Integrated hydrogen peroxide production and organic chemical...

Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...

Reexamination Certificate

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C549S518000, C549S523000

Reexamination Certificate

active

06500969

ABSTRACT:

FIELD OF THE INVENTION
The invention comprises a process for producing organic chemicals by selective oxidation where the selective oxidation reaction is conducted using porous particles comprising specially synthesized nanometer-sized crystallites of supported noble metal catalyst. Classes of chemical substrates which can be selectively oxidized by the process of the invention include alkanes, olefins, alcohols, aromatics, ketones, aldehydes as well as compounds containing mixed functionality and/or heteroatoms such as sulfur or nitrogen.
BACKGROUND OF THE INVENTION
Selective oxidation reactions are a major class of chemical transformations accounting for the production of a wide variety of important chemical products, including epoxides, hydroxylates, alcohols, carbonyl compounds, acids, glycols and glycol ethers, oximes, lactones, and oxygenated sulfur and nitrogen compounds such as sulfoxides, sulfones, nitrones, azo compounds, and other N-oxides. Normally, performing these transformations efficiently and economically requires that a catalyst be used which allows the reaction to occur at a sufficiently high rate (activity) and favors the formation of the desired products (selectivity). Frequently, these catalysts are based, at least in part, on the use of a noble metal constituent such as platinum, palladium, iridium, rhodium, ruthenium, gold, osmium, and the like. Noble metals tend to have favorable activity and selectivity toward desired oxidative reactions. The noble metal may be used as a soluble complex (homogeneous catalyst), but it is also frequently used as a heterogeneous catalyst with the noble metal deposited onto a porous support.
Commonly, selective oxidation reactions are performed utilizing oxygen as the oxidizing agent. However, producing purified oxygen is expensive, requiring large capital investment and operating costs. Also, processes using purified oxygen combined with organic chemical feedstocks may accidentally achieve gas compositions in the explosive range, thereby posing a serious safety hazard. In other cases, selective oxidation processes utilize air as the oxidizing agent. But a major economic problem associated with such processes utilizing air is handling the accompanying undesired large flow of nitrogen which substantially increases process costs. Such oxidation processes can also be prone to forming explosive gas mixtures. Oxidative processes using oxygen or air also tend to suffer from product selectivity problems related to overoxidation of the organic chemical feedstock, normally producing undesired carbon oxides (CO, CO2).
An attractive alternative to using oxygen or air as the oxidizing agent is the use of peroxidic compounds to provide the reactive oxygen needed for oxidative transformations. One common version is the use of organic hydroperoxides as oxidizing agents. These hydroperoxide compounds, typically generated by air- or O2-oxidation of suitable intermediates, are reacted with chemical feedstocks to form oxygenated products and organic by-products. However, these organic by-products represent a significant disadvantage for processes of this type because a large amount of organic material must be recovered, either for recycle or for sale as a secondary product. In some cases, the amount of this secondary product is greater than the amount of the primary oxygenated product, and is typically a less desirable product. For example, conventional production of propylene oxide also results in production of large amounts of styrene or tert-butyl alcohol co-products which typically must be marketed in economically unpredictable markets. Furthermore, processes involving organic hydroperoxide intermediates pose significant safety hazards. Generating hydroperoxides requires reactions of air with organic chemicals which may form explosive mixtures. Furthermore, organic peroxides can themselves be explosive, particularly if they are accidentally concentrated above a certain critical concentration level.
Instead of using organic peroxides, hydrogen peroxide is a known desirable oxidizing agent. The byproduct of oxidation reactions using hydrogen peroxide is typically water, a safe compound that can be easily recovered and reused or disposed. The amount of water on a weight basis is much less than the amount of organic by-product when organic hydroperoxides are used, and thereby represents significant savings in process costs. However, past attempts to develop selective chemical oxidation processes based on hydrogen peroxide have encountered significant difficulties. Conventional hydrogen peroxide production utilizes the anthraquinone process, wherein the anthraquinone is first hydrogenated to hydroanthraquinone and then autoxidized to release hydrogen peroxide and the anthraquinone for recycle. Hydrogen peroxide is generated at low concentrations in the solution, and very large flows of anthraquinone and anthrahydroquinone must be handled in order to produce the desired hydrogen peroxide product. Accordingly, such conventionally produced hydrogen peroxide is generally too expensive for commercial use as an oxidizing agent for selective chemical oxidation processes.
An important alternative to the use of organic peroxides for the oxidation of organic compounds is the generation of hydrogen peroxide directly by the noble metal catalyzed reaction of hydrogen and oxygen. This approach avoids the difficulty of the accompanying large flows of a working solution and can reduce the cost of hydrogen peroxide. The prior art includes a number of catalytic technologies which directly convert hydrogen and oxygen to hydrogen peroxide, but generally utilize a hydrogen/oxygen feed wherein the hydrogen concentration is greater than about 10 mol %. These hydrogen concentrations are well above the flammability limit of about 5 mol % for such mixtures and create a serious process hazard with added process costs and capital equipment costs required to mitigate the explosive hazard. At hydrogen feed concentrations below 5 mol %, the prior art catalysts are not sufficiently active and selective to generate hydrogen peroxide product at a reasonable rate.
Recently, an improved process for direct catalytic production of hydrogen peroxide utilizing an active supported phase-controlled noble metal catalyst has been disclosed in applicants' U.S. Pat. No. 6,168,775 B1, incorporated herein by reference in its entirety. Employing the catalyst and process taught in the '775 patent, the foregoing problems and limitations in the manufacture of hydrogen peroxide have been overcome. Advantageously, the '775 catalyst is highly active and produces hydrogen peroxide from hydrogen and oxygen with superior selectivity over the prior art processes. Of special importance, the process of the '775 patent converts hydrogen and oxygen to hydrogen peroxide with high selectivity wherein the process hydrogen concentration is well below its flammability limit.
Various oxidation processes for organic chemical feedstocks utilizing hydrogen peroxide are known. For example, U.S. Pat. No. 4,701,428 discloses hydroxylation of aromatic compounds and epoxidation of olefins such as propylene using a titanium silicalite catalyst. Also, U.S. Pat. Nos. 4,824,976; 4,937,216; 5,166,372; 5,214,168; and 5,912,367 all disclose epoxidation of various olefins including propylene using titanium silicalite catalyst. European Patent No. 978 316 A1 to Enichem describes a process for making propylene oxide, including a first step for direct synthesis of hydrogen peroxide using a Pd catalyst, and a second step for epoxidation of propylene to form propylene oxide using titanium silicalite (TS-1) catalyst. However, the best hydrogen peroxide product selectivity reported is only 86%, based on the amount of hydrogen converted. In the process second step, the best selectivity of propylene oxide formation is 97%, based on hydrogen peroxide conversion. Therefore, the best overall yield of propylene oxide that can be achieved is 83%, based on hydrogen feed. However, higher yields of oxidized organic produ

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