EP0791644A1

EP0791644A1 - Lubricating oils

Info

Publication number: EP0791644A1
Application number: EP97300876A
Authority: EP
Inventors: Martin BP Chemicals Limited Atkins
Original assignee: BP Chemicals Ltd
Current assignee: BP Chemicals Ltd
Priority date: 1996-02-22
Filing date: 1997-02-11
Publication date: 1997-08-27
Also published as: ID16027A; GB9603753D0; NO970780L; ZA971376B; CA2198073A1; AU1470897A; NO970780D0; JPH09241661A

Abstract

This invention is a process for making lubricating oils of a viscosity index ≥ 120 and a pour point of ≤ -45°C by (a) oligomerizing an olefinic feedstock in the presence of a catalyst comprising an alkyl aluminium halide and an alkyl halide to form a lubricating oil, (b) separating the lubricating oil from the catalyst and (c) optionally catalytically hydrogenating the lubricating oil. The feedstock is a mixture of C7 to C9 1-olefins containing at least 30 % w/w, the mole ratio of the alkyl halide to the alkyl aluminium halide in the oligomerisation catalyst is in the range from 1.0:1 to 20:1, and the oligomerisation reaction is carried out at or below 50°C.

Description

This invention relates to a process for the production of lubricating oils from a mixed feedstock comprising at least heptene.
It is well known to oligomerize 1-olefins to hydrocarbons of higher molecular weight and then to hydrogenate or isomerise the oligomer so formed to produce lubricating oils (See eg) US-A-3763244. In most ofthese cases, the 1-olefins are derived initially from ethylene (by the so called "ethylene chain growth and displacement" method) which is a relatively expensive source for such 1-olefins. Moreover, lubricating oils have been produced by oligomerization of relatively pure 1-olefins (see US-A-31780128 and EP-A-0 468 109). This last document also discloses that once the oligomers have been produced, the oligomers of various 1-olefins can be blended either before or after the hydrogenation or isomerization steps in order to produce the lubricating oils of the desired properties such as viscosity index and pour point. Similarly, US-A-4041098 describes a process for the oligomerisation of 1-olefins using a catalyst comprising an alkyl aluminium halide and an alkyl halide such as tertiary butyl chloride to form lubricating oils. The use of conventional feedstocks such as commercially available 1-olefins such as eg 1-hexene or 1-decene do not give rise to lubricating oils of the desired viscosity index. For instance, a feedstock containing substantially pure olefin such as eg 1-decene gives rise to a lubricant having a relatively high viscosity index but these products comprise exclusively of units which are multiples of 10 as would be expected of oligomers of decene and predominate in discrete units having 30, 40, 50, 60 and 70 carbon atoms. Such a blend, whilst suitable for some purposes, is not an ideal synthetic lubricant since it is desirable for the molecular weight distribution of the components in a synthetic lubricant blend to simulate those of a mineral oil in their dispersity index, ie a standard deviation curve so that there is continuity and gradual blending of the components in the mixture of products. The molecular weight distribution of the products from discrete multiples of 10 described above do not resemble a standard deviation curve and would therefore lack the consistency of properties due to absence of a continuity and gradual blending of closely related oligomers. That is, the blend lacks consistency of properties due to the absence of a continuity and gradual blending of closely related/matched oligomers. Furthermore, the use of a relatively pure single olefin is relatively expensive. It is also known to oligomerize the olefinic products from a Fischer Tropsch synthesis followed by hydrogenation or isomerization of the oligomer to form lubricating oils (see eg Monoolefins, Chemistry & Technology, by F Asinger, pp 900 and 1089 (1968) and published by Pergamon Press). However, these publications relating to use of the Fischer Tropsch products as the source material for the oligomerization step do not indicate the product mix required to achieve the desired oligomer or the catalyst suitable for the oligomerization step. In our prior published EP-A-0583072 we have claimed and described a process for the catalytically oligomerising an olefinic feedstock comprising a mixture of C5 to C18 olefins but having at least 6% w/w of 1-hexene and at least 2.6% w/w of 1-decene to lubricating oils. However, 1-hexene is a valuable monomer which has other uses of greater economic value such as eg as a comonomer in the production of high grade polyolefins, especially polyethylene.
It is therefore the object of the present invention to look at feedstock which would firstly meet the criteria of forming a product with the right blend of components but would also be producible from a relatively inexpensive and commercially available raw material. One such feedstock is the mixture of olefins from a Fischer Tropsch synthesis which is readily available. However, the choice of the feedstock alone is insufficient to achieve this objective since it is also necessary to identify a catalyst system and the oligomerisation conditions which would give rise to the right blend of oligomers.
It has now been found that commercially available olefinic feedstock comprising C7-C9 olefins but which are substantially free of hexenes can be oligomerised to oligomers which can match the properties of those derived from feedstock which contain hexenes.
Accordingly, the present invention is a process for the production of lubricating oils having a viscosity index of at least 120 and a pour point of -45°C or less, said process comprising (a) oligomerizing an olefinic feedstock in the presence of an oligomerization catalyst comprising an alkyl aluminium halide and an alkyl halide to form a lubricating oil, (b) separating the lubricating oil from the oligomerization catalyst, (c) optionally catalytically hydrogenating the lubricating oil in the presence of hydrogen to improve the oxidation stability thereof and (d) recovering the lubricating oil so formed, characterised in that

i. the olefinic feedstock is substantially free of hexenes and comprises a mixture of olefins having 7 to 9 carbon atoms, the amount of heptenes in said mixture being at least 30 % w/w as herein defined
ii. the mole ratio of the alkyl halide to the alkyl aluminium halide in the oligomerisation catalyst is in the range from 1.0:1 to 20:1 and
iii. the oligomerisation reaction is carried out at temperatures at or below 50°C.

The olefinic feedstock is substantially free of hexenes, ie the feedstock has no more than 2% w/w of hexenes, suitably less than 1% w/w and preferably less than 0.5% w/w, and comprises a mixture of olefins having 7 to 9 carbon atoms. In this mixture, the amount of heptenes is at least 30% w/w and may contain in addition octenes and/or nonenes. The olefinic feedstock may contain, in addition to the heptenes, octenes and/or nonenes, other olefins such as eg butenes, pentenes, decenes or higher olefins, preferably 1-decene, provided that the amount of heptenes in the mixture is at least 30% w/w of the total of heptenes, octenes and nonenes in said mixture. In such a mixture the amount of heptenes is preferably from 40 to 75 % w/w, more preferably from 45% to 70% w/w. The olefins in the olefinic feedstock used in general and the heptenes, octenes and nonenes in particular, are preferably 1-olefins. A particularly preferred example of such a feedstock is the olefin stream formed by the Fischer Tropsch synthesis operated in a manner so as to give an olefinic feedstock which comprises a mixture of C7, C8 and C9 1-olefins in a ratio by weight per cent of these respective 1-olefins ranging from 40 to 45 : 30 to 35 : 20 to 25. It is known, for instance, Gasol derived by FTS and described in "Mono-olefins Chemistry & Technology", by F Asinger, page 1089 (1968), published by Pergamon Press, contains about 50% but-2-ene and is said to give poor lubricating materials on polymerization with aluminium chloride. Thus, any unspecified product mix of an unspecified FTS is unlikely to be suitable as feedstock for the process of the present invention.
Normally in a Fischer Tropsch synthesis (hereafter "FTS"), a mixture of carbon monoxide and hydrogen is passed over or through a heated catalyst bed to form a wide variety of hydrocarbons. When the hydrogen content of the reactant mixture is high, the reaction products predominantly contain paraffinic hydrocarbons. However, if the proportion of hydrogen in the reaction mixture is low, the reaction products predominantly contain olefinic hydrocarbons. It is, however, preferable that even in the case where the reaction products of the FTS are predominantly olefins, the reaction conditions of the FTS are controlled to obtain the desired mixture of heptenes, octenes and/or nonenes.
The oligomerization catalyst used is a combination of an alkyl aluminium halide and an alkyl halide. Thus, the alkyl aluminium halide is suitably represented by the generic formula R_nAlX_3- _n, wherein R is a C1-C4 primary, secondary or tertiary alkyl group, preferably a primary or secondary alkyl group, more preferably an alkylaluminium halide (hereafter "AAH"); X is a halogen atom which my be chlorine, bromine or iodine, preferably chlorine; and n is an integer from 1 to 3, preferably 1 to 2. The alkyl halide component of the catalyst suitably has the formula R₃X wherein R and X have the same significance as above and is preferably a tertiary alkyl group eg tert.-butyl chloride (hereafter "TBC"). The AAH is preferably ethyl aluminium dichloride (hereafter "EADC"). The relative mole ratios of alkyl halide to AAH in the oligomerization catalyst is in the range from 1.0:1 to 20:1, preferably from 2.5:1 to 15:1.
The precise concentration of the two catalytic components chosen would depend upon the specific property desired in the final lubricating oil such as eg the viscosity.
The oligomerization is carried out at temperatures at or below 50°C, suitably from ambient temperature, eg 15°C to 50°C, preferably around 0-30°C. The reaction pressures used can be ambient.
The oligomerization is suitably carried out in the presence of a solvent inert under the reaction conditions, preferably a paraffinic hydrocarbon eg n-hexane.
It is preferable to add initially the required amount of TBC to a solution of the olefinic feedstock in an inert solvent and to bring the temperature of this solution to the reaction temperature. Thereafter, a solution of AAH, preferably in the same inert solvent, is added dropwise with continuous stirring to the solution of the olefinic feedstock and TBC over a period of time. After the addition of the EADC solution is completed and a further duration allowed to elapse, the reaction mixture can be neutralised eg by the addition of ammonia, then washed and filtered. The organic products can then be rendered free of the inert solvent by eg evaporation. The above steps can be, if desired, carried out in continuous operation.
The resultant residue is an oligomer. This oligomer is a lubricating oil with important and desirable properties but may contain a small proportion of olefinic groups.
An important aspect of this invention is that by choosing the appropriate feeds, oligomerization catalyst and oligomerization conditions, it is possible to ensure that the oligomer is very low in olefinic groups thereby substantially obviating the need for the subsequent optional hydrogenation step.
The hydrogenation step, when used, is suitably carried out to ensure that any olefinic groups in the oligomer are saturated. The effect of this is to improve the oxidation stability of the lubricating oil formed in step (b). The hydrogenation step in the present case can be carried out using any of the conventional hydrogenation catalysts such as eg Raney nickel or other Group VII or Group VIII metal according to the Periodic Table due to Mendeleef. This step is carried out in the presence of hydrogen. The reaction pressure for this step (including the hydrogen partial pressures) is suitably in the range from 20 to 1000 KPa, preferably from 350 to 750 KPa. The hydrogenation is suitably carried out at a temperature in the range from 0 to 350°C.
The hydrogenated product is separated from the catalyst and any byproducts by well known techniques eg by distillation.
The hydrogenated products of the present invention are excellent lubricants and can be used as such or for blending with other additives in a lubricating oil. The products of the present process can have pour points of below -45°C and viscosity index values above 120.
The present invention is further illustrated with reference to the following Examples:

EXAMPLE 1:

A mixture of 1-heptene (80g, 0.815 moles), 1-octene (10g, 0.089 moles) and 1-nonene (10g, 0.079 moles) was blended with n-heptane (181g) in a reservoir (total mass of 1-olefins 100 g, 0.983 moles). The solution of the resultant 1-olefin blend was cooled to +16°C with stirring at about 1000 rpm. Tert.-butyl chloride (TBC initiator, 6g, 0.065 moles) was added to this blend.
Ethyl aluminium dichloride (EADC catalyst, 0.020 mol) in "hexane" (ex Aldrich Chemicals) solution (1M, 20 ml) was then added to the 1-olefin blend/TBC solution dropwise with stirring over a period of 15 minutes. The reaction temperature increased by 12°C to about 28°C during this addition. The initiator : catalyst ratio of this reaction mixture was thus 3.5.
The oligomerisation reaction was allowed to proceed for 2 hours after the addition of EADC was commmenced, and the reaction was terminated by bubbling anhydrous ammonia gas for 1-2 minutes to deactivate the catalyst. After ammonia addition, the reaction mixture was washed by addition of 100 ml of water and the washed reaction mixture separated from solvents and light polymers by rotary evaporation at 180°C under vacuum for 30 minutes.
The material that remained upon evaporation was a lubricating oil corresponding to a yield of 75% w/w from the 1-olefins. This oil had a kinematic viscosity of 141.1 cSt at 40°C and 16.37 cSt at 100°C, a viscosity index of 123 and a pour point of -48°C.

EXAMPLE 2:

A further Example was carried out using a reactant solution prepared in the same manner as in Example 1 above.
The solution containing 100 g of the olefin blend (0.983 moles) was cooled to + 16°C with stirring as previously in Example 1. The level of TBC initiator added was 9 g (0.097 mol). An EADC solution of the same concentration as used in Example 1 was added dropwise to the 1-olefin blend/TBC solution but the ratio of initiator to catalyst in this Example was 5.0. The reaction was allowed to proceed and the reaction products worked up as previously in Example 1 above. The resultant oil (yield 68.1% w/w) had the following characteristics: kinematic viscosity at 40°C was 99.01 cSt and at 100°C was 12.50 cSt; the viscosity index was 120 and the oil had a pour point of -48°C.

Claims

A process for the production of lubricating oils having a viscosity index of at least 120 and a pour point of -45°C or less, said process comprising (a) oligomerizing an olefinic feedstock in the presence of an oligomerization catalyst comprising an alkyl aluminium halide and an alkyl halide to form a lubricating oil, (b) separating the lubricating oil from the oligomerization catalyst, (c) optionally catalytically hydrogenating the lubricating oil in the presence of hydrogen to improve the oxidation stability thereof and (d) recovering the lubricating oil so formed in steps (b) or (c), characterised in that
i. the olefinic feedstock is substantially free of hexenes and comprises a mixture of olefins having 7 to 9 carbon atoms, the amount of heptenes in said mixture being at least 30 % w/w as herein defined

ii. the mole ratio of the alkyl halide to the alkyl aluminium halide in the oligomerisation catalyst is in the range from 1.0:1 to 20:1 and

iii. the oligomerisation reaction is carried out at temperatures at or below 50°C.
A process according to Claim 1 wherein the olefinic feedstock the feedstock has no more than 2% w/w of hexenes and the amount of heptenes is from 40 to 75 % w/w.
A process according to Claim 1 or 2 wherein the olefins in the olefinic feedstock are 1-olefins.
A process according to any one of the preceding Claims wherein the olefinic feedstock is an olefin stream formed by the Fischer Tropsch synthesis operated in a manner so as to give an olefinic feedstock which comprises a mixture of C7, C8 and C9 1-olefins in a ratio by weight per cent of these respective 1-olefins ranging from 40 to 45 : 30 to 35 : 20 to 25.
A process according to any one of the preceding Claims wherein the alkyl aluminium halide is represented by the generic formula R_nAlX_3- _n, wherein R is a C1-C4 primary, secondary or tertiary alkyl group, X is a halogen atom which my be chlorine, bromine or iodine, preferably chlorine; and n is an integer from 1 to 3.
A process according to any one of the preceding Claims wherein the alkyl aluminium halide is ethyl aluminium dichloride.
A process according to any one of the preceding Claims wherein the alkyl halide in the catalyst has the formula R₃X wherein R is a C1-C4 primary, secondary or tertiary alkyl group, X is a halogen atom which my be chlorine, bromine or iodine.
A process according to any one of the preceding Claims wherein the alkyl halide is tert.-butyl chloride (hereafter "TBC").
A process according to any one of the preceding Claims wherein the relative mole ratios of the alkyl halide to the alkyl aluminium halide in the oligomerization catalyst is in the range from 2.5:1 to 15:1.
A process according to any one of the preceding Claims wherein the oligomerization is carried out at temperatures from 15°C to 50°C.
A process according to any one of the preceding Claims wherein the oligomerization is carried out in the presence of a solvent inert under the reaction conditions.
A process according to any one of the preceding Claims wherein the hydrogenation step, when used, is carried out with a hydrogenation catalyst selected from Raney nickel or other Group VII or Group VIII metal according to the Periodic Table due to Mendeleef.
A process according to Claim 12 wherein the hydrogenation step is carried out in the presence of hydrogen at a reaction pressure (including the hydrogen partial pressures) in the range from 20 to 1000 Kpa and at a temperature in the range from 0 to 350°C.