Continuous polymerization device for the production of polyamide using dibasic acid and dibasic amine

Abstract

A continuous polymerization apparatus for producing polyamide using dibasic acid and dibasic amine, characterized in that it comprises an evaporator, a reaction rectification tower, a flash evaporator, and a polymerizer sequentially connected by piping, wherein the reaction rectification tower comprises a tower boiler and a tower disk section at the upper part of the tower boiler, and wherein the number of tower disks in the tower disk section is 15-30, and wherein the distance between two adjacent tower disks is 400 mm-600 mm, and wherein the height of an overflow weir of the tower disks is 50 mm-300 mm;and wherein the continuous polymerization apparatus further comprises a preheating heat exchanger and a prepolymerization heat exchanger, and wherein the tower disk in the tower disk section near the tower boiler, the preheating heat exchanger and the prepolymerization heat exchanger are connected in series by piping, and wherein the prepolymerization heat exchanger and the tower boiler establish a circulating connection by piping, so that the material enters the preheating heat exchanger, the prepolymerization heat exchanger and the tower boiler in series through the tower disks and can circulate between the prepolymerization heat exchanger and the tower boiler.;

Description

RELATED APPLICATIONThis application claims priority to Chinese Patent Application No. 202410623625.7 filed on May 20, 2024, entitled "Continuous Polymerizer for Producing Polyamide and Continuous Polymerization Process Therefor", which is hereby incorporated by reference in its entirety.TECHNICAL FIELDThe present application relates to the technical field of polyamides, and more particularly to a continuous polymerizer for producing polyamide using dibasic acid and dibasic amine.PRIOR ARTPolyamide (polyamides), abbreviated as PA and generally known as nylon (nylon), is a general term for polymers containing amide groups (-NH-C=O) in the repeating units of the main chain of a macromolecule, the polyamide can generally be obtained by ring-opening a lactam such as nylon 6, or by polycondensation of a dibasic acid and a dibasic amine such as nylon 66.In the production of polyamide by polycondensation of dibasic acid and dibasic amine, conventionally, in industry, the dibasic acid and dibasic amine are first mixed in water in the salt bath in a molar ratio of 1:1 to produce a salt solution having a concentration of 50% by weight, then the physical water and the generated water are gradually removed in the system to complete the polycondensation. However, since the dibasic amine is volatile, it evaporates from the brine during the evaporation and concentration process, resulting not only in imbalance of the carboxylic acid / amine ratio in the brine, which deteriorates the polymerization degree and the performance of the polyamide product, but also in greater loss, which increases the production cost, and at the same time, the evaporated dibasic amine is discharged with the gas phase, resulting in a problem of environmental pollution.CONTENT OF THE PRESENT APPLICATIONFrom the foregoing, in view of the above problem, it is necessary to provide a continuous polymerizer for producing polyamide using dibasic acid and dibasic amine and a continuous polymerization method thereof, wherein the use of the continuous polymerizer for producing polyamide not only ensures the quality of the polyamide product but also reduces loss, reduces the generation of three kinds of wastes and reduces the risk of the process and the running cost.A continuous polymerization apparatus for producing polyamide using dibasic acid and dibasic amine, comprising an evaporator, a reaction rectification tower, a flash evaporator and a polymerizer connected in sequence by piping, wherein the reaction rectification tower comprises a tower vessel and a tower disk section at the upper part of the tower vessel, and wherein the number of tower disks in the tower disk section is 15-30, and wherein the distance between two adjacent tower disks is 400 mm-600 mm, and wherein the height of an overflow weir of the tower disks is 50 mm-300 mm; and wherein the continuous polymerizer further comprises a preheating heat exchanger and a prepolymerization heat exchanger, and wherein the tower plate in the tower plate portion in the vicinity of the tower vessel, the preheating heat exchanger and the prepolymerization heat exchanger are connected by pipings in order, and wherein the prepolymerization heat exchanger and the tower vessel establish a circulating connection by pipings so that the material can enter the preheating heat exchanger, the prepolymerization heat exchanger and the tower vessel in order through the tower plates and circulate between the prepolymerization heat exchanger and the tower vessel.In one embodiment, the number of tower disks is 20-25.In one exemplary embodiment, the distance between two adjacent tower disks is 450 mm-550 mm.In one exemplary embodiment, the height of an overflow weir of the tower disks is 100 mm-200 mm.In one embodiment, a gas phase outlet pipe is provided with an online infrared detector at the top of the reaction rectification tower.In one embodiment, the continuous polymerization apparatus further comprises an on-line dibasic amine refill line used to refill the dibasic amine in real time, and wherein the on-line dibasic amine refill line is connected to the prepolymerization heat exchanger.In an embodiment, the polymerizer includes a polymerizer body, an exhaust pipe connected to the polymerizer body, and a multistage heat exchanger installed in the exhaust pipe.In one embodiment, the number of addition polymerization units is 1 or more than 2.A continuous polymerization process for producing polyamide using dibasic acid and dibasic amine, which uses the continuous polymerization apparatus of polyamide and comprises the following steps:Feeding the brine into the evaporator for evaporation and concentration and then into the reaction rectification tower, wherein the brine after preheating reaches the tower disks in the tower disk section and flows layer by layer to the tower disk in the vicinity of the tower vessel, and wherein then the brine is fed successively into the preheating heat exchanger, the prepolymerization heat exchanger and the tower vessel and then fed successively into the flash evaporator and the polymerizer for flash evaporation polymerization, and wherein the products are granulated to obtain the polyamide products, and wherein the material circulates between the prepolymerization heat exchanger and the tower vessel.In one embodiment, the degree of polymerization of the material conveyed into the preheat heat exchanger is 2 to 3.In the present application, by adjusting the number and the distance of the tower disks and the height of the overflow weir in the reaction distillation tower, the residence time of the salt solution can be extended so that prepolymerization takes place. On the one hand, the concentration of free amine in the brine can be lowered by the prepolymerization, which then reduces the loss of amine in the evaporation and concentration, and on the other hand, as the residence time increases, the gas phase generated by the evaporation and concentration of the tower vessel increases upward, and in the process in which the gas phase comes into contact with the brine in countercurrent for mass and heat transfer, the gas phase can come into full contact with the brine when the free amine in the brine is reduced due to the prepolymerization, the dibasic amine carried in the gas phase can be absorbed by the double role of physical absorption (cooling and condensation) and chemical absorption (reaction with the carboxylic acid in the brine to form carboxylic acid-amine salts), whereby not only the carboxylic acid-amine ratio in the salt solution can be better maintained to ensure the quality of the polyamide products, but the loss and generation of three wastes can also be reduced, making the process more competitive.At the same time, by adding a preheating heat exchanger and a prepolymerization heat exchanger, the present application makes the material enter the preheating heat exchanger for preheating through the tower plate in the vicinity of the boiler and then enter the prepolymerization heat exchanger for evaporation, concentration and prepolymerizing, thus the flow rate and temperature of the hot fluid in the prepolymerization heat exchanger can be decreased, and the deposits in the prepolymerization heat exchanger due to the decomposition of the material and the carbonization caused by the high temperature difference are avoided, so that not only the quality of the polyamide products is ensured, but also the heat exchange efficiency and capacity of the prepolymerization heat exchanger can be ensured, and the process risk and the running costs can be reduced, and the deposits in the prepolymerization heat exchanger due to the decomposition of the material and the carbonization, The heat exchange efficiency and capacity of the prepolymerization heat exchanger caused by the high temperature difference are avoided, so that not only the quality of the polyamide products can be ensured, but also the heat exchange efficiency and capacity of the prepolymerization heat exchanger can be ensured, and the process risk and the running cost can be reduced.BRIEF DESCRIPTION OF THE DRAWINGSIn order to more clearly explain the technical solution in the embodiments of the present application or in the conventional technology, the drawings to be used in the explanation of the embodiments or the conventional technology will be briefly presented below. Obviously, the accompanying drawings described below show only some embodiments of the present application. Those skilled in the art can obtain other accompanying drawings without any creative works based on these accompanying drawings. FIG. 1 is a schematic diagram of a continuous polymerization apparatus for producing polyamide using dibasic acid and dibasic amine according to the present application. FIG. 2 is a schematic diagram showing the structure of a polymerizer in one embodiment of the present application.List of reference characters1 Evaporator 2 Reaction rectification tower 3 Flash evaporator 4 Polymerizer 5 Pelletizer 6 Preheating heat exchanger 7 Prepolymerization heat exchanger 21 Tower disk 22 Tower vessel 2 a Online infrared detector 6 aCirculation pump 41 Polymerizer body 42 Exhaust pipe 43 Heat exchangerDETAILED DESCRIPTIONIn order to facilitate understanding of the present application, the present application will be explained in more detail below. However, it should be understood that the present application may be embodied in many different forms and is not limited to the embodiments or embodiments discussed herein. In contrast, these embodiments or embodiments are provided so that the disclosed content of the present application can be more thoroughly and fully understood.Unless otherwise stated, all technical and scientific terms used in the specification have the same meanings as those commonly understood by those skilled in the technical field of the present application. The terms used in the description of the present application are only for explaining the specific embodiments or embodiments, rather than limiting the present application. The term "and / or" as used herein optionally includes any of two or more related listed items, as well as any combination and all combinations of related listed items, wherein any combination and all combinations include two of the related listed items, multiple of the related listed items, or a combination of all related listed items.As shown in FIG. 1, the continuous polymerization apparatus for producing polyamide using dibasic acid and dibasic amine provided by the present application is mainly used to evaporate and concentrate the salt solution produced from the dibasic acid and the dibasic amine and to remove the physical water and the generated water in the system to complete the polycondensation. Herein, the dibasic acid of the present industrial application refers more broadly to dibasic C4-C12carboxylic acids such as butane diacid, glutane diacid, adipic acid, heptane diacid, octane diacid, nonane diacid, sebacic acid, lauric acid, etc., and the dibasic amine of the present industrial application refers more broadly to dibasic C4-C12amines such as 1,4-butanediamine, 1,5-pentanediamine, 1,6-hexanediamine, 1,7-heptanediamine, 1,8-octanediamine, 1,9-nonanediamine, 1,10-decanediamine, lauryl diamine, etc. The concentration of the salt solution may be in any ratio, Preferably, the dibasic acid and the dibasic amine in the salt bath are mixed at a molar ratio of 1:1 in water to form a salt solution of 50% by weight to 65% by weight.Specifically, the continuous polymerizer comprises an evaporator 1, a reaction rectification tower 2, a flash evaporator 3, and a polymerizer 4 which are connected in sequence by piping.The evaporator 1 serves to evaporate and concentrate the produced brine. More specifically, the brine prepared from the dibasic acid and the dibasic amine enters the evaporator 1 through the pipe a, the evaporator 1 is heated with steam, wherein the temperature of the steam is preferably 100°C-200°C, and the pressure during the heating operation is preferably maintained in a range of 0.1 MPa(g) to 0.25 MPa(g) to allow evaporation and concentration of the brine and to reduce the water content of the brine.The gas phase formed during evaporation and concentration of the brine contains water and a very small amount of dibasic amine, and optionally, the gas phase is discharged from the evaporator 1 through the piping b, cooled and collected by an apparatus such as a cooling tower, and reused for the preparation of the brine to allow reuse of resources, which is green and eco-friendly.The reaction rectification tower 2 comprises a tower vessel 22 and a tower plate portion at the upper part of the tower vessel 22 for receiving the material after evaporation and concentration by the evaporator 1, i.e., the initially concentrated brine, in particular, the material enters the upper preheater of the reaction rectification tower 2 through the pipe c and enters the upper tower plate 21 of the tower plate portion of the reaction rectification tower 2, e.g., the second tower plate 21 or a third tower plate 21 downward from the upper part of the tower after being preheated by the ascending gas phase in the reaction rectification tower 2, and then flows layer by layer through each tower plate 21 and comes into countercurrent contact with the ascending gas phase in the tower, This is done in order to carry out the transfer of material and heat.It should be noted that the number of the tower disks 21 in the tower disk section is usually 8-10, the distance between adjacent tower disks 21 is usually 200 mm-300 mm, and the height of an overflow weir is usually 5 mm-30 mm, but by such a construction, the contact residence time between the material and the gas phase is short and the prepolymerization reaction cannot start on the tower disks, resulting in that free amine in the material easily evaporates after further preheating, resulting in imbalance of the carboxylic acid / amine ratio in the material and not conducive to the speed of the subsequent prepolymerization reaction. Although the lost amine can be adjusted optimally by the salt formation step, it tends to increase the unit consumption of the polymerization and increase the cost, and at the same time, the vapor-evaporated dibasic amine is discharged with the vapor phase, which also brings about the problem of environmental pollution.In this regard, the present application sets the arrangement method of the tower disk 21 in the tower disk section, in particular, the number of the tower disks 21 in the tower disk section of the present application is 15 to 30, preferably 20 to 25, the distance between two adjacent tower disks 21 is 400 mm to 600 mm, preferably 450 mm to 550 mm, and the height of the overflow weir of the tower disk 21 is 50 mm to 300 mm, preferably 100 mm to 200 mm. In the present application, by adjusting the number and the pitch of the tower plates 21 in the reaction rectification tower 2, the time in which the material flows layer by layer to the tower plate 21 in the vicinity of the tower vessel is prolonged, and by adjusting the height of the overflow weir of the tower plates 21 in the reaction rectification tower 2, the residence time of the material in each layer of the tower plates 21 is prolonged, so that the total residence time of the material in the tower is prolonged, which then results in the material already having the preliminary prepolymerization reaction at this stage.By the preliminary prepolymerization reaction, the free amine can be converted into polyamide dimer, whereby the concentration of the free amine in the material can be reduced and the loss of amine during evaporation and concentration can be reduced. At the same time, as the residence time increases, the gas phase produced by the evaporation and concentration of the tower vessel rises, and in the process in which the gas phase comes into contact with the material for mass and heat transfer in countercurrent, the gas phase can come into full contact with the material when the free amine in the material is reduced due to the prepolymerization, the dibasic amine carried in the gas phase can be absorbed by the double role of physical absorption (cooling and condensation) and chemical absorption (reaction with the carboxylic acid in the material to form carboxylic acid-amine salts), whereby not only the carboxylic acid-amine ratio in the material can be more maintained to ensure the quality of the polyamide products, The loss and generation of three wastes can also be reduced, making the process more competitive.Referring to FIG. 1, the continuous polymerization apparatus of the present application further comprises a preheating heat exchanger 6 and a prepolymerization heat exchanger 7, wherein the tower plate 21 in the tower plate portion in the vicinity of the tower vessel, the preheating heat exchanger 6 and the prepolymerization heat exchanger 7 are connected by pipings in order, and wherein the prepolymerization heat exchanger 7 and the tower vessel 22 establish a circulating connection by pipings so that the material can sequentially enter the preheating heat exchanger 6, the prepolymerization heat exchanger 7 and the tower vessel 22 through the tower plates 21 and circulate between the prepolymerization heat exchanger 7 and the tower vessel 22.The preheating heat exchanger 6 serves to receive and preheat the material flowing from the tower plate 21 of the tower plate section in the vicinity of the tower vessel, i.e., the brine realizing the preliminary prepolymerization in the tower plate section. As the material flows through the tower disc 21 in the vicinity of the tower boiler, it enters the preheating heat exchanger 6 through the pipe e to be preheated.Optionally, the material is collected on the tower plate 21 in the vicinity of the tower vessel by means of a collector, e.g. a collector plate, and then connected to the circulation pump 6a to feed it into the preheating heat exchanger 6 for preheating, wherein the circulation pump 6a may be of a pump type usual in industry, e.g. a centrifugal pump, a diaphragm pump, etc., wherein a centrifugal pump is preferred in this application.Optionally, the heat source for the preheat heat exchanger 6 may be a liquid phase heat transfer oil having a temperature of 200°C to 250°C, such as T66 (hydrogenated terphenyl mixture) or other similar heat transfer oils in the industry; or the heat source may be steam having the same temperature to precondition the material to 200°C to 220°C. In view of the fact that the prepolymerization of the material has already occurred in the tower plate portion of the reaction rectification tower 2, in order to avoid clogging and inferior heat transfer effect of the preheating heat exchanger 6 due to the high viscosity material, the preheating heat exchanger 6 of the present application preferably adopts a tube heat exchanger having a high flow rate, and the heat source preferably adopts medium pressure steam heat supply to use its latent heat for further improving the heat transfer effect, thereby achieving the purpose of rapidly preheating the material.The prepolymerization heat exchanger 7 serves to receive the material preheated by the preheating heat exchanger 6 for evaporation and concentration and prepolymerization to achieve the desired concentration and degree of prepolymerization. Specifically, the material preheated by the preheating heat exchanger 6 enters the bottom of the prepolymerization heat exchanger 7 through the pipe f and is forced to be conveyed by the front-end pump and the density difference formed in the prepolymerization heat exchanger 7 to realize the movement of the material inside the prepolymerization heat exchanger 7 and to carry out the evaporation, concentration, and prepolymerization.After preheating by the preheating heat exchanger 6, the prepolymerization heat exchanger 7 only needs to precondition the material to 220° C. to 250° C. However, when the present application adds only the prepolymerization heat exchanger 7, the prepolymerization heat exchanger 7 needs to be heated with heat transfer oil to 280° C. to 300° C., which is not only a large heat loss and is not economical, but also results in the prepolymerization heat exchanger 7 having a high surface temperature and carbonizing and depositing the material under prolonged operation, and the efficiency of heat transfer of the prepolymerization heat exchanger 7 and the material mobility after deposition are significantly reduced, resulting in that emergency shutdown for cleaning is required. This increases the process risk and operating costs and, when the deposit layer penetrates the material, it simultaneously affects the colour and performance of the polyamide product.The present application ensures that, by simultaneously adding a pre-heating heat exchanger 6 and a pre-polymerization heat exchanger 7, the material enters the pre-heating heat exchanger 6 for pre-heating through the final tower plate 21 and then enters the pre-polymerization heat exchanger 7 for evaporation, concentration and pre-polymerization, thus the flow rate and temperature of the hot fluid in the pre-polymerization heat exchanger 7 can be decreased, and the deposits in the pre-polymerization heat exchanger 7 due to the decomposition of the material and the carbonization caused by the high temperature difference are avoided, so that not only the quality of the polyamide products is ensured, but also the heat exchange efficiency and capacity of the pre-polymerization heat exchanger 7 can be ensured, and the process risk and the running cost can be reduced.The tower vessel 22 of the reaction rectification tower 2 serves to receive the material after evaporation, concentration and prepolymerization in the prepolymerization heat exchanger 7 including the gas phase and the liquid phase, in particular, the material obtained in the prepolymerization heat exchanger 7 enters the tower vessel 22 of the reaction rectification tower 2 through the piping g to perform gas-liquid separation, the gas phase is discharged from the reaction rectification tower 2 through the gas phase discharge piping d at the top of the tower after complete heat exchange and absorption of the material on the tower plate 21 in the tower plate portion, a part of the liquid phase enters the flash evaporator 3 through the piping h for further flash evaporation and polymerization reaction, and the other part enters the prepolymerization heat exchanger 7 circulatingly through the piping n.Optionally, the gas phase outlet pipe d at the top of the reaction rectification tower 2 is provided with an online infrared detector 2 ato monitor the content of small multicomponent molecules in the gas phase, in particular the content of dibasic amine, in real time. At the same time, the present application may also be provided with an on-line dibasic amine replenishing line m which is used to replenish the dibasic amine in the prepolymerization heat exchanger 7 in accordance with the monitored changes in the loss of the dibasic amine in real time to maintain the carboxylic acid / amine ratio in the prepolymerization heat exchanger 7 within an appropriate range. It is understood that the on-line dibasic amine replenishing line m may be directly connected to the prepolymerization heat exchanger 7 or to a pipe f through which it is connected to the prepolymerization heat exchanger 7.The flash evaporator 3 assumes a variable diameter serpentine tube which allows the water in the liquid phase material to be progressively evaporated by the resistance of the tubing to achieve a gas-liquid two phase condition while the preliminarily prepolymerized polyamide in the material is further polymerized in the flash evaporator 3. The flash evaporator 3 may heat the material to an arbitrary temperature of 250° C. to 300° C., and the water in the gas-liquid two-phase material may make an arbitrary proportion of 0.1 wt % to 2 wt %.The material obtained by the flash evaporator 3 (gas-liquid two-phase) then enters the polymerizer 4 through the piping k. The polymerizer 4 is used for separating the entering gas-liquid two phase and simultaneously for further removing water in the system under the vacuum system to advance the reaction toward the final polymerization and obtain the polyamide product, wherein the moisture in the polyamide product may be in any proportion of 0.01 wt% to 0.1 wt%. Finally, the product obtained from the polymerizer 4 is granulated by the pelletizer 5 to obtain the polyamide product.In order for the material entering polymerizer 4 to achieve the desired degree of polymerization and molecular weight distribution of the final polyamide product, polymerizer 4 must efficiently and stably remove water from the body while ensuring that the material has a residence time in polymerizer 4 to achieve the final state of the polyamide product.Optionally, the number of polymerizers 4 is 1 or more than 2, preferably 2, and the two polymerizers 4 are independently connected to the flash evaporator 3, so that the production can be switched depending on the actual situation.When the gas-liquid two-phase material enters the polymerizer 4 for separation, it should be avoided that the variations in the liquid level cause a part of the products to be non-uniformly heated and crosslinked and then to be gelized, which in turn deteriorates the quality of the product, and at the same time, further heated and then to be turned into a black dot, which further degrades the quality of the product.The variations in the liquid level are usually caused by variations in vacuum, at present, a large amount of polymerization process vapor in the polymerizer 4 is directly exhausted by a water ring vacuum pump or other similar equipment, further cooled by the spray and other refrigerants, and then discharged. However, when the water of the vapor phase is directly sucked in the polymerizer 4, the water flow of the vapor phase generated at this time has a variation, which results in that the water ring pump of the polymerizer 4 must be constantly adjusted to compensate for the variations due to changes in the amount of the sucked gas, which inevitably deteriorates the degree of vacuum in the polymerizer 4, and the unstable vacuum has a greater effect on the control of the liquid level of the polymerizer 4, which in turn results in that an undesirable cross-linking side reaction occurs in the polymerization and gels and black spots are formed, which requires frequent changing and cleaning. At the same time, the large amount of process steam exhausted from the vacuum pump needs to be cooled by the consumption of circulating spray water or the like, which not only wastes the heat of the process steam but also consumes additional other energy for cooling, resulting in high production cost.For this purpose, as shown in FIG. 2, the polymerizer 4 of the present application preferably comprises a polymerizer body 41, an exhaust pipe 42 connected to the polymerizer body 41, and a heat exchanger 43 installed in the exhaust pipe 42, wherein the number of the heat exchangers 43 is more than 2, including 2, 3, 4, etc., to generate low-pressure steam and hot water by exchanging the heat of the steam with a multistage heat exchanger.Specifically, in the present application, a water ring vacuum pump is used to generate the vacuum of the polymerizer 4, and a multistage heat exchanger 43 is disposed in the exhaust pipe 42 of the polymerizer 4 for heat exchange of the process steam, and a certain amount of low pressure steam and hot water is co-produced using the heat of the process steam; at the same time, the gas phase after cooling by the multistage heat exchanger 43 is mainly a non-condensable gas and a very small part of the process steam, which provides a guarantee for the temperature operation of the vacuum system to avoid unnecessary frequent switching and cleaning due to vacuum fluctuations, at the same time, the process steam heat is further utilized, and also the use of cooling media is reduced. This can reduce the operation and production costs, improve the quality stability of the polyamide product and reduce gels and black spots.The multistage heat exchanger 43 of the present application is a conventional heat exchanger such as a column pipe type, a coil pipe type, etc., which is mainly used to maximize utilization of heat in process steam by setting the multistage heat exchanger 43 to generate low-pressure steam and hot water simultaneously in a stepped manner and to perform secondary segmented heat exchange on the process steam. After sufficient heat exchange, the process vapor, which mainly contains non-condensable gases (nitrogen, amines, etc.) and a small amount of water, is quickly exhausted by a water ring vacuum to a spray tower or similar cooling device for final cooling and then discharged.Referring to Fig. 1, the present application further provides a continuous polymerization process for producing polyamide using the continuous polymerizer, comprising the following steps:Feeding the brine into the evaporator 1 for evaporation and concentration and then into the reaction rectification tower 2, wherein the brine after preheating reaches the tower disks 21 in the tower disk section and flows layer by layer to the tower disk 21 in the vicinity of the tower vessel, and wherein then the brine is fed successively into the preheating heat exchanger 6, the prepolymerization heat exchanger 7 and the tower vessel 22, and then fed successively into the flash evaporator 3 and the polymerizer 4 for flash evaporation polymerization, and wherein the products are granulated to obtain the polyamide products, and wherein the material circulates between the prepolymerization heat exchanger 7 and the tower vessel 22.Optionally, the degree of polymerization of the material fed into the preheating heat exchanger 6 is 2 to 3 in order to avoid the deposits in the prepolymerization heat exchanger due to the decomposition of the material and the carbonization in the prepolymerization heat exchanger 7 caused by the high temperature difference, so that not only the quality of the polyamide products can be secured but also the heat exchange efficiency of the prepolymerization heat exchanger 7 can be secured.Optionally, the water content of the material obtained by the prepolymerization heat exchanger 7 is preferably controlled to 10-12 wt%.The continuous polymerizer of polyamide and the continuous polymerization process therefor will be explained in detail below in connection with specific embodiments.Embodiment 1The adipic acid and hexamethylenediamine are mixed in the salt cold at a 1:1 molar ratio in water to form a salt solution with 50% by weight nylon 66.The brine is fed through the pipe a at a rate of 0.5 m 3 / h to the evaporator 1, which heats the brine to 140°C while maintaining the pressure at 0.2 MPa (g) so that a part of the water is removed from the brine to obtain a material having a water content of 25 wt%, i.e., the preliminarily concentrated brine.The material is conveyed at 0.33 m 3 / h through a pipe c into the reaction rectification tower 2, the reaction rectification tower 2 has 20 tower disks 21, the distance between two adjacent tower disks 21 is 450 mm, and the height of an overflow weir of the tower disk is 150 mm. The material enters the reaction rectification tower 2, passes through a preheater at the top for preheating, then enters a third tower plate 21 in the upper part of the reaction rectification tower 2, and flows through each tower plate 21 one by one, and at the last tower plate 21 in the vicinity of the tower vessel, a preliminarily prepolymerized salt solution is obtained, by sampling, a degree of polymerization of this phase of DP=2-3 is recognized. After the material is collected by the collecting plate, it is fed by the centrifugal pump into the preheating heat exchanger 6 and preheated to 220°C, then it enters the prepolymerization heat exchanger 7 through the pipe f and is heated to 245 °C, the water is further removed, and further prepolymerization is performed to obtain a material having a water content of 10 wt%. Then, the material is conveyed through the pipe g into the tower vessel of the reaction rectification tower 2, after the gas-liquid separation, a part of the liquid phase enters the prepolymerization heat exchanger 7 circulatingly through the pipe n, another part is conveyed into the flash evaporator 3 through the pipe h at a rate of 0.26 m 3 / h, the flash evaporator 3 heats the material to 270° C. to obtain a material having a water content of 0.5 wt %.Then, the material is fed into the polymerizer 4 through the pipe line k at a rate of 0.26 m 3 / hr, and further polymerization is carried out in the polymerizer 4 so as to have a water content of 0.1 % by weight and a relative viscosity of 2.4, and a product is obtained and the product is finally fed to the pelletizer 5 for granulation to obtain a polyamide product. Moreover, the process vapor (0.027 m 3 / hr) generated from the polymerizer 4 is cooled by heat exchange via a multistage heat exchanger 43 in the exhaust pipe 42 and then discharged.Comparative Example 1Comparative Example 1 differs from Embodiment 1 only in that the number of tower disks 21 of reaction rectification tower 2 is 20, the distance between two adjacent tower disks 21 is 200 mm, and the height of an overflow weir is 50 mm.Sampling and analysis of the material entering the prepolymerization heat exchanger 7 shows that no prepolymerization reaction takes place, i.e. the degree of polymerization is 0. At the same time, the trace by the on-line infrared detector of the vapor phase outlet pipe d at the top of the tower shows that under the same amount of vaporization, the peak of the discharged hexamethylenediamine is markedly increased, and according to the analysis of the test after the complete condensation, the amine content in the condensate at the top of the tower in Embodiment 1 is 0.12% and that in the condensate at the top of the tower in Comparative Example 1 is 0.27%. The end group content in the final polyamide product was tested, the end group content was 51 mol / kg in Working Example 1 and 45 mol / kg in Comparative Example 1.From this, it is apparent that when the arrangement methods of the tower plate 21 of the reaction rectification tower 2 are not within the scope of the present application, preliminary prepolymerization reaction cannot occur on the tower plate 21 and the loss of dibasic amine significantly increases, resulting in an increase in COD in the waste water, and in particular, the ammonium-nitrogen compounds in the waste water treatment are complicated. At the same time, loss of a large portion of the amine also leads to degradation of the polyamide product.Moreover, the loss of a large amount of the amine makes it necessary to increase the residence time in the polymerizer 4 in order for the comparative example 1 to reach the desired degree of polymerization / viscosity, and the longer the residence time, the higher the liquid level, the greater the loss of amine, and the fluctuation of the loss amount results in the liquid level being constantly changed, and frequent changes of the liquid level result in an increase in the amount of the polyamide product which is gelatinous and doted black, seriously impairing the quality, particularly after the long-term operation of the embodiment 1, the number of black dots is less than 10 per kg and after the long-term operation of the comparative example 1, more than 20 per kg.Comparative Example 2Comparative Example 2 differs from Embodiment 1 only in that the material passes through the tower disk 21 in the vicinity of the tower boiler and then directly enters the prepolymerization heat exchanger 7 using high-temperature heat transfer oil at 300°C to rapidly heat the material.Since Comparative Example 2 does not use the preheating heat exchanger 6, the temperature and the flow rate of the heat transfer oil of the prepolymerization heat exchanger 7 must be increased considerably, after the conversion of the same production capacity, the total heat in Embodiment 1 is about 430,000 kcal / hr, while the heat of the Comparative Example (including heat loss) required by Comparative Example 2 is 500,000 kcal / hr, namely, the energy consumption is increased by 16%. Moreover, it is seen from the results of the long-term operation that the color of the product of Comparative Example 2 is usually in the range of YI = 5-10, while in Embodiment 1, it is YI = 1-3. The reason is that the higher temperature of the heat transfer oil in the prepolymerization heat exchanger 7 of Comparative Example 2 causes a part of the prepolymers to polymerize rapidly, resulting in a more rapid deposition in the tube of the prepolymerization heat exchanger 7, which leads to decomposition over a longer period of time, and undesirable colors are produced that enter the final product. At the same time, after the prepolymerization heat exchanger 7 is deposited, the heat transfer efficiency is significantly reduced and the flow rate inside the prepolymerization heat exchanger 7 is further lowered, so that it must be shut down finally, which further increases the running cost and the difficulty of purification.Embodiment 2Embodiment 2 differs from Embodiment 1 only in that the process vapor produced (0.027 m 3 / ) is extracted directly by means of a water ring pump for spraying and cooled and then discharged.Embodiment 1 and Embodiment 2 are compared according to long-term operation data, and the results show that the product gel rate of Embodiment 1 is 0.1 ≠ 0.15 ≠ the black dot rate is 0.16 ≠ 0.23 and the facility change time is 7-8 months; and the product gel rate of Embodiment 2 is 0.23 ≠ 0.32 , the black dot rate is 0.2 ≠ 0.29 and the facility change time is 3-4 months.After the calculation of the large production, the polymerizer 4 can continuously generate 1 t / h to 1.5 t / h of 280° C. steam corresponding to about 500,000 kcal / h, and generates heat throughout the year over about 400,000,000 kcal, which is converted into about 500 t SKE / year to 600 t SKE / year of standard coal. A multistage heat exchanger 43 serves for cooling the process steam and simultaneously generates 0.15 t / h of low-pressure steam and 8 t / h of 75° C. of hot water. By implementing the above process scheme, use of circulating water can be reduced and process steam can be simultaneously used to regenerate a certain amount of low-pressure steam and a large amount of high-temperature water, which can be used for other plants in the whole factory, such as trace heating and heat maintenance of piping for hexamethylenediamine, nylon salt. This not only reduces the additional consumption of circulating water, but also reduces the external vapor draw and saves about 2 to 3 million yuans per year of energy consumption.Moreover, comparison of Embodiment 1 and Embodiment 2 shows that after the equipment with the multistage heat exchanger 43, the operation time of the plant is prolonged remarkably and the number of switching and maintenance times of the plant per year is decreased by 1 to 2 times. The costs for the one-time maintenance and production of the plant amount to approximately 1 to 1.5 million yuan. Along with the energy savings and reduced number of plant maintenance, the introduction of the multistage heat exchanger 43 results in a reduction in production cost by about 3.5 to 5 million yuan.The respective technical features of the above embodiments can be combined arbitrarily. In order to simplify the explanation, not all possible combinations of the respective technical features are explained in the above embodiments, but the combinations of the technical features should be considered to be covered by the scope of the description in the case of no conflicts.The above embodiments are only some embodiments of the present application, and the explanations are relatively specific and detailed, but should not be construed as limitations on the scope of the present invention. It should be noted that those skilled in the art can make several improvements and modifications without departing from the concept of the present application. The improvements and modifications are also intended to be considered to be within the scope of the present application. Therefore, the scope of the present application should be defined by the claims.

Claims

A continuous polymerization apparatus for producing polyamide using dibasic acid and dibasic amine, characterized by comprising an evaporator, a reaction rectification tower, a flash evaporator and a polymerizer which are connected in sequence by piping, wherein the reaction rectification tower comprises a tower vessel and a tower plate portion at the upper part of the tower vessel, and wherein the number of tower plates in the tower plate portion is 15-30, and wherein the distance between two adjacent tower plates is 400 mm-600 mm, and wherein the height of an overflow weir of the tower plates is 50 mm-300 mm; and wherein the continuous polymerizer further comprises a preheating heat exchanger and a prepolymerization heat exchanger, and wherein the tower plate in the tower plate portion in the vicinity of the tower vessel, the preheating heat exchanger and the prepolymerization heat exchanger are connected by pipings in order, and wherein the prepolymerization heat exchanger and the tower vessel establish a circulating connection by pipings so that the material can enter the preheating heat exchanger, the prepolymerization heat exchanger and the tower vessel in order through the tower plates and circulate between the prepolymerization heat exchanger and the tower vessel.The continuous polymerization apparatus for producing polyamide using dibasic acid and dibasic amine according to claim 1, wherein the number of the tower disks is 20-25.The continuous polymerization apparatus for producing polyamide using dibasic acid and dibasic amine according to claim 1, wherein the distance between two adjacent tower disks is 450 mm-550 mm.The continuous polymerization apparatus for producing polyamide using dibasic acid and dibasic amine according to claim 1, wherein the height of an overflow weir of the tower disks is 100 mm - 200 mm.The continuous polymerization apparatus for producing polyamide using dibasic acid and dibasic amine according to claim 1, wherein a gas phase outlet pipe at the top of the reaction rectification tower is provided with an online infrared detector.The continuous polymerizer for producing polyamide using dibasic acid and dibasic amine according to claim 5, wherein the continuous polymerizer further comprises a dibasic amine on-line replenishing line used to replenish the dibasic amine in real time, and wherein the dibasic amine on-line replenishing line is connected to the prepolymerization heat exchanger.The continuous polymerizer for producing polyamide using dibasic acid and dibasic amine according to claim 1, wherein the polymerizer comprises a polymerizer body, an exhaust pipe connected to the polymerizer body, and a multistage heat exchanger installed in the exhaust pipe.The continuous polymerization apparatus for producing polyamide using dibasic acid and dibasic amine according to claim 1, wherein the number of the polymerizers is 1 or more than 2.

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