A ternary eutectic solvent for cellulose nanocrystal production: exploring the recyclability and pre-pilot scale-up

Abstract

Deep eutectic solvents (DES) formed using choline chloride (ChCl), p-toluenesulfonic acid (pTSA) of stoichiometry ChCl: pTSA (1:1) and (1:2), and its ternary eutectic mixtures with phosphoric acid (PA) 85% as an additive (ChCl: pTSA: PA) were evaluated for cellulose nanocrystal (CNC) isolation. Initially, the hydrolytic efficiency to produce CNC of each DES was compared before and after adding phosphoric acid by Hammett acidity parameters and the Gutmann acceptor number. Moreover, different DES molar ratios and reaction time were studied at 80°C for CNC optimization. The nanomaterial characteristics were analyzed by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). The ternary eutectic mixture ChCl: pTSA: PA molar ratio (1:1:1.35) was chosen as a suitable recyclable ternary system at the laboratory scale. A CNC yield of about 80% was obtained from the hydrolysis of commercial cellulose in five cycles of recovery, but it dropped to 35% in pre-pilot scaling. However, no variation in the average size of the resulting CNC was observed (132 ± 50 nm x 23 ± 4 nm), which presented high thermal stability (Tmax 362°C) and high crystallinity of about 80% after 3 h of reaction time.

Cationic micelles in deep eutectic solvents: effects of solvent composition

“…Recently deep eutectic solvents formed from p-toluenesulfonic acid (pTSA) with choline chloride (ChCl) at different molar ratios were evaluated by Rodriguez Rodriguez et al 18 comparing both their physical properties and ability to dissolve metal oxides. Other authors have used pTSA:ChCl mixtures at various molar ratios in applications ranging from the extraction of cellulose nanocrystals from biomass 19 or biofuel production 20 to cathode recycling of Li-ion batteries. 21 In water, pTSA is known to cause massive elongation in C 16 TA + micellar systems, causing formation of highly viscous wormlike micelles.…”