Dual mode roll-up effect in multicomponent non-isothermal adsorption processes with multilayered bed packing

Roll-up is a common phenomenon occurring in multicomponent adsorption processes when the concentrations of some components at the outlet of the adsorber exceed their inlet levels. Previous investigations attributed the roll-up effect typically to the displacement of one component by another because of the difference in adsorption affinities or diffusivities. In this work, we report the existence of a peculiar type of roll-up caused by thermal effect solely in our multicomponent non-isothermal breakthrough experiments where the light component CO2 was swept off by a pure thermal wave developed from water vapour adsorption. Even though, the formation of a pure thermal wave is well known, it does not lead to the above roll-up without a multilayered bed packing. To our surprise, a secondary roll-up of CO2 caused by H2O displacement was also observed, since the front of the water concentration wave ran behind its thermal wave in our case. The parameters affecting the formation of this special dual mode roll-up were investigated and summarised. This work will give guidance to the design of multilayered cyclic adsorption processes, e.g. determination of layering ratios and duration of the feed step.