Title

Investigation of Intramolecular Bonding in Four High-Volatile Bituminous Coals Using Wide-Angle X-Ray Scattering Analysis

Date of Award

2006

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry and Biochemistry

First Advisor

David Lee Wertz

Advisor Department

Chemistry and Biochemistry

Abstract

Due to dwindling oil reserves, the feedstock for petrochemical industries needs to change to coal in the future. The smaller hydrocarbon molecules trapped within the macromolecular network of bituminous coals are of particular interest. To optimize coal processing, it is necessary to understand the complex composition and structure of coal as completely as possible. Various analytical methods have shown that coal is most likely a partially layered network of polycyclic aromatic units. The average distance between layers can be determined by means of X-ray scattering analysis. These measurements, together with changes in the X-ray scattering pattern caused by interaction with organic liquids, can provide information about the macromolecular structure and bonding of the coals. The goal of this research was to obtain a better understanding of the structure of four high-volatile bituminous coals by X-ray scattering analysis and molecular modeling, to determine whether differences in the short-range structural domain could be ascertained, and to determine possible origins of any measurable differences. A study of swelling and absorption interactions of the coals with selected organic liquids was also correlated with the X-ray scattering data. X-ray scattering analysis showed distinct differences between the average interlayer distance, and ordering of layers, within the short-range structural domains. Molecular modeling indicated that variations in oxygen and sulfur content are unlikely to be the primary cause of the differences. It was found that the degree of coalification, maceral content, and paleobotanical origin of the coals, have a significant influence on the structure of the short-range structural domain. A detailed structural model of the SRSD could be derived for each of the high-volatile bituminous Argonne Premium Coals. By studying the interaction of the coals with organic liquids, they could be ranked according to relative non-covalent bond strength, and the mechanism of coal swelling, the role of non-covalent bonding, and properties of organic liquids influencing swelling, could be investigated. Evidence of possible ionomeric bonding in coal could be found. Swelling data, in conjunction with molecular modeling, showed that the electrostatic surface potential of organic liquid molecules could be a deciding factor in coal swelling.