Inhibition on de novo synthesis of PCDD/Fs by an N-P-containing compound: Carbon gasification and kinetics.

In this study, an N-P-containing compound (ammonium dihydrogen phosphate (ADP)) and an auxiliary material (CaO) were used to inhibit the formation of polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDD/Fs). ADP significantly inhibited the formation of PCDD/Fs by the inhibition efficiencies of 98.45% for total concentration and 96.55% for toxic concentration. ADP was the best single inhibitor on toxic PCDFs (96.55%), and the inhibition on toxic PCDDs improved after ADP (90.91%) coupled with CaO (95.69%). In the temperature range of 300-350 °C, ADP inhibited the carbon gasification by reducing CO2 and CO (400%-500% (20 K/min)), which could attributed to the formation of Cu2P2O7 and copper nitrides from the Cu deactivation by P and N, respectively. However, the synergy of ADP and CaO decreased CO and CO2 by 200%-300% (20 K/min), because CaO could promote carbon gasification. In addition, the apparent activation energy (Ea) increased from 78.50 kJ/mol to 102.04 kJ/mol with the addition of ADP but decreased to 73.92 kJ/mol after adding ADP and CaO. These results revealed that one inhibition route of de novo synthesis was the inhibition of carbon gasification by ADP, while CaO mainly inhibited de novo synthesis via the consumption of HCl and Cl2. Furthermore, a reaction mechanism function in model fly ash was built as f(α)=2α-1/2/3, which included carbon gasification and de novo synthesis. The results pave the way for further research on the inhibition kinetics of PCDD/F and development of other inhibitors.