Method for the continuous synthesis of zsm-5 zeolite

Abstract

The present invention relates to a method for the continuous synthesis of ZSM-5 zeolite crystals, the method comprising continuously feeding a tubular reactor with a synthesis medium comprising a source of silica, a source of alumina and seeds, rapidly increasing the temperature of the synthesis medium to a value of between 100°C and 300°C, crystallising at a temperature at least equal to or higher than the temperature of the preceding step and continuously recovering the ZSM-5 zeolite crystals.

Description

CONTINUOUS ZSM-5 ZEOLITE SYNTHESIS PROCESS

[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, in particular zeolites with a high silicon content, and very particularly to the continuous preparation of synthetic zeolites with a high silicon content, with high purity and crystallinity levels.

[0002] Zeolites are crystallized aluminosilicates in which the proportion of silicon and aluminum, often referred to as the Si / Al atomic ratio, is highly variable. Furthermore, 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. The synthesis routes are very diverse and more or less easy to implement and conduct, depending on the targeted Si / Al ratio and the desired crystal structure.

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

[0004] However, the currently known ZSM-5 zeolite synthesis routes suffer from numerous drawbacks, including the use of organic structuring agents, relatively long synthesis times, for example from a few dozen hours to a few days, as well as the use of autoclaves, since the synthesis most often requires high temperatures and therefore pressure.

[0005] Furthermore, conventional industrial syntheses of ZSM-5 are most often carried out with large installations, generally with heating of the synthesis gel and / or the reaction medium, by steam injection and / or by double jacket, which requires high energy expenditure and often leads to problems of production regularity.

[0006] Syntheses of ZSM-5 with organic structuring agent are for example described in documents US7244409 and AU2014413311. These syntheses require on the one hand the presence of organic structuring agent in the reaction medium and on the other hand the destruction, generally by calcination, after synthesis of the zeolite, of this organic structuring agent.

[0007] The use of organic structuring agents is therefore harmful to the environment. Furthermore, the use of structuring agents entails high manufacturing costs and an additional industrial step of eliminating said organic structuring agent.

[0008] To overcome these drawbacks, other publications mention syntheses without organic structuring agents, such as publication US2013144100 which describes a synthesis of large-crystal ZSM-5 zeolites. In this description, however, the process uses gluconic acid or its salts as complexing agent(s) for aluminum. Furthermore, the synthesis time (approximately 2 hours to 100 hours) remains too long for efficient, economical and profitable industrial syntheses.

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

[0010] Among the processes carried out continuously in tubular reactors, we can cite in particular international application WO2017216236 and international application WO2018167414, both of which only exemplify syntheses of zeolites with a low Si / Al ratio (chabazite, zeolites A and X).

[0011] The present invention therefore has as its main objective to propose a new method for preparing ZSM-5 zeolite which overcomes the aforementioned drawbacks. In particular, one objective of the present invention is to provide a method for synthesizing ZSM-5 zeolite which is easily industrializable, economical and efficient. Another objective of the invention is to provide a method for synthesizing ZSM-5 zeolite which is easily industrializable, economical and efficient, with short synthesis times. Yet another objective is to provide a method for synthesizing ZSM-5 zeolite which is easily industrializable, economical and efficient, with short synthesis times, the zeolite obtained being in the form of crystals of a size compatible with industrial uses, and in particular sizes larger than nanometric sizes.

[0012] The Applicant has now discovered that the above-mentioned objectives can be achieved in whole or at least in part thanks to the invention which is now detailed in the following description.

[0013] Thus, a first object of the invention consists of a process for the continuous synthesis of ZSM-5 zeolite which does not require the use of an organic structuring agent. The process of the invention also allows syntheses which can be dispensed with a maturing step, and with relatively short crystallization times, generally less than 5 hours, or even less than 4 hours and, even more generally, less than 3 hours. The process according to the present invention is entirely suitable for the continuous synthesis of ZSM-5 crystals.

[0014] In the present invention, and unless otherwise indicated, all ranges of values ​​introduced by the expressions "from ... to ..." or "between .... and ...." or other similar expressions intended to frame two values, are understood to include the limits.

[0015] More particularly, the present invention relates to the process for the continuous synthesis of ZSM-5 type zeolite crystals, said process comprising at least the following steps a) to d): a) continuously feeding a tubular reactor with a synthesis medium comprising a source of silica, a source of alumina and seeds; b) heating the synthesis medium for a duration equivalent to the residence time in at most 1 / 3, preferably 1 / 4, more preferably 1 / 5 of the total length of the tubular reactor, up 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) continuous recovery of ZSM-5 type zeolite crystals, with a size between 0.2 pm and 20.0 pm, preferably between 0.2 pm and 10.0 pm, better still between 0.3 pm and 7.0 pm, advantageously between 0.3 pm and 5.0 pm.

[0016] The ZSM-5 type zeolite crystals obtained by the process of the invention defined above generally have a size of between 0.2 pm and 20.0 pm, preferably between 0.2 pm and 10.0 pm, better still between 0.3 pm and 7.0 pm, advantageously between 0.3 pm and 5.0 pm.

[0017] In the process of the invention, the reactor is a tubular reactor, optionally but preferably provided with one or more stirring systems chosen from mechanical stirring and oscillatory stirring systems, and also combinations of one or more mechanical stirring systems with one or more oscillatory stirring systems. However, for the process of the present invention, only one type of stirring system, either mechanical or oscillatory, is preferred.

[0018] More preferably, the method of the present invention comprises only one stirring system, either mechanical or oscillatory. According to a preferred embodiment, the method of the invention comprises a single mechanical stirring system. According to another preferred embodiment, the method of the invention comprises a single stirring system generated by an oscillatory movement.

[0019] The stirring means may be of any type well known to those skilled in the art, and for example and in a non-limiting manner, when the reactor is a tubular reactor adapted to be operated continuously, this tubular reactor may be provided with restrictions (such as rings, baffles and others), may be equipped with one or more stirring systems (stirring shaft provided with several stirring rotors, cascade of stirrers distributed along the reactor), one or more oscillating or pulsating systems (making it possible to generate a back-and-forth movement of the reaction medium by means of, for example, a piston, membrane, head-to-tail pumps), and others, as well as two or more of these combined techniques.

[0020] In a preferred embodiment of the invention, the method is implemented in a tubular reactor provided with restrictions and equipped with a system for imparting pulsations to the fluid circulating in the reactor, as for example described in application US20090304890 from the company NiTech.

[0021] In a preferred embodiment of the method of the invention, the tubular reactor makes it possible to ensure a continuous flow in a straight line, possibly with one or more curves. The tubular reactor generally and most often has a constant internal diameter which can vary within large proportions, and 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.

[0022] 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, and most preferably between 1 m and 70 m.

[0023] The reactor volume must be adapted according to the zeolite production needs. Typically, it can vary between 0.04 m 3 and 10 m 3 , preferably between 0.05 m 3 and 5 m 3 , with a length / diameter form factor typically greater than 100, preferably greater than 140, more preferably greater than 180. Depending on the geometry of the reactor, the flow rate can typically vary between 0.02 m 3 h -1 and 20 m 3 h' 1 .

[0024] The reactor used for the process of the present invention further comprises at least one heating system for at least a portion of the length of the reactor, as well as optionally a system for insulating all or part of the length of the reactor. The reactor may also comprise one or more ultrasound sources. in order to promote crystallization and / or the formation of well-individualized crystals, i.e. without or with few aggregates.

[0025] Said at least one heating system may be of any type well known to those skilled in the art, and for example chosen from steam injection, by double jacket, by addition of a microwave source, and by combination of one or more of the aforementioned means. The heating system must allow a rapid rise in temperature, up to the crystallization temperature, as will be described later.

[0026] The synthesis medium is prepared continuously, by mixing a source of silica and a source of alumina. This synthesis medium is prepared by mixing the components of said synthesis medium by any means well known to those skilled in the art and more particularly by means of a mixer, for example and preferably a shear mixer of the rotor / stator type.

[0027] By silica source is meant any source well known to those skilled in the art and in particular a solution, preferably aqueous, of silicate, in particular of silicate or orthosilicate of alkali or alkaline-earth metal, for example sodium, or of colloidal silica or even of tetraethyl orthosilicate, the latter not being preferred.

[0028] By source of alumina is meant any source of alumina well known to those skilled in the art and in particular a solution, preferably aqueous, of aluminum sulfate, aluminum nitrate, aluminate, in particular alkali or alkaline earth metal aluminate, for example sodium.

[0029] In a preferred embodiment, the synthesis medium comprises: - a source of silica which is an aqueous solution of silicate or orthosilicate of alkali or alkaline earth metal, for example and preferably sodium, or colloidal silica, and - a source of alumina which is an aqueous solution of aluminum sulfate, aluminum nitrate, aluminate, in particular alkali or alkaline earth metal aluminate, for example sodium.

[0030] By seeds is meant any source of seeds well known to those skilled in the art and in particular a nucleating solution, or zeolite crystals of the MFI type (ZSM-5 or Silicalite-1) or of the MEL type, possibly previously ground or cryo-ground preferably to a submicron size.

[0031] The seeds are introduced continuously, either mixed 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 most preferably carried out upstream of the crystallization step. The percentage by weight 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%.

[0032] The molar ratio SiO2 / AhO3 in the synthesis medium, before introduction of the seeds, is generally between 16 and 400, preferably between 16 and 350, more preferably between 20 and 300, inclusive. The molar ratio H2O / SiO2 is between 1 and 100, preferably between 3 and 90 and more preferably between 5 and 70, inclusive. The molar ratio Na2O / SiO2 is between 0.01 and 0.9, preferably between 0.01 and 0.7, more preferably between 0.01 and 0.5, inclusive.

[0033] According to yet another preferred embodiment, the synthetic medium, before introduction of the seeds, has: - a SiO2 / AhO3 molar ratio of between 16 and 400, preferably between 16 and 350, more preferably between 20 and 300, inclusive, - a molar ratio H2O / SiO2 of between 1 and 100, preferably between 3 and 90 and more preferably between 5 and 70, limits included, and - a Na2O / SiO2 molar ratio is between 0.01 and 0.9, preferably between 0.01 and 0.7, more preferably between 0.01 and 0.5, limits included.

[0034] In one embodiment, the synthesis medium used in the process of the invention may comprise one or more auxiliary agents, such as for example one or more organic solvents, advantageously chosen from water-soluble solvents and for example those chosen from alcohols, advantageously an alcohol chosen from propanol, butanol, pentanol, hexanol, preferably butanol.

[0035] The temperature-raising step can be carried out by 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. The rapid temperature-raising can be simply expressed as a time equivalent to the residence time in at most 1 / 3, preferably 1 / 4, preferably 1 / 5 of the total length of the tubular reactor. This length fraction can, in certain cases, and if desired, be up to 1 / 10 of the total length of the tubular reactor. The temperature-raising can be carried out by any method well known to those skilled in the art and for example by steam injection, by double jacket, or by addition of a microwave source, or by combination of one or more of the aforementioned means.

[0036] The process of the present invention is characterized in particular by the fact that, and this is the main object of the present invention, the heating of the synthesis medium up to the crystallization temperature is carried out very quickly.

[0037] Indeed, it was discovered, quite surprisingly, that this rapid heating allows the production of high-purity zeolite crystals, without impurities, or at least with only a few traces of impurities.

[0038] Thus and as indicated previously, the reaction medium is continuously fed into the tubular reactor and is immediately heated in a heating zone corresponding to a duration equivalent to at most 1 / 3, preferably 1 / 4 and more 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, at a temperature of 100°C to 300°C, continues its advance in the tubular reactor where it crystallizes to form the desired crystals of ZSM-5 zeolite.

[0039] According to the present invention, the crystallization step is carried out at high temperatures, 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.

[0040] The duration of the crystallization step can vary greatly and is generally between a few minutes and several 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.

[0041] It should be understood that thanks to the rapid heating of the synthesis medium for a duration equivalent to the residence time in at most 1 / 3, preferably 1 / 4 and preferably 1 / 5 of the total length of the tubular reactor, up to a value between 100°C and 300°C, as indicated previously, the crystallization duration is equivalent respectively to at least 2 / 3, preferably % and preferably 4 / 5 of the total length of the tubular reactor.

[0042] As previously stated, the flow rate in the tubular reactor can vary greatly and is generally and typically between 0.02 m 3 h' 1 and 20 m 3 h -1 , depending on the geometry of the reactor, the desired synthesis speeds, the different types of equipment used for mixing the starting solutions, for bringing the crystallization temperature up to temperature, and others.

[0043] Yet another advantage of the process of the invention, a direct consequence in particular of the rapid heating up to the crystallization temperature, is realized by very short synthesis times for ZSM-5 crystals, particularly when compared to the industrial synthesis times available today in the prior art.

[0044] Furthermore, the synthesis process of the present invention is a continuous process, which represents a significant advantage over conventional industrial synthesis processes, which generally require large installations, with manufacturing batches that are often not very uniform in terms of the quality of the product manufactured. The continuous process according to the present invention thus provides many advantages as indicated above, to which can be added the reduction in the size of the installations, the reduction in energy costs and the improvement in the consistency of the quality of production.

[0045] The continuous process according to the present invention ensures homogeneous mixing of the reaction medium and in particular during crystallization, which allows the obtaining, in a completely simple and efficient manner, of crystals having a homogeneous particle size and morphology. Thus the process of the invention continuously generates ZSM-5 type zeolite crystals having a Si / Al ratio of 10 to 60, preferably 10 to 50, preferably 12 to 40.

[0046] According to one embodiment, the crystals obtained using the method of the present invention have a size greater than 0.2 pm, and preferably greater than 0.3 pm, inclusive, and, most often, a size between 0.2 pm and 20.0 pm, preferably between 0.2 pm and 10.0 pm, better still between 0.3 pm and 7.0 pm, advantageously between 0.3 pm and 5.0 pm.

[0047] The estimation of the number-average size of zeolite crystals is carried out by observation under a scanning electron microscope (SEM). In order to estimate the size of zeolite crystals on the samples, a set of images is taken at a magnification of at least 5000. The length of at least 200 crystals is then measured using dedicated software, for example the Smile View software from the LoGraMi publisher. The accuracy is around 3%. The ZSM-5 crystals are pure, this purity is verified by the absence of parasitic phases identified by DRX.

[0048] Thus, the crystals obtained according to the process of the present invention are generally and most often characterized by a volume of Dubinin 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. cnr 3 . The volume of Dubinin (or microporous V m / ) is determined in a conventional manner known to those skilled in the art, in particular from the measurement of the adsorption isotherm of a gas at its liquefaction temperature, for example nitrogen, argon, oxygen, and others. Preferably, nitrogen is used.

[0049] Prior to this adsorption measurement, the zeolite crystals of the invention are degassed between 300°C and 450°C for a period of 9 hours to 16 hours, under vacuum. (P < 6.7.10 -4 Pa). For example, for a zeolite with an MFI structure such as ZSM-5, the measurement of the nitrogen adsorption isotherm at 77K is then carried out on a Micromeritics ASAP 2020 type device, taking at least 35 measurement points at relative pressures with a P / Po ratio between 0.002 and 1. The micropore volume is determined according to the Dubinin and Raduskevitch equation from the isotherm obtained, applying the ISO 15901-3:2007 standard. The micropore volume thus evaluated is expressed in cm3 of liquid adsorbent per gram of anhydrous adsorbent. The measurement uncertainty is ± 0.003 g / cm 3 .

[0050] As indicated above, the process of the present invention makes it possible in particular to dispense with the use of an organic structuring agent. In addition to the advantage of simplifying implementation, the absence of the use of a structuring agent significantly reduces the impact on the environment, these organic agents being very often toxic. Another advantage is that the process without a structuring agent avoids an additional step of eliminating the organic structuring agent, thus allowing a reduction in zeolite production costs.

[0051] Without wishing to be bound by theory, it appears that the process of the present invention, in which the reaction medium is rapidly brought to the crystallization temperature, facilitates the obtaining of a well-crystallized, homogeneous and impurity-free material which is characterized by crystals having a relative crystallinity, measured according to the ASTM D5758 standard, of between 95% and 140%, preferably between 95% and 135%, most preferably between 95% and 130%.

[0052] The invention is now illustrated with the aid of the examples which follow and which in no way limit the invention, the scope of which is defined by the claims appended to this description.

[0053] Figures 1, 2 and 3 represent the X-ray diffractograms of the crystals obtained in Examples 1, 2 and 3 respectively. Example 1 (according to the invention): Continuous synthesis of ZSM-5 with seed addition

[0054] The continuous synthesis of ZSM-5 zeolite consists of feeding a tubular reactor with the solution of silicate, aluminate and seeds. A sodium silicate solution of composition 6.9 Na2O - 93 SiC>2 - 951 H2O is prepared. A sodium aluminate solution of composition 1.4 Na2<3 - 1 AI2O3 - 311 H2O is prepared. seeds are made up of ZSM-5 crystals (Alfa AESAR, CAS 1318-02-1) at a rate of 2% by weight relative to the weight of the synthesis medium.

[0055] The synthesis medium is therefore prepared by simultaneously feeding the in-line shear mixer chamber using two pumps: the flow rate of the aluminate solution is equal to 100 g / min and that 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 by means of a double jacket to reach the crystallization temperature of 200°C over a length equivalent to 1 / 6 of the total length of the tubular reactor. The feed rate is fixed in order to guarantee a total residence time in the tubular reactor of 120 minutes. At the end of this synthesis, a pure ZSM-5 zeolite, i.e. with a diffractogram strictly characteristic of an MFI type zeolite, is obtained (see X-ray diffractogram, Figure 1), and has a Dubinin volume of 0.14 g. cm -3 . Example 2 (Comparison): Continuous synthesis of ZSM-5 without the addition of seeds

[0056] In this example of continuous synthesis of ZSM-5 zeolite, a tubular reactor is fed with a sodium silicate solution of composition 6.9 Na2<3 - 93 SiO2 - 951 H2O and a sodium aluminate solution of composition 1.4 Na2<3 - 1 AI2O3 - 311 H2O.

[0057] The synthesis medium is prepared continuously, using a rotor / stator type shear mixer by simultaneously mixing the aluminate solution and the silicate solution. The synthesis medium is therefore prepared by simultaneously feeding the chamber of the Silverson shear in-line mixer using two peristaltic pumps: the flow rate of the aluminate solution is equal to 100 g min' 1 and that of silicate is equal to 450 g min' 1The synthesis medium is heated in the tubular reactor by means of a double jacket to reach the crystallization temperature of 200°C over a length equivalent to 1 / 6 of the total length of the tubular reactor. The feed rate is fixed to guarantee a residence time in the tubular reactor of 120 minutes.

[0058] The X-ray diffractogram (Figure 2) of the product obtained from this synthesis shows that in the absence of seeds an amorphous product is obtained. Example 3 (comparative): Batch synthesis of ZSM-5, with addition of seeds

[0059] Batch synthesis of ZSM-5 zeolite involves introducing a sodium silicate solution, a sodium aluminate solution and seeds into a batch reactor.

[0060] A silicate solution of composition 6.9 Na2O 93 SiC>2 951 H2O is prepared. An aluminate solution of composition 1.4 Na2 <C IAI2O3 311 H2O est préparée. Les semences sont constituées de cristaux de ZSM-5 (Alfa AESAR, CAS 1318-02-1 ) à raison de 2% en poids par rapport au poids du milieu de synthèse.

[0061] The synthesis medium is prepared by mixing the sodium silicate solution, the sodium aluminate solution and then the seeds in the batch reactor. The reactor is then heated to 200°C by a double jacket. The residence time in the reactor is 2 hours.

[0062] The X-ray diffractogram (Figure 3) of the product obtained from this synthesis shows the presence of ZSM-5 of structural type MFI but also the presence of another parasitic phase, a zeolite of structural type MOR.

Claims

CLAIMS 1. Process for the continuous synthesis of ZSM-5 type zeolite crystals, said process comprising at least the following steps a) to d): a) continuously feeding a tubular reactor with a synthesis medium comprising a silica source, an alumina source and seeds; b) heating the synthesis medium for a duration equivalent to the residence time in at most 1 / 3, preferably 1 / 4, more preferably 1 / 5 of the total length of the tubular reactor, up 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) continuous recovery of the ZSM-5 type zeolite crystals.

2. Method according to claim 1, wherein said tubular reactor is provided with one or more stirring systems chosen from mechanical stirring and oscillation stirring system, as well as combinations of one or more mechanical stirring systems with one or more oscillation stirring systems.

3. Method according to claim 1 or claim 2, wherein said tubular reactor has a constant internal diameter of 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. Method according to any one of the preceding claims, in which the seeds are chosen from nucleating solution and zeolite crystals of MFI or MEL type.

5. Method according to any one of the preceding claims, in which the percentage by weight of the seeds relative to the total weight of the synthetic medium is between 0.5% and 20%, preferably between 1% and 10%.

6. Method according to any one of the preceding claims, in which the synthesis medium comprises: - a source of silica which is an aqueous solution of alkali or alkaline earth metal silicate or orthosilicate, or colloidal silica, and - a source of alumina which is an aqueous solution of aluminum sulfate, aluminum nitrate, aluminate, in particular alkali or alkaline earth metal aluminate.

7. Method according to claim 6 in which the synthetic medium, before introduction of the seeds, has: - a SiC AfeOs molar ratio of between 16 and 400, preferably between 16 and 350, more preferably between 20 and 300, inclusive, - a molar ratio H2O / SiO2 of between 1 and 100, preferably between 3 and 90 and more preferably between 5 and 70, limits included, and - a Na2O / SiO2 molar ratio is between 0.01 and 0.9, preferably between 0.01 and 0.7, more preferably between 0.01 and 0.5, limits included.

8. Process according to any one of the preceding claims, in which 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.

9. Process according to any one of the preceding claims, in which the duration of the crystallization step is between a few minutes and several hours, most often for a duration 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 preceding claim, wherein the flow rate is between 0.02 m 3 h' 1 and 20 m 3 h -1 .

11. Method according to any one of the preceding claims, in which the crystals have a relative crystallinity, measured according to the ASTM D5758 standard, of between 95% and 140%, preferably between 95% and 135%, most preferably between 95% and 130%.

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