Development of a continuous intensified process for conversion of hemicellulose sugars into furans using an agitated cell reactor

This study addresses significant process challenges associated with the reactive nature of hemicellulose-derived furan intermediates in aqueous mediums. A continuous agitated cell reactor was used to intensify the extractive reaction using methyl isobutyl ketone as an extractive phase to isolate in situ the furan products obtained by dehydration of hemicellulose sugars in aqueous media, using sulfuric acid as catalyst. The study, as part of a two-stage investigation, examined the influences of reaction temperature (110–140 °C), residence time (30–120 min), catalyst concentration (0.1–0.2 mol L⁻¹) and agitation frequency (2–9 Hz) in a single-phase medium using a definitive screening design of experiment. The aim of this initial experimentation stage was to identify the most statistically significant variables, which would serve as a benchmark for the subsequent evaluation of a biphasic medium. The highest glucose and xylose conversions obtained for single-phase aqueous operation were 30.6% and 61.4%, respectively, achieved for the highest temperature of 140 °C and 120 min residence time. At these conversions, the yield was 3.6% for 5-HMF, and 27.9% for furfural. The low yield was due to the degradation of the reactive intermediate furans in the aqueous phase. Acid concentration and the agitation frequency showed a significant effect on the conversion of the sugars. When using the biphasic extractive reaction system at 125 °C and 120 min residence time, the conversion of glucose and xylose rose to 45.9% and 78.5%, respectively, and the selectivity of 5-HMF (23.1%) and furfural (83.4%) and the yields (10.6% for 5-HMF and 65.5% for furfural) of furan in the biphasic system more than doubled in comparison with the use of single-phase operation. Two industrial hemicellulose hydrolysates were also investigated in a biphasic system, with one achieving maximum yields of 5-HMF and furfural at 21.7% and 37.9%, respectively, influenced by its higher oligomer content. The other stream exhibited furfural and 5-HMF yields of 45.5% and 17.5%, respectively, reflecting a simpler composition and a more favorable C5 sugar profile.