Biodiesel synthesis and kinetic analysis based on MnCO3/Na silicate as heterogeneous catalyst

Abstract

The MnCO3/Na silicate (Mn/Na/Si mole ratio of 4.65:1:1.65) catalyst in the form of solid particles with diameter of 0.99-1.99 mm was used as a catalyst for transesterification of soybean oil in batch autoclave at different conditions: 388-468 K, methanol-to-oil mole ratio 12:1-30:1, catalyst amount based on the mass of oil 0-12.5 %. The complete triacylglycerols (TAG) conversion and high yield of fatty acid methyl ester (FAME) was obtained after 1 h at 458 K, methanol-to-oil mole ratio 30:1 and 10 % of catalyst. Kinetics of transesterification process was analyzed by three models: the simple first order irreversible reaction rate, as well as two more complex models recently reported in literature. The catalyst reuse in transesterification process was tested and the average values of 99.0 % of TAG conversion and 97.5 % of FAME yield were obtained after 8 consecutive runs. Different techniques were used to characterize fresh and used MnCO3/Na silicate catalyst. The determined amounts of leached Na ( lt 500 ppm) and Mn ( lt 20 ppm) in biodiesel phase implied that the homogeneous-heterogeneous process influences the catalyst selectivity, whereby leached Na enables the complete transformation of TAG to FAME.