AGRICULTURAL WASTES

Escalating anthropogenic carbon dioxide (CO₂) emissions necessitate the development of sustainable and cost-effective capture technologies. This research investigates the valorization of corn cobs, an abundant agricultural waste, as a precursor for producing activated carbon (AC) for CO₂ capture via adsorption. The activated carbon was synthesized from corn cobs, sourced from Benin City, Nigeria, using a chemical activation method with potassium hydroxide (KOH). The resulting adsorbent was characterized using Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDS), and Thermogravimetric Analysis (TGA). Adsorption experiments were conducted in a packed column to evaluate CO₂ capture performance. The study systematically assessed the effects of key operational parameters, including contact time, adsorbent dosage, gas flow rate (0.5 and 2.0 L/min), and particle size (100, 250, 500, and >500 µm). Characterization confirmed the synthesis of a porous, carbon-rich material. SEM revealed a rough, heterogeneous surface with significant porosity ideal for adsorption, while EDS confirmed carbon as the predominant element (90.05% atomic concentration). TGA demonstrated high thermal stability, indicating suitability for regeneration cycles. Adsorption studies showed rapid CO₂ uptake, reaching equilibrium in approximately 50-60 minutes. Particle size was identified as a critical factor influencing performance. The 250 µm particle size achieved the highest CO₂ removal efficiency at 48.0%. However, the 100 µm particles exhibited the highest equilibrium adsorption capacity (qₑ) of 2,939 ppm·L/g, attributed to their greater specific surface area. Breakthrough analysis further confirmed that smaller particle sizes (<100 µm) significantly prolonged bed saturation time (approx. 45 minutes) compared to larger particles.This study concludes that corn cob-derived activated carbon is an effective, low-cost, and sustainable adsorbent for CO₂ capture. The 250 µm particle size offers an optimal balance between removal efficiency and practical operational handling. This wasteto-value approach supports circular economy principles and presents a viable pathway for mitigating CO₂ emissions using locally available agricultural residues.

Climate change driven by increasing atmospheric CO₂ concentrations calls for urgent implementation of atmospheric CO2 reduction. However, adsorbents are mostly expensiveand energy-intensive, especially for developing nations. Agricultural wastes, especiallycorncobs, are a sustainable alternative due to their lignocellulosic composition, natural porosity, and abundance as underutilized biomass. This study investigated the CO₂ adsorption potential of chemically activated corn cob-derived adsorbent through packed bed column experiments. Corn cobs were collected, processed, and activated using potassium hydroxide (KOH) at temperatures between 400-600°C. CO₂ gas was generated in-situ via CaCO₃-HCl reactionandpassed through glass columns (2.1 cm diameter, 5 cm bed height) at flowrates of 0.5-2.0L/min. Four particle size ranges (100, 250, 500, and above 500 µm) were evaluated over 60-minute contact periods at ambient temperature (29±2°C). Characterization via SEM-EDS revealed highly porous morphology with 90.05%carboncontent and oxygen-containing functional groups favorable for CO₂ binding. The 100µmparticle size achieved the highest equilibrium adsorption capacity of 5,459 ppm·L/g, while250 µm particles demonstrated optimal removal efficiency of 48.0%. Breakthrough analysisindicated that smaller particles delayed saturation, with 100 µm maintaining effectivenessbeyond 45 minutes compared to 25 minutes for above 500 µm particles. Flowrate influencedperformance, with reduced rates (0.5 L/min) compensating for larger particle sizes byincreasing contact time. These findings reveal that corn bobs are a viable solution for carboncapture.