Modelling equilibrium isotherms for styrene-divinylbenzene ion exchange resins

An equilibrium isotherm, termed the double-selectivity model, is proven to be quite good for fitting equilibrium data of polystyrene-divinylbenzene ion exchangers. It gives excellent mathematical fittings for experimental isotherms which have an inflexion point, and explains the general behavior of other sulfonated styrene DVB exchangers over the whole range of crosslinking degree. Only two fitting parameters are needed and these are linked with the thermodynamical equilibrium constants of areas where DVB or styrene predominates. The model is very simple and can be easily implemented into numerical simulations and supported by a physico-chemical basis.