US2171855A - Dielectric composition - Google Patents

Description

Patented Sept. 5, 1939 UNITED STATES PATENT OFFICE DIELECTRIC OOMPO SITION poration of Delaware N Drawing. Application April 22, 1936, Serial No. 75,890

Claims.

This invention relates to insulating fluids particularly adapted for use in electrical equipment. In electrical apparatus such as transformers, switches, electric bushings, cables, fuses and sim- 5 ilar equipment, it is usual to provide an insulating medium which is ordinarily termed the dielectric liquid. This invention is concerned with certain novel and improved dielectric liquids which possess superior electrical properties, are

0 non-inflammable and do not produce inflammable gases when subjected to decomposition.

A dielectric or insulating liquid in some kinds of electrical equipment such as transformers, serves a dual function. Not only does it act as 5 an insulating medium and so prevent the transfer of' electricity through the dielectric and out of the electrical apparatus, but it also serves to take up and convey to cooling surfaces heat generated within the apparatus. These may be especially 0 provided cooling means or may consist merely of the external surface of the housing in which the apparatus is positioned, which housing is exposed to the external atmosphere. In other electrical apparatus, such as in insulated current carrying 5 cables, the dielectric liquid servesessentially as a non-conductorand not as a heat transfer medium.

In the past it has been customary to use petroleum products. such as the mineral oils, as

D dielectric liquids in electrical equipment. These oils, comprising ordinary parafllnic or naphthenic hydrocarbons or mixtures of these types of hydrocarbons have not proven generally satisfactory. Although possessing certain advantages by 5 reason of their availability and relatively low cost the mineral oils also possess certain very serious disadvantages. These disadvantages, in general, render the use of electrical equipment containing petroleum insulating liquids somewhat hazardous.

One disadvantage of the mineral oils is that they tend to form deposits, generally known as sludge, during the period of their use. This is due to oxidation and decomposition and also re- 5 suits to some extent in the formation of acids which is equally undesirable. The sludging of dielectrics during .use is a serious disadvantage and requires either replacement of the oil or treatment to remove the sludge and revivify the I dielectric. A satisfactory dielectric liquid should not sludge or undergo substantial deleterious change during use and it is one of the objects oi this invention to provide a liquid which does not possess this undesirable disadvantage characteristic of the mineral oils.

The electrical properties of the mineral oils are fairly satisfactory, their power factors being relatively low. However, the dielectric constant of the mineral oils is not as high as might be desired when the oils are used as dielectrics in 5 capacitors. This is not particularly detrimental, however, as a high dielectric constant is not an advantage when the oil is employed as the dielectric liquid in transformers. Generally the power factor of a dielectric is an index of the 1 amount of power dissipated in heat during the operation of a transformer in which the dielectric serves as the insulating material. While the power factor of the mineral oils is sufliciently low, a higher dielectric constant than that possessed by these oils would be desirable in many instances, more especially when the oils are used in condensers as the insulating media.

But by far the most serious disadvantage of the mineral oil is the fact that they are inflammable and upon decomposition yield gases which are also inflammable and explosive when mixed with air. A fireproof insulating liquid is highly desirable since there exists the possibility of a fire occurring in the event a short circuit or similar electrical defect occurs in the electrical apparatus insulated. In the past many fires have been caused by the use of inflammable dielectric liquids. Not only is the flammability of the mineral oils a very series deterrent to their use, but an even greater danger exists, the development of gases which are inflammable and explosive when these oils are subjected to the decomposing in fluence of an electric are. In the event failure occurs within a piece of electrical equipment, particularly one which is operated at high voltage and large current strengths, the dielectric is subjected to an electric are which acts to chemically break down the dielectric. In the past in many installations, particularly in transformers in which the petroleum oils have been used as dielectrics, many dangerous explosions have occurred owing to the development of gases which are both inflammable and explosive when mixed with air, these gases resulting from decomposition of the dielectric. The mineral oils thus present not only a fire hazard but also a potential source of explosive gases. 'An object of this invention is to overcome these disadvantages by the development of a dielectric fluid which is non-inflammable and which does not yield inflammable or explosive products upon decomposition.

In the past these various disadvantages of the mineral oils have been appreciated and attempts have been made to utilize as dielectric liquids certain non-inflammable compositions. Frequently halogenated, more especially, chlorinated, products have been used for this purpose. At present there is electrical apparatus in use employing such non-inflammable dielectric liquids. However, many of these compositions are unsatisfactory for one reason or another, either because of their cost or because their properties, electrical or btherwise, do not render them entirely suitable for dielectric use. In order to overcome these defects in the dielectric compositions known to the prior art we have prepared various new dielectric compositions. These are products which consist essentially of a halogenated aryl nucleus containing an aliphatic substituent, of which the isopropylchloro benzenes are typical compounds. We have found that chlorinated benzenes containing an isopropyl substituent are especially suitable for dielectric use when there are present 3, 4 or 5 atoms of chlorine substituted for hydrogen upon the nucleus per mole of isopropyl benzene. Our invention consists essentially in using as dielectric constituents in electrical equipment various mixtures of isopropyltrichloro benzene, tetrachlorisopropyl benzene, and isopropylpentachloro benzene which are obtainable by chlorinating isopropyl benzene (cumene), the constituents of these mixtures being so selected as to yield a dielectric suitable for the particular use to which it is to be applied.

In our co-pending application, .Serial No. 53,099, filed December 5 1935, we have disclosed the use of various mixtures of trichlorethylbenzene, tetrachlorethylbenzene and pentachlorethylbenzene as dielectric liquids in electrical apparatus. The invention disclosed in this application is to be regarded as, in part, a continuation of that disclosed in our earlier application, and this application bears the relationship of continuation-in-part to our co-pending application. The preparation-pf novel mixtures comprising isopropyltrichloro benzene, isopropyltetrachloro benzene, and isopropylpentachloro benzene and a novel process for preparing mixtures of the chlorinated isopropyl benzenes is disclosed and claimed in our co-pending application, Serial No. 68,919, filed March 14, 1936. That case also discloses the isolation of certain new compounds from the mixtures resulting from the chlorination of isopropyl benzene under conditions disclosed in that application.

There are certain essential requirements which a commercially satisfactory dielectric liquid must meet. The liquid must be stable and must not sludge or require frequent reconditioning. Since many pieces of electrical equipment are subjected to relative extremes of temperature it is desirable that the dielectric liquid be not too viscous at the lower temperatures and essential that it has a relatively high boiling point and not volatilize at or near the higher temperatures to which the electrical equipment may be subjected. Moreover, it must have a relatively low freeze point. This means that the temperature at which solid crystals will begin to deposit in the dielectric liquid must be one which is not too high. While the freeze point or point at which crystals deposit may be somewhat higher than the lowest temperature to which the electrical apparatus may be subjected during use it is essential that complete solidification shall not occur at any temperature encountered during use. Ordinarily-since heat is developed during operation of the electrical device in which the dielectric functions as the insulating medium the temperature of the dielectric will be generalbe low enough to fall within the range generally l regarded as acceptable for dielectric liquids." The properties enumerated are, of course, in addition to what may be termed the chemical requirements, i. e., stability so that the material remains substantially unchanged during use and does not attack metals or any other material which may be immersed in the dielectric, substantial noninflammability, and no tendency to develop inflammable gases upon decomposition. The dielectric liquids forming the subject matter of this application answer all these requirements and in addition are readily manufactured from materials which may be obtained commercially in any desired quantity.

It has been found that cyclic compounds containing an isopropyl constituent such as isopropyl benzene, when suitably chlorinated, possess all the properties requisite in a dielectric liquid. These products are readily prepared by the chlorination of benzene which has previously been reacted with propylene or with isopropyl or normal propyl chloride so as to replace one of the nuclear hydrogen atoms by an isopropyl substituent. We have found that when isopropyl benzene is chlorinated until from 3.0 to 5.0 atoms of chlorine have been introduced per mole of isopropyl benzene a liquid having satisfactory electrical properties and meeting other requirements of commercial dielectric compositions is produced.

Our novel products comprise undersome circumstances mixtures of isopropyltrichloro benzene and isopropyltetrachloro benzene. Under other circumstances but iso-propyltetrachloro benzene and isopropylpentachloro benzene are present. When other amounts of chlorine have been introduced the product may consist of all three isopropylchloro benzenes, the product then constituting primarily a mixture of the isomers of isopropyltrichloro benzene and isopropyltetrachloro benzene with isopropylpentachloro benzene. There are three isomeric isopropyltetrachloro benzenes and six isomeric isopropyltrichloro benzenes. But one isopropylpentachloro benzene is possible.

In preparing dielectric compositions we also contemplate admixing the reaction product of isopropyl benzene and chlorine with various other materials and/or diluents which are now or may be subsequently used as ingredients of dielectric compositions. Thus the products obtainable by the chlorination of cumcne and described in this application may be mixed in varying proportions with diluents such as trichlorbenzenc. Various mixtures of certain of the chlorination products of isopropyl benzene with other dielectricmixtures is described in our co-pending application, Serial No. 103,742, filed October 2, 1936.

The mixture prepared by the direct chlorination of isopropyl benzene until there are present from 3.0 to 5.0 atoms of chlorine per molecule of isopropyl benzene, in accordance with the method described in our previously referred to co-pending application, Serial No. 68,919, may be utilized directly as a dielectric composition in electrical equipment. This product consists generally of a mixture of isopropyltrichloro benzene, isopropyltetrachloro benzene, and isopropylpentachloro benzene. When the amount of chlorine introduced per molecule of isopropyl benliquids. The table which follows, Table 11, gives the properties of the products resulting when from 3.5 to 4.5 atoms of chlorine per mole of isopropyl benzene are introduced. It also gives the properties of selected fractions of the products thus prepared, these fractions having boiling points within various ranges.

TABLE II Properties of certain combined fractions of zene reaches 4.0 atoms or goes above this amount chlorinated isopropyl benzene No. of chlorine atoms per mol 3.5 4.0 4.5

N 0. of fraction I V II III I II III I II III Boiling range of traction. -C.. 270-310 260-310 250-310 270-310 260-310 250-310 270-310 260-310 250-310 Percent wt. of total product in frnction..... 58. 4 73.8 80. 5 57.4 71.7 78. 9 66.7 71. 5 75.9

Density at 96 C- 1. 33 1.32 1. 32 1. 36 l. 35 l. 35 l. 44 1. 43 1. 43 Melting point. C -18 17 23 30 29 35 57 51 50 Freeze point.... ..C.. Below 40 25 -7 7 45 34 30 Flash point ..C.. 180 180 175 180 180 165 Over 200 Over 200 Over 200 Fire point C. None None 223 None None None None None None at which crystals first appear upon cooling.

the product contains but little isopropyltrichioro benzene and consists essentially of isopropyltetrachloro benzene and pentac'hlorisopropyl benzene. The boiling points of the major ortion of the product containing 4.0 chlorine atoms or above generally vary between about 260 C. and 320 0. Upon cooling, solid crystals will ordinarily deposit aproximately within the range of temperatures 10 C. and 40 C.

The mixture prepared by chlorination until the chlorine content ranges from 3.0 to 5.0 atoms of chlorine per molecule of isopropyl benzene may also be split by fractional distillation into various fractions. The table which follows, Table I, will show the amounts, densities, melting points, and boiling points of various fractions separated from the mixtures obtained in accordance with our process by fractional distillation. Our invention contemplates the use of any one of these fractions or any number of them in admixture as ingredients in dielectric compositions intended for use in electrical apparatus.

The freeze pnint is the temperature As will be apparent from the table, the fractions from each one of these products may be combined into the three fractions shown, having boiling points from 270 to 310 C., from 260 to 310 C. and from 250 to 310 C. In this way, fractions of any desired freeze point may be prepared ranging from below 40 C. to 45 C.

Our invention contemplates the use of any one of thes particular fractions having boiling points and melting points within certain definite limits. It will be noted that when 4.5 atoms are present that portion of the product having a boiling point between 270 and 310 C. has a melting point of 57 C. This is so high that the material is not satisfactory by itself for use as a liquid dielectric. If desired, it may be dissolved or incorporated with other ingredientswhich will render the mixture liquid. Thus it may be admixed with other fractions of the product obtainable by chlorinating isopropyl benzene, the freeze point of the resulting composition being lowered thereby. However, for insulating electrical conductors such as TABLE I N umber of Cl atoms per mol Fran- Bolling 3.0 3.5 4.0 4.5 5.0

1011 N range Per Den- Per Den- Per Den Per Den- Per Dencent P sity cent P sity cent P sity cent P sity cent P sity Degrees Degrees Degrees Degrees Degree 1 To 200 8. O 5.0 3. 5 1. 3.0 4.8 35 1. 218 2 200-240 7. 6 Below 20 l. 28 6. 0 8. 7 43 1. 329 4.0 3. 1 52 1.350 3 240-250 7. 1 Below 20 1. 24 7.8 6. 8 57 1.349 5. 7 73 1.39 5. 4 84 l. 445 4 250-260 56. 7 Below 20 1. 23 6. 7 7. 2 54 1. 354 4. 4 85 l. 43 8. 2 98 l. 453 5.. 260-270 9.0 Below 20 1.27 15.4 14.3 58 l. 356 4. 8 85 1.44 6. 7 94 l 457 6... 270-280 6.0 Below 20 1. 30 21. 2 18. 6 32 1.349 7. 3 80 1.44 6. 3 98 l 459 7 280-290 3. 3 Below 20 1. 31 16.8

19. 7 l2 1, 352 6.1 66 l. 44 4. 7 101 l 463 8 290-300 2 l 14. 5 16.1 37 1, 382 11.9 18 1.44 5.1 68 1. 465 9 300-320 2. 9 3. 0 75 41. 4 64 1. 44 49. 1 75 l. 425 Residue 3. 8 .1 11. R 6. G

In view of the fact that, in general, the dielectric properties are improved and the inflammability lowered as the chlorine content increases, we prefer to use fractions having chlorine contents ranging from 8.5 to 4.5 atoms of chlorine per mole of isopropylbenzene. When over 4.5 atoms of chlorine per mole of isopropylbenzene are present the product approaches asolid in its characteristics and is for this reason not so suitable for dielectric compositions which are intended to be wires, and for use in condensers, the solid characteristics of the product boiling between 2'70 and 310 C. when isopropylbenzene is chlorinated until there are approximately 4.5 atoms of chlorine introduced are not objectionable.

All of the mixtures specified are substantially non-inflammable as will be apparent from the values given for the flash points and for the fire points. This applies more especially to all mixtures obtained by chlorinating isopropyl benzene plosive. The electric properties of all.- fractions may be stated to be approximately as fol- I lows:

TABLE III Per cent Dielectric constant at 24 C 4.65 Power factor at 24 C 1. 1 Power factor at 80 C 2.7

.having dielectric properties.

We have found that the fraction having a boiling point within the range 260 to 310 0., prepared by chlorinating lsopropyl benzene until there are from 3.5 to 4.5 atoms of chlorine present per mole of lsopropyl benzene and then separating out this fraction by fractional distillation, is especially useful for lowering the freeze point or viscosity of mixtures containing other materials By admixing various proportions of this fraction with other materials, products may be prepared which have viscosities and freeze points falling within any desired ranges.

When more than about 4.0 atoms of chlorine are present per mole of lsopropyl benzene the product resulting from the chlorination is a solid at room temperature, This product may be rendered liquid'by admixing it with any suitable diluent liquid. Solid dielectric materials have some utility, however, as they are used in condenser installations and as insulating medium for wires and other conductors of electricity, Our invention contemplates the use of our products either as solids or as liquids.

If desired, the freeze point of any of the dielectric liquids prepared as described above may be lowered by the addition of any suitable and well known diluent used for similar purposes in dielectric liquids now known to the art. Thus for example, trichlorbenzene prepared by the direct chlorination of benzene may be employed as diluent or freeze point depressant. The addi-' tion of such a diluent is frequently desirable to decrease the viscosity without affecting the electrical properties to such an extent as to render the liquid no longer suitable for dielectric use.

As is apparent from our previously referred to copending application S. N. 68,919, filed Mar. 14, 1936, the chlorine introduced is substituted on the nucleus in place of the nuclear hydrogen atoms. Tests to determine the presence of chlorine in a side chain, such as digestion with alcoholic caustic and titration to determine change in normality, indicate, conclusively that the lsopropyl side chain is not chlorinated to any appreciable extent.

- prising a mixture of chlorinated lsopropyl benzenes having boiling points falling within the temperature range 260 to 310 C. and containing, a

as a diluent, a mixture of chlorinated lsopropyl benzenes having boiling points falling within the temperature range 250 to 260 C.

2. An electrical insulating composition comprising a mixture of chlorinated lsopropyl benzenes having boiling points falling within the temperature range 2'70 to 310 C. and containing, as a diluent, a mixture of chlorinated lsopropyl benzenes having boiling points falling within the temperature range 260 to 270 C,

3. An electrical insulating composition comprising a mixture of chlorinated lsopropyl benzenes having boiling points falling within the temperature range 270 to 310 C. and containing,

as a diluent, a mixture of chlorinated isopropyl benzenes having boiling points falling within the temperature range 250 to 270 C.

4. The method of insulating elements in electrical apparatus which comprises interposing therebetween nuclear chlorinated isopropylbenzene.

5. The method of insulating elements in electrical apparatus which comprises interposing therebetween lsopropyltrichlorobenzene.

6. The method of insulating elements in electrical apparatus which comprises interposing therebetween isopropyltetrachlorobenzene,

7. The method of insulating elements in electrical apparatus which comprises interposing therebetween isopropylpentachlorobenzene 8. In an electrical apparatus comprising electrically conducting elements, a dielectric medium for insulating said electrically conducting elements which comprises nuclear chlorinated isopropyl benzene.

9. In an electrical apparatus comprising electrically conducting elements, a dielectric medium for insulating said electrically conducting elements which comprises a liquid consisting principally of lsopropyl tetrachlorobenzene-and isopropyl pentachlorobenzene.

10. In an electrical apparatus comprising electrically conducting elements, an electrical insulating composition for insulating said conducting elements which comprises lsopropyl tetrachlorobenzene and lsopropyl trichlorobenzene.

11. In an electrical apparatus comprising electrically conducting elements, an electrical insulating material for insulating said conducting elements which comprises lsopropyl pentachlorobenzene and lsopropyl trichlorobenzene. 12.In an electrical apparatus comprising electrically conducting elements, a dielectric medium for insulating said conducting elements which comprises isopropyl trichlorobenzene, isopropyl tetrachlorobenzene, and lsopropyl pentachlorobenzene. l

13. In an electrical apparatus comprising electrically conducting elements, a dielectric medium for insulating said conducting elements which comprises lsopropyl trichlorobenzene.

14. In an electrical apparatus comprising elec- R15 to be understood that the various composb, trically conducting elements, a dielectric medium tions herein disclosed may be varied somewhat in composition without departing from the scope of our invention. We do not desire that the various numerical proportions and properties of the dielectric liquids and mixtures herein disclosed be construed as restrictive, except as necessitated by the scope of the appended claims.

We claim: 7

1. An electrical insulating composition comfor insulating said conductingelements which comprises isopropyl tetrachlorobenzene.

15. In an electrical apparatus comprising electrically conducting elements, an electrical'insulating material for. insulating said conducting elements which comprises isopropyl pentachlorobenzene. V

' ARTHUR A. LEVINE.

OLIVER W. CASS.