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

Abstract

The adsorption of gases CO2, H2O, methanol, and dimethyl ether (DME) in zeolite H-ZSM-5 in the temperature range of 50-150 degrees 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 degrees C, LCM can be used at higher temperatures, i.e., at or close to the reaction temperature of one-stage DME synthesis (200-300 degrees C), owing to the absence of crystalline-phase transitions up to its melting point (1470 degrees 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.