Statistical optimization to improve N and C efficiency in biochar from model systems

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

Submitted to: Bioresource Technology Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/29/2023
Publication Date: 10/2/2023
Citation: Mainali, K., Sarker, M.I., Mullen, C.A., Jimenez, V.S., Garcia-Perez, M. 2023. Statistical optimization to improve N and C efficiency in biochar from model systems. Bioresource Technology Reports. https://doi.org/10.1016/j.biteb.2023.101646.
DOI: https://doi.org/10.1016/j.biteb.2023.101646

Interpretive Summary: Pyrolysis is a common technique to produce value-added products from biomass including bio-char which can have many different uses. During the pyrolysis two important elements of the materials, nitrogen (N) and carbon (C) are lost in their oxide forms from the products. Especially if the feedstock has high N content as is the case for manures, algae and sewage sludge, retaining N in the bio-char is preferred to avoid emission of pollutants. Nitrogen containing bio-chars can also have specialty uses such as adsorbents because of their unique properties. In this study, different factors of the pyrolysis process have been evaluated and optimized to enhance the retention efficacy of N and C in solid products obtained from pyrolysis. Three factors including temperature, acid concentration and feed stock ratio were combined in this investigation to obtain a solid product containing the highest amount of N and C after pyrolysis.

Technical Abstract: During biomass pyrolysis, nitrogen and carbon are lost in the form of NOX and CO2. Co-carbonization of cellulose (as a carbon source) and nitrogen containing compounds (such as lysine and melamine) was investigated to determine how independent variables interact to maximize N and C conversion efficiency into the solid product. A central composite design was used to select the combinations of temperature, acid concentration, and cellulose to N-compound ratio. Response Surface Methodology (RSM) was used to optimize the variables’ responses. Different statistical models were generated based on experimental data to estimate N and C conversion efficacy. Models were also used to determine the optimal N and C conversion efficiencies in char. In the case of lysine, the best N-conversion efficiency was obtained with a lysine loading of 10 wt.% , an acid impregnation of 4 wt.% and a carbonization temperature of 275 C. Similarly, the best N-efficacy obtaining variables for melamine was a 7 wt.% loading, 4 wt.% acid impregnation and 200 C co-carbonization temperature. Statistical analysis was used to compare the coefficients (R2) in both cases (as predicted vs. actual).