Hydrothermal carbonization of poly(vinyl chloride)

Abstract

Poly(vinyl chloride) (PVC) was subjected to hydrothermal carbonization in subcritical water at 180–260°C. Dehydrochlorination increased with increasing reaction temperature. The release of chlorine was almost quantitative above ∼235°C. The fraction of organic carbon (OC) recovered in the hydrochar decreased with increasing operating temperature from 93% at 180°C to 75% at 250°C. A wide array of polycyclic aromatic hydrocarbons (PAHs) could be detected in the aqueous phase, but their combined concentration amounted to only ∼140μgg−1 PVC-substrate at 240°C. A pathway for the formation of cyclic hydrocarbons and O-functionalized organics was proposed. Chlorinated hydrocarbons including chlorophenols could only be identified at trace levels (low ppb). Polychlorinated dibenzodioxins (PCDDs) and dibenzofurans (PCDFs) could not be detected. The sorption potential of the hydrochar turned out to be very low, in particular for polar organic pollutants. Our results provide strong evidence that hydrothermal carbonization of household organic wastes which can be tied to co-discarded PVC-plastic residues is environmentally sound regarding the formation of toxic organic products. Following these findings, hydrothermal treatment of PVC-waste beyond operating temperatures of ∼235°C to allow complete release of organic chlorine should be further pursued.