JPS59170282A - Method and device for electrolyzing dilute aqueous caustic alkali solution - Google Patents

Abstract

PURPOSE:To perform stably electrolysis for a long period by performing the electrolysis in which polarities are inverted and electricity is conducted in a reverse direction at every conduction of electricity in a positive direction for a prescribed time, reversing the feeding and discharging directions of the electrolyte and performing the similar electrolysis. CONSTITUTION:A dilute caustic alkali soln. is fed into one of the electrode chambers of an electrolytic cell segmented by a cation exchange membrane and a thick aq. caustic alkali soln. is recovered from the other electrode chamber. Fe, Ni or an alloy thereof is used as the electrode material thereof. The electrolysis in which polarities are inverted and electricity is conducted in a reverse direction at every electrolysis by conducting the electricity for a prescribed time in a positive direction is performed for a specified period. Then the feeding and discharging directions of the electrolyte are reversed and the electrolysis in which polarities are inverted and electricity is conducted in a reverse direction at every electrolysis by conducting the electricity for a prescribed time in a negative direction is performed for a specified period.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and an apparatus for electrolyzing a dilute caustic aqueous solution using iron, nickel, or an alloy thereof as an electrode in an electrolytic cell separated by a cation exchange membrane.

Solutions containing caustic alkali are discharged from industrial manufacturing, processing or processing processes. Examples include reaction waste liquid from a chemical reaction process for wings, alkali treatment waste liquid for gold, ion exchange resin recycled brittle liquid, alkali treatment waste liquid in an oil refining process, and the like. Recovery of caustic alkali from these waste liquids is important from the viewpoint of process economics or pollution control.

Therefore, attempts have been made to treat such brittle liquids to recover caustic alkalis and to render them harmless. Most of these caustic-containing brittle liquids are relatively low-0 degree aqueous solutions and contain many other inorganic or organic coexisting substances, so they cannot be recovered for practical, technical, or economic reasons. In many cases, the insect dies without being treated, even after neutralization or other detoxification treatment.

An electrolytic method using a cation exchange membrane is known as an effective means of efficiently recovering caustic alkali from such a bottom liquid. A method for treating alkaline aqueous humor is described in which only alkali is separated and recovered from alkaline wastewater by dialysis, and the wastewater is discharged as neutral.

However, in such electrolytic methods, the electrodes, especially the anode, are required to be highly durable to withstand the oxygen evolution reaction, and are not made of expensive precious metals or are prone to wear and tear and have drawbacks in manufacturing and operation. A certain type of graphite or the like had to be used, and it was hoped that a technologically and economically superior electrolytic technology that could be adopted during the first Qin period would emerge. That is, iron, nickel, and their alloys such as stainless steel are inexpensive and have good workability, and have been conventionally used as TFj and electrodes for electrolyzing caustic aqueous solutions in water electrolysis and the like. However, these can be used in relatively high temperature, highly concentrated aqueous solutions, and about 10% of caustic alkali
At low concentrations below 9C, especially below 55C, problems may occur such as the anode being significantly oxidized due to an increase in electrolytic voltage, oxides being formed on the surface and inactivation, or further elution of the anode surface. It was not possible to apply electrolytic iron, nickel, etc. in a low concentration caustic alkaline aqueous solution as an electrode.
When electrolyzing waste liquid containing organic substances and heavy metals, these impurities may deposit on the redundant electrodes or piping during ion exchange and cause 'I! ! It tended to open while making the progress of tm difficult.

The present invention was made to solve the above-mentioned problems, and its purpose is to stably electrolyze a dilute aqueous caustic alkali solution over a long period of time using inexpensive electrodes made of iron, nickel, etc., and efficiently remove caustic alkali. New′ that can be recovered well! r
To provide a method and its location.

The present invention is an electrolysis method in which a dilute caustic aqueous solution is supplied to one TiP chamber of an electrolytic girder divided from a cation exchange membrane building, a dilute aqueous caustic alkaline solution is recovered from the other electrode chamber, and a dilute aqueous caustic alkaline solution is recovered from the other electrode chamber. In this method, iron, nickel, or an alloy thereof is used as the electrode material, and each time electrolysis is performed by applying current in the positive direction for a predetermined time, the polarity is reversed and current is applied in the opposite direction for a certain period of time. A method for electrolyzing a dilute caustic alkaline aqueous solution, which is characterized in that the direction of supply and discharge of the liquid is reversed, and each time electrolysis is performed by energizing in the negative direction for a predetermined period of time, the polarity is reversed and energizing is performed in the opposite direction for a certain period of time. and its apparatus.

The present invention performs the same electrolysis by periodically reversing the polarity of the electrode with the above-mentioned energization and a predetermined amount of energization, and by operating the electrolyte supply/discharge direction and energization direction for each electrolysis period of a certain period. Toto K has achieved the above objectives and, as detailed below, has developed an excellent product that enables stable electrolysis of dilute alkaline aqueous solutions over long periods of time using inexpensive electrodes made of iron, nickel, etc. It is effective.

The electrolytic cell used in the present invention has an electrode chamber divided by a gate ion exchange membrane, and can be applied to any type such as a monopolar type or a bipolar type.

The electrolyzer shown in FIG. 1 shows the basic type of a monopolar electrolytic cell according to the present invention, in which a cation exchanger 1 is installed to form electrode chambers 2 and 3, and electricity is supplied through electrodes 4 and 5. and perform electrolysis.

FIG. 2 shows an example of a bipolar electrolytic cell according to the present invention, in which VCl'! between end electrodes 4' and 5'! An ion exchange membrane 1 and a multiple f@6 are sequentially provided. 7 indicates an intermediate electrode chamber, and by providing a plurality of 7, a multi-chamber bipolar electrolytic cell f
Of course, it is possible to use it as a tank. In the present invention, the same electrode material can be used for both the anode and the cathode, which is advantageous since there is no need to combine the bipolar Trt decay material, especially when constructing a bipolar electrolytic cell.

As the cation exchange membrane 1, any known cation exchange membrane that can withstand an electrolytic environment can be used, but a fluororesin membrane such as a perfluoro ion exchange membrane with good alkali resistance is particularly suitable for the cation exchange membrane 111.

The electrodes 4 and 5 are made of iron, nickel, or an alloy thereof. Examples of alloy materials include carbon fl, Fe
'--Ni alloy, stainless steel, alloy with Co, Cr or Mo, etc. can be used. The individual electrodes may be made of the same electrode material, or may be made of different electrode materials in combination. An electrolytic cell is usually equipped with a direction for supplying and discharging electrolyte and products. ! The electrolytic device is constructed in a symmetrical shape around the membrane 1 or the electrode 6, and the direction of current flow and the direction of liquid flow can be reversed at any time. In a multi-chamber bipolar electrolytic cell as shown in Figure 2, if an odd number of cation exchange membranes are used, the middle cation exchange membrane will be the center of symmetry, and if an even number is used, the middle bipolar electrode will be the center of symmetry. It lasts forever.

For example, in FIG. 1, tanks 8, 8' piping 9, 9' pumps 10, 10 with the same shape can supply or discharge electrolyte to the left and right m-electrode chambers 2, 3. ', and additionally provide liquid supply pipes 11, 11', exhaust pipes 12, 12', etc. as necessary, thereby constructing an electrolyzer symmetrically with the cation exchange membrane 1 at the center.

Electrodes using iron, nickel, or the like as an electrode material have good conductivity, can be easily formed into any shape such as a rod, plate, net, perforated plate, etc., and are inexpensive. However, when conventional electrolysis methods are used to electrolyze dilute aqueous solutions or waste liquids containing caustic alkali, the I5 electrode surface is oxidized to form oxides, making it difficult to continue electrolysis.

Even if such an electrode is used, the present invention performs electrolysis for a certain period of time, in which the polarity is reversed every time the current is passed in the forward direction for a predetermined period of time, and the current is passed in the reverse direction, and then the direction of supply and discharge of the electrolyte is reversed. This work was made based on the new knowledge that if similar electrolysis was performed using a similar method, the above-mentioned conventional problems would be resolved, and a dilute caustic alkali-containing aqueous solution could be electrolyzed stably for a long period of time.

The energization method of the present invention will be specifically explained with reference to FIG.

First, one of the electrode chambers is used as an anode chamber, and each time electricity is applied in the positive direction for a predetermined time T at a predetermined current value A to perform electrolysis, the chairness is reversed.
Current is applied in the opposite direction at a predetermined current value a for a predetermined time, and this is continued for a predetermined period of time.

Thereafter, the electrode chamber is used as a cathode chamber, and the direction of supply and discharge of the electrolyte is reversed, and electricity is similarly applied in the negative direction for a predetermined time T', and each time electrolysis is performed, the polarity is reversed and a predetermined current value a' is applied. time t
'Electricity is applied in the opposite direction for a certain period of time L'. Thereafter, electrolysis is continued in the same manner.

Although it is not necessarily clear why the above-mentioned effects of the present invention are achieved, progress of deactivation of the electrode can be prevented by periodically applying current in the reverse direction. This is thought to be because the activity is further restored. Also,
Current flow in the opposite direction is also effective in removing and cleaning impurity metals that are reduced and precipitated on the cathode surface and obstacles that are precipitated and adhered to the cation exchange membrane.

On the other hand, since the direction of current flow and the flow direction of the liquid throughout the electrolyzer are periodically reversed every time electrolysis is performed for a certain period of time, the electrochemical effect described above is improved, and at the same time, the physical effect due to backflow of the liquid is reversed. This is thought to be because the removal and cleaning of scale materials deposited on film formation, piping, etc. is performed effectively.

It is desirable that the energization time T, T' at the predetermined current value A, A' in the positive or negative direction is long for the purpose of performing electrolysis, but if it is too long, the electrode will become inactive, and furthermore, by energization in the reverse direction. However, it is difficult to revive the activity, so it is necessary to limit it to a certain period of time.

Generally, if the time is set to about 15 minutes or less, the electrode activity can be restored safely and easily.

On the other hand, the current values a and a' in the opposite direction and the current conduction time tt'
Since energization at
It is preferable to use a small amount of current as long as it is possible to sufficiently restore the electrode activity. Normally, the reverse direction 'P1% a X t
, a'X t' is the energization amount AXT in the positive direction or negative direction
, A'XT' is about 3 to 30%, it has been confirmed that the object of the present invention can be effectively achieved. For example, a =
-A and T is 10 minutes, t is about 18 seconds to 3 minutes according to the present invention.

Electrolysis is carried out for a certain period of time while periodically energizing in the opposite direction, as in ,
This is repeated to continue electrolysis for a long period of time. The period of time during which the electrolysis is continued in a certain direction, or L', can be determined as appropriate, but is generally preferably about 100 to 1000 hours in order to achieve the effects of the present invention.

In the energization pattern shown in Figure 3, the current value should be the same in both the forward and reverse directions: A=A'=-a==-a/)
, each energization time is constant (T=T', t=t'.

When L=L'), the operation is the simplest, as it is only necessary to control the time for switching the polarity. However, each current value A HA'l a
y h's energization time T, T', t, t', electrolysis period,
There is no problem in changing L' as appropriate.

Example 1 An electrolytic cell divided by a cation exchange membrane (trade name Nafion 315, manufactured by DuPont) was constructed as shown in Fig. 1, and both electrodes 4 and 5 had a size of 1 cm x 10 csn. A stainless steel plate (SUS316) with a thickness of 2.5W was used as an electrode material. First, the left electrode chamber 2 is set as the anode chamber, and N
An aOH aqueous solution was supplied as an electrolytic solution, and electrolysis was carried out by periodically applying electricity in the opposite direction according to the electricity supply pattern shown in FIG.

Next, the stain-dissolving solution was supplied to the right electrode chamber 3 by pulp operation, and electrolysis was continued in the same manner by using the electrode chamber 3 as the anode chamber and reversing the direction of flow of the solution and the direction of current supply. Those conditions are as follows.

Supply electrolyte = 2% NaOH aqueous solution Chamber ii discharge liquid: 0.5'jt; Na OH
Aqueous cathode chamber discharge liquid; 12% NaOH aqueous solution electrolysis temperature = 55 °C Current density A = a: 30 A/dm Current application time T = T: 60 seconds Reverse direction t = t: 6 seconds Electrolysis period L = L: 300 hours As a result, the electrolytic treatment could be continued for 3000 hours without any trouble at a total current efficiency of about 71%.

In the case of electrolysis in which electricity was not periodically applied in the reverse direction to the crack, the current efficiency was approximately 86%, but after approximately 100 hours of electrolysis, the electrolysis voltage increased by more than 5V, and electrolysis was continued beyond that point. There was nothing I could do.

Example 2 An electrolytic cell divided by a cation exchange membrane (trade name: Fion 324, manufactured by DuPont) was constructed as shown in Fig. 1, and both electrodes 4 and 5 had a size of 10 mm x 10 m and a thickness. Alkaline wastewater from the Maalox process when producing LPGm using pure nickel plates of 300ml. 11. Continue to collect the NaOH aqueous solution.

The analytical values of the alkaline wastewater were as follows.

NaQH6.0% TOC'20g/l Ca" 20 mg/A Mg"5mg/1 M n++5 mg/L So--20mg/1 This alkaline wastewater is used as an electrolyte and is first supplied to the left electrode chamber 2. The electrode chamber was used as an anode chamber, and electrolysis was carried out according to the energization pattern shown in FIG. 6, while periodically conducting reverse direction rLct. Next, let's operate the valve! 11 electrolytic solution was supplied to the right electrode chamber 3, and electrolysis was continued in the same manner with the electrode chamber 6 set as the positive chamber and the direction of flow of the solution and the direction of current supply reversed.

After reversing the yin/yang of the electrode chamber and starting electrolysis, the F m Na OH aqueous solution obtained in the cathode chamber for 15 minutes was
It was returned to the original waste liquid and only the pure NaOH aqueous solution was recovered.

The conditions for the electric lamp are as follows.

Supply electrolyte Na0HP degree: 6,0% 7411 room discharge liquid Na0Hffi3 degree: G, 69
(.

Cathode chamber discharge liquid: 12% Na OH71
#i'i & Electrolysis temperature: 55℃ Current density A"a: 30A/dm" Current application time T=
T: 60 seconds reverse direction t=t: 6 seconds electrolysis period L=L: 168 hours (1 week) As a result, the total current efficiency was approximately 73%, and it was possible to continue the electrolytic treatment for 4500 hours without any problems. done. In addition, almost no adhesion of the precipitate to the cation exchange membrane was observed.

On the other hand, in the case of electrolysis without periodic energization in the reverse direction, the current efficiency was about 8896, but about 10
After 0 hours of electrolysis, the electrolytic voltage increased by 5 V or more, and electrolysis could not be continued any further.

In addition, if the current is periodically applied in the opposite direction, but the electrode chamber is not periodically reversed, the total current efficiency is approximately 739 (and the initial operation was possible for about 1,500 hours without any problems). However, the electrolytic voltage gradually increased.When the tank was dismantled,
A small amount of non-conductive oxide was observed on the surface of the anode plate.
In addition, it was observed that precipitates, which were thought to be impurities in the supplied alkaline waste liquid, had adhered to the surface of the cation exchange membrane, and the electrical resistance of the ion exchange membrane had increased approximately twice.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing an example of an electrolytic device according to the present invention, FIG. 2 is an explanatory diagram showing another example of an electrolytic device according to the present invention,
FIG. 3 is an explanatory diagram showing an example of an energization pattern for electrolysis according to the present invention. 1: F1 ion exchange membrane 2.3.7: Electrode chamber 4.5: Electrode 8.8: Tank 9.9: Piping 10.10: Pump 11.11': Liquid supply Pipe 12.12: Exhaust pipe

Claims (7)

[Claims] (1) In an electrolysis method in which a dilute aqueous caustic alkaline solution is supplied to one electrode chamber of an electrolytic cell divided by a cation exchange membrane for electrolysis, and a concentrated aqueous caustic alkaline solution is recovered from the other electrode chamber, the electrode Using iron, nickel or their alloy as the material, each time electrolysis is carried out by applying current in the positive direction for a predetermined period of time,
Electrolysis is performed for a certain period of time by reversing the polarity and energizing in the opposite direction. Next, the supply and discharge direction of the electrolyte is reversed, and each time electrolysis is performed by energizing in the negative direction for a predetermined period of time, the polarity is reversed and energization is performed in the opposite direction. A method for electrolyzing a dilute caustic alkaline aqueous solution, which is characterized by carrying out electrolysis with electricity for a certain period of time. (2) The method according to claim (1), wherein the aqueous solution supplied has a caustic alkali concentration of 109 or less. (3) The method according to claim (1) for supplying a caustic alkali treatment waste liquid in a petroleum refining process. (4) The method according to claim (1), wherein the energization time in the positive direction or the negative direction is 15 minutes or less. (5) The amount of energization in the opposite direction is the amount of energization in the positive or negative direction 3
30%. (6) The method according to claim (1), wherein the electrolysis for a certain period is 100 to 1000 hours. (7) In an electrolytic device using an electrolytic cell separated by a cation exchange membrane, both electrodes are made of iron, nickel, or an alloy thereof, and both electrode chambers and their electrolyte supply and discharge mechanisms have the same shape. A dilute alkaline aqueous electrolysis device comprising a symmetrical electrolytic cell centered on a cation exchange membrane or electrode, and capable of reversing the polarity of the electrodes and reversing the direction of supply and discharge of electrolyte at any time.