A preparation method of O-methyl-N-nitroisourea

Abstract

The present invention relates to the technical field of fine chemicals, and proposes a method for preparing O-methyl-N-nitroisourea, comprising the following reaction steps: after urea and dimethyl sulfate react, they react with fuming sulfuric acid and fuming nitric acid in sequence, and then ripen to obtain the first part of O-methyl-N-nitroisourea and mother liquor; after neutralizing the mother liquor, extract, concentrate, and crystallize to obtain the second part of O-methyl-N-nitroisourea; combine the first part of O-methyl-N-nitroisourea and the second part of O-methyl-N-nitroisourea to obtain the total part of O-methyl-N-nitroisourea; the extractant used for the extraction is composed of water, anhydrous ethanol and ethyl acetate in a volume ratio of 1:3 to 5:20. Through the above technical scheme, the problem of low yield in the industrial production of O-methyl-N-nitroisourea in the prior art is solved.

Description

Technical Field

[0001] The invention relates to the technical field of fine chemicals, and in particular to a method for preparing O-methyl-N-nitroisourea. Background Art

[0002] O-methyl-N-nitroisourea is a key intermediate for the synthesis of new low-toxic pesticides such as dimethoate and clothianidin, and has a broad market space. The process of synthesizing O-methyl-N-nitroisourea involves a nitration reaction process. The traditional nitration reaction process usually adopts an intermittent kettle method for production. The reaction releases a large amount of heat, and the time for dripping nitric acid is as long as more than 20 hours. The production cycle is long and the safety risk is high. In addition, the nitration reaction itself is also highly dangerous. In addition, the production process must meet the government's regulatory requirements. The continuous production of O-methyl-N-nitroisourea has become an inevitable option for enterprises.

[0003] Patents CN111362839B, CN113603617A and the 2018 Nanjing University of Science and Technology dissertation "Application of Microchannel Reactors in Nitration of Nitrogen-Containing Compounds" all disclose methods for continuously preparing O-methyl-N-nitroisourea using a microchannel reactor. These documents all use O-methylisourea hydrogen sulfate solid with high purity as raw material, but the market price of O-methylisourea hydrogen sulfate solid product is relatively high, and using it as a raw material is not economical and cannot meet the requirements of industrial production.

[0004] The literature Journal of the American Chemical Society (1954), 76, 4382-5 and JPH2000103775A reported that industrial O-methylisourea is prepared by reacting urea and dimethyl sulfate as raw materials to obtain O-methylisourea with a yield of 60-70%, and then hydrolyzing and concentrating the reaction solution to obtain an aqueous sulfuric acid solution containing O-methylisourea hydrogen sulfate with a yield of 60-70%, and the solution is further separated to obtain O-methylisourea hydrogen sulfate solid. However, the yield of O-methylisourea hydrogen sulfate solid is only 35%-50%, and nearly 20% of the yield is lost to the mother liquor, which will produce sulfuric acid waste liquid containing the product O-methylisourea, thereby causing the double loss of O-methylisourea and sulfuric acid, which is extremely uneconomical and environmentally unfriendly in industry.

[0005] Patent JPH2000103775A reported that the yield of O-methyl-N-nitroisourea nitration reaction can reach more than 90%, but after separation, the yield is less than 75%, and 15% of the yield is lost in the mother liquor. This is because O-methyl-N-nitroisourea is very easy to hydrolyze under acidic conditions. To avoid its hydrolysis, the temperature needs to be lowered to below -10°C. Although lowering the temperature can ensure the stability of O-methyl-N-nitroisourea, it is not industrially feasible. It can be extracted at room temperature after neutralization reaction below -10°C, but O-methyl-N-nitroisourea has low solubility in the extraction solvent, so a large amount of organic solvent is required in the extraction operation, which makes the operation cumbersome and extremely disadvantageous in industry.

[0006] And the sulfuric acid aqueous solution containing O-methylisourea hydrogen sulfate obtained by reaction hydrolysis and concentration of urea and dimethyl sulfate contains unconverted urea, and after adding oleum, white precipitated aminosulfonic acid will be generated. If it is used as the raw material of microchannel continuous nitration reaction, it will block the feed pump and the microchannel reactor. Although the pipeline filter is added, it may still cause a local violent reaction in the reactor, damage the reactor, and bring danger; the presence of excessive urea in the O-methylisourea hydrogen sulfate solution will also produce a large amount of gas with a liquid volume of about 70 times during continuous nitration, occupying the liquid holding volume of the microchannel reactor itself, which is not large, reducing the production capacity of the reactor and increasing equipment investment; the presence of excessive urea increases the consumption of nitric acid and sulfuric acid in the nitration process, and produces many nitration impurities. This makes it extremely difficult to use the O-methylisourea hydrogen sulfate solution obtained by reaction hydrolysis and concentration as a raw material for nitration, so these problems lead to a low yield during the current industrial production of O-methyl-N-nitroisourea. Summary of the invention

[0007] The invention provides a method for preparing O-methyl-N-nitroisourea, which solves the problem of low yield in industrial production of O-methyl-N-nitroisourea in the related art.

[0008] The technical solution of the present invention is as follows:

[0009] The present invention provides a method for preparing O-methyl-N-nitroisourea, comprising the following reaction steps:

[0010] S1, using urea and dimethyl sulfate as raw materials, reacting, hydrolyzing and concentrating to obtain O-methylisourea hydrogen sulfate original solution;

[0011] S2, mixing the original O-methylisourea hydrogen sulfate solution and fuming sulfuric acid, performing a pretreatment reaction, and separating the solid to obtain a pretreated original O-methylisourea hydrogen sulfate solution;

[0012] S3, mixing the pretreated O-methylisourea hydrogen sulfate original solution with fuming nitric acid to carry out nitration reaction to obtain a nitration reaction solution;

[0013] S4, subjecting the nitration reaction liquid to a ripening reaction, and then to quenching, separation, and washing to obtain a first portion of O-methyl-N-nitroisourea and a mother liquor;

[0014] S5, after neutralizing the mother liquor, extracting, concentrating and separating by crystallization to obtain the second part of O-methyl-N-nitroisourea;

[0015] S6, combining the first part of O-methyl-N-nitroisourea and the second part of O-methyl-N-nitroisourea to obtain O-methyl-N-nitroisourea;

[0016] The extractant used for extraction in S5 is composed of water, anhydrous ethanol and ethyl acetate in a volume ratio of 1:3 to 5:20.

[0017] As a further technical solution, the molar ratio of urea to dimethyl sulfate in S1 is 0.8-1.1:1.

[0018] As a further technical solution, the reaction temperature in S1 is 60-90° C., and the reaction time is 2-4 hours.

[0019] As a further technical solution, in S2, the O-methylisourea hydrogen sulfate original solution and fuming sulfuric acid are mixed in an intermittent or autoclave continuous manner, and after a pretreatment reaction, the solid is separated to obtain a pretreated O-methylisourea hydrogen sulfate original solution.

[0020] As a further technical solution, the content of urea in the original O-methylisourea hydrogen sulfate solution is 5.5-9%.

[0021] As a further technical solution, the molar ratio of free sulfur trioxide in the oleum in S2 to urea in the original solution of O-methylisourea hydrogen sulfate is 2.0-2.5:1.

[0022] As a further technical solution, the mass concentration of free sulfur trioxide in the oleum in S2 is 10% to 45%, preferably 22.5%.

[0023] As a further technical solution, the mixing temperature in S2 is 40-90°C, the pretreatment reaction temperature is 70-90°C, the pretreatment reaction time is 0.2-2h, and the solid separation temperature is 10-40°C.

[0024] As a further technical solution, in S3, the pretreated O-methylisourea hydrogen sulfate solution and the fuming nitric acid are synchronously pumped into the microchannel reactor for nitration reaction.

[0025] As a further technical solution, the microchannel reactor is a single set of microchannel nitrification reactor, which is composed of 4 reaction modules, wherein the 2nd and 3rd reaction modules are connected in parallel, and the 1st and 4th reaction modules are connected in series, or 1st reaction module is connected in series, and the 2nd, 3rd, and 4th reaction modules are connected in parallel.

[0026] As a further technical solution, the reaction module of the microchannel reactor is one of a T-shaped structure, a spherical structure, a heart-shaped structure, and a Baguayangyu-shaped structure.

[0027] As a further technical solution, a premixing zone and a reaction zone are set for the nitration reaction in S3, the temperature of the premixing zone is 20-50°C, the temperature of the reaction zone is 50-90°C, and the residence time of the reaction zone is 5-40s.

[0028] As a further technical solution, the nitration reaction in S3 is carried out in a microchannel reactor. The nitration reaction in S3 is first premixed at 20-50° C. in a premixing zone, and then reacted at 50-90° C. in a reaction zone for 5-40 seconds.

[0029] As a further technical solution, the molar ratio of nitric acid in the fuming nitric acid in S3 to O-methylisourea hydrogen sulfate in the pretreated O-methylisourea hydrogen sulfate original solution is 1-1.5:1.

[0030] As a further technical solution, the mass concentration of nitric acid in the fuming nitric acid in S3 is 84-99%.

[0031] As a further technical solution, the aging reaction in S4 can be carried out intermittently in a kettle, or can be carried out continuously in a tubular reactor, preferably in a tubular reactor.

[0032] As a further technical solution, the temperature of the aging reaction in S4 is 0-50° C., and the time of the aging reaction is 10-1440 min.

[0033] As a further technical solution, the temperature of the aging reaction in S4 is 20-40° C., and the aging reaction time is 1-4 hours.

[0034] As a further technical solution, the neutralization is carried out in S5 by a microchannel method, and the neutralization mother liquor is adjusted to a pH of 2.0-7.0 using liquid ammonia or aqueous ammonia at 0-50°C.

[0035] As a further technical solution, in S5, liquid ammonia or ammonia water and the mother liquor are continuously introduced into a microchannel reactor for neutralization, and then extracted, concentrated and crystallized to obtain the second part of O-methyl-N-nitroisourea.

[0036] As a further technical solution, the neutralization temperature in S5 is 0-50° C., and the neutralization pH is 2.0-7.0.

[0037] As a further technical solution, the neutralization temperature in S5 is 0-30° C., and the neutralization pH is 4.0-6.0.

[0038] The working principle and beneficial effects of the present invention are:

[0039] 1. In the present invention, water, anhydrous ethanol and ethyl acetate are used as an extractant to extract and neutralize O-methyl-N-nitroisourea in the mother liquor, which can improve the extraction rate of O-methyl-N-nitroisourea, thereby improving the yield of O-methyl-N-nitroisourea in industrial production.

[0040] 2. The present invention adopts O-methylisourea hydrogen sulfate original solution as raw material and pretreats it, thereby solving many problems that may occur when a microchannel reactor is used to carry out a nitration reaction using solid materials as raw materials. It is more convenient to realize the full process automation of the entire nitration reaction, and produces aminosulfonic acid with a wide range of uses as a by-product, thereby avoiding the generation of waste and reducing production costs, which has both economic and environmental significance.

[0041] 3. The present invention adopts a microchannel reactor, which not only realizes continuous production, but also reduces the liquid holding capacity of the equipment from several cubic meters of traditional reactors to tens of milliliters to hundreds of milliliters, greatly reducing the safety hazards of operation, and the entire reaction time is shortened from more than thirty hours of the kettle type to within a few hours, greatly shortening the reaction time and improving production efficiency. In addition, the strong mass transfer and heat transfer characteristics of the microchannel reactor promote the removal of heat, reduce the consumption of cold, avoid the risk of uncontrolled reaction and explosion, and reduce operating costs.

[0042] 4. The present invention adopts a method of pre-treating the original O-methylisourea hydrogen sulfate solution and feeding the fuming nitric acid in parallel, without preparing the mixed acid in advance, avoiding the safety risks and equipment occupation of the mixed acid configuration, and adopts a pre-mixing and reaction distribution method to optimize the reaction progress, avoid material decomposition, and ensure the high yield of the nitration reaction.

[0043] 5. The present invention preferably uses a tubular reactor for the subsequent aging reaction, which is convenient for the subsequent continuous quenching of the reaction solution, reduces the safety risk of the aging reaction, further reduces the floor space of the nitration equipment, and facilitates the realization of full-process automation.

[0044] 6. The present invention adopts a microchannel reactor to neutralize the nitrated and aged mother liquor, thereby ensuring that the neutralization reaction is achieved at a relatively high temperature without decomposing O-methyl-N-nitroisourea, greatly reducing the cooling energy consumption of the neutralization reaction, making the neutralization reaction feasible for industrial production, further improving the separation yield of the product, and improving the economic benefits of the project. The measures taken by the present invention are more conducive to industrial production, making industrial production more economical and safer. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 The present invention is a schematic diagram of the process connection for the pretreatment of O-methylisourea hydrogen sulfate sulfuric acid solution and nitration reaction with fuming nitric acid to produce O-methyl-N-nitroisourea; wherein reaction modules 1 to 4 represent microchannel reactor reaction modules for nitration reaction.

[0046] Figure 2 The internal structure diagram of the microchannel reactor used in the present invention; wherein a is a straight channel reaction module, b is a Baguayangyu-shaped reaction module, c is a T-shaped structure, d is a spherical structure, and e is a heart-shaped structure. DETAILED DESCRIPTION

[0047] The following will be combined with 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.

[0048] Example 1

[0049] A method for preparing O-methyl-N-nitroisourea comprises the following steps:

[0050] S1. Take urea (20 kmol, 1200 kg) and dimethyl sulfate (25 kmol, 3150 kg) as raw materials, react at 60 °C for 4 hours, and then hydrolyze and concentrate to obtain about 3953 kg of O-methylisourea hydrogen sulfate solution with a urea concentration of 6.1%.

[0051] S2. Under stirring, the original solution of O-methylisourea hydrogen sulfate and oleum containing 22.5wt% free sulfur trioxide are synchronously and continuously pumped into the low-temperature reactor. The flow rate of the original solution of O-methylisourea hydrogen sulfate is 325kg / hr, and the flow rate of oleum is 292kg / hr. The amount of urea in the oleum and the amount of free sulfur trioxide in the original solution of urea are 2.5:1. The temperature of the low-temperature reactor is controlled at 45°C. The low-temperature reaction liquid continuously flows into the high-temperature reactor. The temperature of the high-temperature reactor is controlled at 70°C. The residence time is 2h. The high-temperature treatment liquid enters the treatment liquid temporary storage kettle, is cooled to 10°C, and is filtered to obtain a crude aminosulfonic acid product. The filter cake is refined to produce aminosulfonic acid. The pretreated original solution of O-methylisourea hydrogen sulfate enters the temporary storage tank for the raw material liquid of the nitration reaction to obtain 6732kg of the pretreated original solution of O-methylisourea hydrogen sulfate.

[0052] S3, like Figure 1 In the microchannel reactor shown in FIG. Figure 2 a) simultaneously pumping in a pretreated O-methylisourea hydrogen sulfate original solution and 84 wt% fuming nitric acid, the flow rate of the pretreated O-methylisourea hydrogen sulfate original solution is 4600 g / min, the flow rate of the 84 wt% fuming nitric acid is 1199 g / min, the molar ratio of nitric acid to O-methylisourea hydrogen sulfate in the fuming nitric acid is 1.5:1, controlling the temperature of the mixing zone to 35° C., the temperature of the reaction zone to 60° C., and the residence time in the reaction zone to 20 s, to obtain a nitration reaction solution;

[0053] S4, the nitration reaction liquid from the microchannel reactor enters a tubular reactor with a heat exchange sleeve, and after aging at 20°C for 4 hours, it is continuously entered into a quenching kettle with ice water and water in proportion for quenching, and the temperature of the quenching kettle is controlled below -10°C. The quenching liquid continuously flows out and enters a temporary storage kettle, and is centrifuged and rinsed to obtain the first part of O-methyl-N-nitroisourea and mother liquor;

[0054] S5, the mother liquor enters the temporary storage kettle, and undergoes a neutralization reaction with the liquid ammonia continuously pumped into the microchannel reactor, the neutralization reaction temperature is controlled to be 0°C, the neutralization reaction pH is 4.0, and the neutralized mother liquor is extracted with an extractant composed of water, anhydrous ethanol and ethyl acetate (the volume ratio of water, anhydrous ethanol and ethyl acetate is 1:4:20), concentrated, and crystallized to obtain the second part of O-methyl-N-nitroisourea;

[0055] S6. Combine the first part of O-methyl-N-nitroisourea and the second part of O-methyl-N-nitroisourea to obtain the total part of O-methyl-N-nitroisourea (yield: 1803.3 kg, purity: 97.8%, nitration yield: 95%, total molar yield based on urea: 74.1%).

[0056] Example 2

[0057] A method for preparing O-methyl-N-nitroisourea comprises the following steps:

[0058] S1. Take urea (20 kmol, 1200 kg) and dimethyl sulfate (18 kmol, 2268 kg) as raw materials, react at 80 °C for 3 hours, then hydrolyze and concentrate to obtain about 3241 kg of O-methylisourea hydrogen sulfate solution; the urea concentration is 8.9%.

[0059] S2. Under stirring, the original solution of O-methylisourea hydrogen sulfate and oleum containing 10wt% free sulfur trioxide are synchronously and continuously pumped into the low-temperature reactor. The flow rate of the original solution of O-methylisourea hydrogen sulfate is 325kg / hr, and the flow rate of the oleum is 770kg / hr. The amount of urea in the oleum and the amount of free sulfur trioxide in the original solution of urea are 2:1. The temperature of the low-temperature reactor is controlled at 40°C, and the low-temperature reaction liquid continuously flows into the high-temperature reactor. The temperature of the high-temperature reactor is controlled at 80°C, and the residence time is 1h. The high-temperature treated liquid enters the temporary storage kettle for the treated liquid, is cooled to 20°C, and is filtered to obtain a crude aminosulfonic acid product. The filter cake is refined to produce aminosulfonic acid. The pretreated original solution of O-methylisourea hydrogen sulfate enters the temporary storage tank for the raw liquid of the nitration reaction, and 9990kg of the pretreated original solution of O-methylisourea hydrogen sulfate is obtained.

[0060] S3, like Figure 1 In the microchannel reactor shown in FIG. Figure 2 a) simultaneously pumping in a pretreated O-methylisourea hydrogen sulfate original solution and 90 wt% fuming nitric acid, the flow rate of the pretreated O-methylisourea hydrogen sulfate original solution is 9200 g / min, the flow rate of the 90 wt% fuming nitric acid is 1242 g / min, the molar ratio of nitric acid to O-methylisourea hydrogen sulfate in the fuming nitric acid is 1.3:1, controlling the temperature of the mixing zone to 35° C., the temperature of the reaction zone to 60° C., and the residence time in the reaction zone to 12 s, to obtain a nitration reaction solution;

[0061] S4, the nitration reaction liquid from the microchannel reactor enters a tubular reactor with a heat exchange sleeve, and after aging at 30°C for 3h, it continuously enters a quenching kettle with ice water and water in proportion for quenching, and the temperature of the quenching kettle is controlled below -10°C. The quenching liquid continuously flows out and enters a temporary storage kettle, and is centrifuged and rinsed to obtain the first part of O-methyl-N-nitroisourea and mother liquor;

[0062] S5, the mother liquor enters the temporary storage kettle, and undergoes a neutralization reaction with the liquid ammonia continuously pumped into the microchannel reactor, the neutralization reaction temperature is controlled at 15°C, the neutralization reaction pH is 5.0, and the neutralized mother liquor is extracted with an extractant composed of water, anhydrous ethanol and ethyl acetate (the volume ratio of water, anhydrous ethanol and ethyl acetate is 1:4:20), concentrated, and crystallized to obtain the second part of O-methyl-N-nitroisourea;

[0063] S6. Combine the first part of O-methyl-N-nitroisourea and the second part of O-methyl-N-nitroisourea to obtain the total part of O-methyl-N-nitroisourea (yield: 1715 kg, purity: 98.2%, nitration yield: 95.5%, total molar yield based on urea: 70.8%).

[0064] Example 3

[0065] A method for preparing O-methyl-N-nitroisourea comprises the following steps:

[0066] S1. Take urea (20 kmol, 1200 kg) and dimethyl sulfate (20 kmol, 2520 kg) as raw materials, react at 90 °C for 2 hours, and then hydrolyze and concentrate to obtain about 3453 kg of O-methylisourea hydrogen sulfate original solution; the urea concentration is 7.0%.

[0067] S2. Under stirring, the original solution of O-methylisourea hydrogen sulfate and oleum containing 45wt% free sulfur trioxide are synchronously and continuously pumped into the low-temperature reactor. The flow rate of the original solution of O-methylisourea hydrogen sulfate is 325kg / hr, and the flow rate of oleum is 147kg / hr. The amount of substance ratio of free sulfur trioxide in oleum to urea in the original solution of O-methylisourea hydrogen sulfate is 2.2:1. The temperature of the low-temperature reactor is controlled at 55°C. The low-temperature reaction liquid continuously flows into the high-temperature reactor. The temperature of the high-temperature reactor is controlled at 90°C. The residence time is 0.2h. The high-temperature treatment liquid enters the temporary storage kettle for the treatment liquid, is cooled to 40°C, and is filtered to obtain a crude sulfamic acid product. The filter cake is refined to produce sulfamic acid. The pretreated original solution of O-methylisourea hydrogen sulfate enters the temporary storage tank for the raw liquid of the nitration reaction to obtain 4241kg of the pretreated original solution of O-methylisourea hydrogen sulfate, and the concentration of O-methylisourea hydrogen sulfate is about 63.3%.

[0068] S3, like Figure 1 In the microchannel reactor shown in FIG. Figure 2a) simultaneously pumping in a pretreated O-methylisourea hydrogen sulfate original solution and 90wt% fuming nitric acid, the flow rate of the pretreated O-methylisourea hydrogen sulfate original solution is 18.5kg / min, the flow rate of 98wt% fuming nitric acid is 4.374kg / min, the molar ratio of nitric acid to O-methylisourea hydrogen sulfate in the fuming nitric acid is 1.0:1, controlling the temperature of the mixing zone at 40°C, the temperature of the reaction zone at 80°C, and the residence time in the reaction zone at 5s, to obtain a nitration reaction solution;

[0069] S4, the nitration reaction liquid from the microchannel reactor enters a tubular reactor with a heat exchange sleeve, and after aging at 40°C for 1h, it is continuously entered into a quenching kettle with ice water and water in proportion for quenching, and the temperature of the quenching kettle is controlled below -10°C. The quenching liquid continuously flows out and enters a temporary storage kettle, and is centrifuged and rinsed to obtain the first part of O-methyl-N-nitroisourea and mother liquor;

[0070] S5, the mother liquor enters the temporary storage kettle, and undergoes a neutralization reaction with the liquid ammonia continuously pumped into the microchannel reactor, the neutralization reaction temperature is controlled at 30°C, the neutralization reaction pH is 6.0, and the neutralized mother liquor is extracted with an extractant composed of water, anhydrous ethanol and ethyl acetate (the volume ratio of water, anhydrous ethanol and ethyl acetate is 1:4:20), concentrated, and crystallized to obtain the second part of O-methyl-N-nitroisourea;

[0071] S6. Combine the first part of O-methyl-N-nitroisourea and the second part of O-methyl-N-nitroisourea to obtain the total part of O-methyl-N-nitroisourea (yield: 1805 kg, nitration yield: 96.2%, purity: 98.9%, total molar yield based on urea: 75%).

[0072] Example 4

[0073] Compared with Example 1, the only difference in this example is that the extractant in S5 consists of water, anhydrous ethanol and ethyl acetate in a volume ratio of 1:3:20, and the total amount of O-methyl-N-nitroisourea (yield is 1802.7 kg, nitration yield is 94%, and purity is 96.8%) is finally obtained.

[0074] Example 5

[0075] Compared with Example 1, the only difference in this example is that the extractant in S5 consists of water, anhydrous ethanol and ethyl acetate in a volume ratio of 1:5:20, and the total amount of O-methyl-N-nitroisourea (yield is 1802.9 kg, nitration yield is 94.4%, and purity is 97.2%) is finally obtained.

[0076] Example 6

[0077] Compared with Example 1, the only difference in this example is that the extractant in S5 consists of water, anhydrous ethanol and ethyl acetate in a volume ratio of 1:2:20, and the total amount of O-methyl-N-nitroisourea (yield is 1802.2 kg, nitration yield is 93.1%, and purity is 95.9%) is finally obtained.

[0078] Example 7

[0079] Compared with Example 1, the only difference in this example is that the extractant in S5 consists of water, anhydrous ethanol and ethyl acetate in a volume ratio of 1:6:20, and the total amount of O-methyl-N-nitroisourea (yield is 1802.4 kg, nitration yield is 93.5%, and purity is 96.3%) is finally obtained.

[0080] Example 8

[0081] Compared with Example 1, the only difference between this embodiment and Example 1 is that in S2, fuming sulfuric acid (3555 kg) containing 22.5 wt% of free sulfur trioxide is added dropwise to the original solution of O-methylisourea hydrogen sulfate (3953 kg) under stirring, and the kettle temperature is controlled at 45°C during the dropping process. After the dropping is completed, the temperature is slowly raised to 70°C, kept warm for 2 hours, the carbon dioxide is completely released, the temperature is lowered to 10°C, and filtered to obtain crude aminosulfonic acid. The filter cake is refined to produce aminosulfonic acid, and the pretreated original solution of O-methylisourea hydrogen sulfate enters the temporary storage tank for the raw material liquid of the nitration reaction, and finally the total amount of O-methyl-N-nitroisourea (the output is 1803.4 g, the nitration yield is 95.2%, and the purity is 98%).

[0082] Example 9

[0083] The difference between this embodiment and embodiment 1 is that when the nitration reaction occurs in S3, the connection mode of the four reaction modules in the microchannel reactor is as follows: Figure 2 As shown in b, the total amount of O-methyl-N-nitroisourea (yield: 234.17, yield: 95.1%, purity: 97.9%) was finally obtained.

[0084] Comparative Example 1

[0085] The only difference between this comparative example and Example 1 is that no water and anhydrous ethanol are added to the extractant in S5, and the total amount of O-methyl-N-nitroisourea (yield: 1781.1 kg, nitration yield: 71%, purity: 74%) is finally obtained.

[0086] Comparative Example 2

[0087] The only difference between this comparative example and Example 1 is that no water is added to the extractant in S5, and the total amount of O-methyl-N-nitroisourea (yield: 1736.5 g, nitration yield: 84%, purity: 89.8%) is finally obtained.

[0088] Comparative Example 3

[0089] The only difference between this comparative example and Example 1 is that no anhydrous ethanol is added to the extractant in S5, and the total amount of O-methyl-N-nitroisourea (yield: 1730.4 g, nitration yield: 81%, purity: 86.9%) is finally obtained.

[0090] Comparative Example 4

[0091] The difference between this comparative example and Example 1 is only in S3. In this comparative example, step S3 is

[0092] S3, like Figure 1 In the microchannel reactor shown in FIG. Figure 2 a) simultaneously pumping in a pretreated O-methylisourea hydrogen sulfate original solution and 84wt% fuming nitric acid, the flow rate of the pretreated O-methylisourea hydrogen sulfate original solution is 4600g / min, the flow rate of 84wt% fuming nitric acid is 1199g / min, the molar ratio of fuming nitric acid to O-methylisourea hydrogen sulfate is 1.5:1, no mixing zone is set, the temperature of the reaction zone is 60°C, the residence time of the reaction zone is 20s, and a nitration reaction liquid is obtained, and finally the total O-methyl-N-nitroisourea (yield is 1879.6kg, nitration yield is 89%, and purity is 87.9%) is obtained.

[0093] Comparative Example 5

[0094] The only difference between this comparative example and Example 1 is that in S5, the mother liquor is added to the reactor, liquid ammonia is added under stirring for neutralization reaction, the neutralization reaction temperature is controlled to be 0°C, the neutralization reaction pH is 4.0, and the neutralized mother liquor is extracted with an extractant consisting of water, anhydrous ethanol and ethyl acetate (the volume ratio of water, anhydrous ethanol and ethyl acetate is 1:4:20), concentrated, and crystallized to obtain the second part of O-methyl-N-nitroisourea, to obtain a nitration reaction liquid, and finally to obtain the total part of O-methyl-N-nitroisourea (the output is 1786.8 kg, the nitration yield is 77%, and the purity is 80%).

[0095] In the present invention, compared with Example 1, no water and anhydrous ethanol are added to the extracting agent in Comparative Example 1, no water is added to the extracting agent in Comparative Example 2, and no anhydrous ethanol is added to the extracting agent in Comparative Example 3. As a result, the yield and purity of O-methyl-N-nitroisourea in Comparative Examples 1 to 3 are both lower than those in Example 1, indicating that the extracting agent is composed of water, anhydrous ethanol and ethyl acetate, which can improve the yield and purity of O-methyl-N-nitroisourea in industrial production.

[0096] Compared with Example 1, Examples 4 to 7 changed the volume ratio of water, anhydrous ethanol and ethyl acetate in the extractant. As a result, the yield and purity of O-methyl-N-nitroisourea in Examples 6 to 7 were less than those in Examples 1 and 4 to 5, indicating that when the volume ratio of water, anhydrous ethanol and ethyl acetate in the extractant was 1:3 to 5:20, the yield and purity of O-methyl-N-nitroisourea in industrial production could be further improved, and the yield and purity of O-methyl-N-nitroisourea in Example 1 were greater than those in Examples 4 to 5, indicating that when the volume ratio of water, anhydrous ethanol and ethyl acetate in the extractant was 1:4:20, the yield and purity of O-methyl-N-nitroisourea in industrial production could be further improved. Compared with Example 1, Comparative Example 4 did not set a premixing zone during the nitration reaction. As a result, the yield and purity of O-methyl-N-nitroisourea in Comparative Example 4 were both lower than those in Example 1, indicating that setting a premixing zone and a reaction zone during the nitration reaction can further improve the yield and purity of O-methyl-N-nitroisourea in industrial production.

[0097] Compared with Example 1, Comparative Example 5 changed the way of neutralizing the mother liquor. As a result, the yield and purity of O-methyl-N-nitroisourea in Comparative Example 5 were both lower than those in Example 1, indicating that the nitration reaction in a microchannel reactor can further improve the yield and purity of O-methyl-N-nitroisourea in industrial production.

[0098] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing O-methyl-N-nitroisourea, characterized in that: The reaction steps include: S1, using urea and dimethyl sulfate as raw materials, reacting, hydrolyzing and concentrating to obtain O-methylisourea hydrogen sulfate original solution; S2, mixing the original solution of O-methylisourea hydrogen sulfate with oleum, performing a pretreatment reaction, and separating the solid to obtain a pretreated original solution of O-methylisourea hydrogen sulfate; the molar ratio of free sulfur trioxide in the oleum to urea in the original solution of O-methylisourea hydrogen sulfate is 2.0-2.5:1; the mixing temperature is 40-90° C., the pretreatment reaction temperature is 70-90° C., the pretreatment reaction time is 0.2-2 h, and the temperature for separating the solid is 10-40° C.; S3, mixing the pretreated O-methylisourea hydrogen sulfate solution with fuming nitric acid to carry out a nitration reaction to obtain a nitration reaction solution; the nitration reaction is carried out in a microchannel reactor; S4, subjecting the nitration reaction liquid to a ripening reaction, and then to quenching, separation, and washing to obtain a first portion of O-methyl-N-nitroisourea and a mother liquor; S5, after neutralizing the mother liquor, extracting, concentrating and separating by crystallization to obtain the second part of O-methyl-N-nitroisourea; S6, combining the first part of O-methyl-N-nitroisourea and the second part of O-methyl-N-nitroisourea to obtain O-methyl-N-nitroisourea; The extractant used for extraction in S5 is composed of water, anhydrous ethanol and ethyl acetate in a volume ratio of 1:3 to 5:

20.

2. The method for preparing O-methyl-N-nitroisourea according to claim 1, characterized in that: The molar ratio of urea to dimethyl sulfate in S1 is 0.8-1.1:

1.

3. The method for preparing O-methyl-N-nitroisourea according to claim 1, characterized in that: The nitration reaction in S3 is first premixed at 20-50° C. in the premixing zone, and then reacted at 50-90° C. in the reaction zone for 5-40 seconds.

4. The method for preparing O-methyl-N-nitroisourea according to claim 1, characterized in that: The molar ratio of nitric acid in the fuming nitric acid in S3 to O-methylisourea hydrogen sulfate in the pretreated O-methylisourea hydrogen sulfate original solution is 1-1.5:

1.

5. The method for preparing O-methyl-N-nitroisourea according to claim 1, characterized in that: The temperature of the aging reaction in S4 is 0-50° C., and the time of the aging reaction is 10-1440 min.

6. The method for preparing O-methyl-N-nitroisourea according to claim 1, characterized in that: In the S5, the neutralization is carried out in a microchannel manner, and the neutralization mother liquor is adjusted to a pH of 2.0-7.0 using liquid ammonia or ammonia water at 0-50°C.

7. The method for preparing O-methyl-N-nitroisourea according to claim 1, characterized in that: The mass concentration of free sulfur trioxide in the oleum in S2 is 10% to 45%.

8. The method for preparing O-methyl-N-nitroisourea according to claim 1, characterized in that: The mass concentration of nitric acid in the fuming nitric acid in S3 is 84-99%.

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