[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 zeolites with controlled particle size, monomodal distribution 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, mono- 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] 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 μηι μηι, 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 a reactor you drink lai re with said gel synthesis,

c) first introduction of one or more agent (s) seeding in the tubular reactor or upstream of the tubular reactor,

d) introducing a second or more agent (s), seeding, identical (s) or different (s) in the tubular reactor,

e) carrying out the crystallization reaction in the tubular reactor of the synthesis gel in presence of the agent (s), seeding, forming the reaction medium, f) filtering the reaction medium to recover product crystals.

[0014] The process of the invention is characterized by at least two introductions of agent (s) seeding during the conduct of the crystallization reaction. And step d) can be repeated one, two, three or more times, preferably one, two or three times, more preferably once or twice. At least two introductions are carried out at rate of progress of the different crystallization reaction. At least two introductions can thus be carried out at different times or at different locations of the reactor, particularly in the case of continuous synthesis, for example in a tubular reactor operated continuously.

[0015] In a preferred embodiment of the invention, the first agent introduction (s), seeding is carried out upstream of the reactor, that is to say the one or more agent (s) seeding is (are) mixed (s) to the synthesis gel before introduction into the reactor where the crystallisation takes place.

[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 synthesis gel is introduced into the tubular reactor by any suitable means for transferring a fluid, for example by gravity flow, by siphoning or pumping. Checking the flow of the synthesis gel in the reactor inlet and / or

production reactor outlet crystals can be obtained according to any means known to those skilled in the art and preferably by means of pumps, possibly associated with flow regulators.

[0025] 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 zone reaction 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 (allowing 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. In a preferred embodiment of the invention, the tubular reactor is provided with restrictions and equipped with

[0026] The first introduction of one or more agent (s) seeding in the synthesis gel is preferably carried out upstream of the tubular reactor. In this case the one or more agent (s), seeding is (are) mixed (s) with the synthesis gel prepared in step a) prior to introduction into the tubular reactor. 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 other,

[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 the skilled person and preferably

using a static mixer, which has the advantage of promoting the homogenization of said mixture.

[0029] 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. Crystallisation of the synthesis gel comes into the tubular reactor and is favored by the one or more agent (s) seeding. The tubular reactor comprises a reaction and crystallization medium. Crystallization is also favored by the temperature applied to said reaction medium, but also by any means of agitation, static or dynamic, said reaction medium in the reactor as explained above.

[0030] By "favored" a better seed crystal means and / or a higher crystallization kinetics.

[0031] 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.

[0032] As indicated above, the method of the present invention is characterized in that, further a first introduction (or addition) of agent (s) seeding at least one further addition of agent (s) seeding is carried out during the crystallization step in the reaction medium. The seeding agents are added during the process of the present invention may all be identical or different. Moreover, this step of adding agent (s), seeding may be repeated in the time and / or at other points of the tubular reactor.

[0033] In one embodiment of the inventive method, the tubular reactor comprises, besides a first medium feeding system (s) seeding upstream of the inlet of the tubular reactor, at least one other agent introduction system (s) seeding at least one point of the tubular reactor, it being understood that the agent of introduction (s), seeding can be carried out once or several times in one or more points the tubular reactor.

[0034] For example, and in a particular embodiment of the present invention, a second medium feeding (s), seeding, after starting a first crystallization reaction, allows the starting of the growth of a second population of crystals, thus leading to the synthesis of zeolite crystals with a bimodal distribution. By further repeating the addition of agent (s), seeding, at the same point of introduction after a first agent introduction (s), seeding, or at another point of the tubular reactor, tri distribution is obtained -modale zeolite crystals.

[0035] According to a most preferred aspect of the invention, the method comprises at least two agent additions (s) seeding continuously in one or more points of the tubular reactor.

[0036] 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.

[0037] 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 a different structure. This does not, however, a preferred embodiment of the present invention.

[0038] It may also be envisaged to add an additional synthesis gel in the reaction medium in one or more points of the tubular reactor, as nutrient medium in order to provide the constituent basic elements of the zeolite, particularly the silicon and / or aluminum. The additional synthetic gel has usually a composition similar or even identical to that of the synthesis gel initially introduced. The amount of synthesis gel which may optionally be added is a minor addition relative to the amount initially introduced is less than 50% by weight, preferably less than 30% by weight.

[0039] The process of the invention provides an adjustable multimodal crystal size distribution and controlled through the introduction into at least two time of seeding agents to various parts of the tubular reactor, preferably operating in continued. In a preferred embodiment, the method of the invention is a continuous synthesis process carried out in a tubular reactor in which is inserted at different locations of the tube one or more agent (s) and seeding the synthesis gel ( nutrient solution) to obtain the desired multi-modal particle size distribution.

[0040] The total amount of agent (s) added in the sowing process of the present invention is between 0.005% and 10% by weight relative to the synthesis gel, preferably between 0.01% and 5% and more preferably between 0.01% and 3% by weight relative to the synthesis gel initially introduced into the tubular reactor.

[0041] The one or more agent (s) seeding introduced closer to the inlet of the tubular reactor, that is to say before or just after entering the reactor, will generate larger crystals because growth will have time to be realized while or agent (s) introduced seeding (s) and subsequently in one or more other points of the reactor, will give smaller crystals.

[0042] After the crystallization reaction, the reaction mixture is filtered (step f)) to separate the one hand products crystals and the other mother liquors. This filtration can be performed by any method well known to the skilled person, and for example one or more methods selected from centrifugation, filtration on a filter press, filtration belt filter, rotary filter filtration and the like.

[0043] The crystals obtained after step f) may optionally be subjected to one or more conventional treatments well known to those skilled in the art, such as washing, cation exchange, drying, impregnation, activation, and other, this or these treatments can be performed in batch or continuously, preferably continuously. For example, the crystals may be subjected to one or more washes with water in order to remove residual mother liquors that might still be present.

[0044] The resulting crystals can also be dried according to conventional drying techniques zeolite crystals, for example at temperatures between 40 ° C and 150 ° C, for a duration of between a few minutes and a few hours, typically a few minutes to 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.

[0045] After drying, the zeolite crystals can be used as such, but are preferably activated, again according to conventional techniques well known activation of those skilled in the art, for example at temperatures between 150 ° C and 800 ° C, for a period ranging from several minutes to several hours, and typically from a few minutes to 10 hours.

[0046] The mother liquors from step f) filtration can advantageously be recycled. One advantage of this recycling is thereby enable reducing the consumption of sodium hydroxide by introducing the mother liquor directly in the reaction medium or in the silicate solution or the aluminate solution (which are respectively typically the sources of silica and alumina in step a) of the process) or in the synthesis gel, but may also permit a substantial reduction in power consumption. Before being recycled, the mother liquors may have undergone or not one or more treatments selected from among ultra-filtration, reconcentration, distillation, and others.

[0047] The process of the present invention is very advantageously carried out continuously, although a driving synthesis of zeolite crystal multi-modal distribution in batch mode is also possible.

[0048] Thus, the method of the present invention allows the continuous synthesis, with several solution introductions (s) seeding at different levels, of zeolite crystals with a multimodal particle size distribution, and this in a homogeneous and reproducible and stable manner in the time.

[0049] The determination of the particle size distribution corresponds here to the particle size number distribution diameter of the zeolite crystals. This determination is made from photographs obtained by observation with a scanning electron microscope (SEM). For this we performed a set of photographs at a magnification of at least 3000 is measured using a dedicated software, such as Smile View software LOGRAMI the editor, all the crystals present in the photographs so as to measure at least 300 crystals and then in the number distribution is plotted as a histogram with classes adapted to the particle size of the crystals, e.g., every 0.2 μηη classes for counting micrometric crystals or such classes all 0,

[0050] By "multimodal particle size distribution," a multimodal size distribution means, that is to say having at least two peaks "separate", ie at least two peaks "resolved". The value of the diameter at the top of the peak is called "mode" or "dominant value" and represents the most frequent value of the peak. When distribution has two peaks separated (or resolved), we say that the distribution is bimodal.

[0051] We define the concept of multi-modality from a "criterion" R, referred to as "resolution factor" that characterizes the separation or not superposition of the peaks.

[0052] Les différents pics sont assimilés at gaussienne, caractérisée par son and the mode of a largeur hauteur-δ, de laquelle on peut déduire largeur de la base du pic ω = 1, δ 7.

[0053] 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).

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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 .

[0063] 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.

[0064] 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.

[0065] 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.

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) supplying a tubular reactor with said gel synthesis,

c) first introduction of one or more agent (s) seeding in the tubular reactor or upstream of the tubular reactor,

d) introducing a second or more agent (s), seeding, identical (s) or different (s) in the tubular reactor,

e) carrying out the crystallization reaction in the tubular reactor of the synthesis gel in presence of the agent (s), seeding, forming the reaction medium, f) filtering the reaction medium to recover product crystals.

2. The method of claim 1, wherein step d) is repeated one, two, three or more times, preferably one, two or three times, more preferably once or twice.

3. The method of claim 1 or claim 2, wherein the first agent introduction (s), seeding is carried out upstream of the reactor.

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

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

7. A method according to any preceding claim, wherein an additional synthesis gel is added to the reaction medium in one or more points of the tubular reactor.

8. A method according to any preceding claim, wherein the total amount of agent (s) seed added is between 0.005% and 10% by weight relative to the synthesis gel, preferably between 0.01% and 5% and more preferably between 0.01% and 3% by weight relative to the synthesis gel initially introduced into the tubular reactor.

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

10. 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.