A catalytic oxidation device and method for producing furan ammonium salt

Abstract

The invention relates to the technical field of furan ammonium salt production, and discloses a catalytic oxidation device and method in furan ammonium salt production, which adopts the following equipment: an oxidation kettle, wherein the oxidation kettle controls the oxidation reaction temperature of 65-70°C through steam and circulating water; a sodium nitrate I high-level tank, a sodium nitrate III high-level tank and a sodium nitrate II high-level tank are respectively connected to the oxidation kettle through pipelines, and the sodium nitrate I high-level tank, the sodium nitrate III solution and the sodium nitrate II solution are dripped with precision flow meters and regulating valves, and the pipelines are provided with flow meters and flow regulating valves, and the dripping sodium nitrate I / III flow rate is controlled at 380-400L / h, and the sodium nitrate II flow rate is controlled at 800-850L / h; the phosphoric acid high-level tank is equipped with a weighing module, which is connected to the oxidation kettle through a pipeline; and a hydrochloric acid high-level tank, which is connected to the oxidation kettle through a pipeline. The invention effectively increases the content of oxidized ketoacid from 75-77% to 79-81% by adding a catalyst and changing the raw material ratio, thereby increasing the acetofuran conversion rate and reducing the production cost of furan ammonium salt.

Description

Technical Field

[0001] The invention relates to the technical field of furan ammonium salt production, and in particular to a catalytic oxidation device and method in the production of furan ammonium salt. Background Art

[0002] Furan ammonium salt (English name: SMIA) is currently the main raw material for the production of cephalosporin antibiotics cefuroxime and cefuroxime axetil. Cefuroxime was first successfully developed by Glaxo William's and was first launched in the UK, Ireland, Germany and Italy in 1978 and then sold in many countries and regions around the world. The trade name is "Ciliou". It was approved by the US FDA in 1987 and launched in the United States. Due to its definite efficacy, it is widely used to combat various infections caused by sensitive bacteria. In the 1990s, the drug has become the world's best-selling anti-infective drug with good efficacy. Furan ammonium salt, as a new type of pharmaceutical intermediate, is a key intermediate in the synthesis of the second-generation cephalosporin drug cefuroxime. Its property state is white or off-white crystalline powder, molecular weight 186.17, boiling point: 284.7℃at760mmHg, trans isomer ≦0.5%, chemical name is (z)-2-methoxymethylamino-2-(furan-2-yl) ammonium acetate.

[0003] Keto acid is a key intermediate product in the production of furan ammonium salt and is the core cost step in the entire production of furan ammonium salt. At present, the synthesis of keto acid is to use a mixed reaction of acetofuran, sodium nitrite, water, phosphoric acid, hydrochloric acid, etc. to generate keto acid, which then reacts with methoxyamine to generate oxime acid, and finally the oxime acid reacts with ammonia to obtain the product furan ammonium salt.

[0004] In the industrial production of furan ammonium salt, the conversion rate of acetofuran in the oxidation reaction is the key to determine the production yield of furan ammonium salt. The current oxidation reaction mainly involves oxidation of acetofuran by sodium nitrite, followed by rearrangement and hydrolysis to obtain keto acid. Most of the current keto acid synthesis processes are manually operated, with manual heating, cooling, and manual adjustment of the drip flow rate. At the same time, it is also impossible to monitor the drip flow rate 24 hours a day. Manual operation brings a lot of instability and causes system fluctuations. In addition, the reaction of the existing process purely relies on sodium nitrite itself to oxidize acetofuran, and the rearrangement after oxidation is carried out under the catalysis of phosphoric acid. In the early stage of this reaction mode, the reaction is more violent due to the excessively high acid concentration, the heat release is large, and the risk factor is high. In the mid-term, due to the selection of catalysts during the rearrangement process, the reaction is relatively slow, resulting in a long time for the first two steps, which aggravates the coking of acetofuran under phosphoric acid conditions.

[0005] The invention adopts fully automated heating and cooling operations, and the sodium nitrite dripping regulating valve is interlocked with the flow rate during the dripping process, thereby ensuring the stability of the dripping process and greatly enhancing the operability of the reaction; secondly, acetofuran reacts with sodium nitrite under strong acidic conditions to generate furan hydroxamic acid, and the more acid in this step, the more conducive to improving the conversion rate of acetofuran, but in the early stage, if the H+ concentration is too high, acetofuran will be coked, which is not conducive to the conversion rate of acetofuran, and the amount of acid added needs to consider the optimal pH values ​​of the second rearrangement and the third step hydrolysis, so the acid is diluted with water to a concentration of 18% to 20% for reaction; in the second step, furan hydroxamic acid is rearranged under the action of phosphoric acid to generate (2-furanyl) oxyacetamide, and the addition of metal salt ions can catalyze the rearrangement reaction and promote the rearrangement; in the third step, (2-furanyl) oxyacetamide is hydrolyzed into furanone acid under the protection of sodium nitrite, and the optimal pH value of the hydrolysis reaction in this step is between 2.8 and 3.2. This process meets the production requirements, improves the yield of ketoacid synthesis oxidation reaction and stabilizes production, while also better ensuring production safety and stability, and achieving good safety and economic benefits, so research on this is imminent. Summary of the invention

[0006] The present invention provides a catalytic oxidation device and method in the production of furan ammonium salt, which solves the problems in the background technology.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A catalytic oxidation device in the production of furan ammonium salt adopts the following equipment: an oxidation kettle, wherein the oxidation kettle controls the oxidation reaction temperature at 65-70°C through steam and circulating water; a sodium hypochlorite I high-level tank, a sodium hypochlorite III high-level tank and a sodium hypochlorite II high-level tank are respectively connected to the oxidation kettle through pipelines, and the sodium hypochlorite I high-level tank, the sodium hypochlorite III solution and the sodium hypochlorite II solution are all provided with precision flow meters and regulating valves for dropwise addition, and flow meters and flow regulating valves are provided on the pipelines, and the flow rate of dropwise addition of sodium hypochlorite I / III is controlled at 380-400 L / h, and the flow rate of sodium hypochlorite II is controlled at 800-850 L / h; a phosphoric acid high-level tank is equipped with a weighing module and is connected to the oxidation kettle through a pipeline; a hydrochloric acid high-level tank is connected to the oxidation kettle through a pipeline; an acetyl Furan high-level tank, acetylfuran high-level tank is equipped with a weighing module, the acetylfuran high-level tank is connected to the oxidation kettle via a pipeline; pure water high-level tank, the pure water high-level tank is connected to the oxidation kettle via a pipeline; catalyst high-level tank, the catalyst high-level tank is connected to the oxidation kettle via a pipeline, a heating jacket is installed on the outside of the oxidation kettle, the oxidation kettle and the heating jacket are divided into two parts by a partition, steam inlet pipe and steam outlet pipe are connected to the outer walls of both sides of the heating jacket respectively, the steam inlet pipe and the steam outlet pipe are connected to the two side parts of the partition respectively, a heat exchange conduit is installed inside the oxidation kettle, the steam outlet and steam inlet of the heat exchange conduit extend to both sides of the partition in the heating jacket respectively, and a stirring mechanism is also installed on the oxidation kettle.

[0009] Preferably, the stirring mechanism comprises a rotary motor and a stirring rod, the stirring rod extends to the interior of the oxidation kettle, and a stirring branch is fixed to the outer side of the stirring rod.

[0010] Preferably, a screw is fixed to the bottom end of the stirring rod, and the screw extends into the bottom feed port of the oxidation kettle.

[0011] Preferably, a plurality of annular baffles are evenly distributed from top to bottom inside the heating jacket, and a first through hole is formed on the annular baffle.

[0012] Preferably, the first through holes on adjacent annular baffles are staggered.

[0013] Preferably, pressure valves are installed at the steam inlet positions of the steam exhaust pipe and the heat exchange conduit.

[0014] Preferably, the horizontal height of the steam inlet pipe is greater than the horizontal height of the steam outlet pipe, and the horizontal height of the steam outlet is greater than the horizontal height of the steam inlet.

[0015] A catalytic oxidation method in the production of furan ammonium salts comprises the following steps:

[0016] Step S1: Add water, hydrochloric acid, catalyst, and acetofuran to the oxidation kettle in sequence, wherein the catalyst is prepared by dissolving 15-20 kg of a certain salt in an appropriate amount of water, and the final hydrochloric acid concentration in the kettle is controlled at 18-20%;

[0017] Step S2: close the oxidation kettle vent and tail gas valve, fill the kettle with nitrogen to 0.06-0.07MPa and then vent, repeat 2-3 times;

[0018] Step S3: Turn on the steam to heat the oxidation kettle to 50-52°C, then turn off the steam to heat naturally, and when the feed liquid temperature reaches 62-65°C, add sodium sulfate I dropwise, with the flow rate controlled at 380-400 L / h;

[0019] Step S4: After the addition of sodium sulfate high-level tank I is completed, 200Kg of phosphoric acid is added at one time. After the addition of phosphoric acid, sodium sulfate II is added dropwise at a flow rate of 800-850L / h, and then sodium sulfate III is added dropwise at a flow rate of 380-400L / h. During the addition of sodium sulfate III, the pH value of the feed liquid is controlled at 2.8-3.2.

[0020] The beneficial effects of the present invention are:

[0021] 1. The present invention effectively increases the content of oxidized keto acid from 75-77% to 79-81% by adding a catalyst and changing the raw material ratio, thereby increasing the conversion rate of acetylfuran and reducing the production cost of furan ammonium salt;

[0022] 2. The hot steam can not only exchange heat with the reactants from the outer wall of the oxidation kettle, but also from the inside of the oxidation kettle through the heat exchange pipe, which can effectively improve the heating efficiency and prevent the reactants from being heated unevenly, thereby effectively improving the reaction efficiency;

[0023] 3. By adding a pressure valve, the steam from the steam inlet pipe into the right part of the heating jacket is gathered in the heating jacket. Only when the heating jacket is filled with hot steam and the steam pressure reaches a certain value can it pass through the pressure valve and then enter the heat exchange conduit. Similarly, the hot steam from the left half of the heating jacket entering through the heat exchange conduit will be discharged from the steam discharge pipe only after filling the interior of the heating jacket. The design of the pressure valve can ensure that the hot steam can fill the interior of the heating jacket, thereby improving the heat exchange effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The present invention provides a flow chart of a catalytic oxidation method for producing furan ammonium salts.

[0025] Figure 2 The present invention provides a schematic diagram of the structure of an oxidation kettle of a catalytic oxidation device in the production of furan ammonium salt.

[0026] Figure 3 This is a schematic diagram of an oxidation kettle of a catalytic oxidation device in the production of furan ammonium salt proposed by the present invention, omitting the heating jacket.

[0027] Figure 4 This is a schematic diagram of an oxidation kettle of a catalytic oxidation device in the production of furan ammonium salt proposed by the present invention, omitting the heating jacket.

[0028] Figure 5 This is a schematic diagram of the internal structure of an oxidation kettle of a catalytic oxidation device in the production of furan ammonium salt proposed by the present invention.

[0029] Figure 6 This is a schematic diagram of the internal stirring mechanism of the oxidation kettle of the catalytic oxidation device in the production of furan ammonium salt proposed by the present invention.

[0030] Figure 7 This is a schematic diagram of the heat exchange conduit structure of a catalytic oxidation device in the production of furan ammonium salt proposed by the present invention.

[0031] Figure 8 This is an enlarged cross-sectional view of a pressure valve of a catalytic oxidation device in the production of furan ammonium salt proposed by the present invention.

[0032] Numbers in the figure: 1. Oxidation kettle; 2. Heating jacket; 3. Steam inlet pipe; 4. Steam outlet pipe; 5. Partition; 6. Annular baffle; 7. First through hole; 8. Steam inlet; 9. Steam outlet; 10. Heat exchange conduit; 11. U-shaped connecting pipe; 12. Arc conduit; 13. Rotating motor; 14. Stirring rod; 15. Stirring branch; 16. Screw; 17. Pressure valve; 18. Sealing plate; 19. Second through hole; 20. Elastic telescopic rod; 21. Sealing plug. DETAILED DESCRIPTION

[0033] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0034] Reference Figure 1-8 A catalytic oxidation device for the production of furan ammonium salts, using the following equipment: an oxidation kettle 1, wherein the oxidation reaction temperature of the oxidation kettle 1 is controlled at 65-70°C by steam and circulating water; a sodium hypochlorite I high-level tank, a sodium hypochlorite III high-level tank and a sodium hypochlorite II high-level tank are respectively connected to the oxidation kettle 1 through pipelines, and a sodium hypochlorite I high-level tank, a sodium hypochlorite III solution and a sodium hypochlorite II solution are all provided with precision flow meters and regulating valves for dropwise addition, and flow meters and flow regulating valves are provided on the pipelines, and the flow rate of dropwise addition of sodium hypochlorite I / III is controlled at 380-400L / h, and the flow rate of sodium hypochlorite II is controlled at 800-850L / h; a phosphoric acid high-level tank is equipped with a weighing module and is connected to the oxidation kettle 1 through a pipeline; a hydrochloric acid high-level tank, wherein the hydrochloric acid high-level tank is connected to the oxidation kettle 1 through a pipeline; an acetylfuran high-level tank, wherein the acetylfuran high-level tank is equipped with a weighing module, and the acetylfuran high-level tank is equipped with a weighing module, and the acetylfuran high-level tank is equipped with a weighing module. The furan high-level tank is connected to the oxidation kettle 1 through a pipeline; the pure water high-level tank is connected to the oxidation kettle 1 through a pipeline; the catalyst high-level tank is connected to the oxidation kettle 1 through a pipeline, and a heating jacket 2 is installed on the outside of the oxidation kettle 1. The oxidation kettle 1 and the heating jacket 2 are divided into two parts by a partition 5. The outer walls of the heating jacket 2 on both sides are respectively connected with a steam inlet pipe 3 and a steam outlet pipe 4. The steam inlet pipe 3 and the steam outlet pipe 4 are respectively connected to the two side parts of the partition 5. A heat exchange pipe 10 is installed inside the oxidation kettle 1. The steam outlet 9 and the steam inlet 8 of the heat exchange pipe 10 extend to the two sides of the partition 5 in the heating jacket 2 respectively. A stirring mechanism is also installed on the oxidation kettle 1. Hot steam enters the right half of the heating jacket 2 through the steam inlet pipe 3 ( Figure 2 After the hot steam fills the right half of the heating jacket 2, it enters the heat exchange conduit 10 through the steam inlet 8. The heat exchange conduit 10 is coiled inside the oxidation kettle 1. The hot steam then flows out through the steam outlet 9 and enters the left half of the heating jacket 2 ( Figure 2), after the hot steam fills the left half of the heating jacket 2, it flows out through the steam exhaust pipe 4. The hot steam can not only exchange heat with the reactants from the outer wall of the oxidation kettle 1, but also exchange heat with the reactants from the inside of the oxidation kettle 1 through the heat exchange conduit 10, which can effectively improve the heating efficiency and prevent the reactants from being heated unevenly, thereby effectively improving the reaction efficiency.

[0035] Among them, the stirring mechanism includes a rotating motor 13 and a stirring rod 14. The stirring rod 14 extends to the interior of the oxidation kettle 1, and a stirring branch 15 is fixed to the outside of the stirring rod 14. The rotating motor 13 can drive the stirring rod 14 to rotate, and the material is stirred through the stirring branch 15 to improve the mixing degree of the material, so that the material can be heated more evenly.

[0036] Among them, a screw 16 is fixed to the bottom end of the stirring rod 14, and the screw 16 extends to the bottom discharge port of the oxidation kettle 1. The screw 16 can rotate with the stirring rod 14 to actively discharge the material, which can accelerate the discharge and prevent the discharge port from being blocked.

[0037] like Figure 3 and 4 A plurality of annular baffles 6 are evenly distributed from top to bottom inside the heating jacket 2, and first through holes 7 are provided on the annular baffles 6. The first through holes 7 on adjacent annular baffles 6 are staggered, which can ensure that the flow path of the steam in the heating jacket 2 is S-shaped, increase the steam flow stroke, increase the residence time of the steam in the heating jacket 2, and improve the heating effect of the steam.

[0038] like Figure 2 , 5and 8, a pressure valve 17 is installed at the steam inlet 8 of the steam discharge pipe 4 and the heat exchange pipe 10, a sealing plate 18 is fixed inside the pressure valve 17, a plurality of second through holes 19 are opened on the sealing plate 18, a plurality of elastic telescopic rods 20 are fixed on one side of the sealing plate 18 in the pressure valve 17, a sealing plug 21 is connected to the movable end of the elastic telescopic rod 20, the sealing plug 21 is a truncated cone structure, and the sealing plug 21 corresponds to the second through hole 19 one by one, due to the elastic force of the elastic telescopic rod 20, the sealing plug 21 can be pushed to block the second through hole 19, so that the steam can only pass from right to left, and only when the steam reaches a certain pressure, can it The elastic telescopic rod 20 is compressed to separate the sealing plug 21 from the second through hole 19. This design allows the right part of the steam entering the heating jacket 2 from the steam inlet pipe 3 to gather in the heating jacket 2. Only when the heating jacket 2 is filled with hot steam and the steam pressure reaches a certain value can it pass through the pressure valve 17 and then enter the heat exchange conduit 10. Similarly, the hot steam entering the left half of the heating jacket 2 through the heat exchange conduit 10 will be discharged from the steam exhaust pipe 4 only after filling the interior of the heating jacket 2. The design of the pressure valve 17 can ensure that the hot steam can fill the interior of the heating jacket 2, thereby improving the heat exchange effect.

[0039] like Figure 7 The horizontal height of the steam inlet pipe 3 is greater than the horizontal height of the steam outlet pipe 4, the horizontal height of the steam outlet 9 is greater than the horizontal height of the steam inlet 8, and the heat exchange conduit 10 includes an arcuate conduit 12 and a U-shaped connecting pipe 11. Through the cooperation of the arcuate conduit 12 and the U-shaped connecting pipe 11, the heat exchange conduit 10 can spirally extend upward from the steam inlet 8 and extend to the steam outlet 9 position, and the arcuate conduit 12 is a spiral structure, which can effectively increase the flow distance of the steam inside the oxidation kettle 1 and improve the heat exchange effect.

[0040] A catalytic oxidation method in the production of furan ammonium salts comprises the following steps:

[0041] Step S1: Add water, hydrochloric acid, catalyst, and acetofuran to the oxidation kettle 1 in sequence, wherein the catalyst is dissolved by adding an appropriate amount of water to 15-20 kg of a certain salt, and the final hydrochloric acid concentration in the kettle is controlled at 18-20%;

[0042] Step S2: close the venting and tail gas valves of oxidation kettle 1, fill the kettle with nitrogen to 0.06-0.07 MPa and then vent, repeat 2-3 times;

[0043] Step S3: Turn on the steam to heat the oxidation kettle 1 to 50-52°C, then turn off the steam to heat it naturally, and when the feed liquid temperature reaches 62-65°C, add sodium sulfate I dropwise, and control the flow rate at 380-400 L / h;

[0044] Step S4: After the addition of sodium sulfate high-level tank I is completed, 200Kg of phosphoric acid is added at one time. After the addition of phosphoric acid, sodium sulfate II is added dropwise at a flow rate of 800-850L / h, and then sodium sulfate III is added dropwise at a flow rate of 380-400L / h. During the addition of sodium sulfate III, the pH value of the feed liquid is controlled at 2.8-3.2.

[0045] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0046] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0047] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A catalytic oxidation device for the production of furan ammonium salt, comprising an oxidation kettle (1), a sodium sulfate I high-level tank, a sodium sulfate III high-level tank, a sodium sulfate II high-level tank, a phosphoric acid high-level tank, a hydrochloric acid high-level tank, an acetylfuran high-level tank, a pure water high-level tank, and a catalyst high-level tank, characterized in that: A heating jacket (2) is installed on the outside of the oxidation kettle (1). The oxidation kettle (1) and the heating jacket (2) are divided into two parts by a partition (5). The outer walls of the heating jacket (2) on both sides are connected with a steam inlet pipe (3) and a steam outlet pipe (4). The steam inlet pipe (3) and the steam outlet pipe (4) are connected to the two side parts of the partition (5) respectively. A heat exchange pipe (10) is installed inside the oxidation kettle (1). The steam outlet (9) and the steam inlet (8) of the heat exchange pipe (10) extend to the two sides of the partition (5) in the heating jacket (2) respectively. Hot steam enters the right side of the heating jacket (2) through the steam inlet pipe (3). After the hot steam fills the right half of the heating jacket (2), it enters the heat exchange conduit (10) through the steam inlet (8). The heat exchange conduit (10) is coiled inside the oxidation kettle (1). The hot steam then flows out through the steam outlet (9) and enters the left half of the heating jacket (2). After the hot steam fills the left half of the heating jacket (2), it flows out through the steam discharge pipe (4). The hot steam can not only exchange heat with the reactants from the outer wall of the oxidation kettle (1), but can also exchange heat with the reactants from the inside of the oxidation kettle (1) through the heat exchange conduit (10). The oxidation kettle (1) is also equipped with a stirring mechanism. A plurality of annular baffles (6) are evenly spaced from top to bottom inside the heating jacket (2), each of the annular baffles (6) being provided with first through holes (7), and the first through holes (7) on adjacent annular baffles (6) are staggeredly arranged, and pressure valves (17) are installed at the steam inlet (8) positions of the steam discharge pipe (4) and the heat exchange pipe (10), and a sealing plate (18) is fixed inside the pressure valve (17), and a plurality of second through holes (19) are provided on the sealing plate (18), and the pressure valve (17) is located in the sealing plate (18). A plurality of elastic telescopic rods (20) are fixed to one side of the housing, and the movable ends of the elastic telescopic rods (20) are connected to sealing plugs (21). The sealing plugs (21) are of a truncated cone-shaped structure, and the sealing plugs (21) correspond to the second through holes (19) one by one. Due to the elastic force of the elastic telescopic rods (20), the sealing plugs (21) can be pushed to block the second through holes (19), so that steam can only pass from right to left. Only when the steam reaches a certain pressure can the elastic telescopic rods (20) be compressed, so that the sealing plugs (21) are separated from the second through holes (19).

2. A catalytic oxidation device for producing furan ammonium salt according to claim 1, characterized in that: The stirring mechanism comprises a rotating motor (13) and a stirring rod (14); the stirring rod (14) extends into the interior of the oxidation kettle (1), and a stirring branch (15) is fixed to the outside of the stirring rod (14).

3. A catalytic oxidation device in the production of furan ammonium salt according to claim 2, characterized in that: A screw rod (16) is fixed to the bottom end of the stirring rod (14), and the screw rod (16) extends into the bottom feed opening of the oxidation kettle (1).

4. A catalytic oxidation device for producing furan ammonium salt according to claim 1, characterized in that: The horizontal height of the steam inlet pipe (3) is greater than the horizontal height of the steam outlet pipe (4), and the horizontal height of the steam outlet (9) is greater than the horizontal height of the steam inlet (8).

5. A method for catalytic oxidation in the production of furan ammonium salt, using a catalytic oxidation device in the production of furan ammonium salt as claimed in any one of claims 1 to 4, characterized in that: The following steps are involved: Step S1: Add water, hydrochloric acid, catalyst, and acetofuran to the oxidation kettle (1) in order, wherein the catalyst is prepared by dissolving 15-20 kg of a certain salt in an appropriate amount of water, and the final hydrochloric acid concentration in the kettle is controlled to be 18-20%; Step S2: close the venting and tail gas valves of the oxidation kettle (1), fill the kettle with nitrogen to 0.06-0.07 MPa and then vent, repeating 2-3 times; Step S3: Turn on the steam to heat the oxidation kettle (1) to 50-52°C, then turn off the steam to allow the temperature to rise naturally, and when the feed liquid temperature reaches 62-65°C, add sodium sulfate I dropwise, with the flow rate controlled at 380-400 L / h; Step S4: After the addition of sodium sulfate high-level tank I is completed, 200 kg of phosphoric acid is added at one time. After the addition of phosphoric acid, sodium sulfate II is added dropwise at a flow rate of 800-850 L / h, and then sodium sulfate III is added dropwise at a flow rate of 380-400 L / h. During the addition of sodium sulfate III, the pH value of the feed liquid is controlled at 2.8-3.2.

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