Synthesis system and synthesis process of dinitrotoluene

Abstract

The invention relates to the technical field of nitration, in particular to a synthesis system and a synthesis process of dinitrotoluene. The synthesis system provided by the invention comprises a first-section nitrator, a second-section nitrator, a first-section separator, a second-section separator, a washing tower, an acid mixer, a heat exchanger and a waste acid concentration unit. The first-section nitrator and the second-section nitrator are respectively responsible for introducing a first nitro group and a second nitro group to generate mononitrotoluene and dinitrotoluene. The first-section separator and the second-section separator are used for separating an organic phase and an inorganic phase, so that the product quality is improved, and unreacted acid is recovered. The washing tower is used for treating gas generated in the reaction process, so that emission reaches the standard, and part of acidic substances are recycled. Required mixed acid is provided, and the stability of reaction conditions is ensured. The synthesis system adopts a continuous flow nitration process, has the characteristics of short process flow, uniform raw material dispersion, high conversion rate, high selectivity, few byproducts and the like, and is suitable for large-scale production.

Description

Technical Field

[0001] The invention relates to the technical field of nitration, and in particular to a synthesis system and a synthesis process of dinitrotoluene. Background Art

[0002] DNT (dinitrotoluene, molecular formula C7H6N2O4) and its derivatives can be widely used in many fields such as organic synthesis, fuel, paint and polyurethane. At present, the industrial synthesis of DNT is mainly obtained by reacting toluene and nitric acid under the condition of sulfuric acid as a catalyst. The reaction is divided into two steps, specifically, toluene nitration reaction to generate MNT (mononitrotoluene, molecular formula C7H7NO2), and then MNT further nitration reaction to generate DNT. According to the different production operation time, the existing DNT production process can be divided into two types: intermittent and continuous. According to the form and process route of the nitrator, there are DNT nitration process technologies such as kettle type, pump type, tubular type, ring type, microchannel and adiabatic nitration. The above processes have been applied to a certain extent in actual production. However, the above processes all have problems such as long process flow, low toluene conversion rate and selectivity in one stage, large equipment volume, low nitration liquid phase separation efficiency, difficult phase interface adjustment, low finished product yield, many by-products, serious entrainment of nitration tail gas and high energy consumption. Summary of the invention

[0003] (I) The problem to be solved by the present invention is that the existing synthesis process of dinitrotoluene has problems such as long process flow, low toluene conversion rate and selectivity in the first stage, large equipment volume, low nitration liquid phase separation efficiency, difficult phase interface adjustment, low finished product yield, many by-products, serious entrainment of nitration tail gas and high energy consumption.

[0004] (II) Technical solution

[0005] In order to solve the above technical problems, an embodiment of the present invention provides a synthesis system, including: two nitrifiers, two separators, a washing tower, an acid mixer, a heat exchanger, and a waste acid concentration unit; the two nitrifiers are respectively a first-stage nitrifier and a second-stage nitrifier; the two separators are respectively a first-stage separator and a second-stage separator;

[0006] The first stage nitrifier has a first feed end, a first liquid phase outlet and a first gas phase outlet; the second stage nitrifier has a second feed end, a second liquid phase outlet and a second gas phase outlet; the first stage separator has a third feed end, a third gas phase outlet, a first oil phase outlet and a first acid phase outlet; the second stage separator has a fourth feed end, a fourth gas phase outlet, a second oil phase outlet and a second acid phase outlet; the washing tower has a top outlet, a top liquid inlet, a bottom gas inlet and a bottom liquid outlet; the acid mixer has a fifth feed end and an acid liquid outlet; the heat exchanger has a tube side inlet, a tube side outlet, a shell side inlet and a shell side outlet;

[0007] The first feed end is connected with the raw material pipeline, the spent acid concentration unit and the shell side outlet of the heat exchanger; the third feed end is connected with the first liquid phase outlet; the second feed end is connected with the first oil phase outlet and the bottom liquid outlet; the fourth feed end is connected with the second liquid phase outlet; the fifth feed end is connected with the spent acid concentration unit and the raw material pipeline; the bottom gas inlet is connected with the first gas phase outlet, the second gas phase outlet, the third gas phase outlet and the fourth gas phase outlet, the top outlet is connected with the spent acid concentration unit, and the top liquid inlet is connected with the acid liquid outlet; the tube side inlet is connected with the first acid phase outlet, the tube side outlet is connected with the spent acid concentration unit, and the shell side inlet is connected with the second acid phase outlet.

[0008] Furthermore, the nitrifier includes an upper tube box, a lower tube box, a cylinder, a first liquid receiving tray, a stirring shaft, a push-down stirring paddle, an upper guide tube, a lower guide tube and a tube bundle assembly;

[0009] The upper end of the cylinder is connected to the upper tube box, and the lower end is connected to the lower tube box, and a reaction space is formed between the cylinder, the upper tube box and the lower tube box; the tube bundle assembly includes a plurality of heat exchange tubes, the tube bundle assembly is arranged in the cylinder, the upper guide tube is arranged in the upper tube box, and the lower end of the upper guide tube is connected to the upper end of the tube bundle assembly, the lower guide tube is located in the tube box, and the upper end of the lower guide tube is connected to the lower end of the tube bundle assembly, the upper guide tube and the lower guide tube are coaxial and have the same radial size, and are located between the upper guide tube and the lower guide tube The two ends of the heat exchange tubes in the middle are respectively connected with the upper guide tube and the lower guide tube, and the two ends of the remaining heat exchange tubes are respectively connected with the upper tube box and the lower tube box; the first liquid receiving pan is arranged in the upper tube box and is located above the upper guide tube, the push-down stirring paddle is located in the upper guide tube, the stirring shaft passes through the first liquid receiving pan and is connected with the push-down stirring paddle, the stirring shaft and the push-down stirring paddle are both hollow inside and connected with each other, the stirring shaft is located in the first liquid receiving pan. The area provided with a first opening, and the push-down stirring paddle is provided with a second opening.

[0010] Further, the separator includes a separation chamber, a liquid accumulation plate, a second liquid receiving plate, a disc separator, a hollow shaft, a second motor, a liquid collection separator, and a liquid discharge pipe;

[0011] The liquid accumulation tray is arranged in the separation bin, and divides the interior of the separation bin into a first chamber and a second chamber spaced apart in an upper and lower manner; a guide tube is extended downwardly from the liquid accumulation tray, and the first chamber and the second chamber are connected through the guide tube; the second liquid receiving tray and the disc separator are both located in the first chamber, and the disc separator is located below the second liquid receiving tray, one end of the hollow shaft is connected to the second motor transmission, and the other end passes through the second liquid receiving tray and is connected to the disc separator, the peripheral side of the disc separator is open, and the interior is filled with filler, and the second liquid receiving tray is connected to the disc separator through the hollow shaft; the liquid accumulation separator is located in the second chamber, and the liquid accumulation separator is connected to the lower end of the guide tube, and one end of the drainage pipe is vertically arranged in the second chamber, and the other end extends out of the second chamber.

[0012] Furthermore, the first liquid receiving tray is filled with structured fillers; and the lower end of the lower guide tube is filled with structured fillers.

[0013] Furthermore, the filler in the disc separator is 250Y plate corrugated filler; the polymer liquid separator is filled with 250Y plate corrugated filler.

[0014] Another embodiment of the present invention further provides a process for synthesizing dinitrotoluene, using the synthesis system described in any of the above embodiments;

[0015] The synthesis process of the dinitrotoluene comprises the steps:

[0016] Step S1, transporting toluene and concentrated nitric acid from an upstream raw material pipeline, dilute nitric acid from a waste acid concentration unit, and a first mixed acid separated from a second-stage separator to a first-stage nitrifier, wherein the toluene and concentrated nitric acid are first premixed in a first liquid receiving plate of a nitrifier at one end, and then mixed with the dilute nitric acid and the first mixed acid for reaction; the product in the first-stage nitrifier is a mixture of mononitrotoluene and a first-stage acid phase;

[0017] Step S2, conveying the mixture of mononitrotoluene and the first acid phase to a first separator for separation to obtain mononitrotoluene and the first acid phase;

[0018] Step S3, transporting mononitrotoluene and the second-stage mixed acid from the washing tower to the second-stage nitrifier for mixed reaction, and the product in the second-stage nitrifier is a mixture of dinitrotoluene and the second-stage acid phase;

[0019] Step S4, conveying the mixture of dinitrotoluene and the second-stage acid phase to a second-stage separator for separation to obtain dinitrotoluene and the second-stage acid phase, wherein the second-stage acid phase is the first mixed acid in step S1;

[0020] The first acid phase obtained in step S2 is transported to the waste acid concentration unit through the tube side of the heat exchanger for concentration; the second acid phase obtained in step S4 is transported as the first mixed acid to the first nitrifier through the shell side of the heat exchanger;

[0021] The first mixed acid in step S1 and the second mixed acid in step S3 are both mixed solutions of sulfuric acid and nitric acid;

[0022] The acidic gas generated inside the first-stage nitrifier in step S1, the first-stage separator in step S2, the second-stage nitrifier in step S3 and the second-stage separator in step S4 is transported to the washing tower, and the concentrated sulfuric acid from the waste acid concentration unit and the concentrated nitric acid from the upstream feed line are mixed in the acid mixer to form a third mixed acid which is transported to the washing tower to wash the acidic gas to obtain nitrated tail gas and a second mixed acid, and the nitrated tail gas is transported to the waste acid concentration unit.

[0023] Furthermore, in step S1:

[0024] The volume ratio of the material circulation volume to the withdrawal volume in the first stage nitrifier is 50:1 to 110:1, preferably 70:1 to 90:1;

[0025] The working temperature in the first stage nitrifier is 40°C to 55°C, preferably 45°C to 53°C;

[0026] The working pressure of the first stage nitrifier is -5KPa(G)~500KPa(G), preferably -2KPa(G)~20KPa(G);

[0027] The acid-to-oil mass ratio in the first stage nitrifier is 1.5-4, preferably 2.2-3;

[0028] The nitric acid ratio in the first stage nitrifier is 1 to 1.5, preferably 1.01 to 1.1.

[0029] Furthermore, in step S3:

[0030] The volume ratio of the material circulation volume to the withdrawal volume in the second stage nitrifier is 50:1 to 115:1, preferably 75:1 to 95:1;

[0031] The operating temperature of the second stage nitrifier is 50℃~70℃, preferably 56℃~68℃;

[0032] The working pressure of the second stage nitrifier is -5KPa(G)~500KPa(G), preferably -2KPa(G)~20KPa(G);

[0033] The acid-to-oil mass ratio in the second-stage nitrifier is 1.5 to 3, preferably 1.7 to 2;

[0034] The nitric acid ratio in the second-stage nitrifier is 1 to 1.5, preferably 1.05 to 1.2.

[0035] Furthermore, in step S1:

[0036] The mass concentration of concentrated nitric acid from the upstream raw material pipeline is greater than or equal to 95%, preferably 98%;

[0037] The mass concentration of the dilute nitric acid from the spent acid concentration unit is 40% to 70%, preferably 55% to 65%.

[0038] Furthermore, the mass concentration of concentrated sulfuric acid from the spent acid concentration unit used to form the third mixed acid is greater than or equal to 90%, preferably greater than 93%.

[0039] Beneficial effects of the present invention:

[0040] The synthesis system provided by the present invention comprises: two nitrators, two separators, a washing tower, an acid mixer, a heat exchanger, and a waste acid concentration unit; the two nitrators are respectively a first-stage nitrator and a second-stage nitrator; the two separators are respectively a first-stage separator and a second-stage separator; the first-stage nitrator has a first feed end, a first liquid phase outlet, and a first gas phase outlet; the second-stage nitrator has a second feed end, a second liquid phase outlet, and a second gas phase outlet; the first-stage separator has a third feed end, a third gas phase outlet, a first oil phase outlet, and a first acid phase outlet; the second-stage separator has a fourth feed end, a fourth gas phase outlet, a second oil phase outlet, and a second acid phase outlet; the washing tower has a top outlet, a top liquid inlet, a bottom gas inlet, and a bottom liquid outlet; the acid mixer has a fifth feed end and an acid liquid outlet; the heat exchanger There are a tube-side inlet, a tube-side outlet, a shell-side inlet and a shell-side outlet; the first feed end is connected to the raw material pipeline, the spent acid concentration unit and the shell-side outlet of the heat exchanger; the third feed end is connected to the first liquid phase outlet; the second feed end is connected to the first oil phase outlet and the bottom liquid outlet; the fourth feed end is connected to the second liquid phase outlet; the fifth feed end is connected to the spent acid concentration unit and the raw material pipeline; the bottom gas inlet is connected to the first gas phase outlet, the second gas phase outlet, the third gas phase outlet and the fourth gas phase outlet, the top outlet is connected to the spent acid concentration unit, and the top liquid inlet is connected to the acid liquid outlet; the tube-side inlet is connected to the first acid phase outlet, the tube-side outlet is connected to the spent acid concentration unit, and the shell-side inlet is connected to the second acid phase outlet.

[0041] In the process of synthesizing nitrates, the synthetic raw materials come from the raw material pipeline, the acid liquid produced by the waste acid concentration unit and the acid liquid separated by the second-stage separator. The synthetic raw materials are transported to the first-stage nitrifier through the first feed end for reaction. The product in the first-stage nitrifier is a mixture of an oil phase and an acid phase. The heat in the reaction process is absorbed by the circulating water in the shell of the first-stage separator; the mixture of the oil phase and the acid phase is transported to the first-stage separator for separation; the mixture of the oil phase and the acid phase is discharged from the first-end nitrifier through the first liquid phase outlet and enters the first-stage separator through the third feed end. The mixture of the oil phase and the acid phase is separated by the first-stage separator to obtain an oil phase and an acid phase; the oil phase is discharged from the first-stage separator through the first oil phase outlet and enters the second-stage nitrifier from the second feed end, and the acid phase is discharged from the first acid phase outlet The first stage separator is used for the first stage oil phase and the acid liquid discharged from the bottom liquid outlet of the washing tower enters the second stage nitrifier for further reaction, and the product in the second stage nitrifier is a mixture of the second stage oil phase and the second stage acid phase; the mixture of the second stage oil phase and the second stage acid phase is transported to the second stage separator for separation; the mixture of the second stage oil phase and the second stage acid phase is discharged from the second stage nitrifier through the second liquid phase outlet and enters the second stage separator through the fourth feed end for separation, and the mixture of the second stage oil phase and the second stage acid phase is separated in the second stage separator to obtain the second stage oil phase and the second stage acid phase; the second stage oil phase is discharged from the second stage separator through the second oil phase outlet as the final product and enters the subsequent process, the second stage acid phase is discharged from the second stage separator through the second acid phase outlet, and is transported back to the first stage nitrifier through the tube side of the heat exchanger as a reaction raw material. The gas generated inside the first stage nitrifier is discharged through the first gas phase outlet and enters the washing tower through the bottom air inlet for washing, the gas generated inside the second stage nitrifier is discharged through the second gas phase outlet and enters the washing tower through the bottom air inlet for washing, the gas generated inside the first stage separator is discharged through the third gas phase outlet and enters the washing tower through the bottom air inlet for washing, the gas generated inside the second stage separator is discharged through the fourth gas phase outlet and enters the washing tower through the bottom air inlet for washing; the acid solution formed after the liquid from the waste acid concentration unit and the raw material pipeline is mixed by the acid mixer enters the washing tower through the top liquid inlet as an absorption liquid, is discharged from the bottom liquid outlet after contacting with the gas in the washing tower and is transported to the second stage nitrifier as a reaction raw material in the second stage nitrifier. The synthesis system provided by the present invention adopts a continuous flow nitration process, has the characteristics of short process flow, uniform dispersion of raw materials, high conversion rate, high selectivity, few by-products, etc., and is suitable for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0043] Figure 1 A structural diagram of a synthesis system provided by an embodiment of the present invention;

[0044] Figure 2 A schematic diagram of the structure of a nitrifier provided in an embodiment of the present invention;

[0045] Figure 3 A schematic structural diagram of a separator provided in an embodiment of the present invention.

[0046] Icons: 11-first stage nitrifier; 12-second stage nitrifier; 21-first stage separator; 22-second stage separator; 3-washing tower; 4-heat exchanger; 5-acid mixer; 61-waste acid pump; 62-mixed acid pump; 7-waste acid concentration unit;

[0047] 101-upper tube box; 102-cylinder; 103-lower tube box; 104-first liquid receiving tray; 105-down-push stirring paddle; 106-stirring shaft; 107-upper guide tube; 108-lower guide tube; 109-tube bundle assembly; 110-guide plate; 111-overflow weir;

[0048] 201-separation chamber; 202-liquid accumulation plate; 203-second liquid receiving plate; 204-disc separator; 205-hollow shaft; 206-second motor; 207-liquid collection separator; 208-liquid discharge pipe; 209-adjusting structure; 210-flow guide pipe. DETAILED DESCRIPTION

[0049] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than 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.

[0050] like Figures 1 to 3As shown, one embodiment of the present invention provides a synthesis system, including: two nitrators, two separators, a washing tower 3, an acid mixer 5, a heat exchanger 4, and a waste acid concentration unit 7; the two nitrators are respectively a first-stage nitrator 11 and a second-stage nitrator 12; the two separators are respectively a first-stage separator 21 and a second-stage separator 22; the first-stage nitrator 11 has a first feed end, a first liquid phase outlet, and a first gas phase outlet; the second-stage nitrator 12 has a second feed end, a second liquid phase outlet, and a second gas phase outlet; the first-stage separator 21 has a third feed end, a third gas phase outlet, a first oil phase outlet, and a first acid phase outlet; the second-stage separator 22 has a fourth feed end, a fourth gas phase outlet, a second oil phase outlet, and a second acid phase outlet; the washing tower 3 has a top outlet, a top liquid inlet, a bottom gas inlet, and a bottom gas inlet. and a bottom liquid outlet; the acid mixer 5 has a fifth feed end and an acid liquid outlet; the heat exchanger 4 has a tube side inlet, a tube side outlet, a shell side inlet and a shell side outlet; the first feed end is connected to the raw material pipeline, the spent acid concentration unit 7 and the shell side outlet of the heat exchanger 4; the third feed end is connected to the first liquid phase outlet; the second feed end is connected to the first oil phase outlet and the bottom liquid outlet; the fourth feed end is connected to the second liquid phase outlet; the fifth feed end is connected to the spent acid concentration unit 7 and the raw material pipeline; the bottom gas inlet is connected to the first gas phase outlet, the second gas phase outlet, the third gas phase outlet and the fourth gas phase outlet, the top outlet is connected to the spent acid concentration unit 7, and the top liquid inlet is connected to the acid liquid outlet; the tube side inlet is connected to the first acid phase outlet, the tube side outlet is connected to the spent acid concentration unit 7, and the shell side inlet is connected to the second acid phase outlet.

[0051] The synthesis system provided in this embodiment can be used to synthesize nitrates such as dinitrotoluene, mononitrobenzene, dinitrobenzene, mononitrobenzene and dinitrobenzene. The above-mentioned synthesis system includes two nitrators, two separators, a washing tower 3, an acid mixer 5, a heat exchanger 4 and a waste acid concentration unit 7. The structures of the two nitrators are basically the same, and the structures of the two separators are basically the same. For the convenience of description, the two nitrators are respectively a first-stage nitrator 11 and a second-stage nitrator 12, and the two separators are respectively a first-stage separator 21 and a second-stage separator 22. In the process of synthesizing nitrate, the synthetic raw materials come from the raw material pipeline, the acid liquid produced by the waste acid concentration unit 7 and the acid liquid separated by the second-stage separator 22. The synthetic raw materials are transported to the first-stage nitrifier 11 through the first feed end for reaction. The product in the first-stage nitrifier 11 is a mixture of an oil phase and an acid phase. The heat in the reaction process is absorbed by the circulating water in the shell side of the first-stage separator 21; the mixture of an oil phase and an acid phase is transported to the first-stage separator 21 for separation; the mixture of an oil phase and an acid phase is discharged from the first-end nitrifier through the first liquid phase outlet and enters the first-stage separator 21 through the third feed end. The mixture of an oil phase and an acid phase is separated by the first-stage separator 21 to obtain an oil phase and an acid phase; an oil phase is discharged from the first-stage separator 21 through the first oil phase outlet and enters the second-stage nitrifier 12 from the second feed end, and an acid phase is discharged from the first acid phase outlet. The first oil phase and the acid liquid discharged from the bottom liquid outlet of the washing tower 3 enter the second nitrifier 12 for further reaction, and the product in the second nitrifier 12 is a mixture of the second oil phase and the second acid phase; the mixture of the second oil phase and the second acid phase is transported to the second separator 22 for separation; the mixture of the second oil phase and the second acid phase is discharged from the second nitrifier 12 through the second liquid phase outlet and enters the second separator 22 through the fourth feed end for separation, and the mixture of the second oil phase and the second acid phase is separated by the second separator 22 to obtain the second oil phase and the second acid phase; the second oil phase is discharged from the second separator 22 through the second oil phase outlet as the final product and enters the subsequent process, and the second acid phase is discharged from the second separator 22 through the second acid phase outlet and transported back to the first nitrifier 11 as a reaction raw material through the tube side of the heat exchanger 4.The gas generated inside the first stage nitrifier 11 is discharged through the first gas phase outlet and enters the washing tower 3 through the bottom air inlet for washing, the gas generated inside the second stage nitrifier 12 is discharged through the second gas phase outlet and enters the washing tower 3 through the bottom air inlet for washing, the gas generated inside the first stage separator 21 is discharged through the third gas phase outlet and enters the washing tower 3 through the bottom air inlet for washing, and the gas generated inside the second stage separator 22 is discharged through the fourth gas phase outlet and enters the washing tower 3 through the bottom air inlet for washing; the acid solution formed after the liquid from the waste acid concentration unit 7 and the raw material pipeline is mixed by the acid mixer 5 enters the washing tower 3 through the top liquid inlet as an absorption liquid, and is discharged from the bottom liquid outlet after contacting with the gas in the washing tower 3 and transported to the second stage nitrifier 12 as the reaction raw material in the second stage nitrifier 12. The synthesis system provided in this embodiment adopts a continuous flow nitration process, has the characteristics of short process flow, uniform dispersion of raw materials, high conversion rate, high selectivity, and few by-products, and is suitable for large-scale production.

[0052] Optionally, in this embodiment, a mixed acid pump 62 is provided between the second-stage separator 22 and the heat exchanger 4 , and a waste acid pump 61 is provided between the first-stage separator 21 and the heat exchanger 4 .

[0053] The synthesis system provided by the embodiment of the present invention is as follows: Figures 1 to 3 As shown, the nitrifier includes an upper tube box 101, a lower tube box 103, a cylinder 102, a first liquid receiving tray 104, a stirring shaft 106, a push-down stirring paddle 105, an upper guide tube 107, a lower guide tube 108 and a tube bundle assembly 109; the upper end of the cylinder 102 is connected to the upper tube box 101, and the lower end is connected to the lower tube box 103, and a reaction space is formed between the cylinder 102, the upper tube box 101 and the lower tube box 103; the tube bundle assembly 109 includes a plurality of heat exchange tubes, the tube bundle assembly 109 is arranged in the cylinder 102, the upper guide tube 107 is arranged in the upper tube box 101, and the lower end of the upper guide tube 107 is connected to the upper end of the tube bundle assembly 109, the lower guide tube 108 is located in the tube box, and the upper end of the lower guide tube 108 is connected to the lower end of the tube bundle assembly 109, and the upper The guide tube 107 and the lower guide tube 108 are coaxial and have the same radial size. The two ends of the heat exchange tube located between the upper guide tube 107 and the lower guide tube 108 are respectively connected to the upper guide tube 107 and the lower guide tube 108, and the two ends of the remaining heat exchange tubes are respectively connected to the upper tube box 101 and the lower tube box 103; the first liquid receiving pan 104 is arranged in the upper tube box 101 and is located above the upper guide tube 107, the down-push stirring paddle 105 is located in the upper guide tube 107, the stirring shaft 106 passes through the first liquid receiving pan 104 and is connected to the down-push stirring paddle 105, the stirring shaft 106 and the down-push stirring paddle 105 are both hollow inside and connected to each other, the area of ​​the stirring shaft 106 located in the first liquid receiving pan 104 is provided with a first opening, and the down-push stirring paddle 105 is provided with a second opening.

[0054] In this embodiment, the structures of the first stage nitrifier 11 and the second stage nitrifier 12 are basically the same, except that the upper tube box 101 of the first stage nitrifier 11 is provided with four feed ports for forming the above-mentioned first feed end, and the upper tube box 101 of the second stage nitrifier 12 is provided with two feed ports for forming the above-mentioned second feed end. When the first stage nitrifier 11 is in use, the raw materials transported by the raw material pipeline first enter the first liquid receiving tray 104 for premixing, then enter the upper guide tube 107, mix with the acid liquid from the waste acid concentration unit 7 and the second stage separator 22, and react in the tube bundle assembly 109 to generate a first stage oil phase; when the second stage nitrifier 12 is in use, the first stage oil phase enters the first liquid receiving tray 104, then enters the upper guide tube 107, mixes with the acid liquid from the washing tower 3, and reacts in the tube bundle assembly 109 to generate a second stage oil phase.

[0055] In this embodiment, both ends of the cylinder 102 are open, the upper end of the cylinder 102 is connected to the upper tube box 101 through a flange or other structure, and the lower end of the cylinder 102 is connected to the lower tube box 103 through a flange or other structure. The up and down directions are Figure 2 In the up-down direction, the interior of the cylinder 102 is connected with the interiors of the upper tube box 101 and the lower tube box 103. The tube bundle assembly 109 includes two tube sheets arranged at intervals and a plurality of heat exchange tubes arranged between the two tube sheets; the first liquid receiving tray 104 and the upper guide tube 107 are both located in the upper tube box 101, and the first liquid receiving tray 104 is located above the upper tube box 101, the lower end of the upper guide tube 107 is connected to the tube sheet at the upper end of the tube bundle assembly 109, the lower guide tube 108 is located in the lower tube box 103, the upper end of the lower guide tube 108 is connected to the tube sheet at the lower end of the tube bundle assembly 109, the upper guide tube 107 and the lower guide tube 108 are both cylinders with the same diameter, the upper guide tube 107 and the lower guide tube 108 are coaxially arranged, and the above-mentioned plurality of heat exchange tubes are partially located between the upper guide tube 107 and the lower guide tube 108, and the rest are located in the area outside the upper guide tube 107 and the lower guide tube 108. The push-down stirring paddle 105 is located in the upper guide tube 107, one end of the stirring shaft 106 passes through the first liquid receiving pan 104 and is connected to the push-down stirring paddle 105, and the other end is connected to the driving unit, and the driving unit is used to drive the stirring shaft 106 to rotate, thereby driving the push-down stirring paddle 105 located on the stirring shaft 106 to rotate. The stirring paddle and the stirring shaft 106 are hollow inside, and a first opening is provided on the stirring shaft 106, and a second opening is provided on the stirring paddle to allow the liquid to flow. In this embodiment, preferably, a plurality of guide plates 110 are also provided in the lower tube box 103 along the circumference of the lower tube box 103, for guiding the liquid. The above-mentioned first liquid phase outlet is provided in the upper tube box 101, and an overflow weir 111 is provided at the first liquid phase outlet.

[0056] The synthesis system provided by the embodiment of the present invention is as follows: Figure 1 refer to Figure 3As shown, the separator includes a separation chamber 201, a liquid collecting plate 202, a second liquid receiving plate 203, a disc separator 204, a hollow shaft 205, a second motor 206, a liquid collecting separator 207, and a liquid discharge pipe 208; the liquid collecting plate 202 is arranged in the separation chamber 201, and divides the interior of the separation chamber 201 into a first chamber and a second chamber separated by an upper and a lower space; the liquid collecting plate 202 extends downwardly with a guide pipe 210, and the first chamber and the second chamber are connected through the guide pipe 210; the second liquid receiving plate 203 and the disc separator 204 are both located in the first chamber, and the disc separator 204 is connected to the first chamber. The disc separator 204 is located below the second liquid receiving disc 203, one end of the hollow shaft 205 is transmission-connected to the second motor 206, and the other end passes through the second liquid receiving disc 203 and is connected to the disc separator 204. The peripheral side of the disc separator 204 is open, and the interior is filled with filler. The second liquid receiving disc 203 is connected to the disc separator 204 through the hollow shaft 205; the liquid collecting separator 207 is located in the second chamber, and the liquid collecting separator 207 is connected to the lower end of the guide pipe 210, and one end of the discharge pipe 208 is vertically arranged in the second chamber, and the other end extends out of the second chamber.

[0057] In this embodiment, the separation chamber 201 is a closed cylindrical structure, and a guide tube 210 extends from the lower end of the liquid accumulation plate 202. The liquid accumulation plate 202 is a funnel-shaped structure. The periphery of the liquid accumulation plate 202 is connected to the inner wall of the separation chamber 201, so as to separate the first chamber and the second chamber separated from each other in the upper and lower directions inside the separation chamber 201. The first chamber and the second chamber are connected through the guide tube 210 on the liquid accumulation plate 202. The second liquid receiving plate 203 and the disc separator 204 are arranged in the first chamber, and the drainage pipe 208 for drainage is arranged in the second chamber. The drainage pipe 208 is a bellows. The separation chamber 201 is also provided with an adjustment structure 209 for adjusting the length of the bellows, so as to control the drainage liquid level in the second chamber. The separator provided in this embodiment adopts a combination of super gravity separation and static separation, and has a better separation effect and higher separation efficiency.

[0058] Another embodiment of the present invention further provides a synthesis process of dinitrotoluene, which is used to synthesize dinitrotoluene. The synthesis process of dinitrotoluene adopts the synthesis system described in any of the above embodiments; further, the synthesis process of dinitrotoluene comprises the steps of:

[0059] Step S1, toluene and concentrated nitric acid from the upstream raw material pipeline, as well as dilute nitric acid from the waste acid concentration unit 7 and the first mixed acid separated from the second-stage separator 22 are transported to the first-stage nitrifier 11, and the toluene and concentrated nitric acid are firstly premixed in the first liquid receiving plate 104 of the nitrifier at one end, and then mixed with the dilute nitric acid and the first mixed acid for reaction; the product in the first-stage nitrifier 11 is a mixture of mononitrotoluene and a first-stage acid phase;

[0060] Step S2, conveying the mixture of mononitrotoluene and the first acid phase to a first separator 21 for separation to obtain mononitrotoluene and the first acid phase;

[0061] Step S3, transporting mononitrotoluene and the second-stage mixed acid from the washing tower 3 to the second-stage nitrifier 12 for mixed reaction, and the product in the second-stage nitrifier 12 is a mixture of dinitrotoluene and the second-stage acid phase;

[0062] Step S4, conveying the mixture of dinitrotoluene and the second-stage acid phase to the second-stage separator 22 for separation to obtain dinitrotoluene and the second-stage acid phase, wherein the second-stage acid phase is the first mixed acid in step S1;

[0063] The first acid phase obtained in step S2 is transported to the waste acid concentration unit 7 through the tube side of the heat exchanger 4 for concentration; the second acid phase obtained in step S4 is transported as the first mixed acid through the shell side of the heat exchanger 4 to the first nitrifier 11;

[0064] The first mixed acid in step S1 and the second mixed acid in step S3 are both mixed solutions of sulfuric acid and nitric acid;

[0065] The acidic gas generated inside the first-stage nitrifier 11 in step S1, the first-stage separator 21 in step S2, the second-stage nitrifier 12 in step S3 and the second-stage separator 22 in step S4 is transported to the washing tower 3, and the concentrated sulfuric acid from the waste acid concentration unit 7 and the concentrated nitric acid from the upstream feed line are mixed in the acid mixer 5 to form a third mixed acid, which is transported to the washing tower 3 to wash the acidic gas to obtain nitrated tail gas and a second mixed acid, and the nitrated tail gas is transported to the waste acid concentration unit 7.

[0066] The synthesis process of dinitrotoluene provided in this embodiment is as follows: in a first-stage nitrifier 11, an upstream raw material pipeline transports toluene and concentrated nitric acid through two feed ports of the first-stage nitrifier 11 to a first liquid receiving pan 104 for premixing; dilute nitric acid from the waste acid concentration unit 7 and a first mixed acid from the second-stage separator 22 enter an upper draft tube 107 through the other two feed ports of the first-stage nitrifier 11; toluene and concentrated nitric acid are premixed in the first liquid receiving pan 104 and enter a stirring shaft 106 through a first opening, then enter a push-down stirring paddle 105 through the stirring shaft 106, and finally discharge the push-down stirring paddle 105 from a second opening and enter the upper draft tube 107; in the upper draft tube 107, toluene and concentrated nitric acid are mixed with dilute nitric acid and the first mixed acid, and enter the upper draft tube 107 and the lower draft tube 107 under the action of the push-down stirring paddle 105. 108, and then enter the lower guide tube 108 and the lower pipe box 103 through the heat exchange tube located between the upper guide tube 107 and the lower guide tube 108, and enter the heat exchange tube outside the upper guide tube 107 and the lower guide tube 108 under the action of the guide plate 110 in the lower pipe box 103, and finally enter the upper pipe box 101 from the upper end of the heat exchange tube outside the upper guide tube 107 and the lower guide tube 108, and overflow and discharge the first nitrifier 11 through the first liquid phase outlet; the above-mentioned first mixed acid is a mixed solution of sulfuric acid and nitric acid. Under the condition of sulfuric acid as a catalyst, toluene and nitric acid react in the heat exchange tube to produce mononitrotoluene, and the product in the first nitrifier 11 is a mixture of mononitrotoluene and a first acid phase, mononitrotoluene is a first oil phase, and the first acid phase is mainly waste acid containing sulfuric acid.

[0067] Furthermore, the product of the first stage nitrifier 11 enters a first stage separator 21 for separation to obtain mononitrotoluene and an acid phase; specifically, in the first stage separator 21, the product of the first stage nitrifier 11 first enters the second liquid receiving plate 203, and then flows to the disc separator 204 through the hollow shaft 205, and the second motor 206 drives the disc separator 204 to rotate, thereby realizing the super gravity separation of the product of the first stage nitrifier 11 in the disc separator 204; the product of the first stage nitrifier 11 is initially separated by the disc separator 204 and then passes through the disc separator 204. The peripheral portion leaves the disc separator 204 and enters the liquid-collecting separator 207 through the guide pipe 210 for further separation, and finally is discharged from the liquid-collecting separator 207 to obtain an acid phase and mononitrotoluene, wherein the mononitrotoluene is located above the acid phase. As mentioned above, the acid phase is mainly waste acid containing sulfuric acid, and the acid phase is discharged from the separator 21 through the first acid phase outlet, and enters the waste acid concentration unit 7 through the tube side of the heat exchanger 4 for concentration. Mononitrotoluene is discharged from the separator 21 through the drain pipe 208 in an overflow manner, and enters the second-stage nitrifier 12.

[0068] Furthermore, in the second-stage nitrifier 12, mononitrotoluene enters the first liquid receiving pan 104 through one of the feed ports, and then enters the upper draft tube 107 through the stirring shaft 106 and the push-down stirring paddle 105 in sequence, and the second mixed acid from the washing tower 3 enters the upper draft tube 107 through another feed port; in the upper draft tube 107, the second mixed acid is mixed with mononitrotoluene, and under the action of the push-down stirring paddle 105, enters the heat exchange tube between the upper draft tube 107 and the lower draft tube 108 to fully react, and then enters the lower draft tube 108 through this part of the heat exchange tube between the upper draft tube 107 and the lower draft tube 108, In the lower tube box 103, under the action of the guide plate 110 in the lower tube box 103, it enters the heat exchange tube outside the upper guide tube 107 and the lower guide tube 108, and finally enters the upper tube box 101 from the upper end of the heat exchange tube outside the upper guide tube 107 and the lower guide tube 108, and overflows out of the second-stage nitrifier 12 through the first liquid phase outlet; the above-mentioned second mixed acid is a mixed solution of sulfuric acid and nitric acid. Under the condition of sulfuric acid as a catalyst, mononitrotoluene reacts in the heat exchange tube to generate dinitrotoluene, and the product in the second-stage nitrifier 12 is a mixture of dinitrotoluene and the second-stage acid phase, the dinitrotoluene is the second-stage oil phase, and the second-stage acid phase is a mixture of nitric acid and sulfuric acid.

[0069] Further, the product of the second stage nitrifier 12 enters the second stage separator 22 for separation to obtain dinitrotoluene and the second stage acid phase; specifically, in the second stage separator 22, the product of the second stage nitrifier 12 first enters the second liquid receiving plate 203, and then flows to the disc separator 204 through the hollow shaft 205, and the second motor 206 drives the disc separator 204 to rotate, thereby realizing the super gravity separation of the product of the second stage nitrifier 12 in the disc separator 204; the product of the second stage nitrifier 12 is initially separated by the disc separator 204 and leaves the disc separator 204 through the periphery of the disc separator 204. 04, and enters the polymer-liquid separator 207 through the guide pipe 210 for further separation, and finally discharges from the polymer-liquid separator 207 to obtain a second-stage acid phase and dinitrotoluene, and the dinitrotoluene is located above the second-stage acid phase; the above content mentioned that the second-stage acid phase is mainly a mixed acid containing sulfuric acid and nitric acid, and the second-stage acid phase is discharged from the second-stage separator 22 through the second acid phase outlet, and enters the first-stage separator 21 through the shell side of the heat exchanger 4 as the first mixed acid of the raw material of the first-stage separator 21; dinitrotoluene is discharged from the second-stage separator 22 through the drain pipe 208 in an overflow manner, and enters the subsequent process for further treatment.

[0070] Furthermore, in this embodiment, the first-stage nitrifier 11, the second-stage nitrifier 12, the first-stage separator 21 and the second-stage separator 22 generate acidic gas (nitration gas) during operation, and the acidic gas enters the washing tower 3 for washing; the absorption liquid of the washing tower 3 is concentrated nitric acid diverted from the raw material pipeline and sulfuric acid from the waste acid concentrator, and the concentrated nitric acid and sulfuric acid are mixed in the acid mixer 5 and transported to the washing tower 3, and after fully contacting with the acidic gas, they are discharged from the washing tower 3 from the bottom liquid outlet, and are transported to the second-stage nitrifier 12 as the raw material second mixed acid of the second-stage nitrifier 12, and the nitration tail gas is transported to the waste acid concentration unit 7 for concentration treatment.

[0071] The synthesis process of dinitrotoluene provided by the embodiment of the present invention has the following characteristics: the organic matter content in the first acid phase separated by the first separator 21 is less than or equal to 0.5wt%, and the acid content in the separated mononitrotoluene is less than or equal to 0.7wt%; the toluene conversion rate in the first nitrifier 11 is 97.8%, and the selectivity of toluene to MNT is 97.5%. The conversion rate of the second nitrifier 12 is 100%, and the selectivity of MNT to DNT is more than 99.5%. The organic matter content in the first mixed acid separated by the second separator 22 does not exceed 5wt%, and the acid content in the separated second oil phase does not exceed 1.5wt%. NO in the nitrated tail gas after washing in the washing tower 3 is 100%. X The content does not exceed 10wt%. The second opening is a circular hole, and the diameter of the second opening is 3mm to 15mm, preferably 6mm to 10mm. In the first stage nitrifier 11 and the second stage nitrifier 12, the rotating speed of the hollow stirring shaft 106 is adjustable in the range of 300r / min to 2900r / min, preferably 600r / min to 1500r / min. In the first stage separator 21 and the second stage separator 22, the rotating speed of the hollow shaft 205 is adjustable in the range of 300r / min to 3000r / min, preferably 1000r / min to 1500r / min.

[0072] Furthermore, in the synthesis process of dinitrotoluene provided in an embodiment of the present invention, in step S1:

[0073] The volume ratio of the material circulation volume to the production volume in the first-stage nitrifier 11 is 50:1-110:1, preferably 70:1-90:1; the working temperature in the first-stage nitrifier 11 is 40°C-55°C, preferably 45°C-53°C; the working pressure of the first-stage nitrifier 11 is -5Kpa(G)-500KPa(G), preferably -2KPa(G)-20KPa(G); the acid-oil mass ratio in the first-stage nitrifier 11 is 1.5-4, preferably 2.2-3; the nitric acid ratio in the first-stage nitrifier 11 is 1-1.5, preferably 1.01-1.1.

[0074] In step S3:

[0075] The volume ratio of the material circulation volume to the production volume in the second-stage nitrifier 12 is 50:1-115:1, preferably 75:1-95:1; the operating temperature of the second-stage nitrifier 12 is 50°C-70°C, preferably 56°C-68°C; the operating pressure of the second-stage nitrifier 12 is -5KPa(G)-500KPa(G), preferably -2KPa(G)-20KPa(G); the acid-oil mass ratio in the second-stage nitrifier 12 is 1.5-3, preferably 1.7-2; the nitric acid ratio in the second-stage nitrifier 12 is 1-1.5, preferably 1.05-1.2.

[0076] In step S1:

[0077] The mass concentration of concentrated nitric acid from the upstream raw material pipeline is greater than or equal to 95%, preferably 98%; the mass concentration of dilute nitric acid from the spent acid concentration unit 7 is 40% to 70%, preferably 55% to 65%.

[0078] The above-mentioned nitric acid ratio is the molar ratio or mass ratio between nitric acid and toluene; the material circulation amount refers to the total amount of material circulating in the first-stage nitrifier 11 or the second-stage nitrifier 12, and the production amount refers to the amount of product produced in the first-stage nitrifier 11 or the second-stage nitrifier 12. The acid-oil mass ratio is the ratio of toluene to acidic substances (nitric acid and sulfuric acid).

[0079] In the description of the present invention, it should be noted that the terms "upper", "lower", etc., indicating the orientation or positional relationship are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0080] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installation", "connection" and "connection" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be a connection between the inside of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances. In addition, in the description of the present invention, unless otherwise specified, "plurality" means two or more.

[0081] 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, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A synthesis system, characterized in that: include: Two nitrators, two separators, a washing tower (3), an acid mixer (5), a heat exchanger (4), and a waste acid concentration unit (7); the two nitrators are respectively a first-stage nitrator (11) and a second-stage nitrator (12); the two separators are respectively a first-stage separator (21) and a second-stage separator (22); The first stage nitrifier (11) has a first feed end, a first liquid phase outlet and a first gas phase outlet; the second stage nitrifier (12) has a second feed end, a second liquid phase outlet and a second gas phase outlet; the first stage separator (21) has a third feed end, a third gas phase outlet, a first oil phase outlet and a first acid phase outlet; the second stage separator (22) has a fourth feed end, a fourth gas phase outlet, a second oil phase outlet and a second acid phase outlet; the washing tower (3) has a top outlet, a top liquid inlet, a bottom gas inlet and a bottom liquid outlet; the acid mixer (5) has a fifth feed end and an acid liquid outlet; the heat exchanger (4) has a tube side inlet, a tube side outlet, a shell side inlet and a shell side outlet; The first feed end is connected to the raw material pipeline, the spent acid concentration unit (7) and the shell side outlet of the heat exchanger (4); the third feed end is connected to the first liquid phase outlet; the second feed end is connected to the first oil phase outlet and the bottom liquid outlet; the fourth feed end is connected to the second liquid phase outlet; the fifth feed end is connected to the spent acid concentration unit (7) and the raw material pipeline; the bottom gas inlet is connected to the first gas phase outlet, the second gas phase outlet, the third gas phase outlet and the fourth gas phase outlet, the top outlet is connected to the spent acid concentration unit (7), and the top liquid inlet is connected to the acid liquid outlet; the tube side inlet is connected to the first acid phase outlet, the tube side outlet is connected to the spent acid concentration unit (7), and the shell side inlet is connected to the second acid phase outlet.

2. The synthesis system according to claim 1, characterized in that: The nitrifier comprises an upper tube box (101), a lower tube box (103), a cylinder (102), a first liquid receiving tray (104), a stirring shaft (106), a push-down stirring paddle (105), an upper guide tube (107), a lower guide tube (108) and a tube bundle assembly (109); The upper end of the cylinder (102) is connected to the upper tube box (101), and the lower end is connected to the lower tube box (103); a reaction space is formed between the cylinder (102), the upper tube box (101) and the lower tube box (103); the tube bundle assembly (109) comprises a plurality of heat exchange tubes; the tube bundle assembly (109) is arranged in the cylinder (102); the upper guide tube (107) is arranged in the upper tube box (101), and the lower end of the upper guide tube (107) is connected to the upper end of the tube bundle assembly (109); the lower guide tube (108) is located in the tube box, and the upper end of the lower guide tube (108) is connected to the lower end of the tube bundle assembly (109); the upper guide tube (107) and the lower guide tube (108) are coaxial and have the same radial size; the upper guide tube (107) and the lower guide tube (108) are located between the upper guide tube (107) and the lower guide tube (108); The two ends of the heat exchange tubes between the flow tubes (108) are respectively connected to the upper guide tube (107) and the lower guide tube (108), and the two ends of the remaining heat exchange tubes are respectively connected to the upper tube box (101) and the lower tube box (103); the first liquid receiving tray (104) is arranged in the upper tube box (101) and is located above the upper guide tube (107); the push-down stirring paddle (105) is located in the upper guide tube (107); the stirring shaft (106) passes through the first liquid receiving tray (104) and is connected to the push-down stirring paddle (105); the stirring shaft (106) and the push-down stirring paddle (105) are both hollow inside and connected to each other; the stirring shaft (106) is located in the first liquid receiving tray (104) and is provided with a first opening; and the push-down stirring paddle (105) is provided with a second opening.

3. The synthesis system according to claim 1, characterized in that: The separator comprises a separation chamber (201), a liquid accumulation plate (202), a second liquid receiving plate (203), a disc separator (204), a hollow shaft (205), a second motor (206), a liquid collection separator (207), and a liquid discharge pipe (208); The liquid collecting pan (202) is arranged in the separation chamber (201) and divides the interior of the separation chamber (201) into a first chamber and a second chamber spaced apart from each other; a guide tube (210) extends downward from the liquid collecting pan (202), and the first chamber and the second chamber are connected via the guide tube (210); the second liquid collecting pan (203) and the disc separator (204) are both located in the first chamber, and the disc separator (204) is located below the second liquid collecting pan (203); one end of the hollow shaft (205) is connected to the second motor (2 06) is connected by transmission, and the other end passes through the second liquid receiving plate (203) and is connected to the disc separator (204). The circumferential side of the disc separator (204) is open and filled with fillers. The second liquid receiving plate (203) and the disc separator (204) are connected through the hollow shaft (205); the liquid collecting separator (207) is located in the second chamber, and the liquid collecting separator (207) is connected to the lower end of the guide pipe (210). One end of the discharge pipe (208) is vertically arranged in the second chamber, and the other end extends out of the second chamber.

4. The synthesis system according to claim 2, characterized in that: The first liquid receiving tray (104) is filled with structured fillers; and the lower end of the lower guide tube (108) is filled with structured fillers.

5. The synthesis system according to claim 3, characterized in that: The filler in the disc separator (204) is a 250Y plate corrugated filler; the liquid-collecting separator (207) is filled with a 250Y plate corrugated filler.

6. A process for synthesizing dinitrotoluene, characterized in that: Using the synthesis system according to any one of claims 1 to 5; The synthesis process of the dinitrotoluene comprises the steps: Step S1, toluene and concentrated nitric acid from an upstream raw material pipeline, as well as dilute nitric acid from a waste acid concentration unit (7) and a first mixed acid separated from a second-stage separator (22) are transported to a first-stage nitrifier (11); toluene and concentrated nitric acid are first premixed in a first liquid receiving plate (104) of a nitrifier at one end, and then mixed with the dilute nitric acid and the first mixed acid for reaction; the product in the first-stage nitrifier (11) is a mixture of mononitrotoluene and a first-stage acid phase; Step S2, conveying the mixture of mononitrotoluene and the first acid phase to a first separator (21) for separation to obtain mononitrotoluene and the first acid phase; Step S3, transporting the mononitrotoluene and the second-stage mixed acid from the washing tower (3) to the second-stage nitrifier (12) for mixed reaction, and the product in the second-stage nitrifier (12) is a mixture of dinitrotoluene and the second-stage acid phase; Step S4, conveying the mixture of dinitrotoluene and the second-stage acid phase to a second-stage separator (22) for separation to obtain dinitrotoluene and the second-stage acid phase, wherein the second-stage acid phase is the first mixed acid in step S1; The first acid phase obtained in step S2 is transported to the waste acid concentration unit (7) through the tube side of the heat exchanger (4) for concentration; the second acid phase obtained in step S4 is transported as the first mixed acid through the shell side of the heat exchanger (4) to the first nitrifier (11); The first mixed acid in step S1 and the second mixed acid in step S3 are both mixed solutions of sulfuric acid and nitric acid; The acidic gas generated inside the first-stage nitrifier (11) in step S1, the first-stage separator (21) in step S2, the second-stage nitrifier (12) in step S3 and the second-stage separator (22) in step S4 is transported to the washing tower (3), and the concentrated sulfuric acid from the waste acid concentration unit (7) and the concentrated nitric acid from the upstream feed line are mixed in the acid mixer (5) to form a third mixed acid, which is transported to the washing tower (3) to wash the acidic gas to obtain nitrated tail gas and a second mixed acid. The nitrated tail gas is transported to the waste acid concentration unit (7).

7. The synthesis process of dinitrotoluene according to claim 6, characterized in that: In step S1: The volume ratio of the material circulation volume to the withdrawal volume in the first stage nitrifier (11) is 50:1 to 110:1, preferably 70:1 to 90:1; The working temperature in the first stage nitrifier (11) is 40°C to 55°C, preferably 45°C to 53°C; The working pressure of the first stage nitrifier (11) is -5KPa(G) to 500KPa(G), preferably -2KPa(G) to 20KPa(G); The acid-oil mass ratio in the first stage nitrifier (11) is 1.5 to 4, preferably 2.2 to 3; The nitric acid ratio in the primary nitrifier (11) is 1 to 1.5, preferably 1.01 to 1.

1.

8. The synthesis process of dinitrotoluene according to claim 6, characterized in that: In step S3: The volume ratio of the material circulation volume to the withdrawal volume in the second-stage nitrifier (12) is 50:1 to 115:1, preferably 75:1 to 95:1; The operating temperature of the second stage nitrifier (12) is 50°C to 70°C, preferably 56°C to 68°C; The working pressure of the second stage nitrifier (12) is -5KPa(G) to 500KPa(G), preferably -2KPa(G) to 20KPa(G); The acid-to-oil mass ratio in the second-stage nitrifier (12) is 1.5 to 3, preferably 1.7 to 2; The nitric acid ratio in the second-stage nitrifier (12) is 1 to 1.5, preferably 1.05 to 1.

2.

9. The synthesis process of dinitrotoluene according to claim 6, characterized in that: In step S1: The mass concentration of concentrated nitric acid from the upstream raw material pipeline is greater than or equal to 95%, preferably 98%; The mass concentration of the dilute nitric acid from the spent acid concentration unit (7) is 40% to 70%, preferably 55% to 65%.

10. The synthesis process of dinitrotoluene according to claim 6, characterized in that: The mass concentration of the concentrated sulfuric acid from the spent acid concentration unit (7) used to form the third mixed acid is greater than or equal to 90%, preferably greater than 93%.

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