CATALYST PREPARATION

Abstract: A SiO₂ comprising carrier is treated with a specified silicon compound and thereafter cobalt is emplaced on the carrier by contacting it with a cobalt compound in the presence of an organic liquid. The silicon compounds to be applied have the general formula Si(X) n (Y) m (Z) in which X = halogen, alkoxy or acylocy; Y = H or a hydrocarbyl group; Z = halogen or a nitrogen or oxygen containing group; n = 0-3; n+m = 3.

Description: CATALYST PREPARATION The invention relates to a process for the preparation of catalysts comprising cobalt supported on a silica-containing carrier and also to the use of these catalysts in the preparation of hydrocarbons fran mixtures of carbon monoxide with hydrogen. The preparation of hydrocarbons from a H2tCO mixture by contacting this mixture at elevated temperature and pressure with a catalyst is known in the literature as the Fischer-Tropsch hydrccarbon synthesis. Catalysts suitable for the purpose are those comprising cobalt supported on a silica-containing carrier. Such catalysts can be prepared by contacting a silica-containing carrier with a cobalt compound in the presence of a liquid, then removing the liquid and calcining and activating the composition obtained. In this manner of catalyst preparation part of the cobalt reacts with hydroxy groups occurring at the surface of the silica-containing carrier, thus forming cobalt hydroxysilicates, which coopunds will not be reduced in the subsequent catalyst activation. Consequently, part of the cobalt has no activity for the Fischer-Tropsch synthesis and therefore the catalysts show lower activity than one would have expected in reliance upon their cobalt contents. It has naw been found that this drawback can be overcome by first treating the silica-containing carrier with a compound chosen from a certain group of silicon oowpounds, then contacting the carrier thus treated with a cobalt compound in the presence of an organic liquid and finally, after removal of the organic liquid, calcining and activating the composition obtained. Eligible for the present purpose are silicon compounds having the general formula Si (X) n m (Z), wherein X = halogen, a11cy and/or acyloxy; Y = H and/or a hydrocabyl group; Z = halogen or a nitrogen-containing or an oxygen-containing group; n = 0-3; n+m = 3. The present patent application therefore relates to a process for the preparation of catalysts carprising cobalt on a silica containing carrier, in which a silica-containing carrier is treated with a silicon conpcund of the general formula Si(X)nCY)m(Z), in which the thus treated carrier is contacted with a cobalt compound in the presence of an organic liquid, in which the organic liquid is removed and in which the composition obtained is calcined and activated. Treatment of the carrier with a silicon compound according to the invention can be carried out either in the gaseous phase or in the liquid phase. The preferred treatment time is 1-24 hours and in particular 4-20 hours. The treatment is preferably carried out using a solution of the silicon compound in an organic solvent containing no hydroxyl groups. Suitable solvents are octane, benzene, toluene, xylene, aceonitrile and dimethyl sulfoxide. preference is given to the use of a hydrocarbon or a mixture of hydrocarbons as the solvent. The treatment of the carrier with a solution of a silicon catpund in a solvent is preferably carried out at a temperature of 40-200 C and in particular of 80-150 OC. Said treatment can very suitably be carried out by boiling the carrier and the solution of the silicon compound under reflux. If in the prose s8 according to the invention a silicon compound is used in which halogen, alkoxy or acyloxy occurs as group X, preference is given to chlorine, methoxy or ethoxy and acetyloxy, respectively. If a silicon compound is used in which a hydrocarbyl group occurs as group Y, preference is given to methyl and ethyl. If a silicon compound is used in which as the group Z an oxygen-containing group occurs which does not belong to the alkoxy and acyloxy class, or in which a nitrogen-containing group occurs as group Z, preference is given to -O-Si(Y)3 and -NH- Si(Y)3. In the process according to the invention preference is given to the use of silicon oampounds of the general formula Si (X)2 (Y) (Z), and in particular those in which the two groups X are similar. Examples of suitable silicon impounds which are eligible for use in the process according to the invention that may be mentioned are: Si (OC2H5) 3H = triethyloxysilane; Si (CH3) 3C1 = trimethylchlorosilane; Si(CH3CC0)3H = triacetyloxysilane; SiCl4 = tetrachlorosilane; [{CH3)3Si]2NH = di (trimethylsilyl) amine; [(CH3)3Si]2O = di(trimethylsilyl) di (trimethylsilyl)oxide. The catalysts which are prepared according to the invention oomprise cobalt supported on a silica-containing carrier. Suitable carriers are inter alia silica, silica-alumina and silicamagnesia. Preference is given to the use of silica as carrier. The quantities of cobalt present on the catalysts may vary within wide ranges. It is preferred to prepare catalysts comprising 3-60 parts by weight of cobalt and in particular 5-50 parts by weight of cobalt per 100 parts by weight of carrier material. The catalysts which are prepared according to the invention preferably comprise one or more promotes. Pranoters suitable for the present cobalt catalysts are iron, magnesium, zinc and thorium. It is preferred to prepare catalysts which ocoprise zirconium, titanium, chrcmium or ruthenium as promoter. Special preference is given to the use of zirconium as promoter. The preferred quantity of promoter present on the cobalt catalysts is 0.1-5 parts by weight per 100 parts by weight of carrier. The preparation of catalysts according to the invention which, in addition to cobalt, comprise a promoter is preferably carried out by first depositing the cobalt on the carrier, and after calcination of the cobalt-loaded carrier, the promoter. If desired, the cobalt and the promoter may be deposited on the carrier simultaneously. The deposition of the cobalt is carried out by contacting the carrier which has been treated with the silicon carpund with a cobalt carpound in the presence of an organic liquid. For this purpose use is preferably made of a solution of a cobalt compound in an organic solvent. Very suitable solvents for the purpose are methanol, ethanol and glycol. If the deposition of the cobalt onto the carrier using a solution of a cobalt compound in an organic solvent is carried out in the conventional manner by contacting the carrier for a considerable period of time at room temperature with a relatively dilute cobalt solution, this leads to catalysts in which the cobalt is distributed homogeneously over the carrier, viz. at every point in the catalyst particle the cobalt concentration is virtually the same. A recent investigation into the use of catalysts comprising cobalt supported on a carrier for the preparation of hydrocarbons fran N /CO mixtures has shown that catalysts in which the cobalt distribution over the carrier material is inhomogenous in a specific manner, show higher C5+ selectivities than similar catalysts in which the cobalt is distributed over the carrier homogeneously. It has been found that the desired inhomogeneous cobalt distribution over the carrier is attained by submersing the carrier once or several times in a solution of a cobalt compound in an Organic solvent, removing the liquid from the composition after each submersion, and seeing to it that during each submersion the following relation between viscosity measured at 60 C (v in cS) and temperature (T in K) of the solution, and the submersion time (t in s) is satisfied: log v 104 > 1. In the catalyst preparation according to the t x T invention it is preferred to make use of this finding. The present patent application also relates to the use of the catalysts prepared according to the invention far the conversion of a H2/CO mixture into hydrocarbons. Preparatory to becaning eligible for this purpose, the cobalt catalysts should be activated. This activation can suitably be carried out by con- tacting the catalysts at a temperature between 200 and 350 C with hydrogen or a hydrogen containing gas. The aeeersion of the H2/CO mixture into hydrocarbons by using a catalyst according to the invention is preferably carried out at a temperature of 125-350 C and in particular of 175-275 C and a pressure of 5-100 bar and in particular of 10-75 bar. Further, the conversion is preferably carried out by contacting the H2/CO mixture with a catalyst which is present in the form of a fixed bed. H2/CO mixtures which are eligible to be converted into hydrocarbons according to the invention can very suitably be obtained by steam reforming or partial oxidation starting from light hydrocarbons, such as natural gas. The H2/00 mixture which is converted into hydrocarbons according to the invention preferably has a H2/CO molar ratio higher than 1.5. If the feed has a H2/CO molar ratio lower than 1.5, it is preferred to increase the latter to a value lying between 1.5 and 2.5 and in particular between 1.75 and 2.25, before contacting the feed with the cobalt catalyst. The H2/CO molar ratio of hydregen-poor H2/CO mixtures can be increased by, inter alia, addition of hydrogen, removal of carbon monoxide, mixing with a hydrogen-rich H2/CO mixture or by subjecting the hydrogen-poor H2/00 mixture to the shift reaction. The conversion of the H2/CO mixture according to the invention can suitably be used as an independent process in which unssnverted synthesis gas can be recirculated, if desired. Further, the conversion of the H2/CO mixture according to the invention can very suitably be used as the first step in a step process for the preparation of middle distillates fran H2/CO mixtures. For it has been found that catalysts containing silica or silica-alumina as carrier and cobalt together with zirconium, titanium, chranium and/or ruthenium as catalytically active metals, which catalysts have been prepared by depositing the metals concerned on the carrier material by impregnation and/or kneading, yield a product substantially consisting of unbranched paraffins whose high-boiling part can be converted in high yield into middle distillates by subjecting it to a hydrocracking treatment. Although in the preparation of middle distillates from the product obtained over the cobalt catalyst the part of the product whose initial boiling point lies above the final boiling point of the heaviest middle distillate desired as end product will do as feed for the hydrocracking, the total C5+ fraction of the product prepared over the cobalt catalyst may also be used for the purpose, if desired. The hydrocracking is carried out by contacting the fraction to be treated at elevated temperature and pressure and in the presence of hydrogen with a catalyst containing one or more Group VIII noble metals on a carrier. The hydrocracking catalyst used by preference is a catalyst comprising 0.2-1 %w of platinum or palIdium supported on silica-alumina as carrier. The hydro cracking treatment is preferably carried out at a temperabure of 250-350 C and a pressure of 10-75 bar. invention is now illustrated with the aid of the hollowing example. Exsaple- Catalyst preparation Nine Co/SiO2 catalysts (Catalysts 1-9), some of which had and sane of which had not been promoted with Zr or Ru, were prepared as follows starting fran a gJdbular silica carrier which previously had been calcined at 500 C and then exposed to the air for 24 hours (hereinafter referred to as Silica A). The starting material used for the preparation of Catalysts 1-3 was Silica A as such. For the preparation of Catalysts 4-6, a Silica B was used, and for the preparation of Catalysts 7-9, Silica C, the latter tso silicas having been preipared from Silica A by treatment with a silicon compound. Silica B This silica was prepared by boiling under reflux for 12 haurs a mixture of 20 g of Silica A, 10 g of thiethcsysilane and 200 ml of toluene. The Silica B obtained was filtered off, washed three times with methanol and dried in vacua for 16 hours at 80 OC, Silica C This silica was prepared in substantially the same manner as Silica B, the difference being that now, instead of 20 g of triethoxysilane, 8 g of di(trimethylsilyl)amine was used. Catalysts 1, 4 and 7 These catalysts, which per 100 parts by weight of silica comprised 25 parts by weight of cobalt, were prepared by impregnation of the silica carriers concerned with a solution of cobalt nitrate in ethanol, followed by drying and calcination of the oompositions at 500 C. Catalysts 2, 5 and 8 These catalysts, which per 100 parts by weight of silica comprised 25 parts by weight of cobalt and 0.9 parts by weight of zirconium, were prepared by impregnating the silica carriers cancerned with a solution of cobalt nitrate in ethanol and, after drying and calcination at 500 OC, impregnating the cobalt-loaded carriers with a solution of zirconium nitrate in water, followed by drying and calcination at 500 OC. Catalysts 3, 6 and 9 These catalysts, which per 100 parts by weight of silica comprised 25 parts by weight of cobalt and 0.5 parts by weight of ruthenium, were prepared by impregnating the silica carriers concerned with a solution comprising cobalt nitrate and ruthenium chloride in ethanol, followed by drying and calcination of the catpositions at 500 CC. In the preparation of Catalysts 1-9 the quantity of liquid used in each impregnatian step was of such a volume as to correspond substantially with the pore volume of the carrier. Catalysts testing Catalysts 1-9 were used in nine experiments (Experiments 1-9) in the preparation of hydrorbns from a mixture of carbon monoxide and hydrogen having a H/0O molar ratio 2. The experiments were carried out at a pressure of 20 bar, a temper- ature of 220 C and a space velocity of 600 NI. l.h 1 in a reactor containing a solid catalyst bed. Preceding the testing the catalysts were activated by treatment with hydrogen at 250 C. The results of Experiments 1-9 are given in the table. Of the catalysts mentioned in the table, only catalysts 4-9 are catalysts according to the invention. In the preparation of these catalysts the cobalt was deposited on a silica carrier which had previously been treated with a silicon compound. Catalysts 1-3, where the cobalt was deposited on a non-pretreated carrier, fall outside the scope of the invention. They have been included in the patent application for oomparison. Of the experiments mentioned in the table, only Experiments 4-9 are experiments according to the invention. In these experiments, which were carried out by using catalysts prepared according to the invention, very high activities were observed Experiments 1-3 fall outside the scope of the invention. In these experiments, which were carried out by using catalysts which had not been prepared according to the invention, considerably lower activities were attained. STABLE Experiment Catalyst Catalyst oomposition H2+CO oonversion, No. No. parts by weight %vol 1 1 25 Co/100 SiO2 (A) 55 2 2 25 Co/0.9 Zr/100 SiO2 (A) 60 3 3 25 Co/0.5 Ru/100 SiO2 (A) 63 4 4 25 Co/100 SiO2 (B) 81 5 5 25 Co/0.9 Zr/100 SiO2 (B) 86 6 6 25 Co/0.5 Ru/100 SiO2 (B) 94 7 7 25 Co/100 SiO2 (C) 75 8 8 25 Co/0.9 Zr/100 SiO2 (C) 81 9 9 25 Co/0.5 Ru/100 SiO2 (C) 90

Claims: CLAIMS 1. A process for the preparation of catalysts comprising cobalt supported on a silica-containing carrier, characterized in that a silica-containing carrier is treated with a silicon compound of the general formula Si(X)n(Y)m(Z), wherein X = halogen, alkoxy and/or acyloxy; Y = H and/or a hydrocardyl group; Z = halogen or a nitrgen-contnining or an oxgen-containing group; n = 0-3; num = 3, that the carrier thus treated is contacted with a cobalt cceçcund in the presence of an organic liquid, that the organic liquid is removed and that the composition obtained is calcined and activated. 2. A process as claimed in claim 1, characterized in that the treatment time is 1-24 hours. 3. A process as claimed in claim 2, characterized in that the treatment time is 4-20 hours. 4. A process as claimed in any one of claims 1-3, characterized in that the treatment is carried out using a solution of a silicon carpound in an organic solvent which contains no hydroxy moieties. 5. A process as claimed in claim 4, characterized in that the solvent used is a hydrocarbon or a mixture of hydrtcarbons. 6. A process as claimed in claim 4 or 5, characterized in that the treatment is carried out at a tenperature of 40-200 CC. 7. A process as claimed in claim 6, characterized in that the treatment is carried out at a temperature of 80-150 OC. 8. A process as claimed in any one of claims 4-7, characterized in that the treatment is carried out by boiling the carrier with the solution of the silicon campc{nd under reflux. 9. A process as claimed in any one of claims 1-8, characterized in that a silicon compound is used in which the occurring group X is halogen, alxcxy or acyloxy, which group is present as chlorine, methoxy or ethoxy, or acetyloxy, respectively. 10. A process as claimed in any one of claims 1-9, characterized in that a silicon compound is used which the occurring group Y is a hydrccarbyl group, which group is present as methyl or ethyl. 11. A process as claimed in any one of claims 1-10, characterized in that a silicon compound is used in which the occurring group Z is an oxygen-containing group which des not belong to the alkoxy and acyloxy class, or in which the occurring group Z is a nitrogen-containing group, which group is present as -O-Si(Y)3 or -NH-Si(Y)3 respectively. 12. A process as claimed in any one of claims 1-10, characterized in that use is made of a silicon compound of the general formula Si(X)2(Y) (Z). 13. A process as claimed in any one of claims 1-12, characterized in that per 100 parts by weight of carrier the catalyst carprises 5-50 parts by weight of cobalt and 0.1-5 parts by weight of promoter. 14. A process as claimed in any one of claims 1-13, characterized in that the catalyst comprises one ar more promoters chosen fran zirconium, titanium, chromium and ruthenium. 15. A process as claimed in any one of claims 1-14, characterized in that the carrier is submerged in the solution once or several times, that after each subversion the liquid is removed from the composition, and that during each submersion the following relation between viscosity measured at 60 C (v in cS) and temper- ature (T in CK) of the solution and the submersion time (t in s) is satisfied: logv x 104 > , 1. txT 16. A process for the preparation of catalysts comprising cobalt supported on a silica-containing carrier as claimed in claim 1, substantially as described hereinbefore and in particular with reference to the example. 17. Catalysts which comprise cobalt supported on a silicacontaining carrier and which have been prepared by a process as described in claim 16. 18. A process for the preparation of hydrocarbons by catalytic reaction of carbon monoxide with hydrogen, characterized in that a H2/CO mixture is contacted at elevated temperature and pressure with a catalyst as claimed in claim 17. 19. A process as claimed in claim 18, characterized in that it is used as the first step in a twc-step process for the preparation of middle distillates fran H2/CO mixtures, that in the first step use is made of a catalyst which carprises silica or silica-alumina as carrier and cobalt together with zirconium, titanium, chranium and/or ruthenium as catalytically active metals, which catalyst has been prepared by depositing the metals concerned on the carrier material by imçregnation and/or kneading, and that of the product prepared in the first step at least the part whose initial boiling point lies above the final boiling point of the heaviest middle distillate desired as end product is subjected in the second step to a hydrocracking treatment by contacting it at elevated temperature and pressure with a catalyst comprising one or more noble metals fran Group VIII supported on a carrier. 20. A process for the preparation of hydrscarbcns as claimed in claim 18, substantially as described hereinbefore and in particular with reference to the example. 21. Hydrocecarbons whenever prepared according to a process as described in claim 20.

Inventors: SUDHOLTER, ERNST JAN ROBERT TH TWENTE, Sudhölter, Ernst Jan Robert TH Twente
Applicants: SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V.
Application year: 1985
Main classification: B01J23
IPC codes: C10G3, B01J23, B01J37, C07B61, C07C67, C07C1, B01J31, C10G2, B01J21