Method for recycling sodium sulfate in nitromethane solid waste

Abstract

The invention relates to a method for recycling sodium sulfate in nitromethane solid waste, which comprises the following steps of: adding water into nitromethane solid waste hot water bath for dissolving, and filtering while hot; dropwise adding dilute sulfuric acid into the filtrate, adding an organic solvent, extracting at room temperature, and separating out a water phase; performing gradient cooling crystallization on the water phase, and performing suction filtration to obtain a filter cake; leaching the filter cake with ice water, pulping, and carrying out suction filtration to obtain a wet sodium sulfate product; performing reduced-pressure rotary evaporation and drying on the sodium sulfate wet product to obtain a sodium sulfate product. According to the method, sodium sulfate in the nitromethane solid waste is purified and recycled, the solid waste yield is favorably reduced, the original solid waste is converted into resources for economic conversion, and the problem of solid waste treatment is solved for continuous production of nitromethane. The resource utilization rate is increased, the production cost is reduced, the product quality is improved, the method is environment-friendly, the solid waste treatment problem is radically solved, and solid wastes can be converted into resources to generate economic values.

Description

Technical Field

[0001] The invention belongs to the technical field of three-waste treatment, and specifically relates to a method for recovering and treating sodium sulfate in nitromethane solid waste. Background Art

[0002] At present, the domestic industrial production of nitromethane generally adopts the substitution reaction of dimethyl sulfate and sodium nitrite. The advantages of this synthesis process are relatively mild reaction conditions and high product purity. The reaction for synthesizing nitromethane is as follows:

[0003]

[0004] A large amount of salt by-products are produced during the synthesis of nitromethane. After triple-effect evaporation, concentration and filtration, solid salt is obtained, which contains a large amount of sodium sulfate, sodium nitrite, sodium nitrate, etc. It is impossible to obtain a sodium sulfate product that can be sold on the market, and nitromethane solid waste is often used for treatment. For example, landfill treatment, the waste salt is solidified by concrete and then disposed of by landfill. However, this method may have an impact on the groundwater system due to the high water solubility of the waste salt. High-temperature calcination treatment, calcination at high temperature decomposes and oxidizes the organic matter in the solid waste to achieve the purification of sodium sulfate. However, it has high energy consumption, large equipment investment, and produces a large amount of harmful gases, causing secondary pollution. There are also attempts to further purify sodium sulfate, so that sodium sulfate is supersaturated and precipitated, and then sodium sulfate is obtained by solid-liquid separation, but either the treatment cost is high, or the sodium sulfate obtained by treatment is yellow in color and has a strong odor, which cannot achieve the purpose of commercialization.

[0005] The solid waste from nitromethane production cannot be treated reasonably and effectively, which will limit the industrial upgrading and continuous large-scale production of nitromethane. Summary of the invention

[0006] Purpose of the invention: In view of the problems existing in the prior art, the purpose of the present invention is to provide a method for recovering sodium sulfate from nitromethane solid waste. The method solves the problem that sodium sulfate from nitromethane solid waste in the prior art can be recovered at a low cost, reducing the cost of solid waste treatment. The recovered sodium sulfate can meet the market standard, solving the solid waste problem of nitromethane and laying the foundation for the sustainable industrial production of nitromethane.

[0007] The present invention provides a method for recovering sodium sulfate from nitromethane solid waste, which is achieved through the following technical solutions:

[0008] A method for recovering sodium sulfate from nitromethane solid waste comprises the following steps:

[0009] (1) Dissolve the nitromethane solid waste in water in a hot water bath and filter it while it is hot;

[0010] (2) adding dilute sulfuric acid dropwise to the filtrate, then adding an organic solvent for extraction at room temperature, and separating the aqueous phase;

[0011] (3) gradient cooling the water phase for crystallization and suction filtration to obtain a filter cake;

[0012] (4) washing and slurrying the filter cake with ice water, and draining to obtain a sodium sulfate wet product;

[0013] (5) subjecting the wet sodium sulfate product to reduced pressure rotary evaporation and drying to obtain a sodium sulfate product.

[0014] The present invention uses a byproduct of synthesizing nitromethane by reacting dimethyl sulfate with sodium nitrite to obtain nitromethane solid waste by three-effect evaporation, concentration and filtration. The nitromethane solid waste is dissolved in water in a hot water bath, filtered while hot, and carbon black and oily substances are filtered out to obtain a dark brown filtrate. Dilute sulfuric acid is then added dropwise to control the pH to about 5-6, and impurities such as sodium nitrate and sodium nitrite in the system are neutralized.

[0015] According to the technical solution of the present invention, the temperature of the hot water bath is controlled at 35°C-40°C, specifically 35°C, 36°C, 37°C, 38°C, 39°C, 40°C and the like.

[0016] According to the technical solution of the present invention, the concentration of the dilute sulfuric acid is controlled at 20-30%, specifically 20%, 25%, 30% and the like.

[0017] According to the technical solution of the present invention, the organic solvent is selected from any one of chlorobenzene, toluene, ethyl acetate or ethylene dichloride.

[0018] According to the technical solution of the present invention, the gradient cooling is reduced to 5-10°C, such as 5°C, 6°C, 7°C, 8°C, 9°C, 10°C, etc. Direct cooling and crystallization easily causes impurities to crystallize together, resulting in a yellow product with low purity and cannot be commercially available. The present invention adopts gradient cooling to gradually precipitate sodium sulfate, which can slow down the rate of temperature change during the cooling process, thereby reducing the thermal stress and mechanical stress caused by rapid cooling, which is conducive to the precipitation of purer sodium sulfate. By gradient cooling control, the temperature can be reduced to 5-10°C to achieve sodium sulfate precipitation, without having to drop below 5°C, which will save a lot of energy consumption required to control low temperatures.

[0019] According to the technical solution of the present invention, the gradient cooling controls the cooling rate to be 1°C to 2°C / 5min, such as 1°C / 5min, 2°C / 5min, etc. The present invention controls the speed of gradient cooling, and a cooling rate that is too high or too low is not conducive to the precipitation of the product. If the cooling rate is too fast, the thermal stress will increase, and rapid cooling will produce greater thermal stress. Too fast cooling will lead to crystal structure defects, and too fast cooling rate may not give the crystals enough time to arrange in order, resulting in an increase in crystal structure defects. Too fast cooling will also lead to insufficient phase separation, inhibit the phase separation process, and cause the product purity to decrease. Rapid cooling usually requires more energy input, such as a stronger cooling system, which will increase production costs and reduce energy efficiency. If the cooling rate is too low, the slow cooling process will extend the production cycle, reduce production efficiency, and increase production costs. Maintaining a low temperature state for a long time will also consume a lot of energy, which is not conducive to energy conservation and emission reduction. In addition, too slow a cooling rate may cause excessive growth of grains. Inconsistent or improperly controlled cooling rates may cause product quality fluctuations, affecting the consistency and reliability of the product. Therefore, it is crucial to control the cooling rate during the gradient cooling process. Too high or too low a cooling rate will cause a series of problems.

[0020] According to the technical solution of the present invention, the weight of the ice water accounts for 50%-70% of the solid waste feed amount, such as 50%, 60%, 70%, etc. The present invention adopts the technical solution of ice water elution and pulping to obtain a satisfactory sodium sulfate product. The amount of ice water fed should not be too high, otherwise the sodium sulfate product will be lost. If it is too low, it cannot be fully impurized and the product color will be yellowish. Ice water elution can effectively remove dirt, grease and other impurities, shrink the surface of sodium sulfate, and is beneficial to the crystal form of sodium sulfate after crystallization. Pulping can make the sodium sulfate fully dispersed in water to form a uniform slurry, which is beneficial to obtain a crystalline product with uniform quality.

[0021] According to the technical solution of the present invention, the temperature of the reduced pressure rotary evaporation is controlled at 70°C to 80°C, such as 70°C, 75°C, 80°C, etc.; the pressure of the reduced pressure rotary evaporation is controlled at -0.095MPa to -0.1MPa, such as -0.095MPa, -0.1MPa, etc.; the rotation speed is controlled at 50-100 rpm, such as 50 rpm, 60 rpm, 70 rpm, 80 rpm, 90 rpm, 100 rpm, etc.

[0022] The present invention adopts a technical scheme combining gradient cooling, ice water elution, pulping and vacuum rotary evaporation, and can obtain a pure white sodium sulfate product without adding a decolorizing agent such as diatomaceous earth, activated carbon and the like, thereby reducing the cost of three waste treatment.

[0023] According to the technical solution of the present invention, the filtrate obtained after the suction filtration in step (3) and / or the filtrate obtained after the suction filtration in step (4) is applied to the step (1) to dissolve the nitromethane solid waste. By repeated application, the amount of water used to dissolve the nitromethane solid waste is reduced, the cost of three wastes treatment is reduced, and the amount of wastewater discharged is reduced. In addition, sodium sulfate remains in the filtrate, which can be reused by application, thereby improving the overall product yield. And according to the accumulation of impurities and product quality control, the reasonable number of applications is controlled.

[0024] According to the technical solution of the present invention, the amount of water added in step (1) is 1.6-1.8 times the amount of solid waste. If the amount of water is too much, the product yield will be low, and the amount of mother liquor will increase, which will eventually lead to an increase in wastewater; if the amount of water is too little, hot filtration will filter out part of the by-product sodium sulfate, resulting in an increase in the amount of filter residue, an increase in solid waste, and a decrease in product yield.

[0025] By treating nitromethane solid waste and recovering sodium sulfate through the present invention, the purity of the purified sodium sulfate product can reach more than 98.5%, which fully meets the market standards. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0027] Figure 1 It is nitromethane solid waste;

[0028] Figure 2 The sodium sulfate wet product recovered in Example 1;

[0029] Figure 3 The sodium sulfate dry product recovered in Example 1;

[0030] Figure 4 This is the wet product of sodium sulfate recovered in Comparative Example 6.

[0031] Beneficial Effects

[0032] The present invention purifies and recovers sodium sulfate from nitromethane solid waste, which is beneficial to eliminating solid waste production, converting the original solid waste into resources for economic transformation, and solving the solid waste treatment problem for the sustainable production of nitromethane. The beneficial effects of the patent are mainly reflected in the following aspects:

[0033] 1. Improve resource utilization: By purifying and recovering sodium sulfate from nitromethane solid waste, waste emissions can be effectively reduced, while valuable sodium sulfate can be recycled and reused, improving resource utilization. This not only meets the current requirements of environmental protection and sustainable development, but also brings economic benefits to enterprises.

[0034] 2. Reduce production costs: Traditional treatment methods often consume a lot of chemical reagents or energy. For example, if nitromethane solid waste is sent to hazardous waste treatment, the cost will increase by 300-400 yuan per ton. The purification and recovery method provided by the present invention is efficient and economical. In addition to reducing the cost of hazardous waste treatment, it can also increase the revenue of 150-200 yuan per ton on the market, thereby reducing production costs. This is a significant advantage for enterprises and helps to improve market competitiveness.

[0035] 3. Improve product quality: The purity of the purified and recovered sodium sulfate can reach more than 98.5%, reaching the market standard, with more stable quality and meeting the requirements of industrial applications.

[0036] 4. Environmentally friendly: The technical solution adopted by the present invention does not require further addition of a decolorizing agent for decolorization, thereby reducing further cost investment and reducing secondary pollution caused by the use of a decolorizing agent.

[0037] The present invention recovers the sodium sulfate product in the nitromethane solid waste, which not only solves the problem of solid waste treatment, but also can convert the solid waste into resources to generate economic value.

[0038] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by writing the description and claims.

[0039] The technical solution of the present invention is further described in detail below through embodiments. DETAILED DESCRIPTION

[0040] The following is an explanation of the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0041] Before further describing the specific embodiments of the present invention, it should be understood that the scope of protection of the present invention is not limited to the specific embodiments described below; it should also be understood that the terms used in the examples of the present invention are for describing specific embodiments rather than for limiting the scope of protection of the present invention.

[0042] Unless otherwise defined, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by those skilled in the art. In addition to the specific methods, equipment, and materials used in the embodiments, any methods, equipment, and materials of the prior art that are similar or equivalent to the methods, equipment, and materials in the embodiments of the present invention may be used to implement the present invention, based on the prior art mastery of those skilled in the art and the description of the present invention.

[0043] Embodiment 1:

[0044] Take nitromethane solid waste (such as Figure 1 )400g, add 700g of water, heat to 40℃ in a water bath, stir and dissolve for 30min, filter while hot, add 30% dilute sulfuric acid to the filtrate, control the pH value to about 5-6, after the addition is completed, stir for 30min, add 50g of chlorobenzene, extract at room temperature, stir for 30min, stand and stratify, separate the organic phase, cool the aqueous phase to 5℃ at a rate of 2℃ / 5min, crystallize, filter, add 280g of ice water to the filter cake for leaching and pulping, and filter to obtain a white sodium sulfate wet product (such as Figure 2 ). Vacuum evaporation (-0.095MPa, 100 rpm, 75°C) was performed and dried to obtain a sodium sulfate product (such as Figure 3 )255g, sodium sulfate purity is 98.85%.

[0045] Embodiment 2:

[0046] Take 400g of nitromethane solid waste, add 720g of water, heat the water bath to 35℃, stir and dissolve for 40min, filter while hot, add 20% dilute sulfuric acid to the filtrate, control the pH value to about 5-6, stir for 30min after the addition, add 45g of toluene, extract at room temperature, stir for 30min, stand for stratification, separate the organic phase, cool the aqueous phase to 10℃ at a rate of 1℃ / 5min, crystallize, filter by suction, add 200g of ice water to the filter cake for leaching and pulping, and obtain a white sodium sulfate wet product after suction filtration. Vacuum rotary evaporation (-0.1MPa, 50 rpm, 70℃), dry to obtain 245g of sodium sulfate product, and the purity of sodium sulfate is 98.56%.

[0047] Embodiment 3:

[0048] Take 400g of nitromethane solid waste, add 640g of water, heat the water bath to 38°C, stir and dissolve for 30min, filter while hot, add 25% dilute sulfuric acid to the filtrate, control the pH to about 5-6, stir for 30min after the addition is completed, add 40g of ethyl acetate, extract at room temperature, stir for 30min, stand and stratify, separate the organic phase, cool the aqueous phase to 8°C at a rate of 1°C / 5min, crystallize, filter by suction, add 240g of ice water to the filter cake for leaching and pulping, and obtain a white sodium sulfate wet product after suction filtration. Vacuum rotary evaporation (-0.1MPa, 80 rpm, 80°C) and dry to obtain 250g of sodium sulfate product with a sodium sulfate purity of 98.51%.

[0049] Embodiment 4:

[0050] Take 400g of nitromethane solid waste, add 700g of water, heat the water bath to 40℃, stir and dissolve for 30min, filter while hot, add 30% dilute sulfuric acid to the filtrate, control the pH value to about 5-6, stir for 30min after the addition, add 50g of dichloroethane, extract at room temperature, stir for 30min, stand for stratification, separate the organic phase, cool the aqueous phase to 5℃ at a rate of 2℃ / 5min, crystallize, filter by suction, add 250g of ice water to the filter cake for leaching and pulping, and obtain a white sodium sulfate wet product after filtration. Vacuum rotary evaporation (-0.1MPa, 100 rpm, 80℃), dry to obtain 257g of sodium sulfate product, and the purity of sodium sulfate is 98.80%.

[0051] Embodiment 5:

[0052] Collect all the filtrates of Examples 1-4, take 700g to dissolve 400g of nitromethane solid waste, heat the water bath to 40°C and stir to dissolve for 30min, filter while hot, add 30% dilute sulfuric acid to the filtrate, control the pH value to about 5-6, stir for 30min after the addition is complete, add chlorobenzene 50g, extract at room temperature, stir for 30min, stand for stratification, separate the organic phase, cool the aqueous phase to 5°C at a speed gradient of 2°C / 5min, crystallize, filter by suction, add 280g of ice water to the filter cake for leaching and beating, and obtain a white sodium sulfate wet product after filtering by suction. Vacuum rotary evaporation (-0.095MPa, 100 rev / min, 75°C) and dry to obtain 261g of sodium sulfate product with a sodium sulfate purity of 98.81%.

[0053] Comparative Example 1:

[0054] Take 400g of nitromethane solid waste, add 800g of water, heat the water bath to 40℃, stir and dissolve for 30min, filter while hot, add 30% dilute sulfuric acid to the filtrate, control the pH value to about 5-6, stir for 30min after the addition is completed, add 80g of chlorobenzene, extract at room temperature, stir for 30min, stand for stratification, separate the organic phase, cool the aqueous phase to 5℃ at a rate of 2℃ / 5min, crystallize, filter by suction, add 280g of ice water to the filter cake for leaching and pulping, and obtain a white sodium sulfate wet product after suction filtration. Vacuum rotary evaporation (-0.095MPa, 100 rpm, 75℃) and drying to obtain 225g of sodium sulfate product with a sodium sulfate content of 98.81%.

[0055] Comparative Example 2:

[0056] Take 400g of nitromethane solid waste, add 480g of water, heat the water bath to 40℃, stir and dissolve for 30min, filter while hot, add 30% dilute sulfuric acid to the filtrate, control the pH value to about 5-6, stir for 30min after the addition, add 30g of chlorobenzene, extract at room temperature, stir for 30min, stand and stratify, separate the organic phase, cool the aqueous phase to 5℃ at a rate of 1℃ / 5min, crystallize, filter by suction, add 220g of ice water to the filter cake for leaching and pulping, and obtain a white sodium sulfate wet product after suction filtration. Vacuum rotary evaporation (-0.095MPa, 100 rpm, 75℃), dry to obtain 211g of sodium sulfate product, with a sodium sulfate content of 98.70%.

[0057] Comparative Example 3:

[0058] Take 400g of nitromethane solid waste, add 640g of water, heat the water bath to 38°C, stir and dissolve for 30min, filter while hot, add 25% dilute sulfuric acid to the filtrate, control the pH to about 5-6, stir for 30min after the addition, add 40g of ethyl acetate, extract at room temperature, stir for 30min, stand and stratify, separate the organic phase, cool the aqueous phase to 5°C at a rate of 4°C / 5min, crystallize, filter, add 240g of ice water to the filter cake for leaching and pulping, and filter to obtain a white sodium sulfate wet product. Vacuum rotary evaporation (-0.1MPa, 80 rpm, 80°C) and dry to obtain 261g of sodium sulfate product with a sodium sulfate content of 97.35%.

[0059] Comparative Example 4:

[0060] Take 400g of nitromethane solid waste, add 640g of water, heat the water bath to 38°C, stir and dissolve for 30min, filter while hot, add 25% dilute sulfuric acid to the filtrate, control the pH to about 5-6, stir for 30min after the addition, add 40g of ethyl acetate, extract at room temperature, stir for 30min, stand and stratify, separate the organic phase, cool the aqueous phase to 8°C at a rate of 1°C / 5min, crystallize, filter, add 160g of ice water to the filter cake for leaching and pulping, and filter to obtain a white sodium sulfate wet product. Vacuum rotary evaporation (-0.1MPa, 80 rpm, 80°C) and dry to obtain 252g of sodium sulfate product, which is yellowish in color and has a sodium sulfate content of 95.17%.

[0061] Comparative Example 5:

[0062] Take 400g of nitromethane solid waste, add 640g of water, heat the water bath to 38°C, stir and dissolve for 30min, filter while hot, add 25% dilute sulfuric acid to the filtrate, control the pH to about 5-6, stir for 30min after the addition, add 40g of ethyl acetate, extract at room temperature, stir for 30min, stand and stratify, separate the organic phase, cool the aqueous phase to 8°C at a rate of 1°C / 5min, crystallize, filter by suction, add 320g of ice water to the filter cake for leaching and pulping, and obtain a white sodium sulfate wet product after filtration. Vacuum rotary evaporation (-0.1MPa, 80 rpm, 80°C) and dry to obtain 223g of sodium sulfate product with a sodium sulfate content of 98.72%.

[0063] Comparative Example 6:

[0064] Take 400g of nitromethane solid waste, add 700g of water, heat to 40℃ in a water bath, stir and dissolve for 30min, filter while hot, add 30% dilute sulfuric acid to the filtrate, control the pH value to about 5-6, stir for 30min after the addition, add 50g of chlorobenzene, extract at room temperature, stir for 30min, let stand and separate, separate the organic phase, cool the aqueous phase to 5℃ at a rate of 2℃ / 5min, crystallize, and filter to obtain a yellow wet product (such as Figure 4 ). The product was evaporated under reduced pressure (-0.095 MPa, 100 rpm, 75°C) and dried to obtain 262 g of sodium sulfate with a purity of 95.14%.

[0065] Comparisons 1-6 are selection comparisons of claim optimization conditions. In Comparison 1, too much water is added, and the obtained product yield is low. In Comparison 2, too little water is added, and hot filtration will filter out a portion of the by-product sodium sulfate, resulting in a decrease in product yield. In Comparison 3, the gradient cooling rate is too fast, resulting in a decrease in purity. In Comparison Example 4, the amount of ice water added is too low, resulting in an inability to fully remove impurities, resulting in a yellowish product color, a reduced yield, and a significant decrease in purity. In Comparison Example 5, the amount of ice water added is too high, resulting in a decrease in product yield. In Comparison Example 6, the product obtained without ice water rinsing and pulping is yellow.

[0066] The above is only a specific implementation of the present application, so that those skilled in the art can understand or implement the present application. Various modifications to these embodiments will be apparent to those skilled in the art. Although embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations may be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents. The aforementioned embodiments and methods described in the present invention may vary based on the abilities, experiences and preferences of those skilled in the art.

[0067] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be considered exemplary and non-restrictive in all respects, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims be included in the present invention.

[0068] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A method for recovering sodium sulfate from nitromethane solid waste, characterized in that: The following steps are involved: (1) Dissolve the nitromethane solid waste in water in a hot water bath and filter it while it is hot; (2) adding dilute sulfuric acid dropwise to the filtrate, then adding an organic solvent for extraction at room temperature, and separating the aqueous phase; (3) gradient cooling the aqueous phase for crystallization and suction filtration to obtain a filter cake; (4) washing the filter cake with ice water, beating the filter cake, and filtering the filter cake to obtain a wet product of sodium sulfate; (5) subjecting the wet sodium sulfate product to reduced pressure rotary evaporation and drying to obtain a sodium sulfate product.

2. The recycling method according to claim 1, characterized in that: The temperature of the hot water bath in step (1) is controlled at 35°C-40°C.

3. The recycling method according to claim 1, characterized in that: The concentration of the dilute sulfuric acid in step (2) is controlled at 20-30%.

4. The recycling method according to claim 1, characterized in that: It is characterized in that The organic solvent in step (2) is selected from any one of chlorobenzene, toluene, ethyl acetate or ethylene dichloride.

5. The recycling method according to claim 1, characterized in that: The temperature in step (2) is gradually reduced to 5-10°C.

6. The recycling method according to claim 5, characterized in that: The gradient cooling in step (2) controls the cooling rate to be 1°C to 2°C / 5min.

7. The recycling method according to claim 1, characterized in that: The weight of the ice water in step (2) accounts for 50%-70% of the solid waste input.

8. The recycling method according to claim 1, characterized in that: The filtrate obtained after the suction filtration in step (3) and / or the filtrate obtained after the suction filtration in step (4) is used in step (1) to dissolve the nitromethane solid waste.

9. The recycling method according to claim 1, characterized in that: The temperature of the reduced pressure rotary evaporation is controlled at 70°C to 80°C.

10. The recycling method according to claim 1, characterized in that: The pressure of the reduced pressure rotary evaporation is controlled at -0.095MPa to -0.1MPa. The speed is controlled at 50-100 rpm.

Images