Synthetic method of sodium hydrosulfite

Abstract

The invention discloses a sodium hydrosulfite synthesis method, which realizes efficient and safe production of sodium hydrosulfite by changing raw material selection, charging mode, reaction condition and post-treatment mode based on a reaction mechanism and a reaction crystallization technology of sodium hydrosulfite synthesis. The sodium hydrosulfite product meets the requirement of a superior product and the raw material cost is saved; in addition, the method disclosed by the invention briefly reveals the basic principle of reaction, and provides feasible thinking and conditions for automation of the sodium hydrosulfite process.

Description

Technical Field

[0001] The invention relates to the technical field of sodium hydrosulfite production, and in particular to a method for synthesizing sodium hydrosulfite. Background Art

[0002] Sodium dithionite, also known as sodium hydrosulfite, is an inorganic substance with the chemical formula Na2S2O4, and is a white crystalline powder. Its aqueous solution is unstable and is a strong reducing agent. It is easily oxidized by absorbing oxygen when exposed to air, and is also easily heated by absorbing moisture and deteriorating. It can also clump and emit a pungent sour smell by absorbing oxygen in the air. It is widely used in the food industry and the chemical industry: In the food industry, sodium hydrosulfite is often used as a food preservative. It can prevent food oxidation and extend the shelf life of food. Especially in dried foods such as preserved fruits and dried vegetables, sodium hydrosulfite can effectively prevent color change and flavor loss. In some foods, sodium hydrosulfite is used as a bleaching agent, such as in soy sauce, fruit juice and other foods. In some processed foods, sodium hydrosulfite can inhibit oxidation reactions and prevent food from spoiling.

[0003] In the chemical industry, sodium hydrosulfite is a common reducing agent used to reduce other compounds in chemical reactions. For example, it can reduce certain metal ions. In some industrial applications, sodium hydrosulfite is used as a bleaching agent for bleaching pulp and textiles.

[0004] At present, there are three common methods for synthesizing hydrosulfur powder: 1. Laboratory preparation method: Mix formic acid and NaOH solution dissolved in a mixed solvent of methanol and water, and then introduce SO2 gas to obtain hydrosulfite. Chemical formula: HCOONa + 2SO2 + NaOH = Na2S2O4 + CO2 +H2O, methanol is used as the solvent, in which both the product and the reactant are soluble in methanol, which can reduce the solubility of hydrosulfite in water, because water will reduce polarity after adding methanol, and hydrosulfite has strong polarity and can be precipitated from the solvent, thereby achieving the purpose of convenient separation from the reaction system. Zinc disulfite obtained by absorbing SO2 with Zn(OH)2 suspension reacts with NaOH to obtain the finished product.

[0005] 2. Zinc powder sulfur dioxide method: SO2 reacts with zinc powder monohydrate suspension at 35-45°C to generate zinc dithionite, and the pH value of the reaction end point is 3.0-3.5; then it is added to 18% sodium carbonate (or sodium hydroxide) solution, and reacts at 28-35°C to generate sodium hyposulfite and zinc hydroxide suspension. After the reactants are filtered to remove zinc hydroxide precipitate (recovery of zinc oxide), sodium chloride is added to the filtrate, and cooled to 20°C to crystallize sodium hyposulfite. After filtering out the crystals, dehydrate and dry with alcohol to obtain the product.

[0006] 3. Sodium formate method: First add a certain amount of sodium formate methanol solution into a stainless steel reactor, and neutralize it with sulfur dioxide methanol solution to slightly acidic; then add sulfur dioxide methanol solution (containing about 260g / L SO2) and alkali methanol solution (containing about 170g / L sodium hydroxide) at 70°C, and control the feeding speed so that the temperature does not exceed 83°C. Sodium hyposulfite precipitates in the reaction, and after filtering out the crystals, it is washed, recrystallized, separated, and dried to obtain the finished product.

[0007] However, there are still many problems in the preparation of sodium hydrosulfite: although the laboratory preparation method is convenient and fast, the raw materials are dangerous and the preparation process conditions are difficult to control. Although the zinc powder method produces a large particle size of sodium hydrosulfite, it is expensive. Although the sodium formate method has a simple preparation process and cheap raw materials, the amount of material in the process and the overall reaction time are highly dependent on the operator's experience and are difficult to automate, thus affecting the safe and efficient production of sodium hydrosulfite.

[0008] In summary, there is a need to develop a method for synthesizing sodium formate that is efficient, fast and safe. The present invention is based on the sodium formate method and can produce large-particle sodium formate products efficiently, greenly and safely through different feeding methods and processing means. Summary of the invention

[0009] The purpose of the present invention is to provide a method for synthesizing sodium hydrosulfite to solve the problems raised in the above background technology. To achieve the above purpose, the present invention provides the following technical solutions: A method for synthesizing hydrosulfur powder comprises the following steps: S1, grinding and mixing sodium formate, ethanol and water to obtain a sodium formate alcohol aqueous solution, preheating for standby use; grinding and mixing sodium pyrosulfite and ethanol to obtain a sodium pyrosulfite alcohol solution, preheating for standby use; S2, adding the sodium formate alcohol solution and the sodium pyrosulfite alcohol solution into the reactor, controlling the reactor to stir and heat to the target reaction temperature; S3, adding sulfur dioxide absorption liquid into the reactor, controlling the reactor to stir and heat up to the target reaction temperature, and regularly detecting the pH value in the reactor; S4. When the content of sodium hypochlorite in the reactor no longer increases, the stirring speed is increased, and sulfur dioxide absorption liquid is added dropwise to the reactor according to the detected pH value to control the pH value. After the reaction is completed, the temperature is lowered to obtain a sodium hypochlorite suspension; S5, subjecting the sodium hydrosulfite suspension to rotary evaporation to obtain finished sodium hydrosulfite.

[0010] Preferably, the mass ratio of sodium formate, ethanol, water, sodium metabisulfite and sulfur dioxide added in step S1 and step S3 is 40-50:70-80:20-30:30-40:20-30.

[0011] Preferably, in step S1, the particle size of the ground sodium formate is 150-200 microns; the particle size of the ground sodium metabisulfite is 100-200 microns.

[0012] Preferably, in step S2, the target reaction temperature is 70-85°C.

[0013] Preferably, in step S3, the stirring speed of the reactor is 50-150 rad / min; in step S4, the stirring speed of the reactor is 150-250 rad / min.

[0014] Preferably, in step S4, when the detected pH value reaches 4.8, sulfur dioxide absorption liquid is added dropwise into the reactor to control the pH value.

[0015] Preferably, in step S4, the pH value is controlled in the range of 3.8-4.5 by dripping sulfur dioxide absorption liquid into the reactor.

[0016] Preferably, in steps S2 to S4, the reaction pressure in the reactor is controlled to be 0.1-0.4 MPa.

[0017] Preferably, in step S4, after cooling, the temperature in the reactor is 30-50°C.

[0018] Preferably, in step S5, the temperature of the rotary evaporation treatment is 70-90°C, the rotary evaporation pressure is lower than 0.02 MPa, and the rotary evaporation time is 0.5-2 min.

[0019] The beneficial effects of the present invention are as follows: the method for synthesizing the insurance powder of the present invention, based on the reaction mechanism of insurance powder synthesis and the reaction crystallization technology, realizes the efficient and safe production of insurance powder by changing the raw material selection, feeding method, reaction conditions and post-processing method; enables the insurance powder product to meet the requirements of high-quality products and saves the cost of raw materials; and the present invention briefly reveals the basic principle of the reaction, and provides feasible ideas and conditions for the automation of the insurance powder process. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0021] Figure 1 The present invention is a flowchart of the method for synthesizing the hydrosulfur powder.

[0022] It should be noted that the drawings are not necessarily drawn to scale, but are merely shown in a schematic manner that does not affect the reader's understanding. DETAILED DESCRIPTION

[0023] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] It should be further understood that the term "and / or" used in the present description and the appended claims refers to any and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0025] The present application provides a method for synthesizing hydrosulfur powder, comprising the following steps: S1. Grind and mix sodium formate, ethanol and water to make the particle size of the ground sodium formate reach 150-200 microns, prepare sodium formate alcohol aqueous solution, and preheat for use; Grind and mix sodium metabisulfite and ethanol to make the particle size of the ground sodium metabisulfite reach 100-200 microns, prepare sodium metabisulfite alcohol solution, and preheat for use; Among them, the use of sodium formate meets the Type I index of HGT 5390-2018, the water used is deionized water, and the use of sodium metabisulfite meets the index of superior products in HG / T 2826-2008.

[0026] S2. Add the sodium formate alcohol aqueous solution and the sodium pyrosulfite alcohol solution into the reactor for premixing, control the reactor to stir to mix the materials evenly, and heat to the target reaction temperature of 70-85°C.

[0027] S3. Add sulfur dioxide absorption liquid into the reactor to enter the first stage of reaction. Control the reactor to continue stirring and heat up to the target reaction temperature of 70-85°C, and wait for the first stage of reaction to end. During this period, regularly detect the content of sodium hypochlorite and pH value in the reactor. The content of sodium hypochlorite is detected using the national standard HG / T2074-2011 method.

[0028] S4. When the content of sodium hypochlorite in the reactor no longer increases, the second stage of reaction is entered, the stirring speed is increased, and according to the detected pH value, whenever the pH value reaches 4.8, sulfur dioxide absorption liquid is added dropwise into the reactor, and the amount of sulfur dioxide absorption liquid added each time is 0.5-5% of the total volume of the reaction system to control the pH value within the range of 3.8-4.5; after the reaction is completed, the temperature in the reactor is lowered to 30-50°C to protect the alcohol-water ratio in the sodium hypochlorite suspension and prevent the sodium hypochlorite from being oxidized by air.

[0029] S5. The hydrosulfite suspension is subjected to rotary evaporation to obtain finished hydrosulfite.

[0030] Compared with the traditional method for synthesizing sodium hydrosulfite, the improvement of the technical solution of the sodium hydrosulfite synthesis method of the present application is: (1) The traditional method for synthesizing sodium hydrosulfite generally uses methanol as a solvent, and methyl formate is generated during the reaction. The loss of methyl formate will affect the equilibrium shift of sodium hydrosulfite synthesis, that is, affect the synthesis of sodium hydrosulfite and reduce the yield of sodium hydrosulfite. In addition, since methyl formate has a low boiling point (31.5°C), it will escape immediately once it is generated in the system. Therefore, an additional cold source is required for condensation and reflux in industrial production, which is easy to cause environmental pollution and waste of resources. However, this synthesis method innovatively uses ethanol as a solvent, and produces ethyl formate (54.7°C), a product with a higher boiling point, during the reaction. Therefore, ethyl formate can be condensed and refluxed without using an external cold source, reducing resource waste and environmental pollution.

[0031] (2) This synthesis method grinds sodium formate and sodium metabisulfite in advance to ensure that the particle size is within an appropriate range, which not only ensures smooth feeding, but also improves the effective collision efficiency of molecules and accelerates the reaction rate; and the grains with this particle size can reduce the probability of secondary nucleation during the reaction crystallization process, ensuring that the generated insurance powder reaches the particle size required for high-quality products. In the traditional insurance powder synthesis method using sodium formate as feed material, the raw materials are usually not pre-grinded, which not only easily blocks the pipeline during the production process, but also causes uneven dispersion of the produced insurance powder.

[0032] The synthesis method is suitable for preparing a sodium formate alcohol aqueous solution system and a sodium pyrosulfite alcohol solution (3) system in advance, and preheating them as standby to achieve ready-to-use. When it is necessary to synthesize the sodium hydrosulfite powder, the two pre-prepared systems can be fed into the reactor at any time for reaction, thereby shortening the preparation time of the sodium hydrosulfite powder, and preliminarily solving the problem of traditional reliance on manual experience in feeding, providing ideas and conditions for realizing the automated synthesis production of sodium hydrosulfite.

[0033] (4) The traditional method for synthesizing sodium hypochlorite is to first add sulfur dioxide absorption liquid while feeding, and then heat it up; then add ethylene oxide according to the sodium thiosulfate content to carry out the first stage reaction; in the second stage, add sulfur dioxide absorption liquid according to the pH, and supplement ethylene oxide until the reaction is completed. In this traditional method, the continuous heating and temperature increase will cause sulfur dioxide to escape and methanol to volatilize, which will lead to unstable pressure control and waste of raw materials. According to experimental exploration, the content of sodium hypochlorite is only 1.3% from the completion of feeding to the heating to 78°C; and the added ethylene oxide is also highly dangerous and has great harm to the environment. Therefore, the present synthesis method innovatively selects to first add the sodium formate alcohol aqueous solution and the sodium metabisulfite alcohol solution into the reactor for mixing, and then add the sulfur dioxide absorption liquid after the mixed solution is heated to the target reaction temperature. This adding step or method is different from the traditional way of adding the raw materials and the sulfur dioxide absorption liquid at one time. The present method can reduce the volatilization of alcohol, reduce the amount of sulfur dioxide used, and improve the alcohol-water ratio in the system, thereby shortening the overall insurance powder preparation time and making the prepared insurance powder more stable; there is no need to use ethylene oxide, thereby ensuring production safety and reducing environmental hazards.

[0034] (5) Based on the rules obtained from experiments, this synthesis method summarizes a more appropriate and regular method for adding sulfur dioxide absorption liquid: that is, by slowly adding a small amount of sulfur dioxide absorption liquid, and controlling the amount of sulfur dioxide absorption liquid added each time to be 0.5-5% of the total volume of the reaction system; this addition method can not only solve the problem of excessive local concentration of sulfur dioxide absorption liquid in the traditional production process leading to decomposition of insurance powder products and large-scale generation of by-products, but also solve the problem of strong experience dependence of the insurance powder production process.

[0035] In summary, the method for synthesizing insurance powder of the present application is based on the reaction mechanism of insurance powder synthesis and the reaction crystallization technology, and realizes the efficient and safe production of insurance powder by changing the raw material selection, feeding method, reaction conditions, and post-processing method; the insurance powder product meets the requirements of high-quality products and saves raw material costs; and the present invention briefly reveals the basic principles of the reaction, and provides feasible ideas and conditions for the automation of the insurance powder process.

[0036] Preferably, in step S1 and step S3, the mass ratio of the added sodium formate, ethanol, water, sodium metabisulfite and sulfur dioxide is 40-50:70-80:20-30:30-40:20-30.

[0037] Preferably, in step S3, the stirring speed of the reactor is 50-150rad / min; in step S4, the stirring speed of the reactor is 150-250rad / min. In the traditional method for synthesizing sodium hydrosulfite, a fixed stirring speed is usually used in the entire reaction process, which will result in the inability to quickly mix the materials and efficiently form crystal nuclei during the first stage of the reaction, and the inability to protect the generated large-particle sodium hydrosulfite and inhibit secondary nucleation in the second stage. This synthesis method is based on the principle of reaction crystallization and adopts a slow-first-fast-later stirring speed mode: a slower speed is used in the first stage, which can protect the generated sodium hydrosulfite particles from being destroyed, improve the nucleation efficiency, and ensure that the materials are fully mixed and uniform; a faster speed is used in the second stage, which can solve the problem of uneven solution dispersion and excessive local concentration of sulfur dioxide absorption liquid, avoid the negative impact of a large number of by-products or inhibiting the generation of sodium hydrosulfite, stabilize the material to prevent breakage, and solve the problem of traditional processes destroying large-particle sodium hydrosulfite and inhibiting secondary nucleation.

[0038] Preferably, in steps S2 to S4, the reaction pressure in the reactor is controlled to be 0.1-0.4 MPa; specifically, the present application uses nitrogen to increase the pressure to the reaction pressure, and the reactor is also connected to a condensing reflux device to adjust the reflux temperature and the back pressure valve to control the reaction pressure.

[0039] Preferably, in step S5, the temperature of the rotary evaporation treatment is 70-90°C, the rotary evaporation pressure is lower than 0.02MPa, and the rotary evaporation time is 0.5-2min. The use of the rotary evaporation process to dry the sodium hydroxide suspension can not only reduce the contact between the sodium hydroxide and oxygen in the air, but also reduce the loss of sodium hydroxide; compared with the four-in-one treatment method of filtering, washing, vacuuming and drying in the traditional sodium hydroxide synthesis method, the rotary evaporation can also effectively avoid the crushing of sodium hydroxide particles, ensure the particle size of the finished product, and improve the product quality.

[0040] Based on the inventive concept of the method for synthesizing sodium hydrosulfite of the present application, the technical solution of the present application will be described in detail below in combination with specific embodiments and comparative examples: 1. Implementation Example

[0041] a. Weigh 150g sodium formate, 215ml anhydrous ethanol, and 96ml distilled water, and grind them in a grinder for 1min. The particle size is within the range of 180 microns to obtain a sodium formate alcohol aqueous solution, which is preheated for use. Weigh 128g sodium pyrosulfite and 183ml anhydrous ethanol, and grind them for 1min. The particle size is within the range of 128 microns to obtain a sodium pyrosulfite alcohol solution, which is preheated for use.

[0042] b. Pour the sodium formate alcohol solution and the sodium metabisulfite alcohol solution into the reactor and seal it. Turn on the magnetic stirring at a speed of 60 rad / min and use a water bath to heat the reactor to 78°C.

[0043] c. Add 211 ml of sulfur dioxide absorption liquid, and use nitrogen to increase the pressure to 0.3 MPa after adding; the room temperature during the experiment is 33°C, and condensation reflux is performed without providing an additional cold source; the reactor is connected to a back pressure valve and the pressure is adjusted to 0.3 MPa. Start the first stage reaction, and take the liquid in the reactor to test the pH value every 30 minutes; the reaction time is 230 minutes, until the content of the hydrosulfite reaches the maximum value and no longer increases, and the first stage reaction is over.

[0044] d. Enter the second stage of reaction, adjust the speed to 180rad, take the liquid in the reactor every 30 minutes to test the pH value; according to the real-time detected pH value, when the pH value is 4.8, add sulfur dioxide absorption liquid in small drops, the amount added is 1% of the total volume of the reaction system, and the pH value is adjusted to 4.3; the reaction time is 230min, until the content of the hydrosulfite in the reactor no longer increases, and the second stage of reaction is completed; the temperature in the reactor is reduced to 50℃ for cooling.

[0045] e. Take the suspension in the reaction kettle, put it into a rotary evaporator, and perform rotary evaporation at 80°C to obtain the sodium hypochlorite product. The national standard HG / T2074-2011 method is used for testing. The sodium hypochlorite content in the product is 93.2%, and the particle size meets the standard of superior products. Example

[0046] The synthesis method of this embodiment is the same as that of embodiment 1, except that the mass ratio of sodium formate: ethanol: sodium metabisulfite: sulfur dioxide is 47: 93: 7: 47: 50. The content of sodium hydrosulfite in the product is detected to be 85.4%, and the particle size meets the standard of superior products. Example

[0047] The synthesis method of this embodiment is the same as that of embodiment 1, except that sulfur dioxide absorption liquid is added before the temperature is raised to the target temperature, and then the temperature is raised. The content of sodium hydrosulfite in the product is detected to be 89.2%, and the particle size meets the standard of superior products. Example

[0048] The synthesis method of this embodiment is the same as that of embodiment 1, except that the overall alcohol-water ratio of the reaction system is 78:22. The content of sodium hydrosulfite in the product is detected to be 83.2%, and the particle size meets the standard of superior products. Example

[0049] The synthesis method of this embodiment is the same as that of embodiment 1, except that the reaction temperature is 83° C. The content of sodium hydrosulfite in the product is detected to be 90.1%, and the particle size meets the standard of superior products.

[0050] The synthesis method of this embodiment is the same as that of embodiment 1, except that the reaction temperature is 72° C. The content of sodium hydrosulfite in the product is detected to be 71.5%, and the particle size meets the standard of superior products. Example

[0051] The synthesis method of this embodiment is the same as that of embodiment 1, except that the reaction pressure is 0.2 MPa. The content of sodium hydrosulfite in the product is detected to be 90.9%, and the particle size meets the standard of superior products.

[0052] The synthesis method of this embodiment is the same as that of embodiment 1, except that the reaction pressure is 0.4 MPa. The content of sodium hydrosulfite in the product is detected to be 87.3%, and the particle size meets the standard of superior products. Example

[0053] This example provides two groups of experiments, and the experimental method is the same as the synthesis method of Example 1, except that the first-stage reaction time of one group is 200 minutes, and the content of sodium hydrosulfite in the product is detected to be 84.7%, and the particle size does not meet the standard of high-quality products. The first-stage reaction time of the other group is 260 minutes, and the content of sodium hydrosulfite in the product is detected to be 92.3%, and the particle size meets the standard of high-quality products. Example

[0054] This example provides two groups of experiments. The experimental method is the same as the synthesis method of Example 1, except that the second-stage reaction time of one group is 180 minutes, and the content of sodium hydrosulfite in the product is detected to be 92.1%, and the particle size does not meet the standard of high-quality products. The second-stage reaction time of the other group is 250 minutes, and the content of sodium hydrosulfite in the product is detected to be 91.9%, and the particle size does not meet the standard of high-quality products. Example

[0055] This embodiment provides four groups of experiments. The experimental method is the same as the synthesis method of Example 1. The difference is that in the first group of experiments, the pH value before the addition of sulfur dioxide absorption liquid in the second stage reaction is 4.5, and the content of sodium hypochlorite in the product is detected to be 78.8%, and the particle size meets the standard of superior products.

[0056] In the second set of experiments, the pH value was 5.0 before the addition of sulfur dioxide absorption liquid in the second stage reaction, and the content of sodium hypochlorite in the product was detected to be 91.7%, and the particle size met the standards for superior products.

[0057] In the third group of experiments, the pH value was 4.0 after adding sulfur dioxide absorption liquid in the second stage reaction, and the content of sodium hypochlorite in the product was detected to be 81.5%, and the particle size met the standards of superior products.

[0058] In the fourth group of experiments, the pH value was 4.5 after the sulfur dioxide absorption liquid was added to the second stage reaction, and the content of sodium hypochlorite in the product was detected to be 87.8%, and the particle size met the standards for superior products. Example

[0059] This example provides two groups of experiments. The experimental method is the same as the synthesis method of Example 1, except that the first-stage rotation speed of one group is 50 rad / min, and the content of sodium hydrosulfite in the product is detected to be 90.4%, and the particle size does not meet the standard of high-quality products. The first-stage rotation speed of the other group is 100 rad / min, and the content of sodium hydrosulfite in the product is detected to be 90.2%, and the particle size does not meet the standard of high-quality products. Example

[0060] This example provides two groups of experiments. The experimental method is the same as the synthesis method of Example 1, except that the second stage rotation speed of one group is 150 rad / min, and the content of sodium hydrosulfite in the product is detected to be 92.0%, and the particle size does not meet the standard of high-quality products. The second stage rotation speed of the other group is 200 rad / min, and the content of sodium hydrosulfite in the product is detected to be 92.5%, and the particle size does not meet the standard of high-quality products. Example

[0061] This example provides two groups of experiments. The experimental method is the same as the synthesis method of Example 1. The difference is that one group uses methanol as a solvent, and the content of the insurance component in the product is detected to be 85.6%, and the particle size meets the standard of high-quality products. The other group uses propanol as a solvent, and the content of the insurance component in the product is detected to be 92.2%, and the particle size meets the standard of high-quality products. Example

[0062] This example provides two groups of experiments. The experimental method is the same as the synthesis method of Example 1, except that the temperature of the material after cooling in one group is 40°C, and the content of sodium hydrosulfite in the product is detected to be 89.7%, and the particle size meets the standard of high-quality products. The temperature of the material after cooling in the other group is 60°C, and the content of sodium hydrosulfite in the product is detected to be 85.1%, and the particle size meets the standard of high-quality products. Example

[0063] The synthesis method of this embodiment is the same as that of embodiment 1, except that the rotary evaporation pressure is greater than 0.02 MPa. The content of sodium hydrosulfite in the product is detected to be 91.2%, and the particle size meets the standard of superior products. Example

[0064] This example provides two groups of experiments. The experimental method is the same as the synthesis method of Example 1, except that the rotary evaporation temperature of one group is 70°C, and the content of sodium hydrosulfite in the product is detected to be 85.6%, and the particle size meets the standard of high-quality products. The rotary evaporation temperature of the other group is 90°C, and the content of sodium hydrosulfite in the product is detected to be 82.9%, and the particle size meets the standard of high-quality products. Example

[0065] This example provides two groups of experiments, and the experimental method is the same as the synthesis method of Example 1, except that in one group, 0.5% of the total volume of sulfur dioxide absorption liquid was added in the second stage, and the content of sodium hydrosulfite in the product was detected to be 80.8%, and the particle size met the standard of high-quality products. In the other group, 5% of the total volume of sulfur dioxide absorption liquid was added in the second stage, and the content of sodium hydrosulfite in the product was detected to be 82.4%, and the particle size met the standard of high-quality products.

[0066] (II) Comparative Example Comparative Example 1 This comparative example provides two groups of experiments. The experimental method is the same as the synthesis method of Example 1, except that the target reaction temperature of one group is 88°C. The content of sodium hydrosulfite in the product is detected to be 50.6%, and the particle size meets the standard of high-quality products. The target reaction temperature of the other group is 67°C. The content of sodium hydrosulfite in the product is detected to be 53.1%, and the particle size meets the standard of high-quality products.

[0067] Comparative Example 2 This comparative example provides two groups of experiments, and the experimental method is the same as the synthesis method of Example 1, except that the reaction pressure of one group is 0.5Mpa, and the content of sodium hydrosulfite in the product is detected to be 72.2%, and the particle size meets the standard of high-quality products. The other group does not provide an additional pressure source, and the content of sodium hydrosulfite in the product is detected to be 80.6%, and the particle size meets the standard of high-quality products.

[0068] Comparative Example 3 This comparative example provides two groups of experiments, and the experimental method is the same as the synthesis method of Example 1, except that the first-stage reaction time of one group is 180 minutes, and the content of sodium hydrosulfite in the product is detected to be 78.7%, and the particle size meets the standard of high-quality products. The first-stage reaction time of the other group is 280 minutes, and the content of sodium hydrosulfite in the product is detected to be 83.0%, and the particle size meets the standard of high-quality products.

[0069] Comparative Example 4 This comparative example provides two groups of experiments. The experimental method is the same as the synthesis method of Example 1, except that the second-stage reaction time of one group is 150 minutes, and the content of sodium hydrosulfite in the product is detected to be 81.9%, and the particle size meets the standard of high-quality products. The second-stage reaction time of the other group is 280 minutes, and the content of sodium hydrosulfite in the product is detected to be 76.5%, and the particle size meets the standard of high-quality products.

[0070] Comparative Example 5 This comparative example provides two groups of experiments, the experimental method is the same as the synthesis method of Example 1, the difference is that in one group, the pH value before adding the sulfur dioxide absorption liquid in the second stage is 5.2, and the content of sodium hypochlorite in the product is detected to be 87.1%, and the particle size meets the standard of high-quality products. In the other group, the pH value is controlled to 3.5 after adding the sulfur dioxide absorption liquid, and the content of sodium hypochlorite in the product is detected to be 51.4%, and the particle size meets the standard of high-quality products.

[0071] Comparative Example 6 This comparative example provides two groups of experiments, and the experimental method is the same as the synthesis method of Example 1, except that in one group, during the first stage reaction, the stirring speed of the reactor was 30 rad / min, and the content of sodium hydrosulfite in the product was detected to be 86.6%, and the particle size did not meet the standard of high-quality products. During the first stage reaction of the other group, the stirring speed of the reactor was 180 rad / min, and the content of sodium hydrosulfite in the product was detected to be 86.3%, and the particle size did not meet the standard of high-quality products.

[0072] Comparative Example 7 This comparative example provides two groups of experiments. The experimental method is the same as the synthesis method of Example 1. The difference is that in the second stage reaction of one group, the stirring speed of the reactor is 120 rad / min, and the content of sodium hypochlorite in the product is detected to be 91.1%, and the particle size does not meet the standard of high-quality products. In the second stage reaction of the other group, the stirring speed of the reactor is 280 rad / min, and the content of sodium hypochlorite in the product is detected to be 91.9%, and the particle size does not meet the standard of high-quality products. Comparative Example 8 The synthesis method of this comparative example is the same as that of Example 1, except that the condensation reflux temperature is 50° C. The content of sodium hydrosulfite in the product is detected to be 77.4%, and the particle size meets the standard of superior products.

[0073] Comparative Example 9 This comparative example provides two groups of experiments. The experimental method is the same as the synthesis method of Example 1, except that the rotary evaporation temperature of one group is 95°C, and the content of sodium hydrosulfite in the product is detected to be 71.3%, and the particle size meets the standard of high-quality products. The rotary evaporation temperature of the other group is 60°C, and the content of sodium hydrosulfite in the product is detected to be 78.1%, and the particle size meets the standard of high-quality products.

[0074] Comparative Example 11 This comparative example provides two groups of experiments, and the experimental method is the same as the synthesis method of Example 1, except that in one group, the amount of sulfur dioxide absorption liquid added in the second stage is 10% of the total volume, and the content of sodium hydrosulfite in the product is detected to be 60.5%, and the particle size meets the standard of high-quality products. In the other group, the amount of sulfur dioxide absorption liquid added in the second stage is 0.1% of the total volume, and the content of sodium hydrosulfite in the product is detected to be 77.3%, and the particle size meets the standard of high-quality products.

[0075] Comparative Example 12 This comparative example adopts the production method described in the patent document with patent application number CN201611155475.3 and patent name “A method for continuous production of hydrosulfur powder synthesis”, and the specific steps are as follows: Preparation: Prepare 98% HCOONa by mass, 62% sodium metabisulfite by mass, SO2-CH3OH, SO2 concentration ≥ 370g / L, and 78% by mass of carrier methanol; Feed the bottom material: pressurize the storage tank with inert gas, open the flow meter and feed about 1.8m3 of AE into the synthesis large dropping pot, and start heating; Adjustment: Turn on the steam and when the temperature rises to 76℃ and the pressure is 0.1MPa, open the flow meter valve and add 25L of SO2-CH3OH solution and a certain amount of ethylene oxide to the large dropping pot, and adjust the pH to 4.3; Large dropping: after adjusting for 10min~20min, when the temperature rises to 81℃~82℃, start adding AE and ME to stabilize the pH at 4.4~4.5 and the pressure at 0.2MPa~0.25MPa. When the synthesis large dropping pot reaches 80% (a batch of materials) visually, the bottom tube in the pot is automatically opened to continuously transfer materials to the four small dropping pots A#~D#. During the material transfer process, raw materials AE and ME continue to be added to the synthesis large pot. When the synthesis small dropping pot receives a batch of materials, the second small dropping pot starts to receive materials from the synthesis large dropping pot, and so on; always maintain the time required for the reaction of the four small dropping pots to reach the end point.

[0076] Small drop addition: control the temperature at 82℃~83℃, the pressure at 0.2MPa~0.25MPa, and continuously add 100L of SO2-CH3OH solution at a fast and then slow rhythm, and control the pH at 4.5~4.6 to continuously generate the hydrosulfite to increase the content of hydrosulfite. Visually observe that the synthetic liquid is clear or analyze the content of sodium bisulfite in the clear liquid. When NaHSO3≤10g / L, the small drop addition is completed and the heat preservation operation is started; Insulation: After 10 minutes of insulation, take samples for analysis. When the pH value is ≥4.9 and the sautéed sample hydrochloric acid content is ≥85%, the insulation ends. Cooling and discharging: Discharge when the temperature is 68℃~75℃, pH value ≥4.9, and Na2S203 ≤10g / L.

[0077] 3. Analysis of experimental results The present invention analyzes the experiments and experimental results of the above embodiments and comparative examples, and reveals the technical effects that can be achieved by the method for synthesizing sodium hydrosulfite: 1. Regarding the mass ratio of raw materials: The synthesis process of sodium hydrosulfite is a reversible reaction. An unreasonable raw material ratio will destroy the entire chemical balance during the reaction and affect the efficient production of sodium hydrosulfite.

[0078] Regarding the time of adding the sulfur dioxide absorption liquid in the first stage: the inventors conducted 2. verification through multiple experiments and found that when the sulfur dioxide absorption liquid was added before the reaction temperature was reached, almost no insurance powder was generated, which was sufficient to prove that the addition of the sulfur dioxide absorption liquid did not play a role in generating insurance powder during the heating process; and as the temperature increased, it was observed that there was continuous gas escaping through the connected gas flow meter, and the escaping gas was collected and detected to contain sulfur dioxide. Therefore, the synthesis method of the present invention chooses to arrange the addition time of the sulfur dioxide absorption liquid after the target reaction temperature is reached, which can reduce the escape of sulfur dioxide and promote the positive shift of equilibrium.

[0079] 3. Regarding the amount of sulfur dioxide absorption liquid added in the second stage: the addition of sulfur dioxide affects the balance of the reaction. The sulfur dioxide added in the second stage can also generate sodium hyposulfite. Too little sulfur dioxide added will result in less sodium hyposulfite generated in the second stage and a lower content. Too much sulfur dioxide added will result in too high a solution acidity, causing the sodium hyposulfite to decompose.

[0080] 4. Regarding the alcohol-water ratio: In the production process of sodium hypochlorite, the alcohol-water ratio has always been one of the factors that need to be strictly regulated. Among them, the water content directly affects the effect of the entire reaction; water is both a reaction promoter that can promote the balance to move toward the direction of generating sodium hypochlorite, and a reaction inhibitor that can reverse the reaction, and too high a water content will lead to the decomposition of sodium hypochlorite. The present invention has finally selected a more appropriate alcohol-water ratio through multiple experiments, which can achieve a better reaction effect.

[0081] 5. Reaction pressure and temperature: The reaction pressure and temperature directly affect the balance of the reaction. The present invention has finally selected more appropriate temperature and pressure parameters through multiple experiments, so that the hydrosulfite can be generated more efficiently.

[0082] 6. Regarding reaction time: reaction time directly affects the crystallization of sodium hydrosulfite and the content of the product. In the first stage, sodium hydrosulfite grows on the crystal nucleus. If the reaction time is not enough, the generated sodium hydrosulfite particles are small, and it is difficult to continue to grow into the particle size of high-quality products in the second stage of the reaction process. A longer reaction time will cause the generation of by-products and consume the generated sodium hydrosulfite.

[0083] Regarding the rotation speed: the rotation speed directly affects the dispersion of the solution and the particle size of the insurance powder. During the reaction process, a slower rotation speed can protect the generated insurance powder particles from being destroyed, but a slower rotation speed will cause uneven dispersion of the solution and excessive local concentration of the sulfur dioxide absorption liquid, affecting the generation of insurance powder; on the contrary, a higher rotation speed can solve the problems of uneven dispersion of the solution and excessive local concentration of the sulfur dioxide absorption liquid, but it will face the problem of breaking the insurance powder particles and affecting the particle size of the insurance powder.

[0084] 8. Choice of alcohol: With the increase of molecular weight, the boiling point of a formic acid ester generated by alcohol and formic acid will increase. The formic acid ester needs to be retained in the solution to promote the reaction balance to move toward the direction of generating sodium hypochlorite, so the increase of boiling point is beneficial to the reaction. However, the problem is that the molecular weight of the alcohol increases. When removing the residual alcohol in the later stage, the operating temperature will increase. Increasing the operating temperature will lead to the decomposition of sodium hypochlorite, so ethanol is more suitable.

[0085] 9. For cold material operation: cold material operation can maintain the stability of the alcohol-water ratio in the sodium hypochlorite suspension and protect the sodium hypochlorite from being oxidized by air; too high a cold material temperature will lead to an imbalance in the alcohol-water ratio and decomposition of the sodium hypochlorite; too low a cold material temperature will prompt the reaction to move toward the direction of generating by-products, causing the sodium hypochlorite content to decrease.

[0086] 10. Regarding the temperature and pressure of rotary evaporation: The temperature and pressure of rotary evaporation affect the content of sodium hypochlorite. Too low a rotary evaporation temperature will result in the inability to completely remove the alcohol in the sodium hypochlorite, while too high a rotary evaporation temperature will result in thermal decomposition of the sodium hypochlorite. If the rotary evaporation pressure does not reach the preset value, the sodium hypochlorite will come into contact with air during the rotary evaporation process, causing a certain degree of decomposition.

[0087] Regarding the embodiments of the present invention, it should also be noted that, in the absence of conflict, the embodiments of the present invention and the features therein may be combined with each other to obtain new embodiments.

[0088] The above is only a preferred embodiment of the present invention, and does not limit the present invention in any form. The protection scope of the present invention shall be subject to the protection scope of the claims. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technician familiar with this profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical content disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the scope of the technical solution of the present invention.

Claims

1. A method for synthesizing hydrosulfur powder, characterized in that: The following steps are involved: S1, grinding and mixing sodium formate, ethanol and water to obtain a sodium formate alcohol aqueous solution, preheating for standby use; grinding and mixing sodium pyrosulfite and ethanol to obtain a sodium pyrosulfite alcohol solution, preheating for standby use; S2, adding the sodium formate alcohol solution and the sodium pyrosulfite alcohol solution into the reactor, controlling the reactor to stir and heat to the target reaction temperature; S3, adding sulfur dioxide absorption liquid into the reactor, and regularly detecting the pH value in the reactor; S4. When the content of sodium hypochlorite in the reactor no longer increases, the stirring speed is increased, and sulfur dioxide absorption liquid is added dropwise to the reactor according to the detected pH value to control the pH value. After the reaction is completed, the temperature is lowered to obtain a sodium hypochlorite suspension; S5, subjecting the sodium hydrosulfite suspension to rotary evaporation to obtain finished sodium hydrosulfite.

2. The method for synthesizing hydrosulfur powder according to claim 1, characterized in that: The mass ratio of sodium formate, ethanol, water, sodium pyrosulfite and sulfur dioxide added in step S1 and step S3 is 40-50:70-80:20-30:30-40:20-30.

3. The method for synthesizing hydrosulfur powder according to claim 1, characterized in that: In step S1, the particle size of the ground sodium formate is 150-200 microns; the particle size of the ground sodium pyrosulfite is 100-200 microns.

4. The method for synthesizing hydrosulfur powder according to claim 1, characterized in that: In step S2, the target reaction temperature is 70-85°C.

5. The method for synthesizing hydrosulfur powder according to claim 1, characterized in that: In step S2, the stirring speed of the reactor is 50-150 rad / min; in step S4, the stirring speed of the reactor is 150-250 rad / min.

6. The method for synthesizing hydrosulfur powder according to claim 1, characterized in that: In step S4, when the detected pH value reaches 4.8, sulfur dioxide absorption liquid is added dropwise into the reactor to control the pH value.

7. The method for synthesizing hydrosulfur powder according to claim 1, characterized in that: In step S4, the pH value is controlled in the range of 3.8-4.5 by adding sulfur dioxide absorption liquid dropwise into the reactor.

8. The method for synthesizing hydrosulfur powder according to claim 1, characterized in that: In steps S2 to S4, the reaction pressure in the reactor is controlled to be 0.1-0.4 MPa.

9. The method for synthesizing hydrosulfur powder according to claim 1, characterized in that: In step S4, after cooling, the temperature in the reactor is 30-50°C.

10. The method for synthesizing hydrosulfur powder according to claim 1, characterized in that: In step S5, the temperature of the rotary evaporation treatment is 70-90°C, the rotary evaporation pressure is lower than 0.02MPa, and the rotary evaporation time is 0.5-2min.

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