title: End-of-life treatment of poly(vinyl chloride) and chlorinated polyethylene by dehydrochlorination in ionic liquids.
abstract: There is an urgent need for green technologies to remove halogens from halogenated polymers at the end of their lifetime. Ionic liquids (ILs) were used to dehydrochlorinate and/or dissolve the chlorinated polymers poly(vinyl chloride) (PVC) and chlorinated polyethylene (CPE). The dehydrochlorination activity of an IL depends mainly on its anion and is related to the high hydrogen-bond-accepting ability (β value) of the anion. Different phosphonium ILs successfully dissolve and dehydrochlorinate PVC and CPE at temperatures from 80 °C. PVC is dehydrochlorinated up to 98 % after 60 min in tetrabutylphosphonium chloride ([P4444 ][Cl]) at 180 °C. PVC pieces stabilized by calcium stearate (4 mm(3) ) are dehydrochlorinated more slowly; conversions of 85 and 96 % are reached after 1 and 8 h, respectively. Smaller pieces are dehydrochlorinated faster. High loadings, for example, 0.3 g stabilized PVC in 0.5 g IL, can be applied with only a minor loss of conversion. [P4444 ][Cl] proved to be stable during several consecutive reactions; after each run more than 99 % of the IL can be recovered. The structure of the dehydrochlorinated PVC was studied by (13) C cross-polarization magic-angle spinning NMR and FTIR spectroscopy; the removal of Cl and the formation of double bonds were confirmed. Carefully dehydrochlorinated CPE was processed further by acyclic diene metathesis depolymerization with ethylene and the Hoveyda-Grubbs second-generation catalyst to yield α,ω-dienes such as 1,5-hexadiene and 1,6-heptadiene.
authors.affiliation: Centre for Surface Chemistry and Catalysis, Department of Microbial and Molecular Systems, KU Leuven, Kasteelpark Arenberg 23, box 2461, 3001 Leuven (Belgium).
authors.forename: Daan
authors.initials: D
authors.lastname: Glas
authors.forename: Joris
authors.initials: J
authors.lastname: Hulsbosch
authors.forename: Philippe
authors.initials: P
authors.lastname: Dubois
authors.forename: Koen
authors.initials: K
authors.lastname: Binnemans
authors.forename: Dirk E
authors.initials: DE
authors.lastname: De Vos
mesh_terms: D054879:Halogenation; D007093:Imidazoles / Q000737:chemistry; D052578:Ionic Liquids / Q000737:chemistry; D007700:Kinetics; D020959:Polyethylene / Q000737:chemistry*; D011143:Polyvinyl Chloride / Q000737:chemistry*
chemical_list: D007093:Imidazoles; D052578:Ionic Liquids; C502841:1-butyl-3-methylimidazolium chloride; D011143:Polyvinyl Chloride; D020959:Polyethylene
keywords: chlorine; environmental chemistry; ionic liquids; polymers; waste prevention