NO326144B1 - Methods for clarification, dewatering, retention and drainage by adding a higher active polymer dispersion - Google Patents

Description

Field of the invention

The invention is a method for treating industrial waste water or paper pulp with an effective amount of at least one dispersion of a water-soluble cationic polymer flocculant in which improvements include the addition of said polymer having a concentration of at least 25% to said waste water or paper pulp. The industrial waste is preferably food processing waste water, oily waste water, paper mill waste water and inorganically contaminated waste water. The pulp can be an aqueous cellulose suspension.

Background for the invention

The present invention relates to polymers which are of special value as flocculants for suspensions of organic matter of a proteinaceous or cellulosic nature as found in sewage and industrial plant treatment effluents or in paper mills.

It is generally accepted that such suspended materials, which are hydrophilic in nature and often have specific gravities quite close to that of the aqueous fluids in which they are suspended, are in marked contrast to the more hydrophobic mineral suspensions because they are often found being much more difficult to economically flocculate with chemical reagents prior to a physical dewatering step such as filtration, flotation, sedimentation, dewatering or in the retention of such materials for improvement. These difficulties are particularly noticeable when higher proportions of suspended matter are present, usually involving concentrations of 0.5% by weight and above in which the suspensions take on a paste-like consistency and are often described as sludge or paper pulp.

It is well known that the clarification or dewatering of sewage and industrial sludges and similar organic suspensions can be aided by the use of chemical reagents, added to induce a state of coagulation or flocculation which facilitates the process of solid/liquid or liquid/liquid separation from water. For this purpose, limestone or salts of iron or aluminum have been used. More recently, synthetic polyelectrolytes, especially certain cationic copolymers of acrylamide, have been found to be of interest.

Cationically charged water-soluble or water-dispersible polymers are used in a variety of processes involving the separation of solids or immiscible liquids dispersed or suspended in water from water, and the dewatering of solids containing water. These types of polymers, which may be natural or synthetic, are broadly referred to as coagulants and flocculants. These polymers can be used in such different processes as emulsion breaking, sludge dewatering, raw water clarification, drainage and retention aids in the production of pulp and paper, flotation aids in mining processing and color removal.

Polymers of this type generally work by neutralizing the anionic charge of the suspended solids or liquids to be removed. These solids or liquids can be waste that must be removed from water, or desirable products that are recovered from aqueous systems, such as coal fines that can be coagulated or flocculated and sold as fuel.

In the water treatment field of solid/liquid separation, suspended solids are removed from water by a variety of processes including sedimentation, screening, flotation, filtration, coagulation, flocculation and emulsion breaking among others. In addition, after suspended solids are removed from the water, they must often be dewatered so that they can be further treated or appropriately disposed of. Liquids treated for solids removal often have as little as a few parts per billion of suspended solids or dispersed oils, or may contain large amounts of suspended solids or oils. Solids that are dewatered may contain anywhere from 0.25% solids by weight to 40 or 50% solids by weight. Solid/liquid or liquid/liquid separation processes are designed to remove solids from liquids, or liquids from liquids.

While strictly mechanical devices have been used to perform solid/liquid separation, modern methods often rely on mechanical separation techniques that are enhanced by synthetic and natural cationic polymer materials to accelerate the rate at which solids can be removed from water. These processes include the treatment of raw water with cationic coagulant polymers that precipitate suspended inorganic particles and make the water usable for industrial or municipal purposes. Other examples of these processes include the removal of colored soluble species from paper mill effluent wastes, the use of organic flocculant polymers to flocculate industrial and municipal waste materials, sludge recycling and emulsion breaking.

Regarding the mechanism of separation processes, particles in nature have either a cationic or anionic charge. Accordingly, these particles are often removed by a water-soluble coagulant or flocculant polymer which has a charge opposite to that of the particles. This is referred to as a polyelectrolyte-enhanced solid/liquid separation process in which a water-soluble or dispersible ionically charged polymer is added to neutralize the charged particles or emulsion droplets to be separated. The dosage of these polymers is critical to the performance of the process. If too little ionically charged polymer is used, the suspended particles will not be charge neutralised, and will therefore repel each other. If too much polymer is used, the polymer will be wasted, or worse represent a problem in and of itself.

Examples of such cationic polymers for dewatering include US Patent No. 3,409,546 which describes the use of N-(aminomethyl)-polyacrylamides in conjunction with other cationic polymers for the treatment of sewage sludge; US Patent No. 3,414,514 which describes the use of a copolymer of acrylamide and a quaternized cationic methacrylate ester, JP 61-106072 which describes water-soluble copolymers and another class of cationic polymers used to dewater sludge as described in US Patent No. 3,897,333. Use of polyethyleneimines and homopolymers of cationic acrylates and methacrylates and other cationic polymers such as polyvinylpyridines is also known.

Another example of a cationic polymer useful for sludge treatment is US Patent No. 4,191,645, wherein cationic copolymers are prepared from a nonionic monomer such as acrylamide, and a cationic monomer such as trimethylammonium ethyl methacrylate methyl sulfate quaternary (TMAEM. MSQ) or dimethylaminoethyl acrylate-methylsulfate quaternary (DMAEA.MSQ) is presented. Further examples of polymer treatments for sludge dewatering include the 1,4-dichloro-2-butene-dimethylamine ion chloride polymer as described in US Patent No. 3,928,448 and the block copolymers disclosed in US Patent No. 5,234,604.

Among the treatments that can be used to improve retention and drainage are those described in US Patent Nos. 5,126,014 and 5,266,164.

Despite the variety of commercially available polymers that have been found to be capable of flocculating or coagulating solid sludge, there are various considerations that tend to limit the applicability of these reagents. While it is known for this sludge that economical treatments with these known reagents are possible, it is more often that sludge requires very high and cost-ineffective dosages of reagents for a successful treatment. Furthermore, variations often occur in sludge from any other source. Variations in the supply of material to waste water/sludge/pulp process water and/or in the oxidation conditions that may be involved in the production of this water can, for example, lead to a number of particle types that must be removed. Furthermore, it is not uncommon to encounter sludge which, for one reason or another, cannot be improved by flocculation with any of the known polymeric flocculation agents. It is therefore an object of the invention to provide the subject with a superior method for the dewatering of sludge-containing industrial waste water or in the retention of industrial processing aids.

Summary of the invention

In summary, the invention is explained as set out in the attached set of requirements.

The invention is a method for treating industrial wastewater or paper pulp with an effective amount of at least one dispersion of a water-soluble cationic polymer flocculant in which the improvement comprises the addition of said polymer having a concentration of at least 25% to said wastewater or paper pulp. The industrial waste is preferably food processing waste water, oily waste water, paper mill waste water and inorganically contaminated waste water. The pulp can be an aqueous cellulose suspension.

Description of the invention.

Methods for preparing the polymer dispersion used in the invention are described in detail in US Patents Nos. 5,006,590 and 4,929,655, issued to Kyoritsu Yuki Co., Ltd., Tokyo, Japan and US Patents Nos. 5,708,071 and 5,587,415 issued to Hymo Corporation of Tokyo, Japan. The presentations in these two patents are incorporated herein by reference.

This invention represents a significant improvement in the art of treating aqueous systems with dispersion polymers. As will be shown in the examples, the lower concentration dispersion polymers now used and presented are of poorer quality than the higher concentration dispersion polymers presented herein. The superiority of the polymers presented herein is much more than an increasing additive effect that would be commonly expected by those skilled in the art. The examples illustrate this unexpected greater activity at much lower dosages, which previously could not be predicted.

The monomers

According to the invention, the polymer dispersion is used to treat the produced water prepared from a water-soluble monomer mixture containing at least 5 mol% of a cationic monomer represented by the general formula (I):

wherein R 1 is H or CH 3 ; R 2 and R 3 are each an alkyl group having 1 to 2 carbon atoms; Ai is an oxygen atom or NH; Bi is an alkyl group having 2 to 4 carbon atoms or a hydroxypropyl group and Xi is a counter anion. The above

water-soluble monomer mixture is soluble in the aqueous solution of the anionic salt. However, the polymer generated from the monomer mixture is insoluble in the aqueous anionic salt solution. The polymer of the monomer mixture can also be used as the seed polymer. The seed polymer is described in detail below.

The above-mentioned cationic monomer represented by the general formula (I) is preferably a quaternary ammonium salt obtained by the reaction of benzyl chloride and dimethylaminoethyl acrylate, diethylaminoethyl acrylate, dimethylaminohydroxypropyl acrylate, dimethylaminopropyl acrylate, dimethylaminoethyl methacrylate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate and dimethylaminopropyl methacrylate.

Monomers which are preferably copolymerized with the cationic monomer represented by the general formula (I) include acrylamide, methacrylamide or other N-substituted (meth)acrylamides and the cationic monomers represented by the general formula (II):

wherein R 4 is H or CH 3 ; R 5 and R 6 are each an alkyl group having 1 to 2 carbon atoms; R 7 is H or an alkyl group having 1 to 2 carbon atoms; A 2 is an oxygen atom or NH; B 2 is an alkyl group having 2 to 4 carbon atoms or a hydroxypropyl group and X 2 is a counter anion. Xi and X2 can be anionic counterions such as halides, pseudohalides,

-SO3OCH3 and -OC(0)CH3 among others.

Preferred monomers represented by formula (II) include the ammonium salts of dimethylaminoethyl acrylate, diethylaminoethyl acrylate, dimethylaminopropylacrylamide, diethylaminopropylacrylamide and dimethylhydroxypropylacrylate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, dimethylaminopropyl methacrylate, diethylaminopropyl methacrylate and dimethylhydroxypropyl methacrylate or other N-substituted (meth)acrylamides as well as the quaternized and ethylated salts . Among the more preferred cationic monomers represented by the general formula (II) are the salts and the methylated quaternary salts of dialkylaminoethyl acrylate and dialkylaminoethyl methacrylate. The concentration of the above monomers in the polymerization reaction mixture is suitably in the range of 5 to 30% by weight.

The anionic salts

The anionic salt to be incorporated into the aqueous solution according to the present invention is suitably a sulphate, a phosphate, a chloride or a mixture thereof. Preferred salts include ammonium sulfate, sodium sulfate, magnesium sulfate, aluminum sulfate, ammonium chloride, sodium chloride, ammonium hydrogen phosphate, sodium hydrogen phosphate and potassium hydrogen phosphate. In the present invention, these salts can all be used as an aqueous solution thereof having a combined concentration of 10% or more.

The dispersants

A dispersing polymer (also referred to as a stabilizing polymer) is present in the aqueous anionic salt solution in which the polymerization of the above monomers occurs. The dispersant polymer is a water-soluble high molecular weight cationic polymer. The dispersant polymer is at least partially soluble in the above-mentioned aqueous salt solution. The dispersion polymer is preferably used in an amount of from 1 to 10% by weight based on the total weight of the monomers. The dispersant polymer is composed of 5 mol% or more of a diallyldialkylammonium halide or of a cationic monomer unit represented by the formula (I) or (II). Preferred is the remaining mol% acrylamide or methacrylamide or other N-substituted (meth)acrylamides or diallyldimethylammonium chloride. The performance of the dispersant is not greatly affected by molecular weight. However, the molecular weight of the dispersant is preferably in the range of 10,000 to 10,000,000. According to one embodiment of the invention, a multi-functional alcohol such as glycerine or polyethylene glycol or a chain transfer agent such as sodium formate coexists in the polymerization system. The deposition of the fine particles is smoothly carried out in the presence of these agents.

The dispersion polymers

For the polymerizations, a common water-soluble radical-forming agent can be used, but water-soluble azo compounds such as 2,2'-azobis(2-amidinopropane)hydrochloride and 2,2'-azobis(N,N'-dimethylisobutylamine)hydrochloride are preferred. ride used.

According to one embodiment of the invention, a seed polymer can be added before the beginning of the polymerization of the above-mentioned monomers for the purpose of obtaining a fine dispersion. The seed polymer is a water-soluble cationic polymer which is insoluble in the aqueous solution of the anionic salt. The seed polymer is preferably a polymer produced from the above-mentioned monomer mixture by the method described herein. Nevertheless, the monomer composition of the seed polymer need not always be equal to that of the water-soluble cationic polymer formed during polymerization. However, similar to the water-soluble polymer formed during polymerization, the seed polymer should contain at least 5 mol% of cationic monomer units represented by the general formula (I). According to one embodiment of the invention, the seed polymer used in the polymerization reaction is the water-soluble polymer produced in a previous reaction that used the same monomer mixture.

One aspect of this invention is a method of clarifying wastewater with an effective clarifying amount of at least one dispersion of a water-soluble cationic polymer flocculant; wherein said water-soluble flocculant is added to said wastewater in an effective amount to flocculate suspended solids, the suspended solids are removed, and a clarified water is obtained, said dispersion of said water-soluble cationic polymer flocculant formed from polymerization of vinylic monomers under free-radical- forming conditions in a medium containing water, monomers, stabilizing monomers and an aqueous anionic salt solution; in which said water-soluble cationic poly-merf loculant is polymerized from

a) at least 5 mol% of a cationic monomer selected from the group consisting of: monomers of general formula (I)

wherein Ri is selected from the group consisting of H and CH3, R2 and R3 are selected from the group consisting of Ci-alkyl and C2-alkyl, Ai is selected from the group consisting of 0 and NH, Bi is selected from the group consisting of C2-alkyl, C3-alkyl and hydropropoxy -groups and Xi" is an anionic counterion and monomers of general formula II:

wherein R4 is selected from the group consisting of H and CH3, R5 and C6 are selected from the group consisting of C1-alkyl and C2-alkyl; R 7 is selected from the group consisting of hydrogen atom, C 1 -alkyl and C 2 -alkyl; A 2 is selected from the group consisting of an oxygen atom and NH; B2 is selected from the group consisting of C2-alkyl, C3-alkyl, C4-alkyl and hydroxypropyl and X2~ is an anionic counter with

b) at least 5 mol% of a monomer selected from the group consisting of C1-C10N-alkylacrylamide, C1-C10N, N-dialkylarylamide, C1-C10

N-alkyl methacrylamide, Ci-CioN,N-dialkyl methacrylamide, N-aryl acrylamide, N,N-diaryl acrylamide, N-aryl methacrylamide, N,N-diaryl methacrylamide, N-aryl alkyl acrylamide, N,N-diarylalkyl acrylamide, N- arylalkyl methacrylamide, N,N-diarylalkyl methacrylamide, acrylamide and methacrylamide; and wherein said stabilizing polymer is a cationic polymer which is at least partially soluble in said aqueous solution of said anionic salt, wherein the improvement comprises the addition of said water-soluble cationic flocculant polymer dispersion to said waste water at a concentration of at least 25% by weight polymer dispersion in water.

Another aspect of this invention is a method for dewatering waste water with an effective dewatering amount of at least one dispersion of a water-soluble cationic polymer flocculant; wherein said water-soluble flocculant is added to said wastewater in an effective amount to dewater suspended solids, the suspended solids are removed, and a clarified water is obtained, said dispersion of said water-soluble cationic polymer flocculant formed from polymerization of vinylic monomers under free radical forming conditions in a medium containing water, monomers, stabilizing polymer and an aqueous anionic salt solution; wherein said water-soluble cationic polymer flocculant is polymerized from

a) at least 5 mol% of a cationic monomer selected from the group consisting of monomers of the general formula I:

wherein Ri is selected from the group consisting of H and CH3, R2 and R3 are selected from the group consisting of Ci-alkyl and C2-alkyl, Ax is selected from the group consisting of 0 and NH, Bi is selected from the group consisting of C2-alkyl, C3-alkyl and hydropropoxy -groups, and Xi" is an anionic counterion and monomers of the general formula II:

wherein R 4 is selected from the group consisting of H and CH 3 , R 5 and R 6 are selected from the group consisting of C 1 -alkyl and C 2 -alkyl; R 7 is selected from the group consisting of hydrogen atom, C 1 -alkyl and C 2 -alkyl; A 2 is selected from the group consisting of an oxygen atom and NH; B2 is selected from the group consisting of C2-alkyl, C3-alkyl, C4-alkyl and hydroxypropyl and X2~ is an anionic counter with b) at least 5 mol% of a monomer selected from the group consisting of Ci-CioN-alkylacrylamide, Ci-CioN, N-dialkylarylamide, Ci-CioN-alkylmethacrylamide, Ci-CioN,N-dialkylmethacrylamide, N-aryl-acrylamide, N,N-diarylacrylamide, N-arylmethacrylamide, N,N-diarylmethacrylamide, N-arylalkylacrylamide, N,N- diarylalkylacrylamide, N-arylalkylmethacrylamide, N,N-diarylalkylmethacrylamide, acrylamide and methacrylamide; and wherein said stabilizing polymer is a cationic polymer which is at least partially soluble in said aqueous solution of said anionic salt; wherein the improvement comprises the addition of said water-soluble cationic flocculant polymer dispersion to said waste water at a concentration of at least 25% by weight polymer dispersion in water. Yet another aspect of the present invention is a method for improving retention and drainage of process water in pulp and paper production with an effective amount of at least one dispersion of a water-soluble cationic polymer flocculant; wherein said water-soluble flocculant is added to said process water in an effective amount to improve retention and drainage, said dispersion of said water-soluble cationic polymer flocculant formed from the polymerization of vinylic monomers under free-radical-forming conditions in a medium containing water, monomers, stabilizing monomers and an aqueous anionic salt solution; wherein said water-soluble cationic polymer flocculant is polymerized from a) at least 5 mol% of a cationic monomer selected from the group consisting of: monomers of the general formula I

wherein Ri is selected from the group consisting of H and CH3, R2 and R3 are selected from the group consisting of Ci-alkyl and C2-alkyl, Ai is selected from the group consisting of 0 and NH, Bi is selected from the group consisting of C2-alkyl, C3-alkyl and hydropropoxy -groups, and Xi~ is an anionic counterion and

monomers of the general formula II:

wherein R 4 is selected from the group consisting of H and CH 3 , R 5 and R 6 are selected from the group consisting of C 1 -alkyl and C 2 -alkyl; R 7 is selected from the group consisting of hydrogen atom, C 1 -alkyl and C 2 -alkyl; A 2 is selected from the group consisting of an oxygen atom and NH; B2 is selected from the group consisting of C2-alkyl, C3-alkyl, C4-alkyl and hydroxypropyl and X2~ is an anionic counter with

b) at least 5 mol% of a monomer selected from the group consisting of Ci-CioN-alkylacrylamide, Ci-CioN, N-dialkylarylamide, Ci-Cio

N-alkyl methacrylamide, Ci-CioN,N-dialkyl methacrylamide, N-aryl acrylamide, N,N-diaryl acrylamide, N-aryl methacrylamide, N,N-diaryl methacrylamide, N-aryl alkyl acrylamide, N,N-diarylalkyl acrylamide, N- arylalkyl methacrylamide, N,N-diarylalkyl methacrylamide, acrylamide and methacrylamide;

and wherein said stabilizing polymer is a cationic polymer which is at least partially soluble in said aqueous solution of said anionic salt; wherein the improvement comprises the addition of said water-soluble cationic flocculant polymer dispersion to said waste water at a concentration of at least 25% by weight polymer dispersion in water.

Preferred polymeric flocculants are poly(DMAEA.MCQ/AcAm), poly(DMAEA.BCQ/AcAm) and poly(DMAEA.MCQ/DMAEA.BCQ/AcAm).

For any aspect of this invention, a stabilizing polymer may be polymerized from at least 5 mol% of cationic monomers selected from the group consisting of monomers of the general formula I

wherein Ri is selected from the group consisting of H and CH3, R2 and R3 are selected from the group consisting of Ci-alkyl and C2-alkyl, Ax is selected from the group consisting of 0 and NH, Bi is selected from the group consisting of C2-alkyl, C3-alkyl and hydropropoxy -groups, and Xi~ is an anionic counterion, diallyldialkylammonium halides and monomers with the general formula II:

wherein R 4 is selected from the group consisting of H and CH 3 , R 5 and R 6 are selected from the group consisting of C 1 -alkyl and C 2 -alkyl; R 7 is selected from the group consisting of hydrogen atom, C 1 -alkyl and C 2 -alkyl; A 2 is selected from the group consisting of an oxygen atom and NH; B2 is selected from the group consisting of C2-alkyl, C3-alkyl, C4-alkyl and hydroxypropyl and X2~ is an anionic counterion. A preferred diallyldialkylammonium halide is diallyldimethylammonium chloride (DADMAC).

The waste water can be selected from the group consisting of industrial waste water and municipal waste water. Furthermore, the industrial waste water can be selected from the group consisting of food processing waste water, oily waste water, paper mill waste water and inorganically contaminated waste water. The polymers described herein can be used together with coagulants such as poly(DADMAC), poly(epichlorohydrin/dimethylamine) and inorganic materials.

The polymers according to the present invention were compared with the polymers produced by Derypol S.A. Corporation in Spain. The polymer preparations are available from Derypol S.A. Corporation under the brand name designations DR-2570 (sold in 15% concentration), DR-3000 and DR-4000 (both of which are sold in 20% concentrations).

The following examples are presented to describe preferred embodiments and possibilities in the invention and are not intended to limit the invention unless otherwise stated in the accompanying claims.

Example 1

A 25% polymer solid, 65/25/10 mol% AcAm/DMAEA.

BCQ/DMAEA.

The MCQ dispersion was prepared as follows. A 1500 cc reaction flask was equipped with a mechanical stirrer, thermocouple, cooler, nitrogen purge tube, addition port and heat tape. To this reactor was added 173.7 g of acrylic amide (50% aqueous solution available from Nalco Chemical Co. of Naperville, IL), 158.5 g of dimethylaminoethyl acrylate benzyl chloride quaternary salt (80% aqueous solution, available from Nalco Chemical Co. of Naperville, IL), 45.5 g dimethylaminoethyl acrylate methyl chloride quaternary salt (80% aqueous, available from CPS Chemical Company Old Bridge, N.Y.), 18.8 g glycerin, 45.9 g of the homopolymer of dimethylaminoethyl acrylate methyl chloride quaternary (20% aqueous soln. -ning, available from Nalco Chemical Co. Naperville, IL), 16.7 g of a copolymer of diallyldimethylammonium chloride and dimethylaminoethyl acrylate benzyl chloride quaternary (15% aqueous solution available from Nalco Chemical Co., Naperville, IL), 1.5 g of a 1.0% aqueous solution of sodium bisulfite, 0.5 g of sodium diethylenetriamine pentaacetate (DABERSEEN 503 available from Derpol S.A. in Spain, 45% aqueous solution), 135.0 g of ammonium sulfate and 332.3 g of deionized water. The mixture was then warmed to 35°C under a constant nitrogen purge with stirring at 90 rpm. After 35°C is reached and under a constant purge of nitrogen, 3.7 g of a 1.0% aqueous solution of 2,2'-azobis(N,N'-dimethylisobutyramide)dihydrochloride (WAKO VA-044 available from Wako Chemicals, Dallas, TX) was added to the reaction mixture and the temperature was maintained for about 16 hours. The temperature was then raised to 50°C and 1.5 g of a 10% aqueous solution of ammonium persulfate and 1.5 g of a 10% aqueous solution of sodium bisulfite added. The temperature was maintained for one hour, cooled to ambient temperature, and 45.0 g of ammonium sulfate, 10.0 g of sodium thiosulfate and 10.0 g of acetic acid were added. The final product was a smooth milky white dispersion with a bulk viscosity of 1950 eps. After dilution to 0.5% active polymer, a solution viscosity of 74 eps in 2% aqueous ammonium sulfate was obtained.

Example 2

To determine the increasing effectiveness of the higher polymer solid polymers synthesized according to the method of Example 1 in improving the clarity of wastewater, jar tests were conducted in a pet food production facility. 200 ml samples of untreated effluents were taken from a sump in the plant before the receiving sump. An appropriate amount of polymer was added to the sample at a pH of 7.1. The solution was mixed vigorously for 5 seconds, then slowly for 30 seconds.

The clarity of the supernatant was determined by a visual evaluation with values designated from 1 to 10, with 10 being the most free of solids and most desirable. The flock size is also based on a visual evaluation, in which a larger flock (higher numbers) is more desirable.

Table I illustrates the results of the comparison of polymer A (20% active dispersion polymer DR-3000, available from Derypol S.A. Corporation in Spain) and polymer B (25% active dispersion polymer, synthesized according to the method described in Example 1). The molecular weights of the two polymers were considered to be equal based on the fact that polymer A and polymer B had equivalent reduced specific viscosity readings as recorded in 0.125N NaNO 3 solutions.

The dosages of the products in Table I were adjusted to an equal polymer active basis. Normally one would expect equal performance on an active basis since the polymers are of the same chemical composition and molecular weight, but in this case increased efficiency and activity was evident with polymer B of this invention over that obtained with commercially available polymer A. Superior flock size and water clarity were achieved with polymer B compared to polymer A, therefore a significantly lower treatment dosage can be used.

The surprising results were obtained at 25% concentration values. One skilled in the art familiar with this surprisingly large result would then understand that even higher concentrations would also produce this enhanced effect.

Polymer A = 20% active dispersion polymer DR-3000, available from Derypol S.A. Corporation in Spain.

Polymer B = 25% active dispersion polymer, synthesized according to the method described in example 1.

1 = dosage of polymer listed on an equal active basis.

2 = scale from 1 - 10, where 10 is most desirable as it represents the largest herd size. 3 = scale from 1 - 10, with 10 being the most desirable as it represents the highest clarity.

Example 3

A comparison of the polymers synthesized according to the procedure of Example 1 was also made for effectiveness as a treatment for the purposes of sludge dewatering on a twin feed press in a food production facility.

Polymer A and Polymer B were fed into the food processing wastewater stream using a NALMAT dosing system (available from Nalco Chemical Co., Naperville,

IL) which was previously used for experiments with latex polymers. An initial dilution was performed and the polymer

was prepared as a dilute solution. The solution of polymer B had to be prepared at a lower concentration than polymer A due to the much higher Brookfield viscosity. A primary dilute polymer was initially prepared

with the NALMAT dosing system followed by a second dilution with a static mixer to reach a lower concentration. The two dilution strengths are indicated in Table II's results.

The turbidity of the filtrate released from the belt filter press was measured with a Hach® DR-2000 spectrophotometer. The lower the turbidity reading, the better the performance of the polymer. The cake solids (finished sludge at the outlet of the belt filter press) were determined gravimetrically according to standard procedures. The higher the cake solids, the more effective the treatment in dewatering the removed solids waste water (or sludge). The cake solids can be artificially high when the performance of the polymer is poor and a significant amount of solids is pushed out of the machine. Therefore, the overall performance of the polymer must be considered. Since the performance of a baler is mainly based on visual evaluation, the following parameters were observed: flock size and shape; free drainage zone clarity; wedge zone mud stability (pressing); and press stability (which includes cake tackiness and mat characteristics).

These results are shown in Table II. Improved performance was obtained with polymer B over a commercially available polymer A. As a result of treatment with polymer B, the cake solids were similar to polymer A. However, with polymer B the overall quality was very good, the belt was free of blinding (ie - plugged belt) and the clarity of the filtrate was superior at a lower dosage compared to polymer A. As in example 2, one would normally expect a similar performance on an active basis since the polymers are of the same composition and molecular weight. However, increased efficacy and activity were evident with polymer B according to this invention compared to that obtained with the commercially available polymer A.

N/A = not available.

Polymer A = 20% active dispersion polymer DR-3000, available from Derypol S.A. Corporation in Spain.

Polymer B = 25% active dispersion polymer, synthesized according to the procedure described in Example 1.

1 = dosage of polymer listed on an equal active basis.

2 = listed as solution concentration of active polymer. The first number represents the primary dilution, the second number represents the secondary dilution. 3 = higher percentages of cake solids are more desirable.

4 = lower turbidity is more desirable.

Example 4

The polymers synthesized according to the method of Example 1 were also compared for their ability to dewater sludge during centrifugation from oily grease-containing wastewater at a wastewater disposal facility.

Polymer A and polymer B were fed in-line using a Gear pump. With this type of arrangement, a change in the dosage would automatically lead to a change in the solution strength as shown in table IMPDH.

The clarity of the centrate (the effluent from the centrifuge) and the cake quality were compared qualitatively on a visual basis and the results are summarized in Table III. Very good performance was obtained with both polymers, but that of polymer B was superior.

For Table III, the performance of the polymer was better the lower the value of the centrate clarity. Although centrate clarity was similar between the two polymers at equal dosage, polymer B was superior due to the high cake quality (drier cake, less sticky, less compact) over the dosage range. In this example, as with the previous examples, one would normally expect equal performance on an active basis since the polymers had the same chemical composition and molecular weight. Table III indicates that increased efficiency and activity was demonstrated with polymer B according to this invention compared to that obtained with the commercially available polymer A.

Polymer A = 20% active dispersion polymer DR-3000, available from Derypol S.A. Corporation in Spain.

Polymer B = 25% active dispersion polymer, synthesized according to the procedure described in Example 1.

1 = dosage of polymer listed on an equal active basis.

2 = listed as solution concentration of active polymer.

3 = scale of 0 - 3, 0 represents highest water clarity and is most desirable.

Example 5

The polymers prepared according to the method of Example 1 were also compared for their ability to dewater sludge composed of inorganically contaminated railway soil. A procedure similar to that of Example 2 was used to obtain the results in Table IV.

The dosage of the polymers in Table IV was adjusted to an equal polymer active base. The performance of the polymers was evaluated in terms of floc size (the largest floc size is the most desirable), sludge settling rate (a faster settling rate is more desirable), floc stability against shearing is more desirable) and drainage rate (highest volume of water drained is most desirable). Although one would normally expect equal performance on an active basis since the polymers are of the same chemical composition and molecular weight, Table IV shows that increased efficiency and activity were evident with polymer B over that obtained with commercially available polymer A.

Polymer A = 20% active dispersion polymer DR-3000, available from Derypol S.A. Corporation in Spain.

Polymer B = 25% active dispersion polymer, synthesized according to the procedure described in Example 1.

1 = dosage of polymer listed on an equal basis.

2 = listed as solution concentration of active polymer.

3 = larger herd is more desirable.

4 = faster descent is more desirable.

5 = greater flock stability is more desirable.

6 = faster drainage is more desirable.

Example 6

The polymers synthesized according to the procedure of Example 1 were also compared for their retention and drainage capabilities in a recycled paperboard mill.

Both polymer A and polymer B were fed directly in-line before the pressure screen. A simple static mixer was used to prepare the polymer solution. No aging tank was required.

The performance of the two polymers was evaluated by measuring first pass retention (FPR). FPR is a measure of the amount of fibres, fines and fillers that were retained in the paper sheet and was calculated with the following equation:

A = concentration of inlet box pulp (g/l)

B = concentration of the white water (ie filtrate) (g/l).

It is desirable to have as high a percentage of FPR as possible. As clearly evidenced in Table V, polymer B was more effective than polymer A since a significantly lower dosage of polymer B was required to achieve the same percent FPR as that achieved using polymer A. Again, one would normally expect equal performance on a active base since the polymers are of the same chemical composition and molecular weight, but in this case increased efficiency was evident with polymer B according to the present invention compared to that obtained with commercially available polymer A.

Polymer A = 20% active dispersion polymer DR-3000, available from Derypol S.A. Corporation in Spain.

Polymer B = 25% active dispersion polymer, synthesized according to the procedure described in Example 1. 1 = higher percentages of first pass retention are desired. 2 = dosage of polymer listed on an equal active basis.

Example 7

The polymers synthesized according to the methods of Example 1 were also compared in their ability to dewater oily sludge from a refinery. A sludge sample was collected before the twin belt press was used for dewatering. The polymers were evaluated using a free drainage test carried out as follows: the desired amount of polymer was added to 200 ml of sludge and mixed with 10 inversions using graduated cylinders. The test charge was emptied into a tube resting on top of a filter cloth and timing was immediately started. The free drainage volume achieved after 10 seconds was recorded.

The results are shown in Table VI where the drainage volume at 10 seconds is given. The higher the drained volume, the more efficient the dewatering. As clearly shown in Table IV, polymer B's performance was better than polymer A's on an active basis, because polymer B is both more efficient (higher volume drained) and more effective (less dosage required). Again, one would normally expect equal performance on an active basis because the polymers are of the same chemical composition and molecular weight, but in this case increased efficiency was evident with polymer B of this invention over that obtained with the commercially available polymer A.

Polymer A = 20% active dispersion polymer DR-3000, available from Derypol S.A. in Spain.

Polymer B = 25% active dispersion polymer, synthesized according to the procedure described in Example 1.

1 = dosage of polymer listed on an equal active basis.

2 = higher drainage is more desirable.

Changes can be made in the composition, operation and arrangement of the method according to the present invention described herein without deviating from the concept and scope of the invention as defined in the following claims.

Claims (11)

1. A method for clarifying and dewatering waste water, comprising adding to the waste water an effective amount of a water-soluble cationic polymer dispersion containing at least 25% by weight polymer solids, in which the water-soluble cationic polymer dispersion is prepared by polymerizing monomers under conditions of free radical formation in an aqueous solution of a anionic salt in the presence of two or more stabilizing polymers, characterized in that the monomers are selected from the group consisting of: (a) at least 5 mole percent of a cationic monomer of the formula in which R 1 is selected from the group consisting of H and CH 3 , R 2 and R 3 are selected from C 1 -alkyl and C 2 -alkyl, Ai is 0, Bi is C2-alkyl or C3-alkyl, and Xi~ is an anionic counterion and (b) a monomer of formula: in which R4 is H or CH3, R 5 and R 6 are selected from C 1 -alkyl and C 2 -alkyl, R 7 is H, C 1 - or C 2 -alkyl, and X2~ is an anionic counterion and (c) at least 5 mole percent of acrylamide or methacrylamide, wherein the stabilizing polymers are cationic polymers which are at least partially soluble in the aqueous solution of the anionic salt, the stabilizing polymers comprising: (a) at least one cationic polymer consisting of diallyldimethylammonium chloride and a monomer of the formula in which R 1 is H or CH 3 , R 2 and R 3 are selected from C 1 -alkyl and C 2 -alkyl, Ai is 0, Bi is C2-alkyl or C3-alkyl, and Xi~ is an anionic counterion, and (b) at least one cationic polymer consisting of cationic monomers of formula: in which R4 is H or CH3, R 5 and R 6 are selected from C 1 -alkyl and C 2 -alkyl, R7 is H, C1- or C2-alkyl, A2 is 0, B2 is C2-alkyl or C3-alkyl, and X2~ is an anionic counterion. 2. Method according to claim 1, characterized in that the waste water is selected from industrial waste water and municipal waste water. 3. Method according to claim 2, characterized in that the industrial waste water is selected from food processing waste water, oily waste water, paper mill waste water and inorganically polluted waste water. 4. Method according to claim 1, characterized in that the anionic salt is selected from phosphates, sulphates, chlorides and mixtures thereof. 5. Method according to claim 1, characterized in that it further comprises adding an effective amount of at least one coagulant to the waste water. 6. Method according to claim 1, characterized in that the cationic dispersion polymer is produced from monomers selected from the group consisting of: (a) at least 5 mol percent of dimethylaminoethyl acrylate benzyl chloride quaternary salt, (b) dimethylaminoethyl acrylate methyl chloride quaternary salt, and (c) at least 5 mol percent of acrylamide. 7. Method according to claim 1, characterized in that the stabilizing polymers are a homopolymer of dimethylaminoethyl acrylate-methyl chloride quaternary and a copolymer of dimethylaminoethyl acrylate benzyl chloride quaternary and diallyldimethylammonium chloride. 8. Method for improving retention and drainage in a paper supply, comprising adding to the paper supply an effective amount of a water-soluble cationic polymer dispersion containing at least 25 percent by weight polymer solids, wherein the water-soluble cationic polymer dispersion is prepared with polymerization monomers under conditions of free radical formation in an aqueous solution of a anionic salt in the presence of two or more stabilizing polymers, characterized in that the monomers are selected from the group consisting of: (a) at least 5 mole percent of a cationic monomer of formula in which R 1 is selected from the group consisting of H and CH 3 , R 2 and R 3 are selected from C 1 -alkyl and C 2 -alkyl, Ai is 0, Bi is C2-alkyl or C3-alkyl, and Xi~ is an anionic counterion and (b) a monomer of formula: in which R4 is H or CH3, R 5 and R 6 are selected from C 1 -alkyl and C 2 -alkyl, R7 is H, C1- or C2-alkyl, A2 is 0, B2 is C2-alkyl or C3-alkyl, and X2~ is an anionic counterion and (c) at least 5 mole percent of acrylamide or methacrylamide, wherein the stabilizing polymers are cationic polymers that are at least partially soluble in the aqueous solution of the anionic salt, the stabilizing polymers comprising: (a) at least one cationic polymer consisting of diallyldimethylammonium chloride and a monomer of formula in which R 1 is H or CH 3 , R 2 and R 3 are selected from C 1 -alkyl and C 2 -alkyl, Ai is 0, Bi is C2-alkyl or C3-alkyl, and Xi~ is an anionic counterion, and (b) at least one cationic polymer consisting of cationic monomers of formula: in which R4 is H or CH3, R 5 and R 6 are selected from C 1 -alkyl and C 2 -alkyl, R7 is H, C1- or C2-alkyl, A2 is 0, B2 is C2-alkyl or C3-alkyl, and X2~ is an anionic counterion. 9. Method according to claim 8, characterized in that the anionic salt is selected from phosphates, sulfates, chlorides and mixtures thereof. 10. Method according to claim 8, characterized in that the cationic dispersion polymer is prepared from monomers selected from the group consisting of: (a) at least 5 mole percent of dimethylaminoethyl acrylate benzyl chloride quaternary salt; (b) dimethylaminoethyl acrylate methyl chloride quaternary salt; and (c) at least 5 mole percent of acrylamide. 11. Method according to claim 8, characterized in that the stabilizing polymers are a homopolymer of quaternary dimethylamine ethyl acrylate and methyl chloride and a copolymer of quaternary dimethylaminoethyl acrylate benzyl chloride and diallyldimethylammonium chloride.