CA1185588A

CA1185588A - Preparation of catalyst mixtures

Info

Publication number: CA1185588A
Application number: CA000414054A
Authority: CA
Inventors: Arend Hoek; Martin F.M. Post; Swan T. Sie
Original assignee: Shell Canada Ltd
Current assignee: Shell Canada Ltd
Priority date: 1981-11-12
Filing date: 1982-10-22
Publication date: 1985-04-16
Also published as: FR2515985A1; AU9034182A; BE894980A; GB2110559A; AU549976B2; ZA828227B; NZ202453A; JPS58122041A; DE3241578A1; NL8105117A; FR2515985B1; IT8224160A0; IT1154548B; DE3241578C2; GB2110559B

Abstract

A B S T R A C T

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 sillicate with ZSM-5 structure. Intimate mixing of the catalyst com-ponents 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

~B~

PREPARATIO~ OF CATALYST MIXTURES

The invention relates to a process for the preparation of a catalyst mixture suitable for the conversion of a mix-ture of carbon monoxide and hydrogen into an aromatic hydro-carbon 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 compo-sition which, in addition to zinc, comprises one or more of the metals chromium, copper and aluminium and which compo-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-cates are characterized in that, after one hour's calcina-tion in air at 500C, they have the following properties:
a) thermally stable up to a temperature of at least 600C, b) an X-ray powder dif~raction 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 + o.o6 vs in which the letters used have the following meanings:
VS = very strong 9 S = strong, and c) in the formula which represents the composi'cion of the silicate, expressed in moles of the oxides, and which, in additlon 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/A2O3 molar ratio is higher than 10.
In the present patent application a crystalline sili-cate having a thermal stability of tC should be taken tobe a silicate whose X-ray powder diffraction pattern remains substantially unchanged upon heating to a temperature of tC.
The above-mentioned catalyst mixtures have till now been used in the form of a coarse mixture obtained by mecha-nically mixing particles of the zinc-containing composition and the crystalline silicate, each having an average par-ticle 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 an aromatic hydrocarbon mixture, there still is a desire to enhance this performance, particularly where the Cs~ select ivity and aromatics production are concerned.
On the presumption that the above-mentioned proper-ties of the catalyst mixture might possibly be improved b~ bringing about a more intimate contact between the two components of the mixture9 a number of experiments were carried out using catalysts based on a fine mixture, which 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 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 Cs~selectivity, this was accompanied with a very sharp decrease in activity as well as a decrease in C3~ selec-tivity 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 not lead to the achievement of the object in view (enhance-ment of the catalytic properties of th`e mixture~, an attempt was nevertheless made at attaining a more intimate contact between the components in a different wa~y. 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.

~s~

In the preparation of the present catalyst mixtures by spray-drying the starting material was an aqueous disper-sion 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/C0 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 Cs~ 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 pre-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 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-ding a basic reacting substance to one or more aqueoussolutions 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 Si02/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 dif-fraction pattern. Its strongest lines should be the four lines given in Table A. The complete X~ray powder diffrac-tion pattern of a typical example of a silicate that maybe used in the process according to the invention is given in Table B.

Table B

d(~) Rel. int. d(~)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 7.42 2 3.43 5 6.68 7 3.34 2 6.35 11 3.30 5 5.97 17 3.25 5.70 7 3.05 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 mono-valent organic cation (R) is present or from which -s~

- such a cation is formed during the preparation of the sili-cate, 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 sili-cates 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 proce-dure 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 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 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 NH
ions, and the silicate is converted into the NH4+ form.
The NH41 form of the silicate is converted into the H-~ form by calcination.
In the preparation of ~he catalyst mixtures according to the invention one or more precipitates are used in which zinc is present together with one or more of the me-tals 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 intro-duction, ~ia the precipitates, into the catalyst mixtures to be prepared by spray-drying are zinc-chromium, 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 60-80%. The metal-containing precipitates which, in the process according to the invention, are dispersed in water together with the crystalline silicate, may be S~

prepared by precipitation of the indiviclual 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, preclpitates 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 a~ter 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 precipit-ation 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-precipi-tate formed. It is advisable to allow the metal precipitates to age in the mother liquor for some time and subseauently to wash them thoroughly with water before dispersing them, together with the crystalline silicate, in water. Suitable basic reacting sub-stances 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 metal-t~

containing precipitate and crystalline silicate present in the dispersion from which the catalyst mixture is pre-pared by spray-drying, these are preferably chosen such that a catalyst mixture is obtained which per pbw of sili-5 cate comprises 2.5-12.5 pbw, and more in particular 4-8 pbw, of metal oxides originating in the precipitake. Conditions suitable f`or carrying out the conversion of a H2/CO mix-ture into an aromatic hydrocarbon mixture using a catalyst mixture prepared according to the invention are: a tempe-10 rature of from 200-500C and in particular of from 300-450C, 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 Nl gas/l catalyst/hour. Pre~erably the feed used is a H2/C0 mixture having a H2/C0 molar ratio in the range 15 of from 0.25 to 1Ø Such H2/C0 mixtures may very suitably be prepared by steam gasification of a carbonaceous material, such as coal, at a temperature of from 900-1500C and a pressure of from 10-50 bar.
The conversion of a H2/C0 mixture into an aromatic 20 hydrocarbon mixture described hereinbefore may very suit-ably be used as the first step in a two-step process for the conversion of H2/C0 mixtures into hydrocarbon mix-tures. 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 5~

~or the conversion of a H2/C0 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/C0 mixture into an aromatic hydrocarbon mixture described hereinbefore may further be used very suitably as the first step of a three-step pro-cess for the preparation, inter alia, of middle distillates from a H2/C0 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/C0 molar ratio of from 1.75-2.25. At least that part of the reaction product ~rom 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(N03)2.6 aq and Cr(N03)3O9 aq were dissolved in water in such quantities that a Zn/Cr solution was obtained com-~St~

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 stoi-chiometric quantity of a 10% aqueous NH3 solution, was pumped with stirring through a blending unit which was kept at a temperature of 20C. 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 20C. The solid material was filtered off and washed with water until the wash water was free from N03- 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 120C, grinding the dried material to an average particle size of 0.4 mm and calcining the ground material for one hour in air at 400C.
Catalyst 2 A crystalline aluminium silicate was prepared as follows.
A mixture of NaOH, (C3H7)4NOH, amorphous silica and NaA102 in water, having the molar composition 3Na2- 4-5 [(C3H7)4N]20. 25 SiO2. 0.04 Al203. 450 H20, was heated for 24 hours with stirring in an autoclave at 150C under autogenous pressure. After cooling of the re-action mixture the silicate formed was filtered off, washedwith water until the pH of the wash water was about 8, and dried at 120C. After one hour's calcination in air at 500C
the silicate had the following properties:
a) thermally stable up to a temperature of at least 900C, b) an X-ray powder diffraction pattern substantially corresponding with that given in Table B, and c) an SiO2/Al203 molar ratio of 225.
The silicate was boiled with a 1.0 molar NH4N03 solution, washed with water, boiled again with a 1.0 molar NH4N03 solution and washed with water and dried at 120C. 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 500C.
Catalyst 3 -Catalyst 3 was prepared starting from a crystalline aluminium silicate, which after one hour's calcination in air at 500C, had the following properties:
a) thermally stable up to a temperature of at least 8000C, b) an X-ray powder diffraction pattern substantially corresponding with that given in Table B, and c) an SiO2/Al203 molar ratio of 290.
The silicate was boiled with a 1.0 molar NH4N03 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 120C, pressing and grinding .

.

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the dried material to an average particle size of 0.4 mm and calcining the ground material for one hour in air at 500C.
Catalyst mixture I
This catalyst mixture was prepared by mixing catalyst 1 and catalyst 2 in a weight ratio of 1001.
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 o~ less than 5 micron, mixing the milled ca-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 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-lysts 1 and 3 very intimately in the weight ratio of 5:1 andfinally pressing and grinding the mixture to an average par-ticle size of 0.4 mm.

Portion D of the crystalline silicate was dried for 16 hours at 120C and then calcined in air for one hour at 500C. 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 + Cr2O3 to silicate in the dispersion was 5:1O Finally so much water was stirred into the dispersion that the solids content thereof was 15% w. Settling of the dispersion was prevented by continuous st.irring. The dis-persion thus obtained was spray-dried in air in a counter-current operation using compressed air. The inlet tempe-rature of the air was 300C, the outlet temperature of the air was 120C. The pressure used was 0.4 bar. The powder obtained, which consisted substantially of sphe-rical particles having an average particle size of 50 micron and a bulk density of 1.33 g~ml, was divided into two ~ortions E and F. Catalyst mixture V was prepared from portion E by pressing, grinding to an a~erage par ticle size of 0.4 mm and calcination in air for one hour at 400C. Catalyst mixture VI was prepared from portion F, by calcination in air for one hour at 400C.
Catalyst mixtures I-VI were tested for the prepara-tion of an aromatic hydrocarbon mixture from a H2/C0 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 375C, a pressure of 60 bar and a space velocity of 850 Nl.kg-1.h-1. 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 III IV V

Conversion of syn-thesis gas, %v 60 41 60 45 55 C3~ selectivity, cal-culated on C1 T ~ %W93 89 93 88 93 Cs~ seleckivity, cal-culated on C1~, %w 73 79 63 72 81 Composition of Cs+ product, %w paraffins 25 17 30 2l 6 naphthenes 16 30 10 22 9 aromatics ~ 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, containing 314 ml catalyst. The depth of the catalyst bed in the settled condition was 100 cm. A H2/C0 mixture having a H2/C0 molar ratio of 0.5 was contacted with catalyst mixture VI at a temperature of 380C, 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-1.h-1). The results of this experiment (Experiment 6), averaged over the first 50 hours, are given in Table D.

~ ~ ~ 5 Table D

Experiment No. 6 Catalyst mixture No~ VI
Conversion of synthesis gas, % v 55 C3+ selectivity, calculated on C1+, % w 94 Cs+ selectivity, calculated on C1~, % w 82 Composition of Cs+ product, % w :
paraffins 10 naphtenes 15 aromatics 75 Research octane number (RON-O) of the Cs+ fraction g9 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 cata-lyst 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 upon activity, C3+ selectivity and aromatics pro-duction.
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 o~ the results of Experiment 3 (using a 5:1 coarse catalyst mixture) with those of Experi-ment 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+ selec tivity and aromatics production.
As regards the results mentioned in Table D the follow-ing may be ob~erved. Fluid-bed Experiment 6, carried out using a catalyst mixture prepared according to the invention yielded a very attractive Cs+ product having a high aromatics content and a high octane number.

Claims

C L A I M S

1. A process for the preparation of a catalyst mix-ture, characterized in that a crystalline metal silicate which, after one hour's calcination in air at 500°C, has 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

in which the letters used have the following mean-ings = 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 SiO2, comprises one or more oxides of a trivalent metal A chosen from the group formed by aluminium, iron, gallium, rhodium, chro-mium and scandium, the SiO2/A2O3 molar ratio is higher than 10, is dispersed in water together with one or more precipi-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 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, characterized in that the crystalline silicate has an SiO2/A2O3 molar ratio in the range of from 20 to 500.

4. A process as claimed in claim 1, 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 claim 1, 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 60-80%.

7. A process as claimed in claim 1, 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 H2/CO mixture with a catalyst mixture as prepared according to claim 1.

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 H2/CO mixture has a H2/CO molar ratio in the range of from 0.25 to 1Ø