Solubility of petroleum hydrocarbons in oil/water systems

To elucidate mechanisms, two laboratory-scale experiments were correlated to understand and quantify how oil partitions into the aqueous phase. In the two experiments, free-phase petroleum was exposed to water in an effort to determine aqueous concentrations of various oil components. In the first investigation, an oil/water system was allowed to equilibrate for 16 days. The water column in the system was periodically sampled, and sample analysis was performed by GC-MS. After analyzing for naphthalene and various alkyl-substituted naphthalene compounds, the data was modeled and rate coefficients and the saturation concentrations were predicted. For naphthalene, the modeled saturation concentration was 1.4×10−6 mol/l , the rate coefficient was 0.239 h−1 and the predicted time to reach equilibrium was 19.3 h. For the alkyl-substituted compounds, there was an inverse correlation between both the rate coefficients and saturation concentrations and the degree of alkyl-substitution. In the second investigation, oil/water systems were allowed to equilibrate for 36 h. Various oil loadings (mass of oil/volume of water) were investigated. The mixing energy was twice that of the first experiment. After the 36 h, the water column was sampled and analyzed by GC-MS. There was a direct correlation between the measured total petroleum hydrocarbon (TPH) concentrations in the water and the oil loading. However, there was no such correlation between the naphthalenes and oil loading. It was concluded that the first experiment was a solubility phenomenon while the second experiment also included a colloidal phenomenon.