Effect of ammonium sulfate and urea on PCDD/F formation from active carbon and possible mechanism of inhibition

The effect of ammonium sulfate((NH4)2SO4) and urea(CO(NH2)2) on polychlorinated dibenzo-p-dioxin and dibenzofuran(PCDD/F) formation from active carbon was investigated in this study. Both additives could significantly inhibit PCDD/F formation, and PCDD/F(TEQ)generation was reduced to 98.5%(98%) or 64.5%(77.2%) after 5%(NH4)2SO4or CO(NH2)2was added into model ash, respectively. The inhibition efficiency of PCDDs was higher than the value of PCDFs, however, the reduction of PCDD/F yield was mainly from PCDFs decreasing. In addition, the solid-phase products were reduced more than the gas-phase compounds by inhibitors. By the measurement of chlorine emission in the phase of ion(Cl[Cl-]) and molecule gas(Cl[Cl2]), it was observed that both Cl[Cl-] and Cl[Cl2] were reduced after inhibitors were added into ash. Cl[Cl2] was reduced to 51.0% by urea addition, which was supposed as one possible mechanism of PCDD/F inhibition.