Investigation of methane adsorption on molecular sieve zeolite (from natural materials)

In this study, Kaolin, Bentonite, and Feldspar were used as a low-cost source of Si and Al to synthesize the molecular sieve 13X. The synthesized Zeolites were characterized by XRD, FTIR, SEM, TGA, and BET analysis and used as a suitable adsorbent for CH4 adsorption. The surface areas were 591, 505, 472, and 588 m2/g for natural kaolin (13X-K), bentonite (13X-B), feldspar (13X-F) and commercial molecular sieve 13X (13X–C), respectively. The 13X-K had the highest thermal stability than 13X-B and 13X-F. The adsorption capacities (pressure >20bar) of 13X (kaolin), 13X (bentonite), and 13X(feldspar) were 3.6, 2.4, and 1.95 mmol/g, respectively. The adsorption data were fitted to some isotherms including Langmuir, Freundlich, Sips, BET, and Toth. It was found that the Sips model showed better fitting in comparison to other models. The thermodynamic of adsorption was also investigated; the positive value of ∆S_ads^0 revealed the increased randomness at the solid-solution interface during the gas adsorption. The thermodynamic study also indicated that the adsorption process was exothermic and spontaneous. The adsorption capacities of synthesized 13X samples were compared to other adsorbents; it was found that 13X–K showed considerable performance and can be introduced as a suitable adsorbent for applications on a large scale.