GB1569934A

GB1569934A - Electrical insulating oil compositions

Info

Publication number: GB1569934A
Application number: GB17877/77A
Authority: GB
Original assignee: Nippon Oil Corp
Current assignee: Eneos Corp
Priority date: 1976-05-01
Filing date: 1977-04-28
Publication date: 1980-06-25
Also published as: FR2349929B1; JPS52133600A; DE2719218C2; CA1100304A; JPS6051210B2; DE2719218A1; FR2349929A1

Description

(54) ELECTRICAL INSULATING OIL COMPOSITIONS (71) We, NIPPON OIL CO., LTD., a Japanese company, of 3-12, 1-chome, Nishi shimbashi, Minato-ku, Tokyo, Japan, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a mineral oil-derived electrical insulating oil having improved pour point.

Electrical insulating oils of mineral oil origin have heretofore generally been produced from a naphthenic base crude oil as the starting oil. It has recently been expected to produce from a mixed or paraffinic base crude oil which is available at a relatively low cost in large quantities. However, electrical insulating oils of mixed or paraffinic crude oil origin are disadvantageous in that they have a high pour point.

This invention is applicable to the improvement of all mineral oil-derived electrical insulating oils in pour point and is particularly valuable in improving in pour point electrical insulating oils produced from the mixed or paraffinic base crude oil as the starting oil.

The electrical insulating oil composition of this invention consists essentially of (I) 50 95 parts by weight of a mineral oil-derived electrical insulating oil, (II) 5 - 50 parts by weight of a polyisobutene which is a liquid polymer having an average molecular weight of 200 to 400 and (III) 0.001 - 1.0% by weight of a hydrocarbon pour point depressant, based on the total weight of the oils (I) and (II). Thus, this invention is based on the finding or discovery that the addition of both the components (II) and (III) to the oil (I) exhibits such an unexpectedly great pour point-depressing action on the oil (I) as may not be expected from the addition of the component (II) alone or the component (III) alone to the oil (I).

This invention will be detailed hereinbelow.

The mineral oil-derived electrical insulating oil (I) may be one which is produced from any of naphthenic base, intermediate base and paraffin base crude oils, or may be blends of the oils so produced.

The terms paraffin base, intermediate base and naphthenic base crude oils are used herein to denote crude oil fractions classified by the U.S. Bureau of Mines. The classification is as follows: Classification API gravity API gravity of kerosene of lubricating oil fraction fraction boiling at 275- 300"C/40 mm.Hg Paraffin base crude oil at least 40 at least 30 Intermediate base crude oil 33 - 40" 20 - 30 Naphthenic base crude oil not higher than 33 not higher than 20 Typical of the naphthenic base crude oils are a California crude oil, a Texas crude oil, a Mexico crude oil, a Venezuela crude oil and a Duri crude oil. Typical of the paraffin base crude oils are a Pennsylvania crude oil and a Minas crude oil. Typical of the intermediate base crude oils are a Midcontinent crude oil, an Arabian crude oil and a Khafji crude oil.

This invention is applicable to an electrical insulating oil, as a base oil, of naphthenic, intermediate or paraffinic origin, as previously mentioned.

There have heretofore been known many processes for the preparation of electrical insulating oils from naphthenic base crude oils, the processes including a process comprising hydrofining a mineral oil to effect a 65 - 96% desulfurization and then treating the thus-desulfurized mineral oil with a solid adsorbent (Japanese Patent Gazette No.

18584/61) and a process comprising blending a mineral oil raffinate in hydrogenated form having an aromatic content not higher than 23% by weight with not more than 15% by weight of a lubricating oil having a higher aromatic content than the hydrogenated raffinate (Japanese Patent Gazette No. 3589/66).

Processes for the preparation of electrical insulating oils from paraffin base crude oils include, for example, a process comprising distilling a distillate obtained b dewaxing a vacuum distilled gas oil fraction 5 - 95 % of which boils at 2880 - 399"C (550 - 750"F) and recovering a heart cut thereby obtaining an electrical insulating oil (Japanese Patent Gazette No. 46123/74).

In United States Patent No. 4 008 148, there is described by the a process for the preparation of an electrical insulating oil which comprises refining with furfural or other suitable solvents at 500 - 1000C a distillate having a boiling range of 250 - 400"C at atmospheric pressure obtained by the distillation of a paraffin or intermediate base crude oil at atmospheric pressure or by the distillation at a reduced pressure of a bottom oil obtained by the distillation of the crude oil at atmospheric pressure, to effect a 30 75 wt.% desulfurization thereby obtaining a raffinate, hydrofining the thus obtained oil to remove therefrom 40 - 90 wt.% of the sulfur contained therein, solvent dewaxing the desulfurized oil and, if desired, successively treating the dewaxed desulfurized oil with clay thereby to obtain the electrical insulating oil having a sulfur content of 0.1 - 0.35 wt%, satisfactory oxidation stability, electrical properties and resistance to copper corrosion. The resent inventors also describe in application No. 4975/76 (Serial No.1540126 a process for the preparation of an electrical insulating oil having a total sulfur content of not more than 0.35 wit. %, excellent oxidation stability, thermal stability, corona resistance and corrosion resistance which consists essentially of (I) 80 - 99 parts by weight of a refined oil obtained by solvent refining a distillate contained in a fraction having a boiling range of 230 - 430"C at atmospheric pressure, the fraction being obtained by the distillation of a paraffin or intermediate base crude oil at atmospheric pressure or by the distillation at a reduced pressure of a bottom oil obtained by the distillation of the crude oil at atmospheric pressure, to producea raffinate, hydrofining the raffinate so produced, solvent dewaxing the thus-hydrofined oil and, if desired, treating the dewaxed hydrofined oil with a solid adsorvent thereby to obtain the refined oil having a sulfur content of no higher than 0.25 wt.% and an aromatic content of from more than 25 wt.% to 35 wit. % and (II) 1 -20 parts by weight of a refined oil obtained by treating the lubricating fraction of a mineral oil with a solid adsorbent.

There have been known various processes for the preparation of electrical insulating oils from the various crude oils. typical of them is a process for preparing an electrical insulating oil by either providing a lubricating oil fraction obtained by distilling at a reduced pressure a bottom oil obtained by the distillation of the crude oil at atmospheric pressure or providing a fraction having a boiling range of about 260 - 400"C at atmospheric pressure obtained by deasphalting the bottom oil to obtain a heavy oil, subjecting the thus-obtained heavy oil to hydrogenolysis at a temperature not lower than 350"C and a high hydrogen pressure not lower than 150 kg/cm2G and distilling the thushydrogenolysed oil to obtain a fraction having a boiling range within the range of about 260 - 400"C at atmospheric pressure, and, if necessary, successively dewaxing the fraction with a suitable solvent thereby to prepare the electrical insulating oil. The solvent may be a benzene-toluene-methyl ethyl ketone (vol. ratio, e.g. 25: 25 : 50) mixture.

This invention may of course be applicable not only to electrical insulating oils obtained by the said typical process but also those of mineral oil origin obtained by any other processes, irrespective of the native of the processes.

The second component oil (II) of the electrical insulating oil composition is polyisobutene.

The polyisobutene used herein is a liquid polymer which has an average molecular weight of from 200 - 400, preferably from 250 - 300. The polyisobutene consists mainly or entirely of isobutene and is preferably obtained by polymerizing a C4 (butaneisobutene) fraction, obtained as a by-product when naphtha, for example, is thermocracked in attempts to produce, inter alia ethylene and propylene, at a temperature of from -30 C to 300C in the presence of a Friedel-Crafts type catalyst such as aluminium chloride.

The hydrocarbon pour point depressant which is the component (III) according to this invention, is preferably at least one compound selected from (1) copolymers of ethylene and an a-olefin having the general formula CH2 = CH-R wherein R is an alkyl group having at least one carbon atom, (2) poly- a-olefins (a-olefin polymers), (3) hydrogenated styrene-butadiene copolymers, (4) condensed alkylnaphthalenes and (5) alkylated polystyrenes.

The copolymers (1) of ethylene and an a-olefin include ethylene-propylene copolymers, ethylene-butene-l copolymers and ethylene-hexene-1 copolymers with ethylenepropylene copolymers being particularly preferred. The ethylene. a-olefin copolymers used herein are essentially amorphous oil-soluble ones having a number average molecular weight of usually 10,000 - 200,000, preferably 20,000 - 70,000, and an ethylene content of 30 - 90 mol%, preferably 40 - 80 mol%. The term "essentially amorphous" used herein means that the ethylene- a-olefin copolymers may have some degree of crystallization therein, the degree being usually 0 - 5%, preferably 0 - 2%. In addition, it is preferable that the copolymers have a relatively narrow distribution of molecular weight, the distribution being usually not higher than 8, particularly not higher than 4. The ethylene-ex-olefin copolymers may be produced by known processes. The copolymerization may be effected by reacting ethylene with at least one a-olefin in an inert organic solvent containing an organic solvent-soluble specified homogeneous Ziegler type catalyst at atmospheric or somewhat superatmospheric pressure and at a temperature varying from a somewhat low temperature to a somewhat high temperature. The Ziegler type catalyst which may preferably be used is a coordination catalyst comprising a vanadium compound and an organoaluminum compound such as VOC13 - Al (C2H5) system.

The poly-a-olefin or polymer of a-olefin (2) usable as the component (III) of this invention is a homopolymer or copolymer of a-olefin having the general formula CH2 = CH - R wherein R is any one of alkyl groups which have 7 - 18, preferably 8 16, carbon atoms. The polymer of a-olefin (2) may also be a mixture of a said homopolymer and copolymer.

The polymer or copolymer has side chains which contain the moiety (CH2 )n in which n is at least 6. These polymers of a-olefin may be produced in the presence of the same homogeneous Ziegler type catalyst as the aforesaid ethylene-a-olefin copolymer (1). The polymer of a-olefin has a number average molecular weight of usually 10,000 - 200,000, preferably 20,000 - 70,000 and is essentially amorphous; in addition, it should preferably have a relatively narrow molecular weight distribution.

The hydrogenated styrene-butadiene copolymer (3) usable as the component (III) according to this invention may be produced by a known process such as a process comprising copolymerizing styrene and butadiene in the presence of an alkyl-alkali metal compound, such as butyllithium, as a catalyst and hydrogenating the resulting styrenebutadiene copolymer using a known hydrogenating technique. It is desirable that at least 90%, preferably 100%, of the double bonds contained in the original styrene-butadiene copolymer be hydrogenated.

The hydrogenated styrene-butadiene copolymer (3) is preferably a random copolymer and preferably has an average molecular weight of 10,000 - 200,000, more preferably 20,000 - 70,000. The ratio of content between the styrene units and the butadiene units in the copolymer is 15 - 50: 85-50,referably 25 - 40: 75 - 60.

The condensed alkylnaphthalene (4) usable as the component (III) is a condensate of dichloroparaffin and naphthalene and may be synthesized by a known process using a catalyst such as anhydrous Alp13. The dichloroparaffin usable herein is a dichloride of a paraffin preferably having from 15 - 60 carbon stoms. The condensed alkylnaphthalene usable herein has a molecular weight of several thousands to hundred thousands, usually about 2,000 - 70,000.

The alkylated polystyrene (5) usable as the component (III) according to this invention may be produced by a known process such as a process comprising subjecting styrene to free radical polymerization in the presence of a peroxide, such as benzoyl peroxide, as an initiator. Starting polystyrene for the alkylated polystyrene (5) has a number average molecular weight of 10,000 - 15,000 , preferably 20,000 - 70,000. The starting polystyrene is alkylated by contacting an alkyl halide therewith in the presence of a Friedel-Crafts type catalyst. The alkyl halide is represented by the general formula RX wherein R is an alkyl group having 6 - 20, preferably 8 - 18, carbon atoms and X is a halogen atom.

This invention is based on the finding or discovery that a mineral oil-derived electrical insulating oil - (I) may remarkably be depressed in pour point without impairing the electrical properties thereof by adding thereto a specified component (11) and a hydrocarbon pour point depressant (III) each in a specified proportion.

According to this invention, the blending ratio by weight of the mineral oil-derived electrical insulating oil (I) as the 1st component to the component (II) may be in the range of 50 - 95 : 5 - 50, preferably 60 - 90 : 40 - 10, and more preferably 70 - 85 : 30 - 15. The use of the component (II) in a higher blending ratio than the oil (I) will not be effective in further improving the oil (I) in properties, particularly pour point, nor will it be economical. The use of the components (II) and (I) in a blending ratio of less than 5 : 95 will not be effective in remarkably depressing the pour point of the component (I) although such remarkable depression is characteristic of this invention. In addition, the hydrocarbon pour point depressant (III) as the third component of the insulating oil composition of this invention may be used in amounts of 0.001 - 1.0%, preferably 0.05 0.2%, of the total weight of the components (I) and (II).

Furthermore, the electrical insulating oil composition of this invention may be incorporated with a known antioxidant such as DBPC (di-tert.-butyl-p-cresol), N phenyl- a-naphthylamine, nicotinic acid or hydroquinoline.

This invention will be illustrated by the following non-limitative Example wherein all percentages and parts are by weight unless otherwise specified.

Example There was obtained a distillate having a boiling range of 260 - 380"C at atmospheric pressure and a sulfur content of 2.2 wt.% by distilling an Arabia crude oil at atmospheric pressure to obtain a bottom oil and distilling the thus-obtained bottom oil at a reduced pressure. The distillate so obtained was extracted with furfural in a solvent ratio (furfural/distillate) of 1.3 at an extracting temperature of 75" - 90"C to obtain a raffinate having a sulfur content of 0.8 wt.%. The thus-obtained raffinate was hydrofined at 310 C under a hydrogen pressure of 40 kg/cm2G in the presence of an alumina-carried NiO-Mo03 catalyst (NiO : 3.0 wt.%, Mo03 : 14.0 wt.%) to obtain a hydrofined oil which was dewaxed with a benzene-toluene-methyl ethyl ketone mixed solvent in a solvent ratio (solvent/oil) of 1.6 at a cooling temperature of -30 C and successively treated with clay at 70"C for one hour thereby obtaining an electrical insulating oil (A).

Seventy-five (75) parts of the electrical insulating oil (A) were blended with 25 parts of polyisobutene having an average molecular weight of about 280 to obtain a blended oil (B). The thus obtained blended oil (B) was then incorporated with 0.07% of an essentially amorphous ethylene-propylene copolymer having an average molecular weight of 36,000 and a propylene content of 30 mol% to obtain an electrical insulating oil (C) having the properties shown in the following table I. For comparison, the table shows the properties of a blended oil (D) preparing by incorporating the electrical insulating oil (A) with 0.07% of the ethylene-propylene copolymer. The properties of the insulating oil (A), blended oil (B), final insulating oil (C) and comparative insulating oil (D) are shown in the atable.

TABLE Electrical insulating Blended oil (B) Electrical insulating Blended oil (D) oil (A) oil (C) Electrical insulating Electrical insulating Electrical insulating oil (A) oil (A) oil (A) + + + polyisobutene Polyisobutene Ethylene-propylene + copolymer Ethylene-propylene copolymer Pour point C -25 -27.5 -45 -32.5 Volume resistivity 80 C, #.cm 3.7 x 105 3.8 x 1015 4.1 x 1015 2.7 x 1015 Dielectric loss tangent 80 C, % 0.005 0.004 0.003 0.007 Corrosiveness (140 C x 19 hr) 1 b 1 b 1 b 1 b Steam emulsion number sec (JIS K-2517) 35 35 31 34 Hydrogen gas absorbency mm Oil [Value for 150 min. Value for 50 min.] -24 -47 -46 -45

Claims

WHAT WE CLAIM IS:

1. An electrical insulating oil composition consisting essentially of (I) 50 to 95 parts by weight of a mineral oilsderived electrical insulating oil, (II) 5 to 50 parts by weight of a polyisobutene which is a liquid polymer having an average molecular weight of 200 to 400, and (III) 0.001 to 1.0% by weight of a hydrocarbon pour point depressant, based on the total weight of the oils (I) and (II).

2. An electrical insulating oil composition according to claim 1, wherein the hydrocarbon pour point depressant (III) is at least one selected from (1) copolymers of ethylene and a-olefins having the general formula CH2 = CH-R wherein R is an alkyl group, (2) homopolymers and copolymers of a-olefins having the general formula CH2 =CH-R wherein R is a C7 - 18 alkyl group, the homopolymers or copolymers having side-chains comprising moieties of formula (CH2 )n wherein n is at least 6, (3) hydrogenated styrene-butadiene copolymers, (4) condensed alkylnaphthalenes produced by condensing a dichloro-paraffin and naphthalene and (5) alkylated polystyrenes obtained by the reaction of a polystyrene having a number average molecular weight of 10,000 to 150,000 with an alkyl halide of the formula RX wherein R is an alkyl group having 6 to 20 carbon atoms and X is a halogen atom.

3. An electrical insulating oil composition according to claim 2, wherein the hydrocarbon pour point depressant (III) is an essentially amorphous ethylene-propylene copolymer having anumber average molecular weight of 10,000 to 200,000 and an ethylene content of 30 to 90 mol%.

4. An electrical insulating oil composition according to claim 2, wherein the hydrocarbon pour point depressant (III) is a hydrogenated styrene-butadiene copolymer having a number average molecular weight of 10,000 to 200,000 with a ratio of content between the styrene units and butadiene units in the copolymer being 15 to 80 : 85 to 50.

5. An electrical insulating oil composition according to claim 2, wherein the hydrocarbon pour point depressant (III) is a said homopolymer or copolymer of an a-olefin of general formula CH2 = CH-R wherein R is as defined in claim 3, the homopolymer or copolymer having a number average molecular weight of 10,000 to 200,000.

6. An electrical insulating oil composition according to claim 2, wherein the hydrocarbon pour point depressant (III) is a said condensed alkylnaphthalene having a molecular weight of 2,000 to 70,000.

7. An electrical insulating oil composition according to claim 2, wherein the hydrocarbon pour point depressant (III) is an alkylated polystyrene, the polystyrene, before alkylation, having a number average molecular weight of 10,000 to 150,000.

8. An electrical insulating oil composition according to any one of claims 3 to 5 wherein the hydrocarbon pour point depressant has a number average molecular weight of 20,000 to 70,000.

9. An electrical insulating oil composition according to claim 7, wherein the polystyrene, before alkylation had a number average molecular weight of 20,000 to 70,000.

10. An electrical insulating oil composition as claimed in claim 1, substantially as described in the foregoing Example.

Agents for the Applicants