Energy-Efficient Low-Temperature Alkaline Thermal Graphitization (ATG) of Biomass-Derived Lignin for Porous Graphitic Carbon (PGC) Production
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Conventional graphitization typically requires temperatures exceeding 3000 °C, resulting in high energy consumption and limited sustainability. Lignin, an abundant and aromatic biomass component, has been widely considered non-graphitizable due to its rigid cross-linked structure that restricts atomic rearrangement. This study investigates the energy-efficient alkaline thermal graphitization (ATG) of biomass-derived lignin to produce porous graphitic carbon (PGC) at lower temperatures of 500-700 °C and 900 °C. Lignin was treated with alkali metal carbonates (Li2CO3, Na2CO3, and K2CO3) and a ternary eutectic mixture. Raman spectroscopy and X-ray diffraction (XRD) analyses revealed that Na2CO3 at 900 °C produced the highest degree of graphitic ordering, while K2CO3 promoted pore development through enhanced intercalation and etching. Li2CO3 exhibited the highest gas production, particularly CO, indicating enhanced carbon conversion. The eutectic carbonate system enabled graphitization at significantly reduced temperatures, with 600 °C providing an optimal balance between carbon retention and structural evolution. Process simulation using Aspen Plus and Techno-Economic Analysis (TEA) were conducted to evaluate the process feasibility, indicating that the 600 °C eutectic system offers the most favorable economic performance due to enhanced PGC yield. These findings highlight the potential of lignin as a sustainable carbon feedstock and demonstrate the roles of carbonate salts in biomass graphitization, providing insight into their potential for enabling energy-efficient pathways toward sustainable graphitic carbon.