<p>LTA and FAU zeolites were successfully synthesized from a Venezuelan sodium silicate solution, by hydrothermal crystallization under autogenous pressure at 100°C, with 2–24h crystallization times. The synthesized materials were characterized by XRD, BET specific surface area and SEM. A series of synthesis tests were performed to study the influence of the molar composition of the starting mixture over zeolites crystallization. The effect of crystallization time for a particular synthesis mixture composition was studied for both zeolites types. The reuse as alkaline medium of the mother liquor separated during filtration, and the effect of the aging before crystallization were additionally studied. The experimental result  are in agreement with the crystallization mechanism proposed for zeolites synthesis in liquid phase. The use of a 2SiO2:Al2O3:6.Na2O:240H2O synthesis mixture composition allows obtaining LTA zeolite within 2h of crystallization. For FAU zeolite, no aging period was needed when starting with a 4SiO2:Al2O3:6.6Na2O:264H2O composition. It was possible to synthesize both zeolites with high purity and crystallinity and with adequate water adsorption properties.</p>

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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/m 3 ; and Langmuir surface area, 410.5 m 2 /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 CO 2 , 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.

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