Mineral oils: processes and products – Products and compositions – Lubricating oils
Reexamination Certificate
2000-03-21
2001-11-27
Myers, Helane E. (Department: 1764)
Mineral oils: processes and products
Products and compositions
Lubricating oils
C208S087000, C208S097000, C208S058000, C208S072000, C208S071000, C208S088000, C208S095000, C208S057000
Reexamination Certificate
active
06322692
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to lubricating oil basestocks and to a process for preparing lubricating oil basestocks having a high saturates content, high viscosity indices and low volatilities.
BACKGROUND OF THE INVENTION
It is well known to produce lubricating oil basestocks by solvent refining. In the conventional process, crude oils are fractionated under atmospheric pressure to produce atmospheric resids which are further fractionated under vacuum. Select distillate fractions are then optionally deasphalted and solvent extracted to produce a paraffin rich raffinate and an aromatics rich extract. The raffinate is then dewaxed to produce a dewaxed oil which is usually hydrofinished to improve stability and remove color bodies.
Solvent refining is a process which selectively isolates components of crude oils having desirable properties for lubricant basestocks. Thus the crude oils used for solvent refining are restricted to those which are highly paraffinic in nature as aromatics tend to have lower viscosity indices (VI), and are therefore less desirable in lubricating oil basestocks. Also, certain types of aromatic compounds can result in unfavorable toxicity characteristics. Solvent refining can produce lubricating oil basestocks have a VI of about 95 in good yields.
Today more severe operating conditions for automobile engines have resulted in demands for basestocks with lower volatilities (while retaining low viscosities) and lower pour points. These improvements can only be achieved with basestocks of more isoparaffinic character, i.e., those with VI's of 105 or greater. Solvent refining alone cannot economically produce basestocks having a VI of 105 with typical crudes. Nor does solvent refining alone typically produce basestocks with high saturates contents. Two alternative approaches have been developed to produce high quality lubricating oil basestocks; (1) wax isomerization and (2) hydrocracking. Both of the methods involve high capital investments. In some locations wax isomerization economics can be adversely impacted when the raw stock, slack wax, is highly valued. Also, the typically low quality feedstocks used in hydrocracking, and the consequent severe conditions required to achieve the desired viscometric and volatility properties can result in the formation of undesirable (toxic) species. These species are formed in sufficient concentration that a further processing step such as extraction is needed to achieve a non-toxic base stock.
An article by S. Bull and A. Marmin entitled “Lube Oil Manufacture by Severe Hydrotreatment,” Proceedings of the Tenth World Petroleum Congress, Volume 4, Developments in Lubrication, PD 19(2), pages 221-228, describes a process wherein the extraction unit in solvent refining is replaced by a hydrotreater.
U.S. Pat. No. 3,691,067 describes a process for producing a medium and high VI oil by hydrotreating a narrow cut lube feedstock. The hydrotreating step involves a single hydrotreating zone. U.S. Pat. No. 3,732,154 discloses hydrofinishing the extract or raffinate from a solvent extraction process. The feed to the hydrofinishing step is derived from a highly aromatic source such as a naphthenic distillate. U.S. Pat. No. 4,627,908 relates to a process for improving the bulk oxidation stability and storage stability of lube oil basestocks derived from hydrocracked bright stock. The process involves hydrodenitrification of a hydrocracked bright stock followed by hydrofinishing.
It would be desirable to supplement the conventional solvent refining process so as to produce high VI, low volatility oils which have excellent toxicity, oxidative and thermal stability, fuel economy and cold start properties without incurring any significant yield debit which process requires much lower investment costs than competing technologies such as hydrocracking.
SUMMARY OF THE INVENTION
This invention relates to a lubricating oil basestock produced by a process which comprises:
(a) conducting a lubricating oil feedstock, said feedstock being a distillate fraction, to a solvent extraction zone and under-extracting the feedstock to form an under-extracted raffinate;
(b) stripping the under-extracted raffinate of solvent to produce an under-extracted raffinate feed having a dewaxed oil viscosity index from about 75 to about 105;
(c) passing at least a portion of the raffinate feed to a first hydroconversion zone and processing the raffinate feed in the presence of a non-acidic catalyst at a temperature of from 320 to 420° C., a hydrogen partial pressure of from 1000 to 2500 psig (7.0 to 17.3 mPa), space velocity of 0.2 to 5.0 LHSV and a hydrogen to feed ratio of from 500 to 5000 Scf/B (89 to 890 m
3
/m
3
) to produce a first hydroconverted raffinate;
(d) passing the hydroconverted raffinate from the first hydroconversion zone to a second hydroconversion zone and processing the hydroconverted raffinate in the presence of a non-acidic catalyst at a temperature of from 320 to 420° C. provided that the temperature in the second hydroconversion is not greater than the temperature in the first hydroconversion zone, a hydrogen partial pressure of from 1000 to 2500 psig (7.0 to 17.3 mPa), a space velocity of from 0.2 to 5.0 LHSV and a hydrogen to feed ratio of from 500 to 5000 Scf/B (89 to 890 m
3
/m
3
) to produce a second hydroconverted raffinate;
(e) passing at least a portion of the second hydroconverted raffinate to a hydrofinishing reaction zone and conducting cold hydrofinishing of the second hydroconverted raffinate in the presence of a hydrofinishing catalyst which is at least one Group VIB or Group VIII metal on a refractory metal oxide support at a temperature of from 200 to 360° C., a hydrogen partial pressure of from 1000 to 2500 psig (7.0 to 17.3 mPa), a space velocity of from 0.2 to 10 LHSV and hydrogen to feed ratio of from 500 to 5000 Scf/B (89 to 890 m
3
/m
3
) to produce a hydrofinished raffinate.
The basestocks produced by the process according to the invention have excellent low volatility properties for a given viscosity thereby meeting future industry engine oil standards while achieving good oxidation stability, cold start, fuel economy, and thermal stability properties. In addition, toxicity tests show that the basestock has excellent toxicological properties as measured by tests such as the FDA(c) test.
REFERENCES:
patent: 4764265 (1988-08-01), Bijwaard et al.
patent: 5911874 (1999-08-01), Cody et al.
patent: 5935417 (1999-08-01), Cody et al.
Boate Douglas R.
Cody Ian A.
Demmin Richard A.
Gallagher John E.
Linek Sandra J.
ExxonMobil Research and Engineering Company
Myers Helane E.
Takemoto James H.
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