Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
2000-07-14
2001-10-16
Trinh, Ba K. (Department: 1612)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
C549S532000, C549S533000
Reexamination Certificate
active
06303800
ABSTRACT:
This application is a 371 of PCT/EP98/07862 dated Dec. 3, 1998.
The present invention relates to a process for preparing propene oxide by direct oxidation of propene using oxygen or oxygen-containing gases in the gas phase with or without participation of an additionally added catalyst in a temperature range from 150 to 500° C. in a reactor which is lined or modified with inert materials.
Propene oxide is one of the most important intermediates of the chemical industry; it is required mainly for the preparation of propylene glycols which are mostly processed further to give polyurethanes. Bifunctional polypropylene glycols having high viscosities or mixed adducts of propene oxide and ethylene oxide or the monoalkyl ethers of these compounds are important raw materials which are used for producing a wide variety of products (e.g. antifoams, mold release agents, demulsifiers, brake fluids, metalworking auxiliaries, textile assistants, lubricants and adhesives).
Propene oxide itself is a good solvent for cellulose acetate, nitrocellulose, adhesives, resins and other materials and is used as stabilizer for chlorine-containing polymers, as corrosion inhibitor in cooling fluids and pest control compositions and also as a weed killer and as a disinfection and sterilization agent.
There has hitherto been no satisfactory direct oxidation process for preparing propene oxide, since relatively large amounts of by-products or waste products are always produced in addition to propene oxide itself and these have to be separated off in further work-up steps. Furthermore, in the coupled product processes, a use also has to be available for the coproduct or an appropriate price has to be achieved in order to cover costs.
In the conventional chlorohydrin process, the chlorohydrin prepared from propene and chlorine in aqueous solution is dehydrochlorinated using milk of lime (Ca(OH)
2
). This results in formation of a CaCl
2
solution which, after work-up, is disposed of into the wastewater and represents considerable environmental pollution. In the brine recirculation method, the chlorohydrin is reacted with NaOH from the cell liquid of a chloralkali electrolysis, giving an NaOH/NaCl solution which has to be concentrated and freed of organic substances before it can be returned to the electrolysis cell.
The preparation of propene oxide by indirect oxidation using peroxides or peracids is likewise a two-stage process which differs from the chlorohydrin process in that the coproducts formed are frequently obtained in larger amounts than propene oxide itself and an outlet has to be available for them too. Hydrogen peroxide, organic peracids and organic hydroperoxides are used for the epoxidation of propene. The epoxidation using H
2
O
2
is usually carried out in the liquid phase (e.g. methanol/water) in the presence of a catalyst (MoO
3
) or titanium oxide on SiO
2
or Ti-containing zeolites such as TS-1 (Enichem) at 40-50° C. and a pressure of 4 bar. Propene oxide selectivities of 75-99%, albeit at very low conversions, are reported. Main disadvantages are the high cost of H
2
O
2
and the difficulty of handling it.
In the oxidation by means of organic peracids, use is made of perpropionic acid and peracetic acid (Daicel), and propene oxide and the corresponding carboxylic acid are formed in the liquid phase. In this context, mention should be made of the Bayer-Degussa process in which acetic acid or propionic acid is reacted with the expensive H
2
O
2
to generate the peracids which react with propene to give propene oxide and the corresponding acid. The main disadvantage of this coupled product process is once again the formation of large amounts of the corresponding by-products, i.e. the acids, for which there has to be a market and which lower the flexibility of the process. Oxidation using organic hydroperoxides has gained importance in recent years, since there is increasing demand on the world market for the coproducts formed, especially styrene or methyl tert-butyl ether (MTBE). Hydroperoxides used are preferably tert-butyl hydroperoxide, ethylbenzene hydroperoxide and cumene hydroperoxide, which give isobutene (or methyl tert-butyl ether), styrene and methylstyrene, respectively, as coproducts. The SMPO process of Shell, which produces propene oxide together with styrene in a coupled process, uses a TiO
2
-containing silica gel catalyst (e.g. EP-A-0 345 856). This process is at present profiting from good world market prices for styrene.
Oxidations in the liquid phase, which can be carried out with or without catalyst (homogeneous or heterogeneous) (FR-A-2 115 752, DE-A-4 447 231), do often give better yields than the gas-phase processes, but they are associated with difficult separation tasks, corrosion problems and complicated technologies, so that no industrial-scale use has become known to the present time.
A Canadian publication (CA 986127) describes a gas-phase reaction of propene (93.9%) with oxygen (6.1%) in a glass-lined steel autoclave at a temperature of 226° C. at 5 bar pressure. After 90 minutes, the selectivity to propene oxide is 64% (no indication of the conversion is given). This process has, in particular, the disadvantages of the excessively long residence time and the use of relatively expensive pure oxygen which represents a very high safety risk.
Numerous patents of Odin Corporation (U.S. Pat. Nos. 5,117,011; 5,142,070; 5,241,088; EP-A-0 268 870) disclose processes and reactors for the oxidation of propene in the gas phase under superatmospheric pressure, some of which make use of an alkali metal nitrate melt as catalyst while others proceed in the absence of a catalyst. The best selectivity to propene oxide reported here is 60.8% at a propene conversion of 8.3% (U.S. Pat. No. 5,142,070).
All catalytic and noncatalytic direct oxidation processes for converting propene into propene oxide in the gas phase known in the past have the disadvantage that both the conversions and the selectivities to PO are not very high. For this reason, none of these processes is used industrially at present.
It is therefore an object of the present invention to provide a process for preparing propene oxide by direct oxidation of propene, which process does not have the disadvantages of the known process, i.e. enables propene oxide selectivities of >60% to be achieved without by-products or coproducts in stoichiometric amounts being formed.
It has now surprisingly been found that propene oxide can be prepared very selectively, effectively and inexpensively in a continuous gas-phase process in a reactor lined with inert materials. According to the invention, the inner walls of the reactor and/or internals for directing the gas stream or internals which control the flow of reactants in the tube reactor, e.g. thermocouples, can be coated with an inert material or consist of such a material.
The present invention accordingly provides a process for preparing propene oxide, in which a mixture of propene and oxygen or an oxygen-containing gas is reacted at a temperature in the range from 150 to 500° C., in the presence or absence of a catalyst, in a reactor, wherein all or part of the interior of the reactor is lined with inert materials.
It has surprisingly been found that a tube reactor coated on the inside with inert materials gives better propene oxide yields even without catalyst than does a reactor of the same diameter made of normal standard steel (e.g. V2A). The product selectivity can even be increased here via the moisture and CO
2
content of the air or gas mixture used for oxidation.
For the purposes of the invention, inert materials are materials which undergo only minimal, if any, interactions or chemical reactions with the reactants and allow no chemisorption or physisorption on their surface. Inert materials which are suitable for coating the reactor interior or for coating reactor internals can, for example, be selected from the materials of the following group: one or more noble metals of transition group VIII of the Periodic Table, in particular gold, titanium and tantalum
Dingerdissen Uwe
Maier Wilhelm
Orzesek Holger
Schulz Rolf
Aventis Research & Technologies GmbH & Co KG
Connolly Bove & Lodge & Hutz LLP
Trinh Ba K.
LandOfFree
Method for producing propene oxide does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for producing propene oxide, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for producing propene oxide will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2608829