JP3443900B2 - Separation membrane treatment method - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a treatment method for improving the separation performance of a separation membrane.

[0002]

2. Description of the Related Art Separation membranes are required to have good permeability and separability, and various polymer membrane materials for separating oxygen and nitrogen in the air in a gaseous state have been variously studied. However, those having good permeability had insufficient separability, and those having good separability had insufficient permeability. Therefore, as one of the methods for solving this, a surface treatment by plasma treatment, plasma polymerization, coating, or the like has been studied. For example, JP-A-3-284325 discloses plasma treatment with a fluorine compound of chlorinated lower alkane, and JP-A-62-19206 discloses plasma treatment with chlorine gas. As described above, in the case of plasma processing, the processing gas that has been conventionally used is chlorine gas or fluorine-containing gas, and it is known that the aliphatic hydrocarbon of the present invention having 2 to 4 chlorine-substituted compounds is used as the processing gas. Not not.

[0003]

[Problems to be Solved by the Invention] In the range known to date, the oxygen permeation rate is practical when the polymer film material itself or the coating process or when chlorine gas or fluorine-containing gas is used in the plasma process. The value of the oxygen / nitrogen separation coefficient of the separation membrane, which is high enough to cause no problem, is about 5 at most, which is still insufficient. Further, in the processing such as plasma polymerization, the separation coefficient was improved, but the permeation rate was reduced to 1/10 or less of that before the processing, which was a practical problem. Therefore, an object of the present invention is to obtain a membrane having excellent gas permeability and excellent separability.

[0004]

Means for Solving the Problems The inventors of the present invention have earnestly studied a modification method for further improving the separability of a separation membrane (hereinafter also simply referred to as a membrane), and as a result, the permeation rate was significantly decreased. The present invention has been accomplished by finding a novel plasma processing method that can improve the separability without the need.

That is, the present invention relates to a 4-methyl-pentene-based heavy chain.
The present invention relates to a method for treating a separation membrane, which comprises subjecting a dense layer of a separation membrane having a non-porous dense layer made of coalesce to plasma treatment in the presence of a gas or vapor of a chlorine-substituted saturated hydrocarbon.

The separation membrane in the present invention may have a non-porous dense layer on its surface, and may be a symmetrical membrane (homogeneous membrane) or an asymmetric membrane (heterogeneous membrane). . Asymmetric membranes are preferred. The separation membrane may be a lobe-type asymmetric membrane in which the dense layer and the porous support layer are the same material, or a composite membrane in which the dense layer and the porous support layer are different materials.
The position of the dense layer is not particularly limited, and may be, for example, a film in which a non-porous dense layer is formed on the surface or inside of a porous support, preferably on the surface of the film. The smaller the dense layer, the higher the permeation rate, which is preferable in terms of performance, but a certain thickness is required in terms of strength and durability. Specifically, it is preferably in the range of 0.01 μm to 10 μm. Further, the shape of the membrane is arbitrary, and for example, it may be a flat membrane shape, a tubular shape, or a hollow fiber shape, but the hollow fiber shape is preferable because the surface area can be increased and the module structure can be simplified.

Such a membrane can be obtained by a known method such as a water surface development method, a solvent casting method or the like, a dry spinning method, a wet spinning method or a melt spinning method. It is also possible to obtain these films by compounding such as coating.

Poly-4-methylpente as a material for the dense layer
The -1-polymer is a homopolymer or a copolymer or polymer blend containing 50 mol% or more of 4-methylpentene-1. Olefins are preferred as the copolymerization component.

The general plasma treatment is described in detail in "Polymer surface modification" by Fumio Ide (Modern Editing Co., 1977) and the low-temperature plasma treatment method and JP-A-62-19206. Briefly, the separation membrane to be processed is placed in the space of the plasma state excited by the electric field,
By introducing a plasma species (the chlorine-substituted product of an aliphatic hydrocarbon corresponds to this in the present invention) thereto, it is activated, and the surface of the separation membrane is modified by radicals or ions.

The gas or vapor that is the plasma species used in the treatment is a 2-4 chlorine-substituted aliphatic hydrocarbon, preferably a saturated hydrocarbon-substituted chlorine. As a chlorine-substituted product of an aliphatic saturated hydrocarbon, methane, a chlorine-substituted product of ethane is particularly preferable, for example, dichloromethane, chloroform, carbon tetrachloride, 1,1-dichloroethane, 1,2-dichloroethane, 1,1,1. -Trichloroethane, 1,1,2-trichloroethane, 1,1,1,2-tetrachloroethane and the like can be mentioned. Further, as the 2-4 chlorine-substituted product of the aliphatic unsaturated hydrocarbon, a 2-4 chlorine-substituted product of ethylene is preferable, and for example,
1,1-dichloroethylene, 1,2-dichloroethylene, trichloroethylene, tetrachloroethylene and the like can be mentioned. The 2 to 4 chlorine-substituted product of the aliphatic hydrocarbon used in the present invention may further contain other atoms such as oxygen and bromine, but the chlorine-only product is preferred.

The gas or vapor used as the plasma species may be diluted with a carrier gas (inert gas, oxygen, chlorofluorocarbon, etc.). Alternatively, two or more kinds of gas or vapor may be mixed and used. By using such a gas or vapor as the plasma species, the oxygen permeation rate can be improved to a practical level without causing a significant decrease and the separation coefficient can be improved.

The apparatus used for this plasma treatment may be a known apparatus, and the method of applying an electric field may be either an internal electrode method or an external electrode (no electrode) method.
Plasma is generated by applying a direct current, an alternating current, and a high frequency electric field in the internal electrode method and by operating a high frequency electric field in the external electrode method continuously or in a pulsed manner. Various modes such as glow discharge, corona discharge, and spark discharge can be applied to the plasma generation mode. Regarding the processing conditions such as discharge output, degree of vacuum, gas flow rate, etc., an appropriate range of conditions can be selected depending on the separation membrane to be processed and the gas or vapor used for the processing.

The degree of vacuum in the plasma treatment is 0.01 to 10
The range is about torr, preferably 0.05 to 1 torr, and can be appropriately determined depending on the gas or vapor used. The discharge output is about 1 to 500 W, preferably 10
~ 100W. If the output is too high, the sample (film) itself may be damaged, and if it is too low, the plasma state cannot be sufficiently maintained.

If the treatment time is short, the damage to the sample is small, but the treatment effect does not appear unless it is above a certain level, so 1 second to 30 minutes, preferably 10 seconds to 1
About 0 minutes is good.

In the plasma treatment, the dense layer of the separation membrane to be treated may be treated. Therefore, for example, it is possible to use a method such as a method of performing plasma treatment in a state where a fixed amount of the membrane is focused after forming the separation membrane, or a method of performing plasma treatment on the membrane that continuously moves in the step of forming the separation membrane. it can.

The treatment of the present invention is effective for various separation membranes such as gas separation membranes, liquid separation membranes, gas-liquid contacting separation membranes, etc., but gas separation membranes are particularly preferable. The membrane obtained by the present invention is, for example, the production of oxygen-enriched air or nitrogen-enriched air from air,
It can be used for separation and recovery of carbon dioxide gas, recovery of hydrogen gas, degassing of gas dissolved in liquid, particularly selective degassing, dissolution of gas in liquid, particularly selective dissolution, pervaporation and the like.

The plasma-treated separation membrane was evaluated by measuring the gas permeation rate and the separation coefficient. The unit of gas permeation rate here is cm ³ / cm ² · sec · c
In mHg, it is a practical index in which the film thickness is added to the gas permeability coefficient. The separation coefficient is a value obtained by dividing the oxygen permeation rate by the nitrogen permeation rate. The gas permeation rate and the separation coefficient were measured based on ASTM D1434 (pressure method).

[0018]

EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

Example 1 Using poly-4-methylpentene-1 as an olefin polymer, a hollow fiber heterogeneous membrane having an outer diameter of about 200 μm and a wall thickness of 30 μm was prepared by a melt drawing method. According to a scanning electron microscope (SEM), this heterogeneous film had a non-porous dense layer on the outer surface. The oxygen permeation rate (Q _O2 ) and the separation coefficient of oxygen and nitrogen (Q _O2 / Q _N2 ) of this heterogeneous membrane were 1.2 × 10 ⁻⁵ cm ³ / cm ^{2 respectively.}
-Sec · cmHg was 3.8. This is about 300m long
The yarn length was set to m, a yarn bundle of 60 yarns was fixed, and both ends of the yarn bundle were fixed. The vacuum container for plasma processing has a diameter of 100 mm and a length of 5
A 00 mm quartz container was used. A high-frequency coil that generates plasma is installed around it. The container is provided with a lid for loading and unloading the sample and can be closed by an O-ring to maintain the degree of vacuum. The lid was opened, the yarn bundle of the sample was placed in a vacuum vessel, and the inside of the vacuum vessel was evacuated by a vacuum pump until the pressure reached 0.001 torr. Then, while operating the vacuum pump, carbon tetrachloride serving as a plasma species was introduced through a gas introduction pipe, and the degree of vacuum in the pipe was adjusted to 0.1 torr. When the degree of vacuum became stable, a high frequency power supply and a matching box were operated, a high frequency voltage was applied to the coil, and plasma was generated in the container. Plasma discharge was performed at an output of 50 W for 1 minute.
The oxygen permeation rate of the treated heterogeneous membrane and the separation factor of oxygen and nitrogen were measured. The results are shown in Table 1.

Example 2 The same process as in Example 1 was performed except that chloroform was used as the plasma species. The results are shown in Table 1.

Example 3 The same process as in Example 1 was carried out except that dichloromethane was used as the plasma species. The results are shown in Table 1.

<Example 4> The same treatment as in Example 1 was performed except that trichlorethylene was used as the plasma species. The results are shown in Table 1.

Example 5 The same process as in Example 1 was carried out except that 1,1,1-trichloroethane was used as the plasma species. The results are shown in Table 1.

Comparative Example 1 Hollow fiber made of polydimethylsiloxane (outer diameter 320 μm)
m, wall thickness 80 μm) except that a separation membrane is used.
The same process as in Example 1 was performed. The characteristic before the treatment is that the oxygen permeation rate is 0.5 × 10 ⁻⁵ cm ³ / cm ² · se.
c · cmHg, separation factor was 2. The results are shown in Table 1.

Comparative Example 1 Poly-1-trimethylsilyl-1-propyne powder was dissolved in toluene and a film (thickness 30 μm was prepared by a conventional method.
m) was obtained. Using this as a separation membrane, the same treatment as in Example 1 was performed. The characteristic of the pre-treatment, there are changes over time in the film itself, but decreases the oxygen transmission rate over time, the oxygen permeation rate 20 × after one day elapsed from the film created 10 ^-5 cm ^{3 /} cm ² -Sec-cmHg, separation factor was 1.4. The results are shown in Table 1.

[0026]

[Table 1] (* 1) Unit x 10 ^-5 cm ³ / cm ² · sec · cmHg

<Comparative Example 3 > The same treatment as in Example 1 was performed except that chlorine gas was used as the plasma species. The results are shown in Table 2.

Comparative Example 4 The same treatment as in Example 1 was carried out except that carbon tetrafluoride was used as the plasma species. The results are shown in Table 2.

[0029]

[Table 2] (* 1) Unit x 10 ^-5 cm ³ / cm ² · sec · cmHg

[0030]

By using the treatment method of the present invention, the separation performance can be improved without significantly reducing the gas permeation rate. In particular, a gas separation membrane having an excellent oxygen and nitrogen permeability coefficient ratio can be obtained.

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) B01D 67/00

Claims (4)

(57) [Claims] 1. A dense layer of a separation membrane having a non-porous dense layer made of a 4-methyl-pentene polymer is provided with a gas or vapor of 2 to 4 chlorine-substituted aliphatic hydrocarbon. A method for treating a separation membrane, which comprises performing a plasma treatment below. 2. The treatment method according to claim 1, wherein the 2 to 4 chlorine-substituted product of the aliphatic hydrocarbon is a chlorine-substituted product of the saturated hydrocarbon. 3. The method according to claim 2, wherein the chlorine-substituted product of saturated hydrocarbon is a chlorine-substituted product of methane or ethane. 4. A separation membrane according to claim 1-3 is a hollow fiber membrane
The processing method according to any one of 1.