A method for comprehensive utilization of sulfur dioxide tail gas

Abstract

The present invention relates to a method for comprehensive utilization of sulfur dioxide tail gas, comprising the following steps: 1) adding excessive fluorine gas to the tail gas containing sulfur dioxide for reaction to obtain a mixed gas containing sulfuryl fluoride; 2) adding excessive ammonia gas to the mixed gas for reaction to obtain a mixture, and performing gas, solid, and liquid three-phase separation on the mixture to respectively obtain solid ammonium fluoride, liquid bis(fluorosulfonyl)imide, and residual tail gas, and the residual tail gas is absorbed by acid solution and discharged up to the standard. In the present invention, harmful impurities in the hydrogen fluoride process tail gas are removed and all converted into reusable resources, without generating waste gas or waste residue; the treatment process is simple and easy to implement industrially.

Description

Technical Field

[0001] The present invention belongs to the technical field of tail gas treatment, and particularly relates to a comprehensive utilization method for sulfur dioxide tail gas. Background Art

[0002] In the current preparation process of hydrogen fluoride, whether it is the fluorite method, the fluorosilicic acid method or other methods, due to the influence of raw materials and process control, there will inevitably be a small amount of sulfur dioxide and hydrogen fluoride in the tail gas. The main treatment processes for waste gas include the limestone-gypsum method, the ammonia method, the double-alkali method, etc.

[0003] The limestone-gypsum method uses limestone as a desulfurization absorbent, which reacts with sulfur dioxide in the flue gas to form calcium sulfite, and then reacts with oxygen in the air to form calcium sulfate. This process is simple and has low requirements for equipment. The problem is that calcium sulfate is easy to wrap the limestone, resulting in low absorption efficiency.

[0004] The ammonia method for desulfurization uses ammonia as a sulfur dioxide absorbent. Ammonia reacts with sulfur dioxide to form ammonium sulfite, and then reacts with oxygen to form ammonium sulfate. Since ammonia is volatile in this process, the tail gas after desulfurization contains ammonia, causing secondary pollution.

[0005] Patent CN201811290654.7 provides a process for treating sulfur dioxide in tail gas by the double-alkali method. This process includes a desulfurization unit, a desulfurizer regeneration unit and a by-product recovery unit. By combining the medium circulation solubilization effect and the reaction intensification technology, the inexpensive lime is efficiently regenerated into a sodium alkali absorbent, but the calcium sulfate generated in the process is difficult to recycle, and stacking treatment is easy to cause secondary pollution.

[0006] The above-mentioned schemes all utilize the principle of acid-base neutralization to achieve the removal of impurities in the tail gas, but there are some defects. Summary of the Invention

[0007] In view of the above-mentioned defects existing in the prior art, the present invention provides a comprehensive utilization method for sulfur dioxide tail gas. The specific scheme is as follows:

[0008] A comprehensive utilization method for sulfur dioxide tail gas includes the following steps:

[0009] 1) Adding excessive fluorine gas to the tail gas containing sulfur dioxide for reaction to obtain a mixed gas containing sulfuryl fluoride;

[0010] 2) Adding excessive ammonia gas to the mixed gas for reaction to obtain a mixture. The mixture is subjected to gas-solid-liquid three-phase separation to respectively obtain solid ammonium fluoride, liquid bis(fluorosulfonyl)imide and residual tail gas. The residual tail gas is absorbed by acid solution and then discharged up to standard.

[0011] After adding fluorine gas, it can react quickly with sulfur dioxide at normal temperature and pressure to generate sulfuryl fluoride (SO2F2). Slightly excessive fluorine gas can ensure the full reaction of sulfur dioxide. The reaction equation is:

[0012] SO2 + F2 → SO2F2

[0013] After adding ammonia gas, it first reacts with hydrogen fluoride impurities in the tail gas to generate ammonium fluoride. The excess ammonia gas then reacts with SO2F2 at high temperature to generate liquid bis(fluorosulfonyl)imide (HFSI); at the same time, the remaining fluorine gas reacts with ammonia gas to generate solid ammonium fluoride and nitrogen gas. The total amount of ammonia gas is sufficient for the complete reaction of the three gases of hydrogen fluoride, sulfuryl fluoride, and fluorine gas. The reaction equations are as follows:

[0014] NH3 + HF → NH4F

[0015] 3NH3 + 2SO2F2 → HN(SO2F)2 + 2NH4F

[0016] 8NH3 + 3F2 → N2 + 6NH4F

[0017] After the reaction, the HFSI liquid and ammonium fluoride solid are separated. The remaining gas is then passed into dilute acid to remove the residual ammonia. Only nitrogen gas remains in the tail gas and can be harmlessly discharged. The HFSI liquid and ammonium fluoride solid can be separated respectively. HFSI can react with lithium salts to generate LiFSI. LiFSI is an important electrolyte for lithium batteries, and ammonium fluoride is an important raw material for the fluorine chemical industry, both of which can be reused.

[0018] Preferably, the tail gas is the tail gas generated in the hydrogen fluoride preparation process. The tail gas generated in the hydrogen fluoride preparation process contains sulfur dioxide and hydrogen fluoride, and is suitable for being treated by the method of the present invention.

[0019] Preferably, the reaction temperature in step 2) is controlled at 60 - 90 °C. Controlling the temperature within this range can ensure the complete reaction of ammonia gas with hydrogen fluoride, sulfuryl fluoride, and fluorine gas.

[0020] Preferably, the reaction of the tail gas with fluorine gas in step 1) is carried out in the tail gas pipeline. Specifically, a fluorine gas addition port can be set on the tail gas pipeline, without the need to additionally set up a reactor, reducing the equipment transformation cost. Since the reaction between fluorine gas and sulfur dioxide is violent, the complete reaction of fluorine gas and sulfur dioxide can also be ensured in the tail gas pipeline.

[0021] Preferably, a spoiler is provided in the tail gas pipeline. By setting the spoiler, the turbulence effect in the tail gas pipeline can be improved, and the gas mixing speed can be promoted.

[0022] Preferably, the reaction of the mixed gas with ammonia in step 2) is carried out in a cyclone separator. Specifically, a cyclone separator can be connected to the end of the tail gas pipeline, and an ammonia addition port can be set at the end of the tail gas pipeline or at the inlet of the cyclone separator. Ammonia and the mixed gas are mixed and reacted in the cyclone separator. By controlling the flow rate of the cyclone separator, it is ensured that the contact reaction time of the gas in the cyclone separator is greater than 2 minutes.

[0023] Preferably, the separation of the solid phase, liquid phase and gas phase in step 2) is carried out in a cyclone separator. Since the cyclone separator itself has a centrifugal separation effect, in this solution, it serves as both a reaction vessel and a separation function, separating the solid phase and liquid phase generated after the reaction. The solid and liquid mixture can be further subjected to solid-liquid separation by means such as standing and filtration to obtain solid ammonium fluoride and liquid HFSI products respectively.

[0024] Preferably, the molar ratio of fluorine gas to sulfur dioxide in the tail gas in step 1) is (1.02 - 1.10):1. Within this range, it can ensure that sulfur dioxide reacts completely, and at the same time, the amount of fluorine gas used is relatively low.

[0025] Preferably, the amount of ammonia added in step 2) is determined according to the formula c = (1.02 - 1.1)b + (1.8 - 2)a; where a is the number of moles of sulfur dioxide in the tail gas, b is the number of moles of hydrogen fluoride in the tail gas, and c is the number of moles of ammonia added. Within this range, it can ensure that hydrogen fluoride, sulfuryl fluoride, and fluorine gas react completely, and at the same time, the amount of ammonia used is relatively low.

[0026] Preferably, the acid solution in step 2) is dilute sulfuric acid or dilute phosphoric acid. After absorbing the residual ammonia with dilute sulfuric acid or dilute phosphoric acid, it can be separated out and used as a chemical fertilizer after accumulating to a certain concentration.

[0027] The beneficial effects of the present invention are as follows: The present invention uses fluorine gas to remove sulfur dioxide in the tail gas, with high purification efficiency. After further reacting with ammonia, valuable HFSI and ammonium fluoride products can be prepared. The harmful impurities in the tail gas can be removed and all converted into reusable resources, without generating waste gas or waste residue; moreover, the equipment involved in this solution has a low usage cost, the treatment process using this solution is simple, and it is easy to implement industrially. Brief Description of the Drawings

[0028] Figure 1 It is a process schematic diagram of the present invention. Detailed Embodiments

[0029] Next, the technical solutions in the embodiments of the present invention will be described clearly and completely in conjunction with the embodiments of the present invention. The methods of Examples 1 - 3 are carried out according to the Figure 1 shown process.

[0030] Example 1:

[0031] A comprehensive utilization method for sulfur dioxide tail gas:

[0032] Fluorine gas is added to a tail gas pipeline with a flow rate of 1000 L / min, a sulfur dioxide content of 4113 mg / m 3 , a hydrogen fluoride content of 1106 mg / m 3 . The flow rate of fluorine gas is 1.47 L / min, and the molar ratio of fluorine gas to sulfur dioxide is 1.02:1. After the reaction, ammonia gas is added, with a flow rate of 3.85 L / min. The molar amount of ammonia gas is the sum of 1.02 times the molar amount of hydrogen fluoride and 1.8 times the molar amount of sulfur dioxide. It enters a cyclone separator for reaction at 90 °C, separating out solids and liquids. The remaining gas is then passed into dilute phosphoric acid to remove residual ammonia. The sulfur dioxide content in the tail gas is detected to be 73 mg / m 3 , and hydrogen fluoride and ammonia are not detected.

[0033] Example 2:

[0034] A comprehensive utilization method for sulfur dioxide tail gas:

[0035] Fluorine gas is added to a tail gas pipeline with a flow rate of 1000 L / min, a sulfur dioxide content of 3959 mg / m 3 , a hydrogen fluoride content of 1089 mg / m 3 . The flow rate of fluorine gas is 1.52 L / min, and the molar ratio of fluorine gas to sulfur dioxide is 1.1:1. After the reaction, ammonia gas is added, with a flow rate of 4.11 L / min. The molar amount of ammonia gas is the sum of 1.1 times the molar amount of hydrogen fluoride and 2 times the molar amount of sulfur dioxide. It enters a cyclone separator for reaction at 60 °C, separating out solids and liquids. The remaining gas is then passed into dilute phosphoric acid to remove residual ammonia. The sulfur dioxide content in the tail gas is detected to be 64 mg / m 3 , and hydrogen fluoride and ammonia are not detected.

[0036] Example 3:

[0037] A comprehensive utilization method for sulfur dioxide tail gas:

[0038] Fluorine gas is added to a tail gas pipeline with a flow rate of 1000 L / min, a sulfur dioxide content of 4029 mg / m 3 , a hydrogen fluoride content of 1156 mg / m 3 . The flow rate of fluorine gas is 1.49 L / min, and the molar ratio of fluorine gas to sulfur dioxide is 1.06:1. After the reaction, ammonia gas is added, with a flow rate of 4.05 L / min. The molar amount of ammonia gas is the sum of 1.06 times the molar amount of hydrogen fluoride and 1.9 times the molar amount of sulfur dioxide. It enters a cyclone separator for reaction at 80 °C, separating out solids and liquids. The remaining gas is then passed into dilute sulfuric acid to remove residual ammonia. The sulfur dioxide content in the tail gas is detected to be 68 mg / m 3, hydrogen fluoride and ammonia were not detected.

[0039] The impurity contents before and after tail gas treatment in Examples 1-3 are summarized in the following table. It can be seen from the table that for the tail gas treated by this method, the sulfur dioxide content has dropped to 100 mg / m 3 Below, it meets the emission standards.

[0040]

Claims

1. A method for comprehensive utilization of sulfur dioxide tail gas, characterized in that, It includes the following steps: 1) React excessive fluorine gas with the tail gas containing sulfur dioxide to obtain a mixed gas containing sulfuryl fluoride; 2) React the mixed gas with excessive ammonia to obtain a mixture. The mixture is subjected to three-phase separation of gas, solid and liquid to respectively obtain solid ammonium fluoride, liquid bis(fluorosulfonyl)imide and residual tail gas. The residual tail gas is absorbed by acid solution and then discharged up to the standard.

2. The comprehensive utilization method of sulfur dioxide tail gas according to claim 1, characterized in that: The tail gas in step 1) is the tail gas generated in the hydrogen fluoride preparation process.

3. The comprehensive utilization method of sulfur dioxide tail gas according to claim 1, characterized in that: The reaction temperature in step 2) is controlled at 60 - 90 °C.

4. The method for comprehensive utilization of sulfur dioxide tail gas according to claim 1, characterized in that: The reaction between the tail gas and fluorine gas in step 1) is carried out in the tail gas pipeline.

5. The method for comprehensive utilization of sulfur dioxide tail gas according to claim 4, characterized in that: A spoiler is arranged in the tail gas pipeline.

6. The comprehensive utilization method of sulfur dioxide tail gas according to claim 4, characterized in that: The reaction between the mixed gas and ammonia in step 2) is carried out in a cyclone separator.

7. The method for comprehensive utilization of sulfur dioxide tail gas according to claim 6, characterized in that: The separation of the solid phase, liquid phase and gas phase in step 2) is carried out in a cyclone separator.

8. The comprehensive utilization method of sulfur dioxide tail gas according to claim 1, characterized in that: In step 1), the molar ratio of fluorine gas to sulfur dioxide in the tail gas is (1.02 - 1.10):

1.

9. The method for comprehensive utilization of sulfur dioxide tail gas according to claim 2, wherein: The amount of ammonia added in step 2) is determined according to the formula c = (1.02 - 1.1)b + (1.8 - 2)a; where a is the number of moles of sulfur dioxide in the tail gas, b is the number of moles of hydrogen fluoride in the tail gas, and the added c is the number of moles of ammonia.

10. The method for comprehensive utilization of sulfur dioxide tail gas according to claim 1, characterized in that: The acid solution in step 2) is dilute sulfuric acid or dilute phosphoric acid.

Images