JP2018134611A - Method for producing hollow fiber carbon membrane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a hollow fiber carbon membrane.SOLUTION: A method for producing a hollow fiber carbon membrane includes: preparing a membrane forming stock solution for carbon membrane in which polyphenylene oxide in an amount of 15-40 wt.% in the membrane forming stock solution and lithium chloride in an amount of 0.1-5.0 wt.% with respect to the polyphenylene oxide is dissolved in a solvent capable of dissolving them; molding the membrane forming stock solution for carbon membrane into a hollow shape with the use of a double annular nozzle by a spinning method by a nonsolvent induction separation method; heating the obtained hollow membrane at 150-350°C and subjecting the hollow membrane to infusibilizing treatment; and heating the hollow membrane at 600-800°C in the inert atmosphere or in the vacuum and subjecting the hollow film to carbonization treatment. A method for producing a hollow fiber carbon membrane includes subjecting the surface of the hollow membrane to chemical vapor deposition treatment using hydrocarbon gas after the carbonization.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a method for producing a hollow fiber carbon membrane. More specifically, the present invention relates to a method for producing a hollow fiber carbon membrane using a carbon membrane stock solution containing polyphenylene oxide as a membrane-forming component.

  Conventionally, various organic membranes and inorganic membranes have been proposed as separation membranes. However, although organic films are inexpensive and have excellent moldability, they have low solvent resistance and heat resistance, while ceramic films and other inorganic films have excellent solvent resistance and heat resistance, as opposed to organic films. However, it is expensive and difficult to mold.

  Therefore, in recent years, a carbon film that is an inorganic film and has excellent moldability and is inexpensive has attracted attention. The hollow fiber carbon membrane has pores of a size that allows gas separation, exhibits excellent gas separation performance among various inorganic membranes, and is resistant to high temperatures such as 70 to 150 ° C. where organic membranes cannot be applied. Since it can be used in an environment where chemical resistance is required, its practicality is greatly expected. In addition, the hollow fiber membrane is excellent in pressure resistance and has a large membrane area per unit volume, making it possible to produce a compact separation membrane module.

  So far, as carbon film materials, for example, those using polyphenylene oxide resin (Patent Documents 1 and 2) and those using a resin sulfonated polyphenylene oxide (Patent Documents 3 and 4) have been proposed.

  In general, the carbon film is heated at 600-800 ° C in an inert atmosphere or in vacuum after being subjected to "infusibilization" heating at 150-350 ° C in air, regardless of which organic material is used. It is necessary to perform two-stage heating, such as performing “carbonization treatment”.

  However, the hollow fiber carbon membrane obtained by such a production method has a strength higher than that of the support, for example, as compared with a coated carbon membrane in which the carbon membrane is formed on the support as disclosed in Patent Document 5. Since it is necessary to maintain the strength of the membrane itself only by the strength of the small hollow fiber itself, the strength tends to be smaller than that of the coated carbon membrane.

  Further, in the hollow fiber carbon membrane obtained by the above production method, generation of voids having a size of several μm is confirmed in the cross section, and the presence of such voids can be a decrease in strength of the hollow fiber and a starting point of breakage.

  Therefore, the strength of the obtained hollow fiber carbon membrane is improved, and when a hollow fiber membrane module is produced using the hollow fiber carbon membrane, it is difficult to cause hollow fiber breakage due to handling, and the durability of the module is further improved. It is demanded.

WO 2016/0667900 WO 2016/093357 JP 2009-34614 A JP 2013-94744 A WO2013 / 042262 Japanese Patent Laid-Open No. 7-51551

  The object of the present invention is to use a stock solution for carbon film containing polyphenylene oxide as a main component, and after applying “infusibilization treatment” in air at 150 to 350 ° C., in an inert atmosphere or in vacuum. It is possible to improve the strength of the hollow fiber carbon membrane obtained in the production method of the hollow fiber carbon membrane produced by applying two stages of heating such as “carbonization treatment” of heating at 600 to 800 ° C. An object of the present invention is to provide a method for producing a hollow fiber carbon membrane.

  The object of the present invention is to dissolve polyphenylene oxide in an amount of 15 to 40% by weight in the film-forming stock solution and lithium chloride in an amount of 0.1 to 5.0% by weight with respect to the polyphenylene oxide. A carbon membrane forming stock solution dissolved in a suitable solvent was prepared, and the carbon membrane forming stock solution was formed into a hollow shape by a spinning method by a non-solvent induced separation method using a double annular nozzle. This is achieved by heating the hollow membrane at 150 to 350 ° C. for infusibilization, and further heating at 600 to 800 ° C. in an inert atmosphere or vacuum for carbonization.

  According to the method for producing a hollow fiber carbon membrane according to the present invention, by using a film-forming stock solution in which polyphenylene oxide and lithium chloride in an amount of 0.1 to 5.0% by weight with respect to the polyphenylene oxide are added, There are excellent effects of suppressing the generation of voids in the yarn cross section, preventing the voids from becoming the starting point of breakage, and making it possible to produce a hollow fiber membrane that is difficult to break by handling and easy to handle.

It is a figure which shows the Weibull distribution which represented the result of the tension test done about the hollow fiber membrane obtained by the Example and the comparative example in the graph. It is a figure showing a cross-sectional structure by SEM observation of the hollow fiber membrane obtained in the example It is a figure showing a cross-sectional structure by SEM observation of a hollow fiber membrane obtained in a comparative example

  As the polyphenylene oxide, commercially available products, for example, SABIC product PPO646, Mitsubishi Engineering Plastics products PX100F, PX100L, etc. can be used as they are. % Is used. When the concentration of polyphenylene oxide is higher than this, the raw film forming solution is separated and cannot be spun. On the other hand, when it is lower than this, it may become brittle during firing and a good carbon film may not be obtained.

  Further, lithium chloride in an amount of about 0.1 to 5.0% by weight, preferably about 0.2 to 3.0% by weight, based on polyphenylene oxide is added to the film forming stock solution. Such an addition ratio is determined from the viewpoint that it is possible to produce a hollow fiber carbon membrane in which the occurrence of voids in the cross section of the obtained hollow fiber is almost completely suppressed and the strength is remarkably improved. If the proportion of lithium chloride is less than this, the void suppression effect on the cross section of the hollow fiber membrane obtained by adding lithium chloride will not be sufficiently observed, while if more than this, the polymer concentration of the main component polyphenylene oxide will be As a result, the sufficient gas separation performance cannot be obtained.

  Inclusion of a predetermined amount of lithium chloride in the membrane-forming stock solution can improve the strength of the hollow fiber carbon membrane. As clearly shown in the Weibull distribution of FIG. 1, the hollow fiber membrane obtained using the spinning stock solution to which lithium chloride is added has a reduced probability of breakage.

  That is, the hollow fiber membrane obtained by the production method according to the present invention has no voids in the cross section as shown in FIG. 2, while the hollow fiber membrane produced using a spinning stock solution without adding lithium chloride is As shown in FIG. 3, voids are confirmed in the cross section, and comparing these, it is clear that the strength is improved by adding lithium chloride to the spinning dope.

  As a result, the void does not become the starting point of breakage in the hollow fiber, and it is difficult to break by handling during modularization, and handling becomes easy.

  Preparation of a carbon film-forming stock solution is performed by dissolving polyphenylene oxide and lithium chloride (and additives) in a solvent in which they can be dissolved. Examples of such a solvent include methanol, ethanol, tetrahydrofuran, N, N-dimethylacetamide, N-methyl-2-pyrrolidone and the like, preferably a non-proton such as N, N-dimethylacetamide, N-methyl-2-pyrrolidone and the like. Polar solvents are used.

  Here, since stable spinning cannot be performed if the spinning dope is phase-separated at the time of spinning, the film-forming solution at the time of spinning and film-forming is preferably a phase-stable temperature, preferably [temperature during film-forming temperature for phase separation. ] Whose phase stability is 10 ° C. or more is used.

  The prepared film forming solution is directly or directly idled from the outer tube of a hollow fiber spinning nozzle having a double ring structure by a spinning method using a non-solvent induced phase separation method such as a wet spinning method or a dry wet spinning method. A polyphenylene oxide hollow fiber membrane is formed by extruding inward and, if necessary, simultaneously extruding a core solution that is incompatible with the solvent of the membrane forming solution and the polymer from the inner tube of the spinning nozzle. Here, the core solution and the coagulation bath are mixed with the solvent of the film-forming stock solution, but a solvent incompatible with polyphenylene oxide, for example, water, ethylene glycol, or the like is used. The temperature of the core liquid and the coagulation bath at this time is generally about -20 to 60 ° C, preferably about 0 to 30 ° C.

  The obtained polymer hollow fiber membrane is washed with water as necessary, and then dried, that is, moisture is removed from the polymer portion of the hollow fiber-like product. The drying is not particularly limited as long as the polymer hollow fiber membrane is completely dried, but is generally performed at about 20 to 80 ° C, preferably about 25 to 60 ° C for about 0.5 to 4 hours.

  The dried polymer hollow fiber membrane is subjected to an infusibilization treatment before the carbonization treatment. The infusibilization treatment is performed by performing a heat treatment at a temperature lower than the carbonization temperature such as about 150 to 350 ° C. for about 0.5 to 4 hours. Such infusibilization treatment will particularly improve the performance as a carbon hollow fiber membrane.

Carbonization treatment is carried out by using the obtained precursor polymer hollow fiber membrane in a known manner, for example, containing the precursor polymer hollow fiber membrane in a container, and under reduced pressure of 10 ⁻⁴ atm or less (about 10 Pa or less) or helium or argon gas. The heat treatment is performed in an inert gas atmosphere substituted with nitrogen gas or the like. The heating conditions vary depending on the type of material constituting the precursor polymer, the amount thereof, and the like, but generally it is about 450 to 850 ° C. under a reduced pressure of 10 ⁻⁴ atm or less (about 10 Pa or less) or in an inert gas atmosphere. Preferably, conditions such as about 600 to 800 ° C. and about 0.5 to 4 hours are applied.

  In order to further improve the separation performance of the obtained hollow fiber carbon membrane, chemical vapor deposition (CVD), which is a known technique (see Patent Document 6, etc.), preferably propylene, butane, cyclohexane, etc. CVD treatment using hydrocarbon gas can also be performed. By performing such a CVD process, an effect of achieving higher separation performance is observed.

  Next, the present invention will be described with reference to examples.

Example A film-forming stock solution comprising 34 parts by weight of polyphenylene oxide (SABIC PPO616), 1 part by weight of lithium chloride and 65 parts by weight of dimethylacetamide was prepared. The prepared spinning solution was heated to 150 ° C., and then, using a spinning nozzle having a double ring structure, ethylene glycol was extruded as a core solution into a water coagulation bath, and wet spinning was performed at a spinning speed of 15 m / min. Thereafter, it was dried in an oven at 60 ° C. to obtain a porous polyphenylene oxide hollow fiber membrane having an outer diameter of 1060 μm and an inner diameter of 930 μm.

  Next, the obtained hollow fiber membrane was inserted into a tube made of perfluoroalkoxyalkane resin (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin) and heated in air at 300 ° C. for 1 hour to make it infusible. Treated. Further, the infusibilized hollow fiber membrane is inserted into a quartz tube, heated in a nitrogen atmosphere at a temperature of 650 ° C. for 1 hour, and carbonized to obtain a hollow fiber carbon membrane having an outer diameter of 430 μm and an inner diameter of 370 μm. It was. Using the obtained carbon film, a tensile strength test (based on JIS R7606: 2000) was performed, and the fracture probability was determined from the Weibull distribution. Furthermore, the cross-sectional structure was confirmed by SEM observation.

Comparative Example In the examples, lithium chloride was not used, and a membrane-forming stock solution having a dimethylacetamide content of 66 parts by weight was used, and a hollow fiber carbon membrane of the same size was obtained.

  The comparison results of the Weibull distribution obtained in Examples and Comparative Examples are shown in FIG. 1 (▲: Examples, ◆: Comparative Examples), and the cross-sectional structures by SEM observation are shown in FIG. 2 (Examples) and FIG. Shown in

Claims (3)

  Carbon obtained by dissolving polyphenylene oxide in an amount of 15 to 40% by weight in the film-forming stock solution and lithium chloride in an amount of 0.1 to 5.0% by weight with respect to the polyphenylene oxide in a solvent capable of dissolving them. A membrane-forming stock solution for a membrane is prepared, and the membrane-forming solution for carbon membrane is formed into a hollow shape by a spinning method using a non-solvent induced separation method using a double annular nozzle, and the formed hollow membrane is 150 to 350 A method for producing a hollow fiber carbon membrane, comprising heating at 600C to infusibilize, and further heating at 600 to 800C in an inert atmosphere or vacuum to perform carbonization.   The method for producing a hollow fiber carbon membrane according to claim 1, wherein after the carbonization treatment, a chemical vapor deposition treatment using a hydrocarbon gas is further performed on the surface.   Carbon obtained by dissolving polyphenylene oxide in an amount of 15 to 40% by weight in the film-forming stock solution and lithium chloride in an amount of 0.1 to 5.0% by weight with respect to the polyphenylene oxide in a solvent capable of dissolving them. Membrane stock solution.