Deep eutectic solvent pretreatment of oil palm biomass: Promoted lignin pyrolysis and enzymatic digestibility of solid residues

Guohua Miao; Jung Lin Wong; Jiuan Jing Chew; Deni Shidqi Khaerudini; Jaka Sunarso; Feng Xu

doi:10.1016/j.ijbiomac.2024.138847

Deep eutectic solvent pretreatment of oil palm biomass: Promoted lignin pyrolysis and enzymatic digestibility of solid residues

Int J Biol Macromol. 2024 Dec 24:293:138847. doi: 10.1016/j.ijbiomac.2024.138847. Online ahead of print.

Authors

Guohua Miao¹, Jung Lin Wong², Jiuan Jing Chew², Deni Shidqi Khaerudini³, Jaka Sunarso⁴, Feng Xu⁵

Affiliations

¹ Beijing Key Laboratory of Lignocellulosic Chemistry, Beijing Forestry University, Beijing 100083, PR China.
² Research Centre for Sustainable Technologies, Faculty of Engineering, Computing and Science, Swinburne University of Technology Sarawak Campus, Kuching 93350, Sarawak, Malaysia.
³ Research Center for Advanced Materials, National Research and Innovation Agency, Bld. 440 Kawasan Puspiptek Serpong, South Tangerang 15314, Banten, Indonesia.
⁴ Research Centre for Sustainable Technologies, Faculty of Engineering, Computing and Science, Swinburne University of Technology Sarawak Campus, Kuching 93350, Sarawak, Malaysia. Electronic address: jsunarso@swinburne.edu.my.
⁵ Beijing Key Laboratory of Lignocellulosic Chemistry, Beijing Forestry University, Beijing 100083, PR China. Electronic address: xfx315@bjfu.edu.cn.

PMID: 39725101
DOI: 10.1016/j.ijbiomac.2024.138847

Abstract

Herein, choline chloride/oxalic acid (ChCl/OA) and choline chloride/oxalic acid/ethylene glycol (ChCl/OA/EG) pretreatments of oil palm empty fruit bunches (EFB) and mesocarp fibers (MSF) were conducted to achieve protection of the lignin structure, while improving the enzymatic efficiency of the solid residues. Under the operating conditions of 90 °C and 6 h, ChCl/OA/EG demonstrated a higher lignin extraction selectivity and obtained solid residues with higher hemicellulose content compared to ChCl/OA. The digestibility of glucan and xylan in solid residues obtained using ChCl/OA/EG achieved 98.56 % and 95.63 %, respectively, for EFB and 75.95 % and 88.60 %, for MSF. Uncondensed lignin enriched with 71.79-81.61 % of β-O-4 bonds was obtained from EFB and MSF using ChCl/OA/EG. 2D HSQC NMR and the density functional theory calculation confirmed that substituting the lignin C_α position by ethylene glycol changed the local potentials of the β-O-4 bonds, impeding the attack of protons (H⁺). The higher β-O-4 linkage content in ChCl/OA/EG-Ls led to the formation of several oxygenated alkyl methoxy phenols and alkyl methoxy phenols were promoted during the pyrolysis. Moreover, molecular dynamics simulations showed that the main factor affecting lignin extraction and dissolution in this study was the diffusion coefficient of lignin in DESs.

Keywords: Biomass pretreatment; Enzymatic hydrolysis; Lignin pyrolysis; β-O-4 protection.