Preparation method of high-purity hydroxyl methionine isopropyl ester

Abstract

This invention discloses a method for preparing high-purity hydroxymethionine isopropyl ester, comprising: mixing hydroxymethionine and hydroxymethionine polymer at a mass ratio of 4.0~4.8:1 as raw materials; using molecular sieve drying or isopropanol-water azeotropic dehydration to control the moisture content of the raw materials to below 0.1% to avoid catalyst poisoning; mixing the dehydrated raw materials with isopropanol and preheating to 90~110℃ to obtain a mixture; and feeding the mixture in stages into a container filled with SO4. 2‑ A fixed-bed reactor using ZrO2-SBA-15 mesoporous molecular sieve catalyst was used to carry out alcoholysis reaction at 240~260℃ and 4.5~5.5MPa. The reaction solution was separated and purified by vacuum flash evaporation, short-path distillation, precision distillation and crystallization coupling process to effectively remove light and heavy component impurities, ensuring product purity ≥99.0% and improving reaction selectivity and stability.

Description

Technical Field

[0001] This invention relates to the field of organic ester compound preparation technology, and more specifically to a method for preparing high-purity hydroxymethionine isopropyl ester. Background Technology

[0002] Hydroxymethionine isopropyl ester, as an important feed additive, possesses high stability and excellent bioavailability. The key to its industrial production lies in achieving efficient alcoholysis conversion of hydroxymethionine and its polymers, as well as high-purity product purification. Existing hydroxymethionine ester production processes mostly employ batch reactors, which not only have low reaction efficiency and are prone to side reactions, but also suffer from catalyst poisoning due to moisture in the raw materials, leading to incomplete conversion of the hydroxymethionine polymers. Furthermore, traditional single distillation purification processes cannot effectively remove reaction byproducts, making it difficult to meet the purity and yield requirements for high-end feed additives. Overall, the low alcoholysis conversion efficiency of hydroxymethionine and its polymers, coupled with the difficulty in removing byproducts, ultimately results in insufficient product purity and yield. Summary of the Invention

[0003] The purpose of this invention is to address the problems mentioned in the background section by providing a method for preparing high-purity hydroxymethionine isopropyl ester, ensuring catalyst activity and reaction stability, effectively suppressing the occurrence of isopropanol dehydration side reaction, improving the reaction selectivity of hydroxymethionine isopropyl ester, and ultimately ensuring that the product purity consistently reaches over 99.0% and the yield reaches over 92.0%.

[0004] To achieve the above objectives, the present invention specifically adopts the following technical solution: A method for preparing high-purity hydroxymethionine isopropyl ester includes the following steps: S1. Mix the dehydrated raw material with isopropanol to obtain a mixture, and preheat the mixture to 90~110℃; The raw materials include 88% hydroxymethionine and 20% hydroxymethionine polymer mixed at a mass ratio of 4.0~4.8:1.

[0005] Furthermore, in step S1, the raw material is dehydrated using a 3A molecular sieve or an isopropanol-water azeotropic dehydration process until the moisture content is ≤0.1%, thus avoiding subsequent SO4 emissions. 2- / ZrO2-SBA-15 mesoporous molecular sieve catalyst water poisoning.

[0006] Furthermore, specific methods for dehydration using 3A molecular sieves include: Add 10%~15% of 3A molecular sieve by total mass of raw materials, and dry at 110~130℃ and 0.05~0.1MPa for 2~4 hours until the moisture content of the raw materials is ≤0.1%.

[0007] Furthermore, the reflux ratio of the isopropanol-water azeotropic dehydration is 1.5~2.5:1.

[0008] Furthermore, the mass ratio of the raw material to isopropanol is 1:3.5~4.5.

[0009] S2. The preheated mixture is fed in sections into the SO4-filled container. 2- A fixed-bed reactor using ZrO2-SBA-15 mesoporous molecular sieve catalyst was used to carry out alcoholysis reaction at 240~260℃ and 4.5~5.5MPa.

[0010] Furthermore, the liquid hourly space velocity (LHSV) of the alcoholysis reaction is 0.4–0.6 h⁻¹. -1 .

[0011] Furthermore, in step S2, 65-75% of the preheated mixture is fed from the top inlet of the fixed-bed reactor, and the remaining 25-35% of the preheated mixture is fed from the middle of the fixed-bed reactor. This can effectively control the axial temperature distribution and material concentration gradient of the fixed-bed reactor, suppress intramolecular and intermolecular dehydration of isopropanol to generate side reactions such as isopropyl ether and propylene, thereby improving the selectivity of hydroxymethionine isopropyl ester. Specifically, the alcoholysis reaction of hydroxymethionine and isopropanol is exothermic, and the dehydration of isopropanol is also exothermic. Single-stage feeding can easily cause localized overheating in the upper part of the catalyst bed, and high temperatures accelerate side reactions such as isopropanol dehydration and product decomposition. Staged feeding can disperse the heat of reaction, making the bed temperature more stable, avoiding hot spots, and making the reaction more inclined towards the target esterification / alcoholization pathway, thus improving product selectivity. Mid-stage feeding allows later-added materials to participate in the reaction in the latter half of the bed, shortening their residence time in the high-temperature zone and reducing excessive adsorption and conversion of isopropanol on the catalyst surface.

[0012] S3. The reaction solution obtained after alcoholysis is separated and purified to obtain hydroxymethionine isopropyl ester product.

[0013] Furthermore, the specific method for separation and purification in S3 includes: The reaction solution was subjected to vacuum flash evaporation, short-path distillation, precision distillation and crystallization in sequence; The reduced pressure flash evaporation conditions are 75~85℃ and 8~12kPa. The short-path distillation conditions are 90~110℃ and 0.5~1.5kPa; The precision distillation conditions are 115~125℃, 0.4~0.6kPa, and a reflux ratio of 4~6:1; The crystallization process uses a mixture of isopropanol and water as the crystallization solvent.

[0014] Furthermore, the volume ratio of isopropanol to water is 8~10:1, and the crystallization temperature is 3~12℃.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. In the raw material pretreatment stage, the present invention uses molecular sieve drying or isopropanol-water azeotropic dehydration to strictly control the raw material moisture content to below 0.1%, thereby avoiding water poisoning of the catalyst and ensuring catalyst activity and reaction stability. 2. In the fixed-bed reaction stage, the present invention adopts a segmented feeding mode, which feeds the preheated mixture into the fixed-bed reactor in batches according to a certain proportion, effectively suppressing the occurrence of isopropanol dehydration side reaction and improving the reaction selectivity of hydroxymethionine isopropyl ester. 3. In the separation and purification stage, this invention employs a combination of vacuum flash evaporation, short-path distillation, precision distillation, and crystallization to perform a stepwise deep treatment of the reaction solution, efficiently removing light and heavy component impurities from the system, and ultimately ensuring that the product purity consistently reaches over 99.0% and the yield reaches over 92.0%. Detailed Implementation

[0016] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. The materials and instruments used in the following embodiments are all commercially available.

[0017] A method for preparing high-purity hydroxymethionine isopropyl ester includes the following steps: S1. Mix the dehydrated raw material with isopropanol to obtain a mixture, and preheat the mixture to 90~110℃; The raw materials include 88% hydroxymethionine and 20% hydroxymethionine polymer mixed at a mass ratio of 4.0~4.8:1.

[0018] Furthermore, in S1, the raw material is dehydrated by 3A molecular sieve or isopropanol-water azeotropic dehydration until the moisture content of the raw material is ≤0.1%.

[0019] Furthermore, specific methods for dehydration using 3A molecular sieves include: Add 10%~15% of 3A molecular sieve by total mass of raw materials, and dry at 110~130℃ and 0.05~0.1MPa for 2~4 hours until the moisture content of the raw materials is ≤0.1%.

[0020] Furthermore, the reflux ratio for isopropanol-water azeotropic dehydration is 1.5~2.5:1.

[0021] Furthermore, the mass ratio of the raw material to isopropanol is 1:3.5~4.5.

[0022] S2. The preheated mixture is fed in sections into the SO4-filled container. 2- A fixed-bed reactor using ZrO2-SBA-15 mesoporous molecular sieve catalyst was used to carry out alcoholysis reaction at 240~260℃ and 4.5~5.5MPa.

[0023] Furthermore, the liquid hourly space velocity (LHSV) of the alcoholysis reaction is 0.4–0.6 h⁻¹. -1 .

[0024] Furthermore, in S2, 65-75% of the preheated mixture is fed from the top inlet of the fixed-bed reactor, and the remaining 25-35% of the preheated mixture is fed from the middle of the fixed-bed reactor.

[0025] S3. The reaction solution obtained after alcoholysis is separated and purified to obtain hydroxymethionine isopropyl ester product.

[0026] Furthermore, the specific methods for separation and purification in S3 include: The reaction solution was subjected to vacuum flash evaporation, short-path distillation, precision distillation and crystallization in sequence; The reduced pressure flash evaporation conditions are 75~85℃ and 8~12kPa. The short-path distillation conditions are 90~110℃ and 0.5~1.5kPa; The precision distillation conditions are 115~125℃, 0.4~0.6kPa, and a reflux ratio of 4~6:1; The crystallization process uses a mixture of isopropanol and water as the crystallization solvent.

[0027] Furthermore, the volume ratio of isopropanol to water is 8~10:1, and the crystallization temperature is 3~12℃.

[0028] The present invention will be further described below with reference to specific embodiments and comparative examples.

[0029] Example 1 This embodiment provides a method for preparing high-purity hydroxymethionine isopropyl ester, including the following steps: 1) Raw material pretreatment: Weigh 440g of 88% hydroxymethionine and 100g of 20% hydroxymethionine polymer and mix them evenly. Add 54g of 3A molecular sieve to the mixture and dry it for 3 hours at 120℃ and 0.1MPa. After drying, the moisture content of the raw material is 0.08%. 2) Raw material mixing and preheating: Mix the above dehydrated raw materials thoroughly with 2160g of isopropanol, stir evenly, and then preheat the mixture to 100℃; 3) Fixed-bed reaction: The preheated mixture is fed into a bed filled with SO4 using a segmented feeding method. 2- A fixed-bed reactor using ZrO2-SBA-15 mesoporous molecular sieve catalyst was employed, with 70% of the mixture fed from the reactor inlet and 30% fed from the middle of the reactor bed. The reaction conditions were controlled as follows: reaction temperature 250℃, reaction pressure 5.0 MPa, and liquid hourly space velocity (LHSV) 0.5 h⁻¹. -1 Under these conditions, an alcoholysis reaction is carried out to obtain a reaction solution; 4) Separation and purification: The above reaction solution was processed sequentially as follows: First, vacuum flash evaporation was carried out at 80℃ and 10kPa to recover isopropanol from the system; then, short-path distillation was carried out at 100℃ and 1.0kPa to remove light component impurities from the reaction solution; next, precision distillation was carried out at 120℃, 0.5kPa, and a reflux ratio of 5:1 to obtain the distillation product; finally, the distillation product was recrystallized at 5℃ using an isopropanol-water mixture as the crystallization solvent (the volume ratio of isopropanol to water was 9:1). After recrystallization, the product was filtered and dried to obtain hydroxymethionine isopropyl ester.

[0030] Example 2 This embodiment provides a method for preparing high-purity hydroxymethionine isopropyl ester, including the following steps: 1) Raw material pretreatment: Weigh 400g of 88% hydroxymethionine and 100g of 20% hydroxymethionine polymer, mix them evenly, and dehydrate using isopropanol-water azeotropic dehydration at a reflux ratio of 2:1. The moisture content of the raw material was found to be 0.07%. 2) Raw material mixing and preheating: Mix the above dehydrated raw materials thoroughly with 2250g of isopropanol, stir evenly, and then preheat the mixture to 95℃; 3) Fixed-bed reaction: The preheated mixture is fed into a bed filled with SO4 using a segmented feeding method. 2- A fixed-bed reactor using ZrO2-SBA-15 mesoporous molecular sieve catalyst was employed, with 68% of the mixture fed from the reactor inlet and 32% fed from the middle of the reactor bed. The reaction conditions were controlled as follows: reaction temperature 245℃, reaction pressure 4.8 MPa, and liquid hourly space velocity (LHSV) 0.45 h⁻¹. -1 Under these conditions, an alcoholysis reaction is carried out to obtain a reaction solution; 4) Separation and purification: The above reaction solution was subjected to the following treatments in sequence: First, a vacuum flash evaporation was performed at 80℃ and 10kPa to recover isopropanol from the system; then, a short-path distillation was performed at 100℃ and 1.0kPa to remove light component impurities from the reaction solution; next, a precision distillation was performed at 118℃, 0.45kPa, and a reflux ratio of 4.5:1 to obtain the distillation product; finally, the distillation product was recrystallized at 8℃ using an isopropanol-water mixture as the crystallization solvent (the volume ratio of isopropanol to water was 8.5:1). After recrystallization, the product was filtered and dried to obtain the hydroxymethionine isopropyl ester product.

[0031] Example 3 This embodiment provides a method for preparing high-purity hydroxymethionine isopropyl ester, including the following steps: 1) Raw material pretreatment: Weigh 480g of 88% hydroxymethionine and 100g of 20% hydroxymethionine polymer and mix them evenly. Add 72g of 3A molecular sieve to the mixture and dry it for 2.5h at 130℃ and 0.08MPa. After drying, the moisture content of the raw material is 0.09%. 2) Raw material mixing and preheating: Mix the above dehydrated raw materials thoroughly with 2610g of isopropanol, stir evenly, and then preheat the mixture to 105℃; 3) Fixed-bed reaction: The preheated mixture is fed into a bed filled with SO4 using a segmented feeding method. 2- A fixed-bed reactor using ZrO2-SBA-15 mesoporous molecular sieve catalyst was employed, with 72% of the mixture fed from the reactor inlet and 28% fed from the middle of the reactor bed. The reaction conditions were controlled as follows: reaction temperature 255℃, reaction pressure 5.2 MPa, and liquid hourly space velocity (LHSV) 0.55 h⁻¹. -1 Under these conditions, an alcoholysis reaction is carried out to obtain a reaction solution; 4) Separation and purification: The above reaction solution was subjected to the following treatments in sequence: First, a vacuum flash evaporation was carried out at a temperature of 80℃ and a pressure of 10kPa to recover isopropanol from the system; then, a short-path distillation was carried out at a temperature of 100℃ and a pressure of 1.0kPa to remove light component impurities from the reaction solution; next, a precision distillation was carried out at a temperature of 122℃, a pressure of 0.55kPa, and a reflux ratio of 5.5:1 to obtain the distillation product; finally, the distillation product was recrystallized at 10℃ using an isopropanol-water mixture as the crystallization solvent (the volume ratio of isopropanol to water was 9.5:1). After recrystallization, the product was filtered and dried to obtain the hydroxymethionine isopropyl ester product.

[0032] Comparative Example 1 The difference between this comparative example and Example 1 is that segmented feeding is not used; the preheated mixture is fed into the fixed-bed reactor inlet all at once. All other conditions are the same as in Example 1.

[0033] Comparative Example 2 The difference between this comparative example and Example 1 is that the catalyst is replaced with ordinary SO4. 2- / ZrO2 catalyst (without SBA-15 mesoporous support), all other conditions are the same as in Example 1.

[0034] Comparative Example 3 The difference between this comparative example and Example 1 is that no deep dehydration treatment is performed, while all other conditions are the same as in Example 1.

[0035] Comparative Example 4 The difference between this comparative example and Example 1 is that short-path distillation and precision distillation-crystallization coupling processes are not performed; only vacuum flash evaporation and ordinary distillation are performed. All other conditions are the same as in Example 1.

[0036] The hydroxymethionine isopropyl ester products obtained in Examples 1-3 and Comparative Examples 1-4 were tested, and the test results are shown in Table 1: Table 1. Detection results of Examples 1-3 and Comparative Examples 1-4 As shown in Table 1 and Comparative Example 1, the single-feeding of Comparative Example 1 leads to excessively high isopropanol concentration and long residence time in the upper section of the fixed-bed reactor. At the same time, the heat released by the alcoholysis reaction is concentrated, forming a local overheating zone, which exacerbates the dehydration side reaction of isopropanol under the strong acid catalyst conditions. In contrast, the segmented feeding of the present invention can evenly distribute the material concentration and disperse the heat of reaction, avoiding local overheating and excessive contact of isopropanol with the acidic sites of the catalyst, thereby suppressing side reactions and improving the selectivity and yield of hydroxymethionine isopropyl ester.

[0037] As shown in Table 1 and Comparative Example 2, the SBA-15 mesoporous carrier has a high specific surface area and a regular mesoporous structure, which can effectively disperse SO4. 2- / ZrO2 active sites enhance the acidity and stability of the catalyst while limiting side reactions; ordinary SO4 2- The active sites of the ZrO2 catalyst were unevenly dispersed, and the acidity distribution was unreasonable; while in Comparative Example 2, the catalyst was replaced with ordinary SO4. 2- / ZrO2 catalyst, without SBA-15 mesoporous support; leads to decreased selectivity of main reaction and increased side reaction.

[0038] As shown in Table 1 and Comparative Example 3, the alcoholysis reaction of hydroxymethionine with isopropanol is a reversible reaction. The presence of water will promote the reaction to proceed in reverse. At the same time, water will induce ester hydrolysis side reaction and form an azeotrope with isopropanol, increasing the difficulty of separation. In addition, water will reduce the catalyst activity and further aggravate the occurrence of side reactions. Comparative Example 3 did not undergo deep dehydration treatment, resulting in a significant decrease in product purity and yield.

[0039] As shown in Table 1 and Comparative Example 4, short-path distillation can quickly remove light component impurities (such as unreacted isopropanol and low-boiling-point byproducts) from the reaction solution under mild conditions, avoiding the decomposition of heat-sensitive products. The precision distillation-crystallization coupling process can further remove trace impurities and improve product purity. However, Comparative Example 4 only used vacuum flash evaporation and ordinary distillation, without short-path distillation and precision distillation-crystallization coupling processes, which could not effectively remove impurities from the system, resulting in a significant decrease in product purity and yield.

[0040] In summary, in the raw material pretreatment stage, this invention employs molecular sieve drying or isopropanol-water azeotropic dehydration to strictly control the raw material moisture content to below 0.1%, avoiding water-induced catalyst poisoning and ensuring catalyst activity and reaction stability. In the fixed-bed reaction stage, a segmented feeding mode is adopted, feeding the preheated mixture into the fixed-bed reactor in batches according to a specified ratio, effectively suppressing the occurrence of isopropanol dehydration side reactions and improving the reaction selectivity of hydroxymethionine isopropyl ester. In the separation and purification stage, vacuum flash evaporation, short-path distillation, precision distillation, and crystallization coupling processes are used to perform stepwise deep treatment of the reaction liquid, efficiently removing light and heavy component impurities from the system, ultimately ensuring that the product purity consistently reaches above 99.0%.

[0041] Although embodiments of this application have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of this application, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing high-purity hydroxymethionine isopropyl ester, characterized in that, Includes the following steps: S1. Mix the dehydrated raw material with isopropanol to obtain a mixture, and preheat the mixture to 90~110℃; The raw materials include hydroxymethionine and hydroxymethionine polymer mixed at a mass ratio of 4.0~4.8:1; S2. The preheated mixture is fed in sections into the SO4-filled container. 2- A fixed-bed reactor with ZrO2-SBA-15 mesoporous molecular sieve catalyst was used to carry out alcoholysis reaction at 240~260℃ and 4.5~5.5MPa. S3. The reaction solution obtained after alcoholysis is separated and purified to obtain hydroxymethionine isopropyl ester product.

2. The method for preparing high-purity hydroxymethionine isopropyl ester according to claim 1, characterized in that, In S1, the raw material is dehydrated by 3A molecular sieve or isopropanol-water azeotropic dehydration until the moisture content of the raw material is ≤0.1%.

3. The method for preparing high-purity hydroxymethionine isopropyl ester according to claim 2, characterized in that, Specific methods for dehydration using 3A molecular sieves include: Add 10%~15% of 3A molecular sieve by total mass of raw materials, and dry at 110~130℃ and 0.05~0.1MPa for 2~4 hours until the moisture content of the raw materials is ≤0.1%.

4. The method for preparing high-purity hydroxymethionine isopropyl ester according to claim 2, characterized in that, The reflux ratio for isopropanol-water azeotropic dehydration is 1.5~2.5:

1.

5. The method for preparing high-purity hydroxymethionine isopropyl ester according to claim 1, characterized in that, The hydroxymethionine has a mass fraction of 88%, and the hydroxymethionine polymer has a mass fraction of 20%.

6. The method for preparing high-purity hydroxymethionine isopropyl ester according to claim 1, characterized in that, The mass ratio of the raw material to isopropanol is 1:3.5~4.

5.

7. The method for preparing high-purity hydroxymethionine isopropyl ester according to claim 1, characterized in that, The liquid hourly space velocity (LHSV) for the alcoholysis reaction is 0.4–0.6 h⁻¹. -1 .

8. The method for preparing high-purity hydroxymethionine isopropyl ester according to claim 1, characterized in that, In step S2, 65-75% of the preheated mixture is fed from the top inlet of the fixed-bed reactor, and the remaining 25-35% of the preheated mixture is fed from the middle of the fixed-bed reactor.

9. The method for preparing high-purity hydroxymethionine isopropyl ester according to claim 1, characterized in that, The specific methods for separation and purification in S3 include: The reaction solution was subjected to vacuum flash evaporation, short-path distillation, precision distillation and crystallization in sequence; The reduced pressure flash evaporation conditions are 75~85℃ and 8~12kPa. The short-path distillation conditions are 90~110℃ and 0.5~1.5kPa; The precision distillation conditions are 115~125℃, 0.4~0.6kPa, and a reflux ratio of 4~6:1; The crystallization process uses a mixture of isopropanol and water as the crystallization solvent.

10. The method for preparing high-purity hydroxymethionine isopropyl ester according to claim 8, characterized in that, The volume ratio of isopropanol to water is 8~10:1, and the crystallization temperature is 3~12℃.

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