specific species is an important consideration so that reduction in production cost can
be achieved (Gouveia and Oliveira 2009; Lourinho and Brito 2015; Mata
et al. 2010).
2.4.1.3 Trans-Esterification
After extraction, the oil which is composed of triglycerides when combined with
methanol is the trans-esterification reaction, forming FAMEs (biodiesel) and glycerol (waste product). Trans-esterification is catalysed by acids, alkali and lipolytic
enzymes. Alkaline catalysis is commonly used as it is faster than the acid-catalysed
reaction. Also, because of the high cost of lipolytic enzymes, they are not used
commonly.
As subjection of triacylglycerol (1 mol) with methyl alcohol (3 mol) results in the
formation of 3 mol of methyl esters of fatty acids and 1 mol of glycerol, therefore, the
surplus amount of methanol is applied so as to carry the reaction in the direction of
methyl esters, towards biodiesel. After termination of trans-esterification process,
distillation of excess methanol and its returning back into the process takes place.
The most appropriate temperature is 60–70
C; however, higher temperatures can
also be applied with higher pressures, but it can increase the cost.
During the reaction of methanolysis, the oil used should be completely
dehydrated and lacking free fatty acids as it leads to the soap formation that affects
or reduces the activity of the catalyst and also cause hindrance in the isolation of the
FAME and glycerol. Also, the contact between the alcohol and triacylglycerol can be
improved by vigorous stirring of the reaction system because of poor solubility of
methanol in oil (Meher et al. 2006; Fukuda et al. 2001; Li et al. 2008).
2.4.2 Bacteria
Bacteria are also preferred as an important source for biodiesel production as they are
able to grow rapidly with easy culture method, unlike microalgae which require
larger spaces to culture with prolonged fermentation period. The limitation being
lower lipid accumulation with an average content of about 20–40% as compared to
microalgae because most of the bacteria are not oil producers.
However, some bacterial strains can be used to produce lipids to about 60–70% of
their cellular dry weight, in order to obtain the esters that can constitute biodiesel.
Some species of Actinomycetes, as well as other bacterial genera of Acinetobacter,
Mycobacterium and Streptomyces can be used as these bacteria are capable
of producing triacylglycerol intracellularly to great scales from simple sources of
carbon under growth-restricted conditions. To overcome the major problems of
biodiesel production including geographical and seasonal restrictions of producing
plant oil, and production cost, an extensive research is now been carried out to
engineer Escherichia coli to produce FAEEs for biodiesel production. Microdiesel is
thus considered as an important future fuel totally created by bacteria E. coli.
2 Application of Microorganisms for Biofuel Production
43
be achieved (Gouveia and Oliveira 2009; Lourinho and Brito 2015; Mata
et al. 2010).
2.4.1.3 Trans-Esterification
After extraction, the oil which is composed of triglycerides when combined with
methanol is the trans-esterification reaction, forming FAMEs (biodiesel) and glycerol (waste product). Trans-esterification is catalysed by acids, alkali and lipolytic
enzymes. Alkaline catalysis is commonly used as it is faster than the acid-catalysed
reaction. Also, because of the high cost of lipolytic enzymes, they are not used
commonly.
As subjection of triacylglycerol (1 mol) with methyl alcohol (3 mol) results in the
formation of 3 mol of methyl esters of fatty acids and 1 mol of glycerol, therefore, the
surplus amount of methanol is applied so as to carry the reaction in the direction of
methyl esters, towards biodiesel. After termination of trans-esterification process,
distillation of excess methanol and its returning back into the process takes place.
The most appropriate temperature is 60–70
C; however, higher temperatures can
also be applied with higher pressures, but it can increase the cost.
During the reaction of methanolysis, the oil used should be completely
dehydrated and lacking free fatty acids as it leads to the soap formation that affects
or reduces the activity of the catalyst and also cause hindrance in the isolation of the
FAME and glycerol. Also, the contact between the alcohol and triacylglycerol can be
improved by vigorous stirring of the reaction system because of poor solubility of
methanol in oil (Meher et al. 2006; Fukuda et al. 2001; Li et al. 2008).
2.4.2 Bacteria
Bacteria are also preferred as an important source for biodiesel production as they are
able to grow rapidly with easy culture method, unlike microalgae which require
larger spaces to culture with prolonged fermentation period. The limitation being
lower lipid accumulation with an average content of about 20–40% as compared to
microalgae because most of the bacteria are not oil producers.
However, some bacterial strains can be used to produce lipids to about 60–70% of
their cellular dry weight, in order to obtain the esters that can constitute biodiesel.
Some species of Actinomycetes, as well as other bacterial genera of Acinetobacter,
Mycobacterium and Streptomyces can be used as these bacteria are capable
of producing triacylglycerol intracellularly to great scales from simple sources of
carbon under growth-restricted conditions. To overcome the major problems of
biodiesel production including geographical and seasonal restrictions of producing
plant oil, and production cost, an extensive research is now been carried out to
engineer Escherichia coli to produce FAEEs for biodiesel production. Microdiesel is
thus considered as an important future fuel totally created by bacteria E. coli.
2 Application of Microorganisms for Biofuel Production
43