Binderless low silica X zeolite for methane separation from binary CO2/CH4 biogas stream: A comprehensive experimental and computational study

This study presents the synthesis of binderless Na-LSX (B-Na-LSX) and binderless NaK-LSX (B-NaK-LSX). XRD, SEM, EDS, and N₂ physisorption were used for characterization of samples. Computational modelling of prepared sorbent was performed for the fundamental understanding of zeolite topology and adsorption behaviour. The breakthrough experiments are used to evaluate the adsorption capacities on CO₂/CH₄ (40/60 vol%) binary biogas stream. The results were compared with commercial Na-LSX (C-Na-LSX). The breakthrough adsorption capacity of B-Na-LSX was 3.08 mmol g⁻¹ and 0.29 mmol g⁻¹ of CO₂ and CH₄, respectively, at 300 K and 1 bar. CO₂ sorption capacity of B-Na-LSX was ∼11 % and ∼17 % higher than B-NaK-LSX (2.77 mmol g⁻¹) and C-Na-LSX (2.56 mmol g⁻¹), respectively. DFT study reveals that the higher adsorption of CO₂ over CH₄ was attributed to higher charge transfer from CO₂ to zeolite framework. Dual-bed six-step Pressure Swing Adsorption (PSA) was performed on B-Na-LSX at 6 bar. ∼232 cycles were run with above 98 % of CH₄ purity and ∼74 % of recovery. The life-cycle test of sorbent was studied. It was implied that the designed sorbent is effective to produce the high purity of CH₄ and can be utilized for a longer period for CH₄ production.