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-
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This document is available to the public through the National
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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 300°C, (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. 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 500°C., 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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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
400°C, 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 300°C
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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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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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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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 + 1°C below 350°C and +_ 2°C above 350°C.
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
150°C 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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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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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 (500°C) reached
1n some of the mixed feedstock runs. Subsequent experiments were limited
to 425°C. 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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100
z
Q
o:
UJ
>
8
U
Z
UJ
X
Q.
g
I
z
UJ
o
o:
UJ
Q.
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
-------
z
O
Q:
ui
O
U
UJ
z
UJ
QL
O
I
Z
UI
U
£t
UI
0.
1OO
80
60
Q 4O
2O
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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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
380°C. 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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100
z
o
<7>
QC
y
i
o
UJ
z
u
I
Q.
O
Z
UJ
u
a
it!
20 -
Partial Pr«ssur«f 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 Prti«ur*«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.)
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80
z
O
to
LJ
Z
O
U
LJ
Z
O
o:
EL
h-
Z
LJ
U
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.)
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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 325°C 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 325°C 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 325°C (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 H«S 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 250-350°C. 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 H«S 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 H«S 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-
z
O
to
or
LJ
>
z
O
u
LJ
Z
o:
>-
Q.
z
u
u
or
u
Q.
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
z
g
i?>
CE
u
>
z
O
u
u
z
o:
CL
H-
Z
UJ
U
o:
UJ
CL
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 400°C 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 350°C, 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
O
v>
a:
u
>
z
O
U
u
z
LJ
I
0.
O
I
Z
U
U
a:
LJ
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 300°C, 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 (315°C, 50-TOO bars, NiCoMo/Al-O- catalyst) hydrogenation
ۥ 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 350°C 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 350°C, 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 400°C. 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 200°C to 425°C. 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 250°C) 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 375°C 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 250°C ^
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 250°C ^
3.08
10.8
a. Residence time is calculated based on the superficial gas velocity
at 250°C and 11.2 bars
-------
1.0
K
Z>
0
I/)
LJ
U
UJ
DL
I/)
U.
O
I/}
U
0
2
-z.
u
_
5
cr
>-
Q_
Lu
O
\T>
UJ
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
O
o:
LJ
O
U
u
z
Q
o:
Z
U
u
f£
U
OL
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.)
-------
o
o
Ld
Ld
Q
E
Ld
Q_
tO
Ld
O
9 100
cr
Ld
CL
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.
-------
o
o
LJ
UJ
cr
Ld
Q.
LJ
_J
O
100
Q
rr
LJ
Q_
CL
I/)
LJ
_J
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
o
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 300°C. 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
400°C, equilibrium was established. With piperidine feed, no pyridine
was observed below 300°C but above this temperature its quantity in-
creased steadily at the expense of the piperidine. At 400°C, 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 430°C with the piperidine feed, and at a slightly
lower temperature (about 400°C) 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/Al«0~, below about 275°C piperidine
£ O
was the only reaction product, and the material balance was within a
-------
H
O
in
LI
x
CL "^^
U. 0.2
°
I/)
QJ
Q 0.1
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 300°C and dropped to nearly zero at high tempera-
tures. Ammonia and n-pentane were not observed at 251°C but were found
in appreciable quantities at 295°C. Much greater quantities of ammonia
and other light products appeared at 356°C and 402°C, but a decrease was
observed at 426°C 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 370°C
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 300°C, but in smaller quantities
than with NiMo/AlpO.,. Small quantities of n-pentylamine were observed
in the off-gas from 300-400°C. 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 300°C 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 300°C, 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-
-------
o
(/)
LJ
U
Ld
Q_
CO
Lu
O
tO
LJ
_J
O
1.0
0.8
0.6
LJ
Q
o:
LJ
Q.
Q- 0.4
O
LJ 0.2
_J
O
z
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.
-------
O
Ld
u
Ld
Q_
l/)
L_
O
I/)
Ld
_J
O
2
1.O
0.8
Ld
0: 0.6
Ld
Q_
0.
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
a>
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 400°C. 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
315°C 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 375-400°C 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.
-------
-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
-------
-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
-------
-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 450°C (570-850°F) 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
-------
-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,
-------
-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:
AG°f = 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
-------
-43-
free energy of formation was then found as follows:
AG°f = AH°f - TAS°f (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 1000°K, 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 298°K to 0.1 at 1000°K. 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
-------
-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 1000°K and two orders of magnitude at 500°K.
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
225°C. The equilibrium constants for all the other reactions are favorable
even at temperatures approaching 500°C.
-------
-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.
-------
-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 500°C.
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 500°C. 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
-------
-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 1500°K; 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).
-------
-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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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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