A cobalt-containing multimetallic bimodal pseudoboehmite and a method for preparing the same

Abstract

The application discloses a kind of cobalt-containing multimetal bimodal pseudo-boehmite and its preparation method, and the preparation steps include: when pseudo-boehmite is prepared using hydrothermal method, water-soluble cobalt compound and water-soluble silver compound are added to aluminum source;Then through forming, shade drying, drying and calcination treatment obtain multimetal improved pseudo-boehmite finished product, and non-metal modifier is added in the forming process;Multimetal improved pseudo-boehmite finished product is immersed in potassium citrate solution, and acid-base adjustment is carried out to increase the basicity of carrier;Multimetal improved pseudo-boehmite after acid-base adjustment is used as carrier and is immersed in aqueous solution of molybdenum compound;Finally, after shade drying, drying and calcination, cobalt-containing multimetal bimodal pseudo-boehmite catalyst is obtained.The preparation method designed by the application makes the distribution of cobalt and molybdenum in the catalyst more uniform, and the molybdate impregnation process is simple and controllable, which is conducive to improving the performance of the catalyst.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, specifically to a cobalt-containing polymetallic bimodal pseudoboehmite and its preparation method. Background Technology

[0002] The Claus process for sulfur recovery and low-temperature hydrolysis tail gas treatment technology are the main methods for treating acidic gases containing hydrogen sulfide in industries such as oil refining and natural gas purification. Low-temperature hydrolysis tail gas treatment technology is a key piece of equipment to ensure that sulfur dioxide emissions from the plant's tail gas meet standards, and the low-temperature hydrolysis catalyst is one of the core technologies.

[0003] The low-temperature hydrolysis catalyst converts sulfur-containing substances such as sulfur dioxide, elemental sulfur, and organic sulfur in Claus tail gas into hydrogen sulfide at a reactor inlet temperature of 210-240℃. Sulfur dioxide and elemental sulfur react with hydrogen in the presence of a catalyst to produce hydrogen sulfide, while organic sulfur hydrolyzes into hydrogen sulfide and carbon dioxide. The hydrogenation reaction of sulfur dioxide and elemental sulfur is relatively easy to carry out, with a conversion rate generally close to 100%. The conversion rate of organic sulfur hydrolysis is generally less than 85%, making it the key technology for achieving ultra-low sulfur dioxide emissions in the plant.

[0004] Low-temperature hydrolysis catalysts typically consist of cobalt and molybdenum oxides supported on an alumina substrate. The catalyst preparation process generally begins with substrate molding or the direct use of commercially available alumina substrate, followed by loading of the active components. Because the catalyst contains two active components with significantly different content, the loading process generally employs either stepwise or simultaneous impregnation with cobalt and molybdenum compounds. The inventors have found that traditional stepwise impregnation processes suffer from drawbacks such as long catalyst preparation times and high production costs. Simultaneous impregnation involves significant analytical workload during the reuse of the impregnation solution, has complex impregnation solution preparation processes, and suffers from the problem of alumina substrate dust detachment affecting subsequent impregnation steps. Summary of the Invention

[0005] The technical problem to be solved by this invention is that the cobalt-molybdenum hydrogenation catalyst prepared by the traditional impregnation method has poor cobalt-molybdenum dispersion, which affects the efficiency of organic sulfur hydrolysis. This invention provides a cobalt-containing polymetallic bimodal pseudoboehmite and its preparation method to solve the above problem.

[0006] This invention is achieved through the following technical solution:

[0007] A method for preparing a cobalt-containing polymetallic bimodal pseudoboehmite catalyst includes the following steps:

[0008] Step 1, Preparation of polymetallic modified pseudoboehmite:

[0009] When preparing pseudoboehmite using a hydrothermal method, water-soluble cobalt compounds and water-soluble silver compounds are added to the aluminum source; then, the product is obtained by molding, air drying, drying and calcination to obtain a multi-metal modified pseudoboehmite product, and a non-metallic modifier is added during the molding process;

[0010] Step 2, pH adjustment treatment:

[0011] The polymetallic modified boehmite product was impregnated in potassium citrate solution to adjust the acidity and alkalinity, thereby increasing the alkalinity of the carrier.

[0012] Step 3, impregnation with molybdenum:

[0013] A polymetallic modified boehmite, modified by acid-base regulation, was used as a support and impregnated in an aqueous solution of molybdenum compounds. Finally, the cobalt-containing polymetallic bimodal boehmite catalyst was obtained by air drying, drying, and calcination.

[0014] During the hydrothermal reaction, the reaction temperature is controlled at 100℃-200℃, while for other methods the reaction temperature is controlled at 55℃-100℃, and the final pH value of the reaction solution is 6.5-9.5.

[0015] In step 1, during the molding process, a binder, a pore-forming agent, molding aids, and a non-metallic modifier are added. The binder includes water, nitric acid, oxalic acid, acetic acid, etc.; the pore-forming agent includes polyvinyl alcohol, cellulose, etc.; and the molding aid includes guar gum powder, etc. The molding process uses extrusion molding, which involves mixing, kneading, and extrusion in sequence.

[0016] The addition of silver compounds acts as a co-catalyst, enhancing the selectivity of organic sulfur hydrolysis in the presence of high levels of hydrogen sulfide. The addition of activated carbon modulates the dispersion of several active metals in the catalyst's pore structure, resulting in a more uniform distribution of metal oxides. This prevents the oxide particles from agglomerating, thus avoiding the collapse of primary and secondary pores formed during heat treatment.

[0017] The air-drying process is carried out at room temperature for 1-3 days; the drying process is carried out at 80℃-160℃ for 1-48 hours; and the calcination process is carried out at 400℃-600℃ for 1-12 hours.

[0018] Further optionally, in step 1, the water-soluble cobalt compound includes one or more of cobalt nitrate and cobalt chloride; the water-soluble silver compound includes silver nitrate.

[0019] Further optionally, in step 1, the ratio of cobalt to (cobalt + aluminum + silver) is 0.01-0.04, the ratio of silver to (cobalt + aluminum + silver) is 0.02-0.02, and the remainder is aluminum, with the ratios expressed as oxides by mass.

[0020] Further optionally, in step 1, the non-metallic modulator is activated carbon; the ratio of the amount (mass) of the activated carbon to the polymetallic modified pseudoboehmite product is 0.01 to 0.05.

[0021] Optionally, in step 1, a silicon-containing compound is also added, wherein the silicon-containing compound includes one or more of sodium silicate, water glass, and tetraethyl orthosilicate.

[0022] In the process of preparing modified boehmite by hydrothermal reaction, silicon-containing compounds are added to increase the specific surface area of ​​cobalt-containing boehmite.

[0023] Further optionally, the ratio of silicon to (silicon + cobalt + aluminum + silver) is 0.01 to 0.05, and the ratio is expressed as an oxide mass.

[0024] Further optionally, in step 2, after acid-base modulation, the ratio of potassium to (potassium + silicon + cobalt + aluminum + silver) is 0.001-0.005.

[0025] Further optionally, in step 3, the molybdenum compound includes one or both of ammonium tetramolybdate and ammonium heptamolybdate.

[0026] Further optionally, the added molybdenum has a molybdenum:(molybdenum + carrier) ratio of 0.05-0.20, the ratio being based on the mass of oxide.

[0027] A cobalt-containing polymetallic bimodal pseudoboehmite catalyst was prepared using the method described above for preparing a cobalt-containing polymetallic bimodal pseudoboehmite catalyst.

[0028] The final catalyst product contains (based on oxides) 5%-20% molybdenum, 1%-5% cobalt, and 0.1%-1% silver.

[0029] The present invention has the following advantages and beneficial effects:

[0030] 1. In the preparation process of pseudoboehmite powder material, this invention adds compounds containing cobalt and silver (to improve the low-temperature activity of the catalyst) to make cobalt highly dispersed in the pseudoboehmite powder. Then, the cobalt-containing pseudoboehmite powder is shaped to prepare a bimodal catalyst support. The support is then modified by acid-base adjustment and impregnated with molybdate to prepare a low-temperature hydrogenation hydrolysis catalyst.

[0031] 2. Compared with traditional cobalt-molybdenum-alumina hydrogenation hydrolysis catalysts, the catalyst provided by this invention has a more uniform distribution of cobalt and molybdenum inside the catalyst due to the use of precious metals and special treatment methods (modification with non-metallic modifiers and acid-base modulation treatment). The molybdate impregnation process is simple, which is beneficial to improving catalyst performance. Attached Figure Description

[0032] The accompanying drawings, which are included to provide a further understanding of embodiments of the invention and form part of this application, do not constitute a limitation thereof. In the drawings:

[0033] Figure 1 The distance from the surface of catalyst 2-1 represents the different metal concentrations.

[0034] Figure 2 The distance between catalyst 2-2 and the surface represents different metal concentrations. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0036] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that these specific details are not necessary to practice the invention. In other embodiments, well-known structures, circuits, materials, or methods have not been specifically described in order to avoid obscuring the invention.

[0037] Throughout this specification, references to "an embodiment," "an example," or "an example" mean that a particular feature, structure, or characteristic described in connection with that embodiment or example is included in at least one embodiment of the invention. Therefore, the phrases "an embodiment," "an example," "an example," or "an example" appearing in various places throughout the specification do not necessarily refer to the same embodiment or example. Furthermore, specific features, structures, or characteristics can be combined in one or more embodiments or examples in any suitable combination and / or sub-combination. Moreover, those skilled in the art will understand that the illustrations provided herein are for illustrative purposes and are not necessarily drawn to scale. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0038] Example 1

[0039] This embodiment provides a cobalt-containing multimetallic bimodal pseudoboehmite catalyst, which is prepared by the following method:

[0040] Prepare a mixed solution of aluminum sulfate and cobalt nitrate, with an aluminum sulfate concentration of 0.167 mol / L and a cobalt nitrate concentration of 0.01 mol / L, denoted as solution A. Prepare a mixed solution of sodium aluminate and sodium silicate, with a sodium aluminate concentration of 0.78 mol / L and a sodium silicate concentration of 0.05 mol / L, denoted as solution B. Prepare a solution of silver nitrate with a concentration of 0.1 mol / L, denoted as solution C.

[0041] Solutions A, B, and C were simultaneously added dropwise to a stirred container. After the addition was complete, the solution was transferred to a hydrothermal reactor and aged at 120°C for 6 hours. Then, the solution was washed, filtered, and dried to obtain a cobalt-containing boehmite sample.

[0042] Add 10 kg of cellulose, 15 kg of guar gum powder, 5 kg of activated carbon powder, and 250 L of 10% dilute nitric acid to 500 kg of cobalt-containing boehmite sample. Mix well and knead three times with an extruder. Then extrude the mixture using a 3 mm perforated plate. After air drying for 1 day, dry at 120℃ for 2 hours and then calcine at 500℃ for 4 hours to obtain the intermediate sample of the catalyst support.

[0043] The intermediate sample of this carrier exhibits a bimodal structure, with its pore structure concentrated in the 8-15 nm and 35-45 nm ranges, and a specific surface area of ​​275 m². 2 / g. The support was impregnated with potassium citrate solution in an equal proportion, resulting in a potassium content of 0.5%. It was then dried at 140±10℃ for 12 h and calcined at 400℃ for 6 h to obtain the support. Compared to the unimpregnated support, analysis using vacuum infrared spectroscopy, transmission electron microscopy, and pyridine infrared spectroscopy revealed that the potassium citrate-treated support exhibited newly added hydroxyl infrared peaks on corresponding crystal planes, along with a significant increase in alkalinity of approximately 0.008 mmol / g. Improving the weak alkalinity of the support and increasing the dispersion of cobalt and molybdenum on it, as demonstrated by ammonia dissolution tests under the same conditions, can increase the dispersion of cobalt and molybdenum by 10%-20%, which is beneficial to the hydrolysis performance of the catalyst.

[0044] Using ammonium heptamolybdate as the molybdenum source, a solution D of 450 g / L was prepared. The concentration of the competing adsorbent hexamethylenediamine in the solution was 15%, and the concentration of ammonium heptamolybdate was 17%. The support was immersed in solution D for 2 h, then filtered, air-dried for 2 days, dried at 80 °C for 12 h, and then calcined at 400 °C for 6 h to obtain the catalyst, which was numbered catalyst 1-1.

[0045] In the above process, the acidity / alkalinity of potassium citrate was not changed, and the rest of the process remained unchanged. The catalyst obtained was numbered Catalyst 1-2.

[0046] In the above process, ammonium heptamolybdate is replaced with ammonium tetramolybdate, while the rest of the process remains unchanged. The resulting catalyst is designated as catalyst 1-3.

[0047] In the above process, without adding silver nitrate, and with the rest of the process unchanged, the obtained catalyst is numbered Catalyst 1-4.

[0048] In the above process, without adding cobalt nitrate, and with the rest of the process unchanged, the obtained catalysts are numbered Catalyst 1-5.

[0049] In the above process, without adding ammonium heptamolybdate, and with the rest of the process unchanged, the obtained catalysts are numbered Catalyst 1-6.

[0050] According to the evaluation criteria described later, the optimal combination for this process is cobalt + molybdenum + silver, with potassium citrate modification applied during the process, i.e., catalyst 1-1. Adding silver loading can improve the low-temperature activity of the catalyst.

[0051] Example 2

[0052] This embodiment provides a cobalt-containing multimetallic bimodal pseudoboehmite catalyst, which is prepared by the following method:

[0053] Prepare a mixed solution of aluminum sulfate and cobalt chloride, with an aluminum sulfate concentration of 0.167 mol / L and a cobalt chloride concentration of 0.015 mol / L, denoted as solution A. Prepare a sodium aluminate solution, with a sodium aluminate concentration of 0.78 mol / L, denoted as solution B. Prepare a solution of silver nitrate solution, with a silver nitrate concentration of 0.1 mol / L, denoted as solution C.

[0054] Solutions A, B, and C were simultaneously added dropwise to a stirred container. After the addition was complete, the solution was transferred to a hydrothermal reactor and aged at 160°C for 4 hours. Then, the solution was washed, filtered, and dried to obtain a cobalt-containing boehmite sample.

[0055] Add 20 kg of polyvinyl alcohol, 5 kg of guar gum powder, 5 kg of activated carbon powder, and 300 L of 8% dilute nitric acid to 500 kg of cobalt-containing boehmite sample. Mix well and knead twice with an extruder. Then extrude the mixture using a 5 mm clover-shaped perforated plate. After air-drying for 3 days, dry at 80℃ for 48 h and then calcine at 400℃ for 12 h to obtain the intermediate sample of the catalyst support.

[0056] Following the method in Example 1, the catalyst was treated with potassium citrate, and then a solution D of a certain concentration was prepared using ammonium heptamolybdate as the molybdenum source. The support was immersed in solution D for 8 hours, then filtered, air-dried for 1 day, dried at 110°C for 4 hours, and then calcined at 600°C for 1 hour to obtain catalyst 2-1. The support modified with citric acid and base and loaded with molybdenum also has a bimodal structure, with its pore structure concentrated in the 8-15 nm and 35-45 nm ranges, and a specific surface area of ​​263 m². 2 / g.

[0057] In the above process, the aging time during the hydrothermal reaction was changed to 12 hours, while the rest of the process was not complicated, and catalyst sample 2-2 was obtained.

[0058] Characterization results indicate that an aging time of approximately 4 hours is beneficial for increasing the uniformity of cobalt and molybdenum distribution within the catalyst, which may be a significant reason for the improved activity. Conversely, excessively long aging times may cause crystal agglomeration on the support, which is detrimental to activity.

[0059] The activity comparison of the catalyst samples obtained in Examples 1 and 2 with a commercial low-temperature hydrogenation catalyst (molybdenum oxide, cobalt oxide, and alumina in a ratio of 10:2:88) is shown in Table 1. The test conditions were: reaction temperature 240℃, space velocity 1500 h⁻¹. -1 The catalyst loading was 40 mL, the catalyst particle size was 1.5-2.5 mm, and the gas composition was H2S 0.6%, SO2 0.3%, COS 0.02%, CO2 25%, H2O 30%, H2 2.5%, with N2 as the balance gas. Catalyst 2-1 was preferred in the experiment.

[0060] Table 1 Comparison of sulfur dioxide conversion rate and COS hydrolysis rate of catalysts

[0061] catalyst <![CDATA[SO2 hydrogenation rate, %]]> COS hydrolysis rate, % Comparison Samples ≈100 82.0 Catalyst 1-1 ≈100 85.2 Catalyst 1-2 ≈100 84.2 Catalyst 1-3 ≈100 83.5 Catalyst 1-4 ≈100 84.0 Catalyst 1-5 ≈100 84.5 Catalyst 1-6 ≈100 83.9 Catalyst 2-1 ≈100 87.4 Catalyst 2-2 ≈100 86.0

[0062] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a cobalt-containing polymetallic bimodal pseudoboehmite catalyst, characterized in that, Includes the following steps: Step 1, Preparation of polymetallic modified pseudoboehmite: When preparing pseudoboehmite using a hydrothermal method, water-soluble cobalt compounds and water-soluble silver compounds are added to the aluminum source; then, after molding, air drying, drying and calcination, a multi-metal modified pseudoboehmite product is obtained, and a non-metallic modifier is added during the molding process; Step 2, pH adjustment treatment: The polymetallic modified boehmite product was immersed in potassium citrate solution to adjust its acidity and alkalinity. Step 3, impregnation with molybdenum: A multi-metallic modified boehmite, modified by acid-base regulation, was used as a support and impregnated in an aqueous solution of molybdenum compounds. Finally, the cobalt-containing multi-metallic bimodal boehmite catalyst was obtained by air drying, drying, and calcination. In step 1, the non-metallic modifier is activated carbon; the ratio of the amount of activated carbon to the polymetallic modified pseudoboehmite product is 0.01 to 0.05, and the ratio is expressed by mass.

2. The method for preparing a cobalt-containing multimetallic bimodal pseudoboehmite catalyst according to claim 1, characterized in that, In step 1, the water-soluble cobalt compound includes one or more of cobalt nitrate and cobalt chloride; the water-soluble silver compound includes silver nitrate.

3. The method for preparing a cobalt-containing multimetallic bimodal pseudoboehmite catalyst according to claim 2, characterized in that, In step 1, the ratio of cobalt to (cobalt + aluminum + silver) is 0.01 to 0.04, and the ratio of silver to (cobalt + aluminum + silver) is 0.02, with the ratios expressed as oxide mass.

4. The method for preparing a cobalt-containing multimetallic bimodal pseudoboehmite catalyst according to claim 1, characterized in that, In step 1, a silicon-containing compound is also added, which includes one or more of sodium silicate, water glass, and tetraethyl orthosilicate.

5. The method for preparing a cobalt-containing multimetallic bimodal pseudoboehmite catalyst according to claim 4, characterized in that, The ratio of silicon to cobalt, aluminum and silver is 0.01 to 0.05, and the ratio is based on the mass of oxides.

6. A method for preparing a cobalt-containing multimetallic bimodal pseudoboehmite catalyst according to claim 4, characterized in that, In step 2, after acid-base adjustment, the ratio of potassium to (potassium + silicon + cobalt + aluminum + silver) is 0.001 to 0.005, and the ratio is expressed as the mass of oxides.

7. The method for preparing a cobalt-containing multimetallic bimodal pseudoboehmite catalyst according to claim 1, characterized in that, In step 3, the molybdenum compound includes one or both of ammonium tetramolybdate and ammonium heptamolybdate.

8. The method for preparing a cobalt-containing multimetallic bimodal pseudoboehmite catalyst according to claim 7, characterized in that, The mass of molybdenum added is such that the ratio of molybdenum to (molybdenum + support) is 0.05 to 0.20, and the ratio is based on the mass of oxide.

9. A cobalt-containing polymetallic bimodal pseudoboehmite catalyst, characterized in that, The cobalt-containing multimetallic bimodal pseudoboehmite catalyst was prepared using the preparation method described in any one of claims 1 to 8.

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