Richard A. Bourne

The 24 Principles of Green Engineering and Green Chemistry: “IMPROVEMENTS PRODUCTIVELY”

Samantha Tang, Richard Bourne, Richard Smith and Martyn Poliakoff suggest a condensed 24 Principles of Green Chemistry and Green Engineering, with the mnemonic “IMPROVEMENTS PRODUCTIVELY”

Self‐Optimizing Continuous Reactions in Supercritical Carbon Dioxide

Hands-free optimization: A combination of an automated flow reactor, online analysis, and a control algorithm leads to efficient optimization of reactions to a given product without the need for human intervention.

Cleaner Continuous Photo‐Oxidation Using Singlet Oxygen in Supercritical Carbon Dioxide

High pressure under the spotlight: A new milliliter-scale reactor is developed for using supercritical CO(2) to perform continuous photo-oxidation reactions. Changing from a traditional microliter-scale batch reaction to 8 hours of reaction using the new reactor gives a 3000-fold scale-up of the oxidation of alpha-terpinene (see picture).

Maximising opportunities in supercritical chemistry: the continuous conversion of levulinic acid to γ-valerolactone in CO2

Phase behaviour is manipulated during the hydrogenation of aqueous levulinic acid in supercritical CO(2) to separate almost pure gamma-valerolactone from water and unreacted acid with reduced energy requirements compared to conventional processing.

Real-Time Feedback Control Using Online Attenuated Total Reflection Fourier Transform Infrared (ATR FT-IR) Spectroscopy for Continuous Flow Optimization and Process Knowledge.

The use of automated continuous flow reactors is described, with real-time online Fourier transform infrared spectroscopy (FT-IR) analysis to enable rapid optimization of reaction yield using a self-optimizing feedback algorithm. This technique has been applied to the solvent-free methylation of 1-pentanol with dimethyl carbonate using a γ-alumina catalyst. Calibration of the FT-IR signal was performed using gas chromatography to enable quantification of yield over a wide variety of flow rates and temperatures. The use of FT-IR as a real-time analytical technique resulted in an order of magnitude reduction in the time and materials required compared to previous studies. This permitted a wide exploration of the parameter space to provide process understanding and validation of the optimization algorithms.

Immobilised photosensitisers for continuous flow reactions of singlet oxygen in supercritical carbon dioxide

Photosensitisers have been incorporated into both polymer and aerogel supports for the photochemical generation of singlet oxygen, 1O2, in supercritical carbon dioxide, scCO2. These systems showed high activity and an acceptable lifetime for the photo-oxidation of α-terpinene and of citronellol in continuous reactors over a period of at least 5 h. The most effective photosensitiser was a covalently coupled analogue of tetradi(2,6)chloro-phenylporphyrin (TDCPP) on polyvinyl chloride (PVC). This immobilisation removes the need to separate the photosensitiser from the downstream solution.

Remote-controlled experiments with cloud chemistry

Developing cleaner chemical processes often involves sophisticated flow-chemistry equipment that is not available in many economically developing countries. For reactions where it is the data that are important rather than the physical product, the networking of chemists across the internet to allow remote experimentation offers a viable solution to this problem.

The continuous self aldol condensation of propionaldehyde in supercritical carbon dioxide: a highly selective catalytic route to 2-methylpentenal

The aldol reactions of propionaldehyde and butyraldehyde have been explored in supercritical CO2, scCO2, using an automated continuous flow reactor. The reaction was found to proceed over a variety of heterogeneous acidic and basic catalysts and with increased selectivity compared to using neat reactants.

Continuous catalytic upgrading of ethanol to n-butanol and >C4 products over Cu/CeO2 catalysts in supercritical CO2

n-Butanol (BuOH) often has superior properties as a bio-fuel compared to ethanol (EtOH). However finding sustainable sources of BuOH is proving difficult. In this paper, direct production of BuOH from EtOH is compared over custom-synthesized six Cu catalysts, supported on different solid acids. These catalysts were tested in a continuous flow supercritical CO2 (scCO2) reactor, and were found to catalyse the dehydrogenation, aldol condensation and hydrogenation steps of the so-called Guerbet reaction converting EtOH to BuOH. BuOH yields and selectivities were significantly different over the four catalysts. Cu on high surface area CeO2 showed the best activity for BuOH formation, with yields above 30% achieved with good selectivity. In addition high pressure CO2 is shown to have a positive effect on the reaction, possibly due to the redox cycle of Ce2O3 and CeO2.

Synthesis of antimalarial trioxanes via continuous photo-oxidation with 1O2 in supercritical CO2

The oxidation of an allylic alcohol to its hydroperoxides represents a key step in the synthesis of a series of spirobicyclic, antimalarial trioxanes. Herein, we investigate the continuous photo-oxidation of an allylic alcohol with 1O2 in scCO2, as a ‘green’ alternative to conventional methods, and examine the remaining two steps in the synthesis of antimalarial trioxanes from readily available starting materials.