JP2958030B2 - Separation method of organic solvent mixture - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for separating an organic gas and a liquid mixture using a polymer membrane. More specifically, the present invention relates to a method for separating an organic gas and liquid mixture by using a multilayer composite hollow fiber membrane having excellent gas and liquid permeability, and particularly by a pervaporation method (pervaporation).

(Prior art)

In the pervaporation method, a liquid mixture is supplied to one side of a non-porous polymer membrane and the other side is evacuated to reduce the pressure, or a carrier gas such as an inert gas is supplied to lower the vapor pressure. This is a method of preferentially separating and concentrating components that easily permeate through the membrane. This membrane separation method
It is effective for separating an organic gas from a waste gas or a liquid mixture. In particular, when obtaining a liquid having a purity higher than the azeotropic composition from a liquid mixture having an azeotropic composition (for example, a mixed liquid of water and ethanol), or separation of alcohol from a low-concentration aqueous alcohol solution obtained by fermenting biomass resources It is effective for etc. For such a purpose, it is indispensable to construct a high-performance separation membrane, and at present, its development is urgent.

In the pervaporation method, the components in the mixed gas and the mixed solution are dissolved.
Since it permeates the membrane by the diffusion mechanism, selectivity is developed in the process of dissolving the permeated component to the membrane and in the process of diffusion in the membrane. Therefore, it is said that a material which has an affinity for one component in the mixture and specifically dissolves it has high permselectivity. For example, as a polymer film which selectively permeates alcohol, a silicone rubber film (JP-A-57-1369) is used.
No. 05), a polyacetylene derivative film (JP-A-60-7530)
No. 6) is known.

[Problems to be solved by the invention]

However, in such a membrane material, when the composition of the permselective component (organic solvent) in the mixture increases, the membrane swells significantly due to excessive dissolution in the membrane. As a result, the poorly permeable component also easily permeates, so that a decrease in selectivity cannot be avoided. In order to prevent such a plasticization effect due to film swelling,
Generally, a method of introducing an appropriate cross-linking structure into a membrane polymer or introducing a chain having no affinity for both components of a mixture into a membrane is adopted. The method of controlling membrane swelling by cross-linking has the problem that a large permeation rate cannot be obtained because the diffusion rate of the substance in the membrane decreases, and a method of introducing a chain having no affinity to both components of the mixture In this case, it is difficult to increase the permeation rate because the amount of the permeable component dissolved in the membrane is reduced. In order to increase the transmission speed, thinning is as important as material development. As one of thin film forming techniques, a method of forming a thin film on a porous base material by a coating method or a vapor deposition method has been actively performed. However, in such a method, a substantial thin film cannot be obtained because the thin film material penetrates into the pores of the porous substrate.

In order to avoid this phenomenon, there is a method of filling the pores of the porous substrate with a soluble substance in advance and forming a thin film on the surface and then eluting the soluble substance in the porous substrate. It is difficult to obtain a thin film layer and it is easily damaged, and the risk of defects is extremely high.

[Means for solving the problem]

The gist of the present invention is a multilayer composite hollow fiber membrane in which a separation layer A having a selective separation function and a porous layer B having a reinforcement function are alternately stacked on a mixed solution containing an organic solvent and water, The inner surface and the outer surface are the porous layer B and the separation layer A
Is made of a non-flowable polymer at room temperature and has a thickness of 1 μm.
There is a separation method in which an organic solvent is selectively permeated by a pervaporation method using the following multilayer composite hollow fiber membrane.

The multilayer composite hollow fiber membrane has at least a three-layer structure. The outer surface and the inner surface are made of a porous layer having a reinforcing and protecting function, and the separation layer A serving as an intermediate layer is made of a very thin film having a separating function. Basically, one layer of the separation layer A is sufficient, but a multilayer structure of two or more layers can be arbitrarily performed according to the purpose. If the separation layer A is in the outermost layer, the surface will be damaged during handling and the like, and a defect will be generated in the film, making it impractical. Further, when the permeable substance dissolves in the separation layer A which is exposed on one side and is not physically fixed, the membrane easily swells, and as a result, the poorly permeable component is also permeated and the selectivity is reduced. In addition, since the swelling causes the substantial film thickness to increase, the permeation rate of the permeable component also decreases. On the other hand, when the membrane of the present invention having a separation layer in the middle portion is used, the layer having the separation function is reinforced and protected by the porous layer B, so that there is no such problem.

Further, since the film having the laminated structure does not have to have adhesiveness between layers, there is a feature that selection of a material of each layer is not restricted by adhesiveness. This is not possible with flat membranes and is one of the major features of hollow fiber membranes.

The material used for the separation layer A, which is responsible for the separation function, is a polymer that is non-flowable at room temperature, and is a polymer containing a siloxane component such as a copolymer of silicon and polycarbonate, a copolymer of silicon and arylate, and a polymethyl phthalate. Examples include polysiloxanes such as enylsiloxanes, polyurethanes, and segmented polyurethanes such as urethane and ethylene glycol copolymers. From the viewpoint of high alcohol permeation rate and ease of melt shaping, copolymers containing a siloxane component are preferred. Polymers and segmented polyurethanes are preferred.

The thickness of the separation layer A is preferably 1 μm or less from the viewpoint of increasing the transmission speed and suppressing the swelling of the membrane.

As the polymer used for the porous layer B sharing the reinforcing function, any polymer may be used as long as it can be made porous by a stretching operation. A crystalline polymer having excellent strength is preferred. Specifically, polyethylene, polypropylene, polyolefins such as poly-4-methylpentene-1, and polyvinylidene fluoride,
Crystalline polymers such as tetrafluoroethylene are preferred.
Particularly, polyethylene, polypropylene, and poly-4-methylpentene-1 are preferred materials.

Organic solvents to be separated are alcohol, acetone,
Lactic acid and the like, and methanol and ethanol, which are attracting attention as next-generation energy, are particularly desired.

A mixture containing an organic solvent and water refers to a liquid or a state in which bacterial cells and cell tissues are suspended in a liquid, and contains dissolved substances such as organic substances such as glucose, inorganic salts, and carbon dioxide gas. It can be done even if it is.

The separation characteristics of alcohol and water that normally permeate through a homogeneous membrane include the separation efficiency obtained from the alcohol concentration Cf of the feed solution and the alcohol concentration Cp of the permeate solution, Is defined by The permeation rate of alcohol and water is calculated from the permeation amount of the alcohol solution and the concentration of the permeated liquid.

Hereinafter, the present invention will be described in detail with reference to Examples, but the permeation rate and the separation efficiency described in Examples and Comparative Examples are based on the above definitions.

〔Example〕

Example 1 Concentrically arranged spouts using polyethylene (Hizex2200J manufactured by Mitsui Petrochemical Co., Ltd.) for the polymer material of the inner layer and the outer layer, and segmented polyurethane (10% swelling with respect to a 30 wt% aqueous solution of ethanol) for the polymer material of the intermediate layer. Using a hollow fiber producing nozzle having an outlet, the fiber was spun at a discharge temperature of 160 ° C. and a draft ratio of 1500 to obtain a composite hollow fiber having a three-layer structure. The resulting undrawn yarn had an inner diameter of 230 μm and consisted of three concentrically arranged layers having a thickness of 15, 0.2 and 15 μm, respectively, from the innermost layer.

The hollow undrawn yarn was annealed at 110 ° C. for 8 hours. Further, the annealed yarn is stretched 100% at room temperature, and then thermally stretched in a heating furnace heated to 105 ° C until the total stretching amount becomes 250%, and further thermally stretched in a heating furnace heated to 115 ° C. The stretched yarn thus obtained was relaxed by 30% and heat set to obtain a composite hollow fiber membrane.

The resulting composite hollow fiber membrane has an inner diameter of 200 μm and consists of three layers arranged concentrically with a thickness of 13,0.15 and 13 μm from the innermost layer. On the outer surface, slit-shaped holes each having a size of 0.04 μm were formed.

An ethanol-water mixture having an ethanol concentration of 30 wt% is supplied to the hollow portion of the composite hollow fiber membrane, the pressure on the supply side is reduced to atmospheric pressure, and the pressure on the permeation side outside the hollow fiber membrane is reduced to 5 mmHg.
A permeation experiment was performed by a pervaporation method under the condition that the temperature of the measurement cell was kept at 25 ° C. As a result of measuring the permeation rate of the mixture and the alcohol concentration of the permeate, the permeation rate was 500 (g / m ² · h).
r), the alcohol concentration of the permeate-side mixture was 75 wt%, and the separation efficiency was 7.0.

After the separation experiment by the pervaporation method, the thickness of the composite membrane was measured. As a result, the thickness was 13,0.15 and 13 μm from the inner layer, which was the same as that before the measurement.

Example 2 Poly-4-methylpentene-1 (TPX MX007 manufactured by Mitsui Petrochemical Co., Ltd., heat deformation temperature 90 ° C.) was used for the polymer material of the inner layer and the outer layer.
Silicon and polycarbonate copolymer (dimethylsiloxane content 47 wt%, ethanol 30
The swelling degree is 8% for a wt% aqueous solution) and the discharge temperature is 250
This was spun at a draft of 1000 ° C. to obtain a composite hollow fiber having a three-layer structure. The resulting undrawn yarn had an inner diameter of 250 μm and consisted of three concentrically arranged layers having a thickness of 20, 0.2 and 20 μm, respectively, from the innermost layer.

The hollow undrawn yarn was annealed at 160 ° C. for 1 hour. Further, the annealed yarn is stretched by 50% at room temperature, and subsequently
Hot stretching was performed in a heating furnace heated to 120 ° C. until the total drawing amount reached 250%, and heat setting was performed in a heating furnace heated to 140 ° C. to obtain a composite hollow fiber membrane.

The obtained composite hollow fiber membrane has an inner diameter of 200 μm and consists of three layers arranged concentrically with a thickness of 15,0.1 and 15 μm from the innermost layer, and as a result of observation with an electron microscope,
Slit-shaped holes each having a size of 0.02 μm were formed on the inner surface and the outer surface.

An ethanol-water mixture having an ethanol concentration of 10 wt% is supplied to the hollow portion of the composite hollow fiber membrane, the supply side pressure is reduced to atmospheric pressure, and the pressure on the permeation side outside the hollow fiber membrane is reduced to 5 mmHg.
A permeation experiment was performed by a pervaporation method under the condition that the temperature of the measurement cell was kept at 25 ° C. As a result of measuring the permeation rate of the mixture and the alcohol concentration of the permeate, the permeation rate was 1 (kg / m ² · h
r), the alcohol concentration of the permeate mixture was 30 wt%, and the separation efficiency was 3.85.

After the separation experiment by the pervaporation method, the thickness of each layer of the composite membrane was measured. As a result, the thickness was 15, 0.1 and 15 μm from the inner layer, which was the same as before the measurement.

Comparative Example 1 The same segmented polyurethane as that of the separation membrane material of Example 1 was dissolved in chloroform, cast on a glass plate and dried to produce a cast film having a thickness of 100 μm. Place the film on a porous film (Juraguard 24
00), and a permeation experiment was performed by the pervaporation method under the same conditions as in Example 1. As a result, the transmission speed was 10 (g / m ²
hr), the alcohol concentration of the permeate mixture was 63%, and the separation efficiency was 4.0.

The swelling degree was 13% as a result of calculation by measuring the weight and volume of the film after use.

Comparative Example 2 The same silicon and polycarbonate copolymer as the separation membrane material of Example 2 was dissolved in chloroform, cast on a glass plate and dried to prepare a cast film having a thickness of 100 μm. The film was put on a porous film (Shuragard 2400), and a permeation experiment was performed by the pervaporation method under the same conditions as in Example 2. As a result, the transmission speed is
40 (g / m ² · hr), the alcohol concentration of the permeate mixture is 19.2
% And the separation efficiency was 2.1.

The degree of swelling was 10%, as calculated by measuring the weight of the film after use.

〔The invention's effect〕

In the present invention, since the separation layer uses a composite membrane sandwiched between the porous layers, the swelling of the separation layer is suppressed, and the organic solvent is separated selectively and at a high permeation rate from the mixed solution containing the organic solvent and water. be able to.

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B01D 61/36 B01D 69/12 B01D 69/08

Claims (4)

(57) [Claims] 1. A separation layer A having a selective separation function for a mixed liquid containing an organic solvent and water, and a porous layer B having a reinforcement function.
Are alternately laminated, the inner surface and the outer surface of which are porous layers B, the separation layer A is made of a non-flowable polymer at room temperature, and the film thickness is 1 μm. A separation method in which an organic solvent is selectively permeated by a pervaporation method using the following multilayer composite hollow fiber membrane. 2. The method according to claim 1, wherein the organic solvent is methanol or ethanol. 3. The method according to claim 1, wherein the material of the separation layer A of the multilayer composite hollow fiber membrane is a segmented polyurethane or a polymer containing a siloxane component. 4. The method according to claim 1, wherein the material of the porous layer B of the multilayer composite hollow fiber membrane is polyethylene, polypropylene or poly-4-methylpentene-1.