Effect of emulsion breakage on selectivity in the separation of hydrocarbon mixtures using aqueous surfactant membranes

Abstract

In liquid membrane separation processes emulsion breakage results in non-selective physical mixing of the feed mixture with the receiving solvent phase. In this paper a model is developed for describing the interphase transfer process, which takes emulsion breakage into account. The overall transfer is envisaged as a result of two parallel transfer mechanisms: (i) diffusive transport across the membrane and (ii) non-selective physical mixing of the feed with the receiving phase due to emulsion breakage. For selective removal of aromatics from non-aromatics in a feed mixture the “ideal” selectivity, β, obtained in the absence of non-selective breakage, will he given as the ratio of the products of the distribution coefficients times the diffusivity in the aqueous membrane phase. Experiments were carried out in a batch stirred cell to determine the permeation rates for a benzene-n-heptane mixture. From the experimentally observed selectivities the contribution due to emulsion breakage was estimated. This fractional breakage was in good agreement with values determined independently using a water-insoluble dye tracer technique, lending support to the developed model. Further experiments were carried out with the system 1-methylnaphthalene-dodecane, and breakage-corrected transfer rates were determined. The model developed in this paper, together with the experimental studies, sheds light on the mechanism of liquid membrane permeation and should aid in scaling-up processes for dearomatization of naphtha and kerosine.