Hydrofinishing of petroleum

Abstract

A method of improving the oxidative stability of sulfur and oxygen and/or nitrogen polar material containing lubricating base charge stocks wherein the lubricating base charge stocks are contacted with a nickel-molybdenum on large pore alumina catalyst in the presence of a gas mixture of about 90% hydrogen and 10% hydrogen sulfide under hydrofinishing conditions.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention concerns the production of a lubricant which has superior oxidative stability.

2. Description of the Prior Art

It is well-known that certain types of organic compounds are normally susceptible to deterioration by oxidation through coming into contact with various metal surfaces. For example, it is known that liquid hydrocarbons in the form of fuels or lubricating oils tend to accumulate considerable quantities of water when maintained for long periods of time in storage vessels; and when subsequently brought into contact with metal surfaces in their functional environments, deterioration as a result of oxidation, occurs. As a further example, in modern internal combustion engines and in turbojet engines, lubricants can be attacked by oxygen or air at high temperatures to form acids, heavy viscous sludges, varnish and resins which become deposited on the engine surfaces. As a result, the lubricant cannot perform its required task effectively, and the engine does not operate efficiently. Furthermore, the sludges produced by lubricant deterioration generated by insufficient oxidative stability tend to foul and plug low tolerance hydraulic system components and interconnecting piping and valves. In addition, where such lubricating oils or other oxidation prone materials are incorporated into solid lubricants as in the form of greases, similar results are encountered, thus clearly indicating the necessity for improved methods of treatment which increase the oxidative stability of lubricating oils.

Accompanying the deterioration of lubricants by oxidation is the resultant corrosion of the metal surfaces for which such lubricants are designed and supplied. In the oxidation of a lubricant, acids develop which are corrosive enough to destroy most metals. Moreover, the friction between metal parts increases following lubricant breakdown due to oxidation and leads to excessive metal wear. Increasing demands on lubricants, brought about by larger engines operating at steadily increasing temperatures and pressures, and often at higher speeds, necessitate a constant search for new methods of hydrocarbon treatment which can provide lubricants with increased oxidation resistance.

Due to the lubricant oxidative stability requirements for such newer and larger engines and other rotating or moving equipment lubrication, feedstocks which were previously suitable for lubricant production are presently unsuitable or at best marginal for such uses. Thus at a time when overall lubricant demands are increasing, the amount of suitable lubricant feedstock material is being diminished due to the oxidative stability requirements of newer and larger machinery.

Various antioxidant additives have been developed to help improve lubricant oxidative stability, see for example U.S. Pat. No. 3,399,041 (McCabe). However, such additives are expensive to produce and present metering and mixing problems when added to lubricants.

Accordingly, it is an object of this invention to provide a method whereby the oxidative stability of lubricant chargestocks is improved.

A further object of this invention is to provide for a method of treatment whereby hydrocarbon feedstocks presently of poor or marginal lubricant quality may be upgraded through oxidative stability improvement in order to produce lubricants having sufficiently high anti-oxidation qualities.

A further object of this invention is to provide for a method of treatment whereby the lubricant produced is enhanced in the response to antioxident additives.

Another object of this invention is to provide for a method of lubricant treatment whereby the lubricant produced has sufficient oxidative stability to substantially reduce metals corrosion and wear when employed as a lubricant for such metals.

Other objects and advantages of this invention will become apparent to those skilled in the art upon reading the entire specification including the following detailed description and claims.

SUMMARY OF THE INVENTION

A method of improving the oxidative stability of a sulfur and oxygen and/or nitrogen containing hydrocarbon lubricant base stock has recently been discovered. The method consists of contacting said lubricant base stock with a nickel-molybdenum on large pore alumina catalyst in the presence of a gas mixture of about 90% hydrogen and 10% hydrogen sulfide, said contacting being carried out under hydrofinishing conditions of at temperature of about 200.degree. to 700.degree.F., space velocities of about 0.25 to 10 L.H.S.V. and pressures of about 100 to 2,000 p.s.i.g.; and removing said charge stock from said catalyst following said contacting.

In a preferred embodiment the charge stock has a sulfur content of about 0.01 to 2.5 weight percent, and an oxygen and/or nitrogen polar compound concentration of about 0.0001 to 2.0 weight percent, the viscosity of the lubrication base stock is about 100 SSU to 800 SSU at 100.degree.F the temperature, space velocity and pressure are 300.degree. to 600.degree.F., 1 to 4 L.H.S.V. and 100 to 500 p.s.i.g. respectively.

EXAMPLES 1-36

Two catalysts, one a nickel-molybdenum on alumina and the other a molybdenum on alumina, were obtained as meshed through 8 on 16 mesh/inch. The NiMo/Al.sub.2 O.sub.3 catalyst used is more particularly defined as follows:

Surface Area 57 m.sup.2 /g Ni 2.7% Real Density 4.29 MoO.sub.3 11.7% Particle Density 1.57 Al.sub.2 O.sub.3 86.2% Pore Volume .405 cc/g Pore Diameter 284 A Angstrom: 0-50 50-100 100-200 200-300 300 % of Pore Dia. in Range 22 4 33 10 31

Each catalyst was then sulfided with about 2% H.sub.2 S -- 98% H.sub.2 gas of 500 p.s.i.g. and at about 450.degree.-750.degree.F. For each catalyst, the initial sample was obtained with pure H.sub.2 in the circulating gas and the second sample with H.sub.2 gas containing 10% H.sub.2 S. Temperature was then raised and the third sample obtained with the gas containing 10% H.sub.2 S and the fourth with pure H.sub.2. This alternating procedure was carried on for the remainder of the run. In all cases the product was nitrogen stripped of H.sub.2 S gas at 150.degree.F. The Rotary Bomb Oxidation Test (RBOT) performed on each of the samples is described in ASTM test D 2272 -- 67 1972 Annual Book of ASTM Standards, Part 17 (American Society for Testing and Materials, Phil., Pa. 1972) p. 783.

Results of these examples are compared with an untreated base stock are shown in Tables 1-4 and FIGS. 1-4.

While not wishing to be bound by any particular theory of operability, the following analysis of a suggested mechanism is put forward specifically by way of explaining FIGS. 1-4. FIG. 1 shows the variation of RBOT for a Light Neutral (150 SUS/100.degree.F) Arabian Stock with hydrofinishing temperature. These results indicate that hydrofinishing with NiMo/Al.sub.2 O.sub.3 at 450.degree. in the presence of 10% H.sub.2 S significantly increases RBOT above that obtained with clay percolation. Using NiMo/Al.sub.2 O.sub.3 without H.sub.2 S, this increase is not observed.

FIG. 2 illustrates the fraction of sulfur remaining in the product as a function of hydrofinishing temperature. With both catalysts, the presence of H.sub.2 S in the circulating gas suppresses desulfurization. For NiMo/Al.sub.2 O.sub.3, differences in RBOT stability observed with and without H.sub.2 S in the circulating gas may be attributed to differences in the sulfur content of the hydrofinished products. However, the sulfur and nitrogen content of the hydrofinished products obtained using NiMo/Al.sub.2 O.sub.3 with H.sub.2 S in the circulation gas is nearly the same as that obtained using Mo/Al.sub.2 O.sub.3 with no H.sub.2 S, yet there are substantial differences in their respective RBOT values. A possible explanation for these RBOT differences is that the NiMo/Al.sub.2 O.sub.3 catalyst is more selective for removal of stability reducing oxygen polar compounds than Mo/Al.sub.2 O.sub.3.

The hypothesis that NiMo/Al.sub.2 O.sub.3 has increased activity for oxygen removal is consistent with the observation that the hydrofinished oil has a higher RBOT value than clay percolated oil. Evidence from chromatography and mass spectra indicates that clay percolation is very efficient for removal of stability reducing nitrogen compounds, but is not as efficient for removal of oxygen polar compounds. Light Arabian lube stocks have relatively low nitrogen contents and, therefore, in a very highly furfural treated stock such as the one used in the present study, clay percolation is not as effective as hydrofinishing for RBOT improvement. Therefore, reduced desulfurization due to the presence of H.sub.2 S in the circulating gas coupled with higher oxygen removal selectivity of NiMo/Al.sub.2 O.sub.3 may result in a hydrofinished oil having a higher RBOT stability than that obtained from clay percolation.

Tables 3 and 4 and FIGS. 3 and 4 give the results of hydrofinishing of Mid-Continent Sweet lube stock. Such stocks are relatively high in nitrogen polar compounds, and relatively low in oxygen polar compounds. The presence of H.sub.2 S or the use of NiMo/Al.sub.2 O.sub.3 shows no advantage perhaps because the more difficult to remove nitrogen compounds in this stock, and not the oxygen polars, are the preponderant factor in controlling stability.

It has been found that polar oxygen and nitrogen containing compounds are detrimental to lube oil performance in at least some applications, and that some sulfur compounds are beneficial. It is thus desirable to remove the polar materials without removing sulfur, especially in relatively high sulfur stocks. Since hydroprocessing under relatively mild conditions does not normally remove nitrogen containing material, the ideal charge stock for hydroprocessing should contain relatively small amounts of nitrogen in the furfural treated and dewaxed oil compared to the total amount of polar material. Typical oils may have from 0.1 to 0.6% polar material (which is the material not eluted by pentane from a Florisil (6% H.sub.2 O) chromatographic column) and a nitrogen content of 10 to 100 ppm. Typically the nitrogen materials represent about 30-50 percent of the total polar material, where 100 ppm nitrogen corresponds to about 0.3 to 0.4% nitrogen containing polar material. The presence of H.sub.2 S permits some of the deleterious polar materials to be removed without removing the sulfur compounds. The effectiveness of H.sub.2 S/H.sub.2 hydroprocessing a particular lube stock should therefore increase with a decreasing percentage of nitrogen containing polar material and with increasing sulfur content. A stock such as Arab Light where only about 20-30 percent of the polar material contains nitrogen and with about 0.25 to 0.4% sulfur is ideal for this application.

The development of a good low temperature (300.degree.-600.degree.F.) catalyst for nitrogen removal would extend the application of this technique to virtually all potential lube oil stocks.

TABLE 1 __________________________________________________________________________ HYDROFINISHING OF ARABIAN LIGHT LUBE BASE STOCK NiMo/Al.sub.2 O.sub.3 CATALYST Example No Base Stock 1 2 3 4 5 6 7 8 9 10 __________________________________________________________________________ Temp.,.degree.F. 450 450 500 500 550 550 600 600 650 650 LHSV 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 Pressure,psig Hydrogen 300 252 252 300 300 252 252 300 300 252 Hydrogen 0 28 28 0 0 28 28 0 0 28 Sulfide Sulfur, wt % 0.28 0.25 0.28 0.26 0.20 0.15 0.24 0.17 0.072 0.024 0.074 %Desulfurization 11 0 7 29 46 14 39 74 91 74 Nitrogen, ppm 8.0 7.1 6.0 7.1 7.2 7.2 6.2 6.1 5.6 5.2 5.5 KV at 100.degree.F. 28.65 28.14 28.41 28.29 28.14 27.89 28.26 28.14 28.06 27.55 27.61 KV at 210.degree.F. 5.03 5.02 5.02 5.00 5.01 4.97 5.03 5.02 4.98 4.87 4.98 Aniline 222.3 223.2 223.0 223.3 223.8 223.9 223.5 223.3 224.7 224.5 222.2 Pour Point,.degree.F. -5 -5 -5 -5 -5 0 0 0 0 0 0 Total Acid No. 0.03 0.24 0.09 0.18 0.09 0.04 0.06 0.11 0.05 0.10 0.05 RBOT, Min. 466 440 546 500 375 342 444 375 310 305 328 __________________________________________________________________________

TABLE 2 __________________________________________________________________________ HYDROFINISHING OF ARABIAN LIGHT LUBE BASE STOCK Mo/Al.sub.2 O.sub.3 CATALYST Example No. Base Stock 11 12 13 14 15 16 17 18 19 20 __________________________________________________________________________ Temp., .degree.F. 450 450 500 500 550 550 600 600 650 650 LHSV 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 Pressure, psig Hydrogen 280 252 252 280 280 252 252 280 280 252 Hydrogen 0 28 28 0 0 28 28 0 0 28 Sulfide Sulfur, wt % 0.28 0.27 0.28 0.27 0.25 0.22 0.27 0.24 0.18 0.12 0.18 %Desulfurization 4 0 4 11 21 4 14 36 57 36 Nitrogen, ppm 8.0 6.6 6.2 6.9 5.9 7.9 7.6 7.1 7.5 4.2 6.0 KV at 100.degree.F. 28.65 28.48 28.21 28.25 28.32 28.25 27.85 28.18 27.78 27.65 27.84 KV at 210.degree.F. 5.03 5.03 5.02 5.01 5.02 5.03 5.01 5.05 4.98 4.97 4.98 Aniline 222.3 222.4 223.0 223.0 223.1 223.3 223.1 223.0 223.3 224.0 223.6 Pour Point,.degree.F. -5 -10 -10 0 0 0 0 -5 0 0 0 Total Acid No. 0.03 0.09 0.15 0.13 0.11 0.02 0.03 0.10 0.07 0.18 0.12 RBOT, Min. 466 458 460 457 407 378 428 390 372 312 368 __________________________________________________________________________

TABLE 3 __________________________________________________________________________ (300%/215.degree.F) HYDROFINISHING OF MID CONTINENT SWEET LUBE BASE STOCK NiMo/Al.sub.2 O.sub.3 CATALYST Example No. Base Stock 21 22 23 24 25 26 27 28 __________________________________________________________________________ Temperature, .degree.F. 450 450 500 500 550 550 600 600 LHSV 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 Pressure, psig Hydrogen 280 252 252 280 280 252 252 280 Hydrogen Sulfide 0 28 28 0 0 28 28 0 Sulfur, wt % 0.12 0.10 0.13 0.12 0.081 0.054 0.10 0.073 0.029 Desulfurization 17 0 0 33 55 17 39 76 Nitrogen, ppm 35 32 34 33 31 30 30 28 29 KV at 100.degree.F. 33.68 33.37 33.59 32.84 -- 33.27 33.42 33.33 31.17 KV at 210.degree.F. 5.51 5.50 5.62 5.53 5.46 5.49 5.50 5.47 5.46 Aniline 226.0 225.5 225.0 225.8 225.5 225.8 225.5 225.7 226.1 Pour Point, .degree.F. 20 30 20 25 25 25 25 25 25 Total Acid No. 0.17 0.19 0.28 0.16 0.14 0.11 0.14 0.15 0.16 RBOT, Min 257 333 251 284 293 284 322 312 272 __________________________________________________________________________

TABLE 4 __________________________________________________________________________ HYDROFINISHING OF MID CONTINENT SWEET LUBE BASE STOCK Mo/Al.sub.2 O.sub.3 CATALYST Example No. Base Stock 29 30 31 32 33 34 35 36 __________________________________________________________________________ Temperature, .degree.F. 450 450 500 500 550 550 600 600 LHSV 2.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5 Pressure, psig Hydrogen 280 252 252 280 280 252 252 280 Hydrogen Sulfide 0 28 28 0 0 28 28 0 Sulfur, wt % 0.12 0.11 0.12 0.12 0.11 0.096 0.11 0.10 0.077 Desulfurization 8 0 0 8 20 8 17 36 Nitrogen, ppm 35 29 26 31 32 32 29 31 30 KV at 100.degree.F. 33.68 33.81 33.64 33.61 33.28 33.51 33.49 33.48 33.34 KV at 210.degree.F. 5.51 5.51 5.55 5.53 5.48 5.52 5.22 5.51 5.38 Aniline Point 226.0 225.5 225.5 225.5 225.5 225.5 225.0 225.5 225.5 Pour Point, .degree.F. 20 25 10 10 5 5 20 20 20 Total Acid No. 0.17 0.15 0.07 0.13 0.10 0.08 0.08 0.11 0.13 RBOT, Min. 257 351 260 315 335 332 335 348 310 __________________________________________________________________________

Claims

What is claimed is:

1. A method of improving the oxidative stability of a sulfur-containing hydrocarbon lubricant base stock comprising: contacting said lubricant base stock with a nickel-molybdenum on alumina catalyst having a major fraction of pores at least 100A diameter in the presence of a gas mixture of about 90% hydrogen and 10% hydrogen sulfide, said contacting being carried out under hydrofinishing conditions; and removing said chargestock from said catalyst following said contacting.

2. The method as claimed in claim 1 wherein the sulfur content of said hydrocarbon lubricant base stock is about 0.01 to 2.5 weight percent.

3. The method as claimed in claim 2 wherein the said hydrocarbon lubricant base stock has an oxygen content which is contained in polar compounds and represents about 0.0001 to 2.0 weight percent of said lubricant base stock.

4. The method as claimed in claim 2 wherein said hydrocarbon lubricant base stock has a nitrogen content which is contained in polar compounds and represents about 0.0001 to 2.0 weight percent of said lubricant base stock.

5. The method as claimed in claim 1 wherein said lubricant base stock has a viscosity of about 100 to 800 S.U.S. at 100.degree.F.

6. The method as claimed in claim 5 wherein said temperature is about 200.degree. to 700.degree.F.

7. The method as claimed in claim 5 wherein said space velocity is about 0.25 to 10 L.H.S.V.

8. The method as claimed in claim 5 wherein said pressure is about 100 to 2,000 p.s.i.g.