(179o) Absorption of Carbon Dioxide Into Aqueous Surfactant Solutions

The absorption of carbon dioxide into aqueous surfactant solutions at elevated pressures is of interest in certain military applications. We have conducted a study of the absorption process on a laboratory scale (using beverage cylinders) to better understand the approach to saturation. Since the solubility is pressure-dependent, the interfacial equilibrium composition (XA0) changes over the course of the absorption. We began by studying the diffusion-limited process in which the head space above the quiescent surfactant solution was pressurized with carbon dioxide (with a typical initial pressure of about 55 bar). Experimental data were obtained by recording the gas pressure over time; the decreasing pressure was converted to absorption rate. A Fickian diffusion model was compared with the data.

The rate of absorption under quiescent conditions is impractically slow, so we devised a roller apparatus driven by a variable-speed DC motor. In this manner the pressurized cylinders could be rotated slowly in a horizontal position, providing greater interfacial area and continuous renewal of the liquid at the interface. A model of the resulting liquid flow has been constructed and tested against experimental data. As expected, this arrangement significantly accelerates the approach to saturation, while minimizing the temperature increase resulting from viscous dissipation.