Title of Invention

"PROCESS FOR PRODUCING AN ACTIVE HIGHLY ACIDIC MICROPOROUS SOLID CATALYST"

Abstract

A process for producing an active highly acidic microporous solid catalyst comprising sulphated metal oxide coated with carbon molecular sieves and optionally heteropoly acid and having pore volume in the range of 0.1-0.2 cm3/g and pore size distribution in the range of 25-40 °A, said process comprising : i. providing sulphated zirconia, said sulphated zirconia optionally wetted with solvent; ii. coating the sulphated zirconia with at least one carbon molecular sieve modifying agent/precursors selected from polyfurfuryl alcohol, phenol-formaldehyde resin, polyvinyl alcohol, and polyacrylo nitrile and optionally heteropoly acid; iii. drying the carbon molecular sieve precursor coated sulphated zirconia at a temperature between 100-150°C; iv. calcining the carbon molecular sieve precursor coated sulphated zirconia at a temperature up to 350°C to thereby obtain the sulphated zirconia in the form of shape selective microporous solid catalyst.

Full Text

The present invention relates to a process of preparing an solid catalyst for use in acid catalyzed organic reactions such as Friedel-Craft's reaction, nitration, cyclization. This invention particularly relates to the preparation of catalysts for use in acid catalyzed organic reactions which occur in the microporous range of the catalysts such as nitration of aromatic compounds, cyclization of terpenoids and more particularly relates to the preparation of modified sulfated zirconia catalysts. Laszlo, P. and Pennetraeu, P., J. Org. Chem., 52, 2407, 1987 have shown that copper nitrate supported K-10 clay (see Table 1C) gives the best o:p ratio of 1:7.5 so far reported for nitration of chlorobenzene. However, this catalyst did not give adequate para product, which is an important drug intermediate. Shabtai, J., Lazar, R. and Biron, E., J. Mol. Cat., 27, 35, 1984 have shown that depending on the alkali metal introduced in to the zeolite, the reaction yields either citronellol or isopulegol. With NaX, 85 % isopulegol and 14 % citronellol are obtained at 87 % conversion of citronellal, while with CsX 92 % citronellol is obtained at 77 % conversion. However, this is rather attributed to a difference in pore dimension than to a difference in basicity. Superacids as Catalysts Superacids like K-10 clay, zeolites, silica-alumnia, sulfated metal oxides, like sulfated zirconia, etc. are substances known to have acidity higher than that of 100 % sulfuric acid. Preparation of Sulfated Zirconia (S-ZrO2) A variety of methods have been reported for the preparation of sulfated zirconia. These methods differ mainly in the type of precursor, type of precipitating agent, type of sulfating agent, method of impregnation, calcination temperature, etc. The type of precursor for preparing sulfated zirconia plays a vital role in the final texture and hence, the performance of the catalyst. Various zirconium compounds such as Zr(NO3)4, ZrCl4, zirconium isopropoxide, zirconyl chloride, zirconium oxychloride and sometimes, zirconia itself are used to prepare these catalysts. Various precipitating agents like aqueous ammonium hydroxide, and urea have been reported (Yamaguchi, T. and Tanabe, K., Mater. Chem. Phys., 16, 67, 1986). Sometimes hydrogen sulfide and sulfur dioxide are also used as sulfating agents. Amorphous zirconium hydroxide obtained by the alkaline hydrolysis of the zirconia precursor is usually sulfated before it is crystallized by thermal treatment. The sulfating species most commonly used are sulfuric acid and ammonium sulfate (Sohn, J.R. and Kim, H.W., J. Mol. Catal. 52, 361, 1989). The sulfated species is then thermally crystallized whereby it undergoes phase transformation, the tetragonal phase being stabilized as a result of sulfate incorporation. Sulfated zirconia as such, prepared by co-precipitation of zirconium oxychloride with ammonia followed by sulfation, is a highly superacidic catalyst. Sulfated zirconia, prepared by sol-gel method, is also highly superacidic. However, co-precipitated zirconia is cost effective. Many industrially important reactions have been studied for the use of sulfated zirconia because of its superacidic character. Some of these reactions are Friedel-Crafts alkylation, acylation, condensation, esterification, etherification, nitration, isomerization, cracking, dehydration, oligomerization, etc. But one of the major drawbacks of sulfated zirconia is that it is not a shape selective catalyst. Carbon Molecular Sieves (CMS) and CMS Coated Catalysts Carbon molecular sieves (CMS) are substances which have micro- or mesopores depending on the source and the method of preparation. They are mostly used in the separation of gases like nitrogen and oxygen gas from air, methane and ethane gas, etc. CMS are prepared from coal, by pyroh/sis of precursor polymeric materials like poryacrylonitrile, phenol formaldehyde resin, potyvinylidene chloride, poh/furfuryl alcohol, potyvinyl alcohol, etc. or any combination of the above. CMS prepared by pyrorysis of polymers are found to be inert having absolutely no catalytic activity. The diffusivities of molecules through the ultramicroporous networks of CMS materials display a strong dependence on the critical kinetic diameter of the molecule. Hence the concept of coating carbon molecular sieves on superacids has been explored. Foley, H.C., Perspectives in Molecular Sieve Science, American Chemical Society, 335, 1988, reports that the research groups of Walker and Trimm were the first to have investigated the reactant shape-selectivity of metal containing carbon molecular sieves. Trimm and Cooper (Chem. Commun., 477, 1970; j/. Catal., 31, 287, 1973) and Schmitt and Walker (Carbon, 9, 791, 1971; Carbon, 10, 87, 1972), studied CMS/Pt catalysts for the shape selective hydrogenation of gas phase olefins. There were further developments in this field whereby a composite mixture of inorganic oxides (e.g., SiO2, TiO2, ZrO2, TiO2- ZrO2 etc.) modified with CMS could be used as catalyst. It is the basic objective of the present invention to provide an active highly acidic microporous solid catalyst, the pore dimension of which will favour the selective cyclizations and nitrations. Another objective of the invention is to provide a process for producing tailor made active highly acidic microporous solid catalysts for reaction such as mono-nitration with high para-selectivity, cyclization with high 1-isomer formation. Yet further object of the present invention is directed to selecting the proper solid acid catalysts which would provide improved selectivity towards the formation of the desired products through selective cyclization and nitration. Yet further object of the invention is directed to develop a novel composite catalyst by combining the activity of solid acid catalyst and pore selectivity of CMS. STATEMENT OF INVENTION Thus according to basic aspect of the invention there is provided a process for producing an active highly acidic microporous solid catalyst comprising sulphated metal oxide coated with carbon molecular sieves and optionally heteropoly acid and having pore volume in the range of 0.1-0.2 m3/g and pore size distribution in the range of 25-40°A, said process comprising : i) providing sulphated zirconia, said sulphated zirconia optionally wetted with solvent; ii) coating the sulphated zirconia with atleast one carbon molecular sieve modifying agent/precursors selected from polyfurfuryl alcohol, phenol-formaldehyde resin, polyvinyl alcohol, and polyacrylo nitrile and optionally heteropoly acid; iii) drying the carbon molecular sieve precursor coated sulphated zirconia at a temperature between 100-150°C; and iv) calcining the carbon molecular sieve precursor coated sulphated zirconia at a temperature up to 350°C to thereby obtain the sulphated zirconia in the form of shape selective microporous solid catalyst. Thus according to one aspect of the present invention there is provided an active highly acidic microporous solid catalyst comprising sulfated metal oxide and atleast one of carbon molecular sieve and/or heteropoly acid and having pore volume in the range of 0.1-0.2 m3/g and pore size distribution in the range of 25-40 A. In accordance with a preferred aspect of the invention the active highly acidic microporous sulfated zirconia solid catalyst comprise said sulfated metal oxide and atleast one of said carbon molecular sieve and/or heteropoly acid and having BET surface area in the range of 60-165 m2/g, pore volume in the range of 0.1 to 0.2 m3/g, and pore size distribution in the range of 25-40 A and d-spacing in the range of 1.5 to 3.75 A for all the peaks and in the range of 1.8-3.25 °A for high intensity peaks. The solvent used in step (ii) above for wetting the sulfated zirconia is selected from aliphatic. aromatic, cyclic or chlorinated hydrocarbons, aliphatic alcohols, aliphatic ketones. In the above process depending upon the precursor coating material used in step (ii) the calcining temperature varied. In particular, when the carbon molecular sieve precursor coating material in step ii above used is polyvinyl alcohol the calcination temperature in step iv is 100°C - 350°C and when the precursor coating material step ii above used is dodecatungstophosphoric acid then the calcination temperature in step iv is 200°C - 250°C. The active catalytic phase of the CMS/S-ZrO2 material of the present invention is the solid acid S-ZrO2, which is a well known superacid catalyst whereas the CMS acts as barrier for the bulkier molecules. The carbon molecular sieve of the present invention is synthesized from a precursor material. Examples of preferred precursor materials are polyacrylonitrile, phenol formaldehyde resin, polyvinylidene chloride, polyfurfuryl alcohol, polyvinyl alcohol or any combination of the above. A preferred method of forming the carbon molecular sieves used in the production of the CMS/S-ZrO2 material of the present invention is the pyrolysis of polyvinyl alcohol. However, any known method of forming microporous carbon materials or carbon molecular sieves can be used in the production of CMS/S-Zr02 material of the present invention. The active phases of the HPA/S-ZrO2 material of the present invention are both the Bronsted acid sites of HPA and the Lewis acid sites of S-ZrO2 whereby making them useful for nitration any cyclization reactions. The process of present invention is for the preparation of catalysts of both the types, CMS/S-ZrO2 and HPA/S-ZrO2 catalysts. In particular the process for preparation of the catalysts comprises: preparation of zirconium hydroxide by conventional precipitation technique; treating the zirconium hydroxide formed with sulfating agents such as sulfuric acid, ammonium sulfate, etc., calcining the reaction product at 200-700 °C, to get sulfated zirconia; mixing the sulfated zirconia (after pulverizing) and a solution of a precursor material such as PVA dissolved in water, phenol-formaldehyde dissolved in acetone, HPA disserved in methanol, by incipient wetness technique to get precursor coated sulfated zirconia; drying the precursor coated sulfated zirconia at 100-150 °C; treating the dry precursor coated sulfated zirconia at temperature equal to or less than that used in calcining step for getting sulfated zirconia, in air or in inert atmosphere, upto 4 hours depending on me precursor material used. EXAMPLES The invention, its objective and advantages, will now be illustrated by way of non-limiting examples. Examples are by way of illustration only and in no way restrict the invention. The CMS modified sulfated zirconia catalysts are classified as UDCaT-2 (University of Department of Chemical Technology, University of Mumbai) type of catalysts. Chemicals used in these examples namely, zirconium oxychloride (ZrOCl2.8H2O), dodecatungstophosphoric acid (H3PO4,12WO3.nH2O, molecular weight 2880.17), 25 % ammonia solution (AR Grade) and solvents methanol, benzene, carbon tetrachloride, hexane, cyclohexane were obtained locally from s.d. Fine Chem. Ltd. All the solvents were of AR grade. Poly vinyl alcohol was obtained from Loba Chemie Ltd. (Degree of polymerization: 1700-1800) EXAMPLE 1: Preparation of S-ZrO2[650] S-ZrO2[650] was prepared by the conventional precipitation technique. About 110 g of zirconium oxychloride was dissolved in about 2000 ml of distilled water. This was then filtered to remove any impurities. The solution was then added dropwise simultaneously with 25 % ammonia solution with constant stirring. On addition of both the solution white precipitate of zirconium hydroxide was obtained. The pH of the solution was maintained between 8-10. After complete precipitation, it was allowed to digest for 4 h. The precipitate was then washed and filtered through a buchner funnel. The precipitate was washed and made free of chloride ions and ammonia, as verified from the phenolphthalein and the silver nitrate tests, respectively. This hydroxide was dried in an oven for 24 h at 110 °C. The dried cake was then crushed to obtain the desired particle size. Sulfation of this hydrous zirconia was carried out by percolating a IN sulfuric acid solution through it taken as 15 ml/g of solid hydrous zirconia. The sulfated zirconium hydroxide was then calcined in air at 650 °C for 3 h in a quartz tube to yield the sulfated zirconia catalyst. The catalyst thus obtained was having very good activity for the nitration of chlorobenzene as shown in our co-pending Indian Patent Application entitled "A process for selective nitration of aromatic compounds using UDCaT-2". The catalyst has been further characterized by BET surface area, pore size distribution, pore volume, XRD, SEM and FTIR techniques. This catalyst was found to have a surface area of 100 m2/g by BET method. The pore size of the catalyst was found to be 40 A. The pore volume of the catalyst was found to be 0.107856 cm3/g. SEM of the catalyst shows that the surface was quite smooth which indicates low surface area. For S-ZrO2 the spectra shows a broad peak having shoulder peaks at 1218, 1152, 1066 and 1058 cm'1, which are typical of a chelating bidentate sulfate ion coordinated to metal cation. This structure is stronger than that of usual metal sulfates and due to inductive effect of sulfur oxygen bonds, there is an increase in the Lewis acidity of the Zr4+ metal cation. S-ZrO2 is found to be crystalline in nature and shows a tetragonal structure as can be clearly seen from the XRD pattern. Table 1 gives the d/n and I/I,, values for S-ZrO2. The chemical analysis of the catalyst showed 3.8 % w/w of sulfur. Table 1 XRD analysis of S-ZrO2[650] (Table Removed) EXAMPLE 2: Preparation of Heteropoly Acid (HPA) on S-ZrO2 (HPA/S-ZrO2) The HPA used in this study was dpdecatungstophosphoric acid. 1 g HPA was dissoh/ed in methanol and then impregnated on to 20 g S-ZrO2, as in EXAMPLE 1, followed by drying in an oven at 120 °C for 24 h. This catalyst was then calcined in air at 250 °C for 3 h. The material thus obtained was HPA/S-ZrO2. The x-ray diffraction pattern showed that the catalyst was crystalline in nature. The FT1R peaks in the region 1400-1700 cm-1 indicate the phosphorous linkages that come by way of heteropoly acid deposition. The amount of phosphorous detected in the catalyst was found to be 0.09 % w/w with traces of tungsten. EXAMPLE 3: Preparation of CMS/S-ZrO2 S-ZrO2[650] catalyst was prepared as in EXAMPLE 1. This catalyst was then mixed with poh/vinyl alcohol (PVA) solution (2 g dissolved in 25 ml distilled water at 90 °C with constant stirring) by incipient wetness technique. 2.5 g of sulfated zirconia required 1.3 ml of PVA solution. The mixture was then calcined in air preferably between 350 °C for 3 h. The material, thus obtained, was CMS/S-ZrO2. The catalyst was further characterized by XRD, FTIR, SEM, BET surface area and pore volume. SEM showed that the surface of the catalyst was rough as compared to S-ZrO2 which is probabty due to the CMS coating on the catalyst. XRD analysis of the catalyst showed some additional peaks with respect to that obtained in S- ZrO2. Table 2 shows the XRD results. Similar results were obtained from FTIR spectrum. The BET surface area of this catalyst was found to be 64.30 m2/g. The average pore volume of the catalyst was found to be 0.165 m3/g. The pore size distribution of the catalyst was found to be 29 A. This catalyst was found to give very high selectivity towards the formation of para-product in the nitration reactions as described in our co-pending Indian Patent Application entitled, "A process for,selective nitration of aromatic compounds using UDCaT-2". The catalyst consisted of 1.3 % carbon, 0.5 % hydrogen and about 1 % sulfur. Table 2 XRD analysis of CMS/S-ZrO2 (Table Removed) EXAMPLE 4: Preparation of CMS/HPA/S-ZrO2 HPA/S-ZrO2 catalyst was prepared as in EXAMPLE 2. This catalyst was then mixed with poryvinyl alcohol solution (2 g dissolved in 25 ml distilled water at 90 °C with constant stirring) by incipient wetness technique. The mixture was then calcined at 250 °C for 3 h in air. The material thus obtained was CMS/HPA/S-ZrO2. The catalysts in EXAMPLES 1-4 were found to be high in selectivity towards the formation of para- product as mentioned in the co-pending Indian Patent Application entitled "A process for selective nitration of aromatic compounds using UDCaT-2". EXAMPLE 5: Preparation of Zirconia ZrO2[230-350] ZrO2[230-350] was prepared by the conventional precipitation technique as in EXAMPLE 1 upto to the stage of formation of zirconium hydroxide. This hydroxide was dried in an oven for 24 h at 110 °C. The dried cake was then crushed to obtain the desired particle size. This was then calcined at 350 °C for 3 h. EXAMPLE 6: Preparation of S-ZrO2[230-350] S-ZrO2[230-350] was prepared by the conventional precipitation technique as in EXAMPLE 1 upto the stage of sulfation. The sulfated zirconium hydroxide was then calcined in air at 350 °C for 3 h in a quartz tube to yield the S-ZrO2[230-350] catalyst. The catalyst has been characterized by BET surface area, pore size distribution, pore volume, XRD, FTIR and SEM techniques. This catalyst was found to have a surface area of 160 m2/g by BET method. The pore size of the catalyst was found to be 28 A. The pore volume of the catalyst was found to be 0.115436 cm3/g. It was found to be crystalline in nature. The details of XRD analysis are given in Table 3. The SEM shows that the catalyst surface is smooth as compared to that of CMS/S-ZrO2[230-350]. Here again the FTIR spectrum was found to be very similar to S-ZrO2 except that the peaks were more found to be less intense as compared to S-ZrO2. This can be attributed to the low calcination temperature hence the peaks were not well defined, but still retaining the nature of active site of the catalyst. The catalyst consisted of 4.2 % sulfur. Table 3 XRD analysis of S-ZrO2[230-350] (Table Removed) EXAMPLE 7: Preparation of CMS/S-ZrO2[230-350] S-ZrO2[230-350] was prepared as explained in EXAMPLE 6. This catalyst was then mixed with pofyvinyl alcohol (PVA) solution (2 g dissolved in 25 ml distilled water at 90 °C with constant stirring) by incipient wetness technique. 2.5 g of sulfated zirconia required 1.3 ml of PVA solution. The mixture was then calcined in air at 350 °C for 3 h. The material, Ihus obtained, was CMS/S-ZrO2[230-350]. The catalyst has been characterized by BET surface area, pore size distribution, pore volume, XRD, FTIR, and SEM techniques. This catalyst was found to have a surface area of 145 m2/g by BET method. The pore size of the catalyst was found to be 27 A. The pore volume of the catalyst was found to be 0.108337 cnvVg. It was found to be crystalline in nature from the XRD data and the details are given in Table 4. The SEM shows that the catalyst surface is rough as compared to S-ZrO2[230-350]. This can be attributed to the CMS coating on S-ZrO2[230-350]. The FTIR spectrum of CMS/S-ZrO2[230-350] was found to be very similar to S-ZrO2[230-350] indicating that the nature of active site has not changed even after coating S-ZrO2[230-350] with CMS. The catalyst consisted of 1.3 % carbon, 0.8 % hydrogen and about 1 % sulfur. Table 4 XRD analysis of CMS/S-ZrO2[230-350] (Table Removed) This catalyst was found to be highly selective towards the formation of 1-isopulegol from d-citronellal following selective cyclization of d-citronellal to 1-isopulegol. EXAMPLE 8-11: Preparation of CMS/Solvent/S-ZrO2[230-350] In EXAMPLES 8-11 S-ZrO2[230-350] was prepared as in EXAMPLE 6. 2.5 g of S-ZrO2[230-350] was then soaked in a solvent, as shown in Table 1, to just wetness. This was then mixed with pohyvinyl alcohol (PVA) solution (2 g dissolved in 25 ml distilled water at 90 °C with constant stirring) by incipient wetness technique. 2.5 g of sulfated zirconia required 1-1.5 ml of PVA solution. The mixture was then calcined in air at 350 °C for 3 h. The material, thus obtained, in each example is designated as shown in Table 1. Table 1 Details of EXAMPLES 8-11 (Table Removed) The products of these Examples have given better conversion (except that of EXAMPLE 10). However, in selectivity in cyclization of d-citronellal was slightly low over those Examples in which soaking in solvent is not done, catalyst of EXAMPLE 7 (CMS/S-ZrO2[230-350]). EXAMPLE 12: Preparation of CMS[120]/S~ZrO2[230-350] S-ZrO2[230-350] was prepared as explained in EXAMPLE 6. This was then mixed with poh/vinyl alcohol (PVA) solution (2 g dissoh/ed in 25 ml distilled water at 90 °C with constant stirring) by incipient wetness technique. 2.5 g of sulfated zirconia required 1.3 ml of PVA solution. The mixture was then dried in an oven at 120 °C for 3 h. The material, thus obtained, was CMS[120]/S-ZrO2[230-350]. EXAMPLE 13: Preparation of CMS[230]/S-ZrO2[230-350] S-ZrO2[230~350] was prepared as explained in EXAMPLE 6. This was then mixed with poryvinyl alcohol (PVA) solution (2 g dissolved in 25 ml distilled water at 90 °C with constant stirring) by incipient wetness technique. 2.5 g of sulfated zirconia required 1.3 ml of PVA solution. The mixture was then calcined at 230 °C for 3 h. The material, thus obtained, was CMS[230]/S-ZrO2[230-350]. Catalysts in EXAMPLES 12 and 13 were found to give selectivity as good as that of EXAMPLE 7, in the cyclization of d-citronellaL, following selective cyclization of d-citronellal to 1-isopulegol. However, higher carbonization temperature as that of EXAMPLE 7 is preferred to avoid danger of leaching of the CMS layer. EXAMPLE 14: Preparation of CMS[250]/S-ZrO2 S-ZrO2[650] was prepared as explained in EXAMPLE 1. This was then mixed with poh/vinyl alcohol (PVA) solution (2 g dissolved in 25 ml distilled water at 90 °C with constant stirring) by incipient wetness technique. 2.5 g of sulfated zirconia required 1.3 ml of PVA solution. The mixture was then calcined at 250 °C for 3 h. The material, thus obtained, was CMS[250]/S- ZrO2. Catalyst in EXAMPLE 14 was found to give the same conversion as that of EXAMPLE 3 but the latter is preferred to achieve high selectiviry towards the formation of para- product in nitration of chlorobenzene and toluene following process for selective nitration of aromatic compounds. CHARACTERIZATION OF CATALYSTS CHEMICAL ANALYSIS The results of chemical analysis of the sulfated zirconia catalysts prepared as explained in Examples 1, 3, 6 and 7 are shown in Table 5. Table 5 (Table Removed) SURFACE AREA ANALYSIS The sulfated zirconia catalysts prepared as explained in Examples 1, 3, 6 and 7 show that their BET surface area values are within the range of 60-165 m2/g. PORE VOLUME ANALYSIS Using nitrogen adsorption isotherm pore volume of (he sulfated zirconia catalysts prepared as explained in Examples 1, 3, 6 and 7 was found to be in the range of 0.1-0.2 m3/g. PORE SIZE DISTRIBUTION The pore size distribution of the sulfated zirconia catalysts prepared as explained in Examples 1, 3, 6 and 7 was found to be in the range of 25-40 A. X-RAY DIFFRACTION (XRD) TECHNIQUE The d spacing of the sulfated zirconia catalysts prepared as explained in Examples 1, 3, 6 and 7 was determined and was found to be in the range of 1.5-3.75 A for all the peaks. The d spacing for high intensity peaks was found to be in the range of 1.8-3.25 A. FOURIER TRANSFORM INFRA RED (FTIR) TECHNIQUE The FTIR spectrum was determined for the sulfated zirconia catalysts prepared as explained in Examples 1, 3, 6 and 7 and it was found that the patterns of the spectra of these catalysts were very similar which indicated that the morphology of the catalytic material was retained and was not affected by the carbon molecular sieve coating. WE CLAIM : 1. A process for producing an active highly acidic microporous solid catalyst comprising sulphated metal oxide coated with carbon molecular sieves and optionally heteropoly acid and having pore volume in the range of 0.1-0.2 m3/g and pore size distribution in the range of 25-40 °A, said process comprising : i. providing sulphated zirconia, said sulphated zirconia optionally wetted with solvent; ii. coating the sulphated zirconia with at least one carbon molecular sieve modifying agent/precursors selected from polyfurfuryl alcohol, phenol-formaldehyde resin, polyvinyl alcohol, and polyacrylo nitrile and optionally heteropoly acid; iii. drying the carbon molecular sieve precursor coated sulphated zirconia at a temperature between 100-150°C; and iv. calcining the carbon molecular sieve precursor coated sulphated zirconia at a temperature up to 350°C to thereby obtain the sulphated zirconia in the form of shape selective microporous solid catalyst. 2. A process as claimed in claim 1 wherein the solvent used for wetting the sulphated zirconia is selected from aliphatic, aromatic, cyclic or chlorinated hydrocarbons, aliphatic alcohols, and aliphatic ketones. 3. A process as claimed in claim 1 wherein the heteropoly acid used is dodecatungstophosphoric. 4. A process as claimed in claim 1, wherein said calcining is carried out at between 100°C. and350°C. 5. A process as claimed in claim 1 wherein the solvent used for wetting the sulphated zirconia is selected from carbon tetrachloride, benzene, cyclohexane and hexane. 6. A process for producing an active highly acidic microporous solid catalyst substantially as hereindescribed and illustrated with reference to the accompanying examples.

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