Methods for restoring the operating solution used in hydrogen peroxide production, as well as methods for producing hydrogen peroxide using the restored operating solution.

Abstract

In the production of hydrogen peroxide, a higher alcohol component in an organic solvent changes into a ketone body and increase in the ketone bodies reduces water content of a working solution and causes deterioration of catalytic activity. In addition, increase in the ketone bodies may obstruct stable and safe operation during the production of hydrogen peroxide due to decrease in the solubility of anthrahydroquinones, crystallization, precipitation, etc. The objective of the present invention is to provide a method for improving hydrogen peroxide production efficiency by regenerating an altered substance (ketone body) derived from a polar solvent in the working solution used for the production of hydrogen peroxide by the anthraquinone method to the original alcohol component. Hydrogen peroxide can be produced more efficiently by distilling off the organic solvent component including the ketone body from the working solution which has been used over time and hydrogenating the same under the presence of a metal catalyst to regenerate to the original alcohol component.

Description

The present invention relates to a method for regenerating a working solution used in the production of hydrogen peroxide by the anthraquinone method. More specifically, the invention relates to a method for regenerating a working solution in which altered substances derived from the polar solvent in the working solution are regenerated back to their original polar solvent components by hydrogenation treatment under a metal catalyst, and to a method for producing hydrogen peroxide using the working solution obtained by this treatment method. The main industrial method for producing hydrogen peroxide currently employs anthraquinones as the reaction medium, and is generally called the anthraquinone process. Anthraquinones are used dissolved in a suitable organic solvent. Organic solvents are used alone or in mixtures, but usually a mixture of two types, a polar solvent and a non-polar solvent, is used. The solution prepared by dissolving anthraquinones in an organic solvent is called the working solution. In the anthraquinone process, during the reduction step, anthraquinones in the working solution are hydrogenated in the presence of a catalyst to produce anthrahydroquinones. Then, in the oxidation step, these anthrahydroquinones are oxidized with air or an oxygen-containing gas to return them to anthraquinones, simultaneously generating hydrogen peroxide. The hydrogen peroxide produced in the working solution is usually extracted using water and separated from the working solution. The working solution from which the hydrogen peroxide has been extracted is returned to the reduction step, forming a cyclic process. This process essentially produces hydrogen peroxide from hydrogen and air, making it an extremely efficient and effective process. Hydrogen peroxide is already being produced industrially using this cyclic process. The organic solvent in the working solution also undergoes alteration as it repeatedly cycles through hydrogenation and oxidation, accumulating as by-products. These by-products are mainly ketone bodies formed when higher alcohols, which are polar solvents in the working solution, are dehydrogenated. A working solution containing a large amount of ketone bodies reduces the desired water content it can incorporate. As a result, this can lead to a deterioration in catalytic activity and cause problems with safe and stable operation. The by-products also include oxides and decomposition products of organic solvent components. Specifically, carboxylic acids, polyols, and phenols have been detected. These by-products alter various physical and chemical properties of the working solution, such as its specific gravity, viscosity, and surface tension, and thus cause a decrease in the efficiency of hydrogen peroxide production through the reduction, oxidation, and extraction processes of the working solution. Conventionally, methods have been proposed for removing various by-products from working solutions that have been used for a long time, and for regenerating working solutions. For example, a method is known in which reduced anthraquinones are brought into contact with an alkaline aqueous solution to remove anthraquinone by-products that do not contribute to hydrogen peroxide generation. Similarly, a method is known in which the working solution is treated at 100 to 170°C using solid or aqueous solutions of halides such as aluminum and ammonium to regenerate anthraquinone by-products. Another known method is to treat the working solution with ozone, then extract it with an alkali metal hydroxide aqueous solution, and then bring the extracted and separated working solution into contact with activated alumina or activated magnesia. On the other hand, a method is known for preventing blockage due to crystallization of the distillate when performing a first-stage distillation to separate the organic solvent in the working solution, followed by a second-stage distillation to separate anthraquinones and monoanthracene-based low-boiling-point substances. Furthermore, Patent Document 1 describes a method for producing hydrogen peroxide, which includes a first-stage distillation to recover the organic solvent by distilling the working solution at atmospheric pressure or lower, followed by a second-stage distillation to recover anthraquinones by distilling at a lower pressure, at a temperature of 200°C or higher, and for a residence time of 1 hour or more, and is characterized by treating the working solution prepared from the total distillate with a regenerating catalyst. Patent Document 2 describes a method of removing low-boiling point modifiers derived from an organic solvent by azeotropic distillation with an aqueous alkali solution. Patent Document 3 also describes a method of removing modifiers derived from an organic solvent by distilling an operating solution and subjecting the obtained organic solvent to a contact treatment with water. International Publication No. 2007 / 129769, JP-A No. 2008-87992, JP-A No. 2008-120631 As described above, in the proposed technologies, methods for extracting and removing by-products in the reaction medium and methods for removing deteriorated products derived from the solvent have been reported, but there has been no proposal regarding a method for regenerating and removing a higher alcohol component, which is a polar solvent among organic solvents, that has become a ketone. An increase in the ketone in the operating solution reduces the water content of the operating solution, leading to deterioration of the catalytic activity and further causing an obstacle to safe operation. The object of the present invention is to provide a method for regenerating a ketone derived from a polar solvent in an operating solution that has been used over time in the production of hydrogen peroxide by the anthraquinone method into the original alcohol component and improving the production efficiency of hydrogen peroxide. The present inventors have found that hydrogen peroxide can be efficiently produced by distilling and separating an organic solvent component containing a ketone in an operating solution used for use and hydrogenating this in the presence of a metal catalyst to regenerate it into the original alcohol component, thereby completing the present invention. In other words, the present invention is as follows: 1. A method for regenerating a working solution continuously used in the production of hydrogen peroxide by the anthraquinone method, comprising the steps of: distilling and separating an organic solvent component containing alcohol and the ketone body of the alcohol from the working solution; and hydrogenating the obtained organic solvent component in the presence of a metal catalyst to regenerate alcohol from the ketone body. 2. The method for regenerating a working solution according to item 1, wherein the residual rate of ketone bodies in the organic solvent (= ketone bodies / organic solvent component × 100) is 10% by mass or less by hydrogenating the organic solvent in the presence of a metal catalyst. 3. The method for regenerating a working solution according to item 1, wherein the metal catalyst is a metal compound containing one or more selected from palladium, rhodium, ruthenium, platinum, copper, or chromium. 4. The method for regenerating a working solution according to item 1, wherein the metal catalyst is a metal compound containing copper and / or chromium. 5. The method for regenerating a working solution according to item 1, wherein the amount of the metal catalyst added is 0.05% by mass to 10% by mass relative to the mass of the organic solvent. 6. 1. A method for regenerating the working solution according to item 1, wherein the pressure of the hydrogenation treatment is atmospheric pressure to 10 MPa. 7. A method for regenerating the working solution according to item 1, wherein the hydrogenation temperature of the hydrogenation treatment is 140°C to 230°C. 8. A method for regenerating the working solution according to item 1, wherein the time of the hydrogenation treatment is 0.5 hours to 100 hours. 9. A method for regenerating the working solution according to item 1, further comprising the step of contacting the organic solvent component after the hydrogenation treatment with water and / or an alkaline aqueous solution. 10. A method for producing hydrogen peroxide by the anthraquinone method, characterized by using a working solution regenerated by the method described in any of items 1 to 9. 11. Hydrogen peroxide produced by the production method described in item 10. This invention makes it possible to regenerate and reuse altered substances derived from polar solvents in the working solution, which is expected to reduce solvent usage and, as a result, lower manufacturing costs. Furthermore, it is expected to reduce the risk of catalyst deactivation and enable a more efficient process. The present invention will be described in detail below. The following embodiments are illustrative for illustrating the present invention and are not intended to limit the present invention to these embodiments only. The present invention can be implemented in various forms without departing from its spirit. As mentioned above, a solution prepared by dissolving anthraquinones in an organic solvent is called a working solution. The anthraquinones used in this invention are preferably alkylanthraquinones, alkyltetrahydroanthraquinones, or mixtures thereof. The alkylanthraquinones and alkyltetrahydroanthraquinones used may each be mixtures of multiple alkylanthraquinones and alkyltetrahydroanthraquinones. Examples of alkylanthraquinones include ethylanthraquinone, t-butylanthraquinone, and amylanthraquinone. Examples of alkyltetrahydroanthraquinones include ethyltetrahydroanthraquinone, t-butyltetrahydroanthraquinone, and amyltetrahydroanthraquinone. Both nonpolar and polar solvents can be used as organic solvents, but those containing both are preferred. Examples of nonpolar solvents include aromatic hydrocarbons, such as benzene or benzene derivatives containing alkyl substituents with 1 to 5 carbon atoms. Examples of polar solvents include higher alcohols, carboxylic acid esters, tetrasubstituted ureas, cyclic ureas, and trioctyl phosphates. In this invention, an organic solvent recovered by distillation from a working solution used over time is hydrogenated in the presence of a hydrogenation catalyst (metal catalyst). The metal catalyst is supported on a carrier, and the metal compound is preferably a metal compound containing at least one selected from copper, chromium, palladium, rhodium, ruthenium, or platinum, with a catalyst containing copper and / or chromium being particularly preferred. The catalyst compound is usually in a metallic state, but may also be in the form of an oxide that is easily reduced to a metal under reaction conditions. These metals may also be supported on a carrier. The amount of catalyst is not decisive to the effect of this invention, and only an amount necessary for the hydrogenation reaction to proceed sufficiently is required. The present invention provides a method for producing hydrogen peroxide, which involves separating a working solution that has been used for a long period of time and whose organic solvent components have oxidized and deteriorated due to continuous repeated use, into a reaction medium containing alkylanthraquinones and / or alkyltetrahydroanthraquinones and an organic solvent component containing ketone bodies by distillation, and further regenerating the ketone bodies in the organic solvent component into the original alcohol component by hydrogenation treatment of this organic solvent component under a metal catalyst, and then mixing it with the alkylanthraquinones and / or alkyltetrahydroanthraquinones separated as described above and reusing it for the production of hydrogen peroxide. In addition, organic solvent components recovered from various points in the hydrogen peroxide production process, such as organic solvents recovered from the exhaust gas of the oxidation process, may also be mixed with the working solution or organic solvent components and subjected to distillation and hydrogenation treatment. The working solution used in this invention is one in which the amount of oxidized and degraded organic solvent components has increased due to continuous repeated use. However, when performing a distillation operation to separate the reaction medium from the organic solvent components, there is a concern that abnormal decomposition may occur if hydrogen peroxide remains in the working solution. For this reason, it is preferable that the working solution is in a state in which hydrogen peroxide has been removed by thoroughly contacting it with water before the distillation operation is performed. The water used here is preferably purified water such as distilled water, ion-exchanged water, or water produced by reverse osmosis. Water purified by methods other than those mentioned above is also preferably used. In particular, pure water is preferred as the water used for washing. Generally known methods can be used as means for mixing the working solution and water. For example, stirring, shaking, bubbling with an inert gas, parallel flow and alternating current contact methods are available, but the method is not limited to these, and any method that allows the working solution and water to come into efficient contact is acceptable. There is no significant upper limit to the volume of water to be brought into contact with the working solution; it can be appropriately selected depending on the equipment and work procedures. There is no significant upper limit to the contact time between the working solution and the water; it can be appropriately selected depending on the equipment and work procedures. The contact temperature between the working solution and the water should be in the range of 0°C to 70°C, preferably 10°C to 60°C, and particularly preferably 20°C to 50°C. Within this range, hydrogen peroxide can be efficiently removed. There are no particular limitations on the pressure during the contact process between the working solution and the water, but it is usually advantageous to maintain it at atmospheric pressure. After contact, the water is separated from the working solution and discharged. The working solution, after being used for a long period, is separated by distillation into a reaction medium containing alkylanthraquinones and / or alkyltetrahydroanthraquinones and an organic solvent component. In the distillation operation in this invention, it is preferable to distill the organic solvent component in the working solution at atmospheric pressure or lower, but there are no particular restrictions on the apparatus, and commonly used distillation equipment can be used. Examples include batch distillation apparatuses, continuous distillation apparatuses, and thin-film distillation apparatuses. Specific operating conditions can be those disclosed in International Publication No. 2007 / 129769. The temperature and pressure, which are the distillation conditions, are selected appropriately depending on the solvent used in the working solution and cannot be specified in general terms, but they can be selected from the following conditions. A pressure of 1 kPa to 100 kPa (atmospheric pressure) is suitable, 5 to 80 kPa is more preferable, and 5 to 30 kPa is even more suitable. The temperature is determined as the condition for distillation until the amount of residual solvent is 5% by mass or less. Typically, distillation is considered complete when the temperature has risen by approximately 50 to 100°C from the temperature at which the solvent distillation began. For example, if the solvent begins distilling at a pressure of 13 kPa and a pot temperature of 130°C, the distillation should be terminated when the pot temperature reaches 200°C. <Regeneration of Working Solution> The organic solvent components recovered by distillation in this invention are hydrogenated under a metal catalyst, thereby regenerating the oxidized and degraded organic solvent components back into the original organic solvent components. Any commonly used pressurized reaction equipment can be used as the apparatus, and there are no particular restrictions. Examples include batch reactors and continuous reactors, but batch reactors are preferred. However, it is advantageous for the hydrogenation reaction if the organic solvent components, hydrogenation catalyst, and hydrogen are thoroughly mixed. Generally known methods can be used for mixing. Examples include stirring, shaking, and circulation of the reaction solution, but the method is not limited to these; any method that allows for efficient contact between the organic solvent components, hydrogenation catalyst, and hydrogen is acceptable. <Hydrogenation of Distilled Organic Solvents> In the present invention, the distilled organic solvent is subjected to a hydrogenation reaction. There are no particular restrictions on the amount of hydrogenation catalyst added, as long as there is a sufficient amount for the hydrogenation reaction to proceed. However, the amount of hydrogenation catalyst as a metal component is preferably 0.05 to 10% by mass, more preferably 0.1 to 8% by mass, and particularly preferably 0.2 to 5% by mass, relative to the weight of the organic solvent component. Similarly, there are no particular restrictions on the hydrogenation temperature and hydrogenation pressure. However, the hydrogenation temperature is preferably 100°C to 230°C, more preferably 140°C to 230°C, and particularly preferably 150°C to 210°C. The hydrogenation pressure is atmospheric pressure or higher, preferably 0.8 MPa or higher, more preferably 1.2 MPa or higher, and particularly preferably 1.8 MPa or higher. The upper limit pressure depends on the hydrogenation apparatus, but 10 MPa or lower is preferable for safety reasons. Regarding the hydrogenation time, there are no particular restrictions as long as the hydrogenation reaction is completed, but 0.5 hours to 100 hours is preferred, more preferably 1 hour to 80 hours, and especially preferably 2 hours to 50 hours. The endpoint of the hydrogenation reaction is, for example, when the remaining percentage of ketone bodies in the organic solvent becomes 10% or less, but a lower value is preferable and can be selected as appropriate. More preferably 8% or less, and even more preferably 7% or less. In the present invention, the organic solvent after hydrogenation treatment is removed from the reactor and separated from the hydrogenation catalyst. Generally known methods can be used for separation. For example, filter paper, sintered metal filters, metal fiber filters, resin filters, and centrifugal separation are acceptable, but the method is not limited to these. Any method that efficiently separates the organic solvent components from the hydrogenation catalyst, including the shape of the separation components, is acceptable. In the present invention, the organic solvent components separated by the above method after hydrogenation treatment are more preferably subjected to azeotropic distillation with an alkaline aqueous solution or contact treatment with an alkaline aqueous solution or water. This makes it possible to remove oxidized and degraded products other than ketone bodies, such as dimethylbenzoic acid, alkylphthalic anhydride, aliphatic carboxylic acids, trimethylphenol, and 2,6-dimethyl-4-heptanediol, which cannot be easily removed by distillation and hydrogenation reactions. As for specific operating conditions, the conditions disclosed in Japanese Patent Application Publication No. 2008-87992 and Japanese Patent Application Publication No. 2008-120631 can be applied. In the present invention, the organic solvent component obtained in the above operation is mixed with the reaction medium recovered in the distillation operation or a new reaction medium, and returned to the hydrogen peroxide production process as a working solution for reuse. The present invention will be described in more detail below with reference to examples, but the present invention is not limited thereto. In this invention, pseudocumene (PSC) was used as the aromatic hydrocarbon, which is a nonpolar solvent in the working solution, and diisobutylcarbinol (DIBC) was used as the higher alcohol, which is a polar solvent. The ketone body derived from diisobutylcarbinol was diisobutyl ketone (DIBK), and each organic solvent component was measured using gas chromatography (GC). Among the organic solvent components, other components identified included dimethylbenzoic acid, alkylphthalic anhydride, aliphatic carboxylic acids, trimethylphenol, and 2,6-dimethyl-4-heptanediol, which are altered organic solvents that cannot be regenerated by hydrogenation treatment. <Measurement of Acid Value of Solvents> The acid value of solvents was measured in accordance with JIS-K0070. Specifically, it was done as follows: First, 40 mL of the solvent sample and 20 mL of N / 10 sodium carbonate aqueous solution were added to a flask and weighed, and extracted at 50°C for 15 minutes. The extracted contents were allowed to stand in a separatory funnel, and the resulting sodium carbonate solution layer (lower layer) was washed with 20 mL of pseudocumene. Then, 5 mL of the sodium carbonate solution layer was mixed with pure water to make a 40 mL sample, which was titrated with N / 20 hydrochloric acid. The acid value A of the solvent sample was then determined based on the following formula. A = (B / R - C / S) × N × F × U / V × 1000 (wherein A: acid value (measured acid component (mol / L)), B: blank titration volume (mL), C: sample titration volume (mL), R: blank volume (5 mL), S: titration sample volume (5 mL), N: titrator concentration (0.05 mol / L), F: titrator factor, U: extract volume at extraction (mL), and V: sample volume at extraction (mL).) <Measurement of Water Content of Working Solution> A Karl Fischer MKS-520 manufactured by Kyoto Electronics Industrial Co., Ltd. was used to measure the water content of the prepared working solution. Specifically, the procedure was as follows: First, the prepared working solution was collected in a 2 ml volumetric pipette and injected into a Karl Fischer MKS-520 titration vessel manufactured by Kyoto Electronics Industrial Co., Ltd. The solution was titrated using Aquamicron titrant SS 3 mg as the titrant, and the water content was measured by volumetric titration. <Activity Test of Working Solution> The performance of the working solution obtained by the above process was confirmed using a batch-type evaluation apparatus equipped with a stirring blade, as follows. 1 part by weight of catalyst and 20 parts by weight of working solution were added to the batch-type reaction vessel. After sealing the reaction vessel, the reaction system was purged with hydrogen. The stirring blade was stirred at 1000 rpm for 30 minutes, and the amount of hydrogen absorbed per unit catalyst was measured. The reaction temperature was controlled to 30°C, and the reaction pressure to atmospheric pressure. The catalyst used here was the silica-supported palladium catalyst disclosed in Japanese Patent Application Publication No. 9-271670. Reference Example 1 <Recovery of Organic Solvent Components as Processing Raw Materials> In the first distillation step of the present invention, the working solution used was one that had been used for many years in an actual hydrogen peroxide production apparatus. 2000 ml of the working solution was withdrawn from the hydrogen peroxide production apparatus. The reaction media in the working solution were amylanthraquinone and amyltetrahydroanthraquinone. In the first stage of recovering the organic solvent components, 400 ml of the working solution was pre-charged into a 1000 ml flask equipped with a distillation apparatus, and the temperature was raised from room temperature while controlling the vacuum to 13 kPa. Distillation began when the temperature of the vessel reached 130°C, and as the volume of liquid in the flask decreased, the remaining working solution was added sequentially until the total amount charged reached 2000 ml, at which point the addition was stopped. After stopping the addition of the working solution, distillation was continued until the temperature of the distillation vessel reached 200°C, which took 2 hours, and the organic solvent components were recovered. At this time, the anthraquinones remaining in the flask of the distillation vessel are called the "separated reaction media". GC analysis of the organic solvent components in the separated reaction medium revealed a total concentration of less than 1% by mass. Meanwhile, 1400 ml of organic solvent was recovered. This is referred to as the distillation-recovered solvent. GC analysis of the organic solvent components in this distillation-recovered solvent revealed pseudocumene / diisobutylcarbinol / diisobutylketone to be 62.4% by mass / 11.8% by mass / 25.4% by mass. The acid value of this distillation-recovered solvent was 84 mg-KOH / g (Table 1). <Preparation of Working Solution> The "separated reaction medium" (residue in the boiler after distillation recovery) and the distillation-recovered solvent were mixed to a solid content (amylanthraquinone and amyltetrahydroanthraquinone) concentration of 250 g / L. 5 g of pure water was then added and stirred, and the mixture was allowed to stand at room temperature (20°C to 25°C) for approximately 2 hours to obtain the working solution. The water content of the obtained working solution was 2.4 g / L (Table 1). Considering the preference for the working solution to contain an appropriate amount of water, 5 g of pure water exceeding the saturation water content was added to the mixture beforehand, and the actual water content in the mixture (saturation water content) was also measured. The same procedure was followed in the following examples and reference examples, and the results of the water content evaluation for these examples will be described later. <Activity Test of Working Solution> An activity test was performed on the working solution prepared above. The amount of hydrogen absorbed obtained here was used as the standard, and the relative hydrogen absorption rate was set to 100% (Table 1). Example 1 <Hydrogenation of Distilled Recovery Solvent> 900 g of the above-mentioned distilled recovery solvent and 9 g of N203SD (Cu-Cr-based catalyst) manufactured by JGC Catalysts & Chemicals Co., Ltd. (1% by mass relative to the distilled recovery solvent) were added to an autoclave and a hydrogenation reaction was carried out for 7 hours. The reaction temperature was controlled to 200°C and the reaction pressure to 2.0 MPa. After the hydrogenation reaction was completed, the mixture was allowed to stand until it reached room temperature, and then the catalyst was filtered off using Advantec filter No. 1. The solvent obtained by the hydrogenation reaction of the distilled recovery solvent is called the hydrogenated solvent. GC analysis of the hydrogenated solvent components showed that pseudocumene / diisobutylcarbinol / diisobutylketone = 62.4% by mass / 30.8% by mass / 6.4% by mass. Table 1 shows the GC analysis results of the hydrogenated solvent components over time as the hydrogenation reaction progressed. The acid value of this hydrogenated solvent was 81 mg-KOH / g (Table 1). <Preparation of Working Solution> The "separated reaction medium" (residue in the boiler after distillation recovery) and the hydrogenation solvent were mixed to a solid content (amylanthraquinone and amyltetrahydroanthraquinone) concentration of 250 g / L. 5 g of pure water was then added and the mixture was stirred. The mixture was then allowed to stand at room temperature (20°C to 25°C) for approximately 2 hours to obtain the working solution. The water content of the obtained working solution was 3.6 g / L (Table 1). <Activity Test of Working Solution> An activity test was performed on the obtained working solution. The relative hydrogen absorption rate of this working solution was 153% (Table 1). Example 2 <Hydrogenation of Distilled Recovered Solvent> The hydrogenation treatment of the distilled recovered solvent was carried out for a total of 80 hours under the same conditions as in Example 1, except that the amount of catalyst was controlled to 0.4% by mass relative to the distilled recovered solvent, the reaction temperature was 160°C, and the reaction pressure was 1.6 MPa. The hydrogenated solvent components were pseudocumene / diisobutylcarbinol / diisobutylketone = 62.2% by mass / 30.3% by mass / 6.9% by mass. Table 1 shows the GC analysis results of the hydrogenated solvent components over time as the hydrogenation reaction progressed. The acid value of this hydrogenated solvent was 82 mg-KOH / g (Table 1). <Preparation of Working Solution> The working solution was prepared in the same manner as in Example 1. The water content of this working solution was 3.5 g / L (Table 1). <Activity Test of Working Solution> The activity test of the obtained working solution was performed using the same method as in Example 1. The relative hydrogen absorption rate of this working solution was 151% (Table 1). Example 3 <Hydrogenation of Distilled Recovered Solvent> Hydrogenation treatment of the distilled recovered solvent was carried out for 9 hours under the same conditions as in Example 1, except that the reaction temperature was controlled to 160°C and the reaction pressure to 2.0 MPa. The hydrogenated solvent components were pseudocumene / diisobutylcarbinol / diisobutylketone = 62.3% by mass / 31.1% by mass / 6.1% by mass. Table 1 shows the GC analysis results of the hydrogenated solvent components over time as the hydrogenation reaction progressed. The acid value of this hydrogenated solvent was 82 mg-KOH / g (Table 1). <Preparation of Working Solution> The working solution was prepared in the same manner as in Example 1. The water content of this working solution was 3.6 g / L (Table 1). <Activity Test of Working Solution> The activity test of the obtained working solution was performed using the same method as in Example 1. The relative hydrogen absorption rate of this working solution was 152% (Table 1). Example 4 <Hydrogenation of Distilled Recovered Solvent> The amount of distilled recovered solvent was double that of Example 1, i.e., 1800 g and 14.4 g of catalyst were charged, the reaction temperature was started at 160°C, and after 2 hours from the start of the reaction, the reaction temperature was controlled to rise to 200°C. The hydrogenation treatment of the distilled recovered solvent was carried out in the same manner as in Example 1 for a total of 8.5 hours. The hydrogenation solvent components were pseudocumene / diisobutylcarbinol / diisobutylketone = 62.3 mass% / 30.6 mass% / 6.6 mass%. The GC analysis results of the hydrogenation solvent components over time are shown in Table 1. The acid value of this hydrogenation solvent was 81 mg-KOH / g (Table 1). <Preparation of Working Solution> The working solution was prepared in the same manner as in Example 1. The water content of this working solution was 3.5 g / L (Table 1). <Activity Test of Working Solution> The activity test of the obtained working solution was performed using the same method as in Example 1. The relative hydrogen absorption rate of this working solution was 151% (Table 1). Example 5 <Hydrogenation of Distilled Recovered Solvent> Hydrogenation was carried out for 12.5 hours in the same manner as in Example 1, except that the reaction temperature was controlled to 220°C and the reaction pressure to 1.0 MPa. The hydrogenated solvent components were pseudocumene / diisobutylcarbinol / diisobutylketone = 62.4% by mass / 30.8% by mass / 6.4% by mass. Table 1 shows the GC analysis results of the hydrogenated solvent components over time as the hydrogenation reaction progressed. The acid value of this hydrogenated solvent was 82 mg-KOH / g (Table 1). <Preparation of Working Solution> The working solution was prepared in the same manner as in Example 1. The water content of this working solution was 3.6 g / L (Table 1). <Activity Test of Working Solution> The activity test of the obtained working solution was performed using the same method as in Example 1. The relative hydrogen absorption rate of this working solution was 152% (Table 1). Reference Example 2 <Preparation of Working Solution> First, a mixed solution consisting of 60% by volume of unused pseudocumene and 40% by volume of diisobutylcarbinol was prepared. The components of this mixed solvent were pseudocumene / diisobutylcarbinol / diisobutylketone = 60.8% by mass / 38.1% by mass / 1.0% by mass. The acid value of this mixed solvent was 0 mg-KOH / g (Table 1). 83 g of fresh amylanthraquinone was dissolved in this mixed solvent to a concentration of 0.6 mol / L, and then 5 g of pure water was added and stirred. The solution was then allowed to stand at room temperature (20°C to 25°C) for about 2 hours to obtain the working solution. The water content of the obtained working solution was 4.1 g / L (Table 1). <Activity Test of Working Solution> The activity test of the obtained working solution was performed using the same method as in Example 1. The relative hydrogen absorption rate of this working solution was 168% (Table 1). Reference Example 3 <Hydrogenation of Distilled Recovered Solvent> The same method as in Example 1 was used, except that the reaction temperature was set to 120°C. However, the reaction did not proceed. Reference Example 4 <Hydrogenation of Distilled Recovered Solvent> The same method as in Example 1 was used, except that the catalyst species was SN-750 (Ni-based catalyst) manufactured by JGC Catalysts & Chemicals Co., Ltd., and the reaction temperature was 120°C. However, the reaction did not proceed. Reference Example 5 <Hydrogenation of Distilled Recovery Solvent> The same method as in Example 1 was used, except that the catalyst species was SN-750 (Ni-based catalyst) manufactured by JGC Catalysts & Chemicals Co., Ltd., and the reaction start temperature was 100°C. However, the reaction did not proceed, so after 2 hours from the start of the reaction, the reaction temperature was raised to 160°C. Hydrogen absorption was observed as the reaction temperature increased, so the reaction was continued at 170°C for 2 hours, but at the same time an increase in low-boiling components occurred, and the remaining diisobutyl ketone was 14.3% by mass (Table 1). Example 6 <Alkaline Azeotropic Treatment of Hydrogenated Solvent> The hydrogenated solvent obtained by treating the distillation-recovered solvent under the same conditions as in Example 1 was subjected to alkaline azeotropic treatment by the method disclosed in Japanese Patent Application Publication No. 2008-87992. Specifically, 100 ml of 1.0% sodium hydroxide aqueous solution was charged into a distillation apparatus equipped with a rectification column packed with Melapak and a stirrer, and the hydrogenated solvent obtained by treating the distillation-recovered solvent under the same conditions as in Example 1 was continuously added, and the mixture of hydrogenated solvent and water was distilled off by heating. This mixture was separated in a separation layer, the distilled water was returned to the distillation vessel as reflux water, and only the distilled purified hydrogenated solvent was recovered. The hydrogenated solvent was supplied continuously and the supply was stopped when the total amount reached 1000 ml. The acid value of this purified hydrogenated solvent was 0 mg KOH / g (Table 1). <Preparation of Working Solution> Using the purified hydrogenated solvent obtained by the above method, a working solution was prepared in the same manner as in Example 1. The water content of this working solution was 3.6 g / L (Table 1). <Activity Test of Working Solution> The activity test of the obtained working solution was performed using the same method as in Example 1. The relative hydrogen absorption rate of this working solution was 159% (Table 1). Example 7 <Alkaline Washing of Hydrogenated Solvent> The hydrogenated solvent obtained by treating the distilled recovered solvent under the same conditions as in Example 1 was washed with an alkaline aqueous solution. A 0.5% sodium hydroxide aqueous solution was used as the alkaline aqueous solution. 250 ml of hydrogenated solvent and 100 ml of the above 0.5% sodium hydroxide aqueous solution were placed in a separatory funnel. The hydrogenated solvent and alkaline aqueous solution were preheated to 30°C. The separatory funnel was placed in a shaker (Shaker SA31, manufactured by Yamato Scientific Co., Ltd.) and shaken at a shaking intensity of 280 times / min for 5 minutes. After standing for 60 minutes, the hydrogenated solvent and sodium hydroxide aqueous solution were separated into upper and lower layers. The upper layer of hydrogenated solvent separated from the separatory funnel was recovered. <Water Washing Treatment> After the alkaline washing described above, the recovered hydrogenated solvent was washed with water as follows. The hydrogenated solvent and 100 ml of pure water were placed in a separatory funnel and shaken for 5 minutes using the method described above. After shaking, it was allowed to stand for 60 minutes to separate the hydrogenated solvent from the aqueous layer. The lower aqueous layer was removed, and 90 ml of fresh pure water was added, and the same shaking procedure was performed. After shaking, the aqueous layer was removed in the same manner. The mixture was washed again with water, for a total of three washes. The water temperature was adjusted to 30°C beforehand. The acid value of the purified hydrogenated solvent was 31 mg KOH / g (Table 1). <Preparation of Working Solution> Using the hydrogenated solvent obtained by the above method, a working solution was prepared in the same manner as in Example 1. The water content of the obtained working solution was 3.5 g / L (Table 1). <Activity Test of Working Solution> The activity test of the obtained working solution was performed using the same method as in Example 1. The relative hydrogen absorption rate of this working solution was 158% (Table 1). Example 8 <Water Washing Treatment of Hydrogenated Solvent> The hydrogenated solvent obtained by treating the distilled recovered solvent under the same conditions as in Example 1 was washed with pure water. For the water washing treatment, a counter-flow type 5-stage mixer settler extractor was used, with pure water in a volume ratio of 5 times that of the hydrogenated solvent. The acid value of the purified hydrogenated solvent was 64 mg KOH / g (Table 1). <Preparation of Working Solution> Using the hydrogenation solvent obtained by the above method, a working solution was prepared in the same manner as in Example 1. The water content of this working solution was 3.5 g / L (Table 1). <Activity Test of Working Solution> The activity test of the obtained working solution was performed using the same method as in Example 1. The relative hydrogen absorption rate of this working solution was 155% (Table 1). PSC; Pseudocumene DIBC; Diisobutylcarbinol DIBK; Diisobutylketone As described above, in each example, the hydrogen absorption efficiency was increased by reducing the ketone bodies (DIBK) in the organic solvent component (distilled recovered solvent) of the working solution that had been used for a long time to alcohol. Specifically, while the relative absorption efficiency was 100% in Reference Example 1, where 25.4% by mass of ketone bodies remained in the organic solvent component, in each example, by reducing the ketone bodies in the organic solvent component to 10% by mass or less, specifically to 6-7% by mass, the relative absorption efficiency was improved to 150% or more (see Table 1). This value is close to the 168% in Reference Example 2, which used an unused working solution as a sample. Furthermore, since the hydrogen absorption efficiency in the anthraquinone method is proportional to the hydrogen peroxide production efficiency, it was confirmed that the hydrogen peroxide production efficiency by the working solution is improved by reducing the residual rate of ketone bodies in the organic solvent to 10% by mass or less. Furthermore, the following can be considered as more specific reasons why the hydrogen peroxide production efficiency could be improved. In Reference Example 1, where a large amount of ketone bodies were contained in the organic solvent component, the organic solvent component (distillation recovered solvent) contained only 2.4 g / L of water. In contrast, in each example with a low ketone body content, it was confirmed that the water content reached 3 to 4 g / L, close to the value in Reference Example 2 (4.1 g / L) which used an unused working solution. Thus, an appropriate amount of water can be contained in the working solution with a low ketone body content, which can suppress the generation of free water that can adversely affect hydrogen peroxide production. By suppressing the generation of free water in this way, the hydrogen absorption efficiency was increased, and this can be said to be the main reason why the hydrogen peroxide production efficiency could be improved. In addition, in Examples 6 to 8, where the organic solvent component was contacted with an alkaline aqueous solution or water, the acid value decreased significantly compared to Reference Example 1 and the other examples (see Table 1). From these results, it was confirmed that acidic impurities other than ketone bodies can also be removed by the process of contacting the organic solvent component with an alkaline aqueous solution or water. Furthermore, according to the present invention, it is possible to efficiently regenerate ketone bodies into alcohol. This is because, in the present invention, there is no need for a step to selectively separate only ketone bodies from the working solution. For example, the organic solvent component, including a nonpolar solvent, can be separated from the working solution, and the organic solvent component can be reacted directly with the catalyst. The organic solvent components commonly used in the anthraquinone process can be easily separated from anthraquinones, and the separation of such organic solvent components is much easier than the selective separation of only ketone bodies.

Claims

1. A recovery method for the operating solution continuously used in the anthraquinone hydrogen peroxide production method, characterized by a distillation-separation process of the organic solvent component containing alcohol and its ketone form from the operating solution, and a recovery process of the alcohol from its ketone form by co-catalyzed hydrogenation of the resulting organic solvent component.

2. A recovery method for the operating solution specified in claim 1 that results in a retention rate of ketone in the organic solvent by co-catalyzed hydrogenation of the organic solvent (=ketone / organic solvent component x 100) not exceeding 10% by mass.

3. A recovery method for the operating solution specified in claim 1 where the metal catalyst is a metal compound consisting of one or more selected metals from palladium, rhodium, ruthenium, platinum, copper, or chromium.

4. A recovery method for the operating solution specified in claim 1 where the metal catalyst is a metal compound containing copper and / or chromium. 5.

6. Regeneration methods of the operating solution specified in Claim 1 in which the amount of such metal catalyst added to the mass of such organic solvent is 0.05% by mass - 10% by mass.

7. Regeneration methods of the operating solution specified in Claim 1 in which the hydrogenation pressure is atmospheric pressure - 10 MPa.

8. Regeneration methods of the operating solution specified in Claim 1 in which the hydrogenation temperature is 140°C - 230°C.

9. Regeneration methods of the operating solution specified in Claim 1 in which the hydrogenation time is 0.5 hours - 100 hours.

10. Regeneration methods of the operating solution specified in Claim 1 which include a contact treatment process of the organic solvent components after hydrogenation with water and / or alkaline solution.

10. An anthraquinone-based hydrogen peroxide production method characterized by the use of an operating solution regenerated by one of the methods specified in Claim 1-9.

11. Hydrogen peroxide produced by the production method specified in Claim 10.