5 Principle and Processing of Biodiesel Production
145
Fig. 5.6 Impact of methanol
concentration on reaction
yield
40
50
60
70
80
90
4
5
6
7
8
Yield(%)
Methanol/soybean oil (mole ratio)
that at 6:1, methanol concentration has an optimal impact on the reaction yield. If the
concentration keeps increasing, it has little impact on the reaction equilibrium shift.
Furthermore, as mentioned above, transesterification is mostly a reversible reaction.
Higher methanol concentration will increase the polarity of the reaction system so
as to reduce the reaction speed. More specifically, the biodiesel yield will decrease
slightly. To sum up, at the methanol/soybean oil molar ratio of 6:1, the biodiesel yield
reaches its highest point. Therefore, in the real-world scenario, the methanol/soybean
oil molar ratio should be kept at 6:1.
5.2.7.2 Impact of Reaction Time on Biodiesel Yield
Below is the table showing how reaction time affects biodiesel yield at 60 °C with a
methanol/soybean oil molar ratio of 6:1 at different catalyst (NaOH) concentration
levels.
Figure 5.7 demonstrates that in the initial phase, as reaction time increases, the
yield increases significantly. But after 20 min, the reaction yield begins to fall. As
the reaction continues, the yield gradually approaches a stable value. All this shows
Fig. 5.7 Yield changes over
reaction time at different
catalyst concentration levels
50
55
60
65
70
75
80
85
90
95
10
20
30
60
90
120
Yield (%)
Reaction time (min)
0.90%
1.20%
0.90%