Method for continuously synthesizing ZSM-5 zeolite

Abstract

The present invention relates to a process for the continuous synthesis of zeolite crystals of the ZSM-5 type, comprising continuously feeding a tubular reactor with a synthesis medium comprising a source of silica, a source of alumina and a seed crystal, rapidly heating said synthesis medium to a value between 100 DEG C and 300 DEG C, crystallizing at a temperature at least equal to or higher than the temperature of the previous step, and continuously collecting zeolite crystals of the ZSM-5 type.

Description

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

[0002] Zeolites are crystalline aluminosilicates in which the ratio of silicon to aluminum (commonly referred to as the Si / Al atomic ratio) is highly variable. Furthermore, for the same Si / Al ratio, a variety of crystal structures are possible, and a variety of zeolites with different Si / Al ratios may have the same crystalline structure. The synthetic routes are very diverse and more or less easy to implement and conduct, depending on the target Si / Al ratio and the desired crystalline structure.

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

[0004] However, the ZSM-5 zeolite synthesis routes known today have many disadvantages, among which may be mentioned the use of organic structuring agents, relatively long synthesis times, for example tens of hours to days, and the use of autoclaves, since the synthesis most often requires high temperatures and therefore pressures.

[0005] Furthermore, the conventional industrial synthesis of ZSM-5 is most often carried out using large-scale plants, generally with heating of the synthesis gel and / or the reaction medium by steam injection and / or by jackets; this results in high energy costs and often leads to problems with production regularity.

[0006] The synthesis of ZSM-5 with organic structurants is described, for example, in documents US 7244409 and AU 2014413311. On the one hand, these syntheses require the presence of an organic structurant in the reaction medium, on the other hand, the organic structurant is generally destroyed by calcination after the zeolite synthesis.

[0007] Therefore, the use of organic structurants is harmful to the environment. Furthermore, the use of structurants results in high manufacturing costs and an additional industrial step to remove the organic structurants.

[0008] In order to overcome these disadvantages, other publications mention synthesis without organic structuring agents, such as publication US2013144100, which describes the synthesis of large crystalline ZSM-5 zeolites. However, in this description, the method uses gluconic acid or its salts as aluminum complexing agent. In addition, the duration of the synthesis (about 2 hours to 100 hours) is still too long for an effective, economical and advantageous industrial synthesis.

[0009] Patent US5240892 describes a batch synthesis lasting several hours, wherein the crystallization step is carried out in an autoclave. Patent US6261534 also describes a method for synthesizing ZSM-5 zeolite in the absence of a structuring agent, but in the presence of two metal and non-metal oxide sources in a molar ratio greater than 12. In addition, the synthesis time is long, for example greater than 24 hours.

[0010] Among the processes carried out continuously in a tubular reactor, mention may be made in particular of the international applications WO2017216236 and WO2018167414, both of which illustrate only the synthesis of zeolites with a low Si / Al ratio (chabazite, zeolite A and X).

[0011] Therefore, the main object of the present invention is to propose a new method for preparing ZSM-5 zeolite that avoids the above-mentioned disadvantages. In particular, an object of the present invention is to provide a method for synthesizing ZSM-5 zeolite that is easy to industrialize, economical and effective. Another object of the present invention is to provide a method for synthesizing ZSM-5 zeolite that is easy to industrialize, economical and effective, and the synthesis time is short. Another object is to provide a method for synthesizing ZSM-5 zeolite that is easy to industrialize, economical and effective, and the synthesis time is short, and the zeolite obtained is in crystalline form, the size is compatible with industrial use, and in particular has a size greater than the nano size.

[0012] The applicant has now discovered that the above objects can be achieved in whole or at least in part by means of the invention which is now described in detail in the following description.

[0013] The first subject of the present invention is therefore a process for the continuous synthesis of ZSM-5 zeolites which does not require the use of organic structurants. The process of the invention also allows the synthesis of relatively short crystallization times which can dispense with the aging step and which are generally less than 5 hours, or even less than 4 hours and more generally less than 3 hours. The process according to the invention is fully applicable to the continuous synthesis of ZSM-5 crystals.

[0014] In the present invention, and unless otherwise stated, all value ranges introduced by the expression “from ... to ..." or “between ... and ..." or similar expressions intended to cover two values ​​should be understood to include the endpoints.

[0015] More particularly, the present invention relates to a method for the continuous synthesis of ZSM-5 type zeolite crystals, said method comprising at least the following steps a) to d):

[0016] a) continuously feeding a synthesis medium comprising a silica source, an alumina source and seed crystals into a tubular reactor;

[0017] b) heating the synthesis medium for a period of time corresponding to a residence time in at most 1 / 3, preferably 1 / 4, preferably 1 / 5 of the total length of the tubular reactor to a value between 100° C. and 300° C.;

[0018] c) crystallization at a temperature at least equal to or higher than the temperature of the previous step;

[0019] d) continuously recovering zeolite crystals of the ZSM-5 type, the size of which is 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.

[0020] The ZSM-5 type zeolite crystals obtained by the process of the invention defined above generally have 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] In the process of the present invention, the reactor is a tubular reactor, optionally but preferably equipped with one or more stirring systems, which are selected from mechanical stirring and oscillating stirring systems, and a combination of one or more mechanical stirring systems and one or more oscillating stirring systems. However, for the process of the present invention, only one type of stirring system, mechanical or oscillating, is preferred.

[0022] More preferably, the method of the present invention comprises only one stirring system, mechanical or oscillatory. According to a preferred embodiment, the method of the present invention comprises a single mechanical stirring system. According to another preferred embodiment, the method of the present invention comprises a single stirring system generated by an oscillatory motion.

[0023] The stirring device can be of any type known to the person skilled in the art and, for example and in a non-limiting manner, when the reactor is a tubular reactor suitable for continuous operation, the tubular reactor may be provided with restrictions (e.g. rings, baffles, etc.), may be equipped with one or more stirring systems (a stirring shaft equipped with a plurality of stirring wheels, cascade stirrers distributed along the reactor), one or more oscillation or pulsation systems (allowing to generate a reciprocating motion of the reaction medium by means of, for example, pistons, membranes, head-to-tail pumps), etc., as well as combinations of two or more of these technologies.

[0024] In a preferred embodiment of the invention, the process is carried out in a tubular reactor equipped with restrictions and with a system making it possible to impart pulses to the fluid circulating in the reactor, as described for example in application US20090304890 from NiTech.

[0025] In a preferred embodiment of the process of the invention, the tubular reactor makes it possible to ensure a continuous flow along a straight line, optionally with one or more curves. The tubular reactor generally and most often has a constant internal diameter, which can vary in large proportions and is 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.

[0026] The total length of the tubular reactor may also vary widely and is generally between 0.5 m and 100 m, preferably between 0.8 m and 80 m and preferably between 1 m and 70 m.

[0027] The volume of the reactor should be adjusted according to the zeolite production requirements. Typically, it can be between 0.04 m 3 and 10 m 3 between 0.05 m 3 and 5 m 3 The length / diameter shape factor is typically greater than 100, preferably greater than 140, and more preferably greater than 180. Depending on the geometry of the reactor, the flow rate may typically be between 0.02 m 3 h -1 and 20 m 3 h -1 Changes between.

[0028] The reactor used in the process of the invention further comprises at least one heating system for at least a portion of the reactor length, and optionally a thermal insulation system for all or part of the reactor length. The reactor may also comprise one or more ultrasound sources in order to promote the crystallization and / or formation of well-individualized (that is to say without or with few aggregates) crystals.

[0029] The at least one heating system can be of any type known to those skilled in the art and is selected, for example, from steam injection, through a jacket, by adding a microwave source, and by a combination of one or more of the above means. The heating system must allow a rapid increase in temperature, up to the crystallization temperature, as will be described later.

[0030] The synthesis medium is prepared continuously by mixing a silica source and an alumina source.The synthesis medium is prepared by mixing the components of said synthesis medium by any means known to a person skilled in the art and more particularly by means of a mixer, for example, and preferably a shear mixer of the rotor / stator type.

[0031] Silica source is any source known to the person skilled in the art and in particular a solution, preferably an aqueous solution, of a silicate, in particular a silicate or orthosilicate of an alkali metal or alkaline earth metal, such as sodium, or colloidal silica or tetraethyl orthosilicate, the latter being less preferred.

[0032] Alumina source is understood to mean any alumina source known to the person skilled in the art and in particular solutions, preferably aqueous solutions, of aluminum sulfates, aluminum nitrates, aluminates, in particular alkali metal or alkaline earth metal aluminates such as sodium aluminate.

[0033] In a preferred embodiment, the synthetic medium comprises:

[0034] a silica source which is an aqueous solution of a silicate or orthosilicate of an alkali metal or alkaline earth metal, such as and preferably sodium, or colloidal silica, and

[0035] - A source of alumina which is an aqueous solution of aluminum sulfate, aluminum nitrate, an aluminate, in particular an alkali metal or alkaline earth metal aluminate, for example sodium aluminate.

[0036] The term "seed" is understood to mean any source of seed crystals known to the person skilled in the art, and in particular a nucleating solution, or zeolite crystals of the MFI type (ZSM-5 or Silicalite-1) or MEL type, optionally pre-ground or cryogenically ground to preferably submicron size.

[0037] The seeds are introduced continuously, either in a mixture with the silica source and / or the alumina source, or after the introduction of the silica and alumina sources. The introduction of the seeds is carried out in the most preferred manner upstream of the crystallization step. The weight percentage of the seeds relative to the total weight of the synthesis medium is generally and most often between 0.5% and 20%, preferably between 1% and 10%.

[0038] Before the introduction of the seed crystals, the SiO 2 / Al 2 O 3 The molar ratio is generally between 16 and 400, preferably between 16 and 350, preferably between 20 and 300, including the end values. 2 O / SiO 2 The molar ratio is between 1 and 100, preferably between 3 and 90, and preferably between 5 and 70, including the end values. 2 O / SiO 2 The molar ratio is between 0.01 and 0.9, preferably between 0.01 and 0.7, preferably between 0.01 and 0.5, both inclusive.

[0039] According to another preferred embodiment, before the introduction of the seed crystals, the synthetic medium has:

[0040] - SiO between 16 and 400, preferably between 16 and 350, preferably between 20 and 300 2 / Al 2 O 3 Molar ratios, inclusive,

[0041] - H between 1 and 100, preferably between 3 and 90, and preferably between 5 and 70 2 O / SiO 2 molar ratios, inclusive, and

[0042] - Na between 0.01 and 0.9, preferably between 0.01 and 0.7, preferably between 0.01 and 0.5 2 O / SiO 2 Mole ratios are inclusive.

[0043] In one embodiment, the synthesis medium used in the process of the invention may contain one or more auxiliaries, for example one or more organic solvents, advantageously selected from water-soluble solvents and, for example, those selected from alcohols, advantageously selected from propanol, butanol, pentanol, hexanol, preferably butanol.

[0044] The heating step can be carried out according to any means known to those skilled in the art, provided that the synthesis medium quickly 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 within at most 1 / 3, preferably 1 / 4, preferably 1 / 5 of the total length of the tubular reactor. In some cases, and if necessary, this length fraction can be up to 1 / 10 of the total length of the tubular reactor. Heating can be carried out according to any method known to those skilled in the art and for example by steam injection, by a jacket, or by adding a microwave source, or by combining one or more of the aforementioned means.

[0045] The process of the invention is characterized in particular by the fact, and this is the main object of the invention, that the heating of the synthesis medium up to the crystallization temperature is carried out very quickly.

[0046] In fact, it has been found, quite surprisingly, that such rapid heating makes it possible to obtain zeolite crystals of particularly high purity, without impurities, or at least with only traces of impurities.

[0047] Therefore, and as described above, the reaction medium is continuously fed into the tubular reactor and immediately heated in a heating zone for a duration corresponding to at most 1 / 3, preferably 1 / 4, and preferably 1 / 5, or even up to 1 / 10 of the total length of the tubular reactor. At the end of this heating zone, the reaction medium continues to advance into the tubular reactor at a temperature of 100° C. to 300° C., where it crystallizes to form the desired ZSM-5 zeolite crystals.

[0048] According to the invention, the crystallization step is carried out at an elevated temperature and 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.

[0049] The duration of the crystallization step may vary widely and is generally between a few minutes and a few hours, most often lasting 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.

[0050] It will be appreciated that by virtue of the rapid heating of the synthesis medium over a period of 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, up to values ​​between 100° C. and 300° C., the crystallization time corresponds, as described above, to at least 2 / 3, preferably ¾ and preferably 4 / 5 of the total length of the tubular reactor, respectively.

[0051] As mentioned above, the flow rate in the tubular reactor can vary greatly and is generally and typically in the range of 0.02 m / s. 3 h -1 and 20 m 3 h -1 The preferred method for preparing the crystallization reaction is to use a reactor of a suitable temperature, a reactor having a specific reaction temperature and a specific reaction mixture.

[0052] Yet another advantage of the process of the invention, in particular as a direct result of the rapid heating up to the crystallization temperature, is reflected in the very short duration of the ZSM-5 crystal synthesis, most particularly when compared with the duration of industrial syntheses now available in the prior art.

[0053] Furthermore, the synthesis process of the invention is a continuous process, which represents a considerable (not insignificant) advantage over conventional industrial synthesis processes, which generally require large-sized plants, wherein the production batches are usually not very uniform in terms of the quality of the manufactured product. Thus, the continuous process according to the invention offers many of the advantages described above, to which can be added the regularity of reduced equipment size, reduced energy consumption and improved production quality.

[0054] The continuous process according to the invention ensures a homogeneous mixture of the reaction medium and in particular during crystallization, which makes it possible to obtain crystals with uniform particle size and morphology in a completely simple and effective 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, preferably 12 to 40.

[0055] According to one embodiment, the size of the crystals obtained by means of the process of the invention is greater than 0.2 μm and preferably greater than 0.3 μm, both inclusive, and most often 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.

[0056] The estimation of the number average size of the zeolite crystals is carried out by observation with a scanning electron microscope (SEM). To estimate the size of the zeolite crystals in the sample, a set of images is taken at a magnification of at least 5000. The length of at least 200 crystals is then measured using a dedicated software such as Smile View software from publisher LoGraMi. The accuracy is of the order of 3%. The crystals of ZSM-5 are pure; the purity is verified by the absence of parasitic phases identified by DRX.

[0057] Thus, the crystals obtained according to the process of the invention are generally and most often characterized by a Dubinin volume equal to or greater than 0.10 g.cm -3 , preferably equal to or greater than 0.13 g.cm -3 , preferably equal to or greater than 0.14 g.cm -3 . Dubinin volume (or micropore volume V mi ) is determined in a conventional manner known to the person skilled in the art, in particular from the measurement of the adsorption isotherm at its liquefaction temperature of a gas such as nitrogen, argon, oxygen, etc. Preferably, nitrogen is used.

[0058] Prior to the adsorption measurement, the zeolite crystals of the invention were placed in a vacuum (P<6.7.10 -4 The nitrogen adsorption isotherms at 77 K are then measured on an ASAP 2020 apparatus from Micromeritics at P / P 0 At least 35 measurement points were taken at relative pressures between 0.002 and 1. The micropore volume was determined from the resulting isotherms using the equation of Dubinin and Raduskevitch using standard ISO 15901-3:2007. The micropore volume thus assessed is expressed in cm 3 It is expressed as liquid adsorbent / gram of anhydrous adsorbent. The measurement uncertainty is ±0.003 g / cm 3 .

[0059] As mentioned above, the process of the invention makes it possible in particular to dispense with the use of organic structuring agents. In addition to the advantage of simplifying the implementation, the absence of structuring agents also significantly reduces the impact on the environment, these organic agents being often toxic. Another advantage is that the process without structuring agents avoids the additional step of removing the organic structuring agents, thus allowing to reduce the costs of zeolite production.

[0060] Without wishing to be bound by theory, it appears that the process of the invention, in which the reaction medium is quickly brought to the crystallization temperature, contributes to the production of a well-crystalline, homogeneous and impurity-free material, characterized in that 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%.

[0061] The invention will now be illustrated with the aid of the following examples, which in no way limit the invention, the scope of which is defined by the claims appended to this description.

[0062] Figure 1 , 2 3 and 4 show X-ray diffraction patterns of the crystals obtained in Examples 1, 2 and 3, respectively.

[0063] Example 1 (according to the present invention):

[0064] Continuous synthesis of ZSM-5 with seed addition

[0065] The continuous synthesis of ZSM-5 zeolite involves feeding a solution of silicate, aluminate and seed crystals into a tubular reactor. 2 O-93SiO 2 - 951 H 2 Sodium silicate solution of O. Preparation of composition 1.4 Na 2 O-1Al 2 O 3 - 311 H 2 The seed crystals consisted 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.

[0066] Thus, the synthesis medium is prepared by simultaneously feeding the chamber of an in-line shear mixer with the aid of two pumps: the flow rate of the aluminate solution is equal to 100 g / min and the flow rate of the silicate is equal to 450 g / min. The seeds are added just before entering the tubular reactor. The synthesis medium is heated in the tubular reactor with the aid of a jacket so as 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 so as to ensure a total residence time of 120 minutes in the tubular reactor. At the end of this synthesis, a pure ZSM-5 zeolite is obtained, that is to say a diffraction pattern exhibiting the strict characteristics of an MFI-type zeolite (see X-ray diffraction pattern, Figure 1 ), and has a mass of 0.14 g.cm -3 Dubinin volume.

[0067] Embodiment 2 (comparison):

[0068] Continuous synthesis of ZSM-5 molecular sieve without adding seed crystals

[0069] In this embodiment of continuous synthesis of ZSM-5 zeolite, the composition of 6.9 Na 2 O-93SiO 2 - 951 H 2 Sodium silicate solution with a composition of 1.4 Na 2 O-1Al 2 O 3 - 311 H 2 O sodium aluminate solution is fed into a tubular reactor.

[0070] The synthetic medium was prepared continuously by simultaneously mixing the aluminate solution and the silicate solution using a rotor / stator type shear mixer. Thus, the synthetic medium was prepared by simultaneously feeding the chamber of the Silverson in-line shear mixer using two peristaltic pumps: the flow rate of the aluminate solution was equal to 100 g min -1 , and the silicate flow rate is equal to 450 g min -1 The synthesis medium was heated in the tubular reactor by means of a jacket in order 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 was fixed in order to ensure a total residence time of 120 minutes in the tubular reactor.

[0071] The X-ray diffraction pattern of the product obtained by this synthesis ( Figure 2 ) shows that in the absence of seed crystals, an amorphous product is obtained.

[0072] Embodiment 3 (comparison):

[0073] Batch synthesis of ZSM-5 with seed addition

[0074] The batch synthesis of ZSM-5 zeolite involves introducing a sodium silicate solution, a sodium aluminate solution and seed crystals into a batch reactor.

[0075] Preparation composition is 6.9 Na 2 O 93 SiO 2 951 H 2 O silicate solution. Prepare a composition of 1.4 Na 2 O 1Al 2 O 3 311 H 2 The seeds consisted 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.

[0076] The synthesis medium was prepared by mixing sodium silicate solution, sodium aluminate solution and then seed crystals in a batch reactor. The reactor was then heated to 200° C. by means of a jacket. The residence time in the reactor was 2 hours.

[0077] The X-ray diffraction pattern of the product obtained from this synthesis ( Figure 3 ) shows the presence of ZSM-5 of the MFI structure type, but also the presence of another parasitic phase, a zeolite of the MOR structure type.

Claims

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

2. The process according to claim 1, wherein the tubular reactor is equipped with one or more stirring systems selected from the group consisting of a mechanical stirring system and an oscillating stirring system, and a combination of one or more mechanical stirring systems and one or more oscillating stirring systems.

3. A process according to claim 1 or claim 2, wherein the tubular reactor has a constant inner diameter 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.

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

5. A method according to any one of the preceding claims, wherein the weight percentage of the seeds relative to the total weight of the synthesis medium is between 0.5% and 20%, preferably between 1% and 10%.

6. A method according to any one of the preceding claims, wherein the synthetic medium comprises: a silicon dioxide source which is an aqueous solution of an alkali metal or alkaline earth metal silicate or orthosilicate, or colloidal silicon dioxide, and - Alumina source which is an aqueous solution of aluminum sulfate, aluminum nitrate, aluminate, in particular an alkali metal or alkaline earth metal aluminate.

7. The method of claim 6, wherein prior to introducing the seed crystals, the synthetic medium has: - SiO between 16 and 400, preferably between 16 and 350, preferably between 20 and 300 2 / Al 2 O 3 Molar ratios, inclusive, - H between 1 and 100, preferably between 3 and 90, and preferably between 5 and 70 2 O / SiO 2 molar ratios, inclusive, and - Na between 0.01 and 0.9, preferably between 0.01 and 0.7, preferably between 0.01 and 0.5 2 O / SiO 2 Mole ratios are inclusive.

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

9. The process according to any one of the preceding claims, wherein the duration of the crystallization step is between a few minutes and a few hours, most typically 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. A method according to any one of the preceding claims, wherein the flow rate is between 0.02 m 3 h -1 and 20 m 3 h -1 between.

11. The method according to any one of the preceding claims, 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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