Flow chemistry synthesis and sustvdainability assessment for choline chloride, a deep eutectic solvent constituent

Abstract

The continuous use of traditional solvents is not aligned with green chemistry principles, driving interest in natural deep eutectic solvents (NADES) as sustainable alternatives. This paper presents a two-step continuous-flow process for choline chloride production only from common biomass-derived precursors. Using water as the solvent, the method delivers 99% pure choline chloride and can generate NaCl as a byproduct depending on the base used. With a residence time of just 1 minute, the process reaches full conversion, achieving a 20-fold improvement in productivity compared to batch operation and enabling annual throughputs of up to half a ton per microcapillary. A comprehensive sustainability assessment highlights the advantages of using choline hydroxide (Ch-OH) as the base. When using Ch-OH, the process requires substantially less material and generates no byproducts, leading to a 51% reduction in energy demand and a 24% decrease in overall environmental impacts relative to NaOH. These benefits arise from lower input requirements, reduced wastewater generation, and higher process efficiency. Circularity performance also improves with Ch-OH, and life cycle assessment confirms that increased productivity outweighs the higher impacts associated with its production. Overall, the combined flow chemistry and Ch-OH strategy offers a highly efficient and more sustainable route to choline chloride.