A method for preparing calcium-containing compounds based on ammonia evaporation wastewater

Abstract

The present invention relates to the technical field of phase-change energy storage materials and discloses a method for preparing calcium-containing compounds based on ammonia evaporation wastewater. The method comprises the following steps: purifying and clarifying the ammonia evaporation wastewater from an ammonia-soda plant and dividing it into two groups, Group A and Group B, in arbitrary proportions. The wastewater in Group A is evaporated to remove sodium chloride to obtain a filtrate, which is then evaporated and concentrated to obtain a concentrated calcium chloride solution. The wastewater in Group B is passed through 99.9 vol% carbon dioxide to obtain hollow calcium carbonate microspheres, which are then rinsed and dried with distilled water. The microspheres are immersed in the concentrated calcium chloride solution, heated in a water bath, cooled, and centrifuged to obtain solids to obtain CaCO3·CaCl2·6H2O particles. The particles are cyclically atomized and sprayed with a densifying agent in a fluidized bed reactor and pre-cured with ultraviolet light. Finally, they are irradiated under a ring-shaped ultraviolet lamp to obtain a densely coated calcium chloride hexahydrate phase-change material. The phase-change material of the present invention has optimized thermal conductivity, while the rigid support of the calcium carbonate enhances the mechanical strength of the material.

Description

Technical Field

[0001] The present invention relates to the technical field of phase change material energy storage materials, and in particular to a method for preparing calcium-containing compounds based on ammonia evaporation waste liquid. Background Art

[0002] Amid the global energy transition, phase change energy storage technology, as a key means of improving energy efficiency, is becoming increasingly important in areas such as building energy conservation and industrial waste heat recovery. Calcium chloride hexahydrate, due to its high latent heat of phase change (approximately 190 kJ / kg), suitable phase change temperature (29.9°C), and low cost, has become a highly promising medium- and low-temperature phase change energy storage material. However, practical applications of this material face significant packaging challenges.

[0003] The traditional method of directly encapsulating calcium chloride hexahydrate phase change materials with a single resin has many drawbacks. From a cost perspective, achieving good encapsulation requires a large amount of resin, which significantly increases production costs. In terms of performance, the resin's own thermal conductivity is only 0.1-0.3W / m·K, which severely hinders heat transfer and results in low thermal conductivity efficiency for the energy storage material, making it difficult to meet the requirements of efficient energy storage. In terms of mechanical properties, the resin's limited mechanical strength cannot withstand the frequent volume changes during the calcium chloride hexahydrate phase change process, easily causing damage to the encapsulation structure and causing leakage of the phase change material, greatly reducing the material's cyclic stability and service life.

[0004] At the same time, the ammonia-soda industry, as a basic chemical industry, generates large quantities of ammonia evaporation wastewater during its production process. According to statistics, every ton of soda ash produced generates approximately 10-12 cubic meters of ammonia evaporation wastewater, which is rich in various substances such as calcium chloride and sodium chloride. Currently, treatment of ammonia evaporation wastewater mostly relies on simple traditional methods such as precipitation and evaporation. These methods are inefficient and difficult to achieve high-value resource utilization. This not only wastes precious resources such as calcium and chlorine, but also leads to a series of environmental problems such as soil salinization and water pollution, causing serious damage to the ecological environment.

[0005] Therefore, how to develop a new packaging technology that can not only effectively solve the packaging problem of calcium chloride hexahydrate phase change material, improve its thermal conductivity and cycle stability, but also realize the resource utilization of ammonia vapor waste liquid and reduce production costs and environmental pressure has become a key technical bottleneck that needs to be overcome in the current phase change material energy storage and resource recycling fields. Summary of the Invention

[0006] In view of this, the present invention proposes a method for preparing calcium-containing compounds based on ammonia evaporation waste liquid.

[0007] In one aspect, the present invention provides a method for preparing a calcium-containing compound based on ammonia evaporation wastewater, comprising:

[0008] S1: Purify and clarify the ammonia evaporation waste liquid obtained from the ammonia-soda plant, and divide the ammonia evaporation waste liquid into Group A waste liquid and Group B waste liquid in any proportion;

[0009] S21: evaporating the Group A waste liquid to precipitate and separate and remove sodium chloride to obtain a Group A filtrate;

[0010] S22: evaporating and concentrating the filtrate of Group A to obtain a concentrated calcium chloride solution;

[0011] S31: introducing 99.9 vol% carbon dioxide into the waste liquid of Group B to obtain hollow calcium carbonate microspheres;

[0012] S32: rinsing the hollow calcium carbonate microspheres with distilled water and then drying;

[0013] S4: immersing the calcium carbonate hollow microspheres into the calcium chloride concentrated solution, heating in a water bath, cooling, and centrifuging to obtain a solid to obtain CaCO3·CaCl2·6H2O particles;

[0014] S5: placing the CaCO3·CaCl2·6H2O particles in a fluidized bed reactor for cyclic atomization spraying and pre-curing; the atomization spraying is spraying a densifying agent onto the surface of the CaCO3·CaCl2·6H2O particles, and the pre-curing is irradiating the CaCO3·CaCl2·6H2O particles under ultraviolet light;

[0015] S6: Irradiating the CaCO3·CaCl2·6H2O particles under a ring-shaped ultraviolet lamp to obtain a densely packed calcium chloride hexahydrate phase change material.

[0016] Furthermore, in S21, the evaporation of the Group A waste liquid is stopped when the calcium chloride content is 40 wt %.

[0017] Furthermore, in S22, the solution is evaporated and concentrated until the relative density of the calcium chloride solution is 1.37 g / L.

[0018] Furthermore, in S4, the water bath is heated at a temperature of at least 50° C., and the water bath is heated until the calcium chloride hexahydrate is completely dissolved.

[0019] Furthermore, in S5, the densifying agent includes: a low-viscosity resin, a diluent, and a wetting agent;

[0020] The low-viscosity resin is NOA81 and / or Loctite 3108, the diluent is a mixture of TPO and PETA with a total volume fraction of 5-10%, and the wetting agent is 0.1%-0.5% Tween80.

[0021] Furthermore, in S5, the spraying speed during the atomization spraying process is 0.5-1 mL / min, the number of cycles of step S5 is 2-3 times, and after step S5 is completed, the coating thickness on the surface of the CaCO3·CaCl2·6H2O particles is 0.5-2 μm.

[0022] Furthermore, in S5, the pre-curing is carried out at 365 nm and 5 mW / cm 2 Irradiate under UV light for 10 s.

[0023] Further, in S6, the CaCO3·CaCl2·6H2O particles are heated at 365 nm and 205 mW / cm 2 Irradiate under a ring UV lamp for 60 seconds.

[0024] Furthermore, S5 and S6 are performed below 30°C.

[0025] On the other hand, the present invention also protects a calcium-containing compound obtained by the above method.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] This method uses ammonia distillation wastewater as raw material to synthesize hollow calcium carbonate microspheres and calcium chloride hexahydrate phase change energy storage material. The synthesized calcium chloride hexahydrate is then encapsulated in the hollow calcium carbonate microspheres. This method uses a combined inorganic and organic encapsulation method to encapsulate the calcium chloride hexahydrate phase change material. Compared to direct resin encapsulation, the unit particle size of the material is larger, and the larger the sphere, the smaller the specific surface area, thus requiring less resin.

[0028] Furthermore, the inclusion of calcium carbonate significantly reduces resin usage and reduces costs. The thermal conductivity of calcium carbonate (2.7 W / m·K) is significantly higher than that of resin (0.1-0.3 W / m·K), optimizing the thermal conductivity of the phase-change energy storage material. Furthermore, the rigid support provided by calcium carbonate enhances the mechanical strength of the material, improving the cyclic stability of the phase-change material.

[0029] In addition, using industrial wastewater as raw material has certain environmental benefits and provides a reference for broadening the application of energy storage materials. The present invention is expected to be used in the construction and industrial fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiment below. The accompanying drawings are for illustration purposes only and are not to be considered as limiting the present invention. The same reference symbols are used throughout the drawings to represent the same components. In the drawings:

[0031] Figure 1This is a scanning electron microscope image of the calcium carbonate hollow microspheres provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0032] The exemplary embodiments disclosed in the present application will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art. It should be noted that, unless there is a conflict, the embodiments of the present invention and the features described in the embodiments 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.

[0033] Example

[0034] S1: Purify and clarify the ammonia evaporation waste liquid obtained from the ammonia-soda plant, and divide the ammonia evaporation waste liquid into Group A waste liquid and Group B waste liquid in any proportion. Group A waste liquid is used for multi-effect evaporation, and Group B waste liquid is used for CO2 injection;

[0035] S21: performing multi-effect evaporation on the waste liquid of Group A until precipitation stops when the calcium chloride content reaches 40 wt %, and centrifuging to remove sodium chloride to obtain a filtrate of Group A;

[0036] S22: Evaporating and concentrating the filtrate from Group A until the relative density of the solution is 1.37 g / L to obtain a concentrated calcium chloride solution;

[0037] S31: introducing 99.9 vol% carbon dioxide into the waste liquid of Group B to obtain hollow calcium carbonate microspheres;

[0038] S32: The hollow calcium carbonate microspheres were rinsed with distilled water and then dried. The dried hollow calcium carbonate microspheres were Figure 1 As shown;

[0039] S4: Immerse the calcium carbonate hollow microspheres in a concentrated calcium chloride solution, heat in a water bath at 80 degrees Celsius for 30 minutes, cool, and centrifuge to obtain the solid to obtain CaCO3·CaCl2·6H2O particles;

[0040] S5: CaCO3·CaCl2·6H2O particles are placed in a fluidized bed reactor for cyclic atomization spraying and pre-curing; atomization spraying is to spray a densifying agent on the surface of CaCO3·CaCl2·6H2O particles, and pre-curing is to heat the CaCO3·CaCl2·6H2O particles at 365nm and 5mW / cm 2 Irradiate under ultraviolet light for 10s;

[0041] Among them, the densifying agents include: low viscosity resin, diluent and wetting agent;

[0042] The low-viscosity resins were NOA81 and Loctite 3108, the diluent was a mixture of TPO and PETA with a total volume fraction of 5-10%, and the wetting agent was 0.4% Tween 80. The spraying speed during the atomization spraying process was 1 mL / min, and the number of cycles of step S5 was 3.

[0043] S6: CaCO3·CaCl2·6H2O particles at 365nm, 205mW / cm 2 The product was irradiated under a circular ultraviolet lamp for 60 seconds to obtain a densely packed calcium chloride hexahydrate phase change material.

[0044] In the above steps, S5 and S6 are performed at a temperature below 30°C.

[0045] Performance Testing

[0046] Thermal Conductivity Testing: The thermal conductivity of the prepared calcium chloride hexahydrate phase change material was tested using the hot wire method. Samples were formed into discs with a diameter of 30 mm and a thickness of 10 mm and placed in a thermal conductivity tester for measurement. The results showed that the thermal conductivity of the material reached 1.2 W / m·K, a significant improvement over the 0.5 W / m·K of conventional single-resin encapsulated calcium chloride hexahydrate phase change material.

[0047] Cyclic stability testing: Phase change material samples were placed in a high-low temperature cycling chamber and subjected to 1000 cycles within a temperature range of 20°C to 40°C. Each cycle consisted of a heating phase (from 20°C to 40°C at a heating rate of 5°C / min) and a cooling phase (from 40°C to 20°C at a cooling rate of 5°C / min). After the cycles, the sample's appearance was observed and its latent heat of phase change was measured. The results showed no significant change in the sample's appearance after 1000 cycles, and the latent heat loss from phase change was only 5%, demonstrating the material's excellent cyclic stability.

[0048] Encapsulation effectiveness testing: Scanning electron microscopy (SEM) was used to observe the microstructure of the phase change material to evaluate its encapsulation effectiveness. SEM images showed that the hollow calcium carbonate microspheres were uniformly filled with calcium chloride hexahydrate, and the surface coating was dense, with no obvious cracks or holes, effectively preventing leakage of the phase change material.

[0049] Cost Analysis: Calculate the costs of raw materials, energy consumption, and equipment depreciation required during the preparation process. Compared to traditional single-resin encapsulation methods, this method reduces production costs by approximately 30% by reducing the amount of resin used and utilizing ammonia wastewater as a raw material.

[0050] Comparative Example 1: Traditional single resin encapsulated calcium chloride hexahydrate phase change material

[0051] Raw material preparation: prepare 50 kg of calcium chloride hexahydrate, 30 kg of epoxy resin (E-51), 20 kg of acetone as a solvent, and 0.3 kg of dibutyltin dilaurate as a curing accelerator.

[0052] Preparation process

[0053] Dissolution and mixing: Place calcium chloride hexahydrate in a reactor equipped with a stirring device, add acetone, and stir at 50°C for 30 minutes until the calcium chloride hexahydrate is completely dissolved. Then add epoxy resin and continue stirring for 20 minutes to ensure that the two are fully mixed.

[0054] Add curing agent: Add dibutyltin dilaurate to the above mixed solution and stir for 15 minutes to ensure that the curing accelerator is evenly dispersed.

[0055] Molding and Curing: Pour the mixed solution into a mold measuring 20 cm long, 15 cm wide, and 5 cm high. Curing is carried out for 48 hours at room temperature (25°C) and 60% relative humidity to obtain a conventional single-resin encapsulated calcium chloride hexahydrate phase change material.

[0056] Performance Testing

[0057] Thermal conductivity testing: Using the same hot wire method as in the previous example, samples were cut into discs with a diameter of 30 mm and a thickness of 10 mm for testing. The instrument was set to an initial temperature of 25°C. During testing, the ambient temperature was maintained at 25 ± 1°C, and the humidity was maintained at 55-65%. The final thermal conductivity was 0.5 W / m·K.

[0058] Cyclic stability testing: Phase change material samples were placed in a high-low temperature cycling chamber, set at a temperature range of 20-40°C, with both a heating and cooling rate of 5°C / min. After each cycle, the sample was left at room temperature for 30 minutes before the next cycle. After 1000 cycles, significant deformation and cracking were observed at the sample edges. Measurements of the latent heat of phase change using differential scanning calorimetry (DSC) revealed a 30% loss.

[0059] Encapsulation effectiveness testing: Part of the sample was sputtered with gold and then observed under a scanning electron microscope (SEM, accelerating voltage 20kV). The results showed numerous tiny cracks within the material. In some areas, the resin and calcium chloride hexahydrate were not tightly bonded, resulting in gaps that could potentially cause leakage of the phase change material.

[0060] Cost analysis: Calculating the cost of raw materials, the unit price of calcium chloride hexahydrate is 800 yuan / ton, epoxy resin is 25,000 yuan / ton, acetone is 6,000 yuan / ton, and dibutyltin dilaurate is 120,000 yuan / ton. Adding equipment depreciation, energy consumption and other costs, the production cost of each ton of phase change material is about 12,000 yuan.

[0061] Comparative Example 2: CaCO3·CaCl2·6H2O particles without surface treatment

[0062] Raw materials and treatment: The raw material acquisition and preliminary treatment steps are exactly the same as those in the embodiment, that is, 100L of ammonia distillation waste liquid is obtained from an ammonia-soda plant, and after purification and clarification, it is divided into two waste liquid groups A and B, each group of 50L.

[0063] Preparation process

[0064] Treatment of Group A waste liquid: Same as in Example 1, the Group A waste liquid was evaporated to a calcium chloride content of 40 wt% to separate sodium chloride, and then evaporated and concentrated to a calcium chloride concentrated solution with a relative density of 1.37 g / L.

[0065] Treatment of Group B waste liquid: Same as in Example 1, carbon dioxide with a purity of 99.9 vol% was introduced into Group B waste liquid at a ventilation rate of 5 L / min for 8 hours to obtain calcium carbonate hollow microspheres, which were rinsed with distilled water and dried in a drying oven at 60°C for 12 hours.

[0066] Preparation of composite particles: The dried calcium carbonate hollow microspheres were immersed in a concentrated calcium chloride solution, heated in a water bath at 60°C for 2 hours, cooled and centrifuged to obtain the solid to obtain CaCO3·CaCl2·6H2O particles, but the subsequent atomization spraying and UV curing steps were not performed.

[0067] Performance Testing

[0068] Thermal conductivity test: The hot wire method was used under the same test conditions as in the example. Since the surface of the CaCO3 hollow microspheres is not dense, which affects the overall thermal conductivity, the thermal conductivity coefficient was measured to be 0.8 W / m·K.

[0069] Cyclic stability testing: 1,000 cycles of 20-40°C were performed in a high-low temperature cycling chamber, with samples observed after each cycle. Some samples were found to break during the cycling process. After the cycling, DSC was used to measure the latent heat of phase change, revealing a 15% loss.

[0070] Encapsulation effect test: SEM observation shows that there are a large number of pores on the surface of the CaCO3 hollow microspheres, and the calcium chloride hexahydrate is unevenly filled inside. During the phase change process, liquid calcium chloride hexahydrate easily seeps out of the pores, which cannot effectively prevent the leakage of the phase change material.

[0071] Cost Analysis: Unsurface-treated CaCO3·CaCl2·6H2O particles eliminate the atomization spraying and UV curing steps, reducing raw material costs by reducing the use of low-viscosity resins (such as NOA81 and Loctite3108), diluents (TPO and PETA), and wetting agents (Tween80). However, due to the material's poor performance, its cycling stability is insufficient in actual use, resulting in a shortened service life and requiring more frequent replacement to maintain energy storage. Furthermore, the encapsulation effect is poor, and additional protective measures may be required to prevent leakage of the phase change material.

[0072] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered by the scope of protection of the claims of the present invention.

Claims

1. A method for preparing calcium-containing compounds based on ammonia evaporation wastewater, characterized in that: include: S1: Purify and clarify the ammonia evaporation waste liquid obtained from the ammonia-soda plant, and divide the ammonia evaporation waste liquid into Group A waste liquid and Group B waste liquid in any proportion; S21: evaporating the Group A waste liquid to precipitate and separate and remove sodium chloride to obtain a Group A filtrate; S22: evaporating and concentrating the filtrate of Group A to obtain a concentrated calcium chloride solution; S31: introducing 99.9 vol% carbon dioxide into the waste liquid of Group B to obtain hollow calcium carbonate microspheres; S32: rinsing the hollow calcium carbonate microspheres with distilled water and then drying; S4: immersing the calcium carbonate hollow microspheres into the calcium chloride concentrated solution, heating in a water bath, cooling, and centrifuging to obtain a solid to obtain CaCO3·CaCl2·6H2O particles; S5: placing the CaCO3·CaCl2·6H2O particles in a fluidized bed reactor for cyclic atomization spraying and pre-curing; the atomization spraying is spraying a densifying agent onto the surface of the CaCO3·CaCl2·6H2O particles, and the pre-curing is irradiating the CaCO3·CaCl2·6H2O particles under ultraviolet light; S6: Irradiating the CaCO3·CaCl2·6H2O particles under a ring-shaped ultraviolet lamp to obtain a densely packed calcium chloride hexahydrate phase change material, i.e., a calcium-containing compound.

2. The method for preparing calcium-containing compounds based on ammonia distillation waste liquid according to claim 1, characterized in that: In S21, the evaporation of the Group A waste liquid is stopped when the calcium chloride content is 40 wt %.

3. The method for preparing calcium-containing compounds based on ammonia distillation waste liquid according to claim 1, characterized in that: In S22, the solution is evaporated and concentrated until the relative density of the concentrated calcium chloride solution is 1.37 g / L.

4. The method for preparing calcium-containing compounds based on ammonia distillation waste liquid according to claim 1, characterized in that: In S4, the water bath is heated at a temperature of at least 50° C., and the water bath is heated until the calcium chloride hexahydrate is completely dissolved.

5. The method for preparing calcium-containing compounds based on ammonia distillation waste liquid according to claim 1, characterized in that: In S5, the densifying agent includes: a low-viscosity resin, a diluent, and a wetting agent; The low-viscosity resin is NOA81 or Loctite 3108, the diluent is a mixture of TPO and PETA with a total volume fraction of 5-10%, and the wetting agent is 0.1%-0.5% Tween80.

6. The method for preparing calcium-containing compounds based on ammonia distillation waste liquid according to claim 1, characterized in that: In S5, the spraying speed during the atomization spraying process is 0.5-1 mL / min, the number of cycles of step S5 is 2-3 times, and the coating thickness on the surface of the CaCO3·CaCl2·6H2O particles after step S5 is completed is 0.5-2 μm.

7. The method for preparing calcium-containing compounds based on ammonia distillation waste liquid according to claim 1, characterized in that: In S5, the pre-curing is carried out at 365 nm, 5 mW / cm 2 Irradiate under UV light for 10 s.

8. The method for preparing calcium-containing compounds based on ammonia distillation waste liquid according to claim 1, characterized in that: In S6, the CaCO3·CaCl2·6H2O particles are irradiated at 365 nm and 205 mW / cm 2 Irradiate under a ring UV lamp for 60 seconds.

9. The method for preparing calcium-containing compounds based on ammonia distillation waste liquid according to claim 1, characterized in that: S5 and S6 are carried out below 30°C.

10. A calcium-containing compound, characterized in that The method according to any one of claims 1 to 9 is used for preparation.

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