Investigation of High-Temperature and High-Pressure Gas Adsorption in Zeolite H‑ZSM‑5 via the Langatate Crystal Microbalance: CO2, H2O, Methanol, and Dimethyl Ether

The adsorption of gases CO2, H2O, methanol, and dimethyl ether (DME) in zeolite H-ZSM-5 in the temperature range of 50–150 °C and pressure range of 0–18 bar has been investigated using a high-temperature, high-frequency oscillating microbalance (langatate crystal microbalance, LCM). The determined adsorption data are needed to validate a detailed simulation model, which is meant to assist in the optimization of the preparation of bifunctional core–shell catalysts for one-stage DME synthesis from syngas. Compared to the conventional quartz crystal microbalance (QCM) which is limited to temperatures below 80 °C, LCM can be used at higher temperatures, i.e., at or close to the reaction temperature of one-stage DME synthesis (200–300 °C), owing to the absence of crystalline-phase transitions up to its melting point (1470 °C). Zeolite H-ZSM-5 crystallites have been synthesized on the langatate crystal by steam-assisted crystallization (SAC). The loaded H-ZSM-5 (Si/Al molar ratio 100) on the langatate crystal has been confirmed and characterized with X-ray diffraction (XRD), wavelength-dispersive X-ray spectroscopy (WDX), and scanning electron microscopy (SEM). The adsorption experiments showed that the adsorption of CO2, methanol, and DME in H-ZSM-5 is fitted well by the single site Langmuir model, while the dual-site Langmuir model is needed for the adsorption of H2O in H-ZSM-5. The determined adsorption parameters, i.e., adsorption capacities, adsorption enthalpies, and adsorption entropies, compare well to literature data.