Transformation of Nitrogen and Evolution of N-Containing Species during Algae Pyrolysis

Transformation and evolution mechanisms of nitrogen during algae pyrolysis were investigated in depth with exploration of N-containing products, under variant temperature. Results indicated nitrogen in algae is mainly in the form of protein N (similar to 90%) with some inorganicN. At 400-600 degrees C, protein-N in algae cracked first with algae pyrolysis and formed pyridinic-N, pyrrolic-N, and quaternaryN in char. The content of proteinN decreased significantly, while that of pyrrolic-N and quaternaryN increased gradually with temperature increasing. Pyridinic-N and pyrrolic-N formation was due to deamination or dehydrogenation of amino acids; subsequently, some pyridinic-N converted to quaternaryN. Increasing temperature decreased amides content greatly while increased that of nitriles and Nheterocyclic compounds (pyridines, pyrroles, and indoles) in bio-oil. Amides were formed through NH3 reacting with fatty acids, that underwent dehydration to form nitriles. Besides, NH3 and HCN yields increased gradually. NH3 resulted from ammoniaN, labile amino acids and amides decomposition, while HCN came from nitrile decomposition. At 700-800 degrees C, evolution trend of Ncontaining products was similar to that at 400-600 degrees C. While Nheterocyclic compounds in bio-oil mainly came from pyrifinic-N, pyrrolic-N, and quaternaryN decomposition. Moreover, cracking of pyridinic-N and pyrrolic-N produced HCN and NH3. A mechanism of nitrogen transformation during algae pyrolysis is proposed based on amino acids decomposition.