256446 Membrane Facilitated Stripping of VOCs From Latex
Membranes promise improved efficiency of distillation and gas-liquid contacting operations by increasing the interfacial area per unit volume and by breaking the link between hydrodynamics and flow rates. In particular, membranes allow independent control of flow rates to take best advantage of diffusion and thermodynamic behavior to effect separation without deleterious backmixing or flooding. Although this concept dates from 2003, few commercial developments of this technology have since been reported, apparently because of the challenge involved in displacing existing, more familiar, and already commercially-viable distillation technologies.
To be commercially successful, membranes must overcome a particularly vexing limitation of current technology without adding significant mass transfer resistance or fouling. With this in mind, we introduce a new membrane-based process involving stripping of volatile organic compounds (VOCs) from emulsion polymer latex used in water-borne paint formulations, an application driven by the market’s demand for high-performance paints having little or no odor. Conventional distillation and stripping technology involves direct contact of steam, nitrogen, or air with the surfactant-laden latex. This typically causes severe foaming which necessitates a reduction in throughput and thus compromises productivity of conventional process equipment. By placing a membrane between the liquid and the vapor or gas, foaming is completely eliminated. Moreover, the membrane resistance frequently is negligible.
Thus the use of a membrane offers significant improvement in the stripping of latex products, allowing efficient vapor-liquid or gas-liquid contacting without foaming and permitting a more compact and cost-effective operation. This presentation describes process concepts and presents data demonstrating the utility of the membrane process for stripping latex (Dow patents pending).
Background: G. Zhang and E. L. Cussler, "Hollow Fibers as Structured Distillation Packing," J. Membrane Sci. 2003, 215, 185-193; and "Distillation in Hollow Fibers," AIChE J. 2003, 49, 2344-2351.