JP2717458B2 - Filtration method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a full filtration periodic backwashing system, and more particularly to a full filtration periodic backwash in a microfiltration area where periodic backwashing is performed to maintain a large membrane permeation flux. It relates to a washing system. The whole filtration periodic backwash system of the present invention can be used for various polymers, microorganisms, yeasts,
It is applied to the separation, purification, recovery, concentration, etc. of a fluid containing or suspending fine particles, and in particular, it can be applied to any case where it is necessary to separate the fine particles from a fluid containing fine particles requiring filtration. For example, the present invention can be applied to a case where fine particles are separated from a suspension of a pigment and the like, in addition to various suspensions containing fine particles, a fermentation solution or a culture solution.

[0002]

2. Description of the Related Art Conventionally, techniques for separating a suspended substance from a raw fluid containing the suspended substance using a membrane include, for example, a reverse osmosis method using pressure as a driving force, an ultrafiltration method, and a microfiltration method. There are an electrodialysis method using a potential difference as a driving force and a diffusion dialysis method using a concentration difference as a driving force. These methods are capable of continuous operation, can be separated without significantly changing the temperature and pH conditions during the separation operation, can be purified or concentrated, can be separated over a wide range of particles, molecules, ions, etc., It is economical because the processing capacity can be kept large even in a small plant, and the energy required for the separation operation is small.
In addition, the method is widely used because it is possible to treat a low-concentration raw fluid that is difficult with other separation methods. The membranes used for these separation techniques include polymer membranes mainly composed of organic polymers such as cellulose acetate, cellulose nitrate, regenerated cellulose, polysulfone, polyacrylonitrile, polyamide, and polyimide, and heat resistance and chemical resistance. There is a porous ceramic membrane etc. which is excellent in the durability of ultrafiltration. Ultrafiltration membrane is mainly used for filtration of colloid, and microfiltration for filtration of fine particles of 0.05 to 10μm. Uses a microfiltration membrane having micropores suitable for it. By the way, in recent years, with the advancement of biotechnology, higher purity, higher performance, and higher precision have been required, and the application field of microfiltration or ultrafiltration technology is expanding. However,
In microfiltration or ultrafiltration, when fine particles are separated using a membrane, a cake layer is formed due to the effect of concentration polarization, causing resistance to the flow of the permeated fluid, and resistance due to membrane clogging is increased. There is a problem that the permeation flux decreases rapidly and remarkably, and this is the biggest cause that hinders the practical use of microfiltration or ultrafiltration. Further, the film used therein is easily contaminated, and it is necessary to take measures to prevent it.

[0003] As a filtration method, there is a so-called total filtration method in which all the fluid to be filtered passes through a filter medium (such as a filter cloth or a membrane) and a cake layer to separate fine particles contained in the fluid. In this conventional all-filtration method, a high permeation flux is obtained at a stage where a fluid passes and suspended substances are trapped and separated inside the filtration membrane. When a layer is formed and a large amount of raw fluid is processed, or when the specific resistance of the cake layer to be formed is extremely high, the filtration resistance becomes large, and such total filtration reduces the membrane permeation flux. On the other hand, in the fields of wastewater treatment and filtration of fresh water and pool water, it is known to perform backwashing to recover the permeation flux of a clogged filter. However, this combined filtration and backwashing method is a technology developed in the field of wastewater treatment where the specific resistance of the cake layer is relatively small, so enzymes, beer, wine, sake,
Filtration of fine particles having high specific resistance, such as isolation of bacterial cells from a fermentation solution that produces soy sauce, antibiotics, amino acids, and organic acids such as acetic acid and oxalic acid, is ineffective as it is. At present, for such a liquid, a filtration method using a filter aid such as diatomaceous earth or bentonite is most commonly used. This method is a method in which fine particles of a filter aid are stacked in a block shape to form a microfiltration layer, and the fine particles are filtered through gaps between the particles. Although this method is a sophisticated filtration method that has been used for a long time, it is still a very effective method for filtering a large amount of suspension, but it requires a lot of labor and a lot of industrial waste There is such a problem. For this reason, it has been considered to use a cross flow type filtration system. In this cross-flow filtration method, a raw fluid to be filtered flows in parallel to the membrane surface of the filtration membrane, and the fluid permeates to the opposite side through the filtration membrane, and the flow of the raw fluid and the flow of the permeated fluid are orthogonal to each other. This is why it is so named. In this cross-flow type filtration method, the cake layer formed on the membrane surface is peeled off by the flow of the raw fluid parallel to the membrane, so that the membrane permeation flux is larger than the conventional total filtration method, and a large amount of the raw fluid Can be directly continuously separated, purified, and concentrated, but when a membrane in the microfiltration region that removes particles with a large pure water flux, that is, particles of 0.05 μm or more, is used, the membrane flux rapidly increases. It is difficult to maintain a high membrane permeation flux at the beginning of filtration due to a decrease, and as a result, when compared with the total filtration method and the total permeate volume, the improvement effect is small and insufficient to obtain an economical permeation flux. Met.

[0004]

As described above, the cross-flow filtration method is an advanced separation technique in principle, but the biggest problem, the membrane permeation flux, is lower than that of the conventional total filtration method. Although large, there is a problem that even if this cross-flow method is used as a microfiltration method, a sufficiently high membrane permeation flux cannot be obtained economically. Also, looking at a specific example of the conventional separation of a suspended substance and a fluid, for example, when separating cells from a fermentation broth, the conventional centrifugation method, diatomite filtration, Even if a cross-flow filtration method is used in place of the filtration method, not only does the cake layer formed on the membrane surface and clogging cause a decrease in the membrane permeation flux as the filtration time elapses, but also shearing when circulating the raw fluid There was a problem that the activity of the cells was lost by the force.

[0005] As a method of increasing the permeation flux, the inflow of the raw fluid into the filtration membrane is intermittently stopped in combination with the cross-flow filtration method, or the valve on the permeation fluid side of the filtration membrane is closed, whereby the filtration is performed. The pressure applied perpendicular to the membrane surface of the membrane is intermittently eliminated or reduced, and the pressure is applied from the permeated liquid side of the filtration membrane to flow the fluid from the permeated liquid side to the raw fluid side, so that the raw fluid side of the filtration membrane is removed. Attempts to remove intermittently the cake layer and the adhering layer deposited on the membrane surface have been made as "backwashing", and even when these backwashes are performed, suspended substances desorbed from the filtration membrane are removed. If left in the filtration system, the concentration of the suspension in the raw fluid gradually increases, and in some cases, the viscosity of the raw fluid also increases. There was a problem that the permeation flux did not recover sufficiently.
In addition, when backwashing is performed using a permeate, the membrane permeation amount is reduced by the amount of the backwash substantially, so that there is a problem that a backwash solution that can sufficiently recover the membrane permeation flux cannot be secured. On the other hand, as a method of not lowering the activity of the cells, the cross-flow circulation flow rate is reduced to reduce the shearing force.However, when the shearing force is reduced, the effect of the cross-flow filtration method is reduced. Taking measures not to decrease the body activity, there is a problem that the membrane permeation flux decreases. Further, when a pump having a small shearing force such as a diaphragm pump is used in order to reduce the crushing of bacterial cells by the pump, there is a problem that the pulsation of the pump is large and the effect of the cross flow filtration system is reduced.

[0006] Cake filtration using a filter aid such as diatomaceous earth or perlite has the following problems. That is, prior to filtration, an operation of forming a deposited layer of a filter aid on a filter called a precoat, a process of adding and dispersing a filter aid to a stock solution called a body feed, and washing the cake layer after completion of filtration. There is also a removal step, which requires a lot of manpower. Further, if there is a change in filtration pressure or flow rate during filtration, there is a problem that the cake layer of the filter aid falls off and cannot be filtered, or a large amount of industrial waste is generated.

[0007]

The above problem can be solved by the following method. That is, the pore size of the surface where the undiluted filtration solution first contacts the membrane is 1 to 10 times the volume average diameter of the suspended particles in the undiluted filtration solution, and the pore size of the densest layer of the membrane is 0.8 of the particle size to be removed. This is a filtration method involving periodic backwashing using a microfiltration membrane having anisotropy in the pore diameter in the thickness direction, characterized in that the filtration is not more than twice. The suspended particles in the fermentation broth are
It is made up of fungi such as bacteria, yeasts and mycelia, and aggregate particles composed of proteins and polysaccharides derived from medium components and fermentation metabolites. The average particle size, distribution and concentration vary depending on the type of fermentation liquid, ranging from a submicron region with a small particle size of about 0.1 μm to a large range of several tens μm with a large particle size. Further, since the purpose of filtration differs depending on the product, the minimum particle size to be removed is not uniform. For example, in the case of beer, the particle size is 2 to 5
μm, and the concentration of the suspension is from 0.1 g / liter to 1 g
Per liter. In order to clarify the solution by filtering it, a microfiltration membrane having an average filtration pore size of 1.5 μm or less is required. However, in a membrane such as a nylon membrane formed by the method described in JP-A-55-8887, pores are uniformly distributed in the thickness direction, and all the particles are trapped on the membrane surface and clogged immediately. I do. On the other hand, when the filtration is performed using an anisotropic microfiltration membrane having an average pore diameter of 5 to 30 μm on the inlet side of the filtration and an average pore diameter of the smallest pore layer inside the membrane of 0.3 to 3 μm, the clogging is remarkable. Improved. Furthermore, if the filtration with periodic backwashing is performed using this anisotropic structure membrane, such as filtering for 5 to 60 minutes, then backwashing for several seconds and repeating the filtration again, practically unfiltered young beer is practical. It has been found that effective filtration can be achieved.

[0008] The purpose of filtering alcoholic beverages such as beer and sake is to clarify the liquid and remove various bacteria such as fire-killed bacteria. For the former purpose alone, it is sufficient that the average pore diameter of the minimum pore diameter layer of the anisotropic film is about 1.5 to 0.8 μm to 3 μm. If the latter purpose is also included, the average pore size of the minimum pore size layer of the anisotropic film must be reduced to 0.3 to 0.6 μm. In addition, as in the fermentation of antibiotics, these bacteria are entangled to form large lumps, such as filamentous fungi, and if a small amount of fermentation bacteria falls off in the filtrate, there is no problem in the subsequent process. The average pore size of the minimum pore size layer of the conductive membrane is more preferably as large as 2 to 10 μm. Generally, the average pore size of the minimum pore size layer of the anisotropic film needs to be 0.8 times or less the minimum particle size to be removed. On the other hand, the optimum pore diameter on the inlet side of filtration varies depending on the volume average particle diameter and the distribution of suspended particles in the undiluted solution. The standard value is 1 to 10 times the volume average diameter of the suspended particles, but in most cases, the optimum pore size is in the range of 2 to 6 times.

A microfiltration membrane having an anisotropic structure in which the pore size changes continuously in the thickness direction of the membrane is disclosed in Japanese Patent Publication No. 55-6406 and Japanese Patent Publication No. 1-343619, one side of the membrane. From the surface to the opposite surface, and those having a minimum pore diameter layer inside the membrane, as described in JP-A-62-27006. As a film material, cellulose acetate and polysulfone are known as typical materials forming an anisotropic structure, but vinyl chloride, polyvinylidene fluoride and the like also form an anisotropic structure. Hereinafter, the method for producing the anisotropic film will be described in detail. The production of the microfiltration membrane is performed by dissolving the polymer in a good solvent, a mixed solvent of a good solvent and a non-solvent or a mixture of a plurality of solvents having different degrees of solubility in the polymer to prepare a membrane-forming stock solution. Is cast on a support or directly in a coagulating liquid, and washed and dried. In this case, examples of the solvent for dissolving the polymer include dichloromethane, acetone, dimethylformamide, dimethylacetamide, dimethylsulfoxide, 2-pyrrolidone, N-methyl-2-pyrrolidone, and sulfolane. Examples of the non-solvent to be added to the solvent include cellosolves, alcohols such as methanol, ethanol and isopropanol, ketones such as acetone and methyl ethyl ketone, ethers such as tetrahydrofuran and dioxane, polyethylene glycol, glycerin and ethyl glycol. Polyols and the like. The ratio of the non-solvent to the good solvent may be any range as long as the mixed solution can maintain a uniform state, but is preferably 5 to 50% by weight.

Further, an inorganic electrolyte, an organic electrolyte, a polymer electrolyte or the like, which is called a swelling agent, can be added to control the porous structure. Examples of the electrolyte that can be used in the present invention include metal salts of inorganic acids such as sodium chloride, sodium nitrate, potassium nitrate, sodium sulfate, zinc chloride, and magnesium bromide; organic acid salts such as sodium acetate, sodium formate, and potassium butyrate; and polystyrene sulfonic acid. Polymer electrolytes such as sodium, polyvinylpyrrolidone and polyvinylbenzyltrimethylammonium chloride, and ionic surfactants such as sodium dioctylsulfosuccinate and sodium alkylmethyltaurate are used. Although some of these electrolytes show a certain effect even when added alone to the polymer solution, when these electrolytes are added as an aqueous solution, a particularly remarkable effect may be exhibited.
The amount of the electrolyte aqueous solution to be added is not particularly limited as long as the uniformity of the solution is not lost by the addition, but is usually 0.5% by volume to 10% by volume based on the solvent. The concentration of the aqueous electrolyte solution is not particularly limited, and the higher the concentration, the greater the effect. However, the concentration generally used is 1% by weight to 60% by weight. The polymer concentration as a stock solution is 5 to 35% by weight, preferably 10 to 30% by weight.
It is. If it exceeds 35% by weight, the water permeability of the obtained microporous membrane becomes so small that it has no practical meaning, and it becomes 5% by weight.
If it is smaller than this, a microfiltration membrane having a sufficient separation ability cannot be obtained.

The membrane-forming stock solution prepared as described above is cast on a support, and the polymer solution membrane together with the support is immersed in the coagulation solution immediately after the casting or after a certain period of time. Water is most commonly used as the coagulation liquid, but an organic solvent that does not dissolve the polymer may be used, or two or more of these non-solvents may be used in combination. The support can be arbitrarily selected from those which can be used as a support in the case of manufacturing a microfiltration membrane. However, it is preferable to use a nonwoven fabric because the support does not need to be peeled off. The nonwoven fabric that can be used in the present invention is a general one made of polypropylene, polyester, or the like, and is not limited by the material. The cast film in which the polymer is precipitated in the coagulation bath is then washed with water, washed with warm water, washed with a solvent, etc., and dried.

The membrane thus obtained is assembled into a known module such as a pleated cartridge flat membrane laminated structure cartridge and is subjected to filtration. FIG. 1 is a line diagram for performing filtration while performing periodic backwashing. The filtrate is sent to the filter housing 11 by the pump 12. The filtered filtrate is sent to a filtrate storage tank. When filtration is performed for a certain period of time and the filtration pressure increases, the pump 12 is stopped, and gas is introduced into the primary side of the filter to push out the remaining liquid to the secondary side. Next, the backwash water is sent to the filter housing by the pump 13, and the backwash liquid is pushed out together with the particle cake captured at the backwash liquid outlet. After gas is introduced from the filter secondary side and the remaining backwash liquid is pushed out to the outlet, the filtration is restarted by the pump 12 again. The elimination of backwash water remaining in the housing may be omitted if further purification steps follow, such as antibiotics and amino acids. Water is usually used for the backwashing liquid, but a filtrate may be used in some cases.

It is natural that the cycle of filtration and backwashing is preferably longer, and for that purpose, first, the anisotropic structure of the membrane is important. On the other hand, it is possible to lengthen the cycle also depending on the filtering conditions. It can be achieved by reducing the filtration flux per unit membrane area. As the rate of increase of the filtration pressure decreases as the flux decreases, the rate of increase is less than simply proportional to the flux, so that the required amount of filtration can be obtained without increasing the membrane area much. The appropriate filtration flux cannot be specified because it naturally depends on the type of the fermentation solution and the purpose of filtration. For example, in a beer which has been matured and most of the yeast has settled, the filtration is performed at a flux of 20 L / m ² · min or less. Is preferred.

[0014]

EXAMPLES The present invention will be described in more detail with reference to specific examples, but the present invention is not limited to the examples unless it exceeds the gist of the invention. Example 1 A film forming stock solution was obtained by uniformly dissolving 15 parts of polysulfone (P-3500 manufactured by Amoco), 70 parts of N-methyl-2-pyrrolidone and 15 parts of polyvinylpyrrolidone. It is cast on a glass plate so as to have a thickness of 180 μm.
% For 6 seconds, then immersed in 15 ° C water,
An anisotropic microfiltration membrane with a dense inner layer was obtained. AST
When the pore size was measured by the method of MF316, the average pore size was 1.4 μm. Take a cross-sectional SEM photograph of the membrane,
When the average pore size of the minimum pore size layer and the average pore size of the maximum pore size layer on the surface were compared, the anisotropy ratio was about 1: 8 (referred to as membrane B). Cast using the same film-forming stock solution, 25 ° C, humidity 60
% For 5 seconds, then immersed in 45 ° C water,
An anisotropic microfiltration membrane with a dense inner layer was obtained. AST
When the pore size was measured by the method of MF316, the average pore size was 1.5 μm. Take a cross-sectional SEM photograph of the membrane,
When the average pore size of the minimum pore size layer and the average pore size of the maximum pore size layer on the surface were compared, the anisotropy ratio was about 1:15 (membrane C
).

Example 2 German vise beer (Hefeweizenbie)
r, Oberdorfer) were analyzed. The total amount of the suspension was 0.27 g / L, the number of yeasts was 5 × 10 ⁸ / L, the aggregated polysaccharide was 30 mg / L, the aggregated protein was 70 mg / L, and the size of the yeast was about 5 μm. This beer was used as a stock solution for filtration, and a filtration flux of 50 L / m ² was obtained using two types of membranes formed in Example 1 and an NP membrane (average pore diameter: 1.4 μm, called membrane A) having a uniform structure and manufactured by Pall Corporation. Min, 20 L / m ² · min and 5 L / m ² · min, and the filtration pressure rise curve was measured. The results are shown in FIG. 2, and the description of the reference numerals in FIG.
Shown in

[0016]

[Table 1]

Example 3 The same vise beer as in Example 2 was produced using the film B formed in Example 1 while repeating backwashing under the following conditions. Filtration while backwashing at a filtration flux of 10 L / m ² · min for 3 seconds every 8 minutes and filtering while backwashing at a filtration flux of 20 L / m ² · minute every 4 minutes for 3 seconds FIG. 3 shows the change in the filtration pressure when this was performed. At this time, the backwash was performed using water with a flux of 200
L / m ² · min. As can be seen from the results, the anisotropy ratio of the membrane pore diameter and the filtration flux have a large influence on the rate of increase of the filtration pressure, and a large amount of filtration is possible by performing regular backwashing.

[0018]

According to the present invention, the pore size of the surface where the undiluted filtration solution first contacts the membrane is 1 to 10 times the volume average diameter of the suspended particles in the undiluted filtration solution, and the pore size of the densest layer of the membrane is the same as the particle size to be removed. Filtration of the suspension from the fermentation liquor by a filtration method involving periodic backwashing using a microfiltration membrane having anisotropy in the film thickness direction, characterized by being 0.8 times or less, It can be done efficiently and with high precision.

[Brief description of the drawings]

FIG. 1 is a filtration flow diagram with periodic backwashing.

FIG. 2 is a comparison of the increase in filtration pressure when the anisotropy and flux of the membrane are changed. The description of the reference numerals in the figure is shown in Table 1.

FIG. 3 is a filtration pressure rise curve when filtering while periodically backwashing.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Filter housing 12 Filtration pump 13 Backwashing pump 14 Filtration stock 15 Filtrate storage tank 16 Backwashing liquid 17 Gas supply port 18 Backwashing liquid outlet

Claims (3)

(57) [Claims] 1. The pore size of the surface of the stock solution to be first contacted with the membrane is 1 to 10 times the volume average size of the suspended particles in the stock solution, and the pore size of the densest layer of the membrane is the size of the particle to be removed. A filtration method involving periodic backwashing using a microfiltration membrane having anisotropy in the pore diameter in the thickness direction, which is 0.8 times or less. 2. The pore size of the surface where the undiluted solution first contacts the membrane is 4 to 30 μm, and the pore size of the densest layer of the membrane is 0.8 μm.
The filtration method with periodic backwashing according to claim 1, wherein the filtration solution is an alcohol fermentation suspension. 3. The alcoholic fermentation suspension is beer,
The filtration method with periodic backwashing according to claim 2, wherein the filtration is performed at a flux of 20 L / m ² · min or less.