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Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Chemical Engineering

Year Degree Awarded

Summer 2014

First Advisor

Paul J. Dauenhauer

Subject Categories

Catalysis and Reaction Engineering | Chemical Engineering

Abstract

Increasing demand for renewable and domestic energy and materials has led to an accelerated research effort in developing biomass-derived fuels and chemicals. The North American shale gas revolution can provide a domestic source for the manufacture of four of the five major products of the world chemical industry: methanol, ethylene, ammonia, and propylene. However this emerging domestic resource lacks a conversion pathway to the fifth major chemical building block; the larger C6 aromatics benzene, toluene, and xylene (BTX). One sustainable feedstock for renewable C6 aromatic chemicals is sugars produced by the saccharification of biopolymers (e.g., cellulose, hemicellulose). The catalytic conversion of these sugars to high value commodity chemicals, like p-xylene (used in the production of PET plastics), is currently a research area of great interest. The last step in the production of p-xylene from biomass derived glucose involves the conversion of 2,5-dimethylfuran (DMF) and ethylene to p-xylene, which proceeds via a Diels-Alder cycloaddition followed by dehydration.

This thesis presents a novel catalytic system for the production of p-xylene from DMF and ethylene. Potential transport limitations between the liquid reaction solution and ethylene gas as well as through the pores of the zeolite catalyst have been investigated and altered such that the system is kinetically limited. Competing side reactions have been characterized, and minimized, to achieve high yields of p-xylene. Additionally, a possible mechanism has been developed that takes into account both of the reaction steps: Diels-Alder cycloaddition and dehydration.

Results have demonstrated a 90% yield of p-xylene through optimization of the catalyst and reaction conditions. The production of renewable p-xylene has also been shown to occur at high selectivity and without isomerization to less valuable o,m-xylenes. Careful testing of the principal reaction components revealed the source of isomerization inhibition is very likely the reactant DMF. The precise mechanism of inhibition was further studied through the use of diffuse reflectance infrared spectroscopy (DRIFTS). This study shows preferential binding of DMF over p-xylene to the Brønsted acid sites necessary for promoting isomerization chemistry. Additionally, evidence suggesting a cationic polymerization of DMF on the Brønsted acid sites of H-Y zeolite has been revealed through the use of thermogravimetric analysis (TGA). Reaction kinetics for the Diels-Alder cycloaddition and dehydration steps have also been quantified, revealing first order kinetics in DMF and ethylene. The feasibility of catalyst regeneration has been investigated through the use of x-ray diffraction (XRD) and 27Al-NMR. This analysis indicates that the zeolite catalyst remains structurally sound after reaction and that there is minimal degradation of the catalytically active Brønsted acid sites. Finally, possible reaction mechanisms have been developed through careful manipulation of the reaction system and an in depth understanding of the catalysis. This increased understanding of the transformation of DMF and ethylene to p-xylene will aid in the development of a variety of renewable aromatics from biomass derived furans.

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