6.3.2 Biochemical Conversion Methods
The agro-residues can be converted into different biofuels like ethanol, butanol,
bio-oil, and acetone by using biochemical conversion technologies. Depending on
the product and the process, the microbes like bacteria, fungi, and yeast can be used
in the biochemical conversion process. The selection of microbes depends on the
substrate, process, and end products. The lignin present in the biomass makes
complications, and this biomass is not suitable to produce bioethanol/biobutanol
through the fermentation process.
6.3.2.1 Biomass Pretreatment
The pretreatment is an unavoidable step for lignocellulosic biomass used for lignin
removal and to release the sugars for fermentation. Pretreatment of lignocellulosic
biomass is one of the expensive processes, and it accounts for about 18% of the total
production cost (Zhang and Shahbazi 2011). Since the compositions of agroresidues from different sources may vary with varieties, crops, seasons, and regions.
The major hurdles in the commercialization of agro-residues based biofuels production are the high energy-intensive process and cost involved in different unit
operations. Development of low cost and energy-efficient technologies for
pretreatment, minimum inhibitors production, and sugar loss, fermentation, distillation process are significant challenges for the production of biobutanol from lignocellulosic feedstocks. Therefore, the major hindrance to the commercialization of
alcohol production technology is the biomass pretreatment process.
6.3.2.2 Fermentation Process
Technology for bioethanol production from sugar crops is well established. Furthermore, many bioethanol plants are operated at commercial scale. Meanwhile, a
Fig. 6.2 Different pyrolysis modes and end products yield (source: adapted from Bridgwater 2007)
6 Sustainable Biorefinery Technologies for Agro-Residues: Challenges and. . .
107
The agro-residues can be converted into different biofuels like ethanol, butanol,
bio-oil, and acetone by using biochemical conversion technologies. Depending on
the product and the process, the microbes like bacteria, fungi, and yeast can be used
in the biochemical conversion process. The selection of microbes depends on the
substrate, process, and end products. The lignin present in the biomass makes
complications, and this biomass is not suitable to produce bioethanol/biobutanol
through the fermentation process.
6.3.2.1 Biomass Pretreatment
The pretreatment is an unavoidable step for lignocellulosic biomass used for lignin
removal and to release the sugars for fermentation. Pretreatment of lignocellulosic
biomass is one of the expensive processes, and it accounts for about 18% of the total
production cost (Zhang and Shahbazi 2011). Since the compositions of agroresidues from different sources may vary with varieties, crops, seasons, and regions.
The major hurdles in the commercialization of agro-residues based biofuels production are the high energy-intensive process and cost involved in different unit
operations. Development of low cost and energy-efficient technologies for
pretreatment, minimum inhibitors production, and sugar loss, fermentation, distillation process are significant challenges for the production of biobutanol from lignocellulosic feedstocks. Therefore, the major hindrance to the commercialization of
alcohol production technology is the biomass pretreatment process.
6.3.2.2 Fermentation Process
Technology for bioethanol production from sugar crops is well established. Furthermore, many bioethanol plants are operated at commercial scale. Meanwhile, a
Fig. 6.2 Different pyrolysis modes and end products yield (source: adapted from Bridgwater 2007)
6 Sustainable Biorefinery Technologies for Agro-Residues: Challenges and. . .
107