Green production process of aminoguanidine carbonate

Abstract

The invention belongs to the technical field of environmental protection, and particularly relates to a green production process of aminoguanidine carbonate. The method comprises the following steps: inputting hydrazine hydrate and softened water into a premixer, pumping CO2 into the premixer, controlling the pumping pressure of the CO2 at 0.03-0.05 MPa, stabilizing the pH value of a mixed solution at 5.0-5.5, premixing, respectively pumping the premixed solution and a cyanamide aqueous solution into a Taylor-type tubular reactor, arranging CO2 injection ports on the Taylor-type tubular reactor in sections, respectively injecting CO2 through the CO2 injection ports, and respectively injecting the hydrogen cyanamide aqueous solution through the CO2 injection ports. The pH value of the reaction system is kept at 5.0-5.5 for reaction, and reaction liquid is rapidly cooled to 0-5 DEG C through a tubular heat exchanger and then enters a reaction kettle for crystallization; and after the crystallization is finished, filtering, washing and drying the feed liquid to obtain the product aminoguanidine carbonate. According to the method, efficient, safe and controllable industrial production is realized, the yield is high, the CO2 utilization rate is high, the cost is low, the product purity is high, and the crystal particle size distribution is uniform.

Description

Technical Field

[0001] This invention belongs to the field of environmental protection technology, specifically relating to a green production process for aminoguanidine carbonate. Background Technology

[0002] Aminoguanidine carbonate is an important fine chemical product, mainly used in the synthesis of drugs such as tropidil, propamidine hydrazone, and nifuran hydrazone. The traditional production process of aminoguanidine carbonate uses calcium cyanamide, hydrazine hydrate, ammonium bicarbonate, or sodium bicarbonate as raw materials. The specific process is as follows: First, distilled water is added to calcium cyanamide, and the reaction is maintained at a certain temperature. The residue is filtered off to obtain a cyanamide (calcium) solution. Then, dilute sulfuric acid is added to the cyanamide (calcium) solution to adjust the pH to 6-7. After cooling to room temperature, calcium sulfate is filtered off to obtain a cyanamide solution. Then, 5% hydrazine hydrate is added to the cyanamide solution, and the reaction is maintained at a certain temperature. Ammonium bicarbonate is then added, and the mixture is allowed to stand to precipitate crystals. The crystals are then filtered off to obtain crude aminoguanidine bicarbonate. The crude product is dissolved in acetic acid, and then oxalic acid is added. Calcium oxalate is filtered off, and the filtrate is adjusted to pH 8-9 with ammonia water. A small amount of disodium ethylenediaminetetraacetate is added, and the mixture is filtered until clear. Ammonium bicarbonate solution is then added, and the mixture is allowed to stand to crystallize. The crystals are then filtered off, and the mixture is washed with distilled water and ethanol, and finally filtered off to obtain the finished aminoguanidine carbonate product. This method is complex, has high production costs, and low product yield. The average content of aminoguanidine carbonate produced is 98%, which cannot meet the requirements of high-end product customers.

[0003] Existing technologies disclose the direct reaction of hydrazine hydrate with cyanamide to produce aminoguanidine carbonate, but this requires a 100% excess of cyanamide and yields only 80% to 90%, resulting in high costs, low yields, and safety hazards.

[0004] Chinese patent CN1361764A discloses the reaction of cyanamide aqueous solution and hydrazine hydrate aqueous solution in the presence of CO2, with a preferred pH value of 7-7.3. The amount of cyanamide used is lower than the stoichiometry, and the yield (relative to cyanamide) after the reaction is completed is about 95.0%. However, this patent is under normal pressure. According to the preferred temperature of this patent, it is impossible to reach a lower pH value, which will result in the polymerization of cyanamide. In addition, the amount of hydrazine hydrate is excessive. Excessive hydrazine hydrate is highly toxic and explosive, posing a great safety hazard and risk in the treatment of waste liquid.

[0005] In pharmaceutical and pesticide intermediates, there are high requirements for product particle size. Aminoguanidine carbonate has advantages in terms of particle size (D50) of 40-50 micrometers, and its dissolution rate and stability are relatively good. However, the particle size distribution of aminoguanidine carbonate crystals prepared by existing technologies is uneven and difficult to control within this range.

[0006] In addition, existing preparation processes for aminoguanidine carbonates also suffer from problems such as low CO2 mass transfer efficiency, uneven crystallization, and significant scale-up effects. Summary of the Invention

[0007] To address the problems of traditional batch processes, the purpose of this invention is to provide a green production process for aminoguanidine carbonate. This process employs continuous flow to suppress local over-reaction, achieving efficient, safe, and controllable industrial production with high yield, short reaction time, high CO2 utilization, low raw material cost, high product purity, uniform crystal particle size distribution (D50 = 40-50 micrometers), and excellent dissolution rate and stability.

[0008] This invention provides a green production process for aminoguanidine carbonate, comprising the following steps: (a) Hydrazine hydrate and softened water are fed into a premixer, CO2 gas is pumped into the premixer for premixing, and a premixed liquid is obtained after premixing. (b) The premixed solution obtained in step (a) and the cyanamide aqueous solution are pumped into a Taylor tubular reactor, and CO2 injection ports are set in sections on the Taylor tubular reactor. CO2 is injected into the Taylor tubular reactor through the CO2 injection ports to maintain the pH value of the reaction system between 5.0 and 5.5 and carry out the reaction. (c) The reaction solution obtained in step (b) is rapidly cooled by a tubular heat exchanger and then introduced into the reactor for crystallization; (d) After crystallization, the liquid is filtered, washed and dried to obtain the product aminoguanidine carbonate.

[0009] Preferably, in step (a), the pumping pressure of CO2 gas is controlled between 0.03 MPa and 0.05 MPa to stabilize the pH of the mixture at 5.0 to 5.5 for premixing.

[0010] The inventors discovered that directly reacting hydrazine hydrate and cyanamide releases a large amount of heat. Furthermore, the strong alkalinity of hydrazine hydrate causes cyanamide to polymerize into dicyandiamide, preventing the more expensive cyanamide from fully participating in the preparation of aminoguanidine, resulting in low yield and high cost. Moreover, cyanamide exhibits poor stability under neutral / alkaline conditions and readily dimers into dicyandiamide. Industrial hydrazine hydrate operates at a pH between 8 and 9; at this pH, cyanamide is unstable and readily polymerizes into dicyandiamide. In this invention, hydrazine hydrate and softened water are first fed into a premixer via proportioning pumps for premixing and dilution. After premixing and dilution, CO2 gas is pumped into the premixer, with the pumping pressure controlled between 0.03 MPa and 0.05 MPa. The CO2 flow rate is adjusted via online pH feedback to stabilize the pH of the mixture at 5.0 to 5.5 for premixing. The premixed solution and cyanamide aqueous solution are then pumped into a Taylor tubular reactor, with CO2 injected in stages for reaction. By premixing CO2 gas with hydrazine hydrate and softened water and controlling the pH to be stable at 5.0-5.5, cyanamide can be stably present in the reaction system, which can improve the yield and reduce side reactions. Then, by using a Taylor tubular reactor and selecting an appropriate CO2 injection method, cyanamide has high stability in the reaction system, avoiding polymerization into dicyandiamide. This allows equal amounts of cyanamide and hydrazine hydrate to react and generate a fixed amount of aminoguanidine carbonate, reducing the amount of high-cost cyanamide used, lowering production costs, and increasing the yield. Combined with Taylor vortex flow to enhance mass transfer, continuous reaction is achieved, improving product purity, yield, and carbon dioxide utilization.

[0011] Preferably, step (a) involves closed-loop pH control using an online pH sensor to avoid delays caused by manual intervention.

[0012] Preferably, in step (a), the premixer is a pipeline reactor, the pumping pressure of CO2 gas is 0.03~0.05MPa, and the pH value of the reaction system is stable at 5.0~5.5. Under these conditions, the stability of cyanamide is enhanced, and the reaction of equal amounts of cyanamide and hydrazine hydrate can produce a quantitative amount of aminoguanidine carbonate. The hydrazine hydrate, cyanamide and dicyandiamide contained in the wastewater are all in trace amounts (detected to be below 100ppm), which greatly improves production efficiency and reduces production costs.

[0013] Preferably, in step (a), the concentration of hydrazine hydrate is 80-81%, the mass ratio of hydrazine hydrate to softened water is 1.0:1.0-3.0, the premixing time is 0.5-2.0 hours, and the premixing temperature is 10-40°C.

[0014] Preferably, in step (b), CO2 injection ports are respectively set at the inlet, middle and outlet of the Taylor tubular reactor, that is, CO2 injection ports are set in three sections: front, middle and rear, on the Taylor tubular reactor. CO2 is injected into the Taylor tubular reactor from the inlet, middle and outlet respectively. In order to maintain the pH value of the reaction system between 5.0 and 5.5, the carbon dioxide injection pressure of the three CO2 injection ports needs to be controlled separately. The pressure of the inlet injection port is controlled at 0.045~0.050 MPa, the pressure of the middle injection port is controlled at 0.035~0.040 MPa, and the pressure of the outlet injection port is controlled at 0.025~0.030 MPa. This invention utilizes three injection ports with varying pressures to enhance carbon dioxide participation in the reaction, significantly improving carbon dioxide utilization. The inlet injection port pressure is controlled at 0.045–0.050 MPa, where carbon dioxide demand and consumption are highest. This higher pressure allows for greater carbon dioxide dissolution in the reaction solution, promoting the reaction. The middle injection port pressure is controlled at 0.035–0.040 MPa to continue the reaction and improve conversion rate. The outlet injection port pressure is controlled at 0.025–0.030 MPa to ensure sufficient reaction of unreacted products, further improving conversion rate and purity. This invention also employs continuous flow to suppress localized overreaction and maintains the pH of the reaction system between 5.0 and 5.5, thereby improving product purity and conversion rate.

[0015] Preferably, in step (b), each CO2 injection port on the Taylor tubular reactor is provided with 3 to 5 air inlets. Compared with 1 air inlet, providing 3 to 5 air inlets allows for more complete dispersion of carbon dioxide.

[0016] Preferably, in step (b), the inner cylinder rotation speed of the Taylor tubular reactor is 500-1000 rpm, and the Taylor number (Ta) is ≥50. This invention selects an inner cylinder rotation speed of 500-1000 rpm and a Taylor number (Ta) ≥50 for the Taylor tubular reactor. This causes the fluid to transition from laminar flow to Taylor vortex flow, forming periodic rotating vortex rings. This increases the gas-liquid or liquid-liquid contact area by 5-10 times, improves the dissolution rate of gases such as CO2, increases the mass transfer coefficient K1a by more than 30%, ensures uniform reactant concentration distribution, avoids local over-concentration or dead zones, and improves yield.

[0017] Preferably, in step (b), the reaction conditions are: a total residence time of the reaction solution of 0.5 to 2.0 hours and a reaction temperature of 40 to 50°C. This invention, by precisely controlling the total residence time of the reaction solution to 0.5 to 2.0 hours, the reaction temperature to 40 to 50°C, the Taylor number (Ta) ≥ 50, and the inner cylinder rotation speed to 500-1000 rpm, avoids the mass transfer / heat transfer bottlenecks in traditional scale-up processes.

[0018] In step (b), the flow rate of the cyanamide aqueous solution in the Taylor tubular reactor is 3-4 L / min, and the flow rate of the premixed solution in the Taylor tubular reactor is 5 L / min. At this flow rate ratio, the reaction is more complete, the yield is higher, and the production capacity requirements can be met.

[0019] Preferably, in step (c), the rapid cooling rate is 10~20℃ / min, the temperature is cooled to 0~5℃, and the crystallization time is 1~3 hours. The reactor in step (c) is a stainless steel reactor. By using rapid cooling (10~20℃ / min) to rapidly cool the obtained reaction liquid to 0~5℃ via a tubular heat exchanger, combined with crystallization in the reactor, precise control of the crystal particle size at D50=40-50 μm is achieved, improving crystal particle uniformity and purity, and offering advantages in dissolution rate and stability.

[0020] In step (d), filtration, washing, and drying are performed using a three-in-one filtration, washing, and drying machine. This three-in-one filtration, washing, and drying machine enables continuous solid-liquid separation and reduces solvent residue.

[0021] Step (d) is as follows: After crystallization, the liquid enters the three-in-one centrifugal washing and drying machine and is stirred at a low speed of 10~20 r / min to make the material evenly distributed. After feeding, the feed valve is closed and the filtrate outlet valve is opened. The pressure is gradually increased for filtration, with a pressure ≤0.3MPa. Water is added as washing liquid and stirred at a speed of 20~30 r / min. When the pressure filter is pressed until no liquid flows out of the outlet, the hot water inlet and outlet valves are opened first, and the vacuum valve is opened. Drying is carried out under vacuum. Before discharge, a sample is taken to test the drying loss ≤1.0%. After passing the test, the product aminoguanidine carbonate is discharged.

[0022] Compared with the prior art, the present invention has the following advantages: (1) The existing process adopts batch production process, which requires step feeding, temperature control and crystallization. The operation is cumbersome and inefficient. In addition, the existing process requires continuous carbon dioxide supply, which consumes a large amount of carbon dioxide and is seriously wasteful. It also has problems such as uneven dissolution, large pH fluctuation (affecting the yield, resulting in low yield and many side reactions), and large consumption, which leads to waste of carbon dioxide. This invention addresses the inherent shortcomings of traditional batch processes by providing a green production process for aminoguanidine carbonate. The process involves premixing CO2 gas with hydrazine hydrate and softened water, controlling the CO2 gas injection pressure between 0.03 MPa and 0.05 MPa, and maintaining a stable pH between 5.0 and 5.5. This ensures the stable presence of cyanamide in the reaction system, improving yield and reducing side reactions. A Taylor-type tubular reactor is then employed, and by selecting a suitable CO2 injection method, the cyanamide exhibits high stability within the reaction system, preventing its polymerization into dicyandiamide. This allows for the reaction of equal amounts of cyanamide and hydrazine hydrate to produce a fixed amount of aminoguanidine carbonate, reducing the amount of high-cost cyanamide used, lowering production costs, and increasing yield. The wastewater contains trace amounts of hydrazine hydrate, cyanamide, and dicyandiamide (all below 100 ppm). Combined with Taylor vortex flow to enhance mass transfer, this enables continuous reaction, improving product purity, yield, and carbon dioxide utilization. This invention enables efficient, safe, and controllable industrial production through continuous flow tubular reactor technology. It achieves continuous production throughout the entire process, including pH control, reaction, crystallization, and separation, significantly improving production efficiency, shortening the preparation cycle by more than 40%, and increasing product purity.

[0023] (2) Existing processes have problems such as uneven crystallization particle size in batches, low filtration efficiency, and difficulty in continuous crystallization and separation. This invention uses rapid cooling at 10-20℃ / min to rapidly cool the obtained reaction liquid to 0-5℃ through a tubular heat exchanger, and then crystallizes it in a reaction vessel. This achieves precise control of crystal particle size at D50=40-50 μm, improves crystal particle uniformity and purity, and has good advantages in terms of dissolution rate and stability.

[0024] (3) Existing processes have the problem of high batch operation risks of hydrazine hydrate (flammable and explosive) and cyanamide (highly toxic). This invention reduces the exposure risk by using a closed continuous system, and by selecting appropriate reaction processes and conditions, cyanamide has high stability in this reaction system, avoiding polymerization into dicyanamide. It achieves the reaction of equal amounts of cyanamide and hydrazine hydrate to generate a quantitative amount of aminoguanidine carbonate. The hydrazine hydrate, cyanamide and dicyanamide contained in the wastewater are all in trace amounts (all below 100 ppm after testing), which greatly improves production efficiency and reduces production costs.

[0025] (4) The present invention uses a pipeline reactor to react cyanamide and hydrazine hydrate, while carbon dioxide is introduced in stages, which can improve the reaction efficiency, produce high product purity, high yield, and low cost. The product purity can reach more than 99.5%, which can ensure that carbon dioxide fully participates in the reaction, avoid waste, reduce emissions, and improve process safety and environmental protection.

[0026] (5) The CO2 utilization rate of the present invention is over 90% (the existing batch production process is only 60%), which reduces the raw material cost. The present invention adopts continuous flow to suppress local over-reaction, and the purity is ≥99.5% (the purity of the existing batch production process is about 95%). The yield of the present invention is more than 15% higher than that of the existing technology, and the yield is increased to over 99%, and the reaction time is shortened by 80%. The risk of local overheating and explosion of hydrazine hydrate is avoided. The crystal particle size distribution of the present invention is uniform, and the crystal D50 is 40-50 μm. Attached Figure Description

[0027] Figure 1 This is the mass spectrum of the aminoguanidine carbonate prepared in Example 1; Figure 2 This is the liquid chromatogram of the aminoguanidine carbonate prepared in Example 1; Figure 3 This is the particle size distribution of the aminoguanidine carbonate prepared in Example 1; Figure 4 This is the particle size distribution of the aminoguanidine carbonate prepared in Comparative Example 6. Detailed Implementation

[0028] The present invention will be further illustrated below with specific embodiments. These embodiments are merely illustrative and do not limit the scope of the invention.

[0029] Example 1 A green production process for aminoguanidine carbonate includes the following steps: (1) 45 kg of hydrazine hydrate (concentration of 80%) and 90 kg of softened water were continuously fed into the premixer through a proportional pump for premixing. At the same time, CO2 gas was pumped into the premixer and the pressure was controlled between 0.03 MPa and 0.05 MPa. The flow rate of CO2 was adjusted by online pH feedback to stabilize the pH of the mixture at 5.0 to 5.5. The premixing time was 2.0 hours and the premixing temperature was 15℃. After the premixing was completed, the premixed solution was obtained. (2) The premixed solution obtained in step (1) and 100 kg of a 30% cyanamide aqueous solution were pumped separately into a Taylor tubular reactor. The flow rate of the cyanamide aqueous solution in the Taylor tubular reactor was 3.5. The flow rate of the premixed liquid in the Taylor tubular reactor is 5 L / min. The inner cylinder rotation speed of the Taylor tubular reactor is 800 rpm, and the Taylor number (Ta) is >50. CO2 injection ports are set at the inlet, middle, and outlet of the Taylor tubular reactor. Each injection port contains 5 air inlets. CO2 is injected into the Taylor tubular reactor through the air inlets by pressure reducing valves. The pressure of the front injection port (reactor inlet) is set between 0.045 and 0.050 MPa, the pressure of the middle injection port (reactor middle inlet) is set between 0.035 and 0.040 MPa, and the pressure of the rear injection port (reactor outlet) is set between 0.025 and 0.030 MPa. The pH value of the reaction system is maintained between 5.0 and 5.5. The total residence time of the reaction liquid is 2.0 hours, and the reaction temperature is 40℃. (3) The reaction liquid obtained in step (2) is rapidly cooled to 0°C at a rate of 15°C / min through a tubular heat exchanger and then enters a 500L stainless steel reactor for crystallization. Crystallization is carried out at 0°C for 3 hours. (4) After crystallization, open the feed valve and feed the liquid obtained after crystallization in step (3) into the tank of the three-in-one filter washing and drying machine. Lower the stirring paddle and stir at low speed (stirring speed 15r / min) to make the material evenly distributed. After feeding, close the feed valve and open the filtrate outlet valve. Gradually increase the pressure for filtration. The pressure should be ≤0.3MPa. If air leakage is found in the filter cake, the stirring paddle can be lowered to perform low-speed surface leveling. The washing liquid is introduced into the tank through the washing liquid port. After 50kg of washing liquid is introduced, stop adding. Gradually and slowly lower the stirring paddle and stir at a speed of 25r / min. When there is no liquid flowing out of the outlet after pressure filtration, first open the hot water inlet and outlet valves, open the vacuum valve, and dry under vacuum. Before discharge, take a sample to test the drying loss ≤1.0%. After passing the test, prepare to discharge. First close the heating water valve, slowly open the cooling water valve, slowly lower the stirring paddle, and stir the material to accelerate cooling. At this time, the vacuum pump can be turned on to draw a vacuum and discharge the hot air. Before opening the discharge valve, pure nitrogen gas is introduced for balancing protection. When the pressure is at atmospheric pressure, the material is discharged from the discharge valve by the reverse thrust of the agitator, yielding the product aminoguanidine carbonate. The mass spectrum of the prepared aminoguanidine carbonate is shown below. Figure 1 [M+H]=75.1, which is the molecular weight of aminoguanidine. The liquid chromatogram is shown below. Figure 2 Purity 99.72%, particle size distribution shown in [reference needed]. Figure 3 The crystals have a D50 of 47.3 μm, uniform crystal size distribution, and a D50 between 40 and 50 μm. The yield is 100%.

[0030] Example 2 A green production process for aminoguanidine carbonate includes the following steps: (1) 45 kg of hydrazine hydrate (concentration of 80%) and 90 kg of softened water were continuously fed into the premixer through a proportional pump for premixing. At the same time, CO2 gas was pumped into the premixer to control the pressure between 0.03 MPa and 0.05 MPa. The CO2 flow rate was adjusted by online pH feedback to stabilize the pH of the mixture at 5.0 to 5.5. The premixing time was 1.0 hour and the premixing temperature was 35℃. After the premixing was completed, the premixed liquid was obtained. (2) The premixed solution obtained in step (1) and 100 kg of a 30% cyanamide aqueous solution were pumped separately into a Taylor tubular reactor. The flow rate of the cyanamide aqueous solution in the Taylor tubular reactor was 3.5. The flow rate of the premixed liquid in the Taylor tubular reactor is 5 L / min. The inner cylinder rotation speed of the Taylor tubular reactor is 800 rpm, and the Taylor number (Ta) is >50. CO2 injection ports are set at the inlet, middle, and outlet of the Taylor tubular reactor. Each injection port has 4 air inlets. CO2 is injected into the Taylor tubular reactor through the air inlets by pressure reducing valves. The pressure of the front injection port (reactor inlet) is set between 0.045 and 0.050 MPa, the pressure of the middle injection port (reactor middle inlet) is set between 0.035 and 0.040 MPa, and the pressure of the rear injection port (reactor outlet) is set between 0.025 and 0.030 MPa. The pH value of the reaction system is maintained between 5.0 and 5.5. The total residence time of the reaction liquid is 1.0 hour, and the reaction temperature is 50℃. (3) The reaction liquid obtained in step (2) is rapidly cooled to 2°C at a rate of 20°C / min through a tubular heat exchanger and then enters a 500L stainless steel reactor for crystallization. Crystallization is carried out at 2°C for 2 hours. (4) After crystallization, open the feed valve and feed the liquid obtained in step (3) into the tank of the three-in-one filter washing and drying machine. Lower the stirring paddle and stir at low speed (stirring speed 15r / min) to make the material evenly distributed. After feeding, close the feed valve and open the filtrate outlet valve. Gradually increase the pressure for filtration. The pressure should be ≤0.3MPa. If air leakage is found in the filter cake, the stirring paddle can be lowered to perform low-speed surface leveling. The washing liquid is introduced into the tank through the washing liquid port. After 50kg of washing liquid is introduced, stop adding. Gradually and slowly lower the stirring paddle and stir at a speed of 25r / min. When there is no liquid flowing out of the outlet after pressure filtration, first open the hot water inlet and outlet valves, open the vacuum valve, and dry under vacuum. Before discharge, take a sample to test the drying loss ≤1.0%. After passing the test, prepare to discharge. First close the heating water valve, slowly open the cooling water valve, slowly lower the stirring paddle, and stir the material to accelerate cooling. At this time, the vacuum pump can be turned on to remove the hot air. Before opening the discharge valve, pure nitrogen is introduced for balancing protection. When the pressure is at atmospheric pressure, the material is discharged from the discharge valve by the reverse thrust of the agitator, yielding aminoguanidine carbonate as the product. The yield is 99.98%, the purity is 99.70%, the crystal particle size distribution is uniform, and the crystal D50 is 40-50 μm.

[0031] Comparative Example 1 Comparative Example 1 is basically the same as Example 1, except that in step (1), CO2 gas is not pumped into the premixer to keep the pH of the mixture stable between 7.0 and 7.5.

[0032] The aminoguanidine carbonate prepared in Comparative Example 1 had a yield of 63.0% and a purity of 97.6%.

[0033] Comparative Example 2 Comparative Example 2 is basically the same as Example 1, except that the pumping pressure of CO2 gas in step (1) is controlled at 0.020±0.005MPa and the pH of the mixture is stable between 6.2 and 6.5.

[0034] The aminoguanidine carbonate prepared in Comparative Example 2 had a yield of 83.3% and a purity of 98.90%.

[0035] Comparative Example 3 Comparative Example 3 is basically the same as Example 1, except that: CO2 is not added in step (2), no product is precipitated, and aminoguanidine carbonate cannot be obtained.

[0036] Comparative Example 4 Comparative Example 4 is basically the same as Example 1, except that in step (2), only one CO2 injection port is set at the inlet of the Taylor tubular reactor. The injection port contains 5 air inlets and the pressure of the injection port is set between 0.045 and 0.050 MPa.

[0037] The aminoguanidine carbonate prepared in Comparative Example 4 had a yield of 84.1% and a purity of 98.7%.

[0038] Comparative Example 5 Comparative Example 5 is basically the same as Example 1, except that the pressure of the front, middle and rear inlet of the Taylor tubular reactor in step (2) is set to between 0.035 and 0.040 MPa.

[0039] The aminoguanidine carbonate prepared in Comparative Example 5 had a yield of 96.0% and a purity of 99.32%.

[0040] Comparative Example 6 Comparative Example 6 is basically the same as Example 1, except that in step (3), the cooling rate of rapid cooling is 3℃ / min, the temperature is cooled to 20℃, and crystallization takes 3 hours.

[0041] The aminoguanidine carbonate prepared in Comparative Example 6 had a yield of 80.7% and a purity of 99.62%. The particle size distribution is shown in the figure. Figure 4 The crystal particle size was D50 = 87.79 μm. Comparative Example 6 had a low yield and low purity due to slow cooling rate and high crystallization temperature (20℃), resulting in a larger crystal particle size D50 and lower crystal particle uniformity.

Claims

1. A green production process for aminoguanidine carbonate, characterized in that: Includes the following steps: (a) Hydrazine hydrate and softened water are fed into a premixer, CO2 gas is pumped into the premixer for premixing, and a premixed liquid is obtained after premixing. (b) The premixed solution obtained in step (a) and the cyanamide aqueous solution are pumped into a Taylor tubular reactor, and CO2 injection ports are set in sections on the Taylor tubular reactor. CO2 is injected into the Taylor tubular reactor through the CO2 injection ports to maintain the pH value of the reaction system between 5.0 and 5.5 and carry out the reaction. (c) The reaction solution obtained in step (b) is rapidly cooled by a tubular heat exchanger and then introduced into the reactor for crystallization; (d) After crystallization, the liquid is filtered, washed and dried to obtain the product aminoguanidine carbonate.

2. The green production process for aminoguanidine carbonate according to claim 1, characterized in that: In step (a), the pumping pressure of CO2 gas is controlled between 0.03 MPa and 0.05 MPa to stabilize the pH of the mixture at 5.0 to 5.5 for premixing.

3. The green production process for aminoguanidine carbonate according to claim 1, characterized in that: In step (a), the concentration of hydrazine hydrate is 80-81%, the mass ratio of hydrazine hydrate to softened water is 1.0:1.0-3.0, the premixing time is 0.5-2.0 hours, and the premixing temperature is 10-40℃.

4. The green production process for aminoguanidine carbonate according to claim 1, characterized in that: In step (b), CO2 injection ports are set at the inlet, middle and outlet of the Taylor tubular reactor, respectively, and the carbon dioxide injection pressure of the three CO2 injection ports is controlled respectively. The pressure of the inlet injection port is controlled at 0.045~0.050MPa, the pressure of the middle injection port is controlled at 0.035~0.040MPa, and the pressure of the outlet injection port is controlled at 0.025~0.030MPa.

5. The green production process for aminoguanidine carbonate according to claim 4, characterized in that: In step (b), each CO2 injection port on the Taylor tubular reactor is provided with 3 to 5 air inlets.

6. The green production process for aminoguanidine carbonate according to claim 1, characterized in that: In step (b), the reaction conditions are as follows: the total residence time of the reaction solution is 0.5 to 2.0 hours, and the reaction temperature is 40 to 50°C.

7. The green production process for aminoguanidine carbonate according to claim 1, characterized in that: In step (b), the inner cylinder of the Taylor tubular reactor rotates at 500-1000 rpm, and the Taylor number Ta ≥ 50.

8. The green production process for aminoguanidine carbonate according to claim 1, characterized in that: In step (b), the flow rate of the cyanamide aqueous solution in the Taylor tubular reactor is 3 L ~ 4 L / min, and the flow rate of the premixed solution in the Taylor tubular reactor is 5 L / min.

9. The green production process for aminoguanidine carbonate according to claim 1, characterized in that: In step (c), the rapid cooling rate is 10~20℃ / min, the temperature is 0~5℃, and the crystallization time is 1~3 hours.

10. The green production process for aminoguanidine carbonate according to claim 1, characterized in that: Step (d) is as follows: After crystallization, the liquid enters the three-in-one centrifugal washing and drying machine and is stirred at a low speed of 10~20 r / min to make the material evenly distributed. After feeding, the feed valve is closed and the filtrate outlet valve is opened. The pressure is gradually increased for filtration, with a pressure ≤0.3MPa. Water is added as washing liquid and stirred at a speed of 20~30 r / min. When the pressure filter is pressed until no liquid flows out of the outlet, the hot water inlet and outlet valves are opened first, and the vacuum valve is opened. Drying is carried out under vacuum. Before discharge, a sample is taken to test the drying loss ≤1.0%. After passing the test, the product aminoguanidine carbonate is discharged.

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