Synergistic integration of zeolite engineering and fixed-bed column design for enhanced biogas upgrading: Adsorbent synthesis, CO2/CH4 separation kinetics, and regeneration assessment

Biogas, a renewable energy vector derived from anaerobic digestion of organic waste, requires CO₂ separation to enhance its calorific value for engine fuel. This study integrates CO₂/CH₄ separation in biogas using a novel approach integrating dual chemically-activated zeolites and fixed-bed column purification. Biogas produced via CSTR/ultrafiltration (69 % CH₄, 30 % CO₂, 14 ppm H₂S) was further upgraded using HCl + NaOH and H₂SO₄ + NaOH activated zeolites. Optimal absorption capacity of 97.77 ± 0.01 % was achieved at 140 mesh, 60-minute H₂SO₄ + NaOH activation, 2-hour calcination (400 °C), and 200 mL/min flow rate. Breakthrough was observed at 18.12 min. Langmuir isotherm (R² = 0.9992) and Elovich kinetics (R² = 0.9846) best described the adsorption process. XRD analysis showed significant crystal size reduction post-activation (53.31 nm to 16.90 nm). Notably, BET analysis revealed enhanced surface properties surface area of 286.71 m²/g, pore volume of 0.213 cc/g, and pore diameter of 3.532 Å. An innovative dual-column system with non-isothermal TSA protocol optimized CO₂ adsorption (30 mins) and desorption (17 mins, 40 °C, 100 mL/min), yielding superior near-pure methane biogas (99.29 % CH₄, 0.66 % CO₂, trace H₂S). A methane loss of 2.75 % during upgrading demonstrated high CO₂ selectivity. This synergistic approach presents a promising solution for sustainable biogas purification and engine fuel applications.