Lewis acid/surfactant rare earth trisdodecylsulfate catalysts for biodiesel production from waste cooking oil

This work reports the synthesis, characterization and application of rare earth (La, Ce, Sm and Gd) trisdodecylsulfate materials as Lewis acid-surfactant-combined catalysts for the production of biodiesel from waste cooking soybean oil. All the solid materials showed a bilayer lamellar arrangement with the dodecylsulfate molecules in a head to head, tail to tail packing. The reaction between commercial feedstocks (soybean oil and oleic acid) with ethanol was used separately to study La, Ce, Sm and Gd catalyst activities for transesterification (conversions of 73, 92, 53 and 73%) and esterification (conversions of 87, 80, 75 and 85%) after 1 h, respectively. Among them, cerium(III) trisdodecylsulfate showed the highest catalytic activity (TOF = 29.5 mol h−1 molcat−1) for transesterification, while lanthanum(III) and gadolinium(III) trisdodecylsulfates were the most active for esterification (TOF = 28.7 mol h−1 molcat−1). The application of the studied catalysts for the simultaneous transesterification and esterification reaction of waste cooking oil, containing 8.8 wt.% of free fatty acids (FFAs), with ethanol showed conversions of 76 (3.3 wt.% of FFAs), 79 (5.3 wt.% of FFAs), 81 (2.5 wt.% of FFAs) and 86% (0.0 wt.% of FFAs) after 1 h for La, Ce, Sm and Gd catalysts, respectively. Thus, gadolinium(III) trisdodecylsulfate was the best material for the conversion of waste feedstock to produce biodiesel. However, cerium(III) trisdodecylsulfate was less susceptible to deactivation, exhibiting conversion values of 92, 81 and 77% for the 1st, 2nd and 3rd reaction cycles. The catalysts were characterized by elemental analysis, X-ray powder diffraction (XRD), 1H NMR, thermal analysis (TG/DTG/DTA) and FTIR measurements.

Figure optionsDownload high-quality image (73 K)Download as PowerPoint slideHighlights
► Synthesis of rare earth trisdodecylsulfate Lewis acid-surfactant-combined catalysts.
► Production of biodiesel from waste cooking oil.
► Cerium(III) catalyst showed the highest activity for transesterification.
► Lanthanum(III) and gadolinium(III) materials were the most active for esterification.
► Gadolinium(III) catalyst was the best material for the conversion of waste feedstock.