The influence of adsorption capacity on enhanced gas absorption in activated carbon slurries

The enhanced absorption of gases in aqueous activated carbbon slurries of fine particles is studied with a non-steady-state absorption model, taking into account the finite adsorption capacity of the carbon particles. It has been found that, for the different gas/activated carbon slurry systems studied in the literature, a remarkable similarity exists in the maximum achievable enhancement factor and the minimum solids concentration needed to reach the maximum enhancement. The enhance physical absorption of gases via absorption on the carbon particles, extensively investigated by Alper, is simulated with a penetration-type model. For the O2 and CO2 absorption it is demonstrated that, at the experimental bulk solids concentrations, no enhanced absorption could occur, because the adsorption capacities of these gases on activated carbon is too small. At these low solids concentrations, the enhancement is limited due to a rapid build-up of a layer of saturated particles close to the interface. High interfacial particle concentrations are necessary for any enhancement. It is therefore proposed, also on the basis of the observations in the literature, that the interfacial carbon concentration is much higher than the bulk concentration of the activated carbon particles. It is demonstrated that the non-steady-state absorption model can also be used for modelling enhanced gas absorption (adsorption followed by surface reaction). The absorption of O2 in aqueous Na2S activated carbon slurries is taken as an example.