Title of Invention

A METHOD OF PREPARING ZSM-48

Abstract

A method for preparing ZSM-48 which comprises: (c) preparing a reaction mixture comprising a source of silica, a source of trivalent metal oxide, an alkali metal oxide and a directing agent of ethylenediamine in a solvent phase comprising water, and optionally seed crystals; wherein said mixture, in terms of mole ratios, of dftides, has the following composition ranges: Si02/Me203: 100 to 1500, M2/nO/Si02: 0 to 0.2, RN/Si02: 1.0 to 5.0, OH/Si02: 0 to 0.3, and H20/Si02: 10 to 100, wherein Me is trivalent metal, M is akali metal and RN is ethylenediamine, and (d) maintaining said mixture under crystallization conditions until crystals of said ZSM-48 are formed.

Full Text

FORM 2 THE PATENTS ACT 1970 [39 OF 1970] COMPLETE SPECIFICATION [See Section 10] "A METHOD OF PROCESSING" MOBIL OIL CORPORATION, of 3225 Gallows Road, Fairfax, Virginia 22037, United States of America, The following specification particularly describes the nature of the invention and the manner in which it is to be performed :- The present invention relates to a method for preparing ZSM-48. This invention relates to synthesis of ZSM-48 having a new crystal morphology. U.S. Patent No. 4,423,021 to Rollmann et al. describes a method for synthesizing ZSM-48 using a diamine having four to twelve carbons as the directing agent. The composition is described as a crystalline silicate and it includes very little, if any aluminum. U.S. Patent Nos. 4,397,827 and 4,448,675 to Chu also describes method for synthesizing ZSM-48 including very little, if any, aluminum. The synthesis utilizes a mixture of an amine having from two to twelve carbons and tetramethylammonium compound as the directing agent. U.S. Patent No. 5,075,269 to Degnan et al. describes ZSM-48 prepared with an organic linear diquaternary ammonium compound as the directing agent. The crystal morphology is illustrated in Figures 3 and 4 of the patent and is described as having platelet-like crystal morphology at high silica/alumina molar ratios and aggregates of small irregularly shaped crystals at silica/alumina molar ratios below 200. In 5,075,269 this is compared with the crystal morphology of Rollmann et al. (U.S. Patent No. 4,423,021) in Figure 1 and Chu (U.S. Patent No 4,397,827) in Figure 2. Figures 1 and 2 show a rod-like or needle-like crystal morphology which is random and dispersed. ZSM-48 is also described by R. Szostak, Handbook of Molecular Sieves, Van Nostrand Rheinhold, New York 1992, at pp. 551-553. Organic directing agents suitable for the synthesis of ZSM-48 are listed as diquat-6, bis (N-methylpyridyl)ethylinium, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, 1, 4, 8, 11-tetra-aza-undecane, 1, 5, 9, 13-tetra-aza-undecane, 1, 5, 8, 12-tetra-aza-undecane, 1, 3-diaminopropane, n-propylamine/TMA+, hexane-diamine and triethylamine. There is no suggestion of ethylenediamine. In addition, the crystal habit is described therein as bundles of needles and there is no suggestion of radial morphology. Accordingly, the prior art utilizes relatively complex and expensive organics. It is an object of the present invention to overcome disadvantages of the prior art using a less expensive and more readily available directing agent to make ZSM-48. This reduces manufacturing costs and provides a superior ZSM-48 product. According to the present invention there is provided a method for preparing ZSM-48 which comprises: (a) preparing a reaction mixture comprising a source of silica, a source of trivalent metal oxide, an alkali metal oxide and a directing agent of ethylenediamine in a solvent phase comprising water, and optionally seed crystals; wherein said mixture, in terms of mole ratios of oxides, has the following composition ranges: Si02/Me203: 100 to 1500, M2/nO/Si02: 0 to 0.2, RN/Si02: 1.0 to 5.0, OH/Si02: 0 to 0.3, and H20/Si02: 10 to 100, wherein Me is trivalent metal, M is akali metal and RN is ethylenediamine, and (b) maintaining said mixture under crystallization conditions until crystals of said ZSM-48 are formed. The zeolite ZSM-48 prepared by the method of the present invention, while exhibiting the same X-ray characteristics of the conventionally prepared ZSM-48, frequently possesses a surprisingly different crystal morphology. The ZSM-48 of the present invention is less fibrous than many conventionally prepared ZSM-48 crystals. By fibrous is meant crystals in the form of individual rods or needles, whose length is at least 5 and often at least 10 times their diameter. A ZSM-48 prepared with ethylenediamine directing agent can possess a radial aggregate morphology. The resulting morphology can be described as sea urchin-like. ZSM-48 crystals prepared by conventional prior art methods possess a dispersed or bundled rod or needle-like morphology or platelet morphology. The as-synthesized ZSM-48 product is also low in alkali metal ion, and after calcination to remove the organic, advantageously can be used as an acidic catalyst component without ion exchange. The X-ray diffraction pattern of ZSM-48 has the significant lines shown in Table 1 and is further characterized by the fact that it exhibits only a single line within the range of 11.8 + 0.2 Angstrom units. The presence of only a single line at the indicated spacing structurally distinguishes the material from closely related material such as ZSM-12 (U.S. Patent No. 3,832,449) which has a doublet (two lines) at 11.8 ± 0.2 Angstrom units, and high silica ZSM-12 (U.S. Patent No. 4,104,294) which also exhibits a doublet at 11.8 ± 0.2 Angstrom units. TABLE 1 Characteristics Lines of ZSM-48 d(A) Relative Intensity (I/I0) 11.8+/-0.2 W-VS 10.2+/-0.2 W-M 7.2 +/-0.15 W 4.2 +/-0.08 VS 3.9 +/-0.08 VS 3.6 +/- 0.06 W 3.1 +/-0.05 W 2.85+/-0.05 W These values were determined by standard techniques. The radiation was the K-alpha doublet of copper, and a diffractometer equipped with a scintillation counter with a strip chart pen record was used. The peak heights, intensity (I), and the positions as function of 2 times theta, where theta is the Bragg angle, were read from the spectrometer chart. From these, the relative intensities, 100 I/I0, where I0 is the intensity of the strongest line or peak, and d (obs.), the interplanar spacing in A, corresponding to the recorded lines, were calculated. In Table 1 the relative intensities are given in terms of the symbols W for weak, VS for very strong and W-S for weak-to-strong (depending on the cationic form). Ion exchange of the sodium ion with cations reveals substantially the same pattern with some minor shafts in interplanar spacing and variations in relative intensity. Other minor variations can occur depending on the silicon to aluminum ratio of the particular sample, as well as if it has been subjected to thermal treatment. The composition of the as-synthesized ZSM-48 prepared by the method of the present invention can be identified, in terms of moles of anhydrous oxides per 100 moles of silica as follows: (2 to 10) RN: (0 to 1.0)M2O: (0.06 to l)Me203): (100)SiO2. wherein RN is an ethylenediamine, M is at least one alkali metal cation, Me20 is an oxide of a trivalent metal, e.g., aluminum, titanium, iron, chromium, zirconium, vanadium, molybdenum, arsenic, antimony, manganese, gallium, germanium, boron, etc. or combination thereof. The ZSM-48 of the present invention can be prepared from a crystallization reaction mixture containing a source of silica, an alkali metal (M) oxide or source thereof such as sodium silicate, alkali salt or alkali hydroxide, an organic directing agent of ethylenediamine RN, optionally a source of metal oxides Me203 or source thereof such as alumina gel, aluminum sulfate, iron sulfate, zirconyl chloride, gallium oxide, germania, titanyl chloride, boria, vanadia, chromia, molybdena, etc. and a solvent phase which includes water. Suitable alkali metals include, e.g., sodium, lithium, and potassium. The reaction mixture, in terms of mole ratios of oxides, has the following composition ranges: REACTANTS BROAD PREFERRED Si02/Al203 100 to 1500 150 to 500 M/Si02 0 to 0.4 0.001 to 0.10 RN/Si02 1.0 to 5.0 2.0 to 4.0 OH/Si02 0 to 0.3 0.001 to 0.10 H20/Si02 10 to 100 15 to 40 While it is not intended to be bound by theory, it is believed that the organic directing agent should be present in the crystallizing reaction mixture in an amount sufficient to fill the pores of the zeolite as they are being formed. Ethylenediamine is generally an alkaline liquid soluble in water and which, besides acting as an organic directing agent in the method of the present invention, can also be considered to form part of the solvent phase for crystallization, along with water. It is recognized that a fraction of the amine functional groups may be protonated. The amount of ethylenediamine in the solvent phase of the resulting mixture is important in producing a pure ZSM-48 crystal. In general, if the amount of ethylenediamine in the solvent phase is 20 mole percent or above, the resulting crystal will not be a pure ZSM-48 crystal, i.e., the resulting crystal will contain a different crystalline aluminosilicate, such as ZSM-5. Often, if the amount of ethylenediamine in the solvent phase is less than 8 mole %, the resulting crystal will also not be a pure ZSM-48 crystal, i.e., the resulting product is either less than 100% ZSM-48 crystal or simply amorphous. The optimal amount of RN in the solvent phase is particularly dependent on such parameters as Si02/Me203 ratio, the presence of seeds, (usually added at 1-5%, based on silica) and the OH/Si02 ratio. At very high Si02/Me203 ratio, e.g., above 500, less RN is required, and 5 to 10% may be satisfactory. At lower Si02/Me203 ratio, more RN is required, e.g., 8 to 15%. Crystal morphology is also sensitive to variation in these parameters. For example, lower OH/SiO2 ratios, e.g., below 0.05 are particularly preferred in order to obtain the radial aggregate crystal morphology. The crystallization mixture of the present invention has a pH value preferably from 7 to 14, more preferably from 11 to 13. The crystallization mixture of the present invention is maintained at a temperature range of 100 to 200°C, preferably from 140 to 170°C, until crystals of the material are formed, typically from 0.5 hour to two weeks. Thereafter, the ZSM-48 crystals are separated from the liquid and recovered. The resulting ZSM-48 of the present invention has a low alkali metal ion content, typically containing from O to 1.0, and more usuaiiy from 0.05 to 0.5, sodium ions per unit cell and can be used as an active catalyst without ion exchange. However, if desired, the original cations can be replaced, at least in part, by calcination and/or ion exchange with other cations according to techniques well known in the art. Thus, the original cations can be exchanged into a hydrogen or hydrogen ion precursor form such as ammonium or a form in which the original cation has been replaced by cations of rare earth metals, manganese, calcium, as well as metals of Groups II through VIII of the Periodic Table. Thus, for example, the original cations can be exchanged with ammonium ions or with hydronium ions. Catalytically active forms of these would include, in particular, hydrogen rare earth metals, aluminum, metals of Groups II, e.g., zinc, and VIII, e.g., nickel, platinum and palladium of the Periodic Table and manganese. Typical ion exchange techniques include contacting the zeolite with a salt of the desired replacing cation. Although a variety of salts can be employed, particular preference is given to chlorides, nitrates and sulfates. Representative ion-exchange techniques are disclosed in a wide variety of patents including U.S. Patent Nos. 3,140,249, 3,140,251 and 3,140,253. The ZSM-48 of the present invention can also be used as a catalyst in intimate combination with an additional hydrogenating component such as tungsten, vanadium, molybdenum, rhenium, nickel, cobalt, chromium, manganese, or a noble metal such as platinum or palladium where a hydrogenation-dehydrogenation function is to be performed. Such component can be exchanged into the composition, impregnated therein or physically intimately admixed therewith. Such component can be impregnated in or onto it such as, for example, by, in the case of platinum, treating with a solution containing platinum metal-containing ions. Thus, suitable platinum compounds include chloroplatinic acid, platinous chloride and various compounds containing the platinum ammine complex. The ZSM-48 when employed either as an adsorbent or as a catalyst in one of the aforementioned processes should be dehydrated, at least partially. This can be done by heating to a temperature in the range of 100 to 600°C in an atmosphere, such as air, nitrogen, etc. and at atmospheric pressure from between about 1 and about 48 hours. Dehydration can also be performed at room temperature merely by placing the ZSM-48 type catalyst in a vacuum, but a longer time is required to obtain a sufficient amount of dehydration. As is the case with many catalysts, it is desired to incorporate the ZSM-48 with another material resistant to the temperatures and other conditions employed in organic conversion processes. Such materials include active and inactive materials and synthetic or naturally occurring zeolites as well as inorganic materials such as clays, silica and/or metal oxides. The latter may be either naturally occurring or in the form of gelatinous precipitates or gels including mixtures of silica and metal oxides. Use of a material in conjunction with the composition of the present invention, i.e., combined therewith which is active, tends to improve the conversion and/or selectivity of the catalyst in certain organic conversion processes. Inactive materials suitably serve as diluents to control the amount of conversion in a given process so that products can be obtained economically and without employing other means for controlling the rate of reaction. These materials may be incorporated into naturally- occurring clays, e.g. bentonite and kaolin, to improve the crush strength of the catalyst under commercial operating conditions. Such material, i.e., clays, oxides, etc" function as binders for the catalyst, It is desirable to provide a catalyst having good crush strength because in a petroleum refinery the catalyst is often subjected to rough handling, which tends to break the catalyst down into powder like materials, which cause problems in processing. These clay binders have been employed for the purpose of improving the crush strength of the catalyst. Naturally-occurring clays which can be composited with the ZSM-48 of the present invention include montmorillonite and kaolin families. These families include subbentonites, and kaolins commonly known as Dixie, McNamee, Georgia and Florida clays or others in which the main mineral constituent is halloysite, kaolinite, dickite, nacrite, or anauzite. Such clays can be used in the raw state as originally mined or initially subjected to calcination, acid treatment or chemical modification. Binders useful for compositing with the zeolite of the present invention also include inorganic oxides, notably alumina. In addition to the foregoing materials, the zeolite of the present invention can be composited with a porous matrix material such as silica-alumina, silica-magnesia, silica-zirconia, silica-thoria, silica-beryllia, silica-titania as well as ternary compositions such as silica-alumina-thoria, silica-alumina-zirconia, silica-alumina-magnesia and silica-magnesia-zirconia. The relative proportions of finely divided ZSM-48 and inorganic oxide gel matrix vary widely with the ZSM-48 content ranging from 1 to 90 percent by weight and more usually, particularly when the composite is prepared in the form of beads, in the range of 2 to 70 percent by weight of the composite. Employing a catalytically active form of the composition of this invention which contains a hydrogenation component, reforming stocks can be reformed employing a temperature of 300 to 600°C. The pressure can be from 100 to 1,000 psig (800 to 7000 kPa) but is preferably from 200 to 700 psig (1500 to 4900 kPa). The liquid hourly space velocity is generally from 0.1 to 10, preferably from 0.5 to 4 and the hydrogen to hydrocarbon mole ratio is generally from 1 to 20, preferably from 4 to 12. The catalyst made with the ZSM-48 can also be used for hydroisomerization of normal paraffins, when provided with a hydrogenation component, e.g., platinum, hydroisomerization is carried out at a temperature of 100 to 400°C, preferably 150 to 300°C, with a liquid hourly space velocity between 0.01 and 2, preferably between 0.25 and 0.5 employing hydrogen such that the hydrogen to hydrocarbon mole ratio is between 1:1 and 5:1. Additionally, the catalyst can be used for olefin or aromatic isomerization employing temperatures between 50 and 400°C. The catalyst can also be used for reducing the pour point of distillate fuels and lubricants. This reduction is carried out at a liquid hourly space velocity between 0.5 and 10, preferably between 0.5 and 5, and a temperature between 200 and 450°C, preferably between 250 and 400°C. Other reactions which can be accomplished employing the catalyst of this invention with or without a metal, e.g., platinum, or palladium, include hydrogenation-dehydrogenation reactions and desulfurization reactions, olefin polymerization (oligomerization), aromatic alkylation with C2-C12 olefins or with C1-C12 alcohols, aromatics, isomerization, disproportionation and transalkylation and other organic compound conversion such as the conversion of alcohol (e.g., methanol) to hydrocarbon. The invention will now be more particularly described with reference to the following Examples and the accompanying drawing, which is the X-ray diffraction pattern of the ZSM-48 prepared by the method of Example 1. EXAMPLE 1 To a stirred solution of l.lg of 45% sodium aluminate (19.5% Na20, 25.5% AI2O3) in 270 cc of distilled water, 40 g UltraSil silica (92.4% Si02, 0.4% Na20) was added. To the resultant stirred mixture, 93 g of ethylenediamine was added. The resultant mixture had a pH of approximately 12.1 and can be described by the following mole ratios of ingredients: SiO,/Al203 = 200 Na/Si02 = 200 Diamine/Si02 = 2.5 OH/Si02 = 0.002 H20/Si02 = 25 The resultant mixture contained 9 mole % of ethylenediamine in the solvent (ethylenediamine and water). The mixture was heated for 65 hours at 160°C in an autoclave stirred at 200 rpm, cooled, and filtered. The solid product was then washed with distilled water and dried at 120°C. On analysis, the solid product was identified as ZSM-48 sample having a S1O2/AI2O3 ratio of 190. The ZSM-48 sample contained 0.1 Na ions and 2.3 ethylenediamine molecules per unit cell. The ZSM-48 sample was found to be pure ZSM-48, as shown by the X-ray diffraction pattern in Figure 1. The ZSM-48 sample is crystalline aggregate having sea urchin-like morphology. EXAMPLE 2 The procedure of Example 1 was repeated except the ratios of reactants were as follows: S1O2/AI2O3 = 200 Na/Si02 = 0.02 Diamine/Si02 = 3.0 OH/SiO2 = 0.002 H2O/SiO2 = 18 In this Example, 14 mole % of the solvent was ethylenediamine, and the pH of the starting mixture was 12.4. The resultant product was again a pure ZSM-48 crystal having a Si02/Al203 ratio of 170. The resultant product contained 0.3 sodium ions and 2.6 ethylenediamine molecules per unit cell. EXAMPLE 3 The starting reaction composition and the procedures of Example 2 were repeated except that the crystallization temperature was 149°C. The resultant product was again a pure ZSM-48 crystal. EXAMPLE 4 The Example shows that an excess of ethylenediamine can promote the formation of zeolites other than ZSM-48. The procedures of Example 1 were repeated except that the amount of water was reduced, raising the molar proportion of ethylenediamine in the solvent to 17 mole%. The initial pH was 12.3. The crystallization product was mainly ZSM-48, but it contained a small but evident amount of ZSM-5 contaminant. EXAMPLE 5 This Example shows that a minimum amount of ethylenediamine in the solvent phase is important for rapid and successful ZSM-48 crystallization. The procedure was the same as in Example 1 except that the molar ratios were as follows: Si02/Al203 = 200 Na/Si02 = 0.02 Diamine/Si02 = 1.5 OH/Si02 = 0.002 H20/Si02 = 18 mole % ethylenediamine in solvent (ethylenediamine and water) = 8 The resultant product was incompletely crystallized ZSM-48. It contained only 20% ZSM-48, together with amorphous material. EXAMPLE 6 The procedure of Example 1 was repeated except the molar ratios were as follows: Si02/AI203 = 200 Na/Si02 = 0.02 Diamine/Si02 = 2.0 OH/Si02 = 0.002 H20/Si02 = 30 mole % ethylenediamine in solvent (ethylenediamine and water) = 6 The resultant product is amorphous, after 65 hours at 160°C. WE CLAIM: 1. A method for preparing ZSM-48 which comprises: (c) preparing a reaction mixture comprising a source of silica, a source of trivalent metal oxide, an alkali metal oxide and a directing agent of ethylenediamine in a solvent phase comprising water, and optionally seed crystals; wherein said mixture, in terms of mole ratios, of dftides, has the following composition ranges: Si02/Me203: 100 to 1500, M2/nO/Si02: 0 to 0.2, RN/Si02: 1.0 to 5.0, OH/Si02: 0 to 0.3, and H20/Si02: 10 to 100, wherein Me is trivalent metal, M is akali metal and RN is ethylenediamine, and (d) maintaining said mixture under crystallization conditions until crystals of said ZSM-48 are formed. 2. The method as claimed in claim 1, wherein said mixture has the following composition ranges: Si02/Me203: 150 to 500, M2/nO/Si02: 0.001 to 0.10, RN/Si02: 2.0 to 4.0, OH/Si02: 0.001 to 0.10, and H20/Si02: 15 to 40. 3. The method as claimed in claim 1, wherein the amount of said ethylenediamine is from greater than 5 to less than 20 mole % of the total solvent. 4. The method as claimed in claim 1, wherein the amount of said ethylenediamine is from about 8 to about 15 mole % of the total solvent. 5. The method as claimed in claim 1, wherein the seed crystals are in amount of from about 1 to about 5% based on silica. Dated this the 18th day of July 2000 [RITUSHKA NEGI] OF REMFRY & SAGAR ATTORNEY FOR THE APPLICANTS

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