Abstract
5‐Hydroxymethylfurfural (HMF) is an important biobased platform chemical obtainable in high selectivity by the hydrolysis of fructose (FRC). However, FRC is expensive, making the production of HMF at a competitive market price highly challenging. Here, it is shown that sugar beet thick juice, a crude, sucrose‐rich intermediate in sugar refining, is an excellent feedstock for HMF synthesis. Unprecedented high selectivities and yields of >90 % for HMF were achieved in a biphasic reactor setup at 150 °C using salted diluted thick juice with H2SO4 as catalyst and 2‐methyltetrahydrofuran as a bioderived extraction solvent. The conversion of glucose, obtained by sucrose inversion, could be limited to <10 mol %, allowing its recovery for further use. Interestingly, purified sucrose led to significantly lower HMF selectivity and yields, showing advantages from both an economic and chemical selectivity perspective. This opens new avenues for more cost‐effective HMF production.
Highlights
As a response to the anticipated decrease in fossil fuel reserves, fluctuating crude oil prices, and environmental issues related to the use of fossil resources, their replacement with renewable alternatives is receiving much attention
To ensure low GLC conversion and to avoid excessive humin formation, the temperature was set to 150 8C and an extraction solvent was used.[6a]. The reactions, monitored at different reaction times, were run at equal H2SO4 concentrations (0.05 m, pH 1.6) for MTHF (Figure S1 a in the Supporting Information) and Methyl isobutyl ketone (MIBK) (Figure S2 in the Supporting Information) as well as at a set pH achieved by the careful addition of H2SO4
A higher HMF selectivity was observed when using MTHF compared with MIBK (82 and 75 %, respectively, after 30 min), which was attributed to the higher partition coefficient of HMF in MTHF/ water (P = 1.9; determined experimentally) compared with HMF in MIBK/water (P = 1.0), demonstrating the beneficial effect of more extensive removal of HMF from the acid aqueous phase.[17,27]
Summary
As a response to the anticipated decrease in fossil fuel reserves, fluctuating crude oil prices, and environmental issues related to the use of fossil resources, their replacement with renewable alternatives is receiving much attention. Effective isomerization catalysts are required, and well-known examples are CrCl3 and SnCl4.[22] these catalysts are expensive, toxic, and do not always show the desirable compatibility with the dehydration reaction This method typically requires the use of ionic liquids or other alternative, expensive solvents to obtain high HMF yields from GLC. The second approach relies on the conversion of SUC to HMF (from FRC) and GLC This is possible through careful control of the reaction conditions (Figure 1) by making use of the fact that FRC is significantly more reactive than GLC at temperatures around 140 8C.[6a,23] This allows for GLC to be separated after the reaction and subsequently processed to other biobased chemicals or isomerized to FRC and recycled to the reactor. The results were compared with those obtained for pure SUC, clearly showing the beneficial effect of the use of crude thick juice for HMF and GLC production
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