BACKGROUND OF THE INVENTION:
(Field of the Invention)
The present invention relates to a working medium for
absorption refrigerators, and an absorption refrigerator
using this medium.
(Description of Related Art)
A working medium used generally in conventional
absorption refrigerators is a lithium-bromide/water system.
Water is a cooling medium, and lithium bromide is an
15 absorbing liquid. Accordingly, the water which is the
cooling medium is frozen in an evaporator for generating a
cold energy, the evaporator constituting the absorption
refrigerator. It is therefore difficult that temperature
of a heat medium for transporting the cold energy is
20 adjusted to a temperature below a freezing point of water
in the absorption refrigerator having an ordinary
specification.
International Publication WO 2004/087830 (Patent
Literature 1) discloses an absorption refrigerator in which
25 a cold energy corresponding to the freezing point or lower
5
2
is obtained by using a lithium-bromide/water system working
medium including 1,4-dioxane as an additive which is a
boiling-point-lowering-type organic substance having an
azeotropic point with water.
From the viewpoint of prevention of corrosion of
parts formed of a stainless steel used for the apparatus,
Japanese Patent Application Laid-Open No. Hei 11-080978
(Patent Literature 2) discloses an aqueous solution
composition for an absorption heat pump that contains
10 lithium bromide as a main component, and a molybdate and an
alkali hydroxide as inhibitors, the concentration of the
alkali hydroxide being restricted.
"Kurita Industrial Chemicals Handbook", edited by
Kurita Water Industries chemicals Handbook Editorial
15 Committee (Non Patent Literature 1) describes
aminotrimethylenephosphonic acid which is of a phosphonic
acid type and is widely used as a corrosion inhibitor for
cooling-water systems.
20 SUMMARY OF THE INVENTION:
The working medium of the present invention for
absorption refrigerators is a mixture that is to contact a
carbon steel or a copper alloy that is a structural
material of any one of the absorption refrigerators, and
25 includes water and 1,4-dioxane, and further includes a
5
10
15
20
25
3
corrosion inhibitor. The corrosion inhibitor includes one
or more selected from the group consisting of respective
hydroxides of any alkali metal and any alkaline earth metal,
and respective oxoates.
The present invention makes it possible to restrain a
structural material of an absorption refrigerator which
generates the freezing point of water from being corroded
with a water/dioxane mixed cooling medium used in the
absorption refrigerator.
BRIEF DESCRIPTION OF THE DRAWINGS:
Fig. 1 is a schematic structural view illustrating an
absorption refrigerator for generating a freezing point of
water;
Fig. 2 is a graph showing a dependency of a gas
quantity generated in each corrosion test of a material
SS400 upon a concentration of LiOH which is a corrosion
inhibitor, the corrosion test using a mixed cooling medium
to which LiOH was added;
Fig. 3 is a graph showing a dependency of a gas
quantity generated in each corrosion test of a material
SS400 upon the concentration of Li2Mo04 which is a corrosion
inhibitor, the corrosion test using a mixed cooling medium
to which Li2Mo04 was added; and
Fig. 4 is a graph showing a change with time in a
5
4
corrosion quantity of an oxygen-free copper in mixed
cooling mediums.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS:
A simple substance of each of water and 1,4-dioxane
is not very strong in corrosiveness, or corroding power to
structural materials, for example, a material SS400.
However, a mixed cooling medium in which 1,4-dioxane is
added to water is remarkably increased in corrosiveness
10 thereto. A reason for this increase in the corrosiveness
is based on a matter that the ring structure of 1,4-dioxane
is broken so that the ring is opened to produce a
carboxylic acid or some other. Accordingly, in the case of
configuring an absorption refrigerator by using a 1,4-
15 dioxane/water mixed cooling medium as a cooling medium, it
is indispensable to establish a technique of preventing the
corrosion based on the mixed solvent.
20
Patent Literature 1 never describes any corrosion
inhibitor.
Patent Literature 2 never describes any system using
1,4-dioxane.
An object of the present invention is to restrain a
structural material of an absorption refrigerator, which
generates a freezing point of water, from being corroded
25 with a water/dioxane mixed cooling medium used in the
5
absorption refrigerator.
The present invention relates to an absorption
refrigerator in which a cold energy corresponding to a
solidifying point of water (the freezing point thereof) or
5 lower, particularly to an absorption refrigerator excellent
in a corrosion resistance. The corrosion of a main
structural member of this refrigerator is restrained at a
high level by adding an alkali hydroxide or oxoate to the
cooling medium when a water/dioxane mixed solution is used
10 as a cooling medium (working medium) .
Conventionally, corrosion inhibitors used in coolingwater
are roughly classified into types as described below
on the basis of the mechanism thereof.
(1) Adsorption type: any inhibitor of this type
15 causes a chemical adsorption:
20
[M] + RX: ---> [M] : XR
(2) Oxidation type: any inhibitor of this type causes
a production of a precipitation of a hydroxide:
Mn+ + n: OW ---> [Mn+ ( : OH-) nJ
(3) Precipitation type: any inhibitor of this type
causes a production of a precipitation of a complex:
Mn+ + nRX: - ---> [Mn+ ( : XR-) nJ
In each of these expressions, [M] or Mn+ represents a
Lewis acid; and RX:, :OH-, RX:-, and others are each a Lewis
25 base.
6
However, as described above, a cause for corrosion in
a 1,4-dioxane/water system is that the ring structure of
1,4-dioxane is broken so that the ring is opened to produce
a carboxylic acid or some other. Thus, in order to
5 restrain the corrosion, it is necessary to prevent the
ring-opening of the ring structure of 1,4-dioxane. However,
it cannot be presumed whether or not the corrosion
inhibitors produce an advantageous effect based on a
conventional corrosion-restraining mechanism also in a 1,4-
10 dioxane/water system.
In order to solve the above-mentioned problems, the
inventors have made eager researches to achieve the present
invention. Specifically, by adding an alkali metal
hydroxide, an alkaline earth metal hydroxide or an oxoate
15 to a 1,4-dioxane/water mixed cooling medium which is high
in corrosiveness, the resultant medium can exhibit a
sufficient corrosion-restraining effect to make it possible
to configure the absorption refrigerator using the 1,4-
dioxane/water mixed cooling medium to generate a cold
20 energy corresponding to 0°C or lower. The effect can be
obtained also by using a combination of an alkali metal
hydroxide or alkaline earth metal hydroxide with an oxoate.
Examples of the alkali metal hydroxide are LiOH, NaOH,
KOH, RbOH, and CsOH. These hydroxides each exhibit a
25 corrosion-restraining effect. Of these hydroxides, LiOH,
7
NaOH and KOH are preferred from the viewpoint of the
solubility and the corrosion-restraining effect thereof.
Since LiBr is frequently used as an absorbing liquid, it is
particularly preferred to use a hydroxide of Li which is
5 identical with the alkali metal of LiBr. When the
concentration of the hydroxide of the alkali metal is 0.1 M,
the corrosion-preventing effect is obtained. However, even
when the concentration is 0.02 M which is a lower
concentration than 0.1 M, a sufficient corrosion-
10 restraining effect is obtained. When the hydroxide is
added to the cooling medium in the concentration of 0.1 M
or more, the effect is obtained. However, an improvement
in the effect is small. When the concentration is 0.005 M
or less, the corrosion-restraining effect of the alkali
15 metal hydroxide is small and further the corrosionrestraining
effect is unfavorably lost by the consumption
of the hydroxide. From these matters, the range of optimal
concentrations of the hydroxide is from 0.02 to 0.15 M.
Examples of the alkaline earth metal hydroxide are
20 Be(OH) 2, Mg(OH)2, Ca(OH)2, Sr(OH) 2, and Ba(OH) 2. Of these
hydroxides, Ca(OH) 2 is preferred from the viewpoint of the
solubility and the corrosion-restraining effect thereof.
When the concentration of the hydroxide of the alkaline
earth metal is 0.1 M, the corrosion-preventing effect is
25 obtained. However, even when the concentration is 0.02 M,
8
which is a lower concentration than 0.1 M, a sufficient
corrosion-restraining effect is obtained. When the
hydroxide is added to the cooling medium in the
concentration of 0.1 M or more, the effect is obtained.
5 However, an improvement in the effect is small. When the
concentration is 0.005 M or less, the corrosion-restraining
effect of the alkaline earth metal hydroxide is small and
further the corrosion-restraining effect is unfavorably
lost by the consumption of the hydroxide. From these
10 matters, the range of optimal concentrations of the
hydroxide is from 0.02 to 0.15 M. Ca(OH) 2 has a low
solubility (about 0.02 Mat 25°C) Thus, a saturated
solution thereof may be used.
The addition of the alkali metal hydroxide or
15 alkaline earth metal hydroxide causes a rise in the pH of
the solution, so that the solution exhibits alkalinity.
However, the addition of NH3 or Na2C03 which exhibits
alkalinity in the same way does not produce any corrosionrestraining
effect. In general, by making a solution
20 alkaline, an iron hydroxide is produced on an outer surface
of a metal such as iron steel in the solution, so that the
corrosion of the metal is restrained. However, in a
water/dioxane system, no corrosion-restraining effect is
exhibited even when NH3 or Na2C03 which is an alkali is
25 added to the system. This is because the corrosion9
restraining mechanism in this case is based not on the
production of any iron hydroxide, but on a mechanism of
preventing the ring-opening of the ring structure of 1,4-
dioxane. In other words, any alkali metal hydroxide or
5 alkaline earth metal hydroxide has an effect of preventing
the ring-opening of the ring structure of 1,4-dioxane, but
NH3 or Na2C03 does not have such an effect.
An oxoate is a chemical substance which is other than
any alkali metal hydroxide and any alkaline earth metal
10 hydroxide, and which exhibits an effect of preventing the
ring-opening of the ring structure of 1,4-dioxane.
Examples of the oxoate include molybdates, tungstates,
vanadiates, silicates, phosphates, polyphosphates,
phosphonates, hypochlorites, chlorites, perchlorates, and
15 sulfonates. Specific examples thereof include lithium
molybdate, sodium molybdate, ammonium molybdate, sodium
tungstate, ammonium vanadiate, sodium orthovanadiate,
sodium silicate, sodium metasilicate, sodium phosphonate,
sodium dihydrogenphosphate, ammonium dihydrogenphosphate,
20 sodium hydrogenpyrophosphate, sodium metaphosphate, sodium
polyphosphate, sodium hypochlorite, sodium chlorite, and
sodium perchlorate. As far as the oxoate is any one of
these oxoates, a corrosion-restraining effect is exhibited
without any especial restriction.
25 When the oxoate is added in a concentration of 0.01 M,
10
a corrosion-preventing effect is obtained. Even when the
concentration is 0.002 M which is a lower concentration
than 0.01 M, a sufficient corrosion-restraining effect is
obtained. However, the corrosion-restraining effect is
5 decreased as the concentration is lowered. When the
concentration is 0.002 M or less, the corrosion-restraining
effect is small and further the corrosion-restraining
effect is unfavorably lost by the consumption of the oxoate.
From these matters, the range of optimal concentrations of
10 the oxoate is from 0.002 to 0.01 M. In an ordinary
cooling-water, an oxidizer causes the production of a thin
passive film on the outer surface of a metal to exhibit a
corrosion-restraining effect. However, in a water/dioxane
system, an oxidizer such as hydrogen peroxide, potassium
15 nitrate, sodium nitrite or ceriumammonium nitrate does not
exhibit any corrosion-restraining effect although the
oxoate which is also an oxidizer exhibits the corrosionrestraining
effect. This is because the corrosionrestraining
mechanism of the oxoate is based not on the
20 production of the passive film by the oxidizer, but on the
effect of preventing the ring-opening of the ring structure
of the 1,4-dioxane.
For the same reason, adsorption type corrosion
inhibitors which exhibit a corrosion-restraining effect in
25 an ordinary cooling-water do not exhibit any corrosion11
restraining effect in a water/dioxane system, examples of
the inhibitors including hexamethylenetetramine, thiourea,
hexanethiol, and dimethylhexabenzylamine. 8-quinolinol or
sodium octylpropionate which is a precipitation type
5 corrosion inhibitor does not exhibit any corrosion
inhibitor in a water/dioxane system, either.
10
Fig. 1 is a schematic view illustrating a structure
and connection of units of an absorption refrigerator
preferred for carrying out the present invention.
In Fig. 1, the absorption refrigerator which is a
refrigerator 100 is composed of an evaporator 1, an
absorber 2, a high-temperature regenerator 3, a lowtemperature
regenerator 4, a condenser 5, and a solution
heat exchanger 6. Of these units, the evaporator 1, the
15 absorber 2 and the condenser 5 are kept in a vacuum having
a pressure of several millimeters of mercury. A cooling
medium used in the evaporator 1 is a water/1,4-dioxane
mixed cooling medium (hereinafter referred merely to also
as a "mixed cooling medium") . A molar fraction of water is
20 0.85 when the mixed cooling medium is sealed into the
evaporator 1. In order to relieve a high corrosiveness of
the water/1,4-dioxane mixed cooling medium, LiOH is added
as a corrosion inhibitor to this cooling medium to have a
concentration of 0.3%. An absorption liquid used in the
25 absorber 2 is a concentrated LiBr solution having a very
12
low water vapor pressure. The high-temperature regenerator
3 and the low-temperature regenerator 4 may be collectively
called the "regenerator".
At a lower part of the evaporator 1, a pump 8 is
5 located for spraying the mixed cooling medium that remains
in a bottom part of the evaporator 1 from an upper part of
the evaporator 1. At a lower part of the absorber 2, a
pump 9 is located for spraying the absorption liquid that
remains in a bottom part of the absorber 2 from an upper
10 part of the absorber 2.
When a low-temperature medium is supplied, the
following are sprayed from the upper part of the evaporator
1: the water/1,4-dioxane mixed cooling medium that is
produced in the condenser 5; and the water/1,4-dioxane
15 mixed cooling medium that remains in the bottom part of the
inside of the evaporator 1. Thus, these cooling mediums
are vacuum-evaporated on an outside surface of a cooling
pipe located inside the evaporator 1. By vaporization heat
of the evaporation, the cooling medium inside the cooling
20 pipe is cooled to yield a low-temperature medium.
However, when the vacuum evaporation is continued,
the vacuum degree is lowered by generated vapor of the
mixed cooling medium so that the cooling efficiency is
lowered. Thus, in order to continue the vacuum evaporation
25 efficiently, it is necessary to remove the mixed cooling
13
medium vapor generated in the evaporator 1 to keep the
vacuum. For this purpose, the mixed cooling medium vapor
generated in the evaporator 1 is absorbed into the
concentrated LiBr solution in the absorber 2. The
5 absorption liquid diluted by the absorption of the mixed
cooling medium vapor (diluted solution) is heated in the
solution heat exchanger 6, and subsequently sent to the
high-temperature regenerator 3 and the low-temperature
regenerator 4.
10 In the high-temperature regenerator 3, the absorption
liquid is heated and concentrated by vapor or some other as
one or more heat sources supplied from the outside. Vapor
of the mixed cooling medium thus produced attains the
heating of the low-temperature regenerator 4 to be
15 condensed into the mixed cooling medium. The mixed cooling
medium is sprayed inside the condenser 5. The vapor or the
other as the heat source that has passed through the hightemperature
regenerator 3 turns to condensed water. The
condensed water is used to heat the diluted solution in a
20 drain cooler 7, thereby being further cooled, and then
discharged as a drainage.
The vapor of the mixed cooling medium produced by
heating the absorption liquid in the low-temperature
regenerator 4 is condensed by a cooling-water inside the
25 condenser 5, and subsequently sent to the evaporator 1.
14
The heated cooling-water is cooled by heat-radiation into
the atmosphere in a cooling tower or some other.
In order to verify advantageous effects of the
present invention, a corrosion test of a structural
5 material 88400 was made in a solution prepared by adding
each of various alkalis to a mixed cooling medium to
measure a quantity of a gas generated by the corrosion of
the structural material. An anode reaction of the
corrosion is a dissolution reaction of iron, which is
10 represented by a reaction formula (1) illustrated below. A
cathode reaction paired with the anode reaction is a
hydrogen-gas-generating reaction represented by a reaction
formula (2) illustrated below. The quantity of the
generated hydrogen gas is in proportion with the quantity
15 of the corrosion in this way. Thus, it can be determined
from the quantity of the generated hydrogen gas whether the
degree of the corrosion is large or small.
20
Fe ~ Fe2+ + 2e- (1)
2H+ + 2e- ~ H2 (2)
Each of the corrosion tests and the measurement of
the generated gas quantity in the test were made as
follows:
In the corrosion test, a sealed tube (a glass ample)
made of Pyrex (registered trademark) glass was used. The
25 sealed tube was produced as follows:
15
A test piece (the 88400; a length of 10 mm, a width
of 4 mm, and a thickness of 0.5 mm), and 20 mL of the
above-mentioned alkali-added mixed cooling medium which was
each test liquid were put into a glass tube having a
5 bottom; the glass tube was connected to a vacuum pump;
under a condition of a decreased pressure of 2 mmHg at 298
K, the tube was deaerated for 15 minutes while ultrasonic
vibration was applied to the tube; and then, an opening in
the tube was sealed up to produce the sealed tube. The
10 sealed tube was held in a thermostat having a temperature
kept at 90°C for 500 hours.
After the corrosion test, the glass ample was put
into a glass-ample-crushing vessel connected to a mercury
manometer, and the inside of the crushing vessel was
15 decreased to a pressure of 2 mmHg or less. After the glass
ample was crushed, the generated gas quantity was
calculated out from a variation in the value of the mercury
manometer.
Each of the used test pieces was the 88400 (oxygen-
20 free copper was used for some of tests that will be
described later) . In the present specification, the 88400
was used as a typical example of a carbon steel. However,
the steel material used as the structural material of the
absorption refrigerator is not limited to this material.
25 Thus, the structural material may be any other carbon steel
16
or some other.
Table 1 shows the quantity of the gas (hydrogen)
generated in each of some of the made corrosion tests using,
as its test liquid, the mixed cooling medium to which one
5 of the various alkalis was added. In the test, the molar
fraction of water in the mixed cooling medium was 0.85.
[Table 1]
Gas (hydrogen) quantity generated by corrosion of SS400
immersed in a mixed coolant to which each of various alkalis was added
Comparative
Example 1 Example 2 Example 3 Example 4 Comparative Comparative Comparative
Example 1 Example 2 Example 3 Example 4
Additive: - LiOH LiOH Ca(OH)2 NaOH NH3 NH3 Na2C03 corrosion inhibitor
Concentration (M) - 0.125 0.02 0.02 0.1 1.0 0.1 0.1
Molar fraction 0.85 0.85 0.85
of water
0.85 0.85 0.85 0.85 0.85
pH 5.2 12.0 11.6 12.3 11.2 11.4 11.2 11.5
Generated gas
120 0.4 0.2 0.25 0.15 110 105 95
quantity (ml/dm2)
10 From this table, the following are understood:
Comparative Example 1 shows a result obtained by
investigating the gas quantity generated in one of the made
corrosion tests in the mixed cooling medium to which no
corrosion inhibitor is added. The generated gas quantity
15 is 120 mL/dm2
•
As shown in Example 1, when 0.125 M LiOH is added as
a corrosion inhibitor, the generated gas quantity is 0.4
mL/dm2
. The generated gas quantity in Example 1 is
decreased to 1/300 of that in Comparative Example 1; thus,
17
as compared with Comparative Example 1, Example 1 shows a
remarkably restrained corrosion.
Example 2 demonstrates a case where the LiOH
concentration is made lower than that in Example 1 to be
5 decreased to 0. 02 M. In Example 2, the generated gas
quantity is 0.2 mL/dm2
• Thus, even when the concentration
is decreased, the corrosion quantity can be kept at a low
level.
Examples 3 and 4 demonstrate cases where the cation
10 species of their hydroxide is changed to Ca and Na,
respectively, from Li. Even when the cation species is
changed, the generated gas quantities are 0.25 dL/dm2 and
0.15 mL/dm2
, respectively. Thus, even when the respective
concentrations of these hydroxides are decreased, the
15 resultant corrosion quantities can be kept at a low level.
Comparative Examples 2 and 3 demonstrate cases where
NH3 are added to the mixed cooling medium. The respective
concentrations of NH3 are 1.0 M, and 0.1 M. In these cases,
the respective generated gas quantities are 110 mL/dm2 and
20 105 mL/dm2
• These quantities are at a level equivalent to
the level of the case demonstrated in Comparative Example 1,
where no corrosion inhibitor is added. Thus, the corrosion
is not restrained. The pH of each of these solutions is
about 11 to be equivalent to the pH in each of Examples 1
25 to 4.
5
10
15
18
From these matters, it is unbelievable that the
material SS400 is restrained from being corroded by a
corrosion inhibitor since the corrosion inhibitor is an
alkali.
Comparative Example 4 demonstrates a case where Na2C03
is added. The pH thereof is equivalent to the pH (= 11) in
Examples 1 to 4. However, the generated gas quantity is 95
mL/dm2
• Thus, the corrosion is not restrained in the same
way as in the case of NH3 •
Table 2 shows the gas (hydrogen) quantity generated
in each of the others of the made corrosion tests using, as
its test liquid, the mixed cooling medium into which one of
the various alkalis was added. In the test, the molar
fraction of water in the mixed cooling medium was 0.95.
19
[Table 2]
Gas (hydrogen) quantity generated by corrosion of 88400
immersed in a mixed coolant to which each of various alkalis was added
Comparative
Example 5 Example 6 Example 7 Example 8
Comparative Comparative Comparative
Example 5 Example 6 Example 7 Example 8
Additive: - UOH LiOH Ca(OH)2 NaOH NH3 NH3 Na2C0 corrosion inhibitor 3
Concentration (M) - 0.125 0.02 0.02 0.1 1.0 0.1 0.1
Molar fraction 0.95 0.95 0.95 0.95 0.95 0.95 0.95 0.95
of water
pH 5.4 11.8 11.5 12.0 11.1 11.0 10.9 11.1
Generated gas 80 0.15 0.25 0.08 0.12 75 60 65
quantity (mlldm2)
From this table, the following are understood:
5 Comparative Example 5 shows a result obtained by
investigating the gas quantity generated in one of the made
corrosion tests in the mixed cooling medium to which no
corrosion inhibitor is added. The generated gas quantity
is 80 mL/dm2
•
10 Examples 5 and 6 demonstrate cases where LiOH is
added as the corrosion inhibitor. Equivalently to the
respective corresponding cases shown in Table 1, where the
molar fraction of water is 0.85, the generated gas quantity
is extremely lowered to restrain the corrosion.
15 Example 7 demonstrates a case where Ca(OH) 2 is added
as the corrosion inhibitor. Equivalently to the
corresponding case shown in Table 1, where the molar
fraction of water is 0.85, the generated gas quantity is
extremely lowered to restrain the corrosion.
20
Example 8 demonstrates a case where NaOH is added as
the corrosion inhibitor. Equivalently to the corresponding
case shown in Table 1, where the molar fraction of water is
0.85, the generated gas quantity is extremely lowered to
5 restrain the corrosion.
However, when an alkali is used at a concentration
equivalent to each of the concentrations as described above
but the alkali is NH3 shown in Comparative Example 6 or 7,
or Na2C03 shown in Comparative Example 8, no corrosion-
10 restraining effect is exhibited in the same manner in the
cases where the molar fraction of water is 0.85.
From these matters, it is unbelievable that the
material SS400 is restrained from being corroded by a
corrosion inhibitor since the corrosion inhibitor is an
15 alkali.
Table 3 shows the gas (hydrogen) quantity generated
in each corrosion test equivalent to the above-mentioned
tests, using, as its test liquid, the mixed cooling medium
to which one out of various oxoates was added. In the test,
20 the molar fraction of water in the mixed cooling medium was
0.85. In this Table, Comparative Example 1 is also shown
together.
21
[Table 3]
Gas (hydrogen) quantity generated by corrosion of SS400 immersed
in a mixed coolant to which each of various corrosion inhibitors was added
Comparative
Example 9 Example 10 Example 11 Example 12 Example 13 Example 14
Example 1
C6H5Na03S
Additive: - Li2Mo04 Na3V04 Na2Si03 HNa20 3P (sodium NaCI0 corrosion inhibitor 4 benzenesulfonate)
Concentration (M) - 0.01 0,01 0.01 0.01 0.01 0.01
Molar fraction 0.85 0.85 0.85 0.85 0.85 0.85 0.85
of water
pH 5.2 5.4 5.8 4.8 4.9 5.2 4.7
Generated gas
quantity 120 0.08 0.1 0.25 0.3 0.22 0.18
(ml/dm2)
From this table, the following are understood:
5 Example 9 demonstrates a case where Li2Mo04 is added
as the corrosion inhibitor. As compared with the case
demonstrated as Comparative Example 1, in which no
corrosion inhibitor is contained, this case shows an
extremely lowered generated gas quantity so that the
10 corrosion is restrained.
Example 10 demonstrates a case where sodium
orthovanadiate (Na3V04 ) is added as the corrosion inhibitor.
As compared with the case demonstrated as Comparative
Example 1, in which no corrosion inhibitor is contained,
15 this case shows an extremely lowered generated gas quantity
so that the corrosion is restrained.
Example 11 demonstrates a case where sodium
metasilicate (Na2Si03 ) is added as the corrosion inhibitor.
5
22
As compared with the case demonstrated as Comparative
Example 1, in which no corrosion inhibitor is contained,
this case shows an extremely lowered generated gas quantity
so that the corrosion is restrained.
Example 12 demonstrates a case where sodium
phosphonate (HNa20 3P (disodium hydrogenphosphite) is added
as the corrosion inhibitor. As compared with the case
demonstrated as Comparative Example 1, in which no
corrosion inhibitor is contained, this case shows an
10 extremely lowered generated gas quantity so that the
corrosion is restrained.
Example 13 demonstrates a case where sodium
benzenesulfonate (C6H5Na03S) is added as the corrosion
inhibitor. As compared with the case demonstrated as
15 Comparative Example 1, in which no corrosion inhibitor is
contained, this case shows an extremely lowered generated
gas quantity so that the corrosion is restrained.
Example 14 demonstrates a case where sodium
perchlorate (NaCl04 ) is added as the corrosion inhibitor.
20 As compared with the case demonstrated as Comparative
Example 1, in which no corrosion inhibitor is contained,
this case shows an extremely lowered generated gas quantity
so that the corrosion is restrained.
The corrosion inhibitors in Examples 9 to 14 are
25 collectively called the "oxoate" in the present
23
specification. As demonstrated in these working examples,
when the oxoate is added at various low concentrations, the
oxoate exhibits a remarkable corrosion-restraining effect
in the same manner as in the case of the addition of the
5 alkali even when the oxoate-added mixed cooling medium is
hardly varied in pH.
Table 4 shows a result obtained by making each
corrosion test equivalent to the above-mentioned tests,
using a test liquid in which one out of various absorption
10 type corrosion inhibitors used in ordinary cooling-water
was added to the water/1,4-dioxane mixed cooling medium.
In the mixed cooling medium, the molar fraction of water
was 0.85. The testing temperature was 90°C. In this table,
Comparative Example 1 is also shown together.
15 [Table 4]
Gas (hydrogen) quantity generated by corrosion of 88400 immersed
in a mixed coolant to which each of various adsorption-type corrosion inhibitors was added
Comparative Comparative Comparative Comparative Comparative
Example 1 Example 9 Example 10 Example 11 Example 12
Additive: - C6H12N4 CH4N2S Dimethyl- (hexamethylene- Hexanethiol
corrosion inhibitor tetra mine) (thiourea) hexadecylamine
Concentration (M) - 0.1 0.1 0.1 O.ot
Molar fraction 0.85 0.85 0.85 0.85 0.85
of water
pH 5.2 5.2 5.3 5.0 4.9
Generated gas 120 115 93 120 118
quantity (ml/dm2)
From this table, the following are understood:
Comparative Example 9 demonstrates a case where
24
hexamethylenetetramine, which is used as a corrosion
inhibitor in cooling-water, is added. Even when
hexamethylenetetramine, which exhibits a corrosionrestraining
effect in cooling-water, is added to the
5 water/dioxane mixed cooling medium, this compound does not
exhibit any corrosion-restraining effect in the cooling
medium.
Comparative Example 10 demonstrates a case where
thiourea, which is used as a corrosion inhibitor in
10 cooling-water, is added. Even when thiourea, which
exhibits a corrosion-restraining effect in cooling-water,
is added to the water/dioxane mixed cooling medium, this
compound does not exhibit any corrosion-restraining effect
in the cooling medium.
15 Comparative Example 11 demonstrates a case where
dimethylhexadecylamine, which is used as a corrosion
inhibitor in cooling-water, is added. Even when
dimethylhexadecylamine, which exhibits a corrosionrestraining
effect in cooling-water, is added to the
20 water/dioxane mixed cooling medium, this compound does not
exhibit any corrosion-restraining effect in the cooling
medium.
Comparative Example 12 demonstrates a case where
hexanethiol, which is used as a corrosion inhibitor in
25 cooling-water, is added. Even when hexanethiol, which
25
exhibits a corrosion-restraining effect in cooling-water,
is added to the water/dioxane mixed cooling medium, this
compound does not exhibit any corrosion-restraining effect
in the cooling medium.
5 Table 5 shows a result obtained by making each
corrosion test equivalent to the afore-mentioned corrosion
tests, using a test liquid in which one out of various
oxidation type corrosion inhibitors used in ordinary
cooling-water was added to the water/1,4-dioxane mixed
10 cooling medium. In the mixed cooling medium, the molar
fraction of water was 0.85. The testing temperature was
90°C. In this table, Comparative Example 1 is also shown
together.
[Table 5]
Gas (hydrogen) quantity generated by corrosion of 88400 immersed
in a mixed coolant to which each of various oxidation-type corrosion inhibitors was added
Comparative Comparative Comparative Comparative Comparative
Example 1 Example 13 Example 14 Example 15 Example 16
Additive: - Hydrogen Potassium Sodium Ceriumammonium
corrosion inhibitor peroxide nitrate nitrite nitrate
Concentration (M) - 1.0M 0.1M 0.1M 0.05M
Molar fraction 0.85 0.85 0.85 0.85 0.85
of water
pH 5.2 4.8 5.3 5.5 4.1
Generated gas 120 98 113 105 145
quantity {mlldm2)
15
From this table, the following are understood:
Comparative Example 13 demonstrates a case where
hydrogen peroxide is added to the water/dioxane mixed
26
cooling medium. Even by the addition of hydrogen peroxide,
the peroxide does not exhibit any corrosion-restraining
effect in this cooling medium.
Comparative Example 14 demonstrates a case where
5 nitrate ions (potassium nitrate) are added to the
water/dioxane mixed cooling medium. Even by the addition
of potassium nitrate, which exhibits a corrosionrestraining
effect in cooling-water, the nitrate does not
exhibit any corrosion-restraining effect in this cooling
10 medium.
Comparative Example 15 demonstrates a case where
nitrite ions (sodium nitrite) are added to the
water/dioxane mixed cooling medium. Even by the addition
of sodium nitrite, which exhibits a corrosion-restraining
15 effect in cooling-water, the nitrite does not exhibit any
corrosion-restraining effect in this cooling medium.
Comparative Example 16 demonstrates a case where
nitrate ions (ceriumammonium nitrate) are added to the
water/dioxane mixed cooling medium. Even by the addition
20 of ceriumammonium nitrate, which exhibits a corrosionrestraining
effect in cooling water, the nitrate does not
exhibit any corrosion-restraining effect in this cooling
medium.
Table 6 shows a result obtained by making each
25 corrosion test equivalent to the afore-mentioned corrosion
27
tests, using a test liquid in which one out of various
precipitation type corrosion inhibitors used in ordinary
cooling-water was added to the water/1,4-dioxane mixed
cooling medium. The molar fraction of water in the mixed
5 cooling medium was 0. 85. The test temperature was 90°C. In
this table, Comparative Example 1 is also shown together.
[Table 6]
Gas (hydrogen) quantity generated by corrosion of SS400 immersed
in a mixed coolant to which each of various precipitation-type corrosion inhibitors was added
Comparative Comparative Comparative Comparative
Example 1 Example 17 Example 18 Example 19
Additive: - Ce(N03) 3 8-Qinolinol Sodium octylpropionate
corrosion inhibitor
Concentration (M) - O.Dl 0.1 0.1
Molar fraction 0.85 0.85 0.85 0.85
of water
pH 5.2 4.9 5.0 4.2
Generated gas 120 103 96 89
quantity (ml/dm2)
10 From this table, the following are understood:
Comparative Example 17 demonstrates a case where
cerium nitrate is added to the water/dioxane mixed cooling
medium. Even by the addition of cerium nitrate, the
nitrate does not exhibit any corrosion-restraining effect
15 in this cooling medium.
Comparative Example 18 demonstrates a case where 8-
quinolinol is added to the water/dioxane mixed cooling
medium. Even by the addition of 8-quinolinol, this
compound does not exhibit any corrosion-restraining effect
28
in this cooling medium.
Comparative Example 19 demonstrates a case where
sodium octylpropionate is added to the water/dioxane mixed
cooling medium. Even by the addition of sodium
5 octylpropionate, the salt does not exhibit any corrosionrestraining
effect in this cooling medium.
Table 7 shows a result obtained by making each
corrosion test equivalent to the afore-mentioned corrosion
tests, using a test liquid in which one out of various
10 combinations of an oxoate with an alkali metal hydroxide
was added to the water/1,4-dioxane mixed cooling medium.
In this table, Comparative Example 1 is also shows together.
[Table 7]
Gas (hydrogen) quantity generated by corrosion of 88400 immersed
in a mixed coolant to which each combination of an oxoate and a hydroxide of an alkali metal was added
Comparative Example 15 Example 16 Example 17 Example 18
Example 1
Additive: corrosion - LiOH UOH Ca(OH) 2 NaOH
inhibitor (1)
Concentration (M) 0.1 0.05 0.02 0.1
Additive: corrosion
C6H5Na03S
- Li2Mo04 (sodium Na2V04 HNa20P
inhibitor (2) benzenesulfonate)
Concentration (M) - 0.01 0.01 0.01 0.01
Molar fraction
of water
0.85 0.85 0.85 0.85 0.85
pH 5.2 11.8 11.9 11.5 11.9
Generated gas 120 0.35 0.25 0.32 0.28
quantity (ml/dm2)
15
From this table, the following are understood:
Example 15 demonstrates a case where lithium
29
hydroxide and lithium molybdate are added as corrosion
inhibitors. Example 15 shows an extremely lowered
generated gas quantity as compared with Comparative Example
1, which contains no corrosion inhibitor, so that the
5 corrosion is restrained.
Additionally, in Example 15, the additives are
additives used also for an absorption liquid in the
absorber. For this reason, even when mist of the mixed
cooling medium in the evaporator is blended into the
10 absorption liquid in the absorber, only a small effect is
produced. Thus, it can be mentioned that the corrosion
inhibitors are most preferable corrosion inhibitors.
Example 16 demonstrates a case where lithium
hydroxide and sodium benzenesulfonate are added as
15 corrosion inhibitors. Example 16 shows an extremely
lowered generated gas quantity as compared with Comparative
Example 1, which contains no corrosion inhibitor, so that
the corrosion is restrained.
Example 17 demonstrates a case where calcium
20 hydroxide and sodium orthovanadate are added as corrosion
inhibitors. Example 17 shows an extremely lowered
generated gas quantity as compared with Comparative Example
1, which contains no corrosion inhibitor, so that the
corrosion is restrained.
25 Example 18 demonstrates a case where sodium hydroxide
30
and sodium phosphonate are added as corrosion inhibitors.
Example 18 shows an extremely lowered generated gas
quantity as compared with Comparative Example 1, which
contains no corrosion inhibitor, so that the corrosion is
5 restrained.
Table 8 shows a solidifying point of a solution in
which each of various corrosion inhibitors was added to the
water/dioxane mixed cooling medium. The molar fraction of
water in the mixed cooling medium was 0.85.
10 [Table 8]
Solidifying point of water/dioxane/corrosion-inhibitor solution
Corrosion inhibitors
Molar fraction Corrosion
of water inhibitor: none Li0H(0.05M) LiOH(O.lM) Li2Mo04 (0.01M) Li2Mo04 (0.002M)
0.85 -l5°C -16°C -19°C -17°C -15°C
From this table, the following are understood:
When no corrosion inhibitor is added thereto, the
15 solidifying point of the solution is -15°C.
Also when each of the corrosion inhibitors is added
thereto, the solidifying point is slightly varied. The
solidifying point tends to be lowered by a temperature of 0
to 4 °C. The lowering in the solidifying point does not
20 produce an effect onto the absorption refrigerator of the
present invention. Thus, the addition of the corrosion
inhibitor can keep characteristics of the water/dioxane
31
mixed cooling medium.
Fig. 2 is a graph showing a dependency of the gas
quantity generated in each corrosion test using the mixed
cooling medium to which LiOH was added upon the
5 concentration of the alkali. Each test piece used therein
was a material 88400.
As shown in Fig. 2, by adding LiOH at a concentration
of 0.005 M, the generated gas quantity is abruptly lowered
to about 1/80. Thus, the addition of LiOH at a
10 concentration of at least 0.005 M makes it possible to
restrain the corrosion sufficiently. When the LiOH is
added up to 0.02 M, the generated gas quantity lowers as
the LiOH-added amount is increased. However, at a
concentration of 0.02 M or more, the degree of the lowering
15 in the generated gas quantity is decreased.
20
Fig. 3 shows a dependency of the gas quantity
generated in each corrosion test using the mixed cooling
medium to which Li2Mo04 was added upon the concentration of
Li2Mo04 • Each test piece used therein was a material 88400.
From this figure, it is understood that: as the
concentration of Li2Mo04 added is increased, the generated
gas quantity linearly lowers in a logarithmic manner
thereto. By the addition thereof at a concentration of
0.002 M, the generated gas quantity lowers to about 1/10 of
25 that in the case of no addition of Li2Mo04 ; thus, the
32
corrosion can be sufficiently restrained.
The following will describe results obtained by
making corrosion tests about oxygen-free copper, which is a
structural material other than the material SS400 of the
5 absorption refrigerator.
In each of the corrosion tests, in the same way as in
the above-mentioned SS400 corrosion tests, a sealed tube
made of Pyrex (registered trademark) glass (glass ample)
was produced. The sealed tube was kept in a thermostat
10 having a temperature kept at 90°C over at longest 2000
hours.
After the corrosion test, the test piece was taken
out, and the corrosion quantity thereof was calculated out
from the difference between the mass of the test piece
15 before the corrosion test and that after this test.
20
Fig. 4 is a graph showing a change with time in the
corrosion quantity of oxygen-free copper in the water/1,4-
dioxane mixed cooling medium (molar fraction of water:
0.85) at 90°C.
When no inhibitor (corrosion inhibitor) is added to
the cooling medium, the corrosion quantity rises up
abruptly after 500 hours elapse, so as to increase linearly
with time. By contrast, when the inhibitor of LiOH is
added thereto at a concentration of 0.3% (0.125 M), the
25 corrosion quantity is equivalent to that when no inhibitor
33
coexists with the cooling medium till 500 hours. However,
after 500 hours, the corrosion rate lowers with time. From
this matter, it is understood that the addition of LiOH at
the concentration of 0.3% makes it possible to restrain the
5 corrosion of copper.
Table 9 shows the corrosion quantity obtained when
oxygen-free copper was immersed over 2000 hours in the
mixed cooling medium to which each corrosion inhibitor
other than the 0.3% LiOH was added as the corrosion
10 inhibitor. The molar fraction of water was 0.85, and the
temperature was 90°C. Table 9 also shows the case where no
corrosion inhibitor was added to the medium.
[Table 9]
Corrosion inhibitors
Corrosion
LiOH NaOH NaOH Ca(OH)2
U2Mo04 inhibitor: none NH3 (0.01M)
(0.02M) (0.125M) (0.02M) (0.02M)
+LiOH (0.02M)
(0.125M)
3.0 0.8 0.65 0.85 0.90 0.8 15.5
15
From this table, it is understood that an effect of
restraining the corrosion of copper is exhibited in the
case of lowering the LiOH concentration to 0.02 M, in the
case of adding NaOH or Ca(OH) 2 instead of LiOH, and in the
20 case of adding the combination of LiOH with Li2Mo04 in the
same manner as in the case of using the 0.125M LiOH.
By contrast, when an alkali is added but the alkali
34
is NH3 , no corrosion-restraining effect is exhibited;
conversely, the corrosion is accelerated. This would be
because copper and ammonia form a complex.
For the results in Fig. 4 and Table 9, oxygen-free
5 copper was used as an example of the copper alloy. However,
the copper alloy is not limited thereto, and may be, for
example, 7-3CuNi alloy or 9-1CuNi alloy.
In absorption refrigerators in each of which the
working medium of the lithium-bromide/water system is used
10 to generate the cold energy corresponding to the freezing
point of water or lower, a means for adding 1,4-dioxane to
water as a cooling medium has been hitherto known in order
to make this apparatus simple and small, and attain some
other purpose. However, no technique has been known for
15 decreasing the corrosiveness of the mixed cooling medium in
which 1,4-dioxane is added to water.
According to the present invention, the addition of
the hydroxide of the alkali metal or alkaline earth metal
or the oxoate to the water/dioxane mixed cooling medium
20 makes it possible to decrease the corrosion of the
structural material in the cooling medium largely, and
configure the apparatus using this cooling medium.

WHAT IS CLAIMED IS:
1. A working medium for absorption refrigerators that is
to contact a carbon steel or a copper alloy that is a
5 structural material of any one of the absorption
10
15
20
25
refrigerators,
the working medium comprising:
water; and 1,4-dioxane,
and further comprising a corrosion inhibitor,
wherein the corrosion inhibitor includes one or more
selected from the group consisting of respective hydroxides
of any alkali metal and any alkaline earth metal, and
respective oxoates.
2. The working medium according to claim 1,
wherein the oxoates are molybdates, tungstates,
vanadiates, silicates, phosphates, polyphosphates,
phosphonates, hypochlorites, chlorites, perchlorates and
sulfonates.
3. The working medium according to claim 1,
wherein the selected corrosion inhibitors are lithium
hydroxide and lithium molybdate.
4 . The working medium according to claim 1,
36
having a solidifying point of 0°C or lower .
5. An absorption refrigerator comprising:
an evaporator;
an absorber;
a generator; and
a condenser,
wherein the working medium recited in claim 1 is used
as a tooling medium circulated in the evaporator and the
condenser.
Dated this o.J>h Day of Septemb