Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/4/2013
Publication Date: 9/4/2013
Citation: Cao, X., Ro, K.S., Libra, J.A., Kammann, C.I., Lima, I.M., Berge, N., Li, L., Li, Y., Chen, N., Yang, J., Deng, B., Mao, J. 2013. Effects of biomass types and carbonization conditions on the chemical characteristics of hydrochar. Journal of Agricultural and Food Chemistry. p. 9401-9411. Interpretive Summary: Although there has been a recent surge of interest to improve soil quality using biochar, very little is understood about biochar’s chemical properties which can impact stability. Hydrochar is a biochar made from wet pyrolyzing biomass. This study investigated chemical properties of different hydrochars made from sugar beet and bark mulch. Chemical properties of the two hydrochars prepared from different reaction media (steam vs. water), processing temperatures and reaction times were analyzed using advanced solid state nuclear magnetic resonance spectroscopic techniques along with conventional thermal and wet chemistry methods. Generally higher processing temperature and longer reaction time produced hydrochars with higher aromatic carbons. Water hydrochar contained more abundant aromatic carbons but less carbohydrate carbons than steam hydrochar. These findings are important in understanding the stability of hydrochar when applied to soil as a soil amendment.
Technical Abstract: Effects of biomass types (sugar beet pulp vs. bark mulch) and hydrothermal carbonization (HTC) processing conditions (temperature, residence time, and the phase of reaction medium) on the chemical characteristics of hydrochars were examined by elemental analysis, advanced solid-state nuclear magnetic resonance spectroscopy, and chemical and biochemical oxygen demand measurements. As lignin structures were slightly modified and retained, bark hydrochars were more aromatic than sugar beet hydrochars produced at the same processing conditions. The presence of lignin also resulted in a much lower biochemical oxygen demand (BOD) of bark than sugar beet and the increasing trends of BOD after the HTC processing (likely due to the release of degradable compounds). Compared with those prepared at 200 ºC, 250 ºC hydrochars were more aromatic and depleted of carbohydrates. Increasing residence time from 3 to 20 hr at 250 ºC generally resulted in the enrichment of nonprotonated aromatic carbons. Water hydrochars prepared at 250 ºC contained more condensed aromatic structures than single aromatic rings in lignin, but generally consisted of small aromatic clusters. Both bark and sugar beet pulp underwent deeper carbonization during water HTC (200 ºC, 3 hr) than steam HTC (200 ºC, 3 hr) in terms of more abundant aromatic carbons but less carbohydrate carbons in water hydrochars.