A vertical integrated reaction device and method for continuous synthesis of polyamide

Abstract

The present invention relates to the technical field of polymer production processes, and discloses a vertical integrated reaction device and method for continuous synthesis of polyamide. The device includes a concentrating distillation tower and a vertical polycondensation reaction tower; the vertical polycondensation reaction tower includes, from top to bottom, a central circulation reactor, a first multi-stage tray reactor, and a second multi-stage tray reactor connected in sequence; after being concentrated in the concentrating distillation tower, a polyamide salt solution enters the central circulation reactor for polycondensation; the generated polyamide product is discharged from the conical bottom of the central circulation reactor, enters the first multi-stage tray reactor for further polycondensation reaction, and is obtained from the bottom of the second multi-stage tray reactor. The present invention utilizes a combination of the concentrating distillation tower, the central circulation reactor, and the multi-stage tray reactor to greatly improve the discharge rate and heat exchange efficiency of the reaction byproduct water, thereby realizing large-scale production of polyamide.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer production technology, and in particular to a vertical integrated reaction device and method for continuous synthesis of polyamide. Background Art

[0002] In the industrial production of polyamide, a diacid and a diamine are typically neutralized to form a polyamide salt, which is then used as a raw material for a polycondensation reaction to produce the polyamide. Polyamide salts generate small molecules of water during the polycondensation reaction. The water content in the reaction system affects the reaction rate and the molecular weight of the polymer, so the polycondensation process requires continuous removal of water at high temperatures. The boiling point of diamine at atmospheric pressure is lower than the melting temperature of the polyamide salt and the starting temperature of the polycondensation reaction. To prevent significant volatilization of diamine, which disrupts the equimolar ratio of dicarboxylic acid to diamine, polycondensation is typically performed by heating an aqueous solution of polyamide to above its melting temperature under high pressure.

[0003] The existing process for the continuous polymerization of nylon 66 mainly includes concentration, high-pressure pre-condensation, flash evaporation, atmospheric compression polymerization, and vacuum polycondensation. The above process is the mainstream of the current continuous polymerization process for nylon 66. The high-pressure pre-condensation stage uses a three-stage tubular reactor, which has the following disadvantages: the high-pressure concentration portion of the polyamide salt solution is mainly concentrated in the first stage of the three-stage tubular reactor. The tubular reactor is close to a plug flow reactor, and a sufficiently large heat exchange area cannot be set inside the equipment, and water cannot be discharged in time, so the production capacity of the device cannot be effectively improved.

[0004] In order to overcome the defects in the high-pressure pre-condensation process in the traditional continuous production of polyamide, an improved reaction device of the traditional three-stage tubular reactor was disclosed. Chinese patent CN214810920U discloses a new type of nylon 66 continuous dehydration polymerization U-shaped horizontal structure reaction device improved by Huafeng Company, which sets a heating device at a specific position to achieve the omission of the pilot heating device in the prior art; Chinese patent CN204079857U discloses a new type of nylon 66 polymerization device improved by Huitong Company that connects the outlet of the vertical reactor with the inlet of the U-shaped tube reactor, greatly improving the heating efficiency. Although the above-mentioned device has improved the heat transfer efficiency of the high-pressure pre-condensation process to a certain extent, there are limitations in the process of scaling up the production of the device, and the production capacity cannot be increased.

[0005] CN102746509A discloses a gas-liquid reverse integrated tower reaction device comprising a distillation section and a falling film reaction section using a two-component monomer as raw material. The reaction device is operated at normal pressure and has risks such as large-scale evaporation of diamine and precipitation of unreacted polyamide salts.

[0006] US3296217A discloses a tower reaction device integrating a drop tube and a distillation tray. The reaction on the drop tube of the device is accompanied by a large amount of evaporation of diamine, which is not conducive to the growth of the polyamide molecular chain. Summary of the Invention

[0007] The present invention addresses the defects of polyamide synthesis devices, such as low heating efficiency, inability to be scaled up, and difficulty in further increasing production capacity, and provides a vertical integrated reaction device for continuous synthesis of polyamide. The device can significantly improve heat transfer efficiency, enable large-scale production of polyamide, reach an output of 80,000 tons, and reduce technical costs.

[0008] To achieve the above object, the technical solution adopted by the present invention is:

[0009] A vertical integrated reaction device for continuous synthesis of polyamide, comprising a concentrating distillation tower and a vertical polycondensation reaction tower; the concentrating distillation tower is provided with a material inlet in the middle, a gas phase outlet at the top, and a discharge port at the bottom connected to the upper part of the vertical polycondensation reaction tower; the gas outlet at the top of the vertical polycondensation reaction tower is connected to the lower part of the concentrating distillation tower;

[0010] The vertical polycondensation reaction tower comprises a central circulation reactor, a first multi-stage tray reactor and a second multi-stage tray reactor connected in sequence from top to bottom;

[0011] The central circulation reactor comprises a draft tube located at the center of the reactor and a heating zone consisting of a heat exchange tube bundle, the heating zone being located between the draft tube and the inner wall of the central circulation reactor; the liquid phase material in the central circulation reactor is heated and evaporated in the heating zone and moves upward, and then flows downward in the draft tube to form an internal circulation; the central circulation reactor is provided with a liquid phase inlet and a steam outlet at the top, and has a conical bottom with a liquid phase outlet; the liquid phase outlet at the bottom of the central circulation reactor is connected to the top inlet of the first multi-stage reactor;

[0012] The first multi-stage tray reactor includes n stages of reaction units, each stage of the reaction unit includes a reaction tray, an overflow weir, a downcomer and a heat exchange system;

[0013] The reaction tray is an arched sieve plate perpendicular to the inner wall of the reactor, with one side connected to the inner wall of the reactor and an overflow weir perpendicular to the reaction tray on the top surface of the other side. The bottom of the overflow weir is connected to the downcomer to form the liquid phase outlet of the reaction unit. The heat exchange system is a heat exchange tube laid on the top and / or bottom surface of the reaction tray. The liquid phase outlet of the x-stage reaction unit corresponds to the side of the reaction tray in the x+1-stage reaction unit close to the inner wall of the reactor. A steam outlet is provided above the reactor wall on the side of the liquid phase outlet of each stage reaction unit. The liquid phase outlet of the last stage reaction unit corresponds to the second multi-stage tray reactor.

[0014] The second multi-stage tray reactor includes m stages of reaction units, and the structure of each stage of reaction unit is the same as that of the reaction unit in the first multi-stage tray reactor. The liquid phase outlet of the last stage of reaction unit corresponds to the bottom product outlet of the second multi-stage tray reactor.

[0015] The design principle of the reaction device of the present invention is that: a polyamide salt solution is concentrated as a raw material in a concentration and distillation tower and then enters a vertical polycondensation reaction tower for a polycondensation reaction; a large amount of water in the polyamide salt solution is quickly discharged from the reaction system by utilizing the functions of the central circulation reactor heating zone and the guide tube, thereby improving the polycondensation reaction speed and promoting the increase of the molecular weight of the polyamide; the raw material entering the first multi-stage tray reactor has removed more than 50% of the water in the reaction system and starts a condensation reaction; the reaction time is then extended by the multi-stage tray reactor; a heat exchange system is utilized to achieve uniform temperature distribution in the first multi-stage tray reactor and the second multi-stage tray reactor, with high heat transfer efficiency; and steam outlets are provided in each reaction unit of the multi-stage tray reactor to facilitate the efficient removal of by-product water, thereby promoting the progress of the polycondensation reaction from the perspective of chemical equilibrium, thereby realizing large-scale production of polyamide.

[0016] On the other hand, the water vapor containing diamine produced by the polyamide condensation reaction in the central circulation reactor is returned to the concentration distillation tower for mass transfer and heat transfer, thereby realizing the recovery of diamine, improving the utilization rate of diamine and simplifying the secondary treatment of the water vapor carrying diamine.

[0017] Preferably, the concentrating distillation tower is a tray tower with 8 to 15 trays, with a reboiler at the bottom outlet and a condenser at the top outlet to return the material to the concentrating distillation tower. The condenser reflux ratio is 0.005 to 0.1. The condenser recovers the diamine at this reflux ratio, ensuring that the diamine content carried by the water vapor at the top of the tower is within the required range and minimizing the condenser energy consumption.

[0018] Preferably, the gas phase outlet of the concentration and distillation tower is connected to a low-pressure steam system to reuse the outflowing gas.

[0019] Preferably, the height of the overflow weir is adjustable, and the height of the overflow weir is positively correlated with the residence time of the polyamide polycondensation reaction.

[0020] Preferably, the inclination angle of the conical structure at the bottom of the central circulation reactor from the bottom edge of the cone to the liquid phase outlet at the bottom is 25° to 45°, so that the reaction liquid enters the first multi-stage tray reactor at an appropriate flow rate. When the inclination angle is less than 25°, the reaction liquid flows slowly and the load of the central circulation reactor is large. When the inclination angle is greater than 45°, the evaporated water amount of the reaction liquid does not meet the requirement and enters the first multi-stage tray reactor, which is not conducive to the reaction; the ratio of the inner diameter of the guide tube to the inner diameter of the central circulation reactor is 0.3-0.7, the liquid flows from top to bottom inside the guide tube and from top to bottom outside the guide tube. The appropriate inner diameter size of the guide tube can control the internal and external liquids to maintain a suitable flow rate to form self-circulation.

[0021] Preferably, the inner diameter ratio of the central circulation reactor to the first multi-stage tray reactor is 1.5-2:1. A large amount of water evaporates from the reaction liquid in the central circulation reactor, and the polyamide salt condenses to a certain extent, thereby reducing the volume of the liquid phase entering the first multi-stage tray reactor, reducing the inner diameter of the first-stage tray reactor, increasing the number of reaction stages and the water vapor discharge channel, and facilitating the timely separation of water vapor from the reaction system during the polycondensation reaction. At the same time, each stage of the reaction unit is heated evenly, which is convenient and easy to control.

[0022] Preferably, n is 3-10; m is 3-10; by regulating the number of reaction layers in the two stages, the degree of polymerization of the product can be effectively controlled to meet the production requirements of polyamide materials with different properties.

[0023] Preferably, the reaction tray area accounts for 80-90% of the cross-sectional area of the multi-stage tray reactor, with the remaining area being the liquid phase channels of the reaction units. Preferably, the sieve area ratio of the arched sieve trays in the first multi-stage tray reactor to the arched sieve trays in the second multi-stage tray reactor is 0.3-0.8:1. The reactants in the upper portion of the first multi-stage tray reactor have a relatively low degree of polymerization and a relatively low viscosity of the product. As the reactants continue to move downward, the degree of polymerization increases, and the viscosity also increases. Therefore, the sieve area of the reaction trays in the second multi-stage tray reactor should be increased to facilitate the downward flow of the high-viscosity product.

[0024] Preferably, the heat exchange medium of the heat exchange system is biphenyl or thermal oil.

[0025] Preferably, the heat exchange system of each stage reaction unit is used alone or the multi-stage reaction units are operated in countercurrent series, and the inner walls of the first multi-stage tray reactor and the second multi-stage tray reactor are provided with heat exchange system inlets and outlets to connect the heat exchange system with external pipelines.

[0026] The present invention also provides a method for continuous synthesis of polyamide, which uses the vertical integrated reaction device to continuously synthesize polyamide, comprising the steps of:

[0027] The polyamide salt solution is used as the liquid raw material, enters the concentration distillation tower for concentration, and then is discharged from the bottom and passed into the vertical polycondensation reaction tower for polycondensation reaction;

[0028] The water and diamine produced by the polycondensation reaction of the concentrated polyamide salt solution in the central circulation reactor are discharged from the top of the central circulation reactor and returned to the concentration distillation tower; the produced polyamide product is discharged from the conical bottom of the central circulation reactor, enters the first multi-stage tray reactor to continue the polycondensation reaction, and obtains the polyamide product through the bottom of the second multi-stage tray reactor.

[0029] Preferably, the top pressure of the concentrating distillation tower is 0.12MPa~0.3MPa, and the temperature inside the tower is 115℃~160℃. Under these operating conditions, the polyamide salt solution in the concentrating distillation tower reaches the required concentration for the polycondensation reaction through heat and mass transfer, and the polyamide salt solution does not precipitate in the form of crystals.

[0030] Preferably, the diamine content in the gas discharged from the top of the central circulation reactor is 0.2-1.5%. The gas enters the bottom of the concentrating distillation tower, flows from bottom to top in the concentrating distillation tower, contacts the gas-liquid phase of the polyamide salt solution, and the diamine molecules enter the liquid phase from the gas phase. Finally, the diamine content of the gas discharged from the top of the concentrating distillation tower is less than 0.1%.

[0031] Preferably, the concentration of the polyamide salt solution entering the concentrating distillation tower is 40-65%; the concentration of the concentrated polyamide salt solution is 65-80%, at which concentration the polyamide salt does not precipitate in the form of crystals and reaches a concentration that can undergo polycondensation. In some embodiments, the polyamide salt includes any one or more of caprolactam salt, undecanolactam salt, dodecanolactam salt, butanediamine adipate, pentanediamine adipate, hexamethylenediamine adipate, hexamethylenediamine terephthalate, hexamethylenediamine sebacate, hexamethylenediamine dodecanoate, decanediamine sebacate, and dodecanediamine dodecanoate.

[0032] Preferably, the pressure in the vertical polycondensation reaction tower is 16 to 20 atm. When the pressure is lower than this range, the steam discharged from each reaction section of the vertical polycondensation tower is alkaline, which destroys the equivalent ratio reaction of the reactants. If the pressure is too high, it is not conducive to the discharge of polycondensation water and increases the pressure resistance requirement of the equipment.

[0033] Preferably, the temperature in the central circulation reactor is 200°C to 220°C, and the minimum temperature requirement for the polyamide condensation reaction is 205°C. The condensation reaction is an endothermic reaction. Increasing the temperature can accelerate the reaction rate and accelerate water evaporation. However, when the temperature exceeds a certain limit, it causes excessive volatilization of diamine, destroying the equivalent ratio of the reactants.

[0034] Preferably, the temperature in the first multi-stage tray reactor and the second multi-stage tray reactor gradually increases from top to bottom within the range of 220°C to 260°C; as the reaction proceeds, free diamine almost disappears, the viscosity of the system increases, and the increase in temperature is beneficial to reducing the viscosity of the polymer and facilitating the discharge of water, but too high a temperature will cause the polymer to decompose and produce gel.

[0035] Preferably, the degree of polymerization of the polyamide product is 18-28, which is the same as the product of high-pressure prepolymerization technology and can be used in subsequent polyamide polycondensation processes.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] (1) The vertical integrated reaction device for continuous synthesis of polyamide provided by the present invention returns the water vapor carrying diamine evaporated during the polyamide polycondensation reaction to the concentration and distillation tower for mass transfer and heat transfer, and simultaneously concentrates the aqueous solution of polyamide salt and recovers diamine, thereby improving the utilization rate of diamine and simplifying the secondary treatment of the water vapor carrying diamine.

[0038] (2) The vertical integrated reaction device for continuous synthesis of polyamide provided by the present invention includes a central circulation reactor that facilitates rapid discharge of a large amount of water in the polyamide salt solution from the interior of the reaction system, thereby increasing the polycondensation reaction speed and promoting the increase of the molecular weight of the polyamide.

[0039] (3) Each stage reaction unit of the multi-stage tray reactor included in the neutral integrated reaction equipment of the present invention discharges the gas generated by the reaction in a timely manner, thereby promoting the progress of the polycondensation reaction from the perspective of chemical equilibrium.

[0040] (4) In the present invention, each reaction unit in the multi-stage tray reactor is equipped with a heat exchange system to directly exchange heat with the reaction system or to exchange heat through a heating tray, thereby overcoming the problems of low heat exchange efficiency and difficulty in scaled-up production in the traditional high-pressure pre-condensation process of the tubular reactor, improving the heat transfer efficiency, enabling large-scale production of polyamide, and reducing technical costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 Schematic diagram of the continuous synthesis process of polyamide in a specific embodiment, wherein A represents the concentration and distillation section, and B represents the vertical polycondensation reaction section.

[0042] Figure 2 for Figure 1 The main view of the vertical polycondensation reaction section in the middle B, wherein I represents the central circulation reactor, II represents the first multi-stage tray reactor, III represents the second multi-stage tray reactor, C represents a reaction unit of the first multi-stage tray reactor, and D represents a reaction unit of the second multi-stage tray reactor.

[0043] Figure 3 for Figure 2 Schematic diagram of the structure of the I central circulation reactor.

[0044] Figure 4 for Figure 2 Schematic diagram of the structure of a single reaction unit in C.

[0045] Figure 5 for Figure 2 Schematic diagram of the structure of a single reaction unit in D.

[0046] Figure 6 Schematic diagram of two types of heat exchange systems on a single reaction tower plate.

[0047] Figure 7 Schematic diagram of the arcuate cribriform plate in area C and the arcuate cribriform plate in area D.

[0048] In the figure, T01 is a concentrating distillation tower; E01 is a reboiler; E02 is a condenser; T02 is a vertical polycondensation reaction tower; PL01 is a liquid feedstock flowing into the concentrating distillation tower; PL02 is a concentrated polyamide salt solution flowing into the central circulation reactor for polycondensation; PL03 is a liquid flowing from the central circulation reactor to the first multi-stage tray reactor; PL04 is a polyamide product flowing out; PG01 is a steam flowing out of the concentrating distillation tower; PG02 is a steam flowing from the concentrating distillation tower to the condenser; PG03 is a water and diamine gas flowing from the central circulation reactor to the concentrating distillation tower;

[0049] 1-gas phase outlet of central circulation reactor; 2-liquid phase inlet of central circulation reactor; 3-draft guide tube; 4-heating area; 5-heat exchange tube bundle; 6-conical bottom; 7-liquid phase outlet of central circulation reactor; 8-gas phase outlet of reaction unit; 9-overflow weir; 10, 10a-downcomer; 11, 11C, 11D-reaction tower plate; 12-product outlet; 13-gas phase pressure control valve; 14-liquid phase flow control valve; 15-heat exchange system; 16a, 16b-heat exchange tubes. DETAILED DESCRIPTION

[0050] In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with embodiment. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. Those skilled in the art will make modifications or equivalent substitutions based on understanding the technical solution of the present invention, without departing from the spirit and scope of the technical solution of the present invention, and all should be encompassed within the protection scope of the present invention.

[0051] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if the terms "upper", "lower", "left", "right" and the like indicate directions or positional relationships based on the directions or positional relationships shown in the drawings, it is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction. Therefore, the terms describing the positional relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting this patent. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0052] A vertical integrated reaction device for continuous synthesis of polyamide Figure 1-2As shown, continuous synthesis of nylon 66 is carried out, and the device includes a concentrating distillation tower T01 and a vertical polycondensation reaction tower T02; the concentrating distillation tower T01 is a plate tower containing 8 trays, and the liquid raw material nylon 66 salt solution PL01 flows into the middle of the concentrating distillation tower T01, part of the gas PG01 flows out from the top, and part of the gas PG02 flows out from the top and then flows into the condenser E02 and returns to the concentrating distillation tower T01; after concentration, part PL02 of the nylon 66 salt solution flows into the upper part of the vertical polycondensation reaction tower T02 from the bottom discharge port of the concentrating distillation tower T01, and part flows into the reboiler E01 and returns to the concentrating distillation tower T01.

[0053] like Figure 2-3 As shown, the vertical polycondensation reaction tower T02 includes a central circulation reactor I, a first multi-stage tray reactor II and a second multi-stage tray reactor III connected in sequence from top to bottom;

[0054] The central circulation reactor (1) comprises a draft tube (3) at the center of the reactor and a heating zone (4) consisting of a heat exchange tube bundle (5). The heating zone (4) is located between the draft tube (3) and the inner wall of the central circulation reactor. The draft tube (3) coincides with the reactor's central axis. A concentrated nylon 6,6 salt solution enters the central circulation reactor through the liquid phase inlet (2). It is heated, evaporated, and boiled in the heating zone (4), moving upward. It then flows downward through the draft tube (3), forming an internal circulation. When the gas-liquid mixture reaches the liquid surface, it separates, and the gas escapes into the gas phase space above the reactor. The liquid, under the influence of gravity and gas pressure, flows back into the draft tube (3) and downward, continuing to circulate the liquid phase within the draft tube (3) and the heat exchange tube bundle (5). This circulation fully mixes the liquid phase within the reactor, improving mass transfer efficiency and simultaneously enhancing heat transfer efficiency in the heating zone (4).

[0055] Central circulation reactor 1 produces a large amount of water and a small amount of diamine vapor PG03, which flows out of the central circulation reactor gas phase outlet 1 and returns to the concentrating distillation tower T01. The central circulation reactor liquid phase inlet 2 and the central circulation reactor gas phase outlet 1 are respectively equipped with a liquid phase flow control valve 14 and a gas phase pressure control valve 13 to control the inflow of reactants and the outflow of vapor.

[0056] The initially polycondensed nylon 66 solution is collected through the conical bottom 6 of the central circulation reactor I and enters the reaction tray of the first reaction unit of the first multi-stage tray reactor II through the liquid phase outlet 7 of the central circulation reactor; the central circulation reactor I coincides with the central axis of the first multi-stage tray reactor and the second multi-stage tray reactor and is connected up and down, the diameter ratio of the central circulation reactor I to the first multi-stage tray reactor II is 1.5:1, and the first multi-stage tray reactor and the first multi-stage tray reactor II have the same diameter.

[0057] like Figure 4-7As shown, the first multi-stage tray reactor II includes four reaction units, and each reaction unit includes a reaction tray 11, an overflow weir 9, a downcomer 10 and a heat exchange system 15; the area of the reaction tray 11 is 87% of the cross-sectional area of the multi-stage tray reactor; the heat exchange medium of the heat exchange system is biphenyl, and the inner walls of the first multi-stage tray reactor II and the second multi-stage tray reactor III are provided with heat exchange system inlets and outlets, so that the heat exchange system 15 is connected to the external pipeline, which is not drawn in the figure.

[0058] The reaction tray 11 is an arched sieve plate perpendicular to the inner wall of the reactor, one side of which is connected to the inner wall of the reactor, and the other side of the top surface is provided with an overflow weir 9 perpendicular to the reaction tray 11, and the bottom of the overflow weir 9 is connected to the downcomer 10 to form the liquid phase outlet of the reaction unit; the heat exchange system 15 is a heat exchange pipe 16a laid on the top surface of the reaction tray 11, such as Figure 4 and Figure 6 As shown; the liquid phase outlet of the x-th stage reaction unit corresponds to the side of the reaction tray 11 in the x+1-th stage reaction unit close to the inner wall of the reactor, a steam outlet 8 is provided above the reactor wall on the liquid phase outlet side of each stage reaction unit, and the liquid phase outlet of the downcomer 10a of the last stage reaction unit corresponds to the second multi-stage tray reactor II;

[0059] The second multi-stage tray reactor II includes four reaction units, each of which includes a reaction tray 11, an overflow weir 9, a downcomer 10, and a heat exchange system 15;

[0060] The reaction tray 11 is an arched sieve plate perpendicular to the inner wall of the reactor, one side of which is connected to the inner wall of the reactor, and the other side of the top surface is provided with an overflow weir 9 perpendicular to the reaction tray 11, and the bottom of the overflow weir 9 is connected to the downcomer 10 to form the liquid phase outlet of the reaction unit; the heat exchange system 15 is a heat exchange pipe 16b laid on the bottom surface of the reaction tray 11, such as Figure 5 and Figure 6 As shown; the liquid phase outlet of the x-th stage reaction unit corresponds to the side of the reaction tower plate 11 in the x+1-th stage reaction unit close to the inner wall of the reactor, and a steam outlet 8 is provided above the reactor wall on the liquid phase outlet side of each stage reaction unit. The liquid phase outlet of the last stage reaction unit corresponds to the bottom product outlet 12 of the second multi-stage tower plate reactor.

[0061] Example 1

[0062] A continuous synthesis method for polyamide, the specific process and materials are as follows:

[0063] A nylon 66 salt solution with a mass flow rate of 12,000 kg / h and a mass concentration of 50% enters the concentrating distillation tower, is concentrated in the concentrating distillation tower, and the mass concentration of the nylon 66 salt solution discharged from the bottom is 68%; the top pressure of the concentrating distillation tower is 1.3 atm, the temperature in the tower is controlled at 120°C, the reflux ratio is 0.009, the heat exchange of the top condenser is 30 kW, and the heat exchange of the bottom reboiler is 2,315 kW.

[0064] The concentrated nylon 66 salt solution is pressurized to 18.3 atm by a pressurizing device, heated to 205°C by a heating device (the pressurizing device and the heating device are not shown), and injected into the central circulation reactor through the liquid phase inlet of the central circulation reactor. The reaction temperature in the tower is 214°C. The water and diamine vapor produced by the preliminary polycondensation are discharged from the top of the central circulation reactor and returned to the concentration distillation tower. The gas phase flow rate is adjusted by the gas phase control valve to control the pressure in the central circulation reactor at 18.3 atm.

[0065] The amount of steam discharged from the central circulation reactor is 58% of the total water amount of the polyamide salt solution entering the central circulation reactor, and the hexamethylenediamine content in the steam is about 0.4%. The steam carrying hexamethylenediamine is introduced from the bottom of the concentrating distillation tower, and the steam flow rate at the top of the concentrating distillation tower is 4950 kg / h, and the hexamethylenediamine content is less than 0.01%.

[0066] The liquid-phase polyamide primary polymerization product produced in the central circulation reactor is collected at the conical bottom of the central circulation reactor and enters the first multi-stage tray reactor to continue the polycondensation reaction; the sieve hole area ratio of the bow sieve plate of the reaction tray in the first multi-stage tray reactor and the bow sieve plate of the reaction tray in the second multi-stage tray reactor is 0.5:1.

[0067] The operating temperatures of the four reaction units of the first multi-stage tray reactor are 220°C, 222.5°C, 225°C and 227.5°C respectively; the operating temperatures of the four reaction units of the second multi-stage tray reactor are 230°C, 235°C, 240°C and 245°C respectively. The residence time of the reaction raw materials in the entire tower is controlled at 58 minutes.

[0068] Finally, the product obtained at the bottom of the second multi-stage tray reactor is a nylon 66 melt material with a degree of polymerization of 22, a water content of 9%, and a nylon 66 salt content of 3.8%.

[0069] Example 2

[0070] Using the same equipment as in Example 1, the pressure within the central circulation reactor was controlled at 16.5 atm, with all other conditions remaining the same. The steam discharged from the central circulation reactor accounted for 65% of the total water content of the polyamide salt solution entering the central circulation reactor, and the hexamethylenediamine content in the steam was approximately 0.5%. The steam carrying hexamethylenediamine was introduced from the bottom of the concentrating distillation column, with a steam flow rate of 5224 kg / h at the top of the concentrating distillation column, and the hexamethylenediamine content was less than 0.01%.

[0071] Finally, the product obtained at the bottom of the second multi-stage tray reactor is a nylon 66 melt material with a degree of polymerization of 24, a water content of 8.5%, and a nylon 66 salt content of 3.0%.

Claims

1. A vertical integrated reaction device for continuous synthesis of polyamide, characterized in that: It includes a concentration distillation tower and a vertical polycondensation reaction tower; the concentration distillation tower is provided with a material inlet in the middle, a gas phase outlet at the top, and a discharge port at the bottom connected to the upper part of the vertical polycondensation reaction tower, and the gas outlet at the top of the vertical polycondensation reaction tower is connected to the lower part of the concentration distillation tower; The vertical polycondensation reaction tower comprises a central circulation reactor, a first multi-stage tray reactor and a second multi-stage tray reactor connected in sequence from top to bottom; The central circulation reactor comprises a draft tube located at the center of the reactor and a heating zone consisting of a heat exchange tube bundle, the heating zone being located between the draft tube and the inner wall of the central circulation reactor; the liquid phase material in the central circulation reactor is heated and evaporated in the heating zone and moves upward, and then flows downward in the draft tube to form an internal circulation; the central circulation reactor is provided with a liquid phase inlet and a steam outlet at the top, and has a conical bottom with a liquid phase outlet; the liquid phase outlet at the bottom of the central circulation reactor is connected to the top inlet of the first multi-stage reactor; The first multi-stage tray reactor includes n stages of reaction units, each stage of the reaction unit includes a reaction tray, an overflow weir, a downcomer and a heat exchange system; The reaction tray is an arched sieve plate perpendicular to the inner wall of the reactor, with one side connected to the inner wall of the reactor and an overflow weir perpendicular to the reaction tray on the top surface of the other side. The bottom of the overflow weir is connected to the downcomer to form the liquid phase outlet of the reaction unit. The heat exchange system is a heat exchange tube laid on the top and / or bottom surface of the reaction tray. The liquid phase outlet of the x-stage reaction unit corresponds to the side of the reaction tray in the x+1-stage reaction unit close to the inner wall of the reactor. A steam outlet is provided above the reactor wall on the side of the liquid phase outlet of each stage reaction unit. The liquid phase outlet of the last stage reaction unit corresponds to the second multi-stage tray reactor. The second multi-stage tray reactor comprises m stages of reaction units, the structure of each stage of the reaction unit being the same as that of the reaction unit in the first multi-stage tray reactor, and the liquid phase outlet of the last stage of the reaction unit corresponds to the bottom product outlet of the second multi-stage tray reactor; The tapered structure at the bottom of the central circulation reactor has an inclination angle of 25° to 45° from the bottom edge of the tapered structure to the liquid phase outlet at the bottom end; the inner diameter ratio of the central circulation reactor to the first multi-stage tray reactor is 1.5-2:1; The ratio of the sieve hole areas of the arcuate sieve plates in the second multi-stage tray reactor and the arcuate sieve plates in the first multi-stage tray reactor is 0.3-0.8:

1.

2. The vertical integrated reaction device for continuous synthesis of polyamide according to claim 1, characterized in that: The concentration distillation tower is a plate tower containing 6 to 15 plates. The bottom outlet is provided with a reboiler and the top outlet is provided with a condenser to return the material to the concentration distillation tower. The condenser reflux ratio is 0.005 to 0.

1.

3. The vertical integrated reaction device for continuous synthesis of polyamide according to claim 1, characterized in that: The ratio of the inner diameter of the draft tube to the inner diameter of the central circulation reactor is 0.3-0.

7.

4. The vertical integrated reaction device for continuous synthesis of polyamide according to claim 1, characterized in that: n is 3-10; m is 3-10; And / or, the reaction tray area is 80-90% of the cross-sectional area of the multi-stage tray reactor.

5. The vertical integrated reaction device for continuous synthesis of polyamide according to claim 1, characterized in that: The heat exchange medium of the heat exchange system is biphenyl or thermal oil; And / or, the heat exchange system of each stage reaction unit is used alone or the multi-stage reaction units are operated in countercurrent series, and the inner walls of the first multi-stage tray reactor and the second multi-stage tray reactor are provided with heat exchange system inlets and outlets to connect the heat exchange system with external pipelines.

6. A method for continuous synthesis of polyamide, characterized in that: The vertical integrated reaction device according to any one of claims 1 to 5 is used to continuously synthesize polyamide, comprising the steps of: The polyamide salt solution is used as the liquid raw material, enters the concentration distillation tower for concentration, and then is discharged from the bottom and passed into the vertical polycondensation reaction tower for polycondensation reaction; The water and diamine produced by the polycondensation reaction of the concentrated polyamide salt solution in the central circulation reactor are discharged from the top of the central circulation reactor and returned to the concentration distillation tower; The produced polyamide product is discharged from the conical bottom of the central circulation reactor, enters the first multi-stage tray reactor to continue the polycondensation reaction, and obtains the polyamide product through the bottom of the second multi-stage tray reactor.

7. The method for continuous synthesis of polyamide according to claim 6, wherein: The top pressure of the concentration and rectification tower is 0.12 MPa to 0.3 MPa, and the temperature inside the tower is 115° C. to 160° C.

8. The method for continuous synthesis of polyamide according to claim 6, wherein: The diamine content in the gas discharged from the top of the central circulation reactor is 0.2-1.5%; and / or, the concentration of the polyamide salt solution entering the concentration distillation tower is 40-65%; the concentration of the polyamide salt solution after concentration is 65-80%; And / or, the polyamide salt includes any one or more of caprolactam salt, undecanolactam salt, laurolactam salt, butanediamine adipate, pentanediamine adipate, hexamethylenediamine adipate, hexamethylenediamine terephthalate, hexamethylenediamine sebacate, hexamethylenediamine dodecanoate, decanediamine sebacate, and dodecanediamine dodecanoate.

9. The method for continuous synthesis of polyamide according to claim 6, wherein: The pressure in the vertical polycondensation reaction tower is 16 to 20 atm; and / or, the temperature in the central circulation reactor is 200° C. to 220° C.; the temperature in the first multi-stage tray reactor and the second multi-stage tray reactor gradually increases from top to bottom within the range of 220° C. to 260° C.; And / or, the degree of polymerization of the polyamide product is 18-28.

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