Carbon dioxide has been developed as an alternative process solvent for traditional catalysis and has been successfully commercialised for applications such as hydrogenation and hydroformylation. Suprex has successfully developed reactions in supercritical CO₂ using biocatalysts which have broad applications in the synthesis of natural products for a wide range of formulations. The equipment used is essentially the same as used for extraction and fractionation except that the extractor is replaced either with a stirred batch reactor or a flow reactor.

CO2 Reactions 1

For many applications the substrates and products are sufficiently soluble in supercritical CO₂ alone to achieve very high titres but for some applications where the substrates are more polar an inert co-solvent can be used to achieve greater solubility. Enzymes or whole cells can be used as biocatalysts in scCO₂ and greater stability can often be achieved than in aqueous systems as the water activity is very limited. As a result higher process temperatures can be used and therefore more rapid reaction rates are achieved.

A comparison of a model reaction carried out in n-heptane and scCO2 at 40°C demonstrates the effective replacement of a hydrocarbon solvent with scCO₂ in a batch reactor. Kinetic data from such trials can be used to determine the suitability of a reaction for transfer to a continuous process.

CO2 Reactions 2

For a synthesis to be economically viable continuous processing is highly desirable but initial trials are often carried out in a batch reactor. If a synthesis is successful in a laboratory flow reactor processes can be scaled up to multi kilogram scale. The equipment at Suprex is capable of continuous flow reactions up to 80°C and 400bar .