Catalyst – solid sorbent – or support therefor: product or process – Zeolite or clay – including gallium analogs – Activating treatment
Reexamination Certificate
1999-05-05
2001-09-11
Griffin, Steven P. (Department: 1754)
Catalyst, solid sorbent, or support therefor: product or process
Zeolite or clay, including gallium analogs
Activating treatment
C502S064000, C502S022000
Reexamination Certificate
active
06288004
ABSTRACT:
The present invention relates to a method for improving the catalytic performances of titanium silicalite having general formula (I) and its use in oxidation processes of organic substrates and the amoximation of carbonyl compounds with hydrogen peroxide.
It is known in literature that zeolite compounds with an MFI structure containing titanium (TS-1) are used as catalysts in direct oxidation reactions with hydrogen peroxide of substrates such as aromatic hydrocarbons (U.S. Pat. No. 4,369,783), olefins (EP-100,119), nitrogenated compounds (secondary amines U.S Pat. No. 4,918,194, ammonia U.S Pat. No. 5,320,819) and in amoximation reactions of carbonyl compounds (U.S Pat. No. 4,794,198, EP-496,385).
It is also known in literature that the catalytic performances of zeolite compounds in reactions with hydrogen peroxide can be effectively improved by subjecting these catalysts to suitable activation treatment.
For example the patent EP-230,949 describes a process for the preparation of epoxides from olefins and hydrogen peroxide which uses, as catalyst, a titanium silicalite treated, before or during the epoxidation reaction, with a neutralizing agent.
Among neutralizing agents the European patent discloses the use of organic derivatives of silicon of the X—Si(R)
3
type or hydrosoluble substances deriving from cations of group I or II with varying basic strength.
This process, however, has various limitations deriving, for example, from the reactivity of the organic compounds of silicon. A washing phase is consequently required after the treatment to remove the excess silanizer from the catalyst which, if it is not quantitative, can cause undesired reactions in the epoxidation phase, with the solvents and products formed in the reaction.
As far as the use of basic substances of cations of group I and II is concerned, a limitation derives from their hydrosolubility, making it necessary for a quantity of water to be present in the reaction solvent, right from the beginning, which completely dissolves them, if the neutralization treatment is carried out during the reaction.
U.S. Pat. No. 4,794,198 discloses an amoximation process of carbonyl compounds, in particular cyclohexanone, to the corresponding oximes which uses a titanium silicalite (TS-1) pretreated with aqueous solutions of hydrogen peroxide and/or in the presence of at least 0.5 equivalents/liter of acids having a pKa≦5 (preferably H
2
SO
4
, HCl, HNO
3
, H
3
PO
4
).
Operating according to this process, however, a relatively low productivity, intended as quantity of oxime produced per hour, per weight unit of titanium, is obtained. The production of oximes with good yields therefore implies the necessity of operating with high contents of catalyst and long reaction times, which is disadvantageous from an economic point of view and with respect to separation and purification treatment of the end-products.
In addition, the catalysts activated with the methods described above are specific for each reaction.
It has now been found, according to the present invention, that the catalytic performances of titanium silicalite (TS-1) in the above reactions can be improved if these catalysts are subjected, before use, to an activation treatment in an aqueous medium with hydrogen peroxide, in the presence of fluoride ions or anionic species containing fluorine.
The higher activity and selectivity of the activated catalyst forms the main advantage of the process of the present invention. This in fact simplifies the recovery operations of the products and recycling of the reagents with positive effects on the economy of the process. In addition, the catalysts activated with the method of the present invention have a general validity for all reactions catalyzed by titanium silicalite (oxidation and amoximation).
In accordance with this, a first objective of the present invention relates to a method for improving the catalytic performances of titanium silicalite having formula (I) by the activation of the catalyst (I) in an aqueous medium with hydrogen peroxide, in the presence of precursors of fluoride ions or anionic species containing fluorine.
A further object of the present invention relates to an oxidation process of organic substrates and an amoximation process of carbonyl compounds with hydrogen peroxide which uses, as catalyst, titanium silicalite having formula (I) activated in an aqueous medium with H
2
O
2
in the presence of precursors of fluoride ions or anionic species containing fluorine.
The catalysts used in the process of the present invention are selected from those having general formula (I):
x
TiO
2
.(1−
x
)SiO
2
(I)
wherein x ranges from 0.0001 to 0.04.
The above titanium silicalites can be prepared according to the method described in U.S. Pat. No. 4,410,501 which also specifies their structural characteristics.
Alternatively these catalysts can be used in the form of microspheres with a high mechanical resistance prepared according to the processes described in U.S. Pat. Nos. 4,954,653 and 4,701,428.
It has been observed in fact that amorphous silica, used as ligand of submicronic particles of TS-1, does not jeopardize the effectiveness of the activation process of the catalyst.
Titanium silicalites in which part of the titanium is substituted by other metals such as boron, aluminum, iron and gallium, can also be used. These substituted titanium silicalites and the methods for their preparation are described in European patent applications 226,257, 226,258 and 266,825.
Examples of precursors of fluoride ions which can be used for the purposes of the present invention are selected from hydrofluoric acid, ammonium fluorides, fluorides of alkaline metals (NaF, KF, LiF, KHF
2
) or of other metals soluble in water such as for example AlF
3
.3H
2
O.
In addition, inorganic fluoroderivatives soluble in water can be used in acid form such as for example fluosilicic acid (H
2
SiF
6
), fluoboric acid (HBF
4
) and hexafluophosphoric acid (HPF
6
), or in salified form for example with NH
4
OH.
Among the fluorinated compounds mentioned above, ammonium derivatives are preferred, as the ammonium ion, optionally present as residue in the catalyst, can be more easily eliminated by thermal treatment at temperatures higher than 400° C. Ammonium fluoride and ammonium bifluoride (NH
4
F, NH
4
HF
2
) are particularly preferred.
In order to control the pH of the reaction medium, the aqueous solutions of the fluorine compounds in acid form can be partially basified using for example NH
4
OH.
The concentration of the fluorinated compound in the reaction medium is defined in relation to the concentration and composition of the titanium silicalite. Expressing the reagents in moles of F and Ti respectively, the molar ratio F/Ti can vary from 0.5 to 3.0. Under the preferred conditions in which NH
4
F or H
4
HF
2
are used, this ratio can range from 1.0 to 2.5.
Hydrogen peroxide in aqueous solution at 30-35% by weight is typically used in the activation reaction. The quantity of hydrogen peroxide is regulated in relation to the concentration of the titanium. Under the preferred conditions the molar ratio H
2
O
2
/Ti is such as to range from 3.0 to 15, preferably from 6 to 12.
The combination of fluorinated compound/H
2
O
2
is fundamental as the activation treatment without one of the two reagents is not very effective. The presence of hydrogen peroxide in the reaction system causes an increase in the solubilization degree of Ti (weight % of Ti removed from the titanium silicalite), whose control is a critical point of the activation process.
It has been observed in fact that, in relation to the chemical composition of the catalyst, the type and concentration of the fluorinated compound and the other reaction conditions (temperature and duration of the treatment), the quantity of Ti solubilized, referring to that originally present in the catalyst, can vary from 1 to 60% by weight.
Following the activation treatment, the UV-Vis spectrum of the TS-1 undergoes a modification, more or less distinct, consisting in the appearan
Bagatin Roberto
Balducci Luigi
Bianchi Daniele
Mantegazza Maria Angela
Ungarelli Raffaele
Enichem S.p.A.
Griffin Steven P.
Ildebrando Christina
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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