Experimental and DFT study on the migration and transformation mechanism of nitrogen during the pyrolysis of food waste

Abstract

Pyrolysis technology is an effective way to realize the reduction and recycling of food waste (FW), but the generation of N-containing substances has a great impact on the quality of pyrolysis products and the environment. The present study mainly focused on the migration and transformation mechanism of N during the pyrolysis process of FW, which was investigated by TG-FTIR, GC–MS, and DFT calculation. The experimental results show that NH3 and HCN are the main N-containing gas products, and the N-containing substances in the pyrolysis oil are mainly N-containing heterocycles (21.82%), nitriles (6.43%), and amides (4.00%) at 500 ℃. The proteins in food waste are cleaved into various amino acid molecules at temperatures above 300 ℃. Some amino acid molecules generate NH3 and HCN by removing various groups. Some other amino acid molecules generate N-containing heterocycles, nitriles, amides, and various other N-containing substances by intramolecular de-H2O or intermolecular de-H2O reactions of amino acids or condensation reactions of amino acids with small molecules and transfer to the pyrolysis oil. As the temperature increases, most of the N-containing heterocycles and nitriles will be cleaved and generate HCN.