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

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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°.

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