Ambient and Low-Temperature PVC Dehydrochlorination Using Imidazolium-Based Ionic Liquids for Low-Energy Plastic Waste Recycling

Conventional polyvinyl chloride (PVC) recycling processes require high temperatures (>۴۰۰ °C), leading to excessive energy use and hazardous emissions. This study explores ambient-condition and low-temperature approaches utilizing imidazolium-based ionic liquids (ILs)—۱-methylimidazole, ۱-ethyl-۳-methylimidazolium acetate (EMIM OAc), and ۱-butyl-۳-methylimidazolium chloride (BMIM Cl)—as pretreatment media for PVC plastic wrap. PVC films were contacted with aqueous IL solutions at a ۱:۱ mass ratio and stirred for ۲۴ h at ۲۵ °C, followed by treatment at ۱۱۰ °C for ۸ h. Raman spectroscopy characterized the PVC phase, while FTIR analyzed IL-rich fractions. At ambient conditions, ۱-methylimidazole initiated the onset of dehydrochlorination, evidenced by attenuation of CH₂ deformation bands (~۱,۴۳۰–۱,۴۵۰ cm⁻¹) and appearance of polyene signals (~۱,۵۰۰–۱,۵۲۰ cm⁻¹). In contrast, EMIM OAc and BMIM Cl exhibited stronger C–H stretching and spatially heterogeneous responses between ۱۱,۰۰ and ۱۵,۲۰ cm⁻¹, suggesting dominant plasticization and interfacial rearrangement. At ۱۱۰ °C, EMIM OAc promoted pronounced dehydrochlorination with diminished C–Cl intensity (۵۰۰–۷۰۰ cm⁻¹), enhanced conjugated C=C bands (۱,۵۰۰–۱,۶۱۰ cm⁻¹), and an increased Ipolyene/Ibackbone ratio. BMIM Cl primarily reduced C–H stretching near ۲,۹۰۰–۲,۹۳۰ cm⁻¹ and moderately increased polyene features, implying limited C–Cl scission. FTIR spectra confirmed IL structural integrity, revealing only the disappearance of broad O–H/N–H bands due to moisture loss without signs of degradation. These results demonstrate that imidazolium-based ionic liquids can promote PVC dehydrochlorination and polyene formation at substantially lower temperatures, offering a stable and recyclable route for sustainable PVC recycling.

کلیدواژه ها:

Imidazolium-based pretreatment ، Ionic Liquids ، Low-temperature dehydrochlorination ، Plastic waste recycling ، Polyvinyl chloride