Preparation of 5-HMF in a DES/Ethyl N-Butyrate Two-Phase System

Abstract

In this paper, a two-phase system, formed by oxalic acid/choline chloride-based deep eutectic solvent (DES) and chosen extractants, was used as a dissolution–reaction–separation system, and metal chloride was used as a catalyst to study the degradation of cellulose to produce 5-hydroxymethylfurfural (5-HMF) and glucose. The effects of the amount of organic solvent and the reaction temperature on product yield, the repeated recycling of DES, the comparison between a two-phase system and a homogeneous system, and the mechanism of cellulose degradation to 5-HMF were investigated. The results show that ethyl n-butyrate has the best extraction effect on 5-HMF. Compared with the homogeneous system, the yield of 5-HMF and glucose in the two-phase system is significantly improved. At a temperature of 140 °C and a reaction time of 120 min, the yields of glucose and 5-HMF reached the maximum, which were 23.5% and 29.8%, respectively. After DES was reused three times, the yields of glucose and 5-HMF decreased greatly, indicating that the recycling rate of DES was low.

Acid-Catalyzed Conversion of Cellulose Into Levulinic Acid With Biphasic Solvent System

“…Formic acid is also a by-product of furfural by hydrolysis and fission ( van Zandvoort et al, 2015 ). Yet, in this reaction, the products degraded in the aqueous layer would transfer to the organic layer (GVL), such as HMF and LA, due to the difference in hydrophobicity between the reactants and the products, while the sugars and acids remain in the aqueous layer, which lead to the efficient separation of products and the recovery of solvents ( Mellmer et al, 2019 ; Lang et al, 2020 ). What is more, the proton transition states of acidic protons in polar aprotic solvents, such as GVL and THF, are unstable relative to water, where destabilization of the acidic protons could lead to the increased reactivity of acid-catalyzed reactions ( Wang et al, 2012 ; Mellmer et al, 2019 ).…”

“…The microwave-assisted hydrolysis of bamboo to 5-HMF and furfural is also studied in a dilute acid (H 2 O)/methyl isobutyl ketone (MIBK)biphasic system ( Sweygers et al, 2020 ). Generally, in a biphasic system, the hydrolysis of cellulose to glucose and the further degradation of glucose to 5-HMF occur mainly in the aqueous phase, and the degradation of 5-HMF to LA mainly occurs in the organic phase ( Ghosh et al, 2016 ; Lang et al, 2020 ). This separated reaction medium offers many advantages such as enhancing cellulose solubility, preventing LA from polymerization and concentrating products by using a lower volume of solvent.…”

Deep Eutectic Solvents for the Valorisation of Lignocellulosic Biomasses towards Fine Chemicals

“…Therefore, in this case, the use of DESs acquires importance both for the solubilization issue and the catalytic aspect. A list of DESs that resulted in being efficient in the conversion of cellulose is reported in Table 4 [146,147,154].…”

“…Lang et al [146] reported a two-phase system formed by DES (ChCl/oxalic acid) and chosen solvents in order to overcome problems of the separation of products. Metal chloride (SnCl 4 ) was used as a catalyst to study the degradation of cellulose to produce HMF and glucose.…”

Ionic Liquids in Catalysis

“…By rehydration reaction of the latter, it can be converted into levulinic acid. The process of cellulose degradation towards 5-HMF and glucose in the presence of DES (deep eutectic solvents based on oxalic acid/choline chloride) and metal chlorides (CrCl 3 or SnCl 4 ) has been presented by Zhang's research group [27]. Brønsted acidic ionic liquids based on trimethylamine and sulfuric acid were employed as a solvent and catalyst in the synthesis of bis(2-ethylhexyl) terephthalate which is used as a plasticizer in the manufacture of plastics coming into contact with food.…”