Transesterification reactions of soybean oil with methanol were carried out in an autoclave reactor PARR model 4842, stainless steel, with reaction volume of 300 mL. The reactor was charged with soybean oil, anhydrous methanol (with methanol/oil molar ratio of 8–13) and different amounts of catalyst (3–5 wt.%), heated and stirred for 1 h. The reaction pressure varied between 27 atm at 180 °C and 34 atm at 230 °C. After the reaction finished, the mixture was filtered and transferred to a decanting funnel for phase separation. After 24 h, the glycerin phase was separated and the biodiesel phase was washed with water, decanted and heated at 110 °C to remove humidity and alcohol.
GC analysis was performed on a Shimadzu CG2014 Gas Chromatograph equipped with a flame ionization detector. Determination of free glycerol and mono-, di- and tri-glyceride content was based on EN 14105 standard (using a SGE ID-HT5 column) and the ester content was evaluated by EN 14103 standard (using a Carbowax column).
For evaluating the catalyst reusability, the catalyst after reaction was three times washed with methanol and heated at 200 °C for 18 h to eliminate the interlayer water. Then, a new reaction cycle started with fresh reactants.