A method and system for co-production of ammonia and calcium chloride using ammonium chloride

Abstract

The application discloses a method for co-production of ammonia and calcium chloride by using ammonium chloride, which comprises the following steps: step one, mixing ammonium chloride, mother liquor and water to obtain an ammonium chloride solution; step two, adding calcium oxide into the ammonium chloride solution, and performing reaction at 80-110 DEG C to obtain a reaction liquid; step three, evaporating the reaction liquid of step two at 90-170 DEG C to obtain a concentrated liquid; condensing the gas phase product generated in the reaction process of step two and the evaporation process of step three to obtain ammonia water; step four, performing solid-liquid separation on the concentrated liquid at 155-185 DEG C to obtain sodium chloride impurities and a calcium chloride solution; step five, cooling the calcium chloride solution to 30-50 DEG C, and then performing solid-liquid separation to obtain calcium chloride products and the mother liquor; and the mother liquor is returned to step one. The application can realize high-value utilization of industrial ammonium chloride raw materials containing sodium chloride impurities. The sodium chloride impurities can be efficiently removed on line, and the purity of the main product calcium chloride dihydrate is ensured.

Description

Technical Field

[0001] This invention belongs to the field of chemical production technology, specifically relating to a method and system for co-producing ammonia and calcium chloride using ammonium chloride. Background Technology

[0002] Ammonium chloride is a major byproduct of soda ash production via the combined alkali process. Its limited market capacity and large-scale stockpiling have constrained the development of the soda ash industry. Furthermore, industrial ammonium chloride often contains impurities such as sodium chloride, affecting the quality of its further processed products.

[0003] In existing technologies, using lime (calcium oxide or calcium hydroxide) to decompose ammonium chloride and recover ammonia is a common method. For example, a method using calcium hydroxide to decompose ammonium chloride to recover ammonia and produce a calcium chloride solution as a byproduct. However, this method does not consider the influence of sodium chloride impurities in the raw materials, resulting in a calcium chloride solution with low purity and concentration, and high energy consumption in subsequent processing. Other technologies recover ammonia and calcium chloride from complex solutions, but their processes are complex and mainly target heavy metal impurities in hydrometallurgical systems, and are not directly applicable to the treatment of industrial ammonium chloride containing sodium chloride.

[0004] Furthermore, existing processes primarily focus on ammonia recovery, paying insufficient attention to the form (mostly solution or anhydrous solid) and purity of calcium chloride products, and lack effective and economical methods for removing sodium ions as impurities. Therefore, developing a clean production process that can efficiently process impure ammonium chloride, simultaneously produce high-purity calcium chloride dihydrate and high-value ammonia products, and integrate the processes, has significant industrial value. Summary of the Invention

[0005] This invention aims to overcome the shortcomings of existing technologies and provide a novel, compact, resource-efficient, and environmentally friendly process for the comprehensive utilization of ammonium chloride. The specific objective of this invention is to achieve high-value utilization of industrial ammonium chloride raw materials containing sodium chloride impurities. It achieves efficient online removal of sodium chloride impurities, ensuring the purity of the main product, calcium chloride dihydrate. It enables flexible recovery of ammonia resources, allowing the production of commercial ammonia water or high-purity liquid ammonia. Through mother liquor recycling, it maximizes the utilization of water and useful components within the system, reducing the discharge of waste gas, wastewater, and solid waste.

[0006] A method for co-producing ammonia and calcium chloride using ammonium chloride includes the following steps: Step 1: Mix ammonium chloride, mother liquor, and water to obtain an ammonium chloride solution; Step 2: Add calcium oxide to the ammonium chloride solution and react at 80~110℃ to obtain the reaction solution; Step 3: Evaporate the reaction solution from Step 2 at 90~170℃ to obtain a concentrated solution; The gaseous products generated in the reaction process of step two and the evaporation process of step three are condensed to obtain ammonia water; Step 4: Separate the concentrate into solid and liquid components at 155~185℃ to obtain sodium chloride impurities and calcium chloride solution; Step 5: Cool the calcium chloride solution to 30~50℃, then separate the solid and liquid to obtain calcium chloride product and mother liquor; the mother liquor is returned to step 1.

[0007] Optionally, the mother liquor comprises 30-55 wt% water, 0-2 wt% sodium chloride, and 40-70 wt% calcium chloride.

[0008] Optionally, the ammonium chloride solution contains 30-40 wt% ammonium chloride, 50-70 wt% water, 0-5 wt% sodium chloride, and 4-10 wt% calcium chloride.

[0009] Optionally, in step two, the weight ratio of calcium oxide to ammonium chloride is 0.5 to 0.524; and the reaction time in step two is 1 to 5 hours.

[0010] Optionally, in step three, the condensation temperature is controlled at 40°C, and the concentration of the ammonia solution obtained is 18~25wt%.

[0011] Optionally, the concentrate contains 25-30 wt% water, 60-80 wt% calcium chloride, 0-3 wt% sodium chloride, and 0-1 wt% ammonium chloride.

[0012] Optionally, ammonia water is distilled at a bottom temperature of 160~220℃ and a top pressure of 1.8~2.5 MPa(G) to obtain liquid ammonia product.

[0013] Preferably, the water formed after distillation is sent to step one.

[0014] The present invention also proposes an apparatus for co-producing ammonia and calcium chloride using ammonium chloride, comprising: A mixer is used to mix ammonium chloride, mother liquor, and water to obtain an ammonium chloride solution; A reactor, connected to the mixer, is used to add calcium oxide to an ammonium chloride solution and react at 80-110°C to obtain a reaction solution. An evaporation device, connected to the liquid phase outlet of the reactor, is used to evaporate the reaction liquid from step two at 90~170℃ to obtain a concentrated liquid; A sodium salt filter, connected to the slurry outlet of the evaporation equipment, is used to separate the concentrate into solid and liquid components at 155~185℃ to obtain sodium chloride impurities and calcium chloride solution. A crystallizer, connected to the liquid phase outlet of the sodium salt filter, is used to cool the calcium chloride solution to 30~50°C to crystallize calcium chloride dihydrate. A calcium salt filter is connected to the slurry outlet of the crystallizer, and the mother liquor outlet of the calcium salt filter is connected to the mixer to perform solid-liquid separation, obtaining calcium chloride product and mother liquor; the mother liquor is returned to step one. A condenser, whose inlet is connected to the gas phase outlet of the reactor and the evaporation equipment, is used to condense the gas phase products generated in the reaction process of step two and the evaporation process of step three to obtain ammonia water.

[0015] The present invention also proposes an apparatus for co-producing ammonia and calcium chloride using ammonium chloride, further comprising: a distillation column connected to the outlet of the condenser for producing liquid ammonia.

[0016] Optionally, the water formed after distillation in the distillation column is sent to a mixer.

[0017] Compared with the prior art, the outstanding advantages and beneficial effects of the present invention are as follows: Highly efficient online impurity removal: Innovatively utilizing the common ion effect during the evaporation and concentration process, sodium chloride impurities are pre-crystallized and separated, fundamentally solving the negative impact of sodium ions on the purity of calcium chloride dihydrate products, and can also produce industrial salt as a byproduct, thus improving economic efficiency.

[0018] The product offers flexible solutions and high added value: the ammonia recovery system can be flexibly switched, capable of producing commonly used ammonia water simply and efficiently, or producing higher-value liquid ammonia through distillation, adapting to market demands.

[0019] High resource utilization and environmentally friendly: Through closed-loop circulation of mother liquor, water, unreacted components and intermediate products in the system are fully utilized, achieving near-zero wastewater discharge, which is in line with the concept of green chemical industry.

[0020] High integration of process flow: The reaction, evaporation and impurity removal, crystallization, ammonia recovery and other units are organically coupled, the process is simple and smooth, and the equipment investment and operating costs are relatively low, making it very suitable for the technological transformation and industrial upgrading of existing soda ash enterprises or ammonium chloride production enterprises. Attached Figure Description

[0021] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram of the device in Example 1; Figure 2 This is a schematic diagram of the device in Example 2. Detailed Implementation

[0023] To better understand the above-mentioned objectives, features, and advantages of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.

[0024] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and therefore the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0025] In this invention, the terms "installation," "connection," "linking," and "fixing" should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; "linking" can be a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of these terms in this invention according to the specific circumstances.

[0026] In the description of this invention, it should be understood that the terms "inner" and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or unit referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0027] In the description of this specification, the terms "one embodiment," "some embodiments," "specific embodiment," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0028] This invention proposes a process for the combined production of ammonia and calcium chloride dihydrate from ammonium chloride, comprising the following steps: (1) Preparation and reaction: The ammonium chloride solid is mixed with the mother liquor from the subsequent steps in a mixer to prepare an ammonium chloride solution. The solution is fed into a reactor and reacted with the added calcium oxide solid at a temperature of 80~110℃ to produce ammonia and calcium chloride.

[0029] (2) Ammonia recovery and purification: The gas phase (mainly containing ammonia and water vapor) generated by the reactor and the gas phase (mainly containing ammonia and water vapor) generated by the subsequent evaporation equipment are fed into the condenser together. By quantitatively adding pure water to the condensation system to absorb ammonia, a commercial ammonia solution with a concentration of approximately 20 wt% is directly obtained. Alternatively, the concentrated ammonia gas or ammonia solution obtained from condensation can be introduced into a distillation column and subjected to pressurized distillation to obtain a high-purity liquid ammonia product.

[0030] (3) Impurity separation and evaporation concentration: The calcium chloride liquid material discharged from the reactor is sent to the evaporation equipment for concentration. During the concentration process, the common ion effect of chloride ions is used to cause the sodium chloride impurities carried in the raw material ammonium chloride to crystallize and precipitate due to the decrease in solubility, forming sodium salt slurry.

[0031] (4) Sodium salt separation: The sodium salt slurry obtained in step (3) is sent to a sodium salt filter for solid-liquid separation to obtain industrial sodium chloride by-product (industrial salt) and calcium salt concentrate.

[0032] (5) Calcium chloride crystallization and separation: The calcium salt concentrate obtained in step (4) is sent to a crystallizer and cooled to crystallize, resulting in a calcium salt slurry containing calcium chloride dihydrate crystals. The slurry is then sent to a calcium salt filter for solid-liquid separation to obtain the product calcium chloride dihydrate solid and mother liquor. The mother liquor is returned to the mixer in step (1) for preparing an ammonium chloride solution, thus realizing mother liquor recycling.

[0033] Example 1 This embodiment proposes an apparatus for co-producing ammonia and calcium chloride using ammonium chloride, comprising: Mixer 1 is used to mix ammonium chloride, mother liquor and water to obtain an ammonium chloride solution; Reactor 2, connected to mixer 1, is used to add calcium oxide to ammonium chloride solution and react at 80~110℃ to obtain a reaction solution; Evaporation equipment 3 is connected to the liquid phase outlet of reactor 2 and is used to evaporate the reaction liquid of step two at 90~170℃ to obtain concentrated liquid; Sodium salt filter 4 is connected to the slurry outlet of the evaporation equipment 3 and is used to separate the concentrate into solid and liquid components at 155~185℃ to obtain sodium chloride impurities and calcium chloride solution. Crystallizer 5 is connected to the liquid phase outlet of the sodium salt filter 4 and is used to cool the calcium chloride solution to 30~50°C to crystallize calcium chloride dihydrate. Calcium salt filter 6 is connected to the slurry outlet of the crystallizer 5, and the mother liquor outlet of the calcium salt filter 6 is connected to the mixer 1 to perform solid-liquid separation to obtain calcium chloride product and mother liquor; the mother liquor is returned to step one. The condenser 7, whose inlet is connected to the gas phase outlet of the reactor 2 and the evaporation equipment 3, is used to condense the gas phase products generated in the reaction process of step two and the evaporation process of step three to obtain ammonia water.

[0034] The specific operation steps in this embodiment are as follows: First, in a mixer, 6.9 tons of industrial ammonium chloride (containing approximately 3% NaCl) are mixed with approximately 2.2 tons of mother liquor from a calcium salt filter, approximately 5.1 tons of steam condensate, and approximately 5.9 tons of pure water to prepare an ammonium chloride solution. The mother liquor contains 30 wt% water, 1 wt% sodium chloride, and 69 wt% calcium chloride. The ammonium chloride solution contains 34 wt% ammonium chloride, 58 wt% water, 1.1% sodium chloride, and 6.25 wt% calcium chloride.

[0035] The solution was then pumped into a reactor, and approximately 3.5 tons of calcium oxide powder were added. The mixture was stirred at 95°C for 2 hours.

[0036] The gas phase discharged from the top of the reactor and the gas phase discharged from the top of the evaporator are combined and then enter the condenser. By adjusting the flow rate of the steam condensate discharged from the evaporator to about 5.8 tons, about 10.6 tons of ammonia water with a concentration of 20wt% are directly obtained. The ammonia recovery rate is almost 100%.

[0037] The liquid phase at the bottom of the reactor was fed into a triple-effect evaporation system and concentrated at 120°C to a water content of 27.4 wt%. During the concentration process, sodium chloride crystallized out. The resulting sodium salt slurry was centrifuged at 170°C through a sodium salt filter to obtain approximately 0.2 tons of industrial salt. The resulting concentrated solution contained 27.93 wt% water, 71.79 wt% calcium chloride, 0.28 wt% sodium chloride, and 0.0000015 wt% ammonium chloride.

[0038] The calcium salt concentrate, from which sodium chloride has been removed, is fed into a crystallizer and cooled to below 45°C to precipitate calcium chloride dihydrate crystals. The resulting calcium salt slurry is then separated by a calcium salt filter to obtain approximately 9.26 tons of 99% pure calcium chloride dihydrate product, with a recovery rate close to 100%. Approximately 2.2 tons of filtrate (mother liquor) is returned to the mixer for recycling.

[0039] Example 2 The process is basically the same as in Example 1, except for the ammonia recovery section. In this example, a distillation column 8 is added to the technology of Example 1.

[0040] During the preparation process, the ammonia water collected from the condenser is pressurized to 1.9 MPa and then sent to pressurized distillation column 8. Through distillation, approximately 2.1 tons of liquid ammonia product with a purity of 99.9% is obtained after condensation at the top of the column. The distillation conditions are: top pressure 1.8 MPa (G) and bottom temperature 212°C. Approximately 8.7 tons of pure water are obtained in the bottom reboiler, and this portion of pure water is returned to the mixer for recycling.

[0041] Example 3 Compared to Example 1, the mixer solution was pumped into the reactor, and approximately 3.5 tons of calcium oxide powder were added simultaneously. The mixture was stirred and reacted at 80°C for 4 hours.

[0042] The gas phase discharged from the top of the reactor and the gas phase discharged from the top of the evaporator are combined and then enter the condenser.

[0043] The liquid phase at the bottom of the reactor is fed into a triple-effect evaporation system and concentrated at 170°C to a water content of 28 wt%. During the concentration process, sodium chloride crystals precipitate. The resulting sodium salt slurry is then centrifuged at 155°C through a sodium salt filter.

[0044] The calcium salt concentrate, from which sodium chloride has been removed, is fed into a crystallizer and cooled to below 45°C to precipitate calcium chloride dihydrate crystals. Everything else is the same as in Example 1.

[0045] The results showed that the ammonia recovery rate was 99%, the calcium chloride product purity was 99%, and the recovery rate was 99.5%.

[0046] Example 4 Compared to Example 1, the mixer solution was pumped into the reactor, and approximately 3.5 tons of calcium oxide powder were added simultaneously. The mixture was stirred and reacted at 110°C for 2 hours.

[0047] The gas phase discharged from the top of the reactor and the gas phase discharged from the top of the evaporator are combined and then enter the condenser.

[0048] The liquid phase at the bottom of the reactor is fed into a triple-effect evaporation system and concentrated at 90°C to a water content of 27.1 wt%. During the concentration process, sodium chloride crystals precipitate. The resulting sodium salt slurry is then centrifuged at 185°C through a sodium salt filter.

[0049] The calcium salt concentrate, from which sodium chloride has been removed, is fed into a crystallizer and cooled to below 45°C to precipitate calcium chloride dihydrate crystals. Everything else is the same as in Example 1.

[0050] The results showed that the ammonia recovery rate was 99%, the calcium chloride product purity was 99%, and the recovery rate was 99.5%.

[0051] Comparative Example 1 Compared with Example 1, in this comparative example, the concentrate was subjected to solid-liquid separation at 100°C to obtain sodium chloride impurities and calcium chloride solution.

[0052] The results showed that the ammonia recovery rate was 99%, the calcium chloride product purity was 99%, and the recovery rate was 91%.

[0053] It is evident that excessively low temperatures here can cause calcium chloride to crystallize prematurely, reducing the recovery rate.

[0054] As can be seen from the comparison of the above embodiments and comparative examples, the method of the present invention pre-crystallizes and separates sodium chloride, fundamentally solving the negative impact of impurity sodium ions on the purity of calcium chloride dihydrate products, and can also produce industrial salt as a byproduct, thus improving economic efficiency. Through closed-loop circulation of the mother liquor, water, unreacted components, and intermediate products within the system are fully utilized, achieving near-zero wastewater discharge, which aligns with the concept of green chemistry. The present invention organically couples reaction, evaporation for impurity removal, crystallization, and ammonia recovery units, resulting in a simple and smooth process with relatively low equipment investment and operating costs, making it highly suitable for the technological transformation and industrial upgrading of existing soda ash plants or ammonium chloride production enterprises.

[0055] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for co-producing ammonia and calcium chloride using ammonium chloride, characterized in that, Includes the following steps: Step 1: Mix ammonium chloride, mother liquor, and water to obtain an ammonium chloride solution; Step 2: Add calcium oxide to the ammonium chloride solution and react at 80~110℃ to obtain the reaction solution; Step 3: Evaporate the reaction solution from Step 2 at 90~170℃ to obtain a concentrated solution; The gaseous products generated in the reaction process of step two and the evaporation process of step three are condensed to obtain ammonia water; Step 4: Separate the concentrate into solid and liquid components at 155~185℃ to obtain sodium chloride impurities and calcium chloride solution; Step 5: Cool the calcium chloride solution to 30~50℃, then separate the solid and liquid to obtain calcium chloride product and mother liquor; the mother liquor is returned to step 1.

2. The method for co-producing ammonia and calcium chloride using ammonium chloride according to claim 1, characterized in that, The mother liquor comprises 30-55 wt% water, 0-2 wt% sodium chloride, and 40-70 wt% calcium chloride.

3. The method for co-producing ammonia and calcium chloride using ammonium chloride according to claim 1, characterized in that, The ammonium chloride solution contains 30-40 wt% ammonium chloride, 50-70 wt% water, 0-5 wt% sodium chloride, and 4-10 wt% calcium chloride.

4. The method for co-producing ammonia and calcium chloride using ammonium chloride according to claim 1, characterized in that, In step two, the weight ratio of calcium oxide to ammonium chloride is 0.5 to 0.524; the reaction time in step two is 1 to 5 hours.

5. The method for co-producing ammonia and calcium chloride using ammonium chloride according to claim 1, characterized in that, In step three, the condensation temperature is controlled at 40°C, and the concentration of the ammonia water obtained is 18~25wt%.

6. The method for co-producing ammonia and calcium chloride using ammonium chloride according to claim 1, characterized in that, The concentrate contains 25-30 wt% water, 60-80 wt% calcium chloride, 0-3 wt% sodium chloride, and 0-1 wt% ammonium chloride.

7. The method for co-producing ammonia and calcium chloride using ammonium chloride according to claim 1, characterized in that, It also includes distilling ammonia water at a bottom temperature of 160~220℃ and a top pressure of 1.8~2.5Mpa to obtain liquid ammonia product; Preferably, the water formed after distillation is sent to step one.

8. An apparatus for co-producing ammonia and calcium chloride using ammonium chloride, characterized in that, include: A mixer is used to mix ammonium chloride, mother liquor, and water to obtain an ammonium chloride solution; A reactor, connected to the mixer, is used to add calcium oxide to an ammonium chloride solution and react at 80-110°C to obtain a reaction solution. An evaporation device, connected to the liquid phase outlet of the reactor, is used to evaporate the reaction liquid from step two at 90~170℃ to obtain a concentrated liquid; A sodium salt filter, connected to the slurry outlet of the evaporation equipment, is used to separate the concentrate into solid and liquid components at 155~185℃ to obtain sodium chloride impurities and calcium chloride solution. A crystallizer, connected to the liquid phase outlet of the sodium salt filter, is used to cool the calcium chloride solution to 30~50°C to crystallize calcium chloride dihydrate. A calcium salt filter is connected to the slurry outlet of the crystallizer, and the mother liquor outlet of the calcium salt filter is connected to the mixer to perform solid-liquid separation, obtaining calcium chloride product and mother liquor; the mother liquor is returned to step one. A condenser, whose inlet is connected to the gas phase outlet of the reactor and the evaporation equipment, is used to condense the gas phase products generated in the reaction process of step two and the evaporation process of step three to obtain ammonia water.

9. The apparatus for co-producing ammonia and calcium chloride using ammonium chloride according to claim 8, characterized in that, Also includes: The distillation column, connected to the outlet of the condenser, is used to produce liquid ammonia.

10. The apparatus for co-producing ammonia and calcium chloride using ammonium chloride according to claim 8, characterized in that, Also includes: The water formed after distillation in the distillation column is sent to the mixer.

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