Enhancing CO₂ capture using novel adsorbents derived from palm kernel shell biochar: experimental study, process optimisation, adsorption isotherm and kinetic modelling

The urgent need to mitigate anthropogenic (CO₂) emissions, which have increased from pre-industrial levels of 270 ppm to over 410 ppm, underscores the importance of developing efficient and cost-effective carbon capture technologies. This study addresses this challenge by developing high-performance (CO₂) adsorbents derived from Palm Kernel Shell Biochar (PKSB). A Xerogel (PKSBX) was synthesised from (PKSB), while commercial Activated Carbon (PKSB-AC) was also evaluated in a packed fixed-bed column system. The physicochemical properties of the adsorbents were characterized using Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), Brunauer–Emmett–Teller (BET) surface area analysis, Fourier-Transform Infrared Spectroscopy (FTIR), Thermogravimetric Analysis (TGA), and Elemental Analysis (EA). The (CO₂) adsorption process was optimised by varying the adsorbent mass (10 g, 15 g, 20 g), gas flow rate (100 L/h, 200 L/h, 300 L/h), and contact time (5min, 10 min, 15 min) at 30 °C and an inlet (CO₂) concentration of (95.11 ppm). Response Surface Methodology (RSM) was successfully applied to model and optimise the operational parameters, yielding a highly accurate model (R² = 0.99) for both (PKSBX) and (PKSB-AC). The (RSM) analysis identified a mass weight of (20 g), a flow rate of (100 L/h), and a contact time of (15 min) as the most significant factors influencing adsorption performance for high removal effectiveness of (CO2). Under these optimal conditions, maximum (CO₂) adsorption efficiencies of (89.2%) for (PKSBX) and (84.5%) for (PKSB-AC) were achieved. Although experimental results indicated the highest removal efficiency at (20 g), the statistical model suggested that (10 g) provided comparable performance with improved material efficiency, reflecting a trade-off between adsorption capacity and cost-effectiveness. Fixed-bed modelling using the Thomas and Yoon–Nelson models confirmed enhanced adsorption efficiency at (20 g) of adsorbent weight and (100 L/h) flow rate. At the same time, kinetic analysis indicated conformity to the pseudo-second-order model, suggesting chemisorption as the dominant mechanism. Blended adsorbents comprising (PKSBX+PKSB-AC) in ratios of (70:30), (50:50), and (30:70), respectively, were further tested. Among these, the (70% PKSBX + 30% PKSB-AC) blend exhibited the highest CO₂ removal efficiency (RE = 92.7%), followed by (89.6%) and (89.2%) for the (50:50) and (30:70) blends, respectively at same operating conditions and parameters values of adsorbent weight (20 g), gas flow rate (100 L/h) and (15min.) of contact time, confirming the superior CO₂ affinity of the Xerogel component. Overall, the study demonstrates that (PKSB)-derived materials, particularly (PKSBX) and its blends with (PKSB-AC), are sustainable and highly effective adsorbents for (CO₂) capture, contributing to both agricultural waste valorisation and climate change mitigation.