A method to simultaneously determine sorption isotherms and sorption enthalpies with a double twin microcalorimeter

Sorption of vapors of water, ethanol, and other liquids on solids like pharmaceuticals, textiles and food stuffs are of both practical and theoretical importance. In this article we present a technique to simultaneously measure sorption isotherms and sorption enthalpies. The sample is contained in one end of a sorption vessel. In the other end a vaporizable liquid is introduced to start the measurement. Mass transfer from the liquid to the sample is by vapor diffusion and the rate of mass transfer is calculated from the measured thermal power of vaporization. Simultaneously, the thermal power of sorption is measured and from this one may calculate the differential enthalpy of sorption. The thermal power measurements are made by inserting the sorption vessel in an isothermal double twin microcalorimeter.