In the process of steam explosion, more than 50 % hemicellulose degrades into pentose. Therefore, it is possible to fractionate hemicellulose by washing materials pretreated with steam explosion. As per the analysis in Sect. 4.1, materials pretreated with steam explosion formed porous structure, which enhance the accessibility of a substrate for solvent or other chemicals. So, steam exploded materials are suitable for component fractionation.

Research reveals that lignin could be separated by alkali oxygenation [36]. There­fore, stalk is pretreated with steam explosion-washing-alkali extraction technology to realize fractionation in the component level.

Fig. 4.3 Steam explosion-washing-alkali integrated technology chart

Organic solvent is applied in the process of clean fractionation technology from National Renewable Energy Laboratory [37]. By this way, cellulose, hemicellulose, and lignin in lignocelluloses are also separated. However, compared with organic solvent steam and alkali are cost-competitive. Moreover, alkali solvent could be recycled by nanofiltration.

To improve the yield of hemicellulose [38], corn stalk exploded with steam at severity of logioR0 [min] = 3.05 is pretreated with 0.3-0.5 % dilute sulfuric acid at 110-120 °C for 0.5-1 h. The ratio of dilute acid to solid is 1:5-1:7, and then liquid and solid are separated with spiral extruder. As a result, hemicellulose yield reaches to 30.7 %. Lignin in solid is fractionated with 0.5-2 % NaOH for 2-3 h at 150­160 °C. The ratio of solid to liquid is 1:5-1:7 (based on the hydrolysis residues). The extract liquid is filtrated sequentially with precise filter, ultrafiltration membrane, and nanofiltration membrane. Filtrate from the nanofiltration membrane is a NaOH so­lution that could be reused. Concentrated solution from the ultrafiltration membrane is a lignin solution. The lignin solution is sent to neutralization tank to get lignin precipitation that is washed to get lignin product. The whole chart is as Fig. 4.3.As a result, lignin yields are 16.80 %, and cellulose content in cellulose fraction reaches 63 % from 25.4 %.