Sorption and diffusion of gaseous hydrocarbons in synthetic mordenite

Diffusion coefficients for the C 1 to C 4 paraffin hydrocarbon gases in single crystals of the synthetic zeolite (molecular sieve) sodium mordenite were determined from transient sorption rate and desorption rate measurements over the temperature range 25° to 140°C. and pressure range 0 to 20 cm. Hg, and found to be of the order of 10 −9 to 10 −10 sq. cm./sec. Diffusion coefficients for desorption were from three to sixty times smaller than those for sorption. Activation energies for methane and ethane were 1.7 and 1.9 kcal./mole, respectively. Equilibrium sorption capacity and diffusion coefficients are markedly affected by the conditions of synthesis and by mechanical treatments such as grinding. For propane at 29°C. and at 2.0 cm. Hg pressure, the sorption capacity in 2.5 μ crystals was only 50% of that in 21 by 21 by 33 μ crystals and the diffusion coefficient was only 1/50 of that in the larger crystals. Light mechanical grinding of the larger crystals lowered the sorption capacity 30% and the diffusion coefficient by a factor of 35.