Efficient synthesis of furfural from xylose over HCl catalyst in slug flow microreactors promoted by NaCl addition

Abstract

Efficient synthesis of furfural from xylose over the HCl catalyst in a water-methyl isobutyl ketone biphasic system was achieved in slug flow microreactors, using NaCl as a promotor which facilitates xylose dehydration and suppresses xylose condensation. An optimized furfural yield of 93% was obtained from 1 M xylose over 0.2 M HCl with 10 wt% NaCl at 180 C within 4 min. A comprehensive kinetic model was developed from monophasic experiments in water in microreactors, by incorporating the acidity in water and kinetic constants as a function of the chloride ion concentration. The coupling of kinetic model with furfural extraction, with consideration of phase volume change as a function of temperature and partial phase miscibility, enables to predict the results of biphasic experiments in microreactors where masstransfer limitation was eliminated. The aqueous phase containing HCl and NaCl could be readily recycled and reused multiple times without noticeable performance loss.

Insights into the reaction network and kinetics of xylose conversion over combined Lewis/Brønsted acid catalysts in a flow microreactor

“…The setup and procedure are similar to that reported in our previous work. 19,20,29 Typically, the aqueous feed contained sugars or furfural as well as HCl and (or) AlCl 3 catalyst, and the organic feed was MIBK. Both phases were fed to the microreactor using a binary HPLC pump unit (Agilent 1200 Series).…”

“…We have recently reported the use of a slug flow microreactor for xylose conversion over the HCl catalyst in a water (with 10 wt% NaCl addition)-methyl isobutyl ketone biphasic system, where a promising furfural yield up to 93% was achieved at 180 °C and 4 min. 29 The furfural extraction rate was estimated to be two orders of magnitude higher than the rate of furfural formation or degradation, rendering the reaction under kinetic control.…”

Kinetic and mechanistic aspects of furfural degradation in biorefineries

“…One might argue that acid anions could influence furfural degradation, especially because halides are known to catalyze the dehydration of sugars due to their basic and nucleophilic character, and chloride ions were found to accelerate furfural degradation in aqueous solutions. [44,45] Enslow and coworkers proposed that chloride ions may stabilize oxocarbenium ions, thus promoting the nucleophilic attack on the carbonyl group. However, a catalytic effect of anions, other than chloride has never been described for the degradation of furfural or HMF.…”

Titanium Phosphate Grafted on Mesoporous SBA-15 Silica as a Solid Acid Catalyst for the Synthesis of 5-Hydroxymethylfurfural from Glucose

“…Moreover, water as a green and cheap solvent is more economically and environmentally desirable compared with ionic liquids and polar aprotic organic solvents, despite side reactions occurring in water such as HMF rehydration to formic acid (FA) and levulinic acid, as well as the polymerization of sugars and HMF to humins. To suppress these side reactions, biphasic systems with the addition of a non-reactive organic phase to extract HMF formed in situ in the aqueous reaction phase has been developed and proven effective. − ,− Other challenges that need to be addressed for reactions over solid acid catalysts in water include (i) the deactivation of LAS by hydration in water (e.g., zeolites); (ii) the hydrolytic leaching of active functional groups (e.g., sulfate or phosphate groups on acid-functionalized metal oxides); and (iii) the collapse of porous structures under hydrothermal reaction conditions . Consequently, developing water-tolerant bi-functional solid acid catalysts for glucose conversion in water-organic biphasic systems is of great importance.…”