Catalyst – solid sorbent – or support therefor: product or process – Zeolite or clay – including gallium analogs – Activating treatment
Reexamination Certificate
2000-11-15
2003-11-11
Dunn, Tom (Department: 1725)
Catalyst, solid sorbent, or support therefor: product or process
Zeolite or clay, including gallium analogs
Activating treatment
C502S064000, C502S071000, C502S077000, C423S702000, C423S705000, C423S713000
Reexamination Certificate
active
06645899
ABSTRACT:
The present invention relates to a method for the removal of the templating agent from synthetic zeolites in general, and in particular from silicalite-1 (S-1) and titanium silicalite-1 (TS-1), and from composite materials containing zeolite.
More specifically, the present invention relates to a method for the removal of the templating agent from synthetic zeolites and for their activation as catalysts, which consists in treating the above materials with solvents, in vapor phase and at a low temperature.
The invention also relates to the materials obtained by means of the above processes and to the catalytic processes in which they are used as catalysts.
Zeolites and zeolitic materials are known in literature as basic components for the preparation of catalysts which can be used in numerous reactions of industrial interest.
For example, zeolites of the MFI type with a low content of trivalent hetero-elements, are known in literature as basic material for the preparation of catalysts which can be used in the transposition reaction of oximes to amides (EP 242,960).
Titanium-Silicalites TS-1 are known as materials for the preparation of catalysts which are used in many oxidation reactions among which ammoximation reactions (U.S. Pat. Nos. 4,410,501; 4,794,198).
Beta zeolites are known as materials for the preparation of catalysts which are used in alkylation reactions (EP 687,500).
ZSM-12 zeolites are used in various acid catalysis reactions among which transalkylation reactions of aromatics (U.S. Pat. No. 5,347,061).
Synthetic zeolites are generally prepared by reacting a silicon compound, such as tetra-alkyl-orthosilicate or an inorganic silica source, optionally mixed with another suitable alkoxide of an element different from silicon or a corresponding inorganic compound, in the presence of an organic templating agent, such as a tetra-alkylammonium hydroxide; the reaction mixture may also contain an inorganic base, such as sodium hydroxide.
The reaction mixture is subjected to hydrothermal synthesis in an autoclave at high temperatures until zeolite crystals are formed.
The crystals are then separated from the mother liquor, washed with water and dried.
The zeolite thus obtained contains the organic templating agent which is trapped inside the pores of the zeolite itself.
The zeolites prepared in the presence of an organic templating agent are initially inactive as catalysts.
It is believed that the lack of catalytic activity is due to the presence of the molecules of organic templating agent adsorbed on the internal and external surface of the zeolite.
The removal of the templating agent and consequent activation of the zeolite for use as catalyst generally take place at high temperatures, by calcining the crystals in air, at 550° C., for times ranging from 0.25 to 72 h (U.S. Pat. No. 4,410,501).
It is known however that this method can cause degradation of the crystalline structure or induce more or less marked surface modifications in relation to the different stability of the various types of zeolites.
This leads to the importance of developing alternative methods for removing the templating agent, using lower temperatures.
With these objectives, the U.S. Pat. No. 5,425,934, for example, describes a method for the dealumination and selective removal of organic templating agents from synthetic zeolites. The method consists in the treatment of a zeolite characterized by a ratio SiO
2
/Al
2
O
3
of at least 7:1, with an alcohol (methanol) and an acid (hydrochloric acid), in liquid phase and at a low temperature.
Operating according to the method of U.S. Pat. No. 5,425,934, however, a partial, even if selective, removal of the templating agent is obtained, from a particular group of pores of the zeolitic structure and, moreover, no information is provided as to the catalytic activity of the zeolites obtained by means of this process.
U.S. Pat. No. 5,681,789 discloses a method for the activation of zeolites, containing titanium, which are used as catalysts. In particular, the method consists in treating the zeolites with ozone, at low temperatures and for a time sufficient to reduce the quantity of organic templating agent contained therein.
The zeolites obtained by means of this process, although having catalytic capacities comparable to those obtained by calcination, still contain a substantial quantity of organic templating agent.
A method has now been found which allows the templating agent to be effectively removed from synthetic zeolites and at the same time obtaining materials with catalytic properties similar or improved with respect to those typical of a zeolite prepared according to the methods described in the known art.
In particular, an object of the present invention relates to a process for the removal of the templating agent from synthetic zeolites and for their activation as catalysts, characterized in that the zeolites are preheated to the treatment temperature in a stream of nitrogen and treated in vapor phase with methanol, methyl esters or methyl halides, optionally diluted with another inert solvent, for example toluene, at molar concentrations ranging from 20 to 100%, at temperatures ranging from 250° to 380° C., preferably at atmospheric pressure, obtaining a contact time ranging from 0.1 to 5 s and prolonging the treatment for a time ranging from 0.25 to 72 hours. The contact time refers to the time necessary for the reaction mixture in vapor phase to pass through the catalyst in the reactor.
Reagents for the treatment which can be used are methanol, methyl esters or methyl halides. Among methyl esters, those of acids with up to 4 carbon atoms are particularly suitable; preferred are dimethyl carbonate, methyl acetate and methyl formiate. Among the methyl halides, methyl iodide is preferred.
At the end of the treatment the catalyst is flushed with nitrogen.
The treatment can be carried out in a fixed bed or fluid bed reactor.
All synthetic zeolites can be treated with the process of the invention, in particular the group of porous zeolites of the MFI, MTW and BEA type, in which a portion of silicon atoms of the crystalline structure can be substituted by aluminum atoms or another trivalent element, titanium or another tetravalent element, or vanadium and which contain an organic templating agent in the pores of their structure.
In particular the zeolites which can be conveniently treated with the method of the invention comprise the group of microporous crystalline silicates which contain only silicon and oxygen or also, optionally, at least either titanium or aluminum, in their lattice.
The zeolites from which the templating agent can be removed by means of the method of the present invention can generally be obtained by hydrothermal synthesis in which compounds based on silicon and, optionally, Titanium or Aluminum (all for example in the form of alkoxides or oxides) are reacted at reasonably high temperatures for periods ranging from a few hours to several days in the presence of a base or quaternary ammonium salt, which acts as organic templating agent, and optionally an inorganic base.
Particularly preferred are synthesis zeolites commonly defined as: Silicalite (S-1), having a structure of the MFI type and described in patent EP 242,960, Titanium-Silicalite (TS-1), having a structure of the MFI type and described in U.S. Pat. Nos. 4,410,501 and 4,794,198, Beta Zeolite, having a structure of the BEA type and described in patent EP 687,500, ZSM-5 Zeolite, having a structure of the MFI type and described in U.S. Pat. Nos. 3,702,886 and 5,705,726, ZSM-12 Zeolite, having a structure of the MTW type and described in U.S. Pat. No. 3,832,449.
In addition they contain the organic templating agent used for their synthesis.
The templating agent can be any organic compound capable of directing the construction of the zeolitic structure; as is known in the art, the pore dimension, the structure of the channels and, basically, the arrangement of the atoms in the lattice of the zeolites are influenced by the type, dimension and structure of the templating agen
Buzzoni Roberto
Cesana Alberto
Dalloro Leonardo
Genoni Fausto
Palmery Stefano
Dunn Tom
Enichem S.p.A.
Ildebrando Christina
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