Co-pyrolysis of FeO-poly(vinyl chloride) (PVC) mixtures: Mitigation of chlorine emissions during PVC recycling.

A systematic investigation was conducted onthe co-pyrolysisof FeOand PVC mixtures in temperatures as high as 1373 K upon the development of PVC recycling technology that mitigates chlorine emission. Central to our investigation, PVC decomposition plays the leading role in the co-pyrolysis of FeOand PVC mixtures following a two-stage pattern bifurcated at a temperature of 673 K. In Stage 1, at temperatures 673 K and lower, FeOis chlorinated by chlorine from PVC, resulting in FeCl. The composition of the final solid residue of Stage 1,conjugated polyene, FeCland FeO/FeO, depends on the initial FeOcontent in the mixture. When the temperature is increased to be higher than 673 K, decomposition of conjugated polyene occurs simultaneously with the stepwise reduction of FeO/FeO: FeO → FeO → FeO → Fe. However, in mixtures containing FeOthat is less than 39.6% of the mass, FeOcan coexist with Fe; therefore, the FeO formation step is skipped. Most FeClescapes from the reaction system as vapor, showing the necessity of removing FeClat the end of Stage 1 to avoid harmful substance emission. The presence of FeOcan significantly suppress gaseous emissions, especially HCl originating from PVC decomposition. There was only 0.6% HCl by mass (2.4% PVC base by mass) released when co-pyrolyzing the PVC + 75% FeOmixture due to the complete consumption of PVC and its decomposition products by FeO. After separating FeCl,which is a valuable chemical feedstock, by water-leaching the solid residue obtained at 673 K, the filtered residue,which is a mixture of FeO/FeOand polyene, was confirmedto be suitable for iron-making. The results clearly show the possibility of developing a PVC recycling technology with mitigated chlorine emissions by manipulating the amount of FeOadded.