NZ202453A - Preparing crystalline silicate catalyst and use in preparing aromatic hydrocarbon mixtures - Google Patents

Description

New Zealand Paient Spedficaiion for Paient Number £02453 2024S3 COMPLETE SPECIFICATION PREPARATION OF CATALYST MIXTURES I#We, SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V. Carel van Bylandtlaan 30, The Hague, the Netherlands, a Netherlands Company hereby declare the invention for which Ix^ we pray that a patent may be granted to sccexfus, and the method by which it is to be performed, to be particularly described in and by the following statement: - - 1 - (followed by page la) - |.<t- JJtEPAIIATION OF CATALYDT MIXTURES The invention relates to a process for the preparation of a catalyst mixture suitable for the conversion of a mixture of carbon monoxide and hydrogen into an aromatic hydrocarbon mixture.

^ Mixtures of carbon monoxide and hydrogen can be conver ted into an aromatic hydrocarbon mixture by using a mixture of two catalysts, one of which is a zinc-containing composition which, in addition to zinc, comprises one or more of the metals chromium, copper and aluminium and which compo-10 sition has been prepared by the calcination of one or more precipitates obtained by adding a basic reacting substance to one or more aqueous solutions comprising salts of the metals involved', and the other a crystalline metal silicate having a special structure. The said crystalline metal sili-15 cates are characterized in that, after one hour's calcination in air at 500°C, they have the following properties: a) thermally stable up to a temperature of at least 600°C, b) an X-ray powder diffraction pattern in which the strongest lines are the four lines mentioned in Table A.

Table A d (A) Relative Intensity 11.1 +0.2 S .0 +0.2 S 3.84 + 0.07 VS 3.72 + 0.06 VS 20245 in which the letters used have the following meanings: VS = very strong, S = strong, and c) in the formula which represents the composition of the silicate, expressed in moles of the oxides, and which, 5 in addition to Si02, includes one or more oxides of a trivalent metal A chosen from the group formed by aluminium, iron, gallium, rhodium, chromium and scandium, the Si02/A203 molar ratio is higher than 10.

In the present patent application a crystalline sili-10 cate having a thermal stability of t°C should be taken to be a silicate whose X-ray powder diffraction pattern remains substantially unchanged upon heating to a temperature of t°C The above-mentioned catalyst mixtures have till now been used in the form of a coarse mixture obtained by mecha-15 nically mixing particles of the zinc-containing composition and the crystalline silicate, each having an average particle size in the range of from 0.1 to 0.5 mm. Although the above-mentioned catalyst mixtures show quite an acceptable performance when used for converting a H2/CO mixture into 20 an aromatic hydrocarbon mixture, there still is a desire to enhance this performance, particularly where the C^+ selectivity and aromatics production are concerned.

On the presumption that the above-mentioned properties of the catalyst mixture might possibly be improved 25 by bringing about a more intimate contact between the two components of the mixture, a number of experiments were carried out using catalysts based on a fine mixture, which %02 catalysts had been obtained by grinding each individual original mixture component having an average particle size in the range of from 0.1 to 0.5 mm to an average particle size of less than 5 micron, mixing the resulting powders 5 mechanically, and pressing and grinding the mixture into particles of an average particle size in the range of from 0.1 to 0.5 mm. The results of these experiments were most unsatisfactory. Although an improvement was seen in the C5+selectivity, this was accompanied with a very sharp 10 decrease in activity as well as a decrease in C3+ selectivity and aromatics production.

Although from the above mentioned results one could not but conclude that the chosen manner of bringing about a more intimate contact between the mixture components will 15 not lead to the achievement of the object in view (enhancement of the catalytic properties of the mixture), an attempt was nevertheless made at attaining a more intimate contact between the components in a different way. The method of preparing the mixture chosen for the purpose was spray-20 drying. Spray-drying is a method which for many years past has been in use on a commercial scale for preparing small spherical particles starting from a solid material or mixture of solid materials. The method comprises atomising a dispersion in water of the substance to be spray-dried 25 through a nozzle or from a rotating disc into a hot gas.

This method is particularly suitable for effecting a very intimate contact between various substances. ^^2453 In the preparation of the present catalyst mixtures by spray-drying the starting material was an aqueous dispersion which in addition to the crystalline silicate, comprised a zinc-containing precipitate prepared in the same manner 5 as the precipitate mentioned hereinbefore which had been calcined to form one of the two catalyst components. The small spherical particles obtained during spray-drying were pressed and the pressed material was ground to an average particle size in the range of from 0.1 to 0.5 mm to yield a 10 catalyst having excellent properties for the conversion of a H2/CO mixture into an aromatic hydrocarbon mixture. In comparison with the coarse mixture obtained by mechanical mixing described hereinbefore, the mixture prepared by spray-drying showed both a much higher 05* selectivity and a 15 much higher aromatics production. In view of the previous disappointing results concerning intimate contact between the catalyst components, obtained in the experiments with the catalysts prepared starting from the fine mixture, the result now obtained is considered to be surprising. The pre-20 paration of the present catalyst mixtures by spray-drying is novel.

The present patent application therefore relates to a process for the preparation of a catalyst mixture in which a crystalline metal silicate having the properties 25 mentioned under a)-c) is dispersed in water together with one or more precipitates in which zinc and one or more metals chosen from chromium, aluminium and copper are present, and which precipitates have been obtained by ad- 202453 ding a basic reacting substance to one or more aqueous solutions of salts of the metals involved, and in which from the dispersion thus obtained the desired catalyst mixture is prepared by spray-drying. In view of their 5 form, size and strength, the catalyst particles prepared according to the invention are very suitable for use in a fluidized state.

Although in the process according to the invention crystalline silicates comprising more than one metal A 10 -may be used, preference is given to silicates in which only one metal A is present and in particular to silicates comprising aluminium, iron or gallium as metal A. The crystalline silicates should have an Si02/A2C>3 molar ratio higher than 10. Preferably silicates are used having an 15 Si02/A2C>3 molar ratio lower than 1000 and in particular in the range of from 20 to 500. The crystalline silicates are defined, among other things, by the X-ray powder diffraction pattern. Its strongest lines should be the four lines given in Table A. The complete X-ray powder diffrac-20 tion pattern of a typical example of a silicate that may be used in the process according to the invention is given in Table B. 2°24S3 Table B d(&) Rel. int. d(&) Rel. int. 11.1 57 3.84 (D) 100 .0 (D) 31 3.70 (D) 70 8.93 1 3.63 16 7.99 1 3.47 1 7.42 2 3.43 6.68 7 3.34 2 6.35 11 3.30 .97 17 3.25 1 .70 7 3.05 8 .56 2.98 11 .35 2 2.96 3 4.98 (D) 6 2.86 2 4.60 4 2.73 2 4.35 2.60 2 4.25 7 2.48 3 4.07 2 2.40 2 4.00 4 (D) = doublet The crystalline silicates may be prepared starting from an aqueous mixture comprising the following compounds: one or more silicon compounds, one or more compounds in which a mono-valent organic cation (R) is present or from which 20245? such a cation is formed during the preparation of the silicate, one or more compounds in which a trivalent metal A is present and, if desired, one or more compounds of an alkali metal (M). The preparation is carried out by maintaining 5 the mixture at an elevated temperature until the silicate has formed and subsequently separating 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 10 in the following ratios, expressed in moles of the oxides: M20 : Si02 < 0.35, R20 : Si02 = 0.01-0.5, Si02 : A2O3 > 10, and H20 : Si02 = 5-65.

When in the preparation of the crystalline silicates the starting mixture is an aqueous mixture comprising one or more alkali metal compounds, crystalline silicates may be obtained which comprise alkali metal. Subject to the concentration of the alkali metal compounds in the aqueous 20 mixture, the crystalline silicates obtained may comprise more than 1$ w alkali metal. Since the presence of alkali metal in the crystalline silicates has an unfavourable influence on their catalytic properties, the usual procedure when crystalline silicates have a relatively high 25 alkali metal content, is to reduce this content before using such silicates as catalysts. Reduction of the alkali metal content to about 200 ppmw is sufficient to this end. 2024s3 It has been found that further reduction of the alkali metal content will have virtually no more effect on the catalytic properties of the silicate. The reduction of the alkali metal content of crystalline silicates may very 5 suitably be carried out by treating the silicates once or several times with a solution of an ammonium compound. In this treatment alkali metal ions are exchanges for NHi4+ ions, and the silicate is converted into the NH4+ form. The NH2|+ form of the silicate is converted into the 10 H+ form by calcination.

In the preparation of the catalyst mixtures according to the invention one or more precipitates are used in which zinc is present together with one or more of the metals chromium, aluminium and copper and which precipitates 15 have been obtained by adding a basic reacting substance to one or more aqueous solutions of salts of the metals involved. Examples of metal combinations eligible for introduction, via the precipitates, into the catalyst mixtures to be prepared by spray-drying are zinc-chromium, zinc-20 chromiurn-copper and zinc-aluminium-copper. Preference is given to the use of precipitates which, in addition to zinc, comprise chromium, in particular precipitates in which the atomic percentage of zinc, calculated on the sum of zinc and copper, it is at least 60$ and in particular 25 of from 60-8056. The metal-containing precipitates which, in the process according to the invention, are dispersed in water together with the crystalline silicate, may be i2024 prepared by precipitation of the individual metals, or by co-precipitation of the desired metal combination. Thus, for the preparation of a catalyst mixture in which the metal combination zinc-chromium is to be incorporated via 5 the precipitates, precipitates may be formed starting from an aqueous solution of a zinc salt and an aqueous solution of a chromium salt, by adding a basic reacting substance to each of these solutions, and the two precipitates may be dispersed in water either individually or after previous mixing, together 10 with the crystalline silicate. In the process according to the invention preference is given to the use of a co-precipitate obtained by adding a basic reacting substance to an aqueous solution comprising all the metals involved.. Such a co-precipit-ation is preferably carried out in a blending unit with a 15 continuous supply of an aqueous solution comprising the metal salts involved and an aqueous solution of the basic reacting substance in a stoichiometric quantity, calculated on the metals, and with a continuous discharge of the co-precipi-tate formed. It is advisable to allow the metal precipitates to 20 age in the mother liquor for some time and subsequently to wash them thoroughly with water before dispersing them, together with the crystalline silicate, in water. Suitable basic reacting substances that may be used in the preparation of the metal precipitates are ammonium hydroxide, sodium carbonate and 25 alkali metal hydroxides. The basic reacting substances are preferably used in the form of an aqueous solution.

As regards the ratios between the quantities of metal- 2024s3 containing precipitate and crystalline silicate present in the dispersion from which the catalyst mixture is prepared by spray-drying, these are preferably chosen such that a catalyst mixture is obtained which per pbw of sili-^ cate comprises 2.5-12.5 pbw, and more in particular 4-8 pbw, of metal oxides originating in the precipitate. Conditions suitable for carrying out the conversion of a H2/CO mixture into an aromatic hydrocarbon mixture using a catalyst mixture prepared according to the invention are: a tempe-10 rature of from 200-500°C and in particular of from 300-450°C, a pressure of from 1 — 150 bar and in particular of from 5-100 bar and a space velocity of from 50-5000 and in particular of from 300-3000 N1 gas/1 catalyst/hour. Preferably the feed used is a H2/CO mixture having a H2/CO molar ratio in the range 15 of from 0.25 to 1.0. Such H2/CO mixtures may very suitably be prepared by steam gasification of a carbonaceous material, such as coal, at a temperature of from 900-1500°C and a pressure of from 10-50 bar.

The conversion of a H2/CO mixture into an aromatic 20 hydrocarbon mixture described hereinbefore may very suitably be used as the first step in a two-step process for the conversion of H2/CO mixtures into hydrocarbon mixtures. In that case carbon monoxide and hydrogen present in the reaction product from the first step are contacted 25 in a second step - together with other components of this reaction product, if desired - with a catalyst comprising one or more metal components having catalytic activity 202453 for the conversion of a H2/CO mixture into paraffinic hydrocarbons, which metal components have been chosen from the group formed by cobalt, nickel and ruthenium, care being taken that the feed for the second step has a H2/CO molar 5 ratio of from 1.75-2.25.

The conversion of a H2/CO mixture into an aromatic hydrocarbon mixture described hereinbefore may further be used very suitably as the first step of a three-step process for the preparation, inter alia, of middle distillates 10 from a H2/CO mixture. In that case carbon monoxide and hydrogen present in the reaction product from the first step, are contacted in a second step - together with other components of this reaction product, if desired - with a cobalt catalyst comprising zirconium, titanium or chromium 15 as promoter, care being taken that the feed for the second step has a H2/CO molar ratio of from 1.75-2.25. At least that part of the reaction product from the second step whose initial boiling point lies above the final boiling point of the heaviest middle distillate desired as end product is 20 subjected in a third step to a catalytic hydrotreatment.

The invention is now illustrated with the aid of the following Example.

Example Catalyst preparation.

Preparation of a Zn/Cr precipitate.

Zn(NC>3)2.6 aq and Cr(N03)3.9 aq were dissolved in water in such quantities that a Zn/Cr solution was obtained com- 20245 3 prising 1.15 g ion Zn + Cr per litre and having a Zn/Zn + Cr atomic ratio of 0.67. This solution, together with a stoichiometric quantity of a "\0% aqueous NH3 solution, was pumped with stirring through a blending unit which was kept 5 at a temperature of 20°C. The volume of the blending unit was 350 ml. The ratio of the feed rates was chosen such as to ensure a value for the pH, measured at the outlet of the blending unit, of between 7 and 8. The pumping rates were chosen such as to allow a throughput of 100 1 per hour. The 10 Zn/Cr precipitate obtained was collected and left to age for one hour with stirring at 20°C. The solid material was filtered off and washed with water until the wash water was free from NO3- ions. The N03~-free Zn/Cr precipitate thus obtained was divided into two portions A and B.

Catalyst 1 This catalyst was prepared by drying the above-mentioned portion A of the Zn/Cr precipitate for 16 hours at 120°C, grinding the dried material to an average particle size of 0.4 mm and calcining the ground material for one hour 20 in air at 400°C.

Catalyst 2 A crystalline aluminium silicate was prepared as follows. A mixture of NaOH, (C3Hy)4NOH, amorphous silica and NaA102 in water, having the molar composition 25 3Na20. 4.5 [25 Si02. 0.04 A1203. 450 H20, was heated for 24 hours with stirring in an autoclave at 150°C under autogenous pressure. After cooling of the re- 202453 action mixture the silicate formed was 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 500°C the silicate had the following properties: a) thermally stable up to a temperature of at least 900°C, b) an X-ray powder diffraction pattern substantially corresponding with that given in Table B, and c) an Si02/Al2C>3 molar ratio of 225.

The silicate was boiled with a 1.0 molar NH4NO3 10 solution, washed with water, boiled again with a 1.0 molar NH4NO3 solution and washed with water and dried at 120°C. Catalyst 2 was prepared by pressing and grinding the dried material to an average particle size of 0.4 mm and calcining the ground material for one hour in air'at 15 500°C.

Catalyst 3 Catalyst 3 was prepared starting from a crystalJ.ine aluminium silicate, which after one hour's calcination in air at 500°C, had the following properties: 20 a) thermally stable up to a temperature of at least 800°C, b) an X-ray powder diffraction pattern substantially corresponding with that given in Table B, and c) an Si02/Al203 molar ratio of 290.

The silicate was boiled with a 1.0 molar NH4NO3 solu-25 tion and washed with water. The silicate thus obtained was divided into two portions C and D.

Catalyst 3 was prepared by drying the above-mentioned portion C of the silicate at 120°C, pressing and grinding the dried material to an average particle size of 0.4 mm and calcining the ground material for one hour in air at 500°C. Catalyst mixture I This catalyst mixture was prepared by mixing catalyst 1 5 and catalyst 2 in a weight ratio of 10:1.

Catalyst mixture II This catalyst mixture was prepared by milling each of catalysts 1 and 2 individually in a ball mill to an average particle size of less than 5 micron, mixing the milled ca-10 talysts 1 and 2 very intimately in the weight ratio of 10:1, and finally pressing and grinding the mixture to an average particle size of 0.4 mm.

Catalyst mixture III This catalyst mixture was prepared by mixing catalyst 1 15 and catalyst 3 in a weight ratio of 5:1.

Catalyst mixture IV This catalyst mixture was prepared by milling each of catalysts 1 and 3 individually in a ball mill to an average particle size of less than 5 micron, mixing the milled cata-20 lysts 1 and 3 very intimately in the weight ratio of 5:1 and finally pressing and grinding the mixture to an average particle size of 0.4 mm.

Catalyst mixtures V and,VI Portion D of the crystalline silicate was dried for 25 16 hours at 120°C and then calcined in air for one hour at 500°C. The material thus obtained was dispersed in water using a turbostirrer to give a concentration of 200 g per litre. So much of portion B of the Zn/Cr precipitation was 2024$3 stirred into the dispersion thus obtained that the weight ratio of ZnO + to silicate in the dispersion was :1. Finally so much water was stirred into the dispersion that the solids content thereof was 15% w. Settling of the 5 dispersion was prevented by continuous stirring. The dispersion thus obtained was spray-dried in air in a counter-current operation using compressed air. The inlet temperature of the air was 300°C, the outlet temperature of the air was 120°C. The pressure used was 0.4 bar. The 10 powder obtained, which consisted substantially of spherical particles having an average particle size of 50 micron and a bulk density of 1.33 g/ml, was divided into two portions E and F. Catalyst mixture V was prepared from portion E by pressinggrinding to an average par-15 ticle size of 0.4 mm and calcination in air for one hour at 400°C. Catalyst mixture VI was prepared from portion F, by calcination in air for one hour at 400°C.

Catalyst mixtures I-VI were tested for the preparation of an aromatic hydrocarbon mixture from a H2/CO 20 mixture. Catalyst mixtures I-V were tested in a 50-ml reactor containing a fixed catalyst bed of 7.5 ml volume. In five experiments a H2/CO mixture having a H2/CO molar ratio of 0.5 was passed over each of catalyst mixtures I-V at a temperature of 375°C, a pressure of 60 bar and a space 25 velocity of 850 N1.kg"^.h~1. The results of the experiments, averaged over the first 100 hours, are given in Table C. .?45J Table C Experiment No. 1 2 3 4 Catalyst mixture No.

I II III IV V Conversion of synthesis gas, %v 60 41 60 45 55 C3+ selectivity, calculated on C-| + , %w 93 89 93 88 93 C5+ selectivity, calculated on C-| + , %w 73 79 63 72 81 Composition of C^+ product, %w paraffins 17 21 6 naphthenes 16 22 9 aromatics 59 52 60 57 85 Catalyst mixture VI was tested in a vertically arranged fluid-bed reactor, 175 cm in height and of 500 ml volume, 20 containing 314 ml catalyst. The depth of the catalyst bed in the settled condition was 100 cm. A H2/CO mixture having a H2/CO molar ratio of 0.5 was contacted with catalyst mixture VI at a temperature of 380°C, a pressure of 60 bar and a superficial gas rate of 1.3 cm/s (corresponding with 25 a space velocity of about 850 N1.kg-^.h-1). The results of this experiment (Experiment 6), averaged over the first 50 hours, are given in Table D. 202<$3 Table D Experiment No. 6 Catalyst mixture No. VI Conversion of synthesis gas, % v 55 C3+ selectivity, calculated on C-| + , % w 94 C5+ selectivity, calculated on C-| + , % w 82 Composition of C^+ product, % w paraffins 10 naphtenes 15 aromatics 75 Research octane number (R0N-0) of the C5+ fraction 99 As regards the results mentioned in Table C, the following may be observed: a) Of catalyst mixtures I-V only catalyst mixture V was prepared according to the invention. The other catalyst mixtures fall outside the scope of the invention. They have been included in the patent application for comparison. b) Of Experiments 1-5 only Experiment 5 was carried out using a catalyst mixture prepared according to the invention. c) Comparison of the results of Experiment 1 (using a 10:1 coarse catalyst mixture) with those of Experi ment 2 (using a 10:1 fine catalyst mixture) clearly shows the unfavourable effect of the intimate mixing

Claims (10)

18 upon activity, C3+ selectivity and aromatics production . 5 d) A similar effect may be seen upon comparison of the results of Experiment 3 (using a 5:1 coarse catalyst mixture) with those of Experiment 4 (using a 5:1 fine catalyst mixture). e) Comparison of the results of Experiment 3 (using a 5:1 coarse catalyst mixture) with those of Experiment 5 (using a 5:1 catalyst mixture prepared by spray- of the preparation through spray-drying on selectivity and aromatics production. As regards the results mentioned in Table D the following may be observed. Fluid-bed Experiment 6, carried out using 15 a catalyst mixture prepared according to the invention yielded a very attractive C$+ product having a high aromatics content and a high octane number. 10 drying) clearly shows the highly favourable influence - 19 - . 0 L A I H 0 WHAT 4?'.Vc CLAiM IS; .

1. A process for the preparation of a catalyst mixture, characterized in that a crystalline metal silicate which, after one hour's calcination in air at 500°C, has the following properties: 5 a) thermally stable up to a temperature of at least 600°C, b) an X-ray powder diffraction pattern in which the strongest lines are the four lines mentioned in Table A. Table A 10 d (A) Relative intensity 11.1 . + 0.2 S 10.0 + 0.2 S 3.84+0.07 VS 15 3.72 + 0.06 VS in which the letters used have the following meanings = VS: very strong, S = strong, and c) in the formula which represents the composition of the silicate expressed in moles of the oxides and 20 which, in addition of Si02, comprises one or more oxides of a trivalent metal A chosen from the group ' formed by aluminium, iron, gallium, rhodium, chromium and scandium, the Si02/A203 molar ratio is higher than 10, 25 is dispersed in water together with one or more precipi - 20 - tates in which zinc and one or more of the metals chromium, copper and aluminium are present and which precipitates have been prepared by adding a basic reacting substance to one or more aqueous solutions of salts of the 5 metals involved, and in that from the dispersion thus obtained the desired catalyst mixture is prepared by spray-drying.

2. A process as claimed in claim 1, characterized in that the crystalline silicate comprises only one trivalent 10 metal A chosen from the group formed by aluminium, iron and gallium.

3. A process as claimed in claim 1 or 2, characterized in that the crystalline silicate has an Si02/A203 molar ratio in the range of from 20 to 500. 15

4. A process as claimed in any one of claims 1-3, characterized in that a co-precipitate is used which has been obtained by adding a basic reacting substance to an aqueous solution comprising all the metals involved.

5. A process as claimed in claim 4, characterized in that 20 the co-precipitation is carried out in a blending unit with a continuous supply of an aqueous solution comprising the metal salts involved and an aqueous solution of the basic reacting substance in a stoichiometric quantity calculated on the metals, and with a continuous discharge of the 25 co-precipitate formed.

6. A process as claimed in any one of claims 1-5, characterized in that a precipitate is used which, in addition to zinc, comprises chromium and in which the atomic 202453 21 percentage of zinc, calculated on the sum of zinc and chromium, is 60-8055.

7. A process as claimed in any one of claims 1-6, characterized in that the ratio between the quantities of metal- 5 containing precipitate and crystalline silicate present in the dispersion is chosen sudi that after spray-drying a catalyst mixture is obtained which per part by weight of silicate oanprises 4-8 parts by weight of metal oxides originating in the precipitate.

8. A process for the preparation of an aromatic hydro-10 carbon mixture by contacting a H2/CO mixture with a catalyst mixture as prepared according to any one of claims 1-7.

9. A process as claimed in claim 8, characterized in that the catalyst mixture is used in a fluidized con- 15 dition.

10. A process as claimed in claim 8 or 9, characterized in that the H2/CO mixture has a H2/CO molar ratio in the range of from 0.25 to 1.0.