A melting crystallizer for preparing electronic-grade phosphoric acid, its method and electronic-grade phosphoric acid

Abstract

The present invention relates to a melting crystallizer for preparing electronic-grade phosphoric acid, a method thereof, and electronic-grade phosphoric acid. The melting crystallizer includes a double-layer crystallization shell, a first constant-temperature bath, and a second constant-temperature bath. A cooling pipe is arranged inside the double-layer crystallization shell, and a frustum base is arranged below the cooling pipe. The first constant-temperature bath is connected to the cooling pipe, and the second constant-temperature bath is connected to the double-layer crystallization shell. The melting crystallizer provided by the present invention can effectively prevent crystal blockage of the liquid discharge port by arranging a frustum base at the bottom of the cooling pipe, so that the crystal layer is evenly distributed on the outer wall of the cooling pipe. By cooling the melt inside and outside with a double constant-temperature bath, while the temperature of the cooling medium inside the pipe is reduced to make the crystal layer grow, the temperature of the outer medium is slowly reduced to slowly cool the phosphoric acid liquid, increasing the heat transfer driving force, solving the problem of increasing thermal resistance with the increase of the crystal layer thickness, and effectively improving the crystal layer growth rate.

Description

Technical Field

[0001] The present invention belongs to the technical field of phosphoric acid purification, and relates to a melting crystallizer for preparing electronic-grade phosphoric acid, in particular to a melting crystallizer for preparing electronic-grade phosphoric acid, a method thereof, and electronic-grade phosphoric acid. Background Art

[0002] Electronic-grade phosphoric acid is an ultra-high-purity chemical reagent used in the microelectronics industry, and is widely used in wet cleaning and wet etching in the production process of electronic devices such as integrated circuits, thin-film liquid crystal displays, and silicon wafer lithography. If metal ions or insoluble solids are present in the microcircuit, it may cause large-scale circuit short-circuit scrapping. Therefore, cleaning is required before each step of the electronic device manufacturing process, which poses very high quality requirements for the phosphoric acid used in wet cleaning. The industrial-grade, food-grade, or low-end electronic-grade phosphoric acid obtained by wet or thermal processes still has a large gap from the application requirements of semiconductor component production. Its arsenic, iron, antimony, chromium, nickel, sodium and other ionic impurities will greatly reduce the product quality and use reliability during the circuit board etching process. Therefore, before applying phosphoric acid to high-end electronic components such as electronic circuit boards and liquid crystal screens, further purification must be carried out to obtain ultra-high-purity electronic-grade phosphoric acid.

[0003] The melting crystallization method does not need to introduce a solvent, and can achieve a good purification effect through crystallization-sweating, and has good application prospects. The main problem of this method lies in the selection of the crystallizer. The commonly used crystallization tower type for preparing electronic-grade phosphoric acid is to introduce phosphoric acid into the crystallization tower, and use a cooling medium to cool the raw material phosphoric acid in the crystallizer, so that phosphoric acid crystallizes inside the crystallization tower. The porosity of the phosphoric acid crystal layer obtained by this method is relatively large, resulting in a large amount of mother liquor entrapment, and the mother liquor is not completely discharged during the solid-liquid two-phase separation.

[0004] CN 1843900A discloses a method for preparing electronic-grade phosphoric acid by melting crystallization. First, a film is formed on the surface of the crystallization tube at -45 to -35 °C, and then the temperature is raised to -2 to 10 °C for crystal growth. This method has a low operating temperature and high energy consumption; CN101774555A adopts a dynamic mode - liquid film crystallization method to prepare electronic-grade phosphoric acid, and raises the operating temperature to a suitable temperature range, but the concentration of metal impurity ions in the finally obtained electronic-grade phosphoric acid is still relatively high and still needs further improvement; Chinese patent CN102198937A conducts multi-stage static melting crystallization in a crystallization tower to prepare electronic-grade phosphoric acid, and needs to perform multi-stage crystallization separation operations in the tower, and the preparation period reaches 10 h, with a long operating time.

[0005] A crystallizer with an internal cooling pipe and an outer jacket. The main body of the molten phosphoric acid solution is introduced into the interior of the crystallizer. By cooling the cooling medium in the cooling pipe, crystal layers grow in a layered manner on the outer wall of the cooling pipe, and the amount of mother liquor occluded in the phosphoric acid crystal layer growing on the outer wall of the cooling pipe is greatly reduced. This type of crystallizer is commonly reported in literature for separating isomers, etc., and there are relatively few reports related to the research of electronic-grade phosphoric acid.

[0006] CN 103896231A invented a device for producing electronic-grade phosphoric acid by tubular crystallization. The vertical tubular columns are vertically and parallelly distributed in the crystallization tank, and crystals adhere to the vertical tubular columns. When separating the crystal-liquid two phases, the uncrystallized mother liquor can be completely discharged, effectively reducing the amount of mother liquor occlusion and improving the purification efficiency. However, this set of devices does not consider the problem that the bottom of the crystallizer is prone to crystal blockage of the drain port under static operation.

[0007] In addition, the above improvements to the crystallizer rarely involve the sweating step, that is, in the step of heating and sweating after crystallization in melt crystallization. If static sweating is used, the low sweating efficiency caused by the low liquid flow efficiency in the static state will increase the energy consumption of the whole process, and this problem has not been considered. Summary of the Invention

[0008] In view of the problems existing in the prior art, the present invention provides a melt crystallizer for preparing electronic-grade phosphoric acid, its method, and electronic-grade phosphoric acid. By adding a frustum base to the cooling pipe, it can effectively prevent a large amount of crystal seeds from growing at the bottom and blocking the drain port. When sweating after the crystal layer growth is completed, the cooling pipe with the attached crystal layer can be rotated through the frustum base to achieve heating and rotating sweating, playing a role of "spin-drying", improving the sweating effect, achieving a relatively high impurity ion removal rate, effectively improving the production efficiency, with a moderate operating temperature, greatly reducing the energy consumption, and having good application prospects.

[0009] To achieve this purpose, the present invention adopts the following technical solutions:

[0010] In the first aspect, the present invention provides a melt crystallizer for preparing electronic-grade phosphoric acid, and the melt crystallizer includes a double-layer crystallization shell, a first constant temperature bath, and a second constant temperature bath;

[0011] The interior of the double-layer crystallization shell is provided with a cooling pipe, and a frustum base is arranged below the cooling pipe;

[0012] The first constant temperature bath is connected to the cooling pipe;

[0013] The second constant temperature bath is connected to the double-layer crystallization shell.

[0014] The double-layered crystallization shell of the present invention forms a jacket. By attaching a frustum base to the cooling pipes of the melting crystallizer, the present invention can effectively prevent a large amount of crystal seeds from growing at the bottom and blocking the liquid discharge port. With the arrangement of the first constant-temperature bath and the second constant-temperature bath, the temperatures of the medium in the cooling pipes and the medium in the jacket layer of the melting crystallizer are controlled. The rapid cooling of the medium in the cooling pipes enables the growth of phosphoric acid crystals in a layered manner, and the slow cooling of the medium in the jacket layer can offset the hindrance to heat transfer caused by the growth of the phosphoric acid crystal layer, effectively improving the heat transfer efficiency and achieving the rapid growth of the phosphoric acid crystal layer.

[0015] Preferably, a liquid discharge port and a liquid discharge valve are provided below the double-layered crystallization shell.

[0016] Preferably, the cooling pipes include rotating cooling pipes.

[0017] By rotating the cooling pipes attached with the phosphoric acid crystal layer on the frustum base, the present invention allows the phosphoric acid crystal layer to heat up and rotate for sweating, which plays a role of "spin-drying", improves the sweating effect, and achieves a high impurity ion removal rate.

[0018] Preferably, the frustum base includes a perforated frustum base.

[0019] Preferably, the frustum base includes an arc-shaped frustum base.

[0020] Preferably, the frustum base is externally connected to a speed controller.

[0021] In a second aspect, the present invention provides a method for preparing electronic-grade phosphoric acid using the melting crystallizer as described in the first aspect. The method includes the following steps:

[0022] (1) Perform a constant-temperature precooling treatment on the phosphoric acid melt to obtain precooled phosphoric acid;

[0023] (2) Mix crystal seeds with the precooled phosphoric acid obtained in step (1), cool down for crystallization to obtain crude crystals;

[0024] (3) Heat up the crude crystals obtained in step (2) for sweating to obtain the electronic-grade phosphoric acid.

[0025] By adding crystal seeds, cooling down for crystallization, and heating up for sweating, the present invention obtains a purified electronic-grade phosphoric acid crystal layer, with a short production cycle and low energy consumption.

[0026] Preferably, the time for the constant-temperature precooling in step (1) is 30 - 60 min. For example, it can be 30 min, 40 min, 45 min, 50 min, or 60 min, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0027] Preferably, the temperature of the constant-temperature precooling in step (1) is 12-27°C. For example, it can be 12°C, 15°C, 20°C, 22°C, 25°C or 27°C, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0028] The constant-temperature precooling is divided into internal constant-temperature precooling and external constant-temperature precooling. The present invention adopts a structure of cooling both inside and outside. While the cooling medium inside the tube cools down to make the crystal layer grow, the temperature of the outer medium is slowly decreased to slowly cool the phosphoric acid liquid, increasing the heat transfer driving force, solving the problem of increasing thermal resistance as the crystal layer thickness increases, and effectively improving the crystal layer growth rate.

[0029] The internal constant-temperature precooling is realized by controlling with a first constant-temperature bath connected to the cooling tube, and the temperature of the cooling tube is controlled to be 12-20°C. For example, it can be 12°C, 14°C, 15°C, 16°C or 17°C, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0030] The temperature of the cooling tube in the present invention refers to the temperature of the heat exchange medium inside the cooling tube.

[0031] The external constant-temperature precooling is realized by controlling with a second constant-temperature bath connected to the double-layer crystallization shell, and the temperature of the double-layer crystallization shell is controlled to be 20-27°C. For example, it can be 20°C, 22°C, 24°C, 25°C, 26°C or 27°C, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0032] The temperature of the double-layer crystallization shell in the present invention refers to the temperature of the heat exchange medium in the jacket formed by the double-layer crystallization shell.

[0033] Preferably, the addition amount of the crystal seeds in step (2) is 1-3 g. For example, it can be 1 g, 1.5 g, 2 g, 2.5 g or 3 g, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0034] Preferably, the crystal seeds in step (2) include phosphoric acid crystal seeds.

[0035] The phosphoric acid crystal seeds in the present invention are prepared by rapid quenching in advance and stored at low temperature.

[0036] Preferably, the cooling rate of the cooling crystallization in step (2) is 1-8°C / h. For example, it can be 1°C / h, 2°C / h, 4°C / h, 5°C / h, 7°C / h or 8°C / h, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0037] The cooling rates of the cooling crystallization are divided into internal cooling crystallization and external cooling crystallization. The internal cooling crystallization is realized by controlling a first constant temperature bath connected to a cooling pipe, and the cooling rate is 3-8 °C / h. For example, it can be 3 °C / h, 4 °C / h, 5 °C / h, 7 °C / h or 8 °C / h. The external cooling crystallization is realized by controlling a second constant temperature bath connected to a double-layer crystallization shell, and the cooling rate is 1-5 °C / h. For example, it can be 1 °C / h, 2 °C / h, 3 °C / h, 4 °C / h or 5 °C / h, but it is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0038] The cooling rate of the internal cooling crystallization described in the present invention refers to the cooling rate of the heat exchange medium in the cooling pipe. The cooling rate of the external cooling crystallization described in the present invention refers to the cooling rate of the heat exchange medium in the jacket surrounded by the double-layer crystallization shell.

[0039] Preferably, the time of the cooling crystallization in step (2) is 1-3 h. For example, it can be 1 h, 1.5 h, 2 h, 2.5 h or 3 h, but it is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0040] Preferably, the temperature of the heating and sweating in step (3) is 18-22 °C. For example, it can be 18 °C, 19 °C, 20 °C, 21 °C or 22 °C, but it is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0041] Preferably, the time of the heating and sweating in step (3) is 0.5-2 h. For example, it can be 0.5 h, 0.8 h, 1 h, 1.5 h or 2 h, but it is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0042] Preferably, the heating and sweating in step (3) includes rotational heating and sweating. The rotational heating and sweating is realized by rotating the cooling pipe for heating and sweating.

[0043] Preferably, the rotation speed of the rotational heating and sweating is 20-40 r / min. For example, it can be 20 r / min, 25 r / min, 30 r / min, 35 r / min or 40 r / min, but it is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0044] As a preferred technical solution of the method provided in the second aspect of the present invention, the method includes the following steps:

[0045] (1) Constantly pre-cool the phosphoric acid melt for 30-60 min at a temperature of 12-27 °C to obtain pre-cooled phosphoric acid;

[0046] (2) The seed crystal with a mixed addition amount of 1-3 g and the precooled phosphoric acid obtained in step (1) are cooled and crystallized at a rate of 1-8 °C / h to obtain crude crystals;

[0047] (3) The crude crystals obtained in step (2) are heated and sweated, the temperature is 18-22 °C, and the time is 0.5-2 h to obtain the electronic grade phosphoric acid.

[0048] In a third aspect, the present invention provides an electronic grade phosphoric acid, which is prepared according to the method described in the second aspect.

[0049] Based on the above technical solutions, the beneficial effects of the present invention are as follows:

[0050] (1) The melting crystallizer provided by the present invention can effectively prevent crystal blockage of the liquid discharge port by arranging a frustum base at the bottom of the cooling tube, and make the crystal layer evenly distributed on the outer wall of the cooling tube;

[0051] (2) The melt is cooled inside and outside by using a double constant temperature bath. While the cooling medium in the tube is cooled to make the crystal layer grow, the temperature of the outer medium is slowly reduced to slowly cool the phosphoric acid liquid, increasing the heat transfer driving force, solving the problem of increasing thermal resistance with the increase of the crystal layer thickness, and effectively improving the crystal layer growth rate;

[0052] (3) The rotating heating and sweating can be realized by the cooling tube with adjustable rotation speed, effectively improving the sweating effect;

[0053] (4) Through adding seed crystal, cooling crystallization and heating sweating, a purified electronic grade phosphoric acid crystal layer is obtained, with a short production cycle and low energy consumption. Description of the Drawings

[0054] Figure 1 It is a schematic diagram of the device of the melting crystallizer described in the present invention.

[0055] Among them, 1 - cooling tube, 2 - double-layer crystallization shell, 3 - first constant temperature bath, 4 - second constant temperature bath, 5 - frustum base, 6 - speed controller, 7 - liquid discharge port. Detailed Embodiments

[0056] The present invention will be further described in detail below with reference to the drawings and through specific embodiments. However, the following examples are only simple examples of the present invention, and do not represent or limit the scope of the patent protection of the present invention. The scope of protection of the present invention is subject to the claims.

[0057] Example 1

[0058] This example provides a melting crystallizer for preparing electronic grade phosphoric acid. The schematic diagram of the device of the melting crystallizer is as Figure 1As shown in the figure, it includes: a cooling pipe 1, a double-layer crystallization shell 2, a first constant temperature bath 3 and a second constant temperature bath 4. The aspect ratio of the double-layer crystallization shell 2 is 2:1. A cooling pipe 1 is arranged inside. A frustum base 5 is arranged below the cooling pipe 1, and the diameter of the frustum base 5 is 0.6 times the diameter of the double-layer crystallization shell 2. The first constant temperature bath 3 is connected to the cooling pipe 1. The second constant temperature bath 4 is connected to the double-layer crystallization shell 2. A drain port 7 is arranged below the double-layer crystallization shell 2. The cooling pipe 1 is a rotary cooling pipe. The frustum base 5 is an arc-shaped perforated frustum base with a porosity of 50%, and is externally connected to a speed controller 6.

[0059] Example 2

[0060] This example provides a melting crystallizer for preparing electronic-grade phosphoric acid. The schematic diagram of the device of the melting crystallizer is as shown in Figure 1 As shown in the figure, it includes: a cooling pipe 1, a double-layer crystallization shell 2, a first constant temperature bath 3 and a second constant temperature bath 4. The aspect ratio of the double-layer crystallization shell 2 is 1.5:1. A cooling pipe 1 is arranged inside. A frustum base 5 is arranged below the cooling pipe 1, and the diameter of the frustum base 5 is 0.8 times the diameter of the double-layer crystallization shell 2. The first constant temperature bath 3 is connected to the cooling pipe 1. The second constant temperature bath 4 is connected to the double-layer crystallization shell 2. A drain port 7 is arranged below the double-layer crystallization shell 2. The cooling pipe 1 is a rotary cooling pipe. The frustum base 5 is an arc-shaped perforated frustum base with a porosity of 60%, and is externally connected to a speed controller 6.

[0061] Example 3

[0062] This example provides a melting crystallizer for preparing electronic-grade phosphoric acid. The schematic diagram of the device of the melting crystallizer is as shown in Figure 1 As shown in the figure, it includes: a cooling pipe 1, a double-layer crystallization shell 2, a first constant temperature bath 3 and a second constant temperature bath 4. The aspect ratio of the double-layer crystallization shell 2 is 3:1. A cooling pipe 1 is arranged inside. A frustum base 5 is arranged below the cooling pipe 1, and the diameter of the frustum base 5 is 0.5 times the diameter of the double-layer crystallization shell 2. The first constant temperature bath 3 is connected to the cooling pipe 1. The second constant temperature bath 4 is connected to the double-layer crystallization shell 2. A drain port 7 is arranged below the double-layer crystallization shell 2. The cooling pipe 1 is a rotary cooling pipe. The frustum base 5 is an arc-shaped perforated frustum base with a porosity of 40%, and is externally connected to a speed controller 6.

[0063] Application Example 1

[0064] This application example provides a method for preparing electronic-grade phosphoric acid by using the melting crystallizer described in Application Example 1. The method includes the following steps:

[0065] (1) Keep the phosphoric acid melt at a constant temperature and pre-cool it for 45 min. The temperature of the cooling tube 1 is 18 °C, and the temperature of the double-layer crystallization shell 2 is 23 °C to obtain pre-cooled phosphoric acid;

[0066] (2) Mix 2 g of phosphoric acid crystal seeds with the pre-cooled phosphoric acid obtained in step (1), cool and crystallize for 2 h. The cooling rate of the cooling tube 1 is 4 °C / h, and the cooling rate of the double-layer crystallization shell 2 is 2 °C / h to obtain crude crystals; After mixing for 15 min, a white phosphoric acid crystal layer can be observed on the outer wall of the cooling tube, and then the crude crystals grow on the outer wall of the cooling tube;

[0067] (3) Heat up and sweat the crude crystals obtained in step (2). The rotation speed of the cooling tube 1 is 30 r / min, the temperature is 22 °C, and the time is 1 h to obtain electronic-grade phosphoric acid.

[0068] Application Example 2

[0069] This application example provides a method for preparing electronic-grade phosphoric acid using the melt crystallizer described in Application Example 1. The method includes the following steps:

[0070] (1) Keep the phosphoric acid melt at a constant temperature and pre-cool it for 30 min. The temperature of the cooling tube 1 is 17 °C, and the temperature of the double-layer crystallization shell 2 is 24 °C to obtain pre-cooled phosphoric acid;

[0071] (2) Mix 1 g of phosphoric acid crystal seeds with the pre-cooled phosphoric acid obtained in step (1), cool and crystallize for 3 h. The cooling rate of the cooling tube 1 is 6 °C / h, and the cooling rate of the double-layer crystallization shell 2 is 1 °C / h to obtain crude crystals; After mixing for 15 min, a white phosphoric acid crystal layer can be observed on the outer wall of the cooling tube, and then the crude crystals grow on the outer wall of the cooling tube;

[0072] (3) Heat up and sweat the crude crystals obtained in step (2). The rotation speed of the cooling tube 1 is 30 r / min, the temperature is 20 °C, and the time is 0.5 h to obtain electronic-grade phosphoric acid.

[0073] Application Example 3

[0074] This application example provides a method for preparing electronic-grade phosphoric acid using the melt crystallizer described in Application Example 2. The method includes the following steps:

[0075] (1) Keep the phosphoric acid melt at a constant temperature and pre-cool it for 60 min. The temperature of the cooling tube 1 is 16 °C, and the temperature of the double-layer crystallization shell 2 is 27 °C to obtain pre-cooled phosphoric acid;

[0076] (2) Mix 3 g of phosphoric acid seed crystals with the pre-cooled phosphoric acid obtained in step (1), cool and crystallize for 2 h. The cooling rate of cooling tube 1 is 8 °C / h, and the cooling rate of the double-layer crystallization shell 2 is 4.5 °C / h to obtain crude crystals. After mixing for 15 min, a white phosphoric acid crystal layer can be observed on the outer wall of the cooling tube, and then the crude crystals grow on the outer wall of the cooling tube.

[0077] (3) Heat up and sweat the crude crystals obtained in step (2). The rotation speed of cooling tube 1 is 20 r / min, the temperature is 19 °C, and the time is 2 h to obtain electronic-grade phosphoric acid.

[0078] Application Example 4

[0079] This application example provides a method for preparing electronic-grade phosphoric acid using the melt crystallizer described in Application Example 3. The method includes the following steps:

[0080] (1) Keep the phosphoric acid melt at a constant temperature and pre-cool it for 40 min. The temperature of cooling tube 1 is 12 °C, and the temperature of the double-layer crystallization shell 2 is 24 °C to obtain pre-cooled phosphoric acid.

[0081] (2) Mix 2.5 g of phosphoric acid seed crystals with the pre-cooled phosphoric acid obtained in step (1), cool and crystallize for 1 h. The cooling rate of cooling tube 1 is 5 °C / h, and the cooling rate of the double-layer crystallization shell 2 is 2 °C / h to obtain crude crystals. After mixing for 15 min, a white phosphoric acid crystal layer can be observed on the outer wall of the cooling tube, and then the crude crystals grow on the outer wall of the cooling tube.

[0082] (3) Heat up and sweat the crude crystals obtained in step (2). The rotation speed of cooling tube 1 is 4 r / min, the temperature is 18 °C, and the time is 1.5 h to obtain the electronic-grade phosphoric acid.

[0083] Application Example 5

[0084] This application example provides a method for preparing electronic-grade phosphoric acid using the melt crystallizer described in Application Example 1. Except that the temperature of the double-layer crystallization shell 2 in step (1) is 21 °C and the cooling rate of the double-layer crystallization shell 2 in step (2) is 3 °C / h, the other process steps are the same as those in Application Example 1.

[0085] Application Example 6

[0086] This application example provides a method for preparing electronic-grade phosphoric acid using the melt crystallizer described in Application Example 1. Except that the temperature of cooling tube 1 in step (1) is 19 °C and the cooling rate of cooling tube 1 in step (1) is 5 °C / h, the other process steps are the same as those in Application Example 1.

[0087] Application Example 7

[0088] This application example provides a method for preparing electronic-grade phosphoric acid using the melting crystallizer described in Application Example 1. Except that the cooling tube does not rotate in step (3), the remaining process steps are the same as those in Application Example 5.

[0089] Application Example 8

[0090] This application example provides a method for preparing electronic-grade phosphoric acid using the melting crystallizer described in Application Example 1. Except that the cooling rate of the double-layer crystallization shell 2 in step (2) is 0 °C / h, the remaining process steps are the same as those in Application Example 1.

[0091] Application Example 9

[0092] This application example provides a method for preparing electronic-grade phosphoric acid using the melting crystallizer described in Application Example 1. Except that the cooling rates of both the cooling tube 1 and the double-layer crystallization shell 2 in step (2) are 0 °C / h, the remaining process steps are the same as those in Application Example 1.

[0093] For the electronic-grade phosphoric acid obtained in Application Examples 1-9, the contents of impurities chromium, iron, and arsenic in the crystals were tested using ICP-MS (model iCAP-RQ), and the average growth rate of the phosphoric acid crystal layer was measured using a camera (model Canon EOS 90D). The results are shown in Table 1.

[0094] Table 1

[0095]

[0096] From the results in Table 1, it can be obtained that:

[0097] (1) From Application Examples 1-4, it can be seen that the present invention improves the melting crystallizer for preparing electronic-grade phosphoric acid by adding a frustum base under the cooling tube, connecting the double constant temperature baths to the crystallization shell and the cooling tube respectively, and setting the cooling tube as a rotating cooling tube. The whole device has a simple and reasonable structure, is easy to operate, can effectively improve production efficiency, has a moderate operating temperature, greatly reduces energy consumption, and prepares electronic-grade phosphoric acid.

[0098] (3) From the comparison between Application Examples 5 and 6 and Application Example 1, it can be seen that when the internal and external cooling are carried out simultaneously and a larger cooling rate is adopted, the crystal layer growth rate is fast. This shows that the temperature conditions and cooling rate of the internal and external double constant temperature pre-cooling and temperature control provided by the present invention are beneficial to the preparation of electronic-grade phosphoric acid, and the operating temperature range is moderate, greatly reducing energy consumption.

[0099] (4) From the comparison between Application Example 7 and Application Example 1, it can be seen that when the cooling tube does not rotate during heating and sweating, the purity of the prepared electronic-grade phosphoric acid is low. This shows that the temperature conditions, cooling rate of the internal and external double constant temperature pre-cooling and temperature control, and the rotatable sweating cooling tube provided by the present invention are beneficial to the preparation of electronic-grade phosphoric acid.

[0100] (5) As can be seen from the comparison between Application Example 8 and Application Example 1, when the external double-layer crystallization shell does not undergo slow cooling and only the cooling pipe is used for cooling, the purity of the prepared electronic-grade phosphoric acid is low and the growth rate is slow. This indicates that the internal and external double-cooling and temperature control settings provided by the present invention are conducive to increasing production efficiency and preparing electronic-grade phosphoric acid.

[0101] (6) As can be seen from the comparison between Application Example 9 and Application Example 1, when neither the internal and external cooling pipes nor the double-layer crystallization shell is cooled, the purity of the prepared electronic-grade phosphoric acid is low and the growth rate is slow. This indicates that the cooling conditions provided by the present invention are conducive to increasing production efficiency and preparing electronic-grade phosphoric acid.

[0102] In summary, the present invention improves the melt crystallizer for preparing electronic-grade phosphoric acid by adding a frustum base under the cooling pipe, connecting the double constant temperature baths to the crystallization shell and the cooling pipe respectively, and setting the cooling pipe as a rotating cooling pipe. The whole device has a simple and reasonable structure, is easy to operate, can effectively improve production efficiency, has a moderate operating temperature, greatly reduces energy consumption, and prepares electronic-grade phosphoric acid. By adding crystal seeds, cooling crystallization, and heating sweating, a purified electronic-grade phosphoric acid crystal layer is obtained, with a short production cycle and low energy consumption.

[0103] The applicant declares that the present invention uses the above embodiments to illustrate the detailed structural features of the present invention, but the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must rely on the above detailed structural features to be implemented. Those skilled in the art should understand that any improvement to the present invention, the equivalent replacement of the components selected by the present invention, the addition of auxiliary components, and the selection of specific methods, etc., all fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A method for preparing electronic-grade phosphoric acid using a melt crystallizer, characterized in that, The melt crystallizer includes a double-layer crystallization shell, a first constant-temperature bath and a second constant-temperature bath; A cooling pipe is arranged inside the double-layer crystallization shell, and a frustum base is arranged below the cooling pipe; The first constant-temperature bath is connected to the cooling pipe; The second constant-temperature bath is connected to the double-layer crystallization shell; The method includes the following steps: (1) Perform constant-temperature precooling treatment on the phosphoric acid melt to obtain precooled phosphoric acid; (2) Mix the seed crystal with the precooled phosphoric acid obtained in step (1), cool down and crystallize to obtain crude crystals; (3) Heat up and sweat the crude crystals obtained in step (2) to obtain electronic-grade phosphoric acid.

2. The method according to claim 1, characterized in that, A drain port is arranged below the double-layer crystallization shell.

3. The method according to claim 1, characterized in that, The cooling pipe includes a rotating cooling pipe.

4. The method according to claim 1, characterized in that The frustum base includes a perforated frustum base.

5. The method according to claim 1, characterized in that, The frustum base includes an arc-shaped frustum base.

6. The method according to claim 1, wherein The frustum base is externally connected to a speed control instrument.

7. The method according to claim 1, wherein The time of the constant-temperature precooling in step (1) is 30 - 60 min.

8. The method according to claim 1, wherein The temperature of the constant-temperature precooling in step (1) is 12 - 27 °C.

9. The method according to claim 1, characterized in that, The addition amount of the seed crystal in step (2) is 1 - 3 g.

10. The method according to claim 1, characterized in that, The seed crystal in step (2) includes a phosphoric acid seed crystal.

11. The method according to claim 1, characterized in that The cooling rate of the cooling and crystallization in step (2) is 1 - 8 °C / h.

12. The method according to claim 1, wherein The time of the cooling and crystallization in step (2) is 1 - 3 h.

13. The method according to claim 1, characterized in that, The temperature of the heating up and sweating in step (3) is 18 - 22 °C.

14. The method according to claim 1, wherein The time of the heating up and sweating in step (3) is 0.5 - 2 h.

15. The method according to claim 1, characterized in that The heating up and sweating in step (3) includes rotating heating up and sweating.

16. The method according to claim 15, characterized in that, The rotation speed of the rotating heating up and sweating is 20 - 40 r / min.

17. The method according to claim 1, characterized in that, The method includes the following steps: (1) Perform constant-temperature precooling on the phosphoric acid melt for 30 - 60 min at a temperature of 12 - 27 °C to obtain precooled phosphoric acid; (2) Mix the seed crystal with an addition amount of 1 - 3 g with the precooled phosphoric acid obtained in step (1), and perform cooling and crystallization at a rate of 1 - 8 °C / h to obtain crude crystals; (3) Heat up and sweat the crude crystals obtained in step (2) at a temperature of 18 - 22 °C for 0.5 - 2 h to obtain electronic-grade phosphoric acid.

18. An electronic-grade phosphoric acid, characterized in that, The electronic-grade phosphoric acid is prepared by the method according to any one of claims 1 - 17.

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