| The underlying theme of this thesis is the liquefaction reactivity of a Victorian brown coal. For this study, a chemical-based approach has been adopted. This has resulted in the development and evaluation of a separation method, specifically, for coal derived liquids, which produced stringently defined acid, base and neutral fractions. Similarly the Total Oils and residues have been extensively characterized, by a variety of spectroscopic and chemical techniques. Additionally, a more reliable, GPC-HPLC-based, method for Molecular Weight determinations of heterogeneous mixtures and a Negative Chemical Ionization Mass Spectrometric technique for the analysis of individual phenols, in acid fractions, have also been developed.; The effects of temperature, time and catalysis, on both product yields and characteristics, were investigated, for brown coal hydrogenation. The influence of its structure and rank were ascertained by: (1) comparison with a bituminous coal, liquefied under equivalent conditions; this being the case for the temperature and catalyst studies and (2) a model study, employing diagenetically related geopolymers--softwood and hardwood lignins, and the humic acid fraction of the coal. Furthermore, the effect of liquefaction process was assessed.; These studies have, not only highlighted different aspects of brown coal reactivity; but, also led to a number of important general conclusions. Some examples are: (1) 375(DEGREES)C being both the temperature of maximum oil yield for brown coal and the division between two distinct reaction phases; (2) processes, such as decarboxylation, decarbonylation, dehydration and cleavage of interaryl linkages, being thermally mediated and rank independent, (3) the mode of action of the catalyst being dependent on the structure of the substrate, (4) neutral hydrocarbon material appearing to derive, predominantly, from non-lignin-related structures in the coal, (5) higher rank coals requiring elevated temperatures to display equivalent reactivity to lower rank coals, (6) pyrolysis producing an, appreciably, more aliphatic and hydrocarbon neutral-containing liquid, than hydrogenation, (7) acids being more readily converted, in-situ, to non-polar neutral material, than bases, which are normally inert and (8) dissolution being a function of time and the identification of two chemically discrete periods, about 10 minutes--enabling brown coal liquefaction to be modelled by a system of second-order equations. (Abstract shortened with permission of author.)... |
