ENZYMATIC HYDROLYSIS OF WHEAT STRAW UNDER PRETREATMENT OF IONIC LIQUID BMIMCL AND ALKALI EXTRACTION

摘要

The wheat straw was subjected to an ionic liquid (IL)l-butyl-3-methylimidazolium chloride ([BMIM]C1) pretreatment step to obtain a high conversion of soluble sugars in the enzyme hydrolysis of cellulose. The solubility of native wheat straw in [BMIM]C1 was 4.50%, whereas wheat straw after alkali extraction was 6.01%. Compared with the regenerated fiber from [BMIM]C1 without alkali extraction process, alkali extraction could significantly improve solubility of wheat straw in ionic liquids, as well as dissolution rate. Enzyme hydrolysis of cellulose from different process shows, amounts of lignin and crystallinity are the main factors which influence the hydrolysis rates, and the former has more effect. The surface morphology of regenerated fibre after pretreatment was observed by optical microscope and scanning electron microscope (SEM); the change of crystallinity and crystal form was detected through X-Ray Diffraction (XRD), and we also discussed possible mechanism of pretreatment of ionic liquids. The results show that the wheat straw could be dissolved in ionic liquids [BMIM]C1 and formed transparent amber solution; the alkali extraction can promote the solution of wheat straw in ionic liquids. Recovered fiber was shaped irregularly, and surface was uneven, the surface area was enlarged. Crystallinity of regenerated fibre decreased from 57% to 38%, and changed the crystal form. The dissolution mechanism of cellulose in [BMIM]C1 can be attributed to the nature of the bulky imidazolium cation and the relatively strong electronegativity and small size of the chloride ion. [BMIM]Cl has high hydrogen bond basicity and the anion plays a key role in the dissolution of cellulose. The chloride ion attacks the free hydroxyl groups and deprotonates cellulose.