It doesn't sound like you have a liquid-liquid extraction. It sounds more like you are using a liquid to absorb a component from a gas stream in a standard tray column. Since you are working with a gas and not true vapor-liquid equilibrium, this would be an absorption problem involving Kga values. This involves heat transfer, heat of solution, heat capacity, liquid and gas concentration values, and diffusion values, so it gets complicated. I would use Aspen Ratefrac to model this problem, since hand calculations would be very difficult.
Harold Reed, M.S.
Sirius Technical Services Contract Engineer
For Evonik Corporation
Process Technology and Engineering, Americas