High Temperature Materials and Processes (Jan 2024)
De-chlorination of poly(vinyl) chloride using Fe2O3 and the improvement of chlorine fixing ratio in FeCl2 by SiO2 addition
Abstract
A quantitative investigation of poly(vinyl) chloride (PVC) de-chlorination using Fe2O3, together with the impact of SiO2 addition on the co-pyrolysis of PVC and Fe2O3, was conducted below 673 K in an Ar atmosphere aiming to cut the emission of gaseous Cl⁻ products. It was found that chlorine in PVC can be fixed in FeCl2 by the reaction between PVC and Fe2O3. The co-pyrolysis of PVC and Fe2O3 proceeds in two stages with a temperature boundary of around 543 K. Below 543 K, a direct reaction occurs between PVC and Fe2O3, resulting in a small mass loss ratio and some extent of chlorine fixing ratio in FeCl2. However, above 543 K, PVC starts to decompose to release gaseous H2, HCl, etc., which react with Fe2O3 through two possible pathways to form FeCl2. In Pathway 1, first Fe2O3 is reduced to Fe3O4 by H2, followed by the chlorination of Fe3O4 to FeCl2 by HCl. In Pathway 2, first Fe2O3 is chlorinated to FeCl3 by HCl, followed by the reduction of FeCl3 to FeCl2 by H2. The chlorine fixing ratio in FeCl2 and the volatile generation ratio increase with decreasing PVC content in the initial mixtures. The addition of SiO2 promotes the chlorine fixing ratio in FeCl2 and volatile generation, and the impact gets stronger with decreasing PVC content in the mixtures. The chlorine fixing ratio is increased from 70.8 to 82.6% by SiO2 addition for the mixtures containing 25% PVC, whereas the difference in the chlorine fixing ratio in FeCl2 caused by SiO2 addition is negligible for the mixtures containing 90% PVC. Fayalite (Fe2SiO4) was not detected in the solid residues after the experiments. After separating FeCl2 using water leaching, the filter residue, a composite of iron oxide and conjugated polyene, can be used as a raw material for iron-making.
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