Synthesis of methyl esters from relevant palm products in near-critical methanol with modified-zirconia catalysts

The transesterification and esterification of palm products i.e. crude palm oil (CPO), refined palm oil (RPO) and palm fatty acid distillate (PFAD) under near-critical methanol in the presence of synthesized SO4–ZrO2, WO3–ZrO2 and TiO2–ZrO2 (with various sulfur- and tungsten loadings, Ti/Zr ratios, and calcination temperatures) were studied. Among them, the reaction of RPO with 20%WO3–ZrO2 (calcined at 800 °C) enhanced the highest fatty acid methyl ester (FAME) yield with greatest stability after several reaction cycles; furthermore, it required shorter time, lower temperature and less amount of methanol compared to the reactions without catalyst. These benefits were related to the high acid-site density and tetragonal phase formation of synthesized WO3–ZrO2. For further improvement, the addition of toluene as co-solvent considerably reduced the requirement of methanol to maximize FAME yield, while the addition of molecular sieve along with catalyst significantly increased FAME yield from PFAD and CPO due to the inhibition of hydrolysis reaction.