Methyl carbamate finished product crystallization method
By mixing the reaction crude product of methyl carbamate with the extract, rotary evaporation and concentration under reduced pressure, and adding crystallization additives during cooling and crystallization, the problem of insufficient crystallization purity and efficiency of methyl carbamate in urea alcoholylation method is solved. Achieve efficient and pure crystallization of finished methyl carbamate.
Patent Information
- Application Number
- CN202411717357.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-11-27
- Publication Date
- 2025-02-25
AI Technical Summary
During the preparation of methyl carbamate by urea alcoholylation, the crystal purity of methyl carbamate is insufficient and the crystallization efficiency is not high.
A method for crystallization of methyl carbamate finished product, including mixing the crude reaction product of methyl carbamate with the extract, rotary evaporation and concentration under reduced pressure, and then adding crystallization additives to the concentrated mixture solution to cool and crystallize, and finally The finished methyl carbamate was obtained by suction filtration and drying under reduced pressure.
The crystallization efficiency and purity of the finished product of methyl carbamate is improved, the separation process is simplified, energy consumption is reduced, and the product production efficiency is improved.
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Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of synthesizing methyl carbamate, and in particular relates to a method for crystallizing a methyl carbamate finished product. Background Art
[0002] Methyl carbamate is not only an important raw material for insecticides and herbicides, but also an important intermediate for drug synthesis. It is widely used in various fields such as pesticides, medicines, resin modification, fabric finishing, powder coatings, etc. At present, with the increasing social requirements for green chemistry and environmental protection, the method of preparing methyl carbamate by urea alcoholysis not only has abundant raw material sources and simple reaction steps, but also does not produce highly toxic substances during the production process. The safety of the reaction device is high, which can meet the needs of contemporary society and is widely used in production.
[0003] However, the urea alcoholysis method also has certain defects. For example, the production of methyl carbamate by this method is accompanied by side reactions. The by-products produced by the side reactions are difficult to separate after mixing with methyl carbamate, which is not conducive to the crystallization process of the finished product of methyl carbamate and the improvement of the purity of methyl carbamate crystals. Summary of the invention
[0004] The object of the present invention is to provide a method for crystallizing a methyl carbamate finished product, so as to solve the problems of insufficient purity of methyl carbamate crystals and low crystallization efficiency in the process of preparing methyl carbamate by urea alcoholysis.
[0005] The purpose of the present invention can be achieved by the following technical solutions:
[0006] The present application provides a method for crystallizing a methyl carbamate finished product, comprising the following process steps:
[0007] S1. The crude product of methyl carbamate was mixed with the extract to obtain a mixed solution, and the mixed solution was concentrated by rotary evaporation under reduced pressure, and the dissolution and concentration time was 0.5 to 1 h;
[0008] S2. Add a crystallization aid to the concentrated mixture, cool it to a temperature of 0.1 to 0.2 ° C / min until crystals appear, and maintain the crystallization temperature for 30 to 40 min;
[0009] S3. After the constant temperature is completed, the temperature is lowered to 20-25°C at a rate of 0.5-1°C / min, and then vacuum filtration and drying are performed to obtain the finished methyl carbamate crystals.
[0010] Preferably, the drying temperature in step S3 is 40-50°C.
[0011] Preferably, the crude product of methyl carbamate is prepared according to the following process steps: urea and methanol in a molar ratio of 1:(6-8) are mixed and put into a reactor, stirred for reaction and the temperature is increased to 155-165°C, and the reaction is carried out for 2-3 hours. During the reaction, the generated ammonia gas is discharged 2-3 times. After the reaction is completed, stirring is stopped, and the mixture is naturally cooled to room temperature to obtain a crude product solution; the crude product solution is distilled at 70-80°C, and then dried to obtain the crude product of methyl carbamate.
[0012] The present application adopts urea alcoholysis to prepare a crude reaction product of methyl carbamate. By adopting the above technical scheme, the cooling-dissolution crystallization process of the crude reaction product of methyl carbamate is improved, thereby improving the finished product crystallization efficiency and purity of methyl carbamate. Specifically, the crude product solution obtained by the reaction of urea and methanol is distilled, and the excess methanol is removed to obtain a crude reaction product of methyl carbamate. Further, the crude reaction product of methyl carbamate is added to the extract, dissolved, and concentrated by reduced pressure rotary evaporation. By evaporating part of the extract during the evaporation and concentration process, the concentration of the methyl carbamate product in the solution can be increased, so that the methyl carbamate is kept in a saturated state as much as possible, which is conducive to the subsequent formation of methyl carbamate crystals.
[0013] The concentrated mixed solution is then cooled and crystallized, and a crystallization aid is added during this process. The addition of the crystallization aid can help methyl carbamate form crystals with complete structures, accelerate the growth process of the crystals, and strictly control the impurities and defects in methyl carbamate; after the crystals are produced, the crystals are grown at a constant temperature for a period of time, which is beneficial to maintaining the integrity and dimensional stability of the methyl carbamate crystals and improving the purity of the methyl carbamate crystals.
[0014] After the crystallization is completed, vacuum distillation can achieve good solid-liquid separation, separate the methyl carbamate crystals from the extract, greatly shorten the separation time, and no further high-speed centrifugal separation is required at low temperature, which reduces the separation energy consumption of the product and improves the production efficiency of the product. At a drying temperature of 40 to 50°C, methyl carbamate has high chemical stability and is not prone to decomposition or changes in physical form.
[0015] Preferably, the extract is chloroform and n-hexane in a mass ratio of 1:(3-4).
[0016] Preferably, the mass ratio of the extract to the crude reaction product of methyl carbamate is 100:(30-50).
[0017] By adopting the above technical solution, the extract is a mixture of chloroform and n-hexane. Chloroform is a good solvent for methyl carbamate. Methyl carbamate has high solubility in chloroform and is easy to separate. At the same time, n-hexane is mixed in chloroform. By utilizing the difference in solubility of methyl carbamate and other byproducts in the reaction, such as biuret, in chloroform and n-hexane, impurities can be effectively removed, the solubility of methyl carbamate can be enhanced, the product can be separated and impurities can be removed, and the extraction efficiency and crystal purity of the methyl carbamate finished product crystal can be improved. In addition, n-hexane can well regulate the viscosity of chloroform, improve the fluidity of the extract, and facilitate subsequent separation and recovery.
[0018] Preferably, the pressure of reduced pressure evaporation concentration in step S3 is 0.08-0.09 MPa and the temperature is 45-50°C.
[0019] By adopting the above technical scheme, after the crude reaction product of methyl carbamate is mixed with the extract, the solution is evaporated and concentrated under reduced pressure, and the temperature is controlled within a reduced range to avoid inducing side reactions or thermal decomposition. The reduced pressure condition improves the evaporation efficiency of the extract, and the extract can be removed more efficiently, achieving the purpose of concentration more quickly; concentration can increase the concentration of the solute in the solution, namely methyl carbamate, which is beneficial to controlling and promoting the subsequent formation of crystal nuclei and the growth of crystals, forming larger and uniform crystals, and improving the crystallization efficiency as well as the purity and quality of the finished crystals.
[0020] Preferably, the crystallization aid is long alkyl modified carboxymethyl cellulose.
[0021] Preferably, the raw materials of the long alkyl modified carboxymethyl cellulose include carboxymethyl cellulose and long alkyl acyl chloride in a mass ratio of 1:(3-4).
[0022] Preferably, the long alkyl acid chloride is a C12-C18 alkyl acid chloride.
[0023] Preferably, the mass ratio of the crystallization aid to the extract is (0.05-0.1):100.
[0024] By adopting the above technical solution, in the production process of methyl carbamate, by-products such as biuret and dimethyl carbonate are formed. These by-products and impurities such as urea that are not reacted may exist in the crude reaction product of methyl carbamate mixed with the extract. These impurities will affect the purity of the final methyl carbamate finished crystal. Through the selection of the extract in the early stage and the effect of reduced pressure evaporation and concentration, methyl carbamate can be partially separated from these impurities. Adding a crystallization aid to the mixed solution before cooling and crystallization can well separate impurities during the crystallization process and improve the formation of crystals. Specifically:
[0025] On the one hand, the addition of long alkyl modified carboxymethyl cellulose will not introduce other impurity ions and affect the purity of methyl carbamate. After the addition of long alkyl modified carboxymethyl cellulose, it can be adsorbed on the various crystal faces of the formed crystals during the crystallization process of methyl carbamate, hindering the attachment of impurity molecules on the crystal surface, reducing the interaction between impurity molecules and the crystal surface, and can also wash away the impurities adsorbed on the crystal surface; and the addition of long alkyl modified carboxymethyl cellulose can reduce surface tension, and can effectively inhibit the crystallization process of impurities such as urea and biuret, thereby improving the finished crystal purity of methyl carbamate.
[0026] On the other hand, the adsorption of long alkyl modified carboxymethyl cellulose on the crystal surface can not only hinder the attachment of impurity molecules, but also reduce the interaction between the formed crystals, provide good growth conditions for the growth of crystals, increase the fluidity of the mixed solution, reduce the generation of pseudocrystals or sticky crystals in the crystallization process of methyl carbamate finished products, and effectively improve the state of the formed crystals. At the same time, the crystallization aid can affect the nucleation process of the crystal. The fibrous structure of long alkyl modified carboxymethyl cellulose can provide additional crystallization sites for the crystallization process of methyl carbamate, reduce the energy barrier of the formed crystal nucleus, improve the nucleation conditions and nucleation efficiency of the crystal, and make the crystallization process easier to start. In addition, the groups on the carboxymethyl cellulose chain and the long alkyl chain segments can interact with the molecules of methyl carbamate, help form the initial crystal nucleus, and stabilize the crystal structure being formed, which is conducive to the rapid growth of the crystal of methyl carbamate finished products and improve the integrity of the crystals. After the long alkyl modification, the carboxymethyl cellulose has a certain hydrophobicity, and the compatibility with the extract is increased, which improves the dispersibility of methyl carbamate in the mixed solution, reduces the collision and aggregation between molecules, and is conducive to the crystallization of methyl carbamate finished products.
[0027] Preferably, the long alkyl modified carboxymethyl cellulose is prepared according to the following method: carboxymethyl cellulose and long alkyl acyl chloride are added to a solvent, the temperature is raised to 60-70° C. after mixing, an alkaline catalyst is added, the mixture is stirred for reaction for 4-5 hours, and then cooled to room temperature, and then the long alkyl modified carboxymethyl cellulose is obtained by suction filtration, washing and drying.
[0028] Preferably, the degree of substitution DS of the carboxymethyl cellulose is 0.6 to 1.2.
[0029] Preferably, the solvent includes a combination of one or more of n-heptane, dimethyl sulfoxide, and N,N-dimethylformamide.
[0030] Preferably, the alkaline catalyst comprises a combination of one or more of pyridine, triethylamine, sodium hydroxide and potassium carbonate.
[0031] By adopting the above technical scheme, under the action of a catalyst, the hydroxyl groups on the carboxymethyl cellulose molecular chain can undergo an esterification reaction with the long alkyl acyl chloride, and the long alkyl chain segments are grafted onto the carboxymethyl cellulose molecular chain, thereby improving the hydrophobicity of the carboxymethyl cellulose and further improving the compatibility of the crystallization aid in the extract; at the same time, other hydrophilic groups on the carboxymethyl cellulose can interact with the methyl carbamate in the mixed solution, including hydrogen bonding and electrostatic attraction, so that the crystallization aid can be smoothly adsorbed on the crystals of the methyl carbamate, thereby hindering the attachment of impurity molecules, improving the purity of the finished product crystals, and at the same time helping to form initial crystallization nuclei, stabilizing the crystal structure being formed, and improving the crystallization efficiency.
[0032] Beneficial effects of the present invention:
[0033] 1. In the crystallization process of methyl carbamate in the present application, a mixture of chloroform and n-hexane is selected as the extract. By utilizing the difference in solubility, the product can be analyzed and impurities can be removed. The mixed solution is then concentrated by rotary evaporation under reduced pressure, which can efficiently remove part of the extract and increase the concentration of methyl carbamate in the mixed solution, which is beneficial to control and promote the subsequent formation of crystal nuclei and crystal growth, and improve the crystallization efficiency as well as the purity and quality of the finished crystals.
[0034] 2. The present application further adds a crystallization aid during the crystallization process of methyl carbamate. The crystallization aid is a long-alkyl modified carboxymethyl cellulose, which can be adsorbed on the crystal surface of methyl carbamate, hinder the attachment of by-products and impurity molecules such as unreacted urea to the crystal surface, and can effectively inhibit the crystallization process of impurity molecules, thereby improving the purity of the crystallization of the methyl carbamate finished product; at the same time, the long-chain alkyl modified carboxymethyl cellulose has a certain hydrophobicity and good compatibility with the extract, which can help reduce the collision and aggregation between methyl carbamate molecules and facilitate the smooth progress of the crystallization process; the fibrous structure of the long-alkyl modified carboxymethyl cellulose can also provide additional crystallization sites for the crystallization process of methyl carbamate, reduce the energy barrier of the formed crystal nucleus, improve the nucleation conditions and nucleation efficiency of the crystal, make the crystallization process easier to start, and thus improve the crystallization efficiency of the methyl carbamate finished product. DETAILED DESCRIPTION
[0035] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.
[0036] Preparation Example
[0037] Preparation Example 1: A long alkyl modified carboxymethyl cellulose is prepared according to the following method:
[0038] 10 g of carboxymethyl cellulose (DS=0.9) and 30 g of octadecyl chloride were added to 250 ml of N,N-dimethylformamide, the temperature was raised to 70°C after mixing, 0.5 g of sodium hydroxide was added, the mixture was stirred for 4 h, and then cooled to room temperature. The long alkyl modified carboxymethyl cellulose was obtained by filtration, washing and drying.
[0039] Preparation Example 2, a long alkyl modified carboxymethyl cellulose, is different from Preparation Example 1 only in that the added amount of octadecyl chloride is 40 g.
[0040] Preparation Example 3, a long alkyl-modified carboxymethyl cellulose, is different from Preparation Example 1 only in that an equal amount of dodecanoyl chloride is used to replace octadecyl chloride.
[0041] Preparation Example 4, a long alkyl modified carboxymethyl cellulose, is different from Preparation Example 1 only in that octadecyl chloride is replaced by an equal amount of octyl chloride.
[0042] Example
[0043] Embodiment 1, a method for crystallizing methyl carbamate finished product, comprising the following process steps:
[0044] S1. Mix 1 kg urea and 3.7 kg methanol in a reaction kettle at a molar ratio of 1:7, stir the reaction and raise the temperature to 160°C for 3 hours. During the reaction, the generated ammonia gas is discharged 3 times. After the reaction is completed, stirring is stopped, and the mixture is naturally cooled to room temperature to obtain a crude product solution;
[0045] S2. The crude product solution was distilled at 80°C, and then dried to obtain a crude product of methyl carbamate;
[0046] S3. The crude product of methyl carbamate in a mass ratio of 40:100 was mixed with the extract to obtain a mixed solution, wherein the extract was a mixed solution of chloroform and n-hexane in a mass ratio of 1:4; the mixed solution was concentrated by rotary evaporation under reduced pressure, the dissolution concentration time was 1h, wherein the pressure of the rotary evaporation under reduced pressure was 0.09MPa, and the temperature was 50°C;
[0047] S4. Adding the long alkyl modified carboxymethyl cellulose prepared in Preparation Example 1 to the concentrated mixed solution, wherein the mass ratio of the long alkyl modified carboxymethyl cellulose to the extract is 0.08:100; cooling at a rate of 0.1°C / min to crystallization, and maintaining the crystallization temperature for 30min;
[0048] S5. After the constant temperature is completed, the temperature is lowered to 25°C at a rate of 0.5°C / min, and then vacuum filtration and drying are performed to obtain the finished methyl carbamate crystals.
[0049] Embodiment 2, a method for crystallizing methyl carbamate finished product, comprising the following process steps:
[0050] S1. Mix 1 kg urea and 3.7 kg methanol in a reaction kettle at a molar ratio of 1:7, stir the reaction and raise the temperature to 160°C for 3 hours. During the reaction, the generated ammonia gas is discharged 3 times. After the reaction is completed, stirring is stopped, and the mixture is naturally cooled to room temperature to obtain a crude product solution;
[0051] S2. The crude product solution was distilled at 80°C, and then dried to obtain a crude product of methyl carbamate;
[0052] S3. The crude product of methyl carbamate in a mass ratio of 30:100 was mixed with the extract to obtain a mixed solution, wherein the extract was a mixed solution of chloroform and n-hexane in a mass ratio of 1:3; the mixed solution was concentrated by rotary evaporation under reduced pressure, and the dissolution and concentration time was 0.5h, wherein the pressure of the rotary evaporation under reduced pressure was 0.09MPa and the temperature was 45°C;
[0053] S4. Adding the long alkyl modified carboxymethyl cellulose prepared in Preparation Example 1 to the concentrated mixed solution, wherein the mass ratio of the long alkyl modified carboxymethyl cellulose to the extract is 0.05:100; cooling at a rate of 0.1°C / min to crystallization, and maintaining the crystallization temperature for 30min;
[0054] S5. After the constant temperature is completed, the temperature is lowered to 25°C at a rate of 0.5°C / min, and then vacuum filtration and drying are performed to obtain the finished methyl carbamate crystals.
[0055] Embodiment 3, a method for crystallizing methyl carbamate finished product, comprising the following process steps:
[0056] S1. Mix 1 kg urea and 3.7 kg methanol in a reaction kettle at a molar ratio of 1:7, stir the reaction and raise the temperature to 160°C for 3 hours. During the reaction, the generated ammonia gas is discharged 3 times. After the reaction is completed, stirring is stopped, and the mixture is naturally cooled to room temperature to obtain a crude product solution;
[0057] S2. The crude product solution was distilled at 80°C, and then dried to obtain a crude product of methyl carbamate;
[0058] S3. The crude product of methyl carbamate in a mass ratio of 50:100 was mixed with the extract to obtain a mixed solution, wherein the extract was a mixed solution of chloroform and n-hexane in a mass ratio of 1:4; the mixed solution was concentrated by rotary evaporation under reduced pressure, the dissolution concentration time was 1h, wherein the pressure of the rotary evaporation under reduced pressure was 0.08MPa, and the temperature was 50°C;
[0059] S4. Adding the long alkyl modified carboxymethyl cellulose prepared in Preparation Example 2 to the concentrated mixed solution, wherein the mass ratio of the long alkyl modified carboxymethyl cellulose to the extract is 0.1:100; cooling at a rate of 0.1°C / min to crystallize, and maintaining the crystallization temperature for 30min;
[0060] S5. After the constant temperature is completed, the temperature is lowered to 25°C at a rate of 0.5°C / min, and then vacuum filtration and drying are performed to obtain the finished methyl carbamate crystals.
[0061] Example 4, a method for crystallizing a methyl carbamate product, is different from Example 1 only in that the long alkyl modified carboxymethyl cellulose prepared in Preparation Example 1 is replaced by an equal amount of the long alkyl modified carboxymethyl cellulose prepared in Preparation Example 3.
[0062] Example 5, a method for crystallizing a methyl carbamate product, is different from Example 1 only in that an equal amount of long alkyl modified carboxymethyl cellulose prepared in Preparation Example 4 is used to replace the long alkyl carboxymethyl cellulose prepared in Preparation Example 1.
[0063] Example 6, a method for crystallizing a methyl carbamate product, is different from Example 1 only in that the mass ratio of the long alkyl modified carboxymethyl cellulose obtained in Preparation Example 1 to the extract is 0.03:100.
[0064] Example 7, a method for crystallizing a methyl carbamate product, is different from Example 1 only in that the mass ratio of the long alkyl modified carboxymethyl cellulose obtained in Preparation Example 1 to the extract is 0.12:100.
[0065] Comparative Example
[0066] Comparative Example 1, a method for crystallizing a methyl carbamate product, is different from Example 1 only in that an extract obtained by mixing chloroform and n-hexane in a mass ratio of 1:4 is replaced by an equal amount of chloroform.
[0067] Comparative Example 2, a method for crystallizing a methyl carbamate finished product, differs from Example 1 only in that step S3 is performed according to the following method: a crude reaction product of methyl carbamate in a mass ratio of 40:100 is mixed with an extract to obtain a mixed solution, wherein the extract is a mixed solution of chloroform and n-hexane in a mass ratio of 1:4; the temperature of the mixed solution is raised to 50°C, and stirred and dissolved for 1 hour.
[0068] Comparative Example 3 is a method for crystallizing a methyl carbamate product, which is different from Example 1 only in that an equal amount of carboxymethyl cellulose (DS=0.9) is used to replace the long alkyl modified carboxymethyl cellulose prepared in Preparation Example 1.
[0069] Comparative Example 4 is a method for crystallizing a methyl carbamate product, which is different from Example 1 only in that the long alkyl-modified carboxymethyl cellulose prepared in Preparation Example 1 is replaced by an equal amount of dodecylphenol polyoxyethylene ether.
[0070] Comparative Example 5, a method for crystallizing a methyl carbamate product, comprising the following process steps:
[0071] S1. Mix 1 kg urea and 3.7 kg methanol in a reaction kettle at a molar ratio of 1:7, stir the reaction and raise the temperature to 160°C for 3 hours. During the reaction, the generated ammonia gas is discharged 3 times. After the reaction is completed, stirring is stopped, and the mixture is naturally cooled to room temperature to obtain a crude product solution;
[0072] S2. The crude product solution was distilled at 80°C, and then dried to obtain a crude product of methyl carbamate;
[0073] S3. The crude product of methyl carbamate in a mass ratio of 40:100 was mixed with the extract to obtain a mixed solution, wherein the extract was a mixed solution of chloroform and n-hexane in a mass ratio of 1:4; the mixed solution was concentrated by rotary evaporation under reduced pressure, the dissolution concentration time was 1h, wherein the pressure of the rotary evaporation under reduced pressure was 0.09MPa, and the temperature was 50°C;
[0074] S4. The concentrated mixed solution was cooled at a rate of 0.1 ° C / min to the crystallization temperature, and the crystallization temperature was maintained for 30 min;
[0075] S5. After the constant temperature is completed, the temperature is lowered to 25°C at a rate of 0.5°C / min, and then vacuum filtration and drying are performed to obtain the finished methyl carbamate crystals.
[0076] Performance testing
[0077] The crude reaction product of methyl carbamate and the finished methyl carbamate crystals obtained in the examples and comparative examples were analyzed by gas chromatography, wherein the content of methyl carbamate (MC) was mainly analyzed by FID (hydrogen flame ionization) detector, and the recovery rate of the finished methyl carbamate crystals was calculated.
[0078] The above test results are shown in Table 1:
[0079] Table 1 Sample analysis results
[0080]
[0081]
[0082] According to Table 1, in combination with Example 1 and Example 2 to Example 4, it can be seen that the content of methyl carbamate in the finished crystals of Example 2 to Example 4 and the recovery rate of methyl carbamate are not much different from those of Example 1. The difference between Example 2 to Example 4 and Example 1 is only that the raw materials and the process parameters of the crystallization process are adjusted within the required range, indicating that the finished product crystallization method in Example 2 to Example 4 has no significant effect on the crystallization rate and purity of the obtained methyl carbamate finished product.
[0083] Combining Example 1 and Example 5, it can be seen that the content of methyl carbamate in the finished crystals of Example 5 and the recovery rate of methyl carbamate are slightly lower than those of Example 1. Compared with Example 1, the crystallization aid used in Example 5 is obtained by modifying carboxymethyl cellulose with a short-chain alkyl acyl chloride. The shortening of the alkyl chain segment is not conducive to the improvement of the hydrophobicity of carboxymethyl cellulose. In the process of mixing with the extract, the compatibility of the crystallization aid is poor, and the improvement effect on the nucleation process and crystallization process of methyl carbamate is reduced.
[0084] Combining Example 1, Example 6, Example 7 and Comparative Example 5, it can be seen that the content of methyl carbamate in the finished crystals of Example 6, Example 7 and Comparative Example 5 and the recovery rate of methyl carbamate are lower than those of Example 1, especially Comparative Example 5, which is significantly lower than that of Example 1. The difference between Example 6, Example 7 and Comparative Example 5 and Example 1 is that the addition amount of the crystallization aid is adjusted. In Example 6, the addition amount is reduced, the effect of improving the nucleation and crystallization process performance of methyl carbamate is reduced, and the effect of removing impurities in the solution is weakened, resulting in a decrease in the purity of the finished crystals of methyl carbamate obtained. In Comparative Example 5, no crystallization aid is added, and the improvement effect on the removal of impurities and crystal formation is significantly reduced; while in Example 7, the addition amount is increased, and the excessive addition of the crystallization aid can not only inhibit the crystallization process of impurities, but also inhibit the crystallization process of methyl carbamate in turn, reducing the yield of methyl carbamate.
[0085] Combining Example 1 and Comparative Example 1, it can be seen that the content of methyl carbamate in the finished crystals of Comparative Example 1 and the recovery rate of methyl carbamate are lower than those of Example 1. The extract used in Comparative Example 1 does not add n-hexane to mix with chloroform, the early removal effect of impurity molecules is weakened, the purity of methyl carbamate crystals is reduced, and there is no n-hexane to regulate the viscosity of chloroform, which is not conducive to the subsequent separation of the extract and the finished crystals of methyl carbamate, and the recovery rate of methyl carbamate is reduced.
[0086] Combining Example 1 and Comparative Example 2, it can be seen that the content of methyl carbamate in the finished crystals of Comparative Example 2 and the recovery rate of methyl carbamate are significantly lower than those of Example 1. Compared with Example 1, Comparative Example 2 did not perform reduced pressure rotary evaporation concentration treatment, resulting in a decrease in the dissolved concentration of methyl carbamate in the mixed solution of methyl carbamate and the extract for crystallization, resulting in a significant decrease in the recovery rate, and was not conducive to promoting the crystallization process of methyl carbamate, and the purity of the obtained finished crystals was significantly reduced.
[0087] Combining Example 1, Comparative Example 3 and Comparative Example 4, it can be seen that the content of methyl carbamate in the finished crystals of Comparative Example 3 and Comparative Example 4 and the recovery rate of methyl carbamate are lower than those of Example 1. In Comparative Example 3, carboxymethyl cellulose is not modified. On the one hand, the compatibility between the crystallization aid and the extract is extremely low, making it difficult to control and help the nucleation and crystallization process of methyl carbamate. On the other hand, without the interaction of the long alkyl chain segments, the removal of impurities and the effect of hindering the attachment of impurity molecules to the methyl carbamate crystals are reduced, and the purity of the finished crystals is significantly reduced. In Comparative Example 4, the surfactant dodecylphenol polyoxyethylene ether is used to replace the long alkyl modified carboxymethyl cellulose. Compared with the long alkyl modified carboxymethyl cellulose, the surfactant can only hinder the attachment of impurity molecules to the methyl carbamate crystals to a certain extent. The long alkyl modified carboxymethyl cellulose can also use its unique fiber mesh structure to provide additional crystallization sites for the crystallization process of methyl carbamate, thereby improving the nucleation conditions and nucleation efficiency of methyl carbamate and stabilizing the crystal structure being formed.
[0088] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.
[0089] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.
Claims
1. A method for crystallizing a methyl carbamate product, characterized in that: The process steps include: S1. The crude product of methyl carbamate was mixed with the extract to obtain a mixed solution, and the mixed solution was concentrated by rotary evaporation under reduced pressure, and the dissolution and concentration time was 0.5 to 1 h; S2. Add a crystallization aid to the concentrated mixture, cool it to a temperature of 0.1 to 0.2 ° C / min until crystals appear, and maintain the crystallization temperature for 30 to 40 min; S3. After the constant temperature is completed, the temperature is lowered to 20-25°C at a rate of 0.5-1°C / min, and then vacuum filtration and drying are performed to obtain the finished methyl carbamate crystals.
2. The method for crystallizing methyl carbamate finished product according to claim 1, characterized in that: The crude reaction product of methyl carbamate is prepared according to the following process steps: urea and methanol in a molar ratio of 1:(6-8) are mixed and put into a reactor, stirred for reaction and the temperature is increased to 155-165° C., and the reaction is carried out for 2-3 hours. During the reaction, the generated ammonia gas is discharged 2-3 times. After the reaction is completed, stirring is stopped, and the mixture is naturally cooled to room temperature to obtain a crude product solution; the crude product solution is distilled at 70-80° C., and then dried to obtain the crude reaction product of methyl carbamate.
3. The method for crystallizing methyl carbamate finished product according to claim 1, characterized in that: The extract is chloroform and n-hexane in a mass ratio of 1:(3-4).
4. The method for crystallizing methyl carbamate finished product according to claim 1, characterized in that: The mass ratio of the extract to the crude reaction product of methyl carbamate is 100:(30-50).
5. The method for crystallizing methyl carbamate finished product according to claim 1, characterized in that: The pressure of reduced pressure evaporation concentration in step S3 is 0.08-0.09 MPa and the temperature is 45-50°C.
6. The method for crystallizing methyl carbamate finished product according to claim 1, characterized in that: The crystallization aid is long alkyl modified carboxymethyl cellulose.
7. The method for crystallizing methyl carbamate finished product according to claim 6, characterized in that: The raw materials of the long alkyl modified carboxymethyl cellulose include carboxymethyl cellulose and long alkyl acyl chloride in a mass ratio of 1:(3-4).
8. The method for crystallizing methyl carbamate finished product according to claim 7, characterized in that: The long alkyl acyl chloride is a C12-C18 alkyl acyl chloride.
9. The method for crystallizing methyl carbamate finished product according to claim 7, characterized in that: The long alkyl modified carboxymethyl cellulose is prepared according to the following method: carboxymethyl cellulose and long alkyl acyl chloride are added into a solvent, the temperature is raised to 60-70° C. after mixing, an alkaline catalyst is added, the mixture is stirred for reaction for 4-5 hours, and then the mixture is cooled to room temperature, and then the long alkyl modified carboxymethyl cellulose is obtained by suction filtration, washing and drying.
10. The method for crystallizing methyl carbamate finished product according to claim 1, characterized in that: The mass ratio of the crystallization aid to the extract is (0.05-0.1):100.