Performance of CaX Zeolite for Separation of C2H6, C2H4, and CH4 by Adsorption Process; Capacity, Selectivity, and Dynamic Adsorption Measurements

Adsorption-based process for removal of ethane and ethylene, as the main products of oxidative coupling methane reaction from unreacted methane is discussed. The adsorption equilibrium of methane, ethane, and ethylene was determined experimentally on CaX, the calcium cation exchanged NaX zeolite, by the volumetric measurements in a high pressure setup at three different temperatures. The adsorption isotherms were well modeled by the extended Langmuir-Freundlich isotherm and the adsorbed capacity, adsorption constants, and surface heterogeneity parameter were determined by regression of the model to the isothermal experiments. The results indicated that CaX zeolite would be a selective adsorbent for the separation of ethane, ethylene, and methane from each other at moderate temperatures and pressures. The breakthrough curves of gases were determined in a dynamic adsorption experiment of the gaseous mixture in a fixed bed of CaX zeolites for a feed with similar molar composition of OCM hydrocarbon product. Significant difference of breakthrough times was observed for methane, ethane, and ethylene. It is concluded that construction of an adsorption unit from CaX zeolites at the OCM reactor downstream would be economic and useful for the separation of methane from the C2 products.