WO1991013131A1

WO1991013131A1 - Hydrodewaxing process

Info

Publication number: WO1991013131A1
Application number: PCT/US1991/001079
Authority: WO
Inventors: John W. Ward
Original assignee: Union Oil Company Of California
Priority date: 1990-02-22
Filing date: 1991-02-19
Publication date: 1991-09-05

Abstract

Waxy hydrocarbon feedstocks are hydrodewaxed by contact in the presence of hydrogen under hydrodewaxing conditions with a catalyst devoid of Group VIB metal components and comprising nickel components supported on a mixture of one or more amorphous, inorganic, refractory oxide components and a crystalline, intermediate pore, nonzeolitic molecular sieve having cracking activity, preferably a mixture of alumina and silicalite.

Description

HYDRODEWAXING PROCESS

BACKGROUND OF THE INVENTION

This invention relates to a process for hy- drodewaxing a waxy hydrocarbon feedstock to reduce its normal paraffin content, thereby producing a product hydrocarbon having a relatively low pour point and/or cloud point. It is particularly concerned with a catalytic hydrodewaxing process in which the catalyst contains nickel components but no tungsten or other Group VIB metal components.

Many liquid hydrocarbon feedstocks contain relatively high concentrations of straight and slightly branched chain paraffinic compounds having between 6 and 40 carbon atoms. Some of these long chain com¬ pounds, typically the ones containing 12 or more carbon atoms, tend to crystallize upon cooling of the hydro¬ carbon oil. This crystallization may only take place to the extent that a clear and bright oil becomes dull because of the formation of small crystals, or it may proceed until sufficient crystals are present that they interfere with the flow of the hydrocarbon liquid from one location to another. The temperature at which the waxy compounds begin to crystallize from the solution and impart a cloudy appearance is referred to as the "cloud point" and is determined by standardized test procedures. Similarly, the temperature at which suffi¬ cient crystals form to prevent the hydrocarbon oil from flowing is commonly referred to as the "pour point" and is also determined by standardized test procedures. Examples of feedstocks having relatively high pour points are the raw oil obtained by retorting oil shale, such as the oil shale found in the Colorado River formation in the Western United States, and middle distillates and gas oils derived from highly paraffinic crude oils. Such waxy hydrocarbon feedstocks usually have pour points above 35° F. and frequently have pour points in the range between 50° F. and 140° F. Such high pour points indicate the presence of a relatively high proportion of wax components, i.e., straight chain and slightly branched chain paraffins of high molecular weight.

In order for such waxy hydrocarbon feedstocks to be usable as lubricating base oils, heating oils or diesel fuel, their pour points and/or cloud points must be reduced. Hydrodewaxing is a process typically used to lower the pour point and/or cloud point of waxy hydrocarbon feedstocks by selectively converting the straight chain and slightly branched chain paraffins into lower molecular weight constituents which do not tend to crystallize at low temperatures. One such hydrodewaxing process is disclosed and claimed in U.S. Patent No. 4,790,927 issued to John W. Ward and Timothy L. Carlson, the disclosure of which is hereby incorpo¬ rated by reference in its entirety. According to this patent, waxy hydrocarbon feedstocks, particularly waxy shale oils that have been deashed, dearsenated and hydrotreated, are hydrodewaxed to lower their pour points by contacting the feedstocks with a catalyst containing a Group VIB metal, usually tungsten, prefer¬ ably in combination with a Group VIII metal, such as cobalt and nickel, supported on a mixture of silicalite or other Group IIIA metal-free crystalline silica molecular sieve and an inorganic refractory oxide. Although the examples in U.S. Patent No. 4,790,927 show that the hydrodewaxing catalysts disclosed therein, . which catalysts contain from about 3 to 5 weight per¬ cent nickel components, calculated as nickel oxide, and from about 20 to 22 weight percent tungsten components, calculated as tungsten oxide, supported on mixtures of silicalite and alumina, are highly effective for reduc¬ ing the pour point of certain feedstocks, these cata¬ lysts do have a significant disadvantage in that they contain high concentrations of tungsten which adds significantly to the cost of the catalyst.

Accordingly, it is one of the objects of the present invention to provide a process for hydrodewax¬ ing shale oil, gas oils and other waxy hydrocarbon feedstocks with a catalyst which is less expensive than other hydrodewaxing catalysts now known to be effective for reducing the concentration of normal and slightly branched chain paraffins in such waxy hydrocarbon feedstocks. It is another object of the invention to provide such a process having the further advantage that the hydrodewaxing step can be carried out at a lower temperature because the catalyst has an increased activity for conversion of waxy components into lower boiling components. These and other objects of the invention will become more apparent in light of the following description of the invention.

SUMMARY OF THE INVENTION

In accordance with the invention, it has now been surprisingly found that the pour point and/or cloud point of waxy hydrocarbon feedstocks can be significantly reduced by contacting the feedstock in the presence of hydrogen with a catalyst comprising an intermediate pore, nonzeolitic molecular sieve having cracking activity and relatively small quantities of a nickel component without the need for the catalyst to contain a tungsten or other Group VIB metal component. It has been unexpectedly found that such tungsten-free catalysts have a significantly increased hydrodewaxing activity which enables them to produce a hydrocarbon product having the desired pour point at a much lower temperature than is possible using similar catalysts which can contain up to 30 weight percent tungsten components, calculated as W0₃. Operating at such lower temperatures not only saves money on fuel costs but also results in the yield of a greater proportion of the desired higher boiling constituents. Moreover, it has been found that the catalysts used in the process of the invention are much more stable than catalysts containing a tungsten component as indicated by the ability of such tungsten-free catalysts to produce low pour point products over long periods of time.

A preferred catalyst for use in the hydrode¬ waxing process of the invention will typically contain less than about 12 weight percent nickel components, calculated as NiO, impregnated on a support comprising a mixture of an amorphous, inorganic refractory oxide and a crystalline silica, intermediate pore, nonzeolit¬ ic molecular sieve known as silicalite. In a preferred embodiment, the catalyst contains between about 2 and 8 weight percent nickel components, calculated at NiO, and the amorphous refractory oxide is alumina, all or a portion of which serves as a binder for the silicalite. The product hydrocarbon from the process of the inven¬ tion will normally have boiling characteristics very similar to the feedstock being treated; i.e., the process of hydrodewaxing will have little effect on the branched chain and non-alkylated aromatic hydrocarbons present in the feed. The catalyst will selectively convert the straight chain and slightly branched chain paraffins into lower molecular weight constituents that will not readily crystallize on cooling and therefore will not adversely affect the pour point and/or cloud point of the product hydrocarbon.

When it is desired to produce a low pour point lubricating base oil, the process of the invention is normally conducted such that the overall conversion of 650° F.+ boiling components to components boiling at or below about 600° F. in the hydrodewaxing step is no more than about 25 volume percent, preferably no more than about 15 volume percent. On the other hand, when it is desired to produce a middle distillate such as a heating oil or diesel fuel having both a low pour point and a low cloud point, the process is typically carried out such that the overall conversion of components comprising the waxy hydrocarbon feedstock to components boiling at or below about 300° F. in the hydrodewaxing zone is less than about 30 volume percent, preferably less than about 20 volume percent.

The process of the invention provides a method for converting waxy hydrocarbon feedstocks into lubri¬ cating base oils having substantially reduced pour points without excessive loss of lubricating base oil constituents, or into middle distillates having reduced pour points and/or cloud points without excessive loss of constituents boiling between 300° F. and 700° F. utilizing a catalyst which does not contain an expen¬ sive Group VIB metal component. It has been found that such catalysts have a higher hydrodewaxing activity, a greater stability, and produce higher yields of desired products than similar catalysts containing such Group VIB metal constituents.

DETAILED DESCRIPTION OF THE INVENTION

Feedstocks that can be upgraded in accordance with the process of the invention include waxy raffi- nates and waxy gas oils normally boiling above about 650° F., usually in the range from about 650° F. to about 1100° F. , and/or waxy distillates typically boiling above about 300° F. , usually between about 300° F. and 700° F. Such feedstocks, which can have pour points between about 50° F. and 140° F. , may be treated in the process of the invention to produce lubricating base oils of low pour point, typically at or below about 30° F. , preferably below 20° F., or middle dis¬ tillates of low cloud point, normally below 10° F. Other feedstocks which may be used include waxy hydro¬ carbons derived from shale, tar sands, coal and other carbonaceous solids. Such feedstocks are typically composed of hydro-carbons boiling in the range between 650° F. and 1150° F. and can have pour points as high as between about 70° F. and 150° F. Typically, a shale oil feedstock that is subjected to the process of the invention to produce a lubricating base oil is a full boiling range shale oil or shale oil fraction that has been deashed, dearsenated and catalytically hydrotreat- ed. U.S. Patent No. 4,046,674 discloses a method for carrying out the dearsenation of shale oil, while a typical hydrotreating process and catalyst used therein are taught in U.S. Patent No. 4,428,862. The disclo¬ sures of these two patents are hereby incorporated by references in their entireties. Typically, the process of the invention will be effective in reducing the pour point and/or cloud point of hydrocarbon feedstocks at least 30° F. , quite often at least 60° F., and in some cases by as much as 120° F.

If the waxy hydrocarbon feedstock which is to be subjected to the hydrodewaxing process of the inven¬ tion has a relatively small concentration of nitrogen and sulfur, it can normally be passed directly into the hydrodewaxing reactor where it is contacted in the presence of hydrogen with the hydrodewaxing catalyst. If, however, the feedstock is a waxy shale oil or other hydrocarbon feedstock which contains relatively high concentrations of organonitrogen and/or organosulfur compounds, the feedstock may need to be upgraded by hydrotreatment prior to being subjected to hydrodewax¬ ing. Typically, feedstocks which contain greater than about 0.3 weight percent sulfur, calculated as the element, and/or greater than about 0.01 weight percent nitrogen, calculated as the element, should be subject¬ ed to hydrotreatment to reduce concentrations of orga¬ nosulfur and/or organonitrogen compounds prior to passage into the hydrodewaxing reactor. Normally, the waxy hydrocarbon feedstock is not treated, prior to hydrodewaxing, with a zeolite having a Constraint Index between 1 and 12 in order to remove impurities by sorption.

If a hydrotreatment step is included in the process of the invention, it will typically be carried out at normal hydrogenation conditions of elevated temperature and pressure in a conventional hydrotreat- ing reactor in which the liquid feed is passed down¬ wardly through a packed bed of conventional hydrotreat¬ ing catalyst. Such a catalyst normally comprises an alumina or a silica-alumina support carrying one or more Group VIII metal components and one or more Group VIB metal components in the form of an oxide or a sulfide. Combinations of one or more Group VIB metal oxides or sulfides with one or more Group VIII metal oxides or sulfides are generally preferred. Normally, the preferred metal constituents are either tungsten or molybdenum constituents in combination with either nickel or cobalt components. In addition to a Group VIB metal component and a Group VIII metal component, the hydrotreating catalyst may also contain a phospho¬ rus component. Examples of such hydrotreating cata¬ lysts can be found in U.S. Patent Nos. 4,879,265 and 4,886,582, the disclosures of which are hereby incorpo¬ rated by reference in their entireties.

In accordance with the process of the inven¬ tion, the waxy hydrocarbon feedstock, which may contain all or a portion of the effluent from a hydrotreating reactor, is passed into a hydrodewaxing reactor where it is directed downwardly through a bed of hydrodewax¬ ing catalyst in the presence of hydrogen at elevated temperature and pressure. Normally, the temperature in the hydrodewaxing reactor will range between about 500° F. and about 850° F., preferably between about 600° F. and 800° F. The pressure in the reactor will typically range between about 500 p.s.i.g. and 3000 p.s.i.g., preferably between about 1000 p.s.i.g. and about 2000 p.s.i.g. The rate at which the feedstock is gassed through the reactor in contact with the catalyst parti¬ cles is typically set at a liquid hourly space velocity between about 0.3 and about 8.0 reciprocal hours, preferably between about 0.5 and 3.0. The hydrogen flow rate through the reactor is generally greater than about 500 standard cubic feet per barrel of feedstock, preferably between about 1500 and 10,000 standard cubic feet per barrel. In some cases, it may be preferable to remove all or a substantial proportion of the ammo¬ nia and hydrogen sulfide from the effluent exiting the hydrotreating reactor before the effluent is passed into the hydrodewaxing reactor.

The catalyst used in the hydrodewaxing reactor comprises a nickel component supported on a crystal¬ line, intermediate pore, nonzeolitic molecular sieve having cracking activity, which sieve typically is mixed with and/or bound together by an amorphous, inorganic refractory oxide. The term "molecular sieve" as used herein refers to any material capable of sepa¬ rating atoms or molecules based on their respective dimensions. Molecular sieves include zeolites, micro- porous carbons, porous membranes, aluminas and the like. The term "pore size" as used herein refers to the diameter of the largest molecule that can be sorbed by the particular molecular sieve in question. The measurement of such diameters and pore sizes is dis¬ cussed more fully in Chapter 8 of the book entitled "Zeolite Molecular Sieves" written by D. W. Breck and published by John Wiley & Sons in 1974, the disclosure of which book is hereby incorporated by reference in its entirety. The term "nonzeolitic" as used herein refers to molecular sieves whose frameworks are not formed of substantially only silicon and aluminum atoms in tetrahedral coordination with oxygen atoms. The nonzeolitic molecular sieve component of the catalyst used in the process of the invention is to be distin¬ guished from a "zeolitic" molecular sieve which is a molecular sieve whose framework is formed of substan¬ tially only silicon and aluminum atoms in tetrahedral coordination with oxygen atoms, such as the frameworks present in ZSM-5 zeolites, Y zeolites and X zeolites.

It has been surprisingly found that the cata¬ lysts described above, which comprise a hydrogenation metal constituent containing a nickel component but no tungsten or other Group VIB metal component, are unex¬ pectedly more active for hydrodewaxing than similar catalysts which contain both a nickel hydrogenation component and a tungsten hydrogenation component. It has been found that such tungsten-free catalysts are able to produce, under hydrodewaxing conditions, a hydrocarbon product having a lower pour point than that obtained using similar catalysts which contain tungsten components. Alternatively, it has been found that such tungsten-free catalysts can produce a hydrocarbon product having a pour point equivalent to that possible using its tungsten-containing counterpart but at much lower temperatures where a greater concentration of higher boiling constituents is produced. Thus, the use of such tungsten-free catalysts in the process of the invention yields improved results with both lower catalyst and operating costs.

The nickel components that comprise the hy¬ drogenation constituent of the hydrodewaxing catalyst will normally be present in the form of the metal, the metal oxide or the metal sulfide, and will typically comprise less than about 12 weight percent, calculated as NiO, of the catalyst. Typically, the catalyst will contain between about 1 and about 9.5 weight percent nickel components, calculated as NiO, preferably be¬ tween about 2 and about 8 weight percent, and most preferably between about 3.5 and 6.0 weight percent. As mentioned previously, nickel components will normal¬ ly be the only hydrogenation metal components present in the catalyst. The catalyst is typically substan¬ tially devoid of tungsten components, other Group VIB metal hydrogenation components, and Group VIII metal hydrogenation components other than nickel components.

The intermediate pore, crystalline, nonzeolit¬ ic molecular sieve component of the hydrodewaxing catalyst has a pore size between about 5.0 and 7.0 Angstroms, possesses cracking activity and is normally comprised of 10-membered rings of oxygen atoms. In general, the intermediate pore molecular sieve will selectively sorb n-hexane over 2,2-dimethylbutane. Examples of crystalline, nonzeolitic molecular sieves which may be used in the catalyst include crystalline silicas, silicoaluminophosphates, chromosilicates, aluminophosphates, titanium aluminosilicates, titanium aluminophosphates, ferrosilicates and borosilicates, provided, of course, that the particular sieve chosen has a pore size between about 5.0 and about 7.0 Ang- stroms .

The silicoaluminophosphates which may be used as the intermediate pore, crystalline molecular sieve in the hydrodewaxing catalyst are nonzeolitic molecular sieves comprising a molecular framework of [A10₂] [P0₂], and [Si0₂] tetrahedral units. The different species of silicoaluminophosphate molecular sieves are referred to by the acronym SAPO-n, where "n" denotes a specific structure type as identified by X-ray powder diffraction. The various species of silicoaluminophos¬ phates are described in detail in U.S. Patent No. 4,440,871, the disclosure of which is hereby incorpo¬ rated by reference in its entirety, and one use of these materials is disclosed in U.S. Patent No. 4,512,875, also herein incorporated by reference in its entirety. The silicoaluminophosphates have varying pore sizes and only those that have pore sizes between about 5.0 and 7.0 Angstroms may be used as the interme¬ diate pore molecular sieve in the hydrodewaxing cata¬ lyst. Thus, typical examples of silicoaluminophos¬ phates suitable for use in the catalysts are SAPO-11 and SAPO-41. The silicoaluminophosphates are also discussed in the article entitled "Silicoaluminophos¬ phate Molecular Sieves: Another New Class of Micropor- ous Crystalline Inorganic Solids" published in the Journal of American Chemical Society. Vol. 106, pp. 6093-6095, 1984. This article is hereby incorporated by reference in its entirety.

Other nonzeolitic molecular sieves which can be used as the intermediate pore, crystalline molecular sieve in the hydrodewaxing catalyst are the crystalline aluminophosphates. These molecular sieves have a framework structure whose chemical composition ex¬ pressed in terms of mole ratios of oxides is A1₂0₃ : 1.0 p 0.2 P 0₅. The various species of aluminophos¬ phates are designated by the acronym ALP0₄-n, where n denotes a specific structure type as identified by X- ray powder diffraction. The structure and preparation of the various species of aluminophosphates are dis¬ cussed in U.S. Patent Nos. 4,310,440 and 4,473,663, the disclosures of which are hereby incorporated by refer¬ ence in their entireties. One useful crystalline aluminophosphate is ALP0₄-11.

Two other classes of intermediate pore, crys¬ talline molecular sieves for use in the hydrodewaxing catalyst are borosilicates and chromosilicates. Boro- silicates are described in U.S. Patent Nos. 4,254,297; 4,269,813 and 4,327,236, the disclosures of all three of which are hereby incorporated by reference in their entireties. Chromosilicates are described in detail in U.S. Patent No. 4,405,502, the disclosure of which is also hereby incorporated by reference in its entirety.

Another class of intermediate pore, crystal¬ line molecular sieves for use in the catalyst is the titanium aluminophosphates. Such materials are de¬ scribed in greater detail in U.S. Patent No. 4,500,651, herein incorporated by reference in its entirety, and are designated by the acronym TAPO-n, where the "n" is an arbitrary number specific to a given member of the class. One such material which has a pore size of intermediate dimensions is TAPO-11.

Yet another class of nonzeolitic molecular sieves which can be utilized as the cracking component of the catalyst used in the process of the invention is the titanium aluminosilicates, particularly those described under the acronym TASO-n, where, again, the "n" is an arbitrary number specific to a given member of the class. One such material having a pore size of intermediate dimension is TASO-45. Titanium alumino¬ silicates are described in detail in U.S. Patent No. 4,707,345, the disclosure of which is hereby incorpo¬ rated by reference in its entirety.

A preferable intermediate pore, nonzeolitic molecular sieve for use in the hydrodewaxing catalyst is a crystalline, silica molecular sieve essentially free of Group IIIA metals, in particular aluminum, gallium and boron, with the most preferred silica molecular sieve for use being a material known as silicalite, a silica polymorph that may be prepared by methods described in U.S. Patent No. 4,061,724, the disclosure of which is hereby incorporated by reference in its entirety. The resulting silicalite may be subjected to combustion to remove organic materials and then treated to eliminate traces of alkali metal ions. Silicalite may be characterized as a crystalline molec¬ ular sieve comprising a channel system or pore struc¬ ture of intersecting elliptical straight channels and nearly circular straight channels, with openings in both types of channels being defined by 10-membered rings of oxygen atoms. These openings are normally between about 5.0 and 6.0 Angstroms in maximum cross- sectional dimension. Silicalite is a hydrophobic crystalline, silica molecular sieve having the property under ambient conditions of absorbing benzene, which has a kinetic diameter of 5.85 Angstroms, while reject¬ ing molecules larger than 6.0 Angstroms such as neopen- tane which has a kinetic diameter of 6.2 Angstroms. Silicalite is known to have an X-ray powder diffraction pattern similar to ZSM-5 zeolite, but recently new silicas having X-ray powder diffraction patterns simi¬ lar to ZSM-11 zeolite have been discovered. While ZSM- 11 type silicalites are contemplated for use herein, the preferred silicalite is that having an X-ray powder diffraction pattern similar to ZSM-5 zeolite, a mean refractive index of 1.39 p 0.01 when calcined in air for 1 hour at 600° C. and a specific gravity between about 1.65 and 1.80 grams per cubic centimeter depend¬ ing upon the method of preparation.

It should be emphasized that, although silica¬ lite is similar to members of the ZSM-5 family of zeolites in having a similar X-ray powder diffraction pattern, it is dissimilar in two important aspects. First, silicalite is not a zeolite because it contains only trace proportions of alumina which are present due to the commercial impossibility of removing all contam¬ inant aluminum components from reactants used to pre¬ pare silicalite. ZSM-5 type zeolites, on the other hand, are typically crystallized from hydrogels to which aluminum-containing reactants have been added and, therefore, usually contain substantially more than trace amounts of alumina, normally greater than 1.0 weight percent, calculated as A1₂0₃. Silicalite, however, will normally only contain between about 0.15 and about 0.75 weight percent alumina, calculated as A1₂0₃, with most silicalites containing less than about 0.6 weight percent. Secondly, as disclosed in U.S. Patent No. 4,061,724, neither silicalite nor its sili¬ cate precursors exhibit significant ion exchange properties. Thus, silicalite does not share the zeolit- ic property of substantial ion exchange common to crystalline aluminosilicate zeolites such as ZSM-5 zeolite.

Normally, the crystalline, nonzeolitic, in¬ termediate pore molecular sieve is intimately mixed with one or more amorphous, inorganic, refractory oxide components to form a support upon which the nickel hydrogenation metal component or components are subse¬ quently deposited. The proportion of molecular sieve in the support typically varies in the range of 2 to 90 weight percent. In some cases it may be desirable that the support contain the nonzeolitic molecular sieve in a minor proportion, usually between about 10 and 45 weight percent, and more usually between 20 and 40 weight percent, with 30 weight percent being highly preferred. In another embodiment of the invention, it is preferred that the nonzeolitic molecular sieve comprise a major proportion of the support, usually between about 60 and about 90 weight percent, with 80 weight percent being preferred.

At least part of the refractory oxide portion of the support serves as a binder to hold the molecular sieve cracking component together in the support. A preferred refractory oxide for use as the binder is a dense, low porosity, gamma alumina formed by calcining peptized alumina that has been mixed with the molecular sieve. The binder will typically comprise between about 5 and 30 weight percent, usually between about 10 and 25 weight percent, of the support. When the sup¬ port comprises a minor amount of the intermediate pore molecular sieve, it is preferred that the support contain a refractory oxide diluent in addition to the binder. This diluent may or may not possess some type of catalytic activity and will typically be an amor¬ phous, inorganic refractory oxide such as silica, magnesia, silica-magnesia, zirconia, silica-zirconia, titania, silica-titania, alumina, silica-alumina and combinations thereof. The preferred refractory oxide for use as the diluent is amorphous alumina, most preferably gamma alumina. Typically, the refractory oxide which comprises the diluent component of the support will have a surface area above about 50 m /gram. When an amorphous, inorganic, refractory oxide diluent is utilized as a component of the cata¬ lyst support, it will typically comprise between about 35 and 65 weight percent, preferably between about 45 and 55 weight percent, of the support.

The catalyst used in the process of the inven¬ tion is preferably prepared in particulate form, with cylinders being a preferred shape. One convenient method for preparing the catalyst involves first co- mulling a wetted mixture of the nonzeolitic, intermedi¬ ate pore, molecular sieve cracking component and a precursor of the inorganic refractory oxide binder, usually peptized alumina, in proportions appropriate to what is desired in the final catalyst support. If a refractory oxide diluent is also desired, a precursor of it, such as an alumina gel, hydrated alumina, a silica-alumina hydrogel, a silica sol and the like, is also mixed with the molecular sieve. The comulled mixture is then extruded through a die having openings in the preferred shapes, normally circles, ellipses. three-leaf clovers or four-leaf clovers. Among pre¬ ferred shapes for the die openings are ones that result in particles having surface-to-volume ratios greater than about 100 reciprocal inches. After extrusion, the catalyst support particles are cut into lengths of from 1/16 to 1/2 inch. The resulting particles are dried and calcined at an elevated temperature, normally between about 600° F. and 1600° F., to produce support particles of high crushing strength.

After calcination, the extruded support parti¬ cles are impregnated with a liquid solution containing nickel components in dissolved form, normally an aque¬ ous solution of dissolved nickel nitrate, or other soluble nickel salt to form the catalyst particles. After impregnation, the particles are dried and then calcined in air at temperatures at or above 800° F. for a time period sufficient to convert the metal compo¬ nents to the oxide form. The resulting catalyst parti¬ cles comprise nickel components distributed rather evenly over the intermediate pore molecular sieve cracking component and the amorphous, inorganic, re¬ fractory oxide or oxides.

Alternative methods of introducing the nickel components into the catalyst include mixing an appro¬ priate solid or liquid containing the nickel components with the materials to be extruded through the die. Such a method may prove less expensive and more conven¬ ient on a commercial scale than the impregnation method and will also result in nickel components being inti¬ mately mixed with the crystalline, nonzeolitic, molecu¬ lar sieve cracking component and the amorphous refrac¬ tory oxide component of the support. Regardless of how the nickel component is introduced into the catalyst, its concentration therein will be substantially great¬ er, normally one and one-half to two times greater, than could be achieved by ion exchange with the in¬ termediate pore, nonzeolitic, molecular sieve component of the catalyst.

It is preferred that the nickel constituents of the hydrodewaxing catalyst be converted to the sulfide form prior to use. This may be accomplished by contacting the catalyst in the hydrodewaxing reactor with a gas stream consisting of hydrogen and about 10 volume percent hydrogen sulfide at an elevated tempera¬ ture. Alternatively, if the waxy feedstock with which the catalyst is to be contacted contains organosulfur components, the catalyst may be merely placed in serv¬ ice in the oxide form and under the conditions speci¬ fied previously, the nickel components of the catalyst will be readily converted to the sulfide form in situ. It should be understood, however, that the nickel components of the catalyst can be converted to the sulfide form prior to the catalyst being loaded into the hydrodewaxing reactor by one of several techniques including the one described in U.S. Patent No. 4,719,195, the disclosure of which is hereby incorpo¬ rated by reference in its entirety.

Although the hydrodewaxing catalyst used in the process of the invention may contain more than one crystalline, nonzeolitic molecular sieve cracking component in combination with one or more amorphous, refractory oxide components, it is preferable that only one intermediate pore nonzeolitic molecular sieve, preferably silicalite, be present. Thus, the hydrode- waxing catalyst is usually devoid of crystalline zeolit- ic and nonzeolitic molecular sieves having small and large pore sizes, i.e., pore sizes below about 5.0 Angstroms and greater than 7.0 Angstroms. Also, the preferred catalyst is essentially free of an acid halogen component such as fluorine or chlorine. Pref¬ erably then, the hydrodewaxing catalyst used in the process of the invention consists essentially of nickel components, an intermediate pore, nonzeolitic molecular sieve and one or more amorphous, inorganic, refractory oxide components.

The effluent from the hydrodewaxing reactor has a substantially lower pour point than the feedstock due to the selective conversion by the hydrodewaxing catalyst of straight and slightly branched chain paraf¬ fins in the waxy hydrocarbon feedstock into lower molecular weight, non-waxy components. There is of course some change in the boiling characteristics between the feedstock and the effluent from the hy¬ drodewaxing reactor because hydrodewaxing is a form of hydrocraeking, and hydrocracking by necessity produces hydrocarbons of lowered boiling points. It is, howev¬ er, desirable, in most cases, to minimize the produc¬ tion of components boiling below the initial boiling point of the feedstock.

The hydrodewaxing catalyst of the invention is highly selective for hydrocracking waxy paraffins as evidenced by the substantial drop in pour point achieved in the reactor and the relatively small amount of conversion of high boiling feed components into lower boiling products. Typically, no more than about 15 to 25 volume percent of the high boiling components in lubricating base oils, particularly components boiling above about 650° F. , are converted to lower boiling products. Such low percentage conversions of high boiling components are indicative of efficient hydrogen utilization since the less hydrogen consumed in the unnecessary hydrocracking of non-waxy compo¬ nents, the less costly will be the facilities required to supply hydrogen to the process of the invention.

In addition to having a high hydrodewaxing activity, the catalyst used in the process of the invention is less expensive because it does not contain an expensive Group VIB metal component. Moreover, the catalyst has a high stability as indicated by its long life for the hydrodewaxing reactions required to con¬ vert the waxy feed oils into more valuable products. Virtually no deactivation of the catalyst is detected when utilized under preferred conditions for time periods greater than 30 days.

In some cases, it may be desirable to hydro- treat the effluent from the hydrodewaxing reactor in order to stabilize the product hydrocarbon by hydroge- nating olefins and other unsaturated hydrocarbons which tend to polymerize to form gums and sediments. If hydrotreating of the effluent is desired or required, the effluent will typically be passed downwardly through a bed of conventional hydrotreating catalyst in the presence of hydrogen under conditions such that the unsaturated hydrocarbons that tend to polymerize are saturated. Any conventional hydrotreating catalyst can be used. Such a catalyst will typically be similar to that used to hydrotreat the feedstock to the hydrode¬ waxing reactor, if such a step is necessary, and will typically contain a Group VIB and Group VIII metal component supported on an amorphous, porous, inorganic refractory oxide such an alumina.

The nature and objects of the invention are further illustrated by the following example, which is provided for illustrative purposes and not to limit the invention as defined by the claims. The example demon¬ strates that a catalyst containing nickel components and no Group VIB metal components supported on a mix¬ ture of silicalite and alumina is surprisingly more active and stable for hydrodewaxing than a similar catalyst containing a Group VIB metal.

EXAMPLE

An experimental catalyst was prepared by mixing 80 weight percent silicalite with 20 weight percent peptized

Catapal alumina and a sufficient amount of water to produce an extrudable paste. The silicalite used was obtained from Union Carbide Corporation and contained about 0.5 weight percent alumina, calculated as A1₂0₃. The mixture was mulled and then extruded through a 1/16 inch diameter die in the shape of cylinders. The extruded product was dried and then broken into parti¬ cles varying in length up to 1/2 inch. These particles were then dried and calcined at 900° F. for 1 hour. The dried and calcined extrudate particles were impreg¬ nated with a sufficient amount of a nickel nitrate solution to saturate the pores of the extrudate parti¬ cles. The nickel nitrate solution was prepared by dissolving 43 grams of nickel nitrate [Ni(N0₃)₂6H₂0] in 56 ml of water. The resulting impregnated particles were dried and calcined at 900° F. to produce catalyst particles containing about 5 weight percent nickel components, calculated as NiO.

A comparative catalyst similar to ones dis¬ closed in U.S. Patent Nos. 4,428,862 and 4,790,927 was prepared in the same manner as the experimental cata¬ lyst except the dried and calcined extrudate particles were impregnated by pore saturation with a solution containing both nickel nitrate and ammonium metatung- state. The impregnating solution was made by dissolv¬ ing 55 grams of nickel nitrate and 67 grams of ammonium metatungstate into 86 ml of water. After these impreg¬ nated particles were dried and calcined, the resultant catalyst particles contained 4 weight percent nickel components, calculated as NiO, and 18 weight percent tungsten components, calculated as W0₃.

The experimental and comparative catalysts were evaluated for hydrodewaxing activity utilizing a heavy vacuum gas oil having the properties set forth in Table 1.

TABLE 1

PROPERTIES AND CHARACTERISTICS OF FEEDSTOCK

Gravity, °API 20.5 Distillation. D-1160

Vol % F.

Pour point, ° F. 102 IBP/5 668/741

Sulfur, Wt % 2.97

Nitrogen, wt % 0.085

Hydrogen, wt % 12.0

Carbon, wt % 85.4

Flash point, ° F. 400

Normal paraffins C13 - C36, wt % 4.2 Max/Rec 1055/99.0%

About 77 grams of each catalyst was placed in a labora¬ tory size reactor vessel between two beds of the same hydrotreating catalyst, which catalyst contained 4 weight percent nickel, calculated as NiO, 24 weight percent molybdenum, calculated as Mo0₃, and 7 weight percent phosphorus, calculated as P₂0₅, supported on an amorphous alumina carrier. After loading, the reactor contained a lower bed of hydrotreating catalyst which comprised about 10 volume percent of the total catalyst in the reactor, a top bed of hydrotreating catalyst which comprised about 20 volume percent of the catalyst in the reactor and an intermediate bed of the experi¬ mental or comparative catalyst which comprised 70 volume percent of the total catalyst in the reactor. Prior to passing the heavy vacuum gas oil through the reactor, the catalyst bed system was presulfided by contacting the catalysts in the reactor for 19 hours with a gas consisting of 90 volume percent hydrogen and 10 volume percent hydrogen sulfide flowing at 19 stand¬ ard cubic feet per minute. The temperature in the reactor during the presulfiding step was gradually increased from room temperature to 700° F. At this point, the temperature was lowered to 450° F. and the heavy vacuum gas oil was passed into the reactor, through the first bed of hydrotreating catalyst to lower its concentration of sulfur and nitrogen, through the bed of hydrodewaxing catalyst and then through the second bed or post-treat bed of hydrotreating catalyst to stablize the hydrodewaxed product. The gas oil was passed through the reactor at a liquid hourly space velocity of 1.0 reciprocal hours. The temperature in the reactor was raised from about 450° F. to about 720° F. at a rate of about 50° F. per hour and then main¬ tained at 720° F. for 10 days. The temperature was then raised to 750° F. and maintained at that level for another 5 days. Hydrogen was passed through the reac¬ tor simultaneously with the vacuum gas oil in an amount equal to 5000 standard cubic feet of hydrogen per barrel of oil. The pressure maintained in the reactor was 1000 p.s.i.g. Samples of the effluent product from the reactor were taken at regular intervals during the 15-day run and analyzed. A comparison of the tempera¬ ture required to yield a product pour point of 21° F. for. both the experimental and comparative catalysts and the yield of 650° F.+ material are set forth below in Table 2.

TABLE 2

Experimental Comparative Catalyst Catalyst

Reactor temperature required to yield

21° F. pour point, ° F. 720 750

Yield of 600° F.+ material, vol % 81.9 75.4

As can be seen from Table 2, the experimental catalyst containing nickel constituents, but no tung¬ sten constituents, supported on a mixture of silicalite and alumina was 30° F. more active (750° F. - 720° F.) for reducing the pour point of the vacuum gas oil to 21° F. than the comparative catalyst which contained both nickel and tungsten components on the same sup¬ port. This is a surprising and unexpected result in view of the teachings of U.S. Patents Nos. 4,428,862 and 4,790,927 that a Group VIB metal such as tungsten is required to obtain good hydrodewaxing activity. Obviously, the data in Table 2 show that much greater hydrodewaxing activities may be obtained by not includ¬ ing an expensive tungsten component in the catalyst. This means that a less expensive Group VIB metal-free catalyst can be used in the process of the invention to obtain desired pour points at lower temperatures which further reduces the cost of the hydrodewaxing process. Moreover, since the experimental catalyst was able to accomplish the same pour point reduction at a much lower temperature than the comparative catalyst, it gave a higher yield of desired products; i.e., 81.9 volume percent of products boiling above 600°_*F. versus 75.4 volume percent.

A sampling of the pour point data for products taken from the laboratory reactor during the 720° F. run period as a function of time is set forth in Table 3.

TABLE 3

Experimental Comparative Catalyst Catalyst

Product pour point at base time, ° F. 21 32

Product pour point at base time + 80 hrs, ° F. 21 . 43

Product pour point at base time + 160 hrs, ° F. 21 48

As can be seen from the data in Table 3, the product pour points obtained with the experimental catalyst remained constant over a period of 160 hours or 6 1/2 days while the pour point of products obtained with the comparative catalyst gradually increased with time from 32° F. to 48° F. These data are indicative of the superior stability of the tungsten-free catalyst when used for hydrodewaxing, which stability is also unex¬ pected in view of the teachings of U.S. Patent Nos. 4 , 428 , 862 and 4 , 790 , 927 .

Although this invention has been described in conjunction with an example and by reference to several embodiments of the invention, it is evident that many alterations, modifications and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace within the invention all such alternatives, modifications and variations that fall within the spirit and scope of the appended claims.

Claims

I CLAIM

1. A process for hydrodewaxing a hydrocarbon feedstock containing waxy paraffins which comprises contacting said feedstock in the presence of hydrogen under hydrodewaxing conditions with a catalyst composi¬ tion comprising:

(a) a crystalline, intermediate pore, nonzeo¬ litic molecular sieve having cracking activity; and

(b) a hydrogenation component comprising nickel components but no Group VIB metal components, said nickel components comprising less than about 12 weight percent, calculated as NiO, of said catalyst composition.

2. A process as defined by claim 1 wherein said catalyst composition further comprises an amor¬ phous, inorganic, refractory oxide binder.

3. A process as defined by claim 1 wherein said intermediate pore, nonzeolitic molecular sieve comprises a silicoaluminophosphate molecular sieve.

4. A process as defined by claim 3 wherein said silicoaluminophosphate molecular sieve is SAPO-11 molecular sieve.

5. A process as defined by claim 1 wherein said intermediate pore, nonzeolitic molecular sieve comprises an aluminophosphate molecular sieve.

6. A process as defined by claim 5 wherein said aluminophosphate molecular sieve is A1P0 -11 molecular sieve.

7. A process as defined by claim 1 wherein said intermediate pore, nonzeolitic molecular sieve comprises a titanium aluminophosphate molecular sieve.

8. A process as defined by claim 7 wherein said titanium aluminophosphate molecular sieve is TAPO- 11 molecular sieve.

9. A process as defined by claim 1 wherein said intermediate pore, nonzeolitic molecular sieve comprises a titanium aluminosilicate molecular sieve.

10. A process as defined by claim 9 wherein said titanium aluminosilicate molecular sieve is TASO- 45 molecular sieve.

11. A process as defined by claim 1 wherein said intermediate pore, nonzeolitic crystalline molecu¬ lar sieve comprises a crystalline silica polymorph.

12. A process as defined by claim 11 wherein said crystalline silica polymorph is silicalite.

13. A process as defined by claim 1 wherein said hydrogenation component contains nickel as essen¬ tially the only metal therein.

14. A process as defined by claim 1 wherein said nickel components comprise between about 2 and about 8 weight percent, calculated as NiO, of said catalyst composition.

15. A process as defined by claim 1 wherein said hydrocarbon feedstock is a waxy vacuum gas oil.

16. A process as defined by claim 2 wherein said nickel components are supported on both said inorganic, refractory oxide binder and said nonzeolitic molecular sieve.

17. A process for treating a waxy hydrocarbon feedstock having a pour point above about 50° F. which comprises:

(a) contacting said feedstock in the presence of hydrogen at an elevated temperature above about 500° F. and at an elevated pressure with a catalyst composi¬ tion comprising a nickel component on a support com¬ prising silicalite and an amorphous, inorganic, refrac¬ tory oxide binder, wherein said catalyst composition contains between about 1 and about 9.5 weight percent nickel components, calculated as NiO, and is substan¬ tially devoid of Group VIB metal components; and

(b) recovering a product_^ hydrocarbon having a substantially lower pour point as compared to said waxy hydrocarbon feedstock.

18. A process as defined by claim 17 wherein said inorganic, refractory oxide binder comprises alumina .

19. A process as defined by claim 17 wherein said product hydrocarbon has a pour point below about 30° F.

20. A process as defined by claim 17 wherein said catalyst composition comprises between about 3.5 and 6.0 weight percent nickel components, calculated as NiO.

21. A process as defined by claim 17 wherein the overall conversion of components in said feedstock boiling above about 650° F. to components boiling at or below about 600° F. in said contacting step is no more than about 25 volume percent.

22. A process as defined by claim 18 wherein said support consists essentially of alumina and sili¬ calite.

23. A process as defined by claim 17 wherein said waxy hydrocarbon feedstock is a shale oil.

24. A process as defined by claim 18 wherein said catalyst further comprises an amorphous, inorgan¬ ic, refractory oxide diluent.

25. A process as defined by claim 24 wherein said catalyst comprises between about 20 and 40 weight percent silicalite, between about 10 and 25 weight percent alumina binder and between about 35 and 65 weight percent amorphous, inorganic, refractory oxide diluent.

26. A process as defined by claim 25 wherein said refractory oxide diluent comprises alumina having a surface area greater than about 50 m²/gram.

27. A process as defined by claim 18 wherein said catalyst comprises between about 70 and 90 weight percent silicalite and between about 10 and 30 weight percent alumina binder.

28. A process for upgrading a waxy hydrocar¬ bon feedstock containing organonitrogen components and organosulfur components and having a relatively high pour point, which process comprises:

(a) contacting said waxy hydrocarbon feed¬ stock with hydrogen in the presence of a hydrotreating catalyst in a h'/drotreating zone under conditions such that the concent-ation of organosulfur and organonitro¬ gen compounds is .-educed;

(b) contacting the effluent from said hydro¬ treating zone with ϊ. drogen in the presence of a hy¬ drodewaxing catalyst :_n a hydrodewaxing zone under conditions such that -he pour point of said hydrotreat- ed feedstock from step (a) is reduced, wherein said hydrodewaxing catalyst is substantially free of Group VIB metal components an comprises (1) between about 1 and 9.5 weight percent nickel components, calculated as NiO, (2) an essentially Group IIIA metal-free crystal¬ line silica molecular sieve having pores defined by 10- membered rings of oxygen atoms and (3) an amorphous, inorganic, refractory oxide binder; and

(c) recovering a product hydrocarbon having a reduced pour point and containing a decreased concen¬ tration of organonitrogen and organosulfur components in comparison to said waxy hydrocarbon feedstock.

29. A process as defined by claim 28 wherein the effluent from said hydrotreating zone contains constituents boiling above about 650° F. but less than about 25 volume percent of said constituents are con¬ verted in said hydrodewaxing zone into constituents boiling below 600° F.

30. A process as defined by claim 28 wherein said inorganic, refractory oxide binder comprises alumina.

31. A process as defined by claim 30 wherein said crystalline silica molecular sieve comprises silicalite.

32. A process as defined by claim 31 wherein the pour point of said product hydrocarbon is at least 30° F. lower than the pour point of said waxy hydrocar¬ bon feedstock.

33. A process as defined by claim 31 wherein said waxy hydrocarbon feedstock is a heavy vacuum gas oil.

34. A process as defined by claim 31 wherein said waxy hydrocarbon feedstock is a shale oil.

35. A process as defined by claim 31 wherein the product hydrocarbon recovered in step (c) is subse¬ quently hydrotreated to hydrogenate olefins and thereby stabilize said product.

36. A process as defined by claim 31 wherein said hydrodewaxing catalyst contains between about 3.5 and 6.0 weight percent nickel components, calculated as NiO.

37. A catalyst composition comprising:

(b) a hydrogenation component comprising a nickel component but no Group VIB metal components, wherein said nickel components comprise less than about 12 weight percent, calculated as NiO, of said catalyst composition.

38. A catalyst composition as defined by claim 37 further comprising an amorphous, inorganic, refractory oxide binder.

39. A catalyst composition as defined by claim 38 wherein said nonzeolitic molecular sieve is silicalite and said refractory oxide binder is alumina.