Method for separating and recovering sodium carbonate and sodium chloride in crude hydrazine and concentrating hydrazine and hydrazine hydrate

Abstract

The invention provides a method for separating and recovering sodium carbonate and sodium chloride in crude hydrazine and concentrating hydrazine and hydrazine hydrate. The crude hydrazine comprises hydrazine hydrate, water, sodium carbonate and sodium chloride, and the method comprises the following steps: drawing a solubility phase diagram of a Na2CO3-NaCl-H6N2O ternary system, evaporating the crude hydrazine, dynamically adjusting the amount of evaporated water according to the solubility phase diagram, preventing Na2CO3 from being separated out, and reducing volatilization of hydrazine hydrate at the same time; when a liquid phase point moves to a point E, stopping evaporation to obtain a sodium chloride product, and cooling the primary mother liquor to obtain a sodium carbonate product; and mixing the secondary mother liquor with the crude hydrazine, and performing circular treatment. According to the method, the Na2CO3-NaCl-H6N2O ternary phase diagram is finely constructed, and the influence of the temperature and the hydrazine hydrate concentration on the solubility of the sodium salt is comprehensively evaluated, so that the optimal condition for precipitation of Na2CO3 and NaCl can be accurately identified, high-purity separation and recovery of Na2CO3 and NaCl are realized, and the hydrazine hydrate concentration is effectively improved.

Description

Technical Field

[0001] The invention relates to the technical field of chemical separation, in particular to a method for separating and recovering sodium carbonate and sodium chloride in crude hydrazine and concentrating hydrazine, and a hydrazine hydrate. Background Art

[0002] The urea process for producing hydrazine hydrate is a widely used production process in the chemical industry and has become the primary method for producing hydrazine hydrate in my country. The basic process involves dissolving urea in water to form a urea solution. This solution is then reacted with a mixed solution of sodium hypochlorite and caustic soda in a tubular oxidation reactor in the presence of magnesium sulfate as a promoter, producing a crude hydrazine hydrate product with a hydrazine content exceeding 2%. However, after ultrafiltration and concentration, the resulting hydrazine-containing wastewater contains significant amounts of inorganic impurities such as sodium carbonate and sodium chloride.

[0003] Directly discharging this salty wastewater not only causes significant environmental pollution but also means the loss of sodium carbonate and sodium chloride, a significant waste of resources. Given the importance of sodium carbonate and sodium chloride as basic chemicals in multiple industrial sectors, effectively recycling and utilizing these substances not only reduces production costs but also improves overall resource efficiency and environmental standards.

[0004] For the recovery of inorganic salts in hydrazine-containing wastewater, the current treatment methods mainly include evaporative crystallization and freezing separation. Evaporative crystallization is usually used for the recovery of sodium chloride, while freezing is used for the separation of sodium carbonate. However, both of these traditional methods have certain technical bottlenecks and environmental problems. When controlling the separation point of sodium chloride, the evaporative crystallization method is usually difficult to achieve precise control, which leads to poor crystallization effect of sodium chloride and incomplete separation, thereby causing the loss of sodium salt resources. When the freezing method is used to treat sodium carbonate, due to the difficulty in accurately controlling the freezing temperature, the sodium carbonate crystallization rate is low and the separation is incomplete, which in turn affects the recovery efficiency of sodium carbonate.

[0005] Therefore, a more precise and efficient treatment strategy is urgently needed to solve the problem of separation and recovery of sodium chloride and sodium carbonate in hydrazine-containing wastewater. Summary of the Invention

[0006] The main purpose of the present invention is to provide a method for separating and recovering sodium carbonate and sodium chloride in crude hydrazine and concentrating hydrazine, and a hydrazine hydrate, so as to solve the problem of incomplete separation when separating and recovering sodium carbonate and sodium chloride in hydrazine hydrate production wastewater in the prior art.

[0007] To achieve the above object, according to one aspect of the present invention, a method for separating and recovering sodium carbonate and sodium chloride in crude hydrazine and concentrating hydrazine is provided. The crude hydrazine comprises hydrazine hydrate, water, sodium carbonate and sodium chloride. The method comprises the following steps: step S1, drawing a solubility phase diagram of a Na2CO3-NaCl-H6N2O ternary system: using aqueous solutions with different hydrazine hydrate concentrations as solvent, adding sodium carbonate and sodium chloride thereto, measuring the solubility of the system by adopting an isothermal dissolution equilibrium method, and after obtaining solubility data, drawing a solubility phase diagram of the Na2CO3-NaCl-H6N2O ternary system with different hydrazine hydrate concentrations; wherein the vertex W represents the pure solvent, point A represents the saturated solution of NaCl, point B represents the saturated solution of Na2CO3, and point E represents the co-saturated point of NaCl and Na2CO3; curve AE represents the solubility curve of NaCl in the presence of Na2CO3, curve BE represents the solubility curve of Na2CO3 in the presence of NaCl, area a represents the unsaturated phase area, area b represents the NaCl crystallization area, and area c represents the Na2CO3·10H2O crystallization area. region, with region d representing the eutectic region of NaCl and Na2CO3·10H2O; step S2, separating NaCl: using point L to represent the composition of crude hydrazine, evaporating the crude hydrazine to saturate and precipitate NaCl, performing a first filtration, gradually reducing the water in the system, and dynamically increasing the hydrazine hydrate concentration accordingly. When the liquidus point moves to L1, the intersection of WL and AE, it indicates that NaCl has reached a saturated state; continuing evaporation, NaCl precipitates, and the liquidus point moves from point L1 along AE to point E. The amount of evaporated water is dynamically adjusted according to the solubility phase diagram to prevent the precipitation of Na2CO3 and reduce the volatilization of hydrazine hydrate; when the liquidus point moves to point E, stopping evaporation to obtain a sodium chloride product and a primary mother liquor; step S3, separating Na2CO3: cooling the primary mother liquor to saturate and precipitate Na2CO3, performing a second filtration to obtain a sodium carbonate product and a secondary mother liquor; step S4, mixing the secondary mother liquor with the crude hydrazine for a cyclic treatment to obtain a concentrated hydrazine-containing solution.

[0008] Furthermore, in the solvent, the mass concentration of hydrazine hydrate is 0.01-50%; and / or, in the crude hydrazine, the mass concentration of sodium chloride is 0.01-30%, and the mass concentration of sodium carbonate is 0.01-5%.

[0009] Furthermore, in step S2, the evaporation process is a gradient temperature rising evaporation process.

[0010] Furthermore, during the evaporation process, the initial temperature is 15-25°C, the heating rate is 0.5-4°C / min, the temperature is kept at 3-5°C for 20-40 minutes, and the terminal temperature is 35-45°C.

[0011] Furthermore, step S2 further includes a step of first drying the sodium chloride product; preferably, the first drying temperature is 55-65° C., and the time is 1-3 hours.

[0012] Furthermore, in step S3, the cooling rate is 0.5-4°C / min, and the end temperature is 10-25°C.

[0013] Furthermore, step S3 further includes a step of performing a second drying on the sodium carbonate product; preferably, the second drying temperature is 55 to 65° C., and the time is 1 to 3 hours.

[0014] Furthermore, in the sodium chloride product, the purity of NaCl is ≥99%, preferably 99.5-99.99%.

[0015] Furthermore, in the sodium carbonate product, the purity of Na2CO3 is ≥99%, preferably 99.5 to 99.99%.

[0016] According to another aspect of the present invention, a hydrazine hydrate is provided, wherein the raw material comprises the concentrated hydrazine-containing solution prepared according to the above method.

[0017] In response to the hydrazine-containing wastewater generated in the production of hydrazine hydrate by the urea process, the present invention proposes a method for separating and recovering sodium carbonate and sodium chloride from crude hydrazine and concentrating hydrazine. By carefully constructing the Na2CO3-NaCl-H6N2O ternary phase diagram and comprehensively evaluating the effects of temperature and hydrazine hydrate concentration on the solubility of sodium salts, the optimal conditions for the precipitation of Na2CO3 and NaCl can be accurately identified, achieving high-purity separation and recovery of the two, as well as an effective increase in the concentration of hydrazine hydrate. The concentrated hydrazine-containing solution can be directly reused in the manufacturing process of hydrazine hydrate, forming a closed loop and achieving zero waste discharge. Compared with traditional separation technologies, the present invention not only significantly improves separation efficiency, reduces resource consumption and waste, but also significantly reduces the negative impact on the environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0019] Figure 1 The phase diagram of the Na2CO3-NaCl-H6N2O ternary system at different hydrazine hydrate concentrations at 25°C in Example 1 of the present invention is shown;

[0020] Figure 2 The phase diagram shows the gradient temperature increase evaporation process of hydrazine-containing wastewater in Example 1 of the present invention;

[0021] Figure 3The figure shows the solubility of NaCl and Na2CO3 as a function of temperature in Example 1 of the present invention. DETAILED DESCRIPTION

[0022] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0023] Explanation of terms:

[0024] Isothermal dissolution equilibrium method: a method of determining solubility by measuring the concentration of a solute when it is dissolved to saturation at a constant temperature.

[0025] It should be noted that in the description and claims of the present invention, the terms "first," "second," etc. are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the terms used in this manner are interchangeable where appropriate to describe the embodiments of the present invention.

[0026] As described in the background of the present invention, the prior art has the problem of incomplete separation when separating and recovering sodium carbonate and sodium chloride from hydrazine hydrate production wastewater. In order to solve the above problems, in a typical embodiment of the present invention, a method for separating and recovering sodium carbonate and sodium chloride in crude hydrazine and concentrating hydrazine is provided, wherein the crude hydrazine includes hydrazine hydrate, water, sodium carbonate, and sodium chloride, and the method includes the following steps: step S1, drawing a solubility phase diagram of the Na2CO3-NaCl-H6N2O ternary system: using an aqueous solution with different hydrazine hydrate concentrations as a solvent, adding sodium carbonate and sodium chloride thereto, and determining the solubility of the system by an isothermal dissolution equilibrium method. After obtaining the solubility data, a solubility phase diagram of the Na2CO3-NaCl-H6N2O ternary system with different hydrazine hydrate concentrations is drawn; wherein, vertex W represents a pure solvent, point A represents a saturated solution of NaCl, point B represents a saturated solution of Na2CO3, and point E represents a co-saturated point of NaCl and Na2CO3; curve AE represents the solubility curve of NaCl in the presence of Na2CO3, curve BE represents the solubility curve of Na2CO3 in the presence of NaCl, area a represents the unsaturated phase region, and area b represents the N aCl crystallization area, c area represents Na2CO3·10H2O crystallization area, d area represents NaCl and Na2CO3·10H2O eutectic area; step S2, separation of NaCl: point L represents the composition of crude hydrazine, the crude hydrazine is evaporated to saturate and precipitate NaCl, a first filtration is performed, the water in the system gradually decreases, and the concentration of hydrazine hydrate increases dynamically. When the liquidus point moves to the intersection point L1 of WL and AE, it indicates that NaCl has reached a saturated state; continue evaporation, NaCl is precipitated, and the liquidus point is saturated. The phase point moves from point L1 along AE to point E, and the amount of evaporated water is dynamically adjusted according to the solubility phase diagram to prevent the precipitation of Na2CO3 and reduce the volatilization of hydrazine hydrate. When the liquidus point moves to point E, evaporation is stopped to obtain a sodium chloride product and a primary mother liquor. Step S3: separating Na2CO3: cooling the primary mother liquor to saturate and precipitate Na2CO3, and performing a second filtration to obtain a sodium carbonate product and a secondary mother liquor. Step S4: mixing the secondary mother liquor with crude hydrazine for a circulating treatment to obtain a concentrated hydrazine-containing solution.

[0027] It should be noted that the pure solvent in this application refers to an aqueous solution including hydrazine hydrate, which does not include Na2CO3 and NaCl. This is understandable to those skilled in the art and will not be elaborated here.

[0028] In the method of the present invention, step S1 uses the isothermal dissolution equilibrium method to systematically study the solubility of sodium carbonate and sodium chloride at different hydrazine hydrate concentrations, and then draws a ternary phase diagram covering multiple temperature points. This provides a theoretical basis for subsequent steps, allowing for accurate understanding of the dissolution and precipitation patterns of each salt when processing complex solvent systems, thereby achieving efficient separation. Compared to the prior art that only processes a single aqueous solvent, the present invention requires real-time monitoring of solubility during changes in hydrazine hydrate concentration and draws a dynamic phase diagram, which also provides a theoretical basis for the separation of complex systems.

[0029] Step S2, based on the phase diagram drawn in step S1, realizes the efficient separation of sodium chloride by controlling the evaporation process of crude hydrazine. During the evaporation process, as water decreases, the concentration of hydrazine hydrate increases dynamically, and the system point moves to the saturation point along the WL line. When the system point arrives L1, NaCl begins to saturate and precipitate. By accurately calculating and controlling the evaporation amount, Na2CO3 can be avoided from being precipitated while reducing the volatilization loss of hydrazine hydrate. This process makes full use of the phase diagram information and guides the optimal condition setting of the evaporation process, thereby ensuring the high-purity separation of sodium chloride.

[0030] In step S3, the remaining primary mother liquor after step S2 is cooled to saturate and crystallize the sodium carbonate. This process complements the evaporation step, achieving sequential and independent separation of the salts, improving the purity and efficiency of the separation.

[0031] In step S4, the secondary mother liquor after separation of sodium carbonate is mixed with the original crude hydrazine for recycling. This process not only recovers the unused solvent but also further concentrates the hydrazine hydrate by controlling the conditions, reducing waste liquid discharge and embodying a closed-loop resource utilization.

[0032] Each step of the present invention is closely linked and works together to contribute to the overall separation and recovery process, demonstrating a synergistic effect. "Phase diagram drawing" provides a theoretical basis for the subsequent "inorganic salt separation"; the "sodium chloride separation" and "sodium carbonate separation" steps are sequential and orderly, with the former creating the conditions for the latter and avoiding mutual interference in the salt recovery process; and the "circular treatment" is an extension of the results of the first three steps, achieving both economical and environmentally friendly overall process through resource reuse.

[0033] Unlike existing freezing and evaporative crystallization methods, the core of this invention lies in utilizing the principles of the ternary phase diagram, combined with precise control of evaporation and cooling conditions, to achieve efficient separation of sodium carbonate and sodium chloride in complex solvent systems, avoiding the limitations and non-selective precipitation issues associated with mixed solvent processing. Furthermore, by implementing a recycling process, this invention further increases the concentration of hydrazine hydrate and reduces wastewater discharge, demonstrating comprehensive improvements in resource recovery and environmental friendliness.

[0034] In summary, the present invention provides a method for separating and recovering sodium carbonate and sodium chloride in crude hydrazine and concentrating hydrazine in the face of crude hydrazine produced by urea process, by accurately constructing the Na2CO3-NaCl-H6N2O ternary system phase diagram, comprehensively considering the influence of temperature and hydrazine hydrate concentration on the solubility of sodium salt, analyzing the optimal point for precipitating Na2CO3 and NaCl in the Na2CO3-NaCl-H6N2O three-phase, achieving accurate separation and recovery of NaCl and Na2CO3 (for example: the purity of sodium carbonate and sodium chloride after separation reaches more than 99%), and effectively improving the concentration of hydrazine hydrate, the concentrated hydrazine-containing solution can be reused in hydrazine hydrate production, thereby achieving zero emission, solving the problems of low separation efficiency and waste of resources in the prior art, while reducing environmental pollution and improving resource recycling efficiency. Compared with the prior art, the present invention has a stronger ability to handle complex solvent systems and a better separation effect.

[0035] The method of the present invention is applicable to Na2CO3-NaCl-H6N2O systems of various hydrazine hydrate solubilities. In a preferred embodiment, the mass concentration of hydrazine hydrate in the solvent is 0.01-50%; and / or, in the crude hydrazine, the mass concentration of sodium chloride is 0.01-30%, and the mass concentration of sodium carbonate is 0.01-5%.

[0036] In a preferred embodiment, in step S2, the evaporation process is a gradient temperature evaporation process. This dynamic evaporation process can more precisely control the evaporation rate, more effectively avoid the unexpected precipitation of sodium carbonate, while minimizing the volatilization loss of hydrazine hydrate, ensuring high-purity recovery of sodium chloride, and thus improving the efficiency and economy of the entire separation and recovery process.

[0037] In a preferred embodiment, the initial temperature during the evaporation process is 15-25°C. This range effectively ensures system stability during the initial phase, avoids unnecessary volatilization of hydrazine hydrate due to excessively high temperatures, and lays the foundation for subsequent precise control. To ensure a smoother transition of the system points on the phase diagram, avoid non-selective precipitation of salts due to sudden temperature changes, and more effectively ensure the controllability and efficiency of the separation process, in a preferred embodiment, the heating rate is 0.5-4°C / min. In a preferred embodiment, the temperature is held for 20-40 minutes at intervals of 3-5°C. This gradient heating strategy better balances the relationship between the evaporation rate and the change in salt solubility, ensuring complete precipitation of sodium chloride at the appropriate temperature while avoiding premature saturation precipitation of sodium carbonate, thereby improving separation accuracy and product purity. In a preferred embodiment, the endpoint temperature is 35-45°C. Within this range, it can more effectively promote the precipitation of sodium chloride while preventing premature crystallization of sodium carbonate, which is more conducive to achieving high-purity separation of NaCl and reducing energy consumption.

[0038] In a preferred embodiment, step S2 further includes a first drying step of the sodium chloride product; preferably, the first drying temperature is 55-65° C. and the drying time is 1-3 hours. Within the above range, the drying efficiency and quality of the sodium chloride can be further ensured, moisture and trace impurities attached to the crystal surface can be effectively removed, and the purity and drying speed of the final sodium chloride product can be improved. At the same time, this temperature range is more conducive to maintaining the integrity of the sodium chloride crystal structure and avoiding increased energy consumption and crystal damage caused by excessive high-temperature drying.

[0039] In a preferred embodiment, the cooling rate of the cooling is 0.5 to 4 ° C / min. Under this condition, uniform cooling during the crystallization process can be further promoted, poor crystal growth or dissolution caused by too fast or too slow cooling rate can be avoided, the controllability and consistency of sodium carbonate crystallization can be enhanced, and impurity encapsulation can be more effectively prevented. In order to more effectively promote the formation of sodium carbonate crystals, while avoiding increased energy consumption and reduced efficiency caused by too low a temperature, and ensuring high purity and high recovery of sodium carbonate, in a preferred embodiment, the terminal temperature of the cooling is 10 to 25 ° C, preferably 15 ° C.

[0040] In order to more effectively remove moisture and other impurities that may be adsorbed on the surface of the sodium carbonate crystals, ensure their purity, optimize the drying rate, and avoid the additional energy consumption and production costs that may be introduced by long drying times, in a preferred embodiment, step S3 also includes a second drying step of the sodium carbonate product; preferably, the second drying temperature is 55-65°C and the drying time is 1-3 hours. This temperature range is more conducive to maintaining the chemical stability of the sodium carbonate, preventing decomposition or deterioration during the drying process, and thus achieving efficient and high-quality recovery of the sodium carbonate product.

[0041] The present invention ensures that the separated sodium chloride and sodium carbonate have high purity through the precisely controlled separation and drying process. In a preferred embodiment, the purity of NaCl in the sodium chloride product is ≥99%, preferably 99.5-99.99%; the purity of Na2CO3 in the sodium carbonate product is ≥99%, preferably 99.5-99.99%.

[0042] In order to fully recycle hydrazine hydrate and reduce the loss of raw materials in the production process, in a preferred embodiment, the concentrated hydrazine-containing solution is returned to the hydrazine hydrate production for use.

[0043] In another typical embodiment of the present invention, a hydrazine hydrate is also provided, and the raw material includes a concentrated hydrazine-containing solution prepared according to the above method. The present invention is a concentrated hydrazine-containing solution obtained by refining the phase diagram separation technology, and its hydrazine concentration and purity are significantly improved, which reduces the raw material demand and optimizes resource utilization. Since the method of the present invention effectively removes impurities in wastewater, the stability and efficiency of the concentrated hydrazine-containing solution are enhanced. The hydrazine hydrate product prepared using this high-purity solution as raw material is not only more reliable in quality, but also has improved production efficiency. At the same time, the use of new raw materials is greatly reduced, wastewater discharge is reduced, and the dual goals of cost saving and environmental friendliness are achieved.

[0044] The present application is further described in detail below with reference to specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in this application.

[0045] Example 1

[0046] Step S1, draw the solubility phase diagram of the Na2CO3-NaCl-H6N2O ternary system:

[0047] To a certain amount (100 g) of different hydrazine-containing aqueous solutions (hydrazine hydrate concentrations of 0, 5%, 10%, 15%, and 20%), add Na2CO3 and NaCl in different proportions, stir at 20°C, and after the solid phase no longer dissolves, place it in a constant temperature shaker. Take the clear liquid at regular intervals (4 hours) to analyze the composition. If the composition remains constant, it is considered that the system has reached equilibrium. The equilibrium concentration measured in the solution is the solubility. After obtaining the solubility data, draw a phase diagram for the Na2CO3-NaCl-H6N2O ternary system.

[0048] Figure 1 This is the phase diagram of the Na2CO3-NaCl-H6N2O ternary system at different hydrazine hydrate concentrations at 25°C, where vertex W represents the pure solvent, point A represents the saturated solution of NaCl, point B represents the saturated solution of Na2CO3, and point E represents the co-saturated point of NaCl and Na2CO3; curve AE represents the solubility curve of NaCl in the presence of Na2CO3, curve BE represents the solubility curve of Na2CO3 in the presence of NaCl, area a represents the unsaturated phase area, area b represents the NaCl crystallization area, area c represents the Na2CO3·10H2O crystallization area, and area d represents the NaCl and Na2CO3·10H2O eutectic area.

[0049] Step S2, separation of NaCl:

[0050] Figure 2The present invention is a phase diagram representing the gradient heating evaporation process of hydrazine-containing wastewater. It is known that the salt composition of crude hydrazine is 20.53 wt% NaCl and 3.25 wt% Na2CO3. The solvent includes 2.0 wt% hydrazine hydrate and the remainder is water. Point L represents the composition of the crude hydrazine. The crude hydrazine is gradually heated from 20°C to 40°C at a heating rate of 2°C / min, with a dwell time of 30 min at each 5°C interval to saturate and precipitate NaCl. A first filtration is performed to obtain a sodium chloride product and a primary mother liquor. During the evaporation process, the water in the system gradually decreases, and the hydrazine hydrate concentration increases dynamically. When the evaporation system point reaches the intersection L1 of WL and AE, it indicates that NaCl has reached a saturated state. Evaporation continues, NaCl precipitates, and the liquidus point moves from point L1 along AE to point E. The hydrazine hydrate concentration in the system is measured every 4 hours. The system evaporation point E is calculated based on the phase diagram at the corresponding hydrazine hydrate concentration to prevent Na2CO3 precipitation and reduce the volatilization of hydrazine hydrate. Evaporation is stopped when the liquidus point moves to point E. The filtered sodium chloride was dried at 60° C. for 2 h, and the purity of the sodium carbonate was 99.9% after analysis.

[0051] Step S3, separation of Na2CO3:

[0052] Figure 3 The solubility curve of NaCl and Na2CO3 changes with temperature. As can be seen from the figure, during the cooling process from 40℃ to 15℃, the solubility of NaCl does not change significantly with the decrease in temperature, but the solubility of Na2CO3 decreases significantly with the decrease in temperature. Therefore, after isothermal evaporation separates a portion of NaCl solid, the system can use cooling to separate Na2CO3·10H2O solid. Therefore, the primary mother liquor is gradually cooled from 40℃ to 15℃ at a cooling rate of 2℃ / min to saturate Na2CO3 and precipitate it. It is then filtered to obtain sodium carbonate product (mainly Na2CO3·10H2O) and secondary mother liquor. The filtered sodium carbonate solid is dried at 60℃ for 2h, and analysis shows that the purity of the sodium carbonate is 99.9%.

[0053] In step S4, the secondary mother liquor is mixed with the crude hydrazine for recycling treatment to complete the separation of Na2CO3 and NaCl, and finally a concentrated hydrazine-containing solution is obtained and returned to production.

[0054] Example 2

[0055] The only difference from Example 1 is:

[0056] The composition of the treated crude hydrazine is: NaCl 0.01wt%, Na2CO3 3.25%, hydrazine hydrate 0.01wt% in the solvent, and the rest is water.

[0057] The purity of the separated sodium chloride is 99.5%; the purity of the separated sodium carbonate is 99.9%.

[0058] Example 3

[0059] The only difference from Example 1 is:

[0060] The composition of the treated crude hydrazine is: NaCl 20.53 wt%, Na2CO3 0.01 wt%, hydrazine hydrate 50 wt% in the solvent, and the rest is water.

[0061] The purity of the separated sodium chloride is 99.9%; the purity of the separated sodium carbonate is 99.5%.

[0062] Example 4

[0063] The only difference from Example 1 is:

[0064] In step S2, the crude hydrazine is gradually heated from 15°C to 40°C at a heating rate of 2°C / min, and is kept at 5°C for 30 minutes.

[0065] The purity of the separated sodium chloride is 99.9%; the purity of the separated sodium carbonate is 99.9%.

[0066] Example 5

[0067] The only difference from Example 1 is:

[0068] In step S2, the crude hydrazine is gradually heated from 25°C to 40°C at a heating rate of 2°C / min, and is kept at 5°C for 30 minutes.

[0069] The purity of the separated sodium chloride is 99.9%; the purity of the separated sodium carbonate is 99.9%.

[0070] Example 6

[0071] The only difference from Example 1 is:

[0072] In step S3, the temperature is cooled from 40°C to 25°C at a cooling rate of 2°C / min.

[0073] The purity of the separated sodium chloride is 99.9%; the purity of the separated sodium carbonate is 99.9%.

[0074] Example 7

[0075] The only difference from Example 1 is:

[0076] In step S3, the temperature is cooled from 40°C to 10°C at a cooling rate of 2°C / min.

[0077] The purity of the separated sodium chloride is 99.9%; the purity of the separated sodium carbonate is 99.9%.

[0078] As can be seen from the above, the present invention, by carefully constructing the Na2CO3-NaCl-H6N2O ternary phase diagram and comprehensively evaluating the effects of temperature and hydrazine hydrate concentration on the solubility of sodium salts, can accurately identify the optimal conditions for the precipitation of Na2CO3 and NaCl, achieve high-purity separation and recovery of both, and effectively improve the concentration of hydrazine hydrate. The concentrated hydrazine-containing solution can be directly reused in the manufacturing process of hydrazine hydrate, forming a closed loop and achieving zero waste discharge. Compared with traditional separation technology, the present invention not only significantly improves separation efficiency, reduces resource consumption and waste, but also significantly reduces the negative impact on the environment.

[0079] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for separating and recovering sodium carbonate and sodium chloride from crude hydrazine and concentrating hydrazine, characterized in that: The crude hydrazine comprises hydrazine hydrate, water, sodium carbonate and sodium chloride, and the method comprises the following steps: Step S1, draw the solubility phase diagram of the Na2CO3-NaCl-H6N2O ternary system: Using aqueous solutions of different hydrazine hydrate concentrations as solvents, sodium carbonate and sodium chloride are added thereto, and the solubility of the system is determined by the isothermal dissolution equilibrium method. After obtaining the solubility data, a solubility phase diagram of the Na2CO3-NaCl-H6N2O ternary system with different hydrazine hydrate concentrations is drawn; wherein, vertex W represents the pure solvent, point A represents the saturated solution of NaCl, point B represents the saturated solution of Na2CO3, and point E represents the co-saturated point of NaCl and Na2CO3; curve AE represents the solubility curve of NaCl in the presence of Na2CO3, curve BE represents the solubility curve of Na2CO3 in the presence of NaCl, area a represents the unsaturated phase area, area b represents the NaCl crystallization area, area c represents the Na2CO3·10H2O crystallization area, and area d represents the NaCl and Na2CO3·10H2O eutectic area; Step S2, separation of NaCl: Point L represents the composition of crude hydrazine, and the crude hydrazine is evaporated to saturate and precipitate NaCl. A first filtration is performed, and the water in the system gradually decreases, and the hydrazine hydrate concentration increases dynamically. When the liquidus point moves to the intersection L1 of WL and AE, it indicates that NaCl has reached a saturated state; the evaporation is continued, NaCl precipitates, and the liquidus point moves from point L1 along AE to point E. The amount of evaporated water is dynamically adjusted according to the solubility phase diagram to prevent Na2CO3 precipitation and reduce the volatilization of hydrazine hydrate; when the liquidus point moves to point E, the evaporation is stopped to obtain a sodium chloride product and a primary mother liquor; Step S3, separation of Na2CO3: The primary mother liquor is cooled to saturate and precipitate Na2CO3, and a second filtration is performed to obtain a sodium carbonate product and a secondary mother liquor; Step S4: mixing the secondary mother liquor with the crude hydrazine for a circulation treatment to obtain a concentrated hydrazine-containing solution.

2. The method according to claim 1, characterized in that The mass concentration of hydrazine hydrate in the solvent is 0.01 to 50%; and / or, In the crude hydrazine, the mass concentration of sodium chloride is 0.01-30%, and the mass concentration of sodium carbonate is 0.01-5%.

3. The method according to claim 2, characterized in that In the step S2, The evaporation process is a gradient temperature rising evaporation process.

4. The method according to claim 3, characterized in that During the evaporation process, The initial temperature is 15-25°C, the heating rate is 0.5-4°C / min, the temperature is kept at 3-5°C for 20-40 minutes, and the end temperature is 35-45°C.

5. The method according to any one of claims 1 to 4, characterized in that In the step S2, The step of first drying the sodium chloride product is also included; Preferably, the first drying temperature is 55-65° C., and the time is 1-3 hours.

6. The method according to any one of claims 1 to 5, characterized in that In the step S3, The cooling rate of the cooling is 0.5-4°C / min, and the end point temperature is 10-25°C.

7. The method according to any one of claims 1 to 6, characterized in that In the step S3, The step of subjecting the sodium carbonate product to a second drying step is also included; Preferably, the second drying temperature is 55-65° C. and the time is 1-3 hours.

8. The method according to any one of claims 1 to 7, characterized in that In the sodium chloride product, the purity of NaCl is ≥99%, preferably 99.5-99.99%.

9. The method according to any one of claims 1 to 8, characterized in that In the sodium carbonate product, the purity of Na2CO3 is ≥99%, preferably 99.5-99.99%.

10. A hydrazine hydrate, characterized in that The raw material comprises a concentrated hydrazine-containing solution prepared by the method according to any one of claims 1 to 9.

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