CH 2 –OOC–R 1
CH–OOC–R 2
+ 3R´OH
Catalyst
R 1 –COO–R´
R 2 –COO–R´ +
CH 2 –OH
CH–OH
CH 2 –OOC–R 3
R 3 –COO–R´
CH 2 –OH
Glyceride
Alcohol
Esters
Glycerol
Biodiesel
45
and butanol. The esters have reduced the viscosity and increased volatility
relative to the triglycerides present in vegetable oils. Biodiesel production
methods include acid, alkaline, two-step, supercritical methanol, and ultrasonic methods.
Several catalysts were tried for the purpose of transesterification, for
example, magnesium, calcium oxides, and carbonates of basic and acidic
macroreticular organic resin, alkaline alumina, phase transfer catalysts, sulfuric acids, p-toluene sulfonic acid, and dehydrating agents as co-catalysts
(Agarwal, Bijwe, and Das 2003). The catalysts reported to be effective at room
temperature were alkoxides and hydroxides (Canakci and Van Gerpan 1999).
The biodiesel blend is referred as Bxx, where xx indicates the percentage
amount of biodiesel that is in the B20 blend, which represents the mixture
of 20% biodiesel and 80% diesel. Biodiesel is registered as a fuel and fuel
additive with the United States Environmental Protection Agency (EPA) and
meets clean diesel standards established by the California Air Resources
Board (CARB). Neat biodiesel (B100) has been designated as an alternative
fuel by the Department of Energy and Department of Transportation of the
United States. Most of the countries started using biodiesel as substitute fuel
for diesel and made their own national fuel quality standards for biodiesel.
Biodiesel has been in use in countries such as the United States, European
Union, Germany, Malaysia, Thailand, France, and Italy.
3.2.1 Alkaline Transesterification
Alkaline-catalyzed transesterification process is the commercially well-developed biodiesel production process. Alkaline catalysts (NaOH, KOH) are
used to improve the reaction rate and to increase the yield of the process. To
complete the transesterification stoichiometrically, 3:1 molar ratio of alcohol
to triglycerides is needed. In practice, the ratio needs to be higher to drive the
equilibrium to a maximum ester yield. Since the transesterification reaction
is a reversible process, excess alcohol is required to shift the reaction equilibrium to the products side. Alcohols such as methanol, ethanol, or butanol
are used in the transesterification. Figure 3.1 shows the transesterification
equation of vegetable oils with alcohols.
The alkali-catalyzed transesterification of vegetable oils proceeds faster
than the acid-catalyzed reaction. The first step is the reaction of the base with
Figure 3.1
Transesterification equation.
CH–OOC–R 2
+ 3R´OH
Catalyst
R 1 –COO–R´
R 2 –COO–R´ +
CH 2 –OH
CH–OH
CH 2 –OOC–R 3
R 3 –COO–R´
CH 2 –OH
Glyceride
Alcohol
Esters
Glycerol
Biodiesel
45
and butanol. The esters have reduced the viscosity and increased volatility
relative to the triglycerides present in vegetable oils. Biodiesel production
methods include acid, alkaline, two-step, supercritical methanol, and ultrasonic methods.
Several catalysts were tried for the purpose of transesterification, for
example, magnesium, calcium oxides, and carbonates of basic and acidic
macroreticular organic resin, alkaline alumina, phase transfer catalysts, sulfuric acids, p-toluene sulfonic acid, and dehydrating agents as co-catalysts
(Agarwal, Bijwe, and Das 2003). The catalysts reported to be effective at room
temperature were alkoxides and hydroxides (Canakci and Van Gerpan 1999).
The biodiesel blend is referred as Bxx, where xx indicates the percentage
amount of biodiesel that is in the B20 blend, which represents the mixture
of 20% biodiesel and 80% diesel. Biodiesel is registered as a fuel and fuel
additive with the United States Environmental Protection Agency (EPA) and
meets clean diesel standards established by the California Air Resources
Board (CARB). Neat biodiesel (B100) has been designated as an alternative
fuel by the Department of Energy and Department of Transportation of the
United States. Most of the countries started using biodiesel as substitute fuel
for diesel and made their own national fuel quality standards for biodiesel.
Biodiesel has been in use in countries such as the United States, European
Union, Germany, Malaysia, Thailand, France, and Italy.
3.2.1 Alkaline Transesterification
Alkaline-catalyzed transesterification process is the commercially well-developed biodiesel production process. Alkaline catalysts (NaOH, KOH) are
used to improve the reaction rate and to increase the yield of the process. To
complete the transesterification stoichiometrically, 3:1 molar ratio of alcohol
to triglycerides is needed. In practice, the ratio needs to be higher to drive the
equilibrium to a maximum ester yield. Since the transesterification reaction
is a reversible process, excess alcohol is required to shift the reaction equilibrium to the products side. Alcohols such as methanol, ethanol, or butanol
are used in the transesterification. Figure 3.1 shows the transesterification
equation of vegetable oils with alcohols.
The alkali-catalyzed transesterification of vegetable oils proceeds faster
than the acid-catalyzed reaction. The first step is the reaction of the base with
Figure 3.1
Transesterification equation.