Improving Enzymatic Hydrolysis of Cellulose from Rice Straw Using an Ionic Liquid [EMIM]Ac Pretreatment

Abstract

Lignocellulose represents a key sustainable source of biomass for transformation into biofuels and bio-based products. Unfortunately, the recalcitrance of lignocellulosic biomass poses a major challenge for its sustainable and cost-effective utilization. Overcoming the recalcitrance is therefore an important priority for the development of the lignocellulosic biorefinery. In this work, the ionic liquid, 1-ethyl-3-methylimidazolium acetate, was selected from five ionic liquid candidates for treating rice straw and the potential of accelerating enzymatic hydrolysis. The yield of reducing sugars from rice straw pretreated with this ionic liquid at 120°C for 12 h reached 70.5% after being hydrolyzed enzymatically for 48 h, which was 7-fold higher than that of untreated rice straw and the 1-ethyl-3-methylimidazolium acetate could still be recyclable. The chemical structure and crystalline form of rice straw before and after dissolution were analyzed by Fourier transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy. It showed that the crystalline form of rice straw was partly transformed from cellulose I to cellulose II after 1-ethyl-3-methylimidazolium acetate pretreatment.

Keywords:

• enzymatic hydrolysis
• ionic liquid
• lignin
• pretreatment
• rice straw

Notes

^aThe 1,437 cm⁻¹ band is for CH2 scissoring motion, and the 899 cm⁻¹ band (equivalent to 897 cm⁻¹ absorbance) is for vibrational mode involving C1 and four atoms attached to it, which is characteristic of α-anomers or β-linked glucose polymers (Nelson and O'Connor, 1964); the 1,378 cm⁻¹ band is for C–H bending mode, and the 2,900 cm⁻¹ band is for C–H and CH2 stretching, which is unaffected by changes in crystallinity (Nelson and O'Connor, 1964).