A method for producing high-purity phosphoric acid using a membrane process

Abstract

The present application relates to the technical field of phosphoric acid purification, and particularly relates to a method for producing high-purity phosphoric acid by using a membrane method, comprising the following steps: delivering raw water to a ceramic membrane system for filtration, and delivering the raw water to a ceramic membrane liquid production tank for buffering; sequentially arranging three nanofiltrations and ion exchange resins downstream of the ceramic membrane liquid production tank, and outputting filtrate to a storage tank after the filtrate sequentially passes through the three nanofiltrations and the ion exchange resins for adsorption; periodically detecting the mass fraction of phosphoric acid, the density of acid liquid and the temperature of acid liquid in each liquid production tank; determining whether the acid consistency of the filtrate in the liquid production tank meets preset conditions; if the acid consistency does not meet the preset conditions, determining that the current incoming liquid has abnormal doping, abnormal fluctuation or sensing distortion, so that the liquid production tank enters a re-measurement confirmation mode, and a homogeneous buffering mode or a temporary delivery mode is executed according to a re-measurement result. While stability is ensured, a higher purification effect can be achieved.

Description

Technical Field

[0001] This invention relates to the field of phosphoric acid purification technology, and in particular to a method for producing high-purity phosphoric acid using a membrane process. Background Technology

[0002] Wet-process phosphoric acid, as an important inorganic chemical raw material, has wide applications in various fields. With continuous technological advancements and social development, the market has set stricter standards for the purity of phosphoric acid. Therefore, how to further improve the purity of phosphoric acid, reduce energy consumption, and decrease pollutant emissions are challenges that technical personnel need to overcome. Currently, traditional wet-process phosphoric acid purification technologies include solvent extraction, chemical precipitation, crystallization, electrodialysis, and ion exchange. Solvent extraction requires simple equipment and has a mature process, but the extraction process can cause a certain degree of equipment corrosion, the extractant is flammable and explosive with a high loss rate, and it also produces residual acid as a byproduct. Furthermore, it has stringent installation requirements and high costs. Chemical precipitation cannot completely purify impurity ions and introduces new impurity ions. Solvent precipitation has low purification efficiency and recovery rate. Crystallization is cumbersome and requires strict operation. These shortcomings are the biggest challenges currently facing the deep purification of phosphoric acid.

[0003] Based on the aforementioned problems, physical methods for improving purity using nanofiltration have been developed. For example, in the prior art, Chinese Patent Publication No. CN103303885A discloses a phosphoric acid production process, including the following steps: ultrafiltration of a crude phosphoric acid solution to obtain a primary filtrate; nanofiltration of the primary filtrate to obtain a secondary filtrate and a secondary concentrate. The aforementioned process further purifies the crude phosphoric acid by subjecting it to ultrafiltration and nanofiltration.

[0004] For existing multi-stage filtration technologies, abnormal fluctuations, abnormal doping, or short-term measurement distortions that occur in the previous filtration stage can easily be transmitted to the next filtration stage through continuous transport, causing subsequent membrane stages to operate under incompatible conditions, resulting in unstable operation, increased pollution, or fluctuations in product quality. Summary of the Invention

[0005] Therefore, this invention provides a method for producing high-purity phosphoric acid using membrane technology. This addresses the problem in existing nanofiltration methods for phosphoric acid production, where abnormal fluctuations, abnormal doping, or short-term measurement distortions from the previous filtration stage can easily be transmitted to the next filtration stage through continuous transport. This causes subsequent membrane stages to operate under incompatible conditions, leading to unstable operation, increased contamination, or product quality fluctuations. This invention utilizes the inherent physical properties of phosphoric acid to accurately distinguish between genuine anomalies and detection distortions, avoiding erroneous control actions. While ensuring stable product quality, it also incorporates ion exchange to further enhance purity.

[0006] To achieve the above objectives, the present invention provides a method for producing high-purity phosphoric acid using a membrane process, comprising the following steps:

[0007] Raw water is pumped to a ceramic membrane system for filtration via a booster pump, and the resulting filtrate is then pumped to a ceramic membrane product tank for buffering. Downstream of the ceramic membrane product tank, three nanofiltration stages and an ion exchange resin are sequentially installed. The filtrate is then discharged to a storage tank after being adsorbed by the three nanofiltration stages and the ion exchange resin. Each nanofiltration stage includes a booster pump, a security filter, a high-pressure pump, a nanofiltration membrane, and a product tank connected in sequence.

[0008] The following dynamic control process is configured for the delivery of each product tank:

[0009] The phosphoric acid mass fraction, acid density, and acid temperature are periodically measured in each product tank. A reference density range is determined based on the phosphoric acid mass fraction and acid temperature. The acid phase consistency of the filtrate in the product tank is determined in conjunction with the acid density to see if it meets the preset conditions. If the acid phase consistency does not meet the preset conditions, it is determined that there is abnormal doping, abnormal fluctuation, or sensor distortion in the incoming liquid. The corresponding product tank is then controlled to enter the retest confirmation mode. The cause of non-compliance is determined based on the retest results, and the corresponding product tank is controlled to switch to homogenization buffer mode or temporarily suspend delivery mode.

[0010] Specifically, for the product tank corresponding to the third nanofiltration, the flow rate to the ion exchange resin is adjusted based on its ion distribution.

[0011] The steps to determine whether the acid phase consistency of the filtrate in the product tank meets the preset conditions include:

[0012] The corresponding baseline density range is determined based on the detected phosphoric acid mass fraction and acid solution temperature.

[0013] The detected acid density is compared with the reference density range;

[0014] When the acid density falls within the reference density range, it is determined that the acid phase consistency of the filtrate in the product tank meets the preset conditions.

[0015] When the acid density deviates from the reference density range, it is determined that the acid phase consistency of the filtrate in the product tank does not meet the preset conditions.

[0016] As a preferred technical solution for the method of producing high-purity phosphoric acid using membrane technology, the process of retesting and confirming the mode includes:

[0017] While maintaining the circulation and mixing within the corresponding product tank and temporarily suspending the delivery to the next stage, the phosphoric acid mass fraction, the acid density, and the acid temperature are repeatedly measured at least twice.

[0018] When repeated test results all indicate that the consistency of the acid phase does not meet the preset conditions, it is determined that there is abnormal doping or abnormal fluctuation in the current liquid.

[0019] When at least one repeated detection result indicates that the acid phase consistency recovery meets the preset conditions, it is determined that there is sensing distortion in the current liquid.

[0020] As a preferred technical solution for producing high-purity phosphoric acid using membrane technology, when the acid phase consistency does not meet preset conditions and the deviation of the acid solution density from the reference density range shows a decreasing trend, it is determined that there is an abnormal fluctuation, and the corresponding product tank is controlled to enter the homogenization buffer mode.

[0021] The homogenization buffer mode includes maintaining the circulating mixing in the product tank and controlling the next stage to take liquid at an output slope that is less than the rate of change of the incoming liquid of the previous stage, so that the fluctuating load of the previous stage is buffered by the corresponding product tank before being delivered to the next stage.

[0022] As a preferred technical solution for producing high-purity phosphoric acid using membrane technology, if the acid phase consistency does not meet the preset conditions and the deviation of the acid liquid density from the reference density range shows an increasing trend, it is determined that there is abnormal doping, and the corresponding product tank is controlled to enter the temporarily suspended feeding mode.

[0023] As a preferred technical solution for the method of producing high-purity phosphoric acid using membrane technology, the temporary suspension mode includes reducing or stopping the liquid intake flow rate of the next stage, maintaining the circulation in the current product tank, and resuming delivery to the next stage after the acid phase consistency is restored to meet the preset conditions.

[0024] As a preferred technical solution for the production of high-purity phosphoric acid using membrane technology,

[0025] For the product tank corresponding to the third nanofiltration, after confirming that the acid phase consistency of the filtrate in the product tank meets the preset conditions, the distribution of residual polyvalent metal ion load and alkali metal ion load in the product is detected.

[0026] As a preferred technical solution for the production of high-purity phosphoric acid using membrane technology,

[0027] The distribution of residual polyvalent metal ion load and alkali metal ion load in the product solution is compared with the preset resin protection window.

[0028] When the distribution of residual polyvalent metal ion load and alkali metal ion load in the product solution falls within the resin protection window, the product solution is determined to meet the inlet conditions of the ion exchange resin.

[0029] When the distribution of residual polyvalent metal ion load and alkali metal ion load in the product solution exceeds the resin protection window, the product solution is determined to not meet the inlet conditions of the ion exchange resin.

[0030] As a preferred technical solution for the production of high-purity phosphoric acid using membrane technology,

[0031] When the third nanofiltration product does not meet the inlet conditions of the ion exchange resin, the corresponding product tank is controlled to enter the resin protection mode.

[0032] The resin protection mode includes reducing the flow rate to the ion exchange resin;

[0033] When the acid phase consistency is restored to meet the preset conditions and the distribution of residual polyvalent metal ion load and alkali metal ion load in the product liquid falls within the resin protection window, the flow rate to the ion exchange resin is restored.

[0034] Compared with the prior art, the beneficial effect of the present invention is that it combines membrane method and ion exchange process to achieve a high purification effect. The purified phosphoric acid can meet the quality requirements of food grade and electronic grade phosphoric acid, while not generating secondary pollution.

[0035] In particular, under specific purification process conditions, the phosphoric acid mass fraction, acid density, and acid temperature are not isolated parameters but rather exhibit corresponding physical property relationships. Therefore, this method utilizes the inherent physical properties of the phosphoric acid system to verify the consistency of the filtrate state within the product tank. It determines whether the phosphoric acid mass fraction should correspond to the current density at the current temperature; if the correspondence is disrupted, further analysis can be conducted to determine whether the anomaly originates from the actual incoming liquid or from sensor distortion.

[0036] In particular, this method considers that the operating state of the ion adsorption resin depends not only on the absolute concentration of a single ion, but also on the competitive environment formed by different ions. Therefore, an acceptable competitive occupancy state for the resin is set for the third nanofiltration product. Consequently, the triggering of the resin protection mode is no longer triggered by a single parameter exceeding the limit. Instead, given confirmed acid phase consistency, the method determines whether to limit the flow to protect and better utilize the ion adsorption resin, based on the matching relationship between the ion distribution and the resin protection window, further ensuring process stability. Attached Figure Description

[0037] The accompanying drawings are provided to further understand the technical solutions of the present invention and constitute a part of the specification. They are used together with the embodiments of the present invention to explain the technical solutions of the present invention, and do not constitute a limitation on the technical solutions of the present invention.

[0038] Figure 1 This is a flowchart illustrating a method for producing high-purity phosphoric acid using a membrane process, as described in an embodiment of the present invention.

[0039] Figure 2This is a schematic diagram of the application equipment and basic purification process in an embodiment of the present invention;

[0040] Figure 3 This is a flowchart illustrating the dynamic control process in an embodiment of the present invention. Detailed Implementation

[0041] To make the objectives and advantages of the present invention clearer, the present invention will be further described below with reference to embodiments; it should be understood that the specific embodiments described herein are merely for explaining the present invention and are not intended to limit the present invention.

[0042] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0043] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0044] Please see Figure 2 As shown, to facilitate understanding of the present invention, this embodiment first describes the application equipment and basic purification process of the method for producing high-purity phosphoric acid using membrane technology.

[0045] The application equipment includes raw water tanks, booster pumps, ceramic membrane systems, ceramic membrane product tanks, first-stage nanofiltration (NF) booster pumps, security filters, first-stage NF high-pressure pumps, first-stage NF systems, first-stage NF product tanks, second-stage NF booster pumps, security filters, second-stage NF high-pressure pumps, second-stage NF systems, second-stage NF product tanks, third-stage NF booster pumps, security filters, third-stage NF high-pressure pumps, third-stage NF systems, third-stage NF product tanks, ion exchange resins, purification devices, and purification storage tanks.

[0046] A raw water tank is installed before the booster pump to buffer and homogenize the incoming phosphoric acid mixture, ensuring more stable acid input to subsequent equipment. A booster pump is installed before the ceramic membrane filtration unit to provide power and pressurize it, ensuring better permeation of the phosphoric acid solution. A ceramic membrane filtration system is installed between the booster pump and the ceramic membrane product tank. After initial treatment, its tiny pores intercept impurities in the mixed phosphoric acid solution, preventing fouling of the downstream nanofiltration membrane. A ceramic membrane product tank is installed after the ceramic membrane system, primarily for buffering the incoming solution and ensuring more stable operation of subsequent equipment. A first-stage NF booster pump is installed after the ceramic membrane product tank to provide power and pressurize the nanofiltration unit.

[0047] A security filter, a first-stage NF high-pressure pump, and a first-stage NF system are installed after the first-stage NF booster pump. This system primarily utilizes the characteristics of nanofiltration membrane elements to remove Ca from the phosphoric acid solution. 2+ Mg 2+ Fe 3+ Al 3+ To achieve preliminary purification, divalent and higher-valent polyvalent ions are used.

[0048] A security filter, a secondary NF high-pressure pump, and a secondary NF system are installed after the secondary NF booster pump. This primarily utilizes the characteristics of nanofiltration membrane elements to further remove calcium from the phosphoric acid solution based on these characteristics. 2+ Mg 2+ Fe 3+ Al 3+ To further purify the ions, including divalent and higher-valent ions.

[0049] A security filter, a three-stage NF high-pressure pump, and a three-stage NF system are installed after the three-stage NF booster pump. This is mainly to utilize the characteristics of nanofiltration membrane elements to remove trace ions and impurities that still exist in the phosphoric acid solution.

[0050] Each stage of the NF system is equipped with a product tank, which originally only served the purpose of storage and transportation, but in this embodiment it is also used for the analysis and control of purification stability.

[0051] A multi-stage series ion exchange resin device is installed after the three-stage NF product tank. Special adsorbents are used to adsorb trace amounts of divalent and higher-valent ions in the phosphoric acid solution that have not been retained by nanofiltration, as well as monovalent ions present in the solution, ultimately yielding high-purity phosphoric acid that meets the product requirements for food-grade or electronic-grade phosphoric acid.

[0052] The purification storage tank is set up at the terminal mainly for storing purified phosphoric acid.

[0053] Based on the above embodiments, please refer to Figure 1As shown, this embodiment provides a method for producing high-purity phosphoric acid using a membrane process, comprising the following steps:

[0054] Step S1: Raw water is transported to the ceramic membrane system for filtration by a booster pump, and the resulting filtrate is transported to the ceramic membrane product tank for buffering.

[0055] Step S2: A multi-stage nanofiltration and ion exchange resin are sequentially installed downstream of the ceramic membrane product tank. The filtrate is output to the storage tank after passing through three nanofiltration and ion exchange resin adsorption stages in sequence. Each nanofiltration stage includes a booster pump, a security filter, a high-pressure pump, a nanofiltration membrane, and a product tank connected in sequence.

[0056] See Figure 3 As shown, in this embodiment, to improve the stability of the purification process, the following dynamic control process is configured for the delivery of the product liquid tank:

[0057] Step S01: Periodically check the phosphoric acid mass fraction, acid density, and acid temperature in each product tank;

[0058] Step S02: Determine the baseline density range based on the phosphoric acid mass fraction and acid solution temperature, and determine whether the acid phase consistency of the filtrate in the product tank meets the preset conditions based on the acid solution density.

[0059] Step S03: If the acid phase consistency does not meet the preset conditions, it is determined that the incoming liquid has abnormal doping, abnormal fluctuations, or sensor distortion. The product tank then enters a retest confirmation mode. Based on the retest results, the cause of the non-compliance is determined, and the corresponding product tank is controlled to switch to homogenization buffer mode or temporarily halt delivery mode. In detail, the principle behind the dynamic control process is that the phosphoric acid solution in each product tank is not merely an intermediate storage solution, but rather a state determination node before the results of the previous stage are delivered to the next stage. By correlating and detecting the phosphoric acid mass fraction, acid density, and acid temperature at the state determination node, liquid states unsuitable for continued delivery can be identified before the next stage of liquid extraction, thus preventing abnormal states from directly entering the next processing unit.

[0060] This allows the product tank to not only serve as a buffer volume but also as a pre-transport verification function, thereby improving the continuous stability of the multi-stage membrane separation and resin adsorption process.

[0061] In detail, the steps to determine whether the acid phase consistency of the filtrate in the product tank meets the preset conditions include:

[0062] The corresponding baseline density range is determined based on the detected phosphoric acid mass fraction and acid solution temperature.

[0063] The detected acid density is compared with the baseline density range;

[0064] When the acid density falls within the reference density range, it is determined that the acid phase consistency of the filtrate in the product tank meets the preset conditions.

[0065] When the acid density deviates from the baseline density range, it is determined that the acid phase consistency of the filtrate in the product tank does not meet the preset conditions.

[0066] In some embodiments, the baseline density range is determined based on a pre-established correspondence between phosphoric acid mass fraction, acid solution temperature, and acid solution density. Specifically, multiple phosphoric acid mass fraction ranges and multiple temperature ranges that may occur during the target production process can be selected, and the density of the standard phosphoric acid solution can be calibrated to form a correspondence table, a correspondence curve, or a fitting model. Based on the detection deviation range under historical stable operating conditions, a baseline density range is formed by expanding both sides of the theoretical density value.

[0067] Preferably, the reference density range is not fixed, but can be preset in stages according to the product requirements of different purity levels, the allowable fluctuation range of feed liquid in different processes, and the location of different product tanks. For product tanks close to the upstream membrane separation, the reference density range can be appropriately widened to take into account the objective existence of feed liquid fluctuations; for product tanks corresponding to the third nanofiltration, the reference density range can be appropriately narrowed to improve the accuracy of state determination before entering the ion exchange resin.

[0068] The purpose of this setting is to move away from using a single density value as the sole criterion for judgment, and instead use the allowable density range that matches the current phosphoric acid mass fraction and acid solution temperature as the basis for judgment. This is more in line with the actual physical properties of the phosphoric acid system and improves the accuracy of acid phase consistency determination.

[0069] Specifically, the process of retesting and confirming the mode includes:

[0070] While maintaining the circulation and mixing within the corresponding product tank and temporarily suspending the transfer to the next stage, the phosphoric acid mass fraction, acid density, and acid temperature are measured at least twice.

[0071] When repeated test results all indicate that the acid phase consistency does not meet the preset conditions, it is determined that there is abnormal doping or abnormal fluctuation in the current liquid.

[0072] When at least one repeated test result indicates that the acid phase consistency has recovered to meet the preset conditions, it is determined that there is a sensing distortion in the current liquid. Specifically, if the acid phase consistency anomaly originates from actual abnormal doping or abnormal fluctuations, the corresponding anomaly will usually be persistent during repeated tests within a short period; however, if the acid phase consistency anomaly originates from sensing distortion, at least some of the test values ​​will return to a range consistent with the current phosphoric acid mass fraction and temperature after repeated tests. By setting a retest confirmation mode, unnecessary control actions caused by directly executing flow reduction, shutdown, or long-term buffering based on a single anomaly detection can be avoided, thereby improving the decision-making reliability of the dynamic control process.

[0073] When the acid phase consistency does not meet the preset conditions and the deviation of the acid density from the reference density range shows a decreasing trend, it is determined that there is an abnormal fluctuation, and the corresponding product tank is controlled to enter the homogenization buffer mode.

[0074] The homogenization and buffering mode involves maintaining the circulating mixing within the product tank and controlling the next stage to draw liquid at an output slope that is less than the rate of change of the incoming liquid from the previous stage. This ensures that the fluctuating load of the previous stage is buffered by the corresponding product tank before being delivered to the next stage. "The next stage draws liquid at an output slope that is less than the rate of change of the incoming liquid from the previous stage" means that the rate of change of the liquid flow rate in the next stage is less than the rate of change of the flow rate entering the current product tank from the previous stage, or that the rate of change of the concentration load in the next stage is less than the rate of change of the concentration load at the inlet side of the current product tank.

[0075] When the acid phase consistency does not meet the preset conditions and the deviation of the acid solution density from the reference density range shows an increasing trend, it is determined that abnormal doping exists, and the corresponding product tank is controlled to enter a suspended feed mode. The deviation can be characterized as the distance between the acid solution density and the boundary of the reference density range.

[0076] The temporary suspension mode includes reducing or stopping the liquid intake flow rate of the corresponding booster pump in the next stage, maintaining the circulation within the current product tank, and resuming delivery to the next stage after the acid phase consistency returns to the preset conditions. It should be understood that "upper stage" and "next stage" refer to each nanofiltration and resin adsorption cycle; a single nanofiltration cycle counts as one stage, and resin adsorption counts as one stage.

[0077] To further ensure stability, for the product tank corresponding to the third nanofiltration, after confirming that the acid phase consistency of the filtrate in the product tank meets the preset conditions, the distribution of residual polyvalent metal ion load and alkali metal ion load in the product is also periodically detected.

[0078] The distribution of residual multivalent metal ion load and alkali metal ion load in the product solution was compared with the preset resin protection window.

[0079] When the distribution of residual polyvalent metal ion load and alkali metal ion load in the product solution falls within the resin protection window, the product solution is deemed to meet the inlet conditions of the ion exchange resin.

[0080] When the distribution of residual polyvalent metal ion load and alkali metal ion load in the product solution exceeds the resin protection window, the product solution is deemed not to meet the inlet conditions of the ion exchange resin.

[0081] When the third nanofiltration product does not meet the inlet conditions of the ion exchange resin, the corresponding product tank is controlled to enter the resin protection mode.

[0082] Resin protection modes include reducing the flow rate to the ion exchange resin;

[0083] When the acid phase consistency is restored to meet the preset conditions and the distribution of residual polyvalent metal ion load and alkali metal ion load in the product solution falls within the resin protection window, the flow rate to the ion exchange resin is restored.

[0084] In the above embodiments, before the third nanofiltration product enters the ion exchange resin, the resin faces not a single ionic component, but a competitive adsorption environment composed of residual polyvalent metal ions and alkali metal ions. Different ions have different occupancy tendencies on the resin's active sites. If the concentration of a single ion is used as the sole criterion for deciding whether to allow it to enter the resin, it is difficult to accurately reflect the actual adsorption load at the resin inlet. If, in resin protection mode, the filtrate accumulates to the upper limit of the product tank but still does not reach the resin protection window, the flow rate to the ion exchange resin is restored. Once the standard volume of the product tank (e.g., 50% of the upper limit) is reached, the resin protection mode is re-entered to ensure smooth delivery. This setup reduces the risk of premature occupancy, premature penetration, or decreased polishing capacity of the resin due to unreasonable inlet load.

[0085] In implementation, the resin protection window is preset based on the resin type, effective exchange capacity of the resin bed, purity level of the target product, and the ionic composition range of the third nanofiltration product under historical stable operation phases. Preferably, the combination state of residual polyvalent metal ion load and alkali metal ion load in the third nanofiltration product is first recorded under stable production conditions over multiple cycles. Combined with the ion penetration before and after the resin bed, the composition range of each ion corresponding to the stable adsorption operation range of the resin is determined, and this range is used as the resin protection window.

[0086] For example, the stock solution used in this embodiment (a low-quality phosphoric acid solution produced by the wet-process phosphoric acid process) has the following specifications as shown in Table 1:

[0087] Table 1. Quality of the original solution

[0088]

[0089] A ceramic membrane filtration system is installed between the booster pump and the ceramic membrane product tank. After preliminary treatment at the front end, the system intercepts impurities in the mixed phosphoric acid solution through its tiny pores, preventing fouling of the downstream nanofiltration membrane.

[0090] The water quality data after filtration by the ceramic membrane filtration device is shown in Table 2.

[0091] Table 2. Liquid production indicators of ceramic membrane filtration device

[0092]

[0093] A security filter, a first-stage NF high-pressure pump, and a first-stage NF system are installed after the first-stage NF booster pump. This system primarily utilizes the characteristics of nanofiltration membrane elements to remove Ca from the phosphoric acid solution. 2+ Mg 2+ Fe 3+ Al 3+ For divalent and higher-valent polyvalent ions, based on experimental data, using Ca... 2+ Taking ions as an example, under acidic conditions, the corresponding ion removal rate is as high as 97% or more. The indicators after treatment by the first-stage NF membrane device are shown in Table 3.

[0094] Table 3. Product parameters of the first-stage NF unit (Ca) 2+ )

[0095]

[0096] A security filter, a secondary NF high-pressure pump, and a secondary NF system are installed after the secondary NF booster pump. This primarily utilizes the characteristics of nanofiltration membrane elements to further remove calcium from the phosphoric acid solution based on these characteristics. 2+ Mg 2+ Fe 3+ Al 3+ For divalent and higher-valent polyvalent ions, based on experimental data, using Ca... 2+ Taking ions as an example, under acidic conditions, the ion removal rate of the secondary nanofiltration is as high as 90% or more. The indicators after treatment by the secondary NF membrane device are shown in Table 4.

[0097] Table 4. Product parameters of the secondary NF unit (Ca) 2+ )

[0098]

[0099] A security filter, a three-stage NF high-pressure pump, and a three-stage NF system are installed after the three-stage NF booster pump. This primarily utilizes the characteristics of nanofiltration membrane elements to remove trace ions and impurities remaining in the phosphoric acid solution. Based on experimental data, using Ca... 2+ Taking ions as an example, under acidic conditions, the ion removal rate of the secondary nanofiltration is as high as 90% or more. The indicators after treatment by the tertiary NF membrane device are shown in Table 5.

[0100] Table 5. Product parameters of the third-stage NF unit (Ca) 2+ )

[0101]

[0102] A multi-stage ion exchange resin device is installed after the three-stage NF product tank, using a special adsorbent to adsorb trace amounts of divalent and higher-valent ions (as shown in Table 6) in the phosphoric acid solution that were not retained by nanofiltration, as well as monovalent Na present in the solution. + The ions (as shown in Table 7) are used to obtain high-purity phosphoric acid, which meets the cation requirements for food-grade or electronic-grade phosphoric acid.

[0103] Table 6. Ion Exchange Resin Product Index (Ca) 2+ )

[0104]

[0105] Table 7. Ion Exchange Resin Product Index (Na) + )

[0106]

[0107] In this example, when the acid solution temperature is 20℃, the baseline density value corresponding to the filtrate with a phosphoric acid mass fraction of 29% can be preset to approximately 1.174 g / cm3, and the corresponding baseline density range can be set to 1.171~1.177 g / cm3; the baseline density value corresponding to the filtrate with a phosphoric acid mass fraction of 30% can be preset to approximately 1.181 g / cm3, and the corresponding baseline density range can be set to 1.178~1.184 g / cm3.

[0108] When the acid solution temperature is 25℃, the baseline density value corresponding to the filtrate with a phosphoric acid mass fraction of 29% can be preset to approximately 1.172 g / cm3, and the corresponding baseline density range can be set to 1.169~1.175 g / cm3; the baseline density value corresponding to the filtrate with a phosphoric acid mass fraction of 30% can be preset to approximately 1.179 g / cm3, and the corresponding baseline density range can be set to 1.176~1.182 g / cm3.

[0109] When the acid solution temperature is 30℃, the baseline density value corresponding to the filtrate with a phosphoric acid mass fraction of 29% can be preset to approximately 1.169 g / cm3, and the corresponding baseline density range can be set to 1.166~1.172 g / cm3; the baseline density value corresponding to the filtrate with a phosphoric acid mass fraction of 30% can be preset to approximately 1.176 g / cm3, and the corresponding baseline density range can be set to 1.173~1.179 g / cm3.

[0110] In this example, the resin protection window is Ca. 2+ It is 8–10 mg / L, Na + The concentration is 400–530 mg / L.

[0111] Under the premise of using membrane technology to produce high-purity phosphoric acid for the above-mentioned raw materials, the failure rate of the same equipment is significantly reduced, and the service life of the resin and nanofiltration membrane is also improved.

[0112] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the scope of protection of the present invention.

[0113] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention; various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for producing high-purity phosphoric acid using a membrane process, comprising: Raw water is transported to a ceramic membrane system for filtration via a booster pump, and the resulting filtrate is then transported to a ceramic membrane product tank for buffering. Downstream of the ceramic membrane product tank, three nanofiltration and ion exchange resins are sequentially installed. After the filtrate passes through the three nanofiltration and ion exchange resins for adsorption, it is output to a storage tank. Each nanofiltration process includes a booster pump, a security filter, a high-pressure pump, a nanofiltration membrane, and a product tank connected in sequence. Its characteristic is that the following dynamic control process is configured for the delivery of each product tank: The mass fraction of phosphoric acid, the density of acid solution, and the temperature of acid solution were periodically measured in each product tank. The baseline density range is determined based on the phosphoric acid mass fraction and acid solution temperature. The acid phase consistency of the filtrate in the product tank is then determined based on the acid solution density to see if it meets the preset conditions. If the acid phase consistency does not meet the preset conditions, it is determined that there is abnormal doping, abnormal fluctuation or sensor distortion in the incoming liquid. The corresponding product tank is controlled to enter the retest confirmation mode. The reason for non-compliance is determined according to the retest result, and the corresponding product tank is controlled to switch to homogenization buffer mode or temporarily suspend delivery mode. For the product tank corresponding to the third nanofiltration, the flow rate to the ion exchange resin is reduced based on its ion distribution. The steps to determine whether the acid phase consistency of the filtrate in the product tank meets the preset conditions include: The corresponding baseline density range is determined based on the detected phosphoric acid mass fraction and acid solution temperature. The detected acid density is compared with the reference density range; When the acid density falls within the reference density range, it is determined that the acid phase consistency of the filtrate in the product tank meets the preset conditions. When the acid density deviates from the reference density range, it is determined that the acid phase consistency of the filtrate in the product tank does not meet the preset conditions. When the acid phase consistency does not meet the preset conditions and the deviation of the acid liquid density from the reference density range shows a decreasing trend, it is determined that there is an abnormal fluctuation. The corresponding product tank is controlled to enter the homogenization buffer mode, including: maintaining the circulating mixing in the product tank, and controlling the next stage to take liquid at an output slope that is less than the liquid change rate of the previous stage, so that the fluctuation load of the previous stage is buffered by the corresponding product tank before being delivered to the next stage. If the acid phase consistency does not meet the preset conditions and the deviation of the acid liquid density from the reference density range shows an increasing trend, it is determined that there is abnormal doping, and the corresponding product tank is controlled to enter the temporary feeding mode, including: reducing or stopping the liquid extraction flow rate of the next level, maintaining the circulation in the current product tank, and resuming feeding to the next level after the acid phase consistency recovers to meet the preset conditions.

2. The method for producing high-purity phosphoric acid using a membrane process according to claim 1, characterized in that, The process of retesting and confirming the mode includes: While maintaining the circulation and mixing within the corresponding product tank and temporarily suspending the delivery to the next stage, the phosphoric acid mass fraction, the acid density, and the acid temperature are repeatedly measured at least twice. When repeated test results all indicate that the consistency of the acid phase does not meet the preset conditions, it is determined that there is abnormal doping or abnormal fluctuation in the current liquid. When at least one repeated detection result indicates that the acid phase consistency meets the preset conditions, it is determined that there is sensing distortion in the current liquid.

3. The method for producing high-purity phosphoric acid using a membrane process according to claim 1, characterized in that, For the product tank corresponding to the third nanofiltration, after confirming that the acid phase consistency of the filtrate in the product tank meets the preset conditions, the distribution of residual polyvalent metal ion load and alkali metal ion load in the product is detected.

4. The method for producing high-purity phosphoric acid using a membrane process according to claim 3, characterized in that, The distribution of residual polyvalent metal ion load and alkali metal ion load in the product solution is compared with the preset resin protection window. When the distribution of residual polyvalent metal ion load and alkali metal ion load in the product solution falls within the resin protection window, the product solution is determined to meet the inlet conditions of the ion exchange resin. When the distribution of residual polyvalent metal ion load and alkali metal ion load in the product solution exceeds the resin protection window, the product solution is determined to not meet the inlet conditions of the ion exchange resin.

5. The method for producing high-purity phosphoric acid using a membrane process according to claim 4, characterized in that, When the third nanofiltration product does not meet the inlet conditions of the ion exchange resin, the corresponding product tank is controlled to enter the resin protection mode. The resin protection mode includes reducing the flow rate to the ion exchange resin; When the acid phase consistency is restored to meet the preset conditions and the distribution of residual polyvalent metal ion load and alkali metal ion load in the product liquid falls within the resin protection window, the flow rate to the ion exchange resin is restored.

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