JPS58208116A - Method for regenerating co absorbing liquid - Google Patents

Abstract

PURPOSE:To easily regenerate a CO absorbing liq. with a simple apparatus by reducing Cu<2+> contained in the soln. with a gaseous pole. CONSTITUTION:H<+> and e<-> are generated from H2 at a gaseous pole 1. The e<-> reaches a cathode 3 through an external circuit 4 and reduces Cu<2+> to Cu<+>. The H<+> is transferred from an electrolyte soln. I contg. the H<+> to a soln. IIcontg. Cu<2+> and Cu<+> through a cation exchange membrane 2, and it is neutralized to H2O with OH<->. The overall reaction is a reaction for producing water by reducing O2 absorbed in a CO absorbing liq. by various factors with H2. When CO absorbed in the absorbing liq. is released from the liq. by heating, the aqueous composition of the absorbing liq. can be kept uniform by controlling the partial pressure of steam.

Description

DETAILED DESCRIPTION OF THE INVENTION 7. The present invention relates to a method for regenerating a CO absorption liquid, and more particularly to a method for electrochemically regenerating an oxidized CO absorption liquid. The technology to recover COi from various process waste gases containing CO in order to effectively use it has become an important issue in the chemical industry, steel industry, etc. Conventionally, the process for separating CO from various gases has been, for example, deep cooling. Many methods have been used, such as the separation method and the copper-ammonia method, but the former requires high equipment construction and operating costs, while the latter requires high pressure and is difficult to control the Cu''/Cu2+ ratio of the absorption liquid. There are some problems. In the recently developed COSO BonB process, the absorption liquid deteriorates significantly due to moisture, making handling difficult such as dehumidifying the process gas and sealing the pump. In addition, solvent recovery is a common problem with non-aqueous solvents. The necessary equipment becomes complicated.

However, a solution of CuCt in hydrochloric acid has also been proposed as a CO absorbent.
However, the oxidation of cuprous ions by oxygen is rapid, and the scattering of hydrochloric acid vapor also becomes a problem.

In response, the inventors developed CuCt55-180 as an absorbing liquid that is easy to handle in an aqueous solution system and is resistant to oxidation.
375) i proposed. CLI+02 of these absorption liquids
The oxidation of CLI+ proceeds according to equation (1), and the oxidation rate of CLI+ is 4Cu ''+02 +2HzC
)+4Cu"+40H-(1) 100% of uptake speed-
It has the following characteristics.

By the way, in CO recovery using the absorption liquid method, the absorption liquid is CO
Since it is used in the cycle of absorption → CO dissipation by heating → cooling → CO absorption, once it comes into contact with the processing gas, CO
Although the amount of Cu2+ produced, which has no coordinating force, is minute, it becomes impossible to ignore as the number of turns increases.

Possible methods for reducing the generated Cu2+ to Cu" with CO coordination ability include adding a reducing agent such as S n C, l , z or TiCL3, or using electrolytic reduction. However, the former is (Because the reducing agent concentration gradually increases, it is necessary to separate the used reducing agent from the absorption liquid for repeated use.) In addition to requiring an acid power source, there are problems with anodic oxidation that are common in electrolytic reduction. The present invention aims to solve the problems of Ton et al., and is characterized by electrochemical reduction to Cu''iCu+ using a gas electrode, particularly a hydrogen electrode. 1-12Vi can be easily synthesized from separated and recovered CO by a bodic gas shift reaction, so it is easily available. FIG. 1 is a conceptual diagram of a Cu 2+ reduction device using a gas electrode. In Figure 1, symbol 1 is a gas electrode, 2 is a cation exchange membrane, 3 is a cathode, I is an electrolyte solution containing hydrogen ions, and ■ is a solution containing CLl(ID, CLl(I) ions.The reaction is , H2-'22 at gas electrode 1
H" + 26- (2)
゛ and e- are generated. e- reaches the cathode 3 through the external circuit ■, where Cuν+e −, −2Cu ”
(CLl"'v is reduced by 3+. 1-I+
I1 is sent through the cation exchange membrane 2, and 1"+OH- on the ■ side. -2)!,, 0
(4) It is consumed in large quantities. As a reaction of o-all, it was reduced with 02 crab H2 which was mixed into the absorption liquid due to various factors.
ru02 +2H2ヰ2Hz Of5) This is the formation reaction of female water.

Since twice the amount of water (in moles) as the amount of oxygen used for oxidation is generated, the absorption liquid is slightly diluted after reducing divalent copper in this way, and this H20rt' easily flows out of the system. In the separation and recovery of CO that can be removed by the absorption liquid method, the absorbed CO is desorbed from the absorption liquid by heating. The υ1 thermal temperature is, for example, 8 in the case of CuCt-M g Ct 2-based absorption liquid.
0C or higher, and by controlling the water vapor partial pressure at this temperature, the water composition of the absorption liquid can be kept constant.

The above reduction method is electrochemical reduction, and CLI(I)
It is also true that the monovalent and divalent redox potentials of copper, determined by the activity ratio of /Cu0Il, are more noble than the redox potential of hydrogen. The higher the divalent concentration of the steel, the more noble the monovalent/divalent oxidation-reduction potential of copper becomes, and the difference from the hydrogen electrode potential becomes larger, so that the driving force for reduction also becomes larger. From this, the higher the concentration of divalent copper, the easier the reduction, but since divalent copper has no coordinating power for CO, it is not desirable from the viewpoint of CO absorption.

The present invention solves this problem by removing CO from the bath liquid that has absorbed CO.
By solidifying the complex with Cu4' and separating it from the solution to increase the Cu2+ concentration in the solution and then performing reduction treatment, the Cu2+ concentration during CO absorption is low and the Cu2+ concentration during reduction treatment is kept high. It is what makes things possible. To absorb CO, form a solid complex containing Cu" and CO and separate it from the absorption liquid system, thereby increasing the Cu2+ concentration in the solution. In the case of J1 aqueous absorption liquid, the liquid temperature at the time of absorption should be from about OC. Keep it between about 150 or C
Although it is possible to use the absorption liquid of the eaves by lowering the temperature to the above temperature after O absorption, the above Cu Ct M g CL
Approximately 40C-! when using 2-type absorption liquid. It can be easily carried out within the temperature range of Well, this CuC,4-\J g Cl
The complex shown in formula (6) is precipitated simultaneously with dcO absorption in the two-system absorption liquid, and the liquid becomes a slurry. An example of the flow of the recovery device in equation (6) is shown in FIG. For simplicity, the absorption liquid is Cu.
Let it be CL-MgCt2. The treated gas 10 comes into contact with the absorption liquid in the absorption tower 21, and CO is transferred to the liquid side. The liquid 11 that has absorbed CO and turned into a slurry enters the separator 24 . solid complex 1
3 is sent to a desorption column 22, releases CO, and is circulated as a solution 14. The supernatant liquid 12 separated from the solid complex enters the reduction device 23 and is electrochemically reduced by the method described above. The reduced supernatant liquid 15 is combined with the solution 14 from the desorption column and sent to the absorption column 21.

Example 1 0.1 g of platinum black and 0.4 g of activated carbon powder were thoroughly kneaded with Teflon dispersion and water, and placed on a tantalum mesh.
50r, dried in N2 [Also, the following system was constructed using H2 pole on the electrode and Nafion membrane for the partition.
042N/Pt/H2 The Cuo amount before connecting both pts and starting reduction was 22.6 m mat. both p
When a current of about 100 mA was connected between the two through an ammeter. After 115 minutes, CLIQD's ffkk
I found that it had decreased to 15 mmoA.

Example 2 CuCL-MCAn-(M:
Divalent or trivalent metal, n = 2, 3) Mg
A CA2 solution was prepared and contacted with 1 atmosphere of CO. When the resulting solid was separated and the composition of the supernatant liquid was examined by atomic absorption spectroscopy, it was found that MC1n was υ larger than the original liquid composition, and the Cu(I) and Mg concentrations had decreased (I), indicating that the concentration of MC1n had decreased. I did it.

[Brief explanation of the drawing]

Fig. 1 is a conceptual diagram for explaining the reduction of Cu2'' by a gas electrode, and Fig. 2 is a system diagram showing an embodiment of the present invention. 1... Gas electrode, 2... Cation exchange Membrane, 3... Cathode, 10... Processing gas, 21... Absorption tower, 22
... desorption column, 23 ... reduction device, 24 ... separator.

Claims (1)

[Claims] A method for regenerating a CO absorption liquid, comprising a step of reducing with a Cu''k gas electrode contained in the liquid.