Effect of surfactant type on selectivity for the separation of 1-methylnaphthalene from dodecane using liquid membranes

Abstract

The selective removal of aromatics from kerosine for the purposes of smoke-point improvement and to meet the specifications for aviation turbine fuel is an industrially important operation. The present study is part of a programme for developing an energy-efficient aqueous surfactant membrane process with high selectivities for aromatics removal. In the experimental studies, carried out in a batch mixer-settler unit, the kerosine feed was modelled using a synthetic mixture of 1-methylnaphthalene and dodecane. The objective of the experimental study was to study the influence of the surfactant type on the selectivity for removal of l-methylnaphthalene. Eight different types of surfactants were used in the studies, with HLB (hydrophile-lipophile balance) numbers ranging from 12.8 to 17.8. The selectivity β, defined as the ratio of the mass transfer coefficients for transfer of aromatics to that of the non-aromatics, was determined after correcting for nonselective transport due to emulsion breakage. The selectivity thus obtained correlated very well with W, the work of transfer, which reflects the ease of adsorption of the surfactant to form a monolayer relative to the ease of micellization. For high W (i.e., lower ease of micellization) the selectivities are higher, as might be expected because micelle formation leads to non-selective transport through the membrane barrier. The study sheds light on the appropriate choice of surfactant to obtain increased selectivities.