GB2110559A - Preparation of catalyst mixtures - Google Patents

Abstract

Catalyst mixtures for the single stage conversion of syngas into an aromatic hydrocarbon mixture are prepared by spray drying an aqueous dispersion comprising a basic Zn/Cr containing precipitate and a crystalline metal silicate of specified structure. Intimate mixing of the catalyst components by spray drying gives a catalyst with a strongly improved C5<+>- selectivity and aromatics production. In view of their size, shape and strength the catalyst particles obtained are excellently suitable for application in fluid bed operation.

Description

SPECIFICATION Preparation of catalyst 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 converted 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 composition 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 silicates are characterized in that, after one hour's calcination in air at 5000 C, they have the following properties: a) thermally stable up to a temperature of at least 6000 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 10.0+0.2 S 3.84+0.07 VS 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 which, in addition to SiO2, includes one or more oxides of a trivalent metal A chosen from the group formed by aluminium, iron, gallium, rhodium, chromium, and scandium, the SiO2/A203 molar ratio is higher than 10.

In the present patent application a crystalline silicate having a thermal stability of tOC 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 mechanically 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 abovementioned catalyst mixtures show quite an acceptable performance when used for converting a H2/CO mixture into an aromatic hydrocarbon mixture, there still is a desire to enhance this performance, particularly where the C5+ selectivity and aromatics production are concerned.

On the presumption that the above-mentioned properties of the catalyst mixture might possibly be improved 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 catalysts had been obtained by grinding each invididual 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 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 decrease in activity as well as a decrease in C3+ selectivity and aromatics production.

Although from the above mentioned results one could not conclude that the chosen manner of bringing about a more intimate contact between the mixture components will 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-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 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.

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 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 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 C5+ selectivity and a 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 preparation 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 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 adding 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 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 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 SiO2/A203 molar ratio higher than 10. Preferably silicates are used having an SiO2/A203 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 diffraction pattern of a typical example of a silicate that may be used in the process according to the invention is given in Table B.

Table B drA) Rel. int d(Aj Rel. int.

11.1 57 3.84 (D) 100 10.0 (D) 31 3.70 (D) 70 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 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 monovalent organic cation (R) is present or from which 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 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 in the following ratios, expressed in moles of the oxides: M20: SiO2 < 0.35, R20: SiO2=0.01-0.5, SiO2: A203 > 10, and H20: SiO2=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 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 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.It has been found that further reduction of the alkali metal content wili have virtually no more effect on the catalytic properties of the silicate. The reduction of the alkali metal content of crystalline silicates may very 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 NH4+ ions, and the silicate is converted into the NH4+ form. The NH4+ form of the silicate is converted into the 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 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 zincchromium, zinc-chromium-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 of from 6080%. The metal-containing precipitates which, in the process according to the invention, are dispersed in water together with the crystalline silicate, may be 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 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 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-precipitation is preferably 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 co-precipitate formed. It is advisable to allow the metal precipitates to 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 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 metai-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 silicate comprises 2.512.5 pbw, and more in particular 4-8 pbw, of metal oxides originating in the precipitate.Conditions suitable for carrying out the conversion of a H2CO mixture into an aromatic hydrocarbon mixture using a catalyst mixture prepared according to the invention are: a temperature of from 200-5000C and in particular of from 300--4500C, a pressure of from 1-1 50 bar and in particular of from 5-100 bar and a space velocity of from 50-5000 and in particular of from 300-3000 NI gas/l catalyst/hour.

Preferably the feed used is a H2/CO mixture having a H2CO molar ratio in the range 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 900-1 5000C and a pressure of from 10-50 bar.

The conversion of a H2/CO mixture into an aromatic 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 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 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 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 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 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 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(NO3)2.6 aq and Cr(NO3)3.9 aq were dissolved in water in such quantities that a Zn/Cr solution was obtained comprising 1.1 5 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 10% aqueous NH solution, was pumped with stirring through a blending unit which was kept at a temperature of 200 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 Zn/Cr precipitate obtained was collected and left to age for one hour with stirring at 200C.The solid material was filtered off and washed with water until the wash water was free from NO3 ions. The NO3~-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 1 6 hours at 1200 C, grinding the dried material to an average particle size of 0.4 mm and calcining the ground material for one hour in air at 4000C.

Catalyst 2 A crystalline aluminium silicate was prepared as follows. A mixture of NaOH, (C3H7)4NOH, amorphous silica and NaAIO2 in water, having the molar composition 3Na2O. 4.5 [(C3H,)4N]2O.25 SiO2.

0.04 Awl203.450 H2O, was heated for 24 hours with stirring in an autoclave at 1 500C under autogenous pressure. After cooling of the reaction mixture the silicate formed was fiitered off, washed with water until the pH of the wash water was about 8, and dried at 1200 C. After one hour's calcination in air at 5000C the silicate had the following properties: a) thermally stable up to a temperature of at least 9000C, b) an X-ray powder diffraction pattern substantially corresponding with that given in Table B, and c) an SiO2/AI203 molar ratio of 225.

The silicate was boiled with a 1.0 molar NH4NO3 solution, washed with water, boiled again with a 1.0 molar NH4NO3 solution and washed with water and dried at 1200 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 5000 C.

Catalyst 3 Catalyst 3 was prepared starting from a crystalline aluminium silicate, which after one hours calcination in air at 5000 C, had the following properties: a) thermally stable up to a temperature of at least 8000C, b) an X-ray powder diffraction patter substantially corresponding with that given in Table B, and c) an SiO2/AI203 molar ratio of 290.

The silicate was boiled with a 1.0 molar NH4NO3 solution 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 1200C, 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 5000C.

Catalyst mixture I This catalyst mixture was prepared by mixing catalyst 1 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 catalysts 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 Ill This catalyst mixture was prepared by mixing catalyst 1 and catalyst 3 in a weight ratio of 5:1.

Catalyst mixture IV This catalyst mixture was prepared by milling each of catalyst 1 and 3 individually in a ball mill to an average particle size of less than 5 micron, mixing the milled catalysts 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 Vl Portion D of the crystalline silicate was dried for 1 6 hours at 1 200C and then calcined in air for one hour at 5000 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 stirred into the dispersion thus obtained that the weight ratio of ZnO+Cr203 to silicate in the dispersion was 5:1.

Finally so much water was stirred into the dispersion that the solids content thereof was 1 5% w.

Settling of the dispersion was prevented by continuous stirring. The dispersion thus obtained was spray-dried in air in a countercurrent operation using compressed air. The inlet temperature of the air was 3000C, the outlet temperature of the air was 1200 C. The pressure used was 0.4 bar. The 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 pressing, grinding to an average particle size of 0.4 mm and calcination in air for one hour at 4000C. Catalyst mixture Vl was prepared from portion F, by calcination in air for one hour at 4000C.

Catalyst mixtures 1-VI were tested for the preparation of an aromatic hydrocarbon mixture from a HdCO 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 HdCO mixture having a HdCO molar ratio of 0.5 was passed over each of catalyst mixtures I-V at a temperature of 3750C, a pressure of 60 bar and a space velocity of 850 Nl.k-1.h-'. The results of the experiments, averaged over the first 100 hours, are given in Table C.

Table C Experiment No. 1 2 3 4 5 Catalyst mixture No. I II Ill IV V Conversion of synthesis gas, %v 60 41 60 45 55 C3+ selectivity, calculated on C+,96w 93 89 93 88 93 C6+ selectivity, calculated on C+, %w 73 79 63 72 81 Composition of C6+ product, %w paraffins 25 17 30 21 6 naphthenes 16 30 10 22 9 aromatics 59 52 60 57 85 Catalyst mixture Vl was tested in a vertically arranged fluid-bed reactor, 175 cm in height and of 500 ml volume, containing 314 ml catalyst. The depth of the catalyst bed in the settled condition was 100 cm.A HCO mixture having a HCO molar ratio of 0.5 was contacted with catalyst mixture Vl at a temperature of 3800 C, a pressure of 60 bar and a superficial gas rate of 1.3 cm/s (corresponding with a space velocity of about 850 Nl.kg'l.h'). The results of this experiment (Experiment 6), averaged over the first 50 hours, are given in Table D.

Table D Experiment No. 6 Catalyst mixture No. Vl Conversion of synthesis gas, %v 55 C3+ selectivity, calculated on C1+, %w 94 C6+ selectivity, calculated on C,+ %w 82 Composition of C6+ product, %w paraffins 10 naphthenes 15 aromatics 75 Research octane number (RON-0) of the C6+ 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 Experiment 2 (using a 10:1 fine catalyst mixture) clearly shows the unfavourable effect of the intimate mixing upon activity, C3+ selectivity and aromatics production.

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-drying) clearly shows the highly favourable influence of the preparation through spray-drying on C5+ selectivity and aromatics production.

As regards the results mentioned in Table D the following may be observed. Fluid-bed Experiment 6, carried out using a catalyst mixture prepared according to the invention yielded a very attractive C5+ product having a high aromatics content and a high octane number.

Claims (1)

1. Claims

   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 5000 C, has the following properties: a) thermally stable up to a temperature of at least 6000 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 5

   10.0+0.2 S

   3.84+0.07 VS

   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 which, in addition of Six2, comprises one or more oxides of a trivalent metal A chosen from the group formed by aluminium, iron, gallium, rhodium, chromium and scandium, the SiOJA203 molar ratio is higher than 10, is dispersed in water together with one or more precipitates 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 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 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 SiO2/A203 molar ratio in the range of from 20 to 500.

   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 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 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 percentage of zinc, calculated on the sum of zinc and chromium, is 6080%.

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

   8. A process for the preparation of an aromatic hydrocarbon mixture by contacting a HJCO 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 condition.

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