Environmental Engineering Reference
In-Depth Information
for sodium hydroxide (NaOH) (Fanguri and Hanna 1999). To complete a transesterification
stoichiometrically, a 3:1 molar ratio of alcohol to triglycerides is needed. The reaction can be
catalyzed by alkalis, acids, or enzymes. The alkali include NaOH, potassium hydroxide (KOH),
carbonates, and the corresponding sodium methoxide, sodium ethoxide, sodium peroxide, and
sodium butoxide Sulfuric acid, sulfonic acids, and hydrochloric acid are usually used as acid
catalysis. Lipase can be used as biocatalysts. Alkali-catalyzed transesterification is much faster
than acid-catalyzed transesterification and is most often used commercially (Nelson et al. 1996)
.
According to the quality of the parent oil, the selection of a transesterification process can be made
as shown in Figure 25.1 and it can be explained as follows:
• If the free fatty acid (FFA) content and moisture content of parent vegetable oils are less
than 0.5%, a single-stage transesterification process can be chosen.
• When the FFA content is less than 0.5% but the moisture content is greater than 0.5%, the
moisture content can be removed by heating the oil at 110°C for approximately 1 h with
stirring. Then, the biodiesel can be produced from single-stage transesterification.
Start
1. Determination of
• Free fatty acids (FFA) content and
•Moisture content of raw vegetable oils
2. FFA < 0.5%,
moisture
content < 0.5%
3. FFA < 0.5 %,
moisture
content > 0.5 %
No
Yes
Yes
3a. Heating of oil @
100°C with stirring
for one hour and
removal of moisture
No
5. Single-stage
transesterification
4. FFA > 0.5 %,
moisture
content < 0.5 %
Yes
4a. Two-stage
transesterification
No
4b. Three-stage
transesterification
Stop
FIGure 25.1
Flow chart for the selection of transesterification process.
