Chemical-looping combustion of plastic wastes for in situ inhibition of dioxins

Polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) as toxic by-products are inevitably emitted during conventional air incineration processes of chlorine containing wastes (typically, plastic wastes). The presence of O2 in the conventional waste incineration not only participates in carbon gasification and rearrangement as an oxygen source during the de novo synthesis process of PCDD/Fs, but also promotes chlorination through generating more active Cl2 via Deacon reaction. Chemical looping combustion (CLC), which creates an O2-free atmosphere in the fuel reactor, was proposed to dispose plastic wastes. Comparative experiments [conventional PW incineration vs. in situ gasification-chemical looping combustion (iG-CLC) using CaO-decorated Fe2O3/Al2O3 as oxygen carrier] were conducted to measure the distribution properties of 17 toxic PCDD/Fs congeners. The total amount and toxic equivalency quantity of PCDD/Fs have been reduced by 94 % and 89 %, respectively, in iG-CLC. The absence of O2 in fuel reactor and lower Cl2 yield (due to the restriction of Deacon reaction and effective dechlorination by CaO) lead to the significant inhibition of the PCDD/Fs formation. Chlorine substitution modelling also demonstrated that the chlorine substitution probabilities for the formation of 7 toxic congeners of PCDDs and 10 toxic congeners of PCDFs are significantly reduced in iG-CLC.