Nitrogen Transfer Behavior During Catalytic Fast Pyrolysis Of Sewage Sludge Over ZSM-5

High nitrogen content is the important factor restricting rational resources and sustainable utilization of sewage sludge?SS?.Denitrification and upgrading of SS through catalytic pyrolysis is one of the effective ways for high-efficiency and clean utilization.In the dissertation,catalytic upgrading of pyrolysis volatiles from SS were conducted in a drop tube reactor in order to achieve the removal of organic nitrogen species and directional preparation of light aromatics.The effects of pyrolysis temperature and reaction atmosphere on the product distribution and nitrogen transformation were investigated during non-catalytic fast pyrolysis?NCFP?of SS.Based on comprehensive understanding of the mechanism of nitrogen transformation in NCFP of SS,the effects of pyrolysis temperature on products distributions and nitrogen transfer behavior were investigated during SS catalytic fast pyrolysis?CFP?over zeolite?ZSM-5,Si/Al=25/50/80?.The mechanism of aromatics formation and nitrogen release during CFP of amino acid model compounds with different chemical structures were investigated under the optimal pyrolysis conditions.An in-depth understanding of catalytic pyrolysis mechanism and nitrogen transformation mechanism may provide theoretical basis and technical support for the sustainable utilization of SS resources.The results show that the reductive atmosphere?H₂?improved the formation of gas products and inhibited the formation of tar in comparison to the inert atmosphere?Ar?during NCFP of SS.The reductive atmosphere promoted the thermal decomposition of char N,resulting in a lower char N yield than that under Ar atmosphere.Raising the temperature promoted the release of nitrogen-containing gases.Under all conditions,the production of HCN was quite low,and more N released in the form of NH₃.The thermal decomposition of nitrogenous compounds in SS produced more amines,nitriles,and N-heterocycles under the reductive atmosphere.Above500°C,H₂ further promoted the conversion of nitrogenous compounds to NH₃.The synergistic effect of the reductive atmosphere and high temperature promoted the thermal decomposition of more difficult-to-cleave N-heterocycles,such as piperidines,pyrroles,and pyridines,to generate more NH₃ and HCN,and promoted the conversion of HCN to NH₃.Catalytic upgrading of pyrolysis volatiles from SS pyrolysis show that ZSM-5promoted the removal of volatile nitrogen,converted volatile nitrogen into NH₃,HCN and part of coke N,and a greater amount of aromatics and olefins were prepared.The greater yield of aromatics were obtained over smaller Si/Al ZSM-5?high density of Br?nsted acid sites?with strong denitrification.During CFP of SS,the aromatic carbon yield increased first and then decreased with the increase of pyrolysis temperature.The maximum aromatics yield of 16.4%was obtained over ZSM-5 with Si/Al ratio of 25 at500°C.ZSM-5 promoted the formation of benzene and toluene,and had a high selectivity for aromatics with simple alkyl side chains.CFP of amino acids indicated that amino acids with aromatic ring or saturated hydrocarbon side chain,such as phenylalanine and leucine in SS,favored the formation of aromatics and NH₃.The amino acids with N-ring structure?proline?in SS promoted the formation of N-containing heterocyclic compounds,which were prone to coke on catalyst and inhibited the catalytic cracking of SS to produce more aromatics and NH₃.In addition,excessive aspartic acid of short chain dibasic acid structure in SS was not conducive to the complete thermal decomposition of SS under the optimum pyrolysis condition.