Thermogravimetric kinetic studies of acid and base treated dairy manure as gasification feedstock

Authors: MAINALI, KALIDAS - Oak Ridge Institute For Science And Education (ORISE); Ellison, Candice; Sharma, Brajendra; Sarker, Majher; Mullen, Charles; GARCIA-PEREZ, MANUEL - Washington State University

Submitted to: Energies
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/27/2026
Publication Date: 3/4/2026
Citation: Mainali, K., Ellison, C.R., Sharma, B.K., Sarker, M.I., Mullen, C.A., Garcia-Perez, M. 2026. Thermogravimetric kinetic studies of acid and base treated dairy manure as gasification feedstock. Energies. https://doi.org/10.3390/en19051293.
DOI: https://doi.org/10.3390/en19051293

Interpretive Summary: Conversion of dairy manure into syngas through CO2 gasification offers a sustainable pathway for waste utilization. The study examined how treating dairy manure with phosphoric acid (H3PO4) or sodium hydroxide (NaOH) changes its thermal decomposition behavior during pyrolysis and CO2 gasification. Phosphoric acid had a strong impact. It partially removed hemicellulose and produced a denser, more stable char that reacted more slowly with CO2. This led to higher gasification temperatures, lower syngas production, and higher activation energies. Sodium hydroxide caused only minor changes. It slightly lowered the energy needed for manure to start breaking down during pyrolysis, but this did not improve CO2 gasification. Chars from NaOH-treated manure showed gasification behavior similar to untreated manure, likely because natural minerals reduced sodium’s catalytic effects. Overall, the results show how acid and base pretreatments shape pyrolysis and CO2 gasification reactivity, offering guidance for improving manure conversion in CO2-based pyrolysis and gasification systems.

Technical Abstract: 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 that remained close 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.