Recyclable choline chloride-based deep eutectic solvent pretreatment for accelerated enzymatic digestibility of Triarrhena lutarioriparia

Abstract

Choline chloride (ChCl) is the most common hydrogen acceptor (HBA) used in deep eutectic solvents (DES) due to its low toxicity and biodegradability. In this study, seven types of ChCl-based DESs were used for the pretreatment of Triarrhena lutarioriparia (TL), and the residues after pretreatment were subjected to enzymatic hydrolysis. Characterization techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transformed infrared (FTIR) spectroscopy were used to determine the physical and chemical properties of TL pretreated with DESs. The results demonstrated that ChCl-oxalic acid dihydrate (molar ratio of 2:1; CO2:1) exhibited a good pretreatment ability among the DESs types examined. The optimal TL pretreatment process with CO2:1 was obtained by uniform design (UD) experiments and comprised a solid-liquid ratio of 1:25, temperature of 110 ℃, and time of 5 h, which achieved an enzymatic digestibility of 83.71 %. Furthermore, the cellulose reservation, hemicelluloses removal, and lignin removal still remained over 86 %, 80 % and 67 %, respectively, after being recycled five times. Overall, the CO2:1 pretreatment process was effective for the component separation and enzymatic hydrolysis of TL and will promote the development of a green biological refinery pretreatment process.