Date of Award
Open Access Dissertation
This work set out to investigate biomass derived sugar alcohol upgrading via the removal of oxygen and hydroxyl groups via the hydrodeoxygenation reaction utilizing heterogeneous catalysts. The importance of reaction conditions, catalyst meal loadings, catalyst structure and properties were probed using techniques such as design of experiments, and spectroscopic techniques including Raman and DRIFTS. The state of the art simultaneous hydrodeoxygenation (S-HDO) catalyst ReOx-Pd/CeO2 was investigated and optimized for various sugar alcohol substrates. The kinetics and associated mass transfer were also investigated to give further insight into the reaction over the ReOxPd/CeO2 catalyst.
First, the effects of reaction temperature, pressure and Re loading in the ReOxPd/CeO2 catalyst on S-HDO conversion and selectivity for 1,4-anhydroerythritol and xylitol as substrates was investigated. Simplistic L9 Taguchi design of experiments were utilized to elucidate the associated relationships. The designs showed the significance of reaction temperature on the yield of the reaction and also elucidated a zero-order relation with hydrogen pressure. The zero-order relation with pressure was evaluated and confirmed down to 10 bar H2. Optimum reaction conditions for both the 1,4- anhydroerythritol and xylitol S-HDO reactions were elucidated.
Second, the general reaction kinetics and associated mass transfer of the xylitol SHDO over a ReOx-Pd/CeO2 catalyst was investigated. It was determined that the xylitol concentration was zero-order in the S-HDO reaction to 1,2-dideoxypentitol and 1,2,5-pentanetriol. Over the 120-170 °C temperature range, it was elucidated that a sub-Arrhenius relationship was present for this reaction, in which activation energy was a function of temperature. The activation energy ranged from 10.2–51.8 kJ/mol over the temperature range evaluated and the non-Arrhenius behavior was fully modeled to account for the quantum tunneling present in the reaction. 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 and no limitations were found.
Third, the effects of reaction temperature, pressure and Re loading for sorbitol SHDO was investigated using an L9 Taguchi design and a Box-Behnken design of experiment. The designs were directly compared to determine if the more simplistic Taguchi design could deliver comparable results to the more complex and experimentally intensive Box-Behnken design. The Taguchi design predicted an optimal reaction condition of 170 °C, 10 bar H2, and a 4 wt% Re catalyst, which was experimentally validated. The structure of the ReOx on the catalyst was also investigated as a function of temperature and Re loading using in-situ Raman spectroscopy.
Lastly, the structure of ReOx supported on CeO2 was investigated using in-situ 18O isotopic exchange Raman and DRIFTS spectroscopy. The isotope exchange was utilized to help deconvolute the vibrational bands by tracking the resulting red shifted substituted bands. The ReOx was found to exist in four distinct structures including a di-oxo structure, a mono-oxo species, a mono-oxo species that contains a hydroxyl group, and a cross-linked oligomeric ReOx species. The effect of temperature and Re weight loading on the structure of ReOx was also investigated.
MacQueen, B.(2021). Hydrodeoxygenation of Biomass Derived Sugar Alcohols To Platform Chemicals Using Heterogeneous Catalysts. (Doctoral dissertation). Retrieved from https://scholarcommons.sc.edu/etd/6757