Title of Invention

A PROCESS FOR MANUFACTURING OF MICRO-POROUS ALUMINA CERAMIC DISK MEMBRANES .

Abstract

This invention relates to a method of producing 'micro-porous ceramic membranes' of disk/pellet type for filtration/separation processes/systems comprising the sequential steps of a) mixing/grinding of alumina powders of different sizes and other additives like, pore former, binder, dispersant, stabilizers in a water solvent in a ball mixer using different sizes of alumina balls followed by transferring batch mix in a teflon/nylon or similar jars placed in a pot mill for thorough mixing of the batch for a period of 24 to 48 hours to form a slurry, b) drying the said slurry in ambient conditions on pouring the suspension into 'plaster of paris'/clay moulds or similar and to allow the water to drip out from the slurry yielding 'dry batch composition', c) sieving the said dry batch composition using sieves of 100-200 mesh or similar, to result a binder-mixed batch composition in granular form, d) pressing the resultant granules into the form of green disks/pellets with varied diameter and thickness in stainless steel die/s by processing in an uniaxial pressing machine at varied pressure levels to obtain green disks /pellets, e) drying the said green disks/pellets in an oven maintaining a temperature in the range of 50-120 degC so as to get dry green disks/pellets,

Full Text

The present invention is related to the field of fabrication of micro-porous ceramic membranes, which can be adapted for variety of purposes/applications in particular to the filtration/separation technologies. More particularly, the present invention relates to a methodology for fabricating disk/pellet type alumina ceramic membranes of consistently uniform pore size and its distribution with superior mechanical strength and surface finish through maintenance in the uniformity of thickness of the membrane, all of the said can further be tailored to give rise alumina membranes with predetermined levels of pore size in the range of 0.3 to 0.6 micrometer. The present method also provides a guideline to fabricate alumina ceramic membranes in the entire spectrum of micro-filtration besides the defined range of 0.3 to 0.6 micron. BACKGROUND OF THE INVENTION Membrane based processes are known for numerous applications, each being different in their mode and with separation characteristics. Pressure driven filtration processes, e.g. micro-, ultra- and nano-filtration, reverse osmosis; Concentration driven processes, e.g. gas separation, pervaporation, dialysis; Temperature driven processes, e.g. membrane distillation; Electrically driven processes, e.g. electrodialysis. It also can be used as a support for heterogeneous catalysis reactions and photo-catalysis reactions and processing involving adsorption or absorption reactions. The produced ceramic membranes can further be used as a support material for the fabrication of ultra-filtration, nano-filtration, reverse osmosis membranes. The main criterion considered in membrane filtration/separation process is the ability of the membrane to permeate selectively. Indeed, approximately 60 - 75% of synthetic polymer membranes are today employed as semi-permeable barrier layers. Organic Polymeric membranes have numerous advantages like flexibility to fabricate in the form of tubes and sheets. However they have great limitations like, they are susceptible to biodegradation (organic ones), have relatively short shelf and operating life, less resistant to organic solvents, chlorines, and extreme pH conditions, relatively less mechanical strength. In order to overcome the above-mentioned disadvantages, there is a need to develop new membrane materials, which can overcome the disadvantages of the polymeric/organic membranes, and at the same time, it should provide similar advantages comparable to the polymer/organic membranes. During the past few decades, ceramic membranes have been receiving greater attention because of their advantages over polymeric /organic and metallic membranes. Compared to polymeric based membranes, ceramic membranes exhibit unquestionable advantages, essentially due to their inherent properties. They can withstand high temperatures, high pressure (> 100 bar), abrasion, and chemical attack, which makes them a very good materials for applications in harsh and extreme environments. Recent studies have showed that ceramic membranes exhibit high resistance against microbiological attack. Generally, they are stable up to 1000°C or more under pressure which enable them for high- temperature applications and thereby permitting sterilization operation in biochemical applications. Ceramic membranes can well tolerate chemical / mechanical cleaning, can readily accommodate the abrasion encountered in slurries, and resist the build up of high pressure (up to 30 atm) often used in back flushing techniques. Ceramic membranes have excellent reliability and long operating life. There is no structural deformation even under a wide range of operating conditions. Moreoever, the well-developed production technology provides membranes with high permeability and desired pore size. Due to the stringent operating conditions (wide pH range, repeated vapor sterilization, organic solvents, and temperatures up to 500°C) several industries have thought to immensely benefit from ceramic membranes in the field of agro-foodstuffs industries, biotechnology, biomedicine, paper industries, textile, and petroleum industries. Some membranes, which have been commercialized recently haveunequivocally longer life under harsh industrial conditions and their industrial use have shown a good degree of reliability in several applications. In some cases, the lifespan of membranes is greater than five years and have also significantly decreased the cost of maintenance in industrial facilities. However, even though the basic principles and methodology of ceramic membrane processing have already been known, tailoring/regulating pore size and the distribution of pore size, consistency in the uniformity in thickness of the membranes are still a major task to accomplish. Besides, improvement in mechanical strength and good surface finish despite allowing the membrane to possess a high porosity level is also a major task. The present invention aims to provide a fabrication method to obtain microporous alumina membranes with above-mentioned characteristics. PRIOR ART REFERENCE There are many prior arts reported in the preparation of ceramic membranes. Hay et al. in U.S. Pat. No. 4,968,426 has described the procedure of preparation of strong and durable alpha phase alumina ultrafitration membranes by seeding boehmite sols, and further coating on the support with a thin layer of gel to obtain a final pore size of less than about 500µm. The preparation of membranes by sol gel technology as disclosed by Mori et al. in U.S. Pat. No. 4,770,908 describes a procedure of membrane preparation by disposing a layer of alumina sol on a porous membrane formed by hydroly2ing an alcoholate or a chelate of alumina followed by drying and burning thereof. Anderson, Marc A et al. conducted significant work on preparation of membrane by various procedures reported in EP No.0537944B1, U.S. Pat. No. 5.006,248, U.S. Pat. No. 5.096745, U.S. Pat. No. 5,104,539, U.S. Pat. No. 5,169,576, U.S. Pat No.5,194,200, U.S. Pat. No. 5,208,190, U.S. Pat. No. 5,215,943, U.S. Pat No. 5,610,109, U.S. Pat. No. 5,712,037, and was able to create a stable, transparent metal oxide ceramic membrane, particularly alumina, titanium, and silica based with a narrow pore size distribution and with pore diameter manipulable in the range of 5 - 100 Å. Ail those inventions were based on preparation of membranes using sol-gel or improved sol-gel techniques using different precursors. The same group also invented the procedure (U.S. Pat. No.5,268,101) of preparing combined alumina and silica membranes having high surface area, small pore size with high temperature stability. Various other patent literatures like Van T Veen et al. U.S. Pat.No. 5,089,299, Maier US Pat. No. 5,250,184, Nishio et al. U.S. Pat. No. 5,250,242, de Jong et al. U.S. Pat. No. 5,407,703, Chen et al. U.S. Pat. No. 6,165,553 have described the method of creating membranes suing sol-gel techniques. Liu et ai. in U.S. Pat. No. 5,645,891 has described the method of preparation of mesoporous ceramic membranes by inserting a substrate into the reaction chamber at pressure and thereby allowing the deposition of nucleates on the substrate leading to the formation of a membrane layer therein. Yet in the same patent, it is reported one more method of preparation of ceramic membranes by placing a substrate between two solutions permitting the formation of membrane on the surface by or within the pores of the porous substrate. Webster et al. in U.S. Pat. No. 5,269,926 has disclosed the creation of supported microporous membranes by placing a porous support on one side in a colloidal suspension and drying the other side by exposing it to the drying stream of air or a reactive gas stream so that the particle are deposited on the drying side as membrane. Shimai et al. in U.S. Pat No. 5,405,529 has described yet another method of preparing ceramic filter consisting of bone like structure using ceramic-slurring foaming techniques. Bartton et al. in U.S. Pat. No. 5,935,440 has disclosed a process for treating memebrane comprising a film of crystalline ceramic zeo-type material which process comprises treating the membrane with a silicic acid and or a polysilicic acid or a mixture of the both. Takahashi et al. in U.S. Pat. No. 6,007,800 has described a method of preparation of ceramic porous membrane and ceramic filter by the deposition of titania from titania slurry (1-70% by weight) on the surface on the porous substrate followed by thermally treating the membrane at 100-300°C in an aqueous vapor phase environment. Herrmann et al. in U.S. Pat. No. 6,309,546 discloses various examples of preparing the micro and ultra pore membrane with controlled pore size like, single membrane layer by immersing the substrate in a solution of desired metal (dip coating) followed by sintering to remove organic binder (double dip coating), two layer graded membrane by dip coating, tape casting, screen printing, and finally two layer hybrid membrane on a metallic substrate via spin coating. Fain, Sr, et al. in U.S. Pat. No. 6,649,255 reports an unexpected invention, a process for controlling the ultimate pore size of a fine-pored inorganic membrane, particularly chosen from the group of alumina, zirconia, titania, silica alumina/silica mixtures, can be achieved by depositing one monolayer at a time of an inorganic compound where the layer thickness approximately equals to the size of the molecule, such as metal oxide, metal nitride or the pore walls of the inorganic membrane followed subsequently by drying the membrane. Piner et al. in U.S. Pat. No. 6,528,214 presents yet another method of preparing inorganic membranes by suspending the mixture of fine and coarse particles in a liquid to form a slurry followed by poring the thus prepared slurry into a mould such as one made up of 'Piaster of Paris' thereby obtaining green intermediate product and finally baking, firing or sintering the green intermediate so as to obtain a finished membranes having a density distribution of fine particles that increases in one direction (surface in use) across the finished membrane and a density distribution of the coarse particles that decreases in the same direction across the finished membrane. The method of preparation of ceramic filters or membranes by sol-gel, tape casting methods is believed to suffer from the disadvantage like higher chances for cracks formation on the membrane surface during the binder burn-off and sintering due to large shrinkage ratio between the film and the substrate. Presence of even small cracks, crevices can have a remarkable deleterious effect on the performance of membranes and can render them substantially little value in many operations. This is because in many separation operations the effect of defects is essentially to provide a channel where the un-separated products can pass through. Though some existing methods of membrane preparation like slurry suspension, sol-gel, tape casting claim that a defect free membrane is obtained on a laboratory scale, but attempts to provide a substantially defect free membrane on a larger scale production have proved to be unsuccessful. In the background of aforesaid disadvantages of prior art, the present invention has devised a novel fabrication procedure for the preparation of ceramic membranes, in particular alpha phase of alumina ceramic having a consistent and uniform pore size, uniform pore distribution, uniform thickness appended with superior mechanical strength and surface finish characteristics. OBJECTIVES OF THE INVENTION: Hence, it is the objective of the present invention to provide a fabrication procedure to produce microporous aluminum oxide (alumina) ceramic membranes in the form of disks/pellets with consistently uniform pore size, uniform pore distribution and uniform thickness with superior mechanical strength with surface finish characteristics by varying the same base composition. One of the objective of the present invention is to provide a method for fabrication of ceramic membranes by routes other than sol-gel route, tape casting method, solution or colloidal route, isostatic pressing. Another objective of the present invention is to fabricate ceramic membranes, in disk/pellet forms using alpha phase of aluminum oxide (alumina) in an efficient and predictable manner. Still another objective of the present invention is to fabricate alumina disk/pellet membranes with controlled and uniform pore size and its distribution along with uniform thickness of the membrane. Still further objective of the proposed invention is to provide a fabrication method for generating reproducible and reliable alumina ceramic disk/pellet membranes for its applications in various filtration/separation processes. Yet another objective of the present invention is to define various process parameters for producing the above alumina membranes, which are very significant for the continuous and beneficial production of the process. Yet further objective of the present invention is to provide alumina membrane substrates (supports) for generating ultra-filtration, nano-filtration, hyper- filtration, reverse osmosis membranes by applying further ceramic/polymer layer/s on the support structure thereby generating the said membranes, which has great applications in the other separation/purification technologies. Other objects, novel features, advantages, and applications of the present invention will be better understood in the description that follows. According to the invention there is provided a method of producing 'micro-porous ceramic membranes' of disk/pellet type for filtration/separation processes/systems comprising the sequential steps of a) mixing/grinding of alumina powders of different sizes and other additives like, pore former, binder, dispersant, stabilizers in a water solvent in a ball mixer using different sizes of alumina balls followed by transferring batch mix in a teflon/nylon or similar jars placed in a pot mill for thorough mixing of the batch for a period of 24 to 48 hours to form a slurry, b) drying the said slurry in ambient conditions on pouring the suspension into 'plaster of paris'/clay moulds or similar and to allow the water to drip out from the slurry yielding 'dry batch composition', c) sieving the said dry batch composition using sieves of 100-200 mesh or similar, to result a binder-mixed batch composition in granular form, d) pressing the resultant granules into the form of green disks/pellets with varied diameter and thickness in stainless steel die/s by processing in an uni- axial pressing machine at varied pressure levels to obtain green disks/pellets, e) drying the said green disks/pellets in an oven maintaining a temperature in the range of 50-120 degC so as to get dry green disks/pellets, f) heat treating the dry green disks/pellets in presence of air or similar oxidizing atmosphere in a suitable kiln/furnace in the range of 1558°C. - 1580°C, to get an intermediate membrane disks/pellets and g) heat treating (sintering) the intermediate disks/pellets in presence of air or similar oxidizing atmosphere in a suitable kiln at set temperature/s in the range of 1550°C - 1580°C to result the micro-porous alumina disk/pellet membrances followed by characterization and testing of the resulted micro- porous alumina membranes DETAILED DESCRIPTION OF THE INVENTION: The present invention describes the fabrication of a disk/pellet type ceramic membrane using alpha phase of alumina material that generates consistently uniform pore diameter which is manipulable in the range of 0.3 to 0.6 µm. For the said purpose, alumina powders with different particle size distribution but similar physical and chemical properties along with other additive materials such as binders, dispersants, deflocculant, sintering agent, pore former etc were used as the starting raw materials. In general, the fabrication process starts with a wet-mixing operation using predetermined quantities of the said raw materials using water in a ball mill mixer using nylon pot or a similar kind of container for a mixing period for about 24 to 48 hours. The sequence of addition of the constituents within the raw materials has an important effect on the characteristics of the membrane. As per the present invention, alumina powders were first mixed with water. Then, the dispersant sodium stearate was added to alumina powders to aid good dispersion consistency in the mixture followed by addition of other organic additives, i.e. polyvinyl alcohol, polyethylene glycol, ammonium polyarcylate, carboxymethyl cellulose etc. The mixing is carried out using different sizes of alumina balls in a ball mixer. The alumina balls are used in the present invention to avoid entrainment in the batch composition. However other kinds of balls can be used for mixing the above said raw materials by taking enough precaution to avoid entrainment or contamination of the starting materials from the balls. The aqueous suspension thus obtained after 24 to 48 hours of mixing is poured into a gypsum mould to drain out the solvent (water). The suspension was then dried under controlled conditions ambient or in an oven or both or other means in order to get the dry batch. The drying temperature is kept in the range of 60-100°C. Only water is eliminated during drying as the organic additives that have been incorporated in the batch during processing have decomposition temperature of higher than 600°C. The slurry is dried until the moisture content is reduced to weight % moisture level results over-dried powder, which subsequently looses its binding properties and hence makes the pressing of the powders difficult in the subsequent steps, thereby leading formation of cracks and or pinholes during the green stage. The resultant dry batch is further mixed either of the organic binders, like polyethylene glycol (PEG), carboxymethyl cellulose (CMC), polyvinyl alcohol (PVC) etc or similar, with appropriate quantity in the range of 1-5 weight % using a dry mixer or similar so as to obtain a binder-mixed batch composition that subsequently provides good strength to the uni-axially pressed green disk/pellets. The binder-mixed batch composition is then sieved using a 200 mesh or similar so as to get the binder-mixed batch composition in granular form. The resultant granular composition is then weighed (depending on the thickness of the membrane to be fabricated) and poured in the stainless steel die of desired dimensions depending on the diameter/dimension of the membrane to be fabricated. The granular composition is then uniformly spread over the surface of the die cavity and pressed in the uni-axial direction at definite levels of pressure in order to obtain a predetermined geometrical shape of disk or pellet type. During uni-axial pressing, compaction occurs by crushing of the granules and mechanical redistribution of the particles into a closed packed array. The lubricant and binder usually aid in this redistribution and the binder provides cohesion of the batch material. A compaction pressure in the range of 5000 - 5500 kPa was chosen to ensure breakdown of the granules and uniform compaction during uni-axial pressing. After the above uni-axial pressing, the disks/pellets those obtained are conventionally called as the green disks/pellets. The green disks/pellets need to be carefully dislodged form the die using a suitable scrapping mechanism. These green disks/pellets are dried in an oven in the temperature range of 50-100°C until the moisture content of the body is reduced to <: sufficient care was taken during drying in order to obtain a> homogeneous dry surface. Improper drying or uncontrolled drying can lead to differential shrinkage, resulting in wrapping density gradients, and hence cracks in the green disks/pellets. The dried disks/pellets (moisture contlent refractory-lined high-temperature furnace or any other type of similar furnace at a temperature of in the range of 1550°C - 1580°C in presence of air or any suitable oxidizing atmosphere. The heating rate was maintained constant at 1°C/min till 600°C is reached and the heating rate was increased to 1.5°C/min until the furnace temperature reaches 1000°C where disks/pellets were soaked for 60 min. Further sintering operation was continued by increasing the temperature of the furnace in the range of 1550° to 1580°C at a rate of 2°C/min and the resultant article was soaked at the said temperature for 120 min. In between the temperature of 300 - 600°C organic substances those incorporated in the body start decomposing, certain amount of which decomposes completely and some amount would still be there in the body as un-decomposed carbonaceous matter or soot. The strength of the material is reduced during this period. This soot is subjected to oxidation from about 8O0°C to 1000°C and so-called soot removal is carried out. To remove soot completely during this period, it is necessary to ensure effective supply of air or any oxidizing atmosphere in the firing environment. Sintering starts partly at the end of this oxidation period, the strength is increased slightly over. Active sintering takes place beyond 1300°C and the body goes on skrinking considerably. Therefore, sufficient attention is paid in maintaining uniform temperature throughout the furnace cavity to avoid uneven skrinkage and deformation of the fired membranes. The temperature of the furnace is raised to the specified value (1580°C), and then soaked at this temperature for a period of two hours and then the heating process is terminated. Even when the green body is large temperature differences may occur in different portion of the body. To prevent this, the temperature uniformity around the body particularly at the maximum temperature (1580°C) zone needs to be maintained very strictly. Embodiments construed under the proposed invention is illustrated in the following examples, with the help of accompanying drawings and tables in which Figures 1 to 6 represents pore size distribution of various alumina membrane formed and construed under the scope of the proposed invention. Example 1 A disk/pellet type alumina (AI2O3) membrane was fabricated in accordance with the method of this disclosed invention as follows. In the present invention, alumina (Al2O3 and other raw materials (inorganic type) were used as per the technical specifications furnished in the Table 1, whereas Table 2 shows the technical characteristics of the other additives (organic type) those used along with the said alumina for a batch preparation. As per batch composition, a typical batch composition as per Table 3 was prepared. Different sizes of alumina balls with varying diameters (3mm, 6mm and 9mm) each with a definite quantity was used as a media for mixing/grinding operation of the said batch composition. The batch composition was taken in a Teflon/nylon pot/jar, which was then placed on a mechanical pot mill (in-house fabricated) for the purpose of mixing the batch composition homogeneously, and the speed of the pot mill was kept in the range of 50 - 75 rpm. The composition was allowed to mix in the pot mill for a period of 48 hrs or so in order to ensure homogeneity of the batch composition. The size as well as the quantity of alumina balls in the mixing operation may vary from case to case depending on the batch size, however the main importance in the mixing process is laid to obtain the homogeneity of the batch composition. After the mixing operation, a slurry was formed, which was then transferred into a gypsum mould for drying the slurry under ambient condition. When the moisture content of the said slurry was reduced to less than 7 wt %, the semi- dried slurry was taken out from the mould and sieved the mass with a 200 mesh- size siever, which forms fine granules of the semi-dried slurry. The resultant granules was then poured into the cavity of a stainless stell die (in-house fabricated) and pressed in a uni-axiai pressing machine at a pressure of 5395 kPa in the form of discs having an outer diameter of 57.8 mm, and a thickness of 2.5 mm. The so pressed disks/pellets were identified as green body, which were dried at room temperature for about 30 min, later it was dried in an oven to a temperature not beyond 80°C maintaining a heating rate of 0.5 °C per minute until it reached at 80°C and were subjected to be dried in the said oven until the moisture content of the discs came down to a level of The resultant dried pressed disks / pellets with moisture content were subjected to consolidation or densification (sintering) operation in a refractory-lined high-temperature furnace procured from commercial sources) at a temperature of 1580°C in presence of air. The heating rate was maintained constant at 1.0°C/min till 600°C and the heating rate was increased to 1.5°C/min until the furnace temperature reaches 1000°C where it was soaked for 60 min. Further sintering operation was continued by increasing the temperature of the furnace at 1580°C with a heating rate of 2°C/min and was soaked at 1580°C for 120 min in air. The furnace was then cooled down to 100°C at a uniform rate of 3°C/min after which the further cooling to room temperature was carried by exposing the membrane disc/pellets in ambient atmosphere. Once the said process of sintering was completed, the so derived sample (fired body or micro- porous alumina membranes) was characterized for various physical properties. The microporous alumina membranes thus formed had a bulk density of 2.93 ± 0.05 gm/cc, apparent porosity of 23.6 ± 1%, and a uniform pore radius of 0.3 urn (See Table 3, Table 9 and Figure 1). The normalized flux of water of the thus prepared alumina membranes was found to be 95 l/m2/hr at 100kPa and 26°C (Table 10). Example 2: Another type of alumina membranes were prepared in the same manner as explained in Example 1, except the batch consists with different compositions as represented in the Table 4. The physical properties of the resulted alumina microporous membranes had a bulk density of 2,76 ± 0.05 gm/cc, apparent porosity of 29.9 ± 1%, and a uniform pore radius of 0.37 µm (Table 4, Table 9 and Figure 2). The normalized flux of water of the thus prepared alumina membranes was found to be 167 l/m2/hr at lOOkPa and 26°C (Table 10). Example 3: Further, alumina membranes were prepared in the same manner as explained in Example 2, and as per the composition presented in Table 5. The membranes prepared had a bulk density of 2.70 ± 0.05 gm/cc, apparent porosity of 31.3 ± 1% and a uniform pore radius of 0.41 µm (See Table 5, Table 9 and Figure 3). The normalized flux of water of the thus prepared alumina membranes was found to be 224 l/m2/hr at 100kPa and 26°C (Table 10). Example 4: Further, alumina membranes were prepared in the same manner as explained in Example 3, and as per the composition presented in Table 6. The so-derived had a bulk density of 2.20 ± 0.05 gm/cc, apparent porosity of 46.4 ± 1% and a uniform pore radius of 0.43 µm (See Table 9 and Figure 4). The normalized flux of water of the thus prepared alumina membranes was found to be 224 l/m2/hr at 100kPa and 26°C (Table 10). Example 4: Further, alumina membranes were prepared in the same manner as explained in Example 3, and as per the composition presented in Table 6. The so-derived had a bulk density of 2.20 ± 0.05 gm/cc, apparent porosity of 46.4 ± 1%, and a uniform pore radius of 0.43 µm (Table 6, Table 9 and Figure 4). The normalized flux of water of the thus prepared alumina membranes was found to be 603 l/m2/hr at lOOkPa and 26°C (Table 10). Example 5: Further, alumina membranes were prepared in the same manner as explained in Example 4, and as per the composition presented in Table 7. The so-derived membranes had a bulk density of 2.03 ± 0.05 gm/cc, apparent porosity of 50.8 ± 1%, and a uniform pore radius of 0.53 µm (Table 7, Table 9 and Figure 5). The normalized flux of water of the thus prepared alumina membranes was found to be 777 l/m2/hr at lOOkPa and 26°C (Table 10). Example 6: Further, alumina membranes were prepared in the same manner as explained in Example 5, and as per the composition presented in Table 8. The so-derived membranes had a bulk density of 1.93 ± 0.05 gm/cc, apparent porosity of 53.5 ± 1%, and a uniform pore radius of 0.57 urn (Table 8, Table 9 and Figure 6). The normalized flux of water of the thus prepared alumina membranes was found to be 1340 l/m2/hr at 100kPa and 26°C (Table 10). Sufficient number of alumina membranes were prepared in accordance with examples 1-5 and were subjected to test for evaluation of characterization and validation for their effectiveness in maintaining consistent physical properties. The prepared membranes out of a particular batch exhibited similar values (within the limit) of physical properties like, bulk density, apparent porosity, bulk porosity, pore size, pore distribution, mechanical strength, surface texture, water permeability. The resultant ceramic membranes were characterized in terms of porosity/density measurements, scanning electron microscopy analysis, bubble point test and clarifications in dead-end micro-filtration mode using aqueous bakers yeast solution at different trans-membrane pressure (TMP) in the range of 50-250 kPa. Membranes fabricated in accordance to examples 1-4 were also tested for their effectiveness in filtering feeds of biological origin. For this purpose, 5g/l of 250 ml synthetic bakers' yeast suspension was filtered through the membranes in a dead-end filtration fashion. The transmembrane pressure (TMP) across the membrane was varied in the range of 50-250 kPa and subsequent flux and quality of permeate was determined as a function of time. The concentration of the bakers'yeast in the permeate was sampled using standardized methods. The invention as described and explained hereinabove with illustrated embodiment is in relation to non limiting embodiments which can be adopted, changed and modified within the scope and limit of the appended claims. WE CLAIM 1. A method of producing 'micro-porous ceramic membranes' of disk/pellet type for filtration/separation processes/systems comprising the sequential steps of a) mixing/grinding of alumina powders of different sizes and other additives like, pore former, binder, dispersant, stabilizers in a water solvent in a ball mixer using different sizes of alumina balls followed by transferring batch mix in a teflon/nylon or similar jars placed in a pot mill for thorough mixing of the batch for a period of 24 to 48 hours to form a slurry, b) drying the said slurry in ambient conditions on pouring the suspension into 'plaster of paris'/clay moulds or similar and to allow the water to drip out from the slurry yielding dry batch composition, c) sieving the said dry batch composition using sieves of 100-200 mesh or similar, to result a binder-mixed batch composition in granular form, d) pressing the resultant granules into the form of green disks/pellets with varied diameter and thickness in stainless steel die/s by processing in an uni- axial pressing machine at varied pressure levels to obtain green disks/pellets, e) drying the said green disks/pellets in an oven maintaining a temperature in the range of 50-120 degC so as to get dry green disks/pellets, f) heat treating the dry green disks/pellets in presence of air or similar oxidizing atmosphere in a suitable kiln/furnace in the range of 1558°C. - 1580°C, to get an intermediate membrane disks/pellets and g) heat treating (sintering) of the intermediate disks/pellets in presence of air or similar oxidizing atmosphere in a suitable kiln at set temperature/s in the range of 1550°C - 1580°C to result the micro-porous alumina disk/pellet membrances followed by characterization and testing of the resulted micro- porous alumina membranes 2. A method of producing membranes as claimed in claim i wherein micro- porous alumina ceramic membrane is produced having specific pore size in the range of 0.30 - 0.60 micron. 3. A method of producing membranes as claimed in claim 1 wherein binder is an organic binder and added alone or in combination from the group of polyethelene glycol (PEG), carboxymethyl cellulose (CMC), polyvinyl alcohol (PVC), ammonium polyarcylate in the range of 1-5% as aqueous solution and the dispersant is sodium stearate. 4. A method of producing membranes as claimed in the preceeding claims wherein drying of the slurry is carried out under natural conditions or other means of evaporation of water until the moisture level in the dried composition comes down to 7 weight percent or below. 5. A method of producing membranes as claimed in claim 1 wherein moisture level of the dried green membrane disks/pellets are brought down to 1% level by drying the disks/pellets in an oven in the temperature range of 50- 120 degC. 6. A method of producing membranes as claimed in the preceeding claims wherein the formulations/compositions of the starting raw materials is maintained as per Tables 1 or 2 or 3. 7. A method of producing membranes as claimed in the preceeding claims wherein during uni-axial pressing of the granules, compaction pressure is maintained in the range of 5000 - 5500 kPa, during uniaxial pressing of the granules. 8. A method of producing membranes as claimed in the preceeding claims wherein sintering of the dry green disks/pellets is carried out in two stages of firing, firstly in the range of 1558-1580°C and secondly in the range of 1550- 1580°C followed by furnace cooling to 100°C at a uniform rate of 3°C/min and further cooling to room temperature in ambient atmosphere, the heating rates in the first stage are maintained at 1%/rnin upto 600°C and at 1.5°C/min from 600°C to 1000°C - 1280°C and in the second stage the heating rates are maintained at 2°C/min from 1000°C - 1280°C upto 1550°C - 1580°C, in between the stages of the sintering the disk/pellets are soaked at 1000°C - 1200°C for 60 min and at 1550°C to 1580°C for 120 min. 9. A method of producing membranes as claimed in claim 1 wherein the resultant ceramic membranes were characterized in terms of porosity/density measurements, scanning electron microscopy analysis, bubble point test and clarifications in dead-end micro-filtration mode using aqueous bakers yeast solution at different trans-membrane pressure (TMP) in the range of 50-250 kPa 10. A method of producing micro-porous ceramic membranes of disk/pellet type for filtration/separation processes/systems as herein described and illustrated in the accompanying drawing, tables and examples. This invention relates to a method of producing 'micro-porous ceramic membranes' of disk/pellet type for filtration/separation processes/systems comprising the sequential steps of a) mixing/grinding of alumina powders of different sizes and other additives like, pore former, binder, dispersant, stabilizers in a water solvent in a ball mixer using different sizes of alumina balls followed by transferring batch mix in a teflon/nylon or similar jars placed in a pot mill for thorough mixing of the batch for a period of 24 to 48 hours to form a slurry, b) drying the said slurry in ambient conditions on pouring the suspension into 'plaster of paris'/clay moulds or similar and to allow the water to drip out from the slurry yielding 'dry batch composition', c) sieving the said dry batch composition using sieves of 100-200 mesh or similar, to result a binder-mixed batch composition in granular form, d) pressing the resultant granules into the form of green disks/pellets with varied diameter and thickness in stainless steel die/s by processing in an uniaxial pressing machine at varied pressure levels to obtain green disks /pellets, e) drying the said green disks/pellets in an oven maintaining a temperature in the range of 50-120 degC so as to get dry green disks/pellets,

Documents:

169-KOL-2006-FORM 15.pdf

169-KOL-2006-FORM-27-1.pdf

169-KOL-2006-FORM-27.pdf

169-kol-2006-granted-abstract.pdf

169-kol-2006-granted-claims.pdf

169-kol-2006-granted-correspondence.pdf

169-kol-2006-granted-description (complete).pdf

169-kol-2006-granted-drawings.pdf

169-kol-2006-granted-examination report.pdf

169-kol-2006-granted-form 1.pdf

169-kol-2006-granted-form 18.pdf

169-kol-2006-granted-form 2.pdf

169-kol-2006-granted-form 3.pdf

169-kol-2006-granted-form 5.pdf

169-kol-2006-granted-gpa.pdf

169-kol-2006-granted-reply to examination report.pdf

169-kol-2006-granted-specification.pdf