JPS6148522B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a polymer flocculant, and more particularly to an inexpensive and efficient method for producing a polymer flocculant by applying the Hoffman reaction to polyacrylamide. In general, when an amide compound is treated with a hypohalite in an alkaline state and then heated to 70-90℃ or reacted at a low temperature of 5℃ or less, amines are produced in high yield, which is often referred to as a Hofmann decomposition reaction. Are known. Also, polyacrylamide (hereinafter referred to as
Polyvinylamine, which is an aminated product of PAM (abbreviated as PAM), is also important as a paper strength agent, sedimentation accelerator, polymer flocculant, or colloid titration reagent. Therefore, there have been many attempts to produce polyvinylamine by applying the Hoffman reaction to PAM. However, all of the conventional methods were aimed at improving the amination rate. In general, the Hofmann reaction is a reaction in which a hypohalite is reacted with a carboxylic acid amide, such as PAM, to produce the amine, and can be represented, for example, by the following formula (1). R-CONH ₂ +NaOC+2NaOH →R-NH ₂ +NaC+Na ₂ CO ₃ +H ₂ O...(1) Moreover, this reaction is said to proceed through the following three steps. Since the reaction of → is highly temperature dependent, →
It is common knowledge in the Hoffmann reaction that after the reaction of , the reaction is rapidly heated to 70-90°C to proceed with the transition reaction to . In the reaction of formula (1), R-CONH ₂ , NaOC
The reaction molar ratio of and NaOH is 1:1:2,
In order to efficiently react NaCO in the reaction solution, twice the equivalent or more of NaOH is required. Conventionally, the Hofmann reaction was carried out to increase the amination rate mentioned above, so the initial alkali concentration was increased to increase the reaction efficiency.
There are no examples in which the Hofmann reaction is carried out at mol/mole or less. Also, for the same purpose, high average molecular weight
When PAM is used, the concentration of the reaction solution increases and its apparent viscosity increases, making reaction operations difficult. conducting a reaction. In the Hofmann reaction of PAM, PAM is oxidized by an oxidizing agent such as hypochlorite in the presence of alkali hydroxide, so the chain of the polymer molecule is broken, so the degree of polymerization of the polymer after the Hofmann reaction is It is inevitable that it will decline compared to before. However, especially when the purpose is a flocculant as in the present invention, this decrease in the degree of polymerization is a fatal flaw. That is, the flocculation mechanism when treating wastewater (sewage) using a polymer flocculant is thought to be as follows. In order to separate and dehydrate sludge sludge from wastewater, first, the electric charge of sludge particles is neutralized (coagulation effect).
It is necessary to make the flocs larger and stronger (flocculating action), and it is said that the larger the molecular weight, the greater the effect of this aggregating action.
(Normally, sedimentation accelerators have a molecular weight of several hundred thousand to several million, and flocculants have a molecular weight of several million.) On the other hand, when the Hoffman reaction is applied to PAM, as mentioned above, chain scission of polymer molecules occurs. Therefore, in order to obtain a flocculant, the starting material PAM must have a very high molecular weight. However, in the Hofmann reaction, the viscosity temporarily increases significantly more than the viscosity of the starting material during the haloamidation reaction of → in formula (2). Therefore, for example, the mixing of PAM, hypochlorite and sodium hydroxide becomes non-uniform, making it impossible to produce a flocculant with stable and uniform performance. Therefore, this is the reason why the production of cationic flocculants by the Hoffman reaction of PAM is not widely used, even though it is cheaper and easier to react than other methods. The present invention was made in view of the current situation, and its purpose is to develop a method for producing a polymer flocculant that is inexpensive and has an excellent flocculation effect by applying the Hoffman reaction to polyacrylamide under specific conditions. It is to provide. To summarize the present invention, the method for producing a polymer flocculant of the present invention comprises reacting polyacrylamide and hypohalite in an aqueous solution in the presence of an alkali hydroxide.
It is characterized by reacting polyacrylamide with an average molecular weight of 1.5 million or more with a hypohalite at a temperature of 15 to 30°C at an initial alkaline concentration of 0.3 to 0.95 mol/. As a result of various studies on the conditions of the above-mentioned Hofmann reaction, the present inventors have solved the above-mentioned problems and achieved a remarkable The present invention was achieved by discovering that a polymer flocculant having an aggregating effect can be produced. In the present invention, when PAM is subjected to the Hoffman reaction, PAM with an average molecular weight of 1.5 million or more, preferably 2 million or more is used as a starting material, and the alkali concentration at the start of the reaction is set to an ultra-low concentration of 0.3 to 0.95 mol/, The reaction temperature is 15~30℃, preferably 20~
Perform at 25℃. By reacting under these conditions, the amount of amino groups produced (see Example 1 below) is
Although it is 15 to 36%, it is possible to obtain a product with significantly superior performance as a flocculant. Under these conditions, if the average molecular weight of PAM is less than 1.5 million, the flocculant will not exhibit sufficient coagulating properties, and if the alkali concentration is less than 0.3 mol/mol, the reaction will not proceed;
If the amount exceeds 1 mol/molar, the amount of hypohalite used will increase, which will result in hydrolysis, resulting in a decrease in the molecular weight of PAM and poor agglomeration.Furthermore, the reaction temperature will be 15℃
If it is less than 30°C, the reaction rate will decrease and cooling will be required, and if it exceeds 30°C, the reaction itself will proceed, but the molecular weight of PAM will decrease, resulting in a decrease in cohesiveness. According to the present invention, the Hofmann reaction can be carried out satisfactorily even if the alkali concentration is very low, and the amount of amino groups produced is 40% or less. If the molecular weight can be increased, there is no need to increase the amount of amino groups when used as a flocculant. In the present invention, since the concentration of alkali is low and therefore the concentration of hypohalite is low,
There is less cleavage of the PAM main chain. Furthermore, since it is possible to lower the concentration of PAM, even if the starting material PAM has a high molecular weight of 2 million or more, it can be subjected to the Hoffman reaction, and it is also possible to lower the concentration of PAM. Therefore, the molecular weight of PAM is 150
Even if it is extremely large (more than 10,000 yen), it can be subjected to the Hoffman reaction.
The apparent viscosity of the PAM solution can be reduced, and manufacturing operations are easy. The present inventors measured the viscosity of the flocculant produced when denaturation was carried out by varying the alkali concentration during the Hoffman decomposition reaction, and obtained the results shown in the table below. The viscosity was measured using a Bruckfield viscometer.
Measured at 20°C.

[Table] As is clear from the table, the viscosity decreases significantly when denaturation is carried out with a high alkali concentration, and the viscosity is different between high-molecular PAM and low-molecular PAM. As described above, when the viscosity of PAM is high, the reaction becomes non-uniform, but according to the present invention, it is found that the viscosity can be lowered even by using polymeric PAM. In general, flocculants produced by the Hofmann reaction are strongly alkaline as they are, so it is necessary to neutralize them in consideration of the PH operability of the treated water. Since the reaction is carried out at high concentrations, the amount of acid required for neutralization is small, making it economical. In addition, in the present invention, the reaction can be carried out at a temperature near room temperature, and the necessary Hoffmann reaction can be completed in a short time of about 60 minutes. The amount of amino groups produced during aging reaches a constant value in about 60 minutes. That is, FIG. 1 is a graph showing the relationship between the reaction time and the amount of amino groups in the Hoffman reaction according to the present invention, and it is clear from this graph that the above is supported. A flocculant is generally used after being diluted in order to uniformly contact the sludge particles, but the flocculant produced according to the present invention can be easily diluted, and can be used easily in solution. Because it mainly contains inorganic salts such as sodium chloride, it is resistant to freezing and is advantageous for use in cold regions.Moreover, when sludge coagulates, these inorganic salts flow out into the water and affect sludge treatment. do not have. Next, the present invention and its effects will be explained by examples, but the present invention is not limited by these in any way. The flocculation experiment was conducted using sludge water discharged from a paper mill, that is, paper manufacturing sludge water mainly composed of fine fibers, mixed with excess sludge water generated by the activated sludge treatment method (solid content concentration 2.6% by weight, PH
6.5), dilute and dissolve with water to a pure content of 0.2% (because the flocculant produced by this method contains inorganic substances, when expressing the concentration, it is expressed in terms of PAM, and this is treated as the pure content). After adding a certain amount of flocculant and stirring for 90 seconds at 150 rpm using a jar tester, 1.5 mm was added using a Canadian freeness tester.
Place it in a container fitted with a plate with 400 φ holes per 100 cm ² and leave it for 60 seconds.
This was done by measuring the water content and the concentration of solids flowing out into the water. However, the amount of flocculant added is expressed as the ratio (%) of the pure flocculant to the solid content of sludge water, and the water ratio was calculated using the following formula. Water rate (%) =
Amount of water for 60 seconds (ml) / Amount of sludge water collected (ml) + Coagulant addition volume (ml) Example 1 8.7 g of 24.0% by weight NaOC aqueous solution and 45.0% by weight
A mixture of 5.0 g of NaOH aqueous solution was placed in a 500 ml separable flask and pre-cooled to 15° C. with cold water. To this, a 5.0% by weight PAM aqueous solution [viscosity
2900cps (viscosity of 1% by weight aqueous solution at 20℃,
100.0 g of average molecular weight 6 to 8 million (calculated based on Bruckfield viscosity, same hereinafter) was added with stirring. Since heat is generated, cool the reaction temperature so that it does not exceed 25°C, and leave it at 25°C.
The reaction was continued at ℃ and the Hofmann decomposition reaction was completed in 60 minutes. The molar blending ratio of raw materials, namely PAM:NaOC:NaOH (hereinafter referred to as the molar blending ratio of raw materials) is 1:
0.4:0.8, and the concentration of NaOH at the start of the reaction is
It was 0.51 mol/. This is cooled, and at the same time, 20% by weight Na ₂ SO ₃ aqueous solution is added to reduce unreacted free chlorine. After the reduction is completed, the pH is neutralized to 9.5 to 10.0 with 8.75% by weight HC aqueous solution to produce the final product. It became a thing. The amount of amino groups produced (molar ratio % of amino groups produced to amide groups measured by colloid titration using polyvinyl potassium sulfate, hereinafter the same) is
It was 15.6%. The final product is then purified with water.
Aggregation experiments were conducted after diluting to 0.2%. The results obtained are shown in FIG. (Explanation will be given later together with other examples and comparative examples. The same applies hereinafter.) Example 2 7.0 g of 24.0% by weight NbOC aqueous solution and 45.0% by weight
A mixed solution of 4.1 g of NaOH aqueous solution was placed in a 500 ml separable flask and precooled to 15° C. with cold water. To this, a 4.0% by weight PAM aqueous solution (viscosity
100.0 g (1600 cps; average molecular weight 2.5 to 3 million) was added with stirring. Since heat was generated, cooling was performed to prevent the reaction temperature from exceeding 25°C, and the reaction was continued at 25°C for 30 minutes to complete the Hofmann decomposition reaction. The molar blending ratio of the raw materials was 1:0.4:0.8, and the concentration of NaOH at the start of the reaction was 0.41 mol/mol. Thereafter, reductive neutralization was performed according to Example 1 to obtain a final product. The amount of amino groups produced was 15.2%. Moreover, the results of the aggregation experiment are shown in FIG. Example 3 A mixed solution of 17.7 g of a 24.0% by weight NaOC aqueous solution and 10.1 g of a 45.0% by weight NaOH aqueous solution was placed in a 500 ml separable flask, and an experiment was conducted in accordance with Example 2. The molar mixing ratio of the raw materials was 1:1:2, and the NaOH concentration at the start of the reaction was 0.93 mol/mol. The amount of amino groups produced was 35.6%, and the results of the aggregation experiment are shown in Figure 2. Example 4 8.7 g of 24.0 wt% NaOC aqueous solution and 45.0 wt%
A mixed solution of 5.0 g of NaOH aqueous solution was placed in a separable flask and pre-cooled to 15° C. with cold water. 15 for this
A 5.0 wt% aqueous PAM solution (viscosity
100.0 g (1600 cps; average molecular weight 2.5 to 3 million) was added with stirring. Since heat was generated, cooling was performed to prevent the reaction temperature from exceeding 20°C, and the reaction was continued at 20°C to complete the Hofmann decomposition reaction in 60 minutes. The molar mixing ratio of the raw materials was 1:0.4:0.8, and the concentration of NaOH at the start of the reaction was 0.51 mol/mol. Thereafter, reductive neutralization was performed according to Example 1 to obtain a final product. The amount of amino groups produced was 16.5%, and the results of the aggregation experiment are shown in FIG. Comparative Example 1 8.7g of 24.0% by weight NaOC aqueous solution and 45.0% by weight
A mixture of 5.0 g of NaOH aqueous solution was placed in a 500 ml separable flask and pre-cooled to 15° C. with cold water. Add to this a 5.0% by weight PAM aqueous solution (viscosity
100.0 g (14 cps; average molecular weight 600-900,000) was added with stirring. Since heat was generated, cooling was performed to prevent the reaction temperature from exceeding 25°C, and the reaction was continued at 25°C to complete the Hofmann reaction in 60 minutes. The molar mixing ratio of the raw materials was 1:0.4:0.8, and the concentration of NaOH at the start of the reaction was 0.51 mol/mol. Thereafter, reductive neutralization was performed according to Example 1 to obtain a final product. The amount of amino groups produced was 12.0%, and the results of the aggregation experiment are shown in FIG. Comparative Example 2 17.4g of 24.0% by weight NaC aqueous solution and 45.0% by weight
A mixed solution of 20.0 g of NaOH aqueous solution was placed in a 500 ml separable flask and precooled to 15° C. with cold water.
Add to this a 5.0% by weight PAM aqueous solution (viscosity
100.0 g (1600 cps; average molecular weight 2.5-3.5 million) was added with stirring. Since heat was generated, cooling was performed to prevent the reaction temperature from exceeding 25°C, and the reaction was continued at 25°C to complete the Hofmann reaction in 60 minutes. The molar mixing ratio of the raw materials was 1:1:4, and the concentration of NaOH at the start of the reaction was 2.0 mol/mol. Thereafter, reductive neutralization was performed according to Example 1 to obtain a final product. The amount of amino groups produced was 39.7%, and the results of the aggregation experiment are shown in FIG. Comparative Example 3 A mixed solution of 17.4 g of a 24.0 wt% NaOC aqueous solution and 10.0 g of a 45.0 wt% NaOH aqueous solution was placed in a 500 ml separable flask and precooled to 15°C with cold water. To this was added 100.0 g of a 5.0% by weight aqueous PAM solution (viscosity 2900 cps; molecular weight 6 million to 8 million) heated to 20° C. with stirring. Since heat is generated, cool the reaction temperature so that it does not exceed 25℃, and leave it at 25℃.
The reaction continued for 60 minutes, and the Hofmann decomposition reaction was completed. The molar mixing ratio of the raw materials was 1:1:2, and the NaOH concentration at the start of the reaction was 1.11 mol/mol. Thereafter, reductive neutralization was performed according to Example 1 to obtain a final product. The amount of amino groups produced was 34.7%, and the results of the aggregation experiment are shown in FIG. Comparative Example 4 A mixed solution of 43.4 g of a 24.0 wt% NaOC aqueous solution and 24.9 g of a 45.0 wt% NaOH aqueous solution was placed in a 500 ml separable flask and maintained at -5°C in advance with cold water. To this was added 10.0% by weight cooled to 0°C.
PAM aqueous solution (viscosity 14cps; average molecular weight 600,000-900,000)
100.0g was added with stirring. Since heat is generated, cool the reaction temperature so that it does not exceed 10℃.
The reaction was continued at 10°C, and the Hofmann decomposition reaction was completed in 120 minutes. The molar mixing ratio of the raw materials was 1:1:2, and the concentration of NaOH at the start of the reaction was 1.85 mol/mol. Thereafter, reductive neutralization was performed according to Example 1 to obtain a final product. The amount of amino groups produced was 35.6%, and the results of the aggregation experiment are shown in Figure 2. Next, the results of aggregation experiments in the above examples and comparative examples will be explained. That is, FIG. 2 is a graph showing the relationship between the amount of coagulant added, the water percentage, and the solid content concentration in water in Examples and Comparative Examples of the present invention, and curves A, B, C, and D are graphs for the examples and comparative examples of the present invention, respectively. For examples 1, 2, 3 and 4, curve E,
F, G and H are Comparative Examples 1, 2, 3 and 4 respectively
The case is shown below. As is clear from the graph in FIG. 2, the flocculant produced in this example had a high water content in the treated sludge water, and the concentration of solids that flowed into the water was effectively reduced. It can exhibit an extremely superior flocculating effect compared to the manufactured flocculant. As explained above, by applying the Hofmann reaction to polyacrylamide under specific conditions according to the present invention, a polymer flocculant that is inexpensive, has an excellent flocculating effect, and has the numerous other advantages described above can be produced. can be provided.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between the reaction time and the amount of amino groups in the Hoffman reaction according to the present invention, and Figure 2 is a graph showing the amount of flocculant added, water percentage, and solid content concentration in water in Examples and Comparative Examples of the present invention. This is a graph showing the relationship between

Claims (1)

[Claims] 1. In a method for producing a polymer flocculant in which polyacrylamide and hypohalite are reacted in an aqueous solution in the presence of an alkali hydroxide, the average molecular weight
1. A method for producing a polymer flocculant, which comprises reacting polyacrylamide of 1.5 million or more with a hypohalite at an initial alkali concentration of 0.3 to 0.95 mol/at a temperature of 15 to 30°C.