Cold precipitation-salting-out integrated ammonium chloride preparation method and system

Abstract

The invention relates to a cold precipitation-salting-out integrated ammonium chloride preparation method and system, which comprises the following steps: reducing the temperature of an ammonium chloride-containing solution generated in a combined alkali production process to below 10 DEG C, then adding sodium chloride into the solution while stirring until an ammonium chloride saturated salt solution is formed, standing, then cooling in a stepped manner, and after ammonium chloride crystals are completely separated out, obtaining ammonium chloride. And centrifuging to obtain an ammonium chloride product. Compared with a traditional separation preparation method of cold precipitation and salting-out in sequence, the method has the advantages that the ammonium chloride-containing solution generated in the combined alkali production process is subjected to cold precipitation and salting-out at the same time through one-step operation, so that the process flow is simplified, the time is greatly saved, the production efficiency and the yield are improved, the equipment investment is reduced, and the process operation cost is reduced; and the yield is improved.

Description

Technical Field

[0001] The invention relates to the technical field of soda ash industrial product preparation, and in particular to a cold precipitation-salting-out integrated ammonium chloride preparation method and system. Background Art

[0002] In the traditional alkali production process, after sodium bicarbonate is separated from the mother liquor coming out of the carbonization tower, an ammonium chloride solution is obtained, and then the ammonium chloride solution needs to be further treated to finally obtain ammonium chloride solid. This treatment process involves two processes: cold precipitation and salting out. Cold precipitation and salting out are used to separate ammonium chloride from the mother liquor, mainly because the solubility of sodium chloride and ammonium chloride will change with temperature. Ammonium chloride has a large solubility at room temperature, but a very small solubility at a lower temperature, while the solubility of sodium chloride remains basically unchanged with temperature changes. Therefore, in order to separate sodium chloride and ammonium chloride, salt can be added to the solution first to make the solution a saturated solution, and then the cooling crystallization method can be used to precipitate ammonium chloride in the form of crystals, and then the ammonium chloride can be separated using a centrifuge.

[0003] Chinese patent 2019100009244 discloses "a circulating manufacturing method for co-producing ammonium chloride with baking soda", which adopts five steps of primary precipitation of baking soda, cold crystallization, salting-out crystallization, secondary precipitation of baking soda, and mother liquor circulation to circulate and manufacture baking soda and co-produce ammonium chloride. The yield and nitrogen content of ammonium chloride are improved by two crystallizations of cold crystallization and salting-out crystallization, and the yield and purity of baking soda are improved by two precipitations of baking soda, primary precipitation of baking soda and secondary precipitation of baking soda. The production cost is low, the yield of each product is 95-98%, and the nitrogen content of the obtained ammonium chloride product is about 24%.

[0004] Chinese patent 2021108989746 discloses "a method for efficient separation and comprehensive utilization of mixed salts", wherein a mother liquor F containing NaCl and NH4Cl in a molar ratio of (0.8-2):1 is obtained, sodium chloride is added thereto by using the common ion effect, and then centrifuged after freezing to obtain solid NH4Cl and liquid mother liquor G. Based on the concepts of resource conservation, environmental friendliness, and circular economy, the method aims at solid mixed salts and the phase equilibrium of the water-salt system, and completes the efficient separation of solid mixed salts and the comprehensive utilization of sodium chloride, optimizes the process control conditions, and breaks through the key technologies of efficient separation of mixed salts and comprehensive resource utilization.

[0005] Chinese Patent No. 2017109559043 discloses a "method for cooling the external circulation of a salting-out crystallizer in the production process of soda ash by the combined alkali process". This method adds an external cooler to the salting-out crystallizer to achieve external circulation cooling of the salting-out crystallizer. The steps are as follows: on the basis of retaining the original salting process of the salting-out crystallizer, an external circulation cooling process flow of the salting-out crystallizer is added, an external cooler is configured on the salting-out crystallizer, and a salting-out circulation pump is configured. The salting-out circulation pump is installed on the upper part of the salting-out crystallizer, and the mother liquor in the salting-out crystallization is extracted to the external cooler, and heat exchange and cooling are carried out with the refrigerant medium in the external cooler. The mother liquor goes through the tube side of the external cooler, and the refrigerant medium goes through the shell side of the external cooler. The mother liquor after cooling returns to the central tube of the salting-out crystallizer, dissolves and absorbs the salt added by the salting-out crystallizer, and precipitates ammonium chloride product.

[0006] From the existing process flow, in the process of separating ammonium chloride products, the cold precipitation and salting-out processes are usually implemented separately. Summary of the invention

[0007] The object of the present invention is to provide a cold precipitation-salting out integrated ammonium chloride preparation method and system, which simultaneously performs cold precipitation and salting out on a solution containing ammonium chloride produced in a combined alkali production process, realizes one-step operation, simplifies the process flow, greatly saves time, improves production efficiency and output, reduces equipment investment, reduces process operation costs, and increases output.

[0008] To achieve the above object, the technical solution of the present invention is:

[0009] A cold precipitation-salting out integrated ammonium chloride preparation method, wherein the temperature of a solution containing ammonium chloride produced in a combined alkali production process is reduced to below 10°C, and then sodium chloride is added to the solution while stirring until a saturated ammonium chloride salt solution is formed; the solution is then allowed to stand, and the temperature is then stepped down until ammonium chloride crystals are completely precipitated, and the ammonium chloride product is obtained after centrifugation.

[0010] Further, hydrochloric acid is added to the ammonium chloride-containing solution to adjust the pH of the solution to 7.4-8, and then cold precipitation-salting out is performed.

[0011] Preferably, the step-by-step cooling operation is to keep the temperature for 30 to 60 minutes each time the temperature is reduced by 1 to 2°C.

[0012] In the alkali production process, after sodium bicarbonate is separated from the product coming out of the carbonization tower, a mixed solution containing ammonium chloride and salt remains, which then needs to be further processed to obtain the ammonium chloride product.

[0013] The ammonium chloride solution produced in the above-mentioned combined alkali production process generally contains a small amount of carbonate ions. When sodium chloride is added for salting out, carbonates are bound to precipitate, which will have a certain impact on the purity of the ammonium chloride product and it is difficult to meet the standards of high-quality products.

[0014] The present invention uses hydrochloric acid to adjust the pH value of a solution containing ammonium chloride before cold precipitation and salting out, thereby eliminating the influence of carbonate ions on subsequent ammonium chloride separation and improving product purity.

[0015] The method comprises the following steps: cooling a solution containing ammonium chloride, directly adding salt to the solution, standing the solution, and performing cold precipitation and salting out at the same time; then performing step-by-step cooling, observing the amount of solid precipitation of ammonium chloride, so that the ammonium chloride in the solution is completely separated, improving the yield, and thus separating more ammonium chloride products.

[0016] The present invention also provides a system for the cold precipitation-salting out integrated ammonium chloride preparation method, which comprises:

[0017] A cooling box having a temperature controller thereon;

[0018] A magnetic stirrer is arranged at the bottom of the cooling box;

[0019] The reactor is arranged on the magnetic stirrer in the cooling box; the reactor is provided with a feed inlet, a liquid inlet and a liquid outlet; and a temperature detection device is arranged in the reactor;

[0020] A liquid storage tank connected to the liquid inlet of the reactor through a pipeline and a pump;

[0021] A feeder connected to the feed port of the reactor through a pipeline;

[0022] The centrifuge has an inlet end connected to the liquid outlet of the reactor through a pipeline and a pump, and an outlet end connected to an NH4Cl storage tank and a brine storage tank through a pipeline.

[0023] Preferably, the cooling box is filled with a cooling medium.

[0024] Preferably, the cooling medium is water, ice or an ice-water mixture.

[0025] In the system of the present invention:

[0026] The cooling box is provided with a temperature controller, which can adjust the temperature in the cooling box. The reactor is placed in the cooling box. The temperature of the solution in the reactor is controlled by adjusting the temperature in the cooling box, so that the temperature of the ammonium chloride during cooling and crystallization can be effectively regulated, and multiple step cold precipitation and salting-out operations can be achieved, so as to facilitate the complete precipitation of the ammonium chloride.

[0027] The reactor is placed on a magnetic stirrer. After sodium chloride is added to the reactor, it is stirred by the magnetic force, so that the sodium chloride is quickly dissolved. On the other hand, the crystal size of ammonium chloride is generally affected by the solution temperature. Under the action of the magnetic stirring, the temperature distribution in the solution is more uniform, so that the size of the precipitated ammonium chloride crystals is more uniform.

[0028] Compared with the prior art, the present invention has the following advantages:

[0029] Conventional ammonium chloride separation cold precipitation and salting out are carried out separately. After cold precipitation is completed in the cold precipitation crystallizer, the solution needs to be transferred to the salting out crystallizer. The transfer process may cause solution loss and reduce the yield of ammonium chloride.

[0030] Compared with the traditional separation and preparation method of first cold precipitation and then salting out, the present invention is aimed at the separation of ammonium chloride in the alkali production process, and cold precipitation and salting out are carried out simultaneously, so that the operation is completed in one step, the process flow is simplified, time is greatly saved, production efficiency and output are improved, and equipment investment is reduced, thereby reducing process operation costs.

[0031] Furthermore, the present invention reduces the amount of carbonate in the solution by adjusting the pH value of the solution, avoids the formation of carbonate, and improves the purity of the product, and the purity of the ammonium chloride product finally obtained can be guaranteed to be above 99%. The purity standard of industrial-grade ammonium chloride products is required to be above 95%, and the purity of the ammonium chloride product obtained by the present invention far exceeds the industrial production requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a schematic diagram of the structure of the system embodiment of the present invention. DETAILED DESCRIPTION

[0033] The present invention will be further described below in conjunction with the embodiments and drawings.

[0034] The cold precipitation-salting out integrated ammonium chloride preparation method of the present invention comprises the following steps: lowering the temperature of a solution containing ammonium chloride produced in a combined alkali production process to below 10°C, then adding sodium chloride to the solution while stirring until a saturated ammonium chloride salt solution is formed, allowing the solution to stand, and then stepwise cooling until ammonium chloride crystals are completely precipitated; and then obtaining an ammonium chloride product by centrifugation.

[0035] See also Figure 1 The system for preparing ammonium chloride by cold precipitation-salting out integration of the present invention comprises:

[0036] A cooling box 1, on which a temperature controller is provided;

[0037] A magnetic stirrer 2 is arranged at the bottom of the cooling box 1;

[0038] The reactor 3 is arranged on the magnetic stirrer 2 in the cooling box 1; the reactor 3 is provided with a feed inlet, a liquid inlet and a liquid outlet; and a temperature detection device is arranged in the reactor 3;

[0039] A liquid storage tank 4 is connected to the liquid inlet of the reactor 3 through a pipeline and a pump 7;

[0040] A feeder 5 connected to a feed port of the reactor 3 via a pipeline;

[0041] The inlet of the centrifuge 6 is connected to the liquid outlet of the reactor 3 through a pipeline and a pump 7'; the outlet of the centrifuge 6 is connected to the NH4Cl storage tank 8 and the brine storage tank 9 through a pipeline.

[0042] Example 1

[0043] A cold precipitation-salting out integrated ammonium chloride preparation method, wherein the ammonium chloride solution in the liquid storage tank 4 is transported to the reactor 3 in the cooling box 1 through the water pump 7, the temperature in the cooling box 1 is adjusted to 10° C. through the temperature controller, and the cooling box 1 is allowed to stand for 1 hour. During the standing period, the temperature of the ammonium chloride solution in the reactor 3 is kept balanced with the temperature in the cooling box 1;

[0044] The sodium chloride crystals in the feeder 5 are fed into the reactor 3 in the cooling box 1 until a saturated ammonium chloride salt solution is formed, and the solution is stirred by a magnetic stirrer 2 installed under the reactor 3;

[0045] Subsequently, the temperature in the cooling box 1 is stepped down by the temperature controller, and the temperature is kept for 60 minutes each time the temperature is lowered by 2°C. As the temperature drops, ammonium chloride crystals in the solution gradually precipitate, and the solution with precipitated ammonium chloride crystals is sent into the centrifuge through the water pump 7' to separate and obtain the ammonium chloride product.

[0046] The product contains 99.4% ammonium chloride and 0.6% sodium chloride.

[0047] Example 2

[0048] A cold precipitation-salting out integrated ammonium chloride preparation method, adding hydrochloric acid to the ammonium chloride solution in the liquid storage tank 4, adjusting the solution pH to 7.4, and then transporting the solution to the reactor 3 in the cooling box 1 through the water pump 7, adjusting the temperature in the cooling box 1 to 8°C through the temperature controller, and standing for 1 hour to keep the temperature of the ammonium chloride solution in the reactor 3 balanced with the temperature in the cooling box 1;

[0049] The sodium chloride crystals in the feeder 5 are fed into the reactor 3 in the cooling box 1 until a saturated ammonium chloride salt solution is formed, and the solution is stirred by a magnetic stirrer 2 installed under the reactor 3;

[0050] Subsequently, the temperature in the cooling box 1 is stepped by the temperature controller, and the temperature is kept for 30 minutes each time the temperature is reduced by 1°C. As the temperature changes, ammonium chloride crystals in the solution gradually precipitate, and the solution with precipitated ammonium chloride crystals is sent into the centrifuge through the water pump 7' to separate and obtain the ammonium chloride product.

[0051] The product contains 99.2% ammonium chloride and 0.8% sodium chloride.

Claims

1. A method for preparing ammonium chloride by cold precipitation and salting out, characterized in that: The temperature of the solution containing ammonium chloride produced in the combined alkali production process is lowered to below 10°C, and then sodium chloride is added to the solution while stirring until a saturated salt solution of ammonium chloride is formed; then the solution is allowed to stand and the temperature is lowered step by step until ammonium chloride crystals are completely precipitated, and the ammonium chloride product is obtained after centrifugation.

2. The method for preparing ammonium chloride according to claim 1, wherein Add hydrochloric acid to the solution containing ammonium chloride to adjust the pH of the solution to 7.4-8, and then perform cold precipitation-salting out.

3. The method for preparing ammonium chloride according to claim 1, wherein The specific operation of the step-by-step cooling is to keep the temperature for 30 to 60 minutes each time the temperature is reduced by 1 to 2°C.

4. A system for the cold precipitation-salting out integrated ammonium chloride preparation method as claimed in claim 1, 2 or 3, characterized in that: include: A cooling box having a temperature controller thereon; A magnetic stirrer is arranged at the bottom of the cooling box; The reactor is arranged on the magnetic stirrer in the cooling box; the reactor is provided with a feed inlet, a liquid inlet and a liquid outlet; and a temperature detection device is arranged in the reactor; A liquid storage tank connected to the liquid inlet of the reactor through a pipeline and a pump; A feeder connected to the feed port of the reactor through a pipeline; The centrifuge has an inlet end connected to the liquid outlet of the reactor through a pipeline and a pump, and an outlet end connected to an NH4Cl storage tank and a brine storage tank through a pipeline.

5. The system according to claim 4, characterized in that: The cooling box is filled with cooling medium.

6. The system according to claim 5, characterized in that: The cooling medium is water, ice or an ice-water mixture.

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