Synergetic inhibition of PCDD/F formation from pentachlorophenol by mixtures of urea and calcium oxide

Abstract

h i g h l i g h t s• Mixed CaO/urea have a synergetic inhibition effect for PCDD/Fs formation from PCP.• 5-20% urea reaction systems obtained the better synergetic inhibition effect.• 2,3,7,8-PCDD congeners were the dominant products in eight reaction systems.• Intermediates could promote the acid-base reaction to realize synergetic inhibition. a r t i c l e i n f o b s t r a c tChlorophenols are structurally similar to PCDD/Fs and have been considered as highly potential precursors for PCDD/Fs formation. The suppressing effects of PCDD/F formation from pentachlorophenol (PCP) were investigated on various mass ratios of CaO and urea. The total concentration of 2,3,7,8-PCDD/Fs, mostly dominated by OCDD, was determined to be 48.58-10186 ng/mg in inhibitor-reaction systems, being much lower than that in blank reaction system (75654 ng/mg). Interestingly, compared with pure CaO and urea reaction system, the concentration and TEQ of formed 2,3,7,8-PCDD/Fs in mixed urea/CaO reaction system were lower, especially with 5-20% urea reaction systems being respectively at decrease by 96.5-99.4% and 99.2-99.7%. The suppression efficiency of TEQ in 5-20% urea reaction systems could be always approximately 100% under 250-350• C. These results suggested that mixed inhibitors, especially 5-20% urea inhibitors, have a synergetic inhibition effect for PCDD/Fs formation from PCP. Mixed inhibitor generated several intermediates, involving CO 2 , H 2 O, NH 3 , Ca(OH) 2 , CaCO 3 , HNCO, biuret and ammelide. The complex between PCP and Ca, N-doped species, lower chlorinated phenols and benzenediol, and organic acids were also determined. Synergetic inhibition mechanism may be attributed to accelerated facilitation of acid-base reaction and N doping. The decomposition of PCP itself also contributes to prevent PCDD/Fs formation.

Inhibitory Effect and Mechanism of an N-S-Based Inhibitor (CH4N2S) on PCDD/Fs in Flue Gas and Fly Ash in a Full-Scale Municipal Solid Waste Incinerator

“…It has been widely reported that Cl 2 plays an essential role in the generation of C–Cl bonds, which more effectively promote the chlorination reaction of PCDD/Fs than HCl . Previous studies have tried to determine the inhibition mechanism of sulfur-based inhibitors and reported that sulfur could convert Cl 2 to HCl . As the TG-MS spectra in Figure show, the decomposition products (primary SO 2 and NH 3 with a strong reduction capability) from the inhibitor could react with Cl 2 to generate HCl.…”

“…44 Previous studies have tried to determine the inhibition mechanism of sulfur-based inhibitors and reported that sulfur could convert Cl 2 to HCl. 45 As the TG-MS spectra in Figure 5 show, the decomposition products (primary SO 2 and NH 3 with a strong reduction capability) from the inhibitor could react with Cl 2 to generate HCl. Consequently, the chlorination reaction was effectively suppressed and the organic chlorine content decreased after injection of the inhibitor.…”

Formation, Measurement, and Control of Dioxins from the Incineration of Municipal Solid Wastes: Recent Advances and Perspectives

“…Numerous studies have been conducted to investigate the suppression effects of alkaline compounds on PCDD/F formation. − Liu et al found that CaO could inhibit more than 90% of PCDD/F formation from PCP. CaO could consume acidic compounds such as HCl and Cl 2 resulting from a low concentration of chlorine and weakening the chlorination of PCDD/Fs.…”

Exploring N/S-Based Polymers for Synergistic Inhibition of Multiple Unintentional Persistent Organic Pollutants during Iron Ore Sintering

“…Chemical inhibition is a low-cost and highly efficient technique to reduce UP-POP formation and emissions at the source. , Many previous studies used N/S-based inhibitors, such as urea, NH 3 , amidosulfonic acid, and other S-containing substances. − Inhibitory effects were observed both in the laboratory and in full-scale municipal solid waste incinerators, and the mechanism of action underlying the inhibitory effects of thiourea in combustion flue gas was also clarified. , Lone-pair electrons of N and S in N/S-containing inhibitors are able to form stable complexes with catalytic metals to retard the activity of the catalyst. , Our group previously utilized thiourea in the iron sintering process and achieved total CBz and PCB emission concentration reductions of 78.2 and 83.0%, respectively . The thermal properties and chemical structures of N/S-containing compounds may influence the decomposition of N/S-containing products .…”