Liquid having oxygen absorbing ability, method for producing same, and complex solution containing same

Abstract

A liquid having oxygen absorbing ability, comprising a cobalt-salen complex or a derivative thereof and an ionic liquid formed from an anion having an amine structure and a cation of an aliphatic quaternary phosphonium or ammonium having alkyl chains with each 2-20 carbon atoms, wherein the anion of the ionic liquid is coordinated to a cobalt ion of the cobalt-salen complex or a derivative thereof.

Claims

1. A liquid having oxygen absorbing ability, comprising: a cobalt-salen complex and an ionic liquid formed from an anion having an amine structure and a cation of an aliphatic quaternary phosphonium or ammonium having alkyl chains with each 2-20 carbon atoms, wherein the ionic liquid includes an anion of N-methylglycine; the anion of N-methylglycine of the ionic liquid is coordinated to a cobalt ion of the cobalt-salen complex in an axis direction; the cobalt-salen complex is represented by the general formula (1): ##STR00002## R.sup.1a, R.sup.1b, R.sup.2, and R.sup.3 are the same or different and respectively are a hydrogen atom, a halogen atom, an alkyl or haloalkyl group with 1-6 carbon atoms, an alkoxy group with 1-6 carbon atoms, an acyl group with 1-6 carbon atoms, an amino group, a nitro group, a nitrile group (cyano group), a vinyl group, or an aryl or heteroaryl group with 6-12 carbon atoms; and R.sup.1a and R.sup.1b may bind each other through an atom or an atomic group bound thereto to form a ring structure.

2. The liquid having oxygen absorbing ability according to claim 1, wherein the ionic liquid comprises a cation of trihexyl(tetradecyl)phosphonium.

3. The liquid having oxygen absorbing ability according to claim 1, wherein the cobalt-salen complex is N,N-bis(salicylidene)ethylenediaminocobalt(II).

4. A complex solution having oxygen absorbing ability, comprising the liquid having oxygen absorbing ability according to claim 1 dissolved in a second ionic liquid.

5. The complex solution having oxygen absorbing ability according to claim 4, wherein the second ionic liquid comprises an anion of bis(trifluoromethanesulfonyl)imide.

6. The complex solution having oxygen absorbing ability according to claim 4, wherein the second ionic liquid is trihexyl(tetradecyl)phosphonium bis(trifluoromethanesulfonyl)imide.

7. The complex solution having oxygen absorbing ability according to claim 4, wherein the complex solution having oxygen absorbing ability comprises the liquid having oxygen absorbing ability at a concentration of 1 to 80% by mass in the second ionic liquid.

8. A method for producing the liquid having oxygen absorbing ability according to claim 1.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a schematic view of an absorption test device for measuring the amount of oxygen absorption;

(2) FIG. 2 is an oxygen absorption isotherm of the liquid of Example 1 at a temperature of 30 C.;

(3) FIG. 3 is an oxygen absorption isotherm of the liquid of Example 2 at a temperature of 30 C.; and

(4) FIG. 4 is an oxygen absorption isotherm of the liquid of Example 3 at a temperature of 30 C.

DESCRIPTION OF EMBODIMENTS

(5) The embodiments of the present invention are more specifically described hereinafter. However, the embodiments do not limit the present invention.

(6) The liquid having oxygen absorbing ability (hereinafter also referred to as oxygen absorbing liquid) of the present invention is characterized in that the liquid comprises a cobalt-salen complex or a derivative thereof (hereinafter the complex and the derivative are also collectively referred to as cobalt-salen complex) and an ionic liquid formed from an anion having an amine structure and a cation of an aliphatic quaternary phosphonium or ammonium having alkyl chains with each 2-20 carbon atoms, and the anion of the ionic liquid is coordinated to a cobalt ion of the cobalt-salen complex.

(7) The derivative of the cobalt-salen complex as used herein means a cobalt-salen complex including a substituent introduced in the salen structure (skeleton).

(8) The oxygen absorbing liquid of the present invention is formed from a cobalt-salen complex and an ionic liquid coordinated thereto.

(9) An anion having a basic nitrogen atom is coordinated to the cobalt ion of the cobalt complex in the axis direction and the anion forms the ionic liquid together with a counter cation. The anion used in the present invention preferably has a secondary amine structure because the binding ability of an oxygen molecule coordinated to the other side along the axis direction is stronger when the basicity of the nitrogen on the anion is stronger.

(10) (Cobalt-Salen Complex)

(11) The cobalt-salen complex that may be used in the present invention is a metal complex well known per se having a structure in which salen or a salen derivative having a substituent coordinates to a cobalt(II) ion as a quadridentate ligand, and may be represented by, for example, the general formula (1):

(12) ##STR00001##

(13) wherein R.sup.1a, R.sup.1b, R.sup.2 and R.sup.3 are the same or different and respectively are a hydrogen atom, a halogen atom, an alkyl or haloalkyl group with 1-6 carbon atoms, an alkoxy group with 1-6 carbon atoms, an acyl group with 1-6 carbon atoms, an amino group, a nitro group, a nitrile group (cyano group), a vinyl group or an aryl or heteroaryl group with 6-12 carbon atoms; and R.sup.1a and R.sup.1b may bind each other through an atom or an atomic group bound thereto to form a ring structure.

(14) Various metals may coordinate to the molecule of the cobalt salen or a derivative thereof; however, a cobalt(II) ion is the most preferable because of the absorbing ability of oxygen molecules.

(15) The substituents R.sup.1a, R.sup.1b, R.sup.2 and R.sup.3 in the general formula (1) are hereinafter described.

(16) The halogen atom includes fluorine, chlorine, bromine and iodine.

(17) The alkyl group with 1-6 carbon atoms includes linear and branched alkyl groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, neopentyl and n-hexyl.

(18) The haloalkyl group with 1-6 carbon atoms includes alkyl groups described above in which any hydrogen atom is substituted by the halogen atom described above. Specific examples thereof include fluoromethyl, chloromethyl, bromomethyl, trifluoromethyl and the like.

(19) The alkoxy group with 1-6 carbon atoms includes linear or branched alkoxy groups such as methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, n-pentoxy and n-hexoxy.

(20) The acyl group with 1-6 carbon atoms includes aliphatic acyl groups such as formyl, acetyl, propionyl, butyryl, isobutyryl, valeryl, isovaleryl, pivaloyl and hexanoyl.

(21) The aryl and heteroaryl groups with 6-12 carbon atoms include phenyl, tolyl, xylyl, fluorophenyl, chlorophenyl, bromophenyl, naphthyl and the like.

(22) R.sup.1a and R.sup.1b may be the same or different and may bind each other through an atom or an atomic group bound thereto to form a ring structure, and the substitution position of the substituent R.sup.3 is arbitrary.

(23) The cobalt-salen complex may be produced by, for example, synthesizing salen or a salen derivative by dehydration condensation of a corresponding salicylaldehyde and ethylenediamine in a solvent such as ethanol and reacting the obtained salen or salen derivative as a ligand with a cobalt ion under a basic condition. Alternatively, the cobalt-salen complex may be obtained by adding an acetate salt of cobalt during synthesis of salen or a salen derivative.

(24) By using synthetic raw materials which are salicylaldehyde and ethylenediamine respectively having substituents, various structures of salen derivatives may be obtained.

(25) Substituted salicylaldehydes include dihydroxybenzaldehyde, chlorosalicylaldehyde, bromosalicylaldehyde, fluorosalicylaldehyde, aminosalicylaldehyde, methylsalicylaldehyde, tert-butylsalicylaldehyde, methoxysalicylaldehyde, ethoxysalicylaldehyde and the like.

(26) Substituted ethylenediamines include 1,2-dimethylethylenediamine, 1,1,2,2-tetramethylethylenediamine, 1,2-cyclohexanediamine, 1,2-diphenylethylenediamine and the like.

(27) Cobalt-salen derivatives obtained by combining the above include, in addition to cobalt-salen, namely N,N-bis(salicylidene)ethylenediaminocobalt(II), N,N-bis(salicylidene)-1,2-dimethylethylenediaminocobalt(II), N,N-bis(salicylidene)-1,1,2,2-tetramethylethylenediaminocobalt(II), N,N-bis(salicylidene)-1,2-cyclohexanediaminocobalt(II), N,N-bis(3-methylsalicylidene)ethylenediaminocobalt(II), N,N-bis(5-methylsalicylidene)ethylenediaminocobalt(II), N,N-bis(3-ethoxysalicylidene)ethylenediaminocobalt(II), N,N-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediaminocobalt(II), N,N-bis(3-ethoxysalicylidene)-1,1,2,2-tetramethylethylenediaminocobalt(II) and the like. Among others, N,N-bis(salicylidene)ethylenediaminocobalt(II) is particularly preferred in terms of oxygen absorbing ability.

(28) Cobalt-salen complexes disclosed in Japanese Unexamined Patent Publication No. H6(1994)-340683, Pier Giorgio Cozzi, Metal-Salen Schiff base complexes in catalysis: practical aspects, Chemical Society Reviews, 2004, vol. 33, p. 410-421 and Eric C. Niederhoffer et al., Thermodynamics of Oxygen Binding in Natural and Synthetic Dioxygen Complexes, Chemical Reviews, 1984, vol. 84, p. 137-203 and citations therein may be used.

(29) (Ionic Liquid)

(30) The ionic liquid preferably has a secondary amine structure as the anion as described above and particularly preferably is an N-alkylamino acid corresponding an amino acid having an alkyl chain on the amino group, which is generally used as an anion of an ionic liquid and has a secondary amine structure. The alkyl chain may be any of those with 1-8 carbon atoms. However, because an increased number of carbon atoms increases an effect of steric hinderance upon coordination, the number of carbon atoms is preferably low. The alkyl chain is preferably methyl or ethyl and particularly preferably methyl. The type of amino acid is preferably glycine having the lowest molecular weight by taking the steric effect upon coordination into account. Therefore, the anionic ligand is particularly preferably N-methylglycine (aminoacetic acid).

(31) The cation which is a counter ion of the anion may be phosphonium or ammonium which may be included in common ionic liquid, and is particularly preferably an aliphatic quaternary phosphonium or ammonium having alkyl chains with each 2-20 carbon atoms.

(32) The ionic liquid may be obtained by anion exchange reaction between a compound serving as the anion and a phosphonium salt or an ammonium salt serving as the cation.

(33) The phosphonium salt and the ammonium salt may be tetramethylphosphonium bromide, tetraethylphosphonium bromide, tetrabutylphosphonium bromide, tetrahexylphosphonium bromide, triethylhexylphosphonium bromide, triethyloctylphosphonium bromide, triethyl(2-methoxyethyl)phosphonium bromide, tributyloctylphosphonium bromide, tributyldodecylphosphonium bromide, tributyl(2-methoxyethyl)phosphonium bromide, trihexyldodecylphosphonium bromide, trihexyl(tetradecyl)phosphonium bromide and chlorides corresponding to the above bromides.

(34) Not all combinations of the above phosphonium salts or ammonium salts and anions coordinating in the axis direction of the cobalt complex form liquid at normal temperature. Therefore, among others, triethyloctylphosphonium bromide, tributyloctylphosphonium bromide, trihexyl(tetradecyl)phosphonium bromide which, in combination with an anion, have low melting points and thus easily form ionic liquid are preferred, and trihexyl(tetradecyl)phosphonium bromide which forms ionic liquid in combination with many anions is particularly preferred.

(35) (Production Method of Oxygen Absorbing Liquid)

(36) The oxygen absorbing liquid of the present invention may be produced by mixing the cobalt-salen complex and an ionic liquid formed from an anion having an amine structure and a cation of an aliphatic quaternary phosphonium or ammonium having alkyl chains with each 2-20 carbon atoms under an oxygen-containing atmosphere to dissolve the cobalt-salen complex in the ionic liquid and obtaining a coordination compound of the cobalt-salen complex and the ionic liquid.

(37) The proportion of the cobalt-salen complex and effective components of the ionic liquid may be such that the moles of the cobalt-salen complex and the moles of the effective components of the ionic liquid are almost equivalent, or the moles of effective components of the cobalt-salen complex are excessive.

(38) The coordination compound of the cobalt-salen complex and the ionic liquid may be confirmed according to well-known methods such as comprehensive analyses including ultraviolet-visible spectroscopy, .sup.59Co-NMR spectroscopy and color change.

(39) (Oxygen Absorbing Liquid)

(40) The oxygen absorbing liquid of the present invention selectively binds to oxygen and may adsorb 1 equivalent of oxygen at maximum relative to an equivalent of the complex. Further, the oxygen absorbing liquid allows reversible adsorption and desorption of equivalent of oxygen relative to an equivalent of the complex under conditions in which adsorption and desorption reactions of oxygen proceed repetitively and stably. In order to increase the dispersibility of oxygen in the liquid, it is preferable to mix with a second ionic liquid to decrease the viscosity before use.

(41) Thus, the oxygen absorbing liquid of the present invention is preferably used as a complex solution having oxygen absorbing ability containing the oxygen absorbing liquid dissolved in a second ionic liquid.

(42) The second ionic liquid preferably has similar properties to the oxygen absorbing liquid of the present invention and has a low viscosity. The optimal viscosity depends on the usage form of the oxygen absorbent. It is preferable that the second ion liquid allows preparation of a solution having as high concentration as possible within the range of viscosity allowing easy handling in order to increase the oxygen absorption.

(43) The second ionic liquid may be commonly used ionic liquid.

(44) The cations thereof which are known include imidazolium, pyridinium, pyrrolidinium, phosphonium, ammonium and the like. In the present invention, phosphonium and ammonium are particularly preferred in view of compatibility.

(45) The anions which are well known include tetrafluoroborate, hexafluorophosphonate, trifluoroacetate, trifluoromethanesulfonate, bis(trifluoromethanesulfonyl)imide and the like. In the present invention, bis(trifluoromethanesulfonyl)imide is particularly preferred because it may provide the lowest viscosity.

(46) Thus, the second ionic liquid is particularly preferably trihexyl(tetradecyl)phosphonium bis(trifluoromethanesulfonyl)imide.

(47) The liquid having oxygen absorbing ability of the present invention preferably contains the oxygen absorbing liquid at a concentration of 1 to 80% by mass in the second ionic liquid.

(48) When the concentration of the oxygen absorbing liquid is less than 1% by mass, the obtained oxygen absorbing ability may not be sufficient. When the concentration of the oxygen absorbing liquid exceeds 80% by mass, the complex solution having oxygen absorbing ability may have high viscosity, making handling thereof difficult.

(49) Specific concentrations (% by mass) of the oxygen absorbing liquid include 1, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75 and 80.

(50) The concentration of the oxygen absorbing liquid which is preferable and allows relatively easy handling is 20 to 50% by mass and more preferably 30 to 50% by mass.

EXAMPLES

(51) The present invention is hereinafter specifically described by way of Examples which do not limit the present invention.

Example 1

(52) [Preparation of Ionic Liquid]

(53) To 100 ml of ethanol, 5.64 g (10 mmol) of trihexyl(tetradecyl)phosphonium bromide (produced by Sigma-Aldrich, purity >95%) and 20 g of anion exchange resin (produced by Sigma-Aldrich, Amberlite IBN78 hydroxide form) were added and stirred to carry out hydroxide substitution reaction. Thereafter, the reaction solution was separated by vacuum filtration, an aqueous solution obtained by dissolving 0.98 g (11 mmol) of N-methylglycine (produced by Tokyo Chemical Industry, Co., Ltd., purity >98%) in 20 ml of pure water was added for reaction, the solvent and unreacted matters were removed by concentration under reduced pressure, thereby obtaining 4.88 g of ionic liquid formed from trihexyl(tetradecyl)phosphonium cation and N-methylglycine anion.

(54) [Preparation of Liquid Having Oxygen Absorbing Ability]

(55) The thus-obtained ionic liquid (1.30 g, effective components: 2.3 mmol) and 2.35 g (7.2 mmol) of N,N-bis(salicylidene)ethylenediaminocobalt(II) (produced by Tokyo Chemical Industry, Co., Ltd., purity >95%) were then added to 50 ml of ethanol and stirred at room temperature for 3 hours, the solvent and unreacted matters were removed by concentration under reduced pressure, thereby obtaining 1.82 g of desired liquid having a cobalt-salen complex structure.

(56) By ultraviolet-visible spectroscopy, observation of the developed color and the like, it was verified that the anion of the ionic liquid was coordinated to the cobalt ion of the cobalt-salen complex.

(57) The obtained liquid was stable and no weight change was observed after maintaining the liquid in a solution of trihexyl(tetradecyl)phosphonium bis(trifluoromethanesulfonyl)imide at 100 C. for 10 hours. In addition, no weight change was observed after heating to around 200 C., and thus it was verified that the liquid had high heat resistance for a molecule of an organic molecular component composition, similar to typical ionic liquids.

(58) [Preparation of Complex Solution]

(59) In order to evaluate oxygen absorbing ability of the obtained liquid, the obtained liquid was dissolved in trihexyl(tetradecyl)phosphonium bis(trifluoromethanesulfonyl)imide synthesized according to Dr. Tom Vander Hoogerstraete et al., Selective Single-Step Separation of a Mixture of three Metal Ions by a Triphasic Ionic-Liquid-Water-Ionic-Liquid Solvent Extraction System, Chemistry-A European Journal, 2015, vol. 21, p. 11757-11766, thereby obtaining 6.3 g of complex solution of about 30% by mass.

(60) [Evaluation of Oxygen Absorbing Ability]

(61) By using the absorption test device schematically illustrated in FIG. 1, the oxygen absorption of the obtained liquid was measured.

(62) The absorption test device was internally replaced with nitrogen and 5.25 g of sample solution was introduced into the device with a syringe. The replacement with nitrogen was then further carried out and degassing was performed for 1 hour or more in order to dry the system. Oxygen gas was then introduced at a predetermined pressure of 0 to 20 kPa under a temperature of 30 C., the pressure change due to absorption was measured with a pressure sensor and the oxygen absorption was estimated from the result.

(63) At the tip of the arrow on the right hand side in FIG. 1 is connected to a vacuum pump which is not shown.

(64) The obtained result is shown in FIG. 2. As shown in FIG. 2, it is demonstrated that about 0.5 mol of oxygen was adsorbed relative to 1 mol of the cobalt-salen complex including the ionic liquid coordinated thereto.

(65) It was further verified that oxygen was desorbed by reducing pressure after the above adsorption, thereby verifying that the reaction was reversible.

Example 2

(66) In Example 2, the absorbing ability of a complex solution was evaluated in the same manner as in Example 1 except that the concentration of the liquid having oxygen absorbing ability dissolved in the second ionic liquid was changed from 30% by mass in Example 1 to 50% by mass.

(67) In the same manner as in Example 1, an ionic liquid formed with trihexyl(tetradecyl)phosphonium cation and N-methylglycine anion and 1.95 g of liquid having a cobalt-salen complex structure were obtained.

(68) The obtained solution was dissolved in trihexyl(tetradecyl)phosphonium bis(trifluoromethanesulfonyl)imide synthesized in the same manner as in Example 1, thereby obtaining 1.5 g of complex solution of about 50% by mass.

(69) The oxygen absorption of the obtained complex solution was measured on the device shown in FIG. 1 in the same procedures as in Example 1.

(70) The result is shown in FIG. 3. As shown in FIG. 3, it is demonstrated that about 0.5 mol of oxygen was adsorbed relative to 1 mol of the cobalt-salen complex including the ionic liquid coordinated thereto.

Example 3

(71) In Example 3, the absorbing ability of the liquid having oxygen absorbing ability per se was evaluated without using the second ionic liquid for dissolving the liquid having oxygen absorbing ability as in Examples 1 and 2.

(72) However, it takes time to reach saturation absorption when a solution is not formed, and thus this embodiment is not preferable in practical view point for applications such as oxygen separation because of unfavorable conditions in view of the reaction time including the time for desorption reaction.

(73) In the same manner as in Example 1, an ionic liquid formed with trihexyl(tetradecyl)phosphonium cation and N-methylglycine anion was obtained.

(74) Then, 1.18 g of the obtained ionic liquid and 0.33 g of N,N-bis(salicylidene)ethylenediaminocobalt(II) (produced by Tokyo Chemical Industry, Co., Ltd., purity >95%) were added to 50 ml of ethanol, stirred and mixed at room temperature for 3 hours followed by deoxygenation by nitrogen bubbling for 1 hour and removal of the solvent and unreacted matters by concentration under reduced pressure to obtain 1.25 g of desired liquid having a cobalt-salen complex structure.

(75) By ultraviolet-visible spectroscopy, observation of the developed color and the like, it was verified that the anion of the ionic liquid was coordinated to the cobalt ion of the cobalt-salen complex. Also, by thermal analysis, it was verified that the liquid had high heat resistance of 200 C. or higher.

(76) The oxygen absorption of the obtained complex solution was measured on the device shown in FIG. 1 in the same procedures as in Example 1.

(77) The result is shown in FIG. 4. As shown in FIG. 4, it is demonstrated that about 1 mol of oxygen was adsorbed relative to 1 mol of the cobalt-salen complex including the ionic liquid coordinated thereto.

(78) The following reason may be suggested: when a second ionic liquid is not included, two N-methylglycine anions in ionic liquid formed from trihexyl(tetradecyl)phosphonium cation and N-methylglycine anion coordinate to a cobalt ion in the cobalt-salen complex, and in the presence of oxygen, an oxygen molecule replaces one anion to be coordinated to the cobalt ion, resulting in one oxygen binding per complex. Although an oxygen molecule coordinates to two cobalt-salen complexes to stabilize the structure in case of Examples 1 and 2, an oxygen molecule coordinates to only one cobalt-salen complex in the present Example.

INDUSTRIAL APPLICABILITY

(79) The liquid having oxygen absorbing ability of the present invention may be used in the fields requiring oxygen absorbing materials and oxygen separation membranes for the purposes of separation, concentration, removal, storage and the like of oxygen.