Dealumination and Na activation of natural zeolite for CO 2 adsorption on biogas

In this study, natural zeolites from the Philippines were modified using NaOH heat treatment and NaCl hydrothermal process. Pre-treatment using ferro-filtering and dealumination using different concentrations of HCl acid leaching were prepared prior to sodium activation. Heat treatment was performed using 5M NaOH at 80 °C for 72 hrs while 3 cycle hydrothermal process was performed using 5M NaCl at 10 psi for 1 hr. Diffraction pattern from XRD showed Heulandite (HEU) - Clinoptilolite (CLI) and Mordenite (MOR) framework for raw and acid pre-treated zeolites. There was a shift in HEU characteristic peak from 9.9084° and 8.91 A to 9.6901° and 9.12 A which can be attributed to the decrease of contribution of HEU type zeolite. The decrease in contribution enabled the peak to move towards 9.10 A, value expected for MOR. However, it was found that presence of amorphous phase widens MOR structure on d-spacing 13.45 A that created humps. Reduction of intensity peaks on HEU - CLI on 9.85°, 9.88° and 22.22° regions were observed attributed to acid leaching. The decline on this characteristic peaks implies severe degradation of crystal framework after heavy acid treatment although the framework was stable. Acid treated modified zeolites intensify Si/Al ratio due to dealumination. Sodium uptake along with higher Si/Al ratio was preferred for CO2 adsorption in a mixed gas system of CO2/CH4. Both NaOH heat treatment and NaCl hydrothermal process increase Na uptake as confirmed by EDS but the latter is preferred due to higher Si/Al ratio..