Green solvents and biocatalysis: A bigger picture

Biocatalysis has matured to be used in an ample array of reaction media, from pure aqueous solutions to (water-free) non-conventional media. In most of the applications solvents are needed as reaction media and/or during the downstream unit to extract and purify the product. Aligning processes with the Green Chemistry principles, some green solvents have been introduced. This article discusses critically the environmental impact that solvents may have in a biocatalytic reaction, from the raw material extraction to the solvent synthesis and to its use in biocatalysis and ultimate disposal. Some of the observed impacts – quantified as kg CO₂·kg product⁻¹ – are surely unavoidable, as they depend on the solvent synthesis or on the raw material used. However, the intensification of the biocatalytic reaction (e.g. using higher substrate loadings) and investing efforts in solvent recycling may have a clear impact in the final ecological footprint of the enzymatic process. Instead of qualitatively stating that green solvents are used, experiments in these directions should be performed to provide reaction conditions with minimized environmental metrics for sustainable chemistry.