3.1. Selection of enzyme and effect of enzyme amount
We investigated the effect of enzyme types and amount on
the conversion of biodiesel and glycerol carbonate. Novozym 435,
Lipozyme TL IM, Lipozyme RM IM and Amano AK were loaded with
10% concentration (w/w, based on oil). Initial results showed the
conversions of biodiesel and glycerol carbonate were 77.6% and
16.6% with 10% Novozym 435, respectively. The other enzymes
showed biodiesel conversion below 30%, and did not produce glycerol
carbonate (data not shown).
The enzyme amount has a great influence on the rate of transesterification.
In order to investigate the effect of the amount of
enzyme on the conversion of biodiesel and glycerol carbonate,
experiments were performed in the range of 10–30% Novozym 435
for 48 h. Fig. 2 shows the effect of enzyme amount (10–30%) on the
conversion of biodiesel and glycerol carbonate after 48 h of reaction.
The final conversions for each amount of enzyme were in the
ranges of 77.6–79.8% for biodiesel conversion, and 16.6–36.1% for
glycerol carbonate conversion. In the enzyme concentration range
of 10–30%, the biodiesel conversion was similar and not increased
by further increase in enzyme concentration. For the reactions
at 10–20% enzyme concentration, glycerol carbonate conversion
dramatically increased from 16.6% to 33.1%, and similar trends
of glycerol carbonate conversion were observed at 20% and 30%
enzyme concentration. Therefore, 20% Novozym 435 was chosen
as an optimal enzyme amount for the economically efficient process.
At this condition, the conversions of biodiesel and glycerol
carbonate were 79.3% and 33.1%, respectively.