High-yield non-catalytic supercritical transesterification of soybean oil to biodiesel induced by gradual heating in a batch reactor

Abstract

The non-catalytic synthesis of biodiesel in supercritical methanol from soybean oil was conducted in a batch reactor using three different reaction approaches: (1) process at constant temperature, (2) gradual heating process, and (3) process combining a phase of gradual heating followed by a phase at constant temperature (hybrid process). In the conditions leading to the highest yields of biodiesel during the constant temperature and gradual heating processes (87.5mol% at 320°C and 83mol% at a heating rate of 2.60°C/min, respectively), a considerable degree of thermal decomposition of the biodiesel synthesized (16 and 10wt.%, respectively) was observed. However, the use of a low heating rate (0.51°C/min) and a subsequent maintenance time of 10min at 320°C during the hybrid process completely prevented the onset of thermal decomposition reactions while transforming all glycerides into biodiesel, thus resulting in a yield of biodiesel of 99.9mol%.