Field of the Invention

This invention relates to hydrogenation catalysts and their use in a hydrogenation process which is particularly applicable to the hydrogenation or hydrotreating of lubricant oils, especially synthetic lubricant oils produced by the oligomerization of low molecular weight olefins.

Background of the Invention

Hydrogenation is a well-established process both in the chemical and petroleum refining industries. Hydrogenation is conventionally carried out in the presence of a catalyst which usually comprises a metal hydrogenation component on a porous support material, such as a natural clay or a synthetic oxide. Nickel is often used as a hydrogenation component, as are noble metals such as platinum, palladium, rhenium and iridium. Typical support materials include kieselguhr, alumina, silica and silica-alumina. Depending upon the ease with which the feed may be hydrogenated, the hydrogen pressures used may vary from quite low to very high values, typically from about 791 to 17,339 kPa.

Hydrogenation is an exothermic process and is therefore thermodynamically favored by lower temperatures but for kinetic reasons, moderately elevated temperatures are normally used and for petroleum refining processes, temperatures in the range of 38* to 371 ^β C. are typical.

Hydrogenative treatment is frequently used in petroleum refining to improve the qualities of lubricating oils, both of natural and synthetic origin. Hydrogenation, or hydrotreating as it is frequently termed, is used to reduce residual unsaturation in the lubricating oil, and to remove heteroatom-containing impurities and color bodies. The removal of impurities and color bodies is of particular

significance for mineral oils which have been subjected to hydrocracking or catalytic dewaxing. For both hydroprocessed mineral and synthetic stocks, the saturation of lube boiling range olefins is a major objective.

The polyolefins comprise one class of synthetic hydrocarbon lubricants which has achieved importance in the lubricating oil market. These materials are typically produced by the polymerization (the term oligomerization is often used for the lower molecular weight products which are used as low viscosity basestocks) of alpha olefins typically ranging from 1-octene to 1-dodecene, with 1-decene being a preferred material, although polymers of lower olefins such as ethylene and propylene may also be used, including copolymers of ethylene with higher olefins, as described in U.S. 4,956,122 and the patents referred to there. The poly alpha-olefin (PAO) products may be obtained with a wide range of viscosities varying from highly mobile fluids of about 2cS at 100*C to higher molecular weight, viscous materials which have viscosities exceeding 100 cSt at 100°C. The PAO's are conventionally produced by the polymerization of the olefin feed in the presence of a catalyst such as aluminum trichloride, or boron trifluoride or trifluoride complexes. Processes for the production of PAO lubricants in this way are disclosed, for example, in U.S. Patent Nos 3,382,291 (Brennan) , 4,172,855 (Shubkin) , 3,780,128 (Shubkin), 3,149,178 (Hamilton), 3,742,082 (Brennan), and 4,956,122 (Watts). The PAO lubricants are also discussed in Lubrication Fundamentals, J.G. Wills,

Marcel Dekker Inc., New York, 1980 ISBN 0-8247-6976-7, especially pages 77 to 81. Subsequent to the polymerization, the lubricant range products are hydrogenated in order to reduce the residual unsaturation. In the course of this reaction, the bromine number of the lubricant is reduced from typical values of about 30 or higher for low viscosity PAOs and 5 to 15 for high viscosity PAOs to a value of not more than about 2 or even lower.

A novel type of PAO lubricant has recently been disclosed as having exceptional and advantageous properties. These materials are the HVI-PAO materials which are disclosed in U.S. Patent Nos. 4,827,064 (Wu) , 4,827,073 (Wu) . These materials are produced by the oligomerization of alpha olefins, especially 1-decene, using a reduced Group VI metal oxide catalyst, preferably a reduced chromium oxide catalyst. The HVI-PAO products may be derivatized by reaction with aromatics, as disclosed EP 377305 and higher molecular weight versions prepared by the use of lower oligomerization temperatures, as disclosed in U.S. Patent No. 5,012,020, to which reference is made for a disclosure of the higher molecular weight products. Although the oligomerization process using the reduced metal oxide catalysts produces a material of characteristic structure, residual unsaturation remains in the oligomer product and, like the conventional PAO oligomers, it is subjected to hydrogenation in order to improve its stability as a

lubricant. The hydrogenation is carried out in the same manner as with the conventional PAO-type materials.

The catalysts used for hydrogenating lubricants, whether of mineral oil or synthetic origin, require a strong hydrogenation function provided by the metal component and an effective large pore diameter in the porous support material in order to minimize the diffusion resistance of the bulky lubricant molecules. For reactions with bulky molecules, the optimum ratio of catalytic pore diameter to molecule size is about 1.5:1. Table 1 below shows the optimum pore sizes required for normal alkanes in the C-7 to C-25 range. The table shows that for alkanes in this range, the chain-length varies from 9.9 to 37.6 A so that active hydrogenation catalysts for these materials should have a major amount of their pore volume with pore openings in the range of 15 to 56 A, and preferably with a major amount of this in the range 38 to 56 A.

Table 1 Optimum Pore Size

... Optimum Pore Carbon Number Alkane Length. A - ^■ —*- Diameter. A ( 2 )

1. Based on bond lengths of 1.54 and 1.11 A for C-C and C-H bond lengths, respectively.

2. Based on an optimum ratio of catalyst pore to molecule size ratio of 1.5.

Conventional amorphous support materials such as alumina, silica and silica-alumina, typically have a pore size distribution with most of the pores larger than 50 A and most of these are larger than 100 A. Although these large pores enable the bulky lubricant molecules to traverse the molecular structure of the catalyst freely with little diffusional resistance, the reduced surface area associated with the larger pore sizes diminishes the area which is available for the hydrogenation reactions. It would therefore be desirable to utilize a hydrogenation catalyst which possess a significant amount of its pores in the range of 15 to 60 A, close to the optimum ratio for the lower molecular weight materials making up the bulk of many

synthetic lubricants as well as the lower viscosity mineral oils.

Summary of the Invention

We have now found that another class of catalytic materials - the mesoporous crystalline materials - which have high pore volume, high surface area and controlled pore openings of at least 13 A, is particularly suitable for the hydrogenation of lubricant hydrocarbons, especially synthetic PAO-type materials.

According to the present invention, the hydrogenation process utilizes a catalyst which comprises a hydrogenation function in the form of a metal on a support material which comprises a mesoporous siliceous material with a novel and unique structure and pore geometry described below. These materials are inorganic, porous, non-layered crystalline phase materials which, in their calcined forms exhibit an X-ray diffraction pattern with at least one peak at a d- spacing greater than about 18 Angstrom Units (A) . They also have a benzene adsorption capacity greater than 15 grams benzene per 100 grams of the material at 50 torr and 25*C. In a preferred form, the support material is characterized by a substantially uniform hexagonal honeycomb microstructure with uniform pores having a cell diameter greater than 13 A and typically in the range of 20 to 100 A. Most prominent among these materials is a new crystalline material identified as MCM-41 which is usually

synthesized as a metallosilicate with Brønsted acid sites by incorporating a tetrahedrally coordinated trivalent element such as Al, Ga, B, or Fe within the silicate framework. The preferred forms of these materials are the aluminosilicates although other metallosilicates may also be utilized.

MCM-41 is characterized by a microstructure with a uniform, hexagonal arrangement of pores with diameters of at least about 13 A: after calcination it exhibits an X-ray diffraction pattern with at least one d-spacing greater than about 18 A and a hexagonal electron diffraction pattern that can be indexed with a d ₁₀₀ value greater than about 18 A which corresponds to the d-spacing of the peak in the X-ray diffraction pattern.

A preferred catalyst for the present purpose is an alumina bound crystalline material which has a significant pore volume with pore diameters greater than 200 A. The large diameter pores provide channels for bulky PAO oligomers to transport freely with diminished diffusion resistance to the smaller particles of the crystalline material which provide a large surface area for the hydrogenation reaction. The preferred crystalline materials for use in the present process have pore diameters greater than 15 A and the preferred pore diameters are in the range of 15 to 60 A.

Drawings

Figure 1 of the accompanying drawings is a graphical representation of testing results reported in the Examples below.

Figure 2-6 are Fourier transforms which describe the behavior of an alumina bound MCM-41 catalyst containing palladium when subjected to EXAFS analysis as described in Example 28.

Detailed Description

In the present process, lubricant range hydrocarbons are hydrogenated or hydrotreated or hydrotreated in the presence of a hydrogenation catalyst which comprises a mesoporous crystalline material, preferably with a binder which possesses a significant pore volume having pore diameters greater than 200 A. The process may be carried out with mineral oil lubricants or synthetic hydrocarbon lubricants, of which the PAO materials are preferred, both conventional type PAO's prepared using Friedel-Crafts type catalysts as well as the HVI-PAO materials produced using a reduced Group VIB metal oxide catalyst.

The mineral oil lubricants may generally be characterized as having a minimum boiling point of at least 345"C and usually they will be neutral i.e., distillate, stocks with an end point of not more than 565°C, although residual lube

stocks such as bright stock may also be treated by the same catalytic process. Mineral oil stocks of this kind are typically prepared by the conventional refining process involving atmospheric and vacuum distillation of a crude of suitable composition, followed by removal of undesirable aromatic components by solvent extraction using a solvent such as phenol, furfural or N,N-dimethylformamide (DMF) . Dewaxing to the desired product pour point may be carried out using either solvent dewaxing or catalytic dewaxing techniques and it is particularly preferred that a hydrogenative treatment according to the present invention should follow any catalytic dewaxing treatment in order to saturate lube boiling range olefins which may be produced during the catalytic dewaxing process.

The present process is, however, particularly applicable to the hydrogenative treatment of synthetic lubricating oils, especially the poly alpha-olefins (PAO) including the HVI- PAO type materials. These types of lubricants may be produced by the polymerization or oligomerization procedures described above using Friedel-Crafts type catalysts such as aluminum trichloride, boron trifluoride or boron trifluoride complexes, e.g., with water, lower alkanols or esters in the conventional manner. The HVI-PAO type oligomers may be prepared by the methods described in U.S. 4,827,064 (Wu) , 4,827,073 (Wu) , using a reduced Group VIB metal oxide catalyst, normally chromium on silica. The HVI-PAO materials include the higher molecular weight versions prepared by the use of lower oligomerization

temperatures, as disclosed in U.S. Patent No. 5,012,020, to which reference is made for a full description of these materials and their preparation. Derivatives of the PAO lubricants may be prepared by reaction with aromatics as disclosed, for example, in EP 377305, referred to above. The HVI-PAO materials are characterized by a branch ratio below 0.19 which results from the use of the unique reduced metal oxide catalyst during the oligomerization process.

The lubricant materials are subjected to the hydrogenative treatment in the presence of a catalyst which comprises a metal component for hydrogenation together with the mesoporous crystalline material and, optionally, a binder.

The hydrogenation reaction is carried out under conventional conditions with temperatures from about 38*C to about 371'C. and preferably in the range of 66 ^β C to

260 ^β C. Hydrogen pressure may vary up to about 17,339 kPa but normally will be from about 791 kPa to 10,441 kPa. Hydrogen circulation rates are typically in excess of that required stochiometrically for complete saturation ranging from 200% to 5000% stochiometric excess. Once through circulation is preferred in order to maximize the purity of the hydrogen. Space velocities are typically in the range of 0.1 to 10 LHSV, usually from 1 to 3 LHSV. The products of the hydrogenation reaction have a low degree of unsaturation consistent with the hydrogenative treatment and in most cases the bromine number of the product will be less than 3 and is often less than 1.

Hvdrogenation Catalyst

The catalytic material used in the present invention includes a novel synthetic composition of matter comprising an ultra-large pore size crystalline phase as a support for the metal component of the catalyst. This material is an inorganic, porous, non-layered crystalline phase material which can be characterized (in its calcined form) by an X- ray diffraction pattern with at least one peak at a d- spacing greater than about 18 A with a relative intensity of 100 and a benzene sorption capacity of greater than 15 grams of benzene per 100 grams of the material at 50 torr and 25*C.

The preferred form of the crystalline material is an inorganic, porous, non-layered material having a hexagonal arrangement of uniformly-sized pores with a maximum perpendicular cross-section pore dimension of at least about 13 Angstrom Units (A) , and typically within the range of from about 13 A to about 200 A. A preferred form of this hexagonal crystalline composition, identified as MCM- 41, with the characteristic structure of hexagonally- arranged, uniformly-sized pores of at least 13 A diameter, exhibits a hexagonal electron diffraction pattern that can be indexed with a d ₁₀₀ value greater than about 18 A which corresponds to at least one peak in the X-ray diffraction pattern. This material is described in detail in U.S. Pat. No. 5,098,684, which is hereby incorporated by reference.

Metal Component

Catalyst Metal Component

The hydrogenation catalyst includes a metal as the hydrogenation- dehydrogenation component. The hydrogenation-dehydrogenation component is provided by a metal or combination of metals. Noble metals of Group VIIIA, especially palladium, platinum, rhenium, iridiu or base metals of Groups IVA, VIA and VIIIA, especially chromium, molybdenum, tungsten, cobalt and nickel, may be used. The combination of at least one Group VIA metal such as tungsten with at least one Group VIIA metal such as nickel is particularly preferred for many applications, for example, combinations such as nickel-molybdenum, cobalt- nickel, nickel-tungsten, cobalt-nickel-molybdenum and nickel-tungsten-titanium. For certain applications, where sulfur and other contaminants such as phosphorus are in low concentrations in the feedstock, e.g. sulfur or phosphorous <10 ppm, palladium or platinum is preferred.

The content of the metal component will vary according to its catalytic activity. Thus, the highly active noble metals may be used in smaller amounts than the less active base metals. For example, about 1 wt. percent or less palladium or platinum will be effective and in a preferred base metal combination, about 7 wt. percent nickel and about 2.1 to about 21 wt. percent tungsten, expressed as metal. The present support materials are, however, notable in that they are capable of including a greater proportion

of metal than previous support materials because of their extraordinarily large surface area. The metal component may exceed about 30 percent in a monolayer. The hydrogenation component can be exchanged onto the support material, impregnated into it or physically admixed with it. If the metal is to be impregnated into or exchanged onto the mesoporous support, it may be done, for example, by treating the zeolite with a palladium or platinum metal- containing ion. Suitable platinum compounds include chloroplatinic acid, platinous chloride and various compounds containing the platinum amine complex. The metal compounds may be either 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 can be used. Palladium or platinum compounds in which the metal is in the form of a cation of cationic complex, e.g., Pd(NH_) ₄ Cl ₂ or Pt(NH_) ₄ Cl are particularly useful, as are anionic complexes such as the vanadate and etatungstate ions. Cationic forms of other metals are also very useful since they may be exchanged onto the crystalline material or impregnated into it.

Example 1

A Pd/SiO. catalyst was made by impreganting silica spheres (Shell S-980 C 1.5) with a Pd(NH ₃ ) ₄ Cl ₂ solution using the incipient wetness method. The impregnated spheres were then dried at room temperature for 4 hours, followed by

121°C overnight after which the catalyst was calcined in 5 v/v/min air at 288 ^* C for 3 hours.

Example 2

The three noble metal containing catalysts described above (Pt MCM-41/A1 ₂ 0 ₃ , Pd MCM-41/A1 ₂ 0 ₃ , Pd Si0 ₂ ) were evaluated for hydrogenating a PAO lubricant.

The properties of the three catalysts are summarized in Table 2 below.

Table 2 Catalvst Propert:ies

Pd MCM-41 (1) Pt MCM-41 (1) Pd

Si02 Metal Loading. Wt%

Pd 0.83 0.84

Pt 0.54

Surface Area. m2/g 800 682 330

Pore Volume, cc/g 0.96 0.97 0.88

Pore Distribution.%

<50 A 32 42 0 50-100 A 16 12 41 100-200 A 15 11 32 >200 A 37 35 37

1) Contains 65 wt% MCM-41 and 35 wt% alumina prior to the metal addition.

The MCM-41 materials used in the catalysts containing this crystalline material had a pore opening of 40 A. All three catalysts have 30% pore volume with pore diameters greater than 200 A but the MCM-41 catalysts have 30-40% pore volume with pore diameters less than 50 A.

All catalysts were evaluated in a fixed-bed pilot unit. A poly-alpha olefin (PAO) lube oligomer having the composition shown in Table 3 below was used as the feed.

Table 3 Properties of PAO

Gravity, "API 39.2

Hydrogen, wt% 14.6

Bromine Number 27.3

KV @ 40 ^β C, cS 26.22 KV @100 ^β C, CS 5.253

Viscosity Index 136

The PAO was hydrogenated at 2.0 LHSV, 2515 kPa H ₂ and 890 n.1.1." ¹ of once-through hydrogen circulation rate. Reactor temperature was varied to obtain catalyst activity as a function of temperature. Catalyst activity is measured by the reduction of bromine number of the oil.

The results are summarized graphically in the figure. The PAO feed had a bromine number of 27.3 units and, as shown in the figure, the Pd MCM-41/A1 ₂ 0_ catalyst is the most active catalyst. It achieved the reduction of bromine

number to less than 1 at 177"C, the lowest temperature of the experiments. Pt MCM-41/A1 0 is also quite active. The Pd/SiO catalyst, which does not have pore volume associated with pore openings less than 50 A, is the least active catalyst.

Example 3

MCM-41 As An Unexpected Catalyst Support

A total of five Pd-containing catalysts were tested for hydrogenation of a low-viscosity PAO (nominal 6 cst § 100*c) , including two granular carbon catalysts with >1000 m ² /g surface area. The Pd/MCM-41(65%)/Al ₂ 0 ₃ (35%) catalyst was prepared using the same procedure described in Example 22. The finished Pd MCM-41/A1 ₂ 0 ₃ catalyst had a surface area of 614 m ² /g. Among those catalysts tested, Pd/MCM-41 was the most active catalyst. Although the surface area of the Pd/MCM-41 catalyst was lower than any of the Pd/C catalysts, it produced products with less than 0.1 bromine number at the highest space velocity (7.5 LHSV, Table 4). This high activity of the Pd MCM-41/A1 ₂ 0 ₃ catalyst is unexpected and can not be attributed to support surface area alone. Table 4 summarizes the results.

Table 4

Catalvst Evaluation

Surface

Bromine

Catalyst Pd Support Area LHSV Number

(wt%) (m ² /g) (Hr- ¹ )

A 0.5 A1 ₂ 0 ₃ 35 1 2.7

B 0.5 A1 ₂ 0 ₃ 95 2 3.6

C 0.5 Carbon 1050 1 3.8

D 0.8 Carbon 1200 2 10.9

E 0.8 MCM-41(65%) 614 7.5 <0.1 /Al ₂ 0 ₃ (35%)

Note: Catalysts A, B, C, and D are commercial catalysts.

All experiments in Table 1 were conducted in fixed pilot units at 122'C, 2273 kPa hydrogen partial pressure and a hydrogen circulation rate of 200% excess hydrogen above that calculated for total olefin saturation. Properties of the PAO feed used in the above experiments are listed in Table 5.

Table 5 PAO Properties

Gravity, "API 40

Hydrogen, wt% 14.74

Bromine Number 29.5

KV § 40°C, est 25.61

KV e 100 ^β C, cst 5.19

Viscosity Index 137

Example 4

Wide Operating Conditions for Pd/MCM-41

The Pd MCM-41/A1 ₂ 0 ₃ catalyst can hydrogenate PAO to a very low bromine number at a wide range of operating conditions. A total of five different operating conditions were examined using the nominal 6 cst PAO feed (Table 5) . Table 6, which used a similar Pd MCM-41/A1 ₂ 0 ₃ catalyst identified as the Catalyst E in Table 4, illustrates feasible operation at high space velocities. The product bromine number of the product is less than 2 in each case (which represents over 93% olefin conversion)

Table 6 High Space Velocity Performance

Feed

PAO Case 1 Case 2 Case 3

Conditions

LHSV, Hr ^_1 4 4 8

P _H2 , kPa 1756 1756 1756

Excess H ₂ , % 400 400 400

Temperature, ^• c 128 162 154

Performance

Bromine No. 29.5 1.0 0.1 0.5

Table 7 illustrates feasible operation at very low pressure (Case 1) and low temperature (Case 2) , respectively. The Pd/MCM-41 catalyst used to generate the data in Table 7 was prepared with MCM-41 material having a Si0 ₂ :Al ₂ 0 ₃ ratio of 400:1, compared to 40:1 Si0 ₂ :Al ₂ 0 ₃ ratio for the catalyst used to generate the data in Table 6. The properties of

the 400 : 1 Si0 ₂ : Al ₂ 0 ₃ Pd/MCM-41 catalyst are given in Table 8 .

The nominal 6 cst PAO feed used to generate Table 7 suffered some exposure to air with resulting peroxide contamination. Low peroxide levels, which do not exist in commercial applications, reduced catalyst activity somewhat. However, product bromine numbers less than 3, representing greater than 90% olefin conversion, were obtained in both cases.

Table 7 Low Temperature Performance

Feed

PAO Case 1 Case 2

Conditions LHSV, Hr ^-1 0.3 0.3 P _H2 , kPa 791 6996

Excess H,, % 200 200

Temperature, *C 191 60

Performance Bromine No. 29.5 0.4 2.2

The data of Table 7 were generated in an isothermal pilot unit. Commercial adiabatic experience suggests that a 60 ^* C average temperature (Table 7, Case 2) in an isothermal unit corresponds to an inlet temperature below 38°C in an adiabatic reactor.

Table 8

Pd MCM-41/A1-0, Properties

MCM-41 ⁽¹⁾ 65

A1 ₂ 0 ₃ , Wt% 35

Pd, Wt% 0.77

Na, pp w 175

Surface Area, m2/g 558

( 1) 400 : 1 Si0 ₂ /Al ₂ 0 ₃ ratio

Example 5

Processing High-Viscosity PAO over Pd MCM-41

Pd/MCM-41 was active for hydrogenation of high-viscosity PAO that contains trace amounts of chlorine and water. A nominal 40 cSt PAO was used in the experiments (Table 10) . The Pd MCM-41/A1 ₂ 0 ₃ catalyst was the same catalyst used for Cases 1 and 2 in Table 7 and its properties are given in

Table 8. The experimental results are summarized in Table 9 below.

Table 9

High- -Viscosity PAO Hydrogenat: Lon

Feed PAO Case 1 Case 2

Conditions LHSV, Hr ^-1 1.0 1.0

*H2 4238 1756

Excess H ₂ , % 700 700 Temperature, ^• C 177 232

Performance Bromine No. 12.7 1.0 0.4

Table 10 Properties of High-Viscositv PAO

KV @ 40*C, CSt 400.7 KV @ 100'C, CSt 40.1

Viscosity Index 150

Chlorine, ppmw 132 Water, ppmw 15

Bromine Number 12.7