JP3082263B2 - How to remove colloidal silica - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for removing colloidal silica. More specifically, the present invention relates to a method for removing colloidal silica applied to an open circulation cooling water system or the like.

[0002]

2. Description of the Related Art In an open circulating cooling water system in an industrial plant or an open circulating cooling water system used for cooling equipment, substances dissolved in circulating water are gradually concentrated by evaporation of water in a cooling tower. Calcium in the inside and silica adhere to the heat exchanger tube, causing an obstacle to lower the heat transfer efficiency.

[0003] Among these adhered components, calcium carbonate scale, which is a problem during high concentration operation, is developed by developing a synthetic polymer electrolyte scale inhibitor such as an acrylic acid terpolymer or a maleic acid copolymer to precipitate crystals. By restricting the growth and growth to some extent, its adhesion has been prevented.

[0004] However, with respect to silica, which is another major scale component, prevention of adhesion of silica scale on the heat transfer surface has been conventionally regarded as a very difficult problem. Although there are water treatment devices to solve these problems, they have a large reverse osmosis or ultrafiltration level and are comparable to pure water production devices.

[0005] By the way, there are dissolved silica and colloidal silica (colloidal silica) in the state of existence of silica in water. So-called silica (SiO ₂ ) has a particle size of about 0.001 to 0.001.
A colloid is formed in the form of particles of about 0.1 μm.

JP-B-63-56802 discloses that the average particle size is 80.
Å Polysulfone hollow fiber membranes having a rejection ratio R of 95% or more of colloidal silica are described, but this polysulfone hollow fiber has a slit-shaped fine gap with an average width of 80 to 500 mm on the inner surface and an outer surface with It has micropores with an average pore diameter of 1500 to 3500 mm at a porosity of 10 to 50%, and the inside of the membrane has a microporous structure, so there is no trapping ability in the outer surface layer, and colloidal silica penetrates into the inside of the membrane Has a film structure that is not suitable for cleaning and regeneration.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a polysulfone hollow having excellent cleaning recoverability for removing deposits trapped on the outer surface of a membrane by periodic backwashing and recovering a processing flow rate. It is an object of the present invention to provide a method for removing colloidal silica using an ultrafiltration membrane module.

[0008]

SUMMARY OF THE INVENTION The object of the present invention is as follows.
This is achieved by a method in which the colloidal silica-containing liquid is completely permeated by a filtration method using a polysulfone hollow ultrafiltration membrane module having a dense layer on the outer surface side to remove colloidal silica.

[0009] The polysulfone hollow ultrafiltration membrane having a dense layer on the outer surface side adjusts the time until the polysulfone spinning stock solution discharged from the nozzle by dry-wet spinning or wet spinning comes into contact with the coagulation bath. By a method, a method of adjusting the temperature of a coagulation bath, a method of performing post-treatment such as heat treatment after film formation, etc., a hollow ultrafiltration membrane having a dense layer formed on the outer surface can be obtained. When the tip of the nozzle is submerged in the coagulation bath in the first method, the time required to contact the coagulation bath is the shortest, and the densest dense layer is formed.

The outer diameter of the polysulfone hollow ultrafiltration membrane having a dense layer on the outer surface side is desirably about 0.4 to 0.5 mm. This is because although it is necessary to increase the membrane area for the entire amount of filtration, if a hollow fiber membrane that is too thin is used to increase the total membrane area, potting is difficult and it is difficult to modularize, or the inside of the hollow fiber membrane is difficult. Since the flow path resistance becomes large, the one having an outer diameter of this degree is preferable. In addition, the film thickness is generally about 0.
It is about 05-0.15m.

[0011] Such a polysulfone hollow ultrafiltration membrane is generally made into a module by using about 1,000 to 10,000 pieces, and the whole colloidal silica-containing liquid is permeated through the hollow fiber membrane by a filtration method. Is deposited on the inner surface of the film.

[0012] A decrease in the processing flow rate is observed with an increase in the permeation processing amount.
The processing flow rate can be recovered by cleaning.

[0013]

According to the method of the present invention, colloidal silica can be effectively removed from a liquid containing colloidal silica. The silica deposited on the inner surface of the hollow fiber membrane by the whole filtration method is removed by backwashing, and the processing flow rate decreased with the increase of the permeation processing amount is washed and recovered.

[0014]

Next, the present invention will be described with reference to examples.

EXAMPLE 15 parts by weight of a polysulfone resin, polyvinylpyrrolidone (K9
0) A wet spinning solution comprising 1 part by weight and 84 parts by weight of dimethylformamide was wet-spun from a double annular nozzle having a nozzle tip submerged in a water coagulation bath, using isopropanol as a core liquid, and a dense layer on the outer surface side. A polysulfone hollow fiber membrane (outer diameter 0.4 mm, wall thickness 0.1 mm) having an ultrafiltration level having the following characteristics was obtained.

A module is formed using 500 hollow fiber membranes, and about 1% by weight of colloidal silica adjusted to a particle size of 70 to 90 μm in each hollow fiber membrane (pure water of Nissan Chemical Products Snowtex S) The diluent was subjected to a total external pressure filtration test.

Then, filtration was performed at room temperature under an external pressure of 1 kg / cm ² to deposit silica on the inner surface of the film. The silica rejection was determined from the rate of decrease in the amount of evaporation residue (content of solids) in the stock solution and the permeate. As a result, 97% of the permeate was blocked, from 10 g / l of the stock solution to 0.4 g / l of the permeate.

The initial processing flow rate is 10 cm ³ / cm ² · (kg / cm ² )
· Respect hr, throughput 100 cm ³ / cm ² at ^{5cm 3 / cm 2 · (kg} / cm 2) ·
Although the flow rate and the flow rate were reduced by half, it was confirmed that the processing flow rate was restored to a value of 8 cm ³ / cm ² · (kg / cm ² ) · hr or more by backwashing with pure water.

Claims (1)

(57) [Claims] 1. A method for removing colloidal silica, wherein the colloidal silica-containing liquid is entirely permeated by a filtration method using a polysulfone hollow ultrafiltration membrane module having a dense layer on the outer surface side.