JPS602081B2 - Method for restoring membrane separation properties - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for cleaning objects whose surfaces are contaminated with organic compounds, and in particular, to cleaning semipermeable membranes used in membrane separation methods such as reverse osmosis and ultrafurnace filtration. The present invention relates to a method of cleaning a contaminated layer formed on a pus surface with an aqueous solution of an oxidizing substance adjusted to pH 9 or higher to restore a decreased water permeability.

In general, the main pus separation methods that use pressure as the driving force are reverse osmosis and ultrafiltration. It is well known that the latter is used for the selective separation and concentration of high molecular weight substances such as proteins and low molecular weight substances such as lees and inorganic substances. One of the most important issues in the practical application of these membrane separation methods is how to recover membrane performance from performance degradation caused by membrane surface contamination, and various membrane performance recovery methods have been proposed depending on the liquid to be treated. ing. For example, ■ a method of washing the contaminated layer formed on the membrane surface with a sponge, etc., ■ a method of dissolving and decomposing the contaminated layer with chemicals, ■ a method of flowing the liquid to be treated at a high flow rate, and causing the turbulence of the liquid to cause Method for removing surface contamination: ■ After pressurized operation for a certain period of time, the pressure is released and the contamination formed on the membrane surface is lifted by the backflow of liquid from the outside to the inside of the semipermeable membrane due to osmotic pressure. There are ways to remove it. Among these methods, method (2) may not be applicable depending on the shape of the semipermeable membrane, and also has the disadvantage of easily damaging the membrane surface. Furthermore, with method (1) alone, it is difficult to completely remove the contaminant layer firmly adhered to the film surface, similar to methods (2) and (3). In the method (2) using a drug, the semipermeable membrane is soaked with the drug, so regardless of the shape of the semipermeable membrane, the contaminated layer is completely removed and the membrane performance is restored. The shape of the semipermeable membrane referred to in this item refers to a spiral type, an internal pressure or external pressure tubular type, a hollow fiber type, a flat membrane type, etc. Known methods for cleaning semipermeable membranes with chemicals include a method of cleaning with an alkaline aqueous solution (Tokukan Sho 50-175177) and a method of applying pressure fluctuation after cleaning with a hydrogen peroxide solution (Tokusei Sho 51-13391). ), pH 2.0-4
．． There is a method of washing with a nonionic surfactant adjusted to zero and then washing with an alkali (Japanese Unexamined Patent Publication No. 1986-44, No. 9).

In addition, Japanese Patent Publication No. 49-137455 describes a method for cleaning contaminants in the filter layer of a packing material with an aqueous solution of an oxidizing substance, but as shown in the comparative example below, In some cases, sufficient effects may not be obtained. The inventors
The present invention was completed as a result of intensive research into a method of treating the liquid to be treated, cleaning the semipermeable membrane with a contaminated membrane surface with a drug, and restoring the purulent performance.

That is, when an aqueous solution of an oxidizing substance consisting of sodium hypochlorite or hydrogen peroxide is adjusted to pH 9 or higher, especially pHil ~ 13, an unforeseen synergistic effect may cause the oxidizing substance or alkaline aqueous solution to react individually. We have found that this method is highly effective in removing the contaminant layer formed on the ventral surface that could not be removed and restoring pus performance. Furthermore, the method of the present invention requires a device made of a material that cannot be physically washed with a sponge or other material due to its shape, and that can withstand the above-mentioned aqueous solution containing oxidizing substances adjusted to a pH of ~13 according to the present invention; It is also effective for cleaning instruments contaminated with organic compounds. In the present invention, the treatment liquid that causes membrane contamination refers to, for example, pulp 8E liquid, wastewater from agricultural, livestock, and fisheries processing, and other organic liquids. The pH of the cleaning solution, the type and concentration of oxidizing substances, and the immersion time vary depending on the type of contaminants and the degree of their adhesion to the pus surface. As the oxidizing substance, in the case of an acrylonitrile copolymer membrane, sodium hypochlorite is preferred since it does not damage the membrane. Also, the concentration of oxidizing substances is 0
．． 0.01 to 3 molar, preferably 0.05 to 1 molar. To clean a contaminated membrane, for example, the cleaning water of the present invention may be passed directly through the bag in which the membrane is attached, or the apparatus may be filled with cleaning water, or the contaminated membrane may be removed from the bag and then cleaned using the present invention. Possible methods include immersion in a cleaning solution.
The bonding time may be any time longer than 5 minutes, but preferably,
It is 5 minutes to 2q hours. Applicable membranes of the present invention must be able to withstand the agents used. but,
Even with membrane materials that are decomposed by chemicals, the bonding time is 5 to 1
In the case of a short time of 0 minutes, it is also possible to remove only the contaminated layer without decomposing the membrane. Therefore, the membranes used in the present invention include not only various vinyl polymer, polysulfone, polyamide, and polyphenoxy resin membranes that have alkali resistance and oxidation resistance, but also acetic acid membranes that have weak alkali resistance when the soaking time is short. It is also applicable to cellulose conductor films such as cellulose. Next, examples of the present invention will be shown.

Example 1 Decanter effluent with a total solids content of 3% and a total dissolved solids content of 2.6% discharged from the potato starch production process was passed through an internal pressure tubular type ultrafurnace filtration device (with an inner diameter of 14.5 mm). Membrane area: 7.2〆)
, using membrane type DUY20 manufactured by Daicel (membrane material: acrylonitrile copolymer), flow rate 1〆'hr, operating pressure 3.5
It was concentrated to 1/6 of the liquid temperature under operating conditions of k9/liquid temperature of 1/0.

Table 1 shows the initial state, after one month of continuous operation, and after immersing these membranes in an alkaline aqueous solution with a pH of 13 for 20 hours, and also with a sodium hypochlorite aqueous solution with a pH of 12.3 (effective CI.5 wt%). The membrane separation properties of the membrane soaked for 1 hour were shown. Table 1 Commercially available Na00 aqueous solution (effective 0CIowt omitted) diluted with water, pH 12.3 Disaccharide transmittance = Unurabaken Cod Seismic Intensity X.00) Note that the membrane surface was white before use. But 1
After several months of operation, the color changed to yellowish brown due to membrane surface contamination, and
As shown in the micrograph of FIG. 1, a contamination layer with unevenness was formed on the surface of the film.

The cleaning layer with the NaOCI aqueous solution at pH 12.3 was removed, and the membrane surface became white, and as shown in the micrograph of FIG. 2, the membrane surface became a smooth surface, and no contamination layer was observed. Examples 2 to 4 In Example 1, the ultra-furnace filtration membrane (DUY20 manufactured by Daicel) was used for one month in the ultra-furnace filtration, and the ultra-furnace filtration membrane (DUY20 manufactured by Daicel) was used in the ultra-furnace filtration for 10 days in exactly the same manner as in Example 1. A circular flat membrane with a membrane area of 10.2 mm was cut out from a membrane (DUY30 manufactured by Daicel), and operated at an operating pressure of 3.0 kg' and a liquid temperature of 25 qo using an ultrafiltration device for flat membrane measurement with stock solution circulation. Membrane performance was compared before and after membrane surface cleaning with NaOCI aqueous solution using pure water and 250 pm Eosin yellowish aqueous solution under the following conditions.

The results are shown in Table 2. Membrane separation properties have been restored. Ship Ants
Effective CII. The procedure was carried out in exactly the same manner, except that a 10% 202 water* solution at pH 6.0 was used instead of 5wt%).

As shown in Table 3, the membrane and performance were not fully recovered. Table 3
Example 5 In Example 3, the effective CII. 5wt
% NaOCI aqueous solution, the effective CIO. Exactly the same method was used except that a lwt% NaOCI aqueous solution was used.

The results are shown in Table 4. The membrane separation properties have been fully recovered. Comparative Examples 2 and 3 In Example 3, the effective CII. 5wt
% NaOCI aqueous solution instead of effective CI at pH 8.5
O. lwt% NbOCI aqueous solution (Comparative Example 2) and pH
Chemical cleaning was carried out in exactly the same manner except that an alkaline aqueous solution of No. 13 (Comparative Example 3) was used.

The results are shown in Table 4. The hip separation property has not recovered. Ship Example 6 A membrane subjected to continuous operation for 20 days under the operating conditions of Example 1 was subjected to pHIO. 2. Effective CIO. 05wt% NaOC
The membrane surface was washed by immediately immersing it in an aqueous solution of NaOCI (a commercially available aqueous solution of NaOCI with an effective CII skin t% diluted with water) for 1 hour.

Table 5 shows the water permeation rate with pure water before and after washing. Comparative Example 4 In Example 6, pHIO. 2. Effective CIO. 05w
t% NaOCI aqueous solution instead of pHIO. The same method was used except that the alkaline aqueous solution in step 2 was used.

The results are shown in Table 5. Comparative Example 5 In Example 6, pHIO. 2. Effective CIO. 05M%
of effective CIO. adjusted to pH 8.5. The same method was used except that a 05 wt % NaOCI aqueous solution was used.

. The results are shown in Table 5. Table 5 Example 7 A cloudy liquid with a COD of 200 pm discharged from the manufacturing process of emulsion polymerization of vinyl acetate, acrylate, and acrylonitrile was circulated through a semipermeable membrane made of polysulfone having the membrane separation performance shown in Table 6. Separation treatment was carried out using a flat membrane ultrafurnace filtration device at an operating pressure of 3.0 kg'.

After 20 hours of operation, the semipermeable membrane with reduced water permeation rate was heated to pH 12.5.
Adjusted to 2. The performance of the semipermeable membrane was able to be significantly restored by washing it by soaking it in hydrogen peroxide solution with a concentration of +%.

The results are shown in Table 6.

Comparative Example 6 The same method as in Example 7 was carried out except that an alkaline aqueous solution with a pH of 12.5 was used instead of the hydrogen peroxide solution adjusted to pH 12.5 in Example 7.

The results are shown in Table 6. Comparative Example 7 Instead of using hydrogen peroxide solution adjusted to pH 12.5 in Example 7, 2. The same method as in Example 7 was carried out except that t% Sakaki hydrogen peroxide solution was used.

The results are shown in Table 6. omitted crotch English S L ink Steam White Day debt fart ・ Day hmm hmm under Day inferior

[Brief explanation of the drawing]

Figure 1 is a micrograph of a contaminated membrane surface and a dense section.
FIG. 2 is a microphotograph of the membrane surface after cleaning by the method of the present invention. Figure 1 Figure 2

Claims (1)

[Claims] 1. A semipermeable membrane contaminated with organic substances containing sodium hypochlorite or hydrogen peroxide at a concentration of 0.01 to 3 molar and pH 11.
A method for restoring the membrane separation characteristics of a semipermeable membrane, characterized by washing with washing water consisting of an aqueous solution adjusted to 13.