Title : A prospective life-cycle assessment (LCA) of monomer synthesis: Comparison of biocatalytic and oxidative chemistry
Enzymatic reactions are typically perceived, and sometimes claimed, as being greener than the corresponding chemical conversions. The use of water as reaction medium, the selectivity of enzymes to avoid protection/deprotection steps, and the renewable aspect of enzymes are just a few examples of the presumed benefits of biocatalysis. These assumed environmental benefits are an incentive for the development of such enzymatic processes. They are few methodologies to evaluate the environnemental impact of (bio)chemical reactions. Life cycle assessments (LCAs) are being more widely performed by the scientific community in order to obtain an accurate quantification of the environmental impact of reactions or processes. An LCA is a standardized and internationally recognized tool specifically designed to quantify the environmental impact of a product or service, taking into account its entire life cycle (ISO14044:2006). So far, LCAs are considered as “the best framework for assessing the potential environmental impacts of products currently available” by the European Comission because several environmental impacts are considered.
The goal of the current study is to compare the environmental impact of two synthetic routes for the preparation of lactones. A cradle-to-gate LCA was performed to compare the chemical and biochemical synthesis of lactones obtained by Baeyer-Villiger oxidation (Figure 1). This LCA is prospective since the studied process developement is still at laboratory scale. The results of the LCA show that the impacts of both routes are similar for all the impact categories evaluated (climate change impact, damage to human health, use of primary energy, and ecosystem quality).
Key process performance metrics affecting the environmental impact were evaluated by performing a sensitivity analysis. Recycling of solvents and enzyme was shown to be crucial and to advantage the enzymatic synthesis. Additionally, the climate change impact was demonstrated to be dramatically affected by the source of electricity used (laboratory scale experimentation). The use of renewable electricity is therefore relevant because it can decrease the carbon emissions by 74 %.
The study shows that the LCA methodology, including the sensitivity and the uncertainaty analysis, can be used to usefully support decisions from the early-stage of process development. The environmental impact comparison allows selecting the most promising route for developing a new process. As shown in the sensitivity analysis, the implementation of the recycling of enzyme is relevant from a carbon emission point of view. It is also relevant to identify the key process performance metrics for the improvement of the environmental impact of these reactions.