WATER SORPTION MEASURED BY SORPTION CALORIMETRY

A calorimetric method is described for the determination of adsorption and desorption of adsorptives that are liquid at room temperature, focussing on the sorption of water. Together with the isotherms, the sorption thermodynamics is determined in one experiment by determining the heat flow needed for generating the vapour and the heat flow generated by the adsorption process. An error analysis of the technique shows that reproducibility is good, and that absolute errors in relative vapour pressure and amount adsorbed are typically small. Only at very high loadings where the driving force for evaporation becomes small do larger errors occur in these parameters. The accuracy of the determination of the sorption thermodynamics is less good for the system water/activated carbon. This is partly due to the small net adsorption enthalpy for water in this system. Some proposals for improvement are given. An example of the adsorption of water vapour by activated carbons loaded with increasing amounts of residual surfactant shows the sensitivity of the technique.