JPH0445450B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for purifying brine for electrolysis, particularly for use in an ion exchange membrane method.

It is well known that chlorine and caustic soda are produced by electrolyzing salt water, but the raw salt water often contains impurities such as heavy metals and hardness components such as calcium and magnesium.

In conventional electrolysis using the mercury method or the diaphragm method, even if such impurities were present on the order of several milligrams/milligram, it did not pose a particular problem to the operation. However, in recent electrolysis using ion-exchange membranes, if there are many impurities, it can cause various problems such as a decrease in current efficiency, an increase in electrolysis voltage, or an impact on membrane life due to membrane clogging. There is a growing need for further purification. In particular, calcium and magnesium ions, which are hardness components, are at least
It is necessary to remove it to 0.05mg/or less.

Conventionally, as an industrial purification method for salt water, a method has often been adopted in which sodium carbonate or the like is added to salt water to precipitate and remove hardness components as carbonates. However, in this method, partly because the solubility product of the carbonate produced is relatively large, it is inevitable that a few mg of hardness components remain.

Therefore, as a method to remove as much of the hardness component as possible, in addition to primary purification using the conventional coagulation-sedimentation method,
Secondary purification by adsorption using chelate resins is attracting attention.

However, adsorption methods using chelate resins also have various drawbacks. That is, calcium leak occurs in the initial period when salt water is passed through the chelate resin, and the calcium concentration in the salt water does not fall below 0.05 ppm. To solve this problem, we added 2 chelate resins.
A tower or three towers are used in series, but if two or three towers are installed using chelate resin, the initial equipment cost will be very high. In addition, if the salt water from which initial calcium leaks is passed through the second chelate resin tower, the breakthrough time of the chelate resin in the second tower will be shortened, and the regeneration frequency will increase, resulting in an increase in regeneration chemical costs. There was a drawback. On the other hand, since the chelate resin base for salt water purification is a styrene-divinylbenzene copolymer, it is susceptible to oxidizing agents, and free chlorine generated in the salt water has the drawback of extremely shortening the resin life.

The present inventor conducted extensive studies to solve these problems and develop an advantageous method for purifying salt water.

Normally, chelate resin regeneration treatment removes fine particles and insoluble SS that cause pressure loss, and also makes the particle size distribution of the resin uniform, prevents channeling, and improves contact between salt water and the resin layer. A backwashing step, then, after standing, an elution step to desorb calcium, usually using hydrochloric acid, an extrusion and water washing step, and a step to convert the functional group of the chelate resin from H type to Na type, usually using caustic soda. It is carried out through various steps including extrusion and water washing. After the chelate resin is regenerated in this way, it is purified by passing salt water through it.

When we investigated why calcium leaks during the initial flow of salt water in such a normal regeneration process, we found that the chelate resin contracts when hydrochloric acid is flowing, and swells when caustic soda is flowing. fact, and extrusion after the elution step,
It was discovered that calcium is constantly leaking into the liquid that flows out during the water washing process.

Calcium forms a strong chelate bond with the chelate resin, and is therefore adsorbed into the pores of the chelate resin. As mentioned above, the resin volume of chelate resin contracts when hydrochloric acid is flowing through it, so when hydrochloric acid, which is an eluent, is passed through the chelate resin layer that has adsorbed calcium, the pores contract rapidly. This makes it difficult for the eluent to diffuse into the pores of the chelate resin, making it difficult to completely desorb calcium adsorbed deep into the pores. After that, when caustic soda is passed through in the conversion process to Na type, the chelate resin swells as mentioned above, so the caustic soda also diffuses into the pores, and the calcium remaining inside the pores of the chelate resin becomes water. Accumulates as calcium oxide. When salt water is passed in this state, the chelate resin contracts again and the calcium remaining in the pores is pushed out, so calcium leakage cannot be avoided in the early stages of salt water flow.

Furthermore, when salt water is used in circulation, chlorate gradually accumulates, and if hydrochloric acid, which is an eluent, is passed through the column while chlorate is present in the resin column without being sufficiently washed with water, the chlorate decomposes and generates free chlorine. This free chlorine causes the resin to undergo oxidation and deteriorate, resulting in a very short resin life.

Under the above circumstances, the inventor of the present invention conducted studies to develop an advantageous method for purifying salt water, and as a result, the inventor conducted a study to develop an advantageous method for purifying salt water. Prior to liquefaction, there is a step in which salt water is passed under specific conditions to replace the inside of the chelate resin tower with salt water, and after the purification of the salt water is completed, and prior to the backwashing step, soft water is passed under specific conditions. The inventors have discovered that the objective can be achieved by providing a step of replacing the inside of the chelate resin column with soft water, and have completed the present invention.

That is, in the present invention, when purifying salt water for electrolysis using a chelate resin, the salt water is heated to SV = 10 between the end of reprocessing of the chelate resin and the start of salt water flow.
(Hr ^-1 ) or less to replace the inside of the chelate resin column with salt water, and between the end of salt water flow and the start of regeneration treatment, soft water is passed at a rate of SV = 10 (Hr ^-1 ) or less. This method of purifying brine for electrolysis is characterized by providing a step of replacing the inside of the chelate resin column with soft water by passing the solution through the chelate resin tower, and recycling the dilute brine generated in these two steps as a raw salt solution.

The present invention will be explained in more detail.

The chelate resin used in the present invention may be any ordinary chelate resin for salt water purification, and specific examples include chelate resins having iminodiacetic acid as a functional group, such as Diaion CR-10 (manufactured by Mitsubishi Chemical Corporation),
Revachit OC-1048 (Bayer), Sumikylate MC-30 (Sumitomo Chemical), chelate resins with aminophosphoric acid as a functional group, such as Duolite
Examples include ES-467 (manufactured by Diamond Shamlok).

The method of contact between the salt water and the chelate resin is not limited in any way and may be any method, such as an upward flow or a downward flow. The flow rate of salt water is SV = 2 to 50.
(Hr ^-1 ) is preferable both economically and in order to suppress calcium leakage to an extremely low level, and more preferably SV is about 10 to 40 (Hr ^-1 ).

In order to increase the adsorption capacity and keep calcium leakage low, the pH of the salt water flowing through the solution must be adjusted to
The range of PH = 5 to 13 is preferable, and more preferably PH
= range of 7 to 11. In addition, the temperature of the salt water flowing through the solution should be 10 to
The temperature range is preferably 80°C, more preferably 20 to 70°C.
℃ range.

After purification by passing salt water through it, the chelate resin is subjected to regeneration treatment. In the regeneration process of chelate resin, the salt water replacement step according to the present invention, which is performed prior to the backwashing step, uses soft water and may be carried out in the same direction or in the opposite direction as the liquid flow, but the flow rate is SV = 10.
(Hr ^-1 ) or less. The flow velocity at this time is SV
If it is larger than 10 (Hr ^-1 ), the salt water in the resin will not be completely replaced, and the eluent hydrochloric acid will be passed through with chlorate remaining in the system, decomposing the chlorate and releasing free chlorine. occurs.

In addition, between the end of the regeneration process and the start of brine passage, brine is passed through to replace the inside of the resin column with brine, but the flow rate of brine is SV=10 (Hr ^-1 ) or less. If the speed at this time is higher than SV=10 (Hr ^-1 ), the soft water in the resin will not be completely replaced. In addition, rapid passage of salt water is not preferable because it causes rapid contraction of the resin, which may lead to the resin being crushed.

The dilute brine generated in the above two replacement processes is
It can be reused as a raw salt solution.

Further, the elution step and the step of converting the functional group of the chelate resin from H type to Na type are each performed using hydrochloric acid and a caustic alkali such as caustic soda. The concentration of hydrochloric acid and the concentration of caustic alkali in each step are preferably about 2 to 25% by weight, and the temperature can be about 10 to 80°C, but it is usually carried out at room temperature. The method of drug delivery may be either downward flow or upward flow. In addition, the flow rate of the drug, extrusion, water washing, etc.
It is carried out at SV=2 to 7 (Hr ^-1 ).

When purifying brine for electrolysis using the method of the present invention, the raw brine may be treated as it is, but the method of the present invention may be carried out using the brine that has been previously treated by a known method such as the above-mentioned coagulation-precipitation method. There is no problem with that. Rather, such primary treatment is more preferable in terms of purification effects and the like.

Thus, according to the method of the present invention, it is possible to highly reduce hardness components in salt water, such as calcium and magnesium, which were difficult to remove in the past, and moreover, since the breakthrough time is long, it is stable for a long time. can be used for purification treatment, etc.
Excellent effects can be obtained as a method for purifying salt water for electrolysis.

The present invention will be explained below using examples.

Example 1 In a vinyl chloride resin column (inner diameter 26 mm, height 1500 mm) filled with 500 ml of Duolite ES-467, pure water was poured at SV = 4 (Hr ^-1 ) after the completion of salt water flow.
brine replacement for 60 minutes, then LV=
Backwashing was performed with pure water at 7 (m/Hr) for 30 minutes. Next, 2N-hydrochloric acid was passed at SV=2 (Hr ^-1 ) for 55 minutes, and then pure water was passed at SV=2 (Hr ^-1 ) for 180 minutes. Then add 1N caustic soda at SV=2 (Hr ^-1 )
Pass the medicine for 55 minutes, then add pure water at SV = 4 (Hr ^-1 )
It ran for 60 minutes.

Next, brine for electrolysis after primary purification was passed through this column at SV = 4 (Hr ^-1 ) for 30 minutes, replacing the pure water with salt water, and then continuing to pass brine at SV = 4 (Hr -1 ).
(Hr ^-1 ).

The results are shown in curve A in Figure 1, and there was no leakage of calcium from the initial stage of liquid flow, and treated brine was stably obtained.

After repeating this test 20 times, the physical properties of the resin were analyzed, and no deterioration of the resin due to free chlorine was observed.

Comparative Example 1 In a vinyl chloride resin column (inner diameter 26 mm, height 1500 mm) filled with 500 ml of Duolite ES-467, after the brine was passed through, 2N-hydrochloric acid was added at SV = 2.
(Hr ^-1 ) for 55 minutes, then pure water at SV=2
(Hr ^-1 ) for 180 minutes. Thereafter, 1N caustic soda was passed at SV = 2 (Hr ^-1 ) for 55 minutes, and then pure water was passed at SV = 4 (Hr ^-1 ) for 60 minutes. Next, brine for electrolysis after primary purification was passed through this column at SV = 40 (Hr ^-1 ) for 30 minutes to replace pure water with brine, and then brine was passed through this column at SV = 40 (Hr ^{-1 ). 1} )
The liquid was passed through.

The results are shown by curve B in Figure 1.Although the calcium leakage during steady state was almost the same as in Example 1, the calcium leakage at the initial stage of liquid flow was extremely high.

In addition, LV = 7 (m/Hr) at a rate of 1 out of 5 times.
After repeating this test 20 times while backwashing with pure water for 30 minutes, we analyzed the physical properties of the resin and found that the water content of the resin had increased by 6%, clearly indicating that free Deterioration of the resin due to chlorine was observed.

[Brief explanation of drawings]

Figure 1 shows the calcium leak curve at the initial stage of fluid flow, and the vertical axis is the calcium concentration (mg/
), and the horizontal axis represents the liquid flow rate (//-R). In the figure, curve A shows the calcium leak curve of Example 1, and curve B shows the calcium leak curve of Comparative Example 1.

Claims (1)

[Claims] 1 When purifying salt water for electrolysis using a chelate resin, between the end of the chelate resin regeneration process and the start of the salt water flow, the salt water is passed through the chelate resin tower at a rate of SV = 10 (Hr ^-1 ) or less. During the process of replacing the interior with salt water, and between the end of the salt water flow and the start of regeneration treatment,
A process is provided to replace the inside of the chelate resin column with soft water by passing soft water at a rate of SV = 10 (Hr ^-1 ) or less, and the dilute salt water generated in these two processes is recycled and used as a raw salt solution. A method for purifying salt water for electrolysis, characterized by: