FR2584385A1 - Process for the manufacture of a stabilised alumina-free omega zeolite - Google Patents

Abstract

Process for the manufacture of an omega zeolite with an SiO2/Al2O3 molar ratio greater than 10 and a sodium content lower than 0.3 %. The method of preparation is characterised in that, in a first stage, a synthetic omega zeolite with an SiO2/Al2O3 molar ratio between 6.5 and 10 is subjected to a treatment for the removal of the greater part of its organic cations, lowering the content therein of alkali metals, and in that, in a second stage, the solid obtained is subjected to at least one calcination/acid attack cycle.

Description

 The present invention relates to a process for producing an improved cracking catalyst for heavy petroleum fractions based on stabilized and dealuminated omega zeolite. More specifically, this catalyst is characterized by the presence, for example, of from 3 to 50% by weight of an omega zeolite which is highly depleted of alkaline ions, the overall molecular ratio SiO 2 / Al 2 O 3 of which is greater than or equal to 10, diluted in a matrix based on amorphous silica-alumina and / or clay for example. This new catalyst has comparable conversion and comparable coke production, a selectivity in middle distillates (LO) greater than that of most catalysts of the prior art.

The stabilized and dealuminated omega zeolite prepared according to the present invention has cracking properties with respect to heavy charges which are very interesting and different from those of zeolites of faujasite structure (such as zeolite Y) used in the industrial cracking catalysts of the prior art. . This dealuminated omega zeolite also has the following advantages. a great thermal and hydrothermal stability which is very
interesting considering what has been written previously.

 . an ability to produce little coke.

 excellent selectivity in middle distillates.

 The stabilized and dealuminated omega zeolite used in the catalysts of the present invention is characterized by a SiO 2 / Al 2 O 3 molar ratio greater than 10, a sodium content of less than 0.3% by weight and preferably less than 0.01% by weight. . The stabilized and dealuminated solid retains the X-ray diffraction spectrum of zeolite Q with crystalline parameters a and c less than or equal to 1.84 nm and 0.760 nm, respectively.

Its nitrogen adsorption capacity at 77 K under a partial pressure
P / po equal to 0.19 is greater than 8% by weight and preferably greater than 11% by weight. The solid obtained by the invention has a network of secondary pores whose radii are between 1.5 nm and 14 nm, and preferably between 2 nm and 6 nm. The volume of the secondary pores represents 5 to 50% of the total pore volume of the zeolite.

 The product preparation procedure described above is based on the ion exchange equilibrium with ammonium cations, acid attacks and (or) heat treatments in the presence or absence of water vapor. These treatments have been used in the prior art to stabilize various zeolites. However, the zeolite n is recognized as being very little stable. The preparation of stabilized and dealuminated lithes in particular by the treatments mentioned above has not been successful to date. The decationization and dealumination treatments described in the invention considerably improve the acidic properties of zeolite n, which can then be used as catalyst or catalyst support in reactions such as cracking and hydrocracking.

 The OMEGA zeolite (called ZSM-4 by MOBIL) is the synthetic analogue of MAZZITE which is a natural zeolite.

The zeolite is synthesized in the presence of sodium cations and organic cations generally TMA (tetrapropylammonium) (Dutch Patent No. 6,710,729, US Patent No. 4,241,036). The Molae Naj'IMA ratio is generally close to 4 (T.WEEKS , D. KIMAK, R. BUJALSKI and A. BOLTON,
JCS Farad Trans 1, 72, (1976), 57); LEACH and C. MARSDEN, Catalysis by Zeolites, B. IMELIK ed, 1980, p. 141, Elsevier Amsterdam), and the SiO 2 / Al 2 O 3 molar ratio is in the range 5 to 10 (US Pat 4,241,036, T. WEEKS, D. KIMAK, R. BUJALSKI and
A. BOLTON, JCS. Farad Trans 1.72, 1976, 57, F. LEACH and C. IARSDEN,
Catalysis by Zeolites, B. IMELIK ed., 1980, p. 141, Elsevier Amsterdam; A. ARAYA, T. BARBER, B. LOWE, D. SINCLAIR and A. VARMA, Zeolites, 4, (1984), 263). Zeolite Q crystallizes in the hexagonal system with parameters a and c close to 1.82 nm and 0.76 nm (T. WEEKS,
D. KIMAK, R. BUJALSKI and A. BOLTON, JCS Farad Trans 1, 72, (1976), 57, R. BARRER and H. VILLIGER, Chem Comm. (1969), 65). The structure of the zeolite is formed by the arrangement of gmelinite cages connected to each other along the c axis (W. MEIER, D. OLSON, Atlas of
Zeolites Structures Types, DRUCK + VERLAG AG, Zürich, 1978). The particular arrangement of the gmelinite cages in the zeolite fl, in the structure provides a network of 12-sided canals with a diameter close to 0.74 nm and parallel to the c axis.

With pores of about 0.7 nm in diameter, the zeolite belongs to the category of zeolites with a large porous opening, which makes it particularly attractive for reactions such as cracking and hydrocracking. Although it possesses properties that are interesting in catalysis, the catalytic performances of the zeolite # have been little explored. Only a limited number of reactions such as the isomerization of substituted cyclopropanes (F. LEACH and C. tSARSDEN, Catalysis by Zeolites, B. IMELIK ed, 1980, p.141, Elsevier Amsterdam) or the cracking of n- heptane have been studied (A.Perrota et al., Catal 55, 1978, 240)
For this last reaction, the authors indicate that after + exchange with N114 and calcination at 500 ° C., the zeolite exhibits an initial activity greater than that of zeolite Y. However treated in this way, the zeolite # deactivates extremely rapidly.

The main reason for the limited number of studies devoted so far to the catalytic properties of zeolite Q is the low thermal stability of this zeolite. Indeed it is well known in the scientific literature that the zeolite # in form
NaTMA or NH4TMA can be destroyed (T. WEEKS, D. KIMAK, R. BUJALSKI and A. BOLTON, JCS Farad Transl, 72, (1976), 57) or see its crystallinity considerably diminished (F. LEACH and C. MARSDEN, Catalysis by Zeolites, B. IMELIK ed., 1980, p.141, Elsevier, Amsterdam) by a calcination above 600 ° C. Several reasons have been invoked to account for the fragility of the zeolite nvis with regard to heat treatments. This fragility is due to crystal sizes that are too small (T. WEEKS, D. KIMAK, R. BUJALSKI and A. BOLTON,
JCS Farad Trans 1, 72, (1976), 57 A. ARAYA, T. BARBER, B. LOWE, D.

SINCLAIR and A. VARMA, Zeolites, 4, (1984), 263) or would come from the particular role played by TMA cations in the cohesion of the crystalline framework (T. WEEKS, D. KIMAK, R. BUJALSKI and A. BOLTON,
JCS Farad Trans 1, 72, (1976), 57). The cause of the thermal fragility of the zeolite # remains poorly understood.

Under certain operating conditions, it is possible to partially preserve the crystallinity of the zeolite S2 during heat treatments. However, as will be seen below, the products obtained are not interesting in acid catalysis. The calcination of a natta Q form in a small quantity in a differential thermal analysis apparatus leads to a solid which remains crystallized at 8000C (A. ARAYA, T. BARBER, B. LOWE, D. SINCLAIR and A. VARMA,
Zeolites, 4, (1984), 263); such a solid is not dealuminated and still contains all the starting alkaline cations. Calcination under thick bed conditions of the NH Q form also leads to an increase in thermal stability (T. WEEKS, D.

KIMAK, R. BUJALSKI and A. BOLTON, JCS Farad Trans 1, 72, (1976), 57) but the solids obtained show only a very moderate activity in hydrocracking and isomerization.

As regards the dealumination of the zeolite, several techniques have been proposed. These techniques, which are described below, do not make it possible to obtain solids possessing the desired specifications, in particular the high SiO 2 / Al 2 O 3 ratio combined with the existence of a secondary porous network. In the US patent. Pat 3,937,791 describes the dealumination of various zeolites including zeolite
Q with Cr (III) salts. This method leads to a replacement of aluminum atoms by chromium atoms. There is good dealumination of the structure but also inevitably enrichment with chromium. U.S. Patent No. 4,297,335 proposes a dealumination technique by fluorine gas treatment at high temperature applicable to several zeolites but which causes, in the case of zeolite, In the 100544 patent, the dealumination of many zeolites, including zeolite n, by calcination in the presence of SiCl4 at temperatures below 2000C is described in spite of the fact that it is furthermore established that Higher temperatures are required to dealuminise the zeolites by this technique (BEYER et al catalysis by zeolites (l98o) p.203). The dealumination of the zeolite with SiCl 4 is indeed possible provided that it is placed at elevated temperatures. order of 500 C for example (J. KLINOWSKI, M. ANDERSON and J.

TH0S9S, JCS, Chem. Common. 1983, p. 525, 0. TERASAKI, J. TH0NfAS, G. MILLWARD
Proc. R. Soc. London (A), 395 (1808), 153-64).

However, even under these conditions the increase in the ratio
If / Al is apparently limited since it goes from 4.24 before treatment to 4.5 after treatment (J. KLINOWSKI, M. ANDERSON and
J. THOMAS JCS, Chem. Common. 1983, p. 525). Insofar as the dealumination by SiCl 4 treatment is a method applicable to the Q zeolite, it is essential to underline that this technique irreparably leads to an atom-by-atom replacement of the aluminum of the framework by silicon (H. BEYER and I. BELENYKAJA,
Catalysis by Zeolites, B. IMELIK et al editors (1980), p. 203, Elsevier Amsterdam). A zeolite is thus obtained which remains perfectly microporous. It is not as in the art that it is advocated in the present invention creating a secondary porous network.

The secondary network plays an important role in the transformation of heavy hydrocarbons. Moreover, according to J. KLINOWSKI et al,
JCS, Chem. Common. 1983, p. 525, the dealuminated zeolite by
SiCl4 sees its mesh size increase, which is exactly the opposite of what is obtained by the method of the present invention.

 Finally it appears that in the current state of the art, it is not known to prepare a zeolite Q form stabilized hydrogen, disassembled, low volume mesh and having a secondary porous network. From zeolites Q possessing these properties it is possible to prepare active and selective catalysts for cracking and hydrocracking reactions.

 It has been found in the present invention that it is possible by alternating ion exchanges or acid attacks, and thermal treatments to obtain from a zeolite # resulting from synthesis (in Na-OfA form for example ), the SiO 2 / Al 2 O 3 molar ratio of which is between 6 and 10, a well crystallized hydrogen zeolite Q with a sodium content of less than 0.3% and preferably less than 0.01% by weight and whose SiO 2 / Al 2 O 3 ratio is greater than 10 and sometimes, depending on the use, more than 30 or even 50.

 Ionic exchanges and acid attacks are carried out at temperatures between 0 and 1500C. For ion exchange ionizable salt solutions are used. The acid attacks are carried out in solutions of mineral acids (hydrochloric acid for example) or organic acids (acetic acid for example). The heat treatments are carried out between 400 and 9000C with or without the injection of steam. The product obtained at the end of these various treatment steps has an X-ray diffraction spectrum which is that of zeolite Q (Table 1). The crystalline parameters have the following dimensions: a is preferably in the range 1.814 nm to 1.794 nm, it is preferably in the range 0.760 nm to 0.749 nm. The nitrogen adsorption capacity at 77 K for a pressure partial p / po = 0.19 is greater than 8 Z weight. The porous network is no longer solely micropores but comprises a network of mesopores whose rays measured by the BJH method (see below) are located between 1.5 nm and 14 nm and more particularly between 2 and 6 nm. The volume of the mesopores corresponds to about 5 to 50% of the total pore volume of the zeolite.

 Characterization of the dealuminated zeolites.

The silica-rich zeolite n obtained in the present invention has been characterized by the following techniques
- X-ray diffraction

The equipment used includes: a PHILIPS generator
PW 1130 (35 mA, 35kV), PHILIPS PW 1050 goniometer, CuKce tube (fine focus), graphite crystal back monochromator, autosampler.

From the X-ray diffraction spectra, for each sample, the surface of the bottom was measured on a range (2 e) of 6 to 32 on the one hand, and in the same area, the surface area of the lines in number of pulses for a step-by-step recording of 2 seconds on steps of 0.02 (2 e5.
surface area of the tallied rays is expressed as the total area ratio. The ratios of each treated sample are then compared with a reference standard of the same series as the sample and containing less than or equal to 3% by weight of sodium. Thus, the degree of crystallinity is expressed as a percentage with respect to a reference arbitrarily taken at 100.

 It is important to choose the reference, because in some cases, there may be an exaltation or a decrease in intensity of the lines, depending on the cation content of the samples.

The crystalline parameters were calculated using the least squares method from the formula (hexagonal mesh)

 - Microporosity.

Secondary mesopority is determined by the BJH technique (BARRET, JOYNER, HALENDA, J. Am Chem Soc, 73, (1951), 373) based on the numerical exploitation of the nitrogen desorption isotherm; the total pore volume is taken at a nitrogen pressure such that
P / Po = 0.95, where P is the nitrogen partial pressure of the measurement and
Po the saturation vapor pressure of nitrogen at the temperature of the measurement. The microporous volume is estimated from the amount of nitrogen adsorbed at P / PO = 0.19.

Assays of sodium, silicon and aluminum were performed by chemical analysis.

 Preparation of zeolites n dealuminated.

est situe entre 6.5 et 10.The starting zeolite Q is obtained by synthesis. It contains alkaline cations (generally Na +) and organic cations TMA or TPA cations). The alkali cation ratio (usually TMA or TPA). The ratio of organic cations + alkaline cations is generally in the range 1.0 to 0.50 and the molar ratio

is between 6.5 and 10.

The method used in the present invention to obtain a dealuminated and stabilized zeolite is as follows
Firstly, by the techniques known in the prior art a non-dealuminated Q zeolite free of organic cations and very low alkaline content (sodium content less than 0.3% and preferably 0.01% by weight). possibilities to achieve this flintermediate zeolite is as follows
Elimination of organic cations by calcination with an inert gas plus oxygen mixture (the molar oxygen content is greater than 2% and preferably greater than 10%) at temperatures of between 450 and 65 ° C. and preferably between 500 and 600 ° C. C for a duration greater than 20 minutes.

 - Elimination of the alkaline cations by at least one cationic exchange at a temperature between 0 and 1500C in a solution of an ionizable ammonium salt (nitrate, sulfate, chloride, acetate, etc.) with a molarity of between 3 and 20, and preferably between 4 and 10.

 It is possible to reverse the elimination order of organic cations-elimination of alkaline cations or to omit the step of thermal decomposition of organic cations.

 At the end of this series of treatments, the solid is not dealuminated and contains less than 0.3% and preferably less than 0.01% by weight of sodium.

 The zeolite2 obtained after this first series of treatments is subjected to calcination in the presence or absence of water vapor.

Two techniques can be used
calcination in air or in an inert atmosphere, preferably containing between 5% and 100% of water vapor with total flow rates of between, for example, 0.01 and 100 μl g. The calcination temperature is preferably between 500 and 8500C, the duration of treatment being greater than half an hour and preferably greater than one hour.

 Calcination in a confined atmosphere, that is to say with a zero external gas flow. In this case, the water vapor necessary for the treatment is provided by the product itself (self steaming).

 After calcination, in the presence of any water vapor, the zeolite Q is subjected to at least one acid attack at a temperature of between 0 and 150 ° C. The acids used can be inorganic (hydrochloric acid, nitric acid, hydrobromic acid, sulfuric, perchloric) or organic (acetic or benzoic for example). The normality of the acid is generally between 0.1 and 10 N (preferably between 0.5 and 2.0 N) with a volume / weight ratio expressed in cm3 gas of between 2 and 10. The duration of treatment is greater than half an hour . It is preferable to carry out the acid attack under controlled conditions to avoid the possible degradation of the solid. Thus, the zeolite can first be suspended in distilled water and then the acid can be added in a gradual manner.

To obtain a stabilized zeolite of molar ratio
Si02 / A1203 high (greater than 10) by the present invention, the preferred protocol is often as follows
1) Elimination of organic cations by calcination under air.

 2) Exchange of alkaline (Na +) cations with ammonium cations.

 3) Calcination in the presence of water vapor.

 4) Acid attack.

 To reach the desired SiO 2 / Al 2 O 3 ratio, it is necessary to choose the operating conditions; from this point of view, the most critical parameters are the temperature and the water vapor content retained for step 3), and the severity of step 4) (concentration of acid, nature of acid , temperature). When particularly high SiO 2 / Al 2 O 3 ratios are targeted, for example greater than 30 or 50, it may be necessary to carry out several cycles (calcination-etching).

 The omega zeolite, the characteristics and the preparation of which have just been specified, must be dispersed within an amorphous matrix in order to be used as a cracking catalyst. All matrices known and used for cracking catalysts of the prior art may be suitable. Preferably they will be based on silica-aluminas and clays and may also contain small amounts of various oxides such as alumina, for example.

The stabilized and dealuminated omega zeolite may be introduced into the matrix in hydrogen form or after being exchanged with various alkaline earth metal ions such as 2+ various alkaline earth metal ions such as Mg and Ca or, preferably belonging to the family of rare earths, such as notably La, Ce, Nd, Pr etc ...

This omega zeolite thus stabilized, dealuminated and optionally exchanged with the various cations mentioned above, can be added as a complementary active agent within the matrix of a conventional catalyst already containing one or more other zeolites of different structures, in particular the zeolites of faujasite structure.
X or Y or pentasil type such as ZSM5 or ZSM1. Among the faujasite structures which are best suited for the catalysts containing the dealuminated omega zeolite as the second zeolite structure, there will be mentioned stabilized zeolite Y, commonly called ultrastable or USY, either in hydrogen form or in form exchanged with alkaline earth cations. and especially rare-earths.

 The following examples illustrate the present invention without limiting its scope.

(molaire).Example No. 1 Preparation of a stabilized and dealuminated ratio zeolite #

(molar).

50 g of zeolite # of molar composition 0.90 Na 2 0 0 0 TMA 2 O
Al 2 O 3 8.5 SiO 2 are calcined at 59 ° C. for two hours under a mixture of N 2 + O 2 (flow rate N 2 = 50 lh 1, flow rate O 2 = 5 Ih -1) in order to decompose the TMA cations.

 At the end of the calcination, the zeolite is exchanged three times in 200 cm 3 of 4N NH 4 NO 3 solution at 100 ° C. for 4 hours.

The product obtained referenced OM1 has a sodium content of less than 0.1% by weight.

The decationized OM1 zeolite is calcined under water vapor under the following conditions

<tb> - <SEP> speed <SEP> of <SEP> rise <SEP> in <SEP> temperature <SEP> 100C <SEP> mn
<tb> - <SEP> flow rate <SEP> air <SEP> 4 <SEP> 1h-1 <SEP> g-1 <SEP>
<tb> - <SEP> steam <SEP> water <SEP> 60 <SEP>% <SEP> molar
<tb> - <SEP> temperature <SEP> final <SEP> to <SEP> 6000C, <SEP> step <SEP> 2 <SEP> hours.
<Tb>

After calcination under steam the zeolite # is attacked with the acid according to the protocol given below.

<tb> - <SEP> HCl <SEP> = <SEP> 0.5N
<tb> - <SEP> Ratio <SEP> V / P <SEP> = <SEP> 10 <SEP> cm3 <SEP> solution / g <SEP> solid <SEP> sec
<tb> - <SEP> T <SEP> = <SEP> 800C, <SEP> time <SEP> 4 <SEP> hours <SEP> under <SEP> shake.
<Tb>

The solid OM2 referenced by all these treatments has an X-ray diffraction spectrum of the zeolite # Its physicochemical properties are as follows
Characteristic of the zeolite #: 0M2

<tb><SEP> Diffraction <SEP> X <SEP> Adsorption
<tb> Si0 <SEP>
<tb> AlS3 <SEP> Crystallinity <SEP><SEP> Parameters <SEP> N2 <SEP>
<tb><SEP> 23 <SEP> Z <SEP>
<tb><SEP> moles <SEP> a <SEP> (nm) <SEP> c <SEP> (Z <SEP> wt)
<tb> 12 <SEP> 85 <SEP>% <SEP> 1.813 <SEP> 0.759 <SEP> 11
<Tb>
The ON2 zeolite has a network of secondary mesopores created by the treatments it has undergone. These mesopores are centered around 4 nm in radius.

 By way of example, Table 2 on page 21 gives the characteristics of the X-ray diffraction pattern of an omega zeolite.

Example 2 Preparation of a stabilized and dealuminated ratio zeolite #

From 50 g of decationized OM1 zeolite prepared under the conditions of Example 1, calcination is carried out under steam and then with an acid attack according to the following procedures:
- Calcination under water vapor.

<Tb>

- <SEP> speed <SEP> of <SEP> rise <SEP> in <SEP> temperature <SEP> 100C <SEP> mn
<tb> - <SEP> flow <SEP> air <SEP> 4 <SEP> lh <SEP> 1 <SEP> g
<tb> - <SEP> injection <SEP> of <SEP> steam <SEP> of water <SEP> a <SEP> 400 "C, <SEP> content <SEP> in <SEP> vapor <SEP> of water
<tb><SEP> 70 <SEP>% <SEP> molar
<tb> - <SEP> temperature <SEP> final <SEP> to <SEP> 6500C, <SEP> step <SEP> 2 <SEP> hours.
<Tb>

- Attack acid.

<Tb>

- <SEP> HCl <SEP> 0.5N
<tb> - <SEP> ratio <SEP> V / P <SEP> = <SEP> 10 <SEP> cm3 <SEP> solution / g <SEP> solid <SEP> sec
<tb> - <SEP> T <SEP> = <SEP> 100 C, <SEP> time <SEP> 4 <SEP> hours <SEP> under <SEP> shaking.
<Tb>

 As for the solid OM2 of Example 1, the solid obtained by the previous treatments, referenced OM3 has a diffraction spectrum X typical zeolite # and a network of secondary mesopores centered at 4 nm in radius.

The main physicochemical characteristics of the # OM3 zeolite are as follows

Sur 100 g de zeolithe # de formule molaire 0.90 Na20 0.10TMA20 A1203 8SiO2 on procède à une calcination à 550 C pendant deux heures sous un mélange N2+02 (débit N2 = 70 1h-1 débit 02 = 7 lh ) afin d'éliminer les cations TMA.<tb> SiO2 <SEP> moles <SEP> Diffraction <SEP> X <SEP> Adsorption
<tb> Al203 <SEP> Crystallinity <SEP> Parameters <SEP> Nitrogen
<tb><SEP> Z <SEP> I <SEP> a <SEP> (nm) <SEP> c <SEP> (% <SEP> wt)
<tb><SEP> 20 <SEP> 88 <SEP>% <SEP> 1.811 <SEP> 0.756 <SEP> 14
<tb> Example # 3: Comparative Example.Preparation of a zeolite # form hydrogen report

On 100 g of zeolite # of molar formula 0.90 Na 2 O 0.1 TMA 2 O 2 O 8SiO 2 calcination is carried out at 550 ° C. for two hours under a mixture N 2 + O 2 (flow rate N 2 = 70 1 h -1 flow rate O 2 = 7 lh) in order to eliminate TMA cations.

After calcination the solid is exchanged three times in 500 of a solution of NH4N036N at 1000C for 4 hours. The zeolite obtained is referenced OM4. It has a diffraction spectrum X typical of the zeolite #. Its physicochemical characteristics are as follows

<tb> SiO2 <SEP> Diffraction <SEP> Adsorption
<tb> moles <SEP> Z <SEP>% <SEP> Na <SEP> Crystallinity <SEP> Parameters <SEP> Nitrogen
<tb><SEP> 23 <SEP> p <SEP> Z <SEP> I <SEP> a (nm) c <SEP><Z<SEP> wt)
<tb><SEP> 8 <SEP> 0.04 <SEP> 100 <SEP>% <SEP> 1.818 <SEP> 0.761 <SEP> 12
<Tb>
Unlike the dealuminated zeolites OM3 and OM2, the dealuminated zeolite OM4 does not have a secondary mesoporous network.

Example 4 Preparation of a HY zeolite of SiO 2 / Al 2 O 3 ratio = 12 and crystalline parameter equal to 2.445 nm.

 100 g of NaY zeolite of Na 2 Al 2 O 3 4.7 SiO 2 molar composition are exchanged 3 times in 600 cm 3 of a NH 4 NO 3 N solution at 1000 ° C. for 4 hours. The NH4Y form obtained at the end of these exchanges has a residual sodium content equal to 1% by weight.

The NH4Y zeolite is calcined in the presence of steam at 5500C under the following conditions

<tb> - <SEP> speed <SEP> of <SEP> rise <SEP> in <SEP> temperature <SEP> 200C <SEP> mn <SEP>
<tb> - <SEP> flow <SEP> of air <SEP> 2 <SEP> lh <SEP> lg <SEP> 1 <SEP>
<tb> - <SEP> injection <SEP> of <SEP> steam <SEP> of water <SEP> to <SEP> 4000C, <SEP> content <SEP> molar <SEP> in
<tb><SEP> steam <SEP> water <SEP> equals <SEP> to <SEP> 80 <SEP> Z
<tb> - <SEP> time <SEP> of <SEP> treatment <SEP> to <SEP> the <SEP> temperature <SEP> final <SEP> 4 <SEP> hours.
<Tb>

 At the end of the calcination, the solid is treated in 500 cm3 of a 1N hydrochloric acid solution at 1000C for 4 hours.

The solid obtained at the end of these various steps is a HY zeolite whose physicochemical characteristics are given below.

<Tb>

rétroéchangée aux terres rares.% <SEP> Na <SEP> (wt) <SEP> SiO2 <SEP> Diffraction <SEP> X <SEP> Adsorption
<tb><SEP> Al203 <SEP> Crystallinity <SEP> Parameter <SEP> Z <SEP> wt
<tb><SEP> (moles) <SEP> (%) <SEP> (nm) <SEP> Nitrogen
<tb><SEP> 0.3 <SEP> 12 <SEP> 90 <SEP> 2.445 <SEP> 20 <SEP> Z <SEP>
<tb> Example # 5: (Comparative)
Preparation of a dealuminated ratio zeolite 2

retro-changed to rare earths.

 In a first step, a dealuminated and stabilized zeolite # of SiO 2 / Al 2 O 3 equal to 20 is prepared in accordance with Example 2; a zeolite Q is thus obtained whose physicochemical characteristics are those of OM3 (example n 2).

 On 100 g of zeolite OM3 is exchanged in 1000 cm3 of rare earth rare earth molarity solution equal to 0.15N. The exchange is performed at 1000C for 4 hours. During the exchange period the pH is controlled and maintained between 5 and 5.5.

The composition of the rare earth mixture used to effect the exchange is as follows, by weight
203 = 57% weight
CeO2 = 15 z weight
Nd203 = 21% by weight
Pr6011 = 7% by weight

 At the end of the exchange-one obtained a Re # rare earth zeolite whose total rare earth content is 4.8%. The solid thus exchanged retains the SiO 2 / Al 2 O 3 ratio of OM 3 as well as the X-ray diffraction spectrum of the Q zeolite, it is referred to as OMS.

 By way of example, catalysts could be produced from the zeolites prepared in Examples 1 to 5 by diluting these zeolites, for example by 20% by weight, in an amorphous silica of controlled particle size comparable to that of the zeolites.

Example 6: Hydrothermal aging tests and measurement of the catalytic performances in micro-unit.

 The various zeolites obtained in Examples 1 to 5 are pelletized and then reduced into small aggregates using a crushing machine. The fraction between 40 microns and 200 microns is then collected by sieving.

 Each of the powders thus obtained is subjected to a hydrothermal treatment according to: 8 hours at 7500C under 1 bar of partial pressure of steam.

 After this treatment, the crystalline parameters of the various samples changed. The new values are shown in Table i.

 This example is simply intended to simulate an industrial aging on a new zeolite.

Table 2
Crystalline parameters of various zeolites after treatment
hydrothermally.

<Tb>

<SEP> Characteristics <SEP> 1) <SEP> OM2 <SEP> 2) <SEP> OM3 <SEP> 3) <SEP> OM4 <SEP> 4) <SEP> HY <SEP> 5) <SEP> Re # <September>
<tb><SEP> a <SEP> nm <SEP> 1.801 <SEW> 1.799 <SEW> 1.805 <SEW> 2.430 <SEW> 1.802
<tb><SEP> c <SEP> nm <SEP> 0.752 <SEP> 0.749 <SEP> 0.754 <SEP> / <SEP><SEP> 0.753
<tb> nitrogen adsorption <SEP>
<tb><SEP> P / Po <SEP> = <SEP> 0.19 <SEP> 9 <SEP> 11 <SEP> 10 <SEP> 18 <SEP> 8
<Tb>
TABLE 1
CHARACTERISTICS OF THE DIFFRACTION DIAGRAM X OF A ZEOLITHE #
STABILIZED AND DESALUMINATED PARAMETERS a = 1.800 NM, C = 0.753
PREPARED ACCORDING TO THE INVENTION.

<Tb>

<SEP> d <SEP> ff <SEP> d <SEP> (nm) <SEP> I / I <SEP> max.
<Tb>

<SEP> Cu <SEP> KS <SEP>
<tb> 5.67 <SEP> 1.559
<tb> 9.83 <SEP> 0.900 <SEP> 100
<tb> 11.35 <SEP> 0.779 <SEP> 50
<tb> 13.05 <SEP> 0.678 <SEP> 60
<tb> 15.04 <SEP> 0.589 <SEP> 75
<tb> 16.36 <SEP> 0.542 <SEP> 25
<tb> 17.05 <SEP> 0.520 <SEP> 10
<tb> 19.12 <SEP> 0.464 <SEP> 40
<tb> 20.54 <SEP> 0.432 <SEP> 40
<tb> 22.82 <SEP> 0.390 <SEP> 20
<tb> 23.73 <SEP> 0.375 <SEP> 65
<tb> 24.30 <SEP> 0.366 <SEP> 25
<tb> 24.90 <SEP> 0.358 <SEP> 10
<tb> 25.63 <SEP> 0.3475 <SEP> 40
<tb> 26.27 <SEP> 0.3392 <SEP> 25
<tb> 28.63 <SEP> 0.3117 <SEP> 40
<tb> 29.28 <SEP> 0.3050 <SEP> 25
<tb> 29.78 <SEP> 0.3000 <SEP> 25
<tb> 30.96 <SEP> 0.2889 <SEP> 40
<tb> 31.04 <SEP> 0.2881 <SEP> 40
<tb> 34.16 <SEP> 0.2624 <SEP> 10
<tb> 34.52 <SEP> 0.2598 <SEP> 10
<tb> 34.58 <SEP> 0.2594 <SEP> 10
<tb> 31.01 <SEP> 1.884 <SEP> 10
<Tb>

Claims (5)

 P / Po equal to 0.19-) greater than 8% by weight.  1) A process for preparing an omega zeolite whose molar ratio SiO2 / Al2O3 is greater than 10, the sodium content less than 0.3% by weight, the crystalline parameters "a" and "c" respectively lower than 1.813 nm and 0.760 nm, furthermore having a nitrogen adsorption capacity of 77 X (at partial pressure  greater than 10.

 is between 6.5 and 10, preceded by preparation being characterized in that (a) in a first step, the synthetic zeolite is subjected to a removal treatment of most of the organic cations, while lowering the alkali content to less than 0.3% by weight, by at least one treatment selected from the group consisting of cation exchange and calcination, and (b) in a second stage, the solid is subjected to obtained in the preceding step at least one calcination, then at least one acid attack so as to obtain a molar ratio

 The said omega zeolite being prepared from a synthetic omega zeolite, containing alkaline cations and organic cations, and whose molar ratio  said zeolite having a network of secondary pores (mesopores) whose rays are between 1.5 nm and 14 nm, the volume of the secondary pores being equal to 5 to 50% of the total pore volume of the zeolite, 2) Process according to claim 1 wherein during the second step, the synthetic zeolite is subjected to at least one calcination in air or in an inert atmosphere between 500 and 8500C, the acid attack temperature being between 0 and 1500C . 3) Process according to claim 2 wherein one operates in the presence of steam. 4) Process according to claim 1 wherein during the second step, the synthetic zeolite is subjected to at least one calcination in a confined atmosphere, the acid attack temperature being between 0 and 1500C. 5) Method according to one of claims 2 to 4 wherein the acid attack following the calcination step is carried out in the presence of a normal acid between 0.1 N and 10 N with a volume / weight ratio expressed in cm3 g 1 between 2 and 10.