Method for preparing solid pyrophosphoric acid by adopting belt type crystallization device

Abstract

The invention discloses a method for preparing solid pyrophosphoric acid by adopting a belt type crystallization device, and belongs to the technical field of fine chemical synthesis, the belt type crystallization device comprises a closed box body, a conveyor belt is mounted in the closed box body, a plurality of liquid distribution pipes are arranged above the initial end of the conveyor belt, and the liquid distribution pipes are connected with a liquid outlet pipe at the bottom of a reaction kettle; the conveying belt is wound on the driving cooling roller, the supporting cooling roller and the driven cooling roller, upper cooling boxes and lower cooling boxes are installed between the driving cooling roller and the supporting cooling roller and between the supporting cooling roller and the driven cooling roller, and the upper surfaces of the upper cooling boxes and the lower surfaces of the lower cooling boxes are both in sliding connection with the inner wall of the conveying belt. The liquid pyrophosphoric acid added with the seed crystal is distributed on the conveyor belt in the form of a film, is cooled and crystallized into solid pyrophosphoric acid in the conveying process, and then is scraped off from the conveyor belt through the scraper to form flaky solid pyrophosphoric acid, so that the problem of low crystallization efficiency caused by serious influence on heat transfer due to wall adhesion of materials can be well solved.

Description

Technical Field

[0001] The invention relates to a method for preparing solid pyrophosphoric acid by adopting a belt-type crystallization device, and belongs to the technical field of fine chemical synthesis. Background Art

[0002] Pyrophosphoric acid is an important chemical widely used in food processing, pharmaceutical and plastic additive manufacturing, catalysts, and stabilizers for organic peroxides. With technological advancements, the application of pyrophosphoric acid in new materials, nanomaterials, biotechnology, and other fields is also increasing. Currently, pyrophosphoric acid is available in two forms: liquid and solid. Liquid pyrophosphoric acid is highly acidic and low in purity, with only 52%-68% of the phosphoric acid existing in the form of pyrophosphoric acid, while the remainder exists in the form of tripolyphosphoric acid, tetrapolyphosphoric acid, and a small amount of orthophosphoric acid. Solid pyrophosphoric acid, on the other hand, is highly pure, with 99% of the phosphoric acid existing in the form of pyrophosphoric acid, and the product purity can reach over 99%.

[0003] Solid pyrophosphate has two crystalline forms: Form I pyrophosphate. Form I is stable in ice water and does not readily decompose, but it decomposes into orthophosphoric acid at elevated temperatures. Form I crystals have a melting point of 54.3°C; and Form II pyrophosphate. Form II pyrophosphate is stable at room temperature and has a melting point of 71.5°C. Form I pyrophosphate converts to Form II when heated at approximately 50°C in a sealed tube for several hours.

[0004] Pyrophosphate easily absorbs water and decomposes into phosphoric acid, making it difficult to store. However, Type II pyrophosphate is less hygroscopic than Type I, making it easier to store. Therefore, research into highly stable and pure Type II solid pyrophosphate products is a current research and development focus.

[0005] Existing methods for preparing solid pyrophosphoric acid can be divided into the following two categories: Seeded crystallization: Liquid pyrophosphate is left to crystallize without adding seed crystals, typically over two to three days under ice-water cooling. This method suffers from slow crystallization, resulting in low production efficiency and impracticality for large-scale industrial production.

[0006] Induced crystallization: An appropriate amount (10% to 50% by weight) of Type I or Type II pyrophosphate seed crystals is added to the liquid pyrophosphate under stirring at 30-50°C to induce crystallization. To prevent moisture absorption, crystallization is carried out in a dry nitrogen atmosphere. Yunnan Yuntianhua Co., Ltd. uses this process to produce solid pyrophosphate, using a kneader (CN113896693B). This is a typical method for producing high-purity solid pyrophosphate. While this method offers advantages such as high product yield and quality, a simple production process, and ease of industrialization, it also suffers from several drawbacks: pyrophosphate crystallization is a highly exothermic process, requiring cooling during the crystallization process. However, pyrophosphate has a high viscosity, and as crystallization proceeds, the viscosity increases, rapidly transforming the liquid pyrophosphate into a paste. This paste adheres to the inner walls of the kneader, impairing heat transfer and resulting in poor cooling of the equipment, making it impossible to effectively dissipate the heat released by crystallization. This results in slow crystallization, long crystallization times, high energy consumption, and low production efficiency.

[0007] It can be seen that although the induced crystallization method is the only industrial method for preparing solid pyrophosphoric acid, the use of a kneader as a crystallization equipment has the problem of material sticking to the wall, seriously affecting the heat transfer effect and resulting in low production efficiency. Summary of the Invention

[0008] The present invention addresses the deficiencies in the background technology and provides a method for preparing solid pyrophosphoric acid using a belt crystallization device. Liquid pyrophosphoric acid with seed crystals is distributed on a conveyor belt in a film 2 to 10 mm thick. During the conveying process, the liquid pyrophosphoric acid is cooled and crystallized into solid pyrophosphoric acid. The solid pyrophosphoric acid is then scraped off the conveyor belt by a scraper to form flakes of solid pyrophosphoric acid. This method effectively solves the problem of material sticking to the wall, which seriously affects heat transfer and leads to low crystallization efficiency.

[0009] The present invention specifically adopts the following technical solutions: A method for preparing solid pyrophosphoric acid using a belt crystallization device, the belt crystallization device comprising a sealed box, a conveyor belt with an inclination angle of 5 to 20 degrees installed inside the sealed box, a plurality of liquid distribution pipes provided above the starting end of the conveyor belt, the liquid distribution pipes being connected to the liquid outlet pipes at the bottom of the reactor, and a discharge valve being installed on the liquid outlet pipes; the conveyor belt is wound around an active cooling roller, a supporting cooling roller, and a driven cooling roller, an upper cooling box and a lower cooling box symmetrically arranged in the vertical direction are installed between the active cooling roller and the supporting cooling roller, and between the supporting cooling roller and the driven cooling roller, the upper surface of the upper cooling box and the lower surface of the lower cooling box being both slidably connected to the inner wall of the conveyor belt.

[0010] Furthermore, the active cooling roller, supporting cooling roller and driven cooling roller all include roller shells, which are arranged on the periphery of the driving roller body and the driven roller body, and an annular cooling cavity is formed between the roller shell and the driving roller body and the driven roller body.

[0011] Furthermore, the facing ends of the driving roller body and the driven roller body are connected by threads, and the periphery of the driving roller body and the driven roller body is provided with an annular groove for installing the roller shell; the conveyor belt is wound around the outside of the roller shell, and ribs are provided on both sides of the conveyor belt.

[0012] Furthermore, a hollow drive shaft head is installed inside the drive roller body, and the drive shaft head and the drive roller body are fixedly connected by bolts. A diversion cavity is provided in the end of the drive shaft head close to the drive roller body, and a diversion cone is fixedly installed in the diversion cavity. The diversion cavity is connected to the annular cooling cavity through multiple diversion channels distributed in a circumference, and the diversion channels are opened in the drive shaft head and the drive roller body.

[0013] Furthermore, a hollow driven shaft head is installed inside the driven roller body, and the driven shaft head and the driven roller body are fixedly connected by bolts. A confluence cavity is provided in the end of the driven shaft head close to the driven roller body, and a confluence cone is fixedly installed in the confluence cavity. The confluence cavity is connected to the annular cooling cavity through multiple confluence channels distributed in a circumference, and the confluence channels are opened in the driven shaft head and the driven roller body.

[0014] Furthermore, inlet and outlet interfaces are provided on both sides of the upper cooling box and the lower cooling box, which are used for the entry and exit of cooling medium, and the cooling medium cools the materials on the conveyor belt; arc portions are provided at both ends of the upper cooling box and the lower cooling box, respectively, and the arc portions are adapted to the shape of the cooling roller.

[0015] Furthermore, an adjustment plate is provided above the conveyor belt, which is arranged close to the outlet of the liquid distribution pipe. There is a gap of 2 to 10 mm between the bottom end of the adjustment plate and the upper surface of the conveyor belt. The middle part of the adjustment plate is hingedly installed, and one side of the top of the adjustment plate is connected to the telescopic cylinder B.

[0016] Furthermore, a scraper is provided at the end of the conveyor belt, and the distance between the scraper and the conveyor belt is 0.2 mm; the scraper is driven by a telescopic cylinder A outside the end of the closed box.

[0017] Furthermore, a transversely arranged air collecting pipe is installed on the top of the inner cavity of the closed box, the bottom of the air collecting pipe is connected to a guide plate with an inverted V-shaped structure, the bottom end of the guide plate is connected to the inner wall of the closed box, and the guide plate is used to guide air. An air outlet is provided on the top of the air collecting pipe, and the air outlet passes through the top wall of the closed box, and the air outlet is connected to the inlet of the cooling and dehumidifier; an air inlet is provided at the bottom of the closed box, and the air inlet is connected to the outlet of the cooling and dehumidifier through a pipeline.

[0018] The preparation of solid pyrophosphoric acid using the above-mentioned belt crystallization device comprises the following steps: Step 1: Add liquid pyrophosphoric acid to the reactor, add 5% to 30% seed crystals, start stirring, and stir for 1-2 hours to mix the materials evenly; Step 2: Turn on the cooling dehumidifier to dehumidify the space where the conveyor belt is located, keep the humidity of the space below 30%, and keep the temperature of the space between 5 and 15 degrees Celsius; the cooling medium enters each cooling roller and each cooling box to cool the conveyor belt, and the temperature of the cooling medium is -10 degrees Celsius to 10 degrees Celsius; Step 3: Open the discharge valve and evenly discharge the viscous liquid pyrophosphoric acid onto a conveyor belt with an inclination angle of 5 to 20 degrees through the liquid distribution pipe, and use the adjustment plate to fully spread the material on the conveyor belt. The material thickness is controlled at 2 to 10 mm; the material stays on the conveyor belt for 0.5 to 2 hours; Step 4: Use a scraper to scrape off the flaky material to obtain a flaky solid pyrophosphoric acid product.

[0019] After adopting the above technical solution, the present invention has the following advantages compared with the prior art: The present invention uses a conveyor belt with a cooling function to convey liquid pyrophosphoric acid, and accurately controls the thickness of the material on the conveyor belt. Then, by controlling the speed of the conveyor belt, the residence time of the material on the conveyor belt is controlled, so that the material can be fully cooled and the time for the liquid pyrophosphoric acid to be converted into solid pyrophosphoric acid is accelerated. In the present invention, since the material is distributed on the conveyor belt in the form of a film, the problem of the material easily sticking to the wall and affecting heat transfer when using a kneader as a crystallization device is well solved. Therefore, it has the advantages of high heat transfer efficiency, short crystallization time, high production efficiency, low energy consumption, etc., and is operated in a dehumidified space, which can effectively prevent the material from absorbing moisture and deteriorating.

[0020] The present invention is described in detail below with reference to the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a structural schematic diagram of the belt crystallization device in the present invention; Figure 2 It is a driving diagram of the conveyor belt; Figure 3 It is a schematic diagram of the structure of the cooling roller; Figure 4 This is a schematic diagram of the installation of the gas collecting pipe.

[0022] In the figure, 1-sealed box, 2-reactor, 3-liquid outlet pipe, 4-discharging valve, 5-liquid distribution pipe, 6-conveyor belt, 7-active cooling roller, 8-support cooling roller, 9-driven cooling roller, 10-upper cooling box, 11-lower cooling box, 12-arc-shaped part, 13-scraper, 14-telescopic cylinder A, 15-adjusting plate, 16-telescopic cylinder B, 17-guide plate, 18-gas collecting pipe, 19-air outlet, 20-air inlet, 21-discharge port, 22-roller shell, 23-annular groove, 24-driving roller body, 25-driven roller body, 26-annular cooling chamber, 27-driving shaft head, 28-driven shaft head, 29-diverter chamber, 30-diverter cone, 31-diverter channel, 32-merging chamber, 33-merging cone, 34-merging channel. DETAILED DESCRIPTION

[0023] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, specific embodiments of the present invention are now described with reference to the accompanying drawings.

[0024] like Figure 1-Figure 4 As shown together, the present invention provides a belt crystallization device for preparing solid pyrophosphoric acid, comprising a closed box 1, a conveyor belt 6 with an inclination angle of 5 to 20 degrees installed inside the closed box 1, the conveyor belt 6 is made of 2205 alloy steel, and a plurality of liquid distribution pipes 5 are provided above the starting end of the conveyor belt 6, the liquid distribution pipes 5 are connected to the liquid outlet pipe 3 at the bottom of the reactor 2, and a discharge valve 4 is installed on the liquid outlet pipe 3.

[0025] The conveyor belt 6 is wound around the active cooling roller 7, the supporting cooling roller 8 and the driven cooling roller 9. An upper cooling box 10 and a lower cooling box 11 symmetrically arranged in the vertical direction are installed between the active cooling roller 7 and the supporting cooling roller 8, and between the supporting cooling roller 8 and the driven cooling roller 9. The upper surface of the upper cooling box 10 and the lower surface of the lower cooling box 11 are both slidably connected to the inner wall of the conveyor belt 6.

[0026] The upper cooling box 10 and the lower cooling box 11 are provided with inlet and outlet ports on both sides for the entry and exit of the cooling medium, which cools the materials on the conveyor belt 6. The upper cooling box 10 and the lower cooling box 11 are provided with arc-shaped portions 12 at both ends. The arc-shaped portions 12 are adapted to the shape of the cooling rollers and are used to maximize the contact area with the conveyor belt 6.

[0027] The active cooling roller 7, the supporting cooling roller 8 and the driven cooling roller 9 all include a roller shell 22, which is sleeved on the periphery of the driving roller body 24 and the driven roller body 25, and an annular cooling cavity 26 is formed between the roller shell 22 and the driving roller body 24 and the driven roller body 25.

[0028] The driving roller body 24 and the driven roller body 25 are connected at their facing ends by threads. Ring grooves 23 are provided on the peripheries of the driving roller body 24 and the driven roller body 25 for mounting the roller shell 22. The conveyor belt 6 is wound around the outside of the roller shell 22. Side ribs are provided on both sides of the conveyor belt 6 to prevent material on the conveyor belt 6 from flowing out from either side.

[0029] A hollow drive shaft head 27 is mounted within the drive roller body 24. The drive shaft head 27 and the drive roller body 24 are fixedly connected by bolts. A diverter cavity 29 is provided at the end of the drive shaft head 27 near the drive roller body 24. A diverter cone 30 is fixedly mounted within the diverter cavity 29. The diverter cavity 29 is connected to the annular cooling cavity 26 via a plurality of circumferentially distributed diverter channels 31. The diverter channels 31 are provided within the drive shaft head 27 and the drive roller body 24. The cooling medium flowing into the drive shaft head 27 passes through the diverter cavity 29 and the diverter channels 31 and then enters the annular cooling cavity 26, thereby cooling the conveyor belt 6 and the material on the conveyor belt 6.

[0030] A hollow driven shaft head 28 is mounted inside the driven roller body 25. The driven shaft head 28 and the driven roller body 25 are fixedly connected by bolts. A confluence chamber 32 is provided at the end of the driven shaft head 28 near the driven roller body 25. A confluence cone 33 is fixedly mounted in the confluence chamber 32. The confluence chamber 32 is connected to the annular cooling chamber 26 via a plurality of circumferentially distributed confluence channels 34. The confluence channels 34 are provided in the driven shaft head 28 and the driven roller body 25. The cooling medium in the annular cooling chamber 26 flows into the confluence chamber 32 through the confluence channels 34 and eventually flows back out of the end of the driven shaft head 28.

[0031] An adjustment plate 15 is installed above the conveyor belt 6, near the outlet of the liquid distribution pipe 5. A gap of 2 to 10 mm is maintained between the bottom of the adjustment plate 15 and the upper surface of the conveyor belt 6. The middle portion of the adjustment plate 15 is hinged, and one side of the top of the adjustment plate 15 is connected to a telescopic cylinder B16, which powers the swing of the adjustment plate 15, thereby adjusting the height of the gap between the adjustment plate 15 and the conveyor belt 6.

[0032] A scraper 13 is provided at the end of the conveyor belt 6. Made of 2205 alloy, the distance between scraper 13 and conveyor belt 6 is less than 1 mm, preferably 0.2 mm. Scraper 13 is driven by a telescopic cylinder A14 located outside the end of the sealed box 1, rotating through a predetermined angle. Scraper 13 is used to scrape flaky material off the conveyor belt 6, producing a flaky solid pyrophosphate product.

[0033] A discharge port 21 is provided below the scraper 13 . The discharge port 21 is located at the bottom of the sealed box 1 and is used to collect flaky materials.

[0034] A transversely arranged air collecting pipe 18 is installed at the top of the inner cavity of the closed box 1. The bottom of the air collecting pipe 18 is connected to a guide plate 17 with an inverted V-shaped structure. The bottom end of the guide plate 17 is connected to the inner wall of the closed box 1. The guide plate 17 is used to guide air. An air outlet 19 is provided at the top of the air collecting pipe 18. The air outlet 19 is set through the top wall of the closed box 1 and is connected to the inlet of the cooling dehumidifier. An air inlet 20 is provided at the bottom of the closed box 1. The air inlet 20 is connected to the outlet of the cooling dehumidifier through a pipeline. The cooling dehumidifier is used to dehumidify and cool the space where the conveyor belt 6 is located, keeping the humidity of the space below 30% and the temperature of the space between 5 and 15°C.

[0035] A method for preparing solid pyrophosphoric acid using the above-mentioned belt crystallization device comprises the following steps: Step 1: Add liquid pyrophosphoric acid to the reactor, add 5% to 30% seed crystals, start stirring, and stir for 1-2 hours to mix the materials evenly; Step 2: Turn on the cooling dehumidifier to dehumidify the space where the conveyor belt is located, keep the humidity of the space below 30%, and keep the temperature of the space between 5 and 15 degrees Celsius; the cooling medium enters each cooling roller and each cooling box to cool the conveyor belt, and the temperature of the cooling medium is -10 degrees Celsius to 10 degrees Celsius; Step 3: Open the discharge valve and evenly discharge the viscous liquid pyrophosphoric acid onto a conveyor belt with an inclination angle of 5 to 20 degrees through the liquid distribution pipe, and use the adjustment plate to fully spread the material on the conveyor belt. The material thickness is controlled at 2 to 10 mm; the material stays on the conveyor belt for 0.5 to 2 hours; Step 4: Use a scraper to scrape off the flaky material to obtain a flaky solid pyrophosphoric acid product.

[0036] The liquid pyrophosphoric acid used in the present invention was produced by Wuhan Haorong Biotechnology Co., Ltd., and the seed crystal was solid pyrophosphoric acid produced by Yunnan Yuntianhua Co., Ltd. The melting point tester was produced by Shanghai Yidian Physical Optical Instrument Co., Ltd.

[0037] Example 1 A method for preparing solid pyrophosphoric acid using a belt crystallization device, the process steps are as follows: 200 kg of liquid pyrophosphoric acid was added to the reactor, stirring was started, 10 kg of solid pyrophosphoric acid was added, and stirring was continued for 1 hour; the cooling dehumidifier was turned on to adjust the indoor air humidity to 30%, the indoor temperature to 15°C, and the cooling medium temperature to -10°C; the discharge valve was opened to spread the material on the conveyor belt with a thickness of 2 mm; the material was advanced on the conveyor belt at a speed of 20 meters per hour, the cooling roller had a diameter of 0.4 meters, the conveyor belt had a width of 1.5 meters, and the upper conveyor belt had a length of 10 meters; the material was scraped off by a scraper at the end of the conveyor belt to obtain 210 kg of flaky solid pyrophosphoric acid product, which took 115 minutes. The melting point of the product was detected to be 71.5-71.6°C.

[0038] Example 2 A method for preparing solid pyrophosphoric acid using a belt crystallization device, the process steps are as follows: 200 kg of liquid pyrophosphoric acid was added to the reactor, stirring was started, 20 kg of solid pyrophosphoric acid was added, and stirring was continued for 1 hour; the cooling dehumidifier was turned on to adjust the indoor air humidity to 28%, the indoor temperature to 13°C, and the cooling medium temperature to 0°C; the discharge valve was opened to spread the material on the conveyor belt with a thickness of 4 mm; the material was advanced on the conveyor belt at a speed of 11 meters per hour, the cooling roller had a diameter of 0.4 meters, the conveyor belt had a width of 1.5 meters, and the upper conveyor belt had a length of 10 meters; the material was scraped off by a scraper at the end of the conveyor belt to obtain 220 kg of flaky solid pyrophosphoric acid product, which took 110 minutes. The melting point of the product was detected to be 71.6-71.7°C.

[0039] Example 3 A method for preparing solid pyrophosphoric acid using a belt crystallization device, the process steps are as follows: 200 kg of liquid pyrophosphoric acid was added to the reactor, stirring was started, 30 kg of solid pyrophosphoric acid was added, and stirring was continued for 1 hour; the cooling dehumidifier was turned on to adjust the indoor air humidity to 25%, the indoor temperature to 10°C, and the cooling medium temperature to 5°C; the discharge valve was opened to spread the material on the conveyor belt with a thickness of 6 mm; the material was advanced on the conveyor belt at a speed of 8 meters per hour, the cooling roller had a diameter of 0.4 meters, the conveyor belt had a width of 1.5 meters, and the upper conveyor belt had a length of 10 meters; the material was scraped off by a scraper at the end of the conveyor belt to obtain 230 kg of flaky solid pyrophosphoric acid product, which took 100 minutes. The melting point of the product was detected to be 71.6-71.7°C.

[0040] Example 4 A method for preparing solid pyrophosphoric acid using a belt crystallization device, the process steps are as follows: 200 kg of liquid pyrophosphoric acid was added to the reactor, stirring was started, 40 kg of solid pyrophosphoric acid was added, and stirring was continued for 1 hour; the cooling dehumidifier was turned on to adjust the indoor air humidity to 20%, the indoor temperature to 5°C, and the cooling medium temperature to 10°C; the discharge valve was opened to spread the material on the conveyor belt with a thickness of 8 mm; the material was advanced on the conveyor belt at a speed of 6 meters per hour, the cooling roller had a diameter of 0.4 meters, the conveyor belt had a width of 1.5 meters, and the upper conveyor belt had a length of 10 meters; the material was scraped off by a scraper at the end of the conveyor belt to obtain 240 kg of flaky solid pyrophosphoric acid product, which took 100 minutes. The melting point of the product was detected to be 71.6-71.7°C.

[0041] Example 5 A method for preparing solid pyrophosphoric acid using a belt crystallization device, the process steps are as follows: 200 kg of liquid pyrophosphoric acid was added to the reactor, stirring was started, 50 kg of solid pyrophosphoric acid was added, and stirring was continued for 1 hour; the cooling dehumidifier was turned on to adjust the indoor air humidity to 20%, the indoor temperature to 5°C, and the cooling medium temperature to 10°C; the discharge valve was opened to spread the material on the conveyor belt with a thickness of 10 mm; the material was advanced 4 meters on the conveyor belt in 1 hour, the cooling roller had a diameter of 0.4 meters, the conveyor belt was 1.5 meters wide, and the upper conveyor belt was 10 meters long; the material was scraped off by a scraper at the end of the conveyor belt to obtain 250 kg of flaky solid pyrophosphoric acid product, which took 116 minutes. The melting point of the product was detected to be 71.6-71.7°C.

[0042] Comparative Example 1 5.65 kg of polyphosphoric acid containing 84% by mass of phosphorus pentoxide was placed in a stirred reactor and mixed with 4.35 kg of polyphosphoric acid containing 76% by mass of phosphorus pentoxide. The mixture was heated to 60°C and stirred continuously for 2 hours to obtain pourable pyrophosphoric acid. The mixture was then placed in a kneader and stirred. 0.5 kg of solid pyrophosphoric acid was added. The kneader jacket was cooled to 5°C and stirred for 3 hours. The material was observed to be viscous. Stirring continued for 5 hours until the material became even more viscous. Stirring for 10 hours turned the material into a block solid. Stirring for 12 hours turned it into a powdery granular mixed solid. The melting point of the product was tested to be 71.6-71.7°C.

[0043] Comparative Example 1 required 10 hours to obtain a block product, which had low production efficiency and high cost compared with the examples.

[0044] Comparative Example 2 5.65 kg of polyphosphoric acid containing 84% by mass of phosphorus pentoxide was placed in a stirred kettle and mixed with 4.35 kg of polyphosphoric acid containing 76% by mass of phosphorus pentoxide. The mixture was heated to 60°C and stirred continuously for 2 hours to obtain pourable pyrophosphoric acid. The mixture was then placed in a kneader and stirred. 20 kg of solid pyrophosphoric acid was added and stirring was resumed. The kneader jacket was cooled to -20°C and stirred for 3 hours. The material was observed to be a viscous solid. Stirring continued for 5 hours until the material became even more viscous. Stirring for 7 hours resulted in a lumpy solid. Stirring for 9 hours resulted in a powdery solid. The melting point of the product was tested to be 71.6-71.7°C.

[0045] Comparative Example 2 required 7 hours to obtain a block product, which had low production efficiency and high cost compared with the examples.

[0046] Unless otherwise specified, all percentages used in the present invention are by mass.

[0047] The foregoing is an example of the best mode of carrying out the present invention. Any portion not described in detail herein is common knowledge within the skill of one of ordinary skill in the art. The scope of protection of the present invention is determined by the claims. Any equivalent transformation based on the technical teachings of the present invention is also within the scope of protection of the present invention.

Claims

1. A method for preparing solid pyrophosphoric acid using a belt crystallization device, characterized in that: The belt crystallization device comprises a sealed box (1), wherein a conveyor belt (6) with an inclination angle of 5 to 20 degrees is installed inside the sealed box (1), and a plurality of liquid distribution pipes (5) are provided above the starting end of the conveyor belt (6), and the liquid distribution pipes (5) are connected to the liquid outlet pipe (3) at the bottom of the reactor (2), and a discharge valve (4) is installed on the liquid outlet pipe (3); the conveyor belt (6) is wound around an active cooling roller (7), a supporting cooling roller (8) and a driven cooling roller (9), and an upper cooling box (10) and a lower cooling box (11) are symmetrically arranged in the vertical direction between the active cooling roller (7) and the supporting cooling roller (8), and between the supporting cooling roller (8) and the driven cooling roller (9), and the upper surface of the upper cooling box (10) and the lower surface of the lower cooling box (11) are both slidably connected to the inner wall of the conveyor belt (6).

2. The method for preparing solid pyrophosphoric acid using a belt crystallization device according to claim 1, wherein: The active cooling roller (7), the supporting cooling roller (8) and the driven cooling roller (9) all include a roller shell (22), which is sleeved on the periphery of the driving roller body (24) and the driven roller body (25), and an annular cooling cavity (26) is formed between the roller shell (22) and the driving roller body (24) and the driven roller body (25).

3. A method for preparing solid pyrophosphoric acid using a belt crystallization device as claimed in claim 2, characterized in that: The facing ends of the driving roller body (24) and the driven roller body (25) are connected by threads, and an annular groove (23) for mounting the roller shell (22) is provided on the periphery of the driving roller body (24) and the driven roller body (25); the conveyor belt (6) is wound around the outside of the roller shell (22), and ribs are provided on both sides of the conveyor belt (6).

4. A method for preparing solid pyrophosphoric acid using a belt crystallization device as claimed in claim 3, characterized in that: A driving shaft head (27) with a hollow structure is installed inside the driving roller body (24). The driving shaft head (27) and the driving roller body (24) are fixedly connected by bolts. A diversion cavity (29) is provided in the end of the driving shaft head (27) close to the driving roller body (24). A diversion cone (30) is fixedly installed in the diversion cavity (29). The diversion cavity (29) is connected to the annular cooling cavity (26) through a plurality of diversion channels (31) distributed in a circumferential manner. The diversion channels (31) are opened in the driving shaft head (27) and the driving roller body (24).

5. The method for preparing solid pyrophosphoric acid using a belt crystallization device according to claim 4, wherein: A driven shaft head (28) with a hollow structure is installed inside the driven roller body (25). The driven shaft head (28) and the driven roller body (25) are fixedly connected by bolts. A merging cavity (32) is provided in the end of the driven shaft head (28) close to the driven roller body (25). A merging cone (33) is fixedly installed in the merging cavity (32). The merging cavity (32) is connected to the annular cooling cavity (26) through a plurality of merging channels (34) distributed in a circumferential manner. The merging channels (34) are opened in the driven shaft head (28) and the driven roller body (25).

6. The method for preparing solid pyrophosphoric acid using a belt crystallization device according to claim 1, wherein: Inlet and outlet interfaces are provided on both sides of the upper cooling box (10) and the lower cooling box (11), and the inlet and outlet interfaces are used for the entry and exit of cooling medium, and the cooling medium cools the material on the conveyor belt (6); arc-shaped portions (12) are provided at both ends of the upper cooling box (10) and the lower cooling box (11), and the arc-shaped portions (12) are adapted to the shape of the cooling roller.

7. The method for preparing solid pyrophosphoric acid using a belt crystallization device according to claim 1, wherein: An adjusting plate (15) is provided above the conveyor belt (6). The adjusting plate (15) is provided near the outlet of the liquid distributing pipe (5). A gap of 2 to 10 mm is provided between the bottom end of the adjusting plate (15) and the upper surface of the conveyor belt (6). The middle portion of the adjusting plate (15) is hingedly mounted, and one side of the top of the adjusting plate (15) is connected to the telescopic cylinder B (16).

8. The method for preparing solid pyrophosphoric acid using a belt crystallization device according to claim 1, wherein: A scraper (13) is provided at the end of the conveyor belt (6), and the distance between the scraper (13) and the conveyor belt (6) is 0.2 mm; the scraper (13) is driven by a telescopic cylinder A (14) outside the end of the closed box (1).

9. The method for preparing solid pyrophosphoric acid using a belt crystallization device according to claim 1, wherein: A transversely arranged air collecting pipe (18) is installed on the top of the inner cavity of the closed box (1), and the bottom of the air collecting pipe (18) is connected to a guide plate (17) with an inverted V-shaped structure. The bottom end of the guide plate (17) is connected to the inner wall of the closed box (1), and the guide plate (17) is used to guide air. An air outlet (19) is provided on the top of the air collecting pipe (18), and the air outlet (19) is set through the top wall of the closed box (1). The air outlet (19) is connected to the inlet of the cooling dehumidifier; an air inlet (20) is provided at the bottom of the closed box (1), and the air inlet (20) is connected to the outlet of the cooling dehumidifier through a pipeline.

10. A method for preparing solid pyrophosphoric acid using a belt crystallization device, characterized in that: The preparation of solid pyrophosphoric acid using a belt crystallization device comprises the following steps: Step 1: Add liquid pyrophosphoric acid to the reactor, add 5% to 30% seed crystals, start stirring, and stir for 1-2 hours to mix the materials evenly; Step 2: Turn on the cooling dehumidifier to dehumidify the space where the conveyor belt is located, keep the humidity of the space below 30%, and keep the temperature of the space between 5 and 15 degrees Celsius; the cooling medium enters each cooling roller and each cooling box to cool the conveyor belt, and the temperature of the cooling medium is -10 degrees Celsius to 10 degrees Celsius; Step 3: Open the discharge valve and evenly discharge the viscous liquid pyrophosphoric acid onto a conveyor belt with an inclination angle of 5 to 20 degrees through the liquid distribution pipe, and use the adjustment plate to fully spread the material on the conveyor belt. The material thickness is controlled at 2 to 10 mm; the material stays on the conveyor belt for 0.5 to 2 hours; Step 4: Use a scraper to scrape off the flaky material to obtain a flaky solid pyrophosphoric acid product.

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