A continuous flow synthesis of nitromethane

Abstract

This invention discloses a continuous flow synthesis method for nitromethane. The method includes mixing dimethyl sulfate, nitrite, a catalyst, and water to obtain a mixture; continuously feeding the mixture into a first reactor and reacting it at a first temperature to obtain a first reaction solution; continuously feeding the first reaction solution into a second reactor and reacting it at a second temperature to obtain a second reaction solution; continuously feeding the second reaction solution into a distillation column to obtain crude nitromethane, which is then purified by distillation to obtain the final nitromethane product. Both the first and second reactors are plug flow reactors, and the first temperature is lower than the second temperature. This method provides milder reaction conditions, easier process control, and by refining and precisely controlling the reaction temperatures of the two stages, it reduces the generation of byproducts and energy costs, avoids the safety hazards caused by violent foaming and material surges during the reaction, and significantly improves both process safety and efficiency.

Description

Technical Field

[0001] This invention relates to the field of flow chemical synthesis technology, and more specifically to a continuous flow synthesis method for nitromethane. Background Technology

[0002] Nitromethane is an important organic chemical product and organic synthesis intermediate, characterized by good selectivity, low viscosity, and low volatility. It is widely used in the synthesis of polymer materials and also in the production of explosives, rocket fuels, pesticides, gasoline additives, coatings, textiles, food, and paints. Nitromethane is also a high-performance liquid explosive and can be used as a fuel additive to improve fuel calorific value and reduce pollution. Many important organic chemical products, such as nitro alcohols, can be synthesized from nitromethane, making it an important raw material for the pharmaceutical, pesticide, and dye industries. In recent years, the market demand for nitromethane has been gradually increasing.

[0003] Currently, there are two main synthesis methods for nitromethane: the gas-phase nitration of methane and the reaction of dimethyl sulfate with sodium nitrite. The gas-phase nitration of methane involves spraying dilute nitric acid into a mist to vaporize it, which is then mixed with preheated methane (natural gas) to maintain a specific ratio of nitric acid, methane, and water vapor. The mixed gas enters a pipeline reactor using molten salt as the heating medium, where nitration occurs directly at atmospheric pressure and 450-550℃. The reaction products are condensed and absorbed by water; the resulting aqueous nitromethane solution is distilled to obtain crude nitromethane, which is then washed and purified to obtain the final product. The gas-phase nitration method has high reaction temperatures, requires sophisticated equipment, has low yields, and poses safety hazards due to the high reaction temperatures. The reaction of dimethyl sulfate with sodium nitrite involves adding sodium nitrite and dimethyl sulfate to a reaction vessel. The reaction products are condensed, distilled, cooled to separate layers, and then purified to obtain the final product. Alternatively, sodium nitrite can be reacted with sodium chloroacetate and then heated. Nitrites can also be produced by reacting with haloalkanes. Industrially, other low-carbon alkanes (ethane, propane) can also be directly nitrated in the chlorination phase, but the reaction products are a mixture of nitromethane, nitrobenzene, and nitrobanane, resulting in low yields and difficulties in separation and purification. The reaction of dimethyl sulfate with sodium nitrite is characterized by readily available raw materials, simple process, and low cost, making it a commonly used method in industry. In practice, the traditional process involves a one-pot reaction of dimethyl sulfate and sodium nitrite. However, the temperature in existing batch reactors is difficult to control, leading to violent foaming during the reaction, posing safety hazards such as material overflow and flash explosions. Even with the addition of defoamers, this is difficult to avoid. Furthermore, the accumulation of products and byproducts during the reaction, which cannot be discharged in time, easily leads to reduced product yield and purity. Summary of the Invention

[0004] This invention provides a continuous flow synthesis method for nitromethane, which solves the problem of severe foaming caused by the inability to remove reactants in a timely manner, while also reducing side reactions and improving reaction yield and purity.

[0005] Specifically, the method includes the following steps:

[0006] (1) A mixture is obtained by mixing dimethyl sulfate, nitrite, catalyst and water;

[0007] (2) The mixture obtained in step (1) is continuously fed into the first reactor and reacted at the first temperature to obtain the first reaction liquid;

[0008] (3) The first reaction solution is continuously fed into the second reactor and reacted at the second temperature to obtain the second reaction solution;

[0009] (4) The second reaction liquid is continuously fed into the distillation column to obtain crude nitromethane, which is then distilled to obtain nitromethane product;

[0010] Both the first reactor and the second reactor are plug flow reactors, and the first temperature is lower than the second temperature.

[0011] Specifically, according to the method of the present invention, in step (1), the feeding method is to add a material containing water but not nitrite to a material containing nitrite but not water. Nitrite absorbs a large amount of heat when dissolved in water, consuming most of the heat released by the reaction of nitrite and dimethyl sulfate, thus facilitating the control of the reaction temperature and allowing the reaction in the first reactor to proceed gently.

[0012] Specifically, as provided in step (1) above, the first raw material and the second raw material are provided.

[0013] The first raw material contains dimethyl sulfate, nitrite, and catalyst, but does not contain water; the second raw material contains water but does not contain nitrite.

[0014] or,

[0015] The first raw material contains dimethyl sulfate and nitrite, but does not contain water; the second raw material contains water and catalyst, but does not contain nitrite.

[0016] The second ingredient is added to the first ingredient and mixed.

[0017] A plug flow reactor is a type of tubular reactor in which, under ideal flow conditions, the material exhibits a strictly uniform radial velocity distribution and no axial mixing. The material flows forward like a piston; this flow is called plug flow, and there is no backmixing within the reactor. In actual plug flow reactors, the material flow can approximate this ideal flow to varying degrees.

[0018] According to the method of the present invention, the first stage of the reaction is carried out at low temperature in a first plug flow reactor, and then the first reaction liquid is continuously pumped into a second plug flow reactor for further reaction, and the second reaction liquid is then continuously pumped into a distillation column. This allows for rapid reaction while simultaneously ensuring the rapid removal of products from the reaction system, reducing safety issues such as foaming caused by product aggregation, and greatly promoting the equilibrium of the reaction, thus significantly improving the yield. The reaction between dimethyl sulfate and nitrite can be considered a methylation reaction, and also a nitration reaction. The nitrite ion dissociated from nitrite (e.g., sodium nitrite) acts as an amphiphilic nucleophile. Therefore, in the reaction of nitrite (e.g., sodium nitrite) and dimethyl sulfate to form nitromethane, the nitrogen atom of the nitrite ion attacks the methyl group to form nitromethane, and the oxygen atom attacks the methyl group to form the main byproduct, nitrosomethyl ester. The reaction temperatures required for the removal of the two methyl groups from dimethyl sulfate are different. Considering that dimethyl sulfate hydrolyzes rapidly at high temperatures, the first methyl group of dimethyl sulfate is easily removed, so the first stage needs to be carried out at a lower temperature. However, the removal of the second methyl group is difficult. The second stage requires a reaction at a high temperature to generate the product, and the product needs to be removed from the reaction system as soon as possible to prevent the formation of gaseous byproducts (alkyl nitrites, nitrogen oxides, carbon dioxide, etc.) from causing strong foaming in the reaction medium. Even with the use of defoamers, it is difficult to control the strong foaming phenomenon.

[0019] This invention divides the reaction of nitrite (e.g., sodium nitrite) and dimethyl sulfate into two stages, refining and precisely controlling the reaction temperature of the two stages:

[0020] The main reactions at low temperature in the first stage are:

[0021] (CH3)2SO4+NaNO2→CH3SO4Na+CH3NO2

[0022] The main reactions at high temperature in the second stage are:

[0023] CH3SO4Na+NaNO2→Na2SO4+CH3NO2

[0024] Specifically, according to the method of the present invention, the plug flow reactor is a plug flow reactor with a temperature control system for controlling the preheating temperature, the temperature during the reaction, and the heat removal after the reaction;

[0025] The plug flow reactor is equipped with straight pipes, coils, U-shaped pipes, tubular pipes, or any combination of pipes connected in series or parallel.

[0026] The pipeline material is a metal pipe, a plastic-coated metal pipe, or a plastic pipe, preferably a metal pipe;

[0027] Preferably, the metal pipe is a galvanized pipe, a copper pipe, or a stainless steel pipe;

[0028] Preferably, the plastic-coated metal pipe is an aluminum-plastic composite pipe;

[0029] Preferably, the plastic pipe is a PVC pipe or a PE pipe.

[0030] Specifically, the inner diameter of the pipes in the plug flow reactor The diameter is 1.0-25.0 mm (e.g., 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 14, 15, 20, 25 mm), preferably 2-10 mm; the length is 0.5-15 m (e.g., 0.5, 1.0, 1.5, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 14, 15 m), preferably 0.5-2 m.

[0031] Specifically, the first temperature is 30-50℃ (e.g., 30, 35, 40, 45, 50℃), preferably 30-35℃.

[0032] Specifically, the second temperature is 80-100℃ (e.g., 80, 85, 90, 95, 100℃), preferably 90-100℃.

[0033] The reaction at the first temperature is a low-temperature reaction. Using a conventional reactor will result in the accumulation of dimethyl sulfate. When the temperature reaches the second temperature, the dimethyl sulfate will react rapidly and exothermically. Using a plug flow reactor can effectively solve the problems of material accumulation and rapid, uneven reaction.

[0034] Specifically, the distillation temperature in step (4) is 100-110℃ (e.g., 100℃, 105℃, 110℃), and the distillation is atmospheric distillation.

[0035] Specifically, the reaction pressure inside the first reactor and the second reactor is 0.1-0.2 MPa.

[0036] Specifically, the aforementioned nitrite is sodium nitrite or potassium nitrite, especially sodium nitrite.

[0037] Specifically, the catalyst is a base or a strong base weak acid salt. For example, the base can be sodium hydroxide or potassium hydroxide, and the strong base weak acid salt can be sodium carbonate, sodium bicarbonate, potassium carbonate, or potassium bicarbonate. In one embodiment of the present invention, the catalyst is sodium carbonate.

[0038] Specifically, the molar ratio of dimethyl sulfate to nitrite is 1:2-2.2 (e.g., 1:2, 1:2.05, 1:2.1, 1:2.2), especially 1:2-2.1. Molar ratios of dimethyl sulfate to nitrite below or above the selected range will significantly reduce the yield of nitromethane products.

[0039] Specifically, the mass ratio of catalyst to nitrite is 0.01-0.1:1 (e.g., 0.01:1, 0.02:1, 0.03:1, 0.04:1, 0.05:1, 0.06:1, 0.07:1, 0.08:1, 0.09:1, 0.1:1), particularly 0.02-0.06:1. Too little or too much catalyst will reduce the yield of nitromethane products.

[0040] Specifically, in step (1), the mass ratio of water to nitrite is 0.1-1:1 (e.g., 0.1:1, 0.2:1, 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1), especially 0.3-0.6:1. Too little water will not dissolve the raw material well, while too much water will over-dilute the raw material and hinder the reaction.

[0041] In one embodiment of the present invention, step (4) further includes the step of recovering nitromethane from the bottom liquid of the distillation column. Specifically, the bottom liquid is collected periodically and then distilled in another distillation column to recover crude nitromethane. The crude nitromethane is then distilled alone or by combining two crude nitromethane products to obtain the nitromethane product.

[0042] This invention also proposes the use of a plug flow reactor in the synthesis of nitromethane via the dimethyl sulfate substitution method.

[0043] Specifically, the dimethyl sulfate substitution method refers to the synthesis of nitromethane by reacting dimethyl sulfate with a nitrite (e.g., sodium nitrite) solution through a substitution reaction.

[0044] Specifically, the plug flow reactor has the corresponding definition described above in this invention.

[0045] In the plug flow reactor, the material maintains a continuous and stable flow along the direction of motion, resulting in uniform reaction. The products are quickly carried out of the reaction system after formation, preventing accumulation within the reactor, reducing side reactions, and improving product yield. The equipment used in this invention has a small footprint, high reaction conversion rate, and can achieve continuous feeding and discharging, significantly shortening reaction time. It also boasts a high degree of automation, improved reaction selectivity, increased product yield and purity, and controllable safety risks during online production, eliminating potential safety hazards.

[0046] Beneficial effects

[0047] 1. This invention employs a plug flow reactor. Compared to the one-pot method, this invention offers shorter reaction residence time, more precise controllable temperature range, safer and more reliable process, more stable process control, and higher product yield. Traditional reactor-type production processes suffer from structural drawbacks due to the limitations of the reactor's structure, such as smaller heat exchange area, difficulty in timely product removal, and uncontrolled reaction temperature. The smaller heat exchange area of ​​the reactor leads to the inability to remove heat generated during the reaction in a timely manner, resulting in uncontrolled temperature within the reactor and a high risk of accidents such as reactor overflow and material spillage. The difficulty in timely removal of reaction products can easily lead to backmixing and the generation of byproducts due to product retention within the reactor, resulting in longer reaction times, lower reaction yields, and poor product quality. The difficulty in controlling the reactor temperature can cause safety hazards such as foaming, material spillage, and flash explosions during the reaction process, and foaming and material spillage are difficult to avoid even with the addition of defoamers. Intermittent start-up and shutdown of the reaction process also easily lead to safety accidents.

[0048] 2. This invention specifically employs a feeding method in which a material containing water but not nitrite is added to a material containing nitrite but not water. The endothermic dissolution of nitrite facilitates control of the exothermic reaction temperature, resulting in milder reaction conditions, easier control of the reaction process, and reduced byproduct formation and energy costs.

[0049] 3. This invention employs a method of continuously feeding materials into a first plug flow reactor for reaction, and rapidly feeding intermediate products into a second plug flow reactor for reaction, promoting the advancement of the second-stage reaction equilibrium. The second reaction liquid is quickly carried out of the reaction system and then enters a distillation column, resulting in continuous product output. This increases the yield of the main product, nitromethane, while suppressing the formation of the byproduct, methyl nitrite, and significantly reducing foaming. Compared to the one-pot method, this invention also avoids the risk of flash explosion caused by excessively rapid temperature rise due to material accumulation within the reactor.

[0050] 4. This invention divides the reaction of nitrite and dimethyl sulfate into two stages, refining and precisely controlling the reaction temperature of the two stages. The first and second plug flow reactors can each be configured with multiple reaction tubes in parallel, enabling continuous production where batching, low-temperature reaction, high-temperature reaction, and distillation reactions occur simultaneously in different equipment under automatic control.

[0051] 5. Existing traditional one-pot reaction processes are inconvenient for changing reaction conditions, and the heat released during the reaction cannot be dissipated in time, easily leading to localized overheating. In contrast, the plug flow reactor used in this invention has a large unit heat exchange area, ensuring sufficient and timely heat exchange. Therefore, the reaction temperature is easily controllable, byproduct formation is reduced, and the reaction yield is increased. The yield of the produced nitromethane can reach over 80%, with a purity of over 99.5%.

[0052] 6. Compared to traditional reactor-type reactions, the reaction in the plug flow reactor is more continuous, requires less reaction time, has a higher reaction rate, and is easier to automate and shut off in emergencies. The liquid holdup in the plug flow reactor of this invention is less than 1 / 50 or even 1 / 100 of that in existing reactors, making safety risks controllable, production stable, and yield improved, thus enabling industrial-scale promotion. The raw material cost can be reduced by approximately 1600 yuan per ton of nitromethane produced. Detailed Implementation

[0053] It should be noted that in this application, relational terms such as "first" and "second" are used to distinguish one entity or operation from another. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0054] Unless otherwise defined, all scientific and technical terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art.

[0055] All publications, patents, and published patent specifications cited in this article are incorporated herein in their entirety through citation.

[0056] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0057] The following is an example:

[0058] Example 1

[0059] Add 230 ml of water to 345 g (5 mol) of sodium nitrite, 315.3 g (2.5 mol) of dimethyl sulfate, and 8.6 g of sodium carbonate. After mixing in a static mixing device, pump the mixture into the first plug flow reactor. The reactor contains 26 parallel tubes with an inner diameter of [missing information]. The first plug flow reactor has a pipeline length of 0.5m and is made of stainless steel. The temperature of the hot zone of the first plug flow reactor is controlled at 30℃, the pressure is 0.1MPa, and the flow rate is set at 20mL / min by a temperature control system. The resulting first reaction liquid is continuously pumped into the second plug flow reactor, which has the same structure as the first plug flow reactor. Its hot zone temperature is controlled at 80℃, the pressure is 0.1MPa, and the flow rate is also set at 10mL / min. The resulting second reaction liquid is continuously fed into a distillation column, and the temperature of the distillation column is controlled at 100-110℃. As the reaction liquid continues to enter, continuous distillation continues, and distillation products are continuously produced. After static separation, crude nitromethane is obtained. The bottom liquid of the distillation column is collected from the bottom of the column, and then the crude nitromethane is recovered by distillation in another distillation column. The crude nitromethane products are combined and then purified by distillation to obtain 244.6 grams of nitromethane product with a purity of 99.51% and a yield of 80.14%.

[0060] Example 2

[0061] Add 920 mL of water to 1380 g (20 mol) of sodium nitrite, 1261.3 g (10 mol) of dimethyl sulfate, and 34.5 g of sodium carbonate. After mixing in a static mixing device, pump the mixture into the first plug flow reactor. The reactor contains 16 parallel tubes with an inner diameter of [missing information]. The reactor is 1m long and uses an aluminum-plastic composite pipe. The temperature of the hot zone of the first plug flow reactor is controlled at 40℃, the pressure is 0.15MPa, and the flow rate is set to 100mL / min through a temperature control system. The resulting first reaction liquid is continuously pumped into the second plug flow reactor, which has the same structure as the first plug flow reactor. Its hot zone temperature is controlled at 90℃, the pressure is 0.15MPa, and the flow rate is set to 100mL / min. The resulting second reaction liquid is continuously fed into a distillation column, and the temperature of the distillation column is controlled at 100-110℃. As the reaction liquid continues to enter, continuous distillation is carried out, and distillation products are continuously produced. After static separation, crude nitromethane is obtained. The bottom liquid of the distillation column is collected from the bottom of the column, and then the crude nitromethane is recovered by distillation in another distillation column. The crude nitromethane products are combined and then purified by distillation to obtain 1037.3 grams of nitromethane product with a purity of 99.93% and a yield of 85.02%.

[0062] Example 3

[0063] Add 920 ml of water to 1449 g (21 mol) of sodium nitrite, 1261.3 g (10 mol) of dimethyl sulfate, and 55.2 g of sodium carbonate. After mixing in a static mixing device, pump the mixture into the first plug flow reactor. The reactor contains 10 parallel U-shaped tubes with an inner diameter of [missing information]. The first plug flow reactor has a 2m long pipeline made of copper. The temperature of the hot zone of the first plug flow reactor is controlled at 35℃, the pressure at 0.15MPa, and the flow rate at 400mL / min by a temperature control system. The resulting first reaction liquid is continuously pumped into the second plug flow reactor. The second plug flow reactor has the same pipeline structure as the first, with its hot zone temperature controlled at 100℃, the pressure at 0.15MPa, and the flow rate at 400mL / min. The resulting second reaction liquid is continuously fed into a distillation column, with the distillation column temperature controlled at 100-110℃. As the reaction liquid continues to enter, continuous distillation continues, and distillation products are continuously produced. After settling and separation, crude nitromethane is obtained. The bottom liquid of the distillation column is collected from the bottom of the column and then distilled again to recover the crude nitromethane product. The crude nitromethane products are combined and then further distilled to obtain 1065.6g of nitromethane product with a purity of 99.98% and a yield of 87.34%.

[0064] Example 4

[0065] 27.3 kg of sodium bicarbonate was dissolved in 920 L of water, then 1380 kg (20 kmol) of sodium nitrite and 1261.3 kg (10 kmol) of dimethyl sulfate were added. After mixing in a static mixing device, the mixture was pumped into the first plug flow reactor. The reactor contained 10 parallel coiled tubes with an inner diameter of [missing information]. The first plug flow reactor has a 10m long pipeline made of stainless steel. A temperature control system maintains the hot zone temperature at 35℃, the pressure at 0.2MPa, and the flow rate at 10L / min. The resulting first reaction solution is continuously pumped into a second plug flow reactor, which is identical to the first, with a hot zone temperature controlled at 90℃, and the same pressure and flow rate. The resulting second reaction solution is continuously fed into a distillation column, with the temperature controlled at 100-110℃. As the reaction solution continues to enter, continuous distillation continues, producing distillation products. After settling and separation, crude nitromethane is obtained. The bottom liquid of the distillation column is collected and further distilled to recover the crude nitromethane product. The combined crude nitromethane products are then further purified by distillation to obtain 1050.6 kg of nitromethane product with a purity of 99.92% and a yield of 86.11%.

[0066] Example 5

[0067] Add 1380 kg (20 kmol) sodium nitrite, 1261.3 kg (10 kmol) dimethyl sulfate, and 34.5 kg sodium carbonate to 920 liters of water. After mixing in a static mixing device, pump the mixture into the first plug flow reactor. The reactor contains nine parallel tubes with an inner diameter of [missing information]. The first plug flow reactor has a 5m long pipeline made of stainless steel. A temperature control system maintains the hot zone temperature at 50℃, pressure at 0.2MPa, and flow rate at 400L / min. The resulting first reaction liquid is continuously pumped into a second plug flow reactor, which has the same structure as the first, with a hot zone temperature controlled at 100℃, pressure at 0.2MPa, and flow rate at 400L / min. The resulting second reaction liquid is continuously fed into a distillation column, with the temperature controlled at 100-110℃. As the reaction liquid continues to enter, continuous distillation continues, producing distillation products. After settling and stratification, crude nitromethane is obtained. The bottom liquid of the distillation column is collected and further distilled in another distillation column to recover the crude nitromethane product. The combined crude nitromethane products are then further purified by distillation to obtain 995.6 kg of nitromethane product with a purity of 99.61% and a yield of 81.28%.

[0068] Examples 4 and 5 are examples of industrial production. If continuous production for a longer period of time (such as several days) is required, the next batch of raw materials can be added to the static mixing device after the previous batch of raw materials has almost finished reacting. After thorough mixing, the feeding can continue to achieve this purpose.

[0069] Comparative Example 1

[0070] 1380 g (20 mol) of sodium nitrite, 34.5 g of sodium carbonate, and 920 mL of water were added to a reaction vessel. 1261.3 g (10 mol) of dimethyl sulfate was added dropwise over half an hour. The mixture was stirred and heated, with the temperature controlled below 70 °C. After distillation for 2 hours, the mixture was allowed to stand and separate into layers to obtain crude nitromethane. Further distillation yielded 721.1 g of nitromethane with a purity of 99.51% and a yield of 59.1%.

[0071] Comparative Example 2

[0072] Add 920 ml of water to 1380 kg (20 mol) of sodium nitrite, 1261.3 g (10 mol) of dimethyl sulfate, and 34.5 g of sodium carbonate. After mixing in a static mixing device, pump the mixture into the first plug flow reactor. The reactor contains 16 parallel tubes with an inner diameter of [missing information]. The reactor is 2m long and uses an aluminum-plastic composite pipe. The temperature of the hot zone of the first plug flow reactor is controlled at 50℃ and the pressure is 0.15MPa through a temperature control system. The flow rate is set to 100mL / min. The resulting reaction liquid is continuously fed into the distillation column, and the temperature of the distillation column is controlled at 100-110℃. After the distillation product is allowed to stand and separate into layers, crude nitromethane is obtained. The crude nitromethane is then further distilled to obtain 436.2g of nitromethane product with a purity of 99.22% and a yield of 35.7%.

[0073] Comparative Example 3

[0074] Add 920 ml of water to 1380 kg (20 mol) of sodium nitrite, 1261.3 g (10 mol) of dimethyl sulfate, and 34.5 g of sodium carbonate. After mixing in a static mixing device, pump the mixture into the first plug flow reactor. The reactor contains 16 parallel tubes with an inner diameter of [missing information]. The reactor is 2m long and uses an aluminum-plastic composite pipe. The temperature of the hot zone of the first plug flow reactor is controlled at 80℃ and the pressure is 0.15MPa through a temperature control system. The flow rate is set to 100mL / min. The resulting reaction liquid is continuously fed into the distillation column, and the temperature of the distillation column is controlled at 100-110℃. After the distillation product is allowed to stand and separate into layers, crude nitromethane is obtained. The crude nitromethane is then further distilled to obtain 798.6g of nitromethane product with a purity of 99.56% and a yield of 65.4%.

[0075] It is evident that using a single plug flow reactor to directly heat the reaction to a high temperature of 80°C is similar to the one-pot reaction in Comparative Example 1. Although it can achieve some of the effects of a plug flow reactor, it cannot fully achieve the ideal yield.

[0076] Comparative Example 4

[0077] Add 920 ml of water to 1380 kg (20 mol) of sodium nitrite, 1261.3 g (10 mol) of dimethyl sulfate, and 34.5 g of sodium carbonate. After mixing in a static mixing device, pump the mixture into the first plug flow reactor. The reactor contains 16 parallel tubes with an inner diameter of [missing information]. The tube is 2m long and made of aluminum-plastic composite. The temperature of the hot zone of the first plug flow reactor is controlled at 25℃, the pressure is 0.15MPa, and the flow rate is set to 100mL / min through the temperature control system. However, the target product nitromethane cannot be obtained.

[0078] If the reaction temperature is too low (below 30℃), the reaction cannot proceed; if the reaction temperature is too high (above 100℃), the chemical reaction will be too violent, which is detrimental to controlling production safety.

[0079] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

[0080] The foregoing embodiments and methods described in this invention may vary based on the capabilities, experience, and preferences of those skilled in the art.

[0081] Listing the steps of the method in a certain order in this invention does not constitute any restriction on the order of the method steps.

Claims

1. A method for the continuous synthesis of nitromethane, characterized in that, The method comprises the following steps: (1) mixing dimethyl sulfate, nitrite, catalyst and water to obtain a mixture; (2) continuously feeding the mixture obtained in step (1) into a first reactor to react at a first temperature to obtain a first reaction liquid; (3) continuously feeding the first reaction liquid into a second reactor to react at a second temperature to obtain a second reaction liquid; (4) continuously feeding the second reaction liquid into a distillation column to obtain a crude nitromethane product, and then performing rectification to obtain a nitromethane product; wherein the first reactor and the second reactor are both plug flow reactors, and the first temperature is less than the second temperature; the catalyst is a strong base weak acid salt.

2. The method according to claim 1, wherein: in step (1), a first raw material and a second raw material are provided, the first raw material comprises dimethyl sulfate, nitrite and catalyst, and does not comprise water, and the second raw material comprises water and does not comprise nitrite; or, the first raw material comprises dimethyl sulfate and nitrite, and does not comprise water, and the second raw material comprises water and catalyst, and does not comprise nitrite; the second raw material is added to the first raw material for mixing.

3. The method according to claim 1, wherein: the plug flow reactor is a plug flow reactor with a temperature control system; the plug flow reactor is provided with a straight pipe, a coil pipe, a U-shaped pipe, a tube bank or a combined pipe line formed by connecting any of them in parallel.

4. The method according to claim 3, wherein: the pipe line is made of a metal pipe, a plastic clad metal pipe or a plastic pipe.

5. The method according to claim 4, wherein: the pipe line is made of a metal pipe.

6. The method according to claim 4, wherein: the metal pipe is a galvanized pipe, a copper pipe or a stainless steel pipe.

7. The method according to claim 4, wherein: the plastic clad metal pipe is an aluminum plastic clad pipe.

8. The method according to claim 4, wherein: the plastic pipe is a PVC pipe or a PE pipe.

9. The method according to claim 3, wherein: the inner diameter of the pipe line of the plug flow reactor is 1.0-25.0 mm, and the length is 0.5-15 m.

10. The method according to claim 3, wherein: the inner diameter of the pipe line of the plug flow reactor is 2-10 mm.

11. The method according to claim 3, wherein: the length of the pipe line of the plug flow reactor is 0.5-2 m.

12. The method according to claim 1, wherein: the first temperature is 30-50℃; the second temperature is 80-100℃.

13. The method according to claim 1, wherein: the first temperature is 30-35℃.

14. The method according to claim 1, wherein: the second temperature is 90-100℃.

15. The method according to claim 1, wherein: the reaction pressure in the first reactor and the second reactor is 0.1-0.2 MPa.

16. The method according to claim 1, wherein: the nitrite is sodium nitrite or potassium nitrite.

17. The process as claimed in claim 1, wherein, the strong base weak acid salt is sodium carbonate, sodium bicarbonate, potassium carbonate or potassium bicarbonate.

18. The process as claimed in claim 1, wherein, the molar ratio of dimethyl sulfate and nitrite salt is 1:2 to 2.

2.

19. The process as claimed in any one of claims 1 to 11, wherein, the distillation temperature in step (4) is 100 to 110 °C.

20. The process as claimed in claim 19, wherein, the distillation in step (4) is atmospheric distillation.

21. The process as claimed in claim 19, wherein, step (4) further comprises the step of recovering nitromethane from the column still pot liquid.