Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
2001-03-23
2003-08-05
Trinh, Ba K. (Department: 1625)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
C549S534000, C502S347000, C502S350000
Reexamination Certificate
active
06603028
ABSTRACT:
This application is a 371 of PCT/EP99/05370, filed Jul. 27, 1999.
The present invention relates to a process for the oxidation of hydrocarbons on a catalyst containing silver in the presence of a hydrogen/oxygen mixture.
The direct oxidation of ethene to ethene oxide by molecular oxygen is well known and is used commercially to produce ethene oxide. The typical catalyst for this application contains metallic or ionic silver, optionally further modified with different promoters and activators. Most of these catalysts contain a porous, inert catalyst support with small surfaces such as alpha aluminium oxide, for example, onto which silver and promoters were applied. A review of the direct oxidation of ethene in the presence of supported silver catalysts has been compiled by von Sachtler et al. in Catalysis Reviews: Science and Engineering, 23 (1&2), 127-149 (1981).
It is also known that the silver catalysts and the reaction conditions which have proved to be favourable for ethene oxide production do not lead to comparably good results in the direct oxidation of higher olefins such as propene (U.S. Pat. No. 5,763,630, U.S. Pat. No. 5,703,254, U.S. Pat. No. 5,760,254) and maximum propene oxide selectivities of approx. 50% are achieved. Generally speaking the direct oxidations of these higher olefins with molecular oxygen in the gas phase do not take place below 200° C.—even in the presence of catalysts—and it is therefore difficult selectively to produce oxidation-sensitive oxidation products, such as epoxides, since the secondary reactions of these products often proceed more quickly than the oxidation of the olefins themselves which are used.
U.S. Pat. No. 4,833,260 describes titanium silicalite catalysts which effectively make possible the epoxidation of olefins with the oxidant hydrogen peroxide in the liquid phase. In the silicalites a small part of the lattice silicon is replaced by titanium (U.S. Pat. No. 4,410,501). The high cost of hydrogen peroxide as oxidant precludes large-scale application.
Titanium silicalite-catalyzed epoxidation with pure oxygen as oxidant is successful in the presence of a redox system consisting of alkylanthrahydroquinone and alkylanthraquinone (EP 526,945).
On titanium silicalites containing metallic platinum, propene oxidation is achieved with low yield (approx. 1-2%) and propene oxide selectivities of 60-70% in the liquid phase by means of an in-situ hydrogen peroxide formation with a gas mixture consisting of molecular oxygen and molecular hydrogen (JP-A 92/352771, WO 97/47386, WO 96/023 023). Hydrogenations which take place as secondary reactions lead to large quantities of propane as a by-product and the fact that this is a liquid phase reaction in which the epoxide which is formed is concentrated in the liquid phase makes these processes of little interest as far as industrial use is concerned.
U.S. Pat. No. 5,623,090 describes a gas phase direct oxidation of propene to propene oxide with high selectivity. This is a gold-catalyzed gas phase oxidation with molecular oxygen in the presence of hydrogen. Conventional commercial titanium dioxide, which is coated with finely dispersed gold particles, is used as the catalyst. With identical educt gases, another embodiment uses catalysts in which gold is applied to a support consisting of isolated titanium sites in a silicon dioxide matrix (WO 9800415 A1; WO 9800414 A 1; WO 9800413 A1). These processes all have the disadvantage of being very expensive because of the gold content of the catalyst and are not therefore considered for an industrial use of products such as propene oxide.
The object of the present invention therefore consisted of providing a catalytic process for the oxidation of hydrocarbons which leads to improved selectivities, yields and costs.
It has surprisingly been found that this object may be achieved if hydrocarbons are caused to react in the presence of a hydrogen/oxygen mixture on a catalyst which contains silver and titanium.
The present invention thus relates to a process for the oxidation of hydrocarbons, wherein a mixture containing at least one hydrocarbon, oxygen and hydrogen is converted on a catalyst which contains silver and titanium, wherein the catalyst contains a support containing titanium and silver particles with an average particle size of 0.3 to 100 nm.
In principle the process according to the invention may be applied to all hydrocarbons. The term hydrocarbon is intended to mean saturated or unsaturated hydrocarbons such as alkanes or olefins which may also contain heteroatoms such as N, O, P or S. Hydrocarbons from which those oxidation products, the partial pressure of which is low enough consistently to remove the product from the catalyst are formed, are preferably oxidized. Unsaturated hydrocarbons with 2 to 20, preferably 2 to 10 carbon atoms, particularly ethene, propene, 1-butene, 2-butene, butadiene and pentenes and hexenes are preferred.
The catalyst containing silver contains silver particles which are preferably applied to a support.
The catalyst containing silver contains fine silver particles with average particle sizes of 0.3-100 nm, preferably 0.5-20 nm and particularly preferably 0.5 to 6 nm. The silver content in the catalyst is preferably 0.5-10 wt. %.
Pulverulent and pelletized supports are equally suitable as support materials. Amorphous high-surface support materials with surfaces >50 m
2
/g, preferably >100 m
2
/g, are preferred, particularly those which contain titanium such as titanyl hydrates, zinc oxide hydrate containing titanium, aluminium oxide containing titan ium, titanium dioxides (anatases) or titanium/silicon mixed compounds such as TiO
2
—SiO
2
mixed oxides, titanium silicalites or molecular sieves (zeolites) in which titanium is present finely dispersed in a silicon matrix.
In principle any crystal structure of the titanium oxide may be selected although the amorphous titanium dioxide modification and anatase are preferred. The titanium oxide does not have to be present as pure component but may also be present as complex material, e.g. in combination with other oxides (e.g. titanates). According to our knowledge and without wishing to restrict the invention in any way, the titanium sites in particular which are chemically bonded to silica and/or inorganic silicates represent the catalytically active titanium sites. Furthermore we assume that in active catalysts titanium is present bonded to the silica or silicate in the form of the oxide [e.g. —Si—O—Ti(═O)—O—Si—].
The support materials containing silicon according to the invention advantageously consist of 50%, preferably of 75% and particularly preferably of >90% of the dioxide form of the silicon. In addition to silicon dioxide and silicates the support materials containing silicon according to the invention may also contain other oxides, e.g. aluminium oxide, zirconium oxide etc. Support materials containing silicon with a large specific surface and a high proportion of surface silanol groups are preferably used. The specific surface should be at least 1 m
2
/g, preferably in the range from 25-700 m
2
/g.
Preferred support materials containing silicon are synthetically produced porous silicon dioxides such as silica gels, precipitated silica, precipitated silica gels, silicalites or similar and mixtures thereof for example. Production methods for such synthetically produced silicas are described in “The Colloid Chemistry of Silica and Silicates (R. G. Iler, Cornell University Press, New York, USA, 1955, Chapter VI)”. Examples of these silicas are pyrogenic silicas which are obtained by conversion of silicon tetrachloride or fluoride with hydrogen and oxygen (e.g. Cab-o-sils from Messrs Cabot Corporation or Aerosils from Messrs Degussa).
Crystalline alurninosilicates and silicalites, known as molecular sieves, may also be used as support materials containing silicon. Naturally occurring crystalline silicates may also be used, particularly serpentine (magnesium silicate), clay minerals such as hectorite (lithium magnesium silicate), kaolin, b
Dorf Ernst Ulrich
Schild Christoph
Wegener Gerhard
Weisbeck Markus
Bayer Aktiengesellschaft
Gil Joseph C.
Mrozinski, Jr. John E.
Trinh Ba K.
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