Life Cycle Assessment of the Catalytic Pyrolysis of High‐Density Polyethylene (HDPE) and High‐Impact Polystyrene (HIPS)

Abstract

Pollution by plastics constitutes an urgent problem that demands immediate actions, including development of efficient polymer recycling technologies. In this scenario, the catalytic degradation of plastic wastes constitutes a promising technology, as suitable catalysts can be used to perform cracking reactions and controlled plastic degradation, yielding high quality end products. Catalyst investments are expected to be recovered by benefits related to reduction of reaction temperature and time and by manufacture of higher valued products. However, proper environmental assessment of catalyst usage has yet to be performed in most plastics chemical recycling processes. For these reasons, in the present study, life cycle assessment (LCA) based on system expansion methodologies is carried out to determine the environmental impacts of catalytic pyrolysis transformations of high‐impact polystyrene (HIPS) and high‐density polyethylene (HDPE) using zeolite H‐USY (ultrastable Y) and SO4/SnO2 catalysts, respectively, based on actual collected experimental data to represent conversions and yields. Surprisingly, the obtained results indicate that the use of catalysts for plastic waste degradation reactions can be environmentally disadvantageous sometimes, depending on the blend of obtained products. Therefore, the environmental impact of catalysts on plastics chemical recycling should be carefully assessed to avoid problems derived from positive bias, which assumes that the catalytic process is necessarily better than the noncatalytic counterpart. However, the positive impacts of styrene and olefins recovery can indeed contribute with positive environmental performances of both catalytic and non‐catalytic processes, particularly regarding global warming, acidification, human toxicity, ecotoxicity, eutrophication, and ozone layer depletion.

Total revalorization of high impact polystyrene (HIPS): enhancing styrene recovery and upcycling of the rubber phase

“…[25][26][27][28][29][30][31][32][33][34][35] This can be attributed to the presence of the PB particles, which contribute to the formation of char nuclei during the thermal degradation process and affect the thermal decomposition mechanism, decreasing in turn the styrene yield. [25][26][27][28][29][30][31][32][33][34][35] A possible solution to this problem could be the separation of the rubber particles from the free PS matrix before the pyrolysis process. In a lab context, such fractionation can be carried out employing the Ruffing technique.…”

“…However, in almost all efforts to thermally recycle HIPS, the styrene selectivity and yield are lower than in the thermal degradation of pure PS samples. [25][26][27][28][29][30][31][32][33][34][35] This can be attributed to the presence of the PB particles, which contribute to the formation of char nuclei during the thermal degradation process and affect the thermal decomposition mechanism, decreasing in turn the styrene yield. [25][26][27][28][29][30][31][32][33][34][35] A possible solution to this problem could be the separation of the rubber particles from the free PS matrix before the pyrolysis process.…”