Catalytic hydrogenation, supercritical

In a somewhat different approach, supported-aqueous-phase-catalysts (SAPC, see Chapter 5, Section 5.2.5 of this book) have been combined with supercritical CO2 in catalytic hydrogenation [55], Ruthenium was supported on silica and combined with the ligand TPPTS in water, after which a scC02/H2 phase was applied together with the substrate. Better levels of conversion were obtained using scC02 than the equivalent system with toluene for the hydrogenation of cinnamaldehyde. 

P. G. Jessop, T. Ikariya, R. Noyori, Homogeneous Catalytic Hydrogenation of Supercritical Carbon Dioxide , Nature 1994,368,231-233. 

Biphasic systems containing an ionic liquid and supercritical CO2 have been used effectively for catalytic hydrogenation of alkenes. The ionic liquid phase containing the catalyst could be reused (2/6). 

Catalytic hydrogenation in supercritical carbou dioxide has been studied. The effects of temperature, pressure, and CO2 concentration on the rate of reaction are important. Hydrogenation rates of the two double bonds of an unsaturated ketone on a commercial alumina-supported palladium catalyst were measured in a continuous gra-dient-less internal-recycle reactor at different temperatures, pressures, and C02-to-feed ratios. The accurate control of the organic, carbon dioxide, and hydrogen feed flow rates and of the temperature and pressure inside the reactor provided reproducible values of the product stream compositions, which were measured on-line after separation of the gaseous components (Bertucco et al., 1997). 

The three-phase catalytic hydrogenation of an unsaturated ketone using supercritical carbon dioxide as a solvent was studied in order to simulate the performance of a semi-industrial trickle-bed reactor. It is shown that supercritical CO2 strongly increases the reaction rate (Devetta et al., 1999). 

Hitzler, M. G., Smail, F. R., Ross, S. K., Poliakoff, M. Selective Catalytic Hydrogenation of Organic Compounds in Supercritical Fluids as a Continuous Process. Organic Process Research Development. 1998, 2, 137 - 146. 

Bertucco, A., Canu, P., Devetta, L. Catalytic Hydrogenation in Supercritical C02 Kinetic Measurements in a Gradientless Internal-Recycle Reactor. Ind. Eng. Chem. Res. 1997, 36, 2626 - 2633. 

Aldehydes have been catalytically hydrogenated to alcohol products in a range of supercritical solvents under otherwise mild conditions.314... 

Burk MJ, Feng S, Gross MF et al (1995) Asymmetric catalytic hydrogenation reactions in supercritical carbon dioxide. J Am Chem Soc 117(31) 8277-8278... 

Bertucco A, Canu P., Devetta L., Zwahlen A.G. Catalytic Hydrogenation in Supercritical C02 Kinetic Measurement in a Gradientless Recycle Reactor, Submitted for publication in Industrial and Engineering Chemistry Research, April 1996... 

The Pt-catalyzed enantioselective hydrogenation of ethyl pyruvate to (/ )-ethyl lactate was considerably faster (by a factor of 3-3.5) in supercritical ethane than in the conventional apolar solvent toluene, whereas the enantioselectivity was unaffected. Complete catalyst deactivation was observed in C02, which was shown by FTIR to be due to the reduction of C02 to CO via reverse water gas shift reaction. The catalyst could be regenerated by exposing it to ambient air, while hydrogen treatment was less efficient. This is the first evidence to the limitation of catalytic hydrogenations over Pt metals in supercritical C02. 

Other non-classical reaction media [96] have, in recent years, attracted increasing attention from the viewpoint of avoiding environmentally unattractive solvents and/or facilitating catalyst recovery and recycling. Two examples, which readily come to mind, are supercritical carbon dioxide and room temperature ionic liquids. Catalytic hydrogenation in supercritical C02, for example, has... 

Jessop PG, Ikariya T, Noyori IG (1994) Homogeneous catalytic-hydrogenation of supercritical carbon-dioxide. Nature 368 231-233. 

Ramirez, E. Zgarni, S. Larrayoz, M. A. Recasens, F. Short compilation of published reaction rate data for catalytic hydrogenations in supercritical fluids. Eng. Life Sci. 2002, 2 (9), 257-264. 

Devetta, L. Giovanzana, A. Canu, P. Bertucco, A. Minder, B.J. Kinetic experiments and modeling of a three-phase catalytic hydrogenation reaction in supercritical CO2. Catal. Today 1999, 48 (1 ), 337-345. 

Masaru Watanabe, Hiroshi Inomata, Kunio Aral. (2002). Catalytic hydrogen generation from biomass (glucose and cellulose) with ZrO2 in supercritical water. 22, 405-410. 

There are still many developments in selective hydrogenation, both in terms of new catalysts and process operations. An example of the first is the discovery that Sn-substituted zeolite beta is the most active heterogeneous catalyst for the Meer-wein-Pondorff-Verley reduction of aldehydes and ketones to the corresponding alcohols, with high cis-selectivity (99-100%) in the reduction of 4-alkylcyclohexa-nones [301]. An example of process development is in the heterogeneous catalytic hydrogenation of organic compounds in supercritical fluids (SCFs) [302]. 

Coenen H, Hagen R, Kriegel E. Supercritical extraction and simultaneous catalytic hydrogenation of coal. Fried Krupp Gesellschaft, U.S.A., US 4,485,003, 1984. 

Jessop and co-workers have pointed out that homogeneous catalysis in supercritical fluids can offer high rates, improved selectivity, and elimination of mass-transfer problems.169 They have used a ruthenium phosphine catalyst to reduce supercritical carbon dioxide to formic acid using hydrogen.170 The reaction might be used to recycle waste carbon dioxide from combustion. It also avoids the use of poisonous carbon monoxide to make formic acid and its derivatives. There is no need for the usual solvent for such a reaction, because the excess carbon dioxide is the solvent. If the reaction is run in the presence of dimethy-lamine, dimethylformamide is obtained with 100% selectivity at 92-94% conversion.171 In this example, the ruthenium phosphine catalyst was supported on silica. Asymmetric catalytic hydrogenation of dehydroaminoacid derivatives (8.16) can be performed in carbon dioxide using ruthenium chiral phosphine catalysts.172... 

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