Effects of atmosphere and stepwise pyrolysis on the pyrolysis behavior, product characteristics, and N/S migration mechanism of vancomycin fermentation residue

Vancomycin fermentation residue (VFR) urgently needs proper treatment due to its complex and hazardous nature. Pyrolysis is a promising treatment method, while the product characteristics of VFR pyrolysis remain unclear. Therefore, the influence of different atmospheres and stepwise pyrolysis (including one-stage reaction in N-2 or CO2 and two-stage reaction in N-2) on pyrolysis behavior, product characteristics, and N/S migration mechanism during VFR pyrolysis were investigated for the first time in this work. The results showed that VFR mainly decomposed at 180-600 degrees C, forming non-condensable gas, bio-oil, and biochar. The main released gases included CO2, H2O, NH3, HCN, SO2, and H2S, whereas the N-containing pollutant gas, notably NH3, should be focused due to its high emission (>10 %). Bio-oil was rich in N-containing compounds with a content exceeding 46 %, mainly consisting of Indolizne (9.2-11.5 %), 5H-1-Pyrindine (5.0-9.9 %), and Indole (8.4-9.0 %), and 9-Octadecenamide, (Z)- (1.8-10.1 %). Moreover, the effects of different conditions on the product characteristics were as follows: For the one-stage reaction, compared to N-2, the CO2 atmosphere promoted the formation of alcohols (intended product, increasing 2.2-14.6 %), whereas the two-stage reaction in N-2 inhibited alcohol production (decreasing 1.1-2.5 %). At CO2 condition, the harmless temperature of VFR reduced from 600 degrees C (pyrolysis in N-2) to 400 degrees C. Both CO2 (increasing 0.6-1.5 %) and the two-stage reaction in N-2 (increasing 0.4-1.0 %) retained more N in the solid. Kinetics showed that the pyrolysis process of VFR conformed to diffusion models and reaction order models (F2/D1/F3/D1 for N-2 and F2/D2/F3/D1 for CO2). The VFR transformed to the chemicals and fuels mainly through the deamination, desulfurization, dehydration, decarboxylation, and dehydrogenation reactions. This work provides guidance for harmless disposal and resource utilization during VFR pyrolysis.