JPH0217229B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] This invention relates to a method for treating polyvinyl alcohol-containing water.

[Conventional technology]

Polyvinyl alcohol (hereinafter sometimes referred to as PVA) is used as a raw material or processing agent in the vinylon manufacturing industry, textile processing industry, paper manufacturing industry, polymer manufacturing industry, etc.

Among these, especially in the textile processing industry,
PVA is used as a warp glue and emulsifier, and these are contained in wastewater and flow out of the system.
PVA is a biologically persistent substance with a high COD/BOD ratio, and many factories are struggling to deal with it.

[Problem that the invention seeks to solve]

Conventional methods for treating water containing PVA include oxidative decomposition methods, coagulation-sedimentation methods, and biodegradation methods.

Of these, the coagulation-sedimentation method conventionally involves adding copper, iron, and cobalt salts to PVA-containing water.
A method of generating insolubilized chelate compounds is known, but the problem is that the generated sludge contains heavy metal hydroxides and is difficult to treat and dispose of, such as by dehydration. There is also a method of flocculation treatment using bentonite, activated clay, diatomaceous earth, etc.
In both cases, practical problems remained, such as when the amount added increased, the amount of sludge also increased.

The present invention was completed after intensive research to overcome these problems of the prior art.

[Means for solving problems]

The present invention is a method for treating polyvinyl alcohol-containing water, which is characterized by adding an acid colloid solution of a melamine-aldehyde condensate to polyvinyl alcohol-containing water for flocculation treatment.

Further, the present invention is a method for treating polyvinyl alcohol-containing water, which is characterized in that an acid colloid solution of an alkyl etherified melamine/aldehyde condensate is added to the polyvinyl alcohol-containing water for flocculation treatment.

As mentioned above, the polyvinyl alcohol-containing water targeted by this invention includes vinylon manufacturing industry,
Examples include, but are not limited to, wastewater discharged from the textile processing industry, paper manufacturing industry, polymer manufacturing industry, etc., and in short, any wastewater that contains PVA is subject to the present invention.

The acid colloid solution of the melamine/aldehyde condensate used in this invention is produced by further adding an acid to methylolmelamine obtained by reacting melamine and aldehyde, as shown in the production examples below. Note that, if necessary, it may be obtained by adding an acid to a product obtained by further converting methylolmelamine into an alkyl ether. In this case, when acid is added, the ether decomposes to produce methylolmelamine.

Examples of the aldehyde include formaldehyde, paraformaldehyde, acetaldehyde, and propionaldehyde, with formaldehyde and paraformaldehyde being preferred from the viewpoint of ease of handling and reaction efficiency.

The charging ratio of melamine and aldehyde is 1 to 6 moles of aldehyde per 1 mole of melamine.

However, if the aldehyde exceeds 2.5 moles, the amount of free aldehyde will increase when an acid colloid solution is prepared. Since free aldehydes are a source of COD,
Where COD is a problem, the amount of aldehyde is 2.5
It is preferable that the amount is less than mol.

The methylolmelamine thus obtained does not dissolve in water, but dissolves in an acid solution in a colloidal state. On the other hand, alkyl etherified methylol melamine obtained by further alkyl etherification of methylol melamine is water-soluble and becomes colloidal when an acid is added.

A monobasic acid is suitable as the acid used here. Examples of monobasic acids include mineral acids such as hydrochloric acid and nitric acid, as well as organic acids such as formic acid, acetic acid, lactic acid, and propionic acid. Among these, hydrochloric acid is preferable because a stable colloidal solution can be obtained.

The amount of monobasic acid, especially hydrochloric acid, to be added is about 0.5 to 1.5 mol, preferably 0.7 to 1.3 mol, per 1 mol of melamine.

If the amount of acid added is less than 0.5 mol, sufficient acid colloidal properties cannot be exhibited. on the other hand,
If it exceeds 1.5 mol, the stability of the colloidal solution tends to deteriorate.

A large amount of free aldehyde is present in this acid colloidal solution of methylolmelamine at the initial stage of preparation of the colloidal solution, but when it is left to ripen at room temperature after preparation, the amount of free aldehyde decreases. Ripening can also be accelerated by heating. In the case of room temperature aging, it takes 5 days to 3 months, and in the case of heat aging, it takes about 2 to 3 hours at 50°C.

The amount of the acid colloid solution to be added varies depending on the type of wastewater and the treatment target value, and is appropriately determined by a jar test.

After adding the acid colloid solution to the target water, the pH is adjusted to 7.
Above, it is necessary to adjust preferably to 7-11.
When the pH becomes less than 7, the colloidal state begins to shift again to the dissolved state, and reaction precipitates with polyvinyl alcohol no longer form effectively.

As the acid or alkaline agent used for pH adjustment, known ones such as hydrochloric acid, nitric acid, sodium hydroxide, ammonia, etc. can be selected.

Note that the acid colloid solution may be used by being added to wastewater alone, but it may also be used in combination with an inorganic coagulant such as aluminum sulfate or ferric chloride.
It may be used in combination with an organic coagulant.

As the organic coagulant, polyalkylene polyamines such as polyethyleneimine, water-soluble dicyandiamide-formaldehyde condensates, polydimethyldiallylammonium salts, epihalohydrin-amine condensates, cationized guar gums, and the like can be used.

When an inorganic coagulant and an organic coagulant are used together for water in which a COD component coexists, it is preferable to add an acid colloid solution simultaneously with or after the addition of these agents. If an acid colloid solution is added first, inorganic or organic coagulants can also be removed.
This is not preferable because it may affect COD components.

When an acid colloid solution is added to polyvinyl alcohol-containing water and maintained at a predetermined pH, the acid colloid solution rapidly becomes cloudy and aggregates, and the polyvinyl alcohol also becomes insolubilized.

After this reaction has been carried out sufficiently, the precipitate is separated from the water. In the case of separation by the coagulation filtration method, the suspension may be directly fed to a filtration device filled with an appropriate material.

On the other hand, in the case of coagulation-sedimentation treatment, it is preferable to add an organic polymer flocculant to the suspension, as this will coarsen the flocs and increase the sedimentation rate.

Known organic polymer flocculants can be used, but among them, acrylamide-based ones are preferable, and polyacrylamide, polymethacrylamide, partial hydrolyzate of polyacrylamide or polymethacrylamide, acrylamide or methacrylamide, and others. Copolymers with vinyl monomers such as acrylic acid esters, acrylonitrile, dialkylaminoethyl methacrylate, or quaternized products thereof may be mentioned.

As the precipitation device, a known type such as a circular type or a square type can be used.

[Effect]

In this invention, the removal mechanism of polyvinyl alcohol by the acid colloid solution is unknown, but when the acid colloid solution is added to the target water, the polyvinyl alcohol and the acid colloid solution may react in some way and precipitate in that state. , or first,
It is presumed that the colloidal nature of the acid colloid solution is broken by an increase in pH, causing the acids to associate, and at that time, polyvinyl alcohol is mixed in and becomes insolubilized. Considering that it is treated with an acid colloid solution even though it is not treated with other cationic flocculants, it seems highly likely that not only the ionicity but also the molecule itself is involved in the reaction.

〔Effect of the invention〕

As described above, while the conventional method had some problems during treatment, the method of the present invention allows polyvinyl alcohol to be treated quickly and efficiently with simple operations.

Hereinafter, the effects of the present invention will be clarified by examples using acid colloid liquids obtained in the following production examples.

[Example of production of acid colloid liquid]

63 g (0.5 mol) of melamine and 30 g of paraformaldehyde (as formaldehyde) in 93 ml of distilled water.
1.0 mol) was added, the pH was adjusted to 10.0 with NaOH, and the mixture was heated to 70°C to dissolve the melamine. 70 more
After reacting at °C for 5 minutes, the mixture was left at room temperature and gradually cooled to precipitate methylolated melamine crystals. This precipitate was collected on a Buchner funnel, washed with methanol, and then dried under reduced pressure. Elemental analysis of this dried methylolated melamine revealed that the ratio of melamine to formaldehyde was 1:2.19.

10g (0.05mol) of this methylolated melamine
Add to 100ml of 1.35% hydrochloric acid solution (0.75% melamine)
molar) and stirred to obtain an acid colloid solution. When used in the following example, the product was further left to mature at room temperature for 12 days.

On the other hand, 10 g of the methylolated melamine (0.05
mol) and 0.03 g of citric acid were added to 20 g of methanol and heated under reflux with stirring. Once the methylolmelamine was dissolved, the reaction solution was cooled, neutralized with NaOH dissolved in methanol, and adjusted to pH 8-10. After standing overnight, filter out the precipitate and collect the filtrate at 50°C.
Concentrate under reduced pressure to remove methanol. As a result, a colorless and transparent viscous candy-like substance of methoxymethylolmelamine was obtained.

〔Example〕

Polymerization degree 1900-2100, saponification degree 98.5-99.2 mol%
PVA (manufactured by Kishida Chemical Co., Ltd.) was added to tap water and heated to create a solution containing 100 mg of PVA, which was used as the target water.

500 ml of this target water was collected in a beaker, and after adding a predetermined amount of the drug obtained in the above production example, a sodium hydroxide solution was added as needed to adjust the pH to a predetermined value. After stirring for 2 minutes, the mixture was allowed to stand for 15 hours, and then the amount of PVA in the supernatant water was measured as TOC.

The results are shown in the figure.

In the above, 10 g of the methoxylated melamine/formaldehyde condensate produced in the above production example was used instead of the melamine/formaldehyde condensate.
When an acid colloid solution obtained by adding 78 ml of 1.35% hydrochloric acid solution (0.75 mol of melamine) and stirring was used, similar results to the melamine/formaldehyde condensate were obtained.

Comparative Example In the Example, sulfuric acid, polydimethylamine-epichlorohydrin condensate, dicyandiamide formalin condensate, polyethyleneimine, and chitosan were used instead of the acid colloid solution, and the pH was adjusted to the optimum aggregation pH for each drug. It was processed in the same way.

The results are shown in the figure.

As is clear from the figure, even if conventionally used cationic organic and inorganic flocculants are added,
PVA is hardly removed, whereas in the case of this invention, PVA is removed extremely efficiently.

[Brief explanation of drawings]

The drawing shows the results of an example, and is a diagram showing the relationship between the amount of a chemical added and the removal rate of PVA.

Claims (1)

[Scope of Claims] 1. A method for treating polyvinyl alcohol-containing water, which comprises adding an acid colloid solution of a melamine-aldehyde condensate to polyvinyl alcohol-containing water for flocculation treatment. 2 Acid colloid solution of melamine/aldehyde condensate contains 1 to 6 aldehydes per mole of melamine.
The method for treating polyvinyl alcohol-containing water according to claim 1, which comprises methylolmelamine and an acid in a molar bond. 3. The method for treating polyvinyl alcohol-containing water according to claim 1 or 2, wherein the acid is hydrochloric acid. 4. The method for treating polyvinyl alcohol-containing water according to claim 3, wherein 0.5 to 1.5 moles of hydrochloric acid are added per mole of melamine. 5. A method for treating polyvinyl alcohol-containing water, which comprises adding an acid colloid solution of an alkyl etherified melamine/aldehyde condensate to the polyvinyl alcohol-containing water for flocculation treatment.