Deep Eutectic Solvents as Green Catalysts for Carbohydrate Conversion and Synthesis of Furanic Compounds from Amazonian Cupuaçu Peel (Theobroma grandiflorum)

Abstract

Lignocellulosic biomass is a promising renewable feedstock, but its high recalcitrance requires biotechnological pretreatments to enable conversion into biobased chemicals. This study evaluated deep eutectic solvent (DES) pretreatments to maximize carbohydrate conversion and optimize the production of furanics 5-hydroxymethylfurfural (HMF) and furfural (FF) from cupuaçu peel (CP). Pretreatment was performed with choline chloride (ChCl)-based DES combined with lactic acid (LA), oxalic acid (OA) or ethylene glycol (EG), using ultrasound (US) or autoclave (ATC). Pretreatments with DES proved effective in structurally modifying biomass, as evidenced by Fourier transform infrared (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermogravimetric analyses (TGA). After acid hydrolysis, ChCl:OA + ATC and ChCl:OA + US increased glucose concentrations by 97.90 and 69.72%, respectively, relative to raw CP. Analysis of variance (ANOVA) revealed a significant interaction between DES type and pretreatment method (p < 0.05). The synthesis of HMF and FF from cupuaçu peel hydrolysate was optimized in a DES/ethyl acetate system, achieving yields of 1.46 and 7.80%, respectively, at 120 °C for 150 min. The results show that the integration of DES combined with US and ATC technologies represents a sustainable and promising strategy for the valorization of Amazonian lignocellulosic waste in the context of biorefineries.

Keywords:
DES; lignocellulosic biomass; furanic compounds; green chemistry