A method for preparing food-grade phosphoric acid

Abstract

The application relates to the technical field of food-grade phosphoric acid preparation, in particular to a food-grade phosphoric acid preparation method; the method comprises the following steps: using tributyl phosphate to extract an industrial-grade phosphoric acid solution to obtain an organic phase containing phosphoric acid; performing arsenic removal reaction and filtration on the organic phase and phosphorus pentasulfide to obtain a dearsenated phosphoric acid solution; performing fluorine removal reaction on the dearsenated phosphoric acid solution by using active diatomite under the condition of nitrogen gas being introduced to obtain a defluorinated phosphoric acid solution; performing easy-oxide removal reaction on the defluorinated phosphoric acid solution by using nitrogen gas and an oxidizing agent to obtain a de-easy-oxide phosphoric acid solution; performing desulfurization reaction and filtration on the de-easy-oxide phosphoric acid solution by using a desulfurizing agent to obtain a desulfurized phosphoric acid solution; performing aging treatment, filtration and reverse extraction on the desulfurized phosphoric acid solution to obtain a clear phosphoric acid solution; and performing ultrafiltration and nanofiltration on the clear phosphoric acid solution to obtain a food-grade phosphoric acid solution. The preparation method can improve the impurity removal effect of the food-grade phosphoric acid product under 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 particularly relates to a food-grade phosphoric acid preparation method. BACKGROUND

[0002] Food additives have become an important raw material for improving the color, aroma, taste and other properties of food, and are one of the food additives with the largest use in the current food industry. In food processing, food-grade phosphoric acid can not only improve the organization structure and taste of food, but also can be used as an acidulant, a mineral nutrient enhancer, etc. At present, the production of food-grade phosphoric acid is mainly carried out by wet-process phosphoric acid process, and the wet-process phosphoric acid process mainly uses industrial-grade phosphoric acid as raw material. Most of these industrial-grade phosphoric acid products are formed by industrial-grade phosphoric acid products formed by hydrochloric acid method using hydrochloric acid and low-grade phosphate rock as raw materials. Due to the use of different types of low-grade phosphate rock raw materials, the food-grade phosphoric acid contains many impurities, including silicon carbide, arsenic, fluorine and sulfur elements, and in addition, some food-grade phosphoric acid products also contain easily oxidizable substances such as phosphorous acid and hypophosphorous acid. These easily oxidizable substances can form highly toxic phosphine under heat, 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 easily oxidizable substances needs to be strictly controlled to meet the use scenarios. However, during the removal of arsenic elements from food-grade phosphoric acid products, sodium sulfide or phosphorus pentasulfide products are introduced into the food-grade phosphoric acid products, which undoubtedly increases the desulfurization pressure of the food-grade phosphoric acid products. In addition, in order to promote the complete removal of arsenic, heating is also carried out during the arsenic removal stage, which undoubtedly causes the easily oxidizable substances to be converted into highly toxic phosphine, affecting the safety of the final food-grade phosphoric acid. The traditional methods for removing these harmful substances from food-grade phosphoric acid products include solvent extraction, chemical precipitation, solvent precipitation, crystallization, electrodialysis and ion exchange, etc. However, these methods either have high costs or require strict separation environments, and therefore there is an urgent need to develop a new purification process for food-grade phosphoric acid products.

[0004] At present, the membrane separation method using ultrafiltration membrane combined with nanofiltration membrane can be used to remove the impurities in food-grade phosphoric acid products, and the impurity removal efficiency of food-grade phosphoric acid is about 90%. However, due to the limited treatment capacity of ultrafiltration membrane and nanofiltration membrane and the high quality requirement of industrial-grade phosphoric acid, the impurities in industrial-grade phosphoric acid need to be pretreated first, which undoubtedly increases the cost and energy consumption of the impurity removal stage. In addition, using membrane separation alone cannot remove arsenic elements at one time, and multiple arsenic removal treatments are required, further increasing the energy consumption and power of the removal stage. Moreover, the final arsenic removal efficiency is below 90%, which cannot meet the use requirements of high-purity food-grade phosphoric acid products. SUMMARY

[0005] The application provides a food-grade phosphoric acid preparation method to solve the technical problem of how to improve the impurity removal effect of food-grade phosphoric acid products under the premise of low cost and energy consumption.

[0006] In a first aspect, the application provides a food-grade phosphoric acid preparation method, which comprises:

[0007] extracting an industrial-grade phosphoric acid solution using tributyl phosphate to obtain an organic phase containing phosphoric acid;

[0008] performing a dearsenification reaction on the organic phase containing phosphoric acid and phosphorus pentasulfide and filtering to obtain a dearsenified phosphoric acid solution;

[0009] performing a defluorination reaction on the dearsenified phosphoric acid solution using activated diatomite under the condition of nitrogen gas being introduced to obtain a defluorinated phosphoric acid solution;

[0010] performing a deoxygenate removal reaction on the defluorinated phosphoric acid solution using nitrogen gas and an oxidizing agent to obtain a deoxygenate-removed phosphoric acid solution;

[0011] performing a desulfurization reaction on the deoxygenate-removed phosphoric acid solution using a desulfurizing agent under the condition of nitrogen gas being introduced and filtering to obtain a desulfurized phosphoric acid solution;

[0012] performing aging treatment, filtering and reverse extraction on the desulfurized phosphoric acid solution to obtain a clear phosphoric acid solution;

[0013] performing ultrafiltration and nanofiltration on the clear phosphoric acid solution to obtain a food-grade phosphoric acid solution.

[0014] Optionally, the temperature of the dearsenification reaction is 75-85°C, and the time of the dearsenification reaction is ≥15 min; and / or

[0015] the temperature of the deoxygenate removal reaction is 55-70°C, and the time of the deoxygenate removal reaction is 4.5-5.5 h; and / or

[0016] the temperature of the desulfurization reaction is 30-40°C, and the time of the desulfurization reaction is 60-90 min.

[0017] 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

[0018] the oxidizing agent comprises hydrogen peroxide, the volume V1 of the hydrogen peroxide and the volume V2 of the dearsenified phosphoric acid solution satisfy the relationship V1:V2≥1:60; and / or

[0019] the desulfurizing agent comprises barium carbonate, the mass m3 of the barium carbonate and the mass m4 of the deoxygenate-removed phosphoric acid solution satisfy the relationship

[0020] m3=0.08%×m4×197.35 / 96×Q,

[0021] 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 and the theoretical addition amount M of barium carbonate, Q is 1.0-1.4.

[0022] Optionally, the defluorination of the arsenic-removed phosphoric acid solution is performed using active diatomite under nitrogen flow to obtain a defluorinated phosphoric acid solution, comprising the steps of:

[0023] The arsenic-removed phosphoric acid solution is washed using a dilute alkali solution to obtain a primary defluorinated phosphoric acid solution;

[0024] The primary defluorinated phosphoric acid solution is vacuum concentrated using active diatomite to obtain a secondary defluorinated phosphoric acid mixture;

[0025] The secondary defluorinated phosphoric acid mixture is stripped using saturated steam under nitrogen flow to obtain a defluorinated phosphoric acid mixture.

[0026] Optionally, the temperature of the vacuum concentration is 85-95℃, the pressure of the vacuum concentration is 0.08-0.09MPa, and the time of the vacuum concentration is 1.5-2.5h; and / or

[0027] The temperature of the stripping is 85-95℃, and the time of the stripping is 2.0-3.0h.

[0028] Optionally, the nitrogen flow is 0.5-1.5L / min, and the nitrogen flow is bottom blowing and bubbling.

[0029] Optionally, the temperature of the saturated steam is 90-95℃, and the saturated steam flow is 1.0-2.0L / min.

[0030] Optionally, the mass m5 of the active diatomite and the mass m6 of fluorine in the primary defluorinated phosphoric acid solution satisfy the relationship m5:m6=(2.0-3.0):1.

[0031] Optionally, the aging treatment time is 8-12h; and / or

[0032] The volume of the stripping solution used for the stripping is 2 times the volume of the desulfurized phosphoric acid solution.

[0033] Optionally, the porosity of the ultrafiltration membrane used for the ultrafiltration is ≥50%; and / or

[0034] The nanofiltration membrane used in the nanofiltration has a molecular weight cut-off of 150 Da to 200 Da.

[0035] The above technical solution provided by the embodiments of the present application has the following advantages compared with the prior art:

[0036] The preparation method of the food-grade phosphoric acid provided by the embodiments of the present application first uses tributyl phosphate as an extractant to extract the phosphoric acid component of the industrial-grade phosphoric acid solution into an organic phase, facilitating the subsequent impurity removal reaction; then uses phosphorus pentasulfide as a reducing agent to form hydrogen sulfide gas under the action of phosphoric acid, and the formed hydrogen sulfide gas can convert the arsenic element in the organic phase into arsenic slag, which can be separated from the phosphoric acid solution by filtration; 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 oxidizing agent converts the easily oxidizable substances (phosphorous acid and hypophosphorous acid) into phosphoric acid and converts the aforementioned residual hydrogen sulfide into sulfate ions, thereby reducing the content of the easily oxidizable substances in the phosphoric acid solution; furthermore, in the case of nitrogen introduction, the desulfurizing agent can fully react with the sulfate ions in the phosphoric acid solution to ultimately obtain a pure phosphoric acid solution; finally, through aging treatment, the various impurity components in the phosphoric acid solution are fully reacted to further obtain a pure phosphoric acid solution; then the ultrafiltration and nanofiltration methods are used to further remove the impurity ions introduced in the above process (especially divalent anions and multivalent anions), thereby ultimately obtaining a high-purity phosphoric acid solution product; the preparation method combines the main reactions of extraction, arsenic removal reaction, fluorine removal reaction, easily oxidizable substance removal reaction and desulfurization reaction, and further combines the membrane filtration methods of ultrafiltration and nanofiltration, and the overall preparation method does not require complex reagents and special process conditions, and ultimately can improve the impurity removal effect of the food-grade phosphoric acid product under the premise of low cost. BRIEF DESCRIPTION OF DRAWINGS

[0037] The accompanying drawings, which are incorporated into and form a part of the specification, illustrate one embodiment consistent with the present application and, together with the description, serve to explain the principles of the application.

[0038] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the accompanying drawings needed to be used in the embodiments or prior art description will be briefly introduced as follows, and obviously, other drawings can also be obtained by those skilled in the art without creative labor under the premise of these drawings.

[0039] Figure 1 A food-grade phosphoric acid preparation method provided by the embodiments of the present application is shown in the flowchart.

[0040] Figure 2A food-grade phosphoric acid preparation method provided by the embodiment of the present application is shown in detail in the flowchart. DETAILED DESCRIPTION

[0041] To make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described below in connection with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0042] Various embodiments of the present application can exist in the form of a range; it should be understood that the description in the form of a range is merely for the convenience and brevity, and should not be understood as a hard limit on the scope of the present application; therefore, it should be considered that the described range has disclosed all possible sub-ranges and single values in the range; for example, it should be considered that the range description from 1 to 6 has 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., and single numbers in the range, such as 1, 2, 3, 4, 5 and 6, which applies to any range; in addition, whenever a numerical range is indicated in this document, it refers to any cited number (fraction or integer) in the indicated range.

[0043] In this document, the terms "comprises", "comprising", "includes", "including" or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises, includes or includes elements or steps does not include only those elements or steps but can include other elements or steps not expressly listed or inherent to such process, method, article, or apparatus. The terms "first", "second", "third", etc. are used merely as labels, and are not intended to impose numerical requirements on their objects. The term "and / or", describing the relationship between associated objects, means that there can be three kinds of relationships, for example, A and / or B can mean that A exists alone, A and B exist together, B exists alone; wherein A and B can be singular or plural. "At least one" means one or more, "multiple" means two or more; "at least one" or "at least one of the following" or the like means any combination of the items, including single item or combination of multiple items; for example, "at least one of a, b, or c", or "at least one of a, b, and c", can mean a, b, c, a-b (i.e. a and b), a-c, b-c, or a-b-c, wherein a, b, and c can be single or multiple. The "parts ratio" such as weight parts, mass parts, etc. represents the proportional relationship between components. In the proportional relationship described in this document, the parameters that need to be described in order should be understood as the front item of the proportional formula, and the proportional number should be understood as the rear item of the proportional formula, for example, the mass ratio of substance A, substance B and substance C is 1:2:3, then substance A, substance B and substance C should be corresponding to the proportional number in the proportional formula in the order of description, i.e. the mass of substance A: the mass of substance B: the mass of substance C = 1:2:3.

[0044] Unless otherwise specified, the various raw materials, reagents, instruments and equipment used in this document can be purchased from the market or prepared by existing methods.

[0045] Figure 1 An exemplary flow chart of a food-grade phosphoric acid preparation method provided by the embodiments of the present application is shown;

[0046] As shown in Figure 1 The embodiments of the present application provide a food-grade phosphoric acid preparation method, which comprises:

[0047] S1. Using tributyl phosphate to extract industrial-grade phosphoric acid solution to obtain phosphoric acid-containing organic phase;

[0048] S2. The phosphoric acid-containing organic phase and phosphorus pentasulfide are subjected to arsenic removal reaction and filtration to obtain arsenic-removed phosphoric acid solution;

[0049] S3. Using active diatomite to remove fluorine from the arsenic-removed phosphoric acid solution under the condition of nitrogen gas being introduced to obtain fluorine-removed phosphoric acid solution;

[0050] S4. The defluorinated phosphoric acid solution is subjected to a de-oxidable matter reaction using nitrogen and an oxidizing agent to obtain a de-oxidable matter phosphoric acid solution;

[0051] S5. The de-oxidable matter phosphoric acid solution is subjected to a desulfurization reaction using a desulfurizer under nitrogen and is filtered to obtain a desulfurized phosphoric acid solution;

[0052] S6. The desulfurized phosphoric acid solution is subjected to an aging treatment, filtration and back extraction to obtain a clarified phosphoric acid solution;

[0053] S7. The clarified phosphoric acid solution is subjected to ultrafiltration and nanofiltration to obtain a food-grade phosphoric acid solution.

[0054] It should be noted that after extraction, the obtained organic phase can be washed using a dilute alkali solution to remove the phosphorus pentoxide impurities and part of the fluorine element of the industrial-grade phosphoric acid solution, and the mass fraction of the dilute alkali solution used can be 20%, and the mass of the dilute alkali solution used can be 1.4% of the mass of the organic phase.

[0055] It should be noted that the addition of phosphorus pentasulfide causes the high-valence arsenic of the arsenic-containing substances (arsenic acid or arsenious acid) in the organic phase to be converted into low-valence arsenic, and then the low-valence arsenic reacts with the hydrogen sulfide gas formed by the phosphorus pentoxide to generate arsenic sulfide precipitates, and in addition, the industrial-grade phosphoric acid solution contains lead impurities, which will also form lead sulfide precipitates and be removed in this process.

[0056] It should be noted that the fluorine in the industrial-grade phosphoric acid solution will form fluorosilicic acid under the action of the active diatomite, and the fluorosilicic acid can be heated or concentrated to form silicon fluoride or hydrogen fluoride gas, thereby realizing the separation of fluorine from the de-arsenized phosphoric acid solution.

[0057] It should be noted that the preparation process of the active diatomite is to soak the diatomite in a dilute alkali solution for 20 minutes, and then vacuum dry to form the finished product of active diatomite.

[0058] It should be noted that the defluorinated phosphoric acid solution is subjected to a de-oxidable matter reaction using nitrogen and an oxidizing agent, specifically, nitrogen is first used to aerate the defluorinated phosphoric acid solution, so that the de-oxidable matter of the defluorinated phosphoric acid solution is uniformly distributed and part of the de-oxidable matter is carried out by nitrogen, and then an oxidizing agent is added, which uses the strong oxidizing property of the oxidizing agent to oxidize the de-oxidable matter (hypophosphorous acid or phosphorous acid) of the defluorinated phosphoric acid solution to form phosphoric acid, and at the same time, the hydrogen sulfide formed in the de-arsenization reaction is oxidized to sulfate to reduce the sulfur impurities in the defluorinated phosphoric acid solution.

[0059] It is necessary to point out that the desulfurizer is used to carry out the desulfurization reaction on the de-easily oxidizable phosphoric acid solution under the condition of nitrogen gas being introduced, specifically, under the condition of nitrogen gas being introduced, the desulfurizer can fully form a precipitate with the sulfate radical of the de-easily oxidizable phosphoric acid solution, so as to realize the separation of the sulfur element and the de-easily oxidizable phosphoric acid solution.

[0060] It is necessary to point out that the application embodiment provides a food-grade phosphoric acid preparation method, and 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 finely designed chemical reactions and physical treatment steps, and finally obtain a high-purity food-grade phosphoric acid product. The specific process is as follows:

[0061] ‌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 removal of impurities in the subsequent steps. 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.

[0062] ‌The method then uses phosphorus pentasulfide as a reducing agent, which decomposes to produce hydrogen sulfide gas under the action of phosphoric acid. In this process, the hydrogen sulfide gas formed reacts with arsenic elements in the organic phase to form arsenic slag, which can be easily removed by filtration, thereby significantly reducing the arsenic content in the phosphoric acid solution.

[0063] ‌After removing the arsenic impurities, the method further utilizes the action of nitrogen gas in combination with the hydrophobic interface of the organic phase to convert the fluorine element in the phosphoric acid solution into gaseous silicon fluoride, achieving effective removal of fluorine elements. This step not only improves the purity of phosphoric acid, but also avoids the influence of fluorine elements on subsequent processes.

[0064] ‌The method also uses nitrogen gas and oxidizing agents to convert easily oxidizable substances (such as phosphorous acid and hypophosphorous acid) into phosphoric acid and oxidize residual hydrogen sulfide to sulfate ions. This step not only reduces the content of easily oxidizable substances in the phosphoric acid solution, but also provides favorable conditions for the subsequent desulfurization reaction.

[0065] The method further reduces the content of sulfate ions by introducing nitrogen gas during the desulfurization stage to promote the reaction of the desulfurizer with the sulfate ions in the phosphoric acid solution, thereby obtaining a more pure phosphoric acid solution.

[0066] ‌The method finally includes an aging treatment step to allow the various impurity components in the phosphoric acid solution to fully react, further improving the purity of the phosphoric acid. Subsequently, membrane filtration techniques such as ultrafiltration and nanofiltration are used to effectively remove impurity ions (especially divalent and multivalent anions) that may be introduced during the above process, thereby ensuring that the final phosphoric acid solution product has extremely high purity.

[0067] In summary, the food-grade phosphoric acid preparation method provided by the embodiments of the present application realizes the goal of efficiently removing impurities at low cost by means of main reactions such as extraction, arsenic removal reaction, fluorine removal reaction, easily oxidizable substance removal reaction and sulfur removal reaction, in combination with membrane filtration technologies such as ultrafiltration and nanofiltration, and provides a new train of thought and technical path for the production of food-grade phosphoric acid.

[0068] In some optional embodiments, the temperature of the arsenic removal reaction is 75-85°C, and the arsenic removal reaction time is ≥15 min; and / or

[0069] The temperature of the easily oxidizable substance removal reaction is 55-70°C, and the easily oxidizable substance removal reaction time is 4.5-5.5 h; and / or

[0070] The temperature of the sulfur removal reaction is 30-40°C, and the sulfur removal reaction time is 60-90 min.

[0071] In these embodiments, the temperature of the arsenic removal reaction can be 75-85°C, and the arsenic removal reaction time is ≥15 min, so that the phosphorus pentasulfide fully reacts with the arsenic impurities in the organic phase to effectively remove the arsenic-containing impurities in the organic phase; in addition, the temperature of the easily oxidizable substance removal reaction can be 55-70°C, and the easily oxidizable substance removal reaction time can be 4.5-5.5 h, so that the oxidizing agent fully reacts with the easily oxidizable substance (hypophosphorous acid or phosphorous acid) in the fluorine-removed phosphoric acid solution, and at the same time, the hydrogen sulfide formed in the arsenic removal reaction is oxidized into sulfate to reduce the sulfur impurities in the fluorine-removed phosphoric acid solution; in addition, the temperature of the sulfur removal reaction can be 30-40°C, and the sulfur removal reaction time can be 60-90 min, so that the sulfur removal agent fully forms a precipitate with the sulfate in the easily oxidizable substance-removed phosphoric acid solution, thereby realizing the separation of sulfur and the easily oxidizable substance-removed phosphoric acid solution.

[0072] The temperature of the arsenic removal 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.

[0073] The arsenic removal reaction time can be 15 min, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min or 60 min.

[0074] The temperature of the easily oxidizable substance removal reaction can be 55°C, 58°C, 61°C, 64°C, 67°C or 70°C.

[0075] The easily oxidizable substance removal 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.

[0076] 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.

[0077] The time of the desulfurization reaction can be 60 min, 65 min, 70 min, 75 min, 80 min, 85 min, or 90 min.

[0078] In some alternative 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

[0079] The oxidizing agent comprises hydrogen peroxide, and the volume V1 of the hydrogen peroxide and the volume V2 of the arsenic-removed phosphoric acid solution satisfy the relationship: V1:V2≥1:60; and / or

[0080] The desulfurizer comprises barium carbonate, and the mass m3 of the barium carbonate and the mass m4 of the easily-oxidized substance-removed phosphoric acid solution satisfy the relationship:

[0081] m3=0.08%×m4×197.35 / 96×Q,

[0082] wherein 197.35 is the relative molecular mass of barium carbonate, 96 is the relative molecular mass of a sulfate ion, and Q is the ratio of m3 to the theoretical addition amount M of barium carbonate, and Q is 1.0-1.4.

[0083] In these embodiments, the mass m1 of the phosphorus pentasulfide and the mass m2 of the organic phase can satisfy the relationship: m1:m2=(5-10):100, so that the phosphorus pentasulfide sufficiently reacts with the arsenic impurities of the organic phase to effectively remove the arsenic impurities of the organic phase; in addition, the volume V1 of the hydrogen peroxide and the volume V2 of the arsenic-removed phosphoric acid solution satisfy the relationship: V1:V2≥1:60, so that the oxidizing agent sufficiently reacts with the easily-oxidized substance (hypophosphorous acid or phosphorous acid) of the arsenic-removed phosphoric acid solution, while the hydrogen sulfide formed in the arsenic-removal reaction is oxidized into sulfate to reduce the sulfur impurities of the arsenic-removed phosphoric acid solution; in addition, the mass m3 of the barium carbonate and the mass m4 of the easily-oxidized substance-removed phosphoric acid solution satisfy the relationship: m3=0.08%×m4×197.35 / 96×Q, and Q can be 1.0-1.4, so that the barium carbonate sufficiently forms a precipitate with the sulfate of the easily-oxidized substance-removed phosphoric acid solution, thereby realizing the separation of the sulfur element from the easily-oxidized substance-removed phosphoric acid solution.

[0084] The mass m1 of the phosphorus pentasulfide can be 5, 6, 7, 8, 9, or 10.

[0085] The value of Q can be 1.0, 1.1, 1.2, 1.3, or 1.4.

[0086] It should be noted that, since barium carbonate is difficult to dissolve in aqueous solution, and can react with sulfate in organic phase to form barium sulfate precipitate, these barium sulfate precipitates can be precipitated from the organic phase, so that the sulfate is removed.

[0087] Figure 2 An exemplary food-grade phosphoric acid preparation method provided by the embodiment of the present application is shown in the detailed flowchart;

[0088] In some optional embodiments, as shown in Figure 2 The defluorinated phosphoric acid solution is obtained by using active diatomite under the condition of nitrogen introduction, and includes the following steps:

[0089] S301. The defluorinated phosphoric acid solution is washed by using a dilute alkali solution to obtain a primary defluorinated phosphoric acid solution;

[0090] S302. The primary defluorinated phosphoric acid solution is vacuum concentrated by using active diatomite to obtain a secondary defluorinated phosphoric acid mixture;

[0091] S303. The secondary defluorinated phosphoric acid mixture is stripped by using saturated steam under the condition of nitrogen introduction to obtain a defluorinated phosphoric acid mixture.

[0092] In these embodiments, the defluorinated phosphoric acid solution is first washed by using a dilute alkali solution, so that the trace impurities such as iron, magnesium and aluminum in the defluorinated phosphoric acid solution are converted into precipitates and precipitated by the hydroxide ions in the dilute alkali solution. In addition, the dilute alkali solution can make the fluorine element form a metal salt containing fluorine and sodium. Under the subsequent addition of diatomite, these metal salts containing fluorine and sodium will form sodium fluorosilicate precipitates to achieve the preliminary conversion of the fluorine element. In addition, active diatomite is used in the vacuum concentration stage, which can convert the fluorine in the primary defluorinated phosphoric acid solution into fluorosilicic acid gas by the action of silicon and silicon dioxide in the active diatomite, so as to separate the fluorine element from the primary defluorinated phosphoric acid solution. In addition, the introduction of saturated steam can further make the residual fluorosilicic acid and hydrofluoric acid in the secondary defluorinated phosphoric acid mixture form gas by heating, so as to separate the fluorine element from the primary defluorinated phosphoric acid solution.

[0093] It should be noted that, the nitrogen and saturated steam can be mixedly used, that is, the saturated steam and nitrogen can be simultaneously introduced into the secondary defluorinated phosphoric acid mixture.

[0094] In some optional embodiments, the temperature of the vacuum concentration is 85℃-95℃, the pressure of the vacuum concentration is 0.08MPa-0.09MPa, and the time of the vacuum concentration is 1.5h-2.5h; and / or

[0095] The temperature of the stripping is 85℃-95℃, and the time of the stripping is 2.0h-3.0h.

[0096] In these embodiments, the temperature of the vacuum concentration can be 85℃-95℃, and the pressure of the vacuum concentration can be 0.08MPa-0.09MPa, and the time of the vacuum concentration can be 1.5h-2.5h, so that the active diatomite fully reacts with the fluorine in the primary defluorinated phosphoric acid solution to form fluosilicic acid, facilitating the subsequent stripping; in addition, the temperature of the stripping can be 85℃-95℃, and the time of the stripping can be 2.0h-3.0h, so that the residual fluosilicic 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 realizing the separation of fluorine from the primary defluorinated phosphoric acid solution.

[0097] The temperature of the vacuum concentration can be 85℃, 86℃, 87℃, 88℃, 89℃, 90℃, 91℃, 92℃, 93℃, 94℃, or 95℃.

[0098] The pressure of the vacuum concentration can be 0.08MPa, 0.081MPa, 0.082MPa, 0.083MPa, 0.084MPa, 0.085MPa, 0.086MPa, 0.087MPa, 0.088MPa, 0.089MPa, or 0.09MPa.

[0099] The time of the vacuum concentration can be 1.5h, 1.6h, 1.7h, 1.8h, 1.9h, 2.0h, 2.1h, 2.2h, 2.3h, 2.4h, or 2.5h.

[0100] The temperature of the stripping can be 85℃, 86℃, 87℃, 88℃, 89℃, 90℃, 91℃, 92℃, 93℃, 94℃, or 95℃.

[0101] The time of the stripping can be 2.0h, 2.1h, 2.2h, 2.3h, 2.4h, 2.5h, 2.6h, 2.7h, 2.8h, 2.9h, or 3.0h.

[0102] In some alternative embodiments, the flow rate of the nitrogen introduced is 0.5L / min-1.5L / min, and the nitrogen is introduced in a bottom-blowing bubbling manner.

[0103] In these embodiments, the flow rate of the nitrogen introduced can be 0.5L / min-1.5L / min, and the nitrogen is introduced in a bottom-blowing bubbling manner, so that each reagent can be fully mixed and reacted with the corresponding phosphoric acid solution, thereby effectively removing each impurity element.

[0104] The flow rate of the nitrogen gas 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.

[0105] In some alternative 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.

[0106] 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, so that the residual fluosilicic acid and hydrofluoric acid in the secondary defluorinated phosphoric acid mixture are heated to form gas by the action of the nitrogen gas and the saturated steam, thereby achieving the separation of the fluorine element from the primary defluorinated phosphoric acid solution.

[0107] The temperature of the saturated steam can be 90°C, 91°C, 92°C, 93°C, 94°C, or 95°C.

[0108] The 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.

[0109] In some alternative embodiments, the mass m5 of the active diatomite and the mass m6 of the fluorine in the primary defluorinated phosphoric acid solution satisfy the relationship: m5:m6=(2.0-3.0):1.

[0110] In these embodiments, the mass m5 of the active diatomite 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 active diatomite sufficiently reacts with the fluorine in the primary defluorinated phosphoric acid solution and forms fluosilicic acid, and the subsequent vacuum concentration of the fluosilicic acid causes the fluosilicic acid to form gas, thereby achieving the removal of fluorine from the primary defluorinated phosphoric acid solution.

[0111] The mass m5 of the active diatomite 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.

[0112] In some alternative embodiments, the aging treatment time is 8 h to 12 h; and / or

[0113] The volume of the stripping solution used for the stripping is 2 times the volume of the desulfurized phosphoric acid solution.

[0114] In these embodiments, the time of the aging treatment can be 8h-12h, so that various impurities are sufficiently 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 2 times 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, thereby facilitating the subsequent use of the food-grade phosphoric acid.

[0115] The time of the aging treatment can be 8h, 9h, 10h, 11h or 12h.

[0116] In some alternative embodiments, the porosity of the ultrafiltration membrane used for the ultrafiltration is ≥50%; and / or

[0117] The molecular weight cut-off of the nanofiltration membrane used for the nanofiltration is 150Da-200Da.

[0118] In these embodiments, the porosity of the ultrafiltration membrane used for the ultrafiltration is ≥50%, so that the ultrafiltration membrane has a sufficiently small pore size, which can effectively remove the phosphorus pentoxide impurities in the clarified phosphoric acid solution; in addition, the molecular weight cut-off of the nanofiltration membrane used for the nanofiltration is 150Da-200Da, which can remove the phosphorus pentoxide impurities and various divalent metal ions in the clarified phosphoric acid solution through nanofiltration.

[0119] The molecular weight cut-off of the nanofiltration membrane used for the nanofiltration is 150Da, 160Da, 170Da, 180Da, 190Da or 200Da.

[0120] 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 >2m 3 / h; the nanofiltration can use Duracid acid-resistant nanofiltration membranes.

[0121] The present application will be further described below in conjunction with specific examples. The experimental methods in the following examples are generally determined according to national standards / industry standards; if there is no corresponding national standard / industry standard, the general international standard, conventional conditions or the conditions recommended by the manufacturer are used.

[0122] Example 1

[0123] A food-grade phosphoric acid preparation method comprises:

[0124] S1. Using phosphoric acid tributyl ester to extract the industrial-grade phosphoric acid solution to obtain an organic phase containing phosphoric acid;

[0125] S2. Performing a dearsenification reaction on the organic phase containing phosphoric acid and phosphorus pentasulfide and filtering to obtain a dearsenified phosphoric acid solution;

[0126] S301. washing the dearsenated phosphoric acid solution using a dilute alkali solution to obtain a primary defluorinated phosphoric acid solution;

[0127] S302. vacuum concentrating the primary defluorinated phosphoric acid solution using active diatomite to obtain a secondary defluorinated phosphoric acid mixture;

[0128] S303. stripping the secondary defluorinated phosphoric acid mixture using saturated steam under nitrogen to obtain a defluorinated phosphoric acid mixture;

[0129] S4. subjecting the defluorinated phosphoric acid solution to a de-episulfide reaction using nitrogen and an oxidizing agent to obtain a de-episulfide phosphoric acid solution;

[0130] S5. subjecting the de-episulfide phosphoric acid solution to a desulfurization reaction and filtration using a desulfurizer under nitrogen to obtain a desulfurized phosphoric acid solution;

[0131] S6. subjecting the desulfurized phosphoric acid solution to aging treatment, filtration and back extraction to obtain a clarified phosphoric acid solution;

[0132] S7. subjecting the clarified phosphoric acid solution to ultrafiltration and nanofiltration to obtain a food-grade phosphoric acid solution.

[0133] The temperature of the dearsenation reaction is 80℃, and the time of the dearsenation reaction is 20min;

[0134] The temperature of the de-episulfide reaction is 65℃, and the time of the de-episulfide reaction is 5.0h;

[0135] The temperature of the desulfurization reaction is 35℃, and the time of the desulfurization reaction is 75min.

[0136] The mass m1 of the phosphorus pentasulfide and the mass m2 of the organic phase satisfy the relationship: m1:m2=8:100;

[0137] The oxidizing agent includes hydrogen peroxide, and the volume V1 of the hydrogen peroxide and the volume V2 of the dearsenated phosphoric acid solution satisfy the relationship: V1:V2=1:60;

[0138] The desulfurizer includes barium carbonate, and the mass m3 of the barium carbonate and the mass m4 of the de-episulfide phosphoric acid solution satisfy the relationship:

[0139] m3=0.08%×m4×197.35 / 96×Q,

[0140] 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 and the theoretical addition amount M of barium carbonate, and Q is 1.2.

[0141] The temperature of the vacuum concentration is 90℃, the pressure of the vacuum concentration is 0.085MPa, and the time of the vacuum concentration is 2.0h;

[0142] The temperature of the stripping is 90℃, and the time of the stripping is 2.5h.

[0143] The flow rate of the nitrogen is 1.0L / min, and the nitrogen is bubbled from the bottom.

[0144] The temperature of the saturated steam is 95℃, and the flow rate of the saturated steam is 1.5L / min.

[0145] The mass m5 of the active diatomite and the mass m6 of the fluorine in the primary defluorinated phosphoric acid solution satisfy the relationship: m5:m6=2.5:1.

[0146] The time of the aging treatment is 10h;

[0147] The volume of the stripping solution used in the stripping is 2 times of the volume of the desulfurized phosphoric acid solution.

[0148] The porosity of the ultrafiltration membrane used in the ultrafiltration is 50%;

[0149] The molecular weight cut-off of the nanofiltration membrane used in the nanofiltration is 150Da-200Da.

[0150] Example 2

[0151] Based on the disclosure of Example 1, the following modifications are further made:

[0152] The temperature of the arsenic removal reaction is 75℃;

[0153] The temperature of the de-oxides reaction is 70℃, and the time of the de-oxides reaction is 5.5h;

[0154] The temperature of the desulfurization reaction is 40℃, and the time of the desulfurization reaction is 90min.

[0155] The mass m1 of the phosphorus pentasulfide and the mass m2 of the organic phase satisfy the relationship: m1:m2=10:100;

[0156] The mass m3 of the barium carbonate and the mass m4 of the de-oxides phosphoric acid solution satisfy the relationship:

[0157] m3=0.08%×m4×197.35 / 96×Q,

[0158] In the formula, 197.35 is the relative molecular mass of the barium carbonate, 96 is the relative molecular mass of the sulfate ion, Q is the ratio of m3 and the theoretical addition amount M of the barium carbonate, and Q is 1.4.

[0159] The temperature of the vacuum concentration is 95℃, the pressure of the vacuum concentration is 0.09MPa, and the time of the vacuum concentration is 2.5h;

[0160] The temperature of the stripping is 95℃, and the time of the stripping is 3.0h.

[0161] The flow rate of the nitrogen is 1.5L / min.

[0162] The temperature of the saturated steam is 95℃, and the flow rate of the saturated steam is 2.0L / min.

[0163] The mass m5 of the active diatomite and the mass m6 of the fluorine in the primary defluorinated phosphoric acid solution satisfy the relationship: m5:m6=3.0:1.

[0164] The time of the aging treatment is 12h.

[0165] Example 3

[0166] On the basis of the disclosure of Example 1, the following modifications are further made:

[0167] The temperature of the arsenic removal reaction is 85℃;

[0168] The temperature of the de-epitaxy compound reaction is 55℃, and the time of the de-epitaxy compound reaction is 4.5h;

[0169] The temperature of the desulfurization reaction is 30℃, and the time of the desulfurization reaction is 60min.

[0170] The mass m1 of the phosphorus pentasulfide and the mass m2 of the organic phase satisfy the relationship: m1:m2=5:100;

[0171] The desulfurizer includes barium carbonate, and the mass m3 of the barium carbonate and the mass m4 of the de-epitaxy compound phosphoric acid solution satisfy the relationship:

[0172] m3=0.08%×m4×197.35 / 96×Q,

[0173] In the formula, 197.35 is the relative molecular mass of the barium carbonate, 96 is the relative molecular mass of the sulfate ion, Q is the ratio of m3 and the theoretical addition amount M of the barium carbonate, and Q is 1.0.

[0174] The temperature of the vacuum concentration is 85℃, the pressure of the vacuum concentration is 0.08MPa, and the time of the vacuum concentration is 1.5h;

[0175] The temperature of the stripping is 85℃, and the time of the stripping is 2.0h.

[0176] The flow rate of the nitrogen is 0.5L / min.

[0177] The temperature of the saturated steam is 90℃, and the flow rate of the saturated steam is 1.0L / min.

[0178] The mass m5 of the active diatomite and the mass m6 of fluorine in the primary defluorinated phosphoric acid solution satisfy the relationship: m5:m6=2.0:1.

[0179] The aging treatment time is 8h.

[0180] Comparative Example 1

[0181] Based on the disclosure of Example 1, the following modifications are further made:

[0182] Only ultrafiltration and nanofiltration are used.

[0183] Comparative Example 2

[0184] Based on the disclosure of Example 1, the following modifications are further made:

[0185] The temperature of the arsenic removal reaction is 70℃;

[0186] The temperature of the de-oxides reaction is 50℃, and the time of the de-oxides reaction is 4.0h;

[0187] The temperature of the desulfurization reaction is 25℃, and the time of the desulfurization reaction is 30min.

[0188] Comparative Example 3

[0189] Based on the disclosure of Example 1, the following modifications are further made:

[0190] The temperature of the arsenic removal reaction is 95℃;

[0191] The temperature of the de-oxides reaction is 85℃, and the time of the de-oxides reaction is 6h;

[0192] The temperature of the desulfurization reaction is 60℃, and the time of the desulfurization reaction is 120min.

[0193] Comparative Example 4

[0194] Based on the disclosure of Example 1, the following modifications are further made:

[0195] The mass m3 of the barium carbonate and the mass m4 of the de-oxides phosphoric acid solution satisfy the relationship:

[0196] m3=0.08%×m4×197.35 / 96×Q,

[0197] 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 and the theoretical addition amount M of barium carbonate, and Q is 0.5.

[0198] Comparative Example 5

[0199] On the basis of the disclosure of embodiment 1, the following modifications are further made:

[0200] The mass m3 of barium carbonate and the mass m4 of the deoxidized phosphoric acid solution satisfy the relationship:

[0201] m3 = 0.08% x m4 x 197.35 / 96 x Q,

[0202] In the formula, 197.35 is the relative molecular mass of barium carbonate, 96 is the relative molecular mass of the sulfate ion, Q is the ratio of m3 and the theoretical addition amount M of barium carbonate, and Q is 2.0.

[0203] Related experiments and effect data:

[0204] 1. The food-grade phosphoric acid solution obtained in embodiment 1 was collected, and the content of substances was detected, and the results are shown in Table 1.

[0205] Table 1 Table of food-grade phosphoric acid solution obtained in embodiment 1

[0206] ,

[0207] 2. The food-grade phosphoric acid solutions of each embodiment and comparative example were collected respectively, and the impurity removal rates of each food-grade phosphoric acid solution in the preparation process were detected. The statistics of the removal rates of each substance can refer to the prior art, and the results are shown in Table 2.

[0208] Table 2 Table of removal rates of fluorides, arsenic, sulfur and easily oxidizable substances of each embodiment and comparative example

[0209] ,

[0210] As can be seen from Table 1, the removal rates of fluorides, arsenic, sulfur and easily oxidizable substances of each embodiment can reach more than 95%. In addition, although comparative example 5 also has 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.

[0211] In summary, the food-grade phosphoric acid preparation method provided in the embodiments of the present application realizes the goal of efficiently removing impurities at low cost through main reactions such as extraction, dearsenization reaction, defluorination reaction, deoxidizable substance removal reaction and desulfurization reaction, combined with membrane filtration technologies such as ultrafiltration and nanofiltration, which provides a new idea and technical path for the production of food-grade phosphoric acid.

[0212] The foregoing detailed description of the application has been presented for purposes of illustration and description. Various modifications to the description will be readily apparent to those skilled in the art, and the generic principles defined herein can be applied to other implementations without departing from the spirit or scope of the application. Accordingly, the application is not intended to be limited to the implementations described herein but is to be accorded the widest scope consistent with the principles and novel features to the application.

Claims

1. A food-grade phosphoric acid preparation method, comprising: extracting an industrial-grade phosphoric acid solution using tributyl phosphate to obtain a phosphoric acid-containing organic phase; carrying out a dearsenication reaction on the phosphoric acid-containing organic phase and phosphorus pentasulfide and filtering to obtain a dearsenic phosphoric acid solution; carrying out a defluorination reaction on the dearsenic phosphoric acid solution using activated diatomite under nitrogen gas flow to obtain a defluorinated phosphoric acid solution; carrying out a de-easily oxidized substance reaction on the defluorinated phosphoric acid solution using nitrogen gas and an oxidizing agent to obtain a de-easily oxidized substance phosphoric acid solution; carrying out a desulfurization reaction on the de-easily oxidized substance phosphoric acid solution using a desulfurizer under nitrogen gas flow and filtering to obtain a desulfurized phosphoric acid solution; carrying out aging treatment, filtering and reverse extraction on the desulfurized phosphoric acid solution to obtain a clear phosphoric acid solution; carrying out ultrafiltration and nanofiltration on the clear phosphoric acid solution to obtain a food-grade phosphoric acid solution; the dearsenication reaction is carried out at a temperature of 75-85℃ for a time of ≥15 min; and / or the de-easily oxidized substance reaction is carried out at a temperature of 55-70℃ for a time of 4.5-5.5 h; and / or the desulfurization reaction is carried out at a temperature of 30-40℃ for a time of 60-90 min; 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 oxidizing agent comprises hydrogen peroxide, the volume V1 of the hydrogen peroxide and the volume V2 of the dearsenic phosphoric acid solution satisfy the relationship V1:V2≥1:60; and / or the desulfurizer comprises barium carbonate, the mass m3 of the barium carbonate and the mass m4 of the de-easily oxidized substance 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 a sulfate ion, and Q is the ratio of m3 to the theoretical addition amount M of barium carbonate, Q being 1.0-1.

4. 2.The preparation method of claim 1, wherein the defluorination reaction on the dearsenic phosphoric acid solution using activated diatomite under nitrogen gas flow to obtain a defluorinated phosphoric acid solution comprises the steps of: washing the dearsenic phosphoric acid solution using a dilute alkali solution to obtain a primary defluorinated phosphoric acid solution; vacuum concentrating the primary defluorinated phosphoric acid solution using activated diatomite to obtain a secondary defluorinated phosphoric acid mixture; stripping the secondary defluorinated phosphoric acid mixture using saturated steam under nitrogen gas flow to obtain a defluorinated phosphoric acid mixture. 3.The preparation method of claim 2, wherein the vacuum concentration is carried out at a temperature of 85-95℃, a pressure of 0.08-0.09 MPa, and for a time of 1.5-2.5 h; and / or the stripping is carried out at a temperature of 85-95℃ for a time of 2.0-3.0 h. 4.The preparation method of claim 2, wherein the nitrogen gas is bubbled from the bottom at a flow rate of 0.5-1.5 L / min. ​ ​ 5. The preparation method according to claim 2, wherein the saturated steam has a temperature of 90-95°C and a flow rate of 1.0-2.0 L / min.

6. The preparation method according to claim 2, wherein the mass m5 of the active diatomite and the mass m6 of fluorine in the primary defluorinated phosphoric acid solution satisfy the relationship m5:m6=(2.0-3.0):

1.

7. The preparation method according to claim 1, wherein the aging treatment is performed for 8-12 h; and / or the volume of the stripping solution used in the stripping is 2 times the volume of the desulfurized phosphoric acid solution.

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

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