Multi-reactor synthesis process for zeolite crystals with controlled particle size

Abstract

The present invention relates to a method for preparing zeolite crystals having a multimodal particle size distribution, and whose sizes are between 0.02 µm and 20 µm, said method comprising feeding at least two reactors each with a synthesis gel suitable for forming zeolite crystals, conducting a crystallization reaction, in parallel, in each of the at least two reactors, and mixing the reaction media of the at least two reactors after the commencement of at least one of the crystallization reactions.

Description

[0069] The zeolites that can be prepared according to the process of the present invention can be of any type, and for example, and without limitation, any MFI type zeolite, and in particular silicalite, any MOR type zeolite, OFF type zeolite, MAZ type zeolite, CHA type zeolite and HEU type zeolite, any FAU type zeolite, and in particular Y zeolite, X zeolite, MSX zeolite, LSX zeolite, any EMT type zeolite or any LTA type zeolite, i.e. zeolite A, as well as other zeotypes, such as for example titanosilicalites.

[0070] By MSX (Medium Silica X) zeolite, we mean a FAU-type zeolite having a Si / Al atomic ratio between approximately 1.05 and approximately 1.15, inclusive. By LSX (Low Silica X) zeolite, we mean a FAU-type zeolite having a Si / Al atomic ratio of approximately 1.

[0071] The process according to the invention is particularly suitable for the preparation of zeolites selected from among MFI type zeolites, and in particular silicalite, FAU type zeolites, and in particular zeolite Y, zeolite X, zeolite MSX, zeolite LSX, and LTA type zeolites, i.e. zeolite A, as well as CHA type zeolites and HEU type zeolites.

[0072] The process according to the invention is also particularly well suited to the preparation of any FAU-type zeolite, and in particular X-type zeolite, MSX-type zeolite, and LSX-type zeolite. MFI-type zeolites, and in particular silicalite, can also be very advantageously prepared according to the process of the invention.

[0073] Furthermore, the continuous preparation process of the present invention is not limited to the preparation of the zeolites described above, but also includes the corresponding zeolites with hierarchical porosity. Zeolites with hierarchical porosity are solids comprising a microporous network linked to a mesoporous network, and thus make it possible to reconcile the accessibility properties to active sites of mesoporous zeolites known from the prior art with those of maximum crystallinity and microporosity of so-called "classical" zeolites (without mesoporosity). In this case, specific structuring agents are introduced into the reaction medium of step a), for example, organosilane-type structuring agents as described in document FR 1 357 762.

[0074] The synthesis process of the present invention therefore allows for an easy and economical industrial synthesis of zeolite crystals whose distribution The particle size distribution, at least bimodal, is homogeneous, controlled, and even mastered. Furthermore, it has been observed that the process according to the invention is very stable over time when implemented continuously. These zeolite crystals have very interesting applications in numerous fields.

[0075] Indeed, thanks to the process of the invention, it is now possible to obtain more easily multimodally distributed zeolite crystals in a controlled and homogeneous manner, unlike what would be obtained with mixtures of crystals of different grain sizes.

[0076] The multimodal particle size distribution of the zeolite crystals obtained by the process of the invention makes it possible to obtain crystals exhibiting, in particular, a high apparent density, and especially a higher density compared to crystals with a single-mode particle size distribution. It can indeed be estimated that the small crystals occupy the spaces between the large crystals.

[0077] This high apparent density of the zeolite crystals obtained with the process of the invention makes it possible to obtain very particular adsorption performances, in particular in terms of volumetric adsorption capacity.

[0078] The zeolite crystals obtained with the process of the invention thus find very interesting applications in the field of adsorption, separation, purification of gases, of liquids.By way of non-limiting examples, zeolite crystals obtained according to the process of the present invention can advantageously be used as adsorbent fillers in polymer-based composites, as constituents of agglomerated zeolite adsorbents used in separation or purification processes by adsorption such as pressure- and / or temperature-modulated processes, or in chromatographic separation processes (fixed beds, moving beds, simulated moving beds), in applications as varied as the purification of industrial gases, the separation of nitrogen and oxygen, the purification of natural gas or synthesis gas, or the purification of various petrochemical fractions, the separation of isomers in refining, and others.

[0079] The degree of crystallinity and the purity of the synthesized zeolite are evaluated by X-ray diffraction analysis, a technique known to those skilled in the art by the acronym XRD. This identification is, for example, carried out on a Bruker brand XRD instrument.

[0080] This analysis makes it possible not only to determine the quantity of crystalline phase(s) present, but also to identify and quantify any different zeolites present, each zeolite having a unique diffractogram defined by The positioning of the diffraction peaks and their relative intensities are key factors. Non-crystalline phases are not detected by X-ray diffraction analysis.

[0081] This analysis is also used to determine the degree of crystallinity of the reaction medium in order to assess whether the crystallization reaction has begun. In this case, a sample of the reaction medium is taken, dried at 80°C for 4 hours, and then analyzed by XRD.

[0082] The zeolite crystals (or dried samples) are crushed, then spread and smoothed onto a sample holder by simple mechanical compression. The acquisition conditions for the diffractogram produced on the Bruker D5000 instrument are as follows: • Cu tube used at 40 kV - 30 mA; • size of the slits (diverging, diffusion and analysis) = 0.6 mm; • filter: Ni; • rotating sample device: 15 rpm-1; • measuring range: 3° < 20 < 50°; • pitch: 0.02°; • Counting time per step: 2 seconds.

[0083] The interpretation of the diffractogram obtained is carried out with the EVA software with identification of zeolites using the ICDD PDF-2 database, release 2011.

[0084] The quantity of crystals, by weight, is determined by XRD analysis; this method is also used to measure the quantity of non-crystalline phases. This analysis is performed on a Bruker instrument, and then the quantity by weight of the zeolite crystals is evaluated using Bruker's TOPAS software.

[0085] Crystallinity (or degree of crystallinity) corresponds to the ratio of the sum of the mass fractions of the crystalline phases present, to the total weight of the sample.

[0086] Purity is expressed as a mass percentage of the desired crystalline phase relative to the total weight of the sample.

Claims

DEMANDS 1. A process for preparing zeolite crystals having a multimodal particle size distribution, and having sizes ranging from 0.02 pm to 20 pm, said process comprising at least the following steps: a) preparation of a synthesis gel by mixing at least one source of silica, at least one source of alumina and possibly but preferably at least one aqueous solution of alkali or alkaline earth metal hydroxide, b) feeding at least two reactors, each with a synthetic gel capable of forming zeolite crystals, c) conducting a crystallization reaction, in parallel, in each of the at least two reactors, d) mixing of the reaction media from at least two reactors, and e) filtration of the mixture of reaction media obtained in step d), in order to separate the crystals produced from the mother liquors.

2. A method according to claim 1, wherein the at least two reactors are each fed with a zeolite crystal synthesis gel, the synthesis gels being able to be identical or different.

3. A method according to claim 1 or claim 2, wherein one or more seeding agent(s) are introduced into the synthesis gel(s) upstream or inside at least one of the synthesis reactors or into at least two synthesis reactors.

4. A method according to any one of the preceding claims, wherein the seeding agent is selected from nucleation gels, zeolite crystals, mineral particles of any kind, and others, as well as mixtures thereof.

5. A method according to any one of the preceding claims, wherein the reactors used are stirred reactors for batch mode syntheses and tubular reactors for continuous mode syntheses.

6. A method according to any one of the preceding claims, in which there are 2 or more reactors, of the same or different types, preferably 2, 3, 4 or 5 reactors of the same or different types, preferably again 2 or 3 reactors of the same or different types, preferably again 2 reactors of the same or different types, typically two reactors of the same type.

7. A process according to any one of the preceding claims, operated continuously, in 2, 3 or 4 tubular reactors, preferably in 2 or 3 tubular reactors, typically in 2 tubular reactors.

8. A process according to any one of the preceding claims, wherein the crystallization reaction is carried out at a temperature between 60°C and 200°C, preferably between 80°C and 160°C.

9. A method according to any one of the preceding claims, wherein the crystallization reaction is carried out under a pressure between atmospheric pressure and 1.5 MPa.

10. A method according to any one of the preceding claims, wherein the reaction media of at least two reactors operating in parallel are mixed at any time, provided that the crystallization reaction has started in one of the at least two reactors, preferably in at least two reactors.

11. A process according to any one of the preceding claims, wherein the mother liquors from step e) of filtration are recycled.

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