Room temperature ionic liquids are emerging as alternative solvents which replace the conventional volatile organic solvents. The solvent extraction/liquid membrane process requires substantial amount of solvent as well as stripping of solute from the solvent. In order to reduce the solvent requirement, emulsion liquid membrane technique is proposed for the benzimidazole separation from aqueous solutions using tri-n-octyl methyl ammonium chloride ionic liquid carrier. The distribution coefficient of benzimidazole between aqueous solution and ionic liquid in membrane phase was studied to optimize the external phase pH. Effects of emulsification time, speed of emulsification, internal phase reagent concentration, extractant (carrier) concentration, volume ratio of organic phase to aqueous internal phase and concentration of surfactant (span-80) on the membrane stability as well as contact time, stirring speed, feed concentration. external phase pH and volume ratio of the emulsion to the external phase on the pertraction were studied. The organic phase consists of kerosene and n-heptane as diluent. At optimized conditions, the emulsion was stable up to 140 min, the breakage of internal phase was <0.5 and 97.5% of benzimidazole was extracted within 12 min with a concentration factor of 5. It was found that benzimidazole concentration in external phase increased due to membrane breakage after 12 min. Crown Copyright (C) 2008 Published by Elsevier B.V. All rights reserved.