Catalytic transformations of biomass with Brønsted and Lewis acid zeolites to value-added products
Date
2017
Authors
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Publisher
University of Delaware
Abstract
In this work, Lewis and Brønsted acid zeolites have been applied to transformations of biomass for the synthesis of fuels and chemicals. In the first half of this work, Lewis acid Beta zeolites (Sn-, Zr- and Ti-Beta) were screened for their activity in sugar isomerizations, Meerwein-Ponndorf-Verley (MPV) reduction and etherification. Activity trends of these catalysts varied depending on the chemistry. For isomerization, Sn>Zr~Ti. For MPV reduction, Zr>Sn>Ti. Finally, for etherification, Sn>Zr>Ti. These materials were then studied more in-depth for the MPV reduction of furfural. Hf-Beta, not screened previously, was found to have much higher reaction rates than the other catalysts tested (Zr- and Sn-Beta), despite similar apparent activation energies for the reaction on all three catalysts. ☐ In the next half of this work, a process was developed to make p-ethyltoluene, a precursor to p-methylstyrene, from bio-derived methylfuran. This process involves three steps. First, acylation of methylfuran with acetic anhydride on Brønsted acid zeolite H-[Al]-Beta to form 2-acetyl-5-ethylfuran (2A5EF). Next, hydrodeoxygenation of 2A5EF with hydrogen on copper chromite to form 2-ethyl-5-methylfuran (2E5MF). Finally, Diels-Alder cycloaddition and dehydration of 2E5MF with ethylene on H-[Al]-Beta to form p-ethyltoluene. Overall, this process yields p-ethyltoluene in 53.5% yield at excellent isomer selectivity of 99.5% para. This methodology was then extended to make p-diethylbenzene at 99% para selectivity from furan. ☐ The first step of this process was studied in more detail on Brønsted and Lewis acid zeolites as it is a Friedel-Crafts acylation that is known to be catalyzed by both types of acids. Brønsted acid aluminum zeolites were found to be more effective than Lewis acid zeolites for the acylation of methylfuran and lower aluminum content was found to result in higher turnover per acid site. Lower apparent energies were found on Lewis acidic Sn catalysts, despite higher rates on the Al catalysts. Kinetic isotope effect experiments indicate a similar mechanism on Brønsted and Lewis zeolites with deprotonation as the rate determining step. In flow experiments, gamma-valerolactone solvent was found to significantly increase the reaction rate. ☐ In summary, several catalytic transformations of biomass have been studied on Brønsted and Lewis acid zeolites in batch and continuous flow reactors for the production of fuels and chemicals. Some of these reactions are exceptionally selective, which was exploited to demonstrate the ability to make p-methylstyrene from renewable methylfuran. The activity trends established in this work can be used to choose the best catalyst or sequence of catalysts for transforming renewable biomass feedstocks into valuable products.
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Keywords
Pure sciences, Applied sciences, Biomass, Brønsted, Catalytic transformations, Lewis acid zeolites, Value-added products