A method for wet treatment of ammonium bicarbonate in sodium bicarbonate mother liquor

Abstract

This invention discloses a wet process for treating ammonium bicarbonate in sodium bicarbonate mother liquor, comprising the following steps: 1) collecting sodium bicarbonate mother liquor; 2) transferring the sodium bicarbonate mother liquor to a primary ammonium sodium deposition vessel, adding sodium chloride to react and obtain a primary mixed slurry, then transferring the primary mixed slurry to a secondary ammonium sodium deposition vessel, continuing the reaction to obtain a secondary mixed slurry, then heating the secondary mixed slurry and transferring it to an ammonium sodium separation vessel to react and obtain a tertiary mixed slurry; 3) filtering the tertiary mixed slurry, sending the deammonium-removed mother liquor to prepare ammonium chloride, and returning the crude sodium bicarbonate to the metathesis reaction process to prepare sodium bicarbonate. This invention has low energy consumption and cost, and can effectively improve the nitrogen content and particle size of ammonium chloride. The ammonium chloride prepared from the ammonium chloride-containing filtrate after removing ammonium bicarbonate using this method meets the standards for superior agricultural ammonium chloride in terms of nitrogen content and particle size, greatly improving the product quality of agricultural ammonium chloride.

Description

Technical Field

[0001] This invention relates to the field of mother liquor treatment technology in the preparation process of baking soda, and particularly to a method for wet treatment of ammonium bicarbonate in baking soda mother liquor. Background Technology

[0002] Baking soda, also known as sodium bicarbonate, is an inorganic salt, a white crystalline powder, odorless, with an alkaline taste, and readily soluble in water. It is widely used in the pharmaceutical, food processing, and fire-fighting equipment industries. It is mainly produced by a double decomposition reaction between brine and ammonium bicarbonate, followed by washing, dehydration, and drying. During this reaction, only 75-80% of the ammonium bicarbonate is utilized; the remaining 20-25% dissolves into the baking soda mother liquor obtained after washing and dehydration, resulting in a mother liquor containing large amounts of ammonium chloride, sodium chloride, and ammonium bicarbonate.

[0003] To remove ammonium bicarbonate from baking soda mother liquor and obtain agricultural-grade ammonium chloride, existing technologies have many methods for removing ammonium bicarbonate from baking soda mother liquor. For example, CN201910226450.5 discloses a process for thermally recovering products from mother liquor containing ammonium chloride, sodium chloride, ammonium bicarbonate, and sodium bicarbonate. This includes a method for recovering the gas generated after ammonia removal from the mother liquor: the mother liquor is preheated and then fed into an ammonia stripping tower for ammonia removal. The carbon dioxide and ammonia generated after ammonia removal are sent to an ammonia absorption tower to generate carbon-containing ammonia water. Carbon dioxide is added to the carbon-containing ammonia water in excess to generate ammonium bicarbonate. This process also includes a method for recovering ammonium chloride and sodium chloride from the mother liquor after ammonia removal: sodium chloride is obtained through five-effect cross-flow evaporation, and ammonium chloride is obtained through four-effect flash crystallization. The overflow from the salt thickener and the liquid after centrifugation are sent to a V-effect evaporator for recycling; the overflow from the ammonium thickener and the liquid after centrifugation are pumped into a IV-effect flash crystallizer for recycling.

[0004] The method for removing ammonium bicarbonate in this process involves distillation to first decompose the ammonium bicarbonate into carbon dioxide and ammonia at high temperature, then condensing and absorbing the sublimated carbon dioxide and ammonia, and finally adding carbon dioxide to carbonize and regenerate ammonium bicarbonate. This method for removing ammonium bicarbonate is complex, energy-intensive, requires stringent control conditions, and is costly.

[0005] For example, CN202111449257.1 discloses a method for co-producing ammonium chloride from sodium bicarbonate, including the following steps: 1) Primary precipitation of sodium bicarbonate to obtain crude sodium bicarbonate and crude mother liquor M1; 2) Sodium precipitation: sodium chloride is added to the crude mother liquor M1 to cause the residual ammonium bicarbonate in the crude mother liquor M1 to undergo a double decomposition reaction with sodium chloride again, filtered to obtain refined mother liquor M1 and sodium bicarbonate, and the sodium bicarbonate is returned to step 1); 3) Cold crystallization; 4) Salting-out crystallization; 5) Secondary precipitation of sodium bicarbonate; 6) Mother liquor recycling. Step 2) The specific steps for sodium precipitation are as follows: crude mother liquor M1 and sodium chloride are fed into the first sodium precipitation reactor to undergo a double decomposition reaction again. The mass ratio of ammonium bicarbonate to added sodium chloride in crude mother liquor M1 is 75-95:7. The temperature in the first sodium precipitation reactor is controlled at 22-25℃. The mixture flows through the second sodium precipitation reactor, and the temperature in the second sodium precipitation reactor is controlled at 35-40℃. The sodium precipitation time is 1-1.5h. The slurry after the reaction in the second sodium precipitation reactor is then filtered to obtain refined mother liquor M1 and sodium bicarbonate.

[0006] This method employs a sodium precipitation step (further reacting the residual ammonium bicarbonate in the crude mother liquor M1 with sodium chloride) to further remove ammonium bicarbonate from the sodium bicarbonate mother liquor. However, in practical application, it was found that when using this method to remove ammonium bicarbonate and recover ammonium chloride, the sodium precipitation step only uses two first-stage sodium precipitation reactors for ammonium bicarbonate removal. This results in a low removal rate of ammonium bicarbonate during the precipitation process, leaving a small amount of residual ammonium bicarbonate that has not reacted with sodium chloride. Consequently, the nitrogen content in the recovered ammonium chloride does not meet the standards for agricultural ammonium chloride, and the particle size of the ammonium chloride does not meet the standards for superior grade agricultural ammonium chloride in GB / T2946-2008, thus reducing the product quality of the ammonium chloride. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a simple, low-energy-consumption, low-cost wet treatment method for ammonium bicarbonate in sodium bicarbonate mother liquor that can effectively increase the nitrogen content in ammonium chloride.

[0008] The technical solution adopted by this invention to solve its technical problem is: a method for wet treatment of ammonium bicarbonate in sodium bicarbonate mother liquor, comprising the following steps: 1) collecting sodium bicarbonate mother liquor generated during the preparation of sodium bicarbonate by metathesis reaction; 2) conveying the sodium bicarbonate mother liquor to a primary ammonium sodium deposition vessel, adding sodium chloride and reacting for a period of time to obtain a primary mixed slurry, then conveying the primary mixed slurry to a secondary ammonium sodium deposition vessel, continuing to react for a period of time to obtain a secondary mixed slurry, then heating the secondary mixed slurry and conveying it to an ammonium sodium separation vessel, reacting for a period of time to obtain a tertiary mixed slurry; 3) filtering the tertiary mixed slurry to obtain a deammonium mother liquor containing ammonium chloride, which is sent to prepare ammonium chloride, and the obtained crude sodium bicarbonate is returned to the metathesis reaction process to prepare sodium bicarbonate.

[0009] Furthermore, the sodium bicarbonate mother liquor is reacted in the primary ammonium sodium deposition vessel at a temperature of 20-25°C for a reaction time of 1 hour.

[0010] Furthermore, the amount of sodium chloride added is M, in tons, where M = total amount of NH4HCO3 in sodium bicarbonate mother liquor × 1.35 × 1.2 × 10 -3 The total amount of NH4HCO3 in the sodium bicarbonate mother liquor is expressed in kg. Among them, 1.35 is the ratio of the relative molecular masses of NH4HCO3 to NaCl, and 1.2 is the stoichiometric ratio of ammonium bicarbonate and sodium chloride in the reaction equation to produce sodium bicarbonate and ammonium chloride +20% to ensure that sodium chloride is added in excess.

[0011] Furthermore, when adding sodium chloride to the primary ammonium sodium deposition vessel, it is necessary to add it while stirring.

[0012] Furthermore, the reaction time of the primary mixed slurry in the secondary ammonium sodium deposition vessel is determined based on the removal rate of NH4HCO3 in the mixed slurry.

[0013] Furthermore, when the removal rate of NH4HCO3 in the mixed slurry in the secondary ammonium sodium deposition vessel reaches more than 95%, a secondary mixed slurry is obtained, and the secondary mixed slurry is then transported to the ammonium sodium separation vessel.

[0014] Furthermore, the reaction temperature of the secondary mixed slurry in the ammonium sodium separation vessel is 32-35℃, and the reaction time is 1-3h.

[0015] Furthermore, the secondary mixed slurry is preheated using a heat exchanger before entering the ammonium sodium separation vessel.

[0016] The beneficial effects of the wet treatment method for ammonium bicarbonate in sodium bicarbonate mother liquor of the present invention are as follows: The process of the present invention is simple, with low energy consumption and low cost. By using two sodium ammonium deposition tanks and one sodium ammonium separation tank, the ammonium bicarbonate in the sodium bicarbonate mother liquor can react completely with the added sodium chloride in the two sodium ammonium deposition tanks to generate sodium bicarbonate and ammonium chloride, which effectively increases the nitrogen content in ammonium chloride. Then, by heating the slurry in the sodium ammonium separation tank, sodium bicarbonate and ammonium chloride can be effectively separated, which not only reduces the sodium content in ammonium chloride, but also significantly improves the particle size of ammonium chloride. The ammonium chloride prepared from the ammonium chloride filtrate after removing ammonium bicarbonate using the method of the present invention has a nitrogen content and particle size that meet the standard of superior agricultural ammonium chloride, which greatly improves the product quality of agricultural ammonium chloride. Attached Figure Description

[0017] Figure 1 —This is a process flow diagram of a wet treatment method for ammonium bicarbonate in sodium bicarbonate mother liquor according to the present invention. Detailed Implementation

[0018] The present invention will be further described below with reference to the accompanying drawings and embodiments, but these specific embodiments do not limit the scope of protection of the present invention in any way.

[0019] Example 1

[0020] A method for wet treatment of ammonium bicarbonate in sodium bicarbonate mother liquor, the process flow diagram of which is shown below. Figure 1 As shown, it includes the following steps:

[0021] 1) The sodium bicarbonate mother liquor obtained after a double decomposition reaction using brine and ammonium bicarbonate as raw materials, followed by washing, dehydration, and separation of sodium bicarbonate, is stored in a storage tank. The concentration of NH4HCO3 in the sodium bicarbonate mother liquor is 100 g / L, and the volume of the sodium bicarbonate mother liquor is 4.2 m³. 3 / h;

[0022] 2) The sodium bicarbonate mother liquor is pumped into the primary sodium ammonium deposition vessel using a feed pump. Figure 1 In the sodium ammonium deposition vessel 1), sodium chloride is added and reacted at a temperature of 20-25℃ (specifically 22℃ in this embodiment) for 1 hour while stirring. Utilizing the heat of dissolution generated by NaCl at the low temperature of 20-25℃, the common ion effect causes the complexed ionic state NH4HCO3 + NaCl to undergo another double decomposition reaction to generate NaHCO3 and NH4Cl, which can further remove ammonium bicarbonate from the sodium bicarbonate mother liquor, yielding a primary mixed slurry. The amount of sodium chloride added is M, in tons. Sodium chloride addition M (tons) = total amount of NH4HCO3 in the sodium bicarbonate mother liquor (kg) × 1.35 × 1.2 × 10⁻⁶ -3 = Mass-volume concentration of NH4HCO3 in baking soda mother liquor (g / L) × Volume of baking soda mother liquor (m³) 3 )×1.35×1.2×10 -3 = 100g / L × 4.2m 3 ×1.35×1.2×10 -3 = 0.68 tons;

[0023] Then, the primary mixed slurry is pumped into the secondary ammonium sodium deposition vessel using a feed pump. Figure 1 In the sodium ammonium ammonium deposition vessel 2), the reaction continues for a period of time. During the reaction, the removal rate of NH4HCO3 in the slurry is monitored in a timely manner. The removal rate of NH4HCO3 = the content of NH4HCO3 in the slurry to be tested / the content of NH4HCO3 in the sodium bicarbonate mother liquor × 100%. When the removal rate of NH4HCO3 in the mixed slurry reaches more than 95%, a secondary mixed slurry is obtained.

[0024] By adding a secondary ammonium sodium deposition tank to further treat the primary mixed slurry, not only can NH4HCO3 in the slurry be removed more effectively, but the particle size of the final ammonium chloride product after preparing ammonium chloride from the ammonium chloride filtrate can also be effectively improved.

[0025] The secondary mixed slurry is then pumped into a heat exchanger for preheating and then transported to the sodium ammonium separation vessel. The temperature of the sodium ammonium separation vessel is controlled at 32-35℃ (34℃ in this embodiment). NH4Cl can dissolve at this temperature, allowing it to separate from solid sodium bicarbonate. The reaction takes 1-3 hours (2 hours in this embodiment) until the NH4Cl crystals are completely dissolved, resulting in the tertiary mixed slurry.

[0026] 3) The three-stage mixed slurry is filtered, and the resulting ammonium chloride-containing deammoniation mother liquor is sent to prepare ammonium chloride. The resulting crude sodium bicarbonate is returned to the metathesis reaction process to prepare sodium bicarbonate.

[0027] 4) The specific operation steps for using the ammonium chloride-containing deammonium chloride mother liquor to prepare ammonium chloride are as follows: The method for preparing ammonium chloride from the deammonium chloride mother liquor refers to the cold crystallization and salting-out crystallization method in CN202111449257.1, a method for co-producing ammonium chloride from sodium bicarbonate. Specifically, the deammonium chloride mother liquor is sent to a cold crystallization kettle, where ammonium chloride is precipitated at a temperature of 8-10℃. Ammonium chloride is taken out from the lower crystal outlet, and the supernatant overflows into the salting-out crystallization kettle. After adding salt, ammonium chloride is precipitated at a temperature of 9-11℃. The ammonium chloride settles to the crystal slurry outlet at the bottom of the salting-out crystallization kettle. The ammonium chloride crystal slurry is pumped back to the cold crystallization kettle for crystal growth. The ammonium chloride crystallized from the cold crystallization kettle is combined with the ammonium chloride crystallized from the cold crystallization kettle and dehydrated and packaged by a centrifuge to obtain agricultural ammonium chloride. The mother liquor after centrifugation is recycled to produce sodium bicarbonate.

[0028] Example 2

[0029] The difference between this embodiment and Embodiment 1 is that the temperature of the primary ammonium sodium deposition vessel is 20°C, and the temperature of the ammonium sodium separation vessel is 35°C.

[0030] Example 3

[0031] The difference between this embodiment and Embodiment 1 is that the temperature of the primary ammonium sodium deposition vessel is 25°C, and the temperature of the ammonium sodium separation vessel is 35°C.

[0032] Comparative Example 1

[0033] This comparative example uses the distillation method in the prior art CN201910226450.5 to perform the deammoniation step, and the deammoniation mother liquor after deammoniation is used to prepare ammonium chloride in the same way as the deammoniation mother liquor in Example 1.

[0034] Comparative Example 2

[0035] The difference between this comparative example and Example 1 is that in step 2), the primary mixed slurry obtained by adding sodium chloride to undergo a metathesis reaction is directly pumped into a heat exchanger for preheating and then transported to the ammonium sodium separation vessel. All other operation steps are the same as in Example 1.

[0036] The removal rate of ammonium bicarbonate in sodium bicarbonate mother liquor after treatment in Examples 1-3 and Comparative Examples 1-2 was tested. The removal rate of ammonium bicarbonate was calculated as: (Ammonium bicarbonate content in the deammonium removal mother liquor / Ammonium bicarbonate content in the sodium bicarbonate mother liquor) * 100%. The results are shown in Table 1.

[0037] Table 1. Comparison of ammonium bicarbonate removal rates between the methods of Examples 1-3 and Comparative Examples 1-2

[0038]

[0039]

[0040] As shown in the table above, the ammonium bicarbonate removal rate in the deammonium mother liquor obtained after stepwise treatment using the primary ammonium sodium deposition vessel, secondary ammonium sodium deposition vessel, and ammonium sodium separation vessel of the present invention in Examples 1-3 all reached over 90%. Compared with the deammonium removal treatment using distillation in Comparative Example 1, this significantly improves the ammonium bicarbonate removal rate. Furthermore, in Comparative Example 2, only one ammonium sodium deposition vessel was used to treat the sodium bicarbonate mother liquor, resulting in an ammonium bicarbonate removal rate of only 80%. This is because adding solid salt at low temperature generates a common ion effect, stimulating the precipitation of ammonium chloride, while the secondary ammonium sodium precipitation... The sedimentation tank can further expand the water system space and accelerate the dissolution of solid salts. At the same time, the precipitation of ammonium chloride also produces seed crystals, which also promotes the rapid formation of sodium bicarbonate crystal nuclei by the strong driving force of solid salt dissolution, thus fully eliminating and utilizing ammonium bicarbonate. Therefore, the primary ammonium sodium sedimentation tank can only complete the precipitation of ammonium chloride seed crystals and the metathesis of sodium chloride and ammonium bicarbonate to form NaHCO3. It is difficult to complete the growth of crystal nuclei into coarse particles (NaHCO3). Therefore, only the secondary ammonium sodium sedimentation tank can complete the subsequent particle growth period and further improve the removal rate of ammonium bicarbonate.

[0041] The present invention also used the deammoniation mother liquor obtained by removing sodium bicarbonate mother liquor using the methods of Examples 1-3 and Comparative Examples 1-2 to prepare ammonium chloride. The nitrogen and sodium content and particle size of the ammonium chloride product were then determined, and the results are shown in Table 2.

[0042] Table 2. Comparison of various indicators in the ammonium chloride products prepared from the deammoniation mother liquor obtained during the removal of ammonium bicarbonate using the methods of Examples 1-3 and Comparative Examples 1-2.

[0043]

[0044] As shown in the table above, when the deammonium mother liquor obtained by step-by-step treatment of the first-stage ammonium sodium deposition vessel, the second-stage ammonium sodium deposition vessel, and the ammonium sodium separation vessel of the present invention was used to prepare ammonium chloride, the nitrogen content, sodium content, and particle size of the ammonium chloride all met the standard of superior grade of agricultural ammonium chloride in GB / T 2946-2008. However, the ammonium chloride prepared by the deammonium mother liquor of Comparative Example 1 after deammonium treatment by distillation did not meet the standard of agricultural ammonium chloride. Moreover, in Comparative Example 2, only one ammonium sodium deposition vessel was used for treatment before the ammonium sodium separation vessel. The particle size of the ammonium sodium deposition vessel was significantly smaller than that of Example 1. This indicates that by adding the second-stage ammonium sodium deposition vessel treatment in the present invention, the particle size of agricultural ammonium chloride prepared by the deammonium mother liquor after treatment can be significantly improved. The reason is that the second-stage ammonium sodium deposition vessel can further promote the formation of sodium bicarbonate, improve the removal rate of ammonium bicarbonate, and prevent sodium bicarbonate generated in the subsequent salting-out crystallization of ammonium chloride from mixing into the crystallized ammonium chloride, which would have a great impact on the particle size and quality of ammonium chloride. Therefore, the secondary ammonium sodium deposition vessel can not only effectively remove ammonium bicarbonate, but also ensure the particle size quality of ammonium chloride.

[0045] The present invention also statistically analyzed the energy consumption and cost of the methods for removing ammonium bicarbonate from sodium bicarbonate mother liquor in Examples 1-3 and Comparative Examples 1-2, and the results are shown in the table below:

[0046] Table 3. Comparison of energy consumption and cost for removing ammonium bicarbonate using the methods in Examples 1-3 and Comparative Examples 1-2.

[0047] Processing group Energy consumption (heat consumption in tons of coal) Cost (RMB) Example 1 0.01 10 Example 2 0.01 10 Example 3 0.01 10 Comparative Example 1 0.08 80 Comparative Example 2 0.09 90

[0048] As shown in the table above, compared with Comparative Example 1, the method for removing ammonium bicarbonate from sodium bicarbonate mother liquor in Examples 1-3 of the present invention can significantly reduce energy consumption and cost; while compared with Comparative Example 2, there is no significant difference in energy consumption and cost between the two, but the method of the present invention has better technical effects in removing ammonium bicarbonate and agricultural ammonium chloride than Comparative Example 2.

[0049] It should be noted that this article uses the terms "primary," "secondary," etc., to describe various components, but these components should not be limited by these terms. These terms are only used to distinguish one component from another.

[0050] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method of treating ammonium bicarbonate in a bicarbonate mother liquor in a wet process, characterized by, Includes the following steps: 1) Collect the sodium bicarbonate mother liquor generated during the preparation of sodium bicarbonate using the metathesis reaction; 2) Transfer the sodium bicarbonate mother liquor to the primary ammonium sodium deposition vessel, add sodium chloride and react for a period of time to obtain the primary mixed slurry, then transfer the primary mixed slurry to the secondary ammonium sodium deposition vessel, continue the reaction for a period of time to obtain the secondary mixed slurry, then heat the secondary mixed slurry and transfer it to the ammonium sodium separation vessel, react for a period of time to obtain the tertiary mixed slurry; 3) Filter the tertiary mixed slurry to obtain the ammonium chloride-containing deammonium mother liquor, which is sent to prepare ammonium chloride, and the obtained crude sodium bicarbonate is returned to the metathesis reaction process to prepare sodium bicarbonate.

2. The method for wet treatment of ammonium bicarbonate in sodium bicarbonate mother liquor as described in claim 1, characterized in that, The sodium bicarbonate mother liquor was reacted in the primary ammonium sodium deposition vessel at a temperature of 20-25℃ for 1 hour.

3. The method for wet treatment of ammonium bicarbonate in sodium bicarbonate mother liquor as described in claim 1, characterized in that, The added amount of sodium chloride is M, unit is ton, M = total amount of NH4HCO3 in the baking soda mother liquor × 1.35 × 1.2 × 10 -3 , the total amount of NH4HCO3 in the baking soda mother liquor is kg.

4. The method for wet treatment of ammonium bicarbonate in sodium bicarbonate mother liquor as described in claim 1, characterized in that, When adding sodium chloride to the primary ammonium sodium deposition vessel, it is necessary to stir while adding it.

5. The method for wet treatment of ammonium bicarbonate in sodium bicarbonate mother liquor as described in claim 1, characterized in that, The reaction time of the primary mixed slurry in the secondary ammonium sodium deposition vessel is determined based on the removal rate of NH4HCO3 in the mixed slurry.

6. The method for wet treatment of ammonium bicarbonate in sodium bicarbonate mother liquor as described in claim 5, characterized in that, When the removal rate of NH4HCO3 in the mixed slurry in the secondary ammonium sodium deposition vessel reaches more than 95%, a secondary mixed slurry is obtained, and the secondary mixed slurry is then transported to the ammonium sodium separation vessel.

7. The method for wet treatment of ammonium bicarbonate in sodium bicarbonate mother liquor as described in claim 1, characterized in that, The reaction temperature of the secondary mixed slurry in the ammonium sodium separation vessel is 32-35℃, and the reaction time is 1-3h.

8. The method for wet treatment of ammonium bicarbonate in sodium bicarbonate mother liquor as described in claim 1, characterized in that, The secondary mixed slurry is preheated by a heat exchanger before entering the ammonium sodium separation vessel.

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