Environmental assessment of different strategies to produce rigid polyurethane foams using unrefined crude glycerol

Abstract

Rigid polyurethane foams (PUFs) traditionally rely on crude oil (fossil feedstock). Yet, the increasing concerns over environmental issues have been promoting the use of renewable/recycled feedstocks, such as crude glycerol (CG) derived from bio-based feedstocks, like soybean, rapeseed, palm and waste cooking oil (WCO). In turn, from the perspective of a circular economy, recycling PUF waste to recover its polyol or CG content and use it as a partial substituent of virgin polyol or CG in the production of new rigid PUFs (close-loop recovery), rather than disposing it in landfill, is generally seen as a suitable option. To evaluate that perception, this study compares the environmental impacts of rigid PUF produced using polyol derived from crude oil and unrefined CG derived from bio-based feedstocks, based on life cycle assessment following a cradle-to-grave approach. Three optimised formulations of PUF derived from polyol/CG were considered. Furthermore, recycling of rigid PUF wastes, to recover its polyol/CG, was compared with its disposal in landfill. The results obtained revealed that the different formulations used in this study had distinct impacts depending on the scenarios considered. Moreover, these results have also clearly demonstrated that, overall, the environmental superiority of bio-based feedstocks compared to their fossil feedstock counterpart to produce rigid PUFs cannot always be claimed. Regardless of the scenario considered, the methylene diphenyldiisocyanate (MDI) is the main hotspot for all impact categories other than marine eutrophication (ME), ranging from 50 to 98% of the total impacts. As regards the scenarios involving polyol/CG recovery, the environmental impacts from the polyol/CG recovery process exceeded the environmental benefits from the PUF waste recycling and the inherent partial replacement of virgin polyol/CG. Indeed, the polyol/CG recovery resulted in a slight increase of the total impacts compared to those without polyol/CG recovery. These results highlight the need to carry out further studies to improve the environmental performance related with polyol/CG recovery considering different chemical processes.