Title of Invention

A METHOD OF MAKING A FLUID SEPARATION MATERIAL SUCH AS MEMBRANE OF NANOPORE STRUCTURE

Abstract

A method of making a fluid separation material such as membrane of nanopore structure comprising chemically synthesising a free standing conducting porous polymer membrane of 50 to 10000 microns thick and nanoengineering a nanopore structure in the membrane by chemical or electrochemical doping and dedoping followed by secondary doping to obtain a porosity of 0.01 to 50% and pores in the nanopore sizes of 0.05 to 17 nanometers.

Full Text

FORM 2 THE PATENTS ACT 1970 COMPLETE SPECIFICATION (SEE SECTION 10) TITLE A method of making a fluid separation material such as membrane of nanopore structure APPLICANTS Indian Institute of Technology, Bombay, Powai, Mumbai 400076, Maharashtra, India, an autonomous educational institute established in India under the Institutes of Technology Act 1961 INVENTORS Under Section 28(2) Jayesh Ramesh Bellare, AHasgar Qutub Contractor and Sanjib Niranjan Datta, all Indian nationals and of Indian Institute of Technology, Bombay, Powai, Mumbai - 400076, Maharashtra, India The following specification particularly describes «B4 ascertains the nature of this invention and the manner in which it is to be performed : GRANTED 4 JAN 2001 4-1-2001 This invention relates to a method of making a fluid separation material such as membrane of nanopore structure. A fluid separation membrane may be free standing or supported. A free standing membrane comprises a conducting porous polymer film of 50 to 10000 microns thick having a porosity of 0.01 to 50 % and pores in the sizes 10000 to lOnm. A supported membrane comprises a conducting porous polymer film of 0.01 to 100 microns thick having a porosity of 0.01 to 75% and pores in the sizes of 10000 to 10 nm supported on a porous substrate of 10% to 70% porosity having pore sizes of 10000 to 10 nm. The porous conducting substrate may be of inherent conductivity made of a conducting material. Alternatively the porous substrate may be of induced conductivity made of a non¬conducting material and coated with a conducting material. A free standing membrane is made by casting with a polymer solution obtained by dissolving the respective polymer in a solvent such as ethyl acetate, dimethyl formamide or dimethyl sulfoxide. The polymer may be obtained by dissolving the respective monomer in a solvent such as ethyl acetate, dimethyl formamide or dimethyl sulfoxide and polymerizing it with an oxidant/initiator such as benzoyl peroxide or ammonium peroxydisulfate. Alternatively the polymer may be obtained by heating the respective monomer with catalyst such as vanadium pentoxide or titanium chloride in a reactor at a high temperature of the order of 100 to 200°C and pressures of the order of 10,000 to 20,000 psi. A supported membrane is made by casting the film on the substrate in situ using the respective polymer solution. Permeability of the above membranes is narrow and is usually in the range of 1 to 100 barrers. Selectivity of the above membranes is also narrow and usually in the range of 2 to 1000. Membranes with poor selectivity are costly to use for high degrees of separation as many cascading stages have to be used. A supported membrane is of reduced material cost due to the film being thin and of increased mechanical strength due to the substrate. The selectivity and permeability of a membrane depends on its pore structure. The higher the porosity the greater the permeability and lower the selectivity. Pore structures may be created and/or modified in a polymer membrane by phase inversion, track etching, sintering or chemical doping with dopants such as hydrochloric acid, hydrobromic acid, hydroiodic acid or perchloric acid and dedoping with dedopants such as ammonia. Pore structures created in a polymer membrane by the above techniques cannot be precisely controlled to obtain desired permeability and selectivity because precise control cannot be exercised on such techniques. Besides chemical doping/dedoping of polymer membranes is very slow because the diffusion coefficients of the liquid/solid dopants in the polymer matrix are low. An object of the invention is to provide a method of making a fluid separation material such as membrane which has wide permeability range. Another object of the invention is to provide a method of making a fluid separation material such as membrane which has wide selectivity range. Another object of the invention is to provide a method of making a fluid separation material such as membrane, which is simple and easy to carry out. According to the invention there is provided a method of making a fluid separation material such as membrane of nanopore structure comprising synthesising a conducting porous polymer film and nanoengineering a nanopore structure in the film to obtain a porosity of 0.01 to 50% in the nanopore sizes of 0.05 to 17 nanometers. According to an embodiment of the invention the method comprises chemically synthesising a free standing conducting polymer membrane of 50 to 10000 microns thick and nanoengineering the pore structure in the membrane by chemical or electrochemical doping and dedoping followed by secondary doping to obtain a porosity of 0.01 to 50% and pores in the nanosizes of 0.05 to 17 nanometers. According to another embodiment of the invention the method comprises casting a conducting polymer membrane of 0.01 to 100 microns thick on a porous substrate of 10 to 70% porosity having pore sizes of 10000 to 10 nm with the respective polymer solution and nanoengineering the pore structure in the membrane by chemical or electrochemical doping and dedoping followed by secondary doping to obtain a porosity of 0.01 to 50% having pore sizes of 0.4 to 17 nanometers. The term nanoengineering wherever used in the specification means engineering the pore structure of the film/membrane at atomic/molecular scale/level. The porous substrate may be of inherent conductivity made of a conducting material such as copper, stainless steel, brass or bronze. Alternatively the porous substrate may be of induced conductivity made of a non-conducting material such as polypropylene, polytetrafluoroethylene, cellulosic ester, polycarbonate or ceramics and coated with a conducting material such as gold, platinum, palladium, nickel or copper or mixers or alloys thereof. The conducting polymer film may for example be made of polyaniline, polyacetylene, polypyrrole or polythiophene or polymers derived from substituted monomers thereof. The chemical doping and dedoping and secondary doping may consist of doping with dopants such as hydrochloric acid, hydrobromic acid, hydroiodic acid or perchloric acid and dedoping with dedopants such as ammonia followed by secondary doping with host molecules such as macrocylic organic compounds such as crown ethers and treatment with compatible guest molecules such as alkali/alkaline earth metal ions such as potassium, sodium, strontium or barium. During chemical doping, the dopant is added to the polymer solution at the stage of synthesis of the membrane or prior to the stage of casting of the membrane. At these stages the diffusion coefficient of the dopants in the liquid polymer precursor is high and therefore doping is fast. The interactions of the host and guest molecules between the polymer chains help to control the pore structure precisely to improve selectivity of fluids. The permeability of the membrane obtained by the method of the invention has been found to be 25.3 to 0.000005. The selectivity of the membrane obtained by the method of the invention has been found to be 100-59000. The wide permeability and selectivity ranges of the membrane are indicative of the extent of nanoengineering brought about by the method in the pore structure of the membrane. The high selectivity permits thinner membranes and/or fewer stages of separation thereby reducing cost of the membrane. The method of the invention is also simple and easy to carryout. The membranes of the invention may be used for the separation of liquids such as isomers of o-xylene or m-xylene or gases such as hydrogen, helium, nitrogen, oxygen, carbondioxide or methane. Besides using as membrane, the fluid separation material of the invention also may be used as a sheet or as a coating of uniform or non-uniform thickness. The following experimental examples are illustrative of the invention but not limitative of the scope thereof: Example 1 Aniline (10.0 ml, 0.107 mol) was dissolved in 600 ml of 1M HC1 and the mixture was cooled to below 5°C in an ice bath. A solution (300 ml) of 28.2 g (0.124 mol) ammonium peroxydisulfate in 1 M HCl was prepared and cooled to 5°C in an ice bath. The ammonium peroxydisulfate solution was added to the aniline solution dropwise over a period of 20 minutes with vigorous stirring maintaining the temperature below 5 C in ice bath. After about 2 hours, the precipitate was collected on a buchner funnel and was washed with four portions of 100 ml of 1 M HCl. The precipitate was kept under suction for 15 minutes until significant cracking of the moist filter cake was obtained. The moist polymer cake was doped by suspending with constant stirring in 500 ml of 1 M HCl solution at room temperature for 4 hours. The polymer was filtered on a buchner funnel and dried under dynamic vacuum at room temperature for 48 hours. The dried polymer was dedoped by suspending with constant stirring in 1 litre of 0.1 M NH4OH at room temperature for 3 hours. The polymer was filtered and dried under dynamic vacuum at room temperature for 48 hours to obtain a blue powder, which was grounded into fine powder in a mortar. 1 g of the polymer was swelled in a beaker containing 10 ml of tetrahydrofuran (THF) for 12 hours. The THF was removed by decantation. 15 ml of N-methyl pyrrolidone was added to the swelled polymer and stirred for 12 hours. The polymer solution was filtered and concentrated in a rotary vacuum. The concentrated polymer solution was (1% wt/wt). 4 ml of the concentrated solution was stirred with 50 mM of 18-Crown-6 (1,4,7,10,13,16-hexaoxacyclo-octadecane), for 2 hours. A sintered stainless steel disk having 25 mm diameter and 1 mm thickness and apparent porosity 22% and mean pore size of 0.5 micron was cleaned in a beaker containing 50 ml of pure water and sonicating in an ultrasonic bath for 10 minutes. Sonication was repeated 6 times each time with fresh water. The disk was further cleaned by degreasing in an soxhlet apparatus with acetone for 12 hours. The crown doped polymer solution was spin cast on the cleaned disk and dried at 130°C for 2 hours. The polymer thickness was controlled to 1-10 microns by controlling the spinning parameters. The permeability of the membrane for hydrogen and nitrogen were 0.18 and 0.00000304 barrers respectively, and the selectivity for hydrogen/nitrogen was 59210. Similar membrane made without crown doping gave hydrogen and nitrogen permeability of 25.3 and 0.245 and selectivity of 103. The porosity of the membrane were between 0.1 to 50%. Example 2 The procedure of Example J was repeated and the crown -4 doped cast polymer film was doped with 10 M KCl solution to obtain a potassium (K ) secondary doped supported membrane. The permeability of the membrane for hydrogen and nitrogen were 0.18 and 0.0009 barrers respectively, and the selectivity for hydrogen/nitrogen was 200. We Claim : 1. A method of making a fluid separation material such as membrane of nanopore structure comprising chemically synthesising a free standing conducting porous polymer membrane of 50 to 10000 microns thick and nanoengineering a nanopore structure in the membrane by chemical or electrochemical doping and dedoping followed by secondary doping to obtain a porosity of 0.01 to 50% and pores in the nanopore sizes of 0.05 to 17 nanometers. 2. A method of making a fluid separation material as claimed in claim 1, wherein the membrane has pore sizes of 0.05 to 0.5 nanometers. 3. A method of making a fluid separation material as claimed in any one of claims 1 and 2, wherein the chemical doping and dedoping and secondary doping consists of doping with dopants such as hydrochloric acid, hydrobromic acid, hydroiodic acid or perchloric acid and dedoping with primary dedopant such as ammonia followed by secondary doping with host molecules such as macrocyclic organic compounds such as crown ethers and treatment with compatible guest molecules such as alkali/alkaline earth metal ions such as potassium, sodium, strontium or barium. 4. A method of making a fluid separation material as claimed in any one of claims 1 to 3, wherein the conducting polymer membrane is made of polymers such as polyaniline, polyacetylene, polypyrrole or polythiophene or polymers derived from substituted monomers thereof. 5. A method of making fluid separation material such as membrane of nanopore structure substantially as herein described particularly with reference to Examples 1 and 2. Dated this 2nd day of January 2001. (Karuna Goleria) of DePENNING & DePENNING Agent for the Applicants

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12-mum-2001-cancelled pages(4-1-2001).pdf

12-mum-2001-claims(granted)-(4-1-2001).doc

12-mum-2001-claims(granted)-(4-1-2001).pdf

12-mum-2001-correspondence(3-12-2004).pdf

12-mum-2001-correspondence(ipo)-(9-1-2006).pdf

12-mum-2001-form 1(4-1-2001).pdf

12-mum-2001-form 19(28-8-2003).pdf

12-mum-2001-form 2(granted)-(4-1-2001).doc

12-mum-2001-form 2(granted)-(4-1-2001).pdf

12-mum-2001-form 26(4-1-2001).pdf

12-mum-2001-form 3(4-1-2001).pdf

12-mum-2001-form 8(23-2-2004).pdf

12-mum-2001-power of authority(18-9-2004).pdf