EP3041793A1

EP3041793A1 - Zeolites with hierarchical porosity

Info

Publication number: EP3041793A1
Application number: EP14790186.2A
Authority: EP
Inventors: Serge Nicolas; Ludivine Bouvier; Cécile LUTZ
Original assignee: Carbonisation et Charbons Actifs CECA SA
Current assignee: Arkema France SA
Priority date: 2013-09-02
Filing date: 2014-08-06
Publication date: 2016-07-13
Also published as: CN105431380B; FR3010071A1; FR3010071B1; KR101800527B1; US10071914B2; JP2016526524A; KR20160005054A; TW201517981A; JP6280640B2; CN105431380A; US20180362355A1; US20160176720A1; WO2015028740A1; CN109250727A; US10696559B2; TWI544960B; CN109250727B

Abstract

The present invention concerns Y-type FAU zeolites with hierarchical porosity having an Si/AI atomic ratio strictly greater than 1.4 and less than or equal to 6, having controlled and optimised crystallinity, and having mesoporosity such that the mesoporous outer surface area is between 40 m2. g-1 and 400 m2. g-1. The present invention also concerns the method for preparing said Y-type FAU zeolites with hierarchical porosity.

Description

ZEOLITES WITH HIERARCHISED POROSITY

The present invention relates to the field of zeolites, more particularly zeolites with hierarchical porosity, and in particular zeolites with hierarchical porosity (ZPH) of faujasite structure (FAU) with an atomic ratio Si / Al strictly greater than 1, 4, in particular zeolites of type Y, hereinafter referred to as YPH.

Synthetic zeolites (that is to say non-natural) are of ever increasing interest in the industry, as evidenced by the many recent research work related to obtaining zeolites always more efficient, with synthetic processes always simpler, economic and easy to implement.

In recent years, hierarchical porosity zeolites (ZPH) are the subject of many scientific publications and patent applications. Thus, as early as 2005, the process for synthesizing zeolites with hierarchical porosity with good crystallinity (pure phase, observed by XRD) was described in application WO2007 / 043731, using an organosilane structuring agent.

The product obtained after calcination comprises a zeolite network connected to a network of mesopores of a few nanometers in diameter. The hydrothermal resistance of this product is much better than that of mesoporous solids MCM 41 which allows to consider applications in which a thermal regeneration occurs.

[0005] Other methods for preparing zeolite with hierarchical porosity, that is to say solids comprising a microporous network of zeolite type connected to a mesopore network, have been developed and can be classified in the following way ( reviewed by DP Serrano, C em Soc Rev., (2013), 42, 4004-4035):

• Post-treatment of zeolitic structures that consists of removing atoms from the zeolite network to create mesopores; this can be achieved either by acid treatments which dealuminate the solid followed by a washing with sodium hydroxide which eliminates the aluminic residues formed (J. Pérez-Ramirez et al., Adv Funct Mater., (2012), p 1 - 12) or by treatments that combine the action of an acid with that of a structuring agent that promotes the formation of mesopores (see WO 2013/106816).

• "Hard templating method" or "method of molding" which consists in using a porous network (organic or inorganic) as a mold, this porous network is put into contact with a reaction medium capable of forming a zeolite network by hydrothermal transformation, crystallization of the zeolite is carried out and then the mold is removed either by calcination or by dissolution to generate the mesoporosity (CJH Jacobsen, J. Am. C em. Soc., ( 2000), 122, 71 16-71 17).

Zeolitization of amorphous mesoporous solid such as mesoporous silicas formed according to the sol-gel technique described by M. Matsukata et al., (Top Catal., (1999), 9, 77-92).

• Direct synthesis mentioned at the beginning using a structuring agent of the organosilane type, this type of structurant having the distinction of having on the one hand, an affinity with the silico-aluminas species which form the zeolite network thanks to its silane function and on the other hand, to be able to occupy a space with its long-chain organic function that occupies space and creates mesoporosity when it is eliminated (application WO2007 / 043731).

However, even if the solids obtained according to this direct synthesis method indeed have a hierarchical porosity as shown by the nitrogen adsorption isotherms and the transmission microscopy photos (Angew Chem Int., Ed. 2012), 51, 1962-1965), we find that:

The microporous volume of these hierarchically porous zeolites is significantly lower than that of non-mesoporous zeolites,

The structuring agent modifies the growth rates of the faces of the crystals, which makes it difficult to control the size of the crystals,

The increase of the structurant content aimed at increasing the mesoporous volume leads to a loss of selectivity for the crystallization of a given zeolite, which results in the formation of an undesired mixture of zeolite structures (Y. Meng et al. Asian Journal of Chemistry, 25 (8), (2013), 4423-4426).

One of the objectives of the present invention is to solve at least these three major drawbacks noted for direct synthesis using an organosilane type structuring agent.

Mention may also be made of the following documents, in which the use of structuring agents of the organosilane type and of organosilane derivatives is described, with the aim of synthesizing various zeolitic structures with hierarchical porosity including X and LTA zeolites. .

Thus R. Ryoo [Nature Materials, (2006), vol. 5, p. 718 et seq.) Describes the synthesis of LTA with mesoporosity and later (K. Cho et al., Chem Mater 21, (2009), 5664-5673) the synthesis of LTA-type mesoporous zeolites and their applications to them. catalysis. The diffractograms presented in Figure 2 of K. Cho's article (see above) show that there is no polluting crystalline phase. On the other hand, the decrease in the intensity of the peaks, as soon as there is addition of structuring agent and a fortiori when its quantity increases, proves a degradation of the crystalline framework (low microporosity).

The patent application EP2592049 proposes a zeolite synthesis having a very large and well organized mesoporosity, but with a marked degradation of the crystalline framework (very low microporosity). This method uses a specific structuring agent comprising three ammonium functions.

The work of W. Schwieger {Angew. Chem., Int. Ed., (2012), 51, 1962-1965) concern the synthesis of mesoporous zeolite type FAU (X) implementing a structuring agent. A single example shows the use of TPHAC ([3- (trimethoxysilyl) propyl] hexadecyldimethylammonium chloride as a structuring agent, with a TPHAC / Al ₂ O ₃ mole ratio of 0.06.

The article by Y. Meng (Asian Journal of Chemistry, 25 (8), (2013), 4423-4426) discloses syntheses of mesoporous LTA zeolite using [3- (trimethoxysilyl) chloride). ) propyl] octadecyldimethylammonium (TPOAC), as a structuring agent, and presents a study of various synthesis parameters including the amount of structuring agent used, the alkalinity of the reaction medium and the crystallization temperature.

It appears that an increase in the content of structuring agent which should lead to an increase in the mesoporous volume also has the effect of modifying the growth rates of the zeolite network, thus causing the appearance of other zeolitic crystalline phases and therefore formation of mixtures of zeolitic structures, which is not desired. In addition, the diffractograms in Figure 1 of this article show a lowering of crystallinity.

The aforementioned prior art also shows that the microporous volumes are significantly lower than the microporous volumes of equivalent non mesoporous zeolites (that is to say whose mesoporous outer surface as defined below is strictly less than 40. m ^2, g ^"1 ), which is very penalizing in applications where a high active site content is required.In addition, the size of the crystals is undergone and can not be modified.

Finally, the preparation methods described in the prior art seem to be difficult to industrialize especially because of the high costs they can generate, and because of the synthesis times which are even longer than the desired increase the mesoporosity. As regards more particularly mesoporous Y-type zeolites, the literature provides some references concerning their syntheses implementing post-treatments of zeolites Y.

Thus, for example, the article by U. Lohse et al. (Z. Anorg Allg Chem, 476, (1981), 126-135) describes the creation of a mesopore system of size close to 20 nm in a Y zeolite by steam treatment and then by extraction. with acid. These successive treatments, however, lead to a drastic reduction in the crystallinity of the mesoporous Y zeolite in comparison with the untreated starting zeolite.

[0018] The document US2013 / 0183229, the post-treatment is carried out by introducing an amount of Pluronic ^® (nonionic surfactant) of the same order of magnitude (similar amount by weight) the amount of Y zeolite, then by long treatments, in liquid way, followed by several calcination treatments.

The documents US8486369 and US2013 / 0183231 show post-treatments using a cetyltrimethylammonium halide (CTA) coupled with an acid, and then a steam treatment. Such post-treatments, however, have the major drawbacks of reducing both the crystallinity and the microporous volume of the starting zeolites. They also have the effect of drastically reducing material yields. These effects are all the more marked as the desired formed mesoporous volume is important.

Another example is illustrated by the work of D. Verboekend et al. (Advanced Functional Materials, 22 (5), (2012), 916-928) which have Y zeolites possessing mesopores obtained by a succession of post-treatments. It is indicated (page 919, left column, ^1st §) that these post-treatments strongly degrade the microporosity. This microporosity degradation is however not visible in Table 2, due to the fact that the microporous volume is measured by D. Verboekend (ibid.) Using the t-plot method which measures both the micropore volumes. and small mesopores. Measurement of the microporous volume using the Dubinin-Raduskevitch equation takes into account only micropores with a diameter strictly less than 2 nm (see "Adsorption by powders and porous solids", F. Rouquerol et al., Académie Press, ( 1999), chapter 8.2.2, pages 224-225).

WO2012 / 084276 describes a method for preparing a mesoporous Y zeolite by various basic post-treatments but at the expense of microporosity. These treatments also lead, as claimed, to an increase in the Si / Al atomic ratio by dealumination. Although these methods make it possible to prepare zeolites with hierarchical porosity, as shown by the shape of the nitrogen adsorption isotherms of the solids obtained, it is important to note that these processes use quantities of post-treatment fluids. of the same order of magnitude as the initial zeolite mass with multiple and long operations. In addition, the mass yield of these processes is less than 60% which further penalizes their productivity. These processes are therefore long, expensive and unproductive.

It therefore appears that these documents of the prior art relating to the preparation of Y-type mesoporous zeolites only propose synthetic techniques comprising at least one post-treatment step.

The work of Baoyu Liu et al. {RSC Advances, 3, (2013), 15075-15084) teach the synthesis of hierarchically porous Y zeolites prepared using a sacrificial template. However, these zeolites have microporous volumes which are insufficient in view of the targeted applications using said Y zeolites with hierarchical porosity.

Thus, an object of the present invention is to provide Y-type FAU zeolites with hierarchical porosity combining mesoporosity, high microporous volume, optimal purity and adjustable crystal sizes, and Si / Al atomic ratio strictly greater than 1, 4. Another object of the present invention is to provide an economical, simple and easily industrializable process for the preparation of said zeolites.

The inventors have now discovered that it is possible to prepare Y type mesoporous FAU zeolites by direct route, that is to say without going through the synthesis of a type Y FAU zeolite which would then undergo a or several post-treatments necessary according to the prior art to obtain a certain mesoporosity. Y-type FAU zeolites with hierarchical porosity (YPH) according to the invention have quite interesting characteristics and are thus easily industrialized by a direct route.

Thus, and according to a first aspect, the present invention relates to a zeolite with hierarchical porosity having the following characteristics:

Si / Al atomic ratio strictly greater than 1, 4 and less than 6, preferably between 1, 5 and 5 inclusive, more preferably between 1, 5 and 3 inclusive,

Microporous volume νμρ, in cm ³ . g ^"1 , corresponding to the equation νμρ = \ μρ _κ ± 15%, where λ / μρρ _! represents the microporous volume, in cm ³ .g ^-1 , measured under the same conditions, for a zeolite of the same chemical nature and same structure crystalline, but whose mesoporous outer surface is strictly less than 40 m ² .g ^-1 , and

Mesoporosity such that the mesoporous outer surface is between 40 m ² . g ^"1 and 400 m ^2, g ^{" 1} , preferably between 60 m ² . g ^"1 and 200 m ^2. ^{g" 1} and more preferably between 60 m ² · g ^"1 and 150 m ² ^{.g" 1.}

According to a preferred embodiment, the zeolite according to the present invention is a zeolite of the FAU type, and in particular a zeolite FAU type Y.

The characteristics mentioned above confer on the zeolite according to the present invention, improved properties and quite surprising and interesting, compared to zeolites only microporous or both microporous and mesoporous known from the prior art.

According to a preferred aspect of the present invention, the zeolite with hierarchical porosity has a mean diameter in number of crystals between 0.1 μηη and 20 μηι, preferably between 0.1 μηη and Ι Ο μηι, more preferably between 0.5 μηη and 10 μηη, more preferably between 0.5 μηη and 5 μηη, limits included.

The size of the zeolite crystals according to the present invention is expressed by their number average diameter by observation with a scanning electron microscope (SEM), as indicated below. The present invention also has the advantage of allowing to adjust and adjust this size of crystals, in particular according to the synthesis conditions explained below.

The hierarchically porous zeolite of the present invention furthermore has a controlled crystallinity, which means that the zeolite comprises a pure zeolitic phase, and more precisely constituted by a single zeolite phase or comprising, preferably consisting of, up to 2% by weight, inclusive, of one or more other zeolitic or amorphous phases, called polluting phases (crystallinity determined by XRD, technique described below).

Furthermore, the zeolite with hierarchical porosity according to the invention has optimum crystallinity, that is to say a microporous volume νμρ, corresponding to the equation νμρ = νμρ _κ ± 15%, preferably greater than equation νμρ = \ μρ _κ ± 10%, more preferably to the equation νμρ = \ μρ _κ ± 5%, very particularly preferred to the equation νμρ = νμρ _κ ± 3%, where \ / μρ _κ is the volume microporous measured, under the same conditions, for a zeolite of the same chemical nature and of the same crystalline structure, perfectly crystalline (according to ICDD PDF-2, release 201 1) but not mesoporous in the sense of the invention, that is- that is, whose mesoporous outer surface is strictly less than 40 m ² . g ^"1 . In the present description, all the microporous volumes are expressed in cm ³ . g ^"1. For zeolite of the same chemical nature and of the same crystalline structure, but not perfectly crystalline mesoporous within the meaning of the invention is meant a zeolite prepared in the same conditions, but for which no specific treatment has been employed to create a mesoporosity, either directly (using a structuring agent as described later in the present invention) and / or by post-treatment.

By way of example, mention may be made of "Zeolite Molecular Sieves" by DW Breck, John Wiley and Sons, New York, (1973), Table 4.26, p. 351, where the microporous volume / μρ _κ of a NaY FAU zeolite, not mesoporous, having an Si / Al atomic ratio of between 1.5 and 3, and perfectly crystallized, is equal to 0.34 cm ³ . g ^"1 .

Calculations of the microporous volume and the mesoporous surface are carried out by applying the methods known to those skilled in the art from the nitrogen adsorption isotherm by applying the Dubinin equation as indicated below. Raduskevich, for the microporous volume and the Harkins and Jura t-plot equation for the micro- and meso-porous surface.

The zeolites with hierarchical porosity according to the invention make it possible to reconcile the properties of accessibility to the active sites of the mesoporous zeolites known from the prior art and those of crystallinity and maximum microporosity of the so-called "classical" zeolites (without mesoporosity). . Thus, the hierarchically porous zeolites of the present invention have unexpected properties and open new perspectives as to their fields of industrial applications.

In addition, the zeolites of the present invention may be subjected to one or more cationic exchanges (for example with alkali metal or alkaline earth metal salt (s)) as is well known to those skilled in the art and commonly performed on conventional zeolites.

According to another aspect, the present invention relates to the method for preparing zeolites with hierarchical porosity as just described. The method of the invention has the advantages of being easy to implement, easily transferable on an industrial scale, and this in particular because of the high yields of synthetic materials, the robustness of the process and its speed.

More specifically, the method for preparing the zeolite with hierarchical porosity according to the invention comprises at least the following steps: a) preparing a so-called growth gel for the preparation of a Y-type FAU zeolite, by mixing a source of silica with a source of alumina, at a temperature between 0 ° C and 60 ° C,

b) adding to the growth gel of step a) at least one nucleating agent, at a temperature between 0 ° C and 60 ° C,

c) adding to the reaction medium at least one structuring agent,

d) crystallization reaction by increasing the temperature,

e) filtration and washing of the zeolite crystals obtained, and

f) drying and calcination.

The growth gel used in step a) is well known to those skilled in the art and is perfectly defined for example in DW Breck ("Zeolite Molecular Sieves", John Wiley and Sons, New York, (1973) , pp. 277 ff.).

It should be understood that step c) of adding agent (s) structurant (s) can be operated at the same time as steps a) and / or b) or before and / or after the steps a) and / or b). In all cases, the structuring agent must be present in the reaction medium before step d) of crystallization. However, it is preferred to add the structuring agent after step b). In addition, a latency time (rest time, with or without agitation) can be provided between steps a), b), c) and d).

The process of the present invention is characterized by the use of the seeding technique with at least one nucleating agent well known to those skilled in the art, for example selected from a nucleating gel, a crystal, by for example, a zeolite crystal, a mineral particle of any kind, for example kaolin, meia-kaolin, or other clay, and the like, and mixtures thereof.

Without wishing to be bound by the theory, it is considered that the nucleating agent promotes the orientation of the synthesis to the desired zeolite. In addition, and thanks to the presence of the nucleating agent, it is possible to use a larger amount of structuring agent than that described in the prior art without disturbing or slowing the crystallization of the zeolite network.

According to a preferred aspect, the nucleating agent is a nucleation gel, and more preferably, said nucleating gel comprises a homogeneous mixture of a source of silica (for example sodium silicate), a source of alumina (for example alumina trihydrate), a strong mineral base, such as, for example, sodium hydroxide, potassium hydroxide, or calcium hydroxide to name only the main and most commonly used, and water. In a preferred aspect, the growth gel comprises a homogeneous mixture of a source of silica (for example sodium silicate or colloidal silica, preferably colloidal silica), a source of alumina (for example example alumina trihydrate), a strong mineral base, such as, for example, sodium hydroxide, potassium hydroxide, or calcium hydroxide to name only the main and most commonly used, and water.

The homogeneity of the mixture can be obtained by any method well known to those skilled in the art, and for example and without limitation by means of a paddle stirrer, a mixer, or to using an Archimedean screw type mixer as described in patent EP0818418. Agitators with a high shear rate, for example of the mixer type, are preferred.

By way of nonlimiting example, with an Archimedean screw whose rotation is set at 300 rpm ^"1 , a satisfactory homogeneity is obtained between a few minutes and a few tens of minutes, usually between 20 and 30 minutes. .

The mixture is generally prepared at temperatures between 0 ° C and 60 ° C, preferably between 10 ° C and 40 ° C, and for practical and economic reasons, the mixture is prepared at room temperature, for example at 25 ° C. The homogenization period is then less than 2 hours.

The process of the present invention is further characterized by adding to the growth gel thus obtained at least one nucleating agent, and preferably a nucleating gel, according to the concept defined in the patent. US3947482. The amount of nucleation gel added can vary in large proportions but is generally between 0.1% and 20%, preferably between 0.5% and 15% by weight, more preferably between 1% and 10% by weight. , limits included, relative to the weight of the growth gel.

When the nucleating agent is a zeolite crystal, it is preferably a zeolite crystal of the same nature as the zeolite that it is desired to synthesize. The size of the crystal can vary in large proportions, and for example is typically between 0.1 μηη and 10 μηη. According to a preferred embodiment, the zeolite crystal is introduced in the form of an aqueous suspension. The amount of crystals introduced may also vary in large proportions, but this amount of crystals is generally between 0.1% and 10% by weight relative to the total weight of growth gel.

As indicated above, the process of the present invention is a method of direct synthesis of zeolite with hierarchical porosity, and not a process where the hierarchical porosity results from a post-treatment of an already synthesized zeolite. However, it would not be outside the scope of the invention, by operating a subsequent post-processing step of the zeolite as synthesized.

Thus, the method of the present invention comprises an addition step in the mixture [growth gel / nucleating agent] obtained in step b) of at least one structuring agent.

The structuring agents that can be used are of all types known to those skilled in the art and in particular those described in the application WO2007 / 043731. According to a preferred embodiment, the structuring agent is advantageously chosen from organosilanes and more preferably from [3- (trimethoxysilyl) propyl] octadecyldimethylammonium chloride, [3- (trimethoxysilyl) propyl] hexadecyldimethylammonium chloride, [3- (trimethoxysilyl) propyl] dodecyldimethylammonium chloride, [3- (trimethoxysilyl) propyl] octylammonium chloride, N- [3- (trimethoxysilyl) propyl] aniline, 3- [2- (2-aminoethylamino) ) ethylamino] propyltrimethoxysilane, N- [3- (trimethoxysilyl) propyl] -N '- (4-vinylbenzyl) ethylenediamine, triethoxy-3- (2-imidazolin-1-yl) propylsilane, [3- (trimethoxysilyl) propyl] urea, N- [3- (trimethoxysilyl) propyl] ethylenediamine, [3- (diethylamino) propyl] trimethoxysilane, (3-glycidyloxypropyl) trimethoxysilane, 3- (trimethoxysilyl) methacrylate propyl, [2- (cyclohexenyl) ethyl] triethoxysilane, dodecyltriethoxysilane, hexadecyltrimethoxysilane, aminopropyl) trimethoxysilane, (3-mercaptopropyl) trimethoxysilane, (3-chloropropyl) trimethoxysilane, and mixtures of two or more of them in all proportions.

Among the structuring agents listed above, [3- (trimethoxysilyl) propyl] octadecyldimethylammonium chloride, or TPOAC, is particularly preferred.

It is also possible to use structuring agents of higher molar mass and for example PPDA (Polymer Poly-Diallyldimethylammonium), PVB (PolyVinyl Butyral) and other oligomeric compounds known in the art for increasing the diameter of the mesopores.

The amount of agent (s) structurant (s) can vary in large proportions and in general it is such that the molar ratio agent (s) structurant (s) / AI ₂ 0 ₃ starting is understood between 0.005 and 0.20, preferably between 0.01 and 0.15, more preferably between 0.02 and 0.08 inclusive.

The addition of the structuring agent (s) is carried out with stirring, for example as indicated previously in step a), and then the mixture is subjected to a maturation step, preferably with stirring, always at the same temperature, for example at 25 ° C, for a time varying from a few minutes to several tens of minutes, typically for one hour, with stirring at 300 rpm ^"1 .

After this stage of maturation, the reaction mixture is engaged in step d) of crystallization, still with stirring, but slower, typically between 20 and 100 rpm ^" , for example at 50 rpm ^{" 1} , and increasing the temperature to a value between 60 ° C and 100 ° C, for example 75 ° C. The time required for crystallization is generally between a few hours and several tens of hours, advantageously between 8 hours and 48 hours.

At the end of the crystallization step, the zeolite crystals are extracted from the reaction medium by filtration, and then washed with one or more suitable solvent (s), aqueous and / or organic (s), but preferably aqueous and finally dried between 50 and 150 ° C, according to the usual techniques known to those skilled in the art.

The average size of the crystals may in particular be controlled by adjusting the content of nucleating agent (nucleation gel, or crystals, for example zeolite, or other) relative to the growth gel during step b).

The dried crystals are then subjected to calcination, a step necessary to release both the microporosity (elimination of water) and the mesoporosity (elimination of the structuring agent). The calcination used to eliminate the structuring agent can be carried out according to any calcination method known to those skilled in the art. For example, and in a nonlimiting manner, the calcination of the zeolite crystals comprising the structuring agent can be carried out under an oxidizing and / or inert gas scavenging, with in particular gases such as oxygen, nitrogen, air, a dry air and / or decarbonated oxygen depleted air, optionally dry and / or decarbonated, at a temperature or temperatures above 150 ° C, typically between 180 ° C and 800 ° C, preferably between 200 ° C and 650 ° C ° C, for a few hours, for example between 2 and 6 hours. The nature of the gases, the ramps of temperature rise and the successive stages of temperatures, their durations will be adapted according to the nature of the structuring agent.

It would not be outside the scope of the invention by operating one or more cationic exchanges (for example with alkali metal or alkaline earth metal salt (s)), before or after the drying step and / or calcination (step f)), according to conventional cation exchange techniques.

As indicated above, the synthesis method of the invention is easy to implement and it is performed in a relatively short time, and in particular in a reduced time by a factor of at least 4, with respect to synthesis processes of Hierarchized Porosity Zeolites (ZPH) known from the prior art which are very long due to the inhibitory effect of the organosilane structurant for nucleation and growth of the microporous zeolite network. It has been discovered, quite surprisingly, that the inhibitory effect of the structuring agent (eg TPOAC) is compensated for by the presence of the nucleating agent.

This simplicity and rapidity of synthesis, however, do not affect the quality and properties of zeolites thus obtained. Indeed, thanks to the process of the invention, it is possible to increase the selectivity of the synthesis to a pure zeolite structure (with less than 2% by weight of other crystalline phase (s) pollutant (s) (s)) and to be able to maximize the ratio [microporous volume / mesoporous area] for a given external surface, which is not the case with the methods known from the prior art (see, for example, the work of Y. Meng (ibid.) Shows that an increase in the content of the structuring agent, which should lead to an increase in the mesoporous volume, also has the effect of modifying the growth rates of the zeolite network, thus causing the appearance of other zeolitic crystalline phases and thus the formation of mixtures of zeolitic structures, which is not desired).

Indeed, with the methods of the prior art, the increase of the microporous volume of the zeolite and the maintenance of a high phase purity are achieved only by means of very long crystallization times and relatively low temperatures (<80 ° C). These methods, however, never reach microporous volumes comparable to those of the invention.

Thus, compared with other processes for preparing ZPH, for example by post-treatment, the process of the invention is more productive and less expensive because it is carried out in a single step, of relatively short duration. (less than one day) with a low amount of structuring agent, and therefore globally with a relatively low cost, or at least with a limited additional cost compared to that of a non-mesoporous zeolite synthesis, and much lower than the cost induced by methods of synthesis of ZPH by post-treatment.

The use of these hierarchically porous zeolites is particularly advantageous in industrial processes such as adsorption, ion exchange, separation, and can also be envisaged in all technical fields in which the non-mesoporous zeolites are usually used. The present invention is now illustrated by the following examples which are presented without any intention to limit the various embodiments of the invention.

In the following examples, the physical properties of the zeolite crystals are evaluated by methods known to those skilled in the art, the main of which are recalled below.

Loss of fire of zeolite crystals

The loss on ignition is determined in an oxidizing atmosphere, by calcination of the sample in air at a temperature of 950 ° C ± 25 ° C, as described in standard NF EN 196-2 (April 2006). The standard deviation of measurement is less than 0.1%.

Microporous volume (Dubinin-Raduskevich volume):

The volume of Dubinin-Raduskevich is determined from the measurement of the nitrogen adsorption isotherm at its liquefaction temperature. Prior to adsorption, the zeolite adsorbent is degassed between 300 ° C. and 450 ° C. for a period of between 9 hours and 16 hours under vacuum (P <6.7 × 10 ^-4 Pa). adsorption is then carried out on an ASAP 2020 Micromeritics-type apparatus, taking at least 35 measuring points at relative pressures of Ρ / Ρ0 ratio of between 0.002 and 1. The microporous volume is determined according to Dubinin and Raduskevitch from isotherm obtained by applying the ISO 15901 -3 (2007) standard The microporous volume evaluated according to the Dubinin and Raduskevitch equation is expressed in cm ³ of liquid adsorbate per gram of zeolite The measurement uncertainty is ± 0.003 cm ³ g ^-1 .

Size and morphology of crystals (SEM)

The estimation of the average number diameter of the zeolite crystals is carried out as indicated previously by observation with a scanning electron microscope (SEM).

In order to estimate the size of the zeolite crystals on the samples, a set of images is carried out at a magnification of at least 5000. The diameter of at least 200 crystals is then measured using a dedicated software, for example the Smile View software from the LoGraMi editor. The accuracy is of the order of 3%.

The morphology of the crystals is qualified from SEM photos taken at magnification adapted to the size of the crystals (see Figure 1). Measurement of the mesoporous outer surface (m ^2, g ^'1 ) by the so-called t-plot method:

The t-plot calculation method exploits the data of the adsorption isotherm Q ads = f (Ρ / Ρ0) and makes it possible to calculate the microporous surface. The mesoporous outer surface can be deduced by differentiating with the BET surface which measures the total porous area in m ² . g ^"1 (S BET = S microp + S ext Mesop.).

To calculate the microporous surface by the t-plot method, plot the Q ads curve (cm ^3, g ^"1 ) as a function of t = thickness of the layer dependent on the partial pressure Ρ / Ρ 0 which would be formed on a non-porous reference solid (t log function Ρ / Ρ0: Harkins equation and applied Jura (ISO 15901 -3: 2007)):

[13.99 / (0.034-log (P / P0)) ^A 0.5],

where in the range t between 0.35 nm and 0.5 nm, a line can be drawn which defines an adsorbed Y intercept which allows the microporous surface to be calculated; if the solid is not microporous the line goes through 0.

Observation of the Mesoporous Structure by Transmission Electron Microscopy (TEM)

The powder is dispersed in ethanol: 1 minute under ultrasound. One drop of the solution is deposited on a microscopy grid. The sample is allowed to dry at room temperature. The observation is made with a transmission electron microscope (FEI CM 200) at a voltage of 120 kV.

The magnifications obtained from x 300000 (see Figure 2) make it possible to visualize the presence of the mesopores and to estimate their diameters.

Analysis of the Si / Al atomic ratio of zeolites by X-ray fluorescence

An elemental chemical analysis of the zeolite with hierarchical porosity can be carried out according to various analytical techniques known to those skilled in the art. Among these techniques, mention may be made of the technique of chemical analysis by X-ray fluorescence as described in standard NF EN ISO 12677: 201 1 on a wavelength dispersive spectrometer (WDXRF), for example Tiger S8 of the Bruker company.

X-ray fluorescence is a non-destructive spectral technique exploiting the photoluminescence of atoms in the X-ray domain, to establish the elemental composition of a sample. The excitation of the atoms generally by an X-ray beam or by bombardment with electrons, generates specific radiations after return to the ground state of the atom. The fluorescence spectrum X has the advantage of depending very little on the chemical combination of the element, which offers a precise determination, both quantitative and qualitative. A measurement uncertainty of less than 0.4% by weight is obtained conventionally after calibration for each oxide.

These elementary chemical analyzes make it possible to verify the atomic ratio Si / Al of the zeolite, the uncertainty of measurement of the atomic ratio Si / Al is of ± 5%.

Qualitative and quantitative analyzes by X-ray diffraction

This analysis makes it possible to identify the crystalline phases present in the solid analyzed because each of the zeolite structures has a diffractogram (or diffraction spectrum) that is defined by the positioning of the diffraction peaks and by their relative intensities.

The zeolite crystals are spread and smoothed on a sample holder by simple mechanical compression. The conditions of acquisition of the diffraction spectrum realized on the Bruker D5000 apparatus are as follows:

• Cu tube used at 40 kV - 30 mA;

• size of the slots (divergent, diffusion and analysis) = 0.6 mm;

• filter: Ni;

• rotating sample device: 15 rpm ^"1 ;

• measuring range: 3 ° <2Θ <50 °;

• not: 0.02 °;

• counting time in steps: 2 seconds.

The interpretation of the diffraction spectrum (or diffractogram) obtained is carried out with the EVA software with phase identification using the ICDD PDF-2 base, release 201 1 which makes it possible to highlight a phase perfectly. crystalline.

The amount of zeolite fractions is measured by XRD analysis. This analysis is carried out on a Bruker brand apparatus, then the quantity of zeolite fractions is evaluated using Bruker's TOPAS software.

Example 1

Synthesis of YPH with addition of nucleation gel and growth gel with TPOAC / AI2O3 ratio = 0.04

a) Preparation of the growth gel in stirred reactor with Archimedes screw at 300 rpm ^"1 . In a 3-liter stainless steel reactor equipped with a heating jacket, a temperature probe and an agitator, a growth gel is prepared by adding 1446 g of colloidal silica (Ludox AM-30 containing 30 % by weight of SiO ₂ ) at 25 ° C in an aluminate solution containing 184 g of sodium hydroxide (NaOH), 138 g of alumina trihydrate (Al ₂ O ₃ , 3H ₂ O, containing 65.2% by weight of AI ₂ 0 ₃ ) and 800 g of water at 25 ° C in 25 minutes with a stirring speed of 300 rpm ^"1 .

[0088] The stoichiometry of growth gel is: 2.5 Na ₂ 0 / AI ₂ 0 ₃ / Si0 8.0 _2/1 17H ₂ 0. The homogenization of the gel growth is carried out with stirring at 300 tr.min ^-1 for 25 minutes at 25 ° C.

b) Addition of the nucleation gel

[0089] To the gel growth at 25 ° C with stirring at 300 tr.min ^"1, 61, 2 g of nucleating gel (2% by weight) of composition 12 Na ₂ 0 / AI ₂ 0 ₃ / 10 Si0 _2/180 H ₂ 0 prepared by mixing a sodium silicate and sodium aluminate under stirring for 1 hour at 40 ° C. After 5 minutes of homogenization at 300 tr.min ^"1, the stirring speed is reduced to 100 r ^"1 and continued for 30 minutes.

c) Introduction into the reaction medium of the structuring agent

27.3 g of 60% TPOAC solution in methanol (MeOH) are introduced into the reaction medium with a stirring speed of 300 rpm ^"1 (TPOAC / Al ₂ 0 ₃ molar ratio = 0). , 04). the process is performed at 25 ° C a soaking step for 1 hour at 300 tr.min ^"1 before starting the crystallization.

d) Crystallization

[0091] It lowers the stirring speed to 50 tr.min ^"1 and the set is fixed to the jacket of the reactor to 80 ° C so that the reaction mixture warms up to 75 ° C in 80 minutes. After 22 at 75 ° C., the reaction medium is cooled by circulating cold water in the jacket to stop the crystallization e) Filtration / washing

The solids are recovered on sintered and then washed with deionized water until neutral pH.

f) Drying / Calcination

In order to characterize the product, the drying is carried out in an oven at 90 ° C for 8 hours, the loss on ignition of the dried product is 23% by weight.

The calcination of the dried product necessary to release both the microporosity (water) and the mesoporosity by eliminating the structuring agent is carried out with the following temperature profile: 30 minutes of temperature rise at 200 ° C., then 1 time to bearing at 200 ° C, then 3 hours of temperature rise at 550 ° C, and finally 1.5 hours of bearing at 550 ° C.

A pure mesoporous Y zeolite (identification by X-ray diffraction spectrum) is thus obtained, with an Si / Al atomic ratio determined by X fluorescence equal to 2.6 and a microporous volume equal to 0.330 cm ³ . g ^"1 .

Example 2

Synthesis of YPH with addition of nucleation gel and growth gel with TPOAC / AI2O3 ratio = 0.02

The procedure is as described in Example 1, with a TPOAC / Al ₂ O ₃ molar ratio of 0.02. A pure mesoporous Y zeolite (XRD) with an Si / Al atomic ratio determined by X fluorescence equal to 2.6 and a microporous volume equal to 0.332 cm ^{3 is thus} obtained. g ^"1 .

Example 3:

Synthesis of YPH with addition of nucleation gel and growth gel with TPOAC / AI2O3 ratio = 0.08

The procedure is as described in Example 1, with a molar ratio TPOAC / Al ₂ O ₃ of 0.08. A pure mesoporous Y zeolite (XRD) with an Si / Al atomic ratio determined by X fluorescence equal to 2.6 and a microporous volume equal to 0.320 cm ^{3 is} thus obtained. g ^"1 .

Example 4

Synthesis of YPH from a growth gel prepared with a shear mixer with addition of nucleation gel and a TPOAC / Al ₂ O ₃ ratio = 0.06.

a) Preparation of the growth gel with a deflocculating disk (shear mixer).

The growth gel is prepared in a 3-liter reactor by adding 1136 g of colloidal silica (Ludox AM-30 containing 30% by weight of SiO ₂ ) at 25 ° C. in an aluminate solution containing 145 g. of sodium hydroxide (NaOH), 11 g of alumina trihydrate (Al ₂ O ₃ , 3H ₂ O, containing 65.2% by weight of Al ₂ O ₃ ) and 626 g of water at 25 ° C. 3 minutes with a stirring speed of 2500 rpm ^"1 .

[0099] The stoichiometry of growth gel is: 2.5 Na ₂ 0 / AI ₂ 0 ₃ / Si0 8.0 _2/1 17H ₂ 0. The homogenization of the gel growth is carried out with stirring at 1200 tr.min ^-1 for 5 minutes at 25 ° C.

To carry out the crystallization, the growth gel is transferred to a stirred 3-liter reactor with an Archimedean screw. b) Addition of the nucleation gel

[0101] To the gel growth at 25 ° C with stirring at 300 tr.min ^"1, 101 g of nucleating gel (5% wt) of composition 12 Na ₂ 0 / AI ₂ 0 _3/10 Si0 _2/180 H ₂ 0 ripened for 1 hour at 40 ° C. After 5 minutes of homogenization at 300 tr.min ^"1, the stirring speed was decreased to 100 ^{r" 1} and continued for 30 minutes .

c) Introduction into the reaction medium of the structuring agent

35.2 g of 60% TPOAC solution in methanol (MeOH) are introduced into the reaction medium with a stirring speed of 300 rpm ^" (TPOAC / Al ₂ 0 ₃ molar ratio = 0). , 06). the process is performed at 25 ° C a soaking step for 1 hour at 300 tr.min ^"1 before starting the crystallization.

d) Curing and Crystallization

Maturing is carried out at 25 ° C. at 100 rpm for 10 hours.

[0104] The stirring speed was maintained at 100 r ^"1 and is carried out a temperature rise to 95 ° C over 2 hours. After 36 hours bearing at 95 ° C, the reaction medium is cooled by circulating cold water in the jacket to stop the crystallization.

e) Filtration / washing

f) Drying / Calcination

In order to characterize the product, the drying is carried out in an oven at 90 ° C. for 8 hours. The loss on ignition of the dried product is 22% by weight.

The calcination of the dried product necessary to release both the microporosity (water) and the mesoporosity by eliminating the structuring agent is carried out with the following temperature profile: 30 minutes of temperature rise at 200 ° C., then 1 bearing time at 200 ° C, then 3 hours of temperature rise at 550 ° C, and finally 1.5 hours of bearing at 550 ° C.

There is thus obtained 327 g of anhydrous equivalent solid YPH zeolite; which represents a yield of 97 mol% relative to the amount of aluminum involved.

The Si / Al ratio of YPH determined by X-ray fluorescence is 2.4.

The porosity characteristics (microporous volume, mesoporous outer surface, size of the mesopores) are summarized in Table 1.

The morphology of the crystals is shown in FIG. 1 (SEM photo, magnification x 5000) and the mesoporosity is visualized in FIG. 2 (TEM photo, magnification x 300000). The size of the crystals is between 3 μηη and 7 μηη. Example 5

The procedure is as described in Example 4, with the addition of 10% by weight of the same nucleating gel with respect to the weight of the growth gel so as to reduce the size of the crystals.

The zeolite obtained has a crystal size of between 1 μηη and 3 μηη, that is to say less than the size of the crystals of the zeolite obtained in Example 4.

Comparison of the Characteristics of Hierarchized Porosity Y Zeolite Powders Synthesized in Examples 1, 2, 3 and 4

The results of the characterizations of zeolites with hierarchical porosity are grouped together in Table 1 with a comparison with a reference zeolite Y, CBV 100, marketed by Zeolyst International, and whose average crystal size is 0.6 μηι. .

The porosity characteristics (microporous volume, mesoporous outer surface, mesopore size) are calculated from nitrogen adsorption / desorption isotherms at the temperature of the liquid nitrogen of a previously degassed powder at 300 ° C. C under vacuum. Measurements are made on an ASAP 2020 Micromeritics device.

The microporous volume (cm ^3, g ^-1 ) is calculated according to the Dubinin-Raduskevitch theory The mesoporous outer surface (m ^2, g ^-1 ) is calculated from the t-plot model. The mesopore size distribution is calculated by the Density Functional Theory (DFT) method with the cylindrical Pore model.

The X-ray diffraction makes it possible to identify the crystalline phases present in the powder from the reference spectra (or diffractograms) of the various zeolite structures and to demonstrate the level of crystallinity of the solids produced as a function of the peak intensity.

FIG. 3 shows the diffractogram (a) of the non-mesoporous Y zeolite of reference (CBV 100) and the diffractogram (b) of the YPH zeolite of Example 4. This comparison shows the similarity of the intensities of the diffraction peaks between the reference zeolite and that of the invention (Example 4). This shows that the crystallinity (and therefore the microporous volume) is similar in these two zeolites. The results of the hierarchical porosity Y (YPH) Y zeolites of Examples 1, 2, 3 and 4 are summarized in Table 1 below:

- Table 1 -

Legend:

Zeolite Y CBV 100: Zeolyst International's non-mesoporous zeolite reference, νμρ: microporous volume calculated with Dubinin-Raduskevitch equation.

Sext: external surface deduced from the extrapolation t-plot.

The results presented in Table 1 above show that the morphology of the crystals varies with the TPOAC content. One explanation is the effect of the structuring agent on the growth rates of the different crystal faces.

The synthesis method implemented with the use of a seeding gel and a nucleation gel makes it possible to vary the microporous volume / mesoporous surface distribution while obtaining a pure Y type FAU (Faujasite) zeolite. that is, without observing other crystalline forms.

The method described in the present invention is economically viable, simple to implement on an industrial scale, with a very significant time saving compared to the syntheses described in the prior art. In addition, the synthesis method of the invention makes it possible to obtain quite satisfactory yields, generally greater than 90%, relative to the amount of aluminum involved and which is the element in defect in the gel of synthesis.

Claims

1. A hierarchically porous zeolite having the following characteristics:

Microporous volume νμρ, in cm ³ . g ^"1 , corresponding to the equation νμρ = \ μρ _κ ± 15%, where λ / μρρ! represents the microporous volume, in cm ³ .g ^-1 , measured under the same conditions, for a zeolite of the same chemical nature and of the same crystalline structure, but whose mesoporous outer surface is strictly less than 40 m ² .g ^-1 , and

Mesoporosity such that the mesoporous outer surface is between 40 m ² . g ^"1 and 400m ^2, g ^{" 1} , preferably between 60 m ² . g ^"1 and 200 m ^2. ^{g" 1} and more preferably between 60 m ² · g ^"1 and 150 m ² ^{.g" 1.}

2. A zeolite according to claim 1, which is a zeolite of Faujasite type, and in particular a zeolite Faujasite type Y.

Zeolite according to Claim 1 or Claim 2, having a number-average crystal diameter of between 0.1 μηη and 20 μηη, preferably between 0.1 μηη and 10 μηη, more preferably between 0.5 μηη and 10 μηη, more preferably between 0.5 μηη and 5 μηι, limits included.

A zeolite according to any one of the preceding claims, comprising a pure zeolite phase, and preferably consisting of a single zeolite phase or comprising, preferably up to 2% by weight, inclusive terminal, of a alone or several other zeolitic or amorphous phases.

5. A zeolite according to any one of the preceding claims, and secondly a microporous volume νμρ corresponding to the equation νμρ = \ μρ _κ ± 10%, preferentially to the equation νμρ = \ μρ _κ ± 5%, of very particularly preferred to the equation νμρ = νμρ _κ ± 3%, where \ / μρ _κ represents the microporous volume measured, under the same conditions, for a zeolite of the same chemical nature and of the same crystalline structure, perfectly crystalline but not mesoporous within the meaning of the invention, that is to say whose mesoporous outer surface is strictly less than 40 m ² . g ^"1

6. Process for the preparation of a zeolite according to any one of the preceding claims, comprising at least the following steps:

a) preparing a so-called growth gel for the synthesis of a Y-type FAU zeolite, by mixing a silica source with a source of alumina, at a temperature between 0 ° C and 60 ° C,

c) adding to the reaction medium at least one structuring agent,

d) crystallization reaction by increasing the temperature,

e) filtration and washing of the zeolite crystals obtained, and

f) drying and calcination.

The method of claim 6, wherein the nucleating agent is a nucleation gel.

The process according to claim 7, wherein the amount of nucleation gel added is between 0.1% and 20%, preferably between 0.5% and 15% by weight, more preferably between 1% and 10%. by weight, limits included, relative to the weight of the growth gel.

The method of claim 6, wherein the nucleating agent is a crystal.

10. The method of claim 9, wherein the amount of added crystal is between 0.1% and 10% by weight relative to the total weight of growth gel.

The process of any one of claims 6 to 10, wherein the source of silica is sodium silicate or colloidal silica, and the source of alumina is alumina trihydrate.

12. Process according to any one of claims 6 to 11, wherein the structuring agent is an organosilane.

13. Process according to any one of claims 6 to 12, in which the structuring agent is chosen from [3- (trimethoxysilyl) propyl] octadecyldimethylammonium chloride, [3- (trimethoxysilyl) propyl] hexadecyldimethylammonium chloride. [3- (trimethoxysilyl) propyl] dodecyldimethylammonium chloride, [3- (trimethoxysilyl) propyl] octylammonium chloride, N- [3- (trimethoxysilyl) propyl] aniline, 3- [2- (2-aminoethylamino) ) ethylamino] propyltrimethoxysilane, N- [3- (trimethoxysilyl) propyl] -N '- (4-vinylbenzyl) ethylenediamine, triethoxy-3- (2-imidazolin-1-yl) propylsilane, 1 - [3- ( trimethoxysilyl) propyl] urea, N- [3- (trimethoxysilyl) propyl] ethylenediamine, [3- (diethylamino) propyl] trimethoxysilane, (3-glycidyloxypropyl) trimethoxysilane, 3- (trimethoxysilyl) propyl methacrylate, [2- (cyclohexenyl) ethyl] triethoxysilane, dodecyltriethoxysilane, hexadecyltrimethoxysilane, (3-aminopropyl) trimethoxysilane, (3-mercaptopropyl) trimethoxysilane, (3-chloropropyl) trimethoxysilane, as well as mixtures of two or more of them in all proportions.

14. Process according to any one of Claims 6 to 13, in which the amount of structuring agent (s) is such that the molar ratio of the starting agent (s) / Al ₂ O ₃ is between 0.005 and 0.20, preferably between 0.01 and 0.15, more preferably between 0.02 and 0.08 inclusive.