Separation of paraffins by membrane extraction combined with crystallization

Author： Lipatov D. Myasnikov S. Kulov N.

ISSN： 0040-5795

Source： Theoretical Foundations of Chemical Engineering, Vol.39, Iss.2, 2005-03, pp. : 110-117

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Abstract

An integrated mass-exchange process combining liquid-membrane separation with crystallization from solution is experimentally and theoretically investigated. Experiments on separation of binary mixtures of paraffins that have close properties and form mutual solid solutions are carried out. The maximal degree of separation is attained using an aqueous ethanol membrane containing 65 wt % ethanol. From hexadecane-octadecane and hexadecane-tetracosane mixtures containing 86 mol % hexadecane, crystals containing 96.3 and 99.8 mol % hexadecane, respectively, are obtained. The solubility of hexadecane, octadecane, and tetracosane in aqueous ethanol solutions of various concentrations is experimentally studied over a wide temperature range. Using the solubility data, thermodynamic calculations of the liquid-liquid and liquid-crystals equilibria are carried out for the upper and lower boundaries of the aqueous alcohol membrane. A mathematical model of the integrated process is obtained by compiling a set of equations for the diffusion fluxes of the components in the liquid membrane and expressions describing the phase equilibria at the membrane boundaries. A comparison of the experimental data on the separation efficiency with the results of the calculations shows that the diffusion model adequately describes the main features of the integrated process.