PROCESS FOR THE PREPARATION OF AN AROMATIC HYDROCARBON MIXTURE

Abstract: C₂-C₄ paraffins or hydrocarbon mixtures comprising more than 50 %w of C₂-C₄ paraffins are converted into an aromatic hydrocarbon mixture over a crystalline gallium silicate, having a SiO₂/Ga₂O₃ molar ratio of 25-100 and a Y₂O₃/Ga₂O₃ molar ratio lower than 1 (Y = Al, Fe, Co and/or Cr), and having an X-ray powder diffraction pattern after one hour's calculation in air, in which pattern the strongest lines are shown at interplanar spacings d(Å) of 11.2 ± 0.2; 10.0 ± 0.2; 3.84 ± 0.07; 3.72 ± 0.06.

Description: PROCESS FOR THE PREPARATION OF AN AROMATIC HYDROCARBON MIXTURE The present invention relates to a process for the preparation of an aromatic hydrocarbon mixture, characterized in that paraffins with two, three or four carbon atans per molecule or aliphatic hydrocarbon mixtures consisting more than 50 %w of said paraffins are contracted with a catalyst ccmprising a crystalline gallium silicate which a) has been prepared by crystallization starting fran an aqueous mixture which, in addition to the components needed for the synthesis of the silicate, comprises one or rrore gallium ccmpounds and, if desired, one or more compounds of a trivalent metal Y chosen fran the group formed by alumin ium, iron, cobalt and chromium in such quantities that in the formula which represents the composition of the sili cate expressed in moles of the oxides; the SiO2/Ga2O3 molar ratio is 25-100 and the Y203/Ga203 molar ratio is lower than 1, and b) after one hour's calcination in air at 500 C has an X-ray powder diffraction pattern in which the strongest lines are the four lines mentioned in Table A, TABLE A d( ) 11.1 + 0.2 10.0 + 0.2 3.84 # 0.07 3.72 + 0.06 The gallium present in the catalysts occurs exclusively in the crystalline silicate and has been incorForated therein during the preparation of the silicate by crystallization from the aqueous mixture containing one or more gallium carpounds. The preparation of the crystalline gallium silicates used in the process according to the invention may very suitably be carried out starting from an aqueous mixture containing the following compounds: one or more compounds of an alkali metal (M), one or more organic nitrogen ccmpotnds (RN) which contain an organic cation or fran which an organic cation is formed during the preparation of the silicate, one or more silicon compounds, one or more gallium compounds and, if desired, one or more ccopounds of a trivalent metal Y. The preparation is carried out by maintaining the mixture at an elevated tempera- ture until the silicate has formed and subsequently seating the silicate crystals from the mother liquor and washing, drying and calcining the crystals. In the aqueous mixture from which the silicates are prepared the various compounds should be present in the following molar ratios expressed - with the exception of the organic nitrogen compounds - in moles of the oxides: : SiO2 = 0.01-0.35, RN : SiO2 = 0.02-1.0, SiO2 : Ga2O3 = 25-150, Y203 : Ga2O3 < 1, and H2O : SiO2 = 5-65. In the preparation of the silicates the base mixture may very suitably be a mixture containing a quaternary ammonium compound as the organic nitrogen catund, a sodium compound as the alkali metal compound and amorphous silica as the silicon compound. In the process according to the invention preference is given to the use of crystalline gallium silicates which have been prepared by crystallization fran an aqueous mixture which, apart from possible impurities present in the reaction ponents, contains no compounds of a trivalent metal Y. The silicates prepared as described hereinbefore contain alkali metal ions. By using suitable exchange methods these may be replaced by other cations, such as hydrogen ions or ammonium ions. The crystalline gallium silicates used in the process according to the invention preferably have an alkali metal content of less than 0.05 %w. In the process according to the invention the crystalline gallium silicates may be used per se or ccibined with a binder material, such as kaolin or bentonite. Olefins having two, three or four carbon atoms per molecule can be converted at a relatively low temperature and in high yields into aromatic hydrocarbon mixtures by contacting the olefins with crystalline metal silicates having a similar structure as the gallium silicates used in the process according to the invention have. A similar conversion into aromatic hydrocarbon mixtures of paraffins having two, three or four carbon atoms per molecule and of aliphatic hydrocarbon mixtures which consist more than 50 %w of said paraffins is much more difficult and requires considerably higher temperatures, which accounts for the important role played by cracking reactions and the low yields of C+5 hydrccarbons. In this conversion hydrogen is releaaed. In view of the growing demand for hydrogen for a variety of purposes it is important that in the conversion as much as possible of the hydrogen becomes available as molecular hydrogen and not in the form of hydrogen-rich by-products, such as methane. It has been found that the above-mentioned crystalline gallium silicates show a high C5+ and H2 selectivity. In the process according to the invention the starting material comprises paraffins having two, three or four carbon atoms per molecule or an aliphatic hydrocarbon mixture which consists more than 50 %w of said paraffins. The paraffins with two, three or four carbon atoms per molecule which should constitute more than 50 %w of the feed are ethane, propane, n-butane and issbutane. If the starting material is an aliphatic hydrocarbon mixture which, in addition to the paraffins mentioned, contains other aliphatic hydrocarbons as well, this mixture may contain, inter alia, rtthane, ethene, propene, butene, isobutene, butadiene and paraffins and olefins with five or more carbon atoms per molecule. In the process according to the invention the starting material preferred is a feed which consists more than 75 bw, and in particular substantially ccmpletely, of paraffins having three or four carbon atans per molecule. A feedstock which is very suitable for use in the process is a mixture of paraffins with three and four carbon arans per molecule obtained as a by-product in the production of mineral oil. The liquid hydrocarbon mixtures obtained in the process according to the invention boil substantially in the gasoline range and have a very high octane number. They are therefore excellently suitable for use as motor gasoline or as mixing c- ents for motor gasolines. The process according to the invention is preferably carried out at a temperature of 350-700 C and in particular of 450-650 ac, a pressure of 1-20 bar and in particular of 1-10 bar and a space velocity of 0.1-10 kg.kg-1.hour-1 and in particular of 0.5-5 kg.kg l.hour 1. In the process according to the invention the feed is contacted with a catalyst containing a crystalline gallium silicate which is defined, among other things, by the X-ray powder diffraction pattern which the silicate shows after one hour's calcination in air at 5000C. In this pattern the strongest lines should be the four lines mentioned in Table A. The complete X-ray powder diffraction pattern of a typical example of the present crystalline gallium silicates after one hour's calcination in air at 500 C is given in Table B. TABLE B (d( )) Rel.int. d( ) Rel.int. 11.1 100 3.84 (D) 57 10.0 (D) 70 3.72 (D) 31 8.93 1 3.63 16 7.99 1 3.47 < 1 7.42 2 3.43 5 6.68 7 3.34 2 6.35 11 3.30 5 5.97 17 3.25 1 5.70 7 3.05 8 5.56 10 2.98 11 5.35 2 2.96 3 4.98 (D) 6 2.86 2 4.60 4 2.73 2 4.35 5 2.60 2 4.25 7 2.48 3 4.07 2 2.40 2 4.00 4 (D) = doublet In the crystalline gallium silicates used in the process according to the invention the SiO2/Ga2O3 molar ratio is 25-100. Since investigation has shown that, within these limits, the performance of crystalline gallium silicates having a SiO2/Ga203 molar ratio lower than 60 wfien used as catalysts for the present conversion is indeed excellent, but that this performance is not superior to that of crystalline gallium silicates with a SiO21Ga203 molar ratio higher than 60, it is preferred in the process according to the invention, in view of the high cost of gallium, to use a catalyst containing a crystalline gallium silicate having a SiO2/Ga2O3 molar ratio of at least 60. The invention is now elucidated with the aid of the following exattple. Example Nine crystalline metal silicates (silicates 1-9) were prepared by heating mixtures of NaCH, amorphous silica (C3H7)4NOH and NaAlO2 or Fe(NO3)3 or Ga(NO3)3 in water, in an autoclave under autogenous pressure, at 150 0C for 24 hours. Alter cooling of the reaction mixtures the silicates formed were filtered off, washed with water until the pH of the wash water was about 8 and dried at 120 C. After one hour's calcination in air at--5000C silicates 1-9 had the following properties a) an X-ray powder diffraction pattern substantially corresponding with that mentioned in Table B, and b) SiO2/Al2/O3, SiO2/Fe2O3 and SiO2/Ga2O3 molar - ratios as mentioned in Table C. TABLE C Silicate Molar ratio No SiO2/Al2O3 SiO2/Fe2O3 SiO2/Ga2O3 1 72 --- -- 2 260 3 72 4 200 5 --- --- 46 6 --- --- 70 7 --- --- 120 8 --- --- 180 9 --- --- 350 The molar compositions of the aqueous mixtures fran which silicates 1-9 were prepared may be rendered as follows: w Na2O.9 (C3H7)4NOH.x Al2O3.y Fe2O3.z Ga2O3.25 SiO2. 450 H2O wherein w, x, y, and z have the values given in Table D. TABLE D Silicate No. w x y z 1 1 0.33 - - 2 1 0.06 - - 3 3 --- 0.25 4 1 --- 0.125 5 3 - - 0.5 6 3 --- --- 0.33 7 1 - - 0.2 8 1 - --- 0.125 9 1 --- --- 0.06 From silicates 1-9 were prepared catalysts I-IX, respectively, by boiling silicates 1-9 with a 1.0 molar NH4NO3 solution, washing with water, boiling again with a 1.0 molar NH4NO3 solution and washing, drying at 1200C and calcination at 500 C Catalysts I-IX were tested in ten experiments (Experiments 1-10) in the preparation of C+5 aromatic hydrocarbon mixtures starting fran n-butane (Experiments 1-9) and propane (Experiment 10). The experiments were carried out in a reactor containing a fixed catalyst bed. All the experiments were carried out at a temperature of 5500C, a pressure of 1.5 bar and a space velocity of 2kg,kg-1.hour-1. The results of the experiments are listed in Table E. Table F gives the canpositions of the C5+ products obtained in Experiments 6 and 10, carried out using catalyst VI. TABLE E Feedstock n-butane propane Experiment No 1 2 3 4 5 6 7 8 9 10 Catalyst No. I II III IV V VI VII VIII IX VI Conversion, %w 82 65 12 8 85 90 56 46 41 41 Product selectivity, %w on converted material H2 1.0 0.6 3.5 3.1 5.0 5.0 3.6 1.8 2.0 H2 7.5 C1-C3 73.8 79.1 57.3 55.6 47.2 45.3 65.0 69.8 69.0 C1-C2 38.2 iso-C 4# 5.7 3.4 3.2 2.0 2.0 1.8 5.9 4.6 4.0 C3# 9.2 # C4 9.0 7.5 10.2 29.2 1.4 1.0 4.9 7.6 10.2 #C4 4.0 C5+ 10.5 9.4 25.8 10.1 44.4 46.9 20.6 16.2 14.8 C5+ 41.1 TABLE F Feedstock n-butane propane Experiment No. 6 10 Catalyst No. VI VI Composition of C5+ product, %w benzene 23 27 toluene 41 37 C8 aromatics 21 22 C9 aromatics 3 3 C10+ aromatics 2 2 C11 aromatics 8 7 non-aromatics 2 2 Of the experiments mentioned in Table E only Experiment 5, 6 and 10 are experiments according to the invention. These experiments were carried out using crystalline gallium silicates having a SiO2/Ga2O3 molar ratio in the range between 25 and 100 as catalysts. These catalysts show a high activity and a high H2 and C5+ selectivity. That in Experiment 10 conversion is only 41 %w as compared with 90 %w in Experiment 6 is due to the fact that propane is a feedstock which is much harder to convert than n-butane. Comparison of the results of EXperi- ments 5 (carried out using a crystalline gallium silicate having a SiO2/Ga2O3 molar ratio in the range between 25 and 60) and 6 (carried out using a crystalline gallium silicate having a SiO2/Ca203 molar ratio in the range between 60 and 100) shows that in spite of its lower gallium content this catalyst has a somewhat higher activity and C5+ selectivity than catalyst V. Experiments 1-4 and 7-9 fall outside the scope of the invention. They have been included in the patent application for comparison. Experiments 1 and 2 were carried out using crystalline aluminium silicates as catalysts. These catalysts show a very low H2 and C5+ selectivity. Experiments 3 and 4 were carried out using crystalline iron silicates as catalysts. These catalysts show a very low activity and a low to very low C+ selectivity. Experiments 7-9 were carried out using crystalline gallium silicates having a SiO2/Ga2O3 molar ratio higher than 100. These catalysts show a relatively low activity and a low to very low C5+ selectivity.

Claims: CLAIMS 1. A process for the preparation of an aromatic hydrocarbon mixture, characterized in that paraffins with two, three or four carbon atoms per molecule or aliphatic hydrocarbon mixtures consisting more than 50 %w of said paraffins are contacted with a catalyst comprising a crystalline gallium silicate which a) has been prepared by crystallization starting from an aqueous mixture which, in addition to the components needed for the synthesis of the silicate, comprises one or more gallium compounds and, if desired, one or more compounds of a trivalent metal Y chosen from the group formed by alummium, iron, cobalt and chromium is such quantities that in the formula which represents the composition of the silicate expressed in moles of the oxides, the SiO2/Ga2O3 molar ratio is 25-100 and the Y203/Ga203 molar ratio is loader than 1, and b) after one hour's calcination in air at 500 C has an X-ray powder diffraction pattern in which the strongest lines are the four lines mentioned in Table A, TABLE A d( ) 11.1 + 0.2 10.0 # 0.2 3.84 + 0.07 3.72 + 0.06 2. A process as claimed in clam 1, characterized in that it is applied to a feedstock more than 75 %w of which consists of paraffins having three or four carbon atans per molecule. 3. A process as claimed in claim 2, characterized in that the feedstock consists completely of paraffins having three or four carbon atoms per molecule. 4. A process as claimed in claim 3, characterized in that the feed consists of a mixture of paraffins with three and four carbon atoms per molecule, which has been obtained as a by-product in the prcduction of mineral oil. 5. A process as claimed in any one of claims 1-4, characterized in that it is carried out at a temperature of 350-700 OC, a pressure of 1-20 bar and a space velocity of 0.1-10 kg.kg-1.h-1. 6. A process as claimed in any one of claims 1-5, characterized in that the crystalline gallium silicate has a SiO2/Ga203 molar ratio of at least 60. 7. A process as claimed in any one of claims 1-6, characterized in that the crystalline gallium silicate has been prepared by maintaining an aqueous mixture comprising the following compounds: one or more compounds of an alkali metal (M), one or more organic nitrogen compounds (RN) which contain an organic cation or from which an organic cation is formed during the preparation of the silicate, one or more silicon compounds, one or more gallium compounds and, if desired, one or norse compounds of a trivalent metal Y, in which mixture the various compounds are present in the following molar ratios, expressed - with the exception of the organic nitrogen ccmpcunds - in moles of the oxides: M29 : SiO2 = 0.01-0.35, PN : SiO2 = 0.02-1.0, SiO2 : Ga203 = 25-150, Y203 Ga2O3 < 1, and H2O : SiO2 = 5-65 at an elevated temperature until the silicate has formed, subsequently separating the silicate crystals from the mother liquor and calcining them. 8. A process as claimed in claim 7, characterized in that the aqueous mixture contains a quaternary amnnium compound as the organic nitrogen compounds, a sodium compound as the alkali metal compound and amorphous silica as the silicon compsand. 9. A process as claimed in any one of claims 1-8, characterized in that the crystalline silicate has been prepared by crystallization from an aqueous mixture which, apart from possible impurities present in the reaction components, contains no compounds of a trivalent metal Y. 10. A process as claimed in any one of claims 1-9, characterized in that the crystalline gallium silicate has an alkali metal content of less than 0.05 bw.

Inventors: KIEFFER, EDUARD PHILIP, VAN ERP, WILLIBRORD ADELBERT
Applicants: SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V.
Application year: 1983
Main classification: C07C2
IPC codes: C07C15, B01J29, C07C2