A method for preparing sodium carbonate based on ternary synthesis technology

Abstract

The application relates to the technical field of inorganic chemical synthesis, in particular to a sodium carbonate preparation method based on ternary synthesis technology. The method takes sodium chloride, liquid ammonia and carbon dioxide as ternary raw materials, and through a'segmented carbonization-gradient temperature control crystallization-CO2 closed loop recovery-mother liquor optimization treatment' synergistic process, first, uniform crystal nuclei are induced through low-temperature pre-carbonization, then, sufficient reaction is promoted through medium-temperature deep carbonization, and the crystal structure is optimized by combining gradient cooling crystallization and aging, and the efficient recycling of carbon, ammonia and salt resources is realized. The application improves the carbon dioxide utilization rate and the product purity, optimizes the crystal particle size uniformity, reduces the energy consumption and the environmental protection load, the process is stable and easy to control, and has strong industrialization adaptability, and the obtained sodium carbonate can meet the strict requirements in the fields such as food processing, and has economic and environmental benefits.

Description

Technical Field

[0001] This invention relates to the field of inorganic chemical synthesis technology, and in particular to a method for preparing sodium carbonate based on ternary synthesis technology. Background Technology

[0002] Sodium carbonate, a key raw material in food processing and chemical production, has a huge market demand. Its traditional preparation processes mainly involve the ammonia-soda process and the combined alkali process, both revolving around a ternary system of "sodium chloride-liquid ammonia-carbon dioxide." Sodium bicarbonate is produced through a carbonation reaction, and then calcined to obtain the final sodium carbonate product. While these processes have been industrialized, they have long suffered from imperfect process design. In particular, the carbonation stage often employs a single-stage reaction, with carbon dioxide being introduced into the ammonia-water system all at once. This results in excessively high local gas concentrations during the reaction, affecting reaction uniformity, wasting raw materials, and making it difficult to balance reaction efficiency and product quality.

[0003] The core shortcomings of existing technologies are concentrated in three main areas: reaction regulation, crystallization optimization, and resource recycling. The carbonization reaction lacks precise stage-by-stage control, and the mismatch between carbon dioxide dissolution and reaction rates leads to low utilization. The crystallization process often employs natural or rapid cooling methods, lacking precise control over the thermodynamics and kinetics of crystal growth. This results in uneven sodium bicarbonate crystal size, numerous lattice defects, significant losses during subsequent filtration and separation, and may also affect the purity of the final sodium carbonate product. Simultaneously, the carbon dioxide tail gas generated during calcination is mostly emitted directly without forming an effective closed-loop recovery system, leading to a waste of carbon resources. Furthermore, the recovery efficiency of ammonia and salt resources during mother liquor treatment is limited, and some byproducts are difficult to utilize efficiently, increasing production costs and creating environmental pressure.

[0004] With the increasing demand for high-purity sodium carbonate in the food processing industry, and the industry's development trend towards energy conservation, emission reduction, and resource recycling, existing processes are no longer sufficient to meet the production requirements of "high efficiency, low consumption, high quality, and environmental protection." Although some improved technologies attempt to optimize individual process steps, such as adjusting carbonation temperature or improving filtration equipment, they do not construct a systematic solution from the perspective of reaction mechanism and process synergy. Therefore, they cannot fundamentally solve core problems such as incomplete reaction, uneven crystallization, and low resource utilization. Thus, there is an urgent need to develop a new sodium carbonate preparation technology with strong process synergy, precise control, and high resource recycling efficiency. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and propose a method for preparing sodium carbonate based on ternary synthesis technology.

[0006] To achieve the above objectives, the present invention provides a method for preparing sodium carbonate based on ternary synthesis technology, comprising the following steps: (1) Preparation of ammonia brine: Sodium chloride is dissolved in deionized water to prepare saturated brine, and liquid ammonia is introduced to prepare ammonia brine. The brine is then cooled to 15-20℃ for later use. (2) Segmented carbonization reaction: The cooled ammonia brine is first sent to the pre-carbonization tower, and purified calcination by-product CO2 is introduced for low-temperature pre-carbonization to obtain pre-carbonized liquid; then the pre-carbonized liquid is sent to the deep carbonization tower, and industrial CO2 is introduced for medium-temperature deep carbonization to obtain deep carbonized liquid. (3) Gradient temperature controlled crystallization and solid-liquid separation: After the deep carbonized liquid is subjected to gradient cooling crystallization and aging, solid-liquid separation is performed to obtain sodium bicarbonate filter cake and carbonization mother liquor; (4) Closed-loop recovery and purification of CO2: Sodium bicarbonate filter cake is calcined to obtain sodium carbonate. The tail gas generated by calcination is purified through multiple stages of dust removal, dehydration, ammonia removal and adsorption to obtain purified calcination by-product CO2, which is then recycled in the pre-carbonization stage of (2). (5) Mother liquor recycling and ammonia stripping optimization: The carbonization mother liquor is successively subjected to vacuum stripping to recover ammonia, filtered to recover calcium carbonate, and evaporated and crystallized to recover sodium chloride; (6) Preparation of finished product: The sodium carbonate obtained by calcination is cooled and crushed to obtain the finished sodium carbonate product.

[0007] Preferably, the preparation conditions of the salt ammonia water in (1) are: temperature 40-50℃ and pressure 0.2-0.3MPa.

[0008] Preferably, the molar ratio of NH3:NaCl in the ammonia water in (1) is 1.15-1.2:1.

[0009] Preferably, the reaction conditions for low-temperature pre-carbonization in (2) are: temperature 15-20℃, pressure 0.1-0.2MPa, and the introduction rate of purified calcination by-product CO2 is 0.3-0.4m. 3 / (m 3 ·h), reaction time 1.5-2.5h.

[0010] Preferably, the reaction conditions for the intermediate-temperature deep carbonization in (2) are: temperature 20-30℃, pressure 0.2-0.3MPa, and industrial CO2 injection rate 0.5-0.6m. 3 / (m 3 ·h), reaction time 2-3h.

[0011] Preferably, gradient cooling crystallization in (3) refers to cooling to 20°C at a cooling rate of 1-2°C / h and aging for 1-2h.

[0012] Preferably, in step (3), the solid-liquid separation is performed using a horizontal spiral centrifuge with a rotation speed of 3000-4000 rpm.

[0013] Preferably, the calcination conditions in (4) are as follows: first heat to 100-140℃ at a heating rate of 3-7℃ / min, hold for 1-2 hours, and then heat to 200-230℃ at a heating rate of 5-10℃ / min, hold for 1-2 hours.

[0014] Preferably, the specific steps of the multi-stage purification in (4) are as follows: the tail gas generated by calcination is first removed by a bag filter, then dehydrated by a 5-10℃ low-temperature condenser, then ammonia is removed by a 5wt%-8wt% dilute sulfuric acid scrubbing tower, and finally dehydrated again by silica gel adsorption; the filtration accuracy of the bag filter is ≤1μm.

[0015] Preferably, the specific operation steps in (5) are as follows: add lime milk accounting for 20%-30% of the mass of carbonization mother liquor to the carbonization mother liquor, heat to 60-80℃ and stir to react, collect the generated gas, which is ammonia gas, when the reaction system does not generate gas, cool the reaction liquid to room temperature, filter, recover lime milk, add 5%-10% saturated sodium carbonate solution accounting for the mass of carbonization mother liquor to the filtrate, filter, the filter cake is calcium carbonate precipitate, add 0.1-1mol / L dilute hydrochloric acid solution to the filtrate until no bubbles are generated in the system, then evaporate and crystallize, recover sodium chloride, and return to (1) to prepare saturated brine.

[0016] Preferably, the sodium carbonate product in (6) has a purity of ≥99.6% and a particle size of 200-300 mesh.

[0017] Preferably, the process mechanism of the sodium carbonate preparation method based on ternary synthesis technology in this invention is explained as follows: The process principle of this invention uses sodium chloride, liquid ammonia, and CO2 as the reaction system. By precisely matching the temperature gradient with the reaction stages, the selectivity of the target reaction is enhanced, the crystallization behavior is optimized, and the efficient recycling of carbon and salt ammonia resources is achieved. The specific process flow is explained in stages as follows: The first stage involves the preparation of ammonia brine and the formation of the reaction precursor. The core objective of this stage is to construct a stable "Na" solution. + The "-NH3-H2O" reaction system provides an active precursor for the subsequent carbonization reaction. Sodium chloride completely ionizes upon dissolution in deionized water: NaCl ⇌ Na + +Cl - This forms a saturated brine solution; when liquid ammonia is introduced into it, the ammonia dissolves and weakly ionizes in the aqueous solution: NH3 + H2O ⇌ NH3·H2O ⇌ NH4+ + +OH - By controlling the preparation conditions of ammonia salt solution, the dissolution efficiency of ammonia is ensured, ultimately forming a solution containing Na. + NH4 + Cl - OH -The ammonia brine system lays the foundation for the efficient conversion of CO2, avoiding incomplete carbonization due to insufficient ammonia content, or waste of raw materials and increased load on subsequent ammonia removal caused by excessive ammonia.

[0018] The second stage is the synergistic reaction and crystallization control stage of segmented carbonization, which is the core of this invention. Through a temperature gradient design of "low-temperature pre-carbonization + medium-temperature deep carbonization," the stepwise conversion of CO2 and the directional control of sodium bicarbonate crystallization are achieved. In the pre-carbonization stage, purified calcination byproduct CO2 is introduced. At this stage, the low-temperature environment of the system is conducive to the dissolution of CO2. The dissolved CO2 first reacts with NH3·H2O in the ammonia brine system: CO2 + NH3·H2O → NH4HCO3. The generated ammonium bicarbonate then reacts with Na in the system. + The metathesis reaction NH4HCO3 + NaCl ⇌ NaHCO3↓ + NH4Cl occurs. During this stage, the CO2 introduction rate is controlled to slowly provide the reaction substrate, inducing the formation of fine and uniform sodium bicarbonate crystal nuclei and avoiding disordered crystal growth caused by excessively high local CO2 concentrations. After pre-carbonization, the solution enters the deep carbonization stage, with the temperature raised to 20-30℃ and the pressure adjusted to 0.2-0.3 MPa. Industrial CO2 is then introduced; the medium-temperature environment enhances the reaction kinetics and promotes the remaining Na+ crystal growth. + By fully reacting with CO2, sodium bicarbonate crystal nuclei grow into uniformly sized crystals, ultimately improving the overall utilization rate of CO2 and solving the dual problems of "incomplete reaction and uneven crystallization" in traditional single-stage carbonization.

[0019] The third stage is the kinetic optimization stage of gradient temperature-controlled crystallization. The principle is to precisely control the cooling rate and aging time to regulate the growth process of sodium bicarbonate crystals and improve crystal particle size uniformity. The deeply carbonized feed solution contains a large amount of sodium bicarbonate crystals and unreacted ions. It is fed into a gradient cooling crystallizer and cooled to 20°C at a slow rate of 1-2°C / h. This process reduces the crystal growth rate and avoids crystal breakage and secondary nucleation caused by excessively rapid cooling. Subsequently, it is aged at this temperature for 1-2 hours, utilizing the Ostwald ripening effect to dissolve small crystals and redeposit solute on the surface of larger crystals, further optimizing the crystal particle size distribution. The solid-liquid separation stage uses a horizontal spiral centrifuge at 3000-3500 r / min to achieve efficient separation of the sodium bicarbonate filter cake and the carbonization mother liquor, laying the foundation for subsequent purification and recycling.

[0020] The fourth principle is calcination decomposition and closed-loop CO2 recovery. This stage achieves the conversion of sodium bicarbonate to sodium carbonate and the recycling of carbon resources. The sodium bicarbonate filter cake enters the calcination furnace and undergoes a thermal decomposition reaction: 2NaHCO3 Na₂CO₃ + CO₂↑ + H₂O↑ produces the target product, sodium carbonate. The exhaust gas from calcination contains CO₂, water vapor, trace amounts of NH₃, and dust. Direct emission would waste carbon resources and pollute the environment. Therefore, this invention employs a multi-stage purification process: baghouse dust collector (filtration accuracy ≤ 1μm) removes dust impurities; a 5-10℃ low-temperature condenser condenses and separates water vapor; a 5%-8% dilute sulfuric acid scrubbing tower neutralizes trace amounts of NH₃: 2NH₃ + H₂SO₄ → (NH₄)₂SO₄; finally, silica gel adsorbs trace amounts of moisture entrained in the dilute sulfuric acid, yielding purified byproduct CO₂, which is reused in the pre-carbonization stage, forming a closed loop of "calcination byproduct CO₂ - purification - re-carbonization," significantly reducing the consumption of fresh CO₂.

[0021] Finally, there is the mother liquor recycling and ammonia stripping optimization stage. The core principle is to achieve efficient recovery and recycling of ammonia and salt resources, while recovering by-product calcium carbonate, reducing wastewater discharge and raw material consumption. The treatment process of the carbonation mother liquor in this invention is "recovery of ammonia gas by vacuum stripping → recovery of calcium carbonate by filtration → recovery of sodium chloride by evaporation and crystallization". In the vacuum stripping stage, 20%-30% lime slurry by mass is added to the carbonation mother liquor, and the mixture is heated to 60-80℃ and stirred. The NH4Cl in the mother liquor reacts with the lime slurry: 2NH4Cl + Ca(OH)2 → CaCl2 + 2NH3↑ + 2H2O. The generated ammonia gas is collected and returned to the ammonia brine preparation process for recycling. When the reaction system no longer produces gas, the reaction liquid is cooled to room temperature, filtered to remove unreacted lime slurry, and 5%-10% saturated sodium carbonate solution by mass of the carbonation mother liquor is added to the filtrate. At this point, the Ca in the solution... 2+ With CO3 2- The reaction occurs: CaCl2 + Na2CO3 → CaCO3↓ + 2NaCl. After filtration, the filter cake is calcium carbonate precipitate, realizing the recovery of calcium resources. A dilute hydrochloric acid solution with a concentration of 0.1-1 mol / L is added dropwise to the filtrate until no bubbles are generated in the system. The purpose is to remove excess sodium carbonate. Then, sodium chloride is recovered by evaporation and crystallization and returned to the ammonia brine preparation process for recycling. Finally, the entire process of "salt-ammonia" resource reuse is achieved, which significantly improves the utilization rate of raw materials and reduces the environmental burden.

[0022] The beneficial effects of this invention are: 1. This invention significantly improves the utilization efficiency and reaction uniformity of carbon dioxide through the synergistic design of a segmented carbonization process. The low-temperature pre-carbonization stage enhances the dissolution and gradual reaction of carbon dioxide, avoiding raw material waste caused by excessively high local concentrations; the medium-temperature deep carbonization stage optimizes reaction kinetics, promoting the full combination of sodium ions and bicarbonate ions, reducing the loss of unreacted raw materials from the source. Simultaneously, the closed-loop CO2 recovery and multi-stage purification system realizes the recycling of carbon resources, reducing both the consumption of fresh carbon dioxide and the environmental pressure from exhaust emissions, aligning with the industry's demand for energy conservation and emission reduction, and possessing both economic value and environmental benefits.

[0023] 2. This invention utilizes a gradient temperature-controlled crystallization and aging process to significantly optimize the structure and properties of the product crystals. The slow cooling rate and the heat-preserving aging process result in more regular crystal lattice growth and fewer defects, improving not only the particle size uniformity of sodium bicarbonate crystals but also reducing the adsorption and encapsulation of impurity ions. The resulting sodium carbonate product after subsequent calcination has higher purity and more stable quality, fully meeting the stringent requirements for high-purity raw materials in food processing and other fields. Simultaneously, the uniform crystal structure reduces losses during filtration and washing, simplifies subsequent separation and purification processes, and helps improve overall production efficiency and reduce processing costs.

[0024] 3. This invention achieves efficient recovery and recycling of resources such as ammonia, salt, and calcium throughout the entire process through optimized mother liquor treatment. Precise lime slurry dosage and step-by-step reaction design ensure complete desorption and recovery of ammonia, directional crystallization and reuse of sodium and chloride ions, and the conversion of calcium into high-value calcium carbonate byproducts, avoiding resource waste and wastewater discharge. This resource recycling model significantly reduces raw material consumption costs, minimizes environmental impact during production, and forms a closed-loop system of "raw materials-products-byproducts-recycled raw materials." Simultaneously, no harmful pollutants are generated during the process, aligning with green production principles and enhancing the technology's sustainability and market competitiveness.

[0025] 4. The process design of this invention combines stability and industrial adaptability. Operating parameters are easily controlled and require no special equipment, allowing for upgrades and modifications to existing sodium carbonate production facilities, thus lowering the barrier to entry and reducing investment costs for industrial applications. The parameter ranges for core processes such as segmented carbonation and gradient crystallization are reasonable, minimizing scaling and crystal agglomeration during production, thereby improving continuous operation cycles and production stability. Furthermore, the overall energy consumption is low, requiring no extreme temperature or pressure conditions, reducing energy consumption and equipment maintenance difficulty and wear, making it suitable for large-scale continuous production and possessing broad industrial application value. Attached Figure Description

[0026] Figure 1 This is a process flow diagram of a sodium carbonate preparation method based on ternary synthesis technology according to the present invention. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0028] Example 1: A specific method for preparing sodium carbonate based on ternary synthesis technology, comprising the following steps: (1) Preparation of ammonia brine: Sodium chloride is dissolved in deionized water to prepare saturated brine. Liquid ammonia is introduced into the solution at a molar ratio of NH3:NaCl of 1.15:1. The ammonia brine is prepared at a temperature of 40℃ and a pressure of 0.2MPa. The solution is then cooled to 15℃ for later use. (2) Segmented carbonization reaction: The cooled ammonia brine is first fed into the pre-carbonization tower, and under the conditions of temperature 15℃ and pressure 0.1MPa, it is reacted at a rate of 0.3m 3 / (m 3 The purified calcination byproduct CO2 was introduced at a rate of ·h) for low-temperature pre-carbonization for 1.5h to obtain a pre-carbonized feed liquid. This pre-carbonized feed liquid was then fed into a deep carbonization tower, where it was subjected to a reaction at 20℃ and 0.2MPa at a rate of 0.5m... 3 / (m 3 Industrial CO2 was introduced at a rate of ·h) to carry out medium-temperature deep carbonization for 2h, and a deep carbonization solution was obtained. (3) Gradient temperature controlled crystallization and solid-liquid separation: The deep carbonized liquid is subjected to gradient cooling crystallization (cooled to 20℃ at a cooling rate of 1℃ / h) and aged for 1h. The solid-liquid separation is carried out by a horizontal screw centrifuge at a speed of 3000rpm to obtain sodium bicarbonate filter cake and carbonized mother liquor. (4) Closed-loop recovery and purification of CO2: The sodium bicarbonate filter cake is calcined and heated to 100°C at a heating rate of 3°C / min and held for 1 hour. Then it is heated to 200°C at a heating rate of 5°C / min and held for 1 hour to obtain sodium carbonate. The tail gas generated by calcination is dusted by a bag filter (filtration accuracy ≤1μm), then dehydrated by a 5°C low-temperature condenser, then ammonia is removed by a 5wt% dilute sulfuric acid scrubbing tower, and finally dehydrated by silica gel adsorption to obtain purified calcination by-product CO2, which is then reused in the pre-carbonization stage in (2). (5) Optimization of mother liquor circulation and ammonia stripping: Add lime milk accounting for 20% of the mass of carbonization mother liquor to the carbonization mother liquor, heat to 60℃ and stir to react, collect the generated gas, which is ammonia. When the reaction system does not produce gas, cool the reaction liquid to room temperature, filter, recover lime milk, add 5% of the mass of carbonization mother liquor saturated sodium carbonate solution to the filtrate, filter, the filter cake is calcium carbonate precipitate, add 0.1mol / L dilute hydrochloric acid solution to the filtrate until no bubbles are generated in the system, then evaporate and crystallize, recover sodium chloride, and return to (1) to prepare saturated brine; (6) Preparation of finished product: The sodium carbonate obtained by calcination is cooled and pulverized to 200-300 mesh to obtain the finished sodium carbonate product.

[0029] Example 2: A specific method for preparing sodium carbonate based on ternary synthesis technology, comprising the following steps: (1) Preparation of ammonia brine: Sodium chloride is dissolved in deionized water to prepare saturated brine. Liquid ammonia is introduced according to the molar ratio of NH3:NaCl of 1.18:1. Ammonia brine is prepared under the conditions of temperature 45℃ and pressure 0.25MPa. It is then cooled to 15-20℃ for later use. (2) Segmented carbonization reaction: The cooled ammonia brine is first fed into the pre-carbonization tower, and under the conditions of temperature 18℃ and pressure 0.15MPa, it is reacted at a rate of 0.35m 3 / (m 3 The purified calcination byproduct CO2 was introduced at a rate of ·h) for low-temperature pre-carbonization for 2 hours to obtain a pre-carbonized feed liquid. This pre-carbonized feed liquid was then fed into a deep carbonization tower, where it was subjected to a reaction at 25℃ and 0.25MPa at a rate of 0.55m³ / h. 3 / (m 3 Industrial CO2 was introduced at a rate of ·h) to carry out medium-temperature deep carbonization for 2.5h, and a deep carbonized feed liquid was obtained. (3) Gradient temperature controlled crystallization and solid-liquid separation: After the deep carbonized liquid is crystallized by gradient cooling (cooled to 20℃ at a cooling rate of 1.5℃ / h) and aged for 1.5h, the solid-liquid separation is carried out by a horizontal screw centrifuge at a speed of 3500rpm to obtain sodium bicarbonate filter cake and carbonized mother liquor. (4) Closed-loop recovery and purification of CO2: The sodium bicarbonate filter cake is calcined and heated to 120°C at a heating rate of 5°C / min and held for 1.5h. Then it is heated to 220°C at a heating rate of 7°C / min and held for 1.5h to obtain sodium carbonate. The tail gas generated by calcination is dusted by a bag filter (filtration accuracy ≤1μm), then dehydrated by an 8°C low-temperature condenser, then ammonia is removed by a 7wt% dilute sulfuric acid scrubbing tower, and finally dehydrated again by silica gel adsorption to obtain purified calcination by-product CO2, which is then recycled to the pre-carbonization stage in (2). (5) Optimization of mother liquor circulation and ammonia stripping: Add lime milk accounting for 25% of the mass of carbonization mother liquor to the carbonization mother liquor, heat to 70°C and stir to react, collect the generated gas, which is ammonia. When the reaction system does not produce gas, cool the reaction liquid to room temperature, filter, recover lime milk, add 8% saturated sodium carbonate solution accounting for 8% of the mass of carbonization mother liquor to the filtrate, filter, the filter cake is calcium carbonate precipitate, add 0.5 mol / L dilute hydrochloric acid solution to the filtrate until no bubbles are generated in the system, then evaporate and crystallize, recover sodium chloride, and return to (1) to prepare saturated brine; (6) Preparation of finished product: The sodium carbonate obtained by calcination is cooled and pulverized to 200-300 mesh to obtain the finished sodium carbonate product.

[0030] Example 3: A specific method for preparing sodium carbonate based on ternary synthesis technology, comprising the following steps: (1) Preparation of ammonia brine: Sodium chloride is dissolved in deionized water to prepare saturated brine. Liquid ammonia is introduced according to the molar ratio of NH3:NaCl of 1.2:1. Ammonia brine is prepared under the conditions of 50℃ and 0.3MPa. It is then cooled to 15-20℃ for later use. (2) Segmented carbonization reaction: The cooled ammonia brine is first fed into the pre-carbonization tower, and under the conditions of temperature 20℃ and pressure 0.2MPa, it is subjected to a reaction at a rate of 0.4m 3 / (m 3 The purified calcination byproduct CO2 was introduced at a rate of ·h) for low-temperature pre-carbonization for 2.5h, yielding a pre-carbonized feed liquid. This pre-carbonized feed liquid was then fed into a deep carbonization tower, where it was subjected to a reaction at 30℃ and 0.3MPa at a rate of 0.5m... 3 / (m 3 Industrial CO2 was introduced at a rate of ·h) to carry out medium-temperature deep carbonization for 3h of reaction time, resulting in a deep carbonized feed liquid; (3) Gradient temperature controlled crystallization and solid-liquid separation: The deep carbonized liquid is subjected to gradient cooling crystallization (cooled to 20℃ at a cooling rate of 2℃ / h) and aged for 2h. The solid-liquid separation is carried out by a horizontal screw centrifuge at a speed of 4000rpm to obtain sodium bicarbonate filter cake and carbonized mother liquor. (4) Closed-loop recovery and purification of CO2: The sodium bicarbonate filter cake is calcined and heated to 140°C at a heating rate of 7°C / min and held for 2 hours. Then it is heated to 230°C at a heating rate of 10°C / min and held for 2 hours to obtain sodium carbonate. The tail gas generated by calcination is dusted by a bag filter (filtration accuracy ≤1μm), then dehydrated by a 10°C low-temperature condenser, then ammonia is removed by an 8wt% dilute sulfuric acid scrubbing tower, and finally dehydrated by silica gel adsorption to obtain purified calcination by-product CO2, which is then reused in the pre-carbonization stage in (2). (5) Optimization of mother liquor circulation and ammonia stripping: Add lime milk accounting for 30% of the mass of carbonization mother liquor to the carbonization mother liquor, heat to 80℃ and stir to react, collect the generated gas, which is ammonia. When the reaction system does not produce gas, cool the reaction liquid to room temperature, filter, recover lime milk, add 10% of the mass of carbonization mother liquor saturated sodium carbonate solution to the filtrate, filter, the filter cake is calcium carbonate precipitate, add 1 mol / L dilute hydrochloric acid solution to the filtrate until no bubbles are generated in the system, then evaporate and crystallize, recover sodium chloride, return to (1) to prepare saturated brine; (6) Preparation of finished product: The sodium carbonate obtained by calcination is cooled and pulverized to 200-300 mesh to obtain the finished sodium carbonate product.

[0031] Comparative Example 1: The difference between Comparative Example 1 and Example 2 is that: in step (2), segmented carbonization is not used; instead, the cooled ammonia brine is first fed into the carbonization tower, and under the conditions of a temperature of 25°C and a pressure of 0.25 MPa, it is fed at a speed of 0.55 m 3 / (m 3 Industrial CO2 was introduced at a rate of ·h) to carry out a carbonization reaction for 4.5h, resulting in a carbonized feed liquid.

[0032] Comparative Example 2: The difference between Comparative Example 1 and Example 2 is that gradient cooling crystallization is not used in step (3), but the crystallization is cooled to room temperature naturally and then cooled to 20°C by circulating condensate.

[0033] Performance testing: The sodium carbonate prepared according to the process methods of Examples 1-3 and Comparative Examples 1-2 was subjected to purity and crystal particle size uniformity tests. The crystal particle size uniformity test included the average particle size D50 and the particle size distribution span ((D90-D10) / D50) of the sodium carbonate. The CO2 utilization rate, sodium chloride recovery rate and ammonia recovery rate of the entire process were also tested. The experimental results are shown in Table 1.

[0034] Table 1 Performance Test Results Performance Analysis: As can be seen from the experimental data in Table 1, Examples 1-3 all exhibited excellent overall performance, with Example 2 showing the best overall performance.

[0035] Example 2 demonstrates outstanding purity, which microscopically stems from the synergistic regulation of segmented carbonization and gradient crystallization: In the low-temperature pre-carbonization stage, the low temperature reduces the kinetic energy of CO2 molecules, strengthening the hydrogen bonding between CO2 and water molecules, allowing CO2 to slowly dissolve and gradually react with NH3·H2O. This results in a uniform concentration of NH4HCO3 molecules, preventing molecular aggregation caused by localized supersaturation. In the medium-temperature deep carbonization stage, the medium temperature increases the Na... + With HCO3 - The ion migration rate of the two molecules is high, and they are directionally bonded through ionic bonds to form a well-structured NaHCO3 crystal precursor. Gradient cooling crystallization involves slowly lowering the temperature at a rate of 1.5℃ / h to match the crystal lattice growth rate with the molecular alignment rate, reducing lattice defects, lowering the crystal surface energy, and making it less prone to adsorbing Cl from the mother liquor. - Impurity ions. Comparative Example 1 uses single-stage carbonization, resulting in a large and rapid dissolution of CO2 molecules at the microscopic level, leading to the instantaneous enrichment of NH4HCO3 molecules and Na. + With HCO3 -The crystal lattice formed by rapid bonding is incomplete and easily encapsulates unreacted molecules and impurity ions, resulting in a lower purity than in Example 2. In Comparative Example 2, the natural cooling rate is too fast, and the rapid nucleation of crystals at the microscopic level leads to an increase in lattice defects and adsorption sites on the crystal surface, making it easier to form weak interactions with impurity ions in the mother liquor, resulting in a lower purity than in Example 2.

[0036] Example 2 exhibits the best average particle size adaptation, the microscopic mechanism of which lies in the precise control of the crystallization process: in the segmented carbonization stage, the slowly generated fine NaHCO3 crystal nuclei provide uniform "seeds" for subsequent growth, and the molecular active sites on the surface of the crystal nuclei are evenly distributed; in the deep carbonization stage, the intermediate temperature environment enhances the diffusion rate of solute molecules, making HCO3 - with Na + The crystals continuously and uniformly deposited on the surface of the crystal nuclei, growing along the thermodynamically stable direction. During gradient cooling and 1.5h aging, the Ostwald ripening effect was utilized, resulting in higher surface energy for the smaller crystals, making it easier for molecules to dissolve and migrate to the surface of larger crystals, thus gradually increasing the crystal size and making it more uniform. In Comparative Example 1, the single-stage carbonization process lacked a pre-carbonization crystal nucleus induction step, leading to a disordered crystal nucleus generation rate and competition for solute among numerous small crystal nuclei, resulting in insufficient crystal growth and an average particle size smaller than that of Example 2. In Comparative Example 2, the natural cooling rate process without aging resulted in insufficient time for molecular migration and rearrangement, preventing the crystal nuclei from growing sufficiently, and also resulting in an average particle size lower than that of Example 2.

[0037] The small particle size distribution in Example 2 is primarily due to the uniformity of molecular interactions during the reaction and crystallization processes: segmented carbonization stabilizes the formation rate of NH4HCO3 by controlling the CO2 inlet rate, and Na... + With HCO3 - The ion binding probability is uniform, and the size difference of the initial crystal nuclei is minimal. During gradient cooling, the slow cooling process ensures a consistent temperature gradient across the system, synchronizing crystal growth rates and avoiding differences in crystal growth caused by local temperature fluctuations. Microscopically, uniformly grown crystals have consistent surface energy, reducing agglomeration and further minimizing the particle size distribution span. In Comparative Example 1, single-stage carbonization leads to local enrichment of CO2 molecules, resulting in significant differences in NH4HCO3 concentration in different regions, uneven crystal nucleus size, and amplified differences during subsequent growth, resulting in a much larger particle size distribution span than in Example 2. In Comparative Example 2, the natural cooling rate is uncontrollable, resulting in local temperature gradients within the system, different crystal growth rates in different regions, and no aging process optimization, leading to a larger particle size distribution span than in Example 2.

[0038] The high CO2 utilization rate in Example 2 is closely related to the molecular mechanisms of segmented carbonization and closed-loop recovery at the microscopic level: In the low-temperature pre-carbonization stage, the low temperature reduces the thermal motion rate of CO2 molecules, allowing for a more complete reaction between CO2 and NH3·H2O, and OH...- The increased probability of binding with CO2 molecules promotes the conversion of CO2 to HCO3. - In the intermediate-temperature deep carbonization stage, the intermediate temperature enhances the ion reaction kinetics, making HCO3... - with Na + The combination is more thorough, reducing the escape of unreacted CO2 molecules. The multi-stage purification process of CO2 closed-loop recovery removes impurities such as water vapor and NH3 from the tail gas. The recovered CO2 molecules have high purity and are free from interference by inert molecules when participating in the reaction again, and the reaction efficiency with NH3·H2O is not affected. Comparative Example 1, with its single-stage carbonization without a low-temperature pre-carbonization step, results in insufficient dissolution of CO2 molecules at the microscopic level. The excessively high local concentration causes some CO2 molecules to escape without participating in the reaction, resulting in a lower utilization rate than in Example 2. Comparative Example 2 only changed the crystallization method, without affecting the dissolution and reaction microscopic process of CO2 molecules. Therefore, its utilization rate is close to that of Example 2, but the lack of precise temperature control may cause a small amount of CO2 molecules to escape, resulting in a slightly lower utilization rate.

[0039] Example 2 showed excellent sodium chloride recovery, which was attributed at the microscopic level to the molecular regulation of the optimized mother liquor treatment: adding an appropriate amount of lime slurry to the mother liquor, microscopically, OH groups ionized from Ca(OH)2... - With NH4 + The combination produces NH3·H2O, which decomposes upon heating into NH3 gas, escaping and preventing NH4 from being released. + To Na + Interference with crystallization; the subsequent addition of saturated sodium carbonate solution, causing Ca... 2+ With CO3 2- Ca is removed by forming CaCO3 precipitate through ionic bonding. 2+ Impurities, reduce Ca 2+ With Cl - The effect of interactions on NaCl crystallization; neutralization of excess CO3 by dilute hydrochloric acid 2- Avoid CO3 2- with Na + Combined to form Na2CO3, ensuring Na + With Cl - NaCl crystals are formed through directional bonding via ionic bonds. The mother liquor treatment processes of Comparative Examples 1 and 2 are the same as those of Example 2. The ionic reactions and crystallization mechanisms are the same at the microscopic level, so the recovery rates are close to those of Example 2. However, the single-stage carbonization in Comparative Example 1 may result in a slightly lower NaCl concentration in the mother liquor, and the natural cooling in Comparative Example 2 may result in a slightly higher adsorption of impurity ions in the mother liquor. Therefore, the recovery rates of both examples are slightly lower than those of Example 2.

[0040] The high ammonia recovery rate in Example 2 is due to the microscopic mechanism of the vacuum distillation process and the precise addition of lime slurry: the temperature of 60-80℃ increases the kinetic energy of NH3 molecules, weakens the hydrogen bonding between NH3 and water molecules, and promotes NH3 desorption. The precise addition of lime slurry, microscopically, results in the OH groups generated by the ionization of Ca(OH)2. - Sufficient and uniform amount, with NH4 + The reaction should proceed until NH3·H2O is fully produced, avoiding the presence of OH-. - Insufficient NH4 + Residue. The ammonia stripping processes in Comparative Examples 1 and 2 were completely identical to those in Example 2, with NH4 remaining at the microscopic level. + The desorption and reaction mechanisms are the same, so the ammonia recovery rate is very similar to that of Example 2. However, the single-stage carbonization in Comparative Example 1 may lead to an increase in NH4 in the mother liquor. + The concentration was slightly lower, and the natural cooling of Comparative Example 2 may have resulted in a small amount of NH4 in the mother liquor. + Adsorbed on the crystal surface, the recovery rates were all slightly lower than those in Example 2.

[0041] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing sodium carbonate based on ternary synthesis technology, characterized in that, Includes the following steps: (1) Preparation of ammonia brine: Sodium chloride is dissolved in deionized water to prepare saturated brine, and liquid ammonia is introduced to prepare ammonia brine. The brine is then cooled to 15-20℃ for later use. (2) Segmented carbonization reaction: The cooled ammonia brine is first sent to the pre-carbonization tower, and purified calcination by-product CO2 is introduced for low-temperature pre-carbonization to obtain pre-carbonized liquid; then the pre-carbonized liquid is sent to the deep carbonization tower, and industrial CO2 is introduced for medium-temperature deep carbonization to obtain deep carbonized liquid. (3) Gradient temperature controlled crystallization and solid-liquid separation: After the deep carbonized liquid is subjected to gradient cooling crystallization and aging, solid-liquid separation is performed to obtain sodium bicarbonate filter cake and carbonization mother liquor; (4) Closed-loop recovery and purification of CO2: Sodium bicarbonate filter cake is calcined to obtain sodium carbonate. The tail gas generated by calcination is purified through multiple stages of dust removal, dehydration, ammonia removal and adsorption to obtain purified calcination by-product CO2, which is then recycled in the pre-carbonization stage of (2). (5) Optimization of mother liquor circulation and ammonia stripping: The carbonization mother liquor is successively subjected to vacuum stripping to recover ammonia, filtered to recover calcium carbonate, and finally evaporated and crystallized to recover sodium chloride; (6) Preparation of finished product: The sodium carbonate obtained by calcination is cooled and crushed to obtain the finished sodium carbonate product.

2. The method for preparing sodium carbonate based on ternary synthesis technology according to claim 1, characterized in that, The preparation conditions of the ammonia solution in (1) are: temperature 40-50℃, pressure 0.2-0.3MPa; the molar ratio of NH3:NaCl in the ammonia solution is 1.15-1.2:

1.

3. The method for preparing sodium carbonate based on ternary synthesis technology according to claim 1, characterized in that, The reaction conditions for low-temperature pre-carbonization in (2) are: temperature 15-20℃, pressure 0.1-0.2MPa, and the introduction rate of purified calcination by-product CO2 is 0.3-0.4m. 3 / (m 3 ·h), reaction time 1.5-2.5h.

4. The method for preparing sodium carbonate based on ternary synthesis technology according to claim 1, characterized in that, The reaction conditions for the intermediate-temperature deep carbonization in (2) are: temperature 20-30℃, pressure 0.2-0.3MPa, and industrial CO2 injection rate 0.5-0.6m. 3 / (m 3 ·h), reaction time 2-3h.

5. The method for preparing sodium carbonate based on ternary synthesis technology according to claim 1, characterized in that, The gradient cooling crystallization mentioned in (3) refers to cooling to 20°C at a cooling rate of 1-2°C / h and aging for 1-2h.

6. The method for preparing sodium carbonate based on ternary synthesis technology according to claim 1, characterized in that, In step (3), the solid-liquid separation is performed using a horizontal spiral centrifuge with a rotation speed of 3000-4000 rpm.

7. The method for preparing sodium carbonate based on ternary synthesis technology according to claim 1, characterized in that, The calcination conditions in (4) are as follows: first heat to 100-140℃ at a heating rate of 3-7℃ / min, hold for 1-2 hours, and then heat to 200-230℃ at a heating rate of 5-10℃ / min, hold for 1-2 hours.

8. The method for preparing sodium carbonate based on ternary synthesis technology according to claim 1, characterized in that, The specific steps of the multi-stage purification in (4) are as follows: the tail gas generated by calcination is first removed by a bag filter, then dehydrated by a 5-10℃ low-temperature condenser, then ammonia is removed by a 5wt%-8wt% dilute sulfuric acid scrubbing tower, and finally dehydrated again by silica gel adsorption; the filtration accuracy of the bag filter is ≤1μm.

9. The method for preparing sodium carbonate based on ternary synthesis technology according to claim 1, characterized in that, The specific operation steps in (5) are as follows: add lime milk accounting for 20%-30% of the mass of carbonization mother liquor to the carbonization mother liquor, heat to 60-80℃ and stir to react, collect the generated gas, which is ammonia gas, when the reaction system does not produce gas, cool the reaction liquid to room temperature, filter, recover lime milk, add 5%-10% saturated sodium carbonate solution accounting for the mass of carbonization mother liquor to the filtrate, filter, the filter cake is calcium carbonate precipitate, add 0.1-1mol / L dilute hydrochloric acid solution to the filtrate until no bubbles are generated in the system, then evaporate and crystallize, recover sodium chloride, and return to (1) to prepare saturated brine.

10. The method for preparing sodium carbonate based on ternary synthesis technology according to claim 1, characterized in that, The sodium carbonate product in (6) has a purity of ≥99.6% and a particle size of 200-300 mesh.

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