Permeable polymer membrane for desiccation of gas

Abstract: A permeable polymer membrane, formed of a fluorine type copolymer containing a repeating unit represented by the general formula: (wherein m is 0 or 1 and n is an integer of the value of 2 to 5) and satisfying the relation between the water absorption ratio, W, and the ion-exchange capacity, Q, represented by the following formula: 1.20Q - 1.964<log W<1.20Q - 1.742 (wherein W is , W₁ the dry weight, W₂ the equilibrium weight as immersed in pure water at 25°C, and Q the ion-exchange capacity in meq/g of H form dry resin). This permeable polymer membrane is capable of highly desiccating a gas to a low water content. By the use of the extremely desiccated gas, semiconductor elements, semiconductor devices, intermediates thereof, and new components can be produced with outstanding quality. This permeable polymer membrane can be produced by a heat treatment.

Description: This invention relates to an improved fluorine type permeable polymer membrane suitable for desiccation of gases used in the production of semiconductor components such as silicon wafers, gases used in the production of semiconductor devices, gases used in the production of new articles such as fine ceramics, solar cells, and optical fibers and for desiccation of source gases, carrier gases, and ambient gases used in the chemical vapor deposition (CVD) and physical vapor deposition (PVD) methods applied to the formation of ceramic or metallic thin-films on the surface of such substrates as optical components, precision machine components, general machine components, and heat ray-reflecting glass parts. It is those semiconductor devices called large scale integrated circuit (in the following denoted as LSI) and very large scale integrated circuit (in the following denoted as VLSI) that lead the remarkable growth now taking place in the field of electronics. In the process for the production of their materials and the production of these devices, rare gases such as argon and helium, corrosive gases such as hydrogen chloride and chlorine, and special gases such as silane, arsine, and borane gas are used in addition to such general-purpose gases as nitrogen. Further in the process for the production of semiconductor devices, high integration (super-miniaturization) is advancing rapidly. The lines forming miniature patterns have been gradually losing width and, as a result, microfine dust particles which have not posed any noticeable problem have been manifesting an increasingly conspicuous influence on the yield of products in proportion to the growing degree of integration of LSI's from the present prevalent level of 256 K bits to 1 megabit and further to 4 megabits. The gases used in the production of semiconductors mentioned above, specifically the gases used for silicon wafers as substrates of LSI's and for the operations of epitaxial growth, doping, etching, and cleaning in the processes for production of semiconductor devices have reached the point where they are required to possess purity of the order of 99,99% to 99,999% or higher and, in addition thereto, to possess dryness of not more than 1 ppm of water content and enjoy perfect freedom from floating dust particles. The water present in such a gas induces various hindrances as cited below. The water content, therefore, must be controlled strictly. (1) The water causes corrosion of such metallic components as pipes, valves, and flowmeters used in the production process of semiconductors and consequent formation of fine metal impurities and fine particles (for example, such corrosive gases as HCl gas). (2) The water, in the furnace for the production of semiconductors, is decomposed into H₂ and 0₂ and particularly this 0₂ gives rise to unexpected oxide impurities. (3) The gas itself and the entrained water are chemically combined to give rise to by-produced impurities. (4) The surface of the susceptor used in the furnace is damaged to expose graphite. The high desiccation of a gas mentioned above is important when metallic or ceramic coatings are formed on the surface of such substrates as components in optical devices and components of precision machines. The purity of a gas used in a CVD or PVD method has a serious effect on the construction and physical properties of the coating to be produced. The properties possessed by the produced coating improve in proportion as the purity of the gas is heightened. At present, the method of adsorption by the use of a molecular sieve is partly adopted for the desiccation of gases to be used in the process for the production of semiconductor devices. The molecular sieve is a desiccant second in adsorbing ability to phosphorus pentoxide and rather readily desiccates an ordinary gas to below 1 ppm of water content. This particular desiccant has found extensive utility because it has an advantage that, as a physical desiccant, it refrains from inducing such problems as deliquescence and swelling. It has a disadvantage, however, that its thermal regeneration necessitates an elevated temperature of 200 to 400°C and its repeated use after the thermal regeneration entails occurrence of floating dust particles. Further, the molecular sieve, on exposure to an acid gas such as hydrochloric acid gas, is deteriorated. Although the molecular sieve is available in its acidproof grade, the formation of floating dust particles must be prevented. Thus, the molecular sieve inevitably necessitates attachment of a dust filter. In this case, the molecular sieve is no longer regenerable. As means of desiccating gases, methods which resort to use of polymer membranes are disclosed in U. S. Patent No. 3,735,558 and the specification of Japanese Patent Applicaiton Laid-open Print No. 60,563/1978, for example. Unlike the method of adsorption by the use of the molecular sieve, these methods of permeation through membranes have an advantage that the membranes can be used continuously for a long time without requiring any regeneration. The former method utilizes a polymer particularly possessing a fluorine type sulfonate group and, therefore, is usable even with a corrosive gas. The UK patent application No. 2 051 831 relates to a fluorinated cation exchange membrane containing carboxylic acid groups and sulfonic acid groups, both in the form of a specific pendant structure, the carboxylic acid groups being at least 20% on one surface of the membrane and gradually decreasing towards the inner side of the membrane. The membrane disclosed therein is characterized as being useful in electrolysis of an aqueous alkali metal halide solution. As specific features of the membrane disclosed therein are mentioned excellent electrolysis performance of high current efficiency and low electrolysis voltage and an excellent stability under more severe conditions than those usually employed, whereby the excellent electrolysis performance is reported to be maintained for a long time. Neither of the methods, however, are capable of producing a gas having a water content of not more than 1 ppm and suitable for a process of producing semiconductors. The method of adsorption by the use of a disposable grade molecular sieve is not practicable because of high running costs. In the circumstance, development of a method capable of easily producing a gas highly desiccated to not more than 1 ppm of water content at low running cost without generation of floating dust particles is highly expected by the market. This invention provides a permeable polymer membrane formed of a fluorine type copolymer containing a repeating unit represented by the general formula (I): (wherein m is 0 or 1 and n is an integer of the value of 2 to 5) and satisfying the relation between the water absorption ratio, W, and the ion-exchange capacity, Q, represented by the following formula: 1.20Q - 1.964<log W<1.20Q - 1.742 (wherein W is W 2 - W 1 W 1 , W₁ the dry weight, W₂ the equilibrium weight when immersed in pure water at 25°C, and Q the ion-exchange capacity in meq/g of the dry resin in the H form. Fig. 1 is a graph showing the relation between the temperature of thermal treatment for desiccation and the equilibrium water absorption obtained of a permeable polymer membrane produced in Example 1, Fig. 2 is a graph showing the relation between the water absorption (W) and the ion-exchange capacity (Q) obtained of a permeable polymer membrane of an ion-exchange capacity of 0.8 to 1.1 produced by a thermal treatment of desiccation at a temperature not less than 70°C in Example 1, Fig. 3 is a schematic explanatory diagram of water separating means incorporating therein hollow fibers formed of a permeable polymer membrane according to the present invention. In Fig. 3, 1 stands for a hollow-fiber membrane, 2 for a raw material gas inlet, 3 for a raw material gas outlet, 4 for a purge gas inlet (to be closed for vacuumization), 5 for a purge gas outlet (to serve as an evacuating orifice for vacuumization), 6 for a cell, 7 for a partition panel. Fig. 4 is a graph showing the relation between the change of fiber length and the temperature and Fig. 5 is a graph showing the relation between the highest temperature involving no thermal shrinkage and the temperature of thermal treatment. The permeable polymer membrane of the present invention for high desiccation of a gas is formed of a fluorine type copolymer containing a repeating unit represented by the general formula (I): (wherein m is 0 or 1 and n is an integer of the value of 2 to 5) and satisfying the relation between the water absorption ratio, W, and the ion-exchange capacity, Q, represented by the following formula: 1.20Q - 1.964<log W<1.20Q - 1.742 (wherein W is W 2 - W 1 W 1 , W₁ the dry weight, W₂ the equilibrium weight as immersed in pure water at 25°C, and Q the ion-exchange capacity in meq/g of the dry resin in the H form. The fluorine type copolymer mentioned above is desired to be formed by copolymerizing a fluorinated olefin such as tetrafluoroethylene, trifluoroethylene, perfluorovinyl ether, vinylidene fluoride or vinyl fluoride with a perfluorovinyl ether monomer represented by the formula: (wherein m is 0 or 1 and n is an integer of the value of 2 to 5). Concrete examples of the copolymer meeting this requirement are indicated in U. S. P. 4,329,434, U. S. P. 4,329,435, U. S. P. 3,909,378 and GB -A- 2 051 831. The inventors have found that, of the membranes formed of the fluorine type copolymers containing a repeating unit represented by the general formula (I), permeable polymer membranes which satisfy the relation between the water absorption ratio, W, and the ion-exchange capacity, Q, represented by the following formula: 1.20Q - 1.964<log W<1.20Q - 1.742 (wherein W is W 2 - W 1 W 1 , W₁ the dry weight, W₂ the equilibrium weight as immersed in pure water at 25°C, and Q the ion-exchange capacity in meq/g of the dry resin in the H form produce an excellent effect in thoroughly desiccating a gas. The amount of the sulfonate group incorporated in the aforementioned fluorine type copolymer is desired to fall in the range of 0.5 to 2.5 meq/g of the dry resin in the H form in terms of ion-exchange capacity. By limiting the ion-exchange capacity of the fluorine type copolymer to the range of 0.5 to 2.5 meq/g of H form dry resin, the polymer membrane can be easily produced without notably lowering the speed of permeation of steam or excessively increasing the melting point of the copolymer and the polymer membrane can be enabled to retain its shape stably without a sacrifice of physical strength thereof. Preferably, the ion-exchange capacity falls in the range of 0.8 to 1.8 meq/g of the dry resin in the H form. The membrane of the fluorine type copolymer may be in the shape of a flat sheet, a tube, or a hollow fiber. Among other shapes of membrane, the hollow fiber proves particularly desirable because of large membrane surface area and high treating ability per unit volume. For the purpose of attaining the desiccation at a high degree, the airtightness of the apparatus counts strongly. Also in this respect, the hollow-fiber membrane proves desirable. The thickness of the hollow-fiber membrane is desired to be as small as possible because the membrane's ability to pass steam and its performance improve with the decreasing thickness. The smallest possible thickness of this membrane is fixed by such factors as moldability and pressure-resisting property. The thickness of the membrane is variable with the diameter of the hollow fiber. It is desired to fall in the range of 40 to 60 µm when the hollow fiber has an inside diameter in the range of 400 to 500 µm, for example. The membrane of this invention is produced by forming the fluorine type copolymer described above in the shape of a thin-film, then hydrolyzing the thin-film with an alkali, treating the hydrolyzed thin-film with a strong acid thereby converting the terminal group, SO₂F, of the copolymer to SO₃H, and thereafter subjecting the copolymer to a thermal treatment. The thermal treatment may be carried out, when necessary, by keeping the site of treatment purged with a dry gas such as, for example, nitrogen gas having a water content of not more than 2.5 ppm or keeping the site of treatment under a vacuum. The proper temperature of the thermal treatment is in the range of 60° to 250°C. If the temperature is excessively high, there ensues a possibility that the copolymer will be deprived of the ion-exchange group and consequently of the performance. Preferably, the temperature of the thermal treatment is in the range of 70° to 200°C. By the thermal treatment, the copolymer is caused to undergo shrinkage of some tens of percent and drop of water absorption ratio. As a result, the produced membrane satisfies the relation between the water absorption ratio, W, and the ion-exchange capacity, Q, represented by the following formula: 1.20Q - 1.964<log W<1.20Q - 1.742 (wherein W is W 2 - W 1 W 1 , W₁ the dry weight, W₂ the equilibrium weight as immersed in pure water at 25°C, and Q the ion-exchange capacity in meq/g of dry resin in the H form. The membrane resulting from the thermal treatment desiccates a gas to a level of not more than 5 ppm of water content and further to a level of not more than 1 ppm of water content. In this sense, it is logical to conclude that the membrane obtained by the thermal treatment of the aforementioned copolymer is capable of desiccating a gas to an ultimate level unthinkable by the common knowledge on conventional membranes. The gas to be desiccated may be supplied to either side of the membrane of the fluorine type copolymer. By sweeping the other side of the membrane with a dry purge gas of a lower water content or by reducing the pressure with a vacuum pump, the partial pressure difference which is the driving force for membranous permeation is generated and the desiccation aimed at is accomplished. The dry purge gas of a lower water content is supplied for the purpose of depriving the gas under treatment of the contained water across the membrane and, therefore, is desired to be an inert gas, which reactivity is as low as possible at elevated temperatures. The term "vacuum" as used herein means a pressure lower than the atmospheric pressure, though variable with the pressure of the gas to be supplied. The membrane of the present invention is produced by the thermal treatment. In the case of a flat membrane, whether the membrane has been produced by the thermal treatment or not can be readily decided by testing the membrane for its water absorption ratio. In the case of a membrane in the shape of a thin hollow fiber, since the water absorption ratio is not easily measured, the decision can be attained by testing the membrane for a temperature for starting thermal shrinkage to be described below. A sample of hollow-fiber membrane, with a light weight (heavy enough to pull the fiber straight but not heavy enough to stretch the fiber) hung down from the lower end thereof, is suspended in an air tank. The temperature of the air tank is gradually elevated and the change in the length of the fiber is measured with a reading microscope. Typical results of this measurement are shown in a graph of Fig. 6, wherein the horizontal axis is the scale of temperature and the vertical axis the scale of fiber length. In the graph, L₂₅ denotes a length at 25°C and L t a length at the temperature of t°C. With reference to Fig. 6, the temperature indicated by the arrow, i.e. the highest temperature at which no change of length is caused by elevation of temperature, is defined as "the highest temperature involving no thermal shrinkage." A few samples of hollow-fiber membranes obtained at different temperatures of thermal treatment (t) were tested for their "highest temperatures (T) involving no thermal shrinkage." The results are shown in Fig. 7. The graph indicates the following relation. T = t (1) Thus, the temperature of thermal treatment (t) of a given hollow-fiber membrane can be found by measuring the highest temperature (T) involving no thermal shrinakge. The gas to be desiccated when using the membrane of the present invention is generally a gas which is marketed as contained in a cylinder. This gas has no appreciably high steam content. The steam content of the gas so contained in the cylinder is generally in the range of several ppm to some tens of ppm. At times, the steam content exceeds 100 ppm. Depending on the steam content of a given gas, the surface area of the membrane in the water separating device or the number of membranes used in the device may be suitably varied to effect desiccation to a desired level. Among the gases which can be desiccated by the use of the membrane of this invention for desiccation of a gas is included an epitaxial gas. Concrete examples of the epitaxial gas include HCl, PH₃, B₂H₆, SiCl₄, SiH₂Cl₂, SiHCl₃, SiH₄, Si₂H₆, SiI₄, SiI₂, SiF₄, SnCl₄, SbCl₅, GeH₄, GeCl₄, GeI₄, GeI₂ , TeH₂ , BBr₃ , BCl₃ , PCl₃ , AlCl₃, AsCl₃, (CH₃)₃Al, (C₂H₅)₃Al, (CH₃)₃Sb, (C₂H₅)₃Sb, (CH₃)₃Ga, (C₂H₅)₃Ga, (CH₃)₃As, (C₂H₅)₃As, (CH₃)₂Hg, (C₂H₅)₃Hg, (CH3)3P, and (C₂H₅)₃P, and mixtures thereof. Among other epitaxial gases enumerated above, hydrogen chloride gas, phosphine gas, diborane gas, tetrachlorosilane gas, trichlorosilane gas, dichlorosilane gas, and mixtures thereof are generally used frequently. The effects of the present invention may be summarized as follows. (1) The permeable polymer membrane of the present invention can amply desiccate a gas and retain this ability of desiccation intact for a long time. (2) The desiccation of the gas proceeds without generation of any floating dust. (3) The membrane is proof against corrosion by an acid gas such as hydrogen chloride gas. (4) Unlike the molecular sieve used for adsorption, the membrane can be used continuously for a long time without requiring any regeneration. (5) Various gases such as the gas for the process of producing semiconductor elements, the gas used for the process of producing semiconductor devices, and the gas used for the process of producing new components can be amply desiccated by the membrane of this invention. When the gases so desiccated are used in dry etching, forming oxide coatings, cleaning the surface of semiconductor wafer and the interiors of devices, diffusing impurities on semiconductor wafers or compound semiconductor wafers, and forming coatings on substrates, the semiconductor wafers, the semiconductor devices, the intermediates, and the new components are obtained with improved quality in increased yields. (6) Since gases are desiccated to a fixed water content, the etched products have their quality and yield unaffected by aging. (7) Since the removal of water is effected by the membrane, gases desiccated by the membrane of this invention entrain no dust. The products obtained by the use of gases so dessicated enjoy improvement in both yield and quality. (8) Since the gases being transported have decreased water contents, the pipes used for their transfer are prevented from corrosion and from generation of fine metallic impurities. (9) Since the metallic implements such as pipes, valves, and flowmeters which are used in handling gases are prevented from corrosion by extreme desiccation of the gases, the devices and implements enjoy great addition to their service life and the operation utilizing the devices and implements is less expensive. (10) While water, on decomposition, produces H₂ and O₂, the desiccation with the membrane of this invention prevents this O₂ from giving rise to unexpected oxide impurities. (11) The desiccation with the membrane of the present invention prevents a gas from undergoing a chemical reaction with water and provides a desired effect. (If the water remaining in a gas settles and persists in a very narrow gap within a reactor, the gas such as, for example, SiCl₄ or SiHCl₃ which enters the reactor next chemically reacts with the water and, therefore, fails to fulfil its expected function.) (12) In the case of HCl gas, for example, the desiccation with the membrane of the present invention permits the purity of the HCl gas to be elevated from 99,9 to 99,99% to 99,99 to 99,999%. Thus, inexpensive HCl gas one grade lower can be adopted to permit a notable reduction in the cost of operation. (13) The desiccation with the membrane of the present invention prevents the protective film on the susceptor (a wafer support) in the CVD device from being corroded by HCI gas and the inside graphite from being exposed. Now, the present invention will be described more specifically below with reference to working examples. In the working examples and comparative experiments, the water content of gases was measured with a dew-point meter or moisture meter. Some gases were measured by Karl Fischer's method. EXAMPLE 1: A dry resin in the H form having an ion-exchange capacity of 0.94 meq./g dry resin was obtained by copolymerizing tetrafluoroethylene with The resin so produced was molded at 250°C into the form of a film 500 µm in thickness. This film was hydrolyzed with an alkaline alcohol solution, then subjected to ion exchange with an aqueous hydrochloric acid solution for conversion of the terminal of the side chain to the sulfonate form (H form), and dried in air. The membrane obtained was then dried under heat and vacuum and tested for equilibrium water absorption ratio at 25°C (Fig. 1). It is noted from Fig. 1 that the water absorption ratio fell down notably at the drying temperature of about 70°C or higher and remained substantially fixed at higher drying temperatures. Similarly, permeable polymer membranes having an ion-exchange capacity of 0.8 - 1.1 meq./g were prepared using various kinds of monomer as listed in Table A. Their water absorption ratios are also shown in Table A. From the results, the relation between the ion-exchange capacity and the water absorption ratio of the membrane according to the present invention falls in the range indicated by hatch lines in Fig. 2. EXAMPLE 2: A dry resin in the H form having an ion-exchange capacity of 0.90 meq./g dry resin was obtained by copolymerizing tetrafluoroethylene with With a molding machine provided with a spinneret for the production of hollow fibers, the resin was melt spun at a temperature of 250°C at a rate of 88 m/m to produce a membrane in the form of hollow fibers having an inside diameter of 500 µm and a wall thickness of 60 µm. The hollow fibers were hydrolyzed with an alkaline alcohol solution and then subjected to ion exchange with an aqueous hydrochloric acid solution for conversion of the terminal of the side chain to a sulfonate form (H form), and then dried in air. A bundle of 400 hollow fibers 40 cm in unit length was inserted in a separator of SUS, with the opposite ends fixed in position with epoxy resin, to form a water separator as illustrated in Fig. 1. In the separator, N₂ gas adjusted to a water content of not more than 1 ppm (a dew point of -76°C) and compressed to 5 kg/cm²G was passed through the interiors of the hollow fibers at a flow volume of 0.5 liter/min (the flow volume is expressed as reduced to be under atmospheric pressure; the same is applied hereinafter). N₂ gas adjusted to a water content of not more than 1 ppm (a dew point of -76°C) was supplied at a flow volume of 0.75 liter/min to sweep the outside of the hollow fibers. The separator was placed in a constant temperature bath at 70°C and heated therein for 3 hours. Then, the separator was cooled to room temperature. N₂ gas adjusted to a water content of 31 ppm (a dew point of -52°C) and pressure of 5 kg/cm²G was passed through the interiors of the hollow fibers at a flow volume of 0.5 liter/min and N₂ gas adjusted to a dew point of not more than -76°C (a water content of not more than 1 ppm)was supplied at a flow volume of 0.75 liter/min to sweep the outsides of the hollow fibers. The dew point at the N₂ gas outlet of the separator was found to be not more than -76°C (a water content of not more than 1 ppm). The separator was operated continuously under the existing conditions. After 24 hours' continued operation, the dew point at the N₂ gas outlet was still not more than -76°C (a water content of not more than 1 ppm). As regards the purge gas used outside the hollow fibers, the dew point at the outlet of the separator was found to be -66°C (a water content of 4.6 ppm) when measured after 24 hours' continued operation. After about 1,000 hours' continued operation under the same conditions, the dew point at the N₂ gas outlet was still not more than -76°C (a water content of 1 ppm). The ratio of the amount of water lost by the sampled gas to the amount of water gained by the purge gas was substantially constant at 1.2 : 1 within the range of measurement error. The other membranes of the present invention also exhibited the results similar to those as in Example 2 as shown in Table A. COMPARATIVE EXPERIMENT 1: In the same apparatus as used in Example 2, the same N₂ gas and purge gas were supplied each without the preheating treatment. After 44 hours' continued operation, the dew point of the N₂ gas failed to reach -60°C (a water content of 10.6 ppm). It is also shown in Table A that the membranes which do not belong to this invention exhibit the results similar to those as in Comparative Experiment 1. EXAMPLE 3: A polytetrafluoroethylene copolymer (an ion-exchange capacity of 0.86 meq./g of dry resin in the H form possessing a sulfonate group and containing a repeating unit of the following chemical structure: was molded to produce a membrane in the form of hollow-fibers. The hollow fibers measured 500 µm in inside diameter and 620 µm in outside diameter (60 µm in wall thickness). A module was prepared as illustrated in Fig. 3 by bundling 420 hollow fibers having an effective length of about 38 cm. For comparison, hollow-fiber membranes of regenerated cellulose measuring 150 µm in inside diameter and 175 µm in outside diameter (12.5 µm in wall thickness) was prepared by following the procedure of Example 1 of Japanese Patent Application Laid-open Print No. 152,679/1979. A similar module constructed as illustrated in Fig. 3 was produced by bundling these hollow fibers in a total of 420. These hollow fibers had an effective length of about 38 cm. Commercially available molecular sieves were used for comparison. As a model for the evaluation of yield and quality of etching, five silicon wafers were adopted. After the modules and the molecular sieves had passed HCl gas having a water content of 20 ppm, the silicon wafers were subjected to etching. The outside of the membrane was used as a gas outlet 3 for the module and the purge gas outlet 5 was connected to a vacuum pump. The interior of the module was evacuated to 10⁻² mmHg. On the etched silicon wafers, the numbers of bright points were counted by a mirror test and compared. The bright points are scratches caused by water or fine particles. The results are shown in Table 1. From the data of Table 1, it is noted that the effect of the module of this invention was demonstrated by perfect absence of a bright point. A hollow-fiber membrane of a polytetrafluoroethylene copolymer (an ion-exchange capacity of 0.90 meq./g of dry resin in the H form) containing a repeating unit of the formula: gave substantially the same results as those shown above. EXAMPLE 4: (1) A polytetrafluoroethylene copolymer (an ion-exchange capacity of 0.94 meq./g of dry resin in the H form) possessing a sulfonate group and containing a repeating unit of the following chemical structure: was molded to produce a membrane in the form of hollow fiber (500 µm in inside diameter and 60 µm in wall thickness). The hollow fiber was cut into pieces 40 cm in length. A bundle of 400 cut pieces of hollow fiber was inserted in a casing of SUS, with the opposite ends fixed in position with epoxy resin, to produce a water separator as illustrated in Fig. 3. In the water separator, nitrogen gas adjusted to a water content of not more than 1 ppm and a pressure of 5 kg/cm²G was passed through the interiors of the hollow fibers at a flow volume of 0.5 liter/min. Dry nitrogen gas (purge gas) having a water content of not more than 1 ppm was supplied at a flow volume of 0.75 liter/min under atmospheric pressure to sweep the exteriors of the hollow fibers. The water separator was placed in a constant temperature bath at 70°C and preheated for 3 hours. It was then cooled to room temperature. The nitrogen gas was switched to hydrogen chloride gas which was adjusted to a water content of 50 ppm and compressed to a pressure of 5 kg/cm²G. This hydrogen cholride gas was passed through the interiors of the hollow fibers at a flow volume of 0.5 liter/min. The water content of the hydrogen chloride gas measured at the outlet of the water separator was found to be 3 ppm. The operation of the separator was continued under the existing conditions. Even after 24 hours' continued operation, the water content of the hydrogen chloride gas was still 3 ppm. As regards the purge gas fed to sweep the exteriors of the hollow fibers, the water content measured at the outlet of the water separator after 24 hours' continued operation was found to be 8 ppm. After about 1,200 hours of the operation continued under the same conditions, the water content of the hydrogen chloride gas measured at the outlet of the water separator was still 3 ppm. (2) A hollow-fiber membrane of a polytetrafluoroethylene copolymer (an ion-exchange capacity of 0.90 meq./g of dry resin in the H form containing a repeating unit of the following chemical structure: gave substantially the same results as shown above. EXAMPLES 5-6: With the same water separator as used in Example 4, different raw material gases of different water contents indicated in Table 2 adjusted to the same pressure as in Example 4 were treated and further treated under a varying vacuum condition with the same water separator. The gases resulting from the last treatment were tested for water content. The results are shown in Table 2. Kind and water content of gas Flow volume of gas (vacuum) Time of operation Water content at outlet after desiccation with water separator Example 5 HCl gas 31 ppm 0.5ℓ/min. (1.7x10⁻² mmHg) 18 hr 3 ppm Example 6 H₂ gas 6 ppm 0.5ℓ/min. (380 mmHg) 17 hr Not more than 1 ppm EXAMPLE 7: (1) In the same water separator as prepared in Example 4 (1), nitrogen gas adjusted to a water content of not more than 1 ppm and to a pressure of 5 kg/cm²G was passed at a flow volume of 0.5 liter/min through the interiors of the hollow fibers. Dry nitrogen gas of a water content of not more than 1 ppm (purge gas) under atmospheric pressure was fed at a flow volume of 0.75 liter/min to sweep the exteriors of the hollow fibers. The water separator was placed in a constant temperature bath at 70°C and heated for 3 hours. Then, it was cooled to room temperature. The nitrogen gas was switched to hydrogen chloride gas which was adjusted to a water content of 31 ppm and compressed to a pressure of 5 kg/cm²G. This hydrogen chloride gas was passed through the interiors of the hollow fibers at a flow volume of 0.5 liter/min. The water content of the hydrogen chloride gas measured at the outlet of the water separator was found to be 3 ppm. The operation was continued under the existing conditions. Even after 24 hours' continued operation, the water content of the hydrogen chloride gas at the outlet was still 3 ppm. As regards the purge gas used to sweep the exteriors of the hollow fibers, the water content measured at the outlet of the water separator after 24 hours' continued operation was found to be 5 ppm. After about 1,200 hours' operation continued under the same conditions, the water content of the hydrogen chloride gas measured at the outlet was found to be still 3 ppm. When H₂ gas having a water content of 6 ppm was similarly desiccated with the water separator, there was obtained H₂ gas of high purity amply desiccated to a water content of not more than 1 ppm. EXAMPLES 8-9: With the same water separator as prepared in Example 4 (1), raw material gases which were adjusted to one fixed pressure were treated under a vacuum with the water separator by following the procedure of Example 7. The gases so treated were tested for water content. The results are shown in Table 3 below. Example Kind and water content of gas Flow volume of gas (vacuum) Time of operation Water content at outlet after desiccation with water separator 8 HCl gas 31 ppm 0.5ℓ/min. (1.0x10⁻² mmHg) 18 hr 3 ppm 9 H₂ gas 6 ppm 0.5ℓ/min. (380 mmHg) 17 hr Not more than 1 ppm EXAMPLE 10: In the same water separator as used in Example 4 (1), nitrogen gas adjusted to a water content of not more than 1 ppm and to a pressure of 5 kg/cm²G was passed at a flow volume of 0.5 liter/min through the interiors of the hollow fibers. Dry nitrogen gas (purge gas) having a water content of not more than 1 ppm under atmospheric pressure was fed at a flow volume of 0.75 liter/min to sweep the exteriors of the hollow fibers. The water separator was placed in a constant temperature bath at 70°C and heated therein for 3 hours. It was then cooled to room temperature. The nitrogen gas was switched to phosphine gas which was adjusted to a water content of 30 ppm and compressed to a pressure of 5 kg/cm²G. This phosphine gas was passed through the interiors of the hollow fibers at a flow rate of 0.5 liter/min. The water content of the phosphine gas measured at the outlet of the water separator was found to be not more than 3 ppm. The operation was continued under the existing conditions. After about 800 hours' operation continued under the same conditions, the water content of the phosphine gas at the outlet was found to be still not more than 3 ppm. EXAMPLES 11, 12, 13: With the same water separator as used in Example 4 (1), varying raw material gases of varying water contents indicated in Table 4 were treated, with the raw material gases and purge gases kept under the same pressure, and were further treated under a vacuum by following the procedure of Example 10. The raw material gases were tested for water content at the outlet of the water separator. The results are shown in Table 4. A hollow-fiber membrane obtained by molding a polytetrafluoroethylene copolymer (an ion-exchange capacity of 0.90 meq./g of dry resin in the H form containing a repeating unit of the following chemical structure: gave substantially the same results as those described above. EXAMPLES 14, 15, 16: (1) With the same water separator as used in Example 4 (1), varying raw material gases of varying water contents indicated in Table 5 were treated, with the raw material gases and purge gases kept under the same pressure, and were further treated under a vacuum by following the procedure of Example 7. After the treatment, the gases were tested for water content. The results are shown in Table 5. (2) A hollow-fiber membrane obtained by molding a polytetrafluoroethylene copolymer (an ion-exchange capacity of 0.90 meq./g dry resin in the H from) containing a repeating unit of the following chemical structure: gave substantially the same results as those described above. EXAMPLE 17: (1) With the same water separator as used in Example 4 (1), nitrogen gas adjusted to a water content of not more than 1 ppm and compressed to a pressure of 5 kg/cm²G was passed at a flow volume of 0.5 liter/min through the interiors of the hollow fibers. Dry nitrogen gas (purge gas) of a water content of not more than 1 ppm was fed at a flow volume of 0.75 liter/min to sweep the exteriors of the hollow fibers. The water separator was placed in a constant temperature bath at 70°C and heated therein for 3 hours. It was then cooled to room temperature. The nitrogen gas was switched to CH₄ gas which was adjusted to a water content of 50 ppm and compressed to 5 kg/cm²G. The CH₄ gas was passed through the interiors of the hollow fibers at a flow volume of 0.5 liter/min. The water content of the gas measured at the outlet of the water separator was found to be not more than 1 ppm. In the same manner as described above, H₂ gas was desiccated to a water content of not more than 1 ppm. (2) A hollow-fiber membrane obtained by molding a polytetrafluoroethylene copolymer (an ion-exchange capacity of 0.90 meq./g of dry resin in the H form) containing a repeating unit of the following chemical structure: gave substantially the same results. EXAMPLE 18: A hollow-fiber membrane (500 µm in inside diameter and 60 µm in wall thickness) was produced by molding a polytetrafluoroethylene copolymer (dry resin in the H form having an ion-exchange capacity of 0.90 meq./g of dry resin) possessing a sulfonate group and containing a repeating unit of the following chemical structure: The hollow fiber was cut into pieces of 40 cm. A bundle of 400 cut pieces was inserted in a casing of SUS, with the opposite ends of the bundle fixed in place with epoxy resin, to produce a water separator illustrated in Fig. 3. In the water separator, nitrogen gas adjusted to a water content of not more than 1 ppm and compressed to a pressure of 5 kg/cm²G was passed through the interiors of the hollow fibers at a flow volume of 0.5 liter/min. Dry nitrogen gas (purge gas) having a water content of not more than 1 ppm under atmospheric pressure was fed at a flow volume of 0.75 liter/min to sweep the exteriors of the hollow fibers. The water separator was placed in a constant temperature bath at 70°C and heated therein for 3 hours. It was cooled to room temperature. The nitrogen gas was switched to CH₄ gas which was adjusted to a water content of 50 ppm and compressed to 5 kg/cm²G. The CH₄ gas was passed through the interiors of the hollow fibers at a flow volume of 0.5 liter/min. The water content of the CH₄ gas measured at the outlet of the water separator was found to be not more than 1 ppm. In the same manner, Ar gas was desiccated to a water content of not more than 1 ppm. (2) A hollow-fiber membrane obtained by molding a polytetrafluoroethylene copolymer (H-form dry resin having an ion-exchange capacity of 0.94 meq./g of dry resin) containing a repeating unit of the following chemical structure: gave substantially the same results as those described above. EXAMPLE 19 : In the same water separator as formed in Example 4 (1), nitrogen gas adjusted to a water content of not more than 1 ppm and compressed to a pressure of 5 kg/cm²G was passed at a flow volume of 0.5 liter/min through the interiors of the hollow fibers. Dry nitrogen gas (purge gas) having a water content of not more than 1 ppm under atmospheric pressure was fed at a flow volume of 0.75 liter/min to sweep the exteriors of the hollow fibers. The water separator was placed in a constant temperature bath at 70°C and heated therein for 3 hours. It was cooled to room temperature. The nitrogen gas was switched to arsine gas which was adjusted to a water content of 18 ppm and compressed to a pressure of 5 kg/cm²G. The arsine gas was passed through the interiors of the hollow fibers at a flow volume of 0.5 liter/min. The water content of the arsine gas measured at the outlet of the water separator was found to be not more than 1 ppm. The operation was continued under the existing conditions. After 24 hours' operation continued under the same conditions, the water content of the arsine gas was still not more than 1 ppm. The water content of the arsine gas even after about 170 hours' continued operation was still not more than 1 ppm. EXAMPLES 20-21: With the same water separator as used in Example 20, raw material gases of varying water contents indicated in Table 6 were treated, with the raw material gases and a purge gas kept under the same pressure, and were further treated under a vacuum by following the procedure of Example 19. The water contents of the gases were tested. The results are shown in Table 6.

Claims: A permeable polymer membrane, formed of a fluorine type copolymer containing a repeating unit represented by the general formula: wherein m is 0 or 1 and n is an integer of the value of 2 to 5, being characterized in that it satisfies the relation between the water absorption ratio, W, and the ion-exchange capacity, Q, represented by the following formula: 1.20Q - 1.964 < log W < 1.20Q - 1.742 wherein W is W 2 - W 1 W 1 , W₁ is the dry weight, W₂ is the equilibrium weight when immersed in pure water at 25°C, and Q is the ion-exchange capacity in meq/g of the dry resin in H form. A permeable polymer membrane according to claim 1, wherein m is 1 and n is 3 in said general formula. A permeable polymer membrane according to either of claims 1 or 2, wherein said permeable polymer membrane is in the form of hollow fibers. The use of a permeable polymer membrane according to any of the claims 1 to 3 for the desiccation of a water-containing gas.

Inventors: KAGEURA YOSHIAKI, KOBAYASHI HIROSHI, TERADA EIGO, TOYOMOTO KAZUO, KAGEURA, YOSHIAKI, KOBAYASHI, HIROSHI, TERADA, EIGO, TOYOMOTO, KAZUO
Applicants: ASAHI CHEMICAL IND, ASAHI KASEI KOGYO KABUSHIKI KAISHA
Application year: 1986
Main classification: C08J5
IPC codes: B01D53, C23C16, B01D71, C08J5, C08F214