CA1122198A

CA1122198A - Oxidation stable base oil

Info

Publication number: CA1122198A
Application number: CA000325143A
Authority: CA
Inventors: Jacobus H. Breuker
Original assignee: Shell Canada Ltd
Current assignee: Shell Canada Ltd
Priority date: 1978-05-12
Filing date: 1979-04-09
Publication date: 1982-04-20
Also published as: AU4696279A; SG8583G; GB2024852A; DE2918902A1; AU525249B2; DE2918902C2; GB2024852B; NZ190415A; NL7903668A; NL191519B; NL191519C

Abstract

A B S T R A C T

A base oil composition comprising:
(a) a base oil having a viscosity index of at least 94 obtained by hydrotreating a solvent-extracted raffinate having a viscosity index of at most 92, and (b) a solvent-extracted raffinate having a viscosity index of at most 92, and/or a deasphalted vacuum residue and/or a hydrotreated deasphalted vacuum residue.
shows improved oxidation stability.

Description

OIL COMPOSITIONS

The invention is concerned with improving the oxidation stability of certain base oils.
Base oil, e.g. lubricating oils,transmission fluids or industrial oils~ are prepared from various petroleum feedstocks, e.g. vacuum distillates or de~
asphalted vacuum residues or mixtures thereo~. One important class of base oil is those base oils having a viscosity index (V.I.) of at least 94. Since most feedstocks have a V.I. of below 94j e.g. of from 20 to 85, lt lS important to subject such feedstocks to a processing step which increases the V.I. thereof to at least ~4.
It is possible to increase t'ne V.I.cf a feedstock by solvent extraction alone or by hydrotreating alone or by both solvent extraction and hydrotreating. The present invention is particularly concerned with those base oils prepared by both solvent extraction of the feedstock, e.g. to an extent such that the solvent-, -' extracted raffinate has a V.I. of at most 92, and hydrotreating the solvent-extracted raffinate, e.g.
to an extent such that the resultant base oil has a V.I. of at least 94. One characteristic of such base oils is that they sometimes darken and/or form sludge when exposed to oxygen. This phenomenon is usually described as oxidation instability.
It has now been found that the oxidation stability of such base oils is improved by the addition thereto of a sol~ent-extracted raffinate having a viscosity index of at most 92 and/or by the addition of a de-asphalted vacuum residue and/or a hydrotreated de-; asphalted vacuum residue.
Accordingly, the present invention is concerned with a base oil composition comprising:(a) a base oil having a viscosity index of at least 94 obtained by hydrotreating a solvent-extracted raffinate having a viscosity index of at most 92, and (b) a solvent-extrac~ed raffinate having a viscosity index of at most 92, and/or a deasphalted vacuum residue and/or a hydrotreated deasphalted vacuum residue.
The base oil of the base oil composition may be prepared from an~ suitable petroleum feedstock. As ~z~

stated above the V.I. of such feedstocks is usually from 20 to 85. Examples of suitable feedstocks in-clude vacuum distillates, deasphalted residues of vacuum distillations (deasphalted vacuum residues) and mixtures thereof derived from crude oils, e.g.
paraffinic crude oils. Distillate feedstocks usually ;~ have a V.I. of from 20 to 60 and residual feedstocks - usually have a V.I. of from 60 to 85.
Such feedstocks are then solvent-extracted to in-crease the V.I. Preferably, the ~.I. of the solvent-extracted raffinate is from 75 to 92. In the case of a feedstock already having a V.I. of above 75 it is desirable that it is solvent-extracted to an extent such that the V.I. of the raffinate is at least 5 V.I.
units above the V.I. of the feedstock. Solvent ex-traction is a well known technique and suitable solvents include phenol, furfural or sulphur dioxide. After extraction an aromatic extract and a solvent~extracted raffinate are obtained.
~he solvent-extracted raffinate is then hydro-treated to an extent such that the resultant base oil has a V.I. of at least 94, suitably of from 95 to 110, althou~h the V.I. of the resultant base oil ~ay be as ; high as 120 or higher, e.g. above 140 (extra-high V.I. base oil). Hydrotreating is a well known technique and usually comprises treating the raffinate with hydrogen at a temperature of from 350C to 500C, a pressure of from 60 to 200 bars in the presence of a catalyst using space velocities of from 0.1 to

2.0 kg feed per litre catalyst per hour. Suitable catalysts usually comprise one or more of the metals molybdenum, chromium, tungsten, vanadium, platinum, nickel, copper, iron and cobalt or their oxides and/or sulphides, either supported on a suitable carrier~
such as alumina or silica or unsupported. Particularly advantageous catalysts are the iron transition metals (iron, cobalt and nickel) and the Group VIB metals (chromium, molybdenum and tungsten) especially com-binations of metals from each of these groups, for instance cobalt and molybdenum, nickel and tungsten, and nickel and molybdenum supported on alumina. The catalyst may also contain promoters, such as co~.pounds containing phosphorus, fluorine or borium. Usually the V.I. of the solvent-extracted raffinate is in-creased by at least 5 V.I. units by the hydrotreatment.
It is preferred to add a solvent-extracted raf-finate having a viscosity index of at most 92 to the base oil. Suitable amounts of such raffinates are ; from 0.1 to 20%~r, preferably from 0.1 to 10%w based on the ~reight of the base oil. Suitable solvent ~ :~22~3i~

extracted raffinates having a viscosity index of at most 92 are those prepared as described above for the preparation of the base oil. The petroleum feedstocks, from which such raffinates may be prepared may be vacuum distillates, deasphalted vacuum distillates or mixtures thereof. Various combinations are possible, e.g. a solvent-extracted raffinate derived from a deasphalted vacuum residue may be added to a base oil derived from a vacuum distillate or from a deasphalted vacuum residue, and a solvent-extracted raffinate derived from a vacuum distillate may be added to a base oil derived from a deasphalted vacuum residue or from a vacuum distillate.
The base oil from which the compositions of the present invention are obtained may be~ or may have been, subjected to one or more additional processing ; steps, such as a finishing step and/or a distillation step andlor a dewaxing step. The base oil may be subjected to a distillation step in order to remove the more volatile components therefrom. For example the volatile material boiling below a temperature in the range of from 200 to 550C may be removed. De-waxing serves to decrease the pour point of the feed-stocks by removing wax therefrom and is usually carried out after the hydrotreatment step. Finishing steps :

` -include clay and/or acid treatments and/or hydro-finishing treatment.
In addition, the solvent-extracted raffinate, which is preferably added to the base oil, may be, or may have been, subjected to one or more processing steps, such as a dewaxing step. Tne raffinate may be dewaxed in admixture with the base oil.
The base oil compositions of the present in-vention are suitably used as lubricating oil com-positions for internal combustion engines and maycontain one or more conventional additives~ such as viscosity index improvers, anti-wear/extreme-pressure additives, detergents, anti--rust additives, pour point depressants and other anti-oxidants~ e.g.
secondary amines, and/or other daylight stabilizers, such as quinones (e.g. tetrabutyldipheno~uinone).
The invention will now be illustrated by reference to the follo~ing Examples. In the Examples the ~.I.'s and viscosities were determined on dewaxed samples.
EX~MPLES 1, 2 and 3 ~ base oil was prepared by extracting a vacuum distillate (derived from a light paraffinic crude oil) having a V.I. of 54.5 and a viscosity of 5.03 centi-stokes at 98.9C. The extractant used was furfural and the solvent extracted raffinate had a V.I. of 87 ,. ~

The raffinate thus obtained was treated with hydrogen using a Ni/~.~ alumina supported catalyst, at a temper ature of 361C, a pressure of 90 bar and a space velocity of 1.5 kg feed per litre catalyst per hour.
The hydrotreated base oil was then distilled to re-move components having a boiling point of below about 365C and dewaxed with a mixture (50/50) of methyl-ethylketone (MEK) and toluene. The V.I. and viscosity of the dewaxed and distilled hydrotreated base oil was 95 and 4.27 centistokes at 98.9C respecti.vely.
The final base oil was subjected to an oxidation stability test. This test comprised blow~ng air through the base oil at a temperature of 160C for 168 hours at the end of the test the amount of sl.udge formed, the acidity and the viscosity increase of the base oil were determined. The results (~xample (a)) are given in Table I.
Base oil compositions according to the present invention were then prepared by adding various amounts of a solvent-extracted raffinate having a V.I. of 88 and a viscosity of 40.8 centistokes at 98.9~. The raffinate ~as prepared by ex.tracting a deasphalted vacuum residue ~derived from a light paraffinic crude oil) having a V.I. of 66 and a viscosity of 56.9 centi-stokes at 98.9C with furfural followed by dewaxing ~ . , with a mixture (50/50) of MEK and toluene. The baseoil compositions obtained were subjected to the oxidation stability test as described above. The results (Examples (1) and (2)) are also given in Table I.
Another base oil composition according to the present invention was prepared by replacing the solvent-extracted raffinate with the deasphalted vacuum residue, after dewaxing as described above, from which it was prepared. The base oil composition was also subjected to the oxidation stability test as described above. The results (Example (3)) are . also given in Table I.
,~.` .

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TABLE I

. _ -- ,_, __. r ., ~ . _~
Ex- Additive (%w) on Oxidation stability _ base oil I
ample solvent de- sludge, acid- vis-extract- asphalt- %w on it~J, cosity ed raf- ed vacuum com- mg in-finate residue position 100 g crease : (a) _ _10 3o 510 1 52 ~ 77 ~.2 24 ; 3 _ 2l.9 ~.~ ~ , EXAl~PLE 4 Example 2 was repeated with the differences that the vacuum distillate, from which the base oil was prepared, had a V.I. of 29 and a viscosi.ty o~ 18.0 centistokes at 98.9C, that the solvent-extracted raffinate had a V.I. of 88 and a viscosity of 12.2 centistokes at 98.9C and that the base oil~ after hydrotreatment, had a V.I. of 97 and a viscosity of 10.5 centistokes at 98.9C. The solvent-extracted raffinate added thereto was as described for Example 2. The base oil (Example (b)) and the base oil com-position were subjected to the oxidation stability 2~

test; as described abo.ve. The result;s are given in Table II.
TABLE II
. _ _ .. ._ Ex- Additive (%w) on Oxidation stability ample base oil _ sludge, acid- vis-%w on ity, cosity : com- mg in-~ position eq / crease . . .. _ ___ _ . _ _ . _ (b) _ 0.05 26 360 4 5 0.05 1.4 17 EXAMPLES 5 and 6 A base oil was prepared by extracting a vacuum ~:5 distillate (derived from a paraffinic crude oil) having a V.I. of 48 and a viscosity of 17.~ centi-stokes at 98.9C. The extractant used was furfural and the solvent-extracted raffinate had a V.I of 82 and a viscosity of 13.5 centistokes at 98.9C.
.lO The solvent-extracted raffinate was hydrotreated, distilled and dewaxed as described in Examples l and 2 and the V.I. and viscosity of the dewaxed and distilled hydrotreated base oil was 96 and 10.15 centistokes at 98.9C, respectively. This base oil (Example (c)) ~las then subjected to the oxidation stability test as described above.
Base oil compositions according to the present invention were then prepared by adding to the base oil various amounts of the solvent-extracted raf-finate having a V.I. of 82 and a viscosity of 13.5 centistokes at 98.9C after dewaxing with a mixture (50/50) of MEK and toluene, and also subjected to the oxidation stability test. The results are given in Table III.
TABLE III

Ex- Additive (~w) on Oxidation stability . amplebase oil ~

: . . sludge~ acid- V15-%w on ity, cosity com- mg in-_ t}on es / cr~ase (c) _ nil 14.9 94 0.5 nil 3.6 15 ~:
; 6 3.0 nil 1.7 7-7 . _ _ . ~ . .

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A base oil composition comprising:
(a) a base oil having a viscosity index of at least 94 obtained by hydrotreating a solvent-extracted raffinate having a viscosity index of at most 92, and (b) a solvent-extracted raffinate having a viscosity index of a-t most 92, and/or a deasphalted vacuum residue and/or a hydrotreated deasphalted vacuum residue.

2. A composition as claimed in claim 1, wherein the amount of (b) is from 0.5 to 20%w, based on the weight of (a).

3. A composition as claimed in claim 1, wherein (a) is derived from a vacuum distillate and/or deasphalted vacuum residue.

4. A composition as claimed in claim 1 to 3, wherein (a) is obtained by hydrotreating a solvent-extracted raffinate having a viscosity index of from 75 to 92.

5. A composition as claimed in claim 1, wherein (b) is a solvent-extracted raffinate having a viscosity index of from 75 to 92.

6. A composition as claimed in claim 1, wherein (a) has been subjected to a finishing step and/or a distillation step and/
or a dewaxing step.

7. A composition as claimed in claim 1, wherein (b) has been subjected to a dewaxing step.