DEVELOPMENT OF RE6ENERABLE FIBERS
            FOR REMOVAL OF
   SULFUR DIOXIDE FROM WASTE GASES
                    by
                Ronald W. Fuest
                Merlin P. Harvey
                November 1968
           TECHNICAL REPORT
     Covering the period January I to June 30, 1968
            Contract No. PH 86-68-74


                 Prepared for
       National Center for Air Pollution Control
            Cincinnati, Ohio  45227
               UNIROYAL, INC.
               Research Center

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      DEVELOPMENT OF REGENERABLE FIBERS

FOR REMOVAL OF SULFUR DIOXIDE FROM WASTE GASES
                      by
               Ronald W. Fuest
               Merlin P. Harvey
                November 1968
               UNIROYAL, INC.
              Research  Center

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                                 FOREWORD

     This report coyers work done during the six months period January 1 to
June 30, 1968 which comprised the initial phase of the contract.  The con-
tract has been extended for 12 additional months.

     The work was under the administrative direction of Dr.  J. S.  Lasky.
Dr. R. W. Fuest served as Principal Investigator.

     Mr. E.  D. Margolin of the National  Center for Air Pollution Control
served as Project Engineer.

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                               TABLE OF CONTENTS
       ABSTRACT
       SUMMARY                                                              1
I.     INTRODUCTION                                                         3
II.    CHEMICAL BACKGROUND                                                  5
III.   SCREENING OF BASIC SORBENTS                                         11
       A.  STYRENE/DIMETHYLAMINOPROPYLMALEIMIDE COPOLYMER (SSQ) AND
           2-VINYLPYRIDINE/2-METHYL-5-VINYLPYRIDINE COPOLYMER (GIQ)        11
       B.  POLYETHYLENEIMINE (PEI)                                         15
       C.  POLYVINYLPYRIDINE                                               17
       D.  AMINOPOLYUREA                                                   17
       E.  ANION EXCHANGE RESIN                                            19
       F.  ST YRENE-METHYLVINYLETHER- DIMETHYLAMINOPROPYLMALEIMIDE
           TERPOLYMER (VTQ)                                                19
IV.    FIBERS                                                              21
       A.  POLYPROPYLENE-POLYETHYLENEIMINE FIBERS                          21
       B.  POLYPROPYLENE-SSQ FIBER                                         25
V.     REGENERATION                                                        27
       A.  POLYPROPYLENE-POLYETHYLENEIMINE FIBER                           27
       B.  MULTIPLE SORPTION-REGENERATION WITH SSQ                         27
VI.    SORPTION ISOTHERMS                                                  31
VII.   DISTRIBUTION COEFFICIENTS                                           37
VIII.  EFFECT OF FLOW RATE                                                 39
IX.    EFFECT OF N02                                                       41
X.     EXPERIMENTAL                                                        43
XI.    FUTURE RESEARCH PROGRAM                                             47
XII.   REFERENCES                                                          49

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                              LIST OF FIGURES
Figure
  No.
   1     Sorption of S02 by dry SSQ at 35°C (flow rate - 21.2 ml/min.)     14
   2     Sorption of SC>2 by dry aminopolyurea at 35°C.                     18
   3     Effect of flow rate,  PEI level,  and draw ratio upon rate of
         S(>2 sorption of polypropylene-PEI fiber in the presence of
         water vapor at 35°C.                                               23
   4     S0» sorption of undrawn polypropylene- SSQ fiber in the
         presence of water vapor at 35°C.                                   26
   5     Sorpt ion-regeneration of SSQ                                      29
   6     Dissociation pressure of SSQ-S02  reaction product                 33
   7     Langmuir isotherms for dry SSQ at 55°C.  and 75°C.                 34
   8     Log distribution coefficient vs. 1/T for SSQ                       38
   9     Apparatus for treating sorbent and fiber samples with gas
         mixtures                                                          44
                               LIST  OF TABLES

                                                                          Page
         Sorption of  S02  by  SSQ (g/g)                                       13
         Sorption of  S0»  by  various materials  (g/g)                         15
         S02  sorption of  polypropylene fiber containing  9.1% PEI
         in presence  of water vapor                                         21
  IV     Regeneration of  polypropylene-PEI  fiber                            27
   V     S0_  capacity of  dry SSQ                                            32

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                                 ABSTRACT

     Several basic nitrogen-containing polymers have been evaluated as SO
sorbents for use in melt-spun fibers.  The effect of basicity and amine
nitrogen type upon capacity is discussed.  Preliminary work on the effect
of water vapor, temperature, and flow rate upon the capacity of several
candidate materials has been carried out.  Two candidate sorbents have been
co-spun with polypropylene to form fibers and their sorption properties

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                                   SUMMARY

A.  We have selected several polymeric sorbents with which we have had prior
    experience in our inhouse programs to improve dyeability of fibers.
    These include materials of varying structural types, basicity, and nitro-
    gen content.  All of the materials evaluated are known to be co-spinnable
    with polypropylene.

B.  Samples of these materials have been treated in a flow system with SO--
    nitrogen mixtures containing, in most cases, approximately 10,000 ppm SO^.
    Results with some of these materials are as follows:
         A styrene-dimethylaminopropylmaleimide copolymer (SSQ) was
         evaluated in detail.  It was found that at a temperature of 35°C,
         S02 capacity of 0.190 g/g was obtained.  This  capacity is ~-85% of
         the stoichiometric value (0.223 g/g)  for the 1:1 complex based on
         amine nitrogen content.  At higher temperatures (95°C), the
         capacity was reduced to 0.033 g/g, approximately 157o of stoi-
         chiometric.  The presence of water vapor in the gas stream, however,
         gave a significant increase in capacity at 95°C (0.075 g/g).
         High molecular weight polyethyleneimine (PEI) was also evaluated.
         This material was of interest because of its low equivalent weight,
         which gives a theoretical capacity for the 1:1 complex of 1.47 g/g.
         Capacities as high as 1 g/g have been obtained experimentally in the
         presence of water vapor.  Reversibility with PEI is poor, however.
         A vinylpyridine polymer showed much lower capacity than the alkyl-
         amine polymers.  This is probably due to its weaker basicity, and
         indicates that strong-base polymers are probably necessary for high
         capacity.

C.  Fifteen-denier, round-cross-section, polypropylene  fibers containing
    10-12.5 parts per hundred (phr) of high molecular weight PEI have
    been spun by conventional melt-spinning techniques without great

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    believe that considerably higher loadings are achieveable, but this
    will require investigation of spinning parameters and development of
    specialized spinning techniques.

    No attempts to obtain minimum denier or other than round cross-sectional
    shapes have been made•

D.  Preliminary evaluation of a fiber containing PEI has shown that: capaci-
    ties of about 0.184 g S02 per g PEI, i.e., 0.017 g/g on weight of fiber,
    are obtained under conditions (35°C, presence of water vapor) where a
    capacity of approximately 1 g SO- per g PEI was obtained when the PEI
    was supported on a porous mineral material.  It should be emphasized
    that this fiber does not represent optimum.

E.  Regeneration experiments with dry SSQ show that sorbed SO- can be removed
    from the polymer by flushing with nitrogen at elevated temperatures.
    Work in progress involves carrying samples through several absorption-
    regeneration cycles to determine the degree of cumulative irreversibil-
    ity.  In addition,  we are carrying out regeneration studies on fibers.

F.  We have shown that the presence of water in the gas stream increases the
    SO- capacity of basic nitrogen-containing sorbents.  We are in the pro-
    cess of adding other typical flue gas constituents (e.g., 0„,  NO) to
    our synthetic gas streams to determine the effect of these materials
    on the sorbtive and physical properties of the sorbents,  and to obtain
    information on the selectivity of these sorbents toward SO  in the
    presence of other acidic gases.

G.  Dry SSQ has been shown  to follow the Langmuir adsorption isotherm for

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                             I.  INTRODUCTION

     Sulfur dioxide is one of  the major air pollutants, and it occurs as a
waste product in a number of industrial operations  including the smelting
of ores and the combustion of  coal and oil.  The deleterious effects of
sulfur dioxide in the atmosphere on plant and animal life, as well as on
materials, has been widely documented.

     Considerable effort has been expended in recent years to reduce or
eliminate the discharge of sulfur dioxide into the  atmosphere, and it is
recognized that a technique satisfying the following criteria for treatment
of waste gases to remove S0_ is urgently needed:
          (1)  Low cost, both  in materials and construction.
          (2)  Adaptable for use in combustion units ranging
               in size from small industrial furnaces  to  large
               power plants, as well  as smelters and other
               SO- sources.
          (3)  Regenerable, with economic sulfur recovery.

     Our approach to a solution of this problem involves  the use of basic
nitrogen-containing organic polymers  for the sorption  of  sulfur dioxide,
these sorbents being admixed with a melt-spun synthetic fiber to act as a
strong flexible carrier for them.

     The fibrous form presents several advantages over particulate sorbent
beds - it is tough, flexible and strong, and it can be fabricated into mats,
felts, knitted fabrics and many other assemblies which lend themselves to
the design of continuous processes.   Contact area can  be  made very high,
depending upon the size and cross-sectional shape of the  fiber.

     Over the period from January 1,  1968 to June 30,  1968 we have investi-
gated the feasibility of this  concept for the Bureau of Disease Prevention
and Environmental Control, Public Health Service, under Contract No. PH 86-
68-74.  We have selected and evaluated several basic sorbents which would

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co-spinnability, and regenerability,  and have obtained quantitative data
regarding the effect of temperature and moisture.  Work to determine quali-
tatively the effect of.oxygen and oxides of nitrogen is in progress.  Some

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                          II.  CHEMICAL BACKGROUND

     The consideration of organic amines in either polymeric or small-
molecule form for use as SO- sorbents for treatment of waste gases must
include detailed consideration of the chemistry involved.  Although a
review of all potential reactions involving organic amines and flue gas
components would be beyond the scope of this section, we will discuss the
more obvious reactions.

     Although the interaction of organic amines with SO- was reported as
early as 1843, one of the first systematic studies was carried out by
    (1)
Hill   , in which he studied the reaction of aniline with SO-.  Aniline
was found to form a 1:1 addition compound with SO-, and the decomposition
pressure of this compound was studied over the range of 3.5° to 50°C.
The dissociation pressure was approximately 0.005 atm. at 3.5° and 0.83 atm.
at 50°C.  The heat of dissociation was calculated to be 19,630 cal/mole.  In
the presence of water, normal sulfite and acid sulfite salts were formed
    , and these products had dissociation pressures markedly less than that
of the anhydrous addition compound.  Heating of the anhydrous complex at
100°C for 16 hours in a closed tube gave a colorless solid with no appre-
ciable SO- pressure, indicating that further reaction had occurred to form
a compound in which the SO- was bound in a different manner.

     It is possible that the product found here was a thionamic acid or its
          (2)
amine saltx   .
     Later work with homologs of  aniline, benzidine, phenylene diamines,
                              (3)
n-amylamine and n-heptylaminev  '  showed  that  compounds of SO- and amines
were formed at S0_/amine  ratios of  1:2 and  1:1.  Heats of formation for
several of these,  calculated  by the Clausius-Clapeyron equation, ranged

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amine which were reported as 3,500 cal/mole and 6,400 cal/mole, respectively.
These anomalously low AH values could not be explained.
             has studied the reaction of S02 with N,N-dimethyltoluidines  and
N,N-dimethylaniline and has found AH values to be in the 21,000-24,000  range,
except  for N,N-dimethylaniline (11,600 cal/mole).  A similar study was  carried
out with  trimethylamine^  , which was found to form addition products similar
to those  formed by aromatic amines.  The equilibrium S02 pressure, however,
at 55°C was approximately 0.055 atm, whereas that for aniline was 0.83  atm.
Bright  and Jasper^  ' prepared the 1:1 triethylamine-SO- complex and distilled
it at 93.5°C (751 mm).  This indicates that the dissociation pressure of  this
compound  is less than 0.98 atm  at 93.5°C.  The inference from this is  that
the more  basic amines (trimethylamine, K,  = 4.24; triethylamine, Kfa = 3.35;
vs. aniline, K, = 9.41) form more stable complexes with SO--  Steric factors
are also  important, e.g., the SO- complexes of N, N-dimethyl-p-toluidine and
N,N-dimethyl-m-toluidine are much more stable than that of N,N-dimethyl-o-
toluidine.  This is considered to be due to shielding of the nitrogen by  the
                  (4)
ortho methyl group v ' .  Steric effects will be discussed more fully later.

     From the results of Hill and Fitzgerald,  however,  it also appears  that
subsequent irreversible reaction of SO- with aromatic amines (primary,
secondary, or tertiary) and primary aliphatic amines does not occur rapidly
at temperatures in the 25-50°C range.

     The  reaction of ammonia and aliphatic amines with S00 under anhydrous
                                             st\          2
conditions has been studied spectrochemically^  .  Ammonia reacts spontane-
ously with the evolution of heat to form thionylimide (HNSO), NH.+,  HSO ",
    S3                                                           H      J
S2°5 '   The reaction between methylamine and SO-  produces methylthionyl-
amine (CH^NSO)  and the pyrosulphite t(CH.jNH3)2S205] .   The reaction between
dimethylamine  and S02  was reported to give a material which could be puri-
fied by vacuum distillation without decomposition.   'This product was con-
sidered to be  the molecular complex (CH3)2NH.S02  on the basis of spectral

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     Sulfur dioxide and ammonia have been  shown  to undergo a  redox  reaction
which leads to ammonium sulfamate and  free sulfur    .
     Bateman, Hughes, and Ingold*1  ' and  Byrd^  ' have discussed  the bonding  in
amine-SC^ COItlP°un^s'  It is agreed that  the bonding is between  sulfur  and
nitrogen to  form a  charge-transfer complex:
     Under severe conditions,  S09  is  a powerful oxidizing agent  for many
                 (9)             z
organic compoundsv   ;  for  example,  toluene  is  oxidized  to benzoic acid, and
aniline decomposes  explosively in  the range of 200-400°C under 50-2500 atm
pressure.  It  is considered  that under conditions  suitable  for sorption of
S0« from flue  gases and  regeneration  of  the sorbent,  these  reactions are
negligibly slow.

     Other possible reactions  which could lead to  irreversible reactions of
organic amines with flue gas constituents include:
          1.   Oxidation  of SO- to  SO- by 0. -  particularly  in the
               presence of  water.   It  is  known  that  in a solution of
               sulfurous  acid,  in the  absence of oxygen, dispropor-
               tionation  into sulfuric acid  and free sulfur  will  occur
               whereas  in the presence of oxygen, formation  of sulfuric
               acid  will  occur^   .
               Subsequent  reaction with  amino  groups would  form amine
               sulfate  salts which would not be  thermally regenerable.
               Redox  processes  between SO^  and oxides  of nitrogen.   It
               is possible that oxidation-reduction  reactions between  NO,  0
               and  S09  could occur in a  manner similar to the lead

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              In addition,  the complex equilibria between the oxides of
              nitrogen,  oxygen,  and water can lead to the formation of
              nitric acid which would compete with S02>  probably irre-
              versibly,  for amine sites.
          3.   Reactions  between oxides of nitrogen and amines.   Dragq
              and coworkers have investigated the interaction of nitric
              oxide with amines^   ,  and  reported that primary and sec-
              ondary amines react readily with NO according to the follow-
              ing scheme:
                                            R2NHNO
     The aliphatic tertiary amine,  trimethylamine,  forms an addition compound,
(CH«)~NN909,  which is unstable.   Weaker tertiary amines such as pyridine, a.nd
highly hindered primary amines such a t-butylamine,  do not form addition
compounds.
                                            (12)
     Nitrogen dioxide has also been reported     to  react with amines to form
addition compounds which are stable only at low temperatures,  and as with NO,
do not form with hindered amines,  such as a,  a'-lutidine.  Probably more
important than competition with  S0_ for sorption sites however, is the fact
that N02/N20^ reacts with a variety of organic materials; a few of these
reactions are listed below:
          1.   Nitration of paraffins,  alcohols,  ethers.
          2.   Formation of nitrous  acid esters with  alcohols.
          3.   Nitration of aromatic nuclei,  even at  80°C.
          4.   Formation of nitrous  acid and subsequent reaction with
              amines:
                       HN02 + RNH2  - >  ROH   (deamination)

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              Although tertiary amines are generally considered
              unreactive toward nitrous acid, they sometimes react
              with cleavage of an alkyl group:
                       R2N-CHRj, + HONO

     Although many of these reactions do not occur at appreciable rates at
low temperatures (< 100°C) there may be sufficient reactivity over long
periods of use to severely damage a sorbent system.

     Although these side reactions are all possibilitiess it is difficult to
estimate the relative importance they might have (depending on amine type,
temperature, humidity, concentration of various gases, etc.) or how they
might quantitatively affect regenerability.

     Clearly, tertiary amines are to be preferred on the basis of greater
stability toward a variety of side reactions with S0_ and other agents, and
aliphatic amines are preferable because of their higher basicity and their
generally greater resistance to oxidation by most oxidizing agents,  such as
atmospheric oxygen.  This is not to imply, however, that tertiary aliphatic
amines are completely unreactive with respect to oxidation; nonperoxidic
agents can convert tertiary aliphatic amines to enamines, which are then
subject to further oxidation or hydrolysis:
                          [01                H2°
              R2NCH2CHR'  L J< > R2N-CH=CHR' — =L->> R'CH2CHO + R2NH

     Peroxidic agents or ozone convert  tertiary amines to N-oxides:
     The substitution of alkyl groups on nitrogen generally results in a
maximum in base strength for the secondary amine  and a decrease in basicity
for the tertiary amine.  The order of base strength is:
              R2NH > RNH2 > R3N > NRj

     The basicity of an amine in aqueous solution is not necessarily directly

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amine acts as a proton acceptor.
              R N + H20      N R3NH+ OH"

The same would be true in reactions with Bronsted acids.
              R3N -f 'HX

Reaction with electron acceptors larger than the proton (e.g. S02)
               J      f- \       J    *•
involves close approach of the acceptor molecule to the nitrogen, and  steric
effects (especially the so-called "F-strain") become the dominant factor  in
determining the stability of the complex.

     For example, the stability of amine-'trimethylboron adducts decreases  with
increasing substitution of alkyl groups on the nitrogen much more rapidly
than does the base strength toward protons.
                            	\ n D . xTn 1
              R3B + R; N
                         \
              Amine           \             KJ4 J(CH,),B adduct]
              EtNH2        5.6 x 10"4               0.0705
              Et-NH        9.6 x 10"4               1.22
                                   -4
              Et3N         9.7 x 10          Too highly dissociated to
                                             be measured.
Hence, the order of basicity toward the reference acid trimethylboron becomes:
If the reference acid is tri-tert-butylboron,  steric factors become completely
dominant, and the order of stability is:
                    RNH2
     A discussion of this behavior can be found in the work by Brown and
             (13)
collaborators    .   Although tertiary amines are less basic than the corres-
ponding secondary amines, particularly toward bulky Lewis acids, the much
higher stability toward side reactions would make them the most promising
sorbents,  providing the alkyl groups around the nitrogen are small.

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                     III.   SCREENING OF BASIC SORBENTS

     Our  first  task was  to select  basic nitrogen-containing polymers  which
were known  to be  cospinnable with  fiber-forming materials,  and  to obtain
information regarding the effects  of temperature,  S0_ concentration in  the
gas phase,  and  moisture  upon the capacity and rate of sorption.   A styrene/
dimethylaminopropylmaleimide copolymer (SSQ) and a copolymer of  2-vinyl-
pyridine  with 2-methyl-5-vinylpyridine (GIQ) were  chosen  as typical materials
covering  a  wide range in basicity  from the strongly basic tertiary alkyl
amine  in  SSQ to the relatively weakly basic pyridine nitrogen in  GIQ.
                                                   CH2  - CH - CH2 - CH
          SSQ             ^N\                     GIQ
                        CH3     CH3

     In addition  to  the above  polymers, a number of other polymers were
evaluated and  the results are  included  in this section.

A.  STYRENE/DIMETHYLAMINOPROPYLMALEIMIDE COPOLYMER (SSQ) AND
    2-VINYLPYRIDINE/2-METHYL-5-VINYLPYRIDINE COPOLYMER (GIQ)
     In order  to  gain  some  information  regarding the S09 sorption properties
of SSQ and GIQ, both as the pure materials and in fibers, samples were ex-
posed to pure  SO   at atmospheric pressure, and the weight gain was determined.

1.  S09 Capacity  of  Pure Sorbents

     One gram  samples  each of  SSQ and GIQ were placed in a chamber containing
pure SOy gas at room temperature.  The  samples were weighed at two intervals
to determine SO- uptake.

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g/g
0.435
0.459
so2
Pure SSQ
mole/equiv
1.95
2.06
Uptake

g/g
0.461
0.976

Pure GIQ
mole/equiv
0.81
1.72
                3 hours
               24 hours

     These data indicate that both of these materials form 2:1 complexes with
S0« under the pure gas.  However, these secondary complexes appear to be weak
and do not form to any appreciable extent under conditions where the S02 con-
centration is lower (see Sec. VI).   In addition, such 2:1 complexes have not
been reported for non-polymeric materials and are therefore of little import-
ance to the present work (see Sec. II).

2.  SO  Capacity of Sorbents in Polypropylene Fiber

     Five-gram samples of fibers containing (1) 2 parts per hundred (phr) of
SSQ, (2) 2 phr GIQ, and (3) no S09 acceptor,  were exposed to pure SO- in the
same fashion as above.  At each time interval the weight gain of the blank
was subtracted, and the S0_ sorption of the acceptor in each fiber was calcu-
lated.
                                                   S02 Uptake
               1.75 hours
              18.75 hours
SSQ in
Polypropylene Fiber
g/g
J.410
).410
mole/equiv
1.84
1.84
GIQ in
Polypropylene Fiber
g/g
0.529
0.801
mole/equiv
0.93
1.41
     These results show that the S02 sorption behavior of SSQ and GIQ under
pure S02 in polypropylene fiber is parallel to that of the pure materials.
The fibers used here were spun as part of another program, and contain much
lower levels of acceptor than used in later work.

3.  SQ2 Capacity of SSQ in a Flow System

     The effectiveness of dry SSQ in removing SO  from a S02~N2 gas stream
containing approximately 11,000 ppm S02 was determined at several tempera-

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tures in the range 35-95°C.  In each case a 1 g fixed bed of 60-100 mesh
SSQ was used.

     At each temperature the S02 concentration in the effluent gas remained
below 50 ppm (our lower limit of detection) for a certain time, then rose
rapidly to the feed concentration  (see for example, Figure 1).

     The capacity of SSQ shows a strong temperature dependence.  The break-
through point (where the S02 concentration in the effluent gas reaches that
of the feed gas, and no further sorption of S02 takes place) is reached
earlier at higher temperatures, and the total SO- capacity is consequently
smaller (see Experimental, Sec. X, for the relationship between breakthrough
time and capacity).  For example,  the breakthrough point at 35°C occurs at
approximately 0.190 g/g whereas at 95°C it occurs at 0.033 g/g.  The data
(Table I) also show that at 35°C the SSQ bed is capable of reducing the S02

                                   TABLE I
                        Sorption of S02 by SSQ (g/g)
        	Dry	      Presence of Water Vapor
        1st Appearance    Breakthrough   1st Appearance    Breakthrough
T°C     of S02  (>50 ppm)     Point       of S02  (>50 ppm)      Point
95
85
75
55
35
0.0056
-
0.0636
0.116
0.162
0.0357
0.0602
0.110
0.139
0.187
0.0535
-
-
0.145
0.169
0.0781
-
-
0.185
0.196
      Feed gas  concentration approx.  11000 ppm
      Flow rate 21.2 ml/min.
concentration in a gas  stream  containing approximately 11,000 ppm at a flow
rate of 21.2 ml/min.  to less than 50 ppm until a capacity of 0.162 g/g is
reached.  At 95°C, however, SSQ  can reduce  the SO- concentration in a similar
gas stream to less than 50 ppm until only 0.0056 g/g is sorbed.  In addition,

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 11000

10000




 8000




 6000




 4000




 2000




 >50
              Feed  gas level
E
CL
CL
 eg

O
UJ
         10
     JL
     80    100  120    140   180    200    220   240    260   280

                    Time in Minutes

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if a sample loaded with S02 at a lower temperature  is raised to a higher
temperature, SI
later section.
temperature, S09 is driven off.  Regeneration behavior is described in a
4.  S(>2 Capacity of SSQ in the Presence of Water Vapor
     The reaction of amines with SO- in the presence of water should lead
to a more favorable equilibrium for the reaction, since S09 would be more
tightly bound as the bisulfite or sulfite salt than as the association
    !  (1)
complex   .

     Samples of SSQ were equilibrated with water vapor at room temperature,
then treated with a water-saturated S09-N9 gas mixture and the SQ_ content
                                      ^.  £,                       £.
of the effluent gas stream determined as a function of time. The S0_ capa-
city was significantly increased, particularly at higher temperatures.  At
lower temperatures, where the capacity of the dry polymer is already high,
the improvement was much smaller, as is to be expected (Table I).

B.  POLYETHYLENEIMINE (PEI)
     Montrek 12 (Dow Chemical Co.) polyethyleneimine, a liquid,  was placed
on Chromosorb W (a calcined silica) as a support material at a level of 1 g
Montrek on 5 g of Chromosorb.  At 35°C the breakthrough point occurred at
16.5% of the 1:1 stoichiometric value (Table II).  However, since poly-
ethyleneimine has a very low equivalent weight (43), this is a relatively

                                  TABLE II
                  Sorption of SC>2 by Various Materials (g/g)
PEI on Chromosorb

Benzoylated PEI
GIQ
Aminopolyurea
IRA-400
VTQ
         SOo-N2 mixture   10,000 ppm S02
         Flow rate        21.2 ml/min.
                                        15
35°
150°
35°
35°
35°
31°
95°
75°
Dry Water Vapor
0.246 0.990
0.91
0.100
0.0099
0.074
0.08
0.138
0.188
Stoichiometric
1:1 Capacity
1.47
0.260
0.568
0.164


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high capacity on a weight basis (0.246 g/g).  At 150°C. considerable sorption
of SO. occurred as determined by integration of the time vs. effluent S02
curve (0.91 g/g, 60.9% of stoichiometric), but poor correlation with the
weight gain (0.221 g/g, 14.8% of stoichiometric) was obtained.  Examination
of the sample after the run showed that extensive darkening and degradation
had taken place, and loss of volatile decomposition products probably caused
the discrepancy.

     Polyethyleneimine has been spun into polypropylene fiber at high temper-
atures (about 300°C) without significant decomposition.  The decomposition
observed in the present work is probably due to reaction with S02 at high
temperatures.  The higher capacity for S02 at 150° compared to 35° is
probably due to increased rate of side reactions as discussed in Section II.
Although in its present form PEI is not useful it seems that polyethylene-
imine merits further consideration since: (1) polyethyleneimine and its de-
rivatives made by reaction with alkyl halides, anhydrides, etc. are cospinn-
able with polypropylene; (2) its low equivalent weight gives high potential
S0_ capacity.

     The presence of moisture has a strong effect upon the SO. uptake of
unsubs-tituted PEI.  At 35°C, dry PEI .on Chromosorb reaches the breakthrough
point at a capacity of 0.246 g/g, whereas in the presence of moisture, the
breakthrough occurs at a capacity of about one gram of SO- per gram of PEI
(Table II).  A blank run with Chromosorb W support material alone under the
same conditions showed only an insignificant SO- absorption.

     We prepared a solid derivative of PEI by reaction with benzoyl chloride.
The softening point of this product is 90°C, and the equivalent weight,
determined by titration of the amino groups, is 246.3 (the equivalent weight
of the unsubstituted material is 43).  Thus, somewhat more than half of the
amine nitrogen was benzoylated,  and is inactive.  This material was evaluated
in the presence of water vapor,  and breakthrough was reached at 38.6% of stoi-
chiometric capacity,  a loading of 0.100 g SO- per gram of sorbent.  Thus it
appears that benzoylation of polyethyleneimine to this degree not only raises
the equivalent weight,  thereby reducing the potential capacity, but the remain-
ing free amino groups are less reactive toward SO-, probably because of steric
effects.

-------
     Polyethyleneimine  is 9 highly branched  polymer  containing  primary,
secondary, and tertiary amino groups.   Since primary and  secondary  amino
groups lead to undesirable side  reactions, and may be responsible for  the
extensive decomposition observed at  elevated temperatures,  the  most prom"
ising course may be to  react the polymer with a  lower-alkyl  alkylating
agent to convert all the amino groups  to tertiary amino groups.  This
would, in addition, lead to only a relatively small  increase in equiva-
lent weight.  This is planned for fixture work.

C.  POLYVINYLPYRIDINE
     Polyvinylpyridine  (GIQ) was exposed to  a 11,000 ppm  SO--N- gas stream
at 35° in the same manner as SSQ.  The breakthrough  occurred at only 0.0099
g/g, less than 27. of the stoichiometric 0.568 g/g (Table  II),  This is
probably due to the much weaker  basicity of  the  pyridine  nitrpgen as com-
pared to the tertiary aliphatic  nitrogen of  SSQ,  and a consequently higher
SOj partial pressure of the complex.

D.  AMINOPOLYUREA
     A polyurea containing tertiary  amino  groups was prepared in the labor-
atory by the reaction of 2,4-tolylenediisocyanate w;Lth N-methyl-bis(amino«-
propyl) amine:
The SO   sorption  characteristics  at  35°  are  shown  in  Figure  2.  Comparison
with Figure  1  (SSQ  at  35°)  shows  that  this material does not give as sharp
a rise to  the  breakthrough  point  as  does SSQ.  This indicates that  the
rate of  sorption, at 35°  at least,  is  slower.  In  addition,  only 45%
(.074 g/g) of  stoichiometric capacity  was reached  (Table II)  whereas SSQ
reached  almost 85%  (0.187 g/g)  of stoichiometric under  the same conditipns.

-------
CO
12000
 11000
10000

 8000

 6000

 4000

 2000

<50
                                  Feed  gas level
                                     120  .140    160
                                       Time in Minutes
                                            180   200   220   240

-------
E.  ANION EXCHANGE RESIN
     Dry anion exchange resins have been  studied as  potential  SCL  sorbents
Of the materials studied, the best performance was obtained with Rohm and
Haas IRA-400, a commercial quaternary ammonium chloride anion  exchange resin,
but the S02 concentration range  in this study was much higher  (.018 - 1 atm)
than that used in our work.  We  considered  it of interest  to evaluate this
resin by our method to see how effective  ion exchange resins are in compari-
son with the free-base polymers  we have been evaluating.   Results with poly-
ethyleneimine and SSQ run under  similar conditions show that the anion
exchange resin is definitely inferior to  either SSQ  or PEI (Table  II).  The
quaternary ammonium halide is a  salt, and reaction with S0_ would  require
displacement of the halide:
                  Iffi  (C)        o  x     Iff)    Q
                -iTciu + so     =^  - N^ksor + uci
An anion  exchange  resin  in  the  hydroxyl  form, however,  should react readily
with  S02:
Resins  in the hydroxyl  form have  low thermal  stability, however.

      Free base polymers can form  salts  directly with  S02  in the presence of
water:
                                —NH  HS03

      Ion  exchange  resins,  therefore,  must  depend  upon  secondary  forces  to
bind  S0_,  whereas  with free base resins  true  complex formation takes place.

F.  STYRENE-METHYLVINYLETHER-DIMETHYLAMINOPROPYLMALEIMIDE
    TERPOLYMER  (VTQ)	
      VTQ,  a  terpolymer of  styrene,  methylvinylether, and dimethylamino-
propylmaleimide  (mole  ratios 1:1:2),  has been evaluated in  the absence  of
water vapor  at 95°C and 75°C.   This material  has  a  1:1 stoichiometric S0_

-------
capacity in the same range as SSQ (0.249 g/g for VTQ,  0.223 g/g for SSQ).
Its breakthrough point occurred at 0.138 g/g at 95°C and at 0.188 g/g at
75°C (Table II).  This is substantially better performance than that of
SSQ.  Further work with VTQ is in progress.

-------
                                 IV.   FIBERS

A.  POLYPROPYLENE-POLYETHYLENEIMINE  FIBERS
1.  Spinning
     Spinning  conditions  used were those  designed  for  low  levels of polymeric
additives.  Compatibility with  the polypropylene  (Hercules  Pro-fax 6501 +
heat stabilizer) was  satisfactory, and  good  fibers of  about 15 denier were
obtained.  These fibers contained 9-11% of PEI  by  weight.   Some exploratory
work will be required to  determine the  optimum  conditions and techniques
of S02 acceptor loading and  fiber spinning for  obtaining fibers having the
maximum  amounts of  S0» acceptor consistent with good fiber  properties.

2.  Effect of  Temperature
     S0? sorption experiments were run  on an undrawn 9.17, PEI fiber in the
presence of moisture  at temperatures of 35°,  123°,  and 150°C.  The respective
sorptions are  shown in Table III.  At the two higher temperatures a darken-
ing of the fiber occurred,  indicating decomposition,

                                  TABLE III
          SO-  Sorption of Polypropylene Fiber Containing 9.1% PEI
                       In Presence of Water  Vapor
Temp.
123
150
35
35
35
g/g on fiber
0.0127
0.0189
0.0167
0.00435
0.0253
g/g on sorbent
0.141
0.208
0.184
0.0478
0.228

(degradation apparent)
(degradation apparent)

(dry)
(11.1% PEI in fiber)
             10,000  ppm SO-  in  S02-N2 mixture
             21.2  ml/minute  flow rate

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3.  Effect of Moisture
     S02 sorption of an undrawn 9.1% PEI fiber at 35°G, both dry and in the
presence of moisture, was determined.  The respective sorptions were 0.00435
g/g and 0.0167 g/g (Table III).  This increased sorption of a PEI fiber in
the presence of moisture is in agreement with the results obtained from
samples of pure PEI and SSQ equilibrated with water vapor at room temperature.
High hydrophilicity of fibers may be advantageous in improving their per-
formance as S0_ sorbents.

4.  Drawn vs. Undrawn Fibers
     Drawing of fibers increases the orientation of the polymer chains.
Although the changes in diffusion and sorption properties are complex, and
depend upon many variables, the general effect of orientation is to decrease
the permeability of the polymer matrix to substances such as water    '
However, this decrease in permeability is greater in the direction parallel
to the direction of orientation than normal to it.  To gain some information
on what the magnitude of this effect might be, the SO- capacities of drawn
(3:1) and undrawn samples of a 9.1% PEI fiber in the presence of moisture at
35°C were compared. The respective S0« sorptions were 0.0168 g/g and 0.0147
g/g.  The slightly higher S0_ sorption capacity and faster rate (Figure 3) of
the drawn fiber may be attributable to its greater (1.73-fold) surface area.
It would appear that this effect was sufficiently great to more than offset
any decrease in sorption which might be expected to occur due to an increase
in the orientation of the fiber.  Further work will be needed to establish
the generality and magnitude of the effect of orientation on rate and capacity,

5.  Effect of Polyethyleneimine Level
     In a comparison of the S02 sorption capacity of two undrawn polypropyl-
ene-PEI fibers containing different amounts (1.17. and 11.1%) of PEI, at 35 °C
in the presence of moisture, a positive correlation between the PEI level and
the S02 sorption capacity was observed.  The S02 sorptions were 0.0167 g/g and
0.0253 g/g (Table III).

-------
N>
           10000
            8000
            6000 h
            4000
            2000
               0
                         A PEI on CHROMOSORB  21.2 ml/mm.
                          ® 9.1% PEI  21.2 ml/min.  J-/ draw ratio
                         A 11.1% PEI  2l.2ml/min. undrawn
                          o 9.1 % PEI  21.2 ml/mm. undrawn
40
                               80
100    120    140

  Time in Minutes
160    180   200   220
                     Figure 3. Effect of flow rate, PEI level, and draw ratio upon rate of S02 sorptioa

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6.  Polypropylene Fiber
     As a control, a similar fiber without PEI was spun, and its sorption  of
SO- determined at 35°C in the presence of moisture.  Sorption was negligible,
and the weight gain of the sample was only 0.00093 g/g.
7-  Sorption Rate
     The sharpness of the breakthrough curve, which represents the sharpness
of the advancing front of S0? through the sorbent bed, is dependent upon  the
rate of sorption of S0? by the sorbent (assuming the chemical equilibrium
between the gas and sorbent phases ;Ls favorable).

     Rate-controlling factors can be: 1), the rate of reaction of S02 with
the acceptor polymer; 2), the rate of diffusion of S0? through the sorbent
matrix; 3), the surface area of the sorbent; 4), flow rate of gas through the
bed.  For example, if any of the above factors were highly unfavorable, a
curve such as (1) would be expected,  whereas if equilibration between gas and
sorbent were extremely rapid a curve such as (2) would be expected.  Of course,
the more closely actual curves approach (2), the less SO™ "leakage" and the
more effective the system.
       Effluent
       so2
       Concentration
                                      time
     Dry SSQ and PEI on Chromosorb,  for example,  give curves which approach
type (2) (see Figures 1,  3).

-------
     The effect of flow rate, PEI level, and draw ratio upon the shape of the
breakthrough curves was briefly  investigated (Figure 3).  Increased draw ratio
and increased PEI level both  gave more favorable curves.  In the case of the
drawn fiber, the greater  surface area and  shorter diffusion path through the
fiber are probably responsible,  and  in the case of the higher PEI level, the
diffusivity of SO^ in  the fiber  may  be higher  since the mixture contains more
PEI and less polypropylene, although increased hydrophilicity may also be a
factor.

B.  POLYPROPYLENE-SSQ  FIBER
     In one investigation of  the SO- sorption  capacity of an undrawn poly-
propylene fiber containing 8.337. SSQ in  the presence of moisture; at 35°C, a
high percentage of the 1:1 stoichiometric  capacity was attained.  Although the
sorption did not proceed  with great  rapidity,  it steadily increased, and at
termination of the experiment a  loading  of 0.0136 g S0»/g fiber (0.163 g/g on
SSQ) had been reached  (see Figure 4).  Although the rate was relatively slow
compared to that of  SSQ powder   (cf  Figure 1)  the capacity compares favorably.
Considerations concerning the rate of SO-  sorption were discussed in the pre-
vious section, and it  is  probable that the rate 6f sorption by polypropylene-
SSQ fibers can be increased substantially  by the use of the same techniques.

-------
tsJ
12000
11000
10000


 8000


6000


4000


 2000


 >50
                               Feed gas level

                 20   40   60   80  100      130
                                         Minutes
                                                 160
190
220    250
                          Figure 4. SG2 sorption of undrawn polypropylene-SSQ fiber

-------
                             V.   REGENERATION

A.  POLYPROPYLENE-POLYETHYLENEIMINE FIBER
     The performance  of  an  undrawn  polypropylene-PEI  fiber  (11.1% PEI) in the
presence of moisture  has been  determined  during an SO, sorption-regeneration-
sorption operation  (Table IV).   In  the  initial sorption, breakthrough occurred
at 0.0252 g/g  on  fiber.   During  the regeneration only 0.0097 g/g of the sorbed
S02 was released, probably  indicating irreversible reaction between S0? and
PEI.  A second sorption  under  the same  conditions gave a S00 uptake of only

                                  TABLE  IV
                  Regeneration of PolypromOpJie-PEI Fiber

(1)
(2)
(3)
(4)


Sorption
Loss on regeneration
Residual S02
Second sorption
Total (3 + 4)
g/g on Fiber
0.0252
0.00971
0.0155
0.00874
0.0242
g/g on PEI
0.228;
0.0873
0.141
0.0787
0.220
          Sorption  -  35°C,  10,000  ppm SO_-N_ mixture,  21.2 ml/min, water
                      vapor.
          Regeneration  -  95°C,  N-,  21.2  ml/min,  dry.

0,00874 g/g.  Possible  reasons  for this  behavior have  been discussed earlier
in this report.

B.  MULTIPLE SORPTION-REGENERATION WITH  SSQ
     In accordance  with plans to study the efficiency  of  S02 acceptors in
multiple sorptions  and  regenerations,  the behavior  of  60-100 mesh SSQ in the
presence of moisture  was  investigated in this  respect.  Data were obtained
on four S02 sorptions at  55°C and  three  intervening regenerations at 95°C.

-------
     Feed gas concentrations of 10-12,000 ppm SO,, (saturated with water vapor)
were used for the sorption cycles at 55'C at a flow rate of 21.2 ml/min.  Re-
generation was accomplished by raising the sample temperature to 95°C.and
flushing with dry nitrogen at the same flow rate.

     There is a loss in SO,, capacity with succeeding cycles.  A capacity of
0.181 g/g on the first sorption was reduced to 0.112 g/g on the fourth sorp-
tion.  However, the removal of S02 on each regeneration appears to be fairly
complete (Figure 5).  This would suggest a deactivation of the sorbent by the
process, rather than a cumulative irreversible sorption of S02(as occurs with
PEI).  A possible explanation for this is hydrolysis, leading to subsequent
internal salt formation:
                 N
      Evidence  that water  is  important  in  the deactivation process  is  given  by
work now in  progress where it appears  that dry SSQ can be carried  through
several  cycles without  significant  loss in capacity.

      The data  are somewhat erratic,  especially in the second  regeneration and
the third sorption.  This may be  due to changes  in the moisture  content of
the sample because of changes in  structure which are occurring.
                           Regeneration of SSQ
                                                 Residual S02 After
           Cycle  No.   Sorption  (g S02/g SSQ)     Regeneration (g/g)
              1               0.181                  0.0056
              2               0.158                 -0.0201
              3               0.089                  0.0167
              4               0.112
           Sorption - 55°C, 10-12,000 ppm  S02-N2  mixture,  21.2 ml/min,
                     water vapor.
           Regeneration  -  95°C,  N-,  21.2 ml/min,  dry.

-------
            Sorption
            Regeneration
            Flow Rate
55°, IO-/2000 ppm SOS, Water vapor
95°, N2,  dry
21.2 ml/mm.
o
 CM
o>
.20
,18
.16


.14

.12
.10

.08

06



.04


.02
0

',02

— •
— i
••• i
i
- i
" i
"~ A
-f
• j
i
" J
l
i
"i
_'
'
_'
•
1 ;
1
T
f
<
••
> ->
A
ii
'
1
1
!
f /
/
i V
Ja
/
/
/
/
/
/
/
/
/

ww»
- J
r



A
^•r
<
'
'
•1
P /




, S02
Sorbed


*
/
/
, /
/ f ^
/ '
/
/
'

J
f
/
jr
/
/
/
( 1
/
/
r ^/

S02 Remaining
^ after Regeneration

i i I
                                     4   CYCLE NO.
             Figure 5. Sorption-regeneration of SSQ


-------
                          VI.  SORPTION ISOTHERMS
     The equilibrium constant  for gas-solid  reactions of the type shown below
is equal to the partial pressure of  the gaseous  component
                     =^  Ca°(s)
This is in agreement with the phase rule, C  - P + 2 = degrees of freedom.  In
the above example there are two  solid phases and one gas phase, and there are
two components, hence there is one degree of freedom, i.e., pressure or temper-
ature.  As a result, if the partial pressure of CO- in the system is greater
than the dissociation pressure of CaCO- at a given temperature, the reaction
will proceed to completion.

     In the case of reaction of  SO- with a polymeric amine

          S°
            2(g)
                                                    so2
this treatment does not apply,  since  there  is only one gas phase and one solid
phase present at any time.  A polymeric amine chain  reacted to any degree of
completion would be physically  inseparable  from other chains where the reaction
has proceeded to either a greater or  lesser degree,  i.e., a solid solution is
formed.  This system has two degrees  of freedom, and at constant temperature
the amount of gas sorbed will vary with the partial  pressure.

     The basic difference between an  adsorption process and our SO- sorption
system is that in the Langmuir  equation the maximum  capacity corresponds to a
monomolecular layer of adsorbed molecules on the surface of the adsorbent,
whereas in our system the maximum capacity  is related to the stoichiometric
amount of SO- which can react with the amine sites in the acceptor polymer.

     The sorption of SO  by dry SS.Q was determined at temperatures of 55, 75,
and 95°C under varying SO- partial pressures.  Results are shown in Table V.
The data were obtained by treatment of 1 g  samples of dry SSQ with S02~N2 gas
streams containing various levels of  SO- at a flow rate of 64.0 ml/min.  When
the SO- concentration in the effluent gas was the same as in the feed gas,

-------
                                  TABLE V
                          S02 Capacity of Dry SSQ
                                    95°C
          p S02 (atm)     Weight Gain (Y) (g/g)
          0.00327
          0.00526
          0.00752
          0.0108
          0.0170
0.0113
0.0196
0.0297
0.0360
0.0585
 £/Y
0.290
0.268
0.244
0.300
0.291
          0.000435
          0.00382
          0.00526
          0.00900
          0.0171
          0.0219
  75°C
0.0081
0.0501
0.0644
0.0974
0.119
0.134
0.054
0.0762
0.0817
0.0924
0.144
0.163
          0.000435
          0.00526
          0.0117
          0.0150
          0.0195
  55°C
0.0029
0.129
0.149
0.161
0.163
0.015
0.0407
0.0787
0.0933
0,120
equilibrium was attained.  The S0_ uptake of each sample was determined by
weight gain.  Plots of g S02/g SSQ vs.  equilibrium SO- pressure are shown
in Figure 6.  Sorption at 55° and 75°C shows typical type I (Langmuir)
curves in the S02 pressure range studied, and a plot of p/Y vs. p gives a
straight line (Figure 7).  Capacities at.various pressures were calculated
from the 55°C plot and are shown in Figure 6.

-------
U)
     0.16
     0.14
     0.12
     0.10
     .08
      .06
      .04
      .02
       0
               .002
006
                                          Equilibrium  S02  Pressure  (atm)
,010
.014
.018
                              Figure 6,  Dissociation pressure of SSQ-S02 reaction product.

-------
 .16
 .14
 .12
 .10
.08
.06
.04
.02
      CL
                                            75<
P S09 (atm)
                            1
 1
I
1
I
1
1
I

-------
     At 95°C, however, the capacity vs. pressure curve is nearly linear, and
the points on the p/Y vs. p plot are badly scattered.  It may be that the
curvature of the capacity vs. pressure curve is so slight that it is not dis-
tinguishable with our experimental data, or Langmuir behavior may not be followed
at this temperature,

     The Langmuir adsorption isotherm can be expressed as
                  Y bp
              Y = 1 + bp             Y = g S02 sorbed/g SSQ
                                    Y  = maximum g S02/g SSQ
it follows that                      b = constant
                                     p = partial pressure SO-
The slope of the p/Y vs. p plot equals 1/Y  and the intercept equals 1/Y b.
                                       75°                     55°
              Slope  (l/Ym)*          5.07                    5.49
              Y                      0.197 g/g               0.182 g/g
               m           !
              Intercept  (   b  )*     0.0533                  0.0126
              b            m         95.3                    436.7

              * Determined by  the method of least squares.

     The maximum capacity of 0.182 g/g at 55°C is 81.6% of the stoichiometric
capacity of SSQ (0.223 g/g) and, of course, has meaning only if the Langmuir
isotherm is followed at  much higher S02 pressures.

     A series of log p vs -  plots at various loadings (isosteres) were
made from the data, and  AH of  sorption calculated from the slope of the lines
for several loadings of  SO, on SSQ:

-------
               Isosteric Heat of Sorption of S02 °n Pyy SSQ

                Loading, g/g                AH. Real/mole
                   0.02"                        - 18.3
                   0.06                        - 17.9
                   0.12                        - 14.7

     These figures are in the appropriate range for this type of process,
and show, as expected, that the heat; of sorption is lower at higher
loadings.

-------
                       VII.  DISTRIBUTION COEFFICIENTS
     A rapid method for obtaining thermodynamic distribution coefficients
between SO^ in the gas phase and S0~  in solid sorbents has been investigated.
This method involves  the use of the candidate sorbent as a substrate in a gas
chromatography column^  '     .
     A sample of  S09  is  injected  into  a  helium  carrier gas stream and the
     le of gi
determined.
volume of gas required to carry the sample through the column (V ) is
 If  it  is  assumed the pressure drop through the sample is  negligible
                       V    (S0_ in solid ph^se)
                       V  ~ (S09 in gas phase)
                        S      £•
                   t  = retention time
                    r
                   F  = carrier gas flow rate, ml/min.
                   V  = retention volume
                    r
                   V  = volume of solid absorbent
                    s
                   C  = distribution coefficient

     Determinations were carried out at three temperatures using a 1-1/2"  x
 1/4" O.D. column packed with 0.175 g 60-100 mesh SSQ.
                                                   C
                                                 4800
                                                 1330
                                                  740
     A plot of log C vs. 1/T yields a straight line  (Figure 8).  Work is in
 progress  to determine the usefulness of these data  in evaluation of sorbents.

-------
    8 r-
    7  -
    6  -

    5

    4 h
         o
          o»
          o
1000
    9
    8
    7
    6

    5

    4
                           i/T°Kxi03
                          I     	!
     2.5
2.6
2.7
2.8
2.9
3.0
         Figure 8. Log distribution coefficient vs. 1/T for SSQ

-------
                        VIII.  EFFECT OF FLOW RATE

     One-gram beds of 60-100 mesh SSQ were contacted with a 5200 ppm SO.-N,
gas stream at several flow rates at 55°C.  The loading at breakthrough was
determined.

                                                      Relative Space
                                                      Velocity
Flow Rate
ml/min.
21.2
43.0
87,5
177.0
271.0
g S02/g SSQ
0.139
0.129
0.142
0.128
0.129
                                                           1
                                                           2.06
                                                           4.12
                                                           8.33
                                                          12.78

     The capacities at each  flow  rate agree within + 5 percent, indicating
that equilibrium is attained  in each case.  If  the density of SSQ is con-
sidered to be about 1, the absolute space velocity at a flow rate of 271.0
ml /rain, is 16,260 ml/hr/ml.   Further experiments are being carried out at
higher flow rates to determine where non-equilibrium conditions begin.

-------
                             IX.  EFFECT OF NO-

     Although N02 is a minor constituent of flue gases, higher levels than
those originally present  in the gas  (~. 00025%) might occur because of further
oxidation of NO in  the sorbent bed.  In view of the potential reactivity of
N02 with amine sorbents a brief investigation of the gross effect of NO.
upon SSQ was undertaken.

     A sample of dry SSQ was treated with N02 until 68.4% (0.1601 g/g) of
the stoichiometric  amount was taken up.  This sample was then exposed to a
5260 ppm S02-N2 gas mixture at a  flow rate of 42 ml/min at 55°C.  Break-
through was reached at 0.026 g/g.  Another sample, handled in the same way
but without the N02 treatment broke  through at 0.129 g/g.  Although the NO.
treatment reduced the SO. capacity of the sample, the total number of amine
groups reacting (with N02 and SO,,) was greater (80.1% vs. 58%).  This may be
due to either partial displacement of the NO. by SO. or the affinity of the
remaining free amine sites for SO. is not reduced by the presence of NO. on
other sites as much as if they were occupied by SO..

     Although this  experiment indicates that the presence of NO  may have
serious effects upon the  SO. capacity of materials such as SSQ, it would be
much more informative to  conduct  further experiments in the presence of
relatively low levels of  NO., NO, and other gases and SO. simultaneously;
this would present  a more competitive situation and would approximate the
conditions of service more closely.  In addition, kinetic effects, such as
slow displacement of NO.  by SO. (which would lead to an apparent equilibrium
favoring the NO. complex  over the S02 complex) would be minimized.  Modifica-
tion of our present apparatus will be required to carry out this work.

     Experiments to determine the effect of other flue gas components are
under way.

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                              X.   EXPERIMENTAL

     The apparatus  (Figure 9) for  the determination of SO. concentration con-
sists of a F&M Model  720 dual-column, programmed-temperature chromatograph
with a Leeds and Northrup Speedomax G recorder.  Helium carrier gas is used
at a flow rate of 40  ml/min.  A  25 ml.  gas  sampling loop is used with a Perkin-
Elmer 154-0068 Precision Gas Sampling System.  The chromatographic column is a
1-foot by 1/4-inch  stainless steel tubing packed with W. R. Grace grade 12,
60-100 mesh silica  gel.  At 135°C  the retention times for nitrogen and SO,
are 48 sec. and 209 sec. respectively.  Gas mixtures of S02 and nitrogen
containing 5260 ppm,  435 ppm, and  41 ppm SO- were obtained from the Matheson
Company.  Other gas mixtures are prepared in the laboratory by blending
Linde LC-3 99.997%  nitrogen gas  and Matheson anhydrous grade 99.98% S02-  Flow-
meters are used to  set  the approximate  relative amounts of SO- and N-.  The
actual concentration  of SO- is determined by the area of the SO- peak in the
gas chromatogram.   The  relationship of  peak area to concentration was estab-
lished over a wide  range of SO-  concentration by simultaneous determination of
the SO- content of  a  known volume  of gas by reaction with standardized iodine
solution.

     The apparatus  for  exposing  the sample  to the gas stream consists of a
fan-circulating air oven containing a 6-1/2-foot by 1/4-inch coil of stainless
steel tubing to bring the gas mixture to thermal equilibrium.  This leads to a
14 cm by 10 mm cylindrical stainless steel  chamber.  A weighed amount of the
candidate SO -acceptor  is placed in this chamber and sandwiched between two
wads of glass wool.   The gas passes through this chamber, then out of the oven
to the gas sampling loop of the  G-C.

     The gas containing 41 ppm SO- gives a  barely discernible peak on the G.C.;
this represents our lower limit  of detection.

     In each run the  SO- concentration  in the  feed gas was set at the desired
concentration.  The exact concentration was determined by the gas chromato-
graph.  In most cases the flow rate of  gas  through the samples was 21.2 ml/min.
All SO  acceptors were  screened  to 60-100 mesh particle size.

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Flowmeter
                                         Sample
                                         Chamber
                          Mixing
                          Chamber
H2SO4
'Glass Woo I
 Spray Trap
                                                                      Waste
                                                                      Flowmeter
                                   H2O
                                  Vaporizer
                                                            Gas
                                                       Chromatograph

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     Plots of SO- concentration in the effluent gas vs. time were made and the
SO- taken up by the sample at various time intervals was determined by graphical
integration of the area between the curve and the line drawn at the feed gas
concentration.  In most cases good correlation between the weight gain of the
sample at the breakthrough point and the graphically determined SO- sorption
was obtained.

     In cases where water vapor was used, the gas stream was bubbled through a
gas washing bottle containing water at 25°C  (puori = 0.032 atm) until equilibrium
                                              H/U
between the SO- in the  feed  gas and the SO-  in the water was attained.  Fiber
samples were  immersed in water for 5 minutes, then blotted dry.  Powder samples
were equilibrated with  water vapor by placing them in a desiccator containing
water at  room temperature.   In all cases, excess water on the samples was re-
moved by  the  gas stream in the first few minutes of flow.

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                        XI.  FUTURE  RESEARCH  PROGRAM

A.  SCREENING OF BASIC ABSORBENTS
     Evaluation of absorbents will be  continued with particular emphases on
(1) selectivity toward S02  in the presence of other acidic  flue gas constit-
uents, (2) stability  in operating environment (operating environment shall
consist of flue gas having  the  following  compositions:
                                          Volume  Percent
          Component               Composition I     Composition II
            N2                         74.9               81.7
            C02                        14.7
            H20                         7.25               2.6
            02                          2.8                4.2
            S02                         0.3               11.5
            NO                          0.05
              X
            Fly Ash                     0.2 (wt)           3.  (wt)

and temperatures in the range of 250-300 °F for sorption.  The upper tempera-
ture limit shall be based on thermal regeneration  requirements), (3) high
temperature capacity, and (4) reversibility.

B.  FIBER OPTIMIZATION
     The effect of such variables as fiber denier, cross section, loading of
absorbent, crystallinity and orientation, hydrophilicity, stability, sample
packing and configuration,  etc. on rate and capacity will be determined.

C.  KINETICS
     The effect of SO- concentration,  flow rate,  temperature, and factors
related to fiber optimization upon rate of S02 absorption will be studied.
The data derived in this area will be  obtained in  such a menner that it can
be presented in terms of space velocities and partial pressures of S02>

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D.  REGENERATION
     The more promising fibers will be carried through multiple cycles of
absorption and regeneration to determine what changes in rate or capacity
occur, and to optimize regeneration conditions. Evidence of irreversible
reactions occurring will be sought.  To the extent that such reactions occur,
either during sorption or regeneration, chemical regeneration techniques will
be investigated in addition to thermal regeneration methods.

E.  SCALE-UP
     Promising fibers will be spun in sufficient quantity to permit fabrica-
tion into filter packs for testing with gas mixtures simulating typical S02~
containing waste gases.

F.  PLANT CONCEPTUALIZATION
     In the latter stages of this work, a chemical engineer will be assigned
to this project to develop and outline plant designs for the practical appli-
cation of this method of SO. removal.  Conceptual designs for a source yield-
          6                                                 ;
ing 2 x 10  SCFM flue gas of composition I (previous table) and a source
yielding 1 x 10  SCFM of composition II will be considered, if applicable.
Such conceptualization, will include heat and material balances,  engineering
flow diagram, and sketches of novel and innovative equipment.   The Project
Officer will be called upon to supply guidance and information in this work.

     In addition,  the above engineer and the Project Officer will be consulted
throughout the work to insure that the type of information and data being
accumulated is in a form suitable for engineering calculations,  and further,
that no important points of information are being overlooked.

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                           XII.  REFERENCES

(1).    A. E. Hill, J. Am. Chem. Soc.,  53  2598  (1931).
(la).   See also ref.  (4).
(2).    Houben-Weyl, Methoden der OrganjLschen Chemie. 4th  ed. Vol.  XI/2
        Georg. Thieme Verlag, Stuttgart, 1958,  Chap. V,  p  732.
(3).    A. E. Hill and T. B. Fitzgerald, J. Am.  Chem. Soc.  .57 250  (1935).
(4).    W. E. Byrd, Inorganic Chem.  1  762  (1962).
(5).    A. B. Burg, J. Am. Chem. Soc.  65 1629 (1943).
(5a).   J. R. Bright and J. J. Jasper,  J.  Am. Chem.  Soc. j>5 1262 (1943).
(6).    T. Hata and S. Kinumaki, Nature, 203 1378  (1964).
(7).    J. L. Boivin,  Can. J. Chem. _34 827 (1956).
(8).    L. C. Bateman, E. D. Hughes, C. K. Ingold, J. Chem.  Soc. 243  (1944).
<9).    Selective Oxidation Processes,  A.C.S.,  Washington,  D.C., 1965, p. 52  ff.
(10).   N. V. Sidgwick, The Chemical Elements and  Their  Compounds,  Volume II
        Oxford University Press, London, 1950,  p.  908.
(11).   R. Longhi, R.  0. Ragsdale, and R.  S. Drago,  Inorganic Chem. I  768 (1962)
(12).   P. Gray and A. D. Yoffee, Chem. Revs. 5_5 1069 (1955)
(13).   H. C. Brown and R. B. Johannesen,  J. Am. Chem. Soc.  75  16  (1953)
        and earlier papers in this series.
(14).   R. Cole and H. L. Shulman, Ind. Eng. Chem. 52 859  (1960).
(15a).  S. W. Laskoski and W. H. Cobbs, J. Poly. Sci ^6  21  (1959).
(15b).  A. Peterlin and H. G. Olf, J.  Poly. Sci. Part A-2  4 587 (1966).
(16);   S. Glasstone,  Textbook of Physical Chemistry, second edition
        D. Van Nostrand Company, Inc.,  Princeton,  N.J. 1946 pp  779, 845.
(17).   Dal Nogare and Juvet, Gas-Liquid Chromatography, Interscience
        Publishers, New York, 1962,  pp 9,  364.
(18).   M. A. Muhs and F. T. Weiss,  J.  Am, Chem. Soc. 84 4697 (1962).

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