Synthesis of biomass-derived porous carbon from bean dregs for adsorptive removal and regeneration of trace C4–C6 light alkanes

Abstract

This study investigates the carbonization mechanism of bean dregs and their chemical activation with KOH through gas composition analysis (GC/TG-MS), focusing on the dynamic adsorption behavior of trace C4–C6 alkane mixtures (34 Pa) in simulated oil tank exhaust. During carbonization, cellulose and lignin decomposition yielded low-carbon alkanes, olefins, and biochar, while protein degradation generated HCN, CO, and NO. KOH activation above 400 °C triggered reactions with oxygen-containing surface groups, releasing CH₄ and H₂ (>1 wt%). The optimized activated carbon (NJ-4-700) exhibited a hierarchical pore structure with a BET surface area of 2462 m² g⁻¹, total pore volume of 0.94 cm³ g⁻¹, and 64% microporosity (<10 Å). Equilibrium adsorption experiments revealed a strong correlation between n-hexane uptake and total pore volume (R² = 0.9654). Dynamic breakthrough testing demonstrated exceptional performance for C4–C6 alkane capture, achieving 56.2 mg g_ads⁻¹ at 30 °C with full capacity retention over 10 cycles. A linear relationship between alkane adsorption capacity and sub-nanometer micropore volume (<10 Å, R² = 0.9598) confirmed the critical role of ultra micropores in physisorbing low-concentration light hydrocarbons. This work establishes a pore-structure design principle for efficient VOC removal under industrial emission conditions, providing mechanistic insights into the targeted adsorption of trace alkanes in energy storage applications.