JPS5847205B2 - Flocculant with improved dewatering properties - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a polymer flocculant with improved dehydration properties.

In recent years, the need to purify all kinds of wastewater, including factory wastewater and domestic wastewater, has become increasingly important in order to preserve environmental water quality.

Water treatment has become an important issue in today's human life.

In particular, the treatment of wastewater discharged as a result of production activities has become clearly legally mandated, and for this reason various technologies have been developed regarding wastewater treatment.

The most basic wastewater treatment technology is to remove suspended solids by sedimentation or flotation. is often used as a flocculant.

When the suspended sludge (normally the solid content of this material is 0.5 to 5 weight φ) flocculated by such sedimentation or flotation methods is incinerated or recycled, filtration, centrifugation, etc. Dehydration is common.

At this time as well, we try to improve the dehydration processing ability by adding a chemical called a dehydration aid, but it is often possible to achieve both objectives by using a flocculant during the coagulation and dehydration process. The amount of water used naturally depends on the amount of wastewater involved, but normally one factory uses about 20% of wastewater per day.
In many cases, a small amount of ~10 kg is sufficient.

The flocculants used for this purpose include nonionic,
There are anionic and cationic types, and they are used depending on the target wastewater or its treatment process, and the representative ones are polyacrylamide and its partial hydrolyzate.

Various studies have been conducted to improve the quality of acrylamide-based flocculants, and various proposals have been made, including for the purpose of reducing manufacturing costs.

However, until now, the first urgent task in wastewater treatment has been to eliminate visible suspended solids in the treated water, so even when using polymer flocculants, the flocculation performance during coagulation sedimentation or flotation of raw water has been a problem. Quality improvements were being made in all directions.

It is still clear that the performance of flocculants depends on their molecular weight, and as a result, acrylamide flocculants have also been moving toward higher molecular weights.Today, those with molecular weights of several million are mainstream, and some of them are 1. It is said that there are some that exceed .0 million.

With the spread of water treatment technology, the economic efficiency of the dehydration process has become more important.Usual vacuum filtration and centrifugal dehydration can yield a wet cake with a water content of about 70 to 90mm; -20I) may significantly change the handling properties of the cake, and also greatly change the fuel consumption during incineration and drying.

On the other hand, regarding the flocculant itself, flocculant is usually handled as a powder product due to transportation cost and ease of dissolution operation. We have proposed a method in which an aqueous solution with a monomer concentration of 20 to 25% is polymerized in an adiabatic state by increasing the monomer concentration during polymerization, and if necessary, a partial hydrolysis reaction is carried out substantially simultaneously with the polymerization.

In this high-concentration aqueous solution polymerization method, for example, when polymerizing with a 25% aqueous solution, the productivity in the same polymerization pot is 2.5 times higher than when polymerizing with a low concentration of about 10φ, and there is less water to evaporate. Since the fuel consumption is reduced to 1/3, it is overwhelmingly advantageous economically.

However, when the acrylamide polymer thus obtained was used as a flocculant, the dehydration performance tended to be inferior to that obtained when polymerized at a low concentration.

In addition, polyacrylamide in which 3 to 20 moles of amide groups are substituted with carboxyl groups is in great demand for paper pulp wastewater sludge and aluminum wastewater sludge, but it is also used in filtration dehydration and press dehydration. The moisture content of the dehydrated cake obtained varies depending on the flocculant used.

In the wastewater treatment process, it is often experienced that flocculants with different molecular weights and hydrolysis rates cause differences in treatment results. Even if the decomposition rate and solution viscosity are almost the same and there is no difference in flocculation performance, it has been experienced that there is a difference in performance only in the dehydration process.

It has also been found that the dewatering results are good when uniformly sized and compact flocs are formed by adding a flocculant, while the dehydration rate does not improve when non-uniform flocs or unnecessarily large flocs are formed. It was done.

It is thought that these factors are related to the dissolution state of the flocculant molecules in relation to their dehydration properties, and that the ability to dissolve more uniformly, close to molecular dispersion, produces good results.

Under these circumstances, the present inventors learned that polymer flocculants with excellent flocculating performance are not necessarily excellent as dehydrating agents, and developed methods for improving dehydrating performance or dehydrating properties. As a result of extensive research into achieving both cohesive properties, the present invention was arrived at.

That is, the present invention provides alkylene oxide addition of a compound having active hydrogen in the polymerization system in which the concentration of the monomer is approximately 15% by weight or more when acrylamide or a water-soluble monomer containing a predominant amount of acrylamide is polymerized in an aqueous solution. A monomer is a water-soluble compound (hereinafter abbreviated as polyethylene glycol, etc.) with a molecular weight of about 400 to 20,000 obtained by substituting a compound or its terminal hydroxy hydrogen with a residue of another hydroxy compound or a carboxylic acid residue. This relates to a flocculant with improved dehydration properties, characterized in that it is polymerized in coexistence with a weight of 0.5 to 15% of the total weight of the coagulant, and if necessary, further partially hydrolyzed, and then dried and powdered. be.

Regarding polyethylene glycol, an application has already been filed as an anti-tack agent for acrylamide polymer hydrogel (see Japanese Patent Application No. 51-1599 = JP-A-52-85283). They have discovered that this has the effect of improving the molecular dispersion state during dissolution of the combined dry powder, resulting in improved dehydration properties.

The mechanism of action of this effect of polyethylene glycol etc. is not yet clear, but when polyethylene glycol is dissolved in an aqueous polyacrylamide solution, two-phase separation occurs at a certain point, and the polyacrylamide-
A phenomenon of separation into a water phase and a polyethylene glycol-water phase was observed.

According to literature, it is known that the COOH group of polyacrylic acid and the 101 groups of polyethylene glycol form hydrogen bonds in water under certain conditions.

Therefore, it is highly conceivable that polyethylene glycol has some effect on the spread of polyacrylamide chains in the aqueous medium.

When acrylamide is obtained at a high molecular weight by aqueous polymerization at a concentration on a 15-weight plate, considering that the coordination of the polymer chain formed during polymerization remains in the powder after drying, it is assumed that It is not surprising that the effects of added polyethylene glycol, etc., affect the solubility of the cam powder.

Polyethylene glycol and the like mentioned here are alkylene oxide adducts of compounds having active hydrogen, or those obtained by substituting the terminal hydroxy hydrogen with the residue of another hydroxy compound or a carboxylic acid residue. Of course, those suitable for the intended use herein must be water soluble.

And the molecular weight of this kind of thing is 400 to 20,000
It is preferably 2,000 to 20,000, more preferably 3,000 to 10,000.

Compounds with polyalkylene chains include not only polyethylene glycol, but also compounds with the general formula % formula %) which are addition polymerized with ethylene oxide to alcohol, carboxylic acid, sulfonic acid, etc. R803(CH2CHO)H (where R is CH3, C2
Effects are also recognized in those represented by H5° C3H7y Cl8H37% phenyl and octylphenyl, R' represents CH3, C2H5 and C17H35), and those in which the terminal OH is etherified or esterified.

It has also been found that a similar effect can be expected from a block copolymerized compound of ethylene oxide and propylene oxide, which are known as surfactants.

The molecular weight range of these compounds is as described above, but those with very large molecular weights are not preferable because they increase the viscosity of the monomer solution before polymerization starts, and if they are too small, the concentration of terminal -CH2oH The force N becomes relatively high, and the chain transfer effect due to C-H bonds is exerted, so the force N
Even if it is effective in improving dehydration properties, it is not possible to increase the molecular weight of the polyacrylamide produced.

The amount of polyethylene glycol etc. added is not uniform depending on the various conditions during polymerization, but it is usually about 0% per monomer.
．． Addition of 5 to 15 weight φ is used.

The larger the amount added, the better the effect that is the objective of the present invention, but if it exceeds about 15 weight φ, the effect commensurate with the amount added will no longer be expressed, and on the other hand, it may be difficult to dilute the active ingredient as a flocculant or increase the viscosity of the polymerization system. The disadvantages of this method are that it increases the amount of carbon dioxide, or that chain transfer effects begin to appear.

Various improved methods for polymerizing acrylamide have already been proposed, but it is natural that polymerization at a high concentration is preferred in order to obtain a dry powder product.

When the monomer concentration is about 18 to 25, the form of the produced polymer becomes a semi-solid gel, and when the concentration is about 30 φ or more, the heat generated by polymerization is large, so the polymerization system is held in a thin plate shape and the polymerization is carried out. Although it is necessary to conduct the polymerization process and cool it from the outside, this case has the advantage that continuous polymerization is possible.

In any case, in the case of the present invention, adiabatic polymerization can be carried out.

A known polymerization initiator is used in a known manner.

For example, an initiator system selected from water-soluble peroxides, redox initiators consisting of water-soluble peroxides and reducing agents, or water-soluble azo compounds, or an appropriate combination of these as necessary may be used. .

The flocculants targeted by the present invention include not only nonionic polymers obtained without active modification as acrylamide-based polymers, but also those modified by polymer reaction of the obtained polymers. .

Examples of polymer reactions include partial hydrolysis, Mannich formation, Hofmann degradation, and sulfomethylation.

Further, as a partial hydrolysis reaction, it is of course possible to make a hydrolyzing agent present in the acrylamide polymerization system and hydrolyze the acrylamide during the polymerization process.

Furthermore, in order to further improve the performance as a flocculant, it is known that acrylamide and a copolymerizable monomer are mixed and copolymerized, and of course, in the present invention, the product obtained in this way is also used. It is possible.

Such monomers include (meth)acrylic acid and its salts, (meth)acrylic acid esters, 2-methyl-2
- acryloylpropanesulfonic acid and its salts, dimethylaminoethyl (meth)acrylate and its quaternary salts,
2-Hydroxy-3-methacryloyloxypropyl
Examples include trimethylammonium chloride.

As mentioned above, the flocculant of the present invention can be obtained by polymerizing a monomer concentration of about 15 φ or more, especially 18 φ or more in some cases.

It is not effective when the monomer concentration during polymerization is much lower than this value or when producing a low molecular weight polymer.

In other words, the dry polymer obtained by polymerizing acrylamide using a low-concentration aqueous solution has good solubility in water and good dehydration properties, so the effect of adding polyethylene glycol etc. is not noticeable, and when used as a flocculant. The production of low molecular weight polymers is not very conceivable, but in this case as well, it is meaningless since the solubility of the polymer is inherently good.

Also, when an aqueous polymer solution or gel is directly dissolved and diluted in water, it is not necessary to add polyethylene glycol, etc., because the solubility is better than when dissolving a dry powder, and it is easier to approach a molecularly dispersed state.

Normally, when the molecular weight of a polymer is increased to improve coagulation performance, solubility deteriorates, for example, when the molecular weight is 8 million to 1,000,
It is not unusual for it to take 2 to 4 hours to prepare an aqueous solution with a concentration of about 0.1 to 1 φ from 0.0000 polymer powder, and even if you spend a long time dissolving it, it will not completely dissolve.
Polymers containing mamako'' are also commercially available.

On the other hand, the acrylamide polymer containing polyethylene glycol or the like according to the present invention has a similar molecular weight and completely dissolves within one hour.

When a flocculant is used for dehydration, there are methods such as vacuum filtration, pressure filtration, or centrifugal dehydration as a dehydrator.The flocculant obtained by the present invention can be used in any of the cases, but filtration methods, especially vacuum filtration, are used. It shows particularly excellent performance in this method.

The amount of coagulant used is 0.5 per solid content in the sludge.
Good results are often obtained by adding about 3φ.

Stirring after addition should be done relatively gently to avoid unnecessarily destroying the flocs produced.

In order to obtain the desired effect by adding polyethylene glycol, etc., it is necessary to make it coexist during polymerization; otherwise, the effect observed in the present invention will not be exhibited.

EXAMPLES The present invention will be specifically explained below with reference to Examples.

In addition, various measurements were performed based on the following method.

[Dehydration]

Measured using Nutsche test equipment.

Using a vinylon furnace cloth as the perforation plate, the pressure was reduced by 400 aHg in mercury column from atmospheric pressure using a vacuum pump, and the copolymer 1010
Pour the wastewater sludge to which 00pp vs. liquid) was added all the way into the funnel, and after pouring it, let it suck for 2 minutes, and then calculate the weight (Wwc) of the wet cake formed.

Next, this wet cake is dried in a dryer at 100° C. for 24 hours, the dry cake weight (WDc) after drying is determined, and the cake solid content is calculated according to the following formula.

Cake solid content (Sol, %) = Wp C/Ww c1
00 [Cohesiveness] Take wastewater sludge in a 500 WIl beaker and adjust the pH to 7.
In step 6, add polymer 11) pIII and flocculate it using a jar tester using a conventional method.
Find Q).

[Solution viscosity, ■]

An aqueous solution of the powdered polymer with a concentration of 1φ is prepared and measured using a B-type viscometer under the condition of Arashi 2 rotor 6ppIn.

[Hydrolysis rate, hydr,) By alkaline titration method.

[Wastewater used]

Aluminum wastewater sludge and papermaking wastewater were used.

The main component of aluminum wastewater is aluminum oxide fine particles, and the pH of the raw wastewater is
is 7.6, SS is 60p p)l
is 7.0. SS is 9.7%.

The main components of the suspension in the papermaking wastewater were fine cellulose and inorganic substances, and the pH of the raw wastewater was 6.9 and the SS was 380ppm.

Example 1 A dewar bottle with a capacity of 11 was used as a polymerization vessel, in which 176 grams of acrylamide and the amount of polyethylene glycol (average molecular weight 6,250) listed in the table were dissolved in deionized water.

At this time, the pH was adjusted to 7.0 with a caustic soda solution, and the total pH was adjusted to 8.
001 monomer solution.

The container was equipped with a rubber stopper equipped with a thermometer, a nitrogen gas inlet, a nitrogen gas outlet, and a polymerization initiator inlet, and while the temperature was set at 25°C, nitrogen gas was passed through the monomer aqueous solution to sufficiently deoxygenate it. Later, the polymerization initiator 2,2'-azobis-2
-0.32% aqueous solution of amidinopropane hydrochloride 10- was introduced and all openings were sealed.

After an induction period of several minutes, polymerization began with an exotherm, reaching a maximum temperature of 93-94° C. after about 120 minutes in each case.

The polymer gel was held at this temperature for 14 hours to promote partial hydrolysis of the amide groups.

Next, these polymer gels were mechanically crushed, dried in a hot air drier, and further pulverized in a pulverizer.

All of these powders were soluble in water, and their properties were evaluated according to the method described above.

Example 2 Example 1 was repeated except that the various water-soluble polyalkylene oxide compounds indicated were used in place of polyethylene glycol.

The time required for polymerization of rice paulownia was between 110 and 130 minutes, and the hydrolysis rate was 4.0±0.3 mole φ.

Storms 7 and 8 used a small amount of antifoam.

The performance of the polymer thus obtained is shown in the following table.

Example 3 Example 1 was repeated except that 5φ of polyethylene glycol (PEG) having different average molecular weights were added.

The performance of the obtained polymer was as shown in the following table.

Example 4 Example 1 was repeated except that partial hydrolysis was not performed to obtain a powdered polymer.

The moisture content in the powder was over 9.0.

The viscosity of this polymer at 1% concentration is 2900 cp
s, and the hydrolysis rate was 0.5 mol φ.

The polymer thus obtained exhibited the properties shown in the following table.

Example 5 Acrylamide 176L containing indicated amount of PEG? was polymerized according to Example 1 using a redox initiator of persulfate power 'J 0.032f and dimethylaminopropionitrile 0.032S' in the presence of 7.27 i of boric acid and 4.8 i of caustic soda as a hydrolyzing agent. did.

After the polymerization was completed, the mixture was aged at 90° C. for 14 hours to complete the hydrolysis reaction, and then dried and powdered.

A polymer was obtained in which the water content in the powder was 10.0% and the hydrolysis rate was 13.9 mol.

The performance of this polymer was as shown in the table below.

Example 6 The performance of the same polymers used in Examples 1-3 was measured for the treatment of cotton wastewater.

Specifically, sulfuric acid band 2ooppIn was added to papermaking wastewater, the pH was adjusted to 6.5 with an alkali, and the mixture was subjected to an aggregation test.

The polymer used was lppm (relative to liquid), and the obtained sludge had a pH of 5.8 and an SS' of 3.5.

During dewatering, a polymer was used as a dehydration aid at 100 pP relative to the sludge.

A mixture of the polymer of Comparative Example A4 and PEG having a molecular weight of 6000 was used to treat paper manufacturing wastewater, and its performance was measured.

The following two mixing methods were used. CI) Make a polyhydric solution of powdered polymer of A4 and add 0.0% PEG to 500 WIl of this solution.
15-51 added and stirred and dissolved, CI) A: 4
A mechanically crushed polymer gel was uniformly sprayed with 10 tons of a solution of PEG in an amount equivalent to the above amount, dried and crushed in the same manner as in Example 1, and then redissolved.

Claims (1)

[Claims] 1. In aqueous solution polymerization of acrylamide or a water-soluble monomer containing a predominant amount of acrylamide, alkylene of a compound having active hydrogen in the polymerization system in which the concentration of the monomer is about 15% by weight or more. Molecular weight of oxide adducts or obtained by further substituting the terminal hydroxy hydrogen with residues of other hydroxy compounds or carboxylic acid residues, approximately 400 to 2.
o, oo. 0.5 to 15% of the water-soluble compound to the monomer
A flocculant with improved dehydration properties, characterized in that it is co-polymerized by coexistence, if necessary, further partially hydrolyzed, and then dried and powdered.