CA1117883A

CA1117883A - Process for preparing liquid hydrocarbons

Info

Publication number: CA1117883A
Application number: CA000301470A
Authority: CA
Inventors: Bernardus J. Runderkamp; Nicoline W. Spakman; Lambert Schaper; Swan T. Sie
Original assignee: Shell Canada Ltd
Current assignee: Shell Canada Ltd
Priority date: 1977-05-13
Filing date: 1978-04-19
Publication date: 1982-02-09
Also published as: IT1094830B; AU3600478A; IN147640B; IT7823297A0; DE2820666A1; FR2390491B1; JPS611479B2; FR2390491A1; JPS53140303A; AU514794B2; NL7804899A

Abstract

A B S T R A C T
Process for preparing liquid hydrocarbons. Coal is gasified at 1050 to 2000°C.
The synthesis gas produced is catalytically converted to an aromatic hydrocarbon mixture which is separated into an aromatic liquid fraction and an isobutane fraction.
The isobutane fraction is alkylated.
The alkylate is mixed with the aromatic liquid fraction.

Description

~ 2 -The invention relates to a proce3s for preparing I iqui d hydrocarbons from coal.
Hydrocarbon mixtures boiling in the gasoline range can be obtained, for instance, by straight-run distillation of crude mineral oil, by conversion of heavy mineral oil fractions, for instance, by catalytic cracking, thermal cracking and hydro cracking and by conversion of light mineral oil fractions 3 for inqtance by alkylation.
In view of the increasing need of gasoline and the decreasing reserves of mineral oil there is a great interest in processes having the potentialities of converting carbon-containing materials not based on mineral oil. such as coal, in an economical-ly justified way into hydrocarbon mixtures boiling in the gas-oline range.
It is known that carbon-containing materials, such as coal, can be converted into mixtures of carbon monoxide and hydrogen by gasification. It is further known that mixtures of carbon monoxide and hydrogen can be converted into mixtures of hydrocarbons by contacting the gas mixtures with suitable catalysts. Finally~ it is known that mixtures of paraffins and olefins boiling below the gasoline range can be converted into hydrocarbon mixtures boiling in the gasoline range by contacting the mixtures first mentioned with an alkylation catalyst.
The Applicant has carried out an investigation to examine to what extent the three above-mentioned processes can be used for preparing gasoline ~rom coal. This investigation has shown that gasoline having a high octane number can be prepared from 7~383 coal by combining the t~ree above mentioned processee., pro-~ided that the following conditions are satisfied.
First of all, the gasification of the coal should be carried out at a temperature of from 1050 to 2000C. From the mixture of carbon monoxide and hydrogen thus obtained an aromatic hydrocarbon mixture should then be prepared using a catalyst which contains a crystalline aluminosilicate zeolite having an SiO2/Al203 molar ratio of at least 12 and a constraint index between 1 and 12. Fro~
the aromatic hydrocarbon mixture thus obtained two fractions ~hould then be separated, viz. an isobutane-containing gaseous ~; fraction, which is contacted with an alkylation catalyst and an aromatic liquid fraction boiling in the gasoline range. Finally, a fraction boiling in the gasoline range is separated from the product obtained in the alkylation, and this ~raction is mixed with the gasoline fraction that was separated from the reaction product of carbon monoxide and hydrogen.
If the C2 fraction of the reaction product obtained in the conversion of the H2/C0 mixture has a sufficiently high hydro-carbon content, the process may be improved by steam reforming this C2 ~raction in order to prepare an additional H2/C0 mixture and to mix the latter H2/C0 mixture with the H2tC0 mixture already obtained by gasification of the coal.
The present patent application therefore relates to a proce~ for preparing liquid hydrocarbons from coal, in which a) the coal is aonverted into a mixture of carbon monoxide and hydrogen by gasification at a temperature between 1050 and 2000C;

88;3 b) the mixture of carbon monoxide and hydroyen is con-verted into an aromatic hydrocarbon mixture using a catalyst which contains a crystalline aluminosilicate zeolite having an SiO2/A12O3 molar ratio of at least 12, a constraint index between 1 and 12, a pore size of more than 5 ~, and which freely sorbs n-hexane;
c) an isobutane-containing gaseous fraction and an aromatic liquid fraction boiling in the gasoline range are separated from the aromatic hydrocarbon mixture;
d) the isobutane-containing gaseous fraction is con-verted by alkylation into a product from which a fraction boil-; ing in the gasoline range is separated~ and e) the two fractions boiling in the gasoline range obtained according to c) and d) are mixed.
In the first step of the process according to theinvention a mixture of carbon monoxide and hydrogen is prepared by gasification of coal at a temperature between 1050 and 2000 C.
As a result of the use of this high temperature the synthesis gas prepared contains very little methane, if any at all. In comparison with a process in which in the first step a lower temperature is used, for instance between 800 and 1000C, the process according to the invention gives a higher yield of CO
and H2 per tonne of coal and a higher gasoline yield per tonne of coal. Because of the use of a gasification temperature between 1050 and 2000C the product contains only very small amounts of non-gaseous by-products such as tar, phenols and condensable hydrocarbons, if any at all. The absence of these products also leads to a higher yield of CO

~ :3 1~7~33 and H2 and therefore to a higher gasoline yield than when a lower temperature is used in the gasification step. In addition, no provisions have to be made to remove tar, phenols and condensable hydrocarbons from the synthesis gas, which will promote the economy of the gasoline preparation.
The starting materials in the process according to the invention may, for instance, be: lignite, bituminous coal, sub-bituminous coal, anthracite and coke. With a view to achieving more rapid and complete gasification, it is preferred first to reduce the starting material to powder. The high-temperature gasification is preferably carried out in the presence of oxygen and steam. It is preferred to choose such an oxygen/steam ratio that per part by volume of oxygen from 5 to 150%v steam is present. The oxygen used is preferably preheated before it is contacted with the coal. This pre-heating can ve~y conveniently be carried out by heat exchange, for instance, with the hot product gas prepared according to step a) of the process. By preheating the oxygen is preferably brought to a temperature between 200 and 500C. The reactor in which the gasification is carried out preferably consists of an empty steel vessel lined with a heat-resistant material.
A suitable reactor is described in British Patent 1,501,28~
and Canadian Patent 1,069,305. The high temperature at which the gasification is effected is produced by the reaction of the coal with oxygen and steam. The mixture to be reacted is pre-ferably introduced into the reactor at high speed. A suitable ~3 linear speed is 10 to 100 m/s. The pressure at which the gasi-fication is carried out may vary within wide limits. The absolute pres~ure is preferably 1 to 200 bar. In order to convert as much as possible of the coal introduced into the re~ctor into ga~, the coal particles should remain in the reactor for some time. It has been found that a residence time of from 0.1 to 12 seconds is sufficient for this purpose. After the coal has been converted into gas, the reaction product, which consists sub-stantially of H2, CO, C02 and H20, is removed from the reactor.
This gas, which has as a rule a temperature higher than 110QC, may contain impurities such as ash, carbon-containing solids and hydro-gen sulph~ide. To allow the impurities to be removed fro~ the gas, the latter should first be cooled. This cooling can very suitably be e~fected in a boiler, in which steam is formed with the aid of the waste heat. Although as a rule the solids content of the crude gas that leaves the boiler is low, a further reduction of the solids content may nevertheless be desirable! for instance, if the gas is to be desulphurized. To thls end the gas is preferably con-ducted through a scrubber where it is washed with water. An appara-tus ~or this purpose is described in British patent specification826,209. Such a washing produces a gas containing hardly any solids any more and having a temperature between 20 and 80C. The gas may be purified still further by removal o~ H2S and, if desired, part of the C02. The removal of H2S and C02 is preferably carried out with the aid of the ADIP process or the SULFINOL process, which processes are described in British patent specifications 1,444,963, 1,131,989, 965,358, 957,260 and 972,140.

~7~83 The mixture of carbon monoxide and hydrogen prepared according to the first step of the proce~s according to the invention, is converted in the second ~tep into an aromatic hydrocarbon mixture using a catalyst which contains a crystalline aluminosilicate zeolite of a special class. These zeolites effect a high conversion of aliphatic hydrocarbons into aromatic hydrocarbons in commercially desirable yields and they are in general very active in conversion reactions in which aromatic hydrocarbons are involved. Although they have an uncommonly low alumina content, i.e. a high SiO2~Al203 molar ratio, they are very active, even when the SiO2/Al203 molar ratio is more than 30. This activity is sur-prising because the catalytic activity of zeolites is generally ascribed to the aluminium atoms of the lattice and the cations present in combination with these aluminium atoms. These zeolites retain their crystalline character for a very long time in spite of the presence of steam, even at high temperatures such as those which effect irreversible collapse of the crystal lattice of other zeolites, e.g. those of the X- and A-type. If carbon-con-taining deposits are formed, they can be removed by burning them

2~ at temperatures that are higher than the temperatures usually employed for restoring the activity. In many media zeolites of this group show a very slight caapability of forming coke, as a result of which the operational times between regenerations are very long.
An important property of the crystal structure o~ this class of zeolites is that it provides constrained access to and egre~s from the intracrystalline free space, because the pore 8f3~

. .
size is more than about 5 R and the pore windows are of about the same size as are provided by rings of 10 oxygen atoms.
Obviously, these rings are those formed by the regular arrange-ment of the tetrahedrons forming the anionogenic lattice of the crystalline aluminosilicate, the oxygen atoms themselves being bound to the silicon or aluminium atoms in the centres of the tetrahedrons. In short, the zeolites that are pref2rably used according to the invention have a ratio of silica to alumina of at least 12 and a structure that gives constrained access to the free space in the crystals.
The said ratio of silica to alumina can be determined by usual analyis. This ratio serves the purpose of representing a~ precisely as possible the ratio in the rigid anionogenic lattice of the zeolite crystal, so that aluminium in the binder material or in cationogenic or other form in the channels is excluded. Although zeolites having a molar SiO2/Al203 ratio of at least 12 are suitable, use is preferably made of zeolites having a higher ratio of at least 30 and in particular having an SiO2/Al203 ratio between 60 and 400. After activation, these zeolites obtain an intracrystalline sorptive power for ~;' n-hexane that i5 greater than for water, i.e. they show hydro-phobic properties. It is assumed that this hydrophobic nature is an advantage in the presen4 invention.
The zeolites that are suitable according to the invention freely sorb n-hexane and have a pore size of more than 5 R.
The ~tructure must further provide constrained access to certain large molecules. Sometimes it is possible to infer 1~78133 g from a known crystal structure whether such a constrained access exists. If, for instance, the only pore windows in a crystal are formed by rings of eight oxygen atoms, the access for molecules having a larger cross--section than n-hexane is ex-cluded and then the zeolite is not of the desired type. Zeolites with windows of rings with 10 atoms are preferred, although an excessive puckering or pore blockage may deactivate these zeolites. In general, zeolites with windows of rings with 12 atoms have been found to give no sufficiently constrained access to effect the conversivns desired according to the invention, although as a result of pore blockage or other causes structures are possible here which are active.
Instead of trying to judge from the crystal structure whether a zeolite has the required constrained access or not, a simple constraint index determlnation can be carried out by continuously passin~ a mixture of equal quantities by weight of n-hexane and 3-methylpentane at atmospheric pressure over a small sample, about 1 g or less, o~ the zeolite according to the process given hereinafter. A sample of the zeolite in the form of granules or extrudate is ground to a particle size which is about equal to that of coarse sand and introduced into a glass tube. Before the examination the zeolite is treated for at least 15 minutes with a stream of air of about 538C. The zeolite i3 thereupon purged with helium and the temperature is et at a value between about 285C and about 510C to give a total conversion between 10% and 60%. The mixture of hydro-carbons is passed over the zeolite at a volume vel3city of 1 (i.e. 1 volume of liquid hydrocarbon per volume of zeolite per hour), the mixture being diluted with helium such that the molar ratio of helium to total hydrocarbons is 4:1.
After a running time of 20 minutes a sample of the effluent is taken and analysed (the best way is by gas chromatography) in order to determine the fraction of each of the two hydro-carbons that has not been converted.
The constraint index is calculated as follows:
. . 10lo~ (remaining fraction of n-hexane) Constralnt lndex = ~
1olog (remaining fraction of 3-methylpentane) ; The constraint index approaches the ratio of the velocity constants for cracking the two hydrocarbons. Catalysts which are suitable for the present process are thos containing a zeolite with a constraint index between 1 and 12. For some representative materials, some of which fall outside the scope of the invention, the values for the constraint index (CI) are given below CI
ZSM-5 8.3 ZSM-11 8.7 TMA-offretite 3.7 Beta 0.6 Acid mordenite 0.5 Amorphous silica-alumina 0.6 Erionite 38 ~117~E~3 Examples of zeolites of the class defined here are ZSM-5, ZSM ll, ZSM-12, ZSM-35 and ZSM-38. United States Patent

3,702,886 describes ZSM-5. ZSM-11 is described in United States Patent 3,709,979 and ZSM-12 in United States Patent 3,832,449.
Naturally occurring zeolites may sometimes be con-verted into this type of zeolite hy various activation methods and other t.reatments such as base exchange, steam treatment, alumina extraction and calcination or combinations of these treatments. Of the naturally occurring minerals that may be treated in this way are to be mentioned: ferrierite, brewsterite, stilbite, dachiardite, epistilbite, heulandite and clinoptilolite.
The crystalline aluminosilicate zeolites which are preferably used are ZSM-5, ZSM-ll, ZSM-12~ ZSM-35 and ZSM-38, particular preference being given to ZSM-50 ; According to a preferred aspect of the invention the zeolites used in the catalysts have in the dry hydrogen form a crystal lattice density of at least 1.6 g per cm3. The dry-state density can for known structures be calculated from the number of silicon plus alu~inium atoms per lO00 ~3, as described for instance on page l9 of the article on zeolite structure by W. U. Meier~ This article is to be found in "Proceedings of the Conference on Molecular Sieves", London~ April 1967 published by the Society of Chemical Industry, London, 1968. If the crystal structure is unknown, the density of the crystal lattice can be determined according to classical pycnometer methods. The density may be determined, for instance, by immersing the zeolite 7~83 in the dry hydrogen form in an organic solvent which is not sorbed by the crystal. It may be that the extraordinary, long lasting activity and stability of this class of zeolites is connected with the high density of the anionogenic lattice of the crystal, which is at least 1.6 g per cm3. Obviously, this high density has to be associated with a relatively ~mall free ~pace in the crystal, which may be expected to lead to stabler structures. However, this free space seems to be important as the seat of the catalytic activity.
Below the densities are given of the crystal l~ttice of some representative zeolites, of which some fall outside the scope of the invention.

~78~3 .

Zeolite Volume of cavities, Density of lattice, - - _ cm3!cm3 ____~_cm3 __ Ferrierite 0.28 1.76 Mordenite 0.28 1.7 ZSM--5, -11 0.29 1.79 Dachiardite 0.32 1.72 L 0.32 1.~1 Clinoptilolite 0.34 1.71 Laumontite 0.34 1.77 ZSM-4 (omega) 0.38 1.65 Heulandite 0.39 1.69 P 0.41 1.57 Offretite 0.40 1.55 Levynite 0.40 1.54 Erionite 0.35 1.51 Gmelenite 0.44 1.46 Chabazite 0.47 1.45 A 0.5 1.3 0.48 1.27 In step b) of the process according to the invention a mixture of carbon monoxide and hydrogen should be converted into an aromatic hydrocarbon mixture. Step b) may in itself be carried out a~ a one-step or as a two-step process. In the two-step process the mixture of carbon monoxide and hydrogen is contacted in the first step with a catalyst containing one or more metal components having catalytic activity for the conversion of a H2/CO mixture into hydrocarbons and~or oxygen-containing hydro-- 14 _ carbons. In the second step the product t'nus obtained is conver4ed into an aromatic hydrocarbon mixture by contacting it under aromatization conditions with the crystalline aluminosilicate zeolite. In the one step process the mixture of carbon monoxide and hydrogen is contacted with a b;functional catalyst which contains, in addition to the crystalline aluminosilicate zeolite, one or more metal compounds having catalytic activity for the conversion of a H2/C0 mixture into hydrocarbons and/or oxygen~
containing hydrocarbons. Step b) of the process according to the invention is preferably carried out as a one-step process.
According to step a) in the process according to the invention a H2/C0 mixture is prepared, whose H2/C0 molar ratio, depending on starting material and reaction conditions, may vary within wide limits. Before this mixture is further converted according to step b) its H2/C0 molar ratio can be changed by adding hydrogen or carbon monoxide. The hydrogen content of the mixture may also be increased by subjecting it to the known water gas shift reaction.
As the feed for step b~ of the process according to the invention use is pre~erably made of a gas mixture whose H2/C0 molar ratio is more than 0.4. If the mixture of carbon monoxide and hydrogen used in the process according to the invention as the feed for step b) has a H2/C0 molar ratio of less than 1.0 step b~ is pre~erabl~ carried out as a one-step process by con-tacting the gas with a trifunctional catalyst which contains one or more metal csmponents having catalytic activity for the con-version of a H2/C0 mixture into hydrocarbons and/or oxygen-con~

~7883 taining hydrodarbons ? one or more metal components havinz c~talytic activity for the water gas shift reaction and the crystalline aluminosilicate ~eolite. The ratio in which tne three catalytic functions are present in the catalyst may vary within wide limits and is chiefly determined by the activity of each of t'ne catalytic functions. When use is made of a trifunctional catalyst in step b) of the process according to the invention for conver-ting a H2/C0 ~ixture with a H2/C0 molar ratio of less than 1.0, the object is that of the acyclic hydrocarbons and/or oxygen-con-taining hydrocarbons formed under the influence of a first catalytlc function, as much as possible i3 converted under the influence of a second catalytic function into an aromatic hydrocarbon mixture ~ubstantially boiling in the gasoline range, and that of the water liberated in the conversion of the mixture of carbon monoxide and hydrogen into hydrocarbons and/or in the conversion of oxygen-con-taining hydrocarbons into an aromatic hydrocarbon mixture, as muchas possible reacts under the influence of a third catalytic function with the carbon monoxide present in an excess amount in the mixture of carbsn monoxide and hydrogen with formation of a mixture of hydrogen and carbon dioxide. In the composition of an optimum tri-functional catalyst to be used in step b) of the process accordingto the invention, which catalyst contains a given quantity of a first catalytic function having a given activity, it is therefore possi-ble to do with less of the other catalytic functions according as these ane more active.
Although the trifunctional catalysts that can be used in step b) of the process according to the invention are described in this 17~

patent application as catalysts containing one or more metal com-ponents having catalytic activity for the conversion of a H~CO
mixture into hydrocarbons and one or more metal components having catalytic activity for the water gas shift reaction, this means in no way that metal components each having in themselves one of the two catalytic functions should always separately be present in the catalysts. For, it has been found that metal components and com-binations of metal components having catalytic activity for the conversion of a H2/CO mixture into substantially oxygen containing hydrocarbons as a rule also have sufficient catalytic activity for the water gas shift reaction so that in such a case incorporation of one metal component or one comblnation of metal components into the catalysts will suffice. Examples of such metal components are the metals chosen from the group formed by the metals zinc.
copper and chromium. When use is made of trifunctional catalysts containing these metals in step b) of the process according to the invention, preference is given to catalysts containing combinations of at least two of these metals, for instance the combination zinc-copper, zinc-chromium or zinc-copper-chromium.
Particular preference is given to a trifunctional catalyst containing in addition to the crystalline aluminosilicate zeolite the metal combination zinc-chromium. Metal components and com-bination~ of metal components having catalytic activity for the conversion of a H2/CO mixture into substantially hydrocarbons have as a rule no or insufficient activity for the water gas ~hift reaction. When use is made of such metal components or combinations of metal components in the catalyst, one or more 1117~B3 1'7 separate metal components having catalytic activity for the ~later gas shift reaction should therefore be incorporated therein.
The tri~unctional catalysts which are used in step b) o~
the process according to the invention are preferably composed of two or three separate catalysts, which will for convenlence be designated catalysts X, Y and Z. Catalyst X is the catalyst containing the metal components having catalytic activity for the conversion of a H2/C0 mixture into hydrocarbons and~or oxygen-containing hydrocarbons. Catalyst Y is the crystalline alumino-- 10 ilicate zeolite. Catalyst Z is the catalyst containing the metal component having catalytic activity for the water gas shift reaction. As has been explained hereinbefore the use of a Z-catalyst may be omitted in some cases.
If as the X catalyst a catalyst is used which is capable of converting a H2/C0 mixture into substantially oxygen--con--taining hydrocarbons, preference is given to a catalyst which is capable of converting the H2/C0 mixture into substantially methanol and/or dimethyl ether. For the conversion of a H2/C0 mix-ture into substantially methanol, catalysts containing the metal combinations mentioned hereinbefore are very suitable. If desired.
the said metal combinations may be emplaced on a carrier material.
By introducing an acid function into these catalysts, for instance by emplaclng the metal combination on an acid carrier, it may be effected that apar'c from the conversion of the H2/C0 mixture into methanol a considerable part of the mixture will be converted into dimethyl ether.

, ., 7~3 X-catalysts which are capable of converting a H2/CO
mixture into substantially hydrocarbons are referred to in the literature as Fischer-Tropsch catalysts. Such catalysts often contain one or more metals of the iron group or ruthenium to-gether with one or more promoters to increase the activity and/or selectivity and sometimes a carrier material such as kieselguhr. They can be prepared by precipitation, melting and by impregnation. The preparation of the catalysts containing one or more metals of the iron group, by impregnation, takes place by impregnating a porous carrier with one or more aqueous solutions of salts of metals of the iron group and, optionally, of promoters, followed by drying and calcining the composition.
If in step b) of the process according to the invention use is -~ made of a catalyst combination in which catalyst X is a Fischer-Tropsch catalystr it is preferred to choose for this purpose an iron or cobalt catalyst, in particular such a catalyst which has been prepared by impregnation. Very suitable Fischer-Tropsch catalysts for use in the catalyst combinations accord-ing to the invention are the catalysts prepared by impregnation according to the Netherlands patent application No. 7612.460*.
The catalysts concerned contain per 100 pbw carrier 10-75 pbw of one or more metals of the iron group, together with one or more promoters in a quantity of 1-50% of the quantity of metals of the iron group present on the catalyst, which catalysts have such a specific average pore diameter (p) of at most 10,000 nm and such a specific average particle diameter (d) of at most 5 mm, that the quotient p/d is more than 2 (p in nm and d in mm).

*see also Canadian Patent 1,089,495 ~1~7~3 If in ~tep b) of the procesc according to the inventior. the object is to use a catalyst combination of which X is a Fiscner-Tropsch iron catalyst, it is preferred to choose an iron catalyst containing a promoter combination consisting of an al-kalimetal, a metal that is easy to reduce, such a~ copper or sil-ver and, optionally, a metal that is hard to reduce, such as aluminium or zinc. A very suitable iron catalyst for the present purpo e is a catalyst prepared by impregnation containing iron, potassium and copper on silica as the carrier. If in step b) of the process according to the invention the object is to use a catalyst combination of which X is a Fischer-Tropsch cobalt cataly3t, it is preferred to choose a cobalt catalyst containing a promoter combination con~isting of an alkaline-earth metal and thorium, uranium or cerium. A very suitable Fischer-Tropsch cobalt catalyst for the present pur-pose is a catalyst prepared by impregnation containing cobalt, magnesium and thorium on silica as the carrier. Other very suitable Fischer-Trop~ch cobalt catalysts prepared by impregnation are cataly~ts containing~ in addition to cobalt, one of the elements ¢hromium, titanium, zirconium and zinc on silica as the carrier.
If desired, it is also possible to use in step b) of the process according to the invention catalyst combinations containing an X-catalyst, which is capable of converting a H2~CO mixture into a mixture containing both hydrocarbons and oxygen~containing hydrocarbons in comparable quantities. As a rule, such a catalyst has sufficient catalytic activity for the water gas shift reaction, 80 that the use of a Z-catalyst in the combination can 7~3~3 e omitted. An example of an X-catalyst of thls type is an iron-chromium oxide catalyst. If desired, it is also possible to use in step b) of the process according to the invention catalyst combinations containing two or more X-catalysts, for instance in addition to a catalyst of the X-type which is capable of converting a H2/CO mixture into substantially hydrocarbons, a second catalyst of the X-type which is capable of converting a H2/CO mixture into substantially oxygen-con-taining hydrocarbons.
Z-catalysts which are capable of converting a ~2O/CO
mixture into a H2~CO2 mixture are referred to in the literature as CO shift catalysts. Such catalysts often contain one or more metals of the group formed by iron, chromium, copper, zinc, cobalt, nickel and molybdenum as the catalytically active com-ponent, either as such, or in the form of their oxides or sul-phides. Examples of suitable CO-shift catalysts are the mixed sulphidic catalysts according to the Netherlands patent applications No. 7305340(1) and No. 7304793(2) and the spinel catalysts according to the French patent application No.
7633900(3). If in step b) of the process according to the invention use is made of a catalyst combination in which a Z-catalyst is present, it is preferred to choose a catalyst which contains both copper and zinc, in particular a catalyst in which the Cu/Zn atom ratio lies between 0.25 and 4Ø
In the trifunctional catalysts the catalysts X, Y and, optionally, Z may be present as a mixture, in which in principle, each particle of catalyst X is surrounded by a number of particles of catalyst Y and, optionally, catalyst Z and con-versely. If the process is carried out with use of a fixed catalyst bed, this bed may be (1) see also Canadian Patent 1,018,329 t2) see also Indian Patent 140,246 (3) see also United Kingdom 1,536,652 .1 . ''~3 1~L78~3 ~ 21 ~
built up of alternate ]ayers of particles of cataly~3ts X, Y and, optionally, Z. If the two or three catalyst~ are used as a mixture, this mixture may be a macromixture or a micromixture.
In the first case the trifunctional catalyst consists of two or three kinds of macroparticles of which one kind i5 completely made up of catalyst X, the second kind completely of catalyst Y and, optionally, a third kind completely Or catalyst Z. In the ~econd case the trifunctional catalyst consists of one kind of macroparticles, each macroparticle being made up of a large number of microparticles of each of the catalysts X, Y and, optionally, Z. Trifunctional catalysts in the form of micromixtures may be prepared, for instance, by thoroughly mixing a fine powder ,~ of catalyst X with a fine powder of catalyst Y and, optionally, ; with a fine powder of catalyst Z and shaping the mixture to larger particles, for instance, by extruding or pelletizing. In step b) of the process according to the invention it is preferred to use trifunctional catalysts in the form of micromixtures. The trifunc-tional catalysts may also have been prepared by incorporating the metal components having catalytic activity for converting a H2/C0 mixture into hydrocarbons and/or oxygen-containing hydrocarbons ,, -and, optionally, the metal components having catalytic activity for the water gas shift reaction into the crystalline aluminosilicate ~ zeolite, for instance by impregnation or by ion exchange.
- The crystalline aluminosilicate zeolites which are used in step b) of the process according to the invention are usually prepared from ar aqueous mixture as the starting material which contains the followin~ compounds in a given ratio: one or more ,~;

13117B8~

compounds of an alkali or alkaline earth metal, one or more compounds containing a mono~or bivalent organic cation or lrom which such a cation is formed during the preparation of the zeolite, one or more silicon compounds and one or more aluminium compounds. The preparation is effected by maintaining the mixture at elevated temperature unt l the zeolite has been formed and then separating the crystals of tine zeolite from the mother liquor.
The zeolite~ thus prepared contain alkali and/or alkaline-earth metal ions and mono- and/or bivalent organic cations. Before being used in step b) of the process according to the invention at lea~t part of the mono- and/or bivalent organic cations inkroduced during the preparation are preferably converted into hydrogen ions, for instance by calcining and at least part of the exchangeable mono- and~or bivalent cations introduced during the preparation are preferably replaced by other ions, in particular hydrogen ions, ammonium ions and/or ions of the rare-earth metals.
The crystallin~ aluminosilicate zeolites used in step b) of the process according to the invention preferably have an alkali metal ; content o~ less than 1 %w and in particular of less than 0.05 %w.
If desired, a binder material such as bentonite or kaolin may be incorporated into the catalysts that are used in step b) of the proce~s according to the invention.
Step b) of the process according to the invention is preferably carried out at a temperature of from 200 to 500C and in particular of from 300 to 450C, a pressure of from 1 to 150 bar and in par-ticular of from 5 to 1G0 bar and a space velocity of from 50 to 5000 and in particular of from 300 to 3000 ~l gas~l catalyst/hour.

~117~38~
, , .

Step b) of the process according to the invention can ~ery ~uitably be carried out by pa~sing the feed in upward or in downward direction through a vertically disposed reactor in which a fixed or a moving bed of the trifunctional catalyst concerned is present. Step b) of the process may, for instance, be carried out in the so-called fixed-bed operation~ in bunker-flow operation or in ebulated-bed operation. It is preferred to use catalyst particles then with a diameter between 1 and 5 mm. If desired, step b) of the process may also be carried out in fluidized-bed operation or with the use of a suspension of the catalyst in ahydrocarbon oil. It is preferred to use catalyst particles then with a diameter between 10 and 150 mm.
In the process according to the invention an isobutane-con-taining gaseous fraction and an aromatic liquid fraction boiling in the gasoline range should be separated from aromatic hydro-carbon mixture obtained according to step b). It is preferred to separate the reaction mixture originating from step b) in step c) into a C2 fraction, a propane fraction, an isobutane-containing fraction, an n~butanefraction and an aromatic liquid fraction boiling in the gasoline range. The C2 fraction may be used as fuel gas. If desired, a H2/C0 mixture can be separated from the C2~fractionJ
which mixture may be recirculated to step b). If the hydrocarbon content of the C2 fraction is sufficiently high, it may be preferred to sub~ect it, either after removal of a H2/C0 mixture from it or not, to ~team reforming in order to prepare additional synthesis ; gao., which may be used as feed component for step b). Steam re-forming of the C2 fraction can very suitably be effected by con-L7~83 - 2l~ ~
tacting it together with steam at elevated temperature and pressure with a nickel-containing catalyst. Water which may be formed as a by-product in step b) may, if desired, be used in the proce~s in the steam gasification of the coal and/or in the steam reforming of the C2 fraction~
In step d) of the process according to the invention the isobutane-containing gaseous fraction should be converted by alkylation into a product from which a fraction boiling in the gasoline range can be separated. This alkylation can very con-veniently be effected by contacting the fraction with a strong acid a3 the catalyst, such as sulphuric acid or hydrofluoric acid. Since the gaseous part of the reaction product of step b) usually containq only small amounts olefins, the isobutane-con-taining gaseous fraction which is separated from it will often have too low an olefin content to realize a sufficient conversion of the isobutane present in it by alkylation. It is therefore preferred to increase the olefin content of the fraction before subjecting it to alkylation. An increase in the olefin content of the isobutane-containing fraction can conveniently be effected by mixing it with an olefin-rich stream which may originate from an external source or which has been prepared by dehydrogenation of the paraffins obtained in the process, such as a propane fraction, an n-butane-fraction or an LPG fraction obtained from it by mixing. Dehydro~enation of these fractions can conveniently be effected by contacting them at elevated temperature with a chromium-cortaining catalyst. From the product obtained in the alkylation a fraction boiling in the gasoline range is separated and this 11178i33 fraction is mixed according to ~tep e) of the proce3s accordlng to the inYention with the aromatic liquid fraction obtained in step c) and boiling in the gasoline range. The non-converted isobutane is preferably separated from the product obtained in the alkylation and recirculated to the alkylation reaction. In order to increase the vapour pressure of the gasoline mixture thu~ obtained, light hydrocarbons are preferably added to it.
As light hydrocarbons use can very conveniently be made of n-butane or LPG, which may be obtained as by-products of the process.
Two process schemes for the conversion of coal into aromatic gasoline according to the invention will be explained in more detail hereinafter with the aid of the figures.
Process scheme I (see Fig. 1) The process is carried out in an apparatus comprising succes-sively a gasification section (1), a gas purification section (2), a hydrocarbon synthesis section (3), the first separation section

(4) a steam reforming section (5), an alkylation section (6) and the seco~d separation section (7). A mixture of coal (8), oxygen (9) and steam (10) is gasified and the crude gas (11) is purified.
The purified gas (12) is mixed with a synthesis gas (13) reverted to furtheron and prepared by steam reforming, and the mixture is converted under the influence of a trifunctional catalyst according to the invention into an aromatic hydrocarbon mixture (14). This hydrocarbon mixture i3 separated into a C2~fraction (15) 7 a propane fraction (16) an isobutane fraction (17), an n-butane fraction (18) an an aromatic gasoline fraction (19). The C2~fraction (15) is converted by steam reforming into the synthesis gas (13). The propane fraction (16) and the n-butane fraction ~18) are mixed in-to the LPC fraction (20), which is subsequently separated into two portions (21) and (22) having the same composition. The isobutane fraction (17) is alkylated together with an olefin strea~ (23) originating from an external source and with an isobutane recir-culation stream (24) reverted to later. From the alkylation product (25) the isobutane recirculation stream (24) and a gasoline fraction (26) are separated. The gasoline fraction (26) is mixed with the gasoline fraction (19) and with portion ~22) of the LPG fraction (20~ into gasoline (27).
Process Scheme II (see Fig. 2) The process is carried out in an apparatus comprising succes-sively a gasification section (1), a gas purification section {2), a hydrocarbon synthesis ~ection (3), the first separation section (4) ! a dehydrogenation section (5), an alkylation section (6) and the second separation section (7). A mixture of coal (8), oxygen (9) and steam (10) is gasified, the crude gas (11) is purified and the purified gas (12) is converted under the influence of a tri-functional catalyst accordlng to the invention into an aromatichydrocarbon mixture (13). This hydrocarbon mixture is separated into a C2 fraction (14), a propane fraction (15), an isobutane fraction (16) an n-butane fraction (17) and an aromatic gasoline fraction (18). The propane fraction (15) is separated into two portions (19) and (20). Portion (20) is converted by dehydrogenation into a mixture of propene and propane (21). The n-butane fraction (17) is separated into two portion~ (22) and (23). The isobutane ~7883 fraction (16) is alkylated together with the propane/propene stream (21) and with an isobutane recirculation stream (24) rever-ted to later. From the alkylated product (25) a propane fraction (~6), the i~obutane recirculation stream (24) and a gasoline frac-tion (27) are separated. The propane fraction (26) is mixed with portion (19) of the propane fraction (15) and with portion (23) of the n-butane fraction (17) into the LPG fraction (28). The gasoline ~raction (27) i~ mixed with the gasoline fraction (18) and with portion (22) of n-butane fraction (17) into the gas-oline (29).
The present invention also comprises equipment for carrying out the proce~s according to the invention as shown schematically in Figures 1 and 2.
The invention will now be further explained with the aid of the following examples.
Example I
ZSM-5 (zeolite A) was prepared as follows. A mixture of SiO2, NaAlO2, NaOH and / (C3H7)4N_/OH in water with the molar composition 2 A1203. 9/ (C3H7)4N /20. 29.1 SiO2. 480 H20 was heated for 98 hours in an autoclave at 150C under autogeneous pressure.
After having cooled the reaction mixture, the zeolite formed was filtered off, wa~hed with water until the pH of the wash water was about 8 and dried for two hours at 120C. With zeolite A as the starting material zeolite B was prepared by, successively, cal-cining zeolite A at 500C, boiling with 1.0 molar NH4N03 solution, washing with water, boiling again with 1.0 molar NH4N03 solution ~ ~7~3~3 - 2~ -and washing) drying for two hours at 120C and calcining for four hours at 500C.
Example II
_ _ A catalyst C was prepared by thoroughly mixing equal parts by weight of the following finely powdered materials a) a Fe/Cu/K/SiO2 Fischer-Tropsch catalyst prepared by impregnation;
b) zeolit~ B;
c) a Cu/Zn C0 shift catalyst.
Catalyst C was extruded to particles having a diameter of 1-3 mm.
_~ample III
A catalyst D was prepared by mixing a ZnO-Cr203 composition with zeolite B in a weight ratio of 5:1. Both materials were present in the catalyst in the form of particles having a diameter of 0.15-Q.3 mm. The ZnO-Cr203 composition used catalyses both the reduction of C0 to methanol and the water gas shift reaction.
Exampl_ I~
Bituminouq coal was ground to a particle size of less than 120 micron~ and used as the feed for a high-temperature coal gasifier. Per gramme of coal 0.9 g oxygen and 0.15 g steam were added. The coal gaqification was effected at a temperature of 1500C, a pressure of 30 bar and a residence time of 0.5 s.
The coal conversion was 99~. The gas obtained had the following composition ~5 %v CH4 0.1 C0 64.7 H2 31.8 C2 1.7 1~788:3 The gas further contained about 1.7 ~v H20, COS and H2S.
To re~ove the last-mentioned impurities from the gas, this gas was passed at about 45C through a mixture of diisopropyl amine, sulfolane and water. The resulting synthesis gas, of which the CO/H2 molar ratio was 2.03, was further purified by passing it at 200C over ZnO. The synthe~is gas thus purified was used in Examples V and VI which were carried out according to process ~chemes I and II, respectively.
Example V
The synthesis gas prepared according to Example IV was mixed in a volume ratio of 60:40 with a synthesis gas (II), referted to furtheron, obtained by ~team reforming, and the mixture was con-tacted with catalyst C at a temperature of 280C, a prassure of 30 bar and a space velocity of 1000 l.l-1.h-1. The synthesis gas conversion was 85%. The hydrocarbon mixtu~e obtained had the following composition %w c3 14 n-c4 6 i-C4 8 C5+gasoline 45 The olefin content of both the C3 and the C4 fractions was le~ than 1 %w. The reaction product was separated by cooling into a C2~fraction (including carbon dioxide and unconverted syn-thesis gas) and a C3~fraction. The C2 fraction was mixed with ~7B83 25 %v steam and the mixture was converted into synthes1s gas by contacting it at a temperature of 900C and a pressure of 30 bar with a Ni-containing catalyst. The product was washed with caustic solution to remove C02 and the purified synthesis gas (II) was mixed with the feed gas. The C3+fraction was separated into a propane fraction, an isobutane fraction, an n-butane fraction and a C5+gasoline fraction. The propane fraction and the n-butane fraction were mixed into LPG. The isobutane fraction was mixed with 80 %v of a C3-C5 ole~in mixture originating from an external ~ource and the mixture was converted by contacting it at 40C with a HF alkylation catalyst. By recirculation sf isobutane a constant isobutane/olefin ratio of 14 was maintained in the alkylation reactor. The alkylate which was obtained in 95~ yield was mixed with the gasoline obtained earlier in the process. To bring the vapour pressure of the mixture to the proper value part o~ the LPG was added to it. The gasoline thus obtained had an octane number (CRON) of 91.
Example VI
. .
The synthesis gas prepared according to Example IV was contacted at a temperature o~ 375C, a pressure of 60 bar and a space velocity of 300 l.l-1.h-1 with catalyst D. The synthesis gas conversion was 95%. The reaction developed completely to carbon dioxide. The hydrocarbon mixture obtained had the ~ollowing compo~ition:

1~7883 -- 3~ --~W

n-C4 3 i-C4 8 C5+gasoline 42 The olefin content of both the C3 and the C4 fractions was less than 1 %w. The reaction product was separated by cooling into a C2 fraction (including carbon dioxide and unconverted synthesis gas) and a C3~fraction. The C3~fraction was separated into a propane fraction, an isobutane fraction, an n butane fraction and a C5+
gasoline fraction mainly consisting of aromatics. The propane frac-tion was divided into two egual portions of which one was converted by dehydrogenation at 600C over a Cr203 catalyst into a mixture of propane and propene. The conversion from propane into propene was 30%. The propane~propene mixture thus obtained was mixed with the isobutane fraction and the mixture was converted by contacting it at 40C with a HF alkylation catalyst. From the product obtained in the alkylation a propane fraction an isobutane fraction and a gasoline fraction were separated. By recirculation of isobutane a constant isobutane/olefin ratio of 14 was maintained. The alkylation gasoline yield was 94%. The alkylation gasoline was mixed with the gasoline obtained earlier in the process. To bring the vapour pre~sure of the mixture to the proper value, part of the n-butane fraction was added. The gasoline thus obtained had an octane number (C~ON) of 96. The remaining part o~ both the propane fraction ~78 anà the n-b~ltane fractiorl ooi;~ined from the '`3~ fractiori of ~he hydrocarbon syntdlesis produc'l were rnixed with the propane fraction obtained rrom the alky~ation product, into L.YG.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS

1. A process for preparing liquid hydrocarbons from coal, characterized in that a) the coal is converted into a mixture of carbon monoxide and hydrogen by gasification at a temperature between 1050 and 2000°C;
b) the mixture of carbon monoxide and hydrogen is con-verted into an aromatic hydrocarbon mixture using a catalyst which contains a crystalline aluminosilicate zeolite having an SiO2/A12O3 molar ratio of at least 12, a constraint index between 1 and 12, a pore size of more than 5 A, and which freely sorbs n-hexane;
c) an isobutane-containing gaseous fraction and an aromatic liquid fraction boiling in the gasoline range are separated from the aromatic hydrocarbon mixture;
d) the isobutane-containing gaseous fraction is con-verted by alkylation into a product from which a fraction boiling in the gasoline range is separated, and e) the two fractions boiling in the gasoline range obtained according to c) and D) are mixed.

2. A process as claimed in claim 1, characterized in that the gasification is carried out in the presence of oxygen and steam.

3. A process as claimed in claim 1, characterized in that a coal/oxygen/steam mixture is introduced into a gasification reactor at a linear speed from 10 to 100 m/s.

4. A process as claimed in claim 1, characterized in that the crystalline aluminosilicate has a SiO2/A12O3 molar ratio between 60 and 400.

5. A process as claimed in claim 1, characterized in that a trifunctional catalyst is used in step b).

6. A process as claimed in claim 1, characterized in that step b) is carried out at a temperature from 200 to 500 C, a pressure from 1 to 150 bar and a space velocity from 50 to 5000 Nl gas/l catalyst/hour.

7. A process as claimed in claim l, characterized in that the reaction mixture originating from step b) is separated in step c) into a C2 fraction, a propane fraction, an isobutane-containing fraction, a n-butane fraction and an aromatic liquid fraction boiling in the gasoline range.

8. A process as claimed in claim 1, characterized in that the olefin content of the isobutane-containing fraction obtained in step c) is increased before subjecting it to alkylation in step d).