JPH0363416B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a semipermeable membrane suitable for separating water-soluble organic compounds from a mixed liquid of water/water-soluble organic compounds.

Relationship with Prior Art In recent years, semipermeable membranes have come into widespread use in wastewater treatment, seawater desalination, food industry, medical fields, and the like. Furthermore, in the chemical industry, attempts are being made to utilize semipermeable membranes in the processes of separating, concentrating, and recovering valuable materials. As one such attempt, research began around the mid-1970s on pervaporation, with the aim of separating and purifying organic mixtures that were difficult to separate using conventional distillation methods. Pervaporation is a method in which a mixed liquid is placed on one side of the membrane and the other side is reduced in pressure, or an inert gas is kept at a low vapor pressure, and the pressure difference allows the liquid to permeate. This is a method of separating a mixture by evaporation. For example, it is applied to the separation and fractionation of azeotropic mixtures, solvents with similar boiling points, isomers, etc. As semipermeable membranes used in the pervaporation method, polyvinyl alcohol polymers are used in US Pat. No. 2,953,502, acrylonitrile polymers are used in US Pat. No. 3,726,934, and acrylonitrile polymers are used in US Pat. No. 2,960,462. discloses a composite membrane consisting of ethyl cellulose and polyethylene or cellulose butyl acetate, and JP-A-54-47579 discloses an example of separation of organic substance mixtures using polyvinyl alcohol hollow fibers. Further, JP-A-54-10549 discloses an example of separating organic substances using a separation membrane made of polyolefin, polystyrene, polyvinyl halide, polyvinyl acetal, or the like. However, since both membranes have poor separation efficiency, there is a problem in that even if the organic liquid mixture passes through the polymer membrane once, it cannot be separated and concentrated to the desired concentration. On the other hand, in order to separate and concentrate a water-soluble organic liquid to the desired concentration, it is necessary to pass it through a multilayer membrane, increase the membrane surface area, or make the membrane extremely thin. If this method is to be implemented industrially, the equipment must be enlarged, which has the disadvantage of increasing costs. In the latter case, problems arise in the strength and durability of the membrane.

Purpose of the Invention In order to overcome these drawbacks, it is necessary to develop a semipermeable membrane with excellent separation efficiency, and as a result of intensive research, the present inventors have found that a dextrin-based crosslinked thin membrane has extremely excellent separation properties. We have discovered that this shows the following, and have arrived at the present invention.

An object of the present invention is to provide a semipermeable membrane using a dextrin-based crosslinked membrane with good separation efficiency and excellent permeability. Another object of the present invention is to provide a semipermeable membrane with excellent separation efficiency and high permeability in the separation of organic substances such as by pervaporation.

Structure of the Invention That is, the gist of the present invention is a semipermeable membrane having a crosslinked structure obtained by the reaction of a dextrin-based substance and an isocyanate or epihalohydrin.

Further, preferred embodiments of the present invention include a composite membrane obtained by coating a support with the above reactant, or a membrane obtained by blending the reactant onto a support.

As the support according to the present invention, a porous support having excellent mechanical strength, heat resistance, chemical resistance, and microbial resistance is desirable. Examples of such porous supports include polyvinylidene fluoride, polysulfone, polystyrene, polyacrylonitrile, polypropylene, polycarbonate, polyester,
Examples include polyamide, polyvinyl chloride, and polyvinyl fluoride, with polyvinylidene fluoride and polysulfone being particularly preferred. The pore diameter on the surface of the porous support is not particularly limited, but in order to have particularly high permselectivity, it should be 100 or more.
Something in the range of 1000〓 is desirable. The shape of the porous support is not limited to a flat membrane, but can be used in the form of a tube or hollow fibers, and can be arbitrarily selected. When hollow fibers are used, the permeation area of the membrane can be maximized, so the separation throughput can be increased with a device that is more compact than conventional devices. Furthermore, since hollow fibers have excellent pressure resistance, the film thickness can be made thinner, and therefore the transmittance can be further increased. The hollow fiber preferably has an outer diameter of 5000μ or less, preferably 50 to 500μ. The smaller the outer diameter of the hollow fibers, the better the mechanical strength and pressure resistance, and therefore the thinner the film thickness. In addition, the thickness of the hollow fiber should be as thin as possible in order to increase the amount of permeation, but if it is made thin, the mechanical strength will decrease.
Preferably it is in the range of 10 to 100μ.

Next, the crosslinked thin film of the present invention can be obtained by casting the dextrin reactant solution on a glass plate and then evaporating the solvent on a hot plate or immersing it in water. Methods for forming a thin film of the dextrin reactant on the porous support include a method of casting a dextrin reactant solution onto the porous support, a method of spraying, or a method of dipping the porous support in the solution. There are methods. The dextrins used here are commercially available, and the cyclodextrins include α-cyclodextrin (n=6) and β-cyclodextrin (n=6).
7), γ-cyclodextrin (n=8), etc. The molecular weight of dextrin is not particularly limited. Isocyanates used as crosslinking agents include isophorone diisocyanate, hexamethylene diisocyanate, tolylene-2,4-diisocyanate, 4,4-diphenylmethane diisocyanate, and m-xylylene diisocyanate. As epihalohydrin, epichlorohydrin, epipromhydrin, 1,2-epoxy-4-chlorobutane, 2,3-epoxy-4
-chlorptane, 1,2-epoxy-5-florpentane, 1,2-epoxy-4-bromobutane, 2,3-epoxy-4-bromobutane, 1,
Examples include 2-epoxy-5-bromopentane and 2,3-epoxy-5-bromopentane. In addition, as a solvent for reacting dextrin, dimethyl sulfoxide, N,N-dimethylformamide,
N,N-dimethylacetamide and the like are preferred;
In addition, solvents such as acetone methyl ethyl ketone, chloroform, carbon tetrachloride, and tetrahydrofuran can also be used. The concentration of isocyanate or epihalohydrin in the organic solvent is not particularly limited, but it is preferably used in a range of 5% to 50% by weight. The degree of crosslinking of dextrin can be varied by changing the concentration of isocyanate or epihalohydrin. The crosslinking reaction is carried out at a temperature of 20° C. to 100° C. for a period of 1 hour to 24 hours.

Effects of the invention By using the dextrin crosslinked membrane thus obtained, it is possible to perform efficient separation and concentration with excellent organic matter separation efficiency and high permeation rate by pervaporation, which requires a large amount of energy and large size compared to conventional methods. This method has great advantages over the distillation method, which required several types of equipment, and its industrial merits are extremely large. In particular, water/ethyl alcohol was separated by pervaporation using a semipermeable membrane obtained by coating a polyvinylidene fluoride support membrane with dextrin crosslinked with isophorone diisocyanate. The separation coefficient was found to be higher than ever seen before.

Example Examples of the present invention will be described below.

Example 1 After dextrin was dissolved in dimethyl sulfoxide, isophorone diisocyanate was added under heating to convert the dextrin into urethane. This solution was coated on polyvinylidene fluoride film and air-dried to obtain a film. A permeation experiment was carried out using a 20% by volume aqueous ethyl alcohol solution at 40°C using the pervaporation method. Separation factor α ^H2OEtoH =
1877.2 Water permeation rate QH ₂ O＝2.925×10 ¹ Kg・m
^-2・day ^-1 , ethyl alcohol permeation rate Q _EtpH =
3.117×10 ^-3 Kg・m ^-2・day ^-1 was obtained.

Example 2 A film was prepared by mixing dextrin urethanized with isophorone diisocyanate into polyvinylidene fluoride. Using this membrane, we conducted a permeation experiment using a pervaporation method with a 20% ethyl alcohol aqueous solution at 40°C, and found that the separation coefficient α ^H2OEtoH =
109.0, water permeation rate Q _H2O = 1.741×10 ^-1 Kg・m
^-2・day ^-1 , ethyl alcohol permeation rate Q _EtpH =
3.196×10 ^-4 Kg・m ^-2・day ^-1 was obtained.

Example 3 Using a membrane in which a polypinylidene fluoride film was coated with dextrin urethanized with isophorone diisocyanate, a permeation experiment was carried out using a permeation method using an 80% by volume aqueous ethyl alcohol solution at 40°C. Separation coefficient α ^H2OEtoH = 389.3, water permeation rate QH ₂ O = 9.451×10 ^-1 Kg・m ⁻²・day ⁻¹ ethyl alcohol permeation rate Q _EtpH = 7.711×10 ⁻³ Kg・
It was m ^-3・day ^-1 .

Example 4 Using a membrane in which a polysulfone film was coated with dextrin urethanized with hexamethylene diisocyanate, pervaporation of an 80% by volume aqueous ethyl alcohol solution was carried out at 40°C. Separation coefficient α ^H2OEtoH = 128.4 Water permeation rate 2.910×10 ^-1 Kg・m
^-2・day ^-1 , ethyl alcohol permeation rate Q _EtpH =
It was 5.416×10 ^-3 Kg・m ^-2・day ^-1 .

Example 5 A membrane was prepared by coating a polysulfone film with α-cyclodextrin urethanized with hexamethylene diisocyanate. Using this membrane, a permeation experiment using the pervaporation method of a 90% ethyl alcohol aqueous solution was conducted at 40°C, and the separation coefficient α ^H2OEtoH = 50.8 and the water permeation rate Q _H2O = 1.778×10 ^-1
Kg・m ^-2・day ^-1 , permeation rate of ethyl alcohol
Q _EtpH = 2.492×10 ^-2 Kg·m ^-2 ·day ^-1 was obtained.

Example 6 Dextrin epoxidized with epichlorohydrin was pervaporated using a membrane coated on a polyvinylidene fluoride film. Separation coefficient α ^H2OEtoH = 76.8, water permeation rate QH ₂ O = 1.504×10 ^-1 at 40°C for 80% ethyl alcohol aqueous solution by volume
Kg・m ^-2・day ^-1 , permeation rate of ethyl alcohol,
Q _EtpH = 6.224×10 ^-3 Kg・m ^-2・day ^-1 .

Example 7 A membrane was prepared by coating a polysulfone film with dextrin epoxidized with epichlorohydrin. Using this membrane, a pervaporation experiment of a 50% by volume aqueous ethyl alcohol solution was conducted at 40°C. Separation coefficient α ^H2OEtoH = 17.6, water permeation rate
Q _H2O = 1.443×10 ^-1 Kg・m ^-2・day ^-1 , Ethyl alcohol permeation rate Q _EtpH = 6.507×10 ^-3 Kg・m ^-2・
Got day ^-1 .

Comparative Example After dextran was dissolved in dimethyl sulfoxide, isophorone diisocyanate was added under heating to convert the dextran into urethane. This solution was coated on a polyvinylidene fluoride film and air-dried to obtain a film. of this membrane
The results of a permeation experiment using a 20% ethyl alcohol aqueous solution at 40°C by pervaporation method: Separation coefficient α ^H2OEtoH = 5.0 Water permeation rate Q _H2O = 5.683Kg・m ^-2・day ^-1 Ethyl alcohol permeation rate Q _EtOH = 2.264×
10 ⁻¹ Kg·m ⁻² ·day ⁻¹ , and the separation performance was inferior to that of the dextrin crosslinked membrane.

Claims (1)

[Claims] 1 A semipermeable membrane for pervaporation having a crosslinked structure obtained by reacting dextrin with isocyanate or epihalohydrin.