7.9.2 Biobutanol
Another product obtained from biorefinery and has attracted the attention of scientists as an efficient alternative for gasoline (Bhandiwad et al. 2014) (Fig. 7.2) is
biobutanol.
Microorganisms,
such
as
Clostridium
spp.,
C. saccharoperbutylacetonicum, Clostridium acetobutylicum and C. beijerinckii,
are example of microorganims capabable of produding biobutanol by using sugars
from agricultural residues (Bhandiwad et al. 2014; Nakayama et al. 2011). Similarly,
Thermoanaerobacterium thermosaccharolyticum showed 1.8–5.1 mM n-butanol
production from the overexpression of thl, hbd, crt, bcd, etfA and etfB genes of
bcs operon required for butyryl-CoA formation (Bhandiwad et al. 2014). 7.9 g/L of
n-butanol was produced by coculture of Clostridium thermocellum and Clostridium
saccharoperbutylacetonicum (Nakayama et al. 2011). 7.7 g/L of acetoin and 14.5 g/
L of 2,3-butanediol were reported from Geobacillus strain XT15 from corn steep
liquor at 55
C (Yang et al. 2015).
7.9.3 Hydrogen
It is a carrier of energy having a high potential of being considered as an alternative
for fossil fuel. As it is a clean fuel, it can be used as an internal fuel for combustion
engines in combination with oxygen (Koskinen et al. 2008). Thermophilic microorganisms, e.g. Pyrococcus furiosus, Thermococcus kodakarensis and all Thermotoga
and Caldicellulosiruptor species, have been found to be the good producers of
hydrogen with only the water vapour emission (Verhaart et al. 2010). adhE and
aldH genes are not present in these microorganisms; therefore, they do not produce
ethanol; hence due to hydrogenase, hydrogen production increases. However, Clostridium uzonii strain AK15 and Thermoanaerobacterium aciditolerans AK17 isolated from Iceland during geothermal springs showed good hydrogen production
along with bioethanol (Koskinen et al. 2008).
7.10 Molecular Aspects of Enzymes in Biorefinery
The advances of effective hydrolysis enzymes with advanced properties, e.g. better
interaction with cheap substrates, higher specific activity and higher stability, are
important factors for the industrial production of biofuel. As discussed above,
lignocellulosic plant biomass degradation into their monomeric sugars comprises
two important constituents, i.e. hemicellulose and cellulose (Balat 2011; Pareek et al.
2013; Ulaganathan et al. 2017), and the composite hemicellulose structure needs the
synergistic action of different enzymes, and endo-1,4-β-xylanase plays an important
role to degrade the complex polymer of xylan into oligosaccharides and other
172
N. Bhardwaj and P. Verma
Another product obtained from biorefinery and has attracted the attention of scientists as an efficient alternative for gasoline (Bhandiwad et al. 2014) (Fig. 7.2) is
biobutanol.
Microorganisms,
such
as
Clostridium
spp.,
C. saccharoperbutylacetonicum, Clostridium acetobutylicum and C. beijerinckii,
are example of microorganims capabable of produding biobutanol by using sugars
from agricultural residues (Bhandiwad et al. 2014; Nakayama et al. 2011). Similarly,
Thermoanaerobacterium thermosaccharolyticum showed 1.8–5.1 mM n-butanol
production from the overexpression of thl, hbd, crt, bcd, etfA and etfB genes of
bcs operon required for butyryl-CoA formation (Bhandiwad et al. 2014). 7.9 g/L of
n-butanol was produced by coculture of Clostridium thermocellum and Clostridium
saccharoperbutylacetonicum (Nakayama et al. 2011). 7.7 g/L of acetoin and 14.5 g/
L of 2,3-butanediol were reported from Geobacillus strain XT15 from corn steep
liquor at 55
C (Yang et al. 2015).
7.9.3 Hydrogen
It is a carrier of energy having a high potential of being considered as an alternative
for fossil fuel. As it is a clean fuel, it can be used as an internal fuel for combustion
engines in combination with oxygen (Koskinen et al. 2008). Thermophilic microorganisms, e.g. Pyrococcus furiosus, Thermococcus kodakarensis and all Thermotoga
and Caldicellulosiruptor species, have been found to be the good producers of
hydrogen with only the water vapour emission (Verhaart et al. 2010). adhE and
aldH genes are not present in these microorganisms; therefore, they do not produce
ethanol; hence due to hydrogenase, hydrogen production increases. However, Clostridium uzonii strain AK15 and Thermoanaerobacterium aciditolerans AK17 isolated from Iceland during geothermal springs showed good hydrogen production
along with bioethanol (Koskinen et al. 2008).
7.10 Molecular Aspects of Enzymes in Biorefinery
The advances of effective hydrolysis enzymes with advanced properties, e.g. better
interaction with cheap substrates, higher specific activity and higher stability, are
important factors for the industrial production of biofuel. As discussed above,
lignocellulosic plant biomass degradation into their monomeric sugars comprises
two important constituents, i.e. hemicellulose and cellulose (Balat 2011; Pareek et al.
2013; Ulaganathan et al. 2017), and the composite hemicellulose structure needs the
synergistic action of different enzymes, and endo-1,4-β-xylanase plays an important
role to degrade the complex polymer of xylan into oligosaccharides and other
172
N. Bhardwaj and P. Verma