Synthetic system and process for synthesizing dinitrotoluene

Abstract

The present application relates to the technical field of nitration, in particular to a synthesis system and a synthesis process of dinitrotoluene. The synthesis system comprises a first-stage nitration device, a second-stage nitration device, a first-stage separator, a second-stage separator, a washing tower, an acid mixer, a heat exchanger and a waste acid concentration unit. The first-stage nitration device and the second-stage nitration device are respectively responsible for introducing the first and second nitro groups to generate mononitrotoluene and dinitrotoluene. The first-stage separator and the second-stage separator are used for separating the organic phase and the inorganic phase, improving the product quality and recovering the unreacted acid. The washing tower treats the gas generated in the reaction process, ensures that the emission meets the standard, and recovers part of the acidic substances. The required mixed acid is provided to ensure the stability of the reaction conditions. The synthesis system 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.

Description

Technical Field

[0001] This invention relates to the field of nitration technology, specifically to a synthesis system and a synthesis process for dinitrotoluene. Background Technology

[0002] DNT (dinitrotoluene, molecular formula C7H6N2O4) and its derivatives are widely used in organic synthesis, fuels, paints, and polyurethanes, among other fields. Currently, the industrial synthesis of DNT mainly involves the reaction of toluene and nitric acid under sulfuric acid as a catalyst. The reaction is divided into two steps: toluene nitration to produce MNT (mononitrotoluene, molecular formula C7H7NO2), followed by further nitration of MNT to produce DNT. Depending on the production operation time, existing DNT production processes can be divided into batch and continuous processes. Based on the type of nitrator and the process route, there are various DNT nitration technologies, including batch, pump, tubular, ring, microchannel, and adiabatic nitration. All of these processes have been applied to some extent in actual production. However, these processes all suffer from various problems, such as long process flow, low first-stage toluene conversion and selectivity, large equipment volume, low nitration liquid phase separation efficiency, difficulty in phase interface adjustment, low product yield, numerous by-products, severe 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 conversion rate and selectivity of toluene in the first stage, large equipment volume, low separation efficiency of nitration liquid phase, difficulty in phase interface adjustment, low product yield, many by-products, serious entrainment of nitration tail gas and high energy consumption.

[0004] (II) Technical Solution

[0005] To address the aforementioned technical problems, one embodiment of the present invention provides a synthesis system comprising: two nitrators, two separators, a washing tower, an acid mixer, a heat exchanger, and a waste acid concentration unit; the two nitrators are a first-stage nitrator and a second-stage nitrator; the two separators are a first-stage separator and a second-stage separator.

[0006] 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 scrubbing 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 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 to the raw material pipeline, the waste 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 waste acid concentration unit and the raw material pipeline; the bottom air 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 waste acid concentration unit; the top liquid inlet is connected to the acid outlet; the tube-side inlet is connected to the first acid phase outlet; the tube-side outlet is connected to the waste acid concentration unit; and the shell-side inlet is connected to the second acid phase outlet.

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

[0009] The upper end of the cylindrical body is connected to the upper tube box, and the lower end is connected to the lower tube box, forming a reaction space between the cylindrical body, the upper tube box, and the lower tube box. The tube bundle assembly includes a plurality of heat exchange tubes and is disposed within the cylindrical body. The upper guide tube is disposed within the upper tube box, and its lower end is connected to the upper end of the tube bundle assembly. The lower guide tube is located within the lower tube box, and its upper end is connected to the lower end of the tube bundle assembly. The upper and lower guide tubes are coaxial and have the same radial dimension. The two ends of the heat exchange tubes are respectively connected to the upper guide tube and the lower guide tube, and the two ends of the remaining heat exchange tubes are respectively connected to the upper tube box and the lower tube box; the first liquid receiving plate is located in the upper tube box and above the upper guide tube, the downward-pushing agitator is located in the upper guide tube, the agitator shaft passes through the first liquid receiving plate and is connected to the downward-pushing agitator, the agitator shaft and the downward-pushing agitator are both hollow and interconnected, the agitator shaft has a first opening in the area of ​​the first liquid receiving plate, and the downward-pushing agitator has a second opening.

[0010] Furthermore, the separator includes a separation chamber, a liquid collection tray, a second liquid receiving tray, a disc separator, a hollow shaft, a second motor, a liquid-gathering separator, and a drain pipe;

[0011] The liquid collection tray is located inside the separation chamber, dividing the interior of the separation chamber into a first chamber and a second chamber with vertical spacing. A guide pipe extends downward from the liquid collection tray, and the first chamber and the second chamber are connected through the guide pipe. The second liquid receiving tray and the disc separator are both located in the first chamber, with the disc separator located below the second liquid receiving tray. One end of the hollow shaft is connected to the second motor drive, and the other end passes through the second liquid receiving tray and is connected to the disc separator. The disc separator has an open periphery and is filled with packing material. The second liquid receiving tray and the disc separator are connected through the hollow shaft. The liquid condenser is located in the second chamber and is connected to the lower end of the guide pipe. One end of the drain pipe is vertically installed in the second chamber, and the other end extends out of the second chamber.

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

[0013] Furthermore, the packing material inside the disc separator is 250Y plate corrugated packing; the liquid separator is filled with 250Y plate corrugated packing.

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

[0015] The synthesis process of the dinitrotoluene includes the following steps:

[0016] 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 and the first mixed acid separated from the two-stage separator, are transported to the first-stage nitrifier. Toluene and concentrated nitric acid are first premixed in the first liquid receiving pan of the first-stage nitrifier, and then mixed and reacted with dilute nitric acid and the first mixed acid. The product in the first-stage nitrifier is a mixture of mononitrotoluene and the first-stage acid phase.

[0017] Step S2: The mixture of mononitrotoluene and a first-stage acid phase is fed into a first-stage separator for separation to obtain mononitrotoluene and a first-stage acid phase;

[0018] Step S3: Mononitrotoluene and the second mixed acid from the washing tower are fed into the second-stage nitrator for mixing and reaction. The product in the second-stage nitrator is a mixture of dinitrotoluene and the second-stage acid phase.

[0019] Step S4: The mixture of dinitrotoluene and the two-stage acid phase is fed into a two-stage separator for separation to obtain dinitrotoluene and the two-stage acid phase, which is the first mixed acid in step S1.

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

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

[0022] The acidic gases 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 are transported to the scrubbing tower. The concentrated sulfuric acid from the waste acid concentration unit and the concentrated nitric acid from the upstream feed line are mixed by the acid mixer to form the third mixed acid, which is then transported to the scrubbing tower to wash the acidic gases, resulting in nitration tail gas and the second mixed acid. The nitration tail gas is then transported to the waste acid concentration unit.

[0023] Furthermore, in step S1:

[0024] The volume ratio of material circulation to output in a first-stage nitrifier is 50:1 to 110:1.

[0025] The operating temperature inside the first stage nitrifier is 40℃~55℃;

[0026] The working pressure of the first stage nitrifier is -5KPa(G) to 500KPa(G);

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

[0028] The nitric acid ratio in the first stage nitrifier is 1~1.5.

[0029] Furthermore, the volume ratio of material circulation to output in a first-stage nitrifier is 70:1 to 90:1.

[0030] The operating temperature inside the first stage nitrifier is 45℃~53℃;

[0031] The working pressure of the first stage nitrifier is -2 kPa (G) to 20 kPa (G);

[0032] The acid-to-oil mass ratio in the first stage nitrifier is 2.2-3;

[0033] The nitric acid ratio in the first stage nitrifier is 1.01~1.1.

[0034] Furthermore, in step S3:

[0035] The volume ratio of material circulation to output in the second-stage nitrifier is 50:1 to 115:1.

[0036] The operating temperature of the two-stage nitrifier is 50℃~70℃;

[0037] The working pressure of the two-stage nitrifier is -5KPa(G) to 500KPa(G).

[0038] The acid-to-oil mass ratio in the second-stage nitrifier is 1.5-3.

[0039] The nitric acid ratio in the two-stage nitrifier is 1~1.5.

[0040] Furthermore, the volume ratio of material circulation to output in the second-stage nitrifier is 75:1 to 95:1.

[0041] The operating temperature of the two-stage nitrifier is 56℃~68℃;

[0042] The working pressure of the two-stage nitrifier is -2KPa(G) to 20KPa(G).

[0043] The acid-to-oil mass ratio in the second-stage nitrifier is 1.7-2.

[0044] The nitric acid ratio in the two-stage nitrifier is 1.05~1.2.

[0045] Furthermore, in step S1:

[0046] The mass concentration of concentrated nitric acid from the upstream raw material pipeline is greater than or equal to 95%;

[0047] The mass concentration of dilute nitric acid from the waste acid concentration unit is 40%~70%.

[0048] Furthermore, the concentrated nitric acid from the upstream raw material pipeline has a mass concentration of 98%.

[0049] The mass concentration of dilute nitric acid from the waste acid concentration unit is 55%~65%.

[0050] Furthermore, the concentrated sulfuric acid from the waste acid concentration unit used to form the third mixed acid has a mass concentration greater than or equal to 90%.

[0051] Furthermore, the concentrated sulfuric acid from the waste acid concentration unit used to form the third mixed acid has a mass concentration greater than 93%.

[0052] The beneficial effects of this invention are:

[0053] The synthesis system provided by this invention includes: two nitrators, two separators, a scrubbing tower, an acid mixer, a heat exchanger, and a waste acid concentration unit; the two nitrators are a first-stage nitrator and a second-stage nitrator; the two separators are 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 scrubbing 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... It 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 waste 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 waste acid concentration unit and the raw material pipeline; the bottom air 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 waste acid concentration unit; the top liquid inlet is connected to the acid outlet; the tube-side inlet is connected to the first acid phase outlet; the tube-side outlet is connected to the waste acid concentration unit; and the shell-side inlet is connected to the second acid phase outlet.

[0054] In the process of synthesizing nitrates, the raw materials come from the raw material pipeline, the acid solution generated by the waste acid concentration unit, and the acid solution separated by the two-stage separator. The raw materials are fed into the first-stage nitrator through the first feed end for reaction. The product in the first-stage nitrator is a mixture of a primary oil phase and a primary acid phase. The heat generated during the reaction is absorbed by the circulating water in the shell side of the first-stage separator. The mixture of the primary oil phase and the primary acid phase is then fed into the first-stage separator for separation. The mixture of the primary oil phase and the primary acid phase is discharged from the first-stage nitrator through the first liquid phase outlet and enters the first-stage separator through the third feed end. After separation by the first-stage separator, the mixture of the primary oil phase and the primary acid phase is divided into a primary oil phase and a primary acid phase. The primary oil phase is discharged from the first-stage separator through the first oil phase outlet and enters the second-stage nitrator through the second feed end. The primary acid phase is discharged from the first acid phase outlet. The first stage separator, through the tube side of the heat exchanger, enters the waste acid concentration unit for concentration; the first stage oil phase and the acid discharged from the bottom liquid outlet of the scrubbing tower enter the second stage nitrifier for further reaction, 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 conveyed 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, the mixture of the second stage oil phase and the second stage acid phase is separated into the second stage oil phase and the second stage acid phase; the second stage oil phase, as the final product, is discharged from the second stage separator through the second oil phase outlet 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 conveyed back to the first stage nitrifier through the tube side of the heat exchanger as a reaction feedstock. Gas generated inside the first-stage nitrator is discharged through the first gas phase outlet and enters the scrubbing tower for washing through the bottom inlet. Gas generated inside the second-stage nitrator is discharged through the second gas phase outlet and enters the scrubbing tower for washing through the bottom inlet. Gas generated inside the first-stage separator is discharged through the third gas phase outlet and enters the scrubbing tower for washing through the bottom inlet. Gas generated inside the second-stage separator is discharged through the fourth gas phase outlet and enters the scrubbing tower for washing through the bottom inlet. Liquid from the waste acid concentration unit and the raw material pipeline is mixed in an acid mixer to form an acid solution, which is then used as an absorbent and enters the scrubbing tower through the top inlet. After contacting the gas in the scrubbing tower, the solution is discharged through the bottom outlet and used as a reactant in the second-stage nitrator. The synthesis system provided by this invention adopts a continuous flow nitration process, which has the characteristics of short process flow, uniform raw material dispersion, high conversion rate, high selectivity, and few by-products, making it suitable for large-scale production. Attached Figure Description

[0055] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0056] Figure 1 A structural diagram of the synthesis system provided in an embodiment of the present invention;

[0057] Figure 2 This is a schematic diagram of the structure of a nitrifier provided in an embodiment of the present invention;

[0058] Figure 3 This is a schematic diagram of the separator provided in an embodiment of the present invention.

[0059] Icons: 11-First stage nitrifier; 12-Second stage nitrifier; 21-First stage separator; 22-Second stage separator; 3-Scrubber; 4-Heat exchanger; 5-Acid mixer; 61-Waste acid pump; 62-Mixed acid pump; 7-Waste acid concentration unit;

[0060] 101-Upper tube box; 102-Cylinder body; 103-Lower tube box; 104-First liquid receiving plate; 105-Push-down type agitator; 106-Agitator shaft; 107-Upper guide tube; 108-Lower guide tube; 109-Tube bundle assembly; 110-Guide plate; 111-Overflow weir;

[0061] 201-Separation chamber; 202-Collection tray; 203-Second liquid receiving tray; 204-Disc separator; 205-Hollow shaft; 206-Second motor; 207-Liquid separator; 208-Drain pipe; 209-Adjustment structure; 210-Guide pipe. Detailed Implementation

[0062] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0063] like Figures 1 to 3As shown, one embodiment of the present invention provides a synthesis system, comprising: 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 a first-stage nitrator 11 and a second-stage nitrator 12; the two separators are 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, and a bottom gas inlet. The acid mixer 5 has a fifth feed end and an acid 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 waste 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 outlet; the fourth feed end is connected to the second liquid phase outlet; the fifth feed end is connected to the waste acid concentration unit 7 and the raw material pipeline; the bottom air 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 waste acid concentration unit 7; the top liquid inlet is connected to the acid outlet; the tube-side inlet is connected to the first acid phase outlet; the tube-side outlet is connected to the waste acid concentration unit 7; and the shell-side inlet is connected to the second acid phase outlet.

[0064] The synthesis system provided in this embodiment can be used to synthesize nitrates such as dinitrotoluene, mononitrobenzene, dinitrobenzene, mononitrobenzene, and dinitrobenzene. The synthesis system includes two nitrators, two separators, a scrubbing tower 3, an acid mixer 5, a heat exchanger 4, and a waste acid concentration unit 7. The two nitrators and the two separators have essentially the same structure. For ease of description, the two nitrators are referred to as a first-stage nitrator 11 and a second-stage nitrator 12, and the two separators are referred to as a first-stage separator 21 and a second-stage separator 22. In the process of synthesizing nitrates, the raw materials come from the raw material pipeline, the acid solution generated by the waste acid concentration unit 7, and the acid solution separated by the two-stage separator 22. The raw materials are fed into the first-stage nitrator 11 through the first feed end for reaction. The product in the first-stage nitrator 11 is a mixture of a first-stage oil phase and a first-stage acid phase. The heat generated during the reaction is absorbed by the circulating water in the shell side of the first-stage separator 21. The mixture of the first-stage oil phase and the first-stage acid phase is fed into the first-stage separator 21 for separation. The mixture of the first-stage oil phase and the first-stage acid phase is discharged from the first-stage nitrator through the first liquid phase outlet and enters the first-stage separator 21 through the third feed end. After separation by the first-stage separator 21, the mixture of the first-stage oil phase and the first-stage acid phase are obtained. The first-stage oil phase is discharged from the first-stage separator 21 through the first oil phase outlet and enters the second-stage nitrator 12 through the second feed end. The first-stage acid phase is discharged from the first acid phase outlet. The first phase of the oil phase and the acid solution discharged from the bottom liquid outlet of the washing tower 3 enter the second-stage nitrifier 12 for further reaction. The product in the second-stage nitrifier 12 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 22 for separation. The mixture of the second-stage oil phase and the second-stage acid phase is discharged from the second-stage nitrifier 12 through the second liquid phase outlet and enters the second-stage separator 22 through the fourth feed end for further separation. After separation by the second-stage separator 22, the mixture of the second-stage oil phase and the second-stage acid phase is obtained as the second-stage oil phase and the second-stage acid phase. The second-stage oil phase is discharged from the second-stage separator 22 as the final product through the second oil phase outlet and enters the subsequent process. The second-stage acid phase is discharged from the second-stage separator 22 through the second acid phase outlet and is transported back to the first-stage nitrifier 11 as a reaction feedstock through the tube side of the heat exchanger 4.The gas generated inside the first-stage nitrator 11 is discharged through the first gas phase outlet and enters the washing tower 3 for washing through the bottom inlet. The gas generated inside the second-stage nitrator 12 is discharged through the second gas phase outlet and enters the washing tower 3 for washing through the bottom inlet. The gas generated inside the first-stage separator 21 is discharged through the third gas phase outlet and enters the washing tower 3 for washing through the bottom inlet. The gas generated inside the second-stage separator 22 is discharged through the fourth gas phase outlet and enters the washing tower 3 for washing through the bottom inlet. The liquid from the waste acid concentration unit 7 and the raw material pipeline is mixed in the acid mixer 5 to form an acid solution, which is then used as an absorbent and enters the washing tower 3 through the top inlet. After contacting the gas in the washing tower 3, it is discharged through the bottom outlet and used as a reaction feedstock in the second-stage nitrator 12. The synthesis system provided in this embodiment adopts a continuous flow nitration process, which has the characteristics of short process flow, uniform raw material dispersion, high conversion rate, high selectivity, and few by-products, and is suitable for large-scale production.

[0065] Optionally, in this embodiment, a mixed acid pump 62 is provided between the two-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.

[0066] The synthesis system provided in the embodiments of the present invention, such as 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 plate 104, a stirring shaft 106, a downward-pushing 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, forming a reaction space between the cylinder 102, the upper tube box 101, and the lower tube box 103. The tube bundle assembly 109 includes several heat exchange tubes and is located inside the cylinder 102. The upper guide tube 107 is located inside the upper tube box 101, and its lower end is connected to the upper end of the tube bundle assembly 109. The lower guide tube 108 is located inside the lower tube box 103, and its upper end 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 dimensions. The two ends of the heat exchange tube located between the upper guide tube 107 and the lower guide tube 108 are connected to the upper guide tube 107 and the lower guide tube 108 respectively. The two ends of the remaining heat exchange tubes are connected to the upper tube box 101 and the lower tube box 103 respectively. The first liquid receiving plate 104 is located in the upper tube box 101 and above the upper guide tube 107. The downward-pushing agitator 105 is located in the upper guide tube 107. The stirring shaft 106 passes through the first liquid receiving plate 104 and is connected to the downward-pushing agitator 105. The stirring shaft 106 and the downward-pushing agitator 105 are both hollow and interconnected. The stirring shaft 106 has a first opening in the area located in the first liquid receiving plate 104, and the downward-pushing agitator 105 has a second opening.

[0067] In this embodiment, the structures of the first-stage nitrifier 11 and the second-stage nitrifier 12 are basically the same, the difference being that the upper tube box 101 of the first-stage nitrifier 11 is provided with four feed ports to form the first feed end mentioned above, while the upper tube box 101 of the second-stage nitrifier 12 is provided with two feed ports to form the second feed end mentioned above. When the first-stage nitrifier 11 is in use, the raw material transported by the raw material pipeline first enters the first liquid receiving pan 104 for premixing, and then enters the upper guide tube 107 to mix with the acid from the waste acid concentration unit 7 and the second-stage separator 22, and reacts 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 pan 104, and then enters the upper guide tube 107 to mix with the acid from the washing tower 3, and reacts in the tube bundle assembly 109 to generate a second-stage oil phase.

[0068] In this embodiment, the two ends of the cylinder 102 are open. The upper end of the cylinder 102 is connected to the upper pipe box 101 via a flange or other structure, and the lower end of the cylinder 102 is connected to the lower pipe box 103 via a flange or other structure. The above-mentioned vertical direction is... Figure 2 In the vertical direction, the interior of the cylinder 102 is connected to the interior of the upper tube box 101 and the lower tube box 103. The tube bundle assembly 109 includes two spaced tube sheets and a plurality of heat exchange tubes disposed between the two tube sheets; the first liquid receiving plate 104 and the upper guide tube 107 are both located inside the upper tube box 101, and the first liquid receiving plate 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 inside 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 cylindrical and have the same diameter. The upper guide tube 107 and the lower guide tube 108 are coaxially arranged. Some of the aforementioned heat exchange tubes are located between the upper guide tube 107 and the lower guide tube 108, and the rest are located outside the area of ​​the upper guide tube 107 and the lower guide tube 108. A push-down agitator 105 is located inside the upper guide tube 107. One end of the agitator shaft 106 passes through the first liquid receiving plate 104 and is connected to the push-down agitator 105, while the other end is connected to a drive unit. The drive unit drives the agitator shaft 106 to rotate, thereby causing the push-down agitator 105 located on the agitator shaft 106 to rotate. The agitator and agitator shaft 106 are hollow inside, with a first opening on the agitator shaft 106 and a second opening on the agitator for liquid flow. In this embodiment, preferably, multiple guide plates 110 are also provided along the circumference of the lower tube box 103 for guiding liquid flow. The upper tube box 101 has the aforementioned first liquid phase outlet, and an overflow weir 111 is provided at the first liquid phase outlet.

[0069] The synthesis system provided in the embodiments of the present invention, such as Figure 1 refer to Figure 3As shown, the separator includes a separation chamber 201, a liquid collection tray 202, a second liquid receiving tray 203, a disc separator 204, a hollow shaft 205, a second motor 206, a liquid-gathering separator 207, and a drain pipe 208. The liquid collection tray 202 is located inside the separation chamber 201 and divides the interior of the separation chamber 201 into a first chamber and a second chamber with vertical spacing. A guide pipe 210 extends downward from the liquid collection tray 202, and the first chamber and the second chamber are connected through the guide pipe 210. The second liquid receiving tray 203 and the disc separator 204 are both located in the first chamber. The disc separator 204 is located below the second liquid receiving plate 203. One end of the hollow shaft 205 is connected to the second motor 206 for transmission, and the other end passes through the second liquid receiving plate 203 and is connected to the disc separator 204. The disc separator 204 has an open periphery and is filled with packing material. The second liquid receiving plate 203 and the disc separator 204 are connected through the hollow shaft 205. The liquid separator 207 is located in the second chamber and is connected to the lower end of the guide pipe 210. One end of the drain pipe 208 is vertically installed in the second chamber, and the other end extends out of the second chamber.

[0070] In this embodiment, the separation chamber 201 is a closed cylindrical structure. A guide pipe 210 extends from the lower end of the liquid collection tray 202, which is funnel-shaped. The periphery of the liquid collection tray 202 is connected to the inner wall of the separation chamber 201, thus dividing the interior of the separation chamber 201 into a first chamber and a second chamber spaced vertically. The first and second chambers are connected by the guide pipe 210 on the liquid collection tray 202. A second receiving tray 203 and a disc separator 204 are located in the first chamber, and a drain pipe 208 for draining liquid is located in the second chamber. The drain pipe 208 is a corrugated pipe. The separation chamber 201 is also equipped with an adjustment structure 209 for adjusting the length of the corrugated pipe, thereby controlling the drain liquid level in the second chamber. The separator provided in this embodiment combines gravity separation and static separation, resulting in better separation effect and higher separation efficiency.

[0071] Another embodiment of the present invention provides a synthesis process for dinitrotoluene, wherein the synthesis process for dinitrotoluene employs the synthesis system described in any of the above embodiments; further, the synthesis process for dinitrotoluene includes the following steps:

[0072] In 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 two-stage separator 22, are transported to the first-stage nitrifier 11. Toluene and concentrated nitric acid are first premixed in the first liquid receiving pan 104 of the first-stage nitrifier, and then mixed and reacted with dilute nitric acid and the first mixed acid. The product in the first-stage nitrifier 11 is a mixture of mononitrotoluene and a first-stage acid phase.

[0073] Step S2: The mixture of mononitrotoluene and a first-stage acid phase is fed into a first-stage separator 21 for separation to obtain mononitrotoluene and a first-stage acid phase;

[0074] In step S3, mononitrotoluene and the second mixed acid from the washing tower 3 are fed into the second-stage nitrator 12 for mixing and reaction. The product in the second-stage nitrator 12 is a mixture of dinitrotoluene and the second-stage acid phase.

[0075] In step S4, the mixture of dinitrotoluene and the two-stage acid phase is fed into the two-stage separator 22 for separation to obtain dinitrotoluene and the two-stage acid phase, which is the first mixed acid in step S1.

[0076] In step S2, the first acid phase obtained is transported to the waste acid concentration unit 7 for concentration through the tube side of the heat exchanger 4; 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.

[0077] The first mixed acid in step S1 and the second mixed acid in step S3 are both mixtures of sulfuric acid and nitric acid;

[0078] 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 scrubbing tower 3. The concentrated sulfuric acid from the waste acid concentration unit 7 and the concentrated nitric acid from the upstream feed line are mixed by the acid mixer 5 to form a third mixed acid, which is then transported to the scrubbing tower 3 to scrub the acidic gas, resulting in nitration tail gas and a second mixed acid. The nitration tail gas is then transported to the waste acid concentration unit 7.

[0079] The synthesis process of dinitrotoluene provided in this embodiment involves the following steps: In the first-stage nitrator 11, the upstream raw material pipeline transports toluene and concentrated nitric acid through two inlets of the first-stage nitrator 11 to the first receiving pan 104 for premixing. Dilute nitric acid from the waste acid concentration unit 7 and the first mixed acid from the second-stage separator 22 enter the upper guide tube 107 through the other two inlets of the first-stage nitrator 11. After premixing in the first receiving pan 104, the toluene and concentrated nitric acid enter the stirring shaft 106 through the first opening, then enter the downward-pushing impeller 105 through the stirring shaft 106, and finally exit through the second opening into the upper guide tube 107. In the upper guide tube 107, the toluene and concentrated nitric acid are mixed with the dilute nitric acid and the first mixed acid, and under the action of the downward-pushing impeller 105, they enter the upper guide tube 107 and the lower guide tube. The reaction proceeds fully within the heat exchange tubes between 108 and 107. The product then enters the lower guide tube 108 and lower tube box 103 through this section of heat exchange tubes located between the upper guide tube 107 and lower guide tube 108. Under the action of the guide plate 110 within the lower tube box 103, the product flows into the heat exchange tubes outside the upper guide tube 107 and lower guide tube 108. Finally, it enters the upper tube box 101 from the upper end of the heat exchange tubes outside the upper guide tube 107 and lower guide tube 108, and overflows out of the first liquid phase outlet of the first nitrator 11. The first mixed acid is a mixture of sulfuric acid and nitric acid. Under the condition that sulfuric acid is used as a catalyst, toluene reacts with nitric acid in the heat exchange tubes to produce mononitrotoluene. The product in the first nitrator 11 is a mixture of mononitrotoluene and a first acid phase. Mononitrotoluene is the first oil phase, and the first acid phase is mainly waste acid containing sulfuric acid.

[0080] Furthermore, the product from the first-stage nitrator 11 enters the first-stage separator 21 for separation, yielding mononitrotoluene and a first-stage acid phase. Specifically, within the first-stage separator 21, the product from the first-stage nitrator 11 first enters the second receiving plate 203, and then flows through the hollow shaft 205 to the disc separator 204. The second motor 206 drives the disc separator 204 to rotate, thereby achieving gravity separation of the product from the first-stage nitrator 11 within the disc separator 204. After preliminary separation by the disc separator 204, the product from the first-stage nitrator 11 passes through the disc separator 204... The material exits the disc separator 204 and enters the polymer liquid separator 207 through the guide pipe 210 for further separation. Finally, it exits the polymer liquid separator 207, yielding a first acid phase and mononitrotoluene, with the mononitrotoluene located above the first acid phase. As mentioned above, the first acid phase mainly consists of waste acid containing sulfuric acid. The first acid phase exits the first 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. The mononitrotoluene overflows from the first separator 21 through the drain pipe 208 and enters the second nitrifier 12.

[0081] Furthermore, within the second-stage nitrator 12, mononitrotoluene enters the first receiving plate 104 through one of the inlets, and then sequentially enters the upper guide tube 107 via the stirring shaft 106 and the downward-pushing impeller 105. The second mixed acid from the washing tower 3 enters the upper guide tube 107 through the other inlet. Within the upper guide tube 107, the second mixed acid mixes with mononitrotoluene and, under the action of the downward-pushing impeller 105, enters the heat exchange tube located between the upper guide tube 107 and the lower guide tube 108 for thorough reaction. Afterward, it enters the lower guide tube 108 through this heat exchange tube between the upper guide tube 107 and the lower guide tube 108. Inside the lower tube box 103, under the action of the guide plate 110, the liquid enters the heat exchange tubes outside the upper guide tube 107 and lower guide tube 108, and finally enters the upper tube box 101 from the upper end of the heat exchange tubes outside the upper guide tube 107 and 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 mixture of sulfuric acid and nitric acid. Under the condition that sulfuric acid is a catalyst, mononitrotoluene reacts in the heat exchange tube to generate dinitrotoluene. The product in the second-stage nitrifier 12 is a mixture of dinitrotoluene and the second-stage acid phase. Dinitrotoluene is the second-stage oil phase, and the second-stage acid phase is a mixture of nitric acid and sulfuric acid.

[0082] Furthermore, the product of the second-stage nitrator 12 enters the second-stage separator 22 for separation, yielding dinitrotoluene and a second-stage acid phase. Specifically, within the second-stage separator 22, the product of the second-stage nitrator 12 first enters the second receiving plate 203, and then flows through the hollow shaft 205 to the disc separator 204. The second motor 206 drives the disc separator 204 to rotate, thereby achieving gravity separation of the product of the second-stage nitrator 12 within the disc separator 204. After preliminary separation by the disc separator 204, the product of the second-stage nitrator 12 exits the disc separator 204 through its periphery. 04, and then enters the polymer liquid separator 207 through the guide pipe 210 for further separation, and finally exits the polymer liquid separator 207 to obtain a second-stage acid phase and dinitrotoluene, with the dinitrotoluene located above the second-stage acid phase; as mentioned above, the second-stage acid phase is mainly a mixed acid containing sulfuric acid and nitric acid. 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 as the raw material first mixed acid through the shell side of the heat exchanger 4; the dinitrotoluene is discharged from the second-stage separator 22 by the overflow drain pipe 208 and enters the subsequent process for further processing.

[0083] 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 (nitrated gas) during operation. The acidic gas enters the scrubbing tower 3 for washing. The absorbent in the scrubbing tower 3 consists of concentrated nitric acid from the raw material pipeline and sulfuric acid from the waste acid concentrator. The concentrated nitric acid and sulfuric acid are mixed in the acid mixer 5 and then transported to the scrubbing tower 3. After fully contacting the acidic gas, the mixture is discharged from the bottom outlet of the scrubbing tower 3 and used as the second mixed acid as the raw material for the second-stage nitrifier 12. The nitrification tail gas is then transported to the waste acid concentration unit 7 for concentration treatment.

[0084] The synthesis process of dinitrotoluene provided in this embodiment of the invention has the following characteristics: the organic matter content in the first acid phase separated by the first-stage separator 21 is less than or equal to 0.5 wt%, and the acid content in the separated mononitrotoluene is less than or equal to 0.7 wt%; the toluene conversion rate in the first-stage nitrator 11 reaches 97.8%, and the selectivity for toluene to MNT conversion reaches 97.5%. The conversion rate in the second-stage nitrator 12 is 100%, and the selectivity for MNT to DNT conversion reaches over 99.5%. The organic matter content in the first mixed acid separated by the second-stage separator 22 does not exceed 5 wt%, and the acid content in the separated second oil phase does not exceed 1.5 wt%. NO in the nitration tail gas after washing in the scrubbing tower 3... X The content does not exceed 10 wt%. The second opening is a round hole with a diameter of 3 mm to 15 mm, preferably 6 mm to 10 mm. In the first-stage nitrifier 11 and the second-stage nitrifier 12, the rotational speed of the hollow stirring shaft 106 is adjustable in the range of 300 r / min to 2900 r / min, preferably 600 r / min to 1500 r / min. In the first-stage separator 21 and the second-stage separator 22, the rotational speed of the hollow shaft 205 is adjustable in the range of 300 r / min to 3000 r / min, preferably 1000 r / min to 1500 r / min.

[0085] Furthermore, in the synthesis process of dinitrotoluene provided in this embodiment of the invention, in step S1:

[0086] The volume ratio of material circulation to output 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℃ to 55℃, preferably 45℃ to 53℃; the working pressure in the first-stage nitrifier 11 is -5Kpa(G) to 500KPa(G), preferably -2KPa(G) to 20KPa(G); the acid-to-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 first-stage nitrifier 11 is 1 to 1.5, preferably 1.01 to 1.1.

[0087] In step S3:

[0088] The volume ratio of material circulation to output 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℃ to 70℃, preferably 56℃ to 68℃; the operating 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.

[0089] In step S1:

[0090] 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 waste acid concentration unit 7 is 40% to 70%, preferably 55% to 65%.

[0091] The nitric acid ratio mentioned above refers to the molar ratio or mass ratio between nitric acid and toluene; the material circulation volume refers to the total amount of material circulating in the first-stage nitrifier 11 or the second-stage nitrifier 12; and the output volume refers to the amount of product extracted from 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).

[0092] In the description of this invention, it should be noted that the terms "upper" and "lower," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0093] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linkage" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to a connection within two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances. Furthermore, in the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0094] 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 principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A synthesis system characterized by, The application relates to a nitration device for producing nitric acid, which comprises: two nitration devices, two separators, a washing tower (3), an acid mixer (5), a heat exchanger (4) and a waste acid concentration unit (7); the two nitration devices are a first-stage nitration device (11) and a second-stage nitration device (12); the two separators are a first-stage separator (21) and a second-stage separator (22); the first-stage nitration device (11) is provided with a first feeding end, a first liquid phase outlet and a first gas phase outlet; the second-stage nitration device (12) is provided with a second feeding end, a second liquid phase outlet and a second gas phase outlet; the first-stage separator (21) is provided with a third feeding end, a third gas phase outlet, a first oil phase outlet and a first acid phase outlet; the second-stage separator (22) is provided with a fourth feeding end, a fourth gas phase outlet, a second oil phase outlet and a second acid phase outlet; the washing tower (3) is provided with a top outlet, a top liquid inlet, a bottom gas inlet and a bottom liquid outlet; the acid mixer (5) is provided with a fifth feeding end and an acid liquid outlet; the heat exchanger (4) is provided with a tube side inlet, a tube side outlet, a shell side inlet and a shell side outlet; the first feeding end is communicated with a raw material pipeline, the waste acid concentration unit (7) and the shell side outlet of the heat exchanger (4); the third feeding end is communicated with the first liquid phase outlet; the second feeding end is communicated with the first oil phase outlet and the bottom liquid outlet; the fourth feeding end is communicated with the second liquid phase outlet; the fifth feeding end is communicated with the waste acid concentration unit (7) and a raw material pipeline; the bottom gas inlet is communicated 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 communicated with the waste acid concentration unit (7); the top liquid inlet is communicated with the acid liquid outlet; the tube side inlet is communicated with the first acid phase outlet; the tube side outlet is communicated with the waste acid concentration unit (7); and the shell side inlet is communicated with the second acid phase outlet.

2. The synthesis system of claim 1, wherein, The nitration device comprises an upper pipe box (101), a lower pipe box (103), a cylinder body (102), a first liquid receiving disc (104), a stirring shaft (106), a lower push type stirring paddle (105), an upper flow guide cylinder (107), a lower flow guide cylinder (108) and a pipe bundle assembly (109). The upper end of the cylinder (102) is connected with the upper tube box (101), and the lower end is connected with the lower tube box (103), and the 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 pipes, the tube bundle assembly (109) is arranged in the cylinder (102), the upper flow guide cylinder (107) is arranged in the upper tube box (101), and the lower end of the upper flow guide cylinder (107) is connected with the upper end of the tube bundle assembly (109); the lower flow guide cylinder (108) is located in the lower tube box (103), and the upper end of the lower flow guide cylinder (108) is connected with the lower end of the tube bundle assembly (109); the upper flow guide cylinder (107) and the lower flow guide cylinder (108) are coaxial and have the same radial dimension, the two ends of the heat exchange pipes located between the upper flow guide cylinder (107) and the lower flow guide cylinder (108) are respectively communicated with the upper flow guide cylinder (107) and the lower flow guide cylinder (108), and the two ends of the remaining heat exchange pipes are respectively communicated with the upper tube box (101) and the lower tube box (103); the first liquid receiving disc (104) is arranged in the upper tube box (101) and located above the upper flow guide cylinder (107), the lower push type stirring paddle (105) is located in the upper flow guide cylinder (107), the stirring shaft (106) is connected with the lower push type stirring paddle (105) through the first liquid receiving disc (104), the stirring shaft (106) and the inside of the lower push type stirring paddle (105) are hollow and communicated with each other, the area of the stirring shaft (106) located in the first liquid receiving disc (104) is provided with a first opening, and the lower push type stirring paddle (105) is provided with a second opening.

3. The synthesis system of claim 1, wherein, The separator comprises a separation bin (201), a liquid accumulation disc (202), a second liquid receiving disc (203), a disc separator (204), a hollow shaft (205), a second motor (206), a liquid gathering separator (207) and a liquid discharge pipe (208). The liquid accumulation tray (202) is arranged in the separation bin (201) and separates the inside of the separation bin (201) into a first bin chamber and a second bin chamber which are spaced apart in an up-down direction; the liquid accumulation tray (202) extends downwardly with a flow guide pipe (210), the first bin chamber and the second bin chamber are communicated through the flow guide pipe (210); the second liquid receiving tray (203) and the disc separator (204) are both located in the first bin chamber, the disc separator (204) is located below the second liquid receiving tray (203), one end of the hollow shaft (205) is in transmission connection with the second motor (206), the other end of the hollow shaft (205) penetrates through the second liquid receiving tray (203) and is connected with the disc separator (204), the disc separator (204) is open on the side, the inside of the disc separator (204) is filled with packing, the second liquid receiving tray (203) and the disc separator (204) are communicated through the hollow shaft (205); the liquid gathering separator (207) is located in the second bin chamber, the liquid gathering separator (207) is communicated with the lower end of the flow guide pipe (210), one end of the liquid discharge pipe (208) is vertically arranged in the second bin chamber, the other end of the liquid discharge pipe (208) extends out of the second bin chamber.

4. The synthesis system of claim 2, wherein, The first liquid receiving tray (104) is filled with structured packing; the lower end of the lower flow guide cylinder (108) is filled with structured packing.

5. The synthesis system of claim 3, wherein, The packing in the disc separator (204) is 250Y plate corrugated packing; the liquid gathering separator (207) is filled with 250Y plate corrugated packing.

6. A process for the synthesis of dinitrotoluene, characterized in that, The synthesis system according to claim 2 or 4 is used; The synthesis process of the dinitrotoluene comprises the following steps: In step S1, toluene and concentrated nitric acid from an upstream raw material pipeline, dilute nitric acid from a waste acid concentration unit (7) and first mixed acid separated from a two-stage separator (22) are transported into a one-stage nitrator (11), toluene and concentrated nitric acid are premixed in a first liquid receiving tray (104) of the one-stage nitrator first, and then mixed with dilute nitric acid and the first mixed acid for reaction; the product in the one-stage nitrator (11) is a mixture of mononitrotoluene and one-stage acid phase; In step S2, the mixture of mononitrotoluene and one-stage acid phase is transported into a one-stage separator (21) for separation, mononitrotoluene and one-stage acid phase are obtained; In step S3, mononitrotoluene and second mixed acid from a washing tower (3) are transported into a two-stage nitrator (12) for mixed reaction, the product in the two-stage nitrator (12) is a mixture of dinitrotoluene and two-stage acid phase; In step S4, the mixture of dinitrotoluene and two-stage acid phase is transported into a two-stage separator (22) for separation, dinitrotoluene and two-stage acid phase are obtained, and the two-stage acid phase is the first mixed acid in step S1; In step S2, the one-stage acid phase is transported to the waste acid concentration unit (7) for concentration through the tube side of a heat exchanger (4); in step S4, the two-stage acid phase is transported into the one-stage nitrator (11) as the first mixed acid through the shell side of the heat exchanger (4); The first mixed acid in step S1 and the second mixed acid in step S3 are both mixed liquid of sulfuric acid and nitric acid; The acid gas generated in the first nitration reactor (11) in step S1, the first separator (21) in step S2, the second nitration reactor (12) in step S3 and the second separator (22) in step S4 is transported into the scrubbing tower (3), the concentrated sulfuric acid from the waste acid concentration unit (7) and the concentrated nitric acid from the upstream feed line are mixed by the acid mixer (5) to form the third mixed acid which is transported into the scrubbing tower (3) to wash the acid gas, and the nitration tail gas and the second mixed acid are obtained, and the nitration tail gas is transported into 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 amount to the extraction amount in the first nitration reactor (11) is 50:1~110:1; The working temperature in the first nitration reactor (11) is 40℃~55℃; The working pressure of the first nitration reactor (11) is -5KPa(G)~500KPa(G); The acid / oil mass ratio in the first nitration reactor (11) is 1.5~4; The nitric acid ratio in the first nitration reactor (11) is 1~1.

5.

8. The synthesis process of dinitrotoluene according to claim 7, characterized in that, The volume ratio of the material circulation amount to the extraction amount in the first nitration reactor (11) is 70:1~90:1; The working temperature in the first nitration reactor (11) is 45℃~53℃; The working pressure of the first nitration reactor (11) is -2KPa(G)~20KPa(G); The acid / oil mass ratio in the first nitration reactor (11) is 2.2~3; The nitric acid ratio in the first nitration reactor (11) is 1.01~1.

1.

9. The process for synthesis of dinitrotoluene as claimed in claim 6 wherein, In step S3: The volume ratio of the material circulation amount to the extraction amount in the second nitration reactor (12) is 50:1~115:1; The working temperature of the second nitration reactor (12) is 50℃~70℃; The working pressure of the second nitration reactor (12) is -5KPa(G)~500KPa(G); The acid / oil mass ratio in the second nitration reactor (12) is 1.5~3; The nitric acid ratio in the second nitration reactor (12) is 1~1.

5.

10. The synthesis process of dinitrotoluene according to claim 9, characterized in that, The volume ratio of the material circulation amount to the extraction amount in the second nitration reactor (12) is 75:1~95:1; The working temperature of the second nitration reactor (12) is 56℃~68℃; The working pressure of the second nitration reactor (12) is -2KPa(G)~20KPa(G); The acid / oil mass ratio in the second nitration reactor (12) is 1.7~2; The nitric acid ratio in the second nitration reactor (12) is 1.05~1.

2.

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

12. The synthesis process of dinitrotoluene according to claim 11, characterized in that, The mass concentration of the concentrated nitric acid from the upstream raw material pipeline is 98%; The mass concentration of the dilute nitric acid from the waste acid concentration unit (7) is 55%~65%.

13. The process for synthesis of dinitrotoluene as claimed in claim 6 wherein, The mass concentration of the concentrated sulfuric acid from the waste acid concentration unit (7) for forming the third mixed acid is greater than or equal to 90%.

14. The process for the synthesis of dinitrotoluene according to claim 13, characterized in that, The mass concentration of the concentrated sulfuric acid from the waste acid concentration unit (7) for forming the third mixed acid is greater than 93%.

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