JP3715004B2 - Treatment of acrylamide-containing wastewater - Google Patents

Description

【００１４】
【発明の効果】
以上説明してきたように、本発明の処理法によれば、アクリルアミドを濃厚に含有した排水についても、容易に処理することができる。[0001]
[Industrial application fields]
The present invention relates to an advantageous treatment method for wastewater containing acrylamide.
[0002]
[Prior art]
There are many industrial processes in which wastewater containing acrylamide is discharged, especially acrylonitrile, olefin (or corresponding alcohol), which is called liter reaction, concentrated sulfuric acid to acryloylmethylpropane sulfonic acid, diacetone acrylamide, N-isopropylacrylamide, etc. In the process for producing N-substituted acrylamide derivatives, wastewater containing a few percent of concentrated acrylamide is discharged.
As a method for treating such acrylamide-containing wastewater, for example, as disclosed in JP-B-55-50477, a method using biochemical treatment with activated sludge is known.
[0003]
[Problems to be solved by the invention]
However, the biochemical treatment method is troublesome to maintain and is not suitable as a treatment method for concentrated wastewater, such as requiring large dilution when the salt concentration is high.
This invention makes it a subject to provide the processing method of the acrylamide containing waste_water | drain by the combination of processes, such as superposition | polymerization and a hydrolysis process which are easy to handle in a chemical plant without these faults.
[0004]
[Means for solving the problems]
As a result of earnest research to solve such problems, the present inventors have added alkali to acrylamide-containing wastewater, partially hydrolyzed by heating, and then made acid and weakly acidic, followed by iron-hydrogen peroxide solution. It has been found that acrylamide in the waste water can be suitably removed by polymerizing with such a redox polymerization catalyst and adding the ions of calcium, Mg, etc. to the resulting polymer to precipitate it as an insoluble polymer and removing it by filtration, flotation separation, etc. The present invention has been completed.
The effluent containing acrylamide as used in the present invention refers to effluent containing 0.3 to 3% of acrylamide in the concentration range.
[0005]
Hereinafter, the present invention will be described in detail.
Hydrolysis Step Wastewater containing acrylamide is hydrolyzed in the presence of alkali. Although there is no restriction | limiting in particular as an alkali which can be used, The caustic soda flake or caustic soda aqueous solution which is easy to acquire is especially preferable, and it adjusts to predetermined concentration in addition to waste_water | drain. If the alkali concentration is increased, the hydrolysis rate increases. However, since a large amount of acid is required for neutralization with the acid in the next step, the amount added is 2.5 to 4. mol in molar amount relative to acrylamide. 5 times,> 3 wt% is preferred for the concentration in the wastewater.
The hydrolysis is carried out at a temperature slightly higher than room temperature, for example, around 50 to 70 ° C. while blowing air to remove the generated ammonia. Depending on the reaction conditions, about 80% of acrylamide is hydrolyzed and converted to acrylic acid in a few hours. As will be described later, when alkaline earth metal ions are added to the polymerized polymer and precipitated as an insoluble polymer, the more acrylic acid is obtained, the harder the polymer is obtained and the easier it is to process, but the hydrolysis rate is increased. Therefore, since it takes time and cost, it is sufficient to hydrolyze 70% or more of acrylamide as shown in the experimental examples.
[0006]
Polymerization step After acidity, for example, concentrated sulfuric acid is added to the hydrolyzed waste water to adjust to weak acidity, for example, pH 4 to 4.5, a polymerization reaction is performed. At neutrality, the polymerization rate is slow and the polymerization rate does not increase.
For the polymerization reaction, a known method of redox polymerization can be used.
The ferrous sulfate is preferably ferrous sulfate or ferrous chloride, and the iron ion concentration is preferably 500 to 1000 ppm. After deoxygenation by nitrogen bubbling, hydrogen peroxide (a normal 30% aqueous solution may be used) is added to 2000 to 4000 ppm, the temperature is raised to 40 to 50 ° C., and polymerization is carried out for about 1 hour. Or a polymer mixture is formed. There is no need for nitrogen bubbling once polymerization has begun. Further, the reaction is stopped when hydrogen peroxide decomposition bubbles disappear by heating for about 1 hour. From the amount of residual monomer, the polymerization rate is 97% or more.
Whether the polymer produced is a copolymer or a mixture of polymers of acrylic acid and acrylamide has not been confirmed. However, when alkaline hydrolysis is performed again on the polymer precipitated by adding alkaline earth metal ions described later, ammonia that appears to be derived from acrylamide is generated. Polyacrylamide itself is precipitated even when alkaline earth metal ions are added. The inventors speculate that it is a copolymer because it does not.
[0007]
Separation process By adding alkaline earth metal ions to the waste water subjected to the polymerization reaction, an insoluble polymer is precipitated and separated.
Even if an acid is further added to the waste water after the polymerization reaction, an insoluble polymer is deposited. However, what is deposited in this manner is sticky and sticks to the wall with a high water content, and the separated polymer is difficult to be treated by re-dissolution if washed with water.
The polymer deposited by adding metal polyvalent ions is a low moisture content polymer without adhesion, and can be easily removed by, for example, flotation separation or filtration, and further incinerated.
As the metal polyvalent ions, alkaline earth metal ions are preferable, and calcium is particularly preferable in view of cost and ease of post-treatment, and slaked lime is usually used.
[0008]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples.
Example 1
200 ml of distilled water is put into a flask equipped with a stirrer, 3 g (42 mmol) of acrylamide and 4 g of caustic soda are dissolved, and the reaction is continued for 3 hours at 60 ° C. while bubbling with air under stirring. 5g was added and neutralized. When the reaction solution was analyzed by gas chromatography, 79% of acrylamide was decomposed, and most of it was converted to acrylic acid, and a part was converted to 3-hydroxypropionic acid with water added thereto. The pH of this solution was 4.5 and Mn-COD was 17,000 ppm.
Bubbling was carried out with nitrogen for 10 minutes, 0.5 g of ferrous sulfate heptahydrate and 1.5 g of 30% hydrogen peroxide were added, and the reaction was continued at 45 ° C. for 1.5 hours with stirring. Next, when 1.5 g of calcium hydroxide was added, a grayish brown precipitate floated on the surface of the liquid, and was filtered and washed.
Both acrylamide and acrylic acid in the filtrate were 0.04% or less. The COD of the filtrate was 3,100 ppm.
On the other hand, the weight of the precipitate washed and dried was 3.15 g. The residual polymer in the filtrate was examined by GPC (using Ultrahydrogel 120 column manufactured by Waters), but could not be detected.
The precipitate was again dispersed in 10% caustic soda water, and when heated, the generation of ammonia was observed, so it is considered that amide groups are present in the precipitated polymer.
[0009]
Example 2
A flask was charged with 200 ml of distilled water and 6 g of acrylamide. To this, 8 g of caustic soda was added and heated at 60 ° C. for 3 hours. After cooling to room temperature, the pH was adjusted to 4.5 with sulfuric acid, and after bubbling with nitrogen for 10 minutes, 0.5 g of ferrous sulfate heptahydrate and 1.5 g of 30% hydrogen peroxide were added and stirred while stirring. The reaction was continued for 1.5 hours at ° C. Next, when 3 g of calcium hydroxide was added, a grayish brown precipitate floated on the surface of the liquid, and was filtered and washed. The dry weight of the precipitate was 6.5 g, residual acrylic acid and acrylamide in the filtrate were each 0.04% or less, and no polymer was detected.
[0010]
Example 3
Instead of the acrylamide aqueous solution of Example 1, 200 ml of waste water (1.2% by weight of acrylamide, COD 16,000 ppm) after neutralization of N-isopropylacrylamide synthesis reaction by liter reaction was taken, 4 g of caustic soda was added, and the same as in Example 1 below. The operation was performed.
The COD of the filtrate obtained by adding calcium hydroxide to precipitate a grayish brown precipitate was 3,800 ppm, and acrylamide and acrylic acid were both 0.04% or less. The dry weight of the precipitate was 3.1 g.
[0011]
Comparative Example 1
In Example 1, a polymerization reaction liquid was obtained by carrying out in the same manner as in Example 1 without performing alkaline hydrolysis. Although the viscosity of this solution increased, insoluble precipitate did not precipitate even when 1.5 g of calcium hydroxide was added.
[0012]
Experimental Examples 1-4
A simulated solution prepared by mixing 200 ml of water with acrylic acid (molecular weight 72) and acrylamide (molecular weight 71) at a ratio as shown below to adjust the pH to 4.5 was used for polymerization and precipitation.
Table 1 shows the polymer removal rate (obtained from GPC analysis values before and after adding calcium hydroxide and filtering) and the properties of the precipitate.
[0013]
[Table 1]

[0014]
【The invention's effect】
As described above, according to the treatment method of the present invention, wastewater containing acrylamide in a concentrated manner can be easily treated.

Claims (1)

For wastewater containing acrylamide,
1) By heating in the presence of alkali, acrylamide is partially hydrolyzed and converted to acrylic acid,
2) Next, after acidifying with an acid, a redox polymerization initiator is added and polymerized,
3) adding alkaline earth metal ions to the polymerization solution to precipitate insoluble polymer and separating it;
A method for treating acrylamide-containing wastewater.