Visual observation of the solubility of heavy hydrocarbons in near-critical water

Heavy hydrocarbons (M/sub R/ > 250) have been observed to dissolve in liquid water just below its critical temperature (374 /sup 0/C). Visual measurements of the solution temperatures of hydrocarbon/water systems confined in sealed quartz capillary tubes (autogenous pressure) show unambiguously that even very heavy heavy hydrocarbons (M/sub R/ > 400) form true solutions with water in a temperature-pressure region where both pure components can exist as liquids. The solubilities determined from solution temperatures of three pure hydrocarbons (a straight-chain paraffin, n-tetracosane; a polynuclear aromatic, benzo(e)pyrene; an alkylbenzene, n-nonadecylbenzene) and a naphthene/branched paraffin white oil mixture are reported in the temperature range 320-365/sup 0/C. The solution-temperature-derived solubilities are in agreement with heavy oil fraction solubility data obtained in ''blind'' autoclaves. Solubilities of pure heavy hydrocarbons in water at 350/sup 0/C range from 1 wt % for n-tetracosane to 10 wt % for benzo(e)pyrene. The variation of hydrocarbon solubility in water as a function of temperature and hydrocarbon molecular size and type is discussed by using the concepts of hydrophobic interactions and solubility parameters which have been developed to explain the solubilities of light hydrocarbons in water.