Hydrodynamic and mass transfer of benzene absorption process in bubble column

Abstract

The objective of this work is to study the hydrophobic VOCs absorption process in terms of bubble hydrodynamic and mass transfer parameters in bubble column (4.4 cm in diameter and 30 cm in height). The absorbate used in this work were benzene and the absorbent used in this work were the aqueous solution of non-ionic surfactant and oil-in-water emulsion with non-ionic surfactant, respectively. Moreover, the ranges of surfactant concentrations (0.1, 0.5, 1, 3, 5 CMC), oil-in-water concentrations (50 and 300 mg/L) were analyzed with the gas flow rates applied 0.5, 1.3, 2.2, 3.0 ml/s. The analytical parameters were the VOCs removal efficiency, bubble hydrodynamic parameters, and also the mass transfer parameters. This result has shown that the VOCs removal efficiency obtained in liquid phase containing with oil-in-water emulsion absorbent (47.67%) were greater than those obtained with surfactant absorbent (27.56) and tap water (8.97%). These results relate with the augmentation of benzene solubility in liquid phase due to the lubricant oil and surfactants presence in liquid phase. Moreover, the VOCs removal efficiency obtained experimentally correspond with the overall mass transfer coefficient (K[subscript L]a) that is the product between the interfacial area (a) and the liquid-film mass transfer coefficient (K[subscript L]). It can be stated that, not only the influence of high gas flow rates can caused the increasing of K[subscript L]a and a, but also the decreasing of VOCs removal efficiency due to the desorption or stripping process that related to the power mixing in liquid phase. This desorption phenomena obtained with oil-in-water emulsion was more pronounces than those obtained with other liquid phases. Furthermore, it can be noted that the values of a and K[subscript L] are compensated to each other that can be effected to the K[subscript L]a coefficient in case of liquid phase containing of oil-in-water emulsion and aqueous solution of surfactant. Moreover, small effect of surfactants and oil-in water emulsion on the K[subscript L] coefficients was observed at high concentrations injected in liquid phase. Therefore, the appropriate gas flow rates providing the suitable bubble hydrodynamic condition and also concentrations of surfactant and oil-in-water emulsion as absorbents were essential to provide the high removal efficiency of benzene absorption process. By considering the preparation of absorbent, wastewater treatment, and removal efficiency, it can be concluded that the additional of surfactant at 5 CMC was suggested for absorbent used in this study.