JPS60209205A - Preparation of hollow yarn porous membrane comprising polyvinylidene fluoride - Google Patents

Abstract

PURPOSE:To prepare hollow yarn porous membrane having high roundness and asymmetric structure by extruding a solution comprising polyvinylidene fluoride, PEG, and DMA through an annular nozzle, and guiding the extruded product contg. liquid in the inside as it is into coagulating bath. CONSTITUTION:Polyvinylidene fluoride type polymer is dissolved in a mixed solvent comprising dimethyl acetamide and polyethylene glycol having <=1,000 mol.wt. in 95:5-80:20 proportion to prepare a solution having 5-30wt% concn. The soln, is extruded through an annular nozzle while holding temp. at >=50 deg.C, and a solvent mixture comprising 60:40-40:60 dimethyl acetamide and polyethylene glycol is introduced into the inside of the hollow yarn. After passing the extruded yarn through a space having a specified distance, it is guided into a coagulating bath holding an aq. soln. contg. <20wt% solvent mixture comprising dimethyl acetamide and polyethylene glycol, and heat-treated in the water while restricting the shrinkage to <=10%.

Description

[Detailed Description of the Invention] The invention relates to the production of polyvinylidene fluoride separation membranes.More specifically, the invention relates to the production of polyvinylidene fluoride separation membranes. This invention relates to a filamentous porous membrane.

BACKGROUND ART In recent years, attempts have been made to separate mixed gases and mixed liquids by utilizing the gas selective separation property and liquid selective permeability of polymer membranes. However, the permeation rate of gas or liquid through such polymer membranes is generally very low, and it is quite difficult to carry out fractional concentration of gas or liquid outside of a commercial station. In other words, it is known that the amount of gas or liquid that permeates through a polymer membrane is generally proportional to the area of the polymer membrane, the concentration difference on both sides of the polymer membrane, and the pressure difference, and inversely proportional to the thickness of the polymer membrane. . Membrane thickness and pressure resistance are essentially contradictory properties, and in order to perform gas or liquid separation on a commercial scale using polymer membranes, it is unavoidable to overcome this contradiction, which requires a great deal of effort. It is accompanied by difficulties.
In order to effectively resolve this contradiction, we have developed a method to improve membrane area per unit volume and pressure per unit membrane thickness by making polymer membranes hollow fibers. Attempts have been made to improve pressure resistance per unit film thickness by forming composite films.

There are quite a lot of publications regarding the manufacturing method of polyvinylidene fluoride hollow fiber porous membranes, such as JP-A-S-6693! l
, JP-A-55-696! Ifu, Japanese Patent Publication No. 515-9993
4. As revealed in Japanese Patent Application Laid-open No. 1986-86, etc., all of these methods not only contain surfactants in the membrane-forming stock solution, but also contain surfactants, which are the most important method for producing hollow fiber porous membranes. Warm water is used to coagulate the internal liquid of the hollow fiber, which is a major factor.

In such a case, the solidification rate of the gel-like material linearly extruded from the annular nozzle from the spinning dope is fast, which not only impairs the roundness of the hollow fiber membrane but also damages the dense layer of the hollow fiber membrane, which has an asymmetric structure. The pore size becomes large, which is not preferable. When the roundness of the hollow fibers is impaired, the pressure resistance decreases. Furthermore, when the pore diameter of the narrow layer of a hollow fiber membrane having an asymmetric structure becomes large, the gas separation ability or liquid separation function decreases.

When manufacturing a gas or liquid multi-unit system in which a polymer thin film is supported on the dense layer side of a hollow fiber membrane having an asymmetric structure, a porous hollow fiber fL that serves as a support 1 is used. Regarding 011, the pore size distribution greatly affects the performance of the composite membrane, and when the pore size of the porous hollow fiber membrane is large, the resistance such as pressure drop when gas or liquid permeates is small, and the amount of permeation can be increased. However, on the other hand, when a thin polymer film is formed on the dense layer surface of the porous hollow fiber membrane, the pressure resistance of the thin polymer film decreases, and defects such as pinholes occur in the thin polymer film. An increase in the thickness of the polymer thin film is not necessarily desirable. That is, when separating and concentrating gas or liquid using a composite hollow fiber membrane supporting a thin polymer membrane, the reduction in the thickness of the thin polymer membrane is an important factor in increasing the permeation amount per membrane. In order to substantially increase the pressure resistance of the polymer membrane while reducing the thickness of the membrane, it is desirable to divide the thin polymer membrane through which gas or liquid is permeable into as small a portion as possible and have them supported on the support membrane. In order to achieve this, it is desirable that the micropore diameter of the porous hollow fiber membrane surface that functions as a polymer membrane support has a maximum value of micropore distribution of 50.5100X, and the generation of pinholes can be prevented. desirable.

As a result of intensive research into a method for producing a hollow fiber porous membrane with such a pore size distribution using polyvinylidene fluoride polymer, the yrL6i laxative liquid was prepared from polyvinylidene fluoride polymer 7'-tyt 7'amide and ethylene glycol. the linear body is introduced into the inside of the linear body, the linear body is then guided through a space of a predetermined length, and the linear body is then introduced into a coagulation bath consisting of an aqueous solution containing less than 5% by weight of a mixed solvent. Production of a polyvinylidene fluoride hollow fiber porous membrane having roundness and a maximum micropore distribution with a micropore diameter of 50 to 200X on the hollow fiber membrane surface by a method for producing a polyvinylidene fluoride hollow fiber porous membrane. The present invention was achieved by discovering that the polyvinylidene fluoride hollow fiber porous membrane obtained by such a manufacturing method has an active layer portion with a smooth and dense structure and a supporting layer with a porous sponge structure. It has layer parts. Looking at the cross section of the membrane, the pores in the porous structure are large, and the active layer is small and has a gradient. In this way, an asymmetric separation membrane with different pore size distributions on both sides of the membrane can be obtained. , the throughput will be increased in practical gas or liquid separation operations.

Here, the polyvinylidene fluoride-based polymer in the present invention refers to vinylidene fluoride homopolymer, and for example, biylidene fluoride-tetrafluoride ethylene copolymer,
It means a random or random copolymer of vinylidene fluoride, such as vinylidene fluoride-hexafluorobylene copolymer, ethylene-tetrafluoride ethylene copolymer, etc., or a mixture thereof. Mixtures of these vinylidene fluoride polymers and small amounts of other polymers are also included in the present invention. The best solvent for the polyvinylidene fluoride polymer used in the present invention is a mixed solvent of dimethylacetamide and polyethylene glycol. It is best for polyethylene glycol to have a molecular weight of 1000 or less.

In addition to diethylacetamide (DMAO), dimethylformamide (DM7), diethylformamide (DI?), diethylacetamide (DMAo), and trimethylphosphate can be used as solvents for polyvinylidene fluoride polymers.
) (TMP) M-methylpyrrolidone (IMF), hexamethylphosphoamide (HMPA), tetramethylurea (TMV), etc., but the solubility of the polyfluorinated bi=IJ-dene polymer or the stability of the polymer solution If the molecular weight of the polyethylene glycol exceeds 1000, the solubility of the polyvinylidene fluoride polymer will not only deteriorate, but also the pore size of the polyvinylidene fluoride hollow fiber membrane formed will become too large, which is not desirable. do not have. Dimethylacetamide and polyethylene glyco.

The mixing ratio of 2@:p is 9615 to 801 g by weight.
.

If the range is 9o:1o to 1i15+15, the polymer 11 degree in the solution should be 5 to 3031t%, and if the concentration is less than 1B%, the viscosity of the solution is low and spinning becomes difficult.On the other hand, 30 If the viscosity of the solution exceeds 1%, spinning becomes difficult.The stock solution for film forming should be kept at a high temperature of 50°C or higher to prevent the melt from gelling. Just beforehand, the temperature can be adjusted to the desired temperature.

The membrane-forming stock solution prepared in this way is extruded linearly through an annular nozzle at a temperature higher than the gelling temperature, and at the same time a mixed liquid consisting of dimethylacetamide and ethylene glycol is introduced inside the linear body. Then, the linear body is introduced through a space of a predetermined length into a coagulation bath consisting of an aqueous solution containing less than % to*1 of a mixed solvent consisting of dimethylacetamide and polyethylene glycol.・Dimethyl introduced into the inside of the linear body The mixing ratio of acetamide and ethylene glycol is preferably in the range of 60240 to 40+60 in terms of volume ratio.
If the proportion of diethylacetamide is too high, fiber breakage during spinning will increase and the roundness of the hollow fibers will be impaired.

Furthermore, even if the proportion of ethylene glycol is increased, the coagulation rate becomes too fast11, resulting in breakage and loss of roundness of the hollow fiber membrane. In order to stably spin a perfectly circular hollow fiber membrane, the mixing ratio of dimethylacetamide and ethylene glycol is very important. An aqueous solution containing less than 20% by weight is used, but if the concentration of the mixed solvent becomes too high, the coagulation rate will slow down and the micropore diameter of the dense layer on the outside of the hollow fiber membrane will become too small, resulting in an extreme amount of gas or liquid permeation. If the temperature of the coagulation bath becomes too low, the coagulation rate slows down, and the amount of gas or liquid permeation decreases as described above.Preferably, the temperature is in the range of sO 0 C to 60 0 C.

The hollow fiber porous membrane endowed with an asymmetric structure in this way has a final content of preferably 10% or less! The heat treatment is carried out in water or an aqueous non-solvent mixture at a temperature range of 60°C to 98°C, preferably in a temperature range of 80°C to 9B"0, under a limited shrinkage of 1% or less. is the amount of shrinkage in the direction of maximum shrinkage on the membrane surface, expressed as a percentage of its initial length.When the shrinkage rate exceeds 10%, the amount of gas or liquid permeation decreases significantly. Furthermore, if the heat treatment temperature is lower than 60°C, the hollow fiber membrane structure will not be sufficiently fixed, and the pores will become smaller during drying and the performance of the membrane will deteriorate.

-1, the hollow fiber porous membrane obtained like an ear will eventually become 4
In order to obtain a dry membrane, it is necessary to dry the hollow fiber porous membrane at a temperature below the heat treatment temperature.The drying temperature is the heat treatment temperature. If the temperature is higher than that, structural changes will occur again during the drying process, resulting in a decrease in porosity and deformation of the membrane.Membranes dried below the heat treatment temperature will have almost no change in porosity, and will undergo structural changes again during the drying process. Even when it is returned to water, it maintains the same membrane performance as before drying.

The thus obtained composite membrane, in which a thin polymer film is supported on the surface layer of a polyvinylidene fluoride-based hollow fiber porous membrane, has high pressure resistance and excellent gas or liquid permeability, even though the thin polymer film is extremely thin. 10 films with excellent performance.

Example 1 Polyvinylidene fluoride (Ou Chemical xy*x1oo) 2
Mix 8 parts (weight fraction) of 7.2 parts of dimethyl acetate as a solvent to prepare a homogeneous solution. The temperature was kept at 0°C. This polymer solution is extruded from an annular nozzle for producing hollow fibers using a cap pump, and at the same time, a mixture of equal volumes of 1 dimethylacetamide and ethylene glycol is introduced inside the hollow fibers. After passing through a space of a predetermined length, Put it in warm water at 48℃ and make it 1i41 (lIl).The shape of the hollow fiber is the outer diameter SOOμ, the inner diameter is 0μ, and the water permeability is 10-' cd/ed -s. -csHg
, the porosity was 6 parts%"Q〇' Example 2 The hollow fiber porous membrane obtained in Example 1 was soaked in hot water at 40 to 96 °C under controlled limited shrinkage and free shrinkage of 5% or less. The hollow fiber porous membrane was immersed in water for 10 minutes for heat treatment, and then dried in hot air at 135°C.The performance of the obtained hollow fiber porous membrane is shown in Table 1. The unit of 0 water permeability is 1lI8/lI/-day atm
, the unit of nitrogen permeation is ell/8m? -m @O-cs
The units of Hg and porosity are expressed in %.

Table 1: As a result of measuring the V pore diameter distribution of polyvinylidene fluoride hollow fiber membranes of A8 by electron microscopy and mercury porosimetry, the structure of the hollow fiber membranes shows that the average pore diameter of the surface dense layer is 100 to tooX1. The supporting layer has giant pores of 20 microns or more and pores with a medium pore diameter of 0.1 to 0.6 microns surrounding the giant pores.

Claims (2)

[Claims] (1) Polyvinylidene fluoride polymer is introduced into the inside of a liquid mixture consisting of polyethylene glycol, dimethyl hydroxide, and ethylene glycol, and then a space of a predetermined length is created. a polyvinylidene fluoride hollow fiber porous membrane, characterized in that the linear body is introduced into a coagulation bath consisting of an aqueous solution containing less than ''to% by weight of the mixed solvent. manufacturing method. (2) 60° under limited contraction of 10% or less after solidification
The method according to claim 1, wherein the process is heat-treated in water or an aqueous non-solvent mixture at a temperature of 98°C to 98°C.