[0001] The present invention relates to zeolites, more precisely the field of industrial synthesis of zeolite crystals and more particularly that of industrial continuous synthesis of zeolite crystals.
[0002] The synthesis of the 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] In order to improve the conventional method of crystallizing zeolites in batch, studies have been published on the continuous synthesis process of development. This work aims to overcome or at least mitigate the disadvantages associated with batch processes and in particular to reduce the size of facilities for synthesis, correspondingly decrease energy expenditure and improve the regularity of the quality of production.

[0004] Some studies describe processes called "continuous" synthesis of zeolites that 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 feeds a continuous crystallization reactor; in this case is called method "semi-continuous" as part of the process is conducted in batch reactor (see e.g. Jingxi Ju et al, "Continuous Synthesis of zeolite NaA in a microchannel reactor," Chemical Engineering Journal, 1 16, (2006), 1 15-121; 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 4,848,509 or US 6,773,694);

2) the synthesis medium is continuously prepared using a mixer and shear is crystallized in a batch reactor in a conventional manner (see for example EP0149929 and BE 869,156 documents);

3) the synthesis medium is continuously prepared and fed to a continuous reactor to effect crystallization.

[0005] The first two categories are not strictly speaking processes "continuous" since at least part of the synthesis is performed in batch.

[0006] Among the works of the third category, it appears that the conditions for continuous synthesis are described so always accurate, so it is difficult if not impossible to replicate. In particular, the precise conditions of operation of the process fail to whether and how the risks of contamination of facilities can be effectively avoided.

[0007] Recently, the work of Zhendong Liu et al., In "Continuous flow synthesis of ZSM-5 zeolite on the order of seconds", published in PNAS, 113 (50) December 13, 2016, 14267-14271, offer air vibrator to minimize problems of precipitation and blockage in the preparation of zeolite ZSM-5 (MFI type).

[0008] It remains that the teaching of the prior art for zeolite synthesis continuously is not without many problems. Indeed, one of the constraints of the continuous process is for example related to the crystallization time. Numerous studies conducted today on the synthetic zeolite LTA show that the crystallization time is a few hours at 100 ° C, or only a few seconds for the crystallization of ZSM-5, with the help of water under pressure at extremely high temperature, cf. Zhendong Liu et al., Ibid ..

[0009] It is therefore known that a point of vigilance in the implementation of a method for continuous synthesis containing solids (as is the case in the synthesis of zeolites) is the risk of fouling of reactors, which are usually and mostly tubular reactors, by the accumulation of solids that may involve a drift of the process and high maintenance costs.

[0010] However, and as discussed in the prior art, the implementation of a zeolite synthesis continuous process compared with a batch process, is expected to make gains in energy expenditure, build more compact units so with less investment and produce more consistent quality crystals, thanks to easier control of manufacturing parameters.

[0011] However, one can only note that continuous processes were not specifically developed so far in the synthesis of zeolites. This is probably due in particular to the risk of contamination (as explained above) due to the presence of solids in the reaction medium (as amorphous solid is present in the starting synthesis gel or crystalline solids at the end of synthesis, after crystallization), the difficulties of reconciling crystallization time and quality of the crystals formed. These problems may be magnified if the crystal sizes than hundred nanometers are sought.

[0012] There remains therefore a need for a zeolite synthesis method that can continuously overcome the above drawbacks.

[0013] Thus, the present invention relates to a zeolite synthesis continuous process, said method being performed completely continuously, that is to say in which a gel is prepared continuously and then crystallized continuously without transient batch phase.

[0014] Indeed, it has been surprisingly discovered that the application-specific settings can reduce or even eliminate any risk of contamination of the system, enabling the preparation of zeolites continuously, and this industrially that is to say large-scale, in order to meet the needs of an ever growing market. Still further advantages will be apparent from the description of the invention that follows.

[0015] Thus, the present invention firstly provides a method for preparing zeolite crystals continuously, comprising at least the steps of:

a) providing continuously a composition capable of generating zeolite crystals; b) continuously introducing said composition into at least one reaction zone of crystallization subjected to stirring means, to confer on said composition a flow characterized by a Reynolds number Re on r between 40 and 50000, preferably between 40 and 25000, preferably between 70 and 5000, typically between 100 and 2000, inclusive,

c) continuous recovery of the crystals formed in step b) in a flow characterized by a Reynolds number Re net n between 1 and 1500, preferably between 1 and 1000, more preferably between 5 and 500, typically between 10 and 200, inclusive.

[0016] The net Reynolds number (Re n ) is calculated using the following formula:

Ren = mv.V.D/μ,

where mv is the density of the reaction medium (in kg.nr 3 ), V represents the moving speed of the reaction medium was empty (or "empty bed" in English) in m. s "1 , D is the equivalent diameter of the reactor in meters, and μ represents the viscosity of the reaction medium (in Pa.s or kg.nr 1 . s " 1 ).

[0017] displacement speed of the reaction medium was vacuum V is calculated from the measurement of the volume flow of the reaction medium and the section of the reactor according to the formula: V = Q / S, where Q is the volume flow reaction medium, expressed in m 3 . s ' 1 , and S represents the empty barrel of the section in m 2 .

[0018] The term "equivalent diameter" means the inner size of the reactor measured perpendicular to the direction of the net flow.

[0019] The Reynolds number Re on r , represents the inertial forces relative to viscous forces within the reactor, independently of the net flow.

[0020] Lorsque the agitation by a northeast general.The agitateur Contractor, on the wall, then formulas:

Re r = mv.Nd 2 ^

wherein MV is the density of the reaction medium (in kg.nr 3 ), N represents the speed of rotation of the agitator (in tr.s "1 ), d represents the diameter of the agitator (m) and μ represents the viscosity of the reaction medium (in Pa.s or kg.nr 1 . s "1 ).

[0021] When the agitation is generated by an oscillating movement of the reaction medium of amplitude A (m) and frequency f (in s "1 ), then applying the formula:

Re r = Gin.i.A 2 / m

wherein MV is the density of the reaction medium (in kg.nr 3 ), f represents the frequency of oscillation (in s "1 ), A represents the amplitude of oscillation (m) and μ represents the viscosity of the reaction medium (in Pa.s or kg.nr 1 . s "1 ).

[0022] It is possible to implement many stirring systems, combining for example one or more mechanical stirring systems with one or more oscillatory systems. In such cases, it is preferable or even necessary that the Reynolds number Re on r of each of the stirring systems, taken separately, is within the value range defined above, that is to say between 40 and 50000, preferably between 40 and 25000, preferably between 70 and 5000, typically between 100 and 2000, inclusive.

[0023] It is preferred however, for the process of the present invention, a single type of stirring system, either mechanical or oscillatory. More preferably the method of the present invention includes only one stirring system, either mechanical or oscillatory. According to a preferred embodiment, the method of the invention comprises a single mechanical stirring system. According to another preferred embodiment, the method of the invention comprises a single stirring system generated by an oscillatory movement.

[0024] The densities and viscosities of the reaction medium correspond to the densities and viscosities measured on the composition at the reactor inlet.

[0025] The formation and especially the rapid formation, more specifically the rapid formation and with a high purity, crystals of zeolite is particularly delicate and requires both adequate local stirring (turbulence) to promote adequate transfer material at the solid / liquid interface crystallization for optimal crystallization, and also a sufficiently gentle shaking, not to disrupt the training crystals or disrupt the proper organization of reactive species at the interface.

[0026] If these crystallization conditions are now perfectly controlled and mastered for "batch" mode preparations, it is difficult to combine these two types of continuous agitation without observing deposition phenomena, clogging, or clogging of the equipment, not to mention the quality of the zeolite crystals obtained, and, especially as the crystallization time and space equipment and synthesis equipment must be compatible with economic industrial exploitation.

[0027] In order to avoid these phenomena of fouling, while maintaining an excellent quality of zeolite crystals, the Applicant has now discovered the optimal stirring conditions during the continuous preparation of zeolite crystals, conditions that are characterized by the type of flow to be applied to fluid overall (net number of Reynolds, correlated with the net rate, so the residence time for a given type of reactor) and locally (on Reynolds number).

[0028] Thus, and according to a preferred embodiment of the present invention, the difference between the Reynolds number Re on r and net Reynolds number Re n (that is to say the difference Re r - Re n ) is strictly greater than 50, preferably strictly greater than 100, more preferably strictly greater than 150, and most most preferably strictly greater than 180.

[0029] Thus the process of the present invention to provide an industrial process which benefits from the advantages of the continuous synthesis versus synthesis "batch" conventional, such as better temperature control, compact facilities, maintenance of production, but also and above all has the advantage of limiting the fouling of facilities.

[0030] The composition may generate zeolite crystals 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 any other source of element (s) may constitute a zeolitic framework, e.g. source of phosphorus, titanium, zirconium, and the like. To this composition may be added optionally, but preferably, 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).

[0031] 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.

[0032] 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.

[0033] 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).

[0034] 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.

[0035] According to a preferred embodiment, the method of the present invention enables the preparation of all types of zeolites known to those skilled in the art and for example, and without limitation, any zeolite of the MFI type, and in particular the silicalite, any zeolite type MOR 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 yet any LTA type zeolite, that is to say zeolite; and other zeotypes, such as for example titanosilicalites.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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 synthesis medium, such structuring agents organosilanes type as described in document FR 1,357,762.

[0040] More specifically, the present invention discloses a zeolite crystal preparation process comprising at least the steps of:

1) continuously preparing a composition capable of generating zeolite crystals, to obtain a synthesis medium,

2) addition of seed in the synthesis medium obtained in step 1),

3) carried out continuously and with stirring of the reaction formation of the zeolite crystals, according to stages a), b) and c) defined above,

4) filtering the reaction medium to recover the product crystals;

5) optionally recycling the mother liquors.

[0041] The process of the invention is particularly efficient in terms of energy. Furthermore the process can be implemented with compact installations and especially much less bulky than the known installations of the art for the preparation of zeolites in batch mode.

[0042] The synthesis of step 1 medium) was 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.

[0043] 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).

[0044] 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 .

[0045] The addition of seed in the synthesis medium allows to obtain sufficiently short crystallization times to fit the constraints of a continuous process. The addition of seed can be performed by any means known in the art and for example using a static mixer which has the advantage of promoting the homogenization of the mixture synthesis medium / seed. For seed (also called "seeding agent") means a solid or liquid that promotes the orientation of the synthesis to the desired zeolite.

[0046] The formation of the zeolite crystals (crystallization) is carried out, as indicated above with stirring under flow conditions characterized by a Reynolds number Re on r between 40 and 50,000, preferably between 40 and 25 000 , more preferably between 70 and 5000, typically between 100 and 2000, inclusive. In addition, this crystallization step is advantageously carried out at high temperature, typically at a temperature between 60 ° C and 200 ° C, preferably between 80 ° C and 160 ° C.

[0047] In one embodiment most preferred, the step of forming the zeolite crystals (crystallization step c) described above) is carried out in a tubular reactor and may be carried out under pressure, for example under autogeneous pressure under atmospheric pressure, or more generally at any pressure, typically between atmospheric pressure and 1, 5 MPa.

[0048] After the crystallization step, the crystals obtained are freed from mother liquor, for example by filtration, centrifugation, and other techniques well known to those skilled in the art.

[0049] It is possible, and this represents a preferred embodiment of the present invention to provide a recycling all or part of the mother liquor, that is to say water collected after removal of synthesis, e.g. by filtration, of the solid obtained at the outlet of the continuous reactor. Before being recycled, the mother liquors may have undergone or not one or more treatments selected from among ultra-filtration, reconcentration or distillation.

[0050] The recycling of mother liquor has many advantages, including saving of raw material and recover calories. Thus recycling of mother liquor allows among others to reduce consumption of global energy

synthesis process, the amount of basic solution (e.g. sodium hydroxide) used, etc.

[0051] The crystals obtained at the end of step 4) are optionally subjected to one or several treatments well known to those skilled in the art, such as washing, cation exchange, drying, impregnation, activation, and others, or these treatments can be performed in batch or continuously, preferably continuously.

[0052] The washing is typically a water wash to allow the disposal of residual mother liquors that might still be present.

[0053] Drying may be performed at any temperature and typically at a temperature between 40 ° C and 150 ° C, for a duration of between a few minutes and a few hours, typically between a few minutes and 10 hours. The drying operation at a temperature below 40 ° C may be much longer and so little cost-effective, while a drying temperature higher than 150 ° C may lead to more or less significant deterioration crystals zeolite still moist.

[0054] Activation of the zeolite crystals, which are preferably previously dried, is conventionally carried out at a temperature between 150 ° C and 800 ° C, for a period ranging from several minutes to several hours, and typically a few minutes to 10 hours.

[0055] The synthesis device for operating the process of the present invention may comprise, in an improved embodiment, any suitable means to improve the heat transfer, the transport of material, and others, in the reaction mixture in all or part of the process, for example by additions of source (s) of ultrasound and / or microwaves, to mention only a few ways from those well known to those skilled in the art.

[0056] In a particularly advantageous embodiment, the method of the invention comprises adding one or more times, before, after or during the crystallization step, one or more seeding agents. This addition of agent (s) seeding particular enables substantially accelerate the crystallization step.

[0057] For seeding agent (or seed), is meant a solution or suspension, in liquid form or gel form, a solid or liquid that favors orientation of the synthesis to the zeolite desired. Seeding agents 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 the like, and mixtures thereof.

[0058] 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.

[0059] As indicated above, the synthesis process according to the present invention comprises a continuous crystallization step which is operated in at least one reaction zone of crystallization subjected to stirring means, to confer on said composition a flow characterized by a relative Reynolds number (Re r ) as defined above.

[0060] The agitating means may be of any type well known to those skilled in the art, for example and without limitation, when the reactor is a tubular reactor adapted to be operated in continuous, tubular reactor may be provided with restrictions (such as rings, baffles, and others), can be equipped with a stirring system, a system oscillating or pulsating (for generating a movement back and forth of the reaction medium for example by means piston, membrane), and others, as well as two or more of these combined techniques.

[0061] In a preferred embodiment of the invention, the method is implemented in a tubular reactor, optionally but preferably provided with restrictions and equipped with a system for imparting to the fluid circulating in the reactor of pulses, such as described in US 2009/0304890 the NiTech society. Other systems for obtaining at least one reaction zone wherein the flow is characterized by a relative number of Reynolds (Re r ) as defined above, may also be suitable with the process of the present invention.

[0062] Thus, and according to an embodiment particularly suitable, the method of synthesis according to the present invention is a continuous process effected in a tubular reactor provided with internal restrictions systems and a pulsating device, and operated in special conditions, namely:

- an oscillation amplitude of the pulsating device between 20 mm and 400 mm, preferably between 25 mm and 300 mm, more preferably between 30 mm and 200 mm, and

- an oscillation frequency between 0.1 Hz and 2 Hz, preferably between 0.15 and 1 Hz, 5 Hz, more preferably between 0.4 Hz and 1 Hz.

[0063] The amplitude of oscillation can however vary within wide limits, and preferably, the amplitude is between 0.5D and 3D, preferably between D and 2D, where D is the equivalent diameter of the reactor, as previously defined. Similarly, and in the presence of restrictions within the tubular reactor, the restrictions are preferably spaced by a distance varying between 0.5D and 3D, preferably between D and 2D.

[0064] It has indeed been noticed that, to avoid fouling or at least avoid fouling too fast reactor, it is important, even necessary, to generate local turbulence within the reactor, via movements oscillation applied to the synthesis medium, oscillations whose amplitude must be greater than 20 mm, and preferably between 20 mm and 400 mm, as indicated above.

[0065] In addition, this system pulsations, or oscillatory system can be advantageously coupled to restrictions arranged in all or part of the reactor. According to an embodiment the restrictions are present throughout the tubular reactor in the form of rings, baffles, and others.

[0066] The coupling of these restrictions with appropriate oscillations (whose amplitude and frequency can vary), applied to the reaction mixture in the tubular reactor, to generate a flow characterized by a Reynolds number Re on r included in the range of values previously defined.

[0067] The oscillations imposed on the reaction medium, advantageously accompanied by the presence of restrictions in the reactor used to generate an optimal agitation both axial and radial. This agitation is not only necessary for optimal training of zeolite crystals, but also allows to increase the field of trade within the reaction medium. As another advantage, this agitation also improves the efficiency of heat exchange.

[0068] It has thus been observed that the oscillation amplitude must be sufficient to enable the solids present in the reactor tube to progress in the tube uniformly, clearing restrictions. Too low amplitude can cause fouling, while too high amplitude can affect the quality of crystallization. It appears that the oscillation frequency must be maintained in the appropriate band and defined above, not to incur the effects described above (contamination or poor quality of crystallization). The amplitude is preferably at least equal to the distance between two restrictions. Thus the reactor as a whole can thus be viewed as a cascade of perfectly agitated reactors, one reactor being materialized by

[0069] Another advantage of the process of the present invention is that the change in the oscillation frequency is used to vary the size of the crystals obtained. Indeed, it is possible to reduce the crystal size by increasing the frequency of the oscillator and vice versa to increase the crystal size by decreasing the frequency of the oscillator.

[0070] The method according to the present invention generally allows the synthesis of particle size of zeolite crystals (number average diameter determined by counting on plates SEM) ranging from 0.1 to 20 μηη μηη and preferably ranging from 0, 2 μηη 10 μηι, and more preferably from 0.3 to 8 μηη μηι so most preferably 0.3 m to 5 μηη. The method of the present invention makes it possible to synthesize zeolite crystals having a purity equal to or greater than 98%, and preferably between 98% and 100%.

[0071] Within the reactor comprising at least one rough area are continuously formed crystals, the starting gel and the crystals formed are subjected to a flow in order to advance the starting gel along the reactor and thus permit expulsion of the crystals formed in the reactor outlet. As indicated above, the crystals formed are recovered continuously at the reactor outlet in a flow characterized by the net number of Reynolds (Re n ) defined above, and which corresponds to a flow that can be characterized as laminar flow.

[0072] Thus, to achieve the net number of Reynolds (Re n ) desired, various parameters can be adjusted such that the equivalent diameter of the tubular reactor, and the net flow rate. A number of too high Reynolds net may disrupt the crystallization, for example by preventing the crystallization or by creating crystalline phases other than the desired one. A number of too low Reynolds net may cause a risk of fouling of the reactor continuously.

[0073] The control of the raw material flow to the reactor inlet and / or the production of crystals at the reactor outlet can be obtained according to any means known to those skilled in the art and for example by means of pumps, optionally associated with flow regulators.

[0074] There has thus been shown for example that it is possible to operate without clogging when using a tubular reactor provided with an oscillating system for achieving the relative Reynolds number as defined above, a system of pumps to achieve a Reynolds number of net as defined above.

[0075] A 90-minute residence time allows to obtain zeolite crystals of purity higher than 95%, or even greater than 98% in a reactor length

typically between 1 m and 100 m and a diameter typically of between 0.5 cm and 30 cm. The crystallinity is determined by X-ray diffraction (XRD).

[0076] By operating with a reactor as defined in US Patent Application 2009/0304890 of NiTech company and under the operating conditions of the process of the present invention, no contamination could be observed after 24 hours of continuous operation for zeolite preparation the type X.

[0077] In addition it was possible to decrease the size of the crystals by accelerating the frequency of the oscillator.

[0078] The following examples illustrate the present invention without providing any limitation to the scope of the protection sought which is defined by the appended claims.

Characterization Techniques

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

[0079] The purity of the synthesized zeolite crystals is evaluated by diffraction X-ray analysis, known to the art by the acronym DRX. This identification is performed on a Bruker XRD unit of the brand.

[0080] This analysis identifies the different zeolites present in the adsorbent material for each zeolite has a unique diffraction pattern defined by the positioning of the diffraction peaks and their relative intensities.

[0081] The zeolite crystals are then crushed and spread on a sample holder smoothed by simple mechanical compression.

[0082] The conditions for the acquisition 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.

[0083] 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.

[0084] 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. The purity is expressed in percentage by weight of crystalline desired phase relative to the total weight of the sample.

Example 1 (according to invention): Synthesis of zeolite A continuous

[0085] The continuous synthesis of zeolite A consists in feeding a tubular reactor (inner diameter = 1, 5 cm and length 20 m) with a further synthetic defined medium to which 1% by weight of nucleating gel explained below -after.

[0086] The nucleating gel is prepared by adding a sodium silicate solution at 35 ° C in a sodium aluminate solution at 35 ° C so as to obtain a gel composition: 2.66 Na 2 0 / Al 2 0 3 /1 92 Si0 2 /65 H 2 0.

[0087] The sodium aluminate solution was prepared by dissolving alumina in a boiling sodium hydroxide solution and then cooling to 35 ° C. This solution contains 938.7 g of alumina, 1539.0 g of aqueous solution of sodium hydroxide to 50% by weight and 1542.6 g of water.

[0088] The sodium silicate solution is prepared by mixing 2601 g of sodium silicate with 486 g of aqueous solution of sodium hydroxide to 50% by weight and 2160 g of water and then brought to a temperature 35 ° C .

[0089] The nucleating gel is kept for 2 hours at 35 ° C and then cooled to 25 ° C and stored for 20 hours at 25 ° C. This solution can then be used as seed in the synthesis of zeolite A by adding it continuously in the synthesis medium with a content equal to 1% by weight based on the weight of the synthesis medium.

[0090] The synthesis mixture is prepared using a mixer shearing type rotor / stator in which the rotor diameter is 38.1 mm and the distance the air gap between the rotor and the stator is 0.2 mm. Simultaneously mixing a sodium aluminate solution at 35 ° C and a sodium silicate solution at 35 ° C so as to obtain a gel composition: 3.5 Na 2 0 / AI 2 0 3 / Si0 2.0 2 /175 H 2 0.

[0091] The sodium aluminate solution was prepared by dissolving alumina in a boiling sodium hydroxide solution and then cooling to 35 ° C. This solution contains 31 824 g of alumina, 86 402 g of aqueous solution of sodium hydroxide to 50% by weight and 273 600 g of water.

[0092] The sodium silicate solution was prepared by mixing 91 152 g of sodium silicate with 8641 g of aqueous solution of sodium hydroxide to 50% by weight and 254 880 g of water and then brought to a temperature 35 ° vs.

[0093] To prepare the synthetic medium are simultaneously feeds the in-line mixer of the Silverson shear chamber using two peristaltic pumps: the flow rate of the aluminate solution is equal to 220.5 g. min -1 and that of the solution of silicate is equal to 21, 1 5 g. min -1 . The supply pipes are first filled with water.

[0094] The mixing is carried out with a rotor speed of 5500 tr.min "1 , which corresponds to a shear rate of 54 800 s " 1 . The synthesis medium is continuously fed into the static mixer into which is introduced the nucleating gel at 25 ° C at a rate of 4.32 g. min "1 (1% by weight of the synthesis medium).

[0095] The stream exiting the static mixer consisting of the mixture of the synthesis medium and the nucleating gel has a density of 1200 kg. m "3 and a viscosity of 5 mPa.s. A mass fraction of 1/9 of this stream fed directly to the pulse tube reactor.

[0096] The pulsation tube reactor is initially set temperature by setting the oscillator operation (amplitude 50 mm and frequency 0.4 Hz). Water is first circulated by adjusting the temperature of the oil bath at 108 ° C so as to obtain a temperature within 100 ° C. Then supplies the driver with the mixture of the synthesis medium and nucleating gel carried out using a static mixer 316 stainless steel 125 mm long with 17 elements sold by Fisher Scientific (reference 1 174-41 19) maintaining a 50 mm oscillation amplitude and frequency of 0.4 Hz. with these operating conditions, the net number of Reynolds (Re n ) is equal to 13.7 and the relative number of Reynolds (Re r ) is equal to 240.

[0097] After 24 hours of continuous operation, is not observed on the indication of the pressure gauge installed at the inlet of the tubular reactor, the pressure rise in the system. The feed rate of 2.4 Lh "1 provides a residence time in the tubular reactor of 90 minutes, sufficient residence time to obtain a crystallized LTA zeolite. The reaction mixture taken from the outlet of the tube is then filtered washed with water until pH neutral and dried at 80 ° C and activated at 550 ° C.

[0098] In order to drain the system is circulated to the cold water with 60 Lh rate "1 for 1 hour. The zeolite LTA crystals obtained have a crystallinity of 99%.

Example 2 (Comparative) Synthesis of zeolite A continuous

[0099] In carrying out the continuous synthesis depending on the operating conditions of Example 1 but decreasing the amplitude of the oscillator 20 mm, is then observed, on the indication of the pressure gauge installed at the entry of the tube reactor, increases in pressure after only 2 hours of operation, and which lead to clogging

installation after 3 hours and 15 minutes synthesis. With these operating conditions, the number of net Reynolds is equal to 13.7 and the Reynolds number relative equals 38.

Example 3 (Invention): Synthesis of zeolite X continuously

[0100] [0074] By reproducing the operating conditions of Example 1, and changing the nature of the composition of the starting reaction medium, is carried out a faujasite X-type zeolite synthesis continuously for 24 hours. The zeolite crystals X obtained at the outlet of the tubular reactor have a crystallinity of 99%. The diffraction pattern of these crystals is shown in Figure 1.

CLAIMS
1. A process for preparing zeolite crystals continuously, comprising at least the steps of:

a) providing continuously a composition capable of generating zeolite crystals; b) continuously introducing said composition into at least one reaction zone of crystallization subjected to stirring means, to confer on said composition a flow characterized by a Reynolds number Re on r between 40 and 50000, preferably between 40 and 25000, preferably between 70 and 5000, typically between 100 and 2000, inclusive,

c) continuous recovery of the crystals formed in step b) in a flow characterized by a Reynolds number Re net n between 1 and 1500, preferably between 1 and 1000, more preferably between 5 and 500, typically between 10 and 200, inclusive.

2. The method of claim 1, wherein the difference between the Reynolds number Re on r and the Reynolds number Re net n is strictly greater than 50, preferably strictly greater than 100, more preferably strictly greater than 150, and so most preferably strictly greater than 180.

3. The method of claim 1 or claim 2, for preparing crystals of any zeolite of the MFI type, and in particular silicalite, any zeolite type MOR, OFF type, MAZ type, CHA type and Type ER, all FAU type zeolite, in particular zeolite Y, zeolite X, zeolite MSX, zeolite LSX, any EMT type zeolite or any LTA type zeolite, that is to say zeolite A; and other zeotypes.

4. The method of claim 3, for the preparation of zeolite crystals, where the zeolite is selected from zeolites of type MFI, and in particular the silicalite of type FAU and in particular zeolite Y, zeolite X, zeolite MSX, zeolite LSX, and LTA, that is to say of zeolite A and the CHA zeolites and HEU zeolites.

5. A method according to any preceding claim, comprising at least the steps of:

1) continuously preparing a composition capable of generating zeolite crystals, to obtain a synthesis medium,

2) addition of seed in the synthesis medium obtained in step 1),

3) carried out continuously and with stirring of the reaction formation of the zeolite crystals, according to stages a), b) and c) of claim 1,

4) continuous filtration to separate the mother liquor the crystals obtained, and

5) optionally recycling the mother liquors.

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

7. A method according to any preceding claim, further comprising adding one or more times, before, after or during the crystallization step, one or more seeding agents.

8. The method of claim 8, wherein the seeding agent is selected from a nucleating gel, a crystal, an inorganic particle of any kind, and the like, and mixtures thereof.

9. A method according to any preceding claim, which method es implemented in a tubular reactor possibly provided with restrictions, and equipped with a stirring system, a system oscillating or pulsating, and others, as well as two or more of these combined techniques.

10. A method according to any one of the preceding claims, made in a tubular reactor provided with internal restrictions systems and a pulsating device, and operated under specific conditions, namely:

- an oscillation amplitude of the pulsating device between 20 mm and 400 mm, preferably between 25 mm and 300 mm, more preferably between 30 mm and 200 mm, and

- an oscillation frequency between 0.1 Hz and 2 Hz, preferably between 0.15 and 1 Hz, 5 Hz, more preferably between 0.4 Hz and 1 Hz.