Unlocking the Biofuel Potential of Tamarind Shells through Deep Eutectic Solvent Pretreatment

¹ Biorefinery and Process Automation Engineering Center, Department of Chemical Engineering and Management, The Sirindhorn International Thai German Graduate School of Engineering, King Mongkut’s University of Technology North Bangkok, Bangkok, Thailand.
² Theophane Venard School of Food Biotechnology and Innovation, Assumption University of Thailand, Bangkok, Thailand
³ Department of Biotechnology, Faculty of Applied Science, King Mongkut’s University of Technology North Bangkok, Bangkok, Thailand

^* Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Abstract

Lignocellulosic biomass is a promising feedstock for bioethanol production, but its recalcitrant structure requires efficient pretreatment to improve sugar release. This study valorized tamarind shells, an abundant agricultural residue, for bioethanol production through pretreatment with two deep eutectic solvents (DESs): a ternary DES containing choline chloride, ethylene glycol, and p-toluenesulfonic acid, and a binary DES containing urea and monoethanolamine. Pretreatment significantly modified biomass composition, with the ternary DES removing hemicellulose completely, while the binary DES reduced lignin and partially solubilized hemicellulose. Enzymatic saccharification increased reducing sugar yields from 31.80 mg/g in untreated shells to 183.94 mg/g and 170.50 mg/g for ternary and binary DES-pretreated biomass, respectively. Fermentation of the hydrolysates produced ethanol concentrations of 91.48 mg/g for the ternary DES, and 85.76 mg/g for the binary DES, representing 6.9and 6.4-folds increase over untreated shells (13.34 mg/g). These results demonstrate that DES pretreatment effectively enhances sugar release and ethanol production, highlighting tamarind shells as a sustainable feedstock for bioethanol.