Date of Award
Doctor of Philosophy
Chemical and Biological Engineering
Brent H. Shanks
The overall goal of the present work is to devise a catalyst system, in which novel catalyst and reactor configuration design will be synergistically performed on the dehydration of glucose. We have successfully demonstrated in the following chapters that MCl3-type Lewis acids are effective catalyst to realize the efficient HMF production. Despite a number of reports on this strategy by us and other groups, a generalized frame to understand the intrinsic properties of employed Lewis acids and kinetic information relevant to processing development on this type of catalysts will also be explored in a systematic manner.
After extensively reviewing the challenges and opportunities of HMF production from sugars, we first report the catalytic conversion of glucose in high yields (62%) to HMF using a Lewis acid metal chloride (e.g., AlCl3) and a BrÃ¸nsted acid (HCl) in a biphasic reactor consisting of water and an alkylphenol compound (2-sec-butylphenol) as the organic phase. The conversion of glucose in the presence of Lewis and BrÃ¸nsted acidity proceeds through a tandem pathway involving isomerization of glucose to fructose, followed by dehydration of fructose to HMF. The organic phase extracts 97% of the HMF produced, while both acid catalysts remain in the aqueous phase. Water-compatible lanthanide-based Lewis acids were further tested to be able to catalyze the reaction under near-neutral conditions (pH=5.5) and a moderately high yield of 42 mol% could be obtained. The combined catalytic system also showed effectiveness to convert other polysaccharides to HMF. Furthermore, the aqueous phase was recycled and used for multiple times without significant loss of catalytic performance.
Further effort to understand the factors governing catalyst activities/selectivites was also undertaken. The glucose conversion kinetic profile was used to reflect the Lewis ac id character of different metal ions. It was found that the pH value of the aqueous solution played an important role in controlling the Lewis activities. For the lanthanide chlorides, their Lewis acidity was comparable under the pH values studied (from 2.5 to 5.5). However, the Lewis acidity strength of other metal salts, such as aluminum chloride, showed dependence on the pH value of the solution. Activation energies with various Lewis acids were also calculated with both glucose and fructose to obtain more insight about the strength of the catalyst-substrate interaction as well as the dehydration reaction. The kinetic isotope effect with labeled glucose molecules was also studied to explore a more mechanistic understanding of the dehydration, which likely involves the 2-H atom of the glucose molecule in the transition state.
While understanding the Lewis acidities using homogeneous model catalysts can be insightful, the ultimate practice of catalyst/catalytic processes likely necessitates the development of heteroegeneous catalysts. In this regard, a robust and sustainable catalyst preparation method pyrolizing glucose and taurine in the presence of CNT to obtain a versatile solid acids has been demonstrated. Characterization and textual properties of the catalysts were probed through the utilization of TEM, SEM, TGA, XPS. Additionally, solid state nuclear magnetic resonance(ssNMR) spectroscopy has been exploited to further elucidate the chemical nature of carbon species deposited on the surface of CNT. Al(OTf)3 as a model Lewis acidic metal salt was successfully supported on sulfonic groups tethered CNTs and tested for C6 sugar dehydration for the production of HMF in tetrahydrofuran(THF)/water solvent system with good recyclability.
In addition, an integrated catalytic pathway has also been demonstrated to utilize HMF-derived 1,2,6-hexanetriol as starting materials for the production of nylon 6,6 monomers-adipic acid and hexanediamine. To realize this goal, gold nanoparticle supported on both carbon and metal oxide based materials have been synthesized and tested for 1,6-hexanediol oxidation using molecular oxygen. On the other hand, homogeneous iodine-containing molecules have been exploited for the conversion of 1,6-hexanediol to adiponitrile, which can be subsequently hydrogenated to produce the desired diamine.
Wang, Tianfu, "Catalytic conversion of glucose to 5-hydroxymethylfurfural as a potential biorenewable platform chemical" (2014). Graduate Theses and Dissertations. 13721.