Method of producing expoxides in the gaseous phase

Details Method of producing expoxides in the gaseous phase Method of producing expoxides in the gaseous phase

2001-01-19

2001-11-27

Trinh, Ba K. (Department: 1625)

Organic compounds -- part of the class 532-570 series

Organic compounds

Heterocyclic carbon compounds containing a hetero ring...

C549S531000

Reexamination Certificate

active

06323349

ABSTRACT:

This application claims priority from German Application No. 100 02 514.5, filed on Jan. 21, 2000, the content of which is hereby incorporated here by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method of producing epoxides [oxiranes; literally “olefin oxides”] with 2 to 6 C atoms, especially propene oxide, by gas-phase epoxidation of the corresponding olefin with 2 to 6 C atoms with hydrogen peroxide in the presence of a solid catalyst.
2. Background Information
The epoxidation of olefins such as propene using hydrogen peroxide is successful in the liquid phase using a titanium silicalite catalyst—see U.S. Pat. No. 5,874,596 and DE 197 31 627. A disadvantage of this method is the rapid deactivation of the catalyst by high-boiling byproducts.
The liquid-phase epoxidation of olefins with hydrogen peroxide in the presence of a catalyst containing molybdenum or tungsten is also known—see Weigert et al., Chem.-Ztg. [German=Chemische Zeitung] 99, 19 (1975). The workup of the reaction mixture and the recovery of the catalyst are quite expensive.
The carrying out of the epoxidation in a membrane reactor is also known from CA 2,206,626 A1, in which catalytically active particles are intercalated [inserted] in the composite membrane and a gas phase with the olefin such as propene to be epoxidized is located on the one side of the membrane and on the other side a liquid phase with hydrogen peroxide is located. The catalytically active particles preferably consist of titanium silicalite.
Instead of in the liquid phase, ethylene can also be epoxidized in the gas phase in the presence of a silver-containing catalyst at 200 to 300° C. In this instance, air or molecular oxygen is used as epoxidizing agent instead of hydrogen peroxide (see, e.g., U.S. Pat. No. 4,374,260).
The attempt has also been made to epoxidize lower olefins with hydrogen peroxide in the gas phase, during which hydrogen peroxide is thermally or catalytically activated: Thus, according to G. M. Mamedjarov and T. M. Nagiev (Azerb. Khim. Zh. [Russian=Azerbaizhanskii Khimicheski Zhurnal] ethene and propene can be epoxidized at 500 to 600° C. in a gas phase in the absence of a catalyst. Epoxide yields, that were initially low, were able to be increased by T. M. Nagiev et al. (Neftekhimiya [Russian] 31 (1991), 670-675) by optimization to approximately 50 to 55%. The high reaction temperatures, that oppose an economic process, are disadvantageous.
H. M. Gusenov et al. (Azerb. Khim. Zh. (1984), 47-51) investigated the mechanism of a similar method; however, the gas-phase epoxidation takes place here in the presence of a Si-containing catalyst at 425 to 500° C. Propene and vaporous hydrogen peroxide are supplied to a tubular reactor; the conversion of propene is in a range of 15 to 65%.
T. M. Nagiev et al. (Neftekhimiya 31, (1991), 670-675) teach an improved gas-phase epoxidation in the presence of an Fe-containing catalyst: Propene is epoxidized with hydrogen peroxide to propene oxide using magnetite as catalyst at approximately 250° C. with a yield of about 30%. However, the catalytic service life of 25 h is very low. A longer service life and a further lowering of the reaction temperatures can be obtained with an Fe
III
OH-protoporphyrin catalyst bound to aluminum oxide as carrier. A propene oxide yield of approximately 50% is obtained with this catalyst at a temperature of about 160° C. and a molar dosing ratio of C
3
H
6
:H
2
O
2
:H
2
O=1:0, 2:0,0.8.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a further method for the catalytic gas-phase epoxidation of lower olefins with hydrogen peroxide in which the catalyst should be iron-free (non-ferrous) and wherein the epoxidation can be carried out below 250° C. The term “iron-free” does not exclude here the presence of traces of iron in the catalyst within the scope of customary impurities.
This object is accomplished by a method of producing an epoxide with 2 to 6 C atoms, especially propylene oxide, by gas-phase epoxidation of the olefin to be epoxidized with hydrogen peroxide, comprising bringing the a gaseous mixture containing the olefin, hydrogen peroxide and water into contact with a solid catalyst and the isolating of the epoxide from the reaction mixture, that is characterized in that a compound of an element of the 4th to the 6th subgroup of the periodic table of the elements or arsenic or selenium or a molecular sieve is used as catalyst and the epoxidation is carried out at a temperature below 250° C. in the absence of a liquid phase.
The subclaims are directed to preferred embodiments of the method of the invention.
One class of suitable catalyst concerns molecular sieves, especially synthetic zeolites. An especially preferred catalyst from the family of molecular sieves is based on titanium-containing molecular sieves of the general formula (SiO
2
)
1−x
(TiO
2
)
x
such as titanium silicalite-1 (TS-1) with MFI crystalline structure, titanium silicalite-2 (TS-2) with MEL crystalline structure, titanium beta zeolite with BEA crystalline structure and titanium silicalite-48 with the crystalline structure of zeolite ZSM 48. The TiO
2
content in TS-1 is preferably in a range of 2 to 4%. Titanium silicates are commercially obtainable. Instead of pure titanium silicates combination products can be used that also contain amorphous or crystalline oxides such as SiO
2
, TiO
2
, Al
2
O
3
, ZrO
2
in addition to titanium silicate. Crystallites of titanium silicate can be homogeneously distributed in this instance with the crystallites of the other oxides and form granulates or can be located as the outer shell on a core of other oxides.
Another class of catalysts to be used in accordance with the invention preferably concerns inorganic, especially oxidic compounds containing as catalytically active element one or more elements of the 4th to the 6th subgroup of the periodic table or an arsenic compound or selenium compound. Compounds of titanium, zirconium, vanadium, niobium, tantalum, chromium, molybdenum and tungsten are preferably concerned. The catalytic action is viewed in the fact that, without excluding other mechanisms, hydrogen peroxide is activated by the porous structure of the catalyst and/or the enabling of the catalyst to the reversible formation of peroxo compounds.
Examples of suitable catalysts are vanadium oxides, vanadates, niobium oxide and tantalum oxide and —oxide hydrates as well as H
2
O
2
adducts of the cited oxides and oxide hydrates.
Another especially suitable class of epoxidation catalysts contains molybdenum or tungsten. Examples are MoO
3
and WO
3
, molybdic- and tungstic acids, alkali- and alkaline-earth molybdates and —tungstates in is far as their basicity does not result in a hydrolysis of the epoxide, homo- and heteropolymolybdates and tungstates (=homo-and heteropolyacids) and H
2
O
2
adducts of the cited substance classes such as peroxomolybdic acid, peroxotungstic acid, peroxomolybdates and peroxotungstates that can also be formed in situ during the epoxidation from other Mo and W compounds.
The catalyst is usually particulate; however, the active component can be fixed to the walls of a monolithic carrier with through tubes or slots. Catalysts in granulate, spherical or rod-like form are used with particular advantage. Particulate catalysts can be used in the form of a fixed-bed charge or in the form of a fluid bed.
A gaseous mixture containing an olefin, hydrogen peroxide, water and optionally another gas for rendering inert is passed thereby through the catalytic charge [packing] or is used as a fluid-bed gas. The method can be carried out batchwise or continuously. It is essential that no liquid phase develops during the epoxidation in the reactor that is, on the catalyst. This increases the catalytic service life and reduces the expense of a regeneration.
It can be advantageous, if required, in particular in order to adjust isothermal reaction conditions and to avoid/red

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