Semipermeable membrane devices, and in particular semipermeable ultrafiltration membrane devices, have been employed to concentrate or separate polymeric emulsions or latices. Such latices typically comprise solid polymeric particles dispersed in water or a water-alcohol or other liquid phase. Often such latices contain a surfactant material which has been added during the manufacturing process to disperse the polymeric particles in the liquid phase. Typical latices would include, but not be limited to: styrene-butadiene latices, polyvinyl-chloride latices and the like.
Past commercial attempts to concentrate such latices through the removal of a portion of the liquid phase after manufacture from a permeate zone of a semipermeable membrane device have not been successful. Such lack of success has been due in part to the inability of the semipermeable membranes to maintain the initially or originally high flux rates during the separation or concentration process. Quite often the flux rates rapidly diminish with time to an unsatisfactory or very low flux value, and, therefore, require, such as described in my prior application (now U.S. Pat. No. 3,956,114, issued May 11, 1976), the periodic employment of a solvent in order to help maintain or restore such original flux value. Thus, it is desirable to provide a rapid, simple, and inexpensive process which will permit the concentration of polymeric latices in a semipermeable membrane process, such as a low-pressure, ultrafiltration process, and for such process to operate in a commercially satisfactory and continuous manner without severe flux degradation.
USPTO Backgrounds
USPTO Backgrounds