Comparison of Solid Acid-Catalyzed and Autocatalyzed C5 and C6 Sugar Dehydration Reactions with Water as a Solvent

Abstract

Lignocellulosic sugars are a potential feedstock for fuel and chemical production. The dehydration activity of an activated carbon catalyst was compared to the dehydration activity of homogeneous autocatalyzed xylose, glucose, and fructose dehydration using water as a solvent. Carbon catalysts are highly suitable for dehydration due to their water tolerance. Although furfurals were formed without any added catalyst, the presence of a heterogeneous catalyst affected beneficially the sugar isomerization and acid formation taking place in the same reaction conditions as sugar dehydration. Heterogeneous carbon catalyst guides the reaction towards the dehydration route by suppressing the formation of acids which cause the less selective autocatalytic reaction.

Oxidative Dehydrogenation of Ethylbenzene Over Poly(furfuryl alcohol)-Derived CMK-1 Carbon Replica

“…Recently, Yang et al [10] have described a high catalytic activity of polyacrylamide-based cryogels in the transesterification of fatty glyceride. Furthermore, carbon materials appeared to be effective catalysts in the dehydration of hemicellulosis sugars [11] as well as in the 1,2-dichloroethane (DCE) dechlorination [12]. However, the spatial structure of majority of investigated carbons consists mainly of disordered micropores, which may hinder internal diffusion of reagents during catalytic processes.…”

Heterogeneous Catalytic Conversion of Biobased Chemicals into Liquid Fuels in the Aqueous Phase

“…In chemical reactions, the use of green solvents, which is another interesting area in green chemistry, is included in the 12 Principles of Green Chemistry. Water is a desirable reaction medium for chemical reactions, because it is abundant, inexpensive, nontoxic, nonflammable, and clean; moreover, a variety of organic reactions have been shown to have improved reactivity and selectivity in aqueous solutions . Biomass conversion processes, such as isomerization and dehydration, can be achieved in aqueous media over water‐tolerant solid acid and/or base catalysts.…”

“…To date, many biobased chemicals, such as sugar, furfural/HMF, levulinic acid, fatty acids, polyhydric alcohols, and phenolics, have been converted into high‐quality fuels through heterogeneous catalytic conversions in the aqueous phase. The conversion reactions in this review involve dehydration, isomerization, aldol condensation, ketonization, rehydration, decarboxylation, hydrogenation, and hydrodeoxygenation (HDO).…”

“…Additionally, dehydration and other reactions are favored by different active sites on the heterogeneous acid catalysts (Scheme ), namely, dehydration is catalyzed by both Brønsted acid and Lewis acid sites, whereas isomerization and rehydration are more reactive on Lewis acid and Brønsted acid sites, respectively . Taking into consideration safety, sustainability and selectivity, the heterogeneous acid catalysts show better performance than homogeneous acid catalysts for the high efficiency of the dehydration process . Therefore, proper selection of the catalyst type and designation of the catalyst properties will benefit the desired dehydration reaction.…”

“…Typically, three types of heterogeneous acid catalysts, phosphates, metal oxides, and zeolites, are widely utilized in sugar dehydration reactions that use water as the reaction medium, and the activity of carbon‐based catalysts in aqueous and biphasic systems have also been studied . These catalysts vary in their activities and stabilities during aqueous‐phase dehydration; for instance, phosphates demonstrate predominant selectivity and stability over other catalysts, and zeolite catalysts are easily deactivated because of the adsorption of undesired humin products in the pore structures .…”