Reactive Extraction Enhanced by Synergic Microwave Heating: Furfural Yield Boost in Biphasic Systems

Abstract

Reactive extraction is an emerging operation in the industry, particularly in biorefining. Here, reactive extraction was demonstrated, enhanced by microwave irradiation to selectively heat the reactive phase (for efficient reaction) without unduly heating the extractive phase (for efficient extraction). These conditions aimed at maximizing the asymmetries in dielectric constants and volumes of the reaction and extraction phases, which resulted in an asymmetric thermal response of the two phases. The efficiency improvement was demonstrated by dehydrating xylose (5 wt % in water) to furfural with an optimal yield of approximately 80 mol % compared with 60–65 mol % under conventional biphasic conditions, which corresponds to approximately 50 % reduction of byproducts.

Selectivity switch by phase switch – the key to a high-yield furfural process

“…22 This extraction allows naturally to consider a biphasic system to convert the xylose upon back-extraction into acidic water, but the xylose-to-furfural selectivity under biphasic operation is typically only about 70%. 11 We therefore considered adapting the solvent in which to convert the back-extracted xylose. We started with a solution of PBA 2 X in toluene in the present study.…”

“…Please do not adjust margins Please do not adjust margins toluene-water (pH 1), which is biphasic at the reaction temperature, resulted in only 70 mol% selectivity. 11 To understand the origin of the high furfural selectivity in the former case, the progress of the reaction was followed in time (Fig. 2), showing a fast (< 30 min) release of the sugar from its boronate ester and partitioning into the aqueous phase (upon analysis at room temperature at which the mixtures are always biphasic), followed by a slower conversion of the released xylose into furfural (Fig.…”

“…In contrast, performing the reaction starting from free xylose in water (pH = 1), using the same solvent system and experimental conditions, but in the absence of PBA, gave only a 70 mol% yield of furfural, comparable to the selectivity obtained under commonly applied water-toluene biphasic conditions. 11 This suggests that the PBA, originating from the hydrolysis of PBA 2 X, is an essential component to obtain the high selectivity, even though ester formation is not.…”

“…[1][2][3][4][5][6] To address these problems and enhance the production of furfural, various strategies have introduced an organic solvent in the process. [6][7][8][9][10][11][12][13][14] A common strategy to improve the efficiency of xylose dehydration is to perform the reaction in a biphasic system, [6][7][8][9][10][11][12] with the aim to extract furfural as soon as it is formed and thereby protect it from degradation. 11,12 Accordingly, the xylose-to-furfural selectivity is raised to 65-70 mol%, which is a significant improvement over the 50 mol% observed when xylose is dehydrated in water.…”

“…[6][7][8][9][10][11][12][13][14] A common strategy to improve the efficiency of xylose dehydration is to perform the reaction in a biphasic system, [6][7][8][9][10][11][12] with the aim to extract furfural as soon as it is formed and thereby protect it from degradation. 11,12 Accordingly, the xylose-to-furfural selectivity is raised to 65-70 mol%, which is a significant improvement over the 50 mol% observed when xylose is dehydrated in water. 12 Alternatively, the reaction can be performed under monophasic conditions, using polar aprotic solvents (e.g., DMSO and sulfolane), optionally with limited amounts of water, delivering furfural with a selectivity up to 80-85 mol%.…”