Direct observation of polyvinylchloride degradation in water at temperatures up to 500°C and at pressures up to 700 MPa

Abstract

Degradation of polyvinylchloride (PVC) in high-temperature and supercritical water was studied with a hydrothermal diamond anvil cell to determine phase change characteristics of the reacting polymer with respect to water density. During the reaction period of 500 s, at temperatures between 400 and 5008C and at water densities from 0 to 930 kg/m 3 , PVC particles exhibited clearly defined spreading on the anvil surface that was defined as spread time, S t . The spread times decreased with increasing temperature and the values increased with increasing water density. Analysis of the residues with infrared spectroscopy showed the presence of both polyenes and polyols, whose formation was correlated with water density.From the analyses, nucleophilic substitution of PVC in water was found to be promoted at low temperatures ($ 4008C) and high water densities (>830 kg/m 3 ), whereas the ionic chain dechlorination was promoted at high temperatures (> $ 4508C) and low water densities ($ 750 kg/ m 3 ). A reaction pathway is proposed that shows À ÀOH nucleophilic substitution in competition with ionic chain reaction for dechlorination both of which vary with water density.

Application of Subcritical Water to Dechlorinate Polyvinyl Chloride Electric Wires

“…Therefore, the dechlorination treatment at high pressure and high temperature could break the chemical bonds of the polymeric matrix, favoring PVC degradation. Possible decomposition pathways of PVC have been proposed by several authors [27][28][29].…”

Hydrothermal carbonization of medical wastes and lignocellulosic biomass for solid fuel production from lab-scale to pilot-scale

“…A subsequent stepwise of HCl elimination results in the polyene formation, which is a non-free radical reaction mechanism [30]. Obviously, conjugated double bonds could be created by a ''zipper'' mechanism [31]: once a double bond has formed, the allylic chlorine atom on the C-atom adjacent to the double bond splits off HCl forming two double bonds during the HTC process, which in turn activates adjacent chlorine to propagate the dehydrochlorination process. In aqueous suspensions, PVC In the HTC process, the lignin fragments can be decomposed to phenolics via hydrolysis and further form the phenolic hydrochar via polymerization.…”

Recovery of copper and lead from waste printed circuit boards by supercritical water oxidation combined with electrokinetic process

“…At supercritical conditions (T > 647.3 K, P > 22.1 MPa), water has a high solubility for both organics and oxygen, and organic compounds, oxygen, and water form a single and homogeneous phase, which allows oxidation to proceed rapidly by an elimination of the potential interface mass transport limitations [6,7]. Recently, this technique has been successfully applied to the degradation of waste polymer materials [8,9]. Polymers could be degraded and recovered as monomers or low molecular weight organic compounds in a very short residence time in supercritical water without causing air pollution [9].…”

“…Recently, this technique has been successfully applied to the degradation of waste polymer materials [8,9]. Polymers could be degraded and recovered as monomers or low molecular weight organic compounds in a very short residence time in supercritical water without causing air pollution [9]. Recently, it has been reported that polymers in waste PCBs could be degraded into CO 2 and H 2 O in the SCWO process, and the formation of brominated polycyclic aromatic hydrocarbons (PAHs) was eliminated at the same time [10].…”