Kinetics Study of the Hydrodeoxygenation of Xylitol over a ReOx-Pd/CeO2 Catalyst

Blake Macqueen,Jochen Lauterbach,Bradie S Crandall,Michael Royko,Andreas Heyden,Yomaira J Pagán-Torres

doi:10.3390/catal11010108

Blake Macqueen, Jochen Lauterbach + Show 4 more

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https://doi.org/10.3390/catal11010108

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Abstract

In this study, we elucidate the reaction kinetics for the simultaneous hydrodeoxygenation of xylitol to 1,2-dideoxypentitol and 1,2,5-pentanetriol over a ReOx-Pd/CeO2 (2.0 weight% Re, 0.30 weight% Pd) catalyst. The reaction was determined to be a zero-order reaction with respect to xylitol. The activation energy was elucidated through an Arrhenius relationship as well as non-Arrhenius kinetics. The Arrhenius relationship was investigated at 150–170 °C and a constant H2 pressure of 10 bar resulting in an activation energy of 48.7 ± 10.5 kJ/mol. The investigation of non-Arrhenius kinetics was conducted at 120–170 °C and a sub-Arrhenius relation was elucidated with activation energy being dependent on temperature, and ranging from 10.2–51.8 kJ/mol in the temperature range investigated. Internal and external mass transfer were investigated through evaluating the Weisz–Prater criterion and the effect of varying stirring rate on the reaction rate, respectively. There were no internal or external mass transfer limitations present in the reaction.

Highlights

Lignocellulosic biomass can be utilized to produce various sugars, which can further be upgraded to value-added fuels and chemicals by removing the hydroxyl groups [1,2,3,4]
The simultaneous hydrodeoxygenation (S-HDO) of xylitol produces 1,2-dideoxypentitol and 1,2,5-pentanetriol if one pair of vicinal hydroxyl groups is removed or 1-pentanol and 3-pentanol if two pairs of hydroxyl groups are removed. 1,2-dideoxypentitol and 1,2,5-pentanetriol are value-added chemical building blocks that are between 300 to 5000 times more valuable than xylitol [9]. 1,2,5-pentanetriol can be converted to tetrahydrofurfuryl alcohol and 3-hydroxytetrahydropyran through dehydration [12,13]. 1,2,5-pentanetriol has been produced from D-ribose [14], but xylitol offers a potentially economic path for 1,2,5-pentanetriol and 1,2-dideoxypentitiol production via S-HDO due to the current large-scale production of xylitol
X-ray Fluorescence Spectroscopy (XRF) on the ReOx-Pd/CeO2 catalyst showed that both the Re and Pd were uniformly distributed with standard deviations of 0.075 wt% and 0.054 wt%, respectively

Summary

Introduction

Lignocellulosic biomass can be utilized to produce various sugars, which can further be upgraded to value-added fuels and chemicals by removing the hydroxyl groups [1,2,3,4]. Xylitol is a five-carbon sugar alcohol that can be produced through the hydrolysis of xylan to xylose, followed by fermentation of xylose to xylitol [5,6,7,8]. Xylitol contains five vicinal hydroxyl groups, which can be removed to upgrade xylitol to value-added chemicals. The S-HDO of xylitol produces 1,2-dideoxypentitol and 1,2,5-pentanetriol if one pair of vicinal hydroxyl groups is removed or 1-pentanol and 3-pentanol if two pairs of hydroxyl groups are removed. The DODH removes two vicinal hydroxyl groups and forms a double bond between the carbons previously containing the hydroxyl groups.

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Conclusion