Preparation method of food-grade phosphoric acid

Abstract

The invention relates to the technical field of preparation of food-grade phosphoric acid, in particular to a preparation method of food-grade phosphoric acid. The method comprises the following steps: extracting an industrial-grade phosphoric acid solution by using tributyl phosphate to obtain an organic phase containing phosphoric acid; carrying out arsenic removal reaction on the organic phase and phosphorus pentasulfide, and filtering to obtain an arsenic-removed phosphoric acid solution; under the condition that nitrogen is introduced, active diatomite is used for carrying out a defluorination reaction on the arsenic-removed phosphoric acid solution, and a defluorinated phosphoric acid solution is obtained; performing a readily oxidizable substance removal reaction on the defluorinated phosphoric acid solution by using nitrogen and an oxidizing agent to obtain a readily oxidizable substance removal phosphoric acid solution; carrying out desulfurization reaction on the readily oxidizable oxide-removed phosphoric acid solution by using a desulfurizing agent, and filtering to obtain a desulfurized phosphoric acid solution; carrying out aging treatment, filtration and back extraction on the desulfurized phosphoric acid solution to obtain a clear phosphoric acid solution; and performing ultrafiltration and nanofiltration on the clarified phosphoric acid solution to obtain the food-grade phosphoric acid solution. According to the preparation method, the impurity removal effect of the food-grade phosphoric acid product can be improved on the premise of low cost through a series of technologies.

Description

Technical Field

[0001] The present application relates to the technical field of food-grade phosphoric acid preparation, and in particular to a method for preparing food-grade phosphoric acid. Background Art

[0002] Food additives have become an indispensable and important raw material for improving the color, aroma and taste of food, and are one of the most widely used food additives in the current food industry. In food processing, food-grade phosphoric acid can not only improve the organizational structure and taste of food, but also can be used as an acidulant, mineral nutrition enhancer, etc. At present, the production of food-grade phosphoric acid is mainly carried out through the wet phosphoric acid process, and the wet phosphoric acid process mainly uses industrial-grade phosphoric acid as a raw material. Most of these industrial-grade phosphoric acids are industrial-grade phosphoric acid products formed by the hydrochloric acid method using hydrochloric acid and medium- and low-grade phosphate rock as raw materials. Due to the different types of medium- and low-grade phosphoric acid raw materials used, food-grade phosphoric acid contains many impurities, which mainly include silicon carbide, arsenic, fluorine and sulfur. In addition, some food-grade phosphoric acid products will also contain easily oxidized substances such as phosphorous acid and hypophosphorous acid. These easily oxidized substances will form highly toxic phosphine when heated, affecting the safety of food-grade phosphoric acid products.

[0003] For food-grade phosphoric acid products, the weight content of harmful substances such as arsenic, fluorine, sulfur, and oxidizable substances needs to be strictly controlled to meet its usage scenarios. However, in the stage of removing arsenic from food-grade phosphoric acid products, sodium sulfide or phosphorus pentasulfide products will be introduced into the food-grade phosphoric acid products, which will undoubtedly increase the desulfurization pressure of food-grade phosphoric acid products. In addition, in order to promote the thorough dearsenicization reaction, heating will be carried out in the dearsenicization stage, which will undoubtedly cause the oxidizable substances to be converted into highly toxic phosphine, affecting the safety of the final food-grade phosphoric acid. Traditional methods for removing these harmful substances from food-grade phosphoric acid products include: solvent extraction, chemical precipitation, solvent precipitation, crystallization, electrodialysis, ion exchange, etc., but these methods are either costly to use or require a harsh separation environment. Therefore, it is urgent to develop a new purification process for food-grade phosphoric acid products.

[0004] At present, the impurities of food-grade phosphoric acid products can be removed by using ultrafiltration membranes in combination with nanofiltration membranes, so that the impurity removal efficiency of food-grade phosphoric acid is about 90%. However, due to the limited processing capacity of ultrafiltration membranes and nanofiltration membranes and the high quality requirements for industrial-grade phosphoric acid, it is necessary to pre-treat the impurities of industrial-grade phosphoric acid first, which undoubtedly increases the cost and energy consumption of the impurity removal stage; in addition, it is difficult to remove arsenic at one time by simply using membrane separation, and multiple arsenic removal treatments are required, which further increases the energy consumption and power of the removal stage. And the final arsenic removal efficiency is below 90%, which is difficult to meet the use requirements of high-purity food-grade phosphoric acid products. Summary of the invention

[0005] The present application provides a method for preparing food-grade phosphoric acid to solve the following technical problem: how to improve the effect of removing impurities from food-grade phosphoric acid products under the premise of low cost and energy consumption.

[0006] In a first aspect, an embodiment of the present application provides a method for preparing food-grade phosphoric acid, the method comprising: The industrial-grade phosphoric acid solution is extracted using tributyl phosphate to obtain an organic phase containing phosphoric acid; The organic phase containing phosphoric acid and phosphorus pentasulfide are subjected to a dearsenification reaction and filtered to obtain a dearsenified phosphoric acid solution; The dearsenicized phosphoric acid solution is subjected to a defluorination reaction using activated diatomaceous earth under the condition of nitrogen gas passing to obtain a defluorinated phosphoric acid solution; Using nitrogen and an oxidant to carry out a deoxidation reaction on the defluorinated phosphoric acid solution to obtain a deoxidation phosphoric acid solution; The deoxidized phosphoric acid solution is subjected to a desulfurization reaction and filtered using a desulfurizing agent under the condition of nitrogen gas flow to obtain a desulfurized phosphoric acid solution; The desulfurized phosphoric acid solution is subjected to aging treatment, filtering and stripping to obtain a clarified phosphoric acid solution; The clear phosphoric acid solution is subjected to ultrafiltration and nanofiltration to obtain a food-grade phosphoric acid solution.

[0007] Optionally, the temperature of the arsenic removal reaction is 75° C. to 85° C., and the time of the arsenic removal reaction is ≥15 min; and / or The temperature of the deoxidation reaction is 55°C to 70°C, and the time of the deoxidation reaction is 4.5h to 5.5h; and / or The temperature of the desulfurization reaction is 30° C. to 40° C., and the time of the desulfurization reaction is 60 min to 90 min.

[0008] Optionally, the mass m1 of the phosphorus pentasulfide and the mass m2 of the organic phase satisfy the relationship: m1:m2=(5-10):100; and / or The oxidant comprises hydrogen peroxide, and the volume V1 of the hydrogen peroxide and the volume V2 of the dearsenicated phosphoric acid solution satisfy the relationship: V1:V2≥1:60; and / or The desulfurizing agent includes barium carbonate, and the mass m3 of the barium carbonate and the mass m4 of the deoxidized phosphoric acid solution satisfy the relationship: m3=0.08%×m4×197.35 / 96×Q, In the formula, 197.35 is the relative molecular mass of barium carbonate, 96 is the relative molecular mass of sulfate ion, Q is the ratio of m3 to the theoretical addition amount M of barium carbonate, and Q is 1.0 to 1.4.

[0009] Optionally, the defluorinating reaction of the dearsenicated phosphoric acid solution using activated diatomaceous earth under nitrogen flow to obtain a defluorinated phosphoric acid solution comprises the steps of: The dearsenicated phosphoric acid solution is washed with a dilute alkaline solution to obtain a primary defluorinated phosphoric acid solution; The primary defluorinated phosphoric acid solution is vacuum concentrated using activated diatomaceous earth to obtain a secondary defluorinated phosphoric acid mixture; The secondary defluorinated phosphoric acid mixture is stripped using saturated steam under nitrogen flow to obtain a defluorinated phosphoric acid mixture.

[0010] Optionally, the temperature of the vacuum concentration is 85°C to 95°C, the pressure of the vacuum concentration is 0.08MPa to 0.09MPa, and the time of the vacuum concentration is 1.5h to 2.5h; and / or The stripping temperature is 85°C to 95°C, and the stripping time is 2.0h to 3.0h.

[0011] Optionally, the nitrogen gas has an introduction flow rate of 0.5 L / min to 1.5 L / min, and the nitrogen gas is introduced by bottom blowing and bubbling.

[0012] Optionally, the temperature of the saturated steam is 90° C. to 95° C., and the flow rate of the saturated steam is 1.0 L / min to 2.0 L / min.

[0013] Optionally, the mass m5 of the activated diatomaceous earth and the mass m6 of fluorine in the primary defluorinated phosphoric acid solution satisfy the relationship: m5:m6=(2.0-3.0):1.

[0014] Optionally, the aging treatment time is 8h to 12h; and / or The volume of the stripping solution used in the stripping is twice the volume of the desulfurized phosphoric acid solution.

[0015] Optionally, the porosity of the ultrafiltration membrane used in the ultrafiltration is ≥50%; and / or The molecular weight cut-off of the nanofiltration membrane used in the nanofiltration is 150Da to 200Da.

[0016] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art: The present application provides a method for preparing food-grade phosphoric acid. The method first uses tributyl phosphate as an extractant to extract the phosphoric acid component of an industrial-grade phosphoric acid solution into an organic phase to facilitate the subsequent impurity removal reaction; then phosphorus pentasulfide is used as a reducing agent to form hydrogen sulfide gas from phosphoric acid. The formed hydrogen sulfide gas can convert the arsenic element in the organic phase into arsenic slag, and the arsenic impurities can be separated from the phosphoric acid solution by filtering; then, under the action of nitrogen, the hydrophobic interface of the organic phase cooperates with the nitrogen bubbles to convert the fluorine element in the phosphoric acid solution into gaseous silicon fluoride, thereby achieving the removal of the fluorine element in the phosphoric acid solution; in addition, the combined action of nitrogen and an oxidant is used to convert the easily oxidized substances (phosphorous acid and hypophosphorous acid) into phosphoric acid and the aforementioned residual hydrogen sulfide into sulfate ions, thereby reducing phosphorus. The content of easily oxidized substances in the acid solution; in addition, when nitrogen is introduced, the desulfurizer can fully react with the sulfate ions in the phosphoric acid solution to finally obtain a pure phosphoric acid solution; finally, the various impurity components of the phosphoric acid solution are fully reacted through aging treatment to further obtain a pure phosphoric acid solution; then, ultrafiltration and nanofiltration are used to further remove the impurity ions (especially divalent anions and polyvalent anions) introduced in the above process, so as to finally obtain a phosphoric acid solution product with higher purity; the preparation method uses extraction, dearsenication reaction, defluorination reaction, deoxidation reaction and desulfurization reaction as the main reactions, and then combines ultrafiltration and nanofiltration and other membrane filtration methods. The overall preparation method does not require complex reagents and special process conditions, and can finally improve the effect of removing impurities from food-grade phosphoric acid products at a low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0019] Figure 1 A schematic diagram of a method for preparing food-grade phosphoric acid provided in an embodiment of the present application; Figure 2 A detailed schematic diagram of a method for preparing food-grade phosphoric acid provided in an embodiment of the present application. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0021] Various embodiments of the present application may be presented in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity and should not be understood as a rigid limitation on the scope of the present application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within the range; for example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, which applies regardless of the range; in addition, whenever a numerical range is indicated in this document, it is meant to include any cited numbers (fractions or integers) within the indicated range.

[0022] In this document, the terms including "including" and "including" mean "including but not limited to". Relational terms such as "first" and "second" are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. "And / or" describes the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone; where A and B can be singular or plural. "At least one" means one or more, "plurality" means two or more; "at least one", "at least one of the following" or similar expressions refer to any combination of these items, including any combination of single or plural items; for example, "at least one of a, b, or c", or "at least one of a, b, and c" can all mean: a, b, c, ab (i.e. a and b), ac, bc, or abc, where a, b, and c can be single or plural, respectively. "Parts" such as parts by weight and parts by mass indicate the proportional relationship between the components. In the proportional relationship involved in this article, the parameters that need to be described by proportion should be understood as the first term of the proportional formula in the order of description, and the proportional numbers should be understood as the second term of the proportional formula. For example, if the mass ratio of substance A, substance B and substance C is 1:2:3, then substance A, substance B and substance C should correspond to the proportional numbers in the proportional formula in the order of description, that is, the mass of substance A: the mass of substance B: the mass of substance C = 1:2:3.

[0023] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in this article can be purchased from the market or prepared by existing methods.

[0024] Figure 1 A schematic diagram of a method for preparing food-grade phosphoric acid provided in an embodiment of the present application is exemplarily shown; like Figure 1 As shown, the present application embodiment provides a method for preparing food-grade phosphoric acid, the method comprising: S1. extracting an industrial-grade phosphoric acid solution using tributyl phosphate to obtain an organic phase containing phosphoric acid; S2. subjecting the organic phase containing phosphoric acid and phosphorus pentasulfide to a dearsenification reaction and filtering to obtain a dearsenified phosphoric acid solution; S3. Defluorinating the dearsenicated phosphoric acid solution using activated diatomaceous earth under nitrogen flow to obtain a defluorinated phosphoric acid solution; S4. Using nitrogen and an oxidant to remove the defluorinated phosphoric acid solution to obtain a deoxidized phosphoric acid solution; S5. The desulfurization reaction and filtration of the deoxidized phosphoric acid solution are carried out by using a desulfurizing agent under nitrogen gas flow to obtain a desulfurized phosphoric acid solution; S6. The desulfurized phosphoric acid solution is aged, filtered and stripped to obtain a clarified phosphoric acid solution; S7. The clarified phosphoric acid solution is subjected to ultrafiltration and nanofiltration to obtain a food-grade phosphoric acid solution.

[0025] It should be noted that after extraction, the obtained organic phase can be washed with a dilute alkaline solution to remove phosphorus pentoxide impurities and part of the fluorine element in the industrial-grade phosphoric acid solution. The mass fraction of the dilute alkaline solution used can be 20%, and the mass of the dilute alkaline solution used can be 1.4% of the mass of the organic phase.

[0026] It should be noted that the addition of phosphorus pentasulfide converts the high-valent arsenic in the arsenic-containing substances (arsenic acid or arsenous acid) in the organic phase into low-valent arsenic, which then reacts with the hydrogen sulfide gas formed by phosphorus pentoxide to form arsenic sulfide precipitates. In addition, the industrial-grade phosphoric acid solution contains lead impurities, which will also form lead sulfide precipitates in the process and be removed.

[0027] It should be noted that the fluorine in the industrial-grade phosphoric acid solution will form fluorosilicic acid under the action of activated diatomaceous earth. The fluorosilicic acid can be converted into silicon fluoride or hydrofluoric acid gas by heating or concentration, thereby achieving the separation of fluorine and the dearsenicized phosphoric acid solution.

[0028] It should be noted that the preparation process of the activated diatomite is: soaking the diatomite in a dilute alkaline solution for 20 minutes, and then vacuum drying to form an activated diatomite product.

[0029] It should be noted that the defluorinated phosphoric acid solution is subjected to a deoxidizing reaction using nitrogen and an oxidant. Specifically, the defluorinated phosphoric acid solution is first aerated with nitrogen so that the defluorinated phosphoric acid solution has a uniform distribution of the oxidizable substances and part of the oxidizable substances is taken out by the nitrogen. Then, an oxidant is added to oxidize the oxidizable substances (hypophosphorous acid or phosphorous acid) of the defluorinated phosphoric acid solution to form phosphoric acid by utilizing the strong oxidizing property of the oxidant. Meanwhile, the hydrogen sulfide formed in the dearsenicizing reaction is oxidized to sulfate ions to reduce the sulfur impurities in the defluorinated phosphoric acid solution.

[0030] It should be noted that the desulfurization reaction of the deoxidized phosphoric acid solution is carried out using a desulfurizer when nitrogen is introduced. Specifically, when nitrogen is introduced, the desulfurizer will fully form a precipitate with the sulfate ions of the deoxidized phosphoric acid solution, thereby achieving the separation of elemental sulfur from the deoxidized phosphoric acid solution.

[0031] It should be noted that the present application embodiment provides a method for preparing food-grade phosphoric acid. The core of the preparation method is to extract and purify the phosphoric acid component from the industrial-grade phosphoric acid solution through a series of carefully designed chemical reactions and physical treatment steps, and finally obtain a high-purity food-grade phosphoric acid product. The specific process is: The method first uses tributyl phosphate as an extractant to effectively extract the phosphoric acid component into the organic phase, laying a good foundation for the subsequent removal of impurities. The key to this step is the selection and use of tributyl phosphate, which can effectively improve the extraction efficiency and purity of phosphoric acid.

[0032] The method then uses phosphorus pentasulfide as a reducing agent. Under the action of phosphoric acid, phosphorus pentasulfide decomposes to produce hydrogen sulfide gas. In this process, the hydrogen sulfide gas formed reacts with the arsenic element in the organic phase to form arsenic slag, which can then be easily removed by filtering, thereby significantly reducing the arsenic content in the phosphoric acid solution.

[0033] After removing arsenic impurities, this method further utilizes the effect of nitrogen and the hydrophobic interface of the organic phase to convert the fluorine element in the phosphoric acid solution into gaseous silicon fluoride, thereby effectively removing the fluorine element. This step not only improves the purity of phosphoric acid, but also avoids the influence of fluorine on subsequent processes.

[0034] The method also converts easily oxidized substances (such as phosphorous acid and hypophosphorous acid) into phosphoric acid through the combined action of nitrogen and an oxidant, and oxidizes the remaining hydrogen sulfide into sulfate ions. This step not only reduces the content of easily oxidized substances in the phosphoric acid solution, but also provides favorable conditions for the subsequent desulfurization reaction.

[0035] In the desulfurization stage, this method introduces nitrogen to promote the full reaction between the desulfurizer and the sulfate ions in the phosphoric acid solution, thereby further reducing the content of sulfate ions and obtaining a purer phosphoric acid solution.

[0036] The method also includes an aging step to allow the impurity components in the phosphoric acid solution to fully react to further improve the purity of the phosphoric acid. Subsequently, the impurity ions (especially divalent anions and polyvalent anions) that may be introduced in the above process are effectively removed through membrane filtration technologies such as ultrafiltration and nanofiltration, thereby ensuring that the final phosphoric acid solution product has extremely high purity.

[0037] In summary, the embodiments of the present application provide a method for preparing food-grade phosphoric acid. The preparation method achieves the goal of efficiently removing impurities at low cost through main reactions such as extraction, dearsenicization reaction, defluorination reaction, deoxidation reaction and desulfurization reaction, combined with membrane filtration technologies such as ultrafiltration and nanofiltration, and provides a new idea and technical path for the production of food-grade phosphoric acid.

[0038] In some optional embodiments, the temperature of the arsenic removal reaction is 75° C. to 85° C., and the time of the arsenic removal reaction is ≥ 15 min; and / or The temperature of the deoxidation reaction is 55°C to 70°C, and the time of the deoxidation reaction is 4.5h to 5.5h; and / or The temperature of the desulfurization reaction is 30° C. to 40° C., and the time of the desulfurization reaction is 60 min to 90 min.

[0039] In these embodiments, the temperature of the dearsenification reaction can be 75°C to 85°C, and the time of the dearsenification reaction can be ≥15 minutes, so that phosphorus pentasulfide can fully react with the arsenic impurities in the organic phase to effectively remove the arsenic impurities in the organic phase; in addition, the temperature of the deoxidation reaction can be 55°C to 70°C, and the time of the deoxidation reaction can be 4.5h to 5.5h, so that the oxidant can fully react with the oxidized substance (hypophosphorous acid or phosphorous acid) of the defluorinated phosphoric acid solution, and at the same time, the hydrogen sulfide formed in the dearsenification reaction will be oxidized to sulfate to reduce the sulfur impurities in the defluorinated phosphoric acid solution; in addition, the temperature of the desulfurization reaction can be 30°C to 40°C, and the time of the desulfurization reaction can be 60min to 90min, so that the desulfurizer can fully form a precipitate with the sulfate of the deoxidized phosphoric acid solution, thereby realizing the separation of elemental sulfur from the deoxidized phosphoric acid solution.

[0040] The temperature of the dearsenification reaction can be 75°C, 76°C, 77°C, 78°C, 79°C, 80°C, 81°C, 82°C, 83°C, 84°C or 85°C.

[0041] The dearsenicification reaction time is 15 min, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min or 60 min.

[0042] The temperature of the deoxidation reaction may be 55°C, 58°C, 61°C, 64°C, 67°C or 70°C.

[0043] The deoxidation reaction time can be 4.5 h, 4.6 h, 4.7 h, 4.8 h, 4.9 h, 5.0 h, 5.1 h, 5.2 h, 5.3 h, 5.4 h or 5.5 h.

[0044] The temperature of the desulfurization reaction can be 30°C, 31°C, 32°C, 33°C, 34°C, 35°C, 36°C, 37°C, 38°C, 39°C or 40°C.

[0045] The desulfurization reaction time can be 60 min, 65 min, 70 min, 75 min, 80 min, 85 min or 90 min.

[0046] In some optional embodiments, the mass m1 of the phosphorus pentasulfide and the mass m2 of the organic phase satisfy the relationship: m1:m2=(5-10):100; and / or The oxidant comprises hydrogen peroxide, and the volume V1 of the hydrogen peroxide and the volume V2 of the dearsenicated phosphoric acid solution satisfy the relationship: V1:V2≥1:60; and / or The desulfurizing agent includes barium carbonate, and the mass m3 of the barium carbonate and the mass m4 of the deoxidized phosphoric acid solution satisfy the relationship: m3=0.08%×m4×197.35 / 96×Q, In the formula, 197.35 is the relative molecular mass of barium carbonate, 96 is the relative molecular mass of sulfate ion, Q is the ratio of m3 to the theoretical addition amount M of barium carbonate, and Q is 1.0 to 1.4.

[0047] In these embodiments, the mass m1 of phosphorus pentasulfide and the mass m2 of the organic phase can satisfy the relationship: m1:m2=(5-10):100, so that the phosphorus pentasulfide fully reacts with the arsenic impurities in the organic phase to effectively remove the arsenic impurities in the organic phase; in addition, the volume V1 of hydrogen peroxide and the volume V2 of the dearsenicated phosphoric acid solution satisfy the relationship: V1:V2≥1:60, so that the oxidant fully reacts with the oxidized substance (hypophosphorous acid or phosphorous acid) of the defluorinated phosphoric acid solution, and at the same time, the hydrogen sulfide formed in the dearsenication reaction will be oxidized into sulfate to reduce the sulfur impurities in the defluorinated phosphoric acid solution; in addition, the mass m3 of barium carbonate and the mass m4 of the deoxidized phosphoric acid solution satisfy the relationship: m3=0.08%×m4×197.35 / 96×Q, and Q can be 1.0-1.4, within this relationship, the barium carbonate fully forms a precipitate with the sulfate of the deoxidized phosphoric acid solution, thereby realizing the separation of sulfur element from the deoxidized phosphoric acid solution.

[0048] The mass m1 of the phosphorus pentasulfide can be 5, 6, 7, 8, 9 or 10.

[0049] The value of Q can be 1.0, 1.1, 1.2, 1.3 or 1.4.

[0050] It should be noted that, since barium carbonate is difficult to dissolve in aqueous solution, it can react preferentially with sulfate in the organic phase to form insoluble barium sulfate precipitates. These insoluble barium sulfate precipitates will precipitate out of the organic phase, thereby removing the sulfate.

[0051] Figure 2 A detailed schematic diagram of a method for preparing food-grade phosphoric acid provided in an embodiment of the present application is exemplarily shown; In some optional embodiments, such as Figure 2 As shown, the defluorination reaction of the dearsenicated phosphoric acid solution using activated diatomaceous earth under nitrogen flow to obtain a defluorinated phosphoric acid solution comprises the steps of: S301. Washing the dearsenicated phosphoric acid solution with a dilute alkaline solution to obtain a primary defluorinated phosphoric acid solution; S302. The primary defluorinated phosphoric acid solution is vacuum concentrated using activated diatomaceous earth to obtain a secondary defluorinated phosphoric acid mixture; S303. Stripping the secondary defluorinated phosphoric acid mixture using saturated steam under nitrogen flow to obtain a defluorinated phosphoric acid mixture.

[0052] In these embodiments, the defluorinated phosphoric acid solution is first washed with a dilute alkaline solution, and the trace impurities such as iron, magnesium and aluminum in the defluorinated phosphoric acid solution are converted into precipitates and precipitated through the hydroxide ions of the dilute alkaline solution. In addition, the dilute alkaline solution can cause the fluorine element to form a metal salt containing fluorine and sodium. When diatomaceous earth is subsequently added, these metal salts containing fluorine and sodium will form sodium fluorosilicate precipitates to achieve the initial conversion of the fluorine element; in addition, activated diatomaceous earth is used in the vacuum concentration stage, and the fluorine in the primary defluorinated phosphoric acid solution can be converted into fluorosilicic acid gas through the action of silicon and silicon dioxide of the activated diatomaceous earth, thereby achieving the separation of fluorine element from the primary defluorinated phosphoric acid solution; in addition, the introduction of saturated steam can further heat the residual fluorosilicic acid and hydrofluoric acid in the secondary defluorinated phosphoric acid mixture to form gas, thereby achieving the separation of fluorine element from the primary defluorinated phosphoric acid solution.

[0053] It should be noted that the nitrogen and saturated steam can be used in combination, that is, saturated steam and nitrogen can be simultaneously introduced into the secondary defluorinated phosphoric acid mixture.

[0054] In some optional embodiments, the temperature of the vacuum concentration is 85°C to 95°C, the pressure of the vacuum concentration is 0.08MPa to 0.09MPa, and the time of the vacuum concentration is 1.5h to 2.5h; and / or The stripping temperature is 85°C to 95°C, and the stripping time is 2.0h to 3.0h.

[0055] In these embodiments, the temperature of vacuum concentration can be 85°C to 95°C, the pressure of vacuum concentration can be 0.08MPa to 0.09MPa, and the time of vacuum concentration can be 1.5h to 2.5h, so that the active diatomaceous earth fully reacts with the fluorine in the primary defluorinated phosphoric acid solution to form fluorosilicic acid, which is convenient for subsequent stripping; in addition, the temperature of stripping can be 85°C to 95°C, and the time of stripping can be 2.0h to 3.0h, and the residual fluorosilicic acid and hydrofluoric acid in the secondary defluorinated phosphoric acid mixture are heated to form gas through the action of nitrogen and saturated steam, thereby achieving the separation of fluorine element from the primary defluorinated phosphoric acid solution.

[0056] The temperature of the vacuum concentration may be 85°C, 86°C, 87°C, 88°C, 89°C, 90°C, 91°C, 92°C, 93°C, 94°C or 95°C.

[0057] The pressure of the vacuum concentration may be 0.08 MPa, 0.081 MPa, 0.082 MPa, 0.083 MPa, 0.084 MPa, 0.085 MPa, 0.086 MPa, 0.087 MPa, 0.088 MPa, 0.089 MPa or 0.09 MPa.

[0058] The time of vacuum concentration can be 1.5 h, 1.6 h, 1.7 h, 1.8 h, 1.9 h, 2.0 h, 2.1 h, 2.2 h, 2.3 h, 2.4 h or 2.5 h.

[0059] The stripping temperature may be 85°C, 86°C, 87°C, 88°C, 89°C, 90°C, 91°C, 92°C, 93°C, 94°C or 95°C.

[0060] The stripping time may be 2.0 h, 2.1 h, 2.2 h, 2.3 h, 2.4 h, 2.5 h, 2.6 h, 2.7 h, 2.8 h, 2.9 h or 3.0 h.

[0061] In some optional embodiments, the nitrogen gas has an introduction rate of 0.5 L / min to 1.5 L / min, and the nitrogen gas is introduced by bottom blowing and bubbling.

[0062] In these embodiments, the nitrogen gas introduction flow rate can be 0.5 L / min to 1.5 L / min, and the nitrogen gas is introduced by bottom bubbling. The bottom bubbling method can make each reagent fully mixed and react with the corresponding phosphoric acid solution, so as to ultimately effectively remove each impurity element.

[0063] The nitrogen gas flow rate can be 0.5 L / min, 0.6 L / min, 0.7 L / min, 0.8 L / min, 0.9 L / min, 1.0 L / min, 1.1 L / min, 1.2 L / min, 1.3 L / min, 1.4 L / min or 1.5 L / min.

[0064] In some optional embodiments, the temperature of the saturated steam is 90° C. to 95° C., and the flow rate of the saturated steam is 1.0 L / min to 2.0 L / min.

[0065] In these embodiments, the temperature of the saturated steam can be 90° C. to 95° C., and the flow rate of the saturated steam can be 1.0 L / min to 2.0 L / min. The residual fluorosilicic acid and hydrofluoric acid in the secondary defluorinated phosphoric acid mixture are heated to form gas by the action of nitrogen and saturated steam, thereby achieving separation of fluorine element from the primary defluorinated phosphoric acid solution.

[0066] The temperature of the saturated steam may be 90°C, 91°C, 92°C, 93°C, 94°C or 95°C.

[0067] The inlet flow rate of the saturated steam can be 1.0 L / min, 1.1 L / min, 1.2 L / min, 1.3 L / min, 1.4 L / min, 1.5 L / min, 1.6 L / min, 1.7 L / min, 1.8 L / min, 1.9 L / min or 2.0 L / min.

[0068] In some optional embodiments, the mass m5 of the activated diatomaceous earth and the mass m6 of fluorine in the primary defluorinated phosphoric acid solution satisfy the relationship: m5:m6=(2.0-3.0):1.

[0069] In these embodiments, the mass m5 of the activated diatomaceous earth and the mass m6 of the fluorine in the primary defluorinated phosphoric acid solution can satisfy the relationship: m5:m6=(2.0-3.0):1, so that the activated diatomaceous earth fully reacts with the fluorine in the primary defluorinated phosphoric acid solution to form fluorosilicic acid, which is convenient for subsequent vacuum concentration to form a gas of the fluorosilicic acid, thereby achieving the removal of fluorine from the primary defluorinated phosphoric acid solution.

[0070] The mass m5 of the activated diatomaceous earth can be 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9 or 3.0.

[0071] In some optional embodiments, the aging treatment time is 8h to 12h; and / or The volume of the stripping solution used in the stripping is twice the volume of the desulfurized phosphoric acid solution.

[0072] In these embodiments, the aging treatment time can be 8h to 12h, so that the various impurities are fully separated from the desulfurized phosphoric acid solution, thereby improving the purity of the phosphoric acid solution; in addition, the volume of the stripping solution used for stripping is twice the volume of the desulfurized phosphoric acid solution, which can make the desulfurized phosphoric acid solution transfer from the organic phase to the aqueous phase, facilitating the subsequent use of food-grade phosphoric acid.

[0073] The aging time can be 8h, 9h, 10h, 11h or 12h.

[0074] In some optional embodiments, the porosity of the ultrafiltration membrane used in the ultrafiltration is ≥50%; and / or The molecular weight cut-off of the nanofiltration membrane used in the nanofiltration is 150Da to 200Da.

[0075] In these embodiments, the porosity of the ultrafiltration membrane used in ultrafiltration is ≥50%, so that the ultrafiltration membrane has a sufficiently small pore size to effectively remove the phosphorus pentoxide impurity in the clarified phosphoric acid solution. In addition, the retention molecular weight of the nanofiltration membrane used in nanofiltration is 150Da to 200Da, and the phosphorus pentoxide impurity and various divalent metal ions in the clarified phosphoric acid solution can be removed by nanofiltration.

[0076] The molecular weight cut-off of the nanofiltration membrane used in the nanofiltration is 150 Da, 160 Da, 170 Da, 180 Da, 190 Da or 200 Da.

[0077] It should be noted that the ultrafiltration membrane can be a silicon carbide ceramic membrane, and the clear liquid flux of the silicon carbide ceramic membrane is greater than 2m 3 / h; the nanofiltration can use Duracid acid-resistant nanofiltration membrane.

[0078] The present application is further described below in conjunction with specific examples. The experimental methods in the following examples where specific conditions are not specified are usually measured in accordance with national standards / industry standards; if there are no corresponding national standards / industry standards, they are measured in accordance with common international standards, conventional conditions or conditions recommended by the manufacturer.

[0079] Example 1

[0080] A method for preparing food-grade phosphoric acid, comprising: S1. extracting an industrial-grade phosphoric acid solution using tributyl phosphate to obtain an organic phase containing phosphoric acid; S2. subjecting the organic phase containing phosphoric acid and phosphorus pentasulfide to arsenic removal reaction and filtration to obtain arsenic-removed phosphoric acid solution; S301. Washing the dearsenicated phosphoric acid solution with a dilute alkaline solution to obtain a primary defluorinated phosphoric acid solution; S302. The primary defluorinated phosphoric acid solution is vacuum concentrated using activated diatomaceous earth to obtain a secondary defluorinated phosphoric acid mixture; S303. The secondary defluorinated phosphoric acid mixture is stripped using saturated steam under nitrogen flow to obtain a defluorinated phosphoric acid mixture; S4. Using nitrogen and an oxidant to defluorinate the phosphoric acid solution to obtain a deoxidized phosphoric acid solution; S5. In the case of nitrogen gas passing, the desulfurization agent is used to desulfurize the deoxidized phosphoric acid solution and filter it to obtain a desulfurized phosphoric acid solution; S6. The desulfurized phosphoric acid solution is aged, filtered and stripped to obtain a clarified phosphoric acid solution; S7. The clarified phosphoric acid solution is subjected to ultrafiltration and nanofiltration to obtain a food-grade phosphoric acid solution.

[0081] The temperature of the dearsenicization reaction was 80°C, and the time of the dearsenicization reaction was 20 min; The temperature of the deoxidation reaction is 65°C, and the time of the deoxidation reaction is 5.0h; The temperature of the desulfurization reaction is 35°C, and the time of the desulfurization reaction is 75 minutes.

[0082] The mass m1 of phosphorus pentasulfide and the mass m2 of the organic phase satisfy the relationship: m1:m2=8:100; The oxidant includes hydrogen peroxide, and the volume V1 of the hydrogen peroxide and the volume V2 of the dearsenicated phosphoric acid solution satisfy the relationship: V1:V2=1:60; The desulfurizing agent includes barium carbonate, and the mass m3 of the barium carbonate and the mass m4 of the deoxidized phosphoric acid solution satisfy the relationship: m3=0.08%×m4×197.35 / 96×Q, In the formula, 197.35 is the relative molecular mass of barium carbonate, 96 is the relative molecular mass of sulfate ion, Q is the ratio of m3 to the theoretical addition amount M of barium carbonate, and Q is 1.2.

[0083] The temperature of vacuum concentration was 90°C, the pressure of vacuum concentration was 0.085MPa, and the time of vacuum concentration was 2.0h; The stripping temperature was 90°C and the stripping time was 2.5 h.

[0084] The nitrogen flow rate was 1.0 L / min, and the nitrogen was introduced by bottom bubbling.

[0085] The temperature of saturated steam is 95°C, and the flow rate of saturated steam is 1.5 L / min.

[0086] The mass m5 of the activated diatomaceous earth and the mass m6 of the fluorine in the primary defluorinated phosphoric acid solution satisfy the relationship: m5:m6=2.5:1.

[0087] The aging time is 10h; The volume of the stripping solution used for stripping is twice the volume of the desulfurized phosphoric acid solution.

[0088] The porosity of the ultrafiltration membrane used in ultrafiltration is 50%; The molecular weight cut-off of the nanofiltration membrane used for nanofiltration is 150 Da to 200 Da.

[0089] Example 2 Based on the contents disclosed in Example 1, the following modifications are further made: The temperature of the arsenic removal reaction is 75°C; The temperature of the deoxidation reaction is 70°C, and the time of the deoxidation reaction is 5.5h; The temperature of the desulfurization reaction is 40°C, and the time of the desulfurization reaction is 90 minutes.

[0090] The mass m1 of phosphorus pentasulfide and the mass m2 of the organic phase satisfy the relationship: m1:m2=10:100; The mass m3 of barium carbonate and the mass m4 of the deoxidized phosphoric acid solution satisfy the relationship: m3=0.08%×m4×197.35 / 96×Q, In the formula, 197.35 is the relative molecular mass of barium carbonate, 96 is the relative molecular mass of sulfate ion, Q is the ratio of m3 to the theoretical addition amount M of barium carbonate, and Q is 1.4.

[0091] The temperature of vacuum concentration was 95°C, the pressure of vacuum concentration was 0.09 MPa, and the time of vacuum concentration was 2.5 h; The stripping temperature was 95°C and the stripping time was 3.0 h.

[0092] The nitrogen flow rate was 1.5 L / min.

[0093] The temperature of saturated steam is 95°C, and the flow rate of saturated steam is 2.0L / min.

[0094] The mass m5 of the activated diatomaceous earth and the mass m6 of the fluorine in the primary defluorinated phosphoric acid solution satisfy the relationship: m5:m6=3.0:1.

[0095] The aging time is 12h.

[0096] Example 3 Based on the contents disclosed in Example 1, the following modifications are further made: The temperature of the dearsenicization reaction is 85°C; The temperature of the deoxidation reaction was 55°C, and the time of the deoxidation reaction was 4.5 h; The temperature of the desulfurization reaction is 30°C, and the time of the desulfurization reaction is 60 minutes.

[0097] The mass m1 of phosphorus pentasulfide and the mass m2 of the organic phase satisfy the relationship: m1:m2=5:100; The desulfurizing agent includes barium carbonate, and the mass m3 of the barium carbonate and the mass m4 of the deoxidized phosphoric acid solution satisfy the relationship: m3=0.08%×m4×197.35 / 96×Q, Wherein, 197.35 is the relative molecular mass of barium carbonate, 96 is the relative molecular mass of sulfate ion, Q is the ratio of m3 to the theoretical addition amount M of barium carbonate, and Q is 1.0.

[0098] The temperature of vacuum concentration was 85°C, the pressure of vacuum concentration was 0.08 MPa, and the time of vacuum concentration was 1.5 h; The stripping temperature was 85°C and the stripping time was 2.0 h.

[0099] The nitrogen flow rate was 0.5 L / min.

[0100] The temperature of saturated steam is 90°C, and the flow rate of saturated steam is 1.0 L / min.

[0101] The mass m5 of the activated diatomaceous earth and the mass m6 of the fluorine in the primary defluorinated phosphoric acid solution satisfy the relationship: m5:m6=2.0:1.

[0102] The aging time is 8h.

[0103] Comparative Example 1 Based on the contents disclosed in Example 1, the following modifications are further made: Only ultrafiltration and nanofiltration were used.

[0104] Comparative Example 2 Based on the contents disclosed in Example 1, the following modifications are further made: The temperature of the dearsenicization reaction is 70°C; The temperature of the deoxidation reaction is 50°C, and the time of the deoxidation reaction is 4.0h; The temperature of the desulfurization reaction is 25°C, and the time of the desulfurization reaction is 30 minutes.

[0105] Comparative Example 3 Based on the contents disclosed in Example 1, the following modifications are further made: The temperature of the arsenic removal reaction is 95°C; The temperature of the deoxidation reaction is 85°C, and the time of the deoxidation reaction is 6 hours; The temperature of the desulfurization reaction is 60°C, and the time of the desulfurization reaction is 120 minutes.

[0106] Comparative Example 4 Based on the contents disclosed in Example 1, the following modifications are further made: The mass m3 of barium carbonate and the mass m4 of the deoxidized phosphoric acid solution satisfy the relationship: m3=0.08%×m4×197.35 / 96×Q, In the formula, 197.35 is the relative molecular mass of barium carbonate, 96 is the relative molecular mass of sulfate ion, Q is the ratio of m3 to the theoretical addition amount M of barium carbonate, and Q is 0.5.

[0107] Comparative Example 5 Based on the contents disclosed in Example 1, the following modifications are further made: The mass m3 of barium carbonate and the mass m4 of the deoxidized phosphoric acid solution satisfy the relationship: m3=0.08%×m4×197.35 / 96×Q, In the formula, 197.35 is the relative molecular mass of barium carbonate, 96 is the relative molecular mass of sulfate ion, Q is the ratio of m3 to the theoretical addition amount M of barium carbonate, and Q is 2.0.

[0108] Related experiments and effect data: 1. The food-grade phosphoric acid solution obtained in Example 1 was collected and its substance content was detected. The results are shown in Table 1.

[0109] Table 1 The food grade phosphoric acid solution obtained in Example 1 , 2. The food-grade phosphoric acid solutions of the embodiments and comparative examples were collected respectively, and the impurity removal rates of the food-grade phosphoric acid solutions during the preparation process were detected. The statistics of the removal rates of the various substances can refer to the prior art. The results are shown in Table 2.

[0110] Table 2 The removal rate of fluoride, arsenic, sulfur and oxidizable substances in various examples and comparative examples , As can be seen from Table 1, the removal rates of fluoride, arsenic, sulfur and oxidizable substances in each embodiment can reach more than 95%. In addition, although Comparative Example 5 also has a good impurity removal efficiency, it introduces a large amount of carbonate ions and affects the yield of phosphoric acid, which has a greater impact on product quality.

[0111] In summary, the embodiments of the present application provide a method for preparing food-grade phosphoric acid. The preparation method achieves the goal of efficiently removing impurities at low cost through main reactions such as extraction, dearsenicization reaction, defluorination reaction, deoxidation reaction and desulfurization reaction, combined with membrane filtration technologies such as ultrafiltration and nanofiltration, and provides a new idea and technical path for the production of food-grade phosphoric acid.

[0112] The above description is only a specific implementation of the present application, so that those skilled in the art can understand or implement the present application. It will be apparent to those skilled in the art that various modifications to these embodiments are possible, and the general principles defined in the present application can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown in the present application, but will conform to the widest range consistent with the principles and novel features applied for by the present application.

Claims

1. A method for preparing food-grade phosphoric acid, the method comprising: The industrial-grade phosphoric acid solution is extracted using tributyl phosphate to obtain an organic phase containing phosphoric acid; The organic phase containing phosphoric acid and phosphorus pentasulfide are subjected to a dearsenification reaction and filtered to obtain a dearsenified phosphoric acid solution; The dearsenicized phosphoric acid solution is subjected to a defluorination reaction using activated diatomaceous earth under the condition of nitrogen gas passing to obtain a defluorinated phosphoric acid solution; Using nitrogen and an oxidant to carry out a deoxidation reaction on the defluorinated phosphoric acid solution to obtain a deoxidation phosphoric acid solution; The deoxidized phosphoric acid solution is subjected to a desulfurization reaction and filtered using a desulfurizing agent under the condition of nitrogen gas flow to obtain a desulfurized phosphoric acid solution; The desulfurized phosphoric acid solution is subjected to aging treatment, filtering and stripping to obtain a clarified phosphoric acid solution; The clear phosphoric acid solution is subjected to ultrafiltration and nanofiltration to obtain a food-grade phosphoric acid solution.

2. The preparation method according to claim 1, wherein the temperature of the dearsenification reaction is 75°C to 85°C, and the time of the dearsenification reaction is ≥ 15 min; and / or The temperature of the deoxidation reaction is 55°C to 70°C, and the time of the deoxidation reaction is 4.5h to 5.5h; and / or The temperature of the desulfurization reaction is 30° C. to 40° C., and the time of the desulfurization reaction is 60 min to 90 min.

3. The preparation method according to claim 1, wherein the mass m1 of the phosphorus pentasulfide and the mass m2 of the organic phase satisfy the relationship: m1:m2=(5-10):100; and / or The oxidant comprises hydrogen peroxide, and the volume V1 of the hydrogen peroxide and the volume V2 of the dearsenicated phosphoric acid solution satisfy the relationship: V1:V2≥1:60; and / or The desulfurizing agent includes barium carbonate, and the mass m3 of the barium carbonate and the mass m4 of the deoxidized phosphoric acid solution satisfy the relationship: m3=0.08%×m4×197.35 / 96×Q, In the formula, 197.35 is the relative molecular mass of barium carbonate, 96 is the relative molecular mass of sulfate ion, Q is the ratio of m3 to the theoretical addition amount M of barium carbonate, and Q is 1.0 to 1.

4.

4. The preparation method according to claim 1, wherein the defluorinating phosphoric acid solution is subjected to a defluorinating reaction using activated diatomaceous earth under nitrogen flow to obtain a defluorinated phosphoric acid solution, comprising the steps of: The dearsenicated phosphoric acid solution is washed with a dilute alkaline solution to obtain a primary defluorinated phosphoric acid solution; The primary defluorinated phosphoric acid solution is vacuum concentrated using activated diatomaceous earth to obtain a secondary defluorinated phosphoric acid mixture; The secondary defluorinated phosphoric acid mixture is stripped using saturated steam under nitrogen flow to obtain a defluorinated phosphoric acid mixture.

5. The preparation method according to claim 4, wherein the temperature of the vacuum concentration is 85°C to 95°C, the pressure of the vacuum concentration is 0.08MPa to 0.09MPa, and the time of the vacuum concentration is 1.5h to 2.5h; and / or The stripping temperature is 85°C to 95°C, and the stripping time is 2.0h to 3.0h.

6. The preparation method according to claim 4, wherein the nitrogen gas has an introduction rate of 0.5 L / min to 1.5 L / min, and the nitrogen gas is introduced by bottom blowing and bubbling.

7. The preparation method according to claim 4, wherein the temperature of the saturated steam is 90°C to 95°C, and the flow rate of the saturated steam is 1.0 L / min to 2.0 L / min.

8. The preparation method according to claim 4, wherein the mass m5 of the activated diatomaceous earth and the mass m6 of fluorine in the primary defluorinated phosphoric acid solution satisfy the relationship: m5:m6=(2.0-3.0):

1.

9. The preparation method according to claim 1, wherein the aging treatment time is 8h to 12h; and / or The volume of the stripping solution used in the stripping is twice the volume of the desulfurized phosphoric acid solution.

10. The preparation method according to claim 1, wherein the porosity of the ultrafiltration membrane used in the ultrafiltration is ≥ 50%; and / or The molecular weight cut-off of the nanofiltration membrane used in the nanofiltration is 150Da to 200Da.

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