Liquid purification or separation – Processes – Making an insoluble substance or accreting suspended...
Reexamination Certificate
2000-04-20
2002-06-04
Hruskoci, Peter A. (Department: 1724)
Liquid purification or separation
Processes
Making an insoluble substance or accreting suspended...
C210S728000, C210S734000, C516S174000
Reexamination Certificate
active
06398967
ABSTRACT:
TECHNICAL FIELD
This invention is directed to a method of clarifying water using low molecular weight, low charge cationic dispersion polymers.
BACKGROUND OF THE INVENTION
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, modern methods often rely on mechanical separation techniques that 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 that settle suspended 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, emulsion breaking, drainage aids in the manufacture of pulp and paper and flotation aids in mining processing.
Clarification generally refers to the removal of nonsettleable material by coagulation, flocculation and sedimentation. Coagulation is the process of destabilization of the colloid by neutralization of the surface charge of the colloid. Once neutralized, particles no longer repel each other and can come together to form larger settleable solids. Coagulation is necessary for removal of colloidal sized suspended matter. Flocculation is the process of bringing together the destabilized, “coagulated” particles to form a larger agglomeration or floc for the purpose of increasing the solid-liquid separation process.
Clarification chemicals are typically utilized in conjunction with mechanical clarifiers for the removal of solids from the treated water. The clarification chemicals coagulate and/or flocculate the suspended solids into larger particles, which can then be removed from the water by gravitational settling or flotation.
Depending upon the characteristics of the water being treated, differing chemical types and programs may be utilized. It is conventional to utilize a dual polymer program for clarification of raw water in which an aluminum chemistry is commonly used with an organic coagulant to remove soluble color and other contaminants. Clarification of waste waters can depend on the nature of the solids being removed and the mechanical process. Chemical treatment for waste water clarification is typically employed when colloidal solids need to be removed so that the biochemical oxygen demand, chemical oxygen demand and total suspended solids being discharged to a receiving stream need to be minimized. Typically, this comprises using a low molecular weight cationic coagulant followed by a higher molecular weight flocculant.
Processes for the preparation of high molecular weight cationic dispersion polymer flocculants are described in U.S. Pat. Nos. 5,006,590 and 4,929,655. Use of a cationic dispersion polymer flocculant and a cationic coagulant for clarifying ink-laden water obtained from the recycling of paper stocks is disclosed in commonly assigned U.S. Pat. No. 5,750,034. High molecular weight, high polymer actives cationic dispersion polymers for water clarification, dewatering and retention and drainage are disclosed in commonly assigned U.S. Ser. No. 09/054,980. The use of high molecular weight cationic dispersion polymers as retention and drainage aids in papermaking is disclosed in commonly assigned EPA 97116538.6 and U.S. Ser. No. 09/010,156.
SUMMARY OF THE INVENTION
In its principal embodiment, this invention is directed to a method of clarifying water comprising adding to the water an effective clarifying amount of a low molecular weight water-soluble cationic dispersion polymer prepared by polymerizing one or more cationic monomers and one or more nonionic monomers and one or more chain transfer agents under free radical forming conditions in an aqueous solution of an anionic salt in the presence of a stabilizer polymer, wherein the cationic dispersion has a cationic charge of from about 1.0 mole percent to about 75 mole percent and an RSV of from about 0.2 dl/g to about 6 dl/g.
The cationic dispersion polymers of this invention have superior performance than conventional coagulants for clarifying raw, process and waste waters. The polymers of this invention also show equivalent or improved performance when the polymers are used as a coagulation aid for conditioning sludge for dewatering. The use of these polymers affords removal of particulate materials without the unwanted addition of oils and surfactants contained in conventional latex polymers. Additionally, these polymers require no inverter system and can be introduced to the process stream using simple feeding equipment.
The superior performance of very low molecular weight cationic dispersion polymers having significantly lower cationic charge than conventional coagulants, which typically have a cationic charge of 100 mole percent is unexpected. It is theorized that the mode of action is not solely charge neutralization, but may employ a mechanism of shielding where the anionic charge on the colloidal particle is effectively shielded from the anionic charge of another colloidal particle and the particles can agglomerate.
A further advantage of the cationic dispersion polymer of this invention is that it can be used as the sole treatment agent and the performance is often much greater than the conventional coagulants. Though other treatment agents may be added as adjuncts, they are not required for activity.
In another embodiment, this invention is directed to a method of dewatering sludge comprising adding to the sludge of an effective amount of a low molecular weight water-soluble cationic dispersion polymer prepared by polymerizing one or more cationic monomers and one or more nonionic monomers and one or more chain transfer agents under free radical forming conditions in an aqueous solution of an anionic salt in the presence of a stabilizer polymer, wherein the cationic dispersion has a cationic charge of from about 1.0 mole percent to about 75 mole percent and an RSV of from about 0.2 dl/g to about 6 dl/g.
In another embodiment, this invention is directed to a method for improving retention and drainage performance in a papermaking process comprising adding to a papermaking slurry an effective amount of a low molecular weight water-soluble cationic dispersion polymer prepared by polymerizing one or more cationic monomers and one or more nonionic monomers and one or more chain transfer agents under free radical forming conditions in an aqueous solution of an anionic salt in the presence of a stabilizer polymer, wherein the cationic dispersion has a cationic charge of from about 1.0 mole percent to about 75 mole percent and an RSV of from about 0.2 dl/g to about 6 dl/g.
Further, the aqueous dispersion of this invention, if required in the form of an aqueous solution resulting from dilution with water, can be advantageously used in a number of technological fields as flocculating agents, thickeners, soil conditioners, adhesives, food additives, dispersants, detergents and additives for medicines or cosmetics, among others.
DETAILED DESCRIPTION OF THE INVENTION
Definitions of Terms
As used herein, the following abbreviations and terms shall ha
Cardile Richard P.
Johnson Cathy C.
Sparapany John W.
Zagala Angela P.
Breininger Thomas M.
Hruskoci Peter A.
Martin Michael B.
Nalco Chemical Company
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