Mechanism of Degradation of Liquid Membranes and Washout Characteristics of the Membrane Liquids

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Present study is concerned with separation technique using liquid surfactant membranes(ELM) and supported liquid membranes(SLM).[1] The entrainment of water by emulsified dropletes was examined as well as the droplet breakdown for organic solvent-Span 80 systems. The breakdown of toluene membranes is more than those of higher parafinic hydrocarbons by a factor of 10. Thus it can be concluded that n-dodecane is most suitable as the solvent for ELMs.[2] Stabilities of SLMs impregnated with various organic solvents were tested in terms of the breakthrough time; the results show that the solvent having higher interfacial tension is more stable to washing out of the membrane liquids. Effect of materials and morphology of solid supports on the SLM-stability was examined from the contact angle <theta> of aqueous drop on SLMs. An extrapolating value to cos <theta> ->1 on a plot of cos <theta> versus contact time was introduced as a "critical wetting time", which can quantify the degradation of … More SLMs.[3] Liquid side mass transfer coefficient, <k_c> , in the flow channel through a SLM-device was determined for two types of SLM; flat sheet and hollow fiber modules. The <k_c> -values for the flat type SLM agree well with a theoretical equation for flat plate, while the external <k_c> of the hollow fiber was five to ten times as large as those for the flat plate. Transport coefficients for solute diffusion through the membrane liquid layer have no significant difference among the support polymers having various porosity.[4] In order to obtain higher recovery in SLM-operation, a multilayered flat type SLM was tested for the separation of Cr(VI) from the acid solutions. The addition of Cr(VI) to the stripping solution results in a remarkable improvement of the recovery due to the buffer effect.[5] To enlongate the life-time of SLMs, a regeneration mode of the membrane phase in SLMs was proposed, which utilized a buoyant force of membrane liquid and capillary action. The continuous regenerating SLM was demonstrated for the separation of heavy metals by use of a single hollow fiber module, and also the applicability to a multi-fiber module was confirmed. Less