Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
2002-06-13
2003-07-29
Trinh, Ba K. (Department: 1625)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
C549S523000
Reexamination Certificate
active
06600055
ABSTRACT:
INTRODUCTION AND BACKGROUND
The present invention relates to catalytic epoxidation of olefins with hydrogen peroxide in a continuous flow reaction system.
From EP-A 100 119 it is known that propene can be converted by hydrogen peroxide into propene oxide if a titanium-containing zeolite is used as catalyst.
Unreacted hydrogen peroxide cannot be recovered economically from the epoxidation reaction mixture. Furthermore, unreacted hydrogen peroxide involves additional effort and expenditure in the working up of the reaction mixture. The epoxidation of propene is therefore preferably carried out with an excess of propene and up to a high hydrogen peroxide conversion. In order to achieve a high hydrogen peroxide conversion it is advantageous to use a continuous flow reaction system. Such a reaction system may comprise either one or more tubular flow reactors or an arrangement of two or more flow mixing reactors connected in series. Examples of flow mixing reactors are stirred tank reactors, recycle reactors, fluidized bed reactors and fixed bed reactors with recycling of the liquid phase.
Furthermore the epoxidation of olefins with hydroperoxides is like most oxidation reactions highly exothermic. Thus precautions have to be taken to ensure sufficient removal of the heat generated by the exothermic reaction in order to control the reaction. This problem is especially pronounced in continuous flow systems using fixed bed reactors. Moreover conversion and product selectivity in epoxidation reactions with the effect that efficient temperature control is of uppermost importance.
According to a considerable number of patent disclosures as exemplified by EP-A 230 349, EP-A568 336, EP-A 712 852, EP-A 757 045, JP-A 2-166636, WO 97/47613 and U.S. Pat. No. 5,591,875 the epoxidation reaction of olefins with hydrogen peroxide is performed in a slurry of titanium containing zeolites as catalyst. In this reaction mode temperature control is less difficult and thus a wide range of suitable reaction temperatures from −20° C. to 150° C. are reported in these documents where in the examples temperatures between 0° C. and 85° C. were used.
EP-A 100 119 discloses in addition to reaction in a catalyst slurry the use of a tubular continuous flow reactor with a fixed catalyst bed that is immersed in a cooling bath thermostated at 15° to 20° C.
In WO 97/47614 in example 8 reaction of propene with hydrogen peroxide using a fixed bed tubular reactor having a cooling jacket is described. The temperature of the cooling medium is controlled by a thermostat to be in the range between 0°-5° C. Yield and product selectivity are still insufficient for commercial purposes.
As far as the applicants are aware all of the prior art documents referring to epoxidation of olefins with hydrogen peroxide in tubular fixed bed reactors equipped with cooling means disclose only the temperature of the cooling medium without providing any information with respect to the actual temperature within the reactor. As is known for example from Walter Brötz et.al., Technische Chemie I, Weinheim, 1982, pp 283; the temperature profile with respect to the cross-section of a tubular reactor is parabolic with increasing temperature from the periphery to the center of the reactor in case of exothermic reactions. Additionally the temperature may vary along the axis of the tubular reactor.
EP-A 659 473 describes an epoxidation process wherein a liquid mixture of hydrogen peroxide, solvent and propene is led over a succession of fixed bed reaction zones connected in series in down-flow operation. No temperature control means are present within the reactor to remove the generated heat from the single reaction zones. Thus each reaction zone can be considered as an independent adiabatic reactor. In each reaction zone the reaction is performed to a partial conversion, the liquid reaction mixture is removed from each reaction zone, is led over an external heat exchanger to extract the heat of reaction, and the major proportion of this liquid phase is then recycled to this reaction zone and a minor proportion of the liquid phase is passed to the next zone. At the same time gaseous propene is fed in together with the liquid feed stock mixture, is guided in a parallel stream to the liquid phase over the fixed bed reaction zones, and is extracted at the end of the reaction system in addition to the liquid reaction mixture as an oxygen-containing waste gas stream. Although this reaction procedure enables the propene oxide yield to be raised compared to conventional tubular reactors without the temperature control described in EP-A 659 473, it nevertheless involves considerable additional costs on account of the complexity of the reaction system required to carry out the process.
From U.S. Pat. No. 5,849,937 a process for epoxidation of propene using hydroperoxides especially organic hydroperoxides is known. The reaction mixture is fed to a cascade of serially connected fixed bed reactors in down-flow regime with respect to each single reactor. Similarly to the teaching of EP-A 659 473 in each reactor only partial conversion is accomplished and the reactors are not equipped with heat exchange means. Like in EP-A 659 473 the reaction heat is removed by passing the effluent from each reactor through heat exchangers prior to introducing the reaction mixture to the next fixed bed reactor in series thereby adding to the complexity of the reaction system.
The disadvantages of the reaction systems as discussed in EP-A 659 473 and U.S. Pat. No. 5,849,937 are the complexity and thus the increased costs for investment.
U.S. Pat. No. 5,599,955 refers to an epoxidation reaction in a fixed bed reactor whereby it is evident from example 1 that the reaction mixture is contacted with the titanium silicate catalyst in a temperature range between 40° C. to 60° C. But nevertheless, this reference does not disclose the cooling medium temperature of the cooling means.
In view of the cited prior art an object of the present invention is to provide a process for the epoxidation of olefines that results in improved conversion and product selectivity compared to WO 97/47614 which can be carried out using conventional reaction systems.
SUMMARY OF THE INVENTION
The above and other objects of the present invention can be achieved by a process for the catalytic epoxidation of olefins with hydrogen peroxide in a continuous flow reaction system, wherein the reaction mixture is passed through a fixed catalyst bed within a reactor equipped with cooling means while maintaining a temperature profile within the reactor such that the cooling medium temperature of the cooling means is at least 40° C. and the maximum temperature within the catalyst bed is 60° C. at most.
The present inventors have surprisingly discovered that by conducting the epoxidation reaction in such a way to fulfill the inventive temperature profile requirement an optimized balance between conversion and selectivity can be achieved with a standard reaction system. Thus, a process for epoxidation of olefins with high hydrogen peroxide conversion and product selectivity at low investment costs is available thereby improving the overall economics of the process. Due to the considerably high activation temperature for the epoxidation reaction the process has to be conducted at a certain minimum temperature to achieve economically reasonable conversion. But on the other hand the heat generated by the exothermic reaction has to be effectively removed from the reactor since at increased temperatures unwanted side reactions take place with the result that product selectivity is decreased. While maintaining the temperature profile in the reactor within the inventive very narrow range both goals could be simultaneously achieved.
EP-A-659 473 discloses that in conventional tubular reactors temperature rise in the catalyst bed exceeds 15° C. whereas according to the examples in EP-A-659 473 the temperature rise is 8° C. at most and in the preferred embodiment only 5½° C. Thus according to the teaching of EP-A-659 473 te
Haas Thomas
Hofen Willi
Sauer Jörg
Thiele Georg
Degussa - AG
Smith , Gambrell & Russell, LLP
Trinh Ba K.
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