MODIFICATION OF COAL BY SUBCRITICAL STEAM (PYROLYSIS, EXTRACTION, SWELLING)

It has been discovered at The City College of New York that exposure of coal to steam at temperatures and pressures below the critical point of water alters the coal so as to substantially increase yields obtained in subsequent processing. This hitherto unknown phenomenon has importance both for advancing basic coal science and for improving processes for converting coal to synthetic fuels. This dissertation is a report of an exploration of coal modification by treatment with subcritical steam.;Exploratory studies of the nature of treated coal and the products of its pyrolysis and extraction have been carried out. Solvent swelling studies of treated coal show increased hydrogen bonding in comparison to raw coal.;It is concluded that during treatment coal is partially depolymerized, both thermally and by interaction with steam. Steam could play the physical role of acting to hold open the thermally ruptured structure. It may also react chemically with the coal. Aryl-ether groups may, for example, be hydrolyzed to form phenols. Although these phenols cross-link coal by hydrogen bonding, such bonds are easily disrupted explaining the increase in solvent swelling and the improved yields in pyrolysis and extraction.;In this work, the treatment of Illinois No. 6 coal has been studied in 50 atm. steam. This treatment is effective at temperatures between 320 and 360(DEGREES)C. Liquid yields from the steam pyrolysis of treated coal is more than double the yield from raw coal. Extraction of pretreated coal with pyridine at room temperature yields 1.8 times as much extractable materials as that obtained by extraction of raw coal.