Method for producing titanium chelating agent and titanium chelating agent

Abstract

Provided is a production method for producing, using an industrially advantageous method, a titanium chelating agent that has a flash point of room temperature or higher and can be handled as a non-hazardous material. This method for producing a titanium chelating agent includes: a moisture adjustment step for adding pure water to a liquid mixture of an organic solvent and a titanium chelating compound to adjust the moisture so that the moisture content is 20 mass% to 70 mass%; and a reduced-pressure distillation step for distilling off the organic solvent from the aqueous liquid mixture obtained in the moisture adjustment step under the conditions of a vacuum level of −30 kPa to −100 kPa and a temperature of 30°C to 80°C.

Description

Method for producing titanium chelating agent and titanium chelating agent

[0001] The present invention relates to a method for producing a titanium chelating agent, particularly a method for producing a titanium chelating agent containing a titanium chelating compound having a hydroxycarboxylic acid as a polydentate ligand. The present invention also relates to a titanium chelating agent having a high flash point.

[0002] Titanium chelate compounds are used in a variety of applications, including 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 using a titanium alkoxide as the titanium compound and reacting it with the multidentate ligand (see, for example, Patent Documents 1 to 5).

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

[0004] In order to suppress the hydrolysis reaction of the titanium alkoxide, Patent Documents 2 to 5 describe the reaction of titanium alkoxide with a multidentate ligand such as hydroxycarboxylic acid 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 the addition of ethylene glycol to titanium tetraisopropoxide, followed by the addition of ammonium lactate to obtain a lactic acid chelate titanium compound. Patent Document 4 describes the mixing of lactic acid and isopropyl alcohol, followed by the dropwise addition of titanium isopropoxide to obtain a mixture of titanium isopropoxylactic acid chelate. Patent Document 5 describes a method for producing a titanium chelate compound by diluting titanium alkoxide with a solvent and then reacting it with a hydroxycarboxylic acid.

[0005] Japanese Patent Publication No. 50-5177 Japanese Patent Application Laid-Open No. 05-246936 Japanese Patent Application Laid-Open No. 2015-17219 Japanese Patent Application Laid-Open No. 2015-36390 International Publication No. WO2019-138989 Pamphlet

[0006] When a titanium chelate compound is obtained by reacting a titanium alkoxide with a multidentate ligand in an organic solvent as described above, the organic solvent must be removed or solvent extracted to isolate the titanium chelate compound. The titanium chelate compound may be subjected to thermal history during concentration during the organic solvent removal process, which can cause deterioration of the titanium chelate compound. Furthermore, solvent extraction may not completely recover the titanium chelate compound, resulting in a reduced yield of the titanium chelate compound. 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 chelate compound as a main component, as described in Patent Documents 2 to 5, contain organic solvents such as alcohols, and depending on the content, the flash point may be below room temperature.

[0007] Therefore, there is a need for the development of a chelating agent that has a flash point above 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 that has a flash point above room temperature 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 that has a flash point of 60°C or higher.

[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 chelate compound, since removing the organic solvent by distillation from a titanium chelating agent containing the organic solvent causes the titanium chelate compound to dehydrate and condense. As a result, they have found that by adding 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 the denaturation of the titanium chelate compound, and have thus completed the present invention.

[0009] That is, the present invention provides a method for producing a titanium chelating agent, comprising: a water content adjustment step of adding pure water to a mixture of an organic solvent and a titanium chelate compound to adjust the water content to 20% by mass or more and 70% by mass or less; and a reduced-pressure distillation step of distilling 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 to 80°C.

[0010] According to the present invention, it is possible to provide an industrially advantageous 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.

[0011] The present invention will be described below based on preferred embodiments. The production method of the present invention (hereinafter also referred to as "this production method") is a method for producing a titanium chelating agent, comprising: a water adjustment step (hereinafter also referred to as "this water adjustment step") of adding pure water to a mixture of an organic solvent and a titanium chelate 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") of distilling the organic solvent from the aqueous mixture obtained in the water adjustment step (hereinafter also referred to as "this aqueous mixture") 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 this mixture is an organic solvent that dissolves or disperses the titanium chelate compound. Examples of organic solvents 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 these organic solvents, organic solvents with low flash points are highly effective in rendering them non-hazardous by this production method, and therefore, this production method is particularly suitable. Among these organic solvents, the organic solvents used in producing the titanium chelate compound described below are preferred from the perspective of simplifying the production process of the chelating agent, with alcohols being more preferred. The alcohol is more preferably at least one selected from the group consisting of methanol, ethanol, isopropanol, n-propanol, n-butanol, sec-butanol, tert-butanol, and n-pentanol.

[0013] The titanium chelate compound in this mixture is a compound in which a multidentate ligand having two or more coordination sites is coordinated to tetravalent titanium (hereinafter also referred to as titanium(IV)) through a reaction between the multidentate ligand and titanium(IV). Examples of the multidentate 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 this production method as a catalyst, crosslinker, or the like, titanium chelate compounds in which an amine, hydroxycarboxylic acid, phosphine, or the like is coordinated to titanium are preferred, and titanium chelate compounds in which a hydroxycarboxylic acid is coordinated to titanium are more preferred. Examples of hydroxycarboxylic acids include citric acid, tartaric acid, lactic acid, and glycolic acid.

[0014] Examples of titanium(IV) include titanium tetraalkoxides and titanium tetrahalides, and titanium tetraalkoxides are preferred from the viewpoint of ease of coordination of multidentate ligands. 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 may be, 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 Ls 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 Ls 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, and when m is 1 to 3, m+n is preferably 4 or 5. In the general formula (1), when L is an s-dentate 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, and a group derived from a hydroxycarboxylic acid is preferred from the viewpoint that the titanium chelating agent obtained by the present production method can be suitably used for the above-mentioned applications.

[0017] R １Examples of the alkoxy group represented by the formula (1) include the same alkoxy groups as those mentioned as ligands in titanium alkoxides. 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 one of the nitrogen atoms 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 group in which both nitrogen atoms of the diamine 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 carboxyl group 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 the hydroxycarboxylic acid or the oxygen atom of a carboxyl group in the hydroxycarboxylic acid is coordinated to a titanium atom, or a group in which the oxygen atom of a hydroxyl group in the hydroxycarboxylic acid and the oxygen atom of a carboxyl group in the hydroxycarboxylic acid are bidentately coordinated to a titanium atom. Among these, a group in which the oxygen atom of a hydroxyl group in the hydroxycarboxylic acid and the oxygen atom of a carboxyl group in the 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 with a high flash point and low hazard, it is preferable to apply this production method to a mixture of an organic solvent with a low flash point and a titanium chelate compound. Therefore, the content of the organic solvent in this 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. Furthermore, from the viewpoint of the yield of the chelating agent produced by this production method, the content of the organic solvent in the mixture of the organic solvent and the titanium chelate compound is preferably 70% by mass or less, and more preferably 60% by mass or less, based on 100% by mass of the total amount of the organic solvent and the titanium chelate compound.

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

[0025] When the titanium chelate compound is titanium hydroxycarbonate, the titanium hydroxycarbonate forms a complex with the titanium to hydroxycarboxylic acid molar ratio being 1.5 to 3.5, preferably 2.0 to 3.0. That is, the titanium hydroxycarbonate is a titanium chelate complex in which the hydroxycarboxylic acid is coordinated with titanium in an amount of 1.5 to 3.5 mol, preferably 2.0 to 3.0 mol.

[0026] As a method for producing titanium hydroxycarbonate, for example, a method can be mentioned in which a hydroxycarboxylic acid or its salt 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 from the viewpoint of easy availability of titanium alkoxide.

[0027] The titanium hydroxycarbonate may contain, in addition to the hydroxycarboxylic acid, a coordination compound capable of coordinating with titanium. Examples of such coordination compounds include halogen-containing compounds having a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom; amines having functional groups such as methylamino, ethylamino, propylamino, isopropylamino, butylamino, isobutylamino, t-butylamino, or pentylamino; and phosphines such as trimethylphosphine, triethylphosphine, tributylphosphine, tris-t-butylphosphine, and triphenylphosphine. The amount of the coordination compound other than the hydroxycarboxylic acid that can coordinate with titanium 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 the hydroxycarboxylic acid.

[0028] From the viewpoint of being able to form titanium hydroxycarbonate, a titanium chelate compound that is easily soluble in water, under industrially advantageous conditions, the titanium hydroxycarbonate is preferably 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 four or fewer 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 preferred that 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).

[0030] The solvent used in the first step can be the same organic solvent as described above. In particular, a diluent can stably maintain the titanium alkoxide in a highly fluid state and enhance its reactivity with a hydroxycarboxylic acid. This diluent can be used without removing the diluent when dispersing or dissolving the target titanium chelate compound in a water-containing solvent. Polar organic solvents are preferred for the solvent used in the first step, and alcohols are particularly preferred. Examples of alcohols include methanol, ethanol, isopropanol, n-propanol, n-butanol, sec-butanol, tert-butanol, and n-pentanol. Among these, aliphatic alcohols having 1 to 4 carbon atoms are preferred from the viewpoints of facilitating uniform mixing of the titanium alkoxide and the hydroxycarboxylic acid in a liquid state, enhancing the reactivity of both, and facilitating the synthesis of a water-soluble titanium chelate compound. Furthermore, the use of a monohydric alcohol is preferred from the viewpoint of procurement cost. In particular, the use of 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 is preferred from the viewpoints of compatibility between the chelate compound and the solvent and ease of separation and recovery. As the solvent used in the first step, when the carbon numbers of the alkyl groups in the four alkoxide groups of the titanium alkoxide are different, 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 of a titanium alkoxide are the same, and therefore it is particularly preferable to use a monohydric alcohol having the same carbon number as the alkyl groups in the alkoxide groups of the titanium alkoxide.

[0031] In the diluted solution obtained in the first step, the proportion of titanium alkoxide is preferably 90% by mass or less, in order to fluidize the titanium alkoxide and facilitate mixing with the hydroxycarboxylic acid. Furthermore, the proportion of titanium alkoxide in the diluted solution is preferably 40% by mass or more, in order to effectively increase the yield while reducing the amount of solvent and hydroxycarboxylic acid used. From these perspectives, 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 perspective, 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, per 100 parts by mass of titanium alkoxide.

[0032] The dilution solution may contain components other than the solvent and titanium alkoxide. However, it is more preferable that the dilution solution be substantially free of components other than the solvent and titanium alkoxide, in order to increase the purity of the resulting titanium chelate compound. Specifically, the amount of components other than the solvent and titanium alkoxide in the dilution solution is preferably 10% by mass or less, more preferably 5% by mass or less. If a hydroxycarboxylic acid is present during dilution, it may react violently with the titanium alkoxide, resulting in heat generation. Furthermore, the reaction product formed by the reaction of the hydroxycarboxylic acid with the titanium alkoxide is gel-like, which increases the viscosity of the solution containing the titanium alkoxide and reduces its fluidity. Such a decrease in fluidity may hinder uniform mixing and prevent the desired titanium chelate compound from being obtained. The dilution of the titanium alkoxide with the solvent in the first step is preferably carried out in the absence of a hydroxycarboxylic acid.

[0033] The solvent used in the first step preferably has a low water content, since this can prevent the titanium alkoxide from hydrolyzing before the reaction with the 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 diluting the titanium alkoxide with the solvent in the first step, it is preferable to stir the two.

[0034] The hydroxycarboxylic acid used in the second step is preferably an aliphatic hydroxycarboxylic acid in terms of availability, reactivity with titanium alkoxide, and acquisition cost. For example, monocarboxylic acids include lactic acid, glycolic acid, glyceric acid, and hydroxybutyric acid; dicarboxylic acids include tartronic acid, malic acid, and tartaric acid; and tricarboxylic acids include citric acid and isocitric acid. These aliphatic hydroxycarboxylic acids may be salts with alkali metals, alkaline earth metals, ammonia, and the like. Among α-hydroxycarboxylic acids, at least one selected from lactic acid, tartaric acid, citric acid, and glycolic acid is preferred in terms of their resistance to dehydration reactions with each other and their availability and ease of handling. Lactic acid is particularly preferred because lactic acid, tartaric acid, citric acid, and glycolic acid are liquid at room temperature, easily mixable with a diluted titanium alkoxide solution, and facilitate the production of a titanium chelate compound. As the hydroxycarboxylic acid, the above-mentioned monovalent or divalent carboxylic acid that is not in the form of a salt such as an amine salt of 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 preferably mixed with the diluted solution obtained in the first step in an amount of 1.0 mole or more per 1.0 mole of titanium alkoxide in the diluted solution, from the viewpoint of obtaining a titanium chelate compound having a hydroxycarboxylic acid coordinated therewith in a high yield, and a mixing amount of 3.5 moles or less is preferred, from the viewpoint of suppressing excessive oligomerization of the resulting titanium chelate compound while suppressing the amount of hydroxycarboxylic acid used and increasing productivity. From these viewpoints, the hydroxycarboxylic acid is more preferably mixed with 1.1 moles to 3.3 moles, and even more preferably mixed with 1.2 moles to 3.0 moles per 1.0 mole of titanium alkoxide in the diluted solution.

[0036] In the second step, a coordination compound capable of coordinating with titanium may be added to the dilution solution in addition to the hydroxycarboxylic acid, as long as it does not inhibit the production efficiency of the titanium chelate compound, titanium hydroxycarbonate. Examples of coordination compounds 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 the 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 the hydroxycarboxylic acid. Note that, from the viewpoint of uniformly progressing the reaction when mixing the dilution solution and the 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 the 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 promptly 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. However, 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, it is possible to similarly produce the titanium chelate compound represented by the general formula (1).

[0039] Titanium chelate compounds such as titanium hydroxycarbonate are compounds in which one or more molecules of a polydentate ligand are coordinated to a titanium metal atom. Even when mixed with water, titanium chelate compounds in which a polydentate ligand is coordinated to a titanium metal atom maintain the coordination state of the polydentate ligand, and are therefore likely to inhibit polymerization of titanium atoms.

[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 or the like, as long as it is water-soluble, but it need not necessarily contain substantially any 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 1 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 preferably 5% by mass or less, based on 100% by mass of the total amount of the mixture.

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

[0043] In this water content adjustment step, 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 pure water, the water content in the water mixture is measured or calculated as appropriate, and the addition of pure water is stopped when the water content in the resulting water mixture reaches the above-mentioned range.

[0044] One method for measuring the water content is to sample a portion of the water mixture and determine the water content of the sampled portion using, for example, the Karl Fischer method. When calculating the water content, for example, pure water may be added to the mixture while measuring its amount in the water adjustment step, and the total amount of the mixture and the added pure water may be used as the mass of the water mixture, and the total amount of added pure water may be used as the water content of the water mixture. In this case, the amount of water contained in the mixture is considered negligible, and the mass of the mixture is considered 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 vacuum 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, the organic solvent is preferably distilled off until the content of the organic solvent in the aqueous mixture obtained in the water content adjustment step is preferably from 5 to 50% by mass, more preferably from 10 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, the organic solvent can be efficiently reduced while suppressing denaturation of the titanium chelate compound.

[0047] In this production method, from the viewpoint of reducing the organic solvent concentration in the resulting titanium chelating agent while suppressing denaturation of the titanium chelating compound, it is preferable to repeat the water content adjustment step and the vacuum distillation step multiple times. That is, after performing the water content adjustment step and the vacuum distillation step, it is preferable to repeat the water content adjustment step by adding pure water to the resulting chelating agent again, followed by 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 more of the organic solvent in the mixture can be replaced with water. As a result, the flash point of the resulting chelating agent can be increased, enabling it to be handled as a non-hazardous substance.

[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 as the organic solvent is distilled off, and therefore the water content is adjusted again by adding pure water. In order to effectively dilute the organic solvent and further reduce the alcohol content by vacuum distillation, it is preferable to add pure water in the next vacuum distillation step in an amount equal to or greater than the amount of the distillate distilled off in the immediately preceding vacuum distillation step.

[0049] The titanium chelating agent obtained by this production method is preferably subjected to a subsequent process such as distillation or the 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 subsequent process is preferably 5% by mass or less, more preferably 4% by mass or less, and particularly preferably 3% by mass or less. This subsequent process provides a chelating agent with a high flash point that is not classified as a hazardous material under the Fire Service Act, ensuring safety during transportation and handling.

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

[0051] For example, this production method can produce a titanium chelating agent having a flash point higher than room temperature. From the viewpoint of being classified as a non-hazardous material under the Fire Service Act, the flash point of the titanium chelating agent is preferably 60°C or higher, more preferably 70°C or higher, and it is particularly preferable that no flash point is observed. Note that the flash point is measured by tag closed cup flash point measurement, and no flash point is observed means that the flash point of the titanium chelating agent is sufficiently high in the tag closed cup flash point measurement so that the titanium chelating agent does 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 production 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 production method may include any other optional steps, devices, or functions, or may be replaced with any other steps that produce a similar effect.

[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 400.3 g of tetraisopropoxytitanium(IV) was mixed with 169.3 g of isopropanol to obtain a diluted solution. 422.9 g 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) to the amount of L-lactic acid used was approximately 1:3.

[0056] <Water content adjustment step 1-1> 507.5 g of pure water was added to the obtained titanium lactic acid chelate and stirred to obtain a transparent aqueous solution of titanium lactic acid chelate. The water content of this aqueous solution was 35.0 mass %.

[0057] <Distillation Step 1-1 Under Reduced Pressure> 1500 g of the aqueous solution of lactic acid titanium chelate obtained in the water content adjustment step 1-1 was placed in a 2 L cylindrical separable flask, and the solution was heated to 40°C while stirring. The degree of vacuum in the vessel was adjusted to -90 kPa gauge pressure, and the aqueous solution of lactic acid titanium chelate was subjected to distillation under reduced pressure, distilling off the solvent in an amount equivalent to 40% by mass of the aqueous solution of lactic acid titanium chelate obtained in the water content adjustment step 1-1. The distillate weighed 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] <Water content adjustment step 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] The titanium lactic acid chelate aqueous solution obtained in the water content adjustment step 1-2 was subjected to the same procedure as in the titanium lactic acid chelate aqueous solution obtained in the water content adjustment step 1-2, to obtain a titanium lactic acid chelate aqueous solution. The distillate weighed 628.9 g and had an isopropanol concentration of 5.7% by mass.

[0060] <Water content adjustment step 1-3> 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 the aqueous solution of lactic acid titanium chelate obtained in the reduced pressure distillation step 1-2 to obtain an aqueous solution of lactic acid titanium chelate with a water content of 63.0 mass%.

[0061] <Reduced-pressure distillation step 1-3> The aqueous lactic acid titanium chelate solution obtained in the water content adjustment step 1-3 was subjected to the same operation as in the reduced-pressure distillation step 1-1 to obtain an aqueous lactic acid titanium chelate solution. 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 lactic acid titanium chelate solution, 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 8.0 kg of tetraisopropoxytitanium(IV) was mixed with 3.4 kg of isopropanol to obtain a diluted solution. 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) to the amount of L-lactic acid used was approximately 1:3.

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

[0064] <Distillation step 2-1 under reduced pressure> 30.0 kg of the aqueous solution of lactic acid titanium chelate obtained in the water content 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 adjusted to -90 kPa gauge pressure, and the aqueous solution of lactic acid titanium chelate was subjected to distillation under reduced pressure, distilling off the solvent in an amount equivalent to 40% by mass relative to the mass of the aqueous solution of lactic acid titanium chelate. The distillate was weighed to be 11.9 kg, and the isopropanol concentration was 72.2% by mass. The distillation rate was 40% by mass.

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

[0066] <Water content adjustment step 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 with a water content of 66.9 mass%.

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

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

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

[0070] (Evaluation) <Measurement of Flash Point> 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]

[0072] As shown in Table 1, the titanium chelating agent obtained by this production method did not ignite, whereas the titanium chelating agent obtained by simply 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 production 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. Furthermore, when the concentration of isopropanol was reduced by adding water as in Comparative Example 2, the concentration of the titanium chelate compound in the titanium chelating agent was also low, and the obtained titanium chelating agent could not be used industrially.

Claims

1. 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 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 to 80°C.

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 carried out multiple times.

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 moisture adjustment step is 5% by mass or more and 50% by mass or less.

4. A method for producing a titanium chelating agent according to claim 1 or 2, further comprising the step of adding pure water after the vacuum distillation step so that the concentration of the organic solvent is 5 mass % or less.

5. The method for producing a titanium chelating agent according to claim 1 or 2, wherein the organic solvent is an alcohol.

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. A 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 diluted solution, and then mixing the diluted solution 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. 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.

Images