Note: Descriptions are shown in the official language in which they were submitted.
~(~6~G
F-8865 BACKGROUND OF THE INVENTION
Processes for the conversion of gaseous mixtures comprising
hydrogen and carbon monoxide are known in the prior art. Also
various processes may be employed for the preparation of such
gases. Those of major importance depend either on the partial
combustion of fuel with an oxygen containing gas or on the high
temperature reaction of a selected fuel with steam, or on a
combination of those two reactions. It is known that synthesis
gas will undergo conversion reactions to form reduction products
of carbon monoxide, such as hydrocarbons, at temperatures in
the range of 300 to about 850F, at pressures in the range of
one atmosphere up to about 1000 atmospheres in the presence of
a fairly wide variety of catalysts. The Fischer-Tropsch process
for example, produces a range of liquid hydrocarbons, a portion
of which have been used as relatively low octane gasoline
materials. Catalyst employed in this process and some related
processes include those based on metals and/or oxides of iron,
cobalt, nickel, ruthenium, thorium, rhodium and osmium. On
the other hand, the Fischer-Tropsch processing technology has
been plagued with numerous problems such as deactivation of
the catalyst with sulfur and catalyst regeneration problems.
In addition it has been difficult to find and identify those
conditions which produce liquid hydrocarbons boiling in the
gasoline boiling range containing highly branched paraffins
and substantial quantities of aromatic hydrocarbons required
; to produce high quality gasoline. A number of publications
review the status of the Fischer-Tropsch synthesis art. None
of these publications however provide a satisfactory answer
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1(~61~(~6
for processing synthesis gas to hydrocarbons including those
boiling in the gasoline boiling range where the catalyst is
subjected to continuous or intermittent contact with sulfur.
The present invention is concerned with a recently
discovered and unexpected method for converting synthesis
gas to desired hydrocarbon products including gasoline boiling
range aromatics in the presence of sulfur.
SUMMARY OF THE INVENTION
It has now been discovered that synthesis gas with or
10 without sulfur such as hydrogen sulfide present may be con- -
verted to hydrocarbons by contacting the synthesis gas with a
special catalyst composition which is relatively insensitive
to sulfur and whose activity and selectivity may even be improved
as well as restored after continuous exposure to sulfur in the
synthesis gas feed. The present invention is concerned with
the catalytic conversion of synthesis gas to desired hydro-
carbon products including gasoline boiling range aromatics
wherein the catalyst is continuously or intermittently sub-
jected either by design or by accident to contact with sulfur
components in the synthesis gas.
Thus, the present invention in its broadest aspect ,
relates to a method for converting synthesis gas to hydro-
; carbon components in the gasoline range which comprises con-
tacting synthesis gas at a temperature range of 400 to 1000F
with a carbon monoxide reducing catalyst comprising at least
one of hafnium and zirconium, as metal, oxide or sulfide,
in admixture with a crystalline aluminosilicate zeolite having
a silica to alumina ratio of 12 to 3000 and a constraint index
within the range 1 to 12.
In a particular respect the present invention is con-
cerned with the conversion of synthesis gas comprising hydrogen
and carbon monoxide derived, for example, from coal with or
~ 3 -
~U61~36
without the presence of sulfur therein to form paraffin and
; aromatic hydrocarbons preferably boiling within the qasoline ~ -
boiling range by contacting the syngas with a particular
heterogeneous catalyst mixture relatively insensitive to
sulfur compounds. More particularly, the present
'
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invention is concerned with the conversion of synthesls gascomprising carbon monoxide and hydrogen to hydrocarbon products
~ by contacting a special class of crystalline zeolites represented
; by ZSM-5 in admixture with a carbon monoxide reducing compor.ent
comprising hafnium and/or zirconium, as metal, oxide and/or
sulfide. Molybdenum may be present in admixture therewith.
... .
The synthesis gas may be prepared from rOssil fuels by
- any one of the methods known in the prior art including in situ
gasification processes such as underground combustion of coal
and petroleum deposits. The term fossil fuels is intended to
include anthracite and bituminous coal, lignite, crude petroleum,
shale oil, oil from tar sands, natural gas, as well as fuels
derived by separation or transformation of these materials.
The synthesis gas produced from fossil fuels will often
, ~.!, 15 contain various impurities such as particulates, sulfur, and
~......................................................................... i
` metal carbonyl compounds and will be characterized by a hydrogen
: to carbon oxides (carbon monoxide and carbon dioxide) ratio
,;' !
- which will depend on the fossil fuel and the particular gasifi-
cation technology utilized. In general, it has been essential
; 20 heretofore to purify the raw synthesis gas for the removal of
these impurities. It has now been found however that sulfur in
the syngas (synthesis gas) need not be removed when the catalysts
- of this invention are employed to effect conversion of the syn- i
thesis gas. However, it may be desirable under some conditions
to e~fect a partial removal af the sulfur and complete removal
of other undesired contaminants. In the conversion operations
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- of this invention, it is preferred to adjust the hydrogen to
carbon oxides volume ratio to be within the range of from 0.2
to about 6.0 and more usually adjusted to a 1/1 ratio prior to
contact with the catalyst. The well known water gas shift re-
- 5 action may be used to increase the hydrogen ratio if required
or in the event of a hydrogen rich synthesis gas, it may be
- adjusted by the addition of carbon monoxide and/or carbon
dioxide.
The heterogeneous catalyst mixture of this invention is
one comprising at least two components intimately mixed with
one another and known and referred to as a sulfur insensitive
or sulfur tolerant catalyst mixture. The sulfur tolerant
component may or may not lose some activity in the presence
of sulfur but at least it will reactivate itself substantially
completely simply by removing or reducing the presence of
,,
- sulfur in the syngas feed. Thus in the process of this invention
-~ it is particularly contemplated employing a catalyst mixture
,~ in which the carbon monoxide reducing component is selected
from a class of inorganic substances that are substantially
sulfur insensitive by having activity for the reduction
, of carbon monoxide in the presence of hydrogen to form
:.~ , . .
hydrocarbons and in which the other component is a zeolite
selected from a particular class of crystalline aluminosilicate
characterized by a pore dimension greater than about 5 Angstroms,
a silica to alumina ratio greater than 12, and a constraint index
in the range of 1 to 12. The class of crystalline zeolite so
! classified and identified herein is a class of crystalline
zeolites represented by ZSM-5, ZSM-ll, ZSM-12, ZSM-35 and ZSM-38.
,~
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- - . . ~ .
- , . - : .
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A sulfur tolerant inorganic substance com~ris-'ng one
or more components which may or may not lose activity i- the
presence of sulfur and substantially reactivate itself u~on
removal of sulfur is employed in intimate mixture as se~arate
particles or combined with the crystalline zeolite herein defined
as a single catalyst partlcle. Inorganic substances suitable
for the purposes of this invention include elements of Groups
IIIB and IVB; those which have been found to be particularly
sulfur tolerant in these groups include zirconium and hafnium.
Sul~ur may even act as a promoter for these materials,
.:
Known Fischer-Torpsch synthesis catalysts other than
; thoria have been found to be substantially completely deactivated
by contact with sulfur or compounds of sulfur thereby requiring
their removal from the process since a satisfactory regen~eration
procedure has not been found that will restore the sulfur de-
activated catalyst activity and selectivity. The inorganic sub-
stance may be employed in amounts ranging from about 0.1% up
to about 80 percent by weight and preferably is less than 60
peroent by weieht of the active components of the ~ntimate m~xture.
. :
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The acidic crystalline aluminosilicate component of
the heterogeneous catalyst is characterized by a pore dimension
greater than about 5 Angstroms, i.e., it is capable of sorbing
paraffins having a single methyl branch as well as normal
paraffins, and it has a silica-to-alumina ratio of at least 12.
Zeolite A, for example, with a silica-to-alumina ratio of 2.0
is not useful in this invention, and it has no pore dimension
greater than about 5 Angstroms.
The crystalline aluminosilicates herein referred to,
also known as zeolites, constitute an unusual class of natural
and synthetic minerals. They are characterized by having a
rigid crystalline framework structure composed of an assembly
of silicon and aluminum atoms, each surrounded by a tetrahedron
of shared oxygen atoms, and a precisely defined pore structure.
Exchangeable cations are present in the pores.
The catalysts referred to herein utilize members
of a special class of zeolites exhibiting some unusual properties.
These zeolites induce profound transformations of aliphatic
; hydrocarbons to aromatic hydrocarbons in commercially desirable
yields and are generally highly effective in alkylation, isomeri-
~' zation, disproportionation and other reactions involving aromatic
hydrocarbons. Although they have unusually low alumina contents,
i.e. high silica to alumina ratios, they are very active even
with silica to alumina ratios exceeding 30. This activity
is surprising since catalytic activity of zeolites is generally
attributed to framework aluminum atoms and cations associated
with these aluminum atoms. These zeolites retain their
`:`
106
crystallinity for long periods in spite of the presence of
steam even at high temperatures which induce irreversible
collapse of the crystal framework of other zeolites, e.g. of
the X and A type. Furthermore, carbonaceous deposits, when
formed, may be removed by burning at higher than usual
temperatures to restore activity. In many environments
the zeolites of this class exhibit very low coke forming
capability, conducive to very long times on stream between
burning regenerations.
An important characteristic of the crystal structure
of this class of zeolites is that it provides constrained
i .
access to, and egress from, the intra-crystalline free
space by virtue of having a pore dimension greater than about
, 5 Angstroms and pore windows of about a size such as would
'~ 15 be provided by 10-membered rings of xoygen atoms. It is to
be understood, of course, that these rings are those formed
~i by the regular disposition of the tetrahedra making up the
anionic framework of the crystalline aluminosilicate, the
' oxygen atoms themselves being bonded to the silicon or
,~;
aluminum atoms at the centers of the tetrahedra. Briefly,
` the preferred zeolites useful in type B catalysts in this
invention possess, in combination: a silica to alumina ratio
of at least about 12; and a structure providing constrained
access to the crystalline free space.
The silica to alumina ratio referred to may be
determined by conventional analysis. This ratio is meant to
represent, as closely as possible, the ratio in the rigid
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1(~61~U~;
anionic framework of the zeolite crystal and to exclude
aluminum in the binder or in cationic or other form within
the channels. Although zeolites with a silica to alumina
ratio of at least 12 are useful it is preferred to use
zeolites having higher ratios of at least about 30. Such
zeolites, after activation, acquire an intracrystalline
sorption capacity for normal hexane which is greater than
-~ that for water, i.e., they exhibit "hydrophobic" properties.
It is believed that this hydrophobic character is advantageous
in the present invention.
The zeolites useful as catalysts in this invention --
freely sorb normal hexane and have a pore dimension greater
than about 5 Angstroms. In addition, their structure must
provide constrained access to some larger molecules. It is
sometimes possible to judge from a known crystal structure
whether such constrained access exists. For example, if the
only pore windows in a crystal are formed by 8-membered
rings oxygen atoms, then access by molecules of larger cross-
section than normal hexane is substantially excluded and the
zeolite is not of the desired type. Zeolites with windows
of 10-membered rings are preferred, although excessive
puckering or pore blockage may render these zeolites sub-
stantially ineffective. Zeolites with windows of twelve-
membered rings do not generally appear to offer sufficient
constraint to produce the advantageous conversions desired
in the instant invention, although structures can be con-
ceived, due to pore blockage or other cau~e, that ~ay be
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operative.
Rather than attempt to judge from crystal structure
whether or not a zeolite possesses the necessary constrained
~ access, a simple determination of the "constraint index" may
; 5 be made by continuously passing a mixture of equal weight of
- normal hexane and 3-methylpentane over a small sample,
approximately 1 gram or less, of zeolite at atmospheric
pressure according to the following procedure. A sample of
the zeolite, in the form of pellets or extrudate, is crushed
to a particle size about that of coarse sand and mounted in
a glass tube. Prior to testing, the zeolite is treated with
a stream of air at 1000F for at least 15 minutes. The zeolite
is then flushed with helium and the temperature adjusted
between 550F and 950F to give an overall conversion between
10% and 60%. The mixture of hydrocarbons is passed at 1
liquid hourly space velocity (i.e., 1 volume of liquid hydro-
carbon per volume of catalyst per hour) over the zeolite with /
a helium dilution to give a helium to total hydrocarbon mole
ratio of 4:1. After 20 minutes on stream, a sample of the
effluent is taken and analyzed, most conveniently by gas
chromatography, to determine the fraction remaining unchanged
for each of the two hydrocarbons.
The "constraint index" is calculated as follows:
Constraint Index = log10 (fraction of n-hexane remaining)
log10 (fraction of 3-methylpentane
remaining)
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1()6~806
The constraint index approximates the ratio of the
cracking rate constants for the two hydrocarbons. Catalysts
suitable for the present invention are those which employ
a zeolite having a constraint index from 1.0 to 12Ø
Constraint Index (CI) values for some typical zeolites
; including some not within the scope of this invention are: -
CAS C.I.
- Erionite 38
ZSM-5 8.3
ZSM-ll 8.7
.;
ZSM-35 6.0
~ TMA Offretite 3.7
- ZSM-38 2.0
ZSM-12 2
Beta 0.6
ZSM-4 0 5
Acid Mordenite 0.5
; REY 4
s Amorphous Silica-alumina 0.6
The above-described Constraint Index is an important and
` even critical, definition of those zeolites which are useful to
~ -
catalyze the instant process. The very nature of this parameter
and the recited technique by which it is determined, however, admit
of the possibility that a given zeolite can be tested under somewhat
different conditions and thereby have different constraint indexes.
Constraint Index seems to vary somewhat with severity of operation
(conversion). Therefore, it will be appreciated that it may be
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possible to so select test conditions to establish multiple
constraint indexes for a particular given zeolite which may be
both inside and outside the above defined range of 1 to 12.
Thus, it should be understood that the parameter
and property "Constraint Index" as such value is used herein is
an inclusive rather than an exclusive value. That is, a zeolite
when tested by any combination of conditions within the testing
definition set forth herein above to have a constraint index of
~- 1 to 12 is intended to be included in the instant catalyst
` 10 definition regardless that the sa~e identical zeolite tested under
other defined conditions may give a constraint index value outside
of 1 to 12.
The class of zeolites defined herein is exemplified
. by ZSM-5, ZSM-ll, ZSM-12, ZSM-21, and other similar materials.
Recently issued U.S. Patent 3,702,886 describes ZSM-5. ZSM-ll
.~ is more particularly described in U.S. Patent 3,709,979. ZSM-12is more particularly described in U.S. Patent 3,832,449.
French Specification 74-12078 describes zeolite
compositions, and methods of making such, designated as ZSM-21
which are usef~l in this invention.
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The specific ~eolites described, when prepared
in the presence of organic cations~ are substantially
catalytically inacive, possibly because the intracryst~lline
free space is occupied by organic cations from the forming
solution. They may be activated by heating in an inert
atmosphere at lOOO~F ~or one hour, for example, followed by
base exchange with ammonium salts followed by calcination
at 1000F in air. The presence of organic cations in the
forming solution may not be absolutely essential to the
~ormation of this special type zeolite; however, the presence
of these cations does appear to favor the formation of this
special type of zeolite.` More generally, it is desirable
~~ to activate this type zeolite by base exchange with ammonlum
f~ salts followed by calcination in air at about 1000F for
rrom about 15 minutes to about 24 hours.
Natural zeolites may sometlmes be converted to this
type zeolite by various activation procedures and other
~ !
i trea~ments such as base exchange, steaming, alumina extraction
and calcination, alone or ln combinations. Natural minerals
which may be so treated include ferrierite, brewsterite,
stilbite, dachiardlte, epistilbite, heulandite and clinoptll-
ollte. The pre~erred crystalline aluminosilicates are
ZSM-5, ZSM-ll, ZSM-12 and ZSM-21, wlth ZSM-5 particularly
: preferred.
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~ 6 ~ ~ ~6
The zeolites used as catalysts in this invention
may be in the hydrogen form or they may be base exchanged or
impregnated to contain ammonium or a metal cation complement.
It is desirable to calcine the zeolite after base exchange.
5 The metal cations that may be present include any of the
cations of the metals of Groups I through VIII of the periodic
table. However, in the case of Group IA metals, the cation
content should in no case be so large as to substantially
eliminate the activity of the zeolite for the catalysis being
10 employed in the instant invention. For example, a completely
sodium exchanged H-ZSM-5 appears to be largely inactive for
- shape selective conversions required in the present invention.
In a preferred aspect of this invention, the
zeolites useful as catalysts herein are selected as those
- 15 having a crystal framework density, in the dry hydrogen form,
of not substantially below about 1.6 grams per cubic centi-
meter. It has been fo~nd that zeolites which satisfy all
three of these criteria are most desired. Therefore, the
preferred catalysts of this invention are those comprising
zeolite having a constraint index as defined above of about
1 to 12, a silica to alumina ratio of at least about 12 and a
:
dried cyrstal density of not substantially less than about 1.6
gram per cubic centimeter. The dry density for known structures
; may be calculated from the number of silicon plus aluminum
atoms per 1000 cubic Angstroms, as given, e.g., on page 19
of the article on Zeolite Structure by W. M. Meier. This
paper, the entire contents of which are incorporated herein
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~1~618~6
by reference, is included in "Proceedings of the Conference
Molecular Sieves, London, April, 19S7", published by the
Society of Chemical Industry, London, 1968. When the
crystal structure is unknown, the crystal framework density
may be determined by classical pyknometer techniques. For
example, it may be determined by immersing the dry hydrogen
form of the zeolite in an organic solvent which is not
sorbed by the crystal. It is possible that the unusual
sustained activity and stability of this class of zeolites
is associated with its high crystal anionic framework density
of not less than about 1.6 grams per cubic centimeter. This
high density of course must be associated with a relatively
small amount of free space within the crystal, which might
be expected to result in more stable structures. This free
space, however, seems to be important as the locus of
catalytic activity.
Crystal framework densities of some typical
zeolites including some which are not within the purview
of this invention are:
Zeolite Void Framework
Volume Density
Ferrierite 0.28 cc/cc 1.76 g/cc
Mordenite .28 1.7
i ZSM-5, -11 .29 1.79
i 25 Dachiardite .32 1.72
L .32 1.61
Clinoptilolite .34 1.71
j Laumontite .34, 1.77
; 30 ZSM-4 (Omega) .38 1.65
' Heulandite .39 1.69
;~ P .41 1.57
,. Offretite .40 1.55
Levynite .40 1.54
li 35 Erionite .35 1.51
f' Gmelinite .44 1.46
' Chabazite .47 1.45
A .5 1.3
Y .48 1.27
-15-
The heterogeneous catalysts may be prepared in
various ways. The two components may be separately prepared
in the form of catalyst particles such as pellets or extrudates,
for example, and simply mixed in the required proportions.
The particle size of the individual component particles may
be quite small, for example, from about 20 to about 150 microns,
when intended for use in fluid bed operation; or they may be
as large as up to about 1/2 inch for fixed bed operation.
Or, the two components may be mixed as powders and formed
; 10 into pellets or extrudate, each pellet containing both
components in substantially the required proportions. Binders
such as clays may be added to the mixture. Alternatively,
the component that has catalytic activity for the reduction
of carbon monoxide may be formed on the acidic crystalline
.~ 15 aluminosilicate component by conventional means such as
. "
impregnation of that solid with salt solutions of the desired
metals, followed by drying and calcination. Base exchange of
the acidic crystalline aluminosilicate component also may be
used in some selected cases to effect the introduction of
part or all of the carbon monoxide reduction component. Other
means for forming the intimate mixture may be used, such as:
precipitation of the carbon monoxide reduction component in
the presence of the acidic crystalline aluminosilicate; or
electroless deposition of metal on the zeolite; or deposition
of metal from the vapor phase. Various combinations of the
above preparative methods will be obvious to those skilled
in the art of catalyst preparation. It should be cautioned,
however, to avoid techniques likely to reduce the crystallinity
of the acidic crystalline aluminosilicate.
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:............. - . - , : - :
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It will be recognized from the foregoing descrip-
tion that the heterogeneous catalysts, i.e., the above-described
intimate mixtures, used in the process of this invention, may
; have varying degrees of intimacy. At one extreme, when using
l/2 inch pellets of the carbon monoxide reducing component
`~ mixed with l/2 inch pellets of the acidic crystalline alumino-
~; silicate, substantially all locations within at least one of
the components will be within not more than about lt2 inch of
some of the other component, regardless of the proportions
in which the two components are used. With different sized
pellets, e.g., l/2 inch and 114 inch, again substantially all
locations within at least one of the components will be within
not more than about l/2 inch of the other component. These
examples illustrate the lower end of the degree of intimacy
required for the practice of this invention. At the other
extreme, one may ball mill together acid crystalline alumino-
silicate particles of about O.l micron particle size with
colloidal zinc oxide of similar particle size followed by
~ pelletization. For this case, substantially all the locations
: 20 within at least one of the components will be within not more
than about O.l micron of somé of the other component. This
exemplifies about the highest degree of intimacy that is
' practical. The degree of intimacy of the physical mixture
, may also be expressed as the minimum distance of separation
` 25 of the central points located within the particles of the two
,?; components. This will, on average, be represented by one-half
~ the sum of the average part~-le size for the two components.
.
~-
~ 6
Thus, for the foregoing example illustrating the highest degree
of intimacy, the centers of the particles of either of the
two components will be separated from the nearest particle
of the other component by an average distance of at least
about 0.1 micron. The degree of intimacy of the heterogeneous
catalyst is largely determined by its method of preparation,
but it may be independently verified by physical methods
such as visual observations, examination in an ordinary micro-
scope or with an electron microscope, or by electron microprobe
analysis.
In the process of this invention, synthesis gas is
contacted with the heterogeneous catalyst at a temperature in
the range of from about 400F to about 1000F, preferably from
about 500F to about 850F, at a pressure in the range of
from about 1 to about 1000 atmospheres, preferably from about
3 to about 200 atmospheres, and at a volume hourly space
velocity in the range of from about 500 to,about 50,000 volumes
of gas, at standard temperature and pressure per volume of
catalyst, or equivalent contact time if a fluidized bed is
used. The heterogeneous catalyst may be contained as a fixed
bed, or a fluidized bed may be used. The product stream
; containing hydrocarbons, unreacted gases and steam may be
cooled and the hydrocarbons recovered by any of the techniques
known in the art, which techniques do not constitute part of
this invention. The recovered hydrocarbons may be further
separated by distillation or other means to recover one or more
products such as high octane gasoline, propane fuel, benzene,
toluene, xylenes, or other aromatic hydrocarbons.
., .
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;` 1
Example 1
.
A sample of pure ZrO2 was made by thermal decomposition
of the oxalate thereof. Composite catalysts were made by ball-
milling and pelleting.
Synthesis gas (H2/C0 = 1) was reacted over zirconia
and a zlrconia-ZS~-5 crystalline zeolite composite catalyst
at 1200 psig, 800F and 1.3-1.5 VHSV (gas at standard tempera-
- ture and pressure) (based on ZrO2) or 720-750 ~HSV (based on
total reaction volume). The effect of the ZSM-5 crystalline
zeolite on the reaction product of zirconia appear to be
similar to the effect observed of the zeolite upon a thoria
catalyst. The principal effect observed is the reduction in
methane formation. Some activity enhancement is evidence and
'"! aromatics distribution appears to be similar to that observed
when using a ThO2/ZSM-5 catalyst.
WHSV is the weight of feed/weight of catalyst X time
in hours.
VHSV is the volume of gas/volu~e of catalyst X time
in hours.
STP is identified as standard temperature of 0C and
760 min.Hg.
The effect of H2s on zro2/zsM-5 catalyst activity
was determined and reported in Table 1 below. The initial
portion of the test (Run A) was run without H2S to establish
a base case. The operating conditions were 600 psig, 800F
, . .
q and 1.3 WHSV (based on ZrO2). After 20 hours on stream, about
3 wt.% of H2S was introduced on a continuous basis with the
H2/C0 syngas feed stream. A material balance was obtained after
26 hours continuous exposure to H2S (Run B). Catalytic activity,
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~1)61~
unexpectedly and quite surprisingly~ was unimpaired. A slightly
higher conversion observed in Run B appears to be attributable
to a lower WHSV for the run. The main influence attributable
to H2S appears to be to increase the methane yield (~rom 3.6%
to about 11.2%) and to reduce aromatics formation. A sign~ficant
amount of COS (carbonyl sulfide) was found in the effluent 'hus
` indicating that catalytic activity is also unaffacted by this
substance. The space velocity was then reduced to 0.26 WHSV
(Run C). After an additional 24 hours on stream another material
balance was made (Run C) which revealed a three-fold higher con-
version and little change in selectivity. At the end of Run C,
the H2S was removed from the feed and after an additional 22 hour~
on stream, a product analysis was made. This analysis showed
a drop in methane make and recovery of the catalyst selectivity
for producing aromatics. See Run D. The analysis also showed
a lower conversion which can be partially accounted for in the
use of a somewhat higher (WHSV) space velocity during the
period to obtain a material balance. Catalyst aging may also
be a contributing factor. It is even possible to rationalize
that the H2S in the feed operates as a catalyst promoter. In
any event the production of aromatics in Run D is higher than that
obtalned in F~uns B and C.
.~
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L~.31~ 1
~FFECT OF H2S ON Z~O2/HZSM-5 SYNGAS COI~V~RSION ACTIVI'l'Y
H2/CO = 1, H2S 3 wt%
Run A B C D
¦~ H2S addition
Reaction Conditions
Temperature, F 800 800 800 800
Pressure, psig 600 600 600 600
. WHSV, hr~l (a) 1.3 1.0 0.26 0.34
Time on Stream 20 46 70 92
; Conversion, %
CO 8.o10.6 28.9 16.3
. H2 8.810.7 36.0 13.0
'1 Total Effluent,wt%
. . .
~ Hydrocarbons 2.7 3.7 13.1 6.8
: H O 1.8 1.1 2.8 0.2
' C23.68.214.1 9.1
CO85.8 81.1 64.5 78.1
H26.15.85.3 5.8
Other (b) - 0.1 0.2
., .
Hydrocarbons, wt%
~ Methane 3.6 11.2 10.2 5.5
.' Ethane 7 9 8.5 11.7 12.4
: Ethylene 0.2 0.2 -- --
Propane 12.6 19.6 13.6 12.1
, Propylene 0.1 0.1 -- --
'. i-Butane 1.0 2.1 0.5 0.7
n-Butane o.6 1.4 0.5 0.2
Butenes
C~+ PON - 0.2 0.1
A~omatics 74.0 56.7 63.4 69.1
!
~ (a) WHSV based on ZrO2 component
: (b) Mainly COS (H2S-free basis)
~ -21-
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Example 2
Synthesis gas containing ~ 2.5% H2S was converted
to aromatic hydrocarbons over HfO2/HZSM-5. The catalyst was
found to be resistant to sulfur poisoning. This is demonstrated
in the attached Table 6.
Sulfur (2.5%H2S) was added to the syngas (synthesis
gas) feed (LPA 130B). The results clearly demonstrate the
ability of the catalyst to function in the presence of sulfur.
As previously observed with ThO2/HZSM-5 catalysts, the presence
; 10 of sulfur tends to increase methane slightly with a subsequent
decrease in aromatics.
A catalyst containing 35% TiO2/65% HZSM-5 gives a
conversion of syngas about 1/3 of that achieved with ZrO2 and
` about 1/2 of that achieved with HfO2. Part of this lower
conversion result is attributed to the lower TiO2 content
"
(35%). This TiO2 data is shown in the attached table.
An experiment in which 0.5 wt.% of rare earth elements
~ added to ZrO2/HZSM-5 as a promoter is also shown in the attached
t. le. The rare earth was added aa the chloride salt.
-22-
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-23-
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-24-
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