Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2003-07-17
2004-06-22
Egwim, Kelechi C. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S082000, C525S244000, C525S313000, C525S329400, C525S329700, C525S329800, C525S329900
Reexamination Certificate
active
06753388
ABSTRACT:
TECHNICAL FIELD
This invention is directed to structurally-modified water-soluble polymers prepared by initiating polymerization of an aqueous solution of monomers under free radical polymerization and adding at least one modifier after at least 30% polymerization of the monomers has occurred, and to the use of the polymers as flocculants.
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.
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 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 and the use of polymeric flocculants for the treatment of industrial water, as sludge conditioners for the treatment of municipal water systems, as retention and drainage aids in the manufacture of paper, as chemicals for recovering useful and valuable substances from white water in the papermaking process and in emulsion breaking.
A benchmark test for evaluating the effectiveness of a flocculant is the so-called drainage test in which the polymer is added to sludge and mixed so that the polymer flocculates the sludge. The mixture is then poured through a belt filter press cloth and the rate at which water drains is taken as a measure of polymer performance.
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 that have been found to be capable of flocculating or coagulating sludges, there are various circumstances which tend to limit the usefulness of these reagents. While for certain sludges economical treatments with these known reagents are feasible, more often sludges require very high and cost-ineffective dosages of reagents for successful treatment. Moreover, variations often occur in sludge 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 sludges that are, for some reason, not amenable to flocculation by any of the known polymeric flocculating agents.
Therefore, there is a need for an improved family of polymers that provide better drainage at lower doses in sludge dewatering. Likewise, there is a continuing need for treatments to increase the efficiency of pulp and paper manufacture,
EP 202,780 discloses particulate cross-)inked copolymers of acrylamide with at least 5 mole percent dialkylaninoalkyl acrylate for use as flocculants in high-shear applications.
The addition of a cross-linking agent both at the beginning, and during the polymerization process under conditions such that its availability for reaction is substantially constant throughout the process is disclosed in U.S. Pat. No. 4,950,725.
EP 374,458 discloses water-soluble branched high molecular weight cationic flocculants formed from monomers polymerized in the presence of chain transfer agents such as isopropanol and branching agents such as methylene bisacrylamide, in which the chain transfer agent is added to prevent cross linking. Cross linking can render the polymer insoluble in water.
Addition of chain transfer agent at the conclusion of polymerization of a DADMAC/acrylamide copolymer to produce a linear higher molecular weight copolymer is disclosed in EP 363,024.
U.S. Pat. No. 4,913,775 discloses use of substantially linear cationic polymers such as acrylamide/dimethylaminoethyl acrylate methyl chloride quaternary salt copolymers and bentonite as additives in pulp or paper manufacture.
U.S. Pat. No. 5,393,381 discloses use of a branched cationic polyacrylamide powder such as an acrylamide/dimethylaminoethyl acrylate quaternary salt copolymer and bentonite for paper or cardboard manufacture.
SUMMARY OF THE INVENTION
We have discovered that the late stage addition to a polymerization reaction of a structural modifier as described herein results in formation of a more effective, structurally-modified flocculant. When the structural modifier is a chain-transfer agent, the resulting water-soluble polymers typically have a faster rate of solubilization, higher reduced specific viscosities and are more active than unmodified analogs. This is applicable to cationic, anionic, or nonionic polymers, synthesized using water-in-oil emulsion, dispersion, or gel polymerization techniques.
Accordingly, in its principal aspect, this invention is directed to a water-soluble polymer prepared by initiating polymerization of an aqueous solution of monomers under free radical polymerization conditions to form a polymer solution and adding at least one structural modifier to the polymer solution after at least 30% polymerization of the monomers has occurred.
DETAILED DESCRIPTION OF THE INVENTION
Definitions of Terms
As used herein, the following abbreviations and terms shall have the following meanings.
“AcAm” for acrylamide.
“DADMAC” for diallyldimethylammonium chloride.
“DMAEA” for dimethylaminoethyl acrylate.
“DMAEM” for dimethylaminoethyl methacrylate.
“DMAEA.BCQ” for dimethylaminoethyl acrylate, benzyl chloride quaternary salt.
“DMAEA.MCQ” for dimethylaminoethyl acrylate, methyl chloride quaternary salt.
“EDTA.4Na
+
” for ethylenediaminetetraacetic acid, tetrasodium salt.
“Alfonic®1412-60” is a ethoxylated linear alcohol (60% ethylene oxide), available from Vista Chemical Co., Houston, Tex.
“Span 80” for sorbitan monooleate available from ICI Specialty Chemicals, Wilmington, Del.
“Triton® N-101” for nonylphenoxy po
Guddendorf Tracey M.
Johnson Cathy C.
Maltesh Chidambaram
Sivakumar Ananthasubramanian
Whipple Wesley L.
Breininger Thomas M.
Egwim Kelechi C.
Martin Michael B.
Nalco Company
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