Life cycle assessment applied to bio-based platform molecules: Critical review of methodological practices

Abstract

Bio-based platform molecules are chemicals identified as key agents in the development of circular bioeconomy. Their penetration into the current market would sustain the shift of a chemical industry mainly based on the use of petrochemical feedstock to the use of resources of biological origin. Bio-based platform chemicals have received much attention during the last decades, and thus, there is plenty of literature focused on their production throughout a plethora of different technologies. Nevertheless, most of these procedures lack of maturity and are subject to constraints. Thus, the way to ensure improved environmental sustainability is through the application of tools such as life cycle assessment (LCA). Although the integration of LCA is increasingly common during the design phase of these processes, the diverse modeling options can lead to very unlike results. Converging practices around consensus methodologies would lead to more reliable and comparable results. The purpose of this review is to identify the critical points of divergence that hinder this comparison and try to reconcile them towards the best options within biomass-derived platform chemicals specific context. The performed meta-analysis revealed the existence of three key aspects to be considered in the comparison of LCA studies: cradle-to-gate scope (mostly intermediate chemicals), prospective analysis (technologies under development), and multifunctional processes (biorefineries with several valuable outputs). Regarding the scope, reconciling the temporal scope of the studies with the correct allocation of biogenic carbon fluxes is the aspect that requires a deeper discussion. Evaluating novel technologies (characterized by industrial data scarcity) require careful scaling of the systems, as well as rigorous calculations of the uncertainty of results. Concerning multifunctionality, modelling many flows and their interactions is the most challenging task. Within this context, the consequential perspective seems a more correct approach to capture all the elements of these novel and complex systems, although the lack of data can make it unfeasible in numerous cases. Finally, a limited comparison is performed based on the key aspects previously identified. Thus, broader conclusions are inferred for the most promising routes to produce three bio-based platforms among the selected as a case study: lactic acid (chemo-catalytic transformation of swine manure), succinic acid (fermentative pathways using lignocellulosic biomass), and ethylene (wood gasification).