Insight into Aluminum Sulfate‐Catalyzed Xylan Conversion into Furfural in a γ‐Valerolactone/Water Biphasic Solvent under Microwave Conditions

Abstract

A simple and efficient biphasic system with an earth-abundant metal salt catalyst was used to produce furfural from xylan with a high yield of up to 87.8 % under microwave conditions. Strikingly, the metal salt Al (SO ) exhibited excellent catalytic activity for xylan conversion, owing to a combination of Lewis and Brønsted acidity and its ability to promote good phase separation. The critical role of the SO anion was first analyzed, which resulted in the aforementioned characteristics when combined with the Al cation. The mixed solvent system with γ-valerolactone (GVL) as the organic phase provided the highest furfural yield, resulting from its good dielectric properties and dissolving capacity, which facilitated the absorption of microwave energy and promoted mass transfer. Mechanistic studies suggested that the xylan-to-furfural conversion proceeded mainly through a hydrolysis-isomerization-dehydration pathway and the hexa-coordinated Lewis acidic [Al(OH) (aq)] species were the active sites for xylose-xylulose isomerization. Detailed kinetic studies of the subreaction for the xylan conversion revealed that GVL regulates the reaction rates and pathways by promoting the rates of the key steps involved for furfural production and suppressing the side reactions for humin production. Finally, the Al (SO ) catalyst was used for the production of furfural from several lignocellulosic feedstocks, revealing its great potential for other biomass conversions.

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

“…Conventional solvents, such as methyl isobutyl ketone, tetrahydrofuran (THF), and cyclopentyl methyl ether have been used for this purpose. More recently, bio‐based solvents such as γ‐valerolactone (GVL) and 2‐MeTHF have been applied as greener alternatives.…”

“…Concerning the production of furfural from hemicelluloses, improved furfural yields have been obtained using biphasic systems and microwave‐assisted reactions . Yang et al .…”

“…reported a furfural yield of 64.0 % using microwave heating and a H 2 O/THF biphasic system containing NaCl and AlCl 3 ⋅6 H 2 O at 140 °C . Also by using microwave‐induced reactions, Yang et al . obtained an 87.8 % yield of furfural with a GVL/H 2 O solvent system at 130 °C and Al 2 (SO 4 ) 3 as catalyst .…”

The Effect of Solvent Polarity on Autocatalytic Furfural Production Confirmed by Multivariate Statistical Analysis

“…Increasing the R o and δ P increased both conversion and yield in pure aqueous and organic/water mixtures of sulfolane, γ-butyrolactone, γ-valerolactone, γ-hexalactone, and tetrahydrofuran. [3,9] In biphasic systems using aluminium sulfate as the catalyst, Yang et al hypothesized that as the polarity of a solvent increases, furfural yields increase in γ-valerolactone (GVL), methyl isobutyl ketone, tetrahydrofuran (THF), and 2-methyltetrahydrofuran; [10] however, no direct measure of solvent polarity was provided.Although acid catalysts increase the rate of reaction, furans can be produced through an autocatalytic process (Scheme 1), with the mechanism initiated by the formation of hydronium ions in high temperature water. Using principal component analysis and projection to latent structures, a semi-empirical model was developed that provided estimates of xylose conversion and furfural yield over a range of experimental R o and δ P values.…”

“…[3,9] In biphasic systems using aluminium sulfate as the catalyst, Yang et al hypothesized that as the polarity of a solvent increases, furfural yields increase in γ-valerolactone (GVL), methyl isobutyl ketone, tetrahydrofuran (THF), and 2-methyltetrahydrofuran; [10] however, no direct measure of solvent polarity was provided. Previous research has explored acid-catalyzed reactions in organic solvent mixtures for both monophasic and biphasic systems.…”