JPS5947402B2 - Method for refining orthophosphate ester oil for electrical insulation - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for purifying orthophosphoric acid triester for electrical insulating oil.

As is well known, orthophosphoric acid triester has advantageous properties such as being flame retardant and having a large dielectric constant, unlike mineral oil, but it is inferior in terms of dielectric loss tangent and volume resistivity. It is inferior and cannot be used for electrical insulation as it is commercially available.

The reason for these disadvantageous properties is that orthophosphoric acid diester, orthophosphoric acid monoester (hereinafter referred to as half ester), or phosphoric acid is produced during the synthesis of orthophosphoric acid triester, and this is produced in the oil. This is thought to be due to the fact that they are mixed. In the past, adsorption treatment with acid clay or dehydration treatment has been carried out to separate these substances, but for example, in the case of tricresyl phosphate, as it is commercially available, tan δ is 100% or more and ρ is 1.0j0× 1010 ohm Cm (both 80
Value in °C. same as below. ), breakdown voltage 48KV/2
．． 5-, but even with acid clay treatment (1o0℃, 1 hour), tan δ is 70Cfl,
ρ is 4.5×1010 ohmm, breakdown voltage is 52KV/
2.5wr! This acid clay treated material is further subjected to vacuum dehydration treatment (100℃, 100℃).
-2-Hg), tan δ is 50% and ρ is 8.
0x1010 ohm m, breakdown voltage 52KV/2.5
The improvement is only to a certain degree, and it is still not possible to use it as an electrical insulating oil. It is possible to fractionally distill the crude orthophosphoric acid triester, but since half esters and phosphoric acid have high boiling points, fractional distillation is extremely difficult. It has been considered difficult to separate half ester and phosphoric acid from ester. This invention facilitates the fractional distillation of half ester and phosphoric acid from crude orthophosphoric triester,
The object of the present invention is to provide a refining method that satisfies the characteristics necessary for use as an electrical insulating oil.

30 This invention subjects crude orthophosphoric acid triester to adsorption treatment with one or two types of basic metal oxides,
The method is characterized in that the half ester and phosphoric acid in the orthophosphoric acid triester are separated and removed, and then the remaining half ester and phosphoric acid are fractionated from the orthophosphoric acid triester using a vacuum distillation method.

Here iron, zinc, calcium, magnesium, barium, aluminum, as chemical adsorbents for adsorption treatment.
Select from basic metal oxides such as chromium, lead, and cadmium. The metal oxide powder is packed into a tower and distributed there, or the powder is mixed with crude orthophosphoric acid triester and stirred to perform chemisorption treatment.
When the half ester, phosphoric acid, and other impurities in the crude orthophosphoric acid triester come into contact with the powder, they react and are adsorbed, forming an insoluble or poorly soluble salt. After separating and removing most of the impurities such as half esters in this way, if the orthophosphoric triester is distilled under high vacuum, the remaining half esters and other impurities can be fractionated from the orthophosphoric triester. be able to. In this case, half esters, phosphoric acid, etc. (orthophosphoric triesters) also have high boiling points, so the orthophosphoric triesters after distillation are taken out as a gas phase.
Half esters and the like remain in the liquid phase. Since the distillation is carried out under high vacuum, the distillation temperature can be conveniently lowered than at atmospheric pressure. Next, embodiments of the invention will be described.

The table below shows the electrical properties of each phosphotriester oil purified according to the present invention. A trigram,
In the table below, TCP is tricrediphosphate, C
DP is cresyl phenyl phosphate, TXP is tricylenyl phosphate, MIPP is orthophosphoric triester of monoisopropylphenol, and 0PP (1) is orthophosphoric triester containing 1 mole of orthophenylphenol and 2 moles of cresol. The ester, 0PP (2), each represents an orthophosphoric acid triester containing 2 moles of orthophenylphenol and 1 mole of cresol. For comparison, the characteristics of TCP when only vacuum distillation was performed without chemical adsorption treatment are also listed in the last column. Note that Tan δ is expressed in %, ρ is expressed in ohms m, and breakdown voltage is expressed in KV/2.5TWf1. The chemisorption treatment was also carried out at room temperature. A thin film distillation device (film evaporator) was used as the distillation device. As can be understood from the above table, all of the various orthophosphoric triesters have a Tan δ of 1.5 to 1.9 or less and a ρ of 8.
．． 3~8.7×1012 or more, and the breakdown voltage is 60KV
/2.5wn, which is a significant improvement when compared to untreated products, those treated only with acid clay treatment, those treated with vacuum dehydration, and those treated only with vacuum distillation. It is understood that what is being done.

Needless to say, all of these values are within a range that allows sufficient use as electrical insulating oil. As described above, the refining method of the present invention sufficiently removes half ester, phosphoric acid, and other impurities from crude orthophosphoric acid triester, and maintains its electrical properties as an electrical insulating oil without impairing its flame retardancy. It has the effect of improving it to the extent that it can be used satisfactorily.

Claims (1)

[Claims] 1. Orthophosphoric acid diester in orthophosphoric triester by treating crude orthophosphoric acid triester with a basic metal oxide,
It is characterized by separating and removing the orthophosphoric acid monoester and phosphoric acid, and then fractionating the remaining orthophosphoric acid diester, orthophosphoric acid monoester, and phosphoric acid from the orthophosphoric acid triester by a vacuum distillation method. A method for purifying orthophosphoric acid triester for electrical insulating oil.