Xylose Isomerization with Zeolites in a Two‐Step Alcohol–Water Process

Abstract

Isomerization of xylose to xylulose was efficiently catalyzed by large-pore zeolites in a two-step methanol-water process that enhanced the product yield significantly. The reaction pathway involves xylose isomerization to xylulose, which, in part, subsequently reacts with methanol to form methyl xyluloside (step 1) followed by hydrolysis after water addition to form additional xylulose (step 2). NMR spectroscopy studies performed with (13) C-labeled xylose confirmed the proposed reaction pathway. The most active catalyst examined was zeolite Y, which proved more active than zeolite beta, ZSM-5, and mordenite. The yield of xylulose obtained over H-USY (Si/Al=6) after 1 h of reaction at 100 °C was 39%. After water hydrolysis in the second reaction step, the yield increased to 47%. Results obtained from pyridine adsorption studies confirm that H-USY (6) is a catalyst that combines Brønsted and Lewis acid sites, and isomerizes xylose in alcohol media to form xylulose at low temperature. The applied zeolites are commercially available; do not contain any auxiliary tetravalent metals, for example, tin, titanium, or zirconium; isomerize xylose efficiently; are easy to regenerate; and are prone to recycling.

Dehydration of Xylose to Furfural in Alcohol Media in the Presence of Solid Acid Catalysts

“…However, results reveal that a rapid transformation of xylose ( 1 ) into alkyl xylosides ( 2 ) occurs during the early stages of the reaction. The formation of other types of pentose isomers, such as alkyl ethers of lyxose or xylulose, which are formed under similar reaction conditions, cannot be discarded as these are not resolved in the analysis of the reaction products. However, all these chemical transformations are included and considered within the chemical transformations included in Scheme , though all of them are lumped into single reactions.…”

Fast furfural formation from xylose using solid acid catalysts assisted by a microwave reactor

“…It has been reported previously that SZ possesses Brønsted acid (BA) sites, while Al2O3 presents a combination of BA and Lewis acid (LA) sites. BA are linked to direct pentose dehydration into FUR, and LA tend to isomerize pentoses into chemical intermediates, such as xylulose [12,20,35,[51][52][53]. However, the discussion on the coexistence of BA and LA sites on the surface of SZ and how to properly measure it still continues [54][55][56].…”

Catalytic Isomerization of Biomass‐Derived Aldoses: A Review

“…[59] The same protocol has successfully been appliedt ot he isomerization of xylose into xylulose. [60] Remarkably,t he isomerization of tetroses,t hat is, erythrose and threose to erythrulose,e fficiently proceeds over an H + zeolite in aqueous media. Surprisingly, the reaction rate decreases upon using alcohols as solvents instead of water.…”