Influence of acidic and alkaline aqueous regeneration on enzymatic digestibility of the cellulose fraction recovered from [amim]Cl-treated rice husk

The recalcitrance of lignocelluloses toward enzymatic hydrolysis necessitates pretreatments. Ionic liquid pretreatment with 1-allyl-3-methylimidazolium chloride ([amin]Cl) was applied to risk husk and cellulose-containing fractions were recovered from the ionic liquid solutions by acidic, alkaline, and alkaline–acidic regeneration respectively. Enzymatic hydrolysis of the recovered materials was carried out and results demonstrated that: (i) acidic regeneration was not substantial to ensure enhanced enzymatic digestibility; (ii) alkaline regeneration increased the enzymatic hydrolysis; (iii) alkaline–acidic regeneration led to an almost complete hydrolysis of the carbohydrate fraction. The obtained results were rationalized by means of chromatographic analyses of soluble fractions collected after the different regeneration processes: the removal of hemicellulose, which increased going from the acidic to the alkaline–acidic regeneration, seemed to play a crucial role in enhancing the rice husk saccharification.