(309c) Use of Supercritical Cabon Dioxide for Downstream Processing in Multiphase Whole-Cell Biocatalysis

The biotechnological production of certain bulk and fine chemical has come into scientific as well as industrial interest during the last decades. Besides other approaches, especially whole-cell biocatalysis shows a high potential for the functionalization of hydrocarbons with a high selectivity and efficiency. However, its industrial implementation for the production of hydrophobic compounds, which typically and most easily is accomplished in organic/aqueous emulsion systems, faces major challenges with respect to efficient and cost-effective downstream processing [1-4]. As stable emulsions occur, conventional approaches, such as centrifugation or filtration suffer from insufficient efficiencies in terms of phase separation. Being aware of this, we used an innovative approach to overcome those limitations.

In our work, we considered the stereospecific production of (S)-styrene oxide from styrene. The aqueous/organic biotransformation mixture, containing dioctylphthalate as organic solvent, (S)-styrene oxide as pruduct, octane, styrene and 2-phenylethanol forms a stable emulsion [5]. We propose an integrated approach on phase separation and product purification by applying supercritical carbon dioxide to that mixture.

Optical investigations in a high-pressure variable-volume view cell on phase separation behaviour, and additional experiments analyzing the carbon-dioxide-rich phase directly by GC analysis were performed. As octane and (S)-styrene oxide are more soluble in carbon dioxide than the other components of the biotransformation reaction mixture, they can selectively be extracted by supercritical CO₂. The experimental data of the binary and and multi-component mixtures were modeled using the PC-SAFT Equation of State with satisfying accuracy and will be used for further optimization of phase-separation and extraction steps.

The results indicate, that the use of scCO₂ simplifies the downstream processing of whole-cell biotransformations significantly when compared to conventional approaches.

References

[1] A. Kollmer; Diss. ETH Nr. 12491; Swiss Federal Institute of Technology, 1997, 202

[2] R. G. Mathys; Diss. ETH No. 12013; Swiss Federal Institute of Technology, 1997, 174

[3] A. Schmid, J. S. Dordick, B. Hauer, A. Kiener, M. Wubbolts, and B. Witholt, Nature, 409, 2001, 258-268

[4] H. M. Vansonsbeek, H. H. Beeftink, and J. Tramper, Enzyme and Microbial Technology, 15, 1993, 722-729

[5] S. Panke, M. Held, M. G. Wubbolts, B. Witholt, and A. Schmid, Biotechnology and Bioengineering, 80, 2002, 33-41