Enhanced Conversion of Xylan into Furfural using Acidic Deep Eutectic Solvents with Dual Solvent and Catalyst Behavior

Abstract

An efficient process for the production of furfural from xylan by using acidic deep eutectic solvents (DESs), which act both as solvents and catalysts, is developed. DESs composed of cholinium chloride ([Ch]Cl) and malic acid or glycolic acid at different molar ratios, and the effects of water and γ‐valerolactone (GVL) contents, solid/liquid (S/L) ratio, and microwave heating are investigated. The best furfural yields are obtained with the DES [Ch]Cl:malic acid (1:3 molar ratio)+5 wt % water, under microwave heating for 2.5 min at 150 °C, a S/L ratio of 0.050, and GVL at a weight ratio of 2:1. Under these conditions, a remarkable furfural yield (75 %) is obtained. Direct distillation of furfural from the DES/GVL solvent and distillation from 2‐methyltetrahydrofuran (2‐MeTHF) after a back‐extraction step enable 89 % furfural recovery from 2‐MeTHF. This strategy allows recycling of the DES/GVL for at least three times with only small losses in furfural yield (>69 %). This is the fastest and highest‐yielding process reported for furfural production using bio‐based DESs as solvents and catalysts, paving the way for scale‐up of the process.

Unveiling Modifications of Biomass Polysaccharides during Thermal Treatment in Cholinium Chloride : Lactic Acid Deep Eutectic Solvent

“…Few studies have reported the extraction and valorization of xylans using DES as solvent media [18,35,36] . For instance, a xylan pre‐extraction step from biomass was developed with the mild alkaline‐based [Ch]Cl : Urea aiming at preserving the xylan structure [35] .…”

“…For instance, a xylan pre‐extraction step from biomass was developed with the mild alkaline‐based [Ch]Cl : Urea aiming at preserving the xylan structure [35] . On another perspective, the use of acid‐based DES, such as [Ch]Cl:Oxalic acid and [Ch]Cl:Malic acid, allowed a favorable conversion of xylans into furfural [18] . Although some trends have been reported with acid‐based DES, the fate of hemicelluloses during [Ch]Cl/LA delignification media has not been explored.…”

“…In the case of hemicelluloses, other valorization approaches can be adopted. For instance, xylans can be depolymerized into xylose, which in turn can be converted into platform chemicals, such as furfural and xylitol [16–18] …”

“…Additionally, scarce attention has been given to the fate of hemicelluloses during biomass treatment with this DES, which can be considered of utmost importance for their subsequent valorization. Furthermore, it has been reported that xylans’ structure is maintained in neutral to mild alkaline‐based DES, such as [Ch]Cl/urea, [35] while in the presence of acidic [Ch]Cl‐based DES, comprising oxalic, malic or glycolic acids, xylans are hydrolyzed and favorably converted into furfural [18,36] …”

Aqueous solutions of deep eutectic systems as reaction media for the saccharification and fermentation of hardwood xylan into xylitol

“…Furthermore, they present similar "designer solvent" characteristics (Zhang et al, 2012) given the large variety of HBAs and HBDs that can be used and respective proportions. Over the last few years, the use of DES as greener alternatives to conventional solvents for lignocellulosic biomass processing has attracted increased attention, in areas spanning from delignification (Shen et al, 2019;Soares et al, 2017;Alvarez-Vasco et al, 2016) to high value compounds extraction (Gullón et al, 2019) and their conversion into added value products (Morais et al, 2020).…”