ZEOLITES AND PROCESSES FOR THEIR MANUFACTURE

Abstract: Low temperature hydrothermal treatment of an LTL zeolite-producing mixture produces a colloidal suspension of the zeolite, the suspension may be used as seeds in Al- and Ga-LTL zeolite manufacture.

Description: "Zeolites & Processes for their Manufacture" This invention relates to zeolites of structure type LTL, to processes for the manufacture of such zeolites, and to the use of the zeolites as catalysts and catalyst bases. The zeolites have a 12 membered ring structure with pore dimensions of 0.55 to 0.72 nm. An example of a zeolite of LTL structure type is zeolite L, and processes for the manufacture of zeolite L are described in U.S. Patent No. 3216789, EP-A-219354, and EP-A-595465, the disclosures of all of which are incorporated by reference herein. The two European patent applications, which have extensive prior art discussions to which the reader is referred for more background, and the U.S. Patent list the significant X- ray diffraction data for crystalline zeolite L and give its formula in terms of moles of oxides as 0.9 to 1.3 M 2 / n O:Al 2 0 3 :5.2 to 6.9 Si0 2 :yH 2 0, where M represents an exchangeable cation of valence n, and y represents a value within the range of from 0 to about 9. In Proceedings of the 9th International Zeolite Conference, Ed. von Ball oos et a_l, 1993, p. 297, Xianping Meng et al describe the effect of varying crystallization conditions and reactant ratios on a process for the manufacture of ultrafine (particle size about 30 nm) zeolite L. Products of such a small particle size have advantages over larger particle size products, such as those produced by the procedure of U.S. Patent No. 3216789, when used as a catalyst, or catalyst base, for reactions involving hydrocarbon conversions because of their enhanced ratio of surface area to mass, high diffusion rates and reactivities, and resistance to deactivation by pore plugging and surface contamination. For similar reasons they have advantages in hydrocarbon separations, and are also valuable as starting materials in the manufacture of supported zeolite layers, especially membranes, as described in WO 94/25151, the disclosure of which is also incorporated herein by reference. For the latter purpose, a zeolite having a particle size, whether in the form of agglomerates or single crystals, of at most 100 nm, and advantageously at most 75 nm, is normally required since the zeolite layer is formed by deposition from a colloidal suspension onto a support; if for any reason the suspension is not stable it is unsuitable for the purpose. Although EP-A-595465 describes the product of the inventive process, in which ammonia is used as a co-solvent to water in the zeolite synthesis mixture, as being in mono-crystalline form, and refers to carrying out the hydrothermal treatment at a temperature in the range of 70 to 160°C to yield a product having crystallites of diameter less than about 30 nm, it appears from the description and micrograph in the Application that the product consists of larger agglomerates of the nanocrystals incapable of forming a colloidal suspension. The same is true of the product of EP-A-323893, the small crystallites of which agglomerate into readily recoverable particles (page 2, lines 31 to 33) . It has now surprisingly been found that if a synthesis mixture as described in U.S. Patent No. 3216789 is subjected to heat treatment at a temperature below 100°C a colloidal suspension of zeolite results. The present invention accordingly provides a process for the manufacture of a colloidal suspension of an LTL zeolite, wherein a synthesis mixture having a composition, given in terms of molar proportions with the solid components being calculated in terms of their oxides, in the ranges: K 2 0/(K 2 0 + Na 2 0) from 0.33 to 1:1 (K 2 0 + Na 2 0)/Si0 2 from 0.35 to 0.5:1 Si0 2 /Al 2 0 3 from 10 to 40:1 solvent/ (K 2 0 + Na 2 0) from 15 to 25:1 is subjected to thermal treatment at a temperature below 100°C for a time sufficient to form a colloidal suspension of an LTL zeolite for the solvent. Advantageously, the SiO 2 /Al 2 0 3 ratio is at least 12:1, and advantageously the ratio is at most 28:1. Advantageously, the solvent is water, but the presence of a co-solvent, e.g., ammonia, is not excluded, in which case its molar proportion is included in the specified range. The invention further provides a process for the manufacture of an LTL zeolite of particle size at most 100 nm, wherein the colloidal suspension prepared as described above is washed with water to a pH within the range of 9 to 12, advantageously 10 to 11, and if desired cation exchanged, dried and, if desired, calcined. Advantageously, the resulting zeolite is one having a composition of Formula I 0.9 to 1.3 M 2 / n O:Al 2 0 3 :5.2 to 6.9 Si0 2 I wherein M is an exchangeable cation of valence n. The process of the invention provides either individual crystals or agglomerates which form a colloidal suspension, i.e., the suspension produced directly, or by washing, is a stable one. A stable suspension is one in which settlement does not take place, or one in which any settlement that takes place does so so slowly as to be insignificant over the relevant timescale. Such a suspension is referred to herein aε colloidal. As described above, the zeolites of the invention are primarily aluminosilicates, and will be described herein as such. It is, however, within the scope of the invention to replace aluminium, wholly or partly, with gallium, and partly with boron, iron or other trivalent elements, and silicon may similarly be replaced by germanium or phosphorus. It is also within the scope of the invention to include cations other than potassium and εodium in the synthesis mixture. The sources of the various elements required in the final product may be any of those in commercial use or described in the literature, as may the preparation of the syntheεis mixture. For example, the source of silicon may be a silicate, e.g., an alkali metal silicate, or a tetraalkyl orthosilicate, but there is preferably used an aqueouε colloidal εuεpension of silica, for example one sold by E.I. du Pont de Nemours under the trade name Ludox. Ludox HS-40 is a sodium-containing product, while AS-40 contains very little sodium. The source of aluminium is preferably A1 2 0 3 .3H 2 0, dissolved in alkali. Other aluminium sources include, for example, a water-soluble aluminium salt, e.g., aluminium sulphate, or an alkoxide, e.g., aluminium isopropoxide. The potaεsium source is advantageously potassium hydroxide and the sodium source, if present, is advantageously also the hydroxide. The synthesis mixture is conveniently prepared by mixing two solutionε, one containing the potaεsium and aluminium sources, and the other the silica source, each containing water in a quantity such that, on mixing, the required molar proportions result. Crystallization is effected, either under static conditions or with moderate stirring, and, if desired, under reflux. Thermal treatment (also known as ageing at elevated temperature) at a temperature in the range of from 40 to 97°C is convenient; advantageously from 40 to 95°C and preferably from 40 to 85°C. Although crystallization times are normally described in the prior art aε being longer at lower temperatureε, it has been surprisingly found that, while times from 48 to 500 hours may be used, even at temperatures at the lower end of the present range, times up to 84 hours may suffice. A lower temperature in general gives a smaller particle size zeolite, if other conditions remain constant. By appropriate choice of temperature, agglomerateε of greateεt dimensions in the range of 25 nm to 100 nm may be obtained, with good uniformity of particle sizes. The synthesis mixture may, if desired, be aged at a temperature below that at which crystallization takes place, i.e., at a temperature less than 40°C, for example for up to 2 days. Including this low temperature ageing generally results in a smaller crystallite size, compared with an otherwise similar procedure omitting it. The colloidal suspension, or the crystals obtainable from the suspension, produced by the procesεes described above may be used in a number of applications including the manufacture of thin films on substrates, in which application the crystals may provide a growth-enhancing layer, or as the baεe of the film itself, for example by multiple in-situ crystallization. More especially, however, according to the present invention, the nanometric sized zeolite L particleε may be uεed as seeds in the manufacture of zeolite L. As noted in U.S. Patent No. 3216789, if a synthesis mixture has a composition falling outside a certain range it tends to produce a zeolite other than zeolite L, zeolite L contaminated with other zeolites or with amorphous material, or an amorphous product only. For example, too low an alkalinity results in zeolite W formation, or in zeolite L contaminated with zeolite W. It has previously been proposed, in U.S. Patent No. 5330736, to manufacture zeolite L uεing as seeding gel an amorphous aluminosilicate seeding gel which does not contain zeolite L. The gel is stated to be one which, if heated to 100°C on its own would produce zeolite Y. In the patent, a number of earlier U.S. patents are discussed which are stated to mention the possibility of seeding zeolite L-producing synthesis mixtures with zeolite L seeds. Examples 12 and 13 of U.S. Patent No. 4657749, one referred to in Patent No. 5330736, describe a seeding process, in which seedε of an unspecified particle size zeolite L are used. In a comparison example in U.S. Patent No. 5330736, a preformed crystalline zeolite L of unspecified particle size was used to seed a zeolite L-forming synthesis mixture, with a zeolite T-contaminated zeolite L product resulting. It has now been found that colloidal zeolite L εeeds may εuccessfully be used to promote the formation of zeolite L from a synthesis mixture, even if that mixture is one which, in the absence of colloidal seeds, would give a product other than pure zeolite L. In U.S. Patent No. 5,396,009, there is described a procedure for obtaining zeolite L with a very desirable morphology, one in which crystallites are substantially cylindrical with basal planes so shaped that the ratio of the axial length of curved cylindrical surface to the total length of the crystallite is at least 0.9, and in which the aspect ratio of the length to the diameter is preferably at least 0.5. The crystallites typically have a mean diameter in the region of 0.05 to 0.5 μm. The zeolites described in the U.S. Patent are aluminium-based; syntheεes of gallium-based zeoliteε of εimilar morphology using the same procedure have encountered some difficulties. It has now been found that the addition of a colloidal suspension of zeolite L seeds to a gallium- containing zeolite L-forming synthesis mixture yields pure crystalline Ga-LTL zeolite having reduced contamination by, for example, Zeolite W, and a controlled morphology and particle size. Advantageously, the Ga-LTL zeolite contains lesε than 0.2% by weight alumina. The preεent invention accordingly provides gallium- containing LTL zeolite formed of cylindrical crystallites having basal planes so shaped that the ratio of axial length of curved cylindrical surface to the overall axial length of the crystallites is greater than 0.9 and the aspect ratio of length to diameter is at most 0.5. Advantageously the mean length of the crystallites is lesε than 0.6 μm and advantageously the mean diameter is lesε than 1.5 μm. Because of the reduced acidity of a Ga-LTL zeolite compared with an Al-LTL zeolite of correεponding molar compoεition and similar physical characteristicε, the Ga- LTL provides advantages when used as a catalyεt or catalyεt component, e.g., one admixed with a catalyεt metal, in εeveral hydrocarbon conversions, e.g., aromatization. The present invention alεo provideε a procesε for the manufacture of an LTL zeolite which compriseε forming a εyntheεiε mixture having a composition, given in terms of molar proportions with the solid components calculated in terms of their oxides, in the ranges: K 2 0/ (K 2 0 + Na 2 0) from 0.60 to 1:1 (K 2 0 + Na 2 0)/Si0 2 from 0.18 to 0.36:1 Si0 2 /Al 2 0 3 or Ga 2 0 3 from 5 to 18:1 H 2 0/(K 2 0 + Na 2 0) from 25 to 90:1 and also containing seed crystals of an LTL zeolite of particle size at most 100 nm, and εubjecting the seed- containing synthesis mixture to a hydrothermal treatment at a temperature and for a time sufficient to form an LTL zeolite. Advantageouεly, when A1 2 0 3 is uεed the Si0 2 /Al 2 0 3 ratio iε from 5 to 15; when Ga 2 0 3 iε used the ratio is from 5 to 18. Advantageously, the LTL zeolite is zeolite L. The cryεtalliteε of the reεulting LTL zeolite are advantageously in the form of cylinders with basal planes of εuch a shape that the ratio of axial length of curved cylindrical surface (m) to the overall axial length of the crystallite (h) iε greater than 0.9, and preferably approaches 1. (A geometrically perfect cylinder with completely flat basal planes would have m=h, and m/h=l, while any doming or growths on the basal surfaces mean that h is greater than m.) The cylindrical crystallites advantageously have a mean diameter (d) of at least 0.05 μm, preferably at least 0.1 μm. For certain applications of the crystallites, the diameter of the crystallite is advantageouεly from 0.3 to 1.5 μm, preferably 0.4 to 1.0 μm and the length of the crystallite is advantageously from 0.1 to 0.6 μm, preferably 0.1 μm to 0.3 μm. The aεpect ratio (the ratio of the axial length of the cylindrical εurface to the mean diameter d) iε advantageously leεs than 2, preferably less than 1 and most preferably 0.8 or lesε. For certain applications, the crystallites advantageously have a hockey puck shape (aspect ratio 0.2 to 0.5) or coin εhape (aspect ratio less than 0.2) . A particularly advantageous LTL zeolite of the invention comprises crystalliteε in the form of well-defined, smooth-surfaced cylinders with substantially flat basal planes, i.e., they have a m/h ratio of substantially unity. Preferably the LTL zeolite compriεes cylindrical crystallites wherein at least 80%, preferably at leaεt 90%, of the baεal planes are microscopically flat to within 20 nm, and thus do not exhibit spiral step growths thereon. The LTL zeolite of the invention is characterized by its cylindrical morphology. The terms "cylinder" and "cylindrical" are used herein to describe the shape of a cylinder aε defined in solid geometry, i.e., a solid bounded by a surface generated by a line moving parallel to a fixed line so as to cut a fixed plane curve and by two parallel planeε (baεeε) intersecting the surface. The cylinders will generally be circular cylinders, that iε, with circular cross-section, but in the context of the invention the cylinders may also exhibit some flattening of the cylindrical surface such that the cross-section has polygonal, and particularly hexagonal, character - that is to say, iε in the form of a curvilinear hexagon - and the terms "cylinder" and "cylindrical" as used herein include such forms. It has surprisingly been found that the addition in the form of a colloidal suspension of very small proportions of zeolite seeds is effective to promote crystallization of the desired zeolite from the synthesis mixture without contamination with other crystalline zeolite forms or amorphous material. Because of the small proportions of seed crystals necessary, the seed may be aluminium-based zeolite L in the syntheεiε of Ga- LTL without affecting the εubεtantially gallium-based nature of the resulting product. The resulting particles have a narrow particle size distribution, which is advantageous for the intended uses of the zeolite product. The product of EP-A-142347, which is formed by adding to a synthesis mixture a slurry of seeds of particle size too great to form a colloidal suspenεion, compriεeε material with a wide particle size distribution, e.g., about 1 to 3 μm, and contamination with zeolite W. In contrast to the above-mentioned comparative example in U.S. Patent No. 5330736, which employed about 0.5% by weight of seeds, based on the total synthesis mixture, the procesε of the preεent invention iε effective with ppm proportionε of colloidal seeds, e.g., from 0.005% to 0.10% by weight, based on the weight of the total synthesis mixture, advantageously from 0.015% to 0.05%, conveniently about 0.025%. Although it is within the scope of the invention to employ a greater proportion, no technical advantage appears to result. The seeds, prepared conveniently as described above, advantageously have a particle size within the range of from 25 nm to 100 nm, preferably from 60 to 80 nm. As indicated above, the procedure includeε adding the seeds in the form of a colloidal suspension. It is believed that if the colloidal suspension is evaporated to drynesε the reεulting dried εeedε are changed in an adverse way; in any event a product made using dried seeds tends to be contaminated. Hydrothermal treatment is advantageously carried out at a temperature of 100°C to 180°C, preferably from 150°C to 175°C, for a time advantageously within the range of 4 to 200 hours, preferably for from 20 to 80 hours, advantageously under autogenous presεure. It haε surprisingly been found possible to carry out the thermal treatment with stirring. This iε εurpriεing because in the normal synthetic methods for preparing zeolite L from a low alkaline syntheεis mixture εtirring had to be avoided εince its uεe reεulted in the undeεired formation of Zeolite W. While static conditions are acceptable in small scale operations, on an industrial scale stirring is often required for a commercially viable heating regime. The presence of crystalline nucleating agents, especially the colloidal seeds produced by the first aspect of the present invention, makes it possible to produce zeolite L without contamination by zeolite W in a stirred synthesis mixture. The thermal treatment may accordingly be carried out under static conditions or with stirring. The sources of the various components of the synthesis mixture, other than the seeds, may be as described with reference to the first embodiment of the invention, the formation of the colloidal LTL zeolite suspenεion, while the seeds are advantageously the product of the first embodiment of the invention. By using the seeding process of the invention, zeolite L formation is promoted in, for example, synthesis mixtures that are prone to yield zeolite T or W product, i.e., the seeds act as a structure-directing agent. The invention further provides the use, in a process for the hydrothermal treatment of a synthesis mixture for Zeolite L, of a temperature below 100°C to obtain a colloidal suspension of Zeolite L, or to obtain particles of zeolite L having a greatest dimension of at most 100 nm. The invention further provides the use, in the hydrothermal treatment of a zeolite-forming synthesis mixture, of a colloidal suspenεion of seeds of zeolite L, i.e., of seeds having a greatest dimension of at most about 100 nm, to promote the cryεtallization from the syntheεis mixture of a zeolite L-containing product, advantageously a product consisting esεentially of zeolite L, and preferably a pure zeolite L product. Increasing the concentration of colloidal zeolite L seeds reduces the product particle εize if the conditionε are otherwiεe kept conεtant. The zeolite L produced by the εecond aεpect of the invention, if required after washing, cation exchange and/or calcining, is suitable for use as a catalyst in numerous hydrocarbon converεionε or iε effective in hydrocarbon separations or adsorptionε. The zeolite L material may be used, alone or in admixture with other zeolites, in particulate form or in the form of a layer on a εupport, especially as a membrane. Supported layers may be made by the procedures described in International Application WO 94/25151 and WO 96/01683, the disclosureε of which are incorporated herein by reference. More eεpecially, however, the invention provideε a process for the manufacture of a zeolite L-containing structure comprising a substrate and a zeolite L- containing layer, comprising contacting a face of the substrate with a colloidal suspension of zeolite L, i.e., a suεpenεion in which the particle size is at most about 100 nm, to form an intermediate layer, and subsequently forming on the said face a zeolite L-containing layer by crystallization thereon of zeolite L by hydrothermal treatment of a zeolite-forming synthesiε mixture. Advantageously the synthesis mixture is a pourable gel when it is contacted with the treated face of the substrate. The face of the substrate may be pretreated with a barrier layer forming material, e.g., water, before forming the intermediate layer thereon. Alternatively, the face of the substrate may be dry when the dispersion of zeolite L is applied. The invention also provides a structure comprising a substrate, an intermediate layer, and an upper layer, the intermediate layer comprising zeolite L of a particle size of at most 100 nm, the upper layer comprising zeolite L particles, the particles of zeolite in the upper layer having at least one dimension greater than the dimension of the particles of the intermediate layer. Advantageously, the orientation of at least 75% of zeolite L particles is such that the 12-membered ring pores (the c-axis) lie within 30° of the perpendicular to the plane of the layer. Preferably, the orientation of at least 75% of the zeolite L particles in the upper layer is such that the c-axis of the particles lies within 5° of the perpendicular to the plane of the layer. The LTL zeolite of the present invention may be uεed aε a catalyst baεe and may be uεed in combination with a catalytically active metal in a wide variety of hydrocarbon conversion process. Examples of catalytically active metals include Group VIII metals, e.g., platinum and palladium. A particularly advantageous catalyst composition incorporates from 0.1 to 6.0 wt% (based on the total weight of the composition), preferably from 0.1 to 1.5 wt%, platinum or palladium, since thiε gives excellent results in aromatization. From 0.4 to 1.2 wt% platinum is particularly preferred. Accordingly the invention provides a catalyst comprising the LTL zeolite produced by the seeding proceεε of the invention and a catalytically-active metal. There may alεo be incorporated into the catalyst of the invention as a binder one or more materials substantially inert under the conditions in which the catalyst is to be employed. Such binders may also act to improve the resiεtance of the catalyst to temperature, pressure and attrition. Examples of suitable binders include synthetic or naturally occurring inorganic materials, e.g., clays and/or metal oxides, for example, silica, alumina, titania, and/or zirconia. Examples of naturally occurring clays include those of the montmorillonite and kaolin families, which families include the sub-bentonites and the kaolins commonly known as Dixie, McNamee, Georgia and Florida clays or others in which the main mineral constituent is halloysite, kaolinite, dickite, nacrite, or anauxite. Such clays may be used in the raw state, as originally mined or be subjected to calcination, acid treatment, or chemical modification. Other matrix materials which find particular application in the present invention include porous matrix materials, e.g., silica-alumina, silica-magneεia, silica-zirconia, εilica-thoria, εilica-beryllia, and εilica-titania, as well as ternary compositions, e.g., silica-alumina-thoria, silica- alumina-zirconia, εilica-alumina-magnesia, and silica-magnesia-zirconia. A preferred binder compriseε particleε of zeolitic materialε which materials are disclosed in United States Patent 5,486,348 and International Application WO 96/16004, the disclosures of which are incorporated herein by reference. The LTL zeolite of the present invention may be used in hydrocarbon conversions and has low acidity, advantageous in catalytic applications, e.g., aromatization, where low acid site strength is desired. Hydrocarbon conversions include, for example, cracking, reforming, hydrofining, aromatization, alkylation, transalkylation, dealkylation, dehydrogenation, hydrogenation, dewaxing, hydrodewaxing, alcohol conversion, oligomerization, isomerization and hydrocracking. Of especial importance are hydrocyclization and/or isomerization of aliphatic hydrocarbons in which the hydrocarbons are contacted at a temperature of from 370°C to 600°C, preferably 430° to 550°C, with a catalyst comprising zeolite L of the invention, preferably having at least 90% of the exchangeable cations M as alkali metal ions, and incorporating at least one Group VIII metal having dehydrogenating activity, e.g., palladium or platinum, so as to convert at least part of the aliphatic hydrocarbons into aromatic hydrocarbons. The aliphatic hydrocarbons may be straight or branched chain acyclic hydrocarbons, and particularly paraffins, e.g., hexane, although mixtures of hydrocarbons may alεo be uεed, e.g., paraffin fractions containing a range of alkanes possibly with minor amounts of other hydrocarbons. Cycloaliphatic hydrocarbons, e.g., methylcyclopentane, may also be used. In a preferred aspect the feed to a process for preparing aromatic hydrocarbons, and particularly benzene, compriseε hexanes. The temperature of the catalytic reaction may be from 370° to 600°C, preferably 430° to 550°C and preferably pressures in excess of atmospheric are used, for example up to 2000 KPa, more preferably 500 to 1000 KPa. Hydrogen is employed in the formation of aromatic hydrocarbons, preferably with a molar ratio of hydrogen to feed of less than 10. In a further aspect, the present invention provides a method for the dehydrocyclization and/or isomerization of an aliphatic hydrocarbon comprising contacting the hydrocarbon at a temperature in the range of from 370°C to 600°C with a catalyst so as to convert at least part of the hydrocarbon into an aromatic hydrocarbon, the catalyst comprising a catalytically active metal and gallium-containing LTL zeolite formed of cylindrical crystallites having basal planes εo shaped that the ratio of axial length of curved cylindrical surface to the overall axial length of the crystallite iε greater than 0.9. The following examples illustrate the invention. Comparison Example A Example 1 of U.S. Patent No. 3216789 was repeated. The following two solutions were prepared: Solution A parts by weight KOH pellets, 87.4% purity (Baker) 53.17 Al(OH) 3 , 98.5% purity (Alcoa) 8.20 H 2 0, deionized 57.19 The potasεium and aluminium sources were mixed with the water which was boiled until a clear εolution resulted. After cooling to room temperature, any water losε waε corrected. Solution B parts bv weight Si0 2 , Ludox HS40, 40% Si0 2 by weight 155.54 H 2 0, deionized 23.13 Solution A was quantitatively added to Solution B with stirring. The resulting synthesis mixture had a molar composition of 8.0 K 2 O:Al 2 O 3 :20 Siθ 2 :200 H 2 0 A portion of the synthesis mixture was transferred to a glasε liner, which was placed in a stainless steel autoclave. The autoclave was placed in an oven, which was then heated from room temperature to 100°C over a 2 hours period, and maintained at that temperature for 169 hours. After cooling, the autoclave was opened and the contents of the liner were examined. A product had settled on the bottom leaving a clear mother liquor. The product was washed several timeε with water to reach a pH of 10.2, and then dried in an oven. X-ray diffraction (XRD) showed a pattern characteristic of zeolite KL. Scanning electron microscopy (SEM) shows spherical agglomerates with an average size of 125 nm, as shown in Fig. 1. Examples 1 to 3 The procedure of Comparison Example A was followed up to the preparation of the syntheεiε mixture, but various εamples of the resulting mixture were thermally treated at the temperatures and for the times shown in Table 1 below. Crystallization was effected in polypropylene vessels under reflux conditions. The resulting reaction mixtures were washed with water to a pH of between 10 and 11, and kept in the last wash water. Separation of the product from the final waεh waterε waε effected by high speed centrifugation. In Example 3, a sample was taken from the reaction mixture after 68 hours heating. A portion of this εample and of each of the washed slurry products of the completed experiments was dried and used to obtain X-ray diffraction and SEM data. The XRD and SEM results show that the product of Example 3 was the same after 68 hours as after the complete 164 hour treatment. Table 1 Effect of Crystalliz ;ation Temperature on SEM part ;icle size Cryεtallization Particle Temp. Time, XRD Size, nm Example °C hourε by SEM 1 92.5 408 KL - peak α 75 broadening 2 82.5 432 KL - peak « 50 broadening 3a 72.5 68 KL, extremely « 30 3b 72.5 164 weak pattern « 30 The washed reactor slurries of Example 1 to 3 were transferred to plastics containers and left undisturbed for 7 days. The εuεpended KL products showed no tendency to εettle on the container baεeε. All Exampleε 1 to 3 productε εhowed a very weak but still recognizable XRD pattern of KL, with no amorphous halo whose presence would show contamination by amorphous by-products. A TEM micrograph of the Example 3 product is εhown in Fig. 2. The toluene adsorption properties of the products of Examples 1 to 3 were compared with those of a highly crystalline (as shown by XRD) standard KL product. The resultε are εhown in Table 2. Table 2 Toluene Capacity, wt % Material Micropore* Macropore Standard KL 9.95 0.24 Example 1 8.71 13.31 Example 2 10.65 10.10 Example 3 10.35 10.00 * Wt% Toluene abεorbed after 60 minutes desorption with N 2 , 30°C The results confirm the crystallinity of the products of Examples 1 to 3. Their increased macropore capacity indicates that there are small voids between individual nanometer-sized KL particles. Example 4 A syntheεis mixture with the same molar composition as Comparison Example A and Examples 1 to 3 was aged at 97°C for 74 hours. The aged product was washed with water, separated from the waεh water in a high speed centrifuge, again εuεpended in water and centrifuged and again suspended in water, the process being repeated until the pH of the washwater reached 10.8. Inspection of the suspension after overnight standing showed that a very small proportion of the solid content had settled on the bottom of the vessel. XRD of dried solid product showed the characteriεtic pattern of zeolite L. Scanning and tranεmission electron microεcopy indicated a particle size range of 100 to 110 nm. The example shows that 97°C is close to the upper limit at which colloidal KL cryεtals are formed by the procedure according to the invention. Example 5 The following two εolutions were prepared: Solution A parts by weight KOH pellets, 87.4% purity (Baker) 30.31 Al(OH) 3 , 98.5% pellets (Alcoa) 15.84 H 0, deionized 75.58 The potassium and aluminium sources were mixed with the water which was boiled until a clear solution resulted. The solution was cooled to room temperature and water losε made up. Solution B partε by weight Si0 2 , Ludox HS40 150.24 H 2 0, deionized 115.20 Zeolite L εeedε, 75 nm, 5.49 wt % solids in water 1.7884 The water was added to the colloidal silica, and the resulting liquids mixed in a blender. The seed εuspension was added to the blender contentε, and mixed for 30 seconds. Then Solution A was added and mixed for a further 3 minutes, a thickening gel being obtained. The seedε uεed were obtained as described in Example 1. The molar composition of the syntheεiε mixture was: 2.36 K 2 O:Al 2 O 3 :10 Si0 2 :162 H 2 0 with 252 ppm (0.025%) by weight seeds, based on the total weight of mixture. 326.70 g of syntheεis mixture were transferred to a 300 ml stainless steel autoclave, which waε placed in an oven at room temperature. The oven waε heated over the courεe of 4 hours to 175°C and maintained at that temperature for 66 hours. After cooling, the product was washed 5 times with 750 ml of water, to reach a wash water pH of 9.6. The product was dried at 120°C; the yield was 50.9 g. SEM showed a product consisting of cylindrical crystallites with an average length of 0.6 μm, l/d ratio 1.7, with flat basal planes; SEM indicated that the crystal morphology had all the characteristics of a cylindrical KL species. Figs. 3 and 4 εhow SE micrographs at magnifications of 10,000 and 40,000 respectively. Example 6 and Comparison Example B In these examples, the effect of colloidal εeeds on the product of a synthesiε mixture of alkalinity lower than that of Example 5 was examined. Two synthesis mixtures, both of molar composition: 2.10 K 2 O:Al 2 O 3 :10SiO 2 :160 H 2 0 were prepared, that of Example 5 containing in addition 0.075% by weight of seeds produced as described in Example 1, that of Comparison Example B containing no seeds. Both mixtures were hydrothermally treated in stainlesε steel autoclaves for 80 hours at 150°C. The product of Example 6 was excellently crystalline and pure zeolite L, while that of Comparison B consisted mainly of zeolite W and amorphous material. Example 7 A synthesis mixture with a molar composition of 3.14 K 2 O:0.177 Al 2 O 3 :10 Si0 2 : 159 H 2 0 waε prepared. The K 2 0:A1 0 3 ratio of this syntheεiε mixture was such that if hydrothermally treated on its own a zeolite L heavily contaminated with zeolite T and amorphous material would result. The mixture was, however, seeded with 255 ppm (0.025%) by weight 75 nm KL seed crystalε, prepared aε described in Example 1. The mixture was treated for 80 hours at 170°C in a stainleεs steel autoclave, washed with water to pH 9.5, and dried at 120°C. The product was pure zeolite KL. SEM showed a product of disk-εhaped crystals with flat basal planeε ("hockey puck" type cryεtalε) . Figs. 5 and 6 show SE micrographs at magnifications of 10,000 and 40,000 respectively. Example 8 The following two solutions were prepared: Solution A parts by weight KOH pellets, 87.3% purity (Baker) 62.16 Al(OH) 3 , 98.5% (Alcoa) 32.47 H 2 0, deionized 157.00 Solution B parts by weight Si0 2 , Ludox HS40 308.00 H 2 0, deionized 236.21 Colloidal KL seed suεpension 3.67 (75 nm, 5.49 wt.% solids in water) The solutions were prepared and mixed as described in Example 5. The molar composition of the synthesis mixture was: 2.36 K 2 0 : A1 2 0 3 : 10 Si0 2 : 162 H 2 0 with 253 wt. ppm seeds, based on the total weight of the mixture. The εynthesis mixture was transferred to a 1 litre stirred εtainless steel autoclave. The autoclave was heated up over 8 hours to 150°C with stirring at 80 rpm (tip speed « 0.4 M/S). When the temperature reached ~ 150°C the stirring was stopped and the mixture was kept under quiescent conditionε for 60 hourε at this temperature. The product waε washed several times with water to reach a pH of 10.9 and was dried in an oven at 120°C. XRD showed that the product was excellently crystalline KL without any trace of contaminants such as zeolite W. SEM showed that the product consiεted of very uniform εubmicron cylindrical cryεtals with a length of about 0.4 μm and with flat basal planes. The X-ray diffractogram is given in μm in Fig. 7; SEM micrographs at 10,000X and 40,000X are εhown in Figs. 8 and 9. Comparison Example C This example describes a procedure in accordance with U.S. Patent No. 5,396,009, making gallium-LTL from a syntheεis mixture containing 50 weight ppm of Mg 2+ species. Solution A - potassium gallate solution Component No. Purity Parts by wt. Supplier KOH pellets 1 87.4% 33.34 J.T. Baker Ga 2 0 3 2 99.999% 12.18 Ingal H 0 3 deionized 99.99 Components 1 and 2 were disεolved in 3 with boiling until clear. The solution waε cooled down to room temperature. A portion of component 3 (50.00 parts) was used to transfer the potaεεium gallate εolution quantitatively to the εilicate εolution: Solution B - silicate solution containing 50 wt. ppm Mg 2+ Component No. Puritv Parts by wt. Supplier Ludox HS-40 1 40% Siθ 2 150.29 Du Pont H 2 0 2 D.I. 14.06 Mg 2+ -containling H 2 0 3 Mg 2+ content: 79.49 0.245 mg/g (Mg 2+ -source=Mg(N0 3 ) 2 .6H 2 0) Components 1, 2 and 3 were mixed in a blender for about 2 minutes. The potassium gallate solution (A) was added to the content of the blender. The two solutions were mixed for about 4 minutes. A slightly blueish but clear non gelating mixture waε obtained. The molar composition of the synthesis mixture was: 2.60 K 2 0 : 0.65 Ga 2 0 3 : 10 Si0 2 : 160 H 2 0 The mixture contained 50 wt. ppm Mg 2+ species. 343.96 parts of the synthesis mixture were transferred to a stainless steel autoclave. The autoclave was placed in an oven at room temperature. The oven was heated up to 150°C over 1 hour and kept at this temperature for 39 hours. The product was washed 4 times with 700 parts of water to a pH of 10.4 and was subεequently dried at 120°C for 16 hours. The weight of product obtained was 38.8 parts. According to XRD the product was Gallium LTL slightly contaminated with unreacted gel particles as indicated by the presence of a slight "halo" between 2 theta 20 and 35. SEM confirmed the presence of amorphous material and showed that the particles were large: the diameter was between 1.5 and 3 μm and the length was between 0.7 and 1.0 μm. When Al-LTL crystallizeε in the presence of trace quantities of divalent cations, e.g., Mg 2+ , the particle size and particle εize distribution are very significantly reduced versus the Al-LTL product obtained from the same syntheεiε mixture not containing divalent cations. Comparative Example D The same synthesis mixture as prepared in Example C, but not containing (added) divalent cations and crystallized under the same conditions also gave a large crystal size Ga-LTL contaminated with amorphous material. SEM micrographs of the products obtained in Comparisons C and D are shown in Figs. 10 and 11. Example 9 Synthesis of Ga-LTL in the presence of 50 wt. ppm colloidal LTL seeds. A synthesis mixture with a molar composition of: 2.60 K 2 0 : 0.65 Ga 2 0 3 : 10 Siθ 2 : 160 H 2 0 and containing 50 wt. ppm colloidal LTL seedε was prepared using the same procedure as in Comparison Exampleε C and D. The mixture was crystallized for 39 hours at 150°C. The resulting product was washed several times with water to a pH of 9.6 and was εubεequently dried at 120°C. The product yield (partε product/100 parts gel) was 10.1. XRD showed that the product was excellently crystalline and pure and conεisted of uniform particles with a length of 0.3-0.5 μm and a diameter between 0.5-0.8 μm. The l/d ratio was « 0.6. Example 10 Synthesis of Ga-LTL in the presence of 250 wt. ppm colloidal LTL seeds. A syntheεis mixture with the same molar composition as in Example 9, but containing 250 wt. ppm colloidal seedε, waε cryεtallized in the same way as described in that Example. The resulting product was washed to pH 9.5 and dried at 120°C. The product yield was 10.2. According to XRD the product was excellently crystalline and pure and SEM showed that the product consisted of uniform particles with a length between 0.1 and 0.3 μm and a diameter between 0.2 and 0.5 μm. The l/d ratio was ~ 0.6. The results of Examples 9 and 10 show that colloidal LTL seeds are extremely effective in the formation of Ga- LTL and to control the particle dimensions by adjuεting the εeed level. SEM micrographε of the products obtained in Exampleε 9 and 10 are given in Figs. 12 and 13. Example 11 Synthesis of Ga-LTL from a Ga-enriched synthesis mixture in the presence of 75 wt. ppm seeds. A synthesiε mixture was prepared containing 75 wt. ppm colloidal seeds. In this case the Ga 2 0 3 content of the synthesis mixture was increased by 92% while the alkalinity of the mixture was reduced from K 2 0/Si0 2 = 0.26 to K 2 0/Si0 2 = 0.24. The molar composition was: 2.40 K 2 0 : 1.25 Ga 2 0 3 : 10 Si0 2 : 160 H 2 0 This waε done to inveεtigate the "tolerance" of the syntheεiε to the formation of unwanted zeolite W. The εynthesis mixture was divided between two stainless steel autoclaves. One syntheεiε mixture waε aged for 48 hours at 150°C, while the other was aged for 24 hours at 175 °C. After washing and drying the product yields were for the 150°C synthesis 19.6 and for the 175°C syntheεiε 19.4. According to XRD and SEM the products were excellently crystalline and pure and had an advanced morphology, i.e., microscopically flat baεal planes. X-ray diffractograms and SEM micrographε of both 150°C and 175°C productε are given in Figε. 14 to 17. Examples 12 to 15 In these four examples, various procedures were adopted in the manufacture of supported zeolite-L containing layers. For each example, a porous alpha-alumina diεk was washed for 10 minuteε in n-heptane in an ultraεonic bath, dried for 5 minutes in air, washed for 10 minutes in acetone in the ultrasonic bath and dried in a 50°C oven for 1 hour. The disks for Examples 12 to 14 were then soaked in water for 2 hours under vacuum, and spun-dried for 30 secondε at 4000 r.p.m. This treatment was omitted for Example 15, the disk being kept at 50°C until the next stage. A colloidal εuspension of 75 nm zeolite L seeds was applied dropwise to the surface of the diεks for Examples 13 to 15. The diεks were allowed to stand for 10 seconds with the liquid on the surface and then spun for 30 seconds at 4000 r.p.m. For Examples 13 and 14, the suspenεion contained 9.56% by weight seeds; for Example 15, the concentration waε 0.48% by weight. The seeding step was omitted for Example 12. Synthesiε mixtureε of the following compositions by weight were prepared: Solution A Exs. 12, 13 Exs. 14,15 KOH (Baker, 87.4% purity) 14.47 14.50 Al(OH) 3 (Alcoa) 7.90 7.89 H 2 0, deionized 94.31 94.32 Solution A was prepared as described in Comparison Example A. Solution B Exs. 12, 13 Exs. 14,15 Siθ 2 (Ludox HS40) 75.04 75.00 In each Example, Solution A was quantitatively mixed with Solution B. In Example 13, mixing took place before disk seeding, and so the mixture had time (about 7 minutes) after being poured into an autoclave to become viscous before the Example 12 and 13 disks were immersed; the gel surface was not completely flat. In Examples 14 and 15, the disks were seeded and made ready before the synthesis mixture was made up so when the disks were immersed, treated face down, in the synthesis mixture in the autoclave the gel was still in a pourable state, its surface was flat, and good contact between the seed layer and the gel was achieved. In each Example, the autoclave was heated over 2 hours to 175°C and maintained at that temperature for 24 hours. After allowing the mixture to cool, the autoclave was opened, the supports rinsed with water and washed at 70°C until the conductivity of the washwater was 5 μ Siemens/cm at 70°C (in 200 ml water) and the disks dried at 100°C overnight. Table 3 below summarizes the differences in the procedures used in Examples 12 to 15. Example No. 12 13 14 15 Vacuum immerεion of YES YES YES NO disk in water Seeding (concentration) NO 9.56% 9.56% 0.48% Synthesis mixture gelled YES YES NO NO before disk immerεion The coated diεks were examined by XRD and SEM. XRD showed that in all four cases a layer comprising zeolite L admixed with Zeolite W has grown on the support. When examined by SEM, the product of Example 12 showed a zeolite layer about 30 μm thick. Zeolite L predominates, consiεting of randomly oriented hexagonal cryεtalε with a length between 0.5 and 2.0 μm, l/d ratio about 3. The zeolite W crystals, also randomly oriented throughout the zeolite L layer, are about 30 μm long and 10 μm thick. SEM analysiε of the Example 13 product showed a seed layer of 25 μm thickness on the support, on top of which are deposited first a layer, about 1 to 2 μm thick, of hexagonal Zeolite L crystals, length between 0.5 and 15 μm, l/d ratio about 3, contaminated with Zeolite W crystals, and a second, detachable layer, about 40 μm thick, consisting of large (30 μm x 10 μm) zeolite W crystals embedded in a zeolite L matrix. SEM examination of the Example 14 product did not reveal the seed layer, but a zeolite layer, about 30 μm thick, is formed on a first thin layer (about 2 μm) of zeolite L cryεtalε between 0.5 and 2 μm, l/d ratio about 3, oriented with the c-axis at 60° to 90° to the support surface. The thick zeolite layer is largely zeolite L contaminated with zeolite W. SEM examination of the Example 15 product shows in a large area of the disk a thin layer of zeolite L crystalε (diameter of cross section about 300 nm, l/d ratio about 3) oriented with the c-axis close to 90° to the support surface. (This layer is probably developed from the seed layer, which is not observed.) In some parts of the disk, the layer is overlaid by an easily detachable layer, 30 μm thick, of zeolite L in which large zeolite W crystals are embedded. When subjected to the dye permeation test, Examples 12 to 14 products readily absorbed rhodamine B. The Example 15 product only absorbed the dye at the edge of the disk, indicating that a densely intergrown zeolite layer was formed. Figs. 18 and 19 show the XRD patterns of Examples 14 and 15 products. The εyntheεis mixture in which the disks are immersed may also contain colloidal zeolite L seedε to reduce or avoid zeolite W formation in the layer.

Claims: CLAIMS : 1. A process for the manufacture of a colloidal suspenεion of an LTL zeolite, wherein a synthesis mixture having a composition, given in terms of molar proportions with the solid components being calculated in terms of their oxides, in the rangeε: K 2 0/ (K 2 0 + Na 2 0) from 0.33 to 1:1 (K 2 0 + Na 2 0)/Si0 2 from 0.35 to 0.5:1 Si0 2 /Al 2 0 3 from 10 to 40:1 solvent/ (K 2 0 + Na 2 0) from 15 to 25:1 iε εubjected to thermal treatment at a temperature below 100°C for a time sufficient to form a colloidal suspenεion of an LTL zeolite. 2. A proceεε aε claimed in claim 1, wherein the Si0 2 /Al 2 0 3 ratio iε within the range of from 10 to 28:1. 3. A proceεs as claimed in claim 1, wherein the Si0 2 /Al 0 3 ratio is within the range of from 12 to 28. 4. A process as claimed in any one of claims 1 to 3, wherein thermal treatment is carried out at a temperature within the range of from 40° to 97°C. 5. A procesε as claimed in any one of claims 1 to 4, wherein thermal treatment is carried out for a time within the range of from 48 to 500 hours. 6. A process as claimed in any one of claims 1 to 5, wherein thermal treatment is carried out for a time of at most 84 hours. 7. A proceεs as claimed in any one of claims 1 to 6, wherein the solvent is water. 8. A process as claimed in any one of claims 1 to 7, wherein the colloidal suspension iε washed with water until the wash water has a pH of from 9 to 12, if desired the zeolite is cation exchanged, and if desired calcined. 9. A process as claimed in any one of claims 1 to 7, wherein the resulting zeolite has a composition of the Formula I 0.9 to 1.3 M 2 / n O:Al 2 0 3 :5.2 to 6.9 Si0 2 I wherein M repreεents an exchangeable cation of valence n. 10. Zeolite L of particle size less than 100 nm obtainable, and preferably obtained, by a process as claimed in any one of claims 1 to 9. 11. A process for the manufacture of an LTL zeolite which comprises forming a synthesis mixture having a composition, given in terms of molar proportions with the solid components calculated in terms of their oxides, in the ranges: K 2 0/ (K 2 0 + Na 2 0) from 0.60 to 1:1 (K 2 0 + Na 2 0)/Si0 2 from 0.18 to 0.36:1 Si0 2 /Al 2 0 3 or Ga 2 0 3 from 5 to 18:1 solvent/ (K 2 0 + Na 2 0) from 25 to 90:1 and alεo containing εeed crystals of an LTL zeolite of particle size at most 100 nm, and subjecting the εeed- containing εyntheεiε mixture to a hydrothermal treatment at a temperature and for a time sufficient to form an LTL zeolite. 12. A process as claimed in claim 11, wherein the mixture compriseε aluminum and the Si0 2 /Al 2 0 3 ratio is within the range of from 5 to 15:1. 13. A process as claimed in claim 11, wherein the mixture comprises gallium, and the Si0 2 /Ga 2 0 3 ratio is within the range of from 5 to 18:1. 14. A process as claimed in any one of claims 11 to 13, carried out at a temperature within the range of 100°C to 180°C and/or for a time within the range of from 4 to 200 hourε. 15. A proceεε aε claimed in any one of claimε 11 to 14, wherein from 0.005% to 0.10% by weight of εeeds iε employed, based on the weight of the synthesis mixture. 16. A process aε claimed in any one of claims 11 to 16, wherein the seedε have a particle size within the range of 60 to 80 nm. 17. A procesε as claimed in any one of claims 11 to 16, wherein the solvent is water. 18. A process as claimed in any one of claims 11 to 17, wherein the resulting zeolite is washed with water until the wash water has a pH of from 9 to 12, if desired the zeolite iε cation exchanged, and if desired calcined. 19. A proceεs aε claimed in any one of claimε 11 to 18, which iε carried out with stirring, at least during heating the syntheεiε mixture to the hydrothermal treatment temperature. 20. Zeolite L whenever prepared by a proceεε aε claimed in any one of claimε 11 to 19. 21. The product of claim 20 in the form of a layer on a εupport. 22. The uεe, in a process for the thermal treatment of a synthesis mixture for Zeolite L, of a temperature below 100°C to obtain a colloidal suspension of Zeolite L, or to obtain particles of zeolite L having a greatest dimension of at moεt 100 nm. 23. The uεe, in the hydrothermal treatment of a zeolite-forming synthesiε mixture, of a colloidal εuεpenεion of seeds of zeolite L to promote the crystallization from the syntheεis mixture of a zeolite L-containing product, advantageously a product conεiεting essentially of zeolite L, and preferably a pure zeolite L product. 24. The use of zeolite L obtainable or obtained by the procesε of any one of claims 11 to 18 in particulate or layer form, in hydrocarbon conversion, adεorption or εeparation. 25. Gallium-containing LTL zeolite formed of cylindrical crystallites having basal planes so shaped that the ratio of axial length of curved cylindrical surface to the overall axial length of the crystallites is greater than 0.9 and the aspect ratio of length to diameter is at most 0.5. 26. A process for the manufacture of a zeolite L-containing structure comprising a substrate and a zeolite L-containing layer, comprising applying to a face of the substrate a dispersion of zeolite L of particle size at most 100 nm to form an intermediate layer, and εubεequently forming on the said face a zeolite L- containing layer by crystallization thereon of zeolite L by hydrothermal treatment of a zeolite-forming synthesis mixture. 27. A procesε as claimed in claim 26, wherein the syntheεis mixture is a pourable gel when it is contacted with the said face. 28. A process as claimed in claim 26 or claim 27, wherein the substrate is pretreated with a barrier layer forming material before forming the intermediate layer thereon. 29. A process as claimed in claim 26 or claim 27, wherein the subεtrate iε dry when the diεperεion of zeolite L is applied thereto. 30. A process as claimed in any one of claims 26 to 29, wherein the dispersion of zeolite L has a seed content of at most 1%. 31. A structure comprising a substrate, an intermediate layer, and an upper layer, the intermediate layer comprising zeolite L of a particle size of at most 100 nm, the upper layer comprising zeolite L particles, the particles of zeolite in the upper layer having at least one dimension greater than the dimensions of the particles of the intermediate layer. 32. A structure as claimed in claim 31, wherein the orientation of at least 75% of zeolite L particles iε εuch that the 12-membered ring poreε (the c-axiε) lie within 30° of the perpendicular to the plane of the layer. 33. A εtructure as claimed in claim 32, wherein the orientation of at least 75% of the zeolite L particles in the upper layer is εuch that the c-axiε of the particles lies within 5° of the perpendicular to the plane of the layer. 34. A method for the dehydrocyclization and/or isomerization of an aliphatic hydrocarbon comprising contacting the hydrocarbon at a temperature in the range of from 370°C to 600°C with a catalyst so as to convert at least part of the hydrocarbon into an aromatic hydrocarbon, the catalyεt compriεing a catalytically active metal and gallium-containing LTL zeolite formed of cylindrical crystallites having basal planes so shaped that the ratio of axial length of curved cylindrical εurface to the overall axial length of the crystallite is greater than 0.9. 35. A catalyst compriεing a catalytically active metal and gallium-containing LTL zeolite formed of cylindrical crystallites having basal planes so shaped that the ratio of axial length of curved cylindrical surface to the overall axial length of the cryεtallite is greater than 0.9.

Inventors: ANTHONIS MARC H, MERTENS MACHTELD M, VERDUIJN JOHANNES PETRUS, ANTHONIS, MARC, H., MERTENS, MACHTELD, M., VERDUIJN, JOHANNES, PETRUS
Applicants: ANTHONIS MARC H, EXXON CHEMICAL PATENTS INC, MERTENS MACHTELD M, VERDUIJN JOHANNES PETRUS, ANTHONIS, MARC, H., EXXON CHEMICAL PATENTS INC., MERTENS, MACHTELD, M., VERDUIJN, JOHANNES, PETRUS
Application year: 1996
Main classification: C01B39
IPC codes: B01D71, B01J29, B01J37, C01B39, C07C5