Transesterification of soybean and castor oil with methanol and butanol using heterogeneous basic catalysts to obtain biodiesel

•Transesterification reaction of soybean and castor oil using solid base catalyst.•Higher selectivity to fatty acid esters when butanol was used instead of methanol.•MgO/γ-Al2O3 catalyst showed more than 97% to FABE yield with castor oil.•More than 85% of FABE yield was achieved with ZnO/γ-Al2O3 and castor oil.