Process for the continuous synthesis of ZSM-5 zeolite

Abstract

The present invention relates to a process for the continuous synthesis of ZSM-5 type zeolite crystals, which comprises continuously feeding a synthesis medium comprising a silica source, an alumina source and seeds into a tubular reactor, rapidly heating the synthesis medium to a value between 100°C and 300°C, crystallizing at a temperature at least equal to or higher than the temperature of the previous step, and continuously recovering the ZSM-5 type zeolite crystals.

Description

[Technical Field]

[0001] The present invention relates to the field of zeolites, more particularly to the field of synthetic zeolites, more particularly to the preparation of synthetic zeolites, especially zeolites having a high silicon content, and most particularly to the continuous preparation of synthetic zeolites having a high silicon content with a high level of purity and crystallinity. [Background technology]

[0002] Zeolites are crystalline aluminosilicates with highly variable ratios of silicon and aluminum, often referred to as the Si / Al atomic ratio. Several crystal structures are possible for the same Si / Al ratio, and several zeolites with different Si / Al ratios can have the same crystal structure. Their synthesis routes are highly diverse and more or less easy to implement and perform, depending on the target Si / Al ratio and desired crystal structure.

[0003] In particular, the MFI structure zeolite known as ZSM-5 is a microporous crystalline aluminosilicate that is involved in a variety of industrial applications such as adsorption, catalysis, separation, and ion exchange. Therefore, industry requires relatively large quantities of this synthetically produced ZSM-5 zeolite.

[0004] However, the currently known routes to synthesize ZSM-5 zeolites have many drawbacks, among which can be mentioned the use of organic structuring agents, the relatively long synthesis times, for example from tens of hours to days, and the use of autoclaves, since the synthesis in most cases requires high temperatures and therefore pressures.

[0005] In addition, conventional industrial synthesis of ZSM-5 is mostly carried out in large-scale facilities, generally by heating the synthesis gel and / or reaction medium, by steam injection, and / or by jacketing, which causes high energy costs and often leads to problems with production regularity.

[0006] The synthesis of ZSM-5 with organic structuring agents is described, for example, in documents US 7244409 and AU 2014413311. These syntheses require, on the one hand, the presence of an organic structuring agent in the reaction medium and, on the other hand, the destruction of this organic structuring agent, generally by calcination after the synthesis of the zeolite.

[0007] Therefore, the use of organic structuring agents is harmful to the environment. Furthermore, the use of structuring agents leads to high production costs and an additional industrial step to remove the organic structuring agents.

[0008] To overcome these drawbacks, other publications, such as US2013144100, which describes the synthesis of large-crystalline ZSM-5 zeolite, refer to a synthesis that does not include an organic structuring agent. However, in this publication, the process uses gluconic acid or its salts as an aluminum complexing agent. Furthermore, the duration of the synthesis (approximately 2 to 100 hours) remains too long for an efficient, economical, and profitable industrial synthesis.

[0009] Patent US5240892 describes a batch synthesis lasting several hours, in which the crystallization step is carried out in an autoclave. Patent US6261534 also describes a process for the synthesis of ZSM-5 zeolite without a structuring agent but in the presence of two sources of metal and non-metal oxides in a molar ratio greater than 12. Furthermore, the synthesis times are long, for example, more than 24 hours.

[0010] Among the processes carried out continuously in tubular reactors, mention may be made in particular of International Applications WO2017216236 and WO2018167414, both of which only exemplify the synthesis of zeolites with low Si / Al ratios (chabazite, zeolites A and X). [Prior art documents] [Patent documents]

[0011] [Patent Document 1] U.S. Patent No. 7,244,409 [Patent Document 2] Australian Patent Application Publication No. 2014413311 [Patent Document 3] US Patent Application Publication No. 2013 / 144100 [Patent Document 4] U.S. Patent No. 5,240,892 [Patent Document 5] U.S. Patent No. 6,261,534 [Patent Document 6] International Publication No. 2017 / 216236 [Patent Document 7] International Publication No. 2018 / 167414 Summary of the Invention [Problem to be solved by the invention]

[0012] Therefore, a primary object of the present invention is to propose a new method for preparing ZSM-5 zeolite that avoids the aforementioned drawbacks. In particular, an object of the present invention is to provide a process for synthesizing ZSM-5 zeolite that is easy to industrialize, economical, and efficient. Another object of the present invention is to provide a process for synthesizing ZSM-5 zeolite that is easy to industrialize, economical, efficient, and requires a short synthesis time. Yet another object of the present invention is to provide a process for synthesizing ZSM-5 zeolite that is easy to industrialize, economical, efficient, and requires a short synthesis time, in which the resulting zeolite has a crystalline form with a size suitable for industrial use, in particular a size larger than the nanometer size.

[0013] Applicant has now discovered that the foregoing objects may be achieved in whole or at least in part by the present invention as detailed in the following description. [Means for solving the problem]

[0014] The first subject of the present invention therefore consists in a process for the continuous synthesis of ZSM-5 zeolite, which does not require the use of organic structuring agents. The process of the present invention also makes it possible to dispense with the aging step and allows for a synthesis with relatively short crystallization times, generally less than 5 hours, or even less than 4 hours, more generally even less than 3 hours. The process according to the invention is perfectly suited for the continuous synthesis of ZSM-5 crystals.

[0015] In the present invention, unless otherwise indicated, all ranges of values ​​introduced by the expressions "from ... to ..." or "to ..." or similar expressions intended to encompass two values ​​are understood to include the upper and lower limit values.

[0016] More specifically, the present invention relates to a process for continuous synthesis of ZSM-5 type zeolite crystals, which comprises at least the following steps a) to d):

[0017] a) continuously feeding a synthesis medium comprising a silica source, an alumina source and seeds into a tubular reactor;

[0018] b) heating the synthesis medium to a value between 100°C and 300°C for a period corresponding to the residence time in at most 1 / 3, preferably 1 / 4, preferably 1 / 5 of the total length of the tubular reactor,

[0019] c) a crystallization step at a temperature at least equal to or greater than the temperature of the previous step;

[0020] d) Continuous recovery of zeolite crystals of the ZSM-5 type having a size between 0.2 μm and 20.0 μm, preferably between 0.2 μm and 10.0 μm, better still between 0.3 μm and 7.0 μm, advantageously between 0.3 μm and 5.0 μm.

[0021] The ZSM-5 type zeolite crystals obtained by the process of the invention defined above generally have a size of between 0.2 μm and 20.0 μm, preferably between 0.2 μm and 10.0 μm, better still between 0.3 μm and 7.0 μm and advantageously between 0.3 μm and 5.0 μm.

[0022] In the process of the present invention, the reactor is a tubular reactor, optionally but preferably equipped with one or more stirring systems selected from mechanical stirring systems and vibratory stirring systems, and combinations of one or more mechanical stirring systems and one or more vibratory stirring systems, although only one type of stirring system, either mechanical or vibratory, is preferred for the process of the present invention.

[0023] Even more preferably, the process of the present invention comprises only one agitation system, either mechanical or vibratory. According to one preferred embodiment, the process of the present invention comprises a single mechanical agitation system. According to another preferred embodiment, the method of the present invention comprises a single agitation system generated by a vibratory motion.

[0024] The stirring means may be of any type known to those skilled in the art, for example, but not limited to, if the reactor is a tubular reactor adapted to be operated continuously, this tubular reactor may be equipped with restrictions (for example, rings, baffles, etc.), one or more stirring systems (stirring shaft equipped with several stirring wheels, cascades of stirrers distributed along the reactor), one or more vibration or pulsation systems (for example, pistons, membranes, head-to-tail pumps making it possible to create a reciprocating motion of the reaction medium), etc., as well as a combination of two or more of these techniques.

[0025] In a preferred embodiment of the invention, the process is carried out in a tubular reactor equipped with a restriction and a system making it possible to impart pulsation to the fluid circulating in the reactor, as described, for example, in application US20090304890 from NiTech.

[0026] In a preferred embodiment of the process of the present invention, the tubular reactor makes it possible to ensure a continuous flow in a straight line, optionally with one or more curves. The tubular reactor generally has an internal diameter that can vary in most cases by large percentages, preferably between 1 mm and 1000 mm, preferably between 1 mm and 800 mm, more preferably between 1 mm and 500 mm, for example between 3 mm and 400 mm.

[0027] The total length of the tubular reactor can also vary greatly and is generally between 0.5 m and 100 m, preferably between 0.8 m and 80 m, preferably between 1 m and 70 m.

[0028] The reactor volume should be adapted as a function of the zeolite production requirements. Typically, this is 0.04 m 3 ~10m 3 , preferably 0.05 m 3 ~5m 3 The flow rate may vary from 0.02 m to 1.02 m, with the length / diameter shape factor typically being greater than 100, preferably greater than 140, and more preferably greater than 180. Depending on the reactor geometry, the flow rate may be typically greater than 0.02 m 3 h -1 ~20m 3 h -1 can vary.

[0029] The reactor used in the process of the present invention further comprises at least one heating system for at least a portion of the length of the reactor, and optionally an insulating system for all or a portion of the length of the reactor. The reactor may also comprise one or more ultrasonic sources to promote crystallization and / or the formation of well-individualized crystals (i.e., with no or few agglomerates).

[0030] The at least one heating system can be of any type known to those skilled in the art, for example by steam injection, by jacketing, by adding a microwave source, and by a combination of one or more of the aforementioned means. The heating system must allow a rapid temperature rise up to the crystallization temperature, as described below.

[0031] The synthesis medium is continuously prepared by mixing the silica source and the alumina source, the synthesis medium being prepared by mixing the components of said synthesis medium by any means known to those skilled in the art, more particularly by a mixer, such as a preferably rotor / stator type shear mixer.

[0032] By silica source is meant any source known to those skilled in the art, in particular silicates, in particular silicates or orthosilicates of alkali metals or alkaline earth metals, for example sodium, or colloidal silica, or solutions of tetraethyl orthosilicate, preferably aqueous solutions, the latter being not preferred.

[0033] By alumina source is meant any alumina source known to those skilled in the art, in particular aluminium sulfate, aluminium nitrate, solutions of aluminates, in particular aluminates of alkali metals or alkaline earth metals, for example sodium aluminate, preferably aqueous solutions.

[0034] In a preferred embodiment, the synthetic medium comprises:

[0035] A silica source which is an aqueous solution of a silicate or orthosilicate of an alkali metal or alkaline earth metal, such as preferably sodium, or colloidal silica.

[0036] An alumina source which is an aqueous solution of aluminum sulfate, aluminum nitrate, an aluminate, especially an alkali metal or alkaline earth metal aluminate, such as sodium aluminate.

[0037] The term "seeds" is understood to mean any seed source known to those skilled in the art, in particular nucleation solutions or zeolite crystals of the MFI type (ZSM-5 or silicalite-1) or MEL type, optionally pre-ground or cryo-ground, preferably to submicron size.

[0038] The seeds are introduced in a mixture with the silica and / or alumina sources or continuously after the introduction of the silica and alumina sources. The introduction of the seeds is most preferably carried out upstream of the crystallization step. The weight percentage of the seeds relative to the total weight of the synthesis medium is usually between 0.5% and 20%, preferably between 1% and 10% in most cases.

[0039] The SiO2 / Al2O3 molar ratio in the synthesis medium before the introduction of the seeds is usually 16 to 400, preferably 16 to 350, preferably 20 to 300, inclusive of the upper and lower limits. The H2O / SiO2 molar ratio is 1 to 100, preferably 3 to 90, preferably 5 to 70, inclusive of the upper and lower limits. The Na2O / SiO2 molar ratio is 0.01 to 0.9, preferably 0.01 to 0.7, preferably 0.01 to 0.5, inclusive of the upper and lower limits.

[0040] According to yet another preferred embodiment, the synthesis medium before the introduction of the seeds comprises:

[0041] a SiO2 / Al2O3 molar ratio between 16 and 400, preferably between 16 and 350, preferably between 20 and 300, inclusive;

[0042] a HO / SiO molar ratio of 1 to 100, preferably 3 to 90, preferably 5 to 70, inclusive;

[0043] a Na2O / SiO2 molar ratio of 0.01 to 0.9, preferably 0.01 to 0.7, preferably 0.01 to 0.5, inclusive.

[0044] In one embodiment, the synthesis medium used in the process of the invention may comprise one or more auxiliaries, such as one or more organic solvents advantageously chosen from aqueous solvents, such as alcohols, advantageously chosen from propanol, butanol, pentanol, hexanol, preferably butanol.

[0045] The heating step can be carried out by any means known to those skilled in the art, provided that the synthesis medium rapidly reaches the desired temperature, typically between 100°C and 300°C. Rapid heating can be simply expressed as a time corresponding to a residence time of at most 1 / 3, preferably 1 / 4, and preferably 1 / 5 of the total length of the tubular reactor. This length fraction can, in some cases, be up to 1 / 10 of the total length of the tubular reactor, if desired. Heating can be carried out by any method known to those skilled in the art, for example, by steam injection, by a jacket, or by applying a microwave source, or by combining one or more of the aforementioned means.

[0046] The process of the invention is particularly characterized by the fact that the heating of the synthesis medium to the crystallization temperature, which is the main objective of the invention, is carried out very quickly.

[0047] Indeed, it has been found, quite surprisingly, that this rapid heating makes it possible in particular to obtain zeolite crystals of high purity, with no impurities or at least only minor impurities.

[0048] Thus, as mentioned above, the reaction medium is continuously fed into the tubular reactor and immediately heated in a heating zone corresponding to a duration equal to at most 1 / 3, preferably 1 / 4, preferably 1 / 5, or even at most 1 / 10 of the total length of the tubular reactor. At the end of this heating zone, the reaction medium continues into the tubular reactor at a temperature between 100°C and 300°C, where it crystallizes to form the desired crystals of ZSM-5 zeolite.

[0049] According to the invention, the crystallization step is carried out at elevated temperature under pressure, the pressure being at least equal to the autogenous pressure. Advantageously, the crystallization step is carried out at a temperature ranging from 100°C to 300°C, preferably from 150°C to 220°C, more preferably from 170°C to 210°C, and most preferably from 180°C to 210°C.

[0050] The duration of the crystallization step can vary widely, generally from a few minutes to a few hours, most often from 30 minutes to 5 hours, preferably from 30 minutes to 3 hours, more preferably from 1 hour to 2.5 hours.

[0051] It should be understood that by rapidly heating the synthesis medium to a value between 100°C and 300°C, as indicated above, for a period corresponding to a residence time in at most 1 / 3, preferably 1 / 4, preferably 1 / 5 of the total length of the tubular reactor, the crystallization time corresponds to at least 2 / 3, preferably 3 / 4, preferably 4 / 5, respectively, of the total length of the tubular reactor.

[0052] As indicated above, the flow rate in a tubular reactor can vary widely and is generally and typically in the range of 0.02 m / s to 100 m / s, depending on the reactor geometry, the desired synthesis rate, the different types of equipment used to mix the starting solutions and achieve the crystallization temperature, etc. 3 h -1 ~20m 3 h -1 is.

[0053] Yet another advantage of the process of the present invention, namely, a direct result of the particularly rapid heating up to the crystallization temperature, is realized in the very short duration for the synthesis of ZSM-5 crystals, most particularly when compared to the duration of industrial syntheses available today in the prior art.

[0054] Furthermore, the synthesis process of the present invention is a continuous process, which represents an unimaginable advantage compared to conventional industrial synthesis processes, which generally require large facilities, i.e., batch production processes that are often less uniform in terms of the quality of the products produced. Thus, the continuous process according to the present invention offers many of the advantages indicated above, to which can be added the reduction in the size of the facilities, the reduction in energy consumption, and the improvement in the regularity of the quality of the production.

[0055] The continuous process according to the invention ensures a homogeneous mixture of the reaction medium, in particular during crystallization, which makes it possible to obtain crystals of homogeneous size and morphology in a very simple and efficient manner. Thus, the process of the invention continuously produces ZSM-5 zeolite crystals having a Si / Al ratio of 10 to 60, preferably 10 to 50, and preferably 12 to 40.

[0056] According to one embodiment, the crystals obtained by the process of the invention have a size (limits included) greater than 0.2 μm, preferably greater than 0.3 μm, and in most cases between 0.2 μm and 20.0 μm, preferably between 0.2 μm and 10.0 μm, better still between 0.3 μm and 7.0 μm, advantageously between 0.3 μm and 5.0 μm.

[0057] The number-average size of the zeolite crystals is evaluated by observation with a scanning electron microscope (SEM). To assess the size of the zeolite crystals in the sample, a series of images is taken at a magnification of at least 5000. The lengths of at least 200 crystals are then measured using dedicated software, such as the Smile View software from the publisher LoGraMi. The accuracy is on the order of 3%. The ZSM-5 crystals are pure, and this purity is verified by the absence of parasitic phases identified by DRX.

[0058] Thus, the crystals obtained according to the process of the present invention generally have a density of 0.10 g.cm in most cases. -3 or more, preferably 0.13 g.cm -3 or more, preferably 0.14 g.cm -3 The Dubinin volume (or microporous volume V mi ) is determined by conventional methods known to those skilled in the art, in particular from the measurement of the adsorption isotherms of gases such as nitrogen, argon, oxygen, etc. at their liquefaction temperatures. Nitrogen is preferably used.

[0059] Before this adsorption measurement, the zeolite crystals of the present invention were subjected to vacuum (P<6.7.10 -4The adsorption isotherm is measured at 77 K for a zeolite with MFI structure, such as ZSM-5, using an ASAP 2020 model apparatus manufactured by Micromeritics, obtaining at least 35 measurement points at relative pressures with a P / P ratio between 0.002 and 1. The micropore volume is determined from the resulting isotherm according to the Dubinin and Raduskevitch equation, using standard ISO 15901-3:2007. The micropore volume thus evaluated is expressed as cm of liquid adsorbent per gram of anhydrous adsorbent. 3 The measurement uncertainty is ±0.003 g / cm 3 is.

[0060] As indicated above, the process of the present invention makes it possible to dispense with the use of organic structuring agents in particular. In addition to the advantage of simplified implementation, the lack of use of structuring agents significantly reduces the environmental impact, since these organic agents are often very toxic. Another advantage is that the process without structuring agents avoids the additional step of removing the organic structuring agents, thus reducing the cost of zeolite production.

[0061] Without wishing to be bound by theory, the process of the present invention, in which the reaction medium is rapidly brought to the crystallization temperature, facilitates the production of well-crystallized, homogeneous, impurity-free material characterized by crystals having a relative crystallinity of 95% to 140%, preferably 95% to 135%, and most preferably 95% to 130%, as measured according to standard ASTM D5758.

[0062] The following examples are used to illustrate but not limit the invention, the scope of which is defined by the claims appended hereto. [Brief explanation of the drawings]

[0063] [Figure 1] 1, 2 and 3 show the X-ray diffractograms of the crystals obtained in Examples 1, 2 and 3, respectively. [Figure 2] 1, 2 and 3 show the X-ray diffractograms of the crystals obtained in Examples 1, 2 and 3, respectively. [Figure 3] 1, 2 and 3 show the X-ray diffractograms of the crystals obtained in Examples 1, 2 and 3, respectively. [Example]

[0064] [Example 1 (according to the present invention)] <Continuous synthesis of ZSM-5 with added seeds>

[0065] The continuous synthesis of ZSM-5 zeolite consists of feeding a tubular reactor with a solution of silicate, aluminate, and seeds. A sodium silicate solution with the composition 6.9Na2O-93SiO2-951H2O is prepared. A sodium aluminate solution with the composition 1.4Na2O-1Al2O3-311H2O is prepared. The seeds consist of ZSM-5 (Alfa AESAR, CAS 1318-02-1) crystals in a proportion of 2% by weight based on the weight of the synthesis medium.

[0066] The synthesis medium is therefore prepared by simultaneously feeding it into the chamber of an in-line shear mixer using two pumps. The flow rate of the aluminate solution is equal to 100 g / min, and that of the silicate equal to 450 g / min. Immediately before entering the tubular reactor, seeds are added. The synthesis medium is heated in the tubular reactor using a jacket to reach a crystallization temperature of 200 °C over a length corresponding to 1 / 6 of the total length of the tubular reactor. The feed rate is fixed to ensure a total residence time in the tubular reactor of 120 min. At the end of this synthesis, a pure ZSM-5 zeolite, i.e., a zeolite with a diffractogram strictly characteristic of MFI type zeolite, is obtained (X-ray diffractogram, see Figure 1), with a concentration of 0.14 g.cm. -3 has a Dubinin volume of .

[0067] [Example 2 (Comparison)] <Continuous synthesis of ZSM-5 without adding seeds>

[0068] In this example of the continuous synthesis of ZSM-5 zeolite, a solution of sodium silicate of composition 6.9Na2O-93SiO2-951H2O and a solution of sodium aluminate of composition 1.4Na2O-1Al2O3-311H2O are fed into a tubular reactor.

[0069] The synthesis medium is continuously prepared by simultaneously mixing the aluminate and silicate solutions using a rotor / stator type shear mixer. The synthesis medium is thus prepared by simultaneously feeding them into the chamber of a Silverson in-line shear mixer using two peristaltic pumps. The flow rate of the aluminate solution is equal to 100 g / min, and the flow rate of the silicate solution is equal to 450 g / min. The synthesis medium is heated in the tubular reactor using a jacket to reach a crystallization temperature of 200 °C over a length corresponding to 1 / 6 of the total length of the tubular reactor. The feed rate is fixed to ensure a residence time in the tubular reactor of 120 min.

[0070] The X-ray diffractogram of the product obtained from this synthesis (Figure 2) shows that in the absence of seeds an amorphous product is obtained.

[0071] [Example 3 (Comparison)] <Batch synthesis of seeded ZSM-5>

[0072] The batch synthesis of ZSM-5 zeolite consists of introducing a sodium silicate solution, a sodium aluminate solution and seeds into a batch reactor.

[0073] A silicate solution of composition 6.9Na2O93SiO2951H2O is prepared. An aluminate solution of composition 1.4Na2O1Al2O3311H2O is prepared. The seeds consist of crystals of ZSM-5 (Alfa AESAR, CAS 1318-02-1) in a proportion of 2% by weight relative to the weight of the synthesis medium.

[0074] The synthesis medium is prepared in a batch reactor by mixing sodium silicate solution, sodium aluminate solution, and then seeds. The reactor is then heated to 200°C via a jacket. The residence time in the reactor is 2 hours.

[0075] The X-ray diffractogram of the product obtained from this synthesis (Fig. 3) shows not only the presence of ZSM-5 of MFI structure type, but also of another parasitic phase, zeolite of MOR structure type.

Claims

1. A process for the continuous synthesis of zeolite crystals of the ZSM-5 type, comprising at least the following steps a) to d): a) continuously feeding a synthesis medium comprising a silica source, an alumina source and seeds into a tubular reactor; b) heating the synthesis medium to a value between 100°C and 300°C for a period corresponding to the residence time in at most 1 / 3, preferably 1 / 4, preferably 1 / 5 of the total length of the tubular reactor, c) a crystallization step at a temperature at least equal to or greater than the temperature of the previous step; d) Continuous recovery of zeolite crystals of the ZSM-5 type.

2. 10. The process of claim 1, wherein the tubular reactor is equipped with one or more agitation systems selected from a mechanical agitation system and a vibratory agitation system, and a combination of one or more mechanical agitation systems and one or more vibratory agitation systems.

3. 3. The process of claim 1 or claim 2, wherein the tubular reactor has an internal diameter of from 1 mm to 1000 mm, preferably from 1 mm to 800 mm, more preferably from 1 mm to 500 mm, for example from 3 mm to 400 mm.

4. A process according to any one of claims 1 to 3, wherein the seeds are selected from a nucleation solution and zeolite crystals of MFI or MEL type.

5. The process according to any one of claims 1 to 4, wherein the weight percentage of the seeds relative to the total weight of the synthetic medium is between 0.5% and 20%, preferably between 1% and 10%.

6. The process of any one of claims 1 to 5, wherein the synthesis medium comprises: a silica source which is an aqueous solution of an alkali metal or alkaline earth metal silicate or orthosilicate, or colloidal silica, and an alumina source which is an aqueous solution of aluminum sulfate, aluminum nitrate, an aluminate, in particular an aluminate of an alkali metal or alkaline earth metal;

7. 7. The process of claim 6, wherein the synthesis medium prior to the introduction of the seeds comprises: SiO of 16 to 400, preferably 16 to 350, preferably 20 to 300, inclusive ２ / Al ２ O ３ Molar ratio, H of 1 to 100, preferably 3 to 90, preferably 5 to 70, inclusive ２ O / SiO ２ molar ratio, and Na from 0.01 to 0.9, preferably from 0.01 to 0.7, preferably from 0.01 to 0.5, inclusive ２ O / SiO ２ Molar ratio.

8. 8. The process according to any one of claims 1 to 7, wherein the crystallization step is carried out at a temperature in the range of from 100°C to 300°C, preferably from 150°C to 220°C, more preferably from 170°C to 210°C, and most preferably from 180°C to 210°C.

9. 9. The process according to any one of claims 1 to 8, wherein the duration of the crystallization step is from a few minutes to a few hours, most often for a period varying from 30 minutes to 5 hours, preferably from 30 minutes to 3 hours, more preferably from 1 hour to 2.5 hours.

10. The flow rate is 0.02 m ３ h －１ ~20m ３ h －１ The process according to any one of claims 1 to 9, wherein

11. 11. The process according to any one of claims 1 to 10, wherein the crystals have a relative crystallinity, measured according to standard ASTM D5758, of between 95% and 140%, preferably between 95% and 135%, most preferably between 95% and 130%.

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