Study on the nitrogen migration mechanism during penicillin fermentation residue fast pyrolysis based on the substance transformation and canonical variational theory.

Antibiotic fermentation residue (AR) is not only a kind of hazardous waste, but also a biomass resource that rich in organic matter. The fast pyrolysis of penicillin fermentation residue (PR) and the model compounds was performed in this study. In PR bio-char, protein nitrogen was mainly converted into pyrrole nitrogen and pyridine nitrogen. When the temperature exceeded 500 °C, pyridine nitrogen further converted into quaternary nitrogen. NH3, HCN and HNCO were the main nitrogen-containing compounds in the PR fast pyrolysis gas, among which HNCO was mainly the decomposition product of 2,5-piperazinedione (DKP). The yield of PR bio-oil reached 33.1 wt%, and the content of nitrogen was 8.9 wt% at 600 °C. It was found that the decomposition of glutamic acid and aspartic acid resulted in the formation of several cycloamides in PR bio-oil. The decomposition of histidine led to the formation of imidazole and aromatic imidazole. 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 °C to 700 °C. The DKPs that existed in PR bio-oil were mainly the molecules produced by the condensation between proline and another amino acid, which due to the inhibition of HCNO formation by the proline R-group. With the increase of temperature, the rapid increase in the rate constant of dehydrogenation promoted the formation of indole from aromatic amino acids.