Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Inorganic carbon containing
Reexamination Certificate
2002-01-17
2004-09-14
Bell, Mark L. (Department: 1755)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Inorganic carbon containing
C502S300000, C502S439000, C502S523000, C502S527140, C502S527150, C502S527160, C502S527120, C428S116000, C428S373000, C264S639000, C264S642000, C264S670000, C264S681000, C264S682000, C264S683000
Reexamination Certificate
active
06790806
ABSTRACT:
The invention relates to core/jacket catalyst moldings, a process for their preparation, and their use in the catalysis of reactions of organic compounds.
The present invention relates in particular to a ceramic molding having more than one layer and composed of at least two differently composed, concentrically arranged zones, at least one zone being a catalytically active material.
Many chemical reactions use catalysts to improve the yield and space-time yield of the reaction. In most cases, the catalyst here is employed in the form of a molding in a fixed-bed reactor through which the starting materials are then passed. The moldings used are extrudates, beads, tablets or other agglomerates. These moldings have to have at least a certain stability to mechanical loads, otherwise they would break up in the reactor under the conditions of the reaction. This is one reason for the fact that moldings of this type are rarely composed solely of the catalytically active composition, but mostly comprise an additional component for mechanical stabilization, the support. Another task frequently carried out by the support is to ensure the presence of a certain pore structure, which guarantees rapid transport of the starting materials and products into and out of the molding.
There are various processes for preparing catalysts of this type. For example, an existing molding made from support material may be saturated with a solution of the catalytically active composition, or of a precursor thereof. Depending on the interaction between support and saturating solution, this saturation process produces a particular distribution pattern of the active components over the cross section of the molding. In most cases, the control of this distribution pattern through the expansion of the phases is difficult, and the pattern practically always involves gradients of active component concentration along the penetration path of the active-component precursor. The support may also be combined with the active component at an early stage, prior to the molding process. There is generally then no control of a distribution pattern during the process of producing the molding, but what is achieved is homogeneous and uniform distribution of the active component.
Another preparation method is to apply a layer made from active components to a mostly non-porous ceramic support, applying a powder together with a solution or with a suspension to the support molding. Here, it is possible to some extent to produce an active component layer of well-defined thickness. However, a disadvantage of this type of preparation is the low mechanical bond strength between the support and the layer produced from powder. This type of catalyst is therefore used only in specific gas-phase partial oxidation processes. The layers applied are readily released under higher mechanical loads.
The reactions catalyzed produce intermediates or final products which with prolonged residence time in the vicinity of catalytically active centers react further to form undesirable, yield-reducing byproducts, the catalyst molding has to be structured so as to avoid these prolonged residence times. One possibility here is the use of moldings with only a thin layer made from catalytically active material. Methods for establishing this type of layer or distribution pattern have been described above. However, all of these methods have disadvantages. Either the distribution pattern or the layer thickness cannot be established with precision or the layer applied lacks sufficient mechanical stability. In addition, all of the processes for preparing these catalysts are complicated.
It is an object of the present invention to provide a mechanically stable molding whose layer of catalytically active material has a defined thickness on an inert supporting core, and to provide a process for its preparation.
We have found that this object is achieved by way of a core/jacket catalyst molding with a core made from an inorganic support material and with a jacket made from a catalytically active material, capable of preparation by
coextruding an aqueous molding composition which comprises the support material or a precursor thereof, with an aqueous molding composition which comprises the catalytically active material or a precursor thereof,
then drying the coextrudate, and
then calcining the dried coextrudate.
This catalytically active material preferably catalyzes the hydrogenation dehydrogenation, oxidation, isomerization or polymerization, or addition reactions, substitution reactions or elimination reactions of organic substances. The catalytically active material preferably comprises metals or metal compounds of the 5th to 8th transition group of the Periodic Table, of groups IB or IIB, of the lanthanoids, of the elements Sn, Pb, As, Sb, Bi, Se or Te, or a mixture of these.
In particular, we have found that this object is achieved by preparing the molding from two reaction mixtures, by extruding the two mixtures concentrically through a specific coextrusion die (i.e. ideally in the form of a cylinder within a tubular jacket). The composition for the core of the extrudate here will be composed mainly of a support material which is inert in the particular reaction to be catalyzed, and the composition for the outer layer or, respectively, the outer layers will comprise an active component or precursor thereof.
There has to date been no disclosure of ceramic coextruded moldings in the form of a coextrudate in which a thin-walled jacket composed of catalyst material is extruded onto a cylindrical core so as to give a form-fit.
If ceramic powders are to be capable of extrusion to give moldings, additives are fed to the powder in a compounding step and give the molding composition some degree of plasticity, which in turn is a precondition for the molding process which follows. Once the molding process has been completed, the plasticizer should be capable of being removed from the resultant molding leaving very little residue, since the catalytic properties of its jacket layer are impaired by even small proportions of foreign substances. To obtain a dimensionally stable molding, it is also advantageous for binders, or what are known as bridgers, to be added to the molding compositions. These permit the formation of solids bridges during the final calcining process. As an alternative, or in addition, the powder to be extruded may also be peptized by contact with acids or bases, forming reactive groups on the particle surfaces, these groups then giving the molding increased strength in a subsequent annealing step via formation of solids bridges.
The aqueous molding composition which comprises the support material or comprises a precursor thereof preferably comprises a mixture made from
10-30% by weight
of at least one water-soluble binder,
25-50% by weight
of at least one inorganic support material
or precursor thereof,
2-20% by weight
of at least one peptizing agent,
1-5% by weight
of at least one plasticizer,
20-60% by weight
of water,
where the total amount of the ingredients gives 100% by weight.
The aqueous molding composition which comprises the catalytically active material or comprises a precursor thereof preferably comprises a mixture made from
10-30% by weight
of at least one water-soluble binder,
0-20% by weight
of at least one inorganic support material or
precursor thereof,
10-40% by weight
of at least one catalytically active material or of
a precursor thereof
2-20% by weight
of at least one peptizing agent,
1-5% by weight
of at least one plasticizer,
0.5-2% by weight
of at least one lubricant,
20-60% by weight
of water,
where the total amount of the ingredients gives 100% by weight.
The molding compositions used for this preparation process preferably have essentially the same shrinkage behavior on drying.
Support materials which may be used are preferably oxides, hydroxides or carbonates of the elements B, Al, Ga, Si, Ti, Zr, Zn, Mg or Ca, or a mixture of these. Other suitable support materials are activated car
Anderlik Rainer
Fritz Hans-Gerhard
Hammer Jochen
Hesse Michael
BASF - Aktiengesellschaft
Bell Mark L.
Hailey Patricia L.
Keil & Weinkauf
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