JPH07165776A - Cobalt schiff base complex, complex solution for separating oxygen and method for separating oxygen - Google Patents

Abstract

PURPOSE:To obtain the subject efficiently producible complex, expressed by a specific formula and capable of well separating oxygen at ambient temperature and a small temperature difference according to a temperature-swing method, remarkably improving the energy reduction of a complex solution and the utilization efficiency of the complex and reducing the production cost. CONSTITUTION:This complex is soluble in a solvent, capable of binding to oxygen by absorption thereof and causing the phase separation so as to deposit as a solid phase and expressed by the formula (R1 to R4 each is H, an alkyl or an alkoxy; R5 to R8 each is methyl), preferably N,N'-bis(salicylidene)1,1,2,2- tetramethylethylendiaminocobalt (II). Furthermore, the complex is preferably used as a solution, prepared by dissolving the complex and an axial ligand coordinated with the fifth coordination position in the axial direction of the complex (e.g. a pyridine-based compound containing basic N atom) in a solvent (e.g. 1,2-dichlorobenzene) and capable of absorbing oxygen, thereby binding the complex to the oxygen and depositing the complex as a solid phase.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cobalt Schiff base complex, a complex solution for oxygen separation and an oxygen separation method using the same, and more specifically, it uses a solution of an oxygen complex to remove oxygen from an oxygen-containing gas such as air. The present invention relates to a complex that enables oxygen separation by a temperature fluctuation method at room temperature and a small temperature difference, a solution thereof, and an oxygen separation method using the same.

[0002]

2. Description of the Related Art Conventionally, on the industrial scale, as a method for separating and producing oxygen in air, air is pressurized, cooled, expanded and liquefied, subjected to multiple rectification steps, and subjected to nitrogen and oxygen due to boiling point differences. There is a cryogenic separation method for separating and. However, this method requires a large amount of energy input. Further, it is suitable for the purpose of producing a large amount of high-purity oxygen or nitrogen, but not suitable for small-scale production. In recent years, using an adsorbent such as zeolite or carbon molecular sieves,
There is an adsorption separation method in which oxygen or nitrogen is separated and produced by selectively adsorbing nitrogen or oxygen to the adsorbent. This method has the advantages that the operation is simple and the startup time is short, and it is suitable for the production of relatively small volumes of oxygen and nitrogen. However, this adsorptive separation method is not suitable for large-volume production. Further, there is a drawback that the device becomes large as compared with the production amount of the product. Especially in the case of producing oxygen, there is a drawback that the maximum oxygen concentration is only 95%.

In order to overcome these drawbacks, several methods have recently been proposed for separating oxygen by using a complex that reversibly reacts only with oxygen. In this method, for example, as described in JP-A-58-20296, the complex solution is brought into contact with air at a low temperature of 5 ° C. or lower,
The oxygen in the air is absorbed by the complex solution, and then the oxygen is released from the complex solution at a high temperature of 25 ° C or higher, and this is collected as product oxygen. The complex solution is cooled again to a low temperature of 5 ° C or lower. Absorb oxygen. Hereinafter, the same process is repeated to continuously collect oxygen (temperature fluctuation type chemical absorption method). Another method of this oxygen separation method is that the rate of oxygen binding to the complex changes according to the magnitude of the oxygen partial pressure in the gas phase, so that the temperature of the complex solution is kept constant under high oxygen partial pressure. There is a pressure fluctuation type chemical absorption method in which oxygen is absorbed, and oxygen that has been absorbed under a low oxygen partial pressure is desorbed to separate and collect oxygen. In any case, in this type of method, the complex solution was always treated as a uniform liquid.

[0004]

However, the complex solutions used in these chemical absorption methods have the following drawbacks. Since the conventional complex solution has a low oxygen affinity, it is necessary to cool the complex solution to a temperature of around 0 ° C., and as a result, a large amount of cooling energy is required. Further, the utilization efficiency of the complex is low, and when the complex solution is cooled to 0 ° C. and absorbs oxygen from air at atmospheric pressure, the oxygen bond ratio to the complex is 20.
Only ~ 40%. Furthermore, when absorbing oxygen from air at atmospheric pressure in the absorption tower at a temperature of 0 ° C. and generating oxygen at atmospheric pressure in the diffusion tower, it is necessary to heat the complex solution in the diffusion tower to a temperature of at least 60 ° C. or higher, Here too, a great deal of thermal energy was required. Furthermore, when the composition of the complex solution was determined, the oxygen absorption temperature and the oxygen release temperature were also determined at the same time, and these temperatures could not be changed. Therefore, the environmental heat and the exhaust heat cannot be fully utilized. Further, the complex solution used in the above-mentioned conventional oxygen separation method dimerizes the complex as absorption and desorption of oxygen are repeated, and absorption capacity is deteriorated. Have been taken. However, the dimerization of the complex could not be completely prevented, so that the complex solution could not be used for a long time. Moreover, since the complex concentration of the complex solution could not be made higher than the solubility of the complex in the solvent, the oxygen transport amount (oxygen separation amount) from the absorption tower to the diffusion tower did not reach a practical level. In addition, the solvent of the complex solution must have a high polarity, such as 1-methyl-2-pyrrolidinone (dipole moment 4.09 Debye), in order to accelerate the absorption rate of oxygen. Many of them were hydrophilic. Therefore, the oxygen separation device required equipment for removing water in the raw material gas. In addition, the unit debye of the above dipole moment (Deby
e) is 3.34 × 10 ^-30 Cm (MKS).

The present invention has been made in view of the above circumstances, and provides a complex solution and a complex solution for oxygen separation capable of solving the drawbacks of the conventional temperature fluctuation type chemical absorption method or pressure fluctuation type chemical absorption method, and the above-mentioned complex solution. It is intended to provide the used oxygen separation method.

[0006]

In order to solve such a problem, the cobalt Schiff base complex of the present invention is a complex which dissolves in a solvent and combines with oxygen by absorption of oxygen to cause phase separation which precipitates as a solid phase. Yes, the general formula (A)

[0007]

[Chemical 2]

(Wherein R1, R2, R3 and R4 each represent hydrogen, an alkyl group or an alkoxy group, and R5, R
6, R7 and R8 represent a methyl group. ) Is represented. Further, the oxygen separation complex solution of the present invention is obtained by dissolving the above cobalt Schiff base complex and an axial ligand coordinated to the fifth dentate in the axial direction of the complex in a solvent, and is bound to oxygen by absorption of oxygen. It is characterized in that phase separation occurs as a solid phase. This cobalt Schiff base complex is composed of N, N'-bis (salicylidene) 1,1,2,
2-tetramethylethylenediaminocobalt (II),
N, N'-bis (3-ethoxysalicylidene) 1,1,
2,2-Tetramethylethylenediaminocobalt (I
I), N, N'-bis (4,6-dimethoxysalicylidene) 1,1,2,2-tetramethylethylenediaminocobalt (II), N, N'-bis (3,5-tert-butyl) Salicylidene) 1,1,2,2-tetramethylethylenediaminocobalt (II) is preferable. In addition, as the axial ligand coordinated to the fifth axial site of the cobalt-Schiff base complex, a pyridine compound containing a basic nitrogen atom or an alkylamine compound containing a basic nitrogen atom or a base An imidazole-based compound containing a nitrogen atom is desirable. Also,
The solvent that dissolves the cobalt Schiff base complex and the axial ligand is
A solvent with a dipole moment of 3.5 Debye or less,
2-dichlorobenzene, 3,4-dichlorotoluene,
2,4-dichlorotoluene, 2,3-dichlorotoluene, 2,6-dichlorotoluene, 1,2-dibromobenzene, 2-chloroparaxylene, 4-chloroparaxylene, 1-chloronaphthalene, 1,2,3 , 4-tetrahydronaphthalene, 1-methylnaphthalene, 1,2,3-
Trimethylbenzene, 1,2,3,5-tetramethylbenzene, 1,4-diisopropylbenzene, 4-tert-butyltoluene, tertiary amylbenzene,
One or more selected from normal amylbenzene, phenylcyclohexane, methyl benzoate, normal propyl benzoate, thioanisole and indane, particularly 1,2-dichlorobenzene, 1,2,3, and 1 selected from 4-tetrahydronaphthalene, indane and 2,6-dichlorotoluene
One kind or two or more kinds is preferable. Further, among the above-mentioned respective solvents, one or two or more first solvents selected from 1,2-dichlorobenzene, 1,2,3,4-tetrahydronaphthalene, indane and 2,6-dichlorotoluene. And a second solvent other than these among the above solvents may be mixed and used. Further, it is desirable that the concentration of the cobalt Schiff base complex is higher than 0.1M,
The concentration may be higher than the solubility of the complex. Furthermore, the oxygen separation method of the present invention, an oxygen absorption step of contacting a mixed gas containing air or oxygen to any of the above oxygen separation complex solutions to precipitate the complex bound to oxygen as a solid phase, And an oxygen releasing step of heating the deposited oxygen-bonded complex to release oxygen. It is desirable that this oxygen absorption step be performed under a temperature condition of 0 to 40 ° C. Further, it is desirable to carry out the oxygen releasing step under a temperature condition of 20 to 60 ° C. Furthermore, it is desirable that the oxygen partial pressure of the mixed gas containing air or nitrogen in the oxygen absorption step be 99 Torr or more.

[0009]

The cobalt-Schiff base complex of the present invention is dissolved in a solvent, binds with oxygen by absorbing oxygen, and causes phase separation to be precipitated as a solid phase. As a raw material of a complex solution for oxygen separation having a very high oxygen absorption capacity. It is suitable. The oxygen-separating complex solution of the present invention is obtained by dissolving the above-mentioned cobalt-Schiff base complex and the axial ligand coordinated to the fifth dentate in the axial direction of the complex in a solvent. When it binds with, it becomes a solid phase and precipitates in the solution, and when it is heated to desorb oxygen, a phase separation phenomenon occurs in which it becomes a liquid phase. That is, when air or an oxygen-containing gas is brought into contact with a complex solution consisting of a cobalt Schiff base complex, a specific axial ligand and a solvent, and the complex solution absorbs oxygen, the oxygen-bonded complex to which oxygen is bound is solid. It becomes a phase and precipitates from the solution and solidifies and precipitates. By heating this into a liquid phase, the absorbed oxygen is desorbed, oxygen is obtained, and the complex solution is regenerated. When the phase separation phenomenon is used in the oxygen separation, for example, when oxygen is absorbed from the air at atmospheric pressure at a temperature of 20 ° C., 90% or more of the complex is bound with oxygen to be solid-phased. Is heated to a temperature of 40 to 50 ° C., most of the absorbed oxygen is released to become a liquid phase. As a result, the energy for cooling the complex solution can be reduced and the utilization efficiency of the complex can be improved. Furthermore, when a mixed solvent of a good solvent that easily causes the phase separation phenomenon and a poor solvent that does not easily cause the phase separation phenomenon is used as the solvent for the complex solution, the phase separation elimination temperature can be changed by changing the composition of the complex solution. Can be used, and the energy efficiency of oxygen separation can be significantly improved. Further, the oxygen-bonded complex solidified and precipitated by phase separation has a lower reactivity than the oxygen-bonded complex dissolved in the solution, and the reaction rate of dimerization is also negligible.
As a result, the complex solution can be used repeatedly over a long period of time. The solidification and precipitation of the oxygen-bonded complex due to the phase separation phenomenon means that the oxygen-bonded complex is excluded from the reaction system of the oxygen bond, and the unbonded complex in the complex solution is also phase-separated by the oxygen bond. Excluded outside. Therefore, if there is a solid phase oxygen unbonded complex that exceeds the solubility of the oxygen unbonded complex, the oxygen unbonded complex can be sequentially dissolved in the solution and reacted with oxygen. Therefore, the complex concentration can be used in the reaction at a concentration of solubility or higher, and the oxygen transport amount can be increased to a desired amount.
Furthermore, the conditions relating to the solubility of the solvent are relaxed, and a hydrophobic solvent can be adopted.

The details of the present invention will be described below. The oxygen separation complex solution according to the present invention is composed of the cobalt Schiff base complex represented by the general formula (A), the axial ligand, and the solvent, and causes phase separation. When an axial ligand is added to a complex solution in which the complex of the general formula (A) is dissolved in a solvent, the axial ligand has a fifth axial direction of the complex as shown in the following formulas (1) and (2). Be coordinated to the zodiac.

[0011]

[Equation 1]

[0012]

[Equation 2]

(In the formula, Co represents a cobalt Schiff base complex, B represents an axial ligand, and KB represents an equilibrium bond constant of the cobalt Schiff base complex and the axial ligand.
Represents the concentration of each chemical species. The complex in which the axial ligand (B) is coordinated becomes an oxygen-active complex and reacts with oxygen (O ₂ ) as in the following formula (3).

[0014]

[Equation 3]

Here, 1 represents a liquid phase and g represents a gas phase. When a solvent having a large polarity is used, oxygen bonding is carried out in the complex solution while maintaining the liquid phase without causing a phase change. And the true oxygen bond equilibrium constant at this time (called oxygen affinity) K
i (Torr ⁻¹ ) is represented by the equation (4).

[0016]

[Equation 4]

[0017]

[Equation 5]

[0018]

[Equation 6]

Here, P is oxygen partial pressure (Torr), Cl
Is the concentration of oxygen-bonded complex [B-Co-O ₂ (l)] (mol / l), CB
Is the concentration of unbonded oxygen complex [B-Co (l)] (mol / l), CT is the total complex concentration (mol / l), Y is the ratio of oxygen-bonded complex to all the complexes, and Ki is the phase separation. True oxygen bond equilibrium constant (oxygen affinity) (Torr ^-1 ), where P1 / 2 is the oxygen partial pressure required to bind oxygen to half of all complexes
(Torr) and n represent the Hill coefficient. The Hill coefficient n here means the log (Y /
Y-1), which is the slope of a straight line obtained by plotting logP on the horizontal axis.

Phase separation is considered to occur by the mechanism described below. It is known that in the cobalt-Schiff base complex, when oxygen is bound, the charge density on cobalt moves to the oxygen molecule. As a result, a dipole moment is generated and the polarity of the Co—O ₂ bond increases. The change in the polarity of the complex due to such an oxygen bond has a great influence on the solubility of the complex in a solvent. When the polarity of the solvent of the complex solution is small, the solubility of the complex to which oxygen is bound is smaller than that of the complex not bound to oxygen because the polarity of the complex to which oxygen is bound is large. The amount of the oxygen-bonded complex formed when the complex solution absorbs oxygen is determined by the oxygen affinity and oxygen partial pressure of the complex. in this case,
When the (true) oxygen affinity is sufficiently high, the solubility S of the oxygen-bonded complex is sufficiently low, and the solubility of the oxygen-bonded complex is smaller than the amount Cl of the oxygen-bonded complex formed when the complex solution absorbs oxygen. (S <Cl), the generated oxygen-bonded complex cannot exist in a dissolved state, and is therefore considered to be solidified and precipitated as shown in the following formula (7).

[0021]

[Equation 7]

As mentioned above, l and g represent a liquid phase and a gas phase, respectively, and s represents a solid phase.

Since the equilibrium point of the reaction moves to the right when such a phase separation phenomenon occurs, the reaction of the above formula unilaterally proceeds to the right. As a result, the apparent oxygen affinity Ka of the complex solution becomes larger than the true oxygen affinity Ki. When the amount of the oxygen-bonded complex that is phase-separated and solidified and precipitated is converted into concentration, Cs (mol / l) is given, and the apparent oxygen affinity K is obtained.
a can be expressed by the following equation (8).

[0024]

[Equation 8]

[0025]

[Equation 9]

From the above equation (8), it can be seen that the apparent oxygen affinity Ka due to phase separation depends on the concentration CT of all the complexes and the oxygen partial pressure P. The higher the concentration of the complex and the higher the oxygen partial pressure, the easier the phase separation. When the temperature of the complex solution rises, the solubility S of the oxygen-bonded complex in the solution S
On the other hand, the concentration Cl of the oxygen-bonded complex becomes small, and when the above-mentioned condition for phase separation (S <Cl) is not satisfied, the phase separation phenomenon is eliminated and the complex solution becomes uniform. When the total complex concentration CT is a low concentration at which phase separation does not occur, the true oxygen affinity Ki can be obtained from this complex solution. Based on this true oxygen affinity Ki and the apparent oxygen affinity Ka obtained from the high-concentration complex solution in which phase separation occurs, the solubility S of oxygen complex and the amount Cs of phase separation are (10) and (11).
It can be obtained by a formula.

[0027]

[Equation 10]

[0028]

[Equation 11]

Solubility S and concentration C of the oxygen-bonded complex in a solvent
The temperature Tp of the complex solution when 1 is the same (S = Cl) is defined as the phase separation temperature. When phase separation occurs at a temperature lower than the phase separation temperature Tp, a large amount of oxygen is absorbed because the apparent oxygen affinity Ka is large. Next, when the temperature of the complex solution exceeds the phase separation temperature, the oxygen affinity of the complex solution decreases to a true value, and the absorbed oxygen is released at once. In this way, oxygen can be separated with a small temperature difference near the phase separation temperature. Further, in a complex solution in which phase separation occurs, excess oxygen unbonded complex in a solid state above solubility can be sequentially dissolved in a solvent and reacted with oxygen. This is because when the complex Co (l) dissolved in the solvent reacts with oxygen and is consumed, the concentration CB of the oxygen unbonded complex in the solution decreases. Then, the oxygen unbonded complex Co (s) in the solid state which is not dissolved in the solvent is dissolved to form an oxygen unbonded complex dissolved in the solvent, which reacts with oxygen O ₂ and is represented by a chemical reaction formula. Equation (12) is obtained. And this is repeated. Since this is repeated, the excess oxygen unbonded complex in the solid phase can be sequentially dissolved in the solvent to react with oxygen.

[0030]

[Equation 12]

Therefore, in the complex solution in which phase separation occurs, the reaction of the above formula (12) occurs, so that a complex having a solubility or higher can be added to form an oxygen absorbing solution. Therefore, the amount of oxygen transported from the absorber to the stripper can be increased to a desired amount. Furthermore, the condition of the solvent regarding the solubility is relaxed,
A hydrophobic solvent can be adopted.

The present invention efficiently separates and collects oxygen by utilizing the above-mentioned phase separation. In order to satisfy the conditions of phase separation, the solubility of the oxygen-bonded complex is small and the true oxygen affinity is It is necessary to select a combination of a complex, an axial ligand, and a solvent that will increase the size. The cobalt Schiff base complex according to the present invention is a salicylaldehyde-based Schiff base complex represented by the general formula (A) in which the central metal is cobalt. The complex represented by the general formula (A) has a four-coordinate structure, but when the central metal is cobalt, it has a six-coordinate structure and is a stable complex. That is, when the axial ligand is coordinated to the 5th coordination site in the axial direction of the Schiff base plane, the oxygen binding capacity of the 6th coordination site is enhanced, and oxygen is bound to this to increase the oxygen content. Absorb. There are two types of oxygen-bonded complexes: a monomer in which one molecule of oxygen is bound to one molecule of the complex and a dimer in which one molecule of oxygen is bound to two molecules of the complex. Monomers can reversibly bind or desorb oxygen, but dimers cannot reversibly bind or desorb oxygen. Therefore, in order to prevent the dimerization of the complex, a sterically hindering group may be added to the Schiff base so that the complexes cannot approach each other. In the cobalt Schiff base complex according to the present invention, it is effective that R5, R6, R7 and R8 are methyl groups. Hereinafter, tetramethylethylenediamine in which four methyl groups are added to the diamine portion is referred to as Tmen.

Axial ligands include imidazole compounds, pyridine compounds and alkylamine compounds containing a basic nitrogen atom. Imidazole compounds include 1-methylimidazole and pyridine compounds. 4-dimethylaminopyridine, 4-piperidinopyridine and 4-pyrrolidinopyridine can be preferably used. Among these axial ligands, 4-dimethylaminopyridine is preferable in the present invention.

As a solvent for dissolving the complex and the axial ligand to form a complex solution, a solvent having a dipole moment of 3.5 debye or less and having a small polarity or no polarity is used. From the viewpoint of safety, it is desirable to use a solvent having a high boiling point and a high flash point, which can dissolve the particles. Further, it is desirable to use an aprotic solvent in order to prevent the oxidation of the complex. As such a solvent, 1,2-
Dichlorobenzene, 3,4-dichlorotoluene, 2,4-dichlorotoluene, 2,3-dichlorotoluene, 2,6-dichlorotoluene, 1,2-dibromobenzene, 2-chloroparaxylene,
4-chloroparaxylene, 1-chloronaphthalene, 1,2,3,4-
Tetrahydronaphthalene, 1-methylnaphthalene, 1,2,3-
Trimethylbenzene, 1,2,3,5-tetramethylbenzene,
1,4-diisopropylbenzene, 4-tert-butyltoluene, tertiary-amylbenzene, normal-amylbenzene, phenylcyclohexane, methylbenzoate, normal-propylbenzoate, thioanisole,
Indane or the like can be effectively used. Among these solvents, good solvents that are most likely to cause phase separation are 1,2-dichlorobenzene (dipole moment 2.14 debye), 1,2,3,4-tetrahydronaphthalene (dipole moment 0.6 debye),
Indane and 2,6-dichlorotoluene. Solvents other than these are poor solvents in which phase separation does not occur unless the temperature is set to 20 ° C. or lower or the oxygen partial pressure is 400 Torr or higher. Of the above solvents, 1,2,3-trimethylbenzene and tertiary amylbenzene are solvents with almost no polarity.

[0035]

EXAMPLES The present invention will be specifically described below with reference to examples. (Example 1) The cobalt-Schiff base complex used in this Example was synthesized by synthesizing a Schiff base and a complex formation reaction with cobalt according to a conventional method. The synthesized complexes are shown in Table 1 together with the complex symbols according to the general formula (A).

[0036]

[Table 1]

In the above table, H, CH ₃ , CH ₃ O and tBu represent a hydrogen atom, a methyl group, a methoxy group and a tertiary butyl group, respectively. 4-dimethylaminopyridine or 4-piperidinopyridine was used as the axial ligand. Solvents for dissolving these include 3,4-dichlorotoluene (dipole moment; 2.95 debye), 2,4-dichlorotoluene (dipole moment; 1.70 debye), normal propyl benzoate, 1,2- The dipole moment of dichlorobenzene (dipole moment; 2.14 Debye) etc. is 3.
It was dissolved in a predetermined concentration using a solvent of 5 Debye or less.

Evaluation Test 8 ml of a complex solution having a predetermined concentration was prepared in a vial container from the complex, axial ligand and solvent. This was placed in a constant temperature bath, oxygen was introduced into the gas phase of the vial container, and the complex solution was made to absorb oxygen. At this time, the complex that absorbed and bonded oxygen was solidified and precipitated, and the solution was suspended. Then, the amount of absorbed oxygen AO ₂ (mol) was determined from the volume of the vapor phase of the vial container that was obtained in advance and the amount of change in the oxygen partial pressure of the vapor phase of the vial container. The oxygen absorption amount AO ₂ (mol) and the complex concentration CT
(Mol / l) and the equilibrium oxygen partial pressure P (Torr) were used to determine the oxygen affinity Ka according to the above calculation formula (8). This is shown in Table 2. The four types of complexes shown in Table 2 are: Complex 1: N, N'-bis (salicylidene) 1,1,2,2-
Tetramethylethylenediaminocobalt (II) (hereinafter,
CoSalTmen) Complex 2: N, N'-bis (3-ethoxysalicylidene)
1,1,2,2-Tetramethylethylenediaminocobalt (II) (hereinafter referred to as Co3MeOSalTmen) Complex 3: N, N'-bis (4,6-dimethoxysalicylidene) 1,1,2,2- Tetramethylethylenediaminocobalt (II) (hereinafter referred to as Co4,6DMeOSalTmen) Complex 4: N, N'-bis (3,5-ditertiarybutylsalicylidene) 1,1,2,2-tetramethylethylenediamino Cobalt (II) (hereinafter Co3,5DtBuSal
It is referred to as Tmen).

[0039]

[Table 2]

Next, when desorbing the absorbed oxygen from the complex solution, the temperature in the constant temperature bath was gradually raised. Then, when a certain temperature is reached, the solid phase that has been precipitated previously is dissolved to form a solution and oxygen is desorbed, and the oxygen partial pressure of the gas phase of the vial container becomes the oxygen partial pressure before oxygen absorption. The temperature was defined as the phase separation elimination temperature. When the complex solution was phase-separated, the solution suspended and became a solid-liquid two phase. When the phases were not separated, a uniform liquid phase remained even after absorbing oxygen.

As is clear from Table 2, the oxygen-bonded phase-separated complex according to the present invention is bound to oxygen at room temperature to be solidified and precipitated, and its apparent oxygen affinity is Co3,5DtBuSa.
ltmen 0.1M, axial ligand DMAP (4-dimethylaminopyridine) 1.5 equivalents, solvent 1,2-dichlorobenzene (dipole moment; 2.14 Debye), K at 15 ℃
It was a = 1/47 (Torr ⁻¹ ). Complex is Co4,6DMe
When OSalTmen (0.1 M), the axial ligand is 4 PRP (4-pyrrolidinopyridine) 1.5 equivalents, and the solvent is normal propyl benzoate, phase separation occurs when the complex solution is cooled to 0 ° C., and Ka = 1/381 (Torr ^-1 ).

Next, in order to evaluate the magnitude of the oxygen affinity of the complex solution that absorbs oxygen by the phase separation of the present invention, the complex solution that absorbs oxygen in a liquid phase that does not cause phase separation, which has been conventionally used, is used. The true oxygen affinity Ki of is shown below as a comparative example. (Comparative Example) True oxygen affinity Ki of a complex solution without phase separation
Was determined by measuring the oxygen absorption amount, the concentration of the complex solution, and the oxygen absorption equilibrium pressure. The results are shown in Table 3.

[0043]

[Table 3]

The cobalt Schiff base complex was the same as the complex used in Example 1 above, namely CoSalTmen, Co3.
MeOSalTmen, Co4,6DMeOSalTm
En, Co3,5DtBuSalTmen was used, and MeIm (methylimidazole) was added as an axial ligand in an amount of 1.5 equivalents of the complex, respectively.
A complex solution was prepared by adjusting a concentration of 0.1 M with a solvent of 1-methyl-2-pyrrolidinone (NMP) having a polarity larger than that of 09 Debye and 3.5 Debye. The complex solutions tested as comparative examples in Table 3 above do not solidify and precipitate the oxygen-bonded complex when absorbing oxygen. Since such a complex has a low oxygen affinity, the absorption temperature was tested at a low temperature of 0 ° C. As shown in Table 3, the oxygen affinity Ki at that time is C
o4,6DMeOSalTmen (0.1M), axial ligand M
eIm (1.5 equivalents), when using solvent NMP is the largest, K
i = 1/480 (Torr ⁻¹ ), and the complex Co3.5DtBuS
alTmen (0.1M), axial ligand (1.5 equivalents), solvent N
The time of MP was the smallest, and Ki was 1/2060 (Torr ^-1 ). Comparing this comparative example with the oxygen affinity of the complex solution solidified and precipitated by the oxygen bond in Table 2 of the present invention, the oxygen affinity of the phase-separated complex solution of the present invention is obviously larger than that of the comparative example. The oxygen affinity of the complex solution in which the phase separation was difficult to occur showed almost the same value as the complex of the comparative example.

Example 2 Complex Co3,5DtBuSa
Using ltmen (complex 4) and 4-dimethylaminopyridine (1.5 equivalents) as the axial ligand, this was used as solvent 1,2
The oxygen affinity Ka was measured by using a complex solution dissolved in -dichlorobenzene (dipole moment; 2.14 debye), keeping the amount of oxygen in the gas phase constant, and changing the concentration of the complex. The results are shown in Table 4. When the temperature was 20 ° C. and the complex concentration was 0.05 M, phase separation did not occur. Concentration is 0.
Phase separation did not occur at 20 ° C. at 10 M, but phase separation occurred at a temperature of 15 ° C.

[0046]

[Table 4]

The apparent oxygen affinity Ka is 0.20.
Up to M, it increases as the concentration increases, but 0.20
Above M, almost the same values were obtained. Also, the concentration is
It became clear that 0.1 M or more is preferable. In addition,
When the temperature of the complex solution of 0.35M was raised to 50 ° C. after absorbing oxygen, the phase separation was eliminated and oxygen was desorbed to become a uniform solution. Next, when oxygen is supplied and absorbed using the complex solution at a temperature of 20 ° C. until the equilibrium oxygen partial pressure reaches 160 Torr corresponding to the atmospheric oxygen partial pressure, the apparent oxygen affinity Ka is 1/6 Torr ^−1. The ratio of oxygen-bonded complexes among all the complexes reached 96%.

(Example 3) Co3,5DtB as a complex
uSalTmen (0.2M), 4-dimethylamipyridine (1.5 equivalents) as the axial ligand, and 1,2-dichlorobenzene as the solvent were dissolved, and the oxygen partial pressure Pi immediately before the start of oxygen absorption was changed at a temperature of 20 ° C. The oxygen affinity Ka was measured. The results are shown in Table 5. Phase separation did not occur when the oxygen partial pressure immediately before the start of oxygen absorption was 51 Torr, but phase separation occurred when the oxygen partial pressure was 99 Torr or higher. From this, it was found that the initial oxygen partial pressure of absorption was 99 Torr or more for the phase separation of this complex solution.

[0049]

[Table 5]

(Example 4) Co3,5DtB as a complex
uSalTmen (0.40M), 4-dimethylaminopyridine (1.5 equivalents) as the axial ligand, 1,2-as the solvent
A complex solution was prepared using dichlorobenzene. Complex C
A part of o3,5DtBuSalTmen could not be dissolved in the solution, and the oxygen affinity of the complex solution in the solid state was measured at a temperature of 20 ° C. When the equilibrium oxygen partial pressure was 126 Torr, the apparent oxygen affinity Ka was 1/13 Torr ^-1 , and the oxygen bond ratio to all the complexes was 91%. That is, this is 0.3
This corresponds to that a 6M complex has been reacted and used. Co
Since the solubility of 3,5DtBuSalTmen in 1,2-dichlorobenzene is 0.21M, it is clear that the complex Co3,5DtBuSalTmen remaining in the solid phase was dissolved in the solution and reacted with oxygen. That is, at the beginning of use, even if the complex is added to the solvent at a solubility higher than that of the complex,
As the reaction progresses, oxygen is bound to the complex and used.
It was confirmed that the excess complex was successively dissolved in the solvent and used as a complex solution.

(Example 5) Co3,5DtB as a complex
uSalTmen and 4-dimethylaminopyridine were used as the axial ligands, and these were used as the solvent 1,2-dichlorobenzene (1,
A mixed solvent of 2-DCB) and 2,3-dichlorotoluene (2,3-DCT) was dissolved to form a complex solution, and the phase separation elimination temperature was measured by changing the mixing ratio of this mixed solvent. Table 6 shows that the phase separation elimination temperature decreases as the proportion of 2,3-dichlorotoluene increases.

[0052]

[Table 6]

Example 6 Complex Co3,5DtBuSa
Itmen and 4-dimethylaminopyridine as an axial ligand were dissolved in a solvent 1,2-dichlorobenzene (1,2-DCB) to obtain a complex solution having a complex concentration of 0.02 M and an axial ligand of 2.5 equivalents. Prepared. The true oxygen affinity K in the region where the phase separation of the complex solution does not occur (region where the complex concentration and oxygen partial pressure are low)
i was measured. In addition, a complex solution having a complex concentration of 0.27 M and an axial ligand of 2.5 equivalents was prepared using the same complex, axial ligand and solvent, and the apparent oxygen affinity Ka in the region where the phase separation phenomenon of this complex solution occurs. Was measured. In this measurement, the amount of oxygen was kept constant, and the temperature was measured at 20 ° C to 40 ° C at 5 ° C intervals. Furthermore, the true oxygen affinity Ki and the apparent oxygen affinity K
The solubility S and the phase separation amount Cs of the oxygen-bonded complex were determined using the equations (10) and (11) from a. The results are shown in Table 7.

[0054]

[Table 7]

The apparent oxygen affinity Ka of this complex solution at 20 ° C. is 5.63 × 10 ⁻² Torr ⁻¹ , the true oxygen affinity Ki is 6.10 × 10 ⁻⁴ Torr ⁻¹ , and the apparent oxygen is The affinity Ka was about 100 times as large as the true oxygen affinity Ki. Also, the oxygen-bonded complex Co3 at 20 ° C
The solubility of 5DtBuSalTmen (DMAP) O ₂ was 1.11 × 10 ⁻³ M, which was about 250 times less than the solubility of 0.27M of the complex Co 3,5DtBuSalTmen (DMAP) without oxygen bonding. That is, it was found that the solubility of the oxygen-bonded complex in the solution was sufficiently small, and it was confirmed that phase separation occurred. In addition, from the result that the amount of phase separation is 1.01 × 10 ^-1 M, 3
It was found that 7% of the complex had precipitated. When the oxygen partial pressure is further increased, oxygen is absorbed and the phases are separated, and as shown in Example 4, 90% or more of the complex is bound and absorbed with oxygen.

Example 7 Complex Co4,6DMeOSa
ltmen and the axial ligand 4-piperidinopyridine were dissolved in a solvent normal propyl benzoate to obtain a complex concentration of 0.1.
A complex solution of 1M and 1.5 equivalents of axial ligand was prepared in a glass container, and oxygen was sealed in the gas phase and sealed.
The complex solution was stored in a constant temperature bath at 0 ° C., and the time-dependent change in oxygen affinity of this complex solution at 0 ° C. was examined. The results are shown in Table 8. This complex solution has an apparent oxygen affinity K even after 340 days have passed.
a and the Hill coefficient n were stable, and no evidence of the dimerization reaction was observed.

[0057]

[Table 7]

Example 8 The complex CoS was added to various solvents.
alTmen and the axial ligand 4-dimethylaminopyridine were dissolved so that the complex concentration was 0.25 M and the axial ligand was 1.5 equivalents, and the solvent in which the phase separation phenomenon occurred at 20 ° C. was confirmed by experiments. The solvent that causes the phase separation phenomenon at 20 ℃ is 1,2-
Dichlorobenzene, 1,3-dichlorobenzene, 3,4-dichlorotoluene, 2,4-dichlorotoluene, 2,3-dichlorotoluene, trans-1,2-dichlorocyclohexane, 2,6-dichloroanisole, 2-chloro Paraxylene, 1-chloronaphthalene, 1,2,3,4-tetrahydronaphthalene, indane, 1-methylnaphthalene, dimethylnaphthalene (mixture of isomers), 1,2,3-trimethylbenzene, 1,2,3,5 -Tetramethylbenzene, 1,4-diisopropylbenzene, 4-tert-butyltoluene, tert-amylbenzene, n-amylbenzene, tert-butylbenzene, n-hexylbenzene, methylbenzoate, thioanisole and other solvents for phase separation It was found to be suitable as. Each of these solvents is a solvent having a dipole moment of 3.5 debye or less or a nonpolar solvent and is capable of dissolving the cobalt Schiff base complex and the axial ligand. Further, these solvents are hydrophobic solvents which can be mixed with a very small amount of water but cannot be mixed with a large amount of water. It was not possible to use these hydrophobic solvents as solvents for the complex solution when phase separation did not occur.

(Example 9) In a variety of solvents, the complex Co3,5DtBuSalTmen different from that of Example 8 was added,
Axial ligand 4-dimethylaminopyridine, complex concentration 0.20
M, the axial ligand was dissolved in 1.5 equivalents, and a solvent in which a phase separation phenomenon occurred at 20 ° C. was searched. Solvents that cause phase separation phenomenon are 1,2-dichlorobenzene, 1,2-dibromobenzene, 3,4-dichlorotoluene, 2,3-dichlorotoluene, 1-
Chloronaphthalene, 4-bromoorthoxylene, N, N, 3,5-
Tetramethylaniline, 1,2,3,4-tetrahydronaphthalene, indane, 1-methylnaphthalene, 1,2,3-trimethylbenzene, 1,2,3,5-tetramethylbenzene, 1,4-diisopropylbenzene, These were tertiary amylbenzene, normal amylbenzene, phenylcyclohexane, paramethylisopropylbenzene, 4-tert-butyltoluene, and thioanisole. Each of these solvents is a solvent having a dipole moment of 3.5 debye or less or a nonpolar solvent and is capable of dissolving the cobalt Schiff base complex and the axial ligand. Further, these solvents are hydrophobic solvents which can be mixed with a very small amount of water but cannot be mixed with a large amount of water. It was not possible to use these hydrophobic solvents as solvents for the complex solution when phase separation did not occur.

[0060]

As described above, in the oxygen separation complex solution of the present invention, when the cobalt Schiff base complex binds with oxygen, it becomes a solid phase and precipitates in the solution, and it is heated to desorb oxygen. If this is done, a phase separation phenomenon of liquid phase occurs. That is, when air or an oxygen-containing gas is brought into contact with a complex solution consisting of a cobalt Schiff base complex, a specific axial ligand and a solvent, and the complex solution absorbs oxygen, the oxygen-bonded complex to which oxygen is bound is solid. It becomes a phase and precipitates from the solution and solidifies and precipitates. By heating this into a liquid phase, the absorbed oxygen is desorbed, oxygen is obtained, and the complex solution is regenerated. If such a phase separation phenomenon is used, for example, when contacting with air at atmospheric pressure at a temperature of 20 ° C., 90%
Oxygen is bound to the above complex, and this complex solution is added to 40 to 50
When heated to a temperature of about ℃, most of the absorbed oxygen can be released. As a result, the energy for cooling the complex solution can be reduced, the utilization efficiency of the complex can be significantly improved, and oxygen can be efficiently produced. In addition, the oxygen production system using this complex solution can be simplified and downsized. In addition, when a mixed solvent of a good solvent that easily causes the phase separation phenomenon and a poor solvent that does not easily cause the phase separation phenomenon is used as the solvent for the complex solution, the phase separation elimination temperature can be changed by changing the composition of the complex solution. Can be used, the energy efficiency of oxygen separation can be significantly improved, and the manufacturing cost can be reduced. Further, the oxygen-bonded complex solidified and precipitated by phase separation has a lower reactivity than the oxygen-bonded complex dissolved in the solution, and the reaction rate of dimerization is also negligibly slow. As a result, the complex solution can be used for a long period of time, the replacement of the complex becomes unnecessary, and the manufacturing cost can be reduced. further,
By using the phase separation phenomenon, the concentration of the complex can be made higher than its solubility, and the amount of oxygen transported in the oxygen production system using this complex solution can be increased to a desired amount. In addition, the condition regarding the solubility of the solvent is relaxed, it becomes possible to use a hydrophobic solvent, and the equipment for removing the water in the raw material gas is not required, and the operating conditions of the oxygen production system using this complex solution are applied. The range can be expanded.

Claims (14)

[Claims] 1. A complex which is dissolved in a solvent and combines with oxygen by absorption of oxygen to form a solid phase, which causes phase separation, wherein the complex is represented by the general formula (A): (In the formula, R1, R2, R3 and R4 each represent hydrogen, an alkyl group or an alkoxy group, and R5, R6, R7, R
8 represents a methyl group. ) A cobalt-Schiff base complex represented by: 2. The cobalt-Schiff base complex according to claim 1 and an axial ligand coordinated to the fifth axial dentate of the complex are dissolved in a solvent, and the complex is bound to oxygen by absorption of oxygen and solidified. A complex solution for oxygen separation, which causes phase separation to precipitate as a phase. 3. The cobalt Schiff base complex is N, N ′.
-Bis (salicylidene) 1,1,2,2-tetramethylethylenediaminocobalt (II), N, N'-bis (3
-Ethoxysalicylidene) 1,1,2,2-tetramethylethylenediaminocobalt (II), N, N'-bis (4,6-dimethoxysalicylidene) 1,1,2,2-
Tetramethylethylenediaminocobalt (II), N,
The N'-bis (3,5-tert-butylsalicylidene) 1,1,2,2-tetramethylethylenediaminocobalt (II) selected from N'-bis (3,5-tert-butylsalicylidene). Complex solution for oxygen separation. 4. A pyridine-based compound or an alkylamine-based compound in which the axial ligand coordinated to the fifth axial dentate of the cobalt-Schiff base complex contains a basic nitrogen atom, or The complex solution for oxygen separation according to claim 2 or 3, which is an imidazole-based compound containing a basic nitrogen atom. 5. The oxygen separating complex solution according to claim 2, wherein the solvent for dissolving the cobalt Schiff base complex and the axial ligand is a solvent having a dipole moment of 3.5 Debye or less. 6. The solvent for dissolving the cobalt Schiff base complex and the axial ligand is 1,2-dichlorobenzene, 3,4-dichlorotoluene, 2,4-dichlorotoluene, 2,3-
Dichlorotoluene, 2,6-dichlorotoluene, 1,2
-Dibromobenzene, 2-chloroparaxylene, 4-chloroparaxylene, 1-chloronaphthalene, 1,2,
3,4-tetrahydronaphthalene, 1-methylnaphthalene, 1,2,3-trimethylbenzene, 1,2,3,5
Selected from tetramethylbenzene, 1,4-diisopropylbenzene, 4-tertiarybutyltoluene, tertiary amylbenzene, normal amylbenzene, phenylcyclohexane, methylbenzoate, normalpropylbenzoate, thioanisole, indan It is 1 type or 2 types or more, The complex solution for oxygen separation of Claim 2, 3 or 4 characterized by the above-mentioned. 7. A solvent for dissolving the cobalt-Schiff base complex and the axial ligand is 1,2-dichlorobenzene, 1,2-dichlorobenzene.
3,4-tetrahydronaphthalene, indane, 2,6-
It is 1 type (s) or 2 or more types selected from dichlorotoluene, The complex solution for oxygen separation of Claim 2, 3 or 4 characterized by the above-mentioned. 8. The solvent for dissolving the cobalt-Schiff base complex and the axial ligand is 1,2-dichlorobenzene, 1,2-dichlorobenzene.
3,4-tetrahydronaphthalene, indane, 2,6-
A first solvent, which is one or more selected from dichlorotoluene, and 3,4-dichlorotoluene,
2,4-dichlorotoluene, 2,3-dichlorotoluene, 1,2-dibromobenzene, 2-chloroparaxylene, 4-chloroparaxylene, 1-chloronaphthalene,
1-methylnaphthalene, 1,2,3-trimethylbenzene, 1,2,3,5-tetramethylbenzene, 1,4-
A second or at least one member selected from diisopropylbenzene, 4-tert-butyltoluene, tertiary-amylbenzene, normal-amylbenzene, phenylcyclohexane, methylbenzoate, normal-propylbenzoate, and thioanisole. 3. A mixture of a solvent and the solvent,
3 or 4 oxygen separation complex solution. 9. A cobalt Schiff base complex having a concentration of 0.
The complex solution for oxygen separation according to any one of claims 2 to 8, wherein the complex solution is higher than 1M. 10. The oxygen-separating complex solution according to claim 2, wherein the concentration of the cobalt Schiff base complex is set to a concentration equal to or higher than the solubility of the complex. 11. The oxygen separation complex solution according to any one of claims 2 to 10 is brought into contact with air or a mixed gas containing oxygen to precipitate the complex bound to oxygen as a solid phase. An oxygen separation method comprising an oxygen absorbing step and an oxygen releasing step of heating a deposited oxygen-bonded complex to release oxygen. 12. The oxygen separation method according to claim 11, wherein the oxygen absorption step is performed under a temperature condition of 0 to 40 ° C. 13. The oxygen separation method according to claim 11, wherein the oxygen releasing step is performed under a temperature condition of 20 to 60 ° C. 14. The oxygen separation method according to claim 11, 12 or 13, wherein the oxygen partial pressure of air or a mixed gas containing oxygen in the oxygen absorption step is 99 Torr or more.