Effect of biomass type and pyrolysis temperature on nitrogen in biochar, and the comparison with hydrochar

Abstract

In this paper, two different biomasses (soybean straw and Chlorella) were pyrolyzed at temperatures 300–800 °C to obtain biochars. The impacts of biomass type and pyrolysis temperature on the physical and chemical properties of biochar, especially the effects on nitrogen (N) content and composition, were investigated. Furthermore, the hydrochar obtained from hydrothermal carbonization (HTC) of the same biomass was compared with the pyrolysis biochar. Biochar N content was positively correlated with biomass N content and negatively correlated with pyrolysis temperature. For raw biomass, N mainly existed as protein-N and inorganic-N, which converted to more stable structures through the pyrolysis process, including pyridinic-N, pyrrolic-N, graphitic-N (or quaternary-N) and pyridinicN-O. While in hydrochar, N-containing species mainly include protein-N, pyrrolic-N and pyridinic-N. Biochar had more kinds of N-containing species, more aromatic structures, and higher stability compared with hydrochar.