Abstract:
A process is disclosed for the preparation of an aromatic hydrocarbon mixture from a mixture of carbon monoxide and hydrogen using a mixture of two catalysts; one is a conventional catalyst for the conversion of a CO/H 2  mixture into acyclic oxygen-containing hydrocarbons and the other is a certain crystalline silicate containing at least one element selected from manganese, clacium, magnesium and titanium, and the alumina to silica ratio is greater than 0.005.

Description:
This application is a continuation-in-part of application Ser. No. 095,027, filed Nov. 16, 1979 now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates to a process for the preparation of an aromatic hydrocarbon mixture from a mixture of carbon monoxide and hydrogen using a mixture of two catalysts of which one has the capability of catalysing the conversion of an H 2  /CO mixture into acyclic oxygen-containing hydrocarbons, and the other is a crystalline silicate which has the capability of catalysing the conversion of acyclic oxygen-containing hydrocarbons into aromatic hydrocarbons. 
     It is known to prepare aromatic hydrocarbons from synthesis gas over a mixture of a methanol synthesis catalyst and certain crystalline silicates as disclosed in German patent application No. 2518097 and in U.S. Pat. Nos. 4,086,262 and 4,096,163. However, for commercial application it is highly desirable to employ a process wherein higher selectivity to products boiling in the gasoline range, i.e., pentanes and higher (C 5   + ) is achieved. 
     In an investigation by Applicants concerning the above-mentioned process it was found that the catalyst mixtures show a higher C 5   +  selectivity according as, in the formula hereinafter which shows the composition of the silicate, the value of y is lower. It was found that to reach a C 5   +  selectivity which is acceptable for commercial use of the process, y should be at most 0.005. This finding is the subject of applicants&#39; related Netherlands patent application No. 7811735 and corresponding U.S. patent application Ser. No. 095,025, filed Nov. 16, 1979. Further investigation by Applicants concerning the above-mentioned process has now revealed that also with catalyst mixtures in which a silicate is present whose value of y is greater than 0.005, an acceptable C 5   +  selectivity can be reached, provided that the silicate contains one or more elements selected from the group of manganese, calcium, magnesium and titanium. 
     The invention therefore relates to a process for the preparation of an aromatic hydrocarbon mixture in which a mixture of carbon monoxide and hydrogen is contacted with a mixture of two catalysts of which one is capable of catalysing the conversion of an H 2  /CO mixture into acyclic oxygen-containing hydrocarbons, and the other is a crystalline silicate as defined above, of which, in the formula giving the composition of the silicate, the value of y is more than 0.005, and which contains one or more elements selected from the group of manganese, calcium, magnesium and titanium. 
     SUMMARY OF THE INVENTION 
     According to the invention there is provided a process for the preparation of a hydrocarbon mixture of pentanes and higher containing aromatics, which comprises contacting a mixture of carbon monoxide and hydrogen at elevated temperatures and pressure with a mixture of two catalysts which mixture consists essentially of a catalyst x and a catalyst y, catalyst x being capable of catalysing the conversion of an H 2  /CO mixture into acyclic oxygen-containing hydrocarbons, and catalyst y being a crystalline silicate, which silicate is characterized by having the following properties after 1 hour&#39;s calcining in air at 500° C.: 
     (a) thermally stable up to a temperature above 600° C., 
     (b) an X-ray powder diffraction pattern showing, inter alia, the reflections given in Table A. 
     
                       TABLE A______________________________________Radiation: Cu--Ka          Wavelength 0.15418 nm2 θ      relative intensity______________________________________7.8-8.2        S8.7-9.1        M11.8-12.1      W12.4-12.7      W14.6-14.9      W15.4-15.7      W15.8-16.1      W17.6-17.9      W19.2-19.5      W20.2-20.6      W20.7-21.1      W23.1-23.4       VS23.8-24.1       VS24.2-24.8      S29.7-30.1      M______________________________________ 
    
     where the letters used have the following meanings: VS=very strong; S=strong; M=moderate; W=weak; θ=angle according to Bragg&#39;s law. 
     (c) after evacuation at 2×10 -9  bar and 400° C. for 16 hours and measured at a hydrocarbon pressure of 8×10 -2  bar and 100° C., the adsorption of n-hexane is at least 0.8 mmol/g, the adsorption of 2,2-dimethylbutane at least 0.5 mmol/g, and the ratio ##EQU1## 
     (d) the composition, expressed in moles of the oxides, is as follows: y.(1.0±0.3). M 2  O.y.Al 2  O 3 .SiO 2 , where M=H and alkali metal and y&gt;0.005, and 
     (e) the silicate contains 0.1-10% by weight on the silicate of at least one element selected from the group of manganese, calcium, magnesium and titanium. 
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     The process according to the invention starts from an H 2  /CO mixture. Such a mixture can very 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 900° and 1500° C. and a pressure between 10 and 50 bar. In the process according to the invention the preferred starting material is an H 2  /CO mixture whose molar ratio is between 0.25 and 1.0. 
     The process according to the invention is preferably carried out at a temperature of 200°-500° C. and particularly of 300°-450° C., a pressure of 1-150 bar and particularly of 5-100 bar and a space velocity of 50-5000 and particularly of 300-3000 Nl gas/l catalyst/h. 
     In the process according to the invention a mixture of two catalysts is used, which, for the sake of convenience, will be designated catalysts X and Y. Catalyst X is the one which is capable of catalysing the conversion of an H 2  /CO mixture into acyclic oxygen-containing hydrocarbons and catalyst Y is the crystalline silicate. Catalysts that are preferably used as X-catalysts are those which are capable of converting an H 2  /O mixture into substantially methanol and/or dimethyl ether. Very suitable for the present purpose are catalysts which contain zinc together with chromium. When using such a catalyst, it is preferred to choose one in which the atomic percentage of zinc, based on the sum of zinc and chromium, is at least 60% and in particular 60-80%. The catalyst mixture that is used in the process according to the invention may be a macromixture or a micromixture. In the first case the catalyst mixture consists of two kinds of macroparticles, of which one kind consists completely of catalyst X, and the other kind completely of catalyst Y. In the second case the catalyst mixture consists of one kind of macroparticles, each macroparticle being built up of a great number of microparticles of each of the catalyts X and Y. Catalyst mixtures 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 shaping the mixture into larger particles, for instance, by extruding or tabletting. In the process according to the invention it is preferred to use catalyst mixtures in the form of micromixtures. In view of the required activity of the catalyst mixtures, preferred mixtures are those containing per part by volume of catalyst Y, 1-5 parts by volume of catalyst X. 
     The said crystalline silicates are characterized by having the following properties after 1 hour&#39;s calcining in air at 500° C.: 
     (a) thermally stable up to a temperature above 600° C., 
     (b) an X-ray powder diffraction pattern showing, inter alia, the reflections given in Table A. 
     
                       TABLE A______________________________________Radiation: Cu--Ka          Wavelength 0.15418 nm2 θ      relative intensity______________________________________7.8-8.2        S8.7-9.1        M11.8-12.1      W12.4-12.7      W14.6-14.9      W15.4-15.7      W15.8-16.1      W17.6-17.9      W19.2-19.5      W20.2-20.6      W20.7-21.1      W23.1-23.4       VS23.8-24.1       VS24.2-24.8      S29.7-30.1      M______________________________________ 
    
     where the letters used have the following meanings: 
     VS=very strong; S=strong; M=moderate; W=weak; θ=angle according to Bragg&#39;s law. 
     (c) after evacuation at 2×10 -9  bar and 400° C. for 16 hours and measured at a hydrocarbon pressure of 8×10 -2  bar and 100° C., the adsorption of n-hexane is at least 0.8 mmol/g, the adsorption of 2,2-dimethylbutane at least 0.5 mmol/g, and the ratio ##EQU2## 
     (d) the composition, expressed in moles of the oxides, is as follows: y.(1.0±0.3). M 2  O.y.Al 2  O 3 .SiO 2 , 
     where M=H and alkali metal and O&lt;y≦0.1. 
     The crystalline silicate that is present in the catalyst mixtures as catalyst Y, is defined, inter alia, with reference to the X-ray powder diffraction pattern shown by the silicate after 1 hour&#39;s calcining in air at 500° C. This X-ray powder diffraction pattern should contain, inter alia, the reflections shown 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______________________________________      relative intensity2 θ  (100. I/Io)  description______________________________________8.00       55           SP8.90       36           SP9.10       20           SR11.95      7            NL12.55      3            NL13.25      4            NL13.95      10           NL14.75      9            BD15.55      7            BD15.95      9            BD17.75      5            BD19.35      6            NL20.40      9            NL20.90      10           NL21.80      4            NL22.25      8            NL23.25      100.sup.(x)  SP23.95      45           SP24.40      27           SP25.90      11           BD26.70      9            BD27.50      4            NL29.30      7            NL29.90      11           BD31.25      2            NL32.75      4            NL34.40      4            NL36.05      5            BD37.50      4            BD45.30      9            BD______________________________________ .sup.(x) I.sub.o = intensity of the strongest separate reflection present in the pattent. 
    
     The letters used in Table B for describing the reflections have the following meanings: 
     SP=sharp; SR=shoulder; NL=normal; BD=broad; θ=angle according to Bragg&#39;s law. 
     The crystalline silicates which are used in the catalyst mixtures can be prepared from an aqueous mixture as the starting material which contains the following compounds: 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 aluminum compounds. The preparation takes place 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 aqueous mixture from which the silicates are prepared, the various compounds should be present in the following molar ratio, expressed in moles of the oxides: 
     M 2  O:(R) 2/n  O=0.1-20, 
     (R) 2  O:SiO 2  =0.01-0.5, and 
     SiO 2  :Al 2  O 3  &lt;200; n is the valency of R. 
     In the preparation of the silicates it is preferred to start from a basic mixture in which M is present in a sodium compound and R in a tetrapropylammonium compound. 
     In view of the required stability of the catalyst mixtures in the process according to the invention preference is given to silicates having an average crystallite size of less than 300 nm and in particular of less than 1000 nm. The average crystallite size of the silicates can be adjusted with the aid of the molar ratio of (R) 2/n  O to SiO 2  in the starting mixture, in the sense that silicates with a lower average crystallite size are obtained according as the molar ratio of (R) 2/n  O to SiO 2  in the starting mixture is chosen higher. 
     In the process according to the invention preference is given to silicates of which, in the formula giving the composition of the silicate, the value of y is 0.01-0.02. In the formula which gives the composition of the silicates, the value of y can be adjusted with the aid of the molar ratio of SiO 2  to Al 2  O 3  in the starting mixture, in the sense that silicates with a lower value for y are obtained according as the molar ratio of SiO 2  to Al 2  O 3  in the starting mixture is chosen higher. 
     The silicates prepared in the way described above contain alkali metal ions and organic cations. By using suitable exchange methods the alkali metal ions can be replaced by other cations, such as hydrogen ions or ammonium ions. Organic cations can be very suitably converted into hydrogen ions by calcining the silicates. The crystalline silicates which are used in the catalyst mixtures preferably have an alkali metal content of less than 1% w and particularly less that 0.05% w. If desired, a binder material such as bentonite or kaolin may be incorporated into the catalyst mixtures. 
     In the process according to the invention a catalyst mixture should be used whose crystalline silicate component contains one or more elements selected from the group of manganese, calcium, magnesium and titanium. Particularly preferred are silicates containing manganese. Preferably a catalyst mixture is used whose silicate component contains one or more of the above elements in an amount of 0.1-10% w and particularly of 0.5-5% w, based on the silicate component in the mixture. Incorporation of the elements into the silicate component may take place in various ways, for instance by ion exchange or by impregnation. It is preferred to use in the process a catalyst mixture in which incorporation of the elements into the silicate component has taken place by impregnating this component with an aqueous solution of one or more salts of the elements concerned, followed by drying and calcining of the silicate. 
     The process according to the invention can very suitably be carried out by conducting the feed in upward or downward direction through a vertically mounted reactor, in which a fixed or a moving bed of the catalyst mixture concerned is present. The process may, for instance, be carried out by conducting a feed in upward direction through a vertically mounted catalyst bed, using such a gas rate that expansion of the catalyst bed occurs. If desired, the process can also be carried out using a suspension of the catalyst mixture in a hydrocarbon oil. Depending on whether 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 μm, respectively. 
    
    
     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 SiO 2 , Na 2  AlO 2 , NaOH and [(C 3  H 7 ) 4  N]OH in water with the molar composition 1.5 Na 2  O.Al 2  O 3 . 2.25[C 3  H 7 ) 4  N] 2  O. 37.5 SiO 2 . 675 H 2  O was heated for 48 hours in an autoclave at 150° C. 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&#39;s calcining in air at 500° C. silicate A had the following properties: 
     (a) thermally stable up to a temperature above 800° C.; 
     (b) an X-ray powder diffraction pattern substantially equal to the one given in Table B; 
     (c) after evacuation for 16 hours at 2×10 -9  bar and 400° C. and measured at a hydrocarbon pressure of 8×10 -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, the ratio ##EQU3## 
     (d) the composition, expressed in moles of the oxides, is 0.025 M 2  O. 0.025 Al 2  O 3 .SiO 2 , where M=H and Na. 
     From silicate A, which had an average crystallite size of 250 nm, a silicate B was prepared by boiling the material calcined at 500° C. with 1.0 molar NH 4  NO 3  solution, washing with water, boiling again with 1.0 molar NH 4  NO 3  solution and washing, drying for 2 hours at 120° C. and calcining for 1 hour at 500° C. 
     With silicate B as the starting material seven silicates (silicates C-I) were prepared, which contained 1-3%w of one of the following elements: magnesium, calcium, titanium, manganese, molybdenum, chromium and cerium. The preparation was effected by impregnating samples of silicate B with an aqueous solution of a salt of the element concerned, followed by drying and calcining of the impregnated material. 
     Eight catalyst mixtures (I-VIII) were prepared by mixing a ZnO-Cr 2  O 3  composition with each of the silicates B-I. The atomic Zn percentage of the ZnO-Cr 2  O 3  composition based on the sum of Zn and Cr was 70%. The catalyst mixtures all contained per part by volume of silicate, 4 parts by volume of the ZnO-Cr 2  O 3  composition. 
     Catalysts mixtures I-VIII were tested for the one-step preparation of an aromatic hydrocarbon mixture from an H 2  /CO mixture. The testing was carried out in a 50-ml reactor in which a fixed catalyst bed with a volume of 7.5 ml was present. An H 2  /CO mixture with an H 2  /CO molar ratio of 0.5 was conducted for 48 hours at a temperature of 375° C., a pressure of 60 bar and a space velocity of 1000 1.1 -1 .h -1  over the catalyst. The results of these experiments are given below: 
     
         ______________________________________  Exp. No.Catalyst 1      2      3    4    5    6    7    8mixture No.    I      II     III  IV   V    VI   VII  VIII______________________________________Elementdeposited onthe silicate    --     Mg     Ca   Ti   Mn   Mo   Cr   Ce% W ofelement oncatalyst --     2.8    2.1  1.3  3.0  1.9  1.1  2.0Averagecompositionof the C.sub.1.sup.+product, % WC.sub.1  3      2      3    3    2    4    3    4C.sub.2  3      2      3    3    2    4    4    5C.sub.3  25     16     17   21   16   29   29   19C.sub.4  16     15     6    7    12   13   13   17C.sub.5.sup.+    53     64     71   67   68   50   52   56Averagecompositionof the C.sub.5.sup.+product, % Wacyclic  12     21     19   13   27   10   9    13hydrocarbonsnaphthenes    3      8      7    3    13   2    2    4aromatics    85     71     74   84   59   88   89   83______________________________________