Page 77 - Materials Chemistry, Second Edition

58 Life Cycle Assessment of Wastewater Treatment

FIGURE 4.2 Scum-to-Biodiesel Demo Facility developed at University of Minnesota.

yield, break the emulsion for better water/oil separation, and further remove
impurity from the scum oil, thus speeding up the esterification reaction in
the following acid-catalyzed esterification process. When the acid solution
is introduced into the raw scum oil, it first mixes with the raw oil for 0.5 h
at 60°C. The mixture is then allowed to settle for about half an hour to col-
lect the oil in the upper phase and sediment/water in the lower phase. The
energy is required to heat up the scum oil, to remove the water in the exit
oil, and for mixing.
3. Acid-catalyzed esterification: In this step, the FFA is reacted with methanol
to form fatty acid methyl ester (FAME) with the catalyst H SO . Methanol
2
4
(30% of oil weight) and 98% sulfuric acid (5% of oil weight) are added to
the oil and mixed for 1 h at 60°C. Then, the mixture is allowed to settle
for 0.5 h to separate FAME from excess methanol and acid. The FAME
collected is dried at 105°C to remove all water. The total energy use in this
process includes heat for maintaining the reaction at 60°C for 1.5 h, heat to
remove water from the raw oil, and power for mixing. After acid-catalyzed
esterification, the scum oil would meet the criteria as a feedstock for base-
catalyzed transesterification.
4. Base-catalyzed transesterification: In this process, the triglyceride in the
raw scum oil is converted to FAME with base catalysts, that is, potassium
methoxide (CH OK). Methanol and CH OK are first mixed with raw oil
3
3
from the acid esterification at 60°C for 0.5 h. The mixture is then sent to
a rotary evaporator to remove excess methanol. The energy use in this