JPH0788322B2 - Method for producing diarylalkane mixture having low freezing point - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a diarylalkane mixture having a low freezing point. More specifically, the present invention relates to a method for producing a diarylalkane mixture having a low freezing point by effectively utilizing diphenylmethane having a high freezing point and a low utility value in the related art. The obtained diarylalkane mixture is effective as an electrical insulating oil having excellent low temperature properties.

(Prior art and its problems) Diphenylmethane has not been used so far in the fields where its freezing point is as high as 25 ° C and a low freezing point is required, for example, in fields such as electric insulating oil and heat transfer oil. Meanwhile 1,
The freezing point of 1-diphenylethane is -18 ° C, which is considerably low, but it is still insufficient by itself.

The mixture of diphenylmethane and 1,1-diphenylethane has a lower freezing point to some extent than that of a single compound due to the melting point decrease, but since the freezing point of diphenylmethane is too high, the utility value of the mixture of both is limited. I have no choice.

However, both diphenylmethane and 1,1-diphenylethane have high aromaticity and are originally excellent diarylalkanes as electrical insulating oils.

Therefore, the present inventors have completed the present invention by researching for the purpose of improving the freezing point of a mixture of diphenylmethane and 1,1-diphenylethane in order to improve the low temperature characteristics as an electric insulating oil. is there.

(Structure of Invention) That is, the present invention provides at least diphenylmethane and
A diarylalkane mixture consisting of 1,1-diphenylethane is contacted with an alkylbenzene having at least one alkyl group having 1 to 4 carbon atoms at a reaction temperature of 180 to 400 ° C in the presence of a ZSM-5 type zeolite catalyst, and then obtained. A process for producing a diarylalkane fraction having a low freezing point, which is substantially free of diphenylmethane and contains 1,1-diphenylethane and other diarylalkanes, which comprises recovering the obtained reaction mixture by distillation.

Further, the present invention will be described in detail.

The diarylalkane mixture of the present invention contains at least 2% by weight of 1,1-diphenylethane based on diphenylmethane. More preferably, it contains at least 5% by weight. If it is less than 2% by weight, the effect of the present invention of lowering the freezing point cannot be expected, which is not preferable.
The upper limit of 1,1-diphenylethane is not particularly limited, but it is not economical to use a large amount of 1,1-diphenylethane, which is an excellent substance originally having a low melting point. Further, the degree to which the melting point of the obtained diarylalkane mixture is lowered tends to be small. Therefore, it is customary to use 1,1-diphenylethane in an amount of up to 50% by weight, preferably up to 40% by weight, based on diphenylmethane.

To the extent that the objects of the present invention are not hindered, diphenylmethane and
A diarylalkane other than 1,1-diphenylethane can be appropriately included in the reaction.

The alkylbenzene to be reacted with the diarylalkane mixture consisting of a mixture of diphenylmethane and 1,1-diphenylethane is an alkylbenzene having at least an alkyl group having 1 to 4 carbon atoms. Specific alkyl groups are alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl and tert-butyl. Alkylbenzenes having 1 to 4 of these alkyl groups are used in the present invention. These alkylbenzenes are specifically toluene, ethylbenzene, xylene and the like. Especially preferred is toluene. These alkylbenzenes can be reacted alone or as a mixture of two or more.

The supply amount of alkylbenzene in the reaction system is 0.5 to 20, preferably 1 to 10 in terms of molar ratio of alkylbenzene to diphenylmethane. In any case outside this range, the effect of the present invention of lowering the freezing point of the diarylalkane mixture, which is the object of the present invention, cannot be expected, which is not preferable.

The synthetic zeolite catalyst of the present invention has a Sio ₂ / Al ₂ o ₃ molar ratio of 20.
The above is the crystalline synthetic aluminosilicate zeolite in which the inlet of the main cavity is a 10-membered oxygen ring. Examples of such zeolites include ZSM-5 type synthetic zeolite in which the main cavity has a 10-membered oxygen ring, as well as zeolite zeta 1 and zeolite zeta 2. That is, the zeolite of the present invention is characterized by comprising a 10-membered oxygen ring. Conventional synthetic zeolites such as linde A and erionite have 8-membered oxygen rings, and mordenite, linde X-type and Y-type zeolites have 12-membered oxygen rings.

These conventional zeolites having an 8-membered oxygen ring or a 12-membered oxygen ring are not suitable for the method of the present invention because of their structure different from that of the present invention.

The crystalline synthetic zeolite used in the present invention has a structural characteristic that the inlet of the main cavity is composed of a 10-membered oxygen ring, Sio ₂ / Al ₂
o Any crystalline synthetic aluminosilicate having a ₃ molar ratio of 20 or more can be used. Particularly preferably, ZS
M-5 type synthetic zeolite, for example, ZSM-5, ZSM-1
1, known as ZSM-22, ZSM-23, ZSM-35, ZSM-38, ZSM-48, etc. These ZSM-5 type synthetic zeolites are
Both have structural characteristics that the entrance of the main cavity is composed of a 10-membered oxygen ring. A further particularly preferred synthetic zeolite is ZSM-5. The composition and manufacturing method of these ZSM-5 type zeolites are
Both are described in the following patent publications.

ZSM-5: U.S. Patent No. 3702886 ZSM-11: U.S. Patent No. 3709979 and Japanese Patent Publication No. 53-23280 ZSM-22: U.S. Patent No. 4481177 ZSM-23: U.S. Patent Nos. 4076842 and 4490342 ZSM-35 : JP-A-53-144500 ZSM-38: U.S. Pat.No. 4046859 ZSM-48: U.S. Pat.No. 4423021 Zeolite Zeta 1: JP-A-51-67299 Zeolite Zeta 2: JP-A-51-67298 Main cavity Structurally-synthesized zeolites with 10-membered oxygen rings at their inlets generally have a high Sio ₂ / Al ₂ o ₃ molar ratio, which is usually above 20. In some cases, the Sio ₂ / Al ₂ o ₃ molar ratio is very high, and zeolites such as 1600 or more are also effective. Further, in some cases, it is also possible to use a zeolite which is substantially free of aluminum, that is, the Sio ₂ / Al ₂ o ₃ molar ratio is infinite. Thus, "high silica" zeolites are also included in the definition of the present invention. This Sio ₂ / Al ₂ O ₃ molar ratio is measured by a usual analytical method such as an atomic absorption method. This ratio represents a value as close as possible to that in the hard anion framework of the zeolite crystals, excluding aluminum in the cations and other forms in the binder or channels.

A structure in which the entrance of the main cavity consists of a 10-membered oxygen ring is usually confirmed by X-ray diffraction. For example, preferred as the catalyst of the present invention
Each of the ZSM-5 type synthetic zeolites has a unique characteristic X-ray diffraction pattern (for details, see the above patent publication).

However, instead of using the X-ray diffraction analysis method, a measurement value that is a control index can be used instead of the X-ray diffraction method. That is, the 10-membered oxygen ring of the present invention has a control index of 1
It can also be defined as being ~ 12 synthetic zeolites. here,
The control index is shown by a specific measuring method in JP-A-56-133223. This index indicates the degree to which the pore structure of zeolite crystals controls the approach of molecules having a larger cross-sectional area than n-paraffin. The measurement method is
As disclosed in the publication, n-hexane and 3-methylpentane are adsorbed on zeolite under a constant condition, and the adsorption amount is calculated. A typical control index is as follows.

Control index ZSM-5 8.3 ZSM-11 8.7 ZSM-35 4.5 Amorphous silica / alumina 0.6 As an example of the method for producing the zeolite of the present invention, a method for synthesizing ZSM-5 will be described. First, tetrapropylammonium hydroxide or A reaction raw material containing tetra-n-propyl ammonium bromide, sodium oxide, aluminum oxide, silicon oxide and water is prepared. The composition is within the range described in the above publication, and the reaction mixture is heated to perform hydrothermal synthesis. The crystals obtained after the synthesis are calcined in air to obtain a zeolite ZSM-5 catalyst. Here, the method using aluminum oxide is described, but it is also proposed to synthesize ZSM-5 containing substantially no aluminum atom. In the above method, a method using tetrapropylammonium hydroxide or tetra-n-propylammonium bromide has been described. For example, as a method for synthesizing ZSM-5, various organic cations or organic compounds as precursors thereof may be used. It has been proposed to use this instead. Examples of this are, for example, ammonia, trialkylmethylammonium cation, triethyl-n-
Propyl ammonium cation, C _2-9 primary monoalkylamine, neopentylamine, di- and trialkylamines, alkanolamines, C _5-6 -alkyldiamines, C _3-12 -alkylenediamines, ethylenediamine,
Hexamethylenediamine, C _3-6 diol, ethylene or propylene glycol, 1,4-dimethoxycyclohexane, hydroquinone, ethylene oxide and ammonia, n-dodecylbenzene sulfonate, cyclopentadienyl phthalocyanine complex, 2-aminopyridine, ethylene Examples thereof include carboxylic acids such as glycol dimethyl ether, dioxane, dioxolane, tetrahydrofuran and tartaric acid. Further, it has even been proposed that ZSM-5 is added as a seed during crystallization to produce even without adding the above-mentioned organic cation or an organic compound as a precursor thereof.

The zeolite used in the reaction contains, for example, sodium ions and other metal ions due to the reaction raw materials at the time of synthesis. Alkali metals such as Na and other metals include alkaline earth metals such as calcium and magnesium, and 3
Ion exchanged with a valent metal can also be used. Furthermore, a crystalline synthetic aluminosilicate zeolite modified by impregnation with magnesium, boron, potassium, phosphorus or a compound thereof, for example, ZSM-5 type zeolite can also be used. These ion exchange methods or modification methods can be performed by conventionally known methods.

As described above, the crystalline synthetic zeolite of the present invention can contain various metals, but it is called so-called hydrogen type zeolite (HZSM-5) or acid type zeolite in which metal ions are ion-exchanged with hydrogen ions. Synthetic zeolites are preferred for the method of the invention. A typical hydrogen-type zeolite is to heat a catalyst containing an organic cation at the time of catalyst preparation under an inert atmosphere, for example, at about 540 ° C. for 1 hour, and then ion-exchange with a mineral acid such as ammonium salt or hydrochloric acid,
For example, it is activated by firing at about 540 ° C., and so-called hydrogen type zeolite is obtained.

In addition, steam treatment or coke treatment can be carried out if necessary.

The reaction temperature of the present invention is 170 to 500 ° C, preferably 200 to 350 ° C.
Is. If the reaction temperature is lower than this range, the conversion rate becomes low, and therefore it is not practical. Further, if the reaction temperature is higher than this, side reactions increase, which is not preferable.

The reaction may be carried out in the gas phase, but in order to keep the activity of the catalyst for a long time, it is preferable to carry out the reaction in the liquid phase. Therefore, the reaction pressure is in the range of atmospheric pressure to 50 Kg / cm ² , and it is preferable to set the pressure sufficient to keep the reaction liquid in the liquid phase at the reaction temperature. The reaction system of the present invention may be a flow system or a batch system.

In the batch system, the reaction time is selected from the range of 0.5 to 50 hours depending on the reaction temperature and other reaction conditions. If the reaction time is shorter than this, the reaction rate will be low. Further, even if the reaction time is made longer than necessary, it is not preferable because it only increases side reactions.

The LHSV in the case of a flow reaction type is 0.2 to 20, preferably 0.5 to 10. When LHSV is smaller than this, side reactions increase, and the yield per fixed time decreases, which is not preferable. If LHSV is too large, the reaction will not proceed and will flow out of the system, which is not preferable.

In the present invention, the added alkylbenzene is disproportionated with diphenylmethane or 1,1-diphenylethane to obtain a monocyclic aromatic hydrocarbon such as benzene and a diarylalkane having at least one alkyl group.

For example, in the case where toluene is used as the alkylbenzene, toluene is disproportionated mainly with diphenylmethane in this case, and as a result, benzyltoluene and benzene are produced. In the present invention, as the benzyltoluene thus produced, the m-form having the lowest freezing point among the three types of positional isomers is selectively produced. Also 1,1
-Part of diphenylethane disproportionates with toluene 1
-Phenyl-1-tolylethane and benzene are obtained.
In addition, ditolylmethane is also produced as a byproduct.

Originally, the melting point of 1,1-diphenylethane added before the reaction was considerably low, and therefore, the components in the obtained diarylalkane mixture were the same as the unreacted 1,1-diphenylethane other than unreacted diphenylmethane. It is a feature of the method of the present invention that its melting point, including that of diphenylmethane, is much lower than that of diphenylmethane.

For example, the reaction of the present invention can be carried out by using a silica solid
When the alumina catalyst is used, the selectivity of the m-form is low, and the same applies to the Y-type zeolite. Friedel-Crafts catalysts such as aluminum chloride are not preferable because a large proportion of heavy components are by-produced.

Therefore, in order to obtain a mixture with a low freezing point, at least unreacted diphenylmethane is separated off from the diarylalkane mixture obtained by the process according to the invention.

That is, after completion of the reaction, the diarylalkane mixture is recovered from the reaction mixture, but it is important that at least unreacted diphenylmethane is substantially separated and removed from the diarylalkane mixture. As mentioned above, when diphenylmethane has a high melting point and contains it, it raises the freezing point of the diarylalkane mixture, so that at least diphenylmethane is substantially removed from the reaction mixture. If necessary, other diarylalkanes such as ditolylmethane may be separated and removed.
However, in order to achieve a low freezing point, since it is expected that the melting points of the respective components will be lowered, the diarylalkane fraction obtained by distillation and unreacted 1,1
It is necessary that the mixture contains at least one other diarylalkane in addition to diphenylethane.

The method of separating and removing diphenylmethane can be achieved by simple distillation because diphenylmethane usually has the lowest boiling point among the diarylalkanes contained in the obtained reaction mixture. Specifically, for example, after distilling off unreacted alkylbenzene and benzene or alkylbenzene as a by-product from the reaction mixture, diphenylmethane may be distilled off from the obtained diarylalkane mixture, or unreacted from the reaction mixture. It is also possible to remove diphenylmethane together with alkylbenzene and other light components.

The diarylalkane fraction produced by the method of the present invention has a low freezing point and is therefore excellent in low-temperature characteristics, and is therefore useful as an electrical insulating oil for impregnation of oil-immersed electrical equipment, particularly as an impregnated oil for oil-immersed capacitors. Among them, it is suitable for impregnating an oil-impregnated capacitor in which plastic is used as at least a part of an insulating material or a dielectric material. As the plastic, polyolefins such as polypropylene and polyethylene are used in addition to polyester and polyvinylidene fluoride, and polyolefins such as polypropylene are particularly suitable. The oil-impregnated capacitor suitably impregnated with the electrical insulating oil produced by the present invention is obtained by winding a metal foil as a conductor such as aluminum and a plastic film as the insulating material or the dielectric material and impregnating the insulating oil. Or a metal plastic film in which a metal vapor layer as a conductor such as aluminum or zinc is formed on the plastic film as the insulating material or the dielectric material, together with a plastic film or insulating paper, if necessary. It is an oil-immersion condenser manufactured by winding and impregnating. When used as an electric insulating oil, a conventionally known electric insulating oil, for example, phenylxylylethane, alkylbiphenyl, alkylnaphthalene, 1,
1-Diphenylethylene and the like can be appropriately mixed in an arbitrary ratio.

(Effects of the Invention) A diarylalkane mixture having a low freezing point is produced by using diphenylmethane, which has a high melting point and is not suitable for electrical insulating oil or heat transfer oil, as a starting material. The diarylalkane fraction produced according to the present invention has excellent low-temperature properties and is suitable for impregnation of electric insulating oil, particularly oil-immersed electrical equipment. The present invention will be described in detail below with reference to examples.

(Example) Example 1 A reaction vessel having an internal volume of 250 ml was charged with 200 ml of hydrogen type ZSM-5 (12 to 14 mesh) and dried at 480 ° C for 3 hours while sending dry nitrogen.

Reaction temperature 270 ° C, pressure 20 atm (under nitrogen atmosphere) LHSV = 1.0
Then, a mixed solution of 2 mol of toluene to 1 mol of diphenylmethane and 0.1 mol of 1,1-diphenylethane was passed through the oil.

The reaction liquid passed through the oil was analyzed by a gas chromatogram method, and the composition of the reaction liquid during a certain oil passing time was examined. The results are shown in Table 1.

In addition, benzene, toluene and diphenylmethane were distilled off under reduced pressure from the reaction solution to convert them to atmospheric pressure.
A diarylalkane mixture containing mainly benzyltoluene and 1,1-diphenylethane as fractions having a boiling point of 0 to 280 ° C was obtained. The freezing point of this mixture was measured and is shown in Table 2. From the results in this table, it can be seen that the diarylalkane mixture obtained by the method of the present invention has a much lower freezing point than the starting material mixture of diphenylmethane and 1,1-diphenylethane.

The freezing point is measured by placing the liquid to be measured in a test tube, aging it with a temperature cycle of 10 ° C for a week in a temperature cycle that is high during the day and low at night, and then leave it at the measurement temperature for 1 week and visually inspect it. The freezing point was determined based on the temperature at which it was observed that the entire test tube was solidified.

Example 2 The reaction was performed in the same manner as in Example 1 except that ethylbenzene was used instead of toluene. The freezing point of the diarylalkane mixture as a fraction obtained by distillation under reduced pressure and having a boiling point and atmospheric pressure of 270 to 293 ° C. is also shown in Table 2.

Example 3 Example 1 except that o-xylene was used instead of toluene.
The reaction was performed in the same manner as in. The freezing point of the diarylalkane mixture as a fraction having a boiling point of 270 to 295 ° C. at atmospheric pressure obtained by vacuum distillation is also shown in Table 2.

Table 2 freezing point ℃ diphenylmethane +25 1,1--18 starting mixture ^{* -1} -20 Example 1 -40 below Example 2 -40 or less Example 3 -40 or less * -1: diphenylmethane 1 used in the reaction starting materials Mol to 1,1
Mixture of 0.1 mol of diphenylethane.

(Insulating oil test) Two 14-micron-thick biaxially oriented polypropylene films were stacked and wound with an aluminum foil as an electrode,
A model capacitor having a capacity of 0.4 μF was manufactured.

The five compositions in the above table were impregnated respectively with 1,1-diphenylethane, the starting mixture ^{* -1} , the mixture of Examples 1-3. After cooling for 1 week by a temperature cycle of −40 ° C. in the daytime and −50 ° C. in the night, the sample was left at −40 ° C. for 1 week for measurement. For the measurement, 10 model capacitors of the same impregnated oil were charged and the voltage was increased at a potential gradient of 10 V / μ at -40 ° C, and the number of capacitors destroyed at each potential was determined. The results are shown in the table below. In addition,
Diphenylmethane and 1,1-diphenylethane were not specifically tested because their low temperature properties were clearly inferior to the fractions of the invention. From the results in the following table,
It can be seen that the electric insulating oil of the present invention has excellent low temperature characteristics.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location // C07B 61/00 300 (56) References JP-A-61-267530 (JP, A) JP 62-148431 (JP, A) JP-A-63-222129 (JP, A) CHEMICAL ABSTRACTS Vol. 105 78573v

Claims (6)

[Claims] 1. A diarylalkane mixture comprising at least diphenylmethane and 1,1-diphenylethane,
A substance comprising contacting with an alkylbenzene having at least one alkyl group having 1 to 4 carbon atoms at a reaction temperature of 180 to 400 ° C in the presence of a ZSM-5 type zeolite catalyst, and then recovering the obtained reaction mixture by distillation. Of producing a diarylalkane fraction having a low freezing point, which does not contain diphenylmethane and contains 1,1-diphenylethane and other diarylalkanes. 2. The production method according to claim 1, wherein the alkylbenzene is toluene. 3. A diarylalkane mixture containing at least 2% by weight of 1,1-diphenylethane with respect to diphenylmethane as a starting material.
The manufacturing method according to the item. 4. A diarylalkane mixture comprising at least diphenylmethane and 1,1-diphenylethane,
It is contacted with an alkylbenzene having at least one alkyl group having 1 to 4 carbon atoms at a reaction temperature of 180 to 400 ° C in the presence of a ZSM-5 type zeolite catalyst, and then is recovered by distillation, which is substantially free of diphenylmethane. 1,1-
A method for producing an electrically insulating oil, which is a diarylalkane fraction containing diarylethane and other diarylalkanes. 5. The production method according to claim 4, wherein the alkylbenzene is toluene. 6. A diarylalkane mixture containing at least 2% by weight of 1,1-diphenylethane with respect to diphenylmethane as a starting material.
The manufacturing method according to the item.