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Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Chemical Engineering

Year Degree Awarded

2016

Month Degree Awarded

February

First Advisor

Wei Fan

Second Advisor

William Curtis Connor Jr.

Third Advisor

Scott M. Auerbach

Subject Categories

Catalysis and Reaction Engineering | Chemical Engineering | Other Materials Science and Engineering

Abstract

The need for sustainable production of everyday materials in addition to declining reserves of petroleum-based feedstocks has motivated research into the production of renewable aromatic chemicals from biomass. We have proposed a multistep pathway to produce renewable p-xylene from lignocellulosic biomass using heterogeneous catalysts. The pathway includes formation of glucose by saccharification of cellulose, isomerization of glucose into fructose, dehydration/hydrogenolysis for production of 2,5-dimethylfuran (DMF), and final step for producing p-xylene from reacting DMF with ethylene.

Lewis acid zeolite catalysts (e.g. Sn-BEA, a tin containing molecular sieve with zeolite BEA structure) exhibited critical roles in the pathway because of its excellent catalytic activity for the conversion of glucose into fructose by intramolecular hydride transfer reaction and the production of p-xylene from DMF by cycloaddition/dehydration reactions. However, the development of Sn-BEA is a grand challenge due to the lengthy crystallization time (up to 40 days) and unknown structure of acid site. In this work, a highly reproducible seeded growth approach was invented to significantly shorten the crystallization time. It is demonstrated that the seed crystals effectively reduce the induction time of crystallization and lower the energy barrier by bypassing the nucleation stage. Crystallization kinetic studies reveal the highly crystalline Sn-BEA catalyst can be obtained in 3 hours at 200 °C with similar catalytic activity in isomerization reaction of glucose compared to conventional Sn-BEA. The discovery is important for rational synthesis of heteroatom containing zeolites.

Zr-, Sn-, and Ti-BEA Lewis acid zeolite catalysts were employed in production of p-xylene from DMF and ethylene. It was found that these Lewis acid catalysts are able to catalyze the tandem reaction consisting of Diels-Alder cycloaddition and dehydration reactions to form p-xylene. Zr-BEA shows the best performance with improved recalcitrance to deactivation compared to Brønsted acid zeolite catalyst (Al-BEA), reaching 76 % yield to p-xylene at 99 % conversion of DMF. Zr-BEA also features high p-xylene production rate due to its catalytic activity for both cycloaddition and dehydration reactions. The results provide an approach to rational develop bi-functional (Lewis+Brønsted acids) catalysts for the tandem reaction pathway to efficiently produce p-xylene and many other aromatics.

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