RU2406713C2 - Diammonium phosphate synthesis method - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to a method for synthesis of diammonium phosphate which has antiseptic properties. The method involves mixing phosphoric acid and spent sulphuric acid from petrochemical production in amount of 25-30 kg per ton of phosphoric acid and industrial sulphuric acid until attaining 6.5-7.0 % SO₃ content in the mixture, step by step neutralisation of ammonia with the mixture of acids until molar ratio NH₃/H₃PO₄ = 1.4, and then to 1.75, granulation, drying the product and subsequent cleaning of exhaust gases in two steps, at the first step of which ammonium phosphate pulp with molar ratio NH₃/H₃PO₄ = 0.4 -0.5 is fed, and at the second step - a mixture of acids and an additional antifoaming agent PG-3 in amount of 0.5-2 g per ton of the end product.

EFFECT: method prevents foaming of absorption solutions and enables to obtain diammonium phosphate having antiseptic properties, with high efficiency of the process.

1 tbl, 2 ex

Description

The invention relates to a method for producing diammonium phosphate (DAP), which has antiseptic properties and is widely used in agriculture as nitrogen-phosphorus fertilizer for various types of soils.

A known method of producing diammonium phosphate [1], comprising mixing phosphoric acid with sulfuric acid, stepwise neutralizing ammonia with the obtained mixture of acids to a molar ratio of NH ₃ / H ₃ PO ₄ = 1.4, and then up to 1.75, granulation, drying, classification of the finished product and subsequent purification of the exhaust gases in two stages. According to the known method, phosphoric acid is mixed with sulfuric acid to obtain in the mixture the ratio of SO ₃ : P ₂ O ₅ = 1: 9-15, which is achieved by adding 86-120 kg of sulfuric acid in terms of monohydrate (100% H ₂ SO ₄ ) per 1000 kg P ₂ O ₅ . The waste gases are cleaned in two stages, the first of which is pulp of ammonium phosphates with a molar ratio of NH ₃ / H ₃ PO ₄ = 0.4-0.6, and the second stage is fed with extraction phosphoric acid and the cleaning is carried out until the sanitary standard is reached ammonia content in exhaust gases. This method of producing diammonium phosphate can increase the yield of the finished product fraction 2-4 mm, to achieve sanitary standards of ammonia in the exhaust gases.

The disadvantage of this method of producing DAF is the inability to obtain fertilizer with antiseptic properties.

The closest in technical essence and the achieved result is a known method for producing diammonium phosphate [2], including mixing phosphoric acid with sulfuric acid, stepwise neutralization of ammonia with a mixture of acids to a molar ratio of NH ₃ / H ₃ PO ₄ = 1.4, and then up to 1.75 , granulation, drying and subsequent cleaning of the exhaust gases in two stages. The mixture of acids serves spent sulfuric acid containing 8-10% wt. in terms of carbon of organic compounds, in the amount of 52-60 kg of sulfuric acid in terms of monohydrate per 1 ton of P ₂ O ₅ (or 35-40 kg of spent sulfuric acid (natural) per 1 ton of phosphoric acid). Ammonium phosphate pulp with a molar ratio of NH ₃ / H ₃ PO ₄ = 0.4-0.6 is fed to the first stage of exhaust gas purification, and an acid mixture containing phosphoric acid with the addition of spent sulfuric acid at a ratio in the sulfuric mixture is fed to the second stage and phosphoric acid equal to 1: (1.5-4), respectively. As sulfuric acid, spent sulfuric acids of various petrochemical industries containing 75-85% H ₂ SO ₄ and 8-10% organic compounds in terms of carbon (hereinafter referred to as USC) are used. The mixture of phosphoric and sulfuric acids supplied to the second stage of purification is characterized by a high content of spent sulfuric acid, OSK is introduced in an amount of 220-580 kg (natural) per 1 ton of phosphoric acid. The known method allows to obtain fertilizer with antiseptic properties. The supply of a mixture of phosphoric and sulfuric acids with a high content of spent sulfuric acid to the second stage of gas purification leads to stable foaming of the absorption solutions.

The main disadvantage of this method is the abundant foaming of absorption solutions, which leads to a decrease in the productivity of the process. A disadvantage of the known method is the complexity of the process due to the need for preliminary preparation of two mixtures of phosphoric and sulfuric acids of different compositions for their subsequent supply to the neutralization and the second stage of purification of exhaust gases, respectively.

We set the task, while maintaining the advantages of the known method, to eliminate the above disadvantages and to obtain fertilizer with antiseptic properties.

The problem is achieved in the proposed method for producing diammonium phosphate, including the mixing of sulfuric and phosphoric acids, the stepwise neutralization of ammonia with the mixture to a molar ratio of NH ₃ / H ₃ PO ₄ = 1.4, and then to 1.75, granulation, drying and classification of the finished product and subsequent purification of the exhaust gases in two stages, the pulp of ammonium phosphate with a molar ratio of NH ₃ / H ₃ PO ₄ = 0.4-0.5 is fed to the first stage of purification,

and on the second - the resulting mixture of phosphoric and sulfuric acids and

additionally enter the reagent - antifoam PG-3 in the calculation of 0.5-2 g per 1 ton of the finished product. To prepare a mixture of acids, sulfuric acid is used technical and spent sulfuric acid containing organic compounds, and 25-30 kg of spent sulfuric acid are pre-introduced per 1000 kg of phosphoric acid, and then technical sulfuric acid is supplied with a concentration of 92.5-95% H ₂ SO ₄ until the final SO ₃ content in the mixture of acids is 6.5-7.0%.

The essence of the method is as follows. Production extraction phosphoric acid (hereinafter referred to as EPA) with a concentration of 48-52% P ₂ O ₅ and a content of 3.5-4.5% sulfuric acid in terms of SO _{3 is} pre-mixed with the estimated amount of spent sulfuric acid in the calculation of 25-30 kg OSK per 1 t. The mixture of acids is stirred for at least 1 hour and a sample of the resulting mixture of acids is analyzed for the content of SO ₃ . Then, by introducing a calculated amount of technical sulfuric acid, the content of SO ₃ in the mixture of acids is adjusted to 6.5-7.0%. The resulting mixture of phosphoric, spent and industrial sulfuric acids is sent to diammonium phosphate, the mixture is divided into two streams, the first stream is directed to the stepwise neutralization of ammonia, the second stream to the second stage of purification of exhaust gases. To this stage of gas purification to suppress foaming, an additional 0.5-2 g of defoamer PG-3 is added per one ton of the finished product - diammonium phosphate.

The use of a mixture of phosphoric and sulfuric acids containing organic compounds in the second stage of exhaust gas purification leads to foaming. Of the many reagents studied, the antifoam PG-3, produced according to TU 10 of the Russian Federation 717-92 with a melting point of no higher than 53 ° C and representing polyglycerol fatty acids, has the greatest efficiency of defoaming. Defoamer PG-3 is available in the form of cream tablets to a light brown color. The reagent consumption in the calculation of 0.5-2 g per 1 ton of the finished product eliminates foaming. The consumption of antifoam PG-3 in the calculation of 0.5-2 g per 1 ton of the finished product is selected experimentally. The antifoam is introduced into the collection of the second stage of purification of exhaust gases, which then with the absorption solution enters the collection of the first stage of purification, where foaming is also eliminated.

To achieve standard quality indicators for the content of nitrogen (18% N) and phosphorus (47% P ₂ O ₅ ) in DAF, it is necessary to strictly maintain the sulfuric acid content in terms of SO ₃ in the mixture of acids. When using extraction phosphoric acid with a concentration of 48-52% P ₂ O _{5, the} optimal SO ₃ content in the mixture is 6.5-7.0%, and diammonium phosphate composition is obtained: 18% N and 47% P ₂ O ₅ . With an increase in the content of SO ₃ in the mixture of acids above 7.0% in the finished product, the phosphate component decreases below 47% P ₂ O ₅ . The decrease in the content of SO ₃ in the mixture of acids below 6.5% leads to an increase in phosphate component of 47% P ₂ O ₅ in the finished product.

In the known method for producing DAF (prototype), the regulation of the nutrient content in the finished product is achieved using two different mixtures of phosphoric and sulfuric acids.

Maintaining the consumption of spent sulfuric acid, containing 8-10% of organic compounds in terms of carbon, in the range of 25-30 kg (natural) per 1 ton of phosphoric acid provides diammonium phosphate with antiseptic properties. Reducing the consumption of spent sulfuric acid below 25 kg leads to a decrease in the antiseptic properties of the finished product. An increase in the consumption of spent sulfuric acid above 30 kg leads to foaming, respectively, to a decrease in productivity.

The method is illustrated by the following examples, presented below and in the table.

Example 1 (prototype). 2126 kg of phosphoric acid with a concentration of 53% are mixed in a collection with 61.9 kg of OSK with a concentration of 84% H ₂ SO ₄ and containing 10% wt. organic component in terms of carbon. The OSK content is 52 kg in terms of monohydrate per 1 ton of P ₂ O ₅ . The resulting mixture is fed into a tubular reactor, where it is neutralized with ammonia to a molar ratio of NH ₃ / H ₃ PO ₄ = 1.4. The temperature of the pulp of ammonium phosphate in the Converter is 145 ° C. The resulting pulp is fed to an ammonizer granulator, where ammonia is further ammoniated to a molar ratio of 1.75 and granulated. Next, the fertilizer mixture is sent to a drying drum and dried to a moisture content in the product of not more than 1.2%. The dried granular product goes into classification. The exhaust gases after the ammonia granulator and the drying drum enter the first purification stage, where they are irrigated with a pulp of ammonium phosphates with a molar ratio of NH ₃ / H ₃ PO ₄ = 0.4. Further, the exhaust gases enter the absorber of the second stage of purification, where they are cleaned with a mixture of phosphoric and OSK to the sanitary norm. A mixture of acids obtained by mixing 1 part by weight is fed to the second stage of purification. phosphoric acid and 0.58 parts by weight spent sulfuric acid (ratio of H ₂ SO ₄ : H ₃ PO ₄ = 1: 1.5). Get 2300 kg of the finished product composition: P ₂ O ₅ - 46.2%, N - 18.1%. The process is accompanied by steady foaming in the collections of absorption liquids of the second and first stages of purification of exhaust gases, overfilling of the foam from the collectors, and stopping of pumping equipment.

EXAMPLE 2 37.24 t phosphoric acid concentration of 52% P ₂ O ₅ and 3.5% SO ₃ premixed with 1.12 m collection of spent sulfuric acid concentration of 84% H ₂ SO ₄ containing 10% of the organic component in in terms of carbon. The content of spent sulfuric acid is 30 kg per 1 ton of phosphoric acid. The mixture was stirred for 2 hours and a sample was taken for analysis. The composition of the preliminary mixture: 50.5% P ₂ O ₅ , 5.4% SO ₃ . Then add 0.86 tons of industrial sulfuric acid with a concentration of 93% H ₂ SO ₄ , get 39.22 tons of a mixture of acids (phosphoric, spent and technical sulfuric acids) with a concentration of 49.4% P ₂ O ₅ and 6.95% SO ₃ . The resulting mixture is divided into two streams, one part in an amount of 35 tons is fed to the collector, where it is mixed with the absorption solution after the first stage of purification of the exhaust gases to obtain a reaction mass. The rest of the mixture of acids in an amount of 4.22 tons is fed to the second stage of purification of exhaust gases. The reaction mass from the collection is fed into a tubular reactor, where it is neutralized with ammonia to a molar ratio of NH ₃ / H ₃ PO ₄ = 1.4. The temperature of the pulp of ammonium phosphate in the Converter is 145 ° C. The resulting pulp is fed to an ammonizer granulator, where ammonia is further ammoniated to a molar ratio of 1.75 and granulated. Next, the fertilizer mixture is sent to a drying drum and dried to a moisture content in the product of not more than 1.2%. The dried granular product goes into classification. The finished product yield is 40 tons. The exhaust gases after the granulator-granulator and the drying drum enter the first purification stage, where they are irrigated with a pulp of ammonium phosphates with a molar ratio of NH ₃ / H ₃ PO ₄ = 0.4. Further, the exhaust gases enter the absorber of the second purification stage, where they are cleaned with a mixture of phosphoric and sulfuric acids to the sanitary standard (20 mg NH ₃ / m ^{3 of} exhaust gases). In the collection of absorption solution of the second stage of purification add defoamer PG-3 in an amount of 80 g. The consumption of antifoam is 2 g per 1 ton of the finished product. The absorption solution of the second stage of purification is fed into the collector of the first stage, then in the form of a pulp of ammonium phosphates is sent to the collector to obtain a reaction mass. The process of purification of exhaust gases proceeds without foaming. Get a darkened diammonium phosphate composition: 18.0% N, 47.0% P ₂ O ₅ with antiseptic properties.

Using the proposed method will allow to obtain diammonium phosphate with antiseptic properties at high process performance and use the spent sulfuric acid - a waste of petrochemical industries.

Information sources

1. RF patent №2122989, С05В 7/00, 1998

2. RF patent No. 2157355, С05В 7/00, 1999

Claims (1)

A method of producing diammonium phosphate, comprising mixing phosphoric acid with spent sulfuric acid from petrochemical plants containing organic compounds, stepwise neutralizing ammonia with a mixture of acids to a molar ratio of NH ₃ / H ₃ PO ₄ = 1.4, and then to 1.75, granulation, drying and subsequent purification of the exhaust gases in two stages, the first of which is fed a pulp of ammonium phosphates with a molar ratio of NH ₃ / H ₃ PO ₄ = 0.4-0.5, and the second is a mixture of phosphoric and spent sulfuric acid, characterized in that to mix with phosphoric acid to technical sulfuric acid is supplied thoroughly, and 0.5-2 g of PG-3 antifoam per 1 ton of the finished product is introduced into the second exhaust gas purification stage, and 25-30 kg of spent sulfuric acid per 1 is preliminarily mixed with phosphoric acid t phosphoric acid, sulfuric acid further technical - content achieving up to 6,5-7,0% SO ₃ in the mixture of acids.