Preparation method of caprolactam hydrofining catalyst capable of being stored in deoxygenated water for long time

Abstract

The invention discloses a preparation method of a catalyst suitable for caprolactam hydrofining, the caprolactam hydrofining catalyst prepared by the method, and a caprolactam hydrofining method adopting the catalyst. According to the present invention, after the surface treatment of the catalyst, the hydration reaction between the water molecules and the carrier (alumina) can be effectively inhibited so as to substantially improve the stability of the carrier pore structure in the water phase, such that the long-time storage of the catalyst under the deoxygenated water sealing condition is achieved, and the reduction state and deoxygenated water sealing supply form becomes possible.

Description

Technical Field

[0001] This invention relates to a method for preparing a catalyst suitable for the hydrogenation purification of caprolactam, belonging to the fields of catalysis science and chemical engineering technology. Background Technology

[0002] Caprolactam is an important chemical raw material for the production of nylon-6 fiber and engineering plastics. Its production process involves many types of raw materials and is complex. More than 30 kinds of impurities are introduced by the ammonium oxime reaction and rearrangement reaction. Although the content of these impurities is low, they seriously affect the quality of the finished caprolactam, especially when it is used as a raw material for high-speed spinning, where the requirements for impurity content are more stringent.

[0003] The hydrorefining process mainly involves hydrogenating unsaturated substances in impurities with properties similar to caprolactam, allowing them to be removed in subsequent evaporation and distillation units. Currently, there are three main caprolactam hydrorefining processes in domestic industrial projects: slurry bed, magnetically stabilized bed, and fixed bed. The technology described in this invention refers to catalysts and their preparation methods suitable for fixed bed hydrogenation processes. Fixed bed hydrogenation processes are gradually gaining acceptance among caprolactam manufacturers due to their simple process, ease of operation, and stable performance. However, since the catalyst is used in a liquid environment, manufacturers generally prefer to purchase catalysts in a "reduced state + deoxygenated water storage" state. This eliminates the need for online activation before catalyst use, saving energy, reducing consumption, and saving time. However, the "reduced state + deoxygenated water sealing" supply method presents new requirements for catalyst preparation technology: Since the support for caprolactam hydrogenation refining catalysts is generally alumina, the main impurities in the catalyst, potassium oxide and sodium oxide, will cause the soaking solution to exhibit weak alkalinity. In a weakly alkaline environment, alumina will slowly undergo a hydration reaction, damaging the support structure and even causing white substances to precipitate and cover the catalyst surface, affecting the catalyst's structural stability and catalytic activity. This phenomenon significantly shortens the catalyst's storage period, generally requiring it to be no more than 3 months, causing inconvenience for users who need to prepare stock in advance.

[0004] Chinese patent application No. 202210674761.X discloses a catalyst for the hydrogenation refining of caprolactam, which consists of 27-33 wt% NiO, 2-5 wt% molybdenum oxide, 1-4 wt% additives, 2-5 wt% titanium oxide, and the balance being aluminum oxide. The hydrogenation reaction is carried out under the conditions of 0.4-0.6 MPa and 40-60℃, and the PM value of the caprolactam aqueous solution can reach more than 30,000s.

[0005] Chinese patent application No. 202310941050.9 (CN117065756A) discloses a caprolactam hydrogenation refining catalyst with a composition of 12~30wt% Ni and a rare earth oxide modified alumina as a support. It can withstand the corrosion of weakly acidic or weakly alkaline caprolactam aqueous solutions for a long time and its strength can remain stable when immersed in aqueous solutions with pH values ​​of 4 and 10. However, it does not mention the changes in the pore structure of the support or the changes in hydrogenation performance after immersion.

[0006] Chinese patent application No. 202011259627.0 discloses a catalyst for the hydrogenation refining of caprolactam. The main active component is loaded onto a support by impregnation, and then a precipitant is used to deposit the active component in the pores of the support. The catalyst product is obtained through washing, filtration, drying, primary calcination, molding, secondary calcination, and reduction. After a long-term evaluation experiment of 2000 hours, the PAN value at the hydrogenation outlet is stable below 1.8.

[0007] Chinese patent application No. 201710034646.5 discloses a hydrorefining catalyst with a main structure consisting of an active material outer surface layer and a metal alloy core. The catalyst is composed of 40-65 wt% Ni, 35-60 wt% aluminum, 0.1-2 wt% Nb, and 0-10 wt% modifying elements. It exhibits high activity in the hydrorefining of high-concentration caprolactam. In Example 6, under conditions of 100°C, 1.0 MPa, and a mass hourly space velocity (HHSV) of 3.0 h⁻¹, the PM value at the hydrogenation outlet can reach over 30,000 s⁻¹.

[0008] In summary, currently, industrially available fixed-bed caprolactam hydrogenation catalysts are generally supplied in a passivated state, requiring online activation before use. The hydrogen volume hourly space velocity (HHSV) required for activation is typically 500–1000 h⁻¹. -1 The total activation time is generally 5-7 days. Given that the caprolactam hydrogenation refining reaction system is an aqueous environment, this invention provides a catalyst preparation method that allows for a "reduced state + deoxygenated water sealing" supply format. Furthermore, the catalyst can be stored in an aqueous environment for extended periods, maintaining stable support properties and pore structure, with minimal changes in catalyst strength and hydrogenation performance. This eliminates the need for online activation in industrial caprolactam plants, achieving cost reduction and efficiency improvement. Summary of the Invention

[0009] The purpose of this invention is to address the shortcomings of existing caprolactam hydrogenation refining catalysts by providing a method for preparing a catalyst product that can be used in a fixed-bed hydrogenation reactor, can be stored for a long time in an aqueous environment, and achieves a "reduced state + deoxygenated water sealing" supply form. The catalyst preparation method according to this invention is based on the previous patent application "CN117065756A" with the addition of three processing steps (5) to (7), specifically: (1) Aluminum sol and rare earth metal salt are uniformly mixed to obtain slurry I, in which the solid content of aluminum oxide and rare earth metal salt is 20-40%; slurry I is spray-dried and granulated to obtain solid microsphere powder. A portion of solid microsphere powder was calcined to obtain rare earth oxide modified alumina, wherein the mass ratio of alumina to rare earth metal elements contained in the rare earth oxide in the rare earth oxide modified alumina was (15~50): 1. In step (1), the portion of solid microsphere powder taken accounts for 40%-70% of the total mass of the solid microsphere powder; (2) Add the rare earth oxide modified alumina and the structural additive to water and mix them evenly to obtain slurry II, wherein the mass ratio of the structural additive to the rare earth oxide modified alumina is (0.15~0.6):1, preferably (0.18~0.56):1; (3) Add nickel salt aqueous solution to slurry II and stir thoroughly to obtain slurry III; add precipitant to slurry III to deposit the reaction product of the precipitation reaction on the carrier, wash, dry, calcine and pulverize to obtain solid catalyst powder, wherein the Ni content is 15~35wt% of the mass of solid catalyst powder, preferably 20~30wt%; (4) Take the remaining solid microsphere powder from step (1) and mix it evenly with the solid catalyst powder, binder, and lubricant from step (3). Optionally, dilute nitric acid is added, and the mixture is shaped to obtain a shaped catalyst. The amount of binder added is 5-15 wt% of the mass of the solid catalyst powder, preferably 5-10 wt%, and the amount of lubricant added is 3-7 wt% of the mass of the solid catalyst powder, preferably 3-5 wt%. The obtained shaped catalyst was placed in a constant temperature and humidity chamber at a constant temperature of 25~50℃ and a humidity of 90~97% for 72~168h. After drying and calcination, crude oxidized caprolactam hydrogenation refining catalyst was obtained. (5) At 35~45℃, aluminum dihydrogen phosphate, phosphoric acid and sodium molybdate are dissolved in deionized water to prepare a surface treatment solution. The concentrations of each component are 15~25g / L, 6~15g / L and 0.5~1g / L, respectively. The final pH value of the solution is adjusted to 2.8~3.5 using phosphoric acid or sodium hydroxide to form a surface treatment solution. After preparation, the solution is allowed to stand for 2~4 hours, during which the temperature is maintained at 35~45℃. (6) Immerse the crude catalyst obtained in step (4) into the surface treatment solution obtained in step (5). The liquid surface should completely submerge the crude catalyst. During the immersion, the temperature should be maintained at 35~45℃ and the immersion time should be 8~12 minutes. (7) After the impregnation in step (6) is completed, the catalyst sample is taken out and dried and calcined to obtain the surface-treated caprolactam hydrogenation refining catalyst. (8) The catalyst obtained in step (7) is reduced by hydrogen at 450~600℃ for 2~10 hours and sealed in deoxygenated water to obtain a reduced caprolactam hydrogenation refining catalyst, which can be stored for a long time without much impact on the support structure and hydrogenation performance, thus truly achieving worry-free water-sealed reduced state supply.

[0010] Preferably, in step (5), the preferred concentrations of aluminum dihydrogen phosphate, phosphoric acid, and sodium molybdate are 16~20 g / L, 8~12 g / L, and 0.6~0.8 g / L, respectively.

[0011] Preferably, the conductivity of the deionized water in step (5) and the deoxygenated water in step (8) is required to be less than 5 μs / cm.

[0012] Preferably, the drying temperature in step (7) is 100~120℃ and the calcination temperature is 500~600℃.

[0013] According to another aspect of the present invention, the present invention provides a catalyst for the hydrogenation and refining of caprolactam, the catalyst being prepared by the above-described preparation method.

[0014] According to another aspect of the present invention, the present invention provides a method for hydrogenating caprolactam, the method comprising: hydrogenating caprolactam in a fixed-bed hydrogenation reactor containing the caprolactam hydrogenation catalyst according to the present invention.

[0015] Beneficial effects The catalyst according to the present invention, after surface treatment, can effectively suppress the hydration reaction between water molecules and the support (alumina), thereby greatly improving the stability of the support pore structure in the aqueous phase, thus enabling the catalyst to be stored for a long time under deoxygenated water sealing conditions, making the "reduced state + deoxygenated water sealing" supply form possible. Attached Figure Description

[0016] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0017] Figure 1 The image shows the pore size distribution of the catalyst prepared in Example 1. Figure 2 This is a pore size distribution diagram of the catalyst prepared in Example 2; Figure 3 The pore size distribution diagram is shown for the catalyst prepared in Comparative Example 1. Figure 4 The pore size distribution diagram is shown for the catalyst prepared in Comparative Example 2. Figure 5 The images show the catalysts prepared in Examples 1 and 2, and Comparative Examples 1 and 2, after a 600-day immersion experiment. Detailed Implementation

[0018] The present invention will now be described in detail. Before proceeding with the description, it should be understood that the terminology used in this specification and the appended claims should not be construed as limited to its general or dictionary meaning, but rather should be interpreted according to the meaning and concept corresponding to the technical aspects of the invention, based on the principle that the inventors are allowed to appropriately define the terms for the best interpretation. Therefore, the description presented herein is merely a preferred example for illustrative purposes and is not intended to limit the scope of the invention. It should be understood that other equivalents or modifications can be obtained from it without departing from the spirit and scope of the invention.

[0019] In this document, the terms “comprising,” “including,” “having,” “containing,” or any other similar terms are open-ended conjunctions intended to cover non-exclusive inclusions. For example, a composition or article containing a plurality of elements is not limited to those listed herein, but may also include other elements not explicitly listed but typically inherent to the composition or article. Furthermore, unless explicitly stated to the contrary, the term “or” is inclusive, not exclusive. For example, the condition “A or B” is satisfied in any of the following cases: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); A and B are both true (or exist). Moreover, in this document, the terms “comprising,” “including,” “having,” and “containing” should be interpreted as specifically disclosed and simultaneously cover closed or semi-closed conjunctions such as “composed of” and “substantially composed of.”

[0020] In this document, all features or conditions defined in the form of numerical ranges or percentage ranges are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible secondary ranges and individual values ​​within those ranges, particularly integer values. For example, a range description of "1 to 8" should be considered as specifically disclosing all secondary ranges such as 1 to 7, 2 to 8, 2 to 6, 3 to 6, 4 to 8, 3 to 8, etc., particularly secondary ranges defined by all integer values, and should be considered as specifically disclosing individual values ​​within those ranges such as 1, 2, 3, 4, 5, 6, 7, 8, etc. Unless otherwise specified, the foregoing interpretation applies to all content throughout this invention, regardless of its scope.

[0021] If a quantity or other numerical value or parameter is expressed as a range, a preferred range, or a series of upper and lower limits, it should be understood that this document has specifically disclosed all ranges consisting of any upper or preferred value of that range and the lower or preferred value of that range, regardless of whether such ranges are separately disclosed. Furthermore, when a range of numerical values ​​is mentioned herein, unless otherwise stated, the range shall include its endpoints and all integers and fractions within the range.

[0022] In this document, numerical values ​​are to be understood as having a precision with significant digits, provided that the purpose of the invention can be achieved. For example, the number 40.0 should be understood to cover a range from 39.50 to 40.49.

[0023] The following embodiments are merely examples illustrating implementations of the present invention and do not constitute any limitation on the present invention. Those skilled in the art will understand that modifications made without departing from the spirit and concept of the present invention fall within the protection scope of the present invention. Unless otherwise specified, the reagents and instruments used in the following embodiments are commercially available products.

[0024] Example 1: The preparation process of the crude catalyst is as described in "Steps 1-5" of Example 1 in patent CN117065756A. The crude catalyst is then further processed as follows, and the resulting crude catalyst is designated "Catalyst #1". The further processing steps are as follows: (1) At 35℃, aluminum dihydrogen phosphate, phosphoric acid, and sodium molybdate were dissolved in deionized water to prepare a surface treatment solution with the following concentrations: 16 g / L, 8 g / L, and 0.6 g / L, respectively. The final pH of the solution was adjusted to 3.5 using phosphoric acid or sodium hydroxide. The surface treatment solution was then allowed to stand for 2 hours after preparation, with the temperature maintained at 35℃ during this period.

[0025] (2) Immerse the crude catalyst No. 1 in the surface treatment solution obtained in step (1). The liquid surface should completely submerge the catalyst sample. During the immersion, the temperature should be maintained at 35°C and the immersion time should be 8 minutes.

[0026] (3) After the impregnation in step (2), the catalyst sample was taken out and dried at 100°C for 6 hours and calcined at 500°C for 3 hours to obtain the surface-treated caprolactam hydrogenation refining catalyst.

[0027] (4) The catalyst obtained in step (3) was reduced with hydrogen at 480°C for 4 hours and then sealed in deoxygenated water to obtain a reduced caprolactam hydrogenation refining catalyst, which was numbered "self-made 1#".

[0028] Example 2: The preparation process of the crude catalyst follows steps 1-5 of Example 2 in patent CN117065756A, and is further processed as follows. The resulting crude catalyst is designated as "Catalyst #2". The further processing steps are as follows: (1) At 45℃, aluminum dihydrogen phosphate, phosphoric acid, and sodium molybdate were dissolved in deionized water to prepare a surface treatment solution with the following concentrations: 20 g / L, 12 g / L, and 0.8 g / L, respectively. The final pH of the solution was adjusted to 2.8 using phosphoric acid or sodium hydroxide. The surface treatment solution was then allowed to stand for 2 hours after preparation, with the temperature maintained at 45℃ during this period.

[0029] (2) Immerse the crude catalyst No. 2 in the surface treatment solution obtained in step (1). The liquid surface should completely submerge the catalyst sample. During the immersion, the temperature should be maintained at 45°C and the immersion time should be 12 minutes.

[0030] (3) After the impregnation in step (2), the catalyst sample was taken out and dried at 120°C for 6 hours and calcined at 550°C for 4 hours to obtain the surface-treated caprolactam hydrogenation refining catalyst.

[0031] (4) The catalyst obtained in step (3) was reduced with hydrogen at 500°C for 6 hours and sealed in deoxygenated water to obtain a reduced caprolactam hydrogenation refining catalyst, which was numbered "self-made 2#".

[0032] Comparative Example 1: The catalyst preparation process was carried out in accordance with the patent “CN117065756A Example 1”, and the resulting catalyst sample was numbered “Self-made 3#”.

[0033] Comparative Example 2: The catalyst preparation process was carried out in accordance with the patent “CN117065756A Example 2”, and the resulting catalyst sample was numbered “Self-made 4#”.

[0034] Performance testing and results analysis The hydrogenation performance of the catalysts in Examples 1-2 and Comparative Examples 1-2 was tested. The caprolactam aqueous solution used in the test was taken from the inlet process feed liquid of the hydrogenation reactor of the industrial caprolactam refining unit. The test results after 72 hours of reaction are listed in Table 1.

[0035] The catalyst samples from Examples 1-2 and Comparative Examples 1-2 were immersed in deoxygenated water for 600 days. The pore size distribution of the catalyst samples before and after immersion was tested using nitrogen adsorption-desorption method, and the state of the catalyst samples was observed. See details below. Figures 1-5 .

[0036] Hydrogenation performance tests were conducted on the self-made catalyst samples 1#~4# after 600 days of soaking. The caprolactam aqueous solution used in the test was taken from the inlet process feed liquid of the hydrogenation reactor of the industrial caprolactam refining unit. The test results after 72 hours of reaction are listed in Table 1.

[0037] Table 1

[0038] The PAN value characterizes the content of reducing impurities in caprolactam aqueous solution; a lower value indicates a lower content of reducing impurities. Table 1 shows that the PAN values ​​at the hydrogenation outlet of Examples 1-2 and Comparative Examples 1-2 are consistently between 1.0 and 1.2, indicating that the hydrogenation performance of the catalyst samples remains essentially unchanged after surface treatment according to this invention. Furthermore, the hydrogenation performance of the catalyst samples from Examples 1-2 remained at a normal level after 600 days of immersion, while the hydrogenation performance of the comparative catalyst samples under the same conditions showed a significant decrease. This indicates that the catalyst samples prepared according to this invention can be stored in deoxygenated water for a long time while maintaining stable hydrogenation performance.

[0039] from Figures 1-4 From the perspective of pore structure, the pore size of Examples 1 and 2 decreased slightly after immersion, which was due to residual water molecules in the pores; the changes in pores in Comparative Examples 1 and 2 were more significant, which was due to the superposition of residual water molecules in the pores and the precipitation of hydrated alumina particles. Figure 5 As seen in the catalyst state diagram, after 600 days of soaking, catalysts in Comparative Examples 1 and 2 showed a large amount of white precipitates in the soaking solution. This was caused by the slow hydration reaction between the alumina support and water, resulting in the formation of hydrated alumina, which led to the local erosion and collapse of the catalyst support. In contrast, the soaking solutions of catalysts in Examples 1 and 2 were clean and transparent, without any white suspended matter. This indicates that the catalyst samples prepared by the method of this invention have a certain shielding effect on water, greatly slowing down the occurrence of the hydration reaction.

[0040] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing a catalyst suitable for the hydrogenation purification of caprolactam, comprising: (1) Aluminum sol and rare earth metal salt are uniformly mixed to obtain slurry I, in which the solid content of aluminum oxide and rare earth metal salt is 20-40%; slurry I is spray-dried and granulated to obtain solid microsphere powder. A portion of solid microsphere powder was calcined to obtain rare earth oxide modified alumina, wherein the mass ratio of alumina to rare earth metal elements contained in the rare earth oxide in the rare earth oxide modified alumina was (15~50):

1. In step (1), the portion of solid microsphere powder taken accounts for 40%-70% of the total mass of the solid microsphere powder; (2) Add the rare earth oxide-modified alumina and structural additive to water and mix them evenly to obtain slurry II, wherein the mass ratio of structural additive to rare earth oxide-modified alumina is (0.15~0.6):1; (3) Add nickel salt aqueous solution to slurry II and stir thoroughly to obtain slurry III; add precipitant to slurry III to deposit the reaction product of the precipitation reaction on the support, wash, dry, calcine and pulverize to obtain solid catalyst powder, wherein the Ni content is 15~35wt% of the mass of solid catalyst powder; (4) Take the remaining solid microsphere powder from step (1) and mix it evenly with the solid catalyst powder, binder, and lubricant from step (3). Selectively add dilute nitric acid and shape it to obtain a shaped catalyst. The amount of binder added is 5-15 wt% of the mass of the solid catalyst powder, and the amount of lubricant added is 3-7 wt% of the mass of the solid catalyst powder. The obtained shaped catalyst was placed in a constant temperature and humidity chamber at a constant temperature of 25~50℃ and a humidity of 90~97% for 72~168h. After drying and calcination, crude oxidized caprolactam hydrogenation refining catalyst was obtained. (5) At 35~45℃, aluminum dihydrogen phosphate, phosphoric acid and sodium molybdate are dissolved in deionized water to prepare a surface treatment solution. The concentrations of each component are 15~25g / L, 6~15g / L and 0.5~1g / L, respectively. The final pH value of the solution is adjusted to 2.8~3.5 using phosphoric acid or sodium hydroxide to form a surface treatment solution. After preparation, the solution is allowed to stand for 2~4 hours, during which the temperature is maintained at 35~45℃. (6) Immerse the crude catalyst obtained in step (4) into the surface treatment solution obtained in step (5). The liquid surface should completely submerge the crude catalyst. During the immersion, the temperature should be maintained at 35~45℃ and the immersion time should be 8~12 minutes. (7) After the impregnation in step (6) is completed, the catalyst sample is taken out and dried and calcined to obtain the surface-treated caprolactam hydrogenation refining catalyst. (8) The catalyst obtained in step (7) is reduced by hydrogen at 450~600℃ for 2~10 hours and sealed in deoxygenated water to obtain the reduced caprolactam hydrogenation refining catalyst, which can be stored for a long time, thereby realizing the supply of water-sealed reduced state.

2. The preparation method according to claim 1, characterized in that, In step (2), the mass ratio of the structural additive to the rare earth oxide modified alumina is (0.18~0.56):

1.

3. The preparation method according to claim 1, characterized in that, In step (3), the Ni content is 20-30 wt% of the solid catalyst powder.

4. The preparation method according to claim 1, characterized in that, In step (4), the amount of binder added is 5 to 10 wt% of the mass of the solid catalyst powder; the amount of lubricant added is 3 to 5 wt% of the mass of the solid catalyst powder.

5. The preparation method according to claim 1, characterized in that, In step (5), the preferred concentrations of aluminum dihydrogen phosphate, phosphoric acid, and sodium molybdate are 16~20 g / L, 8~12 g / L, and 0.6~0.8 g / L, respectively.

6. The preparation method according to claim 1, characterized in that, The conductivity of the deionized water in step (5) and the deoxygenated water in step (8) is less than 5 μs / cm.

7. The preparation method according to claim 1, characterized in that, In step (7), the drying temperature is 100~120℃ and the calcination temperature is 500~600℃.

8. A catalyst for the hydrogenation and refining of caprolactam, said catalyst being prepared by the preparation method according to any one of claims 1 to 7.

9. A method for hydrogenating and purifying caprolactam, the method comprising: Caprolactam is hydrogenated in a fixed-bed hydrogenation reactor containing a caprolactam hydrogenation refining catalyst according to claim 8.

Images