Effect of different operation conditions on PCDD/F inhibition by ammonium dihydrogen phosphate: concentrations, distributions and mechanisms

Abstract

Phosphorus-containing compounds are considered as the potential alternatives of traditional inhibitors for suppressing the formation of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), but the suppression characteristics are scarcely studied. In this study, ammonium dihydrogen phosphate (ADP) was selected as the inhibitor to inhibit the PCDD/F formation via de novo synthesis at 350 °C. The influence of oxygen content and addition method on PCDD/F inhibition was systematically investigated by means of statistical analysis and morphological characterization. The results showed that oxygen enhanced the formation of PCDD/Fs from 1470 ng g⁻¹ (9.78 ng I-TEQ g⁻¹) to 2110 ng g⁻¹ (14.8 ng I-TEQ g⁻¹). ADP significantly inhibited the PCDD/F formation, with inhibition efficiencies ranging from 82.0% to 97.7%. Herein, a higher oxygen content and the premixed way intensified the suppression effect. Dibenzo-p-dioxin (DD)/dibenzofuran (DF) chlorination was proven to be effectively suppressed while chlorophenol (CP) route was not obviously influenced. With the addition of ADP, Cl source was significantly reduced and the formation of organic Cl was effectively inhibited. Also, it decreased the proportion of C–O/C=N and C=O, revealing the efficient inhibition of carbon oxidation. Meanwhile, the formation of copper phosphate and copper pyrophosphate was observed in XPS (X-ray photoelectron spectroscopy) spectra, indicating that the catalytic metal Cu was chelated and passivated by ADP. The premixed way had a better effect on reducing Cl resources, inhibiting oxidation and chelating metals, due to the direct contact with inhibitor. However, the separation method could only depend on the decomposed gases, resulting in a lower inhibition efficiency.

Graphical abstract