Development and optimization of palm kernel shell activated carbon blended with xerogel for SO2 capture: experimental, isotherms, and kinetic studies

The rapid expansion of palm oil production has generated significant quantities of palm kernel shells (PKS), a waste by-product that poses environmental challenges. Similarly, sulphur dioxide (SO2), a major pollutant from fossil fuel combustion, contributes to respiratory health issues, acid rain, and economic burdens due to healthcare and industrial maintenance. This study addresses both concerns by developing a blend of adsorbents derived from PKSB to efficiently capture SO2 emissions. The hybrid material, combining activated carbon (PKSAC) and xerogel (PKSX) produced via a sol-gel process, exhibited superior structural and adsorption properties. Comprehensive characterization using Brunauer-Emmet Teller (BET) the pore Size for the (PKSB, PKSAC, and PKSX) was 2.177, 1.877, and 16.525 (nm), respectively. Thermo gravimetric analysis (TGA) lower mass loss and higher thermal stability of PKSAC and PKSX indicate more carbonaceous, stable structures, which favour SO2 adsorption by providing enhanced surface area and thermally resilient active sites. Fourier Transform Infrared (FTIR) the stronger and sharper peaks (e.g., around 3300 cm¹, 1630 cm¹) in PKSAC and PKSX suggest the presence of more active oxygenated and acidic surface groups, enhancing SO2 binding via chemisorption or physisorption mechanisms. Scanning Electronic Microscope (SEM) the SEM image shows a highly porous surface structure with interconnected channels, indicating a welldeveloped porous network. This morphology is favourable for gas adsorption applications such as SO2 capture. X-ray Diffraction (XRD) analysis revealed a characteristic broad peak around 29 = 20-30° for all samples, including xerogel, activated carbon, and biochar. This pattern indicates the amorphous (low-crystallinity) nature of these materials. The observed structural features confirm their suitability for SO2 adsorption applications. Adsorption performance was assessed using a packed fixed-bed column system under varying adsorbent weights and flow rates. A Response Surface Methodology (RSM) model employing a Box-Behnken Design (BBD) was used to optimize key operational parameters: contact time (10-15 minutes), adsorbent mass (10-20 g), and flow rate (100-300 L/h). Under optimal conditions—20 g of adsorbent, a flow rate of 100 L/h, and a 20-minute contact time—removal efficiencies of 84%, 89%, and 91% were achieved using PKSAC, PKSX, and their 30:70 blend, respectively. The experiments were conducted with an SO2 concentration of 50 ppm. The correlation coefficient (R2) was used to assess the equation's suitability. The PKSAC-PKSX blend is the major contributor to SO2 capture and is utilized to investigate both physisorption and chemisorption interactions between SO2 gas and the blend. The PKSACX adsorption processes are suit both the pseudo-first and pseudosecond order models. This indicates that throughout the adsorption process, both physisorption and chemisorption occur. Kinetic studies revealed the adsorbent's dual physisorption and chemisorption mechanisms, with Thomas and Yoon-Nelson models providing the best fit. This research underscores the potential of PKS-derived hybrid adsorbents as a sustainable and cost-effective solution for SO2 mitigation, offering promising applications in pollution control and waste valorisation.