Hydrophobic composite Pd-membrane catalyst useful for...

Details Hydrophobic composite Pd-membrane catalyst useful for... Hydrophobic composite Pd-membrane catalyst useful for...

2000-09-05

2002-09-10

Griffin, Steven P. (Department: 1754)

Catalyst, solid sorbent, or support therefor: product or process

Catalyst or precursor therefor

Metal, metal oxide or metal hydroxide

C502S004000, C502S333000

Reexamination Certificate

active

06448199

ABSTRACT:

FIELD OF INVENTION:
This invention relates to a novel hydrophobic composite Pd-membrane catalyst, useful for non-hazardous direct oxidation of hydrogen by oxygen to hydrogen peroxide, and its method of preparation. This invention particularly relates to a novel tubular hydrophobic composite Pd-membrane catalyst comprising Pd-metallic membrane and inorganic porous membrane, useful for non-hazardous direct oxidation of hydrogen by oxygen to hydrogen peroxide while avoiding premixing of feed hydrogen and oxygen gases and its method of preparation. The present invention also relates to a process for the preparation of the hydrophobic composite Pd-membrane catalyst
The membrane catalyst of this invention could be 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 explosive hydrogen-oxygen or air mixture.
BACKGROUND AND PRIOR ART DESCRIPTION OF THE INVENTION
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.
Hydrophilic Catalysts for Direct Oxidation of H
2
by O
2
to Hydrogen Peroxide
A 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 reabsorbed 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].
Hydrophobic Catalysts for Direct Oxidation of H
2
by O
2
to Hydrogen Peroxide
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, following are the 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 catalyst for the direct oxidation of hydrogen by oxygen to hydrogen peroxide 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 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.
Pd-Containing Membrane Catalyst for Oxidation of H
2
by O
2
to Hydrogen Peroxide
In order to avoid the explosion hazards due to the formation of explosive hydrogen-oxygen or hydrogen-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 dated 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 and dissolved oxygen to form hydrogen peroxide and water as a by product. In this process, the membrane used for hydrogen diffusion is a Pd-containing metallic tube, which is self supporting with thickness high enough to avoid collapse of the metallic structure. For the high thickness Pd metallic membrane tube, the flux of hydrogen diffusion through the Pd-membrane is extremely small and hence not of practical interest for producing hydrogen peroxide. Moreover, palladium-silver alloy and gold platted palladium or palladium-silver alloy catalyst membrane of this process have extremely poor selectivity for the oxidation of hydrogen to hydrogen peroxide; the selectivity of hydrogen peroxide, based upon the amount of hydrogen consumed was reported to be 1.44% and less than 1.0%, when the Pd-containing metallic membrane tube was pretreated with stannic chloride followed by hydrolysis and without the pretreatment, respectively. Su

Affiliated with

Also associated with

Rating

Hydrophobic composite Pd-membrane catalyst useful for... does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Hydrophobic composite Pd-membrane catalyst useful for..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Hydrophobic composite Pd-membrane catalyst useful for... will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2829844