FORM 2
THE PATENTS ACT, 1970
(39 OF 1970)
&
THE PATENT RULES, 2003
COMPLETE SPECIFICATION
(See section 10 and rule 13)
TITLE OF THE INVENTION
"A PROCESS FOR MANUFACTURE OF A CATALYST SUPPORT BY IN SITU FORMATION OF SHELL TYPE REFRACTORY OXIDE ON A SPHERICAL INERT
INORGANIC OXIDE SURFACE"
We, INDIAN PETROCHEMICALS CORPORATION LIMITED, a Government Company incorporated under the Companies Act, 1956, of P. O. Petrochemicals, District Vadodara -391 346, Gujarat, INDIA.
The following specification particularly describes the invention and the manner in which it is to be performed.


Field of invention
The present invention relates to a process for the manufacture of a catalyst support. More particularly, the present invention relates to a process for the manufacture of a spherical catalyst support consisting of a thin annular shell of a catalytically active material in gamma alumina formed in situ on and bonded to a non-active inert core. In particular, the present invention relates to a process for in-situ formation of shell type refractory oxide layer on spherical inter inorganic oxide surface. Prior Art
Most of the hydrocarbon conversion processes use catalysts containing platinum as main active metal along with promoters and modifiers deposited on active spherical alumina support. All components are uniformly dispersed throughout the alumina support. These kinds of catalysts are mainly used in dehydrogenation of hydrocarbons, especially, normal paraffins-, particularly, higher alkanes such as normal decane which are converted to decenes.
U.S. Pat No. 3,878,131 and U.S. Pat. No. 3,761,531 disclose catalysts consisting of a platinum metal, a tin oxide component and a germanium oxide component. A Group VA metallic component, e.g arsenic, antimony and an alkali or alkaline earth component are dispersed on an alumina carrier material with all the components distributed evenly on the carrier. U. S. Pat. Nos. 3,558,477 and 3,562,147 also disclose catalytic composites containing a platinum group component and a rhenium component on a refractory oxide support. These references disclose that the best results are achieved when the platinum group component and rhenium component are uniformly distributed throughout the catalyst.
However, it is also known that in these processes selectivity towards desirable products is inhibited by larger residence time of the feed or/and the products at the active matrix of the catalyst. Hence, a catalyst composition on the periphery of the spherical catalyst support was envisaged. Thus U.S. Pat No. 4,716,143 describes a catalyst in which the platinum group metal is deposited in an outer layer (about 400 u.) of the support- U.S. Pat No. 4,786,625 discloses a catalyst in which the platinum is deposited on the surface of the support where as the modifier metal is evenly distributed throughout the support. U.S. Pat No. 3,897,368 describes a method for the production of a noble metal catalyst where the noble metal is platinum and the platinum is deposited selectively upon the external
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surface of the catalyst. However, this disclosure describes the advantages of impregnating only platinum on the exterior layer and utilizes a specific type of surfactant to achieve the surface impregnation of the noble metal.
Layer of-active metal oxide coated on oxide support is disclosed in U.S. Pat No. 4,077,912 and 4,255,253 Combination of the active metal oxide were also used in the coating. W098/14274 discloses a catalyst which comprises a catalytically inert core material on which is deposited and bonded a thin shell of material containing active sites.
U.S. Pat No. 5,516,740 discloses a thin outer shell of catalytic material bonded to an inner core of catalytically inert material. The outer layer coating comprises of finely divided catalytically active material in slurry of colloidal boehmite/pseudo boehmite which is then calcined to convert the boehmite/pseudo boehmite into gamma, alumina thereby bonding it to the inert core. The colloidal boehmite/pseudo boehmite is produced by mixing boehmite/pseudo boehmite with a solvent such as water, ketone, alcohol, ether, etc. The boehmite/pseudo boehmite is present in the solvent at a level of 10 to 20% boehmite in solvent producing colloidal boehmite/ pseudo boehmite. The outer core has catalytic metals such as platinum dispersed on it. This patent further discloses that the outer layer material contains the catalytic metal prior to it being coated onto the inner core.
US Patents 6,177,381, 6,187,981 and 6,280,608 disclose another method of preparation of layered catalysts. The layer of alumina is applied onto the inner core inert spheres by forming slurry of the preformed gamma alumina. Slurry of alumina was prepared by mixing the aluminum sol with the preformed gamma alumina powder. Aluminum sol used in the patent was made by dissolving aluminum metal in hydrochloric acid. The gamma alumina was prepared by well known oil drop method. The slurry also contains an organic bonding agent, which claimed to aid in the adhesion of the layer material to the inner core. Polyvinyl alcohol (PVA), hydroxy propyl cellulose, methyl cellulose and carboxy methyl cellulose were used as organic bonding agents. The amount of organic has been found that by using an organic bonding agent as described above, the attrition loss is less than about 10 wt. % of the outer layer. The thickness of the outer layer varies from about 40 to about 400 microns. Objects of the invention
It is an object of the present invention to provide a process for the manufacture of a spherical catalyst support consisting of a thin annular shell of a catalytically active material in gamma alumina formed in situ on and bonded to a non-active inert core.
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It is another object of the present invention to provide a process for in-situ formation of shell type refractory oxide layer on spherical inter inorganic oxide surface.
It is yet another object of the present invention to provide a novel process for the synthesis of annular shell type catalyst support with minimum attrition. Summary of the invention
Towards meeting the above and other objects of the invention, the applicants have developed a process for the preparation of an annular shell type inorganic oxide, which differs from the prior art in several ways. The catalyst carrier comprises an inner core such alpha alumina and an outer layer such as gamma alumina. The outer layer has a thickness of about 100 to about 500 microns. The outer shell is prepared by in-situ formation of surface layer by using intermediate alumina such as boehmite, a water-soluble polymer, hydrasol and an organic bonding agent such as polyvinyl alcohol. The process of in-situ formation ensures the bond between the layer and the inner core thereby minimizing attrition loss of the material.
The process of the present invention typically comprises forming an annular shell type catalytically active material such as gamma alumina on a spherjcjtLparticle of inert material having surface active sites e.g. alpha alumina, by using intermediate alumina phase boehmite along with a water soluble polymer as binder in conjunction with a mixture of pseudo boehmite precursor i.e. hydrosol and an organic binder and neutralizing the coated core by soaking in ammounium chloride and ammonia solutions, washing drying and calcining to convert the boehmite / pseudo boehmite into mesoporous gamma alumina thereby forming a bond between the thin annular shell of catalytically active gamma alumina and the inert, non-active core. Phenomenon of cross linking takes place between organic and inorganic binders to enable it to hold the boehmite particles together. This method ensures in-situ synthesis of gamma alumina on the inert core surface. The in-situ formation of gamma alumina ensures bonding of annular layer to the inert e.g. alpha alumina core, Spherical carrier made by this technique, containing an outer shell of thickness of around 400 microns and quantity 40 wt % of the overall support weight inclusive of inert core, is suitable for paraffin dehydrogenation catalysts. Advantage of annular shell catalysts is that the catalytically active material is present only in the thin shell and not throughout the entire particle, and thus, less catalytically active material is needed, based on the total weight of catalyst, as against conventional catalysts with a uniform distribution on active component throughout the particle. The shell type spherical carrier and the catalysts prepared using shell type support thus prepared in the invention
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can be used in a variety of hydrocarbon conversion processes, which include, but not limited to alkylation of both aromatics and isoparaffms, hydrocracking, cracking isomerization, hydrogenation, dehydrogenation and oxidation. The layered spherical catalyst will be of most benefit to processes where the activity or selectivity of the catalyst is limited by intra-particle diffusion resistance of product or reactants.
The layered catalysts of this invention can also be used in oxidation reactions. These oxidation reactions include :
1. Partial oxidation of hydrocarbon streams, such as naphtha or methane, to generate synthesis gas (CO+H2),
2. Selective oxidation of hydrogen produced from endothermic dehydrogenation reactions such as ethyl benzene to styrene; and
3. Oxidation of methane, ethane or carbon monoxide to clean up flue gas emissions from combustion processes.
Accordingly, the present invention provides a process for the manufacture of a catalyst support consisting of a thin annular shell of catalytically active material in gamma alumina formed on and bonded to an inert, non-active core, said process comprising wetting an inert non-active core with colloidal aluminum sol, spraying a bohemite/pseudo bohemite powder along with a powder of water soluble polymer binder on said coloidal aluminum sol wetted inert core to form a coating thereon, neutralising the coated core, and calcining the coated core to convert the bohemite/pseudo bohemite into gamma alumina thereby forming a bond between the thin annular shell of preformed catalytically active material in gamma alumina and the inert, non-active core. Description of the preferred embodiments
The present invention relates to an annular shell catalyst support prepared by w-" situ formation of surface layer, the annular shell catalyst carrier consisting of an inner core, an outer layer bonded to the said inner core with minimum attrition loss based on the weight of the outer layer and, the outer layer consist an outer refractory inorganic oxide.
Another embodiment of the invention is a process for preparing the annular shell catalyst support described above, the process essentially comprising the steps of: in-situ formation of gamma alumina by coating an inner core with a combination of intermediate phase of inorganic oxide along with a water soluble polymer both in powder form and alumina precursor hydrosol along with an organic bonding agent both in solution form, drying the coated core at room temperature, soaking the spheres in ammonium chloride and subsequently in dilute ammonia solution to convert the hydrosol to pseudo-
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boehmite, washing the spheres free from remains of ammonia and converting this to boehmite by drying the coating at 120 C for 2 to 4 hrs and subsequently converting it to gamma alumina by calcining the spheres at a temperature of about 400°C to about 900°C for a time sufficient to decompose all the organic support.
As stated, the present invention relates to an annular shell catalyst support, a process for preparing the support. The annular shell catalyst support comprises an inner core composed of a material, which has substantially lower or negligible adsorptive capacity for catalytic metal precursors, relative to the outer layer. Examples of the inner core materials include, but are not limited to, refractory inorganic oxides, silicon carbide and metals. Examples of refractory inorganic oxides include without limitation alpha alumina, theta alumina, cordierite, zirconia, titania, silica and mixtures thereof. A preferred inorganic oxide is alpha alumina, These materials which form the inner core can be formed into a variety of shapes such as pellets, extrudates, spheres or irregularly shaped particles although not all materials can be formed into each shape. Preparation of the inner core can be done by means known in the art such as oil dropping, pressure molding, metal forming, palletizing, granulation, extrusion, rolling methods. A spherical inner core is preferred. The inner core whether spherical or not has an effective diameter of about 0.05 mm to about 5 mm and preferably from about 0.8 mm to about 3 mm. Once the inner core is prepared, it is calcined at temperature of about 400°C to about 1500°C.
When the inner core is composed of a refractory inorganic oxide (inner refractory oxide), it is necessary that the outer refractory inorganic oxide be different from the inner refractory oxide. Additionally, it is required that the inner refractory inorganic oxide has a substantially lower adsorptive capacity for catalytic metal precursors relative to the outer refractory inorganic oxide.
The inner core is now coated with a layer of a refractory inorganic hydroxyl oxide which is different from the inorganic oxide which may be used as the inner core and will be referred to as the outer refractory inorganic hydroxy oxide or boehmite or intermediate phase of inorganic oxide. This outer refractory hydroxyl oxide is one which has good porosity, has a surface area of at lest 20 m2/g and preferably at least 150 m2 /g, an apparent bulk density of about 0.2 g/ml to about 1.0 g/ml, particle size of about 1 micron to 30 microns and is chose from the group consisting of boehmite alumina, gamma alumina, delta alumina, eta alumina, theta alumina, having pores greater than 60°A diameter. Preferred refractory inorganic hydroxy-oxide is boehmite alumina.
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The coating is applied by spraying, onto the spherical inert core, alternatively a powder combination of intermediate phase of inorganic oxide with a water soluble polymer and alumina precursor hydrosol along with an organic bonding agent both in solution form, drying the coated core at room temperature, soaking the spheres in ammonium chloride and subsequently in dilute ammonia solution to convert the hydrosol to pseudo-boehmite, washing the spheres free from remains of ammonia and converting this to boehmite by drying the coating at 120°C for 2 to 4 hrs and subsequently converting it to gamma alumina by calcining the spheres at a temperature of about 400 C to about 900 C for a time sufficient to decompose all the organic matter and have bonding of outer layer to the inner core to provide a annular shell support.
An advantages of this process is that during washing of the wet pseudo boehmite layered shell with water, no part of the components of the shell dissolve mainly because of the presence of the cross linked polymer.
It is essential in this process that intermediate inorganic oxide is mixed with a water polymer powder having COOH functional group. The purpose of this polymer is to have a cross linking, with the alumina sol and become insoluble to hold the inorganic oxide intermediate particles on to the inert spherical support surface. Examples for these water soluble polymers include but are not limited to PMAA, PAA and co polymers of acrylates. The amount of polymer added to the inorganic oxide intermediate can be between 0.1 wt % to 15 wt % of the inorganic oxide intermediate.
It is also required that the process contain an organic bonding agent which aids in the adhesion of the layer material to the inner core. Examples of this organic bonding agent include but are not limited to polyvinyl alcohol (PVA), bydroxy propyl cellulose, methyl cellulose and carboxy methyl cellulose. The amount of organic bonding agent which is added to the alumina sol will vary considerable from about 0.1 wt % to abut 4 wt %.
Binders which can be used to increase the mechanical strength of the alumina
coated spheres are substances such as acacia gum, alginic acid and aginates,
carboxymethycellulose, ethylcellulose, gelatine, hydroxyproylcellulose,
hydroxypropylmethylcellulose, methylcellulose, zanthan gum, pectin, tragacanth, microcrystaUine, cellulose, hydroxyethylcellulose, ethylhydroxyethyicellulose, sodium carboxymethylcellulose, polyethylene glycols, polyvinylpyrrolidone, polyvinyl alcohol, polyacryiic acid, vinylpyrrolidone-vinyl acetate copolymers, fructose,
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methylhydroxyethylcellulose. The use of polymethacrylic acid in a concentration of 1 205 relative to the boehmite powder, is particularly advantageous.
How strongly the outer layer is bonded to the inner core can be measured by the amount of layer material lost during an attrition text, i.e. attrition loss. Loss of the second refractory oxide by attrition is measured by agitating the shell coated support, collecting the fines and calculating an attrition loss. It has been found that by using a water soluble polymer in the cross linking process as described above, there is minimum loss on attrition. Finally, the thickness of the outer layer varies from about 50 to about 500 microns, preferably from about 40 microns to about 400 microns and more preferably from about 30 microns to about 300 microns. Surface area of the coated shell support varies between 40 to about 80 m2/g preferably from about 50 to about 70 m2/g. Depending on the particle size of the outer refractory inorganic oxide intermediate, it has been found that using a narrow particle size distribution improves compactness of the outer layer on the inner core. It appears that cross linking of water soluble polymer with alumina sol aid in making the surface peptized inorganic oxide intermediate to bind,to the core. This results in minimum loss of the outer layer by attrition. The sol contains an inorganic bonding agent selected from an alumina-bonding agent, a silica bonding agent or mixtures thereof Examples of silica bonding agents include silica sol and silica get, while examples of alumina bonding agents include alumina sol, aluminum chloride and aluminum nitrate. The inorganic agents are converted to alumina or silica in the finished composition. The amount of inorganic bonding agent varies from about 3 to about 30 wt % as the oxide, and based on the weight of the intermediate particles and spraying the sol alternatively onto the inner core spheres placed in a rotating pan to have the particles evenly coated. The thickness of the layer can vary considerably, but usually is form about 50 to about 500 microns preferably from about 50 to about 400 microns and most preferably from about 50 microns to about 300 microns. It should be pointed out that the optimum layer thickness depends on the use for the catalyst and the choice of the outer refractory oxide particle size. Once the inner core is coated with the layer of outer refractory inorganic oxide, the resultant layered support is dried at room temperature for 16 to 24 hrs to let the adhesives used to set. Subsequent to this the spheres are soaked in ammonium chloride solution for having buffer ammonia in the shell which will be further treated with ammonia solution to convert the alumina sol to pseudo boehmite. The said ammonium chloride solution concentration could be between 2 to 30% preferably 20%.
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The ammonia solution used in this process has a pH between 8 and 11 most preferably between 9 and 10. Advantage of this process is that both solutions can be recycled and reused by appropriately maintaining the concentrations.
The wet spheres as mentioned here are dried at about 100°C to about 320°C for a time of about 1 to about 24 hours and then calcined at a temperature of about 400°C to about 900°C for a time of about 0.5 to about 10 hours to effectively bond the outer layer to the inner core and provide annular shell type catalyst support. Of course, the drying and calcining steps can be combined into one step.
The present invention will now be described in greater detail with reference to the following examples which are intended to illustrate this invention and are not intended to limit the generally and scope of the invention as set out in the appended claims.
EXAMPLE 1
Commercial crystalline boehmite of particle size 25 microns was taken (20 gms). To it was added 2 gms of poly methacrylic acid (PMAA: molecular weight 50,000) powder of the same particle size. The mixture was sieved together for number of times to get a thoroughly mixed powder. A solution was prepared by mixing 250g of an aluminum sol (20 wt.% AliO*) and 25g of a 4% aqueous solution of PVA. This solution was sprayed onto 20g of alpha alumina cores having an average diameter of about 1.05mm by using a rotating plate granulating and coating apparatus. The above mentioned boehmite powder mix was sprayed on to these sphere. The sequence of solution and powder spraying was repeated till the 22g powder was coated on to the core spheres to give a final outer layer of about 400 microns and 40 wt% gamma alumina on overall support. This layered spherical support was dried at room temperature over night. Two solutions of ammonium chloride 20% concentration and ammonia solution with pH around 8 were prepared. The coated spheres were first soaked in ammonium chloride solution for one hour, decanted and soaked in ammonia solution for 1 hour decanted again and washed with cold deionized water till the spheres are free from ammonia. Thereafter the spheres were dried at 120 C for 2 hours and then calcined at 615°C for 4 hours in order to convert the pseudo boehmite in the outer layer into gamma alumina.
EXAMPLE 2
The procedure of Example -1 was repeated, except that the polymeric binder was not added in the powder mixture and after granulation and coating, the layered spherical
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support had an outer layer of about 400 microns in thickness. The coated spheres were first soaked in ammonium chloride solution for one hour, decanted and soaked in ammonia solution. The alumina coatings on the spheres started to crumble and dislodge from the surface of the inert core. This indicates that the cross linking between the polymeric binder and the alumina sol is essential to hold the boehmite powder onto the inert core.
EXAMPLE -3
From the results of Example-2, it appeared necessary to form a cross linkage between polymeric binder and alumina sol. Coated spheres were prepared as given in the Example 1, After soaking and washing in water, the spheres were dried. During calcinations it has been observed that the polymeric binder with narrow range of molecular weight polymer burnout occur at small range of temperature resulting in abrupt burnout causing surface coating crack. For gradual binder burnout, wide range molecular weight polymer was employed i.e., 10000 to 50000. In-order to avoid cracking of the surface layer, calcinations temperature programming (150'C @ 10°C/min hold 2 hr&*t that, 350°C @ 10°C/min hold at 350°C for 2 hrs and 600°C @ lOt/min and hold at that 4 hrs) was also adjusted in such a way that slow out-diffusion of combustion products was facilitated.
EXAMPLE-4
Alumina intermediate (Boehmite) was coated on alpha alumina spheres as mentioned in Example-1 except that the polymer binder used was a powdered copolymer of acrylic acid-methacrylic acid.
EXAMPLE - 5
The shell type support was prepared according to Example 1. Catalyst preparation described here is as per the US 5677260. Wherein, alumina was first impregnated with an aqueous solution prepared by dilute Lithium nitrate and ferric nitrate to result 0.6 wt% Li and 0.2 wt% Fe with respect to coated alumina. The impregnated alumina spheres were dried in an oven and then calcined at 600°C for 4 hrs.
The resulting lithium containing alumina was impregnated with platinum, tin and indium by contacting an aqueous solution (1:1 solution : support volume ratio) containing chloroplatinic acid, tin chloride, Indium nitrate and 10% hydrochloric acid (based on coated support weight) to result in 0.4 wt% Pt, 0.5 wt% Sn, and 0.4 wt°/o In. The
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impregnated composite was dried and calcined at 600°C for 4 hrs. This catalyst was made free from residual chloride by suitably treating it with ammonia solution drying and calcining of the same resulted in final catalyst, further the obtained catalyst was reduced in flowing hydrogen at 500°C for 4 hrs. Elemental analysis showed that this catalyst contained wt% 0.093 Platinum, 0.063 Tin, 0.05 Indian and 0.06 Lithium based on the whole catalyst mass.
EXAMPLE-6
The catalyst of Example - 5 was tested for dehydrogenation activity. In a 2.54 cm reactor, lcc of catalyst was placed and n-decane was flown over the catalyst at atmospheric pressure under hydrogen flow with H2: Hydrocarbon molar ratio of 6:1 and a liquid hourly space velocity LHSV of 20 hr"\ The reaction was carried out at a fixed reactor temperature of 450°C. The total normal olefins concentration in the product was monitored. For comparing the performance of the shell type of catalysts.
An examination of the platinum levels across the catalyst showed that the platinum distribution of the invention is contained essentially within the exterior layer of the catalyst particle. Platinum concentration remains constant through out the radius in alumina of 400 microns thickness on the outer surface of the core. Hence the present invention can therefore be regarded as catalyst surface-impregnated with platinum as the concentration of platinum in the 400 micron surface layer is constant.
The results of these tests are set forth in Table-1 below. The data presented in Table 1 represents the normal paraffin conversion as a function of number of hours on-stream. The normal paraffin conversion is defined at the weight percent of the components in the fresh feed which actually underwent some kind of reaction divided by the total weight of the feed. A range of selectivity is also given for the catalyst. The selectivity is the weight percent of the converted product, which was actually converted into the desired normal olefin. Table - 1

Hours on stream % of feed converted
1 14.7
2 14.0
3 13.7
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4 13.7
5 13.6
_. ...
TNO Selectivity 94.0 - 96.0 (% Olefins)
EXAMPLE-7
Coated refractory oxide attrition is measured by tumbling the shell coated support in an attrition test instrument by taking known quantity of the sample, collecting the fines and calculating percentage loss. The dry coated spheres were soaked or non-soaked, dried and calcined before conducting the attrition test.
The results of the attrition test are summarized in Table 2.
Table-2 Effect of soaking the dry coated spheres in ammonia solution on Attrition

Sample Percent Loss by weight
Based on total amount Based on layer
With PMAA and ammonia soaking 1.05 2.63
With PMAA and without soaking 17.9 44.86
The data in Table - 2 shows that converting alumina sol to pseudo-boehmite by soaking the dried spheres in ammonia solution greatly improves the attrition Joss of coated spheres.
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We claim:
1. A process for the manufacture of a catalyst support consisting of a thin annular shell of catalyiically active material in gamma alumina formed on and bonded to an inert, non-active core, said process comprising wetting an inert non-active core with colloidal aluminum sol, spraying a boehmite/pseudo boehmite powder along with a powder of water soluble polymer binder on said colloidal aluminum sol wetted inert core to form a coating thereon, neutralising the coated core, and calcining the coated core to convert the boehmite/pseudo boehmite into gamma alumina thereby forming a bond between the thin annular shell of preformed catalytically active material in gamma alumina and the inert, non-active core.
2. A process as claimed in claim 1 wherein said inert non-acdve core comprises alpha alumina.
3. A process as claimed in claim 1 or 2 wherein the thickness of annular layer of gamma alumina ranges from 10 to 500 microns.
4 A process as claimed in any preceding claim wherein the quantity of thin annular layer of
gamma alumina ranges from 10 to 60 wt% of the overall support weight inclusive of inert
core.
5 A processes claimed in any preceding claim wherein said calcining comprises heating the
coated particle in air at a temperature in the range of from 500"C to 600°C for from 1 to 24
hours.
6. A piocess as claimed in any preceding claim wherein said catalyst support is further heated at a temperature greater than about 500°C for a time sufficient to substantially remove said polymer from said product.
7 A process as claimed in any preceding claim wherein said binder comprises methacryJic acid.
8. A process as claimed in any preceding claim wherein said wetting and spraying steps are repeated till boehmite/pseudo boehmite of a thickness of about 25 u. is coated on said inner core.
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9. A process as claimed in any preceding claim wherein said neutralising of said coated core is carried out by soaking the coated core first in ammonium chloride solution for one hour and followed by soaking ammonium solution for one hour.
10 A process as claimed in claim 9 wherein prior to said calcination, said neutralised coated cotes are washed with deionised water till the coated cotes are free of amnmonia.
11. A process for the manufacture of a catalyst support substantially as herein described with reference to the forgoing Examples.