CA1140909A

CA1140909A - Process for the preparation of fischer-tropsch catalysts

Info

Publication number: CA1140909A
Application number: CA000350343A
Authority: CA
Inventors: Michael A.M. Boersma; Lambert Schaper
Original assignee: Shell Canada Ltd
Current assignee: Shell Canada Ltd
Priority date: 1979-07-13
Filing date: 1980-04-22
Publication date: 1983-02-08
Also published as: NL190603B; IT8023379A0; NL190603C; BE884144A; AU538927B2; ZA804155B; GB2053016A; DE3026175A1; FR2460712A1; FR2460712B1; NL7905479A; JPS6352937B2; IT1131956B; AU6029780A; JPS5621648A; GB2053016B; DE3026175C2

Abstract

A B S T R A C T

A PROCESS FOR THE PREPARATION OF FISCHER-TROPSCH
CATALYSTS

Fischer-Tropsch catalyst. A SiO2-supported Cr-promoted Fe-catalyst has been prepared by impregnation and reduction at high temperature. Eydrocarbons are prepared from H2-poor syngas with the use of this catalyst.

Description

--" 114~9~9 ;-A ~ROCESS FOR THE PREPARATION
OF FISCHER-TROPSCH
CATALYSTS

The invention relates to a process for the preparation of Fischer-Tropsch catalysts.
The preparation of hydrocarbons from a mixture of car bon monoxide and hydrogen by contacting this mixture at elevated temperature and pressure with a catalyst is re-ferred to in the literature as the hydrocarbon synthesis according to Fischer-Tropsch. Catalysts which are often used for this purpose contain one or more metals from the iron group together with one or more promoters and sometimes a carrier material. The preparation of the Fischer-Tropsch catalysts can, in principle be carried out in three ways, viz. by precipitation, by melting or by impregnation. The preparation of the catalysts by precipitation briefly con-sists in an aqueous solution of a salt of a metal from the iron group, to which, if desired, a salt of a promoter and a carrier material may have been added, being rendered alkaline, resulting in the precipitation of the catalyst.
One or more promoters and a carrier material may be added to this precipitate. The preparation of the catalysts by melting is effected, for instance, for iron catalysts by fusing iron oxide with one or more promoter oxides. Both tne precipitation route and the melting route are not very attractive procedures for the preparation of the Fischer-Tropsch catalysts, since their reproducibility is small.

" ~

ll~O9V9 The precipitation route has the additional disadvantage that it takes up a great deal of time, whilst the melting route requires much energy. Moreover, the catalytic pro-perties of the catalysts prepared by melting and by preci-5 pitation, particularly the activity and stability are un-satisfactory. A much more attractive procedure for the pre-paration of the Fischer-Tropsch catalysts is the impregna-tion route. It is easy to carry out, gives well reproducible results and, as a rule, leads to catalysts with high activi-ty and stability. The impregnation route briefly consistsin a porous carrier being impregnated with one or more aqueous solutions of salts of one or more metals from the iron group and of one or more promoters, followed by drying, calcining and reducing of the composite. Many elements, such as alkali metals, alkaline-earth metals, metals from group ~I B, Ti, Zr, Th, V, Mn and Cu, are eligible promoters for the catalysts prepared by impregna-tion. As the carrier materials for the catalysts prepared by impregnation amorphous as well as crystalline materials, may be used. Suitable carriers are, inter alia, silica, alumina, zirconia, thoria, boria and combinations thereof, such as silica-alumina and silica-magnesia and furtAer zeolites, such as mordenite, faujasite and zeolite-omega.

The Applicant has carried out an extensive investiga-tion concerning the preparation of hydrocarbons from H2~C0 mixtures with an ~2~C0 molar ratio smaller than 1.0, using Fischer-Tropsch catalysts prepared by impregnation. In the above-mentioned conversion the behaviour of these catalysts ` :~14~909 was found to be greatly dependent on the ~ollowing factors:
1. the nature o~ the metal from the iron group and the load used,

2. the nature of the promoter and the load used, 5 3. the nature o~ the carrier, and 4. the temperature treatment used.
Catalysts prepared by impregnation were found to have - a very high activity and a very high stability for the con-Yersion of H2/C0 mixtures with an H2~C0 molar ratio smaller than 1.0, if they contain 10-40 pbw iron and 0.25-10 pbw chromium per 100 pbw silica and have been reduced at a tem-perature of 350-750C. These are novel catalysts.
The present patent application therefore relates to a process for the preparation of novel catalysts, in which catalysts containing 10-40 pbw iron and 0.25-10 pbw chromium per 100 pbw silica are prepared by impregnating a silica carrier with one or more aqueous solutions of salts of iron and of chromium, followed by drying the composite, calcining it and reducing it at a temperature of 350-750C. The patent application further relates to the use of these catalysts for the preparation of hydrocarbons with an H2~C0 mixture with an H2tC0 molar ratio smaller than 1.0 as the starting material.
~hen for the above-mentioned application use is made of catalysts pxepared according to the invention, preferred catalysts are those cor.taining 20-35 pb~ iron and 0.5-5 pbw chromium per 100 pbw silica. Further, preference is given to catalysts which contain, in addition to iron and chromium . ~i4!~)~09 a selectivity promoter. Suitable selectivity promoters are the alkali metals, in particular potassium. In addition to iron and chromium it is preferred in the catalyst prepara-tion according to the invention to incorporate 1-5 pbw 5 potassium per lOQ pbw silica into the catalyst by impregna-tion.
In the preparation of the catalysts the metal salts can be deposited on the carrier in one or more steps. Between the impregnation steps the material is dried and optionally, 10 calcined. Impregnation in more than one step may be necessa-ry for the preparation of catalysts with a high metal load.
The metal salts may be deposited on the carrier separately or together from one solution. An attractive method of de-positing the metal salts on the carrier is the dry impreg-15 nation technique, according to which a carrier is contactedwith an aqueous solution of the salts concerned, which aqueous solution has a volume which is substantially the same as the pore volume of the carrier. Sorption of the aqueous solution by the carrier can be facilitated by heating the mixture. If this method is chosen for the prepration of catalysts with a high metal load, it may be necessary to carry out more than one dry impregnation and to dry the material between the separate impregnation steps and, optionally, to calcine it. The calcination is prefer-ably carried out at a temperature of 350-700C. The catal~st preparation is finished with a reduction. This reduction is carried out at a temperature of 350-700C with a hydrogenous gas, e.g. a mixture of hydrogen and nitrogen. The reduction is preferably carried out at a temperature of 350-500C.

-`` 1 1 4V 9 ~ 9 The catalysts prepared according to the invention are pre-eminently suitable for the preparation of hydrocarbons from an H2/C0 mixture with an H2/C0 molar ratio smaller than l.Q. Such H2~CO mixtures can very suitably 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 oils produced from tar sànd and bituminous shale. The steam gasification is prefer-ably carried out at a temperature of from 900 to 1500C and a pressure of from 10 to 50 bar.
The preparation of hydrocarbons from an H2~C0 mixture with an H2~C0 molar ratio smaller than 1.0, using a Fischer-Tropsch catalyst according to the invention is preferably carried out at a temperature of from 200 to 350C and in partilcular of from 250 to 350c, a pressure of from 10 to 70 bar a~nd in particular of from 20 to 50 bar and a space velocity of from 500 to 5000 and in particular of from 500 to 2500 Nl gas/1 catalyst/h. The hydrocarbon preparation according to the invention can very suitably be carried out by conducting the feed in upward or downward direction through a vertically mounted reactor in which a fixed or a moving bed of the catalyst concerned is present.
The invention will now be explained with reference to the following example.
Example Six catal~sts (A-C and 1-3~ were prepared and tested for the hydrocarbon synthesis according to Fischer-Tropsch.
The preparation of t~.e catalysts was effected b~ impregnating 114U~09 a silica or alumina carrier with aqueous solutions contain-îng one or more of the following salts: iron nitrate, chro-mium nitrate and potassium nitrate. In all impregnations the dry impregnation technique was used. The reduction of the catalysts was carried out at atmospheric pressure with an H2tN2 mixture in a volume ratio of 3:1 at a superficial gas rate of 1.6 m~s. Further details about the preparation of the individual catalysts are given below.
Catalyst A
This catalyst was prepared by impregnating a silica carrier first with a solution of KNO3, followed by drying at 120C and calcining for two hours at 400C, and then impregnating with a solution of Fe(N03)3 and Cr(N03)3, followed by drying at 120C, calcining for two hours at 500C and reduction at 280C.
Catalyst 1 The preparation of this catalyst was performed in sub-stantially the same way as the preparation of catalyst A, the difference being that the reduction was carried out at 400C.
Catalyst B
The preparation of this catalyst was performed in sub-stantially the same way as the preparation of catalyst A, the differences being that alumina was used as the carrier and that the reduction was carried out at 400C.
Catalyst C
The preparation of this catalyst was performed in sub-stantially the same way as the preparation of catalyst 91)9 A, the differences be,ing that in the second impregnation a solution was used which did not contain chromium and that the reduction was carried out at 400C.
Catalyst 2 This catalyst was prepared by impregnating a silica carrier with a solution of Fe(NO3~3, Cr(NO3~3 and KN03, followed by drying at 120C, calcining for two hours at 500C and reduction at 40oc.
Catalyst 3 The preparation of this catalyst was performed in sub-stantially the same way as the preparation of catalyst A, the differences being that in the first impregnation a solution with a higher concentration of K was used, that in the second impregnation a solution with higher concentrations of Fe and Cr was used, and that the reduction was carried out at 400C. The composition of the catalysts is shown in Table A.
Table A
Cat. No. Composition expressed in pbw, Fe Cr K SiO2 2 3

3 35 1.5 2.75 100 ---~., `` ll~V9()9 The testing of the catalysts A-C and 1-3 ~or the hydrocarban synthesis according to Fischer-Tro~sch with synthesis gas with an H2tC0 molar ratio of 0.5 as the starting material was performed in a 250-ml reactor which contained a catalyst bed with a volume of 50 ml. The experi-ments were carried out at a temperature of 280C, a pressure of 30 bar and a space velocity of 1000 Nl.l l.h 1.
The results of these experiments are shown in Table B.
Table B
Exp. No. Cat. No. Conversion of the synthesis gas, a~ter 25 h after 500 h 3 C . 69

4 1 91 90 After run hour 500 experiment 4 was continued for another 500 hours with catalyst 1. By gradually increasing the reaction temperature the conversion of the synthesis gas was maintained at 90~. At run hour 1000 the temperature was 290C.
Of the experiments mentioned in Table B only experi-ments 4-6 were carried out with catalysts prepared according to the invention. In these experiments the catalysts showed both.a very high activity and a very high stability. The e~periments 1-3 were carried out with catalysts which outside the scope o~ the inYentiOn. They have been included in the patent application for comparison.
Catalyst A had been reduced at too low a temperature.
Catalyst B did not contain silica. Catalyst C did not contain chromium. The results of experiments 1-3 show that these catalysts had a low activity.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for the preparation of Fischer-Tropsch catalysts, characterized in that catalysts containing 10-40 pbw iron and 0 25-10 pbw chromium per 100 pbw silica are prepared by impregnating a silica carrier with one or more aqueous solutions of salts of iron and of chromium, followed by drying the composite, calcining it and reducing it at a temperature of 350-750°C.

2. A process according to claim 1, characterized in that a catalyst is prepared containing 20-35 pbw iron per 100 pbw silica, and 0.5-5 pbw chromium per 100 pbw silica.

3. A process according to claim 1, characterized in that a catalyst is prepared containing 1-5 pbw potassium per 100 pbw silica.

4. A process according to claim 1, characterized in that the calcination is carried out at a temperature of 350-700°C.

5. A process for the preparation of hydrocarbons from an H2/CO mixture, characterized in that an H2/CO mixture with an H2/CO molar ratio smaller than 1.0 is contacted at elevated temperature and pressure with a catalyst containing.
10-40 pbw iron and 0.25-10 pbw chromium per 100 pbw silica, said catalyst being prepared by impregnating a silica carrier with one or more aqueous solutions of salts of iron and of chromium, by drying the composite, calcining it and reducing it at a temperature of 350-750°C.

6. A process according to claim 5, characterized in that the preparation of the hydrocarbons from the H2/CO mixture is carried out at a temperature of from 200-350°C, a pressure of from 10-70 bar and a space velocity of from 500 to 5000 Nl gas/l catalyst/h.