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US 4,720,346 AGranted
Flocculation processes
AssigneeAllied Colloids Limited
InventorsPeter Flesher, David Farrar, John R. Field
Life of this patent
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AssigneeAllied Colloids Limited
InventorsPeter Flesher, David Farrar, John R. Field
Estimating the term…
When flocculating an aqueous suspension of suspended solids using a high molecular weight synthetic polymeric flocculant, the shear stability of the flocs is increased if the polymeric material includes polymeric particles of below 10 .mu.m dry size. The flocculated solids can therefore be subjected to shear without increasing the amount of discrete suspended solids in the aqueous medium and generally they are subjected to shear by shearing the aqueous medium containing them, either before dewatering, generally on a centrifuge, piston press or belt press, or by continuously agitating them, for instance in a chemical reaction medium. The polymeric material is generally formed by mixing into water polymeric particles made by reverse phase or emulsion polymerization in the presence of added cross linking agent. Alternatively, particles insolubilized by insoluble monomer may be used. A reverse phase dispersion of water soluble polymer may be used if the particles remain undissolved, e.g. if they are added in the absence of an oil in water emulsifying agent.
A process for flocculating an aqueous suspension of suspended solids comprising, adding to the suspension a flocculating amount of a synthetic polymeric flocculant material to form thereby an aqueous medium containing flocculated suspended solids and in which the said polymeric flocculant material at the time of addition to the suspension has a specific viscosity (measured by a capilliary flow viscometer at 34.degree. C. on a 0.5% solution in deionised water) above 10 and comprises polymeric particles that have a dry size of below 10 .mu.m, the polymeric material is added in a floc stabilising amount, and the flocculant solids are subjected to shear in the presence of the aqueous medium substantially without increasing the amount of suspended solids in the aqueous medium to reduce the size and increase the shear stability of said flocculated suspended solids.
A process in which an aqueous suspension of suspended solids is flocculated by adding to the suspension a flocculating amount of a synthetic polymeric flocculant material to form thereby an aqueous medium containing flocculated suspended solids and in which the said polymeric flocculant material at the time of addition to said suspension has a specific viscosity (measured by a capilliary flow viscometer at 34.degree. C. on a 0.5% soluton in deionized water) above 10, and is formed by polymerization of a monomer selected from the group consisting of water soluble acrylic acid salt, water soluble 2-acrylamido methyl propane sulphonic acid salt, dialkylaminoalkyl (meth) acrylates and their quaternary or acid addition salts, and dialkylaminoalkyl (meth) acrylamides and their quaternary or acid addition salts, and blends of any such monomer with acrylamide and has been made by polymerization in the presence of added diethylenically unsaturated cross linking agent in an amount of from 1 to 100 ppm and is in the form of polymeric particles that are water insoluble but water swellable and that have a dry size of below 10 .mu.m, the aqueous medium containing the flocculated solids is subjected to shear substantially without increasing the amount of suspended solids in the aqueous medium to reduce the size and increase the shear stability of said flocculated suspended solids, the amount of the polymeric material that is added to the suspension is from 50 to 150% of the amount that gives maximum floc size after the application of shear to the aqueous medium, and the aqueous medium is then dewatered on a centrifuge, piston press or belt press.
Dependencies are inferred from the claim text.