JPH06105247B2 - Method and apparatus for measuring solution saturation point - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for measuring a saturation point of a solution and an apparatus thereof.

(Background of the Invention) In a device using water such as a boiler, a cooling tower, and a desulfurization process of exhaust gas, in which water is significantly evaporated, when a component contained in water becomes saturated, a component having a limit solubility is piped. It adheres to the equipment surface such as to form a scale.
If such scale is deposited, the pipe may be clogged, the thermal conductivity may be deteriorated, and the operation may have to be stopped to remove the scale.

Therefore, in the above apparatus and the like, it is extremely important for equipment management to measure whether or not the solution state is in a state where scale is generated, that is, whether or not it reaches a saturated state.

There are various methods such as a method for measuring a saturated concentration of an aqueous solution and a method for monitoring, such as a method based on measurement of enthalpy change, a method by colorimetric analysis, and a method of measuring electric conductivity. These measure changes that occur physically and chemically, but the measurement is generally complicated.

In particular, in order to measure the saturation point of calcium sulfate in an aqueous solution that is a source of scale that accumulates on the above pipes, it takes a considerable time to measure the saturation point when other chemical components are mixed. . Conventionally, a completely computerized chemical analysis method was used to measure the saturation point of calcium sulfate,
The concentration of calcium ion and sulfate ion in equilibrium with garcium sulfate is determined by chemical analysis, and the saturation concentration of calcium sulfate is calculated by this method. There is a problem that analysis time of ~ 5 hours is required.

(Object of the Invention) The present invention has been made to solve the above problems.
An object of the invention is to provide a saturation point measuring method and an apparatus therefor capable of obtaining a saturation point of a compound having a limit solubility in a solvent in a short time.

(Means for Solving the Problems) In the present invention according to the above object, a step of diluting a solution (stock solution) in which a compound having a limit solubility is dissolved, and a crystal structure of the same compound part (target compound) as the above compound Passing the diluted solution through a column filled with a solid solution having a tracer incorporated therein at a fixed ratio, dissolving the target compound and the tracer in the diluted solution, and saturating the diluted solution with the target compound; The tracer concentration of the diluted solution saturated with the target compound is measured, and from the concentration of the tracer, the amount of the target compound necessary to saturate the diluted solution is measured, and the measured amount of the target compound and the diluted solution are measured. The method is characterized by including the step of determining the saturation point of the stock solution from the dilution degree of.

The stock solution is preferably an aqueous solution of calcium sulfate, and the solid solution is preferably a eutectic of calcium sulfate and chromic acid or a salt thereof.

In addition, the above solid solution was added to the first aqueous solution of potassium chromate and calcium chloride whose pH was adjusted to about 7 and the second aqueous solution in which potassium sulfate was dissolved in hot water was quickly added while stirring and The suspension is suitably prepared by decanting the supernatant, washing the precipitate with a saturated aqueous solution of calcium sulfate, and then dehydrating.

Further, in the present invention, in a saturation point measuring device for measuring a saturation point of a solution (stock solution) in which a compound having a limit solubility is dissolved, a supply source for supplying a diluted solution of the stock solution, and a compound identical to the above compound ( A column filled with a solid solution in which a tracer is incorporated in a certain ratio in the crystal structure of the target compound), liquid feeding means for sending the diluted solution from the supply source to the solid solution of the column, and passing through the solid solution. It is characterized by comprising a measuring means for measuring the tracer concentration in the diluted solution and determining the saturation point of the compound in the stock solution from the measured value.

(Examples) Hereinafter, preferred examples of the present invention will be described in detail.

In FIG. 1, 10 is a dilute solution, in which the solution to be measured is diluted with a predetermined amount of solvent. For example, if the solution to be measured is an aqueous solution of calcium sulfate, dilute with water. Diluted solution 10 is valved by pipe 12 14
And the valve 14 is connected by a pipe 16 to a pump 18. 20 is a saturated solution, which is connected to the valve 14 by a pipe 22. Pump 18 is connected to valve 26 by line 24. 28 is a column in which a packing material 30 composed of a solid solution of a tracer and a target compound
Is filled. 32 is a flow cell of the spectrometer. An adjustment plunger 34 is provided at the top of the column 28,
The size of the space in which the packing 30 of the column 28 is accommodated can be adjusted. The valve 26 is connected to the column 28 by a pipe 36 which is connected to the flow cell by a pipe 38.
Connected to 32. The valve 26 is also connected to the pipe 38 by a bypass pipe 40. 42 is a discharge pipe.

The diluted solution 10 obtained by diluting the solution to be measured is in the column 28,
Filling material consisting of solid solution of target compound and tracer
Through which the diluted solution is saturated with the target compound and also the tracer is eluted. The diluted solution then flows into the flow cell 32, where the concentration of the tracer in the solution is measured by the spectrometer. From this measured value, the saturation point of the target compound in the solution to be measured before dilution is determined as described later.

The choice of the type of tracer is determined by whether or not the concentration of the tracer can be easily and accurately measured, and whether or not a solid solution is formed with the target compound at a constant ratio. For example, if the tracer develops a color in a solution like chromic acid, the tracer concentration can be continuously monitored by flowing it through a flow cell of a spectrometer. The saturation point or relative saturation point of the stock solution can be determined from the measured tracer concentration and the degree of dilution (level).

In particular, in the present invention, the relative saturation point of calcium sulfate in solution can be determined directly and quickly without directly analyzing a particular component, such as calcium sulfate.

Although calcium sulfate was used as an example of the target compound and chromic acid was used as the tracer here, it is needless to say that it can be applied to a combination of another target compound having a limit solubility and another tracer.

As mentioned above, this method uses tracer technology to directly measure the amount of calcium sulphate required to saturate a dilute solution of a pre-diluted stock solution. The dilute solution is passed through a column packed with a packing of calcium sulfate solid solution with a tracer incorporated into the crystal structure. Chromic acid or its salt is used as a tracer, and pure water is used for dilution. The diluted solution passing through the column directly flows into the flow cell of the spectrometer, where the concentration of dissolved chromic acid is measured. The amount of calcium sulfate is then calculated based on the known amount of chromic acid in solid solution. Since chromic acid is bound as an intrinsic solid solution in the crystal structure of calcium sulfate, the amount of chromic acid dissolved is proportional to the amount of dissolved calcium sulfate.

The flow rate through the column and the contact conditions with the packing in the column are set so that the calcium sulfate is saturated as the diluted solution passes through the column. The amount of calcium sulphate in the filler that is leached to saturate the diluted solution depends on the solubility of calcium sulphate in the solution and the saturation point at that time.

Determining the saturation point of a stock solution requires a dilute solution of two or more stock solutions.

The saturation point is expressed as a function of the degree of dilution, and as a reciprocal number at the point on the X axis of the calibration curve drawn by the data corresponding to the amount of calcium sulfate required to saturate the diluted solution.

To measure with the device shown in FIG.
Thus, a saturated solution 20 of the target compound, eg calcium sulphate, is bypassed through the column 28 by means of a tube 40 and fed directly to the measuring device, eg the flow cell 32 of the spectrometer. Next, operate the valve 14 to adjust the saturated solution 20
Instead of flowing the diluted solution 10 through the tube 40 into the flow cell 32.

When the tracer is chromic acid, the maximum absorption wavelength of chromic acid is 338 nm, but the pH of the solution changes to dichromic acid, which also changes the maximum absorption wavelength, so it is necessary to control the PH of the sample. .

Next, the valve 26 is operated to allow the diluted solution 10 to pass through the packing material in the column 28, and the absorbance is measured. Here, the measurement is repeated by diluting at least two kinds of stock solutions.

When the absorbance is not measured, the saturated solution 20 is sent to the column 28 and the diluted solution that has been flown before is washed out in order to stabilize the next measurement.

In the example, the column 28 had a diameter of 6 mm, and the packing 30 was packed in the column 28 so that the height thereof was about 20 mm. The volume of the plunger 34 provided on the upper portion of the column 18 decreases as the packing material 30 melts, but the packing material 30 can be pressed down by lowering the plunger 34. The fill 30 is preferably replaced when approximately 1/3 of the original volume has dissolved.

In this example, a spectrometer equipped with a low volume flow cell having a length of 1 cm and a volume of 0.014 ml was used, and the absorbance was recorded in a recorder.

Usually, the above process is performed at room temperature (25 ° C), but it can be performed at 40 to 60 ° C or lower (necessary for measuring calcium sulfate in the desulfurization step).

As is clear from the above, what is important in the present invention is to use a solid solution of the target compound and the tracer. The solid solution is prepared by a method compatible with its target compound and tracer. In the case of calcium sulphate and a tracer that can be detected by a colorimetric method, for example chromic acid or chromium as its salt, its solid solution is prepared according to the invention as follows.

a. An aqueous solution containing potassium chromate (K ₂ CrO ₄ ) and calcium chloride (CaCl ₂ ) in pure water is heated to about 50 ° C, and the pH is 6.5.
Or adjust to about 7.

b. Dissolve potassium sulfate in hot water and add to the above solution quickly with vigorous stirring.

c. Stir the precipitate formed in this solution, for example at 50 ° C. for 2 hours.

d. Then let the solution stand. Decant and discard the supernatant. The precipitate is further washed with a saturated solution of calcium sulfate. Then, it is filtered and dehydrated.

This gives a solid solution containing 2-3% by weight of chromic acid. This solid solution is preferably stored in a closed container.

Specific examples will be shown below.

Put 1600 ml of pure water in a 4 liter flask and dissolve 360 g of potassium chromate (K ₂ CrO ₄ ). While stirring the solution, add 24 mL of calcium chloride (CaCl ₂ · 2H ₂ O) to 600 ml of pure water.
Add 0 g of dissolved liquid. The CaCl ₂ solution is cooled below 50 ° C. before adding it to the K ₂ CrO ₄ solution. PH of the mixed solution is 1M-HC
Adjust the solution to 6.5-7 and then heat to 50 ° C.

Next, a solution prepared by dissolving 180 g of potassium sulfate (K ₂ SO ₄ ) in 1200 ml of pure water is added to the above CaCl ₂ / K ₂ CrO ₄ solution, taking care not to raise the temperature below 50 ° C. The mixed solution is stirred for about 2 hours while maintaining the temperature range of 40 to 50 ° C. After heating and stirring, the solution is left to stand. The supernatant is decanted and a saturated solution of calcium sulfate is added to the precipitate.
After stirring, the mixture is left to stand and the supernatant is decanted. The procedure of adding water, mixing, allowing to stand and decanting is repeated several times until the supernatant becomes pale yellow.

The solid solution of calcium sulfate containing 2-3% by weight of chromic acid thus obtained was placed in a column of 6 mm in diameter of about 20 mm.
The height of filling.

A saturated solution of calcium sulfate is passed through the flow cell.

The spectrometer output is adjusted using a solution of known concentration.

Dilute saturated solutions of calcium sulfate to make 90%, 70% and 50% saturated levels of solutions. The amounts of calcium sulphate required to re-saturate these solutions 1 at 25 ° C are 1.54, 4.61 and 7.68 mmol respectively.

By measuring these standard solutions, a calibration curve for the amount of dissolved calcium sulfate is determined and its linearity is evaluated.

This calibration curve can be used to determine the amount of calcium sulfate required to saturate the diluted solution.

Dilute a portion of the stock solution with pure water at room temperature of 25 ℃
Make a diluted solution of 0.5. A portion of the diluted solution is run directly into the flow cell for blank correction of absorbance. The absorption wavelength at this time is 338 nm. The diluted solution is then flowed through the column packed with packing at a flow rate of 1-2 ml / min. The diluted solution discharged from the column enters the flow cell, and the amount of chromic acid dissolved in the diluted solution is measured with a spectrometer.

Then, a saturated calcium sulfate solution is passed through the column to wash out and dilute the previously used diluted solution.

Dilute a portion of the stock solution to prepare second and third diluted solutions with dilutions of 0.7 and 0.9. These second and third diluted solutions are passed through the column and flow cell in the same manner as above.

Thus, the amount of chromic acid (and calcium sulfate) dissolved in each diluted solution is determined through the diluted solutions having three different dilutions of the stock solution. Determined by the measurement of the spectrometer,
The amount of calcium sulfate dissolved to saturate the diluted solution is plotted against the degree of dilution, and the saturation point of the undiluted stock solution can be immediately known from this figure.

At least two different dilutions are required, but it is preferred to use three different dilutions of dilute solution as described above. The absorbance obtained in this experiment is plotted as a function of dilution as shown in FIG. A straight line connects the data points and extends until it reaches the X axis. Thus, a curve (or straight line) is drawn between the values of the optimal data and extrapolates to the X axis (zero dissolved amount of calcium sulfate from the solid solution). This extrapolation value, the dilution value, represents the dilution of the stock solution in equilibrium with calcium sulfate.

Extensive theoretical calculations on solution composition show that for practical purposes, the reciprocal dilution is the relative saturation point of the sample.

The reciprocal of the extrapolation on the X axis, the dilution, gives the practical relative saturation of the stock solution supplied with the sample solution. In this example, the relative saturation was 1.06.

The data in this example use additional dilute solutions detailed in Figure 2 and other dilutions.

When the tracer cannot be measured by the colorimetric method, another measuring means is adopted according to the present invention. That is, the amount of tracer (and the amount of newly eluted target compound) in the solution when the diluted solution is saturated with the target compound due to the dissolution of the solid solution of the target compound and the tracer is measured.

What is important in this invention is that the saturation point of a solution of a compound having a critical solubility, such as calcium sulfate, can be determined practically, quickly and easily.

Further, in the above, the measurement of the solubility of calcium sulfate in pure water was shown, but in the present invention, other chemical components are present as seen in the measurement of calcium sulfate in the waste gas desulfurization step. Can also determine the amount of target compound. In FIG. 2, the data in the case of the calcium sulfate aqueous solution containing magnesium chloride at various concentrations are shown by circles and triangles. MgCl ₂ is a component contained when salsium sulfate is dissolved in water.

The concentration of the stock solution can be easily determined by measuring the concentration of the tracer.

Therefore, since the concentration and the saturation point of the stock solution are measured, the scale adhesion prevention can be easily controlled.

Although various embodiments of the present invention have been described above, the present invention is not limited to the above embodiments,
Of course, many modifications can be made without departing from the spirit of the invention.

(Effect of the invention) As described above, according to the present invention, the saturation point of the target compound can be known by measuring the concentration of the tracer, which is easy to measure, without directly measuring the target compound such as calcium sulfate. This is useful when it is difficult to directly measure the concentration of the target compound.

In particular, it is possible to easily measure the concentration and saturation point of the calcium sulfate aqueous solution, and it is possible to suitably carry out control to prevent scale adhesion to pipes and the like.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a preferred embodiment of the device of the present invention, and FIG. 2 is a graph plotting the absorbance of various diluted solutions. 10 …… diluted solution, 20 …… saturated solution, 12,16,22,24,36,38 …… tube 14,26 …… valve, 18 …… pump, 28 …… column, 30 …… packing material (solid solution) ), 32 …… Flow cell.

Claims (4)

[Claims] 1. A step of diluting a solution (stock solution) in which a compound having a limit solubility is dissolved, and a tracer is incorporated at a constant ratio in the crystal structure of the same compound (target compound) as the above compound. Pass the diluted solution through a column packed with solid solution,
A step of dissolving the target compound and the tracer in the diluted solution and saturating the diluted solution with the target compound, and measuring the tracer concentration of the diluted solution saturated with the target compound, and saturating the diluted solution from the concentration of this tracer The method of measuring a saturation point of a solution, comprising the steps of: measuring the amount of the target compound required for the step 1 and determining the saturation point of the stock solution from the measured amount of the target compound and the degree of dilution of the diluted solution. 2. The method for measuring the saturation point of a solution according to claim 1, wherein the stock solution is an aqueous solution of calcium sulfate and the solid solution is a eutectic of calcium sulfate and chromic acid or chromate. 3. The solid solution is rapidly added to a first aqueous solution of potassium chromate and calcium chloride whose pH is adjusted to about 7 while stirring and a second aqueous solution of potassium sulfate dissolved in warm water. After that, let stand and decant the supernatant liquid,
The method for measuring the saturation point of a solution according to claim 2, wherein the precipitate is prepared by washing the precipitate with a saturated aqueous solution of calcium sulfate and then dehydrating it. 4. A saturation point measuring device for measuring a saturation point of a solution (stock solution) in which a compound having a limit solubility is dissolved, wherein a supply source for supplying a diluted solution of the stock solution and a compound identical to the above compound ( A column filled with a solid solution in which a tracer is incorporated at a fixed ratio in the crystal structure of the target compound), a liquid feeding means for sending the diluted solution from the supply source to the solid solution of the column, and a passage through the solid solution An apparatus for measuring a saturation point of a solution, comprising a measuring means for measuring a tracer concentration in the diluted solution, and determining a saturation point of the compound in the stock solution from the measured value.