EP0625125A1 - Zsm-48 zeolite synthesis method - Google Patents

Abstract

Process for the synthesis of zeolites of the ZSM-48 type, in the absence of nitrogenous organic agent, by hydrothermal reaction of a mixture containing a source of tetravalent silicon, hydroxide ions, water and a glycol and optionally a source of trivalent aluminum. The zeolites obtained are useful as selective organophilic catalysts and adsorbents.

Description

 PROCESS FOR THE SYNTHESIS OF ZSM-48 TYPE ZEOLITHS

This invention relates to a process for the synthesis of zeolites of the ZSM-48 type and their use as a selective organophilic catalyst and adsorbent.

The probable structure of the ZSM-48 zeolite was proposed in 1985 by Schlen et al. (Zeolites, 5, 355, 1985). It is a zeolite of orthorho bic or pseudo-orthorhombic symmetry (a = 1.424, b = 2014, c = 0.840 nm) having unidirectional channels, of 0.53 x 0.56 nm, delimited by cycles of ten tetrahedra.

The zeolites whose structure corresponds to the topology of type ZSM-48, known to date, are EU-2, EU-ll and ZBM-30 (P. Jacobs and J. Martens, Synthesis of high silica aluminosilicate zeolites , Stud. Surf. Sci. Catal., 33, 275, 1987). They are solids of interest for the catalytic transformation of hydrocarbons and organic compounds and for adsorption.

The synthesis of zeolites of the ZSM-48 type is described in several patents and publications in the scientific literature, the main ones of which are summarized in Table 1. The zeolites of the ZSM-48 type are prepared by hydrothermal crystallization of reactive alkaline gels of aluminosilicates or silicates. The syntheses are carried out in the presence of one or more nitrogenous organic agents such as alkylamines, diamines, tertiary, quaternary and bis-quaternary alkyl ammoniums or pyrrolidine. In a publication (Stud. Surf. Sci. Catal. 49A, 291, 1989) Huo Qisheng et al. Describe a synthesis of ZSM-48 in the presence of tetramethylammonium bromide and / or crystals for sowing silica sodalite in a non-medium. aqueous where the solvent consists of a mixture of ethylene glycol and n-butanol. At the end of the synthesis, the organic agent finds itself trapped in the porosity of the zeolite and its elimination, necessary to release the volume TABLE 1

Bibliographical references on the synthesis of zeolites type ZSM-48

microporous zeolite, is carried out by an oxidative calcination at a temperature generally above 500 ° C. This calcination stage has a certain number of drawbacks because, in addition to its energy cost, it can cause degradation of the crystal structure and it is accompanied by the release of nitrogen oxides which it is imperative to treat for environmental reasons. In addition, the cost of syntheses is increased because the organic agent is generally the most expensive component of the preparation. The use of crystals for sowing as described in the publication by Huo Qisheng et al. does not constitute an economic synthesis route because it requires the use of a very large amount of organic solvent (Siθ ₂ / Ethylene glycol / Butanol≈ 1/10/6) and a duration of the syntheses of 50 days at 180 ° C .

We have now found a process for the synthesis of a zeolite of the ZSM-48 type in an aqueous medium which does not use an organic nitrogen agent, and does not require the addition of crystals already formed. The zeolite precursor can be transformed into zeolite without calcination, by a simple moderate heat treatment. This treatment does not lead to degradation of the crystal structure. The zeolite obtained has remarkable thermal and chemical stability. The process for the synthesis of a ZSM-48 type zeolite according to the invention is characterized in that a reaction mixture composed of a source of tetravalent silicon and hydroxide ions, water and a glycol (G) of general formula G = H0 ((CH ₂ ) _n -0) H where n = 2, 3 or 4 and m = 1, 2 or 3. This mixture is maintained at a temperature above 80 ° C. and under a pressure at least equal to the vapor pressure of the solution for a time sufficient to effect the crystallization of the reaction mixture into a zeolite precursor, then the enzéolite precursor is transformed by removing the glycol and the water retained in the porosity .

Without wishing to be limited by a theoretical explanation, we believe that it is the use of an adequate amount of glycol to modify the solubility of silica in the crystallization gel which makes synthesis possible. providing a degree of supersaturation which is particularly favorable for this type of structure.

The reaction mixture may optionally contain a source of trivalent aluminum. The hydroxide ions are derived from compounds of formula M (OH) _n where M is a cation of valence n, n being generally 1 or

2. M is generally an alkali metal from group IA of the periodic table, an alkaline earth metal or an organic compound, such as a quaternary ammonium.

The molar ratios of reactants in the reaction mixture allowing the crystallization of a zeolite of the ZSM-48 type are specified in Table 2.

Among the sources of tetravalent silicon which can be used in the preparation of the reaction mixture, mention may be made of finely divided solid silicas in the form of hydrogels, aerogels or colloidal suspensions, water-soluble silicates such as alkali silicates, hydrolyzable silicic esters such as that orthosilicates, tetraalkyl formula Si (OR) ₄ wherein R is alkyl to C ₄ such as methyl and ethyl.

The silicon source is used in the form of a true aqueous solution, in the case of water-soluble silicates, or else of an aqueous suspension which may be colloidal, in the case of finely divided silicates.

The traces of aluminum present in the silicon source do not interfere with crystallization. Aluminum can also be deliberately incorporated into the synthesis in the form of aluminum salts such as sulphate, nitrate, chloride, fluoride, acetate, aluminum oxides and hydroxides, aluminates and in particular alkali alu inates, aluminum esters such as the aluminum trialkoxides of formula Al (OR) ₃ in which R denotes a C1 to C4 alkyl radical such as methyl, ethyl, propyl or butyl. The mixing of the ingredients constituting the reaction mixture can be carried out in any order.

Advantageously, an alkaline solution is first prepared by dissolving the strong base in water. The strong base is generally potash or soda in pellets. To this alkaline solution is added the glycol and then the source of silicon. These two operations are generally carried out at room temperature.

The whole is transferred to an autoclave. The mixture is heated under autogenous pressure until the zeolite has completely crystallized. The reaction time is generally between 10 and 150 hours. The temperature varies between 80 and 200 ° C.

The duration of the synthesis can be shortened by adding to the reaction medium crystallization seeds. The germs are obtained by grinding a zeolite of the ZSM-48 type. In the absence of seeds, it is also advantageous to subject all or part of the reaction mixture to ripening at a temperature below the crystallization temperature. Some of the properties of the final solid, such as the size and morphology of the crystals may be affected by these modifications, but the crystal structure and the adsorption characteristics remain unchanged.

The crystals obtained are the precursor of the zeolite consisting of the zeolite trapping in its pores and cavities the water of hydration, cations and glycol. These crystals are separated from the reaction medium by filtration, washed with distilled or deionized water, until washing waters are obtained at neutral pH. The washed crystals can then be dried at a temperature between room temperature and 90 ° C, preferably around 70 ° C.

The stoichiometric composition of the zeolite precursor expressed in moles of oxides is as follows: a M g. b AI ₂ O ₃ . Siθ ₂ . cH ₂ θ.dG n where - M is a cation with valence n, in general an alkali metal from group IA of the Periodic Table of the Elements, an alkaline earth metal or a quaternary ammonium. M is preferably potassium or sodium. G is a glycol molecule.

- a goes from 0 to 0, 1

- b goes from 0 to 0, 1 - c goes from 0 to 1

- d goes from 0 to 1

The X-ray diffraction pattern of the precursor of zeolite ZSM-48 is described in Table 3.

The X-ray diffractogram was obtained by a conventional method using K alpha copper radiation and an amplifying detector. The signal intensities are recorded as a function of their position expressed in two theta, where theta is the Bragg angle. These data lead to the relative intensities and the reticular distances, d (nm) in nanometers which are characteristic of the crystal structure. The values may differ slightly depending on the size of the crystals and their hydration state, but in general the X-ray diffractogram is a characteristic of the structure concerned.

Table 3 X-ray diffractogram of a ZSM-48 d (nm) zeolite precursor I / Imax

1.171 0.3

1.014 0.15

0.715 0.05

0.606 0.07

0.582 0.13

0.520 0.10

0.463 0.05

0.418 0.8

0.387 1.0

0.361 0.15 0.337 0.05 0.307 0.06 0.283 0.14 0.271 0.02 0.262 0.03 0.247 0.03 0.242 0.03 0.238 0.03 0.234 0.03 0.209 0.02 0.206 0.05

The zeolite is obtained from the precursor by liberation from its cavities and channels.

In the case of ZSM-48 type zeolites synthesized according to the methods of the prior art, the cavities and channels contain nitrogenous organic bases. The porosity can only be released by calcination, by thermally degrading the structuring molecules.

The porosity of the ZSM-48 zeolite prepared according to the invention is released by treatments at moderate temperature, sufficient to cause the departure of the water and glycol molecules. A simple air drying is sufficient.

The use of ethylene glycol is particularly advantageous because it can be removed by drying at a temperature below 200 ° C.

Obviously, when less volatile organic agents replace ethylene glycol such as diethylene glycol and triethylene glycol, higher temperatures are necessary for the release of the porosity of the zeolite. It should be noted that the drying thus described in two stages can be advantageously substituted by a drying in a single stage, which leads directly from the washed crystals to the final zeolite.

The zeolite thus obtained has an X-ray diffraction spectrum substantially equal to that of the precursor, except for some variations in intensity of the peaks at small angles.

The crystallinity and the adsorption capacities of the zeolite are retained after heat treatment and hydrothermal prolonged or after treatment with acid or basic solutions. Before use, the zeolite can be subjected to a treatment aimed at eliminating traces of cations, generally alkaline cations which may be present. The zeolites obtained according to the invention are suitable as organophilic adsorbents, allowing the separation of "organic molecules from water.

In their protonated form or after exchange with cations, they can be used as catalysts or catalyst components for catalytic conversion reactions of hydrocarbon compounds.

The following examples illustrate the invention without, however, limiting it. EXAMPLE 1 This example describes a general method for preparing a zeolite of the ZSM-48 type according to the invention and its use as an adsorbent.

2.38 grams of potassium hydroxide (KOH, Carlo Erba RLE) are dissolved in a 500 ml stainless steel autoclave containing 31 ml of deionized water and 154 grams of ethylene glycol (Labosi for analyzes) are added. Then added 50 grams of silica sol at 42% by weight of silica (Ludox AS-40, Dupont de Nemours) with vigorous stirring. Given the presence of traces (0.014% by weight) of aluminum in the silica source, the stoichiometry of the crystallization gel is as follows:

0.06 K ₂ O, 0.00038 AI2O ₃ , Siθ ₂ , 9.4 H ₂ O, 7 C2H ₆ O ₂

Stirring is continued for an hour and a half, then the autoclave is closed and the temperature is raised to 150 ° C. while maintaining stirring at 300 rpm (rotations per minute). After 48 hours, the zeolite crystals are collected by filtration, washed with water and dried in an oven at 70 ° C. in air for 12 hours.

The solid presents an X-ray diffractogram corresponding to that of Table 3.

The weight of solid, dried at 70 ° C., collected in this synthesis is 19.8 grams, which corresponds to a yield relative to the committed silica of 91%. Voluetric analysis by nitrogen adsorption at 77 K

2 leads to a specific area of 130 m / g after degassing of the solid at 350 ° C.

This zeolite adsorbs 0.1% by weight of water (5 torr, 25 ° C), and 4.7% by weight of methanol (15 torr, 25 ° C).

After calcination under air flow at 850 ° C for ten hours, the zeolite retained its crystallinity, evaluated by X-ray diffraction, and its specific surface at

2 the nitrogen is 120 m / g. ^• These data illustrate the selectivity of the zeolites of the invention for the organic molecules of small kinetic diameter and excellent thermal stability. EXAMPLE 2 This example illustrates a method of synthesizing the zeolite according to the invention from a medium richer in alkali and in the absence of agitation during crystallization.

In the 120 ml stainless steel autoclave containing 16 ml of deionized water, 1.6 grams of potassium hydroxide (KOH, Carlo Erba RLE) are dissolved and 77 grams of ethylene glycol (Labosi for analyzes) are added. 25 grams of silica sol containing 42% silica (Ludox AS-40, Dupont de Nemours) are then added with vigorous stirring. Given the presence of traces (0.014% by weight) of aluminum in the silica source, the composition of the crystallization gel obtained is as follows: 0.08 K2O, 0.00038 AI2O3, Siθ2, 9.4 H2O, 7 CH ₄ (0H) 2

Stirring is continued for an hour and a half, then the autoclave is closed and it is transferred to an oven previously brought to 170 ° C. After 7 days the zeolite crystals are recovered by filtration, washed with water and dried in an oven at 70 ° C in air for 12 hours.

The solid has an X-ray diffractogram corresponding to that of Table 3. The weight of solid, dried at 70 ° C, obtained in this synthesis, is 7.6 grams which corresponds to a yield relative to the silica used for 72%. EXAMPLE 3:

This example illustrates a synthesis of zeolite according to the invention in which the content of ethylene glycol in the starting gel and the crystallization temperature have been reduced.

3.76 grams of potassium hydroxide (KOH, Carlo Erba RLE) are dissolved in a 500 ml stainless steel autoclave containing 50 ml of deionized water and 105 grams of ethylene glycol (Labosi for analysis) are added. Then added 80 grams of silica sol at 42% by weight of silica (Ludox AS-40, Dupont de Nemours) with vigorous stirring. Given the presence of traces (0.014% by weight) of aluminum in the silica source, the stoichiometry of the crystallization gel is as follows: 0.06 K ₂ 0, 0.00038 AI2O3 ,, Siθ2, 9.4 H2O , 3 C2H6O2

Stirring is continued for an hour and a half, then the autoclave is closed and the temperature is raised to 140 ° C. while maintaining stirring at 300 rpm (rotations per minute). After 4 days the zeolite crystals are collected by filtration, washed with water and dried in an oven at 70 ° C in air for 12 hours.

The solid presents an X-ray diffractogram corresponding to that of Table 3.

The weight of solid, dried at 70 ° C., collected in this synthesis is 27.4 grams, which corresponds to a yield relative to the committed silica of 89%.

EXAMPLE 4:

This example illustrates a synthesis of zeolite according to the invention from a medium richer in aluminate. 2.76 grams of potassium hydroxide (KOH, Carlo Erba RLE) and 0.12 grams of aluminum hydroxide (Al (OH) 3, Merck) are dissolved in a 200 ml stainless steel autoclave containing 41 ml of deionized water. ) and 66 g of ethylene glycol (Labosi for analyzes) are added. 9.2 g of silica (Siθ2, Aerosil Serva) are then added with vigorous stirring. The composition of the crystallization gel obtained is as follows 0.16 K2O, 0.005 AI2O3, SiO2, 15 H2O, 7 C2H4 (0H) 2

Stirring is continued for two hours, then the autoclave is sealed and it is transferred to an oven previously brought to 170 ° C. After 6 days the zeolite crystals are collected by filtration, washed with water and dried at 70 ° C in air for 12 hours.

The solid has an X-ray diffractogram corresponding to that of Table 3. The weight of solid, dried at

70 ° C, obtained in this synthesis is 8.0 grams, which corresponds to a yield relative to the committed silica of

87%.

EXAMPLE 5 This example illustrates a synthesis of zeolite according to the invention from a medium in which the ethylene glycol has been replaced by diethylene glycol and in the absence of stirring during crystallization.

0.37 grams of sodium hydroxide (NaOH, Prolabo Normapur) are dissolved in a 120 ml stainless steel autoclave containing 11 ml of deionized water and 93 g of diethylene glycol (Aldrich) are added. 17.6 g of silica sol containing 42% by weight of silica (Ludox AS-40, of silica sol with 42% by weight of silica (Ludox AS-40, Dupont de Nemours) are then added with vigorous stirring. given the presence of traces (0.014% by weight) of aluminum in the silica source, the composition of the crystallization gel obtained is as follows:

0.04 Na ₂ θ, 0.00038 AI ₂ O ₃ , Siθ ₂ , 9.4 H ₂ O, 7 C ₄ H ₁₀ O ₃

Stirring is continued for an hour and a half, then the autoclave is closed and it is transferred to an oven previously brought to 170 ° C. After 5 days the zeolite crystals are collected by filtration, washed with water and dried in an oven at 70 ° C in air for 12 hours.

The solid has an X-ray diffractogram corresponding to that of Table 3. The weight of solid, dried at

70 ° C, collected at the end of this synthesis is 6.0 grams, which corresponds to a yield compared to the silica involved of 81%.

EXAMPLE 6 This example illustrates a synthesis of zeolite according to the intervention from a medium in which the ethylene glycol has been replaced by triethylene glycol.

0.20 grams of sodium hydroxide (NaOH, Prolabo) are dissolved in a stainless steel autoclave containing 6.2 ml of water Normapur) and 74 g of triethylene glycol (Aldrich) are added. Then added 10 grams of silica sol at 42% by weight of silica (Ludox AS-40, Dupont de Nemours) with vigorous stirring. Given the presence of traces (0.014% by weight) of aluminum in the silica source, the composition of the crystallization gel obtained is as follows

0.04 Na2θ, 0.00038 AI2O3, Si0 ₂ , 9.4 H2O, 7 C6H14O4

Stirring is continued for an hour and a half, then the autoclave is sealed and transferred to an oven brought to 170 ° C. After 5 days the zeolite crystals are collected by filtration, washed with water and dried in an oven at

70 ° C in air for 12 hours.

The solid has an X-ray difractogram corresponding to that of Table 3. The weight of solid, dried at 70 ° C., collected in this synthesis is 2.68 grams, which corresponds to a yield relative to the committed silica of

64%.

EXAMPLE 7:

The catalytic activity of zeolites according to the invention was evaluated as a fresh additive of an industrial FCC catalyst, called in short ECAT (for Equilibrium

Catalyst), in a MAT catalytic test micro-unit (for

Micro Activity Test).

The additive obtained in Example 3 is mechanically mixed in an amount of 5 and 10% by weight with the ECAT catalyst. The ability of each catalyst (ECAT, ECAT + 5% additive ZSM-48, ECAT + 10% ZSM-48) to convert a heavy load of hydrocarbons is then determined under the following conditions: quantity of catalyst = 3 g weight ratio catalyst / charge = C / O = 6 duration of injection = 20 s WHSV = 30 h-1 temperature = 530 "C The hydrocarbon charge used has the following characteristics: density 15 ° C = 0.9226

% weight S = 2.460

% carbon weight Conradson = 0.29 refractive index (20 ° C) = 1.5099 simulated distillation (° C) initial weight 272

370

442

491 517

Comparison of catalytic performances

The results obtained with the industrial cracking catalyst ECAT and the two catalysts comprising an additive based on ZSM-48 are collated in Table 4 below:

Table 4 ECAT catalyst ECAT ECAT

5% weight ZSM-48 + 10% weight ZSM-48

These results show that the catalysts containing a fresh additive based on ZSM-48, prepared according to the invention, make it possible to obtain a significantly higher conversion and markedly improved yields compared with a conventional catalyst for cracking ECAT. In particular, the yields of propylene and of C4 are improved. The yields of gasoline, diesel (LCO) and heavy fraction (residue) are lower. These selectivity changes are interesting for an increase in the octane number of gasolines, and demonstrate the advantage of adding an additive of the ZSM-48 type in accordance with the invention to an industrial catalytic cracking catalyst.

Claims

1) Process for the synthesis of a zeolite of the ZSM-48 type, characterized in that a reaction mixture composed of a source of tetravalent silicon of hydroxide ions, of water and of a glycol (G) of general formula G = H0 ((CH2) _n 0) mH where n = 2, 3 or 4 and m = 1, 2 or 3, this mixture is maintained at a temperature above 80 ° C and under a pressure at least equal to the vapor pressure of the solution for a sufficient time to effect the crystallization of the reaction mixture as a zeolite precursor by elimination of the glycol and of the water.

2) Process according to claim 1 characterized in that the reaction mixture contains a source of trivalent aluminum.

3) Method according to claim 1 or 2 characterized in that the hydroxide ions are derived from compounds of formula M (OH) _n where n is equal to 1 or 2.

4) Method according to claim 3 characterized in that M is an alkali or alkaline earth metal or an organic compound such as quaternary ammonium.

5) Method according to claim 4 characterized in that M is sodium or potassium.

6) Method according to one of claims 1 to 5 characterized in that the reaction mixture contains a source of trivalent aluminum.

7) Method according to one of claims 1 to 4 characterized in that the molar ratios of reactants in the reaction mixture corresponds to:

8) Method according to one of claims 1 to 7 characterized in that the source of tetravalent silicon is solid silica in the form of hydrogel, airgel or colloidal suspension, a water-soluble silicate such as alkali silicates, such as sodium silicate, and hydrolysable silicic esters such as tetra alkyl orthosilicates of the formula Si (oR) 4, wherein R denotes an alkyl Ci Ac ₄ as ethyl or ethyl.

9) Method according to claim 6 characterized in that the trivalent aluminum source is an aluminum salt such as sulfate, nitrate, chloride, fluoride, acetate, aluminum oxides and hydroxides, aluminates and in particular alkali aluminates , aluminum esters such as the aluminum trialkoxides of formula Al (OR) 3 in which R denotes a C1 to C4 alkyl radical.

10) Method according to one of claims 1 to 9 characterized in that the reaction mixture is maintained for a period of 10 to 150 hours at a temperature between 80 and 200 ° C.

11) ZSM-48 type zeolite precursor characterized in that its stoichiometric composition expressed in moles of oxides corresponds to a M ₂ • b AI2O3. Siθ2.c H2θ.dG n where M is a cation of value n, n being equal to 1 or 2, and G is a glycol molecule G = HO ((CH2) nO) m where n = 2, 3 or 4 and m = 1, 2 or 3

- a ranges from 0 to 0.1 - b ranges from 0 to 0.1

- it goes from 0 to 1

- d goes from 0 to 1 and whose X-ray diffraction diagram is described in the following table: d (nm) I / Imax

1.171 0.3

1.014 0.15

0.715 0.05

0.606 0.07 0.582 0.13 0.520 0.10

0.463 0.05

0.418 0.08

0.387 1.00 0.361 0.15

0.337 0.05

0.307 0.06

0.283 0.14

0.271 0.02 0.262 0.03

0.247 0.03

0.242 0.03

0.238 0.03

0.234 0.03 0.209. 0.02

0.206 0.05

12) Application of the zeolite obtained by the process according to claims 1 to 10 as organophilic adsorbents. 13) Application of the zeolite obtained by the process according to claims 1 to 10 in their protonated form or after exchange with cations as catalysts for the conversion of hydrocarbon compounds.