Mass transfer studies in liquid membrane hydrocarbon separations

The effects of operating parameters on mass transfer coefficients of benzene permeating through liquid surfactant membranes have been studied. The study indicates that major resistance to mass transfer lies in the aqueous membrane phase. Mixing intensities used in forming the emulsion and dispersing it in the external phase have relatively less influence. Using a simple membrane film model approach, these mass transfer coefficients can be predicted within reasonable limits. The membrane film thickness to be used in these predictions varies with the holdup of micro phase in the emulsion, and can be estimated from the recently proposed equation of Kataoka et al. 1. Introduction ~ Liquid membranes were first introduced by Li in 1968 [1,2], and are increasingly becoming important in low energy separation processes. Liquid membranes offer the principle advantages of higher selectivities and surface areas over conventional extraction and solid membrane processes. Liquid membranes, also known as "double emulsions", are of two types, o/w/o and w/o/w emulsions (o=oil; w=water). In the formation of a liquid membrane system, an emulsion of two immiscible phases is prepared, and this is dispersed into a third continuous phase. The encapsulated phase in the emulsion and the third phase are generally miscible, and the interstitial liquid between the phases acts as a liquid membrane. Surfactants or additives are added to the membrane phase to maintain stability, permeability and selectivity. Liquid membrane hydrocarbon separations may be effected by a separation mechanism based on differential permeation rates through the membrane due to differences in solubility and/or diffusion coefficients of components in the membrane. Further, significant enhancement of rates and selectivities can be achieved by encapsulating or trapping a reactive species inside the micro-droplets which will convert the solute species into a nonpermeating product; this *To whom correspondence should be addressed. 0376-7388/90/$03.50 @ 1990 - Elsevier Science Publishers B.V