RU2368567C1 - Method of obtaining edible ammonium phosphates - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to methods of obtaining edible ammonium phosphates, more specifically to monoammonium phosphate and diammonium phosphate from wet-process phosphoric acid, which are widely used in the food industry. The method of obtaining edible ammonium phosphates from evaporated wet-process phosphoric acid involves neutralisation with ammonia, crystallisation of ammonium phosphate from ammonium phosphate solution, separation of crystals from the mother solution with recycling of the latter. According to the invention, the evaporated phosphoric acid is diluted to concentration 23-25% P₂O₅. Calcium carbonate is added at ratio CaO/P₂O₅ = (0.03-0.05) : 1. The obtained mixture is neutralised in two stages, first to pH = 1.6-2.0 and then to pH = 4.2-4.5. The formed pulp is filtered with separation of ammonium phosphate solution. Monoammonium phosphate is crystallised. Crystals separated from the mother solution are dissolved in water and the solution is evaporated. The obtained purified ammonium phosphate solution is divided into two streams, one of which is channeled for production of monoammonium phosphate through crystallisation, and the second is ammoniated until obtaining diammonium phosphate. Evaporation is done and diammonium phosphate crystals are separated.

EFFECT: method increases cost effectiveness, simplifies process of purifying wet-process phosphoric acid, allows for obtaining high quality edible phosphates, versatile technology, which allows for obtaining two different products - monoammonium phosphate and diammonium phosphate in a single process.

3 cl, 1 tbl, 1 ex

Description

The invention relates to methods for producing food-grade ammonium phosphates, namely monoammonium phosphate (MAP) and diammonium phosphate (DAP) from extraction phosphoric acid (EPA), which are widely used in the food industry. Thus, MAF is used as an improver of flour and bread in the production of liquid rye starter cultures. DAF is used in the production of baker's yeast, in the production of processed cheeses as a baking powder, and in the production of edible alcohol it acts as a source of phosphorus.

Since the use of these products in the food industry requires high purity, they are mainly obtained on the basis of thermal phosphoric acid (TFA).

Numerous methods are known for producing MAF and DAP based on thermal phosphoric acid (TFA).

For example, auto USSR No. 1057415, cl. C01B 25 / 28.1983; RF patent No. 2220904, CL 01B 25/28, 2004; Chem. Prom., 1981, No. 6, pp. 12-15; Pozin M.E. Technology of mineral salts, part 2., Chemistry, L., 1970, p. 1086.

It should be noted that in order to obtain food ammonium phosphates from TPA, it must first be cleaned of impurities of lead and arsenic, which many methods are also aimed at, for example, RF patent No. 2100273, С01В 25/234, 1997; Patent No. 2209178, С01В 25/234, 2003.

But given that TPA is much more expensive than EPA due to high energy costs, obtaining food or reactive DAF from purified TPA is very problematic from the point of view of economic feasibility.

In addition, the production of TPA in Russia is currently absent, it is produced only in the city of Taraz (Republic of Kazakhstan), and the production of TPA is limited.

The use of EPA for the production of food phosphates implies its thorough purification and, first of all, from those components, the content of which is limited by regulatory documents for the corresponding products. So, of the impurities contained in EPA, the composition of food-grade DAF in accordance with GOST 8515-75 regulates the presence of fluorides, lead and arsenic.

A method has been developed and implemented for the production of MAF partially containing DAP from EPA (22-25% P ₂ O ₅ ), in which phosphoric acid containing up to 25% P ₂ O _{5 is} neutralized with ammonia with preliminary release of iron, aluminum phosphates and other impurities, followed by by evaporation of a solution of ammonium phosphates. In this method, the initial phosphoric acid containing an excess of sulfuric acid is treated with soda to separate silicofluoride, then the solution is neutralized with ammonia at a temperature of about 100 ° C until monoammonium phosphate containing diammonium phosphate impurities of not more than 15% is formed to precipitate iron and aluminum compounds from the solution, which separated by filtration, and the purified solution is evaporated and crystallized in this form or with preliminary complete neutralization with ammonia (ed. St. USSR No. 92149, 1952).

The disadvantage of this method is that the result is crystalline MAF, with a fluorine content of more than 0.001%, which does not meet the requirements of GOST for food additives.

The closest in technical essence and the achieved result to the claimed invention is a method for producing food diammonium phosphate from evaporated EPA, including neutralization with ammonia, crystallization of ammonium phosphate from ammonium phosphate solution, separation of crystals from mother liquors with utilization of the latter. According to this method, the extraction phosphoric acid (EPA) is preliminarily purified by tributyl phosphate, and then the re-extract is defluorinated by evaporation.

For this purpose, a solution containing NH ₄ ⁺ at a ratio of NH ₃ to the sum of all impurities in the acid equal to 1.5 kg / kg is introduced into the EPA preliminarily purified by the organic extractant EPA at the concentration stage for deep post-treatment; neutralization with ammonia is carried out to the ratio NH ₃ : H ₃ PO _{4 is} about 1.8, and the mother liquor after separation is completely withdrawn from the stage of production of diammonium phosphate (DAF) for disposal (RF patent No. 2277509 from 11/18/2004, CL 01/25/28. A method for producing food-grade diammonium phosphate from purified extraction phosphoric acid. Kochetkov SP Lembrikov V .M, Levin B.V. et al.).

By the specified method receive DAP containing (%): P ₂ About ₅ - 52.2; NH ₃ 23.5; F - not less than 0.001%.

The disadvantage of this method is the significant technical, manufacturing and human costs necessary for the preparation of EPA suitable for the production of food-grade DAF. It is enough to imagine that only in order to obtain 53% of P ₂ O ₅ phosphoric acid, purified from impurities of fluorine, other heavy metals and arsenic, 2 separate productions are organized: extraction of phosphoric acid with tributyl phosphate and a concentration unit - defluorination of phosphoric acid, which contains TBP after purification: 39% P ₂ O ₅ ; 0.07% F; 0.12% SO ₄ ^2- ; 0.04% Fe; 0.035% Al; 0,0004% As; 0,0009% Pb. The use of this technology ultimately leads to the high cost of a marketable product.

In addition, only one DAF product can be obtained using this technology.

The objective of the invention is to increase efficiency, simplifying the process at the stage of purification of EPA from impurities and obtaining higher quality food phosphates in terms of the content of basic substances, as well as the creation of a flexible technology that allows, in one process, to obtain two different products of MAP and DAP.

The problem is solved in a method for producing edible ammonium phosphates from one stripped off extraction phosphoric acid, including neutralization with ammonia, crystallization of ammonium phosphate from ammonium phosphate solution, separation of crystals from mother liquors with utilization of the latter. According to this method, one stripped off phosphoric acid is diluted to a concentration of 23-25% P ₂ O ₅ , calcium carbonate is introduced into it at a ratio of CaO / P ₂ O ₅ = (0.03-0.05): 1, then the resulting mixture is neutralized in two stages, first to a pH of 1.6-2.0, then to a pH of 4.2-4.5, the resulting pulp is filtered to separate the ammonium phosphate solution, monoammonium phosphate is crystallized, the crystals separated from the mother liquor are dissolved in water and the solution is evaporated, the resulting purified evaporated ammonium phosphate solution is divided into two streams, one of which is directed to the receiving mono-ammonium phosphate is crystallized, and the second is ammoniated to obtain diammonium phosphate, crystals of diammonium phosphate are evaporated and separated.

The main difference of the claimed invention is the method of purification of EPA from impurities by preliminary dilution of evaporated EPA with water, the introduction of calcium salt and fractional supply of ammonia water with its specific costs.

It is advisable to neutralize the use of ammonia water, and the separation of the purified ammonophosphate solution into streams is carried out depending on the need for a specific ammonium phosphate.

The utilization of the mother liquor separated at the stage of primary crystallization of monoammonium phosphate is carried out by mixing it with the precipitate obtained after filtration of the pulp with a pH of 4.2-4.5 and processed into nitrogen-phosphorus fertilizers by known methods.

The method is as follows, one stripped off (not pretreated TBP) EPA containing: P ₂ About ₅ - 50.6%; F -0.19%; SO ₄ - 2.34%; CaO - 0.66%; Fe - 0.48%, diluted with water to a concentration of 23-25% P ₂ O ₅ and calcium carbonate is sequentially introduced into it with a flow rate of 25-35 kg / t evaporated EPA, ammonia water to a pH of 1.6-2.0 in the first stage and pH of 4.2 to 4.5 in the second stage. The liquid phase - ammonium phosphate solution - is separated from the precipitate by filtration or centrifugation and sent to evaporation, crystallization of monoammonium phosphate and centrifugation. The mother liquor is returned to the sediment pulp, granulation of the resulting mixture and drying to obtain high-quality phosphate-nitrogen fertilizer.

The crystals of monoammonium phosphate after the first stage of crystallization are dissolved in deionized water, evaporated to a concentration of 48-50% P ₂ O ₅ and sent to the second stage crystallization of monoammonium phosphate and centrifugation. To obtain diammonium phosphate evaporated to a concentration of 48-50% by P ₂ O _{5, the} solution of monoammonium phosphate is saturated with gaseous ammonia to pH 8.0-8.2 and fed to crystallization and centrifugation.

Moreover, mother liquors after the second stage of crystallization of mono- and diammonium phosphates are returned to mixing with the solution after dissolution of the first crystals of mono-ammonium phosphate or to the production of feed ammonium phosphates. The proposed method allows you to:

- get crystals of food MAF with a moisture content of 1.9% after a centrifuge of the following composition,%:

P ₂ O ₅ water. - 60.7; NH ₃ 14.4; F is 0,0002; Pb - 1 × 10 ^-4 ; As - 1 × 10 ^-4 ; Hg-1 x 10 ^-5 ; Cd - 1 × 10 ^-5 ; the pH of the 5% solution is 4.2; humidity - 1.9%;

- get crystals of food DAP with a moisture content of 2.2% after a centrifuge, the following composition,%:

P ₂ O ₅ water. - 52.6; NH ₃ 25.16; F≤0,00025; Pb - 1 × 10 ^-4 ; As - 1 × 10 ^-4 ; Hg - 1 × 10 ^-5 ; Cd - 1 × 10 ^-5 ; the pH of the 5% solution is 8.3;

- ammophos of the following composition, in terms of dry product,%: P ₂ O ₅ - 53.6; N - 10.5; CaO - 12.6; F 1.18; SO ₄ 2.4; Fe - 2.8;

- mother liquor crystallization MAF (%):

P ₂ O ₅ - 18.9; F is 0.0012; NH ₃ - 4.4; SO ₄ - 1.47; CaO - n / a; Fe - 0.0024; d = 1.18

- mother liquor crystallization DAP (%):

P ₂ O ₅ - 22.6; F is 0.0010; NH ₃ 8.2; SO ₄ - 1.67; CaO - n / a; Fe - 0.0016; d = 1.27.

The essence of the method is as follows: one stripped off phosphoric acid, without treating it with TBP is diluted with one stripped off EPA to a concentration of 23-25% P ₂ O ₅ , which allows to organize the process flow: for example, at a concentration of P ₂ O ₅ equal to, for example, 27% , the process of neutralization with calcium carbonate occurs with the formation of a stable foam, the destruction of which takes a long time (more than 30 minutes); at a concentration of P ₂ O ₅ equal to, for example, 21%, excessive dilution of the system takes place, which in subsequent operations requires excessive energy costs.

The introduction of calcium carbonate into the diluted solution of EPA makes it possible to isolate the main amount of fluorine (up to 0.0026% in the ammonium phosphate solution separated from the precipitate) in the form of calcium fluoride, the solubility of which is significant during subsequent ammonization of the system to a pH of 4.2-4.5 into the insoluble precipitate lower than the solubility of sodium silicofluoride. This is due to the fact that calcium carbonate is introduced into the acidic solution in such a way that, at a flow rate of 25-35 kg / t of evaporated EPA, only soluble monocalcium phosphate is formed in the liquid phase, but there is practically no precipitation of calcium sulfate and, therefore, there is no cost overrun CaCO ₃ . Further, in the process of neutralization, part of the calcium, including that contained in the initial EPA (0.66% CaO), passes into dicalcium phosphate, but the necessary amount of calcium ions remains so that when fluorine hydrofluoric acid during ammonolysis is first transferred to ammonium silicofluoride by reaction

H ₂ SiF ₆ + 2NH ₄ OH = (NH ₄ ) ₂ SiF ₆ + 2H ₂ O,

and then to ammonium fluoride by reaction

(NH ₄ ) ₂ SiF ₆ + 4NH ₄ OH = 6NH ₄ F + SiO ₂ + 2H ₂ O,

conduct deep defluorination by reaction

Ca (H ₂ PO ₄ ) ₂ + 2NH ₄ F = CaF ₂ + 2NH ₄ H ₂ PO ₄ .

Another role of calcium carbonate is to create the so-called “Pillows” made of crystals of calcium phosphate, on which iron, aluminum phosphates, calcium fluoride and silicon dioxide will be deposited, which creates the conditions for obtaining well filtering precipitates.

The choice of the optimal consumption of calcium carbonate, equal to CaO / P ₂ O ₅ = (0.03-0.05): 1, is due to the fact that when the flow rate is less than 0.03: 1, the fluorine content in the ammonium phosphate solution (AMPF) increases to 0, 01%, while the filtration performance of the phosphate precipitate isolated at pH 4.2-4.5 decreases from 12.0 to 7.3 t / m ² day; at a flow rate of more than 0.05: 1, due to an increase in the yield of insoluble precipitate, there is a decrease in the recovery of P ₂ O ₅ from EPA to AMPF from 82.9 to 77.4%.

Ammonization of EPA with ammonia water is more expedient because when gaseous ammonia is introduced, the concentration of P ₂ O ₅ in the liquid phase of the pulp increases significantly, which leads to excess solubility of ammonium phosphate and salting out in the form of crystals with an insoluble precipitate, i.e. to direct losses of a valuable product.

Fractional ammonization was performed in such a way that ammonia water was supplied to the first stage to a pH of 1.6–2.0 (approximately 2/3 of the total ammonia consumption), and the remainder to the second stage to a pH of 4.2–4.5. This is because such a process leads to the formation of pseudocrystalline crystals of iron and aluminum phosphates in the first stage of the embryos, while the starting silica does not have a colloidal structure, does not cover the fabric, and does not interfere with the filtration of insoluble sediment. A decrease in pH (to 1.4) leads to a decrease in the filterability of the precipitate by about 10%, and an increase in pH (to 2.2) contributes to a significant precipitation of phosphates, which increases its moisture content from 53.3 to 61.2%, reducing the recovery of P ₂ About ₅ in AMFR by about 2.4%.

The pH value of the second stage of neutralization (4.2-4.5) is due to the need to obtain, for subsequent operations, AMPF containing mainly monoammonium phosphate: at pH 4.2, the solution contains 98% MAF and 2% DAP, at pH 4.5, respectively 95 and 5; and at a pH of 4.8 - 80 and 20. This is due to the fact that the presence of DAP in MAF leads to losses of ammonia and the need to capture it during subsequent operations of evaporation of AMPF, which is undesirable, as it complicates the process. So, the dissociation pressure at 100 ° C above MAF is almost zero, above DAF - 5 mm RT. Art., and at 125 ° C it increases, respectively, to 0.05 and 30 mm.

At a pH of less than 4.2, the reaction of AMPH formation does not end, part of the phosphate ions may be in a different form, the system is unstable, which negatively affects the subsequent operations of evaporation of AMPF and obtaining crystals of MAP and DAP.

Using the proposed method will allow to increase the efficiency of the process due to its simplification, in particular the elimination of sites of extraction of phosphoric acid TBP, washing and re-extraction and the process of defluorination; get phosphates of higher quality by the content of basic substances, which is evident when comparing the data of the prototype and the data given in the example and table of this method. In addition, the receipt of two products at the same time (MAF and DAF) in any ratio will expand the range of products, without making changes to the technological and hardware schemes.

The method is illustrated by the following examples.

Example 1

The process was carried out in a rector of 3 m ³ in a batch mode. 1000 kg of EPA (P ₂ O ₅ - 50.6%; F - 0.19%; SO ₄ - 2.34%; CaO - 0.66%; Fe - 0.48%) was diluted with 1000 kg of water at a temperature of 35 -40 ° C for 10 min and served in dilute acid (25.3% P ₂ O ₅ ) for 20 min (10 min supply), at 35-40 ° C 30 kg of calcium carbonate to a CaO / P ₂ ratio O ₅ = 0.03. The pH of the system was 0.12. Then, in 2017 kg of the suspension, ammonia water was introduced into the first stage in the amount of 400 kg of a 20.7% solution of NH ₃ to a pH of 1.6, at a temperature of 35-40 ° C, with a feed time of 20 minutes and an agitation time of 10 minutes. In the resulting 2417 kg suspension, 221 kg of a 20.7% solution of NH _{3 was} added to the second stage of neutralization to a pH of 4.5, at a temperature of 35-40 ° C, with a feed time of 30 minutes and an agitation time of 30 minutes, 2638 kg of pulp was sent for filtration, while received 2295 kg of ammonium phosphate solution (AMPF) containing,%: P ₂ O ₅ - 18.29; NH ₃ 4.8; F is 0.0026; SO ₄ 0.85; CaO - 0.12; Fe - 0.0009 and 343 kg of insoluble sediment, which is an ammophos with a moisture content of 53.3%, containing, in terms of the dried product,%: P ₂ O ₅ - 54.2; N - 9.5; CaO - 12.6; F 1.18; SO ₄ - 2.4; Fe - 2.8.

At the next stage, 2295 kg of AMPF was directed to evaporation up to 995 kg, while 995 kg of crystal pulp was formed (crystals began to precipitate before the system was cooled, during evaporation), which were sent for cooling and crystallization at a temperature of 16-20 ° C, for 8 hours. After centrifugation, 650 kg of MAF crystals and 345 kg of a mother liquor containing,%, P ₂ O ₅ - 18.2 were obtained; F is 0.0013; NH ₃ 8.3; SO ₄ - 4.0; CaO - 0.33; Fe - 0.0035; d = 1.18; pH 4.4 (transition P ₂ O ₅ from EPA - 12%), which was directed to mixing with a wet insoluble precipitate, granulation and drying. MAF crystals (650 kg) were dissolved in 1320 kg of deionized water; in this case, 1970 kg of solution was obtained, which was sent for evaporation and 704 kg of MAF crystal pulp were obtained; it was divided into 2 equal parts, 352 kg of crystal pulp each. The first part was cooled, sent for centrifugation, and 257.6 kg of MAF crystals and 94.4 kg of crystallization mother liquor were obtained.

The composition of the crystals,%: P ₂ About ₅ water. - 60.7; NH ₃ 14.4; F is 0,0002; Pb - 1 × 10 ^-4 ; As - 1 × 10 ^-4 ; Hg - 1 × 10 ^-5 ; Cd - 1 × 10 ^-5 ; the pH of the 5% solution is 4.2; W - 1.9.

The composition of the mother liquor,%: P ₂ O ₅ - 18.9; F is 0.0012; NH ₃ - 4.4; SO ₄ - 1.47; CaO - n / a; Fe - 0.0024; d = 1.18.

The second part of the pulp of MAF crystals was also cooled, 364 kg of ammonia water were introduced into it and evaporation was carried out at a temperature of 70-80 ° С to 440 kg; the pulp was cooled and sent for centrifugation. At the same time, 260 kg of DAF crystals and 180 kg of crystallization mother liquor were obtained. The composition of the crystals,%: P ₂ About ₅ water. - 52.6; NH ₃ 25.16; F≤0,00025; Pb - 1 × 10 ^-4 ; As - 1 × 10 ^-4 ; Hg - 1 × 10 ^-5 ; Cd - 1 × 10 ^-5 ; the pH of the 5% solution is 8.3; W - 2.2

The composition of the mother liquor,%: P ₂ O ₅ - 22.6; F is 0.0010; NH ₃ 8.2; SO ₄ - 1.67; CaO - n / a; Fe - 0.0016; d = 1.27.

The influence of other parameters on the technological parameters of the process are presented in table 1

As can be seen from the table, the claimed limits of the technological parameters allows to obtain products that are stable in quality.

Composition of EPA: P ₂ O ₅ - 50.6%; F - 0.19%; SO ₄ - 2.34%; CaO - 0.66%; Fe - 0.48% No. The concentration of H ₃ PO ₄ ,% P ₂ O ₅ CaO / P ₂ O ₅ pH
Stage 1 pH
2 stage The quality of the crystals,% Laf DAF P ₂ O ₅ water NH ₃ F W PH 5% P ₂ O ₅ water NH ₃ F W PH 5% one 23.0 0.04 1.8 4.35 60.5 14.3 0,0002 2.0 4.1 52.6 25.1 0,0002 2.2 8.3 2 24.0 0.04 1.8 4.35 60.7 14,4 0,0002 1.7 4.1 52.7 25,2 0,0002 2.1 8.2 3 25.0 0.04 1.8 4.35 60.7 14,4 0,0002 1.7 4.1 52.6 25,2 0,0002 2.2 8.3 four 24.0 0,03 1.8 4.35 60.8 14.5 0,0002 1,5 4.1 52,5 25.0 0,0002 2.1 8.2 5 24.0 0.04 1.8 4.35 60.5 14.2 0,0002 2.0 4.1 52.6 25.1 0,0002 2.1 8.2 6 24.0 0.05 1.8 4.35 60.6 14,4 0,0002 1.8 4.1 52,5 25.0 0,0002 2.2 8.3 7 24.0 0.04 1,6 4.35 60,4 14.2 0,0002 2.1 4.1 52.6 25.1 0,0002 2.1 8.4 8 24.0 0.04 1.8 4.35 60.6 14,4 0,0002 1.8 4.1 52.6 25.1 0,0002 2.2 8.3 9 24.0 0.04 2.0 4.35 60.6 14,4 0,0002 1.8 4.1 52.6 25.1 0,0002 2.2 8.3 10 24.0 0.04 1.8 4.2 60.7 14,4 0,0002 1.7 4.0 52.7 25,2 0,0002 2.2 8.4 eleven 24.0 0.04 1.8 4.35 60.6 14,4 0,0002 1.8 4.1 52.7 25.2 0,0002 2.0 8.2 12 24.0 0.04 1.8 4,5 60.7 14,4 0,0002 1.7 4.2 52.6 25.1 0,0002 2.2 8.3

Claims (3)

1. A method of producing food ammonium phosphates from one stripped off extraction phosphoric acid, including neutralization with ammonia, crystallization of ammonium phosphate from ammonium phosphate solution, separation of crystals from mother liquors with utilization of the latter, characterized in that one stripped off phosphoric acid is diluted to a concentration of 23-25% P ₂ O ₅ , calcium carbonate is introduced into it at a ratio of CaO / P ₂ O ₅ = (0.03-0.05): 1, then the resulting mixture is neutralized in two stages, first to a pH of 1.6-2.0, then to pH 4.2-4.5, the resulting pulp is filtered with separation ammonium phosphate solution, monoammonium phosphate is crystallized, the crystals separated from the mother liquor are dissolved in water and the solution is evaporated, the obtained purified ammonium phosphate solution is divided into two streams, one of which is directed to obtain monoammonium phosphate by crystallization, and the second is ammoniated to obtain diammonium phosphate, the crystals are evaporated and separated . 2. The method according to claim 1, characterized in that ammonia water is used to neutralize, and the separation of the purified ammonium phosphate solution into streams is carried out depending on the need for a specific ammonium phosphate. 3. The method according to one of claims 1 and 2, characterized in that the disposal of the mother liquor separated at the stage of primary crystallization of monoammonium phosphate is carried out by mixing it with the precipitate obtained after filtering the pulp with a pH of 4.2-4.5, and process nitrogen-phosphorus fertilizers by known methods.