GB2037316A - Process for the preparation of aromatic hydrocarbon mixtures - Google Patents

Abstract

A C3/C4 fraction obtained as a by-product in the preparation of aromatic gasoline from synthesis gas over a crystalline aluminium or iron silicate comprising catalyst system, is converted into aromatic gasoline by partial oxidation or partial dehydrogenation followed by conversion over a crystalline aluminium or iron silicate catalyst of the partial oxidation or dehydrogenation product. <IMAGE>

Description

SPECIFICATION Process for the preparation of hydrocarbons The invention relates to a process for the preparation of a hydrocarbon mixture boiling in the gasoline range from a mixture of carbon monoxide and hydrogen.

Hydrocarbon mixtures boiling in the gasoline range may, inter alia, be obtained by straight-run distillation of crude mineral oil, by conversion of heavier crude mineral oil fractions, for instance by catalytic cracking, thermal cracking and hydrocracking, and by conversion of lighter mineral oil fractions, for instance by alkylation. To improve the octane number of the hydrocarbon mixtures thus obtained, they are often subjected to catalytic reforming, which increases the aromatic content.

In view of the decreasing mineral oil reserves, there is a great interest in processes for the conversion, in an economically justified way, of carbon-containing materials not based on mineral oil, such as coal, into hydrocarbon mixtures boiling in the gasoline range. lt is desirable that the said hydrocarbon mixtures have a sufficiently high octane number so that they can be used as gasoline without any further refining.

It is known that carbon-containing Is-such as coal can be converted into mixtures of carbon monoxide and hydrogen by gasification. It is also known that mixtures of carbon monoxide and hydrogen can be converted into mixtures of hydrocarbons by contacting the gas mixtures with suitable catalysts. It is further known that paraffinic hydrocarbons can be converted by partial dehydrogenation or partial oxidation into olefinic hydrocarbon mixtures and oxygen-containing hydrocarbon mixtures, respectively. Finally, it is known that aromatic hydrocarbon mixtures boiling in the gasoline range can be prepared by contacting olefinic hydrocarbon mixtures and oxygen-containing hydro-carbon mixtures with suitable catalysts.

The Applicant has carried out an investigation to find out to what extent the above-mentioned processes can be used in the preparation of gasoline from a mixture of carbon monoxide and hydrogen. Itwas found in this investigation that gasoline with a high octane number can be prepared in-a high yield from a mixture of carbon monoxide and hydrogen by a combination of the above-mentioned processes, provided that the following conditions are satisfied.

First of all, an aromatic hydrocarbon mixture should be prepared from the mixture of carbon monoxide and hydrogen by using a catalyst which contains a crystalline silicate, which silicate is characterized in that it has the following properties after 1 hour's calcining in air at 500 C: (1) thermally stable at a temperature above 600 C, (2) an X-ray powder diffraction pattern showing, inter alia, the reflections given in Table A.

TABLE A Radiation Cu-Ka Wavelength 0.15418 nm 2 0 relative intensity 7.8- 8.2 S 8.7- 9.1 M W 12.4-127 W 14.61409 W 15.415.7 W 15.8-16.1 W 17.6-17.9 W 19.2-19.5 W 20.2-20.6 W 20.721.1 W 23.1-23.4 VS 23.8-24.1 VS 24.2-24.8 S 29.7-30.1 M where the letters used have the following meanings: VS = very strong; S=strong; M=moderate; W=weak; 0 = angle according to Bragg's law.

(3) after evacuation at 2x 10-9 bar and 400 C for 16 hours and measured at a hydrocarbon pressure of 8x10-2 bar and 100 C, the adsorption of n-hexane is at least 0.8 mmol/g, the adsorption of 2,2dimethylbutane at least 0.5 mmol/g and the ratio adsorption of n-hexane at least 1.5.

adsorption of 2,2-dimethylbutane (4) the composition, expressed in moles of the oxides, is as follows V (1.0i0.3) M20.y(a Fe2O3. b Al203). SiO2 where M = Hand alkali metal a + b = 1, a30, bÓ,and O < y s 0.1 Then, from the aromatic hydrocarbon mixture thus obtained a gaseous fraction containing propane and/or butane and a liquid fraction boiling in the gasoline range should be separated. Next, the gaseous fraction should be subjected to partial dehydrogenation or partial oxidation. Subsequently the olefinic or oxygen-containing product thus obtained is converted into an aromatic hydrocarbon mixture using a crystalline silicate as defined above as the catalyst.Finally, a fraction boiling in the gasoline range is separated from the last-mentioned aromatic hydro-carbon mixture.

The present patent application therefore relates to a process for the preparation of a hydrocarbon mixture boiling in the gasoline range from a mixture of carbon monoxide and hydrogen, in which (a) the mixture of carbon monoxide and hydrogen is converted into an aromatic hydrocarbon mixture using a catalyst which contains a crystalline silicate as defined hereinbefore, (b) from the aromatic hydrocarbon mixture a gaseous fraction containing propane and/or butane and a liquid fraction boiling in the gasoline range are separated, (c) the gaseous fraction is subjected to partial dehydrogenation or partial oxidation, (d) the olefinic or oxygen-containing product obtained according to (c) is converted into an aromatic hydrocarbon mixture boiling in the gasoline range using a crystalline silicate as defined hereinbefore as the catalyst, and (e) from the aromatic hydrocarbon mixture obtained according to (d) a fraction boiling in the gasoline range is separated.

The process according to the invention starts from an H2/CO mixture. Such a mixture may conveniently be prepared by steam gasification of a carbon-containing material. Examples of such materials are brown coal, anthracite, coke, crude mineral oil and fractions thereof, and oils recovered from tar sand and bituminous shale. The steam gasification is preferably carried out at a temperature between 1000 and 2000"C and a pressure between 10 and 50 bar. In the process according to the invention the preferred starting material is an H2/CO mixture whose molar ratio is between 0.25 and 1.0.

The H2/CO mixture is converted in step (a) of the process into an aromatic hydrocarbon mixture using a catalyst which contains a crystalline silicate belonging to a special class. Although in steps (a) and (d) of the process silicates may be used which contain both iron and aluminium (a > 0 and b > 0), preference is given to the use of silicates which contain either iron only (an 1 and b=O) or aluminium only (a=O and b=1). Step (a) may in itself be carried out as a one-step or a two-step process. In th two-step process the H2/CO mixture is preferably contacted in the first step with a catalyst which contains one or more metal components having catalytic activity for the conversion of an H2/CO mixture into acyclic hydrocarbons.In the second step the product thus obtained is converted into an aromatic hydrocarbon mixture by contacting it under aromatization conditions with the crystalline silicate. In the one-step process the H2/CO mixture is contacted with a bifunctional catalyst which contains, in addition to the crystalline silicate, one or more metal components having catalytic activity for the conversion of an H2/CO mixture into acyclic hydrocarbons and/or oxygen-containing hydro-carbons. Step (a) of the process according to the invention is preferably carried out as a one-step process.

The process according to the invention starts from an H2/CO mixture whose H2/CO molar ratio may vary within wide limits. Before this mixture is converted according to step (a), its H2/CO molar ratio may also be changed by addition of hydrogen or carbon monoxide. The hydrogen content of the mixture may be increased by subjecting the mixture to the known water-gas shift reaction. If the H2/CO mixture that is used in the process as the feed for step (a) has an H2/CO molar ratio of less than 1,0 step (a) is preferably carried out using a catalyst which contains one or more metal components having catalytic activity forthe water-gas shift reaction.When step (a) is carried out as a two-step process, the H2/CO mixture with an H2/CO molar ratio of less than 1.0 is preferably contacted in the first step with a bifunctional catalyst which contains one or more metal components having catalytic activity for the conversion of an H2/CO mixture into acyclic hydrocarbons and one or more metal components having catalytic activity for the water-gas shift reaction and the product thus obtained is converted in the second step into an aromatic hydrocarbon mixture by contacting it under aromatization conditions with the crystalline silicate. When step (a) is carried out as a one-step process, the H2/CO mixture with an H2/CO molar ratio of less than 1.0 is preferably contacted with a trifunctional catalyst which contains one or more metal components having catalytic activity for the conversion of an H2/CO mixture into acyclic hydrocarbons and/or oxygen-containing hydrocarbons, one or more metal components having catalytic activity for the water-gas shift reaction and the crystalline silicate.

Although the trifunctional catalysts which may be used in step (a) of the process are described in this patent application as catalysts which contain one or more metal components having catalytic activity for the conversion of an H2/CO mixture into acyclic hydrocarbons and/or oxygen-containing hydrocarbons, and one or more metal components having catalytic activity for the water-gas shift reaction, this does not mean that separate metal components which each have one of the two catalytic functions should always be present in the catalysts, since it has been found that metal components and combinations of metal components having catalytic activity for the conversion of anH2/CO mixture into substantially oxygen-containing hydrocarbons have, as a rule, also sufficient catalytic activity for the water-gas shift reaction, so that 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 zinc, copper and chromium. When trifunctional catalysts which contain these metals are used in step (a) of the process, a trifunctional catalyst is preferred which contains, in addition to the crystalline silicate, the metal combination zinc-chromium. Metal components and metal combinations of metal components having catalytic activity for the conversion of an H2/CO mixture into substantially hydrocarbons have as a rule no or insufficient activity for the water-gas shift reaction.When such metal components or combinations of metal components are used in the catalyst for the first step of the two-step process or in the catalyst for the one-step process, it will therefore be preferred, when using feeds with an H2/CO molar ratio of less than 1.0, to incorporate one or more separate metal components having catalytic activity for the water-gas shift reaction into the catalyst.

When an H2/CO mixture with an H2/CO molar ratio of less than 1.0 is used as the feed for step (a) of the process, this step is preferably carried out as a one-step process using a trifunctional catalyst which is composed of two or three separate catalysts, which, for the sake of convenience, will be designated catalysts X, Y and Z. Catalyst X is the one which contains the metal components having catalytic activity for the conversion of an H2/CO mixture into acyclic hydrocarbons and/or oxygen-containing hydrocabons. Catalyst Y is the crystalline silicate. Catalyst Z is the one which contains the metal components having catalytic activity for the water-gas shift reaction. As explained hereinbefore, the use of a Z-catalyst may in certain cases not be necessary.

If as the X-catalyst a catalyst is used which is capable of converting an H2/CO mixture into substantially oxygen-containing hydrocarbons, it is preferred to choose a catalyst which is capable of converting the H2/CO mixture into substantially methanol and/or dimethyl ether. For the conversion of an H2/CO mixture into substantially methanol, catalysts containing the above-mentioned metal combinations (chosen from the group consisting of Cu, Zn or Cr) are very suitable. X-catalysts which are capable of converting an H2/CO mixture into substantially acyclic hydrocarbons are known in the literature as Fischer-Tropsch catalysts.

Such catalysts often contain one or more metals from the iron group or ruthenium together with one or more promotors to increase the activity and/or selectivity. If in step (a) 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. If desired, it is also possible to use in step (a) of the process according to the invention catalyst combinations which contain a catalyst X which is capable of converting an H2/CO mixture into a mixture which contains both hydrocarbons and oxygen-containing hydrocarbons in comparable quantities.As a rule, such a catalyst also has sufficient catalytic activity forthe water-gas shift reaction, so that the use of a catalyst Z in the combination can be omitted. An example of an X-catalyst of this type is an iron-chromium oxide catalyst.

Z-catalysts which are capable of converting an H2O/CO mixture into an H2/CO2 mixture are referred to in the literature as CO-shift catalysts. If a Z-catalyst is used in step (a) of the process according to the invention, it is preferred to choose for this purpose a catalyst which contains the metal combination copper-zinc.

The trifunctional catalysts are preferably used as a mixture. This mixture may be a macromixture or a micro-mixture. in the first case the trifunctional catalyst consists of two orthree kinds of macroparticles, of which one kind consists completely of catalyst X, the second kind completely of catalyst Y and the third kind, if present, completely of catalyst Z. In the second case the trifunctional catalyst consists of one kind of macroparticles, each macroparticle being built up of a great number of microparticles of each of the catalysts X, Y and, optionally,Z. In step (a) of the process it is preferred to use trifunctional catalysts in the form of micromixtures.

The crystalline silicate that is used in step (a) and step (d) of the process is defined, inter alia, with reference to the X-ray powder diffraction pattern of the silicate after 1 hour's calcining in air at 500"C. This X-ray powder diffraction pattern should show, inter alia, the reflections given in Table A. The complete X-ray powder diffraction pattern of a typical example of a silicate eligible for use according to the invention is shown in Table B (Radiation: Cu-Ka; wavelength: 0.15418 nm).

TABLE B 2 0 relative intensity description (100.1/lo) 8.00 55 SP 8.90 36 SP 9.10 20 SR 11.95 7 NL 12.55 3 NL 13.25 4 NL 13.95 10 NL 14.75 9 BD 15.55 7 BD 15.95 9 BD 17.75 5 BD 19.35 6 NL 20.40 9 NL 20.90 10 NL 21.80 4 NL 22.25 8 NL 23.25 100X) SP 23.95 45 SP 24.40 27 SP 25.90 11 BD 26.70 9 BD 27.50 4 NL 29.30 7 NL 29.90 11 BD 31.25 2 NL 32.75 4 NL 34.40 4 NL 36.05 5 BD 37.50 4 BD 45.30 9 BD X) lo = intensity of the strongest separate reflection present in the patter.

The letters used in Table B for describing the reflections have the following meanings: SP = sharp; SR = shoulder; NL = normal; BD = broad; 0 = angle according to Bragg's law.

The crystalline silicates may be prepared from an aqueous mixture as the starting material which contains the following compounds in a given ratio: one or more compounds of an alkali metal (M), one or more compounds containing an organic cation (R) or from which such a cation is formed during the preparation of the silicate, one or more silicon compounds and one or more aluminium and/or iron compounds. The preparation is performed by maintaining the mixture at elevated temperature until the silicate has been formed and subsequently separating the crystals of the silicate from the mother liquor. In the preparation of the silicates it is preferred to start from a base mixture in which M is present in a sodium compound and R in a tetrapropylammonium compound.

The silicates prepared as described above contain alkali metal ions and organic cations. When suitable exchange methods are used, the alkali metal ions can be replaced by other cations, such as hydrogen ions or ammonium ions. Organic cations can very conveniently be converted into hydrogen ions by calcining the silicates. The crystalline silicates which are used in the catalysts preferably have an alkali metal content of less than 1 %w, and in particular of less than 0.05 %w.

Step (a) of the process is preferably carried out at a temperature of 200-500"C and in particular of 300-450"C, a pressure of 1-50 bar and in particular of 5-100 bar and a space velocity of 50-5000 and in particular of 300-3000 N1 gas/1 catalyst/h.

Step (a) of the process can very conveniently be carried out by conducting the feed in upward or downward direction through a vertically mounted reactor in which a fixed or a moving catalyst bed is present. Step (a) of the process may, for instance, be carried out by conducting the feed in upward direction through a vertically mounted catalyst bed, at such a gas rate that expansion of the catalyst bed takes place. If desired, step (a) of the process may also be carried out using a suspension of the catalyst in a hydrocarbon oil. Depending on whether step (a) of the process is carried out with a fixed catalyst bed, an expanded catalyst bed or a catalyst suspension, preference is given to catalyst particles with a diameter between 1 and 5 mm, 0.5 and 2.5 mm and 20 and 150 cm, respectively.

From the aromatic hydrocarbon mixture obtained according to step (a), a gaseous fraction containing propane and/or butane and a liquid fraction boiling in the gasoline range should, according to the invention, be separated in step (b). Preferably the reaction mixture eriginating from step (a) is separated in step (b) into a C2 fraction, a C3/C4 fraction and a C+ gasoline fraction. The C2 fraction may be used as fuel gas. If desired, from the C2 fraction an H2/CO mixture may be separated, which may be recycled to step (a).If the hydrocarbon content of the C2- fraction is sufficiently high, it may be preferable to subject this fraction, either with an H2/CO mixture present or after its removal, to steam reforming in order to prepare additional synthesis gas which can be used as feed component for step (a). The steam reforming of the C2 fraction may very conveniently be effected by contacting this fraction together with steam at elevated temperature and pressure with a nickel-containing catalyst.

In the process according to the invention the gaseous fraction containing propane and/or butane should be subjected in step (c) to partial dehydrogenation or partial oxidation. Partial dehydrogenation of the gaseous fraction may be effected by contacting this fraction at elevated temperature with a chromium-containing catalyst. Partial oxidation of the gaseous fraction may be effected by treating the fraction, optionally in the presence of a catalyst, at elevated temperature with a less than theoretical quantity of oxygen, As a rule, in the partial oxidation CO is formed, which may be used, if desired, as feed component for step (a).

In the process according to the invention the olefinic or oxygen-containing product obtained according to step (c) should be converted in step (d) into an aromatic hydrocarbon mixture by contacting it under aromatization conditions with a silicate as defined hereinbefore. From the product prepared according to step (d) a fraction boiling in the gasoline range is separated in step (e).

The conversion of the olefinic or oxygen-containing product obtained according to step (c) over the crystalline silicate may, in principle, be effected in two ways. The product prepared according to step (c) may be contacted in a separate reactor with the crystalline silicate or, alternatively, if step (a) of the process according to the invention is carried out as a two-step process, the-product prepared according to step (c) can very conveniently be mixed with the product ofthe first step.

An attractive embodiment of the process according to the invention is one in which the conversion of the product prepared according to step (c) is carried out by contacting this product in step (d) in a separate reactor with the crystalline silicate, separating from the product prepared according to step (d) a gaseous fraction containing propane and/or butane and a liquid fraction boiling in the gasoline range, and recyling the gaseous fraction to step (c).

A process scheme for the conversion of synthesis gas into aromatic gasoline according to the invention will be explained below in more detail with reference to the drawing.

Process scheme (see figure) The process is carried out in an apparatus which comprises, in succession, a methanol synthesis unit (1), an aromatization unit (2), a separation unit (3), a partial oxidation unit (4), another aromatization unit (5) and another separation unit (6). An H2/CO mixture (7) is converted into methanol (8). The methanol stream is divided into two portions (9) and (10). Portion (9) is aromatized. The aromatized product (10) is separated into a C2 fraction (11), a C3/C4 fraction (12) and a C5+ gasoline fraction (13). The C3/C4 fraction (12) is mixed with a C3/C4fraction (14) and the mixture (15) is partially oxidized. The partially oxidized product (16) is mixed with methanol portion (10), and the mixture (17) is aromatized.The armatized product (18) is separated into a C2 fraction (19), a C3/C4fraction (14) and a C5+ gasoline fraction (20).

The present patent application also comprises an apparatus for carrying out a process according to the invention as shown schematically in the figure.

The invention will now be explained with reference to the following example.

EXAMPLE A crystalline silicate (silicate A) was prepared as follows. A mixture of SiO2, Fe(NO3)3, NaOH and [(C3H7)4N]OH in water with the molar composition 8 Na2O.Fe203.12[(C3H7)4N]2O.200 SiO2. 3750 H2Owas heated for 48 hours in an autoclave at 150oC 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 120"C. After 1 hour's calcining in air at 500"C silicate A had the following properties: (a) thermally stable up to a temperature above 900"C (d) an x-ray powder diffraction pattern substantially equal to the one given in Table B.

(c) after evacuation for 16 hours at 2x10-9 bar and 400"C and measured at a hydrocarbon pressure of 8x10-2 bar and 100 C, the adsorption of n-hexane is 1.2 mmol/g. the adsorption of 2,2-dimethylbutane 0.7 mmol/g and the ratio adsorption of n-hexane 1.7, and adsorption of 2,2-dimethylbutane (d) the composition, expressed in moles of the oxides, is 0.0054 M2O. 0.0054 Fe2O3. SiO2, where M=H and Na.

From silicate A, which had an average crystallite size of 225 nm, a silicate B was prepared by boiling the material calcined at 500"C with 1.0 molar NH4NO3 solution, washing with water, boiling again with 1.0 molar NH4NO3 solution and washing, drying for 2 hours at 120 C and calcining for 1 hour at 500"C.

A crystalline silicate (silicate C( WAS PREPARED IN SUBSTANTIALLY THE SAME WAY AS SILICATE A, the difference being that for the preparation of silicate C the starting material was an aqueous mixture which contained Na2A1 02 instead of Fe(NO2)3 and which had the following molar composition: 16 Na2O.Fe203.72[(C3H7)4N]2O.400 Six2.7200 H2O.

After 1 hour's calcining in air at 500"C silicate C was completely identical to silicate A as regards X-ray powder diffraction pattern and adsorption behaviour.

Silicate C was thermally stable up to a temperature above 800"C. The composition of silicate C (after calcining), expressed in moles of the oxides, was as follows: 0.0035 M2O. 0.0035 Al2O3.SiO2, where M=H and Na.

From silicate C, which had an average crystallite size of 240 nm, a silicate D was prepared in the same way as described above for the preparation of silicate Bfrom silicate A.

Two catalyst mixtures (I and It) were prepared by mixing a ZnO-Cr203 composition with silicate B and with silicate D, respectively. The atomic Zn percentage of the ZnO-Cr2O3 composition based on the sum of Zn and Cr was 70%. The catalyst mixtures both contained per part by volume of silicate, 2 parts by volume of the ZnO-Cr2O3 composition.

Catalyst mixtures I (prepared with silicate B) and II (prepared with silicate D) were used in a process for the preparation of an aromatic hydrocarbon mixture boiling in the gasoline range, with an H2/CO mixture with an H2/CO molar ratio of 0.5 as the starting material. To this end the H2/CO mixture was converted in one step into an aromatic hydrocarbon mixture by conducting it at a temperature of 375"C, a pressure of 60 bar and a space velocity of 200 1.1-1.h-1 over a fixed bed with a volume of 7.5 ml ofthe catalyst mixture concerned, which was present in a 50-ml reactor. The product thus obtained was separated into a C2 fraction, a C3/C4 fraction and a C+ gasoline fraction.The C3/C4 fraction was partially dehydrogenated and the product thus obtained was aromatized by contacting it at a temperature of 375"C, a pressure of 30 bar and a space velocity at 2 kg.kg-'.h-' with silicate B or silicate D. The product thus obtained was separated into a C4 fraction and a C+ gasoline fraction.

The results of these experiments are given below.

Experiment No. 1 2 Conversion of the H2/CO mixture carried out using catalyst mixture No. I Composition of the aromatic hydrocarbon mixture prepared from the H2/CO mixture (Cl'),%w C2 10 7 C3/C4 26 32 64 64 61 Composition of the C5+fraction, prepared from the H2/CO mixture, %w acyclic hydrocarbons 20 18 naphthenes 18 16 aromatics 62 66 Average conversion of C3/C4 paraffins into C3/C4 olefins, % 33 34 Aromatization of the partially dehydrogenated C3/C4fraction carried out using silicate No. B D Yield of C5+fraction, calculat ted on C1+, %w 6 8 Aromatics content of the last-mentioned C5+fraction, %w 85 88

Claims (1)

1. A process for the preparation of a hydrocarbon mixture boiling in the gasoline range from a mixture of carbon monoxide and hydrogen, characterized in that: (a) the mixture of carbon monoxide and hydrogen is converted into an aromatic hydrocarbon mixture using a catalyst which contains a crystalline silicate, which silicate is characterized in that it has the following properties after 1 hour's calcining in air at 5000C: (1) thermally stable at a temperature above 60D C, (2) an X-ray powder diffraction pattern showing, inter alia, the reflections given in Table A.

TABLE A Radiation: Cu-Ka Wavelength 0.15418 nm 26 relative intensity

7.8- 8.2 S

8.7- 9.1 M 11.812.1 W 12.4-12.7 W 14.6-14.9 W 15.4-15.7 W 15.8-16.1 W 17.6-17.9 W 19.2-19.5 W

20.2-20.6 W 20.7-21.1 W 23.1-23.4 VS 23.8-24.1 VS 24:2-24.8 S 29.7-30.1 M where the letters used have the following meanings: VS = very strong; S=strong; M=moderate; W=weak; 0 = angle according to Bragg's law.

(3) after evacuation at 2x 10-9 bar and 400"C for 16 hours and measured at a hydrocarbon pressure of 8x10-2 bar and 100 C, the adsorption of n-hexane is at least 0.8 mmol/g, the adsorption of 2,2dimethylbutane at least 0.5 mmol/g and the ratio adsorption of n-hexane adsorption of 2,2-dimethylbutane at least 1.5.

(4) the composition, expressed in moles of the oxides, is as follows y (1 .0t0.3) M2O. y(a Fe2O3. b Al203). SiO2 where M = H and alkali metal a + b = 1, a 3 O, b > 0, and O < y 0.1 (b) from the aromatic hydrocarbon mixture a gaseous fraction containing propane and/or butane and a liquid fraction boiling in the gasoline range are separated, (c) the gaseous fraction is subjected to partial dehydrogenation or partial oxidation, (d) the olefinic or oxygen-containing product obtained according to (c) is converted into an aromatic hydro-carbon mixture using a crystalline silicate as defined under (a) as the catalyst, and (e) from the aromatic hydrocarbon mixture obtained according to (d) a fraction boiling in the gasoline range is separated.

2. A process according to claim 1, characterized in that step (a) is carried out at a temperature of 200-500"C, a pressure of 1-150 bar and a space velocity of 50-5000 N1 gas/1 catalyst/h.

3. A process according to claim 2, characterized in that step (a) is carried out at a temperature of 300-450"C, a pressure of 5-100 bar and a space velocity of 300-3000 N1 gas/l catalyst/h.

4. A process according to any one of claims 1 -3, characterized in that the aromatic hydrocarbon mixture originating from step (a) is separated in step (b) into a C2 fraction, a C3/C4fraction and a C+ gasoline fraction and that the C3/C4 fraction is used as feed for step (e).

5. A process according to any one of claims 1 -4, characterized in that the product prepared according to step (c) is contacted in step (d) in a separate reactor with the crystalline silicate, from the product prepared according to step (d) a gaseous fraction containing propane or butane and a liquid fraction boiling in the gasoline range are separated, and the gaseous fraction is recycled to step(c).

6. A process for the preparation of a hydrocarbon mixture boiling in the gasoline range, substantially as described hereinbefore and in particular with reference to the example.

7. A process for the preparation of a hydrocarbon mixture boiling in the gasoline range, substantially as described herein before and in particular with reference to the drawing.

8. Hydrocarbon mixtures boiling in the gasoline range, prepared according to a process as described in any one of claims 1-7.