Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
2002-09-05
2004-11-02
Dentz, Bernard (Department: 1625)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
C502S209000
Reexamination Certificate
active
06812351
ABSTRACT:
The present invention relates to a catalyst for preparing maleic anhydride by heterogeneously catalyzed gas-phase oxidation of a hydrocarbon having at least four carbon atoms, which comprises a catalytically active composition comprising vanadium, phosphorus and oxygen and has an essentially hollow cylindrical structure.
The present invention further relates to a process for preparing maleic anhydride by heterogeneously catalyzed gas-phase oxidation of a hydrocarbon having at least four carbon atoms using the catalyst of the present invention.
Maleic anhydride is an important intermediate in the synthesis of &ggr;-butyrolactone, tetrahydrofuran and 1,4-butanediol, which are in turn used as solvents or are further processed to give, for example, polymers such as polytetrahydrofuran or polyvinylpyrrolidone.
The preparation of maleic anhydride by heterogeneously catalyzed gas-phase oxidation of hydrocarbons is generally carried out using pelletized catalysts, i.e. solid cylinders, comprising phosphorus, vanadium and oxygen. Such catalysts are described, for example, in the U.S. Pat. Nos. 5,275,996 and 5,641,722.
In the study on the partial oxidation of n-butane to maleic anhydride over catalysts comprising phosphorus, vanadium and oxygen reported by T. P. Wellauer et al., Chem. Eng. Sci., Vol. 41, No. 4, 1986, pages 765 to 772, it was found that rings having the geometry 8 mm×5 mm×5 mm (external diameter×height×diameter of the internal hole) display an about 65% higher heat removal from the catalyst bed per unit volume compared to the 3 mm×3 mm pellets (diameter×height) customarily used in industry. According to the simulations described, the yield of maleic anhydride can also be increased by 5-7% by use of the 5 mm×8 mm×5 mm rings (“hollow cylinders”) rather than 2.5 mm×2.5 mm pellets (“solid cylinders”).
A number of publications on the preparation of maleic anhydride by heterogeneously catalyzed gas-phase oxidation of hydrocarbons have described the use of catalysts comprising phosphorus, vanadium and oxygen and having an annular (hollow cylindrical) structure. Thus, U.S. Pat. No. 4,713,464 discloses rings having the geometry 5 mm×4 mm×2 mm, EP-A 0 593 646 discloses rings having the geometry 8 mm×8 mm×4 mm, U.S. Pat. No. 4,795,818 discloses rings having the geometry 6.35 mm×3.18 mm×3.18 mm and U.S. Pat. No. 5,296,436 discloses rings having the geometry 4.763 mm×4.763×1.588 mm.
U.S. Pat. No. 4,283,307 describes a catalyst structure comprising vanadium, phosphorus and oxygen and having the shape of a hollow cylinder whose external diameter is from 3.969 to 4.762 mm, whose height is 3.969 to 4.762 mm and whose internal diameter is from 0.888 to 7.925 mm. The diameter of the internal hole of the hollow cylinder is usually from 30 to 50% of the external diameter, with the height and external diameter preferably being equal. In the examples, a hollow cylindrical structure having the geometry 3.969 mm×3.969 mm×1.587 mm is disclosed. Compared to 3.969 mm×3.969 mm pellets having an identical active component, an increase in yield of maleic anhydride of up to 24% relative was obtained when using the hollow cylinders.
U.S. Pat. No. 5,168,090 discloses a catalyst structure for the preparation of maleic anhydride by heterogeneously catalyzed gas-phase oxidation of hydrocarbons which has at least one ordered cavity in the outer surface, a geometric volume V
geo
of from 30 to 67% of the theoretical volume V
overall
which the cavity-free, solid structure of the same external diameter and the same height would have and a ratio of the geometric surface area A
geo
to the geometric volume V
geo
of at least 20 cm
−1
. The hollow cylinders described as a comparative example have a height of 4.76, 4.29 and 4.14 mm, an external diameter of 4.76 mm in each case and an internal diameter of 1.58 mm in each case.
It is an object of the present invention to find a catalyst for the preparation of maleic anhydride by heterogeneously catalyzed gas-phase oxidation of hydrocarbons which is easy to produce, displays a low pressure drop together with sufficiently high mechanical stability and makes possible a high hydrocarbon throughput over the catalyst compared to the catalysts of the prior art and at the same time makes possible a high conversion, a high selectivity, a high yield and therefore a high space-time yield.
We have found that this object is achieved by a catalyst for preparing maleic anhydride by heterogeneously catalyzed gas-phase oxidation of a hydrocarbon having at least four carbon atoms, which comprises a catalytically active composition comprising vanadium, phosphorus and oxygen and has an essentially hollow cylindrical structure, wherein the hollow cylindrical structure has (a) a ratio of the height h to the diameter of the continuous hole d
2
of not more than 1.5 and (b) a ratio of the geometric surface area A
geo
to the geometric volume V
geo
of at least 2 mm
−1
.
For the purposes of the present invention, an essentially hollow cylindrical structure is a structure which essentially comprises a cylinder having a continuous hole going through from one end face to the other. The cylinder has two essentially parallel end faces and an outer curved surface, with the cross section of the cylinder, i.e. parallel to the end faces, being essentially circular. The cross section of the continuous hole, i.e. parallel to the end faces of the cylinder, is likewise essentially circular. The continuous hole is preferably located centrally in the end faces, but other spatial arrangements are not excluded.
The term “essentially” indicates that deviations from the ideal geometry, for example slight deformations of the circular structure, end faces which are not perfectly parallel, chipped corners and edges, surface roughness or notches in the outer curved surface, the end faces or the internal surface of the continuous hole are allowed for in the catalyst of the present invention. Within the accuracy of tableting technology, circular end faces, a circular cross section of the continuous hole, parallel end faces and macroscopically smooth surfaces are preferred.
The essentially hollow cylindrical structure can be described by an external diameter d
1
, a height h as the distance between the two end faces and a diameter of the internal hole (continuous hole) d
2
. The three parameters mentioned are in each case the mean values for the hollow cylinder. This applies particularly in the case of deviations from the ideal geometry.
The catalyst of the present invention has a ratio of the height h to the diameter of the continuous hole d
2
of not more than 1.5. The ratio h/d
2
is preferably from 0.5 to 1.5, particularly preferably from 1.0 to 1.5.
As a further characteristic property, the catalyst has a ratio of the geometric surface area A
geo
to the geometric volume V
geo
of at least 2 mm
−1
. For the purposes of the present invention, the geometric surface area A
geo
is the calculated surface area of all exposed surfaces of the hollow cylinder, including the internal curved surface of the continuous hole, on the basis of the abovementioned parameters d
1
, h and d
2
. The geometric volume V
geo
is the calculated volume of the hollow cylinder on the basis of the abovementioned parameters d
1
, h and d
2
. In the calculation of both quantities, no account is therefore taken of either pores or, for instance, notches or roughness in the exposed surfaces. The ratio A
geo
/V
geo
is preferably from 2 to 3 mm
−1
, particularly preferably from 2 to 2.5 mm
−1
.
In a preferred embodiment, the catalyst of the present invention additionally has a ratio of the geometric volume V
geo
of the hollow cylindrical structure to the theoretical volume V
overall
of a corresponding solid cylinder having the same height h and the same external diameter d
1
of not more than 0.85. Here, the theoretical volume V
overall
of a corresponding solid cylinder having the same height
Storck Sebastian
Tenten Andreas
Weiguny Jens
BASF - Aktiengesellschaft
Dentz Bernard
Keil & Weinkauf
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