Date of Completion

4-29-2015

Embargo Period

10-25-2015

Keywords

• Heterogeneous catalysis • Biomass • Catalytic pyrolysis • Coke characterization • Coke formation chemistry

Major Advisor

George M. Bollas

Associate Advisor

Julia A. Valla

Associate Advisor

Steven L. Suib

Associate Advisor

Richard S. Parnas

Associate Advisor

Luyi Sun

Field of Study

Chemical Engineering

Degree

Doctor of Philosophy

Open Access

Open Access

Abstract

Thermochemical conversion of biomass via pyrolysis can play an important role in renewable fuel production. Introduction of catalyst in biomass pyrolysis is an effective way to upgrade the quality of bio-oil via de-oxygenation reactions. However, in catalytic pyrolysis, char and coke are formed via primary decomposition of biomass and secondary catalytic reactions of pyrolysis intermediates, respectively. The formation of coke and char is the main reaction competing with the production of favorable aromatic compounds and can significantly deteriorate catalyst activity. Control of coke and char formation during pyrolysis could be possible through innovative catalyst and process designs, in which fundamental understanding of the formation mechanisms of char and coke should be viewed as a prerequisite. This study utilizes various experimental and modeling techniques in order to measure and interpret the physicochemical characteristics of char and coke and gain mechanistic insights of their origins during biomass catalytic pyrolysis. This study includes design and testing of a conical spouted bed reactor for in-situ biomass catalytic pyrolysis, investigation of the effect of key operating parameters on pyrolysis product distribution, characterization of char and coke structures and a structured model compound exploration of coke formation mechanisms. It is shown that char and coke have different origins. They cannot be lumped as one, since they occupy different locations on the catalyst surface and, thus, contribute differently to catalyst deactivation. Char, a product from thermal reactions, forms as an external layer on the catalyst surface and in its macropores, whereas coke, a catalytic product, forms inside the zeolite micropores. By studying the coke formation using biomass model compounds, it is concluded that the chemical structure of coke depends on its chemical precursors. The formation of coke from olefins, aromatic hydrocarbons and aromatic oxygenates are all directly related to the so-called “hydrocarbon pool” mechanism, following mainly hydrogen transfer and cyclization reactions.

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