Process for the industrial production of 5,5-dimethylhydantoin disodium salt

Abstract

The application discloses an industrial production method of 5,5-dimethylhydantoin disodium salt and belongs to the technical field of fine chemical intermediate synthesis. In view of the problems of uneven solid-liquid mass transfer and heat transfer, easy material ring-opening hydrolysis caused by long-time residence of a strong alkali system, many by-products, poor product stability and the like existing in a traditional kettle type production process, the application adopts a micro-channel continuous industrialization reaction process, and combines with steps such as fine pretreatment, accurate proportioning and impurity removal of raw materials to quickly complete a neutralization and salt formation reaction of 5,5-dimethylhydantoin and liquid alkali. The application has the advantages of simple and controllable process, high production efficiency and stable operation, and the prepared product is high in purity and stable in storage, and has high industrialization popularization value.

Description

Technical Field

[0001] This invention relates to the field of industrial production technology of fine organic sodium salts, specifically to an industrial production method of 5,5-dimethylhydantoin disodium salt. Background Technology

[0002] 5,5-Dimethylhydantoin sodium salt, also known as 5,5-dimethylhydantoin sodium salt, is a heterocyclic organic sodium salt obtained from 5,5-dimethylhydantoin through an alkaline neutralization reaction. It is also an important precursor raw material for the preparation of halogenated hydantoin disinfectants, preservative intermediates, water treatment stabilizers, and polymer curing agents. In industrial applications, it mainly exists in two forms: monosodium salt and disodium salt. The disodium salt has the characteristics of excellent water solubility and high reactivity, making it the preferred product for industrial production. This substance has a stable heterocyclic skeleton structure, but it is prone to ring-opening hydrolysis side reactions under conditions such as high temperature and strongly alkaline systems. Therefore, as an intermediate material, the purity, color, and stability of 5,5-dimethylhydantoin sodium salt directly determine the quality and storage stability of downstream end products.

[0003] Currently, the industrial preparation of sodium 5,5-dimethylhydantoin generally adopts the traditional stirred tank batch neutralization process. Specifically, 5,5-dimethylhydantoin and liquid alkali are added to the reaction vessel, and the corresponding sodium salt product is obtained by long-term stirring and neutralization, heat preservation and aging, and concentration and crystallization.

[0004] All existing patented technologies employ the aforementioned batch reactor system to prepare sodium dimethylhydantoin and use it for the synthesis of halogenated hydantoin. Among them, patent CN202511640858.X discloses a method for the co-production of dibromohydantoin and bromochlorohydantoin. This process uses a stirred reactor, where 5,5-dimethylhydantoin and liquid alkali are dissolved by prolonged stirring at 20–25°C to prepare a sodium hydantoin solution in situ. After the sodium salt is prepared, it is not filtered, purified, or subjected to stabilization and aging treatment; instead, bromine is directly added dropwise to the same reactor for 2–3 hours to synthesize dibromohydantoin. This process relies on conventional batch reactor stirring and mixing, which suffers from problems such as uneven solid-liquid mixing, localized strong alkaline environments, and localized high temperatures. This easily leads to sodium salt hydrolysis, generating impurities that are introduced into the final product, resulting in low purity and substandard color of the finished product. Patent CN202210370330.X discloses a clean synthesis method for dibromohydantoin. In this process, 5,5-dimethylhydantoin, caustic soda, and sodium bromide are added to a reactor in one go. The sodium salt mixture is obtained by stirring and neutralizing in a reactor. The subsequent bromination reaction is completed by a reactor circulation system. The entire process is a batch reactor operation with an overall reaction time of 2 to 4 hours. This process uses sodium salt preparation only as a pre-treatment auxiliary step before the bromination reaction and does not perform precise temperature control during the reaction process. As a result, there are also problems such as uneven material mixing, multiple side reactions, and substandard purity and color of the finished product. Patent CN202610527346.2 discloses a clean synthesis method and apparatus for dibromohydantoin. This process still uses a traditional reactor as the core reaction equipment. First, the preparation of 5,5-dimethylhydantoin sodium salt is completed in the reactor. Then, the synthesis of dibromohydantoin is completed by combining electrolytic coupling drop bromine method. Due to the inherent defects of the reactor reaction, the reaction process has more side reactions and a large amount of impurities, which ultimately leads to low purity and poor quality of the final product.

[0005] In summary, existing batch processes for preparing 5,5-dimethylhydantoin sodium salt generally have inherent technical defects, as follows:

[0006] 1. Prone to local hot spots and frequent side reactions. Traditional batch reactors rely on macroscopic stirring to achieve mass and heat transfer. The material mixing rate is slow and the heat transfer is delayed. The heat released during acid-base neutralization is concentrated and cannot be dissipated quickly. The system is prone to forming local hot spots of 35-55℃, which triggers the ring-opening hydrolysis of hydantoin heterocyclic imine bonds, generating small molecule impurities such as acetone, urea, and trace amounts of cyanate. Ultimately, this results in the finished product turning yellow, having low light transmittance, and being unable to improve product purity.

[0007] 2. Long reaction cycle and low production efficiency. The solid-liquid mass transfer resistance of the batch system is large and the reaction rate is limited. The neutralization and ripening reaction of a single batch takes as long as 2 to 3 hours. The production cycle is long and the single batch capacity is limited, which cannot meet the needs of large-scale continuous industrial production.

[0008] 3. Poor batch stability and low product consistency. Intermittent production relies on manual feeding and manual control of heating and cooling cycles. Deviations in material mixing, reaction temperature, and reaction time between different production batches result in significant fluctuations in the color, purity, and storage stability of the finished product, making it impossible to meet the stable supply requirements of high-end, refined products.

[0009] 4. Significant degradation and short service life of finished products during storage. Sodium salt products prepared by existing processes retain trace amounts of hydrolysis impurities and have microscopic stress defects in their molecular structure. During long-term storage, they are prone to discoloration, stratification, and a decrease in the effective components, resulting in poor product storage stability.

[0010] In summary, conventional production methods using conventional raw materials and equipment consistently fail to address the core issues of poor adaptability to concentration fluctuations, uncontrollable side reactions, weak product stability, and low batch-to-batch consistency. Therefore, developing an industrial production process that can adapt to fluctuations in industrial raw materials, precisely control impurities, prevent degradation, ensure high stability, and enable continuous mass production is of significant practical importance. Summary of the Invention

[0011] The purpose of this invention is to overcome the combined technical defects of existing conventional production processes and provide an industrial production method for 5,5-dimethylhydantoin disodium salt.

[0012] To achieve the above objectives, the present invention adopts the following technical solution:

[0013] An industrial production method for 5,5-dimethylhydantoin disodium salt, characterized by comprising the following steps:

[0014] S1. Pulverize 5,5-dimethylhydantoin with a purity ≥99.0% to 80-120 mesh, and prepare a suspension with a mass fraction of 22%-28% by mixing it with high-purity deionized water with a conductivity ≤5μS / cm. Stir at 22℃ and 150r / min for 30min to obtain a uniform, stable and sediment-free suspension system.

[0015] S2. The silicon carbide microchannel reactor is pre-cooled to 20-25℃ and kept at a constant temperature for 30 minutes. The temperature deviation throughout the reaction is ≤±0.5℃. The single-channel pore size of the reactor is 0.8-1.2mm, and the specific surface area is ≥1200m² / m³.

[0016] S3. An online refractometer is used to detect the actual concentration of industrial liquid alkali in real time. The control system feeds back and automatically adjusts the alkali feed flow rate to keep the molar ratio of 5,5-dimethylhydantoin to NaOH constant at 1:2.02. The 5,5-dimethylhydantoin suspension and liquid alkali are fed synchronously and continuously through dual-channel metering pumps with a metering accuracy of ±0.5%. The feed flow rate of the DMH suspension is controlled at 120-180 L / h. The material stays in the microchannel for 8-12 seconds to react, quickly completing the low-temperature non-degradable neutralization and salt formation.

[0017] S4. The reaction output is filtered online through a 0.2μm titanium alloy precision filter to remove solid and colloidal impurities. The filtrate is stirred and matured at 20℃ for 20 minutes to regulate the molecular structure and eliminate micro-stress.

[0018] S5. The aging solution is concentrated under vacuum at a vacuum degree of -0.085 to -0.09 MPa and a kettle temperature of ≤55℃. After constant temperature crystallization at 5 to 10℃ for 2 hours and low temperature vacuum drying at 50℃, 5,5-dimethylhydantoin disodium salt solid product is obtained.

[0019] Compared with existing technologies, this invention abandons the traditional batch batch production process and adopts online refractive real-time concentration detection and flow adaptive adjustment technology, combined with a continuous flow microchannel reaction system, to completely avoid reaction deviations caused by raw material concentration fluctuations. At the same time, it suppresses the hydantoin degradation side reaction from the reaction mechanism, and significantly improves product purity, color and long-term storage stability. Attached Figure Description

[0020] Figure 1 This is a schematic flow diagram of an industrial production method for 5,5-dimethylhydantoin disodium salt provided by an embodiment of the present invention. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of the present invention. Where specific techniques or conditions are not specified in the embodiments, they are performed in accordance with the techniques or conditions described in the literature in the art, or in accordance with the product manual.

[0022] Example 1

[0023] This embodiment represents the optimal parameter combination, suitable for conventional industrial continuous production. Specific steps are as follows: S1, Prepare a 25% (w / w) 5,5-dimethylhydantoin suspension, stir at 22°C and 150 rpm for 30 min; S2, Pre-cool the microchannel reactor to 22°C, maintain constant temperature for 30 min, controlling temperature deviation ±0.3°C; S3, Turn on the online refractometer to monitor the liquid alkali concentration in real time, the system automatically adjusts the flow rate to maintain a molar ratio of 1:2.02, the suspension feed flow rate is 150 L / h, the dual-feed accuracy is ±0.3%, and the material reaction residence time is 10 s; S4, Remove impurities online using a 0.2 μm titanium alloy filter, mature at 20°C for 20 min; S5, Concentrate under vacuum of -0.09 MPa and at a reactor temperature of 52°C, crystallize at 8°C for 2 h, and vacuum dry at 50°C.

[0024] Test results: Product purity 99.62%, single-pass yield 99.71%, solution transmittance 99.35%, total degradation impurities (acetone + urea) not detected, purity fluctuation range of 0.06% for 10 consecutive batches, effective content decay of 0.11% after 6 months of storage at room temperature, product color is white, without yellowing, clumping, or layering.

[0025] Example 2

[0026] The process steps are the same as in Example 1, with the following differences: DMH suspension mass fraction 22%, reaction temperature 20℃, material residence time 12s, and feed flow rate 120L / h, suitable for small-batch production of high-end fine products.

[0027] Test results: Product purity 99.45%, single-pass yield 99.63%, solution transmittance 99.12%, total degradation impurity content 0.008%, batch fluctuation range 0.08%, 6-month storage degradation 0.14%, product appearance clean and flawless.

[0028] Example 3

[0029] The process steps are the same as in Example 1, with the following differences: DMH suspension mass fraction 28%, reaction temperature 25℃, material residence time 8s, feed flow rate 180L / h, and the system runs stably for 8 hours, making it suitable for large-scale industrial production.

[0030] Test results: Product purity 99.38%, single-pass yield 99.58%, solution transmittance 99.05%, total degradation impurity content 0.010%, batch fluctuation range 0.09%, 6-month storage degradation 0.17%, no equipment blockage, no operating condition drift, and excellent mass production stability.

[0031] Example 4

[0032] Industrial non-standard liquid alkali with a concentration fluctuation of ±5% was selected, and the online dynamic ratio control of the present invention was adopted. The remaining parameters were the same as in Example 1 to verify the process's adaptability to fluctuations in industrial raw materials.

[0033] Test results: Product purity 99.51%, single-pass yield 99.65%, total degradation impurity content 0.009%, batch fluctuation range 0.07%, and attenuation of 0.13% after 6 months of storage; the data showed no significant difference from the product produced with standard raw materials, proving that the dynamic ratio of this invention can perfectly adapt to the concentration fluctuation of industrial raw materials and solve the pain point of poor raw material adaptability in the industry.

[0034] Comparative Example 1

[0035] Using the existing mainstream industrial batch process, the same raw materials as in the example were selected, the molar ratio of DMH to NaOH was fixed at 1:2.02, the mixture was stirred and neutralized at room temperature for 2.5 hours, and then kept warm for 1 hour. The subsequent filtration, concentration, crystallization and drying processes were completely consistent with those in Example 1, eliminating post-processing interference.

[0036] Test results: Product purity 97.75%, single-pass yield 96.12%, solution transmittance 92.35%, total degradation impurity content 0.86%, fluctuation range of 1.23% over 10 consecutive batches, slight yellowing and layering after 3 months of storage at room temperature, content decay of 1.82% after 6 months. The product quality is poor and the batches are extremely unstable, making it unsuitable for high-end applications.

[0037] Comparative Example 2

[0038] Using the same microchannel equipment and operating parameters as in this invention, but without the online refractive dynamic ratio function, a manual fixed flow ratio is used, and industrial liquid alkali with concentration fluctuations is used. The remaining steps are completely consistent with Example 4.

[0039] Test results: Product purity 98.42%, single-pass yield 97.85%, total degradation impurity content 0.32%, batch fluctuation range 0.75%, 6-month storage degradation 0.65%; due to the inability to adapt to the fluctuation of liquid alkali concentration, single sodium salt residue and local side reactions occurred, and the product stability decreased significantly, proving that conventional microchannel equipment without the dynamic control process of this invention cannot achieve high-quality production.

[0040] Comparative Example 3

[0041] The equipment, proportions, and flow parameters are the same as in Example 1, except that the reaction temperature is increased to 35°C and the low-temperature constant temperature control is cancelled to simulate the conventional microchannel extensive production mode.

[0042] Test results: Product purity 98.15%, single-pass yield 97.52%, total degradation impurity content 0.58%, 6-month storage decay 0.92%, product slightly yellowed, high temperature conditions directly induced a large number of hydantoin hydrolysis side reactions, proving that precise low temperature isothermal control is the core key to suppressing side reactions.

[0043] Comparative Example 4

[0044] The remaining parameters are the same as in Example 1, except that the material residence time is extended to 25 seconds to simulate the production condition of excessively long residence time in conventional microchannels.

[0045] Test results: Product purity 98.63%, single-pass yield 98.21%, total degradation impurity content 0.25%, 6-month storage decay 0.53%; the strong alkaline system still caused trace degradation even after prolonged residence, which demonstrates the inventiveness and necessity of the 8-12s transient reaction of this invention.

[0046] Data Comparison Summary

[0047] Based on the measured data from the above multiple examples and comparative studies, it is clear that simply relying on the conventional neutralization reaction of 5,5-dimethylhydantoin with sodium hydroxide, or directly using general-purpose microchannel equipment for continuous reaction with fixed parameters, cannot effectively solve the practical problems in industrial production. Traditional batch reactor processes have long reaction cycles and uneven heat exchange, easily leading to product hydrolysis and deterioration, high impurity content, low product purity and yield, and significant quality differences between different production batches, resulting in poor product storage stability. Ordinary microchannel processes only simplify the production process and do not precisely control core influencing factors such as fluctuations in industrial alkali concentration, reaction temperature deviations, and material residence time, still resulting in problems such as ratio imbalance and side reaction proliferation, failing to meet the requirements of high-end industrial production. The core improvement of this invention, which distinguishes it from existing conventional processes, lies in addressing the problems existing in industrial mass production by employing online real-time refractive concentration detection combined with flow self-regulation technology to achieve dynamic and precise constant reaction molar ratio, while simultaneously using a microchannel reactor for the reaction. Data shows that this invention can effectively avoid quality deviations caused by fluctuations in raw material concentration, significantly suppress the formation of hydantoin hydrolysis byproducts, and significantly improve product purity, yield, and transmittance. It also greatly improves batch consistency and long-term storage stability. Compared to traditional processes and conventional microchannel processes, this invention forms a complete optimized process suitable for stable and high-quality industrial production, possessing substantial innovative and industrial practical value.

Claims

1. An industrial method for producing 5,5-dimethylhydantoin disodium salt, characterized in that, Includes the following steps: S1. Pulverize 5,5-dimethylhydantoin with a purity ≥99.0% to 80-120 mesh, and prepare a suspension with a mass fraction of 22%-28% by mixing it with high-purity deionized water with a conductivity ≤5μS / cm. Stir at 22℃ for 30 min. S2. The silicon carbide microchannel reactor is pre-cooled to 20-25℃ and kept at a constant temperature. The single-channel pore size of the reactor is 0.8-1.2mm, and the specific surface area is ≥1200m² / m³. S3. An online refractometer is used to detect the actual concentration of industrial liquid alkali in real time. The control system feeds back and automatically adjusts the alkali feed flow rate to keep the molar ratio of 5,5-dimethylhydantoin to NaOH constant at 1:2.

02. The 5,5-dimethylhydantoin suspension and liquid alkali are fed synchronously and continuously through dual metering pumps and reacted in the microchannel for 8-12 seconds to complete the neutralization and salt formation. S4. The reaction discharge is filtered online to remove solid impurities, and the filtrate is stirred and matured at 20°C. S5. The aging liquid is concentrated under vacuum, crystallized, and dried to obtain the solid product of 5,5-dimethylhydantoin disodium salt.

2. The method according to claim 1, characterized in that, In step S1, the stirring speed is 150 r / min.

3. The method according to claim 1, characterized in that, In step S2, the isothermal stabilization time is 30 min, and the reaction temperature deviation is ≤ ±0.5℃.

4. The method according to claim 1, characterized in that, In step S3, the feed accuracy of the dual-metering pump is ±0.5%, and the feed flow rate of the 5,5-dimethylhydantoin suspension is 120-180 L / h.

5. The method according to claim 1, characterized in that, In step S4, an online filtration process using a 0.2μm titanium alloy precision filter is employed, with a curing time of 20 minutes.

6. The method according to claim 1, characterized in that, In step S5, the vacuum concentration is performed at a vacuum level of -0.085 to -0.09 MPa, a vessel temperature of ≤55℃, a crystallization temperature of 5 to 10℃, a time of 2 hours, and a drying temperature of 50℃.

7. The 5,5-dimethylhydantoin disodium salt prepared by the method according to any one of claims 1 to 6, characterized in that, Purity ≥ 99.2%, yield ≥ 99.5%, content decay < 0.2% after 6 months of storage at room temperature in a sealed container.

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