Dimerization of fatty acid methyl ester using Brönsted–Lewis acidic ionic liquid as catalyst

The dimerization of fatty acid methyl ester was investigated using Brönsted–Lewis acidic ionic liquids (ILs) as catalysts. It is found that IL (3-sulfonic acid)-propyl-triethylammonium chlorozincinate [HO3S–(CH2)3–NEt3]Cl–ZnCl2 (x = 0.64, x: molar fraction of ZnCl2, x = moles of ZnCl2/(moles of ZnCl2 + 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 °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 Brönsted and Lewis acid sites enhanced the catalytic performance of the IL.

► Brönsted-Lewis acidic IL efficiently catalyzes the FAME dimerization.
► Acid active sites selectively catalyze different reaction steps.
► Synergetic effect of IL enhances its catalytic activity.
► Product is easily separated and IL catalyst is of good reusability.