Chemistry of inorganic compounds – Oxygen or compound thereof – Peroxide
Reexamination Certificate
2000-09-05
2002-08-13
Griffin, Steven P. (Department: 1754)
Chemistry of inorganic compounds
Oxygen or compound thereof
Peroxide
C502S004000, C502S339000
Reexamination Certificate
active
06432376
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a novel membrane process for the production of hydrogen peroxide by non-hazardous direct oxidation of hydrogen by oxygen, without the formation of an explosive hydrogen and oxygen gas mixture, using a novel hydrophobic composite Pd-membrane catalyst.
The membrane process of this invention is capable of being used in the chemical industries for the production of hydrogen peroxide by the direct oxidation of hydrogen by oxygen to hydrogen peroxide, which is an environmentally clean process, in a safe manner without any chance of forming hazardous explosive hydrogen-oxygen or air mixture.
BACKGROUND OF THE INVENTION
Currently most widely practiced commercial scale production of hydrogen peroxide is based on an auto oxidation process employing alkyl anthraquinone as the working material. This process involves reduction of alkyl anthraquinone dissolved in an organic working solution to alkyl anthraquinol. The alkyl anthraquinol is oxidized by air to produce alkyl anthraquinone, which is recycled in this process, and hydrogen peroxide. This process comprises a number of operations involving reduction, oxidation, and separation by aqueous extractions, refining and concentration, making the process complex. Apart from the requirements of high capital and operation costs, this process has following limitations and disadvantages:
Non-selective in hydrogenation, hence loss of anthraquinone.
Difficulties in separation of hydrogenation catalyst and degradation products.
Need for the regeneration of used hydrogenation catalyst.
Need for the removal of organic matters from the extracted H
2
O
2
solution.
Waste treatment and disposal of undesired side products of the cyclic process. Hence there is great need for developing an environ friendly process for H
2
O
2
production.
PRIOR ART REFERENCES
Since the disclosure in U.S. Pat. No. 1,108,752 by Henkel et al. that palladium is a catalyst promoting the formation of hydrogen peroxide and water from a mixture of hydrogen and oxygen, a number of palladium containing catalysts, useful for the direct oxidation of hydrogen by oxygen to hydrogen peroxide, have been disclosed by many inventors.
Direct Oxidation of H
2
by O
2
to Hydrogen Peroxide over Hydrophillic Pd-Catalysts Using a Mixed Feed of H
2
and O
2
U.S. Pat. No. 4,832,938 by Gosser et al. disclosed a Pt—Pd bimetallic catalyst supported on a carbon, silica or alumina support for making hydrogen peroxide from direct combination of hydrogen and oxygen in an aqueous reaction medium. Later, a German patent Ger. Offen. DE 4,127,918 A1 by Lueckoff et al. disclosed a supported palladium gold catalyst for the manufacture of hydrogen peroxide from hydrogen and oxygen in aqueous medium; the catalyst contains 5-95 wt % Au and is supported on carbon. A number of platinum Group metal containing catalysts: (1) Pt-Group metal on high surface area support, such as carbon, silica or alumina (Ref. U.S. Pat. No. 5,169,618); (2) Pt-Group catalyst on solid acid carrier (Ref. Eur. Pat. Appl. EP 504,741, A1); (3) Pt-Group element supported on Nb- or Ta oxide (Ref. PCT Int. Appl. WO 9,412,428 A1); (4) Sn- modified Pt-Group metals supported on catalysts carriers (Ref. Eur. Pat. Appl. EP 621,235 A1); (5) Pt-Group metal catalyst supported on hydrophilic support (Ref. U.S. Pat. No. 5,399,334); for the oxidation of hydrogen to hydrogen peroxide are known in the prior art.
The above mentioned Pd- or Pt-Group metal containing catalysts are hydrophilic in nature, and hence the aqueous reaction medium used in the oxidation of hydrogen to hydrogen peroxide over these catalysts is in close contact with the catalyst surface. Because of the close contact between the catalyst and the reaction medium, the hydrogen peroxide, which is formed by the reaction between hydrogen and oxygen on the catalyst and then absorbed in the reaction medium due to the high affinity between hydrogen peroxide and water, is readsorbed on the catalyst from the reaction medium and converted to water and oxygen, and thereby the selectivity for hydrogen peroxide in the process is drastically reduced, when the above mentioned catalysts are used in the oxidation of hydrogen to hydrogen peroxide. Earlier, Fu et al. has also found that only the Pd catalysts supported on hydrophobic carbon support are selective towards hydrogen peroxide formation in the oxidation of hydrogen [Ref. L. Fu et al., Stud. Surf. Sci. Catal., 72(1992)33-41].
Direct Oxidation of H
2
by O
2
to Hydrogen Peroxide over Hydrophobic Pd-Catalysts Using a Mixed Feed of H
2
and O
2
A few Pt-Group or Group VIII metal catalysts deposited on hydrophobic support, useful for the oxidation of hydrogen to hydrogen peroxide, are also known in the prior art.
A Japanese patent Jpn. Kokai Tokyo Koho JP 01133909 A2 by Kyora disclosed a Pt-Group metal catalyst carried on a hydrophobic support such as porous and hydrophobic Teflon support. Chuang in an European patent EP 3660419 A1 disclosed a Group VIII metal catalyst deposited on a hydrophobic support for the manufacture of hydrogen peroxide by reacting hydrogen with oxygen in an aqueous medium. Later, Chuang has disclosed a Group VIII metal on a partially hydrophobic and partially hydrophilic support, such as Pd on fluorinated carbon, as a catalyst for the oxidation of hydrogen to hydrogen peroxide, in PCT Int. Appl. WO 9314025 A1.
Although, the hydrophobic support used in these catalysts provides some hydrophobic character to the Pd- or Group VIII metal catalysts, there are following disadvantages and limitations of the use of hydrophobic support for depositing the metal catalysts: 1) It is difficult to deposit catalytically active components from aqueous solution on a hydrophobic support as there is no wetting of the surface of hydrophobic support by aqueous solution. 2) Hydrophobic support, such as teflon and other hydrophobic polymer support, is thermally unstable at the calcination temperatures, above 300° C., normally employed for decomposing the precursor compounds of catalytically active components of the catalyst. 3) Because of the deposition of catalytically active components, which are hydrophilic in nature, on hydrophobic support, the hydrophobic character of the support is lost completely or at least partially.
Apart form the above mentioned disadvantages and/or limitations, the most important disadvantage of the prior art processes using the above mentioned hydrophobic and hydrophillic catalysts for the direct oxidation of hydrogen by oxygen to hydrogen peroxide in a high pressure slurry reactor is that the feed oxygen and hydrogen gases are mixed before or during the reaction. Since hydrogen when mixed with oxygen or air forms an explosive or a flammable mixture for a very wide range of hydrogen concentration in both oxygen and air, the above mentioned prior art processes are highly hazardous, particularly at the high pressure used in the prior art process. Flammability limits of hydrogen in oxygen and air at the atmospheric pressure are as follows: 4.0-94% H
2
in oxygen, and 4.0 to 75.0% H
2
in air. The flammability limits are widen with increasing the pressure.
The explosion hazards in the direct oxidation of hydrogen by oxygen to hydrogen peroxide can be totally eliminated if the direct mixing of feed hydrogen and oxygen gases and/or the formation of H
2
—O
2
or air mixture during the reaction are avoided by some means.
Non-hazardous Direct Oxidation of H
2
by O
2
to Hydrogen Peroxide Using Pd-Membrane Catalyst
In order to avoid the explosion hazards due to the formation of explosive hydrogen-oxygen or air mixture, a use of Pd metallic membrane catalyst for the oxidation of hydrogen by oxygen to hydrogen peroxide has also been disclosed in the prior art.
U.S. Pat. No. 4,393,038, Jul. 12, 1983) discloses hydrogen peroxide production process in which hydrogen is diffused through a palladium metallic membrane permeable to hydrogen, preferably a gold plated palladium-silver metallic alloy membrane tube, into an aqueous solution containing ions of a stabilizing nature a
Choudhary Vasant Ramchandra
Gaikwad Abaji Govind
Sansare Subhash Dwarkanath
Council of Scientific & Industrial Research
Griffin Steven P.
Medina Maribel
Samuels Gauthier & Stevens
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