The glycerol stream leaving the separator is composed only by about 50%wt
glycerol. It contains also methanol, catalyst, and soap. The first step in glycerol
refining is to add acid to split the soaps into FFAs and salts. The free fatty acids are
not soluble in the glycerol and will rise to the top, so that they can be removed and
recycled. The salts generally remain with the glycerol. The methanol mixed with the
glycerol is removed by flash-vacuum distillation or conventional distillation. A
purity of approximately 85% is reached; this allows to sell the glycerol to a refiner.
Glycerol refining can be performed using vacuum distillation or ion exchange
processes. A purity comprised between 99.5%wt and 99.7%wt is achieved.
The methanol that is removed from the methyl ester and from glycerol is mixed
with water after separation has been performed. This water should be removed in a
distillation column before the methanol is recycled into the process.
1.4
Bioethanol
1.4.1 Production of Ethanol from Sucrose
Sugar cane, sugar beet, and sweet sorghum are crops which contain sugars, which
can be used as feedstock for ethanol production. Their main advantages are high
yield of sugar per hectare and low conversion costs.
Fig. 1.4 First-generation biodiesel production flow sheet (Van Gerpen 2005)
10
P. Bartocci et al.
glycerol. It contains also methanol, catalyst, and soap. The first step in glycerol
refining is to add acid to split the soaps into FFAs and salts. The free fatty acids are
not soluble in the glycerol and will rise to the top, so that they can be removed and
recycled. The salts generally remain with the glycerol. The methanol mixed with the
glycerol is removed by flash-vacuum distillation or conventional distillation. A
purity of approximately 85% is reached; this allows to sell the glycerol to a refiner.
Glycerol refining can be performed using vacuum distillation or ion exchange
processes. A purity comprised between 99.5%wt and 99.7%wt is achieved.
The methanol that is removed from the methyl ester and from glycerol is mixed
with water after separation has been performed. This water should be removed in a
distillation column before the methanol is recycled into the process.
1.4
Bioethanol
1.4.1 Production of Ethanol from Sucrose
Sugar cane, sugar beet, and sweet sorghum are crops which contain sugars, which
can be used as feedstock for ethanol production. Their main advantages are high
yield of sugar per hectare and low conversion costs.
Fig. 1.4 First-generation biodiesel production flow sheet (Van Gerpen 2005)
10
P. Bartocci et al.