Percolation of gases into (K, Ca)–A zeolites and their cation distribution

Abstract

The sorption capacity of (K_12–2xCa_x)–A zeolite was measured as a function of its composition, for O₂, N₂ and Ar at 77 and 90 K, and for n-butane at 298 and 323 K. The molecular sieving character of the zeolite changed gradually from 3A to 5A in a range of 4 ⩽x⩽ 6, in contrast to the case of the (Na, Ca)–A system.

Using the percolation process theory, the concentration of windows permeable to these gases is deduced as a function of x. Results show that there are three kinds of window, i.e., an open window unblocked by any cation, a window blocked by K⁺ and that blocked by Ca²⁺. O₂, N₂ and Ar cannot pass through the windows blocked by either K⁺ or Ca²⁺ at 90 K, while n-butane can pass through that blocked by Ca²⁺ but only few of those blocked by K⁺ at 298 K.

The site selectivity of Ca²⁺ is discussed and the diagram of cation distribution in (K, Ca)–A, which had been provisionally proposed previously, is refined.