Continuous polymerization device for preparing polyamide with dibasic acid and diamine, and continuous polymerization process therefor

Abstract

A continuous polymerization device for preparing a polyamide with a dibasic acid and a diamine, and a continuous polymerization process therefor. The continuous polymerization device comprises an evaporator (1), a reactive distillation column (2), a flash evaporator (3), and a polymerizer (4) connected in sequence, wherein the number of trays (21) in a tray (21) section of the reactive distillation column is 15-30, the spacing between two adjacent trays (21) is 400mm-500mm, and the height of an overflow weir of the reactive distillation tower (2) is 50-300mm. The continuous polymerization device further comprises a preheating heat exchanger (6) and a pre-polymerization heat exchanger (7), wherein the pre-polymerization heat exchanger (7) and a column bottom (22) are in cyclical communication by means of piping, so that materials sequentially enter the preheating heat exchanger (6), the pre-polymerization heat exchanger (7), and the column bottom (22) by means of the trays (21), and then cyclically flow between the pre-polymerization heat exchanger (7) and the column bottom (22).

Description

Continuous polymerization equipment for preparing polyamide by using diacid and diamine and continuous polymerization process thereof

[0001] Related applications

[0002] The present application claims priority to the Chinese patent application No. 202410623625.7, filed on May 20, 2024, and entitled "Continuous polymerization equipment for preparing polyamide and continuous polymerization process thereof", the content of which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0003] The present application relates to the technical field of polyamide, in particular to a continuous polymerization equipment for preparing polyamide by using diacid and diamine and a continuous polymerization process thereof. BACKGROUND

[0004] Polyamide (PA), commonly known as Nylon, is a general term for high polymers containing amide groups (-NH-C=O) in the repeating units of the main chain. It can be obtained by ring opening of lactam, such as Nylon 6, or by polycondensation of diacid and diamine, such as Nylon 66.

[0005] In the preparation of polyamide by polycondensation of diacid and diamine, the typical industrial method is to mix diacid and diamine in a molar ratio of 1:1 in water in a salt pool to prepare a 50wt% salt solution, and then gradually remove the physical water and generated water in the system to complete the polycondensation. However, because diamine is volatile, it will be volatilized from the salt solution during evaporation and concentration, which not only affects the polymerization degree and performance of the polyamide product due to the imbalance of the carboxylic acid / amine ratio in the salt solution, but also increases the production cost due to the large loss, and the volatilized diamine will cause environmental pollution problems when it is discharged in the gas phase.

[0006] SUMMARY

[0007] Therefore, it is necessary to provide a continuous polymerization equipment for preparing polyamide by using diacid and diamine and a continuous polymerization process thereof, which can not only ensure the quality of the polyamide product, but also reduce the loss, the generation of three wastes, the process risk and the operating cost.

[0008] A continuous polymerization equipment for preparing polyamide by using diacid and diamine, comprising an evaporator, a reaction rectification tower, a flash evaporator and a polymerizer connected in sequence by pipelines, wherein the reaction rectification tower comprises a tower kettle and a tray section at the upper part of the tower kettle, the number of trays in the tray section is 15 to 30, the distance between adjacent two trays is 400mm to 600mm, and the height of the overflow weir of the tray is 50mm to 300mm.

[0009] The continuous polymerization device further comprises a preheating heat exchanger and a prepolymerization heat exchanger, the tray near the tower kettle in the tray section, the preheating heat exchanger and the prepolymerization heat exchanger are sequentially communicated by pipelines, and the prepolymerization heat exchanger is circularly communicated with the tower kettle by a pipeline, so that the material sequentially enters the preheating heat exchanger, the prepolymerization heat exchanger and the tower kettle through the tray, and circularly flows between the prepolymerization heat exchanger and the tower kettle.

[0010] In one embodiment, the number of trays is 20 to 25.

[0011] In one embodiment, the distance between two adjacent trays is 450 mm to 550 mm.

[0012] In one embodiment, the height of the overflow weir of the tray is 100 mm to 200 mm.

[0013] In one embodiment, an online infrared detector is arranged on the overhead gas phase outlet pipeline of the reaction rectifying tower.

[0014] In one embodiment, the continuous polymerization device further comprises a diamine online supplement pipeline for supplementing diamine in real time, and the diamine online supplement pipeline is communicated to the prepolymerization heat exchanger.

[0015] In one embodiment, the polymerizer comprises a polymerizer body, an exhaust pipeline communicated with the polymerizer body, and a multi-stage heat exchanger arranged in the exhaust pipeline.

[0016] In one embodiment, the number of polymerizers is one or more than two.

[0017] A continuous polymerization process for preparing polyamide from a diacid and a diamine, which is carried out by using the continuous polymerization device for preparing polyamide, comprising the following steps:

[0018] The salt solution is transported to an evaporator for evaporation and concentration, then transported to a reaction rectifying tower, preheated, and then reaches the trays of the tray section, and then flows to the trays near the tower kettle, and then sequentially transported to the preheating heat exchanger, the prepolymerization heat exchanger and the tower kettle, and then sequentially transported to the flash evaporator and the polymerizer for flash evaporation and polymerization, and the product is granulated to obtain a polyamide product, wherein the prepolymerization heat exchanger and the tower kettle have a material circulating flow.

[0019] In one embodiment, the degree of polymerization of the material transported to the preheating heat exchanger is 2 to 3.

[0020] The application can prolong the residence time of the salt solution by adjusting the number, spacing and overflow weir height of the trays in the reactive distillation column, so that the salt solution can be preliminarily polymerized. On the one hand, the preliminary polymerization can reduce the concentration of free amine in the salt solution, thereby reducing the loss of amine during evaporation and concentration. On the other hand, after the residence time is prolonged, the gas phase generated by evaporation and concentration in the column can fully contact the salt solution during the process of countercurrent contact for mass transfer and heat transfer. When the free amine in the salt solution is reduced due to preliminary polymerization, the binary amine entrained in the gas phase can be absorbed through the dual action of physical absorption (cooling and condensation) and chemical absorption (reaction with carboxylic acid in the salt solution to form carboxylic acid amine salt), which can not only better maintain the ratio of carboxylic acid / amine in the salt solution to ensure the quality of the polyamide product, but also reduce the loss and the generation of three wastes, making the process more competitive.

[0021] Meanwhile, by adding a preheating heat exchanger and a pre-polymerization heat exchanger, the material can first enter the preheating heat exchanger for preheating through the tray close to the column, and then enter the pre-polymerization heat exchanger for evaporation and concentration and pre-polymerization, which can reduce the flow and temperature of the hot fluid of the pre-polymerization heat exchanger, avoid the scaling of the pre-polymerization heat exchanger caused by decomposition and carbonization of the material due to high temperature difference, and not only ensure the quality of the polyamide product, but also ensure the heat exchange efficiency and capacity of the pre-polymerization heat exchanger, reduce the process risk and operating cost. BRIEF DESCRIPTION OF DRAWINGS

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the application, and other drawings can be obtained by those skilled in the art without creative labor.

[0023] Fig. 1 is a schematic diagram of a continuous polymerization equipment for preparing polyamide from binary acid and binary amine according to the application.

[0024] Fig. 2 is a schematic diagram of the structure of a polymerizer according to an embodiment of the application.

[0025] In the figure: 1, evaporator; 2, reactive distillation column; 3, flash evaporator; 4, polymerizer; 5, granulator; 6, preheating heat exchanger; 7, pre-polymerization heat exchanger; 21, tray; 22, column still; 2a, online infrared detector; 6a, circulating pump; 41, polymerizer body; 42, exhaust pipe; 43, heat exchanger. DETAILED DESCRIPTION

[0026] For the purposes of promoting an understanding of the principles of the application, the application will now be described more thoroughly. It will be understood, however, that the application can be carried out in many different forms and should not be considered limited to the embodiments or examples set forth in this disclosure. Rather, these embodiments or examples are provided so that this disclosure will convey the principles and applications of the application to those skilled in the art.

[0027] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description of the application herein is for the purpose of describing particular embodiments or examples only and is not intended to be limiting of the application. As used herein, the term "and / or," used in the context of a list of two or more items, means that any single one of the listed items can be present or any two or more of the listed items can be present in any combination. Portions of the disclosure will be described with initial reference to FIG. 1, which illustrates a continuous polymerization apparatus for preparing polyamides from diacids and diamines, according to embodiments of the present application.

[0028] As shown in FIG. 1, the continuous polymerization apparatus for preparing polyamides from diacids and diamines, according to embodiments of the present application, is mainly used for evaporating and concentrating the prepared salt solution of diacids and diamines, removing the physical water and generated water in the system, and completing the polycondensation. In the present application, the diacids are broadly defined as C4-C12 dicarboxylic acids, such as succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, dodecanedioic acid, etc. The diamines are broadly defined as C4-C12 diamines, such as 1,4-butanediamine, 1,5-pentanediamine, 1,6-hexanediamine, 1,7-heptanediamine, 1,8-octanediamine, 1,9-nonanediamine, 1,10-decanediamine, dodecanediamine, etc. The concentration of the salt solution can be any ratio, and preferably, the diacids and diamines are mixed in a molar ratio of 1:1 in water in the salt pool to form a 50wt%-65wt% salt solution.

[0029] Specifically, the continuous polymerization apparatus includes an evaporator 1, a reaction rectification tower 2, a flash evaporator 3, and a polymerizer 4 connected in sequence by pipelines.

[0030] The evaporator 1 is used for evaporating and concentrating the prepared salt solution. Specifically, the prepared salt solution of diacids and diamines enters the evaporator 1 through a pipeline a, and the evaporator 1 is heated using steam. The temperature of the steam is preferably 100°C to 200°C, and the pressure is preferably maintained in the range of 0.1 MPa(g) to 0.25 MPa(g) during the heating process, so that the salt solution is evaporated and concentrated, and the water content of the salt solution is reduced.

[0031] The gas phase generated in the evaporation and concentration process of the salt solution includes water and a very small amount of binary amine. The gas phase is discharged from the evaporator 1 through the pipeline b and is collected by cooling tower or the like, and is recycled for preparation of the salt solution, so that the resources can be recycled and green environmental protection is achieved.

[0032] The reaction rectification column 2 includes a column still 22 and a tray section above the column still 22, which is used to receive the material after evaporation and concentration in the evaporator 1, i.e. the salt solution after preliminary concentration. Specifically, the material enters the top preheater of the reaction rectification column 2 through the pipeline c, is preheated by the ascending gas phase in the reaction rectification column 2, and then enters the upper tray 21 of the tray section of the reaction rectification column 2, such as the second or third tray 21 from the top of the column, and then flows through each tray 21 layer by layer and is countercurrently contacted with the ascending gas phase in the column for mass transfer and heat transfer.

[0033] It should be noted that the number of trays 21 in the tray section is generally 8 to 10, the spacing between adjacent trays 21 is generally 200 to 300 mm, and the height of the overflow weir is generally 5 to 30 mm. However, such a setting makes the contact residence time of the material with the gas phase short, and the pre-polymerization reaction cannot start on the tray, which leads to the free amine in the material being easily volatilized after further preheating, causing the imbalance of the carboxylic acid / amine ratio in the material, which is not conducive to the rapid progress of the subsequent pre-polymerization reaction. Although the lost amine can be optimized and adjusted in the salt formation stage, the unit consumption of polymerization is often increased, the cost is increased, and the binary amine volatilized into the gas phase is also brought to the environment pollution problem.

[0034] To this end, the present application adjusts the setting mode of the trays 21 in the tray section. Specifically, the number of trays 21 in the tray section of the present application is 15 to 30, preferably 20 to 25, the spacing between adjacent two trays 21 is 400 to 600 mm, preferably 450 to 550 mm, and the height of the overflow weir of the tray 21 is 50 to 300 mm, preferably 100 to 200 mm. By adjusting the number and spacing of the trays 21 in the reaction rectification column 2, the time for the material to flow to the trays 21 close to the column still is prolonged, and by adjusting the height of the overflow weir of the trays 21 in the reaction rectification column 2, the residence time of the material in each tray 21 is prolonged, so that the overall residence time of the material in the column is prolonged, and thus the material undergoes preliminary pre-polymerization reaction in this stage.

[0035] Through the initial prepolymerization reaction, the free amine can be converted into a polyamide dimer, which can reduce the concentration of free amine in the material, and then reduce the loss of amine during evaporation and concentration. At the same time, after the residence time is prolonged, the gas phase generated by the evaporation and concentration of the tower kettle rises in the tower and contacts the material in countercurrent to carry out the mass transfer and heat transfer process, which can fully contact the material. When the free amine in the material is reduced due to the initial prepolymerization, the binary amine entrained in the gas phase can be absorbed through the dual action of physical absorption (cooling and condensation) and chemical absorption (reacting with the carboxylic acid in the material to form a carboxylic acid amine salt), which can not only better maintain the ratio of carboxylic acid / amine in the material to ensure the quality of the polyamide product, but also reduce the loss and reduce the generation of three wastes, making the process more competitive.

[0036] Continuing to refer to FIG. 1, the continuous polymerization device described in the present application further comprises a preheating heat exchanger 6 and a prepolymerization heat exchanger 7, the tray 21 near the tower kettle in the tray section, the preheating heat exchanger 6 and the prepolymerization heat exchanger 7 are sequentially communicated by pipelines, and the prepolymerization heat exchanger 7 is in circulation communication with the tower kettle 22 through a pipeline, so that the material sequentially enters the preheating heat exchanger 6, the prepolymerization heat exchanger 7 and the tower kettle 22 through the tray 21, and can circulate between the prepolymerization heat exchanger 7 and the tower kettle 22.

[0037] The preheating heat exchanger 6 is used to receive the material flowing out of the tray 21 near the tower kettle in the tray section, that is, the salt solution in which the initial prepolymerization is achieved in the tray section, and preheat it. Specifically, when the material flows to the tray 21 near the tower kettle, it enters the preheating heat exchanger 6 through the pipeline e for preheating.

[0038] Optionally, the material is collected at the tray 21 near the tower kettle by a collector such as a collection tray, and then delivered to the preheating heat exchanger 6 by a circulating pump 6a for preheating. The circulating pump 6a can be a common type of pump in the industry, such as a centrifugal pump, a diaphragm pump, etc. The centrifugal pump is preferred in the present application.

[0039] Optionally, the heat source of the preheating heat exchanger 6 can be a liquid-phase heat-conducting oil of 200-250℃, such as T66 (hydrogenated triphenyl mixture) or other similar heat-conducting oils in the industry; or the heat source can be steam of the same temperature, which can preheat the material to 200-220℃. Considering that the material has undergone initial prepolymerization in the tray section of the reaction rectifying tower 2, in order to avoid blockage and poor heat exchange effect of the preheating heat exchanger 6 caused by high-viscosity material, the preheating heat exchanger 6 of the present application preferably adopts a high-flow-rate coiled tube heat exchanger, and the heat source preferably adopts medium-pressure steam heating, which uses its latent heat to further enhance the heat exchange effect, so as to achieve the purpose of rapidly preheating the material.

[0040] The pre-polymerization heat exchanger 7 is used to receive the material preheated by the preheating heat exchanger 6 to evaporate, concentrate and pre-polymerize to achieve the desired concentration and pre-polymerization degree. Specifically, the material preheated by the preheating heat exchanger 6 enters the bottom of the pre-polymerization heat exchanger 7 through the pipeline f, is forced to move in the pre-polymerization heat exchanger 7 by the front-end pump and the density difference formed in the pre-polymerization heat exchanger 7, and is evaporated, concentrated and pre-polymerized.

[0041] After being preheated by the preheating heat exchanger 6, the pre-polymerization heat exchanger 7 only needs to preheat the material to 220-250°C. However, if only the pre-polymerization heat exchanger 7 is added in the present application, the pre-polymerization heat exchanger 7 needs to use 280-300°C heat conducting oil for heating, which not only has large heat loss and is not economical and practical, but also makes the surface temperature of the pre-polymerization heat exchanger 7 high. If the material is run for a long time, it will be carbonized and scaled. After scaling, the heat exchange efficiency of the pre-polymerization heat exchanger 7 and the flowability of the material will be greatly reduced, resulting in the need for emergency shutdown and cleaning, increasing the process risk and operating cost. At the same time, if the scale falls into the material, it will affect the color and performance of the polyamide product.

[0042] The present application can reduce the flow and temperature of the heat fluid of the pre-polymerization heat exchanger 7 by simultaneously adding the preheating heat exchanger 6 and the pre-polymerization heat exchanger 7, so that the material enters the preheating heat exchanger 6 first to be preheated, and then enters the pre-polymerization heat exchanger 7 to be evaporated, concentrated and pre-polymerized. This can avoid scaling of the pre-polymerization heat exchanger 7 caused by decomposition and carbonization of the material due to high temperature difference, which can not only ensure the quality of the polyamide product, but also ensure the heat exchange efficiency of the pre-polymerization heat exchanger 7 and the production capacity, and reduce the process risk and operating cost.

[0043] The reactor column 2 is used to receive the material evaporated, concentrated and pre-polymerized in the pre-polymerization heat exchanger 7, including gas phase and liquid phase. Specifically, the material obtained in the pre-polymerization heat exchanger 7 enters the reactor column 2 through the pipeline g to be separated into gas phase and liquid phase. The gas phase is discharged from the reactor column 2 through the overhead gas phase outlet pipeline d after being fully heat exchanged and absorbed with the material on the tray 21 in the tray section. The liquid phase is partially introduced into the flash evaporator 3 through the pipeline h for further flash evaporation and polymerization reaction, and the other part is recycled into the pre-polymerization heat exchanger 7 through the pipeline n.

[0044] Optionally, the overhead gas phase outlet pipeline d of the reactor column 2 is provided with an online infrared detector 2a for real-time monitoring of the content of multi-component small molecules in the gas phase, especially the content of diamine. At the same time, the present application can also be provided with a diamine online supplement pipeline m to supplement diamine into the pre-polymerization heat exchanger 7 in real time according to the loss change of the diamine obtained by monitoring, so that the ratio of carboxylic acid / amine in the pre-polymerization heat exchanger 7 is within a suitable range. It can be understood that the diamine online supplement pipeline m can be directly connected to the pre-polymerization heat exchanger 7, or can be connected to the pipeline f and then connected to the pre-polymerization heat exchanger 7 through the pipeline f.

[0045] The flash evaporator 3 uses a variable-diameter coil pipe to gradually evaporate the water in the liquid-phase material through pipe resistance to reach a gas-liquid two-phase state, and the initially pre-polymerized polyamide in the material further polymerizes in the flash evaporator 3. The flash evaporator 3 can heat the material to any temperature of 250-300°C, and the water content in the gas-liquid two-phase material can be any ratio of 0.1-2wt%.

[0046] The material (gas-liquid two-phase) obtained through the flash evaporator 3 enters the polymerizer 4 through pipe k, the polymerizer 4 is used to separate the entering gas-liquid two-phase, further remove water in the system under a vacuum system, promote the reaction to proceed to final polymerization, and obtain a polyamide product, wherein the water content of the polyamide product can be any ratio of 0.01-0.1wt%. Finally, the product obtained through the polymerizer 4 is granulated through the pelletizer 5 to obtain a polyamide product.

[0047] The material entering the polymerizer 4 needs to reach the polymerization degree and molecular weight distribution required by the final polyamide product, and the polymerizer 4 needs to efficiently and stably remove water in the body while ensuring the residence time of the material in the polymerizer 4 to reach the final state of the polyamide product.

[0048] Optionally, the number of the polymerizer 4 is 1 or more than 2, preferably 2, and the two polymerizers 4 are respectively and independently connected to the flash evaporator 3, so that the production can be switched according to the actual situation.

[0049] When the gas-liquid two-phase material enters the polymerizer 4 for separation, it is necessary to avoid the crosslinking of part of the product due to uneven heating caused by liquid level fluctuation, which will become gel, and the gel itself will affect the product quality, and continue to be heated to become black spots, further reducing the product quality.

[0050] The fluctuation of the liquid level is generally caused by the fluctuation of the vacuum. At present, a large amount of polymerization process steam in the polymerizer 4 is directly extracted by a water ring vacuum pump or other similar equipment, and then discharged after further cooling by spraying and other cooling means. However, the gas-phase water flow generated at this time fluctuates, which causes the water ring pump of the polymerizer 4 to need to be constantly adjusted to balance the fluctuation caused by the change of the air extraction amount, which inevitably affects the vacuum degree in the polymerizer 4. Unstable vacuum has a great influence on the liquid level control of the polymerizer 4, which in turn leads to unexpected crosslinking side reactions of polymerization, producing gel and black spots, and frequent switching and cleaning are required. At the same time, a large amount of process steam extracted by the vacuum pump needs to be cooled by circulating spraying water or other similar means, which not only wastes the heat of the process steam, but also consumes other energy for cooling, resulting in high production cost.

[0051] To this end, please refer to Figure 2, the preferred polymerizer 4 of the present application comprises a polymerizer body 41, an exhaust pipe 42 in communication with the polymerizer body 41, and heat exchangers 43 built in the exhaust pipe 42, the number of heat exchangers 43 is 2 or more, including 2, 3, 4, etc., so that the steam is heat-exchanged by the multi-stage heat exchangers to produce low-pressure steam and hot water.

[0052] Specifically, the present application uses a water ring vacuum pump to establish a vacuum in the polymerizer 4, and sets multi-stage heat exchangers 43 in the exhaust pipe 42 of the polymerizer 4 to heat-exchange the process steam, and uses the heat of the process steam to co-produce a certain amount of low-pressure steam and hot water; at the same time, the gas phase cooled by the multi-stage heat exchangers 43 is mainly non-condensable gas and a small part of process steam, which provides a guarantee for the temperature operation of the vacuum system, and can avoid unnecessary frequent switching and cleaning caused by vacuum fluctuations, and further utilizes the heat of the process steam, and reduces the use of cooling medium. Therefore, the operation and production costs can be reduced, the quality stability of the polyamide product can be improved, and the gel and black spots can be reduced.

[0053] The multi-stage heat exchangers 43 of the present application are conventional heat exchangers, such as tube type, pipe type, etc., which mainly produce low-pressure steam and hot water by setting multi-stage heat exchangers 43, and perform secondary segmented heat exchange on the process steam to maximize the use of the heat in the process steam. After sufficient heat exchange, the process steam mainly contains non-condensable gas (nitrogen, amine, etc.) and a small amount of water, which is rapidly extracted by the water ring vacuum to the spray tower or other similar cooling means for final cooling and discharge.

[0054] Continuing to refer to Figure 1, the present application also provides a continuous polymerization process for preparing polyamide by using the continuous polymerization device, which comprises the following steps:

[0055] The salt solution is transported to the evaporator 1 for evaporation and concentration, then transported to the reaction rectification column 2, preheated to reach the tray 21 in the tray section, and then flow layer by layer to the tray 21 close to the column bottom, and then transported to the preheating heat exchanger 6, the prepolymerization heat exchanger 7 and the column bottom 22 in turn, and then transported to the flash evaporator 3 and the polymerizer 4 for flash evaporation and polymerization, and the product is granulated to obtain a polyamide product, wherein there is a material circulation flow between the prepolymerization heat exchanger 7 and the column bottom 22.

[0056] Optionally, the polymerization degree of the material transported to the preheating heat exchanger 6 is 2 to 3, which can avoid the decomposition and carbonization of the material in the prepolymerization heat exchanger 7 due to high temperature difference, thereby preventing the prepolymerization heat exchanger from scaling, ensuring the quality of the polyamide product, and ensuring the heat exchange effect of the prepolymerization heat exchanger 7.

[0057] Optionally, the water content of the material obtained by the prepolymerization heat exchanger 7 is preferably controlled at 10wt%-12wt%.

[0058] Hereinafter, the continuous polymerization apparatus of the polyamide and the continuous polymerization process thereof will be further described by the following specific examples.

[0059] Example 1

[0060] Adipic acid and hexamethylene diamine were mixed in a molar ratio of 1:1 in water to form a 50wt% nylon 66 salt solution.

[0061] The salt solution was transported through pipe a at a speed of 0.5m 3 / h to evaporator 1, which heated the salt solution to 140°C, with the pressure kept at 0.2MPa(g), to remove part of the water from the salt solution, to obtain a material with a water content of 25wt%, i.e. a preliminarily concentrated salt solution.

[0062] The material was transported through pipe c at a speed of 0.33m 3 / h to reaction rectifying column 2, which had 20 trays 21, with the distance between adjacent two trays 21 being 450mm, and the height of the overflow weir of the tray being 150mm. After entering reaction rectifying column 2, the material was first preheated in the top preheater, and then entered the third tray 21 in the upper part of reaction rectifying column 2, and flowed through each tray 21 layer by layer, to obtain a preliminarily prepolymerized salt solution at the last tray 21 close to the column bottom, with the degree of polymerization DP=2-3 detected by sampling. The material was collected by the collection tray, and then transported by the centrifugal pump to preheating heat exchanger 6 to be preheated to 220°C, and then entered prepolymerization heat exchanger 7 through pipe f to be heated to 245°C, to further remove water and carry out further prepolymerization, to obtain a material with a water content of 10wt%. The material was then transported through pipe g to the column bottom of reaction rectifying column 2, and after gas-liquid separation, part of the liquid phase was circulated into prepolymerization heat exchanger 7 through pipe n, and the other part was transported through pipe h at a speed of 0.26m 3 / h to flash evaporator 3, which heated the material to 270°C, to obtain a material with a water content of 0.5wt%.

[0063] The material was then transported through pipe k at a speed of 0.26m 3 / h to polymerizer 4, and further polymerization was carried out in polymerizer 4, so that the water content reached 0.1wt%, and the relative viscosity reached 2.4, to obtain the product, which was finally transported to pelletizer 5 to be pelletized, to obtain the polyamide product. In addition, the process steam (0.027m 3 / h) generated by polymerizer 4 was cooled by multi-stage heat exchanger 43 in exhaust pipe 42, and then discharged.

[0064] Comparative Example 1

[0065] The difference between Comparative Example 1 and Example 1 is only that the number of trays 21 of the reactive distillation column 2 is 20, the distance between adjacent two trays 21 is 300 mm, and the height of the overflow weir is 50 mm.

[0066] Through sampling analysis, it is found that the material entering the prepolymerization heat exchanger 7 has no prepolymerization reaction, i.e., the degree of polymerization is 0. At the same time, according to the tracking of the online infrared detector of the overhead gas phase outlet pipeline d, under the same evaporation amount, the out-of-peak of hexamethylenediamine is obviously enhanced. According to the test analysis after full condensation, the amine content of the overhead condensate water of Example 1 is 0.12%, and the amine content of the overhead condensate water of Comparative Example 1 is 0.27%. The end group content in the final polyamide product is tested, and the end group in Example 1 is 51 mol / kg, and the end group in Comparative Example 1 is 45 mol / kg.

[0067] Therefore, when the arrangement of the trays 21 of the reactive distillation column 2 is not within the scope of the present application, the preliminary prepolymerization reaction cannot occur on the trays 21, the loss of diamine is obviously increased, which leads to the increase of COD in the waste water, and the ammonia nitrogen compounds are more troublesome in waste water treatment. At the same time, the loss of a large proportion of amine also leads to the decrease of the quality of the polyamide product.

[0068] In addition, the loss of a large proportion of amine makes it necessary to increase the residence time in the polymerizer 4 for Comparative Example 1 to reach the target degree of polymerization / viscosity, and the longer the residence time is, the higher the liquid level is, and the greater the loss of amine is. In addition, the loss proportion fluctuates, which leads to the constant change of the liquid level. The frequent change of the liquid level can lead to the increase of the proportion of gelation and black spots of the polyamide product, which seriously affects the quality. Specifically, after long-term operation of Example 1, the number of black spots is less than 10 per kg, and after long-term operation of Comparative Example 1, the number of black spots is more than 20 per kg.

[0069] Comparative Example 2

[0070] The difference between Comparative Example 2 and Example 1 is only that the material directly enters the prepolymerization heat exchanger 7 after passing through the tray 21 close to the column still, and the prepolymerization heat exchanger 7 uses high-temperature heat-conducting oil at 300°C to rapidly heat the material.

[0071] Since the preheating heat exchanger 6 is not used in Comparative Example 2, the temperature and flow of the heat conducting oil of the pre-polymer heat exchanger 7 are greatly increased. According to the same capacity calculation, the total heat of Example 1 is about 430,000 Kcal / h, while the heat of the heat conducting oil (including heat loss) of Comparative Example 2 is about 500,000 Kcal / h, which is an increase of 16% compared with the same period. In addition, according to the long-term operation results, the color of the product of Comparative Example 2 is generally YI = 5-10, while the YI of Example 1 is 1-3. This is because the high temperature of the heat conducting oil of the pre-polymer heat exchanger 7 of Comparative Example 2 causes the rapid polymerization of part of the pre-polymer, resulting in the rapid fouling of the pre-polymer heat exchanger 7, which leads to decomposition after long-term operation, resulting in unnecessary color entering the final product. At the same time, after the fouling of the pre-polymer heat exchanger 7, the heat exchange efficiency is greatly reduced, and the flow rate in the pre-polymer heat exchanger 7 is further slowed down, which eventually forces the shutdown, further increasing the operation cost and cleaning difficulty.

[0072] Example 2

[0073] The difference between Example 2 and Example 1 is that the process steam (0.027m 3 / ) is discharged after being extracted by a water ring pump and then sprayed and cooled.

[0074] After comparing the long-term operation data of Example 1 and Example 2, the product gel rate of Example 1 is 0.1‰-0.15‰, the black point is 0.16‰-0.23‰, and the equipment switching time is 7-8 months; the product gel rate of Example 2 is 0.23‰-0.32‰, the black point is 0.2‰-0.29‰, and the equipment switching time is 3-4 months.

[0075] According to the large production calculation, the polymerizer 4 can continuously produce 1t / h to 1.5t / h of 280℃ steam, about 500,000 Kcal / h, about 400,000 million Kcal of heat per year, and about 500tce / year to 600tce / year of standard coal. The multi-stage heat exchanger 43 is set to cool the process steam, while generating 0.15t / h of low-pressure steam and 8t / h of 75℃ hot water. Through the implementation of the above process scheme, the use of circulating water can be reduced, and a certain amount of low-pressure steam and a large amount of high-temperature water can be regenerated by using the process steam, which can be used for other devices in the whole plant, such as hexamethylene diamine, nylon salt, etc. The heat tracing and heat preservation of the pipeline can not only reduce the additional use of circulating water, but also reduce the purchase of external steam, which can save energy consumption of about 2 million yuan to 3 million yuan per year.

[0076] In addition, according to the comparison between Embodiment 1 and Embodiment 2, after the multi-stage heat exchanger 43 is provided, the operation time of the equipment is obviously longer, and the number of switching and maintenance of the equipment per year is reduced by 1-2 times. Generally, the single maintenance and production cost of the equipment is about 1 million yuan to 15 million yuan. Combined with the energy consumption saving and the reduction of the number of equipment maintenance, the implementation of the multi-stage heat exchanger 43 can reduce the production cost by about 3.5 million yuan to 5 million yuan per year.

[0077] The technical features of the above-described embodiments can be combined in any manner. In order to make the description simple, all possible combinations of the technical features in the above-described embodiments are not described, but as long as the combinations of the technical features do not contradict, they should be considered as within the scope of the present disclosure.

[0078] The above-described embodiments only express several implementation manners of the present application, and the description is relatively specific and detailed, but it should not be understood as a limitation on the scope of the patent. It should be pointed out that for those skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are all within the protection scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. A continuous polymerization apparatus for producing a polyamide from a dibasic acid and a dibasic amine, characterized by, The continuous polymerization device comprises an evaporator, a reaction rectifying tower, a flash evaporator and a polymerizer connected in sequence by pipelines, wherein the reaction rectifying tower comprises a tower kettle and a tower tray section in the upper part of the tower kettle, the number of tower trays in the tower tray section is 15 to 30, the distance between adjacent two tower trays is 400 mm to 600 mm, and the height of the overflow weir of the tower tray is 50 mm to 300 mm; The continuous polymerization device further comprises a preheating heat exchanger and a prepolymerization heat exchanger, the tower trays in the tower tray section close to the tower kettle, the preheating heat exchanger and the prepolymerization heat exchanger are connected in sequence by pipelines, and the prepolymerization heat exchanger is connected to the tower kettle by a pipeline in circulation, so that the material enters the preheating heat exchanger, the prepolymerization heat exchanger and the tower kettle in sequence through the tower trays and can flow in circulation between the prepolymerization heat exchanger and the tower kettle.

2. The continuous polymerization apparatus for producing a polyamide using a dibasic acid and a dibasic amine according to claim 1, wherein, The number of tower trays is 20 to 25.

3. The continuous polymerization apparatus for producing polyamide using a dibasic acid and a dibasic amine according to claim 1, wherein, The distance between adjacent two tower trays is 450 mm to 550 mm.

4. The continuous polymerization apparatus for producing polyamide using a dibasic acid and a dibasic amine according to claim 1, wherein, The height of the overflow weir of the tower tray is 100 mm to 200 mm.

5. The continuous polymerization apparatus for producing polyamide using a dibasic acid and a dibasic amine according to claim 1, wherein, An online infrared detector is arranged on the gaseous phase outlet pipeline of the reaction rectifying tower.

6. The continuous polymerization apparatus for producing a polyamide using a dibasic acid and a dibasic amine according to claim 5, wherein, The continuous polymerization device further comprises a diamine online supplement pipeline for supplementing diamine in real time, and the diamine online supplement pipeline is connected to the prepolymerization heat exchanger.

7. The continuous polymerization apparatus for producing polyamide using a dibasic acid and a dibasic amine according to claim 1, wherein, The polymerizer comprises a polymerizer body, an exhaust pipe connected to the polymerizer body and a multi-stage heat exchanger arranged in the exhaust pipe.

8. The continuous polymerization apparatus for producing polyamide using a dibasic acid and a dibasic amine according to claim 1, wherein, The number of polymerizers is one or more than two.

9. A continuous polymerization process for producing a polyamide using a dibasic acid and a dibasic amine, using the continuous polymerization apparatus for polyamide as claimed in claim 1, characterized by, The method comprises the following steps: The salt solution is transported to the evaporator for evaporation and concentration, then transported to the reaction rectifying tower, reaches the tower trays of the tower tray section after preheating, and then flows to the tower trays close to the tower kettle layer by layer, and then transported to the preheating heat exchanger, the prepolymerization heat exchanger and the tower kettle in sequence, and then transported to the flash evaporator and the polymerizer for flash evaporation and polymerization, and the product is granulated to obtain a polyamide product, wherein the material flows in circulation between the prepolymerization heat exchanger and the tower kettle.

10. The continuous polymerization process for the production of polyamide from a diacid and a diamine according to claim 9, wherein, The polymerization degree of the material transported to the preheating heat exchanger is 2 to 3.

11. The continuous polymerization apparatus for producing a polyamide using a dibasic acid and a dibasic amine according to claim 9, wherein, The number of tower trays is 20 to 25.

12. The continuous polymerization apparatus for producing a polyamide using a dibasic acid and a dibasic amine according to claim 9, wherein, The distance between adjacent two tower trays is 450 mm to 550 mm.

13. The continuous polymerization apparatus for producing a polyamide using a dibasic acid and a dibasic amine according to claim 9, wherein, The height of the overflow weir of the tower tray is 100 mm to 200 mm.

14. The continuous polymerization apparatus for producing a polyamide using a dibasic acid and a dibasic amine according to claim 9, wherein, An online infrared detector is arranged on the gaseous phase outlet pipeline of the reaction rectifying tower.

15. The continuous polymerization apparatus for producing a polyamide from a diacid and a diamine according to claim 14, wherein, The continuous polymerization device further comprises a diamine online supplement pipeline for supplementing diamine in real time, and the diamine online supplement pipeline is connected to the prepolymerization heat exchanger.

16. The continuous polymerization apparatus for producing a polyamide using a dibasic acid and a dibasic amine according to claim 9, wherein, The polymerizer comprises a polymerizer body, an exhaust pipe connected to the polymerizer body and a multi-stage heat exchanger arranged in the exhaust pipe.

17. The continuous polymerization apparatus for producing a polyamide using a dibasic acid and a dibasic amine according to claim 9, wherein, The number of polymerizers is one or more than two.

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