Another approach is to use an organic or aqueous–organic solvent mixture
with addition of an inorganic acid catalyst (H2SO4 or HCl), which is used to
break the internal lignin and hemicellulose bonds. These methods are usually
referred to as organosolv processes [29]. In these cases the hydrolysed
lignin is dissolved and recovered in the organophilic phase. It is important
to thoroughly wash the material prior to enzymatic hydrolysis and fermentation,
as the solvents may act as inhibitors. Solvents that are used are typically
methanol, ethanol, acetone, ethylene glycol, triethylene glycol and phenol.
Some of these substances are explosive and highly inflammable and thus difficult
to handle.