Chemical apparatus and process disinfecting – deodorizing – preser – Chemical reactor – Including solid – extended surface – fluid contact reaction...
Reexamination Certificate
1999-10-27
2003-02-25
Knode, Marian C. (Department: 1764)
Chemical apparatus and process disinfecting, deodorizing, preser
Chemical reactor
Including solid, extended surface, fluid contact reaction...
C422S211000, C422S221000, C422S171000, C422S177000, C422S179000, C422S180000, C422S198000, C502S527110, C502S527180, C502S527190, C502S527240
Reexamination Certificate
active
06524541
ABSTRACT:
Heterogeneously catalyzed pyrolysis reactions, such as the pyrolysis of formylalanine nitrile (FAN) to vinylformamide and prussic acid, are usually carried out on loose beds of catalyst packing elements coated with the catalytically active substance. Such beds of packing elements have the disadvantage of relatively large pressure loss. In spite of identical depths of the catalyst bed, the pressure losses can vary, meaning that, on use of multi-tube reactors, different pressure losses in the individual reaction tubes can arise under certain circumstances. This can result in non-uniform temperature and residence time of the reactants in the individual reaction tubes, which can have an adverse effect on reaction conversion and reaction yield.
It is known that at temperatures >350° C., energy transport due to radiation increases greatly compared with thermal heat conduction in gases, meaning that at these temperatures, a high proportion of heat transfer takes place by radiation. However, beds of packing elements frequently have only low radiation transparency, meaning that a pronounced radial temperature profile can arise in the reaction tube. This problem has only been solved in part by use of substantially radiation-transparent packing elements, for example Hiflow rings. An unequal radial temperature distribution partly arises simply because the radiation intensity decreases with increasing radiation path. Correspondingly, in exothermic reactions, the temperature is the highest in the reactor core and the lowest in the immediate vicinity of the reactor wall, while in endothermic reactions, the reverse temperature conditions arise. However, different temperatures mean different reaction rates, with the consequence that radial concentration profiles of the starting material and product corresponding to the radial temperature profile can occur, which have an adverse effect on the reaction yield.
Reactor material and packing material have different coefficients of thermal expansion. During heating, the reaction tube expands, and the catalyst bed settles in the tube and is partially crushed by the tube during cooling thereof This catalyst fracture results in an increase in pressure loss, with the result that the bed must be changed frequently.
Packing elements of fragile material can, in addition, only be introduced into a water-flooded reactor, which means that filling of the reactor with the catalyst and replacement of the catalyst bed are complex. In the case of supported catalysts doped with water-soluble substances, such as the supported Al
2
O
3
catalysts doped with potassium carbonate that are used for the pyrolysis of formylalanine nitrile, the doping can only take place in the reactor after the reactor has been filled with the catalyst packing elements, with drying being necessary before and after impregnation. This procedure is extremely complex.
It is an object of the present invention to provide catalyst structures (moldings) which do not have the abovementioned disadvantages.
We have found that this object is achieved by a molding (catalyst structure) for chemical apparatuses which is formed from at least two closed frames and one or more cross-pieces connecting these frames, where the frames are arranged at a distance from one another in a single plane or in a plurality of parallel planes about an (imaginary) molding axis which is perpendicular to the plane(s) and passes through the center points of the frames.
The frames can be arranged in a single plane or in a plurality of parallel planes, where a plurality of frames arranged in the same plane are arranged at a distance from one another and one inside the other. In one embodiment, the molding is formed from at least three frames arranged in at least two parallel planes. For example, one plane may have two frames lying one inside the other, with a further plane having only one frame.
Preference is given to a molding for chemical apparatuses which is formed from at least four closed frames and one or more cross-pieces connecting these frames, where the frames are arranged one inside the other at a distance from one another in at least two parallel planes about an (imaginary) molding axis which is perpendicular to the planes and passes through the center points of the frames, and each plane has at least two frames.
Chemical apparatuses are, for example, tubular reactors, tube-bundle reactors, distillation columns or gas scrubbers. The moldings according to the invention can be used therein as catalysts, catalyst supports or packing elements which promote heat and/or mass transfer.
The closed frames, cross-pieces or the entire molding can have a compact, porous or other structure. For example, the frames can be hollow inside. The closed frames can have any desired geometry.
The frames can have a circular geometry. Closed frames having a circular geometry are also referred to as rings. Closed frames having a geometry other than circular are thus structures corresponding to rings which have another geometry instead of circular.
The frames can have a geometry which is delimited exclusively by curved lines. Besides circular geometry, the frames can have, for example, an oval geometry.
The frames can have edges and corners. The frames can have, for example, the geometry of polygons. Polygons are triangles, quadrangles, pentagons, etc.
The frames can have, for example, star-shaped geometry or the geometry of a rosette (wave line closed in a circular manner).
The frames preferably have essentially the extension of the tube cross section, a certain play being necessary during insertion of the molding (catalyst structure) into the reaction tube. Through corresponding choice of the frame geometry, the molding can be matched to the cross section of the reaction tube.
In general, but not necessarily, reaction tubes have a circular cross section. Preferred frame geometries are therefore those whose periphery is delimited by a circle. Preferred frames having a polygonal geometry are therefore those whose corners are on an arc.
Particularly preferred frames have high symmetry. Particularly preferred frames having a polygonal geometry therefore have the geometry of regular polygons. Regular polygons are squares, triangles, pentagons, hexagons, etc., having sides of equal length. Of these, particular reference is given to frames having at least 5 sides.
Particular preference is given to frames having a circular geometry (rings).
In a preferred embodiment of the moldings (catalyst structures) according to the invention, the frames of adjacent planes are not congruent with respect to an (imaginary) parallel shift along the common axis of the frames. The incongruence of the frames counters the formation of laminar flow profiles in the reaction tube and thus promotes mass transfer in the radial direction.
The frames are incongruent, for example, if they have different shapes. Thus, one plane can have hexagonal frames and the plane above or below can have pentagonal or hexagonal frames. The frames are also incongruent if, although having the same geometry and size, they are each oriented differently in the planes. For example, adjacent planes can have frames of regular hexagonal geometry which are rotated by an angle of between 1° and 59° with respect to one another.
The frames are also incongruent if, although having the same geometry and orientation, they have different sizes. In a preferred embodiment of the moldings according to the invention, frames of identical geometry, but decreasing size, with no two frames having the same size, are oriented the same way in each of two planes, but are arranged in the sequence of size alternately in the upper and lower of the two planes. Particular preference is given to an arrangement in which the frames in adjacent planes are arranged on gaps, i.e. the size of the frames differs in such a way that a frame in one plane is arranged above or below the gap formed by the next-largest and next-smallest frame in the plane above or below.
The moldings (catalyst structures) according to the invention ha
BASF - Aktiengesellschaft
Keil & Weinkauf
Knode Marian C.
Ridley Basia
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