Environmental assessment of a novel ionic-liquid based method for recycling of PVC in composite materials

Waste PVC is scarcely recycled due to its high chlorine content and its use in composite materials, which reduces the applicability of conventional waste treatment methods, including thermal, mechanical and chemical recycling. For this reason, alternative treatment options are being developed to increase the recyclability of waste PVC. This paper focuses on one such option which utilises ionic liquids (ILs) for material separation and dehydrochlorination of PVC contained in composite materials. Taking blisterpacks used as a packaging for medicines as an example of a composite material, the paper presents for the first time the life cycle environmental impacts of this novel PVC recycling method, in comparison with thermal treatment (low-temperature pyrolytic degradation of PVC). Three ILs were considered for the PVC recycling process: trihexyl(tetradecyl)phosphonium chloride, bromide and hexanoate. The results suggested that the impacts of the process using the first two ILs were comparable, while the system with hexanoate-based IL had 7-229 % higher impacts. Compared to the thermal treatment of waste blisterpacks, the IL assisted process had significantly higher impacts (22-819 %) in all 18 categories considered due to the greater heat requirements and the IL losses. Reducing the latter would lower most impacts by 8-41 %, while optimising the energy requirements would reduce the impacts by 10-58 %. Moreover, recovering HCl would increase significantly the environmental sustainability of the process, resulting in net-negative impacts (savings) in most categories. Overall, these improvements would lead to lower or comparable impacts to those of the thermal treatment. The findings of this study will be of interest to the polymer, recycling and related industries, as well as to process developers.