Organic compounds -- part of the class 532-570 series – Organic compounds – Cyclopentanohydrophenanthrene ring system wherein two...
Reexamination Certificate
2000-08-28
2003-02-18
Pryor, Alton (Department: 1616)
Organic compounds -- part of the class 532-570 series
Organic compounds
Cyclopentanohydrophenanthrene ring system wherein two...
C552S501000, C423S587000
Reexamination Certificate
active
06521767
ABSTRACT:
The present invention relates to a process for the suspension hydrogenation of anthraquinone compounds in a special reactor for preparing hydrogen peroxide by the anthraquinone process. In the hydrogenation process of the present invention, an anthraquinone compound or a mixture of two or more thereof are brought into contact with a suspension catalyst and a hydrogen-containing gas phase in a special reactor as is comprehensively described in DE-A 196 11 976. This special reactor contains fittings having openings or channels which have a particular hydraulic diameter.
Virtually all the hydrogen peroxide produced worldwide (>2 million metric tons/a) is produced by the anthraquinone process.
The process is based on the catalytic hydrogenation of an anthraquinone compound to form the corresponding anthrahydroquinone compound followed by reaction of the latter with oxygen to form hydrogen peroxide and subsequent isolation of the hydrogen peroxide formed by extraction. The catalysis cycle is closed by renewed hydrogenation of the anthraquinone compound which has been formed again in the oxidation step.
An overview of the principal reactions is given in the scheme below:
In this reaction, the anthraquinone compounds are generally dissolved in a mixture of a plurality of organic solvents. The resulting solution is referred to as the working solution. In the anthraquinone process, this working solution is generally passed continuously through the above-described steps of the process.
An overview of the anthraquinone process is given in Ullmanns Encyclopedia of Industrial Chemistry, 5th Edition, Vol. A13, pp. 447-456.
A particularly important step in the anthraquinone process is the hydrogenation step in which the anthraquinone compound present in the working solution is hydrogenated in the presence of a catalyst to form the corresponding anthrahydroquinone compound.
The present invention relates to this hydrogenation step of the anthraquinone process.
This catalytic hydrogenation can be carried out in suspension or in a fixed bed in various types of reactor. The prior art is detailed, for example, in EP 0 672 617.
In a fixed-bed process, the hydrogen-containing gas phase and the working solution are passed in cocurrent or countercurrent through a reactor which is charged with a supported catalyst coated with noble metal. The catalyst used loses activity over time and therefore has to be regenerated or replaced. For this purpose, the fixed-bed catalyst first has to be removed from the reactor and fresh or regenerated catalyst has to be installed. This is very time-consuming and expensive.
In industry, the hydrogenation step is therefore primarily carried out in the suspension mode since a drop in the activity of the catalyst can be countered by continuous introduction and bleeding-off of the catalyst.
In its most general form, the suspension hydrogenation is carried out in a reactor in which there are present the working solution in which at least one catalyst is suspended and, in addition, a hydrogen-containing gas phase.
The technology of suspension reactors in general is comprehensively described in Ullmanns Enzyklopädie der technischen Chemie, 4th Edition, Volume 3, pp. 494-518.
Some reactors which are used for the suspension hydrogenation of anthraquinone compounds are described in Ullmanns Enzyklopädie der technischen Chemie, 4th Edition, Volume 17, pp. 700-702. These include stirred vessels, bubble columns and moving bed reactors.
As catalysts for the suspension hydrogenation of anthraquinone compounds, use is made of either suspension catalysts or supported suspension catalysts. The latter comprise a metal layer on a support particle. Supported suspension catalysts have the advantage that the particle diameters of from 0.06 to 0.15 mm simplify the recirculation of the catalyst to the reactor compared to unsupported suspension catalysts. In addition, they are generally, in terms of their activity, less sensitive to thermal stresses and poisoning than are pure catalysts.
The suspension hydrogenation of an anthraquinone compound using a loop reactor containing palladium black as catalyst is described in U.S. Pat. No. 4 428 923.
In DE-C 938 252, the hydrogenation of the anthraquinone compound is carried out in a bubble column containing tubular internal fittings in which the introduction of hydrogen into the lower part of each tube leads to upward flow of the working solution in the tubes. The catalyst used is a supported, palladium suspension catalyst (e.g. 2% of Pd on activated aluminum oxide).
The basic problem in suspension reactions is to ensure sufficient contact of the reactants with the catalyst particles which are suspended in the liquid phase.
Suspension reactors require the introduction of mechanical energy, which is, for example, introduced by means of stirrers, nozzles or rising gas bubbles, to suspend the solid particles. Increasing this mechanical energy input above that required for suspension leads, however, to no appreciable improvement in the mass transfer between the liquid and the suspended solid particles since the achievable relative velocity exceeds the sedimentation velocity only insignificantly.
A decisive factor for economical operation of an anthraquinone process is a high space-time yield in the hydrogenation step.
The space-time yield is the amount of product formed per unit catalyst volume and per unit time.
Using the reactors which have hitherto been used according to the prior art for the suspension hydrogenation of anthraquinone compounds for preparing hydrogen peroxide it has not always been possible to achieve sufficiently high space-time yields.
It is an object of the present invention to provide a process for the suspension hydrogenation of an anthraquinone compound using a reactor which has hitherto not yet been used for this hydrogenation.
We have found that this object is achieved by the process described in the claims. In this process for carrying out the suspension hydrogenation of an anthraquinone compound or a mixture of two or more thereof in a reactor in which there is present the working solution in which at least one catalyst is suspended and, in addition, a hydrogen-containing gas phase, the working solution and the gas phase are, in the reactor, passed at least partly, i.e. part of their volume for part of their path, through a fitting having openings or channels whose hydraulic diameter is from 0.5 to 20 mm, preferably from 1 to 10 mm, particularly preferably from 1 to 3 mm. The hydraulic diameter is defined as the ratio of 4 times the cross section of the opening and its circumference.
The choice of the channel width which is ideal in an individual case depends primarily on the viscosity of the liquid passed through, the size of the suspended particles and the type of gas phase. The more viscous the liquid, the greater the channel widths have to be. For liquids having dynamic viscosities of from 10×10
−5
to 200×10
−5
standard s/m
2
, hydraulic diameters in the range from 1 to 4.5 mm are optimal.
In this way, higher space-time yields are obtained than in conventional reactors for the suspension hydrogenation of anthraquinone compounds.
For the purposes of the present process, the hydrogenation step is generally carried out at from about 20 to 120° C., preferably from about 30 to 80° C. The pressures employed are generally from about 1 to 20 bar, preferably from about 2 to 10 bar.
The hydrogenation can be carried out using either pure hydrogen or a hydrogen-containing gas.
The hydrogenation is generally carried out to a conversion of from about 50 to 70% in order to achieve a higher selectivity of, in general, >90%, preferably >95%.
The term “anthraquinone compound” includes, in principle, all anthraquinone compounds and the corresponding tetrahydroanthraquinone compounds which can be used for the anthraquinone process for preparing hydrogen peroxide. Anthraquinone compounds which are preferably used for the process of the present invention are 2-alkylanthraquionone such as 2-ethyl-, 2-tert-butyl
Böttcher Arnd
Bröcker Franz Josef
Henkelmann Jochem
Kaibel Gerd
Rütter Heinz
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