Production Of Renewable Aromatic Chemicals From Biomass-Derived Furans Through Brønsted Acid Zeolites

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Production Of Renewable Aromatic Chemicals From Biomass-Derived Furans Through Brønsted Acid Zeolites

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Renewable chemicals remain a major need for society as a whole with the eventual extinction of petroleum sources. Though natural gas resources may curtail our energy demand in the foreseeable future, larger carbon-based chemicals are necessary to replace aromatics used in the production of essential polymers and plastics. The most promising choice stems from biomass, as it is cheap and its monomers are similarly structured to those of plastics. This thesis focuses on thermochemical routes to plastics precursors through the use and understanding of zeolite acid catalysts. Specifically, the conversion of biomass-derived 2,5-dimethylfuran (DMF) and ethylene for the production of p-xylene, and water byproduct, with H-Y and H-BEA zeolite catalysts was investigated. This reaction is completed through a two-step reaction pathway: (1) homogeneous Diels-Alder cycloaddition of ethylene and DMF to form an instable cycloadduct intermediate and (2) an acid-catalyzed dehydration of the cycloadduct to form water and p-xylene. Activation energies and reaction rate orders using an H-BEA catalyst were examined and two regimes were found. The first regime, at low acid site concentration, is dehydration limited and the rate of reaction scales linearly with acid site concentration. The second regime, at high acid site concentration, is cycloaddition limited; the reaction rate is zero order with respect to acid site concentration. The high selectivities achieved to p-xylene in this reaction were puzzling and attempts were made to understand the underlying mechanism. Under these reaction conditions, p-xylene should readily isomerize and disproportionate to form other aromatics products. However, none of these products are formed. Upon further adsorption investigations using techniques such as Solid State MAS NMR, FT-IR, and TGA, as well as computational calculations, it was found that the hydrolysis product of DMF, 2,5-hexanedione, preferentially adsorbed onto the zeolite acid sites, protecting them from p-xylene adsorption and reaction. The dehydration reaction still occurred due to the fact that the cycloadduct adsorbed as strongly as 2,5-hexanedione. With this new observation of the ability for an inert species to inhibit reaction of preferred products, a new chemistry was tested. Cyclohexanol dehydration to cyclohexene using an H-BEA catalyst was investigated with and without the addition of an inert chemical DMF/hexanedione. It was found that the addition of the inert increased the yield of cyclohexene by inhibiting its reaction to oligomers. A more general model and approach was developed to use competitive adsorption with an inert as a tool for increasing reaction yields. A new technique for acid site counting in solid acid catalysts was discovered. Reactive Gas Chromatography (RGC) allows for the automated, sensitive and simple counting of acid sites in zeolites with use of a modified gas chromatograph. Counting acid sites in zeolites is essential for the comparison of two catalysts of differing acid site densities and acid sites. The validity of this new technique, which uses the robust method of alkylamine decomposition, was determined with comparison to literature values and those from in situ pyridine titration experiments. Finally, a new application for the RGC, known as Size Exclusion Reactive Gas Chromatography (SE-RGC) was invented for the purpose of understanding and predicting the size of molecules relative to the size of zeolite pores. It is apparent that the zeolitic community needs better measures for understanding the ability for a molecule to fit into a pore. Here, multiple sizing methods (kinetic diameter, van der Waal diameter and minimal enclosing cylinder diameter) were investigated. Though minimal enclosing cylinder was the most accurate predictor, it was found each of these methods overpredicted molecular size, when compared to results using SE-RGC. FT-IR experiments will next be completed to more fully understand molecule fitting in zeolites.


University of Minnesota Ph.D. dissertation. July 2018. Major: Chemical Engineering. Advisor: Paul Dauenhauer. 1 computer file (PDF); xiii, 155 pages.

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Vinter, Katherine. (2018). Production Of Renewable Aromatic Chemicals From Biomass-Derived Furans Through Brønsted Acid Zeolites. Retrieved from the University Digital Conservancy,

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