JPH03288533A - Microporous membrane - Google Patents

Abstract

PURPOSE:To economically separate respective suspended components from a liquid containing various suspended substances in an extremely efficient manner by enhancing the permeation flux of pure water by setting the surface pore size and surface porosity of a filter membrane to specific values. CONSTITUTION:When suspended substances are separated from a liquid containing suspended substance, the surface pore size of a microporous membrane enhancing the recovery properties of permeation flux after the backwashing operation used for the purpose of enhancing the permeation flux is pref. set to a size preventing the penetration of the suspended substances into the membrane, that is, may be smaller than the size of the suspended substances and this surface pore size is set to about 0.01-10mum. Further, the permeation flux of pure water at 25 deg.C is set to 2X10<-3>m<3>/m<2>.sec/atm or more. By this method, respective suspended components are efficiently and economically separated, recovered, purified and conc. from the liquid containing various suspended substances.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to the structure and characteristics of a microporous membrane (hereinafter referred to as a filtration membrane), and in particular to a filtration method for maintaining a large membrane permeation flux. The present invention relates to a filtration membrane used for.

The filtration membrane of the present invention is applied to the separation, purification, recovery, concentration, etc. of fluids containing or suspending various polymers, microorganisms, yeast, and fine particles, and in particular, fluids containing fine particles that require filtration. It can be applied in any case where it is necessary to separate fine particles from, for example, various suspensions containing fine particles, fermentation liquids, culture liquids, etc., as well as from suspensions of pigments, etc. It is also applied to gas purification by separating and removing fine particles from suspended gas containing fine particles, for example, sterilizing nitrogen gas to be filled into medical ampoules, and nitrogen gas to be filled as positive pressure gas into ultrapure water production equipment. It can also be applied to the production of dust-free, sterile gas, or dust-free, microorganism-free air for air conditioning in IC manufacturing lines.

(Prior Art) Conventionally, techniques for separating suspended solids from a raw fluid containing suspended solids using a membrane include, for example, reverse osmosis, ultrafiltration, microfiltration, which uses pressure as a driving force. There are electrodialysis methods that use a potential difference as a driving force, and diffusion dialysis methods that use a concentration difference as a driving force. These methods can be operated continuously, can separate, purify, or concentrate without significantly changing the temperature or pH conditions during the separation operation, can separate a wide range of particles, molecules, and ions, and are small and compact. It is economical because a large processing capacity can be maintained even with a blunt, the energy required for separation operation is small, and it is possible to process low-concentration raw fluids that are difficult to use with other separation methods, so it is widely implemented. There is. The membranes used in these separation techniques include polymer membranes mainly made of organic polymers such as cellulose acetate, cellulose nitrate, regenerated cellulose, polysulfone, polyacrylonitrile, polyamide, and polyimide, as well as membranes with heat resistance, chemical resistance, etc. There are porous ceramic membranes with excellent durability, ultrafiltration membranes are mainly used for colloid filtration, and precision filtration membranes have micropores suitable for filtration of fine particles. A microfiltration membrane is used.

In recent years, with the progress of biotechnology, higher purity, higher performance, and higher precision have been required, and the fields of application of precision filtration or ultrafiltration technology are expanding. However, when fine particles are separated using a membrane in microfiltration or ultrafiltration, a cake layer forms due to the influence of concentration polarization, creating resistance to the flow of the permeate.
There is also the problem that the resistance due to membrane clogging increases and the membrane permeation flux suddenly and significantly decreases.
This was the biggest reason for preventing the practical application of precision filtration or ultrafiltration. Furthermore, the membrane used therein is easily contaminated, and measures to prevent this are required. As a filtration method, all the fluid to be filtered passes through the filter medium (filter cloth, membrane, etc.) and the cake layer i! There is a so-called dead-end filtration system that separates fine particles contained in a fluid. In this dead-end filtration system, in order for the fluid to pass through and the suspended solids to be separated, fluid pressure is required to overcome the resistance of the filter media and cake layer that impedes fluid flow. In a-filtration, if such punto-end filtration is performed, the membrane permeation flux becomes small. For this reason, it was considered that the cross-flow type filtration method could also be applied to the precision filtration method. In this cross-flow type filtration method, the raw fluid to be filtered is passed parallel to the membrane surface of the filtration membrane in the axial direction of the membrane, and the fluid is filtered to the opposite side through the filtration membrane. This is a filtration method in which the fluid flows parallel to the filtration membrane, and the filtered fluid flows perpendicularly to the IIt membrane-passing surface, so called because the two flows are exactly perpendicular to each other.

In this cross-flow type filtration method, the cake layer formed on the membrane surface is stripped off by the flow of raw fluid parallel to the membrane, so the membrane permeation flux is larger than in the conventional dead-end type filtration method, and a large amount of It is possible to directly and continuously separate, purify, and concentrate raw fluids, and there is no need for flocculation agents to improve filterability. Micropore diameter and purpose @! It has the advantage that extremely pure filtration fluid can be obtained by controlling the interaction with the filtrate.

(Question B that the invention attempts to solve) As mentioned above, the cross-flow filtration method is an advanced separation technology in principle, but the biggest problem is Wi! Although the permeation flux is larger than that of dead-end filtration methods, it is very effective!
! Even if this cross-flow one-way method was adopted as the iM method, there was a problem in that a sufficiently high membrane permeation flux could not be obtained.

In addition, looking at specific examples of conventional methods for separating suspended solids and bacterial bodies, for example, when separating bacterial bodies from an unsightly fermented liquid, conventional methods include centrifugation, cake filtration, and diatomaceous earth filtration. Primary filtration, such as the method, and secondary filtration, such as the precision filtration method, are used together, and during this time, yeast that is prone to aggregate sedimentation is used for sedimentation separation, and the yeast is reused. In this separation of bacterial cells, it is difficult to make the process continuous, and products such as enzymes strongly adsorb to the filter aid, reducing the recovery rate. This method has the problem that the membrane permeation flux decreases as the filtration time passes due to the cake layer formed on the membrane surface and clogging of the membrane, and furthermore, the activation of bacterial cells is lost due to the centrifugation method.

For example, in the biological treatment of sewage, the activated sludge produced contains a large amount of water, so it is first concentrated before further treatment. Those larger in size than the turbidity and colloid components are coagulated and sedimented, and metal ions among the dissolved components are insolubilized as hydroxides, oxides, sulfides, etc., and the particles are made to a size larger than that of the colloids and then sedimented. Solid-liquid separation of activated sludge is performed by separating the concentrate and further separating the liquid from the concentrate obtained here. However, in order to carry out advanced treatment in the concentration of activated sludge, the vast amount of time required for sedimentation is required. Equipment is required, the process is complicated,
The operation and management of solid-liquid separation required advanced technology, and there were various problems such as the need for a vast area to dispose of the vast amount of sludge generated.

In order to solve these problems, conventional methods have been used to intermittently stop the flow of raw fluid into the filtration membrane, or to close the valve on the permeate side of the filtration membrane. By intermittently removing or reducing the pressure, or by applying pressure from the permeate side of the filtration membrane to flow the fluid from the permeate side to the raw fluid side, the membrane surface on the raw fluid side of the filtration membrane is deposited. Attempts have been made to intermittently remove cake layers and adhesion layers called "backwashing." However, when such backwashing is performed, in the case of rigid particles with small adsorption and bonding forces between the cake layer, adhesion layer and membrane, after backwashing, the permeation flux decreases to the permeation flux at the initial stage of filtration. However, in the case of highly adsorbent and highly compressible materials such as yeast and microorganisms,
Even if "backwashing" was performed, the cake layer and adhesion layer could not be sufficiently removed, so the permeation flux did not recover and gradually decreased, and as a result, it was not possible to obtain an economical permeation flux.

(Means and effects for solving the problem) The present invention has been made in order to solve the problems in the prior art described above, and is a novel and practical method that has a high membrane permeation flux. The purpose is to provide a microporous membrane.

That is, the present invention is characterized in that the filtration membrane has a high pure water permeation flux characteristic and a high surface porosity for the purpose of separating suspended matter and liquid from a suspension containing suspended matter.

The present invention will be explained in detail below.

The present invention is a filtration membrane that increases the recovery of permeation flux after backwashing operation, which is used for the purpose of increasing permeation flux when separating suspended solids and liquid from a fluid containing suspended solids. It concerns the structure and characteristics of.

The characteristics of the present invention are to increase the pure water permeation flux of the filtration membrane,
This is because the surface porosity has been increased. The surface pore size of the filtration membrane is preferably a size that does not allow the suspended IIA substance to enter the membrane, ie, it is sufficient that it is smaller than the size of the suspended solids. The effect of the present invention is remarkable in the area belonging to microfiltration membranes,
The surface pore diameter is about 0.01 μm to 10 μm, and the effect is particularly large when the surface pore diameter is in the range of 0.05 to 3 μm.

In order to increase the permeation flux, the cake layer and adhesion layer need to be stripped off from the membrane surface when "backwashing" is performed, which intermittently eliminates or reduces the pressure applied perpendicular to the membrane surface of the filtration membrane. However, if the bonding force between the cake layer, adhesion layer and the film is large, it is not possible to partially or almost remove the cake layer or adhesion layer, and it is necessary to reduce these bonding forces.

In addition, during "backwashing" in which fluid permeates from the permeate side to the source fluid side, if the permeation resistance of the filtration membrane is large, the force applied in the direction of peeling off the cake layer and adhesion layer decreases, and as above, the cake layer , it was not possible to remove the adhesion layer. The present invention is characterized in that the surface porosity of the filtration membrane is increased to reduce the contact area between the cake layer, the adhesion layer, and the iIt filtration membrane as a method of reducing the bonding force between the cake layer, the adhesion layer, and the membrane surface. be. In addition, by increasing the pure water permeation flux of the filtration membrane, that is, by lowering the membrane permeation resistance, a cake layer is formed during backwashing.
It is characterized in that it does not reduce the force in the direction in which N is stripped off.

The present invention is not limited to the case of performing a "backwash" operation, but can extremely increase the flux of the raw fluid by using a cross-flow type filtration method,
When the shearing force for stripping off the cake layer or adhering layer is extremely large, such as in a rotating cylindrical filter, the effect is significant even without backwashing.

A cross-flow filtration method using the filtration membrane of the present invention is shown in FIG. FIG. 2 shows a cross-sectional view of a cross-flow filter, showing suspended solids forming a cake layer on the membrane surface.

The amount of fluid passing through a filtration membrane per unit time is measured in terms of that fluid, but since the amount varies depending on the area of the filtration membrane, the flow rate is divided by the area of the membrane, and the amount is calculated as the filtration flux [unit: 2m/sec].

The filtration membrane used in the present invention has micropores, the pore size of which is 10 μm or less, preferably 5 μm or less. Select pore size.

The suspended matter referred to herein includes both inorganic and organic substances, including microorganisms and yeast, and when an ultrafiltration membrane is used as the filtration membrane, it also includes proteins, polymers, and the like.

The fluid to be filtered may be a gas in addition to a liquid, but it is particularly frequently used for liquids. Any fine particles contained in the liquid can be removed as long as they can be removed by filtration, but since coarse particles can be separated and removed by ordinary filtration, it is most effective to separate and remove fine particles. Further, the shape of the membrane does not matter whether it is a flat membrane or a tubular 1 hollow system.

(Control I of surface pore diameter and surface porosity ratio) The surface pore diameter and surface porosity ratio are determined by, for example, Japanese Patent Application Laid-Open No. 63-1
In the case of No. 39929, control is possible by changing the atmosphere after casting the film-forming stock solution with a casting coater and before immersing it in a coagulation bath containing water. That is, when using a film-forming stock solution in which 15 parts of polysulfone (P-3500 manufactured by IC1), 70 parts of N-methyl 2-pyrrolidone, and 15 parts of polyvinylpyrrolidone were uniformly dissolved, the solution was mixed with water at 20°C after casting. Conditioned air is supplied to the surface during immersion in the bath, but microporous membranes formed by increasing the humidity of the conditioned air, increasing the air supply speed, and lengthening the supply time of the conditioned air. The surface pore size and surface porosity can be increased.

(Example) Example-1 A suspension in which Escherichia coli (IF○-3301) was dispersed in 0.9 wt% physiological saline at a content of 1 dry g/1 was used as a suspension, and the nominal pore size was 0.2 μm. Cross-flow filtration was performed using the microfiltration membrane by changing the pure water permeation flux and surface porosity. The precision filtration membrane used was disclosed in Japanese Patent Application Laid-Open No. 1983-13.
One made of polysulfone made by the method described in No. 9929 (1.2.3 in Fig. 6), one made of polysulfone made by Hohiro described in JP-A No. 56154051 ( 45) described in Figure 6,
Those made of polyamide prepared by the method described in JP-A No. 55-8887 (6..7 in Fig. 6)
．． 8), polyamide made by the method described in JP-A-57-202330 (9 in Figure 6), polyvinylidene made by the method described in JP-A-54-16382 2. Made of fluoride (10.11 shown in Figure 6), Special Publication 1986-1986
The module used was a thin-layer waveguide type module with an effective membrane area of 100 cd, which was made of cellulose acetate prepared by the method described in No. 06 (12.13 in Figure 6), and the experimental conditions were as follows. Pressure difference 0.5kg/cj
, the flow rate of the raw fluid was 101/sin, and the liquid temperature was 25°C. After the filtration started, the pump that sent the raw fluid was stopped intermittently to perform backwashing. For backwashing, run the pump for 150 seconds and stop for 30 seconds.
Operated in seconds.

Figure 3 shows the change in i3 flux over time, and Figure 4 shows the change in average permeation flux over time for the iIt membrane made of polysulfone. The average permeation flux at the start of filtration is designated as Javo, and the ratio to the average permeation flux at each time is shown in FIG.

The recoverability of permeation flux is determined by the ratio of average permeation flux J av/J
Judgment was made based on the time T until avo reached 0.75. That is, the larger the value of T, the better the recovery of the permeation flux, and as a result, the higher the permeation flux can be obtained.

Figure 6 shows the results when various membranes with different surface porosity and pure water permeation flux were used. As a result, the pure water permeation flux is
10-3rd/rd ・sec (△P=0.5kg
/ cd) or 2 X 10-3rrr/n(
・sec ・atm or more and the surface porosity is 30% or more, the value of T is large and the permeation flux recovery is good, that is, the permeability i! It became clear that 5 fluxes were obtained.

(Effects of the Invention) According to the present invention, a high membrane permeation flux can be obtained in a filtration method that basically involves backwashing, thereby separating each suspended component from a liquid containing various suspended substances. , recovery, purification,
Concentration etc. can be carried out extremely efficiently and economically. Furthermore, it is possible to make the process continuous and downsize the equipment, and by utilizing the selectivity of the membrane, it is possible to continuously and selectively separate only the target substance, making it possible to remove yeast and bacterial cells from the reaction solution. Immobilization enables reaction in bioreactors,
Compared to conventional techniques, it is easier to manage operations, can be operated at higher concentrations, and does not require special cleaning to restore membrane permeability.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram showing the concept of the cross-flow filtration method using the present filtration membrane. circulate through. At this time, the pressure of the suspension is adjusted by a pressure regulating valve 8. This pressure is read by a pressure gauge 4, and the flow rate of the liquid is read by a flow meter 9. Backwashing is performed by stopping the pump 3. 6 is a flow path for the separated liquid, 7 is a pressure gauge, and 10 is a storage tank for the separated liquid. FIG. 2 is a cross-sectional view of the interior of the cross-flow filter, showing a state in which suspended matter forms a cake layer on the surface of the filter membrane. FIG. 3 shows the change in permeation flux over time when backwashing is performed periodically. FIG. 4 shows the change over time in the average permeation flux of a filtration membrane made of polysulfur water when the same operation as in FIG. 3 is performed. FIG. 5 shows the change over time in the ratio of the average permeation flux shown in FIG. 4 to the permeation flux at the initial stage of filtration, and also shows T, which is an index indicating the recoverability of the permeation flux. FIG. 6 shows the influence of pure water permeation flux and surface porosity on T of various filtration membranes.

Claims (1)

[Claims] 1. A microporous membrane used for the purpose of separating suspended matter and liquid from a suspended matter dispersion, the surface pore size of which is 0.01 μm.
m or more and 10 μm or less and pure water permeation flux at 25°C is 2×
A microporous membrane having a rate of 10^-^3m^2/m^2·sec/atm or more. 2. The microporous membrane according to claim 1, which has a surface porosity of 30% or more.