Catalyst – solid sorbent – or support therefor: product or process – Zeolite or clay – including gallium analogs – And additional al or si containing component
Reexamination Certificate
1999-10-29
2002-01-08
Griffin, Steven P. (Department: 1754)
Catalyst, solid sorbent, or support therefor: product or process
Zeolite or clay, including gallium analogs
And additional al or si containing component
C502S063000, C502S071000, C502S077000
Reexamination Certificate
active
06337296
ABSTRACT:
The present invention relates to a process for the preparation of catalysts based on MFI-type zeolite prepared in spheroidal form and active in transposition reactions of oximes to amides.
More specifically, the present invention relates to a process for the preparation of catalysts based on MFI-type zeolites, suitable for use in gas phase in fluid-bed and entrained-bed reactors.
The invention also relates to catalysts obtained by the above processes.
Zeolites of the MFI type, in particular those with a high silica/alumina ratio (U.S. Pat. No. 4,359,421) and, more generally, those with a low content of trivalent heteroelements (patent EP 242.960), are known in literature as basic material for the preparation of catalysts which can be used in the transposition reaction of oximes to amides.
Among these reactions, those carried out in gas phase which use solids based on zeolites are of particular importance. For example, the patent EP 234.088 describes a method for the preparation of &egr;-caprolactam which consists in putting cyclohexanonoxime, in gaseous state, in contact with crystalline alumino-silicates having well-defined physico-chemical characteristics and preformed in the form of granules (24-48 mesh).
Although they consist of active component alone, these materials have limited possibilities of being used in industrial reactors; in fact, if fluid-bed or entrained-bed reactors are used for the catalytic process, the catalysts should preferably be in the form of microspheres, with an average diameter of 30-100 &mgr;m and characterized by a high resistance to interparticle attrition and attrition against the walls of the reactors; if, on the other hand, fixed-bed reactors are used, the catalysts should have the typical forms for this technology (speres, tablets, etc.) with dimensions of approximately a few millimeters and characterized by a good mechanical stress resistance.
The cohesion between the individual and submicronic particles of the microcrystalline zeolitic material is generally poor and consequently resistance to attrition and mechanical stress is normally obtained by combining the zeolitic material with compounds of an inorganic nature (ligands) in forming phase.
Catalysts based on zeolites, suitable for use in fluid-bed or entrained-bed reactors and with the characteristics listed above, are widely described in the known art and are mainly used in catalytic cracking processes (FCC catalysts, Fluid Catalytic Cracking).
The forming of the above catalysts, when microspheres with a diameter <100 &mgr;m are required, is usually carried out with the well-known spray-drying technique.
Silicas and aluminum oxides in the colloidal state or silico-aluminates are used as ligands to give the microspheres a higher mechanical resistance to attrition; the quantities of the above ligands in the resulting catalytic compositions is normally less than 30% by weight.
The use of siliceous ligands in spherulization processes of MFI-type zeolitic materials suitable for the transposition reaction of oximes to amides, however, is not widely used as amorphous silica is not completely inactive in the above reactions.
It is known in fact that this compound may significantly jeopardize the selectivity of the zeolitic catalyst and deteriorate the catalytic performance due to the formation of organic pitches.
It has been observed, for example, that silica gels characterized by the presence of hydroxylic groups with a low acidity, have a high activity, low selectivity and rapid formation of pitch in transposition reactions of cyclohexanonoxime to &egr;-caprolactam [Catalysis Letters 17 (1993), 139-140; Catalysis Today 38 (1997), 249-253].
To overcome this problem patent EP 576.295 suggests, for example, preforming the zeolitic material in a spherical form by spray-drying without any addition of ligands and subjecting the microspheres, in a subsequnent process phase, to thermal treatment in water to increase their hardness.
A process has now been found for the preparation of catalysts based on zeolitic materials and siliceous ligands, suitable for use in reactions of oximes to amides, which overcomes the drawbacks of the known art.
In particular, the present invention relates to a process for the preparation of catalysts based on MFI-type zeolitic compounds and siliceous ligands characterized in that submicronic particles of zeolite are incorporated into a ligand obtained by the acid hydrolysis of silicon alkoxide.
The innovative aspect of the invention basically consists in the use of oligomeric species of silica synthesized in an acid medium as ligands of MFI-type zeolitic materials.
The catalysts obtained by the process of the invention have a high resistance to attrition and mechanical stress and an excellent catalytic activity.
In particular, the siliceous ligands used, consisting of oligomeric species of silica synthesized by the acid hydrolysis of silicon alkoxides, overcome the disadvantages deriving from their use in the transposition reaction of oximes to amides, because they do not interact in the reaction itself.
This behaviour is in distinct contrast with that of catalysts containing ligands prepared in an alkaline medium, as described, for example, in U.S. Pat. No. 4,859,785 (hydrolysis of silicon alkoxides with organic bases), or basic solutions of colloidal silicons, known commercially under the trade-name of “Ludox”.
It has also been found that the ligands used in the process of the invention can also be advantageously used in the known forming operations of zeolitic materials into spherical form.
In particular, the ligands of the invention have been used in emulsifying/gelation techniques, which consist in dispersing the submicronic particles of zeolitic material in the acid solution of the siliceous ligand and subjecting the resulting mixture to emulsification and gelation in an organic medium.
With this technique, catalytic compositions are obtained in spherical form and with morphological-granulometric, physico-chemical characteristics and resistance to attrition suitable for use in the transposition reactions of oximes to amides in fluid-bed or entrained-bed reactors.
In particular, the catalytic compositions based on MFI-type zeolite which are obtained, consist of microspheres with an average diameter varying from 20 to 200 &mgr;m and are characterized by a content of siliceous ligand (expressed as SiO
2
) equal to or higher than 30% by weight, an external surface area (A.S.E.) varying from 60 to 80 m
2
/g, a specific volume of the micro and mesopores varying from 0.2 to 0.3 ml/g and 0.1 to 0.4 ml/g respectively, bulk density values ranging from 0.7 to 0.85 g/ml and resistance to attrition, expressed as D.I. (Davison Index) less than or equal to 6.
The above catalysts significantly differ from those known in the art in their high content of siliceous ligand (≧30%), thus confirming the low catalytic activity of the ligand in transposition reactions of oximes to amides.
A further object of the invention consists of a process for the catalytic transposition of oximes to amides characterized in that the reaction is carried out in the presence of the catalysts of the invention.
In particular, the catalysts obtained by the emulsification/gelation technique have morphological-granulometric, physico-chemical characteristics and resistance to attrition suitable for use in transposition reactions of oximes to amides in fluid-bed or entrained-bed reactors.
The emulsification/gelation technique used for forming the catalysts of the present invention comprises in particular the following steps:
preparation of siliceous oligomers by the hydrolysis of silicon alkoxides;
mixing said oligomers with an aqueous or hydroalcohol dispersion of submicronic particles of MFI-type zeolite acidified to pH≦5;
spherulization of the resulting mixture.
In the preparation of the siliceous oligomers, silicon alkoxides are used as silica precursors, such as for example tetra-ethyl-orthosilicate (TEOS). The hydrolysis of these compounds in an aqueous medium catalyzed by acids, as wel
Balducci Luigi
Buzzoni Roberto
Dalloro Leonardo
De Alberti Giordano
Enichem S.p.A.
Griffin Steven P.
Ildebrando Christina
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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