Dimerization of fatty acid methyl ester using Bronsted-Lewis acidic ionic liquid as catalyst

The dimerization of fatty acid methyl ester was investigated using Bronsted-Lewis acidic ionic liquids (Is) as catalysts. It is found that IL (3-sulfonic acid)-propyl-triethylammonium chlorozincinate [HO(3)S-(CH(2))(3)-NEt(3)]Cl-ZnCl(2) (x = 0.64, x: molar fraction of ZnCl(2), x = moles of ZnCl(2)/(moles of ZnCl(2) + moles of ammonium salt) was of good catalytic performance. Under the optimum conditions m(biodiesel):m(IL) 15:1, biodiesel 15 g, reaction temperature 240 degrees C, and reaction time 5 h, the yield of product dimeric acid methyl ester was 96.8%. The reusability of IL was good and after it was used five times, the dimeric acid methyl ester yield was still more than 94%. Otherwise, a synergetic effect of Bronsted and Lewis acid sites enhanced the catalytic performance of the IL. (C) 2011 Elsevier B.V. All rights reserved.