Bioresource Technology 333 (2021) 125195 Available online 23 April 2021 0960-8524/© 2021 Elsevier Ltd. All rights reserved. Recent advances in green solvents for lignocellulosic biomass pretreatment: Potential of choline chloride (ChCl) based solvents Chung Loong Yiin a, * , Kok Liang Yap a , Andrian Zi En Ku a , Bridgid Lai Fui Chin b , Serene Sow Mun Lock c , Kin Wai Cheah d , Adrian Chun Minh Loy e , Yi Herng Chan f a Department of Chemical Engineering and Energy Sustainability, Faculty of Engineering, Universiti Malaysia Sarawak (UNIMAS), Kota Samarahan 94300, Sarawak, Malaysia b Department of Chemical Engineering, Faculty of Engineering and Science, Sarawak Campus, Curtin University Malaysia, Miri 98009, Sarawak, Malaysia c CO 2 Research Center (CO2RES), Department of Chemical Engineering, Universiti Teknologi PETRONAS, 32610 Seri Iskandar, Malaysia d Energy and Environment Institute, University of Hull, Cottingham Road, Kingston upon Hull HU6 7RX, United Kingdom e Chemical Engineering Department, Monash University, 3180, Victoria, Australia f PETRONAS Research Sdn. Bhd. (PRSB), Lot 3288 & 3289, Off Jalan Ayer Itam, Kawasan Institusi Bangi, 43000 Kajang, Selangor, Malaysia HIGHLIGHTS G R A P H I C A L ABSTRACT • Identifed green solvents of current in- terest for biomass pretreatment. • Discussed formation, types, materials and design methodologies of green solvents. • Reviewed potential applications of choline chloride (ChCl) based green solvents. • Existing challenges of green solvents are emphasized for future research. A R T I C L E INFO Keywords: Lignocellulosic biomass Pretreatment Green solvents Choline chloride Biomass-to-energy ABSTRACT Biomass wastes exhibit a great potential to be used as a source of non-depleting renewable energy and synthesis of value-added products. The key to the valorization of excess lignocellulosic biomass wastes in the world lies on the pretreatment process to recalcitrant barrier of the lignocellulosic material for the access to useful substrates. A wide range of pretreatment techniques are available and advances in this feld is continuously happening, in search for cheap, effective, and environmentally friendly methods. This review starts with an introduction to conventional approaches and green solvents for pretreatment of lignocellulosic biomass. Subsequently, the mechanism of actions along with the advantages and disadvantages of pretreatment techniques were reviewed. The roles of choline chloride (ChCl) in green solvents and their potential applications were also comprehensively reviewed. The collection of ideas in this review serve as an insight for future works or interest on biomass-to- energy conversion using green solvents. * Corresponding author. E-mail addresses: clyiin@unimas.my (C.L. Yiin), kokliang1@live.com.my (K.L. Yap), andrianku@live.com (A.Z.E. Ku), bridgidchin@curtin.edu.my (B.L.F. Chin), sowmun.lock@utp.edu.my (S.S.M. Lock), K.Cheah@hull.ac.uk (K.W. Cheah), adrianminh@gmail.com (A.C.M. Loy), chan.yiherng@petronas.com.my (Y.H. Chan). Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech https://doi.org/10.1016/j.biortech.2021.125195 Received 8 March 2021; Received in revised form 14 April 2021; Accepted 15 April 2021