EPA 600/2 75 063
October 1975
Environmental Protects Technolo&v Series
                 CATALYTIC  DESULFURiZATIOK AND
                                       DENITROGENATIQN
                                   Indystriai Environmental Research Laboratory
                                         Office of Research and Development
                                        U.S. Environmental Protection Agency
                                  Research Triangle Park, North Carolina 27711

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                   RESEARCH  REPORTING SERIES


Research reports  of  the  Office  of Research and Development,
U.S. Environmental Protection Agency,  have been grouped into
five series.  These  five broad  categories  were established to
facilitate  further development  and application of environmental
technology.  Elimination of traditional  grouping was consciously
planned to  foster technology transfer  and  a maximum interface in
related fields.   The  five series  are:

          1.  Environmental Health Effects Research
          2.  Environmental Protection Technology
          3.  Ecological Research
          4.  Environmental Monitoring
          5.  Socioeconomic Environmental  Studies

This report has been  assigned to  the ENVIRONMENTAL PROTECTION
TECHNOLOGY  series.  This series describes  research performed
to develop  and demonstrate  instrumentation, equipment and
methodology to repair or prevent  environmental degradation from
point and non-point sources of  pollution.   This work provides the
new or improved technology  required for  the control and treatment
of pollution sources  to  meet environmental quality standards.

                      EPA REVIEW NOTICE

This report has been reviewed by the U. S. Environmental Protection
Agency, and  approved for publication.  Approval  does not signify that
the contents necessarily reflect the views and policies of the Agency, nor
does mention of trade names or commercial products constitute endorse-
ment or recommendation for use.
This document is available  to  the  public  through the National
Technical Information Service,  Springfield,  Virginia  22161.

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                           EPA-600/2-75-063
   CATALYTIC  DESULFURIZATION

       AND  DENITROGENATION
                     by
    Charles N. Satterfield, Michael Modell,
  Jerome F. Mayer, and Joseph F. Cocchetto

     Massachusetts Institute of Technology
     Department of Chemical Engineering
         77 Massachusetts Avenue
       Cambridge, Massachusetts 02139

             Grant No. R-800897
           ROAPNo. 21ADD-053
         Program Element No.  1AB013
    EPA Project Officer: William J. Rhodes

 Industrial Environmental Research Laboratory
   Office of Energy, Minerals, and Industry
     Research Triangle Park, NC 27711
                Prepared for

U.S. ENVIRONMENTAL PROTECTION AGENCY
      Office of Research and Development
           Washington, DC  20460


                October 1975

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                           TABLE OF CONTENTS

                                                                       Page

1.  SUMMARY	      1

2.  INTRODUCTION	      3

3.  APPARATUS AND PROCEDURE	      6

4.  RESULTS: INTERACTIONS BETWEEN HDS OF THIOPHENE AND
    HDN OF PYRIDINE	     10

    4.1  HDS of Thiophene	     10
    4.2  HDN of Pyridine	     14
    4.3  Effect of Other Additives	     20

5.  A MODEL FOR THE HDS OF THIOPHENE IN PRESENCE
    OF PYRIDINE	     22

6.  PYRIDINE HYDRODENITROGENATION: AN EQUILIBRIUM
    LIMITATION ON THE FORMATION OF PIPERIDINE
    INTERMEDIATE	     25

    6.1  Introduction	     25
    6.2  Results and Discussion	     26
         6.2.1   The Equilibrium Limitation	     26
         6.2.2  Product Distribution	     32

    6.3  Comparison with Previous Studies	     37

7.  THERMODYNAMIC EQUILIBRIA OF SELECTED HETERO-
    CYCLIC NITROGEN COMPOUNDS WITH THEIR HYDRO-
    GENATED DERIVATIVES	     38

    7.1  Heterocyclic Nitrogen Compounds in Petroleum	     38
    7.2  Hydrodenitrogenation Mechanisms	     40
    7.3  Calculation Procedures	     42
    7.4  Estimates of Reliability	     43
         7.4.1   Single-Ring Compounds	     43
         7.4.2  Multi-ring Compounds	     43
    7.5  Results and Discussion	     44
         7.5.1   Single-Ring Compounds	     44
         7.5.2  Multi-Ring Compounds	     47
         7.5.3  Effect of Operating Conditions	     54

    7.6  Conclusions	     54

8.  NOTATION	     56

9.  LITERATURE CITED	     57
                                   iii

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                              LIST OF TABLES
                                                                         Page
Table I     Catalysts Used                                                 8
Table II    Experimental Conditions for Results Depicted in Figures       13
Table III   Experimental Conditions for HDN Studies                       27
Table IV    Representative Heterocyclic Nitrogen Compounds                39
Table V     Postulated HDN Mechanisms of Representative Heterocyclic
            Nitrogen Compounds                                            41
                                    iv

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 Figure 1:
 Figure 2:
                            LIST OF FIGURES
           Schematic Diagram of Apparatus
           Thiophene HDS with CoMo/Al203 Catalyst (Experimental  Conditions
                Given in Table II)
           Thiophene HDS in Mixed Feedstocks with CoMo/Al9CL Catalyst
                                                          0
                (Experimental Conditions Given in Table II)
                Given in Table II)
           Pyridine HDN on MiMo/AO- Catalyst (Experimental Conditions
                Given in Table II)
Figure 3:

Figure 4:  Thiophene HDS with NiMo/Al203 Catalyst (Experimental  Conditions

Figure 5:

Figure 6:
           Pyridine HDN in Presence of H2S (NiMo/Al203 Catalyst).  Data
                points are for H2S.  Solid lines show results in presence
                of thiophene feed (See Figure 5).
           Pyridine HDN with NiW/(Si02-Al203) Catalyst (Experimental
                Conditions Given in Table II)
           Effect of Additives on Thiophene HDS at 300C, (Other Experi-
                mental Conditions Given in Table II)
Figure 7:

Figure 8:

Figure 9:  Product Distribution for Pyridine  HDN  Runs  Over  NiMo/AUO

Figure 10:
                Catalyst
           Comparison of Experimental and Equilibrium Pyridine  Conversion
                (Experimental  Conditions Given in Table II)
Figure 11: Comparison of Experimental and Equilibrium Quantities of
                Pyridine and Piperidine for HDN Over NiMo/Al?Oo Catalyst
                                                            t. O
Figure 12: Comparison of .Experimental, arid Equilibrium Quantities of
                Pyridine and Piperidine for HDN Over CoMo/Al203 Catalyst
Figure 13: Product Distribution for Pyridine HDN Runs Over CoMo/Al90^
                                                                  - O
                Catalyst

Figure 14: Product Distribution for Piperidine HDN Runs  Over NiMo/Al203
                Catalyst
Page
  7

 11

 12

 15

 16
                                                                             18
 19
 21
                                                                             28
                                                                             29
                                                                             30
                                                                             31
                                                                             33
                                                                            35

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                         LIST OF FIGURES (Cont'd)
Figure 15: Product Distribution for Piperidine HDN Runs Over CoMo/Al203
                Catalyst                                                     36
Figure 16: Thermodynamics of Pyridine HDN                                    45
Figure 17: Thermodynamics of Pyrrole HDN                                     46
Figure 18: Calculated Pyridine/Pi peridine Equilibrium                        48
Figure 19: Thermodynamics of Quincline HDN                                   49
Figure 20: Thermodynamics of Isoquinoline HDN                                50
Figure 21: Thermodynamics of Indole HDN                                      51
Figure 22: Thermodynamics of Acridine HDN                                    52
Figure 23: Thermodynamics of Carbazole HDN                                   53
                                   vi

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                                  -1-
                              1.  SUMMARY

     The hydroprocessing of fuels containing relatively large amounts
of organonitrogen compounds will become increasingly important in the
future in the upgrading of synthetic fuels from oil shale and coal  or
processing of lower grades of crude petroleum.   Organosulfur compounds
are always also present and the inhibiting effect of organonitrogen
compounds on catalytic hydrodesulfurization is  established.  However
very little has been published on the effect of organosulfur compounds
on hydrodenitrogenation.  These two groups of effects were explored
using as model compounds thiophene and pyridine which represent some
of the less reactive organosulfur and organonitrogen compounds re-
spectively.

     Studies were made with a flow microreactor at temperatures of  200
to 500C., 4.4 and 11.2 bars pressure,on commercial catalysts consisting
of CoMo/Al203, NiMo/Al203, NiW/Al203 and NiW/Si02-Al203.   Pyridine
hydrodenitrogenation (HDN) is more difficult than thiophene hydrode-
sulfurization (HDS).  We find that pyridine inhibits the HDS reaction
as previously reported, but sulfur compounds have a dual  effect on  HDN.
At low temperatures, thiophene inhibits the reaction by competing with
pyridine for hydrogenation sites on the catalyst.  This retards the
hydrogenation of pyridine to piperidine, reducing the overall reaction
rate.  At high temperatures the dominant effect is interaction of
hydrogen sulfide, an HDS reaction product, with the catalyst to improve
its hydrogenolysis (hydrocracking) activity. This increases the rate of
piperidine hydrogenolysis, which is rate-determining at the latter  con-
ditions, and enhances the overall  rate of HDN.

     From studies of HDN of pyridine and piperidine in the absence  of
sulfur compounds we have established that equilibration between pyridine
and piperidine, the first product formed in the overall series of
hydrodenitrogenation (HDN) reactions of pyridine, can be  a rate-limiting

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                                   -2-
factor under some conditions.  Thus on a commercial  NiMo/AUO., catalyst
at 11 bars pressure a maximum in the pyridlne HDN rate occurs  at about
400C, caused by a thermodynamlc limitation on the allowable concentra-
tion of p1per1d1ne.  N1Mo/Al203 appears to have greater hydrogenatlon-
dehydrogenatlon activity than CoMo/AKO, but CoMo/AO- appears to  have
                                     Co            fc  O
greater hydrogenolysis activity than NiMo/AlpO-, at least at about  300C
and below.

     Thermodynamic analysis of the principal steps in  the reaction  of
other representative heterocyclic nitrogen compounds (pyrrole, quinollne,
1soqu1nol1ne, Indole, acridine, and carbazole) reveals that under some
significant reaction conditions the overall HDN rate of these  compounds
may likewise be at least partly governed by the equilibrium of the
first step, the hydrogenatlon of the N-containing ring.   There is no
significant thermodynamic limitation on the principal  subsequent steps
or on the reaction as a whole.

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                                   -3-
                           2.  INTRODUCTION
     Hydrodesulfurization (HDS), which is accompanied by some hydro-
denitrogenation (HDN), is an important commercial process for removal
of organosulfur compounds from petroleum feedstocks.  The overall
chemical reactions involved are:
         /Organo-sulfur compound
          Organo-nitrogen compound
                                    + u            ) Hydrocarbon +
                                          catalyst
NH
Sulfided cobalt-molybdenum on alumina or nickel-molybdenum on alumina are
typical catalysts.  Several excellent reviews of HDS reactions and pro-
cesses are available (Schuman and Shalit, 1970;  Schuit and Gates, 1973;
Weisser and Landa, 1973a).

     Hydrodenitrogenation will become increasingly important in the
future to lower the organonitrogen content of synthetic crudes ex-
tracted from oil shale, some coals or certain low-grade naturally-
occurring petroleum, which contains large amounts of both sulfur and
nitrogen.  HDS and HDN occur simultaneously at suitable temperatures
and pressures, but the reactions interact with each other in ways which
are little understood.  As will be shown, under  some circumstances mutual
inhibition occurs, under others, HpS enhances HDN.  This work was under-
taken to elucidate these interactions by study of the HDS/HDN reactions
of mixtures of thiophene and pyridine on four commercial hydrotreating
catalysts.  Some studies of HDN of pyridine and  pyrrole were also made.
These compounds were chosen because they are representative of classes
of sulfur and nitrogen compounds in petroleum and synthetic fuels which
are difficult to desulfurize and denitrogenate by hydrogenation.

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                                    -4-
     Studles on HDS of thlophene and HDN of pyrldine have revealed
 substantial Information about the reaction mechanisms for these com-
 pounds  Individually, although 1t is not too clear how these may be
 affected by pressure or by the nature of the catalyst.  From studies
 at  1 atmosphere over chromia and supported cobalt molybdate catalysts,
 Owens and Amberg,  (1961) proposed the following for the desulfurization
 of  thlophene:
   o
 +H9                    +H,                +H9
TO-^      C4H6     ^     C4H8   ^   C4H10
Their results specifically indicated that the first step, at least under
their conditions, 1s cleavage of a C-S bond rather than hydrogenatlon of
thlophene.  The reaction rate has been described by a Langmuir-Hinshelwood
expression in which thlophene and hydrogen sulfide compete for catalyst
sites (Satterfield and Roberts, 1968).  Hydrogen sulfide also inhibits
the subsequent hydrogenation steps.

     Pyridine 1s less reactive than thiophene.  From studies on a supported
nickel cobalt molybdenum catalyst at 750 to 1500 psig, McIlvMed (1971)
concluded that the mechanism of pyridlne denitrogenation is
                                                 +H,
                                     C5H11NH2    -*> C5H12 + NH3
D1sproportionat1on reactions of piperldine and pentyl amine also occur
(Sonnemans et al., 1972).  The rate of pyridlne denitrogenation can also
be described by a Langmuir-Hinshelwood model in which adsorbed nitrogen
compounds have a strong inhibiting effect on the rate.

     Pyrrole has seldom been used in HDN studies since its  instability
makes handling difficult.

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                                   -5-
     Previous studies on simultaneous HDS/HDN indicate that nitrogen
compounds inhibit the HDS process.  In tests of 35 different crude
oil fractions, Kiovsky and Berg (1964) concluded that the nitrogen
content of the feedstock was the most important variable affecting
catalyst HDS activity.  Doelman (1962) studied the HDS of a cycle oil
fraction (3.8 wt. % sulfur) to which he added pyridine and quinoline.
With the processing conditions used, sulfur removal from the original
cycle oil was 98%, while in the presence of the nitrogen compounds
(1.0 wt. % nitrogen in feedstock) sulfur removal was 94%.  Kirsch et al.,
(1959) experimented with a synthetic gasoline (0.4 wt % sulfur) blended
from heptane, heptene, and thiophene.  With their experimental conditions
sulfur removal from this feedstock was 79%, while addition of pyridine
(0.1 wt. % nitrogen in feed) reduced this to 59%.  Ahuja et al. (1970)
also observed pyridine inhibition of thiophene HDS over catalysts other
than cobalt-molybdenum-alumina.

     Two studies using pure compounds have also shown the detrimental
effect of nitrogen compounds on HDS.  Desikan and Amberg (1964) observed
that pyridine poisoned thiophene HDS on a presulfided CoMo/AlpO^ catalyst
in a manner indicating that there were two sites which have HDS activity.
Pyridine apparently poisons these sites to different extents.  Lipsch
                                                                          V
and Schuit (1969) also reported that pyridine poisons thiophene HDS,
using a CoMo/AO., catalyst that was prereduced but not presulfided,
but the effect was not great as that of Desikan and Amberg.  Both these
studies utilized pulsed reactors, so the results are mainly qualitative.

     The effects of sulfur compounds on HDN are only poorly understood.  A
patent by Gerald (1957) claimed the addition of a sulfur compound in great
excess over the organo nitrogen present to improve nitrogen removal  over a
catalyst containing molybdenum, attributed to the possible formation or
maintenance of a particular sulfided form of the catalyst.  A recent study
by Goudriaan et al. (1973) reported that hydrodenitrogenation of pyridine
over a CoMo/AO, catalyst was enhanced if the catalyst were presulfided
rather than being reduced in hydrogen.  In the presence of hydrogen  sulfide
in molar excess over the pyridine, the nitrogen removal  was further  increased,
attributed to an enhancement of the hydrocracking activity of the catalyst
by the hydrogen sulfide.

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                                       -6-
                      3.  APPARATUS AND PROCEDURE

     The apparatus  (Figure 1) centered around a steady-state flow micro-
reactor.  An infusion pump (Harvard Apparatus Company) fed a liquid feed
(thiophene, pyridine, or a mixture of these compounds) to the system
through a length of heated capillary which served as a vaporizer.  Pre-
purified grade hydrogen was passed through a DEOXO purifier and molecular
sieve (type 4A) drying column to remove traces of oxygen and water.  The
hydrogen and vaporized reactants were then mixed and flowed through several
feet of preheater tubing before entering the reactor.

     The reactor was a stainless steel tube (0.5 cm i.d., 11 cm long) bent
into a U-shape and packed with catalyst.  Catalyst particles were commercial
extrudates crushed and sieved to 20/24 mesh.  A typical catalyst charge was
1.5 grams, and a single charge was used throughout an entire series of ex-
periments.  Table I shows the catalysts used.  Each was activated prior
to the first experimental run by treatment with a mixture of hydrogen
sulfide (10%) and hydrogen (90%) according to a temperature-time program
specified by the manufacturer.

     The reactor and pre-heater tubing were immersed in a fluidized
sand bath which served as a constant temperature medium.   Reactor
temperature was monitored with a thermocouple mounted in the exit gas
stream so that its tip was just above the end of the catalyst bed.
Temperature was controlled to + 1C below 350C and +_ 2C above 350C.

     Samples were taken from the reactor effluent stream with a gas
sampling valve (Carle model 2014) and injected into a Varian 2820 gas
chromatograph.   The sampling valve was mounted in an oven heated to
150C to prevent condensation of reactants or products.  The columns
used in the chromatograph were 20-foot Carbowax 20M on Chromosorb W.
These highly polar column packings separated the reactants (thiophene,
pyridine) very well, but the light reaction products (butanes, ammonia,
hydrogen sulfide, etc.) were unresolved and appeared as a single peak.
Since hydrogen was used as the carrier gas in the chromatograph, the

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                              SOAP-FILM
                              FLOWMETER
                                  FLOW RATE
                                  CONTROL
                                  VALVE
                            0
                                                      PRESSURE
                                                      GAUGE
        VALVE
        OVEN
        INTEGRATOR
      	1 o oCZJooj	
RECORDER
              A
                                                                             H,
                                                       REACTOR
                                                                  SYRINGE PUMP
                                 FLUID
                                 BED
                                 FURNACE
GAS CHROMATOGRAPH
                                             AIR
HEATED LINE
SHUT-OFF VALVE
METERING  VALVE
                            Figure 1. Schematic diagram of apparatus.

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                               -8-
                             TABLE  I
                          Catalysts Used
Manufacturer
American
Cyanamid
American
Cyanamid
Harahaw
( /
Designation
and Type
Aero HDS-2A,
CoMo/Al203
Aero II1JS-3A,
NlMo/Al203 to
Ni.4303, ft)
N1W/A1203 '
Surface, n
Area u'
270 m2/g
180 m2/g
152 ra2/g
Harshuw
Ni430l
NiW/(Si02-Al203)
228 in /g
                                                            Bulk
                                                           Density
                          (2)
                                                           0.531  8/cc
                                                           0.684  g/cc
                                                          0.765  8/cc
0.847 g/cc
Notes ;

(1)  -  Surface area reported by manufacturer

(2)  -  Bulk density of 20/24 mesh fraction uoed in experiments

(3)  -  Analysis indicated the oupport composition was:
        66% Si0>  34% A10
(a)  3.1 wtlNIO; 15.0 WU Mo03

(b)  6% Nickel and 19% tungsten,  as metal  content

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                                  -9-
hydrogen in samples of the reaction mixture did not appear on the
chromatograms.  Peak areas were determined with an electronic digital
integrator.

     A single experimental run consisted of determining the steady state
fractional  conversion of thiophene and of pyridine at each of several
different reactor temperatures for a fixed quantity of catalyst, feedstock,
pressure and total molar gas flow rate (hydrogen plus heterocyclic com-
pounds) .  In a series of experimental runs pressure, quantity of catalyst
and gas flow rate were held constant but the ratio of thiophene and pyridine
to each other and to hydrogen was varied from run to run.   The feed rate of
hydrogen was consequently adjusted slightly to keep the total molar flow
rate constant as feed rates of thiophene and pyridine were changed.
Hydrogen was always present in great excess, the mole ratio of hydrogen
to heterocyclic compound varied from 22 to 90.

     The raw data taken during a run were the reactant peak areas
(thiophene, pyridine) and the overall flow rate through the system.
Fractional  conversions of the reactants were calculated for each re-
action temperature of interest by taking the ratio of thiophene and
pyridine peak areas to those found when no reaction was occurring.

     The results showed very good reproducibility.  The fractional con-
versions observed under a given set of conditions could be reproduced  in
separate experimental runs.  With the analytical procedure used, however,
a mass balance over the system was not possible.  Application of cor-
relations for heat transfer limitations (Mears, 1971) and  mass transfer
limitations (Satterfield, 1970) to worst-case conditions showed that no
significant temperature or concentration gradients existed in the reactor.
Further details on experimental procedures are given by Mayer (1974).

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                                   -10-
4.  RESULTS;  INTERACTIONS BETWEEN HDS OF THIOPHENE AND HDN OF PYRIDINE

4.1  HDS of Thlophene
     Figures  2 and 3 show the percent conversion of thlophene obtained
over a series of experimental runs using pure thiophene or mixed thlophene/
pyrldlne feedstocks, each studied over a wide range of temperature.  (See
Table II for a summary of experimental conditions).  The entire series of
experiments was carried out with one catalyst charge.  No reaction of the
pyrldlne occurred 1n any of these runs.  As shown 1n Figure 2, with pure
thlophene feedstocks, the fractional conversion of thlophene Increased as
Initial partial pressure was decreased, and further analysis showed that
the rate was nearly zero order with respect to Initial partial pressure
over this range of conditions.

     The presence of pyrldlne 1n the feedstock has a severe Inhibiting
effect on HDS, and changes the order of the HDS reaction, as 1s evident
by comparison of the results with pure thlophene and those with mixtures
of thlophene and pyrldlne.  Comparison of runs 3/50 and 3/52 with 3/55
and 3/56 (Figure 2) shows that 1n the presence of pyrldlne the observed
conversion of thlophene was Independent of the Initial concentration,
Indicating a rate expression which is first order with respect to Initial
thlophene partial pressure.  Run 3/71, done as a reproduclblHty test
(compare to 3/29, 3/35) after completion of the mixed feedstock experi-
ments, showed an approximately 10% loss in HDS activity of the catalyst.
This was the only permanent catalyst deactlvation observed and it probably
was caused by coke formation at the very high temperatures (500C) reached
1n some of the mixed feedstock runs.  Subsequent experiments were limited
to 425C.  The inhibiting effect of pyrldlne was reversible.

     Figure 3 shows the effect of varying the ratio of pyrldlne to
thlophene, keeping the Initial partial pressure of the two heterocyclic
compounds constant at 142 torr.  Small additions of pyrldlne have a major
Inhibiting effect but larger additions do not depress the rate further.

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          Partial Pressures at
          Reactor Inlet.bars

            Tniophene pyr Kline Run Ho
           O 0.189

           D O.O76
                     3/29.3/^35

                     3/38.3A41

                     3M3.3M4

                       3/75
                      0.130  3/5O.3/5
                     = 4.4  bars
_  Pressure
g   4O -
    20
       1OO
                       2OO    -*        3OO            400


                                     TEMPERATURE, C

                         Figure 2. Thiophene HDS with CoMo/Al2O3 Catalyst.


                         (Experimental conditions given in Table n.
                                                                 5OO

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            I                I

  Liquid Feedstock (mole*)

Thiophene  Pyridme  Run No.

X 95 *

 60*
        100
               40*
                                                       Pure  TNophene
                                                       Feedstock
  3/75

3/5O.3/52

3/55.3/56

3/59. 3/62 /

  3/64
                       2OO            3OO

                                TEMPERATURE, C
                       4OO
                                                          5OO
               Figure 3. Thiophene HDS in mixed feedstocks with CoMo/Al2O3 Catalyst.

                       (Experimental conditions given in Table n.)

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                                               Table II
                        Experimental  Conditions for Results Depicted in Figures
Figure #:
Pressure, bars:
Catalyst:
Liquid Feed Rate,
ml/hr
Hydrogen Feed Rate,,
av. , cc(STP)/min
Residence Time, ^
sec.
2,3
4.4
1.31 g
(=2.46cc)
CoMo/Al203
20/24 mesh
1.30 to 6.53
714
0.52 to 0.32
4,5
11.2
1.48 g
(*2.17cc)
NiMo/Al203
20/24 mesh
0.65 to 2.60
271
3.1 to 2.1
8
4.4
1.49 g
(=2.85cc)
CoMo/Al203
16/28 mesh
2.60
350
** 1
7
11.2
1.48 g
NiW/Si02-Al203
20/24 mesh
0.65 to 2.6
273
2.44 to 1.65
10
11.2
1.48g
CoMo/Al203 i NiW/Al203
20/24 'mesh
0.65 to 2.6
273
3.77 to 2.55 2.65 to 1.80
1.  Based on superficial  linear velocity at reaction conditions (varies inversely with temperature).

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                                   -14-
      Flgure 4 shows the results of a similar series of runs, but at
 higher  pressure  (11.2 bars) and longer contact times, and using a
 catalyst.  HDN did occur 1n these runs, and those results will be discussed
 Immediately below.  As was observed at the lower pressure on the CoMo/AO,
 catalyst, adding an equlmolar amount of pyrldlne to a thlophene feedstock
 significantly reduces the fractional conversion of thiophene (compare 5/26
 with  5/13, 5/16), while further Increments of pyrldine have very little
 additional effect (compare 5/34 and 5/36 with 5/26).  As with the CoMo/Al203
 catalyst, 1n the presence of large quantities of pyrldlne the HDS of thlo-
 phene follows nearly first order rate behavior, with conversion approximately
 Independent of initial thlophene concentration (compare 5/29 and 5/31 with
 5/26).  Similar studies with N1W/A1203, N1W/S102-A1203 and CoMo/Al203
 catalysts at the same conditions (Mayer, 1974, pp.  86-87) showed virtually
 identical results to those obtained with N1Mo/Al203.  Although the same
weight of each catalyst was used 1n this comparison the surface area per
unit weight and the concentration of the active ingredients were somewhat
different on different catalysts, so that a detailed comparison cannot be
made quantitatively.

     In summary the principal  observations on the HDS reaction are
 (1) small additions of pyridlne cause a major Inhibition of the HDS of
thlophene but larger additions have little effect,  (2) thlophene HDS is
zero order 1n the absence of pyrldlne and first order in the presence
of substantial  quantities, and (3)  there 1s no significant difference
between the behavior of the four catalysts studied.

4.2  HDN of Pyridine
     Figure 5 presents the results  for the HDN of pyridlne alone on a
NiMo/AlgO-j catalyst and in mixtures with thlophene  as discussed above.
Pyrldine is much less reactive than thlophene.   The maximum pyrldlne
conversion ever observed was 50%, whereas thlophene could be 100%
converted.  The effect of temperature on HDN 1s unusual  1n that the
fractional conversion goes through  a maximum and turns downward above
380C.  This 1s probably because of the onset of a  thermodynamlc limit-
ation on the reaction as discussed  below.   Comparison of runs 5/34 and

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                               -15-
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it!
20 -
       Partial  Prssurf at React ot>

       Inlet ( bars )                 ,i


        Thiophene Pyridine  Run No.

         .124       0      5/13.5/16

         .122      .122     9110

       A  .366      .123     3/29,5/31

       +  .122      .366     5/34,5/36


       Tbtol Prtiur*11.2 bars
                                                           I
        100
               200
300         400


TEMPERATURE ,  C
500
600
                         Figure 4. Thiophene HDS with NiMo/Al203 Catalyst.

                         (Experimental conditions given in Table II.)

-------
                    -16-
80
z
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U

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O
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EL
h-
Z
LJ
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cr
LJ
Q.
60
20
       I             I
Partial  Pressures at
Inlet  ( bars)
    Thiophene  Pyridine
    0         .123
 V 0.123       .122
 A 0.366       .123
 4- 0.122       .366
Reactor

   Run No
   5/8,5/11,5/38
   5/26
   5/29 ,5/31
   5/34, 5/36
          Total
          Pressure
                   TI.2 bars
    100        200         300        400
                  TEMPERATURE, C
         Figure 5. Pyridine HDN with NiMo/Al203 Catalyst.
         (Experimental conditions given in Table II.)

-------
                                   -17-
 5/36 with  run 5/26 and other observations Indicate that the HDN reaction
 here 1s  between zero and first order over the entire temperature range.

     The effect of thlophene on HDN 1s two-fold.  Below 325C the
 presence of  the sulfur compound Inhibits the HDN reaction, 1n that
 lower  fractional pyrldlne conversions were observed with mixed feed-
 stocks than  with pure pyrldlne feedstocks.  Above 325C the presence
 of  thlophene enhances the HDN reaction.  However, thlophene Itself 1s
 probably not responsible for the enhancement effect since 1t 1s more
 than 60% converted to hydrogen sulflde at 325C (see Figure 4).  To
 determine  the role of hydrogen sulflde, three runs were performed with
 a pure pyrldlne feedstock at 10.3 bars total pressure but with a hydrogen
 sulflde  partial pressure of 0.358 bar or 0.0046 bar 1n the reaction gas
 (Figure  6).  With the higher H2S partial pressure the results duplicated
 those  of runs 5/29 and 5/31, thus confirming the hypothesis that hydro-
 gen sulflde, not thlophene, 1s responsible for the enhancement effect
 on  HDN.  With 0.0046 bar H2$, Inhibition effects similar to those ob-
 served with  thlophene appear but enhancement of HDN at the higher
 temperatures, although evident, 1s much reduced in magnitude from that
 observed 1n  the other runs.

     The effect of HS 1s corroborated by the observation of Goudrlaan
 (1974  p. 157) on the hydrodenltrogenatlon of pyrldlne on a CoMo/AlgO,
 catalyst at  75 bars pressure and 250-350C.  With a previously sulfided
 catalyst,  a  2 to 6 fold Increase 1n HDN activity was found 1n the pre-
 sence  of 4 bar pressure of HS over that found 1n the absence of HgS.

     Similar studies were made with the other three catalysts.  As with
 the N1Mo catalyst, 1n the presence of thlophene a maximum was observed
 with CoMo/Al203 or N1W/A1203 but somewhat different behavior occurred
 on NIW/SIO-AlO  (Figure 7).  These effects will be discussed below.
     The enhancement of HDN by HS may be associated with the maintenance
of the catalyst 1n a completely sulflded state which has better HDN
activity since the catalyst loses sulfur 1n the presence of hydrogen
alone, as shown by some simple experiments.   Correctly sulflded

-------
   100
                      -18-
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80
60
     40
     20
Inlet  Partial Pressure , bars




   H2S    Pyridine     Run

O  0.35ft   0.118      6/35,6/38

D  0.0046  0.120     6/41
             Pyridine /Thiophene

               Feedstocks

             Runs 5/26, 5/29,5/31
        Pure  Pyridine

          Feedstocks

        Runs 5/8, 5/11,

               5/38
                                              \
       100        200         300         400

                      TEMPERATURE,C


                Figure 6. Pyridine HDN in presence of H2S.


                   (NiMo/AlzOa Catalyst.)

-------
                      -19-
     80
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H-
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                                           T
             Partial
60
40
20
                 Pressures  at
                       (bars )
                     Reactor  Inlet
   Thiophene

     0
  0.124

A  0.371

t  0,126
        100
Pyridine

0.123
0.123

0.123,

0.368
Run  NO.

6/18 , 6/20

6/6

6/9 , 6/11

6/13,6/16
                200         300

                   TEMPERATURE C
                                 400
           Figure 7. Pyridine HDN with NiW/(Si02 - AI203) Catalyst.

             (Experimental conditions given in Table II.)

-------
                                  -20-
CoMo/Al203 had a sulfur content of 1.9 to 2.1 wt. % S, but after ex-
posure to H2 at either 300 or 400C for 35 to 40 hours this was reduced
to 1.0%.

     Some scouting experiments (Mayer, p. 100, 1974) indicated that HDN
activity will drop rapidly just after H,,S 1s removed from the reactant
gas stream but further prolonged exposure to hydrogen will have little
further effect beyond the initial decline.  For example, at 350C, on
CoMo/Al203 catalyst, a 50/50 thiophene-pyridine feed gave a 31% conver-
sion of pyridlne and 93% conversion of thiophene.  With pyrldlne alone
at the same conditions, about 18% conversion was obtained after a freshly
sulfided catalyst had been exposed to the pyridine-hydrogen mixture for
only 1 hour, which dropped to 16% conversion after 38 hours.  The rate
of sulfur loss from the catalyst was not established quantitatively,
but chromatographic analyses showed appearance of substantial  H2S in
the exit gas during the first hour at a rapidly decreasing rate.  The
active sulfur-containing species on the catalyst surface must be un-
stable and rapidly decomposed 1n the absence of sufficient sulfur in
the feed gas.

4.3  Effect of Other Additives
     A few runs under limited conditions were performed with pyrrole,
with results as shown in Figure 8.  Although pyrrole 1s non-basic,  1t
exhibits almost exactly the same Inhibiting effect as pyridine.   Work
with pyrrole is difficult experimentally because of its thermal  de-
composition so no further studies were made with 1t.

     Dilution of the feedstock with 1,3,5 triethyl benzene showed a  mild
Increase in thiophene conversion, a trend that was also observed for
pure thiophene feedstock as the initial  reaction partial  pressure was
decreased.  These results indicate that the reaction rate is close  to
zero order in Initial thiophene concentration and that the aromatic
compound 1s essentially Inert under these sets of circumstances.

-------
                   -21-
Z
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a:
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0.
O
I
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CL
         MOLE  PERCENT  THIOPHENE  IN

                        FEEDSTOCK

        100        90          80          70
    80
60
          I

        Zero  Order
        Reaction
I
20
                    ADDITIVE  TYPE

                  + = 1,3,5 -Triethylbenzene

                  A = Pyrrole            

                   = Pyridine
                    10
                             20
     30
         MOLE  PERCENT  ADDITIVE IN

                     FEEDSTOCK
 Figure 8. Effect of additives on Thiophene HDS at 300C, 50 psig (other
 experimental conditions given in Table   II.)

-------
                                   -22-
     5.  A MODEL FOR THE HDS OF THIOPHENE IN PRESENCE OF PYRIDINE
     The HDS of tMophene 1s Inhibited by H2S and a-kinetic expression
for this reaction on CoMo/Al203 catalyst was developed by Satterfleld and
Roberts (1968) from studies with a differential reactor.  Present data for
thlophene HDS alone could be most readily compared with that expression
for studies at low fractional conversion (<20%).  These showed quite good
agreement (Mayer, 1974).

     Present data were Insufficient to construct a complete kinetic model
for HDS 1n the presence of pyrldlne.  Nevertheless certain features of a
satisfactory model can be developed from the following considerations.
The Inhibition of thlophene HDS by pyrldlne 1s presumably caused by
competition between these compounds for active sites on the catalyst.
The pattern of Inhibition can be Interpreted 1n terms of a two-site
model analogous to that of Desikan and Amberg (1964).  It 1s postulated
that two kinds of sites (Type I and Type II) on sulflded catalysts are
capable of catalyzing the HDS reaction.  Type I sites are postulated to
be very active and to be responsible for the majority of the HDS activity
with pure thlophene feedstocks, but to be extremely sensitive to basic
nitrogen compounds.  In the absence of pyrldlne, the rate 1s approximately
zero order 1n thlophene.  In the presence of sufficient quantities of
pyrldlne, these sites will be completely blocked and, therefore, Inactive
for HDS.

     In terms of a Langmu1r-H1nshelwood model, the results are consistent
with the following rate expression:
                                                                    (3)
where Kj TpT  1 and Kj ppp  Kj TpT  (For a more complete model  a term
for H2S should be Included 1n the denominator and the adsorptlvlty of HgS
relative to thlophene and pyrldlne should be considered.)

-------
                                  -23-
     Type II sites are postulated to have less  HDS  activity,  but  to  be
less susceptible to poisoning, and therefore are responsible  for  the
HDS activity of the catalyst after all  Type I sites are  blocked.  Thiophene
and pyridine probably compete for Type  II sites, but the competition is
less one-sided than on Type I sites.

     Under moderate-to-high concentrations of pyridine,  the rate  of
HDS is first order in thiophene and relatively  insensitive to variations
in pyridine concentration.  These results are consistent with the
following rate expression:

                                             f(pu  )                 (4)
                                 + K   pPp
where KJJ TpT  1 and KJJ ppp  1

The total rate of HDS is:

               r = rr + rn                                         (5)

In the absence of pyridine, the type I  sites  carry  the  reaction.  That is
kj  kjj, or
                   kT
               r = L_ x  f(p  )                                     (6)
                   KI,T      H2

On the other hand, type II sites  are much  less  sensitive  to  pyridine
poisoning.  Thus, in the presence of pyridine,
                                                                    (7)
               r = *"  x f(FV  +  knPi   x
     The inhibiting effects  of  pyridine on  thiophene HDS found here follow
the same trends observed by  investigators studying  the effects of nitrogen
compounds on the HDS of real  or simulated petroleum feedstocks.  These

-------
                                  -24-
results Indicate that sulfur removal  by HDS from feedstocks having a
high nitrogen content will be more difficult than sulfur removal  from
conventional, low-nitrogen feedstocks.  This means more severe and
consequently, more expensive processing conditions will be required,
such as higher pressures, higher temperatures and longer contact  times,

-------
                                  -25-
     6.  PYRIDINE HYDRODENITROGENATION: AN EQUILIBRIUM LIMITATION
                ON THE FORMATION OF PIPERIDINE INTERMEDIATE
6.1  Introduction
     The mechanism of HDN of pyridine is given by Equation 2.   Focussing
on steps 1, 2 and 3, the equilibrium between pyridine and piperidine can
affect the overall rate of reaction if step 3, hydrogenolysis  of the C-N
bortd, is slower than step 1 and if conditions are such that the equi-
librium concentration of piperidine is severely limited.  The  rate of
hydrogenolysis of the C-N bond (and the overall HDN rate) is then less
than it would be if there were no significant thermodynamic limitation
on the concentration of piperidine.  However, if step 1  were rate-
limiting, piperidine would react as it forms and the position  of the
ring-saturation equilibrium would not influence the overall HDN rate.

     Equilibrium towards piperidine becomes less favorable at  higher
temperatures and lower hydrogen pressures.  Under the reaction conditions
of Mcllvried (315C, 50-TOO bars, NiCoMo/Al-O- catalyst) hydrogenation
                                            O
was rapid and step 3 was rate-limiting.  Equilibrium of  steps  1 and 2
was far to the right.  Stengler et al. (1964), as reported by  Goudriaan
(1974), stated that on a NiW/A^O., catalyst at 50 bar, step 3  was rate-
limiting below 350C and step 1 at higher temperatures.   In a  very
recent study on CoMo/A^O, catalyst at 80 bars, Goudriaan (1974) con-
cluded that the equilibrium of steps 1 and 2 may begin to limit the
overall rate of reaction at temperatures higher than 350C, and Sonnemans
and co-workers (1973, 1974) discuss its implications for the mechanism of
pyridine HDN.  The study of simultaneous HDN and HDS (Sections 4, 5)
found, unexpectedly, that the conversion of pyridine over some catalysts
dropped with an increase in temperature above about 400C.   This effect
apparently has not been previously reported in HDN studies  and it can be
interpreted in terms of the development of an unfavorable equilibrium
for the initial  saturation step at higher temperatures.

     For this portion of the study, liquid pyridine or piperidine was
pumped into the reactor system, vaporized, and mixed with hydrogen

-------
                                   -26-
 before entering the  reactor.  A gas chromatograph equipped with Pennwalt
 223  analytical columns was used for quantitative analysis of the reactor
 off-gas.  Catalysts  were commercial NiMo/AlpO-s or CoMo/AlpOg as used
 previously, crushed  and sieved to provide a 20/24 mesh size for study.
 A  single  charge of each catalyst was used for all experiments.  All
 studies were made at a total pressure of 11.2 bars and temperatures
 varied from about 200C to 425C.  A great excess of H2 was present
 at all times.  The ranges of reactant partial pressure and space velocity
 (expressed here as a superficial residence time calculated for 250C) are
 given in  Table III.  The analytical columns provided good separation of
 the  heavier components (pyridine, piperidine, n-pentylamine), but the
 light reaction products such as ammonia and n-pentane, though they
 appeared  as separate peaks on the chromatograms, were not resolved.
 Injection of known pyridine-piperidine solutions covering the full  range
 of compositions indicated that the quantitative analysis of these com-
 ponents always involved absolute errors less than 0.5 mole per cent.
 Further details are  given by Cocchetto (1974).

 6.2  Results and Discussion
 6.2.1  The Equilibrium Limitation: The percent conversions of pyridine
 as a function of temperature agreed closely with those we found in the
 previous studies for similar residence times.  As before, greater con-
versions were obtained with NiMo/Al^Og than with CoMo/AlgOg over the
entire temperature range investigated but even with NiMo/AlgOo the con-
version of pyridine reached a maximum of only 2B% at about 375C and
 then dropped (Figure  9).   With piperidine HDN however, conversion
 increased with temperature on both catalysts, ultimately to the 100%
 level.

     In order to focus on  the reversible pyridine-piperidine reaction, Figure 10,
Figure 1.1  (for NiMo/Al203) and Figure 12 (for CoMo/AlgOj) compare the
experimentally observed ratios of piperidine to pyridine plus piperidine
in the reactor effluent with the calculated equilibrium ratios (Cocchetto,
1974) as a function of temperature, for both pyridine HDN runs and piper-
idine HDN runs.  The equilibrium curve corresponds to the hydrogen  partial
pressure of 11.1  bars.  Figure 11  shows that for pyridine HDN, the amount

-------
                                  -27-
                                Table III
                Experimental Conditions for HDN Studies
                       Total Pressure =11.2 bars
Catalyst
NiMo/Al203
CoMo/Al203
    Reaction of Pyridine
Partial  Pressure at Reactor
       Inlet, bars
           0.13
           0.56
           0.55
Superficial Residence Time
    (sec) at 250C ^
          3.04
          3.92
          7.91
Catalyst
NiMo/Al203
CoMo/Al203
     Reaction of Piperidine
  Partial  Pressure at Reactor
         Inlet, bars
            0.12
            0.60
Superficial Residence Time
    (sec) at 250C ^
          3.08
         10.8
a.  Residence time is calculated based on the superficial  gas velocity
    at 250C and 11.2 bars

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 1.0
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1
	 1
2
0.8
0.2
         O  Pyridinc

         A  Pipcridinc

       	Cracked  Products

            ( by  Difference  )
                                                                   CO
                                                                   ao
    100
200
300
4OO
500
                                 TEMPERATURE ,C


               Figure 9. Product distribution for Pyridine HDN over NiMo/Al2O3 Catalyst.

-------
                              -29-
    100
z
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O
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      80
     60
      40
     20
       0
               Equilibrium  Line
                         H
 Data  Points

 Ni Mo/AI2O3

 CoMo/AI2O3

A Ni W /  AI2O3

-I- Ni W
                                Catalyst
                                Catalyst
                                Catalyst
                                Catalyst
         100
                     200          300

                       TEMPERATURE  C
                                    400
   Figure 10. Comparison of experimental and Equilibrium Pyridine conversion
        (Experimental conditions given in Table n.)

-------
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 o
   Ld
Ld
Q

E
Ld
Q_
tO
Ld

O
   9   100
   cr
   Ld
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   Q_
   LO
   Ld

   O
Ld

5
cc

CL

CO
Ld

O
         80
60
         40
         2O
CALCULATED  EQUILIBRIUM


        2~     N
                H

Total  Pressure =112  bars
Hydrogen  Pressure 11.1 bars

Feed
O   Pyridine
A   Pipcridine
                                                                                                   CO
                                                                                                   o
                                                                                                   i
            100
                             200              30O

                                       TEMPERATURE,C
                                                         4OO
                                                                    5OO
                Figure 11. Comparison of experimental and Equilibrium quantities of Pyridine
                and Piperidine for HDN over NiMo/Al2O3 Catalyst.

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LJ
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      100
Q

rr
LJ
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CL

I/)
LJ
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O
   LJ
    80
Total  Pressure = 11.2 bars

Hydrogen Pressure =10.6 bars

Feed

O,0 Pyridine

A   Piperidine


        CALCULATED  EQUILIBRIUM
                                                                                          CO
                                                                                          I'
9  20
cr

o_


LJ  10
_J
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     0
          150
                 200
                              30O

                   TEMPERATURE , C
4OO
450
               Figure 12. Comparison of experimental and Equilibrium quantities of Pyridine
               and Piperidine for HDN over CoMo/Al203 Catalyst.

-------
                                  -32-
 of  piperidine  in  the off-gas increased at the expense of pyridine as the
 temperature was increased to nearly 300C.  At this point, the equilibrium
 begins  to  shift from piperidine to pyridine, and the observed quantities
 of  piperidine  began to decrease with temperature.  Above approximately
 400C,  equilibrium was established.  With piperidine feed, no pyridine
 was observed below 300C but above this temperature its quantity in-
 creased steadily  at the expense of the piperidine.  At 400C, equilibrium
 was again  established.  At high temperatures, equilibrium was established
 starting with  either pyridine or piperidine.

     The results  shown in Figure 12 are quite similar, the two sets of
 data for pyridine feed representing two different residence times.  The
 pyridine-piperidine reaction was generally farther from equilibrium with
 CoMo/Al203 than with NiMo/Al203, although the activities of the two
 catalysts  cannot be precisely compared here since different partial
 pressures  of reactant were used in the two cases.  Equilibrium was
 finally established at 430C with the piperidine feed, and at a slightly
 lower temperature (about 400C) starting with pyridine.  The results in
 the two figures clearly show the reversibility of pyridine saturation
 in the  initial step of its hydrodenitrogenation.

 6.2.2   Product Distribution: Some information about the relative hydro-
 genation and hydrogenolysis activities of the two catalysts can be gleaned
 from the product distributions as a function of temperature.  For pyridine
 HDN Figure  9 shows results over NiMo/AUO, and Figure 13 over CoMo/AlgO-j.
 No n-pentylamine was detected in the reactor effluent and the light re-
 action  products (ammonia, n-pentane) could not be analyzed for quanti-
 tatively.  The sum of ammonia, nitrogen-containing side products, and
 hydrocarbons such as n-pentane was determined by a material balance
 between the moles of pyridine fed to the reactor and the moles of
 pyridine and piperidine found in the products and is shown as the dashed
 lines.  Ammonia was the principal  nitrogen-containing cracked product,
 but at higher temperatures several light products other than ammonia
 and n-pentane appeared.  With NiMo/Al0~, below about 275C piperidine
                                      O
was the only reaction product, and the material  balance was within a

-------


H
O
in
LI
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QJ
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2


0
1

"^^S^ ' '
^^  	 	
^^^ ^
o
O  Pyridine
 A A Piperidine 
	 Cracked Products
( by Difference ) s
 ' 

-
^
 ^ 
.** ' .  
^^A~-^ ^~^f^l\.^'
i^-^^^^^^^^^1"^"""*^ ^^^^^11^^
JT^^r^^^^1^^ I ^^^^A^ AA
00 200 3OO 4OO
TEMPERATURE ,C





CO
CO
1
7











Figure 13. Product distribution for Pyridine HDN over CoMo/Al203 Catalyst.

-------
                                   -34-
few percent.  The amount of piperidine in the reactor effluent reached
a maximum just below 300C and dropped to nearly zero at high tempera-
tures.  Ammonia and n-pentane were not observed at 251C but were found
in appreciable quantities at 295C.  Much greater quantities of ammonia
and other light products appeared at 356C and 402C, but a decrease was
observed at 426C consistent with the downturn in pyridine conversion.
With CoMo/Al203 less piperidine was always formed than with NiMo/Al203
at the same temperature and the ratio of cracked products to piperidine
was higher.

     Figures 14 and 15 are analogous to Figures  9  and 13 and show the
product distribution as a function of temperature for piperidine HDN
over NiMo/Al203 or CoMo/Al203.  With NiMo/Al203 up to about 40% of the
piperidine was dehydrogenated to pyridine but the conversion of piperi-
dine to cracked products (dashed line) reached a maximum at about 370C
and then decreased.  This behavior is similar to the downturn in pyridine
conversion observed for this same catalyst.   With CoMo/Al203 (Figure 15)
pyridine was again formed only above 300C,  but in smaller quantities
than with NiMo/AlpO.,.  Small  quantities of n-pentylamine were observed
in the off-gas from 300-400C.  With both catalysts ammonia was the
principal nitrogen-containing cracked product, and was produced in greater
quantity than n-pentane.  Qualitative examination of chromatogram peaks
revealed trends consistent with the quantities of cracked products as
calculated by difference.

     Below 300C only cracked products were  formed with both NiMo/Al203
and CoMo/Al203, since the dehydrogenation of piperidine to pyridine was
thermodynamically unfavorable.  Comparison of the product distributions
for pyridine and piperidine HDN over each catalyst suggest that below
about 300C, the hydrogenation of pyridine to piperidine was easier
than piperidine hydrogenolysis for NiMo/Al^, but hydrogenolysis was
easier than hydrogenation for CoMo/AlgO.,. This could account for the
low activity of CoMo/Al203 for pyridine HDN  at low temperatures.   The
larger quantities of pyridine formed with NiMo/Al203 than with CoMo/Al203
for piperidine HDN also imply that the former catalyst had greater de-
hydrogenation activity.  This is consistent  with the fact that the piper-

-------
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Lu
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tO
LJ
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    1.0
   0.8
   0.6
LJ
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Q- 0.4
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LJ 0.2
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     0
             A  Piperidine

             O  Pyridine

           	Cracked  Products
                ( by Difference
       100
                                                                                                 CO
                                                                                                 CJ1
                                              I
                          200                30O

                                  TEMPERATURE  C
                                                                    40O
500
            Figure 14.  Product distribution for Piperidine HDN over NiMo/Al203 Catalyst.

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O
Ld

u
Ld
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L_
O

I/)
Ld
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2
       1.O
       0.8
    Ld
0: 0.6
Ld
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0-0.4


LO
Ld

O 0-2
2
 A  Pipcridine

 O  Pyridine

	Cracked  Products
    ( by Di ffcrcncc )

          100
              200               300

                TEMPERATURE  C
400
                                   i
                                  CO
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                                   i
                                                                                   50O
               Figure 15. Product distribution for Piperidine HDN over CoMo/Al203 Catalyst.

-------
                                  -37-
 idine dehydrogenation reaction was closer to equilibrium with MiMo/AO.,
than with CoMo/AlpO^ (compare Figures 11 and 12).

6.3  Comparison with Previous Studies
     Sonnemans et al. (1972) studied pyridine HDN over reduced CoMo/AO,
at 60 bars hydrogen partial pressure and Goudriaan (1974) at 80 bars
pressure.  No downturn in pyridine conversion was observed, though it
appeared that the pyridine/piperidine equilibrium may have been established
at 400C.  At the higher hydrogen pressures the equilibrium is much more
favorable for piperidine than at the 11  bars hydrogen pressure used in
the present study.  The product distributions shown in Figures 9  and 13
exhibit the same trends as the distributions reported by Sonnemans and
Goudriaan, except for the downturn.

     Mcllvried (1971) studied the hydrodenitrogenation of pyridine at
315C and pressures of 50 to 100 bars on a NiCoMo/AlgOg catalyst.   He
did not analyze for piperidine in his products but he observed that the
nitrogen content of the total product was about the same for a given set
of reaction conditions starting with either pyridine or piperidine.  In
his case the rate of hydrogenation of the pyridine ring was presumably
rapid relative to subsequent steps and at his higher pressure there was
no thermodynamic limitation on the concentration of piperidine that
could exist in equilibrium with pyridine.  Here the rates of hydrogena-
tion of pyridine to piperidine and of the hydrogenolysis step both
appeared to affect the overall rate at the lower temperatures.  At the
higher temperatures the rate-limiting step was solely hydrogenolysis of
piperidine present in low concentration  because of a thermodynamic
limitation.  The maximum in pyridine conversion at 375-400C is caused
by the decrease in the equilibrium concentration of piperidine with
increased temperature being more important than the increase in the
kinetic rate constant for piperidine cracking.

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                                  -38-
         7.  THERMODYNAMIC EQUILIBRIA OF SELECTED HETEROCYCLIC NITROGEN
                   COMPOUNDS WITH THEIR HYDROGENATED DERIVATIVES
           \
     It was shown above that thermodynamics could cause a limitation on
the rate of HDN of pyridine under some circumstances.  The objective of
this portion of the study was to extend these conclusions concerning the
implications of thermodynamics to consideration of various steps involved
in HDN of a group of representative heterocyclic nitrogen compounds found
in natural and synthetic liquid fuels.

7.1  Heterocyclic Nitrogen Compounds in Petroleum
     The heterocyclic nitrogen in petroleum and synthetic crudes is in-
corporated in five- or six-membered rings, most of which are unsaturated.
Some representative compounds are shown in Table IV.  These can be either
basic or non-basic.  Pyridines and saturated heterocyclic ring compounds
(indoline, hexahydrocarbazole) are generally basic, while pyrroles tend to
be non-basic.

     The small quantities of non-heterocyclic nitrogen compounds present
in liquid fules include anilines, aliphatic amines, and nitriles.   These
compounds are easier to denitrogenate by catalytic hydrogenation than
the relatively unreactive heterocyclic compounds so they are not a serious
problem.

   .  Qader et al. (1968) reported that pyridines, quinolines, pyrroles,
indoles, and carbazoles are the principal  heterocyclic nitrogen structures
present in low temperature coal tars.  Indoles, pyridines, and their higher
benzologs were reported in a California petroleum (Snyder, 1970).   In this
same study it was found that the nitrogen content increases with increasing
boiling point (molecular weight) of the petroleum fractions.  One- and two-
ring heterocyclic compounds (pyridines, quinolines) predominate in the
lighter fractions while the large multi-ring structures accumulate in the
heavier fractions.  Similar observations have resulted from studies of
shale oils.  Dinneen (1962) found that the nitrogen content of Colorado
shale oil fractions increases continuously from about 1% (by weight) in

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                                  -39-
                                TABLE  IV
             Representative Heterocyclic Nitrogen  Compounds
Name

Pyrrole

 Indole

 Carbazole

 Pyridine

 Quinoline

 Isoquinoline

Acridine


Pyrrolidine
                     f
 Indoline

Hexahydrocarbazole

Piperidine

1,2,3,4 - Tetrahydroquinoline

1,2,3,4 - Tetrahydroisoquinoline
                                 Formula
                                C4H5N
                                 C12HgN
                                 C,H,N
                                  b  o
                                 C9H?N
                                 C9H?N
                                 C13HgM
                                 C8H9N
 Structure
   I?
    H
    (Si
CoToToj
   H

   


   H

   H
      11

   OQ
                                                           NH
9,10 - Dihydroacridine

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                                   -40-
naphtha to over 2% in residuum.  Pyridines and pyrroles account for most
of the nitrogen in the naphtha fraction; pyridines, indoles, quinclines,
tetrahydroquinclines, and more complex ring compounds are present in the
heavier gas oil fraction.

     The general conclusion from HDN kinetic studies that the multiring
heterocyclic compounds are more difficult to denitrogenate than the lower
molecular weight single- and double-ring compounds indicates that the
higher boiling fractions which contain the most nitrogen also contain it
in a form which is most difficult to remove.

7.2  Hydrodenitrogenation Mechanisms
     In present commercial practice hydrodenitrogenation proceeds in-
cidentally to catalytic hydrodesulfurization at elevated temperatures
and pressures.  Most experimental work on HDN has been done at tempera-
tures from 300 to 450C (570-850F) and pressures of 250-6000 psig.

     In general hydrodenitrogenation of heterocyclic nitrogen compounds
proceeds via saturation of the heterocyclic ring, followed by ring
fracture at a carbon-nitrogen bond.  Nitrogen is then removed from the
resulting amine or aniline as ammonia.  Ideally, HDN should selectively
hydrogenate only the heterocyclic rings, avoiding saturation of desirable
aromatics and olefins and minimizing hydrogen consumption.

     Postulated HDN mechanisms of representative heterocyclic nitrogen
compounds are shown in Table V.   The mechanisms proposed for the following
compounds are supported by experimental work: pyrrole (Smith, 1957), pyridine
(Mcllvried, 1971; Sonnemans et al., 1972, 1973, 1974), indole (Aboul-Gheit
and Abdou, 1973; Hartung et al., 1961), quinoline (Aboul-Gheit and Abdou,
1973; Doelman.and Vlugter, 1963; Madkour et al., 1969), and isoquinoline
(Doelman and Vlugter, 1963; Madkour et al., 1969).  Side reactions also
occur.  Sonnemans et al. (1972) reported disproportionate reactions in
pyridine HDN and with two-ring compounds, aromatic ring saturation may
occur, sometimes followed by ring fracture and  scission of the saturated
heterocyclic ring at a carbon-carbon or "aniline-type" carbon-nitrogen

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                                 -41-

                              TABLE  V

                Postulated HDN Mechanisms of Representative
                     Heterocyclic Nitrogen Compounds
              H
     +2H,
 H
rojni+2H2
      +2H,
+H,
                            C3H7
                            NHo
   +H2    ^^C2H5
C3H7
                              + NH.
                  NH
                                      or
                                             CH.
             C2H5
                    NH,
                      +H
                                NH,
                                                        +NH,
oSo-^ o
                    H
                                    NH,
                                                         OH-
                                            NH,
          +H,
                              +H,

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                                  -42-
 bond  rather  than  at  the weaker aliphatic carbon-nitrogen bond.  Inter-
 conversion between quincline and indole can even occur.  The formation
 of  3-cyclohexylethyl amine, n-octylamine, N-ethylcyclohexylamine, 3-phenyl-
 ethylamine,  and quinoline from indole HDN  (Hartung et al., 1961) can be
 attributed to  such side reactions.

      The mechanisms  proposed for carbazole and acridine are the ideal
 HDN mechanisms for these compounds, but they must be regarded as tentative.
 Home and McAfee  (1960) consider the denitrogenation of carbazole to
 biphenyl plausible,  but also indicate that saturation of an aromatic
 ring .prior to  nitrogen removal is a possibility.  Flinn et al. (1963)
 suggest that one of  the carbazole aromatic rings is hydrogenated and
 cracked to form an alkylated indole or indoline, which then denitrogenates
 by the usual mechanism.  No information on the mechanism of acridine HDN
 was found.

 7.3   Calculation Procedures
      Based on the proposed HDN mechanisms for the heterocyclic nitrogen
 compounds considered in this study, the thermodynamic equilibrium con-
 stants for the stepwise and overall HDN reactions were calculated from
 the corresponding standard free energy changes.  Details of the cal-
 culations are given by Cocchetto (1974).

      In most cases the free energies of formation of the relevant compounds
were  not available in the literature, so  they were estimated, using the
group contribution methods of Benson et al. (1969) and van Krevelen and
Chermin (1951).  The van Krevelen method  resulted in direct estimation
of the standard free energy of formation  of a compound as  a function of
temperature:

                     AGf = A + BT                                    (8)

The constants A and B are assumed to be additive functions  of the atomic
groups comprising the compound.   Several  of the original van Krevelen
group contributions were rederived from more recent data to improve the
accuracy of the estimations.   Benson's method estimates  the standard heat
of formation and the corresponding standard entropy change.  The standard

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                                  -43-
free energy of formation was then found as follows:

                      AGf = AHf - TASf                             (9)

where AH0,. = standard heat of formation of a compound
      AS.c = standard entropy change for the formation of a
             compound from its elements.
Benson's method is generally more accurate than the method of van Krevelen,
and is preferred for this reason.  Unfortunately, Benson's method was not
entirely applicable to all of the compounds encountered in this study, so
some estimates had to be based primarily on van Krevelen's method.  As
much relevant thermodynamic data as could be found was compared with
estimated values to determine the reliability of results.  The ideal gas
law was assumed and all species were taken to be in the gas phase.

7.4  Estimates of Reliability
7.4.1  Single-Ring Compounds: Standard heats and free energies of forma-
tion, at temperatures up to 1000K, for pyridine, pyrrole, their hydro-
genated derivatives, and ammonia are available in the literature.  These
data were used to calculate the thermodynamic equilibrium constants for
the major steps in the pyridine and pyrrole HDN mechanisms and for the
overall reactions.  We estimate the absolute errors in the logarithms
of the equilibrium constants for the hydrogenation steps to vary from
about 0.4 at 298K to 0.1 at 1000K.  The accurate free energies of
formation for ammonia and the normal hydrocarbons do not introduce any
significant errors in the results.  The data for the aliphatic amines,
however, are of questionable accuracy.  Comparison of these data with
the free energies, of formation estimated from the methods of Benson et al.
(1969) and van Krevelen and Chermin (1951) suggests that the literature
values may be high by several kcal/mole.  Thus the equilibrium constants
calculated for the hydrogenolysis reactions (step 2) could be low by one
or two orders of magnitude, while those for the denitrogenation reactions
(step 3) could be high to the same degree.

7.4.2  Multi-ring Compounds:  The calculations for the multi-ring hetero-
cyclic compounds are based primarily upon estimated standard free energies

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                                   -44-
 of  formation  since  these data could not be found for most of the relevant
 compounds.  Standard free energies of formation for ammonia and the hydro-
 carbon  products, with the exception of diphenylmethane, were found in the
 literature and were used in preference to less reliable estimations.

     The results are generally less reliable than those for the single-
 ring compounds.  Errors in the estimated free energies of formation for
 diphenylmethane and the amine intermediates are less than 1 kcal/mole
 over the temperature range considered.  These estimates are based on the
 relatively accurate Benson method which unfortunately is not completely
 applicable to the unsaturated and saturated heterocyclic nitrogen com-
 pounds.  Free energy of formation estimates for these compounds, based
 on modified van Krevelen method, could be in error by several  kcal/mole.
 As a result, calculated equilibrium constants for the hydrogenolysis
 reactions and the overall HDN reactions could be in error by one order
 of magnitude at 1000K and two orders of magnitude at 500K.

     The equilibrium constants for the denitrogenation reactions (step 3)
 are more accurate since heterocyclic nitrogen compounds are not involved.
 The equilibrium constants for the ring-saturation reactions are less re-
 liable because both unsaturated and saturated nitrogen heterocyclic com-
 pounds are present.  The results for quinoline and isoquinoline are more
 reliable than the results for indole and the three-ring compounds,  due to
 better estimates of the free energies of formation.

 7.5  Results and Discussion

 7.5.1  Single-Ring Compounds:  Figures 16 and 17 present the common  loga-
rithms of the equilibrium constants for pyridine and pyrrole HDN respec-
tively as a function of the reciprocal  of the absolute temperature.  The
equilibrium constants in both  figures always decrease with increasing
temperature, consistent with the fact that all  the reactions are exo-
thermic.  For both pyridine and pyrrole, the equilibrium constants  for
the initial  ring-saturation steps are favorable (K > 1, log K > 0)  at low
temperatures but become unfavorable (K < 1,  log K < 0) above approximately
225C.   The equilibrium constants for all  the other reactions  are favorable
even at temperatures approaching 500C.

-------
                             -45-
                               T.C
O
O
               600     300
                               100
 14.0

 12.0

 10.0

  8.0

  6.0

  4.0

  2.0

  0.0

 - 2.0

 -4.0

 -6.0

 -8.0

-10.0
                                             H
                            (2) (>H2 =  C5H11NH2
                               H
                            (3) C5H11NH2+H2=:C5H12+NH3
                            <4)<8)*5Ha=C9Hia*'NH3
             1.0
                      2.0
                  1000/T ,  K
3.0
4.0
                                      -1
            Figure 16. Thermodynamics of Pyridine HDN.

-------
                          -46-
                         T. C
         600     300
100
 16.0 -
-8.0
       1.0.
                 4.0
                    1000/T , K
         Figure 17. Thermodynamics of Pyrrole HDN.

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                                  -47-
     There is generally a change in the total number of moles upon
reaction, so pressure as well as temperature can affect the equilibria.
Elevated pressure shifts the ring-saturation equilibria to the right
(toward saturation) since the corresponding reactions are accompanied
by a reduction in number of moles.  Figure 18 shows, for example, the
effect of temperature and pressure on the pyridine/piperidine equili-
brium, which emphasizes the importance of hydrogen pressure.

7.5.2  Multi-Ring Compounds: Calculated thermodynamic equilibrium con-
stants for the overall reactions and the steps in the HDN mechanisms
of qu.inoline, isbquinoline, indole, acridine, and carbazole are presented
in Figures 19 through 23.  These are analogous to Figures 16 and 17 for
the single-ring compounds.  Qualitatively, the results for both the two-
and the three-ring compounds are similar to the results for the single-
ring compounds (note that the mechanism proposed for carbazole HDN does
not include an initial ring-saturation step).  The equilibrium constants
for the ring saturation reactions are favorable only at low temperatures;
those for the hydrogenolysis, denitrogenation, and overall reactions are
favorable at temperatures as high as 500C.

     The relatively large uncertainties in some estimated equilibrium
constants do not significantly affect these qualitative conclusions.
The only exception is the equilibrium constant for the initial step in
the proposed carbazole HDN mechanism (see Figure 23), for which there is
considerable uncertainty.  This reaction involves the hydrogenolysis of
a resonance-stabilized pyrrole ring rather than a saturated or at least
partially saturated heterocyclic ring, as in the other compounds con-
sidered.  This initial step appears to be easier thermodynamically than
ring saturation, but it is questionable whether the pyrrole ring in
carbazole can be broken under HDN conditions prior to some degree of
saturation.  If the carbazole HDN mechanism involves some initial sat-
uration of the aromatic rings, the equilibrium for this saturation step
should be similar to the equilibria for the saturation steps in the HDN
of the other heterocyclic compounds.

-------
 o
 o
UJ
z
UJ
(/)
UJ
UJ

5.
o:
UJ
Q.
UJ

O
UJ
z
Q
o:
UJ

O
         100
      80
60
          40
          20
                                                                  HYDROGEN  PARTIAL

                                                                  PRESSURE = 10O  ATM
                 HYDROGEN   PARTIAL

                 PRESSURE =11 ATM
                PYRIDINE

                	I
                                                                                                        oo
                                                                                                        i
                              H

                            PIPERDINE
                     200
 300             400

TEMPERATURE  ,C
                                                                     500
                                                                                600
                            Figure 18. Calculated Pyridine/Piperidine Equilibrium.

-------
                        -49-
                            T,C
 o
c5"
o
             600    300
100
     14.0 -
     12.0 -
   -10.OI	I
                       1000 / T ,  K


               Figure 19. Thermodynamics of Quinoline HDN.

-------
                              -50-
                             T,C
            600    300
                             100
 o
6
o
  14.0



  12.0



  10.0



   8.0



   6.0



   4.0



   2.0



   0.0



 - 2.0



 - 4.0



 - 6.0



 -8.0



-10.0



-12.O
                                                  CH2CH2NH2

                                                  CH3
                                                      "CH,
                                     i
           1.0          2.0          3.0


                          1000/T, K~1


                 Figure 20. Thermodynamics of Isoquinoline.
                                              4.0

-------
                          -51-
                             T,   C
             600      300           100
     14.0

     12.0

     10.O

      8.0

      6.0

      4.0

      2.0

*    0.0
 O
O   -2.0
O
     -4.0

     -6.0

     -8.0

    -10.0

   '-12.0
            1.0
 H
r-CaHs
^NH2
 IN
 H|
20             3.0
                 4
              O
                              4.0
                            1000 / T,  K~'
                Figure 21. Thermodynamics of Indole HDN.

-------
                           -52-
                           T,  G
      12.0

      10.0

       8.0

       6.0

       4.0

       2.0

       0.0

O   -2-0
_J
     -4.0

     -6.0

     -8.0

     -10.O

     -12.0

     -1 4.0
 o
6
              600  400     200
                                    100
               M  I    I
                          (4
                                         I
            10            20            30
                         100O/T, K~1
             Figure 22.  Thermodynamics of Acridine HDN.
                                                     4 O

-------
                        -53-
 o
O
O
  14.0


  12.0


  10.0


   8.0


   6.0


   4.0


   2.0


   0.0


  -2.0



  -4.0


 -6.0


 -8.O


-10.0
                             T.C
              600  400     200     100
                     I   I
                        (0> H2=T (bj    TO) + N H3
                         o)+2H,(o
                                  ''
            1.0
                      2.0
3.0
4.0
                         1000 / T  , K~1
              Figure 23. Thermodynamics of Carbazole HDIM.

-------
                                   -54-
7.5.3  Effect of Operating Conditions: Increasing total pressure does
not  improve the denitrogenation equilibria, since there is no change in
the  number of moles upon reaction.  The equilibrium constants for the
hydrogenolysis steps and the overall HDN reactions are all very large at
lower temperatures, but some decrease to about unity (log K = 0) as the
temperature increases to 500C.  At this temperature only moderate pres-
sure (10 atm) shifts these equilibria completely to the right.  The
initial heterocyclic ring-saturation step, however, is reversible; that
is, appreciable quantities of both the saturated and the unsaturated
heterocyclic compounds can be present at equilibrium within the relevant
range, of temperature and pressure.  Decreasing the temperature or in-
creasing the pressure shifts this equilibrium to the right, toward
saturation.

     The extent to which increased pressure can be used to overcome an
unfavorable equilibrium constant depends, of course, on the number of
moles of hydrogen consumed in the ring saturation step.  Saturation of
pyridine to piperidine requires three moles of Hp while hydrogenation
of indole to indoline requires only one.  For an unfavorable equilibrium
constant of say, 0.001 and a hydrogen partial pressure of 100 atm, the
equilibrium piperidine/pyridine mole ratio is 1000, the indoline/indole
ratio is only 0.1.  Thus the elevated hydrogen pressure shifts the
pyridine/piperidine equilibrium completely to the right but fails to
make the indole/indoline equilibrium favorable for hydrogenation.  Since
the slope of log K versus 1/T is proportional to the enthalpy change on
reaction, this also increases with the number of moles of hydrogen con-
sumed in the hydrogenation step, which increases the exothermicity per
mole of heterocyclic compound.  Consequently the equilibrium concentration
of the initial hydrogenated species is most sensitive to both pressure and
temperature for those heterocyclic compounds consuming the greatest amount
of hydrogen in the initial  step.

7.6  Conclusions
     The mechanism for the hydrodenitrogenation of heterocyclic nitrogen
compounds involves reactions in series.  Only the first step in this re-

-------
                                  -55-
action sequence is difficult thermodynamically.  As a result, the effect
of thermodynamics on overall HDN depends on the kinetics of the various
steps in the mechanism.

     If the initial heterocyclic ring-hydrogenation step is rate-limiting,
the hydrogenated heterocyclic compound reacts as soon as it is formed and
the position of the hydrogenation equilibrium for the initial step does
not affect the overall HDN rate.  If hydrogenolysis (cracking) (step 2) is
rate-limiting, the reversible initial step can achieve equilibrium.  The
partial pressure of the saturated heterocyclic compound (the reactant for
step 2) then depends on the position of the saturation equilibrium.  The
overall HDN rate in this case is the rate of hydrogenolysis, which in a
simplified model depends on a temperature-dependent kinetic rate constant
and on the partial pressure of the saturated heterocyclic compound, gov-
erned by the equilibrium of the first step.  An increase in temperature
increases the kinetic rate constant but decreases the equilibrium con-
stant for the first step, decreasing the partial pressure of the reactant
for the hydrogenolysis reaction.  Thus the rate may go through a maximum
with increased temperature.  A potential thermodynamic limitation exists
in most HDN mechanisms under those sets of circumstances in which hydro-
genolysis of the C-N bond is slower than the rate of hydrogenation of the
original heterocyclic ring and the equilibrium concentration of the hydro-
genated compound is substantially limited.

-------
                                 -56-

                         8.  NOTATION

 k    intrinsic rate constant
 K    adsorption coefficient
 p    partial  pressure
 r    instantaneous reaction rate
 H2   hydrogen
 P    pyridine
 T    thiophene
I,II  type I,  type II HDS sites

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                                  -57-
                       9.  LITERATURE CITED

Aboul-Gheit, A.K., and I.K. Abdou, J. Inst. Petrol., London,  59_,  188 (1973).
Ahuja, S.P., M.L. Derrien, and J.F. LePage, "Activity and Selectivity of
     Hydrotreating Catalysts," Ind. Eng.  Chem.  Prod. Res. Develop.,
     9_, 272 (1970).
Benson, S.W., F.R. Cruickshank, D.M. Golden, G.R.  Haugen, H.E.  O'Neal,
     A.S. Rodgers, R. Shaw, and R. Walsh, Chem.  Rev., 69_, 279 (1969).
Beugeling, T., M. Boduszynski, F. Goudriaan and J.W.M.  Sonnemans,  "Gas-
     Liquid Chromatographic Analysis of Products formed by the  Hydro-
     genolysis of Pyridine," Anal. Lett.. 4_, 727 (1971).
Cocchetto, J.F., "Thermodynamic Equilibria of Heterocyclic Nitrogen
     Compounds with Their Hydrogenated Derivatives," S.M. Thesis,
     Mass. Inst. of Tech., 1974.
Desikan, P., and C.H. Amberg, "Catalytic Hydrodesulphurization  of
     Thiophene V.  The Hydrothiophenes.  Selective Poisoning  and  Acidity
     of the Catalyst Surface," Can. J. Chem.. 42_,  843 (1964).
Dinneen, G.U., Proc. Am.  Petrol.  Inst.. 42_ (8), 41 (1962).
Doelman, J., "De Verwijdering van Zwavel  en Stikstof mit Minerale  Olien
     door Katalytisch Hydrogeneren," Ph.D. thesis, Delft Technological
     University, Delft, Netherlands (1962).
     See also, J. Doelman and J.C. Vlugter, "Model Studies on the
     Catalytic Hydrogenation of Nitrogen-Containing Oils," 6th  World
     Petr. Cong., Ill, Paper 12,  p. 247 (1963).
Flinn, R.A., O.A. Larson, and H.  Beuther, Hydrocarbon Proc. & Petrol.
     Refiner.. 42_ (9), 129 (1963).
Gerald, C.F., "Purification of Petroleum Distillates,"  U.S. Patent
     2,790,751, April 30, 1957.
Goudriaan, F., "Hydrodenitrogenation of Pyridine," doctoral thesis,
     Twente Technical Institute,  The Netherlands,  1974.

-------
                                   -58-
                         LITERATURE CITED (Cont'd)


Goiidriaan, F., H. Gierman and J.C. Vlugter, "The Effect of Hydrogen
     Sulfide on the Hydrodenitrogenation of Pyridine," J. Inst. Petrol.,
     London. 59 (565), 41 (1973).
Hartung, G.K., D.M. Jewell, O.A. Larson, and R.A. Flinn, J.  Chem.  Eng.
     Data, 6_, 477 (1961).
Home, W.A., and J. McAfee, Advances in Petroleum Chemistry  and Refining,
     K.A. Kobe and J.J. McKetta, Jr., editors, Vol.  3, p. 228 (Interscience,
     New York (I960)).
Kiovsky, J.R., and L. Berg, paper presented at 52nd  Natl. AIChE meeting,
     Memphis (1964).
Kirsch, F.W., H. Shalit and H.  Heinemann, "Effect of Nitrogen Compounds  on
     Hydrodesulfurization of Petroleum Fractions," Ind.  Eng.  Chem., 5J_,
     1379 (1959).
Lipsch, J.M.J.G., and G.C.A. Schuit, "The CoO-Mo03-Al203 Catalyst.   III.
     Catalytic Properties," J.  Catal.. 15_, 179 (1969).
McCandless, F.P., and L.  Berg,  "Hydrodenitrogenation of  Petroleum  using
     a Supported Nickelous  Chloride-Gaseous  Chloride Catalyst System,"
     Ind. Eng. Chem. Process Des. Develop.,  9_, 110 (1970).
McCullough, J.P., et al., "Pyridine: Experimental and Calculated Chemical
     Thermodynamic Properties between 0 and  1500K;  a revised Vibrational
     Assignment," J. Am.  Chem.  Soc., 79_, 4289 (1957).
Mcllvried, H.G., "Kinetics  of the Hydrodenitrification of Pyridine,"
     Ind. Eng. Chem. Process Des. Develop.,  10.,  125  (1971).
Madkour, M.M., B.H.  Mahmoud, I.K. Abdou, and J.C. Vlugter, "The Effect of
     Chlorides on the Hydrogenation of Nitrogen  containing Model Substances,"
     J. Indian Chem. Soc..  46.  720 (1969).
Mayer, Jerome F., "Interactions between Hydrodesulfurization  and Hydrode-
     nitrogenation Reactions,"  Sc.Di Thesis, Mass.  Inst.  of Tech.,
          Cambridge, Mass., (1974).
Mears, D.E., "Diagnostic  Criteria for Heat Transport Limitations in Fixed
     Bed Reactors,"  J. Catal.,  20, 127 (1971).
Owens, P.J., and C.H. Amberg, "Thiophene Desulfurization by a Microreactor
     Technique," Advan. Chem. Ser., 33, 182  (1961).

-------
                                   -59-
                            LITERATURE CITED (Cont'd)

 Qader,  S.A.,. W.H. Wiser, and G.R.  Hill, Ind. Eng. Chem., Proc. Des. Develop.,
      7., 390  (1968).
 Satterfield,  C.N., Mass Transfer in Heterogeneous Catalysis, pp. 141-148,
      M.I.T. Press, Cambridge (1970).
 Satterfield,  C.N. and J.F. Cocchetto, "Pyridine Hydrodenitrogenation:  An
      Equilibrium Limitation on the Formation of Piperidine Intermediate,"
      AIChE ^.  (in press).
 Satterfield,  C.N. and G.W. Roberts, "Kinetics of Thiophene Hydrogenolysis
      on  a Cobalt-Molybdate Catalyst," AIChE J.. 14, 159 (1968).
 Schuit,  G.C.A., and B.C. Gates, "Chemistry and Engineering of Catalytic
      Hydrodesulfurization," AIChE J., 19, 417 (1973).
 Schuman, S.C., and H. Shalit, "Hydrodesulfurization," Catal. Rev., i,
      245 (1970).
 Scott,  D.W.,  "Piperidine: Vibrational Assignment, Conformational
      Analysis, and Chemical Thermodynamic Properties, J. Chem. Thermo-
      dynamics, 3_, 649 (1971).
 Smith, H.A., pp. 231-234 in Catalysis. Vol. V,  P.H. Emmett, Ed.s (Reinhold,
      New York, (1957)).
 Snyder, L.R., Am. Chem.  Soc.  Div.  Petrol.  Chem.  Preprints. 4_ (2), C43  (1970).
 Sonnemans, J., F. Goudriaan and P.  Mars,  "The Hydrogenolysis of Pyridine
     on Molybdenum Oxide Containing Catalysts,"  Fifth Intl. Cong, on Catal.,
      Palm Beach Fla.  (1972),  paper  78.
 Sonnemans, J., W.J.  Neyens and P. Mars,  "IV.  The Conversion of Piperidine,"
     J. Cat. 34, 230 (1974).
 Sonnemans, J., G.H.  Van  der Berg and P. Mars, "The Mechanism of Pyridine
     Hydrogenolysis  on Molybdenum-Containing  Catalysts,"  II.   "Hydrogena-
     tion of Pyridine to Piperidine," J.  Cat. 31, 220 (1973).
Stengler, W., J. Welker  and E.  Leibnitz,  Freiberger Forchungsh.   329A
     51  (1964).
Tanatarov, M.A., R.A.  Faskhutdinov, M.E.  Levinter and 1.6.  Akmetov, "The
     role of sulfidization of an alumina-cobalt-molybdena  catalyst
     in the sulfidization of  thermally cracked gasoline,"  Int.  Chem. Eng..
     12, 85 (1972).

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                                  -60-
                         LITERATURE CITED (Cont'd)

van Krevelen, D.W., and H.A.G.  Chermin,  Chem.  Eng.  Sci..  1, 66  (1951).
Weisser, 0., and S. Landa, Sulfide Catalysts,  Their Properties  and Appli-
     cations, pp. 118-354, Pergamon Press,  New York (1973a).
Weisser, 0., op. cit., p.  60 (19735).

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                                     -61-
                                 TECHNICAL REPORT DATA
                           (Please read Instructions on the reverse before completing)
 1. REPORT NO.
   EPA-600/2-75-063
                            2.
                                                        3. RECIPIENT'S ACCESSION NO.
 4. TITLE AND SUBTITLE
 Catalytic Desulfurization and Denitrogenation
                                                        5. REPORT DATE
                                                        October 1975
                                                        6. PERFORMING ORGANIZATION CODE
 7. AUTHOH(S)
 Charles  N. Satterfield, Michael Modell, Jerome F.
 Mayer, and Joseph F. Cocchetto
                                                        8. PERFORMING ORGANIZATION REPORT NO
 9. PERFORMING OROANIZATION NAME AND ADDRESS
 Massachusetts Institute of Technology
 Department of Chemical Engineering
 77 Massachusetts Avenue
 Cambridge, Massachusetts  02139
             10. PROGRAM ELEMENT NO.
             1AB013; ROAP 21ADD-053
             11. CONTRACT/GRANT NO.
             Grant R-800897
 12. SPONSORING AGENCY NAME AND ADDRESS
 EPA, Office of Research and Development
 Industrial Environmental Research Laboratory
 Research Triangle Park, NC 27711
             13. TYPE OF REPORT AND PERIOD COVERED
             Final; 6/72-7/75
             14. SPONSORING AGENCY CODE
 15. SUPPLEMENTARY NOTES
 16. ABSTRACT The reporf giV6s results of a study of catalytic desulfurization and denitro-
 genation, using thiophene and pyridine as model compounds because they represent
 some of the less reactive organosulfur and organonitrogen compounds.  When
 thiophene is hydrodesulfurized simultaneously with the hydrodenitrogenation of
 pyridine  (200 to 500 C, 4.4 and 11.2 bars pressure, commercial catalysts), the
 two reactions are  mutually inhibitive at lower temperatures.  At high temperatures,
 H2S  (a hydrodesulfurization reaction product) enhances the hydrodenitrogenation
 rate. The  report  proposes mechanisms to explain these observations.  In hydrode-
 nitrogenation of pyridine and other heterocyclic nitrogen compounds, the rate may be
 at least partly governed by the equilibrium of the first step,  the hydrogenation of the
 N-containing ring.
 7.
                              KEY WORDS AND DOCUMENT ANALYSIS
                 DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS  C. COSATI Field/Group
 Air Pollution
 Desulfurization
  atalysis
 Thiophenes
 Pyridines
Air Pollution Control
Stationary Sources
Denitrogenation
13 B
07A, 07D

07C
 8. DISTRIBUTION STATEMENT
 Unlimited
                                           19. SECURITY CLASS (This Report)
                                           Unclassified
                                                                    21. NO. OF PAGES
                              67
                                           20. SECURITY CLASS (This page)
                                           Unclassified
                                                                    22. PRICE
EPA Form 2220-1 (9-73)

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