Effect of NaCl/MgCl2 on generation of NOx precursors during aspartic acid pyrolysis: A experimental and theoretical study

Abstract

This work studied the effect of NaCl/MgCl2 on the evolution of nitrogen during aspartic acid pyrolysis, focusing on the transformation pathways in molecular level. The generation of NOX precursors and other volatiles were detected by TG-FTIR, UV, and GC–MS. Notably, density functional theory was used to evaluate energy barrier and rate-determining step during pyrolysis. The yields of NH3, HCN, and HNCO were inhibited by NaCl/MgCl2 addition, especially on the second releasing stage (333–468 °C). The result of theoretical simulations showed that the rate-determining step in six pathways of aspartic acid pyrolysis was changed by NaCl/MgCl2 addition, especially for MgCl2, and the optimum generation pathway for nitrogen–containing products changed from NH3 formation to DKP formation. The highest energy barrier of NH3 and HCN generation increased to 327 kJ/mol and 432 kJ/mol after the addition of NaCl and MgCl2, respectively, leading to their lower release than raw aspartic acid. In addition, the presence of NaCl/MgCl2 decreased the energy barrier for the substitution of the amino group with the hydroxyl group, especially for NaCl, resulting in the fact that more nitrogen was retained in the char. The results first revealed how the NaCl/MgCl2 affected the nitrogen transformation during aspartic acid pyrolysis under molecular level.