WO2024120073A1

WO2024120073A1 - Continuous-flow synthesis method for nitromethane

Info

Publication number: WO2024120073A1
Application number: PCT/CN2023/128567
Authority: WO
Inventors: 田童; 黄进虎; 丁红林; 李延升; 鲁力; 时嘉鸿
Original assignee: 湖北富博化工有限责任公司; 湖北远大富驰医药化工股份有限公司
Priority date: 2022-12-06
Filing date: 2023-10-31
Publication date: 2024-06-13
Also published as: CN117466740A

Abstract

Disclosed in the present invention is a continuous-flow synthesis method for nitromethane. The method comprises: mixing dimethyl sulfate, nitrite, a catalyst and water to obtain a mixture, continuously feeding the obtained mixture into a first reactor, and reacting at a first temperature to obtain a first reaction solution; continuously feeding the first reaction solution into a second reactor, and reacting at a second temperature to obtain a second reaction solution; continuously feeding the second reaction solution into a distillation column to obtain a nitromethane crude product, and rectifying to obtain a nitromethane product, wherein the first reactor and the second reactor are both plug flow reactors, and the first temperature is lower than the second temperature. According to the method, the reaction conditions are mild, and the reaction process is easy to control; and by refining and accurately controlling the reaction temperatures of the two reaction stages, generation of by-products and energy consumption costs are reduced, potential safety hazards caused by violent foaming and fast material overflow in the reaction process are avoided, and the process safety and efficiency are greatly improved.

Description

A continuous flow synthesis method of nitromethane

Technical Field

The invention relates to the technical field of flow chemical synthesis, and in particular to a continuous flow synthesis method of nitromethane.

Background technique

Nitromethane is an important organic chemical product and organic synthesis intermediate. It has the characteristics of good selectivity, low viscosity and low volatility. It is widely used in the synthesis of polymer materials, and can also be used in the production of explosives, rocket fuels, pesticides, gasoline additives, coatings, textiles, food and paint industries. Nitromethane is also a liquid explosive with good performance. At the same time, it can be used as a fuel additive to improve the fuel's combustion value and reduce pollution. Many important organic chemical products, such as nitro alcohols, can be synthesized using nitromethane as a raw material. Therefore, it is also an important raw material for the pharmaceutical, pesticide and dye industries. In recent years, the market demand for nitromethane has gradually increased.

At present, there are two main methods for synthesizing nitromethane, namely, methane vapor nitration and dimethyl sulfate and sodium nitrite reaction. Methane vapor nitration: spray dilute nitric acid into mist to gasify it, and mix it with preheated methane (natural gas) to keep a certain ratio of nitric acid, methane and water vapor. The mixed gas enters a pipeline reactor with molten salt as the heating medium, and is directly nitrated under normal pressure and 450-550 ° C. The reaction product is condensed and absorbed by water, and the obtained nitromethane aqueous solution is distilled to obtain crude nitromethane, and then washed and distilled to obtain the finished product. The vapor phase nitration method has a high reaction temperature, high equipment requirements, low yield, and high reaction temperature has safety hazards. Dimethyl sulfate and sodium nitrite reaction method: sodium nitrite and dimethyl sulfate are added to the reactor for reaction, and the reaction product is condensed, distilled, cooled and layered, and then distilled to obtain the finished product. In addition, sodium nitrite can also be reacted with sodium chloroacetate and then heated. It is obtained by the reaction of nitrite and alkyl halide. In industry, other low-carbon alkanes (ethane, propane) can also be used to directly chlorine-phase nitrate The reaction product is a mixture of nitromethane, nitroethane and nitropropane, with low yield and difficult separation and purification. The reaction method of dimethyl sulfate and sodium nitrite has the characteristics of easy availability of raw materials, simple process and low cost, and is currently a method commonly used in industry. In specific implementation, the traditional process is a one-pot reaction of dimethyl sulfate and sodium nitrite, but the temperature of the existing kettle reactor is difficult to control, resulting in violent foaming during the reaction process, which brings about potential safety hazards of material impact and flash explosion, which is difficult to avoid even with the addition of a defoamer. In addition, during the reaction process, the product and by-products cannot be discharged in time due to the aggregation, which easily leads to a decrease in product yield and purity.

Summary of the invention

The present invention provides a continuous synthesis method of nitromethane, which solves the problem of serious foaming caused by failure to remove reaction materials in time, reduces the occurrence of side reactions accordingly, and improves the reaction yield and purity.

Specifically, the method comprises the following steps:

(1) mixing dimethyl sulfate, nitrite, a catalyst, and water to obtain a mixture;

(2) continuously feeding the mixture obtained in step (1) into a first reactor, reacting at a first temperature to obtain a first reaction solution;

(3) continuously feeding the first reaction liquid into the second reactor and reacting at a second temperature to obtain a second reaction liquid;

(4) continuously feeding the second reaction liquid into a distillation tower to obtain a crude nitromethane product, and then rectifying the crude nitromethane product;

Wherein, the first reactor and the second reactor are both plug flow reactors, and the first temperature is lower than the second temperature.

In particular, according to the method of the present invention, the material adding method in step (1) is to add the material containing water but not containing nitrite to the material containing nitrite but not containing water. The nitrite dissolving in water will absorb a large amount of heat, consuming most of the heat released by the reaction of nitrite and dimethyl sulfate, so it is beneficial to control the reaction temperature and make the reaction in the first reactor proceed gently.

Specifically, as in the above step (1), a first raw material and a second raw material are provided,

The first raw material comprises dimethyl sulfate, nitrite, and a catalyst, but does not comprise water, and the second raw material comprises water but does not comprise nitrite;

or,

The first raw material comprises dimethyl sulfate and nitrite, but does not comprise water, and the second raw material comprises water and a catalyst, but does not comprise nitrite;

Add the second raw material to the first raw material and mix.

Plug flow reactor refers to a type of tubular reactor, that is, under ideal flow conditions, the flow reactor has a strictly uniform radial velocity distribution, and there is no axial mixing, the material flows forward like a piston, this flow is called plug flow, there is no back mixing in the reactor. The flow in the actual plug flow reactor can be close to this ideal flow to varying degrees.

According to the method of the present invention, the first stage reaction is carried out in the first plug flow reactor at low temperature, and then the first reaction liquid is continuously pumped into the second plug flow reactor for reaction, and the second reaction liquid is continuously pumped into the distillation tower. While reacting quickly, the product is quickly taken out of the reaction system, reducing safety issues such as foaming caused by product aggregation, and greatly promoting the reaction balance, greatly improving the yield. The reaction of dimethyl sulfate and nitrite can be considered as a methylation reaction, and also a nitration reaction. The nitrite ion dissociated from nitrite (such as sodium nitrite) serves as an amphiphilic nucleophile. Therefore, for the reaction of nitrite (such as sodium nitrite) and dimethyl sulfate to generate nitromethane, nitromethane is generated when the nitrogen atom of the nitrite attacks the methyl group, and the main byproduct nitrosomethyl ester is generated when the oxygen atom attacks the methyl group. The reaction temperature required for dimethyl sulfate to remove two methyl groups is different. Considering that dimethyl sulfate hydrolyzes rapidly at high temperature, the first methyl group of dimethyl sulfate is easily removed, so the first stage needs to be carried out at a lower temperature. However, it is difficult for the second methyl group to leave. The second stage needs to react at a higher temperature to generate products, and the products need to be taken out of the reaction system as soon as possible to avoid the formation of gaseous by-products (alkyl nitrites, nitrogen oxides, carbon dioxide, etc.) that will cause strong foaming of the reaction medium. Even with the use of defoaming agents, it is difficult to control the strong foaming phenomenon.

The present invention divides the reaction of nitrite (e.g. sodium nitrite) and dimethyl sulfate into two stages: The reaction temperature of the two stages is refined and precisely controlled:

The main reactions at low temperature in the first stage are:
(CH ₃ ) ₂ SO ₄ +NaNO ₂ →CH ₃ SO ₄ Na+CH ₃ NO ₂

The main reactions of the second stage high temperature are:
CH ₃ SO ₄ Na+NaNO ₂ →Na ₂ SO ₄ +CH ₃ NO ₂

Specifically, according to the method of the present invention, the plug flow reactor is a plug flow reactor with a temperature control system, which is used to control the preheating temperature, the temperature during the reaction and the heat removal after the reaction;

The plug flow reactor is provided with straight tubes, coils, U-shaped tubes, tube arrays or any combination of these in series or in parallel.

The pipe material is a metal pipe, a plastic-coated metal pipe or a plastic pipe, preferably a metal pipe;

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

Preferably, the plastic-clad metal tube is an aluminum-plastic composite tube;

Preferably, the plastic tube is a PVC tube or a PE tube.

Specifically, the inner diameter of the pipeline of the plug flow reactor is The thickness of the elastic modulus is 1.0-25.0 mm (for example, 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 (for example, 0.5, 1.0, 1.5, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 14, 15 m), preferably 0.5-2 m.

Specifically, the first temperature is 30-50°C (eg, 30, 35, 40, 45, 50°C), preferably 30-35°C.

Specifically, the second temperature is 80-100°C (eg, 80, 85, 90, 95, 100°C), preferably 90-100°C.

The reaction at the first temperature is a low-temperature reaction. After the reaction using a conventional reactor, dimethyl sulfate will accumulate. When the temperature reaches the second temperature, dimethyl sulfate will react rapidly and release heat violently. The use of a plug flow reactor can well solve the problem of material accumulation and rapid and uneven reaction.

Specifically, the distillation temperature in step (4) is 100-110°C (e.g., 100°C, 105°C, 110°C), and the distillation is atmospheric pressure distillation.

Specifically, the reaction pressure in the first reactor and the second reactor is 0.1-0.2 MPa.

Specifically, the above-mentioned nitrite is sodium nitrite or potassium nitrite, especially sodium nitrite.

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.

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. The molar ratio of dimethyl sulfate to nitrite below or exceeding the selected range will significantly reduce the yield of the nitromethane product.

Specifically, the mass ratio of the catalyst to the 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), especially 0.02-0.06: 1. Too low or too high a catalyst dosage will reduce the yield of the nitromethane product.

Specifically, the mass ratio of water to nitrite in step (1) 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 cannot dissolve the raw materials well, and too much water will over-dilute the raw materials and cannot react well.

In one embodiment of the present invention, step (4) further comprises the step of recovering nitromethane from the bottom liquid of the distillation tower, specifically, collecting the bottom liquid at regular intervals, and then recovering the nitromethane crude product by distillation in another distillation tower, and distilling the nitromethane crude product alone or combining two nitromethane crude products to obtain a nitromethane product.

The invention also proposes the use of a plug flow reactor in synthesizing nitromethane by a dimethyl sulfate substitution method.

Specifically, the dimethyl sulfate substitution method refers to the synthesis of nitromethane by using dimethyl sulfate and a nitrite (such as sodium nitrite) solution to undergo a substitution reaction.

Specifically, the plug flow reactor has the above corresponding definitions of the present invention.

During the reaction process of the plug flow reactor, the material keeps a continuous and stable flow along the direction of movement. The product is uniformly taken out of the reaction system quickly after being generated, and does not accumulate in the reactor, thereby reducing the occurrence of side reactions and improving the product yield. The equipment used in the present invention occupies a small area, has a high reaction conversion rate, can realize continuous feeding and discharging, can greatly shorten the reaction time, has a high degree of automation, improves reaction selectivity, improves product yield and product purity, and has controllable online production safety risks, eliminating potential safety hazards.

Beneficial Effects

1. The present invention adopts a plug flow reactor. Compared with the one-pot method, the present invention has a short reaction residence time, a more precise controllable reaction temperature range, a safe and reliable process, stable process control, and a high product yield. Due to the structural limitations of the reactor, the traditional reactor production process has some structural disadvantages, such as a small heat exchange area, difficulty in timely removal of products, and uncontrolled reaction temperature. The small heat exchange area of the reactor will lead to the inability to remove the heat generated in the reaction process in time, and the temperature in the reactor is not controlled, which is prone to accidents such as splashing the reactor and splashing the materials due to the increase in the temperature in the reactor; the reaction products are not easy to be removed in time, and it is easy to generate by-products due to the product staying in the reactor, resulting in back mixing, long reaction time in the reactor, low reaction yield, and poor product quality. If the temperature of the reactor is not easy to control, it will lead to safety hazards such as foaming, splashing, and flash explosion in the reaction process, and the problem of foaming and splashing is difficult to avoid even if a defoaming agent is added. Intermittent reaction startup and shutdown are also prone to cause safety accidents.

2. The present invention particularly adopts a feeding method in which a material containing water but not containing nitrite is added to a material containing nitrite but not containing water. The heat absorption of nitrite dissolution is conducive to the control of the exothermic temperature of the reaction, the reaction conditions are milder, the reaction process is easy to control, and the generation of by-products and energy consumption costs are reduced;

3. The present invention adopts a method of continuously inputting materials into the first plug flow reactor for reaction, quickly feeding the intermediate product into the second plug flow reactor for reaction, promoting the advancement of the reaction balance in the second stage, quickly taking the second reaction liquid out of the reaction system, and then entering the distillation tower, and the product is continuously produced, thereby increasing the yield of the main product nitromethane while suppressing the generation of the by-product methyl nitrite, and greatly reducing the foaming phenomenon. Compared with the one-pot method, the method of the present invention also avoids the risk of flash explosion caused by the rapid increase in the temperature of the materials in the reactor;

4. The present invention divides the reaction of nitrite and dimethyl sulfate into two stages, and refines and accurately controls the reaction temperature of the two stages. The first plug flow reactor and the second plug flow reactor can be respectively configured with multiple reaction tubes in parallel, so as to realize the continuous production of automatic control of batching-low temperature reaction-high temperature reaction-distillation reaction in different equipment at the same time;

5. The existing traditional one-pot reaction process is inconvenient to change the reaction conditions, and the heat released by the reaction cannot be discharged in time, which is easy to cause local overheating. The plug flow reactor used in the present invention has a large unit heat exchange area, sufficient and timely heat exchange, so the reaction temperature is easy to control, the generation of by-products is reduced, and the reaction yield is improved. The yield of nitromethane produced can reach more than 80%, and the purity is more than 99.5%.

6. Compared with the traditional reactor reaction, the reaction continuity of the plug flow reactor is stronger, the reaction time required is shorter, the reaction rate is higher, and it is easier to achieve automatic control and emergency shutdown. The liquid holding capacity in the plug flow reactor of the present invention is less than 1/50 or even 1/100 of the existing reactor, the safety risk is controllable, the production is stable, the yield is improved, and it can be promoted industrially. The production of each ton of nitromethane product can save about 1,600 yuan in raw material costs.

Detailed ways

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 entity or operation. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the sentence "includes a ..." does not exclude the presence of other identical elements in the process, method, article or device including the element.

Unless otherwise defined, all scientific and technical terms used in the present invention have the same meanings as commonly understood by one of ordinary skill in the art to which the present invention relates.

[00136] Various publications, patents, and published patent specifications are cited herein, the disclosures of which are incorporated by reference in their entireties.

The technical solution of the present invention will be clearly and completely described below in conjunction with 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.

The examples are as follows:

Example 1

230 ml of water was added with 345 g (5 mol) of sodium nitrite, 315.3 g (2.5 mol) of dimethyl sulfate, and 8.6 g of sodium carbonate, mixed in a static mixer and pumped into the first plug flow reactor. The reactor contained 26 parallel tubes with an inner diameter of The pipeline of the first plug flow reactor is 0.5m long and made of stainless steel. The temperature of the hot zone of the first plug flow reactor is controlled at 30°C, the pressure is 0.1MPa, and the flow rate is set to 20mL/min through the temperature control system. The obtained first reaction liquid is continuously pumped into the second plug flow reactor. The structure of this reactor is the same as that of the first plug flow reactor. The temperature of its hot zone is controlled at 80°C, the pressure is 0.1MPa, and the flow rate is also set to 10mL/min. The obtained second reaction liquid is continuously fed into the distillation tower, and the temperature of the distillation tower is controlled at 100-110°C. As the reaction liquid continues to enter, continuous distillation is continuously carried out, and the distillation product is continuously produced. After static stratification, a crude nitromethane product is obtained, and the bottom liquid is collected from the bottom of the distillation tower, and then another distillation tower is used to distill and recover the crude nitromethane product. The crude nitromethane products are combined and distilled again to obtain 244.6 grams of nitromethane product with a purity of 99.51% and a yield of 80.14%.

Example 2

920 ml of water was added with 1380 g (20 mol) of sodium nitrite, 1261.3 g (10 mol) of dimethyl sulfate, and 34.5 g of sodium carbonate, mixed in a static mixer and pumped into the first plug flow reactor. The reactor contained 16 parallel tubes with an inner diameter of The length is 1m, and an aluminum-plastic composite pipe is selected. The temperature of the hot zone of the first plug flow reactor is controlled at 40°C, the pressure is 0.15MPa, and the flow rate is set to 100mL/min through the temperature control system. The first reaction liquid is continuously pumped into the second plug flow reactor. The structure of this reactor is the same as that of the first plug flow reactor. The temperature of its hot zone is controlled at 90°C, the pressure is 0.15MPa, and the flow rate is set to 100mL/min. The second reaction liquid is continuously fed into the distillation tower to control the temperature of the distillation tower. The temperature was controlled at 100-110° C., as the reaction liquid continued to enter, continuous distillation was continuously carried out, and distillation products were continuously produced. After static stratification, crude nitromethane was obtained. The bottom liquid was collected from the bottom of the distillation tower, and then distilled and recovered by another distillation tower to obtain the crude nitromethane product. The crude nitromethane products were combined and distilled again to obtain 1037.3 grams of nitromethane product with a purity of 99.93% and a yield of 85.02%.

Example 3

920 ml of water was added with 1449 g (21 mol) of sodium nitrite, 1261.3 g (10 mol) of dimethyl sulfate, and 55.2 g of sodium carbonate, mixed in a static mixer and pumped into the first plug flow reactor. The reactor contained 10 parallel U-shaped tubes with an inner diameter of The pipeline of the first plug flow reactor is 2m long and a copper tube is selected. The temperature of the hot zone of the first plug flow reactor is controlled at 35°C, the pressure is 0.15MPa, and the flow rate is set to 400mL/min through a temperature control system. The obtained first reaction liquid is continuously pumped into the second plug flow reactor. The pipeline structure of the second plug flow reactor is the same as that of the first plug flow reactor. The temperature of its hot zone is controlled at 100°C, the pressure is 0.15MPa, and the flow rate is set to 400mL/min. The obtained second reaction liquid is continuously fed into the distillation tower, and the temperature of the distillation tower is controlled at 100-110°C. As the reaction liquid continues to enter, continuous distillation is continuously carried out, and the distillation product is continuously produced. After static stratification, a crude nitromethane product is obtained, and the bottom liquid is collected from the bottom of the distillation tower, and then another distillation tower is used to distill and recover the crude nitromethane product. The crude nitromethane products are combined and then distilled to obtain 1065.6 grams of nitromethane product with a purity of 99.98% and a yield of 87.34%.

Example 4

27.3 kg of sodium bicarbonate was dissolved in 920 liters of water, and then 1380 kg (20 kmol) of sodium nitrite and 1261.3 kg (10 kmol) of dimethyl sulfate were added, mixed in a static mixer and pumped into the first plug flow reactor. The reactor contained 10 parallel coils with an inner diameter of The first plug flow reactor has a pipeline length of 10m and is made of stainless steel. The temperature of the hot zone of the first plug flow reactor is controlled at 35°C, the pressure is 0.2MPa, and the flow rate is set to 10L/min through the temperature control system. The first reaction liquid is continuously pumped into the second plug flow reactor. The reactor is the same as the first plug flow reactor, and its hot zone temperature is controlled at 90°C, and the pressure and flow rate are also the same. The second reaction liquid is continuously fed into the distillation tower to control the distillation. The tower temperature is controlled at 100-110°C. As the reaction liquid continuously enters, continuous distillation is continuously carried out, and the distillation product is continuously produced. After static stratification, a crude nitromethane product is obtained. The bottom liquid is collected from the bottom of the distillation tower, and then distilled and recovered by another distillation tower to obtain a crude nitromethane product. The crude nitromethane products are combined and distilled again to obtain 1050.6 kg of nitromethane product with a purity of 99.92% and a yield of 86.11%.

Example 5

920 liters of water were added with 1380 kg (20 kmol) of sodium nitrite, 1261.3 kg (10 kmol) of dimethyl sulfate, and 34.5 kg of sodium carbonate, mixed in a static mixer and pumped into the first plug flow reactor. The reactor contained 9 parallel tubes with an inner diameter of The pipeline of the first plug flow reactor is 5m long and made of stainless steel. The temperature of the hot zone of the first plug flow reactor is controlled at 50°C, the pressure is 0.2MPa, and the flow rate is set to 400L/min through the temperature control system. The obtained first reaction liquid is continuously pumped into the second plug flow reactor. The structure of this reactor is the same as that of the first plug flow reactor. The temperature of its hot zone is controlled at 100°C, the pressure is 0.2MPa, and the flow rate is set to 400L/min. The obtained second reaction liquid is continuously fed into the distillation tower, and the temperature of the distillation tower is controlled at 100-110°C. As the reaction liquid continues to enter, continuous distillation is continuously carried out, and the distillation product is continuously produced. After static stratification, a crude nitromethane product is obtained, and the bottom liquid is collected from the bottom of the distillation tower, and then another distillation tower is used to distill and recover the crude nitromethane product. The crude nitromethane products are combined and distilled again to obtain 995.6 kg of nitromethane product with a purity of 99.61% and a yield of 81.28%.

Embodiments 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 is nearly completed, and the feeding can be continued after sufficient mixing to achieve this purpose.

Comparative Example 1

1380 g (20 mol) of sodium nitrite, 34.5 g of sodium carbonate and 920 ml of water were added to the reaction vessel respectively, and 1261.3 g (10 mol) of dimethyl sulfate was added dropwise within half an hour. The mixture was stirred and heated. The temperature was controlled below 70°C. After distillation for 2 hours, crude nitromethane was obtained after static stratification. The crude nitromethane product was then distilled to obtain 721.1 g of nitromethane with a purity of 99.51% and a yield of 59.1%.

Comparative Example 2

920 ml of water was added with 1380 kg (20 mol) of sodium nitrite, 1261.3 g (10 mol) of dimethyl sulfate, and 34.5 g of sodium carbonate, mixed in a static mixer and pumped into the first plug flow reactor. The reactor contained 16 parallel tubes with an inner diameter of The length is 2m, and an aluminum-plastic composite pipe is selected. The temperature of the hot zone of the first plug flow reactor is controlled at 50°C through a temperature control system, the pressure is 0.15MPa, and the flow rate is set to 100mL/min. The obtained reaction liquid is continuously fed into the distillation tower, and the temperature of the distillation tower is controlled at 100-110°C. After static stratification of the distillation product, a crude nitromethane product is obtained. The crude nitromethane product is further distilled to obtain 436.2 grams of nitromethane product with a purity of 99.22% and a yield of 35.7%.

Comparative Example 3

920 ml of water was added with 1380 kg (20 mol) of sodium nitrite, 1261.3 g (10 mol) of dimethyl sulfate, and 34.5 g of sodium carbonate, mixed in a static mixer and pumped into the first plug flow reactor. The reactor contained 16 parallel tubes with an inner diameter of The length is 2m, and an aluminum-plastic composite pipe is selected. The temperature of the hot zone of the first plug flow reactor is controlled at 80°C through a temperature control system, the pressure is 0.15MPa, and the flow rate is set to 100mL/min. The obtained reaction liquid is continuously fed into a distillation tower, and the temperature of the distillation tower is controlled at 100-110°C. After static stratification of the distillation product, a crude nitromethane product is obtained. The crude nitromethane product is further distilled to obtain 798.6 grams of nitromethane product with a purity of 99.56% and a yield of 65.4%.

It can be seen that only one plug flow reactor is used to directly heat up to a high temperature of 80°C for reaction, which is similar to the one-pot reaction in Comparative Example 1. Although it can exert a certain effect of a plug flow reactor, it cannot fully achieve the ideal yield.

Comparative Example 4

920 ml of water was added with 1380 kg (20 mol) of sodium nitrite, 1261.3 g (10 mol) of dimethyl sulfate, and 34.5 g of sodium carbonate, and the mixture was mixed in a static mixer and then pumped into the first plug flow reactor. The reactor contained 16 parallel tubes with an inner diameter of The length is 2m, and the aluminum-plastic composite pipe is selected. The temperature of the hot zone of the first plug flow reactor is controlled at 25℃ and the pressure is 0.15MPa through the temperature control system. The speed was set to 100 mL/min, and the target product nitromethane could not be obtained.

If the reaction temperature is too low (below 30°C), the reaction cannot proceed; if the reaction temperature is too high (above 100°C), the chemical reaction is too violent, which is not conducive to controlling production safety.

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 principle of the present invention should be included in the protection scope of the present invention.

The aforementioned embodiments and methods described in the present invention may be varied based on the ability, experience and preference of those skilled in the art.

In the present invention, merely listing the steps of the method in a certain order does not constitute any limitation on the order of the method steps.

Claims

A continuous synthesis method of nitromethane, characterized in that it comprises the following steps:

(1) mixing dimethyl sulfate, nitrite, a catalyst, and water to obtain a mixture;

(2) continuously feeding the mixture obtained in step (1) into a first reactor, reacting at a first temperature to obtain a first reaction solution;

(3) continuously feeding the first reaction liquid into the second reactor and reacting at a second temperature to obtain a second reaction liquid;

(4) continuously feeding the second reaction liquid into a distillation tower to obtain a crude nitromethane product, and then rectifying the crude nitromethane product;

Wherein, the first reactor and the second reactor are both plug flow reactors, and the first temperature is lower than the second temperature.
The method according to claim 1, characterized in that

The material adding method of step (1) is to add the material containing water but not containing nitrite into the material containing nitrite but not containing water.
The method according to claim 1, characterized in that

The plug flow reactor is a plug flow reactor with a temperature control system;

The plug flow reactor is provided with straight tubes, coils, U-shaped tubes, tube arrays or any combination of these in series or in parallel.
The method according to claim 3, characterized in that

The pipe material is a metal pipe, a plastic-coated metal pipe or a plastic pipe, preferably a metal pipe;

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

Preferably, the plastic-clad metal pipe is an aluminum-plastic composite pipe;

Preferably, the plastic tube is a PVC tube or a PE tube.
The method according to claim 3, characterized in that

The inner diameter of the pipeline of the plug flow reactor The thickness is 1.0-25.0 mm, preferably 2-10 mm; the length is 0.5-15 m, preferably 0.5-2 m.
The method according to claim 1, characterized in that

The first temperature is 30-50°C, preferably 30-35°C;

The second temperature is 80-100°C, preferably 90-100°C.
The method according to claim 1, characterized in that

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

The nitrite is sodium nitrite or potassium nitrite;

The catalyst is a base or a salt of a strong base and a weak acid;

Preferably, the base is sodium hydroxide or potassium hydroxide;

Preferably, the strong base and weak acid salt is sodium carbonate, sodium bicarbonate, potassium carbonate or potassium bicarbonate.
The method according to claim 1, characterized in that

The molar ratio of dimethyl sulfate to nitrite is 1:2-2.2.
The method according to any one of claims 1 to 5, characterized in that

The distillation temperature in step (4) is 100-110° C.;

Preferably, the distillation in step (4) is atmospheric distillation;

Preferably, step (4) further comprises the step of recovering nitromethane from the bottom liquid of the distillation tower.