JPS6096781A - Regeneration of potassium hydroxide electrolyte - Google Patents

Abstract

PURPOSE:To convert K2CO3 to KOH to regenerate the same, by concentrating KOH electrolyte high in content of K2CO3 as impurities while introducing the conc. electrolyte into a filtering electrolytic cell having a diaphragm to allow K2CO3 to be deposited to the diaphragm and adding water to said electrolyte to perform electrolysis. CONSTITUTION:In an aqueous KOH solution used as the electrolyte of an alkali fuel battery, K2CO3 is formed as an impurity byproduct through the reaction with CO2 in air during use. This aqueous KOH solution containing K2CO3 is introduced into a precipitation tank 18 from an alkali fuel battery 17 and subjected to evaporative concn. or receives the addition of a highly conc. aqueous KOH solution to precipitate K2CO3. The suspension containing precipitated K2CO3 is introduced into the anode chamber 5 of a filtering electrolytic cell 1 having an Ni-anode 2, an iron cathode 3 and an asbestos diaphragm 4. The aqueous KOH solution passes the diaphragm 4 to enter a cathode chamber 6 while K2CO3 forms a precipitation layer 7 on the diaphragm 4. The residual solutions in both chambers 5, 6 are withdrawn while water is introduced into both chambers and the diluted solution is electrolyzed by the electrodes 2, 3 to convert K2CO3 to KOH which is, in turn, reutilized as the electrolyte of the alkali fuel battery.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for regenerating potassium hydroxide electrolyte.

More specifically, it relates to a regeneration method that separates and removes potassium carbonate that accumulates as a by-product from a potassium hydroxide aqueous solution used as an electrolyte in alkaline fuel cells, converts it into potassium hydroxide, and reuses it. .

fuel cells that use hydrogen and oxygen-containing gases as fuel;
Among these, alkaline fuel cells have particularly high conversion efficiency into electric power and are highly desirable as power generation systems. But as the only drawback.

Carbon dioxide gas contained in the hydrogen and oxygen-containing gases used as fuel is absorbed into the potassium hydroxide electrolyte, producing carbonates and reducing the performance of the potassium hydroxide electrolyte, which is a major problem in practical use. It was becoming a problem.

Conventionally, carbon dioxide gas in hydrogen- and oxygen-containing gases used as fuel has been almost completely removed. They tend to require the use of complex and excessive amounts of equipment and energy.

It was difficult to put it into practical use due to economic reasons.

The present invention differs from the conventional measures and treatment methods and provides a method for treating a used electrolyte and regenerating potassium carbonate contained in the electrolyte into potassium hydroxide and hydrogen. It is.

The present invention involves extracting an electrolytic solution of an aqueous potassium hydroxide solution containing potassium carbonate from an alkaline fuel cell body that uses hydrogen and oxygen-containing gas as fuel, and evaporating and concentrating the electrolytic solution.

a first step of obtaining an aqueous potassium hydroxide solution containing solid potassium carbonate by adding an aqueous potassium hydroxide solution having a higher concentration than the potassium hydroxide in the aqueous solution;

It has an anode and a cathode and is permeable to liquid.

In an overcharged tank partitioned into an anode chamber and a cathode chamber by a diaphragm that does not allow air bubbles and potassium carbonate solids to pass through.

By introducing the above potassium hydroxide aqueous solution containing the potassium carbonate solid into the anode chamber and leaching the potassium hydroxide aqueous solution through the diaphragm to the cathode chamber side, the potassium carbonate solid is precipitated on the surface of the diaphragm on the anode chamber side. After the lamination is formed, the second step consists of replacing the liquid in both electrode chambers with water and passing direct current to both electrodes to electrolyze the potassium carbonate solid deposited on the surface of the diaphragm on the anode chamber side. This is a method for regenerating potassium hydroxide electrolyte.

The following superior effects can be achieved compared to the case where

Compared to theory, only one series of processing is required.

(2) In the event that the processing system malfunctions, the alkaline fuel cell main body must be stopped in the case of processing fuel gas, but in the present invention, the main body does not need to be stopped and can be stored in a tank or the like.

(3) Compared to gas processing, processing can be performed using small-capacity equipment.

Next, one aspect of the present invention will be explained in more detail.

FIG. 1 is a schematic diagram of the regeneration process of potassium hydroxide electrolyte according to the present invention.

First, the first step will be explained.

Crude hydrogen gas containing carbon dioxide gas is supplied as power generation fuel to the alkaline fuel cell 17 using an aqueous potassium hydroxide solution as an electrolyte through gas conduit '50, and oxygen-containing gas also containing carbon dioxide gas is supplied through gas conduit 31. . Specific examples of crude hydrogen gas include methane steam reforming gas, methanol steam reforming gas, and iron manufacturing gas. The composition of methane or methanol steam reforming gas is +'H275~80
VOt4co220-25vot%. These gases are separated in advance by a separator 19 that uses a hydrogen gas separation membrane, which is known for its low energy consumption, although its ability to separate carbon dioxide gas is incomplete.
Part 1, for example, 1/ro Osho, can be removed and used. However, by-product hydrogen gas generated in the subsequent electrolytic process can also be used. Specific examples of the oxygen-containing gas include air and pure oxygen. By supplying crude hydrogen gas and oxygen-containing gas to the fuel cell 17, power generation is performed in the alkaline fuel cell 17 by the reaction between H2 and 02.

Crude hydrogen gas and carbon dioxide gas in the air are absorbed into an aqueous potassium hydroxide solution used as an electrolyte to become potassium carbonate. When the content of potassium carbonate in the potassium hydroxide aqueous solution exceeds 10% by weight, the alkaline fuel cell
This will impede the power generation function of the Therefore, the electrolytic solution is continuously or intermittently discharged from the fuel cell 17 so that the potassium carbonate concentration in the electrolytic solution does not exceed the above concentration, and an amount of potassium hydroxide aqueous solution commensurate with the discharged amount is supplied to the fuel cell 17. It is preferable to do so. As the newly supplied sodium hydroxide aqueous solution, it is preferable to use one obtained in the second step described below. The electrolytic solution discharged from the fuel cell 17 is introduced into the crystallization tank 18.

Methods for crystallizing the potassium carbonate contained include a method of evaporation and concentration, or a method of adding a potassium hydroxide aqueous solution having a higher concentration than the potassium hydroxide in the above aqueous solution.

The former method includes a heating evaporation concentration method usually used in industrial operations. There are no particular restrictions on the operating conditions at this time, but for the purpose of post-processing.

Usually, it is appropriate to carry out the reaction under normal pressure to reduced pressure and at about 100'C or less.

As for the evaporation method, a single-effect type may be used, but in order to save heating energy, a multiple-effect type is preferable.

Also, self-vapor compression method, single stage or multi-stage flood
The evaporation method can be carried out in a batch, semi-batch or continuous manner, but which one is appropriate depends mainly on the scale of the treatment at the time.

Decide by considering.

As the latter method, a method can be adopted in which an aqueous potassium hydroxide solution is added to an aqueous potassium hydroxide solution containing potassium carbonate so that the solubility of potassium hydroxide is greater than the solubility of potassium hydroxide in a potassium carbonate-potassium hydroxide-water system. . The greater the amount of high concentration potassium hydroxide aqueous solution added, the more potassium carbonate precipitates are generated.

In this way, the suspension obtained by crystallizing 60 to 95 weight percent of the potassium carbonate contained is slowly cooled to 90°C or less, preferably 80'C or less, passes through the teaching tube 8, and is passed through the second tube. Sent to the process.

In the second step, the potassium carbonate solid is converted to potassium hydroxide, which is treated in a two-stage operation in the same equipment. In other words, the filtration and separation operation of solid potassium carbonate in the former stage and the electrolytic operation of potassium carbonate in the latter stage are carried out.

In the present invention, specific examples of the material of the anode 2 used include lead, nickel, nickel-plated iron plate, 9% Ni steel, 5% Nl steel, and 18-8 stainless steel. Among these, nickel is preferably used.

Further, specific examples of the materials used for the cathode and electrode 6 include lead and iron.

The diaphragm 4 used in the present invention must be one that allows the potassium hydroxide aqueous solution to pass through, but does not allow hydrogen, carbon dioxide gas, and oxygen bubbles, and potassium carbonate solids to pass therethrough, and must meet the following requirements. Narahiko. That is, 1Tit alkaline.

Acid resistance, reduction resistance, and oxidation resistance; strength that can withstand a pressure difference of 1 Kg/ctA or more between the anode chamber 5 and cathode chamber 6; heat resistance that can withstand 90 to 100°C The size of the eyes is 1 μm or more and 50 μm or less; and the deposited layer 7 has good adhesion retention.

Specific examples of materials for the diaphragm 4 that meet these requirements include polymeric materials such as asbestos, polytetrafluoroethylene, polyvinyl chloride, polyvinylidene chloride, and polyacrylonitrile, and asbestos using these polymeric materials as a base material. Examples include those pre-coated with

An anode 2 and a cathode 6 are provided at both ends of the filtration electrolytic cell 1, respectively.
is provided. The filtration electrolytic cell 1 is partitioned into an anode chamber 5 and a cathode chamber 6 by a diaphragm 4 installed in the center.

The teaching pipe 9 of the cathode chamber 6 of the filtering electrolytic cell 1 is closed, and a suspension of an aqueous potassium hydroxide solution containing solid potassium carbonate is introduced through the teaching pipe 8 of the anode chamber 5.

The liquid components of the suspension sent to the anode chamber 5 leak into the cathode chamber 6 through the pores of the diaphragm 4 . in this case.

The gas exhaust pipe 10 of the anode chamber 5 is closed, and the gas exhaust pipe 11 of the cathode chamber B is left open. In order to maintain a uniform suspension state, in the anode chamber side circulation line 12 of the anode chamber 5.

It is also possible to circulate the suspension in the anode chamber 5.

The leachate component leached into the cathode chamber 6 is sent to a storage tank 14 for an aqueous potassium hydroxide solution via a cathode side circulation line 13 or a teaching pipe 9 and a second circulation line 13. At this time, the solid potassium carbonate in the suspension adheres to the surface of the diaphragm 4 on the anode chamber side, forming a deposited layer 7. At this time, the appropriate pressure for feeding the suspension into the anode chamber 5 is 1 atm to several atm.

The pressure in the cathode chamber 6 is set to 1 a'tm or reduced pressure. The temperature is usually room temperature to about 90°C.

Under such operations, the thickness of the deposited layer 7 on the surface of the potassium carbonate solid diaphragm 4 on the anode chamber 5 side is 0.5 mm or more and 10 mm or less, preferably 0.5 mm or more and 5 mm or less. The suspension is fed through the liquid conduit 8 until the

After forming the deposited layer 7, the potassium hydroxide solution on the cathode chamber 6 side is extracted through the liquid conduit 9 and transferred to the storage tank 14 for potassium hydroxide aqueous solution.

On the other hand, the suspension in the anode chamber 5 and the anode side circulation line 12 is removed through the liquid conduit 20 by opening the gas discharge pipe 10.

Then, into the anode chamber 5 and the cathode chamber 6, respectively.

Pure water is fed through liquid conduit 20 and liquid conduit 21.

To prevent backflow of the liquid, pure water is passed through the liquid conduit 20 so that the liquid level in the anode chamber 5 is at least 10 cm higher than the liquid level in the cathode chamber 6.
I will send it in.

After making these preparations, electrolysis is started by passing direct current electricity through the two electrodes 2 and 3.

For DC electricity, a voltage of 2.0 to 265 cm is appropriate.

The current density is 3-40A/dm2. In particular, 5 to 20 A/d
Preferably, it is m2.

In the cathode chamber B, potassium carbonate in the potassium carbonate solid deposit layer 7 is gradually dissolved and decomposed by electrolysis and converted into potassium hydroxide, and ions are accumulated therein. Also, from the gas outlet 11 of the cathode chamber B.

The generated H2 gas is exhausted.

In the cathode chamber 6, the potassium hydroxide component gradually increases. Pure water is fed into the cathode chamber B through the liquid conduit 21 so that the concentration of the potassium hydroxide aqueous solution is adjusted to 60% by weight or less, preferably 15% by weight or more.

Further, the potassium hydroxide aqueous solution in the cathode chamber 6 is drained to the storage tank 14 while maintaining a predetermined liquid level.

The extracted potassium hydroxide aqueous solution is adjusted to an appropriate concentration and is circulated to the alkaline fuel cell 17 via the liquid conduit 63. Normally, the concentration of an aqueous solution of potassium hydroxide obtained by regeneration by electrolysis is:

A dilute solution of 30% by weight or more is also required. The filtrate obtained in the previous filtration step is a solution with a concentration of 30% by weight or more, so by appropriately mixing and adjusting the two, it is adjusted to a predetermined concentration for the alkaline fuel cell 17. The liquid is circulated through the liquid conduit 6 to the dialkali fuel cell 17.

Both electrode chambers5. The liquid B is appropriately circulated through the circulation line 12.13, and the liquid temperature in the electrode chambers 5 and 6 is between room temperature and 90°C.
2 Preferably, the temperature is kept constant in the range of 40 to 80°C.

As the pure water used in the electrolysis step, when a heating evaporation concentration method is employed in the first step, it is also possible to condense the evaporated water and use it.

In the electrolysis stage, a mixed gas of carbon dioxide and oxygen gas is discharged to the atmosphere through the gas discharge pipe 10 of the anode chamber 5. Also,
Hydrogen gas is released from the gas exhaust pipe 11 in the cathode chamber B, and can be used as fuel for the alkaline fuel cell 17.

Next, examples will be shown.

Example 1 Aqueous solution 1 containing 0% by weight of potassium hydroxide and 10% by weight of potassium carbonate taken out from an alkaline fuel cell 17
t is heated to 95 to 100°C in a crystallization tank 18, water is evaporated, and concentrated to 0.6 t of an aqueous solution with a potassium hydroxide concentration of 50 parts by weight and a potassium carbonate concentration of 17 parts by weight. and cooled to 50°C to obtain a suspension of aqueous potassium hydroxide solution containing solid potassium carbonate. L.

Anode 2 made of nickel and cathode 5 made of iron.
and effective area 10c made of asbestos.
A filtration electrolytic cell 1 with a capacity of 150 CC was used, which was partitioned into an anode chamber 5 and a cathode chamber 6 by a diaphragm 4 of m×10 Cm. The entire amount of the above suspension was introduced into the anode chamber 5. A liquid component whose main component is potassium hydroxide.

The potassium carbonate solid was leached through the diaphragm 4 into the cathode chamber 6 and deposited on the anode chamber 5 side of the diaphragm 4. 'The thickness at this time was about 4 baskets. After this, two bipolar chambers 5.6 are connected to liquid conduits 20. The remaining liquid was drained through the liquid conduit 9. Next, pure water is poured into the anode chamber 5 and the cathode chamber 6 through the liquid conduit 20.
and the liquid conduit 21, respectively, and the circulation line 12.
．． It was circulated through 13. The liquid level in the anode chamber 5 was kept 10 nm higher than the liquid level in the cathode chamber B. Next, 9 double electrodes 2. DC electricity 2.5 V, 5 A/drr? energized to cause an electrolytic reaction. After about 10 hours, the generation of carbon dioxide gas from the anode chamber 5 decreased and most of the solid potassium carbonate was electrolyzed.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of the regeneration process of potassium hydroxide electrolyte according to the present invention. 1... Filtering electrolytic cell, 2... Anode, 3... Cathode. 4...Diaphragm, 5...Anode chamber, 6...Cathode chamber, 7.
...Sedimentary layer, 17...Alkaline fuel cell, 18...
・Crystallization tank, 19...Membrane separation type patent applicant Ube Industries, Ltd.

Claims (1)

[Claims] An electrolytic solution of an aqueous potassium hydroxide solution containing potassium carbonate is extracted from an alkaline fuel cell body that uses hydrogen and oxygen-containing gas as fuel. A first step of obtaining an aqueous potassium hydroxide solution containing solid potassium carbonate by evaporating and concentrating the electrolyte or adding an aqueous potassium hydroxide solution having a higher concentration than the potassium hydroxide in the aqueous solution, and It has an anode and a cathode and is permeable to liquid. In a filtered electrolytic cell separated into an anode chamber and a cathode chamber by a diaphragm that does not allow air bubbles and potassium carbonate solids to pass through. The potassium hydroxide aqueous solution containing the potassium carbonate solid obtained in the first step is introduced into the anode chamber, and the potassium hydroxide aqueous solution is leached through the diaphragm to the cathode chamber side, so that carbonate is formed on the surface of the diaphragm on the anode chamber side. After forming a deposited layer of potassium solids, the liquid in both electrode chambers is replaced with water, and direct current is passed through both electrodes to electrolyze the potassium carbonate solids deposited on the surface of the diaphragm on the anode chamber side. A method for regenerating a potassium hydroxide electrolyte, comprising the steps of: