Improving Nitrogen Retention in Algal Biochar Pyrolysis by Co-Pyrolysis with Glucose

Algal biomass is a promising pyrolysis feedstock, however, large amounts of nitrogen-containing compounds (NH3, HCN, horizontal ellipsis ) are emitted during its conversion. These emissions can be decreased by incorporating nitrogen in the biochar's carbon matrix via co-pyrolysis. This study investigates whether adding glucose (GL) to the microalgae, Arthrospira sp. (SP), increases the nitrogen fixation in the solid biochar. Moreover, scalable (co-) pyrolysis experiments are linked with micro-scale pyrolysis. Using hyphenated pyrolysis (Py-GC-MS, TG-IR) and characterization (CHNS, XPS, and Raman) techniques the phenomena associated with the incorporation of nitrogen in the biochars are unraveled. Co-pyrolyzing SP and GL increased biochar yields and nitrogen retention, which is attributed to Maillard reactions occurring in the initial pyrolysis stages. In conclusion, this study provides evidence that co-pyrolysis of microalgae and reducing sugars is a more sustainable strategy to produce algae-based biochar. The co-pyrolysis of glucose and microalgae increases the amount of nitrogen retention during thermochemical conversion. This phenomenon is caused by Maillard reactions during the initial pyrolysis stages. Ultimately, this yields heterocyclic nitrogen-rich biochar, demonstrating the potential of co-pyrolyzing nitrogen-rich biomass streams with sugar-rich compounds as a strategy to reduce hazardous emissions from pyrolysis.image