The kinetics of the enzymatic conversion of coconut oil to biodiesel (fatty acid alkyl esters) have been investigated using ethanol and 1% (w/v) lipase at 50 °C. Coconut oil is being evaluated for biofuel production and
an enzymatic process was selected to minimize side reactions (such as saponification) which can occur with
the alkali-catalysed route if free fatty acid (FFA) concentration is significant. Rate data comparison showed
that the NaOH-promoted conversion was about 2 orders of magnitude faster than the lipase-catalysed system
but resulted in saponification/partial solidification of the reaction mixture. Analysis also revealed that the
ratios of the kinetic constants for ester:glycerol (1:1.12) and that for ester:ethanol (1:3.11) during enzymatic
transesterification are in agreement with reaction stoichiometry. Additionally, FFA esterification rates were
higher (1.5 to 2.5) than triglyceride transesterification rates under similar conditions. Supplementation
with ultrasonics at 43 kHz also permitted nearly 20-fold improvement in conversion rate. The study also
demonstrated that withSaccharomyces cerevisiae, the growth yield on glycerol of 0.77 g g
−1
is greater
than that usually found for growth of yeast on glucose (viz. 0.4–0.45 g g
−1
). Thus, opportunities for process
enhancement exist through the use of increased enzyme concentrations, ultrasound techniques and growth
of yeast on residual by-product glycerol