Submitted to: Journal of Analytical & Applied Pyrolysis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 29, 2013
Publication Date: April 16, 2013
Citation: Uchimiya, M., Orlov, A., Ramakrishnan, G., Sistani, K. 2013. In situ and ex situ spectroscopic monitoring of biochar's surface functional groups. Journal of Analytical & Applied Pyrolysis. 102:53-59. Interpretive Summary: Biochar is an agricultural waste-derived value added product that will benefit the farming practice by increasing crop yield, reducing runoff contamination, and by allowing producers to reduce carbon footprint. Cost-effective conversion of biomass to biochar is the key to utilizing biochar in the field scale. This study examined real-time infrared monitoring of biochar production as a way of optimizing the pyrolysis parameters. The results indicated that the developed method can be used to estimate the pyrolysis conditions necessary for achieving desirable biochar properties for soil amendment at minimal time and cost.
Technical Abstract: A number of studies described the higher heating temperature (HHT) as the primary pyrolysis parameter dictating the biochar property: surface functional group and fixed carbon contents, O/C, H/C ratios, and Brunauer-Emmett-Teller (BET) surface area. In order to produce desirable biochar properties with minimal time and cost, the slow pyrolysis system must be optimized for additional parameters, especially the residence time at HHT and the heating rate. In this study, kinetics of biomass slow pyrolysis was investigated in real time using a time-resolved (0.5 s) in situ Diffuse Reflectance Infrared Fourier Transform (DRIFTs) to continuously monitor the changes in surface functionality. The greatest change in surface functionality was observed at 200-500 °C from both in situ DRIFTs (during heating up at 10 °C min-1 to reach HHT) and ex situ (after a set residence time at HHT) proximate, ultimate, ATR-FTIR, and 1H NMR analyses of representative (slow/fast pyrolysis and activated) biochars. The FTIR spectral features at respective temperatures during in situ pyrolysis matched HHT of post-production analysis, and suggested that 20 min residence time was sufficiently long to fully carbonize the lignocellulosic biomass investigated. Regardless of pyrolysis conditions, there was a linear correlation between parameters attributable to aromatic characteristics: (1) baseline FTIR absorbance and (2) H/C ratio with the fixed carbon content of biochar. In situ monitoring of the surface functional groups can provide a rapid means of estimating the residence time, heating rate, HHT and other essential pyrolysis parameters required to achieve desirable aromaticity and to optimize biochar property at minimal time and cost.