Effect of various potassium agents on product distributions and biochar carbon sequestration of biomass pyrolysis.

Biomass to biochar through pyrolysis is promising for carbon-negative biomass energy. Potassium could enhance biochar formation whereas the difference among potassium agents has not been understood. Herein, 13 potassium agents were adopted, and the product compositions and carbon distributions of slow and intermediate pyrolysis were investigated. Results show that neutral agents have a weak influence on the products, while high-basicity agents enhance biochar formation, decrease organics yields, and promote H 2 generation (9–144 cm3/g) and phenols selectivity (64–79 area%). Especially, due to the anion properties, borate and phosphates deviate from the basicity tendency; acetate contributes to increasing acetic acid selectivity (up to 43 area%) while oxidizing agents promote CO 2 and H 2 O yields. Potassium performs obvious enhancement of biochar carbon sequestration, increasing by 2–49 % for intermediate pyrolysis and -8–51 % for slow pyrolysis with biochar carbon retention reaching 55 % and 77 %, respectively. Meanwhile, the thermally unstable phases of biochar were also generated. General correlation analysis indicates that CO yields and phenols selectivity highly relate to biochar carbon retention. This study sheds light on the key role of acid-base properties and anion properties, and provides insight into AAEM-catalytic biomass pyrolysis. [Display omitted] • Acid-base properties of additives have essential influence on pyrolysis products. • Anion properties such as cross-linking cause differences in specific products. • Slow pyrolysis benefits biochar carbon sequestration and phenols selectivity. • Promotion of cross-linking by potassium lowers biochar thermal stability. • Key roles of potassium in cross-linking and polycondensation are revealed. [ABSTRACT FROM AUTHOR]