Method for treating exhaust gas of AHF synthesis of lithium battery electrolyte organic fluorine additive

Abstract

The application discloses a tail gas treatment method for lithium battery electrolyte organic fluorine additive AHF synthesis, and the tail gas from the AHF synthesis is condensed and recovered by a-15 DEG C refrigerant, and then enters a synthesis tail gas pipeline; the synthesis tail gas from the synthesis tail gas pipeline is indirectly cooled to below-50 DEG C by a-70 DEG C low-temperature refrigerant under the suction of an induced draft fan; after most of the organic fluorine compounds and hydrogen fluoride are condensed and recovered, the tail gas enters a washing unit to remove hydrogen fluoride, an adsorption unit to remove organic fluorine compounds, and a denitration unit to remove nitrogen, and is then discharged. The method is simple, clean and environmentally friendly, effectively realizes the recycling of pollution components, ensures the stable, efficient and long-term operation of the system, and is low in operation cost.

Description

Technical Field

[0001] This invention belongs to the field of chemical waste gas treatment, and relates to the treatment of waste gas pollutants generated in the production process of the organic fluorine chemical industry. Specifically, it is a method for treating waste gas generated during the synthesis of organic fluorine additives for lithium battery electrolytes using the AHF method. Background Technology

[0002] Lithium-ion battery electrolyte is one of the key materials in batteries, and a small amount of additives can effectively compensate for some of the shortcomings of the electrolyte itself. Fluorine has strong electronegativity and weak polarity. Fluorine-containing additives can improve the oxidation resistance of the electrolyte at the positive electrode, and at the same time, they can reduce the electrolyte before the solvent at the negative electrode interface, inhibiting further decomposition of the electrolyte. Fluorine-containing additives can improve the non-flammability of the electrolyte and improve battery safety performance; fluorine-containing additives also have advantages such as good electrode wettability and improved electrolyte conductivity [Shao Junhua, Kong Dongbo. Research progress of fluorine-containing additives for lithium-ion battery electrolytes. Battery, April 2017].

[0003] In recent years, fluorine materials have been widely used in new energy fields such as solar cells, lithium-ion batteries, fuel cells, wind power, and nuclear power due to their excellent properties. Especially in the field of lithium-ion batteries, the strong electron-withdrawing effect of fluorine helps to increase the reduction potential of solvent molecules on the carbon anode surface, optimize the solid electrolyte interface film, improve the compatibility between the electrolyte and activated carbon materials, and thus stabilize the electrochemical performance of the electrode. Meanwhile, organofluorine compounds are organic solvents with high or no flash points. Adding these organofluorine compounds to the electrolyte reduces flammability, greatly improving the thermal stability of the electrolyte and the safety of the lithium battery. Therefore, organofluorine compounds are used as additives in various electrolytes for lithium batteries [Song Xin, Wu Zesheng, Yang Qiangqiang, et al. Research progress on novel fluorine-containing additives for lithium-ion battery electrolytes. Power Technology, 2017, No. 10]. Chen Yongkun et al. studied 1,2,3-trifluorobenzene. 1,2,3-trifluorobenzene can improve the battery's room temperature cycling, high temperature cycling, and low temperature discharge performance, reduce interfacial impedance, and has no negative impact on the battery's high-temperature storage performance. These properties of trifluorobenzene are mainly attributed to its improvement effect on the positive and negative electrode interfaces, thereby affecting film formation at the positive and negative electrode interfaces and reducing interfacial impedance [Chen Yongkun, Xie Tian. Research on 1,2,3-trifluorobenzene as an electrolyte additive. Guangdong Chemical Industry, 2020, No. 6]. Organic fluorine materials contain F... - It can reduce the surface tension of the electrolyte on the surface of the active material and increase the wetting speed. At the same time, the benzene rings it contains have a protective effect on the positive electrode, effectively preventing Fe... 2+The dissolution of the electrolyte improves the cycle performance of the battery; trace amounts of fluorinated surfactants can effectively reduce the surface tension of the electrolyte on the surface of the active material and increase the wetting speed, while having virtually no effect on the electrochemical performance [Qin Kai, Sun Xinhua, Yang Liangjun, et al. Research on the improvement of the wetting performance of electrolyte in high-energy-density lithium iron phosphate batteries. Power Technology, 2020, 44(08)].

[0004] In recent years, with the continuous development of applications for organofluorine materials, the market demand for fluorobenzene products, the main raw materials for the synthesis of organofluorine materials, has further increased. Currently, there are two main industrial production methods for fluorobenzene: the Schiemann reaction and the anhydrous hydrogen fluoride (AHF) method. The Schiemann reaction was the earliest method for synthesizing fluorobenzene, but it has been gradually phased out due to its high cost, low yield (56%), unsafe open-flame heating, and the release of large amounts of toxic BF3 gas during thermal decomposition, which is difficult to recover. The core technology of the AHF method is that the synthesis reaction is carried out in a liquid anhydrous hydrogen fluoride system. Because of the polarity of hydrogen fluoride molecules and the strong electronegativity of fluorine, it is not only an excellent solvent for electrolytes but also a superacid system. In anhydrous hydrogen fluoride, not only can aniline dissolve through salt formation, but sodium nitrite can also dissolve in this solvent, readily undergoing a diazotization reaction. Since the diazonium salt decomposition reaction is carried out in anhydrous hydrogen fluoride, the formation of the byproduct phenol is greatly suppressed. Therefore, the yield of fluorobenzene in the AHF method reaches 80%.

[0005] The AHF process yields high production rates of fluorobenzene-based organofluorine materials, but it generates high-concentration HF, NOx, and fluorinated organic compounds in the synthesis tail gas. This tail gas has complex pollutant components and high pollutant concentrations, making purification and treatment difficult and severely restricting the development of the organofluorine chemical industry. Summary of the Invention

[0006] The purpose of this invention is to solve the above-mentioned technical problems and provide a method for treating the tail gas of the AHF synthesis of organic fluorine additives for lithium battery electrolytes that is simple in process, clean and environmentally friendly, effectively realizes the recovery and utilization of pollutant components, ensures system stability, high efficiency, long-term operation, and low operating cost.

[0007] The method of this invention is as follows: the synthesis tail gas of the AHF method is condensed and recovered by a -15℃ refrigerant to recover some organic fluorine compounds and hydrogen fluoride components before entering the synthesis tail gas pipeline. The synthesis tail gas from the synthesis tail gas pipeline is indirectly cooled to below -50℃ by a -70℃ low-temperature refrigerant in a cryogenic unit under the suction of an induced draft fan. After condensation and recovery of most of the organic fluorine compounds and hydrogen fluoride, it enters the washing unit to remove hydrogen fluoride, the adsorption unit to remove organic fluorine compounds, and the denitrification unit to remove and purify before being discharged.

[0008] The synthesis exhaust gas is cooled by exchanging heat with the cryogenic exhaust gas exiting the cryogenic unit through a primary cooling heat exchanger before being sent back into the cryogenic unit.

[0009] The cryogenic unit includes multiple cryogenic heat exchangers, which take turns performing condensation and defrosting processes. The synthesis exhaust gas flows sequentially through the series of cryogenic heat exchangers undergoing condensation before entering the scrubbing unit.

[0010] The synthesis exhaust gas in the exhaust pipe is divided into two streams. The first stream of synthesis exhaust gas is cooled by the primary cooling heat exchanger and then sent to the series-connected cryogenic heat exchangers in the condensation process for condensation. The second stream of synthesis exhaust gas is sent to the cryogenic heat exchangers in the defrosting process as a defrosting medium for defrosting.

[0011] The first stream of synthesis exhaust gas accounts for 70-90% of the total synthesis exhaust gas volume, and the second stream of synthesis exhaust gas accounts for 30-10% of the total synthesis exhaust gas volume.

[0012] The cryogenic heat exchanger has multiple enhanced cooling sections. In each enhanced cooling section, a refrigerant circulation pump is used to return the refrigerant from the downstream to the upstream.

[0013] The washing unit includes a multi-stage water washing tower, a primary alkaline washing tower, and a water washing demister in series. The cryogenic tail gas, after being condensed and having removed most of the organic fluorine compounds and hydrogen fluoride, is sequentially washed by the multi-stage water washing tower, alkaline washed by the primary alkaline washing tower, and demistered by the water washing demister. After removing 99.99% of the hydrogen fluoride, it enters the adsorption unit to remove organic fluorine compounds.

[0014] The multi-stage water washing tower consists of a primary water washing tower and a primary alkali washing tower that operate alternately.

[0015] Both the primary water washing tower and the primary alkali washing tower are equipped with two circulating liquid tanks at their bottoms: one is a circulating alkali tank, and the other is a circulating spray water tank. When operating as a primary water washing tower, the circulating spray liquid is collected in the circulating spray water tank and then returned to the tower. When operating as a primary alkali washing tower, the circulating spray liquid is collected in the circulating alkali tank and then returned to the tower.

[0016] Monitor the sodium fluoride concentration in the circulating alkali tank of the tower that is working as a primary alkali scrubbing tower. When it exceeds 3wt%, the cryogenic tail gas entering the scrubbing unit is directly switched to be introduced into the tower. At the same time, the circulating liquid tank of the tower is switched, and the circulating spray water in the circulating spray water tank is introduced into the tower for circulating spraying. That is, the alkali scrubbing function of the tower is switched to the primary water scrubbing function.

[0017] At the same time, the original first-stage water washing tower is switched to a first-stage alkali washing tower, and the tail gas from the last-stage water washing tower is introduced into the tower. At the same time, the circulating liquid tank of the tower is switched, and the circulating alkali solution in the circulating alkali solution tank is introduced into the tower for circulating spraying.

[0018] When used as a primary water scrubbing tower, circulating alkali solution is continuously and evenly discharged from the corresponding circulating alkali solution tank into the corresponding circulating spray water tank. Discharge is stopped when the discharge reaches 50-60% of the total circulating alkali solution volume, and then fresh sodium hydroxide solution is added to the circulating alkali solution tank to the original level.

[0019] Deionized water is continuously and evenly added to the water washing and demisting tower, and a portion of the washing water discharged from the bottom of the tower enters the multi-stage water washing tower in a reverse direction.

[0020] The amount of deionized water added is controlled according to the hydrogen fluoride content in the cryogenic exhaust gas entering the washing unit, so as to ensure that the hydrogen fluoride concentration in the liquid phase discharged from the washing unit is greater than 40%.

[0021] The adsorption unit includes at least two resin adsorption towers, one for adsorption and the other for desorption, alternating between the two. 10-20% by volume of the adsorption tail gas from the other resin adsorption tower is introduced into the desorbed resin adsorption tower to cool the resin adsorption layer until the set temperature is reached, and then it enters the subsequent denitrification unit together with the remaining adsorption tail gas.

[0022] The desorption exhaust gas from the adsorption unit is condensed by a condenser and then heat-exchanged by a purified exhaust gas heat exchanger before being reused as defrosting gas for the cryogenic unit.

[0023] The denitrification unit includes a denitrification heat exchanger, a tail gas heater, an ammonia addition device, a pipeline mixer, and a denitrification reactor. The adsorption tail gas from the adsorption unit is heated by exchanging heat with the purified tail gas in the denitrification heat exchanger, and then heated to above 170°C by the tail gas heater. Ammonia is added by the ammonia addition device, and finally the mixture is evenly mixed by the pipeline mixer before entering the denitrification reactor for denitrification and purification. The purified tail gas is then sent to the denitrification heat exchanger to exchange heat with the adsorption tail gas.

[0024] The purified exhaust gas from the denitrification heat exchanger is divided into two parts. One part is directly mixed with the adsorption exhaust gas after it has been heated by the denitrification heat exchanger and participates in the exhaust gas circulation to dilute the concentration of nitrogen oxides in the exhaust gas entering the denitrification reactor. The other part is cooled and dehumidified by exchanging heat with the desorbed exhaust gas in the purified exhaust gas heat exchanger and then discharged through the chimney.

[0025] Addressing the challenges of complex and highly concentrated pollutant components in synthesis tail gas, where purification treatment is not only costly but also wasteful of resources, this invention breaks with traditional treatment concepts by proposing a cryogenic condensation and direct reuse technology. The synthesis tail gas is cooled to below -50°C using a -70°C refrigerant, recovering nitrogen dioxide, organofluorine compounds, hydrogen fluoride, etc., which are then returned to the production process to participate in the synthesis reaction again, achieving resource utilization. The reason for cryogenic condensation to below -50°C is based on the understanding that at this temperature, almost all nitrogen dioxide, over 70% of hydrogen fluoride, and over 90% of organofluorine compounds are condensed. Cryogenic condensation enables timely and on-site resource utilization of pollutant components, resulting in high efficiency and low cost. The condensed pollutant components originate from raw materials, reaction products, or byproducts required in the synthesis of organofluorine compounds. Returning these components to the reaction system after condensation effectively inhibits side reactions and improves the conversion rate of reactants.

[0026] In addition to HF, the exhaust gas from the synthesis of organofluorine compounds also contains a large amount of organofluorine compounds, nitrogen oxides, and small amounts of VOCs. To remove or recycle these pollutants and obtain anhydrous HF at the source, this invention, based on the physical properties and characteristics of these components, creatively proposes a cryogenic heat exchanger refrigerant internal circulation scheme, forming an enhanced cooling section within the cryogenic heat exchanger. By adjusting the circulation rate, different cooling effects can be obtained, achieving different condensation rates for pollutants and improving the condensation and interception effect of pollutants in the synthesis exhaust gas.

[0027] Among these pollutants, nitrogen dioxide has a melting point of -11℃ and a boiling point of 21℃; nitric oxide has a melting point of -163.6℃ and a boiling point of -151℃; HF has a melting point of -83℃ and a boiling point of 19.54℃; and organofluorine compounds generally have melting points below -40℃. When the exhaust gas is cryogenically cooled to -50℃, nitrogen dioxide and some organofluorine compounds condense, and more than 70% of HF also condenses. During the condensation process, nitrogen dioxide and organofluorine compounds will frost up inside the cryogenic heat exchanger, blocking the exhaust gas flow channels. To mitigate the frost clogging problem, this invention makes the following improvements:

[0028] (1) The exhaust gas enters the cryogenic heat exchanger and exchanges heat with the refrigerant in the opposite direction. The refrigerant is forced to circulate back in the cryogenic heat exchanger, forming enhanced cooling sections corresponding to hydrogen fluoride, organic fluorinated compounds and nitrogen dioxide respectively. By setting up a refrigerant circulation pump, the higher temperature refrigerant downstream is returned to the upstream, forming a condensation section with a small temperature difference corresponding to the melting point temperature of the pollutant components, so as to ensure that the pollutant components are fully condensed and do not solidify and blockage.

[0029] (2) Utilizing the high-temperature gas circulation defrosting within the exhaust gas purification system. First, the high-temperature desorbed exhaust gas from the resin adsorption unit is used as the defrosting heat source, which not only recovers the organic fluorine compounds in the desorbed exhaust gas but also achieves efficient defrosting. Second, the original synthesis exhaust gas is used as the defrosting heat source, which not only initially cools the synthesis exhaust gas and recovers the frost cooling capacity but also achieves the defrosting effect. Part of the original synthesis exhaust gas is introduced into the cryogenic heat exchanger that needs to be defrosted, and after defrosting, it returns to the cryogenic heat exchanger for further condensation.

[0030] The effects of this improvement are as follows:

[0031] (1) Stepwise condensation and recovery of contaminant components reduces frost blockage during the cryogenic process and improves system operational stability.

[0032] (2) Forced circulation of refrigerant is carried out to make full use of the cold energy of refrigerant, increase the temperature of refrigerant exiting the cryogenic heat exchanger, and then exchange heat with the cryogenic tail gas at a lower temperature (-50℃) after cryogenic cooling, thereby improving the efficiency of refrigerant cold energy utilization.

[0033] (3) Fully recover the cold energy from frost formation.

[0034] (4) No external defrosting medium is required to achieve efficient defrosting.

[0035] (5) During the cryogenic process, most of the nitrogen dioxide condenses back into the synthesis reactor, which increases the concentration of nitrogen dioxide in the reactor liquid, inhibits the occurrence of the side reaction <2HNO2→NO+NO2+water>, and improves the utilization rate of HNO2.

[0036] In order to efficiently recover the HF component in the exhaust gas and eliminate the scaling and clogging problems that exist in the absorption process using sodium hydroxide solution, this invention creatively proposes a scheme for functional conversion of the absorption equipment, which involves periodically switching between the primary water scrubbing tower and the primary alkaline scrubbing tower for alternating use.

[0037] By setting the cycle of the alkaline washing stage in the alkaline washing tower, the functions of the alkaline washing tower and the first-stage water washing tower can be switched periodically, i.e., switching between the "alkaline washing" and "water washing" functions. The improvement effect is as follows:

[0038] (1) Completely eliminate scaling and clogging problems. Sodium fluoride has a solubility of only 3.85% in water (10℃), making it easy to adhere to the surface of the packing material and the contact surfaces of the pump impeller and the inner wall of the absorption tower, forming scale that clogs the equipment. By switching, the original circulating alkaline solution is replaced with circulating spray water, and the original low-concentration hydrogen fluoride tail gas is replaced with high-concentration hydrogen fluoride tail gas. As the circulating spray water circulates, the concentration of hydrogen fluoride increases, and the pH value of the absorbent solution decreases. The sodium fluoride scale that originally adhered to the surface of the packing material and the contact surfaces of the pump impeller and the inner wall of the absorption tower dissolves into the hydrogen fluoride aqueous solution, achieving online descaling without the need to introduce external descaling agents.

[0039] (2) Obtaining high-concentration HF products improves the recovery rate of fluorine. This is because during the washing and absorption of HF in the tail gas, the HF concentration decreases with each of the first to fourth stages of washing, leading to a decrease in the washing absorption efficiency. The ionization process of HF in dilute solution can be represented as HF + H₂O → H₃O + +F - Because of F - It is a strong proton acceptor, while H3O + It is a relatively strong proton donor, H3O + With F - The ions bond with each other through hydrogen bonds to form relatively stable ion pairs. These ion pairs are difficult to ionize. HF exhibits weak acidity in dilute solutions. During the absorption process, there is a gas-liquid equilibrium concentration of HF. Therefore, there is a certain amount of HF residue in the tail gas. Alkali washing can thoroughly absorb the HF components in the tail gas. Then, by converting the function of the absorption equipment, the fluorine in the scale layer can be further dissolved and recovered.

[0040] Furthermore, based on the HF concentration in the exhaust gas entering the washing unit, the amount of deionized water supplied to the water washing demister is controlled, thereby controlling the amount of washing liquid discharged sequentially from the water washing demister to the multi-stage water washing towers, so as to ensure that the concentration of the washing liquid entering the first-stage water washing tower reaches more than 40% after absorbing the HF in the exhaust gas, thus ensuring the liquid phase balance of the system.

[0041] When too much deionized water is added to the water washing demister, the amount of liquid phase discharged from the washing unit will increase, and the HF content in the discharged liquid phase product will be low. In this case, the amount of deionized water added should be reduced. If the amount of deionized water added is too low, it will affect the defluorination effect of the upstream water washing tower and increase the defluorination load of the alkaline washing tower.

[0042] Furthermore, while converting the function of the absorption equipment, two circulating liquid tanks were cleverly set up for each of the first-stage water washing tower and the alkali washing tower: one for circulating alkali solution and the other for circulating spray water. When used as the first-stage water washing tower, the circulating spray liquid returns to the circulating spray water tank; when used as the alkali washing tower, the circulating spray liquid returns to the circulating alkali solution tank. During water washing, the circulating alkali solution from the alkali washing stage is continuously and evenly discharged into the circulating spray water tank in use. Discharge is stopped when the discharge reaches 50-60% of the total circulating alkali solution volume, and then fresh sodium hydroxide solution is added to the circulating alkali solution tank to the original level. The benefits of this improvement are:

[0043] (1) It can ensure the complete recovery of fluorine components in the system and zero discharge of fluorine components.

[0044] (2) No fluoride-containing wastewater is generated, saving wastewater treatment investment and operating costs, and greatly simplifying the treatment process of fluoride components in tail gas.

[0045] Furthermore, in order to achieve the ultimate recovery of organofluorine compounds, the present invention innovatively proposes the following improvements in the resin adsorption unit:

[0046] (1) Adsorption tail gas circulation cooling. 10-20% of the washing tail gas from another resin adsorption tower is refluxed into the resin adsorption tower after desorption to cool the resin adsorption layer. The washing tail gas, after being heated by heat exchange in the resin layer, is mixed with the remaining 80-90% of the adsorption tail gas and enters the subsequent denitrification unit. The reason for cooling the resin adsorption layer after desorption is that the lower the temperature of the resin during adsorption, the better the adsorption. This avoids the washing tail gas being heated when it enters due to the high temperature of the resin adsorption layer in the early stage of adsorption, resulting in a fast tail gas flow rate, short adsorption time, and a decrease in the adsorption rate of fluorobenzene. The reason for using partial adsorption tail gas reflux cooling is to cool the resin at a lower cooling rate to avoid rapid cooling affecting the service life of the resin.

[0047] (2) After the resin desorption tail gas (mainly composed of organic fluorine compounds and nitrogen oxides) is condensed and dehydrated, it is then heated by heat exchange with the purified tail gas after SCR denitrification, and then returned to the synthesis reactor for stirring and temperature adjustment.

[0048] The effects of this improvement are as follows:

[0049] (1) The cold and heat sources of the internal medium of the system are fully utilized. The cold energy of the adsorption tail gas at a lower temperature is recovered by cooling the resin adsorption tower after desorption through the reflux of the adsorption tail gas; the heat enthalpy of the purified tail gas at a higher temperature is recovered by exchanging heat with the desorption tail gas and the purified tail gas after SCR denitrification; the heat enthalpy required for heating and pyrolysis of the synthesis reaction vessel liquid is saved by stirring the desorption tail gas after heat exchange and heating.

[0050] (2) Fully recover and utilize the pollutants such as organic fluorine compounds and nitrogen oxides contained in the exhaust gas.

[0051] Furthermore, this invention innovatively proposes a purified exhaust gas recirculation technology for SCR denitrification treatment of the adsorption exhaust gas after resin adsorption. Specifically, the purified exhaust gas from the denitrification heat exchanger is divided into two parts. One part is directly mixed with the heated adsorption exhaust gas and participates in the exhaust gas recirculation. The other part is cooled and dehydrated by exchanging heat with the desorption exhaust gas in a purified exhaust gas heat exchanger before being discharged through a chimney. The effects of this technology are as follows:

[0052] (1) In terms of system operation stability, by circulating the purified tail gas, the fluctuation range of NOx content in the adsorbed tail gas entering the denitrification reactor is reduced, the impact of NOx concentration fluctuation in the inlet gas on the catalyst is mitigated, which is conducive to the stability of the SCR denitrification reaction process.

[0053] (2) Through the circulating dilution effect of the purified tail gas, the temperature fluctuation of the adsorbed tail gas entering the reactor will also be reduced, thereby improving the system's operational stability. The improved system operational stability can effectively reduce system operating costs and extend the catalyst's service life.

[0054] (3) By monitoring the NOx concentration in the purified tail gas online and adjusting the amount of ammonia injected into the adsorption tail gas, the circulation of the purified tail gas also controls the fluctuation of ammonia content in the tail gas entering the denitrification reactor, which is conducive to the stability of the SCR denitrification reaction process, improves the denitrification effect, and reduces ammonia escape.

[0055] (4) The purified exhaust gas of each row is exchanged with the desorbed exhaust gas at a lower temperature, so that some of the moisture in the purified exhaust gas is condensed. The condensation process also absorbs the ammonia component in the flue gas, reducing ammonia escape.

[0056] (5) By circulating the purified exhaust gas, the concentration of nitrogen oxides is diluted, thus avoiding violent local reactions in the reactor and damage to the catalyst.

[0057] This invention enables the recovery and utilization of pollutant components in synthesis tail gas, fully recovers waste heat and waste cooling capacity, has a relatively simple process route, is environmentally friendly, has high pollutant purification efficiency, low operating costs, and enables the equipment to operate stably for a long time. Attached Figure Description

[0058] Figure 1 : Process flow diagram of this invention.

[0059] The cryogenic unit includes: synthesis tail gas pipe SL1, cryogenic tail gas pipe SL2, primary cooling tail gas pipe SL3, primary cooling heat exchanger SL7, cryogenic heat exchanger SL8, SL9, SL10, cryogenic condensate tank SL11, refrigerant circulation pump SL12, and purified tail gas heat exchanger SL13.

[0060] Washing induced draft fan XD1, primary alkali washing tower XD2A, primary water washing tower XD2B, secondary water washing tower XD3, tertiary water washing tower XD4, quaternary water washing tower XD5, water washing demisting tower XD6, storage tank below the tower XD8, water washing circulating pump XD11, alkali discharge pump XD12.

[0061] Resin adsorption tower SX1, reflux cooling fan SX3, spray cooling tower SX4, desorption tail gas condenser SX5, gas-liquid separator SX7;

[0062] Denitrification heat exchanger XT3, circulating fan XT4, tail gas circulation regulating valve XT5, tail gas heater XT8, denitrification reactor XT9, pipeline mixer XT10, ammonia addition device XT11. Detailed Implementation

[0063] The process of the present invention will be further explained below with reference to the accompanying drawings:

[0064] Taking the tail gas from the synthesis of organic fluorine additives in lithium battery electrolytes via the AHF method in a certain project as an example, the project's production line contains 60 AHF method reactors for the synthesis of organic fluorine additives (not shown in the attached diagram), with an annual production capacity of 4,000 tons of organic fluorine compounds.

[0065] Each synthesis reactor operates intermittently. Although the volume and composition of the exhaust gas emitted from each reactor vary at different stages of the synthesis reaction, the large number of reactors results in a relatively stable volume and composition of the exhaust gas after mixing. The volume of the synthesis exhaust gas is 1000–2000 Nm³. 3 / h, the main components of the exhaust gas are: HF: 160~170g / Nm 3 Organofluorine compounds: 2000–3000 mg / Nm 3 NOx: 12000–20000 mg / Nm³ 3 It contains a small amount of VOCs; the rest is nitrogen.

[0066] The AHF synthesis tail gas, after being condensed by a -15°C refrigerant to recover some organic fluorine compounds and hydrogen fluoride components, enters the synthesis tail gas pipeline SL1. Under the suction of an induced draft fan, it passes through the primary cooling heat exchanger SL7 and exchanges heat with the cryogenic tail gas exiting the cryogenic unit at below -50°C, lowering the temperature of the synthesis tail gas to -10°C. Simultaneously, the temperature of the cryogenic tail gas rises to -30°C. The synthesis tail gas then passes through the primary cooling tail gas pipeline SL3 into the cryogenic unit, where it is indirectly cooled to below -50°C by a -70°C low-temperature refrigerant. After condensation and recovery of most of the organic fluorine compounds and hydrogen fluoride, it sequentially enters the scrubbing unit for hydrogen fluoride removal, the adsorption unit for organic fluorine compound removal, and the denitrification unit for denitrification purification before being discharged. The condensate collected in the primary cooling heat exchanger SL7 flows into the primary condensate tank SL6.

[0067] Among them, see Figure 1The cryogenic unit includes multiple cryogenic heat exchangers, specifically three cryogenic heat exchangers SL8, SL9, and SL10 in this embodiment. The inlet and outlet ports of these three heat exchangers are connected in parallel via pipes, and they are also connected in series via pipes. Switching valves are installed on both the parallel and series connection pipes to switch between parallel and series operation of the cryogenic heat exchangers, alternating between condensation and defrosting. In other words, the three cryogenic heat exchangers take turns performing condensation-condensation-defrosting. The cryogenic heat exchanger operates alternately, with the condensation-condensation-defrosting process controlled by setting upper and lower limits for the pressure difference between the inlet and outlet exhaust gases. When the pressure difference exceeds the upper limit, the refrigerant is cut off, and the heat exchanger enters the defrosting stage. When the pressure difference falls below the lower limit, refrigerant is introduced, and the heat exchanger enters the cryogenic operating stage. This process is repeated alternately (this is existing technology and will not be detailed). The synthesis exhaust gas flows sequentially through the series of cryogenic heat exchangers undergoing condensation before entering the scrubbing unit via cryogenic exhaust gas pipe SL2. The defrosted exhaust gas is then introduced into the cryogenic heat exchanger undergoing condensation to condense and recover organic fluorinated compounds and hydrogen fluoride. The condensate collected by the cryogenic heat exchanger is sent to the cryogenic condensate tank SL11.

[0068] Preferably, the synthesis tail gas from the synthesis tail gas pipeline SL1 is split into two streams. The first stream of synthesis tail gas is cooled by the primary cooling heat exchanger SL7 and then sent to the cryogenic unit for condensation. The second stream of synthesis tail gas is sent as a defrosting medium to the cryogenic heat exchanger undergoing defrosting (the switching process is completed by the corresponding connected pipes and valves). The first stream of synthesis tail gas accounts for 70-90% of the total synthesis tail gas volume, and the second stream accounts for 10-30%. Here, partial synthesis tail gas defrosting is used, which saves refrigerant and improves defrosting efficiency (direct contact defrosting), while also saving the system investment required for introducing external defrosting medium.

[0069] The cryogenic heat exchanger has three enhanced cooling sections. Each enhanced cooling section has a refrigerant outlet downstream, connected to the upstream refrigerant inlet via a refrigerant circulation pump SL12. The synthesis exhaust gas and condensate come into counter-current contact. The enhanced cooling sections respectively enhance the condensation of hydrogen fluoride, organic fluorinated compounds, and nitrogen dioxide components, improving the condensation and interception effect of pollutants in the synthesis exhaust gas.

[0070] See also Figure 1In this embodiment, the washing unit includes four-stage water washing towers XD2B, XD3, XD4, and XD5 connected in series, a primary alkaline washing tower XD2A, and a water washing demister XD6. After condensation and recovery of most of the organic fluorine compounds and hydrogen fluoride, the cryogenic tail gas is sequentially washed by the four-stage water washing towers XD2B, XD3, XD4, and XD5, alkaline washing by the primary alkaline washing tower XD2A, and demister XD6 to remove 99.99% of the hydrogen fluoride before entering the adsorption unit to remove organic fluorine compounds.

[0071] Here, through the control of pipelines and valves, the first-stage water washing tower XD2B (i.e., the first-stage water washing tower of this scheme) and the first-stage alkaline washing tower XD2A in the multi-stage water washing tower can be switched to work alternately. That is, the first-stage water washing tower XD2B can be switched to the first-stage alkaline washing tower, and at the same time, the first-stage alkaline washing tower XD2A can be switched to the water washing tower. The bottom of the first-stage water washing tower XD2B and the first-stage alkaline washing tower XD2A are respectively provided with two circulating liquid tanks, one is a circulating alkaline liquid tank XD20, and the other is a circulating spray water tank XD21. When working as a first-stage water washing tower, the circulating spray liquid is collected through the corresponding circulating spray water tank XD21 and then returned to the tower. When working as a first-stage alkaline washing tower, the circulating spray liquid is collected through the circulating alkaline liquid tank XD21 and then returned to the tower. The above control can be completed through corresponding pipeline connections and valve switching, which is existing technology and will not be described in detail.

[0072] The preferred method is as follows: monitor the sodium fluoride concentration in the circulating alkali tank of the tower XD2A, which is used as the first-stage alkali washing tower. When it exceeds 3%wt, the cryogenic tail gas that entered the original first-stage water washing tower is directly switched to be introduced into this tower. At the same time, the circulating liquid tank of this tower is switched, and the circulating spray water in the circulating spray water tank XD21 is introduced into the tower for circulating spraying. Finally, this tower is switched to be used as the first-stage water washing tower.

[0073] Simultaneously, the original primary water scrubbing tower is switched to a primary alkali scrubbing tower. The exhaust gas from the final primary water scrubbing tower (the fourth primary water scrubbing tower in this scheme) is introduced into this new tower. At the same time, the circulating liquid tank of this tower is switched, and the circulating alkali solution from the circulating alkali solution tank XD20 is introduced into the tower for circulating spraying. Since sodium fluoride has a solubility of only 3.85% in water (10℃), it easily adheres to the surface of the packing material and the contact surfaces of the pump impeller and the inner wall of the absorption tower, forming scale that clogs the equipment. Through this switching, the original circulating alkali solution is replaced with circulating spray water, and the original low-concentration hydrogen fluoride exhaust gas is replaced with high-concentration hydrogen fluoride exhaust gas. As the circulating spray water circulates, the concentration of hydrogen fluoride increases, and the sodium fluoride scale layer originally adhering to the surface of the packing material and the contact surfaces of the pump impeller and the inner wall of the absorption tower dissolves into the hydrogen fluoride aqueous solution, achieving online descaling without the need for external descaling agents. This also ensures complete recovery of the system's fluorine components and zero external discharge.

[0074] When used as a primary water scrubbing tower, circulating alkali solution is continuously and uniformly discharged from the corresponding circulating alkali solution tank XD20 via the alkali discharge pump XD1 into the corresponding circulating spray water tank XD21. Discharge is stopped when the discharged amount reaches 50-60% of the total circulating alkali solution volume, and then fresh sodium hydroxide solution is added to the circulating alkali solution tank XD21 to the original level. Deionized water is uniformly and continuously added to the water scrubbing and demisting tower XD6, and a portion of the washing water discharged from the bottom of the tower is sequentially and counter-currently entered into the multi-stage water scrubbing tower for use as circulating spray water.

[0075] The external washing liquid phase inlet pipe of the washing unit is connected to the circulating alkali tank XD20 of the first-stage alkali washing tower and the bottom storage tank of the water washing demister XD6. The circulating spray water tank XD21 of the first-stage water washing tower XD2B and the first-stage alkali washing tower XD2A is equipped with an external liquid phase outlet pipe. When the first-stage water washing tower XD2B is used to draw out hydrofluoric acid products with an HF concentration of 40wt% or more.

[0076] Based on the HF concentration in the exhaust gas entering the washing unit, the amount of deionized water supplied to the water washing demister XD6 is controlled, thereby controlling the amount of washing liquid discharged sequentially from the water washing demister XD6 to the upstream multi-stage water washing towers. This ensures that the concentration of the washing liquid entering the first-stage water washing tower XD2B reaches more than 40% after absorbing the HF in the exhaust gas, thus ensuring the liquid phase balance of the system.

[0077] Because if too much deionized water is added to the water washing demister XD6, it will increase the amount of liquid phase discharged from the washing unit, and the HF content in the discharged liquid phase product will be low. In this case, the amount of deionized water added should be reduced. If the amount of deionized water added is too low, it will affect the defluorination effect of the preceding water washing tower and increase the defluorination load of the first-stage alkaline washing tower XD2A.

[0078] See Figure 1 The adsorption unit includes at least two resin adsorption towers SX1, one for adsorption and the other for desorption, alternating between the two. 10-20% by volume of adsorption tail gas from the other resin adsorption tower is introduced into the desorbed resin adsorption tower to cool the resin adsorption layer until a set temperature is reached. This tail gas then enters the subsequent denitrification unit along with the remaining adsorption tail gas. The desorption tail gas from the adsorption unit is cooled to -5 to 0°C by a condenser and dehydrated. After indirect heat exchange via a purified tail gas heat exchanger SX13, it is used as defrost gas for the cryogenic unit's defrost piping.

[0079] The condensation device includes a gas-liquid separator SX7, a spray cooling tower SX7, and a desorption tail gas condenser SX5 connected in sequence. The desorbed tail gas is condensed by the gas-liquid separator SX7, the spray cooling tower SX7, and the desorption tail gas condenser SX5 in sequence and then sent to the purified tail gas heat exchanger SX13. The liquid phase (or condensate) drawn from the gas-liquid separator SX7, the spray cooling tower SX7, and the desorption tail gas condenser SX5 enters the oil-water separation tank SX11 to separate and recover fluorobenzene, which is then sent to the fluorobenzene product tank SX12 to obtain the fluorobenzene product.

[0080] See Figure 1 The denitrification unit includes a denitrification heat exchanger XT3, a tail gas heater XT8, an ammonia device XT11, a pipeline mixer XT10, an ammonia addition device XT11, and a denitrification reactor XT9. The adsorption tail gas from the adsorption unit is heated by exchanging heat with the purified tail gas in the denitrification heat exchanger XT3, and then heated to above 170°C by the tail gas heater XT8. After ammonia is added by the ammonia addition device XT11, it enters the denitrification reactor XT9 for denitrification and purification. The purified tail gas is divided into two parts. One part is directly mixed with the adsorption tail gas heated by the denitrification heat exchanger XT3 and sent to the tail gas heater XT8 through the circulating fan XT4 and the tail gas circulation regulating valve XT4 to participate in tail gas circulation, diluting the nitrogen oxide concentration in the tail gas entering the denitrification reactor. The other part is cooled and dehumidified by exchanging heat with the desorbed tail gas through the circulating fan XT4 and the purified tail gas heat exchanger SL13, and then discharged through the chimney.

[0081] After purification, the HF recovery rate is above 99.99%; the organic fluorine compound recovery rate is above 99.9%; the NOx removal rate is above 99.95%, and the outlet NOx is below 100 mg / Nm3.

[0082] After purification, approximately 2,000 tons of HF and about 20 tons of organofluorine compounds can be recovered annually.

Claims

1. A method for treating the tail gas from the AHF synthesis of organic fluorine additives in lithium battery electrolytes, wherein the tail gas from the AHF synthesis is condensed at -15°C with a refrigerant to recover part of the organic fluorine compounds and hydrogen fluoride components before entering the synthesis tail gas pipeline, characterized in that... The synthesis tail gas from the synthesis tail gas pipeline is indirectly cooled to below -50°C by a -70°C low-temperature refrigerant in the cryogenic unit under the suction of the induced draft fan. After condensation and recovery of most of the organic fluorine compounds and hydrogen fluoride, it enters the washing unit to remove hydrogen fluoride, the adsorption unit to remove organic fluorine compounds, and the denitrification unit to remove and purify before being discharged. The washing unit includes a multi-stage water washing tower, a primary alkaline washing tower, and a water washing demisting tower connected in series. The multi-stage water washing tower consists of a primary water washing tower and a primary alkali washing tower that operate alternately. The bottom of both the primary water washing tower and the primary alkali washing tower is equipped with two circulating liquid tanks: one is a circulating alkali tank and the other is a circulating spray water tank. When operating as a primary water washing tower, the circulating spray liquid is collected in the circulating spray water tank and then returned to the tower. When operating as a primary alkali washing tower, the circulating spray liquid is collected in the circulating alkali tank and then returned to the tower. Monitor the sodium fluoride concentration in the circulating alkali tank of the tower that is working as a primary alkali scrubbing tower. When it exceeds 3wt%, the cryogenic tail gas entering the scrubbing unit is directly switched to be introduced into the tower. At the same time, the circulating liquid tank of the tower is switched, and the circulating spray water in the circulating spray water tank is introduced into the tower for circulating spraying. In other words, the alkali scrubbing function of the tower is switched to the primary water scrubbing function. At the same time, the original first-stage water washing tower is switched to a first-stage alkali washing tower, and the tail gas from the last-stage water washing tower is introduced into the tower. At the same time, the circulating liquid tank of the tower is switched, and the circulating alkali solution in the circulating alkali solution tank is introduced into the tower for circulating spraying.

2. The method for treating tail gas from the synthesis of organic fluorine additives in lithium battery electrolytes using the AHF method as described in claim 1, characterized in that, The synthesis exhaust gas is cooled by exchanging heat with the cryogenic exhaust gas exiting the cryogenic unit through a primary cooling heat exchanger before being sent back into the cryogenic unit.

3. The method for treating tail gas from the synthesis of organic fluorine additives in lithium battery electrolytes using the AHF method as described in claim 1 or 2, characterized in that, The cryogenic unit includes multiple cryogenic heat exchangers, which take turns performing condensation and defrosting processes. The synthesis exhaust gas flows sequentially through the series of cryogenic heat exchangers undergoing condensation before entering the scrubbing unit.

4. The method for treating tail gas from the synthesis of organic fluorine additives in lithium battery electrolytes using the AHF method as described in claim 3, characterized in that, The synthesis tail gas from the synthesis tail gas pipeline is divided into two streams. The first stream of synthesis tail gas is cooled by the primary cooling heat exchanger and then sent to the series-connected cryogenic heat exchangers in the condensation process for condensation. The second stream of synthesis tail gas is sent to the cryogenic heat exchangers in the defrosting process as a defrosting medium for defrosting.

5. The method for treating the tail gas from the synthesis of organic fluorine additives in lithium battery electrolytes using the AHF method as described in claim 4, characterized in that, The first stream of synthetic tail gas accounts for 70-90% of the total synthetic tail gas volume, and the second stream of synthetic tail gas accounts for 30-10% of the total synthetic tail gas volume.

6. The method for treating tail gas from the synthesis of organic fluorine additives in lithium battery electrolytes using the AHF method as described in claim 3, characterized in that, The cryogenic heat exchanger has multiple enhanced cooling sections, and each enhanced cooling section uses a refrigerant circulation pump to return the refrigerant from the downstream to the upstream.

7. The method for treating tail gas from the synthesis of organic fluorine additives in lithium battery electrolytes using the AHF method as described in claim 1, characterized in that, In the washing unit, the cryogenic tail gas, after being condensed to remove most of the organic fluorine compounds and hydrogen fluoride, is sequentially washed by a multi-stage water washing tower, an alkaline washing tower, and a water washing demisting tower. After removing 99.99% of the hydrogen fluoride, it enters the adsorption unit to remove organic fluorine compounds.

8. The method for treating tail gas from the synthesis of organic fluorine additives in lithium battery electrolytes using the AHF method as described in claim 1, characterized in that, When used as a primary water scrubbing tower, circulating alkali solution is continuously and evenly discharged from the corresponding circulating alkali solution tank into the corresponding circulating spray water tank. Discharge is stopped when the discharge reaches 50-60% of the total circulating alkali solution volume, and then fresh sodium hydroxide solution is added to the circulating alkali solution tank to the original level.

9. The method for treating the tail gas from the synthesis of organic fluorine additives in lithium battery electrolytes using the AHF method as described in claim 1, characterized in that, Deionized water is continuously and evenly added to the water washing and demisting tower, and a portion of the washing water discharged from the bottom of the tower enters the multi-stage water washing tower in a reverse direction.

10. The method for treating tail gas from the synthesis of organic fluorine additives in lithium battery electrolytes using the AHF method as described in claim 1, characterized in that, The adsorption unit includes at least two resin adsorption towers, one for adsorption and the other for desorption, alternating between the two. 10-20% by volume of the adsorption tail gas from the other resin adsorption tower is introduced into the desorbed resin adsorption tower to cool the resin adsorption layer until the set temperature is reached, and then it enters the subsequent denitrification unit together with the remaining adsorption tail gas.

11. The method for treating tail gas from the synthesis of organic fluorine additives in lithium battery electrolytes using the AHF method as described in claim 10, characterized in that, The desorption exhaust gas from the adsorption unit is condensed by a condenser and then heat-exchanged by a purified exhaust gas heat exchanger before being reused as defrosting gas for the cryogenic unit.

12. The method for treating tail gas from the synthesis of organic fluorine additives in lithium battery electrolytes using the AHF method as described in claim 1, characterized in that, The denitrification unit includes a denitrification heat exchanger, a tail gas heater, an ammonia addition device, a pipeline mixer, and a denitrification reactor. The adsorption tail gas from the adsorption unit is heated by exchanging heat with the purified tail gas in the denitrification heat exchanger, and then heated to above 170°C by the tail gas heater. Ammonia is added by the ammonia addition device, and finally the mixture is evenly mixed by the pipeline mixer before entering the denitrification reactor for denitrification and purification. The purified tail gas is then sent to the denitrification heat exchanger to exchange heat with the adsorption tail gas.

13. The method for treating tail gas from the synthesis of organic fluorine additives in lithium battery electrolytes using the AHF method as described in claim 12, characterized in that, The purified exhaust gas from the denitrification heat exchanger is divided into two parts. One part is directly mixed with the adsorbed exhaust gas after it has been heated by the denitrification heat exchanger and participates in the exhaust gas circulation to dilute the concentration of nitrogen oxides in the exhaust gas entering the denitrification reactor. The other part is cooled and dehumidified by exchanging heat with the desorbed exhaust gas in the purified exhaust gas heat exchanger and is then discharged through the chimney.

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