Catalytic direct production of hydrogen peroxide from...

Details Catalytic direct production of hydrogen peroxide from... Catalytic direct production of hydrogen peroxide from...

2001-05-29

2003-06-10

Langel, Wayne A. (Department: 1754)

Chemistry of inorganic compounds

Oxygen or compound thereof

Peroxide

C549S518000, C549S523000, C549S531000

Reexamination Certificate

active

06576214

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention pertains to production of hydrogen peroxide by catalytic direct synthesis from hydrogen and oxygen-containing feedstreams. It pertains particularly to a process for directly producing hydrogen peroxide (H
2
O
2
) product utilizing an active supported noble metal phase-controlled catalyst in a liquid medium containing an organic solvent and water for providing high activity and product selectivity to the process, and can utilize feedstreams containing low safe hydrogen concentrations below their lower flammability limit.
Demand for hydrogen peroxide product has been growing globally at about 6% annually, and in North America at about 10% annually. Such demand growth is due primarily to the enviromnental advantages of hydrogen peroxide usage, which upon decomposition releases only oxygen and water. Hydrogen peroxide is an effective replacement for chlorine in pulp and paper bleaching, water treatment and other environmental processes, and meets the growing product demand and need for a simple environmentally friendly and cost effective process that can be located on-site for the pulp, paper and other manufacturing facilities. The hydrogen peroxide presently being produced commercially uses a known anthraquinone process which has low yields and some safety problems. Also, transportation of hydrogen peroxide from a production site to an end-user facility is an important safety issue due to the risk of explosion of hydrogen peroxide by its violent decomposition.
Many attempts have been made to produce hydrogen peroxide directly from hydrogen and oxygen-containing feedstreams, because such a process not only has potential for significantly reducing production cost, but also provides an alternative production process which avoids the present use of toxic feedstock and working solutions. For such direct catalytic production of hydrogen peroxide, the feedstreams are hydrogen and air which are clean and environmentally harmless. Such direct catalytic process generates no waste and is cost efficient due to its inherent simplicity, and the hydrogen peroxide product can be used directly as a bleaching agent in pulp and paper processes. However, such proposed direct production technology has not yet been commercialized, as the major problems for the known such processes are (1) hazardous operating conditions (with the feed hydrogen partial pressure within the flammable or explosive range), (2) low reaction rates, and (3) low catalytic product selectivity.
Although the direct catalytic synthesis of hydrogen peroxide product has attracted much attention and many patents have been issued, none of the patented processes have been commercially feasible due to low catalyst activity and low selectivity for the hydrogen peroxide product. Until the early 1990's most of these patents utilized as feed gas at least 10% hydrogen in air or oxygen, which is within the flammabiltiy limits for the H
2
/O
2
mixture. Due to increasing safety concerns, the recent approach has been to utilize feedstreams having hydrogen concentration below about 5 vol. %. However, at such low hydrogen concentration, the catalysts used must be much more active to achieve an acceptable production rate for hydrogen peroxide. Highly dispersed palladium on various support materials has been used to enhance the catalytic activity. However, the dispersion methods used have not adequately controlled the crystal phase of the palladium, and the desired improvement in selectivity towards hydrogen peroxide product has not been achieved. A main problem in preparing a highly selective catalyst for hydrogen peroxide production is how to consistently control the formation of desired metal phase such as phase 110 or 220, etc. in the catalyst.
Most of the known prior processes for direct hydrogen peroxide catalytic synthesis are based on use of an aqueous liquid medium for conducting the synthesis reaction, as hydrogen peroxide is generally produced commercially as an aqueous product. Use of organic compounds in combination with hydrogen peroxide can raise safety concerns related to the unintended formation of organic peroxides which can be fire or explosion hazards, especially if accidentally concentrated for example by precipitation. However, there are some prior art patents disclosing direct synthesis of hydrogen peroxide in liquid mediums that include an organic solvent. One class of such prior art processes involves the use of a liquid medium consisting of a two-phase mixture of water and an organic solvent which is immiscible with water. In general, the operating principle of such prior art processes is that the peroxide synthesis catalyst is contained in the organic phase, such that hydrogen peroxide synthesis occurs in this phase. But the resulting hydrogen peroxide product is poorly soluble in that phase, so the peroxide is extracted into the aqueous phase, segregating the product from the catalyst and preventing undesired product degradation.
U.S Pat. No. 4,128,627 discloses hydrogen peroxide being synthesized in a two-phase mixture using a homogeneous palladium-based catalyst which is insoluble in water, with preferred organic solvents being 1,2-dichlorobenzene, chlorobenzene and xylene. A critical function of the organic solvent component is to dissolve the homogeneous catalyst, which is insoluble in the aqueous phase. The best results reported are a hydrogen peroxide product concentration of only 0.45 wt % and a product yield of only 11.59 g H
2
O
2
/g Pd/hr, but requiring an undesirably high hydrogen feed concentration of 97.2 vol. %. In U.S. Pat. No. 4,336,240, it is disclosed that when the organic solvent is a fluorocarbon or halofluorocarbon such as 1,1,2-trichloro-trifluoroethane, a somewhat higher hydrogen peroxide product concentration of 3.2 wt % is achieved, but at a reduced yield of only 0.99 g H
2
O
2
/g Pd/hr, and again with very high hydrogen concentration in the feed gas.
U.S. Pat. Nos. 4,347,231 and 4,347,232 utilize the same two-phase liquid medium concept using homogeneous iridium-based and palladium-based catalysts, respectively, and preferred organic solvents are toluene, xylene, and chlorinated solvents such as dichloromethane. Again, the key operating principle is that the organic solvent is present to dissolve the water-insoluble homogeneous catalyst, and the water phase is present to extract the peroxide product away from the organic phase. The best results were 1.7% H
2
O
2
product concentration and 89 g H
2
O
2
/g Pd/hr yield, but with undesired high hydrogen feed concentrations of 50 vol. % which are well above the explosion limit.
For U.S. Pat. No. 5,399,334 a two-phase liquid reaction medium is used, wherein the organic solvent is a halogenated organic, especially hydrocarbons substituted by at least three fluorine atoms. The best results reported were only 0.8 wt. % H
2
O
2
product concentration at a yield of 266 g H
2
O
2
g Pd/hr, or 3.5 wt % H
2
O
2
product concentration at a yield 194 g H
2
O
2
/g Pd/hr.
Another group of prior art processes in which organic solvents are used as at least part of the liquid medium for direct catalytic hydrogen peroxide synthesis is those patents where only a single liquid phase is present. For example, U.S. Pat. No. 3,361,533 utilizes a liquid mixture of water with a soluble organic solvent such as alcohol or ketone, with acetone being mentioned as the best organic solvent, and the catalyst is a heterogeneous supported noble metal, especially palladium (Pd). A high hydrogen feed concentration of 16.7 vol. % is used, which is well above the flammability limit and close to the explosion limit, but the hydrogen peroxide yield was only 4.86 g H
2
O
2
g Pd/hr.
U.S. Pat. No. 4,007,256 utilizes a one-phase liquid reaction medium consisting of water mixed with an organic nitrogen-containing compound such as acetonitrile, and a supported palladium catalyst. A high hydrogen feed concentration of 50 vol. % was used, again well above the explosive limit, and the best hydrogen peroxide product concentration was 6.4 wt %, with a

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