JPH0118954B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for concentrating an aqueous polymer solution. Specifically, the present invention relates to a method for concentrating an aqueous polymer solution using a porous diaphragm. In particular, the present invention relates to a method for concentrating a dilute aqueous polymer solution to an intermediate concentration. Water-soluble polymer compounds are sometimes obtained as dilute aqueous solutions, which are often required to be concentrated into products. For example, when manufacturing gelatin, collagen from animal skin, bone, etc. is extracted with hot water to give a concentration of 2 to 10% (concentration as anhydrous gelatin,
In this specification, gelatin concentrations are as anhydrous unless otherwise specified. ) is obtained, concentrated to an intermediate concentration in an evaporator, and further concentrated to a 25-30% gelatin solution in a special evaporator to produce a product. However, such evaporative concentration methods consume a large amount of energy. Furthermore, since the salts present in the extract are transferred directly to the concentrate, a desalting step may be required between the extraction step and the concentration step depending on the salt content allowed in the product. Furthermore, since scale generally occurs in the evaporator, the aqueous gelatin solution leaving the evaporator must be filtered before being supplied to the subsequent evaporator. The present invention provides a method to avoid these difficulties. The present invention allows a dynamic film to be formed on the wall surface of an inorganic porous diaphragm by flowing alumina sol, zirconium oxychloride, or polyacrylic acid under high pressure along the wall surface of the inorganic porous diaphragm. An aqueous polymer solution characterized in that an aqueous gelatin solution, an aqueous polyethylene glycol solution or an aqueous polyacrylamide solution is passed under pressure along a dynamic membrane, and a part of the water in the aqueous solution is expelled to the outside through the dynamic membrane. The gist is the concentration method. To explain the present invention in more detail, when an aqueous polymer solution is passed under pressure along one side of an inorganic porous diaphragm, water and salts pass through the diaphragm, but substantially no polymer compound is passed through the diaphragm. This method takes advantage of the phenomenon that the membrane does not pass through the diaphragm. The porous diaphragm has a pore diameter of 0.02 to 2.0 μm, preferably 0.05 to 0.2 μm, and is made of metal, ceramics, glass,
Materials made of inorganic materials such as carbon are used. Such an inorganic porous diaphragm has high mechanical strength, and is rich in heat resistance and chemical resistance. Since aqueous polymer solutions generally have high viscosity at low temperatures, it is often desirable to handle them at elevated temperatures. Therefore, having a diaphragm with high heat resistance brings great operational benefits. Similarly, the high chemical resistance of the diaphragm makes it possible to eliminate the clogging by treating the diaphragm with chemicals when the diaphragm becomes clogged. A preferred membrane is a sintered metal oxide such as alumina. When an aqueous polymer solution is passed under pressure along such an inorganic porous diaphragm, the polymer compound is deposited on the diaphragm surface and forms a dynamic membrane, allowing water to pass through the diaphragm but blocking the passage of the polymer compound. be done. In the present invention, the surface of the porous diaphragm is precoated with an inorganic compound before use. For example, aqueous solutions of inorganic compounds such as various metal (hydr)oxides, sodium aluminate, and zirconium oxychloride are deposited in a fluid state on the membrane surface to form a dynamic membrane, which is then used in the method of the present invention. Dynamic membranes with such inorganic compounds deposited generally have a large permeation flux, that is, a large amount of permeated water per unit area of the diaphragm and per unit time, when used for concentrating polymer solutions.
And it is hard to cause clogging. Furthermore, even when clogging occurs, the deposited layer of inorganic compounds can be easily peeled off from the diaphragm and the diaphragm can be regenerated by treating it with an alkaline aqueous solution or the like. Furthermore, the performance of the membrane can be modified to further increase the separation capacity by depositing an aqueous solution of a polymer compound in a fluidized state on top of the deposited inorganic compound. When these inorganic and polymeric compounds are deposited under high pressure, the resulting dynamic membrane has salt separation ability. Therefore, when desalting is desired at the same time as concentrating an aqueous gelatin solution, the pressure is low, usually 25 Kg/cm ² G or less, preferably 10 to 20 G.
Deposited under a pressure of Kg/cm ² G. Preferably, alumina sol is deposited because the generated dynamic membrane has a high permeation flux and a low salt separation ability. The targets of the concentration operation in the method of the present invention are aqueous solutions of synthetic polymer compounds such as polyethylene glycol and polyacrylamide, and aqueous solutions of natural polymer compounds such as gelatin. In particular, the present invention is suitable for concentrating a gelatin extract obtained by extracting animal bones, skins, etc. with warm water to an 18-22% aqueous solution. The higher the temperature, the lower the viscosity of the gelatin extract, which makes it easier to operate and the higher the permeation flux, so it is passed under pressure through a channel equipped with a porous diaphragm at as high a temperature as possible without deteriorating the gelatin.
It is usually preferable to operate at a temperature of 40 to 90°C, particularly around 60°C. A suitable operating pressure is 5 to 25 kg/cm ² G. In this range, the higher the pressure, the greater the permeation flux, but even if the pressure is increased to 25 kg/cm ² G or more, the permeation flux does not change much. The preferred operating pressure is 10-20 Kg/cm ² G. In addition, the speed at which the gelatin extract flows in the flow channel in a direction parallel to the diaphragm surface is
0.5 to 3 m/sec is suitable. Generally, the higher the speed, the higher the permeation flux, but even if the speed is 3 m/sec or more, the increase in the permeation flux is small. A preferred speed is 1-2 m/sec. The concentration of the gelatin aqueous solution also greatly affects the permeation flux, and the higher the concentration, the smaller the permeation flux. Therefore, it is not very advantageous to concentrate the gelatin extract to the final concentration required for commercialization by the method of the present invention, but rather to concentrate the gelatin extract to an intermediate concentration of 18 to 22% by the method of the present invention. Advantageously, it is then concentrated to a final concentration, such as in a conventional thin film evaporator. When an aqueous gelatin solution is allowed to flow through the flow path constituted by the porous diaphragm described above under the above-mentioned conditions, water is removed through the diaphragm and the gelatin is concentrated. In addition, this water contains almost the same concentration of salt as the gelatin aqueous solution used as the raw material. Therefore, according to the method of the present invention, the salt content of gelatin can be reduced simultaneously with concentration. Furthermore, some of the gelatin passes through the diaphragm along with water, but the molecular weight distribution of gelatin in the permeate is
The molecular weight distribution of gelatin in the stock solution is skewed toward the lower molecular weight side. This indicates that organic impurities in gelatin are selectively removed through the diaphragm. Therefore, according to the method of the present invention, gelatin purification effects can be achieved at the same time as concentration. Although the above explanation has mainly been given by taking the concentration of an aqueous gelatin solution as an example, it is clear from the Examples described later that the present invention can also be applied to the concentration of other polymer compounds. Next, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to the following Examples unless it exceeds the gist thereof. Example 1 A porous hollow cylinder made of ceramic with an inner diameter of 2 mm, an outer diameter of 5 mm, and a length of 500 mm with one end closed (the pore diameter in the surface layer is about 0.1 μm and the pore diameter in the inner layer is larger) was prepared as shown in Figure 1. A concentrator was constructed by inserting it into the outer cylinder. Sodium chloride is added to the water from the sample inlet.
A solution containing 0.05 mol and 0.5 g of alumina sol (trade name, Alumina Sol-200, manufactured by Nissan Chemical Co., Ltd.) was supplied at room temperature under a pressure of 20 Kg/cm ² G, and the solution was fed inside the device at a speed of 3 m/sec for 30 minutes. It was distributed. Next, after washing the inside of the apparatus by flowing demineralized water at room temperature under the same pressure of 20 kg/cm ² G, 0.05 mol of sodium chloride and polyacrylic acid (trade name, Dulymer AC-10L, molecular weight 20,000 ~
A solution containing 0.1 g of Nippon Pure Chemical Industries, Ltd. 40000 was circulated at room temperature, 20 Kg/cm ² G, and 3 m/sec for 30 minutes. Note that the pH of the polyacrylic acid aqueous solution was raised sequentially from PH2.5 to PH7.0 using hydrochloric acid and caustic soda. Furthermore, demineralized water was circulated to clean the inside of the apparatus, and a concentrating apparatus was prepared which was equipped with a ceramic porous diaphragm having a precoated layer of alumina sol and polyacrylic acid. A solution of commercially available food grade gelatin dissolved in warm water was passed through this concentrator at a rate of 3 m/sec at 20 kg/cm ² G and 80° C. to concentrate the aqueous gelatin solution. The relationship between the concentration of the gelatin aqueous solution supplied to the device and the amount of water permeation per unit outer surface area of the diaphragm is expressed as
The figure shows the concentration of the supplied gelatin aqueous solution and the gelatin separation rate [1-{gelatin concentration in permeated water (g/-
water)/gelatin concentration in the feed solution (g/-
Figure 3 shows the relationship with water)}]×100. Note that FIGS. 2 and 3 show cases in which a diaphragm is used that is pre-coated with alumina sol but not pre-coated with polyacrylic acid, and a diaphragm in which neither alumina sol nor polyacrylic acid is pre-coated. The results are also listed. Example 2 Using a concentrating device similar to that shown in Fig. 1, which contained 18 porous hollow cylinders similar to those used in Example 1 and arranged in parallel at intervals, commercially available food grade gelatin was concentrated. Concentration was carried out. The diaphragm was pre-coated with alumina sol in the same manner as in Example 1. Concentration is 20Kg/cm ² G, 60
The gelatin solution was concentrated from 6.64% to 25.54% by operating at 0.6 m/sec at a speed of 0.6 m/sec and recycling the gelatin solution flowing out of the concentrator. The results are shown in Table 1.

[Table] The molecular weight distribution of gelatin in the raw material solution, concentrated solution and permeated solution was measured by gel permeation chromatography, and the results are shown in FIGS. 4 to 6. The measurement conditions are as follows. Packing material: Cephadex G-200 Filling dimensions: Diameter 15 mm, length 200 mm Sample: 1000 ppm aqueous solution of gelatin, 2 ml Developing solution: Demineralized water Flow rate: 8 to 10 ml/hr Temperature: Room temperature Detector: Total carbon meter These The results show that if gelatin is concentrated using the method of the present invention, ash content in gelatin can be removed (desalted).
It can be seen that both are achieved at the same time. Furthermore, it can be seen that gelatin purification effects can also be achieved because relatively low molecular weight components in gelatin flow out into the permeate. Example 3 A solution of 0.05 mol of sodium chloride and 10 ^-4 mol of zirconium oxychloride (ZrOCl ₂ ) in 1 mol of water was added to the concentrator used in Example 1 at room temperature at 80° C.
It was supplied under a pressure of Kg/cm ² G and allowed to flow through the apparatus at a speed of 3 m/sec for 30 minutes. Then increase the operating pressure to 80Kg/
Washing with demineralized water was carried out in the same manner as in Example 1 except that cm ² G was used.
Polyacrylic Acid Precoat - A demineralized water wash was performed to deposit a precoat layer of zirconium oxychloride and polyacrylic acid onto the porous ceramic membrane. A dilute aqueous solution of polyethylene glycol was passed through this concentrator under conditions of room temperature, 10 kg/cm ² G, and 3 m/sec. The results are shown in Table 2.

[Table] Example 4 Example 3 except that a concentrating device was used in which the polyacrylic acid precoating operation was omitted in Example 3.
Polyethylene glycol was concentrated in the same manner as described above. The results are shown in Table 2. Example 5 Into the concentrator used in Example 1, 0.05 mol of sodium chloride and zirconium oxychloride were added in 1 part of water.
A solution containing 10 ^-4 mol was supplied at room temperature under a pressure of 80 Kg/cm ² G, and was allowed to flow through the apparatus at 3 m/sec for 30 minutes. Next, demineralized water was passed through at 80 kg/cm ² G for washing. A 357 ppm aqueous solution of polyacrylamide (molecular weight 2 x 10 ⁵ - 3 x 10 ⁵ ) was added to this concentrator at 25°C.
The flow was conducted at 3 m/sec. FIG. 7 shows the relationship between operating pressure, separation rate, and permeation flux.

[Brief explanation of drawings]

FIG. 1 is a schematic vertical cross-sectional view of a concentrator used in Examples. In the figure, 1 is an outer cylinder, 2 is a ceramic hollow cylinder, 3 is a sample inlet, 4 is a concentrated liquid outlet, and 5 is a permeated liquid outlet. FIG. 2 is a graph showing the relationship between the concentration of gelatin aqueous solution and permeation flux in Example 1. In the figure, (○) is when a diaphragm without precoating is used, (●) is when a diaphragm is used with alumina sol precoating, and (△) is when a diaphragm is used with alumina sol and polyacrylic acid precoating. Each case is shown below. Third
The figure is a graph showing the relationship between the concentration of gelatin aqueous solution and separation rate in Example 1. The symbols in the figure are the same as in FIG. FIG. 4 is a chromatogram of gelatin gel permeation chromatography used in Example 2. The figure also shows polyethylene glycol (molecular weight) obtained under the same conditions.
The chromatogram of an equal mixture of 1000 and 20000 is also shown with a dashed line. FIGS. 5 and 6 are chromatograms of gelatin in the concentrate and permeate obtained in Example 2. FIG. 7 is a graph showing the relationship between the operating pressure, separation rate, and permeation flux of the polyacrylamide aqueous solution in Example 5.

Claims (1)

[Claims] 1. The wall surface of the inorganic porous diaphragm is created by flowing alumina sol, alumina sol and polyacrylic acid, zirconium oxychloride, or zirconium oxychloride and polyacrylic acid under high pressure along the wall surface of the inorganic porous diaphragm. A dynamic membrane is formed on the membrane, and a gelatin aqueous solution, a polyethylene glycol aqueous solution, or a polyacrylamide aqueous solution is passed under pressure along the obtained dynamic membrane, and a part of the water in the aqueous solution is expelled to the outside through the dynamic membrane. A method for concentrating an aqueous polymer solution, characterized by: