Transformation and regulation of nitrogen and sulfur during pyrolysis of oily sludge with N/S model compounds

Pyrolysis of oily sludge (OS) is an alternative for energy recovery with less pollutants. However, the migration of nitrogen and sulfur during pyrolysis process remain challenges for environmental concern and subsequent utilization of the recovered fuel. In this work, stage pyrolysis experiments of polyacrylamide (PAM) and sodium dodecyl sulfonate (SDS) under OS surroundings were conducted in a thermogravimetry-mass spectrometry-infrared spectroscopy and a fixed reactor to investigate the transformation behaviors of N/S-containing pollutants. Ca(OH)₂ and Fe₂O₃ were then used as inhibitors to regulate nitrogen and sulfur behaviors. Results showed that 3,3 dimethylpyrrolidine-2,5-dione (C₆H₉NO₂), glutarimide (C₅H₇NO₂) and NH₃ were the primary N-containing pollutants in liquid and gaseous products, which were generated from PAM via deamination reactions at 200–400 °C. SO₂ was the dominant S-containing pollutant, which was generated from SDS via desulfonation at temperature below 300 °C. The dosage of Ca(OH)₂ catalyzed the deamination and cracking reactions, and thus led to more N/S-containing pollutants. Fe₂O₃ suppressed the N/S-containing pollutants significantly because it could increase the energy barrier of N/S-containing pollutants and fix the released NH₃ and SO₂ into solid residues. This work facilitated the understanding of the nitrogen and sulfur transformation behaviors and would provide a possible regulatory strategy for clean fuel recovery.