The sorption of ammonium chloride vapour in zeolites. Part II. Mixture of hydrogen chloride and ammonia

Abstract

The high-temperature sorption of vaporized ammonium chloride has been studied in the four zeolites H–mordenite (H–Zeolon), H–Y, Na–Y, and K–L. The vaporized ammonium chloride can be considered as a 1 : 1 mixture of NH₃ and HCl. The theory of the way in which a zeolite sorbent can perturb the solid ⇌ vapour equilibrium has been considered and a method of analysis of the total sorption isotherm to give the partial isotherms of NH₃ and HCl has been developed and applied.

All the total isotherms were of Type IV in Brunauer's classification, corresponding with uptake in a limited pore volume of the two compounds (NH₃ and HCl) which interact strongly. As the isotherms approached saturation of the zeolite the amounts of each component approached the 1 : 1 ratio found in NH₄Cl. This is taken to mean formation of intracrystalline NH₄Cl. For small uptakes disproportionation of the gas phase was found with H–mordenite and H–Y, both of which chemisorbed NH₃ on H-sites and thus enriched the gas phase in HCl. In the cation-bearing zeolites Na–Y and K–L an initial chemisorptive exchange with HCl resulted in formation of some H-sites, which then reacted with NH₃. As a result some initial disproportionation was observed with K–L, but this was very slight with Na–Y.

The isotherm based on a virial equation of state has been extended to mixtures and tested using the reversible isotherm of NH₄Cl in H–mordenite at 230°.