Effects of Pressure on the Cloud Point of Nonionic Surfactant Solutions and on the Solubilization of Hydrocarbons

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Abstract
Cloud points in 1.0 wt% aqueous solutions of penta- and hexa(oxyethylene) dodecyl ether increase monotonously with an increase of pressure up to 150 MPa. The elevation of the cloud-point temperature with pressure was 1.05×10−7 and 1.09×10−7 K Pa−1 for respective surfactant. Both volume and enthalpy changes on the separation of the surfactant-rich phase had the positive values. The rise of cloud points on compression is attributable to the enhancement of the hydrogen bonds formation between water and ether oxygens of the poly(oxyethylene) group and partly to the disruption of the “hydrophobic bonding.” The cloud-point temperature at conscant pressure and the cloud-point pressure at constant temperature were also examined as a function of the amount of solubilizate such as hexane and octane. There was an optimum pressure at a given temperature, as well as an optimum temperature at a given pressure, at which the solubilizing power of surfactant is maximum.