Latex concentration/recovery

Membrane-retained components are collectively called concentrate or retentate. Materials permeating the membrane are called filtrate, ultrafiltrate, or permeate. It is the objective of ultrafiltration to recover or concentrate particular species in the retentate (eg, latex concentration, pigment recovery, protein recovery from cheese and casein wheys, and concentration of proteins for biopharmaceuticals) or to produce a purified permeate (eg, sewage treatment, production of sterile water or antibiotics, etc). Diafiltration is a specific ultrafiltration process in which the retentate is further purified or the permeable sohds are extracted further by the addition of water or, in the case of proteins, buffer to the retentate. 

GeneraL Claiiflcation and thickening duties, recycling of pigment dispersions, latex product recovery and concentration. 

The main distinguishing features of evaporated latex is that 100% mbbet recovery is achieved, but unlike the other methods, the nonmbbets ate also concentrated. The most weU-known evaporated latex is Standard Revertex (trade name from Revertex). 

During 1973, at a chloroprene polymerization plant in the United States, airborne concentrations of chloroprene were found to range from 14 to 1420 ppm [50-5140 mg/m ] in the make-up area, from 130 to 6760 ppm [470-24 470 mg/m in the reactor area, from 6 to 440 ppm [22-1660 mg/m ] in the monomer recovery area and from 113 to 252 ppm [409-912 mg/ni l in the latex area (Infante et al., 1977). Concentrations in the air inside a Russian polychloroprene rubber plant were 14.5-53.4 mg/m (Mnatsakayan et al., 1972). In a Russian chloroprene latex manufacturing facility, chloroprene concentrations varied from 1 to 8 mg/m (Volkova et al., 1976). 

Figure 6. Variation of recovery with successive injections of a 357 nm polystyrene latex at a surfactant concentration of 6mM SLS.

ASSI Frovifors Bruk, Board mill, Frovifors, Sweden In 1991, two CR filters were installed at ASSl Frovifors Bruk board mUl in Frovifors (Sweden) to concentrate and recover the waste latex coating from an air-knife coater. The 50 kg/mol cutoff polysulfone membrane produces a flux of 200 L/(m h). The mUl uses Ti02 pigment, which makes the recovery process extremely economical. The UF operates at a constant concentrate sohds concentration of 20% continuously for 10 days between cleanings [1,130]. When concentrating a standard coating color effluent steady flux of 120 L/(m h) at a coating color concentration of 10%-15% (50 L/(m h) at 40%) is achieved [36]. 

Concentration of latex particles in water and recovery of latex particles from wastewaters (painting processes, for example). 

UF has also been used to clean up polymerization kettle wash waters before disposal. The dilute latex can be concentrated from 0.5 to 25%, thus reducing the volume to be hauled away to /so of the original volume. In some cases, the waste latex is recycled for reformulation. Where there is a significant sewer tax, UF is an economical alternative even without recovery of the latex. The dilution of latex during polymerization kettle rinse-down may deplete the surfactant on the polymer particles or introduce multivalent ions, resulting in decreased latex stability. Adjustment of pH or addition of surfactant can prevent coagulation of the latex on the membrane. 

Ultrafiltration is used in many different processes at the present time. Some of these are separation of oil-water emulsions, concentration of latex particles, processing of blood and plasma, fractionation or separation of proteins, recovery of whey proteins in cheese manufacturing, removal of bacteria and other particles to sterilize wine, and clarification of fruit juices. 

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