Advantages and thermodynamic limitations of the experimental sorption isosteric method

Abstract

A review of advantages and thermodynamic limitations present in the sorption isosteric method (SIM) showed that SIM does not guarantee a constant adsorbed amount. Isosteres computed considering ideal gas behavior show that in SIM the mass of gas in the system dead volume increases as equilibrium pressure increases due to desorbed materials. SIM is useful and effective in obtaining highly accurate thermodynamic data for sorption of gases by microporous and nanoporous materials at low temperatures and pressures. At high temperatures and pressures desorption is not negligible, therefore SIM can not be applied. The errors in the calculation of the isosteric heat using SIM can be reduced using traditional experimental procedures such as adsorption isobars and isotherms to generate isosteres at high temperatures and pressures. Alternatively, corrections by pressure and temperature or an experiment that, after each temperature increase, allows gas dosage to compensate for the amount of mass desorbed would guarantee a constant adsorbed amount and, therefore, isosteric behavior by direct measurements.

A review of advantages and thermodynamic limitations present in the sorption isosteric method (SIM) showed that SIM does not guarantee a constant adsorbed amount. Isosteres computed considering ideal gas behavior show that in SIM the mass of gas in the system’s dead volume increases as equilibrium pressure increases due to desorbed materials. SIM is useful and effective in obtaining highly accurate thermodynamic data for sorption of gases by microporous and nanoporous materials at low temperatures and pressures. At high temperatures and pressures desorption is not negligible, therefore SIM can not be applied. The errors in the calculation of the isosteric heat using SIM can be reduced using traditional experimental procedures such as adsorption isobars and isotherms to generate isosteres at high temperatures and pressures. Alternatively, corrections by pressure and temperature or an experiment that, after each temperature increase, allows gas dosage to compensate for the amount of mass desorbed would guarantee a constant adsorbed amount and, therefore, isosteric behavior by direct measurements.