Thermodynamic study of the linde sieve 5A + ethane system

Abstract

The heat capacities of two samples of sieve containing ethane have been measured from ∼55 to ∼290 K. Below 150 K difficulty was experienced as a consequence of the very slow rate of approach to thermal equilibrium: only above this temperature are the results considered to be reliable and only these are reported. The samples, for which the mean number of sorbate molecules per cavity (〈n〉) was 4.750 and 2.707, each showed a large “hump”, similar to those found for the sieve 5A + methane systems, in the plot of heat capacity contribution of the sorbate against temperature. The temperatures at which the maxima occurred were ∼210 and ∼250 K, respectively, for the two samples. Consideration is given to the possibility of these “humps” being due to the presence in the same sample of cavities having various cation occupancies, and hence offering different sorption potentials to the sorbate. The Schottky-like anomaly so generated can be fitted approximately to the data for the previously reported sieves 5A + methane system as well as to that for the sieve + ethane system. Sorption isotherms were measured for ethane over the range 194.6 to 300 K, from which the isosteric heat was evaluated and found to increase from 25.19 kJ mol^–1 at 〈n〉= 1 to 34.10 kJ mol^–1 at 〈n〉= 4.