Phosphorous acid evaporation and concentration process

Abstract

This invention belongs to the field of oxyacid synthesis technology of phosphorus, specifically relating to a phosphorous acid evaporation and concentration process. The phosphorous acid evaporation and concentration process involves processing crude phosphorous acid through an evaporation and concentration system to obtain a finished phosphorous acid product. The evaporation and concentration system includes a first-stage falling film evaporator, a second-stage falling film evaporator, and a third-stage falling film evaporator connected in sequence. An auxiliary agent is added from the third-stage falling film evaporator, including polyethylene glycol diamine, N,N-diethylhydroxylamine, and sodium succinate sulfonate. This invention, by designing an evaporation and concentration system and using auxiliary agents, further reduces the residual hydrogen chloride content in the crude phosphorous acid product, obtaining a high-purity finished phosphorous acid product. This finished phosphorous acid product can be used in fields requiring high purity, such as semiconductor wafer cleaning agents.

Description

Technical Field

[0001] This invention belongs to the field of phosphorus oxyacid synthesis technology, specifically relating to a phosphorous acid evaporation and concentration process. Background Technology

[0002] Phosphorous acid, with the chemical formula H3PO3, has a melting point of 73.6℃ and a boiling point of 200℃. It is readily soluble in water and ethanol and has broad application prospects in the production of plastic stabilizers, flame retardants, phosphate fertilizer supplements, glyphosate intermediates, and corrosion inhibitors and scale inhibitors in water treatment. Currently, the industrial preparation of phosphorous acid mainly consists of basic steps such as phosphorus trichloride hydrolysis, falling film absorption, atmospheric / negative pressure evaporation deacidification, and crystallization separation. If residual hydrogen chloride is not completely removed during deacidification, the chloride ion content in the finished product will exceed the standard, affecting product stability and application performance. Traditional batch evaporation deacidification processes suffer from high energy consumption and limited production capacity. In particular, during the later stages of concentration, the reduced moisture and increased viscosity in batch evaporation processes lead to insufficient hydrogen chloride removal, resulting in a large residual amount. The resulting phosphorous acid product cannot meet the high purity requirements of products such as wafer cleaning agents.

[0003] Chinese patent CN114940484A discloses a process for preparing phosphorous acid by cascade falling film evaporation, (1) the obtained phosphorous acid solution is evaporated at a flow rate of 0.8~1.2m 3 The feed solution is continuously fed into a falling film evaporator at a flow rate of / h for concentration. The concentration conditions are: temperature 135~150℃, pressure -0.095~-0.075MPa. The resulting first-stage concentrate flows by gravity into a buffer tank. During feeding, when the buffer tank level reaches 3m... 3 (1) Stop feeding into the falling film evaporator; (2) Add pure water continuously to the primary concentrate in (1) at a flow rate of 90~120kg / h, wherein the volume ratio of the primary concentrate to pure water is 1:(8~11); (3) The diluted primary concentrate is concentrated by self-circulation in the falling film evaporator, and the secondary concentrate is obtained after repeating the water circulation concentration 2~3 times. The conditions for secondary concentration are: temperature 130~140℃, pressure -0.095~-0.075MPa; (4) Add the secondary concentrate to the crystallization kettle and cool and crystallize at 54~57℃; (5) Centrifuge and dehydrate the crystallized secondary concentrate to obtain phosphorous acid product. The mass concentration of the phosphorous acid solution is 65~70%.

[0004] The patent requires a high concentration of phosphorous acid in the feed, which needs to be limited to 65-70%, thus limiting its industrial application. In addition, pure water needs to be added multiple times during the evaporation and concentration of phosphorous acid, further increasing energy consumption and production costs. Summary of the Invention

[0005] The purpose of this invention is to provide a phosphorous acid evaporation and concentration process, which further reduces the residual amount of hydrogen chloride during the evaporation and concentration of crude phosphorous acid to obtain a high-purity phosphorous acid product. This phosphorous acid product can be used in fields with high purity requirements, such as semiconductor wafer cleaning agents.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] The phosphorous acid evaporation and concentration process of the present invention involves processing crude phosphorous acid through an evaporation and concentration system to obtain finished phosphorous acid. The evaporation and concentration system includes a first-stage falling film evaporator, a second-stage falling film evaporator, and a third-stage falling film evaporator connected in sequence. An auxiliary agent is added from the third-stage falling film evaporator, which includes polyethylene glycol diamine, N,N-diethylhydroxyamine, and sodium succinate sulfonate.

[0008] in:

[0009] The evaporation and concentration system also includes a crude product pipeline, a scraped film evaporator, and a phosphorous acid product pipeline. An auxiliary agent pipeline is connected to the three-stage falling film evaporator. The crude phosphorous acid product enters the first-stage falling film evaporator, the second-stage falling film evaporator, and the third-stage falling film evaporator sequentially through the crude product pipeline for evaporation and concentration. At the same time, the auxiliary agent enters the third-stage falling film evaporator through the auxiliary agent pipeline, and finally undergoes evaporation and concentration in the scraped film evaporator. The product is then discharged through the phosphorous acid product pipeline to obtain the finished phosphorous acid product.

[0010] The crude phosphoric acid product is sequentially fed into a primary falling film evaporator, a secondary falling film evaporator, a tertiary falling film evaporator, and a scraped film evaporator for evaporation and concentration via the crude product pipeline. The finished phosphoric acid product is then discharged via the finished product pipeline. Simultaneously, the additives are fed into the tertiary falling film evaporator via the additives pipeline.

[0011] The feed flow rate of the crude phosphorous acid product is 1.2~1.5 m³ / h. 3 The feed rate is 65~90℃, and the crude phosphorous acid product mass percentage is 45~55wt%.

[0012] The mass ratio of the crude phosphorous acid product, polyethylene glycol diamine, N,N-diethylhydroxylamine, and sodium succinate sulfonate is 1500:(0.35~0.55):(0.9~1.5):(2.5~3.5).

[0013] The aspect ratio of the first-stage falling film evaporator is (20~25):1, the aspect ratio of the second-stage falling film evaporator is (25~30):1, and the aspect ratio of the third-stage falling film evaporator is (40~50):1.

[0014] The first-stage falling film evaporator, the second-stage falling film evaporator, and the third-stage falling film evaporator are equipped with jackets; a second-stage steam buffer tank is connected between the jackets of the first-stage falling film evaporator and the second-stage falling film evaporator; a third-stage steam buffer tank is connected between the jackets of the second-stage falling film evaporator and the third-stage falling film evaporator; and a first-stage steam buffer tank is also connected to the jacket of the first-stage falling film evaporator.

[0015] The vacuum degree of the first-stage falling film evaporator is 525~600 mmHg, and the jacket temperature is 120~125℃; the vacuum degree of the second-stage falling film evaporator is 525~600 mmHg, and the jacket temperature is 125~135℃; the vacuum degree of the third-stage falling film evaporator is 525~600 mmHg, and the jacket temperature is 135~140℃.

[0016] The operating temperature of the scraped film evaporator is 135~140℃, the vacuum degree inside the evaporator is 5~10kPa, and the residence time is 50~60s.

[0017] The first-stage falling film evaporator, the second-stage falling film evaporator, and the third-stage falling film evaporator are connected in the middle with falling film evaporation exhaust gas pipelines, and the scraped film evaporator is connected at the top with scraped film evaporation exhaust gas pipelines.

[0018] The scraped film evaporator is equipped with a jacket, and the steam pipeline connects the jacket of the scraped film evaporator, the second compressor, and the jackets of the first-stage falling film evaporator, the second-stage falling film evaporator, and the third-stage falling film evaporator; the first compressor is connected between the first-stage steam buffer tank and the second-stage steam buffer tank.

[0019] Compressor 1 and Compressor 2 can appropriately pressurize the steam, improve the heat transfer efficiency of the steam, and reduce heat loss.

[0020] Different falling film evaporators require different length-to-diameter ratios. This is because if the ratio is too small, the Reynolds number of the liquid flow within the tube is insufficient, making it difficult to form a stable and uniform liquid film. Partial drying of the tube walls (i.e., dry wall phenomenon) may occur, leading to a decrease in heat transfer efficiency. Insufficiently wetted tube walls will also increase in temperature, causing coking or scaling of the material. If the ratio is too large, the liquid film thickness gradually decreases over long flow distances. After exceeding the critical length, the liquid film ruptures, forming dry spots, resulting in a decrease in heat transfer efficiency. The actual effective evaporation length is limited by heat flux density; excessively long pipe ends may not effectively transfer heat due to an insufficiently thin or nonexistent liquid film, resulting in wasted heat exchange area.

[0021] This invention first designs a three-stage falling film evaporator along the crude product feed path, combined with a three-stage steam pressurization cycle, which improves operational flexibility. Compared to single-stage falling film evaporation, this invention can adapt to crude products with different proportions of phosphorous acid without requiring equipment replacement, resulting in greater production flexibility. Furthermore, the order in which steam enters the three-stage falling film evaporator is reversed compared to the order in which the crude product enters. On the one hand, this reverse order improves heat transfer efficiency, thereby reducing equipment size and increasing space utilization; on the other hand, in counter-current mode, high-concentration (phosphorous acid concentration) crude product contacts high-temperature steam, while low-concentration crude product contacts low-temperature steam. This method effectively matches the increasing boiling point rise effect as hydrogen chloride evaporates, improving heat utilization efficiency. The same amount of steam can evaporate more water, thereby removing more hydrogen chloride. At the same time, the invention further designs a three-stage steam pressurization cycle. The compressor pressurizes the steam and sends it back to the first, second, and third stage falling film evaporators as a heat source, forming a closed loop of heat energy recovery. On the one hand, this reduces steam waste, and on the other hand, it further matches the boiling point rise effect of crude phosphoric acid, reducing heat loss. In particular, it reduces the risk that a small amount of phosphoric acid is carried away by falling film evaporation in traditional single-stage falling film evaporation, further improving the yield.

[0022] The beneficial effects of this invention are as follows:

[0023] Sodium succinate sulfonate possesses hydrophobic octyl chains at both ends and a hydrophilic sulfonic acid group in the middle. The octyl chains distributed on both sides of the hydrophilic group endow sodium succinate sulfonate with good flexibility and fluidity, allowing it to distribute between the liquid phase and the inner wall of the equipment to form a film structure. This promotes the flow of the phosphorous acid-containing liquid film, which in turn facilitates the formation of a thinner and more uniform liquid film in the falling film evaporator, thus promoting the volatilization and removal of hydrogen chloride. The hydrophilic sulfonic acid group of sodium succinate sulfonate is easily ionized, which can guide N,N-diethylhydroxyamine into the film structure. N,N-diethylhydroxyamine can interact with the inner wall metal through its hydroxyl groups, preventing phosphorous acid crystallization and scaling, maintaining the heat transfer efficiency of the evaporator, and promoting the volatilization and removal of hydrogen chloride. Polyethylene glycol diamine is a long-chain amine compound. Its outer groups can bind to N,N-diethylhydroxyamine and sodium succinate sulfonate through hydrogen bonding and other interactions, allowing the polyethylene glycol diamine to be embedded in the membrane structure. The long chain generates a steric hindrance effect, which reduces the viscosity of crude phosphorous acid and promotes the flow and volatilization of hydrogen chloride molecules.

[0024] Meanwhile, N,N-diethylhydroxylamine can effectively remove metal oxides such as copper and cobalt, making it an important functional component that meets the high requirements of wafer cleaning agents. The long alkyl segments of polyethylene glycol diamine adsorb onto the wafer surface to form a thin film, which acts as a buffer, preventing grinding particles or chemical byproducts from directly contacting the silicon substrate. This protective layer formed during wafer grinding and rinsing reduces the probability of mechanical damage such as scratches and corrosion. Sodium succinate sulfonate provides low surface tension and good wettability, enabling the liquid film to form a thinner and more uniform film on the wafer surface, accelerating the removal of particles and residual films, increasing the cleaning rate, and reducing energy consumption.

[0025] The synergistic effect of N,N-diethylhydroxyamine, polyethylene glycol diamine, and sodium succinate sulfonate reduces the viscosity of the crude phosphorous acid product in the later stage of evaporation and concentration, further forming a thinner and more uniform liquid film on the inner wall of the evaporator, thereby promoting the evaporation of hydrogen chloride and water. Attached Figure Description

[0026] Figure 1 This is a flow chart of the phosphorous acid evaporation and concentration process;

[0027] The system includes: 1. Primary falling film evaporator; 2. Secondary falling film evaporator; 3. Tertiary falling film evaporator; 4. Scraped film evaporator; 5. Primary steam buffer tank; 6. Secondary steam buffer tank; 7. Tertiary steam buffer tank; 8. Compressor 1; 9. Compressor 2; 10. Crude product pipeline; 11. Falling film evaporation exhaust gas pipeline; 12. Phosphorous acid finished product pipeline; 13. Auxiliary agent pipeline; 14. Scraped film evaporation exhaust gas pipeline; 15. Steam pipeline. Detailed Implementation

[0028] The present invention will now be described and illustrated in detail with reference to the embodiments.

[0029] Example 1

[0030] like Figure 1 As shown, crude phosphoric acid is processed by an evaporation and concentration system to obtain finished phosphoric acid. The evaporation and concentration system includes a first-stage falling film evaporator 1, a second-stage falling film evaporator 2, and a third-stage falling film evaporator 3 connected in sequence. An additive is added from the third-stage falling film evaporator 3.

[0031] The evaporation and concentration system also includes a crude product pipeline 10, a scraped film evaporator 4, and a phosphorous acid finished product pipeline 12. An auxiliary agent pipeline 13 is connected to the three-stage falling film evaporator 3. The crude phosphorous acid product enters the first-stage falling film evaporator 1, the second-stage falling film evaporator 2, and the third-stage falling film evaporator 3 in sequence through the crude product pipeline 10 for evaporation and concentration. At the same time, the auxiliary agent enters the third-stage falling film evaporator 3 through the auxiliary agent pipeline 13, and finally undergoes evaporation and concentration in the scraped film evaporator 4. The product is then discharged through the phosphorous acid finished product pipeline 12 to obtain the finished phosphorous acid product.

[0032] Jackets are installed on the first-stage falling film evaporator 1, the second-stage falling film evaporator 2, and the third-stage falling film evaporator 3; a second-stage steam buffer tank 6 is connected between the jacket of the first-stage falling film evaporator 1 and the jacket of the second-stage falling film evaporator 2; a third-stage steam buffer tank 7 is connected between the jacket of the second-stage falling film evaporator 2 and the jacket of the third-stage falling film evaporator 3; and a first-stage steam buffer tank 5 is also connected to the jacket of the first-stage falling film evaporator 1.

[0033] The first-stage falling film evaporator 1, the second-stage falling film evaporator 2, and the third-stage falling film evaporator 3 are connected in the middle by a falling film evaporation exhaust gas pipeline 11, and the scraped film evaporator 4 is connected at the top by a scraped film evaporation exhaust gas pipeline 14.

[0034] The scraped film evaporator 4 is equipped with a jacket. The steam pipeline 15 connects the jacket of the scraped film evaporator 4, the compressor 9, and the jackets of the first-stage falling film evaporator 1, the second-stage falling film evaporator 2, and the third-stage falling film evaporator 3. The compressor 8 is connected between the first-stage steam buffer tank 5 and the second-stage steam buffer tank 6.

[0035] like Figure 1 As shown, start steam line 15, compressor 8, and compressor 9, with the crude phosphorous acid product feed flow rate at 1.4 m³ / s. 3 At a feed temperature of 90℃ and a flow rate of 1 / h, 0.4 parts of polyethylene glycol diamine, 1.1 parts of N,N-diethylhydroxylamine, and 3.5 parts of sodium succinate sulfonate were mixed with the crude phosphoric acid product (obtained through preliminary vacuum evaporation) at a feed pump to obtain the additive. The crude phosphoric acid product was then fed sequentially into the first-stage falling film evaporator 1, the second-stage falling film evaporator 2, and the third-stage falling film evaporator 3 via the crude product pipeline 10. Simultaneously, the additive was fed into the third-stage falling film evaporator 3 via the additive pipeline 13 and mixed with the crude phosphoric acid product. Both were then fed into the scraped film evaporator 4 for evaporation and concentration, and discharged through the finished phosphoric acid product pipeline 12 to obtain the finished phosphoric acid product.

[0036] The first-stage falling film evaporator 1 has an aspect ratio of 22:1, the second-stage falling film evaporator 2 has an aspect ratio of 28:1, and the third-stage falling film evaporator 3 has an aspect ratio of 46:1. By adjusting the opening of each valve in the steam pipeline 15 and the power of the two compressors, the vacuum degree of the first-stage falling film evaporator 1 is 600 mmHg, and the jacket temperature is 122℃; the vacuum degree of the second-stage falling film evaporator 2 is 600 mmHg, and the jacket temperature is 135℃; the vacuum degree of the third-stage falling film evaporator 3 is 600 mmHg, and the jacket temperature is 138℃; the operating temperature of the scraped film evaporator 4 is 140℃, the vacuum degree inside the evaporator is 5 kPa, and the residence time is 50 s; after the temperature stabilizes, the phosphorous acid product pipeline 12 is cut into the product storage tank to collect the phosphorous acid product.

[0037] The primary steam buffer tank 5, secondary steam buffer tank 6, and tertiary steam buffer tank 7 are connected to the steam jackets of each stage of the falling film evaporator to stabilize the steam pressure and make the heating temperature more stable and precise. The hydrogen chloride-containing waste gas from the falling film evaporation is sent to the post-treatment via the falling film evaporation waste gas pipeline 11, and the waste gas from the scraped film evaporation is sent to the post-treatment via the scraped film evaporation waste gas pipeline 14.

[0038] Samples were taken from the outlet of the finished phosphoric acid pipeline 12. The test results showed that the mass concentration of the finished phosphoric acid was 99.58 wt% and the residual chlorine content was 4.3 ppm.

[0039] Example 2

[0040] like Figure 1 As shown, after cleaning and purging the equipment used in Example 1 with clean air for 1 hour, steam line 15, compressor 8, and compressor 9 were turned on, with the crude phosphoric acid product feed flow rate at 1.2 m³ / h. 3 At a feed temperature of 65℃ and a flow rate of 1 / h, 0.35 parts of polyethylene glycol diamine, 1.5 parts of N,N-diethylhydroxylamine, and 2.5 parts of sodium succinate sulfonate were mixed with the crude phosphoric acid product (obtained by preliminary vacuum evaporation) in a feed pump to obtain the additive. The crude phosphoric acid product was then fed into the first-stage falling film evaporator 1, the second-stage falling film evaporator 2, and the third-stage falling film evaporator 3 sequentially via the crude product pipeline 10. Simultaneously, the additive was fed into the third-stage falling film evaporator 3 via the additive pipeline 13 and mixed with the crude phosphoric acid product. Both were then fed into the scraped film evaporator 4 for evaporation and concentration, and discharged through the finished phosphoric acid product pipeline 12 to obtain the finished phosphoric acid product.

[0041] The first-stage falling film evaporator 1 has an aspect ratio of 20:1, the second-stage falling film evaporator 2 has an aspect ratio of 25:1, and the third-stage falling film evaporator 3 has an aspect ratio of 50:1. By adjusting the opening of each valve in the steam pipeline 15 and the power of the two compressors, the vacuum degree of the first-stage falling film evaporator 1 is 525 mmHg, and the jacket temperature is 120℃; the vacuum degree of the second-stage falling film evaporator 2 is 525 mmHg, and the jacket temperature is 125℃; the vacuum degree of the third-stage falling film evaporator 3 is 525 mmHg, and the jacket temperature is 140℃; the operating temperature of the scraped film evaporator 4 is 138℃, the vacuum degree inside the evaporator is 7 kPa, and the residence time is 55 s; after the temperature stabilizes, the phosphorous acid product pipeline 12 is cut into the product storage tank to collect the phosphorous acid product.

[0042] The primary steam buffer tank 5, secondary steam buffer tank 6, and tertiary steam buffer tank 7 are connected to the steam jackets of each stage of the falling film evaporator to stabilize the steam pressure and make the heating temperature more stable and precise. The hydrogen chloride-containing waste gas from the falling film evaporation is sent to the post-treatment via the falling film evaporation waste gas pipeline 11, and the waste gas from the scraped film evaporation is sent to the post-treatment via the scraped film evaporation waste gas pipeline 14.

[0043] Samples were taken from the outlet of the finished phosphoric acid pipeline 12. The test results showed that the mass concentration of the finished phosphoric acid was 99.62 wt% and the residual chlorine content was 4.6 ppm.

[0044] Example 3

[0045] like Figure 1 As shown, after cleaning and purging the equipment used in Example 1 with clean air for 1 hour, steam line 15, compressor 8, and compressor 9 were turned on, with the crude phosphorous acid product feed flow rate at 1.5 m³ / h. 3 At a feed temperature of 80℃, using 50wt% crude phosphoric acid (obtained through preliminary vacuum evaporation) as 1500 parts by weight, 0.55 parts of polyethylene glycol diamine, 0.9 parts of N,N-diethylhydroxylamine, and 3 parts of sodium succinate sulfonate were mixed with the crude phosphoric acid in a feed pump to obtain the additive. The crude phosphoric acid was then fed sequentially into the first-stage falling film evaporator 1, the second-stage falling film evaporator 2, and the third-stage falling film evaporator 3 via the crude product pipeline 10. Simultaneously, the additive was fed into the third-stage falling film evaporator 3 via the additive pipeline 13 to be mixed with the crude phosphoric acid. Both were then fed into the scraped film evaporator 4 for evaporation and concentration, and discharged through the finished phosphoric acid pipeline 12 to obtain the finished phosphoric acid product.

[0046] The first-stage falling film evaporator 1 has an aspect ratio of 25:1, the second-stage falling film evaporator 2 has an aspect ratio of 30:1, and the third-stage falling film evaporator 3 has an aspect ratio of 40:1. By adjusting the opening of each valve in the steam pipeline 15 and the power of the two compressors, the vacuum degree of the first-stage falling film evaporator 1 is 550 mmHg, and the jacket temperature is 125℃; the vacuum degree of the second-stage falling film evaporator 2 is 550 mmHg, and the jacket temperature is 130℃; the vacuum degree of the third-stage falling film evaporator 3 is 550 mmHg, and the jacket temperature is 135℃; the operating temperature of the scraped film evaporator 4 is 135℃, the vacuum degree inside the evaporator is 10 kPa, and the residence time is 60 s. After the temperature stabilizes, the phosphorous acid product pipeline 12 is cut into the product storage tank to collect the phosphorous acid product.

[0047] The primary steam buffer tank 5, secondary steam buffer tank 6, and tertiary steam buffer tank 7 are connected to the steam jackets of each stage of the falling film evaporator to stabilize the steam pressure and make the heating temperature more stable and precise. The hydrogen chloride-containing waste gas from the falling film evaporation is sent to the post-treatment via the falling film evaporation waste gas pipeline 11, and the waste gas from the scraped film evaporation is sent to the post-treatment via the scraped film evaporation waste gas pipeline 14.

[0048] Samples were taken from the outlet of the finished phosphoric acid pipeline 12. The test results showed that the mass concentration of the finished phosphoric acid was 99.60 wt% and the residual chlorine content was 4.2 ppm.

[0049] Comparative Example 1

[0050] Without adding sodium succinate sulfonate, the rest of the equipment installation and operation are the same as in Example 1. After testing, the mass concentration of the finished phosphorous acid product is 97.91 wt%, and the residual chlorine content is 45.8 ppm.

[0051] Comparative Example 2

[0052] Without adding N,N-diethylhydroxylamine, the rest of the equipment installation and operation were the same as in Example 1. The mass concentration of the finished phosphorous acid product was 98.26 wt%, and the residual chlorine content was 53.2 ppm.

[0053] Comparative Example 3

[0054] Without adding polyethylene glycol diamine, the installation and operation of the remaining equipment are the same as in Example 1. After testing, the mass concentration of the finished phosphorous acid product is 98.53 wt%, and the residual chlorine content is 40.3 ppm.

[0055] Comparative Example 4

[0056] Without adding sodium succinate sulfonate, N,N-diethylhydroxylamine, and polyethylene glycol diamine, and with the rest of the equipment installed and operated as in Example 1, the mass concentration of the finished phosphorous acid product was 97.14 wt%, and the residual chlorine content was 115.9 ppm.

[0057] Comparative Example 5

[0058] The scraped film evaporator was not installed, and the installation and operation of the rest of the equipment were the same as in Example 1. After trial operation, it was found that the water content and chlorine residue of the finished phosphoric acid product were significantly higher than those in Example 1, with the chlorine residue being 76 ppm.

[0059] Comparative Example 6

[0060] No compressor was installed, and the direction of high-temperature steam feed was the same as that of crude phosphoric acid feed. The installation and operation of the rest of the equipment were the same as in Example 1. After trial run, it was found that the mass loss of the finished phosphoric acid was slightly greater than that in Example 1, and the residual chlorine content could not be stabilized at ≤50ppm, which was difficult to meet the requirements of formal production. When compared with Example 1, it was found that the steam consumption of Comparative Example 2 was about 13~16% greater than that of Example 1.

[0061] Comparative Example 7

[0062] The length-to-diameter ratio of the first-stage falling film evaporator and the third-stage falling film evaporator is the same, both being 46:1. The installation and operation of the remaining equipment are the same as in Example 1. During the trial run, it was found that the water content and chlorine residue of the finished phosphoric acid product were slightly higher than in Example 1. This is because the crude phosphoric acid product in the first-stage falling film evaporator has a high water content and low viscosity. When the length-to-diameter ratio is too large, the liquid film flows faster and its thickness gradually decreases during the downward flow, resulting in liquid film rupture and the formation of dry spots, which leads to a decrease in heat transfer efficiency.

[0063] Comparative Example 8

[0064] The three-stage falling film evaporator was a dismantled and spared falling film evaporator with a length-to-diameter ratio of 12:1. The installation and operation of the remaining equipment were the same as in Example 1. During trial operation, it was found that the inner wall of the three-stage falling film evaporator was prone to scaling, and the residual chlorine content of the finished phosphoric acid was unstable, resulting in significant phosphoric acid loss, generally ≥3.8 wt%. This was because the viscosity of the crude phosphoric acid increased. When the length-to-diameter ratio was too small, the crude phosphoric acid could not form a stable and uniform liquid film inside the tubes, leading to dry wall phenomena on some tube walls, resulting in unstable heat transfer and scaling.

Claims

1. A phosphorous acid evaporation and concentration process, wherein crude phosphorous acid product is processed by an evaporation and concentration system to obtain finished phosphorous acid product, characterized in that, The evaporation and concentration system includes a first-stage falling film evaporator (1), a second-stage falling film evaporator (2), and a third-stage falling film evaporator (3) connected in sequence; additives are added from the third-stage falling film evaporator (3), including polyethylene glycol diamine, N,N-diethylhydroxyamine, and sodium succinate sulfonate.

2. The phosphorous acid evaporation and concentration process according to claim 1, characterized in that, The evaporation and concentration system also includes a crude product pipeline (10), a scraped film evaporator (4), and a phosphorous acid finished product pipeline (12). An auxiliary agent pipeline (13) is connected to the three-stage falling film evaporator (3). The crude phosphorous acid product enters the first-stage falling film evaporator (1), the second-stage falling film evaporator (2), and the third-stage falling film evaporator (3) in sequence through the crude product pipeline (10) for evaporation and concentration. At the same time, the auxiliary agent enters the third-stage falling film evaporator (3) through the auxiliary agent pipeline (13), and finally evaporates and concentrates in the scraped film evaporator (4), and is discharged through the phosphorous acid finished product pipeline (12) to obtain the finished phosphorous acid product.

3. The phosphorous acid evaporation and concentration process according to claim 1, characterized in that, The feed flow rate for crude phosphorous acid is 1.2~1.5 m³ / h. 3 The feed rate is 65~90℃, and the crude phosphorous acid product mass percentage is 45~55wt%.

4. The phosphorous acid evaporation and concentration process according to claim 1, characterized in that, The mass ratio of crude phosphorous acid, polyethylene glycol diamine, N,N-diethylhydroxylamine, and sodium succinate sulfonate is 1500:(0.35~0.55):(0.9~1.5):(2.5~3.5).

5. The phosphorous acid evaporation and concentration process according to claim 2, characterized in that, The length-to-diameter ratio of the first-stage falling film evaporator (1) is (20~25):1, the length-to-diameter ratio of the second-stage falling film evaporator (2) is (25~30):1, and the length-to-diameter ratio of the third-stage falling film evaporator (3) is (40~50):

1.

6. The phosphorous acid evaporation and concentration process according to claim 2, characterized in that, Jackets are installed on the first-stage falling film evaporator (1), the second-stage falling film evaporator (2) and the third-stage falling film evaporator (3); a second-stage steam buffer tank (6) is connected between the jacket of the first-stage falling film evaporator (1) and the jacket of the second-stage falling film evaporator (2); a third-stage steam buffer tank (7) is connected between the jacket of the second-stage falling film evaporator (2) and the jacket of the third-stage falling film evaporator (3); a first-stage steam buffer tank (5) is also connected to the jacket of the first-stage falling film evaporator (1).

7. The phosphorous acid evaporation and concentration process according to claim 6, characterized in that, The vacuum degree of the first-stage falling film evaporator (1) is 525~600 mmHg, and the jacket temperature is 120~125℃; the vacuum degree of the second-stage falling film evaporator (2) is 525~600 mmHg, and the jacket temperature is 125~135℃; the vacuum degree of the third-stage falling film evaporator (3) is 525~600 mmHg, and the jacket temperature is 135~140℃.

8. The phosphorous acid evaporation and concentration process according to claim 2, characterized in that, The working temperature of the scraped film evaporator (4) is 135~140℃, the vacuum degree is 5~10kPa, and the residence time is 50~60s.

9. The phosphorous acid evaporation and concentration process according to claim 2, characterized in that, The first-stage falling film evaporator (1), the second-stage falling film evaporator (2), and the third-stage falling film evaporator (3) are connected in the middle by a falling film evaporation exhaust gas pipeline (11), and the scraped film evaporator (4) is connected in the top by a scraped film evaporation exhaust gas pipeline (14).

10. The phosphorous acid evaporation and concentration process according to claim 2, characterized in that, A jacket is installed on the scraped film evaporator (4), and the steam pipeline (15) connects the jacket of the scraped film evaporator (4), the compressor (9), and the jackets on the first-stage falling film evaporator (1), the second-stage falling film evaporator (2), and the third-stage falling film evaporator (3); the compressor (8) is connected between the first-stage steam buffer tank (5) and the second-stage steam buffer tank (6).

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