Graphitic Biocarbon from Metal-Catalyzed Hydrothermal Carbonization of Lignin

Lignin is a high-volume byproduct from the pulp and paper industry and is currently burned to generate electricity and process heat. The industry has been searching for high value-added uses of lignin to improve the process economics. In addition, battery manufacturers are seeking nonfossil sources of graphitic carbon for environmental sustainability. In this work, lignin (which is a cross-linked polymer of phenols, a component of biomass) is converted into graphitic porous carbon using a two-step conversion. Lignin is first carbonized in water at 300°C and 1500 psi to produce biochar, which is then graphitized using a metal nitrate catalyst at 900-1100°C in an inert gas at 15 psi. Graphitization effectiveness of three different catalysts - iron, cobalt, and manganese nitrates - is examined. The product is analyzed for morphology, thermal stability, surface properties, and electrical conductivity. Both temperature and catalyst type influenced the degree of graphitization. A good quality graphitic carbon was obtained using catalysis by Mn(NO3)2 at 900°C and Co(NO3)2 at 1100°C.