A system and method for producing dimethyl carbonate

Abstract

The embodiment of the present application provides a system and method for preparing dimethyl carbonate, and relates to the technical field of chemical industry. The system for preparing dimethyl carbonate comprises: a premixer, which is used for reacting nitrogen monoxide with oxygen to generate a first product comprising nitrogen oxides; a synthesis tower, which is used for reacting methanol and the first product to generate a second product comprising methyl nitrite; a carbonyl synthesis reactor, which is used for performing carbonyl synthesis catalytic reaction on the second product and carbon monoxide to generate a third product comprising nitrogen monoxide and dimethyl carbonate; and an absorption tower, which is provided with an absorbent, and the absorbent is used for absorbing dimethyl carbonate and converting into a liquid fourth product comprising dimethyl carbonate and a gaseous fifth product comprising nitrogen monoxide. Through the above system, the danger caused by excessively violent reaction in the production process is reduced, and the safety of production is improved.

Description

Technical Field

[0001] This application relates to the field of chemical technology, and in particular to a system and method for preparing dimethyl carbonate. Background Technology

[0002] Dimethyl carbonate (DMC), due to its presence of carbonyl, methyl, and methoxy functional groups, can participate in various types of reactions such as carbonylation, transesterification, and addition. Furthermore, DMC itself is non-toxic, harmless, and environmentally friendly, making it a widely used chemical raw material. Its production is characterized by safety, convenience, low pollution, and ease of transportation, leading to its widespread use in cosmetics, lithium-ion battery electrolytes, pharmaceuticals, pesticides, fertilizers, and detergents.

[0003] In the methanol oxidative carbonylation process for producing dimethyl carbonate, nitric oxide, methanol, and oxygen are first introduced into a synthesis unit to react and generate methyl nitrite. Then, methyl nitrite reacts with carbon monoxide to generate dimethyl carbonate.

[0004] However, in the above process, oxygen and nitric oxide mix rapidly and undergo a strong exothermic oxidation reaction to generate nitrogen oxides. At the same time, under high temperature conditions, methanol and nitrogen oxides will further react to generate methyl nitrite. Furthermore, the decomposition of methyl nitrite at high temperature will generate a large amount of heat of decomposition, leading to a rapid increase in temperature and pressure in the synthesis unit and causing the reaction to run away from control. Summary of the Invention

[0005] This application provides a system and method for preparing dimethyl carbonate, which solves the problem that when nitric oxide, methanol and oxygen are introduced into a synthesis device for reaction, the reaction is violent and easily leads to runaway reaction.

[0006] In a first aspect, embodiments of this application provide a system for preparing dimethyl carbonate, comprising:

[0007] A premixer for reacting nitric oxide with oxygen to produce a first product comprising nitrogen oxides;

[0008] A synthesis tower is connected to the premixer and a methanol feed tank is connected to the synthesis tower for reacting methanol and the first product to produce a second product including methyl nitrite.

[0009] A carbonyl synthesis reactor, connected to the synthesis tower, is used for a carbonyl synthesis catalytic reaction between a second product and carbon monoxide to produce a third product including nitric oxide and dimethyl carbonate.

[0010] An absorption tower is connected to the carbonyl synthesis reactor. The absorption tower is equipped with an absorbent for absorbing dimethyl carbonate and converting it into a liquid fourth product including dimethyl carbonate and a gaseous fifth product including nitric oxide.

[0011] In one possible implementation, a preprocessor is also included, connected to the absorption tower, to absorb residual methanol in the fifth product to form a sixth product comprising nitric oxide.

[0012] In one possible implementation, the preprocessor is connected to the premixer to pass the sixth product into the premixer for recycling as a raw material.

[0013] In one possible implementation, a cooler is also included, and a circulating pump is also provided on the synthesis tower. One end of the cooler is connected to the circulating pump, and the other end is connected to the synthesis tower to circulate and cool the synthesis tower.

[0014] Secondly, embodiments of this application provide a method for preparing dimethyl carbonate, using a system for preparing dimethyl carbonate, the method comprising:

[0015] Nitric oxide and oxygen are passed into a premixer to react and produce a first product including nitrogen oxides.

[0016] The first product is fed into a synthesis tower, and methanol is introduced into the synthesis tower to react the methanol with the first product to produce a second product including methyl nitrite.

[0017] The second product and carbon monoxide are fed into the carbonyl synthesis reactor to cause the second product and carbon monoxide to undergo a carbonyl synthesis catalytic reaction to produce a third product including nitric oxide and dimethyl carbonate.

[0018] The third product is passed into an absorption tower so that it comes into contact with the absorbent in the absorption tower to form a liquid fourth product including dimethyl carbonate and a gaseous fifth product including nitric oxide.

[0019] In one possible implementation, after the third product is passed into the absorption tower, the fifth product is further passed into a preprocessor to absorb residual methanol in the fifth product, forming a sixth product containing nitric oxide.

[0020] In one possible implementation, after the fifth product is fed into the preprocessor, the sixth product is fed into the premixer for recycling as a raw material.

[0021] In one possible implementation, the methanol content in the sixth product is less than 1000 ppm; and in the premixer, the volume ratio of the oxygen introduced to the nitric oxide in the sixth product is 1:5 to 1:8.

[0022] In one possible implementation, when the nitric oxide and oxygen are introduced into the premixer for reaction, the method further includes: detecting the current concentration C1 of the oxidant in the premixer and the current temperature T1 in the premixer;

[0023] The preset reaction temperature in the premixer is T, and the preset concentration of the oxidant is C;

[0024] When T < T1 < T+30℃ or C < C1 < C+3%, reduce the oxygen input and lower the temperature of the premixer; when T1 ≥ T+30℃ or C1 ≥ C+3%, stop the oxygen input and lower the temperature of the premixer.

[0025] In one possible implementation, when the first product is fed into the synthesis tower, the mass ratio of methanol to the first product is 4:1 to 10:1; and the feed temperature of the methanol is 5 to 30°C.

[0026] The methanol is introduced into the synthesis tower from the top, and the first product is introduced into the synthesis tower from the bottom and comes into countercurrent contact with the methanol so that the methanol absorbs the heat released by the reaction.

[0027] This application provides a system and method for preparing dimethyl carbonate. The system involves reacting nitric oxide with oxygen in a premixer to generate a first product including nitrogen oxides. The first product is then reacted with methanol in a synthesis tower to generate methyl nitrite. The methyl nitrite is then reacted with carbon monoxide in a carbonyl synthesis reactor to generate more methyl nitrite. Finally, the methyl nitrite is liquefied and separated in an absorption tower. By decomposing the methyl nitrite preparation reaction into two separate, stepwise reactions in two different devices, the simultaneous introduction of combustibles such as methanol during oxygen feeding can be avoided. This prevents the strong exothermic oxidation reaction between oxygen and nitric oxide, which could lead to further heat generation from the decomposition of methyl nitrite at high temperatures, potentially causing a runaway reaction and improving the controllability and safety of the production process. Attached Figure Description

[0028] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0029] Figure 1 This is a schematic diagram of the system for preparing dimethyl carbonate provided in this application;

[0030] Figure 2 This is a flowchart of the method for preparing dimethyl carbonate provided in this application.

[0031] Explanation of reference numerals in the attached figures:

[0032] 100. Premixer; 200. Synthesis tower; 210. Cooler; 220. Circulation pump; 300. Methanol feed tank; 400. Carbonyl synthesis reactor; 500. Absorber; 600. Preprocessor; 700. Compressor; 800. Preheater.

[0033] The accompanying drawings illustrate specific embodiments of this application, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the concept in any way, but rather to illustrate the concept of this application to those skilled in the art through reference to particular embodiments. Detailed Implementation

[0034] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this application as detailed in the appended claims.

[0035] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0036] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "fixation," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between components; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise expressly limited. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0037] In this application, unless otherwise expressly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "on top of," and "over" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0038] Dimethyl carbonate (DMC), due to its presence of carbonyl, methyl, and methoxy functional groups, can participate in various types of reactions such as carbonylation, transesterification, and addition. Furthermore, DMC itself is non-toxic, harmless, and environmentally friendly, making it a widely used chemical raw material. Its production is characterized by safety, convenience, low pollution, and ease of transportation, leading to its widespread use in cosmetics, lithium-ion battery electrolytes, pharmaceuticals, pesticides, fertilizers, and detergents.

[0039] There are several production processes for dimethyl carbonate (DMC), including the phosgene method, transesterification method, methanol oxidation carbonylation method, urea alcoholysis method, and direct carbon dioxide oxidation method. Among these, the CO gas-phase oxidation carbonylation method for synthesizing DMC has advantages such as simple raw material preparation and low process cost, making it a relatively advanced method for DMC synthesis.

[0040] In the methanol oxidative carbonylation process for producing dimethyl carbonate, nitric oxide, methanol, and oxygen are first introduced into a synthesis unit to react and generate methyl nitrite. Then, methyl nitrite reacts with carbon monoxide to generate dimethyl carbonate.

[0041] However, in the above process, oxygen and nitric oxide mix rapidly and undergo a strong exothermic oxidation reaction to generate nitrogen oxides. At the same time, under high temperature conditions, methanol and nitrogen oxides will further react to generate methyl nitrite. Furthermore, the decomposition of methyl nitrite at high temperature will generate a large amount of heat of decomposition, leading to a rapid increase in temperature and pressure in the synthesis unit and causing the reaction to run away from control.

[0042] This application provides a system and method for preparing dimethyl carbonate. The system involves reacting nitric oxide with oxygen in a premixer to generate a first product including nitrogen oxides. The first product is then reacted with methanol in a synthesis tower to generate methyl nitrite. The methyl nitrite is then reacted with carbon monoxide in a carbonyl synthesis reactor to generate more methyl nitrite. Finally, the methyl nitrite is liquefied and separated in an absorption tower. By decomposing the methyl nitrite preparation reaction into two separate stepwise reactions in two different devices, the simultaneous introduction of combustibles such as methanol during oxygen feeding can be avoided. This prevents the strong exothermic oxidation reaction between oxygen and nitric oxide, which could lead to further heat generation from the decomposition of methyl nitrite at high temperatures, thus improving the controllability and safety of the production process.

[0043] The technical solution of this application and how the technical solution of this application solves the above-mentioned technical problems are described in detail below with specific embodiments. These specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described again in some embodiments. The embodiments of this application will now be described with reference to the accompanying drawings.

[0044] In a first aspect, embodiments of this application provide a system for preparing dimethyl carbonate, referring to... Figure 1 Systems for preparing dimethyl carbonate include:

[0045] Premixer 100 is used to react nitric oxide with oxygen to produce a first product including nitrogen oxides;

[0046] Synthesis tower 200 is connected to premixer 100. A methanol feed tank 300 is connected to synthesis tower 200 to supply methanol and the first product to react and produce a second product including methyl nitrite.

[0047] A carbonyl synthesis reactor 400 is connected to a synthesis tower 200 and is used for a carbonyl synthesis catalytic reaction between the second product and carbon monoxide to produce a third product including nitric oxide and dimethyl carbonate.

[0048] An absorber tower 500 is connected to a carbonyl synthesis reactor 400. An absorbent is installed in the absorber tower 500 to absorb dimethyl carbonate and convert it into a liquid fourth product including dimethyl carbonate and a gaseous fifth product including nitric oxide.

[0049] The reaction in the premixer 100 is: 2NO + O2 = 2NO2;

[0050] NO2 + NO = N2O3

[0051] The reaction in synthesis tower 200 is: CH3OH + N2O3 → CH3ONO + HONO;

[0052] CH3OH + HONO → CH3ONO + H2O

[0053] The reaction in carbonyl synthesis reactor 400 is as follows:

[0054] CH3ONO + CO → (CH3O)2CO + 2NO

[0055] By decomposing the reaction for preparing methyl nitrite into two separate stepwise reactions, it is possible to avoid the simultaneous introduction of combustibles such as methanol when oxygen is fed in. This prevents the strong exothermic oxidation reaction between oxygen and nitric oxide from causing methyl nitrite to decompose at high temperatures and generate further heat, which could lead to a runaway reaction and improve the controllability and safety of production.

[0056] In one possible implementation, a preprocessor 600 is also included, which is connected to an absorption tower 500 to absorb residual methanol in the fifth product to form a sixth product comprising nitric oxide.

[0057] The preprocessor 600 is filled with 4A molecular sieve to separate methanol, thereby reducing the methanol content in the fifth product.

[0058] Furthermore, the preprocessor 600 is connected to the premixer 100 to pass the sixth product into the premixer 100 for recycling as raw material.

[0059] The gas generated in the carbonyl synthesis reactor 400 is processed by the preprocessor 600 to absorb methanol, reducing the methanol content in the fifth product to a safe range to form the sixth product. The sixth product is then fed into the preprocessor 600 as a raw material for recycling. Controlling the methanol content in the sixth product reduces the content of combustibles in the system before oxygen feeding and avoids the exothermic reaction of nitrogen oxides and methanol to form methyl nitrite, thus reducing the safety risks of the premixer 100 and the synthesis tower 200.

[0060] In one possible implementation, a cooler 210 is also included, and a circulating pump 220 is also provided on the synthesis tower 200. One end of the cooler 210 is connected to the circulating pump 220, and the other end is connected to the synthesis tower 200 to circulate and cool the synthesis tower 200.

[0061] The methanol feedstock tank 300 is connected to the top of the cooling tower, and the methanol feed temperature in the methanol feedstock tank 300 is lower than the temperature of the first product. The premixer 100 is connected to the bottom of the synthesis tower 200, and the first product enters the synthesis tower 200 from the bottom, with the flow direction of the first product opposite to that of the methanol. During the reaction between the first product and methanol, the lower-temperature methanol carries away some of the heat generated by the reaction, thus playing a cooling role and preventing the reaction from getting out of control.

[0062] Furthermore, by setting up a circulation pipeline on the synthesis tower 200, and installing a circulation pump 220 and a cooler 210 on the circulation pipeline, the temperature of the bottom liquid in the synthesis tower 200 can be reduced by the external cooler 210, thereby achieving the effect of cooling.

[0063] The top of the synthesis tower 200 has an exhaust port to discharge a portion of the gas as purge gas, thereby balancing the reaction and controlling the pressure. Specifically, by volumetric flow rate, the purge gas in the synthesis tower 200 accounts for 0.05% to 1% of the total volume of the second product, more preferably 0.05% to 0.5% of the total volume of the second product.

[0064] Furthermore, a compressor 700 and a preheater 800 are also provided between the synthesis tower 200 and the carbonyl synthesis reactor 400. The compressor 700 compresses the second product, and after preheating by the preheater 800, it is introduced into the carbonyl synthesis reactor 400 to maintain the temperature of the reaction raw materials in the carbonyl synthesizer and improve the efficiency of the carbonyl synthesis reaction.

[0065] Secondly, embodiments of this application provide a method for preparing dimethyl carbonate, referring to... Figure 1 and Figure 2 Using the above-described system for preparing dimethyl carbonate, a method for preparing dimethyl carbonate includes:

[0066] Nitric oxide and oxygen are passed into premixer 100 to react and produce a first product including nitrogen oxides.

[0067] The first product is fed into synthesis tower 200, and methanol is introduced into synthesis tower 200 to react with the first product to produce a second product including methyl nitrite.

[0068] The second product and carbon monoxide are fed into the carbonyl synthesis reactor 400 to cause the second product and carbon monoxide to undergo a carbonyl synthesis catalytic reaction to produce a third product including nitric oxide and dimethyl carbonate.

[0069] The third product is introduced into the absorption tower 500 so that it comes into contact with the absorbent in the absorption tower 500 to form a liquid fourth product including dimethyl carbonate and a gaseous fifth product including nitric oxide.

[0070] Furthermore, after the third product is fed into the absorption tower 500, the process also includes feeding the fifth product into the preprocessor 600 to absorb the residual methanol in the fifth product, forming a sixth product containing nitric oxide.

[0071] Furthermore, after the fifth product is fed into the preprocessor 600, the process also includes feeding the sixth product into the premixer 100 for recycling as raw material.

[0072] The sixth product is recycled as a raw material. The fifth product contains gases such as nitric oxide, methyl nitrite, and methanol. After the methanol is separated by the molecular sieve in the preprocessor 600, the methanol content in the sixth product is reduced to below 1000 ppm, thereby avoiding the possibility of methanol reacting in the premixer 100 and causing the reaction to runaway in the premixer 100.

[0073] The use of preprocessor 600 to reduce the methanol content in the fifth product before oxygen feed can reduce the content of combustibles in the system before oxygen feed, and at the same time avoid the exothermic reaction between nitrogen oxides and methanol in the fifth product to form methyl nitrite, thereby reducing the safety risks of premixer 100 and synthesis tower 200.

[0074] In one possible implementation, the methanol content in the sixth product is less than 1000 ppm; in the premixer 100, the volume ratio of the oxygen introduced to the nitric oxide in the sixth product is 1:5 to 1:8.

[0075] Furthermore, the methanol in the fifth product is absorbed by the preprocessor 600, so that the methanol content in the sixth product is less than 500 ppm. The oxygen introduced into the premixer 100 is pure oxygen, and the volume ratio of oxygen to nitric oxide in the sixth product is 1:5 to 1:6. This controls the amount of oxygen introduced, reducing the possibility of oxygen entering the synthesis tower 200 and improving the safety of the synthesis tower 200.

[0076] In one possible implementation, when nitric oxide and oxygen are introduced into the premixer 100 for reaction, the method further includes: detecting the current concentration C1 of the oxidant in the premixer 100 and the current temperature T1 in the premixer 100.

[0077] The preset reaction temperature in the premixer 100 is T, and the preset concentration of the oxidant is C;

[0078] When T < T1 < T+30℃ or C < C1 < C+3%, reduce the oxygen input and lower the temperature of the premixer 100; when T1 ≥ T+30℃ or C1 ≥ C+3%, stop the oxygen input and lower the temperature of the premixer 100.

[0079] An oxidant detector and a temperature detector are installed in the premixer 100, wherein the oxidant detector is an online instrument for detecting nitrogen oxides and oxygen. This includes NO. X Online infrared analyzers and laser oxygen analyzers, in which the sum of the detected values ​​for nitrogen oxides and oxygen is the oxidant concentration.

[0080] The premixer 100 is also equipped with a controller, which presets the reaction temperature to T and the oxidant concentration to C. When T < T1 < T+30℃ or C < C1 < C+3%, the controller reduces the oxygen input and lowers the temperature of the premixer 100; when T1 ≥ T+30℃ or C1 ≥ C+3%, the controller stops the oxygen input and lowers the temperature of the premixer 100.

[0081] By controlling the oxygen flow rate of the premixer 100 and decomposing the overall reaction into multiple steps, a segmented control method is adopted. Temperature and oxidant concentration are monitored online in the premixer 100, and the monitoring of oxygen feed and temperature in the premixer 100 is combined to achieve stable operation of the process over a long period of time.

[0082] Specifically, the carbonyl synthesis reactor 400 is packed with a supported Pd-based catalyst. The supported Pd-based catalyst, calculated by weight of the total catalyst, has a Pd loading of 0.1% to 2 wt%, more preferably 0.5% to 2 wt%. The support comprises one or a mixture of several of alumina, silica, hydrotalcite, and spinel.

[0083] The second product and carbon monoxide are heated in a preheater 800 to bring them to the reaction temperature. For example, the carbonylation catalytic reaction temperature is 80–130°C; furthermore, the reaction temperature can be set to 100–130°C for better reaction results.

[0084] The absorbent in the absorption tower 500 is preferably dimethyl oxalate and methanol. The mass ratio of the absorbent to dimethyl carbonate in the third product is 1:1 to 3:1, or even better, 1:1 to 2:1, to achieve good absorption while reducing the amount of absorbent used.

[0085] In one possible implementation, when the first product is fed into the synthesis tower 200, the mass ratio of methanol to the first product is 4:1 to 10:1; the feed temperature of methanol is 5°C to 30°C.

[0086] Methanol is introduced into synthesis tower 200 from the top, and the first product is introduced into synthesis tower 200 from the bottom and comes into countercurrent contact with methanol so that the heat released by the reaction is absorbed by the methanol.

[0087] In one specific cyclic embodiment, carbon monoxide and the second product are mixed and preheated in a preheater 800. The introduced gas, by volume, contains 10.0% carbon monoxide, 15.0% methyl nitrite, 4.0% nitric oxide, 5.0% methanol, 1.7% carbon dioxide, and 63.9% nitrogen, and contains some impurities. The mixed gas is introduced at 6000 Nm³. 3 A flow rate of [flow rate] / h is fed into preheater 800 for heating. After preheating to 100℃, it is added to tubular carbonyl synthesis reactor 400. Carbonyl synthesis reactor 400 consists of 5000 tubes with a diameter of 30.5mm and a length of 8000mm. The upper two-thirds of the length of the reaction tubes is filled with carbonyl synthesis palladium catalyst, in which the Pd loading is 0.5wt%, and alumina is used as the support. The carbonyl synthesis reaction occurs under the conditions of reaction temperature 115℃ and reaction pressure 0.5MPaG to produce dimethyl carbonate, producing a third product containing dimethyl carbonate.

[0088] The third product is added as a gas to the lower part of an absorber 500 with an inner diameter of 1600 mm and a height of 8000 mm, packed with Pall rings, under heated conditions. Dimethyl oxalate is added from the top of the absorber 500 at a flow rate of 1500 kg / h. The liquid component at the bottom of the absorber 500 has a flow rate of 3392 kg / h and consists of a condensed liquid fraction of 44.6 wt% dimethyl oxalate, 42.6 wt% dimethyl carbonate, and 3.0 wt% methanol. The vapor phase at the top of the column is the fifth product, flowing at a velocity of 5328 Nm. 3 The fifth product, discharged at a rate of / h, comprises, by volume, 4.5% carbon monoxide, 3.4% methyl nitrite, 18.0% nitric oxide, 4.5% methanol, 1.9% carbon dioxide, and 71.9% nitrogen—a non-condensable gas fraction. This fifth product is then introduced into preprocessor 600, which has a capacity of 3m³. 3 The mixture is packed with 4A molecular sieves and heated to 30°C to separate methanol, reducing the methanol content in the sixth product to 800 ppm. The sixth product is then passed into a premixer 100 with an oxygen feed rate of 190 Nm³. 3 / h, reacting in premixer 100 to produce a first product containing nitrogen oxides, which, by volume, contains 4.5% carbon monoxide, 3.4% methyl nitrite, 5.5% nitrogen oxides, 8.0% nitric oxide, 1.9% carbon dioxide and 71.9% nitrogen.

[0089] In the above reaction process, the content of organic compounds (including carbonates, methanol, nitrites, oxalates, etc.) in the gas and liquid phases was analyzed using a gas chromatograph 8090 equipped with an HP-VOC capillary column to determine the volume content of each component in the gas and liquid phases at each stage.

[0090] The first product is added to the bottom of a synthesis tower 200 with a diameter of 6300 mm and a height of 10000 mm, packed with 350Y packing. Methanol is added at the top of the synthesis tower 200 at a flow rate of 26000 kg / h. The circulating gas contacts the methanol countercurrently, and a methanol solution containing 36 wt% water is discharged from the bottom of the synthesis tower 200. Further, the methanol and aqueous solution in the synthesis tower 200 can be passed into a methanol dehydration tower to obtain dehydrated methanol, which can be used as part of the methanol feed to the synthesis tower 200. The second product discharged from the top of the synthesis tower 200 is divided into two parts. The first part is compressed by compressor 700 and supplied as raw material to the carbonyl synthesis reactor 400. The other part is discharged at 5 Nm³. 3 The flow rate is / h as the purge gas emission.

[0091] The reaction conditions in premixer 100 are a temperature of 80°C and an oxidant concentration of 5.5%, while the temperature in preprocessor 600 is 30°C. The temperature and oxidant concentration within premixer 100 are controlled as follows:

[0092] When the temperature inside the premixer 100 reaches 90°C, reduce the oxygen flow rate to 0.8 times the original flow rate. At the same time, reduce the temperature of the preprocessor 600 to 25°C. When the temperature inside the premixer 100 drops to 85°C, gradually increase the oxygen feed rate.

[0093] When the temperature inside the premixer 100 reaches 110°C, the oxygen feed is cut off, and the reaction stops. At the same time, nitrogen is urgently introduced for purging. When the temperature inside the premixer 100 drops to 50°C, the oxygen flow rate is gradually restored to the original return flow rate, and the original production process is resumed.

[0094] When the oxidant concentration in the premixer 100 reaches 7.5%, the oxygen flow rate is reduced to 0.8 times the original return flow rate. Simultaneously, the temperature of the preprocessor 600 is reduced to 25°C. When the oxidant concentration in the premixing reactor reaches 8.5%, the oxygen feed is cut off, and the reaction stops. At the same time, nitrogen is urgently introduced for purging. The cooling devices for the premixer 100 and preprocessor 600 are existing technologies and will not be described in detail here.

[0095] This application provides a method for preparing dimethyl carbonate. The method involves reacting nitric oxide with oxygen in a premixer 100 to generate a first product containing nitrogen oxides. This first product is then reacted with methanol in a synthesis tower 200 to generate methyl nitrite. The methyl nitrite is then reacted with carbon monoxide in a carbonyl synthesis reactor 400 to generate more methyl nitrite. The methyl nitrite is liquefied and separated in an absorption tower 500. A fifth gaseous product generated in the absorption tower 500 is passed into a preprocessor 600 to absorb residual methanol, and then back into the premixer 100 for recycling. By decomposing the reaction for preparing methyl nitrite into two separate devices and proceeding stepwise, the simultaneous introduction of combustibles such as methanol during oxygen feeding avoids the possibility of a runaway reaction due to the strong exothermic oxidation reaction between oxygen and nitric oxide, which could also cause methyl nitrite to decompose at high temperatures. This improves the controllability and safety of the production process.

[0096] Finally, it should be noted that other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein, and is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of the invention is limited only by the appended claims.

Claims

1. A system for preparing dimethyl carbonate, characterized in that, include: A premixer (100) is used to supply nitric oxide to react with oxygen to produce a first product including nitrogen oxides; A synthesis tower (200) is connected to the premixer (100), and a methanol feed tank (300) is connected to the synthesis tower (200) for reacting methanol and the first product to produce a second product including methyl nitrite. A carbonyl synthesis reactor (400), connected to the synthesis tower (200), is used for a carbonyl synthesis catalytic reaction of a second product and carbon monoxide to produce a third product including nitric oxide and dimethyl carbonate; An absorber (500) is connected to the carbonyl synthesis reactor (400). An absorbent is provided in the absorber (500) for absorbing dimethyl carbonate and converting it into a liquid fourth product including dimethyl carbonate and a gaseous fifth product including nitric oxide. It also includes a preprocessor (600) connected to the absorption tower (500) to absorb residual methanol in the fifth product to form a sixth product including nitric oxide; The preprocessor (600) is connected to the premixer (100) to pass the sixth product into the premixer (100) for recycling as raw material; It also includes a cooler (210), and a circulating pump (220) is also provided on the synthesis tower (200). One end of the cooler (210) is connected to the circulating pump (220), and the other end is connected to the synthesis tower (200) to circulate and cool the synthesis tower (200).

2. A method for preparing dimethyl carbonate, characterized in that, Using the system for preparing dimethyl carbonate as described in claim 1, the method comprises: Nitric oxide and oxygen are passed into a premixer (100) to react and produce a first product including nitrogen oxides; The first product is fed into a synthesis tower (200), and methanol is introduced into the synthesis tower (200) to react the methanol with the first product to produce a second product including methyl nitrite. The second product and carbon monoxide are fed into the carbonyl synthesis reactor (400) to cause the second product and carbon monoxide to undergo a carbonyl synthesis catalytic reaction to produce a third product including nitric oxide and dimethyl carbonate. The third product is introduced into the absorption tower (500) so that the third product comes into contact with the absorbent in the absorption tower (500) to form a liquid fourth product including dimethyl carbonate and a gaseous fifth product including nitric oxide.

3. The method for preparing dimethyl carbonate according to claim 2, characterized in that, After the third product is passed into the absorption tower (500), the process further includes: The fifth product is passed into a preprocessor (600) to absorb the residual methanol in the fifth product, forming a sixth product containing nitric oxide.

4. The method for preparing dimethyl carbonate according to claim 3, characterized in that, After the fifth product is passed into the preprocessor (600), the process further includes: The sixth product is fed into the premixer (100) and recycled as a raw material.

5. The method for preparing dimethyl carbonate according to claim 3, characterized in that, The methanol content in the sixth product is less than 1000 ppm; in the premixer (100), the volume ratio of the oxygen introduced to the nitric oxide in the sixth product is 1:5 to 1:

8.

6. The method for preparing dimethyl carbonate according to claim 2, characterized in that, When nitric oxide and oxygen are introduced into the premixer (100) for reaction, the method further includes: detecting the current concentration C1 of the oxidant in the premixer (100) and the current temperature T1 in the premixer (100); The preset reaction temperature in the premixer (100) is T, and the preset concentration of the oxidant is C; When T < T1 < T+30℃ or C < C1 < C+3%, reduce the oxygen input and lower the temperature of the premixer (100); when T1 ≥ T+30℃ or C1 ≥ C+3%, stop the oxygen input and lower the temperature of the premixer (100).

7. The method for preparing dimethyl carbonate according to claim 2, characterized in that, When the first product is fed into the synthesis tower (200), the mass ratio of methanol to the first product is 4:1 to 10:1; the feed temperature of methanol is 5 to 30°C. The methanol is introduced into the synthesis tower (200) from the top, and the first product is introduced into the synthesis tower (200) from the bottom and comes into countercurrent contact with the methanol so that the methanol absorbs the heat released by the reaction.

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