Green approach on pretreatment of rice straw using deep eutectic solvent for lignin recovery and efficient hydrolysis

The use of green processes to recover valuable products from lignocellulosic biomass has gained attention in recent years. In this work, rice straw biomass was pretreated using a natural deep eutectic solvent (NADES), composed of naturally occurring reagents, namely, choline chloride (ChCl) and L-( +)-tartaric acid (TA). The NADES-ChCl/TA was investigated as a potential solvent for the fractionation of rice straw into cellulose-enriched material (CEM) with simultaneous lignin recovery. During the process development, the variables considered were temperature, time, and DES concentration with the experimental range of 96–140 °C, 100–180 min, and 14–40 v/v%, respectively. The experimental design facilitates the mixing of NADES-ChCl/TA with water, resulting in a lower viscosity of NADES which enables effective contact of NADES with rice straw biomass. The qualitative assessment of lignin removal from rice straw was observed using ATR/FT-IR spectra and X-ray diffraction. The pretreated rice straw during enzymatic hydrolysis showed a 6.5 times higher fermentable sugar yield than the untreated sample. The NADES-ChCl/TA showed excellent recyclability up to 8 cycles. The designed process could be considered a viable alternative to conventional biorefinery processes.