Study Of Nitrogen Transformation And Catalytic Denitrogenation During Fast Pyrolysis Of Sewage Sludge

Fast pyrolysis of sewage sludge(SS) was conducted in a fixed-bed tube quartz reactor to investigate the effects of pyrolysis conditions on products and nitrogen distribution. Ni/Al2O3, Co Mo/Al2O3, dolomite, limonite and zeolite catalysts were employed to understand the effects of catalyst, temperature and atmosphere on product composition during catalytic pyrolysis of SS, and a series of advanced analysis techniques were introduced to investigate the structure of nitrogen. The results indicate that raising pyrolysis temperature decreased char yield, but increased the yield of gaseous product, and tar yield reached to a maximum of 55.8%(daf) at 500 oC. The formation of NH3 was attributed to the decomposition of proteins, HCN yield increased while raising pyrolysis temperature. For tar composition, the yields of aliphatics and oxygen containing species(OCS) decreased while nitrogen containing species(NCS) and arenes yields increased by raising temperature. Large amounts of NCS were detected in tar, including N-heterocyclic species, lactams, amines, amines and nitriles. Aromatic nitriles yield increased while aliphatic nitriles yield decreased when raising pyrolysis temperature. Ni/Al2O3 catalyst showed satisfactory activity for tar decomposition.With Ni/Al2O3, total yield of gaseous product increased significantly, especially for CH4 yield. When limonite was used, the yields of NCS and OCS in tar were relatively high. Dolomite can definitely increase OCS yield while zeolite showed unconspicuous influence on tar composition. With catalytic reforming of Co Mo/Al2O3 on volatiles, the yields of NCS and OCS decreased while arenes yield increased significantlly. For Co Mo/Al2O3, high temperature promoted the decomposition of NCS and OCS, and favors the formation of arenes. Furthermore, Co Mo/Al2O3 was found to be active enough for decomposition of indoles and nitriles, and decomposition of indole resulted in the increase of pyrrole yield were proposed. Above 600 oC, Co Mo/Al2O3 showed satisfactory activity on pyrrole decomposition. However, zeolite was found to be active enough for removal of pyridines. H2 atmosphere restrained the decomposition of NH3 to N2 with all catalysts while Ar atmosphere promoted the transformation of NH3 to N2.