Method for synthesizing ethylene urea through cyclization dehydration of ethylenediamine carbamate

Abstract

The invention relates to the field of chemical industry, and discloses a method for synthesizing ethylene urea through cyclization dehydration of ethylenediamine carbamate, which comprises the following steps: 1) mixing ethylenediamine carbamate, 1, 3-dimethyl-2-imidazolinone and a tin-titanium-based composite catalyst for reaction; 2) centrifuging to obtain a solid phase which is the tin-titanium-based composite catalyst and ethylenediamine carbamate; the obtained liquid phase is 1, 3-dimethyl-2-imidazolinone, ethylene urea and water; 3) washing and filtering the solid phase to obtain a tin-titanium-based composite catalyst solid and an ethylenediamine carbamate aqueous solution, and drying the aqueous solution to obtain ethylenediamine carbamate; 4, the liquid phase is extracted and separated through diethyl ether, 1, 3-dimethyl-2-imidazolinone is obtained after diethyl ether is removed through evaporation, ethylene urea is obtained after ethylene urea and water are obtained in a water phase, and the method has the advantages of being high in atom economy, mild in reaction condition, low in energy consumption and high in yield.

Description

Technical Field

[0001] This invention relates to the field of chemical engineering, and more particularly to a method for synthesizing ethylenediamine carbamate by cyclization and dehydration. Background Technology

[0002] Vinylurea, with its advantages of low toxicity, high polarity, and high safety, is widely used in the resin industry, pharmaceutical and chemical industry, textile industry, and paint, coating and adhesive industries. Vinylurea can be used as a formaldehyde scavenger to remove residual formaldehyde from fabrics. It also has applications in the synthesis of chiral microporous materials from achiral precursors, the preparation of aryl and heteroaryl N-acylurea via microwave-assisted palladium-catalyzed carbonylation reactions, the synthesis of highly water-soluble peptides based on human neutrophil elastase inhibitors, the synthesis of antibacterial heterocycles, Pd-catalyzed reactions forming CN bonds with heteroaryl toluenesulfonates, and the oxidative amidation reactions of activated alkenes. Furthermore, vinylurea can be added to metals as a corrosion inhibitor to suppress metal corrosion. With technological advancements and the expansion of its application areas, the vinylurea market will continue to grow and has broad market prospects.

[0003] In 1886, E. Fischer first reported the synthesis of ethylene urea by heating diethyl carbonate and ethylenediamine. Various methods have since been developed, categorized by the different raw materials used: phosgene method, carbon oxide method, carbonate method, carbon dioxide method, and urea method. Domestic and international patents and literature also report different synthetic methods for ethylene urea. Japanese Patent JP620265268A reports the use of phosgene as a carbonyl donor, reacting with ethylenediamine in an aqueous sodium hydroxide solution to generate ethylene urea, which is then distilled and recrystallized from chloroform to obtain ethylene urea. Chinese Patent CN200910019125.8 describes the reaction of ethylenediamine and urea in a continuous or batch reactor until ammonia production is significantly reduced or stopped, with excess ethylenediamine recovered, and the resulting condensate mixture evaporated and collected to obtain ethylene urea. Chinese Patent CN202210211220.3 describes the use of urea compounds from TDI tar residue and ethylenediamine for aminolysis to obtain diaminotoluene and ethylene urea-based organic chemical intermediates. By using a stepwise feeding method, TDI tar residue is aminolyzed with ethylenediamine. The aminolysis products are then purified by salting out with saturated brine, solvent extraction with organic solvents, reduction with hydrazine hydrate, and recrystallization. Chinese patent CN202510406203.9 describes a reaction using ethylenediamine, dimethyl carbonate, and an ionic liquid catalyst to obtain primary ethyleneurea; the ionic liquid catalyst used is 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium bromide, 1-ethyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazolium bromide, 1-butyl-3-methylimidazolium tetrafluoroborate, or 1-ethyl-3-methylimidazolium tetrafluoroborate. Chinese patent CN202210664278.3 describes the conversion of ethylenediamine and CO2 into ethyleneurea using a sulfur-containing compound catalyst and under supercritical conditions. Chinese patent CN201310483582.9 describes a process in which aminosulfonic acid catalyst, methanol solvent, ethylenediamine, and dimethyl carbonate are added to a reactor sequentially. The reaction temperature is 20–80°C, the reaction time is 1–5 h, and the temperature is further increased to 120–180°C. After reacting for 10–24 h, ethylene urea is generated.

[0004] Of the aforementioned methods for preparing ethylene urea, the phosgene method has been phased out due to its inherent limitations. The synthesis of ethylene urea from CO2 and CO with ethylenediamine requires stringent conditions, typically extremely high pressure, and places very strict demands on chemical equipment. The carbonate method offers milder reaction conditions, but requires a suitable catalyst, and the reactant carbonate is expensive, which also limits its application. Overall, the CO2 and urea methods utilize readily available and inexpensive raw materials, offering advantages in both raw material availability and environmental friendliness, making them the two most industrially promising methods for preparing ethylene urea.

[0005] Traditional industrial methods typically use ethylenediamine and urea as raw materials for a direct condensation reaction. The production process involves batching, reaction synthesis, crystallization, spin drying, and intermittent drying. The main problems are that the reaction needs to be carried out at high temperatures (180-220℃), leading to serious side reactions (such as ethylenediamine polymerization, formation of biuret, melamine, etc.), low product yield (usually 60-80%), dark product color, high impurity content, difficult subsequent purification, and high energy consumption. It also produces a large amount of ammonia, requiring additional treatment.

[0006] The CO2 method is not yet widely used in production, therefore, it is necessary to develop catalyst systems with high activity, good selectivity, low cost, and environmental friendliness to ultimately achieve industrial production. The principle of the ethylenediamine and carbon dioxide route (via ammonium carbamate): Ethylenediamine (EDA) reacts with CO2 to first produce ethylenediamine carbamate (EDA·CO2), which then undergoes dehydration and cyclization under heating to form ethylene urea. This route has high atom economy and theoretically produces only water. However, existing technologies suffer from the following problems: low dehydration efficiency, long reaction time, and the dehydration and cyclization of ammonium carbamate salts requires high temperatures (~150-200℃), resulting in a slow process, high energy consumption, and low production efficiency. During dehydration, side reactions such as over-dehydration, ring-opening, or polymerization may occur, affecting the purity and yield of the final product. Existing methods require the addition of catalysts to accelerate the reaction or lower the temperature. Existing catalysts (such as inorganic acids like phosphoric acid and sulfuric acid) suffer from strong corrosivity, poor selectivity, and difficulty in product separation; solid acid catalysts (such as molecular sieves) are prone to deactivation and have poor regeneration performance; homogeneous catalysts are difficult to recover and reuse. This increases costs, the catalyst may become deactivated and difficult to recover, and it may contaminate the product or generate waste residue. Therefore, how to efficiently achieve uniform heating of solid salt, effective removal of moisture, and prevention of by-product formation are the challenges in process scale-up. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention provides a method for synthesizing ethylene urea through the cyclization and dehydration of ethylenediamine carbamate. This method features high atom economy (derived from the CO2 route), mild reaction conditions, significantly reduced energy consumption, and high yield. Compared to the traditional urea method and existing CO2 routes, it is more economical and environmentally friendly.

[0008] The specific technical solution of the present invention includes: a method for synthesizing ethylene urea by cyclization and dehydration of ethylenediamine carbamate, comprising the following steps: 1) A cyclization dehydration reaction was carried out by mixing ethylenediamine carbamate, solvent 1,3-dimethyl-2-imidazolinone and tin-titanium-based composite catalyst.

[0009] In step 1), the present invention uses a supported catalyst, which, compared with a liquid catalyst, is beneficial for the subsequent separation and recovery of the catalyst and has advantages such as low cost and high activity.

[0010] 2) Centrifuge the reactants from 1) to obtain a solid phase consisting of a tin-titanium-based composite catalyst and unreacted ethylenediamine carbamate; and a liquid phase consisting of 1,3-dimethyl-2-imidazolinone, ethylene urea, and water.

[0011] In step 2), this invention utilizes the difference in compatibility between ethylene urea, water, 1,3-dimethyl-2-imidazolinone, and ethylenediamine carbamate to achieve separation of the product from the raw materials and solvent through simple centrifugation. Unreacted ethylenediamine carbamate and catalyst can be separated from the solvent 1,3-dimethyl-2-imidazolinone and the reaction products (ethylene urea, water) under ambient temperature and pressure conditions.

[0012] 3) Wash and filter the solid phase from 2). The resulting solid is a tin-titanium-based composite catalyst for recycling. The resulting liquid is an aqueous solution of ethylenediamine carbamate, which is dried to obtain ethylenediamine carbamate for recycling.

[0013] In step 3), the present invention further utilizes the water-soluble property of ethylenediamine carbamate to achieve the separation and recycling of ethylenediamine carbamate and catalyst.

[0014] 4) Extract the liquid phase from 2) with diethyl ether. The resulting upper oil phase is a mixture of 1,3-dimethyl-2-imidazolinone and diethyl ether. Distill the low-boiling diethyl ether to obtain the high-boiling 1,3-dimethyl-2-imidazolinone. The resulting lower aqueous phase is a mixture of ethylene urea and water. Distill the low-boiling water to obtain the high-boiling ethylene urea.

[0015] In step 4), this invention utilizes the differences in compatibility and boiling points of ethylene urea, water, 1,3-dimethyl-2-imidazolinone, and the extractant diethyl ether for extraction and distillation separation. 1,3-Dimethyl-2-imidazolinone is soluble in diethyl ether. At atmospheric pressure, the boiling point of diethyl ether is 34.6℃, while that of 1,3-dimethyl-2-imidazolinone is approximately 225-226℃, thus achieving low-energy separation at atmospheric pressure. Ethylene urea is a polar compound, while diethyl ether is a weakly polar organic solvent. According to the principle of "like dissolves like," the two have poor compatibility, and ethylene urea has extremely low solubility in diethyl ether. At atmospheric pressure, the boiling point of water is 100℃, and the boiling point of ethylene urea is 252-254℃. However, under reduced pressure conditions (355-525 mmHg), the corresponding boiling point of water is 80-90℃. Therefore, reduced pressure distillation can effectively separate and purify ethylene urea.

[0016] Preferably, in step 1), the mass ratio of the ethylenediamine carbamate, 1,3-dimethyl-2-imidazolinone and the tin-titanium-based composite catalyst is 10-15:150-170:2-3; more preferably, it is 10:160:2.

[0017] Preferably, in step 1), the preparation method of the tin-titanium-based composite catalyst is as follows: hydrochloric acid solution and dimethyl tin oxide are mixed and stirred, and titanium dioxide is added during stirring to form an emulsion. Hydrochloric acid and water are evaporated to obtain a solid tin-titanium-based composite catalyst, wherein the content of dimethyl tin oxide is 30-40 wt%.

[0018] This invention utilizes a wet chemical method, employing an impregnation deposition method to synthesize a tin-titanium based composite catalyst in situ. Specifically, this invention leverages the soluble nature of dimethyltin oxide in hydrochloric acid to prepare its aqueous solution, which is then loaded onto titanium dioxide powder. The hydrochloric acid is then removed by distillation, achieving dispersion of the dimethyltin oxide. Furthermore, the use of a supported catalyst facilitates subsequent separation and recovery, offering advantages such as low cost and high activity.

[0019] Preferably, in step 1), the content of dimethyl tin oxide in the tin-titanium-based composite catalyst is 30-40 wt%. Since the water absorption rate of the support is 55-60%, excessively high dimethyl tin oxide loading will cause pore blockage, resulting in low utilization of the active component; conversely, excessively low dimethyl tin oxide loading will result in fewer catalytic active sites, leading to a decrease in conversion rate.

[0020] Preferably, in step 1), the mass ratio of the hydrochloric acid solution to dimethyl tin oxide is 1.5-2.0:1; the concentration of the hydrochloric acid solution is 35-40 wt%; more preferably, the mass ratio of the hydrochloric acid solution to dimethyl tin oxide is 2:1; the concentration of the hydrochloric acid solution is 37 wt%.

[0021] Preferably, in step 1), the mass ratio of the titanium dioxide to the hydrochloric acid solution and the total dimethyltin oxide is (0.8-1.2):1.

[0022] Preferably, in step 1), the evaporation temperature is 100-110°C.

[0023] Preferably, in step 1), the ethylenediamine carbamate is a solid or a paste. The ethylenediamine carbamate is prepared by reacting ethylenediamine-aqueous solution, ethylenediamine-ethanol solution, or ethylenediamine-1,3-dimethyl-2-imidazolinone solution with CO2 at 25-50°C, followed by filtration, washing, and drying. More preferably, it is prepared by reacting ethylenediamine-1,3-dimethyl-2-imidazolinone solution with CO2 gas at 35°C, followed by filtration, washing, and drying.

[0024] Preferably, in step 1), the reaction conditions are as follows: a batch reaction is adopted, the temperature is increased to 170-200℃ at a rate of 10-15℃ / h, the reaction is kept at a constant temperature for 18-24h, the pressure is 0.5-1.0MPa, after the reaction is completed, the temperature is lowered to room temperature, the pressure is reduced, and the reaction material is discharged.

[0025] Preferably, in step 4), the distillation conditions for the mixture of 1,3-dimethyl-2-imidazolinone and diethyl ether are: atmospheric pressure and temperature 40-50℃.

[0026] Preferably, in step 4), the distillation conditions for the mixture of ethylene urea and water are: pressure 355-525 mmHg and temperature 80-90℃.

[0027] Compared with the prior art, the beneficial effects of the present invention are: (1) In this invention, ethylenediamine carbamate, 1,3-dimethyl-2-imidazolinone, and a tin-titanium-based composite catalyst are mixed and subjected to a cyclization dehydration reaction to prepare ethyleneurea. Utilizing the differences in miscibility and boiling points, the catalyst and solvent can be recovered, and the ethyleneurea purified. This invention provides a novel process for producing ethyleneurea via ethylenediamine and carbon dioxide (via ammonium carbamate), which has the advantages of mild reaction conditions, low energy consumption, simple process, and high yield.

[0028] (2) This invention uses an impregnation deposition method to synthesize tin-titanium based composite catalysts in situ. It utilizes the characteristic that dimethyltin oxide is soluble in hydrochloric acid to prepare an aqueous solution, which is then loaded onto titanium dioxide powder. The hydrochloric acid is then removed by distillation to achieve the dispersion of dimethyltin oxide. At the same time, the use of a supported catalyst is beneficial for subsequent separation and recovery, and has the advantages of low cost and high activity. Attached Figure Description

[0029] Figure 1 This is a process flow diagram for Example 1. Detailed Implementation

[0030] The present invention will be further described below with reference to embodiments.

[0031] General Implementation Examples A method for synthesizing ethylene urea by cyclization and dehydration of ethylenediamine carbamate includes the following steps: 1) A cyclization dehydration reaction was carried out by mixing ethylenediamine carbamate, solvent 1,3-dimethyl-2-imidazolinone and tin-titanium-based composite catalyst.

[0032] In some preferred embodiments, in step 1), the mass ratio of the ethylenediamine carbamate, 1,3-dimethyl-2-imidazolinone and tin-titanium-based composite catalyst is 10-15:150-170:2-3; more preferably 10:160:2.

[0033] In some preferred embodiments, in step 1), the preparation method of the tin-titanium-based composite catalyst is as follows: hydrochloric acid solution and dimethyltin oxide are mixed and stirred, titanium dioxide is added during stirring to form an emulsion, hydrochloric acid and water are evaporated to remove them, and a solid tin-titanium-based composite catalyst is obtained.

[0034] In some preferred embodiments, in step 1), the content of dimethyl tin oxide in the tin-titanium-based composite catalyst is 30-35 wt%. The mass ratio of the hydrochloric acid solution to dimethyl tin oxide is 1.5-2.0:1; the concentration of the hydrochloric acid solution is 35-40 wt%; more preferably, the mass ratio of the hydrochloric acid solution to dimethyl tin oxide is 2:1; the concentration of the hydrochloric acid solution is 37 wt%. The mass ratio of titanium dioxide to the total mass of hydrochloric acid solution and dimethyl tin oxide is (0.8-1.2):1. The evaporation temperature is 100-110℃.

[0035] In some preferred embodiments, in step 1), the ethylenediamine carbamate is a solid or a paste. The ethylenediamine carbamate is prepared by reacting ethylenediamine-aqueous solution, ethylenediamine-ethanol solution, or ethylenediamine-1,3-dimethyl-2-imidazolinone solution with CO2 at 25-50°C, followed by filtration, washing, and drying. More preferably, it is prepared by reacting ethylenediamine-1,3-dimethyl-2-imidazolinone solution with CO2 gas at 35°C, followed by filtration, washing, and drying.

[0036] In some preferred embodiments, in step 1), the reaction conditions are as follows: a batch reaction is adopted, the temperature is increased to 170-200℃ at a rate of 10-15℃ / h, the reaction is kept at a constant temperature for 18-24h, the pressure is 0.5-1.0MPa, after the reaction is completed, the temperature is lowered to room temperature, the pressure is reduced, and the reactants are discharged.

[0037] 2) Centrifuge the reactants from 1) to obtain a solid phase consisting of a tin-titanium-based composite catalyst and unreacted ethylenediamine carbamate; and a liquid phase consisting of 1,3-dimethyl-2-imidazolinone, ethylene urea, and water.

[0038] 3) Wash and filter the solid phase from 2). The resulting solid is a tin-titanium-based composite catalyst for recycling. The resulting liquid is an aqueous solution of ethylenediamine carbamate, which is dried to obtain ethylenediamine carbamate for recycling.

[0039] 4) Extract the liquid phase from 2) with diethyl ether. The resulting upper oil phase is a mixture of 1,3-dimethyl-2-imidazolinone and diethyl ether. Distill the low-boiling diethyl ether to obtain the high-boiling 1,3-dimethyl-2-imidazolinone. The resulting lower aqueous phase is a mixture of ethylene urea and water. Distill the low-boiling water to obtain the high-boiling ethylene urea.

[0040] In some preferred embodiments, in step 4), the distillation conditions for the mixture of 1,3-dimethyl-2-imidazolinone and diethyl ether are: atmospheric pressure and temperature 40-50°C.

[0041] In some preferred embodiments, in step 4), the distillation conditions of the mixture of ethylene urea and water are: pressure 355-525 mmHg and temperature 80-90℃.

[0042] Specific embodiments and comparative examples Example 1 The process flow of this embodiment is as follows: Figure 1 As shown, the specific steps include the following: (1) Weigh 10 mL of 37 wt% hydrochloric acid and 5 g of dimethyltin oxide and put them into a stirred reactor. Stir thoroughly to form a mixture of hydrochloric acid and dimethyltin oxide. Add 10 g of titanium dioxide powder during continuous stirring to form an emulsion. Put the emulsion into an evaporation flask and evaporate it at 100 °C to remove hydrochloric acid and water. The tin-titanium based composite catalyst is obtained in the evaporation flask.

[0043] (2) Weigh 10g of ethylenediamine carbamate (derived from ethylenediamine-1,3-dimethyl-2-imidazolinone solution and CO2 absorption), 2g of tin-titanium-based composite catalyst and 160g of 1,3-dimethyl-2-imidazolinone solvent and add them to the reactor. After checking the airtightness, replace with nitrogen and close all inlet and outlet valves of the reactor while maintaining a slightly positive pressure.

[0044] (3) Heat the temperature to 180℃ at a rate of 15℃ / h, and keep the temperature constant at 180℃ for 20 hours at a pressure of 0.5MPa and a rotation speed of 350rpm. After the reaction is completed, cool the temperature to room temperature and slowly open the drain.

[0045] (4) The discharged reaction material is separated into liquid and solid phases in a separator. The solid phase is washed and filtered with deionized water to obtain the recovered tin-titanium-based composite catalyst, in which the content of dimethyl tin oxide is 35 wt%.

[0046] (5) The liquid phase was extracted and separated with diethyl ether. The upper layer was a mixture of 1,3-dimethyl-2-imidazolinone and diethyl ether as the oil phase. The mixture was further distilled at atmospheric pressure and 40°C to separate the low-boiling-point diethyl ether, and the bottom layer was a high-boiling-point 1,3-dimethyl-2-imidazolinone. The lower layer was a mixture of ethylene urea and water as the aqueous phase. The mixture was further distilled under reduced pressure at a vacuum of 525 mmHg and a temperature of 90°C to separate the low-boiling-point water, and the bottom layer was a high-boiling-point ethylene urea.

[0047] Example 2 The difference compared to Example 1 is that the reaction time was 22 hours at a constant temperature of 180°C.

[0048] Specifically, the following steps are included: (1) Same as Example 1.

[0049] (2) Same as Example 1.

[0050] (3) Heat the temperature to 180℃ at a rate of 15℃ / h, and keep the temperature constant at 180℃ for 22 hours at a pressure of 0.5MPa and a rotation speed of 350rpm. After the reaction is completed, cool the temperature to room temperature and slowly open the drain.

[0051] (4) Same as Example 1.

[0052] (5) Same as Example 1.

[0053] Example 3 The difference compared to Example 1 is that the reaction time was 24 hours at a constant temperature of 180°C.

[0054] Specifically, the following steps are included: (1) Same as Example 1.

[0055] (2) Same as Example 1.

[0056] (3) Heat the temperature to 180℃ at a rate of 15℃ / h, and keep the temperature constant at 180℃ for 24 hours at a pressure of 0.5MPa and a rotation speed of 350rpm. After the reaction is completed, cool the temperature to room temperature and slowly open the drain.

[0057] (4) Same as Example 1.

[0058] (5) Same as Example 1.

[0059] Example 4 The difference from Example 3 is that the isothermal reaction temperature is 170°C.

[0060] Specifically, the following steps are included: (1) Same as Example 3.

[0061] (2) Same as Example 3.

[0062] (3) Heat the temperature to 170℃ at a rate of 15℃ / h, and keep the temperature constant at 170℃ for 24 hours at a pressure of 0.5MPa and a rotation speed of 350rpm. After the reaction is completed, cool the temperature to room temperature and slowly open the drain.

[0063] (4) Same as Example 3.

[0064] (5) Same as Example 3.

[0065] Example 5 The difference from Example 3 is that the isothermal reaction temperature is 200°C.

[0066] Specifically, the following steps are included: (1) Same as Example 3.

[0067] (2) Same as Example 3.

[0068] (3) Heat the temperature to 200℃ at a rate of 15℃ / h, and keep the temperature constant at 200℃ for 24 hours at a pressure of 0.5MPa and a rotation speed of 350rpm. After the reaction is completed, cool the temperature to room temperature and slowly open the drain.

[0069] (4) Same as Example 3.

[0070] (5) Same as Example 3.

[0071] Example 6 The difference from Example 3 is that the ethylenediamine carbamate is obtained by ethylenediamine-water solution and CO2 absorption.

[0072] Specifically, the following steps are included: (1) Same as Example 3.

[0073] (2) Weigh 10g of ethylenediamine carbamate (the source of ethylenediamine carbamate is obtained by ethylenediamine-water solution and CO2 absorption), 2g of tin-titanium-based composite catalyst and 160g of 1,3-dimethyl-2-imidazolinone solvent and add them to the reactor. After checking the airtightness, replace with nitrogen and close all inlet and outlet valves of the reactor while maintaining a slightly positive pressure.

[0074] (3) Same as Example 3.

[0075] (4) Same as Example 3.

[0076] (5) Same as Example 3.

[0077] Example 7 The difference from Example 3 is that the ethylenediamine carbamate is obtained by ethylenediamine-ethanol solution and CO2 absorption.

[0078] Specifically, the following steps are included: (1) Same as Example 3.

[0079] (2) Weigh 10g of ethylenediamine carbamate (derived from ethylenediamine-ethanol solution and CO2 absorption), 2g of tin-titanium composite catalyst and 160g of 1,3-dimethyl-2-imidazolinone solvent and add them to the reactor. After checking the airtightness, replace with nitrogen and close all inlet and outlet valves of the reactor while maintaining a slightly positive pressure.

[0080] (3) Same as Example 3.

[0081] (4) Same as Example 3.

[0082] (5) Same as Example 3.

[0083] Example 8 The difference from Example 3 is that 15g of ethylenediamine carbamate and 3g of tin-titanium-based composite catalyst were added.

[0084] Specifically, the following steps are included: (1) Same as Example 3.

[0085] (2) Weigh 15g of ethylenediamine carbamate (derived from ethylenediamine-1,3-dimethyl-2-imidazolinone solution and CO2 absorption), 3g of tin-titanium-based composite catalyst and 160g of 1,3-dimethyl-2-imidazolinone solvent and add them to the reactor. After checking the airtightness, replace with nitrogen and close all inlet and outlet valves of the reactor while maintaining a slightly positive pressure.

[0086] (3) Same as Example 3.

[0087] (4) Same as Example 3.

[0088] (5) Same as Example 3.

[0089] Example 9 The difference from Example 3 is that 10g of ethylenediamine carbamate and 3g of tin-titanium-based composite catalyst were added.

[0090] Specifically, the following steps are included: (1) Same as Example 3.

[0091] (2) Weigh 10g of ethylenediamine carbamate (derived from ethylenediamine-1,3-dimethyl-2-imidazolinone solution and CO2 absorption), 3g of tin-titanium-based composite catalyst and 160g of 1,3-dimethyl-2-imidazolinone solvent and add them to the reactor. After checking the airtightness, replace with nitrogen and close all inlet and outlet valves of the reactor while maintaining a slightly positive pressure.

[0092] (3) Same as Example 3.

[0093] (4) Same as Example 3.

[0094] (5) Same as Example 3.

[0095] Example 10 The difference compared to Example 3 is that the pressure of the isothermal reaction is 1.0 MPa.

[0096] Specifically, the following steps are included: (1) Same as Example 3.

[0097] (2) Same as Example 3.

[0098] (3) Heat the temperature to 180℃ at a rate of 15℃ / h, and keep the temperature constant at 180℃ for 24 hours at a pressure of 1.0MPa and a rotation speed of 350rpm. After the reaction is completed, cool the temperature to room temperature and slowly open the drain.

[0099] (4) Same as Example 3.

[0100] (5) Same as Example 3.

[0101] Comparative Example 1 Compared with Example 3, the difference is that the reaction solvent was changed from 1,3-dimethyl-2-imidazolinone to water, and the product was directly distilled under reduced pressure after filtration.

[0102] Comparative Example 2 Compared with Example 3, the difference is that the catalyst is changed to a tin-titanium-aluminum based composite catalyst, and 10g of titanium dioxide powder is replaced with 5g of alumina powder and 5g of titanium dioxide powder.

[0103] Specifically, the steps include the following: (1) Weigh 10 mL of 37 wt% hydrochloric acid and 5 g of dimethyltin oxide and place them in a stirred reactor. Stir thoroughly to form a mixture of hydrochloric acid and dimethyltin oxide. During continuous stirring, add 5 g of alumina powder and 5 g of titanium dioxide powder to form an emulsion. Place the emulsion in an evaporation flask and evaporate at 100 °C to remove hydrochloric acid and water. The evaporation flask yields a tin-titanium-aluminum based composite catalyst.

[0104] (2) Same as Example 3.

[0105] (3) Same as Example 3.

[0106] (4) Same as Example 3.

[0107] (5) Same as Example 3.

[0108] Comparative Example 3 Compared with Example 3, the difference is that the catalyst is changed to a tin-titanium-zirconium-based composite catalyst, wherein 10g of titanium dioxide powder is replaced with 5g of zirconium oxide powder and 5g of titanium oxide powder.

[0109] Specifically, the steps include the following: (1) Weigh 10 mL of 37 wt% hydrochloric acid and 5 g of dimethyltin oxide and place them in a stirred reactor. Stir thoroughly to form a mixture of hydrochloric acid and dimethyltin oxide. During continuous stirring, add 5 g of zirconium oxide powder and 5 g of titanium dioxide powder to form an emulsion. Place the emulsion in an evaporation flask and evaporate at 100 °C to remove hydrochloric acid and water. The evaporation flask yields a tin-titanium-zirconium-based composite catalyst.

[0110] (2) Same as Example 3.

[0111] (3) Same as Example 3.

[0112] (4) Same as Example 3.

[0113] (5) Same as Example 3.

[0114] Comparative Example 4 The difference from Example 3 is that the tin-titanium based composite catalyst is changed to zinc acetate.

[0115] Specifically, the steps include the following: (1) Weigh 10g of ethylenediamine carbamate (derived from ethylenediamine-1,3-dimethyl-2-imidazolinone solution and CO2 absorption), 2g of zinc acetate catalyst and 160g of 1,3-dimethyl-2-imidazolinone solvent and add them to the reactor. After checking the airtightness, replace with nitrogen and close all inlet and outlet valves of the reactor while maintaining a slightly positive pressure.

[0116] (2) Same as Example 3.

[0117] (3) Same as Example 3.

[0118] (4) Same as Example 3.

[0119] Comparative Example 5 The difference compared to Example 3 is that no tin-titanium-based composite catalyst is added.

[0120] Specifically, the steps include the following: (1) Weigh 10g of ethylenediamine carbamate (obtained by ethylenediamine-1,3-dimethyl-2-imidazolinone solution and CO2 absorption) and 160g of 1,3-dimethyl-2-imidazolinone solvent and add them to the reactor. After checking the airtightness, replace with nitrogen and close all inlet and outlet valves of the reactor while maintaining a slightly positive pressure.

[0121] (2) Same as Example 3.

[0122] (3) Same as Example 3.

[0123] (4) Same as Example 3.

[0124] Comparative Example 6 The difference from Example 3 is that the tin-titanium based composite catalyst is changed to dimethyltin oxide.

[0125] Specifically, the steps include the following: (1) Weigh 10g of ethylenediamine carbamate (derived from ethylenediamine-1,3-dimethyl-2-imidazolinone solution and CO2 absorption), 2g of dimethyl tin oxide catalyst and 160g of 1,3-dimethyl-2-imidazolinone solvent and add them to the reactor. After checking the airtightness, replace with nitrogen and close all inlet and outlet valves of the reactor while maintaining a slightly positive pressure.

[0126] (2) Same as Example 3.

[0127] (3) Same as Example 3.

[0128] (4) Same as Example 3.

[0129] Comparative Example 7 The difference from Example 3 is that the content of dimethyl tin oxide in the tin-titanium-based composite catalyst is 20 wt%.

[0130] Specifically, the steps include the following: (1) Weigh 10 mL of 37 wt% hydrochloric acid and 3 g of dimethyltin oxide and put them into a stirred reactor. Stir thoroughly to form a mixture of hydrochloric acid and dimethyltin oxide. Add 12 g of titanium dioxide powder during continuous stirring to form an emulsion. Put the emulsion into an evaporation flask and evaporate it at 100 °C to remove hydrochloric acid and water. The tin-titanium based composite catalyst is obtained in the evaporation flask.

[0131] (2) Same as Example 3.

[0132] (3) Same as Example 3.

[0133] (4) Same as Example 3.

[0134] (5) Same as Example 3.

[0135] Comparative Example 8 The difference from Example 3 is that the content of dimethyl tin oxide in the tin-titanium-based composite catalyst is 50 wt%.

[0136] Specifically, the steps include the following: (1) Weigh 10 mL of 37 wt% hydrochloric acid and 7.5 g of dimethyltin oxide and place them in a stirred reactor. Stir thoroughly to form a mixture of hydrochloric acid and dimethyltin oxide. Add 7.5 g of titanium dioxide powder during continuous stirring to form an emulsion. Place the emulsion in an evaporation flask and evaporate at 100 °C to remove hydrochloric acid and water. The tin-titanium based composite catalyst is obtained in the evaporation flask.

[0137] (2) Same as Example 3.

[0138] (3) Same as Example 3.

[0139] (4) Same as Example 3.

[0140] (5) Same as Example 3.

[0141] Performance Comparison The data for each embodiment and each comparative example are shown in Table 1: Table 1 As shown in Table 1, the methods in Examples 1-10 of this invention can achieve high conversion rates of ethylenediamine carbamate and high yields of ethylene urea. The optimal conditions were as follows: Example 7: 10 g ethylenediamine carbamate, 2.0 g tin-titanium-based composite catalyst, 160.0 g solvent 1,3-dimethyl-2-imidazolinone; reaction temperature 180°C, rotation speed 350 rpm, reaction time 24 hours; corresponding to an ethylenediamine carbamate conversion rate of 85.0% and an ethylene urea yield of 82.8%.

[0142] In Comparative Example 1, water was used as the solvent, and the accelerated hydrolysis of dimethyltin oxide led to catalyst deactivation. Comparative Examples 2 and 3 used titanium aluminum oxide and titanium zirconium oxide as supports, respectively, which did not promote catalytic performance. Comparative Example 4 used zinc acetate as the catalyst, and its catalytic activity was lower than that of dimethyltin oxide. Comparative Example 5 did not add any catalyst, and the cyclization reaction was poor. Comparative Example 6 used unsupported dimethyltin oxide, resulting in poor dispersibility and reduced catalytic activity. In Comparative Examples 7 and 8, both excessively high and low levels of dimethyltin oxide in the tin-titanium-based composite catalysts were detrimental to the cyclization reaction.

[0143] Unless otherwise specified, the raw materials and equipment used in this invention are all commonly used in the field; unless otherwise specified, the methods used in this invention are all conventional methods in the field.

[0144] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, alterations, and equivalent transformations made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for synthesizing ethylenediamine carbamate by cyclization and dehydration, characterized in that... include: 1) Mix ethylenediamine carbamate, 1,3-dimethyl-2-imidazolinone and tin-titanium composite catalyst and react them; 2) Centrifuge the reactants to obtain a solid phase consisting of a tin-titanium-based composite catalyst and ethylenediamine carbamate; and a liquid phase consisting of 1,3-dimethyl-2-imidazolinone, ethylene urea, and water. 3) The solid phase was washed and filtered to obtain a tin-titanium-based composite catalyst solid and an aqueous solution of ethylenediamine carbamate. The aqueous solution was dried to obtain ethylenediamine carbamate. 4) The liquid phase was separated by extraction with diethyl ether. The resulting oil phase consisted of 1,3-dimethyl-2-imidazolinone and diethyl ether. After evaporating the diethyl ether, 1,3-dimethyl-2-imidazolinone was obtained. The resulting aqueous phase consisted of ethylene urea and water. After evaporating the water, ethylene urea was obtained.

2. The preparation method according to claim 1, characterized in that: In step 1), the mass ratio of the ethylenediamine carbamate, 1,3-dimethyl-2-imidazolinone and tin-titanium-based composite catalyst is 10-15:150-170:2-3.

3. The preparation method according to claim 1 or 2, characterized in that: In step 1), the preparation method of the tin-titanium-based composite catalyst is as follows: hydrochloric acid solution and dimethyltin oxide are mixed and stirred, titanium dioxide is added during stirring to form an emulsion, hydrochloric acid and water are evaporated to remove them, and a solid tin-titanium-based composite catalyst is obtained.

4. The preparation method according to claim 3, characterized in that: In step 1), the content of dimethyl tin oxide in the tin-titanium-based composite catalyst is 30-40 wt%.

5. The preparation method according to claim 3, characterized in that: In step 1), The mass ratio of the hydrochloric acid solution to dimethyltin oxide is 1.5-2.0:1; The concentration of the hydrochloric acid solution is 35-40 wt%. The mass ratio of the titanium dioxide to the hydrochloric acid solution and the total dimethyl tin oxide is (0.8-1.2):

1.

6. The preparation method according to claim 3, characterized in that: In step 1), the evaporation temperature is 100-110℃.

7. The preparation method according to claim 1 or 2, characterized in that: In step 1), the ethylenediamine carbamate is a solid or a paste. The ethylenediamine carbamate is obtained by reacting ethylenediamine-aqueous solution, ethylenediamine-ethanol solution, or ethylenediamine-1,3-dimethyl-2-imidazolinone solution with CO2 at 25-50°C, followed by filtration, washing, and drying.

8. The preparation method according to claim 1 or 2, characterized in that: In step 1), the reaction conditions are as follows: a batch reaction is adopted, the temperature is increased to 170-200℃ at a rate of 10-15℃ / h, the reaction is kept at a constant temperature for 18-24h, the pressure is 0.5-1.0MPa, after the reaction is completed, the temperature is reduced to room temperature, the pressure is reduced, and the reaction materials are discharged.

9. The preparation method according to claim 1, characterized in that: In step 4), the distillation conditions for the 1,3-dimethyl-2-imidazolinone and diethyl ether are: atmospheric pressure and temperature 40-50℃.

10. The preparation method according to claim 1 or 9, characterized in that: In step 4), the distillation conditions for ethylene urea and water are: pressure 355-525 mmHg and temperature 80-90℃.

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