Note: Descriptions are shown in the official language in which they were submitted.
- 1 -
134U?~4
OIL-FILLED CAPACITOR
BACKGROUND OF THE INVENTION
Field of the Invention
This :invention relates to an oil-filled capacitor
which is impregnated 'with an electrical insulating oil that
is prepared frorn the ~by-product oil fractions obtained in
the process to prepare ethylbenzene. Furthermore, the
invention relatE:s to an oil-filled capacitor which is
impregnated with an electrical insulating oil comprising
a specific fraction or its mixture derived from the
above-mentioned by-product oil.
Description of the Prior Art
It is well known that a heavy by-product oil is
produced in the process to prepare ethylbenzene by reacting
benzene with ethylene in the presence of an alkylation
catalyst as disclosed in, for example, U. S. Patent
Nos. 4,108,788; 4,111"825; and 4,228,024.
In the same reference, it is described that the
fraction having a boi7Ling range of 275 to 420°C is useful as
an electrical insulating oil.
The present inventors recovered the fraction
described in the abovE: reference by distillation and used it
for the impregnation of oil-filled capacitors made by using
polypropylene film. However, it was found out that capacitors
having excellent characteristics cannot always be made,
while the reason for this has not yet been clear.
- 2 -
130?~1
The above by-product oil obtained from the
ethylbenzene prE:paration process, however, inevitably
contains various uncertain compounds that cannot be
determined by analysis, as the general characters of the
materials of this kind. The kinds and quantities of these
undeterminable compounds are not fixed and, in addition, the
boiling points of these compounds are close to or overlapped
with one another. Accordingly, it is impossible to isolate
any component only by distillation from the by-product oil.
In the case that a fraction having a certain
boiling point is recovered, the boiling point of the fraction
is indicated by the distilling temperature of the fraction.
In practice, however, the efficiency of the distillation
generally depends upon the distilling conditions such as
the number of theoretical plates of distillation apparatus,
reflux ratio, bottom temperature and other temperature
distribution in a distillation column, and the rate of
distillation. Even when the distillation temperatures,
that is, the boiling points are the same, the kinds and
quantities of components in distilled fractions are liable
to vary largely.
Owing to the complexity of the origin of
by-product oil and operational factors in the distillation
of by-product oi:L, it is supposed that an electrical
insulating oil having excellent characteristics cannot
be obtained only by a simple measure of distillation.
3 - ~34~'~~~
E~RIEF :SUMMARY OF THE INVENTION
In view of the above facts, the present inventors
have carried out extensive studies on the preparation of
oil-filled capacitors using such by-product oils.
It is, therefore, the primary object of the
present invention to provide an oil-filled capacitor which
is impregnated with an electrical insulating oil having
excellent electrical characteristics that is prepared from
the by-product oil in the ethylbenzene preparation.
Another object of the present invention is to
provide an oil-filled capacitor which can be produced at low
cost without difficulty.
In accordance with the present invention, the
oil-filled capacitor is composed of, at least partially,
a dielectric substance of plastics material and it is,
of course, impregnated with an electrical insulating oil.
The oil is characterized in that it comprises 0 to 1000 by
weight, of a fraction A containing components boiling within
the range of 268 to 2.'5°C (atmospheric pressure basis) and
100 to Oo by weight of= a fraction B containing components
within the range of 280 to 310°C. These fractions are those
recovered by distillation from the heavy by-product oil which
is produced in the preparation of ethylbenzene by alkylating
benzene with ethylene in the presence of an alkylation
catalyst and the ratio of the integrated intensity as
chemical shift a.t 120 to 155 ppm of the spectrum measured
by C13 NMR method to t:he total integrated intensity at
- 4 -
0 to 155 ppm of the spectrum is 80o or higher with regard
to the fraction A and the same ratio is 72% or higher with
regard to the fraction B.
The objects and features of the present invention
will become more apparent in the following description.
DETAILED DESCRIPTION OF THE INVENTION
The method t:o prepare ethylbenzene by alkylating
benzene with ethylene in the presence of an alkylation
catalyst is widely carried out industrially as a method
for preparing th.e raw material of styrene monomer. The
by-product oil referred to in the present invention is
obtained from such a process for preparing ethylbenzene.
More particularly, a liquid phase alkylation
method or a vapor phase alkylation method is generally used
for reacting benzene with ethylene. In the liquid phase
alkylation method, a F'riedel-Crafts catalyst such as aluminum
chloride or a Br~nste~i acid such as p-toluenesulfonic acid
or hydrofluoric acid is used. In the vapor phase alkylation
method, a synthetic ze:olite such as ZSM-5 or phosphoric acid
carried on an appropriate carrier is used. The reaction
temperatures are. genez-ally selected from the range of 20 to
175°C in the lic,uid phase alkylation method and 250 to 450°C
in the vapor phase alkylation method.
Through the above reaction, an alkylation product
is obtained. This alkylation product comprises unreacted
benzene, the aimed ethylbenzene, polyethylbenzene and
a heavy by-product oil. The alkylation product is then
_ 5 - ~3~~'~5~
subjected to the removal of catalyst, neutralization and
washing with water as occasion demands according to the
conventional method. The by-product oil used in the present
invention is then obtained by removing the unreacted benzene,
ethylbenzene, and polyethylbenzene by distillation. Because
the by-product oil contains tarry substances and in order to
facilitate the below-described distillation operation, the
by-product oil is previously subjected to rough distillation
at a reduced pressure to obtain a fraction covering a temper-
ature range broader than that of the aimed fractions. This
fraction obtained in the rough distillation is not especially
limited as far as it covers the aimed temperature range.
That is, the fraction is selected from the range in
distilling temperatures of 255 to 420°C (atmospheric
pressure basis).
From the above by-product oil, the fraction A
containing components having a boiling temperature range
of 268 to 275°C (atmospheric pressure basis) and another
fraction B containing components having a boiling temperature
range of 280 to 310°C (atmospheric pressure basis) are
obtained by precision fractional distillation.
As described above, various undeterminable compounds
are contained in the by-product oil from ethylbenzene. When
heated, these compounds are liable to polymerize, decompose
or isomerize. Furthermore, the by-product oil itself is heavy
and high in boiling point. Accordingly, the distillation of
the by-product oil must be done under reduced pressures.
- 6 -
When it is subjected to distillation at atmospheric
pressure, the fvorego:ing ratios of .integrated . intensities
cannot reach.the level of 80~ or higher in the fraction A
and the level of 72~ or. higher in. the fraction B. Or, even
when the ratio~~ reach these values, the characteristics of_
the electrical insulating oil .is quite poor. The sufficient.
degree of the :reduced pressure may be 200 mmHg or lower, and
preferably not higher than 5.0 mmHg. It is undesirable in
view of economy.to.reduce the pressure to excess. The
precision fractional distillation. can be carried out either
in continuous c>r in batch wise operation using one or a
plurality of distillation columns. The distillation is
carried out by regul,3ting the distilling conditions, for
example, the number of theoretical plates of distillation
column, the bottom temperature and other temperature
distribution in the column, the rate of distillation,
and other factors, so as to meet the foregoing conditions.
It is necessary to use a~distillation apparatus ofgenerally
10 or mode, prEsferably 20 br more;. in the theoretical number
of plates. In ~t:he event that ahe obtained fraction contains
substantially no components boiling, within the above-mentioned'
temperature range, the. ratios ne.Yer reach these values andv
the electrical characteristics, of the by-product oil cannot
be improved. ~~ccordingly, the distillation conditions are
to be selected,.
It i:~ inevitable that the ratio of the integrated
intensity as~chem-ical shift at 120 to 155.ppm of the spectrum
- 7 -
measured by C13 NMR method to the total integrated intensity
at 0 to 155 ppm of the spectrum is 800 or higher with regard
to the fraction A and the same ratio is 72% or higher with
regard to the fraction. B. In connection with the electrical
insulating oil used in the present invention, quite excellent
electrical characteristics are exhibited by the constituents
of the fraction A or those of the fraction B or the syner-
gistic effect of both the fractions A and B. In the case
that the ratio of the integrated intensity of the spectrum
measured by C13 NMR method is lower than 80% in the fraction
A or the ratio is lower than 72s in the fraction B, such the
synergistic effect cannot be expected.
The electrical insulating oil used in the present
invention can comprise the above-described fraction A or the
fraction B. It is, however, preferable that the electrical
insulating oil comprises a mixture of both the fractions.
That i;s, the preferable electrical insulating oil
used for impregnating the oil-filled capacitor is a mixture
of 10 to 800, more preferably 20 to 70%, by weight of the
fraction A and 90 to 20%, more preferably 80 to 30%, by
weight of the fraction B; and the ratio of the integrated
intensity as chemical shift at 120 to 155 ppm of the spectrum
measured by C13 IVMR method to the total integrated intensity
at 0 to 155 ppm of the spectrum is 800 or higher with regard
to said fraction A and the same ratio is 720 or higher with
regard to said f_~action B.
- 1340' ~4
In the case that the proportion of the fraction A
is less than lOs by weight, that is the proportion of the
fraction B is more than 90a by weight, it is less desirable
because the corona discharge characteristic of the capacitor
which is impregnated with such an electrical insulating oil
is impaired. On the other hand, if the proportion of the
fraction A exceeds 80o by weight, that is the proportion of
the fraction B is less than 20o by weight, it is also less
desirable because: the low temperature characteristics of
the capacitor which is impregnated with such an electrical
insulating oil is impaired.
The elE:ctrical insulating oil prepared as described
above is refined if need be and it is used as an impregnating
oil for oil-f ille:d capacitors . The ref fining can be done in
the process of di.still<~tion of the by-product oil.
Furthermore, in ~~ccord<3nce with uses, it is possible to use
the electrical insulating oil by mixing it with well known
diaryl alkanes, alkyl biphenyls, alkyl naphthalenes and so
forth in arbitrary proportions.
The oil-filled capacitor of the present invention
is the one in which at least a part of dielectric substance
is composed of a plastics film. As the plastics films,
those of polyolefins such as polyethylene, polypropylene
and polymethylpentene are desirable. Among them, the film
made of polypropylene i.s most preferable. For example,
the oil-filled capacitor of the present invention is made
by winding a metal foil. such as aluminum foil together with
1340r1~~
polypropylene film, and if necessary also with insulating
paper, and impregnating it with the above-described
electrical insulating oil according to the conventional
method. The oil-filled capacitor in which a metallized
plastics film is wound together with a plastic film or
insulating paper and then impregnated with an electrical
insulating oil is also covered by the present invention.
The dei=ermination in C13 NMR method will be
described. The measuring temperature is generally the room
temperature. A fraction to be measured is dissolved into a
solvent of deutero chloroform to prepare a solution of 10 to
20% by volume. The frequency of measurement can be varied
properly, for example, measurement is done at 67.8 MHz.
In the obtained C:13 NMR spectrum, the integrated intensity
between 120 to 155 ppm in chemical shift on the basis of
tetramethylsilane is measured and then the ratio (%) of this
value to the integrated intensity of the total spectrum
(0 to 155 ppm) excluding that of the solvent, is obtained.
The numeral on the first decimal place is rounded. In order
to improve the quantitative accuracy, the measurement is
generally done by the proton complete decoupling method
with eliminating the nuclear overhauser effect.
The present ~_nvention will be described in more
detail with reference t:o the example of the invention.
1340~~~
- 10 -
E X A M P L E
- Alkylation of Benzene -
From the liquid phase alkylation process to
prepare ethylbenzene by alkylating benzene with ethylene in
the presence of aluminum catalyst, an alkylation product was
obtained. The alkylation product consisted of 43.Oo of
unreacted benzene, 11.8% of ethylbenzene, 18.3% of polyethyl-
benzene and 7.60, all by weight, of heavy by-product oil.
The unreacted benzene, ethylbenzene, and polyethylbenzene
were removed by distillation. The remained by-product oil
was a viscous black substance. This by-product oil was
distilled at a reduced pressure of 10 mmHg to obtain a
fraction (hereinafter referred to as "recovered fraction")
of 255 to 420°C in distilling temperature (atmospheric
pressure basis).
The following fractions were separated from this
recovered fraction.
Fraction A
To the bottom of precision fractional
distillation column was fed 1600 lit. of the recovered
fraction and fraci_ional distillation was carried out at
reduced pressure of 5 to 15 mmHg to obtain a fraction A
of 268 to 275°C (atmospheric pressure basis) in distilling
temperature.
Packed column:
Diameter.: 400 mm Height: 10.4 m
Theoret :cal number of plates : 25
- 11 -
Fraction B
The recovered fraction was distilled using the
above distillation column in the like manner as the above to
obtain a fraction B of 280 to 310°C (atmospheric pressure
basis) in distilling temperature.
Fraction A-1
To the bottom of the following distillation column
was fed 1600 lit. of the recovered fraction and fractional
distillation was carried out under a reduced pressure below
the atmospheric pressure by not less 250 mmHg to obtain a
fraction A-1 of 268 to 275°C (atmospheric pressure basis)
in distilling temperature.
Packed column:
Diameter: 400 mm Height: 4.0 m
Theoretical number of plates: 5
Fraction B-1
The recovered fraction was distilled using the
above distillation column in the like manner as the above to
obtain a fraction. B-1 of 280 to 310°C (atmospheric pressure
basis) in distilling temperature.
- Measurement by C13 NMR Method -
Measurement was carried out at the room temperature
using a C13 NMR measuring apparatus of Model GX-270 made by
Japan Electron Optics Laboratory Co., Ltd. Each fraction
was dissolved in a solvent of deutero chloroform to prepare
solutions of 15% concentration. The frequency of measurement
was 67.8 MHz.
- 12 -
In order to improve the quantitative accuracy, the
measurement was done by the proton complete decoupling method
with eliminating the nuclear overhauser effect.
In the obtained C13 NMR spectrum, the ratio of
integrated intensity of 120 to 155 ppm in chemical shift to
the total integrated intensity of the spectrum (0 to 155 ppm)
was obtained with regard to each fraction. The results of
them are shown in the following Table 1. The standard for
the chemical shift was tetramethylsilane.
- Compatibility with Polypropylene Film -
Polypropylene films (14 micrometer thick) that
were cut into a certain shape, were soaked in the respective
fractions at 80°C for 72 hours. After that, the films were
taken out and the percentages of changes in volumes of the
films were measured, the results of which are shown in Table
1. The smaller value, i.e. the smaller volume change
indicates the excellence in size stability, which means
that the relevant oil is good in the adaptability to the
polypropylene film.
- MeasuremE~nt of Corona Starting Voltage (CSV)
and Corona Ending Voltage (CEV)
A two-p:Ly polypropylene film (each 14 micrometer
thick) as a dielectric substance and aluminum foil as an
electrode were pui= together in layers and wound according to
the ordinary method to obtain model capacitors for oil
impregnation.
_ 13 _ ~3~~~~~
The model capacitors were impregnated with each
fraction in vacuo to obtain oil-filled capacitors of 0.4
microfarad in electrostatic capacity.
The corona starting voltages and corona ending
voltages of these capacitors at 25°C were measured.
The results are ;shown in Table 1.
Life Test for Capacitors -
A two-ply polypropylene film (each 14 micrometer
thick) as a dielectric substance and aluminum foil as an
electrode were put together in layers and wound according
to the ordinary method to obtain model capacitors for oil
impregnation.
The model capacitors were impregnated with each
fraction in vacuo to obtain oil-filled capacitors of 0.4
microf arad in electrostatic capacity.
These capacitors were applied with prescribed AC
voltages at -35°c~ and the time lengths until the capacitors
were broken down were measured to estimate the lives of
capacitors. In i=his case, the potential gradients were
initiated from 60 V/~ and raised by 10 V/~ at every 48
hours, where the numbers of broken capacitors were counted.
The numbers of c<~pacitors that were used for the test were
respectively 10. The :results are shown in the following
Table 2.
It wil:L be understood from the results in tables,
the fraction A and the fraction B are superior to the
recovered fraction even when they are used singly.
- 134U?~~
By mixing the fraction. A and the fraction B, the corona
discharge characteristics at the low temperature and the
lives of the oil-filled capacitors can be improved as
compared with the use of a single fraction A or fraction B.
Furthermore, in the fractions in which the ratios
of integrated intensities of C13 NMR method are less than
80% or 72%, it is apparent that the synergistic effect
between the fractions A and B cannot be exhibited.
- 15 -
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T a b 1 a 2
Life Test at -35°C
(Number of: Capacitors Broken Down)
Insu- F~otential Gradient (V/~)
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