Towards value-added chemicals: Technical and environmental life cycle assessment evaluation of different glycerol valorisation pathways

Abstract

Biodiesel is acknowledged as the most appropriate biofuel to decarbonise the transport sector and combat climate change. The ever-increasing biodiesel production via transesterification results in large amount of glycerol (e.g., 10 kg of glycerol for every 100 kg of biodiesel). Converting glycerol into value-added goods is perceived to be a viable way to lower the high cost of producing biodiesel and expand its market share. The current study examines the technical and environmental aspects of bio-hydrogen, bio-syngas, acrolein, propylene glycol, epichlorohydrin, bio-methanol and bio-ethanol synthesis. CHEMCAD process simulation software was used to perform the modelling and simulation aspects considering a glycerol flowrate of 100 kg/h. The environmental study is based on primary and secondary data and is carried out using the Life Cycle Assessment methodology and the LCA for Experts software, using ReCiPe as the impact assessment method. The technical evaluation points towards glycerol conversion to propylene glycol and bio-methanol production as the best approaches given the relatively low energy requirements, increased purity (>97 wt%) and steadily growing product market. Bio-methanol exhibits the best environmental performance among all examined scenarios, providing the lowest impact in eight out of eleven categories studied while placing second in terms of FETP impact. Glycerol conversion towards propylene glycol seems as the second-best conversion route as it generates the lowest score in regards to GWP impact (0.31 kg CO₂ eq./ kg_product). Ultimately, the most effective methods for valorizing glycerol and improving the production of biodiesel by lowering the expenses related to its manufacturing are glycerol reforming toward bio-methanol and propylene glycol.