Methyl carbamate synthesis post-treatment method
The post-treatment method of synthesis of methyl carbamate in urea alcoholylation, including high-temperature treatment and the use of zinc ion-loaded molecular sieve, solves the problem of reaction residue recovery, and improves the purity of the product and the environmental protection of the process.
Patent Information
- Application Number
- CN202411694514.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-11-25
- Publication Date
- 2025-02-14
AI Technical Summary
During the synthesis of methyl carbamate in urea alcoholylation, side reactions are difficult to suppress, resulting in a large number of reaction residues, resulting in waste of resources and environmental pollution.
A post-treatment method for methyl carbamate synthesis, including atmospheric distillation to remove methanol raw materials, and underpressure distillation to obtain methyl carbamate product and reaction production residue. The residue was then treated with a temperature under a nitrogen atmosphere and the unreacted urea was converted into biuret. Then, zinc ion-loaded molecular sieve was added to the pretreatment solution, and the coordination reaction was carried out to adsorb impurities, and finally the high-purity methyl carbamate was recovered by recrystallization.
Effectively recover and improve the purity of methyl carbamate, reduce resource waste and environmental pollution, and improve the environmental protection and economicality of the synthesis process.
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Figure BDA0005151789220000091
Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of methyl carbamate synthesis, and particularly relates to a post-synthesis treatment method for methyl carbamate. Background Art
[0002] Methyl carbamate is an important fine chemical with high chemical activity and certain biological activity. It is the simplest compound of carbamates and is widely used in the fields of medicine, pesticides, dyes and compound intermediates.
[0003] There are many methods for synthesizing methyl carbamate at present, among which urea alcoholysis is green and environmentally friendly, has simple reaction steps, low raw material cost, and has a very broad market application prospect. However, the urea alcoholysis method is difficult to suppress side reactions during the reaction process, and after the reaction is completed and the methyl carbamate product is separated, there will be a large amount of reaction residues. If it is not recycled, it will not only cause a waste of resources, but also cause serious environmental pollution. Therefore, the post-processing process of the reaction solution is also very important in the process of synthesizing methyl carbamate. Summary of the invention
[0004] The object of the present invention is to provide a post-treatment method for methyl carbamate synthesis, so as to solve the problem of recycling the reaction residue produced by preparing methyl carbamate by urea alcoholysis.
[0005] The purpose of the present invention can be achieved through the following technical solutions:
[0006] The present invention provides a post-treatment method for methyl carbamate synthesis, comprising the following process steps:
[0007] S1. preparing methyl carbamate by alcoholysis of urea to obtain a reaction kettle liquid, distilling the kettle liquid at atmospheric pressure to remove residual methanol raw material, and then distilling under reduced pressure to obtain methyl carbamate product and reaction production residue;
[0008] S2. In a nitrogen atmosphere, the temperature of the reaction residue was raised to 160-170°C, kept constant for 20-30 min, then the temperature was lowered to 140-145°C, and the reaction was continued at a constant temperature for 4-5 h to obtain a pre-treated solution;
[0009] S3. Add zinc ion loaded molecular sieve to the pretreatment solution, adjust the temperature to 35-45 ° C, stir and reflux for 7-8 hours, stand and centrifuge, filter to obtain methyl carbamate residual solution;
[0010] S4. The obtained methyl carbamate residual liquid is recrystallized to obtain the residual methyl carbamate product for recycling.
[0011] Preferably, the addition amount of the zinc ion loaded molecular sieve is 3-6%.
[0012] Preferably, the raw materials for preparing methyl carbamate by urea alcoholysis method include urea and methanol in a molar ratio of 1: (6-8).
[0013] Preferably, the reaction temperature for preparing methyl carbamate by urea alcoholysis is 150-165° C., and the reaction time is 2-3 h.
[0014] In the process of preparing methyl carbamate by urea alcoholysis, urea will condense to form biuret at high temperature. After the reaction is completed, the methanol raw material and the methyl carbamate product are removed by distillation. The reaction residue is mainly composed of unreacted urea, biuret generated by side reactions, and methyl carbamate that has not been completely extracted. At this time, if the methyl carbamate in the reaction residue is directly recovered and subjected to extraction-crystallization treatment, the methyl carbamate extracted from the residue has low purity and cannot be used directly.
[0015] By adopting the above technical scheme, the reaction residue is first heated under a nitrogen atmosphere to react, and the purpose of this step is to thermally condense the unreacted urea in the reaction residue to form biuret. The reaction is divided into two steps. The first step is to quickly start the urea condensation reaction at high temperature, and the second step is to lower the temperature to continue the reaction, while suppressing the side reactions of the condensation reaction, generating biuret compounds as much as possible, and preventing the thermal decomposition of methyl carbamate in the system.
[0016] Secondly, in the pretreatment liquid obtained by the reaction, urea molecules have been converted into biuret. Further, a zinc ion-loaded molecular sieve is added to the pretreatment liquid, and the biuret originally existing in the system and the biuret obtained by the conversion of urea will react with the zinc ions. Specifically, the carbonyl oxygen atom in the biuret will react with the zinc ions loaded on the molecular sieve, and the structure of the formed coordination compound is stable. The biuret in the system is gradually adsorbed on the zinc ion-loaded molecular sieve by the reaction, and then the molecular sieve in the system is removed by centrifugal filtration to obtain a methyl carbamate residual liquid.
[0017] Finally, the residual methyl carbamate solution is recrystallized. At this time, there are no other impurities in the system, and the methyl carbamate obtained by recrystallization has high purity and can be directly recycled.
[0018] If biuret is directly discharged, it will have a toxic effect on the germination and growth of seeds in the ecosystem. The post-treatment method provided by the present invention can not only improve the recovery rate of methyl carbamate, but also prevent the biuret in the residue from polluting the environment.
[0019] Preferably, the raw materials of the zinc ion loaded molecular sieve include NaY type molecular sieve and soluble zinc salt in a mass ratio of 1:(2-2.5).
[0020] Preferably, the soluble zinc salt includes a combination of one or more of zinc sulfate heptahydrate, zinc nitrate hexahydrate, zinc acetate dihydrate, and zinc chloride.
[0021] By adopting the above technical scheme, the present invention loads zinc ions by modifying NaY type molecular sieve, and NaY type molecular sieve has a larger effective pore size compared to other molecular sieve types, which is conducive to zinc ions exchanging sodium ions on the molecular sieve, thereby increasing the loading amount of zinc ions. And the content of biuret in the reaction production residue of the present invention is low, and the coordination reaction activity between biuret and zinc ion can be improved by using multi-aperture, large specific surface area, high selectivity and adsorption activity of NaY type molecular sieve, and the enrichment of biuret on zinc ion loaded molecular sieve is accelerated, thereby realizing the removal of biuret in the reaction production residue, and improving the purity of methyl carbamate.
[0022] Preferably, the zinc ion loaded molecular sieve is prepared according to the following method: a soluble zinc salt is added to distilled water to dissolve, and then a NaY type molecular sieve is added, and the mixture is stirred and refluxed at 90 to 100° C. for 4 to 6 hours, and then cooled, filtered, washed and dried to obtain the zinc ion loaded molecular sieve.
[0023] By adopting the above technical solution, soluble zinc salt is dissolved in water to form zinc ions. The molecular sieve has a unique three-dimensional pore structure and a large specific surface area. At a set temperature, zinc ions will exchange ions with sodium ions on the surface of the NaY type molecular sieve, thereby achieving zinc ion loading. The obtained zinc ion loaded molecular sieve has high selectivity and reactivity, which is conducive to the adsorption of biuret on the surface of the molecular sieve and coordination with zinc ions.
[0024] Preferably, the recrystallization to obtain the residual methyl carbamate product comprises the following steps: mixing the methyl carbamate residual liquid with the extract, raising the temperature to 45-50° C., stirring for 50-60 minutes and filtering, cooling the filtrate naturally and standing for 20-40 minutes, then filtering out the methyl carbamate crystals in the solution, and finally drying to obtain the residual methyl carbamate product.
[0025] Preferably, the extracting liquid comprises a combination of one or more of chloroform, dichloromethane and ethyl acetate.
[0026] By adopting the above technical scheme, after removing impurities from the reaction production residue, in order to further effectively recover the methyl carbamate product in the residue, a recrystallization treatment is performed. After the obtained methyl carbamate residual liquid is mixed with the extract, the methyl carbamate is dissolved in the extract, the temperature is appropriately increased to increase the solubility of the methyl carbamate, and then the solution is naturally cooled, and the methyl carbamate will gradually precipitate crystals, thereby realizing the recovery and utilization of the methyl carbamate product in the reaction production residue, and the methyl carbamate product obtained has high purity and no other impurities while improving the yield of methyl carbamate, and can be used directly.
[0027] Beneficial effects of the present invention: the present invention adopts urea alcoholysis method to prepare methyl carbamate, and the generated reaction production residue is post-processed for further recycling. Specifically, the residual urea is first converted into biuret through two-step high-temperature treatment, and then the biuret is adsorbed and coordinated by zinc ion-loaded molecular sieve to remove impurity molecules in the residue, and finally the remaining solution is recrystallized to recover the methyl carbamate in the reaction production residue, which can not only improve the recovery rate of methyl carbamate in the process of synthesizing methyl carbamate, but also improve the purity of the obtained methyl carbamate. DETAILED DESCRIPTION
[0028] 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.
[0029] Preparation Example
[0030] Preparation Example 1: A zinc ion loaded molecular sieve is prepared according to the following method:
[0031] 23g of zinc nitrate hexahydrate was added to 1000ml of distilled water to dissolve, and then 10g of NaY molecular sieve (average specific surface area of 735m 2 / g), stirred and refluxed at 98°C for 5h, and then cooled, filtered, washed and dried to obtain the zinc ion loaded molecular sieve.
[0032] Preparation Example 2, a zinc ion loaded molecular sieve, prepared according to the following method:
[0033] 20 g of zinc sulfate heptahydrate was added to 1000 ml of distilled water to dissolve, and then 10 g of NaY molecular sieve was added, and the mixture was stirred and refluxed at 98° C. for 5 h, and then cooled, filtered, washed and dried to obtain the zinc ion loaded molecular sieve.
[0034] Preparation Example 3, a zinc ion loaded molecular sieve, is different from Preparation Example 1 only in that the amount of zinc nitrate hexahydrate added is 25 g.
[0035] Preparation Example 4, a zinc ion loaded molecular sieve, is different from Preparation Example 1 only in that an equal amount of X-type molecular sieve (particle size of 1.6 to 2.5 mm) is used to replace the NaY-type molecular sieve.
[0036] Preparation Example 5, a zinc ion loaded molecular sieve, is different from Preparation Example 1 only in that the amount of zinc nitrate hexahydrate added is 15 g.
[0037] Preparation Example 6, a zinc ion loaded molecular sieve, is different from Preparation Example 1 only in that the amount of zinc nitrate hexahydrate added is 30 g.
[0038] Example
[0039] Embodiment 1, a method for post-treatment of methyl carbamate synthesis, comprising the following process steps:
[0040] S1. Put urea and methanol in a molar ratio of 1:7 into a high-pressure reactor, set the reaction temperature to 160°C, stir the reaction for 3 hours, discharge the generated ammonia gas 3 times during the reaction, turn off the heating after the reaction, let the reactor cool naturally to room temperature, discharge the material, distill at 75°C and normal pressure to remove the residual methanol raw material, and then distill under reduced pressure at 125°C and -0.93MPa to obtain methyl carbamate product and reaction production residue;
[0041] S2. In a nitrogen atmosphere, the temperature of the reaction residue was raised to 165 ° C, kept constant for 30 min, then the temperature was lowered to 145 ° C, and the reaction was continued at a constant temperature for 4 h to obtain a pre-treated solution;
[0042] S3. 5% of the zinc ion-loaded molecular sieve prepared in Preparation Example 1 was added to the pretreatment solution, the temperature was adjusted to 40 ° C, the reaction was stirred and refluxed for 7h, and after standing, centrifuged and filtered to obtain a residual solution of methyl carbamate;
[0043] S4. The obtained methyl carbamate residual liquid is mixed with chloroform in a volume ratio of 1:1.5, the temperature is raised to 50°C, stirred for 60 minutes and then filtered, the filtrate is naturally cooled and allowed to stand for 30 minutes, then the methyl carbamate crystals in the solution are filtered out, and finally the residual methyl carbamate product is obtained by drying and recycled.
[0044] Embodiment 2, a method for post-treatment of methyl carbamate synthesis, comprising the following process steps:
[0045] S1. Put urea and methanol in a molar ratio of 1:6 into a high-pressure reactor, set the reaction temperature to 165°C, stir the reaction for 2h, discharge the generated ammonia gas 3 times during the reaction, turn off the heating after the reaction, let the reactor cool naturally to room temperature, discharge the material, distill at 75°C and normal pressure to remove the residual methanol raw material, and then distill under reduced pressure at 125°C and -0.93MPa to obtain methyl carbamate product and reaction production residue;
[0046] S2. Under a nitrogen atmosphere, the temperature of the reaction residue was raised to 160 ° C, kept constant for 30 min, then lowered to 145 ° C, and kept constant for 5 h to obtain a pretreated solution;
[0047] S3. 5% of the zinc ion-loaded molecular sieve prepared in Preparation Example 1 was added to the pretreatment solution, the temperature was adjusted to 40 ° C, the reaction was stirred and refluxed for 7h, and after standing, centrifuged and filtered to obtain a residual solution of methyl carbamate;
[0048] S4. The obtained methyl carbamate residual liquid is mixed with chloroform in a volume ratio of 1:1.5, the temperature is raised to 50°C, stirred for 60 minutes and then filtered, the filtrate is naturally cooled and allowed to stand for 30 minutes, then the methyl carbamate crystals in the solution are filtered out, and finally the residual methyl carbamate product is obtained by drying and recycled.
[0049] Embodiment 3, a method for post-treatment of methyl carbamate synthesis, comprising the following process steps:
[0050] S1. Put urea and methanol in a molar ratio of 1:8 into a high-pressure reactor, set the reaction temperature to 150°C, stir the reaction for 3 hours, discharge the generated ammonia gas 3 times during the reaction, turn off the heating after the reaction, let the reactor cool naturally to room temperature, discharge the material, distill at 75°C and normal pressure to remove the residual methanol raw material, and then distill under reduced pressure at 125°C and -0.93MPa to obtain methyl carbamate product and reaction production residue;
[0051] S2. In a nitrogen atmosphere, the temperature of the reaction residue was raised to 170 ° C, kept constant for 20 min, then lowered to 140 ° C, kept constant for 5 h to obtain a pretreated solution;
[0052] S3. 5% of the zinc ion-loaded molecular sieve prepared in Preparation Example 1 was added to the pretreatment solution, the temperature was adjusted to 40 ° C, the reaction was stirred and refluxed for 7h, and after standing, centrifuged and filtered to obtain a residual solution of methyl carbamate;
[0053] S4. The obtained methyl carbamate residual liquid is mixed with chloroform in a volume ratio of 1:1.5, the temperature is raised to 50°C, stirred for 60 minutes and then filtered, the filtrate is naturally cooled and allowed to stand for 30 minutes, then the methyl carbamate crystals in the solution are filtered out, and finally the residual methyl carbamate product is obtained by drying and recycled.
[0054] Example 4, a method for post-treatment of methyl carbamate synthesis, is different from Example 1 only in that, in step S3, 6% of the zinc ion-loaded molecular sieve prepared in Preparation Example 2 is added to the pretreatment solution.
[0055] Example 5, a method for post-treatment of methyl carbamate synthesis, is different from Example 1 only in that, in step S3, 3% of the zinc ion-loaded molecular sieve prepared in Preparation Example 3 is added to the pretreatment solution.
[0056] Example 6, a method for post-treatment of methyl carbamate synthesis, is different from Example 1 only in that the zinc ion-loaded molecular sieve prepared in Preparation Example 1 is replaced by an equal amount of the zinc ion-loaded molecular sieve prepared in Preparation Example 4.
[0057] Example 7, a method for post-treatment of methyl carbamate synthesis, is different from Example 1 only in that the zinc ion-loaded molecular sieve prepared in Preparation Example 1 is replaced by an equal amount of the zinc ion-loaded molecular sieve prepared in Preparation Example 5.
[0058] Example 8, a method for post-treatment of methyl carbamate synthesis, is different from Example 1 only in that the zinc ion-loaded molecular sieve prepared in Preparation Example 1 is replaced by an equal amount of the zinc ion-loaded molecular sieve prepared in Preparation Example 6.
[0059] Example 9, a method for post-treatment of methyl carbamate synthesis, is different from Example 1 only in that the addition amount of the zinc ion-loaded molecular sieve prepared in Preparation Example 1 is 1%.
[0060] Example 10, a method for post-treatment of methyl carbamate synthesis, is different from Example 1 only in that the addition amount of the zinc ion-loaded molecular sieve prepared in Preparation Example 1 is 8%.
[0061] Comparative Example
[0062] Comparative Example 1, a method for post-treatment of methyl carbamate synthesis, is different from Example 1 only in that step S2 is carried out according to the following method: under a nitrogen atmosphere, the temperature of the reaction residue is raised to 165° C., and the reaction is carried out at a constant temperature for 4 hours to obtain a pretreatment liquid.
[0063] Comparative Example 2, a method for post-treatment of methyl carbamate synthesis, is different from Example 1 only in that step S2 is carried out according to the following method: under a nitrogen atmosphere, the temperature of the reaction residue is raised to 145° C., and the reaction is carried out at a constant temperature for 5 hours to obtain a pretreatment liquid.
[0064] Comparative Example 3, a method for post-treatment of methyl carbamate synthesis, comprising the following process steps:
[0065] S1. Put urea and methanol in a molar ratio of 1:7 into a high-pressure reactor, set the reaction temperature to 160°C, stir the reaction for 3 hours, discharge the generated ammonia gas 3 times during the reaction, turn off the heating after the reaction, let the reactor cool naturally to room temperature, discharge the material, distill at 75°C and normal pressure to remove the residual methanol raw material, and then distill under reduced pressure at 125°C and -0.93MPa to obtain methyl carbamate product and reaction production residue;
[0066] S2. Add 5% of the zinc ion-loaded molecular sieve prepared in Preparation Example 1 to the reaction residue, adjust the temperature to 40 ° C, stir and reflux the reaction for 7h, stand and centrifuge, filter to obtain a residual solution of methyl carbamate;
[0067] S4. The obtained methyl carbamate residual liquid is mixed with chloroform in a volume ratio of 1:1.5, the temperature is raised to 50°C, stirred for 60 minutes and then filtered, the filtrate is naturally cooled and allowed to stand for 30 minutes, then the methyl carbamate crystals in the solution are filtered out, and finally the residual methyl carbamate product is obtained by drying and recycled.
[0068] Comparative Example 4 is a method for post-treatment of methyl carbamate synthesis, which is different from Example 1 only in that the zinc ion-loaded molecular sieve prepared in Preparation Example 1 is replaced by an equal amount of NaY molecular sieve.
[0069] Comparative Example 5, a method for post-treatment of methyl carbamate synthesis, comprising the following process steps:
[0070] S1. Put urea and methanol in a molar ratio of 1:7 into a high-pressure reactor, set the reaction temperature to 160°C, stir the reaction for 3 hours, discharge the generated ammonia gas 3 times during the reaction, turn off the heating after the reaction, let the reactor cool naturally to room temperature, discharge the material, distill at 75°C and normal pressure to remove the residual methanol raw material, and then distill under reduced pressure at 125°C and -0.93MPa to obtain methyl carbamate product and reaction production residue;
[0071] S2. The obtained reaction residue was mixed with chloroform in a volume ratio of 1:1.5, the temperature was raised to 50°C, the mixture was stirred for 60 minutes and then filtered. The filtrate was naturally cooled and allowed to stand for 30 minutes, and then the methyl carbamate crystals in the solution were filtered out. Finally, the residual methyl carbamate product was obtained by drying.
[0072] Performance testing
[0073] 1. Calculate the total recovery of methyl carbamate obtained in the embodiments and comparative examples;
[0074] 2. The residual methyl carbamate product finally obtained from the reaction residue in the embodiment and the comparative example was analyzed by gas chromatography, and the content of methyl carbamate (MC) in the product was obtained by FID (hydrogen flame ionization) detector analysis.
[0075] The above test results are shown in Table 1:
[0076] Table 1 Test results
[0077]
[0078] According to Table 1, in combination with Example 1 and Example 2 to Example 5, it can be seen that the recovery rate of the methyl carbamate product of Example 2 to Example 5 and the purity of the methyl carbamate product recovered from the production residue are not significantly changed compared to Example 1. Compared with Example 1, Example 2 to Example 5 are only adjustments within the range of the process parameters in the synthesis and post-treatment of methyl carbamate, so the recovery rate and purity of Example 2 to Example 5 are not much changed compared to Example 1.
[0079] Combining Example 1 and Example 6, it can be seen that the recovery rate and purity of Example 6 are both lower than those of Example 1. In Example 6, X-type molecular sieve is used to replace NaY-type molecular sieve as a carrier of zinc ions, and the number of pores and the reaction activity of X-type molecular sieve are not high. The content of biuret in the reaction production residue in the present invention is not high, and NaY-type molecular sieve can better meet the adsorption and coordination reaction of low-content biuret on the molecular sieve.
[0080] In conjunction with Example 1, Example 7, Example 8 and Comparative Example 4, it can be seen that the recovery and purity of Example 7, Example 8 and Comparative Example 4 are reduced to a certain extent compared to Example 1, and Comparative Example 4 decreases significantly. The zinc ion loading capacity in the zinc ion loaded molecular sieve adopted in Example 7 decreases, and the coordination reaction effect between biuret decreases, and the residual biuret can affect the purity of methyl carbamate in the final methyl carbamate product, and the molecular sieve adopted in Comparative Example 4 does not load zinc ions, and the purity decreases significantly. The addition amount of soluble zinc salt is increased in Example 8, but the active sites on the molecular sieve surface are limited, which is not conducive to the loading of zinc ions, and finally affects the yield and purity of methyl carbamate.
[0081] It can be seen from Example 1, Example 9 and Example 10 that the recovery and purity of Example 9 and Example 10 are all decreased compared to Example 1. In Example 9, the addition of zinc ion-loaded molecular sieve is reduced, and the adsorption coordination effect of biuret in the residue is reduced, and the residual biuret affects the yield and purity. In Example 10, the addition of zinc ion-loaded molecular sieve is increased, and the addition of molecular sieve is too much and agglomerates in the system, which is not conducive to the removal of biuret in the system.
[0082] In combination with Example 1 and Comparative Examples 1 to 3, it can be seen that the yield and purity of Comparative Examples 1 to 3 are significantly reduced compared with those of Example 1. The reason is that, in Comparative Examples 1 to 3, the process parameters of the temperature increase reaction in step S2 are changed compared with Example 1, wherein Comparative Example 1 only performs a high-temperature constant temperature reaction in the first step, resulting in gradual thermal decomposition of methyl carbamate in the system, affecting the yield, and also causing a large number of side reactions, resulting in a decrease in yield. In Comparative Example 2, only a temperature reduction constant temperature reaction is performed in the second step, and the urea condensation reaction rate is slow, which is not conducive to the complete decomposition and subsequent removal of urea, affecting the purity of the obtained methyl carbamate product. In Comparative Example 3, no temperature increase treatment is performed, and urea will continue to remain in the reaction residue, affecting the yield and purity.
[0083] Combining Example 1 and Comparative Example 5, it can be seen that the yield and purity of Comparative Example 5 are significantly lower than those of Example 1. In Comparative Example 5, the reaction residue is directly recrystallized to precipitate methyl carbamate, but the urea and biuret residues in the system will seriously affect the purity of methyl carbamate, resulting in a significant decrease in the yield of methyl carbamate.
[0084] 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.
[0085] 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 post-treatment method for methyl carbamate synthesis, characterized in that: The process steps include: S1. preparing methyl carbamate by alcoholysis of urea to obtain a reaction kettle liquid, distilling the kettle liquid at atmospheric pressure to remove residual methanol raw material, and then distilling under reduced pressure to obtain methyl carbamate product and reaction production residue; S2. In a nitrogen atmosphere, the temperature of the reaction residue was raised to 160-170°C, kept constant for 20-30 min, then the temperature was lowered to 140-145°C, and the reaction was continued at a constant temperature for 4-5 h to obtain a pre-treated solution; S3. Add zinc ion loaded molecular sieve to the pretreatment solution, adjust the temperature to 35-45 ° C, stir and reflux for 7-8 hours, stand and centrifuge, filter to obtain methyl carbamate residual solution; S4. The obtained methyl carbamate residual liquid is recrystallized to obtain the residual methyl carbamate product for recycling.
2. The post-processing method for methyl carbamate synthesis according to claim 1, characterized in that: The raw materials of the zinc ion loaded molecular sieve include NaY type molecular sieve and soluble zinc salt in a mass ratio of 1:(2-2.5).
3. The post-processing method for methyl carbamate synthesis according to claim 2, characterized in that: The soluble zinc salt includes one or more combinations of zinc sulfate heptahydrate, zinc nitrate hexahydrate, zinc acetate dihydrate, and zinc chloride.
4. The post-processing method for methyl carbamate synthesis according to claim 2, characterized in that: The zinc ion loaded molecular sieve is prepared according to the following method: adding a soluble zinc salt to distilled water to dissolve, then adding a NaY type molecular sieve, stirring and refluxing at 90-100° C. for 4-6 hours, and then cooling, filtering, washing and drying to obtain the zinc ion loaded molecular sieve.
5. The post-processing method for methyl carbamate synthesis according to claim 1, characterized in that: The added amount of the zinc ion loaded molecular sieve is 3-6%.
6. The post-processing method for methyl carbamate synthesis according to claim 1, characterized in that: The raw materials for preparing methyl carbamate by the urea alcoholysis method include urea and methanol in a molar ratio of 1: (6-8).
7. The post-processing method for methyl carbamate synthesis according to claim 1, characterized in that: The reaction temperature for preparing methyl carbamate by the urea alcoholysis method is 150-165° C., and the reaction time is 2-3 hours.
8. The post-processing method for methyl carbamate synthesis according to claim 1, characterized in that: The method of recrystallizing to obtain the residual methyl carbamate product comprises the following steps: mixing the residual methyl carbamate liquid with the extract, raising the temperature to 45-50° C., stirring for 50-60 minutes and filtering, cooling the filtrate naturally and standing it for 20-40 minutes, filtering out the methyl carbamate crystals in the solution, and finally drying to obtain the residual methyl carbamate product.
9. The post-processing method for methyl carbamate synthesis according to claim 8, characterized in that: The extract comprises a combination of one or more of chloroform, dichloromethane and ethyl acetate.