Probing the effects of fructose concentration on the evolution of humins during fructose dehydration

Abstract

5-Hydroxymethylfurfural (HMF), considered as a “sleeping giant” of sustainable chemistry, is generally produced by fructose dehydration. Till now, high HMF yields have been achieved, whereas large-scale production of HMF is...

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

“…This variation of carbon balance revealed the formation and transformation of DFAs during fructose transformation. 14 As evidence, the ESI-MS spectra of the reaction mixture quenched at 2 min confirmed the formation of DFAs ([2Fru-2H 2 O + Na] + , m / z = 347) via progressive dehydration of the [2Fru-H 2 O + Na] + species ( m / z = 365) (Fig. 3).…”

“…57,58 If the degradative condensation was the only way for carbon loss, then the theoretical carbon balance (TCB) should reach 100%. 14 However, the lower TCB in all solvent cases indicated the concurrence of etherification–dehydration–condensation of fructose and/or HMF to humins proceeding by the dehydration and condensation of difructose species formed from intermolecular etherification of fructose. 14,59 In Table 1, the percent of carbon loss from the etherification–dehydration–condensation path was evaluated by 100-TCB, whereas the carbon loss from the degradative condensation path was quantified by the TCB–ACB.…”

“…14 However, the lower TCB in all solvent cases indicated the concurrence of etherification–dehydration–condensation of fructose and/or HMF to humins proceeding by the dehydration and condensation of difructose species formed from intermolecular etherification of fructose. 14,59 In Table 1, the percent of carbon loss from the etherification–dehydration–condensation path was evaluated by 100-TCB, whereas the carbon loss from the degradative condensation path was quantified by the TCB–ACB. Obviously, both 100-TCB and TCB–ACB were decreased by the presence of CTAB in DIO–H 2 O mixed solvents or pure DIO, which illustrated that the humin formation via etherification–dehydration–condensation and degradative condensation of fructose/HMF were simultaneously alleviated by CTAB.…”

“…46,47 However, in our previous study, we found that the increase of fructose concentration mainly led to the aggravation of humin formation via the etherification–dehydration–condensation of fructose at the initial reaction stage, wherein DFAs acted as both reversibly protective species for HMF formation and intermediate species for humin formation. 14,48 As such, to effectively inhibit the humin formation during the acid-catalyzed conversion of high-concentration fructose, the reaction system should be designed to favor fructose dehydration while stabilizing the DFA intermediate species or inhibiting their formation.…”

“…[6][7][8][9] Among others, the polymerized side-products called humins are the most intractable substances because their formation not only increases the energy consumption for separation, but also leads to equipment blockage, catalyst deactivation, and the loss of biomass-derived carbons. 10,11 Notably, the formation of humins becomes more severe in the conversion of high-concentration fructose, [12][13][14] which further lowers the economic feasibility of HMF synthesis. Until now, satisfactory HMF yields have always been achieved at low fructose concentrations (<10.0 wt%).…”