Promoting the production of 5-hydroxymethylfurfural from high-concentration fructose by creating micro-reactors in a mixed solvent

The severe formation of humins during the conversion of high-concentration fructose is a crucial bottleneck restricting the large-scale production of 5-hydroxymethylfurfural (HMF) from fructose. Herein, we report an efficient catalytic system for the conversion of high-concentration (10.0-60.0 wt%) fructose into HMF by creating micro-reactors with cetyltrimethylammonium bromide (CTAB) in a mixed solvent of 1,4-dioxane and water (DIO-H2O), wherein the formation of humins is remarkably restrained. The micro-reactors were composed of reversed micelles constructed by the assembly of amphiphilic CTAB in the mixed solvent (VDIO/VH2O = 95/5). The confinement of fructose and bromine anions within the hydrophilic moiety of the micro-reactors enabled facile interactions between fructose and Br- ions, thereby enlarging the promotional effect of Br- ions on fructose-to-HMF dehydration via accelerating the deprotonation of oxocarbenium ion intermediates. Afterwards, the hydrophobic moiety assisted in the transfer of HMF into the organic solvent outside the micro-reactor protected HMF from further rehydration or condensation to humins. The competitive degradation and condensation of oxocarbenium ion intermediates to humins were significantly mitigated, resulting in high HMF yield (70.3%) and TOF (186.0 h-1) after reacting high-concentration (50.0 wt%) fructose at 140 degrees C within 15 min. This work highlights the utilization of a multifunctional micro-reactor to fix the reaction zone and facilitate mass transfer, thereby providing a valuable guidance for designing effective catalytic systems for future HMF biorefineries.

Automated summary

A catalytic system using micro-reactors composed of CTAB was developed to convert high-concentration fructose into HMF. The formation of humins was effectively restrained, resulting in high HMF yield and TOF. This work provides valuable guidance for designing effective catalytic systems for future HMF biorefineries.