A method for preparing polyphosphoric acid

Abstract

This application provides a recyclable magnetic microsphere catalyst supported on a strong acid and its application in the preparation of polyphosphoric acid. Using this catalyst, polyphosphoric acid can be prepared from wet-process phosphoric acid at a lower temperature, and the catalyst can be effectively recovered.

Description

Technical Field

[0001] This invention relates to the field of chemical engineering, and more specifically to a method for producing polyphosphoric acid. Background Technology

[0002] Polyphosphoric acid (PPA), also known as polyphosphate, tetraphosphate, or polyphosphoric acid, is a colorless, transparent, viscous liquid inorganic acid. It is corrosive, classified as a secondary inorganic acid, and is hygroscopic and does not crystallize. It can hydrolyze with water to form orthophosphoric acid. Typically, phosphoric acid molecules undergo dehydration and cross-linking to form polyphosphoric acids of varying degrees of cross-linking. A mixture of polyphosphoric acids with different degrees of cross-linking forms polyphosphoric acid. Its melting point is 48–50°C, boiling point is 856°C, density is 2100 kg / m³, and relative molecular weight is 337.93. Its representative formula is H₆P₄O₃. 13 The concentration of H3PO4 is an important indicator of polyphosphoric acid, with commonly used concentrations being 105%, 110%, and 115%. Polyphosphoric acid has a wide range of applications in the pharmaceutical, fragrance, leather, and chemical industries. It is also used as a cyclizing agent, acidifying agent, dehydrating agent, and catalyst in organic synthesis and petrochemicals. In addition, polyphosphoric acid can be used as a substitute for orthophosphoric acid.

[0003] There are two existing processes for producing polyphosphoric acid: the wet process and the thermal process (see references US6616906, CN107128888A, US2839408, CN101531354A, CN103818890A, US4309394A, CN101269805A, etc.). The thermal process for producing polyphosphoric acid mainly utilizes traditional thermal phosphoric acid production equipment with supplemental cooling. The wet process for producing polyphosphoric acid involves purifying wet-process phosphoric acid, then heating and concentrating it in a single-stage or multi-stage evaporator to remove moisture. Compared to the thermal process, the wet process produces a lower-cost product, but it has a higher impurity content and is prone to overheating during concentration, limiting its application. Using catalysts such as sulfonic acid, solid acid, and acidic clay to catalyze the dehydration of organic acids to produce polyacids or esters is an effective method (see literature CN101735035A, "Research on the synthesis of ethyl acetate by catalytic dehydration of alcoholic acids" and "Research on the process of synthesizing dimer acids and producing oleic acid by catalytic clay", etc.). However, when using acid as a catalyst, how to recover the corresponding catalyst after the preparation of polyphosphoric acid becomes a problem that needs to be solved.

[0004] In view of this, in order to solve the problem that the preparation of polyphosphoric acid in traditional processes requires a large amount of energy and that the catalyst is difficult to recover when it is used, the present invention provides a recyclable magnetic microsphere catalyst supported on strong acid and the application of the catalyst in the preparation of polyphosphoric acid. Using the catalyst, polyphosphoric acid can be prepared at a lower temperature using wet phosphoric acid as raw material, and the catalyst can be effectively recovered. Summary of the Invention

[0005] The purpose of this invention is to overcome the above-mentioned disadvantages and provide a method for preparing polyphosphoric acid that is simple in process, mild in conditions, and has recyclable catalyst.

[0006] The present invention provides a method for producing polyphosphoric acid, comprising the following steps:

[0007] (1) Ferric chloride hexahydrate, sodium acetate and polyethylene glycol are dissolved in ethylene glycol and reacted. After the reaction is completed, the product is magnetically recovered to obtain iron oxide particles.

[0008] (2) Add iron(III) oxide to fructose solution, disperse evenly and react. After the reaction is complete, the product is magnetically recovered, washed with ethanol and dried. The dried product is calcined in nitrogen atmosphere to prepare magnetic carbon-based microspheres.

[0009] (3) Mix magnetic carbon-based microspheres with sufficient concentrated sulfuric acid to carry out sulfonation reaction. After the reaction is completed, collect the product by magnetic force, wash with water until neutral and dry to obtain magnetic microspheres loaded with sulfonic acid.

[0010] (4) Add phosphophosphoric acid and a catalytic amount of magnetic microspheres to the reactor for polymerization. After the polymerization reaction is completed, cool to room temperature and magnetically recover the catalyst to obtain colorless and transparent polyphosphoric acid.

[0011] Further, in step (1), the mass ratio of ferric chloride hexahydrate, sodium acetate and polyethylene glycol is 1:5 to 8:1 to 3, and the mass-volume ratio of ferric chloride hexahydrate to ethylene glycol is 1:50 to 100, g:mL;

[0012] Furthermore, the reaction temperature in step (1) is 200–250°C, and the reaction time is 5–10 hours;

[0013] Furthermore, in step (2), the molar ratio of ferric oxide to fructose is 1:0.05-0.1, g:mol;

[0014] Furthermore, in step (2), the reaction temperature is 200–250°C and the reaction time is 5–10 hours;

[0015] Furthermore, the calcination temperature in step (2) is 400–800°C, and the calcination time is 3–6 hours;

[0016] Furthermore, in step (3), the mass ratio of magnetic carbon-based microspheres to concentrated sulfuric acid is 1:6 to 10, and the sulfonation reaction temperature is 100 to 150°C;

[0017] Furthermore, the amount of catalyst used in step (4) is 5-10%;

[0018] Furthermore, the reaction conditions in step (4) are: vacuum degree 0.05~0.1Mpa, reaction temperature 100~150℃, rotation speed 300~500rpm, and reaction time 3~6 hours.

[0019] Preferably, in step (1), the mass ratio of ferric chloride hexahydrate, sodium acetate, and polyethylene glycol is 1:5:1.5, and the mass-to-volume ratio of ferric chloride hexahydrate to ethylene glycol is 1:50-80, g:mL;

[0020] Preferably, the reaction temperature in step (1) is 200–220°C and the reaction time is 5–7 hours;

[0021] Preferably, in step (2), the molar ratio of ferric oxide to fructose is 1:0.08-0.1, g:mol;

[0022] Preferably, the reaction temperature in step (2) is 200–220°C and the reaction time is 5–8 hours;

[0023] Preferably, the calcination temperature in step (2) is 400-600℃ and the calcination time is 6 hours;

[0024] Preferably, in step (3), the mass ratio of magnetic carbon-based microspheres to concentrated sulfuric acid is 1:6-8, and the sulfonation reaction temperature is 120-150℃;

[0025] Preferably, the amount of catalyst used in step (4) is 5-7%;

[0026] Preferably, the reaction conditions in step (4) are: vacuum degree 0.05~0.08Mpa, reaction temperature 120~130℃, and reaction time 4~5 hours.

[0027] Compared with the prior art, the present invention has obvious advantages and effects. The magnetic microsphere catalyst prepared can greatly save energy consumption loss in the wet polyphosphoric acid process, and the obtained magnetic microsphere catalyst is easy to recover and can be used in the reaction.

[0028] Attached Description

[0029] Figure 1 These are electron microscope images of the prepared magnetic microspheres;

[0030] Figure 2The image shows the XRD pattern of the prepared magnetic microspheres.

[0031] Figure 3 The image shows the IR spectrum of the prepared magnetic microspheres.

[0032] Figure 4 This describes the magnetic attraction behavior of the prepared magnetic microspheres. Detailed Implementation

[0033] Example 1: Preparation of Catalyst

[0034] Accurately weigh 5g of ferric chloride hexahydrate, 27g of sodium acetate and 7.5g of polyethylene glycol. Dissolve the above substances in 300mL of ethylene glycol. After the substances are fully dissolved, transfer the solution to a 500mL hydrothermal reactor and react at 220℃ for 7 hours. After the reaction has cooled completely, collect the product magnetically, wash and dry it to obtain iron oxide particles.

[0035] Weigh 1g of the iron oxide particles prepared above, add them to 300mL of 0.3mol / L fructose solution, stir and disperse evenly, then transfer to a 100mL hydrothermal reactor and react at 220℃ for 6h. After the reaction is completed, collect the reaction product magnetically, wash thoroughly with ethanol and dry. Calcine the dried product at 500℃ for 4h in a nitrogen atmosphere to obtain magnetic carbon-based microspheres.

[0036] 1g of the calcined magnetic carbon-based microspheres were mixed with 8g of concentrated sulfuric acid and sulfonated at 120°C for a period of time. After cooling, the product was collected magnetically, washed with water until neutral, and dried to obtain dried magnetic microspheres loaded with sulfonic acid.

[0037] The morphology of the prepared magnetic microspheres was characterized using scanning electron microscopy (SEM, Nova 400 Nano), the diffraction peaks were characterized using X-ray diffraction (XRD, XPert Pro MPD), and the infrared characteristics were characterized using Fourier transform infrared spectroscopy (FT-IR, Vertex 70). The results are as follows: Figure 1-3 As shown, the prepared magnetic microspheres have a relatively symmetrical spherical structure with a particle size between 1.1 and 1.3 μm, a relatively uniform particle size distribution, and good dispersibility. In the XRD diffraction pattern, characteristic diffraction peaks of iron(III) oxide appeared at 2θ = 30.36°, 35.61°, 43.49°, 53.47°, 56.90°, and 62.68°. In the infrared spectrum, a stretching vibration peak of iron(III) oxide appeared at 580 cm⁻¹, and symmetric and antisymmetric stretching vibration peaks belonging to sulfonic acid groups appeared at 1038 cm⁻¹ and 1156 cm⁻¹, indicating that the prepared magnetic microspheres retained iron(III) oxide and introduced sulfonic acid groups.

[0038] In addition, the microspheres prepared in this embodiment were compared with those prepared by adding only fructose and concentrated sulfuric acid without adding iron oxide. When the two were placed on a magnetic rack, it was found that the microspheres in this embodiment were completely adsorbed on one side of the EP tube wall, while the solution in the comparative example was milky white, indicating that the microspheres could not be magnetically reclaimed (the shadow near the magnetic rack was due to the lighting during the shooting).

[0039] Example 2: Preparation of polyphosphoric acid

[0040] 20g of 85% phosphoric acid was added to a polymerization reactor, followed by 1g of the magnetic microspheres prepared in Example 1. The system was evacuated to a vacuum of 0.08 MPa, and the reaction was carried out at 120°C and 300 rpm for 3 hours. After the reaction, the mixture was cooled to room temperature, and the catalyst was magnetically recovered to obtain colorless and transparent polyphosphoric acid. The obtained polyphosphoric acid contained 83.7% P2O5 and <0.5 ppm iron, meeting the standards.

Claims

1. A method for producing polyphosphoric acid, comprising the following steps: (1) Ferric chloride hexahydrate, sodium acetate and polyethylene glycol are dissolved in ethylene glycol and reacted. After the reaction is completed, the product is magnetically recovered to obtain iron oxide particles. (2) Add iron oxide particles to fructose solution, disperse evenly and react. After the reaction is completed, the product is magnetically recovered, washed with ethanol and dried. The dried product is calcined in nitrogen atmosphere to prepare magnetic carbon-based microspheres. (3) Mix magnetic carbon-based microspheres with sufficient concentrated sulfuric acid to carry out sulfonation reaction. After the reaction is completed, collect the product by magnetic force, wash with water until neutral and dry to obtain magnetic microsphere catalyst loaded with sulfonic acid. (4) Phosphoric acid and a catalytic amount of magnetic microsphere catalyst loaded with sulfonic acid are added to the reactor for polymerization. After the polymerization reaction is completed, the mixture is cooled to room temperature and the magnetic microsphere catalyst loaded with sulfonic acid is magnetically recovered to obtain colorless and transparent polyphosphoric acid.

2. A method for producing polyphosphoric acid as described in claim 1, characterized in that: In step (1), the mass ratio of ferric chloride hexahydrate, sodium acetate and polyethylene glycol is 1:5~8:1~3, and the mass-volume ratio of ferric chloride hexahydrate to ethylene glycol is 1:50~100, g:mL; the reaction temperature in step (1) is 200~250℃, and the reaction time is 5~10 hours. In step (2), the mass molar ratio of iron oxide particles to fructose is 1:0.05~0.1, g:mol; the reaction temperature in step (2) is 200~250℃, and the reaction time is 5~10 hours; the calcination temperature in step (2) is 400~800℃, and the calcination time is 3~6 hours. In step (3), the mass ratio of magnetic carbon-based microspheres to concentrated sulfuric acid is 1:6~10, and the sulfonation reaction temperature is 100~150℃; The amount of magnetic microsphere catalyst loaded with sulfonic acid in step (4) is 5~10%; the reaction conditions in step (4) are: vacuum degree 0.05~0.1MPa, reaction temperature 100~150℃, rotation speed 300~500rpm, and reaction time 3~6 hours.

3. A method for producing polyphosphoric acid as described in claim 2, characterized in that: In step (1), the mass ratio of ferric chloride hexahydrate, sodium acetate and polyethylene glycol is 1:5:1.5, and the mass-volume ratio of ferric chloride hexahydrate to ethylene glycol is 1:50~80, g:mL; the reaction temperature in step (1) is 200~220℃, and the reaction time is 5~7 hours; In step (2), the molar ratio of iron oxide particles to fructose is 1:0.08~0.1, g:mol; the reaction temperature in step (2) is 200~220℃, and the reaction time is 5~8 hours; the calcination temperature in step (2) is 400~600℃, and the calcination time is 6 hours. In step (3), the mass ratio of magnetic carbon-based microspheres to concentrated sulfuric acid is 1:6~8, and the sulfonation reaction temperature is 120~150℃; The amount of magnetic microsphere catalyst loaded with sulfonic acid in step (4) is 5~7%; the reaction conditions in step (4) are: vacuum degree 0.05~0.08MPa, reaction temperature 120~130℃, and reaction time 4~5 hours.

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