Preparation process of high-purity sodium hydrosulfite

Abstract

The invention relates to the technical field of chemical production, in particular to a preparation process of high-purity sodium dithionite, which specifically comprises the following steps: step 1, preparing suspension liquid from solid sodium formate and sodium pyrosulfite; 2, carrying out a synthetic reaction on the suspension, a side reaction inhibitor and methanol in a mass ratio of (2-5): (1-3): 1, and removing by-products generated in the reaction by using low-pressure flash steam; the synthesis reaction comprises the following steps: starting nitrogen purging, pressurizing to 0.4-0.6 MPa, heating to 75-85 DEG C, adding a gas-liquid mixture of sulfur dioxide, reacting for 70-80 minutes under a water bath condition, pressurizing to 1.0-1.8 MPa, cooling, reacting, preserving heat, cooling, and carrying out filter pressing to obtain a filter cake; 3, adding the filter cake into a methanol solution, and carrying out low-frequency ultrasonic treatment to obtain a mixed solution; 4, modified stearate is added into the mixed solution for treatment, filter pressing is conducted again, drying is conducted, and sodium dithionite is obtained; according to the process, the synthetic reaction rate is high, and the prepared sodium hydrosulfite is high in purity, large in particle size and not prone to decomposition.

Description

Technical Field

[0001] The present invention belongs to the technical field of chemical production, and particularly relates to a preparation process of high-purity sodium dithionite. Background Art

[0002] Sodium dithionite is also called sodium hydrosulfite, also known as "sodium hydrosulfite", which is an inorganic substance in the form of white crystalline powder. It is used as a bleaching agent and deoxidizer in fields such as textiles, medicine, and food. However, compared with other deoxidizers, it has higher safety and less damage to things such as clothes; generally, sodium dithionite has two states, one is the dihydrate salt with crystal water, and the other is anhydrous sodium dithionite. The former can be obtained by high-temperature dehydration to get the latter; its chemical property is strong reducibility, so it is easy to be oxidized and is an unstable substance. It may be oxidized or decomposed under oxygen-containing conditions, high-temperature conditions, acidic conditions, and humid environments, decomposing to produce sulfur dioxide gas. And because it has strong reducibility, it is easy to be oxidized to sodium sulfite and sodium sulfate. Therefore, it is easy to deteriorate during the process of industrial production; and the sodium dithionite product is affected by the production process, and it is easy to cause too small particle size and then easy to decompose. Moreover, the product with poor particle size has a large amount of dust and many impurities, affecting the quality of the product.

[0003] At present, there are three production processes for sodium dithionite. One is the zinc powder method; the second is the solid formate method, and the third is the sodium amalgam method; the most common synthesis process of sodium dithionite is the solid formate method, which is obtained by reacting excessive solid formate with sulfur dioxide and sodium-containing compounds through the reaction medium of methanol aqueous solution. The reaction temperature can be as high as 85 °C, while the decomposition temperature of sodium dithionite is 90 °C. Therefore, sulfur dioxide gas is easily decomposed during the reaction process, affecting the purity and yield of sodium dithionite and causing relatively large pollution at the same time. At present, the method to improve the purity of sodium dithionite is through salting-out recrystallization, that is, anhydrous sodium dithionite is converted into crystalline sodium dithionite dihydrate through an alkaline solution, dispersed with saturated brine and then dehydrated. This method has cumbersome steps and large consumption of raw materials and is not conducive to industrial production; other methods also include alcohol precipitation method, which increases the pH value of crude sodium dithionite through an alkaline solution, and then mixes it with the suspension of sodium dithionite synthesized by the solid formate method to precipitate sodium dithionite. However, this method has a large consumption of reagents, high operation difficulty, and easy loss of equipment when the pH value is too high; and in the preparation of sodium dithionite, solid formate and sodium metabisulfite are usually prepared into a suspension, which will result in too small particle size of the prepared sodium dithionite, easy decomposition, and affect the purity of the prepared sodium dithionite. Summary of the Invention

[0004] Aiming at the above problems, the purpose of the present invention is to provide a preparation process of high-purity sodium dithionite.

[0005] The technical content of the present invention is as follows:

[0006] The present invention provides a preparation process for high-purity sodium dithionite, comprising the following steps:

[0007] Step 1: Prepare a suspension;

[0008] The suspension is prepared by ultrasonically oscillating solid sodium formate and methanol at a mass ratio of 11-15:22-29 to form a uniform suspension; then adding a mixed solution containing sodium metabisulfite, methanol and water with a mass ratio of 4:50-60:18-22 and mixing evenly;

[0009] The preparation of the mixed solution is to heat water to 90-100 °C under closed conditions, add sodium metabisulfite and stir evenly, then cool to 50-60 °C and add methanol for mixing; Ultrasonic oscillation can increase the particle size and uniformity of solid sodium formate, control the crystal grain size and directionality, and improve the consistency and uniformity of the crystal growth rate of sodium dithionite.

[0010] Step 2: Perform a synthesis reaction on the suspension, a side reaction inhibitor and methanol at a mass ratio of 2-5:1-3:1, and remove the by-products generated during the reaction with low-pressure flash steam; The synthesis reaction is to purge with nitrogen and pressurize to 0.4-0.6 MPa, heat to 75-85 °C, then add a gas-liquid mixture of sulfur dioxide and react for 70-80 min under a water bath condition, and then increase the pressure to 1.0-1.8 MPa and cool down for the reaction. After the reaction, keep warm and cool, and filter press to obtain a filter cake; The water bath condition and the pressure increase and temperature decrease in the later stage of the reaction can regulate the temperature to promote crystal growth;

[0011] The cooling reaction is carried out under the conditions of a temperature of 50-60 °C and a rotation speed of 150-250 rpm for stirring reaction for 30-40 min; By reducing the generation of crystal nuclei and increasing the crystal growth rate, it promotes the generation of large-particle crystals and can inhibit the generation of by-products;

[0012] The side reaction inhibitor is ethylene oxide and 1,2-epoxypropane with a mass ratio of 11-14:2-6; It can react with sodium thiosulfate, reduce the generation of by-products, promote the reduction reaction, reduce the oxidation decomposition reaction, and 1,2-epoxypropane can promote the crystallization of sodium dithionite;

[0013] Ethylene oxide can react with sodium thiosulfate to reduce the decomposition reaction of sodium dithionite caused by sodium thiosulfate, but ethylene oxide will cause the pH of the solution to increase, and will consume water and methanol, resulting in a high addition amount; 1,2-epoxypropane can react with sodium thiosulfate without affecting the raw materials and reagents. After the two are compounded, it can further promote the reduction reaction;

[0014] The gas-liquid mixture of sulfur dioxide is a sulfur dioxide solution and sulfur dioxide gas. The flow rate of the sulfur dioxide gas is 90 L / s to 100 L / s, and the addition amount of the sulfur dioxide liquid is 3-5 wt% of the suspension; by combining the advantages of gas-liquid reaction and liquid-liquid reaction, the mass transfer efficiency is improved, thereby improving the reaction uniformity and reaction rate, and promoting the growth of crystals; gaseous sulfur dioxide can reduce the concentration of carbon dioxide and promote the forward formation reaction of sodium dithionite;

[0015] Step 3: Add the filter cake into a methanol solution and perform low-frequency ultrasonic treatment to obtain a mixed solution;

[0016] The low-frequency ultrasonic treatment is carried out at a frequency of 10-15 KHz for 5-10 min; low-frequency ultrasound can promote the dissolution of small-particle-size sodium dithionite;

[0017] Step 4: Add the mixed solution to the modified stearate, perform infrared treatment, then filter press again and dry to obtain sodium dithionite;

[0018] The addition amount of the modified stearate is 3-4 mol / L;

[0019] The preparation of the modified stearate is obtained by mixing a macromolecular stearate and ethyl acetate at a solid-liquid ratio of 11-18:6-9 g / mL and heating at 70-80 °C for 10-15 min; the modified stearate has high dispersibility, can promote the recrystallization of sodium dithionite while reducing the crystal water, and the added modified stearate can evenly wrap sodium dithionite, increase the powder diameter, and improve the stability and purity of sodium dithionite;

[0020] The wavelength of the infrared treatment is 1-4 μm, the power is 700-800 W, the temperature is 40-60 °C, and the treatment time is 2-3 h; the infrared treatment can assist in removing crystal water, and the obtained anhydrous salt has higher stability.

[0021] The beneficial effects of the present invention are as follows:

[0022] In the preparation process of high-purity sodium dithionite provided by the present invention, a uniform suspension of solid sodium formate and sodium metabisulfite is prepared through ultrasonic oscillation and hydrothermal pre-dissolution, and then raw materials such as a side reaction inhibitor are added for hydrothermal synthesis reaction. During the synthesis process, after pressurization and heating and then cooling and pressurization, the crystal growth of the product is regulated. The added side reaction inhibitor can inhibit the side reactions during the synthesis reaction and minimize the generation of by-product impurities. A sulfur dioxide gas-liquid mixture is used in the reaction process to improve the mass transfer efficiency of the reaction and promote the forward progress of the reaction. Then, the sodium dithionite obtained by pressure filtration is dissolved by low-frequency ultrasound in a methanol solution to promote the dissolution of fine powder. After standing, a modified stearate is added to promote recrystallization and stably wrap the generated sodium dithionite. The sodium dithionite prepared by the preparation process of sodium dithionite of the present invention has large particle size, few impurities and high purity. The process of the present invention is relatively simple, has high production efficiency, ensures the quality of the prepared sodium dithionite, can regulate the crystallization rate of sodium dithionite during the process, the prepared product has good particle size, low proportion of fine powder, few impurities, good quality, purity above 90%, meets the food-grade standard, and has high stability and a long storage period. Brief Description of the Drawings

[0023] Figure 1 Shows the stability changes of the sodium dithionite prepared in Example 1 and Comparative Example 4. Detailed Description of the Invention

[0024] The present invention will be further described in detail below through specific implementation cases and the description of the drawings. It should be understood that these examples are only used to illustrate the present invention and not to limit the protection scope of the present invention. After reading the present invention, various equivalent modifications of the present invention by those skilled in the art all fall within the scope defined by the appended claims of this application.

[0025] Unless otherwise specified, all raw materials and reagents of the present invention are raw materials and reagents on the conventional market.

[0026] Example 1

[0027] A preparation process of high-purity sodium dithionite

[0028] Step 1: Prepare a suspension: Ultrasonically oscillate solid sodium formate and methanol at a mass ratio of 13:25 to form a uniform suspension, and then add a mixed solution containing sodium metabisulfite, methanol and water for mixing;

[0029] The preparation of the mixed solution is to heat water to 95°C in a closed condition, add sodium metabisulfite and stir evenly, then cool to 55°C and add methanol for mixing. Among them, the mass ratio of sodium metabisulfite, methanol and water is 4:55:20;

[0030] Step 2: Synthesize the suspension, side reaction inhibitor, and methanol in a mass ratio of 3:2:1. Purge with nitrogen and pressurize to 0.5 MPa. After heating to 80 °C, add a gas-liquid mixture of sulfur dioxide and react for 75 min under a water bath condition. Then increase the pressure to 1.4 MPa and carry out a stirring reaction for 35 min at a temperature of 55 °C and a rotation speed of 200 rpm, followed by a cooling reaction. After the reaction, keep warm and cool, and filter press to obtain a filter cake. The by-products generated during the reaction are removed by low-pressure flash steam;

[0031] The side reaction inhibitor is composed of ethylene oxide and 1,2-epoxypropane with a mass ratio of 13:4;

[0032] The gas-liquid mixture of sulfur dioxide is composed of a sulfur dioxide solution and sulfur dioxide gas. The flow rate of sulfur dioxide gas is 95 L / s, and the addition amount of sulfur dioxide liquid is 4 wt% of the suspension;

[0033] Step 3: Add the filter cake into a methanol solution and perform 13 KHz low-frequency ultrasonic treatment for 8 min to obtain a mixed solution;

[0034] Step 4: Add the mixed solution with a modified stearate added amount of 3.5 mol / L and perform infrared treatment at a wavelength of 3 μm, a power of 750 W, a temperature of 50 °C, and a treatment time of 2 h. After filter pressing again, dry to obtain sodium dithionite;

[0035] The preparation of the modified stearate is obtained by mixing a macromolecular stearate and ethyl acetate at a solid-liquid ratio of 14:8 g / mL and heating at 75 °C for 13 min.

[0036] Example 2

[0037] A preparation process of high-purity sodium dithionite

[0038] Step 1: Prepare a suspension: Ultrasonically oscillate solid sodium formate and methanol in a mass ratio of 11:22 to form a uniform suspension, and then add a mixed solution containing sodium metabisulfite, methanol, and water and mix well;

[0039] The preparation of the mixed solution is to heat water to 90 - 100 °C under a closed condition, add sodium metabisulfite and stir evenly, then cool to 50 - 60 °C and add methanol to mix. Among them, the mass ratio of sodium metabisulfite, methanol, and water is 4:50:18;

[0040] Step 2: Perform a synthesis reaction on the suspension, side reaction inhibitor, and methanol in a mass ratio of 2:1:1. Purge with nitrogen and pressurize to 0.4 MPa. After heating to 75 °C, add a gas-liquid mixture of sulfur dioxide and react for 70 min under a water bath condition. Then increase the pressure to 1.0 MPa and carry out a stirring reaction for 30 min at a temperature of 50 °C and a rotation speed of 150 rpm for cooling reaction. After the reaction, keep warm and cool, and filter press to obtain a filter cake. By-products generated during the reaction are removed with low-pressure flash steam;

[0041] The side reaction inhibitor is composed of ethylene oxide and 1,2-epoxypropane in a mass ratio of 11:2;

[0042] The gas-liquid mixture of sulfur dioxide is a sulfur dioxide solution and sulfur dioxide gas. The flow rate of the sulfur dioxide gas is 90 L / s, and the addition amount of the sulfur dioxide liquid is 3 wt% of the suspension;

[0043] Step 3: Add the filter cake into a methanol solution and perform low-frequency ultrasonic treatment at 10 KHz for 5 min to obtain a mixed solution;

[0044] Step 4: Add the mixed solution with a modified stearate added amount of 3 mol / L and perform infrared treatment. The wavelength is 1 μm, the power is 700 W, the temperature is 40 °C, and the treatment time is 2 h. After filter pressing again, dry to obtain sodium dithionite; The preparation of the modified stearate is to mix macromolecular stearate and ethyl acetate in a solid-liquid ratio of 11:6 g / mL and heat at 70 °C for 10 min;

[0045] Example 3

[0046] A preparation process of high-purity sodium dithionite

[0047] Step 1: Prepare a suspension: Ultrasonically oscillate solid sodium formate and methanol in a mass ratio of 15:29 to form a uniform suspension; then add a mixed solution containing sodium metabisulfite, methanol, and water and mix evenly;

[0048] The preparation of the mixed solution is to heat water to 100 °C under a closed condition, add sodium metabisulfite and stir evenly, then cool to 60 °C and add methanol to mix. Among them, the mass ratio of sodium metabisulfite, methanol, and water is 4:60:22;

[0049] Step 2: Perform a synthesis reaction on the suspension, side reaction inhibitor, and methanol in a mass ratio of 5:3:1. Purge with nitrogen and pressurize to 0.6 MPa. After heating to 85 °C, add a gas-liquid mixture of sulfur dioxide and react for 80 min under a water bath condition. Then increase the pressure to 1.8 MPa and carry out a stirring reaction for 40 min at a temperature of 60 °C and a rotation speed of 250 rpm for cooling reaction. After the reaction, keep warm and cool, and filter press to obtain a filter cake. By-products generated during the reaction are removed with low-pressure flash steam;

[0050] The side reaction inhibitor is composed of ethylene oxide and 1,2-epoxypropane with a mass ratio of 14:6;

[0051] The gas-liquid mixture of sulfur dioxide is sulfur dioxide solution and sulfur dioxide gas. The flow rate of sulfur dioxide gas is 100 L / s, and the addition amount of sulfur dioxide liquid is 5 wt% of the suspension;

[0052] Step 3: Add the filter cake into a methanol solution and perform low-frequency ultrasonic treatment at 15 KHz for 10 min to obtain a mixed solution;

[0053] Step 4: Add the mixed solution to the modified stearate with an addition amount of 4 mol / L and perform infrared treatment. After that, at a wavelength of 4 μm, a power of 800 W, a temperature of 60 °C, and a treatment time of 3 h, filter press again and dry to obtain sodium dithionite; The preparation of the modified stearate is to mix macromolecular stearate and ethyl acetate at a solid-liquid ratio of 18:9 g / mL and heat at 80 °C for 15 min.

[0054] Example 4

[0055] A preparation process of high-purity sodium dithionite

[0056] Step 1: Prepare a suspension: Ultrasonically oscillate solid sodium formate and methanol at a mass ratio of 12:23 to form a uniform suspension; then add a mixed solution containing sodium metabisulfite, methanol, and water and mix well;

[0057] The preparation of the mixed solution is to heat water to 90 °C under closed conditions, add sodium metabisulfite and stir evenly, then cool to 60 °C and add methanol to mix. Among them, the mass ratio of sodium metabisulfite, methanol, and water is 4:50:22;

[0058] Step 2: Perform a synthesis reaction on the suspension, the side reaction inhibitor, and methanol at a mass ratio of 3:1:1. Open nitrogen purge and pressurize to 0.4 MPa. After heating to 85 °C, add the gas-liquid mixture of sulfur dioxide and react for 70 min under water bath conditions. Then increase the pressure to 1.3 MPa and perform a stirring reaction at a temperature of 50 °C and a rotation speed of 250 rpm for 30 min for cooling reaction. After the reaction, keep warm and cool, filter press to obtain a filter cake, and remove the by-products generated during the reaction with low-pressure flash steam;

[0059] The side reaction inhibitor is composed of ethylene oxide and 1,2-epoxypropane with a mass ratio of 12:3;

[0060] The gas-liquid mixture of sulfur dioxide is sulfur dioxide solution and sulfur dioxide gas. The flow rate of sulfur dioxide gas is 100 L / s, and the addition amount of sulfur dioxide liquid is 3 wt% of the suspension;

[0061] Step 3: Add the filter cake into a methanol solution and perform low-frequency ultrasonic treatment at 15 KHz for 5 min to obtain a mixed solution;

[0062] Step 4: Add the mixed solution with a modified stearate added at a dosage of 4 mol / L and perform infrared treatment. After that, at a wavelength of 1 μm, a power of 800 W, a temperature of 40 °C, and a treatment time of 3 h, filter press again and dry to obtain sodium dithionite; the preparation of the modified stearate is to mix a macromolecular stearate and ethyl acetate at a solid-liquid ratio of 12:7 g / mL and heat at 70 °C for 15 min.

[0063] Example 5

[0064] A preparation process of high-purity sodium dithionite

[0065] Step 1: Prepare a suspension: Ultrasonically oscillate solid sodium formate and methanol at a mass ratio of 14:28 to form a uniform suspension; then add a mixed solution containing sodium metabisulfite, methanol, and water and mix well;

[0066] The preparation of the mixed solution is to heat water to 90 °C under closed conditions, add sodium metabisulfite and stir evenly, then cool to 55 °C and add methanol to mix. Among them, the mass ratio of sodium metabisulfite, methanol, and water is 4:60:18;

[0067] Step 2: Perform a synthesis reaction on the suspension, a side reaction inhibitor, and methanol at a mass ratio of 4:2:1. Open nitrogen purging and pressurize to 0.5 MPa. After heating to 85 °C, add a gas-liquid mixture of sulfur dioxide and react for 75 min under a water bath condition. Then increase the pressure to 1.0 MPa and perform a stirring reaction at a temperature of 60 °C and a rotation speed of 150 rpm for 40 min for a cooling reaction. After the reaction, keep warm and cool, and filter press to obtain a filter cake. The by-products generated during the reaction are removed by low-pressure flash steam;

[0068] The side reaction inhibitor is composed of ethylene oxide and 1,2-epoxypropane at a mass ratio of 13:5;

[0069] The gas-liquid mixture of sulfur dioxide is a sulfur dioxide solution and sulfur dioxide gas. The flow rate of the sulfur dioxide gas is 90 L / s, and the addition amount of the sulfur dioxide liquid is 4 wt% of the suspension;

[0070] Step 3: Add the filter cake into a methanol solution and perform low-frequency ultrasonic treatment at 10 KHz for 5 min to obtain a mixed solution;

[0071] Step 4: Add the mixed solution to the modified stearate with an addition amount of 3.5 mol / , and perform infrared treatment. After that, the wavelength is 4 μm, the power is 800 W, the temperature is 45 °C, and the treatment time is 2 h. After filtration again and drying, sodium dithionite is obtained; the preparation of the modified stearate is to mix macromolecular stearate and ethyl acetate at a solid-liquid ratio of 17:8 g / mL and heat at 70 °C for 13 min.

[0072] Comparative Example 1

[0073] The difference between Comparative Example 1 and Example 1 is that the suspension in Comparative Example 1 is prepared by mixing equal amounts of raw materials, and the others remain unchanged.

[0074] Comparative Example 2

[0075] The difference between Comparative Example 2 and Example 1 is that in the synthesis reaction of step 2 in Comparative Example 2, the reaction is carried out under uniform pressure and temperature, hydrothermal treatment is not used, and gaseous sulfur dioxide is used instead of the gas-liquid mixture of sulfur dioxide, and the others remain unchanged. Specifically: Step 2: The suspension, a side reaction inhibitor composed of ethylene oxide and 1,2-epoxypropane with a mass ratio of 13:4, and methanol are subjected to a synthesis reaction at a mass ratio of 3:2:1. The by-products generated during the reaction are removed by low-pressure flash steam; the synthesis reaction is to purge with nitrogen and pressurize to 0.5 MPa, heat to 80 °C, then add sulfur dioxide gas and react for 75 min, the flow rate of the sulfur dioxide gas is 95 L / s, and then react for 35 min. After the reaction, it is kept warm and cooled, and filtered to obtain a filter cake.

[0076] Comparative Example 3

[0077] The difference between Comparative Example 3 and Example 1 is that in Comparative Example 3, an equal amount of ethylene oxide is used as the side reaction inhibitor, and the others remain unchanged.

[0078] Comparative Example 4

[0079] The difference between Comparative Example 4 and Example 1 is that in Comparative Example 4, steps 3 and 4 are not carried out, and direct drying treatment is performed, and the others remain unchanged.

[0080] I. Detect the particle size of the sodium dithionite prepared in the example, and the detection results are shown in Table 1.

[0081] Table 1 Particle size distribution of sodium dithionite

[0082]

[0083] As can be seen from Table 1, the particle size of the sodium dithionite prepared by the present invention is relatively large. From Comparative Example 1, it can be seen that homogenizing the suspension in the early stage of the reaction can improve the quality of the reaction product. From Comparative Example 2, it can be seen that by regulating the temperature and pressure and through the gas-liquid co-reaction of sulfur dioxide in the present invention, improving the mass transfer efficiency of the reaction can improve the synthesis efficiency of sodium dithionite, reduce the decomposition rate, and increase the particle size of sodium dithionite. From Comparative Example 3, it can be seen that the side reaction inhibitor in the synthesis process can reduce the occurrence of side reactions and reduce the decomposition of large-particle sodium dithionite. From Comparative Example 4, it can be seen that in the process of the present invention, Steps 3 and 4 improve the content and stability of large-particle sodium dithionite by redissolving the fine powder of sodium dithionite and stably coating it with modified stearate salt.

[0084] Second, take 5 mg of the sodium dithionite prepared in the examples and comparative examples respectively, and prepare a standard solution with a concentration of 5.00 mg / L. Pour 2% hydrochloric acid solution (10 ml) into the standard solution, and slowly add it drop by drop with a burette until the color does not change. The color of the solution changes from red to purple and no longer changes. Then use an excessive amount of sodium hydroxide solution to calibrate the burette to eliminate the acidity error, record the volume of sodium hydroxide consumed, and at the same time adjust the ratio of hydrochloric acid and sodium hydroxide. Calculate the consumption of sodium dithionite according to the total amount of hydrochloric acid, the amount of sodium hydroxide used, and the amount of barium sulfate produced. That is, 1 mol of sodium dithionite can produce a precipitate with 2 mol of barium chloride, calculate the actual content (mg / g) of sodium dithionite, which is the content of sodium dithionite in the standard solution, calculate the purity of sodium dithionite, and then calculate the yield of sodium dithionite according to the input amount of raw materials such as solid sodium formate. The results are shown in Table 2.

[0085] Table 2 Yield and purity of sodium dithionite

[0086]

[0087]

[0088] As can be seen from Table 2, the sodium dithionite prepared by the method of the present invention has a high yield and high purity; from Comparative Example 1, it can be seen that in the initial stage of preparing sodium dithionite in the present invention, solid sodium formate and sodium metabisulfite are respectively pre-dissolved by physical energy and hydrothermal treatment to obtain a homogenized suspension, which can improve the uniformity and reaction performance of the synthesis reaction and increase the output of high-purity sodium dithionite; from Comparative Example 2, it can be seen that in the synthesis reaction, through a constant temperature water bath and the regulation of temperature and pressure, and by improving the mass transfer efficiency of sulfur dioxide, the synthesis reaction of sodium dithionite is promoted, the crystal size is increased, the crystal nuclei are reduced, and sodium dithionite is not easily decomposed to produce other products; from Comparative Example 3, it can be seen that compared with a single side reaction inhibitor, ethylene oxide and 1,2-epoxypropane have a stronger reaction on sodium thiosulfate, improving the yield and purity of sodium dithionite; from Comparative Example 4, it can be seen that the recrystallization in the later stage of the reaction does not affect the yield of sodium dithionite and increases the yield.

[0089] III. The physical and chemical properties of the sodium dithionite prepared in Example 1 were detected, and the detection results are shown in Table 3.

[0090] Table 3 Physical and Chemical Properties of Sodium Dithionite

[0091]

[0092]

[0093] As can be seen from Table 3, the sodium dithionite prepared by the present invention has good physical and chemical properties, with less impurity content and can meet the food-grade standard.

[0094] IV. The sodium dithionite prepared in Example 1 and Comparative Example 4 was placed in the same open environment for six weeks, and the stability of sodium dithionite was detected. The results are as Figure 1 shown. It can be seen that the sodium dithionite prepared by the present invention is subjected to recrystallization treatment. By removing crystal water, large-particle-size crystals and stable packaging for sodium dithionite, the prepared sodium dithionite is not easily decomposed and has a longer storage period.

[0095] In summary, in the process of the present invention, through the uniform pre-dispersion treatment of raw materials before the reaction, the control of reaction factors such as temperature and pressure during the reaction, and the adoption of recrystallization and the hydrophobic and stable packaging treatment of the reaction products, sodium dithionite with less fine powder, high purity and not easily decomposed is obtained.

Claims

1. A process for preparing high-purity sodium dithionite, characterized in that: The following steps are involved: Step 1: preparing a suspension of solid sodium formate and sodium pyrosulfite; Step 2: The suspension, the side reaction inhibitor and methanol are subjected to a synthesis reaction at a mass ratio of 2-5:1-3:1, and the by-products produced in the reaction are removed by low-pressure flash steam; The synthesis reaction is to start nitrogen purging and pressurize to 0.4-0.6MPa, heat to 75-85°C, add sulfur dioxide gas-liquid mixture and react for 70-80min under water bath conditions, then increase the pressure to 1.0-1.8MPa and cool to react, keep warm and cool after the reaction, and filter to obtain a filter cake; Step 3: adding the filter cake into a methanol solution and subjecting it to low-frequency ultrasonic treatment to obtain a mixed solution; Step 4: Add the modified stearate to the mixed solution and then perform infrared treatment, filter press again and dry to obtain sodium dithionite.

2. A process for preparing high-purity sodium dithionite according to claim 1, characterized in that: The preparation method of the suspension in step 1 is to ultrasonically oscillate solid sodium formate and methanol in a mass ratio of 11-15:22-29 to form a uniform suspension; then add a mixed solution containing sodium pyrosulfite, methanol and water in a mass ratio of 4:50-60:18-22 to mix well.

3. A process for preparing high-purity sodium dithionite according to claim 2, characterized in that: The mixed solution is prepared by heating water to 90-100° C. under closed conditions, adding sodium pyrosulfite, stirring evenly, cooling to 50-60° C., and then adding methanol and mixing.

4. A process for preparing high-purity sodium dithionite according to claim 1, characterized in that: The side reaction inhibitor in step 2 is ethylene oxide and 1,2-propylene oxide in a mass ratio of 11-14:2-6.

5. A process for preparing high-purity sodium dithionite according to claim 1, characterized in that: The cooling reaction in step 2 is carried out by stirring the reaction at a temperature of 50-60° C. and a rotation speed of 150-250 rpm for 30-40 minutes.

6. A process for preparing high-purity sodium dithionite according to claim 1, characterized in that: The low-frequency ultrasonic treatment in step 3 is carried out at a frequency of 10-15 KHz for 5-10 min.

7. A process for preparing high-purity sodium dithionite according to claim 1, characterized in that: The sulfur dioxide gas-liquid mixture in step 3 is sulfur dioxide liquid and sulfur dioxide gas, the flow rate of sulfur dioxide gas is 90L / s-100L / s, and the addition amount of sulfur dioxide liquid is 3-5wt% of the suspension.

8. A process for preparing high-purity sodium dithionite according to claim 1, characterized in that: The amount of modified stearate added in step 4 is 3-4 mol / L.

9. A process for preparing high-purity sodium dithionite according to claim 1, characterized in that: The modified stearate described in step 4 is prepared by mixing macromolecular stearate with ethyl acetate at a solid-liquid ratio of 11-18:6-9 g / mL and heating at a temperature of 70-80° C. for 10-15 minutes.

10. The process for preparing high-purity sodium dithionite according to claim 1, characterized in that: The infrared treatment in step 4 has a wavelength of 1-4 μm, a power of 700-800 W, a temperature of 40-60° C., and a treatment time of 2-3 h.

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