Hydrogen chloride removal from hydrogen gas by adsorption on hydrated ion-exchanged zeolites

Hydrogen chloride is found in important hydrogen gas streams of the chemical industry and needs to be removed for safety and environmental concerns. Here, a systematic study is presented on HCl removal from hydrogen gas by adsorption on zeolites, including cation free and high cation loaded materials, as well as ion-exchanged zeolites (with alkali, alkaline earth and transition metal ions). The HCl removal performance was studied by a fixed-bed breakthrough method under high gas velocities (> 0.3 m/s), at high pressures (30 bar) and at room temperature, and with low HCl concentrations (< 200 ppm). The zeolite screening indicated that the 13X zeolite outperforms the other tested materials. The ion-exchanged X zeolites were extensively characterized via SEM-EDX, XRD, ATR-FTIR, TGA and argon adsorption isotherms. The results revealed that the ion-exchange was successfully achieved with expected tendencies in XRD and ATR-FTIR spectra, and porosities. The breakthrough experiments demonstrated that the hydration of the zeolite prior HCl adsorption improves the hydrogen gas purification performance. The characterization after HCl adsorption supports the hypothesis that HCl is taken up by the material by forming salt molecules within the zeolite cavities by reaction with the cations and, which is, moreover, enhanced by the presence of pre-adsorbed water. The type of cation present in the zeolite framework structure notably affected the HCl removal adsorption capacity as well as uptake rate. Among the ion-exchanged zeolite samples, the Zn2+ form exhibited the highest adsorption capacity at saturation, attributed to the over-exchange of the zeolite cations. The investigation revealed important parameters such as cation radius, atomic mass and electronegativity, which played a noteworthy role in defining the HCl removal performance of ion-exchanged zeolites.