Countercurrent multi-layer stirring nitration tower suitable for aromatic hydrocarbon liquid-liquid nitration reaction

Abstract

The invention discloses a countercurrent multi-layer stirring nitration tower suitable for aromatic hydrocarbon liquid-liquid nitration reaction, annular distributors are arranged at the top and the bottom of a middle reaction zone of the nitration tower, the top annular distributor is connected with a heavy phase feed inlet, and the bottom annular distributor is connected with a light phase feed inlet, so that two-phase countercurrent contact reaction is realized; multiple groups of heat exchange tube layers are arranged in the middle of the reaction area to realize multi-section temperature control; meanwhile, on the basis of the structure arrangement of the nitration tower, the size of the internal structure of the nitration tower is subjected to formula limitation on the basis of reaction heat and reaction efficiency. The nitration tower provided by the invention can realize the countercurrent reaction of the raw material and the acid phase, effectively avoids the problems occurring during concurrent flow, enables the reaction rate to be more uniform, is provided with multi-section temperature control, is more convenient in temperature control, and also can reduce the use amount of acid to a certain extent.

Description

Technical Field

[0001] The invention belongs to the technical field of nitration towers, and in particular relates to a countercurrent multi-layer stirring nitration tower suitable for liquid-liquid nitration reaction of aromatic hydrocarbons. Background Art

[0002] The aromatic nitration process is common in the chemical industry. The mononitro and dinitro compounds produced are intermediates for a large number of chemical products, especially in the fields of medicine and dyes.

[0003] The nitration reaction of aromatics is a highly exothermic reaction, so the heat exchange capacity of the reactor is required to be high, otherwise there is a risk of reaction temperature runaway, reducing the safety of the device; at the same time, the reaction is basically a heterogeneous reaction, and the mixing effect of the reactor is required to be high. It is necessary to increase the contact area and improve the mass transfer effect, otherwise it will lead to a low reaction rate in the later stage, prolong the reaction time, increase the reactor volume, and be unfavorable to the cost. 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 nitration are mainly the following:

[0005] Tank reactors are generally intermittent processes, and raw materials are often added in batches, with long feeding time, long reaction cycle, small production volume, poor heat exchange capacity and mass transfer capacity, and large acid consumption, which is not conducive to cost and environmental protection;

[0006] In a continuous tubular reactor, aromatic raw materials and mixed acid are generally fed together and flow in the tube in parallel, which results in a high reaction rate at the beginning and a large heat release, which reduces the safety of the reactor. In the latter stage of the reaction, due to the low concentration of sulfuric acid and raw materials, it takes a long time to achieve a high conversion rate, which increases the volume of the reactor.

[0007] Micro-tube reactor nitrification is one of the better methods at present. The large heat exchange area provided by the micro-tube can effectively solve the heat release problem in the nitrification process. However, this method has a small processing capacity, high cost and limited application range.

[0008] Multi-stage nitration: This method connects multiple reactors in series to allow the acid phase and the organic phase to be countercurrently nitrated between the reactors. This method consumes less acid and the final nitration product has a higher purity. However, it requires more equipment and occupies a large area. In fact, the acid phase and the organic phase in a single reactor still flow in the same direction. Summary of the invention

[0009] In view of the above problems, the object of the present invention is to provide a countercurrent multi-layer stirred nitration tower for liquid-liquid nitration of aromatic hydrocarbons.

[0010] The specific technical solutions are as follows:

[0011] A countercurrent multi-layer stirring nitration tower suitable for liquid-liquid nitration reaction of aromatic hydrocarbons is divided into a tower top stratification zone, a tower middle reaction zone and a tower bottom stratification zone by a partition plate, the inner wall of the tower middle reaction zone is evenly provided with multiple layers of sieve plate rings from top to bottom, the top and bottom sieve plate rings are evenly provided with first distribution holes, and the top and bottom sieve plate rings are respectively provided with annular distributors on the inner rings, and the annular distributors are evenly provided with second distribution holes, the annular distributor of the top sieve plate ring is connected to the heavy phase feed port, and the annular distributor of the bottom sieve plate ring is connected to the light phase feed port. The nitrifying tower is connected to the upper and lower sieve plate rings, and multiple temperature control sections are arranged between the sieve plate rings in the middle. Multiple groups of heat exchange tube layers are arranged in each temperature control section. The inlet and outlet of the heat exchange tube layers in each temperature control section are connected to a group of cooling water inlet and outlet pipe groups. The temperature control is achieved by the distribution of the heat exchange tube layers and the control of the cooling water flow rate. The cooling water inlet and outlet pipe groups extend from the stratification area at the top of the tower into the reaction area in the middle of the tower, and vertically pass through the multiple layers of sieve plate rings and are sealed and connected with the sieve plate rings at the bottom. A multi-layer stirring mechanism is also arranged inside the nitrifying tower, and the multi-layer stirring mechanism extends from the top of the nitrifying tower through the multiple layers of sieve plate rings to the stratification area at the bottom of the tower.

[0012] Furthermore, the multi-layer stirring mechanism includes a motor, a rotating shaft and multi-layer stirring paddles evenly arranged on the rotating shaft. One end of the rotating shaft is connected to the motor, and the other end extends from the top of the nitrification tower through the multi-layer sieve plate ring to the stratification area at the bottom of the tower.

[0013] Furthermore, a cooling coil is provided in the nitration tower. If the acid phase in the reaction system is a heavy phase, the cooling coil is arranged in the stratification zone at the bottom of the tower. If the acid phase in the reaction system is a light phase, the cooling coil is arranged in the stratification zone at the top of the tower. The cooling coil can control the stratification of the acid and organic phases to ensure that the organic phase will not solidify.

[0014] Furthermore, the cooling water inlet and outlet pipe group includes a cooling water inlet pipe and a cooling water outlet pipe, and each group of heat exchange tube layers includes a plurality of heat exchange coils arranged in parallel.

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

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

[0017] Wherein D2 is the inner diameter of the nitrification 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 spacing height between adjacent sieve plate rings (1), m;

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

[0019]

[0020]

[0021] Where a represents the ratio of the superficial liquid velocity to the flooding point liquid velocity, ranging from 0.5 to 0.7; V A 、V S is the volume flow rate of aromatic raw materials and mixed acid, m 3 / s;u A 、u S is the flooding velocity of the aromatic feed phase and the mixed acid phase, m / s; is the flooding retention rate; L R is the two-phase flow ratio; u K is the characteristic speed, m / s; σ is the interfacial tension between the two phases, N / m; ρ A , S They are the density of aromatic 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 acceleration of gravity, m / s 2 ; N is the rotation speed of the stirring blade (63), r / s; N P is the power factor, which can be 1-3 in the nitrification system.

[0022] Furthermore, the height H of the reaction zone in the middle of the tower is calculated as follows:

[0023]

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

[0025] Furthermore, the height of the top layered area and the bottom layered area is the same, and the calculation formula of the layered area height is as follows:

[0026]

[0027] Where H1 represents the height of the stratified area, m; d p is the average diameter of the aromatic feed phase droplets, m.

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

[0029]

[0030] In the formula, A, 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 cooling water and materials in the tower, ℃, d i d ois the inner and outer diameters of the heat exchange coil, m; a1, a2, a3 are the number of heat exchange coils in each heat exchange tube layer, the number of heat exchange tube layers 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 They are the convection heat transfer coefficient inside the heat exchange coil in the reaction zone and the convection heat transfer coefficient outside the tube, W / m 2 K; λ, λ i , o is the thermal conductivity of the heat exchange coil, the thermal conductivity of the cooling water in the tube, and the thermal conductivity of the mixed phase outside the tube, W / m·K; υ is the kinematic viscosity of the mixed phase outside the heat exchange coil, m 2 / s;Pr i , Pr o are the Prandtl number of cooling water in the heat exchange coil and the Prandtl number of the mixed phase outside the tube; Re is the Reynolds number in the heat exchange coil, V is is the ratio of the viscosity at the cooling water wall temperature in the heat exchange coil to the current viscosity, b is the width of the stirring paddle blade, m; P is the power consumed by the unit mass of the stirred liquid, W.

[0031] Furthermore, a light phase discharge port is provided in the tower top stratification zone, and a heavy phase discharge port is provided at the bottom of the tower bottom stratification zone.

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

[0033] 1) The nitration tower of the present invention is composed of three parts: a tower top stratification zone, a tower middle reaction zone, and a tower bottom stratification zone. Therefore, in the continuous operation process, the nitration reaction and the separation of materials in different phases can be realized in the same device, the reaction and separation coupling is realized, the production efficiency is improved, and the pollution and danger that may be caused by material transmission are reduced;

[0034] 2) The nitration tower of the present invention can realize the countercurrent reaction between the raw material and the acid phase, effectively avoiding the problems that occur during the forward flow. At the beginning, the acid concentration is low and the raw material concentration is high, and at the end, the acid concentration is high and the raw material concentration is low, so that the reaction rate is more uniform, the temperature control is more convenient, and the acid dosage does not need to be increased during the reaction to ensure that the acid concentration in the later stage of the reaction is sufficiently high. The rate in the later stage of the reaction can also be maintained at a high level with a small initial acid amount, thereby reducing the amount of acid in disguised form; for raw materials that need dinitration, such as chlorobenzene, the nitric acid concentration is low in the front section of the reaction zone, which is adapted to the low nitric acid concentration requirement of the mononitration reaction; the nitric acid concentration is high in the back section of the reaction zone, which is adapted to 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, which has a higher space utilization rate than heat exchange methods such as jackets and traditional coils, 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 to improve the convective heat transfer coefficient in the tube;

[0036] 4) The heat exchange tube configuration plays a role similar to the baffle in the stirred tank in the compartment. The combination of heat exchange tube + stirring paddle can destroy the circumferential motion trajectory of the fluid, eliminate the vortex phenomenon, avoid axial stratification of the reaction system, and simply rotate the reactor axially without mixing (making the reaction effect poor), thereby enhancing the turbulence of the fluid in the compartment and improving the convective heat transfer coefficient outside the tube. Moreover, under this heat exchange tube configuration, the cooling water inlet and outlet tube group can be stuck in the gap formed by the bending of the heat exchange tube, which is easy to fix the heat exchange tube, improve its structural strength, and improve safety performance;

[0037] 5) The present invention divides the heat exchange tube layer arranged between the sieve plate rings into multiple sections to form multiple temperature control zones for separate temperature control, thereby improving the flexibility of temperature control: in the strong exothermic section at the highest reactant concentration in the middle of the reaction zone, the cooling water flow rate and heat exchange area are increased to enhance the heat exchange capacity (the average concentration is highest in the middle position of the countercurrent process) to avoid temperature runaway and improve safety; in the section where the nitric acid concentration is the lowest and the reaction rate is slower at the aromatic feed, the cooling water flow rate is appropriately reduced to maintain a higher temperature to accelerate the reaction; in the section where the nitric acid concentration is the highest at the acid phase feed, the cooling water flow rate is appropriately increased to maintain a lower temperature to avoid the decomposition of nitric acid into nitrogen oxides due to excessively high temperature, resulting in a decrease in product yield. For some nitration reactions whose reaction selectivity is sensitive to temperature, such as mononitration products that are prone to generate dinitration byproducts when the temperature is too high, and the temperature of the dinitration product will affect the nitro substitution position, the flexible temperature control capability can avoid these situations and effectively improve the yield of the target product.

[0038] 6) The present invention has stratification zones at both the top and the bottom of the tower, and no external separation device is required. At the same time, the device itself is tower-shaped, which reduces the floor space.

[0039] 7) The present invention specifically sets a heat exchange coil in the acid phase stratification zone (which may be a heavy phase or a light phase according to different systems). Since the solubility of the aromatic nitration product in the acid is relatively large, the spent acid from the reaction zone is cooled to precipitate the dissolved nitration product therein. By controlling the appropriate cooling temperature, it is possible to ensure that the acid phase precipitates the nitration product as much as possible while ensuring that the precipitated nitration product is still in a molten state, so that it can be separated from the acid phase due to the density difference.

[0040] 8) The present invention applies a multi-layer stirring system to the nitration reaction device, ensuring uniform mixing of materials in the entire reaction zone. At the same time, the configuration of the nitration tower ensures that even if the stirring fails, the acid phase and the organic phase will still flow in the opposite direction, thus avoiding to a certain extent the dangerous situation of local overheating of the reaction zone due to severe stratification in the reaction zone. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is a cross-sectional structural schematic diagram of the present invention;

[0042] Figure 2 It is a schematic diagram of the three-dimensional structure of the heat exchange tube layer of the present invention;

[0043] Figure 3 Schematic diagram of the bending angle of the heat exchange coil;

[0044] Figure 4 is a cross-sectional schematic diagram of a heat exchange tube layer;

[0045] Figure 5 It is a schematic diagram of the three-dimensional structure of the sieve plate ring and distributor at the bottom.

[0046] In the figure: 1. sieve plate ring; 11. first distribution hole; 12. annular distributor; 121. second distribution hole; 2. heavy phase feed port; 3. light phase feed port; 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 port; 8. heavy phase discharge port; 9. cooling coil. DETAILED DESCRIPTION

[0047] The present invention is further described below in conjunction with the accompanying drawings and embodiments, but the protection scope of the present invention is not limited thereto.

[0048] like Figure 1 As shown, a countercurrent rotary disc nitration reaction tower suitable for liquid-liquid nitration reaction of aromatic hydrocarbons is divided into a tower top stratification zone, a tower middle reaction zone and a tower bottom stratification zone by a partition plate. The interior of the tower middle reaction zone is evenly provided with multiple layers of sieve plate rings 1 from top to bottom, as shown in FIG. Figure 5As shown, the bottom sieve plate ring 1 is evenly provided with first distribution holes 11, and the inner ring is provided with an annular distributor 12, and the annular distributor 12 is evenly 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 to the heavy phase feed port, and the annular distributor 12 of the bottom sieve plate ring 1 is connected to the light phase feed port 3. A plurality of temperature control sections are provided between the middle sieve plate rings 1, and a plurality of groups of heat exchange tube layers 4 are provided in each temperature control section. The inlet and outlet of the heat exchange tube layer 4 in each temperature control section are connected to a group of cooling water inlet and outlet pipe groups 5. Multi-stage temperature control is achieved by controlling the distribution of the heat exchange tube layer 4 and the cooling water flow rate. The cooling water inlet and outlet pipe groups 5 extend from the top stratification zone of the tower into the middle reaction zone of the tower, and vertically pass through the multi-layer sieve plate rings 1 and are sealed and connected to the bottom sieve plate ring 1, as shown in FIG. 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 group of heat exchange tube layers 4 includes a plurality of heat exchange coils 41 arranged in parallel. The heat exchange coils 41 are serpentine circular frames, such as Figure 3 As shown, the angle of its serpentine bending is Angle, the nitrification tower is also provided with a multi-layer stirring mechanism 6, which includes a motor 61, a rotating shaft 62 and a multi-layer stirring paddle 63 evenly arranged on the rotating shaft 62, one end of the rotating shaft 62 is connected to the motor 61, and the other end extends from the top of the nitrification tower through the multi-layer sieve plate ring 1 to the bottom of the stratification area at the bottom of the tower. A cooling coil 9 is also provided in the nitric acid tower. If the acid phase in the reaction system is a heavy phase, the cooling coil 9 is arranged in the stratification area at the bottom of the tower. If the acid phase in the reaction system is a light phase, the cooling coil 9 is arranged in the stratification area at the top of the tower. A light phase discharge port 7 is provided in the stratification area at the top of the tower, and a heavy phase discharge port 8 is provided at the bottom of the stratification area at the bottom of the tower.

[0049] like Figure 4 As shown, 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] Wherein D2 is the inner diameter of the nitrification 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 spacing height between adjacent sieve plate rings 1, m;

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

[0055]

[0056]

[0057] Where a represents the ratio of the superficial liquid velocity to the flooding point liquid velocity, ranging from 0.5 to 0.7; V A 、V S is the volume flow rate of aromatic raw materials and mixed acid, m 3 / s;u A 、u S is the flooding velocity of the aromatic feed phase and the mixed acid phase, m / s; is the flooding retention rate; L R is the two-phase flow ratio; u K is the characteristic velocity, m / s; σ is the interfacial tension between the two phases, N / m; ρ A , S They are the density of aromatic 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 acceleration due to gravity, which is 9.81m / s 2 ; N is the stirring blade 63 speed, r / s; N P is the power factor, which can be 1-3 in the nitrification system.

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

[0059]

[0060] Wherein, H represents the height of the reaction zone in the middle of the tower, m; t is the reaction residence time, s.

[0061] The height of the top layered area and the bottom layered area is the same. The calculation formula of the layered area height is as follows:

[0062]

[0063] Where H1 represents the height of the stratified area, m; d p is the average diameter of the aromatic feed phase droplets, m.

[0064] like Figure 3 As shown, the angle of the serpentine bend is The angle is related as follows:

[0065]

[0066] In the formula, A, 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 cooling water and materials in the tower, ℃, d i d ois the inner and outer diameters 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 They are the convection heat transfer coefficient inside the reaction zone heat exchange coil 41 and the convection heat transfer coefficient outside the tube, W / m 2 K; λ, λ i , o is the thermal conductivity of the heat exchange coil 41, the thermal conductivity of the cooling water in the tube, and the thermal conductivity 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 cooling water in the heat exchange coil 41 and the Prandtl number of the mixed phase outside the tube; Re is the Reynolds number in the heat exchange coil 41, V is is the ratio of the viscosity of the cooling water wall temperature in 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 by the stirred liquid per unit mass, W.

[0067] Example 1

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

[0069] The mass concentration of nitric acid and sulfuric acid used as raw materials is 98%; the feed flow rate of p-nitrochlorobenzene is 0.355 mol / s, and the feed temperature is 90°C; the feed flow rates of nitric acid and sulfuric acid are 0.373 mol / s and 0.8875 mol / s, respectively, and they are fed at 40°C after mixing.

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

[0071] Tower size parameters

[0072] Physical parameters of materials V A 、V s , A , S , μ S By consulting the database, the ratio of the apparent liquid velocity to the flooding point liquid velocity is taken as 0.6, and the power factor N P Take 1.2, the average diameter of the aromatic feed phase droplets d p Take 0.0004m and the interfacial tension σ between the two phases is 0.055N / m.

[0073] Based on the above data, we first assume that the inner diameter D2 of the nitrification tower is 0.22 m. By using equations (1)-(9), we can calculate D2=0.2176 m. Therefore, D2 is determined to be 0.22 m, and the corresponding D, D1, and h are 0.11 m, 0.15 m, and 0.051 m, 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, including 30+1=31 sieve plate rings; and H1 = 0.058m is obtained by formula (11).

[0075] Heat exchange structure size parameters

[0076] The nitration process of p-nitrochlorobenzene is a typical process with a fast initial stage and a slow later stage. Therefore, the heat load of the reaction is divided into two sections, corresponding to the lower and upper temperature control sections, and the cooling water is taken at 32°C at the inlet and 40°C at the outlet. The first temperature control section has a large heat release, a short time, a low nitric acid concentration, and a temperature control of 95°C; the second section has a small heat release, a long time, a high nitric acid concentration, and a temperature control of 80°C. Since the heat release is mainly concentrated in the first section, the maximum heat load in the tower is calculated according to the first section, Q is taken as 30000W, and the average heat transfer temperature difference Δt between the cooling water and the material in the tower is 59.91°C.

[0077] Physical parameters of materials λ, λ i , o ,υ,Pr i , Pr o By consulting the database, the Reynolds number Re in the heat exchange coil 41 is taken as 7000, and the ratio of the viscosity of the cooling water wall temperature in the heat exchange coil 41 to the current viscosity V is Take 1.

[0078] Calculate the first temperature control section with the largest heat load: Assume the heat exchange structure size: 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 coil 41 in the heat exchange tube layer 4 is Heat exchange coil 41d o d i They are 6 mm and 4 mm respectively, and the blade width b of the stirring paddle 63 is 0.005 m.

[0079] A = 1.83 m is obtained by equations (12)-(16) 2 , A * =2.14m 2 (The thermal resistance of the heat exchange coil 41 is small, so it can be ignored. Item); finally calculate area margin = (A * -A) / A=17%, meeting the design requirements.

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

[0081] Nitric and sulfuric acid mixture and molten p-nitrochlorobenzene are added from the heavy phase feed port 2 and the bottom light phase feed port 3 of the nitration tower respectively through the annular distributor 12 to carry out countercurrent nitration reaction.

[0082] There are two temperature control sections consisting of heat exchange tube layers 4 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, and leaves through two cooling water outlet pipes 52, so that the temperature of the first temperature control section at the bottom of the tower is maintained at 95°C, and the temperature of the second temperature control section at the top is maintained at 80°C, 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 the density of the acid phase) and leaves from the light phase outlet 7 to obtain 2,4-dinitrochlorobenzene with a molar fraction greater than 99.50%. The waste acid is cooled to 50° C. through the cooling coil 9 at the bottom of the tower, and the precipitated 2,4-dinitrochlorobenzene continues to rise to the top of the tower. The waste acid leaves from the heavy phase outlet 8 and is sent to other sections for recovery and treatment.

[0084] Comparative Example 1

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

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

[0087] Comparative Example 2

[0088] A two-step graded reaction was carried out in a flask with a molar ratio of p-nitrochlorobenzene: nitric acid: sulfuric acid = 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°C molten p-nitrochlorobenzene raw material, 50°C waste acid after the second step reaction, and 0.021 mol of fresh 30°C nitric acid are put into a first-step nitration kettle for reaction, and the temperature is controlled at 95°C; the second step is that the organic phase after the first step reaction, 0.125 mol of fresh sulfuric acid, and 0.0315 mol of fresh nitric acid are put into a second-step nitration kettle for reaction, and the temperature is controlled at 95°C. The organic phase obtained at the end of the second step reaction, i.e., the final product, is analyzed by liquid chromatography.

[0090] According to the analysis results, the first step of the two-step reaction took 6 minutes, the second step took 13 minutes, and the final molar fraction of 2,4-dinitrochlorobenzene was 99.53%.

[0091] Example 2

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

[0093] The mass concentration of nitric acid and sulfuric acid used as raw materials is 98%; the feed flow rate of raw material chlorobenzene is 0.9 mol / s, and the feed temperature is 30°C; the feed flow rates of nitric acid and sulfuric acid are 1.89 mol / s and 3.6 mol / s, and they are fed at 30°C after mixing.

[0094] According to the small test device, at a temperature of 75°C and the same feed molar ratio, the conversion rate of chlorobenzene was 98.21% after 8 minutes of reaction, which was basically stable. Therefore, the residence time of the reaction in this example was 8 minutes.

[0095] Tower size parameters

[0096] Physical parameters of materials V A 、V S ,σ,ρ A , S , μ S By consulting the database, the ratio of the apparent liquid velocity to the flooding point liquid velocity is taken as 0.5, and the power factor N P Take 1.6, the average diameter of the aromatic feed phase droplets d p Take 0.0003m, and the interfacial tension σ between the two phases is 0.04N / m.

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

[0098] Heat exchange structure size parameters

[0099] The chlorobenzene nitration process is divided into two processes: mononitration and dinitration. The mononitration process is faster and releases a lot of heat; the dinitration requires a relatively higher temperature and is more difficult to react. The heat load of the reaction is divided into three sections, corresponding to the lower, middle and upper temperature control sections, and the cooling water is taken at 32°C at the inlet and 40°C at the outlet. The nitric acid concentration in the first temperature control section is low, and the temperature is controlled at 85°C; the nitric acid concentration in the second section is relatively high, the reaction releases a lot of heat, and the temperature is controlled at 75°C; the third section is close to the nitric acid feed, the concentration is high, and too high a temperature can easily lead to its decomposition, and the temperature is controlled at 60°C. 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, Q is taken as 110000W, and the average heat transfer temperature difference Δt between the cooling water and the material in the tower is 38.86°C.

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

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

[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 the reactions in these two sections is much smaller than that in the second section, and the structural parameters are the same as those in the second section.

[0103] Nitric and sulfuric acid mixture and chlorobenzene are added from the heavy phase feed port 2 and the bottom light phase feed port 3 of the nitration tower respectively through the annular distributor 12 to carry out countercurrent nitration reaction.

[0104] There are three temperature control sections consisting of heat exchange tube layers 4 in the tower. Cooling water enters from three cooling water inlets and enters the heat exchange tube layers 4 of the three temperature control sections through three cooling water inlet pipes 51, and leaves through three cooling water outlet pipes 52, so that the temperature of the first temperature control section at the bottom of the tower is maintained at 85°C, the temperature of the second temperature control section in the middle is maintained at 75°C, and the temperature of the third temperature control section at the top is maintained at 60°C, and the pressure is normal pressure.

[0105] 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 leaves from the light phase outlet 7. The waste acid is cooled to 30°C through the cooling coil 9 at the bottom of the tower. The precipitated 2,4-dinitrochlorobenzene continues to rise to the top of the tower. The waste acid leaves from the heavy phase outlet 8 and is sent to other sections for recovery and treatment.

[0106] Example 3

[0107] The nitration tower of the present invention 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 a raw material for nitration to obtain N-(2-nitro-4-(benzyloxy)phenyl)acetamide.

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

[0109] According to the small test device, at a temperature of 65°C and the same feed molar ratio, the conversion rate of N-(4-(benzyloxy)phenyl)acetamide was 97.35% after 9 minutes of reaction, which was basically stable. Therefore, the residence time of the reaction in this example was 9 minutes.

[0110] Tower size parameters

[0111] Physical parameters of materials V A 、V S ,σ,ρ A , S , μ S By consulting the database, the ratio of the apparent liquid velocity to the flooding point liquid velocity is taken as 0.7, and the power factor N P Take 1.5, the average diameter of the aromatic feed phase droplets d p Take 0.0003m and the interfacial tension σ between the two phases is 0.035N / m.

[0112] The calculation process is the same as that of Example 1, D2=0.42m, D=0.21m, D1=0.281m, h=0.079m, H=3.16m, H1=0.055m, 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 releases a lot of heat. 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 sections, corresponding to the four temperature control sections from bottom to top, and the cooling water is taken at 32℃ at the inlet and 40℃ at the outlet. The temperature of the four temperature control sections is controlled at 65℃. 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, Q is 45000W, and the average heat transfer temperature difference Δt between the cooling water and the material in the tower is 28.82℃.

[0115] Physical parameters of materials λ, λ i , o 、v、Pr i , Pr o By consulting the database, the Reynolds number Re in the heat exchange coil 41 is taken as 7000, and the ratio of the viscosity of the cooling water wall temperature in the heat exchange coil 41 to the current viscosity V is Take 1.

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

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

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

[0119] There are four temperature control sections consisting of heat exchange tube layers 4 in the tower. Cooling water enters from four cooling water inlets and enters the heat exchange tube layers 4 of the four temperature control sections through four cooling water inlet pipes 51, and leaves through four cooling water outlet pipes 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 falls to the bottom of the tower (the density of the organic mixture is greater than the density of the acid phase) and leaves from the heavy phase outlet 8, and the waste acid leaves from the light phase outlet 7 to other sections for treatment.

[0121] Table 1 Purity summary of products of different embodiments and comparative examples

[0122] Example Molar ratio of sulfuric acid to nitric acid 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, when the residence time of Example 1 using the nitrating tower of the present invention is 10 min, the molar ratio of sulfuric acid to nitric acid only needs 2.38 to obtain a 2,4-dinitrochlorobenzene product with a purity of 99.50%; in contrast, when other conditions are substantially the same, the molar ratio of sulfuric acid to nitric acid of 2.86 is required to reach 99.03% in Comparative Example 1 using the one-step method, and the reaction rate is limited by the lower reactant concentration and the sulfuric acid concentration is also relatively low. The product purity is relatively low at the same residence time, and the sulfuric acid consumption is also large; and when other conditions are substantially the same, when Comparative Example 2 using the two-step method is 2.38 and the total residence time is 19 min, the product purity is 99.53%, the sulfuric acid consumption is reduced relative to the one-step method, and the product purity is also high, but because the reaction needs to be carried out in two steps, the total residence time of the two steps is long, and two reaction equipments are required. In summary, the nitration tower of the present invention has low sulfuric acid consumption and high product purity compared with the kettle type and tubular reactors represented by the one-step method; and has a short total residence time and a small footprint compared with the multi-stage reactor represented by the two-step method.

[0124] The above is based on the ideal embodiment of the present invention. Through the above description, relevant personnel can make various changes and modifications without deviating from the scope of the invention. The technical scope of this invention is not limited to the content in the specification, but must be determined according to the scope of the claims.

Claims

1. A countercurrent multi-layer stirred nitration tower suitable for liquid-liquid nitration of aromatic hydrocarbons, characterized in that: The tower is divided into a tower top layering zone, a tower middle reaction zone and a tower bottom layering zone by a partition plate. The inner wall of the tower middle reaction zone is evenly provided with multiple layers of sieve plate rings (1) from top to bottom. The top and bottom sieve plate rings (1) are evenly provided with first distribution holes (11). The top and bottom sieve plate rings (1) are respectively provided with annular distributors (12) on their inner rings. The annular distributors (12) are evenly provided with second distribution holes (121). The annular distributors (12) of the top sieve plate ring (1) are connected to a heavy phase feed port (2). The annular distributors (12) of the bottom sieve plate ring (1) are connected to a light phase feed port (3). The middle sieve plate ring (1) is connected to a light phase feed port (4). (1) is provided with a plurality of temperature control sections, each temperature control section is provided with a plurality of groups of heat exchange tube layers (4), the inlet and outlet of the heat exchange tube layers (4) in each temperature control section are connected to a group of cooling water inlet and outlet pipe groups (5), and multi-stage temperature control is achieved by the distribution of the heat exchange tube layers (4) and the control of the cooling water flow rate, the cooling water inlet and outlet pipe groups (5) extend from the top stratification area of ​​the tower into the middle reaction area of ​​the tower, and vertically pass through the multi-layer sieve plate ring (1) and are sealedly connected with the bottom sieve plate ring (1), and a multi-layer stirring mechanism (6) is also provided inside the nitration tower, and the multi-layer stirring mechanism (6) extends from the top of the nitration tower through the multi-layer sieve plate ring (1) to the bottom of the stratification area at the bottom of the tower.

2. A countercurrent multi-layer stirring nitration tower suitable for liquid-liquid nitration reaction of aromatic hydrocarbons as claimed in claim 1, characterized in that: The multi-layer stirring mechanism (6) comprises a motor (61), a rotating shaft (62) and multi-layer stirring paddles (63) uniformly arranged on the rotating shaft (62); one end of the rotating shaft (62) is connected to the motor (61), and the other end extends from the top of the nitrification tower through the multi-layer sieve plate ring (1) to the bottom of the stratification zone at the bottom of the tower.

3. A countercurrent multi-layer stirring nitration tower suitable for liquid-liquid nitration reaction of aromatic hydrocarbons as claimed in claim 2, characterized in that: A cooling coil (9) is also provided in the nitric acid tower. If the acid phase in the reaction system is a heavy phase, the cooling coil (9) is provided in the stratification zone at the bottom of the tower. If the acid phase in the reaction system is a light phase, the cooling coil (9) is provided in the stratification zone at the top of the tower.

4. A countercurrent multi-layer stirring nitration tower suitable for liquid-liquid nitration reaction of aromatic hydrocarbons as claimed in 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 group of heat exchange pipe layers (4) comprises a plurality of heat exchange coils (41) arranged in parallel.

5. A countercurrent multi-layer stirring nitration tower suitable for liquid-liquid nitration reaction of aromatic hydrocarbons as claimed in claim 1, characterized in that: The relationship between the parameters of the sieve plate ring (1) satisfies the following formula: Wherein D2 is the inner diameter of the nitrification 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 spacing height between adjacent sieve plate rings (1), m; The inner diameter D2 of the nitrification tower is calculated by the following formula Where a represents the ratio of the superficial liquid velocity to the flooding point liquid velocity, ranging from 0.5 to 0.7; V A 、V S is the volume flow rate of aromatic raw materials and mixed acid, m 3 / s;u A 、u S is the flooding velocity of the aromatic feed phase and the mixed acid phase, m / s; is the flooding retention rate; L R is the two-phase flow ratio; u K is the characteristic speed, m / s; σ is the interfacial tension between the two phases, N / m; ρ A , S They are the density of aromatic 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 acceleration of gravity, m / s 2 ; N is the rotation speed of the stirring blade (63), r / s; N P is the power factor, which can be 1-3 in the nitrification system.

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

7. A countercurrent multi-layer stirring nitration tower suitable for liquid-liquid nitration reaction of aromatic hydrocarbons as claimed in claim 5, characterized in that: The height of the top layer area and the bottom layer area is the same, and the calculation formula is as follows: Where H1 represents the height of the top layer area or the bottom layer area of ​​the tower, m; d p is the average diameter of the aromatic feed phase droplets, m.

8. A countercurrent multi-layer stirring nitration tower suitable for liquid-liquid nitration reaction of aromatic hydrocarbons as claimed in claim 5, characterized in that: The heat exchange coil (41) is a serpentine circular frame, and the angle of its serpentine bending is The angle is related as follows: In the formula, A, 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 cooling water and materials in the tower, ℃, d i ,d o are the inner and outer diameters of the heat exchange coil (41), m; a1, a2, and 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 convection heat transfer coefficient inside the reaction zone heat exchange coil (41) and the convection heat transfer coefficient outside the tube, W / m 2 K; λ, λ i , o is the thermal conductivity of the heat exchange coil (41), the thermal conductivity of the cooling water in the tube, and the thermal conductivity 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 in the heat exchange coil (41) and the Prandtl number of the mixed phase outside the tube, respectively; Re is the Reynolds number in the heat exchange coil (41), V is is the ratio of the viscosity at the wall temperature of the cooling water in the heat exchange coil (41) to the current viscosity, b is the blade width of the stirring paddle (63), m; and P is the power consumed per unit mass of the stirred liquid, W.

9. A countercurrent multi-layer stirring nitration tower suitable for liquid-liquid nitration reaction of aromatic hydrocarbons as claimed in claim 4, characterized in that: A light phase discharge port (7) is provided at the top layering zone of the tower, and a heavy phase discharge port (8) is provided at the bottom of the bottom layering zone of the tower.

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