CA1113508A - Conversion of synthesis gas to aromatic hydrocarbons - Google Patents

Abstract

CONVERSION OF SYNTHESIS GAS
TO AROMATIC HYDROCARBONS

ABSTRACT OF THE DISCLOSURE

Synthesis gas is converted to aromatic hydrocarbons over an intimate mixture of catalysts comprising a first component of ZnO-Cr2O3 mixed catalyst, characterized by catalytic activity for the reduction by hydrogen of carbon monoxide, wherein the Zn:Cr atomic ratio is less than about 4:1 and a second component selected from a selective class of acidic crystalline alumino-silicates having a silica:alumina ratio greater than 12:1 and a pore dimension greater than about 5 Angstroms.

Description

Field of the In~entlon `
. Thl~ invention ic concerned w$th an im~roved prooess for convertlng synthesls gas, l.e. mixtures of.~aseous car~on . oxldes with hydrogen or hydro~en donors, to hydrocarbon mixtures. ..
This in~entlon is parti.cularly concerned with a process for .
converting synthesis gæs to hydrocarbon ~ixtures rlch ln aromætlc hydrocarbons. In another aspect,.this i.nvention is concerned with providlng novel catalysts for the conversion of synthesls . ~

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gas to hydrocarbon mixtures rich in aromatic hydrocarbons.

Prior Art Processes for the conversion of coal and other hydro-carbons such as natural gas to a gaseoùs mixture consisting essentially of hydrogen and carbon monoxide, or of hydrogen and carbon dioxide, or of hydrogen and carbon mon~xide and carbon dioxide, are well known. Although various processes may be employed for the gasificiation, those of major importance depend either on the partial combustion of the fuel with an oxygen-containing gas or on the high tempera-ture reaction of the fuel with steam, or on a combination of these two reactions. An excellent summary of the art of gas manufacture r including synthesis gas, from solid and liquid fuels, is given in Encyclopedia of Chemical Technology, Edited by Kirk-Othmer, Second Edition, Volume 10, pages 353-433, (1966), Interscience Publishers, New York, New York. The techniques for gasification of coal or other solid, liquid or gaseous fuel are not considered to be per se inventive here.
It would be very desirable to be able to effectively convert synthesis gas, and thereby coal and natural gas, to highly valued hydrocarbons such as motor gasoline with high octane number, petrochemical feedstocks, liquefiable petroleum fuel gas, and aromatic hydrocarbons. It is well known that synthesis gas will undergo conversion to form reduction products of carbon monoxide, such as hydrocarbons, and/or oxygen containing compounds such as methanol at from about 300F to about 850F

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under from about one to one thousand atmospheres pressure, over a fairly wide variety of catalysts. The Fisher-Tropsch process, for example, which has been most exten-sively studied, produces a range of liquid hydrocarbons, a portion of which have been used as low octane gasoline.
The types of catalysts that have been studied for this and related processes include those based on metals, oxides or other compounds of iron, cobalt, nickel, ruthenium, thorium, rhodium and osmium. Methanol synthesis processes, for example, use catalysts composed of mixtures of two or more oxides and in particular use ZnO base and CuO base mixed catalysts. A review of catalytic processes for the synthesis of methanol from mixtures containing CO and H2 is given in Emmett, P.H., Catalysis III, N.Y., Reinhold, 1955. Chapter 8, pages 349-411, by G. Natta, Synthesis of Methanol.
The wide range of catalysts and catalyst modifications disclosed in the art and an equally wide range of conver-sion conditions for the reduction of carbon monoxide by hydrogen provide considerable flexibility toward obtaining sele~ted boiling~range products. Nonetheless, in spite of this flexibility, it has not proved possible to make such selections so as to produce liquid hydrocarbons in the gasoline boiling range which contain highly branched paraffins and substantial quantities of aromatic hydro- - -carbons, both of which are desired for high quality gasoline, or to selectively produce aromatic hydrocarbons particularly rich in the benzene to xylenes range. A
review of the status of this art is given in "Carbon 3Q Monoxide-Hydrogen Reactions", Encyclopedia of Chemical Technology, Edited by Kirk-Othmer, Second Edition, Volume ' ~;13S~

4, pages 446-488 and Volume 13, pages 370-398.
Interscience Publishers, New York, N.Y.
Recently it has been discovered that synthesis gas may be converted to oxygenated organic compounds and these then converted to higher hydrocarbons, particularly high octane gasoline, by catalytic contact of the synthesis gas with a carbon monoxide reduction catalyst followed by contacting the conversion products so produced with a special type of zeolite catalyst in a separate reaction zone. This two-stage conversion is described in Canadian Patent No. l,035,297.
Still more recently, it has been discovered that synthesis gas may be converted to hydrocarbon mixtures useful in the manufacture of heating oils, gasoline, aromatic hydrocarbons, and chemical intermediates by : catalytic contact with an imtimate mixture of: (l) carbon monoxide hydrogen reduction catalyst comprising a methanol synthesis catalyst and (2) a special type of zeolite catalyst comprising an acidic crystalline aluminosilicate having a silica:alumina ratio greater than 12 and a pore dimension greater than about 5 Angstroms. This one-staa~
conversion is described in U.S. Patent 4,077,866.
It is an object of the present invention to provide an improved process for converting fossil fuels to a hydro-carbon mixture that contans large quantities of highlydesirable constituents. It is a further object of this invention to provide a more efficient method for converting a mixture of gaseous carbon oxides and hydrogen to a mixture of hydrocarbons.

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It is a further object of this invention to provide an improved method for converting synthesis gas to a hydro-carbon mixture rich in aromatic hydrocarbons. It is a further object of this invention to provide novel catalysts for the conversion of synthesis gas to a hydrocarbon mixture rich in aromatic hydrocarbons.

BRIEF SUMMARY OF THE INVENTION
It has been discovered that valuable hydrocarbon mixtures may be produced by reacting synthesis gas, i.e., mixtures of hydrogen gas with gaseous carbon oxides, or the equivalents of such mixtures, in the presence of certain heterogeneous catalysts comprising intimate mixtures of at least two components. U.S. Patent No.
4,077,866 discloses the selective production of light paraffins from synthesis gas using catalysts comprising a methanol synthesis-~omponent and an acidic crystalline aluminosilicate component of selected characteristics.
The present invention is based on the further discovery that a class of chromium oxide catalyst with or without 2Q the presence of zinc oxide and referred to as a methanol synthesis catalyst, as will be more fully described here-inafter, may be modified such that aromatics are produced when this catalyst is used in conjunction with an acidic crystalline aluminosilicate catalyst of selected characteristic.

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It has now been ~ound that aromatics can be syntheslzed from syngas by shi~tlng the metals ratio of a zinc oxide-chromia catalyst away ~rom an optimum for methanol synthesis; specifi-cally, this is accomplished by providing a Zn:Cr ratio less than about 4:1. When the methanol synthesis catalyst component is mixed with the special acidic crystalline aluminosilicate com-ponent herein defined, the catalyst mixture will convert synthesis gas to a mixture of about equal parts of LPG and aromatics with minimal methane production. This intimate catalyst mixture thus produces highly desirable aromatic and LPG products with good selectivity and does so with extraordinarily high conversion per pass. Furthermore, when the preferred class of acidic crystal-line aluminosilicate component is used In the intimate mixture, cataIytic activity is sustained for unusually long periods of time and the sromatic hydrocarbons produced are rlch in toluene and xylene. The catalyst o~ this invention is also air regenerable and has shift capability.
In yet another aspect, the present invention ls based on a~further findlng in that when the components of the càtalyst 20 ~ composltion comprising ZnO, Cr~03, Al203 and acid ZSM-5 crystal-llne zeollte are~æub~ected to grindlng to obtain an unusually ~flne 8tate of 9u~divislon (' 80 mesh) before mixing and pelleting, -the yield of aromatics was markedly increased at the expense of ~ C3~plus (+) pararfins.

Il 25~ ` ~ DETAILED DESC~IPTI~N AND PREFERRED EMBODIMENTS
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Synthesls gas for use in this invention consiits of a mixturs af hydrogen gas ~ith gaæeouæ carbon oxides lncludlng ~:~ :
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carbon monoxide and carbon dloxide. By way of lllustration, a typical purified synthesis gas will have the composition, on a water-free basis, in volume percentages, as follows: hydrogen, 51; carbon monoxide, 40; carbon dioxide, 4; methane, l; and nitrogen, 4.
The synthesis gas may be prepared from fossil fuels by any of the known methods, including such in situ gasification processes as the underground partial combustion of coal and petroleum deposits. The term fossil fueIs, as used herein, is intended to include anthracite and bituminous coal, lignite, crude petroleum, shale oil, oil from tar sands, natural gas, as well as fuels derived from simple physical separations or more profound transformations of these materials, including coked coal, petro-~ leum coke, gas oil, residua from petroleum distillation, and two or more of any of the foregoing materials in combination. Other carbonaceous fuels such as peat, wood and cellulosic waste materials also may be used.
The raw synthesls gas produced from fossil fuels will ,- ¢ontain ~arious lmpurities such as particulates, sulfur, and metal ~arbonyi compounds, and will be characterized by a hydrogen-, to-carbon oxldes ratio which will depend on khe fossil fuel and the~particular gasificatlon technology utllized. In general, lt ; is des~irable for the efficiency of subsequent conversion steps ~to purify the raw synthesis gas by the removal of impurities.
i 2~5 Techniques for such purlfication are known and are not part of thi~ lnvention. It is preferred to ad~ust the hydrogen-to-carbon oxldes ~olume ratlo to be within the range of from 0.2 to 6.0 ~¦prlor eo u ln eh1s in~erelon~ Should the pur1f1ed synthe~1s ~ : . .' . .. ' .
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gas be excessively rich in carbon oxides, it may be brought wlthin the preferred ran~e by the well-known water-gas shlft reaction.
On the other hand, should the synthesis gas be excessively rich in hydrogen, it may be ad~usted into the preferred range by the addition of carbon dioxide or carbon monoxide. Purified synthesis gas ad~usted to contain a volume ratio of hydrogen-to-carbon oxides of from 0.2 to 6.o will be referred to as ad~usted synthesis gas.
It is contemplated that the synthesis gas for use in I0 thIs invention includes art-recognized equivalents to the already described mixtures of hydrogen gas with gaseous carbon oxides.
Mixtures of carbon monoxide and steam, for example, or of carbon dioxide and hydrogen, to provide ad~usted synthesis ~as by in situ reaction, are contemplated.
The heterogeneous catalysts of this invention comprise at least two components lntimately mixed, and in which one com-ponent is selected from the class of ZnO-Cr2O3 substances that have catalytic actlvity for the reduction by hydrogen of carbon monox~ide wherèin the Zn:Cr atomic ratio is less than than about 4:I, and ln which the other component is a class of acidic crystal-I ~ Ilne~ aluminosillcate characterlzed by a pore dimension greater than about 5 Angstroms, a slllca-to-alumina ratio of at least 12 wd c w r-lnt lndex w:thln the ran6e of l to 12.

. . ''' ' ,' ' ~ : ., ',, 1:L135U~3 . ` ' : ' The ZnO-Cr2O3 substance or component characterized by catalytic activity for the reduction by hydrogen of carbon monoxide may be selected from any of the art-recognized ZnO-Cr2O3 mixed catalysts for producing hydrocarbons, oxygenated products, or mixtuIes thereo~, from synthesis gas, subject only to the further restriction that the Zn:Cr ra~io of the mixed catalyst systems be less than about 4:1. Preferably, the Zn:Cr atomic ratio is within the range from about 3.8:I tQ 0:1.
Examples of these mixed catalyst systems include mechanical mixtures of ZnO and Cr203, mixtures of ZnO~Cr2O3 (zinc chromite~
and ZnO, calcined mixtures of coprecipitated zinc and chromium hydroxides or çarbonates, and thermally decomposed mixtures of zinc and chromium acetates.
The ZnO-Cr2O3 mixed catalyst component should in all cases constitute ~rom 0.05 to 99 percent by weight, and preferably from 1: percen~ to ~5 percent of the intimate mixture. The ZnO-Cr~03 mixed catalyst component may be furnished as elemental metals or as corresponding metal compounds.
The aciaic crystalline aluminosilicate componen~ of ~20 ~ the heterogen~ous catalyst is characterized by a pore dimension greater than about 5 Angstroms, i.e., it is c pable of sor~ing paraffins having a single methyl branch as well as normal paraffins, and it has a si}ica-to-alumina ratio of at least 12.
Z¢olite A, ~or example, with a silica-to-alumina ratio of 2.0 is not useful in this invention, it has no pore dLmension greater than about 5 Angstroms.
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Th~ 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 aliphàtic 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 e~en with silica to alumina ratios excPeding 30. This activity is surprising since catalytic activity of zeolites is generally attributed to framework aluminum atoms and cations associated l with these aluminum atoms. These zeolites retain their ;20 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 typ~. Furthermore, carbonaceous deposits, when formed, may be removed by burning at higher than usual tempera-tures to restore activity. In man~ environments the zeolites of this class exhibit very low coke forming capability, conducive to very long ~imes on stream between burning regenerations.
An important characteristic of the crystal structure of this class of zeolites is that it provides constrained ' -10'_ , :::

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access to, and egress from, the intra-crystalline free space by virtue of having a pore dimension greater than about S
Angstroms and pore windows of about a size such as would be provided by lO-membered rings of oxygen atoms. It is to be understood, of course, that these rings are those formed by the regular disposition of the tetrahedra making up the anlonic framework of the crys~alline aluminosilicate, the oxygen ato~s themselves being bonded to the silicon or aluminum atoms at the centers of the tetrahedra. ~riefly, 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 providinq constrained access to the crystal-line free space.
The silica to alumina ratio referred to may be determined by conventional analysis. This ratio i5 meant to represent, as closely as possible, the ratio in the rigid 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, a~ter activation, acquire . an intracrystalline sorption capacity for normal hexane which is greater than that for water, i.e., they exhlbit "hydrophobic"
properties. It is believed that this hydrophobic character is advantageous in the present invention.
The zeolites useful as catalysts in this invention fr~eely so~b normal hexane and have a pore dimension greater than about S Angstroms~ In addition, their structure must provide constrained access to some lasger molecu~es. It is ' ~ ' ~' - .
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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 ri~gs 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 excessiYe puckering or pore blockage may render these zeolites substantially in-ef~ective~ Zeolites with windows of twel~e-membered rings do not generally appear to offer sufficient constraint to produce the advantageous conversions desired in the instant invention, although structures can be conceived, due to pore blockage or other cause, that may be operative.
Rather than att~mpt to judge from crystal structure whether or not a zeolite possesses the necessaxy constrained access, a sLmple determination of the "constrain~ index" may be made by continuously passing a mixture of equal weight of normal hexane and 3-methylpentane o~er a small sample, approxi-mately 1 gram or lessl 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 o~erall conversion between 10 percent and 60 percent.
The mixture of hydrocarbons is passed at 1 liquid hourly space ~elocity ti.é., 1 volume of liquid hydrocarbon per ~olume of ¦~
¦ c~taly~ er hour) over the zeolite with a helium di1ution to ` - 12 - `
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l~l3s~a 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:

Constramt . loglØ.(fract.ion o .n.-hexane remaining) bx log10 (fraction of 3-methylpentane remainin~) The constxaint index approximates the ratio of the crac~ing rate constants for the two hydrocarbons. Catalysts - 10 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 ~
TMA Offretite 3.7 ZSM-38 2.0 .
ZSM-12 - 2.
Beta 0.6 `
. ZSM-4 0.5 ~cid Mordenite 0.5 REY 0~4 Amorphous Silica-alumuna 0.6 . ~he above-described Constraint Index is an important and even criti.cal, definition of those zeolites which are .
useful to catalyze the instant process.. The v~ry nature of this parameter and the recited technique by which it is determ_ned . - 13 - .
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lil3s~a 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 possible to so select test conditions to establish multiple con-straint indexes for a particular given zeolite which may be both inside and outside the above defined range of l 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 l to 12 is intended to be included in the instant catalyst definition regardless that the same identical zeolite tested under other defined ~;
conditions may give a constraint index value outside of l to 12.
The class of zeolites defined herein is exemplified by ~ZSM-5, ZSM-ll, ZSM-12, ZSM-35 and ZSM-38, and other -~
; similar materials. U.S. Patent 3,702,886 describes and claims ZSM-5, while ZSM-11 is more particularly described in U.S. Patent 3,709,979, and ZSM-12 is more particularly described in U.S. Patent 3,832,449. The subject of ZSM-35 is described in U.S. Patent 4,016,245, and ZSM-38 is -described in U.S. Patent 4,046,859.
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, ~13S~8 The specific zeolites described, when prepared in the presence of organic cations, are substantially catalytic-ally inactive, possibly because the intracrystalline free space is occupied by organic cations ~rom the forming solution. They may be activated by heating in an inert atmosphere at 1000F for one hour, for example, followed by base exchange with ammonium salts followed by calcin-ation at 1000F in air. The presence of organic cations in the forming solution may not be absolutely essential lQ to the formation 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 ammon1um salts followed by calcination in air at about 1000F for from about 15 minutes to about 24 hours.
Natural zeolites may sometimes be converted to this type zeolite by various activation procedures and other treatments such as base exchange, steaming, alumina extrac-2Q tion and calcination, alone or in combinations. Naturalminerals which may be so treated include ferrierite, brewsterite, stilbite, dachiardite, epistilbite, heulandite and clinopti}olite. The preferred crystalline aluminosili-cates are ZSM-5, ZSM-ll, ZSM-12, ZSM-35 and ZS~-38, with ZSM-5 particularly preferred.
The zeolites used as catalysts in this invention may be i~n the hydrogen form or they may be base exchanged or im-pregnated to contain ammonium or a metal cation complement.
It is desirable to calcine the zeolite after base exchange.
- 3Q The metal cations that may be present include any of the ' .

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ll ` 1~13S~3 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 ~roup IA metals, the cation content should in no case be so large as to substanti~lly eliminate the activity of the zeolite for the catalysis being employed in the instant Lnvention. For example, a completely sodium exchanged ~-ZSM-5 appears to be largely inactive for shape selective conversions required in the present invention.
In a preferred aspect of this inven~ion, the zeolites useful as catalysts herein are selected as those having a crystal framework density, in the dry hydrogen form, of not substantially below abou~ 1.6 grams per cubic centLmeter. It has been found 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 crystal 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~ - -.
is included in "Proceedings of the Conference Molecular Sieues, London, April 1967", published by the Society o~ Chemical Industry, ~ondon, 1968. When the crystal structure is unknown, the crystal framework density may be d~termined by c}assical pyknom~ter techniques. For example, it may be determi~
by immersing the dry hydrogen form of the zeolite in aD organic 901vent which is not sorbed by the crystal. It is possible . - .... .
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~!l 1~13S~i3 that the unusual .s.ustained activi.ty 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 centLmeter. 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 ~ncluding some which are not within the purview of this invention -:
are:

. Void Framework Zeolite Volume Density _ Ferrierite 0.~8 cc/cc 1.76 g/cc . 15 Mordenite .28 1,7 ZSM-5, -11 .29 1.79 Dachiardite .32 1,72 L .32 1,61 Clinoptilolite .34 1.71 ~20 Laumontite .34 1.77 ZSM~4 ~Omega) .38 1.65 ~eulandite .39 1.69 P .41 1.57 Offretite .40 1.55 Levynite .40 1.54 Erionite .35 1~51 . Gmelinite .44 1.46 . Chabazite .47 1.45 A .5 1.3 .
3~ Y .48 1.27 I The intimate mixture of 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 . 17 .
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` ~135~8 extrudates, for example, and simply mixed in the required pro-portions. 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 aslarge as up to about 1/2 inch for fixed bed operation. Or, the two components may be mixed as powders and formed into pellets or extrudate, each pellet containing both components in substantially the required proportions. Binders such as alumina, zirconia, silica, titania, magnesia, etc., may be present. Alumina is ~10 particularly preferred because, as shown by the Examples, it has a desirable catalytic effect on the synthesis gas conversion.
Alternatively, the ZnO-Cr203 component that has catalytic activity for the reduction of carbon monoxide may be formed on the acidic crystalline aluminosilicate component by conventional means such as impregnation of that solid with salt solution of the desired metals, followed by drying and calcination. Base exchange of the acidic crystalline aluminosilicate component a}so may be used in some selected cases to effect the introduction o~ part or all of the carbon monoxide reduction component. Other means for ~20 forming the intLmate mixture may be used, such as: precipitation of the carbon monoxide reduction component in the presence of the acidic crystalline aluminosilicate; or e ectroless deposition of metal on the zeolite; or deposition of me~al ~rQm the vapor phase. Various combinations o~ the above preparative methods will be obvious to those skilled in the art of catalyst prepara-tion. It should be cautioned, however, to avoid technlques liXely to reduce the crystallinity of the acidic crystalline alumino-f silicate.
It will be recognized from the foregoing description that the heterogeneous catalysts, i.e., the above-described intimate mixtures, used in the process of this invention, may ~ .' .~ '.', ; l~

1~135~3 have varying degrees of intimacy At one extreme, when using lJ2 inch pellets of the ZnO-Cr2O3 carbon monoxide reducing component mixed with 1/2 inch pellets of the acidic crystalline aluminosilicate, substantially all locations within at least one of the components will be within not more than about 1/2 inch of some of the o~her component, regardless of the proportions in which the two components are used. With different sized pellets, e.g., 1/2 inch and 1/4 inch, again substantially all locations within at least one of the components will be within not more than about 1/2 inch of the other component. These examples illustrate the lower end of the degree of intimacy required for the practice ~f this inventio~. At the other extreme, one may ball mill together acid crystalline alumino-silicate particles of about 0.1 micron particle size with chromia: wi;th or without zi:nc oxide o~ s~ r- particle size followed by pelletization. For this case, substantially all the locations within at least one of the components will be within no~ more than about 0.1 micron of some of the other component. This ex~mplifies about the highest degree of intimacy that is practical. The degree of intimacy of the physical mixture may also be expressed as the minLmum distance of separation 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 particle si2e for the two components. Thus, for the foregoin~ example illustrating the highest degree o~ 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 a~erage distance of at least about 0.1 micron. The degree of intimacy of the het~eneouc ., . . '' . ':
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' ' -il ~135 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 microscope 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 400~F to about lOOO~F, preferably from about 500F to about 900F, at a pressure in the range of from about 1 to about 1000 atmospheres, preferably from about 10 to about 300 atmospheres, and at a volume hourly space velocity in the range of from about S00 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 ~15 used, The heterogeneous catalyst may be contained as a fixed bed, or a 1uidized bed may be used. ~he product stream containinç . .
hy~rocarbons, unreacted gases and steam may be cooled and the and the hydrocarbons recovered by any of the techniques known in the art, which techniques do not constitute part of 2Q this invention. The recovered hydrocarbons may be further separat~d by distillation or other means to recover benzene, toluene, ylenes, or other aromatic hydrocarbons.

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Synthesis gas having a H2~C0 ratlo of 1 was reacted at 12~0 psig, 8QoF, and about 1 ~HS~ over a series of catalysts.
The catalysts were prepared ~y coprecipitation of zinc-chromium nitrate solutions with NH3. The catalysts containing alumina Examples 1-6 and 10-13~ were prepared by introducing' alumina to the solution as the nitrate or acetate before preclpitation.
The prec'ipitates were washed, dried at lQ0C, calcined in air overn~ht' at 538C, combIned with HZSM-5, and then pelletized.
10, Exposing the prepared catalyst to flowing gas tH2CO-1~ at operating conditions ~1200 psig, 800F~ overnight was sufficient for actlvation. Results and catalyst compositions are described in Table I. Catalyst components of 60~8~ mesh size were pelleted and resized by grinding to provide cataIyst particles of 10/30 ~15 mesh particle size.
,, In Examples 1-4 and 6 tsee Table I~, the Zn to Cr ratio was varled while maintaining a constant Cr to Al ratio. Conver-, sions and selectivities are plotted against the atom percent of ~Zn and Cr (Al- and ZS~-5-free basis) in Figure 1. The composition of a typical commercial zinc chromite methanol synthesls catalyst , tHarshaw Zn - Q302~ is also indicated on Figure 1. It can be seen from the plot that aromatics selectlvity is a strong ,~, function of the Zn~Cr ratio, and that vlrtually no aromatics are formed at Zn~Cr ratios optimized for,methanol synthesis. As "'~ ,, ~25 the Cr content increases~ aromatics content rises sharply and passes through a maxlmum. An inverse correlation of conversion and aromatics selectivity is evident, indicating that aromatiza-tion i~ slower than the'competitive hydrogenation reactions : ::

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under the reaction conditlons. Only traces of methanol or di-methyl ether were detected in the product. A typical aromatics distribut~on is shown in Table II; the overall distribution is 84.4 percent A6-Alo t8.5 percent durene) and 15.6 percent All+.
The effect of changing the Zn/Cr ratio at constant Al can be seen from the results of Examples 4, 11, and 12 in Table I.
The effect is almost identical to that shown in Figure 1 for the relationship between the Zn/Cr ratio and the Cr/Al ratio.
Examples 7-9 in Table I show the effect of the Zn/Cr ratio in the absence of Al. Figure 2 is a plot of conversions and selectivities as a function of the atom percent of Zn and Cr (again on an Al- and ZSM-5 free ba~is). Completely different i correlations from those of Figure 1 are evident but indicate that Al has a catalytic function and is not simply an inert 1 15 dlluent.
! The effect of Al content at a constant Zn/Cr ratio is I shown by ~xamples 4~ 8, 10, and 13 and is plotted in Figure 3.
, The aromatlc selectivity maximum is again apparent and is further evldence that Al plays an active role.
Alr regenerability of the catalyst composition of thls invention was qualitatively demonstrated on one catalyst sample: the spent catalyst from Example 4 was placed in a muf~le furnace and calcined in air at 1000F overnight. The catalyst was retested tsee Example 5, Table I~ and showed a 5 percent 095 in CO conversion actlv~ty.

: , : "

` - 22 -. ' I ' ' ' i .. .
: .. . ...

' ~135~'f3f TABLE I
Syngas Conversion Over Z~fCrZSM-5 -- Effect of Alumina ~XAMPLE 1 2 5 4 5 6 7 8 9 10 11 12 13 RW ~PA - 282 A 291 A 294 A 302 A 302-fAlA 300 A 257 A 313 A 299 A 319 A 316 a ~1~ A 318 A
ff AT~YS~ O~HP '~ S
ZnOf 0,030.10 0.160,17 0.270.61 00.360.70 0,31 0.53 0.0- 0.11 Cr203 0.520.48 0.440.-10.410.17 o.a30.54 0.200.48 0.15 0.6~ 0.28 ; A123 0.350.32 0.300,22 0.220.12 0 0 00,11 0.22 0.22 0.44~ ZSM-~ 0.100.~0 0.100.10 O.L0~f.100.170.10 0.10 0,10 0.10 0.10 0.10 fRE.~CTSO~,f ~ tf~oqs T~ 800 - - - - - - -P, p-lg - - - - - 1200 - - - - - - -I N~/C0 . cRsv, hr~l 14901690 1690 15~30182020501680 1840 2845 2020 2450 1750 1840 f~HSV, hr~ 1.01.11.0 1.11.11.1 1.01.21,61.01,20 91 0 ~ S~S, hr 19 19 19 19 20 16 19 lB 19 ~019 i2 io CO~V~A5If~N, %
C0 66,455,9 46.9 41.636.484.6 23.574.~ 79.8 6~.1 79.2 ~.3 39.6 ~2 26.334.7 31.2 23.~2~.262.4 21.456.5 64.6 51.3 51.6 32.1 15.3 HO n~ f,# c 37.026.6 23.3 17.a~16,1 ~5.~16.2 39.442.8 35.7 U.3 2~.1 19.1 liC DrSTlU8flifT~ON, wr 1C .
M-th~fna 2.13.1-3.3 3.42.36.7 2.03.17.03.27.~8 24.2 E~h~n- 26.515.6 15.1 12.616.215.1 12.28,815.4 9.7 10.7 10 9 9.6

2- ~fbylffffne o.l0.20.~ 0.20.30.2 0.30.10.10.10.2 - 0 2 Prop~n- 13.215.8 15.0 15.613.117.5 8.826.3 13.6 28.9 14.9 27.6 lS l Propyl-mff ~0.10.10.1 4.10.10.1 0.10.10.10.10.1 - 0.1 Efutffffnffff- 6.16.6 6,0 5.6 4.727.0 4~426.9 21.6 26.7 25 4 13.1 ~ 2 8Ut~f~- _ _ _ _ _ _ _ _ _ Cs~ P0~ 10.34.41.~ 4.13.327.12.518.6 Y3.916.3 34.2 6,5 .S
3u Arff'ffffffff-tlff ff 41.7 54.2 56.6 58.460.0 6.3 69.716.1 8.3lS.0 7.138.7 59.1 . .
.' . ' . T~BLE II
Aromatics Distribution Example 4 , , wf. % .:
,35 3~nz~n~ ~ 0.1 Toluens 2 . 0 Ethylbenz-n- 0.1 Xyleno~ 12.1 :
Tr~' M~ ]~enZoneJ
,40 ' 1, 2, 3 3.4 . 1, 2, 4 26.3 .
, 3, 5 , 10.1 :
~tr~ Me benz~nes ~, 2, 3, 4 3.6 . . .
~45 ~. 1, 2, 3, 5 17.0 1, 2, 4, 5 ~dursn~) 8.5 Othg.. ~10 1.3 : A ll 15 . 6 -23- ' ~:

. . ..
., ',, ' , "

" ..11 ' 1~

.
These examples are identical to the previous Examples except that zirconia was substituted for alumina as the binder for the intimate oatalyst mixture. Results and catalyst compositions are shown in Table III and Figure 4 is a plot of the results. The plot is similar to Figure 2 (Al-free catalysts) and indicates that ZrO2 has little or no catalytic effect on the zinc chromite catalyst.
~ .

TABLE III
Syngas Conversion over ZnCr ZSM-5 - Effect of Z-rconia .
~ PA - ' 308 A 307 ~ 305 B
C~YST COMP'N, PTS.
ZnO 0.03 0.46 0.21 CS23 0 . 56 O. 13 0 . 3~3 Zr2 0.31 0.31 0.31 ZSM-5 0 . 10 0 . 10 O .10 REACT~ON CONDI~ON9 .
q'- F _ 800 ~
'20 ~i/cPo1g ~ ~OO _ GHSV, hs-~: 1670 2880 2320 W85V, hr~l 1.1 1. 4 1. 0 ~ . ...
~I!OS, hr la 18 24 ~9~
co 61.8 33.0 71,6 . ~
~2 36.2 6a.0 50.7 ..
HC XtEW, X C 34.2 4S.9 53.5 . , .
~C DIST~tSBaTIOl~. WrX
Meth~na ~ 3 . 0 5 . 9 3 . O
Ethan- 19. 7 13 .1 11. 7 Ethylena O .1 0 . 2 0 .
Propane 19.8 13.6 21.2 Propylon~ : 0.1 0.2 . 0.1 E~utane9 9 .1 22 .1 24. 3 ~35 Sutene9 - - -Cs+ PO~ 6.7 37.2 20.2 Aso~atlc~ 41. 5 7 . 7 19 . 4 .
. ' :`' ~: . . .
- 24 - ' , 1~135~c~

A further significant aspect of this invention is the recognition that a methanol synthesis catalyst of the type herein-before defined will provide unexpectedly even more aromatic product components than hereinbefore recognized by the slmple expedient of grinding the individual components of the final catalyst composition to an unusually flne state of subdi~ision less than 80 mesh such as to about 200 mesh or finer before mixing and pelleting the components to form particles of the catalyst composition. Generally, the pelleted catalyst particles will be in the range o~ 40 to 100 microns for use in a fluid catalyst operation and of larger particle size in the range of 10 to 30 ; mesh for a fixed catalyst bed operation.
In the following examples 17, 18 and 19, identified in Table IV below, synthesis gas ~H2~CO=l) was reacted at 1200 psig, 800~F and passed at 1780 GHS~ (gas hourly space velocity) over catalysts consistlng of 16% ZnO, 44% Cr203, 30% A1203 and 10%
HZSM-5 by welght. In example 17 (Run LPA 332A), the catalyst wa~ a physical mixture of 60/80 mesh particles o~ each of the metal component and the ZSM-5 crystalline zeolite component.
~y 60/80 mesh ls meant that the particles will pass through a 60 me9h 8creen but will be retained on an 80 mesh screen. In examples 18 and 19 (Runs LPA ~28A and 328B respectively~, the ; metal and HZSM-5 components were separately milled to ~-200 mesh) and then mixed and pelleted to form particles of catalyst in the range af 10~30 mesh.
, ' ' . ' 1~135~
TABLE IV
SYNGAS AROMATIZATION O~ER Zn-Cr-Al/ZSM-5 H2~CO=1, 1200 psig, 800F

. 5 Component Particle Size60~80 10~30 mesh parti-: (Mesh) cles formed from -200 mesh components GHSV, hr 1 1780 1780 1740 TOS, hr. 19 19 42 .
Conversion, mole %
~H2 ~ CO] 44.1 37.7 32.9 :
Hydrocarbons, wt.% -Methane 3.g 2.5 3.5 Ethane 12.8 12.2 13.6 Ethylene 0.-3 0.1 0.6 Propane 22.6 9.9 9.4 Propylene 0.3 ~0.1 0.2 Butanes 15.5 3.3 4.2 Butenes ~ ~
C5~ PON 10.9 1.9 4.0 Aromatics 33.7 70.1 64.5 Aromatios Distribution,wt% : -'~ A6 ~ Alo 89.3 83.6 87.1 All 10.7 16.4 12.9 ~1 - 2~ -~1 ` -:
., .: ; : , , . , ~ , `'I

It will be observed from the data presented in Table IV
that examples 18 and 19 produced higher yields of aromatics than the larger particle material used as catalyst in Run 17. It is thus concluded that for any given catalyst composltion, preparing the catalyst from finer mesh component, finer than 80 mesh and more, preferably at least 200 mesh, provides a catalyst mixture having a greater selectivity for producing aromatics.

.

.: . . . - ~ .

Claims (7)

WE CLAIM:

1. In a process for forming hydrocarbons by converting syngas comprising hydrogen and carbon oxides with a catalyst com-position comprising a methanol synthesis catalyst component in admixture with a crystalline zeolite component comprising a silica-to-alumina ratio greater than 12, a pore dimension greater than about 5 Angstroms and a constraint index in the range of 1 to 12, the method for improving the yield of formed aromatics which comprises admixing each of the components of the catalyst comprising the methanol catalyst component and the crystalline zeolite component in a fine state of sub-division less than 80 mesh and thereafter pelleting the mixed finely ground material to form particles of the catalyst composition of a particle size less than 10 mesh.

2. The process of claim 1 wherein the methanol synthesis catalyst comprising zinc oxide and chromium oxide is one providing a Zn:Cr ratio less than 4:1.

3. The process of claim 1 wherein the catalyst com-position comprises from 20 to 60 weight percent of alumina.

4. The process of claim 1 wherein the crystalline zeolite component of the catalyst composition is in an amount less than the methanol synthesis catalyst component.

5. The process of claim 1 wherein the individual catalyst components are about 200 mesh before mixing and pelleting.

6. The process of claim 1 wherein the catalyst com-position is formed into particles suitable for use in fluid catalyst reaction zone.

7. The process of claim 1 wherein the catalyst com-position is formed into particles of a size in the range of 10 to 30 mesh.