Thermogravimetric Kinetic Studies of Acid and Base Treated Dairy Manure as Gasification Feedstock

The influence of phosphoric acid (H3PO4) and sodium hydroxide (NaOH) impregnation on the pyrolysis and CO2 gasification behavior of dairy manure was evaluated using thermogravimetric analysis (TGA), with kinetic parameters assessed through iso-conversional kinetic analysis (Frieman method). H3PO4 pretreatment altered early decomposition by partially removing hemicellulose and promoting the formation of thermally stable, condensed char structures. The resulting chars exhibited reduced CO2 reactivity, as evidenced by higher gasification temperatures, lower syngas yields, and elevated activation energies, indicating hindered CO2 diffusion and slower Boudouard reaction kinetics. In contrast, NaOH pretreatment caused only minor changes in both pyrolysis and gasification behavior. A slight reduction in pyrolysis activation energy suggested Na+ catalyzed bond-cleavage reactions; however, this effect did not enhance CO2 gasification reactivity. Chars produced from NaOH-treated manure exhibited slightly higher activation energies during CO2 gasification and syngas yields, which remained close to or slightly above those of raw manure, attributed to complex mineral interactions that diminish the catalytic influence of sodium. Overall, these findings clarify how acid and base chemical pretreatments govern char evolution and carbon-CO2 reactivity, providing a foundation for optimizing pretreatment strategies and reactor conditions for manure conversion in CO2-based pyrolysis and gasification systems.