Supercritical hydrogenation

Details Supercritical hydrogenation Supercritical hydrogenation

1999-02-18

2000-12-05

Killos, Paul J.

Organic compounds -- part of the class 532-570 series

Organic compounds

Amino nitrogen containing

564420, 564448, 564449, 568799, 568835, 568880, 568881, 585250, 585263, 585264, 585266, C07C20900, C07C 3700, C07C 500

Patent

active

06156933&

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to a method of hydrogenating organic compounds. More specifically the present invention relates to heterogeneous catalytic hydrogenation of organic compounds under conditions of continuous flow of the reactants in a continuous flow reactor. The hydrogenation is performed under supercritical or near-critical conditions.
Hydrogenation is a commercially very significant process and enjoys widespread use in the food industry to produce amongst other things edible oils and spreads, and in the fine chemicals, plastics, pharmaceuticals and agricultural industries as a synthetic tool.
Although the use of supercritical fluids as reaction media has been disclosed for a limited number of synthetic organic reactions, the synthetic uses disclosed so far have involved heterogeneous or homogeneous batch systems or homogeneous continuous flow systems and suffer a number of disadvantages.
Catalytic hydrogenation under supercritical conditions is known from WO 94/06738 which discloses a process for manufacturing alcohols by liquid phase heterogeneous catalytic hydrogenation of mono- or dicarboxylic acids or their esters in a liquid inert hydrogen carrier such as a hydrocarbon. In this patent, hydrogenation is preferably carried out under supercritical conditions and is performed in a fixed-bed reactor or a batch autoclave. The process requires a high ratio of hydrogen with respect to the material to be hydrogenated and this is achieved by decreasing the concentration of the starting material in the reaction medium. The alcohol product is separated from dissolved hydrogen on depressurising the mixture. The presence of such an excess of hydrogen presents an explosion risk and is therefore unacceptable for large scale synthesis, unless of course the quantity of carboxylic acid is decreased to such an extent that the amount of hydrogen present does not pose a significant risk. However in this case the quantity of carboxylic acid which can be hydrogenated renders the process useless for large scale synthesis.
The Journal of the American Chemical Society 190495, 117 (31), 8277 discloses asymmetric catalytic hydrogenation reactions in supercritical carbon dioxide using a homogenous chiral rhodium catalyst in a batch-type process. A small-scale reactor is charged with the compound to be hydrogenated and carbon dioxide at a pressure of approximately 3000 psig and hydrogen gas at 200 psig. Significant enantiomeric excesses are claimed for hydrogenations performed under these conditions but the product nevertheless requires purification to separate the catalyst from the product after reaction.
EP-A-0652202 discloses a method for producing formic acid or formic acid derivatives in a reaction employing carbon dioxide in the supercritical state as the reaction medium. The reaction may be performed in the presence of a homogeneous or heterogeneous catalyst. In this patent, the supercritical carbon dioxide medium represents one of the reactants and is consumed during the process. The carbon dioxide is mixed with hydrogen at a relatively high pressure to produce formic acid, or with an active hydrogen group-containing compound to produce a formic acid derivative in a continuous process.
A method for the direct oxidation of benzene or other aromatic hydrocarbons into phenols is disclosed in WO 9420444. In this method, the aromatic hydrocarbon is dissolved in a mixture of supercritical carbon dioxide, molecular oxygen, and hydrogen as a reducing gas. The oxidation is performed under pressure in the presence of a palladium-containing catalyst and the reaction mixture is homogenous, hence avoiding the use of an inefficient 2-phase system. The carbon dioxide separated from the reaction mixture is vaporised and may be re-used in the oxidation of a new batch of aromatic hydrocarbons.
WO 9522591 discloses a process for the continuous hydrogenation of unsaturated fats, fatty acid or fatty acid esters under supercritical conditions on a shaped platinum-group metal catalyst in a solid bed constructed from an inert support

REFERENCES:
patent: 3969382 (1976-07-01), Zogel

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