Method for preparing phosphorous acid crystal from yellow phosphorus by one-step method and phosphorous acid crystal

Abstract

The invention relates to the technical field of inorganic phosphorus chemical industry, in particular to a method for preparing phosphorous acid crystals from yellow phosphorus through a one-step method and phosphorous acid crystals. Dispersing agents are dissolved in water and heated, yellow phosphorus is added, stirring and ultrasonic treatment are started after the yellow phosphorus is melted, the stirring rate, the ultrasonic frequency and the temperature are maintained, then catalysts are added into the solution, oxidizing agents are dropwise added, and stirring and ultrasonic treatment are conducted; continuously reacting to obtain a yellow transparent aqueous solution, namely a phosphorous acid aqueous solution; cooling the phosphorous acid aqueous solution to room temperature, filtering, and concentrating at normal pressure to obtain a phosphorous acid concentrated solution; carrying out ultrasonic treatment on the phosphorous acid concentrated solution, cooling to room temperature, scattering phosphorous acid seed crystals, sealing, crystallizing at a set temperature, taking out, and filtering to obtain crystals; and washing the obtained crystal with vaporous water, and drying in a vacuum drying oven to obtain the phosphorous acid crystal. The method solves the problem that phosphorous acid crystals are difficult to obtain in a conventional crystallization mode in the existing method for preparing phosphorous acid by a one-step method of yellow phosphorus.

Description

Technical Field

[0001] The present invention relates to the technical field of inorganic phosphorus chemical industry, and particularly relates to a method for preparing phosphorous acid crystals by a one-step method from yellow phosphorus and phosphorous acid crystals. Background Art

[0002] Phosphorous acid (H3PO3) is a fine phosphorus chemical product with great market prospects, mainly used for the preparation of phosphites, phosphite esters, glyphosate pesticides, etc., and is also widely used in the production of chemical products such as industrial water treatment agents, polymer stabilizer intermediates, flame retardants, pharmaceuticals, and corrosion and scale inhibitors. At present, the mainstream process for industrial production of phosphorous acid is the hydrolysis method of phosphorus trichloride, that is, phosphorus trichloride reacts with water to generate phosphorous acid and by-product hydrochloric acid (PCl3 + 3H2O → H3PO3 + 3HCl). Since phosphorus trichloride comes from the chlorination of yellow phosphorus (2P + 3Cl2 = 2PCl3), it is actually a two-step process for preparing phosphorous acid from yellow phosphorus. However, this method has many disadvantages: firstly, both reactions are strongly exothermic reactions, the process is dangerous, and the operation needs to be strictly regulated; secondly, this process is a chlorine-containing process, and the presence of chlorine and hydrochloric acid leads to a harsh on-site environment and serious equipment corrosion; in addition, the atom economy is poor, chlorine is only used for synthesis requirements, and finally it is discharged in the form of hydrochloric acid, making it difficult to balance and utilize.

[0003] To solve the above problems, a patent (ZL202110453239.4) has proposed a method for preparing phosphorous acid by a one-step method from yellow phosphorus. This method uses hydrogen peroxide as an oxidant and has the advantages of a short process, chlorine-free environmental protection, and good atom economy. However, the obtained phosphorous acid aqueous solution has a complex composition, containing impurities such as phosphorous acid, phosphoric acid, hypophosphorous acid, and catalyst elemental iodine, and it is difficult to obtain phosphorous acid crystals by conventional crystallization methods. Usually, it is necessary to neutralize with an alkali to form phosphite and then crystallize.

[0004] However, if the phosphorous acid solution can be directly crystallized into phosphorous acid crystals for sale as a solid product, compared with liquid products, it is beneficial to save packaging and transportation costs and also beneficial to meet the needs of the downstream market. Therefore, developing a method that can directly crystallize phosphorous acid crystals from the phosphorous acid aqueous solution prepared by the one-step method of yellow phosphorus has important industrial application value and market prospects. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for preparing phosphorous acid crystals by a one-step method from yellow phosphorus and phosphorous acid crystals, which solves the problem that it is difficult to obtain phosphorous acid crystals by conventional crystallization methods in the existing one-step method for preparing phosphorous acid from yellow phosphorus.

[0006] To achieve the above purpose, the present invention provides a method for preparing phosphorous acid crystals by a one-step method from yellow phosphorus, including the following steps:

[0007] S1. Dissolve the dispersant in water and heat it up. Add yellow phosphorus. After the yellow phosphorus melts, start stirring and ultrasonic treatment, and maintain the stirring rate, ultrasonic frequency and temperature. Then add a catalyst to the solution, dropwise add an oxidant, and continue the reaction to obtain a yellow transparent aqueous solution, that is, obtain an aqueous solution of phosphorous acid;

[0008] S2. Cool the aqueous solution of phosphorous acid to room temperature and then filter it, and concentrate it under normal pressure to obtain a concentrated solution of phosphorous acid;

[0009] S3. Ultrasonic the concentrated solution of phosphorous acid and then cool it to room temperature. Sprinkle in the phosphorous acid crystal seeds, and seal and place it in a set temperature for crystallization. After taking it out, filter it to obtain crystals;

[0010] S4. Wash the obtained crystals with atomized water, and then place them in a vacuum drying oven for drying to obtain phosphorous acid crystals.

[0011] Preferably, in the step S1, the dispersant is one or more of PEG400, alkyl glycoside, sodium dodecyl benzene sulfonate, carboxymethyl cellulose, cetyl trimethyl ammonium bromide. The dispersant is preferably cetyl trimethyl ammonium bromide.

[0012] Preferably, in the step S1, the catalyst is elemental iodine or hydroiodic acid, and the oxidant is hydrogen peroxide.

[0013] Preferably, in the step S1

[0014] The mass ratio of the dispersant to yellow phosphorus is 0.05 - 0.2:1;

[0015] The mass ratio of water to yellow phosphorus is 8 - 12:1;

[0016] The mass ratio of the catalyst to yellow phosphorus is 0.001 - 0.003:1;

[0017] The mass ratio of the oxidant to yellow phosphorus is 5.5 - 6.6:1.

[0018] Preferably, in the step S1, the stirring rate is 300 - 400 rpm, the ultrasonic frequency is 20 - 40 KHz, the temperature is 55 - 70 °C, the oxidant is dropped within 1 - 1.5 h, and the reaction continues for 0.5 - 1 h.

[0019] Preferably, in the step S2, the temperature for concentration under normal pressure is 90 - 95 °C.

[0020] Preferably, in the step S3, the ultrasonic time is 15 - 45 min, the addition amount of the phosphorous acid crystal seeds is 0.5 - 1.5% of the concentrated solution of phosphorous acid, the crystallization time is 2 - 6 h, and the set temperature is -5 - -20 °C.

[0021] Preferably, in step S4, the number of times of atomized water washing is two, the vacuum degree is 0.08 - 0.09 MPa, and the drying temperature is 60 - 70 °C.

[0022] A phosphorous acid crystal is prepared by using the method for preparing a phosphorous acid crystal by the one-step yellow phosphorus method described above.

[0023] Compared with the prior art, the present application has the following advantages:

[0024] 1. By adding a dispersant and controlling other reaction conditions, the present invention solves the problems of uneven dispersion caused by the insolubility of yellow phosphorus in water, small contact area between yellow phosphorus and the oxidant, and low reaction rate, in order to improve the conversion efficiency of yellow phosphorus in the liquid-phase reaction system, eliminate the by-product of hypophosphorous acid, and make the phosphorous acid aqueous solution obtained contain only the by-product of phosphoric acid, creating favorable conditions for the subsequent separation of phosphorous acid. It has been proved by experiments that a small amount of hypophosphorous acid will interfere with the crystallization of phosphorous acid to varying degrees.

[0025] 2. The present invention preferably uses cetyltrimethylammonium bromide (CTAB) as the yellow phosphorus dispersant. The long-chain alkyl group and Br- in the CTAB molecule have a synergistic effect on the adsorption of iodine, so that CTAB has a strong adsorption capacity for iodine. It will form a yellow complex with elemental iodine. After the reaction is completed, the CTAB adsorbed with elemental iodine spontaneously precipitates from the obtained phosphorous acid aqueous solution, and the yellow phosphorus dispersant CTAB and the catalyst I2 are cleverly separated by simple filtration. In this way, the composition of the obtained phosphorous acid aqueous solution is greatly simplified to mainly phosphorous acid, phosphoric acid and water, which greatly improves the crystallization rate and shortens the crystallization time.

[0026] 3. When other yellow phosphorus dispersants are selected in the present invention, although they will not precipitate and remain in the reaction solution, their crystallization time is relatively long, but they can be removed together with phosphoric acid by subsequent atomized water washing of the crystals. The washing process is less difficult than that of other dispersants, and a large amount of phosphorous acid will not be lost due to a large number of washing times.

[0027] 4. The present invention adopts a crystallization method, which can reduce the content of phosphoric acid impurities in phosphorous acid crystals to less than 0.6%, meeting the requirements of qualified product indicators. The current industry standard for phosphorous acid (HG / T 2520-2023) stipulates that the content of phosphoric acid impurities should not be higher than 0.6%, which is formulated based on the phosphorous acid obtained by the hydrolysis process of phosphorus trichloride. Since the content of phosphoric acid impurities in the phosphorous acid obtained by the hydrolysis process of phosphorus trichloride is extremely low, it is not difficult to meet the requirement of not being higher than 0.6%. In the process of preparing phosphorous acid by the one-step method of yellow phosphorus in the present invention, the content of phosphoric acid impurities reaches about 10% of phosphorous acid, and it is generally difficult to reduce it to the required index by ordinary crystallization. Ultrasonic waves are added during the crystallization process, so that phosphoric acid is highly dispersed, thereby reducing its viscosity. When phosphorous acid crystallizes, the phosphoric acid attached to the surface of phosphorous acid crystals is greatly reduced, thus avoiding negative impacts on crystal precipitation. In the subsequent process, it is further washed with atomized water, and finally the content of phosphoric acid impurities attached to phosphorous acid crystals is further reduced; since other impurities are all lower than 0.01%, therefore, the content of phosphoric acid impurities in the phosphorous acid prepared by the present invention is not higher than 0.6%. Description of the Drawings

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art.

[0029] Figure 1 It is the 31P NMR spectrum of the phosphorous acid crystals prepared in Example 2 of the present invention.

[0030] Figure 2 It is the 31P NMR spectrum of the phosphorous acid crystals prepared in Example 3 of the present invention.

[0031] Figure 3 It is the 31P NMR spectrum of the phosphorous acid crystals prepared in Example 4 of the present invention.

[0032] Figure 4 It is the process flow chart of the present invention. Detailed Embodiments

[0033] The following will describe in detail the embodiments of the present invention. The examples of the embodiments are shown in the drawings. The embodiments described below with reference to the drawings are exemplary and are intended to explain the present invention, but should not be construed as a limitation to the present invention.

[0034] Example 1:

[0035] Please refer to Figure 4 , wherein, Figure 4 It is the process flow chart of the present invention.

[0036] A method for preparing phosphorous acid crystals by the one-step method of yellow phosphorus of the present invention includes the following steps:

[0037] S101: Dissolve the dispersant in water and heat it up. Add yellow phosphorus. After the yellow phosphorus melts, start stirring and ultrasonic treatment, and maintain the stirring rate, ultrasonic frequency and temperature. Then add a catalyst to the solution, dropwise add an oxidant, and continue the reaction to obtain a yellow transparent aqueous solution, that is, obtain an aqueous solution of phosphorous acid;

[0038] S102: Cool the aqueous solution of phosphorous acid to room temperature and then filter it, and concentrate it under normal pressure to obtain a concentrated solution of phosphorous acid;

[0039] S103: Ultrasonic the concentrated solution of phosphorous acid and then cool it to room temperature. Sprinkle in phosphorous acid seeds, and seal and place it in a set temperature for crystallization. After taking it out, filter it to obtain crystals;

[0040] S104: Wash the obtained crystals with atomized water, and then dry them in a vacuum drying oven to obtain phosphorous acid crystals.

[0041] Specifically, in step S101, the dispersant is one of PEG400, alkyl glycoside, sodium dodecyl benzene sulfonate, carboxymethyl cellulose, cetyl trimethyl ammonium bromide; the dispersant is preferably cetyl trimethyl ammonium bromide; the catalyst is elemental iodine or hydroiodic acid, and the oxidant is hydrogen peroxide; the mass ratio of the dispersant to yellow phosphorus is 0.05 - 0.2:1; the mass ratio of water to yellow phosphorus is 8 - 12:1; the mass ratio of the catalyst to yellow phosphorus is 0.001 - 0.003:1, and the mass ratio of the oxidant to yellow phosphorus is 5.5 - 6.6:1; the ultrasonic frequency is 20 - 40KHz; the temperature is 55 - 70°C; the oxidant is added dropwise within 1 - 1.5h; continue the reaction for 0.5 - 1h; the stirring rate is 300 - 400rpm;

[0042] In step S102, the temperature for concentration under normal pressure is 90 - 95°C;

[0043] In step S103, the ultrasonic time is 15 - 45min, the addition amount of seeds is 0.5 - 1.5% of the concentrated solution of phosphorous acid; the crystallization time is 2 - 6h; the set temperature is -5 - -20°C;

[0044] In step S104, the number of times of washing with atomized water is two, the vacuum degree is 0.08 - 0.09MPa, and the drying temperature is 60 - 70°C.

[0045] Example 2:

[0046] 1.2 g of cetyltrimethylammonium bromide (CTAB) was dissolved in 170 g of water to obtain a colorless transparent solution, which was heated to 55 °C and poured into a four-necked round-bottom flask. Then 20 g of yellow phosphorus was added. After it melted, stirring and ultrasonic treatment were started. The stirring rate was 300 rpm and the ultrasonic frequency was 20 KHz. Then 0.04 g of iodine (I₂) was added, and at the same time, 110 g of 30% hydrogen peroxide was added dropwise within 1 h. The reaction continued for 0.5 h to obtain a yellow transparent aqueous solution, and the yellow phosphorus reacted completely. After detection by ³¹P NMR, the ratio of phosphorous acid to phosphoric acid was 9.025:1, and there was no hypophosphorous acid.

[0047] After the yellow transparent aqueous solution (phosphorous acid aqueous solution) was cooled to room temperature, it was filtered to separate the yellow CTAB-I₂ complex formed by CTAB and iodine (the chelate formed by CTAB and iodine can be removed by filtration). The filtrate was concentrated at normal pressure at 92 °C to obtain 60 g of concentrated solution. After ultrasonic treatment for 15 min, it was cooled to room temperature, 0.5 g of phosphorous acid crystal seeds were added, and it was sealed and crystallized in a -10 °C refrigerator for 2 h.

[0048] It was taken out, filtered, and the filter cake (wet crystals) was washed with atomized water. Finally, it was placed in a vacuum drying oven at 60 °C and dried for 2 h to obtain 10.2 g of phosphorous acid crystals. After detection by ³¹P NMR 31 the ratio of phosphorous acid to phosphoric acid was 1:0.005, as Figure 1 shown.

[0049] Example 3:

[0050] 1 g of cetyltrimethylammonium bromide (CTAB) was dissolved in 170 g of water to obtain a colorless transparent solution, which was heated to 55 °C and poured into a four-necked round-bottom flask. Then 20 g of yellow phosphorus was added. After it melted, stirring and ultrasonic treatment were started. The stirring rate was 400 rpm and the ultrasonic frequency was 40 KHz. Then 0.04 g of iodine (I₂) was added, and at the same time, 110 g of 30% hydrogen peroxide was added dropwise within 1.3 h. The reaction continued for 0.5 h to obtain a yellow transparent aqueous solution, and the yellow phosphorus reacted completely. After detection by ³¹P NMR, the ratio of phosphorous acid to phosphoric acid was 9.450:1, and there was no hypophosphorous acid.

[0051] After the yellow transparent aqueous solution (phosphorous acid aqueous solution) was cooled to room temperature, it was filtered to separate the yellow CTAB-I₂ complex formed by CTAB and iodine. The filtrate was concentrated at normal pressure at 93 °C to obtain 57 g of concentrated solution. After ultrasonic treatment for 30 min, it was cooled to room temperature, 0.6 g of phosphorous acid crystal seeds were added, and it was sealed and crystallized in a -15 °C refrigerator for 4 h.

[0052] It was taken out, filtered, and the filter cake (wet crystals) was washed with atomized water. Finally, it was placed in a vacuum drying oven at 60 °C and dried for 2 h to obtain 14.5 g of phosphorous acid crystals. After detection by ³¹P NMR 31 the ratio of phosphorous acid to phosphoric acid was 1:0.003, asFigure 2 as shown

[0053] Example 4:

[0054] 1 g of cetyltrimethylammonium bromide (CTAB) was dissolved in 170 g of water to obtain a colorless transparent solution, which was heated to 55 °C and poured into a four-necked round-bottom flask. Then 20 g of yellow phosphorus was added. After it melted, stirring and ultrasonic treatment were started. Then 0.04 g of elemental iodine (I₂) was added. At the same time, 110 g of 30% hydrogen peroxide solution was added dropwise within 1.4 h, and the reaction was continued for 0.5 h to obtain a yellow transparent aqueous solution, and the yellow phosphorus reacted completely. By ³¹P NMR detection, the ratio of phosphorous acid to phosphoric acid was 9.828:1, and there was no hypophosphorous acid.

[0055] Wait for the yellow transparent aqueous solution (phosphorous acid aqueous solution) to cool to room temperature and filter to separate CTAB and elemental iodine (CTAB-I₂ yellow complex). The filtrate was concentrated at 95 °C under normal pressure to obtain 55 g of concentrated solution. After ultrasonic treatment for 45 min and cooling to room temperature, 0.5 g of phosphorous acid crystal seeds were added and the mixture was sealed and crystallized in a refrigerator at -15 °C for 6 h. It was taken out and filtered, and the filter cake (wet crystals) was washed with atomized water. Finally, it was placed in a vacuum drying oven at 60 °C and dried for 2 h to obtain 18.3 g of phosphorous acid crystals. By 31 ³¹P NMR detection, the ratio of phosphorous acid to phosphoric acid was 1:0.007, as Figure 3 shown

[0056] Figures 1 - 3 Phosphorous acid crystals obtained from Example 2 to Example 4 respectively 31 ³¹P NMR phosphorus spectrum detection spectrograms. The spectrograms show that by using the processes and control conditions such as the preparation of phosphorous acid solution, the post-treatment of phosphorous acid solution, and the crystallization of phosphorous acid solution described in the present invention, the content of phosphoric acid impurities in the obtained phosphorous acid crystals is low, there are no obvious other impurities, the purity of the phosphorous acid crystals is high, and the product meets the index requirements of first-class products in the industrial phosphorous acid industry standard (HG / T 2520 - 2023).

[0057] Example 5:

[0058] 1 g of carboxymethyl cellulose was dissolved in 170 g of water to obtain a colorless transparent solution, which was heated to 55 °C and poured into a four-necked round-bottom flask. Then 20 g of yellow phosphorus was added. After it melted, stirring and ultrasonic treatment were started. Then 0.04 g of elemental iodine (I₂) was added. At the same time, 110 g of 30% hydrogen peroxide solution was added dropwise within 1.5 h, and the reaction was continued for 0.5 h to obtain a yellow transparent aqueous solution, and the yellow phosphorus reacted completely. By 31 ³¹P NMR detection, the ratio of phosphorous acid to phosphoric acid was 9.003:1, and there was no hypophosphorous acid.

[0059] The yellow transparent aqueous solution (phosphorous acid aqueous solution) was cooled to room temperature and filtered. The filtrate was concentrated at normal pressure at 95 °C to obtain 57 g of concentrated solution. After ultrasonic treatment for 30 min, it was cooled to room temperature, 0.6 g of phosphorous acid seed crystals were added, and it was sealed and crystallized in a refrigerator at -15 °C for 4 h. It was taken out and filtered, and the filter cake (wet crystals) was washed with atomized water. Finally, it was placed in a vacuum drying oven at 60 °C and dried for 2 h to obtain 16.7 g of phosphorous acid crystals.

[0060] Example 6:

[0061] 1 g of sodium dodecylbenzenesulfonate was dissolved in 170 g of water to obtain a colorless transparent solution, which was heated to 55 °C and poured into a four-necked round-bottom flask. Then 20 g of yellow phosphorus was added. After it melted, stirring and ultrasonic treatment were started. Then 0.04 g of elemental iodine (I2) was added, and at the same time, 110 g of 30% hydrogen peroxide solution was added dropwise within 1.5 h, and the reaction was continued for 0.5 h to obtain a yellow transparent aqueous solution, and the yellow phosphorus reaction was complete. By 31P NMR 31 detection, the ratio of phosphorous acid to phosphoric acid was 8.942:1, and there was no hypophosphorous acid.

[0062] The yellow transparent aqueous solution (phosphorous acid aqueous solution) was cooled to room temperature and filtered. The filtrate was concentrated at normal pressure at 95 °C to obtain 57 g of concentrated solution. After ultrasonic treatment for 30 min, it was cooled to room temperature, 0.6 g of phosphorous acid seed crystals were added, and it was sealed and crystallized in a refrigerator at -15 °C for 4 h. It was taken out and filtered, and the filter cake (wet crystals) was washed with atomized water. Finally, it was placed in a vacuum drying oven at 60 °C and dried for 2 h to obtain 13.2 g of phosphorous acid crystals.

[0063] Example 7:

[0064] 1 g of alkyl polyglycoside was dissolved in 170 g of water to obtain a colorless transparent solution, which was heated to 55 °C and poured into a four-necked round-bottom flask. Then 20 g of yellow phosphorus was added. After it melted, stirring and ultrasonic treatment were started. Then 0.04 g of elemental iodine (I2) was added, and at the same time, 110 g of 30% hydrogen peroxide solution was added dropwise within 1.2 h, and the reaction was continued for 0.5 h to obtain a yellow transparent aqueous solution, and the yellow phosphorus reaction was complete. By 31P NMR 31 detection, the ratio of phosphorous acid to phosphoric acid was 8.051:1, and there was no hypophosphorous acid.

[0065] The yellow transparent aqueous solution (phosphorous acid aqueous solution) was cooled to room temperature and filtered. The filtrate was concentrated at normal pressure at 93 °C to obtain 57 g of concentrated solution. After ultrasonic treatment for 30 min, it was cooled to room temperature, 0.6 g of phosphorous acid seed crystals were added, and it was sealed and crystallized in a refrigerator at -15 °C for 4 h. It was taken out and filtered, and the filter cake (wet crystals) was washed with atomized water. Finally, it was placed in a vacuum drying oven at 60 °C and dried for 2 h to obtain 12.8 g of phosphorous acid crystals.

[0066] Example 8:

[0067] 1 g of cetyltrimethylammonium bromide (CTAB) was dissolved in 170 g of water to obtain a colorless transparent solution, which was then heated to 55 °C and poured into a four-necked round-bottom flask. Then, 20 g of yellow phosphorus was added. After it melted, stirring and ultrasonication were started. Next, 0.04 g of elemental iodine (I₂) was added, and at the same time, 110 g of 30% hydrogen peroxide was added dropwise over 1 h. The reaction was continued for 0.5 h to obtain a yellow transparent aqueous solution, and the yellow phosphorus reacted completely. By ³¹P NMR detection, the ratio of phosphorous acid to phosphoric acid was 9.450:1, and there was no hypophosphorous acid.

[0068] After the yellow transparent aqueous solution (phosphorous acid aqueous solution) was cooled to room temperature, it was filtered to separate CTAB and elemental iodine (CTAB-I₂ yellow complex). The filtrate was concentrated at normal pressure at 90 °C to obtain 57 g of concentrated solution. It was cooled to -15 °C and crystallized for 2 h to obtain 9.3 g of phosphorous acid crystals. After detection, the content of phosphoric acid impurities reached 2.2%.

[0069] Example 9:

[0070] 170 g of water was heated to 55 °C and poured into a four-necked round-bottom flask. Then, 20 g of yellow phosphorus was added. After it melted, stirring and ultrasonication were started. Next, 0.04 g of elemental iodine (I₂) was added, and at the same time, 110 g of 30% hydrogen peroxide was added dropwise over 1 - 1.5 h. The reaction was continued for 0.5 h to obtain a yellow transparent aqueous solution, and the yellow phosphorus did not react completely. By ³¹P NMR detection, the ratio of phosphorous acid to phosphoric acid was 6.025:1, and there was no hypophosphorous acid.

[0071] After the yellow transparent aqueous solution (phosphorous acid aqueous solution) was cooled to room temperature, it was filtered. The filtrate was concentrated at normal pressure at 90 - 95 °C to obtain 57 g of concentrated solution. After ultrasonication for 30 min, it was cooled to room temperature, 0.6 g of phosphorous acid seed crystals were added, and it was sealed and placed in a -15 °C refrigerator for crystallization for 4 h. The seed crystals were taken out and completely dissolved, and no phosphorous acid crystals were obtained.

[0072] Example 10:

[0073] Experiment on the effect of hypophosphorous acid on the crystallization of phosphorous acid

[0074] Commercially available 99% pure phosphorous acid crystals were dissolved in water to prepare a phosphorous acid solution with a concentration of 75 - 80% (the phosphorous acid reagent was purchased from Sinopharm Chemical Reagent Co., Ltd.). Different contents of hypophosphorous acid (hypophosphorous acid was purchased from Sinopharm Chemical Reagent Co., Ltd.) and phosphoric acid (phosphoric acid was purchased from Sinopharm Chemical Reagent Co., Ltd.) were added respectively. After ultrasonication and crystallization at -10 °C, their crystallization was observed. The results are shown in Table 1 below.

[0075] Table 1 Effect of hypophosphorous acid with different concentrations on the crystallization of phosphorous acid

[0076] Hypophosphorous acid content in phosphorous acid solution 0.1％ 0.2％ 0.4％ 0.8％ 1％ Phosphoric acid content in phosphorous acid solution 1％ 2％ 4％ 8％ 10％ Crystallization temperature -10℃ -10℃ -10℃ -10℃ -10℃ Crystallization time 2h 2h 2h 2h 2h Ultrasonic condition None Yes None Yes Yes Hypophosphorous acid content in phosphorous acid crystal 0.05 0.08 0.25％ 0.4％ Phosphorous acid does not crystallize Phosphoric acid content in phosphorous acid crystal 0.3％ 0.3％ 0.8％ 1.2％ Phosphorous acid does not crystallize

[0077] Table 1 results verify that hypophosphorous acid and phosphoric acid present in the phosphorous acid solution will affect the crystallization of phosphorous acid.

[0078] The above-disclosed are only one or more preferred embodiments of the present application, and the scope of rights of the present application cannot be limited thereby. Those of ordinary skill in the art can understand all or part of the processes of implementing the above embodiments, and equivalent changes made according to the claims of the present application still fall within the scope covered by the present application.

Claims

1. A method for preparing phosphorous acid crystals from yellow phosphorus in one step, characterized in that: The following steps are involved: S1. The dispersant is dissolved in water and heated, yellow phosphorus is added, stirring and ultrasound are started after the yellow phosphorus melts, and the stirring rate, ultrasonic frequency and temperature are maintained, and then a catalyst is added to the solution, an oxidant is added dropwise, and the reaction is continued to obtain a yellow transparent aqueous solution, that is, a phosphorous acid aqueous solution is obtained; S2. The phosphorous acid aqueous solution was cooled to room temperature, filtered, and concentrated at normal pressure to obtain a phosphorous acid concentrate; S3. The phosphorous acid concentrate is cooled to room temperature after ultrasonic treatment, phosphorous acid seed crystals are sprinkled in, and sealed and placed at a set temperature for crystallization, and then taken out and filtered to obtain crystals; S4. Wash the obtained crystals with mist water, and then dry them in a vacuum drying oven to obtain phosphorous acid crystals.

2. The method for preparing phosphorous acid crystals by one-step process of yellow phosphorus as claimed in claim 1, characterized in that, In step S1, the dispersant is one or more of PEG400, alkyl glycoside, sodium dodecylbenzene sulfonate, carboxymethyl cellulose, and hexadecyltrimethylammonium bromide.

3. The method for preparing phosphorous acid crystals by one-step process of yellow phosphorus as claimed in claim 1, characterized in that, In step S1, the catalyst is elemental iodine or hydroiodic acid, and the oxidant is hydrogen peroxide.

4. The method for preparing phosphorous acid crystals by one-step process of yellow phosphorus as claimed in claim 1, characterized in that, In step S1 The mass ratio of dispersant to yellow phosphorus is 0.05 ～ 0.2:1; The mass ratio of water to yellow phosphorus is 8 ～ 12:1; The mass ratio of catalyst to yellow phosphorus is 0.001 ～ 0.003:1; The mass ratio of oxidant to yellow phosphorus is 5.5 ～ 6.6:

1.

5. The method for preparing phosphorous acid crystals by one-step process of yellow phosphorus as claimed in claim 1, characterized in that, The stirring rate in step S1 is 300 ～ 400rpm, ultrasonic frequency 20 ～ 40KHz, temperature is 55 ～ 70℃, oxidant at 1 ～ The addition was completed within 1.5 h, and the reaction was continued for 0.5 ～ 1h.

6. The method for preparing phosphorous acid crystals by one-step process of yellow phosphorus as claimed in claim 1, characterized in that, The temperature of atmospheric pressure concentration in step S2 is 90 ～ 95℃.

7. The method for preparing phosphorous acid crystals from yellow phosphorus in one step as claimed in claim 1, characterized in that: The ultrasonic time in step S3 is 15 ～ 45min, the amount of phosphorous acid seed added is 0.5 of the phosphorous acid concentrate ～ 1.5%, crystallization time is 2 ～ 6h, set temperature to -5 ～ -20℃.

8. The method for preparing phosphorous acid crystals by one-step process of yellow phosphorus as claimed in claim 1, characterized in that, In step S4, the number of mist water washing is two times, and the vacuum degree is 0.08 ～ 0.09MPa, drying temperature is 60 ～ 70℃.

9. Phosphorous acid crystals prepared by the method for preparing phosphorous acid crystals from yellow phosphorus in one step as claimed in any one of claims 1 to 9.

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