Method for regenerating catalysts and method for producing unsaturated ester compounds

Abstract

To provide a regeneration method that can sufficiently restore catalytic performance while suppressing the hydrolysis of the hydrolyzable support constituting the catalyst. [Solution] A catalyst for producing an unsaturated ester compound in the presence of a co-catalyst, in which an olefin, a carboxylic acid, and oxygen are passed through a catalyst supported on a hydrolyzable carrier, palladium and optionally a metalloid, and a method for cleaning a catalyst whose activity has decreased after being used in a reaction, characterized in that the co-catalyst dissolved in the cleaning solution is 500,000 ppm or less.

Description

Technical Field

[0001] The present invention relates to a method for regenerating a catalyst in which a palladium-containing metal is supported on a hydrolyzable carrier, which is used for producing an unsaturated ester compound from an olefin, a carboxylic acid and oxygen in the presence of a cocatalyst, and a method for producing an unsaturated ester compound using the catalyst regenerated by the regeneration method.

Background Art

[0002] As a catalyst for producing an unsaturated ester compound from an olefin, a carboxylic acid and oxygen, a catalyst in which a palladium-containing metal is supported on various carriers is known. The optimal combination of the type of carrier and the type of palladium-containing metal has been proposed depending on the type of olefin as a raw material, the reaction form, and the reaction conditions. For example, in a catalyst for producing vinyl acetate from ethylene, a catalyst in which palladium and gold are supported on a silica carrier is often used.

[0003] Generally, the reaction activity of a catalyst gradually decreases and deteriorates due to long-term use, repeated use, or use under severe reaction conditions. There are various factors for deterioration. For example, elution and desorption of catalyst components, coking due to deposition of coke, resin, etc., decrease in the active surface due to sintering and aggregation of supported metals, change in pore structure, adhesion of poisoning substances, and alteration of catalyst components due to change in metal valence. Even in a catalyst supporting a palladium-containing metal or the like, such deterioration causes a decrease in the productivity of the unsaturated ester compound, making it difficult to continuously use the catalyst from an economic perspective. In addition, palladium is a noble metal, and often a noble metal is also used as a metal used as a second metal component used in combination with palladium. Replacing the deteriorated catalyst with a new one is also economically disadvantageous. Therefore, it is desired to regenerate and reuse the catalyst.

[0004] Various regeneration methods have been proposed to address the degradation factors. Examples include heating and firing in an oxygen atmosphere to burn off coking and toxic substances, restoring the non-uniform valency of the metal to the same level as a new catalyst through an oxidation-reduction process, and cleaning with a solvent to remove coking.

[0005] In Patent Document 1, in the regeneration of a catalyst used to produce allyl acetate by passing isoprene, acetic acid, and oxygen through a palladium catalyst, the catalyst's activity is restored by removing the coking by washing with water or an organic solvent and then re-attaching a co-catalyst. In Patent Document 2, the catalyst's activity is restored by washing the catalyst with water and / or alcohol, then heating and calcining it in an oxygen atmosphere to burn off the coking, and then reducing the metal. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 4-131136 [Patent Document 2] Japanese Patent Application Publication No. 50-51094 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] However, according to the inventors' studies, when a catalyst using a hydrolyzable support such as silica is washed using the method described in Patent Document 1 or 2, alkali metal salts and / or alkaline earth metal salts added as co-catalysts may dissolve into the washing solution at high concentrations. This accelerates the dissolution of the hydrolyzable support and promotes the dissolution and desorption of the supported metal, resulting in insufficient recovery of catalytic activity. Furthermore, repeated regeneration treatment can lead to a decrease in the physical strength of the catalyst itself, making it unsuitable for reuse. In addition, there is the problem that it is not economically viable as it becomes difficult to recover the supported precious metal. Moreover, the method described in Patent Document 2 involves a heating step, which has the problem of promoting aggregation and sintering of the supported metal.

[0008] The object of the present invention is to provide a method for regenerating a catalyst, which has a palladium-containing metal supported on a hydrolyzable support, used to produce unsaturated ester compounds from olefins, carboxylic acids, and oxygen, that can sufficiently restore the catalytic performance while suppressing the hydrolysis of the hydrolyzable support constituting the catalyst, and a method for producing unsaturated ester compounds using the catalyst regenerated by this method. [Means for solving the problem]

[0009] As a result of diligent research to achieve the above objective, the inventors realized the importance of controlling the catalyst cleaning conditions so that the concentration of the co-catalyst in the cleaning solution is below a specific value. They found that by performing such a cleaning method, hydrolysis of the support can be reduced and the elution and desorption of the supported metal can be suppressed, thus completing the present invention.

[0010] In other words, the present invention is as follows. [1] A method for regenerating a catalyst having a palladium-containing metal supported on a hydrolyzable carrier, which was used to produce an unsaturated ester compound from an olefin, a carboxylic acid and oxygen in the presence of a co-catalyst, comprising a washing step of washing the catalyst with a washing solution such that the concentration of the co-catalyst in the washing solution that comes into contact with the catalyst is 500,000 ppm or less. [2] A method for regenerating the catalyst according to [1], wherein the cleaning solution is water, a weakly basic aqueous solution, or a mixture of water and an organic solvent. [3] The method for regenerating a catalyst according to [1] or [2], wherein the co-catalyst is an alkali metal salt and / or an alkaline earth metal salt. [4] A method for regenerating any of the catalysts described in [1] to [3], wherein the co-catalyst is potassium acetate. [5] A method for regenerating any catalyst according to [1] to [4], wherein the palladium-containing metal contains, in addition to palladium, at least one metal selected from the group consisting of platinum group elements and group 11 elements of the periodic table as a secondary metallic component. [6] A method for regenerating any catalyst from [1] to [5], wherein the palladium-containing metal contains palladium and gold. [7] A method for regenerating a catalyst according to any of [1] to [6], comprising a pretreatment step of reducing co-catalysts attached to or adsorbed onto the catalyst with an organic solvent before the washing step. [8] A method for regenerating any catalyst according to [1] to [7], wherein the olefin is a branched olefin and the carboxylic acid is a carboxylic acid having 1 to 8 carbon atoms. [9] A method for regenerating the catalyst of [8], wherein the branched olefin is isobutylene and / or methallyl acetate.

[10] A method for regenerating the catalyst of [8] or [9], wherein the carboxylic acid having 1 to 8 carbon atoms is acetic acid. A method for producing an unsaturated ester compound from an olefin, a carboxylic acid, and oxygen in the presence of a co-catalyst, using a catalyst regenerated by one of the catalyst regeneration methods described in [1] to

[10] . [Effects of the Invention]

[0011] According to the catalyst regeneration method of the present invention, the catalytic performance can be fully restored while suppressing the hydrolysis of the hydrolyzable support constituting the catalyst. [Modes for carrying out the invention]

[0012] The present invention relates to a method for regenerating a catalyst, in which a palladium-containing metal is supported on a hydrolyzable carrier, used to produce unsaturated ester compounds from olefins, carboxylic acids, and oxygen in the presence of a co-catalyst, and comprising a washing step of washing the catalyst with a washing solution so that the concentration of the co-catalyst in the washing solution that comes into contact with the catalyst is 500,000 ppm or less. Furthermore, if necessary, a pretreatment step may be performed before the washing step to reduce the amount of co-catalyst impregnated or adsorbed onto the catalyst using an organic solvent.

[0013] (catalyst) The catalyst regenerated by the method of the present invention is a palladium-containing metal supported on a hydrolyzable carrier. The palladium-containing metal contains palladium as an essential component. The palladium-containing metal may consist only of palladium, or it may contain, in addition to palladium, at least one metal selected from the group consisting of platinum group elements and group 11 elements of the periodic table as a secondary metallic component, and may also contain components other than the aforementioned secondary metallic component. The palladium may be metallic palladium or a palladium compound, but metallic palladium is preferred. The palladium compound is not particularly limited, but examples include palladium chloride, palladium acetate, palladium nitrate, palladium sulfate, sodium palladate chloride, potassium palladate chloride, and barium palladate chloride. In addition to palladium, the palladium-containing metal may also include at least one platinum group element such as ruthenium, rhodium, osmium, iridium, or platinum, or an element from Group 11 of the periodic table such as gold, silver, or copper, as a secondary metallic component. Among these, from the viewpoint of increasing production efficiency, copper and gold are preferred as secondary metallic components, with gold being more preferred. The form of the secondary metallic component contained in the catalyst is not particularly limited, and examples include elemental metals; compounds such as nitrates, carbonates, sulfates, organic acid salts, and halides. From the viewpoint of exhibiting high catalytic activity, the content of the secondary metal component among the metal components supported on the hydrolyzable carrier is preferably 0.001 to 10 parts by mass, and more preferably 0.05 to 5 parts by mass, per 1 part by mass of palladium. Furthermore, a co-catalyst, as described later, may be attached to the hydrolyzable support bearing these metals.

[0014] A hydrolyzable carrier on which a palladium-containing metal is supported is a carrier containing hydrolyzable components, such as a carrier where the entire carrier is hydrolyzable (e.g., silica, silica gel, diatomaceous earth, pumice, montmorillonite); or a carrier containing hydrolyzable components such as silica-alumina. These may be used individually or in combination of two or more. Furthermore, if necessary, the above hydrolyzable carrier may be combined with an inorganic carrier such as alumina, calcia, magnesia, zirconia, titania, zeolite, or activated carbon, or a non-hydrolyzable carrier such as polystyrene, polyethylene, polyamide, or cellulose, within a range that does not impair the effects of the invention. From the viewpoint of better demonstrating the effects of the present invention, it is preferable that the hydrolyzable carrier contains silica. The silica content in the hydrolyzable carrier is preferably 50% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and may be 100% by mass. The silica may be crystalline or amorphous, and may contain impurities.

[0015] There are no particular restrictions on the shape of the hydrolyzable support, and it can be appropriately selected depending on the reaction type. Specific shapes include spherical, powder, and pellet forms, with spherical being particularly preferred. When the hydrolyzable support is spherical, there are no restrictions on the particle size, but it is preferably 1 to 10 mm. If the particle size is 10 mm or less, the raw materials can penetrate sufficiently into the catalyst, allowing the reaction to proceed more effectively. If the particle size is 1 mm or more, the support can more easily exert its function.

[0016] There are no particular restrictions on the method for preparing a catalyst in which a palladium-containing metal is supported on a hydrolyzable support. For example, it can be obtained by sequentially carrying out the following steps (1) to (4). Furthermore, if a co-catalyst is to be attached to the catalyst, it can be obtained by carrying out step (5) following steps (1) to (4).

[0017] Process (1) A step of impregnating a carrier in an aqueous solution of a palladium salt and a compound containing a transition metal of Group 11 of the platinum group and / or the periodic table to obtain a catalyst precursor A Step (2) A step of contacting the catalyst precursor A obtained in step (1) with an aqueous solution of an alkali metal salt without drying to obtain a catalyst precursor B Step (3) A step of contacting the catalyst precursor B obtained in step (2) with a reducing agent such as hydrazine or formalin to obtain a catalyst precursor C Step (4) A step of washing and drying the catalyst precursor C obtained in step (3) with water Step (5) A step of contacting and drying the catalyst obtained in step (4) with an aqueous solution of a promoter to attach the promoter

[0018] (Method for producing an unsaturated ester compound) The unsaturated ester compound can be produced by reacting an olefin, a carboxylic acid, and oxygen in the presence of a catalyst in which a palladium-containing metal is supported on a promoter and a hydrolyzable carrier. The catalyst may be a new (unused) catalyst, a deteriorated catalyst before regeneration, a catalyst regenerated by the regeneration method of the present invention, or a catalyst regenerated by a method different from the present invention. From the viewpoint of catalytic activity, it is preferable to use a new (unused) catalyst. On the other hand, from the viewpoint of achieving both economic efficiency and catalytic activity, it is preferable to use a catalyst regenerated by the regeneration method of the present invention. That is, a method for producing an unsaturated ester compound from an olefin, a carboxylic acid, and oxygen in the presence of a promoter using a catalyst regenerated by the catalyst regeneration method of the present invention is also one of the present inventions. The catalyst in this production method only needs to contain a catalyst regenerated by the catalyst regeneration method of the present invention, and a new (unused) catalyst, a deteriorated catalyst, or a catalyst regenerated by a method different from the present invention may be used in combination.

[0019] (Promoter) The co-catalyst used in the production of unsaturated ester compounds may be used in a state where it is supported on the catalyst beforehand, or it may be charged into the reaction apparatus together with the reaction raw material mixture. Examples of co-catalysts include hydroxides, nitrates, carboxylates, or carbonates of alkali metals such as sodium, potassium, and cesium; and hydroxides, nitrates, carboxylates, or carbonates of alkaline earth metals such as magnesium, calcium, and barium. These co-catalysts may be used individually or in combination of two or more. Among these, alkali metal salts and / or alkaline earth metal salts are preferred from the viewpoint of availability and reaction activity, with alkali metal salts being preferred. Furthermore, salts of carboxylic acids are preferred as co-catalysts, alkali metal salts of carboxylic acids are more preferred, and potassium acetate is even more preferred.

[0020] There are no particular restrictions on the amount of co-catalyst used when supporting it on the catalyst, but the amount of co-catalyst used is preferably 1 to 20 parts by mass, and more preferably 3 to 15 parts by mass, per 100 parts by mass of the total sum of the mass of the hydrolyzable carrier and the amount of co-catalyst used.

[0021] (Raw materials and products) The olefin used as a raw material for the unsaturated ester compound is not particularly limited as long as it is a compound having at least one carbon-carbon double bond, and may be an aliphatic olefin or an aromatic olefin, but it is preferable to be an aliphatic olefin. The olefin may be a linear olefin or a branched olefin, but it is preferable to be a branched olefin. The olefin may be a monosubstituted olefin or a polysubstituted olefin with two or more substitutions, but it is preferable to be a polysubstituted olefin with two or more substitutions, and more preferably a disubstituted olefin. The olefin may have a functional group, and examples of such functional groups include a hydroxyl group, a carboxyl group, an aldehyde group, a keto group, an amino group, and the like. Examples of the olefins include linear aliphatic olefins such as ethylene, propylene, 1-butene, 2-butene, 2-pentene, 3-pentene, butadiene, 1,5-hexadiene, allyl acetate, and ethyl acrylate; branched aliphatic olefins such as isobutylene, 2-methyl-1-butene, 2-methyl-2-butene, ethyl methacrylate, and methallyl acetate; linear aromatic olefins such as styrene, p-chlorostyrene, and allylbenzene; and branched aromatic olefins such as α-methylstyrene. From the viewpoint of availability, olefins having 2 to 8 carbon atoms are preferred, and from the viewpoint of productivity, aliphatic olefins having 2 to 4 carbon atoms are more preferred. Even more preferred is isobutylene. Furthermore, when isobutylene is used, methallyl acetate, which is a monoester compound of isobutylene, may also be included. By including methallyl acetate, diester compounds can be produced efficiently. That is, it is particularly preferable that the olefin is isobutylene and / or methallyl acetate.

[0022] There are no particular restrictions on the carboxylic acid used as a raw material for the unsaturated ester compound, but examples include formic acid, acetic acid, propionic acid, n-butyric acid, isobutyric acid, n-valeric acid, and isovaleric acid. From the viewpoint of availability and productivity, carboxylic acids having 1 to 8 carbon atoms are preferred, carboxylic acids having 1 to 4 carbon atoms are more preferred, and acetic acid is even more preferred.

[0023] (oxygen) For the production of unsaturated ester compounds, atomic and / or molecular oxygen can be used, with molecular oxygen being preferred. When molecular oxygen is used, it is preferable to use it as a mixed gas with an inert gas such as nitrogen, argon, helium, and carbon dioxide. In this case, it is more preferable to adjust the oxygen concentration so that the gas does not become explosive in the reaction system. Methods for supplying molecular oxygen or a gas mixture containing molecular oxygen to a reaction system include supplying it to the liquid phase, supplying it to the gas phase, or supplying it to both the liquid and gas phases. When supplying molecular oxygen or a gas mixture containing molecular oxygen to a reaction system, it is preferable to supply it so that the partial pressure of oxygen is within the range of 0.01 to 200 atmospheres (gauge pressure), more preferably 0.1 to 100 atmospheres (gauge pressure).

[0024] (solvent) In the method for producing unsaturated ester compounds, where a carboxylic acid, olefin, and oxygen are passed through in the presence of a catalyst and a co-catalyst, there are no restrictions on the reaction mode (gas phase or liquid phase), but a liquid phase reaction is preferred as it is less likely to generate coking. The reaction in the liquid phase can be carried out with or without a solvent. Examples of solvents that can be used in the liquid phase reaction include hydrocarbons (aliphatic hydrocarbons and aromatic hydrocarbons, etc.) such as hexane, heptane, methylcyclohexane, and benzene; heterocyclic compounds such as pyridine and quinoline; ethers such as diethyl ether, tetrahydrofuran, methyl-tert-butyl ether, and cyclopentyl methyl ether; ketones such as acetone, methyl ethyl ketone, and isobutyl methyl ketone; esters such as carboxylic acid esters, diethyl carbonate, and propylene carbonate; amides such as dimethylformamide and dimethylacetamide; nitriles such as acetonitrile and benzonitrile; and alcohols such as methanol, ethanol, isopropyl alcohol, and phenol. These may be used individually or in combination of two or more. When a solvent is used in the above reaction, there are no particular restrictions on the amount of solvent used as long as it does not adversely affect the reaction. However, the amount of solvent used is usually about 0.1 to 1000 times the total mass of the carboxylic acid and olefin, and from the viewpoint of productivity, 0.4 to 100 times is preferable.

[0025] There are no particular restrictions on the number of ester groups in the resulting unsaturated ester compound. Depending on the starting material (olefin), monoester compounds or diester compounds, and in some cases triester compounds, tetraester compounds, and mixtures thereof may be produced. Furthermore, there are no particular restrictions on the ester bond position. For example, using isobutylene and acetic acid as starting materials yields a mixture of methallyl acetate (a monoester compound) and 2-methylene-1,3-propanediol diacetate (a diester compound).

[0026] (Reaction conditions) In the method for producing unsaturated ester compounds, the amount of carboxylic acid used is preferably more than 1 mole and 50 moles or less per mole of olefin. The amount of carboxylic acid used (amount used per mole of olefin) is more preferably 2 moles or more, even more preferably 2.5 moles or more, and can also be 5 moles or more, 10 moles or more, or 20 moles or more. Furthermore, the amount of olefin used is more preferably 45 moles or less, even more preferably 40 moles or less, and even more preferably 35 moles or less. Using more than 1 mole of carboxylic acid results in better production efficiency. Using 50 moles or less of carboxylic acid shortens the process of recovering excess carboxylic acid, which is economically advantageous.

[0027] The reaction conditions in the method for producing unsaturated ester compounds, such as reaction temperature, reaction pressure, and reaction time, can be appropriately set according to the type and combination of carboxylic acid, olefin, and solvent used as needed, the composition of the catalyst, and are not particularly limited. For example, the reaction temperature is preferably in the range of 80 to 200°C. Setting the reaction temperature to 80°C or higher prevents the reaction rate from becoming too slow, allowing for the efficient production of unsaturated ester compounds. A reaction temperature of 90°C or higher is more preferable, and around 100°C is even more preferable. On the other hand, setting the reaction temperature to 200°C or lower reduces the likelihood of side reactions, including combustion, allowing for the efficient production of unsaturated ester compounds and suppressing corrosion of the reaction apparatus by carboxylic acid. A reaction temperature of 180°C or lower is more preferable, and 160°C or lower is even more preferable.

[0028] The reaction method for producing unsaturated ester compounds may be continuous or batch, and is not particularly limited. For example, if a batch reaction is used, the catalyst may be charged into the reactor all at once along with the raw materials. If a continuous reaction is used, the catalyst may be pre-filled into the reactor or continuously charged into the reactor along with the raw materials. The catalyst may be used in any form: fixed bed, fluidized bed, or suspension bed.

[0029] (Method for regenerating degraded catalysts) The catalyst regeneration method of the present invention includes a washing step of washing a catalyst (sometimes referred to as a degraded catalyst) that has deteriorated in performance after being used in the production of an unsaturated ester compound with a washing solution. Water, a weakly basic aqueous solution, or a mixture of water and an organic solvent is preferred as the washing solution. There are no restrictions on the weakly basic aqueous solution that can be used; examples include aqueous solutions of alkali metals such as sodium, potassium, and cesium nitrates, carboxylates, or carbonates; and alkaline earth metals such as magnesium, calcium, and barium nitrates, carboxylates, or carbonates. The pH of the weakly basic aqueous solution is preferably 13 or less, more preferably 10 or less, and even more preferably 8 or less. There are no restrictions on the organic solvent that can be used; examples include organic acids such as acetic acid and propionic acid, or alcohols such as ethanol, propanol, isopropyl alcohol, and butanol. One type of organic solvent may be used, or two or more types may be mixed and used. Furthermore, the washing may be performed multiple times using one or two or more types of washing solutions. From the viewpoint of suppressing hydrolysis of hydrolyzable carriers, the upper limit of the pH of the cleaning solution is preferably 13 or less, more preferably 10 or less, and even more preferably 8 or less. From a similar viewpoint, the lower limit of the pH of the cleaning solution is preferably 3 or more, more preferably 5 or more, even more preferably 6 or more, and particularly preferably 7 or more. From the viewpoint of availability and efficiency of removing caulking material, the cleaning solution is preferably water, a mixture of water and ethanol, or an aqueous solution of potassium acetate, more preferably water or a mixture of water and ethanol, and even more preferably water.

[0030] In the catalyst cleaning process, if the concentration of co-catalysts that flow from the catalyst into the cleaning solution that comes into contact with the catalyst becomes high, it promotes the hydrolysis of the hydrolyzable support and consequently causes the detachment of the supported metal. Therefore, it is necessary to clean the catalyst so that the concentration of co-catalysts in the cleaning solution that comes into contact with the catalyst is 500,000 ppm or less. The aforementioned concentration is preferably 100,000 ppm or less, more preferably 10,000 ppm or less, even more preferably 5,000 ppm or less, and particularly preferably 1,000 ppm or less. The concentration of co-catalysts in the cleaning solution that comes into contact with the catalyst is preferably 500,000 ppm or less for 80% or more of the catalyst cleaning time, more preferably 500 ppm or less for 95% or more of the catalyst cleaning time, and may always be 500,000 ppm or less throughout the catalyst cleaning process. In this specification, "ppm" means "mass ppm". The aforementioned concentration can be measured by the method described in the examples.

[0031] There are no particular restrictions on the specific cleaning method, as long as it ensures that the concentration of co-catalysts in the cleaning solution that comes into contact with the catalyst is 500,000 ppm or less. Examples include (1) a batch method in which the degraded catalyst is immersed in the cleaning solution in a container such as a beaker and stirred as needed, and (2) a flow method in which the cleaning solution is circulated through the degraded catalyst in a reaction tube. In the batch method (1), to control the concentration of co-catalysts in the cleaning solution to 500,000 ppm or less, it is necessary to take measures such as increasing the amount of cleaning solution used to immerse the degraded catalyst, or shortening the immersion time in the cleaning solution and increasing the number of times the cleaning solution is replaced. In the flow method (2), to control the concentration of co-catalysts in the cleaning solution to 500,000 ppm or less, it is necessary to take measures such as controlling the flow rate of the cleaning solution. Due to the ease with which the concentration of co-catalysts in the cleaning solution can be controlled to a low level, cleaning using the flow method (2) is more preferable. There are no particular restrictions on the temperature of the washing solution during washing, but 5 to 70°C is preferred, and 10 to 40°C is more preferred. Above 5°C, the washing effect tends to be superior, and below 70°C, the hydrolysis rate of the support slows down, the supported metal is less likely to detach, and the physical strength of the support is less likely to decrease even after repeated regeneration. In addition, sintering of the supported metal is less likely to progress, and the recovery of activity tends to be superior.

[0032] The end of the cleaning process is considered to be when the color of the cleaning solution in contact with the catalyst changes from brown to clear or very pale yellow. For example, when cleaning the catalyst using a flow method, the end of the cleaning process is determined by the color of the cleaning solution that flows out of the column packed with the catalyst. When cleaning the catalyst using a batch method, the end of the cleaning process is determined by the color of the supernatant liquid in which the catalyst is dispersed. More specifically, the end of the cleaning process is considered to be when the maximum optical density of the cleaning solution in contact with the catalyst, measured by UV-Vis, is 1 or less in the 250-600 nm range.

[0033] The catalyst regeneration method of the present invention may include a pretreatment step before the washing step in which co-catalysts attached to or adsorbed on the catalyst are reduced with an organic solvent. This pretreatment step can be performed by washing the catalyst with an organic solvent, and the washing method can be the method described above for the catalyst washing step. The organic solvent used here is preferably one that does not cause hydrolysis of the support, and examples include organic acids such as acetic acid and propionic acid; esters such as ethyl acetate, butyl acetate and isopropyl acetate; and alcohols such as ethanol, propanol, isopropyl alcohol and butanol. Among these, alcohols are preferred from the viewpoint of washing and removal efficiency of co-catalysts, and ethanol is more preferred. Performing this pretreatment step is preferable because it allows for a lower concentration of co-catalysts in the washing step, and further suppresses the hydrolysis of the hydrolyzable support.

[0034] The catalyst regeneration method of the present invention may include a step of attaching a co-catalyst to the catalyst after the washing step, if necessary. If the co-catalyst is not added to the reaction raw material mixture during production, it is necessary to attach the co-catalyst to the previously regenerated catalyst. This co-catalyst re-supporting step can be performed by contacting the regenerated catalyst with an aqueous solution of the co-catalyst and drying it, thereby re-supporting the co-catalyst.

[0035] The catalyst regeneration method of the present invention may include a drying step after a washing step or a co-catalyst re-supporting step, if necessary. Examples of drying methods include hot air drying, vacuum drying, and natural drying. The drying step is preferably performed at 20-150°C under reduced pressure or atmospheric pressure in a nitrogen atmosphere or vacuum drying, more preferably at 40-100°C under reduced pressure or atmospheric pressure in a nitrogen atmosphere or vacuum drying, and even more preferably at 40-60°C vacuum drying. Drying in an oxygen-free environment makes it less likely for the supported metal to oxidize, and the initial activity tends not to decrease. In addition, drying time is shorter at temperatures above 20°C, and sintering of the supported metal is less likely to be promoted at temperatures below 100°C, and hydrolysis does not progress easily during drying, so the catalyst life tends to be longer.

[0036] The catalyst regeneration method of the present invention preferably does not include a heat treatment step at 150°C or higher, more preferably does not include a heat treatment step at 120°C or higher, even more preferably does not include a heat treatment step at 100°C or higher, and in some cases particularly preferably does not include a heat treatment step at 60°C or higher. By excluding a heat treatment step at temperatures above the above, sintering of the supported metal is less likely to be promoted, and hydrolysis is less likely to progress during drying, thus tending to extend the catalyst life. [Examples]

[0037] The present invention will be specifically described by examples and comparative examples, but the present invention is not limited thereto.

[0038] (Analysis conditions) The amounts of palladium and gold supported in the prepared catalyst, as well as the concentrations of co-catalysts, silicon, gold, and palladium in the washing solution that came into contact with the catalyst, were analyzed using ICP (Thermo Fisher Scientific). The yield and selectivity of the unsaturated ester compounds were determined using NMR (JEOL, 400 MHz).

[0039] (Preparation of catalyst) A silica support (5 mmφ) of 250 mL (144 g) was immersed in an aqueous solution containing 4.00 g (13.6 mmol) of sodium tetrachloropalladate and 3.90 g (9.5 mmol) of tetrachloroaurate tetrahydrate, and allowed to absorb all the water. Subsequently, 200 mL of an aqueous solution containing 16 g (131 mmol) of sodium metasilicate was added, and the mixture was allowed to stand for 20 hours. After that, 9.50 g (190 mmol) of hydrazine monohydrate was added to reduce the palladium salt and gold salt to metal. After washing the reduced catalyst with water, it was dried at 110°C for 4 hours to prepare the catalyst (loading amount: Pd 0.66 mass%, Au 0.78 mass%).

[0040] (Preparation of degradation catalyst) A liquid-phase flow reactor equipped with a gas inlet and a sampling port was packed with 28 g of the catalyst. A reaction solution, a mixture of acetic acid / methallyl acetate / ethyl acetate / potassium acetate in a ratio of 3.39 / 13.53 / 83.02 / 0.051 mol%, was passed through the reactor at a rate of 0.5 mL / min. A mixed gas of oxygen / nitrogen (molar ratio) was supplied to the liquid phase from the bottom of the reaction tube at a rate of 100 mL / min, while the temperature of the reaction tube was raised to 100°C. The reaction was then carried out for 50 hours while maintaining the pressure of the reaction system at 0.8 MPaG. The unsaturated ester compounds produced were quantified from the NMR of the reaction solution, and the conversion rate was calculated.

[0041] (Evaluation of catalyst performance) A liquid-phase flow reactor equipped with a gas inlet and a sampling port was packed with 28 g of regenerated catalyst. A reaction mixture of acetic acid / methallyl acetate / ethyl acetate / potassium acetate in a ratio of 3.39 / 13.53 / 83.02 / 0.051 mol% was passed through the reactor at a rate of 0.5 mL / min. A mixed gas of oxygen / nitrogen = 8 / 92 (molar ratio) was supplied to the liquid phase from the bottom of the reaction tube at a rate of 100 mL / min, while the temperature of the reaction tube was raised to 100°C. The reaction was then carried out for 5 hours while maintaining the pressure of the reaction system at 0.8 MPaG to obtain the reaction solution. The unsaturated ester compounds produced were quantified from the NMR of the reaction solution, and the conversion rate and selectivity were calculated. From these values, the space-time yield (STY) [g / L·hr] of 2-methylene-1,3-propanediol diacetate was determined. In addition, the catalyst and the cleaning solution were visually observed during the cleaning process to evaluate whether or not the catalyst had disintegrated (i.e., whether or not particles larger than 0.1 μm were present in the cleaning solution).

[0042] [Reference example 1] (Performance evaluation of a new catalyst) The performance of new catalysts prepared using the method described in "Preparation of Catalysts" was evaluated using the method described above. The results are shown in Table 1.

[0043] [Reference example 2] (Performance evaluation of degraded catalysts) The performance of the degradation catalyst prepared by the method described in "Preparation of Degradation Catalyst" was evaluated using the method described above. The results are shown in Table 1.

[0044] [Example 1] (Catalyst regeneration) 28 g of degraded catalyst in the reaction tube was washed with water at a flow rate of 5 mL / min for 30 hours. The maximum co-catalyst concentration in the washing solution (calculated from the potassium concentration) was 82.7 ppm, and the maximum silicon concentration derived from the hydrolysis of the support was 10.1 ppm. After washing, it was vacuum-dried at 40°C for 12 hours.

[0045] [Analysis and performance evaluation of regenerated catalysts] The performance of the catalyst regenerated as described in Example 1 was evaluated using the method described above. The results are shown in Table 1.

[0046] [Example 2] (Catalyst regeneration) 28 g of degraded catalyst in the reaction tube was washed with ethanol at a flow rate of 5 mL / min for 30 hours. Then, water / ethanol = 20 / 80, water / ethanol = 40 / 60, water / ethanol = 60 / 40, and water / ethanol = 80 / 20 were sequentially passed through at a flow rate of 5 mL / min for 1 hour each, and then water was passed through at a flow rate of 5 mL / min for 3 hours to wash the catalyst. The maximum co-catalyst concentration (calculated from potassium concentration) in the washing solution was 94.1 ppm, and the maximum silicon concentration derived from hydrolysis of the support was 6.5 ppm. After washing, the catalyst was vacuum-dried at 40°C for 12 hours.

[0047] [Analysis and performance evaluation of regenerated catalysts] The performance of the catalyst regenerated as described in Example 2 was evaluated using the method described above. The results are shown in Table 1.

[0048] [Example 3] (Catalyst regeneration) 28 g of degraded catalyst removed from the reaction tube was impregnated with 150 mL of water and allowed to stand for 1 hour to dissolve the coking material, and the washing solution was removed. This procedure was repeated 6 times. The maximum co-catalyst concentration in the washing solution (calculated from the potassium concentration) was 2,580 ppm, and the maximum silicon concentration derived from the hydrolysis of the support was 40.9 ppm. After washing, the catalyst was vacuum-dried at 40°C for 12 hours.

[0049] [Analysis and performance evaluation of regenerated catalysts] The performance of the catalyst regenerated according to Example 3 was evaluated using the method described above. The results are shown in Table 1.

[0050] [Example 4] (Catalyst regeneration) 28 g of degraded catalyst removed from the reaction tube was immersed in 30 mL of water and allowed to stand for 1 hour to dissolve the coking material, after which the washing solution was removed. This procedure was repeated 6 times. The maximum co-catalyst concentration in the washing solution (calculated from the potassium concentration) was 13,820 ppm, and the maximum silicon concentration derived from the hydrolysis of the support was 219 ppm. After washing, the catalyst was vacuum-dried at 40°C for 12 hours.

[0051] [Analysis and performance evaluation of regenerated catalysts] The performance of the catalyst regenerated as described in Example 4 was evaluated using the method described above. The results are shown in Table 1.

[0052] [Example 5] (Catalyst regeneration) 28 g of degraded catalyst removed from the reaction tube was impregnated with 30 mL of 5% potassium acetate aqueous solution and allowed to stand for 1 hour to dissolve the coking material. This procedure was repeated 6 times. The maximum co-catalyst concentration in the washing solution (calculated from the potassium concentration) was 9,210 ppm, and the maximum silicon concentration derived from hydrolysis of the support was 108 ppm. After washing, the catalyst was vacuum-dried at 40°C for 12 hours.

[0053] [Analysis and performance evaluation of regenerated catalysts] The performance of the catalyst regenerated according to Example 5 was evaluated using the method described above. The results are shown in Table 1.

[0054] [Comparative Example 1] (Catalyst regeneration) 28 g of the degraded catalyst, removed from the reaction tube, was impregnated with 30 mL of a 70% by mass (saturated) potassium acetate aqueous solution and allowed to stand for 1 hour to dissolve the coking material. This procedure was repeated 6 times. Black powder of the supported metal floated in the washing solution, indicating that the catalyst was degrading.

[0055] [Table 1]

[0056] In Examples 1-5, where the concentration of the co-catalyst in the cleaning solution that came into contact with the catalyst was 500,000 ppm or less, no catalyst breakdown was observed, and the catalytic activity was significantly restored. On the other hand, in Comparative Example 1, where the concentration of the co-catalyst in the cleaning solution that came into contact with the catalyst was greater than 500,000 ppm, the catalyst broke down, and the performance of the catalyst could not be evaluated.

Claims

1. A method for regenerating a catalyst, in which a palladium-containing metal is supported on a hydrolyzable carrier, used to produce an unsaturated ester compound from an olefin, a carboxylic acid, and oxygen in the presence of a co-catalyst, comprising a cleaning step of washing the catalyst with a washing solution such that the concentration of the co-catalyst in the washing solution that comes into contact with the catalyst is 500,000 ppm or less.

2. The method for regenerating a catalyst according to claim 1, wherein the cleaning solution is water, a weakly basic aqueous solution, or a mixture of water and an organic solvent.

3. The method for regenerating a catalyst according to claim 1, wherein the co-catalyst is an alkali metal salt and / or an alkaline earth metal salt.

4. The catalyst regeneration method according to claim 1, wherein the co-catalyst is potassium acetate.

5. The method for regenerating a catalyst according to claim 1, wherein the palladium-containing metal contains, in addition to palladium, at least one metal selected from the group consisting of platinum group elements and group 11 elements of the periodic table as a secondary metallic component.

6. The method for regenerating a catalyst according to claim 1, wherein the palladium-containing metal contains palladium and gold.

7. The method for regenerating a catalyst according to claim 1, further comprising a pretreatment step of reducing co-catalysts attached to or adsorbed onto the catalyst with an organic solvent before the washing step.

8. The method for regenerating a catalyst according to claim 1, wherein the olefin is a branched olefin and the carboxylic acid is a carboxylic acid having 1 to 8 carbon atoms.

9. The method for regenerating a catalyst according to claim 8, wherein the branched olefin is isobutylene and / or methallyl acetate.

10. The method for regenerating a catalyst according to claim 8, wherein the carboxylic acid having 1 to 8 carbon atoms is acetic acid.

11. A method for producing an unsaturated ester compound from an olefin, a carboxylic acid, and oxygen in the presence of a co-catalyst, using a catalyst regenerated by the catalyst regeneration method described in claims 1 to 10.

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