Reactions of Model Compounds with Supercritical Water

The possible use of supercritical fluid extraction (SFE) of coal to obtain cleaner, more versatile fluid products is of significant interest. Some fluids have the opportunity to participate as reactants at process conditions, which may yield extracts of very different compositions than those obtained from other treatments and which will be dependent on the fluid used. Thermodynamic consideration of SPE leads to the prediction that the enhanced solubility (volatility) of the solute may be several orders of magnitude(1-3). Thus, this method combines many of the advantages of distillation with those of extraction. However, despite the interest in SPE, only a few studies have reported the basic chemistry that may be taking place during coal extraction at these conditions(4-8). The current program is concerned with nitrogen removal from, and the rupture of carbon-carbon bonds between, aromatic rings in model compounds thought to be representative of structures found in fossil fuels. Because of the difficulty of removing heterocyclic nitrogen, experiments were initiated by extensively examining the reactivities of quinoline and isoquinoline, as well as brief examinations of the reactivities of other compounds(4). The selection of water as the fluid was based on its physical and chemical properties(9) and on the observation that a few studies of SFE of coal using water as the fluid have given encouraging results(l0.11). Zinc chloride was chosen as a catalyst because of its reported catalytic activity for hydrocracking aromatic structures(l2). This paper discusses the results of a study of the reactions of supercritical water (SW) with organic compounds that were found, or postulated, to be intermediates in the reaction of isoquinoline with SW. Since the isoquinoline reaction produced significant yields of ethyl benzene and o-xylene(4) it was assumed that benzylamine (BA) would be representative of the intermediate structure formed after the initial bond rupture in the heterocycle. It was found that benzaldehyde, benzylidenebenzylamine (BBA) and benzyl alcohol were intermediates in the BA-SW reaction(5). thus these are the primary subjects of the current study.