JPH10260173A - Measuring method for refrigerant for refrigerating machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a measuring method Mo concentration which is not affected by LiBr and can easily, speedily, and accurately analyze the concentration of an Mo inhibitor at the site where a refrigerating machine is used. SOLUTION: In this measuring method of Mo concentration in an LiBr liquid for a refrigerating machine containing Li2 and MoO4 as a corrosion inhibitor, an LiBr liquid, which is the object to be measured, is sampled, and hydrochloric acid and L(+)-ascorbic acid are added to it to reduce hexavalent Mo into pentavalent Mo and to reduce trivalent Fe, which interferes with measurements, into divalent Fe. Then, a thiocyanate solution is added to produce a thiocyanic acid-molybdenum complex to detect Mo concentration in the LiBr liquid by a colorimetric analysis.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a refrigerant for an absorption refrigerator.
Used as a corrosion inhibitor_TwoMoO _FourIncluding
Of the refrigerant liquid for the refrigerator for detecting the Mo concentration in the LiBr liquid
Related to the measurement method.

[0002]

2. Description of the Related Art Li used as a refrigerant for an absorption refrigerator
Li ₂ MoO ₄ is added to the Br solution as a corrosion inhibitor. Li ₂ MoO ₄ in the LiBr aqueous solution has low solubility and a small effective concentration range as a corrosion inhibitor, and the concentration changes during use.
And it is necessary to grasp accurately. Conventionally, as a method for determining Mo, permolybdate spectrophotometry, thiocyanate extraction spectrophotometry, dithiol extraction spectrophotometry, and the like, when measuring Mo in a high-concentration LiBr solution, Li
Under the influence of Br, stable color development was not obtained, and accurate measurement could not be performed. As a method for solving such a problem, a method using a thioglycolate has been proposed (Japanese Patent Application Laid-Open No. 8-105835). This method has drawbacks such as the fact that the thioglycolic acid used emits offensive odor, and the absorbance differs even if the Mo concentration is the same depending on the LiBr concentration, so that it is necessary to correct the LiBr concentration. In addition, as a method for measuring Mo with high accuracy in the presence of high concentration LiBr, there is an IPC emission spectrometric method. However, this method requires special equipment and is not suitable for quick and simple on-site measurement.

[0003]

The thiocyanate absorptiometry in the analysis of Mo is known, but the LiBr liquid for the absorption refrigerator contains Fe (iron) which is a corrosion product, In the conventional thiocyanate absorptiometry, the color tone of the coloring solution changes due to the high concentration of LiBr, or Fe develops simultaneously with Mo, and the developed Fe gradually fades, so that a stable absorbance cannot be obtained. An accurate measurement could not be made. On the other hand, the Mo inhibitor (usually added in the form of Li ₂ MoO ₄ ) added to the LiBr solution of the refrigerator suppresses the corrosive action of LiBr,
During operation, it is consumed for forming a protective film, and gradually ages and its concentration changes. In order to maintain the corrosion inhibitory effect, it is necessary to appropriately control the concentration of the Mo inhibitor, and there has been an urgent need to develop a simple, quick and highly accurate method for measuring the Mo inhibitor at the site of use. In view of the above prior art, the present invention
It is an object of the present invention to provide a method for measuring a refrigerant liquid for a refrigerator, which is not affected by iBr, and enables a concentration analysis of a Mo inhibitor to be performed simply, quickly and accurately at a use site of the refrigerator.

[0004]

Means for Solving the Problems The present inventors have proposed LiBr.
As a result of various investigations on the method for measuring the Mo concentration in the liquid, the hexavalent Mo in the liquid was reduced to pentavalent with hydrochloric acid-L (+)-ascorbic acid, and then measured by thiocyanate spectrophotometry. The present inventors have found that the above objects can be achieved by doing so, and have completed the present invention.

[0005] That is, the present invention relates to the use of Li as a corrosion inhibitor.
A method for measuring the Mo concentration in a LiBr solution for a refrigerator containing ₂ MoO ₄ , wherein a LiBr solution to be measured is collected,
Addition of hydrochloric acid and L (+)-ascorbic acid to add hexavalent Mo
Is reduced to pentavalent and trivalent Fe
Is reduced to divalent, a thiocyanate solution is added to generate a thiocyanate-molybdenum complex, and colorimetric analysis is performed to detect the Mo concentration in the LiBr solution. It is a measuring method. In a preferred embodiment of the method of the present invention, coexistence of copper in a sample solution is provided.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS LiBr for absorption refrigerators is usually 30
Used in an aqueous solution of 55 wt% of the concentration range, Li ₂ MoO ₄ is added at a concentration of 100~300ppm a corrosion inhibitor. The present invention is to perform colorimetric analysis after adding a potassium thiocyanate solution to the LiBr solution to form a color, and to easily and quickly determine the concentration of the Mo inhibitor in the high concentration range of the LiBr concentration of 30 to 55% by weight. Accurate quantitative evaluation can be performed.

Hereinafter, the method of the present invention will be described according to a process. Although the amount of the sample collected is set to about 1 g for convenience of explanation, it is needless to say that the amount can be appropriately changed according to the situation at the time of analysis. In the method of the present invention, first, LiB for a refrigerator including Li ₂ MoO ₄ as a corrosion inhibitor is used.
About 1 g of the r solution is collected, and hydrochloric acid and L (+)-ascorbic acid are added to reduce hexavalent Mo to pentavalent and to reduce trivalent Fe, which hinders measurement, to divalent. In the measurement, the generation of bromine is suppressed by using hydrochloric acid for reducing Mo from hexavalent to pentavalent and adjusting the acid concentration.
By adding (+)-ascorbic acid, it is possible to prevent interference with iron, and a stable result is obtained.

The amount of hydrochloric acid to be added is 5 (1 + 1) hydrochloric acid (equal volume mixture of concentrated hydrochloric acid and water) per g of LiBr solution of the sample.
If it is 10 to 10 ml, a stable absorbance can be obtained. The amount of L (+)-ascorbic acid added was LiBr
If it is 20 mg or more per 1 g of liquid, hexavalent Mo can be reduced to pentavalent Mo without being affected by Fe. A preferable range of the addition amount is about 30 to 100 mg.

Hydrochloric acid and L (+)-ascorbic acid are added to the sample, stirred and dissolved, and then an aqueous solution of potassium thiocyanate is added to form a thiocyanic acid-molybdenum complex, which is diluted to a fixed amount (for example, 20 ml). The Mo concentration can be measured by performing colorimetric analysis.
The addition amount of potassium thiocyanate is 5% in a 25% by weight aqueous solution.
A stable absorbance can be obtained at about 7 ml. As the thiocyanate, sodium thiocyanate, ammonium thiocyanate and the like can be used in addition to potassium thiocyanate.

[0010] Further, a water-soluble copper compound such as copper sulfate is added at the time of coloring operation with thiocyanate to add a trace amount (10 μm).
g or more) of copper, the color development reaction is promoted, the reaction is completed instantaneously, and the measurement time can be reduced and the measurement accuracy can be improved.

Since the absorption maximum of the thiocyanate-molybdenum complex is around 460 nm regardless of the presence or absence of LiBr, a certain amount of the LiBr solution is sampled as described above, and hydrochloric acid, L (+)-ascorbic acid and thiocyanate are used. After coloring by adding an acid salt solution, the absorbance at a specific wavelength around 460 nm is measured with a spectrophotometer. The measurement device usually uses an absorptiometer, but if a portable photoelectric colorimeter that uses a filter for setting the measurement wavelength is used for the absorbance measurement, the Mo inhibitor can be easily measured at the site where the absorption refrigerator is used. Is possible.

[0012] The present invention relates to MoO ₄ ^{2- of} LiBr solution for refrigerators.
Is developed with a thiocyanate to perform colorimetric analysis.
That is, hydrochloric acid and L (+)-ascorbic acid are added to the LiBr solution to reduce Mo from hexavalent to pentavalent, and to reduce trivalent Fe ions, which hinder measurement, to divalent. Is added to form a thiocyanate-molybdenum complex, which develops a reddish brown color. This complex is stable for at least 100 minutes and has a LiBr concentration of 30 to 55% by weight.
Shows a constant absorbance without being affected by changes in the LiBr concentration in the range of.

[0013] The method of the present invention is characterized by utilizing the reducing power of L (+)-ascorbic acid. However, if a reducing agent having a strong reducing power is used, hexavalent Mo is reduced to trivalent Mo. As a result, the coloring of Mo itself becomes weak. Also,
If the reducing power is too weak, the reduction of trivalent Fe becomes insufficient and F
The effect of e cannot be prevented.

[0014]

EXAMPLES The method of the present invention will be described more specifically with reference to the following examples. (Experimental Example 1) 100 ppm of Li ₂ MoO ₄ and 50 p
55 wt% LiBr aqueous solution containing pm Fe ³⁺ 1
g, a predetermined amount of hydrochloric acid, L (+)-ascorbic acid,
The color was developed by adding potassium thiocyanate and copper, and 20
The amount was adjusted to milliliters, and the absorbance at 460 nm was measured to determine the appropriate range of each addition amount. The effects of the amounts of hydrochloric acid, potassium thiocyanate, L (+)-ascorbic acid and copper added are shown in Tables 1 to 4, respectively.

[0015]

[Table 1]

[0016]

[Table 2]

[0017]

[Table 3]

[0018]

[Table 4]

From the results shown in Tables 1 and 2, hydrochloric acid (1 + 1) and potassium thiocyanate were added in an aqueous solution of 5 to 10 ml and 25% by weight, respectively, per 1 g of the LiBr aqueous solution used as the refrigerant for the refrigerator. It is understood that a stable absorbance can be obtained by adding 5 to 7 ml. Also, from Table 3, it can be seen that the effect of Fe can be suppressed if the amount of L (+)-ascorbic acid added is 20 mg or more per 1 g of the LiBr aqueous solution, and a sufficiently stable result can be obtained at about 30 to 100 mg. Further, from Table 4, it can be seen that stable color development can be obtained in a short time by coexisting 10 μg or more of Cu ions per 1 g of the LiBr aqueous solution.

Experimental Example 2 100 ppm Li ₂ MoO
₄ containing 30%, 40%, and 55% by weight, respectively, of L
1 g of an iBr aqueous solution was collected, 5 ml of hydrochloric acid (1 + 1) containing 4 μg / ml of Cu, 50 mg of L (+)-ascorbic acid and 25% by weight of potassium thiocyanate
5 ml of an aqueous solution was added to develop color, adjusted to 20 ml, and the absorbance at 460 nm was measured. The results are as shown in Table 5, and it can be seen that a constant value of the absorbance is obtained regardless of the LiBr concentration in the range of LiBr concentration 30 to 55% by weight which is used as a normal refrigerator refrigerant.

[0021]

[Table 5]

Example 1 1 g of LiBr solution for refrigerator
Dispense into a test tube (25 ml) with a stopper
Then, 50 mg of L (+)-ascorbic acid was added, and
5 ml of hydrochloric acid (1 + 1) containing μg / milliliter
Was added. Roll the test tube 6-7 times to stir the liquid,
After dissolving L (+)-ascorbic acid, potassium thiocyanate
5 ml of aqueous solution (25% by weight)
The liquid volume was adjusted to 20 ml. Absorbance of the solution
Is a photoelectric colorimeter with a 460 nm filter (Tokyo, Japan)
Measured by ANA-18A manufactured by Kodensha Co., Ltd.
Li using the calibration curve _TwoMoO_FourCalculate the concentration
Was. As a result, the LiBr solution Li_TwoMoO_FourDark
The degree was 62 ppm (μg / g). In addition, LiBr
Take 1 ml of liquid and measure the specific gravity separately.
The weight may be converted. The calibration curve was determined by the following method.

(Preparation of Calibration Curve) 1 g of LiBr (55% by weight) was placed in five test tubes with stoppers each having a scale of 25 ml.
And a Li ₂ MoO ₄ aqueous solution (50 μg Li
₂ MoO ₄ / ml) at 0, 1.0, 2.0,
3.0, 4.0 milliliters were added. Next, 50 mg of L (+)-ascorbic acid was added, and 5 ml of hydrochloric acid (1 + 1) containing 2 μg / ml of Cu was added. The test tube was turned over 6 to 7 times to stir the solution, and after dissolving L (+)-ascorbic acid, 5 ml of potassium thiocyanate solution (25% by weight) was added, and the solution was adjusted to 20 ml with pure water. Was. A photoelectric colorimeter (manufactured by Tokyo Koden Co., Ltd.) in which a filter of 460 nm was set for the absorbance of the solution
ANA-18A) to prepare a calibration curve.

(Example 2, Comparative Example 1)
In the LiBr solution of the refrigerator operating at three locations, including the solution
Li _TwoMoO_FourThe method of the present invention and ICP emission spectrometry
(Measurement device: Seiko SPS 1200VR, measurement wave
Table 6 shows the results of measurement at 202.03 nm. table
From FIG. 6, the measured values of both are in good agreement, and the method of the present invention shows that
Quick and simple Mo inhibitor in LiBr solution for collection chiller
It has been confirmed that the method is sufficiently applicable as an analytical method.

[0025]

[Table 6]

Comparative Example 2 LiBr solution (LiBr concentration 55.6% by weight, Fe
8.3 ppm) into four test tubes (25 ml) each with a scale and a stopper.
And 1.25 ml were collected, and pure water was added to make 10 ml. Sulfuric acid (1 + 1) in each test tube
1 ml of an equal volume mixed solution of concentrated sulfuric acid and water, 5 ml of a 25% by weight aqueous solution of potassium thiocyanate and 50 g of stannous chloride were dissolved in 200 ml of hydrochloric acid (1 + 1) and made up to 500 ml with pure water. And made up to 20 ml with pure water. The obtained sample solution was measured at 460 nm using a spectrophotometer.
Was measured for absorbance. Table 7 shows changes in absorbance for 5 to 20 minutes after color development. From Table 7, it can be seen that the change in absorbance with time is large in this method, and a stable measurement result cannot be obtained.

[0027]

[Table 7]

[0028]

According to the method of the present invention, hexavalent Mo in a liquid is reduced to pentavalent with hydrochloric acid-L (+)-ascorbic acid, and then absorbed by measuring by thiocyanate absorptiometry. The concentration of the Mo inhibitor in the LiBr solution for the refrigerator can be simply, quickly and accurately measured at the site where the refrigerator is used without being affected by the concentration of LiBr or the Fe content. Further, by allowing a small amount of Cu to coexist at the time of measurement, more rapid measurement is possible.

Claims (2)

[Claims] 1. A method for measuring the Mo concentration in a LiBr solution for a refrigerator containing Li ₂ MoO ₄ as a corrosion inhibitor, wherein a LiBr solution to be measured is collected, and hydrochloric acid and L (+) −
After reducing hexavalent Mo to pentavalent by adding ascorbic acid and reducing trivalent Fe which interferes with measurement to divalent, a thiocyanate solution is added to form a thiocyanate-molybdenum complex. And colorimetric analysis of M in the LiBr solution
o A method for measuring a refrigerant liquid for a refrigerator, comprising detecting a concentration. 2. The method for measuring a refrigerant liquid for a refrigerator according to claim 1, wherein copper coexists in the sample liquid.