SIMULTANEOUS ABSORPTION OF VAPOR PHASE POLYCYCLIC AROMATIC HYDROCARBON AND CARBON DIOXIDE IN ANIONIC SURFACTANT SOLUTIONS

Abstract

The goal of this work was to investigate whether the solubility of vapor phase polycyclic aromatic compounds (PAHs) and CO₂ in water could be enhanced by adding anionic surfactant during the absorption process. Naphthalene was the PAH surrogate and sodium dodecyl sulfate (SDS) was the anionic surfactant. A series of batch experiments in an absorption cell were performed at 50°C with the surfactant concentration both lower than and higher than the critical micelle concentration (CMC). The experimental findings indicate that the CMC was not a function of pH at values of 3, 5 and 7. Furthermore, at surfactant concentrations less than the CMC, naphthalene apparent solubility increased slightly. On the other hand, the equilibrium naphthalene or CO₂ apparent solubility increased linearly, in proportion to the surfactant concentration at concentrations greater than the CMC. This is due to the solubilization effect of micelles, which were formed by the surfactant at concentrations above the CMC. During simultaneous absorption of the two, the presence of CO₂ only slightly decreased naphthalene apparent solubility, while the apparent solubility of CO₂ was drastically reduced in the presence of naphthalene. As the magnitude of the micelle solubilization effect was greater than the reduction of the mass transfer coefficient in the presence of the surfactant, the total gas absorption rate increased. When the surfactant concentration was 0.1 M, the enrichment factor (the ratio of the solubility in surfactant solution to that in water) values of naphthalene both with and without CO₂ increased to 9.05 and 8.60, respectively. These experimental findings demonstrate that anionic surfactant may be applied to increase the removal efficiency of hydrophobic compounds and CO₂ through either a spray or packed tower.

Keywords:

• Critical micelle concentration
• Solubilization
• Enrichment factor
• Greenhouse effect

ACKNOWLEDGMENT

The authors would like to thank the National Science Council of the Republic of China for financially supporting this research under Contract No. NSC 89-2211-E-002-031.