A method for separating and purifying mixed acid from phosphorus chloride tail gas.

Abstract

This application relates to the field of chemical production technology, specifically disclosing a method for separating and purifying mixed acid from phosphorus-containing chloride tail gas. The method utilizes the principle of chemical equilibrium and the property differences between hydrochloric acid and phosphorus-containing inorganic acids to achieve the enrichment of phosphorus-containing inorganic acids and the removal of hydrogen chloride. Furthermore, a two-stage absorption tower is used to separately absorb the escaping hydrogen chloride, effectively separating the mixed acid into two high-value-added chemical products. This provides a new pathway for the recycling of mixed acid and effectively overcomes the hidden dangers of existing mixed acid treatment methods.

Description

Technical Field

[0001] This application relates to the field of chemical production technology, and more specifically, it relates to a method for separating and purifying mixed acid from phosphorus chloride tail gas. Background Technology

[0002] Phosphorus chlorides are important chemical raw materials with wide applications in the chemical industry. Currently, chemical plants generate tail gas containing phosphorus chlorides during the production process. Phosphorus chlorides are highly toxic, and to prevent air pollution or poisoning, these tail gases require harmless treatment. Since phosphorus chlorides readily react with water, chemical plants typically use water as an absorbent to absorb the phosphorus chloride tail gas. After reacting with water, phosphorus chlorides produce oxyacids corresponding to the valence state of the phosphorus element and hydrogen chloride, resulting in a mixed acid of hydrochloric acid and phosphorus-containing inorganic acids.

[0003] Under current processes, once the mixed acid reaches a total acid concentration of 31 wt%, hydrogen chloride approaches dissolution-precipitation equilibrium, after which the mixed acid can no longer absorb hydrogen chloride produced in subsequent reactions. If the reaction continues, a large amount of newly generated hydrogen chloride will escape, causing a sharp increase in tail gas treatment pressure. Since the existing processes of production enterprises cannot separate phosphorus-containing inorganic acids and hydrochloric acid, these mixed acids must be treated by third parties, often at high costs. Third parties, considering factors such as transportation convenience and recycling costs, will not accept mixed acids with excessively low concentrations, typically only accepting mixed acids with a total acid concentration of around 31 wt%. Even these mixed acids that meet the requirements of third parties are ultimately only used to formulate low-value-added products such as descaling agents. Furthermore, some mixed acid treatment companies, in order to save on treatment and transportation costs, even secretly discharge imported mixed acids into the wild, severely damaging the ecological environment.

[0004] Regarding the aforementioned technologies, the inventors believe that in existing processes, hydrochloric acid and phosphorus-containing inorganic acids in mixed acid cannot be easily separated, making it difficult for production enterprises to effectively recycle and reuse them, which has become a burden that production enterprises cannot ignore. Furthermore, the meager profits from the preparation of low-value-added products from mixed acid make it difficult to prevent third-party illegal discharge of mixed acid, posing a potential threat to the ecological environment. Summary of the Invention

[0005] In related technologies, the separation of mixed acids is quite difficult, making it hard for production enterprises to effectively recycle and reuse them, greatly increasing their burden. Furthermore, mixed acids can currently only be used to produce low-value-added products and pose a potential threat to the ecological environment. To address these shortcomings, this application provides a method for separating and purifying mixed acids from phosphorus-containing chloride tail gas.

[0006] This application provides a method for separating and purifying mixed acid from phosphorus chloride tail gas, employing the following technical solution: A method for separating and purifying mixed acid from phosphorus chloride tail gas includes the following steps: (1) Add primary absorbent to the primary absorption tower, and then introduce phosphorus chloride tail gas into the primary absorption tower for reaction under the drive of nitrogen. At the same time, extract the primary acid solution generated at the bottom of the primary absorption tower for extraction and spray it back into the primary absorption tower, and continuously monitor the water content in the primary acid solution; the primary absorbent is pure water or unsaturated hydrochloric acid solution. (2) Add secondary absorbent to the secondary absorption tower and transport the tail gas generated by the primary absorption tower to the secondary absorption tower. Extract the secondary acid generated at the bottom of the secondary absorption tower and spray it back into the secondary absorption tower. Continuously monitor the tail gas generated by the secondary absorption tower. (3) When the water content in the absorbent drops to 1-15wt%, stop the back spraying of the first-stage absorber and introduce pure nitrogen into the first-stage absorber to drive away the remaining gas. Collect the first-stage acid solution discharged from the first-stage absorber to obtain phosphorus-containing inorganic acid; collect the second-stage acid solution discharged from the second-stage absorber to obtain hydrochloric acid.

[0007] By adopting the above technical solution, this application utilizes the characteristic that phosphorus-containing chlorides readily react with water. Phosphorus-containing chlorides are continuously introduced into the primary absorption tower, and water is used in the secondary absorption tower to absorb the exhaust gas discharged from the primary absorption tower. As the phosphorus-containing chlorides continue to dissolve, the chlorides in the primary absorbent gradually reach a dissolution-volatilization equilibrium. Subsequently, all the hydrogen chloride produced by the reaction of the phosphorus-containing chlorides with water volatilizes into the gas phase, while the water in the primary absorbent is continuously consumed. With the consumption of water, the hydrogen chloride originally dissolved in the water is also gradually released. Since the phosphorus-containing inorganic acid cannot volatilize, it continuously accumulates in the primary absorbent, thus maintaining the ionization equilibrium of hydrogen chloride: HCl(aq)⇌H₂O. + +Cl -The volatile-dissolution equilibrium "HCl(g) ⇌ HCl(aq)" continuously shifts to the left. When the water content in the absorbent drops to 15 wt%, the mass fraction of dissolved chloride ions in the absorbent is less than 5 / 1000. In cases where impurity chloride ions are not a concern, it can completely replace general industrial-grade phosphoric acid. As the water content further decreases, hydrogen chloride will further precipitate, eventually compressing the chloride ion mass fraction to below 5 / 100,000, easily meeting the requirements of GB / T GB 2091-2008 stipulates the requirements for high-grade industrial-grade phosphoric acid. In the second absorption tower, due to the high solubility of hydrogen chloride in water, the hydrogen chloride volatilized during the reaction in the first absorption tower can completely dissolve in the second absorption liquid, ultimately converting into highly pure hydrochloric acid. The method in this application utilizes the principle of chemical equilibrium and the property differences between hydrochloric acid and phosphorus-containing inorganic acids to achieve the enrichment of phosphorus-containing inorganic acids and the removal of hydrogen chloride. Furthermore, the secondary absorption tower separately absorbs the escaping hydrogen chloride, effectively separating the mixed acids into two high-value-added chemical products. This provides a new approach for the recycling of mixed acids and effectively overcomes the hidden dangers of existing mixed acid treatment methods.

[0008] Preferably, the phosphorus-containing chloride is a trivalent phosphorus-containing chloride and / or a pentavalent phosphorus-containing chloride.

[0009] By adopting the above-mentioned technical solutions, trivalent and pentavalent phosphorus chlorides are the most prevalent forms of phosphorus chlorides and are also important substances that need to be recovered and utilized in exhaust gases. The process of this application can effectively regenerate the mixed acid formed by these phosphorus chlorides into high-value-added chemical products, transforming waste that originally required expensive third-party outsourcing into high-value-added chemical products, thereby effectively overcoming the practical difficulties faced by production enterprises.

[0010] Preferably, the phosphorus-containing chloride is at least one of phosphorus trichloride, phosphorus oxychloride, and phosphorus pentachloride.

[0011] By adopting the above technical solution, and considering the presence of air (oxygen) mixed in the gas flow, phosphorus trichloride will undergo the following reaction in the primary absorbent: (1) PCl3+3H2O→H3PO3+3HCl; (2) 2PCl3+O2+6H2O→2H3PO4+6HCl; Phosphorus pentachloride and phosphorus oxychloride will react as follows in the primary absorbent: (3) 4H2O+PCl5→H3PO4+5HCl; (4) POCl3+3H2O→H3PO4+3HCl; Through the above reaction, these phosphorus-containing chlorides are converted into hydrochloric acid and phosphoric acid / phosphorous acid, and further separated in subsequent steps to obtain two high-value-added products.

[0012] Preferably, the phosphorus-containing chloride is further subjected to arsenic removal treatment according to the following steps before being introduced into the primary absorption tower: Phosphorus-containing chlorides are heated to a gaseous state to obtain phosphorus-containing chloride vapor. The phosphorus-containing chloride vapor is then passed through copper powder and subjected to distillation. After the distillation is completed, the arsenic removal process is finished.

[0013] By adopting the above technical solution, trace amounts of arsenic trichloride may be mixed in with phosphorus-containing chlorides. Arsenic trichloride is difficult to completely remove by simple distillation alone. This application uses copper as a reducing agent, which can reduce arsenic trichloride to elemental arsenic without affecting the phosphorus-containing chlorides, while copper is oxidized to cuprous chloride. Since elemental arsenic is easily separated from phosphorus trichloride during distillation, this method can ensure that the arsenic content of the finished phosphoric acid meets the requirements for electronic-grade phosphoric acid.

[0014] Preferably, the phosphorus-containing chloride is a mixture of phosphorus trichloride and at least one pentavalent phosphorus-containing chloride.

[0015] By employing the above technical solution, when the phosphorus-containing chloride contains both trivalent and pentavalent phosphorus, the resulting phosphorus-containing inorganic acid is a mixture of phosphorous acid and phosphoric acid. After slow oxidation with oxygen, a relatively pure phosphoric acid product can ultimately be obtained.

[0016] Preferably, in step (3) of the method for separating and purifying phosphorus-containing chloride tail gas mixed acid, after obtaining the phosphorus-containing inorganic acid, an oxidation treatment is performed as follows: The phosphorus-containing inorganic acid is loaded into a bubbling and stirring absorption tower. A mixture of ozone and air is passed into the phosphorus-containing inorganic acid for bubbling and stirring. At the same time, the phosphorus-containing inorganic acid is extracted and sprayed back into the bubbling and stirring absorption tower until trivalent phosphorus can no longer be detected in the phosphorus-containing inorganic acid. Continue to pass the mixed gas for 120-150 minutes to end the oxidation treatment.

[0017] By adopting the above technical solution, this application uses a mixture of ozone and air to oxidize phosphoric acid, achieving a rapid conversion of phosphorous acid to phosphoric acid without introducing impurities. Furthermore, under the catalysis of hydrogen ions, ozone also has a certain oxidizing effect on chloride ions, further reducing the chloride ion content in phosphoric acid and enabling phosphoric acid to more fully meet the requirements of GB / T 2091-2008 for superior grade industrial phosphoric acid.

[0018] Preferably, in the oxidation treatment step (3), hydrogen peroxide is added to the phosphorus-containing inorganic acid.

[0019] By adopting the above technical solution, hydrogen peroxide itself is liquid and will not escape from the liquid phase in a short time like a mixed gas. Therefore, the oxidation of phosphorous acid can be achieved efficiently by mixing the mixed gas with hydrogen peroxide, and a relatively pure phosphoric acid product can be obtained.

[0020] Preferably, in the oxidation treatment step (3), the phosphorus-containing inorganic acid is heated to 55-90°C.

[0021] By adopting the above technical solution, this application has optimized the temperature range of phosphorus-containing inorganic acids, within which the oxidation of phosphorous acid can be achieved quickly and fully.

[0022] Preferably, in the oxidation treatment step (3), the phosphorus-containing inorganic acid is heated to 75-90°C.

[0023] By adopting the above technical solution, this application has selected a preferred temperature range for phosphorus-containing inorganic acids, which helps to fully realize the oxidation of chloride ions by ozone within this temperature range.

[0024] Preferably, in step (3), when the water content in the absorbent is detected to drop to 1-2 wt%, the subsequent operations are continued.

[0025] By adopting the above technical solution, this application has optimized the water content range in the absorbent. Within this range, the residual chloride ion concentration in the phosphorus-containing inorganic acid is already at an extremely low level. Combined with oxidation treatment, a phosphoric acid product with a chloride ion content far lower than that of the superior grade can be obtained.

[0026] In summary, this application has the following beneficial effects: 1. The method of this application utilizes the principle of chemical equilibrium and the property differences between hydrochloric acid and phosphorus-containing inorganic acids to achieve the enrichment of phosphorus-containing inorganic acids and the removal of hydrogen chloride. Moreover, the escaped hydrogen chloride is absorbed separately through a two-stage absorption tower, which effectively achieves the separation of mixed acids into two high-value-added chemical products. This provides a new way for the recycling of mixed acids and effectively overcomes the hidden dangers of the original treatment methods for mixed acids.

[0027] 2. This application uses a mixture of ozone and air to oxidize phosphoric acid-containing inorganic acids, which can achieve the conversion of phosphorous acid to phosphoric acid at a relatively fast rate without introducing impurities. Furthermore, under the catalysis of hydrogen ions, ozone also has a certain oxidizing effect on chloride ions, which can further reduce the chloride ion content in phosphoric acid-containing inorganic acids, allowing phosphoric acid to more fully meet the requirements of GB / T 2091-2008 for superior grade industrial-grade phosphoric acid.

[0028] 3. This application optimizes the water content range in the absorption liquid, so that the residual chloride ion concentration in the phosphorus-containing inorganic acid is at an extremely low level. Combined with oxidation treatment, a phosphoric acid product with a chloride ion content far lower than that of the superior grade can be obtained. Detailed Implementation

[0029] The present application will be further described in detail below with reference to the embodiments and comparative examples. The raw materials involved in the present application can all be obtained commercially. Example

[0030] Examples 1-3 The following description uses Example 1 as an example.

[0031] Example 1 In this embodiment, the phosphorus-containing chloride is phosphorus trichloride, and both the primary and secondary absorbents are pure water. The volume of both the primary and secondary absorbents is 8 ml. 3 The nitrogen flow rate in the exhaust gas is 269.8 kg / h, the phosphorus chloride flow rate is 154.5 kg / h, and the arsenic content in the exhaust gas is 0.0001 μg / L. To balance the heat released during the reaction and dissolution processes, in this embodiment, a water circulation cooling device is used to continuously cool the primary and secondary absorption towers, maintaining the temperature at 20°C.

[0032] This embodiment provides a method for separating and purifying mixed acid from phosphorus chloride tail gas, including the following steps: (1) Add primary absorbent to the primary absorption tower, and then introduce phosphorus chloride tail gas into the primary absorption tower for reaction under the drive of nitrogen. At the same time, extract the primary acid liquid generated at the bottom of the primary absorption tower for extraction and spray it back into the primary absorption tower, and continuously monitor the water content in the primary acid liquid. (2) Add secondary absorbent to the secondary absorption tower and transport the tail gas generated by the primary absorption tower to the secondary absorption tower. Extract the secondary acid generated at the bottom of the secondary absorption tower and spray it back into the secondary absorption tower. Continuously monitor the tail gas generated by the secondary absorption tower. (3) When the water content in the absorbent drops to 15wt%, stop the back spraying of the first-stage absorber and introduce pure nitrogen into the first-stage absorber to drive away the remaining gas. Collect the first-stage acid liquid discharged from the first-stage absorber to obtain phosphorus-containing inorganic acid; collect the second-stage acid liquid discharged from the second-stage absorber to obtain hydrochloric acid.

[0033] As shown in Table 1, the main difference between Examples 1-3 is that the subsequent operations are started under different moisture content conditions in step (3) (hereinafter referred to as the target moisture content).

[0034] Table 1 Target Moisture Content sample Example 1 Example 2 Example 3 Example 4 Example 5 Target moisture content / % 15 10 5 2 1

[0035] Example 6 The difference between this embodiment and Embodiment 5 is that the primary absorbent is 3wt% dilute hydrochloric acid (prepared directly from deionized water and hydrogen chloride).

[0036] Example 7 The difference between this embodiment and Embodiment 5 is that the primary absorbent is 8 wt% dilute hydrochloric acid (prepared directly from deionized water and hydrogen chloride).

[0037] Example 8 The difference between this embodiment and Embodiment 5 is that phosphorus pentachloride is used as the phosphorus-containing chloride.

[0038] Example 9 The difference between this embodiment and Embodiment 7 is that phosphorus oxychloride is used as the phosphorus-containing chloride.

[0039] Example 10 The difference between this embodiment and Embodiment 5 is that, before the phosphorus-containing chloride is introduced into the primary absorption tower, it undergoes arsenic removal treatment according to the following steps: Phosphorus-containing chlorides are heated to a gaseous state to obtain phosphorus-containing chloride vapor. The phosphorus-containing chloride vapor is then passed through copper powder and subjected to distillation. After the distillation is completed, the arsenic removal process is finished.

[0040] Example 11 The difference between this embodiment and Example 10 is that the phosphorus-containing chloride is a mixture of phosphorus trichloride and phosphorus pentachloride in a 1:1 molar ratio. In step (3) of the phosphorus-containing chloride tail gas mixed acid separation and purification method, after obtaining the phosphorus-containing inorganic acid, it is further oxidized according to the following method: The phosphorus-containing inorganic acid, preheated to 55°C, is loaded into a bubbling and stirring absorption tower. A mixture of ozone and air at a volume ratio of 1:4 is introduced into the phosphorus-containing inorganic acid at a flow rate of 50 L / h for bubbling and stirring. Simultaneously, the phosphorus-containing inorganic acid is extracted and injected back into the bubbling and stirring absorption tower. The oxidation process continues until trivalent phosphorus is no longer detectable in the phosphorus-containing inorganic acid. The mixture is then introduced for another 120 minutes to complete the oxidation process.

[0041] Example 12 The difference between this embodiment and embodiment 11 is that after trivalent phosphorus cannot be detected in the phosphorus-containing inorganic acid, the mixed gas is continued to be passed for 135 minutes before the oxidation treatment is ended.

[0042] Example 13 The difference between this embodiment and embodiment 11 is that after trivalent phosphorus cannot be detected in the phosphorus-containing inorganic acid, the mixed gas is continued to be passed for 150 minutes before the oxidation treatment is ended.

[0043] Example 14 The difference between this embodiment and embodiment 13 is that in the oxidation treatment step (3), hydrogen peroxide is added to the phosphorus-containing inorganic acid. The hydrogen peroxide is added in the form of 20wt% hydrogen peroxide, and the volume ratio of hydrogen peroxide to phosphorus-containing inorganic acid is 1:20.

[0044] Example 15 The difference between this embodiment and embodiment 14 is that in the oxidation treatment step (3), the phosphorus-containing inorganic acid is heated to 65°C.

[0045] Example 16 The difference between this embodiment and embodiment 14 is that in the oxidation treatment step (3), the phosphorus-containing inorganic acid is heated to 75°C.

[0046] Example 17 The difference between this embodiment and embodiment 14 is that in the oxidation treatment step (3), the phosphorus-containing inorganic acid is heated to 80°C.

[0047] Example 18 The difference between this embodiment and embodiment 14 is that in the oxidation treatment step (3), the phosphorus-containing inorganic acid is heated to 90°C. Comparative Example

[0048] Comparative Example 1 The difference between this comparative example and Example 1 is that when the concentration of hydrogen chloride in the primary absorbent reaches 22 wt%, the introduction of phosphorus-containing chloride is stopped, resulting in a mixed acid with a total acid content of 31 wt%.

[0049] Comparative Example 2 This comparative example provides 85wt% industrial-grade phosphoric acid (first-class product) as a control.

[0050] Comparative Example 3 This comparative example uses commercially available industrial-grade hydrochloric acid as a control. Performance testing methods

[0051] I. Phosphorus-containing inorganic acids The components of the phosphorus-containing inorganic acids produced in the first absorption tower were tested, including arsenic content and chloride ion content. The test standards and results are shown in Table 2.

[0052] II. Hydrochloric acid The hydrochloric acid produced in the second absorption tower was tested for its composition. The test items included hydrochloric acid content, appearance, ignition residue, free chlorine, sulfate, heavy metals, arsenic, iron and other indicators. The results are shown in Table 3.

[0053] Table 2. Test standards and results for phosphoric acid composition. sample <![CDATA[The content of H3PO4 ≥ 85.0%]]> Chloride ion content ≤0.5wt% Chloride ion content ≤ 0.0005 wt% Chloride ion content ≤1mg / kg Arsenic content ≤100μg / kg Example 1 conform to conform to Does not meet Does not meet Does not meet Example 2 conform to conform to Does not meet Does not meet Does not meet Example 3 conform to conform to Does not meet Does not meet Does not meet Example 4 conform to conform to Does not meet Does not meet Does not meet Example 5 conform to conform to Does not meet Does not meet Does not meet Example 6 conform to conform to Does not meet Does not meet Does not meet Example 7 conform to conform to Does not meet Does not meet Does not meet Example 8 conform to conform to Does not meet Does not meet Does not meet Example 9 conform to conform to Does not meet Does not meet Does not meet Example 10 conform to conform to Does not meet Does not meet conform to Example 11 conform to conform to conform to Does not meet conform to Example 12 conform to conform to conform to Does not meet conform to Example 13 conform to conform to conform to Does not meet conform to Example 14 conform to conform to conform to Does not meet conform to Example 15 conform to conform to conform to Does not meet conform to Example 16 conform to conform to conform to conform to conform to Example 17 conform to conform to conform to conform to conform to Example 18 conform to conform to conform to conform to conform to Comparative Example 1 Does not meet Does not meet Does not meet Does not meet Does not meet Comparative Example 2 conform to conform to conform to Does not meet Does not meet Table 3. Test Standards and Results of Hydrochloric Acid Components sample HCl content ≤ 36% ≤ 38% Appearance ≤10 Black Zeng Residue on ignition ≤0.002wt% Free chlorine ≤ 0.0002% Sulfate ≤ 0.00005% Arsenic ≤ 0.00001% Iron ≤ 0.0001% Example 1 conform to conform to conform to conform to conform to conform to conform to Example 2 conform to conform to conform to conform to conform to conform to conform to Example 3 conform to conform to conform to conform to conform to conform to conform to Example 4 conform to conform to conform to conform to conform to conform to conform to Example 5 conform to conform to conform to conform to conform to conform to conform to Example 6 conform to conform to conform to conform to conform to conform to conform to Example 7 conform to conform to conform to conform to conform to conform to conform to Example 8 conform to conform to conform to conform to conform to conform to conform to Example 9 conform to conform to conform to conform to conform to conform to conform to Example 10 conform to conform to conform to conform to conform to conform to conform to Example 11 conform to conform to conform to conform to conform to conform to conform to Example 12 conform to conform to conform to conform to conform to conform to conform to Example 13 conform to conform to conform to conform to conform to conform to conform to Example 14 conform to conform to conform to conform to conform to conform to conform to Example 15 conform to conform to conform to conform to conform to conform to conform to Example 16 conform to conform to conform to conform to conform to conform to conform to Example 17 conform to conform to conform to conform to conform to conform to conform to Example 18 conform to conform to conform to conform to conform to conform to conform to Comparative Example 1 Does not meet Does not meet Does not meet Does not meet Does not meet Does not meet Does not meet Comparative Example 3 conform to conform to Does not meet Does not meet Does not meet Does not meet Does not meet Based on Examples 1-18 and Comparative Examples 1-2, and referring to Table 2, it can be seen that Examples 1-18 and Comparative Example 2 both meet the requirements of phosphoric acid content ≥85.0% and chloride ion content ≤0.5%, while the mixed acid of Comparative Example 1 does not meet these requirements. The mixed acid of Comparative Example 1 represents a mixed acid obtained through conventional processes. Because such mixed acid cannot achieve a single composition, its applications are limited, and its economic value is low.

[0054] Although the phosphoric acid obtained in Examples 1-10 did not meet the requirement of chloride ion content ≤0.0005wt%, it was very close to this indicator. Starting from Example 11, due to the use of ozone in the oxidation process, chloride ions were further removed, thus meeting the requirement of chloride ion content ≤0.0005wt%, and it could completely replace high-grade industrial-grade phosphoric acid. From Example 16 onwards, due to further optimization of the temperature, chloride ion removal was more thorough, thus meeting the requirement of chloride ion content ≤1mg / kg (i.e., the standard requirement for electronic-grade phosphoric acid).

[0055] Although the phosphoric acid prepared in Examples 1-9 did not meet the requirement of arsenic content ≤100μg / kg (i.e., the standard requirement of electronic grade phosphoric acid), the examples starting from Example 10 all met this requirement. This is because after copper powder reduction and distillation, arsenic has been fully removed in elemental form.

[0056] As can be seen from Examples 1-18 and Comparative Examples 1 and 3, and Table 3, the hydrochloric acid prepared in this application can meet the requirements of electronic grade hydrochloric acid.

[0057] The above embodiments are merely explanations of this application and are not intended to limit it. After reading this specification, those skilled in the art can make modifications to the embodiments of this application without contributing any inventive step, but such modifications are protected by patent law as long as they are within the scope of the claims of this application.

Claims

1. A method for separating and purifying mixed acid from phosphorus chloride tail gas, characterized in that, Includes the following steps: (1) Add primary absorbent to the primary absorption tower, and then introduce phosphorus chloride tail gas into the primary absorption tower for reaction under the drive of nitrogen. At the same time, extract the primary acid solution generated at the bottom of the primary absorption tower for extraction and spray it back into the primary absorption tower, and continuously monitor the water content in the primary acid solution; the primary absorbent is pure water or unsaturated hydrochloric acid solution. (2) Add secondary absorbent to the secondary absorption tower and transport the tail gas generated by the primary absorption tower to the secondary absorption tower. Extract the secondary acid generated at the bottom of the secondary absorption tower and spray it back into the secondary absorption tower. Continuously monitor the tail gas generated by the secondary absorption tower. (3) When the water content in the absorbent drops to 1-15wt%, stop the back spraying of the first-stage absorber and introduce pure nitrogen into the first-stage absorber to drive away the remaining gas. Collect the first-stage acid solution discharged from the first-stage absorber to obtain phosphorus-containing inorganic acid. The secondary acid solution discharged from the secondary absorption tower is collected to obtain hydrochloric acid.

2. The method for separating and purifying mixed acid from phosphorus-containing chloride tail gas according to claim 1, characterized in that, The phosphorus-containing chloride is a trivalent phosphorus-containing chloride and / or a pentavalent phosphorus-containing chloride.

3. The method for separating and purifying mixed acid from phosphorus-containing chloride tail gas according to claim 2, characterized in that, The phosphorus-containing chloride is at least one of phosphorus trichloride, phosphorus oxychloride, and phosphorus pentachloride.

4. The method for separating and purifying mixed acid from phosphorus-containing chloride tail gas according to claim 3, characterized in that, Before being introduced into the primary absorption tower, the phosphorus-containing chloride undergoes arsenic removal treatment according to the following steps: Phosphorus-containing chlorides are heated to a gaseous state to obtain phosphorus-containing chloride vapor. The phosphorus-containing chloride vapor is then passed through copper powder and subjected to distillation. After the distillation is completed, the arsenic removal process is finished.

5. The method for separating and purifying mixed acid from phosphorus-containing chloride tail gas according to claim 2, characterized in that, The phosphorus-containing chloride is a mixture of phosphorus trichloride and at least one pentavalent phosphorus-containing chloride.

6. The method for separating and purifying mixed acid from phosphorus-containing chloride tail gas according to claim 5, characterized in that, In step (3) of the method for separating and purifying mixed acid from phosphorus chloride tail gas, after obtaining phosphorus-containing inorganic acid, an oxidation treatment is performed as follows: The phosphorus-containing inorganic acid is loaded into a bubbling and stirring absorption tower. A mixture of ozone and air is passed into the phosphorus-containing inorganic acid for bubbling and stirring. At the same time, the phosphorus-containing inorganic acid is extracted and sprayed back into the bubbling and stirring absorption tower until trivalent phosphorus can no longer be detected in the phosphorus-containing inorganic acid. Continue to pass the mixed gas for 120-150 minutes to end the oxidation treatment.

7. The method for separating and purifying mixed acid from phosphorus-containing chloride tail gas according to claim 6, characterized in that, In the oxidation treatment step (3), hydrogen peroxide is also added to the phosphorus-containing inorganic acid.

8. The method for separating and purifying mixed acid from phosphorus-containing chloride tail gas according to claim 7, characterized in that, In the oxidation treatment step (3), the phosphorus-containing inorganic acid is heated to 55-90℃.

9. The method for separating and purifying mixed acid from phosphorus-containing chloride tail gas according to claim 8, characterized in that, In the oxidation treatment step (3), the phosphorus-containing inorganic acid is heated to 75-90℃.

10. The method for separating and purifying mixed acid from phosphorus-containing chloride tail gas according to claim 6, characterized in that, In step (3), when the water content in the absorbent is monitored to drop to 1-2 wt%, the subsequent operations are continued.