JPH0444362B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD OF THE INVENTION The present invention relates to a method of producing an electrical insulating oil useful as a replacement for polychlorinated biphenyl (PCB). Conventional Technology Conventionally, PCB, which has a high dielectric constant and is chemically stable, has been widely used in electrical insulating oil, but it has been replaced with other compounds because of its strong toxicity. As an alternative, the ethyl derivative of biphenyl is used exclusively, which compound is prepared by transalkylation of biphenyl with ethylbenzene or polyethylbenzene. Incidentally, the raw material biphenyl used in this reaction is produced by condensation dehydration of benzene, and ethylbenzene or polyethylbenzene is produced by ethylating benzene. Benzene, which is a raw material for these, can be obtained by separating hydrocarbon oil containing alkylbenzene obtained by reforming naphtha or other methods from a product obtained by hydrodealkylation. As described above, the production of ethyl derivatives of biphenyl requires many steps and is economically disadvantageous. On the other hand, the above-mentioned hydrodealkylated hydrocarbon oil containing alkylbenzene contains benzene, toluene, etc., which are useful raw materials for various petrochemical products.
Xylene (referred to as ``BTX'') was separated and recovered, and the remainder was used as fuel without any use. Problems to be Solved by the Invention The present invention aims to solve the above problems, and aims to provide an economically advantageous method for producing electrical insulating oil through extremely simple steps. Means for Solving the Problems In order to solve the above problems, the present inventors have made extensive studies and found that benzene, toluene, xylene, etc. The remaining fraction, which was separated and collected, contained large amounts of biphenyl, etc., and it was discovered that a product alkylated with lower olefins can be used as a substitute for PCBs, and is also excellent as an electrical insulating oil. The present invention has been made based on the above findings, and the method for producing electrical insulating oil of the present invention involves hydrodealkylating a hydrocarbon oil containing alkylbenzene, and recovering and separating benzene, toluene, and xylene from the residual oil. It consists of alkylating part or all of the above with a lower olefin in the presence of a Friedel-Crafts catalyst or a solid acid catalyst. The present invention will be explained in detail below. In the hydrodealkylation process of alkylbenzene, reformed oil, crude gasoline obtained from an ethylene plant, other cracked gasoline,
Hydrocarbon oil containing alkylbenzene, such as toluene and xylene, is used as a raw material. These raw materials are heated under hydrogen pressure of 35 to 70 kg/cm ² G.
Catalytic hydrodealkylation at a temperature of 550 to 650°C using a catalyst such as Cr-MO or chromia-alumina, or without using a catalyst.
Hydrodealkylation is carried out thermally at a temperature of 500 to 800°C under hydrogen pressure of 10 atmospheres or more. Light hydrocarbons such as methane and ethane are separated from this dealkylated product using a stabilizer, and if necessary, the product is subjected to clay treatment and the like before being introduced into a rectification column. In this rectification column, benzene is recovered as a product, and in some cases, toluene and xylene are also recovered. On the other hand, the residual oil remaining in the kettle from which this benzene, etc. has been recovered has conventionally been recycled again as a raw material. However, in the present invention, the recycled kettle residual oil is partially extracted or the kettle residual oil obtained without recycling is alkylated with a lower olefin.
It is preferable to further separate and recover toluene, xylene fractions, etc. from this pot residual oil to obtain a fraction having a boiling point of 140° C. or higher. All of the residual oil from which benzene, toluene, xylene, etc. are recovered can be used, but if desired, this residual oil can be further separated by distillation and a portion thereof can be used. The residual oil thus prepared is treated with a Friedel-Crafts catalyst, such as anhydrous aluminum chloride.
Lower olefins such as ethylene, propylene, Contact reaction with butene, isobutene, etc. The reaction conditions in this case are the same as those for normal alkylation reactions. For example, when anhydrous aluminum chloride is used as a catalyst, the amount of catalyst is 0.1 to 5% by weight based on the residual oil, the reaction temperature is room temperature to 200°C, especially 75 to 170°C, and the amount of lower olefin is 0.5 to 5% by weight. Under the conditions of 5 mol/residual oil, and when using a solid acid catalyst, the amount of catalyst relative to the residual oil
0.1 to 5% by weight, reaction temperature 120℃ or higher, especially
It is preferable to carry out the reaction under the conditions of 140 to 300°C and an amount of lower olefin of 0.5 to 5 mol/residual oil. Among these catalysts, Friedel-Crafts catalysts have problems with corrosion of the equipment, treatment and disposal of the catalyst after use, and furthermore, very small amounts of halogen ions remain in the product, which may cause product damage. Although it is not very preferable because it lowers the electrical resistance and causes slight coloring of the product, it has the advantage that the reaction conditions are milder and the reaction rate is faster than that of solid acid catalysts. In addition, the activity of solid acid catalysts such as silica-alumina, synthetic zeolite, and natural zeolite decreases when used for a long period of time;
The catalyst can be regenerated by firing in the atmosphere at a temperature of . Furthermore, if the catalyst is regenerated at a temperature of 850°C or higher, the activity of the catalyst tends to be deactivated, and it is almost impossible to regenerate the catalyst at a temperature of 400°C or lower. The contact with the lower olefin in the above alkylation reaction is preferably carried out by continuously blowing the olefin in gaseous form into the liquid residual oil in which the catalyst is dispersed. The catalyst is removed from the alkylated product oil obtained in this manner by a method such as decantation, centrifugation or hyperseparation, and unreacted substances and alkylated oil are further separated. The resulting alkylated oil is a mixture consisting mainly of mono-, di-, and trialkylated biphenyl products, and small amounts of mono-, di-, and trialkylated naphthalenes and other hydrocarbons. This alkylated oil is prepared into the desired fraction according to the use,
It is used as an electrical insulating oil, but generally the boiling point is
Preferably, it is prepared by distillation separation at a temperature of 265 to 350°C. The effects of the method of the present invention will be specifically described below using Examples and Comparative Examples. Example (Preparation of alkylated oil) A reformed oil with a boiling point of 80 to 150°C was hydrodealkylated using a chromia-alumina catalyst at a temperature of 600°C under a hydrogen pressure of 50 kg/cm ² ·G. The fraction was separated by distillation to obtain a dealkylated oil with a boiling point above 140°C. The low boiling fraction was removed from this dealkylated oil by distillation. Next, the residual oil from which the low boiling point fraction was removed was treated in a flask under the catalyst and reaction conditions listed in the upper column of Table 1.
While stirring, olefin gas was continuously blown into the reactor to cause a reaction. The results are shown in the lower column of Table 1.

[Table] (Evaluation of electrical insulating oil) The alkylated oil obtained in Experimental Example 3 was fractionally distilled, and the evaluation test shown in Table 2 was conducted using the oil having a boiling point of 265 to 320°C as an electrical insulating oil. The test method is JIS C 2320-
78R "Electrical Insulating Oil", page 4, "5. Test Methods" was used. Using this result as an example,
They are listed in Table 2 together with the specified values for Type 4, No. 1 (alkylnaphthalene) and Type 5 (alkyldiphenylethane) in "Table 2. Quality" on page 3 of the same JIS. As is clear from the results, all the standard values for electrical insulation for alkylnaphthalenes, alkyl diphenylethanes, etc. are satisfied, and in particular, the dielectric breakdown voltage greatly exceeds the standard values.

【table】

[Table] Effects of the Invention As described above, the present invention has the special effect of being able to economically advantageously produce high-quality electrical insulating oil by an extremely simple method.

Claims (1)

[Claims] 1 Hydrocarbon oil containing alkylbenzene is hydrodealkylated to collect and separate benzene, toluene, and xylene. Part or all of the residual oil is converted into alkyl benzene by lower olefin in the presence of a Friedel-Crafts catalyst or a solid acid catalyst. A method for producing electrical insulating oil, characterized by: