Solvent effects in supercritical extraction of coal

The specific physical and chemical characteristics of supercritical solvents and solvent mixtures that can affect the yield and the properties of coal extracts were investigated experimentally. Strong non-ideal interactions, such as polar bonding and hydrogen transfer, as well as synergistic interactions in multi-component solvent mixtures, were shown to produce large deviations from the simple, density-driven supercritical solubility. These interactions can be manipulated to optimise supercritical coal extraction by reducing the severity of the extraction conditions. Physical and chemical changes occurring in the coal structure during supercritical solvent extraction were also examined.