JPH0440222A - Multilayer composite separation membrane - Google Patents

Abstract

PURPOSE:To enlarge the effective membrane area of a separation layer and to increase transmission speed by receiving the separation layer in a porous layer as a layer whose cross section has a corrugated shape. CONSTITUTION:A porous layers B1 having reinforcing function are arranged to inner and outer surfaces. The porous layers B1 are formed using a material capable of being made porous by stretching operation such as polyethylene or polypropylene. A separation layer A2 having separating function is formed between the porous layers B1 as a layer whose cross section has a corrugated shape to be laminated to the porous layers B1. The separation layer A2 is formed from a silicone polymer or a polyolefin. The polymer materials of the respective layers A, B are alternately laminated so that the layer A has a corrugated shape to form a precursor of a composite mombrane in a molten state and the precursor is subjected to annealing treatment if necessary and subsequently subjected to stretching treatment to make the layers B porous. By this method, the effective membrane area of the separation layer A is made large.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a high-performance multilayer composite separation membrane used for gas separation, solvent separation, degassing, etc.

[Prior Art] Since ancient times, many methods have been developed and repeatedly improved in techniques for separating and purifying substances. Membrane separation technology is one such technology, and looking at the history of its improvements, the major trends in technological development have been the development of superior membrane materials and the development of thin film technology to increase separation efficiency.

As one of the thin film forming technologies, the method of forming a thin film on a porous base material by coating method or vapor deposition method is widely used. The thin film material invaded the pores, making it difficult to obtain a substantial thin film. In addition, to overcome this drawback, there is a method in which the pores of the porous base material are filled in advance with a soluble substance, a thin film layer is formed on the surface, and then the soluble substance within the porous base material is eluted. be. However, even with this method, it is difficult to obtain a homogeneous thin film layer, the thin film layer is easily damaged during the elution process, the thin film layer is easy to peel off from the obtained composite film, and there are limitations on the membrane form that can be applied. There was a problem.

A multilayer composite hollow fiber membrane disclosed in JP-A No. 62-1404 is known as a membrane structure that can be produced industrially by thinning a separation membrane. As shown in FIGS. 4 and 5, the membrane structure of these composite membranes is such that a porous layer 1 having a reinforcing function and a separation layer 2 having a separating function are alternately laminated.

[Problem B to be solved by the invention] However, as is clear from FIGS. 4 and 5, the membrane structure of these composite membranes is such that the separation layer 1 which takes charge of the separation function is
However, in a hollow fiber type composite membrane, they are housed concentrically, and in a plain clothes type composite membrane, they are housed in a planar shape in the porous layer 2, which has a reinforcing function.

One of the performance indicators of a multilayer composite separation membrane is the permeation rate, but in order to increase the permeation rate if the membrane material is the same, it is necessary to make the separation layer thinner and increase the membrane area of the separation layer. is important. Furthermore, it is also important to set the pore diameter, porosity, and film thickness of the porous layer that performs the reinforcing function so as not to cause permeation resistance.

As the separation layer is made thinner, the rate of occurrence of film defects increases, so there is a limit to forming a V# film. Therefore, increasing the effective membrane area of the separation layer is a very effective means.

[Means for Solving the Problems] In other words, the present invention provides a multilayer composite separation system in which separation layers A having a separation function and porous layers B having a reinforcing function are alternately laminated, and both sides of the layers are composed of porous layers B. A multilayer composite separation membrane characterized in that the separation layer A is housed in the porous layer B as a layer having a corrugated cross section! It is a membrane.

[Function] The present invention increases the effective membrane area and increases the permeation rate by making the separation layer a layer with a corrugated cross section while maintaining the external appearance of the multilayer composite separation membrane as before. The present invention provides a multilayer composite separation membrane that is higher than that of conventional multilayer composite separation membranes.

Hereinafter, the multilayer composite separation membrane (hereinafter abbreviated as "composite membrane") of the present invention will be explained with reference to the drawings.

FIG. 1 shows an example of a cross-sectional view of a hollow fiber-like composite membrane, and FIG. 2 shows an example of a cross-sectional view of a film-like composite membrane. As described above, the membrane form of the composite membrane of the present invention may be either a hollow fiber membrane or a flat membrane. A porous layer B having a reinforcing function is arranged on the inner surface and the outer surface or on the inner and outer surfaces, and these porous layers B
A separation layer A having a separation function between the two is formed as a layer having a corrugated cross section and has a laminated membrane structure.

That is, the composite membrane of the present invention has at least a three-layer structure. Basically, one layer of the separation layer A is sufficient, but it may have a multilayer structure of two or more layers depending on the purpose. In a separation membrane, the layer that performs the separation function is the most important, and if this separation layer is the outermost layer, there is a risk of scratches on the surface during handling, but in the composite membrane of the present invention, the layer that performs the separation function is stored in the porous layer. There is no such danger because the separation layer is arranged in a closed manner.

Membrane performance (separation performance) as a composite membrane depends on the membrane thickness and membrane area of separation layer A housed in the porous layer, if the porosity, pore diameter, and thickness of the porous layer are the same. It is determined. Therefore, by making the separation layer A thinner and increasing the area of the membrane to be accommodated, the membrane performance can be improved. There are limits to how to reduce the film thickness depending on the manufacturing method, material, etc. Also,
The thinner the film is, the greater the risk of film defects occurring.

Therefore: When the formation of a membrane approaches its limit, or in order to reduce the risk of membrane defects and improve membrane performance as a composite membrane, it is necessary to It is effective to increase the membrane area.

In the composite membrane of the present invention, in order to increase the membrane area of the separation layer, conventionally, when observed in its cross section, a flat membrane exhibits an almost linear shape (Fig. 5), or a smooth circular or elliptical shape. The separation layer, which was in the form of a cylindrical membrane (FIG. 4), is now formed as a layer with a corrugated cross section. Here, the form having a waveform is typically a sine wave, but examples include a pulse wave shown in Fig. 2 and a triangular wave shown in Fig. 3. It's okay. In addition, when the composite membrane is a hollow fiber membrane, the cross section of the separation layer has these waveforms, and the membrane forms a closed circular or elliptical layer as a whole.

In addition, the form having a corrugated shape as referred to in the present invention refers to the above-mentioned form in which the membrane area is increased by at least 20% compared to the case where the separation layer of the composite membrane of the same size is a simple plain cloth or a simple smooth cylindrical membrane. It means that it has a waveform form.

Furthermore, the term "waveform in cross section" does not necessarily mean that the waveform appears on any cut surface of the composite membrane.
It is sufficient if the waveform appears on a specific cut plane. Normally,
Waveforms appear on the cut plane perpendicular to the stretching direction when manufacturing the composite membrane of the present invention. Furthermore, the separation layer A is housed in the porous layer B, which means that the interface between the porous layer B and the separation layer has a surface morphology having a waveform approximately the same as that of the separation layer, and the inner layer is in close contact with the porous layer B. This refers to a state where no special voids exist between the porous layer and the separation layer.

The separation layer A is a part having a separation function, and is preferably as thin as possible in order to maintain a high permeation rate. Therefore, if the thickness of this separation layer exceeds 2.0 μm, the significance of making the composite film thinner is diminished. On the other hand, the lower limit of the thickness of the separation layer is not particularly limited, but is approximately 0.005 μm.
It is preferably at least 0.01 μm, more preferably at least 0.01 μm.

The position range in which the separation layer A is housed in the porous layer B is 1 μm, more preferably 2 μm from the outer surface of the porous layer B, in order to protect the separation layer A from damage during handling.
It is preferable to store it in a part that is more than m inside.

The porous layer B having a reinforcing function is a layer that not only serves as reinforcement and protection but also is effective in preventing film defects when the separation layer A is made thin. When making the separation layer A thinner in a composite membrane, the thinner the separation layer A becomes, the more likely defects will occur in the separation layer A unless the pore diameter of the porous layer B is set small. Therefore, a preferable porous structure of the porous layer B is such that the separation function of the separation layer A can be fully expressed without the occurrence of membrane defects, and furthermore, it does not become a resistance to the expression of the separation function of the separation layer A. 0.005~0.5μm
, preferably 0.01-0.3 μm, porosity 20-9
0%, preferably 30-70%, and the thickness of the entire composite membrane is 1
0 to 1000 μm, preferably 20 to 500 μl. If the pore diameter is less than 0.005 μm, the resistance to permeation of the substance to be separated increases, and if it exceeds 0.5 μm, it tends to cause membrane defects in the separation layer. If the porosity is less than 20%, the ratio of the separation layer facing the pore openings of the porous layer will be too small, and the effective utilization rate of the separation layer will decrease significantly, and if it exceeds 90%, it will be difficult to reinforce and maintain the composite membrane. Become. If the thickness of the composite membrane is less than 10 μm, the strength tends to be insufficient.

In order to increase the membrane area of the separation layer housed in a wave-like manner in the porous layer, it is advantageous to increase the membrane thickness of the composite membrane.
If it exceeds 000 μm, the resistance of the substance to be separated in the porous layer tends to be excessive. Note that the pore diameter referred to here is
The pore diameter is measured using a mercury porosimeter and the pore volume is expressed as % from the relationship between the pore diameter and the pore volume.

Polymer A used for separation layer A in the composite membrane of the present invention
Examples include silicone polymers such as silicone rubber and copolymers of silicone and polycarbonate; polyolefin polymers such as poly-4-methylpentene-1 and linear low-density polyethylene; perfluoroalkyl fluorine-containing polymers; polyurethane. Polymers: Cellulose polymers such as ethyl cellulose: polyphenylene oxide, 4-vinylpyridine; and copolymers of these polymers; and mixtures thereof.

As for the polymer B used for the porous layer B, any polymer may be used as long as it is a material that can be made porous by a stretching operation, but polyethylene, polypropylene, and poly(4-4) may be used.
- Polyolefins such as methylpentene-1; and crystalline polymers such as halogen-containing polyolefins such as polyvinylidene fluoride and tetrafluoroethylene are preferred.

The composite membrane of the present invention is manufactured, for example, as follows.

A precursor of a composite film in which polymer B' and polymer A' are alternately laminated so that the polymer A' layer has a corrugated cross section is melt-formed at a temperature of 150°C to 30°C.
It is formed in the range of 0''C and the draft ratio in the range of 5 to 9000.

The melt-formed composite membrane precursor is optionally annealed and then stretched to make the layer of polymer B' porous. As a method for forming pores by stretching, a known method used for polyolefins can be adopted. That is, microcracks are generated in the polymer B' layer to whiten it by a small amount of stretching at around room temperature, and then the pores can be enlarged and the flower shape can be stabilized by heating stretching. During this time, polymer A° is not made porous, so as the stretching ratio increases, fl
It is made into li.

The stretching conditions are not particularly limited either, and optimal conditions can be set depending on the type of polymer; for example, for Polymer B.

When using polyethylene, the cold stretching conditions are 40 to 200% at room temperature, and the hot stretching conditions are 80 to 1%.
The total stretching ratio is 10 at 25°C, preferably 90 to 105°C.
A condition of approximately θ˜300% is adopted. Furthermore, to improve thermal stability, the temperature is 80-125°C, preferably 1
Fixed length or relaxation heat treatment may be performed at 05 to 120°C.

[Example] Examples will be explained below.

Example 1 The outer surface of the outer layer and the inner surface of the inner layer formed a concentric circle, and an intermediate layer (separation layer) was arranged between the outer layer and the inner layer to form a closed circular layer having a corrugated shape. High-density polyethylene with a density of 0.968 g/cc and a melt index value of 5.5 (manufactured by Mitsui Petrochemical Co., Ltd., HIZEX 2200J) is used as the polymer material supplied to the outer and inner layers of a hollow fiber manufacturing nozzle with two discharge ports. Segmented polyurethane (manufactured by Thermedex, Tecoflex EG-8OA) is used as the polymer material supplied to the intermediate layer.
with a discharge temperature of 165°C and a winding speed of 205 m/l.
Melt spinning was carried out using ll1n. The obtained hollow undrawn yarn has a membrane form as shown in Fig. 1, and has a three-layer structure in which the intermediate layer is a closed circular layer with a corrugated shape and is housed within a polyethylene layer, and has an inner diameter of 230 μm and a membrane thickness. The distance from the inner and outer surfaces of the intermediate layer located on the innermost surface side and the outermost surface side was 5 μm, respectively, and the thickness of the intermediate layer was 1.0 μm. This hollow undrawn yarn was annealed at 115° C. for 1 hour. Next, the annealed system was cold stretched to 140% at room temperature, followed by hot stretching in a heating furnace heated to 105°C until the total stretching ratio reached 170%, and further 140%.
Relaxation heat setting was performed in a heating furnace heated at 20° C. so that the total stretching ratio was 100%.

As a result of evaluating the membrane performance of the composite hollow fiber membrane thus obtained, the porosity was 40.2%, and the average pore diameter was 0.155μ.
m, the inner diameter was 200 utn, the film thickness was 30 μm, the thickness of the intermediate layer was 0.7 μm, and the distances from the inner and outer surfaces of the intermediate layers located on the innermost and outermost surfaces were 3.0 μm. Furthermore, when the air permeation rate of the obtained composite hollow fiber membrane was measured, the oxygen permeation rate (QO2) at room temperature was 1.
47X 10-5cm3/cm2-sec-cmHg,
Nitrogen permeation rate (QN2) is 5.37X 10-'c+n
'/cm2・sec''cmHg, and the separation coefficient (QO
2/QN2) was 2.7. The porosity and average pore diameter were measured with a mercury porosimeter, and from the relationship between pore diameter and pore volume, the pore diameter when the pore volume was expressed as % was taken as the average pore diameter. Further, the thickness of the intermediate layer was measured by electron microscopic observation.

Comparative Example 1 The same polymer as in Example 1 was used for spinning under the same spinning conditions using a hollow fiber manufacturing nozzle having three discharge ports arranged concentrically. The obtained hollow undrawn yarn had an inner diameter of 23
0 μm, respectively 17.54z+o from the innermost layer,
It consists of three layers as shown in FIG. 3 arranged concentrically with thicknesses of 1.0 .mu.m and 16.5 .mu.m. This hollow undrawn yarn was subjected to annealing, cold stretching, hot stretching, and relaxation heat setting in the same manner as in Example 1, and the membrane performance was evaluated. As a result of evaluating the obtained composite hollow fiber membrane, it was found that the porosity was 40.2%, the average pore diameter was 0.155 μm, and the inner diameter was 200 μm, and the thicknesses were 15.0 μm, 0.7 μm, and 14.3 μm from the innermost layer, respectively. It consisted of three layers arranged in concentric circles.

In addition, when the air permeation performance of the obtained composite hollow fiber membrane was measured, the oxygen permeation rate (QO2) was 8.65X at room temperature.
10-'cm3/cm"sec-cmHg, nitrogen permeation rate (QN2) is 3.20X 10-'cm3/cm2-
sec-cm) Ig, and the separation coefficient (QO2/QN2
) was 2.7.

[Effects of the Invention] As is clear from the examples, in the multilayer composite separation membrane of the present invention, the separation layer is housed in the porous layer as a layer having a waveform. Even if the pore structure and separation layer thickness are the same as conventional multilayer composite separation membranes, the gas permeation performance is about 1.7 times higher, indicating that the membrane performance has improved due to the increased membrane area of the separation layer. It was planned.

Further, by using the composite membrane of the present invention, it is possible to further downsize various membrane modules using conventional composite membranes.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of a multilayer composite separation hollow fiber membrane of the present invention in which a separation layer is housed in a porous layer in a wave shape, and FIGS. 2 and 3 show a separation layer in a porous layer. FIG. 2 is a schematic cross-sectional view of the multi-layer composite separate uniform of the present invention packed in a pulsed wave or triangular shape. FIGS. 4 and 5 are schematic cross-sectional views of a conventional multilayer composite 1 m membrane.

Claims (1)

[Claims] 1) In a multilayer composite separation membrane in which a separation layer A having a separation function and a porous layer B having a reinforcing function are alternately laminated, and both surfaces thereof are composed of the porous layers B, the separation layer A has a corrugated cross section. 1. A multilayer composite separation membrane characterized in that the layer having the following structure is housed in a porous layer B.