ZEOLITH PREPARATION PROCESS

CONTINUOUS USING ULTRASONICS

The present invention relates to an intensified process for the continuous preparation of crystals of zeolites of high crystallinity, of controlled size and with a low level of aggregation.

The term "intensified process" means that the process implemented is:

- an accelerated process compared to the prior art (faster crystallization) and / or

- A method making it possible to reduce, or possibly eliminate, a grinding step subsequent to the recovery of the solid (usually grinding on the dried powder).

The synthesis of zeolite crystals (or more simply "zeolite synthesis" in the remainder of this presentation) is carried out in a conventional manner in the industry in a large stirred "batch" reactor, generally with heating of the gel. of synthesis and / or of the reaction medium by injection of steam and / or by double jacket. The preparation of the synthetic gel consists in mixing a solution of sodium aluminate with a solution of sodium silicate, this mixing being able to be carried out either in an installation upstream of the crystallization reactor or directly in the crystallization reactor.

[0004] In order to improve the conventional process for the crystallization of zeolites in batch, studies have been published on the development of continuous synthesis processes. This work aims to overcome or at least lessen the drawbacks associated with batch processes and in particular to reduce the size of the installations necessary for the synthesis, to decrease the energy expenditure as a consequence and to improve the regularity of the quality of the production.

[0005] Continuous synthesis methods are still little known today, and little used industrially. However, some studies describe so-called “continuous” zeolite synthesis processes, which can be classified into three categories:

1) the synthesis medium is first prepared in a batch reactor in a conventional manner then this gel reservoir continuously supplies a crystallization reactor; in this case, we then speak of a “semi-continuous” process since part of the process is carried out in a batch reactor (see for example Jingxi Ju et al, “Continuous synthesis of zeolite NaA in a microchannel reactor”, Chemical Engineering Journal, 1 16, (2006), 115-121; Shumovskii et al., “Continuous process for the production of zeolite in pulsation apparatus”, Chemical and Petroleum Engineering, 31 (5-6), (1995), 253-256;

Zhendong Liu et al., "Ultrafast Continuous-flow synthesis of crystalline microporous AIP04-5", Chem. Mater., 2-7, (2014); US 4848509 or also US 6773694);

2) the synthesis medium is prepared continuously using a shearing mixer and is then crystallized in a batch reactor in a conventional manner (see for example documents EP0149929 and BE 869156);

3) the synthesis medium is prepared continuously and feeds a reactor continuously in order to carry out crystallization.

[0006] The first two categories are therefore not strictly speaking “continuous” processes since at least part of the synthesis is carried out in batch.

Among the works of the third category, it appears that the continuous synthesis conditions are not always described very precisely, so that it is difficult, if not impossible, to reproduce them. In particular, the precise conditions for carrying out the process do not make it possible to know precisely which parameters are necessary to apply to reduce the crystallization time, or to accelerate the crystallization, to make the crystallization faster, to avoid the formation of aggregates as much as possible, while avoiding the formation of impurities, in particular unwanted crystalline phases.

[0008] Furthermore, it is already known to use ultrasound to assist the synthesis of zeolite, in order to promote the formation of “nuclei” (germs) which will serve as primers for the growth of the solid. Ultrasound is used in particular for the so-called low-temperature ripening phase (“aging”) prior to crystallization, which is carried out at a higher temperature.

[0009] The literature available on the subject, however, relates only to batch processes and ultrasound is only applied cold (maximum temperature at 50 ° C - 70 ° C), essentially on the mixture of reagents (synthetic gel) during the ripening phase. The application of ultrasound at a higher temperature, for intensified continuous zeolite preparation processes, i.e. where the nucleation rate should be as high as possible, is however neither described nor suggested in prior art.

[0010] Document CN 103848436 describes a conventional synthesis of zeolite A, in batch, with a long maturing time, greater than 20 hours, at 35-45 ° C then crystallization between 80 and 120 ° C and sonication at 20-50 Hz for 10 to 30 minutes. The ripening time required in this synthesis makes this process incompatible with the economic requirements associated with an industrial process. The application of ultrasound is presented in a possible washing step

Document CN105271298 describes for its part a process for upgrading coal gangue, composed of alumina and silica, which makes it possible to crystallize an LTA-type zeolite. In this process, a first heat treatment is necessary to “activate” the gangue which is then mixed with water under ultrasound irradiation. Then the reaction medium is subjected to a maturing step, then crystallization takes place by heating the reaction medium. However, this process does not correspond to an intensified process, within the meaning of the present invention, in particular due to the fact that the ultrasonic irradiation stage is carried out for the preparation of the activated gangue in aqueous medium.

[0012] The work of Askari et al. summarize the effect of ultrasound on the synthesis of different types of zeolites in the article “Effects of ultrasound on the synthesis of zeolites: a review”, J. Porous Mater., (2013), 20, 285-302. This article refers in particular to the references cited below, with the details of the operating conditions relating to ultrasound.

[0013] The article "Effects of ultrasound on zeolite A synthesis", Andac et al., Microporous and Mesoporous Materials, 79, (2005), 225-233, shows that the application of ultrasound at 35 kHz by immersing the synthesis reactor, in batch, in an ultrasonic bath during the maturing phase and the crystallization phase, accelerates the synthesis of zeolite.

The article "Synthesis of MCM-22 zeolite by an ultrasonic-assisted aging procedure", Wang et al., Ultrasonics Sonochemistry, 15, (2008), 334-338, shows the contributions of an exposure to ultrasound during the initial ripening of the gel for the synthesis of MCM-22 type zeolites prepared in batch, in particular in terms of reduction of the synthesis time, reduction of the content of structuring agent required in the formulation and increase in the diversity of MCM zeolites -22 obtained.

In "Ultrasonic-Assistance and Aging Time Effects on the Zeolitation Process ofBZSM-5 Zeolite", Abrishamkar et al., Z. Anorg. Allg. Chem., (2010), 636, 2686-2690, the ultrasound applied during the ripening step prior to crystallization shortens the crystallization time of a BZSM-5 zeolite (ZSM-5 zeolite isomorphically substituted with boron) prepared in batch. Ultrasound is applied at a frequency of 40 kHz and a power of 50 W, at room temperature.

[0016] The article "Static and Ultrasonic-assisted Aging Effects on the Synthesis of Analcime Zeolite", Azizi et al., Z. Anorg. Allg. Chem., (2010), 636, 886-890, shows the advantage of subjecting to ultrasound, during the ripening phase, the analcim zeolite synthesis gel to reduce the crystallization time. The synthesis temperature is 25 ° C, and no indication of the ultrasonic bath is provided (frequency / power conditions). The duration of batch synthesis is also totally incompatible with an economically feasible industrial synthesis.

[0017] The article “Ultrasonic pretreatment for hydrothermal synthesis of SAPO-34 nanocrystals”, Askari et al., Ultrasonics Sonochemistry, 19, (2012), 554-559, describes the hydrothermal synthesis, in batch, of SAPO- nanocrystals. 34 ultrasonically assisted during the ripening phase (at a frequency of 24 kHz and at a temperature maintained at 50 ° C).

Finally, the effect of ultrasound on the batch synthesis of EMT zeolite nanocrystals is studied as a function of time in the article "Effects of ultrasonic irradiation on crystallization and structural properties of EMT-type zeolite nanocrystals", Eng-Poh Ng et al., Materials Chemistry and Physics, 159, (2015), 38-45. The synthesis temperature is 25 ° C and the applied ultrasound frequency is 47 kHz.

A similar teaching emerges from the article "Effect of ultrasound pretreatment on the hydrothermal synthesis of SSZ-13 Zeolite", Mu et al., Ultrasonics-Sonochemistry, 38, (2017), 430-436, for the synthesis in batch of SSZ-13 zeolite. The ultrasound bath is at a temperature of 35 ° C, and the frequency is set at 40 kHz.

[0020] All of these so-called batch techniques are however completely incompatible with an intensified, continuous process, one of the main criteria of which is the acceleration of the rate of crystallization. In order to accelerate the crystallization rate as much as possible, one possibility is to prepare the zeolite crystals at a temperature ideally above 70 ° C, preferably above 75 ° C, more preferably above 80 ° C. Under these conditions, the synthesis time is reduced and allows access to a more economical preparation process.

The objective of increasing the crystallization temperature is to accelerate the growth kinetics of the crystals in order to reduce the duration of crystallization. The drawback of such a crystallization, known as “hot crystallization”, is that it remains difficult to carry out, and can, when it is badly carried out, lead to a degradation of the crystallinity of the solid formed or a co-crystallization of phases. unwanted. The application of ultrasound to further improve this step therefore remains to be explored.

[0022] To further accelerate crystallization, the technique of applying ultrasound remains to be explored. In fact, ultrasound could improve the speed of material transport at the solid / liquid crystallization interface by exacerbated local agitation in the reaction medium.

Furthermore, it is known that a point of vigilance in the implementation of a continuous synthesis process containing solids (as is the case in the synthesis of zeolites) is the risk of fouling reactors, which are generally and most often tubular reactors, by the accumulation of solids which may involve process drift and high maintenance costs.

One can think that if the continuous processes have not developed particularly so far in the synthesis of zeolites, this is probably due in particular to the risk of fouling due to the presence of solids in the reaction medium ( either amorphous solids present from the start in the synthesis gel, or crystalline solids at the end of synthesis, after crystallization), to the difficulties of reconciling crystallization time and quality of the crystals formed. These difficulties may be further amplified during the synthesis of crystals of sizes greater than a hundred nanometers.

[0025] Certain publications relate the application of ultrasound in order to simulate agitation of the reaction medium or even to disintegrate clusters of materials, agglomerates of crystals and others.

Thus, for example, it is reported in "Sonofragmentation: Effect of Ultrasound Frequency and Power on Particle Breakage", Jordens et al., Cryst. Growth Des., (2016), 16 (11), 6167-6177, on the interest of fragmenting paracetamol crystals, in a liquid medium, using ultrasound under various conditions. It is not however a question of disagglomeration of crystals, but of fracture of crystals which thus lose their integrity. This sonofragmentation treatment is carried out on previously isolated crystals, and therefore separately from the step of forming said crystals (crystallization).

We can also cite the work of JM Kim et al. ("Acoustic influence on aggregation and agglomeration of crystals in reaction crystallization of cerium carbonate", Colloids Surf. A Physicochem. Eng. Asp., (201 1), 375, pp. 193-199), and by B. Gielen et al. . ("Agglomeration Control during Ultrasonic Crystallization of an Active Pharmaceutical Ingredient", Crystals, (2017), 7, 40) which focus on the effects of sonication and ultrasound, in batch, on the state of agglomeration of crystals of organic compounds or mineral salts.

[0028] There therefore remains a need for an intensified process for the continuous preparation of crystals of highly crystalline zeolite, said crystals having a controlled size and being poorly aggregated, said process also exhibiting good efficiency both economically and in terms of energy plan, and particularly suited to the industrial scale.

[0029] Thus, the present invention relates to an intensified, continuous process for the synthesis of zeolite crystals, said process comprising a continuous supply of a gel prepared continuously, said gel then being continuously crystallized, said process comprising in minus an application of ultrasound.

In the process of the present invention, it should be understood that the gel crystallization step is carried out continuously, that is to say without a transient phase in batch.

It has in fact been surprisingly discovered that the application of ultrasound during an intensified continuous synthesis process of zeolite crystals makes it possible to obtain crystals of very high purity and / or to reduce, or optionally eliminate a grinding step subsequent to the recovery of the solid (usually grinding on the dried powder) well known to those skilled in the art.

[0032] The use of ultrasound thus makes it possible to achieve an intensification of the continuous zeolite synthesis process, which is efficient and economically viable from an industrial point of view, that is to say on a large scale , in order to be able to meet the zeolite needs of an ever-growing market. Still other advantages will appear in the light of the description of the invention which follows.

The process of the present invention makes it possible in particular to synthesize very high purity zeolite crystals, that is to say having a purity equal to or greater than 95%, preferably equal to or greater than 98%, and of more preferably between 98% and 100%, as determined by quantitative DRX analysis.

The method according to the present invention generally allows the synthesis of zeolite crystals of particle size (average diameter in number determined by counting on SEM images) which can range from 0.05 μm to 20 μm, preferably from 0.1 μm to 20 μm, more preferably still being able to range from 0.2 μm to 10 μm, and more preferably from 0.3 μm to 8 μm, very preferably from 0.3 μm to 5 μm.

The aggregation of the crystals is evaluated by measuring the sizes using the technique of particle size analysis by laser diffraction with an apparatus of the Malvern Mastersizer 3000 type, as explained for example by Jordens et al., Ibid.

More specifically, the present invention relates to a process for the preparation of zeolite crystals continuously, comprising at least the following steps:

a) continuous supply of a composition capable of generating zeolite crystals;

b) continuous introduction of said composition into at least one crystallization reaction zone subjected to ultrasound, and

c) continuous recovery of the crystals formed in step b).

For the purposes of the present invention, the term “composition capable of generating zeolite crystals” means any type of composition well known to those skilled in the art depending on the type of zeolite to be prepared. Such a composition typically comprises at least one source of silica and at least one source of alumina and / or any other source.

element (s) which can constitute a zeolitic framework, such as for example a source of phosphorus, titanium, zirconium, and the like.

Preferably, the "composition capable of generating zeolite crystals" comprises a gel prepared continuously, as mentioned above. According to a very particularly advantageous embodiment of the present invention, the composition capable of generating zeolite crystals consists of the continuously prepared gel defined above.

Thus, the gel prepared continuously comprises at least one source of silica and a source of alumina and / or any other source of element (s) which can constitute a zeolitic framework, such as for example a source of phosphorus, of titanium, zirconium, and the like.

To this composition can be added optionally, but preferably, at least one aqueous solution of alkali metal or alkaline earth metal hydroxide, preferably of alkali metal, typically sodium and / or even organic structuring agents (" structure-directing agent ”or“ template ”in English).

By "source of silica" is meant any source well known to those skilled in the art and in particular a solution, preferably aqueous, of silicate, in particular of alkali or alkaline earth metal silicate, for example of sodium , or even colloidal silica.

By "source of alumina" is meant any source of alumina well known to those skilled in the art and in particular a solution, preferably aqueous, of aluminate, in particular of alkali metal or alkaline metal aluminate. earthy, eg sodium.

The concentrations of the various solutions of silica and alumina are adapted according to the nature of the source of silica, of the source of alumina, of the respective proportions of the sources of alumina and of silica to which are added the solution of alkali metal or alkaline earth metal hydroxide and / or one or more organic structuring agents, according to the knowledge of those skilled in the art. In particular, information on the chemical nature of the organic structuring agents to be used depending on the zeolite to be synthesized can be found on the site of the “International Zeolite Association” (www.iza-online.org), for example and in a non exhaustive of tetramethylammonium (TMA), tetra-n-propylammonium (TPA), methyltriethylammonium (MTEA).

The respective concentrations and proportions of the various solutions of silica and alumina are known to those skilled in the art or can be easily adapted by those skilled in the art depending on the nature of the zeolite that is to be prepared, to based on data from the literature.

[0045] Thus, the intensification of the process results from the use of ultrasound, in other words the intensification of the process results from the application at one or more places along the continuous process of frequency ultrasound and well-defined power, with the power and frequency varying from one ultrasound source to another, fulfilling one or more of the following objectives:

accelerate the rate of crystallization (reduce the time of crystallization)

break up the aggregates of crystals at the end of synthesis, when the solid is still in suspension in the mother liquors (avoid or reduce the grinding phase in the solid state)

Ultrasound is applied at at least one point of the continuous synthesis of the zeolite crystals, for example in the crystallization zone (to promote crystal formation) and / or in the end of synthesis zone (to disintegrate possible aggregates of crystals), but also in the ripening zone, etc.

Ultrasound can be applied continuously, or sequenced or alternately or a combination of these different methods.

The application of ultrasound in a liquid medium creates acoustic cavitation. This acoustic cavitation in the liquid medium depends on a large number of sonochemical parameters (such as for example frequency, power, geometry of the reactor, and others), and on the operating conditions (such as for example pressure, temperature, dissolved gas, and others) which directly affect the sonochemical effects obtained.

Ultrasound is generally produced by a device called a transducer, in particular based on the properties of piezoelectric materials, which makes it possible to convert electrical energy into mechanical energy. This mechanical vibration is transmitted into the reaction medium in the form of an acoustic wave. Piezoelectric transducers use the inverse piezoelectric effect of natural or synthetic single crystals such as quartz or ceramics such as barium titanate. These materials are easily machinable in the form of discs, plates or rings on the faces of which are fixed two metal electrodes. Thus, when an electric voltage is applied to these electrodes, the material expands or compresses depending on the orientation of the voltage with respect to the polarization of the material,

Other types of ultrasound emissions are possible, for example from magnetostrictive transducers based on ferromagnetic materials placed under an alternating magnetic field. In addition, as the phenomenon of cavitation can be induced by ultrasound, it is conceivable that this phenomenon is induced by other techniques such as by hydrodynamic cavitation. Combinations of two or more of these techniques can of course be implemented in the process of the present invention.

[0051] Devices Ultrasonic adapted to the needs of the invention may for example be selected from the transducer device to devices, such as those marketed for example by Weber Ultrasonics, under the names Sonopush ® Duotransducer HD Multi Sonoplate , Flow-Through Cell, or even those marketed by the Hielscher company, for example the UP200S, to name only a few of them, without however being limiting.

The frequency of the ultrasound applied largely depends on the desired effect and the nature of the medium to which they are applied. This frequency is generally between 10 kHz and 5 MHz, preferably between 10 kHz and 1.5 MHz, more preferably between 15 kHz and 1 MHz, very particularly preferably between 15 kHz and 500 kHz, typically between 15 kHz and 200 kHz.

Likewise, the acoustic power of the ultrasound which is dissipated in the medium depends largely on the desired effect and on the nature of the medium to which the ultrasound is applied. This acoustic power is directly linked to the electrical power supplied by the generator. The electric power supplied by the generator is generally between 3 W and 500 W, preferably between 5 W and 400 W, more preferably between 8 W and 300 W.

[0054] According to a preferred embodiment, and when the desired effect is the reduction in the duration of the synthesis, the ultrasound applied is applied with relatively low powers, typically powers less than 100 W. In this case, the ultrasound is applied. crystal size (number average diameter) tends to decrease when the power of the applied ultrasound increases. According to another preferred embodiment, and when the desired effect is the disintegration of crystals, the ultrasounds applied are applied with higher powers, typically powers greater than 100 W. In this case, the size of the agglomerates decreases with the increase in power. power of applied ultrasound.

Likewise, the ultrasound exposure time of the continuous synthesis medium can vary widely depending on the desired effect, depending on the nature of the reaction medium and others. Thus, and according to a preferred embodiment of the process according to the present invention, the fraction of the time of exposure to ultrasound relative to the residence time of the reaction medium in the continuous reactor is between 0.05% and 50%, preferably between 0.1% and 30%, more preferably 0.1% and 20%, better still between 0.1% and 10%, limits included.

As indicated above, the ultrasound can be applied continuously, in a sequenced or alternating manner, the application continuously at one or more points throughout the continuous synthesis process being however preferred. Any other combination of ultrasound applications, with variations in application time and / or variations in frequency, or even variations in power are of course possible and within the reach of those skilled in the art. Thus, the duration of exposure to ultrasound, as well as the power of the ultrasound applied per unit volume of gel, have an influence on the crystallization kinetics and on the disintegration of the zeolite crystals. Crystals tend to form faster with increasing exposure time and / or applied power. Likewise,

The process of the present invention can be carried out at any temperature that a person skilled in the art will know how to adapt according to the type of zeolite to be produced and the degree of intensification of the desired process. According to a preferred embodiment, the method according to the invention is carried out at a temperature between 70 ° C and 180 ° C, preferably between 75 ° C and 160 ° C, more preferably between 80 ° C and 140 ° C. .

At temperatures below 60 ° C, the process will be too slow for the needs of an intensive industrial process, so that temperatures above 60 ° C, or even above 70 ° C, and even above 80 ° C are particularly suitable. Reaction temperatures even higher than 180 ° C could theoretically be applied, the industrial process could however under such conditions be regarded as not very profitable.

According to a very particularly preferred aspect of the present invention, the reaction temperature can be advantageously set between 75 ° C and 180 ° C, preferably between 80 ° C and 140 ° C to obtain an optimal compromise between degree of intensification of the process and purity of the crystals obtained.

The method of the present invention can optionally comprise one or more steps of adding seed (s) to the reaction medium.

The addition of seed to the synthesis medium makes it possible to obtain even greater crystallization kinetics in order to be compatible with the constraints of a continuous process. The seed addition (s) can or can be made by any means known to those skilled in the art and for example using a static mixer, which has the advantage of promoting homogenization of the mixture of synthesis medium / seed. By seed (also called “seeding agent”) is meant a solid or a liquid which promotes the orientation of the synthesis towards the desired zeolite. In a particularly advantageous embodiment, the method of the invention comprises the addition, in one or more times, before, after or during the crystallization step, of one or more seeding agents.

By seeding agent (or seed) is meant a solution or a suspension, in liquid form or in gel form, of a solid or of a liquid which promotes the orientation of the synthesis towards the zeolite desired. The seeding agents are well known to those skilled in the art and are, for example, chosen from nucleation gels, zeolite crystals, mineral particles of any kind, and others, as well as their mixtures.

[0064] According to a preferred aspect, the seeding agent is a nucleation gel and more preferably, said nucleation gel comprises a homogeneous mixture of a source of silica (for example sodium silicate), a source of 'alumina (for example alumina trihydrate), optionally but advantageously a strong mineral base, such as for example sodium, potassium or calcium hydroxide to name only the main and most commonly used, and water . One or more structuring agents, typically organic structuring agents, can also optionally be introduced into the nucleation gel.

Thus, the application of ultrasound in the process for the continuous preparation of zeolite crystals allows a substantial intensification of this continuous synthesis, by allowing shorter synthesis times and also reduced energy consumption.

In addition, and if desired, the method of the invention can comprise a step allowing the elimination or at least the reduction of the post-grinding step by ultrasonic irradiation at the end of the synthesis, where the crystals are usually “dry” ground after filtration and drying, the drying step having the effect of making the aggregates more resistant, and therefore more difficult to disrupt. The application of ultrasound according to the process of the present invention makes it possible to disintegrate in a humid environment, before separation of the mother liquors, which makes it possible to reduce the overall energy balance of the process.

It has also been discovered, quite surprisingly, in the continuous process of the present invention, that the application of ultrasound also makes it possible to reduce or even eliminate any risk of clogging of the system. . The use of ultrasound consequently further facilitates the preparation of zeolite crystals continuously, and this, in an industrial manner. Thus the process of the present invention makes it possible to propose an industrial process which benefits from the advantages of

continuous synthesis by minimizing or even eliminating the problems linked to the clogging of the installations.

In general, the process of the present invention allows the preparation of any type of zeolite known to those skilled in the art and for example, and in a nonlimiting manner, any MFI type zeolite, and in particular silicalite, any MOR type zeolite, OFF type, MAZ type, CHA type and HEU type, any FAU type zeolite, and in particular Y zeolite, X zeolite, MSX zeolite, LSX zeolite, any EMT type zeolite or even any zeolite of LTA type, that is to say zeolite A, as well as other zeotypes, such as, for example, titanosilicalites.

The term MSX zeolite (Medium Silica X) is understood to mean an FAU type zeolite having an Si / Al atomic ratio of between approximately 1.05 and approximately 1.15, limits included. The term LSX (Low Silica X) zeolite is understood to mean a zeolite of FAU type having an Si / Al atomic ratio equal to approximately 1.

The process according to the invention is particularly suitable for the preparation of zeolites chosen from zeolites of MFI type, and in particular silicalite, of FAU type, and in particular Y zeolite, X zeolite, MSX zeolite, LSX zeolite, and of LTA type, that is to say of zeolite A, as well as zeolites of CHA type and zeolites of HEU type.

The process according to the invention is also very particularly suitable for the preparation of any FAU type zeolite, and in particular X zeolite, MSX zeolite, LSX zeolite. MFI type zeolites, and in particular silicalite, can also be very advantageously prepared according to the process of the invention.

In addition, the continuous preparation process of the present invention is not limited to the preparation of the zeolites described above, but also includes the corresponding zeolites with hierarchical porosity. The zeolites with hierarchical porosity are solids, well known to those skilled in the art, comprising a microporous network linked to a network of mesopores, and thus make it possible to reconcile the properties of accessibility to the active sites of mesoporous zeolites known in the art. prior and those of maximum crystallinity and microporosity of the so-called “classic” zeolites (without mesoporosity). For the synthesis of such zeolites with hierarchical porosity, use is generally made of specific so-called structuring agents which are introduced into the synthesis medium,

According to another aspect, the present invention relates to the use of ultrasound, during the synthesis of zeolite crystals continuously at a reaction temperature of between 70 ° C and 180 ° C, preferably between 75 ° C and 160 ° C, more preferably between 80 ° C and 140 ° C, said ultrasound being used at a frequency between

10 kHz and 5 MHz, preferably between 10 kHz and 1.5 MHz, more preferably between 15 kHz and 1 MHz, very particularly preferably between 15 kHz and 500 kHz, typically between 15 kHz and 200 kHz.

The following examples illustrate the invention without however limiting the scope defined by the claims appended to the description of the present invention.

Characterization techniques

Qualitative and quantitative analysis by X-ray diffraction (XRD)

The purity of the zeolite crystals synthesized is evaluated by X-ray diffraction analysis, known to those skilled in the art by the acronym DRX. This identification is carried out on a DRX device of the Bruker brand.

This analysis makes it possible to identify the different zeolites present in the adsorbent material because each of the zeolites has a unique diffractogram defined by the positioning of the diffraction peaks and by their relative intensities.

The zeolite crystals are ground and then spread and smoothed on a sample holder by simple mechanical compression.

The conditions for acquiring the diffractogram produced on the Bruker D5000 device are as follows:

• Cu tube used at 40 kV - 30 mA;

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

• filter: Ni;

• rotating sample device: 15 rpm 1 ;

• measuring range: 3 ° <20 ° <50 °;

• step: 0.02 °;

• counting time per step: 2 seconds.

The interpretation of the diffractogram obtained is carried out with the EVA software with identification of the zeolites using the ICDD PDF-2 database, release 2011.

The amount of crystals, by weight, is determined by XRD analysis, this method is also used to measure the amount of non-crystalline phases. This analysis is carried out on an apparatus of the Bruker brand, then the amount by weight of the zeolite crystals is evaluated by means of the TOPAS software from the Bruker company. The purity is expressed as a percentage by mass of the desired crystalline phase relative to the total weight of the sample.

Crystallinity analysis

The crystallinity of the zeolite crystals is estimated by conventional methods such as measurements of Dubinin volumes (adsorption of liquid nitrogen at 77 K), or the toluene adsorption indices (adsorption capacities of toluene at a relative pressure of 0.5 at 25 ° C after exposure for 2 hours, as described in patent application EP11 16691 A or patent US6464756 B).

Example 1: Continuous process without ultrasound at 80 ° C

Zeolite X crystals in sodium form (NaX) are prepared from solutions of sodium aluminosilicate and sodium silicate, with a step of adding a seeding agent. Thus, 100 ml of reaction medium are prepared by mixing the solutions of sodium silicate and sodium aluminosilicate at 80 ° C. in a mixer at high shear rate.

Crystallization takes place at 80 ° C for 2 hours, by circulating the reaction medium at a flow rate of 60 mL.min 1 to pass it through a tubular reactor 0.5 cm in diameter and 22, 5 cm in length, said reactor being equipped with a plate transducer located outside the tube, but which remains inactive for this example.

Example 2: Continuous process with ultrasound at 80 ° C

Zeolite X crystals in sodium form (NaX) are prepared from solutions of sodium aluminosilicate and sodium silicate, with a step of adding a seeding agent. As in the previous example, 100 ml of reaction medium are prepared by mixing the solutions of sodium silicate and sodium aluminosilicate at 80 ° C. in a mixer at high shear rate.

Crystallization takes place at 80 ° C for 2 hours, by circulating the reaction medium at a flow rate of 60 mL.min 1 to pass it through a tubular reactor 0.5 cm in diameter and 22, 5 cm long which is, for the purposes of this example, exposed to ultrasound generated using the plateau transducer whose frequency is equal to 34.5 kHz. The electric power of the generator is fixed at 40 W.

Ultrasound is applied continuously only at the level of the tubular reactor, which corresponds to a continuous circulation of the synthetic gel with a point irradiation with ultrasound.

Figures 1 and 2 show that in the absence of ultrasound, the zeolite crystals allowing to achieve an adsorption of toluene (T50) of about 24% are obtained after 120 minutes (Example 1, Figure 1 ). With the application of ultrasound (Example 2, Figure 2), the zeolite crystals making it possible to achieve an adsorption of toluene (T50) of about 24% are obtained from 80 minutes, which demonstrates the very great interest of the The use of ultrasound for the intensified process for the preparation of continuous zeolite crystals according to the present invention. It is therefore observed that the synthesis time can be greatly reduced (1/3 less time in Example 2) by applying ultrasound, without degrading the adsorption properties of the zeolite obtained. This corresponds to an intensification of the process for preparing zeolites,
CLAIMS

1. Intensified, continuous process for the synthesis of zeolite crystals, said process comprising a continuous supply of a continuously prepared gel, said gel then being continuously crystallized, said process comprising at least one application of ultrasound.

2. Method according to claim 1, comprising at least the following steps: a) continuous supply of a composition capable of generating zeolite crystals;

b) continuous introduction of said composition into at least one crystallization reaction zone subjected to ultrasound, and

c) continuous recovery of the crystals formed in step b).

3. The method of claim 1 or claim 2, wherein the ultrasound is applied at at least one point of the continuous synthesis of the zeolite crystals.

4. Method according to any one of the preceding claims, in which the ultrasound is applied continuously, or sequenced or alternately or a combination of these different methods.

5. Method according to any one of the preceding claims, wherein the frequency of the ultrasound applied is between 10 kHz and 5 MHz, preferably between 10 kHz and 1.5 MHz, more preferably between 15 kHz and 1 MHz, from very particularly preferably between 15 kHz and 500 kHz, typically between 15 kHz and 200 kHz.

6. Method according to any one of the preceding claims, in which the electric power supplied by the ultrasound generator is between 3 W and 500 W, preferably between 5 W and 400 W, more preferably between 8 W and 300. W.

7. Process according to any one of the preceding claims, in which the fraction of the time of exposure to ultrasound relative to the residence time of the reaction medium in the continuous reactor is between 0.05% and 50%, preferably. between 0.1% and 30%, more preferably 0.1% and 20%, better still between 0.1% and 10%, limits included.

8. Process according to any one of the preceding claims, in which the reaction temperature is between 70 ° C and 180 ° C, preferably between 75 ° C and

160 ° C, more preferably between 80 ° C and 140 ° C.

9. Method according to any one of the preceding claims, further comprising one or more steps of adding seed (s) to the reaction medium.

10. Process according to any one of the preceding claims, further comprising an ultrasound irradiation step at the end of synthesis, in a humid medium, before separation of the mother liquors.

11. Process according to any one of the preceding claims, in which the zeolite crystals prepared are crystals of zeolite chosen from zeolites of MFI type, zeolites of MOR type, zeolites of OFF type, zeolites of MAZ type, CHA type zeolites, HEU type zeolites, FAU type zeolites, EMT type zeolites, LTA type zeolites, and titanosilicalites.

12. Process according to any one of the preceding claims, in which the zeolite crystals prepared are crystals of zeolite chosen from zeolite X, zeolite MSX and zeolite LSX.

13. Process according to any one of the preceding claims, in which the zeolite crystals prepared are zeolite crystals with hierarchical porosity.

14. Use of ultrasound, during the synthesis of zeolite crystals continuously at a reaction temperature between 70 ° C and 180 ° C, preferably between 75 ° C and 160 ° C, more preferably between 80 ° C and 140 ° C, said ultrasound being used at a frequency between 10 kHz and 5 MHz, preferably between 10 kHz and 1.5 MHz, more preferably between 15 kHz and 1 MHz, very particularly preferably between 15 kHz and 500 kHz, typically between 15 kHz and 200 kHz.