Liquid purification or separation – Processes – Making an insoluble substance or accreting suspended...
Reexamination Certificate
1999-09-08
2001-04-17
Hruskoci, Peter A. (Department: 1724)
Liquid purification or separation
Processes
Making an insoluble substance or accreting suspended...
C162S189000, C210S727000, C210S734000, C210S928000, C516S172000
Reexamination Certificate
active
06217778
ABSTRACT:
TECHNICAL FIELD
This invention concerns a method of clarifying industrial waste water using a high molecular weight water-soluble anionic or nonionic dispersion polymer.
BACKGROUND OF THE INVENTION
Water-soluble polymeric flocculants are commonly used for clarifying suspensions of organic matter of a proteinaceous or cellulosic nature such as those found in sewage and industrial plant treatment effluents or in paper mills.
These suspended materials are hydrophilic in nature and often have specific gravities quite close to the aqueous liquors in which they are suspended, and differ in a marked way with more hydrophobic mineral suspensions in that they are frequently much more difficult to flocculate economically with chemical reagents prior to a physical dewatering step such as filtration, flotation, sedimentation or dewatering. These difficulties are particularly noticeable when higher proportions of suspended matter are present, commonly involving concentrations of 0.5 percent by weight and upwards where the suspensions take on a paste-like consistency and are commonly described as sludges.
It is well known that the clarification or dewatering of sewage and industrial sludges and similar organic suspensions may be aided by chemical reagents, added in order to induce a state of coagulation or flocculation which facilitates the process of solid/liquid or liquid/liquid separation from water. For this purpose, lime or salts of iron or aluminum have been utilized. More recently synthetic polyelectrolytes, particularly certain cationic and anionic copolymers of acrylamide, have been found to be of interest.
These types of polymers, which may be natural or synthetic, are broadly termed coagulants and flocculants. These polymers can be utilized in such diverse processes as emulsion breaking, sludge dewatering, raw and waste water clarification, drainage and retention aids in the manufacture of pulp and paper, flotation aids in mining processing and color removal.
In the water treatment field of solids/liquid separation, suspended solids are removed from water by a variety of processes, including sedimentation, straining, flotation, filtration, coagulation, flocculation, and emulsion breaking among others. Additionally, after suspended solids are removed from the water they must often be dewatered so that they may be further treated or properly disposed of. Liquids treated for solids removal often have as little as several parts per billion of suspended solids or dispersed oils, or may contain large amounts of suspended solids or oils. Solids being dewatered may contain anywhere from 0.25 weight percent solids, to 40 or 50 weight percent solids material. Solids/liquid or liquid/liquid separation processes are designed to remove solids from liquids, or liquids from liquids.
While strictly mechanical means have been used to effect solids/liquid separation, modem methods often rely on mechanical separation techniques which are augmented by synthetic and natural polymeric 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 which settle suspended inorganic particulates 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 recovery and emulsion breaking.
Regarding the mechanism of separation processes, particles in nature have either a cationic or anionic charge. Accordingly, these particles often are removed by a water soluble coagulant or flocculant polymer having a charge opposite to that of the particles. This is referred to as a polyelectrolyte enhanced solids/liquid separation process, wherein 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. Too little ionically charged polymer, and the suspended particles will not be charge neutralized and will thus still repel each other. Too much polymer, and the polymer will be wasted, or worse, present a problem in and of itself.
Notwithstanding the variety of commercially available polymers which have been found to effect solids/liquid separation, there are various circumstances which tend to limit the usefulness of these reagents. While for certain waste waters economical treatments with these known reagents are feasible, more often very high and cost-ineffective dosages of reagents are required for successful treatment. Moreover, variations often occur in waste water from any one source. For example, variations in the supply of material to the waste water/sludge/paper furnish process water and/or in the oxidizing conditions that may be involved in the production of these waters lead to a variety of particle types which must be removed. Furthermore, it is not uncommon to encounter solids which are, for some reason, not amenable to flocculation by any of the known polymeric flocculating agents. It is therefore an object of the invention to provide to the art a superior method for clarifying and dewatering industrial waste water.
Commonly assigned U.S. Pat. No. 5,605,970 discloses a process for preparing certain high-molecular weight anionic polymer dispersions. Commonly assigned U.S. Pat. No. 5,837,776 discloses certain high molecular weight anionic flocculants and a process for their preparation. A process for the production of a water-soluble polymer dispersion in the presence of a dispersant, wherein the dispersant may be a poly(2-acrylamido-2-methyl propane sulfonic acid (AMPS)) or a copolymer having 30 or more mole percent of AMPS is disclosed in EP 0 183 466.
SUMMARY OF THE INVENTION
In its principal aspect, this invention is directed to a method of clarifying and dewatering industrial waste water comprising adding to the waste water an effective amount of a high molecular weight water-soluble anionic or nonionic dispersion polymer wherein the dispersion polymer has a bulk Brookfield viscosity of from about 10 to about 25,000 cps at 25° C. and comprises from about 5 to about 50 weight percent of a water soluble polymer prepared by polymerizing under free radical forming conditions in an aqueous solution of a water-soluble salt in the presence of a stabilizer:
i. 0-100 mole percent of at least one anionic monomer, and,
ii. 100-0 mole percent of at least one non-ionic vinyl monomer;
wherein the stabilizer is an anionic water soluble polymer having an intrinsic viscosity in 1M NaNO
3
of from about 0.1-10 dl/g and comprises from about 0.1 to about 5 weight percent based on the total weight of the dispersion, and the water soluble salt is selected from the group consisting of ammonium, alkali metal and alkaline earth metal halides, sulfates, and phosphates and comprises from about 5 to about 40 weight percent based on the weight of the dispersion.
DETAILED DESCRIPTION OF THE INVENTION
“Monomer” means a polymerizable allylic, vinylic or acrylic compound.
“Anionic monomer” means a monomer as defined herein which possesses a net negative charge. Representative anionic monomers include acrylic acid, methacrylic acid, 2-acrylamido-2-methyl-1-propanesulfonic acid, acrylamidomethylbutanoic acid, maleic acid, fumaric acid, itaconic acid, vinyl sulfonic acid, styrene sulfonic acid, vinyl phosphonic acid, allyl sulfonic acid, allyl phosphonic acid, sulfomethylated acrylamide, phosphonomethylated acrylamide and the water soluble alkali metal, alkaline earth metal, and ammonium salts thereof. The choice of anionic monomer is based upon several factors including the ability of the monomer to polymerize with the desired comonomer, the use of the produced polymer, and cost. A preferred anionic monomer is acrylic acid.
In certain instances, it may be possible to chemically modify a non-ionic monomer component contained in the dispersion polymer of the invention after
Hurlock John R.
Maltesh Chidambaram
Maury Elise E.
Shing Jane B. Wong
Breininger Thomas M.
Hruskoci Peter A.
Martin Michael B.
Nalco Chemical Company
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