Submitted to: Energy and Fuels
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/24/2010
Publication Date: 1/20/2011
Citation: Cao, X., Ro, K.S., Chappell, M., Li, Y., Mao, J. 2011. Chemical structures of swine-manure chars produced under different carbonization conditions investigated by advanced solid-state 13C nuclear magnetic resonance (NMR) spectroscopy. Energy and Fuels. 25:388-397. Interpretive Summary: Recently in the scientific community, there has been a surge of interest to improve soil quality using biochar. However, very little is understood about biochar chemical properties which can impact soil fertility. This study investigated the chemical properties of different biochars made from swine manure using advanced solid-state nuclear magnetic resonance spectroscopic techniques. Pyrochar was produced from heating dried swine solid at 620°C for 2 hrs under no oxygen condition (pyrolysis); hydrochar was produced from treating swine solid slurry (20% solid + 80% water) at 250°C and about 1000 psi for 20 hrs in a stainless steel vessel. Both hydrochar and pyrochar showed significantly different chemical structures than the raw swine manure with decreased carbohydrate components and increased aromatic components. Due to higher pyrolysis temperature, the dominant component of the pyrochar was aromatics, providing resistance to microbial degradation and stability. These findings are important in understanding the soil-biochar interactions, the stability of biochar, and the greenhouse gas emission characteristics when these chars are applied to soil as a soil amendment.
Technical Abstract: Two types of swine manure chars, hydrothermally-produced hydrochar and slow-pyrolysis pyrochar, and their raw swine manure solid were characterized using advanced 13C solid-state nuclear magnetic resonance (NMR) spectroscopy. Compared with the parent raw swine manure, both hydrochars and pyrochar displayed significantly different structural features, with lower carbohydrate groups but higher aromatic/olefinic groups. The chemical structures of hydrochar also varied with different processing conditions. Washing hydrochar with acetone removed the soluble intermediates deposited on the hydrochar. Aromaticity increased for both citric-acid pre-wash and citric-acid catalyzed hydrochars. Pyrochar was structurally different from hydrochars. The dominant component of pyrochar was aromatics whereas that of hydrochars was alkyl moieties. The aromatic cluster size of pyrochar was larger than those of hydrochars. Slow pyrolysis at 620°C provided deeper carbonization than hydrothermal processes.