JPH0347521A - Separation membrane and usage thereof - Google Patents

Abstract

PURPOSE:To obtain a separation membrane which can be utilized in a membrane distillation type separation method of a liquid-liquid system and a gas-liquid system and is improved in water-permeability by constituting the separation membrane of a hydrophobic porous membrane wherein hydrophilic substance is stuck on the surface of the fine holes. CONSTITUTION:A separation membrane is constituted by sticking hydrophilic substance (e.g. glycerin) on the surfaces of the fine holes of a hydrophobic porous membrane made of polytetrafluoroethylene, etc. The mean pore diameter of the fine holes is preferably regulated to a range within about 20Angstrom and about 0.1mum. Further the rate of amount of stuck hydrophilic substance for the weight of membrane material is preferably regulated to a range within about 0.01-5wt.%. This separation membrane is utilized in the membrane separation method of a liquid-liquid system wherein water contained in liquid is separated while holding the temp. as driving force of separation. Furthermore this separation membrane is utilized in the membrane separation of a gas-liquid system wherein liquid is supplied to the primary side of this membrane and the secondary side is held in a vapor phase and steam passed through this membrane is cooled and collected. As a result, the separation membrane is obtained which is excellent in water-permeability.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a separation membrane used in a membrane separation method for removing or concentrating and separating water from various liquids containing water as a composition, and a method for using the same.

(Prior art) Ultrapure water is used as process water for drug manufacturing in the pharmaceutical industry, washing water for ampules for injections, water for preparing injections, washing water in semiconductor factories, double water in nuclear power plants, etc. In line with technological developments such as improvements in the degree of integration of semiconductors, there is a need for more highly purified water.

Membrane separation technology, which has developed rapidly in recent years, is widely used in fields related to water treatment and water production, and the above-mentioned ultrapure water production technology has made rapid progress in recent years with the introduction of reverse osmosis membranes and ultrafiltration membranes. ing.

(Problem to be solved by the invention) However, currently, the required specifications for ultrapure water for electronics have become extremely sophisticated in response to the dramatic increase in semiconductor integration density, and the development of conventional methods is insufficient. It is said that On the other hand, conventional membrane separation methods are difficult or unreliable for dual water treatment in nuclear power generation or the production of ultrapure water for water preparation for injections. In other words, for the removal of radioactive substances contained in the primary cooling water of nuclear power plants, the reverse osmosis method or the so-called membrane distillation method that has been attempted in the past cannot be said to have a sufficient removal rate, and even more efficient methods are needed. , an economical removal method is desired. In the production of water for injection, it is important to remove pyrogenic substances called pyrogenes, but reverse osmosis membranes currently being considered remove harmful high-molecular-weight substances, but do not allow them to pass through the membrane. It has been pointed out that low molecular weight substances combine to form pyrogenic substances after passing through the membrane, and in addition, this pyrogen has an effect on the human body even in trace amounts below the detection limit, so separation that can be eliminated in principle is not possible. Application of the law is necessary.

Regarding methods for producing ultrapure water in these fields, research has recently begun on the application of a new membrane separation technology called membrane distillation or vapor permeation, which is different from reverse osmosis membranes and ultrafiltration membranes. It's here. A reverse osmosis membrane or an ultrafiltration membrane is a separation method in which the permeated components are always in a liquid state during the permeation process and do not involve a phase change. On the other hand, in the membrane distillation method and the vapor permeation method, since a hydrophobic microporous membrane is used, the membrane does not get wet with the primary liquid, and the permeated substance is
It is thought that it evaporates at the liquid film interface on the next side, enters the fine pores of the film in a gaseous state, and diffuses to the secondary side. In this way, the membrane distillation method and vapor permeation method involve a phase change from a liquid state to a gas state during the permeation process, so in principle, non-volatile substances contained in raw water can enter the secondary side of the membrane. It has the characteristic that it is possible to completely prevent it.

However, the average pore diameter that has been studied so far is 0.
With so-called microporous membranes in the range of 1 to 5 μm, it has been difficult to achieve the expected removal rate because nonvolatile substances accompany the permeated vapor as mist and permeate to the secondary side. Taking this into consideration, the present inventors have researched a method using an ultrafiltration level membrane with a small average pore size that does not have large pores that allow impurities to pass through, but the water permeation rate is low. Therefore, it was necessary to improve the transmission speed.

(Means for Solving the Problems) The present invention has the following configuration in order to eliminate the drawbacks of the above-mentioned prior art.

That is, the present invention relates to a separation membrane characterized by comprising a hydrophobic porous membrane with a hydrophilic substance attached to the surface of micropores, and a method for using the same.

The material polymer for the hydrophobic porous membrane used in the present invention includes:
For example, tetrafluoroethylene, polyvinylidene fluoride, polypropylene, polysulfone, polyethersulfone and copolymers and mixtures thereof, copolymers and mixtures of polyacrylonitrile and fluorine-based polymers, and poly(ethylenetetrafluoroethylene) copolymers. Examples include merging. In addition, the average pore size of the membrane is preferably 10 Å or more and 5 μm or less, but depending on the type of dissolved substances in the raw water and the specifications of the manufactured water, a membrane with a smaller pore size may exhibit the characteristics of the present invention. can. However, if the average pore size is small, even if the hydrophilic substance has the effect of promoting water passage, the permeation rate will be small (so that, except for special purposes, it is preferable that the pore size is 20 Å or more. Although the water permeability is high, due to the pore size distribution that inevitably exists when approaching 5 μm, the liquid supplied to the primary side of the membrane easily permeates through the membrane even in a partially liquid state, resulting in effective membrane separation. In other words, it is more preferable that the average pore diameter is in the range of 20 to 0.1 μm.

Furthermore, in order to improve water permeability, it is necessary to have a larger volume porosity within the above-mentioned preferred pore diameter range and to have relatively large pores inside the membrane. Volume porosity is usually 20%
As mentioned above, it is preferably 40% or more, and as long as the mechanical properties of the membrane are not impaired, the higher the content, the more advantageous.

Examples of hydrophilic substances include alcohols such as glycerin, polyethylene glycol, and polyhydric alcohols;
Examples include deliquescent substances such as lithium chloride and magnesium chloride, various polysaccharides, and surfactants.

Regarding the state of adhesion of the hydrophilic substance, it is preferable that the surface of the membrane micropores is uniformly covered with the hydrophilic substance, but empirically, at least 30% or more of the total surface area of the micropores should be covered. For example, it is thought that the effect of promoting water permeability will appear. On the other hand, if the amount of deposits increases, the micropores will be blocked and the permeation rate will be significantly reduced, so the thickness of the deposits is preferably 20% or less of the average pore diameter. Therefore, the specific amount of adhesion cannot be clearly determined because the average pore diameter and volume porosity vary depending on the membrane material and membrane forming conditions, but for the ultrafiltration level membrane that can be used in the present invention, ,
The ratio of the amount of hydrophilic substance attached to the weight of the membrane material is 0.01
Preferably, the amount is in the range from 5 to 5 wt%.

The method of attaching a hydrophilic substance to the surface of the micropores of such a membrane is to dissolve the hydrophilic substance in a solvent at an appropriate concentration, impregnate the membrane with the solution, allow it to penetrate into the membrane's micropores, and then evaporate the solvent. to form a thin layer of hydrophilic substance on the surface of the micropores of the membrane. Furthermore, depending on the application, if only the hydrophilic substances adhering to the outer surface of the membrane are washed away with a solvent, the hydrophilic substances will exist only on the surface of the membrane's micropores, and the permeation mechanism of this separation method will be eliminated. It is thought that the attached substance will not be eluted into the liquid to be separated and will make the membrane difficult to wet. The concentration of the solution cannot be easily determined because the relationship between the concentration of the solution and the thickness of the deposit changes in a complex manner depending on the influence of the distribution coefficient and pore size distribution of the hydrophilic substance in the membrane and the type of solvent. , empirically, from 0.01 to 10 wt%
In particular, it is considered preferable that the content be in the range of 0.02 to 2.5 wt%. The solvent used may be any solvent as long as it does not dissolve the membrane material, but a highly volatile solvent that can be relatively easily evaporated after impregnation is preferred.

[Example] Next, the present invention will be explained with examples.

Example 1 The gas-liquid separation method was performed as shown in FIG. That is, 2000 cc of raw water is put into the supply liquid tank 1, heated to 40° C. by the heat exchanger 3, and then supplied to the primary side of the module 4 at a flow rate of 400 ml1m1n-1. Nitrogen is supplied to the secondary side at a flow rate of 250 ccmin' (25°C), and the secondary side pressure is adjusted to 640 mm using the vacuum pump 19 and pressure regulator 8.
Maintained at Hg. At this time, the vapor that permeated through the membrane was collected by liquid nitrogen traps 6 and 7.The membrane had an average pore size of 300
A polyvinylidene fluoride membrane was used, and polyethylene glycol was used as the hydrophilic substance.

For impregnation, 0.1wt of polyethylene glycol
% methanol solution, air-dried, and then vacuum-dried before use.

The raw water was tap water, and when it was allowed to permeate for 3 hours, the average water permeation rate was Q, 2kgm-''h-', and the specific resistance of the permeated water was 18MΩ·Cm1TOC was 0.Q3ppm.

Comparative Example 1 A similar permeation experiment was conducted using the membrane used in Example 1 before polyethylene glycol was attached, and the average water permeation rate was 0.10 kgm-2h-
'Met.

Example 2 An experiment on the liquid-liquid separation method was carried out by the method schematically shown in FIG. That is, the stock solution is adjusted to a temperature higher than the secondary side liquid temperature from the supply liquid tank 1, and is supplied to the membrane module 4 and circulated.

On the other hand, on the secondary side of the membrane, the same liquid as the stock solution is circulated and supplied from the permeate tank 5 at a predetermined temperature. At this time, the water component in the primary side circulating liquid evaporates at the liquid membrane interface and permeates in a gaseous state to the secondary side using the water vapor pressure difference generated by the temperature difference on both sides of the membrane as a driving force.

The membrane used was a polyvinylidene fluoride membrane with an average pore size of 250 pores. The hydrophilic substance is glycerin; 5. It was impregnated with a 1% OW acetone solution, and then dried under vacuum and used for experiments.

Comparative Example 2 A similar permeation experiment was conducted using the membrane used in Example 2 before glycerin was attached, and the average water permeation rate was 0. It was 5 kgm-2h'.

[Effects of the Invention] According to the present invention, it is possible to provide a porous membrane with improved water permeability that can be used in membrane distillation type separation methods for liquid-liquid systems and gas-liquid systems, and a method for producing the same. can.

[Brief explanation of drawings]

FIG. 1 is a diagram schematically showing a gas-liquid membrane separation experimental apparatus used in an example of the present invention. 1 is a supply liquid tank, 2
3 is a feed liquid circulation pump, 3 is a feed liquid heat exchanger, 4 is a membrane module, 5 is a needle valve for adjusting the flow rate of inert gas,
6.7 and 13 are cold traps. 8 is a pressure regulator, 19 is a vacuum pump, and 9 and 10 are inlets and outlets of the feed liquid to the membrane module. Reference numeral 12 indicates an inlet for supplying inert gas to the membrane module, and reference numeral 11 indicates an outlet for permeated vapor from the membrane module. 14.15.16.17 and 18 are cooks. FIG. 2 is a diagram schematically showing a liquid-liquid membrane separation experimental apparatus used in an example of the present invention. 21 is a supply (or primary) liquid tank, 22 is a feed liquid circulation pump, 23 is a feed liquid side heat exchanger, 24 is a membrane module, and 29 and 30 are the inlet and outlet of the feed liquid side module, respectively. 25 is a permeate (or secondary) liquid tank, 26 is a permeate side heat exchanger, 27 is a pressure regulating valve, 28 is a permeate side circulation pump, and 31 and 32 are the inlet and outlet of the permeate side membrane module, respectively.

Claims (3)

[Claims] (1) A separation membrane comprising a hydrophobic porous membrane with a hydrophilic substance attached to the surface of micropores. (2) A method of using a separation membrane, characterized in that the separation membrane according to claim 1 is used in a liquid-liquid membrane separation method in which water in a liquid is separated using temperature as a driving force for separation. (3) A gas-liquid system in which the separation membrane according to claim 1 is supplied with a liquid to the primary side of the membrane, and the secondary side is maintained in a gas phase to cool and collect water vapor passing through the membrane. A method of using a separation membrane, characterized in that it is used in a membrane separation method.