Mass transfer coefficient determination in three biphasic systems (water–ionic liquid) using a modified Lewis cell

Baeyer–Villiger bioconversion productivity of the cyclic ketone (±)-cis-bicyclo [3.2.0] hept-2-en-6-ona by the biocatalyst Escherichia coli TOP10 pQR239 in a multiphase system can be limited by mass transport. Mass transfer rates through the liquid–liquid interface depend on the volumetric mass transfer coefficient (kA) and the substrate and product partition coefficients. In situ experimental determination of the volumetric mass transfer coefficient in a partitioning bioreactor is complex. In this work, the substrate (kS) and product (kP) global mass transfer coefficients were determined in a modified Lewis cell in three water–ionic liquids systems. The ionic liquids used were butylmethylpyrrolidinium bis(trifluoromethylsulfonyl)imide [MeBuPyrr][BTA], trioctylmethylammonium bis(trifluoromethylsulfonyl)imide [OMA][BTA] and 1-butyl-3-metyl-imidazolium hexafluorophosphate [BMIM][PF6]. The maximum kS and kP values obtained were 4.35 × 10−5 and 1.21 × 10−5 m s−1 for water-[MeBuPyrr][BTA] system; 1.53 × 10−5 and 7.84 × 10−6 m s−1 for water-[OMA][BTA] system, respectively; and kS values up to 1.01 × 10−5 m s−1 were found for the water-[BMIM][PF6] system. The association among the mass transfer coefficients and the physicochemical properties (interfacial tension, viscosity and density) and the thermodynamics (partition coefficients) are analysed and discussed. Finally, the volumetric mass transfer coefficients (kSA and kPA) were calculated using interfacial areas (A) of the dispersed ionic liquid phase estimated from the “Sauter” mean drop diameter (d32) in a one litre stirred tank partitioning bioreactor.

► We determine mass transfer coefficients in three biphasic water–ionic liquid systems.
► We used a modified Lewis cell to determine global mass transfer coefficients.
► We studied three ionic liquids with different physicochemical properties.
► Hydrodynamics and thermodynamics influenced global mass transfer coefficients.
► We also estimated volumetric mass transfer coefficients in a stirred tank bioreactor.