of microalgal lipids at 60 °C for 3 h with catalyst loading of 25% and the yield of
biodiesel reported was 97.7% (Zhang et al. 2012). Syazwani et al. (2015) performed
a study using CaO catalyst synthesized from angel wing shells in transesterification
of N. oculata lipids. Yield of 84.1% was reported with 9% catalyst concentration
and 1:150 molar ratio of lipids to methanol in a period of 1 h. Leaching of the
heterogeneous catalyst into the final biodiesel product can be one of the concerns
related to the use of these catalysts. There are many heterogeneous catalysts used
for transesterification of edible oil and non-edible oil, but more thorough research
needs to be performed for their application on microalgal lipids, as only limited
information was observed in the literature for the algal lipids.
5.1.3 In situ Transesterification
In situ transesterification is the process where the extraction and transesterification
reaction are carried out simultaneously. It has an advantage over conventional
process as only a single step is required instead of two seperate steps of extraction
and reaction. This approach of combination leads to intensification as it requires
minimal amount of solvent, lesser reaction time, and easy separation of the products. The state of biomass is crucial in this approach as more amount of biodiesel is
produced from dry biomass as compared to wet dry biomass.
Mechanically Catalyzed In situ Transesterification
The mechanically catalyzed in situ transesterification involves the use of mechanical processes based on the use of microwave (MW), ultrasound (US), and autoclave. These processes help in improving the surface area and local temperature of
mixture leading to increased penetration of solvents to cells which further helps in
enhanced extraction of lipids from microalgae. Microwave-assisted direct transesterification study was performed with dried Nannochloropsis and yield of 80.1%
was reported under processing conditions of 1:12 (w/v) ratio of algae to methanol,
2% by weight KOH loading, and reaction time of 2–4 min at 60–65 °C (Patil et al.
2011a). Another study reported that with use of ultrasound, 91–96% yield was
obtained in 20 min–2 h time with 1:105 to 1:315 algae to methanol molar ratio. The
reaction time required for US is typically more as compared to MW (Ehimen et al.
2012), though the scale up prospects for MW need to be carefully evaluated.
Chemically Catalyzed In situ Transesterification
The chemically catalyzed reaction involves no use of mechanical energy. An
important precondition of the chemical catalyst-based approach is that the process
requires the use of dried biomass. Feedstock containing water more than 31.7%
exhibit inhibition to transesterification reaction (Ehimen et al. 2010). These
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S. Joshi and P. Gogate
biodiesel reported was 97.7% (Zhang et al. 2012). Syazwani et al. (2015) performed
a study using CaO catalyst synthesized from angel wing shells in transesterification
of N. oculata lipids. Yield of 84.1% was reported with 9% catalyst concentration
and 1:150 molar ratio of lipids to methanol in a period of 1 h. Leaching of the
heterogeneous catalyst into the final biodiesel product can be one of the concerns
related to the use of these catalysts. There are many heterogeneous catalysts used
for transesterification of edible oil and non-edible oil, but more thorough research
needs to be performed for their application on microalgal lipids, as only limited
information was observed in the literature for the algal lipids.
5.1.3 In situ Transesterification
In situ transesterification is the process where the extraction and transesterification
reaction are carried out simultaneously. It has an advantage over conventional
process as only a single step is required instead of two seperate steps of extraction
and reaction. This approach of combination leads to intensification as it requires
minimal amount of solvent, lesser reaction time, and easy separation of the products. The state of biomass is crucial in this approach as more amount of biodiesel is
produced from dry biomass as compared to wet dry biomass.
Mechanically Catalyzed In situ Transesterification
The mechanically catalyzed in situ transesterification involves the use of mechanical processes based on the use of microwave (MW), ultrasound (US), and autoclave. These processes help in improving the surface area and local temperature of
mixture leading to increased penetration of solvents to cells which further helps in
enhanced extraction of lipids from microalgae. Microwave-assisted direct transesterification study was performed with dried Nannochloropsis and yield of 80.1%
was reported under processing conditions of 1:12 (w/v) ratio of algae to methanol,
2% by weight KOH loading, and reaction time of 2–4 min at 60–65 °C (Patil et al.
2011a). Another study reported that with use of ultrasound, 91–96% yield was
obtained in 20 min–2 h time with 1:105 to 1:315 algae to methanol molar ratio. The
reaction time required for US is typically more as compared to MW (Ehimen et al.
2012), though the scale up prospects for MW need to be carefully evaluated.
Chemically Catalyzed In situ Transesterification
The chemically catalyzed reaction involves no use of mechanical energy. An
important precondition of the chemical catalyst-based approach is that the process
requires the use of dried biomass. Feedstock containing water more than 31.7%
exhibit inhibition to transesterification reaction (Ehimen et al. 2010). These
70
S. Joshi and P. Gogate