Conversion of Shizochitrium limacinum microalgae to biodiesel by non-catalytic transesterification using various supercritical fluids.

Biodiesel was synthesized from Schizochitrium limacinum microalgae with different methylating agents namely, methanol, dimethyl carbonate and methyl acetate. The reactions were conducted at 518-643 K at 20 MPa and methylating agent to algae ratio at 10:1. The reaction time was varied between 10 and 80 min. Conversions of >90% was observed within 40 min at 543 K for methanol system. However, the conversions were considerably lower for other systems and only 50% was observed with dimethyl carbonate after 30 min at 643 K, and 40% conversion with methyl acetate after 40 min at 643 K. The rate constants were obtained by pseudo-first order kinetic model. Based on the variation of rate constants with temperature, Arrhenius equation was used to determine the activation energy of all the three reaction systems. The reaction rates were the highest and lowest for the reaction with methanol and methyl acetate, respectively.