weak HC1
                     Quenched
                     Reaction
                     Products
                                Quench Vessel
X
HC1 Absorber
ttH\


CU


luench Liquid



^J
/





v.
i





\





J
f












Aque










Cooler

aus Lays












sr










^
)








Cooler °

X^™^*.^


Steam \^ _^/

Organic Chlor"1' c
Layer


                                                                                   Decanter
                                                                                                          St
                        Chlorohydrocarbon Recycle
                                                         Steam
                                                                        Vaporizer
                                                            Heavy Ends to
                                                            Waste Treatment

-------
lorine
ovback
1 ntnn
           Recycle
           Blower
                     HC1
                     H20    x"
           Azeotrope
           Recycle

                                                Partial
                                                Condensers 1
                          Anhydrous
                            HC1
                          Product
                                   HC1 Stripper

                   o
                    Pump
le

             Mixed
             Chlorocarbons
earn

Slowbaclc Column
Pump
      Steam
                                           CC14
                                         Refining
                                          Column
                                    Steam

                                                       Carbon
                                                    Tetrachloride
                                                       Product
        Bottoms Recycle
                                               C2C14
                                              Refining
                                               Column
                                                    Perchloroethylene
                                                        Product
                                                                                    FIGURE2.3
                                                                SCIENTIFIC DESIGN PROCESS FOR MANUFACTU
                                                                P6RCHLOROETHYLENE AND CARBON TETRACHL
                                                                          BY CHLORINAT1ON OF PROPANE
                                                                                        21

-------
     The quenched reaction products are pumped to a decanter.  A por-




tion of the upper aqueous hydrochloric acid layer from the decanter,




is cooled to 50°C, and passed through the hydrochloric acid absorber




for reuse in the quench vessel.  The remainder of the upper layer is




sent to a chlorine blowback column and then pumped to a hydrochloric




acid stripper.  The overhead from the stripper is passed through two




partial condensers and collected as anhydrous hydrogen chloride,




which is a by-product of the process.




     The bottoms from the hydrochloric acid stripper consist of the




20 percent hydrochloric acid azeotrope which is used as the absorp-




tion liquid in the hydrochloric acid absorber.  The gases passing




through the hydrochloric acid absorber include the unquenched gases




emitted from the quench vessel and from the chlorine blowback column.




They are compressed in a recycle blower, partly condensed, and passed




through a knockdown column which separates entrained liquid from the




gas stream.  The chlorine gas is recycled to the chlorination fur-




nace.  The separated liquid is returned to the quench vessel.




     The organic chloride bottom layor from the decanter is sent to a




blowback column where it is stripped of dissolved hydrogen chloride,




chlorine, and low-boiling chlorohydrocarbons.  The stripped gas is




combined with the gases from the quench vessel and the chlorine blow-




back column and recycled.  The mixed chlorohydrocarbon liquid is




pumped to a carbon tetrachloride refining column where product carbon




tetrachloride is recovered as an overhead product.  The bottoms from
                                 23

-------
the column are sent to a perchloroethylene refining column where

product perchloroethylene is recovered as an overhead product.

     The bottoms from the perchloroethylene column are sent to a

vaporizer from which the volatile chlorohydrocarbons are returned as


recycle to the chlorination furnace.  The bottoms from the vaporizer


consist of heavy ends which are sent to waste treatment.

2.4  Manufacture of Vinyl Chloride Monomer (VCM) and Ethylene
     Bichloride (EDC), (The "Balanced" Process)

     The balanced ethylene feedstock route to vinyl chloride monomer

(VCM) is currently used for over 90 percent of the world's listed 35


billion Ibs per year of VCM capacity and for about 92 percent of the

VCM produced in the United States (McPherson, et al., 1979).  Three
                      %
principal steps are involved in this process, as follows:


       •  The direct chlorination of ethylene to EDC  -


          CH2 - CH2 + C12   	  C1CH2CH2C1

       •  The thermal dehydrochlorination of EDC to VCM


          and hydrogen chloride (HC1)

          C1CH2CH2C1     425-550°     CK2 - CHC1 + HC1

       •  The oxychlorination of ethylene with hydrogen


          chloride and air or oxygen in the presence of  I


          a catalyst to form EDC.


          CH2 =« CH2 + 2HC1 + 1/2 02 ^5^323°G"

          C1CH2CH2C1 + H20
                                 24

-------
     It is referred to as the "balanced" process because all of the

HC1 from the dehydrochlorination of EDC is used for the oxychlorina-

tion step.  Ethylene dichloride is obtained for sale by increasing

production in the -direct chlorination section unless a supply of

hydrogen chloride from another process is available as feed for the

oxychlorination process.

     2.4.1  Stauffer Balanced Process for the Manufacture of Vinyl
            Chloride Monomer (VCM) and Ethylene Dichloride (EDC)

     The Stauffer Chemical Company balanced- process for the manufac-

ture of VCM and EDC will be used for illustration.  It uses an air-

based, fixed bed oxychlorination plant.  A schematic diagram of the

process is shown in Figure 2.4 (McPherson, et al., 1979; Reich, 1976;

Anonymous, 1973).  Since details of operating conditions are not

available for this process, operating data from similar types of

processes are presented.
                                                     «
     In the Stauffer process, the direct chlorination of ethylene

proceeds by adding ethylene and chlorine to a reactor containing a

suspension of ferric chloride in ethylene dichloride.  Ethylene

dichloride of 99.7 percent purity is produced (Sherwood, 1962).  The

reaction is carried out at 5 atmospheres pressure with the reactants

entering the chlorinator at 30°C and leaving at 46°C.  The EDC from

the direct chlorination reactor is combined with  the EDC from

oxychlorination and sent to the EDC purification  section.
                                 25

-------
SOURCE :
McPherson,  ec
                     DIRECT
                     CHLORINATION
                     SECTION
BWF Steam
4_J
                                                                                  OXYCHLORINATION SI
                                                                       UBULAR FIXED-BED  CATALYTIC RJ

                                                                              BFW Steam
                                                                 LA
                                              O       CD
       cw
                                 H
                                 Z C£
                               HMO
                               o o: (-
                               U) O O
                               OS J <
                               M X (d
       Chlorine
       Ethvlene
       Air
^v  1979
i

-------
  ION
  TORS  NO. 1,2 4 3
  earn
          Chlorine
                                                   SECONDARY
                                                   SEPARATOR
                                                 EDC
 'YROLYSIS
 •TJRNACE     QUENCH
           COLUMN
                                     DISTILLATION
                                     COLUMN
sposal
EDC
RECYCLE
                                             VCM
                                             DISTILLATION
                                             COLUMN
                                                          EDC
iRMAL DEHYDROCHLORINATION
     SECTION
                                  VCM PURIFICATION SECTION
                                                                              F1GURE2.4
                                                        STAUFFER BALANCED PROCESS FOR THE MANUFACTU
                                                                 VINYL CHLORIDE MONOMER (VCM) AND
                                                                 ETHYLENE DICHLORIDE (EDC) BY DIRECT
                                                         CHLORINAT10N AND OXYCHLORINATION OF ETHYLE^
                                                      EDC FOLLOWED BYTHERMAL DEHYDROCHLORINATION

                                                                                     27

-------
     The oxychlorination  section combines HC1 from the EDC thermal




dehydrochlorination  section with fresh ethylene and air in three




tubular fixed-bed  catalytic reactors operating in series.  The tem-




perature is '.maintained below 325°C, generally in.a range of 225-




325°C.  Pressures  of  1 to  15 atmospheres are used.  The catalyst




generally -consists of cupric chloride and sodium or potassium chlo-




ride deposited  on  alumina.  The three reactors are packed with cata-




lyst of increasing activity from reactor No. 1 to reactor No. 3 to




achieve better  temperature control.  In the Stauffer process, ethy-




lene and air are fed  in excess of stoichiometric requirements to




assure high HC1 conversion.  The heat of reaction is removed by gen-




eration of steam on  the shell side of each reactor.




     The effluent  from reactor No. 3 is cooled to condense the EDC.



The unreacted ethylene gas is separated from the EDC in a phase




separator.  The ethylene  flows into a chlorination reactor where-it




is combined with chlorine  to produce more EDC.  The off-gas stream




from the chlorination reactor is cooled with plant cooling water and




.refrigeration, and passed  through a primary and secondary separator




before exiting  the process.  This process reduces the residual




ethylene concentration in  the vent gas to as low as 10 ppm.  EDC




recovered from  the primary and secondary separators is sent to the




EDC purification section.




     EDC used to make vinyl chloride by dehydrochlorination must be




of high purity, normally greater than 99.5 percent, since the thermal
                                  29

-------
dehydrochlorination process is susceptible to inhibition and fouling

by trace amounts of impurities.  EDC from three sources is combined

for purification:  EDC from direct chlorination, EDC from oxychlori-

nation, and EDC recovered  from the thermal dehydrochlorination step.
                 I
The combined EDC streams are fed to a washer where ferric chloride

may be removed with a water wash.  Chloral and other water extract-

able impurities are removed by washing with a caustic solution.

     Effluent from the washer is fed. to a light ends distillation

column where low boiling impurities and water are removed as an over-

hea-d stream.  The bottoms  from the light ends column are fed to a

heavy ends distillation column where pure dry EDC is taken off over-

head.  At this point EDC may be' recovered as product for sale or sent
                    %
to the thermal dehydrochlorination section.  The bottoms*'from the

heavy ends column are sent to-another column where useful heavy ends,

e.g., perchloroethylene, are separated from tars which go to waste

disposal.

     The purified EDC is preheated in the economizer section of the

pyrolysis furnace, and then vaporized with steam.  EDC vapor is

heated to dissociation temperature in the tubes of the pyrolysis fur-

nace to give a mixture of vinyl chloride and hydrogen chloride.  Fur-

nace temperature and pressure are normally maintained at 500-550°C

and 25 to 30 atmospheres respectively.  Residence time is between 2

and 30 seconds.  EDC conversion levels of 50 to 55 percent are

achieved, with selectivities to VCM of 96 to 99 percent.
                                 30

-------
     The exit stream from the pyrolysis furnace is sent to a quench




column where it is cooled by vaporization of a liquid mixture of EDC




and VCM.  Rapid cooling or quenching of the reaction mixture is




important because if the cooling is done too slowly, there are




substantial yield losses to heavy ends and tarsi  The exit stream




from the quench column flows through a condenser and into a phase




separator. The exit streams from the phase separator are sent to the




HC1 distillation column where HC1 gas is separated overhead and sent




to the oxychlorination section.  A portion of the liquid stream from




the phase separator is used as quench in the quench column.  The




bottoms from the HC1 distillation column are sent to the VCM distil-




lation column.  Purified VCM is taken overhead and condensed to give




VCM product.  VCM is easily liquified and is usually handled as a




liquid under 5 to- 8 atmospheres pressure.  The bottoms from the VCM




column are sent to the EDC purification section.




2.5  Manufacture of Chlorophenols




     The commercial process for the chlorination of phenol to




chlorophenols is a semi-batch process.  Figure 2.5 is a schematic




illustration of the process.  At the beginning of the reaction,




phenol is charged into two batch reactors—a primary reactor and a




secondary scrubber reactor.  Chlorine is added only to the primary




reactor.




     The temperature of the phenol in the primary reactor at the




start of chlorination is in the range of 65-130°C (generally 105°C).
                                 31

-------
LO
N>
                          Anhydrous
                          Aluminum
                          Chloride
                                                                                                              W.i i or
              Chlorine
IIC1
| UKILIIX
J DIUIN
uct
ol
lorophenol
lorophenol
Dlchlorophenol
1




[— *~







CA
z
1 ABSORPTIO:
-*- VC'II



<
                                                                  2 ,'i ,(>-Trli lilorophenol
                                                                  2,3,^,6-Tetrachlorophcnol
                                                     X
                                                                                                                             Conccntrntetl
                                                                                                                             Hydrochloric
                                                                                                                             Ac 1.1
                                                                                                                            HEOYCLE
                                                                                                                            PUMP
Hot Cons To
Unsce Disposal
                                                                   FIGURE 2.5
                                                 CHLORINATION PROCESS FOB MANUFACTURE OF
                                                               CHLOHOPHENOLS

-------
The reactor pressure is maintained at about 1.3 atmospheres.  A small




amount of anhydrous aluminum chloride is added as catalyst to the




primary reactor when chlorination has .proceeded to the dichlorophenol




stage, as determined by analysis.  If 2,4,6- trich^lorophenol and




2,3,4,6-tetrachlorophenol are desired as products, the reaction is




stopped when the melting point of the reactor contents reaches 95 °C




(about 2 t'o 3 hours).  At that point, the reactor contents are sent




to a batch vacuum distillation column for separation of the two prod-'




ucts.




     If pentachlorophenol is the desired product, the chlorination is




continued and the reaction temperature is progressively increased to




maintain a. differential temperature of 10°C over the product melting




point.  The total period of chlorination is generally 8-10 hours.




Chlorination' is stopped when the reactor contents have a melting




point of at least 174°C and contain at least 95 percent of chlori-




nated phenols.  For technical grade pentachlorophenol, no further




purification is required.




     The off-gas from the primary reactor, consisting of unreacted




chlorine and hydrogen chloride, is passed into a scrubber reactor




where sufficient phenol is present to ensure complete reaction of the




chlorine.  Catalyst is not used in the scrubber reactor.  The scrub—




ber reactor is used to manufacture monochlorophenol and dichloro-




phenol.  The reactor operates at about 1.3 atmospheres pressure.
                                  33

-------
     For production of raonochlorophenols, the temperature in the




scrubber reactor is maintained at about 70°C.  When one atom of chlo-




rine has combined with one molecule of phenol, as determined by




analysis, the reactor contents are charged to a batch vacuum distil-





lation column for separation of o-chlorophenol and p-chlorophenol.




     When 2,A-dichlorophenol is the desired product the scrubber




reactor is operated at a higher temperature, between 90° and 120°C.




After two atoms of chlorine have combined with one atom of phenol,




as shown by analysis, the reactor contents are charged to two batch




vacuum distillation columns operated in series for separation of the




reactor product components.




     The off-gas from the scrubber reactor consists mainly of hydro-




gen chloride with entrained phenols and chlorinated phenols.  The gas




is passed through a condensing trap where the entrained phenols and




chlorinated phenols separate from the gas stream and are returned'' to




the scrubber reactor.  The hydrogen chloride gas flows to an absorp-




tion tower where it is absorbed in water.  Hydrochloric acid is taken




off from the lower portion of the tower, and recirculated by means of




a pump until hydrochloric acid of the desired concentration is ob-




tained.  The acid is directly suitable for commercial use.  The vent




from the absorption tower releases water vapor containing traces of




hydrogen chloride.  The operation of the batch vacuum distillation




columns proceeds as follows:
                                 34

-------
     Batch distillation column number 1 receives the contents of the




scrubber reactor.  The components of the reactor contents are removed




sequentially.  The column is operated at about 110 mm Hg pressure.




If the reactor contents are monochlorophenol, opthochlorophenol is




taken overhead first at about 104°C, and condensed and recovered as




product. Unchlorinated phenol is then recovered at about 111°C and




recycled to  the reactors as needed.  The third overhead stream is




p-chlorophenol, which distills at about 145°C.  It is condensed and




recovered as product.




     If the reactor contents are primarily dichlorophenol,  the dis-




tillation column is operated to recover monochlorophenols first, then




2,4-dichlorophenol at 1508C.




     The bottoms from column 1 consist of 2,6-dichlorophenol and




2,4,6-trichlorophenol.  This stream is sent to column 2 along with




the trichlorophenol and tetrachlorophenol mixture from the  primary re-




actor.  Column 2 operates at 60 mm Hg.  In column 2, 2,6-dichloropher




nol is removed as an overhead stream at 135°C, condensed, and re-




cycled to the primary reactor for further chlorination.  2,4,6-




trichlorophenol is recovered next at about 160°C and collected as




product.  The final overhead stream is 2,3,4,6-tetrachlorophenol,




which distills at about 190°C.  It is condensed and collected as




product.  The bottoms from column 2 consist of a mixture of penta-




chlorophenol and polynuclear polychlorinated tars.  This mixture is




disposed of as waste.
                                35

-------
 2.6   Manufacture of Allyl Chloride (Shell Process)


      A flow diagram of a commercial scale allyl chlorile plant, as


 developed by the Shell Chemical Company, is illustrated in Figure 2.6


 (Fairbairn,  Cheney, and Cherniavsky,  1947; Pilorz,  1964).   Wet pro-


 pylene from storage is chilled by passage through a bayonet type


 cooler immersed in dry propylene.  The chilling causes condensation


 of water which is subsequently removed in a coalescer.  The separated


 water is periodically drawn off.   :The propylene then passes through a


 drier packed with activated alumina where residual  water is removed.


 The  drier system includes two driers  which operate  alternately so


 that one is being regenerated while the other is operating. The dried


 propylene then flows to the dry propylene storage tank.
                                             \

      In the dry storage tank the pjropylene is vaporized in the pro-


 cess of providing refrigeration for chilling the wet propylene.  The


 gaseous propylene flows through a heater prior to mixing with gaseous


 chlorine and entering the reactor.  Normally the feed will contain


 about 4 moles of propylene per mole of chlorine.  The reaction tem-


 perature is maintained at between 500 and 510°C and the pressure in


 the  reactor is about 1 atmosphere gauge pressure.  Residence time is


 a  few seconds.   Because carbonaceous  material accumulates  in the re-

i

 actor, it is necessary to clean the reactor about once every two


 weeks.  Therefore, two reactors are commonly provided so 'that one is


 in operation while the other is being cleaned.
                                  36

-------
                                                                          LIQUID

                                                                          KNOCK-OUT

                                                                          POT
   LIQUID
   PROPYLENE

   STORAGE
WET PROPYLENE

   STORAGE
DRY PROPYLENE

   STORAGE
o     o
  LIQUID
  CHLORINE
  TANK CAR
                     CHLORINE

                     VAPORIZER
                                                                                              PUMP

-------
      HYDROGEN
      CHLORIDE
      ABSORBER
          • Water
  20° Be
  Hydrochloric
  Acid
      REBOILER
                                                CONDENSER
o
REFLUX
DRUM
   REBOILER
REFLUX
DRUM
                                                           Allyl
                                                           Chloride
                                                           To
                                                           Storage
                 REBOILER
P RETRACTIONATOR
                     DISTILLATION
                     COLUMN NO.  1
                DISTILLATION
                COLUMN NO. 2
                        Heavy
                        Ends
                        To
                        Storage
                                                                   FIGURE2.6
                                                CHLORINAT10N PROCESS FOR THE MANUFACTURE OF
                                                        ALLYL CHLORIDE FROM PROPYLENE
                                                                      37

-------
     The  reaction product  is  cooled  and  fed  directly  to  a  prefrac-



 tionator  where  excess  propylene  and  byproduct  hydrogen chloride  is




 separated as  an overhead product from the  organic  chlorides.   Liquid




 propylene,  cooled to -408C by self-vaporization  in a  propylene flash




 drum,  is  used as reflux in the  prefractionator.




     The  propylene and hydrogen  chloride mixture from the  prefrac-




 cionator  flows  through an  absorber where commercial strength  hydro-




 chloric acid  is produced.   Liquid propylene  is used to-remove  the




 heac of absorption in  this process.   The propylene leaving  the ab-




 sorber is scrubbed with caustic  to remove  residual hydrogen chloride.




 It  then passes  through a liquid  knockout pot to  remove entrained




 water  before  being compressed,  liquified,  and  returned to wet  propy-




 lene storage.  Gaseous, propylene generated in  the  propylene flash  *




 drum and  during regeneration  of  the  driers is  also recycled through




 the compressor  to wet  propylene  storage.




     The  organic chlorides from  the  bottom of  the  prefractionator are



 refined in two  distillation columns  operating  in series.   In  the




'first  distillation column, residual  propylene  and  light  ends  such as




 isopropyl chloride and 2-chloropropene are removed as overhead prod-




 uct.   The bottoms from the first column  are  fractionated in the




 second column where allyl  chloride is removed  as the  overhead  prod-




 uct.   The bottoms from the second column consist primarily  of  dichlo-




 ropropene and dichloropropane.
                                  39

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2.7  Manufacture of Mono- and Dichlorobenzenes



     Monochlorobenzenes and dichlorobenzenes are produced commer-



cially by a continuous process in which liquid benzene is chlorinated



with chlorine in the presence of anhydrous ferric chloride catalyst.



The production of monochlorobenzene is favored by maintaining the



reaction temperature below 50°C.



     Figure 2.7 is a schematic diagram of the process.  Chlorine, an-



hydrous ferric chloride, and dry benzene are continuously fed to a



reactor.  The reaction temperature is maintained at between 308C and



50°C, partly by circulating the reactor contents through a cooler,



and partly by vaporizing some of the reactant mixture.  The vapor
                                                              *


stream from the reactor consists of hydrogen chloride, unreacted



chlorine, inerts, benzene, and some chlorinated benzene.  T^e =treani



is first scrubbed with a refrigerated stream of chlorinated benzenes



in an organic absorber to recover the benzene and chlorobenzenes.'1  It



is then scrubbed with water in a hydrogen chloride absorber system.



The hydrogen chloride absorber system consists of a hydrogen chloride



absorber, a tail gas scrubber, and a residual gas neutralizer.  In



the hydrogen chloride absorber, the gas stream is scrubbed with a



dilute hydrochloric acid stream, and commercial strength hydrochloric



acid is produced.  The inert gas stream from the absorber (tail gas)



containing unabsorbed hydrogen chloride, passes through a tail-gas



scrubber which removes most of the remaining hydrogen chloride in the



gas stream.  The hydrogen chloride solution from the tail gas
                                 40

-------
                                                                                                      Make-up —
                                                                                                      Water
                                                                                                          CW~~'
Chlorine
FeCl3
Catalyst
                                                                                      ORGANIC
                                                                                      ABSORBER
                                                                                               HC1
                                                                                               ABSORBER
                                                                    water
                                                        Caustic      Wash
                                                        Wash
                                          CRUDE
                                          CHLOROBENZENE
                                          DISTILLATION
                                          COLUMN
     Ref
Cooler or Condenser
Using Cooling Water

Refrigerated Cooler
Reboiler

 Reflux Drum
                                                      J  C Ejector Pump

-------
    Make-up
    Caustic
    Organics
    for Recycle
                     Salt +
                     Caustic
                     Solution
                     to Waste
                     Treatment
        p-DICHLOROBENZENE
        CRYSTALLIZATION
                                                              p-dichlorobenzene
                                                              Crytals to Recovery
                                                              and Packaging
                              Solvent grade
                              o,p-Dichlorobenzene
                              to Separation
                              and Recovery
  Hydrochloric
  Acid to
  Storage
VENT
                Monochlorobenzene
                to Storage
        MDNOCHLOROBENZENE
        RECOVERY COLUMN
                                To o-dichlorobenzene
                                Storage
DICHLOROBENZENE-
ISOMER SEPARATION
COLUMN
                                                     Trichlorobenzene
                                                     Isomers and
                                                     Heavier Compounds
                                                     To Storage
      Wastewater
                                                 FIGURE 2.7
                            MANUFACTURE OF MONO- ANO DICHLOROBE
                                        CHLORINAT10N OF BENZENE

                                                      41

-------
scrubber flows into a settler in which condensed organic compounds




are separated and recovered for recycle.  Part of the dilute acid




solution from the separator is used as the scrubber .medium in the




hydrogen chloride absorber and the remainder is mixed with fresh




make-up water and used as the scrubber medium in the tail-gas scrub-




ber.  The inert gas stream from the tail-gas scrubber contains traces




of hydrogen chloride.  It is scrubbed with a caustic solution before




discharge to the atmosphere.




     The liquid stream from the reactor (crude chlorobenzene) con-




tains chlorinated benzenes, unreacted benzene, dissolved hydrogen




chlqride, and spent catalyst.  The stream is distilled in a crude




dichlorobenzene vacuum distillation column.  The benzene, hydrogen




chloride, and most of the monochlorobenzene and dichlorobenzenes are




removed overhead in the column.  The column bottoms contain the cat-




alyst, some dichlorobenzene, and the more highly chlorinated benzena.




The bottom stream is washed with caustic and water to separate the




organics from the catalyst.  The organics are dried and fed to the




dichlorobenzene isomer separation column and the spent caustic and




wash water streams containing catalyst salts are disposed of.




     The overhead stream from the crude distillation column is passed




through a hydrogen chloride stripper where dissolved hydrogen chlo-




ride is boiled off.  The hydrogen chloride stream from the stripper




contains some organics.  It is mixed and processed with the gas




stream from the reactor.  The organic absorber bottoms stream is also
                                43

-------
processed through the hydrogen chloride stripper to remove dissolved




hydrogen chloride.




     The hydrogen chloride free bottoms-stream from the hydrogen




chloride stripper is then processed through a series of distillation




columns to recover benzene and the product chlorinated benzenes.




Benzene is recovered as an overhead product from the benzene recovery




column and recycled to  the reactor.




     The bottoms from the benzene recovery column consist of mixed




chlorobenzenes.  The stream is distilled in a monochlorobenzene re-




covery column where monochlorobenzene is recovered as an overhead




product.  The bottoms from the monochlorobenzene recovery column are




distilled in a dichlorobenzene isomer separation column.




     The overhead product fron the isomer separation column consists




primarily- of para-dichlorobenzene and some ortho- and meta-dichloro-




benzene.  Purified para-dichlorobenzene is recovered from this stream




by fractional crystallization.  Residual liquid from the crystalliza-




tion process consists of a mixture of ortho-, para- and meta-dichlo-




robenzene which is separated by distillation into solvent grades of




ortho-and para-dichlorobenzene.




     The bottoms from the isomer separation column are separated by




distillation into an ortho-dichlorobenzene product stream and a




stream containing a mixture of trichlorobenzene isomers and more




highly chlorinated benzene compounds.
                                 44

-------
3.0  IDENTIFICATION OF CONTAMINANTS FORMED IN CHLORINATTON AND RE-
     LATED UNIT PROCESSES

     In this section, contaminants that may be formed during the man-

ufacturing processes described in Section 2 are identified on the

basis of the process chemistry.  Details of the process chemistry

were obtained from the open literature and from personal knowledge

and experience.  In predicting possible contaminants, considera-

tion was given to the presence of impurities in the raw materials,

process operating conditions, the stability of the compounds on

exposure to the environment, and the use of additives.

     Four unit processes are described,*as follows:

     •  Direct chlorination, in which chlorine reacts directly with a
        hydrocarbon

     •  Hydrochlorination of alcohol, in which chlorine from hydrogen
        chloride replaces the hydroxyl group on the alcohol

     •  Oxychlorination, in which hydrogen chloride is catalytically
        oxidized, making the chlorine atom available for addition to
        the hydrocarbon

     •  Dehydrochlorination, in which hydrogen chloride is removed
        from a chlorinated hydrocarbon to make an unsaturated
        compound

3.1  Direct Chlorinatipn  •

     Six of the manufacturing processes described in section 2

involve the unit process of direct chlorination:  chlorination of

methane, manufacture of carbon tetrachloride and perchloroethylene,

manufacture of vinyl chloride monomer and ethylene dichloride,

manufacture of chlorophenols, manufacture of allyl chloride and
                                45

-------
manufacture of chlorobenzenes.  The chemistry of these processes can




be characterized by the following three types of chlorination




reactions:




     •  Free radical chain reactions




     •  Electrophilic  aromatic  substitution reactions




     •  Addition reaction to a  double bond




In the first two types of reactions, a chlorine atom replaces a




hydrogen  atom on the hydrocarbon, and hydrogen chloride is formed as




a by-product.  In  the  third  type of reaction, both chlorine atoms of




the chlorine molecule  are added to the hydrocarbon fo-rming a




saturated chlorohydrocarbon.




     3.1.1  Chlorination of Methane




     The  direct chlorination of methane proceeds by a free radical




chain reaction involving an  initiation reaction, propagation re-




actions,  and termination reactions.  In the initiation reaction,




chlorine  molecules break, apart  under the influence of heat or light




into chlorine radicals.




                        Cl - Cl -£—   2 Cl-                  (1)




Propagation reactions  consist of the reaction of a chlorine radical




with methane or a  chloromethane to generate hydrogen chloride and a




methyl radical or  a chloromethyl radical, and the reaction of a




methyl radical or  a chloromethyl radical with chlorine to form a




methyl chloride and a  chlorine  radical.




     CH4  + Cl-         	     HC1 + CH3                       (2)




     CH3 + Cl - Cl    	    CH3C1 + Cl-                      (3)







                                 46

-------
     CH3C1 + Cl-        	   HC1 + CH2C1                   (4)

     CH2C1 + Cl - Cl   	   CH2C12 H- Cl-                  (5)

     CH2C12 + Cl-       	   HC1 + CHC12                   (6)

     CHC12 + Cl - Cl   	   CHC13 + Cl-                   (7)

     CHC13 + Cl-        	   HC1 + CC13                    (8)

     CC13-+ Cl - Cl    	  CC14 + Cl-                     (9)

Termination involves  the reaction of two  free radicals.  Termination

reaction products include Cl,, CH-jCl, CH?C12, CHC13> CC14, CH3 - CH3,

CH3 - CH9C1, CH3 - CHC1,,*, CH3 - CC13, CH2C1 - CHnCL*. CH,C1 -

CHCi.,, Qi?Cl - CC13,  CHC1, -CHC12, CHCl^ -CC13> and CCl-j - CClj.

To a much lesser extent,  the two-carbon termination products can

themselves act as reactants and occasionally undergo terminations to

form longer chain carbon compounds.

     Chlorinated methanes are somewhat unstable when exposed to air

and water.  Decomposition products include carbon dioxide, hydrogen

chloride, phosgene, methanol, and chlorine.  In hot water (180°C),

methylene chloride forms carbon monoxide  and formic acid.  In the

presence of iron and  water, chloroform reacts with oxygen to produce

hydrogen peroxide, phosgene, and hydrogen chloride (Hardie, 1974):

                                       +H20
     CHC13 + 02     Fe_        C13COOH 	 C13COH + H202  (10)

     C13COH        	    COC12 + HC1                     (11)
*This compound is a precursor of vinyl chloride  (CH2 = CHC1).   It
 is possible that at high temperatures, a very small  amount of vinyl
 chloride will form.

-------
The above reaction is accelerated by the presence of base.  In


wate-r, phosgene (COC^) decomposes rapidly into carbon dioxide and


hydrogen chloride.  Carbon tetrachloride forms hexachloroethanes,


perchloroethylene, and chloromethanes when exposed to high tempera-


ture  steam.


      Stabilizers are commonly added to the chloromethanes to inhibit


decomposition.  Phenolic compounds or amines are used in methylene


chloride.  Stabilizers for chloroform include absolute alcohol,


methylated spirits, thymol, t-butyl phenol, and n-octyl phenol.


Stabilizers for carbon tetrachloride are alkyl cyanamides, diphenyl


amines, ethyl acetate, ethyl cyanide, fatty acid derivatives,


hexamethylene tetramine, resins and amines, thiocarbamide, and


guanidine (Hardie, 1964).


      3.1.2  Chlorination of Mixed Hydrocarbons and Chlorohydrocarbons


      The direct chlorination of mixed hydrocarbons and chloro-
                                                                   •»

hydrocarbons is used to manufacture perchloroethylene (tetrachloro-


ethylene, 1,1,2,2-tetrachloroethylene) and carbon tetrachloride.  The


feedstock for the process consists of a mixture of aliphatic hydro-


carbons ranging from methanes to butanes.  The process operates at


pyrolytic or near pyrolytic temperature (500-650°C), which is high


enough to pyrolyze the Chlorohydrocarbons formed.  The chemical


process can be analyzed in two stages.  In the first stage the feed-


stock hydrocarbons are completely chlorinated (perchlorinated) in a


free  radical chain reaction.  In the second stage, chlorinated com-


pounds are partially pyrolyzed to yield the final product.


                                 48

-------
     A generalized  reaction  sequence  for  Che  first  stag-;  is  as  fol-
lows:
1.  C1-C1   	    2  Cl-
            Heat
                      Initiation
2.  R-C-H + Cl-	 H-C1 +  R-C
3.  R-C- + C1-C1 	R-C-C1 + Cl-
                                          Propagation
             C1-C1
 .   R
R'  - R"
6,  R'. -r Cl-
 R' - Cl
Termination
     Specific examples of reactions which may  occur  are:
CH4 + , C12
              Heat
  CC14 -I- 4HC1
C4H6C14 •(• 6 C12  	  C4C110 +  6HC1
                 Heat
                        (12)
                                              (13)
NOTE:  R'  and R"   are any hydrocarbon  or  chlorohydrocarbon  radi-
cals.  Steps 2 and 3  together  form a cycle  which  can  generate  hun-
dreds or thousands of product molecules,  depending  upon  the process
conditions.  A termination step halts  two chains  simultaneously.

                                 49

-------
     Hie generalized  reaction sequence for partial pyrolysis is




          CC13 - CC12  -  R   	  R-  4- CC13 - CC12               (14)


                            Heat




          R- + CC13  -  CC12	 R-C1 4- CC12 - CC12              (15)




    ific examples of  partial pyrolysis reactions which may occur are




          cci3K:ci2^;ci3	cci4 + cciz = cci2                 (16)




             2 CC13-CC13	2 CC14 4- CC12 = CC12               (17)




      cci3K:ci2-<:ci2-<:ci3	cci3K:ci3 4- cci2 = cci2            (is)




    Other  possible  combinations exist, all of which ultimately lead




   CC14 and  C2Cl/f.   All of  these reactions stem from fragmenta-




  )ti of  Che  intermediates to yield CC13 - CC13 which then reacts




  "yield the  final  products  (equation 17).  Molecules which fail to




  •rolyze completely,  ultimately end up as the "heavy ends.




      3.1.3   High Temperature Propylene Chlorination




      Propylene will react  with chlorine to produce a number of dif-




 erent compounds.   The  predominant reaction at 500°C is the free




 'adical reaction which  results in the production of allyl chloride:




 "12  =  CHCH3'+ C12	CK2 = CHCH2C1 4- HC1                       (19)






The  allyl  chloride  may'also  be chlorinated to 1,3-dichloropropene




(Hearne, 1953).
                 m



      At temperatures too low for free radical formation (below




200°C), the  chlorine will add across the double bond to produce
                                50

-------
1,2-dichloropropane unless a free radical-producing catalyst has been

added.  Even at 500°C or above, this reaction takes place to an

appreciable degree (Fairbairn et al., 1947).  Similarly, the HC1

present may add across the double bond to produce isopropyl chloride

(Fairbairn et al. , 1947).

      A'likely reaction pathway to  allyl chloride at high (500°C)

temperatures is:

      C1-C1	 2 Cl-              Initiation                     (1)
           Heat
      Cl- + CH2 - CH-CH3	HC1 + CH2 = CH-CH2

      C1-C1 + CH2 - CH-CH2	Cl- + CH2 = CH-CH2
                                             Cl

and termination^of the  chains  shown in 20a and b.
Propagation
(20a)

(20b)
    A process which probably takes place simultaneously is as fol-

lows :
      CH2 = CH-CH3 + C12  -  CH2-^H-CH3                       (21)
                                Cl  Cl

      CH2-CH-CH3 - Cl- + CH2-CH-CH3                              (22)
      Cl  Cl             Cl
      Cl- + CH2-CH-CH3 - ^HCl + CH2-CH = CH2                     (23)
           Cl  '                 Cl
     The former (chain) mechanism can lead to the formation of

products larger than butanes in a manner analogous to that described

earlier for chlorination of methanes and mixed hydrocarbons.
                                51

-------
      The major side reactions are:
     CH2 » CH-CH3 + HC1	CH3-CH-CH3+ CH3CH2CH2C1                (24)
                               Cl

     PH-I— CU—/*"-    -  tri-M _L /"
-------
      A pathway to benzene formation is as follows:

     2 CII2 - CH-CH2	CH2 - CH-CH2-CH2-CH = CH2
          (27)
     CH2
     CHo
CH-CH2-CH2-CH = CH2 + 1/2 C12  	

      CH2 = CH-CH-CH2-CH = CH2 +^HC1
               Cl

CH-CH-CH2-CH =• CH2	CH2 - CH-CH = CH-CH
   Cl
+ HC1
CH2
                                                 (28)


                                                 (29)
                \\  //
F\
                                                                '(30)
                       + h Cl,
                                                  + HC1
          (31)
                                              cr
                                                    HCl
          (.32)
                    Cl

    Propylene is commercially available as a highly purified  com-

pound,  but it may contain detectable quantities of propane, ethane,

ethylene, and carbonyl sulfide.  The hydrocarbon impurities will  be

chlorinated in a free radical reaction to yield the respective

chlorohydrocarbons.  Ethylene will also undergo a chlorine addition

reaction.  Thus, all the mono- and dichlorinated isomers  of these

hydrocarbons are likely to be present in the process streams,

although in very small quantities.
                                 53

-------
      Carbonyl sulfide (COS) is likely to be present only in trace

quantities.  COS is a relatively stable compound but at 500°C there

nay be enough dissociation for its reaction with chlorine to reach

equilibrium:

         2 COS + 3 C12 "	  2 COC12 + S2C12                     (33)

On the.basis of free energy considerations, it is expected that the

equilibrium proceeds toward the right at low temperatures, and to the
            i
left at the high temperatures of the allyl chloride production

process.  However, even if some phosgene and sulfur chloride were

formed when che temperature is dropped during the quench, they would

be destroyed by water in the scrubber.  Therefore, phosgene or sulfur

chloride are not expected to be found in process streams downstream

of the scrubber.

     Following che chlorination step, the reaction products are

scrubbed with water to recover HC1 as hydrochloric (muriatic) acid.N-.

None of che other products (with the exception of phosgene, if

present) is broken down or removed by water.  The final caustic

scrubber removes traces of HC1, producing NaCl.

     Allyl chloride may also be produced by a low temperature

(200°C) catalytic process (Rust, 1942).  It is not expected that the

substances present in the catalytic process will be different from

chose in the high temperature process except for the addition of

catalyst fragments.  Among the different catalysts which may be used

are organo metallic compounds, azo compounds, organic peroxides, and

organic free radical compounds.

                                 54

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      3'1«4  Ethylene Chlorination


       The direct chlorination  of ethylene  is  an  addition  reaction in


which chlorine adds  to  the  double bond  of ethylene  to  form a


saturated dichloride  (ethylene  dichloride).  The  reaction  proceeds


with the aid of a Lewis  acid  catalyst,  as follows:


     -    - -—• d        ..     -  & Q
     :C1 - Cl:    FeGl3   :C1  -  Cl - FeCl3                          (34)
                    ..     ..    S                       0
                    :C1  -  Cl  - FeCl3   H2C -  CH2 +  FeCl4           (35)
                          ©              ©
                        •  CH2  -
                   Cl"   •  Cl"    Cl"

                                                                  (36)
     Under noraal  reaction  conditions,  Che  yield  of  ethylene


..-.•.-ride is greater  than  99  percent.


      Impurities in  the  ethylene  feedstock  include methane  and  ethane


••..lc>. should pass  through the  system  unchanged.


     3.1.5  Chlorobenzenes


     The direct chlorination of benzene  is  an  electrophilic aromatic


substitution reaction.   Benzene is  a  source of electrons  and  thus


reacts with electron seeking reagents  (electrophilic reagents).  The


reaction is believed co  proceed as  follows:


     1.  Chlorine  is polarized by a Lewis acid catalyst:

              ..'     V         -    -©   ©
        •Cl - Cl:     FeCl3 	 'Cl  -  Cl  - FeCl3                  (34)
         —    •*          j      ••   *•         w
                                 55

-------
        .e positive  chlorine (electrophile) reacts with the benzene

        :arbonium  ion:
            + :Cl-Cl-FeCl3    	   f|   *| +  Feci,            (37)
      \ hydrogen  ion  is  subsequently abstracted from the carbonium

      negative  chloride  ion to form hydrogen chloride and

      ;e  the  ferric  chloride:
           H  Cl
                       /-v              ^^
                                                              (38)



     ie remaining  hydrogen  atoms on the ring can be sequentially

     jted by  chlorine  forming  a total of twelve chlorinated

     ds:   monochlorobenzene, three dichlorobenzenes, three

    (robenzenes,  three tetrachlorobenzenes, pentachlorobenzene, and

    Lorobenzene.   The  extent to which polychlorinated compounds are

    depends  on  the  reaction temperature, the molar ratio of

   ie to  chlorine, the catalyst used, and the reactor residence

    Low  temperature,  short residence time, and high mole ratio of

  ne to  chlorine  favor'the production of monochlorobenzene.

  :hlorobenzene  is the preferred product at 40-45°C.  Poly-

  robenzenes  are  produced in more abundance at 75-858C (Brunjes,

  ).   The  use  of  Fuller's earth (Hardie, 1964) or magnesium iron

 linum silicate  (Darragh, 1949) as a catalyst reduces the pro-

 tion of dichlorobenzenes.   However, it is not possible to entirely

initiate polychlorinated benzene byproducts (Hardie, 1964).


                              56

-------
       The presence of chlorine on the benzene ring influences the
      :f subsequent chlorination and the attachment position of the
      quent chlorine atoms on the ring.  The chlorine inhibits sub-
     >nt reaction and is orVho-para directing.  Thus, the products of
    lorination are principally ortho- and para-dichlorobenzene with
    ' minor -amounts of meta dichlorobenzene :
      ci                    ci            ci         ci
                      3    r        .     "cl    ^            (39)
                      Para   CI         Ortho      Meta
   2,4-trichlorobenzene is the predominant trichlorination product.
  . also is  present in only minor amounts.
     Impurities in benzene are usually less than 0.5 percent
  Hancock,  1975).   The impurities are mostly toluene' and aliphatics
 such as n-heptane, with boiling points close to that of benzene.
 Thiophene  is  also often present as an impurity  (Hancock, 1975).
 Toluene can be chlorinated under the conditions of the reaction in a
 manner  similar to that of benzene.  Toluene, in fact, is more re-
 active  than benzene towards electrophilic substitution.  It is not
 expected that the methyl group of the toluene would be chlorinated.
The heptane and other aliphatic impurities in the benzene are ex-
pected  to  go  through the reaction unchanged.  Thiophene reacts with
chlorine but  does not alter the course of the main reaction:
                                    s
                                 57

-------
      Downstream processing of the reactor product includes a caustic




wash and a water wash of a mixture of catalyst and polychlorinated




benzenes.  It is anticipated  that reactions could take place between




hydroxide ion and dichlorobenzene to a  limited extent, producing




phenols, polyhydroxy benzenes, chlorophenols, and related compounds.




      A-very minor  side reaction could  occur between hydroxide ion




and a chlorobenzene as  follows:
                 Cl
                                           OH
                     4- NaOH
NaCl-
       Dichlorobenzenes  may  react  as  follows:
            Cl
                Cl
                      NaOH
                                           OH
                                                 NaCl
                                                                  (41)
                 (42)
             Cl
                 Cl
                    4- 2 NaOH
                                         OH
                 (43)
                      NaOH
                                                NaCl
                                                                  (44)
                    4- 2NaOH
                                             4- 2NaCl
                                                                  (45)
                                   53

-------
     If phenol gets recycled to the "reactor, chlorophenols will
result, as follows:
                OH
                      + 3C1.
      Further products are:
                OH                  ci
                              Cl    1   OH
                                        3HC1
                                                       (46)
Cl

Cl
Cl
0


Cl
                              Cl
                                           Cl
                              Cl
                            OH
OH
                                                                 (47)
                              Cl  ^ 'Cl
                                   Cl
               OH                 Cl

     The hydrolysis of chlorobenzene with caustic to produce phenol

is normally a high pressure, high temperature reaction.  Thus,  it is

not expected that very much phenol or other oxygenated compounds will

form under the conditions encountered in the caustic and water  wash

steps.

      The ferric chloride will react with the caustic and water to  N •>

produce ferric hydroxide and sodium chloride.  Metal impurities

present in the ferric chloride will also react to form metallic

hydroxides.

     3.1.6  Chlorophenols

     The direct chlorination of phenol,' like that of benzene, is an

electrophilic, aromatic substitution reaction.  The hydroxyl group is

rate-enhancing relative to benzene, and is a strong ortho-para

director.  Thus the chlorination of phenol yields ortho- and para-

chlorophenols.  The rate of chlorination of phenol is 1.1 x 10^

times the rate of benzene chlorination (Reiche et al., 1975).
                                 59

-------
     The direct chlorinaticm of phenol with chlorine proceeds  in

steps and can lead to seven chlorinated phenols,  as  shown below:
           OH
                    OH
               OH
                          C1
                                  70°C
                           C12     70°C
                                               OH
                                                   Cl
                                             +  HC1
                                           ortho-Chlorphenol
                                              HC1
                                               Cl
                                           para-Chlorophenol
                            OH            OH
                               ,C1     C
                                                                 (48)
                                                        (49)
                                                            2HC1
                                                                 (50)
                                     Cl
        ortho-Chlorophenol   2,4-Dichlorophenol   2,6-Dichlorophenol
                OH
                       C1
       Cl

para-Chlorophenol
                               90°C
                                      OH
                                                   Cl
                                                        HC1
                                                        (51)
                                               Cl
                                           2,4-Dichlorphenol
                                60

-------
                         ,

                         2     105°C
          2 ,4-Dichlorophenol
          2 ,6-Dichlorophenol
Cl,   A1^3

  2   130°C-
                                              OH
                                         Cl
                           Cl
                                                        HC1
                       Cl

                 2,4,6-Trichlorophenol
                                                     HC1
                       Cl
                2,4,6-Trichlorophenol
        2,4,6-Trichloropheno1
                                                    + HC1
               2,3,4,6-Trichlorophenol
               OH
                                        Cl
                        Cl,
                  'Cl
     A1C13

2  130^185°C
         2 ,3 ,4,6-Tetrachlorophenol-
                               +. HC1
                 Pentachlorophenol
                                           (52)
                                                                 (53)
                                                                 (54)
                                          (55)
     As seen in equations (48) and (49), phenol chlorinates at 70°C
                                <*

to both-ortho-chlorophenol and para-chlorophenol.  On further chlori-


nation at 90°C, ortho-chlorophenol yields both 2,4- and 2,6-dichloro-


phenol (equation 50), while para-chlorophenol yields mainly 2,4-di-


chlorophenol (equation 51). "To chlorinate beyond the dichlorophenol
                                ' 61

-------
stage at an acceptable rate, anhydrous aluminum chloride is added as

catalyst,   For commercial chlorinations a preferred amount of cata-


lyst is 0.0075 mole of aluminum chloride per mole of phenol.  Both

2,4- and 2,6-dichlorophenol yield 2,4,6-trichlorophenol on chlorina-.


tion at 105°C in the presence of aluminum chloride catalyst (equa-

tions 52 and 53).  The temperature is increased from 1058C to 130°C

for the chlorination of 2,4,6-trichlorophenol to 2,3,4,6-tetrachloro-

phenol (equation 54).


     To obtain pentachlorophenol, the temperature is increased pro-

gressively (from about 130°C to 185°C) to maintain a differential


temperature of 10°C over  the product melting point (equation 55).

      The action of aluminum chloride in the synthesis of
                                   "*•-,-
2,4,6-trichlorophenol from 2,4-dichlorophenol is shown in equations


56 to 59 as follows:
                A1C1
  6+     6-
C1-C1	A1C13
                                                                  (56)
              OH
                 Cl        6+
                    + C1--C1 -
                       -   (57)
                   Cl   ,°H Cl
                                                                  (58)
                                 62

-------
              (A1C1.)~ +--H+ 	^.  A1CL, + HC1                (59)
                   4/   r-**         ^      3
     The high temperatures used in the manufacture of the higher

chlorinated phenols result in side reactions that produce many

contaminants.  Most of the available information pertains to penta-

chlorophenol.  Commercial technical grade pentachlorophenol contains

4 to 10 percent 2,3,4,6-tetrachlorophenol, traces of 2,4,6-triehioro-

phenol, chlorinated dibenzo-p-dioxins, chlorinated dibenzofurans,

chlorophenoxy chlorophenols, chlorodiphenyl ethers, and chlorohydroxy-

diphenyl ethers.  Analyses of pentachlorophenol have revealed that
        •v,^

the principal chlorodioxin and chlorodibenzofuran contaminants are
   *
those containing six to eight chlorine atoms.  The highly toxic

2,3,7,8-tetrachlarodibenzo-p-dioxin (TCDD) has not been identified in

any sample of pentachlorophenol that has been analyzed (U.S. EFA,

1978).

      Analysis results for a commercial-grade pentachlorophenol

(Dowicide 7, Sample 9522 A) produced by the Dow Chemical Company in

June 1970, and a purified grade of pentachlorophenol, prepared by dis-

tillation of Dowicide 7, are given in Table III (U.S EPA, 1978).

     Chlorodioxins may result from condensation reactions of ortho-

subs tituted chlorophenoxy radicals (Kulka, 1961).  Chlorophenoxy

radicals are produced from decomposition of polychlorocyclohexa-

dienone (2,3,4,4,5,6-hexachlorocyclohexa-2,5-dien-l-one) which is

                                  63

-------
                             TABLE
                 COMPOSITION OF COMMERCIAL-GRADE AND
                PURIFIED-GRADE PENTACHLOROPHENOL (PGP)
                                     ANALYTICAL RESULTS
COMPONENT
Pen tachlorophenol
2,3 ,4., 6-Tetrachlorophenol
2 ,4,6-Trichlorophenol
Chlorinated phenoxyphenols
Octachlorodioxins
Hep cachlcrodioxins
Hexachlorodioxins
Octachlorodibenzofurans
Hep tachlorodibenzo f-urans
Hexac hlo ro dibenz o f tirans
Commercial
(Dowicide 7)
88.4%
4.4%
0.1%
6.2%
2500 ppm
125 ppm
4 ppm
80 ppm
80 ppm
30 ppm
Purifiedb
(Dowicide EC-7)
89.8%
10.1%
0.1%
	
15 . 1 ppm
6 . 5 ppm
1.0 ppm
1,0 ppm
1.8 ppm
1 . 0 ppm
Sample 9522 A, 1970
 Technical-grade PC? purified by distillation
SOURCE:  U.S. EPA, 1978
                                64

-------
produced by overchlorination of tri-, tetra- or pentachlorophenol

(see equation 60 below).  The chlorophenoxy radical (an electrophile)

attacks electronegative  sites (ortho or para positions) on a poly-

chlorophenol molecule  to  form chlorophenoxy chlorophenols (see equa-

tion 61 below) which undergo further reaction to form chlorodioxins

(see equation 62 below)  (U.S. EPA,  1978).
                                   0
                         C1-
                                           heat
Pentachlorophenol
                 9
                 2,3,4,5,6-
                                                      ci
                                                  Chlorophenoxy
                       hexachlorocyclohexa-   radical
                       2,5-dien-l-one
                        PH           PI         C.1
                                  a  chlorophenoxy chlorophenol
                                                                  (61)
                                 1,2,3,4,6,7,8,9-octachlorodibenzo-p-dioxin

     Similar reactions  may be  written  starting with  2,4,6-trichloro-

 phenol  and  2,3,4,6-tetrachlorophenol.

 3.2  Hydrochlorination  of  Methanol

     The  reaction of  a~n alcohol with hydrogen chloride involves

 substitution in which the  chloride  group  replaces  the  OH group on  the

 alcohol:
R - C - OH
    H
                   HCl
                               R - C  - Cl + H20
(63)
                                  65

-------
    The reaction is catalyzed by Lewis acids such as alumina, cuprous

chloride, or zinc chloride.  The process for manufacturing methyl

chloride from methanol is represented by:

                     catalyst
     CH3 - OH + HC1    	  CH3 - Cl + H20                      (64)
                      heat

    The reaction produces no organic side products.  Methanol of

greater than 99.9 percent purity is commercially available (Hardie,

1964).  Possible impurities include methyl ether and acetone.  If the

methyl chloride is used to make more highly chlorinated methanes by

direct chlorination, any acetone in the methyl chloride can react to

fora chloroketones.  The methyl ether can react with chlorine to form

chloroethers.

3.3  Oxychlorination

     The overall equation for the oxychlorination of ethylene is:

                              catalyst
     2 CH2 = CH2' + 02 + 4 HC1	2CH2 " ?H2 + 2H20          (65)
                                       Cl    Cl



Either air or pure oxygen may be used as the source of oxygen.  The

reaction catalyst  is commonly copper chloride and sodium or potassium

chloride deposited on alumina or other suitable support media.  Other

catalysts that have been described in- the patent literature are rare

earth metal chlorides, sulfate salts, and ferric- chloride (McPherson,
                                 66

-------
1979).   The reaction mechanism is still unclear at this time.  The

following pathway has been suggested (Rothon, 1972):

     CH2 - CH2 + 2 CuCl2	CH2 - CH2 + 2 CuCl                   (66)
                            Cl    Cl


     2 CuCl + 1/2 02	CuOCuCl2                                (67)



     CuOCuCl2 + 2HC1	2 CuCl2 + H20                           (68)



A number of side reactions can occur leading to the formation of

ethyl chloride ('by addition of HC1 to ethylene), polychlorinated

hydrocarbons, and vinyl  chloride:
                                •
     CH2 = CH2 + HC1	CH3 - CH2C1                             (69)


     CH3 - CH2C1     CuCl2    Higher-chlorinated products,  e.g., (70)

       CH3 - CHC12, CH2C1 - CHC1, also, smaller
       products, e.g., CC14 by fragmentation.
                  heat
              5
           Cl"
CH2 - CH2            HC1 + CH2  = CHC1                      (71)
Cl
    Other unsaturated chlorohydrocarbons are also possible, e.g.,
     CH3 - CC13  ^I±l   HC1 + CH2 = CC12                         (72)



     Aldehydes can also be formed by reaction of chlorinated and

unchlorinated hydrocarbons with oxygen.
                                 67

-------
     R - CH + 1/2 02	R - <2 - H                              (73)

     Chloral (CC13  - C - H)  and acetaldehyde (CH3 - C - H)
in particular have been identified as present in the process streams.

    The sodium or potassium chloride serves to increase the yield of

ethylene dichloride by inhibiting the formation of ethyl chloride

(Rothon, 1972).  Byproduct formation can also be minimized by main-

taining the temperature below 3259C.

     The hydrogen chloride used in the oxychlqrination process may

contain acetylene as an impurity as a result of being generated from

downstream dehydrochlorination of ethylene chloride to make vinyl

chloride.  The acetylene can react to form highly chlorinated by-

products.  Sorae companies selectively hydrogenate the acetylene to

ethylene and ethane in order to minimize this occurrence (McPherson,

1979).

3.4  Dehydrochlorination (Pyrolysis) of Ethylene Dichloride

     The dehydrochlorination of ethylene dichloride operates at py-

rolytic (500°C) temperatures to produce vinyl chloride:

     CH2 - CH2 	 CH2 --CHC1 + HC1                             (74)
     6l    Cl  heat

The reaction proceeds by a free radical mechanism, e.g.,

     Cl    Cl              Cl
     CH- - CH2	CH2C1 - CH + H-                    Initiation

             Cl
     CH2C1 - CH2 + H- 	  HC1 + CH2C1 - CH2        Propagation
                                 63

-------
    CH2C1 ~ CH2	CH = CH2 + H-                          Propagation
                   Cl

    R-  +  R1	R-R                                       Termination

where R-and R'. are any two free radicals.

     By-products from the pyrolysis reaction  include acetylene,

ethylene, chloroprene, vinylidene chloride,  1,1-dichloroethane,-

chlorofo'na, carbon tetrachloride, 1,1,1-trichloroethane , and other

compounds (McPherson, 1979).
                                  69

-------
4.0  COMPARISON OF CONTAMINANTS AND WASTE DISCHARGES FOR CHLORINATIOH
     PROCESSES

     In this section, the manufacturing processes described in this

report are compared with respect  to the nature of the substances pre-

sent in the process streams and the types of wastes generated.

4.1  Comparison of Chlorination Processes with Respect to Process
     Stream Contaminants

     The kinds of substances  that are likely to be found in the

process streams associated with the manufacture of chlorinated organic

compounds depends on  the composition of the feedstock naterials, the

types of reactions  that can occur at the  operating conditions, and  the

nature of product recovery and purification steps.  In section 3., the
                                                             •
likely process stream constituents  for  each of the product/processes

were identified on  the basis  of the known process chemistry.  Table IV

lists these process  stream constituents by generic name for each

product/process.  Table V identifies those reaction products  that are-.

on  the U.S. Environmental Protection Agency list  of priority

pollutants.

     All of  the desired products  of  the processes are on  the  list of

priority pollutants.  However, most  of  the processes produce, as

by-products  or  contaminants  and waste products, several additional

compounds  that are  on the  list.   Ethylene dichloride produced by  the

direct chlorination of  ethylene  is  an exception.  Under the  usual

conditions  of  the  reaction  it is  not expected  to  produce  any  by-

products.   However,  if  more  severe  reaction  conditions  are imposed
                                  71

-------
                         I AHI.F I V
LISTIN'  OF SUUSTAN"tS  PilLStNl  IN CIILOMINAIION I'KIICI.SS SVKhANS
                                                                        llvilrnrlilorl | Onvclilorl- |llrliy<
Proceua Stream Conatl tueiita
Chlor lut
Hydro... cklorld.
Saturated hydrocarbons
llnsaturatcd hydrocarbon*'
Ararat Ic hydrocarbona
A 1 echo la
A Idt-livdea and kcton«a
t-.ihera
Phunola

Carbon dioxide
Carbon monoxide
but unit ed cUlorohydro-
carbona
Cli 1 or liinr r»l 
-------
                                                                                    TAIILF.  IV )
U)
               Proceaa Scream ConetItuenta   /
                                                                                                                                          llvdrnclilnrt  Oxyclilorl-  HrhvJrot
                                                                                                                                           iia i ion    I   nai Ion    I   r ln.it I

CMorlnafrd ethers
Cli lor Inai ed pit c no Is
Q,,.no,«.
<:ti loroqulnonea
Cli 1 orod loxina
Cli lor tnarud ptieny lei tiers
Cltlor Inal ed b«iicofuran
Ca rhony 1 «ulf Ide
S.il f>irlc acid
C.....I.-
Hianl Salia








K
M













K





k
«
H









K
K
K

X
K
«





•
H

X
~~

X
X
X



K
.







K
X
X









M
M









K


-------
                                                                                                                1AIII.F V


                                                                                          I'HIOHITV  POLLUTANTS FKOM'CIILOK INA IKK  PHOCLSSES
                                                                                                                      . .        ,
                                                                                                             Dlii-ci  Milor la.i; in

7
                                                                                                                                    7   Sulni II ni lun

                                                                                                                                   /        Hi-ncllon
             Ox ycli Iff! -  IK*liv
X
K
K
•
K
/ -C*
/ /

X
X
X
K
K
M
K
X
X
K
X
K
X
X
/ -»
/ ^

«
X
X
K
X
K
K
K
X
K
K
K
K
-
/ 
-------
                     TAIIII  V  «:,il Ion
ltly.Jrcirlil.irl-]
1 M.ll Illll |
Oxyclilnr 1 -
flat Ion
lldiy.lro.liln
r 1 n.i 1 Ion
free  Kadlc.il ftetictloa
 /   SuliNi Jtut Joti
/        HCACIIon
                                   ,
-------
                                                                                 TABLE V (CONCUIDHI)
o\
                                                                                      IHrfct Chloi liuit Ion
                                                                   Free HuJIc.l
                                                                     React Ion
 //s,ii.«i a,.i i,
/	Heactlui.
Priority Pollutant*
Phenols
Plienol
2 CUlorophenol
2,^ Dl chloropltcaol
Peacachlorophenol
2,4.6 Tclclilorophenol
Met.l.
Copper
Zinc

/ -?
/ tf










/ /










/ ^"










/ />A










/ /

X
X
«
K
X
X
K

•f
/ /

_•_
*
H
X
X
X
X


/ /







It
X

/ /







X


/ ^











-------
e'S«> higher reaction temperatures, free radical reactions will take




place and result in the formation of numerous saturated and unsatu-




rated hydrocarbons of various molecular weights with and without




chlorine attached,  this is observed in the case of allyl chloride




production where an olefin, propylene, is chlorinated .under conditions




favorable to free radical formation so that an unsaturated chloro-




hydrocarbon, allyl chloride, is produced.  The nature of free radical




reactions is such that polychlorinated hydrocarbons are formed.  Free




radical reactions involving olefins also tend to result in the forma-




tion of aromatic compounds, e.g., benzenes and chlorobenzenes (see




section 3.1.3).  Also, although the free radical reaction of olefinic




hydrocarbons predominates at the higher temperatures, the addition




reaction proceeds to a limited extent so that saturated chlorinat-d




compounds' will be produced as by-products.




     Commercial feedstocks contain impurities.  In the case of ethy-




lene, the major impurities are methane and ethane.  These saturated




hydrocarbons do not undergo addition reactions and therefore would




pass through the reaction unchanged.  However, under conditions favor-




able to free radical formation, they will react to form saturated




chlorohydrocarbons and higher molecular weight saturated hydrocarbons.




Higher molecular weight olefin impurities will react similarly to the




ethylene.



     Hydrogen chloride is not a by-product of the addition reaction




but will be formed if free radical reactions take place.
                                 77

-------
     The hydrochlorination of methanol to form methyl chloride is also

a. process that is relatively clean, producing a small amount of by-

products.  The priority pollutants that are present in the process,  in

addition to the product methyl chloride, are heavy metals from the

catalyst used.  The methanol feedstock may contain oxygenated organics

as impurities, e.g., methyl ether and acetone.  These compounds are

inert in the hydrochlorination process.  However, if they are present

in the product methyl chloride, and the methyl chloride is subse-

quently chlorinated to make more highly chlorinated methanes, the

methyl ether and acetone will also chlorinate to form chloromethyl

ethers and chloroketones, respectively.

     The direct chlorination of methane and mixed hydrocarbons and the

dehydrochlorination of ethylene dichloride to produce vinyl chloride

are fres radical reactions.  The processes produce numerous by-

products with various,degrees of chlorination, various molecular

weights, and various levels of unsaturation.  All of the processes

liberate hydrogen chloride as a major product.  The chlorination of

the mixed hydrocarbons to produce perchloroethylene and carbon

tetrachloride, and  the' dehydrochlorination of ethylene dichloride to

produce vinyl chloride take place at pyrolytic temperatures.  The high

temperatures promote the fragmentation of molecules to smaller mole-

cules and unsaturated compounds.  Thus, in the chlorination of mixed
                                                                    \
hydrocarbons, molecules such as octachloropropane break down into
                                 78

-------
carbon tetrachloride and perchloroethylene.  In the dehydrochlorina-




ti.on of ethylene dichloride, acetylene, carbon tetrachloride, and




methyl chloride are among the by-products of the reaction.  The




unsaturated compounds present in these processes will also have a




tendency to combine to form aromatic compounds as described earlier




for the-high temperature chlorination of propylene.




     The chlorination of aromatic compounds by a substitution re-




action results in the formation of each of the possible chlorinated




aromatic compounds and hydrogen chloride.  The amount of each of the




chlorinated compounds formed depends on the reaction conditions




(e.g., higher degrees of chlorination are favored by high tempera-




tures) , and high chlorine to aromatic mole ratio.  Also some loca-




tions of the aromatic ring may be more susceptible to substitution




than others, (e.g., the presence of the hydroxyl group on the phenol




molecule promotes the substitution of chlorine in an ortho or para




position).  The nature- of the aromatic feedstock compound influences




the nature of the side reactions that may occur-  Alkyl substituted




benzenes (e.g., toluene, which may be an impurity in benzene), can




be chlorinated on the alkyl group by a free radical mechanism under




conditions that promote free radical formation.  This would not be




an expected occurrence under the reaction conditions described in




this report for production of mono and dichlorobenzenes.  Chlorinated




phenols tend to form chlorinated benzo-p-dioxins, chlorinated diben-




zofurans , chlorophenoxy chlorophenols, and chlorodiphenyl ethers.
                                 79

-------
     The oxychlorination process can result in the formation of a wide




variety of chlorinated hydrocarbons, saturated and unsaturated, and of




various molecular weights.  The presence of oxygen in the process also




promotes the formation of oxygenated compounds (e.g., chloral and




acetaldehyde).  Some carbon dioxide and carbon monoxide is also



formed.




     Product recovery and purification steps in the manufacture of




chlorinated hydrocarbons almost always include a washing step using




water or caustic.  Because 'chlorinated compounds could possibly under-




go hydrolysis reactions, particularly at elevated temperatures, the




washing step can cause the formation of additional contaminants..




Crude chlorobenzene,. for example, is washed with caustic.  1,2,4-




Trichlorobenzene that may be present in the crude stream can react




with caustic to. form a chlorinated phenolic compound.  Less chlori-




nated benzenes requi're more severe conditions (e.g., higher tempera-




tures)  to form phenols.




     Several of the processes use catalysts.  In some cases the cata-




lyst is in a fixed or fluidized bed and is only minimally present as a




contaminant in the process streams (e.g., the copper catalyst in oxy-




chlorination of ethylene)..  In other cases, the catalyst is spent dur-




ing the process and must be separated from the reactor product stream




(e.g., ferric chloride in chlorobenzene manufacture).  The catalyst in




this case presents a continuous disposal problem.
                                 80

-------
     Additional substances may be found in process or waste streams




as the result of the use of additives to stabilize the product (e.g.,




phenol may be added to vinyl chloride to inhibit polymerization during



storage).




     The chlorine and caustic used in the process may contain contami-




nants that end up-in process and/or waste streams.  Mercury can be a




contaminant if the chlorine and caustic were derived from a mercury




cell.  Carbon tetrachloride and other chlorinated organic substances




may be present as contaminants in chlorine made with graphite anodes




(Edwards, 1968). Metallic anodes do not cause such impurities




(Lowenheim and Moran, 1975).




4.2  Pollutant Discharges from Chlorination Processes




     4.2.1  Emissions to the Atmosphere




     The direct chlorination processes  for chloromethanes,  perchloro-




ethylene and carbon tetrachloride, vinyl chloride, allyl chloride,




chlorophenol, and chlorobenzene produce hydrogen chloride gas as a  "- >




aajor by-product.  The hydrogen chloride gas is usually scrubbed with




water and recovered as a water solution for subsequent sale.  The




hydrogen chloride gas contains some non-water-soluble and nonconden-




sible gases which will be'vented  from the scrubber system.   This emis-




sion will usually contain residual low-molecular weight hydrocarbons,




unreacted chlorine, hydrogen chloride,  and inert  gases and air that




enter with the raw materials or become  entrained  during processing ?




     The oxychlorination process has a  gaseous  emission due  to the




use of air or oxygen  in  the process.  When air  is  used, nitrogen  from
                                  81

-------
the air straam is vented and will carry residual lew molecular weight



hydrocarbons.  When oxygen is used, the unreacted oxygen is recycled



to the reactor; however, a small, portion of this recycle stream is



continuously purged to prevent a buildup of inerts.  This stream will




also carry residual low molecular weight hydrocarbons; however, since




the stream volume is smaller than for the air based process, the pol-



lutant discharge is correspondingly less.




     Emissions to the air also occur from distillation column vents




and from storage tanks.  The manufacture of pentachlorophenol may




result in particulate emissions during the processing and packaging of



solid pentachlorophenol.




     4.2.2  Wastewater Discharges




     A caustic and/or water-washing step is used to remove catalyst




and/or impurities from process streams in the processes for man-




ufacture of chloromethanes, allyl chloride,'et'hylene dichloride (both




processes), vinyl chloride, methyl chloride bv hydrochlorination. and



chlorobenzenes.  Thus, in these processes a spent caustic and waste




water will be generated which will contain dissolved organics, metal



salts from catalysts, sodium chloride, and chlorine as hypochlorite.




In addition, hydrolysis products of the chlorohydrocarbons will be




present, such as phenols in the chlorobenzene wash, and methanol and




formic acid in the chloromethane wash.
     An intermittent wastewater discharge is likely to occur from the



chlorination processes which produce hydrogen chloride as a
                                82

-------
by-product.  During start-up, shut down, or process upsets, an off-

grade hydrochloric acid solution may be produced which is not saleable

and must be disposed of. • The hydrochloric acid is often neutralized

by passage through a bed of•limestone, oyster shells, clam shells, or
                                                            I
in a neutralization system employing lime as the neutralizing reagent

and discharged.  The neutralized effluent will contain dissolved salts

of the heavy metal impurities in the neutralizing reagent [e.g.,

FeCl3, PbCl2, AlCla].

     4.2.3  Liauid Orzanic Wastes

     A distillation residue consisting of polychlorinated compounds

and high molecular weight organic compounds is produced in all pro-
   »
cesses except the hydrochlorination of methanol.  The direct chlo-

rination of ethylene should not produce any appreciable amount of

residue unless the reaction temperature goes out of control and some

free  radical reactions occur-  The distillation residue from penta-

chlorophenol production will contain spent catalyst.

     4.2.4  Solid Waste and Sludges

     The processes involving catalysts are likely to  generate solid

wastes and/or sludges that must be disposed of.  In the case of the

direct chlorination of ethylene and the direct chlorination of ben-

zene, the catalyst is washed from the product with caustic. Treatment

of the spent caustic will produce a sludge containing metal salts.

The catalyst for the oxychlorination process and the hydrochlorination

process is in a fixed bed.  Some of the catalyst may be carried out in
                                 83

-------
 the  reactor product stream as a result of attrition and will end up in

 the  subsequent caustic wash streams.   The catalyst bed does, however,

 have a finite life and must be replaced periodically.  The spent cata-

 lyst must  then be disposed of.

      4.2.5  Other Wastes
                                  »
      Gulfuric acid is used to dry process streams in the manufacturing

 processes  for methyl chloride by hydrochlorinatioa and for chlorome-

 thanes by direct chlorination.  A spent acid stream containing organic

 compounds  is thus generated by these processes.

      Periodic cleaning of process equipment also results in a resi-
                                                          »
 due  that must be disposed of.  The reactors in the allyl chloride

 process must be cleaned of an accumulation of carbonaceous residue

 biweekly.   Other processes are .likely to generate a similar residue.

 although the rate of accumulation of such residue varies from process
.!»»»• >^V3>">'- . .
 to process.  Distillation equipment is also likely to accumulate such

 residues,  particularly in the reboiler and bottom section of the col-

 umn.
                                   84

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5.0  CONCLUSIONS




     This  study of  f0ur  unit  processes used to produce chlorinated




hydrocarbons,  shows that the  unit  process of direct chlorination can




be subdivided  into  three distinct  groups with regard to the types of



by-products  and/or  contaminants present in the process and waste




streams-.   The  groupings,  based on  the reaction type, are as follows:



     •  Free radical reactions




     •  Electrophilic aromatic substitution reaction




     •  Addition  reaction to  a double bond




The high temperature, uncatalyzed  dehydrochlorination unit process is



a free radical reaction.   By-products and/or contaminants in the



process and  waste streams  from the manufacture of products by




uncatalyzed, high temperature dehydrochlorination are similar t« those



produced in  the free  radical  direct chlorination unit process.




     The processes  of hydrochlorination and oxychlorination each have




their own unique characteristics with regard to byproduct and con-



taminant generation.




     The characteristics of each unit process and subgroup of a unit




process is described  below.




5.1'  Direct Chlorination and Dehydrochlorination




     5.1.1  Free Radical Reactions including Dehydrochlorination




     The compounds  discussed in this report that are produced by a




free radical reaction are  chloromethanes, carbon tetrachloride,
                                85

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perchloroethylene, allyl chloride, and vinyl chloride.  In free radi-


cal chlorination processes, side reactions occur Chat can result in


the formation of a wide assortment of chlorinated and unchlorinated


hydrocarbons.  The amount of any particular compound that will be


formed is determined by the reaction conditions.  Polychlorinated com-


pounds and high molecular weight compounds are favored by increased


reaction temperature; however, at pyrolytic temperatures, cracking


will occur producing smaller molecules, unsaturated compounds, and


aromatic compounds.  The major by-product of free radical chlorina-


tions is hydrogen chloride.  For each chlorine atom added to a hydro-


carbon molecule by a free radical reaction, one molecule of hydrogen


chloride is produced.  The hydrogen chloride may be absorbed in water


to make a commercial grade muriatic (hydrochloric) acid, collected as
      •

an anhydrous product, used directly in an associated .process such as


hydrochlorination or oxychlorination, or neutralized and disposed of


with wastewater.


     Waste discharges from free radical chlorinations usually include


an inert gas purge stream from the hydrogen chloride recovery opera-


tion; a spent caustic and/or wastewater stream from washing steps


designed to remove acid and soluble impurities from process streams; a


speit sulfuric acid waste from process stream drying operations; and a


distillation column residue.  Accumulations of carbonaceous material


from reactors and distillation column reboilers are periodical!/ re-


moved and disposed of.  A wastewater stream may also be produced as a


result of the need to dispose of unmarketable hydrochloric acid.
                                 36

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      The inert gas purge stream may contain unreacted feedstock



 materials (low molecular weight hydrocarbons and chlorine),  hydrogen




 chloride, and low molecular weight chlorohydrocarbons.   The  spent




 caustic and wastewater may contain hydrocarbons, chlorohydrocarbons,




 chloride salts, and products of the hydrolysis of chlorohydrocarbons



 (e.g.,  methanol, formic acid, phenols).   The neutralized waste  hydro-




 chloric acid stream may contain salts of heavy metals.   The  spent acid




 may contain hydrocarbons and chlorohydrocarbons.  The distillation



 column  residue will consist primarily Of high molecular  weight  and •




 polychlorinated hydrocarbons.




      5.1.2  Eleetrophilic Aromatic Substitution Reactions



      The ring chlorination of phenol and benzene are  electrophilic




 aromatic substitution reactions.  The ring chlorination  of aromatic




 compounds is promoted by a Lewis acid catalyst and relatively low




 temperatures.  All possible ring-chlorinated compounds of the feed




 compound are likely to be present in the process and  waste streams,




 although the quantity of any particular compound depends on  the



.reaction conditions.    Hydrogen chloride is the major by-product  of




 this process.  For each atom of chlorine added to the aromatic  ring,




 one molecule of hydrogen chloride is formed.  Substituent groups  on




 the feedstock aromatic compound may participate in reactions that form




 additional byproducts.  Chlorinated phenols, for example, form




 benzofurans, quinones, and dioxins.



      Waste streams from ring chlorination of aromatic compounds




 usually include an inert gas purge stream from the hydrogen  chloride
                                  87

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recovery operation, wastewater  from a caustic wash or acid neutrali-
zation operation, and_a distillation column residue.  Accumulations of




carbonaceous material from reactors and distillation column reboilers




may also be periodically removed and disposed of.  A wastewater stream




nay also be^produced as a result, of the need to_dispase__of__unmarket-



able hydrochloric acid.




     The -inert gas purge stream may contain unreacted aromatic hy-



drocarbons, chlorine, hydrogen chloride, and volatile chlorinated




aromatic compounds.  The wastewater will contain some of these same




compounds, plus inorganic salts  from neutralization and/or spent cata-




lyst residue, and products of hydrolysis of the chlorinated hydrocar-




bons, e.g., phenols, and quinones.  The neutralized waste hydrochloric




acid stream may contain salts of heavy metals.  The distillation



column residue will contain  polychlorinated aromatic compounds, and




other reaction side products (e.g., residues from chlorophenol manu-




facture may contain benzofurans and dioxins).  It may also contain




catalyst residue not previously removed.




     5.1.3  Addition Reaction to a Double Bond




     The direct chlorination of  ethylene is the addition process de-




scribed in this report.  In  the  addition reaction,  two chlorine atoms




add to the olefin compound at the double bond to form a saturated




chlorohydrocarbon.  The addition reaction occurs under relatively mild



conditions in the presence of a Lewis acid catalyst and does  not re-




sult in the formation of by-products.  However, a spent catalyst waste
                                  88

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is generated  in  the  process.  At high  temperatures, olefins can react



with chlorine  to  form  unsaturated chlorides by a free radical reac-



tion.  Both the  addition  reaction and  the free radical reaction will



occur at the high temperatures, with the free radical reaction be-



coming increasingly  dominant as the temperature increases.  The main



waste discharge  from this  process is a spent caustic solution which



will contain  hydrocarbons,  chlorohydrocarbons, hydrolysis products of
                                                           *


chlorohydrocarbons,  and spent catalyst residues.



5.2  Hydrochlorination



     The hydrochlorination of methanol with hydrogen chloride in the



presence of a  catalyst (e.g., zinc chloride), is described in this ee-



port.  The only  by-product of this reaction is water;

                                      •

     The wastes  from this  process include the water generated by the



reaction, and  a spent  caustic solution which was used to remove  resi-



'HffifT'-actcP'an'd  impurities  from the product stream.  The waste will



contain some feedstock and product, hydrolysis products of the chloro-



hydrocarbon product, and  probably some catalyst residues.  The cata-



lyst in this process does  not require  continuous renewal; however, it



is anticipated that  it will be replaced  periodically, and therefore



there will periodically be  a spent catalyst waste  from the  process.



5.3  Oxychlorination



     The oxychlorination of ethylene to  make ethylene dichloride is



described in  this report.   The by-products of the  oxychlorination  of



olefins are primarily  chlorinated derivatives of the olefin and their
                                 39

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breakdown products, and oxygenated hydrocarbons and chlorohydrocarbons




sucTi as acetaldehyde and chloral.  Some carbon monoxide and carbon



dioxide is also produced.




     Waste discharges from  this  process are a gaseous emission of




inert gases, a spent caustic waste, and a  distillation column residue.




     The amount of gaseous  emission depends on whether air or oxygen



is used.  The inert gas will contain  some  volatile hydrocarbons and



chlorohydrocarbons, and unreacted hydrogen chloride.  The spent




caustic will contain organics  including aldehydes and chlorinated




aldehydes, some catalyst residue, and hydrolysis products of the



chlorinated hydrocarbons.   The distillation column residue will con-




sist primarily of polychlorinated hydrocarbon derivatives of the




feedstock.
                                  90

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