FR2629443A1 - Zeolites of MFI structure based on silica and titanium oxide, catalysts containing them and process for the manufacture of the latter - Google Patents

Abstract

The present invention relates to a zeolite of MFI structure based on silicon oxide and titanium oxide, and to the process for the manufacture of this compound. The zeolite of the invention has the formula: (Si96-xTix)O192 in which x is between 0.1 and 6. It is obtained by crystallisation, in aqueous medium and in the presence of fluoride anion, of a reaction mixture containing a source of titanium oxide and a source of silicon oxide. The zeolite of the invention is especially useful as a catalyst for the conversion of organic compounds.

Description

 the present invention relates to editions based on silica and titanium oxide.

It relates more particularly to structure zeolites
MFI, and a method of synthesizing them.

 Zeolites are crystallized tectosilicates. The structures are constituted by assemblies of T 'tetrahedrons forming a three-dimensional framework by the pooling of oxygen. In aluminosilicate zeolites which are the most common, T represents tetravalent silicon as well as trivalent aluminum. cavities and channels of molecular dimensions of this framework accommodate cations offsetting the charge deficit related to the presence of trivalent aluminum in tetrahedra. Some rare zeolites are also known where silicon is replaced by tetravalent germanium. Similarly trivalent elements such as gallium and more rarely boron or beryllium can substitute for aluminum.

 In general, the composition of the zeolites can be represented by the empirical formula M2 / nO; Y2O3; XZO2 in the dehydrated and calcined state. Z and Y respectively represent the tetravalent and trivalent elements of the TO4 tetrahedra; ; M represents an electropositive element of valence n such as an alkaline or alkaline earth metal and constituting the compensation cations; x can vary from 2 to theoretically the infinite in which case the zeolite is a crystallized silica.

 Each type of zeolite has a distinct porous structure.

The variation in pore sizes and shapes from one type to another results in changes in the adsorbent properties. Only molecules with certain dimensions and shapes are able to enter the pores of a particular zeolite. Because of these remarkable characteristics zeolites are particularly suitable for the purification or separation of gaseous or liquid mixtures such as selective adsorption hydrocarbon separation.

 The chemical composition with, in particular, the nature of the elements present in the TO4 tetrahedra and the nature of the exchangeable compensation cations, is also an important factor intervening in the selectivity of the adsorption and especially in the catalytic properties of these products. They are used as catalysts or catalyst supports in the cracking, reforming and modification of hydrocarbons as well as in the preparation of many molecules.

 Many zeolites exist in nature: they are aluminosilicates whose availability and properties do not always meet the requirements of industrial applications. As a result, the search for products with novel properties has led to the synthesis of a wide variety of zeolites essentially of the aluminosilicate type. Among the numerous examples of this type, mention may be made of: meditation A (US Pat. No. 2,882,243), zeclite X (US Pat. No. 2,882,244), zeolite Y (US Pat. No. 3,313,0007), zeolite L (French Patent No. 1224154). , zeolite T (French patent N 1223775), zeolite ZSM5 (US Patent No. 3702886), zeolite ZSM12 (US Patent No. 3832444), zeolite ZSM48 (European Patent No. 0015132).

 Titanium-containing zeolites have also been proposed in TO4 tetrahedra. By way of illustration, mention may be made of French patents N 2 471 950, European N 104 107, 100 119 and US Pat. No. 3,329,481. However, the binding of titanium in a crystalline system is rather of the octahedral rather than the tetrahedral type. substitution of silicon with titanium in the structure of a zeolite is very difficult to obtain in aluminosilicates.

 The zeolites are generally obtained from a reaction mixture which is converted, in a hydrothermal medium, by a dissclutin-recrystallization process, the crystalline precipitate being, after separation and drying, calcined to give an active zeolite.

 The reaction mixture contains reagents capable of supplying the elements T to be incorporated into the framework of the zeolite, these reagents are generally aqueous gels containing oxides or hydroxides of the T elements.

 It also contains a mobilizer promoting the dissolution of these reagents and the transfer from the aqueous phase of crystals of edits in formation, and a structuring agent allows tact, by its incorporation, the formation of microporous spaces and a stabilization of zeclite.

 As a mobilizer, the hydroxide ions are used. Thus, the reaction media generally have a pH greater than 10 in order firstly to dissolve the silica sources and the other sources of the T elements, and secondly to facilitate the transfer of the soluble species to the developing educt. training.

 Zeolites containing easily soluble species in a basic medium, such as, for example, aluminum, are very well synthesized by this method.

 However, it appears very difficult to incorporate titanium into the TO4 tetrahedra of the zeolite framework when the reaction medium is basic.

 Moreover, in a basic medium, the metastable zeolites can only be obtained if the reaction medium is supersaturated with active species. This results in rapid nucleation - leading to zeolite crystals of small size, without the possibility of easy control of the size of these crystals.

In addition, synthetic processes using basic reaction mixtures require the use of alkali and alkaline earth cations as a compensating cation. These cations often have to be removed subsequently because they affect the catalytic and adsorptive properties of the zeolite. This elimination is generally carried out by repeated exchanges of ions with NH 4 + cations. The zeolite containing the ammonium cations is then calcined to eliminate them in the form of
NH3.

 The aim of the invention is, in particular, to remedy these inconveniences by proposing a zeolite of the pentasil family similar to zeolites of the MFI type based on silica and titanium oxide, and a process for synthesizing this type of zeolite. it is produced from neutral or acidic reaction mixtures which make it possible, in particular, to incorporate titanium in the framework of the zeolite in a large proportion as well as zeolite crystals of totally controlled dimensions. This zeolite may hereafter be called titanozeosilite.

dans laquelle:
x est compris entre 0,1 et 6 environ.To this end, the subject of the invention is a zeclite of MFI structure containing silica and titanium oxide and having, after calcination, the following formula:

in which:
x is from about 0.1 to about 6.

 the zeolite of the invention has a monoclinic crystalline system and an X-ray diffraction pattern defined in Table I.

 In this table, the extreme values of the different equi-lattice distances dhkl are given and corresponding to the titanium limit concentrations incorporated into the framework of the zeolite, or more precisely to the Ti / Si ratio.

 In fact, the identification of the zeolites of the invention with an MFI structure can be especially and advantageously carried out by establishing their x-ray diffraction pattern.

 This diffraction pattern can be obtained using a diffractometer using the conventional powder method with copper Kdu radiation. From the position of the diffraction peaks represented by the angle 2 #, we calculate, by the Drags relation, the characteristic dhk.l reticular equi-distances of the sample. The estimation of the measurement error # (dhkl) on dhkl is calculated, according to the absolute error b (29) assigned to the measurement of 2 #, by the Bragg relation.An absolute error # (2 # ) equal to # 0.20 is currently accepted. The relative intensity I / Io assigned to each dhkl value is estimated from the height of the corresponding diffraction peak. A scale of symbols is often used to characterize this intensity: FF = very low, F = fcrt, mF = medium to high, m = average, mf = medium to low, f = low, ff = very low.

TABLE I
x-ray diffraction pattern
Extreme values I / Io Extreme values I / Io
dhkl (nm) dhkl (nm)
1,110-1,128 F-FF 0.3785-0.3845 mF
0.991-1.012 F-FF 0.3735-0.3795 m
0.972-0.986 f 0.3715-0.3775 m
0.895-0.906 ff 0.3705-0.3765 m
0,803-0,813 ff 0,3645-0,3700 f
0.741-0.753 ff (large) 0.3610-0.3670 f
0.704-0.715 ff (broad) 0.3470-0.3525 ff
0.666-0.678 f 0.3430-0.3485 f (f)
0.632-0.643 f 0.3415-0.3470 f (f)
0.595-0.605 mf 0.3385-0.3439 ff
0.589-0.598 f 0.3341-0.3394 f (f)
0.568-0.577 mf 0.3290-0.3345 f (broad)
0.565-0.574 f (shoulder) 0.3240-0.3292 f
0.555-0.564 f 0.3045-0.3099 f (f)
0.534-0.543 f 0.33020-0.3068 f
0.531-0.539 f (f) 0.2978-0.3026 f
0.510-0.518 ff 0.2952-0.2999 ff (shoulder)
0.302-0.808 ff 0.2944-0.2991 f
0.496-0.504 mf 0.2914-0.2961 ff
0.485-0.493 ff 0.2852-0.2898 ff (large)
0.468-0.476 ff 0.2774-0.2818 ff
0.459-0.466 f 0.2722-0.2766 ff (large)
0.444-0.451 f 0.2676-0.2720 ff
0.433-0.441 f 0.2606-0.2548 ff
0.423-0.431 f 0.2586-0.2627 ff
0.4055-0.4125 ff 0.2844-0.2383 ff (large)
0.3986-0.4045 f 0.2508-0.2548 ff
0.3835-0.3905 F 0.2478-0.2518 f
0.3805-0.3865 mF
According to another characteristic of the invention, the educt contains fluorine, the concentration of fluorine is advantageously between 0.01 and 0.8% by weight after calcination.

 However, the fluorine can be removed without changing the structure of the zeolite according to the invention.

The invention also relates to a process for synthesizing a zeolite according to the invention, this method comprises
(i) preparing a reaction mixture in an aqueous medium
containing at least one source of silicon oxide, a
source of titanium oxide, fluoride ions, and a
structuring agent, the pF. of this reaction mixture being
between about 1.5 and about 10.5,
(ii) the crystallization of this reaction mixture and the
recovery of the crystalline precipitate, and
(iii) calcining it at a higher temperature
at 450 C.

The X-ray diffraction pattern given in the table
I is that of a zeolite subjected to calcination as indicated above.

 The use of fluoride ions in the reaction medium, which act as a mobilizing agent, makes it possible to solubilize the T (Si and Ti) species in a medium having a pH of less than 10. Thus, it is possible to NH4 + ions can be used as compensation cations, which can be completely removed, if desired, during calcination.

 In addition, the crystallization taking place in a medium at pH below 10, the nucleation rate is slower. Thus, it is possible to obtain crystals of zeolites controlled by controlling the nucleation rate.

 the molar ratios between the different species in the reaction medium are included for Ti / Si between about 1.3 to about 0.002, F / Si between about 10 and about 0.04, H2c / Si between about 400 and about 4 and for about structuring agent with respect to the silicon species between about 2 and about 0.02.

 Advantageously, the molar ratio Ti / Si is between 1 and 0.01, F / Si between E and 0.05, H, Q / Si between Li0 and 6 and between the structering agent and the silicon species between 1 and 0.04.

 Many sources of silica can be used. By way of example, mention may be made of silicas in the form of hydrogels, aerogels, colloidal suspensions, silicas resulting from precipitation from solutions of soluble silicates or hydrolysis of silicic esters such as Si (OC2H5) 4 or complexes such as Na2SiF5, silicas prepared by extraction and activation treatments of natural or synthetic crystalline compounds such as aluminum silicates, aluminosilicates, clays. It is also possible to use hydrolysable tetravalent silicon compounds such as silicon halides.

 Among the sources of titanium oxide, mention may be made, for example, of crystallized or amorphous titanium oxides and hydroxides, the tetraflent titanium compounds being capable of being hydrolyzed, such as the halides (TiCl 4), the alcoholates, the soluble salts of titanium such TiOSO4, (NH4) 2 TiO (c2o4) 2.

 It is also possible to use as sources of silica or of titanium oxide, compounds comprising the elements Si and Ti such as, for example, glasses or gels based on the oxides of these two elements.

 The sources of silica and titanium oxide can be engaged in soluble form or pulverulent solids but also in the form of agglomerates such as, for example, pellets, extruded can be converted into zeolite of desired structure without changing shape.

The fluoride anions can be introduced in the form of hydrofluoric acid, of salts such as, for example, NHJF, NH4HF2,
NH (C3H7) 3F, N (C3H7) 4F, hydrolysable compounds releasing fluoride anions in the reaction medium, such as, for example SiF4, (NH4) 2SiF6, (NH4) 2Ti F6 or the like.

 Ammonium fluoride or acidic ammonium fluoride are preferred salts. Indeed these salts are very soluble and bring no undesirable element and; in addition, they are easily removable in f-n crystallization.

Suitable structuring agents for the invention - amines of formula I

in which
R1, R1, R3, identical or different, represent a group
allyl, preferably a propyl or butyl group.

quaternary ammonium compounds of formula II

in which
R1, R2, R3, R4, which are identical or different, represent
alkyl groups, preferably propyl groups or
butyl.

compounds of formulas T and II in which nitrogen has
been replaced by a phosphorus atom.

 According to a preferred feature of the invention, the structuring agents are tripropylamine or compounds which can provide tetrapropylammonium cations.

 Advantageously, the structuring agent is added to the reaction mixture in the form of a salt of an amine or of a quaternary ammonium providing the abovementioned cations.

 According to another characteristic of the invention, the reaction mixture may comprise a co-mobilizing agent of tetravalent titanium in a molar ratio with respect to silicon of between 3 and 0.01 and advantageously between 2 and 0.04.

 Suitable co-mobilizing agents for the invention are, for example, oxalic acid and its salts, acetylacetene, tartaric acid and its salts.

 The crystallization of the zeolite can be obtained by heating the reaction mixture at a temperature of between about 50 ° C. and about 240 ° C., preferably between 75 ° C. and 225 ° C. for the time required for crystallization, according to a standard procedure. zeolite synthesis and known to those skilled in the art. As an indication, the heating time can be between 6 hours and 500 hours.

 This heating and crystallization are preferably carried out in a vessel or autoclave coated with a layer such as, for example, polytetrafluoroethane.

 The reaction mixture can be stirred or not.

 After crystallization, the precipitate obtained is collected, for example, by filtration.

 This precipitate is then heated after a possible drying, at a temperature above 4500C, preferably above 5000C, in order to decompose by calcination or thermal decomposition the organic species contained in the precipitate, such as, for example, the structuring agent, the compensation cations (NH4,).

 The titanozeosilites of the invention are selective adsorbents.

These compounds also have the important characteristic of possessing catalytic properties which allow their use as catalyst or catalyst support for reaction reactions of various organic compounds such as, for example:
Alkylation of hydrocarbons such as benzene and toluene, isomerization of paraffins and naphthenes, conversion of ethers or alcohols to hydrocarbons, oxidation, disproportionation of aromatic compounds such as toluene, reforming, cracking and hydrocracking, polymerization of acetylenic compounds, hydrogenation and dehydrogenation of hydrocarbons, dehydration of aliphatic compounds, conversion of aliphatic carbonyl compounds or olefins, ethanation.

The subject of the invention is also a crystalline product of the zeolite type with a MFI structure based on silica and on titanium oxide obtainable by the process comprising
(i) preparing a reaction mixture in an aqueous medium
containing at least one source of silica, a source
of titanium oxide, fluoride ions and an agent
structuring, the pH of the reaction mixture being understood
between about 1.5 and 1.5.

(ii) crystallization of the reaction mixture and
recovery of the crystalline precipitate.

 The molar ratios of the different species in the reaction medium are those indicated above.

 The crystalline precipitate is advantageously washed to remove impurities and especially cations or anions not hooked or incorporated into the structure.

 This manipulable product is in particular and mainly used for the production of MFT type zeolite by calcination under appropriate conditions and determined according to the desired use of the zeolite.

 Other objects, features and details of the invention will appear more clearly in view of the following examples given solely for information and illustrative purposes.

Example 1
13.8 g of Tio @ type anatase are dissolved in 51.8 g of an aqueous solution containing 50% HF. This solution is added 12.5 g of silica Aerosil (SiO2). After mixing, a second solution obtained by dissolving 27.8 g of tetrapropylammonium bromide (TPABr) in 44.5 g of water is added and the mixture is stirred. An aqueous ammonia solution is then added with stirring until the FH is between 6 and 6.5. This gives a homogeneous gel to which is added 0.25 g of a zeolite MFI structure as crystallization seeds.

the molar ratios in the reaction mixture are
Ti / Si = 0.83; F / Si = 6.2; TPA + / Si = 0.5; NH4 + / Si = 3.3
H2O / Si = 28.

the reaction mixture is transferred to an autoclave wrapped with polytetrafluoroethane and heated for 2 days at 170 ° C.
After filtration, washing with hot water and drying, 8.3 g of pure MFI type zeolite, or titanozeosilite identified by the X-ray diffraction pattern, are obtained on the calcined product.

The values measured for dhkl and I / Io are in accordance with the values in Table I.

 The talc of the crystals is between 0.5 and 5 m. After calcination at 550 ° C. for 4 hours, the chemical analysis of the product obtained gives an Si / Ti ratio of 26, an F content of 0.14%.

Example 2
12.5 g of Si (OC 2 H 5) 4 and then 3 × 10 6 of Ti (OC 4 H 9) 4 in a solution containing 32.4 g of water, 4 g of TPA-Br and 1.1 g are poured slowly with vigorous stirring. of NH4F. 0.072 g of crystals of MFI structure are added as seeds. the pH is 7.5.

The molar composition of the gel thus obtained is characterized by the following molar ratios
Ti / Si = 0.25; F / Si = 0.5; TPA + / Si = 0.25; NH4 / Si = 0.5
H2O / Si = 30.

This gel is heated in an autoclave coated with polytetrafluoroethane (PTFE) for 5 days at 200 ° C. The pH of the medium at the opening of the autoclave is 8.3. After separation and washing with hot water, 4.9 g of solid are obtained whose raciocristalographic analysis reveals that it is essentially zeolite of the type
MFI with a crystalline impurity of the anatase type. Polarizing microscope examination also shows the presence of amorphous material.

Example 3
A mixed gel containing the Si and Ti elements is prepared, producing a mixture containing 0.1 mol of Si (OC 2 H 5) 4 and 0.00125 mol of Ti (OC 4 H 9) 4 to which 2 of acetonyl acetone, 2 g of n butanol and 150 g of water. the mixture, heated at reflux for 3 hours, is converted into a colloidal suspension which is then evaporated and dried at 80 ° C. 6.2 g of a mixed gel (SiO.sub.2, TiO.sub.2) are thus obtained with a Si / Ti molar ratio = 80.

The 1.85 g of the above mixed gel is dispersed with 0.040 g of MFT-type zeolite (seeds) in an aqueous solution containing 0.54 g of TPA-Br, 0.11 g of NH4F and 16.2 g of water. The reaction mixture, yes to the following molar composition, is reduced to 1 mol of SiO 2
1 Sio2; 0.0125 TiO2; 0.08 TPA-Br; 0.1 NH4F; H 2 O is heated for 4 days at 200 ° C., the crystallized solid is separated by filtration, washed and dried and then calcined for 3 hours at 550 ° C.

 X-ray crystallographic analysis shows that it is a zeclite of the pure MFI type with an X-ray diffraction pattern in accordance with that of Table T. The chemical analysis gives a Si / Ti = 95 molar ratio.

Examples 4
Four identical reaction mixtures are carried out according to the following wedding ceremony
2.72 g of Ti (OC 4 H 9) 4 are hydrolyzed in 20 ml of water, stirring this mixture for 6 hours. The precipitate is obtained and filtered and then dissolved in 20 ml of water in the presence of 2.02 g of oxalic acid (C 2 H 2 O 4). To this solution of titanium oxalate is added a solution containing 5.33 g of tetrapropylammonium bromide (TPA-Br), 1.48 g of ammonium fluoride (NH4F) and 23.2 g of water.

After mixing, 4.8 g of silica are dispersed in the solution.
Aercsil 130. The molar composition reduced to one mole of silica of the reaction mixture is as follows
1 Sio2; 0.1 TiO2; 0.2 C 2 H 2 O 4; 0.25 TPA-Br; 0.5 NH4F; H2o.

 The four reaction mixtures are then crystallized at 200 ° C. in autoclaves coated internally with PTFE according to the procedures given in Table II.

Table II - operating conditions
Test Germs (1) Agitation Duration Phases obtained
4a O e not 2 days 35% eeolite type MFT 65%
amorphous and impurities
4b 2% no 1 day 75% """+ 25%
amorphous and impurities
4c 2% no 2 days> 90b zeolite type MFT
4d 2% -year 1 day> 90 8 "" MFT (1) Germs consist of a type MFI zeolite.

The quantity added is indicated in% by weight relative to
the weight of silica involved.

After crystallization, the solid phases are separated by filtration, washed with water and dried at 40 ° C. After calcination at 550 ° C. for 4 hours, the solid phases are identified by their X-ray diffraction spectrum. It can be seen that the formation of zeolites of the MFI type (titanozeosilite) is faster in the presence of germs and in agitated medium. The chemical analysis carried out on the product of Example 4c gives an area ratio
Si / Ti overall of 25. The estimate of the Si / Ti molar ratio in the zeolite framework can be made from the measurement of these relative displacements of the diffraction peaks. We then find a value equal to about 60.

 The X-ray diffraction pattern of the zeolite obtained in Example 4c is shown in Table IV.

Examples 5
The 7 tests of Example 5 show that the crystallization of the MFI type zeolite (titanozeosilite) as well as the incorporation of the Ti element into the framework of the zeolite can be controlled by varying the amounts of mobilizer (F- ) and Ti-specific mobilizer (oxalic acid) They were made with reaction mixtures similar to those used in Example 4. In the Eh to 5f tests, the use of lower amounts of oxalic acid and that the absence of oxalic acid in the Eg test results in incomplete dissolution of the precipitate obtained after hydrolysis of Ti (OC 4 H 9) 4. They all contain 2% of crystallization seeds. The molar compositions reduced to one mole of silica thus killing the pH are shown in Table III.

Table III n Sio2 Tio2 TPA-Br NH4F C2H2o4 H2o Initial pH Final pH Si / Ti estimated 52 1 0, 0.08 0.5 0.2 30 4 7 75 5b 1 0.1 0.08 0.3 0, 1 0.05 0.25 0.05 30 6 6 50 5d 1 0.1 0.08 0.1 0.1 30 3 5 45 5e 1 0.1 0.08 0 , 1 0.05 30 4 5.5 80 5f 1 0.1 0.08 0 0.05 30 1.5 3.5 amorphous 5g 1 0.1 0.08 0 0 30 6 6 amorphous
The 7 reaction mixtures were heated for 4 days at 2000C in unstirred autoclaves and lined with PTFE.

After filtration, washing and drying, the solids were calcined for 4 hours in an open crucible.

 Radiocrystallographic examination of the 7 samples shows that, with the exception of the products 5f and g, well crystallized MFT (titanozeosilite) type zeolites which may contain some impurities have been obtained.

 The estimation of the Si / Ti ratio (last column of Table III) was made from the measurement of the relative displacement of the diffraction peaks.

 Examination of these results leads to several conclusions. On the one hand, the presence of the mobilizer (F-) is necessary to obtain the crystallization. On the other hand, the Si / T ratio can be modified by varying the amounts of mobilizer (F-) and co-mobilizer (COOH) 2 involved. Too large or too small quantities of these last two constituents are less favorable to the incorporation of the element Ti in the framework of the zeolite.

Example 5
Example 6 illustrates the use of acetylacetone as a specific co-mobilizer in place of oxalic acid.

0.8 g of acetylacetone are mixed with 1.36 g of Ti (oc 4 H 9) 4 and a solution containing 0.37 g of NH 4 F and 0.85 g of TPA-Br in 23 g of H2O is added with vigorous stirring and then 2.40 g. g of aeroosil silica and 0.040 g of seeds (MFI zeolite). The molar composition reduced to mole of silica is then:
1 Sio2; 0.1 TiO2; 0.08 TPA-Br; 0.25 NH4F; 0.2 acetylacetone; 50 H2o.

 Crystallization of the reaction mixture is carried out under the same conditions as for the tests of Example 5. After separation and calcination, a crystallized solid is obtained, the X-ray diffraction pattern of which is in accordance with that of Table I. / Ti in the framework is estimated by measuring the relative displacement of the diffraction peaks at a value close to 45.

Comparative Example 7
For comparison, a porous synthetic material was prepared according to the method described in French Patent No. 2,471,950 and called TS1 in this document.

The process involves a basic solution, using as mobilizing agent OH ions
227.5 g of tetraethylorthosilicate are placed in a pyrex glass vessel equipped with a stirrer and kept under a CO free atmosphere and 7.5 g of tetraethyltitanate are added, followed by a progressive addition of 500 g of a solution to 20% by weight of tetrapropylammonium hydroxide.

 the mixture is stirred for about 1 hour before heating accelerates the hydrolysis and evaporation of the ethyl alcohol.

After 5 hours of heating at 80-90 C is added water. The homogeneous opalescent solution is transferred to a stainless steel autoclave equipped with a stirrer. The mixture is heated to 165 ° C. and kept stirred at this temperature under its own pressure for a period of 10 days. The autoclave is then cooled, and the mass of fine crystals obtained is recovered. After washing the crystals with water, they are dried and then calcined for 6 hours.
The X-ray diffraction spectrum for the calcine product corresponds to that indicated in Table I of Patent FR 2 471 930.

 Table IV below shows the X-ray diffraction spectra of the zeolite according to the invention obtained in Example 4c and that of the product of Comparative Example 7.

 The differences in spectra between these two products are obvious and clearly show that the zeolite obtained with fluoride ions as the mobilizing agent, contains titanium elements in its framework. This difference is concretized by the crystalline system obtained which is monoclinic for a zeolite of the invention, and orthorhombic for a silicalite of titanium obtained in basic medium.

Table IV
Comparison of the corresponding RX diffraction diagrams
Has a titanozeosilite (example 4cç and a silicalite
of titare according to comparative example 7

<tb> Titanozeosilite <SEP> Silicalite <SEP> of <SEP> Titanozeosilite <SEP> Silicalite <SEP> from
<tb><SEP> (eg <SEP> 4c) <SEP> titanium <SEP> (eg <SEP> 7) <SEP> (eg <SEP> 4c) <SEP> titanium <SEP> (ex. <SEP> 7)
## EQU1 ## / Io
<tb><SEP> 1.12 <SEP> F-FF <SEP> 0.114 <SEP> FF <SEP> 0.462 <SEP> f
<tb><SEP> 1.00 <SEP> F-FF <SEP> 0.999 <SEF> F <SEP> 0.446 <SEP> ff
<tb><SEP> 0.98 <SEP> f <SEP> 0.974 <SEP> m <SEP> 0.436 <SEP> f <SEP> 0.4360 <SEP> f
<tb><SEP> 0.90 <SEP> ff <SEP> 0.426 <SEP> f <SEP> 0.4260 <SEP> mf
<tb><SEP> 0.805 <SEP> ff <SEP> 0.4084 <SEP> ff
<tb><SEP> 0.746 <SEP> f <SEP> 0.4008 <SEP> f
<tb><SEP> 0.709 <SEP><SEP> 0.3859 <SEP> F <SEP> 0.3855 <SE> F
<tb><SEP> 0.571 <SEQ> F <SEP> 0.5702 <SEQ> f <SEP> 0.3826 <SEQ> mF <SEP> 0.3819 <SE> F
<tb><SEP> 0.637 <SEP> f <SEP> 0.6362 <SEP> mf <SEP> 0.3806 <SEP> mF
<tb><SEP> 0.500 <SEP> fm <SEP> 0.5993 <SE> mf <SEP> 0.3759 <SE> m <SE> 0.3751 <SE> F
<tb><SEP> 0.594 <SEP> f <SEP> 0.3742 <SEP> m
<tb><SEP> 0.573 <SEP> f (m) <SEP> 0.5698 <SEP> f <SEP> 0.3718 <SEP> m <SEP> 0.3720 <SEP> F
<tb><SEP> 0.570 <SEP> epal @ <SEP><SEP> 0.3663 <SEP> f <SEP> 0.3646 <SEP> m
<tb><SEP> 0.559 <SEP> f <SEP> 0.5574 <SEP> f <SEP> 0.3627 <SEP> f
<tb><SEP> 0.538 <SEP> f (f) <SEP> 0.3448 <SEP> f (f) <SEP> 0.3444 <SEP> f
<tb><SEP> 0.534 <SEP> f (f) <SEP> 0.3431 <SEP> f
<tb><SEP> 0.513 <SEP> ff <SEP> 0.3396 <SEP> ff
<tb><SEP> 0.504 <SEP> ff <SEP> 0.5025 <SEP> f <SEP> 0.3357 <SEP> f (f)
<tb><SEP> 0.498 <SEP> mf <SEP> 0.4980 <SEP> f <SEP> 0.3317 <SEP> f <SEP> 0.3318 <SEP> f
<tb><SEP> 0.488 <SEP> ff <SEP> 0.3256 <SEP> f
<tb><SEP> 0.471 <SEP> ff
<Tb>
EXAMPLE 8
The zeolite of the invention can be used as adsorbent, catalyst and / or catalyst support for many applications.

 By way of example, its use as a catalyst of the selective dehydration reaction of ethylbutynol in methylbutenyne has been tested.

 30 g of catalyst prepared according to Example 1 are added in 300 ml of 0.1N hydrochloric acid. This mixture is heated to 600C and maintained at this temperature with stirring for 4 hours.

 The catalyst is recovered by filtration and washed with water. After drying in an oven at 1000C, the catalyst is ground.

 This catalyst is arranged in a column between two beds of glass beads, and maintained at 5000C overnight for activation.

 The methylbutynol is fed continuously into the column, under a nitrogen atmosphere, at a temperature of 2800 ° C and a gas flow rate of 16 l / h.

 The recovered product is analyzed by gas chromatography.

 The percentage of methylbutenyl in the exit mixture is about 85% for a reaction time of about 2 hours.

 With a conventional gamma alumina catalyst, this level is about 65%.

 These results show that the catalyst of the invention has a better selectivity.

 However, the conversion efficiency of methylbutynol is lower for the catalyst of the invention than the alumina catalyst.

Claims (16)

 1. A zeolite of MFI structure characterized in that it is based on silicon oxide and titanium oxide, and has the following formula, after caloination:  (Si96-x Tix) o192  in which: x is between 0.1 and 6  and in that it has a monoclinic structure and an X-ray diffraction pattern defined in Table I.  2. Zeolite according to claim 1, characterized in that it contains between 0.01 and 0.8% of fluorine by weight, after calcination.  3. A method of manufacturing a zeolite according to one of the preceding claim, characterized in that it comprises the following steps  (i) Preparation of a reaction mixture in aqueous medium  containing at least one source of silicon oxide,  a source of titanium oxide, fluoride ions,  a structuring agent with Ti / Si molar ratios  between 1.5 and 0.002, F / Si between 10 and 0.04,  H2O / Si between 400 and 4, structuring agent / Si between 2 and  0.02 and a pH of between 10.3 and 1.5.  (ii) Crystallization of the reaction mixture.  (iii) Recovery and calcination of the crystalline precipitate  at a temperature above  4. Method according to claim 3, characterized in that the molar ratio Ti / Si in the reaction mixture is between i and 0.01.  5. Method according to claim 3 or 4, characterized in that the molar ratio F / Si in the reaction mixture is between 6 and 0.06.  5. Method according to one of claims 3 to 5, characterized in that the molar ratio H2o / Si is between 100 and  7. Process according to one of the rev-ndications 3 to 6, characterized in that the ratio structuring agent / Si is between 1 and 0.04.  8. Method according to one of claims 3 to 7, characterized in that the silicon oxide and the titanium oxide have a common source.  9. Method according to one of claims 3 to 7, characterized in that the structuring agent mentioned above is chosen from the group comprising  tertiary amines of formula I

 in which  R2, R3 identical or different represent a group  alkyl, preferably a propyl or butyl group. quaternary ammonium compounds of formula II

 in which  R1, R2, R3, R4, which are identical or different, represent the  allyl groups, preferably the propyl groups or  butyl.  compounds of formula T or TI in which the nitrogen has  been replaced by a phosphorus atom.  10. Method according to one of claims 3 to 7 or 9, characterized in that the source of silicon oxide is selected from the group comprising hydrogels, aerogels, colloidal suspensions of silica, silicic esters, soluble silicates in water, silica extracted from natural or synthetic crystalline compounds, hydrolysable tetravalent compounds or ifum, such as silicon halides, and in that the source of titanium oxide is selected from the group consisting of oxides and hydroxides crystallized or amorphous natural or synthetic titanium, halides, alkoxides, its water soluble titanates.  11. Method according to one of claims 3 to 10, characterized in that the aforementioned reaction mixture comprises at least one co-mobilizing agent of titanium in a molar ratio with respect to silicon of between 3 and 0.01, preferably between 1 and 0.04.  12. Process according to claim 11, characterized in that the co-mobilizing agent is chosen from the group comprising oxalic acid and its salts, acetylacetone, tartaric acid and its salts.  13. Method according to one of claims 3 to 12, characterized in that the fluoride ions are added to the reaction mixture in the form of hydrofluoric acid, ammonium fluoride or amines, hydrolyzable compounds releasing the anions fluorides.  14. Process according to claim 13, characterized in that the hydrolysable compounds are fluorinated salts containing silicon or titanium, chosen from the group comprising titanium fluorides, silicon fluoride, ammonium and titanium double fluoride, and fluoride. double ammonium and silicon.  15. Crystalline compound containing silica and titanium oxide, characterized in that it can be obtained by the process comprising the following steps:  (i) Preparation of a reaction mixture in aqueous medium  containing at least one source of silicon oxide,  a source of titanium oxide, fluoride ions,  a structuring agent with Ti / Si molar ratios  between 1.5 and 0.002, F / Si between 10 and 0.04,  H2O / Si between 400 and 4 and structurant / Si between 2 and 0.02  and a pH of between 10.5 and 5.  (ii) Crystallization of the reaction mixture.  (iii) Recovery of the crystalline precipitate.  16. Catalyst for the dehydration of methylbutynol to methylbutenyne, characterized in that it contains a zeolite according to one of claims 1 or 2.