Estimating the organic oxygen content of biochar

• Published in: Scientific reports Vol. 10; no. 1; p. 13082
• Main Authors: Bakshi, Santanu, Banik, Chumki, Laird, David A.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 04.08.2020; Nature Publishing Group
• Subjects: 639/4077; 639/638; 704/106; 704/172; Acids; Biomass; Carbonates; Cellulose; Charcoal; Chemistry; Environmental modeling; Humanities and Social Sciences; multidisciplinary; Polyethylene glycol; Pyrolysis; Raw materials; Science; Science (multidisciplinary)
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/s41598-020-69798-y

The organic O content of biochar is useful for assessing biochar stability and reactivity. However, accurately determining the organic O content of biochar is difficult. Biochar contains both organic and inorganic forms of O, and some of the organic O is converted to inorganic O (e.g., newly formed carbonates) when samples are ashed. Here, we compare estimates of the O content for biochars produced from pure compounds (little or no ash), acid-washed biomass (little ash), and unwashed biomass (range of ash content). Novelty of this study includes a new method to predict organic O content of biochar using three easily measured biochar parameters- pyrolysis temperature, H/C molar ratio, and %biochar yield, and evidence indicating that the conventional difference method may substantially underestimate the organic O in biochar and adversely impact the accuracy of O:C ratios and van Krevelen plots. We also present evidence that acid washing removed 17% of the structural O from biochars and significantly changes O/C ratios. Environmental modelers are encouraged to use biochar H:C ratios.