EMergy and Green Chemistry: do they speak the same language? An integrated assessment applied to the production of lactic acid

In the world of sustainability assessment, several methods have been adopted, but rarely systematically defined or compared. This can lead to conceptual and operational problems when different languages and approaches are attributed the same semantic valence, related to the concept of sustainability, thus weakening the power of scientific analysis in directing consumption and global development. In this work, two languages, taken from Emergy Accounting (EMA) and Green Chemistry (GC), are compared through the case study of a chemical production process. Furthermore, a more precise definition of sustainability and greenness is proposed. Two production routes for racemic lactic acid were compared using both approaches: the first based on the fermentation of glucose from biomass and the second based on the fermentation of glycerol, main byproduct of the biodiesel industry. With the EMA, the diagrams of the two systems were analyzed and the transformities of the final product and of some reactants (butanol, zeolite) were estimated. For the GC study, some of the main metrics were calculated (atom economy, E-factor, reaction mass efficiency, mass intensity) and a semi-quantitative evaluation with EcoScale was performed. The main features, pros and cons of the two languages were compared, highlighting that EMA and GC provide different, but easily complementary, information about the same system, thus can be used concurrently to deepen the significance of sustainability evaluations.