Continuous nitration method of naphthalene disulfonic acid compound

Abstract

The invention relates to a continuous nitration method of naphthalene disulfonic acid compounds, and belongs to the technical field of organic synthesis. According to the invention, the solution containing the naphthalene disulfonic acid compound and the nitric acid solution are continuously input into the tubular reactor, and continuous nitration of the naphthalene disulfonic acid compound is carried out at a low temperature, so that the safety of the nitration process is ensured, the reaction time can be obviously shortened, the reaction selectivity can be improved, and the reaction efficiency can be improved.

Description

Technical Field

[0001] This invention relates to the field of organic synthesis technology, and in particular to a continuous nitration method for naphthalene disulfonic acid compounds. Background Technology

[0002] Naphthalene sulfonic acid nitro compounds are dye intermediates prepared by dissolving naphthalene disulfonic acid compounds (such as 2,7-naphthalene disulfonic acid) in sulfuric acid solution and then reacting them with nitric acid solution. Currently, the preparation process mainly uses batch nitration in a reactor, but this process has the following drawbacks: (1) The nitration reaction is highly exothermic, and the batch operation leads to local overheating of the reactor, which easily causes "runaway temperature" phenomenon; (2) Each batch of reaction needs to go through steps such as feeding, heating, holding, cooling and discharging, which is a long cycle and has low equipment utilization; (3) The mass transfer efficiency is low, the reaction is uneven, and the reaction selectivity is low.

[0003] Therefore, it is essential to develop a continuous nitration method for naphthalene disulfonic acid compounds to ensure the safety of the nitration process while improving the efficiency and selectivity of the nitration reaction. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a continuous nitration method for naphthalene disulfonic acid compounds.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A continuous nitration method for naphthalene disulfonic acid compounds includes the following steps:

[0007] A solution containing naphthalene disulfonic acid compounds and a nitric acid solution are continuously fed into a tubular reactor to carry out a nitration reaction; the nitration reaction temperature is not higher than 50°C; the naphthalene disulfonic acid compounds include 2,7-naphthalene disulfonic acid;

[0008] The reaction products are continuously discharged from the tubular reactor and collected.

[0009] This invention involves continuously feeding a solution containing naphthalene disulfonic acid compounds and a nitric acid solution into a tubular reactor to carry out continuous nitration of the naphthalene disulfonic acid compounds at a relatively low temperature (≤50℃). While ensuring the safety of the nitration process, this invention can significantly shorten the reaction time, improve the reaction selectivity, and increase the reaction efficiency.

[0010] Preferably, the tubular reactor includes a reactor shell, an inlet pipe, an outlet pipe, and several reaction pipes. The reactor shell is a hollow structure with openings at both ends. Sealing gaskets are respectively provided at the two open ends of the reactor shell. The two sealing gaskets and the reactor shell together form an inner cavity. Several reaction pipes are arranged in the inner cavity. The several reaction pipes are connected in series to form a reaction channel. The inlet end of the reaction channel is connected to the inlet pipe, and the outlet end of the reaction channel is connected to the outlet pipe.

[0011] The reactor shell is provided with a medium inlet and a medium outlet that communicate with the inner chamber.

[0012] More preferably, a PTFE rod is disposed inside the reaction tube, and the PTFE rod is provided with a plurality of convex rings arranged at intervals along its axial direction. An annular groove is formed between any two adjacent convex rings along the axial direction of the PTFE rod. The convex ring is provided with a connecting groove extending along its axial direction. The connecting groove extends along the axial direction of the convex ring and communicates with the connecting groove adjacent to it, so that a flow channel is formed between the inner wall of the reaction tube and the PTFE rod; the connecting grooves on any two adjacent convex rings are staggered.

[0013] This invention involves staggering the connecting grooves on any two adjacent convex rings, thereby forming a tortuous flow channel between the inner wall of the reaction tube and the PTFE rod. This creates turbulence within the reaction tube, allowing the solution containing naphthalene disulfonic acid compounds and the nitric acid solution to mix thoroughly within the tortuous flow channel. This improves mass transfer efficiency and enables the continuous nitration method described in this invention to be carried out at lower temperatures. While ensuring nitration safety, this method reduces side reactions, increases reaction rate, improves reaction selectivity, and enhances the conversion rate of naphthalene disulfonic acid compounds.

[0014] Compared with the prior art, the method provided by the present invention is simple and easy to implement, with mild conditions. The mixing and reaction of the solution can be achieved through a tubular reactor without the need for other auxiliary equipment (such as a stirrer, ultrasonic generator, etc.).

[0015] More preferably, the inner chamber is provided with two guide plates, and the guide plates are provided with a plurality of guide holes. Each guide hole includes two through holes and a guide groove. The two through holes are connected through the guide groove. The reaction tube is inserted into the through hole. The inner wall of the through hole is sealed and fixedly connected to the outer wall of the reaction tube. The reaction tube is connected to the guide holes on the two guide plates to form the reaction channel.

[0016] More preferably, the reactor shell is provided with support rings near its two open ends, the guide plate is disposed between the support rings and the sealing gasket, and is tightly fitted to the support rings and the sealing gasket, respectively, and the sealing gasket is provided with a pressure plate on its surface opposite to the guide plate.

[0017] It is understood that the present invention does not impose any particular restrictions on the dimensions of the components in the tubular reactor, and can be designed according to actual needs. For example, the length of the reaction tube is 0.5 to 2 m, the inner diameter of the reaction tube is 15 to 30 mm, the wall thickness of the reaction tube is 0.5 to 3 mm, the difference between the inner diameter of the reaction tube and the diameter of the PTFE rod's convex ring is 0 to 0.1 mm, the depth of the connecting groove (i.e., its radial dimension on the PTFE rod) is 0.1 to 0.3 times the diameter of the convex ring, the width of the connecting groove (i.e., its axial dimension on the PTFE rod) is 0.01 to 0.1 times the length of the PTFE rod, the depth of the annular groove (i.e., its radial dimension on the PTFE rod) is 0.1 to 0.3 times the diameter of the convex ring, and the opening width of the annular groove (i.e., its dimension on the outer circumference of the convex ring) is 0.1 to 0.3 times the diameter of the convex ring.

[0018] This application significantly improves the conversion rate and reaction selectivity of naphthalene disulfonic acid compounds by controlling process parameters such as nitration reaction temperature, reaction residence time, molar ratio of sulfuric acid to naphthalene disulfonic acid compounds in sulfuric acid solution, and molar ratio of nitric acid to naphthalene disulfonic acid compounds.

[0019] Preferably, the temperature of the nitration reaction is 5 to 45°C. For example, the temperature of the nitration reaction can be 5°C, 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, or any two of these values.

[0020] More preferably, the temperature of the nitration reaction is 15–25°C.

[0021] Preferably, the molar ratio M between the nitric acid in the nitric acid solution and the naphthalene disulfonic acid compound in the solution containing the naphthalene disulfonic acid compound is 2 ≤ M ≤ 2.5. For example, the value of M can be 2, 2.1, 2.2, 2.3, 2.4, 2.5, or a range consisting of any two sets of values.

[0022] For further optimization, 2.2≤M≤2.5.

[0023] Preferably, the residence time of the solution containing naphthalene disulfonic acid and the nitric acid solution in the tubular reactor is t, where 40s ≤ t ≤ 120s. For example, the value of t can be 40s, 50s, 60s, 70s, 80s, 90s, 100s, 110s, 120s, or any range of two such values.

[0024] Further optimization is performed where 60s ≤ t ≤ 120s.

[0025] For an even better fit, 80s≤t≤100s.

[0026] Preferably, the solution containing naphthalene disulfonic acid compounds comprises naphthalene disulfonic acid compounds and sulfuric acid solution, wherein the molar ratio of sulfuric acid to naphthalene disulfonic acid compounds in the sulfuric acid solution is (9-12):1.

[0027] For example, the molar ratio of sulfuric acid to the naphthalene disulfonic acid compound in the sulfuric acid solution can be 9:1, 10:1, 11:1, 12:1, or any two of these molar ratios.

[0028] More preferably, the molar ratio of sulfuric acid to the naphthalene disulfonic acid compound in the sulfuric acid solution is (10-11):1.

[0029] More preferably, the sulfuric acid solution contains 90-98% sulfuric acid by mass. For example, the sulfuric acid solution may contain 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or any two of these values.

[0030] More preferably, the sulfuric acid solution contains 95-98% sulfuric acid by mass.

[0031] Preferably, the mass percentage of nitric acid in the nitric acid solution is 90-99%. The mass percentage of nitric acid in the nitric acid solution can be 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or any two of these values.

[0032] More preferably, the mass percentage of nitric acid in the nitric acid solution is 95-97%.

[0033] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0034] This invention continuously feeds a solution containing naphthalene disulfonic acid compounds and a nitric acid solution into a tubular reactor to carry out continuous nitration of the naphthalene disulfonic acid compounds at a lower temperature. While ensuring the safety of the nitration process, it can significantly shorten the reaction time, improve the reaction selectivity, and increase the reaction efficiency. Attached Figure Description

[0035] Figure 1 This is a process flow diagram for the continuous nitration of naphthalene disulfonic acid compounds;

[0036] Figure 2 This is a cross-sectional view of a tubular reactor.

[0037] Figure 3 This is a partial assembly diagram of the reaction tube and the PTFE rod;

[0038] Figure 4 This is a partial front view of a PTFE rod;

[0039] Figure 5 This is a partial rear view of a PTFE rod;

[0040] Figure 6 This is a schematic diagram showing the disassembled components of the tubular reactor, including the guide plate, sealing gasket, and pressure plate.

[0041] In the diagram, 1-tubular reactor, 11-reactor shell, 111-medium inlet, 112-medium outlet, 12-reaction tube, 13-sealing gasket, 14-inner chamber, 15-PTFE rod, 151-convex ring, 152-annular groove, 153-connecting groove, 16-guide plate, 17-support ring, 19-pressure plate, 2-first storage tank, 3-second storage tank, 4-input pipe, 5-output pipe, 6-first metering pump, 7-second metering pump. Detailed Implementation

[0042] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0043] It should be noted that the terms "first" and "second" in this invention are used for descriptive purposes only and should not be construed as indicating the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. All directional indicators (such as "up" and "down") in this invention are only used to explain the relative positional relationships and movements between components in a specific orientation (as shown in the accompanying drawings). If the specific orientation changes, the directional indicator will change accordingly. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion.

[0044] The present invention provides the following embodiments to facilitate understanding of the invention. These embodiments are provided not to limit the scope of the claims.

[0045] The method provided in the following embodiments is achieved by means of, Figures 1-6 The apparatus shown includes a tubular reactor 1, a first storage tank 2, and a second storage tank 3. The tubular reactor 1 is connected to an inlet pipe 4 and an outlet pipe 5. The inlet pipe 4 is connected to the first storage tank 2 via a pipe and a first metering pump 6. The inlet pipe 4 is connected to the second storage tank 3 via a pipe and a second metering pump 7. The outlet pipe 5 is connected to a collection container via a pipe. Control valves are respectively installed on the inlet pipe 4 and the outlet pipe 5. The first storage tank 2 stores a solution containing naphthalene disulfonic acid compounds, and the second storage tank 3 stores a nitric acid solution.

[0046] The tubular reactor 1 includes a reactor shell 11 and several reaction tubes 12. The reactor shell 11 is a hollow structure with openings at both ends. Sealing gaskets 13 are respectively provided at the two opening ends of the reactor shell 11. The two sealing gaskets 13 and the reactor shell 11 together form an inner chamber 14. Seventeen reaction tubes 12 are arranged in the inner chamber 14. The seventeen reaction tubes 12 are connected in series to form a reaction channel. The inlet end of the reaction channel is connected to an input pipe 2, and the outlet end of the reaction channel is connected to an output pipe 3.

[0047] The reactor shell 11 is provided with a medium inlet 111 and a medium outlet 112 that communicate with the inner chamber 14;

[0048] A PTFE rod 15 is provided inside the reaction tube 12. The PTFE rod 15 is provided with a number of convex rings 151 arranged at intervals along its axial direction. An annular groove 152 is formed between any two adjacent convex rings 151 along the axial direction of the PTFE rod 15. A connecting groove 153 is provided on the convex ring 151 extending along its axial direction. The connecting groove 153 extends along the axial direction of the convex ring 151 and communicates with the adjacent connecting groove 153. The inner wall of the reaction tube 12 and the annular groove 152 and the connecting groove 153 on the PTFE rod form a flow channel.

[0049] The reaction tube 12 is 1m long, has an inner diameter of 19mm, a wall thickness of 1.25mm, and is made of silicon carbide; the PTFE rod 15 is 1m long, has a convex ring diameter of 18.9mm, an annular groove 152 has a depth of 3mm, an opening width of 5mm, a connecting groove 153 has a width of 5mm, and a connecting groove 153 has a depth of 3mm.

[0050] The sealing gasket 13 is made of PTFE.

[0051] The connecting grooves 153 on any two adjacent convex rings 151 are located on both sides of the central axis of the PTFE rod 15.

[0052] The reactor shell 11 is provided with support rings 17 near its two opening ends. A guide plate 16 is provided between the support rings 17 and the sealing gasket 13. The guide plate 16 is tightly fitted with the support rings 17 and the sealing gasket 13 respectively. A pressure plate 19 is provided on the side of the sealing gasket 13 facing away from the guide plate 16. The side wall of the reactor shell 11, the sealing gasket 13, the guide plate 16 and the pressure plate 19 are sequentially fastened together by bolts and nuts.

[0053] The inner chamber 14 is provided with two guide plates 16 and two support rings 17. The support rings 17 are integrally formed and connected to the inner chamber 14. The guide plates 16 are disposed between the support rings 17 and the sealing gasket 13. Each of the two guide plates 16 is provided with 9 guide holes. Each guide hole includes two through holes 161 and a guide groove 162. The two through holes 161 are connected through the guide groove 162. The two ends of the reaction tube 12 are respectively inserted into the through holes 161 of the two guide plates 16. The inner wall of the through hole 161 is sealed and fixedly connected to the outer wall of the reaction tube 12. The 17 reaction tubes 12 are connected in series through the guide holes on the two guide plates 16 to form the reaction channel. One end of the input tube 4 passes through the mounting holes on the corresponding pressure plate 19 and the corresponding sealing gasket 13 in sequence and then connects to the inlet end of the reaction channel. One end of the output tube 5 passes through the mounting holes on the corresponding pressure plate 19 and the corresponding sealing gasket 13 in sequence and then connects to the inlet end of the reaction channel. The outer wall of the input pipe 4 is sealed and fixedly connected to the inner wall of the corresponding mounting hole, and the outer wall of the output pipe 5 is sealed and fixedly connected to the inner wall of the corresponding mounting hole.

[0054] The reactor shell 11 is equipped with a temperature sensor for monitoring the temperature of the inner chamber;

[0055] In use, the solution containing naphthalene disulfonic acid compounds is regulated by the first metering pump 6, and the input flow rate of nitric acid solution is regulated by the second metering pump 7.

[0056] The reactor shell 11 is provided with a medium inlet 111 and a medium outlet 112 communicating with the inner chamber 14. The medium inlet 111 is connected to the water bath via a pipe, a transfer pump, and a flow regulating valve, and the medium outlet 112 is connected to the water bath via a pipe. Before each embodiment is implemented, the transfer pump is started to input water from the water bath into the inner chamber 14, and the temperature inside the inner chamber 14 is pre-adjusted to the required reaction temperature. During each embodiment, the water input flow rate is adjusted by the flow regulating valve, and / or the water temperature is adjusted by the water bath, thereby achieving temperature regulation of the inner chamber 14.

[0057] The conversion rate of 2,7-naphthalenedisulfonic acid and the selectivity of 1,8-dinitro-3,6-naphthalenedisulfonic acid in the following examples were tested. The test method was as follows: the collected reaction product was diluted with pure water by an appropriate factor and then filtered through a filter membrane with a pore size of 0.22 μm. The filtrate was used as a sample and tested by high performance liquid chromatography. The conversion rate of 2,7-naphthalenedisulfonic acid and the selectivity of 1,8-dinitro-3,6-naphthalenedisulfonic acid were calculated. The results are shown in Tables 1 to 6.

[0058] The test conditions are as follows:

[0059] The chromatographic column was a 4.6×150mm Extend-C18;

[0060] The detection wavelength is set to 254nm;

[0061] Column temperature set to 30℃;

[0062] The mobile phase is 10 g·L -1 Lithium sulfate solution;

[0063] Flow rate set to 1 mL·min -1 ;

[0064] The detector is an SPD-16;

[0065] The injection volume was 10 μL;

[0066] The running time is 30 minutes.

[0067] Example 1

[0068] This embodiment provides a continuous nitration method for naphthalene disulfonic acid compounds, including the following steps:

[0069] Start the first metering pump 6 to continuously input the solution containing naphthalene disulfonic acid compounds from the first storage tank 2 into the reaction channel of the tubular reactor 1. When the solution containing naphthalene disulfonic acid compounds fills the first reaction tube (the first reaction tube is the reaction tube closest to the input tube 4 among the 17 reaction tubes connected in series), start the second metering pump 7. Under the action of the first metering pump 6 and the second metering pump 7, the solution containing naphthalene disulfonic acid compounds and the nitric acid solution continuously enter the reaction channel of the tubular reactor 1 to carry out the nitration reaction.

[0070] The solution containing naphthalene disulfonic acid compounds is prepared by mixing naphthalene disulfonic acid compounds and sulfuric acid solution. The molar ratio of sulfuric acid to naphthalene disulfonic acid compounds in the sulfuric acid solution is 10:1, the mass percentage of sulfuric acid in the sulfuric acid solution is 98%, and the mass percentage of nitric acid in the nitric acid solution is 95%.

[0071] The nitration reaction is carried out at a temperature of 15°C, and the residence time of the solution containing naphthalene disulfonic acid and the nitric acid solution in the tubular reactor is 80 seconds.

[0072] In step S1, the input flow rates of the solution containing naphthalene disulfonic acid and the nitric acid solution are controlled by the first metering pump and the second metering pump, respectively, so that the input flow rate of the solution containing naphthalene disulfonic acid is 2.8 L / h, and the molar ratio of naphthalene disulfonic acid in the solution to nitric acid in the nitric acid solution is 2.2.

[0073] The reaction products are continuously discharged from tubular reactor 1, and the discharged reaction products are collected.

[0074] Examples 2-6

[0075] The difference between Examples 2-6 and Example 1 is that the residence times of the solutions containing naphthalene disulfonic acid compounds and nitric acid solutions in tubular reactor 1 in Examples 2-6 are shown in Table 1.

[0076] Table 1

[0077]

[0078] Examples 7-11

[0079] The difference between Examples 7-11 and Example 1 is that the nitration temperatures in Examples 7-11 are shown in Table 2.

[0080] Table 2

[0081]

[0082] Examples 12-15

[0083] The difference between Examples 12-15 and Example 1 is that the molar ratios of naphthalene disulfonic acid compounds and sulfuric acid in the sulfuric acid solution in Examples 12-15 are shown in Table 3. In Example 12, a blockage occurred in the reaction tube during the process due to the excessive viscosity of the material.

[0084] Table 3

[0085]

[0086] Examples 16-18

[0087] The difference between Examples 16-18 and Example 1 is that the mass percentage of nitric acid in the nitric acid solution in Examples 16-18 is shown in Table 4.

[0088] Table 4

[0089]

[0090] Examples 19-23

[0091] The difference between Examples 19-23 and Example 1 is that the mass percentage of nitric acid in the nitric acid solution in Examples 19-23 is shown in Table 5.

[0092] Table 5

[0093]

[0094]

[0095] Example 24

[0096] The difference between this embodiment and Embodiment 1 is that no PTFE rod is placed in the reaction tube in this embodiment. In this embodiment, the molar ratio of sulfuric acid to naphthalene disulfonic acid compound in the sulfuric acid solution is 10:1, the mass percentage of sulfuric acid in the sulfuric acid solution is 98%, and the mass percentage of nitric acid in the nitric acid solution is 95%. The temperature of the nitration reaction is 15°C, and the residence time of the solution containing naphthalene disulfonic acid compound and the nitric acid solution in the tubular reactor is 80s. The molar ratio of naphthalene disulfonic acid compound in the solution to nitric acid in the nitric acid solution is 2.2.

[0097] Example 25

[0098] The difference between this embodiment and Embodiment 1 is that no PTFE rod is placed in the reaction tube in this embodiment. In this embodiment, the molar ratio of sulfuric acid to naphthalene disulfonic acid compound in the sulfuric acid solution is 10:1, the mass percentage of sulfuric acid in the sulfuric acid solution is 98%, and the mass percentage of nitric acid in the nitric acid solution is 95%. The temperature of the nitration reaction is 15°C, and the residence time of the solution containing naphthalene disulfonic acid compound and the nitric acid solution in the tubular reactor is 160s. The molar ratio of naphthalene disulfonic acid compound in the solution containing naphthalene disulfonic acid compound to nitric acid in the nitric acid solution is 2.2.

[0099] Table 6

[0100]

[0101] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A continuous nitration method for naphthalene disulfonic acid compounds, characterized in that, Includes the following steps: A solution containing naphthalene disulfonic acid compounds and a nitric acid solution are continuously fed into a tubular reactor to carry out a nitration reaction; the nitration reaction temperature is not higher than 50°C; the naphthalene disulfonic acid compounds include 2,7-naphthalene disulfonic acid; The reaction products are continuously discharged from the tubular reactor and collected.

2. The continuous nitration method for naphthalene disulfonic acid compounds as described in claim 1, characterized in that, The tubular reactor includes a reactor shell, an inlet pipe, an outlet pipe, and several reaction pipes. The reactor shell is a hollow structure with openings at both ends. Each of the two opening ends of the reactor shell is provided with a sealing gasket. The two sealing gaskets and the reactor shell together form an inner cavity. Several reaction pipes are arranged in the inner cavity and are connected in series to form a reaction channel. The inlet end of the reaction channel is connected to the inlet pipe, and the outlet end of the reaction channel is connected to the outlet pipe. The reactor shell is provided with a medium inlet and a medium outlet that communicate with the inner chamber.

3. The continuous nitration method for naphthalene disulfonic acid compounds as described in claim 2, characterized in that, The reaction tube contains a PTFE rod, which has several convex rings spaced apart along its axial direction. An annular groove is formed between any two adjacent convex rings along the axial direction of the PTFE rod. Each convex ring has a connecting groove extending along its axial direction. The connecting groove extends along the axial direction of the convex ring and communicates with its adjacent connecting groove, so that a flow channel is formed between the inner wall of the reaction tube and the PTFE rod. The connecting grooves on any two adjacent convex rings are staggered.

4. The continuous nitration method for naphthalene disulfonic acid compounds as described in claim 2, characterized in that, The inner chamber is provided with two guide plates, and the guide plates are provided with a plurality of guide holes. Each guide hole includes two through holes and a guide groove. The two through holes are connected through the guide groove. The reaction tube is inserted into the through hole. The inner wall of the through hole is sealed and fixedly connected to the outer wall of the reaction tube. The reaction tube is connected to the guide holes on the two guide plates to form the reaction channel.

5. The continuous nitration method for naphthalene disulfonic acid compounds as described in claim 4, characterized in that, The reactor shell is provided with support rings near its two opening ends. The guide plate is disposed between the support ring and the sealing gasket, and is tightly fitted to the support ring and the sealing gasket respectively. The sealing gasket is provided with a pressure plate on its side surface opposite to the guide plate.

6. The continuous nitration method for naphthalene disulfonic acid compounds as described in claim 1, characterized in that, The nitration reaction is carried out at a temperature of 5–45°C.

7. The continuous nitration method for naphthalene disulfonic acid compounds as described in claim 1, characterized in that, The molar ratio M between the nitric acid in the nitric acid solution and the naphthalene disulfonic acid compound in the solution containing the naphthalene disulfonic acid compound is 2 ≤ M ≤ 2.

5.

8. The continuous nitration method for naphthalene disulfonic acid compounds as described in claim 1, characterized in that, The residence time of the solution containing naphthalene disulfonic acid and the nitric acid solution in the tubular reactor is t, where 40s ≤ t ≤ 120s.

9. The continuous nitration method for naphthalene disulfonic acid compounds as described in claim 1, characterized in that, The solution containing naphthalene disulfonic acid compounds includes naphthalene disulfonic acid compounds and sulfuric acid solution, wherein the molar ratio of sulfuric acid to naphthalene disulfonic acid compounds in the sulfuric acid solution is (9-12):

1.

10. The continuous nitration method for naphthalene disulfonic acid compounds as described in claim 1, characterized in that, The nitric acid solution contains 90-99% nitric acid by mass.

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