Stephen K. Ross

Chemical reactions in supercritical carbon dioxide: from laboratory to commercial plantThis work was presented at the Green Solvents for Catalysis Meeting held in Bruchsal, Germany, 13–16th October 2002.

The application of supercritical carbon dioxide in continuous, fixed bed reactors has allowed the successful development of a variety of industrially viable synthetic transformations. The world’s first, multi-reaction, supercritical flow reactor was commissioned in 2002 as a direct result of the successful collaboration between the Clean Technology Group at the University of Nottingham and the fine chemicals manufacturer, Thomas Swan & Co. Ltd. We highlight the development of this project from laboratory to plant scale, particularly in the context of the hydrogenation of isophorone. Phase data for the system; isophorone + H2 + CO2, are presented for the first time. Overall, we present a progress report about an on-going Green Chemistry initiative that has successfully forged strong links between Industry and Academia.

Continuous catalytic asymmetric hydrogenation in supercritical CO2

Continuous hydrogenation in supercritical fluids has been shown to be a technically viable alternative to traditional batch-wise methodologies. Clearly, the next stage of development of this technology is the application of immobilised enantioselective catalysis in the preparation of optically active products. Enantioselective hydrogenation has been successfully carried out in supercritical carbon dioxide using batch-type reactors but has yet to be efficiently carried out continuously. Here we examine an established method of catalyst immobilisation and demonstrate its suitability for application in continuous reactors using supercritical carbon dioxide as solvent.

Continuous reactions in supercritical fluids; a cleaner, more selective synthesis of thymol in supercritical CO2

Continuous fixed-bed catalytic Friedel–Crafts alkylation of m-cresol with different alkylating agents, isopropanol (IPA) and propylene, has been carried out using supercritical CO2, scCO2, as an alternative and more environmentally friendly reaction medium, for the synthesis of the fine chemical thymol. Both a solid Lewis acid catalyst (γ-Al2O3) and a solid Bronsted acid catalyst (Nafion® SAC-13) have been investigated over a range of reaction conditions to optimise yield and selectivity for thymol. The reaction product distribution was found to be related to the type of catalyst employed. This is likely to have been due to the different reaction pathways through which the reaction occurred, a direct Friedel–Crafts alkylation in the case of Bronsted type acids and a Fries rearrangement when employing the Lewis catalyst. The new technique of 2DCOR-GC analysis was employed to establish the order of formation of the different species generated in the reaction over the two catalysts in scCO2.

Friedel–Crafts alkylation in supercritical fluids: continuous, selective and clean

Continuous Friedel–Crafts alkylation of mesitylene, C6H3Me3, and anisole, C6H5OMe, with propene or propan-2-ol has been carried out in supercritical propene or CO2 using a heterogeneous polysiloxane-supported solid acid Deloxan® catalyst in a small fixed bed reactor (10 ml volume); 100% selectivity for mono-alkylated products with 50% conversion could be obtained by adjusting the reaction parameters, e.g. temperature, pressure, flow rates, etc.