Influence of Pickering emulsion composition on continuous lipase-catalyzed oxyfunctionalization of α-pinene: A comparative study of water- and deep eutectic solvent -based systems

This work investigates the continuous oxyfunctionalization of α-pinene in Pickering emulsions (PEs) using Candida antarctica lipase B (CalB). Building on earlier work demonstrating peracid formation in water-based PEs, the present work evaluates the full reaction sequence in both water- and deep eutectic solvent (DES)–based PEs and examines how dispersed-phase composition, phase fraction, nanoparticle concentration and enzyme concentration influence reaction performance and emulsion stability. Water-based PEs were strongly affected by hydrolysis of α-pinene oxide, leading to reduced yields and droplet shrinkage. DES-based PEs, especially glyceline, avoided this side reaction and provided substantially higher stability due to their viscosity, hydrogen-bonding networks and lower interfacial tension. Although DES oxidation affected isolated peracid synthesis, this became negligible during full oxyfunctionalization because rapid epoxidation dominated peracid consumption. Glyceline-based PEs achieved higher yields, reaction rates and space–time yields than water-based systems and remained stable under continuous operation. Phase fraction and particle concentration had contrasting effects in water- and DES-based PEs, governed by hydrolysis in the former and mass-transfer limitations or interfacial crowding in the latter. Enzyme-saturation behavior differed between systems, with optimal CalB concentrations of 7.5 g L⁻¹ dp in water-based PEs and 15 g L⁻¹ dp in glyceline-based PEs. These results identify DES-based PEs as robust media for efficient continuous CalB-catalyzed oxyfunctionalization and provide key design principles for tuning multiphasic biocatalytic processes. Preliminary sustainability and techno-economic assessments further indicated that the glyceline-based system offers advantages in terms of material utilization, reactor productivity and catalyst utilization relative to the water-based system.