JP2015013276A - Method of evaluating performance of ion exchange resin and method of determining replacement time - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a simple method of evaluating the performance of an ion exchange resin by determining equilibrium and kinetic parameters for the ion exchange reaction and a method of determining a replacement time for the ion exchange resin using the parameters obtained by the evaluation method.SOLUTION: The performance of an ion exchange resin is evaluated by mixing a salt aqueous solution of a specified concentration with a specified quantity of a regeneration type ion exchange resin to bring the salt aqueous solution in contact with the ion exchange resin, measuring the time-dependent change the electric conductivity of the salt aqueous solution after the mixing contact and evaluating the performance of the ion exchange resin on the basis of the measurement value. Preferably, a mass transfer capacity coefficient and a selectivity coefficient are determined so that a calculated value of the electric conductivity calculated on the basis of concentrations of individual ions in the aqueous solution brought into contact with the ion exchange resin fit mol electric conductivities of individual ions and measurement value of the electric conductivity.

Description

  The present invention relates to a method for evaluating the performance of an ion exchange resin and a method for determining a replacement time.

  In a pure water apparatus using an ion exchange resin (hereinafter, simply referred to as a resin), replacement with a new resin due to a decrease in the performance of the resin used involves an increase in water production cost. It is desirable to use for a long time. On the other hand, the purpose of pure water production using an ion exchange resin is to collect only a necessary amount of pure water having water quality that satisfies the standard according to its use at an optimum regeneration frequency. Therefore, the quality of the pure water to be manufactured should not be reduced, and the amount of water collected should not be reduced.

  Therefore, it is desired to perform resin replacement in an optimal period of use before causing problems such as deterioration in water quality and reduction in water collection due to contamination and deterioration that the ion exchange resin undergoes over time.

There are the following 1) to 4) as conventional techniques for a method for determining the replacement time of an ion exchange resin.
1) Based on the past operation data of the ion exchange resin tower, assuming that the rate of decrease in the sampling rate is assumed to be constant in advance, and periodically performing resin replacement at a time when it is assumed that the required sampling rate cannot be obtained. There is. Since this method does not have a quantitative evaluation scale, the replacement is performed on the safe side, that is, with a margin in the performance of the ion exchange resin, and the cost tends to be reduced.
2) Samples of the ion exchange resin are collected from the ion exchange tower during periodic open inspections, and the evaluation indices (total exchange capacity, neutral salt decomposition capacity, reaction rate, moisture content, crushing strength, etc.) of the ion exchange resin are obtained. A method of exchanging the resin is also widely performed when a tendency to decrease in performance is confirmed by measuring and comparing with a new resin index value. However, although it is possible to know the deterioration of the resin performance over time by measuring the numerical change of such an index, the evaluation of the direct and quantitative influence on the device performance such as product water quality and water sampling amount is performed. This is difficult, and this also leads to safe operation and high costs.

In addition, these indicators show only relative evaluations compared to new products, and the quality of pure water in individual water purifiers with different raw water quality and equipment conditions, product pure water requirement water quality, and sampled water volume It was difficult to make a direct and quantitative determination of how it affects the amount of water collected.
3) Japanese Patent Application Laid-Open No. 2002-48776 (Patent No. 4600617) describes a method for determining an exchange time using a decrease in mass transfer coefficient (MTC), which is a kinetic parameter of an ion exchange resin, as an index. However, since the parameters defined here are irreversible first-order kinetic parameters that do not take into account the equilibrium theory, it is not possible to accurately represent the ion-exchange reaction rate affected by the concentration of the adsorbed solid side ions. . For this reason, there has been a drawback that it cannot be used for simulation of an apparatus scale. As a result, this also did not exceed the range of the relative evaluation scale of the resin.
4) A control device that calculates the total ion load from the electric conductivity and ion concentration of the water to be treated of the ion exchange device, predicts and calculates the water sampling capacity of the ion exchange device, and controls the regeneration operation. -55082. If this method is used, it is possible to estimate in real time the predicted water withdrawal capacity of the ion exchange device. However, since the influence of the performance deterioration of the ion exchange resin cannot be reflected, it cannot be used for determining the replacement time.

JP 2002-48776 A JP-A-6-55082

  The object of the present invention is not a relative evaluation using the performance evaluation items of the ion exchange resin, but a simple ion exchange resin performance evaluation method for obtaining equilibrium and kinetic parameters of the ion exchange reaction, and this method. Another object of the present invention is to provide a method for determining the replacement time of an ion exchange resin using the parameters.

  The method for evaluating the performance of the ion exchange resin of the present invention is a method in which a salt aqueous solution having a predetermined concentration and a predetermined amount of a regenerative ion exchange resin are mixed and contacted, and the electrical conductivity of the salt aqueous solution after the mixed contact is changed over time. And the performance of the ion exchange resin is evaluated based on the measurement result.

  As the salts, alkali metal halides are preferable.

  In one embodiment of the performance evaluation method of the ion exchange resin of the present invention, the change in electrical conductivity over time is converted into a change curve over time in the halide ion concentration in the case of an anion exchange resin, and an alkali in the case of a cation exchange resin. Convert to a time course curve of metal ion concentration. In this case, it is preferable to determine the overall mass transfer capacity coefficient (Kfav) and the selection coefficient (K) from the concentration change curve with time and the exchange capacity of the ion exchange resin actually measured separately. In particular, the summary substance is such that the calculated electrical conductivity and the measured electrical conductivity are based on the concentration of each ion in the aqueous solution mixed and contacted with the ion exchange resin and the molar electrical conductivity of each ion. It is preferable to determine the moving capacity coefficient and the selection coefficient.

  The ion exchange resin replacement time determination method of the present invention is based on the product of the ion exchange resin exchange capacity, the overall mass transfer capacity coefficient determined by the above-described ion exchange resin performance evaluation method, and the selection coefficient. It is characterized by determining the replacement time.

  By using the equilibrium and kinetic parameters obtained based on the present invention, it is possible to perform a simulation in consideration of the raw water quality, equipment conditions (liquid velocity, space velocity) and regeneration conditions. The quality of water and the amount of water collected can be evaluated.

It is a graph which shows a simulation result. It is a graph which shows a simulation result. It is a graph which shows a simulation result. It is a graph which shows experimental data. It is a graph which shows a simulation result. It is a graph which shows a simulation result.

  The method for evaluating the performance of the ion exchange resin of the present invention is a method in which a salt aqueous solution having a predetermined concentration and a predetermined amount of a regenerative ion exchange resin are mixed and contacted, and the electrical conductivity of the salt aqueous solution after the mixed contact changes with time. And the performance of the ion exchange resin is evaluated based on the measurement result.

  As the salts, alkali metal halides, particularly NaCl, are suitable. This aqueous salt solution preferably has a concentration prepared by the following method (3).

[Test procedure]
In order to evaluate the performance of the ion exchange resin of the ion exchange resin apparatus according to the method of the present invention, a part of the ion exchange resin is sampled during the periodic open inspection of the ion exchange resin apparatus, and the following (1) to (7) It is preferable to carry out a batch ion exchange test (measurement test of change over time in the electric conductivity of the aqueous solution when the ion exchange resin is poured into an aqueous salt solution).

(1) The exchange capacity (q _T [meq / mL]) of the collected ion exchange resin is measured.

(2) The collected ion exchange resin is regenerated (H type for cation exchange resin, OH type for anion exchange resin).

(3) Accurately measure a certain amount (v [mL]) of regenerated ion exchange resin and multiply the exchange capacity measured in (1) by the measured resin capacity (maximum ion exchangeable amount ( q _T × v [meq]) is calculated. Then, 20 to 90%, preferably 20 to 75%, more preferably 30 to 50% of the maximum ion exchangeable amount of NaCl corresponding to the measured resin capacity (v [mL]) is preferably 2 It is dissolved in ultrapure water of ˜50 times, particularly preferably 10 to 30 times. This is because the selection coefficient may not be accurately obtained unless it is performed below the saturated adsorption amount of the actual ion exchange resin.

  If the NaCl concentration is too high, the excess NaCl affects the ultimate electrical conductivity, making it difficult to see the effect of adsorption of the ion exchange resin. On the other hand, if the amount is too small, the adsorption rate of the ion exchange resin is too fast, making it difficult to observe the change.

(4) The aqueous solution obtained in (3) above is placed in a container equipped with a stirrer. The volume of the container is preferably about 1.1 to 5.0 times the volume of the solution. Various containers such as a cylindrical shape and a round bottom are used, but it is preferable to use a round bottom flask so that the liquid is uniformly stirred.

  It is important that the container containing the NaCl aqueous solution, the amount of liquid to be put in, and the shape / size and rotation speed of the stirrer impeller are always constant. (Note that the rotational speed depends on the diameter of the impeller, but the peripheral end speed is preferably selected from the range of the rotational speed that is 1 to 10 times the sedimentation speed of the resin particles. The surface area becomes larger and the Kfav becomes larger than the actual size.If the rotational speed is too small, uniform stirring cannot be achieved. Usually, it is about 600 to 800 rpm.) The overall mass transfer capacity coefficient Kfav, which is the kinetic parameter to be calculated, corresponds to the overall mass transfer capacity coefficient when the ion exchange column is filled with the resin and passed through the water, and at what liquid linear velocity is used. When conducting simulations when water is passed with actual raw water quality and equipment conditions, the overall mass transfer capacity coefficient obtained in the batch test is corrected with the liquid line speed actually used in operation. This is because there is a need.

In the evaluation of the anion exchange resin, the pH of the solution changes from neutral to alkaline with the adsorption of Cl ions. Therefore, when the test solution is kept in contact with the atmosphere, carbon dioxide (CO ₂ ) in the atmosphere is absorbed, and for this reason, when the anion resin is evaluated from the point that affects the data to be measured, It is desirable that the container in which the gas is put be purged with an inert gas (for example, N 2, Ar, etc.) while purging with an inert gas.

(5) After putting NaCl aqueous solution in the container of said (4), an electrical conductivity meter is inserted in a liquid.

(6) The regenerative ion exchange resin measured in (3) above is charged as quickly as possible into a container with a stirrer in which an aqueous NaCl solution is stretched as in (4). Specifically, a method of pushing in using ultrapure water having the same capacity as the resin capacity to be charged is preferable. Since the change in electrical conductivity appears immediately after charging, it is preferable that the charging is completed within 5 seconds, preferably within 2 seconds. However, the resin charging method in the present invention is not limited to this.

(7) The resin charging completion time in (6) is set to time zero, and the change with time in the electrical conductivity accompanying the progress of the ion exchange reaction of the resin is measured. In such a batch-type ion exchange reaction test, it is most preferable to track the change in the concentration of the cation of interest in the case of a cation exchange resin and the change in concentration of the anion of interest in the case of an anion exchange resin over time. However, the ion exchange reaction rate is very fast, and there is no online analysis method for tracking the concentration change in real time. Further, as the ion exchange reaction proceeds, the pH of the test solution also changes. However, the pH meter requires time for measurement, and the actual ion exchange reaction rate cannot be traced. Therefore, in the present invention, the progress of the ion exchange reaction of the resin is measured by measuring the electrical conductivity.

  In the above example, NaCl is used. However, the salt is not limited to this, and any alkali metal halide can be used without any problem. Preferred are NaCl and KCl.

  Moreover, it is preferable that the volume ratio (salt aqueous solution / ion exchange resin) of salt aqueous solution and ion exchange resin is 2-50, especially 10-30. This is because if the amount of the salt aqueous solution is too large, the amount of change is small, and if it is too small, the dispersion state may become non-uniform.

  Furthermore, in the above example, the case where the ion exchange resin is charged into the aqueous salt solution has been described. However, the aqueous salt solution may be charged after the ion exchange resin is placed in a container with a stirrer. In either case, the change over time in electrical conductivity due to the ion exchange reaction between the aqueous salt solution and the ion exchange resin is measured.

  The overall mass transfer capacity coefficient and the selection coefficient are obtained by comparing the measured value of the electrical conductivity with time and the calculated value of the electrical conductivity by the following calculation.

[Calculation formula of electrical conductivity]
The target ion in the test solution in the batch ion exchange test described above (in the following, the case where NaCl is used as the salt is exemplified. When NaCl is used, the target ion is Cl ⁻ ion in the anion exchange resin and in the cation exchange resin. The mass balance equation of Na ⁺ ions is expressed by the following equation (1).
(1) Liquid side material balance

（２） 樹脂側物質収支

(2) Resin-side material balance

（３） イオン平衡関係

(3) Ion equilibrium relationship

(6) Exchange capacity In the case of an anion exchange resin, its exchange capacity q _{Total anion} is measured in advance by a predetermined method _, and in the case of a cation exchange resin, its exchange capacity q _{Total cation} is measured in a predetermined method. Used for analysis.

(7) Solution of simultaneous equations For the anion exchange resin and the cation exchange resin, the selection coefficient is set as an equilibrium parameter and the overall mass transfer capacity coefficient is set as a kinetic parameter as follows. As will be described later, the values of these parameters are set (fitted) so that the calculated value of calculated electrical conductivity matches the measured value of electrical conductivity. For example, the electric conductivity is calculated by changing various parameter values, and the value when the calculated value and the electric conductivity measurement value match is set as the parameter value.

In the case of an anion exchange resin, the formula (1), the formula (2), the formula (3-1), the formula (4), and the formula (5) are changed. In the case of a cation exchange resin, the formula (1), the formula (2), By simultaneously solving Equations (3-2), (4), and (5) under the following conditions, the concentration of each ion species at any time θ, that is, C _H , C _Na , C _OH , _CCl is determined. As described above, this concentration measurement value is affected by parameters.
<In the case of cationic resin>
C _Na = C _{Na, 0} at θ = 0 (6-1-1)
C _Cl = C _{Cl, 0} at θ = _{0 to} θ (6-1-2)
Where C _{Na, 0} : Initial concentration of Na
C _{Cl, 0} : Initial concentration of Cl <In the case of anionic resin>
C _Na = C _{Na, 0} at θ = ₀₋ θ (6-2-1)
C _Cl = C _{Cl, 0} at θ = 0 (6-2-2)
Where C _{Na, 0} : Initial concentration of Na
C _{Cl, 0} : Initial concentration of Cl

  The molar electrical conductivity of each ion at room temperature (25 ° C.) is given in the chemical handbook as follows.

In general, the electrical conductivity EC _SO1 of an aqueous solution is expressed by the following equation (7) based on the ionic species, ion concentration, and molar electrical conductivity of ions in the aqueous solution.

In this equation (7), ion concentrations C _Na , C _Cl , C _H , C _OH , C _{HSiO 3} obtained by solving the above simultaneous equations (these ion concentrations are the above-mentioned parameters (total mass transfer capacity coefficient and selection coefficient)). And the molar electrical conductivity of Table 1 above are substituted. Then, the above parameters (overall mass transfer capacity coefficient and selection coefficient) are determined so that the electrical conductivity calculated by the equation (7) matches the measured value of the change over time in the batch type ion exchange test. And the exchange time of an ion exchange resin is judged from the exchange capacity measured value measured by said (1), and the general mass transfer capacity | capacitance coefficient and selection coefficient which were calculated | required by (2)-(7).

  Specifically, for example, the total mass transfer capacity coefficient, the selection coefficient, and the exchange capacity of a new ion exchange resin are each set to 1, and the total mass transfer capacity coefficient, the selection coefficient, and the exchange capacity of the ion exchange resin after use are three. When the product of the parameters falls below the specified value, it is determined that it is time to replace. This specified value is preferably a value selected from 0.001 to 0.01.

[Reference Example 1]
Using a new strong basic anion exchange resin (SA12A, manufactured by Mitsubishi Chemical Corporation), a batch ion exchange test was performed under the same conditions as in Example 1 described later.

The resin property values of new SA12A are as follows. The manufacturer's catalog value is used for the selection coefficient of (OH, Cl) among these physical property values. The overall mass transfer capacity coefficient K _f a _v is a value obtained by fitting the batch ion exchange test results.

The time change (calculated value) of the concentration C ^{* in} equilibrium with the Cl concentration and the adsorption amount in the solution in the batch test calculated using these values is shown in FIG. In addition, FIG. 2 shows the time change (calculated value) of Cl concentration, adsorption amount and electric conductivity in the solution in the batch test, and FIG. 3 shows the pH change (calculated value) in the batch test.

The solid line in FIG. 1 shows the time change of the Cl concentration in the aqueous solution when the ion exchange resin is brought into contact with the NaCl aqueous solution. The dotted line indicates the calculation result of the Cl concentration (virtual concentration) in the aqueous solution in equilibrium with the resin adsorption amount by increasing the adsorption concentration in the resin by adsorbing Cl ions in the aqueous solution. The difference between the two at an arbitrary time is the ion exchange rate driving force ((C _i −C _i ^* ) in the equation (1)). As shown in FIG. 1, as a matter of course, the driving force decreases with the passage of time, and the ion exchange rate decreases.

The initial rate of change in electrical conductivity when the ion exchange resin is brought into contact with the NaCl aqueous solution is affected by the overall mass transfer coefficient K _f a _v which is the ion exchange rate constant of the ion exchange resin. On the other hand, the ultimate electrical conductivity is the electrical conductivity at the time when NaCl has almost reached equilibrium adsorption, and is affected by the exchange capacity and the selection coefficient.

[Example 1]
Using a new SA12A and SA12A actually used for 3 years (hereinafter sometimes referred to as a used product), a batch ion exchange test was performed according to the following procedures (1) to (7).

≪Batch ion exchange test procedure≫
(1) The exchange capacity (q _T ) of each ion exchange resin was measured.
The replacement capacity of the new SA12A was 1.29 eq / L. The exchange capacity of SA12A used for 3 years was 0.56 eq / L.
(2) Each ion exchange resin was sufficiently passed with a 4% -NaOH aqueous solution and then rinsed with ultrapure water overnight to obtain an OH type.
(3) A certain amount (v = 10 [mL]) of the regenerated ion exchange resin was accurately measured.

The exchange capacity measured in the above (1), the NaCl (117 mg) corresponding to 35% of the maximum ion-exchangeable amount obtained by multiplying the resin volume taken the balance _{(q T × v [meq]} ), weighed Was dissolved in ultrapure water (200 mL) 100 times the resin volume (v [mL]) to prepare a 0.01 mol / L NaCl aqueous solution.
(4) The total amount (200 mL) of the NaCl aqueous solution obtained in (3) above was placed in a container with a stirrer (volume 300 mL round bottom flask). The stirrer impeller had a semicircular shape, a diameter of 20 mm, and a rotation speed of 600 rpm. Stirring was performed while purging the container with N ₂ gas.

(5) The immersion type electrode (ES-51 manufactured by Horiba, Ltd.) was inserted into the NaCl aqueous solution (200 mL) in the container of (4).
(6) The regenerative ion exchange resin measured in (3) above was pushed into the container with a stirrer in (5) within 2 seconds using 10 mL of ultrapure water.
(7) The resin charging time in (6) was set to time zero, and the change with time in the electrical conductivity accompanying the progress of the ion exchange reaction of the resin was measured. The result is shown in FIG.

As shown in FIG. 4, there is no significant difference between the new product and the used product in the change in electrical conductivity immediately after the ion exchange resin is charged. On the other hand, the ultimate electrical conductivity is remarkably different between new and used products. Therefore, when the resin is deteriorated, not only the rate constant changes, equilibrium and exchange capacity q _T is adsorbed properties, it can be seen that there is a case where the selected coefficient changes.

[Parameter setting based on comparison between calculated and measured electrical conductivity]
Using the exchange capacity measurements, the overall mass transfer capacity coefficient was 0.25 (1 / sec), the selectivity coefficient was K 2 ^Cl _OH = 22, and the change in electrical conductivity of the batch test was calculated. The results are shown in FIG. As shown in FIG. 5, with this selection coefficient K ^Cl _OH = 22, the electric conduction between the new SA12A (exchange capacity 1.29 [eq / L]) and the product used (0.56 [eq / L]). There was little difference in degrees.

  Then, the ultimate electrical conductivity was calculated by changing various selection coefficients. The results are shown in FIG. As shown in FIG. 6, the ultimate electrical conductivity decreases as the value of the selection coefficient is set smaller. In the case of the deteriorated SA12A having an exchange capacity of 0.56 eq / L, when the selection coefficient is set to 0.4 (−), it is recognized that the calculated value of electrical conductivity matches the measured value (fitting). It was. As a result, the calculated value and the measured value of the electrical conductivity aging curve matched. It should be noted that by changing the parameter, the judgment of whether the calculated value curve matches the actual value curve can be made by the least square method or the parameter that minimizes the sum of the absolute value of the actual value and the calculated value error at each time. It is performed by a known method such as determination.

  Thus, the performance degradation of the ion exchange resin may be caused not only by changes in the overall mass transfer capacity coefficient, which is a kinetic parameter, but also by changes in the exchange capacity and the selection coefficient, which are equilibrium parameters.

[Example 2]
Using a new strong basic anion exchange resin (manufactured by LANXESS, M500) and M500 actually used for 3 years, a batch ion exchange test was conducted under the same conditions as in Example 1, and the exchange capacity and overall mass transfer capacity. Coefficients and selection coefficients were determined. The results are shown in Table 2.

≪Judgment of ion exchange resin replacement time≫
The exchange time of the ion exchange resin can be determined from the exchange capacity measured in the above (1) and the general mass transfer capacity coefficient and the selection coefficient obtained as described above.

  Specifically, for example, the total mass transfer capacity coefficient, the selection coefficient, and the exchange capacity of a new ion exchange resin are each set to 1, and the total mass transfer capacity coefficient, the selection coefficient, and the exchange capacity of the ion exchange resin after use are three. When the product of the parameters falls below the specified value, it is determined that it is time to replace. This specified value is preferably a value selected from 0.001 to 0.01. However, the threshold for these judgments varies depending on the quality of raw water and the required water quality.

  In the above examples, the overall mass transfer capacity coefficient and the selection coefficient were determined by fitting. In the graph of the electrical conductivity and the salt concentration with time, which are actually measured values, 10 to 10 of the equilibrium reached conductivity from the initial value. The overall mass transfer capacity coefficient may be calculated from the rate of change (slope) when it changes to 70%, preferably 20 to 50%.

  In addition, the selection coefficient may be determined using Equation 3-1 or Equation 3-2 from the supernatant composition of the solution that has reached equilibrium.

  Further, the replacement time of the ion exchange resin is determined by the product of three parameters, but is determined using a breakthrough prediction simulation described in paragraphs [0031]-[0045] of Japanese Patent Application Laid-Open No. 2012-205996. You can also

Claims (6)

  A salt aqueous solution having a predetermined concentration and a predetermined amount of a regenerative ion exchange resin are mixed and contacted, and the change over time of the electrical conductivity of the salt aqueous solution after the mixed contact is measured, and ion exchange is performed based on the measurement result. A method for evaluating the performance of an ion exchange resin, characterized by evaluating the performance of the resin.   2. The method for evaluating the performance of an ion exchange resin according to claim 1, wherein the salt is an alkali metal halide.   The time-dependent change in electrical conductivity is converted into a time-dependent curve of halide ion concentration in the case of an anion exchange resin, and is converted into a time-change curve of alkali metal ion concentration in the case of a cation exchange resin. The performance evaluation method of the ion exchange resin of Claim 1 or 2.   4. The performance of the ion exchange resin according to claim 3, wherein an overall mass transfer capacity coefficient (Kfav) and a selection coefficient (K) are determined from the concentration change curve and the exchange capacity of the ion exchange resin actually measured separately. Evaluation method.   The overall mass transfer capacity coefficient and the selection coefficient are determined so that the calculated electric conductivity calculated based on the concentration of each ion in the aqueous solution and the molar electric conductivity of each ion and the measured electric conductivity are fitted. The method for evaluating the performance of an ion exchange resin according to claim 4.   A resin exchange time is determined by the product of the exchange capacity of the ion exchange resin, the overall mass transfer capacity determined by the performance evaluation method of the ion exchange resin according to claim 5, and a selection coefficient. Replacement time judgment method.

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