Synthesis and Granulation of a 5A Zeolite-Based Molecular Sieve and Adsorption Equilibrium of the Oxidative Coupling of Methane Gases

This work presents a detailed description of the synthesis of a 5A zeolite and its further granulation into molecular sieve beads. The XRD spectrum of synthesized crystals showed the characteristic peaks of a type A sodium zeolite, and XRF results of the ion-exchanged material with a calcium chloride solution allowed us to verify the formation of a 5A zeolite structure. The analysis of SEM images indicated that the granulated process generated a core–shell structure with suitable mechanical properties for industrial use. The granulated material exhibited similar properties (roundness, 96%; crush strength, 57 N; packing density, 607 kg/m³; and Langmuir surface area, 410.5 m²/g) to most commercial molecular sieves. However, its lower water sorption capacity (0.142 kg/kg) reveals that zeolite adsorption is affected by the cementing material. Adsorption equilibrium studies at different temperatures with oxidative coupling of methane (OCM) effluent gases indicated that the material showed a higher affinity for CO₂, followed by ethylene, ethane, and methane, whereas nitrogen was barely retained. The affinity trend was in agreement with the observed heats of adsorption, which were in the range of 13–30 kJ/mol for tested gases. Isotherms were fitted with a Langmuir model, and adsorption parameters were obtained. Regressed equilibrium equations can be used for further modeling of a swing adsorption separation for OCM effluent gases.