Hydrothermal Dehydration of Monosaccharides Promoted by Seawater: Fundamentals on the Catalytic Role of Inorganic Salts

Abstract

In biorefining, the conversion of carbohydrates under subcritical water conditions is a field of extensive studies. In particular, the hydrothermal decomposition of benchmark C6- and C5-monosaccharides, i.e., D-glucose and D-xylose, into furanics and/or organic acids is fully considered. Herein, we propose to establish the fundamentals of the decomposition of D-glucose and D-xylose under subcritical water conditions in the presence of specific salts (i.e., NaCl and KI) and in seawater. Our results demonstrated that the introduction of inorganic salts was found to modify sugars dehydration yields. Different NaCl concentrations from 0.21 to 1.63 mol L −1 promoted the conversion of D-xylose to 2-furfural (2-F) from 28 to 44% (molar yield). NaCl also improved 5-hydroxymethylfurfural (5-HMF) generation from D-glucose as well as rehydration of 5-HMF to levulinic and formic acid. KI favored other pathways toward formic acid production from D-glucose, reaching 20% in the upper concentration. Compared to a solution of equivalent NaCl concentration, seawater enhanced selectivity toward lactic acid which was raised by 10% for both monosaccharides, and sugars conversion, especially for D-glucose whose conversion was increased by 20%. 5-HMF molar yield around 30% were achieved from D-glucose in seawater at 211°C and 20 bars after 15 min.

Direct Brønsted Acid-Catalyzed Dehydration of Glucose to HMF in Methyl Isobutyl Ketone

“…In recent years, the enhancing effects of metal halides on the reactivity and selectivity of dehydration reactions have been extensively explored. − These promotional effects are prevalent in chloride salts with potassium or sodium cations. They are attributed to the stabilization of protonated transition states by the ions and the destabilization of the catalyst and reactants by disrupting solvation. , Here, we evaluate the impact of potassium chloride on the rate and selectivity of glucose dehydration with HCl in MIBK.…”

Microwave‐Assisted Production of 5‐Hydroxymethylfurfural from Glucose

“…First, the aqueous solution of inorganic salts helps to create a biphasic solvent mixture, which facilitates the separation of HMF in the organic phase from the aqueous phase. Second, inorganic cations may also act as Lewis acids while inorganic anions may stabilize carbocation intermediates or catalyze side reactions [26,27] . Furthermore, it has been recently proposed that inorganic salts contribute to the increase in HMF yield by enhancing the fructose dehydration step in organic solvents [28,29] .…”

“…Second, inorganic cations may also act as Lewis acids while inorganic anions may stabilize carbocation intermediates or catalyze side reactions. [26,27] Furthermore, it has been recently proposed that inorganic salts contribute to the increase in HMF yield by enhancing the fructose dehydration step in organic solvents. [28,29] In order to elucidate whether a certain combination of inorganic cation and anion would result in an optimal HMF yield in our microwave-assisted transformation from glucose, we decided to systematically vary the inorganic cations and anions used in the reaction.…”

Catalytic Hydroconversion of 5‐HMF to Value‐Added Chemicals: Insights into the Role of Catalyst Properties and Feedstock Purity

“…Specific inorganic salts can also be considered to be HMF impurities since they are commonly used to accelerate monosaccharides conversion to HMF, or as agent to fortify extraction in two-phasic conditions. [94][95][96][97][98][99] The effect of various sulfate salts addition on the conversion was also investigated by the same research group (Figure 5a). A comparable decrease in DMF conversion was observed when replacing H 2 SO 4 with a sulfate salt in the identical concentration soluble in 2-propanol, for example ZnSO 4 or MgSO 4 .…”

“…In addition, experiments with water addition showed that H 2 O played a negligible role in obstructing Ru's hydrogenation ability, likely only affecting the equilibrium between DMTHF and 2,5‐HDO. Specific inorganic salts can also be considered to be HMF impurities since they are commonly used to accelerate monosaccharides conversion to HMF, or as agent to fortify extraction in two‐phasic conditions [94–99] . The effect of various sulfate salts addition on the conversion was also investigated by the same research group (Figure 5a).…”