CA1117054A

CA1117054A - Process for preparing gasoline from coal

Info

Publication number: CA1117054A
Application number: CA000317067A
Authority: CA
Inventors: Lambert Schaper; Swan T. Sie
Original assignee: Shell Canada Ltd
Current assignee: Shell Canada Ltd
Priority date: 1977-12-01
Filing date: 1978-11-29
Publication date: 1982-01-26
Also published as: IT1101468B; FR2410667B1; GB2009778A; GB2009778B; AU526078B2; ZA786718B; NL173281C; IN148826B; FR2410667A1; DE2851685A1; IT7830351A0; NL7713271A; JPS5485202A; AU4205178A; BE872149A; NL173281B

Abstract

ABSTRACT OF THE DISCLOSURE
Process for preparing gasoline from coal. Coal is gasified at a temperature of from 1050°C to 2000°C to a mixture of CO and H2. The mixture is converted to a hydrocarbon mixture over a catalyst containing a crystalline iron silicate. From the hydrocarbon mixture isobutane and an aromatic gasoline fraction are separated. The isobutane is converted by alkylation into a product from which a gasoline fraction is separated. The two gasoline fractions are mixed.

Description

~7~54 PROCESS FOR PREPARING HYDROCARBONS

The invention relates to a process for preparing liquid hydrocarbons from coal.
Hydrocarbon mixtures boiling in the gasoline range can be obtained, for instance, by straight-run distillation of crude S mineral oil, by conver~;on of heavier mineral oil fractions, for instance, by catalytic cracking, thermal cracking and hydro-cracking, and by conversion of lighter mineral oil fractions, for instance by alkylation.
In view of the increasing need of gasoline and the decreas;ng 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 economically justified way into hydrocarbon mixtures boiling in the gasoline 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

-2~ 7~

~or p~eparing gasoline Erom coal. This investigation has sh~wn thae ~asoline having a high octane number can be prepared from coal ~ combining the three above-mentioned processes, provided ~ha~ e following cond;tions are satisfied.
First of all, an aromatic hydrocarbon mixture shou]d be ?repared from the mixture of carbon monoxide and hydrogen obtained by gasification of coal, using a catalyst containing a crystalline silicate which a) is rhermally stable to temperatures above 600 C, b) after dehydration at 400C in vacuum, is capable of adsorbing more than 3 %w water at 25C and saturated water vapour pressure, and c) in dehydrated form, has the following overall composition, ex?ressed in moles of the ox;des (1.0 + 0.3)(R)2/nO./ a Fe203-b A1203.c Ga203_7-Y(d SiO2 + e GeO2), where R= one or more mono-or bivalent cations, a ~, 0.1, b ~ 0, c ~ 0, a + b + c= 1, Y ~, 10, d 3 0.1, e ?, 0, d + e= 1, and n= the valency of R.
From the aromatic hydrocarbon mixture thus obtained two fractions should 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 i9 separated from the product obtained in the alkylation, and this fraction is mixed with the gasoline fraction that was separated from the reaction product of carbon monoxide and hydrogen.
The present patent application therefore relates to a process for preparing liquid hydrocarbons from coal, in which ~1~7~54 a) the coal is converted into a mixture of carbon monoxide and hydrogen by gasification at a temperature of from 1050C to 2000C;
b) the mixture of carbon monoxide and hydrogen is converted into an aromatic hydrocarbon mixture using a catalyst which contains a crystalline silicate, such as defined hereinbefore;
c) from the aromatic hydrocarbon mixture an isobutane-containing gaseous fraction and an aromatic liquid fraction boiling in the gas-oline range are separated;
d) the isobutane-containing gaseous fraction is converted by alkyl-ation 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 accord-ing to c) and d) are mixed.
In the first step of the process according to the invention a mixture of carbon monoxide and hydrogen is prepared by gasification of coal. This gasification is carried out at a temperature between 1050 and 2000C. 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 high-temperature gasification 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 and H2 and therefore to a higher gasoline yield than when a lower temp-erature is used in the gasifi-:1117054 cation 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 re-duce the starting material to powder. The gasification is prefer-ably carried out in the presence of oxygen and steam. It is prefer-red to choose such an oxygen/steam ratio that per part by volume ofoxygen from 5 to 150%v steam is present. The oxygen used is pre-ferably preheated before it is contacted with the coal. This pre-heating can very 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 gasif-ication is carried out preferably consists of an empty steel vessel lined with a heat-resistant material. A suitable reactor is de-scribed in British Patent 1,501,284 and in Canadian Patent 1,069,305.
The high temperature at which the gasification is effected is pro-duced by the reaction of the coal with oxygen and steam. The mix-ture to be reacted is preferably introduced into the reactor at high speed. A suitable linear speed is 10 to 200 m/s. The pressure at which the gasification is carried out may vary within wide lim-its. The absolute pressure is preferably 1 to 200 bar. In order to convert as much as possible of the coal introduced into the reactor into gas, the coal particles should remain in the reactor 1117~54 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, CO2 and H2O, is removed from the reactor.
This gas, which has as a rule a temperature higher than 1000C, may contain impurities such as ash, carbon-containing solids and hydro-gen sulphide. To allow the impurities to be removed from the gas, the latter should first be cooled. This cooling can very suitably be effected 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 sol-ids content may nevertheless be desirable, for instance, if the gas is to be desulphurized. To this end the gas is preferably conducted through a scrubber where it is washed with water. An apparatus for this purpose is described in British patent specification 826,209.
Such a washing produces a gas containing hardly any solids any more and having a temperature between 20 and 80C. The gas may be puri-fied still further by removal of H2S and, if desired, part of the CO2. The removal of H2S and CO2 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.
The mixture of carbon monoxide and hydrogen prepared according to the first step of the process according to the in-vention, is converted in the second step into an aromatic hydro-carbon mixture using a catalyst which contains a crystalline sili-cate of a special class. These æeolites effect a high conversion ~7Q54 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. In the process according to the invention preference is given to the use of silicates in which no gallium and germanium are present, in other words: silicates of which, in the above-mentioned overall composition, c and e are 0. Such silicates are the subject of Netherlands published patent application No. 7613957*. Further, in the process according to the invention preference is given to the use of silicates of which, in the above-mentioned overall compo-sition, a is greater than 0.3, and in particular of which a is greater than 0.5. Particular preference is given to silicates in which no aluminium is present, in other words: silicates of which, in the above-mentioned overall composition, b is o. It should be noted that in the silicates used in the process according to the invention, y is preferably less than 600 and in particular less than 300. Finally, in the process according to the invention preference is given to silicates whose X-ray powder diffraction pattern has, inter alia, the reflections given in Table A of Netherlands patent application No. 7613957*.
In step b) of the process according to the invention a mixture of carbon monoxide and hydrogen should be converted into *see also U.K. Patent 1,555,928 - 5a -1~17054 an aromatic hydrocarbon mixture. Step b) may in itself be earried out as 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-earbons. In the seeond step the product thus obtained i9 eonverted into an aromatic hydrocarbon mixture by contacting it under aromatization conditions with the crystalline silicate. In the one-step process the mixture of earbon monoxide and hydrogen is eontaeted with a bifunetional eatalyst whieh eontains, in addition to the erystalline silieate, one or more metal eomponents having eatalytie aetivity for the eonversion of a H2/CO mixture into hydroearbons and/or oxygen-eontaining hydroearbons. Step b) of the process according to the invention is preferably carried out as a one-step process.
According to step a) in the proces3 according to the invention a H2/CO mixture is prepared, whose H2/CO
molar ratio, depending on starting material and reaction conditions~
may vary within wide limits. Before this mixture is further eonverted aeeording to step b) its H2/CO molar ratio can be ehanged by adding hydrogen or earbon monoxide. The hydrogen eontent of the mixture may also be inereased by subjeeting it to the known water gas shift reaetion.
- 25 As the feed for step b) of the proeess aeeording to the invention use is preferably made of a gas mixture whose H2/CO
molar ratio is more than 0.4. If the mixture of earbon monoxide and hydrogen used in the proeess aeeording to the invention as the feed for step b) has a H2/CO molar ratio of less than 1.0, step b) is preferably earried out a~ a one-step process by eon-taeting the gas with a trifunetional eatalyst whieh eontains one or more metal eomponents having catalytie activity for the eon-version of a H2/CO mixture into hydroearbons and/or oxygen-eon-taining hydroearbons, one or more metal eomponents having eatalytie aetivity for the water gas shift reaetion and the erystalline silieate. The ratio in whieh the three eatalytie 11~7054 functions are presene in the catalyst may vary within wide limits and is chiefly determined by the activity of each of the 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 mixture 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 catalytic function, as much as possible is converted under the influence of a second catalytic function into an aromatic hydrocarbon mixture substantially 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 convers;on of oxygen-con-ta;ning hydrocarbons into an aromatic hydrocarbon mixture, as much as possible reacts under the inftuence of a third catalytic function with the carbon monoxide present in an excess amount in the mixture of carbon 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 according to the invention, which catalyst contains a given quantity of a first catalytic function having a given activity, it is therefore possible to do with ]ess of the other catalytic functions according as these are more active.
Although the trifunctional catalysts that can be used in step b) of the process according to the invention are described in this patent application as catalysts containing one or more metal components having catalytic activity for the conversion of a H2/CO mixture into hydrocarbons and/or oxygen-containing hydrocarbons and one or more metal components having catalytic activity for the water gas shift reaction, this means in no way that separate 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 combinations of metal components having catalytic act;vity for the conversion of a H2/CO mixture into substant;ally 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 combination 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 silicate the metal combination ~inc-chromium. Metal components and combinations 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 shift reaction. When use is made of such metal components or combinations of metal components in the catalysts, one or more separate metal components having catalytic activity for the water gas shift reaction should therefore be incorporated therein.
The trifunctional catalysts which are used in step b) of the process according to the invention are preferably composed of two or three separate catalysts, which will for convenience be designated catalysts X, Y and Z. Catalyst X is the catalyst containing the metal components having catalytic ~ctivity for the conversion of a H2/CO mixture into hydrocarbons and/or oxygen-containing hydrocarbons. Catalyst Y is the crystalline silicate.
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/CO mixture into substantially oxygen-con-taining hydrocarbons, preference is given to a catalyst which iscapable of converting the H2/CO mixture into substantially methanol and/or dimethyl ether. For the conversion of a H2/CO mixture into substantially methanol, catalysts containing the metal combinations mentioned hereinbefore are very suitable. If desired, the sa;d metal combinations may be emplaced on a carrier material. By introducing an acid function into these catalysts, for instance by emplacing the lll~Q5~

metal combination on an acid carrier, it may be effected that apart from the conversion of the H2/CO mixture into methanol a consider-able part of the mixture will be converted into dimethyl ether.
X-catalysts which are capable of converting a H2/CO mix-ture into substantially hydrocarbons are referred to in the liter-ature as Fischer-Tropsch catalysts. Such catalysts often contain one or more metals of the iron group or ruthenium together with one or more promoters to increase the activity and/or selectivity and sometimes a carrier material such as kieselguhr. They can be pre-pared by precipitation, melting and by impregnation. The prepar-ation 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 calcin-ing 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 catalyst, it is preferred to choose for this purpose an iron or cobalt catalyst, in particular such a catalyst which has been prepared by impregnation. ~ery suitable Fischer-Tropsch catalysts for use in the catalyst combinations accordingto the Netherlands published patent application No. 76.12460*. 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 *see also Canadian Patent 1,089,495 _ g _ .

11~7Q54 is more than 2 (p in nm and d in mm).
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 iron catalyst, it is preferred to choose an iron catalyst containing a promoter combination consisting of an alkali metal, a metal that is easy to reduce, such as copper or silver and, option-ally, a metal that is hard to reduce, such as aluminium or zinc. A
very suitable iron catalyst for the present purpose 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 catalyst, it is preferred to choose a cobalt catalyst containing a promoter combination consisting of an alkaline-earth metal and thorium, uranium or cerium. A very suitable Fischer-Tropsch cobalt catalyst for the present purpose is a catalyst prepared by impregnation containing cobalt, magnesium and thorium on silica as the carrier. Other very suitable Fischer-Tropsch cobalt catalysts prepared by impregnation are catalysts containing, in addition to cobalt, one of the elements chromium, 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, so that the use of a Z-catalyst in the combination can be omitted. An example of an X-catalyst of this type is an iron-chromium oxide catalyst. If de-1117~54 sired, it is also possible to use in step b) of the process accord-ing 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-containing hydrocarbons.
Z-catalysts which are capable of converting a H2O/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 component, either as such, or in the form of their oxides or sulphides. Examples of suitable CO-shift catalysts are the mixed sulphidic catalysts accord-ing to the Netherlands published patent applications No. 7305340 and No. 7304793 (see also Canadian Patent 1,018,329 and Indian Pat-ent 140,246) and the spinel catalysts according to the French pub-lished patent application No. 7633900*. 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 atomatic 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 conversely. If the *see also U.K. Patent 1,536,652 1~17054 process is carried out with use of a fixed catalyst bed, this bed may be built up of alternate layers of particles of catalysts X, Y al~d, optionally, Z. If the two or three catalysts 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 is completely made up of catalyst X, the second kind completely of catalyst Y and, optionally, a third kind completely of catalyst Z. In the second case the tri-functional 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. ~rifunctional catalysts in the form of micromixtures may be prepared, for in-stance, by thoroughly mixing a fine powder of catalyst X with a fine powder of catalyst Y and, optionally, with a fine powder of cat-alyst 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 trifunctional catalysts may also have been prepared by incorporating the metal components having catalytic activity for converting a H2/CO mixture into hydrocarbons and/or oxygen-containing hydrocarbons and, optionally, the metal components having catalytic activity for the water gas shift re-action into the crystalline silicate, for instance by impregnation or by ion exchange.
The crystalline silicates which are used in step b) of the process according to the invention are usually - lla -1117~54 prepared from an aqueous mixture as the starting msterial which contains the following compounds in a given ratio: one or more compounds of an alkali or alkaline-earth metal, one or more compounds contain;ng a mono-or bivalent organic cation or from which such a cation i9 formed during the preparation of the silicate, one or more silicon compounds, one or more iron compounds, and, optionally, one or more aluminium, gallium and/or germanium compounds. The preparation is effected by maintain;ng the mixture at elevated temperature until the silicate has been formed and then separating the crystals of the silicate from the mother liquor.
The silicates 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 least part of the mono- and/or bivalent organic cations introduced 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 crystalline silicates used in step b) of the process according to the invention preferably have an alkali metal content of 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 process according to the invention.
Step b) of the process accorddng 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 100 bar and a space velocity of from 50 to 5000 and in particular of from 300 to 3000 Nl gas/l catatalyst/hour.
Step b) of the process according to the invention can very suitably be carried out by passing 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 ~17054 or in ebulated-bed operation. It is preferred to use catalyst part;cles then with a diameter between I 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 ;n a hydrocarbon oil. It is preferred to use catalyst particles then with a diameter between 10 and 150 f~m.
In the process according to the invention an isobutane-con-taining gaseous fraction and an aromatic liquid fraction bo;ling in the gasoline range should be separated from aromatic hydro-carbon mixture obtained according to step b). It i9 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-butane fraction and an aromatic liquid fraction boiling in the gasoline range. The C2 fraction may be used as fuel gas. If desired, a H2/CO mixture can be separated from the C2 fraction, which mixture may be recirculated to step b)~ If the hydrocarbon content of the C2 fraction is sufficiently high, it may be preferred to subject it, either after removal of a H2/CO mixture from it or not, to steam reforming in order to prepare additional synthesis 20 gAS, which may be used as feed component for step b). Steam re-forming of the C2 fraction can very suitably be effected by con-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 process 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 whicb a fract;on boiling in the

3~ gasoline range can be separated. This alkylation can very con-veniently be effected by contacting the fraction with a strong acid as the catalyst, such as sulphuric acid or hydrofluoric acid. Since the gaseous part of the reaction product of step b) usually contains only small amounts of olefins, the isobutane-con-taining gaseous fraction which is separated from it will oftenhave 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-contain;ng 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. Dehydrogenation of these fractions can conven;ently be effected by contacting them at elevated temperature with a chromium-containing catalyst. From the product obtained in the alkylation a fraction boiling in the gasoline range is separated and this fraction is mixed according to step e) of the process according to the invention with the aromatic liquid fraction obtained in step c) and boiling in the gasoline range. The non-converted isobutane ;s preferably separated from the product obtained in the alkylation and recirculated to the alkylation reactor. In order to increase the vapour pressure of the gasoline mixture thus 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 successively a gasification section (1), a gas purification section (2), a hydro-carbon synthesis section (3), the first separation section (4), a steam reforming section (5), an alkylation section (6) and the second 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 11~7054 hydrocarbon mixeure is separated into a C2 fraction (15), a propane fraction (16), an isobutane fraction (17), a n-butane fraction (18) and an aro~atic gasoline fraction (19). The C2 fraction (15) is converted by steam reforming into the synthesis gaY (13). The propane fraction (16) and the n-butane fraction (18) are mixed into the LPG 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 stream (23) originating from an external source and with an isobutane recir-culation stream (24) reverted to later. From the alkylationproduct (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 ;s carried out in an apparatus comprising succes-sively a gasification section (1), a gas purification section (2)9 a hydrocarbon synthesis section (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) i3 converted under the influence of a tri-functional catalyst according to the invention into an aromatic hydrocarbon mixture (13). This hydrocarbon mixture is separated into a C2 fraction (14), a propane fraction (15), an isobutane fraction (16) a n-butane fraction (17) and an aromatic gasoline fraction (18). The propane fraction (15) is converted by dehydrogenation into a mixture of propene and propane (19).
The n-butane fraction (17) is separated into two portions (20) and (21). The isobutane fraction (16) is alkylated together with the propane/propene stream (19) and with an isobutane recirculation stream (22) reverted to later. From the alkylated product (23)a propane fraction (24), the isobutane recirculation stream (22) and a gasoline fraction (25) are separated. The propane fraction (24) is mixed with portion (21) of the n-butane fraction (17) into the ~ 35 LPG fraction (26). The gasoline fraction (25) is mixed with the 1117C~54 gasoline fraction (18) and with portion (20) of n-butane fraction (17) into the gasoline (27).
The present patent application also comprises an apparatus for carrying out the process according to the invention as shown schematically in Figure 2.
The invention will now be further explained with the aid of the following examples.
Example I
A crystalline iron silicate (silicate A) was prepared as follows. A mixture of Fe(NO3)3, SiO2, NaNO3 and [(C3H7)4N]OH in water with the molar composition Na2O. 1.5 [(C3H7)4N~2O. 0.125 Fe2O3. 25 SiO2. 468 H2O was heated for 48 hours in an autoclave at 150C under autogenous pressure. After the reaction mixture had cooled down, the silicate formed was filtered off, washed with water until the pH of the wash water was about 8 and dried for two hours at 120C. Silicate A thus prepared had the following chemical composition 0-8 [(C3H7)4N]2 0 3 Na2O 2 3 2 The silicate had an X-ray powder diffraction pattern substantially as given in Table B of Netherlands published patent application No. 7613957*. The silicate was thermally stable to temperatures higher than 900C and was capable, after dehydration at 400C, of adsorbing in vacuum 7% w water at 25C and saturated water vapour pressure. With silicate A as the starting material silicate B was prepared by, successively, calcining silicate A at 500C, boiling with 1.0 molar NH4NO3 solution, washing with water, boiling again with 1.0 molar NH4NO3 solution and washing, drying for two hours at 120C and calcining for four hours at 500C.
*see also U.K. Patent 1,555,928 1~17(~

le I I
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 impreg-nation;
b) silicate B;

- 16a -ff. ~
..?_ -' 1~70~4 c) a Cu/~n CO shi~t catalyst.
Catalyst C was extruded to particles having a diameter of 0.15-0.3 mm.
Example III
A catalyst D was prepared by mix;ng a ZnO-Cr203 composition with siLicate B in a weight ratio of 3:1. Both materials were present in the catalyst in the form of particles having a diameter of 0.15-0.3 mm.
The ZnO-Cr203 composition used catalyses both the reduction of CO
to methanol and the water gas shift reaction.
Example IV
Bituminous coal was ground to a particle size of less than 120 microns 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 gasification was effected at a temperature of 1500C, a pressure of 30 bar and a residence time of 0.5 5.
The coal conversion was 99%. The gas obtained had the following composition %v CH4 0.1 CO 64.7 H2 31.8 C02 1.7 The gas further contained about 1.7 %v H20, COS and H2S.
To remove 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 200 C over ZnO. The synthesis gas thus purified was used in Examples V and VI which were carried out according to process schemes I and II, respectively.
Example V
The synthesis gas prepared according to Example IV was mixed in a volume ratio of 65:35 with a synthesis gas (II), reverted to furtheron, obtained by steam reforming, and the mixture was con-tacted with catalyst C at a temperature of 280C, a pressure of 30 bar and a space velocity of 1000 1.1 .h . The synthesis gas ~117~54 conversion was 85%. The hydrocarbon mixture obtained had the ~ollowing composition %w Cl 10 n-C4 3 i-C4 4 C5 gasoline 58 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 fract;on tincluding carbon dioxide and unconverted syn-thesis gas) and a C3 fraction. The C2 fraction was mixed with 25 ~v steam and the mixture was converted into synthesis gas by contacting it at a temperature of 900C and a pressure of 30 bar with a Ni-containing catalys~. 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, a 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 olefin mixture originating from an external source and the mixture was converted by contacting it at 40C with a HF alkylation catalyst. By recirculation of 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 of the ~PG was added to it. The gasoline thus obtained had an octane number (CRON) of 89.

Example VI
The synthesis gas prepared according to Example IV was contacted at a temperature of 375C, a pressure of 60 bar and a space velocity of 275 1.1 .h with catalyst D. The synthesis gas conversion was 94~. The hydrocarbon mixture obtained had the following composition:

~w Cl 3 n-C4 5 i-C4 7 C5 gasoline 64 The olefin content of both the C3 and the C4 fractions was 'ess ehan 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 f-action, an isobutane fraction, a n-butane fract;on and a C5 gasoline f action mainly consisting of aromatics. The propane fract;on was converted by dehydrogenation at 600C over a Cr203 catalyst into a mixture of propane and propene. The conversion from propane into propene was 32%. 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 fract;on and a gasoline fraction were separated. By recirculation of isobutane a constant isobutane/olefin ratio of 14 was maintained. The alkylation gasoline yield was 95%. The alkylation gasoline was mixed with the gasoline obtained earlier in the process. To bring the. vapour pressure of the mixture to the proper value, part of the n-butane fraction was added. The gasoline thus obtained had an octane number (CRON) of ~4. The remaining part of the n-butane fraction obtained from the C3 fraction of the hydrocarbon synthesis product were mixed with the propane fraction obtained from the alkylation product, into LPG.

Claims

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

l. 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°C and 2000°C;
(B) the mixture of carbon monoxide and hydrogen is con-verted into an aromatic hydrocarbon mixture using a catalyst con-taining a crystalline silicate which (1) is thermally stable to temperatures above 600°C, (2) after dehydration at 400°C in vacuum, is capable of adsorbing more than 3% w water at 25°C and saturated water vapour pressure, and (3) in dehydrated form, has the following overall composition, expressed in moles of the oxides (1.0 + 0.3) (R)2/n 0.[a Fe2O3. b Al2O3. c Ga2O3].
y(d SiO2 + e GeO2), where R = one or more mono- or bivalent cations, a ? 0.1, b ? 0 c ? 0 a + b + c = 1 y ? 10 d ? 0.1 e ? 0 d + e = 1, and n = the valency of R

(C) from the aromatic hydrocarbon mixture an isobutane-containing gaseous fraction and an aromatic liquid fraction boiling in the gasoline range are separated, (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 according to claim 1 characterized in that the catalyst used in step (B) contains a crystalline silicate in which, in the formula which gives the overall composition, c and e are equal to 0.
3. A process according to claim 1 characterized in that the catalyst used in step (B) contains a crystalline silicate of which, in the formula which gives the overall composition, a is equal to 1.
4. A process according to claim 1 characterized in that the catalyst used in step (B) contains a crystalline silicate of which, in the formula which gives the overall composition, y is less than 600.
5. A process according to claim 1 characterized in that the olefins content of the isobutane-containing fraction is increased before subjecting it to alkylation.
6. A process according to claim 1 characterized in that to increase the vapour pressure light hydrocarbons, preferably n-butane or LPG, obtained as by-products of the process, are added to the gasoline obtained by mixing the fractions boiling in the gaso-line range and prepared according to steps (C) and (D).
7. A process according to claim 6 wherein the light hydro-carbons used to increase the vapour pressure are n-butane or LPG.