Characteristics Of Pyrolysis Products Of Penicillin Fermentation Residue And Mechanism Of Bio-oil Catalytic Denitrification

Antibiotic fermentation residue(AR)is an organic hazardous waste and a potential safety hazard to the environment and human health.Pyrolysis is an effective method that decompose the residual antibiotics remaining in AR and convert AR into valuable products.However,nitrogen affects the utilization of bio-oil.Clarifying the product characteristics and nitrogen migration mechanism of AR during pyrolysis will be helpful for the resource utilization of AR.In this paper,the changes of their 2D surface morphology,3D surface morphology and internal pore structure with the pyrolysis temperature were analyzed using the fractal dimension method,respectively.Results indicated that the release of volatiles during pyrolysis resulted in a large number of slit-shaped microporous structures on the surface of pyrolysis char.The results showed that the pyrolysis char obtained at 500℃ had the highest fractal dimension value,and the pyrolysis char had the prospect of further activation and modification to prepare for activated carbon.The yield of PR bio-oil reached the maximum value of 28.4 wt%and the content of N-containing compounds was 38.9%in the fast pyrolysis process at 500℃,which lead to the potential of further resource utilization.The cyclization of nitrogen from the protein/amino acids in penicillin fermentation residue(PR)facilitated the generation of pyrrole and pyridine.When heating to 600-700℃,the pyridine and pyrrole in pyrolysis chars could produce quaternary nitrogen groups through condensation,and generate HCN through the secondary thermal cracking at the same time.Amide,amine,pyridine,and indole were the principal nitrogenous species.It was found that the decomposition of glutamic acid and aspartic acid resulted in the formation of several cycloamides in PR fast pyrolysis bio-oil.The decomposition of histidine led to the formation of imidazoles and aromatic imidazoles.The formation and transformation processes of main N-containing compounds in bio-oils were analyzed by using quantum chemical calculations.The results of the quantum chemical calculations indicated that 2,5-piperazinedione(DKP),a nitrogen-containing intermediate produced by the pyrolysis of PR,could decompose into nitriles,amides,and amines.The reaction rate constants in the pathways of DKP decomposition were evaluated by the canonical variational theory(CVT).It was indicated that the pathway of HNCO formation has the highest reaction rate in the PR fast pyrolysis ranging from 400℃ to 700℃,and the activation energy of the rate control step in this pathway was 447.83 kJ/mol.The DKPs that existed in PR fast pyrolysis bio-oils were mainly the molecules produced by the condensation between proline and another amino acid,which due to the inhibition of DKP decomposition by the proline R-group.In this study,in order to further reduce the nitrogen content,the effects of M/HZSM-5(M=Fe,Co,Ni,Cu,Zn,Mo,Zr,Ag and Ce)metal catalysts with metal oxide content of 10 wt%on the catalytic removal of N and O by PR under the condition of fast pyrolysis were discussed.The N content in the mixed catalytic bio-oil decreased from 10.09 wt%to Zn/HZSM-5(6.98 wt%),Co/HZSM-5(7.1 wt%),Cu/HZSM-5(7.18 wt%)and Ce/HZSM-5(7.18 wt%).The separated catalytic pyrolysis not only has good nitrogen removal effect,but also Ag/HZSM-5,Mo/HZSM-5,Ce/HZSM-5 and Fe/HZSM-5 can reduce O content from 9.77 wt%to 3.75 wt%,6.86 wt%,8.39 wt% and 8.54 wt%,respectively.