Nitrogen, methane, and ethane sorption on activated carbon

Joule-Thomson (JT) sorption cryocoolers rely on sorption compressors that provide a continuous flow with predetermined high and low pressures without any vibration emission. These cryocoolers may operate with different fluids, in accordance with the desired cold temperature. Nitrogen, methane, and ethane are prevalent candidate fluids for sorption cryocoolers, providing cold temperatures of about 80 K, 120 K, and 185 K, respectively. In order to develop a sorption compressor it is necessary to know the sorption characteristics of the fluid on the selected adsorbent. In this work we present experimental sorption measurements of the mentioned fluids on a commercial pelleted activated carbon. The Langmuir, Freundlich, and Sips models are fitted to the experimental results and further modified to incorporate the temperature dependence, in order to extend the prediction of sorption properties into wider ranges of temperature and pressure. It appears that each fluid has a different model that best fits its characteristics. Finally, the isosteric heat of adsorption is calculated for the three mentioned fluids as a function of the adsorption coverage and polynomial regressions are obtained for it.