Effect of membrane purification and concentration of sucrose in sugar beet molasses for the production of 5-hydroxymethylfurfural

Production of 5-hydroxymethylfurfural from sugar beet molasses as feed-stock should in theory be a straight-forward process: first, hydrolysis of sucrose, followed by dehydration of fructose, but is in reality challenging. The enzyme-catalysed sucrose hydrolysis is inhibited by impurities and the dehydration of fructose has low conversions. In this study, pretreatment of crude molasses through purification using membrane filtration was investigated. The pretreatment process was evaluated with respect to the sucrose hydrolysis reaction rates and for the downstream 5-hydroxymethylfurfural production. Results from the ultra-/nanofiltration experiments showed good filtration fluxes (11–34 L/m² h bar), high flux recovery after being heavily fouled (>80%) and ability to purify sucrose. The sucrose hydrolysis results showed an improved reaction rate for nanofiltered molasses (concentrate), while the ultrafiltration permeate showed no major difference from the crude molasses, indicating that the inhibitory compounds are of low molecular weight. Furthermore, the ultrafiltered molasses showed highly efficient fructose conversion (near 100%) and 5-hydroxymethylfurfural selectivity of 57% in the biphasic acid-catalysed dehydration, in contrast to only 49% fructose conversion in the crude molasses.