Page 94 - Lignocellulosic Biomass to Liquid Biofuels

70 Lignocellulosic Biomass to Liquid Biofuels

structure of lignin. Finally, an efficient method of removing hemicellulose
and lignin has been introduced to make the cellulose accessible to hydro-
lytic enzyme when then can convert it to monosaccharide [12]. There are
several limitations of conventional pretreatment methods, such as use of
irradiation, chemical cost, and high electricity consumption. In compari-
son to this the use of different ionic liquids as pretreatment medium can
well dissolve cellulose or lignin in it owing to its cationic and anionic
structure. Finally, it will remove lignin successfully as well as alter the
crystalline structure of cellulose [13]. The property of the solvent can be
determined by the way suitable cation and anion is selected; this process
transforms it as designer solvent before being implemented in the field of
green synthesis chemistry for its commendable performances [14]. Mai
et al. [15] summarized different chemical processes, such as distillation
(distillation of ionic liquid and distillation of volatile solutes/impurities in
ionic liquid), induced phase separation (salting out, introduction of CO 2 ,
and changing the temperature), extraction (solvent extraction and CO 2
extraction), adsorption (adsorption/desorption and chromatography),
reverse osmosis, pervaporation, magnetic separation, membrane-based
processes [nanofiltration (NF), electrodialysis] and centrifugation, to
recover and recycle ionic liquid so that the ionic liquid-based lignin
recovery can become an industrially suitable procedure. The main stages
involved in lignin recovery route are mixing of biomass powder with
ionic liquid in a specific ratio, stirring and heating at high temperature for
a certain time period which is then followed by the removal of lignin
from ionic liquid-based lignin solution by precipitation. Some organic
antisolvents and recycling of ionic liquid are used after evaporation of
antisolvent for the recovery of final product. Though lignin can be recov-
ered from poplar wood biomass by only alkaline pretreatment, with cer-
tain ionic liquid followed by NaOH, it is possible to gradually increases
lignin yield [16]. Lignin is also recovered from softwood (pine) as well as
hardwood (Eucalyptus) dissolved in imidazolium-based acetate and chloride
ionic liquid. Further categorization of recovered lignin showed 31%
recovery of lignin [17]. Moghaddam et al. [18] isolated and determined
physicochemical characteristics of sugarcane bagasse lignin using IL 1-
butyl-3-methylimidazolium chloride, [b mim ]Cl, and also 1-butyl-
3 methylimidazolium methyl sulfonate, [b mim ][CH 3 SO 3 ], with HCl as
catalyst. The differences in the extraction productivity of organic solvents
are due to the changes in their conductivity as well as dielectric constant.
NaOH is used to eliminate lignin from carbohydrate-enriched material as