3.4. Effect of water addition
The water content is one of the key factors to determine the
reaction rate as well as conversion of biodiesel and glycerol carbonate.
The effect of additional water content was studied in the range
of 0–3.0% for 48 h of reaction, and the results are given in Fig. 5.
The sample without water addition was used as control, for which
biodiesel conversion was 93.3%, and glycerol carbonate conversion
was 43.5%.
The biodiesel conversions were 92.5% and 96.4% and glycerol
carbonate conversions were 82.4% and 92.1% as the additional
water contents were 0.5% and 0.7% respectively. Biodiesel conversion
decreased from 93.4% to 66.1% as the additional water content
was increased from 1.0% to 3.0%. In conditions of 0.7% and 1.0%
water content, the glycerol carbonate conversion was the same.
However, over 1.0% additional water content, glycerol carbonate
conversion decreased. From above results, 0.7% was selected as
an optimal condition for the additional water content and conversions
of biodiesel and glycerol carbonate were 96.4% and 92.1%,
respectively.
In a similar study, the addition of water showed various effects
on enzyme activity and transesterification reaction when glycerol
carbonate was synthesized from oil and DMC [26,33,34]. Several
studies have reported that water content has a great influence on
the coproduction of biodiesel and glycerol carbonate [33–36]. A little
water could improve enzyme activity by increasing the amount
of active sites. When there was more than an optimum level of
water, hydrolytic reactions were encouraged and the transesterification
yield decreased [35]. If the water layer is sufficiently large,
the transfer of the acyl group to the active site will be prevented
which leads to a decrease in conversion [36].