Reaction product of naphthenic acids useful as insulating oil

Abstract

An insulating composition useful as insulating oil, which can be substituted for PCB and yet has excellent characteristic properties for insulation comparable to PCB, can be obtained by heating naphthenic acids alone or a mixture of naphthenic acids and a saturated, aliphatic carboxylic acid or a saturated aliphatic aldehyde, at a temperature of 200.degree.-700.degree.C, under a pressure of 0.1 - 10 atm, and in the presence of a specified catalyst, followed by neutralization treatment and removal of low boiling fractions.

Description

DESCRIPTION OF THE INVENTION

The present invention relates to a composition useful as an insulating oil in various kinds of electric instruments such as cable, condenser, transformer, etc. More particularly, it relates to a composition useful as an insulating oil, obtained by catalytically reacting naphthenic acids alone or a mixture of naphthenic acids and saturated aldehydes having 2 to 18 C or other kinds of saturated carboxylic acids having 2 to 18 C and subjecting the resulting reaction product to post-treatment.

Heretofore, polychlorobiphenyls (which are a mixture of compounds having different chlorine contents and will be hereinafter abbreviated to PCB) have been widely used as an insulating oil, due to its flame-proof property and superior electric characteristics.

PCB, however, particularly those having a large number of chlorine atoms attached are hardly decomposed in the nature and remain on the surface of the earth for a long period of time, and may enter a human body. When they enter a human body, they are dissolved in the fat of the body and scarcely discharged from the body. Thus, they are gradually accumulated in it and have a great possibility of intoxication upon the body. Accordingly, the use of PCB has recently come to be inhibited or prohibited in Japan.

As for insulating oils, the following characteristics are required:

1. good heat-stability,

2. high dielectric constant,

3. low tan .delta.,

4. high dielectric breakdown voltage, etc.

PCB is a very excellent insulating oil provided with these characteristics, but has the above-mentioned serious drawback. Thus, it has become necessary to develope an insulating oil which is substituted for PCB and yet has an excellent property. As for substances useful for insulating oils except for PCB, there are mineral oils, polybutene and organosiloxane.

Among these, mineral oils obtained from crude oils have a low dielectric constant, and their tan .delta. as well as volume resistivity are also insufficient.

Polybutene is much more stable at higher temperatures than insulating oils of mineral oils, vegetable oils, etc. and hardly oxidizable, and hence the use of polybutene in various kinds of electric instruments has been proposed. However, when polybutene is used in a condenser which is to be used under a potential stress in a closed state at an extremely high temperature, or other apparatuses of such kinds, the polybutene insulator is insufficient in life characteristic and liable to undergo thermal and electrochemical deterioration during the use for a long period of time. Thus, its electric characteristics are reduced and insulation breakdown is brought about within a short period of time.

Further, organosiloxane which has been noted in respect of its excellent characteristics, also has a tendency that its superior insulating property is lost due to chemical and electrochemical actions at high temperatures.

Furthermore, a drawback common to these substitutes for PCB is a low dielectric constant. Namely, the dielectric constant of PCB is 5 - 6, whereas those of mineral oils, polybutene and organosiloxane are 2.5, 2.5 and 2.7, respectively, that is, about half of that of PCB. Accordingly, it is very difficult to use these insulating oils for electric instruments under a high voltage and large capacity.

Thus, the advent of a new insulating oil which can substitute for these insulating oils and yet has more excellent characteristics, has been extremely desired.

The object of the present invention is to provide such a new insulating oil.

After strenuous studies, we have found that a reaction product obtained from naphthenic acids alone or a mixture of naphthenic acids and saturated aldehydes having 2 to 18 C or other kinds of saturated carboxylic acids having 2 to 18 C, has excellent characteristics as an insulating oil which are comparable to those of PCB.

BRIEF DESCRIPTION OF THE DRAWINGS

The figures show infrared absorption spectra of compositions according to the invention.

The present invention resides in a composition useful as an insulating oil, obtained by heating naphthenic acids alone or a mixture of naphthenic acids and a saturated aliphatic carboxylic acid having a carbon number of 2 to 18 or a saturated aliphatic aldehyde having a carbon number of 2 to 18, at a temperature of 200.degree. - 700.degree.C, under a pressure of 0.1 - 10 atm, and in the presence of as a catalyst, an oxide selected from the group consisting of zirconium oxide, thorium oxide, lithium oxide, scandium oxide, yttrium oxide, alumina and oxides of rare earth elements of lanthanum and atomic numbers 58 - 71; subjecting the resulting oily product to neutralization treatment with an aqueous alkaline solution; and removing from the product thus treated, fractions having a boiling point of 150.degree.C/100 mmHg or lower, by distillation.

The above-mentioned reaction is principally a decarboxylation reaction between two molecules of naphthenic acids themselves or naphthenic acids and a saturated aliphatic carboxylic acid of C.sub.2 - C.sub.18 or a saturated aliphatic aldehyde of C.sub.2 - C.sub.18, and the resulting reaction product is composed mainly of ketones.

Formation of ketones from naphthenic acids is known, that is, described in e.g. the following literatures:

1. Zelinsky: Berichte, 1924, 57-B, p. 1932

2. Ipatiev: Brennstoff Chemie, 1930, p. 175

3. Ipatiev: Berichte, 1930, 63-B, p. 329

4. British Pat. No. 1,191,854

5. U.S. Pat. No. 3,466,334

The decarboxylation reaction of the present invention can be expressed by the following three equations (1), (2) and (3):

in these equations, R -- COOH, R.sub.0 -- COOH and R.sub.0 -- CHO mean naphthenic acids, a saturated aliphatic carboxylic acid and a saturated aliphatic aldehyde, respectively.

The naphthenic acids to be used in the present invention are those obtained by subjecting distillates from crude oil to extraction with an alkaline solution followed by sulfuric acid treatment, and having an acid value of 80 - 250, preferably 140 - 230. Such naphthenic acids are on sale, and it is well known that they are a mixture of various kinds of cycloalkyl compounds, that is to say, they contain cyclopentyl acetic acid, methylcyclopentyl acetic acid, cyclopentyl caproic acid, cyclopentyl stearic acid, cyclohexyl propionic acid, cyclohexyl caproic acid, dicyclopentyl acetic acid, dicyclopentyl dodecanoic acid, etc.

The saturated aliphatic carboxylic acid can be straight chain or branched.

The saturated aliphatic aldehyde can be also straight chain or branched.

The mixing ratio by mol of the saturated aliphatic carboxylic acid or the saturated aliphatic aldehyde to naphthenic acids is 5 or less based on one mol of naphthenic acids as calculated for convenience sake from the acid value of naphthenic acids.

It is preferable that the raw material (naphthenic acids or a mixture of naphthenic acids and the saturated, aliphatic carboxylic acid or aldehyde) is preheated and fed into a reaction tube containing a catalyst, at a rate of 0.1 - 30 g/hr/g of catalyst, preferably 0.1 - 5 g/hr/g of catalyst.

The above-mentioned decarboxylation reaction is carried out at a temperature of 200.degree. - 700.degree.C, preferably 300.degree. - 500.degree.C and under a pressure of 0.1 - 10 atm.

Further, the decarboxylation reaction can also be well carried out in the coexistence of water (steam). In this case, the ratio of water to the reaction material is 30 times or less by mol, preferably 15 times or less.

The reaction product after the decarboxylation reaction is subjected to neutralization treatment a few times with a sufficient amount of an aqueous alkaline solution to remove unreacted carboxylic acids, followed by removal of low boiling fractions of 150.degree.C/100 mmHg or lower, by distillation to give an oily substance as residue. As for the aqueous alkaline solution, aqueous solutions of NaOH, Na.sub.2 CO.sub.3, KOH, Ca(OH).sub.2, etc. can be illustrated.

The resulting oily substance can be used as insulating oil, as it is, or in the form of a blend thereof with another component such as other kinds of insulating oils, e.g. mineral oils, polybutene, organosiloxane, alkylbenzenes, paraffins, high molecular wegith dialkylketones, etc., additives, e.g. antioxidant, rustinhibitor, etc. It is preferable that a trace of water contained in the oily substance is removed therefrom in advance or at the time of using it, by molecular shieve or the like means.

The oily substance has as high a dielectric constant at 4 - 6, and excellent heat-stability, low volatility and electric characteristics, and is suitable particularly for the application fields as dielectric liquid, impregnating liquid, etc. for electric instruments such as condenser, transformer, cable, switch, reactor, circuit-breaker or the like.

The present invention is further illustrated by the following examples, but they should not be construed to limit the present invention.

EXAMPLE 1

50 g of activated carbon was introduced into 300 ml of 50% by weight aqueous solution of thorium nitrate. Deaeration and impregnation were carried out using a water bath at 90.degree. - 100.degree.C for 3 hours. After drying at 110.degree.C, heat treatment was carried out at about 300.degree.C for 3 hours to decompose thorium nitrate into thorium oxide. The thorium oxide - activated carbon catalyst thus obtained contained 13% by weight of thorium oxide. 20 g of the catalyst was filled in a silica tube having an inner diameter of 23 mm and a length of 630 mm. Commercial naphthenic acids having an acid value of 220, preheated to 380.degree.C was fed into the silica tube. At the same time, nitrogen gas as a carrier gas at a rate of 40 cc/min. and an equimolecular amount of water to naphthenic acids. The mol number of naphthenic acids were calculated from the acid value for convenience sake. The reaction was carried out at 480.degree.C under the atmospheric pressure. The feeding rate of naphthenic acids was 2 g/hr/g of catalyst.

The resulting reaction product was subjected to neutralization treatment three times with a sufficient amount of an aqueous solution of NaOH to remove unreacted naphthenic acids. The resulting product was distilled to remove low boiling fraction of 150.degree.C/20 mmHg or lower. The residual oil is the objective product for the present invention.

The yield of the oily product based on the weight of naphthenic acids used was 83% by weight after 5 hours, from which time the reaction proceeded in a stationary state. As the reaction time was further prolonged, the yield decreased due to reduction in the catalyst activity. The yield was 67% by weight after 100 hours and 53% by weight after 300 hours. The acid value of the oily product after 5 hours' reaction was 0.2.

According to infrared absorption spectra measurement of the oily product, the spectra had an intensive absorption of carbonyl group. In view of the above-mentioned acid value, it was presumed that the oily product was ketone compounds.

The characteristic properties of the oily product as an insulating oil are shown in Table 1.

FIG. 1 of the accompanying drawings shows the infrared absorption spectra of the oily product obtained by 5 hours' reaction and post-treatment.

EXAMPLE 2

Example 1 was repeated except that commercial naphthenic acids having an acid value of 200 was substituted.

The oily product thus obtained had an acid value of 0.3. According to infrared absorption spectra measurement, it was presumed that ketone compounds were formed. The yield of the product was 80% by weight after 5 hours' reaction. The characteristic properties of the product are shown in Table 1.

EXAMPLE 3

Example 1 was repeated except that naphthenic acids having an acid value of 160 was substituted.

The oil product thus obtained had an acid value of 0.3. It was presumed that ketone compounds were formed. The yield of the product was 79% by weight after 5 hours' reaction. The characteristic properties of the product are shown in Table 1.

EXAMPLE 4

Zirconium hydroxide was heated at 500.degree.C for 3 hours to give zirconium oxide, which was pelletized into pellets of 3 mm .times. 3 mm. 20 g of the pellets were filled in the reaction tube of Example 1.

A mixture of commercial naphthenic acids having an acid value of 140 and acetic acid, having a mixing ratio by mol of 1:1 was preheated to 380.degree.C and fed into the reaction tube at a feeding rate of 1 g/hr/g of catalyst. At the same time, an equimolecular amount of water to acetic acid and nitrogen gas as a carrier gas at a rate of 40 c.c./min. were fed into the tube. The reaction was carried out at 480.degree.C under the atmospheric pressure.

The resulting reaction product was subjected to neutralization treatment three times with a sufficient amount of an aqueous solution of NaOH to remove unreacted acids. The resulting product was distilled to remove low boiling fraction of 150.degree.C/20 mmHg or lower. The residual oil is the objective product for the present invention.

The yield of the oil product based on the weight of the mixture used, of naphthenic acids and acetic acid was 75% by weight after 5 hours' reaction. (In the following Examples using a mixture as raw materials, the yields were also calculated based upon the weight of the mixture.) The oil product had an acid value of 0.5. According to infrared absorption spectra measurement, the spectra had an intensive absorption of carbonyl, thus it was presumed that the oily product was ketone compounds. The characteristic properties of the oil are shown in Table 1.

EXAMPLE 5

Example 4 was repeated except that a mixture of naphthenic acids having an acid value of 140 and isobutyraldehyde was used in a mixing ratio of 1:1 by mol, and water was used in an amount of twice the mols of isobutyraldehyde.

The yield of the resulting oil product was 85% by weight after 5 hours' reaction. The oily product had an acid value of 0.2. According to infrared absorption spectra measurement, the spectra had an intensive absorption of carbonyl, thus it was presumed that the oily product was ketone compounds. (Isobutyraldehyde was removed as a low boiling fraction.) The characteristic properties of the oily product are shown in Table 1. FIG. 2 of the accompanying drawings shows the infrared absorption spectra of the oily product.

EXAMPLE 6

Example 4 was repeated except that a mixture of commercial naphthenic acids having an acid value of 160 and caproic acid was used in a mixting ratio of 1:1 by mol, and water was used in an amount of 10 times the mols of caproic acid.

The yield of the resulting oily product was 81% after 5 hours' reaction. The oily product had an acid value of 0.5. According to infrared absorption spectra measurement, the spectra had an intensive absorption of carbonyl group, thus it was presumed that the oily product was ketone compounds. The characteristic properties of the oily product are shown in Table 1.

EXAMPLE 7

Example 4 was repeated except that a mixture of commercial naphthenic acids having an acid value of 220 and 2-ethylhexanoic acid was used in a mixing ratio of 1:1 by mol, and water was used in an amount of 5 times the mols of 2-ethylhexanoic acid.

The yield of the resulting oily product was 73% by weight after 5 hours' reaction. The oil product had an acid value of 0.3. According to infrared absorption spectra measurement, an intensive absorption of carbonyl was observed in the spectra, thus it was presumed that the oily product was ketone compounds. The characteristic properties of the oily product are shown in Table 1.

Table 1 __________________________________________________________________________ Characteristic Composition as insulating oil of the present invention properties.sup.1 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example __________________________________________________________________________ 7 Viscosity 3000 cst 5000 cst 9500 cst 20 cps 31 cps 35 cps 37 cps (temperature) 38.degree.C 38.degree.C 38.degree.C 20.degree.C 20.degree.C 20.degree.C 20.degree.C Flash point .degree.C 192 188 183 153 157 160 155 Dielectric 5.1 4.5 4.1 4.9 4.8 5.1 5.2 constant (50 c/s) 100.degree.C 100.degree.C 100.degree.C 100.degree.C 100.degree.C 100.degree.C 100.degree.C tan .delta. 0.5> 0.5> 0.5> 0.5> 0.5> 0.5> 0.5> (%, 50 c/s) 100.degree.C 100.degree.C 100.degree.C 100.degree.C 100.degree.C 100.degree.C 100.degree.C Volume resistivity 3.times.10.sup.13 < 3.times.10.sup.13 < 3.times.10.sup.13 < 3.times.10.sup.13 < 3.times.10.sup.13 < 3.times.10.sup.13 < 3.times.10.sup.13 < (.OMEGA.-cm) Insulation breakdown voltage 30 < 30 < 30 < 30 < 30 < 30 < 30 < (KV/mm) __________________________________________________________________________ .sup.1 According to JIS-C-2320 (JIS : Japanese industrial standards)

EXAMPLE 8

Example 1 was repeated except that 25 g of an activated alumina (Al- 0104T 1/8 inch (trade name) made by Harshaw Chemical Co., U.S.A.) was used as the catalyst.

The yield of the resulting oil product was 72% by weight after 5 hours' reaction. The acid value of the oil product was 0.3. The infrared absorption spectra of the oil product was similar to those of Example 1. The characteristic properties of the oil product as an insulating oil were also similar to those of Example 1 except that viscosity: 2,800 cst (38.degree.C), dielectric constant: 4.9 (50 c/s, 100.degree.C), and flash point: 184.degree.C.

EXAMPLE 9

300 g of the activated alumina used in Example 8 was impregnated with 140 ml of an aqueous solution containing 85 g of samarium nitrate. The resulting mixture was heated on a steam bath for 3 hours with stirring to evaporate water, and further dried in an oven at 120.degree.C for 24 hours. Then, heat-treatment was carried out at 450.degree.C, for 4 hours. The catalyst thus obtained contained 16.5% by weight of samarium oxide.

25 g of the catalyst was filled in the tube used in Example 1, and reaction and post-treatment were carried out as in Example 1.

The yield of the resulting oily product based on the weight of naphthenic acids was 85% by weight after 5 hours' reaction. The acid value of the product was 0.2. Further, according to infrared absorption spectra measurement, an intensive absorption of carbonyl group was observed.

The characteristic properties of the oily product were as follows:

Viscosity: 2700 cst (38.degree.C), dielectric constant:

4.8 (50 c/s, 100.degree.C), and flash point: 183.degree.C.

Other properties were similar to those of Example 1.

EXAMPLE 10

Lithium nitrate was heated at about 850.degree.C in a stream of hydrogen gas to give lithium oxide, which was pelletized into pellets of 3 mm .times. 3 mm. 25 g of the pellets as a catalyst were filled in the reaction tube used in Example 1. A mixture as raw materials, of commercial naphthenic acids having an acid value of 160 and isobutyric acid at a mixing ratio of 1:1 by mol was preheated at 370.degree.C and fed into the reaction tube. The reaction was carried out at 480.degree.C. No water was fed in the reaction, but, as the result of analysis, formation of a small amount of water was observed.

Post-treatment was carried out as in Example 1. The yield of the resulting oily product 79% by weight, and the acid value was 0.4. According to infrared absorption spectra measurement, an intensive absorption of carbonyl was observed. The characteristic properties of the oily product were similar to those of Example 6 except that viscosity: 33 cps and dielectric constant: 5.2. Flash point was not measured.

EXAMPLE 11

Pellets of zirconium oxide were dipped into a 20% aqueous solution of lanthanum nitrate, followed by drying on a hot water bath and then heat-treated at 450.degree.C for 3 hours. The catalyst thus obtained contained 13% by weight of lanthanum oxide. 23 g of the catalyst was filled in the reaction tube used in Example 1. A mixture of commercial naphthenic acids having an acid value of 220 and 2-ethyl-hexanoic acid in a mixing ratio of 1:1 by mol was preheated to 370.degree.C and fed into the tube at a feeding rate of 1.2 g/hr/g of catalyst. At the same time, water in an amount of twice the mols of 2-ethyl-hexanoic acid and nitrogen gas as a carrier gas at a flow rate of 40 c.c./min. were fed. The reaction was carried out at 480.degree.C under the atmospheric pressure.

The reaction product was subjected to neutralization treatment with a sufficient amount of NaOH to remove unreacted acids and then low boiling fraction of 150.degree.C/30 mmHg or lower was removed to give an oily substance as a residue.

The yield of the resulting oil product was 78% by weight after 5 hours' reaction, and the acid value was 0.2. According to infrared absorption spectra measurement, an intensive absorption of carbonyl was observed. The viscosity of the oily product was 4500 cst (38.degree.C) and the dielectric constant was 5.0 (50 c/s, 100.degree.C). The tan .delta., volume resistivity and insulation breakdown voltage were similar to those of Example 1.

COMPARATIVE REFERENCE

The characteristic properties of insulating oils other than PCB are shown in Table 2.

It can be seen from the comparison between Tables 1 and 2 that the composition as insulating oil of the present invention has very excellent characteristic properties.

Table 2 ______________________________________ Characteristic Insulating oil properties.sup.1 Mineral oil.sup.2 Polybutene Paraffin ______________________________________ Viscosity 22.3 cst 3000 sus 28.4 cst (temperature) 20.degree.C 99.degree.C 20.degree.C Flash point (.degree.C) 146 193 155 Dielectric constant 2.15 2.2 2.30 (50 c/s) 80.degree.C 26.degree.C 80.degree.C tan .delta. 0.01 -- 0.005 (%, 50 c/s) 80.degree.C 80.degree.C Volume resistivity (.OMEGA.-cm) 3.5.times.10.sup.15 -- 5.0.times.10.sup.15 Insulation breakdown voltage (KV/mm) 31.0 35 36.0 ______________________________________ .sup.1 According to JIS-C-2320 .sup.2 JIS, No. 1 oil

Claims

What is claimed is:

1. A composition useful as an insulating oil obtained by heating naphthenic acids alone or a mixture of naphthenic acids and a saturated aliphatic carboxylic acid having a carbon number of 2 to 18 or a saturated aliphatic aldehyde having a carbon number of 2 to 18, at a temperature of 200.degree. - 700.degree.C, under a pressure of 0.1 - 10 atm, and in the presence of, as a catalyst, an oxide selected from the group consisting of zirconium oxide, thorium oxide, lithium oxide, scandium oxide, yttrium oxide, alumina and oxides of rare earth elements of lanthanum and atomic numbers 58 - 71; subjecting the resulting oily product to neutralization treatment with an aqueous alkaline solution; and removing from the product thus treated, fractions having a boiling point of 150.degree.C/100 mmHg or lower, by distillation.

2. A composition useful as an insulating oil according to claim 1, wherein, when said mixture is used as raw materials, the mixing ratio by mol of said saturated aliphatic carboxylic acid or aldehyde to said naphthenic acids is 5 or less based upon one mol of said naphthenic acids as calculated from the acid value thereof.