JP3000369B2 - Method for regenerating oxygen absorbing complex and method for separating oxygen using oxygen absorbing complex solution - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for regenerating an oxygen-absorbing complex and a method for separating oxygen using an oxygen-absorbing complex solution. The present invention relates to a method for regenerating a degraded complex to an original state and recovering the oxygen separating ability in separating oxygen from oxygen.

[Conventional technology]

In general, cryogenic method and pressure fluctuation method (PSA) using an adsorbent are used to separate and produce oxygen in air on an industrial scale.
Is often used. The former is a method in which air is liquefied and nitrogen and oxygen are separated through a multi-stage rectification process, and high-purity oxygen or nitrogen can be produced, but has a drawback that a large amount of energy is required.

The latter is a method of separating oxygen or nitrogen by selectively adsorbing nitrogen or oxygen on the adsorbent using an adsorbent such as zeolite or carbon molecular sieves. This method has the advantage of simple operation, but has the disadvantage that the apparatus is large and that when producing oxygen, the maximum oxygen concentration is only 95%.

To overcome these drawbacks, several methods have been proposed that utilize complexes that react only reversibly with oxygen.

For example, in the method described in JP-A-59-20296, the complex solution is brought into contact with air at a low temperature of 5 ° C. or less, oxygen in the air is absorbed by the complex solution,
At the above-mentioned high temperature, oxygen is released from the complex solution and is collected as product oxygen. The complex solution is cooled again to a low temperature of 5 ° C. or less to absorb oxygen. Hereinafter, the same process is repeated to continuously generate oxygen (temperature fluctuation type absorption method).

[Problems to be solved by the invention]

However, the oxygen separation method using the above complex solution has a disadvantage that the complex solution is deteriorated, and the one having the longest life in the past was only about 100 days. Moreover, since the complex solution is expensive, the method using the complex solution could not surpass the cryogenic method and the PSA method.

Accordingly, the present invention provides an oxygen-absorbing complex that can re-activate a degraded complex solution in a temperature fluctuation absorption method or a pressure fluctuation absorption method using a complex solution and can substantially semi-permanently extend the life of the complex solution. It is an object of the present invention to provide a regeneration method and a method for separating oxygen using an oxygen-absorbing complex solution.

[Means for solving the problem]

In order to achieve the above object, a method for regenerating an oxygen-absorbing complex according to the present invention comprises a salicylaldehyde in which the absorption of oxygen at a relatively low temperature and the release of oxygen at a relatively high temperature are performed by a monomerization reaction. In a solution containing a system Schiff-based oxygen-absorbing complex in an aprotic solvent, when the oxygen-absorbing complex is deteriorated, the solution is heated to 50 to 170 ° C., which is a temperature higher than the temperature at which oxygen is released in the monomerization reaction. Heating to regenerate the deteriorated oxygen-absorbing complex, and
It is characterized in that the oxygen partial pressure of the gas phase in contact with the solution during heating is reduced.

Further, the method for separating oxygen using the oxygen-absorbing complex solution of the present invention comprises a salicylaldehyde-based method in which the absorption of oxygen at a relatively low temperature and the release of oxygen at a relatively high temperature are performed by a monomerization reaction. In the method of preparing a Schiff-based oxygen-absorbing complex in an aprotic solvent, the oxygen degraded by heating the whole or a part of the solution to 50 to 170 ° C., which is a temperature higher than the release temperature of oxygen in the monomerization reaction, is used. It is characterized by regenerating the absorption complex.

The oxygen-absorbing complex to be used in the present invention has a general formula (Wherein, R ¹ , R ² , and R ³ each represent hydrogen, an alkoxy group, an alkyl group, or a phenyl group; R ⁴ represents hydrogen or a methyl group;
R ⁵ , R ⁶ , R ⁷ and R ⁸ each represent hydrogen, an alkyl group or a phenyl group, and M represents iron, cobalt or nickel. ) And a salicylaldehyde-based Schiff base complex.

This complex has a four-coordinate structure, but usually has a six-coordinate structure and is a stable complex.

That is, when an axial ligand is coordinated to the fifth coordination site of these complexes, the oxygen coordination ability of the sixth coordination site is enhanced, and oxygen coordinates there to absorb oxygen. I do.

As the axial ligand, those containing a basic nitrogen atom can be used, and for example, imidazole-based, pyridine-based, alkylamine-based, and the like can be used.

Examples of the imidazole-based axial ligand include imidazole, 1-methylimidazole, 1,1'-dodecamethylenediimidazole, 3-methyl-1,1'-dodecyldiimidazolium iodide, 4- (imidazole-1 -Yl) phenol, laurylimidazole, 1-benzoylimidazole and the like.

Further, pyridine-based axial ligands include pyridine, 4
-Dimethylaminopyridine, 3-pyridinepropanol, 4- (1-butylpentyl) pyridine, 3-butylpyridine, 1,2-di (4-pyridyl) ethane and the like.

Further, as the alkylamine-based axial ligand, n-
Butylamine, iso-butylamine, neopentylamine and the like can be mentioned.

On the other hand, as the solvent for dissolving the complex, any type of polar (hydrophilic) or nonpolar (hydrophobic) solvent can be used as long as it is an aprotic solvent that can dissolve the complex and the axial ligand. Those having a high boiling point and a high flash point are desirable for the reasons described later. Examples of these include 1-methyl-2-
Examples thereof include pyrrolidinone, N, N'-dimethylformamide, propylene carbonate, dimethyl sulfoxide, N, N'-dimethylacetamide, sulfolane, ortho-dichlorobenzene, and γ-butyrolactone.

The complex solution comprising the complex, the axial ligand, and the solvent usually absorbs oxygen at a temperature of 5 ° C. or less, and at a temperature of normal temperature or more,
Releases absorbed oxygen. This is the principle of oxygen production by the temperature fluctuation absorption method.

Further, if the temperature is kept at, for example, 0 ° C. and the oxygen partial pressure of the gas phase in contact with the complex solution is increased, oxygen is absorbed, and if the oxygen partial pressure of the gas phase is reduced by a vacuum exhaust device or the like, the absorbed oxygen is absorbed. Is released. This is the principle of oxygen production by the pressure fluctuation absorption method.

As described above, when the temperature or pressure is changed, the complex in the complex solution reversibly absorbs and releases oxygen by a monomerization reaction as shown in the following formula (1).

BLM + O ₂ BLM-O ₂ (1) (wherein L is the complex, B is an axial ligand, M is a central metal,
O ₂ represents oxygen. However, when the absorption and release of oxygen are repeated, the oxygen absorbing ability of the complex solution gradually decreases, and eventually the oxygen absorbing ability disappears. The speed at which this oxygen absorption capacity decreases,
That is, the deterioration rate of the complex solution differs depending on the type of the complex, the axial ligand and the solvent used. Assuming that the time until the initial oxygen absorption capacity of the complex solution is reduced to half is the lifetime, the one with a short lifetime is several seconds, and the one with a long lifetime is several months.

The equilibrium multiplier Ko ₂ of the oxygen bond is represented by the following equation (2), and it is generally known that a complex solution having a large Ko _{2 has} a high deterioration rate.

(In the formula, L, B, M, and O ₂ are the same as above.) Deterioration of the above complex solution includes dimerization reaction, hydrogen abstraction reaction in tetradentate ligand, oxidation of axial ligand, oxidation of central metal The present inventor has found that as a result of various experiments, the main cause of degradation is the following equation (3).
It was found that the reaction was a dimerization reaction shown in FIG.

BLM-O ₂ + MLB → BLM-O ₂ -MLB (3) (where L, B, M, and O ₂ are the same as above) For example, when the central metal is cobalt, it is always Magnetic (x _p > 0), but diamagnetic (x _d <0,
| x _p / x _D | ≒ 10 ² ) can be Floriani (Journal of Che
mical Society (A), 946 (1969)).

That is, the magnetic susceptibility of the complex solution having absorbed oxygen decreases with the passage of time, and finally becomes x 、 0.
Indicates that the reaction has progressed.

In contrast, 0 ° C and 70 ° C
When temperature fluctuations are given periodically during the initial period, deterioration progresses and magnetic susceptibility decreases at the beginning of the start, but after that, the degree of deterioration becomes constant at about 50%, and it is observed that the progress of deterioration stops. Was. From this result, it is considered that when temperature fluctuation is given to the complex solution, in the heating step, a part of the dimer which is a degradation product is regenerated to a monomer.

That is, as shown in the following formula (4), it is considered that the complex which has deteriorated to a dimer as shown in the right side of the formula is regenerated to the initial structure shown in the left side of the formula by heating.

(In the formula, L, B, M, and O ₂ are the same as above, and △ represents heating.) Thus, the present inventor conducted an experiment to confirm the above fact by measuring the oxygen absorption capacity. When the solution is allowed to stand for 4 days at 0 ° C. after absorbing oxygen, the oxygen absorbing ability is virtually lost, but when the temperature fluctuates between 0 ° C. and 50 ° C. and oxygen is absorbed and released, the initial number It was confirmed that the oxygen absorption and desorption rapidly decreased in ten cycles, and then became constant after that, and that the progress of the degradation stopped. The result is
This is in good agreement with the susceptibility measurement results described above.

Furthermore, these results indicate that a similar phenomenon could be observed even when the type of complex, the type of axial ligand, and the type of solvent were changed. That is, it has been found that the phenomenon of regeneration of the complex by heating is not specific to a specific complex solution but a general phenomenon.

Assuming that the equilibrium reaction of the above formula (4) generally holds, if the heating temperature is increased and the generated oxygen is removed from the system, the equilibrium point moves to the left side of the formula (4) and the dimerization on the right side of the formula It is expected that the rate at which objects will regenerate into monomers will increase. In particular, it has been found that when the heating temperature is 100 ° C., the equilibrium point of the equation (4) moves sufficiently to the left under the atmosphere, that is, even when the oxygen partial pressure is about 160 Torr.

From these facts, it was confirmed that the dimer, which is a degradation product in the complex solution, could be returned to a monomer by a heating operation at about 100 ° C. and regenerated. Furthermore, by applying such a regeneration method, when oxygen in the air is separated and collected by the temperature fluctuation type absorption method or the pressure fluctuation type absorption method, every one cycle of oxygen absorption / release or a certain number of cycles By heating the whole or a part of the complex solution to an appropriate temperature every time, the complex solution having reduced oxygen absorbing ability can be regenerated into an active monomer, and the oxygen separating ability can be maintained for a long period of time. It is possible to do.

In the heating and regeneration step, the heating temperature is set to 170 ° C.
If it is higher, the complex or the axial ligand or the solvent may be decomposed, and even when the decomposition is not performed, the low-molecular-weight axial ligand or the solvent has a high vapor pressure, so that it evaporates and disperses during heating, The composition of the complex solution may change. On the other hand, when the heating temperature is lower than 50 ° C., the equilibrium point of the above formula (4) cannot be sufficiently moved to the left, and effective regeneration cannot be performed. Therefore, the heating temperature is preferably between 50 ° C. and 170 ° C., more preferably around 100 ° C.

Further, it is preferable to select an axial ligand or a solvent having a high boiling point in order to prevent evaporation and loss. Furthermore,
When a heating operation is performed, oxygen is generated along with the decomposition of the dimer into a monomer, so that the partial pressure of the gas phase oxygen in contact with the complex solution increases. Therefore, in order to prevent danger of ignition or explosion, it is preferable to use an axial ligand or a solvent having a high flash point. Furthermore, depending on the type of the complex solution, when heated to around 100 ° C., the amount of generated oxygen is large, and the partial pressure of gaseous oxygen in contact with the complex solution becomes high, so that the leftward reaction of the formula (4) does not proceed. There is. In such a case, the operation of regenerating the dimer can be effectively performed by lowering the gaseous phase oxygen partial pressure using a vacuum exhaust device or the like.

The above-mentioned complex, axial ligand and solvent are given as examples, and the scope of the present invention is not limited to these.

〔Example〕

Hereinafter, the present invention will be described in more detail based on examples.

Example 1 (N, N'-bis (4-methoxysalicylidene) -1,2-diamino-2-methylpropanato) cobalt (II) [Co (4-MeOSal) Dmen] synthesized by a conventional method. And 3-methyl-1,1'-dodecyldiimidazolium iodide [Im (CH ₂ ) ₁₂ ImMe ⁺ I ⁻ ] And dissolved in N, N-dimethylformamide [DMFd7],
1 ml of a complex solution having a complex concentration of 0.1 M and an axial ligand of 1.5 equivalent was prepared.

Next, the complex solution was heated to 0 ° C. and oxygen gas was added for 15 minutes.
After bubbling for a minute to sufficiently absorb oxygen, the complex solution was transferred to a sample tube for magnetic susceptibility measurement, and the upper gas phase of the complex solution was replaced with air and sealed. The magnetic susceptibility x of the complex solution was measured by the Evans method using a nuclear magnetic resonance apparatus.

As a result, as shown by the line A in FIG. 1, the degree of deterioration of the complex solution was measured by x / x _{0 based on} the magnetic susceptibility x ₀ immediately after the preparation of the complex solution. When stored, x / x ₀ <0.1 after 6 days.

This complex solution was heated to a temperature of 100 ° C. for 1 hour in a state of being kept in the sample tube, that is, under an atmospheric pressure condition where the oxygen partial pressure was about 160 Torr. After cooling, the magnetic susceptibility was measured at 0 ° C., and it was recovered to x / x ₀ = 0.80. This is indicated by point B in FIG.

Example 2 The same complex solution as in Example 1 was prepared and stored in an adiabatic bath (period: 3 hours / cycle) with a temperature range of 0 ° C. and 70 ° C., and the temperature fluctuated periodically. The magnetic susceptibility was measured by the method. The measurement temperature of the magnetic susceptibility was set to 0 ° C. irrespective of the temperature at which the complex solution was taken out from the adiabatic tank. As a result, as shown by the line C in FIG. 1, x / x ₀ decreases for the first two days, but thereafter becomes constant at about x / x ₀ = 0.5, and further deterioration of the complex solution is recognized. I couldn't.

After heating this complex solution in the sample tube in the same manner as in Example 1, when the susceptibility was measured at 0 ° C., it was recovered to x / x ₀ = 0.91. This is shown in FIG.
Indicated by

Example 3 20 ml of the same complex solution as in Example 1 was placed in a cell having a total volume of 37 ml, the gas phase was evacuated, a known amount of oxygen gas was introduced at a temperature of 0 ° C., and the pressure change of the oxygen gas was measured. Then, the equilibrium constant Ko ₂ of the oxygen bond was obtained. As a result, Ko ₂ immediately after the preparation of the complex solution was 0.18 cmHg ^-1 . After keeping the complex solution at 0 ° C. for 4 days, Ko ₂ was measured again and found to be 1 × 10 ^-3 cmHg ^-1 . , And had substantially lost oxygen absorption capacity.

The complex solution having lost the oxygen absorbing ability was taken out to another container and heated at 100 ° C. for 1 hour while bubbling argon gas. When the equilibrium constant Ko ₂ of the oxygen bond was measured at 0 ° C. after cooling, it was 0.03 cm ³ Hg ⁻¹ , indicating that the oxygen absorbing ability was restored.

Example 4 The same complex as in Example 1 and 4-dimethylaminopyridine [DMAP] were dissolved in 1-methyl-2-pyrrolidine [NMP], and a complex solution having a complex concentration of 0.1 M and 1.5 equivalents of an axial ligand was 9 ml.
Was prepared.

This complex solution was placed in a glass cell having a volume of 20 cm ³ ,
The vessel was set in a temperature variable bath capable of giving a temperature fluctuation between 0 ° C. and 50 ° C. with a time cycle, and the upper part of the cell was connected to a vessel (16 cm ³ ) provided with a pressure element.

When the cell is cooled, the oxygen in the container is absorbed and the container pressure is reduced. When the cell is heated, oxygen is released from the complex solution, and the container pressure is increased. Based on this pressure change, the amount of oxygen absorbed and released by the complex solution was calculated.

The initial oxygen absorption / desorption amount was Q ₀ , the second and subsequent absorption / desorption amounts were Q (c), and the degree of deterioration of the complex solution was measured by Q (c) / Q ₀ . Here, c represents the number of cycles. As a result, as shown in FIG. 2, although it rapidly deteriorates in the initial tens of cycles, Q (c) / Q ₀ becomes 0.5 after the 60th cycle.
It became constant around 5.

After this complex solution repeats oxygen absorption and desorption 200 times,
The complex solution was taken out to another container and heated at 100 ° C. for 1 hour while bubbling argon gas. After the cooling, oxygen absorption and desorption was again performed between 0 ° C. and 50 ° C., and the value was close to the initial oxygen absorption and desorption amount Q ₀ (this is indicated by A in FIG. 2). Thereafter, the deterioration rapidly progressed for several tens of cycles as in the initial stage, but thereafter, Q (c) / Q ₀ = 0.55
It became constant before and after.

Furthermore, after the complex solution has been repeatedly absorbed and released 370 times of oxygen, the complex solution is again taken out to another container, and is removed under the atmosphere, that is,
The mixture was heated to 100 ° C. for 1 hour under the condition that the oxygen partial pressure was about 160 Torr. After cooling, oxygen absorption and desorption was again performed between 0 ° C. and 50 ° C., indicating a value close to the initial oxygen absorption and desorption amount Q ₀ (this is indicated by B in FIG. 2). Subsequent changes in oxygen absorption and release were the same as before.

After the complex solution was repeatedly absorbed and desorbed oxygen 800 times in total, the same heating operation was performed, but the same result was obtained (this is indicated by C in FIG. 2).

Example 5 As a complex, (N, N'-bis (4-methoxysalicyldene) -2,3-diamino-2,3-dimethylbutanato) cobalt (II) [Co (4-MeOSal) Tmen] And 4-dimethylaminopyridine [DMA as an axial ligand
P] and 1-methyl-2-pyrrolidinone [NM
P], a complex solution with a complex concentration of 0.1 M and an axial ligand of 5.0 equivalents
9 ml were prepared.

Using this complex solution, the same operation as in Example 4 was performed except that the temperature was varied between -20 ° C and + 25 ° C, and the same result was obtained.

Example 6 In Example 5, the axial ligand was changed to 3-methyl-1,1′-
Dodecyl imidazolium iodide [Im (CH ₂ ) ₁₂ ImM
e ⁺ I ^-] where is was operated in the same manner except for changing the, it was possible to obtain similar results.

Example 7 As a complex, (N, N'-bis (3-tert-butylsalicylidene) -2,3-diamino-2,3-dimethylbutanato) cobalt (II) [Co (3-tBuSal) Tmen ] 4-dimethylaminopyridine [DMAP] as an axial ligand,
Using 1-methyl-2-pyrrolidinone [NMP] as a solvent, 9 ml of a complex solution having a complex concentration of 0.1 M and 10.0 equivalents of an axial ligand was prepared.

When the same operation as in Example 5 was performed using this complex solution, the same results as in Example 4 were obtained.

Example 8 The same operation as in Example 4 was performed, except that the solvent was changed to ortho-dichlorobenzene [o-DCB] and the axial ligand was changed to 1.5 equivalents. did it.

Example 9 (N, N'-bis (3,5-di-tert-butylsalicylidene) -2,3-diaminobutanato) cobalt (II) [Co3,5-DtBuSalBn-Meso] as a complex 4-dimethylaminopyridine [DMAP] as an axial ligand,
Using 1-methyl-2-pyrrolidinone [NMP] as a solvent, 9 ml of a complex solution having a complex concentration of 0.1 M and 1.5 equivalents of an axial ligand was prepared. When the same operation as in Example 4 was performed using this complex solution, similar results were obtained.

Example 10 (N, N'-bis (salicylidene) -1,2-diaminopropanato) cobalt (II) [CoSalPn] as a complex As an axial ligand, laurylimidazole [Im (C
H ₂ ) ₁₂ ] and 9 ml of a complex solution having a complex concentration of 0.3 M and an axial ligand of 5.0 equivalents were prepared using 1-methyl-2-pyrrolidinone [NMP] as a solvent. Using this complex solution, Example 5
By performing the same operation as in the above, similar results could be obtained.

The following table summarizes the complex solutions used in each of the above examples.

[Effects of the Invention] As described above, according to the method for regenerating an oxygen-absorbing complex of the present invention, it is possible to regenerate a degraded complex solution by a simple and easy operation. By regenerating the complex solution of the oxygen separation method using, the complex solution can be used for a long period of time, and the cost in oxygen separation can be significantly reduced.

Further, in order to prevent the dimerization reaction, attempts have been made to add a sterically hindered group to the complex so that the complexes cannot approach each other. However, in this method, it is difficult to completely prevent the dimerization reaction, The cost of synthesizing the complex becomes extremely high, and it is not industrially practical. Therefore, using the regeneration operation of the present invention, even a complex having a simple structure can be used with a substantially semi-permanent life. In particular, since the complex solution given as an example can absorb and release oxygen near normal temperature and normal pressure,
Oxygen can be separated with lower energy than before.

[Brief description of the drawings]

FIG. 1 is a diagram showing a change in magnetic susceptibility in Examples 1 and 2, and FIG. 2 is a diagram showing a change in oxygen absorption / release amount in Example 4.

Continuation of front page (56) References JP-A-2-296703 (JP, A) JP-A-1-9802 (JP, A) JP-A-61-174286 (JP, A) JP-A-53-123392 (JP, A) , A) JP-A-51-122690 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B01D 53/14-53/18

Claims (3)

(57) [Claims] 1. A solution containing a salicylaldehyde-based Schiff-based oxygen-absorbing complex in an aprotic solvent in which oxygen is absorbed at a relatively low temperature and oxygen is released at a relatively high temperature by a monomerization reaction. In the method, when the oxygen-absorbing complex is deteriorated, the solution is heated to 50 to 170 ° C., which is a temperature higher than the temperature at which oxygen is released in the monomerization reaction, to regenerate the deteriorated oxygen-absorbing complex. A method for regenerating an oxygen-absorbing complex. 2. The method for regenerating an oxygen-absorbing complex according to claim 1, wherein the oxygen partial pressure of a gas phase in contact with said solution is reduced during heating. 3. A solution containing a salicylaldehyde-based Schiff-based oxygen-absorbing complex in an aprotic solvent, wherein the absorption of oxygen at a relatively low temperature and the release of oxygen at a relatively high temperature are performed by a monomerization reaction. In the method of separating oxygen by a temperature fluctuation absorption method or a pressure fluctuation absorption method using
An oxygen-absorbing complex solution characterized in that the entire or a part of the solution is heated to 50 to 170 ° C., which is a temperature higher than the temperature at which oxygen is released in the monomerization reaction, to regenerate the deteriorated oxygen-absorbing complex. The method of separating oxygen used.