Pyrolysis behavior of antibiotic residues and the mechanism of nitrogen evolution

The pyrolysis experiments of penicillin residues at different temperatures (300–700 ℃) were carried out in a fixed bed to study the yield of three-phase products and the morphology and distribution of nitrogen at different pyrolysis temperatures. The mechanism of the pyrolysis reaction of amino acids (aspartic acid, histidine and glutamic acid) contained in the bacterial residues and 2, 5-piperazinedione (DKP) was investigated by ReaxFF molecular dynamics simulations. The results show that the yield of gas increases with the increase of temperature, while the char shows a declining trend. The yield of oil increases to a maximum of 42.3% at 500 ℃ and then decreases as temperature increase. The pattern of nitrogen content in the product with temperature is consistent with the trend of yield. Compared with H₂ and hydrocarbon gases, CO₂ and CO aere more easily produced at low temperatures. Amides are the main nitrogenous compounds in oil, and the proportion of amides gradually decreases as the pyrolysis temperature increases. The deamination reaction of amino acids is the main source of NH₃, and dehydration cyclization occurs between amino acid molecules to produce DKP-like compounds. Gases such as NH₃, HCN, HNCO and R-NH, R-NH-R radicals are generated during the pyrolysis of DKP. Nitrogen-containing radicals combine with other radicals or undergo cyclization to form amides, ketones and other compounds present in oil and char.