7
Aside from the competition between food and fuel, another main concern regarding
first generation of biofuels is deforestation. For example, massive tracts of peatland
and rainforest have been cleared all for the plantation of palm oil [21]. Therefore,
first generation of biofuels is the least favoured source of energy, due to disagreements regarding the final greenhouse gas emissions, energy balance and doubtful
social sustainability [14, 16, 22].
3.2 Second Generation
Second-generation biofuels (biofuel SG or biofuel 2.0) are obtained from non- food
biomass such as lignocellulosic feedstock materials like straw, cereal, residues and
forests. Therefore cellulose is the primary component of the biomass feedstock for
second-generation biofuels which are also known as cellulosic fuels [23, 24]. Since
the second generation of biomass feedstock does not require the use of agricultural
land, the issue of fuel versus food is undebatable [25, 26]. The major advantages of
second-generation biofuels over first generation biofuels are as follows [27, 28]:
• An abundant and wide range of feedstocks can be processed.
• They are more efficient and need less farmland.
• They have a better environmental performance.
• They have lower costs.
3.3 Third Generation
Third-generation biofuels are formed from microalgae and microbes as alternative
energy resources [14, 29]. However, cellulose fermentation is defined as a thirdgeneration biofuel process which is used to produce bioethanol [30]. Microalgae are
unicellular or multi-cellular photosynthetic microorganisms. Microalgae can convert sunlight and CO 2 into lipids, carbohydrates and a large amount of proteins.
Also, it removes phosphorus and nitrogen from wastewater and fertilizer, resulting
in pollution reduction [31, 32]. There are several processes for the conversion of
algae into biofuels such as liquefaction, pyrolysis, gasification, anaerobic digestion,
extraction, fermentation and transesterification [16, 33–35].
Second-generation biofuels have some drawbacks, such as their pre-treatment
requirement and the need for facilities on a large scale with complex processes and
relatively low production yields. These reasons have prevented the full commercialization of second- generation biofuels [36, 37]. However, third-generation biofuels
to some extent do not need as sophisticated methods of production, large-scale
facilities and high amounts of energy. Therefore, third generation can be considered
a viable source of renewable energy depending on its final end use [25].
Thermochemical Conversion of Biomass and Upgrading of Bio-Products to Produce…
Aside from the competition between food and fuel, another main concern regarding
first generation of biofuels is deforestation. For example, massive tracts of peatland
and rainforest have been cleared all for the plantation of palm oil [21]. Therefore,
first generation of biofuels is the least favoured source of energy, due to disagreements regarding the final greenhouse gas emissions, energy balance and doubtful
social sustainability [14, 16, 22].
3.2 Second Generation
Second-generation biofuels (biofuel SG or biofuel 2.0) are obtained from non- food
biomass such as lignocellulosic feedstock materials like straw, cereal, residues and
forests. Therefore cellulose is the primary component of the biomass feedstock for
second-generation biofuels which are also known as cellulosic fuels [23, 24]. Since
the second generation of biomass feedstock does not require the use of agricultural
land, the issue of fuel versus food is undebatable [25, 26]. The major advantages of
second-generation biofuels over first generation biofuels are as follows [27, 28]:
• An abundant and wide range of feedstocks can be processed.
• They are more efficient and need less farmland.
• They have a better environmental performance.
• They have lower costs.
3.3 Third Generation
Third-generation biofuels are formed from microalgae and microbes as alternative
energy resources [14, 29]. However, cellulose fermentation is defined as a thirdgeneration biofuel process which is used to produce bioethanol [30]. Microalgae are
unicellular or multi-cellular photosynthetic microorganisms. Microalgae can convert sunlight and CO 2 into lipids, carbohydrates and a large amount of proteins.
Also, it removes phosphorus and nitrogen from wastewater and fertilizer, resulting
in pollution reduction [31, 32]. There are several processes for the conversion of
algae into biofuels such as liquefaction, pyrolysis, gasification, anaerobic digestion,
extraction, fermentation and transesterification [16, 33–35].
Second-generation biofuels have some drawbacks, such as their pre-treatment
requirement and the need for facilities on a large scale with complex processes and
relatively low production yields. These reasons have prevented the full commercialization of second- generation biofuels [36, 37]. However, third-generation biofuels
to some extent do not need as sophisticated methods of production, large-scale
facilities and high amounts of energy. Therefore, third generation can be considered
a viable source of renewable energy depending on its final end use [25].
Thermochemical Conversion of Biomass and Upgrading of Bio-Products to Produce…