MIXED ZEOLITE HYDRODEWAXING CATALYSTS

Abstract: A catalytic dewaxing process using a mixed zeolite cata­ lyst which combines the following components: a first zeolitic catalyst having a Constraint Index not less than 1, a second, different, catalytic component of specified characteristics, and a hydrogenation component.

Description: This invention relates to a process for dewaxing a hydrocarbon feedstock and particularly to a process for dewaxing using a catalyst containing, in combination, a zeolite with Constraint Index greater than 1, a second, different zeolite having a Constraint Index of 1-12 and a hydrogenation component. Refining suitable petroleum crude oils to obtain a variety of lubricating oils which function effectively in diverse environments has become a highly developed and complex art. Although the broad principles involved in refining are qualitatively understood, the art is encumbered by quantitative uncertainties which require a considerable resort to empiricism in practical refining. Underlying these quantitative uncertanties is the complexity of the molecular constitution of lubricating oils. Because lubricating oils for the most part are based on high boiling petroleum fractions, the molecular weights of the hydrocarbon constitutents are high and these constituents display almost all conceivable structure types. This complexity and its consequences are referred to in well-known treatises, such as, for example, "Petroleum Refinery Engineering", by W. L. Nelson, McGraw-Hill Book Company, Inc., New York, NY, 1958 (Fourth Edition). The process of refining to isolate lubricant stock consists of a set of subtractive unit operations which removes the unwanted components. The most important of these unit operations include distillation, solvent refining and dewaxing, which basically are physical separation processes in the sense that if all the separated fractions were recombined, one would reconstitute the crude oil. For the preparation of a high grade distillate lubricating oil stock, the current practice is to vacuum distill an atmospheric tower residuum from an appropriate crude oil as the first step. This step provides one or more raw stocks within the boiling range of about 450° (230°C) to 1050°F (565°C). After preparation of a raw stock of suitable boiling range, it is extracted with a solvent, e.g., furfural, phenol, sulfolane, or chlorex, which is selective for aromatic hydrocarbons, and which removes undesirable components. The raffinate from solvent refining is then dewaxed, for example, by admixing with a solvent, such as a blend of methyl ethyl ketone and toluene. The mixture is chilled to induce crystallization of the paraffin waxes, which are then separated from the raffinate. Sufficient quantities of wax are removed to provide the desired pour point for the raffinate. Other processes, such as hydrofinishing or clay percolation, may be used if needed to reduce the nitrogen and sulfur content or improve the color of the lubricating oil stock. Viscosity Index (VI) is a quality parameter of considerable importance for distillate lubricating oils to be used in automotive engines and aircraft engines subject to wide variations in temperature. This index indicates the degree of change of viscosity with temperature. A high VI of 100 indicates an oil that does not change much in viscosity with changes in temperature. Measurement of the Saybolt Universal Viscosity of an oil at 100° (38°C) and 210°F (100°C), and referral to correlations, provides a measure of the VI of the oil. For purposes of the present invention, whenever VI is referred to, it is meant the VI as noted in the Viscosity Index tabulations of the ASTM (D567), published by ASTM, 1916 Race Street, Philadelphia, PA, or equivalent. Catalytic techniques are now available for dewaxing of petroleum stocks. A process of that nature developed by British Petroleum is described in The Oil and Gas Journal , dated January 6, 1975, at pages 69-73. See also in. U. S. Patent No. 3,668,113. U. S. Patent No. Re. 28,398 describes a process for catalytic dewaxing with a catalyst comprising zeolite ZSM-5. Such a process combined with catalytic hydrofinishing is described in in. U. S. Patent No. 3,894,938. U. S. Patent No. 3,755,138 describes a process for mild solvent dewaxing to remove high quality wax from a lube stock, which is then catalytically dewaxed to specification pour point. U. S. Patent No. 4,053,532 is directed towards a hydrodewaxing operation involving a Fischer-Tropsch synthesis product utilizing ZSM-5 type zeolites. U. S. Patent No. 3,956,102 is connected with a process involving the hydrodewaxing of petroleum distillates utilizing a ZSM-5 type zeolite catalyst. U. S. Patent No. 4,247,388 describes dewaxing operations utilizing ZSM-5 type zeolites of specific activity. U. S. Patent No. 4,222,855 describes dewaxing operations to produce lubricating oils of low pour point and of high VI utilizing zeolites including ZSM-23 and ZSM-35. U. S. Patent No. 4,372,839 describes a method for dewaxing crude oils of high wax content by contacting the oils with two different zeolites, e.g., ZSM-5 and ZSM-35. U. S. Patent No. 4,419,220 describes a dewaxing process utilizing a Zeolite Beta catalyst. Despite all these improvements, it would be beneficial if even better dewaxing processes were available. Accordingly, the present invention provides a process for catalytically dewaxing a hydrocarbon feedstock comprising contacting said feedstock with a dewaxing catalyst, said dewaxing catalyst comprising, in combination: a zeolite catalyst having a Constraint Index not less than 1, a zeolite selected from zeolite Y, mordenite, ZSM-4 and ZSM-20; and a hydrogenation component, recovering a dewaxed product. The zeolite Y may be ultrastable Y, dealuminised Y or rare earth Y: the mordenite may be TEA mordenite. The dewaxing catalyst may further comprise a binder of alpha alumina, silica, silica-alumina and/or naturally-occurring clay. The present process may be used to dewax a variety of feedstocks ranging from relatively light distillate fractions up to high boiling stocks, such as whole crude petroleum, reduced crudes, vacuum tower residua, propane deasphalted residua, e.g., brightstock, cycle oils, FCC tower bottoms, gas oils, vacuum gas oils, deasphalted residua and other heavy oils. The feedstock will normally be a C₁₀+ feedstock since lighter oils will usually be free of significant quantities of waxy components. The process is particularly useful with waxy distillate stocks, such as gas oils, kerosenes, jet fuels, lubricating oil stocks, heating oils, hydrotreated oil stock, furfural-extracted lubricating oil stock, and other distillate fractions which pour point and viscosity must be maintained within certain specification limits. Lubricating oil stocks, for example, will generally boil above 450°F (230°C), more a easily above 600°F (315°C). For purposes of this invention, lubricating oil or lube oil is that part of a hydrocarbon feedstock having a boiling point of 600°F (315°C) or higher as determined by ASTM D-1160 test method. In general, hydrodewaxing conditions include a temperature between about 450°F (230°C) and 750°F (400°C), and a pressure between atmospheric and 21,000 kPa (0 and 3000 psig), preferably between 800 and 7,000 kPa (100 and 1000 psig). The liquid hourly space velocity (LHSV), i.e, volume of feedstock per volume of catalyst per hour, is generally 0.1 to 20 and preferably 0.2 to 4, and the hydrogen-to-feedsotck ratio is generally 50 to 1,400 v/v, volumes of H₂ per volume of liquid (400 and 800 SCFB) and preferably 140 to 700 (8000 and 4000 SCFB). When some hydrocracking is desired, rather than just dewaxing, slightly higher temperatures may be used, typically 230-500°C, but preferably 315-454°C. The catalytic dewaxing process of this invention may be conducted by contacting the feed with a fixed, slurry bed or a transport bed, of catalyst. For purposes of this invention, the term "zeolite" is meant to represent the class of porotectosilicates, i.e., porous crystalline silicates that contain silicon and oxygen atoms as the major components. Other components may be present in minor amounts, usually less than 14 mole % and preferably less than 4 mole %. These components include aluminum, gallium, iron, boron and the like, with aluminum being preferred, and used herein for illustration purposes. The minor components may be present separately or in mixtures. The silica-to-alumina (SiO₂/Al₂O₃) mole ratio referred to may be determined by conventional analysis. This ratio represents the ratio in the rigid anionic framework of the zeolite crystal. Zeolites having ratios of 10:1 and much higher silica-to-alumina mole ratios, i.e., ratios of up to at least 500:1 and higher, may be used. In fact, zeolites as otherwise characterized herein but which are substantially free of aluminum, i.e., having silica-to-alumina mole ratios up to and including infinity, are found to be useful and even preferable in some instances. Such "high silica" zeolites are intended to be included within this description. The novel class of zeolites, after activation, acquire an intra-crystalline sorption affinity for normal hexane which is greater than that for water, i.e., they exhibit "hydrophobic" properties. Some of the zeolites useful herein are termed medium or intermediate pore zeolites and have an effective pore size of generally less than about 6 angstroms, such as to freely sorb normal hexane. In addition, the structure must provide constrained access to larger molecules. It is sometimes possible to judge from a known crystal structure whether such constrained access exists. Large pore zeolites, are well known to the art and have a pore size sufficiently large to admit the vast majority of components normally found in a feed chargestock. These zeolites have a pore size in excess of 6 angstroms and are represented by, e.g., zeolite Y, Mordenite, ZSM-4 and ZSM-20. A convenient measure of the extent to which a zeolite provides control molecules of varying sizes to its internal structure is the Constraint Index of the zeolite. The method by which Constraint Index is determined is described fully in U. S. Patent No. 4,016,218, to which reference is made for details of the method. Constraint Index (CI) values for some typical materials, and patents describing some of these materials are: Constraint Index seems to vary somewhat with severity of operation (conversion) and the presence or absence of binders. Likewise, other variables, such as crystal size of the zeolite, the presence of occluded contaminants, etc., may affect the Constraint Index. This explains the range of Constraint Index for zeolites, such as ZSM-5, ZSM-12 and ZSM-34. A preferred first component zeolite is selected from the family of ZSM-5 zeolites, e.g., ZSM-5, ZSM-11, ZSM-23 and ZSM-35, with ZSM-5 being particularly preferred. Combined with the above-mentioned zeolite is a second, different zeolite selected from Ultrastable Y, Dealuminized Y, Rare Earth Y, Mordenite, TEA Mordenite, ZSM-4 and ZSM-20. A further component of the dewaxing catalyst is a hydrogenation-dehydrogenation component (referred to, for convenience, as a hydrogenation component) which is generally a metal or metals of Groups IB, IIB, VA, VIA or VIIIA of the Periodic Table (IUPAC and U. S. National Bureau of Standards approved Table, as shown, for example, in the Chart of the Fisher Scientific Company, Catalog No. 5-702-10). The preferred hydrogenation components are the noble metals of Group VIIIA, especially platinum, but other noble metals, such as palladium, gold, silver, rhenium or rhodium, may also be used. Combinations of noble metals, such as platinum-rhenium, platinum-palladium, platinum-iridium or platinum-iridium-rhenium, together with combinations with non-noble metals, particularly of Groups VIA and VIIIA are of interest, particularly with metals such as cobalt, nickel, vanadium, tungsten, titanium and molybdenum, for example, platinum-tungsten, platinum-nickel or platinum-nickel-tungsten. Base metal hydrogenation components may also be used, especially nickel, cobalt, molybdenum, tungsten, copper or zinc. Combinations of base metals, such as cobalt-nickel, cobalt-molybdenum, nickel-tungsten, cobalt-nickel-tungsten or cobalt-nickel-titanium, may also be used. The metal may be incorporated into the catalyst by any suitable method, such as impregnation or exchange, onto the zeolite. The metal may be incorporated in the form of a cationic, anionic or neutral complex, such as Pt(NH₃)₄²+, and cationic complexes of this type will be found convenient for exchanging metals onto the zeolite. Anionic complexes are also useful for impregnating metals into the zeolites. The amount of the hydrogenation-dehydrogenation component is suitably from 0.01 to 25% by weight, normally 0.1 to 5% by weight especially for noble metals, and preferably .3 to 1% by weight, although this will, of course, vary with the nature of the component. For example, less of the highly active noble metals, particularly platinum, are required than of the less active metals. The original cations associated with each of the crystalline silicate zeolites utilized herein may be replaced by a wide variety of other cations according to techniques well known in the art. Typical replacing cations include hydrogen, ammonium, alkyl ammonium and metal cations, including mixtures of the same. Of the replacing metallic cations, particular reference is given to cations of metals such as Rare Earth metals, manganese, as well as metals of Groups II A and B of the Periodic Table, e.g., zinc, and Group VIII of the Periodic Table, e.g., nickel, platinum and palladium. Typical ion exchange techniques are to contact the particular zeolite with a salt of the desired replacing cation. Although a wide 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. Alternatively, the metallic catalyst component can be incorporated into the zeolite by impregnating the zeolite with a solution of the metal or metal compounds or complexes, followed by stripping of the solvent employed. Metallic component incorporation can also be accomplished by sorbing metal compounds or complexes into the zeolite. Thus, such materials as nickel carbonyl or rhodium carbonyl chloride can be sorbed from solution or from the gas phase into the zeolite structure. Following contact with a solution of the desired replacing cation, the zeolite is then preferably washed with water and dried at a temperature ranging from 150°F (70°C) to 600°F (320°C) and thereafter calcined in air, or other inert gas at temperatures ranging from 500°F (230°C) to 1500°F (820°C) for periods of time ranging from 1 to 48 hours or more. It has been further found that catalysts of improved selectivity and other beneficial properties may be obtained by subjecting the zeolite to treatment with steam at elevated temperatures ranging from 500°F (230°C) to 1200°F (650°C) and preferably 750°F (400°C) to 1000°F (540°C). The treatment may be accomplished in an atmosphere of 100% steam or an atmosphere consisting of steam and a gas which is substantially inert to the zeolites. A similar treatment can be accomplished at lower temperatures and elevated pressure, e.g., 350°-700°F (180°-370°C) at 10 to 200 atmospheres. The crystalline silicate zeolite utilized in the process of this invention is desirably employed in intimate combination with one or more hydrogenation components in an amount between about 0.1 and about 25% by weight, such as tungsten, vanadium, zinc, molybdenum, rhenium, nickel, cobalt, chromium, manganese, or a noble metal such as platinum or palladium. Such component can be exchanged into the composition, impregnated thereon or physically intimately admixed therewith. Such component can be impregnated into or onto the zeolite, such as, for example, in the case of platinum, by treating the zeolite with a platinum metal-containing ion. Thus, suitable platinum compounds include chloroplatinic acid, platinous chloride and various compounds containing the platinum amine complex. The compounds of the useful platinum or other metals can be divided into compounds in which the metal is present in the cation of the compound and compounds in which it is present in the anion of the compound. Both types of compounds which contain the metal in the ionic state can be used. A solution in which platinum metals are in the form of a cation or cationic complex, e.g., Pt(NH₃)₄Cl₂, is particularly useful. Prior to use, the zeolites should be dehydrated at least partially. This can be done by heating to a temperature in the range of 390° to 1110°F (200° to 600°C) in an inert atmosphere, such as air, nitrogen, etc., and at atmospheric or subatmospheric pressures for between 1 and 48 hours. Dehydration can also be performed at lower temperatures merely by using a vacuum, but a longer time is required to obtain sufficient amount of dehydration. The catalysts of this invention are typically prepared by mulling together from about 5 to 60% by weight, preferably 20 to 40% by weight, most preferably 32.5% by weight of each zeolite catalyst and from 0 to about 50% by weight, preferably 0 to 40% by weight, most preferably 35% by weight, binder alpha alumina monohydrate. During the mulling process, a sufficient amount of water containing H₂PtCl₆ or Pt(NH₃)₄(NO₃)₂ is added slowly to the dry mulling mixture. The mulling process is continued for 20 minutes or until the mixture is uniform. The mixture is then extruded and dried at 230°F (110°C) for approximately 3 hours. The extrudates are crushed and sized to 0.25 to 0.60 mm (30/60 mesh) material and calcined in air at 1000°F (540°C) for 3 hours. The catalyst thus produced contains from 0.1 to 2% by weight, preferably 0.3 to 1% by weight of finely dispersed platinum. It is to be understood that metal cations other than platinum may be incorporated into the catalyst. In the Examples which follow the chargestock was a light neutral lubricating oil chargestock having the following properties: Example 1 (Comparative) This Example 1 illustrates the effect of steamed Ni/ZSM-5 (SiO₂/Al₂O₃ = 70) catalyst on the chargestock as it was passed over the catalyst. The catalyst was steamed for about 6 hours at about 900°F (480°C) and loaded into a 15/32'' (1.16 cm) interior diameter fixed-bed reactor, with a spiral preheater and a 3-zone furnace for good temperature control. After the reactor temperature was lowered to the desired setting, the chargestock was passed over the catalyst along with hydrogen under the controlled process conditions which are recited in Table 1. The product stream leaving the reactor was passed through a heated trap, a cold-water trap, and a gas-sampling bomb. The gas samples were analyzed by conventional procedures. The results are recited in Table 1. Example 2 (Comparative) This Examples illustrates the effect of a 0.5% Pt/ZSM-5 (SiO₂/Al₂O₃ = 70) catalyst on the chargestock. The platinum catalyst was reduced in situ at 900°F (480°C) and 2,900 KPa (400 psig of hydrogen) for one hour before introducing the feed into the reactor. The conditions and results of Example 2 is shown in Table 2. Example 3 (Comparative) This Example illustrates the effect of 0.5% Pt/Z SM-5/ ZSM-12 on the chargestock. The catalyst was prepared by compositing 32.5 parts ZSM-5 (SiO₂/Al₂O₃ = 70), 32.5 parts ZSM-12 (SiO₂/Al₂O₃ = 54) and 35 part alumina. The extrudates were reduced to 1/16'' (.16 cm) by a hydraulic ram extruder and were processed to hydrogen form by conventional means. The platinum was incorporated onto the composite catalyst via chloroplatinic acid impregnation with carbon dioxide saturation. The catalyst was then subjected to air calcination at 900°F (480°C) for 3 hours. The final composition of the catalyst was as follows: The run conditions and results are shown in Table 3. Examples 4-5 These Examples illustrate the effect of 0.5% Pt/ZSM-5/TEA Mordenite on the chargestock. The catalyst was prepared by compositing 32.5 parts NH₄ from ZSM-5 (SiO₂/Al₂O₃ = 70, treated by standard nitrogen precalcination and ammonium exchange steps), 32.5 parts NH₄ from TEA Mordenite (Si/Al = 25.7, treatments similar to ZSM-5), and 35 parts alpha-Al₂O₃ monohydrate. The mixture was mulled together with water added to yield about a 50% solids content. After 30 minutes, the mix was dried, formed and sized to 0.71 to 1.41 mm (14/25 mesh). Platinum was then added and the sample calcined in a manner similar to that previously described for the catalyst of Example 3. The final composition of the catalyst was as follows: The run conditions and results are shown in Table 4. Examples 6-9 These Examples illustrate the effect of 0.5% Pt/ZSM-5/Deal Y on the chargestock. The preparation procedures for this catalyst is similar to that described for the catalyst of Examples 4 and 5. The final composition of the chargestock was as follows: The run conditions and results are shown in Table 5 following: Comparative results are summarized below in Table 6, based upon data at about 20°F (-7°C) pour point for steamed Ni/ZSM-5, Pt/ZSM-5/ZSM-12, Pt/ZSM-5/Deal Y and Pt/ZSM-5/TEA-M, and 5°F pour point for Pt/ZSM-5. Compared to the conventionally used lube dewaxing catalyst (Ni/ZSM-5) at about a -7°C(20°F) pour point, the Pt/ZSM-5/ZSM-12 catalyst improved product VI by 1-2 numbers and lube yield by 4-5 wt %, respectively, Pt/ZSM-5/TEA Mordenite improved VI by 5-6 numbers and lube yield by 5-6 wt % over Ni/ZSM-5 and Pt/ZSM-5/ Deal Y improved VI by about 4 numbers and lube yield by about 4 wt %. The data for steamed Ni/ZSM-5, Pt/ZSM-5/ZSM-12 and Pt/ZSM-5/TEA Mordenite can be correlated to a -7°C(20°F) pour point based on one number in VI for each -15°C(5°F) pour point increase. Thus, the product processed with steamed Ni/ZSM-5 would have a VI of about 93.8 at 20°F pour, the product processed with Pt/ZSM-5/ZSM-12 would have a VI of about 95.4 at 7°C(20°F) pour, and the product processed with Pt/ZSM-5/TEA Mordenite would have a VI of about 99.4 at 20°F pour. With regard to the platinum catalysts, Pt/ZSM-5/ZSM-12 had approximately a 3 wt % increase in lube yield and a 1 number increase in VI over Pt/ZSM-5; Pt/ZSM-5/TEA Mordenite had approximately a 4-5 wt % increase in lube yield and a 4-5 number increase in VI over Pt/ZSM-5; and Pt/ZSM-5/Deal Y had approximately a 2-3 wt % increase in lube yield and a 3-4 number increase in VI over Pt/ZSM-5.

Claims: A process for catalytically dewaxing a hydrocarbon lubricating oil feedstock comprising contacting the feedstock with a dewaxing catalyst, the dewaxing catalyst comprising, in combination: (a) a zeolite having a Constraint Index not less than 1; (b) a zeolite selected from zeolite Y, Mordenite, ZSM-4 and ZSM-20; and (c) a hydrogenation component; and recovering a dewaxed product. The process of claim 1, wherein the zeolite from group (a) has a Constraint Index from 1 to 12. The process of claim 1 or claim 2 wherein the zeolite from group (a) is selected from ZSM-5, ZSM-11, ZSM-12, ZSM-22 ZSM-23, ZSM-34, ZSM-35, ZSM-38, ZSM-48 TMA Offretite and Erionite. The process of any preceding claim wherein the mordenite is TEA mordenite. The process of any preceding claim wherein the zeolite Y is ultrastable Y, dealuminised Y or rare-earth Y. The process of any preceding claim wherein the hydrogenation component is a noble metal. The process of claim 6 wherein the noble metal is platinum or palladium. The process of any preceding claim wherein the dewaxing catalyst further comprises a binder of alpha-alumina, silica, silica-alumina, naturally-occurring clays or mixtures thereof.

Inventors: CHESTER, ARTHUR WARREN, MCHALE, WILLIAM DEPAUL, YEN, JEFFREY HSING-GAN
Applicants: MOBIL OIL CORPORATION
Application year: 1985
Main classification: C10G45
IPC codes: B01J29, C10G73, C10G45