JPH0530484B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] This invention uses, for example, an aromatic polyimide hollow fiber membrane having gas separation performance to separate water vapor from a mixed gas of organic compound vapor such as alcohol, ketone, ether, etc. and water vapor. This invention relates to an improved gas separation method for removing such substances. [Description of the Prior Art] Recently, hollow fiber membranes made of aromatic polyimide having gas separation performance have been used to separate water vapor or vapor of at least one organic compound from a mixed vapor of organic compounds or a mixed vapor of organic compounds containing moisture. Kawara gas separation methods are being proposed. However, in general, aromatic polyimide resins have high resistance to organic chemicals as well as heat resistance, so it is thought that the hollow fiber membranes made of aromatic polyimide can be suitably used for the gas separation described above. When it comes into contact with an organic compound, it swells, expands, or contracts, which causes the various problems mentioned above when performing gas separation. That is, aromatic polyimide hollow fiber membranes are generally produced by using a large number of the hollow fiber membranes to form a fiber bundle, and then solidifying and fixing both ends of the fiber bundle together with a curable resin or the like to form a fiber bundle element. A gas separation device is manufactured in which the yarn bundle element is housed and fixed in a sealed container for gas separation, and is used for the above-mentioned gas separation. When repeated contact with an aromatic polyimide hollow fiber membrane having both ends fixed, the expansion and contraction of the aromatic polyimide hollow fiber membrane causes bending of the hollow fiber membrane in the gas separation device. This may cause the arrangement of the fiber bundle to be significantly deformed, or a portion of the hollow fiber membrane may be severed, or
There is a problem in that the gas separation performance of the hollow fiber membrane itself often deteriorates (in particular, the gas permeation rate decreases, etc.). [Problems to be Solved] As described above, this invention solves the problem when the fiber bundle element of the aromatic polyimide hollow fiber membrane fixed in the gas separation device interrupts or repeats contact with the organic compound vapor. Another object of the present invention is to provide a gas separation method that does not cause bending of the hollow fiber membrane, deformation of the arrangement of the fiber bundle, cutting of the hollow fiber membrane, or deterioration of the gas separation performance of the hollow fiber membrane. [Means for solving the problem] This invention supplies a mixed gas (mixed vapor) containing an organic compound to the outside of an aromatic polyimide hollow fiber membrane having gas separation performance, and In a method of continuously performing gas separation by selectively permeating at least one gas component of the mixed gas into the interior of the hollow fiber membrane, (a) before first introducing the mixed gas to the outside of the hollow fiber membrane, , after reducing the pressure in the hollow of the hollow fiber membrane, supplying the mixed gas to start gas separation; and (b) introducing the mixed gas in order to interrupt or terminate the gas separation. At the time of stopping, a replacement gas that does not substantially contain organic compounds and/or water vapor is introduced to the outside of the hollow fiber membrane to replace the gas that was present outside the hollow fiber membrane during the gas separation. The present invention relates to a gas phase membrane separation method characterized in that after replacing the gas with a mixed gas, the reduced pressure inside the hollow fiber membrane is released and gas separation is interrupted or terminated. Hereinafter, each requirement of the present invention will be explained in more detail with reference to the drawings. As the hollow fiber membrane made of aromatic polyimide,
A solution of aromatic polyamic acid (or aromatic polyimide) obtained by polymerizing (and imidizing) an acid component such as aromatic tetracarboxylic acid or its acid dianhydride and an aromatic diamine component is used. hand,
A hollow fiber membrane for gas separation with an asymmetric structure (a hollow fiber membrane having an integrated homogeneous layer and a porous layer) formed by a wet membrane forming method using a coagulating liquid, or an aromatic polyimide solution can be used. A composite hollow fiber membrane manufactured by forming a thin homogeneous layer made of aromatic polyimide on the outer surface of a porous hollow fiber membrane made of
In addition, hollow fiber membranes having sufficient gas separation performance as described above for water vapor can be preferably mentioned. Examples of the aromatic diamine include 3,
7-diamino-2,8-dimethyl-dibenzothiophene, 3,7-diamino-2,6-dimethyl-
Dibenzothiophene, 2,8-diamino-3,7
Diamino-dibenzothiophenes such as -dimethyl-dibenzothiophene, 3,7-diamino-2,8-diethyl-dibenzothiophene, 3,7-
Diamino-2,8-dimethyl-diphenylene sulfone, 3,7-diamino-2,8-diethyl-diphenylene sulfone, 3,7-diamino-2,8
-dipropyl-diphenylene sulfone, 2,8-
Diamino-3,7-dimethyl-diphenylenesulfone, 3,7-diamino-2,8-dimethoxy-
Diamino-diphenylene sulfones such as diphenylene sulfone, 4,4'-diamino-diphenyl sulfone, 3,3'-diamino-diphenyl sulfone, 3,5-diamino-diphenyl sulfone,
Diamino-diphenyl sulfones such as 3,4'-diamino-diphenyl sulfone, 4,4'-diamino-diphenyl sulfide, 3,3'-diamino-
Diamino-diphenyl sulfides such as diphenyl sulfide, 3,5-diamino-diphenyl sulfide, 3,4'-diamino-diphenyl sulfide, 3,7-diamino-thioxanthene-
5,5-dioxide, 2,8-diamino-thioxanthene-5,5-dioxide, 3,7-diamino-thioxanthone-5,5-dioxide, 2,
8-diamino-thioxanthone-5,5-dioxide, 3,7-diamino-phenoxatin-5,
5-dioxide, 2,8-diamino-phenoxatin-5,5-dioxide, 2,7-diamino-
Diamino-thioxanthene or its derivatives such as thianthrene, 2,8-diamino-thianthrene, 3,7-diamino-10-methyl-phenothiazine-5,5-dioxide;
Examples include aromatic diamines having a sulfur atom such as aminophenoxy)phenyl]sulfide and bis[(p-aminophenoxy)phenyl]sulfone. Other aromatic diamines other than the above-mentioned sulfur-containing aromatic diamines include, for example, 4,4'-diamino-diphenyl ether, 3,3'-dimethyl-4,4'-diamino-diphenyl ether, 3 ，
Diphenyl ether compounds such as 3'-diethoxy-4,4'-diamino-diphenyl ether, 3,3'-diamino-diphenyl ether, 4,4'-diamino-diphenylmethane, 3,3'-diamino-
Diphenylmethane compounds such as diphenylmethane, 4,4'-diamino-benzophenone, 3,
Benzophenone compounds such as 3'-diamino-benzophenone, 2,2-bis(3-aminophenyl)propane, 2,2-bis(4-aminophenyl)propane, 2,2-bis[4-(4'-aminophenoxy)phenyl ] 2,2-bis(phenyl)propane compounds such as propane, and o-,
Mention may also be made of m-, p-phenylenediamine, 3,5-diaminobenzoic acid, 2,6-diaminopyridine, o-tolidine, and the like. The aromatic tetracarboxylic acid components used in the production of the aromatic polyimide include 3,3',
4,4'-biphenyltetracarboxylic acid, or 2,3,3',4'-biphenyltetracarboxylic acid,
Or their dianhydrides, or biphenyltetracarboxylic acids such as lower alcohol esters thereof, 3,3',4,4'-benzophenonetracarboxylic acid, or 2,3,3',4'- Benzophenonetetracarboxylic acids such as benzophenonetetracarboxylic acid, their dianhydrides, or lower alcohol esters thereof; and pyromellitic acids such as pyromellitic acid, its dianhydrides, or its esters. be able to. In particular, in this invention, an aromatic polyimide obtained from an aromatic tetracarboxylic acid component containing 50 to 100 mol%, especially 80 to 100 mol% of biphenyltetracarboxylic acids, and the above-mentioned aromatic diamine component. has excellent solubility in organic solvents such as phenolic compounds, so hollow fiber membranes made of such aromatic polyimides are useful for preparing stable spinning dopes and improving spinnability. This is suitable from the viewpoint of hollow fiber membrane production. The aromatic polyimide hollow fiber membrane used in this invention is made of aromatic polyamic acid (polyimide precursor) obtained from the above-mentioned aromatic diamine component and aromatic tetracarboxylic acid component, or an organic solvent-soluble aromatic polyimide. A solution containing homogeneously dissolved in an organic solvent is used as a dope solution for film forming, and is extruded from a hollow fiber spinning nozzle to form a hollow fiber-like thin film of the dope solution. A dry film forming method that mainly involves a drying process to remove the solvent from the hollow fiber membrane and solidify it, or a wet film forming method that forms a film by bringing a hollow fiber-like thin film of the dope into contact with a coagulating liquid and coagulating it. It can be formed into a hollow fiber membrane to produce an aromatic polyimide hollow fiber membrane. The aromatic polyimide hollow fiber membrane used in this invention has a ``ratio of gas permeation rates of water vapor and ethanol (PH ₂ O / PCH ₃ CH ₂ OH)'' measured and calculated by the gas permeation test method described below. ” permselectivity (gas separation performance) of 80 or more, preferably
An aromatic polyimide hollow fiber membrane having a molecular weight of 100 or more, more preferably about 110 to 10,000 is preferred. The hollow fiber membrane has a water vapor permeation rate (PH ₂ O; according to the gas permeation test method described below) at 100°C of about 1×10 ^-5 cm ³ /cm ² ·sec·cmHg or more, especially 1×
It is preferably about 10 ⁻⁴ to 5×10 ⁻² cm ³ /cm ² ·sec·cmHg. In this invention, for example, as shown in FIG.
Gas separation is performed using a gas separation device 1 in which a specific gas separation membrane (a bundle of aromatic polyimide hollow fiber membranes) 2 is built into and fixed in a sealed container 6 for gas separation. The sealed container has an "exhaust port 5 for permeated gas (water vapor, etc.) that has passed through the gas separation membrane" and a "replacement gas (purge gas) or raw material gas supply port" which are in communication with the gas permeation side of the gas separation membrane 2. Any sealed container (for example, a cylindrical container) having a "mixed gas supply port 3" and a "replacement gas or non-permeable gas discharge port 4" may be used. Both ends of the membrane (filament bundle of hollow fiber membranes) 2 are disk-shaped resin walls 7 formed by solidifying a suitable thermosetting resin such as elastomer resin, acrylate resin, epoxy resin, or phenol resin. 7' to form a hollow fiber membrane element, and each hollow fiber membrane penetrates inside the resin wall so that the holes inside the hollow fiber membrane are connected to the outside of the resin wall. Further, as shown in FIG. 1, the hollow element is attached to the inner wall of the sealed container 1 using adhesive or the like at the resin walls 7, 7' if necessary. The method of the present invention uses a gas separation device incorporating the aromatic polyimide hollow fiber membrane described above, and as shown in FIG. A mixed gas containing vapor of At least one component of the mixed gas that selectively permeates the thread membrane 2 (for example, water vapor, etc.)
is preferably discharged from the permeate gas outlet 5 under a reduced pressure of 1 to 300 Torr (along with the aforementioned purge gas), and on the other hand, the mixed gas (non-permeate gas) that has not permeated through the hollow fiber membrane is converted into a non-permeate gas. (a) Before first introducing the mixed gas to the outside of the hollow fiber membrane 2 of the gas separation device 1 described above, when separating the mixed gas by discharging it from the outlet 4, After reducing the pressure in the hollow of the thread membrane 2 to preferably 1 to 300 Torr, supplying the mixed gas,
When starting gas separation and further (b) stopping the introduction of the mixed gas into the gas separation device 1 in order to interrupt or end the gas separation, an organic compound is added to the outside of the hollow fiber membrane 2. After introducing a replacement gas that does not substantially contain the gas and replacing the mixed gas that existed outside the hollow fiber membrane during the gas separation, the reduced pressure inside the hollow fiber membrane 2 is released. The gas separation is started and stopped by equalizing the pressure between the outside and inside of the hollow fiber membrane and interrupting or terminating the gas separation. As the replacement gas which does not substantially contain the organic compound and/or water vapor, the vapor of the organic compound may be used in an amount of 1% by volume or more, especially . A replacement gas that does not contain more than 5% by volume, or a gas that does not contain more than 1% by volume of organic compound vapor and no water vapor.
The dry gas does not contain 2000 ppm or more, particularly 1000 ppm or more, and suitable examples thereof include dry air or replacement gases such as neon gas, argon gas, and nitrogen gas. In order to replace the mixed gas outside the hollow fiber membrane with a replacement gas that does not substantially contain organic compounds, the operating temperature is not particularly limited, but is preferably 0 to 200°C, particularly 5 to 200°C. The operating temperature may be about 150°C, and the operating time for gas replacement is the time until the concentration of organic compound vapor around the outside of the hollow fiber membrane no longer affects the expansion and contraction of the hollow fiber membrane. , preferably for 5 to 120 minutes, especially for 10 to 60 minutes
It only takes about a minute. The "mixed gas containing organic compound vapor" used in this invention includes hydrocarbons, natural gas, petroleum gas, methanol, ketones, ethers,
A mixed gas or water vapor containing at least two components such as esters as main components is a hydrocarbon, natural gas, petroleum gas, methanol, ketone,
In a mixed gas mainly composed of ether, ester, etc., at the temperature and pressure during dehumidification, the content is close to the saturated state (e.g., the saturation of water vapor in the mixed gas that is the raw material gas at the temperature during dehumidification) It is preferable that the mixed gas is contained at a content rate of at least 70% or more of the saturated content rate. In this invention, the pressure of the mixed gas supplied to the gas separation device is not particularly limited and can be within a wide range since gas separation can be adjusted by the pressure at the time of discharge of the permeated gas. However, in the present invention, it is preferable that the pressure of the permeated gas that has permeated into the hollow interior of the hollow fiber membrane is at a reduced pressure of about 1 to 300 Torr, so the pressure of the supplied mixed gas is around normal pressure or It may be under any pressure, especially about 0.5Kg/cm2 ^or more, preferably 1 to 10
Kg/cm ² , more preferably about 1.5 to 5 Kg/cm ² , is preferable in order to make gas separation efficient. In addition, the amount of the mixed gas supplied is such that the ratio of supply to the effective area of the gas separation membrane (relative to the effective membrane area of the hollow fiber) is approximately 0.005 to 100 ^{cm 3} /cm ² ·sec, particularly 0.01 to 10 cm ³ It is preferable that the supply amount be about 1/cm ² ·sec. [Example] In this invention, a gas permeation test was carried out using a gas separation device as shown in Fig. 1, which is equipped with a bundle of hollow fiber membranes made of each aromatic polyimide, and a mixed gas containing water vapor was tested. is supplied to the gas separation device, the inside of the hollow fiber is maintained at reduced pressure with a vacuum pump, and the vapor (gas) that permeates through the hollow fiber membrane is transferred to dry ice.
The ethanol concentration in the collected material was analyzed by gas chromatography, and the amount of water was measured by subtracting the ethanol content from the total amount of collected material. The water vapor permeation rate of the thread membrane was calculated. Example 1 A tetracarboxylic acid component consisting only of 3,3',4,4'-biphenyltetracarboxylic dianhydride,
4,4'-diaminodiphenyl ether 60 mol%,
3,5-diaminobenzoic acid 30 mol%, and 4,
A halogenated phenol solution of aromatic polyimide obtained by polymerizing and imidizing an aromatic diamine component consisting of 10 mol% of 4'-diaminodiphenylmethane in a halogenated phenol melt is used, and the solution is poured into a hollow cavity. An aromatic polyimide hollow fiber membrane (outer diameter: 545 μm, inner diameter: approximately 408 μm) having gas separation performance was prepared by extraction from a yarn spinning nozzle and produced by a wet spinning method. 100 of the above-mentioned hollow fiber membranes are bundled, and both ends of the fiber bundle are tightly bonded with epoxy resin and cured to form a resin wall to form a fiber bundle element of the hollow fiber membrane (the length of the part effective for gas separation; 20cm), place and fix the yarn bundle element in a sealed container, and approximately
A gas separation device of the type shown in the figure was manufactured. The gas separation device described above was connected to the test equipment, and the hollow interior of the hollow fiber membrane was first reduced to a pressure of approximately 3 mmHg, and then the mixed gas (mixed steam) was heated to 100°C from the gas separation device's mixed gas (mixed steam) supply port 3. A water-ethanol mixed vapor (80% by weight ethanol) was continuously fed along the outside of the hollow fiber membrane (bundle of hollow fiber membranes) 2 in the gas separation device for about 60 hours. While the mixed vapor flows along the outside of the hollow fiber membrane in the gas separation device, the permeate gas that has permeated the tube wall of the hollow fiber membrane passes through the hollow interior of the hollow fiber membrane and flows into the gas separation device. The permeated gas was taken out from the outlet 5, condensed and collected in a trap containing dry ice and ethanol. When 60 hours have elapsed, the supply of mixed steam is stopped, and instead nitrogen gas is supplied from the gas supply port 3 of the gas separation device along the outside of the hollow fiber membrane for about 60 minutes. After expelling the mixed vapor and the permeate gas inside the hollow fiber membrane to remove the vapor of the organic compound in the gas separation device, the reduced pressure inside the hollow fiber membrane was released. The gas separation operation substantially similar to that described above was repeated four more times for a total of 300 hours. After all of the above gas separation operations were completed, the gas separation apparatus was divided and the condition of the fiber bundles of the hollow fiber membranes was examined, but virtually no abnormalities or changes in appearance were found. Table 1 shows the water vapor permeation rate (PH ₂ O; cm ³ /cm ²・sec・mmHg) and permselectivity (PH ₂ O/PCH ₃ CH ₂ OH) at each stage in the gas separation operation. . Comparative Example 1 Before reducing the pressure inside the hollow fiber membrane of the gas separation device, a water-ethanol mixed vapor was supplied, and the mixed vapor was not replaced with nitrogen gas at all, and the supply of the mixed vapor was stopped. However, gas separation was carried out in the same manner as in Example 1, except that the reduced pressure inside the hollow fiber membrane was released. After all the gas separation operations described above were completed, the gas separation device was disassembled and the condition of the fiber bundle element of the hollow fiber membrane was inspected. However, there was no slack in the fiber bundle of the hollow fiber membrane, and each hollow fiber The membranes were in a strongly stretched state, and two of the 100 hollow fiber membranes had become thinner and torn near the resin wall. Table 1 shows the water vapor permeation rate (PH ₂ O; cm ³ /cm ²・sec・mmHg) and permselectivity (PH ₂ O/PCH ₃ CH ₂ OH) at each stage in the gas separation operation. .

[Actions and effects of the present invention]

This invention provides for bending of the hollow fiber membrane when the fiber bundle element of the aromatic polyimide hollow fiber membrane fixed in the gas separation device is repeatedly brought into contact with and interrupted with the vapor of the organic compound as described above. The start and stop operations of gas separation are devised so that the arrangement of the fiber bundles is not deformed, the hollow fiber membranes are not cut, or the gas separation performance of the hollow fiber membranes is not degraded. According to the gas separation method, it is possible to prevent damage to the aromatic polyimide hollow fiber membrane, bending and deformation of its fiber bundle elements, and furthermore, a sudden decrease in the gas selective permeability of the hollow fiber membrane. It has this effect.

[Brief explanation of the drawing]

FIG. 1 is a sectional view schematically showing a gas separation device incorporating a fiber bundle of aromatic polyimide hollow fiber membranes used in the present invention. 1; Gas separation device; 2; Aromatic polyimide hollow fiber membrane (fiber bundle); 3; Mixed gas of raw materials (mixed vapor)
supply port, 4; non-permeable gas discharge port, 5; permeable gas discharge port, 6; sealed container, 7; resin wall.

Claims (1)

[Scope of Claims] 1. A mixed gas containing an organic compound is supplied to the outside of an aromatic polyimide hollow fiber membrane having gas separation performance, and at least one of the mixed gases is supplied from the outside of the hollow fiber membrane to the inside. In a method of continuously performing gas separation by selectively permeating gas components, (a) before first introducing the mixed gas to the outside of the hollow fiber membrane, the inside of the hollow fiber membrane is depressurized; (b) when stopping the introduction of the mixed gas in order to interrupt or terminate the gas separation, the hollow fiber membrane is After introducing a replacement gas that does not substantially contain organic compounds and/or water vapor to the outside and replacing the mixed gas that was present outside the hollow fiber membrane in the gas separation, the hollow fiber A gas phase membrane separation method characterized by releasing the reduced pressure inside the membrane and interrupting or terminating gas separation.