A process for efficient conversion of fructose into 5-hydroxymethylfurfural in ammonium salts

Low melting systems consisting of ammonium salts and highly concentrated fructose were used for the conversion of fructose into 5-hydroxymethylfurfural (HMF). Not only acting as solvents, at sufficiently high temperatures, the ammonium salts themselves could also catalyse the dehydration of fructose to HMF. Among those salts, tetraethyl ammonium chloride (TEAC) was found to be the most efficient solvent-catalyst, demonstrated by its ability to achieve 81.3% HMF yield with 33.3 wt% fructose concentration at 120 °C. 79.2% HMF yield was obtained with 50 wt% fructose concentration in the TEAC/fructose system using 5 mol% NaHSO4·H2O as a co-catalyst. A semi continuous biphasic system of TEAC/fructose/NaHSO4·H2O melt using tetrahydrofuran (THF) to recover HMF was proposed and demonstrated in a laboratory scale process operating at 120 °C. The impurities in the HMF recovered, involving TEAC and NaHSO4·H2O, were determined using 1H NMR, elemental analysis and ICP-OES.

Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (87 K)Download as PowerPoint slideHighlights► Tetraethyl ammonium chloride achieved 81.3% HMF yield in a 33 wt% fructose solution. ► Adding NaHSO4 as co-catalyst achieved 79.2% HMF yield in a 50 wt% fructose solution. ► The separation of HMF was successfully achieved in a THF/TEAC biphasic system.