JP2008229612A - Porous membrane for cell suspension filtering - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide the production apparatus of chemical products by a continuous fermentation method stably keeping high productivity over a long period of time with a simple operation condition. <P>SOLUTION: The continuous fermentation apparatus of the present invention separates fermentation cultivation liquid into filtrate and unfiltered liquid by the separation membrane, recovers chemical products being the desired fermentation product, from the filtrate, and holds or circulates the unfiltered liquid to the fermentation cultivation liquid. The porous membrane which has high water permeability and high cell suppressing efficiency, hardly causes clogging, and is negatively charged, is installed in the fermentation tank. While filtering by low pressure difference through the membrane, productivity of the chemical products by fermentation can be stably and greatly enhanced at a low cost. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a porous membrane for cell suspension filtration suitable for water treatment such as drinking water production, water purification treatment, waste water treatment, and the food industry.

  In recent years, porous membranes have been used in various fields such as water treatment fields such as drinking water production, water purification, and wastewater treatment, and food industry. For example, in the field of water treatment such as drinking water production, water purification treatment, and wastewater treatment, porous membranes have been used to remove impurities in water as an alternative to conventional sand filtration and coagulation sedimentation processes.

  In the wastewater treatment field, an activated sludge membrane filtration process using a porous membrane is widely used in order to separate flocified sludge content and moisture from a microorganism aggregate called activated sludge. In the food industry field, porous membranes are used for the purpose of separating and removing yeasts used for fermentation and concentrating treatment stock solutions.

  However, when these porous membranes for cell suspension liquid filtration are operated without a washing operation, a reduction in filtration flow rate and filtration efficiency due to clogging of the membrane becomes a serious problem. Several methods have been proposed for the prevention of clogging of microorganisms and cultured cells, such as washing of separation membranes and setting of filtration conditions (Patent Documents 1, 2, and 3). In order to do this, gas such as air and nitrogen, water, and liquid such as filtered membrane permeated water are added to the culture solution, so the substance production capacity of microorganisms and cultured cells changes, so the culture state is optimized. There existed the subject that it was difficult to maintain and the filtration membrane apparatus for microbial cell separation became complicated.

If adhesion of microorganisms or cultured cells to the membrane surface can be suppressed, high water permeability operation can be performed with low energy, so that processing efficiency is increased, and the physical cleaning process can be simplified, so that cleaning costs can be suppressed. Patent Documents 4, 5, 6, and 7 attempt to charge the membrane near neutral in order to avoid ion adsorption, but the fouling resistance is not sufficient.
JP 58-47485 A Japanese Patent Laid-Open No. 62-138184 JP-A-6-98758 Japanese Patent Laid-Open No. 10-66845 JP-A-2-90990 JP-A-11-179176 JP 2004-290830 A

  An object of the present invention is to filter cell suspensions that can stably maintain high productivity over a long period of time and achieve high water permeability even when used for solid-liquid separation of cell suspensions. It is to provide a porous membrane.

In order to achieve the above object, the porous membrane for filtering a cell suspension according to the present invention has an average pore diameter in the range of 0.01 μm or more and less than 1 μm, and a standard deviation of the average pore diameter of 0.1 μm or less. It is characterized by including an anionic resin.

  According to the present invention, clogging of the membrane is remarkably suppressed with simple operating conditions, and cell suspension can be filtered stably for a long time at low cost.

  The average pore diameter of the membrane used in the present invention is 0.01 μm or more and less than 1 μm. When the average pore diameter is within this range, when animal cells, yeast, filamentous fungi, or the like are used, clogging is small, and stable filtration is possible without leakage of cells into the filtrate. When bacteria smaller than animal cells, yeasts, and filamentous fungi are used, the average pore size is 0.4 μm or less, and the average pore size is 0.2 μm or less. is there. If the average pore diameter is too small, the water permeation rate may be lowered, so that it is usually preferably 0.02 μm or more, more preferably 0.04 μm or more. As described above, the conventional filtration method balances the separation performance and the water permeability by controlling the average pore diameter. Theoretically, if the water permeation amount is increased, rapid separation becomes possible, but the separation selectivity for selectively retaining desired microorganisms and cultured cells is lowered.

  Here, the average pore diameter can be obtained by measuring and averaging the diameters of all pores that can be observed within a range of 9.2 μm × 10.4 μm in a scanning electron microscope observation at a magnification of 10,000 times. it can. The standard deviation σ of the pore diameter is preferably 0.1 μm or less. The standard deviation σ of the pore diameter is Nk, which is the number of pores that can be observed within the above-mentioned range of 9.2 μm × 10.4 μm, and the measured diameter is Xk, and the average pore diameter is X (ave). It computed from Formula (1) below.

  The porous membrane for cell suspension liquid filtration of the present invention comprises an anionic resin. By including an anionic resin, the membrane of the present invention is negatively charged.

  In general, the solid content of the cell suspension is covered with an extracellular polymeric substance (biopolymer) layer secreted by microorganisms. It is a neutrally charged functional group such as a hydroxyl group, or a positively charged functional group such as an amino group. It was thought that negatively charged functional groups such as carboxyl groups and carboxyl groups were dispersed (Shinji Ohba, Hiroaki Takeyama, Yoichi Nagase, Chemical Engineering 10 (2002) 61-70.). However, paying attention to the fact that microorganisms and cultured cells that are the main separation targets in the present invention are generally negatively charged, the membrane surface is less likely to be clogged by the repulsive force with the negatively charged membrane. Thus, it has been found that the peeling coefficient and membrane resistance of the porous membrane can be reduced. As a result, even when the charged porous membrane is installed in the reaction tank, continuous filtration operation can be performed at a lower rate of increase in the transmembrane pressure difference than in the past.

  In addition to this, the membrane of the present invention to which a negative charge is added can be expected to improve the separability due to the charge repulsion in addition to the size separation ability due to the average pore diameter. When the membrane surface is charged, substances with the same charge polarity as the membrane can repel the membrane, thereby retaining such charged substances in the fermentation reaction layer without passing through the membrane pores. . While showing high separation selectivity compared to uncharged membranes, water permeability is not sacrificed.

In the porous membrane used in the present invention, the permeability of the culture solution is one of the important points, and the pure water permeability coefficient of the porous membrane before use can be used as the permeability index. When the pure water permeability coefficient of the porous membrane was calculated by measuring the water permeability at a head height of 1 m using purified water at 25 ° C. by a reverse osmosis membrane, 2 × 10 ⁻⁹ m ³ / m ² / s / Pa It is preferable that it is above, and if it is 2 × 10 ⁻⁹ or more and 6 × 10 ⁻⁷ m ³ / m ² / s / Pa or less, a practically sufficient amount of permeated water can be obtained.

  The surface roughness of the porous membrane used in the present invention is a factor that affects the clogging of the separation membrane. When the surface roughness is 0.1 μm or less, the separation coefficient and membrane resistance of the separation membrane may be reduced. And continuous fermentation can be carried out with a lower transmembrane pressure difference. In addition, the low surface roughness can be expected to reduce the shearing force generated on the membrane surface during filtration of microorganisms and cultured cells, the destruction of microorganisms or cultured cells is suppressed, and the porous membrane is clogged. It is considered that stable filtration is possible for a long time by being suppressed. Here, the surface roughness can be measured under the following conditions using the following atomic force microscope (AFM).

Apparatus: Atomic force microscope (Digital Instruments Co., Nanoscope IIIa)
Condition: Probe SiN cantilever (manufactured by Digital Instruments)
Scan mode Contact mode (in-air measurement), underwater tapping mode (underwater measurement)
Scanning range 10 μm, 25 μm square (measurement in air), 5 μm, 10 μm square (measurement in water)
Scanning resolution 512 × 512
Sample preparation: For measurement, the membrane sample was immersed in ethanol at room temperature for 15 minutes, then immersed in RO water for 24 hours, washed, and then air-dried.

The surface roughness d _rough of the film was calculated by the following formula (2) from the height in the Z-axis direction at each point by AFM.

  The material of the porous membrane for cell suspension liquid filtration in the present invention includes an anionic resin, and is not particularly limited as long as separation performance and water permeation performance according to the quality of water to be treated and its use can be obtained. From the viewpoint of separation performance such as water permeation performance and dirt resistance, a porous membrane including a porous resin layer is required. In addition, woven fabrics and non-woven fabrics made of organic fibers such as cellulose fibers, cellulose triacetate fibers, polyester fibers, polypropylene fibers, and polyethylene fibers, and porous substrates and inorganic resin layers made of inorganic materials But it ’s okay.

  As a separation membrane for realizing the present invention, an organic polymer membrane can be used. The organic polymer membrane is a separation membrane basically composed of an organic polymer material, for example, an organic fiber. In many cases, a non-woven fabric or a macroporous structure porous organic base material and a porous resin layer having a pore size smaller than the pore size of the porous organic base material are combined. However, the present invention is not limited to this film structure.

  Although it does not specifically limit with anionic resin, Ethylene unsaturated carboxylic acid resin, ethylene unsaturated sulfonic acid resin, and ethylene unsaturated phosphonic acid resin are mention | raise | lifted.

  Examples of the ethylenically unsaturated carboxylic acid resin include acrylic acid resin, methacrylic acid resin, crotonic acid resin, α-methylcrotonic acid resin, hexenoic acid resin, and itaconic acid resin.

  Examples of the ethylenically unsaturated sulfonic acid resin include styrene sulfonic acid resin, acrylic sulfonic acid resin, methacryl sulfonic acid resin, vinyl sulfonic acid resin, and 2-acrylamido-2-methylpropane sulfonic acid resin.

  Examples of the ethylenically unsaturated phosphonic acid resin include vinyl phosphonic acid resin and vinyl phenyl phosphonic acid resin.

  Here, the material other than the anionic resin may be polyethylene resin, polypropylene resin, polyvinyl chloride resin, polyvinylidene fluoride resin, polysulfone resin, polyether sulfone resin, polyacrylonitrile resin, cellulose resin, cellulose triacetate resin, etc. It may be a mixture of these resins.

  Among them, preferred are polyvinylidene fluoride resins excellent in physical durability and chemical durability, and polyacrylate resins and / or polymethacrylate resins, and more preferred are polyvinylidene fluoride resins.

  The polyvinylidene fluoride resin is a resin containing a vinylidene fluoride homopolymer and / or a vinylidene fluoride copolymer. A plurality of types of vinylidene fluoride copolymers may be contained. Examples of the vinylidene fluoride copolymer include a copolymer of vinylidene fluoride and at least one selected from the group consisting of vinyl fluoride, tetrafluoroethylene, hexafluoropropylene, and ethylene trifluoride chloride. . Among these, vinylidene fluoride homopolymer is more preferably used from the viewpoint of film forming property, chemical durability, and cost.

  As anionic resin, the anionic resin of ethylene unsaturated carboxylic acid resin, ethylene unsaturated sulfonic acid resin, and ethylene unsaturated phosphonic acid resin are generally hydrophilic and can be formed by mixing with hydrophobic resin. However, when used in water, only the hydrophilic resin is gradually eluted, and the charged state cannot be maintained for a long time.

  On the other hand, it is known that, for example, polymethacrylate resin is compatible with polyvinylidene fluoride resin at a molecular level (SP Nunes, KV Peinemann, Journal of Membrane Science 1992, 73 P25). It is possible to easily copolymerize the polyvinylidene fluoride resin with a water-soluble ethylenically unsaturated carboxylic acid, ethylene unsaturated sulfonic acid, ethylene unsaturated phosphonic acid and the like. Therefore, the polyacrylate resin and the polymethacrylate resin function as a compatibilizer in the polyvinylidene fluoride resin, and the anionic resin can be dispersed without being eluted.

  That is, the resin for compatibilizing the polyvinylidene fluoride resin and the anionic resin is not particularly limited as long as they are compatibilized, and specific examples include polyacrylate resin and polymethacrylate resin.

  Although it does not specifically limit with polyacrylate resin, for example, acrylics, such as methyl acrylate, ethyl acrylate, n-butyl acrylate, iso-butyl acrylate, tert-butyl acrylate, 2-ethylhexyl acrylate, glycidyl acrylate, hydroxyethyl acrylate, hydroxypropyl acrylate A homopolymer of an acid ester monomer, a copolymer thereof, and a copolymer with another copolymerizable vinyl monomer are shown.

  Although it does not specifically limit with polymethacrylate resin, For example, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, iso-butyl methacrylate, tert-butyl methacrylate, 2-ethylhexyl methacrylate, glycidyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, etc. A homopolymer of a methacrylic acid ester monomer, a copolymer thereof, and a copolymer with another copolymerizable vinyl monomer are shown. Among these polyacrylic ester resins and polymethacrylic ester resins, polymethyl methacrylate is more preferably used from the viewpoint of compatibility with polyvinylidene fluoride resin, film-forming property, and cost.

  Here, it is thought that the higher the content of anionic resin in the membrane, the more clogging can be suppressed with respect to the cell suspension, but if it is too high, the anionic resin will elute into the water and the durability and removal performance of the membrane Decreases. Although the lower limit depends on the type of anionic resin, the performance of the present invention can be exhibited when the anionic resin is contained in the film in an amount of 1% by weight or more, preferably 1.5% by weight or more. The anionic resin content is calculated from the charged composition of the anionic resin component in the film after film formation. Solvents, surfactants and other solvents that are eluted during film formation are the values after film formation. It is not included in the film.

  The porous membrane of the present invention may be a flat membrane or a hollow fiber membrane. In the case of a flat membrane, the thickness is selected according to the application, but for example, it is selected in the range of 20 μm to 5000 μm, preferably 50 μm to 2000 μm. As described above, it may be formed of a porous substrate and a porous resin layer. At that time, either the porous resin layer permeates the porous base material or the porous resin layer does not permeate the porous base material, and it is selected according to the application. The thickness of the porous substrate is selected in the range of 50 μm to 3000 μm. In the case of a hollow fiber membrane, the inner diameter is selected in the range of 200 μm to 5000 μm, and the film thickness is selected in the range of 20 μm to 2000 μm. Moreover, the woven fabric and knitting which made the organic fiber or the inorganic fiber the cylinder shape may be included.

  The porous membrane of the present invention can be made into a separation membrane element by combining with a support. The form of the porous membrane element is not particularly limited, but a porous membrane element in which a support plate is used as a support and the porous membrane of the present invention is disposed on at least one surface of the support plate is suitable for the membrane element of the present invention. This is one of the forms. In this embodiment, since it is difficult to increase the membrane area, it is also preferable to dispose a porous membrane on both sides of the support plate in order to increase the water permeability.

  In the present invention, the transmembrane pressure difference at the time of filtering the cell suspension may be any condition as long as microorganisms, cells and medium components are not easily clogged, but the transmembrane pressure difference is from 0.1 kPa to 20 kPa. Range. As the driving force of filtration, it is possible to generate a transmembrane differential pressure in the porous membrane by siphon using the liquid level difference (water head difference) of cell suspension and porous membrane treated water. As a driving force, a suction pump may be installed on the porous membrane treated water side, or a pressure pump may be installed on the cell suspension side of the porous membrane. The transmembrane pressure can be controlled by changing the liquid level difference between the cell suspension and the porous membrane treated water, and when using a pump, it can be controlled by the suction pressure. The side pressure can be controlled by the gas or liquid pressure introduced. When performing these pressure controls, the pressure difference on the cell suspension side and the pressure difference on the porous membrane treated water side can be used as the transmembrane pressure difference and used to control the transmembrane pressure difference.

  The present invention will be described more specifically with reference to the following examples. However, the present invention is not limited thereby.

  The membrane resistance of the porous membrane in the examples was measured as follows.

The basic filtration experiment apparatus pressurizes the reservoir tank with nitrogen gas, and the permeated water per unit time permeating from the stirring type cell (Amicon (registered trademark) 8010, effective membrane area 4.1 cm ² manufactured by Millipore) is electronically balanced. It is the structure monitored by this. (Chia-Chi Ho, AL Zydney, Journal of Colloid and Interface Science, 2002.232 P389). The electronic balance is connected to a computer and the membrane resistance is calculated from the change in weight over time. The membrane surface was given a membrane surface flux by rotation of a magnetic stirrer attached to the stirring cell, the stirring speed of the stirring cell was always adjusted to 600 rpm, the evaluation temperature was 20 ° C., and the evaluation pressure was 10 kPa.

  The membrane resistance is a resistance generated when the liquid to be filtered is filtered through a membrane, and is generally defined by the following formula (3).

R = ΔP / (μJ) (Formula 3)
R: Membrane resistance [1 / m]
ΔP: membrane filtration pressure [Pa]
μ: Viscosity of membrane filtrate [Pa · s]
J: Membrane filtration flux [m / s]
Here, μ may directly measure the viscosity of the membrane filtrate, but may be converted from the temperature according to the following formula (4).

μ × 10 ³ = F · exp [(1 + BT) / (CT + DT ² )] (Formula 4)
Here, F = 0.01257187, B = −0.005806436, C = 0.001130911, D = −0.000005723952, and T is the absolute temperature [K]. That is, when the Celsius temperature is σ [° C.], it is expressed as T = σ + 273.15.

Example 1
Polyvinylidene fluoride homopolymer (PVDF, weight average molecular weight 358,000), copolymer of methyl methacrylate and methacrylic acid (P (MMA-MAA), weight average molecular weight 22,000, copolymer molar ratio 7: 3) ), N, N-dimethylformamide (DMF, manufactured by Mitsubishi Rayon Co., Ltd.), polyoxyethylene sorbidan monostearate (T-60V, manufactured by Sanyo Chemical Industries, Ltd.), ethylene glycol (EG, Wako Pure Chemical Industries, Ltd.) Each of these was used, and these were sufficiently stirred and mixed and dissolved at a temperature of 100 ° C. with the following composition to prepare a film forming stock solution.

PVDF: 16.0% by weight
P (MMA-MAA): 1.0% by weight
T-60V: 8.0% by weight
EG: 4.0% by weight
DMF: 71.0% by weight
Next, the film-forming stock solution is cooled to 40 ° C., applied to a nonwoven fabric made of polyester fiber having a density of 0.48 g / cm ³ and a thickness of 220 μm, and immediately immersed in a water coagulation bath at 25 ° C. for 5 minutes. A porous substrate on which a porous resin layer was formed was obtained.

This porous substrate was immersed in hot water at 95 ° C. for 2 minutes to wash out DMF, and a porous membrane for cell suspension liquid filtration was obtained. About the produced said separation membrane, content of anionic resin is 1.76 weight%, a pure water permeability coefficient is 54 * 10 < ^-9 > m < ³ > / m < ² > / s / Pa, an average pore diameter is 0.02 micrometer, Membrane surface The roughness was 0.06 μm, and the membrane resistance R during filtration of 0.01 m was 11.76 [1 / m]. The measurement results of the membrane resistance are shown in FIG.

Comparative Example 1
The same procedure as in Example 1 was conducted except that PVDF was changed to 17.0% by weight without adding P (MMA-MAA) of Example 1. The pure water permeability coefficient is 44 × 10 ⁻⁹ m ³ / m ² / s / Pa, the average pore diameter is 0.1 μm, the membrane surface roughness is 0.15 μm, and the membrane resistance R at the time of 0.01 m filtration is 19.47. [1 / m]. The measurement result of the film resistance measured under the same conditions as in Example 1 is shown in FIG.

  According to the charged porous membrane of the present invention, the rate of increase in membrane resistance could be suppressed to about one half compared to the conventional product (Comparative Example 1) that has no charge.

Example 2
Example 1 was the same as Example 1 except that the stock solution composition of Example 1 was changed as follows. P (MMA-NaSS) is a copolymer of sodium styrenesulfonate (NaSS, manufactured by Wako Pure Chemical Industries, Ltd.) and MMA (weight average molecular weight 34,000, copolymer molar ratio 8: 2).

PVDF: 16.0% by weight
P (MMA-NaSS): 1.0% by weight
T-60V: 8.0% by weight
EG: 4.0% by weight
DMF: 71.0% by weight
The pure water permeability coefficient is 59 × 10 ⁻⁹ m ³ / m ² / s / Pa, the average pore diameter is 0.03 μm, the membrane surface roughness is 0.2 μm, and the membrane resistance R during filtration of 0.01 m is 12.83. [1 / m].

Example 3
The same procedure as in Example 1 was carried out except that PVDF was changed to 16.5% by weight and P (MMA-MAA) was changed to 1.0% by weight without adding P (MMA-MAA) in Example 1. The pure water permeability coefficient is 42 × 10 ⁻⁹ m ³ / m ² / s / Pa, the average pore diameter is 0.1 μm, the membrane surface roughness is 0.15 μm, and the membrane resistance R at the time of 0.01 m filtration is 18.21. [1 / m].

It is a figure explaining the relationship between film resistance and fouling.

Claims (6)

A porous membrane for filtering a cell suspension having an average pore diameter in the range of 0.01 μm or more and less than 1 μm and a standard deviation of the average pore diameter of 0.1 μm or less, comprising an anionic resin A porous membrane for filtering a cell suspension. The porous membrane for cell suspension liquid filtration according to claim 1, comprising a polyvinylidene fluoride resin and a resin that compatibilizes the polyvinylidene fluoride resin and the anionic resin. The porous membrane for cell suspension liquid filtration according to claim 1 or 2, wherein the resin for compatibilizing the polyvinylidene fluoride resin and the anionic resin is an acrylate resin or a methacrylate resin. The porous membrane for cell suspension liquid filtration according to any one of claims 1 to 3, wherein the anionic resin is an ethylene unsaturated carboxylic acid resin, an ethylene unsaturated sulfonic acid resin, or an ethylene unsaturated phosphonic acid resin. The pure water permeability coefficient is 2 × 10 ⁻⁹ m ³ / m ² / s / Pa or more and 6 × 10 ⁻⁷ m ³ / m ² / s / Pa or less, or the cell according to claim 1. A porous membrane for suspension. The porous membrane for cell suspension liquid filtration according to any one of claims 1 to 5, wherein the membrane surface roughness is 0.1 µm or less.

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