CATALYST FOR SYNTHESIS OF HYDROCARBONS FROM SYNTHESIS GAS, PROCESS OF PREPARATION OF CATALYST Field of the invention The present invention relates to a catalyst useful in the synthesis of hydrocarbons from synthesis gas. The present invention also relates to a process for the preparation of a catalyst useful for the production of hydrocarbons from synthesis gas. The present invention particularly relates to preparation of a catalyst for production of wax from synthesis gas. The invention finds its usage in synthesising hydrocarbons, specifically wax, using Fisher- Tropsch Synthesis.

Background of the invention Synthesis gas, or"syngas, "is a mixture of gases prepared as feedstock for a chemical reaction; for example, carbon monoxide and hydrogen to make hydrocarbons or organic chemicals, or hydrogen and nitrogen to make ammonia.

The conversion of mixtures of carbon monoxide and hydrogen, for example synthesis gas or syngas, is commonly referred to as Fischer-Tropsch synthesis (FTS). Germany produced 15% of its fuels by Fisher Tropsch Synthesis, in addition to chemicals including waxes as by product. The first commercial Fisher Tropsch Synthesis operation used cobalt catalyst which was later referred with iron catalyst. Fischer-Tropsch synthesis was used extensively in Germany during World War II.

There is considerable incentive for use of the process in the conversion of coal to liquid fuels and for conversion of natural gas to liquid fuels. Liquid fuels are more easily transported and utilized than coal. Conversion of natural gas to liquid makes transportation and storage more feasible. Sasol operates commercial Fischer-Tropsch plants in South Africa which employ an iron catalyst (for example Oil and Gas Journal, Jan. 20,1992, p. 53). A large commercial plant using Shell Oil technology has been recently placed in production in Malaysia. These commercial operations typically employ fixed-bed reactor systems; e. g. conversion of natural gas to transportation fuels via The Shell Middle Distillate Synthesis Process by S. T. Sie, etal, Catalysis Today 8, (1991) (371-394).

In principle, all catalysts that are active for Fisher-Tropsch synthesis can be used in slurry reactor systems. The objective of catalyst choice is to obtain the highest possible selectivity of desired liquid hydrocarbon products and the highest possible activity. Iron catalysts have been preferred because of low cost and good activity. However, better catalyst- reactor systems are desired. U. S. Pat. No. 5,162, 284 to Soled et al. describes a copper promoted cobalt manganese spinel catalyst.

Common Fischer-Tropsch catalysts are cobalt, and iron (for example, "The Fischer-<BR> Tropsch Synthesis, "by R. B. Anderson, Academic Press (1984), p. 2). Other Group VIII metals such as ruthenium and osmium are also active. Other metals that have been investigated as primary catalyst components include rhenium, molybdenum, and chromium, but these have very low or no activity and produce primarily methane.

The activity of supported cobalt catalysts can be enhanced, or the performance modified, by the addition of a variety of metals. Exemplary metals include copper (U. S. Pat.

Nos. 5,302, 622 and 5,162, 284), cerium (U. S. Pat. Nos. 3,888, 792; 4,657, 885; 4,801, 573 and 4,880, 763), rhenium (U. S. Pat. Nos. 4,088, 671; 4, 558, 030; 4,568, 663; 4,801, 573 and 4,880, 763) and manganese (U. S. Pat. No. 5,162, 284). Precious metals include platinum, iridium, ruthenium and rhodium (U. S. Pat. Nos. 5,302, 622; 5,059, 574 and 5,102, 851). In addition to enhancing catalyst activity, promoters are added to achieve specific results, e. g., to enhance liquid hydrocarbon production, to suppress methane production, etc. for example, the discussion in U. S. Pat. No. 4,880, 763. U. S. Pat. No. 5,302, 622 references French Patent Application No. 91/07, 634 that describes a catalyst containing cobalt, at least one additional element chosen from molybdenum and tungsten and at least one element chosen from elements including ruthenium and copper.

A series of Shell patents (U. S. Pat. Nos. 4, 522, 939 ; 4, 499, 209; 4, 587, 008 and 4,686, 238) disclose supported cobalt-silica catalysts promoted with zirconium, titanium or chromium. These catalysts are designed for fixed bed operation. Their effectiveness is dependent on the specific nature of metal incorporation on the support, i. e., by sequential impregnations and/or kneading.

U. S. Pat. Nos. 4,801, 573 and 4, 880, 763 recite the use of small amounts of promoter oxides chosen from elements in Groups IIIB, IVB and VB (including zirconia but no promotional effect on either activity or selectivity was shown). US Patent No: 5639798 relates to catalysts having improved activity for the production of hydrocarbons from hydrogen and carbon monoxide and to an improved hydrocarbon synthesis process. Specifically, this invention relates to a catalyst comprising cobalt supported on an inorganic oxide promoted by molybdenum and or molybdenum and zirconium.

US Patent No. 4542122 discloses the development of cobalt-titania or Thorium promoted cobalt-titania catalysts wherein cobalt or cobalt and thoria is composited or dispersed upon titania containing support. The titania is in rutile phase. Reference may be made to US Patent No. 4568663 wherein rhenium is added to cobalt-titania to improve the activity. US Patent No. 5140050 discloses the use of titania in rutile phase. A catalyst for

linear paraffins and olefins by dispersing cobalt, alone or with a metal promoter, particularly rhenium, as a thin catalytically active film upon a particular titania or titania containing support with rutile : anatase ratio=3: 2 was developed. In US Patent No: 5128377 also, the catalyst is prepared by spray coating the cobalt-precursor.

US Patent No: 5036032 discloses a process wherein the support was made by impregnating the molten cobalt salt and the supports were selected from silica, magnesia, alumina, silica-alumina, titania and mixtures thereof. Reference is also made to US Patent No: 4952406 wherein a catalyst comprising titania support has been developed in which inorganic oxide binders from the group consisting of alumina and zirconia has been incorporated. The titania has specific surface area and pore volume and has rutile: anatase weight ratio of al least about 3: 2 to about 100 ; 1 and higher.

Fischer-Tropsch processes using iron-based catalysts including cobalt as a co-catalyst, are known to produce gaseous and liquid hydrocarbons containing C2-C4 olefins. Because of the importance of C2-C4 olefins, particularly as feed stocks for the chemical industry, modifications of the Fischer-Tropsch process are constantly being pursued toward the goals of maximizing C2-C4 olefin selectivity while maintaining high catalyst activity and stability under the reaction conditions. The main thrust of the efforts in this area has been in the area of new catalyst development.

Reference is made to US Patent No: 4,532, 229 which describes that the use of relatively stable iron carbonyl complexes e. g. Bis (dicarbonylcyclopentadienyliron), and lower melting cobalt carbonyl complexes, facilitates production of mixed metal catalysts for conversion ofCO/H2 to alpha-olefins. The decomposition of these materials can be achieved in a controlled manner resulting in an excellent alpha-olefins synthesis catalyst in Fischer- Tropsch processes. The process is generally carried out by placing the iron and cobalt carbonyl complex materials in a liquid hydrocarbon used as a slurry liquid Reference is also made to US Patent No: 4,670, 475 a rhenium promoted cobalt catalyst has been described, especially a rhenium and thoria promoted cobalt catalyst, and process for the conversion of methanol to hydrocarbons. Methanol is contacted, preferably with added hydrogen, over said catalyst, or synthesis gas is contacted over said catalyst to produce, at reaction conditions, an admixture of C10 + linear paraffins and olefins. These hydrocarbons can be further refined to high quality middle distillate fuels, and other valuable products such as diesel fuel, jet fuel, lubes and speciality solvents, particularly premium middle distillate fuels of carbon number ranging from about C10 to about C20.

The reference J. C. S. Chem. Comm. p. 428-430 (1983) describes complexes such as HFeCo3 (C0) 2 which can effectively be supported on basic supports such as silica modified by amino donor functions. The complexes are described as yielding active Fischer Tropsch catalysts giving rise to an unusual hydrocarbon product distribution.

It has been found that the addition of magnesium together with zirconium on an inorganic oxide support, preferably titanium oxide, substantially increases the effectiveness of cobalt catalysts useful for the conversion of synthesis gas to hydrocarbons.

The above-mentioned processes for development of catalysts suffers from low activity, requiring multiple steps at low syn gas throughput.

Objects of the invention The main object of the invention is to provide a novel catalyst useful in the synthesis of hydrocarbons from synthesis gas which obviates the drawbacks of the prior art enumerated above.

It is another object of the invention to provide a process for the preparation of a catalyst, useful for synthesis of wax from synthesis gas which obviates the drawbacks as detailed above.

Another object of the invention is to produce a catalyst having high selectivity.

Yet another object of the invention is to provide a process for the synthesis of hydrocarbons from synthesis gas which is simple and economically efficient.

Summary of the invention Accordingly the present invention provides a process for preparation of a catalyst, useful for synthesis of hydrocarbons from synthesis gas which comprises addition of Magnesium Nitrate and Cobaltous Nitrate in a desired proportion in the range of 1: 1.5 to 1: 3.0 (w/w) to an appropriate amount of distilled water in the range of 1.5 to 3.5 litres so as to yield 8 to 15 wt % of the solution; warming the said solution at a temperature in the range of 60 to 90 degree Celsius under continuous stirring; addition of 8 to 15 wt % of sodium bicarbonate solution drop wise till the pH of the said solution reads in the range of 7.5 to 8.5 under continuous stirring, maintaining the temperature of the solution in the range of 60 to 90 degree Celsius; addition of ground mixture of Zirconium oxide and Titania in a proportion in the range of 1 : 4 to 1 : 6 (w/w) under stirring for a time period in the range of 20 to 50 minutes; filtering the resultant solution under vacuum; washing the residue with demineralised water to make it nitrate free; transferring the solid mass to a porcelain basin and drying in an oven at temperature in the range of 65 to 80 degree Celsius for a time period

in the range of 6 to 15 hours; cooling the mass and preparing pellets of size 10 mm x 4 mm & crushing to small pieces of-6+14 mesh (BSS) size.

In an embodiment of the present invention titania used is preheated at temperature in the range of 500 to 600 degree Celsius for a time period in the range of 12 to 20 hours.

In another embodiment of the present invention the nitrate free test is performed using conventional brown ring test.

The preferred catalyst contain from about 5% to 50% cobalt and from about 0.1% to 10% magnesium or magnesium and zirconium. Specifically, the improved catalyst comprises magnesium and cobalt and an titania support, the catalyst containing from about 2% to 50% cobalt and from about 0.1% to 15% magnesium and optionally from about 0.1% to 10% zirconium, based on the total weight of the catalyst, the weight ratio of magnesium to cobalt being from about 0.02 to 0.25 and the support having a particle size range of about 5 to 250 microns.

Detailed description of the invention The process of the invention comprises preparation of a catalyst useful for synthesis of hydrocarbons from synthesis gas, by the addition of Magnesium Nitrate and Cobaltous Nitrate in a desired proportion in the range of 1: 1.5 to 1: 3.0 (w/w) to an appropriate amount of distilled water in the range of 1.5 to 3.5 litres so as to yield 8 to 15 wt % of the solution ; warming the said solution at a temperature in the range of 60 to 90°C under continuous stirring ; addition of 8 to 15 wt % of sodium bicarbonate solution drop wise till the pH of the said solution reads in the range of 7.5 to 8. 5 under continuous stirring, maintaining the temperature of the solution in the range of 60 to 90°C ; addition of ground mixture of Zirconium oxide and Titania in a proportion in the range of 1: 4 to 1: 6 (w/w) under stirring for a time period in the range of 20 to 50 minutes; filtering the resultant solution under vacuum; washing the residue with demineralised water to make it nitrate free ; transferring the solid mass to a porcelain basin and drying in an oven at temperature in the range of 65 to 80°C for a time period in the range of 6 to 15 hours; cooling the mass and preparing pellets of size 10 mm x 4 mm and crushing to small pieces of-6+14 mesh (BSS) size.

Titania is preferably preheated at temperature in the range of 500 to 600°C for a time period in the range of 12 to 20 hours. The nitrate free test is performed using conventional brown ring test. The preferred catalyst contain from about 5% to 50% cobalt and from about 0.1% to 10% magnesium or magnesium and zirconium. Specifically, the improved catalyst comprises magnesium and cobalt and an titania support, the catalyst containing from about 2% to 50% cobalt and from about 0.1% to 15% magnesium and optionally from about 0.1%

to 10% zirconium, based on the total weight of the catalyst, the weight ratio of magnesium to cobalt being from about 0.02 to 0.25 and the support having a particle size range of about 5 to 250 microns.

The novelty of the present invention lies in preparing the catalyst, having titania in anatase phase only and having high yield and high selectivity under environment-friendly condition, using minimum number of steps in comparison to prior art processes and the inventive step lies in non-obvious steps of the process of the preparation.

The following examples are given by way of illustration of the present invention and should not be construed to limit the scope of the present invention.

Example-1 185 grams of cobaltous nitrate hexahydrate and 79.5 grams of magnesium nitrate hexahydrate were added to 2.66 litres of distilled water to yield 10 wt % of the solution (Solution A). 62.5 grams of titania (pre heated at 560°C for 16 hours) and 12.5 grams of zirconium oxide were mixed and ground.

Solution A was warmed at 80°C under continuous stirring and 10 wt % sodium bicarbonate solution, at 80°C, was added drop wise till pH of the solution became 8, where heating and addition of sodium carbonate were stopped. The ground mixture of titanium oxide and zirconium oxide was added to the solution and stirring continued for 30 minutes.

The resulting solution was filtered under vacuum using a vacuum pump and washed with 20 liters of demineralised water to make it nitrate free (this was checked by conventional brown ring test). The solid mass was transferred to a porcelain basin and dried in a moisture oven at 70 5°C for 10 hours. It was cooled and prepared as pellets of size (10 mm x 4mm) and crushed to small pieces, sized to-6 +14 mesh (BSS).

Example-2 126.5 grams of cobaltous nitrate hexahydrate and 50.5 grams of magnesium nitrate hexahydrate were added to 2.66 litres of distilled water to yield 10 wt % of the solution (Solution A). 100 grams of titania (preheated at 500°C for 13 hours) and 20 grams of zirconium oxide were mixed and ground.

Solution A was warmed at 90°C under continuous stirring and 10 wt % sodium carbonate solution, at 90°C, was added drop wise till pH of the solution became 8, where heating and addition of sodium bicarbonate were stopped. The ground mixture of titanium oxide and zirconium oxide was added to the solution and stirring continued for 40 minutes.

The resulting solution was filtered under vacuum using a vacuum pump and washed with 20 liters of demineralised water to make it nitrate free (this was checked by conventional brown

ring test). The solid mass was transferred to a porcelain basin and dried in a moisture oven at 70 5°C for 09 hours. It was cooled and prepared as pellets of size (10 mm x 4 mm) and crushed to small pieces, sized to-6 +14 mesh (BSS).

Example-3 130 grams of cobaltous nitrate hexahydrate and 52 grams of magnesium nitrate hexahydrate were added to 2.66 litres of distilled water to yield 10 wt % of the solution (Solution A). 100 grams of titania (preheated at 500°C for 13 hours) and 20 grams of zirconium oxide were mixed and ground.

Solution A was warmed at 80°C under continuous stirring and 10 wt % sodium carbonate solution, at 80°C, was added drop wise till pH of the solution became 8, where heating and addition of sodium bicarbonate were stopped. The ground mixture of titanium oxide and zirconium oxide was added to the solution and stirring continued for 40 minutes.

The resulting solution was filtered under vacuum using a vacuum pump and washed with 20 liters of demineralised water to make it nitrate free (this was checked by conventional brown ring test). The solid mass was transferred to a porcelain basin and dried in a moisture oven at 70 + 5°C for 09 hours. It was cooled and prepared as pellets of size (10 mm x 4 mm) and crushed to small pieces, sized to-6 +14 mesh (BSS).

The main advantages of the present invention are : 1. The process is very simple.

2. The operating conditions are easy to manage.