The temperature dependence of deuterium NMR spin-lattice and spin-spin relaxation time data for ethane and ethene adsorbed in zeolite NaA was presented for sorbate loadings in the range of 1 to 4 molecules/cavity. Analytical expressions relating these data to the dynamics of the sorbate molecules were derived. Simultaneous fitting of the temperature dependence of both T1 and T2 data for each sorbate loading provided estimates of the correlation time characterizing translational, rotational, and librational motions of the sorbate within the zeolite. The NMR data were consistent with ethane having a higher mobility than ethene within the zeolite. Data derived from the NMR study were used as input to a Monte Carlo lattice dynamics model, which predicted adsorption and transport characteristics of the sorbate-zeolite system. Desorption events from adsorption sites were characterized by a correlation time of the form, τ = τoexp[E/(RT)], and the probability of the sorbate attempting an inter-cage jump was assumed to be of the form, pw = pwoexp[-Δ/RT], where τo and pwo were constants and E and Δ were the activation energies characteristic of the respective processes. From the NMR analysis, it was found that ethane transport was characterized by values of τo, E, pwo and Δ of 2.6 x 10-9s, 16kJ/mol, 0.48 and 7.8kJ/mol, respectively, while the corresponding values for ethene were 2.0 x 10-11s, 27kJ/mol, 0.105 and 8.5kJ/mol. Predictions of the concentration dependence of ethene self-diffusivity were shown to be in excellent agreement with existing experimental data. The Monte Carlo lattice dynamics model was also used to predict the self-diffusion coefficients of ethane and ethene within a binary ethane-ethene mixture.

Adsorption and Transport of Ethane and Ethene in Zeolite NaA: 2H NMR and Monte Carlo Lattice Dynamics Studies. L.F.Gladden, J.A.Sousa-Gonçalves, P.Alexander: Journal of Physical Chemistry B, 1997, 101[48], 10121-7