Kinetics of Aqueous Phase Dehydration of Xylose into Furfural Catalyzed by ZSM-5 Zeolite

Abstract

ZSM-5 zeolite in H + form with an average pore size of 1.2 nm was used for aqueous phase dehydration of xylose to furfural at low temperatures; that is, from 413 to 493 K. The selectivity in furfural increased with the temperature to a value of 473 K. Beyond this temperature, condensation reactions were significant and facilitated by the intrinsic structure of ZSM-5. A reaction mechanism that included isomerization of xylose to lyxose, dehydration of lyxose and xylose to furfural, fragmentation of furfural to organic acids, oligomerization of furfural to bi-and tridimensional furilic species, and complete dehydration of organic acids to carbonaceous deposits was developed, and the associated kinetic parameters were estimated. The rate of furfural production was found to be more sensitive to temperature than the rates of side reactions, with an estimated activation energy of 32.1 kcal/mol. This value correlated well with data in the literature obtained by homogeneous catalytic dehydration.

Synthesis of Furfural from Xylose by Heterogeneous and Reusable Nafion Catalysts

“…The ln k vs. 1/T Arrhenius plots (Figure 4) produced activation energy values of 86.4 and 89.3 kJ mol À1 , respectively, for Nafion 117 at 5 % and 20 % catalyst weight loading. These energy values are lower than other liquid acid catalysts such H 2 SO 4 (134 kJ mol À1 ) [20] and HCl (142 kJ mol À1 ), [21] and the heterogeneous catalyst zeolite ZSM-5 (134 kJ mol À1 ) [6] used in xylose conversion. Nafion 117 could accelerate the reaction due to its high acidity as a superacid and its ability to stabilize the protonated xylose transition state through coordination to the polyanionic Nafion network.…”

“…[6,7,12] Indeed, water played an important role in xylose dehydration by Nafion 117, as shown in Figure 5. Nafion 117 could tolerate a water content of up to 10 % in DMSO without significant loss of activity, as an average furfural yield of 56 % was obtained with 89 % xylose conversion.…”

“…[19] As such, mordenites with 0.7 nm pore size tend to exhibit higher selectivity than faujasites with 1.3 nm pore sizes. [4] For heterogeneous zeolite ZSM-5 (1.2 nm pore size) [6] and faujasites, the deposition of furfural oligomers inside catalyst pores is the primary source of catalyst deactivation. However, even with the deposition of carbonaceous materials on the surface of the Nafion, the reactivity and reusability of the catalyst remained high after repeated runs (vide infra).…”

“…These heterogeneous catalysts are often solid acids characterized by strong Brønsted acidity, high surface area, and are thermally stable at the high temperatures required for rapid xylose dehydration to furfural. Zeolites generally produce lower reaction yields [4][5][6] whereas heteropolyacids require lower substrate-to-catalyst loading to obtain moderate yields (63 %). [7] Sulfonic-acid-functionalized MCMs (Mobil catalytic materials) have 91 % xylose conversion and 82 % furfural selectivity, but require 24 h of reaction with diminishing catalyst activity for consecutive runs.…”

Carbocatalytic dehydration of xylose to furfural in water

“…1) [1]. Use of solid acids such as zeolites [3][4][5], heteropolyacids [6], and sulfonic acid functionalized-Mobil Catalytic Materials (MCMs) [7] with strong Brö nsted acidity, high surface area and thermal stability have been attempted. Nafion, a sulfonated tetrafluoroethylene-based fluoropolymer-copolymer [8], has also been proven as an effective and reusable catalyst for the conversion of xylose to furfural [9].…”