Promotion of carbon dioxide adsorption using a zeolite-coated monolith with acoustic excitation

CO2-separation technology is required in various industrial plants to reduce CO2 emissions. A method for promoting adsorption via acoustic excitation is proposed, and the effects of acoustic excitation on CO2 physisorption are investigated using a monolith coated with zeolite. The monolith is placed in a flow duct, where a CO2 + N2 gas mixture is flowed and acoustic resonance occurs due to acoustic excitation by speakers. Observations show that the time required to achieve a certain amount of adsorption can be reduced. Moreover, the mass transfer coefficient estimated based on a linear driving-force model increases as acoustic excitation is intensified, which indicates the promotion of adsorption. In particular, the promotion is intensified when the monolith is placed at the anti-node of the velocity fluctuations of the acoustic resonance. The measured velocity field in the wake of a monolith cell shows flat and high velocity profiles occurring periodically under acoustic excitation, which indicates that high-velocity CO2 gas flows near the cell wall in the monolith. Moreover, the effects of acoustic excitation on the CO2 concentration field in a planar jet comprising a CO2 + N2 gas mixture are investigated using a background-oriented Schlieren method. The result shows varying distributions of CO2 concentration with time under acoustic excitation, where the CO2 concentration around the jet exit is indicated to become periodically larger compared with the baseline case without sound. This indicates the possibility of enhanced CO2 concentration in the monolith with acoustic excitation, which can contribute to promotion of CO2 adsorption.