Application of natural deep eutectic solvents in biomass pretreatment, enzymatic saccharification and cellulosic ethanol production

Authors: KUMAR, ADEPU - Sardar Patel Renewable Energy Research Institute; PARIKH, BHUMIKAS - Sardar Patel Renewable Energy Research Institute; Liu, Zonglin; COTTA, MICHAEL - Former ARS Employee

Submitted to: Materialstoday: Proceedings
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/26/2018
Publication Date: 12/26/2018
Citation: Kumar, A.K., Parikh, B., Liu, Z., Cotta, M.A. 2018. Application of natural deep eutectic solvents in biomass pretreatment, enzymatic saccharification and cellulosic ethanol production. Materialstoday: Proceedings. 5(11):23057-23063 pt. 2. https://doi.org/10.1016/j.matpr.2018.11.035.
DOI: https://doi.org/10.1016/j.matpr.2018.11.035

Interpretive Summary: Cellulosic ethanol production from lignocellulosic materials commonly requires a pretreatment procedure to allow costly enzymes to release fermentable sugars. Currently available acid or alkaline pretreatment methods generate harmful side products which may inhibit subsequent fermentation and also contaminated the environment. Development of renewable, bio-degradable and nontoxic green solvents is needed to maintain a healthy environment and protect the ecosystem. ARS scientists in collaboration with scientists from India developed a new pretreatment method applying low-cost green solvent derived from plant metabolites. The newly developed pretreatment procedures, using green solvent, released fermentable sugars close to the maximum level of reducing sugars obtained by chemical pretreatment. Using an ARS patented enzyme-producing yeast strain, this process yielded a high titer of cellulosic ethanol in a very short period of time from rice straw. It not only reduced the cost, but also significantly improved cellulosic ethanol conversion efficiency. This research provided a novel method of using a plant-based material to expedite advanced biofuels production from plant biomass. Outcomes of this research impact the prospects of economical lignocellulose-to-fuels and chemicals conversion and will likely influence the research and development strategies of both academia and industry.

Technical Abstract: Currently a revolutionary transition is needed in use of greener solvents in chemical industries for a more sustainable world. Natural Deep Eutectic Solvents (NADES) are recently developed as one of these types of new solvents considered as bio-based Ionic liquids (ILs) or Deep Eutectic Solvents (DES). Foreseeing the potential applications of NADES in diverse areas of research, here we have evaluated the applicability of NADES reagents in cellulosic ethanol production from lignocellulosic biomass residue rice straw using Cellic Ctec2 and cellobiose-fermenting yeast strain Clavispora NRRL Y-50464. Enzymatic saccharification of NADES pretreated rice straw produced maximum reducing sugars of 389 g/L was achieved at 40 % solids loading and 12 FPU/g of cellulase enzyme in 48 h. This was marginally less when compared to mild-alkali pretreated rice straw where maximum reducing sugars of 414 g/L was achieved at similar solids and enzyme loading. Besides, increase in solids loading from 10 % to 40 % increased the rate of sugars production significantly in both batch and fed-batch saccharification. Subsequently with the yeast strain NRRL Y-50464 an ethanol production of 36.7 g/L was achieved within 36 h from the soformed reducing sugars (at 8 % measured glucose concentration) with a conversion efficiency of 90.1%.