A continuous tubular oxidation reactor for p-nitrobenzoic acid

Abstract

The present application relates to the technical field of tubular reactor, in particular to a continuous tubular oxidation reactor for p-nitrobenzoic acid, comprising: an initial oxidation pipe, a middle section oxidation pipe and a deep oxidation pipe, the initial oxidation pipe, the middle section oxidation pipe and the deep oxidation pipe are all provided with a jet oscillation assembly at the starting end; the initial oxidation pipe, the middle section oxidation pipe and the deep oxidation pipe are distributed from top to bottom, and the inner diameter gradually decreases and the pitch gradually increases; the jet oscillation assembly comprises a jet nozzle and an oscillation cavity, which strengthens mass transfer and produces oscillation mixing; the reactor adopts a three-stage oxidation pipe segmented design, the pipe diameter and the pitch of each stage are adapted to the requirements of different reaction stages, and the temperature is controlled by an external jacket to provide a precise and suitable environment for the reaction; the initial oxidation stage is adapted to the corresponding structure to realize steady flow and mild heat exchange and reduce the initial pressure drop; the main oxidation stage produces suitable secondary flow through a reasonable structure to strengthen radial mixing and heat transfer, eliminate local hot spots and avoid abnormal reaction.

Description

Technical Field

[0001] This invention relates to the field of tubular reactor technology, and more specifically to a continuous tubular oxidation reactor for p-nitrobenzoic acid. Background Technology

[0002] Nitrobenzoic acid has three isomers: ortho, meta, and para. It is obtained by oxidizing p-nitrotoluene. The oxidizing agent can be sodium dichromate, air, manganese ore powder, nitric acid, etc. Using p-nitrotoluene as a raw material, in the presence of sulfuric acid, the oxidation reaction is carried out with sodium dichromate at 55°C to produce p-nitrobenzoic acid.

[0003] Patent application CN202022759658.4 discloses a continuous tubular oxidation reactor for p-nitrobenzoic acid, comprising a feeding section, a mixing section, a low-temperature reaction section, a high-temperature reaction section, and a cooling section. Materials are transported within the tubular reactor via pressure differential. This patent demonstrates the application of a tubular reactor in the production of p-nitrobenzoic acid, which can replace a reaction vessel for continuous operation, offering superior reaction efficiency and purity compared to a reaction vessel.

[0004] Tubular reactors have high mass transfer efficiency in production. However, in industrial scale-up, the increase in tube diameter can lead to a loss of mass transfer efficiency, which can easily cause local overheating, increased backmixing, and product crystallization in the later stages of the reaction. To solve these problems, a static mixer is usually added to compensate for the loss of mass transfer efficiency. Summary of the Invention

[0005] To address the aforementioned shortcomings of existing technologies, this invention provides a continuous tubular oxidation reactor for p-nitrobenzoic acid, which effectively solves the problem of reduced mass transfer efficiency in industrial scale-up processes of existing technologies.

[0006] To achieve the above objectives, the present invention provides the following technical solution: The present invention provides a continuous tubular oxidation reactor for p-nitrobenzoic acid, comprising a frame, including an initial oxidation tube, a middle oxidation tube, and a deep oxidation tube mounted on the frame, wherein the starting ends of the initial oxidation tube, the middle oxidation tube, and the deep oxidation tube are all provided with jet oscillation components; The initial oxidation tube, the middle oxidation tube, and the deep oxidation tube are distributed from top to bottom, with the inner diameter gradually decreasing and the pitch gradually increasing. The jet turbulence assembly includes a jet nozzle and a turbulence chamber, which enhances mass transfer and produces turbulent mixing.

[0007] Furthermore, the jet oscillation assembly includes a contraction-expansion type jet nozzle and a self-excited oscillating pulse jet nozzle one. The self-excited oscillating pulse jet nozzle one is installed at the starting end of the initial oxidation tube, and the contraction-expansion type jet nozzle is installed at the end of the self-excited oscillating pulse jet nozzle one.

[0008] Furthermore, the jet oscillation assembly also includes a tapered and expanded nozzle one and a self-excited oscillating pulse jet nozzle two. The end of the initial oxidation tube is connected to a bend, which is distributed downwards and fixedly connected to the tapered and expanded nozzle one. The self-excited oscillating pulse jet nozzle two is fixedly connected to the bottom end of the tapered and expanded nozzle one. The beginning end of the tapered and expanded nozzle one matches the bend of the initial oxidation tube, and the end end matches the self-excited oscillating pulse jet nozzle two, which is used to enhance the flow rate and strengthen mass transfer, and to generate oscillating mixing.

[0009] Furthermore, the jet oscillation assembly also includes a second converging and expanding nozzle. The end of the middle section oxidation tube is connected to a bend, the bottom of which is distributed downwards and fixedly connected to the second converging and expanding nozzle. The first end of the second converging and expanding nozzle matches the bend of the middle section oxidation tube, and the end matches the third self-excited oscillating pulse jet nozzle, which is used to enhance the flow rate and strengthen mass transfer. The bottom end of the second converging and expanding nozzle is fixedly connected to the third self-excited oscillating pulse jet nozzle, which is used to generate oscillation mixing.

[0010] Furthermore, the initial oxidation tube, the intermediate oxidation tube, and the deep oxidation tube are all equipped with jacketed temperature control on the outside, and SMA flexible spiral strips are fixed inside the initial oxidation tube, the intermediate oxidation tube, and the deep oxidation tube.

[0011] Furthermore, both ends of the SMA flexible spiral are fixedly connected to limiting rings, which are located within the flanges at the ends of the initial oxidation tube, the intermediate oxidation tube, and the deep oxidation tube. The diameter of the SMA flexible spiral is smaller than the inner diameter of the initial oxidation tube, the intermediate oxidation tube, and the deep oxidation tube, allowing it to float and rotate slightly.

[0012] Furthermore, the initial oxidation tube, the intermediate oxidation tube, and the deep oxidation tube have multiple spiral-shaped guide grooves at their starting ends to guide the liquid flow out of the jet agitation component and drive the SMA flexible spiral strip.

[0013] Furthermore, the AF phase transition temperatures of the three SMA flexible spiral strips correspond to the initial oxidation tube, the intermediate oxidation tube, and the deep oxidation tube, and the SMA flexible spiral strips are affected by the temperature of the external jacket.

[0014] The technical solution provided by this invention has the following advantages compared with the known prior art: 1. Each oxidation tube in this reactor is equipped with an integrated SMA flexible spiral strip, allowing for slight floating. Under the influence of fluid flow, the SMA flexible spiral strip generates low-frequency micro-vibrations and slight rotation, continuously disturbing the near-wall flow field and reducing the deposition and scaling of p-nitrobenzoic acid microcrystals on the tube wall. Compared to the drawbacks of traditional reactors that require periodic shutdowns for cleaning hard scale, this structure significantly extends the shutdown and cleaning cycle, reducing equipment maintenance frequency. Furthermore, the SMA flexible spiral strip is made of an elastic, temperature-resistant, and corrosion-resistant titanium-nickel-based shape memory alloy, ensuring safe and reliable use, further reducing maintenance costs and complexity, and guaranteeing long-term stable operation of the reactor.

[0015] 2. The reactor employs a three-stage oxidation tube segmented design, with each segment's tube diameter and pitch adapted to the requirements of different reaction stages. Combined with external jacket temperature control, this provides a precise and suitable environment for the reaction. The initial oxidation stage utilizes a corresponding structure to achieve stable flow and gentle heat exchange, reducing initial pressure drop. The main oxidation stage generates appropriate secondary flow through a rational structure, enhancing radial mixing and heat transfer, eliminating local hot spots, and preventing abnormal reactions. The deep oxidation stage uses a specific structure to increase axial flow velocity and tube wall shear force, reducing centrifugal wall-throwing effects, minimizing crystal adhesion, and balancing reaction efficiency with subsequent cleaning and unclogging. The synergistic effect of each stage ensures a stable and efficient reaction, improving product conversion.

[0016] 3. Each oxidation tube is equipped with a jet turbulence assembly at its starting end. Combined with the tube structure at different stages, this assembly forces fluid acceleration in various flow environments, significantly enhancing mass transfer. The jet nozzles employ a coaxial contraction-expansion design, forcing the organic phase and oxidant to collide and shear, breaking up droplets into a uniformly dispersed system. Downstream, a self-excited oscillation chamber generates periodic vortices and transient cavitation bubbles through self-excited oscillation. Upon collapse, these bubbles release micro-jet streams and shock waves, breaking up aggregates and further preventing scaling. This assembly increases turbulence intensity, reduces dispersed phase size, and shortens the mixing path. Compared to static mixing tubes, it significantly improves mixing efficiency and reaction uniformity, effectively ensuring stable product quality. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0018] Figure 1 This is a schematic diagram of the overall structure of the present invention; Figure 2 This is a schematic diagram of the initial oxidation tube, the intermediate oxidation tube, and the deep oxidation tube of the present invention; Figure 3This is a schematic diagram of the initial connection between the oxidation tube and the jet oscillation assembly of the present invention; Figure 4 This is a schematic diagram showing the separation of the deep oxidation tube and the SMA flexible spiral strip according to the present invention; Figure 5 For the present invention Figure 4 Enlarged view of point A in the middle; Figure 6 This is a schematic diagram showing the unfolded inner wall of the initial oxidation tube, the middle oxidation tube, and the deep oxidation tube of the present invention. Figure 7 This is a half-sectional view showing the connection relationship between the flange and the limiting ring of the present invention.

[0019] The labels in the diagram represent: 1. Initial oxidation tube; 2. Intermediate oxidation tube; 3. Deep oxidation tube; 4. Contraction-expansion jet nozzle; 5. Self-excited oscillating pulse jet nozzle one; 6. Gradually contracting and expanding nozzle one; 7. Self-excited oscillating pulse jet nozzle two; 8. Gradually contracting and expanding nozzle two; 9. Self-excited oscillating pulse jet nozzle three; 10. SMA flexible spiral strip; 11. Guide groove; 12. Limiting ring. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0021] The present invention will be further described below with reference to embodiments.

[0022] Reference Figures 1 to 6 Example: A continuous tubular oxidation reactor for p-nitrobenzoic acid includes an initial oxidation tube 1, a middle oxidation tube 2, and a deep oxidation tube 3. Each of the three tubes has an externally fitted temperature-controlled jacket. Each of the three tubes also has an SMA flexible spiral strip 10 fixed inside. The two ends of the SMA flexible spiral strip 10 are connected to limiting rings 12 at cross points. (Refer to...) Figure 7The limiting ring 12 is located inside the flange at the end of the initial oxidation tube 1, the intermediate oxidation tube 2, or the deep oxidation tube 3. After the flange is installed at the end of the initial oxidation tube 1, the intermediate oxidation tube 2, or the deep oxidation tube 3, it clamps the limiting ring 12 together with the end of the initial oxidation tube 1, the intermediate oxidation tube 2, or the deep oxidation tube 3, and ensures that the limiting ring 12 has a slight range of motion, allowing the SMA flexible spiral strip 10 to float and rotate slightly. The starting ends of the initial oxidation tube 1, the intermediate oxidation tube 2, and the deep oxidation tube 3 are all provided with jet agitation components. The initial oxidation tube 1, the intermediate oxidation tube 2, and the deep oxidation tube 3 are distributed from top to bottom, with the inner diameter gradually decreasing and the pitch gradually increasing. The jet agitation component includes a jet nozzle and an agitation chamber, which enhances mass transfer and generates agitation mixing.

[0023] It is important to note that Figure 1 and Figure 2 Only one arrangement of the initial oxidation tube 1, the intermediate oxidation tube 2, and the deep oxidation tube 3 is shown. Horizontal and winding arrangements are mature technologies in this field, so no further limitations are made here.

[0024] The initial oxidation tube 1, which forms the main body of the initial oxidation stage, has a specification of DN80-100. The intermediate oxidation tube 2 has a specification of DN50-60, and the deep oxidation tube 3 has a specification of DN30-40. In the early stage of the reaction, the small pitch can increase radial mixing and heat exchange. In the middle stage of the reaction, a medium pitch is used for strong mass transfer and heat exchange. In the later stage of the reaction, when products precipitate, a large pitch and small diameter are used to increase the flow rate and prevent scaling. The initial oxidation tube 1, intermediate oxidation tube 2, and deep oxidation tube 3 are all equipped with SMA flexible spiral strips 10. Under fluid flow, they generate low-frequency micro-vibration and slight rotation, continuously disturbing the near-wall flow field and reducing the deposition and scaling of p-nitrobenzoic acid microcrystals in the tube wall. Traditional backwashing is ineffective against hard scale, so periodic shutdown cleaning is required. With the configuration of SMA flexible spiral strips 10, it is difficult for scale to be deposited in the tube wall, which can extend the shutdown cleaning cycle. Moreover, the SMA flexible spiral strips 10 are made of elastic, temperature-resistant, and corrosion-resistant titanium-nickel-based shape memory alloy, which is relatively safe and has a low maintenance cycle.

[0025] In the production of p-nitrotoluic acid by nitric acid oxidation, p-nitrotoluene is used as a raw material, nitric acid is added, and oxidation is carried out under precise temperature conditions. The reaction temperature is controlled by the jackets outside the initial oxidation tube 1, the intermediate oxidation tube 2, and the deep oxidation tube 3. The initial oxidation tube 1 corresponds to the initial oxidation stage, and the temperature should be controlled at 60-80℃ to prepare for the reaction. The intermediate oxidation tube 2 corresponds to the main oxidation stage, and the temperature is controlled at 100-120℃. The deep oxidation tube 3 corresponds to the deep oxidation stage, and the temperature is controlled at 120-160℃.

[0026] The initial oxidation tube 1, intermediate oxidation tube 2, and deep oxidation tube 3 have different diameters and pitches. In the early stage of the reaction, flow stabilization and heat exchange are required. The initial oxidation tube 1, with its larger diameter and smaller pitch, is suitable for conditions with low material viscosity and mild exothermic reaction. The dense spiral facilitates compact arrangement, mild heat exchange, and reduces the initial pressure drop. The intermediate oxidation tube 2 has a medium diameter and pitch. The reaction is the most vigorous and the heat release is the largest. The constant pitch can generate a suitable secondary flow, enhance radial mixing and heat transfer, and eliminate local hot spots. The deep oxidation tube 3 has a small diameter and a large pitch. In the deep oxidation tube 3, a large amount of product precipitates and is prone to adhering to the wall and forming scale. The small diameter can increase the axial flow velocity and the shear force of the tube wall, while the large pitch weakens the centrifugal wall-throwing effect, reduces crystal adhesion, and facilitates subsequent unblocking and cleaning.

[0027] It should be noted that a matching metering pump, filter, etc. need to be installed at the front end of the initial oxidation tube 1, and temperature and pressure measuring devices and matching safety valves should be installed in the initial oxidation tube 1, the intermediate oxidation tube 2 and the deep oxidation tube 3 to ensure overall safety. Since this part belongs to the prior art and is not within the scope of protection of this application, it will not be further limited or restricted here.

[0028] The jet oscillation components are distributed at the starting ends of the initial oxidation tube 1, the intermediate oxidation tube 2, and the deep oxidation tube 3. With different tube diameters and pitches, the initial oxidation tube 1, the intermediate oxidation tube 2, and the deep oxidation tube 3 force the fluid to accelerate in different flow environments, thereby enhancing the mass transfer effect. A self-excited oscillation chamber is set downstream of the jet nozzle. The self-excited oscillation mode generates periodic vortices. The pulse jet forms transient cavitation bubbles in the chamber. When the bubbles collapse, they release micro-jet streams and shock waves, breaking up the aggregates. The coaxial jet can enhance the turbulence intensity. The oscillation chamber also reduces the size of the dispersed phase to the micron level, thereby improving the mixing efficiency and reaction uniformity. Compared with the static mixing tube, the mixing path can be shortened and the mixing effect is enhanced.

[0029] Specifically, the jet oscillation assembly includes a self-excited oscillating pulse jet nozzle 5 connected to the starting end of the initial oxidation tube 1, and a contraction-expansion type jet nozzle 4 fixedly connected to the end of the self-excited oscillating pulse jet nozzle 5 (the end away from the initial oxidation tube 1). The contraction-expansion type jet nozzle 4 connects two raw materials, and the center of the contraction-expansion type jet nozzle 4 carries the organic phase, while the outer ring carries nitric acid or other oxidants.

[0030] The contraction-expansion jet nozzle 4 is the jet nozzle in the jet turbulence assembly. It is coaxially contraction-expansion and has a three-section design. The center of the contraction section carries the p-nitrotoluene organic phase, the outer ring carries nitric acid, and the throat is the narrowest point. The two phases are forced to collide, shear, and break the droplets. In the expansion section, the pressure rises, and the vortex ring further breaks up the droplets, forming a uniformly dispersed system. It works in conjunction with the downstream self-excited oscillating pulse jet nozzle 5. The self-excited oscillating pulse jet nozzle 5 has a cavity diameter ratio of 2.3-3.3 and a length-to-diameter ratio of 0.6-0.7. It generates 20-200Hz pressure pulses through vortex shedding, periodically disturbing the flow field, matching the boundary layer shedding frequency with the reaction time scale, and forming a cavitation effect. The combination of the two can simultaneously enhance macroscopic and microscopic mixing, thus strengthening the mixing effect.

[0031] It should be noted that the contraction-expansion jet nozzle 4 and the self-excited oscillating pulse jet nozzle 5 are matched with the initial oxidation tube 1, and the jet velocity should be controlled at 1.5 m / s to avoid excessive backmixing in the low-speed section. The length-to-diameter ratio of the self-excited oscillating pulse jet nozzle 5 is preferably 0.65 to match the mild reaction kinetics.

[0032] Specifically, the jet oscillation assembly also includes a tapered and expanding nozzle 6 and a self-excited oscillating pulse jet nozzle 7. The end of the initial oxidation tube 1 is connected to a bend, which is distributed downward and fixedly connected to the tapered and expanding nozzle 6. The self-excited oscillating pulse jet nozzle 7 is fixedly connected to the bottom end of the tapered and expanding nozzle 6. The beginning of the tapered and expanding nozzle 6 matches the bend of the initial oxidation tube 1, and the end matches the self-excited oscillating pulse jet nozzle 7. This is used to enhance the flow rate and strengthen mass transfer, and to generate oscillating mixing. The jet turbulence assembly also includes a tapered and expanding nozzle 28. The end of the middle section oxidation tube 2 is connected to a bend, with the bottom of the bend facing downwards and fixedly connected to the tapered and expanding nozzle 28. The beginning of the tapered and expanding nozzle 28 matches the bend of the middle section oxidation tube 2, and the end matches the self-excited oscillating pulse jet nozzle 39, which is used to enhance the flow rate and strengthen mass transfer. The bottom of the tapered and expanding nozzle 28 is fixedly connected to the self-excited oscillating pulse jet nozzle 39, which is used to generate turbulent mixing.

[0033] The intermediate oxidation tube 2 and the deep oxidation tube 3 correspond to the main oxidation section and the deep oxidation section, respectively. Their mixing requirements gradually decrease. The gradually narrowing and expanding nozzle 1 6 and the gradually narrowing and expanding nozzle 2 8 can be Laval nozzles or Venturi mixers. The cavity diameter ratio and length-to-diameter ratio of the self-excited oscillating pulse jet nozzle 1 5, the self-excited oscillating pulse jet nozzle 2 7, and the self-excited oscillating pulse jet nozzle 3 9 are similar, but the volume of the self-excited oscillating pulse jet nozzle 2 7 and the self-excited oscillating pulse jet nozzle 3 9 should decrease step by step. Among them, the volume of the oscillation cavity inside the self-excited oscillating pulse jet nozzle 3 9 should be the same as that of the self-excited oscillating pulse jet nozzle 1 5. To avoid pulse attenuation caused by high-viscosity materials, the material, after being accelerated and mixed by the gradually expanding and contracting nozzle 6, enters the middle section oxidation tube 2 after being further mixed by the self-excited oscillating pulse jet nozzle 7. It then enters the gradually expanding and contracting nozzle 8 at the end of the middle section oxidation tube 2. After being accelerated by the gradually expanding and contracting nozzle 8 and mixed by the self-excited oscillating pulse jet nozzle 9, it enters the deeper oxidation tube 3 with a smaller diameter for deep oxidation. Finally, the material coming out of the deep oxidation tube 3 needs to be quickly cooled in the condenser. After being cooled to about 60°C, it enters the gas-liquid separator to collect the products and treat the waste gas.

[0034] Specifically, the initial oxidation tube 1, the intermediate oxidation tube 2, and the deep oxidation tube 3 have multiple spiral-shaped guide grooves 11 at their starting ends. The depth of the guide grooves 11 extends from the end of the tube wall inwards, changing from deep to shallow. That is, the groove is deepest at the opening position and gradually extends smoothly into the tube, forming a smooth and unobstructed groove. This groove is used to guide the liquid flow out of the jet agitation component and drive the SMA flexible spiral strip 10.

[0035] Furthermore, the AF phase transition temperatures of the three SMA flexible spiral strips 10 correspond to those of the initial oxidation tube 1, the intermediate oxidation tube 2, and the deep oxidation tube 3, and the SMA flexible spiral strips 10 are affected by the temperature of the external jacket.

[0036] The initial oxidation tube 1 operates at a temperature of 60-80℃. The AF phase transition temperature of the SMA flexible spiral strip 10 inside the initial oxidation tube 1 can be 70℃. The jacket outside the initial oxidation tube 1 can control the temperature fluctuation within a range of ±5℃ during the oxidation process. The SMA flexible spiral strip 10 inside the initial oxidation tube 1 contracts and twists when the temperature is higher than the AF; it rebounds and resets when the temperature is lower. Repeated, periodic temperature control allows the SMA flexible spiral strip 10 to generate controllable periodic torsional vibration, enhancing disturbance near the tube wall and reducing crystallization on the tube wall. Similarly, the jackets outside the intermediate oxidation tube 2 and the deep oxidation tube 3 can also utilize temperature control to control the periodic contraction and rebound of the SMA flexible spiral strip 10 within them. Correspondingly, the intermediate oxidation tube 2 and the deep oxidation tube 3... The AF phase transition temperature of the SMA flexible spiral strip 10 inside the oxidation tube 3 should also match the working temperature of the intermediate oxidation tube 2 and the deep oxidation tube 3. It should be the midpoint between the working temperatures of the intermediate oxidation tube 2 and the deep oxidation tube 3. In this way, the temperature fluctuations generated by the jacket will always be within the working temperature range of the intermediate oxidation tube 2 and the deep oxidation tube 3. Moreover, since the temperature change is small, the impact on the oxidation reaction is weak. On this basis, the guide grooves 11 distributed at 15° to 20° on the inner side of the starting end of the initial oxidation tube 1, the intermediate oxidation tube 2 and the deep oxidation tube 3 guide the liquid flow to form a swirling flow along the tube wall. The swirling flow impacts the SMA flexible spiral strip 10 and generates a certain driving force, causing the SMA flexible spiral strip 10 to rotate slightly, increasing the disturbance near the tube wall, and further reducing the crystallization of the product in the tube wall.

[0037] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions will not cause the essence of the corresponding technical solutions to deviate from the protection scope of the technical solutions of the embodiments of the present invention.

Claims

1. A continuous tubular oxidation reactor for p-nitrobenzoic acid, comprising a frame, characterized in that, include: An initial oxidation tube (1), a middle oxidation tube (2), and a deep oxidation tube (3) are installed on a stand. The starting ends of the initial oxidation tube (1), the middle oxidation tube (2), and the deep oxidation tube (3) are all equipped with jet oscillation components. The initial oxidation tube (1), the middle oxidation tube (2) and the deep oxidation tube (3) are distributed from top to bottom, with the inner diameter gradually decreasing and the pitch gradually increasing. The jet agitation assembly includes a jet nozzle and an agitation chamber, which enhances mass transfer and produces agitated mixing. The initial oxidation tube (1), the middle oxidation tube (2) and the deep oxidation tube (3) are all filled with SMA flexible spiral strips (10). The initial oxidation tube (1), the middle oxidation tube (2) and the deep oxidation tube (3) have multiple spiral-shaped guide grooves (11) at their starting ends, which are used to guide the liquid flow out of the jet agitation component and drive the SMA flexible spiral strips (10). Both ends of the SMA flexible spiral strip (10) are fixedly connected to limiting rings (12). The limiting rings (12) are located inside the flanges at the ends of the initial oxidation tube (1), the middle section oxidation tube (2) and the deep oxidation tube (3). The diameter of the SMA flexible spiral strip (10) is smaller than the inner diameter of the initial oxidation tube (1), the middle section oxidation tube (2) and the deep oxidation tube (3), and it can float and rotate slightly.

2. The continuous tubular oxidation reactor for p-nitrobenzoic acid according to claim 1, characterized in that, The jet oscillation assembly includes a contraction-expansion jet nozzle (4) and a self-excited oscillating pulse jet nozzle (5). The self-excited oscillating pulse jet nozzle (5) is installed at the starting end of the initial oxidation tube (1), and the contraction-expansion jet nozzle (4) is installed at the end of the self-excited oscillating pulse jet nozzle (5).

3. The continuous tubular oxidation reactor for p-nitrobenzoic acid according to claim 2, characterized in that, The jet turbulence assembly also includes a tapered and expanded nozzle one (6) and a self-excited oscillating pulse jet nozzle two (7). The end of the initial oxidation tube (1) is connected to a bend, which is distributed downward and fixedly connected to the tapered and expanded nozzle one (6). The self-excited oscillating pulse jet nozzle two (7) is fixedly connected to the bottom end of the tapered and expanded nozzle one (6). The beginning of the tapered and expanded nozzle one (6) matches the bend of the initial oxidation tube (1), and the end matches the self-excited oscillating pulse jet nozzle two (7), which is used to enhance the flow rate and strengthen mass transfer, and to generate turbulent mixing.

4. The continuous tubular oxidation reactor for p-nitrobenzoic acid according to claim 3, characterized in that, The jet turbulence assembly also includes a tapered and expanding nozzle two (8), the end of the middle section oxidation tube (2) is connected to a bend, the bottom end of the bend is distributed downward and fixedly connected to the tapered and expanding nozzle two (8), the head end of the tapered and expanding nozzle two (8) is matched with the bend of the middle section oxidation tube (2), and the end end is matched with the self-excited oscillating pulse jet nozzle three (9) to enhance the flow rate and strengthen mass transfer. The bottom end of the tapered and expanding nozzle two (8) is fixedly connected to the self-excited oscillating pulse jet nozzle three (9) to generate turbulent mixing.

5. The continuous tubular oxidation reactor for p-nitrobenzoic acid according to claim 1, characterized in that, The initial oxidation tube (1), the middle oxidation tube (2) and the deep oxidation tube (3) are all equipped with jacketed temperature control.

6. The continuous tubular oxidation reactor for p-nitrobenzoic acid according to claim 5, characterized in that, The AF phase transition temperatures of the three SMA flexible spiral strips (10) correspond to the initial oxidation tube (1), the middle oxidation tube (2) and the deep oxidation tube (3), and the SMA flexible spiral strips (10) are affected by the temperature of the external jacket.

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