3.2. Effect of molar ratio of DMC to soybean oil
The molar ratio of DMC to soybean oil is one of the important
variables. To determine the optimal molar ratio of DMC to soybean
oil, experiments of various molar ratios were investigated. The
results at 48 h are shown in Fig. 3. The conversion of biodiesel and
glycerol carbonate increased effectively by increasing the molar
ratio of DMC to soybean oil from 5:1 to 10:1. As can be seen in
Fig. 3, the biodiesel conversion increased from 66.2% to 93.3% with
increasing molar ratio of DMC to soybean oil over the range from 5:1
to 10:1. The glycerol carbonate conversion increased from 19.2% to
43.5%. On the other hand, the increase of the molar ratio of DMC to
soybean oil from 15:1 to 20:1 decreased the biodiesel conversion
(79.4%, 76.2%) and glycerol carbonate conversion (33.1%, 32.1%).
The conversions of biodiesel and glycerol carbonate decreased at
molar ratios of DMC to oil over 10:1. According to these results,
the molar ratio of 10:1 was chosen considering both conversion of
biodiesel and glycerol carbonate.
In this solvent-free system, high molar ratio of DMC to soybean
oil was used in order to drive the reaction toward and to inhibit the
reversible reaction. This effect can be attributed to that excessive
DMC also dilute the oil concentration in the reaction system, thus
the collision frequency of oil and lipase was reduced [25,30]. As
similar results, the optimal molar ratio of DMC to soybean oil was
6:1 in a t-butanol solvent system [15] and the optimal molar ratio
of DMC to palm oil was 10:1 in a solvent free-system [25].