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Study of Hydrophobic VOCs Absorption Mechanism in a Bubble Column: Bubble Hydrodynamic Parameters and Mass Transfer Coefficients

The absorption mechanism of hydrophobic Volatile Organic Compounds (benzene) was investigated in a small bubble column. Effects of gas spargers (orifice size), gas flow rates, and absorbents (tap water, aqueous solution with non-ionic surfactant, and lubricant oily-emulsion) were analyzed in terms of absorption efficiency, bubble hydrodynamic, and mass transfer parameters. The results showed that the presence of non-ionic surfactant and lubricant oil affected the bubble hydrodynamic phenomena and the interfacial area (a) and the mass transfer parameters (volumetric mass transfer coefficient, kLa, and liquid-side mass transfer coefficient, kL). Absorption efficiencies of aqueous solutions with the previous substances as absorbents were significantly greater than those of tap water. These experimental results relate to the augmentation of benzene solubility in the liquid phase (absorbents) due to the presence of oily-particles and surfactant molecules. Moreover, high gas flow rates can decrease the VOCs absorption efficiency due to desorption mechanisms, associated with the mixing power in the liquid phase. Finally, it has been suggested that gas spargers with an orifice size smaller than 0.65 mm, 1 cm/s gas superficial velocity, and 50 mg/l lubricant oily-emulsion or 5 CMC non-ionic surfactant aqueous solutions are of optimal design and operation for hydrophobic VOCs absorption in the bubble column used in this study.