Method for producing titanium chelating agent, and titanium chelating agent

Abstract

To provide a production method for producing, by an industrially advantageous method, a titanium chelating agent that has a flash point equal to or higher than room temperature and can be handled as a non-hazardous material.SOLUTION: The production method of a titanium chelating agent includes: a water content adjustment step for adding pure water to a liquid mixture of an organic solvent and a titanium chelating compound to adjust the water content to 20-70 mass%; and a reduced-pressure distillation step for distilling off the organic solvent from the aqueous liquid mixture obtained in the water content adjustment step under the conditions of a vacuum level of -30 kPa to -100 kPa and a temperature from 30°C to 80°C inclusive.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for producing a titanium chelating agent, and more particularly to a method for producing a titanium chelating agent containing a titanium chelating compound having a hydroxycarboxylic acid as a multidentate ligand. The present invention also relates to titanium chelating agents having high flash points. [Background technology]

[0002] Titanium chelate compounds are used in various applications such as various crosslinking agents, catalysts, dispersants, etc. Titanium chelate compounds are compounds in which a multidentate ligand is coordinated to titanium, and are usually synthesized by reacting a titanium alkoxide with the multidentate ligand (e.g., Patent Documents 1 to 5).

[0003] Patent Document 1 describes a method in which a hydroxycarboxylic acid such as lactic acid is reacted with titanium tetraalkoxide in the presence of water, and then a base such as amine ammonia, caustic soda, or potassium carbonate is added to neutralize the reaction and form a salt. However, in the method described in Patent Document 1, the hydroxycarboxylic acid is reacted with titanium tetraalkoxide in the coexistence of water, which may cause hydrolysis of the titanium tetraalkoxide and result in a poor yield of the titanium chelate compound.

[0004] In order to suppress the hydrolysis reaction of the titanium alkoxide, in Patent Documents 2 to 5, the reaction between titanium alkoxide and a multidentate ligand such as hydroxycarboxylic acid is carried out in an organic solvent. Patent Document 2 describes the addition of tetraisopropyl titanate to lactic acid in petroleum ether to obtain a titanium derivative of lactic acid. Patent Document 3 describes adding ethylene glycol to titanium tetraisopropoxide, and then adding ammonium lactate to obtain a titanium lactic acid chelate compound. Patent Document 4 describes mixing lactic acid and isopropyl alcohol, and then adding titanium isopropoxide dropwise to obtain a titanium isopropoxy lactic acid chelate mixture. Patent Document 5 describes a method for producing a titanium chelate compound by diluting a titanium alkoxide with a solvent and then reacting it with a hydroxycarboxylic acid. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 50-5177 [Patent Document 2] Japanese Patent Application Publication No. 05-246936 [Patent Document 3] JP 2015-17219 A [Patent Document 4] JP 2015-36390 A [Patent Document 5] International Publication WO2019-138989 Brochure Summary of the Invention [Problem to be solved by the invention]

[0006] When a titanium chelate compound is obtained by reacting a titanium alkoxide with a multidentate ligand in an organic solvent as described above, it is necessary to remove the organic solvent or to perform solvent extraction in order to isolate the titanium chelate compound. In the process of removing the organic solvent, the titanium chelate compound may be subjected to a thermal history during concentration, which may cause deterioration of the titanium chelate compound. In addition, the titanium chelate compound may not be completely recovered by solvent extraction, and the yield of the titanium chelate compound may decrease. Therefore, the titanium chelate compound is often not isolated, and the mixture of the organic solvent and the titanium chelate compound is used as a chelating agent for the above-mentioned applications. However, the titanium chelating agents containing a titanium chelating compound as a main component as described in Patent Documents 2 to 5 contain an organic solvent such as an alcohol, and depending on the content, the flash point may be below room temperature.

[0007] Therefore, there is a demand for the development of a chelating agent that has a flash point that is equal to or higher than room temperature, is as high as possible, and has reduced hazards. An object of the present invention is to provide an industrially advantageous method for producing a titanium chelating agent which has a flash point of room temperature or higher and can be treated as a non-hazardous material under the Fire Service Act. Another object of the present invention is to provide a titanium chelating agent having a flash point of 60° C. or higher. [Means for solving the problem]

[0008] The present inventors have investigated a method for producing a titanium chelating agent having a high flash point while suppressing the denaturation of the titanium chelating compound, since removing the organic solvent by distillation from a titanium chelating agent containing the organic solvent causes the titanium chelating compound to denature due to dehydration condensation or the like. As a result, the inventors discovered that by incorporating a certain amount of water before distilling off the organic solvent, it is possible to produce a titanium chelating agent having a high flash point by replacing the organic solvent with water while suppressing denaturation of the titanium chelating compound, and thus completed the present invention.

[0009] That is, the present invention provides a method for producing a titanium chelating agent, comprising: a moisture adjustment step of adding pure water to a mixture of an organic solvent and a titanium chelating compound to adjust the moisture content to 20% by mass or more and 70% by mass or less; and a reduced-pressure distillation step of distilling off the organic solvent from the water mixture obtained in the moisture adjustment step under conditions of a degree of vacuum of -30 kPa to -100 kPa and a temperature of 30°C or more and 80°C or less. Effect of the Invention

[0010] According to the present invention, there can be provided a method for producing a titanium chelating agent which has a high flash point and can be treated as a non-hazardous material under the Fire Service Act in an industrially advantageous manner. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The present invention will be described below based on its preferred embodiments. The production method of the present invention (hereinafter also referred to as "this production method") is a production method for a titanium chelating agent, which includes a water content adjustment step (hereinafter also referred to as "this water content adjustment step") in which pure water is added to a mixture of an organic solvent and a titanium chelating compound (hereinafter also referred to as "this mixture") to adjust the water content to 20% by mass or more and 70% by mass or less, and a reduced pressure distillation step (hereinafter also referred to as "this reduced pressure distillation step") in which the organic solvent is distilled from the water mixture (hereinafter also referred to as "this water mixture") obtained in the water content adjustment step under conditions of a degree of vacuum of -30 kPa to -100 kPa and a temperature of 30°C to 80°C.

[0012] The organic solvent in the mixture is an organic solvent that dissolves or disperses the titanium chelate compound. Examples of the organic solvent include alkanes, alcohols, esters, ketones, ethers, and the like. Examples of alkanes include hexane, heptane, octane, nonane, and decane. Examples of alcohols include methanol, ethanol, isopropanol, n-propanol, n-butanol, sec-butanol, tert-butanol, and n-pentanol. Examples of esters include methyl acetate, ethyl acetate, and butyl acetate. Examples of ketones include acetone, methyl ethyl ketone, dimethyl ketone, diethyl ketone, and methyl isobutyl ketone. Examples of ethers include ethylene glycol monomethyl ether, ethylene glycol dimethyl ether, dimethyl ether, diethyl ether, and dipropyl ether. Among the organic solvents, organic solvents with low flash points are more effective in making them non-hazardous by the present production method, and therefore the present production method can be suitably applied. Among the organic solvents, the organic solvents used in producing titanium chelate compounds described below are preferred from the viewpoint of simplifying the production process of the chelating agent, and alcohol is more preferred. As the alcohol, at least one selected from the group consisting of methanol, ethanol, isopropanol, n-propanol, n-butanol, sec-butanol, tert-butanol, and n-pentanol is more preferred.

[0013] The titanium chelate compound in the mixture is a compound in which a polydentate ligand having two or more coordination sites is coordinated to titanium (IV) by a reaction between the polydentate ligand and tetravalent titanium (hereinafter also referred to as titanium (IV)). Examples of the polydentate ligand include diamine compounds, dicarboxylic acid compounds, hydroxycarboxylic acid compounds, diketone compounds, and diphosphine compounds. From the viewpoint of using the chelating agent obtained by the present production method as a catalyst, crosslinking agent, and the like, the titanium chelate compound is preferably a titanium chelate compound in which an amine, a hydroxycarboxylic acid, a phosphine, or the like is coordinated to titanium, and more preferably a titanium chelate compound in which a hydroxycarboxylic acid is coordinated to titanium. Examples of the hydroxycarboxylic acid include citric acid, tartaric acid, lactic acid, and glycolic acid.

[0014] Examples of titanium (IV) include titanium tetraalkoxide and titanium tetrahalide, and titanium tetraalkoxide is preferred from the viewpoint of ease of coordination of a multidentate ligand. Examples of titanium tetraalkoxides include tetramethoxytitanium(IV), tetraethoxytitanium(IV), tetra-n-propoxytitanium(IV), tetraisopropoxytitanium(IV), tetra-n-butoxytitanium(IV), and tetraisobutoxytitanium(IV).

[0015] The titanium chelate compound in the mixture is, for example, a titanium chelate compound represented by the following formula (1). Ti(R 1 )m(L)n (1) In the formula, R 1 represents an alkoxy group, a hydroxyl group, a halogen atom, an amino group, or a phosphine, and when a plurality of groups are present, they may be the same as or different from each other. L represents a group derived from a multidentate ligand, and when a plurality of groups are present, they may be the same as or different from each other. m represents an integer of 0 to 3, n represents an integer of 1 to 3, and m+n is 3 to 6. When m is 0, m+n is preferably 3; when m is 1 or more and 3 or less, m+n is preferably 4 or 5. In the general formula (1), when L is an s-coordinate ligand (where s is a positive integer), the coordination number of titanium is represented by m+s×n, and is preferably 6.

[0016] Examples of L include a group derived from a diamine compound, a group derived from a dicarboxylic acid compound, a group derived from a hydroxycarboxylic acid compound, a group derived from a diketone compound, and a group derived from a diphosphine compound. From the viewpoint that the titanium chelating agent obtained by the present production method can be suitably used for the above-mentioned applications, a group derived from a hydroxycarboxylic acid is preferred.

[0017] R 1 Examples of the alkoxy group represented by the formula (I) include the same alkoxy groups as those mentioned as the ligand in the titanium alkoxide. Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom. Examples of the amino group include a methylamino group, an ethylamino group, a propylamino group, an isopropylamino group, a butylamino group, an isobutylamino group, a t-butylamino group, and a pentylamino group. Examples of the phosphines include trimethylphosphine, triethylphosphine, tributylphosphine, tris-t-butylphosphine, and triphenylphosphine. In the formula (1), R 1 When is a hydroxyl group, it may be a hydroxyl group derived from water produced by further reacting an alcohol with the hydroxycarboxylic acid used in the production of titanium hydroxycarbonate described below with titanium alkoxide.

[0018] Examples of the group derived from a diamine compound represented by L include a group in which any nitrogen atom of the diamine is coordinated to a titanium atom, or a group in which both nitrogen atoms of the diamine are bidentately coordinated to a titanium atom. Among these, a diamine group in which both nitrogen atoms are bidentately coordinated to a titanium atom is preferred.

[0019] Examples of the group derived from a dicarboxylic acid compound represented by L include a group in which one of the carboxyl groups of the dicarboxylic acid is coordinated to a titanium atom, or a group in which both carboxyl groups of the dicarboxylic acid are bidentately coordinated to a titanium atom. Among these, a group in which both carboxyl groups of the dicarboxylic acid are bidentately coordinated to a titanium atom is preferred.

[0020] Examples of the group derived from a hydroxycarboxylic acid represented by L include a group in which the oxygen atom of a hydroxyl group in a hydroxycarboxylic acid or the oxygen atom of a carboxyl group in a hydroxycarboxylic acid is coordinated to a titanium atom, or a group in which the oxygen atom of a hydroxyl group in a hydroxycarboxylic acid and the oxygen atom of a carboxyl group in a hydroxycarboxylic acid are bidentately coordinated to a titanium atom. Among these, a group in which the oxygen atom of a hydroxyl group in a hydroxycarboxylic acid and the oxygen atom of a carboxyl group in a hydroxycarboxylic acid are bidentately coordinated to a titanium atom is preferred.

[0021] Examples of the group derived from a diketone compound represented by L include a group in which one of the carbonyl groups of the diketone is coordinated to a titanium atom, or a group in which both carbonyl groups of the diketone are bidentately coordinated to a titanium atom. Among these, a group in which both carbonyl groups of the diketone are bidentately coordinated to a titanium atom is preferred.

[0022] Examples of the group derived from a diphosphine compound represented by L include a group in which one of the phosphorus atoms of the diphosphine is coordinated to a titanium atom, or a group in which both phosphorus atoms of the diphosphine are bidentately coordinated to a titanium atom. Among these, a group in which both phosphorus atoms of the diphosphine are bidentately coordinated to a titanium atom is preferred.

[0023] Since the purpose of this production method is to produce a titanium chelating agent having a high flash point and low danger, it is preferable to apply this production method to a mixture of an organic solvent having a low flash point and a titanium chelating compound. Therefore, the content of the organic solvent in the mixture is preferably 40% by mass or more, and more preferably 50% by mass or more, based on 100% by mass of the total amount of the organic solvent and the titanium chelate compound. In addition, from the viewpoint of the yield of the chelating agent by the present production method, the content of the organic solvent in the mixture of the organic solvent and the titanium chelate compound is preferably 70 mass% or less, and more preferably 60 mass% or less, with the total amount of the organic solvent and the titanium chelate compound being 100 mass%.

[0024] As described above, the titanium chelate compound is obtained by reacting the titanium (IV) with the multidentate ligand in an organic solvent. The obtained titanium chelate compound may be isolated once, and then mixed with an organic solvent to be used as the present mixture. Alternatively, titanium (IV) may be reacted with a multidentate ligand in an organic solvent, and the titanium chelate compound may be used as the present mixture without being isolated. As the titanium chelate compound, titanium hydroxycarbonate, in which L in the above formula (1) is a group derived from a hydroxycarboxylic acid, is preferred from the viewpoint of excellent handleability and ease of application to applications such as catalysts and crosslinking agents.

[0025] When the titanium chelate compound is titanium hydroxycarbonate, the titanium hydroxycarbonate forms a complex with a molar ratio of hydroxycarboxylic acid to titanium of 1.5 to 3.5, preferably 2.0 to 3.0. In other words, titanium hydroxycarbonate is a titanium chelate complex in which hydroxycarboxylic acid is coordinated with titanium at 1.5 to 3.5 mol, preferably 2.0 to 3.0 mol.

[0026] Examples of methods for producing titanium hydroxycarbonate include a method in which a hydroxycarboxylic acid or a salt thereof is reacted with a titanium alkoxide in which four alkoxy groups are coordinated to the titanium atom, using an alcohol as a reaction solvent. The four alkoxy groups coordinated to the titanium atom in the titanium alkoxide may be the same or different, but it is preferable that they are the same in terms of easy availability of titanium alkoxide.

[0027] The titanium hydroxycarbonate may have a coordination compound capable of coordinating with titanium other than hydroxycarboxylic acid. Examples of such coordination compounds include halogen atom-containing compounds having fluorine atom, chlorine atom, bromine atom, and iodine atom, amines having functional groups such as methylamino group, ethylamino group, propylamino group, isopropylamino group, butylamino group, isobutylamino group, t-butylamino group, and pentylamino group, and phosphines such as trimethylphosphine, triethylphosphine, tributylphosphine, tris-t-butylphosphine, and triphenylphosphine. The amount of the coordination compound capable of coordinating with titanium other than hydroxycarboxylic acid is preferably 1.0 mol or less, more preferably 0.5 mol or less, and most preferably 0.3 mol or less, per 1.0 mol of hydroxycarboxylic acid.

[0028] From the viewpoint of being easily soluble in water and capable of forming titanium hydroxycarbonate, which is a titanium chelate compound, under industrially advantageous conditions, it is preferable that the titanium hydroxycarbonate is obtained by a production method including a first step of diluting titanium alkoxide with a solvent to obtain a diluted solution, and a second step of mixing the diluted solution with a hydroxycarboxylic acid to obtain a mixture.

[0029] The alkoxy group, which is a ligand of the titanium alkoxide used in the first step, may be linear or branched, but preferably has 4 or less carbon atoms in terms of reactivity with hydroxycarboxylic acid and ease of synthesis of a water-soluble titanium chelate compound. From these viewpoints, it is particularly preferable that the titanium alkoxide is at least one selected from, for example, tetramethoxytitanium(IV), tetraethoxytitanium(IV), tetra-n-propoxytitanium(IV), tetraisopropoxytitanium(IV), tetra-n-butoxytitanium(IV), and tetraisobutoxytitanium(IV).

[0030] The solvent used in the first step may be the same organic solvent as described above. In particular, it is a diluent that can stably keep titanium alkoxide in a highly fluid state and increase the reactivity with hydroxycarboxylic acid, and when the target titanium chelate compound is to be dispersed or dissolved in a water-containing solvent, it can be used without removing the diluent. For this reason, the solvent used in the first step is preferably a polar organic solvent, and particularly, an alcohol. Examples of alcohol include methanol, ethanol, isopropanol, n-propanol, n-butanol, sec-butanol, tert-butanol, and n-pentanol. Among them, an aliphatic alcohol having 1 to 4 carbon atoms is preferred from the viewpoint of easily mixing titanium alkoxide and hydroxycarboxylic acid in a liquid state uniformly, easily increasing the reactivity of both, and easily synthesizing a water-soluble titanium chelate compound. In addition, it is preferable to use a monohydric alcohol as the alcohol in terms of acquisition cost. In particular, it is preferable to use a monohydric alcohol having an alkyl group with the same number of carbon atoms as at least one of the alkyl groups in the alkoxide group of the titanium alkoxide in terms of compatibility between the chelate compound and the solvent and separation and recovery. As the solvent used in the first step, when the alkyl groups in the four alkoxide groups of the titanium alkoxide have different carbon numbers, it is preferable to use a monohydric alcohol having the same carbon number as the alkyl group in at least one alkoxide group of the titanium alkoxide, and it is more preferable to use a mixture of monohydric alcohols having the same carbon number as the alkyl groups in the four alkoxide groups of the titanium alkoxide. Usually, the four alkoxide groups in the titanium alkoxide are the same, and therefore it is particularly preferable to use a monohydric alcohol having the same number of carbon atoms as the alkyl group in the alkoxide group in the titanium alkoxide.

[0031] In the diluted solution obtained by the first step, the ratio of titanium alkoxide is preferably 90% by mass or less in order to fluidize the titanium alkoxide and make it easier to mix with hydroxycarboxylic acid. In addition, the ratio of titanium alkoxide in the diluted solution is preferably 40% by mass or more in order to effectively increase the yield while suppressing the amount of solvent and hydroxycarboxylic acid used. From these points of view, the amount of titanium alkoxide in the diluted solution is more preferably 50% by mass or more and 85% by mass or less, and particularly preferably 60% by mass or more and 80% by mass or less. From the same point of view, the amount of solvent in the diluted solution is preferably 10 parts by mass or more and 150 parts by mass or less, and more preferably 15 parts by mass or more and 100 parts by mass or less, relative to 100 parts by mass of titanium alkoxide.

[0032] The dilution liquid may contain components other than the solvent and the titanium alkoxide, but it is more preferable that the dilution liquid does not substantially contain components other than the solvent and the titanium alkoxide in order to increase the purity of the obtained titanium chelate compound, etc. Specifically, the amount of the components other than the solvent and the titanium alkoxide in the dilution liquid is preferably 10% by mass or less, more preferably 5% by mass or less. If hydroxycarboxylic acid is present during dilution, it may react violently with titanium alkoxide, generating heat. In addition, the reaction product produced by the reaction of hydroxycarboxylic acid with titanium alkoxide is gel-like, and the viscosity of the solution containing titanium alkoxide increases, resulting in low fluidity. Such a decrease in fluidity may prevent uniform mixing, and the desired titanium chelate compound may not be obtained. The dilution of titanium alkoxide with a solvent in the first step is preferably carried out in the absence of hydroxycarboxylic acid.

[0033] The solvent used in the first step preferably has a low water content in order to prevent hydrolysis of titanium alkoxide before the reaction with hydroxycarboxylic acid. From this viewpoint, the solvent used in the first step preferably has a water content of 10% by mass or less, more preferably 5% by mass or less. When the titanium alkoxide is diluted with the solvent in the first step, it is preferable to stir the two.

[0034] As the hydroxycarboxylic acid used in the second step, aliphatic hydroxycarboxylic acids are preferred in terms of availability, reactivity with titanium alkoxide, and availability cost. For example, monovalent carboxylic acids include lactic acid, glycolic acid, glyceric acid, and hydroxybutyric acid, divalent carboxylic acids include tartronic acid, malic acid, and tartaric acid, and trivalent carboxylic acids include citric acid, isocitric acid, and the like. These aliphatic hydroxycarboxylic acids may be salts with alkali metals, alkaline earth metals, ammonia, and the like. At least one selected from lactic acid, tartaric acid, citric acid, and glycolic acid is preferred in terms of the fact that hydroxycarboxylic acids are unlikely to undergo dehydration reaction with each other, and in terms of availability and ease of handling among α-hydroxycarboxylic acids. In particular, lactic acid is preferred in terms of the fact that lactic acid, tartaric acid, citric acid, and glycolic acid are liquid at room temperature, and are easily mixed with a dilute solution of titanium alkoxide, and titanium chelate compounds can be easily produced. As the hydroxycarboxylic acid, the above-mentioned monovalent or divalent carboxylic acid not in the form of a salt such as an amine salt of a hydroxycarboxylic acid is preferred from the viewpoints of ease of waste liquid treatment and resistance to coloration.

[0035] In the second step, the hydroxycarboxylic acid is mixed in the dilution obtained in the first step in an amount of 1.0 mole or more per 1.0 mole of titanium alkoxide in the dilution, from the viewpoint of obtaining a high yield of the titanium chelate compound coordinated with the hydroxycarboxylic acid, and it is preferable to mix 3.5 moles or less in order to suppress the excessive oligomerization of the titanium chelate compound obtained while suppressing the amount of hydroxycarboxylic acid used, thereby increasing productivity. From these viewpoints, it is more preferable to mix 1.1 moles or more and 3.3 moles or less, and even more preferable to mix 1.2 moles or more and 3.0 moles or less, per 1.0 mole of titanium alkoxide in the dilution.

[0036] In the second step, other than the hydroxycarboxylic acid, a coordination compound capable of coordinating with titanium may be added to the dilution liquid within a range that does not inhibit the production efficiency of the titanium chelate compound titanium hydroxycarbonate. Examples of the coordination compound capable of coordinating with titanium include the same halogen atom-containing compounds, amines, and phosphines as described above. When a coordination compound capable of coordinating with titanium other than hydroxycarboxylic acid is added, the amount added is preferably 1.0 mol or less, more preferably 0.5 mol or less, and most preferably 0.3 mol or less, per 1.0 mol of hydroxycarboxylic acid. Note that, from the viewpoint of uniformly progressing the reaction when mixing the diluent and hydroxycarboxylic acid in the second step, it is preferable not to add additional titanium alkoxide that is not diluted in a solvent.

[0037] The first step of mixing the solvent and titanium alkoxide, and the second step of mixing the resulting diluted solution with hydroxycarboxylic acid can both be carried out at room temperature of 0° C. or higher and 40° C. or lower. The first and second steps are preferably carried out continuously, for example by adding hydroxycarboxylic acid or its salt to the diluted solution obtained immediately after the first step to start the second step. From the viewpoint of suppressing side reactions between the hydroxycarboxylic acid and titanium alkoxide, the first and second steps are preferably carried out separately, and it is more preferable to carry out the second step immediately after the completion of the first step.

[0038] The first and second steps can produce titanium hydroxycarbonate, which is a type of titanium chelate compound. By changing the hydroxycarboxylic acid in the above method to a multidentate ligand such as a diamine compound, a dicarboxylic acid compound, a diketone compound, or a diphosphine compound, the titanium chelate compound represented by the general formula (1) can be similarly produced.

[0039] The titanium chelate compound such as titanium hydroxycarbonate is a compound in which one or more molecules of a polydentate ligand are coordinated to a titanium metal atom. In this way, the titanium chelate compound in which a polydentate ligand is coordinated to a titanium metal atom maintains the coordination state by the polydentate ligand even when mixed with water, and polymerization between titanium atoms is easily suppressed.

[0040] The titanium chelate compound in the mixture may contain a polymer such as an oligomer in which titanium atoms are bonded to each other via oxygen atoms, etc., to the extent that it has water solubility, but it does not have to substantially contain a polymer such as an oligomer. For example, even if the monomer and oligomer of the titanium chelate compound are present in equal amounts, it is sufficient that the oligomer has a low degree of polymerization and is water soluble. When the mixture contains a polymer such as an oligomer, the molar ratio of the monomer of the titanium chelate compound represented by formula (1) to the oligomer of the titanium chelate compound in the mixture is preferably 1 mole or less of the oligomer per mole of the monomer, more preferably 0.8 moles or less, and even more preferably 0.5 moles or less.

[0041] The mixture can be obtained as described above. The mixture may contain unreacted hydroxycarboxylic acid in addition to the oligomer. When the mixture contains unreacted hydroxycarboxylic acid, the content of unreacted hydroxycarboxylic acid in the mixture is preferably 10% by mass or less, particularly 5% by mass or less, based on the total amount of the mixture being 100% by mass.

[0042] In the moisture adjustment step, pure water is added to the mixture to adjust the moisture content in the aqueous mixture obtained by the moisture adjustment step to 20 to 70% by mass. In the moisture adjustment step, it is preferable to add pure water to adjust the moisture content in the aqueous mixture to 25 to 60% by mass. If the moisture content in the aqueous mixture obtained by the moisture adjustment step is less than 20% by mass, the titanium chelate compound is likely to be denatured in the reduced pressure distillation step described below. Furthermore, if the moisture content after moisture adjustment exceeds 70% by mass, the organic solvent is not sufficiently removed in the reduced pressure distillation step described below, which is industrially disadvantageous. The water content is a value when the mass of the aqueous mixture obtained in the water adjustment step is taken as 100% by mass.

[0043] In the water content adjustment step, the pure water may be added to the mixture all at once or dropwise. The dropwise addition may be continuous or intermittent. During the addition of the pure water, the water content in the water mixture is appropriately measured or calculated while the pure water is added, and the addition of the pure water is stopped when the water content in the resulting water mixture falls within the above range.

[0044] When measuring the water content, a part of the water mixture is sampled, and the water content in the water mixture is determined from the water content of the sampled part of the water mixture by, for example, the Karl Fischer method. When the water content is calculated, for example, the amount of pure water added to the mixture in the water adjustment step is measured, and the total amount of the mixture and the added pure water is regarded as the mass of the water mixture, and the total amount of added pure water is regarded as the water content in the water mixture. In this case, the amount of water contained in the mixture is considered to be negligible, and the mass of the mixture is considered to be unchanged before and after the water adjustment step.

[0045] Next, the aqueous mixture obtained in the water content adjustment step is subjected to a vacuum distillation step in which the organic solvent is distilled off at a gauge pressure of -30 kPa to -100 kPa and a temperature of 30°C to 80°C. The gauge pressure in the vacuum distillation step is preferably -40 kPa to -95 kPa. The temperature in the vacuum distillation step is preferably 35°C to 75°C. By distilling off the organic solvent under these conditions, the organic solvent can be distilled off while suppressing denaturation of the titanium chelate compound. From the viewpoint of efficiently distilling off the organic solvent, it is preferable to stir the aqueous mixture during the vacuum distillation step.

[0046] In this vacuum distillation step, it is preferable to distill off the organic solvent until the content of the organic solvent in the aqueous mixture obtained in the water adjustment step is preferably 5% by mass to 50% by mass, more preferably 10% by mass to 45% by mass. By distilling off the organic solvent under the vacuum distillation conditions described above until the concentration of the organic solvent in the aqueous mixture falls within this range, it is possible to efficiently reduce the amount of the organic solvent while suppressing the denaturation of the titanium chelate compound.

[0047] In the present production method, it is preferable to repeat the water content adjustment step and the vacuum distillation step multiple times from the viewpoint of reducing the concentration of the organic solvent in the obtained titanium chelating agent while suppressing the denaturation of the titanium chelating compound. That is, it is preferable to repeat the water content adjustment step of adding pure water to the obtained chelating agent again after performing the water content adjustment step and the vacuum distillation step, and then to repeat the vacuum distillation step. It is more preferable to repeat the water content adjustment step and the vacuum distillation step two to three times. By repeating the water content adjustment step and the vacuum distillation step multiple times, a larger amount of organic solvent can be distilled off, and a larger amount of organic solvent in the mixture can be replaced with water. As a result, the flash point of the obtained chelating agent can be increased and it can be handled as a non-hazardous material.

[0048] When the water content adjustment step and the vacuum distillation step are carried out multiple times, the water content of the titanium chelating agent obtained in the vacuum distillation step is reduced at the same time as the organic solvent is distilled off, so the water content is adjusted again by adding pure water. In order to dilute the organic solvent well and further reduce the alcohol content by vacuum distillation, it is preferable to add the same mass or more of the pure water distilled in the vacuum distillation step carried out immediately before in the next moisture adjustment step.

[0049] The titanium chelating agent obtained by this production method is preferably subjected to a post-process such as distillation or addition of water to further reduce the concentration of the organic solvent. The concentration of the organic solvent in the chelating agent obtained by the post-process is preferably 5% by mass or less, more preferably 4% by mass or less, and particularly preferably 3% by mass or less. By such a post-process, a chelating agent having a high flash point and not being a hazardous material under the Fire Service Act can be obtained, ensuring safety during transportation and handling.

[0050] In the latter step, it is preferable to add pure water from the viewpoint of ease of operation. By adding pure water, the concentration of the organic solvent in the obtained titanium chelating agent can be preferably 5% by mass or less, more preferably 4% by mass or less, and particularly preferably 3% by mass or less. Since it has a high flash point, it can be classified as a non-hazardous material under the Fire Service Act, and safety can be ensured during transportation and handling.

[0051] For example, the present production method can provide a titanium chelating agent having a flash point higher than room temperature. The flash point of the titanium chelating agent is preferably 60° C. or higher, more preferably 70° C. or higher, and particularly preferably non-flammable, from the viewpoint of being classified as a non-hazardous material under the Fire Service Act. The flash point is a flash point measured by a tag closed cup flash point measurement, and the absence of a flash point means that the flash point of the titanium chelating agent was sufficiently high in the tag closed cup flash point measurement, and the titanium chelating agent did not ignite.

[0052] The titanium chelating agent of the present invention obtained by the above steps can be usefully used as various crosslinking agents, catalysts, dispersants, etc.

[0053] Although the present manufacturing method and the chelating agent having a high flash point have been described above, the present invention is not limited to the configuration of the above embodiment. The present manufacturing method may additionally have any other steps, devices, or functions, or may be replaced with any other steps that produce the same effect. EXAMPLES

[0054] The present invention will be described below with reference to examples, but the scope of the present invention is not limited to these examples.

[0055] Example 1 <Production of Lactic Acid Titanium Chelate> A diluted solution was obtained by mixing 400.3 g of tetraisopropoxytitanium(IV) with 169.3 g of isopropanol. 422.9 g of L-lactic acid (purity 90 mass%) was added to this diluted solution and stirred to obtain a lactic acid titanium chelate. The molar ratio of the amount of tetraisopropoxytitanium(IV) used to the amount of L-lactic acid used was about 1:3.

[0056] <Moisture adjustment process 1-1> 507.5 g of pure water was added to the obtained lactic acid titanium chelate and stirred to obtain a transparent aqueous solution of lactic acid titanium chelate, the water content of which was 35.0% by mass.

[0057] <Decompression distillation step 1-1> 1500 g of the aqueous solution of lactic acid titanium chelate obtained in the moisture adjustment step 1-1 was placed in a 2 L cylindrical separable flask, and the aqueous solution of lactic acid titanium chelate was heated to 40°C while stirring. The vacuum degree in the vessel was set to -90 kPa in gauge pressure, and the aqueous solution of lactic acid titanium chelate was subjected to reduced pressure distillation treatment, and an amount of solvent equivalent to 40% by mass of the aqueous solution of lactic acid titanium chelate obtained in the moisture adjustment step 1-1 was distilled off. The distillate was weighed to be 588.6 g, and the isopropanol concentration was 65.3% by mass. The isopropanol in the distillate was the total amount of isopropanol added during the production of the lactic acid titanium chelate and isopropanol liberated from tetraisopropoxytitanium (IV).

[0058] <Moisture adjustment process 1-2> 588.6 g of pure water having the same mass as the distillate was added to the aqueous solution of lactic acid titanium chelate obtained in the reduced pressure distillation step 1-1 to obtain an aqueous solution of lactic acid titanium chelate with a water content of 60.6 mass %.

[0059] <Reduced pressure distillation step 1-2> The titanium lactic acid chelate aqueous solution obtained in the moisture adjustment step 1-2 was subjected to the same operation as in the reduced pressure distillation step 1-1 to obtain a titanium lactic acid chelate aqueous solution. The distillate weighed was 628.9 g, and the isopropanol concentration was 5.7 mass%.

[0060] <Moisture adjustment process 1-3> To the aqueous solution of lactic acid titanium chelate obtained in the reduced pressure distillation step 1-2, 628.9 g of pure water having the same mass as the distillate obtained in the reduced pressure distillation step 1-2 was added to obtain an aqueous solution of lactic acid titanium chelate having a water content of 63.0 mass %.

[0061] <Reduced pressure distillation step 1-3> The aqueous solution of lactic acid titanium chelate obtained in the water content adjustment step 1-3 was subjected to the same procedure as in the reduced pressure distillation step 1-1 to obtain an aqueous solution of lactic acid titanium chelate. The distillate was weighed to be 793.2 g, and no isopropanol was detected. 793.2 g of pure water was added to the obtained aqueous solution of lactic acid titanium chelating agent, and the mixture was filtered through a mesh screen to obtain a lactic acid titanium chelating agent. No isopropanol was detected from the obtained lactic acid titanium chelating agent.

[0062] Example 2 <Production of Lactic Acid Titanium Chelate> A diluted solution was obtained by mixing 8.0 kg of tetraisopropoxytitanium(IV) with 3.4 kg of isopropanol. 8.5 kg of L-lactic acid (purity 90% by mass) was added to this diluted solution and stirred to obtain a lactic acid titanium chelate. The molar ratio of the amount of tetraisopropoxytitanium(IV) used to the amount of L-lactic acid used was about 1:3.

[0063] <Moisture adjustment process 2-1> 10.1 kg of pure water was added to the obtained lactic acid titanium chelate and stirred to obtain a transparent aqueous solution of lactic acid titanium chelate, the water content of which was 35.0% by mass.

[0064] <Reduced pressure distillation step 2-1> 30.0 kg of the aqueous solution of lactic acid titanium chelate obtained in the moisture adjustment step 2-1 was placed in a 30 L reactor equipped with a vacuum pump, and the aqueous solution of lactic acid titanium chelate was heated to 40°C while stirring. The degree of vacuum in the vessel was set to -90 kPa in gauge pressure, and the aqueous solution of lactic acid titanium chelate was subjected to reduced pressure distillation treatment, and an amount of solvent equivalent to 40% by mass relative to the mass of the aqueous solution of lactic acid titanium chelate was distilled off. The amount of the distillate was 11.9 kg, and the isopropanol concentration was 72.2% by mass. The distillation rate was 40% by mass.

[0065] <Moisture adjustment process 2-2> 11.9 kg of pure water having the same mass as the distillate removed in the reduced pressure distillation step 2-1 was added to the aqueous solution of lactic acid titanium chelate obtained in the reduced pressure distillation step 2-1 to obtain an aqueous solution of lactic acid titanium chelate with a water content of 63.5 mass %. <Reduced pressure distillation step 2-2> The titanium lactic acid chelate aqueous solution obtained in the moisture adjustment step 2-1 was subjected to the same operation as in the reduced pressure distillation step 2-1 to obtain a titanium lactic acid chelate aqueous solution. The distillate was weighed to be 4.9 kg, and the isopropanol concentration was 20.4 mass%. The distillation rate was 17 mass%.

[0066] <Moisture adjustment process 2-3> 4.9 kg of pure water having the same mass as the distillate obtained in the reduced pressure distillation step 2-2 was added to the aqueous solution of lactic acid titanium chelate obtained in the reduced pressure distillation step 2-2 to obtain an aqueous solution of lactic acid titanium chelate having a water content of 66.9 mass %.

[0067] <Reduced pressure distillation step 2-3> The titanium lactic acid chelate aqueous solution obtained in the moisture adjustment step 2-3 was subjected to the same operation as in the reduced pressure distillation step 2-1 to obtain a titanium lactic acid chelate aqueous solution. The distillate was weighed to be 2.5 kg, and the isopropanol concentration was 0.9 mass%. The distillation rate was 8 mass%. 2.5 kg of pure water was added to the obtained aqueous solution of lactic acid titanium chelating agent, and the mixture was filtered through a mesh screen to obtain a lactic acid titanium chelating agent having an isopropanol concentration of 1.7% by mass.

[0068] Comparative Example 1 The aqueous solution of lactic acid titanium chelating agent was obtained in the <moisture adjustment step 1-1> of Example 1. The isopropanol concentration of this lactic acid titanium chelating agent was 33.9% by mass.

[0069] Comparative Example 2 12.2 kg of pure water was added to the lactic acid titanium chelate obtained in <Production of lactic acid titanium chelate> of Example 1 to obtain a lactic acid titanium chelate agent with an isopropanol concentration of 5% by mass. However, the concentration of the lactic acid titanium chelate in the obtained lactic acid titanium chelate agent was about 5% by mass, which was too low relative to the amount of solvent, making it difficult to use industrially.

[0070] (evaluation) <Flash point measurement> The flash points of the samples obtained in the examples and comparative examples were measured using a tag closed-type automatic flash point tester (ATG-7 model, manufactured by Tanaka Scientific Instruments Co., Ltd.). The results are shown in Table 1.

[0071] [Table 1]

[0072] As shown in Table 1, the titanium chelating agent obtained by this manufacturing method did not ignite, whereas the titanium chelating agent obtained by only adjusting the water content as in Comparative Example 1 had a low flash point of 19°C. Therefore, the titanium chelating agent obtained by this manufacturing method can be said to be a non-hazardous material under the Fire Service Act, and has a flash point of 60°C or higher. In addition, when the concentration of isopropanol is reduced by adding water as in Comparative Example 2, the concentration of the titanium chelating compound in the titanium chelating agent is also low, so the obtained titanium chelating agent could not be suitably used industrially.

Claims

1. a moisture adjusting step of adding pure water to the mixed solution of the organic solvent and the titanium chelate compound to adjust the moisture content to 20% by mass or more and 70% by mass or less; a reduced pressure distillation step of distilling off the organic solvent from the aqueous mixture obtained in the water content adjustment step under conditions of a degree of vacuum of −30 kPa to −100 kPa and a temperature of 30° C. or higher and 80° C. or lower; A method for producing a titanium chelating agent having the formula:

2. The method for producing a titanium chelating agent according to claim 1 , wherein the water content adjustment step and the reduced pressure distillation step are performed multiple times.

3. 3. The method for producing a titanium chelating agent according to claim 1 or 2, wherein the reduced pressure distillation step is a step of distilling off the organic solvent until the organic solvent in the aqueous mixture obtained in the water adjustment step is 5% by mass or more and 50% by mass or less.

4. 3. The method for producing a titanium chelating agent according to claim 1, further comprising the step of adding pure water after the vacuum distillation step so that the concentration of the organic solvent is 5% by mass or less.

5. 3. The method for producing a titanium chelating agent according to claim 1, wherein the organic solvent is an alcohol.

6. 6. The method for producing a titanium chelating agent according to claim 5, wherein the alcohol is at least one selected from the group consisting of methanol, ethanol, isopropanol, n-propanol, n-butanol, sec-butanol, tert-butanol, and n-pentanol.

7. 3. The method for producing a titanium chelating agent according to claim 1 or 2, wherein the titanium chelate compound is obtained by diluting a titanium alkoxide with an organic solvent to obtain a dilution, and then mixing the dilution with a hydroxycarboxylic acid.

8. The method for producing a titanium chelating agent according to claim 7, wherein the titanium alkoxide is at least one selected from the group consisting of tetramethoxytitanium(IV), tetraethoxytitanium(IV), tetra-n-propoxytitanium(IV), tetraisopropoxytitanium(IV), tetra-n-butoxytitanium(IV) and tetraisobutoxytitanium(IV).

9. 9. The method for producing a titanium chelating agent according to claim 7 or 8, wherein the hydroxycarboxylic acid is at least one selected from the group consisting of citric acid, tartaric acid, lactic acid and glycolic acid.

10. A titanium chelating agent having a flash point of 60°C or higher in a TAG closed cup flash point test.

11. The titanium chelating agent according to claim 10, which shows no ignition in a tag closed cup flash point measurement.

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