The sorption of ammonium chloride vapour in zeolites. Part I. Hydrogen chloride and ammonia

The sorption of anhydrous hydrogen chloride and of ammonia was studied at temperatures in the range 190–320° in molecular sieve zeolites, as part of an investigation of the uptake of ammonium chloride vapour in a similar temperature range.When hydrogen chloride was sorbed in porous crystals it reacted in part with them. In decationated zeolites a small amount of aluminium was released from the aluminosilicate framework. In cation-bearing zeolites there was also considerable exchange of cations by hydrogen. In addition in porous aluminosilicates in which the silica : alumina ratio was less than ca. 5 some lattice breakdown occurred, which was ascribed to attack on Si–O–Al bonds. Because of these reactions isotherms of hydrogen chloride were irreversible.Isotherms of ammonia were reversible except those in H–Y. Chemisorption occurred in H–Y and H–Zeolon, forming the ammonium zeolites. Isosteric heats of sorption and differential entropies of sorbed ammonia showed that Na–Y, H–Zeolon, and K–L were energetically heterogeneous to ammonia. Isotherms in Na–Y and K–L were very well described by the isotherm equation based on a virial equation for sorbed ammonia. The activity coefficient of zeolitic ammonia was examined as a test for isotherm models.