GB2141733A - Improved catalytic hydrodewaxing process - Google Patents

Abstract

The presence of ammonia with hydrogen sulfide in the hydroconversion zone is shown to activate zeolite catalysts for hydrodewaxing or isomerization dewaxing.

Description

SPECIFICATION Improved catalytic hyd rodewaxing process The present invention is concerned with reducing wax content of hydrocarbon fractions by conversion of straight or slightly branched paraffin hydrocarbons contained therein. The conversion is accomplished by shape selective dual function catalysts in the presence of hydrogen, a technique aptly designated catalytic hydrodewaxing.

More particularly, the invention is concerned with a novel method of improving catalyst activity during catalytic hydrodewaxing.

It has long been recognized that long straight chain paraffin hydrocarbons containing upwards of about 1 8 carbon atoms will crystallize from a solution of petroleum hydrocarbons at substantially higher temperatures than the freeze point of other hydrocarbons of like boiling points. A fraction separated from a waxy crude oil by distillation will be incapable of flow from a vessel at a temperature such that the wax crystals formed will inhibit such flow. Such temperature is the pour point of the hydrocarbon fraction. Lubricants and liquid fuels can not be used in the intended manner at temperatures below the pour point. Difficulties due to poor pumpability and clogging of filters can be encountered at higher temperatures due to suspended wax crystals in the oil.

Dewaxing of lubricating oils has been practiced for many years by chilling the oil, usually in a solvent, and separating the wax crystals, as by filters, centrifuges and the like. A more recent development is catalytic hydrodewaxing in which a mixture of hydrogen and waxy hydrocarbon fraction is contacted at conversion conditions of temperature and pressure with a shape selective porous solid catalyst having acid activity for cracking with or without a metallic hydrogenation/ dehydrogenation catalyst. The porous solid catalyst is characterized by uniform pores which will admit only straight chain or straight and slightly branched chain paraffinic compounds and therefore converts only those compounds so admitted. Aluminosilicate zeolites having pores of a dimension to admit long chain paraffinic compounds in the nature of petroleum are examples of acid catalysts which can be used.These zeolites crack the wax molecules to lower molecular weight compounds of lower boiling range which will not crystallize at the same pour point as the original wax and which may be removed by distillation, if desired. Among the zeolites proposed for this process, mention may be made of mordenite and zeolities of the ZSM-5 family.

The preferred zeolites for catalytic hydrowaxing are those having shape selective properties similar to that of zeolite ZSM-5 as described for that purpose in United States Patent Re.

28,398 to Chen et al. Catalytic hydrodewaxing techniques are effective to reduce pour points and cloud point of fuels and lubricants. One such dewaxing process employing zeolite beta is described in U.S. Patent 4,419,220 wherein hydrocarbon feedstocks such as distillate fuel oils and gas oils are dewaxed by isomerizing the waxy components over the zeolite beta catalyst.

The process may be carried out in the presence or absence of hydrogen.

Typically, the hydrodewaxed effluent is separated from unused hydrogen, ammonia, hydrogen sulfide and gaseous hydrocarbons and the hydrogen is recycled to the reactor. It is known that ammonia formed by nitrogen compounds in the hydrocarbon feed will impair the activity of catalysts for hydrocracking. Accordingly, catalytic hydrodewaxing processes are often run with either fresh hydrogen or scrubbed recycled streams containing very little ammonia and hydrogen sulfide.

A hydrocracking catalyst which is used in the treatment of petroleum fractions such as heavy distillates and residua which have a relatively high organic nitrogen content will decline in activity with use due to the ammonia which is formed from the nitrogen compounds. United States Patent No. 4,255,251 discloses that the activity of a hydrocracking catalyst comprising a hydrogenating component supported on a cracking component such as an acidic aluminosilicate zeolite for the conversion of heavy hydrocarbon oils can be partially restored by contacting the catalyst with a mixture of an oxygen-containing gas such as air, water vapor, and sulfur dioxide at an elevated temperature in the range of 200"C to 425"C.

United States Patent No. 3,804,742 discloses a process of producing lubricating oil and gasoline by hydrocracking a petroleum feedstock boiling above 350"C using a catalyst of a hydrogenating metal and an alkali metal deficient faujasite in the presence of NH3 and H2S which are preferably produced by treating a nitrogen and sulfur containing feedstock in a preliminary catalytic denitrogenation and desulfurization step. The patent discloses that the presence of NH3 and H2S has the effect in reducing catalyst activity, at least temporarily, and consequently, process conditions have to be more severe to obtain a given level of conversion.

United States Patent No. 3,778,365 discloses a process for upgrading a high boiling, nitrogen-containing feedstock in the presence of H2 by hydrocracking with a crystalline zeolite catalyst containing a mixture of nonnoble metal hydrogenation components in which the catalyst has been activated prior to contact with the feedstock with ammonia. The catalyst can be ammoniated in the presence of sulfur, provided that the partial pressure of the ammonia is at least about 1.5 times as great as the partial pressure of the generated hydrogen sulfide.

In accordance with the present invention catalytic hydrodewaxing processes, including processes wherein waxy compounds are isomerized, using an aluminosilicate cracking catalyst, optionally containing a hydrogenating component, are improved by processing the waxy hydrocarbon fraction in the presence of controlled amounts of both ammonia and hydrogen sulfide. It has now been discovered that maintaining effective quantities of ammonia and hydrogen sulfide in the hydroconversion zone produces an activity gain.

Typical waxy hydrocarbon feedstocks comprise nitrogen and sulfur-containing compounds which are converted to ammonia and hydrogen sulfide during hydrocracking. The generated ammonia and hydrogen sulfide along with excess hydrogen are separated from the dewaxed effluent and form the recycle stream. In accordance with the present invention, about 2-500 ppmV of ammonia and sufficient hydrogen sulfide to provide a H,S/NH3 mole ratio of at least 0.5 are maintained in the reacton zone by controlling the amount of ammonia and hydrogen sulfide contained in the recycle.Inasmuch as it has been suggested to run catalytic hydrodewaxing processes with either fresh hydrogen or scrubbed recycle streams containing very small amounts of ammonia and hydrogen sulfide which heretofore have been considered catalyst "poisons", a substantial economic advantage can be achieved by eliminating the step of scrubbing the hydrogen gas recycle stream free of ammonia and hydrogen sulfide as is possible in the present invention. An additional advantage of the catalytic hydrodewaxing process of the present invention lies in the increase in catalytic activity which has been found and which thus results in longer catalyst cycle times.

The novelty of the catalytic hydrodewaxing process of this invention is predicated upon the controlled addition of ammonia and hydrogen sulfide into the process stream and the effect such addition of ammonia and hydrogen sulfide has on the activity and aging of the hydrodewaxing catalyst. The term "dewaxing" as used in the specification and the claims is used in its broadest sense as intended to mean the removal of those hydrocarbons which readily solidify (waxes) from petroleum stocks. The charge stocks used as feed to the process include heavy distillates or residua, such as feed to the process include heavy distillates or residua, such as coke distillates.

whole crudes, atmospheric residua, vacuum residua, tar sand oil, shale oil, and heavy cycle gas oils and the like. Generally, hydrocarbon feeds which can be treated include lubricating oil stocks as well as those that have a freeze point or pour point problem, i.e., petroleum stocks boiling above about 350"F. The dewaxing is carried out under hydrocracking, isomerization or hydroisomerization conditions.

In accordance with the present invention, a waxy hydrocarbon feed is brought into contact, under dewaxing conditions, with hydrogen and a catalyst comprising a crystalline aluminosilicate zeolite having a silica-to-alumina ratio of at least about 1 2 and a constraint index within the approximate range of 1 to 12. Non-limiting examples of useful crystalline aluminosilicate zeolites include ZSM-5, ZSM-1 1, ZSM-12, ZSM-23, ZSM-35, ZSM-38, ZSM-48 and zeolite beta.

The synthesis and characteristics of zeolite ZSM-5 are described in United States Patent No.

3,702,886, issued November 14, 1972.

The synthesis and characteristics of zeolite ZSM-11 are described in United States Patent No.

3,709,979, issued January 9, 1973.

The synthesis and characteristics of zeolite ZSM-12 are described in United States Patent No.

3,832,449, issued August 27, 1974.

The synthesis and characteristics of zeolite ZSM-23 are described in United States Patent No.

4,076,842.

The synthesis and characteristics of zeolite ZSM-35 are described in United States Patent No.

4,016,245, issued April 5, 1977.

The synthesis and characteristics of zeolite ZSM-38 are described in United States Patent No.

4,046,849.

The synthesis and characteristics of zeolite ZSM-48 are discussed in United States Patent No.

4,375,573.

The synthesis and characteristics of zeolite beta are described in United States Patent Nos.

3,308,069 and Re 28341.

Although the zeolites herein described have unusuallv low alumina contents, i.e., hiqh silicato-alumina ratios, they are very active even when the silica-to-alumina ratio exceeds 30. The activity is surprising since catalytic activity is generally attributed to framework aluminum atoms and cations associated with these aluminum atoms. These catalysts retain their crystallinity for long periods in spite of the presence of steam and high temperature which induces irreversible collapse of the framework of other zeolites, e.g., of the X and A type. Furthermore, cabonaceous deposits when formed, may be removed by burning at higher than usual temperature to restore activity. In many environments the zeolites of this class exhibit very low coke forming capability, conducive to very long times on stream between burning regenerations.

An important characteristic of the crystal structure of the zeolites for use herein is that they provide constrained access to, and egress from, the intracrystalline free space by virtue of having a pore dimension greater than about 5 Angstroms and pore windows of about a size such as would be provided by 10-membered rings of oxygen atoms. It is to be understood, of course, that these rings are those formed by the regular disposition of the tetrahedra making up the anionic framework of the crystalline aluminosilicate, the oxygen atoms themselves being bonded to the silicon or aluminum atoms at the centers of the tetrahedra. Briefly, the preferred type catalysts useful in this invention possess, in combination: a silica-to-alumina ratio of at least about 12; and a structure providing constrained access to the crystalline free space.

The silica-to-alumina ratio referred to may be determined by conventional analysis. This ratio is meant to represent as closely as possible, the ratio in the rigid anionic framework of the zeolite crystal and to exclude aluminum in the binder or in cationic or other form within the channels. Although catalysts with a silica-to-alumina ratio of at least 1 2 are useful, it is preferred to use catalysts having higher ratios of at least about 30. Such catalysts, after activation, acquire an intracrystalline sorption capacity for normal hexane which is greater than that for water, i.e., they exhibit "hydrophobic" properties. It is believed that this hydrophobic character is advantageous in the present invention.

The type of zeolites useful in this invention freely sorb normal hexane and have a pore dimension greater than about 5 Angstroms, or, if elliptical in pore shape, at least the size of the pores in ZSM-5. 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. For example, if the only pore windows in a crystal are formed by 8-membered rings of oxygen atoms, then access to molecules of larger cross-section of normal hexane is excluded and the zeolite is not of the desired type. Windows of 10-membered rings are preferred, although, in some instances, excessive puckering or pore blockage may render these catalysts ineffective. 12-membered rings do not generally appear to offer sufficient constraint to produce the advantageous conversions. Also, structures can be conceived due to pore blockage or other cause, that may be operative.

Rather than attempt to judge from the crystal structure whether or not a catalyst possesses necessary constrained access, a simple determination of the "constraint index" may be made by passing continuously a mixture of an equal rate of normal hexane and 3-methylpentane over a small sample, approximately 1 gram or less of catalyst at atmospheric pressure according to the following procedure. A sample of the catalyst, in the form of pellets or extrudate, is crushed to a particle size about that of coarse sand and mounted in a glass tube. Prior to testing, the catalyst is treated with a stream of air at 1000"F for at least 15 minutes. The catalyst is then flushed with helium and the temperature adjusted between 550"F and 950"F to give an overall conversion between 10% and 60%.The mixture of hydrocarbons is passed at 1 liquid hourly space velocity (i.e., 1 volume of liquid hydrocarbon per volume of catalyst per hour) over the catalyst with the helium dilution to give a helium to total hydrocarbon mole ratio ratio of 4:1.

After 20 minutes on stream, a sample of the effluent is taken and analyzed, most conveniently by gas chromatography, to determine the fraction remaining unchanged for each of the two hydrocarbons.

The "constraint index" is calculated as follows: log,0(fraction of n-hexane remaining) Constraint Index log10(fraction of 3-methylpentane remaining) The constraint index approximates the ratio of the cracking rate constants for the two hydrocarbons. Catalysts suitable for the present invention are those having a constraint index in the approximate range of 1 to 1 2. Constraint Index (Cl) values for some typical catalysts, including those useful herein, are: Crystalline Aluminosilicate Cl ZSM-5 8.3 ZSM-11 8.7 ZSM-12 2.0 ZSM-23 9.1 ZSM-35 4.5 ZSM-38 2.0 Beta 1.5 ZSM-4 0.5 H-Zeolon 0.5 REY 0.4 Erionite 38 It is to be realized that the above constraint index values typically characterize the specified zeolites but that such are the cumulative result of several variables used in determination and calculation thereof.Thus, for a given zeolite depending on the temperature employed within the aforenoted range of 50'to 950"F, with accompanying conversion between 10% and 60%, the constraint index may vary within the indicated approximate range of 1 to 12. Likewise, other variables such as the crystal size of the zeolite, the presence of possibly occluded contaminants and binders intimately combined with the zeolite may affect the constraint index. It will accordingly be understood by those skilled in the art that the constraint index, as utiiized herein, while affording a highly useful means for characterizing the zeolites of interest is approximate, taking into consideration the manner of its determination, with the probability, in some instances, of compounding variable extremes.However, in all instances, at a temperature within the above-specified range of 550"F to 950"F, the constraint index will have a value for any given zeolite of interest herein within the approximate range of 1 to 1 2.

The specific zeolites described, when prepared in the presence of organic cations, are catalytically inactive, possibly because the intracrystalline free space is occupied by organic cations from the forming solution. They may be activated by heating, for example, in an inert atmosphere at 1000"F for 1 hour, followed by base exchange with ammonium salts and by calcination at 1000"F in air. The presence of organic cations in the forming solution may not be absolutely essential to the formation of this type zeolite; however, the presence of these cations does appear to favor the formation of this special tupe of zeolite. More generally, it is desirable to activate this type catalyst by base exchange with ammonium salts followed by calcination in air at about 1000"F for from about 15 minutes to about 24 hours.

Natural zeolites may sometimes be converted to this type zeolite catalyst by various activation procedures and other treatments such as base exchange, steaming, alumina extraction and calcination, in combinations. Natural minerals which may not be so treated include ferrierite, brewsterite, stilbite, dachiardite, epistilbite, heulandite and clinoptilolite. The preferred crystalline aluminosilcates are ZSM-5, ZSM-11, ZSM-12, ZSM-23, ZSM-35 and ZSM-38, ZSM-48 and zeolite beta, with ZSM-5 and zeolite beta particularly preferred.

In a preferred aspect of this invention, the catalysts hereof are selected as those having a crystal framework density, in the dry hydrogen form, of not substantially below about 1.6 grams per cubic centimeter. It has been found that zeolites which satisfy all three of these criteria are most desired for the present process. Therefore, the preferred catalysts of this invention are those having a constraint index as defined above of about 1 to about 12, a silica-to-alumina ratio of at least about 1 2 and a dried crystal density of not less than about 1.6 grams per cubic centimeter. The dry density for known structures may be calculated from the number of silicon plus aluminum atoms per 1000 cubic Angstroms, as given, e.g., on page 1 9 of the article on Zeolite Structure by W. M. Meier.This paper, the entire contents of which are incorporated herein by reference, is included in "Proceedings of the Conference on Molecular Sieves, London, April, 1 967," published by the Society of Chemical Industry, London, 1 968. When the crystal structure is unknown, the crystal framework density may be determined by classical pyknometer techniques. For example, it may be determined by immersing the dry hydrogen form of the zeolite in an organic solvent which is not sorbed by the crystal, or in mercury under pressure (mercury porosimeter). It is possible that the unusual sustained activity and stability of this class of zeolite is associated with its high crystal anionic framework density of not less than about 1.6 grams per cubic centimeter. This high density, of course, must be associated with a relatively small amount of free space within the crystal, which might be expected to result in more stable structures. This free space, however, is important as the locus of catalytic activity.

Crystal framework densities of some typical zeolites are: Void Framework Ferrierite 0.28 cc/cc 1.76 g/cc Mordenite .28 1.7 ZSM-5, - 11 .29 1.79 Dachiardite .32 1.72 L .32 1.61 Clinoptilolite .34 1.77 Laumontite .34 1.77 ZSM-4 .38 1.65 Heulandite .39 1.69 P .41 1.57 Offretite .40 1.55 Levynite .40 1.54 Erionite .35 1.51 Gmelinite .44 1.46 Chabazite .47 1.45 A .5 1.3 Y .48 1.27 When synthesized in the alkali metal form, the zeolite is conveniently converted to the hydrogen form, generally by intermediate formation of the ammonium form as a result of ammonium ionic exchange and calcination of the ammonium form to yield the hydrogen form.

In addition to the hydrogen form, other forms of the zeolite wherein the original alkali metal has been reduced to less that about 1.5 percent by weight may be used. Thus, the original alkali metal of the zeolite may be replaced by ion exchange with other suitable ions of Groups IB to VIII of the Periodic Table, including, by way of example, nickel, copper, zinc, palladium, calcium or rare earth metals.

In practicing the desired conversion process, it may be desirable to incorporate the abovedescribed crystalline aluminosilicate zeolite in another material resistant to the temperature and other conditions employed in the process. Such matrix materials include synthetic or naturally occurring substances 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. Naturally occurring clays which can be composited with the zeolite can include those of the montmorillonite and kaolin families, which families include the sub-bentonites 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 anauxite. Such clays can be used in the raw state as originally mined or initially subjected to calcination, acid treatment or chemical modification.

In addition to the foregoing materials, the zeolites employed herein may be composited with a porous matrix material, such as alumina, silica-alumina, silica-magnesia, silica-zirconia, silicathoria, 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 matrix may be in the form of a co-gel. The relative proportions of zeolite components and inorganic oxide gel matrix may vary widely with the zeolite content ranging from between about 1 to about 99 percent by weight and more usually in the range of about 5 to about 80 percent by weight of composite.

Conditions for hydrodewaxing will be generally those described in United States Patent Re.

28,398, of United States Patent No. 3,700,585. Process conditions include a temperature within a range of about 450"F to about 1 000'F and a pressure which will range between about 100 and 3000 psig, preferably from 200 to 700 psig. Liquid hourly space velocity will generally range between about 0.1 and 10 volumes of liquid feed per volume of catalyst per hour, preferably 0.5 to 4. Hydrogen is supplied at a ratio of 1 to 20 moles of hydrogen per mole of total hydrocarbon charge, preferably a mole ratio of 4 to 1 2 H2/HC.

Conditions for isomerization dewaxing will be generally those described in United States Patent No. 4,419,220. Process conditions include a temperature of from 200"C to 540"C, a pressure of from atmospheric to 25000 kPa and an LHSV of from 0.1 to 20 hr.

The catalysts employed in this invention are constituted by a zeolite as described above in intimate combination with a hydrogenating component such as tungsten, vanadium, molybdenum, rhenium, nickel, cobalt, chromium, manganese, or noble metals such as platinum or palladium. The hydrogenating component may be either in metallic form or as an oxide, sulfide, or telluride thereof. The hydrogenating component can be exchanged into the zeolite compo sition, impregnated therein or physically intimately mixed therewith. Such a component can be impregnated in or onto the zeolite such as, for example, by, in the case of platinum, 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 the metal 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 cation complex, e.g., Pt(MH3)4C12 is particularly useful.

The present invention is based on the recent discovery that the activity of an aluminosilicate zeolite catalyst used in catalytically hydrodewaxing a hydrocarbon feed can be enhanced by maintaining effective quantities of ammonia and hydrogen sulfide in the conversion zone.

Applicable levels of ammonia maintained in the conversion zone will range from about 2-500 ppmV. A sufficient amount of hydrogen sulfide must also be present. Thus, an amount of hydrogen sulfide to provide a H3S:NH3 mole ratio of at least about 0.5 is preferred. Preferably, the applicable levels of ammonia and hydrogen sulfide are generated from the hydrocracking of the feed in the hydroconversion zone, separated from the effluent, and included in the hydrogen gas recycle stream. External sources of NH3 or H2S may be provided, if required. The amounts of NH3 and H2S required to provide any desired degree of catalyst improvement can be readily determined (within the applicable levels) by comparative experiments if necessary. Preferably, it has been found that about 5 to about 300 ppmV of ammonia in the conversion zone achieves an activity gain.About 10 to about 1 50 ppmV of ammonia represents the most preferred amounts to be present in the hydroconversion zone. The amounts of NH3 and H2S added into the reaction zone either from recycle and/or external sources will vary depending on the nitrogen and sulfur content of the waxy feed and the H2 recycle to make-up ratio. For example, a waxy hydrocarbon charge stock containing about 400 to about 500 ppm by weight nitrogen and about 0.4 to about 0.5 percent by weight sulfur yields about 50 ppmV ammonia and about 0.5 percent by weight sulfur yields about 50 ppmV ammonia and about 500 ppmV hydrogen sulfide in the conversion zone at equilibrium with a 1:1 recycle to make-up ratio in which the H2 recycle stream is substantially free of NH3 and H2S.In the present invention, the NH3 and H2S are preferably separated from the effluent along with H2 and recycled into the conversion zone without scrubbing the recycle stream of these compounds rather than added from external sources.

The amounts of NH3 by weight relative to the hydrocarbon feed at the reactor inlet that are applicable in accordance with the present invention comprise generally .00007 to .02%, preferred .0002-.01 %, and most preferred .0004 to .005%.

Insomuch as catalystic hydrodewaxing processes are often run with either fresh hydrogen or scrubbed recycle streams containing very small amounts of ammonia and hydrogen sulfide, an important economic advantage can be achieved by the present invention in eliminating scrubbing of the recycle stream.

The following examples illustrate the improved process of the present invention.

EXAMPLE 1 This example run was made in a continuous microunit, charging Shengli vacuum gas oil having the following properties: Gravity, "API 34.9 Gravity, Specific 0.8504 Pour point, "F + 70 Sulfur, wt. % 0.44 Nitrogen, ppm 440 Boiling Range, "F IBP 467 5% 544 10% 544 30% 567 50% 647 70% 687 90% 752 95% 777 Reaction conditions were 600 psig, 1 LHSV, and 2500 SCF H2/bbl, temperature adjusted to get +10"F pour point. At 14 days on stream, 130 ppm by weight NH3 was dissolved in the charge (equivalent to 340 ppmV in hydrogen stream), resulting in a 25"F activity loss over a 38 hour period. Upon removal of the NH2 activity returned to the same point before the addition.

This example shows that the aged catalyst is deactivated by a low concentration of NH2 alone.

EXAMPLE 2 This run was made in a continuous pilot plant unit, charging the same Shengli vacuum gas oil used in Example 1. Results are summarized in the table below: Recycle Gas Single Pass Pure H2 Days on Stream 33-54 55-76 Pressure, psig 585 585 LHSV 1.1 1.1 Fresh H2 Makeup, SCFB 2500 1200 Recycle Gas, SCFB - 1600 Recycle Gas H2 Purity, Vol % 90 Recycle Gas H2S, ppmV - 1000 Recycle Gas NH3, ppmV - 100 Temperature, "F 765") 763'2' 330"F+ Product Pour Point, "F 0(" - 15(2) (1) at 54 days on stream (2) at 56 days on stream It can be seen that addition of 100 ppmV NH3 and 1000 ppmV H2S in the recycle stream (equivalent to 20 ppm by weight NH3 and 500 ppm by weight H2S in the gas oil feed) at 55 days on stream resulted in a 15"F lower pour point.

This example shows that the aged catalyst not only is not deactivated by the addition of low concentrations of NH3 plus H2S, but is actually activated.

Claims (10)

1. In a process for reducing the wax content of hydrocarbon feedstocks in which the feedstocl < is contacted in a hydroconversion zone with a shape selective dewaxing zeolite catalyst in the presence of hydrogen at an elevated temperature and pressure, the improvement which comprises; providing effective quantities of ammonia and hydrogen sulfide in the hydroconversion zone, said effective quantities comprising from about 2-500 ppmV ammonia and an H2S/NH3 mole ratio of at least about 0.5.

2. The improvement of claim 1 wherein said shape selective dewaxing catalyst comprises an aluminosilicate zeolite having a silica-to-alumina mole ratio of at least about 1 2 and a constraint index within the approximate range of 1 to 1 2.

3. The improvement of claim 2 wherein said elevated temperature is within the range from about 450"F to about 1000oF and said elevated pressure ranges between about 100 and 3000 psig and the feedstock has a liquid hourly space velocity of about 0.1 to 1 0.

4. The improvement of claim 2 wherein said effective amount of ammonia comprises at least about 5 to about 300 ppmV in the hydroconversion zone.

5. The improvement of claim 4 wherein said effective amount of ammonia comprises at least about 10 to about 1 50 ppmV in the hydroconversion zone.

6. The improvement of claim 2 wherein the mole ratio of ammonia to hydrogen sulfide in the hydroconversion zone is about 0.5 to about 100.

7. The improvement of claim 2 wherein said effective quantity of ammonia is provided in the hydroconversion zone by a nitrogen-containing feedstock which produces ammonia at the process conditions, said generated ammonia being separated from the effluent and recycled into the hydroconversion zone.

8. The improvement of claim 2 wherein the effective quantities of ammonia present in the hydroconversion zone is provided at least in part from an external source.

9. The improvement of claim 2 wherein said dewaxing catalyst is ZSM-5 or zeolite beta.

10. The improvement of claim 9 wherein said dewaxing catalyst contains a metal hydrogenating component.