Abstract
A two-step process combining the (equilibrium) glucose isomerization to fructose with selective dehydration of fructose in the obtained sugar mixture to 5-hydroxymethylfurfural (HMF), where glucose is largely unconverted and recycled, represents an attractive concept to increase the overall efficiency for HMF synthesis. This work presents experimental and modelling studies on the conversion of such fructose-glucose mixture to HMF using the sulfuric acid catalyst in a water-methyl isobutyl ketone biphasic system under a wide range of conditions (e.g., temperature, catalyst and sugar concentrations). Through detailed product analyses and ESI-MS spectroscopy, the excess formation of formic acid (together with humins) by the direct sugar/HMF degradation was confirmed and included in the reaction network (neglected in most literatures). The kinetic modelling based on batch experiments in monophasic water well describes the measurements thereof, whereas distinct deviations were found in the prediction of typical literature kinetic models. The incorporation of HMF equilibrium extraction into the developed kinetic model, with consideration of phase volume change as a function of temperature and partial phase miscibility, enables to predict reaction results in the biphasic system in batch. This kinetic model allows to optimize conditions for HMF synthesis that are favored in continuous reactors with minimized back mixing. Based on the model implications, the biphasic system was optimized with slug flow microreactors to better address process intensification and scale-up aspects. Using a simulated fructose-glucose mixture feedstock to represent commercially available high fructose corn syrups, a maximum HMF yield of 81% was obtained at 155 °C over 0.05 M H2SO4 at a residence time of 16 min in the microreactor, with 96% fructose conversion and over 95% of glucose remaining unconverted.
Highlights
The steadily depleting fossil resource and growing environmental concern over CO2 emission have promoted worldwide research atten tions on utilizing lignocellulosic biomass as a green and sustainable feedstock for chemical industry
The possible interaction between glucose and fructose leading to humins is excluded by the fact that no distinct increase of the glucose and fructose conversions was observed compared with the cases starting from only glucose or fructose, as experimentally proven in the work by Tan-Soetedjo et al [36] aiming at the sucrose conversion to HMF in water
In order to develop a process that allows the integration with and upgrading of the industrial processes producing fructose-glucose mix tures in the current bio refinery, experimental and kinetic modeling studies on the conversion of fructose-glucose mixture were performed in this work using sulfuric acid as the catalyst in both monophasic water and biphasic water-methyl isobutyl ketone (MIBK)
Summary
The steadily depleting fossil resource and growing environmental concern over CO2 emission have promoted worldwide research atten tions on utilizing lignocellulosic biomass as a green and sustainable feedstock for chemical industry. HMF is typically produced in good yields by the acid catalyzed dehydration of hexoses such as glucose and fructose [14]. The techno-economic analysis indicates that glucose is a more attractive feedstock due to its higher abundance and much cheaper price compared with fructose [15].
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