Table 2.

Conditions for lignin extraction used for second-stage pretreatments (170 °C, 1 h, liquid:solid = 7:1 by v/w)

Methods	Extraction solvent	Catalyst	Washing procedure	Lignin precipitation	Ref.
Organosolv	Ethanol/water 50/50 by wt	1% H2SO4	Ethanol/water, 50/50 by wt then hot water	10× volume of hot water	[15]
Soda-AQ	14 wt% active alkali in water	0.1% AQ	Hot water	Adjusting pH to 2.0	[23]
Hydrotrope	30 wt% sodium salicylate in water	0.17% formic acid	Hot water	10× volume of hot water	[26]