WO1998022389A1

WO1998022389A1 - Method for production of hexagonal faujasite with low consumption of organic additive, and use of this as a catalyst for alkylation

Info

Publication number: WO1998022389A1
Application number: PCT/NO1997/000306
Authority: WO
Inventors: Rune Wendelbo; Michael Stöcker; Hanne Junggreen; Helle B. Mostad
Original assignee: Nyfotek As
Priority date: 1996-11-22
Filing date: 1997-11-18
Publication date: 1998-05-28
Also published as: NO964988L; NO304183B1; AU5418198A; NO964988D0

Abstract

The invention relates to a method of preparing a hexagonal faujasite consisting of small plate formed crystals with a thickness of less than 0.3 microns and a width of less than 1.3 microns, by adding to a reaction mixture comprising SiO2, Al2O3 and Na2O, an amount of 18 crown ether to achieve a molar ratio of 18 crown ether to Al of less than 0.1, thereafter keeping the mixture at room temperature for 1 to 3 days and then at a temperature of between 80 and 105 °C for at least 15 days, the container being rotated 'head over' during the whole period, thereafter recovering the crystalline product formed in an appropriate way. The reaction mixture has the composition, on a molar basis, of 10.5-11.5 SiO2; Al2O3; 2-3 Na2O; 120-160 H2O; 0.11-0.199 C12H24O6 wherein C12H24O6 is added in the form of 18 crown ether. The invention also relates to the use of the hexagonal faujasite prepared in accordance with the above as an alkylation catalyst, especially in the alkylation of aliphatic compounds, particularly as a catalyst in the alkylation of iso-butane with 2-butene.

Description

Method for production of hexagonal faujasite with low consumption of organic additive, and use of this as a cats- lyst for alkylation.

The invention relates to a method of preparing the zeolitic material hexagonal faujasite having a small crystallite size, with a low organic additive requirement, together with the use of same in a process wherein isobutane is alkylated with 2-butene into a product having a high content of C₈ isomers.

Zeolites are inorganic crystalline substances consisting of silicon and aluminum oxide and optionally other elements. In nature, zeolites occur primarily in transformed volcanic deposits. They may, however, also be prepared synthetically. The main feature distinguishing zeolites from other oxides is their microporosity, having pores of from .3 to .8 nm in a single-, two- or three- dimensional network. The pore channels of the zeolites allow the motion of molecules and ions, giving the zeolites their unique position as adsorbents, ion exchangers and catalysts. The said characteristics are utilized i.a. in the cracking of oils into gasoline, in separating air into nitrogen and oxygen, in gas drying, water purification, fine chemicals and specialty chemicals preparation etc. The zeolites, existing with hydrophobic as well as hydrophilic characteristics, may have pore volumes of up to .3 ml/g. Two examples of zeolitic compounds demonstrate the importance of controlled synthesis conditions to the compositions of the zeolites. 1) Naturally occuring erionite, crystallized in the course of thousands of years at low temperatures and slightly alkaline pH: K₂₀₂Na_{1 9} Ca., ₂₅Mg₀₆₃Fe₀₅₃AI₉₃₁Si_{26 16}O₇₂(H₂O)₁₀₄; and 2) a synthetic A zeolite, crystallized for 6 hours at 90°C and pH > 14:

NaAISi0₄(H₂0)_x wherein x varies from 0 to 2, depending on humidity and temperature.

About 50 different zeolites occur in nature, many of which having been known for a long time. However, zeolites utilized in industry are in most cases prepared synthetically. Up to now, about 50 novel structures (in addition to the naturally occuring zeolites) have additionally been prepared synthetically, some of which being zeolitic aluminophosphates and silico-alumino phosphates. Novel structures and variants are emerging continuously, and also new variants of known zeolites, together with novel and more economic methods of preparation. Moreover, there has been considerable progress with regard to the preparation of zeolites which are more or less tailored for particular purposes. The most important applications established for zeolites are as catalysts, adsorbents, ion exchangers and drying agents, the first great breakthrough being attained when starting using Y zeolites as catalysts in the catalytic cracking of oils into gasoline about 30 years ago. This is quantitatively still the most important application of zeolites in terms of volume, amounting to a consumption of more than 60,000 metric tons/year.

The introduction of zeolites in the petroleum industry gradually altered many processes, leading to power saving and economically favorable innovations. In New Zealand, e.g. a large plant has been operated for the conversion of methanol into gasoline, using the Mobil ZSM 5 zeolite as catalyst. Particularly useful are zeolites for a form selective catalysis, the pore diameters of the crystals being essential to the ability of molecules to pass through the pore openings. An example is the selective methylation of toluene into p- xylene by passing over the zeolite ZSM-5. Analogous to this, a particular titanium containing zeolite (TS-1) is used as an oxidation catalyst, combined with shape selectivity.

Further industrially established applications of zeolites are based on their ion exchanging and adsorbing abilities. Zeolites have cation exchanging capacities of up to about 7 meq/g, the cation selectivities varying somewhat from one zeolite to another. The A zeolite is e.g. utilized in phosphate free detergents, contributing to water softening by binding Ca and Mg ions, substituting with its Na ions. At present, this represents the most extensive use of zeolites, viz. above 400,000 metric tons/year.

Most zeolites have hydrophilic characteristics, such zeolites being highly suitable as drying agents, since, because of their polar nature, they easily absorb water (and other polar substances) from the environment. In the so-called

«pressure swing» process, air can be separated by adsorbing N₂ onto an A zeolite under pressure. In deodorants, air cleaners, cat sands and paper diapers, zeolites may be used both as dessicants and deodorants. These examples illustrate the wide and varied market for such materials.

Zeolites having a high Si0₂/Al₂0₃ ratio are especially attractive because of their generally higher thermal stability as compared with corresponding materials having a low Si0₂/Al₂0₃ ratio. In the case of zeolites belonging to the faujasite family, the thermal stability increases with increasing Si0₂/Al₂0₃ ratio. The said ratio must be at least higher than 6 in order to be useful in processes such as e.g. a catalytic cracking requiring that the zeolite be burned intermittently in order to be free from coke deposited in the pores during the process. With almost no exception, the synthesis of zeolites are carried out by mixing reactive sources of silicon and aluminum with a strongly basic aqueous alkaline solution and optionally (but not in every case) other reagents. Such other reagents may be organic additives acting as so-called templates in which the zeolitic structure is supposed to grow around organic ions or molecules. The organic additives, growing into such a structure, are removed, leaving behind a microporous structure which, if crystalline with a continuous pore system, according to definition, is a zeolite, provided it is able to absorb water into its pore system. Frequently, but not in all conditions, the reagent mixture will form a gel and may then be referred to as a gel. Often, such a gel, with all reagents added, may be referred to as a synthesis gel. The complete mixture may, however, more generally be referred to as a reaction mixture which may take the form of a gel or be a solution, a sol or a precipitate with a clear solution or sol above the precipitate.

From the literature, e.g. from US Patents Nos. 5,451 ,391 and 4,891 ,200, it is known that zeolites can be prepared from raw materials containing oxides or from other compounds containing silicon and aluminum by reacting such materials with a relatively concentrated basic solution for a sufficient time, usually hours to weeks, and at a sufficiently high temperature, usually above 70°C. It would frequently be disadvantageous to have present substances other than Si oxide, Al oxide, water and hydroxide. However, selected substances other than the said substances may also assist in directing the synthesis towards products desired. A Y zeolite was e.g. prepared according to US Patent 3,130,007, Example 1 , by dissolving 5 g of sodium aluminate containing 39% by weight of Na₂0 and 44% by weight of Al₂0₃; and 22 g of sodium hydroxide containing 77.5% by weight of Na₂0, in 89.5 ml of distilled water. To this solution, 124.2 g of an aqueous colloidal silica sol containing 29.5% by weight of Si0₂ was added, obtaining a mixture with the composition of 13.9 Na₂0: Al₂0₃: 28.2 Si0₂: 471 H₂0, which was homogenized by stirring. The said mixture was entrapped in a sealed glass container, which was placed in a water bath at 100°C for 21 hours, whereupon the product was recovered by filtering, washing and drying. Chemical analysis showed the product to have a formula corresponding to 0.92 Na₂0: Al₂0₃: 4.0 Si0₂: 7.0 H₂0. Thus, one problem of the above method is that a substantial portion of the reagents are not incorporated into the product, representing undesirable costs.

In US Patent 4,178,352, a method is disclosed for the preparation of a Y zeolite with a minimum excess of reagents present in the reaction mixture, by first preparing a «seeding slurry» with the composition of 16 Na₂0: 1.2 Al₂0₃: 15 Si0₂: 320 H₂0, being allowed to stand for 48 hours, whereupon 155 g of the slurry was mixed with 438 g of a sodium silicate solution with a Si0₂/Na₂0 ratio of 3.25 and 100 g of sodium aluminate solution containing 17.9% by weight of Na₂0 and 22% by weight of Al₂0₃. To this solution, 132.5 g of water was added. Thereafter, 193.3 g of an alum solution containing 8.3% by weight of alumina was added with stirring. The mixture was heated at 100°C for 9 hours, whereupon the product was recovered by filtering, washing and drying. Chemical analysis showed the product to have a formula corresponding to 12.8% of Na₂0, 23.2% of Al₂0₃ and 63.9% of Si0₂.

Several other patents disclose similar methods for the preparation of Y zeolites, e.g. US Patents Nos. 3,574,538 and 4,166,099, the patent literature thus covering methods for the preparation of a Y zeolite with high crystallinity, viz. US Patent 4,436,708; with a high Si to Al ratio, e.g. US Patent No. 4,714,501 , DE 2,324,235 and DE 2,425,267; a preparation with the use of inexpensive reagents, e.g. US Patents Nos. 3,639,099 and 4,400,366 and EP 0,128,766 A2; and a preparation with a proper utilization of reagents, e.g. US Patent No. 4,178,352, etc. In addition to a Y zeolite, which is a pure cubic faujasite having a Si0₂ to Al₂0₃ ratio of more than 3 up to 6.5, a number of zeolites are known belonging to the faujasite family, e.g. zeolite X, which is a pure cubic feujasite with a Si0₂ to Al₂0₃ ratio of below 3. Moreover, a method is known from European Patent No. s 0,364,352 B1 and US Patent No. 5,098,683 for the preparation of a cubic faujasite, analogous to zeolite Y, with a Si0₂ to Al₂0₃ ratio of more than 6.5 up to 10, the basis for which being a gel consisting of silica, alumina, sodium hydroxide, water and the crown ether 1 ,4,7,10,13-pentaoxacyclopentadecane, generally referred to as «15-CROWN-5» or «15-crown ether». Similarly, according to the o two latter patents, together with US Patent No. 5,393,511 , a method was disclosed for the preparation of a hexagonal faujasite, and more precisely the hexagonal zeolite which was later on referred to as EMC-2, also, according to its so-called structural code, referred to as EMT, wherein E and M denote EMC and T denotes «Two». s The structural code EMT has been determined by the « International Zeolite

Associations Structure Commision», said code now being generally used and acknowledged when referring to hexagonal faujasites having characteristics similar to those of the hexagonal faujasite prepared according to European Patent No. 0,364,352 B1. The said hexagonal faujasite has a Si to Al ratio of from more 0 than 3 and up to 5, corresponding to a Si0₂ to Al₂0₃ ratio of from more than 6 up to 10. It can be prepared in a manner similar to that of the cubic fujasite discussed above, from a gel consisting of silica, alumina, sodium hydroxide, water and crown ether, however, with the use of the crown ether 1 ,4,7, 10,13, 16-hexaoxacycloocta- decane, generally referred to as «18-CROWN-6» or «18 crown ether» and not as 5 «15-CROWN-5». The three dimensional crystal lattice of the hexagonal faujasite is constructed of Si0₂ and AI0₂ tetrahedral units having a hexagonal symmetry, further containing replaceable cations, preferably Na⁺ ions. The diameters of the pore openings are in one direction 7.1 x 7.1 A and in the two other directions 7.4 x 6.5 A. In the preparation of the crystal lattice, one or more organic additives have 0 also been added, which are retained in the pores of the crystallized end product, the formula of which thus being be indicated as follows: mR:(Si₂₄._yAl_yNa_z)0₄₈ wherein «R» represents at least one organic additive present in the intracrystalline pore system; m is the number of moles of «R» present for each mole of (Si_24. _yAl_yNa O^ and m has a value of about 1 , the lowest value reported in the literature being 0.9. The hexagonal faujasite is prepared according to EP 0364352B1 from a reaction mixture consisting of silica, alumina, sodium hydroxide, water and the crown ether 1 ,4,7,10,13,16-hexaoxacyclooctadecane, generally referred to as «18-CROWN-6» or «18 crown ether», in the ratio 4-40 Si0₂; Al₂0₃; 1-16 NaOH; 80-400 H₂0; .2-8.0 «18-CROWN-6», by mixing together reactive sources of the different components and thereafter crystallizing at a temperature of below 150°C and preferably in the range 100 to 120°C for at least 48 hours and usually for more than one week. The crystalline product is then separated from the mother liquor by centhfuging or filtering and is thereafter dried. From the literature, it is known that when carrying out a corresponding synthesis without the addition of 18-CROWN-6, the product will be the Y zeolite or a different zeolite such as e.g. gismondine; with the synthesis carried out according to prior art techniques, if the ratio of 18-CROWN-6 to Al₂0₃ is lower than .2, the product will be a pure Y zeolite or a mixture of a Y zeolite with different zeolites other than the hexagonal faujasites.

In addition to the pure cubic faujasite and the pure hexagonal faujasite, a number of different crystal mixtures are known consisting of more or less inter- grown domains of a hexagonal and cubic structure. Each of the said compounds is characterized partly by the way in which it was prepared and frequently by using an organic additive that is different from what is used in the preparation of other similar materials, and partly by their characteristic X-ray diffractograms and optionally by other characteristics. A characteristic of great importance is the crystal size and to a certain degree the form of the crystal; said characteristics depending i.a. on the synthesis conditions and reagents and on the way in which the different phases grown together. Thus, it is quite possible for two compounds having similar X-ray diffractograms to be quite different with regard to their catalytic and adsorbent characteristics. A lot of examples are known of e.g. a crystalline compound with small crystals being a better catalyst than a corresponding compound consisting of large crystals. Examples of compounds belonging to the faujasite family and comprising cubic as well as hexagonal components are: ECR-30, as disclosed in EP 0,315,461 A2; ZSM-20, as disclosed in US Patent 3,972,983; ZSM-3, as disclosed in US Patent 3,415,736; and CSZ-1 , as disclosed in GB 2,076,793A. The hexagonal faujasite EMC-2 is a member of the faujasite family of zeolites having a close relationship with the zeolites Y, ECR- 30, ECR-32, ZSM-3, ZSM-20, CSZ-1. A common feature of the said compounds is their identical X-ray reflections in an X-ray diffraction characterization. However, the different reflections have mutually different intensities, reflecting differing ratios of the hexagonal and cubic components and also reflecting the sizes of the domains comprising a pure hexagonal and a pure cubic component, respectively. With X-ray diffraction characterization, the intensity ratio of the 15 A reflection to the 14 A reflection is an important indicator for distinguishing the different compounds from each other, since the 15 A reflection only occurs with the hexagonal component, whereas the 14 A reflection occurs with both components (the 15 A reflection denotes the reflection occuring with a hexagonal faujasite at 2 theta values of between 5.6 and 5.9; the 14 A reflection denotes the corresponding reflection between 2 theta = 6.0 and 6.2 in accordance with table 1). Unfortunately, no reflection occurs with the cubic component only. However, by considering the ratio of the intensities of the two reflections mentioned, one may get a true picture of the quantitative ratios of the two components, since it is known that in the case of a pure hexagonal faujasite of the type EMC-2, the ratio of the 15 A reflection to the 14 A reflection is about 2.5.

A hexagonal faujasite is a zeolite type which, since first reported in 1989, has been paid great attention because of its high potential as a catalyst in different processes, also having other possible utilities such as e.g. an adsorbent and a ion exchanger. A factor having so far been a bar to the commercial utilization of the hexagonal zeolites, is the high costs of the raw materials for its preparation, especially the costly reagent 18 crown ether. A second factor is the fact that 18 crown ether is regarded to be toxic. Thus, it is desirable to reduce the handling of this chemical as far as possible and at least to such a degree that the mother liquor will contain a minimum concentration of 18 crown ether when separating the zeolite upon completion of the synthesis. o

A method of preparing a hexagonal faujasite of the type EMC-2 in accordance with EP 0,364,352B1 comprises reaction mixtures containing a ratio of 18 crown ether to Al of down to .1. According to the patent examples, however, it is demonstrated that in practice, with the technique according to EP 0,364,352B1 , it is only possible to prepare hexagonal faujasites from reaction mixtures with a ratio of 18 crown ether to Al of down to .25. Admittedly, the preparation of a hexagonal faujasite from reaction mixtures containing a ratio of 18 crown ether to Al of down to .15 has been reported by S.L. Burkett and M.E. Davis in Microporous Materials, 1 (1993), pages 265 to 282, without stating the product purity or yield. It is, moreover, reported by J. Weitkamp, R. Schumacher and U. Weiss, Chem.-lng.-Techn., 64 (1992) 1109, that by reducing the amount of 18 crown ether by 25% as compared with the prior art, a product was obtained having small crystals with a diameter of below 1 micron. However, with a ratio of 18 crown ether to Al of below 0.35, a product was prepared comprising the cubic faujasite. With the present invention, we have now demonstrated that it is possible to prepare the hexagonal faujasitic zeolite with a 18 crown ether to Al ratio of down to .07, yielding a hexagonal faujasite having substantially less than one molecule of 18 crown ether for each of the large cavities of the zeolite structure, as opposed to what is the opinion of people with ordinary skill in the art, i.e. that this is not possible. The said feature is demonstrated by the following calculation:

The unit cell of hexagonal faujasite contains 96 T atoms, i.e. 96 Si and Al atoms in a tetrahedral coordination in the crystal lattice.

* A unit cell further comprises 4 large cavities (supercages).

^* Thus, there are 24 T atoms and 48 oxygen atoms per supercage. ^* According to the literature, the hexagonal faujasite comprises a maximum

Al content corresponding to the formula Na₆AI₆Si₁₈0₄₈ per supercage, with an equivalent weight of 1572.

^* According to the prior art, there is one 18 crown ether molecule with molecular weight 264 in each supercage. ^* The equivalent weight of the structure per supercage containing one 18 crown ether molecule is then 1572 + 264 = 1836. * The 18 crown ether thus represents 14.4% of the weight of dry hexagonal faujasite containing 18 crown ether in its pores.

* The mole ratio of crown ether to Al would then be at least .167 in a dry hexagonal faujasite of the said formula.

From the above, it would appear that a crown ether to Al₂0₃ ratio of .33, corresponding to a 18 crown ether to Al ratio of .167, represents a critical limit. At lower 18 crown ether to Al ratios, there would no longer be one crown ether molecule in each cavity, or a correspondingly lower yield may be obtained of the product with one crown ether molecule in each supercage. EP 0,364,352B1 claims (claim 2) the protection of a hexagonal faujasite prepared from reaction mixtures having a 18 crown ether to Al ratio of down to .1 (corresponding to a 18 crown ether to Al₂0₃ ratio of down to .2), without any basis in the examples. However, the examples do not demonstrate the preparation of hexagonal faujasites with the use of reaction mixtures having a ratio of 18 crown ether to Al of below .25 (corresponding to a 18 crown ether to Al₂0₃ ratio of below .5).

As would appear from the above, a need exists for preparing hexagonal faujasites more economically. Thus, it would be interesting to consider some parameters. The most important parameter would be to reduce the consumption of the most costly reagent, i.e. the 18 crown ether, partly because this will represent immediate cost savings. However, the savings of minimizing the handling of a toxic reagent would perhaps be still more important, especially if the residual solution separated from the crystalline product upon completion of the synthesis does not contain any residue of such reagent. In similar cases, the expenses for the purification of such residual solutions have appeared to represent up to 50% of the total production costs.

The object of the invention has been to prepare a hexagonal faujasite, and more precisely the hexagonal faujasite EMC-2, more economically than was heretofore possible with prior art techniques. This object, together with other objects of the invention, are achieved with the method disclosed below. The invention is further characterized and defined by the accompanying patent claims. The invention disclosed represents a breakthrough with regard to cost reductions in the preparation of hexagonal faujasites, since we have succeeded in preparing a hexagonal faujasite using the most expensive reagent (i.e. the 18 crown ether) in an amount corresponding to a 18 crown ether to Al ratio of .07 in the reaction mixture, as demonstrated in Example 1. A further advantage of the low 18 crown ether requirement, in addition to the savings due to the reduced use of such expensive reagent, is the fact that, in practice, all 18 crown ether added ends up in the pores of the crystalline product. Thus, the spent mother liquor to be discarded would not contain significant amounts of 18 crown ether, such that the destruction or disposal of the liquor would not require the same degree of care as with prior art methods. A still further advantage of the present preparation method is the fact that a hexagonal faujasite is obtained having a substantially smaller crystal size than that obtained with conventional methods. In the art of catalysis, the crystal size of the catalyst is, in many instances, crucial to the economics of a process.

In the preparation of a hexagonal faujasite with a small crystal size, with a low requirement of organic additives, in accordance with the invention, a colloidal silica sol is blended with an alkaline solution of NaOH and NaAI0₂, together with a suitable amount of water. The choice of silica source is critical, since it is not possible according to the invention to use e.g. water glass or solid silica as the silica source, whereas the choice of the aluminum source is not critical, since each aluminum source which may be brought into solution in a strong base is usable. However, NaAI0₂ is the most suitable compound for such purpose, since it is readily soluble. The base content is critical, since such content determines the pH of the solution and thus determines the solubility of Si and Al. It has been proved that a hexagonal faujasite can only be prepared with a small crystal size and with a low requirement of organic additives with the use of NaOH and not with other bases. Further, the water content has also been proved to be critical, determining partly the pH of the solution and thus indirectly the solubility of Si and Al. Following the addition of each of the reagents mentioned, some homogenization is required; however, it has appeared advantageous and adequate to agitate the mixing container for approx. 1 minute following each addition. The same also applies to the addition of the organic additive added in the end of the reaction, which must in any case be the 18 crown ether and must not contain significant amounts of impurities from the preparation process, such as e.g. BF₃.

In accordance with the invention, the ratio of added 18 crown ether to Al must be less than .1. With a ratio of .05 or lower, however, it has not been possible to prepare a pure hexagonal faujasite. Thus, the preferred ratio of the added amount of 18 crown ether to Al is about .07.

When adding the 18 crown ether to the reaction mixture, it has appeared necessary to crush it into a powder prior to the addition. It has, however, appeared unfavourable to add it in a melted form. In order to prepare a hexagonal faujasite with the addition of 18 crown ether to Al in a ratio of below .1 in the reaction mixture, it is essential that the said mixture be made with a composition of the different reagents within relatively narrow limits, such that, on completing the addition of all reagents, the complete reaction mixture (the synthesis gel) would have a compostition, on a molar basis, within the following limits:

10.5-11.5 Si0₂; Al₂0₃; 2-3 Na₂0; 120-160 H₂0; 0.11-0.19 C₁₂H₂₄0₆ It has appeared essential, following the addition of all reagents, that the reaction mixture be kept at room temperature for several hours, preferably for 48 hours or longer, before heating. During this period, during the subsequent heating and during the period wherein the reaction mixture is kept at high temperature, it is essential that the reaction mixture be kept in continuous motion to maintain its homogeneity. Following the addition of all reagents, the reaction mixture is, therefore, kept in a relatively oblong container which is placed on a rotating shaft mounted into an oven, rotating at a sufficient speed to keep the reaction mixture in motion, thereby maintaining its homogeneity. Shaking the mixture or stirring it in a stationary container is not sufficient, since some separation of the reaction mixture cannot be prevented, with solid particles enriched towards the bottom of the container. The most appropriate way for the reaction mixture to be maintained homogeneous is by rotating the container with the mixture «head over». In order to really keep the reaction mixture in a continuous motion, it is thus also essential that the viscosity of the mixture is sufficiently low for such purpose. This is achieved with the reaction mixture having a water content which is not substantially lower than that of the examples. It is also essential that the total mass of the reaction mixture is sufficiently large to be kept in motion. With rotation «head over» and a water content as indicated, the said mass should exceed 10 grams and preferably be above 20 grams. If the container with the reaction mixture is not rotated such as stated above, it would no longer be possible to prepare a pure hexagonal faujasite with the addition of 18 crown ether arriving at a crown ether to Al ratio of less than .1.

After keeping the reaction mixture at room temperature for preferably 48 hours, it is heated by heating the oven comprising the container with the reaction mixture to the crystallization temperature desired. This temperature must be between 80 and 105°C, the preferred temperature being 90 to 95°C. If the said temperature exceeds 105°C, it would no longer be feasible to prepare a pure hexagonal faujasite with the addition of 18 crown ether arriving at a crown ether to Al ratio of less than .1. In order to achieve a total crystallization of the hexagonal faujasite with the addition of 18 crown ether arriving at a crown ether to Al ratio of less than .1 in the reaction mixture, it is essential to keep the mixture at the crystallization temperature for at least 15 days and preferably at least 20 days. However, slightly shorter periods would be possible by maintaining the alkali content and the crystallization temperature in the upper ranges of the intervals as indicated above. After completing the crystallisation, the crystalline product may be recovered in any suitable way, e.g. by centrifuging or filtering. The product is subsequently washed in pure water until free from base or at least until the pH of the washing liquor is at 9 or lower. Thereafter, the product is dried e.g. in a heating cabinet, e.g. at 100°C. In order to obtain a product that may be used as a catalyst or an absorbent, the organic additive entrapped in the pores of the product must be removed. Such removal is preferably carried out by burning in air at a temperature of above 350°C, most preferably at a temperature of 500 to 600°C.

Having demonstrated the preparation of hexagonal faujasites with a ratio of 18 crown ether to Al of essentially below .1 , this is well below what has up to now been documented in the literature and is also outside the composition range claimed in EP 0,364,352B1. Thus, our invention i.a. consists in a synthesis method making it possible to prepare a pure hexagonal faujasite with the addition of 18 crown ether arriving at a crown ether to Al ratio of substantially below .1. This is surprising, since it implies that the 18 crown ether is not present in each cavity of the hexagonal faujasitic structure, such as has up to now been believed to be essential in order to stabilize the structure of hexagonal faujasites. Different zeolites are usually distinguished by having a set of reflections at certain 2 theta angles in their characteristic X-ray diffractograms, yielding together a characteristic pattern. Thus, X-ray diffraction gives the possibility of identifying or determining semi-quantitatively the contents of different phases of a crystalline material, no other methods being available which are suitable for such identification of crystalline substances in a powder form. The method also gives an approximate measure of the contents of other phases in samples mainly containing e.g. a hexagonal faujasite. It is, however, difficult to quantify a cubic faujasite in a sample mainly comprising hexagonal faujasite, since all X-ray reflections of cubic faujasites are overlapped by hexagonal faujasite reflections. The intensity ratios of different reflections must therefore be considered. In order to determine the ratios expected for a pure hexagonal faujasite and for mixtures of hexagonal and cubic faujasites in different proportions, theoretical X-ray diffractograms have been simulated for different «intergrowths» or mixtures of the two phases, assuming the absence of water, carbon or organic substances in the pores and the absence of a preferred orientation of the crystals in the hypothetic preparation simulated. The programme used in the simulation was «DIFFaX», developed by M.M.J. Treacy, M.W. Deem and J.M. Newsam in 1991. As the basis for the simulation, the common centrosymmetric layer of the two structures was taken as the starting point, together with an ideal pure Si0₂ formulation, combined with the two cubic and the single hexagonal «stacking operations)), the inter- growth of the two layers being assumed to be statistically quite arbitrary. The result of the simulation was that, in ideal conditions such as those discussed above, in the case of a pure EMC-2, the intensity ratio of the 15 A to 14 A reflections would be about 2.5. In practice, however, positive and negative deviations from this ratio may be observed, due to the absence of ideality, the said deviations being in the order of .5 to .6, without having any basis for deciding with certainty whether or not a pure EMC-2 is present. Of course, with the use of this method for the quantification of different phases it is presupposed that the samples analyzed are prepared in such a manner that the crystals do not have a preferable orientation in the preparation.

From the above, it would appear that an X-ray diffraction characterization is fundamental for the identification of different materials of the faujasite family, especially for distinguishing one compound from the other. In order to distinguish different compounds of the faujasite family, the problem is that the reflections of the different phases overlap, i.e. have the same 2 theta values. The different compounds may therefore only be distinguished by varying the ratios of the intensities of different reflections, the so-called 15 A and 14 A reflections and their intensity ratios demonstrating this feature. The zeolitic materials ZSM-3, ASM-20 and EMC-2 have e.g. the same reflections. In the case of ZSM-3, however, the intensity ratio of the 15 A reflection to the 14 A reflection is considerably less than 1. Further, in the case of ZSM-20, the intensity ratio of the 15 A reflection to the 14 A reflection is from .8 to 1.2, whereas, as indicated above, the reflection of EMC-2 would be about 2.5. The said features do not appear from the data represented in European Patent No. 0,364, 352B1 , US Patent 5,098,683 or US Patent 5,393,511 , the said patents stating only an approximate intensity ratio. It appears, however, from the publications: 1) F. Delprato et al., Proc. NATO-workshop 1989. Plenum Press 1989; and 2) F.Delprato, L.Delmotte, J.L.Guth and L.Huve, Zeolites, 10, (1990) 546, revealing the diffractograms of EMC-2 (a hexagonal faujasite). From the said figures, it would appear that the intensity ratio of the 15 A reflection to the 14 A reflection of EMC-2 (a hexagonal faujasite) is about 1.3 to about 1.6, viz. lower than would be expected theoretically. Since, as mentioned, the said values may be taken as an indication of the ratio of cubic to hexagonal faujasite, it would seem as if the products discussed contain a cubic faujasite. There may, however, also be other factors influencing the results, such as e.g. the preferred orientation of the crystals in the prepartions analyzed.

A hexagonal faujasite prepared with a low use of organic additives and with such additive having been burnt away in air, the sample being dry, is characterized i.a. by its X-ray diffractogram comprising reflections with positions and intensities within the limits stated in Table 1 , and further characterized by the so-called 15 A reflection between 2 theta = 5.6 and 5.9 being the strongest of all reflections, there being no other reflections with an intensity of above 55% of the strongest reflection in the range of 2 theta = 3.0 and 11.1 when using a powder X- ray diffraction on the test preparation having non-oriented crystals, a constant slit opening in the appparatus and a Cu-Kα X-ray irradiation.

TABLE 1

2 theta d-spacing (A) l/lo OO

5.6 to 5.9 15.2 to 15.5 100

6.0 to 6.2 14.3 to 14.6 30 to 55

6.4 to 6.6 13.4 to 13.7 10 to 25

8.4 to 8.6 10.3 to 10.5 < 5

9.9 to 10.2 8.7 to 8.9 15 to 35

10.8 to 11.1 8.0 to 8.2 5 to 15

A hexagonal faujasite prepared with a low requirement of organic additives is a material with a small crystal size as compared with a hexagonal faujasite prepared according to the prior art, the former product consisting of small crystals with plate configuration having a thickness of below 0.3 microns and a width of below 1.3 microns.

The main feature distinguishing our preparation method from methods described in literature is the rotation of the autoclave in a self-produced rotor during the whole crystallization, ensuring a continuous homogenization of the reaction mixture. To use autoclave rotation in the synthesis of zeolites is known, but the use of such rotation has not been reported in connection with the synthesis of a hexagonal faujasite. In EP 0,364,352B1 it is mentioned that the autoclave can be statitionary or be shaken («agitation») during the period until starting the heating; this is, however, not mentioned with regard to the crystallization itself. In this connection, it is essential that the autoclave is adequately large and the viscosity of the reaction mixture is adequately low such that homogenization can really occur on rotating the autoclave. Such adaptation has been a part of the work making the present invention feasible. We have, moreover, used a special choice of particularly useful reagents. It has also appeared critical to crush the 18 crown ether crystals into a powder until addition to the reaction mixture. Further, it has appeared advantageous to keep the mixture at room temperatur for 48 hours, preferably longer, until starting heating. We have also demonstrated that a hexagonal faujasite prepared with a low requirement of organic additives according to our method has good catalytic qualities in an alkylation, especially in the alkylation of aliphatic compounds, and particularly as a catalyst in the alkylation of iso-butane with 2-butene. The invention is illustrated by the following examples:

EXAMPLE 1

A sample of a hexagonal faujasite with a low organic additive requirement was prepared by first preparing a solution of sodium aluminate and sodium hydroxide in water by adding 21.9 g of water to 4.7 g of NaAI0₂ (Riedel de Haen) and 2.9 g of NaOH (KEBO) and stirring overnight with a magnetic stirrer. This solution was then blended with 54.8 g of 30% silica sol (DuPont Ludox LS30) in a 250 ml plastic bottle and homogenized by shaking the bottle for 1 min. Finally, 0.94 g of 18-CROWN-6 crown ether (Parish) was added and the bottle was again shaken for 1 min. A gel was now formed with the formula, on a molar basis, corresponding to

11 Si0₂; Al₂0₃; 2.7 Na₂0; 136 H₂0; 0.14 C₁₂H₂₄0₆ After mixing, the gel was filled into a Teflon container having an inner volume of 160 ml. The Teflon container with its contents was then placed in a steel autoclave which was mounted in an Al block on a rotating shaft in a kitchen oven wherein the autoclave was rotated «head over». The autoclave was then rotated at a speed of about 12 revolutions per minute for 48 hours at room temperature. The temperature was then set at 90°C, the autoclave being further rotated at this temperature for 4 weeks, whereupon it was removed and its contents were filtered. The solid product was washed several times with distilled water and then dried over night at 100°C. The dry product weight was 18.9 g. A sample of the dried product was analyzed with thermal gravimetry, showing a weight loss of 14% between 20 and 330°C, representing water in the pore structure. Between 330 and 430°C, an additional weight loss of 5.6% was recorded, substantially representing burnt off material from the crown ether. On the basis of the above values, the ratio of crown ether in the structure was determined to be less than 0.5 crown ether molecule per supercage in the structure. This result also shows that, within the measurement inconsistency, all of the 18 crown ether from the reaction mixture is held in the pores of the crystalline product. A second sample of the dried product was thereafter calcined by heating to

550°C for 5 hours in a stream of dry air. The calcined product was analyzed with X-ray diffraction, giving reflections (d-spacing in A) at angles (2-theta) with relative intensities (%l) as set out in Table 2 below.

TABLE 2

2 theta —d— %i

5.738 15.3906 100.00

6.076 14.5344 50.16

6.490 13.6068 13.30

8.450 10.4556 3.38

10.022 8.8185 29.99

10.903 8.1080 11.12

11.781 7.5056 12.32

13.630 6.4914 1.96

14.875 5.9508 3.49

15.460 5.7268 13.30

15.680 5.6469 6.65

16.566 5.3468 3.71

17.034 5.2010 5.23

18.617 4.7622 3.60

20.282 4.3748 9.81

22.001 4.0367 4.58

23.159 3.8374 7.85

23.529 3.7779 9.27

25.679 3.4662 4.80

26.991 3.3007 9.92

28.654 3.1128 3.16

30.725 2.9076 4.80

31.363 2.8499 8.18

34.323 2.6105 2.73

On the basis of the X-ray data according to Table 2, the product was identified as a hexagonal faujasite of the type EMC-2. Chemical analysis with a microprobe showed the calcined sample to comprise 69.3% of Si0₂, 18.2% of Al₂0₃ and 11.9% of Na₂0, corresponding to the formula, on a molar basis, of 6.5 Si0₂; Al₂0₃; 0.54 Na₂O.

The ratio of Si0₂ to Al₂0₃ was also determined with ²⁹Si-nuclear magnetic resonance. With nuclear magnetic resonance, the ratio of Si0₂ to Al₂0₃ is determined in the crystal lattice itself, giving a ratio of 7.1 , which is in acceptable conformity with the result of the microprobe determination.

The micropore volume was determined to .26 ml/g with nitrogen adsorption. This pore volume corresponds to 100% or approx. 100% of a crystalline material, indicating that the sample comprises approx. 100% of a hexagonal faujasite of the type EMC-2. Analysis with scanning electron microscopy reveals that the product consists of crystals in a plate form with the typical dimensions: thickness 0.1 to 0.2 microns, width 0.3 to 1 micron. The total of the analysis results indicate that the sample contains approx. 100% of a hexagonal faujasite of the type EMC-2 with an adequate crystallinity and small crystals. 5

EXAMPLE 2

A further sample of the hexagonal faujasitic zeolite was prepared according to the same formula as for Example 1 , however, with all amounts scaled down by 60% and with the addition of 3 g of extra water. After mixing, the reaction mixture o was filled into a Teflon container with an inner volume of 60 ml, whereupon the Teflon container with its contents were placed in a steel autoclave. The further handling was as described for Example 1 , however, the crystallization period was extended to 37 days. Thereafter, a sample was removed, filtered and washed several times with distilled water and then dried overnight at 100°C. 5 The dried product was then calcined by heating at 550°C for 5 hours in a stream of dry air. The calcined product was analyzed with X-ray diffraction, giving reflections at angles and with relative intensities as set out in Table 3 below. TABLE 3

2 theta ___d— %i

5.754 15.3479 100.00

6.086 14.5114 43.54

6.500 13.5879 12.48

10.044 8.7995 20.32

10.926 8.0911 11.32

11.835 7.4716 9.87

14.965 5.9151 3.19

15.480 5.7195 13.06

15.720 5.6326 6.68

17.029 5.2024 6.53

18.659 4.7516 4.50

20.326 4.3655 9.43

22.039 4.0299 6.24

23.200 3.8307 10.30

23.561 3.7728 11.18

24.540 3.6245 4.50

27.027 3.2964 9.29

28.622 3.1162 3.77

30.801 2.9005 6.24

31.130 2.8706 7.26

31.407 2.8460 6.82

33.703 2.6572 3.77

34.492 2.5982 3.77

39.165 2.2982 2.61

On the basis of the X-ray data of Table 3, the product was identified as a hexagonal faujasite of the type EMC-2. The micropore volume was determined to be 0.27 ml/g with nitrogen adsorption. This pore volume is in conformity with 100% or approx. 100% of crystalline materiale, indicating that the sample contains approx. 100% of a hexagonal faujasite of the type EMC-2.

Analysis with scanning electron microscopy reveals that the product consists of crystals with a plate configuration, having the typical dimensions: thickness .1 to .2 microns, width .4 to 1.2 microns. The total analysis results indicate that the sample contains approx. 100% of a hexagonal faujasite of the type EMC-2 with an adequate crystallinity and small crystals.

EXAMPLE 3 A further sample of the hexagonal faujasitic zeolite was prepared according to the same formula as for Example 1 , the reaction mixture being diluted with 8 g of extra water.

Following 8 days of crystallization at 90°C, a sample was removed, washed, filtered and dried at 100°C overnight. The dried product was then calcined by heating at 550°C for 5 hours in a stream of dry air. The calcined product was analyzed with X-ray diffraction, giving reflections at angles and with relative intensities as indicated in Table 4 below.

TABLE 4

2 theta —d— %i

5.794 15.2409 100.00

6.135 14.3942 30.66

6.555 13.4737 12.73

10.112 8.7407 19.78

10.969 8.0595 10.88

11.862 7.4543 8.53

13.812 6.4062 3.09

15.002 5.9006 2.97

15.513 5.7073 11.25

15.814 5.5994 6.43

17.131 5.1717 4.70

18.686 4.7448 3.58

20.367 4.3568 9.02

22.110 4.0171 10.38

23.613 3.7646 8.90

24.690 3.6029 4.33

25.717 3.4613 3.71

26.463 3.3653 3.71

27.092 3.2886 6.30

28.673 3.1108 4.45

29.678 3.0077 2.84

30.841 2.8968 5.56

31.163 2.8676 7.05

On the basis of the X-ray data of Table 4, the product was identified as a hexagonal faujasite of the type EMC-2. The micropore volume was determined to .28 ml/g with nitrogen adsorption. This pore volume is in conformity with 100% or approx. 100% of a crystalline material, indicating that the sample contains approx. 100% of a hexagonal faujasite of the type EMC-2. Analysis with scanning electron microscopy showed the product to be comprised of crystals having plate configuration with the typical dimensions of: thickness .1 to .2 microns, width .2 to 1 micron. The total analysis results indicate that the sample contains approx. 100% of a hexagonal faujasite of the type EMC- 2, with an adequate crystallinity and small crystals.

EXAMPLE 4

A further sample of the hexagonal faujasitic zeolite was prepared by first preparing a solution of sodium aluminate and sodium hydroxide in water by adding 29.8 g of water to 3.63 g of NaAI0₂ (Riedel de Haen) and 2.58 g of NaOH (KEBO), stirring overnight with a magnetic stirrer. This solution was then blended with 42,1 g of 30% silica sol (DuPont Ludox LS30) in a 250 ml plastic bottle and homogenized by shaking the bottle for 1 min. Finally, 1.008 g of 18-CROWN-6 crown ether (Parish) was added, shaking the bottle again for 1 min. A gel was now formed having the formula, on a molar basis, of

10.9 Si0₂; Al₂0₃; 2.93 Na₂0; 153 H₂0; 0.198 C₁₂H₂₄0₆ After mixing, the gel was filled into a Teflon container having an inner volume of 160 ml. The Teflon container with its contents was then placed in a steel autoclave which was mounted into an Al block on a rotating shaft in a kitchen oven. The autoclave was then rotated at about 12 rev./min. for 53 hours at room temperature. Thereafter, the temperature was set at 100°C and the autoclave was rotated further at this temperature for 16 days, whereupon it was removed and its contents filtered. The solid product was washed several times with distilled water and then dried overnight at 100°C. The dry product weight was 14.7 g. The dried product was then calcined by heating at 550°C for 5 hours in a stream of dry air. A sample was then analyzed with X-ray diffraction, giving reflections at angles and with relative intensities as shown in Table 5 below. TABLE 5

2 theta _._d— %i

5.802 15.2210 100.00

6.142 14.3773 54.46

6.537 13.5106 11.74

10.100 8.7510 32.28

10.967 8.0606 11.74

11.680 7.5703 7.39

11.855 7.4588 14.44

14.960 5.9172 3.99

15.517 5.7060 13.97

15.720 5.6326 9.39

17.087 5.1848 4.69

18.645 4.7551 3.64

20.357 4.3590 8.22

22.107 4.0177 4.34

22.737 3.9076 4.23

23.233 3.8254 6.81

23.619 3.7637 7.63

25.715 3.4616 3.05

27.070 3.2912 8.69

28.690 3.1089 2.70

20.706 3.0049 2.23

30.797 2.9009 6.57

31.118 2.8717 6.34

31.443 2.8428 7.16

34.400 2.6048 3.05

38.018 2.3649 2.35

The results show that this sample essentially consists of a hexagonal faujasite of the type EMC-2, further containing traces of Y zeolite and Gmelinite. EXAMPLE 5 (Comparative Example)

In an attempt to prepare the hexagonal faujasitic zeolite according to European Patent No. 0,364, 352B1 with a 18 crown ether to Al₂0₃ ratio of 1.0, a solution was prepared of sodium aluminate and sodium hydroxide in water, by adding 25.5 g of water to 4.0 g of NaAI0₂ (Riedel de Haen) and 2.5 g of NaOH (KEBO), stirring overnight with a magnetic stirrer. This solution was then blended with 45.7 g of 30% silica sol (DuPont Ludox LS30) in a 250 ml plastic bottle and homogenized by shaking the bottle for 1 min. Finally, 6,1 g of 18-CROWN-6 crown ether (Parish) was added, and the bottle was again shaken for 1 min. A gel was now formed with the formula, on a molar basis, of:

10 Si0₂; Al₂0₃; 2.3 Na₂0; 140 H₂0; 1.0 C₁₂H₂₄0₆ After mixing, the gel was filled into a Teflon container having an inner volume of 160 ml. The Teflon container with its contents was then placed in a steel autoclave which was mounted in a stationary heating block made of Al, wherein the autoclave was held for 20 hours at room temperature. The temperature was then set at 100°C, the autoclave being further kept at this temperature for 8 days, whereupon a sample was withdrawn and filtered. The sample was washed several times with distilled water and then dried overnight at 100°C. The dried sample was analyzed with X-ray diffraction, giving reflections characteristic of a hexagonal faujasite with relatively low intensities, indicating that the crystallization of the sample was not complete. The residue of the synthesis mixture was further crystallized for 1 week, whereupon it was filtered, washed and dried and then calcined at 550°C in air. The calcined sample was analyzed with X- ray diffraction, giving reflections at angles and with relative intensities as shown in Table 6 below. TABLE 6

2 theta —d— %i

5.815 15.1856 100.00

6.191 14.2648 50.45

6.599 14.3839 37.09

10.122 8.7315 17.21

11.006 8.0323 25.52

11.885 7.4404 22.85

13.241 6.6810 3.26

15.523 5.7037 14.24

15.822 5.5966 12.46

16.699 5.3046 9.20

17.139 5.1695 19.88

18.129 4.8893 10.09

18.681 4.7459 14.24

19.668 4.5100 10.98

19.947 4.4476 15.13

20.341 4.3622 24.93

22.121 4.0152 12.17

22.721 3.9104 8.61

23.222 3.8272 17.51

24.675 3.6050 13.65

25.794 3.4511 8.31

26.466 3.3650 8.01

27.060 3.2924 16.91

28.694 3.1086 9.79

31.048 2.8780 18.99

31.524 2.8356 9.20

32.211 2.7767 9.50

The X-ray data shown in Table 6 demonstrate that the synthesis product was a hexagonal faujasite as disclosed in European Patent No 0.364.352 B1. Chemical analyzes with microprobe showed a Si:AI ratio of the product of 3.9, the nitrogen adsorption showing a micropore volume of .27 ml/g. Analysis with scanning electron microscopy showed the product to consist of crystals with plate configuration, having the typical dimensions as follows: thickness .6 to .8 microns, width 3 to 4 microns. The total analysis results shows the sample to contain approx. 100% of a hexagonal faujasite of the type EMC-2, with an adequate crystallinity and relatively large crystals.

EXAMPLE 6 (Comparative Example) In an attempt to prepare the hexagonal faujasitic zeolite according to

European Patent No. 0.364.352B1 , the same method was used as that of Example 5, with the exception that the amount of 18 crown ether added was reduced to one third, the ratio of 18 crwon ether to Al₂0₃ thus being .33. Thus, the composition of the synthetis mixture was then, on a molar basis: 10 Si0₂; Al₂0₃; 2.4 Na₂0; 140 H₂0; .33 C₁₂H₂₄0₆

After mixing, the gel was filled into a Teflon container having an inner volume of 160 ml. The Teflon container with its contents were then placed in a steel autoclave which was mounted in a stationary heating block made of Al, and left for 20 hours at room temperature. The temperature was then set at 110°C and the autoclave was kept at this temperature for 8 days, whereupon a sample was withdrawn and filtered. The solid product was washed several times with distilled water and then dried overnight at 100°C.

The dried sample was analyzed with X-ray diffraction, giving reflections characteristic of a hexagonal cubic faujasite (Y zeolite) with low intensities, indicating that the sample was only partly crystallized.

The remainder of the synthesis mixture was further crystallized for 1 week, whereupon a new sample was withdrawn and treated as above. The sample was then analyzed with X-ray diffraction, giving reflections at angles and with relative intensities as set out in Table 7 below. _2g

TABLE 7

2 theta ___d— %!

5.823 15.1641 34.38

6.123 14.4233 100.00

6.526 13.5330 13.25

10.086 8.7631 13.25

11.842 7.4669 40.69

12.417 7.1227 6.94

12.821 6.8989 5.36

15.599 5.6759 29.02

17.127 5.1731 5.05

18.652 4.7534 21.45

20.322 4.3663 39.12

22.767 3.9026 8.52

23.602 3.7665 41.64

25.740 3.4583 9.46

27.031 3.2959 28.71

27.760 3.2110 7.89

29.624 3.0131 6.94

30.739 2.9062 18.93

31.391 2.8473 29.34

32.449 2.7569 8.52

34.103 2.6269 10.73

34.680 2.5845 7.57

The X-ray data of Table 7 reveal that the synthesis product consisted of a mixture of mainly a Y zeolite and minor parts of a hexagonal faujasite and the gmelinite and gismondine zeolites. Thus, it is demonstrated that the preparation method as disclosed in European Patent No. 0.364.352 B1 in stationary conditions does not work with a low 18 crown ether content in the synthesis gel.

In order to investigate whether the portion of hexagonal faujasite would increase with a longer crystallization period, the remainder of the gel was further crystallized, withdrawing samples of the contents after 23 and 33 days. The results indicated that the Y zeolite continued to be the main component and that the portion of hexagonal faujasite did not increase with time.

EXAMPLE 7 (Comparative Example)

A synthesis was carried out precisely as in Example 6, with the exception of the autoclave being rotated in our self-produced rotor at 12 rev./min. On the basis of X-ray diffraction analysis of samples taken after 8 and 15 days, respectively, the samples were identified to consist of a hexagonal faujasitic zeolite, illustrating, as compared with Example 6, the importance of the synthesis mixture being continuously homogenized by rotating the autoclave «head over» throughout the crystallization period.

EXAMPLE 8 10 g of the hexagonal faujasitic zeolite prepared according to Example 1 were calcined in air at 550°C for 5 hours. It was then ion exchanged with lanthanum by ion exchanging the zeolite with La(N0₃)₃ according to a standard method described in literature, by keeping the zeolite in suspension in distilled water, adding dropwise a La(N0₃)₃ solution while stirring the suspension with magnetic stirrer.

Thus, the hexagonal faujasitic zeolite is ion exchanged to a La content of 40%, defined as (atomic % of La)/(atomic % of Al/2.5)^*100% based on the hypothesis of each La atom having an average charge of +2.5.

The alkylation of isobutane/2-butene with the use of the above ion exchanged hexagonal faujasitic zeolite as a catalyst was carried out in a 300 ml liquid phase semi-batch stirring autoclave. 5.3 g of ion exchanged and calcined (at 450°C) catalyst were filled into the reactor and dried until adding 227 ml isobutane. The mixture was heated to 80°C under a N₂ pressure of 0.5 MPa. 20 ml of 2-butene were then added, with a feeding rate of .167 ml/min, the addition of 2- butene ceasing after 120 minutes. The mixture was stirred at 1200 rev./min. The hydrocarbon content of the reactor was analyzed at 30 minutes intervals, the results being shown in Table 8. TABLE 8

YTime 120 min. 150 min. 210 min. 240 min. 270 min. selectivity 1.6 1.9 2.1 1.8 1.5 yield 1.2 1.4 1.5 1.4 1.2

2-butene 77 76 73 77 79 conversion

The times stated are the times taken from the start of the experiment. The selectivity is defined as grams of C₅-C₈ paraffins per gram of 2 butene reacted. The yield is defined as grams of C₅-C₈ paraffins per gram of 2 butene added and the 2-butene conversion as the weight percent of butene reacted, based on the total amount added.

The results as shown in Table 8 demonstrate that a hexagonal faujasite with a low requirement of organic additives is useful as a catalyst in the alkylation of isobutane with 2-butene.

Claims

1. A method for the preparation of a hexagonal faujasite in the form of small crystals having a platelet configuration, with a thickness of less than .3 microns and a width of less than 1.3 microns, characterized by adding to a reaction mixture comprising Si0₂, Al₂0₃ and Na₂0, an amount of 18 crown ether to achieve a molar ratio of 18 crown ether to Al of .05 to .1 , thereafter keeping the mixture at room temperature for 1 to 3 days and then at a temperature of 80 to 105°C for at least 15 days, rotating the container during the whole period, whereupon the crystalline product formed is recovered in an appropriate way.

2. The method according to claim 1 , characterized by using a reaction mixture with the composition, on a molar basis, of

10.5-11.5 Si0₂; Al₂0₃; 2-3 Na₂0; 120-160 H₂0; 0.11-0.199 C₁₂H₂₄0₆ wherein C₁₂H₂₄0₆ is added in the form of 18 crown ether.

3. The method according to claims 1 or 2, characterized by carrying out the rotation by placing the reaction mixture in an oblong container or an autoclave mounted into an oven, which is rotated «head over» at a speed sufficient to keep the synthesis mixture in continuous motion.

4. The method according to any one of claims 1 to 3, characterized by carrying out the mixing of the starting materials by blending a colloidal silica sol with a solution of NaOH and NaAI0₂ and water, and then adding the 18 crown ether.

5. The use of a hexagonal faujasite prepared according to any one of claims 1 to 4 as an alkylation catalyst, especially in the alkylation of aliphatic compounds, particularly as a catalyst in the alkylation of iso-butane with 2-butene.