CA1180312A

CA1180312A - Process for the preparation of crystalline silicates

Info

Publication number: CA1180312A
Application number: CA000407161A
Authority: CA
Inventors: Willibrord A. Van Erp; Martin F.M. Post
Original assignee: Shell Canada Ltd
Current assignee: Shell Canada Ltd
Priority date: 1981-07-27
Filing date: 1982-07-13
Publication date: 1985-01-02
Also published as: NL8103532A; AU549792B2; NZ201367A; ZA825293B; AU8636682A

Abstract

A B S T R A C T
Al-containing (C)rystalline (I)ron (S)ilicate with a SiO2/Fe2O3 mol. ratio of 75-300 and a SiO2/Al2O3 mol. ratio of less than 2000 and having a crystal structure which is similar to that of ZSM-5 is prepared from an Al-containing base mixture comprising butylamine (BUAM). The stability of a ZnO-Cr2O3/CIS catalyst mixture - on basis of CIS
prepared via the BUAM route - in the direct gasoline synthesis can be considerably increased by incorporating a small amount of an aluminium compound in the ?se mixture from which the CIS component is prepared.

Description

3:~

PROCESS FOR THE PREPARATION OF CRYSTALLINE
. SILICATES

The invention relates to a process for the preparation of crystalline silicates having improved catalytic properties.
Mixtures of carbon monoxide and hydrogen can be converted into aromatic hydrocarbon mixtures by the use of a mixture of two catalysts, one having the property of catalyzing the conversion of a H2/CO
mixture into oxygen-containing organic compounds, and the other being a crystalline iron silicate capable of catalyzing the conversion of oxygen-con-taining organic compounds into aromatic hydrocarbons.
The said crystalline iron silicates are characterized in that~ after one hour's calcination in air at 500C, they have the ~ollowing properties:
a) thermally stable up to a temperature o~ at least 600C;
b) an X-ray powder diffraction pattern in which the strongesi lines are the four lines listed in Table A:

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TA~LE A

d(~)Relative intensity 11.1 ~ 0.2 VS
10.0 ~ 0.2 VS
3.84 ~ 0.07 S
3.72 ~ 0.06 S

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, the SiO2~Fe203 molar ratio is 75-30C.
In the present patent application a crystalline silicate having a thermal stability of at least tC
should be taken to be a silicate whose X-ray powder diffraction pattern remains substantially unchanged upon heating to a temperature of tC.
The crystalline silicates used in the catalyst mixtures may be prepared starting from an aqueous mixture comprising the following compounds: one or more compounds of an alkali metal (M), one or more amines of the general formula R1R2R3N, in which R1 is an alkyl group and R2 and R3 are an alkyl group or a hydrogen atom, one or more silicon compounds with a high SiO2 content and one or more compounds.
comprising iron in the trivalent form. In the ~8V3 present patent application silicon compounds with a high SiO2 content should be taken to be silicon com-pounds which, a~ter drying at 120C and calcinatio~
at 500C, yield a product with a SiO2 content hi~her than 90%w. The crystalline silicates are prepared by maintaining the mixture at an elevated temperature until the crystalline silicate has formed, separating the ~tter from the mother liquor and calcining i~. In the aqueous mixture from which the silicates are prepared, the various compounds should be present in the following molar ratios, expressed - ~ith the ex-ception of the amine~ - in moles of the oxides:
M20 : SiO2 = 0.01 - 0.35, R1R2R3N : SiO2 = 0.04 - 2.0, SiO2 : Fe203 = 50 400, and H20 : SiO2 = 5 - 65.
An investigation carried out by the Applicant into the application of the above-mentioned catalyst mixtures for the preparation of aromatic hydrocarbon mixtures from H2/C0 mixtures, has shown that the presence of aluminium in the crystalline iron silicates has a great influence upon the stability of the catalyst mixtures. The catalyst mixtures have been found to have an exceptionally high stabili~y, when the crystalline iron silicate present thereïn contains such a quantity of aluminium that in the formula ~8~3~

representing the composition of the silicate expressed in moles of the oxides the SiO2/A1203 molar ratio is lower than 2000.
In the present patent application the term "crystalline iron silicate" relates both to crystal-line silicates ~lhich comprise only iron as the tri-valent metal and to crystalline silicates which, in addition to iron, comprise aluminium, provided that in the formula which represents the composition of the silicate expressed in moles of the oxides the Fe203/A1203 molar ratio is higher than 1Ø The aluminium-containing crystalline iron silicates are prepared starting from an aqueous mixture which, in addition to the aforementioned compounds, contains one or more aluminium compounds. The quantity of aluminium compounds present in the aqueous mixture should be such that the SiO2/A1203 molar ratio is 50 - 4000. The preparation of aluminium-containing crystalline iron silicates as mentioned hereinabove, starting from an aqueous mixture containing one or more amines of the general formula R1R2R3N and one or more silicon compounds having a high SiO2 content, is new.
The present patent application therefore rèlates to a process for the preparation of crystalline iron silicates, characterized in that, after one hour's ~8~3~

calcination 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 diffraction pattern in which the strongest lines are the ~our lines listed in Table A, and c) in the formula which represents the composition of the silicate expressed in moles of the oxides, the SiO2~Fe203 molar ratio is 75-300~ the SiO2/A1203 molar ratio is below 2000 and the Fe203/A1203 molar ratio is higher than 1Ø
The preparation is carried out by maintaining an aqueous mixture comprising the following com-pounds: one or more compounds of an alkali metal(M), one or more amines of the general formula R1R2R3N, one or more silicon compounds having a high SiO2 content, one or more compounds in which iron is present in the trivalent form and one or more aluminium compounds, in which mixture the various compounds are present in the following molar ratios, expressed -with the exception o~ the amines - in moles of the oxides:

~ ~ ~V 3~ 2 M2o : SiO2 = 0.01 - 0-35 3 R1R2R3N : SiO2 = 0.04 - 2.0 SiO2 : Fe203 = 50 - 4, SiO2 : Al23 = 50 - 4000, and H2o : SiO2 = 5 - 65 at an elevated temperature until the crystalline silicate has formed and subsequently separating the crystalline silicate from the mother liquid and calcining it. Preferably, the H20/SiO2 molar ratio in the aqueous mixture is below 0.12.
The silicates prepared according to the in-vention are defined, among other things, by the X-ray powder diffraction pattern that they show after one hour's calcination in air at 500C. In this pattern the strongest lines should be the four lines listed in Table A. The complete X-ray powder diffraction pattern of a typical example of a silicate prepared according to the invention is given in Table B.

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TABLE B

d(~) Rel. int. d(~) Rel int.
11.1 loo 3.84 (D) 57 10.0 (D) 70 3. 70 ( D) 31 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. g7 17 3.25 5.70 7 3.05 8 5.56 lo 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.~0 2 4.25 7 2.48 3 4.07 2 2.40 2 4.00 4 (D) = doublet The prepatation of the silicates may be carried out at an atmospheri.c pressure as well as at an elevated pressure. If the reaction temperatures used lie above the boiling point of the mixture, the reaction is 5 preferably carried out in an autoclave under autogenous pressure. The silicates are preferably prepared by maintaining the mixture for at least four hours at a temperature between 90 and 300C and in particular at a temperature between 125 and 175C. After the formation of the silicates, the crystals are separated from the mother liquor, for instance by filtration, decantation or centri:~ugation. The mass of crystals is then washed with water and finally dried and calcined.
As examples of suitable compounds that can be used in the preparation of the silicates according to the in~ention may be mentioned nitrates, carbon-ates, hydroxides and oxides of alkali metals; amorphous solid silicas, silica sols, silica gels and silicic acid; oxides, hydroxides, normal salts and complex salts of trivalent iron, linear and branched alkyl-amines. In the preparation of silicates according to the invention the starting mixture is preferably an aqueous mixture in which M is present in a sodium compound and R1R2R3N is a linear primary alkylamine having 3-5 carbon atoms in the alkyl group, in particular n-butylamine.
As regards aluminium which, in the preparation of the crystalline iron silicates according to the invention, should be present in the aqueous mixture, the following may be noted. The silicon compounds with a hign SiO2 content eligible from the economical 33~'~

point of view for the preparation on a te.chnical scale of crystalline iron silicates according to the invention, usually contain a small proportion of aluminium as an impurity~ At least part of this aluminium is found in the iron silicate prepared.
This means that the use of such silicon compounds as the starting material results in crystalline iron silicates in which the formula representing the com-position of the silicate expressed in moles of the oxides, in addition to SiO2 and Fe203,also contains A1203. However, the SiO2/A1203 molar ratio is usually considerably higher than 2000. For instance, from silicon compounds with a normal aluminium con-tamination of 50-100 ppmw as the starting material, crystalline iron silicates are obtained having a SiO2/A1203 molar ratio of 5000-20,000. Regarding the .incorporation of aluminium into the aqueous mixtures from which the crystalline iron silicates are prepared according to the invention there are, basically, two possibilities. The starting mixture may be an aqueous mixture comprising a silicon com-pound which is contaminated with aluminium to such an extent that a crystalline iron silicate is obtained having the desired SiO2/A120~ molar ratio below 2000.
For instance, from silicon compounds with a high aluminium contamination - of about 1000 ppmw - as the star~ing material, crystalline iron silicates are obtained having a SiO2/A1203 molar ratio of 500-1000.
The aqueous mixture may also be made to contain such a proportion of one or more aluminium compounds that, while any quantity of aluminium already present in the silicon compound used is taken account of, a crystal-line silicate is obtained having the desired SiO2tA1203 molar ratio below 2000. Examples of suitable aluminium compounds which~ in the preparation of the crystalline iron silicates, may be incorporated into the aqueous mixture include aluminium hydroxide, aluminium sul-phate, sodium aluminate and amorphous alumina.
Silicates prepared according to the invention may be used~ among other things, as adsorbing agents and extracting agents, as drying agents, as ion ex-changers and as catalysts or catalyst carriers for use in a variety of catalytic proGesses, in particular the catalytic preparation of aromatic hydrocarbons from acyclic compounds.
If the silicates prepared according to the in-vention are to be used as catalysts or catalyst car-riers, the alkali metal content of these silic2tes should preferahly be reduced beforehand to less than 0.1 and in particular to less than 0.01%w. The reduction of ~he alh-ali metal content of the silicates may very suitably be carried out by contacting the silicates 31;~

once or several times with an aqueous solution con-taining ammonium ions. The NH4~ silicates thus ob-tained may be calcined to form the H~ silicates.
When the crystalline iron silicates are used as catalysts they may, if desired, be comblned with a binder material, such as bentonite or kaoline.
As explained hereinabove, the silicates pre-pared according to the invention find an important application in catalyst mixtures to be used for the preparation of an aromatic hydrocarbon mixture from a H2/C0 mixture. H2/C0 mixtures may be prepared by steam gasification of a carbon-containing material.
Examples of such materials are brown coal, anthracite, coke, crude mineral oil and fractions thereof and also oils obtained from tar sand and bituminous shale.
The steam gasification is preferably carried out at a temperature between 900 and 1500C and a pressure be-tween 10 and 50 bar. For the preparation of the aromatic hydrocarbon mixture the starting material is preferably a H2/C0 mixture with a H2/C0 molar ratio between 0.25 and 1Ø The preparation of the aromatic hydrocarbon mixture from a H2/C0 mixture using a catalyst mixture comprising a crystalline iron silicate prepared according to the invention, is preferably carried out at a temperature of from 200-500C and in particular of from 300-450C, a 3~

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.
The two catalysts present in the catalyst mlxture used in the preparation of the aromatic hydrocarbon mixture from a H2/C0 mixture will for the sake of brevity hereinafter he referred to as catalysts X
and Y. Catalyst X is the catalyst capable of catalyzing the conversion of a H2/C0 mixture into oxygen-contain-ing organic compounds and catalyst Y is the crystal-line iron silicate prepared according to the in-vention. ~or use as catalysts X preference is given to catalysts capable of converting a H2/C0 mixture into substantially methanol and/or dimethyl ether.
If it is the object to prepare a product substantially consisting of hydrocarbons boiling in the gasoline range, the catalyst X used may very suitably be a catalyst which comprises zinc together with chromium.
When such a catalyst is used, it is preferably chosen to be a catalyst in which the atomic percentage of zinc, calculated on the sum of zinc and chromium, is at least 60% and in particular 60-80%. If the object is to prepare not only hydrocarbons boiling in the gasoline range, hut also a fuel gas wi~h a high calorific value, the catalyst X used` may very suit-ably be a catalyst comprising zinc together with ~8V~

copper. Preference is given to the use o~ a catalyst mixture which, per part by volume of catalyst Y, com-prises 1-5 pbv of catalyst X.
The conversion described hereinabove using a mixture of a crystalline iron silicate prepared ac-cording to the invention and a catalyst capable of catalyzing the conversion of a H2/C0 mixture into oxygen-containing organic compounds, can very suit-ably be carried out as the first step of a two-step process for the conversion of H2/C0 mixtures into hydrocarbon mixtures. In this case carbon monoxide and hydrogen present in the reaction product from the first step are contacted in a second step, if desired, together with other components of this reaction product, with a catalyst comprising one or more metal components having catalytic activity for the conversion of a H2/C0 mixture lnto 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/C0 molar ratio of 1.75-2.25.
The conversion described hereinabove, using a mixture of a crystalline iron silicate prepared ac-cording to the invention and a catalyst capable of catalyzing the conversïon of a H2/C0 mixture ïnto oxygen-containing organic compounds, can very suit-ably be. used as the first s.tep of a three-.s.tage process for preparing, inter alia, middle dlstillates from a H2/CO mixture. I.n this case carbon manoxide and hydrogen present in .the reaction product from the fi.rst step are contacted in a second step, if desired, to.gether with other components of this reaction product, 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 1.75-2.25. An example of a suitable catalyst for use in the second step is a catalyst which comprises 10-40 pbw of cobalt and 0.25-5 pbw of zirconium, titanium or chromium per 100 pbw of silica and has been prepared by impre~nation of a silica carrier with one or more aqueous solutions of salts of cobalt and zirconium, titanium or chromium~ followed by drying of the com-position, calcination at 350-700C and reduction at 200-350C. At least that part of the reaciion product from the second step whose initial boiling point lies above the final boiling polnt of.the heaviest middle distillate desired as e~d-product, is subjected in a thlrd step, to a catalytic hydro-trea`tment.
The invention is.now illustrated with the aid of the following example.
EXAMPLE
Three crystalline iron silicates (silicates 1-3) were prepared from aqueous mixtures of NaOH, C4~9N~2, ~8V3~ ;~

amorphous silica I (for silicates 2 and 3) or amorphous silica II (for si.licate 1) and, optionally, amorphous alumina (for silicate ~). Furt.her, two crystalline aluminium silicates (sIlicates 4 and 5) were prepared from aqueous mixtures of NaOH, C4H9N~ , amorphous silica I and amorphous alumina. The preparation was carried out by heating the aqueous mixtures in an autoclave with stirring and under autogenous pressure for 120 hours at 150C. After 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 120C. After one hour's cal-cination in air at 500C~ silicates 1-5 had the fol-lowing propert;es:
a) thermally stable up to a temperature of at least b) an X-ray powder diffraction pattern substantially corresponding to that given in Table B, and c) a value of the SiO2/Fe203 and SiO2/Al203 molar 20ratios as stated in Table C.

TABLE C

Silicate SiO2/Fe203 SiO2/Al203 No. molar ratio molar ratio _

2 115 2570

3 130 560

4 - 540 Amorphous silica I used in the preparation of silicates 2-5 comprised 280 ppmw of aluminium and, after drying at 120C and calcination at 500C, yielded a product consistin~ of 99.9%w of SiO2. Amorphous silica II used in the preparation of silicate 1 com-prised 70 ppmw of aluminium and, after drying at 120C
and calcination at 500C, yielded a product consisting of ~9.7%w of SiO2.
The molar composition of the aqueous mixtures from which silicates 1-5 were prepared may be rendered as follows . 2 4 9 2 2 3 Y 2 3 sio2.450 H20, where x and y have the values given in Table D.

3 ~'~

TABLE D

Silicate No. x y 1 0.20 0.002 2 0.20 o.oo8 3 0.20 0.041 4 . - 0.041 - 0.075 From silicates 1-5 were prepared silicates 6-10, respectively, by boiling silicates 1-5 with a 1.0 molar NH4N03 solution, washing with water, boiling again with a 1.0 molar NH4N03 solution~ and washing, drying at 120C and calcination at 500C. Five catalyst mixtures (catalyst mixtures A-E) were sub-sequently prepared by mixing a ZnO-Cr203 composition with each of silicates 6-10. The atomic Zn percentage of the ZnO-Cr203 composition, calculated on the sum Df Zn and Cr, was 70%. All the catalyst mixtures comprised 10 pbw of the ZnO-Cr203 composition per pbw of silicate.
Catalyst mixtures A-E were tested for the preparation of an aromatic hydrocarbon mixture from a H2/C0 mixture. The test was carried out in a 50-ml reactor containing a fixed catalyst bed of 7.5 ml volume. In fi-~e experiments a H2/CO mixture having a H2/C0 molar ratio of 0.5 was passed over each of catalyst mixtures A-E at a temperature of 375C~ a pres.sure of 60 bar and a space velocity of 1000 Nl.l 1.h 1. All these experiments yielded a product the C5 fraction of which consisted more than 30%w of aromatics. Furth.er results of the experiments are given in Table E.

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a) ~ Q)~
o o~ s ~. ~ o ` oo U~
I ~ ~
+ ~ O
.,~ ~ ~o o V rl ~ ~
. _._ a)- ~ o ~ c~ c~ o~
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, ~ ~
+ rl a~ o . ~ ~ ~o o .
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~ ~ ~ V o .~ o v~ u~ =r ~ o o J~ X tQ
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'd ~x a) o ¢ m v ~ ~3 ~ æ

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I ~ ~ o ~I ~ ~ 3 x Q) a) ~i Of the silicates lis:ted in Table C onl~ crystal-line iron silicate 3 ~as prepared according to the invention. Crystalline iron silicates 1 and 2 and crystalline aluminium silicates 4 and 5 fall outside the scope of the invention. They have been included in the present patent application for comparison.
Of the experiments listed in Table E only Experiment 3 was carried out using a catalyst comprising a crystal-line iron silicate prepared according to the in-vention. Experiments 1, 2, 4 and 5 fall outside the scope of the invention. They have been included in the patent application ~or comparison. On the results given in Table E the following may be remarked:
a) The results of Experiments 1 and 2 show that catalyst mixtures comprising a crystalline iron silicate havin~ a low aluminium content (SiO2/A1203 molar ratio > 2000), show a high initial activity and a very high selectivity.
The stability of these catalyst mixtures remains susceptible o~ improvement.
b) The result of Experiment 3 shows that raising the Al-content of the crystalline iron silicate to an SiO2/A1203 molar ratio ~ 2000, yields a very substantial improvement of the stabili~y, while the high initial activity and the very high seIectivity are preserved.

c) The catalyst mixture us.ed in Experiment 4.com-prised a crystalline aluminium silicate, in which the SiO2/A1203 molar ratio was chosen such that it corresponded with:that of the crystalline iron silica~e in the catalyst mixture used in Ex-periment 3. The resul~s. of Experiment 1~ s.how. that this catalyst mixture has a low initial act.ivity and a very low s:tability.
d) The catalyst mixture used in Experiment 5 com-prised a crystalline aluminium silicate in which the SiO2/A1203 molar ratio was chosen such that with this catalyst mixture an initial activity could be attained corresponding to that of the catalyst mixture used in Experiment 3. The results of Experiment 5 show that the stability of the catalyst mixture used remains very low.
Comparison of the results of Experiments 5 and 4 shows that reduction of the SiO2/A1203 molar ratio of the crystalline aluminium silicate leads to a considerable reduction in the C5 select~
ivity of the catalyst mixture.

Claims

C L A I M S

1. A process for the preparation of crystalline iron silicates which, after one hour's calcination in air at 500°C, 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 four lines listed in Table A are the strongest lines:
TABLE A
d(.ANG.) Relative intensity 11.1 ? 0.2 VS
10.0 ? 0.2 VS
3.84 ? 0.07 S
3.72 ? 0.06 S
in which the letters. used have the following meanings: VS = very strong; S = strong, and c) in the formula which represents the composition expressed in moles of the oxides, the SiO2/Fe2O3 molar ratio is 75-300, the SiO2/Al2O3 molar ratio is lower than 2000 and the Fe2O3/A12O3 molar ratio is higher than 1.0, characterized in that an aqueous mixture comprising the following com-pounds: one or more compounds of an alkali metal (M), one or more amines of the general formula R1R2R3N, where R1 is an alkyl group and R2 and R3 are an alkyl group or a hydrogen atom, one or more silicon compounds which, after dry-ing at 120°C and calcination at 500°C, yield a product having an SiO2 content of more than 90%w, one or more compounds in which iron occurs in the trivalent form and one or more aluminium com-pounds, in which mixture the compounds are present in the following molar ratios, expressed - with the exception of the amines - in moles of the oxides:
M20 : SiO2 = 0.01-0.35, R1R2R3N : SiO2 = 0.04-2.0, SiO2 : Fe2O3 = 50-400, SiO2 : Al2O3 - 50-4000, and H2O : SiO2 = 5-65, is maintained at an elevated temperature until the crystalline silicate has formed and the latter is subsequently separated from the mother liquor and calcined.

2. A process as claimed in claim 1, characterized in that the M2O/SiO2 molar ratio of the aqueous mixture is lower than 0.12.

3. A process as claimed in claim 1 or 2, characterized in that the alkali metal compound used is a sodium com-pound and the R1R2R3N compound used is n-butylamine.

4. A process as claimed in claim 1, characterized in that the aqueous mixture is kept for at least 4 hours at a temperature between 90 and 300°C.

5. A process as claimed in claim 1, characterized in that the required quantity of aluminium has been introduced into the aqueous mixture by the use of a heavily aluminium-contaminated silicon compound and/or by the addition of a separate aluminium compound.

6. A process for the preparation of an aromatic hydrocarbon mixture from a H2/CO mixture, characterized in that the H2/CO
mixture is contacted with a mixture of two catalysts, one of which is capable of catalyzing the conversion of a H2/CO mixture into oxygen-containing organic compounds, the other being a crystalline iron silicate as prepared in claim 1.

7. A process as claimed in claim 6, characterized in that as the catalyst capable of catalyzing the conversion of a H2/CO mixture into oxygen-containing organic compounds, a composition is used which comprises zinc together with chromium or copper.

8. A process as claimed in claim 6 or 7, characterized in that the H2/CO mixture has a H2/CO molar ratio between 0.25 and 1Ø