A countercurrent multilayer stirred nitration tower suitable for liquid-liquid nitration of aromatic hydrocarbons

Abstract

The application discloses a countercurrent multilayer stirring nitration tower suitable for aromatic hydrocarbon liquid-liquid nitration reaction, which is provided with annular distributors at the top and bottom of the middle reaction zone of the tower, the top annular distributor is connected with a heavy phase feeding port, the bottom annular distributor is connected with a light phase feeding port, two-phase countercurrent contact reaction is realized, and multistage temperature control is realized by arranging multiple groups of heat exchange pipe layers in the middle of the reaction zone; meanwhile, based on the structure of the nitration tower, the size of the internal structure of the nitration tower is limited by formula based on reaction heat and reaction efficiency. The nitration tower can realize countercurrent reaction of raw materials and acid, effectively avoids problems in parallel flow, makes the reaction rate more uniform, realizes multistage temperature control, temperature control is more convenient, and the acid consumption can be reduced to a certain extent.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of nitration tower, and particularly relates to a countercurrent multilayer stirring nitration tower suitable for liquid-liquid aromatic hydrocarbon nitration reaction. BACKGROUND

[0002] Aromatic hydrocarbon nitration process is widely used in the chemical industry, and the generated mononitro and dinitro compounds are intermediates of a large number of chemical products, especially widely used in the fields of medicine and dye.

[0003] The aromatic hydrocarbon nitration reaction is a strong exothermic reaction, so the heat exchange capacity of the reactor is required to be high, otherwise there is a risk of reaction temperature out of control, reducing the safety of the device; at the same time, the reaction is basically a heterogeneous reaction, so the mixing effect of the reactor is required to be high, the phase contact area needs to be increased, and the mass transfer effect needs to be improved, otherwise the reaction rate will be small in the later period, the reaction time will be prolonged, the reactor volume will be increased, which is not conducive to the cost, and at the same time, in order to ensure the conversion rate of the reaction, more acid needs to be consumed, and more waste acid is generated.

[0004] At present, the reactors used for aromatic hydrocarbon nitration mainly include the following types:

[0005] The kettle type reactor is generally used for batch process, the raw material is usually added in batches, the feeding time is long, the reaction period is long, the production capacity is small, the heat exchange capacity and mass transfer capacity are poor, and the acid consumption is also large, which is not conducive to cost and environmental protection;

[0006] The continuous pipe type reactor generally feeds the aromatic hydrocarbon raw material and mixed acid together, and the two flow in the pipe, which leads to a very high reaction rate at the beginning and a large heat release, reducing the safety of the reactor, and in the later period of the reaction, the conversion rate is high due to the low concentration of sulfuric acid and raw material, and the reaction time is long, increasing the reactor volume;

[0007] The micro-pipe reactor nitration is one of the relatively excellent methods, the large heat exchange area provided by the micro-pipe can effectively solve the heat release problem in the nitration process, but this method has small processing capacity and high cost, so the application range is limited;

[0008] The multistage nitration method connects multiple reactors in series, so that the acid phase and the organic phase flow countercurrently between the reactors, the acid consumption is small, and the purity of the nitration product obtained is high, but the equipment is more, the occupied area is large, and actually the acid phase and the organic phase still flow parallelly in a single reactor. SUMMARY

[0009] In view of the above problems, the purpose of the present application is to provide a countercurrent multilayer stirring nitration tower for liquid-liquid aromatic hydrocarbon nitration reaction.

[0010] The specific technical scheme is as follows:

[0011] The application discloses a countercurrent multilayer stirring nitration tower suitable for aromatic hydrocarbon liquid-liquid nitration reaction, which is divided into a top layered zone, a middle reaction zone and a bottom layered zone by a partition plate, the inner wall of the middle reaction zone is uniformly provided with multilayer sieve plate rings from top to bottom, the top sieve plate ring and the bottom sieve plate ring are uniformly provided with first distribution holes, and the inner ring of the top sieve plate ring and the bottom sieve plate ring is respectively provided with an annular distributor, the annular distributor is uniformly provided with second distribution holes, the annular distributor of the top sieve plate ring is connected with a heavy phase feeding port, the annular distributor of the bottom sieve plate ring is connected with a light phase feeding port, a plurality of temperature control sections are arranged between the middle sieve plate rings, a plurality of heat exchange pipe layers are arranged in each temperature control section, and a group of cooling water in-out pipe groups are connected with the inlets and outlets of the heat exchange pipe layers in each temperature control section; temperature control is realized by the distribution of the heat exchange pipe layers and the control of the cooling water flow; the cooling water in-out pipe groups extend into the middle reaction zone from the top layered zone and are vertically connected with the bottom sieve plate ring in a sealing mode; and the nitration tower is further provided with multilayer stirring mechanisms, which extend from the top of the nitration tower to the bottom layered zone through the multilayer sieve plate rings.

[0012] Further, the multilayer stirring mechanism comprises a motor, a rotating shaft and multilayer stirring paddles uniformly arranged on the rotating shaft, one end of the rotating shaft is connected with the motor, and the other end extends from the top of the nitration tower to the bottom layered zone through the multilayer sieve plate rings.

[0013] Further, the nitration tower is further provided with cooling coils, the cooling coils are arranged in the bottom layered zone if the acid phase in the reaction system is a heavy phase, and the cooling coils are arranged in the top layered zone if the acid phase in the reaction system is a light phase; the cooling coils can control the separation of the acid and the organic phase and ensure that the organic phase will not solidify.

[0014] Further, the cooling water in-out pipe group comprises a cooling water inlet pipe and a cooling water outlet pipe, and each heat exchange pipe layer comprises a plurality of parallel heat exchange coils.

[0015] Further, the relationship among the four size parameters in the interval between the sieve plate rings satisfies the following formula:

[0016] D = 0.5D2, D1 = 0.67D2

[0017] In the formula, D2 is the inner diameter of the nitration tower, m; D1 is the inner diameter of the sieve plate ring (1), m; D is the diameter of the stirring paddle (63), m; and h is the interval height between adjacent sieve plate rings (1), m.

[0018] The inner diameter D2 of the nitration tower is calculated by the following formula

[0019]

[0020]

[0021] Wherein, a represents the ratio of the apparent liquid velocity to the flooding liquid velocity, ranging from 0.5 to 0.7; V A , V S is the volume flow rate of the aromatic hydrocarbon raw material and mixed acid, m 3 / s; u A , u S is the flooding velocity of the aromatic hydrocarbon raw material phase and mixed acid phase, m / s; is the liquid flooding holdup; L R is the two-phase flow ratio; u K is the superficial velocity, m / s; σ is the interfacial tension, N / m; ρ A , ρ S are the densities of the aromatic hydrocarbon raw material phase and mixed acid phase, kg / m 3 ; μ S is the viscosity of the mixed acid phase, Pa·s; g is the gravitational acceleration, m / s 2 ; N is the rotational speed of the stirring paddle (63), r / s; N P is the power factor, which can be 1-3 under the nitration system.

[0022] Further, the calculation formula of the height H of the middle reaction zone of the tower is as follows:

[0023]

[0024] Wherein, H represents the height of the middle reaction zone of the tower, m; t is the reaction residence time, s.

[0025] Further, the top and bottom layered zones of the tower have the same height, and the calculation formula of the height of the layered zone is as follows:

[0026]

[0027] Wherein, H1 represents the height of the layered zone, m; d p is the average diameter of the droplets of the aromatic hydrocarbon raw material phase, m.

[0028] Further, the heat exchange coil is a serpentine circular frame, and the angle of the serpentine bending is , and the relationship is as follows:

[0029]

[0030] Wherein, A and A * are the heat exchange area required to meet the reaction heat load and the actual heat exchange area, m 2 ; Q is the reaction heat load, W; Δt is the average heat transfer temperature difference between the cooling water and the material in the tower, ℃, d i , d om is the inner and outer diameter of the heat exchange coil, °; a1, a2, a3 are the number of heat exchange coil layers in each heat exchange pipe, the number of heat exchange pipe layers in each temperature control section, and the number of temperature control sections, respectively; m is the inner and outer diameter of the heat exchange coil, °; a1, a2, a3 are the number of heat exchange coil layers in each heat exchange pipe, the number of heat exchange pipe layers in each temperature control section, and the number of temperature control sections, respectively; i m is the inner and outer diameter of the heat exchange coil, °; a1, a2, a3 are the number of heat exchange coil layers in each heat exchange pipe, the number of heat exchange pipe layers in each temperature control section, and the number of temperature control sections, respectively; o m is the inner and outer diameter of the heat exchange coil, °; a1, a2, a3 are the number of heat exchange coil layers in each heat exchange pipe, the number of heat exchange pipe layers in each temperature control section, and the number of temperature control sections, respectively; 2 m is the inner and outer diameter of the heat exchange coil, °; a1, a2, a3 are the number of heat exchange coil layers in each heat exchange pipe, the number of heat exchange pipe layers in each temperature control section, and the number of temperature control sections, respectively; i m is the inner and outer diameter of the heat exchange coil, °; a1, a2, a3 are the number of heat exchange coil layers in each heat exchange pipe, the number of heat exchange pipe layers in each temperature control section, and the number of temperature control sections, respectively; o m is the inner and outer diameter of the heat exchange coil, °; a1, a2, a3 are the number of heat exchange coil layers in each heat exchange pipe, the number of heat exchange pipe layers in each temperature control section, and the number of temperature control sections, respectively; 2 m is the inner and outer diameter of the heat exchange coil, °; a1, a2, a3 are the number of heat exchange coil layers in each heat exchange pipe, the number of heat exchange pipe layers in each temperature control section, and the number of temperature control sections, respectively; i m is the inner and outer diameter of the heat exchange coil, °; a1, a2, a3 are the number of heat exchange coil layers in each heat exchange pipe, the number of heat exchange pipe layers in each temperature control section, and the number of temperature control sections, respectively; o m is the inner and outer diameter of the heat exchange coil, °; a1, a2, a3 are the number of heat exchange coil layers in each heat exchange pipe, the number of heat exchange pipe layers in each temperature control section, and the number of temperature control sections, respectively; is m is the inner and outer diameter of the heat exchange coil, °; a1, a2, a3 are the number of heat exchange coil layers in each heat exchange pipe, the number of heat exchange pipe layers in each temperature control section, and the number of temperature control sections, respectively;

[0031] Further, the top layer of the tower is provided with a light phase discharge port, and the bottom layer of the tower is provided with a heavy phase discharge port.

[0032] The beneficial effects of the present application are:

[0033] 1) The nitration tower of the present application is composed of a top layer, a middle reaction zone and a bottom layer, so that the nitration reaction and the separation of different phase materials can be realized in the same device during continuous operation, the reaction and separation are coupled, the production efficiency is improved, and the pollution and danger caused by material transmission are reduced;

[0034] 2) The nitration tower of the present application can realize countercurrent reaction of raw materials and acid, effectively avoiding the problems in parallel flow, the acid concentration is low at the beginning and the raw material concentration is high, the acid concentration is high at the end and the raw material concentration is low, so that the reaction rate is more uniform, the temperature control is more convenient, the acid consumption does not need to be increased to ensure that the acid concentration is high enough in the later stage of reaction, the rate in the later stage of reaction can also be maintained at a high level under less initial acid amount, which reduces the consumption of acid; for raw materials that need to be dinitrated, such as chlorobenzene, the nitric acid concentration is low in the front section of the reaction zone, which meets the low nitric acid concentration requirement of mononitration reaction; the nitric acid concentration is high in the rear section of the reaction zone, which meets the high nitric acid concentration requirement;

[0035] 3) The present invention uses a heat exchange tube layer composed of a multi-layer serpentine ring frame for temperature control. Compared with heat exchange methods such as jackets and traditional coils, it has a higher space utilization rate and can provide a larger heat exchange area. The serpentine ring-shaped twisted heat exchange tube can provide a larger heat exchange area due to multiple bends, and can also enhance the turbulence of the cooling water flowing in the tube, thereby increasing the convective heat transfer coefficient in the tube.

[0036] 4) The heat exchange tube configuration acts like a baffle in a stirred tank within the compartment. The combination of heat exchange tubes and agitator can disrupt the circumferential motion of the fluid, eliminate swirling, and prevent axial stratification of the reaction system. In the case of the reactor simply rotating axially without mixing (resulting in poor reaction effect), the turbulence of the fluid in the compartment is enhanced, and the convective heat transfer coefficient outside the tubes is increased. Moreover, with this heat exchange tube configuration, the cooling water inlet and outlet pipes can be stuck in the gaps formed by the bends of the heat exchange tubes, making it easier to fix the heat exchange tubes, improving their structural strength, and enhancing safety performance.

[0037] 5) This invention divides the heat exchange tube layer arranged between the sieve plate rings into multiple segments, forming multiple temperature control zones for independent temperature control, thus improving the flexibility of temperature control: In the strongly exothermic section in the middle of the reaction zone where the reactant concentration is highest, the cooling water flow rate and heat exchange area are increased to enhance heat exchange capacity (the average concentration is highest in the middle position during countercurrent flow), avoiding temperature runaway and improving safety; in the section at the aromatic feed where the nitric acid concentration is lowest and the reaction rate is slower, the cooling water flow rate is appropriately reduced to maintain a higher temperature and accelerate the reaction; in the section at the acid phase feed where the nitric acid concentration is highest, the cooling water flow rate is appropriately increased to maintain a lower temperature, preventing excessively high temperatures from causing nitric acid to decompose into nitrogen oxides and reducing product yield. For some temperature-sensitive nitration reactions, such as mononitration products which easily generate dinitration byproducts at excessively high temperatures, and the temperature of dinitration products affecting the nitro substitution position, flexible temperature control can avoid these situations and effectively improve the yield of the target product.

[0038] 6) The present invention has layered zones at both the top and bottom of the tower, eliminating the need for external separation devices. At the same time, the device itself is a tower type, reducing the floor space required.

[0039] 7) This invention specifically sets up a heat exchange coil in the acid phase stratification zone (which may be a heavy phase or a light phase depending on the system). Since the aromatic nitration products have a relatively high solubility in acid, cooling the waste acid from the reaction zone can precipitate the dissolved nitration products. By controlling an appropriate cooling temperature, it can be ensured that the acid phase precipitates nitration products as much as possible while ensuring that the precipitated nitration products are still in a molten state, so that they can separate from the acid phase due to the density difference.

[0040] 8) The application applies multi-layer stirring system to nitration reaction device, which ensures uniform mixing of materials in the whole reaction zone, and the configuration of the nitration tower ensures that acid phase and organic phase will flow reversely even if stirring fails, which to some extent avoids the risk of local overheating of the reaction zone due to serious stratification in the reaction zone. BRIEF DESCRIPTION OF DRAWINGS

[0041] Figure 1 is a sectional view of the structure of the application;

[0042] Figure 2 is a perspective view of the heat exchange tube layer of the application;

[0043] Figure 3 is a schematic view of the bending angle of the heat exchange coil;

[0044] Figure 4 is a sectional view of the heat exchange tube layer;

[0045] Figure 5 is a perspective view of the sieve ring and distributor at the bottom.

[0046] In the figure: 1, sieve ring; 11, first distribution hole; 12, annular distributor; 121, second distribution hole; 2, heavy phase feed inlet; 3, light phase feed inlet; 4, heat exchange tube layer; 41, heat exchange coil; 5, cooling water inlet and outlet pipe group; 51, cooling water inlet pipe; 52, cooling water outlet pipe; 6, multi-layer stirring mechanism; 61, motor; 62, rotating shaft; 63, stirring paddle; 7, light phase discharge outlet; 8, heavy phase discharge outlet; 9, cooling coil. DETAILED DESCRIPTION

[0047] The application will be further described below in combination with the drawings and examples, but the protection scope of the application is not limited thereto.

[0048] As shown in Figure 1 , a countercurrent rotating disc nitration reaction tower suitable for aromatic liquid-liquid nitration reaction is divided into a top stratification zone, a middle reaction zone and a bottom stratification zone by a partition, and the middle reaction zone is uniformly provided with multiple sieve rings 1 from top to bottom, as shown in Figure 5As shown, the bottom sieve plate ring 1 is uniformly provided with first distribution holes 11, and the inner ring is provided with an annular distributor 12, which is uniformly provided with second distribution holes 121. The structure of the top sieve plate ring 1 is the same as that of the bottom sieve plate ring 1. The annular distributor 12 of the top sieve plate ring 1 is connected with the heavy phase feed port, and the annular distributor 12 of the bottom sieve plate ring 1 is connected with the light phase feed port 3. The middle sieve plate rings 1 are provided with a plurality of temperature control sections. Each temperature control section is provided with a plurality of heat exchange pipe layers 4. The inlet and outlet of the heat exchange pipe layer 4 in each temperature control section is connected with a group of cooling water inlet and outlet pipe groups 5. Through the distribution of the heat exchange pipe layer 4 and the control of the cooling water flow, multi-stage temperature control is realized. The cooling water inlet and outlet pipe group 5 extends into the middle reaction zone of the tower from the layered zone at the top of the tower and vertically penetrates through the multiple sieve plate rings 1 and the bottom sieve plate ring 1 in a sealing manner, as shown in Figure 2 As shown, the cooling water inlet and outlet pipe group 5 includes a cooling water inlet pipe 51 and a cooling water outlet pipe 52. Each heat exchange pipe layer 4 includes a plurality of parallel heat exchange coils 41. The heat exchange coil 41 is a serpentine circular frame, as shown in Figure 3 As shown, the angle of the serpentine bending is The angle between the two adjacent sieve plate rings 1 is 30°-60°, and the angle between the two adjacent sieve plate rings 1 is 30°-60°. The nitration tower is further provided with a plurality of stirring mechanisms 6. The stirring mechanism 6 includes a motor 61, a rotating shaft 62, and a plurality of stirring paddles 63 uniformly arranged on the rotating shaft 62. One end of the rotating shaft 62 is connected with the motor 61, and the other end extends from the top of the nitration tower to the bottom of the layered zone at the bottom of the tower through the multiple sieve plate rings 1. The nitric acid tower is further provided with a cooling coil 9. If the acid phase in the reaction system is the heavy phase, the cooling coil 9 is arranged in the layered zone at the bottom of the tower. If the acid phase in the reaction system is the light phase, the cooling coil 9 is arranged in the layered zone at the top of the tower. The layered zone at the top of the tower is provided with a light phase discharge port 7, and the layered zone at the bottom of the tower is provided with a heavy phase discharge port 8.

[0049] As shown in Figure 4 The relationship between the four size parameters in the interval between the sieve plate rings 1 satisfies the following formula:

[0050]

[0051] D = 0.5D2 (2)

[0052] D1 = 0.67D2 (3)

[0053] In the formula, D2 is the inner diameter of the nitration tower, m; D1 is the inner diameter of the sieve plate ring 1, m; D is the diameter of the stirring paddle 63, m; h is the interval height between the adjacent sieve plate rings 1, m;

[0054] The inner diameter D2 of the nitration tower is calculated by the following formula

[0055]

[0056]

[0057] In the formula, 'a' represents the ratio of the apparent liquid velocity to the flooding point liquid velocity, ranging from 0.5 to 0.7; V A V S For aromatic feedstock and mixed acid volumetric flow rate, m 3 / s;u A u S , where m / s is the flooding rate of the aromatic feedstock phase and the mixed acid phase. For flooding retention rate; L R The two-phase flow ratio; u K ρ is the characteristic velocity, m / s; σ is the interfacial tension between the two phases, N / m; A ρ S The densities of the aromatic feedstock phase and the mixed acid phase are respectively, in kg / m³. 3 μ S ρ is the viscosity of the mixed acid phase, Pa·s; g is the acceleration due to gravity, taken as 9.81 m / s². 2 N represents the stirring speed of the impeller at 63 r / s; N P This is the power factor, which can be 1-3 in nitration systems.

[0058] The formula for calculating the height H of the reaction zone in the middle of the tower is as follows:

[0059]

[0060] In the formula, H represents the height of the reaction zone in the middle of the tower, in meters (m); t is the residence time of the reaction, in seconds (s).

[0061] The height of the top and bottom stratification zones is the same. The formula for calculating the height of the stratification zone is as follows:

[0062]

[0063] In the formula, H1 represents the height of the layered zone, in meters (m); d p denoted as the average diameter of the aromatic feedstock droplets, in meters (m).

[0064] like Figure 3 As shown, the angle of the serpentine bend is The included angle, and its relationship is:

[0065]

[0066] In the formula, A, A * These are the required heat transfer area and the actual heat transfer area, respectively, in meters. 2 Q represents the reaction heat load, in W; Δt represents the average heat transfer temperature difference between the cooling water and the material inside the tower, in °C, d. i d om is the inner and outer diameter of the heat exchange coil 41; a1, a2, a3 are the number of heat exchange coils 41 in each heat exchange tube layer 4, the number of heat exchange tube layers 4 in each temperature control section, and the number of temperature control sections, respectively; m is the inner and outer diameter of the heat exchange coil 41; a1, a2, a3 are the number of heat exchange coils 41 in each heat exchange tube layer 4, the number of heat exchange tube layers 4 in each temperature control section, and the number of temperature control sections, respectively; i m is the inner and outer diameter of the heat exchange coil 41; a1, a2, a3 are the number of heat exchange coils 41 in each heat exchange tube layer 4, the number of heat exchange tube layers 4 in each temperature control section, and the number of temperature control sections, respectively; o m is the inner and outer diameter of the heat exchange coil 41; a1, a2, a3 are the number of heat exchange coils 41 in each heat exchange tube layer 4, the number of heat exchange tube layers 4 in each temperature control section, and the number of temperature control sections, respectively; 2 m is the inner and outer diameter of the heat exchange coil 41; a1, a2, a3 are the number of heat exchange coils 41 in each heat exchange tube layer 4, the number of heat exchange tube layers 4 in each temperature control section, and the number of temperature control sections, respectively; i m is the inner and outer diameter of the heat exchange coil 41; a1, a2, a3 are the number of heat exchange coils 41 in each heat exchange tube layer 4, the number of heat exchange tube layers 4 in each temperature control section, and the number of temperature control sections, respectively; o m is the inner and outer diameter of the heat exchange coil 41; a1, a2, a3 are the number of heat exchange coils 41 in each heat exchange tube layer 4, the number of heat exchange tube layers 4 in each temperature control section, and the number of temperature control sections, respectively; 2 m is the inner and outer diameter of the heat exchange coil 41; a1, a2, a3 are the number of heat exchange coils 41 in each heat exchange tube layer 4, the number of heat exchange tube layers 4 in each temperature control section, and the number of temperature control sections, respectively; i m is the inner and outer diameter of the heat exchange coil 41; a1, a2, a3 are the number of heat exchange coils 41 in each heat exchange tube layer 4, the number of heat exchange tube layers 4 in each temperature control section, and the number of temperature control sections, respectively; o m is the inner and outer diameter of the heat exchange coil 41; a1, a2, a3 are the number of heat exchange coils 41 in each heat exchange tube layer 4, the number of heat exchange tube layers 4 in each temperature control section, and the number of temperature control sections, respectively; is m is the inner and outer diameter of the heat exchange coil 41; a1, a2, a3 are the number of heat exchange coils 41 in each heat exchange tube layer 4, the number of heat exchange tube layers 4 in each temperature control section, and the number of temperature control sections, respectively;

[0067] Example 1

[0068] The nitration tower of the present application is used for preparing 2,4-dinitrochlorobenzene, and molten p-nitrochlorobenzene is used as raw material for nitration to obtain 2,4-dinitrochlorobenzene.

[0069] In the example, the mass concentration of the raw material nitric acid and sulfuric acid is 98%; the feeding flow rate of the raw material p-nitrochlorobenzene is 0.355 mol / s, and the feeding temperature is 90°C; the feeding flow rates of the nitric acid and the sulfuric acid are 0.373 mol / s and 0.8875 mol / s, respectively, and the mixture is fed at 40°C.

[0070] According to the small-scale experimental device, the conversion rate of p-nitrochlorobenzene is 99.49% at 95°C and under the same feeding molar ratio after 10 minutes of reaction. Therefore, the residence time of the reaction in the example is t=10 min.

[0071] Tower size parameters

[0072] Material property parameters V A , V s , ρ A , ρ S , μ S The a value of the ratio of the apparent liquid velocity to the flooding point liquid velocity is 0.6, the power factor N P is 1.2, the average diameter d p of the aromatic hydrocarbon raw material phase droplets is 0.0004 m, and the interfacial tension σ of the two phases is 0.055 N / m.

[0073] Based on the above data, we first assume that the inner diameter D2 of the nitration tower is 0.22m. We then calculate D2 = 0.2176m using equations (1)-(9). Therefore, D2 is determined to be 0.22m, and the corresponding D, D1, and h are 0.11m, 0.15m, and 0.051m, respectively.

[0074] Based on the obtained D2, H = 1.48m is obtained by formula (10); H is divided by h and the result is rounded up to obtain the number of compartments as 30; h is multiplied by 30 to obtain the corrected H = 1.53m, which includes 30+1 = 31 sieve rings; H1 = 0.058m is then obtained by formula (11).

[0075] Heat exchange structure dimensional parameters

[0076] The nitration of p-nitrochlorobenzene is a typical process characterized by rapid initial reaction and slow subsequent reaction. Therefore, the heat load of the reaction is divided into two stages, corresponding to the lower and upper temperature control sections. The cooling water inlet temperature is set at 32℃ and the outlet temperature at 40℃. The first temperature control section releases more heat, has a shorter duration, and a lower nitric acid concentration, so the temperature is controlled at 95℃. The second stage releases less heat, has a longer duration, and a higher nitric acid concentration, so the temperature is controlled at 80℃. Since the heat release is mainly concentrated in the first stage, the maximum heat load in the tower is calculated based on the first stage, with Q set at 30000W. The average heat transfer temperature difference Δt between the cooling water and the material in the tower is 59.91℃.

[0077] Material properties λ, λ i , λ o 、υ、Pr i Pr o According to the database, the Reynolds number Re inside heat exchanger coil 41 is 7000, and the ratio V of the viscosity of the cooling water inside heat exchanger coil 41 at the wall temperature to the current viscosity is... is Take 1.

[0078] Calculations are performed for the first temperature control section with the highest heat load: First, assume the following heat exchange structure dimensions: the number of heat exchange tube layers 4 in the temperature control section is a2 = 10, the number of heat exchange coils 41 in each heat exchange tube layer 4 is a1 = 6, and the bending angle of the heat exchange coils 41 in the heat exchange tube layer 4 is... heat exchanger coil 41 d o d i The diameters are 6mm and 4mm respectively, and the blade width of the 63 stirring paddle is b = 0.005m.

[0079] A = 1.83m is obtained by using equations (12)-(16). 2 A * =2.14m 2 (The thermal resistance of heat exchanger coil 41 is relatively small and can be ignored) (Item); Finally, calculate the area margin = (A) * -A) / A = 17%, which meets the design requirements.

[0080] The number of heat exchange layer tubes 4 in the second temperature control section is 20, the reaction heat release in this section is much less than that in the first section, and the structural parameters are the same as those of the second section.

[0081] The nitro-sulfur mixed acid and the molten p-nitrochlorobenzene are added from the heavy phase feeding port 2 and the light phase feeding port 3 at the bottom of the nitration tower respectively through the annular distributor 12 to carry out the countercurrent nitration reaction.

[0082] Two temperature control sections composed of heat exchange tube layers 4 are arranged in the tower, cooling water enters from two cooling water inlets and enters the heat exchange tube layers 4 of the two temperature control sections through two cooling water inlet pipes 51 respectively, and exits through two cooling water outlet pipes 52 respectively, so that the temperature of the first temperature control section at the lower part of the tower is maintained at 95℃, and the temperature of the second temperature control section at the upper part is maintained at 80℃, and the pressure is normal pressure.

[0083] The 2,4-dinitrochlorobenzene generated by the reaction rises to the top of the tower (the density of the organic mixture is less than that of the acid phase) and exits from the light phase outlet 7, and the molar fraction of the obtained 2,4-dinitrochlorobenzene is greater than 99.50%, the waste acid is cooled to 50℃ by the cooling coil 9 at the bottom, the precipitated 2,4-dinitrochlorobenzene continues to rise to the top of the tower, and the waste acid exits from the heavy phase outlet 8 to be treated in other sections.

[0084] Comparative Example 1

[0085] A one-step reaction was carried out in a nitration kettle with a p-nitrochlorobenzene: nitric acid: sulfuric acid molar ratio of 1:1.05:3, the total amount of p-nitrochlorobenzene was 0.05 mol, the total amount of nitric acid was 0.0525 mol, and the total amount of sulfuric acid was 0.15 mol, and the reaction temperature was 95℃. The samples taken during the reaction were analyzed by liquid chromatography.

[0086] According to the analysis results, the molar fraction of 2,4-dinitrochlorobenzene at 10 min, 15 min, 20 min, 25 min, and 30 min of the reaction was 99.03%, 99.38%, 99.49%, 99.56%, and 99.63% respectively, it can be seen that under the same conditions, the molar fraction of 2,4-dinitrochlorobenzene reached 95.5% in about 20 min, and the reaction rate in the later stage was limited by the lower concentration of reactants and sulfuric acid, so the reaction time was prolonged.

[0087] Comparative Example 2

[0088] A two-step fractional reaction was carried out in a flask with a p-nitrochlorobenzene: nitric acid: sulfuric acid molar ratio of 1:1.05:2.5. The total amount of p-nitrochlorobenzene was 0.05 mol, the total amount of nitric acid was 0.0525 mol, and the total amount of sulfuric acid was 0.125 mol.

[0089] The reaction is divided into two steps, the first step is that 0.05 mol of 90℃ molten p-nitrochlorobenzene raw material, 50℃ waste acid after the second step reaction, 0.021 mol of fresh 30℃ nitric acid are put into a one-step nitration kettle to react, and the temperature is controlled at 95℃; the second step is that the organic phase after the first step reaction, 0.125 mol of fresh sulfuric acid, 0.0315 mol of fresh nitric acid are put into a two-step nitration kettle to react, and the temperature is controlled at 95℃. The organic phase obtained after the second step reaction, i.e. the final product, is analyzed by liquid chromatography.

[0090] According to the analysis results, the reaction time of the two-step method is 6 min for the first step and 13 min for the second step, and the molar fraction of the final 2,4-dinitrochlorobenzene is 99.53%.

[0091] Example 2

[0092] The nitration tower of the application is used to prepare 2,4-dinitrochlorobenzene, and chlorobenzene is used as raw material for nitration to obtain 2,4-dinitrochlorobenzene.

[0093] Among them, the mass concentration of nitric acid and sulfuric acid used in the raw material is 98%; the feeding flow of chlorobenzene raw material is 0.9 mol / s, and the feeding temperature is 30℃; the feeding flow of nitric acid and sulfuric acid is 1.89 mol / s and 3.6 mol / s respectively, and the mixed feeding temperature is 30℃.

[0094] According to the small-scale experimental device, under the condition of the same feeding molar ratio and a temperature of 75℃, the conversion rate of chlorobenzene is 98.21% at 8 min, which is basically stable. Therefore, the residence time of the reaction in this example is taken as 8 min.

[0095] Tower size parameters

[0096] Physical property parameters of the material V A , V S , σ, ρ A , ρ S , μ S The ratio a of the apparent liquid velocity to the flooding point liquid velocity is taken as 0.5 by consulting the database, the power factor N P is taken as 1.6, the average diameter d p of the aromatic hydrocarbon raw material phase droplet is taken as 0.0003 m, and the interfacial tension σ is taken as 0.04 N / m.

[0097] The calculation process is the same as that of Example 1, D2=0.26 m, D=0.13 m, D1=0.174 m, h=0.057 m, H=2.223 m, H1=0.049 m, the number of compartments is 39, and the number of sieve plate rings is 40.

[0098] Heat exchange structure size parameters

[0099] The nitration process of chlorobenzene is divided into mononitration and dinitration: the mononitration process is faster and has large heat release; the dinitration process needs relatively higher temperature and is more difficult. The heat load of the reaction is divided into three sections, corresponding to the lower, middle and upper three temperature control sections, and the cooling water is taken at an inlet temperature of 32℃ and an outlet temperature of 40℃. The nitric acid concentration in the first temperature control section is low, and the temperature control is at 85℃; the nitric acid concentration in the second section is relatively high, and the reaction has large heat release, so the temperature control is at 75℃; and in the third section, since it is close to the nitric acid feeding position, the concentration is high, and too high temperature can easily lead to decomposition of the nitric acid, so the temperature control is at 60℃. Since the heat release is mainly concentrated in the second section, the maximum heat load in the tower is calculated according to the second section, and the cooling water has a heat transfer temperature difference Δt of 38.86℃ with the average temperature of the materials in the tower.

[0100] The physical property parameters λ, λ i , λ o , υ, Pr i , Pr o The Reynolds number Re in the heat exchange coil 41 is taken as 10000 by consulting the database, and the ratio V is of the wall temperature viscosity of the cooling water in the heat exchange coil 41 to the current viscosity is taken as 1.

[0101] The second temperature control section with the largest heat load is calculated, and the calculation process is the same as that of Example 1. The number of heat exchange tube layers 4 in the temperature control section a2 is 20, the number of heat exchange coils 41 in each heat exchange layer a1 is 7, and the bending angle of the heat exchange coil 41 in the heat exchange tube layer 4 is The d o , d i of the heat exchange coil 41 are 5mm and 4mm respectively, and the width of the blade of the stirring paddle 63 b is 0.02m.

[0102] The number of heat exchange tube layers 4 in the first temperature control section is 14, and the number of heat exchange tube layers 4 in the third temperature control section is 5. The heat release of these two sections is much smaller than that of the second section, and the structural parameters are the same as those of the second section.

[0103] The nitro-sulfur mixed acid and chlorobenzene are added through the annular distributor 12 from the heavy phase feeding port 2 and the bottom light phase feeding port 3 of the nitration tower respectively to carry out countercurrent nitration reaction.

[0104] Three temperature control sections composed of heat exchange tube layers 4 are arranged in the tower, cooling water enters from three cooling water inlets, and passes through three cooling water inlet pipes 51 to enter the heat exchange tube layers 4 of the three temperature control sections respectively, and then passes through three cooling water outlet pipes 52 to leave, so that the temperature of the lower first temperature control section in the tower is maintained at 85℃, the temperature of the middle second temperature control section is maintained at 75℃, and the temperature of the upper third temperature control section is maintained at 60℃, and the pressure is normal pressure.

[0105] The 2,4-dinitrochlorobenzene generated in the reaction rises to the top of the column (the density of the organic mixture is less than the density of the acid phase) and exits from the light phase outlet 7, and the waste acid is cooled to 30°C by the cooling coil 9 at the bottom of the column, and the 2,4-dinitrochlorobenzene separated out continues to rise to the top of the column, and the waste acid exits from the heavy phase outlet 8 to be treated in other sections.

[0106] Example 3

[0107] The nitration column of the present application is used to prepare N-(2-nitro-4- (benzyloxy) phenyl) acetamide, and N-(4-(benzyloxy) phenyl) acetamide dissolved in 1,2-dichloroethane is used as the raw material to perform nitration to obtain N-(2-nitro-4- (benzyloxy) phenyl) acetamide.

[0108] In the formula, the mass concentration of the nitric acid used as the raw material is 65%; the feeding amount of the raw material N-(4-(benzyloxy) phenyl) acetamide and 1,2-dichloroethane is 0.9 mol / s and 14.4 mol / s respectively, and the two are pre-mixed and dissolved, and are fed at 50°C; the feeding flow rate of the nitric acid is 2.25 mol / s, and the nitric acid is fed at 30°C.

[0109] Under the same feeding molar ratio, according to the small-scale experimental device, the conversion rate of N-(4-(benzyloxy) phenyl) acetamide is 97.35% at 9 min, and is basically stable. Therefore, the residence time of the reaction in this example is taken as 9 min.

[0110] Column size parameters

[0111] Physical property parameters V of the materials A , V S , σ, ρ A , ρ S , μ S The ratio a of the apparent liquid velocity to the flooding point liquid velocity is taken as 0.7 by consulting the database, the power factor N P is taken as 1.5, the average diameter d p of the aromatic hydrocarbon raw material phase droplets is taken as 0.0003 m, and the interfacial tension σ is taken as 0.035 N / m.

[0112] The calculation process is the same as that in Example 1, D2=0.42 m, D=0.21 m, D1=0.281 m, h=0.079 m, H=3.16 m, H1=0.055 m, the number of compartments is 40, and the number of sieve plate rings is 41.

[0113] Heat exchange structure size parameters

[0114] The nitration process of N-(4-(benzyloxy)phenyl)acetamide is fast and exothermic. At the same time, when the temperature is too high, by-products are easily generated, which seriously affects the product quality and reduces the yield. The heat load of the reaction is divided into four stages, corresponding to the four temperature control stages from bottom to top. The cooling water inlet temperature is 32°C and the outlet temperature is 40°C. The temperature of the four temperature control stages is controlled at 65°C. Since the heat release is mainly concentrated in the second stage, the maximum heat load in the tower is calculated according to the second stage, Q is 45000W, and the average heat transfer temperature difference between the cooling water and the tower material is Δt = 28.82°C.

[0115] The physical property parameters of the material are λ, λ i , λ o , v, Pr i , Pr o The heat transfer tube 41 in the tube has a Reynolds number Re of 7000, and the ratio of the wall temperature viscosity of the heat transfer tube 41 in the tube to the current viscosity V is is 1.

[0116] The second temperature control stage with the largest heat load is calculated, and the calculation process is the same as in Example 1. The number of heat transfer tube layers 4 in the temperature control stage a2 = 19, the number of heat transfer coils 41 in each heat transfer tube layer 4 a1 = 4, and the bending angle of the heat transfer coils 41 in the heat transfer tube layer 4 The d o , d i of the heat transfer coil 41 are 5mm and 4mm respectively, and the width of the stirring paddle 63 b = 0.004m.

[0117] The number of heat transfer tube layers 4 in the first, third and fourth temperature control stages is 7. The heat release of the three stages is much smaller than that of the second stage, and the structural parameters are the same as those of the second stage.

[0118] Since the acid phase density is less than the organic phase in this example, the two raw material phase feeding positions are opposite: N-(4-(benzyloxy)phenyl)acetamide dissolved in dichloroethane, and nitric acid added from the top heavy phase feeding port 2 and the bottom light phase feeding port 3 of the nitration tower through the annular distributor 12 for countercurrent nitration reaction.

[0119] Four temperature control stages composed of heat transfer tube layers 4 are provided in the tower, cooling water enters from four cooling water inlets, and passes through four cooling water inlets 51 to enter the heat transfer tube layers 4 of the four temperature control stages, and exits through four cooling water outlets 52, so that the temperature in the tower is maintained at 65°C, and the pressure is normal pressure.

[0120] The N-(2-nitro-4-(benzyloxy)phenyl)acetamide generated by the reaction is also dissolved in dichloroethane and descends to the bottom of the tower (the density of the organic mixture is greater than the density of the acid phase) to exit from the heavy phase outlet 8, and the waste acid exits from the light phase outlet 7 to go to other sections for treatment.

[0121] Table 1: Summary of product purity for different examples and comparative examples

[0122] Example Sulfuric acid to nitric acid molar ratio Residence time (min) Product purity (%) Example 1 2.38 10 99.50 Comparative Example 1 2.86 10 99.03 Comparative Example 2 2.38 19 99.53

[0123] As can be seen from Table 1, for Example 1 using the nitration tower of the present application, a 2,4-dinitrochlorobenzene product with a purity of 99.50% can be obtained at a residence time of 10 min with a sulfuric acid to nitric acid molar ratio of only 2.38; as a comparison, Comparative Example 1 using a one-step method can achieve a purity of 99.03% under substantially the same conditions, but requires a sulfuric acid to nitric acid molar ratio of 2.86, the rate in the later stage of the reaction is limited by the lower reactant concentration and the relatively low sulfuric acid concentration, the product purity is also relatively low under the same residence time, and the sulfuric acid consumption is also relatively large; and Comparative Example 2 using a two-step method can achieve a product purity of 99.53% under substantially the same conditions, but requires a sulfuric acid to nitric acid molar ratio of 2.38 and a total residence time of 19 min, the sulfuric acid consumption is relatively low compared to the one-step method, and the product purity is also relatively high, but since the reaction needs to be carried out in two steps, the total residence time is relatively long, and two reaction devices are required. In summary, compared to the one-step method represented by the kettle type and tube type reactors, the nitration tower of the present application has a low sulfuric acid consumption and a high product purity; compared to the two-step method represented by the multi-stage reactor, the total residence time is short and the footprint is small.

[0124] Based on the ideal embodiments of the present application, the above description, relevant personnel can make various changes and modifications without deviating from the scope of the present application. The technical scope of the present application is not limited to the contents of the specification, and must be determined according to the scope of the claims.

Claims

1. A countercurrent multistage stirred nitration column suitable for liquid-liquid nitration of aromatic hydrocarbons, characterized in that, The tower is divided into a top layered zone, a middle reaction zone and a bottom layered zone by a partition, the inner wall of the middle reaction zone is uniformly provided with multiple layers of sieve plate rings (1) from top to bottom, the top and bottom sieve plate rings (1) are uniformly provided with first distribution holes (11), and the inner rings of the top and bottom sieve plate rings (1) are respectively provided with annular distributors (12), the annular distributors (12) are uniformly provided with second distribution holes (121), the annular distributor (12) of the top sieve plate ring (1) is connected with a heavy phase feed port (2), the annular distributor (12) of the bottom sieve plate ring (1) is connected with a light phase feed port (3), multiple temperature control sections are arranged between the middle sieve plate rings (1), multiple groups of heat exchange pipe layers (4) are arranged in each temperature control section, and a group of cooling water inlet and outlet pipe groups (5) are connected to the inlet and outlet of the heat exchange pipe layer (4) in each temperature control section; the multiple-stage temperature control is realized by the distribution of the heat exchange pipe layer (4) and the control of the cooling water flow; the cooling water inlet and outlet pipe groups (5) extend into the middle reaction zone from the top layered zone and are vertically connected to the bottom sieve plate ring (1) in a sealing manner; and multiple layers of stirring mechanisms (6) are further arranged in the nitration tower, the multiple layers of stirring mechanisms (6) extend from the top of the nitration tower to the bottom of the bottom layered zone through the multiple layers of sieve plate rings (1).

2. A countercurrent multi-layer agitated nitration column suitable for liquid-liquid nitration of aromatic hydrocarbons according to claim 1, characterized in that, The multiple layers of stirring mechanisms (6) comprise a motor (61), a rotating shaft (62) and multiple layers of stirring paddles (63) uniformly arranged on the rotating shaft (62), one end of the rotating shaft (62) is connected with the motor (61), and the other end of the rotating shaft (62) extends from the top of the nitration tower to the bottom of the bottom layered zone through the multiple layers of sieve plate rings (1).

3. A countercurrent multi-layer agitated nitration column suitable for liquid-liquid nitration of aromatic hydrocarbons according to claim 2, characterized in that, The cooling coil (9) is further arranged in the nitration tower, if the acid phase in the reaction system is a heavy phase, the cooling coil (9) is arranged in the bottom layered zone, and if the acid phase in the reaction system is a light phase, the cooling coil (9) is arranged in the top layered zone.

4. A countercurrent multi-layer agitated nitration column suitable for liquid-liquid nitration of aromatic hydrocarbons according to claim 1, characterized in that, The cooling water inlet and outlet pipe group (5) comprises a cooling water inlet pipe (51) and a cooling water outlet pipe (52), and each heat exchange pipe layer (4) comprises multiple parallel heat exchange coils (41).

5. A countercurrent multi-layer agitated nitration column suitable for liquid-liquid nitration of aromatic hydrocarbons according to claim 1, characterized in that, The relationship between the related parameters of the sieve plate ring (1) satisfies the following formula: In the formula, D2 is the inner diameter of the nitration tower, m; D1 is the inner diameter of the sieve plate ring (1), m; D is the diameter of the stirring paddle (63), m; and h is the interval height between adjacent sieve plate rings (1), m. The inner diameter D2 of the nitration tower is calculated by the following formula wherein a represents the ratio of superficial liquid velocity to flooding liquid velocity, ranging from 0.5 to 0.7; V A , V S is the volume flow rate of aromatic feedstock and mixed acid, m 3 / s; u A , u S is the flooding velocity of aromatic feedstock phase and mixed acid phase, m / s; is the liquid flooding holdup; L R is the two-phase flow ratio; u K is the superficial velocity, m / s; σ is the interfacial tension, N / m; ρ A , ρ S are the densities of aromatic feedstock phase and mixed acid phase, kg / m 3 ; μ S is the viscosity of mixed acid phase, Pa·s; g is the acceleration of gravity, m / s 2 ; N is the rotational speed of stirring paddle (63), r / s; N P is the power factor, which can be taken as 1-3 under the nitration system.

6. A countercurrent multi-layer agitated nitration column suitable for liquid-liquid nitration of aromatic hydrocarbons according to claim 5, characterized in that, The calculation formula of the height H of the middle reaction zone is as follows: In the formula, H represents the height of the middle reaction zone, m; and t is the reaction residence time, s.

7. A countercurrent multi-layer agitated nitration column suitable for liquid-liquid nitration of aromatic hydrocarbons according to claim 5, characterized in that, The top layered zone and the bottom layered zone have the same height, and the calculation formula is as follows: wherein H1 represents the height of the top section or the bottom section of the column, m; d p Dp is the average diameter of the liquid phase droplets of the aromatic feed, m.

8. A countercurrent multi-layer agitated nitration column suitable for liquid-liquid nitration of aromatic hydrocarbons according to claim 5, characterized in that, The heat exchange coil (41) is a serpentine circular frame, and the angle of the serpentine bending is The included angle is related by the formula: In the formula, A, A * are the required heat exchange area and the actual heat exchange area, respectively, to meet the reaction heat load, m 2 ; Q is the reaction heat load, W; Δt is the average heat transfer temperature difference between the cooling water and the material in the column, °C, m i , d o is the inner and outer diameter of the heat exchange coil (41), m; a1, a2, a3 are the number of heat exchange coils (41) in each heat exchange tube layer (4), the number of heat exchange tube layers (4) in each temperature control section, and the number of temperature control sections, respectively; is the bending angle of the heat exchange tube, °; α i , α o are the heat transfer coefficient of the reaction zone heat exchange coil (41) inside the tube and the heat transfer coefficient outside the tube, W / m 2 ·K; λ, λ i , λ o are the heat transfer coefficient of the heat exchange coil (41), the heat transfer coefficient of the cooling water inside the tube, and the heat transfer coefficient of the mixed phase outside the tube, W / m·K; υ is the kinematic viscosity of the mixed phase outside the heat exchange coil (41), m 2 / s; Pr i , Pr o are the Prandtl number of the cooling water inside the heat exchange coil (41) and the Prandtl number of the mixed phase outside the tube, respectively; Re is the Reynolds number of the heat exchange coil (41), V is is the ratio of the viscosity at the wall temperature of the cooling water inside the heat exchange coil (41) to the current viscosity, b is the blade width of the stirring paddle (63), m; P is the power consumed per unit mass of the stirred liquid, W.

9. A countercurrent multi-layer agitated nitration column suitable for liquid-liquid nitration of aromatic hydrocarbons according to claim 4, characterized in that, The top layered zone is provided with a light phase discharge port (7), and the bottom layered zone is provided with a heavy phase discharge port (8).

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