E-Factor Meets Climate-Factor: Translating Waste into Global Warming Potential for Early-Stage (Bio)catalytic Reactions

Developed by Roger Sheldon, the E-Factor has become a crucial environmental metric to assess the impact of chemical reactions and represents a foundational pillar of the concept of Green Chemistry (which was coined some years later). Subsequent additions to the E-Factor were the “complete E-Factor” (incorporating water and solvent wastes), the “Environmental Quotient”, to discern between the real burden of different wastes, and the “E+-Factor” to add the energy environmental impact contribution. To measure all wastes under the same unit, the “Climate Factor” or “C-Factor” (expressed as kg CO2 kg product–1), also coined as Total Carbon Dioxide Release (TCR) or Global Warming Potential (GWP), may be used. This paper provides equations that translate the complete E-Factor directly into the C-Factor by considering the CO2 released in (i) producing the energy invested in the reaction (for the upstream and downstream); (ii) the wastewater treatment; and (iii) solvent incineration. Given the mild reaction conditions applied in biocatalysis, the energetic environmental impact is often less relevant than the CO2 generated during wastewater treatment or during solvent incineration. Process intensification to generate higher product titers to use less water and solvents appears mandatory to lower the environmental impact. Under the same environmental unit (CO2), processes can be benchmarked in a fairer manner.