Process for producing an electrical insulating oil composition

Abstract: The present invention relates to an improved electrical insulating oil composition which has excellent electrical characteristics and is suitable for use in impregnating electrical appliances in which plastic dielectric material is used, and further relates to electrical appliances impregnated with such a composition. The electrical insulating oil composition is produced by bringing a by-product oil fraction mainly containing components having boiling points in the range of 260 to 330°C (atmospheric pressure basis) into liquid-liquid contact with an organic polar solvent; said by-product oil fraction being formed by alkylating benzene or toluene with ethylene in the presence of an alkylation catalyst and then distilling the alkylation product; and said electrical insulating oil composition being characterized in that the ratio of the integrated intensity as chemical shift at 120 to 155 ppm of the spectrum measured by ¹³C NMR method to the total integrated intensity at 0 to 155 ppm of said spectrum is 70% or higher.

Description: BACKGROUND OF THE INVENTION Field of the Invention This invention relates to a process for producing an electrical insulating oil composition by bringing, into liquid-liquid contact with a polar solvent, a by-product oil fraction formed in the manufacture of ethylbenzene, ethyltoluene, cumene and the like. Description of the Prior Art It has been known that a heavy by-product oil is produced in the process to prepare ethylbenzene, ethyltoluene and the like by alkylating benzene, toluene and the like. For example, it is disclosed in U.S. Patent No. 4,111,825 to use, as an electrical insulating oil, a by-product oil of a benzene manufacture process by alkylating benzene with ethylene in the presence of, for example, an aluminum chloride catalyst, and similarly, U.S. Patent No. 4,568,793 discloses that a by-product oil of an ethyltoluene manufacture process by alkylating toluene with ethylene is used as an electrical insulating oil. On the other hand, oil-filled electrical appliances such as oil-filled capacitors recently have a noticeable tendency toward small size and lightweight, and in reply to this tendency, plastic materials for insulators and dielectrics have been developed and are now used together with or in place of conventional insulating papers. Electrical insulating oils with which electrical appliances are impregnated also involve various problems in being used together with the above-mentioned plastic materials. That is, conventional electrical insulating oils, for example, refined mineral oils, polybutenes, alkylbenzenes and the like are not satisfactorily applied to plastic materials of polyolefins such as polypropylene, polymethylpentene and polyethylene which are used in the oil-filled electrical appliances. Some of these conventional electrical insulating oils dissolve or swell these plastic materials to deteriorate insulating power of the oil-filled electrical appliances on occasions. None of the electrical insulating oils disclosed in the above-mentioned publications are preferable for the reason just described. For example, the above-mentioned publication, U.S. Patent No. 4,568,793 disclosing the by-product oil of ethyltoluene refers to the excellent applicability of the oil to the plastic materials, but this oil is not always satisfactory and leaves room for further improvement. This unsatisfactory effect would be due to some causes, and one of them is based on the by-product containing many components, the chemical structures of which are still unidentified. These unidentified components are inevitably contained in the by-product oil even when distillation is performed elaborately, and they cannot be identified. In order to improve the properties of by-product oil fractions used in electric insulators the heavy by-product oils of the alkylation of benzene with ethylene are preferably subjected to a vacuum distillation to recover a distillate fraction boiling at 280 to 310°C. In the 13 C NMR analysis of the distillate fraction the ratio of the spectral peak surface area (120 to 150 ppm) to the total surface area (0 to 155 ppm) is preferably 0.72 or higher (JP-A-63-75090). A similar distillation method for preparing an electrical insulating oil from the heavy by-product oil fraction produced in the preparation of ethyl benzene by alkylating benzene with ethylene is described in EP-A-0 260 702. The inventors of the present application have found that certain components in the by-product oil deteriorate electrical properties of the by-product itself, for example, the compatibility with the plastic materials. With regard to the components in question, perfect identification of their structures is in fact impossible. Although the perfect removal of these components therefrom would not be impossible, in such a case, extremely precise distillation is required, which is not economical. BRIEF SUMMARY OF THE INVENTION In view of the hereinbefore discussed situation, the present inventors have made researches to remove unpreferable components present in a by-product oil and to thereby improve electrical properties of the by-product oil, and as a result, this invention has been achieved. That is, this invention is directed to a process for producing an electrical insulating oil composition which comprises subjecting a by-product oil fraction mainly containing components having boiling points in the range of 260 to 330°C (based on atmospheric pressure) to liquid-liquid extraction with an organic polar solvent, said by-product oil fraction having been formed by alkylating benzene or toluene with ethylene in the presence of an alkylation catalyst to obtain an alkylated product mixture composed of unreacted benzene or unreacted toluene, ethyl benzene or ethyl toluene, polyalkyl benzenes and heavy components and then distilling said alkylated product, wherein said electrical insulating oil composition is recovered as an extract and wherein said liquid-liquid extraction with the organic polar solvent is performed until said electrically insulating oil composition shows a ratio of the integrated intensity as chemical shift at 120 to 155 ppm of the spectrum measured by 13 C NMR method to the total integrated intensity at 0 to 155 ppm of said spectrum of 70 % or higher. The aforesaid by-product oil fraction is formed by first preparing an alkylated product composed of unreacted benzene or unreacted toluene, ethylbenzene or ethyltoluene, polyalkylbenzenes and heavy components by alkylating benzene or toluene with ethylene in the presence of an alkylation catalyst, and then distilling off unreacted benzene or unreacted toluene, ethylbenzene or ethyltoluene and most of polyalkylbenzenes from the alkylated product. The electrical insulating oil composition obtained by the process of this invention is such that the ratio of the integrated intensity as chemical shift at 120 to 155 ppm of the spectrum measured by 13 C NMR method to the total integrated intensity at 0 to 155 ppm of the spectrum is 70% or higher. DETAILED DESCRIPTION OF THE INVENTION A process is now practiced on -an industrial scale in which benzene and toluene are alkylated with the aid of an alkylation catalyst to prepare ethylbenzene and ethyltoluene which are raw materials in the field of petrochemistry. The by-product oil used in this invention can be exemplified by those which are formed in such a manufacturing process. To say more specifically, the above-mentioned alkylation is usually performed in accordance with a liquid phase alkylation process or a gaseous phase alkylation process. In the case of the liquid phase alkylation process, there are used a Friedel-Crafts catalyst such as aluminum chloride and a Brnsted acid such as sulfuric acid, toluenesulfonic acid and hydrofluoric acid, and in the gaseous phase alkylation process, a synthetic zeolite, for example, ZSM-5 type zeolite such as ZSM-5 and a suitable carrier supporting phosphoric acid are used. The reaction temperature is usually in the range of 20 to 180°C in the case of the liquid phase alkylation process, and it is in the range of 250 to 450°C in the case of the gaseous phase alkylation process. After the alkylation reaction, there can be obtained an alkylated product which is composed of unreacted benzene or toluene, the aimed ethylbenzene or ethyltoluene, additionally polyalkylbenzene other than ethyltoluene such as polyethylbenzene or polyethyltoluene, and heavy components. The used catalyst, if necessary, is removed from the alkylated product, followed by neutralizing and water washing. Next, distillation under reduced pressure or atmospheric pressure is carried out to remove, from the alkylated product, unreacted benzene or toluene, aimed ethylbenzene or ethyltoluene, and most of a polyalkylbenzene other than ethyltoluene such as polyethylbenzene or polyethyltoluene, thereby obtaining a by-product oil fraction. The by-product may be directly prepared by distillation from the alkylated product, or may be recovered by distilling off alkylbenzenes as light components from the alkylated product, removing tars as heavy components to once recover a by-product oil, and distilling this by-product oil again. In any case, the by-product which will be treated in this invention mainly contains components having boiling points (atmospheric pressure basis) in the range of 250 to 350°C, preferably 260 to 330°C. Depending upon the limited boiling point, the by-product oil fraction is supposed to be a hydrocarbon mixture containing partially polyethylbenzene and polyethyltoluene, and additionally containing indane derivatives, diaryl or triarylalkane derivatives and polyalkylpolyphenyl derivatives, and so forth. With regard to the by-product oil fraction which contains components having boiling points lower than 250°C and the by-product oil fraction which contains components having boiling points higher than 350°C, their electrical properties are on a low level and cannot be improved even when they are treated by the liquid-liquid contact treatment of this invention. The above-mentioned alkylated product contains very heavy components such as tarry substances, but the latter can be removed therefrom by setting the boiling point within the above range. The thus obtained by-product oil fraction is not always satisfactory as a raw material for the oil-filled electrical appliances, because of the existence of some components, structures of which have not been identified yet, as described above. Thus, in this invention, the by-product oil fraction is brought into liquid-liquid contact with an organic polar solvent. This contact treatment remarkably improves the electrical properties of the by-product oil fraction. The organic polar solvent used in the liquid-liquid contact of this invention preferably has a solubility parameter, as defined in Encyclopedia of Chemical Technology, Kirk-Othmer, 3rd Ed.,Vol.21,pp.377,386,387,390, of 5.1 x 10 -3 (J/m 3 ) 0.5 or higher. Typical examples of the organic polar solvents include alcohols such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutanol and furfuryl alcohol, glycols such as ethylene glycol, propylene glycol, diethylene glycol and triethylene glycol, ketones such as acetone and methyl ethyl ketone, Cellosolves such as ethylene glycol monomethyl ether and ethylene glycol monoethyl ether, ethers such as furfural, sulfolane, dimethylsulfoxide (DMSO), acetonitrile, N-methylpyrrolidone (NMP) and dimethylformamide (DMF). They may be used singly or in a mixture thereof. Moreover, the addition of a suitable amount of water to the organic solvent is preferable because of increasing the effect of the above-mentioned contact treatment, and the amount of water to be added is in the range of 50 wt% or lower, preferably 40 wt% or lower, with respect to the organic solvent. In the presence of the above-mentioned polar solvent, the by-product oil fraction is subjected to the liquid-liquid contact treatment. As an actual means for the liquid-liquid contact, there is used, for example, a liquid-liquid extraction or an extractive distillation. In the liquid-liquid extraction in the presence of the polar solvent, the desired electrical insulating oil is recovered as an extract. Therefore, after the extraction with the aid of the polar solvent, the desired electrical insulating oil can be recovered by a suitable procedure, for example, by the distillation and the addition of a third component to separate the polar solvent therefrom. Also in point of the feature that the aimed electrical insulating oil is recovered as the extract, the liquid-liquid contact of this invention should be apparently distinguished from a mere solvent purification technique which is used for the electrical insulating oil comprising mineral oils. The liquid-liquid extraction can be carried out by the use of a usual batch type or continuous type counter flow extraction tower, a multi-stage extraction tower or the like. After the liquid-liquid extraction, the used polar solvent is separated and removed in an ordinary manner, thereby obtaining the electrical insulating oil. The aforesaid extractive distillation can be accomplished by adding the above-mentioned polar solvent to the by-product oil fraction, followed by a usual extractive distillation. For example, the extractive distillation is achieved by first introducing the organic polar solvent through an inlet in the vicinity of the top of a distillation tower thereinto, and then distilling the by-product oil fraction, while the latter is in contact with the solvent present allover in the tower. In the liquid-liquid contact with the polar solvent, thecompositionof the obtained oil depends upon the kind of the polar solvent used and other conditions such as the extraction temperature and the amount of the polar solvent with respect to the by-product oil fraction. In general, for example, the extraction temperature is in the range of 10 to 150°C, and the amount of the polar solvent is in the range of 1 to 30 parts by weight per part by weight of the by-product oil fraction. Furthermore, in the extractive distillation, the polar solvent is used in an amount of 1 to 30 parts by weight per part by weight of the by-product oil fraction, and in general, 20 or more separation stages are preferably employed under a reduced pressure of 100 mmHg or lower. In this invention, the above-mentioned conditions for the liquid-liquid contact operation should be selected so that an electrical insulating oil may be obtained in which the ratio of the integrated intensity as chemical shift at 120 to 155 ppm of the spectrum measured by 13 C NMR method to the total integrated intensity at 0 to 155 ppm of the spectrum is 70% or higher, preferably 72% or higher. When the above defined ratio is lower than 70%, the effect of the liquid-liquid contact treatment with the organic polar solvent cannot be obtained sufficiently. As described hereinbefore, the by-product oil fraction used as a starting material in the process of this invention is the hydrocarbon mixture containing the structurally unidentified components, and even by the liquid-liquid contact of this invention, all of these unidentified components are not removed therefrom. However, since the ratio of the integrated intensities by the 13 C NMR method is specified, the unpreferable unidentified components are eliminated therefrom, and the remaining components interact with each other so as to exert a synergistic effect. Thus, the aforesaid procedure can provide an electrical insulating oil having excellent electrical properties. A conventional solvent purification for the insulating oil is different from that of this invention in that the conventional case intends to prepare raffinate. In addition, the conventional purification technique contemplates decreasing the amount of aromatics, but in the liquid-liquid contact of this invention, the amount of aromatics is rather finally increased. Also in this point, the liquid-liquid contact of this invention should be distinguished from the conventional technique. Here, reference to the 13 C NMR method will be made. The measurement temperature is usually ordinary temperature. A fraction which is a sample to be measured is dissolved in deuterated chloroform which is a solvent for the measurement so that the concentration of the fraction may be 10 to 20% by volume. The frequency for the measurement can be suitably changed but it is, for example, 67.8 MHz. In the obtained 13 C NMR spectrum, the integrated intensity as chemical shift at 120 to 155 ppm thereof is determined, using tetramethylsilane as standard, and the ratio (%) of the thus obtained value to the total integrated intensity at 0 to 155 ppm of the total spectrum except that of the solvent, is calculated. The calculated value is rounded at the first decimal place. In order to improve the quantitative reliability of the measurement, there is usually employed a proton perfect decoupling process in which the nuclear Overhauzer effect is eliminated. The thus prepared electrical insulating oil is then purified, if necessary, and is preferably used as an oil with which capacitors are impregnated. Moreover, the electrical insulating oil produced by this invention may be mixed with conventional electrical insulating oils, for example, diarylalkane, alkylbiphenyl or alkylnaphthalene in an optional ratio in compliance with uses and other conditions. The electrical insulating oil composition produced by this invention can be employed as an impregnating material for oil-filled electrical appliances such as oil-filled capacitors and oil-filled cables. The oil-filled capacitors for which the composition can be preferably applied are those in which at least a part of dielectric is composed of a plastic material. Preferable examples of the plastic materials include polyolefins such as polyethylene and polymethylpentene, and a more preferable one is polypropylene. For example, the oil-filled capacitors can be manufactured by first winding a polypropylene film together with a metal foil such as an aluminum foil which is a conductor, if necessary, using an insulating paper, and then impregnating the wound material with the above-mentioned electrical insulating oil in an ordinary manner. Furthermore, the above-mentioned suitable capacitors include oil-filled capacitors manufactured by the other procedure in which a metallized plastic film such as a metallized polypropylene film is wound together with an insulating paper or a plastic film, and is then impregnated with the electrical insulating oil. In oil-filled capacitors using a plastic material, physical properties of the by-product oil fraction which are not always suitable for impregnation are remarkably improved, and hence oil-filled capacitors impregnated with the electrical insulating oil produced by this invention are excellent in corona discharge properties, low-temperature properties and the like. Now, this invention will be described in detail in reference to examples. EXAMPLES - By-Product Oil Fraction A - From a process of alkylating benzene with ethylene in the presence of aluminum chloride in accordance with a liquid phase alkylation method to prepare ethylbenzene, an alkylated product was obtained which was composed of 43.0% by weight of unreacted benzene, 11.8% by weight of ethylbenzene, 18.3% by weight of polyethylbenzene and 7.6% by weight of heavier components. Distillation was then carried out to remove unreacted benzene, ethylbenzene and polyethylbenzene from this alkylated product. A by-product oil which was the residue of the alkylated product contained tarry substances and was black and viscous. This oil was further distilled under reduced pressure, thereby recovering by-product oil fraction A shown in Table 1. - By-Product Oil Fraction B - From a process of alkylating toluene with ethylene at a reaction temperature of 450°C by the use of the synthetic zeolite ZSM-5 produced in the manner described in U.S. Patent No. 3,926,782, (H + type; silica/alumina molar ratio = 60) as a catalyst in order to prepare ethyltoluene, an alkylated product was obtained which was composed of unreacted toluene, ethyltoluene, polyethyltoluene and a by-product oil. This alkylated product was distilled to remove therefrom a fraction having a boiling point of less than 250°C and containing unreacted toluene, ethyltoluene and polyethyltoluene, whereby a by-product oil was recovered. Successively, a by-product oil fraction B having a boiling point range shown in Table 1 was obtained from the thus recovered by-product oil. - Liquid-Liquid Extraction - Extraction Process I: A polar solvent and a by-product oil fraction were mixed with each other in a weight ratio of 1:1, and the mixture was then shaken sufficiently in a separatory funnel and a raffinate was removed therefrom. Afterward, the mixture was washed with n-hexane to recover, as a raffinate, an oil from which the used polar solvent had been removed. This operation was repeated thrice, thereby obtaining an electrical insulating oil. Extraction Process II: A polar solvent and a by-product oil fraction were mixed with each other in a weight ratio of 1:1, and the mixture was then shaken sufficiently in a separatory funnel and a raffinate was removed therefrom. Afterward, the used polar solvent was removed by flash distillation. This operation was repeated thrice, thereby recovering an electrical insulating oil from the by-product oil fraction. - Measurement by 13 C NMR Method - Each fraction was dissolved in a solvent of deuterated chloroform so that the concentration of the fraction might be 15%, and measurement was then carried out at room temperature by the use of a GX-270 model 13 C NMR measuring device made by JEOL, Ltd. Frequency: 67.8 MHz In this case, in order to heighten quantitative reliability of the measurement, there was employed a proton perfect decoupling process in which a nuclear Overhauzer effect had been eliminated. In an obtained 13 C NMR spectrum, there was sought the ratio (%) of an integrated intensity as chemical shift at 120 to 155 ppm the spectrum to the total integrated intensity at 0 to 155 ppm thereof. The results are shown in Table 1. In this case, tetramethylsilane was employed as the standard of the chemical shift. - Compatibility with Polypropylene Film - Polypropylene films (thickness 14 microns) cut into a predetermined shape were dipped in each fraction at 80°C for 72 hours, and after they were taken out therefrom, swelling ratios (%) of the films were then calculated from measured values of the films before and after the dipping step. The results are shown in Table 2. The smaller the values of the swelling ratios are, the greater the effect of inhibiting the films from swelling is, which means that dimensional stability of the films is excellent and which further means that the compatibility with polypropylene is good. - Measurement of Corona Starting Voltage: CSV and Corona Ending Voltage: CEV - As a dielectric, a sheet comprising two polypropylene films each having a thickness of 14 microns was used, and an aluminum foil which was an electrode was wound with and laminated to the sheet in an ordinary manner in order to prepare model capacitors for oil impregnation. These capacitors were impregnated with the respective fractions under vacuum to prepare oil-filled capacitors each having a capacitance of 0.4 microfarad. For each of these capacitors, a corona starting voltage and a corona ending voltage were measured at a temperature of -35°C. The results are shown in Table 2. - Lifetime Test of Capacitors - As a dielectric, a sheet comprising two polypropylene films each having a thickness of 14 microns was used, and an aluminum foil which was an electrode was wound with and laminated to the sheet in an ordinary manner in order to prepare model capacitors for oil impregnation. These capacitors were impregnated with the respective fractions under vacuum to prepare oil-filled capacitors each having a capacitance of 0.4 microfarad. Afterward, a predetermined alternating voltage was applied to each of these capacitors at -35°C and a time was measured until the capacitor was broken, and a lifetime of each capacitor was sought. In this case, a potential gradient was increased from a level of 80 V/µ by 10 V/µ every 48 hours, and at this time, the number of the broken capacitors was counted. The number of the capacitors at the start was 10 in each case. The results are shown in Table 2. Insulating Oil No. By-Product Oil Fraction (Boiling Point,°C) Polar Solvent Extraction Method Ratio (%) 1 By-Product Oil Fraction A (265-320°C) Methanol with 10% of Water II 80.9 2 do Ethanol with 10% of Water I 80.7 3 do Methyl Cellosolve I 80.0 4 do Diethylene Glycol I 80.4 5 do Triethylene Glycol I 80.1 6 do Sulfolane with 10% of Water I 80.1 7 do DMSO with 5% of Water II 80.3 8 do NMP with 20% of Water II 80.3 9 do IPA with 30% of Water I 80.7 10 do Furfural I 80.5 11 do Acetonitrile I 80.6 12 do Acetone with 30% of Water II 80.1 13 do DMF I 80.1 14 By-Product Oil Fraction B (275-310°C) Triethylene Glycol I 78.0 15 Diphenyl Ethane 16 1-Phenyl-1-ethylphenylethane 17 By-product Oil Fraction A (unextracted) 18 By-product Oil Fraction B (unextracted)

Claims: A process for producing an electrical insulating oil composition which comprises subjecting a by-product oil fraction mainly containing components having boiling points in the range of 260 to 330°C (based on atmospheric pressure) to liquid-liquid extraction with an organic polar solvent, said by-product oil fraction having been formed by alkylating benzene or toluene with ethylene in the presence of an alkylation catalyst to obtain an alkylated product mixture composed of unreacted benzene or unreacted toluene, ethyl benzene or ethyl toluene, polyalkyl benzenes and heavy components and then distilling said alkylated product, wherein said electrical insulating oil composition is recovered as an extract and wherein said liquid-liquid extraction with the organic polar solvent is performed until said electrically insulating oil composition shows a ratio of the integrated intensity as chemical shift at 120 to 155 ppm of the spectrum measured by 13 C NMR method to the total integrated intensity at 0 to 155 ppm of said spectrum of 70 % or higher. The process according to Claim 1, wherein the solubility parameter of said organic polar solvent is 5.1 x 10 -3 (J/m 3 ) 0.5 or higher. The process according to any one of Claims 1 or 2, wherein said organic polar solvent is selected from the group consisting of lower alcohols such as methanol, ethanol and 2-propanol, ketones such as acetone, ethers such as furfural, cellosolves such as methyl cellosolve, glycols such as diethylene glycol and triethylene glycol, dimethylsulfoxide (DMSO), N-methylpyrrolidone (NMP), sulfolane, acetonitrile, the corresponding water-containing solvents and mixtures thereof. The process according to any one of Claims 1 to 3, wherein said organic polar solvent contains 0 to 50 wt% of water.

Inventors: DOHI HIDEYUKI, ENDO KEIJI, KAWAKAMI SHIGENOBU, SATO ATSUSHI, DOHI, HIDEYUKI, ENDO, KEIJI, KAWAKAMI, SHIGENOBU, SATO, ATSUSHI
Applicants: NIPPON PETROCHEMICALS CO LTD, NIPPON PETROCHEMICALS COMPANY, LIMITED
Application year: 1988
Main classification: H01B3
IPC codes: C10M109, H01G4, H01B3