Green synthesis process of anhydrous sodium phosphite capable of being used as antioxidant

Abstract

The invention discloses a green synthesis process of anhydrous sodium phosphite capable of being used as an antioxidant, and relates to the technical field of chemical engineering, and the green synthesis process comprises the following steps: firstly, adding anhydrous phosphorous acid and methanol into a reactor to obtain an anhydrous phosphorous acid-methanol solution; then slowly dropwise adding a sodium methoxide solution into the anhydrous phosphorous acid-methanol solution, stopping dropwise adding the sodium methoxide solution when the pH value of the solution in the reactor is 6-9, and cooling the solution in the reactor to 20 DEG C to obtain a reaction product; separating the reaction product through a solid-liquid separation device to obtain a filtrate and a filter cake; distilling and recovering the filtrate to obtain recovered methanol; carrying out vacuum drying on the filter cake to obtain anhydrous sodium phosphite; according to the green synthesis process of the anhydrous sodium phosphite capable of being used as the antioxidant, by strictly controlling reaction conditions, generation of by-products is effectively reduced, the output of wastes is reduced, and environmental pollution is relieved; meanwhile, methanol is recycled, the green chemistry concept is met, and sustainable development of the chemical industry is facilitated.

Description

Technical Field

[0001] The invention relates to chemical technology, and in particular to a green synthesis process of anhydrous sodium phosphite which can be used as an antioxidant. Background Art

[0002] Sodium phosphite and sodium hypophosphite are both new products of phosphates, which are widely used in the chemical and material fields, mainly as various reducing agents. Because sodium phosphite has weaker reducing properties than sodium hypophosphite and is more stable, it can replace sodium hypophosphite as a reducing agent to a certain extent, and has better stability and safety. It is used as an antioxidant and anti-yellowing agent in the field of polymer materials, such as polyamide and polyester, to prevent the degradation of materials caused by shear stress and thermal stress during processing, and to extend the service life of materials under thermal aging conditions.

[0003] The existing synthesis process of sodium phosphite is not only complicated, but also the products produced are all sodium phosphite with crystal water, generally with five crystal waters. Because the crystal water carried is more, the specific gravity of its active substances is only 58.3%, which significantly affects its use effect as an antioxidant. On the basis of the above process, to obtain anhydrous sodium phosphite, a more complicated crystal water removal process is required. Therefore, a simple, green and environmentally friendly technical method for synthesizing anhydrous sodium phosphite is provided, which has important social and economic value. Summary of the invention

[0004] The purpose of the present invention is to provide a green synthesis process of anhydrous sodium phosphite which can be used as an antioxidant, so as to solve the problem that the synthesis process of sodium phosphite in the prior art is not only complicated, but also the products produced are all sodium phosphite with crystal water.

[0005] In order to achieve the above object, the present invention provides the following technical solution: a green synthesis process of anhydrous sodium phosphite which can be used as an antioxidant, comprising:

[0006] S1. First, add anhydrous phosphorous acid and methanol into a reactor, and stir until the anhydrous phosphorous acid is completely dissolved to obtain an anhydrous phosphorous acid-methanol solution;

[0007] S2, then slowly adding sodium methoxide solution to the anhydrous phosphorous acid-methanol solution, when the pH value of the solution in the reactor is 6-9, stopping the addition of sodium methoxide solution, and cooling the temperature of the solution in the reactor to 20° C. to obtain a reaction product;

[0008] S3, separating the reaction product through a solid-liquid separation device to obtain a filtrate and a filter cake; distilling and recovering the filtrate to obtain recovered methanol;

[0009] S4, vacuum drying the filter cake to obtain a white solid powder, i.e., anhydrous sodium phosphite.

[0010] Furthermore, the mass of methanol added to the reactor in S1 is 0.2 to 5 times the mass of anhydrous phosphorous acid.

[0011] Furthermore, the mass of methanol added to the reactor in S1 is 0.5 to 2 times the mass of anhydrous phosphorous acid.

[0012] Furthermore, the mass fraction of sodium methoxide in the sodium methoxide solution in S2 is 10% to 50%.

[0013] Furthermore, the mass fraction of sodium methoxide in the sodium methoxide solution in S2 is 25% to 35%.

[0014] Furthermore, the reaction temperature when the sodium methoxide solution is added dropwise in S2 is 20°C to 80°C.

[0015] Compared with the prior art, the green synthesis process of anhydrous sodium phosphite that can be used as an antioxidant provided by the present invention can effectively reduce the generation of by-products, reduce the amount of waste generated, and alleviate environmental pollution by strictly controlling the reaction conditions; at the same time, the solvent methanol can be recycled, which is in line with the concept of green chemistry and is conducive to the sustainable development of the chemical industry;

[0016] This process reduces production costs, avoids dependence on high temperature and high pressure, reduces energy consumption and equipment costs, improves product purity and quality, and enhances market competitiveness and added value. It is easy to operate, has a simple process, does not require high equipment, is easy to operate and control, reduces the skill requirements for operators, and improves production efficiency. The raw material quality requirements are relatively loose, and production flexibility and stability are enhanced, reducing production risks. It avoids dangerous conditions of high temperature and high pressure, reduces safety risks, ensures the safety of operators, creates a safe production environment, and is conducive to the long-term and stable development of the enterprise. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For ordinary technicians in this field, other drawings can also be obtained based on these drawings.

[0018] Figure 1 A schematic diagram of the overall synthesis process provided by an embodiment of the present invention;

[0019] Figure 2 A schematic diagram of the synthesis process principle provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0020] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0021] Embodiment 1:

[0022] See also Figure 1-Figure 2 , a green synthesis process of anhydrous sodium phosphite which can be used as an antioxidant, comprising:

[0023] S1. First, add anhydrous phosphorous acid and methanol into a reactor and stir until the anhydrous phosphorous acid is completely dissolved to obtain an anhydrous phosphorous acid-methanol solution; the mass of methanol added to the reactor is 0.2 to 5 times the mass of the anhydrous phosphorous acid;

[0024] S2, then slowly adding sodium methoxide solution to the anhydrous phosphorous acid-methanol solution, when the pH value of the solution in the reactor is 6-9, stopping the addition of sodium methoxide solution, and cooling the temperature of the solution in the reactor to 20°C to obtain a reaction product; the mass fraction of sodium methoxide in the sodium methoxide solution is 10%-50%; the reaction temperature when adding the sodium methoxide solution is 20°C-80°C;

[0025] S3, separating the reaction product through a solid-liquid separation device to obtain a filtrate and a filter cake; distilling and recovering the filtrate to obtain recovered methanol;

[0026] S4, vacuum drying the filter cake to obtain a white solid powder, i.e., anhydrous sodium phosphite.

[0027] The specific implementation method is as follows: S1, firstly, 82 g (1.0 mol) of anhydrous phosphorous acid is added to a three-necked flask equipped with a mechanical stirrer, a thermometer and a reflux condenser, and then an equal amount of anhydrous methanol is added, and the mechanical stirring device is started, and stirring is continued until the anhydrous phosphorous acid is completely dissolved in the methanol to obtain an anhydrous phosphorous acid-methanol solution;

[0028] Anhydrous phosphorous acid is dissolved in anhydrous methanol. If too little methanol is added, the anhydrous phosphorous acid is difficult to dissolve, affecting the reaction operation; if too much methanol is added, the production efficiency is reduced, the cost is increased, and it has no economic value. Therefore, the mass of methanol added to the reactor is 0.2 to 5 times the mass of anhydrous phosphorous acid.

[0029] S2. Then, slowly add a 30% sodium methoxide solution to the anhydrous phosphorous acid-methanol solution, and treat the entire reaction process in a water bath to effectively control the reaction temperature to 20-80° C. During this process, the pH value of the system needs to be closely monitored. When the pH reaches 7.0, the addition of the sodium methoxide solution is immediately stopped. At this time, a total of 306 g (1.7 mol) of sodium methoxide has been consumed. After completing the above steps, the obtained mixture is cooled to 20° C. to obtain a reaction product;

[0030] Under stirring, slowly add sodium methoxide to the reaction system, and control the pH of the product by controlling the molar ratio of anhydrous phosphorous acid and sodium methoxide. This is the key to the antioxidant application effect of the final product. If the pH of the final product is too low, it may cause corrosion to the equipment in the application scenario; if the pH of the final product is too high, the strong alkalinity may have a negative impact on the application process. For example, when the product is used in combination with a hindered phenolic antioxidant, the strong alkalinity will accelerate the oxidation of the phenolic antioxidant and color the product.

[0031] Therefore, the pH of anhydrous sodium phosphite used as an antioxidant is more suitable between 6-9, and the optimal control range is between 7-8; the concentration of sodium methoxide used is between 10%-50%. Too low a concentration affects production efficiency; too high a concentration is inconvenient to use. It is worth noting that the reaction between sodium methoxide and phosphorous acid is an acid-base neutralization reaction, which is significantly exothermic. The dripping speed needs to be controlled to prevent the heat from being released too quickly and causing loss of control. During the reaction, the heat generated by the reaction needs to be continuously removed by cooling water, and the temperature should be controlled between 20-80°C.

[0032] S3, filtering the reaction product through a suction filtration device to obtain a filtrate and a filter cake; distilling and recovering the filtrate to obtain recovered methanol; the recovered methanol recovered in this step can be used for the next preparation of anhydrous sodium phosphite;

[0033] S4. The obtained filter cake was placed in a vacuum drying oven and dried at 70° C. for four hours to finally obtain 115.8 g of a white powdery substance, which is anhydrous sodium phosphite that can be used as an antioxidant, with a yield of about 97%.

[0034] Embodiment 2:

[0035] See also Figure 1-Figure 2 This embodiment provides a technical solution based on the first embodiment: a green synthesis process of anhydrous sodium phosphite that can be used as an antioxidant, comprising:

[0036] S1. First, add anhydrous phosphorous acid and methanol into a reactor and stir until the anhydrous phosphorous acid is completely dissolved to obtain an anhydrous phosphorous acid-methanol solution; the mass of methanol added to the reactor is 0.5 to 2 times the mass of the anhydrous phosphorous acid;

[0037] S2, then slowly adding sodium methoxide solution to the anhydrous phosphorous acid-methanol solution, when the pH value of the solution in the reactor is 6-9, stopping the addition of sodium methoxide solution, and cooling the temperature of the solution in the reactor to 20°C to obtain a reaction product; the mass fraction of sodium methoxide in the sodium methoxide solution is 25%-35%; the reaction temperature when adding the sodium methoxide solution is 20°C-80°C;

[0038] S3, separating the reaction product through a solid-liquid separation device to obtain a filtrate and a filter cake; distilling and recovering the filtrate to obtain recovered methanol;

[0039] S4, vacuum drying the filter cake to obtain a white solid powder, i.e., anhydrous sodium phosphite.

[0040] The specific implementation method is as follows: S1, firstly, 82 g (1.0 mol) of anhydrous phosphorous acid is added to a three-necked flask equipped with a mechanical stirrer, a thermometer and a reflux condenser, and 82 g of anhydrous methanol is added, and the mixture is stirred until the anhydrous phosphorous acid is completely dissolved to obtain an anhydrous phosphorous acid-methanol solution;

[0041] S2, then, slowly dropwise add 30% sodium methoxide to the anhydrous phosphorous acid-methanol solution, and treat with a water bath to effectively control the reaction temperature to 20-80°C. When the pH is 8.0, stop dropwise adding the sodium methoxide solution. At this time, the consumption of sodium methoxide is 325 g (1.8 mol). After completing the above steps, cool the resulting mixture to 20°C to obtain a reaction product;

[0042] S3, filtering the reaction product through a suction filtration device to obtain a filtrate and a filter cake; distilling and recovering the filtrate to obtain recovered methanol; the recovered methanol recovered in this step can be used for the next preparation of anhydrous sodium phosphite;

[0043] S4. The obtained filter cake was placed in a vacuum oven and dried at 70°C for four hours to obtain 118 g of white solid powder, which was anhydrous sodium phosphite that could be used as an antioxidant, with a yield of 97%.

[0044] Embodiment three:

[0045] See also Figure 1-Figure 2 This embodiment provides a technical solution based on the first embodiment: a green synthesis process of anhydrous sodium phosphite that can be used as an antioxidant, comprising:

[0046] S1. Add 82 g (1.0 mol) of anhydrous phosphorous acid to a three-necked flask equipped with a mechanical stirrer, a thermometer and a reflux condenser, add 82 g of recovered methanol recovered after the filtrate distillation in Example 2, and stir until the anhydrous phosphorous acid is completely dissolved to obtain an anhydrous phosphorous acid-methanol solution;

[0047] S2, then slowly add 30% sodium methoxide solution to the anhydrous phosphorous acid-methanol solution, and treat the entire reaction process in a water bath to effectively control the reaction temperature to 20-80° C. When the pH is 8.0, stop adding the sodium methoxide solution, and the consumption of the sodium methoxide solution is 325 g (1.8 mol). After completing the above steps, cool the resulting mixture to 20° C. to obtain a reaction product;

[0048] S3, filtering the reaction product through a suction filtration device to obtain a filtrate and a filter cake; distilling and recovering the filtrate to obtain recovered methanol; the recovered methanol recovered in this step can be used for the next preparation of anhydrous sodium phosphite;

[0049] S4. The obtained filter cake was placed in a vacuum oven and dried at 70° C. for four hours to obtain 117.8 g of white solid powder, which was anhydrous sodium phosphite that could be used as an antioxidant, with a yield of 97%.

[0050] Embodiment 4:

[0051] See also Figure 1-Figure 2 This embodiment provides a technical solution based on the first embodiment: a green synthesis process of anhydrous sodium phosphite that can be used as an antioxidant, comprising:

[0052] S1. First, 82 g (1.0 mol) of anhydrous phosphorous acid was added to a three-necked flask equipped with a mechanical stirrer, a thermometer and a reflux condenser, and 82 g of anhydrous methanol was added, and the mixture was stirred until the anhydrous phosphorous acid was completely dissolved to obtain an anhydrous phosphorous acid-methanol solution;

[0053] S2, then, slowly adding a 30% concentration of sodium methoxide solution to the anhydrous phosphorous acid-methanol solution, and treating the entire reaction process in a water bath to effectively control the reaction temperature to 20-80° C., when the pH is 8.5, stop adding the sodium methoxide solution, at which time the consumption of the sodium methoxide solution is 360 g (2.0 mol), after completing the above steps, cool the resulting mixture to 20° C. to obtain a reaction product;

[0054] S3, filtering the reaction product through a suction filtration device to obtain a filtrate and a filter cake; distilling and recovering the filtrate to obtain recovered methanol; the recovered methanol recovered in this step can be used for the next preparation of anhydrous sodium phosphite;

[0055] S4. The obtained filter cake was placed in a vacuum oven and dried at 70° C. for four hours to obtain 122 g of white solid powder, which was anhydrous sodium phosphite that could be used as an antioxidant, with a yield of 96.8%.

[0056] Embodiment five:

[0057] This embodiment provides a technical solution based on Embodiment 1, Embodiment 2, Embodiment 3 and Embodiment 4: testing the antioxidant effect of the synthesized anhydrous sodium phosphite.

[0058] The raw materials were mixed according to the weight ratio of the raw materials listed in Table 1 to prepare the required test samples. Each test sample was placed in a 250° C. high-temperature extruder for extrusion treatment, and then a color plate sample was quickly made.

[0059] Table 1 Recipe

[0060]

[0061] Among them, antioxidant H10 is a similar product of Brüggemann of Germany, which can be used in polymer materials, such as polyamide and polyester, to prevent the degradation of materials caused by shear stress and thermal stress during processing. Its role includes preventing the degradation and discoloration of polymer materials during processing and extending the service life of materials under thermal aging conditions. Therefore, antioxidant H10 is used as control 1.

[0062] To ensure the accuracy and consistency of color, the advanced DATACOLOR 850 colorimeter is used to conduct detailed color tests on the newly produced color plates. In particular, the samples that have not been dried are used as standard references for color measurement, and their initial color measurement data are recorded.

[0063] After the initial color test is completed, the color plate samples are transferred to an oven that meets the GB / T 11026.4 standard for aging. Aging is continued for 2 hours at a strictly controlled temperature of 140°C to simulate the color changes that may be encountered during long-term use. After the aging process is completed, the color plate is carefully removed from the oven and left to cool for 1 hour under standard ambient conditions to ensure that the color plate temperature returns to room temperature and eliminate the influence of temperature on color measurement.

[0064] After cooling, the color plate was tested again using the DATACOLOR 850 colorimeter, and the color data of the color plate after aging was recorded in detail. By comparing the color measurement data before and after aging, the color stability and change trend of the color plate under specific conditions can be accurately evaluated, providing an important reference for subsequent product improvement and quality control. The evaluation indicators for the color stability and change trend of the color plate under specific conditions include CIE DL, CIE Da, CIE Db, CIE DE and CMC DE indicators, and the specific test results are as follows.

[0065] 1. The brightness difference (CIE DL) between each test sample and the standard sample and its description under D65 10 Deg light source; CIE DL is the brightness difference, which indicates the difference between two color samples in the brightness (L*) dimension; the specific test results are as follows:

[0066] Test No. Current light source name CIEDL DL Description 1 D65 10 Deg 1.08 Shallow 2 D65 10 Deg 1.06 Shallow 3 D65 10 Deg 1.06 Shallow 4 D65 10 Deg -0.06 Darker Comparison 1 D65 10 Deg 1.07 Shallow Comparison 2 D65 10 Deg -0.11 Darker

[0067] D65 10 Deg is one of the CIE standard light sources, which simulates the spectral power distribution of sunlight at noon in the northern hemisphere, and the color temperature is about 6500K; 10 Deg represents a 10-degree field of view, which is used to simulate the viewing angle of the human eye when observing an object at a certain distance; in CIE DL, a positive value indicates that the sample is brighter than the standard sample, and a negative value indicates that the sample is darker than the standard sample;

[0068] "Lighter" in the DL description means that the color of the sample is brighter or lighter than the standard sample. In the above table, the CIE DL values ​​of test numbers 1, 2, 3 and control 1 are all positive and close to 1.07, which are described as "lighter"; "Darker" means that the color of the sample is darker or darker than the standard sample. In the above table, the CIE DL values ​​of test number 4 and control 2 are negative, which are -0.06 and -0.11 respectively, and are described as "darker".

[0069] The CIE DL values ​​of samples No. 1, 2, 3 and control 1 are very close, which means that they have little difference in brightness from the standard sample and are all brighter than the standard sample, so the color looks lighter.

[0070] Test No. 4 and Control 2, the CIE DL values ​​of these two samples are negative, indicating that they are darker in brightness than the standard sample, and therefore the color appears darker, among which the CIE DL value of Control 2 is more negative than that of Test No. 4, indicating that its color is darker.

[0071] Through these data, the brightness performance of different samples under D65 10 Deg light source can be determined, thereby evaluating the antioxidant effect of anhydrous sodium phosphite.

[0072] 2. Under D65 10 Deg light source, the red-green color difference (CIE Da) between each test sample and the standard sample and its description; CIE Da is the red-green color difference, which indicates the difference between two color samples in the red-green (a*) dimension; the specific test results are as follows:

[0073] Test No. Current light source name CIE Description 1 D65 10 Deg -0.29 Greener 2 D65 10 Deg -0.27 Greener 3 D65 10 Deg -0.27 Greener 4 D65 10 Deg -0.49 Greener Comparison 1 D65 10 Deg -0.28 Greener Comparison 2 D65 10 Deg -0.53 Greener

[0074] CIE Da represents the difference between the sample and the standard sample in the red-green (a*) dimension. A negative value means that the sample is greener than the standard sample. "Greener" in the Da description means that the color of the sample is greener than the standard sample. In the above table, the CIE Da values ​​of all test samples are negative and are described as "greener".

[0075] For test numbers 1, 2, 3 and control 1, the CIE Da values ​​of these samples are very close, namely -0.29, -0.27, -0.27 and -0.28 respectively, which means that they have little difference from the standard sample in the red and green dimensions and are all greener than the standard sample; for test number 4 and control 2, the CIE Da values ​​of these two samples are -0.49 and -0.53, which are more negative than other samples, indicating that their colors are greener than the standard sample.

[0076] Through these data, the red and green performance of different samples under D65 10 Deg light source can be determined, thereby evaluating the antioxidant effect of anhydrous sodium phosphite.

[0077] 3. Under D65 10 Deg light source, the yellow-blue difference (CIE Db) between each test sample and the standard sample and its description; CIE Db is the yellow-blue difference, which indicates the difference between two color samples in the yellow-blue (b*) dimension; the specific test results are as follows:

[0078]

[0079]

[0080] CIE Db represents the difference between the sample and the standard sample in the yellow-blue (b*) dimension. A positive value means that the sample is yellower than the standard sample. "Yellower" in the Db description means that the color of the sample is more yellow than the standard sample. In the above table, the CIE Db values ​​of all test samples are positive and are described as "yellower".

[0081] For test numbers 1, 2, 3 and control 1, the CIE Db values ​​of these samples are very close, namely 1.37, 1.35, 1.36 and 1.37 respectively, which means that they have little difference from the standard sample in the yellow-blue dimension and are all yellower than the standard sample.

[0082] Test No. 4 and Control 2, the CIE Db values ​​of these two samples are 2.03 and 2.35, which are larger than the other samples, indicating that their colors are yellower than the standard sample.

[0083] Through these data, the yellow-blue color performance of different samples under D65 10 Deg light source can be determined, thereby evaluating the antioxidant effect of anhydrous sodium phosphite.

[0084] 4. Under D65 10 Deg light source, the total color difference (CIE DE) and CMC color difference (CMC DE) between each test sample and the standard sample, as well as the judgment results based on these color difference values; CIE De total color difference represents the overall difference between two color samples in the CIELab color space; CMC De is the CMC color difference, which is the color difference value calculated based on the CMC color difference formula, which takes into account the sensitivity of the human eye to different color differences. The specific test results are as follows:

[0085]

[0086]

[0087] CIE DE represents the total color difference between the sample and the standard sample in the CIELab color space, calculated using the CIE1976 color difference formula. The smaller the value, the smaller the color difference. CMC DE represents the color difference between the sample and the standard sample in the CIELab color space, calculated using the CMC color difference formula. The CMC formula takes into account the sensitivity of the human eye to different color differences. The smaller the value, the smaller the color difference.

[0088] In the judgment result, "qualified" means that the color difference of the sample is within the acceptable range, that is, the values ​​of CIE DE and CMC DE are less than or equal to a preset threshold; "unqualified" means that the color difference of the sample exceeds the acceptable range, that is, the value of CIE DE or CMC DE is greater than the preset threshold.

[0089] For test numbers 1, 2, 3 and control 1, the CIE DE values ​​of these samples were 1.77, 1.75, 1.76 and 1.76, respectively, and the CMCDE values ​​were 1.45, 1.43, 1.44 and 1.44, respectively, all of which were within the acceptable range and were judged to be "qualified".

[0090] Test No. 4 and Control No. 2, the CIE DE values ​​of these two samples were 2.09 and 2.41, and the CMC DE values ​​were 2.19 and 2.52, respectively, which were beyond the acceptable range and were judged as "unqualified".

[0091] Through these data, the color difference of different samples under D65 10 Deg light source can be judged. From the above results, the antioxidant effect of the anhydrous sodium phosphite obtained according to the present invention is close to that of Brueggemann H10.

[0092] The above description is only by way of illustration of certain exemplary embodiments of the present invention. It is undoubted that those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the above drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A green synthesis process of anhydrous sodium phosphite which can be used as an antioxidant, characterized in that: include: S1. First, add anhydrous phosphorous acid and methanol into a reactor, and stir until the anhydrous phosphorous acid is completely dissolved to obtain an anhydrous phosphorous acid-methanol solution; S2, then slowly adding sodium methoxide solution to the anhydrous phosphorous acid-methanol solution, when the pH value of the solution in the reactor is 6-9, stopping the addition of sodium methoxide solution, and cooling the temperature of the solution in the reactor to 20° C. to obtain a reaction product; S3, separating the reaction product through a solid-liquid separation device to obtain a filtrate and a filter cake; distilling and recovering the filtrate to obtain recovered methanol; S4, vacuum drying the filter cake to obtain a white solid powder, i.e., anhydrous sodium phosphite.

2. The green synthesis process of anhydrous sodium phosphite as an antioxidant according to claim 1, characterized in that: The mass of methanol added to the reactor in S1 is 0.2 to 5 times the mass of anhydrous phosphorous acid.

3. The green synthesis process of anhydrous sodium phosphite that can be used as an antioxidant according to claim 1, characterized in that: The mass of methanol added to the reactor S1 is 0.5 to 2 times the mass of anhydrous phosphorous acid.

4. The green synthesis process of anhydrous sodium phosphite that can be used as an antioxidant according to claim 1, characterized in that: The mass fraction of sodium methoxide in the sodium methoxide solution S2 is 10% to 50%.

5. The green synthesis process of anhydrous sodium phosphite which can be used as an antioxidant according to claim 1, characterized in that: The mass fraction of sodium methoxide in the sodium methoxide solution S2 is 25% to 35%.

6. The green synthesis process of anhydrous sodium phosphite which can be used as an antioxidant according to claim 1, characterized in that: The reaction temperature when the sodium methoxide solution is added dropwise in S2 is 20°C to 80°C.

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