Co-adsorption of 1,2-dichloroethane and 1-bromo,2-chloroethane on zeolite ZSM-5 from the liquid and vapour phases, using the Myers-Prausnitz-Dubinin model

The adsorption/co-adsorption of 1,2-dichloroethane (DCA) and 1-bromo,2-chloroethane (BCA) from the vapour and the liquid phases by zeolite ZSM-5 at ambient temperature is reported, using Dubinin's theory and the recent Myers-Prausnitz-Dubinin (MPD) theory. For adsorption from the liquid phase, the activity coefficients in the adsorbed and the liquid states are the same and no selectivity is observed. This is confirmed by the absence of an excess enthalpy of immersion of ZSM-5 into the mixtures. Adsorption from the vapour phase proceeds in two stages, as indicated by double Dubinin-Astakhov (DA) plots. If one considers only the domain of high relative pressure, co-adsorption is described by the MPD theory. The agreement between calculated and experimental compositions of adsorbate can be improved by using, as a first and good approximation, the activity coefficients of the liquid–solid equilibrium at the same composition. A good agreement is also observed between the enthalpies of immersion calculated from the DA equation and the experimental integral heats of adsorption. However, for vapour mixtures ZSM-5 shows selectivity in favour of the more volatile compound, 1-bromo,2-chloroethane. This probably results from adsorption at low pressures and could be due to differences in kinetics.