JPS5854632B2 - How to treat pulp wastewater - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a method for treating pulp wastewater in which inorganic substances in the wastewater are separated and organic substances are concentrated by bringing the wastewater discharged from a pulp manufacturing process into contact with an amphoteric ion exchange membrane under pressure. It is about the method.

In recent years, environmental conservation issues have come into sharp focus, and consideration has been given to adopting a method of concentrating and combusting pulp wastewater for the purpose of reducing the amount of pollutants generated from the pulp manufacturing process.

Regarding cooking wastewater, which contains extremely high concentrations of pollutants among various pulp wastewaters, a concentrated combustion method has traditionally been adopted, as seen in the recovery process of cooking chemicals in Kraft pulping. It is coming.

On the other hand, the amount of wastewater generated in the pulp bleaching process is significantly larger than that of cooking wastewater, but the concentration of pollutants is lower than that of cooking wastewater, so currently it is generally discharged using the coagulation sedimentation method or activated sludge method. Removes pollutants from the liquid.

However, it is difficult to remove most of the pollutants in the wastewater with this treatment method.
In recent years, there has been increasing momentum to adopt a method of mixing bleaching wastewater with cooking wastewater and concentrating and burning the organic matter contained therein.

However, it is difficult to mix the bleaching effluent with the cooking effluent and combust it in a concentrated manner for a number of reasons as described below.

Firstly, as mentioned above, the amount of bleaching effluent generated is significantly larger than that of cooking effluent, so in order to collect it in the existing cooking effluent recovery process, it must be pre-concentrated by some method. It is necessary to keep

Second, since chlorine-based chemicals are generally used for pulp bleaching, chlorine ions are present in the bleaching liquid, so if the bleaching liquid is burned in a recovery boiler in the cooking chemical recovery process of the Kraft pulping process, for example, the system As a result, chlorine ions accumulate in the equipment, causing corrosion of the equipment.

Therefore, it is necessary to concentrate the bleaching effluent before mixing it with the cooking effluent and to separate and remove as much chlorine ion as possible.

Thirdly, for the cooking effluent generated, for example, in the manufacture of pulp using the calcium-based sulfide process,
In this case, when the thermal alkali refining effluent from the pulp bleaching and refining process is mixed with the cooking effluent and burned, sodium content is brought in from the thermal alkali refining effluent. It is known that this lowers the melting point of the incinerated ash, causing problems in the operation of the incinerator.

Therefore, in order to mix and burn the thermal alkaline refining effluent with the cooking effluent from the calcium-based sulfide process,
- It is necessary to remove IJum as much as possible.

In this way, in order to send the waste liquid generated in the pulp bleaching and refining process to the cooking waste liquid recovery process and recover it, it is essential to perform concentration and inorganic substance separation in advance.

On the other hand, it has not been possible to separate organic and inorganic substances by concentration using vacuum evaporation using a multi-effect tank, which has been conventionally used in the recovery process of cooking waste liquid.

Further, it is impossible to selectively separate and remove inorganic substances even by pressure concentration methods such as reverse osmosis and ultrafiltration.

As mentioned above, there are many opinions on the effectiveness of the method of burning the wastewater generated in the pulp bleaching and refining process together with the cooking wastewater in the cooking wastewater recovery process from the viewpoint of drastically reducing the amount of pollutants generated. However, it has not yet been put into practical use because an appropriate concentration method and method for separating and removing inorganic substances have not been established.

In view of the existence of the above-mentioned problems, the inventors of the present invention have conducted intensive studies to solve the problems, and as a result, they have successfully removed inorganic substances and organic substances from the waste liquid generated in the pulp bleaching and refining process using an amphoteric ion exchange membrane. Invented a method of concentration.

The amphoteric ion exchange membrane referred to in Tsuzumi refers to an ion exchange membrane that has both a cation exchange group and an anion exchange group in the membrane.

Acidic groups such as sulfonic acid groups and carboxylic acid groups can be used as cation exchange groups, and examples of anion exchange groups include phosphonium groups, sulfonium groups, quaternary ammonium groups, tertiary amine groups, secondary amine groups, and A basic group such as a class amine group can be used.

Amphoteric ion exchange membranes having ion exchange groups such as these can be obtained by copolymerizing a monomer with an acidic group with a monomer having a basic group, or by polymerizing a cation exchange membrane or an anion exchange membrane with an opposite charge. It can be prepared by impregnating with ions and polymerizing in the membrane, or by introducing ion exchange groups after forming the base film, but the finished membrane contains anion exchange groups and cation exchange groups. must be made so that they do not mix uniformly.

For example, the method of homogeneously introducing anion exchange groups into polystyrene, forming a film, and then introducing cation exchange groups is unsuitable for the treatment of pulp wastewater, as will be described later.

By bringing the thus produced amphoteric ion exchange membrane into contact with pulp wastewater and applying pressure to the wastewater side, inorganic compounds dissolved in the wastewater selectively permeate through the membrane. As a result, most of the organic matter is rejected from permeation, making it possible to separate the inorganic matter and concentrate the organic matter.

The cause of this phenomenon has not yet been sufficiently theoretically elucidated, so there is no other way than to estimate it based on experimental results, but it can be determined as follows.

When an amphoteric ion exchange membrane is brought into contact with an aqueous solution of an inorganic substance and pressure is applied to the solution side, the membrane potential short-circuits between adjacent fixed ions of opposite signs in the membrane, resulting in a phenomenon known as piezodialysis. As a result, inorganic substances are promoted to permeate through the membrane and concentrated on the permeate side.

On the other hand, in the case of pulp wastewater, most of the organic substances dissolved therein are substances derived from lignin and hemicellulose in wood, and more than the inorganic substances dissolved in the wastewater.
Its molecular weight is so large that it cannot pass through the membrane.

Therefore, it is considered that when the pulp waste liquid is brought into contact with the amphoteric ion exchange membrane and pressurized continuously, organic substances are concentrated on the feed liquid side, and inorganic substances are selectively transferred to the permeate side.

Examples of using amphoteric ion exchange membranes for desalination from seawater and desalination and purification of organic matter have been known, but such membranes were not suitable for use in pulp wastewater treatment as in the present invention. .

For example, the method of L. Platt et al. (``Die A
ngewandte Makromolekulare
ChemieJ Vol. 19, pp. 135-155, 197
The membrane prepared in 1998) is based on a blend of styrene-butadiene copolymer and vinylpyridine-butadiene copolymer, but these two copolymers do not mix molecularly in the blended state. Because the polyvinylpyridine part and the polystyrene part undergo microphase separation, cracks occur at the phase boundaries during the subsequent ion exchange group introduction process or during membrane use, resulting in the formation of numerous pinholes in the membrane, which impairs the separation performance. inferior in terms of

Dissolve polyamine obtained by reacting trimethylamine with partially chloromethylated mata polystyrene.
A method of introducing sulfonic acid groups after film formation is also known (
"Membrane" Vol. 3, No. 4, pp. 289-294, 1978
However, crosslinking reactions occur during chlormethane miniaturization and during reaction with amines, resulting in the formation of insoluble polymers, making it difficult to form a uniform film.

Furthermore, it has been pointed out that the separation behavior of inorganic salts in this membrane differs significantly depending on the type and concentration of coexisting organic acids.

(“Membrane” Vol. 3, No. 5, pp. 367-373, 197
8) Since the properties of pulp effluent vary greatly depending on the operating conditions, amphoteric ion exchange membranes having the above-mentioned properties are unsuitable for the treatment of pulp effluent.

The above properties are thought to be due to the almost uniform mixture of anion exchange groups and cation exchange groups. Zwitterion obtained by copolymerization of a monomer with a group that can become a cation exchange group and a monomer that has a group that can become a cation exchange group, or a copolymerization of a basic monomer and a monomer that has a group that can become a cation exchange group. In the exchange membrane, the secondary monomers do not show complete alternating copolymerizability, so no problem arises due to uniform mixture of amphoteric ion exchange groups.

Furthermore, since it was not a blend of different polymers, no pinholes caused by microphase separation were observed.

The device used for the above-mentioned pulp wastewater treatment can be selected from among the known pressurized concentration devices used in reverse osmosis and ultrafiltration methods depending on the shape of the membrane, such as flat membrane or tubular type. can do.

The operating pressure varies depending on the properties of the pulp waste liquid to be treated, but is usually in the range of 10 to 150 kg/kg, and the temperature during treatment is suitably between 20°C and 80°C.

EXAMPLES The present invention will be explained in detail below with reference to examples, but the present invention is not limited to the following examples.

Example 1 20 g of polyvinyl chloride was dissolved in a mixed solvent consisting of 15 g of dioxane, 15 g of dimethyl sulfoxide, and 70 g of dimethyl formamide, and the solution was coated onto a glass plate to a thickness of 0.15 to 0.20 mm using a film applicator.

This product was left at 20'C for 60 seconds to evaporate part of the solvent, and then immersed in a 70% methanol aqueous solution for 3 hours to gel.

During this time, the temperature of the gelling bath was maintained at 25°C. The porous polyvinyl chloride film thus obtained was washed with water and dried to serve as a support for an amphoteric ion exchange membrane.

100g of styrene monomer and 100g of 4-vinylpyridine
2 g of benzoyl peroxide dissolved in 2 g of hydroxyethyl cellulose! : 120 g of water containing 25 g of salt
0ml and polymerized at 80°C for 7 hours while stirring.

Washed and dried styrene-4-vinylpyridine copolymer 1
Transfer 0g to a container filled with methyl bromide vapor and heat to 70℃ for 4 hours.
The mixture was held for 8 hours and quaternized.

This product was dissolved in a mixed solvent consisting of 300 g of chloroform, 300 g of cyclohexanol, and 600 g of ethanol.

The above-mentioned porous polyvinyl chloride film attached to the glass plate was immersed vertically in this solution, then immediately pulled up and dried at room temperature for 24 hours.

The sample was then immersed in a 97% sulfuric acid bath and left to stand for 48 hours while maintaining the bath temperature at 40°C to carry out sulfonation.

After washing the amphoteric ion exchange membrane prepared by the above method with water,
% saline solution, further washed with water, and installed in the test cell of the pressurized concentrator shown in the figure.

The effective membrane area of this test cell is 20 ffl.

The operating pressure is 4oK/=, and the feed liquid is approximately 5oK parallel to the membrane surface.
The flow rate of the high-pressure metering pump was set to flow at a speed of m/min.

When operated under these conditions, the rate at which water permeates through the membrane is 25
It was t/i time.

Isometric mixture of thermal alkaline purification wastewater and alkaline extraction wastewater collected from the bleaching and refining process of hardwood sulfide pulp 3
Concentration operation was carried out at a treatment temperature of 20 to 25°C using t, and Table 1 shows the concentrations of effective substances and common salt in the concentrate at each concentration ratio.

In the table, the total organic carbon concentration of wastewater is used as an index of the concentration of organic matter, and for comparison, a commercially available reverse osmosis membrane (trade name, DD
The results of concentrating S-995) in the test cell shown in the figure under the same conditions are also shown.

This table shows that when an amphoteric ion exchange membrane is used, organic matter concentration and salt separation are effectively performed, whereas when a reverse osmosis membrane is used, the organic matter concentration behavior is almost the same as the former. However, it was found that the salt was not separated and removed at all, making the organic nature of the present invention clear.

Example 2 Method of applying 100 g of 2-vinyl 5-ethylpyridine to art materials (Industrial Chemistry Magazine Vol. 64, p. 587, 1961)
120g of styrene monomer
2.5 g of azobisisobutyronitrile was added and polymerized at 60° C. for 20 hours.

10 g of this copolymer was dissolved in a mixed solvent consisting of 300 g of chloroform and 700 g of ethanol, and an anion exchange membrane was formed on the porous polyvinyl chloride film in the same manner as shown in Example 1. An amphoteric ion exchange membrane was prepared and installed in the test cell of the apparatus shown in the figure.

Using 3 tons of alkaline extraction wastewater collected from the bleaching process of hardwood kraft pulp, the concentration ratio was 4.0 under the same conditions as in Example 1.
It was concentrated up to 5 times.

The results are shown in Table 2.

Table 2 also shows the results of concentration using the same reverse osmosis membrane used in Example 1, and the effectiveness of the present invention is clear.

The method of displaying the concentration factor, the concentration unit of total organic carbon and salt is the 1st
Same as table.

[Brief explanation of drawings]

The figure is a flow chart of the pressurized concentrator used in the examples. In the figure, 1: Supply liquid tank, 2: High pressure metering pump, 3 Nibble filter, 4 = Pressure gauge, 5: Valve, 6: Pressure regulator, 7: Test cell.

Claims (1)

[Claims] 1 Copolymerization of a monomer having a group that can become an anion exchange group and a monomer that has a group that can become a cation exchange group, or a basic monomer and a cation while applying pressure to the waste liquid discharged from the pulping process. A method for treating pulp wastewater for separating inorganic substances and concentrating organic substances, which comprises bringing it into contact with an amphoteric ion exchange membrane obtained by copolymerizing with a monomer having a group that can serve as an exchange group.