(41b) Membranes, Phase Interfaces and Separations: Novel Techniques and Membranes -- an Overview
Membranes and phase interfaces share a close relation in separations.The phase interface may be fluid-fluid,fluid-solid or solid-solid. In conventional membrane separations,two phase interfaces exist on two sides of the membrane, two solid-fluid interfaces for solid membranes. Conventional equilibrium separations however have only one phase interface.Such an interface in gas-liquid, vapor-liquid, liquid-liquid, subcritical/supercritical fluid-liquid separation systems may be created by immobilization at a membrane pore mouth as in membrane contactor-based nondispersive separations. Recreation of conventional membrane separation is achieved by having two fluid-fluid phase interfaces immobilized on two sides of a porous membrane(as in SLM,ILM,SGM,osmotic distillation,membrane distillation)or on two contiguous porous membranes(as in CLM).Membrane emulsification/sparging/degassing leads to dispersion-based creation of phase interfaces and contacting.Antisolvent crystallization via dispersion/mixing through membrane pores creates new solid-liquid interfaces. Convective transport through membrane pores provides efficient solid-liquid contacting in membrane chromatography.The membrane pore's large L/D ratio and presence of ligands on pore surfaces create an easily accessed high-surface area solid-liquid sorbent interface.Convection through membrane channel and lateral diffusion through membrane pores overcome deficiencies of micron-sized sorbent filled beds and allow solid-gas contacting. Membranes having high aspect ratio flakes create flat solid-solid phase interfaces which can yield high selectivity via large tortuosity. Flat membranes can create many liquid-solid membrane interfaces when stacked on top of one another as in internally-staged ultrafiltration. Stacking of flat membranes in membrane chromatography generates very high L/D solid-liquid interfaces on the pore surfaces. Bonding/adhesion of solid-solid phase interface is critical in making microporous and mixed matrix membranes.Compatibilized interface between zeolites and the polymer matrix is essential for mixed matrix membranes. Interface rupture in polymer blends under stress can generate microporosity in a film. The critical role played by phase interfaces and membranes vis-a-vis many separations will be highlighted.