JPH0699037A - Method for recovering gaseous co2 in alkaline liquid - Google Patents

Abstract

PURPOSE:To recover gaseous CO2 with good efficiency and large diffusivity by separating gaseous CO2 from alkaline liquid with dissolved gaseous CO2 by electrodialysis. CONSTITUTION:After nonvolatile acid such as sulfuric acid is added to liquid with absorbed carbon dioxide, the mixture is transferred to a gas-liquid separator 3 and the gaseous CO2 gasified there is separated. Next, the liquid from which carbon dioxide has been separated is fed to an electrodialysis tank 2. In the tank a cation exchange membrane 7 and an anion exchange membrane 6 are installed on the cathode 5 side and on the anode 4 side respectively. First the liquid is put in between the ion exchange membranes 6, 7 each. Then, cations in the liquid is attracted to the cathode 5 side and permeates the cation exchange membrane 7 to move to the cathode 5 side. And since nonvolatile acid radicals, carbonate radicals and bicarbonate radicals in the liquid are cations, they permeate the anion exchange membrane 6 to move to the anode 4 side. On the anode 4 side, the carbonate radicals and bicarbonate radicals that remain with the increase in acid are turned into gaseous CO2. And the liquid and liquid leaving the anode 5 side are recycled as additional acid and an absorbent respectively.

Description

Detailed Description of the Invention

[0001]

The present invention relates to carbon dioxide gas (hereinafter referred to as CO ₂
Abbreviated) is recovered from the alkaline solution in which CO ₂ is recovered.

[0002]

2. Description of the Related Art As one method for separating and recovering carbon dioxide gas in a gas, as shown in FIG. 6, a carbon dioxide gas absorption device for absorbing carbon dioxide gas into a liquid by an absorber using an alkali or amine, and its absorption. It is composed of a carbon dioxide emission device that emits from the liquid.

As a method of releasing carbon dioxide gas from the absorbing liquid, there are a method of lowering the solubility of dissolved carbon dioxide gas by raising the temperature and volatilizing it, and a method of releasing it at a pressure lower than the absorption pressure. As the above method, a method of adding an acid to promote gasification of carbonate radicals is considered.

[0004]

The conventional methods for releasing absorbed carbon dioxide gas have the following problems. (1) Among the diffusion methods by pressure change, for example, the method of absorbing at a high pressure and releasing at a constant pressure has a problem that the energy required to pressurize a huge gas amount is large, and the absorption at a normal pressure is also required. In the method of decompressing and then dissipating, since steam is generated by decompressing, there is a problem that efficiency is poor because a large partial pressure difference between carbon dioxide gas of liquid and gas cannot be obtained.

(2) In the method of absorbing at low temperature and dissipating at high temperature, since the dissipating temperature is as high as about 120 ° C., there is a problem that steam is generated and efficiency is low, and amines such as absorbents are used. Therefore, there is a problem that the solvent is expensive and the solvent is deteriorated.

(3) The method using an acid has a problem that the running cost is high because a large amount of the acid and the carbon dioxide absorbing solution are required.

[0007] In view of the above-mentioned state of the art, the present invention is a method of absorbing C absorbed in an alkaline solution which has few problems as in the prior art.
It is intended to provide an O ₂ recovery method.

[0008]

The present invention provides (1) a method for recovering carbon dioxide gas in an alkaline liquid, wherein the carbon dioxide gas is separated from the alkaline liquid in which the carbon dioxide gas is dissolved by electrodialysis.

(2) An alkali characterized in that a non-volatile acid is added to an alkaline solution in which carbon dioxide is dissolved to partially separate and recover the carbon dioxide, and the residual alkaline solution is electrodialyzed to separate the carbon dioxide. Recovery method of carbon dioxide in liquid

(3) The method for recovering carbon dioxide gas in an alkaline liquid according to the above 1 or 2, wherein electrolytic dialysis incorporating a cation exchange membrane and / or an anion exchange membrane is used.

[0011]

[Function] In general, CO ₂ is absorbed in the absorption tower (NaOH,
(KOH etc.) as shown in the following formula, and is absorbed by the absorbing liquid. CO ₂ + MOH → MHCO ₃ (M: alkali metal) The MHCO ₃ solution thus produced is electrodialyzed in an electrodialysis tank to decompose and is separated into a CO ₂ solution and an alkaline solution.
CO ₂ is recovered as a gas in the produced CO ₂ solution in the gas-liquid separation tank, and the solution after recovering CO ₂ and the alkaline solution are combined and reused for absorbing CO ₂ .

Before electrodialyzing the MHCO ₃ solution formed by absorbing CO ₂ as described above, a non-volatile acid (hydrochloric acid, sulfuric acid, nitric acid, hydrofluoric acid, etc.) is added to obtain the following formula. It is also possible to volatilize most of the CO ₂ in response to the above and then electrodialyze. _{MHCO 3 + HAc → MAc + HCO} 3 - + H
⁺ (Where, Ac: ^{_{acid) HCO 3 - + H + →}} CO 2 + H 2 O

According to electrodialysis, the cations in the liquid move to the cathode side, and the carbonate radicals remaining as acid move to the anode side.
Separated into O ₂ solution and alkaline solution. It is preferable to provide a cation exchange membrane and / or an anion exchange membrane in the electrodialysis tank in order to assist the movement and separation of these ions.

[0014]

【Example】

(Example 1) Hereinafter, the present invention will be specifically described with reference to the drawings showing an embodiment thereof. FIG. 1 is a basic flow chart showing the treatment method according to the present invention, wherein 1 is a carbon dioxide absorption tower, 2 is an electrodialysis tank, and 3 is a gas-liquid separator.

FIGS. 2, 3 and 4 are combination diagrams of the electrodialysis tank 2 and the gas-liquid separator 3 according to the embodiment of the present invention. In FIGS. 2 to 4, 1 to 3 are the same parts as FIG. 4 is an anode, 5 is a cathode, 6 is an anion exchange membrane, and 7 is a cation exchange membrane.
Since the anion exchange membrane 6 of FIGS. 2 to 4 is positively charged, it has a characteristic that anions easily pass but cations do not pass easily, and the cation exchange membrane 7 is negatively charged. Therefore, it has a characteristic that cations easily permeate but anions hardly permeate, and the combinations of FIGS. 2 to 4 can be considered by this combination.

FIG. 2 shows a method of supplying a liquid having absorbed carbon dioxide gas to an electrodialysis tank 2 having an anion exchange membrane 6 incorporated therein. Since carbonate radicals and bicarbonate radicals in the supplied liquid are anions, After passing through the anion exchange membrane 6 and moving to the side of the anode 4, as a result, the concentration of carbonate groups becomes high on the side of the anode 4 and a part thereof becomes gas.

FIG. 3 shows a system in which carbon dioxide gas is absorbed and the liquid is supplied to an electrolytic dialysis tank 2 in which a cation exchange membrane 7 is incorporated, and cations such as alkali metal ions in the supplied liquid are cation exchanged. It permeates through the membrane 7 and moves to the cathode 5 side. As a result, the pH on the anode 4 side decreases and the carbonate radical is gasified.

FIG. 4 shows a system for supplying to the electrodialysis tank 2 in which two cation exchange membranes 7 are incorporated. The cations in the liquid supplied between the two cation exchange membranes 7 are cations. Although it permeates the ion exchange membrane 7 and moves to the cathode 5 side, carbonate and bicarbonate do not easily permeate the cation exchange membrane 7 and therefore do not move in any direction. Therefore, at the anode 4, hydrogen ions are generated by electrolysis of water, and the hydrogen ions permeate the cation exchange membrane 7 and move between the membranes in which carbonate radicals and bicarbonate radicals exist, resulting in high pH. Then carbon dioxide gas is generated. The advantage of this method is that the oxygen gas generated at the anode 4 is less likely to be mixed in the carbon dioxide gas as compared with the previous two methods.

EXAMPLE 2 Another example of the present invention will be specifically described with reference to FIG. 5, those parts which are the same as those corresponding parts in FIGS. 2 to 4 are designated by the same reference numerals.

The liquid which has absorbed the carbon dioxide gas is added with a non-volatile acid such as sulfuric acid (described later) and then enters the gas-liquid separator 3 to separate the gasified carbon dioxide gas. The liquid after separation of carbon dioxide is supplied to the electrodialysis tank 2. The electrodialysis tank 2 is equipped with a cation exchange membrane 7 on the cathode 5 side and an anion exchange membrane 6 on the anode 4 side, and the liquid first enters between the ion exchange membranes. Since the cations in the liquid are pulled toward the cathode 5 side, they penetrate the cation exchange membrane 7 and move to the cathode 5 side. Further, since the non-volatile acid group, carbonate group and bicarbonate group in the liquid are anions, they permeate the anion exchange membrane 6 and move to the anode 4 side. The liquid from which both the cations and the anions have been removed is used as the supply liquid to the anode 4 and the cathode 5.

On the side of the anode 4, the carbonic acid and bicarbonate remaining due to the increase in the acid become carbon dioxide gas. Therefore, the liquid produced from the side of the anode 4 enters the gas-liquid separator 3 to separate and recover the carbon dioxide gas, Is an acid (eg sulfuric acid) for addition to the carbon dioxide gas absorbent
The liquid discharged from the cathode 5 side is recycled as a carbon dioxide absorbing liquid.

Although oxygen may be generated at the anode 4, this oxygen can be separated from the recovered carbon dioxide gas by inserting a cation exchange membrane between the anion exchange membrane 6 and the anode 4. Further, in the cathode 5, the cation exchange membrane 7 and the cathode 5
By inserting an anion exchange membrane between the two, it is possible to prevent hydrogen, which may be generated, from mixing with the regenerated alkali.

[0023]

As described above, according to the present invention,
It is possible to dissipate absorbed carbon dioxide without using heat and pressure fluctuations. Alkali metal hydroxide with high ionicity is suitable for the chemical used as an absorbent, and it is easy to decompose and the price is high. There is an advantage in that it is not necessary to use, the carbon dioxide emission rate from the liquid is large because an acid is used if necessary, and the chemicals do not need to be replenished because they can be reused. The effect is remarkable.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a basic flow of the present invention.

FIG. 2 is an explanatory diagram of the first embodiment of the present invention.

FIG. 3 is an explanatory diagram of a second embodiment of the present invention.

FIG. 4 is an explanatory diagram of a third embodiment of the present invention.

FIG. 5 is an explanatory diagram of a fourth embodiment of the present invention.

FIG. 6 is an explanatory view of a mode in which carbon dioxide gas is diffused from a conventional carbon dioxide gas absorption liquid.

Claims (3)

[Claims] 1. A method for recovering carbon dioxide gas in an alkaline liquid, wherein the carbon dioxide gas is separated from the alkaline liquid in which the carbon dioxide gas is dissolved by electrodialysis. 2. An alkaline liquid, wherein a non-volatile acid is added to an alkaline liquid in which carbon dioxide is dissolved to partially separate and recover carbon dioxide, and the residual alkaline liquid is electrodialyzed to separate carbon dioxide. Method of recovering carbon dioxide in the inside. 3. The method for recovering carbon dioxide gas in an alkaline solution according to claim 1 or 2, wherein electrolytic dialysis incorporating a cation exchange membrane and / or an anion exchange membrane is used.