[0001] The present invention relates to zeolites, more precisely the field of industrial synthesis of zeolite crystals and more particularly that of the industrial synthesis of controlled particle size zeolite crystals.
[0002] The synthesis of zeolite crystals (or simply "synthetic zeolite" in the remainder of this disclosure) is conventionally carried out in the reactor industry in "batch" stirred large, usually with heating the gel synthesis and / or the reaction medium by injection of steam and / or jacket. The preparation of the synthesis gel comprises mixing a sodium aluminate solution with sodium silicate solution, this mixture can be carried out either in an upstream installation of the crystallization reactor or directly into the crystallization reactor.

[0003] It is then often necessary to perform a low-temperature curing phase, generally at a temperature below 40 ° C for a longer or shorter duration, usually varying in a few tens of minutes to a few dozen hours , depending on the desired type of zeolitic structure. This phase allows ripening form seeds that give, by their growth, the zeolite crystals after the crystallization stage carried out at higher temperature.

[0004] The addition of seeds in the synthesis gel (seeding process), however, eliminates this phase of curing at low temperatures. Under these conditions, it is possible to control the average crystal size by adjusting the amount of seed introduced into the synthesis gel and thus form a reaction mixture capable of forming zeolite crystals.

[0005] It is thus possible, or at least theoretically possible to obtain zeolite crystals of different sizes, ranging for example from a few tens or a few hundreds of nanometers to several tens of micrometers, it being understood that synthesis reaction, with an own operating conditions for this synthesis, leads to the formation of crystals relatively well controlled particle size zeolite, usually unimodal particle size distribution characterized by a more or less wide.

[0006] However, the areas of use of zeolites are now more and more varied and require increasingly sophisticated technology, so it is often necessary to have controlled particle size zeolites, unimodal, bimodal or multimodal, and whose width at mid-height (FWHM or "Full Width at Half Maximum", FWHM in English) can be adjusted and controlled.

[0007] It may indeed be necessary today to be able to offer crystal controlled particle size zeolite, especially particle size control, for example in order to increase the compactness, density, and others, according to the intended applications. In these applications, it is also often required to replace worn zeolites, and therefore it is essential to be able to replace these zeolites used by new zeolites with the same size characteristics.

[0008] Thus Wanted versatile synthetic methods for obtaining zeolites with particle size distributions, bi- or multi-modal, well controlled and especially controlled, that is to say, repeatable over time.

[0009] It is known synthetic processes leading to particle size distribution in zeolite crystals relatively narrow unimodal. However, besides the fact that it is often difficult to reproduce with great precision successive synthesis (often syntheses "batch") identical to recover the same size characteristics, these techniques do not generally allow obtaining multimodal particle size distributions.

[0010] In order to obtain different sizes of zeolite crystals, well defined, it could be envisaged to produce physical mixtures of zeolite crystals in unimodal distribution perfectly well defined. Mixtures of zeolite crystals, that is to say, physical mixtures of dry powders, are actually unsatisfactory; it is indeed very difficult to obtain homogeneous mixtures of crystals with particle sizes ranging from tens of nanometers to several tens of micrometers.

[0011] There therefore remains a need for a controlled particle size zeolite crystal preparation method, a controlled particle size, monomodal or multimodal particle size distribution, with an adjustable LMH, and particle size of between a few tens of nanometers and a few tens of micrometers.

[0012] The Applicant has now found that it is possible to achieve in whole or at least in part the objectives described above by the method described below and which forms a first object of the present invention. Other advantages and other objects still appear in the description of the invention that follows.

[0013] The applicant has now discovered that multimodal particle size distributions crystals reproducible and homogeneous zeolite (stable during the entire production) can be easily obtained by mixing the reaction media from multiple synthesis reactors, late or being crystallization, which produce different sizes of crystals, and by adjusting the proportions of introduced reaction media.

[0014] In order to ensure good control of the multi-modal particle size distribution of zeolite crystals, the method of the present invention comprises:

- Parallel production in at least two different synthesis reactors, zeolite crystals of different particle size distributions, and

- The mixture, after starting of the crystallization reaction, that is to say during the crystallization reaction or at the end of crystallization, the reaction media (zeolite crystal suspensions thus produced) of the at least two different reactors, in proportions resulting in the desired multi-modal particle size distribution.

[0015] Thus, the present invention firstly relates to a zeolite crystal preparation method having a multimodal particle size distribution, and whose sizes are comprised between 0.02 and 20 μηη μηη, said method comprising at least the following steps :

a) preparation of a synthesis gel by mixing at least one silica source, at least one source of alumina and optionally but preferably at least an aqueous solution of alkali metal hydroxide or alkaline earth,

b) feeding at least two reactors each with a synthesis gel capable of forming zeolite crystals,

c) conducting a crystallization reaction, in parallel, in each of at least two reactors,

d) mixing of the reaction media of at least two reactors, and

e) filtering the mixture of the reaction media obtained in step d), to separate the product crystals from the mother liquors.

[0016] The synthesis gel may be any type of well known composition the skilled person depending on the type of zeolite to prepare and typically comprises at least one silica source and at least one source of alumina, and / or another source of element (s) may constitute a zeolitic framework, e.g. source of phosphorus, titanium, zirconium, and the like. It is also possible, even preferable, to add at least an aqueous solution of alkali metal hydroxide or alkaline earth metal, preferably alkali metal, typically sodium and / or organic structuring agents ( "structure-directing agent "or" template "in English).

[0017] The silica source is any well-known source of the art and in particular a solution, preferably aqueous, silicate, particularly alkali metal silicate or alkaline earth metal, eg sodium, or colloidal silica.

[0018] The alumina source is any source of alumina is well known to those skilled in the art and in particular a solution, preferably aqueous, aluminate, in particular alkali metal or alkaline earth aluminate, for example sodium.

[0019] The concentrations of the various solutions of silica and alumina are suitable depending on the nature of the silica source, the alumina source, the respective proportions of the sources of alumina and silica which are added the solution of alkali metal hydroxide or alkaline earth metal and / or one or more organic templating agents, according to the knowledge of those skilled in the art. Be found including information on the chemical nature of the organic structuring agents to possibly use based on the zeolite synthesized on the site of the "International Zeolite Association" (www.iza-online.org), for example and so not comprehensive tetramethylammonium (TMA), tetra-n-propyl (TPA), the methyltriethylammonium (MTEA).

[0020] The respective concentrations and proportions of the various solutions of silica and alumina are known to those skilled in the art or can be readily adapted by those skilled in the art depending on the nature of the zeolite it is desired to prepare, from the literature data.

[0021] The step of synthesis gel) is prepared as described above by mixing sources of silica and alumina in a basic medium. This mixture is advantageously carried out in a shearing type mixer "rotor-stator", that is to say a shear mixer comprising a rotor rotating at high speed and the blend is passed through a stator whose geometry can vary.

[0022] The level of shear is defined by the shear rate in s γ "1 which is equal to the peripheral speed of the rotor divided by the thickness of the air gap between the rotor and the stator. The peripheral speed V p is calculated from the rotation speed V r and the diameter of the rotor according to the relationship: V p = V r π d r (expressed in m s. "1 ), where V r is the rotational speed expressed in rpm. s "1 , d r is the rotor diameter (in m) and γ is equal to V p / e, where e is the distance of the air gap between the rotor and the stator (in m).

[0023] The shear rate applied generally is between 10 000 s "1 and 200 000 s " 1 , preferably between 10 000 s "1 and 100 000 s " 1 .

[0024] The at least two reactors are supplied in step b) with each a synthesis gel zeolite crystals by any suitable means for transferring a fluid, for example by gravity flow, by siphoning or pumping. Control flow

the synthesis gel at the inlet of each of the at least two reactors and / or the production of crystals of output each of the at least two reactors may be obtained by any means known to those skilled in the art and preferably by means pumps, possibly associated with flow regulators.

[0025] The at least two reactors are each fed by a synthesis gel zeolite crystals. The synthesis gels may be the same or different, that is to say, they can be prepared from various silica and alumina solutions introduced in different concentrations and proportions and known to those skilled in the art or can be easily adapted by the skilled person depending on the nature of the zeolite that is desired to prepare, from the literature data.

[0026] A preferred embodiment of the method of the present invention comprises introducing one or more agent (s) in the seed or the gel (s) synthesis upstream or inside of at least one synthesis reactor or in at least two synthesis reactors. By seeding agent is meant a solution or suspension, in liquid form or gel form, a solid or liquid that favors orientation of the synthesis to the desired zeolite. Such solid and liquid that promote the orientation of the synthesis towards the desired zeolite are well known to those skilled in the art and are for example selected among the nucleating gels, zeolite crystals, the inorganic particles of any kind, and others, as well as mixtures thereof.

[0027] According to a preferred aspect, the seeding agent is a nucleating gel and more preferably, said nucleation gel comprises a homogeneous mixture of a silica source (e.g. sodium silicate), a source alumina (e.g. alumina trihydrate), optionally but preferably a strong inorganic base, such as for example sodium hydroxide, potassium or calcium to mention only the main and most commonly used, and water . One or more structuring agents, typically organic structuring agents, may also optionally be introduced into the nucleation gel.

[0028] The mixture of the agent (s), seeding with the synthesis gel can be performed by any technique well known to those skilled in the art and preferably using a static mixer, which the advantage of encouraging the homogenization of said mixture.

[0029] The reactors used may be of any type well known to those skilled in the art and adapted to the type of synthesis envisaged, for example stirred reactor for batch syntheses and tube reactor for syntheses in continuous mode. In the method of the present invention are generally 2 or more reactors, types

identical or different, preferably 2, 3, 4 or 5 reactors of identical or different types, more preferably 2 or 3 reactors of identical or different types, more preferably two reactors of identical or different types, typically two identical types of reactors .

[0030] Further preferred carry out the process continuously, and in this case we use preferably 2, 3 or 4 tubular reactors, more preferably 2 or 3 tubular reactors, typically two tubular reactors.

[0031] The term "stirred reactor" means a reactor equipped with a stirring system, typically provided with one or more agitators mounted on the same axis or different axes, for example and not limited to agitator (s) to pale, mixer (s) or type mixer auger and optionally provided with one or more against baffles or baffle arrangements.

[0032] The term "tubular reactor" means a reactor or a system of reactors having length to diameter ratios (or equivalent diameter) greater than 3, preferably greater than 10 and more preferably greater than 50, and defining a reaction zone of crystallization subjected at least partially to an agitating means, whether mobile agitation, passive systems such as against baffles, restrictions, rings or baffles or oscillating system or pulsating ( for generating a movement back and forth of the reaction medium for example by means of a piston, diaphragm), and others, as well as two or more of these combined techniques.

[0033] In a preferred embodiment of the invention, the tubular reactor is provided with restrictions and equipped with a system for imparting to the fluid circulating in the reactor of pulses, such as described in application US 2009/0304890 NiTech of society.

[0034] Step c) of conducting crystallization of reactions is carried out according to methods known to those skilled in the art, that is to say either by curing / crystallization from a synthesis gel, or by direct crystallization after seeding with different types of seeds. The seeded process is preferred in that it allows better control of the size of the crystals produced.

[0035] The crystallization reactions are carried out in parallel, each in a reactor, and may be carried out simultaneously and / or sequenced manner and / or sequentially, preferably simultaneously.

[0036] The crystallization reaction is generally carried out at high temperature, that is to say at a temperature between 60 ° C and 200 ° C, preferably between 80 ° C and 160 ° C. The crystallization of the synthesis gel comes most often spontaneously in

reactor and is favored by the one or more agent (s) added seed (s) to said gel synthesis. Crystallization is also favored by the temperature applied to the synthesis gel, but also by any means of agitation, static or dynamic, of the synthesis gel in the reactor as explained above.

[0037] By "favored" a better seed crystal means and / or a higher crystallization kinetics.

[0038] The crystallization reaction can be performed under pressure, for example under autogenous pressure, atmospheric pressure, or more generally at any pressure, typically between atmospheric pressure and 1, 5 MPa.

[0039] The reactions of the at least two reactors operating in parallel are then mixed at any time, since the crystallization reaction began in one of the at least two reactors, preferably in at least two reactors and this, in the proportion which provides the desired multi-modal distribution.

[0040] It is considered that the crystallization reaction started to the reactor since the degree of crystallinity, analyzed by X-ray diffraction (XRD) on a sample taken from said reactor and then dried at 80 ° C for 4 hours, is greater than 5%, preferably greater than 10%, more preferably greater than 30%, and most preferably greater than 50%.

[0041] When the syntheses are carried out in continuous mode, and for each of the reactors which are preferably tubular reactors, the synthesis gel is prepared preferably continuously using a shear mixer operating continuously. In the synthesis gel, it is then possible to introduce by any suitable means described above and one or more agent (s) seeding continuously to inoculate and control the size of crystals to be obtained after crystallization.

[0042] It is also conceivable to operate with the seeding agents and / or synthesis of various kinds of gels in order to obtain crystals of zeolites themselves of different structures. The method of the present invention can indeed be implemented to synthesize zeolite crystals of different structures.

[0043] Several reactors (at least two) operate in parallel, to suitable timber, to adjust the proportion of different size classes of the zeolite crystals. The reaction media continuously produced in these reactors and contain the zeolite crystals are mixed continuously since the crystallization reaction started in one of at least two reactors, preferably in at least two

reactors and in a proportion which provides the desired multi-modal distribution.

[0044] According to a preferred embodiment, the method of the present invention is carried out in continuous mode. In contrast to batch mode, the continuous mode provides the advantage of facilitating the adjustment of the multi-modal distribution by controlling the flow rates of each tubular reactor.

[0045] The process of the present invention is characterized in that are performed in parallel at least two syntheses of zeolite crystals, the reaction media are combined since the crystallization reaction began in one of the at least two reactors, preferably in at least two reactors and in a proportion which provides the desired multi-modal distribution.

[0046] The mixture of the reaction media can be performed by any method well known to those skilled in the art, particularly suitable methods are those that allow an efficient and homogeneous mixing of aqueous media in which solid particles are suspended. Among the usable methods include, by way of non-limiting example, those implementing a static mixer, or any other type of mixer blades, vanes, baffles, or a simple system pipelines that join in one (e.g. tube "Y" in the case of two reactors). It is also possible to combine one or more mixing techniques.

[0047] Blending of the reaction media containing the zeolite crystals in the form of liquid suspensions provides after filtration / washing and drying a homogeneous mixture of zeolite crystals in terms of particle size distribution. This result can not be obtained easily, that is to say economically and with good reproducibility when mixing the dried zeolite crystals of different sizes. Indeed, in this case, there are often segregation inherent in mixing dry zeolite crystals of different sizes, so different individual masses.

[0048] The reaction mixtures from step c) of crystallization are different in that they contain different zeolite crystals, either in size or in kind or in kind and size. however it is preferred to use the method of the invention for the synthesis of a single crystalline form of zeolite, however with different particle size distributions, so as to obtain the zeolite crystals with a bimodal or multimodal particle size distribution.

[0049] The skilled person can easily understand the flexibility afforded by the process of the invention, for generating populations of zeolite crystal size distributions monitored and controlled.

[0050] For example the respective flow rates and / or the respective quantities of each of the reaction media can be adjusted to adjust the proportions of each of the reaction media used in the mixture of step d) and thus easily control the desired particle size distribution of mixture of zeolite crystals at the end of the process of the present invention.

[0051] The method of the invention thus provides an adjustable multimodal crystal size distribution and controlled by mixing several reaction media, each of which is derived from a synthesis which parameters require a well defined and controlled granulometry .

[0052] Grâce au procédé de l'invention, il est maintenant possible de préparer sur le plan industriel des cristaux de zéolithe, avantageusement en continu, en réglant finement la distribution de la taille en nombre des cristaux de zéolithe. Il est ainsi possible d'obtenir une production industrielle aisée, efficace et économique de cristaux de zéolithe avec une distribution granulométrique multimodale réglable et maîtrisée, c'est-à-dire reproductible, stable dans le temps.

[0053] Dans un mode de réalisation préféré, le procédé de l'invention est un procédé de synthèse en continu d'un mélange de cristaux de zéolithe présentant une distribution granulométrique bimodale, ledit procédé étant réalisé dans deux réacteurs tubulaires travaillant en parallèle avec des conditions de synthèse différentes de manière à produire des cristaux de granulométrie différente, les sorties des deux réacteurs étant réunies au moyen d'une tubulure en forme de « Y ».

[0054] Selon un aspect préféré de la présente invention, les réactions de synthèses des cristaux de zéolithe sont opérées en présence d'un ou plusieurs agent(s) d'ensemencement, tels que définis ci-dessus.

[0055] À l'issue de l'étape d) de mélange, le mélange desdits milieux réactionnels est filtré pour séparer les cristaux produits d'une part et les eaux-mères d'autre part. Cette filtration peut être réalisée selon toute méthode bien connue de l'homme du métier, et par exemple par une ou plusieurs méthodes choisies parmi centrifugation, filtration sur filtre presse, filtration sur filtre à bande, filtration sur filtre rotatif et autres.

[0056] Les cristaux obtenus à l'issue de l'étape e) peuvent éventuellement être soumis à un ou plusieurs traitements classiques et bien connus de l'homme du métier, tels que lavage, échange cationique, séchage, imprégnation, activation, et autres, ce ou ces

traitements pouvant être effectués en batch ou en continu, avantageusement en continu. Par exemple les cristaux obtenus peuvent être soumis à un ou plusieurs lavages à l'eau, de façon à éliminer les eaux-mères résiduelles qui pourraient encore être présentes.

[0057] Les cristaux obtenus peuvent également être séchés, selon les techniques classiques de séchage de cristaux de zéolithe, par exemple à des températures comprises entre 40°C et 150°C, pendant une durée pouvant varier entre quelques minutes et quelques heures, typiquement entre quelques minutes et 10 heures. L'opération de séchage à une température inférieure à 40°C pourrait s'avérer beaucoup plus longue et ainsi peu rentable économiquement, tandis qu'une température de séchage supérieure à 150°C pourrait conduire à une détérioration plus ou moins importante des cristaux de zéolithe encore humides.

[0058] Après le séchage, les cristaux de zéolithe peuvent être utilisés tels quels, mais ils sont avantageusement activés, là encore selon les techniques classiques d'activation bien connues de l'homme du métier, par exemple à des températures comprises entre 150°C et 800°C, pendant une durée variant de quelques minutes à quelques heures, et typiquement de quelques minutes à 10 heures.

[0059] Les eaux-mères issues de l'étape e) de filtration peuvent avantageusement être recyclées. Un des avantages de ce recyclage est de permettre ainsi la réduction de la consommation d'hydroxyde de sodium en introduisant les eaux-mères directement dans le milieu réactionnel d'un des au moins deux réacteurs ou dans la solution de silicate ou encore dans la solution d'aluminate (typiquement qui sont respectivement les sources de silice et d'alumine dans l'étape a) du procédé) ou encore dans le gel de synthèse, mais peut aussi permettre une réduction substantielle de consommation énergétique. Avant d'être recyclées, les eaux-mères peuvent avoir subi ou non un ou plusieurs traitements choisis parmi l'ultra-filtration, la reconcentration, la distillation, et autres.

[0060] Le procédé de la présente invention est très avantageusement réalisé de manière continue, de préférence de manière complètement continue, c'est-à-dire sans étape en mode batch.

[0061] Ainsi, et selon un mode de réalisation du procédé de la présente invention, chaque réacteur délivre une fraction granulométrique donnée et avantageusement étroite, déterminée par la qualité et la quantité d'agent(s) d'ensemencement introduites dans le gel de synthèse. La quantité totale d'agent(s) d'ensemencement ajoutée dans le procédé de la présente invention représente entre 0,005% et 10% en poids par rapport au gel de synthèse, de préférence entre 0,01 % et 5% et de manière encore préférée entre 0,01 % et 3% en poids par rapport au gel de synthèse introduit au départ dans chaque réacteur. Par la suite, les différents milieux réactionnels sont mélangés pour obtenir une distribution de taille multimodale qui est la somme des différentes fractions monomodales produites dans chacun des réacteurs de synthèse.

[0062] Ainsi, le procédé de la présente invention permet-il la synthèse, avantageusement en continu, de cristaux de zéolithe à distribution granulométrique multimodale, et ceci de manière homogène et reproductible, stable dans le temps.

[0063] La détermination de la distribution granulométrique correspond ici à la distribution granulométrique en nombre du diamètre des cristaux de zéolite. Cette détermination est réalisée à partir de clichés obtenus par observation au microscope électronique à balayage (MEB). Pour cela on effectue un ensemble de clichés à un grossissement d'au moins 3000. On mesure à l'aide d'un logiciel dédié, par exemple le logiciel Smile View de l'éditeur LoGraMi, l'ensemble des cristaux présents sur les clichés de façon à mesurer au moins 300 cristaux puis on trace la distribution en nombre sous la forme d'un histogramme avec des classes adaptées à la granulométrie des cristaux, par exemple des classes tous les 0,2 μηη pour le comptage de cristaux micrométriques ou par exemple des classes tous les 0,02 μηη pour le comptage de cristaux de quelques dizaines de nanomètres.

[0064] Par « distribution granulométrique multimodale », on entend une distribution de taille multimodale, c'est-à-dire présentant au moins deux pics « séparés », autrement dit au moins deux pics « résolus ». La valeur du diamètre au sommet du pic, est appelée « mode » ou encore « valeur dominante », et représente la valeur la plus fréquente du pic. Lorsqu'une distribution présente deux pics séparés (ou résolus), on dit que la distribution est bimodale.

[0065] On définit la notion de multi-modalité à partir d'un « critère » R, dénommé « facteur de résolution » qui caractérise la séparation ou non superposition des pics.

[0066] Les différents pics sont assimilés à une gaussienne, caractérisée par son mode d et sa largeur à mi-hauteur δ, de laquelle on peut déduire la largeur de la base du pic ω = 1 ,7 δ.

[0067] The resolution factor R 2 adjacent peaks A and B is defined conventionally (see eg "fundamental concepts of chromatography" Marie-Paule Bassez: http://chemphys.u-strasbg.fr/mpb /teach/chromato1/img0.html) using the following equation:

R = 2 (dB - dA) / (Da + DA),

where dA and dB respectively are the modes of the peaks A and B (in μηη) and ωΑ and ωΒ are respectively the widths of the base of the peaks A and B (in μηι).

[0068] Generally, two peaks are considered solved, or completely separated, when the value of R is greater than 1, 5. In the context of the present invention, a particle size distribution has a difference of mode when the resolution R factor is greater than 0.5. In this description, it is considered that the particle size distribution is multimodal since at least two peaks are resolved. When the particle size distribution includes only two peaks resolved, it is called bimodal particle size distribution.

[0069] The method according to the present invention thus allows the production of a zeolite whose crystals have a bimodal particle size distribution or multimodal, controlled, or controlled, this production can be very easily carried out industrially, allowing production quantities important such controlled particle size zeolites or controlled, and this with costs well below those observed production, for example with productions by conventional methods known today.

[0070] Zeolites which may be prepared according to the method of the present invention may be of any type, for example, and without limitation, any zeolite of the MFI type, and in particular silicalite, any MOR type zeolite, of type OFF, type MAZ, type CHA and type ER, any zeolite type FAU and in particular zeolite Y, zeolite X, zeolite MSX, zeolite LSX, any EMT type zeolite or any LTA type zeolite, c ' is to say zeolite A, and other zeotype, such as, for example titanosilicalites.

[0071] The zeolite MSX (Medium Silica X), a FAU-type zeolite having an atomic ratio means an Si / Al of between about 1 05 and about 1: 15, inclusive. By zeolite LSX (Low Silica X) is meant a FAU-type zeolite having an atomic ratio Si / Al equal to about 1.

[0072] The process of the invention is particularly suitable for the preparation of zeolite selected from MFI-type zeolites, and in particular the silicalite of type FAU and in particular zeolite Y, zeolite X, zeolite MSX, zeolite LSX, and LTA is to say zeolite A, and the CHA zeolites and HEU zeolites.

[0073] The process of the invention is further especially suitable for the preparation of any type FAU zeolite, in particular zeolite X, zeolite MSX, zeolite LSX. MFI-type zeolites, including silicalite, can also be very advantageously prepared by the process of the invention.

[0074] In addition, the preparation process in continuous of the present invention is not limited to the preparation of the zeolites described above, but also includes the corresponding zeolites with a hierarchical porosity. Zeolites hierarchical porosity are solid with a microporous network linked to a mesoporous network, and thus possible to reconcile the accessibility properties to the active sites of mesoporous zeolites known from the prior art and those of crystallinity and maximum of micropores zeolites "classic" (without mesoporosity). In this case, specific structuring agents are introduced into the reaction medium of step a), e.g. structuring agents organosilanes type as described in document FR 1,357,762.

[0075] The synthesis method of the present invention therefore allows an easy and economical industrial synthesis of zeolite crystals whose particle size distribution at least bimodal, is homogeneous, controlled or controlled. In addition, it has been observed that the method according to the invention is very stable over time when it is implemented continuously. These zeolite crystals are of all uses is interesting in many application areas.

[0076] In fact, by the method of the invention, it is now possible to obtain more easily multimodal distribution of zeolite crystals in a controlled manner and consistent, unlike what would be obtained with mixtures of crystals of various sizes .

[0077] The multimodal particle size distribution of the zeolite crystals obtained by the process of the invention allows to obtain crystals having a particularly high bulk density, and particularly higher compared to crystals of monomodal particle size distribution. One can indeed feel that the small crystals occupy the spaces between the large crystals.

[0078] This high bulk density of the zeolite crystals obtained with the process of the invention allows to obtain adsorption performance quite specific, in particular in terms of volume adsorption capacity.

[0079] The zeolite crystals obtained with the process of the invention thus find application quite interesting in the field of adsorption, separation, purification of gasses, liquids. In way of nonlimiting examples, the zeolite crystals obtained according to the process of the present invention can advantageously be used as adsorbent fillers in polymer composites, as constituting agglomerated zeolitic adsorbents used in the methods of separation or purification by adsorption such as the methods modulated pressure and / or temperature or in chromatographic-type separation processes (fixed beds, moving beds, moving beds simulated), in applications as varied as purification of industrial gases,

natural or synthesis gas, or the purification of various petrochemical fractions, the separation of isomers in the refining, and the like.

[0080] The crystallinity, as well as the purity of the synthesized zeolite are evaluated by diffraction X-ray analysis, known to the art by the acronym XRD technique. This identification is made for example on a Bruker XRD unit of the brand.

[0081] This analysis allows not only to determine the amount of phase (s) crystalline (s) present (s), and also to identify and quantify any different zeolites herein, each of the zeolites having a unique diffraction pattern defined by the positioning of the diffraction peaks and their relative intensities. Non-crystal phases are not detected by the diffraction X-ray analysis

[0082] This analysis is also used to determine the reaction medium degree of crystallinity in order to assess if the crystallization reaction has begun. In this case a sample of the reaction medium is removed, dried at 80 ° C for 4 hours and then analyzed by XRD.

[0083] The zeolite crystals (or dried samples) are then crushed and spread on a sample holder smoothed by simple mechanical compression. The vesting conditions of the diffraction performed on the Bruker D5000 are:

• Cu tube used at 40 kV - 30 mA;

• size slits (divergent, disseminating and analytical) = 0.6 mm;

• filter: Ni;

• rotating sample device 15 tr.min "1 ;

• measuring range: 3 ° <2Θ <50 °;

• Step: 0.02 °;

• counting time per step: 2 seconds.

[0084] The interpretation of the resulting diffraction pattern is made with EVA software with identification of zeolites using the base ICDD PDF-2, release 1 201.

[0085] The amount of crystals, by weight, is determined by XRD analysis, this method is also used for measuring the amount of non-crystalline phases. This analysis is performed on a device of the Bruker brand, and the amount by weight of the zeolite crystals is assessed using the TOPAS software Bruker.

[0086] The crystallinity (or crystallinity level) corresponds to the ratio of the sum of the mass fractions of the crystalline phases present, based on the total weight of the sample.

[0087] The purity is expressed in percentage by weight of crystalline desired phase relative to the total weight of the sample.

CLAIMS

1. zeolite crystal preparation method having a multimodal particle size distribution, and whose sizes are comprised between 0.02 and 20 μηη μηη, said method comprising at least the steps of:

a) preparation of a synthesis gel by mixing at least one silica source, at least one source of alumina and optionally but preferably at least an aqueous solution of alkali metal hydroxide or alkaline earth,

b) feeding at least two reactors each with a synthesis gel capable of forming zeolite crystals,

c) conducting a crystallization reaction, in parallel, in each of at least two reactors,

d) mixing of the reaction media of at least two reactors, and

e) filtering the mixture of the reaction media obtained in step d), to separate the product crystals from the mother liquors.

2. The method of claim 1, wherein the at least two reactors are each fed by a synthesis gel zeolite crystals, synthetic gels can be identical or different.

3. The method of claim 1 or claim 2, wherein one or more agent (s) are introduced in the seed or the gel (s) synthesis upstream or inside at least one of the reactors synthesis or in at least two synthesis reactors.

4. A method according to any preceding claim, wherein the seeding agent is selected from nucleating gels, zeolite crystals, the inorganic particles of any kind, and the like, and mixtures thereof.

5. A method according to any preceding claim, wherein the reactors used are stirred reactors for synthesis batch and tubular reactors for synthesis in the continuous mode.

6. A method according to any preceding claim, wherein there are two or more reactors of identical or different types, preferably 2, 3, 4 or 5 reactors of identical or different types, more preferably two or three reactors of identical or different types, more preferably two reactors of identical or different types, typically two reactors of identical types.

7. A method according to any preceding claim operated continuously in two, three or four tubular reactors, preferably in 2 or 3 tubular reactors, typically in two tubular reactors.

8. A method according to any preceding claim, wherein the crystallization reaction is performed at a temperature between 60 ° C and 200 ° C, preferably between 80 ° C and 160 ° C.

9. A method according to any preceding claim, wherein the crystallization reaction is performed at a pressure between atmospheric pressure and 1, 5 MPa.

10. A method according to any preceding claim, wherein the reaction media of at least two reactors operating in parallel are mixed at any time, since the crystallization reaction began in one of the at least two reactors , preferably in at least two reactors.

11. A method according to any preceding claim, wherein the mother liquor from step e) filtration are recycled.

12. A method according to any preceding claim, wherein the zeolite crystals are crystals of zeolite selected from zeolites of type MFI, MOR type zeolites, zeolites OFF, MAZ type zeolites, CHA-type zeolites, the HEU zeolites, zeolites of type FAU, EMT type zeolites, the LTA type zeolites and other zeotypes.