Removal Of Nitrogen And Formation Of Light Aromatics During Catalytic Pyrolysis Of Sewage Sludge Over Modified HZSM-5

Sewage sludge?SS?,a kind of low-grade biomass with a wide range of sources,has high utilization value.Developing green conversion technology of SS can not only obtain green bioenergy,but also provide a solution of increasing SS volume and environmental issues caused by SS.Pyrolysis is one of the most promising technologies for the preparation of biofuels and high value-added chemicals from SS,while the high nitrogen content restricts the utilization of bio-oil from SS.In the dissertation,catalytic upgrading of pyrolysis volatiles from SS was conducted for the conversion of organic component in SS to high value-added chemicals.The effects of different metal-loaded?Ni and Co?HZSM-5 catalyst with different metal loading?0.3-3.0 wt.%?on the catalytic fast pyrolysis?CFP?product distribution and nitrogen transfer during CFP process were investigated.The effects of two atmospheres?steam and Ar?and different pyrolysis temperatures on the CFP behavior and nitrogen migration during CFP were mainly studied.The influence of steam on the inhibition of coke deposited on the catalyst and the distribution of nitrogen in product were investigated.Proposed reaction mechanism and catalytic mechanism of SS CFP over metal-loaded HZSM-5.The results show that the presence of metals caused the slight decrease in Oil-C?carbon in bio-oil?yield and the increase in gas yield and total carbon yield of aromatics.Ni-loaded HZ has a better performance than Co-loaded one in improving the carbon yield of aromatics,while the maximum yield of 11.2%was obtained over 0.5Ni-HZ.Metal-loaded HZSM-5 promoted the formation of monocyclic aromatics rather than polycyclic aromatics and Ni significantly enhanced the selectivity of benzene.With the addition of Ni and Co,more nitrogen was released as NH₃ or fixed in solids.NH₃ yield increased by raising the metal loading,and the highest NH₃ yield of 36.8%was obtained over 3.0Ni-HZ.Ni and Co promoted the cracking reactions during CFP to generate more H radicals,which have advantages to the ring-opening of N-containing heterocycles in SS to produce aromatics and NH₃.The distribution of SS product under steam atmosphere was similar to that under Ar atmosphere,and more carbon was transferred to the gaseous product.Compared with the Ar atmosphere,the presence of steam resulted in decrease of coke yield on the catalyst by inhibiting the formation of polycyclic aromatic hydrocarbons,and the water gas shift reaction could be another reason.The gas yield was increased due to the incorporation of steam,and the increase in H₂ and CO was the most.The influence of metal-loaded HZSM-5 on the product distribution of the SS CFP was not changed by steam incorporation.The entire carbon yield of light aromatics in bio-oil obtained under steam atmosphere was reduced compared to that under Ar atmosphere,but the presence of steam increased the selectivity of benzene?B?.The selectivity of B was increased by2.8%at 700 ^oC over HZSM-5 due to the incorporation of steam.Metal-loaded HZSM-5 could also enhance B selectivity and decrease toluene?T?selectivity under steam atmosphere.By the presence of steam,9.6%of the highest total carbon yield of light aromatics was obtained over 0.5Ni-HZ.Steam injection promoted the migration of nitrogen into the gaseous product?NH₃ and HCN?during the CFP of SS,which significantly increased the NH₃ yield and did not change the effect of the metal-supported HZSM-5 catalyst on nitrogen transfer at the same time.The NH₃ yield reached 39.2%and 37.8%over 0.5Ni-HZ and 0.5Co-HZ,respectively.