FR3090616A1 - Process for the preparation of an LTL structural type zeolite - Google Patents

Abstract

The invention relates to a process for the preparation of an LTL structural type zeolite comprising at least the following steps: i) mixing, in an aqueous medium until a precursor gel is obtained, of a zeolite of LTA structural type of a nitrogenous organic compound chosen from 1,5-bis (methylpiperidinium) pentane dihydroxide, 1,6-bis (methylpiperidinium) hexane dihydroxide and 1,7-bis (methylpiperidinium) heptane dihydroxide, at least one source of at least one alkali and / or alkaline-earth metal M of valence n, n being an integer greater than or equal to 1, the mixture having the following molar composition: (SiO2 (LTA)) / (Al2O3 ( LTA)) between 2 and 100, H2O / (SiO2 (LTA)) between 1 and 22, R / (SiO2 (LTA)) between 0.05 and 0.2, M2 / nO / (SiO2 (LTA) ) between 0.33 and 1; ii) the hydrothermal treatment of said precursor gel obtained at the end of step i) at a temperature between 120 ° C and 220 ° C, for a period of between 6 hours and 3 days. Figure 1 to be published

Description

Description

Title of the invention: Process for preparing an LTL structural type zeolite

Technical area

The present invention relates to a new process for the preparation of a LTL structural type zeolite. This new process makes it possible to synthesize a zeolite of structural type LTL by conversion / transformation under hydrothermal conditions of a zeolite of structural type LTA. In particular, said new process makes it possible to carry out the synthesis of a zeolite of structural type LTL, from a zeolite of structural type LTA used as a source of silicon and aluminum and of a specific organic or structuring molecule comprising two quaternary ammonium functions, chosen from 1,5-bis (methylpiperidmium) pentane, 1,6-bis (methylpiperidmium) hexane and 1,7-bis (methylpiperidmium) heptane, in its dihydroxide form. Said LTL structural type zeolite obtained according to the process of the invention advantageously finds its application as a catalyst, adsorbent or separation agent.

Prior art

[0002] Crystallized microporous materials, such as zeolites, are solids widely used in the petroleum industry as a catalyst, catalyst support, adsorbent or separation agent. Although many microporous crystal structures have been discovered, the refining and petrochemical industry is always looking for new zeolitic structures which have particular properties for applications such as purification or separation of gases, conversion of carbonaceous or other species.

The LTL structural type zeolites include in particular the Linde Type L zeolite. The LTL structural type zeolite has a one-dimensional pore system delimited by twelve tetrahedra TO ₄ or T is Si or Al. Many synthetic methods of LTL structural type zeolites, in particular Linde Type L zeolite, without the use of organic structuring agents are known (US 3,867,512; US 4,544,539; US 4,956,166; US 5,242,675; US 5,330,736 and US 5,491,119).

Cho HS et al. observed that the addition of a crown ether makes it possible to block the growth of the LTL zeolite crystals along the crystallographic axis c, the SiO ₂ / Al ₂ O ₃ ratio of the zeolite obtained is 7 (Crystal Growth & Design, 17, 9, (2017), 4516-4521).

Xie D. et al. obtained clusters of LTL zeolite nanocrystals by hydrothermal conversion of the UAE zeolite (US 2016/0059225) with SiO ₂ / Al ₂ O ₃ ratios exemplified between 6.14 and 6.81.

Lupulescu A. I. et al. studied the effect of adding organic molecules (ZGM Zeolite Growth Modifiers) such as: 1-ethyl-1-methylpyrrolidinium bromide, poly (diallyldimethylammonium) chloride, ethanol, propylamine, to synthesis on crystal morphology zeolite LTL (Journal of the American Chemical Society, 135, 17, (2013), 6608-6617).

Carr CS et al. synthesized an LTL zeolite with an SiO ₂ / Al ₂ O ₃ ratio of less than 3 using the Igepal CO-720 in nonionic emulsion (Chemistry of Materials, 17, 24, (2005), 6192-6197).

There is still a need for a method of preparing a LTL structural type zeolite having a high purity.

Summary of the invention

The invention relates to a process for the preparation of an LTL structural type zeolite comprising at least the following steps:

I) mixing in an aqueous medium until a precursor gel is obtained, a zeolite of LTA structural type having a molar ratio SiO _{2 (LTA} ) / A1 ₂ O _{3 (LTA} ) of between 2 and 100, of a nitrogenous organic compound chosen from 1,5-bis (methylpiperidinium) pentane dihydroxide, 1,6-bis (methylpiperidinium) hexane dihydroxide and 1,7-bis (methylpiperidinium) heptane dihydroxide, at least one source of at least one alkali and / or alkaline earth metal M of valence η, n being an integer greater than or equal to 1, the mixture having the following molar composition:

(SiO ₂ ( _LTA )) / (A1 ₂ O _{3 (LTA)} ) between 2 and 100,

H ₂ O / (SiO ₂ (lta)) between 1 and 22,

R / (SiO ₂ (lta)) between 0.05 to 0.2,

M _{2 / n} O / (SiO ₂ (lta)) between 0.33 and 1,

In which SîO _{2 (} lta) denotes the molar amount of SiO ₂ provided by the LTA zeolite, and A1 ₂ O ₃ (lta) denotes the molar amount of A1 ₂ O ₃ provided by the LTA zeolite, R denotes the amount molar of said nitrogenous organic compound, M _{2 / n} O denotes the molar amount expressed in the form of alkali metal and / or alkaline earth metal oxide provided by said source of M;

Ii) hydrothermal treatment of said precursor gel obtained in Tissue from step i) at a temperature between 120 ° C and 220 ° C, for a period of between 6 hours and 3 days, to obtain said type zeolite structural LTL.

Preferably, the nitrogenous organic compound is l, 6-bis (methylpiperidinium) hexane dihydroxide.

Advantageously, the SiO ₂ / Al ₂ O ₃ molar ratio of the zeolite obtained is between 2 and 20, preferably between 2 and 15.

Preferably, the LTA structural type zeolite incorporated in the mixture of step i) has a molar ratio (SiO ₂ (lta)) / (A1 ₂ O _{3 (LTA)} ) of between 2 and 40, preferably between 2 and 25, preferably between 2 and 3, preferably between 2.0 and 3.0 and even more preferably between 2.0 and 2.5.

Preferably, the H ₂ O / (SiO _{2 (LTA)} ) molar ratio in the mixture of step i) is between 5 and 20.

Preferably, the R / (SiO _{2 (LTA)} ) molar ratio in the mixture of step i) is between 0.06 and 0.1.

Preferably, the molar ratio M _{2 / n} O / (SiO _{2 (LTA)} ) in the mixture of step i) is between 0.33 to 0.5 and preferably between 0.35 and 0.45.

Preferably, M is chosen from lithium, sodium, potassium, calcium, magnesium and their mixtures. Preferably, M is potassium.

Preferably, the source of at least one alkali and / or alkaline earth metal M is potassium hydroxide.

In a particular embodiment, the mixture of step i) may comprise at least one additional source of an oxide XO ₂ , X being one or more tetravalent element (s) chosen in the group formed by the following elements: silicon, germanium, titanium, so that the molar ratio XO ₂ / SiO _{2 (LTA)} is between 0.1 and 33, and preferably between 1 and 25, the content of SîO _{2 (L} ta) in said ratio being the content provided by the LTA structural type zeolite. Preferably, X is silicon.

In this embodiment, the mixture of step i) advantageously has the following molar composition:

(XO ₂ + SiO _{2 (} lta)) / A1 ₂ O _{3 (LTA)} between 2 and 40, preferably between 4 and 25

H ₂ O / (XO ₂ + SiO _{2 (LTA)} ) between 1 and 22, preferably between 5 and 20

R / (XO ₂ + SiO _{2 (LTA)} ) between 0.05 to 0.2, preferably between 0.06 and 0.1

M _{2 / n} O / (XO ₂ + SiO _{2 (LTA)} ) between 0.33 and 1, preferably between 0.33 to 0.5, and preferably between 0.35 and 0.45 .

Preferably, in the particular embodiment of the invention, the LTA structural type zeolite has a SiO _{2 (LTA)} / A1 ₂ O _{3 (LTA)} molar ratio of between 2 and 3, preferably between 2 , 0 and 3.0 and very preferably a SiO _{2 (LTA)} / A1 ₂ O 3 (lta) molar ratio of between 2.0 and 2.5.

Advantageously, the precursor gel obtained at the end of step i) has a molar ratio of the total amount expressed in tetravalent element oxides to the total amount expressed in trivalent element oxides between 2 and 100 , preferably between 2 and 40.

Seeds of a zeolite of the LTL structural type, preferably having a SiO ₂ / Al ₂ O ₃ molar ratio of between 2 and 20, can be added to the mixture of step i), preferably in quantity between 0.01 and 10% by mass relative to the total mass of the sources of said tetravalent (s) and trivalent (s) element (s) in anhydrous form present in the mixture, said crystalline seeds not being taken into account in the total mass of the sources of the tetravalent and trivalent elements.

Step i) may include a step of ripening the mixture at a temperature between 20 and 100 ° C, with or without stirring, for a period between 30 minutes and 48 hours.

The hydrothermal treatment of step ii) can be carried out, preferably under autogenous pressure, at a temperature between 120 ° C and 220 ° C, preferably between 150 ° C and 195 ° C, for a period of time included between 6 hours and 3 days, preferably between 8 hours and 2 days, even more preferably between 12 hours and 1 day.

The zeolite obtained at the end of step ii) can advantageously be filtered, washed, and dried at a temperature between 20 and 150 ° C, preferably between 60 and 100 ° C, for a period between 5 and 24 hours to obtain a dried zeolite.

The dried zeolite can then be calcined at a temperature between 450 and 700 ° C for a period between 2 and 20 hours, the calcination may be preceded by a gradual rise in temperature.

The invention also relates to a LTL structural type zeolite with an SiO ₂ / A1 ₂ O ₃ ratio of between 2 and 20, preferably between 2 and 15, capable of being obtained by the preparation process described above, and showing an X-ray diffraction pattern after calcination on which the following average values of d _hld and relative intensities are measured:

[0039]

[Tables 1]

2 theta (°) dhkl (Â) Irel 2 theta (°) dhkl (Â) Irel 5.549 15,913 EL 25,561 3,482 f 9,614 9,193 ff 26,188 3,400 ff 11,107 7,960 ff 27,109 3,287 f 11,754 7.523 f 27,986 3.186 mf 14.701 6.021 f 29.07 3,069 f 15.207 5.822 ff 29,653 3.010 ff 19,291 4,597 mf 30,677 2.912 mf 20,094 4.415 ff 31,472 2,840 ff 20,444 4.341 ff 31.995 2,795 ff 22,653 3.922 m 33.506 2.672 ff 23.337 3,809 ff 33,735 2,655 f 24.28 3,663 f 34,182 2.621 ff

Where FF = very strong: F = strong; m = medium; mf = medium weak; f = weak; ff = very weak.

the relative intensity ύι being given in relation to a relative intensity scale where a value of 100 is assigned to the most intense line of the X-ray diffraction diagram: f '<15; 15 <f <30; 30 <mf <50; 50 <m <65; 65 <F <65; FF> 85.

List of Figures

Figure 1 shows the chemical formulas of organic nitrogen compounds which can be chosen as a structuring used in the synthesis process according to the invention.

FIG. 2 represents the X-ray diffraction diagram of the zeolite, of structural type LTA, obtained according to example 2.

FIG. 3 represents the X-ray diffraction diagram of the zeolite, of the LTL structural type, obtained according to Example 3.

FIG. 4 represents a scanning electron micrograph (SEM) of the zeolite, of structural type LTL, obtained according to example 3.

Ligure 5 shows the X-ray diffraction diagram of a mixture of LTL structural type and ERI structural type zeolites obtained according to Example 4.

Other features and advantages of the synthesis method according to the invention will appear on reading the following description of nonlimiting examples of embodiments, with reference to the appended figures and described below.

Description of the embodiments

The present invention relates to a new process for preparing a zeolite of LTL structural type, by conversion / transformation under hydrothermal conditions of a zeolite of LTA structural type with a particular SiO ₂ / Al ₂ O ₃ ratio, in presence of a specific organic nitrogenous or structuring compound chosen from l, 5-bis (methylpiperidinium) pentane, l, 6-bis (methylpiperidinium) hexane, l, 7-bis (methylpiperidinium) heptane, in its form dihydroxide.

In particular, the Applicant has discovered that the specific nitrogenous or structuring organic compound, that is to say l, 5-bis (methylpiperidinium) pentane, 1,6-bis (methylpiperidinium) hexane or l , 7-bis (methylpiperidinium) heptane, in its dihydroxide form, mixed with a zeolite of structural type LTA having a molar ratio SiO ₂ ( _LT A) / Al ₂ O ₃ ( _LTA ) between 2 and 100, used as source of silicon and aluminum, in the presence or not, of an additional supply, within said mixture, of at least one source of at least one tetravalent element XO ₂ , leads to the production of a precursor gel d '' an LTL structural type zeolite having a molar ratio of the total amount expressed in oxides of tetravalent elements to the total amount expressed in oxides of trivalent elements between 2 and 100, preferably between 2 and 40, then at production of a high purity LTL structural type zeolite, the total amount of tetrava element oxides slow representing the sum of the content of SiO ₂ coming from the zeolite of structural type LTA and the content of XO ₂ coming from the possible additional source of an oxide XO ₂ , in the case where an addition of at least one additional source of an oxide XO ₂ is produced. Any other crystallized or amorphous phase is generally and very preferably absent from the crystallized solid consisting of the zeolite of structural type LTL, obtained at the end of the preparation process.

An advantage of the present invention is to provide a new preparation process allowing the formation of a zeolite of structural type LTL from a zeolite of structural type LTA, said process being carried out in the presence of a specific organic structuring agent, 1,5-bis (methylpiperidinium) dihydroxide pentane, 1,6-bis (methylpiperidinium) dihydroxide hexane or 1,7-bis (methylpiperidinium) heptane dihydroxide.

Advantageously, the material obtained by the method according to the invention, from a zeolite of structural type LTA, is a zeolite of structural type LTL having a molar ratio SiO ₂ / Al ₂ O ₃ of between 2 and 20 , preferably between 2 and 15. Another advantage of the process according to the present invention is to provide a zeolite of structural type LTL of high purity. More particularly, the zeolite according to the invention is a zeolite of structural type LTL of purity greater than or equal to 90%, preferably greater than or equal to 95%, preferably greater than or equal to 97% and more preferably still greater than or equal 99.8%.

An additional advantage of the process according to the invention is to provide a high purity LTL structural type zeolite with very reasonable production costs.

The present invention more specifically relates to a new process for preparing a zeolite of LTL structural type comprising at least the following steps:

I) the mixture in aqueous medium, of a zeolite of structural type LTA having a molar ratio SîO ₂ ( _L ta) / A1 ₂ O ₃ ( _L ta) between 2 and 100, of a nitrogenous organic compound , also called a specific structuring agent, chosen from l, 5-bis (methylpiperidinium) pentane dihydroxide, l, 6-bis (methylpiperidinium) hexane dihydroxide and l, 7-bis (methylpiperidinium) heptane dihydroxide, preferably 1,6-bis dihydroxide (methylpiperidinium) hexane, at least one alkali metal and / or one alkaline earth metal M of valence η, n being an integer greater than or equal to 1, the mixture having the following molar composition:

(SiO ₂ (lta)) / (A1 ₂ O ₃ (lta)) between 2 and 100, preferably between 2 and 40, preferably between 2 and 25, preferably between 2 and 3, in particular between 2.0 and 3.0, and even more preferably between 2.0 and 2.5

H ₂ O / (SiO ₂ (lta)) between 1 and 22, preferably between 5 and 20

R / (SiO _{2 (LTA} )) between 0.05 to 0.2, preferably between 0.06 and 0.1

M _{2 / n} O / (SiO ₂ (lta)) of between 0.33 and 1, preferably between 0.33 to 0.5 and preferably between 0.35 and 0.45,

In which SiO _{2 (LT} A) is the molar amount of SiO ₂ , oxide of the tetravalent element Si, provided by the zeolite LTA, and A1 ₂ O _{3 (L} ta) is the molar amount of A1 ₂ O ₃ , oxide of the tetravalent element Al, provided by the zeolite of structural type LTA, H ₂ O is the molar amount of water present in the mixture, R is the molar amount of said nitrogenous organic compound, M _{2 / n} O is the molar quantity expressed in the form of an alkali metal and / or alkaline earth metal oxide provided by said source of M and where M is one or more alkali and / or alkaline earth metal (s), preferably chosen ( s) among lithium, sodium, potassium, calcium, magnesium and their mixtures, very preferably M being potassium, step i) being carried out for a period allowing a homogeneous mixture called precursor gel;

Ii) the hydrothermal treatment of said precursor gel obtained at the end of step i) at a temperature between 120 ° C. and 220 ° C. for a period of between 6 hours and 3 days, until crystallization, in particular of said LTL structural type zeolite.

The preparation process according to the invention therefore makes it possible to adjust the SiO ₂ / Al ₂ O ₃ ratio of the precursor gel containing a zeolite of structural type LTA as a function of the additional supply or not, within the mixture of step i), also called reaction mixture, of at least one source of at least one tetravalent element XO ₂ .

Another advantage of the present invention is to allow the preparation of a precursor gel of a zeolite of LTL structural type having a molar ratio SiO ₂ / Al ₂ O 3 identical to or greater than the molar ratio SiO ₂ ( _LTA ) / A1 ₂ O _{3 (LTA)} of the starting LTA structural type zeolite.

According to the invention, in the molar composition of the mixture of step i) and in the whole of the description:

SiO _{2 (LTA)} designates the molar amount of SiO ₂ provided by the zeolite of structural type LTA, and A1 ₂ O _{3 (LTA)} designates the molar amount of A1 ₂ O ₃ provided by the zeolite of structural type LTA,

XO ₂ denotes the molar quantity of the additional tetravalent element (s), expressed in oxide form,

H ₂ O denotes the molar amount of water present in the mixture,

R denotes the molar amount of said nitrogenous organic compound,

M _{2 / n} O denotes the molar quantity expressed in the oxide form of the element M provided by the source of alkali metal and / or alkaline earth metal, n being an integer greater than or equal to 1.

According to the present invention, the expression "between ... and ..." means that the limit values of the interval are included in the range of values described. If this was not the case and the limit values were not included in the range described, such precision will be provided by the present invention.

According to the invention, step i) comprises mixing, in aqueous medium, a zeolite of LTA structural type having a SiO _{2 (LTA)} / A1 ₂ O _{3 (LTA)} molar ratio of between 2 and 100, of an organic nitrogen compound chosen from l, 5-bis (methylpiperidmium) pentane dihydroxide, l, 6-bis (methylpiperidmium) hexane dihydroxide and l, 7-bis (methylpiperidmium) heptane dihydroxide at least one source of at least one alkali metal and / or one alkaline earth metal M of valence η, n being an integer greater than or equal to 1, the mixture having the following molar composition:

(SiO ₂ ( _LTA )) / (A1 ₂ O ₃ ( _LTA) ) between 2 and 100, preferably between 2 and 40, preferably between 2 and 25, preferably between 2 and 3, in particular between 2.0 and 3.0, more preferably between 2.0 and 2.5

H ₂ O / (SiO ₂ (l _TA )) between 1 and 22, preferably between 5 and 20

R / (SiO ₂ (lt _A )) between 0.05 to 0.2, preferably between 0.06 and 0.1

M _{2 / n} O / (SiO ₂ (IIa)) between 0.33 and 1, preferably between 0.33 to 0.5 and preferably between 0.35 and 0.45.

Preferably, said organic nitrogen compound, or specific structuring agent, used in step i) of the process according to the invention is l, 6-bis (methylpiperidinium) hexane in its dihydroxide form, and the metal (s) (aux) alkaline (s) and / or alkaline-earth M is (its) chosen (s) among lithium, sodium, potassium, calcium, magnesium and their mixtures, M being preferably potassium.

In a particular embodiment of the invention, step i) comprises mixing, in aqueous medium, a zeolite of LTA structural type, preferably having a molar ratio SiO ₂ (lta / A1 ₂ O _{3 (LTA} ) of between 2 and 3, preferably between 2.0 and 3.0 and very preferably between 2.0 and 2.5, of at least one additional source of an oxide XO ₂ so that the molar ratio XO ₂ / SiO _{2 (LTA)} is between 0.1 and 33, of an organic nitrogen compound chosen from 1,5-bis dihydroxide (methylpiperidinium) pentane, 1,6-bis dihydroxide ( methylpiperidinium) hexane and 1,7-bis (methylpiperidinium) heptane dihydroxide, preferably 1,6-bis (methylpiperidinium) hexane dihydroxide, at least one source of at least one alkali metal and / or one alkali metal earthy M of valence η, n being an integer greater than or equal to 1, the mixture having the following molar composition:

(XO ₂ + SiO ₂ (lta)) / A1 ₂ O _{3 (LTA} ) between 2 and 40, preferably between 4 and 25

H ₂ O / (XO ₂ + SîO _{2 (} lta)) between 1 and 22, preferably between 5 and 20

R / (XO ₂ + SiO _{2 (LTA)} ) between 0.05 to 0.2, preferably between 0.06 and 0.1

M _{2 / n} O / (XO ₂ + SiO _{2 (LTA)} ) of between 0.33 and 1, preferably between 0.33 to 0.5, preferably between 0.35 and 0.45

In which X is one or more tetravalent element (s) chosen from the group formed by the following elements: silicon, germanium, titanium, preferably X is silicon, XO ₂ is the molar quantity of said oxide XO ₂ provided by said additional source, SiO _{2 (LTA)} is the molar amount of SiO ₂ provided by the structural type zeolite LTA, and A1 ₂ O _{3 (LTA)} is the molar amount of A1 ₂ O ₃ provided by zeolite LTA, R is the molar amount of said nitrogenous organic compound, and M _{2 / n} O is the molar amount of one or more alkali and / or alkaline-earth metal (s) in oxide form, said ( said alkali and / or alkaline-earth metal (s) being chosen from lithium, sodium, potassium, calcium, magnesium and the mixture of at least two of these metals, so very preferred M is potassium.

Step i) makes it possible to obtain a homogeneous precursor gel.

According to the invention, a zeolite of LTA structural type having a SiO ₂ (LTA) / Al ₂ O _{3 (L} TA) molar ratio of between 2 and 100, preferably between 2 and 40, preferably between 2 and 25, preferably between 2 and 3, preferably between 2.0 and 3.0 and even more preferably between 2.0 and 2.5, is incorporated into the reaction mixture for carrying out the step (i) as a source of silicon and aluminum element.

The structural type LTA zeolite can be obtained by any method known to those skilled in the art and can be used in its sodium form or any other form or a partial or total exchange of sodium cations with other alkaline or alkaline earth cations whether or not followed by a calcination step.

A zeolite of the preferred LTA structural type at the start advantageously has a SiO ₂ (lta / A1 ₂ O _{3 (LTA)} molar ratio of between 2 and 3, preferably between 2.0 and 3.0, and so even more preferred between 2.0 and 2.5 A structure-type zeolite having such a molar ratio is easily obtained and its synthesis which does not require a structuring organic compound is economical. Among the sources of LTA with a SiO ₂ / Al ratio ₂ O ₃ between 2 and 3, preferably between 2.0 and 3.0, the following commercial zeolites can be used: Siliporite 3Â or Siliporite 4Â produced by Arkema, or Zeolum A-3 or Zeolum A-4 produced by Tosoh.

Any other zeolite of LTA structural type obtained by techniques well known to those skilled in the art can be used as a source of LTA zeolite in the synthesis of the zeolite of LTL structural type.

According to the invention, the organic nitrogen compound of step i) of the process according to the invention is incorporated in the mixture for the implementation of step (i), as an organic structuring agent. Said organic nitrogen compound is an organic compound comprising two quaternary ammonium functions. It is chosen from 1.5-bis (methylpiperidinium) pentane dihydroxide, 1.6-bis (methylpiperidinium) hexane dihydroxide and 1.7-bis (methylpiperidinium) heptane dihydroxide, preferably said organic structuring agent being 1,6-bis dihydroxide (methylpiperidinium) hexane. The anion associated with the quaternary ammonium cations present in the structuring organic species for the synthesis of a zeolite of structural type LTL according to the invention is T anion hydroxide.

According to the invention, at least one source of at least one alkali and / or alkaline-earth metal M of valence n, is used in the mixture of step i), n being an upper integer or equal to 1, M being preferably chosen from lithium, potassium, sodium, magnesium and calcium and the mixture of at least two of these metals. Most preferably, M is potassium.

Preferably, the source of at least one alkali and / or alkaline earth metal M is potassium hydroxide.

In a particular embodiment of the invention, at least one additional source of an oxide XO ₂ , X being one or more tetravalent element (s) chosen from the group formed by the elements following: silicon, germanium, titanium, and preferably X is silicon, so that the molar ratio XO ₂ / SîO _{2 (L} ta) is between 0.1 and 33, and preferably between 1 and 25, the content in SiO ₂ (lta) in said ratio being the content provided by the zeolite of structural type LT A, is used in the mixture of step i).

The addition of at least one additional source of an oxide XO ₂ makes it possible in particular to adjust the molar ratio XO ₂ / A1 ₂ O ₃ of the precursor gel of a zeolite of structural type LTL obtained at the end from step i).

In this particular embodiment of the invention, the starting LTA structural type zeolite has a SiO _{2 (LTA)} / A1 ₂ O _{3 (LTA)} molar ratio of between 2 and 3, even more preferably between 2 and 2.5.

The source (s) of the said element (s) tetravalent (s) can be any compound comprising the element X and which can release this element in aqueous solution in reactive form .

When X is titanium, Ti (EtO) ₄ is advantageously used as the source of titanium. In the preferred case where X is silicon, the source of silicon can be any one of said sources commonly used for the synthesis of zeolites, for example powdered silica, silicic acid, silica colloidal, dissolved silica or tetraethoxysilane (TEOS). Among the powdered silicas, it is possible to use precipitated silicas, in particular those obtained by precipitation from an alkali metal silicate solution, pyrogenic silicas, for example CABO-SIL or Aerosil and silica gels. It is possible to use colloidal silicas having different particle sizes, for example with an average equivalent diameter of between 10 and 15 nm or between 40 and 50 nm, such as those sold under the registered trademarks such as LUDOX. Preferably, the source of silicon is CAB-O-SIL.

Step (i) of the process according to the invention consists in preparing a mixture in an aqueous medium containing a zeolite of structural type LTA, optionally a source of an oxide XO ₂ , at least one nitrogenous organic compound R, R being 1,6-bis (methylpiperidmium) hexane dihydroxide in the presence of at least one source of one or more alkali and / or alkaline-earth metal (s), in order to obtain a precursor gel for a zeolite structural type LTL. The amounts of said reagents are adjusted as indicated above so as to give this gel a composition allowing the crystallization of a zeolite of structural type LTL.

Optionally, an additional source of an oxide of a trivial element Y ₂ O ₃ can advantageously be incorporated into the reaction mixture of step i) of the process of the invention.

It may be advantageous to add seeds of a zeolite of structural type LTL to the mixture of said step i) of the process of the invention in order to reduce the time necessary for the formation of the crystals of a zeolite of the type structural LTL and / or the total crystallization time. Said crystal seeds also promote the formation of said LTL structural type zeolite to the detriment of impurities. Such seeds comprise crystallized solids, in particular crystals of a zeolite of structural type LTL, preferably having a molar ratio SiO ₂ / Al ₂ O ₃ of between 2 and 20, preferably between 2 and 15. The crystalline seeds are generally added in a proportion of between 0.01 and 10% of the total mass of the sources of said tetravalent (s) and trivalent (s) element (s) in anhydrous form present in the mixture of step i), said crystalline seeds not being taken into account in the total mass of the sources of the tetravalent and trivalent elements. Said seeds are also not taken into account to determine the composition of the mixture of step i) and / or the gel, defined further, that is to say in the determination of the different molar ratios of the composition of mixed.

Step i) of mixing is carried out until a homogeneous mixture (or reaction mixture or even precursor gel) is obtained, preferably for a duration greater than or equal to 30 minutes, preferably with stirring. any system known to those skilled in the art, with low or high shear rate.

At the end of step i), a homogeneous precursor gel is obtained.

It may be advantageous to implement a ripening of the reaction mixture before hydrothermal crystallization, during said step i) of the process of the invention, in order to better control the size of the zeolite crystals of structural type LTL obtained after crystallization during step ü). Said ripening also promotes the formation of said LTL structural type zeolite to the detriment of impurities. The reaction mixture matures during said step i) of the process of the invention can be carried out at ambient temperature or at a temperature between 20 and 100 ° C. with or without stirring, for a period advantageously between 30 minutes and 48 hours.

In accordance with the invention, step ii) comprises a hydrothermal treatment of said precursor gel obtained at the end of step i), to form said zeolite of structural type LTL crystallizes.

According to step (ii) of the method according to the invention, the precursor gel obtained at the end of step i) is subjected to a hydrothermal treatment, advantageously carried out at a temperature between 120 ° C and 220 ° C, preferably between 150 ° C and 195 ° C, for a period of between 6 hours and 3 days, preferably between 8 hours and 2 days, even more preferably between 12 hours and 1 day, until that said LTL structural type zeolite crystallizes.

The precursor gel is advantageously placed under hydrothermal conditions under an autogenous reaction pressure, until the complete crystallization of a zeolite of structural type LTL. Gas, for example nitrogen, can advantageously be added to the reactor.

The reaction is generally carried out with stirring or in the absence of stirring, preferably with stirring. As the stirring system, any system known to a person skilled in the art can be used, for example, inclined blades with counter blades, stirring turbines, Archimedes screws, spit-type stirring.

At the end of the reaction, after implementation of said step ii) of the preparation process according to the invention, the solid phase advantageously formed of a zeolite of structural type LTL is preferably filtered, washed and then dried. The drying is generally carried out at a temperature between 20 and 150 ° C, preferably between 60 and 100 ° C, for a period between 5 and 24 hours.

The crystallized material, advantageously composed of the zeolite of structural type LTL, after the drying step, is then ready for subsequent steps such as calcination and ion exchange. For these steps, all the conventional methods known to those skilled in the art can be used.

The dried zeolite can then be advantageously calcined. The dried zeolite, preferably calcined, is generally analyzed by X-ray diffraction. The X-ray technique makes it possible to verify that the zeolite obtained is advantageously the structural type of LTL. This X-ray technique also makes it possible to determine the purity of said zeolite obtained by the process of the invention.

Very advantageously, the process of the invention leads to the formation of a high-purity LTL structural type zeolite. The LTL structural type zeolite according to the invention preferably has a purity greater than or equal to 90%, preferably greater than or equal to 95%, very preferably greater than or equal to 97%, and furthermore more preferred greater than or equal to 99.8%. Advantageously, said LTL structural type zeolite according to the invention is free from any other crystallized or amorphous phase.

The loss on ignition of said zeolite obtained after drying and before calcination is generally between 5 and 25% by weight. According to the invention, loss of ignition (PAL) is understood to mean the percentage of loss of mass undergone by a solid compound, a mixture of solid compounds or a paste, preferably in the case of the present invention by said zeolite of structural type. LTL prepared, during a heat treatment at 1000 ° C for 2 hours, in a static oven (muffle type oven), relative to the mass of the solid compound, of the mixture of solid compounds or of the initial paste , preferably in the case of the present invention with respect to the mass of dried LTL structural type zeolite tested. The loss on ignition generally corresponds to the loss of solvent (such as water) contained in the solids, but also to the elimination of organic compounds contained in the solid mineral constituents.

The calcination step of a zeolite, advantageously of the LTL structural type, obtained according to the method of the invention is preferably carried out at a temperature between 450 and 700 ° C for a period between 2 and 20 hours. The LTL structural type zeolite obtained at the end of the calcination step is devoid of any organic species and in particular of the organic structuring agent R.

According to the invention, the analysis by X-ray diffraction, carried out on the solid obtained at the end of said calcination step makes it possible to verify that the solid obtained by the process according to the invention is indeed a zeolite of structural type LTL and that its purity is preferably greater than or equal to 90%, preferably greater than or equal to 95%, very preferably greater than or equal to 97% and even more preferably greater than or equal to 99.8%. In this case, the solid obtained (after calcination) presents the X-ray diffraction diagram including at least the lines listed in Table 2. Preferably, the X-ray diffraction diagram does not contain other lines of significant intensity ( i.e. more than about three times the background noise) than those listed in Table 2.

This diffraction diagram is obtained by radiocrystallographic analysis using a diffractometer using the conventional method of powders with the Και radiation from copper (λ = l, 5406Â). From the position of the diffraction peaks represented by the angle 20, we calculate, by the Bragg relation, the reticular equidistances d _hld characteristic of the sample. The measurement error A (d _hld ) on d _hk ; is calculated using the Bragg relation as a function of the absolute error A (20) assigned to the measurement of 20. An absolute error A (20) equal to plus or minus 0.02 ° is commonly accepted. The relative intensity I _re i assigned to each value of d ^ i is measured according to the height of the corresponding diffraction peak. The X-ray diffraction diagram of the crystalline solid of structural type LTL according to the invention comprises at least the lines with the values of d _hld given in Table 2. In the column of d _hld , the mean values of the distances between the lines are indicated. -reticular in Angstroms (Â). Each of these values must be assigned the measurement error A (d _hk i) between plus or minus 0.6Â and plus or minus 0.01Â.

[0114]

[Paintings!]

2 theta (°) dhkl (Â) Irel 2 theta (°) dhkl (Â) Irel 5.549 15,913 EL 25,561 3,482 f 9,614 9,193 ff 26,188 3,400 ff 11,107 7,960 ff 27,109 3,287 f 11,754 7.523 f 27,986 3.186 mf 14.701 6.021 f 29.07 3,069 f 15.207 5.822 ff 29,653 3.010 ff 19,291 4,597 mf 30,677 2.912 mf 20,094 4.415 ff 31,472 2,840 ff 20,444 4.341 ff 31.995 2,795 ff 22,653 3.922 m 33.506 2.672 ff 23.337 3,809 ff 33,735 2,655 f 24.28 3,663 f 34,182 2.621 ff

Where-FF - “- very-strong -: - F- = ^! -fort ^; ; -m - = 'môyen -;' mf- = -moyen'fsibfe '? f' = - fa! bte -; - ff '= - irès-weak. ·

Untensity ^ feÎatived ^ 'est'dQnnBe-eh'fapport'à'Urie-é & helie'dfotensïté'feiative'OÙdl'''attribré' '* value-of-100 -à-la-raie-ia- | ^ us-infcMise -of-the-diagram-of-acSiMi-of-X-rays -'- ff- <15 ·: ··

15 '<f'<30-; - 30 ^; - <- mf '<50 -;' 50- <m - <- 65 -: - S5 '<F - <- 65'; - FF -> - 85.1i

Table 2: Average values of d ^ i and relative intensities measured on an X-ray diffraction diagram of the crystallized solid obtained by the process according to the invention and calcined

The SiO ₂ / Al ₂ O ₃ molar ratio of the zeolite obtained by the process according to the invention is calculated after determination of the amount of the silicon and aluminum elements included in said zeolite of structural type LTL by ray fluorescence spectrometry X (LX). X-ray fluorescence spectrometry (LX) is a chemical analysis technique using a physical property of matter, X-ray fluorescence. It allows the analysis of the majority of chemical elements from Beryllium (Be) in concentration ranges from a few ppm to 100%, with precise and reproducible results. X-rays are used to excite the atoms in the sample, which causes them to emit X-rays with energy characteristic of each element present. The intensity and energy of these X-rays are then measured to determine the concentration of the elements in the material.

It is also advantageous to obtain the protonated form of the LTL structural type zeolite obtained by the process according to the invention. Said hydrogen form can be obtained by carrying out an ion exchange with an acid, in particular a strong mineral acid such as hydrochloric, sulfuric or nitric acid, or with a compound such as chloride, sulphate or ammonium nitrate . The ion exchange can be carried out by suspending said zeolite of structural type LTL in one or more times with the ion exchange solution. Said zeolite can be calcined before or after ion exchange, or between two stages of ion exchange. The zeolite is preferably calcined before the ion exchange, in order to remove any organic substance included in the porosity of the zeolite, insofar as the ion exchange is thereby facilitated.

The LTL structural type zeolite obtained by the process of the invention can be used after ion exchange as an acid solid for catalysis in the fields of refining and petrochemicals. It can also be used as an adsorbent or as a molecular sieve.

Examples

The invention is illustrated by the following examples which are in no way limiting in nature.

Example 1: Preparation of the organic structuring agent 1.6-bis (methylpiperidinium) hexane dihydroxide (structuring agent R),

50 g of 1,6-dibromohexane (0.20 mole, 99%, Alfa Aesar) are added to a 1 L flask containing 50 g of N-methylpiperidine (0.51 mole, 99%, Alfa Aesar) and 200 mL of ethanol. The reaction medium is stirred and brought to reflux for 5 hours. The mixture is then cooled to room temperature and then filtered. The mixture is poured into 300 ml of cold diethyl ether then the precipitate formed is filtered and washed with 100 ml of diethyl ether. The solid obtained is recrystallized from an ethanol / ether mixture. The solid obtained is dried under vacuum for 12 hours. 71 g of a white solid are obtained (ie a yield of 80%).

The product has the expected N NMR spectrum. N NMR (D ₂ O, ppm / TMS): 1.27

(4H, m); 1.48 (4H, m); 1.61 (4H, m); 1.70 (8H, m); 2.85 (6H, s); 3.16 (12H, m).

18.9 g of Ag ₂ O (0.08 mol, 99%, Aldrich) are added to a teflon beaker of

250 ml containing 30 g of the structuring agent of 1,6-bis (methylpiperidinium) hexane dibromide (0.07 mol) prepared and 100 ml of deionized water. The reaction medium is stirred protected from light for 12 hours. The mixture is then filtered. The filtrate obtained is composed of an aqueous solution of 1,6-bis dihydroxide (methylpiperidinium) hexane. The assay of this species is carried out by proton NMR using formic acid as a standard.

Example 2: Preparation of a LTA structural type zeolite,

In a beaker (beaker 1), 3.063 g of sodium aluminate (Carlo Erba) are mixed with 4.922 g of sodium hydroxide (purity 98% by weight, Aldrich) and with 30 g of deionized water, the preparation obtained is kept under stirring for 10 minutes. In another beaker (beaker 2), 7.085 g of sodium silicate (Chemistry plus) are mixed with 4.922 g of sodium hydroxide (purity 98% by weight, Aldrich) and with 30 g of deionized water, the preparation obtained is stirred for 5 minutes. The preparation obtained in beaker 1 is poured into beaker 2. The reaction mixture is stirred for 3 minutes. The molar composition of the precursor gel is as follows: 1 SiO ₂ : 0.5 A1 ₂ O ₃ : 4.6 Na ₂ O: 115 H ₂ O, ie an SiO ₂ / Al ₂ O ₃ ratio of 2. After homogenization, the precursor gel obtained is then transferred to an autoclave. The autoclave is closed and then heated to 100 ° C. without stirring for 2 hours. The autoclave is then cooled by quenching in ice water and the crystallized product obtained is filtered, washed with deionized water and then dried overnight at 100 ° C. The loss on ignition of the dried solid, measured after 2 hours at 1000 ° C., is 18.02%. The solid product is analyzed by X-ray diffraction and identified as consisting of an LTA structural type zeolite with a purity greater than 99% by weight. The X-ray diffraction diagram performed on the calcined solid is given in Ligure 2. The solid product has an SiO ₂ / Al ₂ O ₃ molar ratio of 2 as determined by X-ray fluorescence.

Example 3: Preparation of a zeolite of the LTL structural type according to the invention · [0129] 3.4 g of an aqueous solution of 1,6-bis dihydroxide (methylpiperidmium) hexane (18.36% in by weight) prepared according to Example 1 were mixed with 5.186 g of a 20% by weight aqueous solution of potassium hydroxide (purity 98% by weight, Prolabo). The mixture obtained is kept under stirring for 5 minutes. 0.450 g of a zeolite of structural type LTA (SiO ₂ / Al ₂ O ₃ = 2) are added to the synthesis mixture and kept under stirring for 5 minutes. Subsequently, 1.329 g of smoked CabO-Sil M5 silica (100% by weight SiO ₂ , Cabot), corresponding to a SiO ₂ (Cab-O-Sil) / SiO ₂ (LTA) molar ratio of 2.97 are incorporated. in the synthesis mixture which is kept stirring for two hours, at room temperature (about 22 ° C). The precursor gel obtained has the following molar composition: 1 SiO ₂ : 0.05 A1 ₂ O ₃ : 0.08 R: 0.38 K ₂ O: 15.5 H ₂ O, i.e. a SiO ₂ / Al ₂ O ratio ₃ of 20. The mixture is then transferred, after homogenization, to an autoclave. The autoclave is closed and then heated for 12 hours at 180 ° C. with stirring at 35 rpm with a rotisserie system. The autoclave is then cooled by quenching in ice water and the crystallized product obtained is filtered, washed with deionized water and then dried overnight at 100 ° C. The solid is then introduced into a muffle furnace where a calcination step is carried out: the calcination cycle includes a rise of 1.5 ° C./min in temperature to 200 ° C., a plateau at 200 ° C. maintained for 2 hours, a temperature rise of 1 ° C / min to 550 ° C followed by a plateau at 550 ° C maintained for 8 hours then a return to room temperature.

The calcined solid product is analyzed by X-ray diffraction and identified as consisting of a zeolite of the LTL structural type, with a purity greater than 99% by weight. The X-ray diffraction diagram performed on the calcined solid is given in Figure 3. The image of scanning electron microscopy (SEM) performed on the calcined LTL structural type solid is given in Figure 4. The product has a SiO ₂ / Al ₂ O ₃ molar ratio of 2.76 as determined by X-ray fluorescence.

Example 4: Preparation of a mixture of LTL and ERI structural type zeolite (comparative example),

3.0 g of deionized water were mixed with 5.526 g of an aqueous solution at 20% by weight of potassium hydroxide (purity 98% by weight, Prolabo). The mixture obtained is kept under stirring for 5 minutes. 0.480 g of a zeolite of structural type LTA (SiO ₂ / Al ₂ O ₃ = 2) are added to the synthesis mixture and kept under stirring for 5 minutes. Subsequently, 1.428 g of Cab-O-Sil M5 smoked silica (100% by weight SiO ₂ , Cabot), corresponding to a molar ratio SiO ₂ (Cab-O-Sil) / SiO ₂ (LTA) of 2.97 are incorporated into the synthesis mixture which is stirred for two hours at room temperature (about 22 ° C). The precursor gel obtained has the following molar composition: 1 SiO ₂ : 0.05 A1 ₂ O ₃ : 0.38 K ₂ O: 15.5 H ₂ O, ie a SiO ₂ / Al ₂ O ₃ ratio of 20. The mixture is then transferred, after homogenization, to an autoclave. The autoclave is closed and then heated for 24 hours at 180 ° C. with stirring at 35 rpm with a toumebroche system. The autoclave is then cooled by quenching in ice water and the crystallized product obtained is filtered, washed with deionized water and then dried overnight at 100 ° C. The solid is then introduced into a muffle furnace where a calcination step is carried out: the calcination cycle includes a rise of 1.5 ° C./min in temperature to 200 ° C., a plateau at 200 ° C. maintained for 2 hours, a temperature rise of 1 ° C / min to 550 ° C followed by a plateau at 550 ° C maintained for 8 hours then a return to room temperature.

The calcined solid product is analyzed by X-ray diffraction and identified as consisting of a mixture of zeolites of structural type LTL and of structural type ERI. The X-ray diffraction diagram performed on the calcined solid is given in Figure 5. The relative mass composition of zeolites of structural type LTL and of structural type ERI present in the solid, is determined using a similar method to ASTM D3906 03. By comparing the intensities of the peaks of the X-ray diagram, located at 29.07 2 theta, it can be deduced that the solid obtained is composed of 60% ERI and 40% LTL.

It appears that without the particular structuring agent (1,6-bis (methylpiperidinium) hexane) in the reaction mixture, the material obtained is not a zeolite of structural type LTL, of high purity, that is to say ie of purity greater than or equal to 90%.

Claims (1)

Claims [Claim 1] Process for the preparation of a zeolite of structural type LTL comprising at least the following steps: i) mixing, in an aqueous medium until a precursor gel is obtained, of a zeolite of structural type LTA having a molar ratio SiO ₂ (lta) / A1 ₂ O _{3 (} lta) between 2 and 100, of a nitrogenous organic compound chosen from l, 5-bis (methylpiperidinium) pentane dihydroxide, l, 6-bis (methylpiperidinium) dihydroxide hexane and 1,7-bis (methylpiperidinium) heptane dihydroxide, from at least one source of at least one alkali and / or alkaline earth metal M of valence η, n being an integer greater than or equal to 1, the mixture having the following molar composition: (SiO _{2 (LT} A)) / (Al ₂ O _{3 (LT} A)) between 2 and 100, H ₂ O / (SiO ₂ ( _LTA )) between 1 and 22, R / (SiO ₂ ( _LT A)) between 0.05 and 0.2, M _{2 / n} O / (SiO ₂ (lta)) between 0.33 and 1, in which SiO _{2 (LT} A) denotes the molar amount of SiO ₂ provided by the zeolite of structural type LTA, and A1 ₂ O _{3 (LTA )} denotes the molar amount of A1 ₂ O ₃ provided by the zeolite of structural type LTA, R denotes the molar amount of said organic nitrogen compound, M _{2 / n} O denotes the molar amount expressed in the form of an alkali metal and / or metal oxide alkaline earth provided by said source of M; ii) hydrothermal treatment of said precursor gel obtained in Tissue from step i) at a temperature between 120 ° C and 220 ° C, for a period of between 6 hours and 3 days, to obtain said zeolite of structural type LTL. [Claim 2] Method according to claim 1 one of the preceding claims, in which the SiO ₂ / Al ₂ O ₃ molar ratio of the zeolite obtained is between 2 and 20, preferably between 2 and 15. [Claim 3] Method according to one of the preceding claims, in which the nitrogenous organic compound is 1,6-bis (methylpiperidinium) hexane dihydroxide. [Claim 4] Method according to one of the preceding claims, in which the zeolite of structural type LTA incorporated in the mixture of step i) has a molar ratio (SiO ₂ (lta)) / (A1 ₂ O _{3 (LTA} )) between 2 and 40, preferably between 2 and 25, preferably between 2 and 3, preferably between 2.0 and 3.0 and even more preferably between 2.0 and 2.5. [Claim 5] Method according to one of the preceding claims, in which the H ₂ O / (SiO ₂ (lta)) molar ratio in the mixture of step i) is between 5 and 20. [Claim 6] Method according to one of the preceding claims, in which the molar ratio R / (SiO _{2 (LTA)} ) in the mixture of step i) is between 0.06 and 0.1. [Claim 7] Method according to one of the preceding claims, in which the molar ratio M _{2 / n} O / (SiO _{2 (LTA} )) in the mixture of step i) is between 0.33 to 0.5 and preferably between 0.35 and 0.45. [Claim 8] Method according to one of the preceding claims, in which M is chosen from lithium, potassium, sodium, magnesium and calcium and the mixture of at least two of these metals, preferably M being potassium. [Claim 9] The method of claim 4, wherein the source of at least one alkali and / or alkaline earth metal M is potassium hydroxide. [Claim 10] Method according to one of the preceding claims, in which the mixture of step i) comprises at least one additional source of an oxide XO ₂ , X being one or more tetravalent element (s) chosen from the group formed by the following elements: silicon, germanium, titanium, so that the XO ₂ / SiO ₂ molar ratio _(LTA) is between 0.1 and 33, and preferably between 1 and 25, the SiO ₂ content _(LTA ) in said ratio being the content provided by the zeolite of structural type LTA ,. [Claim 11] Process according to Claim 10, in which the mixture of stage i) has the following molar composition: (XO ₂ + SiO _{2 (} lta)) / A1 ₂ O _{3 (LTA)} between 2 and 40, preferably between 4 and 25 H ₂ O / (XO ₂ + SiO _{2 (LTA)} ) between 1 and 22, preferably between 5 and 20 R / (XO ₂ + SiO _{2 (LTA)} ) between 0.05 and 0.2, preferably between 0.06 and 0.1 M _{2 / n} O / (XO ₂ + SiO ₂ ( _LTA) ) between 0.33 and 1, preferably between 0.33 to 0.5, and preferably between 0.35 and 0.45. [Claim 12] Method according to one of Claims 10 to 11, in which X is silicon. [Claim 13] Process according to one of Claims 10 to 12, in which the zeolite of structural type LTA of stage i) has a molar ratio SiO ₂ (lta / A1 ₂ O ₃ (lta) of between 2 and 3, preferably between 2.0 and 3.0 and preferably a SiO ₂ (lta / A1 ₂ O _{3 (LTA} ) molar ratio of between 2.0 and 2.5. [Claim 14] Method according to one of the preceding claims, in which the precursor gel obtained at the end of step i) has a molar ratio of the total amount expressed in tetravalent element oxides to the total amount expressed in element oxides trivalent between 2 and 100, preferably between 2 and 40. [Claim 15] Method according to one of the preceding claims, in which crystalline seeds of a zeolite of structural type LTL, preferably having a SiO ₂ / Al ₂ O ₃ molar ratio of between 2 and 20, are added to the mixture of step i), preferably in an amount of between 0.01 and 10% of the total mass of the sources of said tetravalent (s) and trivalent (s) element (s) in anhydrous form present in the mixture, said crystalline seeds not being taken into account in the total mass of the sources of tetravalent and trivalent elements. [Claim 16] Method according to one of the preceding claims, in which step i) comprises a step of maturing the mixture at a temperature between 20 and 100 ° C, with or without stirring, for a period of between 30 minutes and 48 hours. [Claim 17] Method according to one of the preceding claims, in which the hydrothermal treatment of stage ii) is carried out under autogenous pressure, at a temperature between 120 ° C and 220 ° C, preferably between 150 ° C and 195 ° C, for a duration of between 6 hours and 3 days, preferably between 8 hours and 2 days, even more preferably between 12 hours and 1 day. [Claim 18] Method according to one of the preceding claims, in which the zeolite obtained at the end of step ii) is filtered, washed and dried at a temperature between 20 and 150 ° C, preferably between 60 and 100 ° C , for a period of between 5 and 24 hours to obtain a dried zeolite. [Claim 19] The method of claim 18 wherein the dried zeolite is then calcined at a temperature between 450 and 700 ° C for a period between 2 and 20 hours, the calcination may be preceded by a gradual rise in temperature. [Claim 20] Structural type LTL zeolite with a SiO ₂ / Al ₂ O ₃ molar ratio between 2 and 20, obtained by the preparation process according to claim 19, for which the mean values of d _hld and relative intensities measured on a ray diffraction diagram X are as follows: [Tables3] 2 theta (°) dhkl (Â) Irel 2 theta (°) dhkl (Â) Irel 5.549 15,913 FF 25,561 3,482 f 9,614 9,193 ff 26,188 3,400 ff 11,107 7,960 ff 27,109 3,287 f 11,754 7.523 f 27,986 3.186 mf 14.701 6.021 f 29.07 3,069 f 15.207 5.822 ff 29,653 3.010 ff 19,291 4,597 mf 30,677 2.912 mf 20,094 4.415 ff 31,472 2,840 ff 20,444 4.341 ff 31.995 2,795 ff 22,653 3.922 m 33.506 2.672 ff 23.337 3,809 ff 33,735 2,655 f 24.28 3,663 f 34,182 2.621 ff where FF - = - very-strong '; - F - = - strong -; - m - = - medium-? mf - = - moderate! · weak -; - f - = - low - - - ff - = - frès -low! · intensity · relalive- fjg-being-given-in-relation-to-a-scale-of-relative-intensity-where-it is · assigned- a-value-of-100 · B -ia · stripe-the-more-intensely-of-diagramme- of diffraction X-des ^rayons-: ff <O -, - 15- <f <30 - - 3G <-mf- <50-? ; -50- <m - <- 65 -; - 65- <F - <- 85 -; - FF -> - 85.y