Regeneration method of palladium catalyst for fixed-bed hydrogen peroxide production

Abstract

This invention belongs to the field of catalyst regeneration technology, specifically relating to a method for regenerating palladium catalysts used in fixed-bed hydrogen peroxide production. The regeneration method includes the following steps: (1) immersing the palladium catalyst to be regenerated in solvent A for initial washing to obtain a palladium catalyst after initial washing; (2) adjusting the pH of the water to 6-7, then adding hydrogen peroxide to prepare a hydrogen peroxide solution with a concentration of 0.05-0.5 wt.%, immersing the initially washed palladium catalyst in the above hydrogen peroxide solution to obtain a palladium catalyst cleaned with hydrogen peroxide; (3) immersing the hydrogen peroxide-cleaned palladium catalyst in solvent B for a second washing, followed by water washing and drying to obtain a regenerated palladium catalyst. The regeneration method of this invention is simple to operate, has low regeneration costs, and can deeply clean impurities covering the surface and micropores of the palladium catalyst. The regenerated palladium catalyst has high activity and a long service life.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of catalyst regeneration, and particularly relates to a regeneration method of a palladium catalyst for fixed-bed production of hydrogen peroxide. BACKGROUND

[0002] Hydrogen peroxide is an important chemical product and is widely used in papermaking, textile, chemical synthesis, military industry, electronics, food processing, medicine, environmental protection, metallurgy and other fields. The production methods of hydrogen peroxide mainly include electrolysis method, anthraquinone method, isopropyl alcohol method and direct synthesis of hydrogen and oxygen, among which the anthraquinone method is the most commonly used production method.

[0003] The anthraquinone hydrogenation reaction belongs to a gas-liquid-solid three-phase catalytic reaction, and is divided into two categories of fixed-bed reactor and fluidized-bed reactor according to the static or dynamic state of the catalyst. The fixed-bed anthraquinone method mainly includes four processes of hydrogenation, oxidation, extraction and post-treatment, among which the catalytic hydrogenation is the key step of the production of hydrogen peroxide by the anthraquinone method. The palladium catalyst used in this step is easily coated with substances such as anthraquinone and aluminum oxide powder, which reduces the activity of the palladium catalyst. Therefore, it is necessary to clean the impurities coated on the surface of the palladium catalyst to restore its hydrogenation performance.

[0004] The Chinese invention patent application with the publication number CN113289694A discloses a method for regenerating a palladium catalyst in the production of hydrogen peroxide by the anthraquinone method. The method regenerates the palladium catalyst through steps of water vapor purging, solvent soaking, alkaline solution soaking, pure water washing, nitrogen drying and the like. However, it only cleans the impurities on the surface of the palladium catalyst and cannot deeply clean the impurities in the micropores of the palladium catalyst.

[0005] The Chinese invention patent application with the publication number CN110075866A discloses a regeneration method of a palladium catalyst. The method regenerates the palladium catalyst through steps of impurity removal, acid solution soaking, alkaline solution soaking, palladium supplementing and calcination. The regeneration method is relatively complex, and it also does not involve the cleaning of the impurities in the micropores of the palladium catalyst.

[0006] Therefore, it is necessary to study an effective regeneration method for the impurities coated on the surface and in the micropores of the palladium catalyst. SUMMARY

[0007] In view of the deficiencies of the prior art, the purpose of the present application is to provide a regeneration method of a palladium catalyst for fixed-bed production of hydrogen peroxide, which is simple to operate, can deeply clean the impurities coated on the surface and in the micropores of the palladium catalyst, and has high activity and long service life after regeneration.

[0008] The regeneration method of the palladium catalyst for fixed-bed production of hydrogen peroxide, according to the present application, comprises the following steps:

[0009] (1) the palladium catalyst to be regenerated is soaked in solvent A for primary washing to obtain the palladium catalyst after primary washing;

[0010] (2) the pH value of water is adjusted to 6-7, hydrogen peroxide solution with a concentration of 0.05-0.5wt.% is prepared by adding hydrogen peroxide, and the palladium catalyst after primary washing is soaked in the hydrogen peroxide solution to obtain the palladium catalyst after hydrogen peroxide washing;

[0011] (3) the palladium catalyst after hydrogen peroxide washing is soaked in solvent B for secondary washing, and the catalyst is washed with water and dried to obtain the regenerated palladium catalyst.

[0012] In the present application, the palladium catalyst to be regenerated is the non-sulfur-poisoned palladium catalyst used in the anthraquinone fixed-bed hydrogen peroxide production process.

[0013] In the anthraquinone fixed-bed hydrogen peroxide production process, anthraquinone by-products and alumina powder will coat the surface and micropores of the palladium catalyst after long-term production and use, resulting in a decrease in the activity of the palladium catalyst, mainly manifested in a decrease in the hydrogenation capacity of the palladium catalyst, and the conventional control methods such as increasing the working temperature and pressure cannot meet the production requirements, at which time the hydrogenation capacity of the palladium catalyst needs to be recovered by regeneration. In addition, the raw materials used by hydrogen peroxide manufacturers may be contaminated with trace amounts of sulfur compounds during production and storage, resulting in sulfur poisoning of the palladium catalyst.

[0014] Since the principle of sulfur poisoning is that sulfur-containing compounds react with the active centers of the palladium catalyst to form stable sulfur-palladium bonds with the palladium active sites, which will cause the activity of the palladium catalyst to decrease rapidly; and the non-sulfur-poisoned palladium catalyst is due to the gradual accumulation of impurities on the surface and pores of the palladium catalyst, which coats the active sites, thereby causing the activity of the palladium catalyst to decrease slowly. Therefore, if the activity of the palladium catalyst decreases sharply within a few hours, it is considered that the palladium catalyst is sulfur-poisoned, which can be qualitatively determined by detecting the sulfur content of each material; if the activity of the palladium catalyst decreases linearly or slowly within a few months, it is considered that the palladium catalyst is ordinary deactivated, which can be regenerated by the method of the present application.

[0015] In step (1), the solvent A used for primary washing is one of methanol and ethanol; the volume-to-mass ratio of the solvent A used for primary washing to the palladium catalyst to be regenerated is (3-10) ml:1 g; and the time for primary washing is 1-10 h.

[0016] Methanol and ethanol are used as solvents in the present application to perform primary washing on the sulfur-poisoned palladium catalyst, which can remove part of the organic matter coated on the surface of the palladium catalyst, exposing part of the palladium active sites, facilitating the subsequent hydrogen peroxide washing, so that the hydrogen peroxide solution can fully contact the palladium and produce gas for cleaning the impurities in the micropores.

[0017] Compared with the conventional water vapor washing, the washing mode of the present application has lower requirement for equipment and is more energy-saving; compared with the washing using aromatic hydrocarbon organic solvent, the washing solvent used in the present application can quickly clean the organic matters on the surface of the palladium catalyst, and both methanol and ethanol are miscible with water, so that the hydrogen peroxide solution can directly contact with the surface of the palladium catalyst during the subsequent treatment, which is beneficial to the oxidation reaction, while the aromatic hydrocarbon organic solvent is not miscible with water, and will remain on the surface of the palladium catalyst after washing, which affects the contact reaction of the palladium catalyst with the hydrogen peroxide.

[0018] In step (2), when the pH value of the water is greater than 7, sulfuric acid, nitric acid or phosphoric acid is used to adjust the pH value of the water to 6-7.

[0019] In step (2), the volume-to-mass ratio of the hydrogen peroxide solution to the palladium catalyst to be regenerated in step (1) is (4-10) ml:1 g.

[0020] In step (2), the soaking time is 2-8 h.

[0021] In the present application, the hydrogen peroxide solution is used to clean the palladium catalyst to be regenerated, and the hydrogen peroxide is easily decomposed into water and oxygen under the action of palladium, and the oxygen forms bubbles on the surface of the palladium catalyst and in the pores of the palladium catalyst, and the bubbles can further remove the impurities covering the outer surface and the pore surface of the palladium catalyst by breaking, so that the palladium catalyst is thoroughly cleaned. The concentration of the hydrogen peroxide solution should not be too high, because the high-concentration hydrogen peroxide is decomposed violently, which affects the strength of the catalyst, and a large amount of bubbles generated will lead to palladium removal, which affects the activity of the regenerated palladium catalyst.

[0022] In step (3), the solvent B used for the secondary washing is hot water at 90-100℃; the volume-to-mass ratio of the solvent B used for the secondary washing to the palladium catalyst to be regenerated in step (1) is (3-10) ml:1 g; and the secondary washing time is 1-5 h.

[0023] In step (3), pure water is used for the water washing, and the water washing is performed for 1-7 times, and the single soaking time is 10-30 min, and the volume-to-mass ratio of the pure water used for the single soaking to the palladium catalyst to be regenerated in step (1) is (1-5) ml:1 g.

[0024] In step (3), the drying can be performed by natural air-drying, or by nitrogen blowing, or by heating drying, and the drying is performed until no water remains.

[0025] In the present application, the palladium catalyst is subjected to secondary washing after the cleaning by the hydrogen peroxide solution, so that the impurities cleaned out of the micropores attached to the surface of the palladium catalyst can be removed, and then the palladium catalyst is further cleaned by water washing.

[0026] Compared with the prior art, the present application has the following beneficial effects:

[0027] (1) The present application is directed to the non-sulfur-poisoned palladium catalyst used in the anthraquinone fixed bed hydrogen peroxide production process. The impurities coated on the surface of the palladium catalyst are cleaned using a solvent first, and the palladium on the surface is exposed. Then the palladium catalyst is cleaned in the hydrogen peroxide aqueous solution, and the bubbles generated by the decomposition of hydrogen peroxide are used to clean the impurities coated on the outer surface and the pores of the palladium catalyst, so that the palladium catalyst is regenerated.

[0028] (2) The regeneration method of the present application is simple, does not use water vapor cleaning, does not use organic solvents such as aromatic hydrocarbons and alkaline solution cleaning, the regeneration process is simple and easy to operate, the generated waste liquid is less and easy to recover and treat, the covered impurities on the outer surface and the inner surface of the pores of the palladium catalyst can be cleaned deeply, and the regenerated palladium catalyst has high activity and long service life. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 The appearance picture of the fresh palladium catalyst used in the examples;

[0030] Figure 2 The appearance picture of the palladium catalyst to be regenerated used in the examples;

[0031] Figure 3 The appearance picture of the regenerated palladium catalyst of Example 1;

[0032] Figure 4 The appearance picture of the regenerated palladium catalyst of Comparative Example 2;

[0033] Figure 5 The reaction state diagram of the palladium catalyst to be regenerated used in the examples in the hydrogen peroxide solution (prepared by adding hydrogen peroxide in the sulfuric acid solution with pH value of 6.0, concentration of 0.25wt.%);

[0034] Figure 6 The reaction state diagram of the regenerated palladium catalyst of Example 1 in the hydrogen peroxide solution (prepared by adding hydrogen peroxide in the sulfuric acid solution with pH value of 6.0, concentration of 0.25wt.%);

[0035] Figure 7 The reaction state diagram of the regenerated palladium catalyst of Comparative Example 2 in the hydrogen peroxide solution (prepared by adding hydrogen peroxide in the sulfuric acid solution with pH value of 6.0, concentration of 0.25wt.%). DETAILED DESCRIPTION

[0036] The present application will be further described below in conjunction with examples. The raw materials used in the examples, unless otherwise specified, are all conventional commercial raw materials; the process methods used in the examples, unless otherwise specified, are all conventional methods in the art.

[0037] The palladium catalyst to be regenerated used in the example is a non-sulfur-poisoned palladium catalyst generated in the anthraquinone hydrogen peroxide production process, and the hydrogenation efficiency of the fresh agent of the palladium catalyst is 8.01 g (H2O2) / L, and the appearance picture is shown in FIG. 1, and it can be seen that the surface is clean. After being used in industrial production for 1 year, the hydrogenation efficiency of the palladium catalyst gradually decreases to 4.5 g (H2O2) / L, and it is confirmed to be a non-sulfur-poisoned palladium catalyst through elemental analysis, and the appearance picture is shown in FIG. 2, and it can be seen that the surface is covered with a large amount of impurities. Figure 1 Figure 2

[0038] Example 1

[0039] The palladium catalyst to be regenerated is regenerated, and the regeneration method is as follows:

[0040] (1) 10 g of the palladium catalyst to be regenerated is soaked in 30 ml of ethanol for 2 h, and after the surface of the palladium catalyst is not obviously covered with organic impurities, the ethanol washing solution is separated to obtain the palladium catalyst after the first washing;

[0041] (2) First, sulfuric acid is added to pure water to adjust the pH value of the water to 6.0, and then hydrogen peroxide is added to prepare a hydrogen peroxide solution with a concentration of 0.25 wt.%, and then 10 g of the palladium catalyst after the first washing is added to 40 ml of the hydrogen peroxide solution, and soaked for 2 h to obtain the palladium catalyst after hydrogen peroxide cleaning;

[0042] (3) The palladium catalyst after hydrogen peroxide cleaning is soaked in 30 ml of hot water (temperature between 90-100°C) for 2 h, and after the organic impurities in the micropores of the palladium catalyst are cleaned, the hot water washing solution is separated, and then pure water is added for soaking and washing 3 times, 20 ml of pure water is used for each time of soaking, and the soaking time for each time is 20 min, and finally the water is poured out and dried at room temperature to obtain the regenerated palladium catalyst.

[0043] Example 2

[0044] The palladium catalyst to be regenerated is regenerated, and the regeneration method is as follows:

[0045] (1) 10 g of the palladium catalyst to be regenerated is soaked in 100 ml of methanol for 10 h, and after the surface of the palladium catalyst is not obviously covered with organic impurities, the methanol washing solution is separated to obtain the palladium catalyst after the first washing;

[0046] (2) First, nitric acid is added to water to adjust the pH value of the water to 6.5, and then hydrogen peroxide is added to prepare a hydrogen peroxide solution with a concentration of 0.5 wt.%, and then 10 g of the palladium catalyst after the first washing is added to 100 ml of the hydrogen peroxide solution, and soaked for 8 h to obtain the palladium catalyst after hydrogen peroxide cleaning;

[0047] ​​(3) The oxidized palladium catalyst is soaked in 100 ml of hot water (temperature between 90-100°C) at 100°C for 5 h, the organic impurities in the micropores of the palladium catalyst are cleaned, the hot water washing solution is separated, and then the palladium catalyst is soaked in pure water for washing 7 times, 10 ml of pure water is used for each time of soaking, and the soaking time is 10 min each time. Finally, the washing solution is discarded, and the regenerated palladium catalyst is obtained after air drying at room temperature.

[0048] Example 3

[0049] The palladium catalyst to be regenerated is regenerated by the following method:

[0050] (1) 10 g of the palladium catalyst to be regenerated is soaked in 50 ml of ethanol for 1 h, until there is no obvious organic impurity covering the surface of the palladium catalyst, the methanol washing solution is separated, and the palladium catalyst after the first washing is obtained;

[0051] (2) Hydrogen peroxide solution with a concentration of 0.05 wt.% is prepared by adding hydrogen peroxide to water with a pH value of 7.0, and the palladium catalyst after the first washing is added to 50 ml of the above hydrogen peroxide solution and soaked for 5 h, to obtain the palladium catalyst after hydrogen peroxide cleaning;

[0052] (3) The oxidized palladium catalyst is soaked in 50 ml of hot water (temperature between 90-100°C) at 100°C for 1 h, the organic impurities in the micropores of the palladium catalyst are cleaned, the hot water washing solution is separated, and then the palladium catalyst is soaked in pure water for washing 1 time, 50 ml of pure water is used for each time of soaking, and the soaking time is 30 min each time. Finally, it is filtered and air dried at room temperature to obtain the regenerated palladium catalyst.

[0053] Comparative Example 1

[0054] The difference between this comparative example and Example 1 is only that the concentration of the hydrogen peroxide solution prepared in step (2) is 1.0 wt.%.

[0055] Comparative Example 2

[0056] The palladium catalyst to be regenerated is regenerated by the following method:

[0057] (1) 10 g of the palladium catalyst to be regenerated is soaked in 50 ml of ethanol for 1 h, until there is no obvious organic impurity covering the surface of the palladium catalyst, the methanol washing solution is separated, and the palladium catalyst after the first washing is obtained;

[0058] (2) The palladium catalyst after steam washing is placed in 20 ml of aromatic hydrocarbon solvent and soaked at 50°C for 2 h to obtain the palladium catalyst after aromatic hydrocarbon solvent washing;

[0059] (3) The aromatic hydrocarbon solvent washed palladium catalyst was immersed in 20 ml of sodium hydroxide solution (pH 12) at 40°C for 2 h to obtain the alkali solution washed palladium catalyst;

[0060] (4) The alkali solution washed palladium catalyst was immersed in pure water for washing 4 times, 20 ml of pure water was used for each time, and the immersion time was 20 min each time to obtain the water washed palladium catalyst;

[0061] (5) The water washed palladium catalyst was dried at 100°C for 2 h to obtain the regenerated palladium catalyst.

[0062] The regenerated palladium catalysts of each example and comparative example, fresh palladium catalyst and sulfur poisoned palladium catalyst were subjected to performance evaluation, and the evaluation method was as follows:

[0063] (1) Palladium content: The palladium catalyst was ground and dried in an electric heating drying box at 110°C, about 0.1-0.2 g of sample was dissolved with a mixture of H2SO4 and H3PO4, after cooling to room temperature, EDTA solution was added, and after fully shaking, anhydrous Na2SO3 solution was added, and KI solution was added for color development. The above solution was measured at a specified wavelength with a reagent blank as a reference solution by a spectrophotometer to determine the absorbance and calculate the palladium content.

[0064] (2) Hydrogenation efficiency: 10 g of palladium catalyst was loaded, 200 ml of working solution was circulated (the working solution was composed of Ar: trioctylphosphine = 3.4:1, and the solute was diethylanthraquinone with a concentration of 50 g / L), the running temperature was 70°C, the pressure was 0.3 Mpa, the circulation amount was 1.8 L / h, and the activity value was obtained by taking 10 ml of working solution every 3 h, oxidizing and extracting, and titrating with potassium permanganate, and then taking the average value.

[0065] (3) Compressive strength: tested according to standard GB 3635-1983.

[0066] The evaluation results are shown in Table 1.

[0067] Table 1 Performance evaluation results of palladium catalyst

[0068]

[0069] As can be seen from Table 1, the hydrogenation efficiency of the regenerated palladium catalysts of Example 1, Example 2 and Example 3 is well recovered, the palladium content is not obviously reduced, the compressive strength is basically consistent with that of the fresh palladium catalyst, and the regeneration process is stable and controllable. Compared with Example 1, the hydrogen peroxide solution in Comparative Example 1 has a higher concentration, the reaction between the palladium catalyst and the hydrogen peroxide solution is more violent, more gas is generated at a faster rate, which has a slight influence on the strength of the palladium catalyst, and the rapid falling of impurities can cause the palladium on the surface of the palladium catalyst to fall off, resulting in a slight decrease in the palladium content and a lower hydrogenation efficiency; the conventional regeneration method in Comparative Example 2 has more steps, the recovery effect of the hydrogenation efficiency is general, and the water vapor treatment and the alkali treatment can reduce the strength of the palladium catalyst, and the palladium content detection shows that the regeneration process can also cause obvious palladium falling off.

[0070] In addition, in order to more intuitively compare the cleaning effects of the regeneration method of the application and the conventional regeneration method, the hydrogen peroxide reaction test is performed on the palladium catalyst to be regenerated and the palladium catalysts regenerated in Example 1 and Comparative Example 2, that is, the palladium catalyst is added into a hydrogen peroxide solution (prepared by adding hydrogen peroxide into a sulfuric acid solution with a pH value of 6.0, and the concentration is 0.25wt.%), and the reaction state thereof is observed. The appearance pictures of the palladium catalysts regenerated in Example 1 and Comparative Example 2 are shown in Figure 3 、 Figure 4 respectively; the reaction states of the palladium catalyst to be regenerated and the palladium catalysts regenerated in Example 1 and Comparative Example 2 in the hydrogen peroxide are shown in Figure 5 、 Figure 6 、 Figure 7 respectively.

[0071] As can be seen from Figure 3 and Figure 4 , the palladium catalysts regenerated by the regeneration method of the application (Example 1) and the conventional regeneration method (Comparative Example 2) both show a clean appearance. However, the recovery effect of the hydrogenation efficiency of the palladium catalyst regenerated by the conventional regeneration method (Comparative Example 2) is much lower than that of Example 1. The hydrogen peroxide reaction test result shows that when the palladium catalyst to be regenerated is reacted in the hydrogen peroxide solution, almost no gas is emitted, which is because the surface of the palladium catalyst is covered by organic matter, and the hydrogen peroxide cannot be decomposed (reaction Figure 5 ); when the palladium catalyst regenerated in Example 1 is reacted in the hydrogen peroxide solution, the decomposed gas is easy to escape, and less gas is attached to the surface of the palladium catalyst, indicating that the organic matter in the surface layer and the micropores of the palladium catalyst is cleaned relatively cleanly, and there is basically no residual organic matter (reaction Figure 6 ); when the palladium catalyst regenerated in Comparative Example 2 is reacted in the hydrogen peroxide solution, the gas generated by decomposition is obviously attached to the surface of the palladium catalyst and cannot be separated in time, and part of the palladium catalyst floats in the solution due to too much gas, indicating that the conventional regeneration method is difficult to clean the organic matter in the micropores of the palladium catalyst, and the residual organic matter hinders the escape of the gas.

Claims

1. A method for the regeneration of a palladium catalyst for the production of hydrogen peroxide in a fixed bed, characterized in that: The method comprises the following steps: (1) soaking the palladium catalyst to be regenerated in solvent A for primary washing to obtain a palladium catalyst after primary washing; (2) adjusting the pH value of water to 6-7, adding hydrogen peroxide to prepare a hydrogen peroxide solution with a concentration of 0.05-0.5wt.%, and then soaking the palladium catalyst after primary washing in the hydrogen peroxide solution to obtain a palladium catalyst after hydrogen peroxide washing; (3) soaking the palladium catalyst after hydrogen peroxide washing in solvent B for secondary washing, and then washing with water and drying to obtain a regenerated palladium catalyst; In step (1), the palladium catalyst to be regenerated is a non-sulfur-poisoned palladium catalyst used in an anthraquinone hydrogen peroxide production process; In step (1), the solvent A used for primary washing is one of methanol and ethanol; In step (2), the volume-to-mass ratio of the hydrogen peroxide solution to the palladium catalyst to be regenerated in step (1) is (4-10) ml:1g; In step (3), the solvent B used for secondary washing is hot water with a temperature of 90-100℃.

2. The method for regenerating a fixed bed of a palladium catalyst for producing hydrogen peroxide according to claim 1, characterized by: In step (1), the volume-to-mass ratio of the solvent A used for primary washing to the palladium catalyst to be regenerated is (3-10) ml:1g.

3. The method for regenerating a fixed bed of a palladium catalyst for producing hydrogen peroxide according to claim 1, characterized by: In step (1), the time for primary washing is 1-10h.

4. The method for regenerating a fixed bed of a palladium catalyst for producing hydrogen peroxide according to claim 1, characterized by: In step (2), when the pH value of water is greater than 7, sulfuric acid, nitric acid or phosphoric acid is used to adjust the pH value of water to 6-7.

5. The method for regenerating a fixed bed of a palladium catalyst for producing hydrogen peroxide according to claim 1, characterized by: In step (2), the soaking time is 2-8h.

6. The method for regenerating a fixed bed of a palladium catalyst for producing hydrogen peroxide according to claim 1, characterized by: In step (3), the volume-to-mass ratio of the solvent B used for secondary washing to the palladium catalyst to be regenerated in step (1) is (3-10) ml:1g.

7. The method of claim 1, wherein the method is characterized by: In step (3), the time for secondary washing is 1-5h.

8. The method for regenerating a fixed bed of a palladium catalyst for producing hydrogen peroxide according to claim 1, characterized by: In step (3), when washing with water, the palladium catalyst is soaked in pure water for 1-7 times, with a single soaking time of 10-30min, and the volume-to-mass ratio of the pure water used for single soaking to the palladium catalyst to be regenerated in step (1) is (1-5) ml:1g.

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