Biocatalytic Reactive Extraction in Micellar Two-Phase Systems: Implementation in a Continuous Process

Aqueous non-ionic surfactant solutions split into two phases above the so called cloud point temperature (CPT). Thereby an aqueous phase coexists with a surfactant-rich phase. This phenomenon is applied for separation processes like the cloud point extraction (CPE) for treatment of waste water or the purification of valuable compounds. Due to its mild operating conditions (low salt concentrations, low temperature) and the biocompatibility of many surfactants the cloud point extraction is generally considered as a promising method in biotechnological downstream processes. Recent studies describe the simultaneous biocatalysis combined with micellar extraction. However, this reactive extraction was not performed as a continuous process so far [1].

In this work, an aqueous micellar two-phase system containing the non-ionic surfactant Tergitol NP-7 is used to perform a biocatalytic reaction with a simultaneous separation of the products. The biocatalytic hydrolysis of penicillin G to phenylacetic acid (PAA) and 6-aminopenicillanic acid (APA) is used as a model reaction. Thereby, APA distributes predominantly into the aqueous phase while PAA accumulates in the surfactant-rich phase.

The liquid-liquid equilibrium of the aqueous micellar two-phase system changes during the reaction process since penicillin G elevates and PAA depresses the CPT. Moreover, the production of PAA decreases the pH which influences both, reaction kinetics and equilibrium composition as well as reactant distribution.

A pH-dependent study of the partition equilibrium of all compounds was performed to define the operating window for the reactive extraction process. Furthermore, the biocompatibility of Tergitol NP-7 with respect to the enzyme stability and activity was proven. Consequently, the biocatalytic reactive extraction was performed for the first time in a continuous countercurrent extraction column. The results prove the biocatalytic reactive extraction as a feasible alternative for biotechnological processes.

References: [1] Wang et al., Bioprocess Biosyst Eng (2006) 29: 157-162