Different types of catalyzed transesterification can be adopted (Lam et al. 2010):
1. Homogeneous base catalyst
2. Heterogeneous base catalyst
3. Homogeneous acid catalyst
4. Heterogeneous acid catalyst
5. Enzymes
State-of-the-art biodiesel production usually is done using base catalyst (e.g.,
KOH or NaOH). In that case reaction time can vary between 0.33 and 2 hours and
yields are between 88% and 98% (Lam et al. 2010; Liu et al. 2010). Catalyst loading
is between 1 and 6%wt, while methanol excess is between 7:1 and 9:1, expressed in
molar ratio. Temperature can range between 60 and 87
C (Lam et al. 2010). Also
two-step catalysis can be a solution: first acid catalyst, then followed by basic
catalysis.
Homogeneous acid catalyst usually can use H 2 SO 4 or HCl. Heterogeneous basic
catalysis can be performed using basic zeolites, alkaline earth metal oxides (e.g.,
CaO), and hydrotalcites. Heterogeneous acid catalyst can be zirconium oxide
(ZrO 2 ), titanium oxide (TiO 2 ), tin oxide (SnO2), zeolites, sulfonic ion-exchange
resin, sulfonated carbon-based catalyst, and heteropoly acids (HPAs) (Lam et al.
2010).
Enzyme catalysts lipases can be produced from several microorganisms, such
as Mucor miehei (Lipozyme IM 60), Pseudomonas cepacia (PS 30), C. antarctica
(Novozyme 435), Bacillus subtilis, Rhizopus oryzae, and Penicillium expansum
(Lam et al. 2010; Liu et al. 2010, 2011a, b; Yan et al. 2014; Fan et al. 2016, 2017;
Su et al. 2016; Li et al. 2017).
1.3.2 Biodiesel Production Process Diagram
Figure 1.4 shows the flow sheet of the production processes used for biodiesel.
Based on Fig. 1.4 scheme, it is assumed that alcohol, catalyst, and oil are inserted
in the reactor and agitated for approximately 1 h at 60
C. Small plants often use
batch reactors (Stidham et al. 2000), while larger plants (higher than 4 million liters/
year) use continuous stirred-tank reactors (CSTR) or plug flow reactors operated in
continuous mode (Assman et al. 1996).
Once methyl ester has been produced, it must be separated from the glycerol
(through phase separation because glycerol is much heavier). Methyl esters undergo
a neutralization step and then pass through a methanol stripper. A vacuum flash
process or a falling film evaporator can be used for this purpose. Before washing
with water, acid is added to the biodiesel to neutralize any residual catalyst and to
split any soap that may have formed during the reaction. Soaps react with the acid to
form water-soluble salts and FFAs. The salts are removed during the water washing
step. The water washing step removes traces of catalyst, soap, salts, methanol, or free
glycerol remained in the biodiesel. After the wash process, remaining water is
removed from the biodiesel by flash-vacuum distillation.
1 Biofuels: Types and Process Overview
9
1. Homogeneous base catalyst
2. Heterogeneous base catalyst
3. Homogeneous acid catalyst
4. Heterogeneous acid catalyst
5. Enzymes
State-of-the-art biodiesel production usually is done using base catalyst (e.g.,
KOH or NaOH). In that case reaction time can vary between 0.33 and 2 hours and
yields are between 88% and 98% (Lam et al. 2010; Liu et al. 2010). Catalyst loading
is between 1 and 6%wt, while methanol excess is between 7:1 and 9:1, expressed in
molar ratio. Temperature can range between 60 and 87
C (Lam et al. 2010). Also
two-step catalysis can be a solution: first acid catalyst, then followed by basic
catalysis.
Homogeneous acid catalyst usually can use H 2 SO 4 or HCl. Heterogeneous basic
catalysis can be performed using basic zeolites, alkaline earth metal oxides (e.g.,
CaO), and hydrotalcites. Heterogeneous acid catalyst can be zirconium oxide
(ZrO 2 ), titanium oxide (TiO 2 ), tin oxide (SnO2), zeolites, sulfonic ion-exchange
resin, sulfonated carbon-based catalyst, and heteropoly acids (HPAs) (Lam et al.
2010).
Enzyme catalysts lipases can be produced from several microorganisms, such
as Mucor miehei (Lipozyme IM 60), Pseudomonas cepacia (PS 30), C. antarctica
(Novozyme 435), Bacillus subtilis, Rhizopus oryzae, and Penicillium expansum
(Lam et al. 2010; Liu et al. 2010, 2011a, b; Yan et al. 2014; Fan et al. 2016, 2017;
Su et al. 2016; Li et al. 2017).
1.3.2 Biodiesel Production Process Diagram
Figure 1.4 shows the flow sheet of the production processes used for biodiesel.
Based on Fig. 1.4 scheme, it is assumed that alcohol, catalyst, and oil are inserted
in the reactor and agitated for approximately 1 h at 60
C. Small plants often use
batch reactors (Stidham et al. 2000), while larger plants (higher than 4 million liters/
year) use continuous stirred-tank reactors (CSTR) or plug flow reactors operated in
continuous mode (Assman et al. 1996).
Once methyl ester has been produced, it must be separated from the glycerol
(through phase separation because glycerol is much heavier). Methyl esters undergo
a neutralization step and then pass through a methanol stripper. A vacuum flash
process or a falling film evaporator can be used for this purpose. Before washing
with water, acid is added to the biodiesel to neutralize any residual catalyst and to
split any soap that may have formed during the reaction. Soaps react with the acid to
form water-soluble salts and FFAs. The salts are removed during the water washing
step. The water washing step removes traces of catalyst, soap, salts, methanol, or free
glycerol remained in the biodiesel. After the wash process, remaining water is
removed from the biodiesel by flash-vacuum distillation.
1 Biofuels: Types and Process Overview
9