Key intermediates in nitrogen transformation during microwave pyrolysis of sewage sludge: A protein model compound study

The nitrogen transformations with attention to NH3 and HCN were investigated at temperatures of 300–800 °C during microwave pyrolysis of a protein model compound. The evolution of nitrogenated compounds in the char, tar and gas products were conducted. The amine-N, heterocyclic-N and nitrile-N compounds were identified as three important intermediates during the pyrolysis. NH3 and HCN were formed with comparable activation energies competed to consume the same reactive substances at temperatures of 300–800 °C. The deamination and dehydrogenation of amine-N compounds from protein cracking contributed to the formation of NH3 (about 8.9% of Soy-N) and HCN (6.6%) from 300 to 500 °C. The cracking of nitrile-N and heterocyclic-N compounds from the dehydrogenation and polymerization of amine-N generated HCN (13.4%) and NH3 (31.3%) between 500 and 800 °C. It might be able to reduce the HCN and NH3 emissions through controlling the intermediates production at temperatures of 500–800 °C.