A method for preparing polyphosphoric acid by using superfine powder of phosphorus pentoxide

Abstract

The application provides a novel polyphosphoric acid preparation method, which comprises the following steps: (1) ball milling P2O5 solid into P2O5 superfine powder with a required particle size; (2) taking the P2O5 superfine powder obtained in step (1) and water as raw materials, putting the raw materials into a reaction kettle according to a certain molar ratio, controlling reaction temperature, reaction time, stirring speed and reaction kettle pressure, and performing a polymerization reaction, so that a colorless transparent viscous liquid, i.e. polyphosphoric acid, is finally obtained.

Description

TECHNICAL FIELD

[0001] The present application relates to the chemical industry, in particular to a production method of polyphosphoric acid, more particularly to a method for preparing polyphosphoric acid by reacting water and ultrafine powder of diphosphorus pentoxide. BACKGROUND

[0002] Polyphosphoric acid (PPA for short) is also known as polymeric phosphoric acid, tetraphosphoric acid or polyphosphoric acid, which is a colorless transparent viscous liquid inorganic acid. Polyphosphoric acid can be widely used in pharmaceuticals, perfumes, leather and chemical industry, and used as a cyclizing agent, acidifying agent, dehydrating agent and catalyst in organic synthesis and petrochemical industry. In addition, polyphosphoric acid can also be used as a substitute for orthophosphoric acid, which can be diluted to obtain different concentrations of phosphoric acid according to needs, and has advantages that ordinary orthophosphoric acid cannot match: (1) It has supercooling property, and can remain liquid state and is not easy to crystallize even at much lower temperature, so it is convenient for transportation and storage; (2) Polyphosphoric acid is less corrosive than orthophosphoric acid; (3) Because of the high content of polyphosphoric acid, the transportation cost per unit weight is 40-50% less than that of orthophosphoric acid; (4) It has chelation effect, which can make metal ions in the solution form chelates and stably exist in the acid.

[0003] The existing production methods of polyphosphoric acid include wet process and thermal process. Wet polyphosphoric acid is mainly obtained by single-stage / multi-stage evaporation or electrolysis of wet-process phosphoric acid to remove water. For example, patent US6616906 and CN107128888A report a method for preparing polyphosphoric acid by high-temperature heating and concentration, and patent US2839408 reports a method for preparing polyphosphoric acid by electrolytic concentration. The cost of polyphosphoric acid prepared by wet process is relatively low, but the impurity content of the product is high. In addition, over-heating phenomenon is easy to occur in evaporation concentration, and explosive gas is easy to produce in electrolytic concentration, which limits the application of wet process. Therefore, thermal process is mainly used in China.

[0004] The production of thermal polyphosphoric acid is mainly based on the traditional production process of thermal phosphoric acid, supplemented by the absorption of water or dilute phosphoric acid. The process can be seen from the following flow: yellow phosphorus combustion - absorption hydration - first absorption - secondary absorption - finished product. The yellow phosphorus is combusted in air to obtain phosphorus pentoxide gas, which is absorbed by water / acid circulation, and polyphosphoric acid is generated while being cooled. Such methods have one-step generation, i.e., liquid phosphorus is sprayed into a combustion hydration tower with compressed air, and the cold acid forms an acid film along the tower wall surface, while the combustion gas is cooled, and the phosphorus pentoxide is polymerized with phosphoric acid to generate polyphosphoric acid. There are also two-step production methods of combustion and hydration. For example, document CN101269805 discloses a preparation method of polyphosphoric acid, which first concentrates 80-85% phosphoric acid and then polymerizes with P2O5 to generate polyphosphoric acid. Although the polymerization reaction temperature is only 80°C, the phosphoric acid needs to be concentrated at high temperature, which has high energy consumption. CN101531354A and CN103818890A disclose a method for preparing polyphosphoric acid by absorbing P2O5 gas with dilute phosphoric acid. The raw materials used are all high-temperature P2O5 gas, and dilute phosphoric acid is needed for absorption, which has high cost.

[0005] It can be seen that the production process of thermal polyphosphoric acid in the prior art effectively reduces the process energy consumption (from the traditional concentration temperature of 800-1000°C to the dehydration polymerization reaction temperature of 200-300°C), but the required energy consumption is still high. In addition, the existing thermal process uses P2O5 gas and recycled 85% dilute acid for reaction, which needs multiple cycles to prepare polyphosphoric acid, and the process flow and time are long. The 85% dilute acid needs to be prepared by P2O5 hydration. Due to the low absorption efficiency of the hydration process, the water consumption of the whole process is large. It can be seen that the method for preparing polyphosphoric acid by the existing thermal process still has the defects of large water consumption, high energy consumption, and long time. SUMMARY

[0006] In order to solve the defects of expensive raw materials, large water consumption, high energy consumption, and long time in the preparation of polyphosphoric acid in the prior art, a new method for preparing polyphosphoric acid is provided. The method uses phosphorus pentoxide ultrafine powder prepared by ball milling and water as raw materials, controls the reaction temperature, temperature, and stirring rate, and finally obtains a colorless transparent viscous liquid as polyphosphoric acid.

[0007] The technical scheme of the present application is as follows:

[0008] (1) Ball milling of phosphorus pentoxide solid to obtain phosphorus pentoxide ultrafine powder with a desired particle size;

[0009] (2) using the ultra-fine phosphorus pentoxide powder obtained in step (1) and water as raw materials, putting the raw materials into a reaction kettle according to a certain molar ratio, controlling the reaction temperature, reaction time, stirring rate and reaction kettle pressure, and performing a polymerization reaction to obtain a colorless transparent viscous liquid, which is polyphosphoric acid.

[0010] Preferably, the particle size of the ultra-fine phosphorus pentoxide powder obtained by ball milling is 0.2-2 microns, further, the particle size of the ultra-fine phosphorus pentoxide powder obtained by ball milling is 0.2-1 micron, further, the particle size of the ultra-fine phosphorus pentoxide powder obtained by ball milling is 0.2 microns.

[0011] Preferably, the molar ratio of the ultra-fine phosphorus pentoxide powder to water is 1:1.5-2.2, further, the molar ratio of the ultra-fine phosphorus pentoxide powder to water is 1:1.8-2.0, further, the molar ratio of the ultra-fine phosphorus pentoxide powder to water is 1:1.8.

[0012] Preferably, the temperature of the polymerization reaction is 120-180℃, further, the temperature of the polymerization reaction is 130-160℃, further, the temperature of the polymerization reaction is 130℃.

[0013] Preferably, the pressure of the polymerization reaction is 0.01-0.1 Mpa, further, the pressure of the polymerization reaction is 0.05-0.1 Mpa, further, the pressure of the polymerization reaction is 0.08 Mpa.

[0014] Preferably, the time of the polymerization reaction is 2-8 h, further, the time of the polymerization reaction is 2-6 h, further, the time of the polymerization reaction is 2 h.

[0015] Preferably, the polymerization reaction is performed under stirring, and the stirring rate is 300-800 rpm, further, the stirring rate is 300-500 rpm, further, the stirring rate is 300 rpm.

[0016] Preferably, the method further comprises the following step: (3) after the polymerization reaction is completed, the obtained liquid is aged, and the aging time is 12-24 h, further, the aging time of the polymerization reaction is 12 h.

[0017] The preparation method of the present application can complete the reaction of phosphorus pentoxide hydration to phosphoric acid and then polymerization to polyphosphoric acid in one pot at a lower temperature than the prior art by ball milling phosphorus pentoxide into fine powder to increase its contact area with water and utilizing the large amount of reaction heat released in the hydration process, thereby reducing the amount of water used, fully utilizing the hydration heat, saving energy consumption, having the advantages of simple preparation method, environmental protection and low cost, and being suitable for large-scale production and industrial production. DETAILED DESCRIPTION

[0018] In order for those skilled in the art to better understand the technical solutions of the present application, the present application will be further described in detail below with reference to specific embodiments.

[0019] Example 1

[0020] 158g of phosphorus pentoxide solid with a purity of 99.9% and an arsenic content of 15ppm was ball-milled to obtain 0.2-micron phosphorus pentoxide ultrafine powder; the phosphorus pentoxide ultrafine powder was then added to a polymerization reactor equipped with an electric stirrer together with 18g of water, and a polymerization reaction was carried out under the conditions of 130°C, 300rpm and 0.08Mpa, with a reaction time of 2h; after the reaction was completed, the product was aged for 18h and then lowered to room temperature to obtain a colorless transparent viscous liquid, which was polyphosphoric acid.

[0021] It was detected that the P2O5 content in the polyphosphoric acid was 83%.

[0022] Example 2

[0023] 158g of phosphorus pentoxide solid with a purity of 99.9% and an arsenic content of 15ppm was ball-milled to obtain 0.2-micron phosphorus pentoxide ultrafine powder; the phosphorus pentoxide ultrafine powder was then added to a polymerization reactor equipped with an electric stirrer together with 18g of water, and a polymerization reaction was carried out under the conditions of 150°C, 300rpm and 0.08Mpa, with a reaction time of 2h; after the reaction was completed, the product was aged for 18h and then lowered to room temperature to obtain a colorless transparent viscous liquid, which was polyphosphoric acid.

[0024] It was detected that the P2O5 content in the polyphosphoric acid was 88.3%.

[0025] Example 3

[0026] 158g of phosphorus pentoxide solid with a purity of 99.9% and an arsenic content of 15ppm was ball-milled to obtain 0.2-micron phosphorus pentoxide ultrafine powder; the phosphorus pentoxide ultrafine powder was then added to a polymerization reactor equipped with an electric stirrer together with 18g of water, and a polymerization reaction was carried out under the conditions of 150°C, 300rpm and 0.08Mpa, with a reaction time of 4h; after the reaction was completed, the product was aged for 24h and then lowered to room temperature to obtain a colorless transparent viscous liquid, which was polyphosphoric acid.

[0027] It was detected that the P2O5 content in the polyphosphoric acid was 87.6%.

[0028] Comparative Example 1

[0029] The phosphorus pentoxide ultrafine powder of 0.2 mm was obtained by ball milling 158 g of phosphorus pentoxide solid with a purity of 99.9% and an arsenic content of 15 ppm; the phosphorus pentoxide ultrafine powder and 18 g of water were added into a polymerization reactor with an electric stirrer, and a polymerization reaction was carried out at 130°C, 300 rpm and 0.08 MPa, the reaction time was 2 h, after the reaction, the product was aged for 18 h and then cooled to room temperature, a colorless transparent viscous liquid was obtained, the content of P2O5 in the viscous liquid was 77%, and the total content of orthophosphoric acid and pyrophosphoric acid was 85.3% and the total content of tripolyphosphoric acid and tetrapolyphosphoric acid was about 14.7% according to TLC detection analysis.

[0030] Comparative Example 2

[0031] 158 g of phosphorus pentoxide solid with a purity of 99.9% and an arsenic content of 15 ppm was directly added into a polymerization reactor with an electric stirrer without grinding, and a polymerization reaction was carried out at 130°C, 300 rpm and 0.08 MPa, the reaction time was 2 h, after the reaction, the product was aged for 18 h and then cooled to room temperature, a relatively dilute liquid was obtained; the obtained liquid was reheated to 130°C, and a further reaction was carried out at 300 rpm and 0.08 MPa for 12 h, after the reaction, the product was aged for 18 h and then cooled to room temperature, a colorless transparent viscous liquid was obtained, the content of P2O5 was 70.0%, the average polymerization degree was only 0.837, the content of orthophosphoric acid was 97.4%, a small amount of pyrophosphoric acid was present, and no tripolyphosphoric acid, tetrapolyphosphoric acid and the like were detected.

[0032] As can be seen from the above data, the preparation method of the present application can complete the reaction of phosphorus pentoxide hydration to phosphoric acid and then polymerization to generate polyphosphoric acid in one pot at a lower temperature than the prior art by ball milling the phosphorus pentoxide to fine powder to increase the contact area with water and utilizing the large amount of reaction heat released in the hydration process, the water consumption is reduced, the hydration heat is fully utilized, the energy consumption is saved, and the preparation method is simple, environmentally friendly and low in cost, and is suitable for large-scale production and industrial production.

Claims

1. A method for preparing polyphosphoric acid, characterized in that it comprises the following steps: (1) ball-milling solid phosphorus pentoxide into phosphorus pentoxide ultrafine powder with a desired particle size; (2) using the phosphorus pentoxide ultrafine powder obtained in step (1) and water as raw materials, carrying out a polymerization reaction in a reaction kettle according to a certain molar ratio of the raw materials, controlling the reaction temperature, reaction time, stirring rate and reaction kettle pressure, and finally obtaining a colorless transparent viscous liquid, which is polyphosphoric acid; wherein the particle size of the phosphorus pentoxide ultrafine powder obtained by ball-milling is 0.2 microns; the molar ratio of the phosphorus pentoxide ultrafine powder to water is 1:1.8; the temperature of the polymerization reaction is 150°C; the pressure of the polymerization reaction is 0.08 Mpa; the time of the polymerization reaction is 2 hours; the polymerization reaction is carried out under stirring, and the stirring rate is 300 rpm; the method further comprises the following step: (3) after the polymerization reaction is completed, the obtained liquid is aged for 12 hours.

2. The method according to claim 1, characterized in that the particle size of the phosphorus pentoxide ultrafine powder is 0.1-0.3 microns.

3. The method according to claim 1, characterized in that the molar ratio of the phosphorus pentoxide ultrafine powder to water is 1:1.5-1:

2.

4. The method according to claim 1, characterized in that the temperature of the polymerization reaction is 140-160°C.

5. The method according to claim 1, characterized in that the pressure of the polymerization reaction is 0.05-0.1 Mpa.

6. The method according to claim 1, characterized in that the time of the polymerization reaction is 1-3 hours.

7. The method according to claim 1, characterized in that the stirring rate is 200-400 rpm.

8. The method according to claim 1, characterized in that the aging time of the obtained liquid is 10-14 hours.