Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
2003-03-04
2004-09-14
Trinh, Ba K. (Department: 1625)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
C549S529000, C549S541000
Reexamination Certificate
active
06790969
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for regenerating a zeolite catalyst and to an integrated process for preparing an epoxide in which the regeneration according to the present invention is carried out.
2. Description of the Background
It is known from the prior art that the catalytic activity of heterogeneous catalysts for the oxidation of organic compounds in the liquid phase, in particular the epoxidation of organic compounds having at least one C—C double bond using a hydroperoxide in the presence of a zeolite catalyst, decreases as the run time increases and the corresponding catalysts then have to be regenerated.
Accordingly, processes for regenerating zeolite catalysts are already known from the prior art. On this subject, reference may be made to WO 98/55228 and the prior art cited therein. In this prior art, essentially two different procedures for catalyst regeneration are proposed.
1. If the catalyst is used in suspension, it is firstly separated from the liquid reaction product and transferred to a regeneration apparatus suitable for the regeneration and is regenerated there by thermal treatment in the presence of oxygen;
2. If the catalyst is used as a fixed bed, the liquid phase is drained or pumped out and the catalyst is regenerated by thermal treatment in the absence of oxygen either in the reactor itself or in a separate regeneration apparatus.
Furthermore, regeneration by treatment of the catalyst with a liquid which is an oxidizing agent, e.g. hydrogen peroxide, at elevated temperature has been described a number of times, for example in DE-A 195 28 220 and WO 98/18555.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a further improved, in particular more effective, process for the regeneration of zeolite catalysts, which can be integrated without problems into continuous and integrated processes for preparing epoxides of the type under discussion here and which leads to opening or changeover of the reactors without long shutdown times and downtimes. In particular, this process should be suitable for regenerating zeolite catalysts which are used in an oxidation in the fixed-bed mode. The regeneration process of the present invention should especially substantially prevent or at least greatly reduce the formation of a hot spot in a catalyst bed during regeneration, since such local overheating of the catalyst has an adverse effect on the activity or mechanical stability of the catalyst when it is subsequently reused in the integrated process of the present invention for the oxidation of an alkene.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
We have found that this object is achieved by the process of the present invention for regenerating a zeolite catalyst.
The present invention accordingly provides a process for regenerating a zeolite catalyst, which comprises thermal treatment of the catalyst at above 120° C. in the presence of a gas stream comprising hydrogen.
The regeneration time is preferably chosen so that the catalyst regains at least 85% of its original activity.
In the process of the present invention, it is possible to regenerate either catalysts in powder form as are used in suspension or catalysts in the form of shaped bodies, e.g. extrudates, packed in a fixed bed, or catalysts crystallized on meshes, e.g. stainless steel or Kanthal, or packing or coated catalysts comprising an inner core of SiO
2
, &agr;-Al
2
O
3
, strongly calcined TiO
2
or steatite and an active catalyst shell comprising a zeolite.
If the catalyst has been used in the suspension mode, it firstly has to be separated from the reaction solution by a separation step, e.g. filtration or centrifugation. The at least partially deactivated pulverulent catalyst obtained in this way can then be regenerated. The steps carried out at elevated temperatures during the regeneration process are preferably carried out in rotary tube furnaces in the case of such pulverulent catalysts. In the regeneration of a catalyst which is used in the suspension mode, particular preference is given, for the purposes of coupling the reaction in the suspension mode and the regeneration process of the present invention, to removing part of the at least partially deactivated catalyst continuously from the reaction, regenerating it externally by means of the process of the present invention and reintroducing the regenerated catalyst into the reaction in the suspension mode.
Apart from the regeneration of catalysts in powder form, the process of the present invention can also be employed for regenerating catalysts in the form of shaped bodies, for example those packed in a fixed bed. In the regeneration of a catalyst packed in a fixed bed, the regeneration is preferably carried out in the reaction apparatus itself without the catalyst having to be removed and reinstalled, so that it is subjected to no additional mechanical stress. In the regeneration of the catalyst in the reaction apparatus itself, the reaction is firstly interrupted, any reaction mixture present is removed, the regeneration is carried out and the reaction is subsequently continued.
The regeneration of the present invention proceeds essentially identically in both the regeneration of pulverulent catalysts and the regeneration of catalysts in shaped form.
The process of the present invention is particularly suitable for regeneration in a fixed-bed reactor, especially a tube reactor or a shell-and-tube reactor. The terms “tube reactor” and “shell-and-tube reactor” refer to parallel assemblies of many channels in the form of tubes, where the tubes can have any cross section. The tubes are fixed in space relative to one another, preferably have a spacing between them and are preferably surrounded by a jacket (shell) which encloses all the tubes. In this way, for example, a heating or cooling medium can be passed through the shell so that all tubes are uniformly heated/cooled.
Furthermore, the individual tubes within the tube reactor or shell-and-tube reactor which is preferably employed have a length of preferably from about 0.5 to 15 m, more preferably from 5 to 15 m and in particular from about 8 to 12 m.
The catalyst preferably remains in the reactor during regeneration. The process of the present invention can also be employed for regenerating zeolite catalysts located in a plurality of reactors connected in parallel or in series or (at least partly) in parallel and in series.
The regeneration of the present invention is carried out at above 120° C., preferably above 350° C. and in particular at from 400° C. to 650° C.
The regeneration gases used are in principle subject to no restrictions as long as the regeneration can be carried out so that the catalyst in the interior of the reactor does not become so hot as a result of, for example, combustion of the organic deposits present thereon that the pore structure of the catalyst and/or the reactor is/are damaged, the formation of explosive gas mixtures is prevented and the regeneration gas comprises hydrogen. The regeneration is preferably carried out so that a hot spot at which the temperature is increased by from 10 to 20° C., preferably not more than 20° C., is formed within the catalyst bed.
In a particularly preferred embodiment, the regeneration gas comprises carbon dioxide or hydrogen or carbon dioxide and hydrogen, in each case possibly in combination with CO. The content of CO
2
and/or hydrogen during the regeneration is from 0.1 to 100% by volume, preferably from 0.5 to 20% by volume and more preferably from 1 to 5% by volume.
The regeneration gas may further comprise other inert gases, e.g. nitrogen, noble gases such as argon or helium, hydrocarbons such as methane or ethane and natural gas.
The zeolite catalysts regenerated in the present process are subject to no particular restrictions.
Zeolites are, as is known, crystalline aluminosilicates having ordered channel and cage structures in which micropores, preferably smaller than about 0.9 nm, are present. The framework of such zeolite
Ba&bgr;ler Peter
Harder Wolfgang
Möller Ulrich
Rehfinger Alwin
Rieber Norbert
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Trinh Ba K.
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