Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
2002-10-04
2003-12-30
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
06670492
ABSTRACT:
PRIOR ART
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, fluidised bed reactors and fixed bed reactors with recycling of the liquid phase.
In order to achieve a high reaction velocity as high a propene concentration as possible in the liquid phase is necessary. The reaction is therefore preferably carried out under a propene atmosphere at elevated pressure.
The decomposition of hydrogen peroxide with the formation of molecular oxygen always occurs to a slight extent as a secondary reaction on the titanium silicalite catalyst. In order to be able to operate the epoxidation process reliably on an industrial scale the oxygen that is formed must be removed from the reaction system. This is effected most simply by flushing the oxygen out with a propene waste gas stream.
EP-A 659 473 describes an epoxidation process that combines these features. In this connection a liquid mixture of hydrogen peroxide, solvent and propene is led over a succession of fixed bed reaction zones connected in series, wherein the liquid phase 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. The individual reaction zones behave as flow mixing reactors on account of the liquid recycling over the fixed bed. 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. Furthermore, the described raised yield can only be realised if the propene oxide contained in the waste gas stream is recovered. This necessitates an additional process stage, which in turn adds further to the costs of the process.
The object of the present invention is accordingly to provide a simple inexpensive process for the epoxidation of olefins with hydrogen peroxide, with which high conversions can be achieved combined with a high product yield and which can be carried out using conventional reaction systems.
SUBJECT OF THE INVENTION
This object is achieved by a process for the catalytic epoxidation of olefins with hydrogen peroxide in a continuous flow reaction system wherein a gaseous phase containing an olefin and a liquid phase containing the hydrogen peroxide are present in the reaction system and the gaseous phase is fed in countercurrent to the liquid phase.
An important advantage of the countercurrent arrangement according to the invention is the reduction in the amount of propene oxide that is discharged from the reaction system together with the oxygen-containing propene waste gas stream, and the resultant decreased expenditure on recovering propene oxide from this waste gas stream. As small a loss of propene oxide as possible is desired in order to achieve a high product yield according to the invention.
The countercurrent arrangement according to the invention of gaseous olefin and liquid reaction mixture in the reaction system may be accomplished in various ways depending on the chosen reaction system. In this connection reaction systems are suitable in which there is no complete back-mixing relative to the overall system, i.e. reaction systems whose residence time spectrum exhibits a maximum, or reaction systems involving plug flow.
If the epoxidation of olefins is carried out in a tubular flow reactor, then the gas stream containing the olefin is guided in countercurrent to the liquid phase within the reactor. In this connection the liquid stream is preferably led from the top downwards through the reactor, while the olefin flows from the bottom upwards through the reactor in the form of a gas stream. The reactor may be operated as a bubble column with a continuous liquid phase, as well as a trickle reactor with a continuous gas phase. The catalyst may be employed either as a suspension in the liquid phase or in the form of a fixed bed, wherein the fixed bed may be designed both as a random catalyst packing as well as an ordered packing of coating monoliths or distribution bodies. Preferably a tubular flow reactor is used as a fixed bed reactor with a random catalyst packing and continuous liquid phase.
In order to be able to operate the process continuously when changing and/or regenerating the epoxidation catalyst, two or more tubular flow reactors may if desired also be operated in parallel or in series in the aforedescribed manner.
If the epoxidation of olefins is carried out in a succession of two or more tubular flow reactors connected in series, the substance streams of liquid phase and gaseous phase within a flow reactor may be guided either in co-current or in countercurrent, the substance streams being guided in countercurrent between the tubular flow reactors.
In an alternative embodiment the reaction system may comprise several reactors connected in series that are chosen independently of one another from flow mixing reactors and tubular flow reactors, the substance streams of liquid phase and gaseous phase being guided in countercurrent between the reactors. For example, flow mixing reactors and tubular flow reactors may also be used in combination within the reaction system consisting of reactors connected in series. Preferably, in this connection one or more flow mixing reactors are connected in series with a final tubular flow reactor. The particular advantage of such a reaction system is that the heat of reaction can be particularly easily extracted from the flow mixing reactors in which the major proportion of the reaction turnover takes place. The use of a final tubular flow reactor ensures that the hydrogen peroxide conversion takes place as fully as possible. Stirred tank reactors, recycle reactors, jet reactors with liquid circulation, or fixed bed reactors with a liquid circulation over the fixed bed are for example suitable as flow mixing reactors.
Using the process according to the invention olefins can be epoxidised that are at least partially in the gaseous phase under the chosen reaction conditions. This applies in particular to olefins with 2 to 6 carbon atoms. The process according to the invention is most particularly suitable for the epoxidation of propene to propene oxide.
For economic reasons it would be preferred for an industrial scale process to use propene not in a pure form but as a technical mixture with propane that as a rule contains 1 to 15 vol. % of propane. Since propene is consumed in the epoxidation reaction, propane accumulates in the gas stream during its passage through the reaction system, which in the case of a co-current flow arrangement leads to a decrease in the reaction velocity and to differences in the generation of heat through the exothermal epoxidation reaction along the chain of reactors. T
Hofen Willi
Thiele Georg
Degussa - AG
Smith Gambrell & Russell
Trinh Ba K.
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