biological process to be applied (Doherty et al. 2011; Menon and Rao 2012; Lange et
al. 2013). An effective pretreatment method should be cost effective, require less
energy input, catalyst recovery, and recycle, avoid inhibitors’ formation, and recovery of lignin and hemicellulose fraction as well as treatment of waste. Chemical
pretreatments are most studied processes, and these are generally used in pulp and
paper industry. Pretreatment is a prerequisite for feasibility of processes based on
plant polysaccharides. Delignification is essential in pulp and paper mill industry and
for biofuel production. Pulp and paper and plant polysaccharide-based industries are
the major sources of lignin. The major types of lignin generated through different
pretreatment processes applied in industries are Kraft lignin, lignosulphonates, soda
lignin, and organosolv lignin.
4.2.3 Lignin Structure and Characterization
The exact structure of natural lignin is still unknown, but with the advancement in
analytical technique some linkages commonly found in lignin have been revealed.
The linkages are formed between oligomer–monomer, oligomer–oligomer, and
monomer–monomer coupling reactions (Ralph et al. 2004). There are various
interunit linkages observed in lignin polymer as shown in Fig. 4.3.
Fig. 4.3 Common interunit linkages found in highly complex three dimensional lignin polymer
(Longe et al. 2016)
88
M. Kumar et al.
al. 2013). An effective pretreatment method should be cost effective, require less
energy input, catalyst recovery, and recycle, avoid inhibitors’ formation, and recovery of lignin and hemicellulose fraction as well as treatment of waste. Chemical
pretreatments are most studied processes, and these are generally used in pulp and
paper industry. Pretreatment is a prerequisite for feasibility of processes based on
plant polysaccharides. Delignification is essential in pulp and paper mill industry and
for biofuel production. Pulp and paper and plant polysaccharide-based industries are
the major sources of lignin. The major types of lignin generated through different
pretreatment processes applied in industries are Kraft lignin, lignosulphonates, soda
lignin, and organosolv lignin.
4.2.3 Lignin Structure and Characterization
The exact structure of natural lignin is still unknown, but with the advancement in
analytical technique some linkages commonly found in lignin have been revealed.
The linkages are formed between oligomer–monomer, oligomer–oligomer, and
monomer–monomer coupling reactions (Ralph et al. 2004). There are various
interunit linkages observed in lignin polymer as shown in Fig. 4.3.
Fig. 4.3 Common interunit linkages found in highly complex three dimensional lignin polymer
(Longe et al. 2016)
88
M. Kumar et al.