The conversion of 2,3-butanediol to methyl ethyl ketone over zeolites
Abstract
The interest in investigating the conversion of 2,3-butanediol (2,3-BDL) to methyl ethyl ketone (MEK) over zeolites originates from the idea of synthesizing value-added chemicals by utilizing biomass-generated 2,3-BDL as the feed. Our specific objective here is to understand the catalytic and reaction variables that control the 2,3-BDL to MEK dehydration over a selection of zeolites, since previous findings suggested that biomass to MEK is a viable process. In the present study, a three-pronged approach was implemented to study the effects of temperature, zeolite structure, acid site density, and site acidity on the conversion of 2,3-BDL. First, vapor phase kinetic studies performed utilizing a differential reactor apparatus under specific temperature-programmed or isothermal flow conditions revealed the concurrent formation of pinacol rearrangement and intermolecular dehydration, and that the product distribution from these two pathways depended on pore size. Second, in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) analysis at RT elucidated the dehydration of 2,3-BDL to MEK, the dissociation of the cyclic ketal of 2,3-BDL and MEK, and the absence of aldol dimerization of MEK over zeolites. When combined with temperature step desorption/reaction (TSD/TSR), in-situ DRIFTS revealed aldol condensation of MEK, the formation of coke species with aromatic and/or polyenic nature, and the removal of adsorbed MEK species in larger pore materials by cyclic ketal formation. Characterization of the zeolites with atomic absorption spectroscopy (AAS), 29Si and 27Al magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy, and pyridine titration coupled with in-situ DRIFTS revealed that zeolites having similar structures and Si/Al ratios could have very different Al site distributions. These subtle differences may account for the lack of product formation observed in the isothermal flow experiments on some catalysts.
Degree
Ph.D.
Advisors
Tsao, Purdue University.
Subject Area
Chemical engineering|Organic chemistry|Analytical chemistry
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