A method and device for continuous production of two-component polyamide monomer solution

Abstract

The invention relates to the technical field of polymer production, and discloses a continuous production method and device for a two-component polyamide monomer solution, comprising the following steps: step 1, dicarboxylic acid, diamine and water are continuously fed into a first reactor for reaction, part of the first product obtained is returned to the first reactor through a first heat exchanger, and part of the first product is fed into a second reactor; step 2, dicarboxylic acid and diamine are supplemented in the second reactor for continuous reaction to obtain a second product; part of the first product is returned to the second reactor through a second discharge pump through a second heat exchanger, and part of the first product is fed into a salt preparation tank; step 3, dicarboxylic acid and diamine are supplemented in the salt preparation tank, and the two-component polyamide monomer solution is continuously discharged from the bottom; the invention realizes heat exchange with the outside through the circulation of reactor products, and the endothermic effect and the exothermic effect of the whole process are mutually utilized, thereby reducing the energy consumption cost of the concentration process in the traditional polyamide process, and directly obtaining a high-concentration polyamide salt solution.

Description

Technical Field

[0001] The invention relates to the technical field of polymer production, and in particular to a continuous production method and device for a two-component polyamide monomer solution. Background Art

[0002] Polyamide is formed by polycondensation of dicarboxylic acid and diamine. In order to obtain a polymer with a high enough molecular weight, it is required that adipic acid and hexamethylenediamine have an equal molar ratio during the polycondensation reaction. If any one of the components is excessive, the molecular chain composed of carboxylic acid end groups and amine end groups will be blocked by the excessive component, thereby terminating the growth of the chain. Therefore, in industrial production of polyamide, dicarboxylic acid and diamine are usually neutralized into salts first, and then polyamide salt is used as a raw material for polycondensation to produce polyamide. The concentration of the raw material two-component polyamide monomer aqueous solution has a certain influence on the speed of the polycondensation reaction. A high concentration of polyamide salt aqueous solution is conducive to accelerating the polymerization speed, shortening the polymerization time, and increasing the output of the polymer per unit time. Therefore, before the polycondensation reaction is carried out, the concentration of the polyamide salt aqueous solution is usually required to reach more than 65%.

[0003] The "Basic Knowledge of Nylon 66 Production" published by China Textile Industry Press introduces the continuous production process of nylon 66 introduced by Liaoyang Petrochemical from Rhone-Poulenc on page 52 and the continuous polymerization process of nylon 66 introduced from Asahi Kasei of Japan on page 76. Both of them prepare nylon 66 salt with a mass concentration of about 50% at room temperature, and remove excess water by heating to increase the concentration of raw nylon 66 salt. The above-mentioned pretreatment process of polyamide salt has the following disadvantages: there is a large amount of water in the aqueous solution of low-concentration polyamide salt. Before polycondensation, most of the water is removed by evaporator, for example, the water content is reduced by 15% to 30%, and a large amount of energy is consumed in the process of the polyamide salt aqueous solution from low concentration to high concentration.

[0004] In order to overcome the shortcomings of the traditional polyamide raw material two-component polyamide monomer concentrated solution preparation production process, patent US4233234A discloses a circulation system invented by BASF for producing polyamide salt solution from alkane dicarboxylic acid and alkane diamine, and constructs a first mixing zone and a second mixing zone to introduce alkane diamine respectively to produce a 45-65wt% polyamide salt solution. This patent reduces equipment expenses, but the raw material for producing polyamide still needs to be evaporated and concentrated.

[0005] Patent CN111821714A discloses a continuous concentration system for refined salt for polyamide, which obtains refined salt with a solid content of 60 to 90 wt%. The water vapor in the refined salt stripping tower is used for heat exchange with the refined salt preheater, which saves energy by at least 30% compared with the traditional concentration process. The above patent recycles the water vapor generated by the concentration of the polyamide salt solution, thereby reducing the energy consumed in the process. However, the effective energy in the water vapor energy is too low, and the efficiency of the secondary utilization is limited, and there is also a large amount of energy loss. Summary of the invention

[0006] The present invention aims at the problem of high energy consumption of evaporation and concentration in the preparation process of polyamide salt, and provides a continuous production method of a two-component polyamide monomer solution. The method does not require an evaporation and concentration process, and directly prepares a high-concentration polyamide salt solution, thereby greatly reducing energy consumption and lowering production costs.

[0007] To achieve the above object, the technical solution adopted by the present invention is:

[0008] A method for continuously producing a two-component polyamide monomer solution comprises the steps of:

[0009] Step 1, dicarboxylic acid, diamine and water are continuously introduced into a first reactor to react and obtain a first product; the first product is discharged from the bottom, partially passes through a first discharge pump and returns to the first reactor through a first heat exchanger, and partially enters a second reactor;

[0010] Step 2, adding dicarboxylic acid and diamine to the second reactor to further react with the product of the first reactor to obtain a second product; the second product is partially returned to the second reactor through the second heat exchanger from the bottom discharge port through the second discharge pump, and partially enters the salt preparation tank;

[0011] Step 3, adding dicarboxylic acid and diamine to the salt preparation tank, and continuously discharging from the bottom to obtain a two-component polyamide monomer solution;

[0012] The discharge ports of the first reactor, the second reactor and the salt preparation tank are all provided with pH detectors. The feed port of each reaction tank is connected to the pH detector line of its discharge port, and the feed amount of dicarboxylic acid and diamine is adjusted according to the pH value of the discharge.

[0013] In the present invention, dicarboxylic acid and diamine react in two reactors, and heat is exchanged with the outside world through the circulation of reactor products. The endothermic effect and the exothermic effect of the whole process are mutually utilized, thereby reducing the energy consumption cost of the concentration process in the traditional polyamide process. Energy exchange is performed by heating or cooling the circulating stream, so that the temperature and concentration in the reactor are evenly distributed, and the crystallization and precipitation of the two-component polyamide monomer during the reaction process are effectively controlled to directly obtain a high-concentration polyamide salt solution.

[0014] More specifically, the preparation process of the polyamide salt solution includes two endothermic processes and one exothermic process, wherein the dissolution process of the dicarboxylic acid absorbs heat, and the neutralization reaction process of the dicarboxylic acid and the diamine releases heat. When the dicarboxylic acid feed amount of the first reactor accounts for a higher proportion of the total dicarboxylic acid feed amount of the first reactor and the second reactor, or the temperature required to be maintained in the first reactor is relatively low, the first reactor as a whole presents an exothermic process, and therefore a small amount of heat energy is removed from the product circulating stream by using the first heat exchanger; in order to maintain the salt-forming system from precipitating polyamide salt crystals, the system temperature needs to be increased, and this process absorbs heat. When the heat released by the reaction of the neutralization process of the dicarboxylic acid and the diamine in the second reactor is not enough to compensate for the energy required to increase the system temperature, the second reactor as a whole presents an endothermic process; otherwise, the second reactor as a whole presents an exothermic process, and energy is exchanged between the salt-forming system in the second reactor and the environment through the second heat exchanger, thereby achieving the process of energy transfer in or out. This enables the mutual utilization of the endothermic and exothermic effects of the entire process, reduces the energy consumption cost of the concentration process in the traditional polyamide process, and exchanges energy by heating or cooling the circulating stream to make the temperature and concentration in the reactor evenly distributed. By effectively controlling the crystallization and precipitation of the two-component polyamide monomer during the reaction, a high-concentration polyamide salt solution is directly obtained to save process energy consumption and reduce production costs.

[0015] In some embodiments, the dicarboxylic acid includes a C6-C16 aliphatic or aromatic dicarboxylic acid; and the diamine includes a C4-C12 aliphatic diamine.

[0016] In some embodiments, the dicarboxylic acid includes one or more of 1,6-hexanedioic acid, 1,8-octanedioic acid, 1,10-decanedioic acid, 1,12-dodecane dioic acid, terephthalic acid, and naphthalene dicarboxylic acid; preferably, the dicarboxylic acid is adipic acid;

[0017] In some embodiments, the diamine includes one or more of 1,6-hexanediamine, 1,8-octanediamine, 1,10-decanediamine, 1,12-dodecanediamine, 2-methyl-1,5-pentanediamine, 2-methyl-1,6-hexanediamine, 2-methyl-1,8-octanediamine or 2,5-dimethylhexanediamine, m-xylylenediamine, and p-xylylenediamine. Preferably, the diamine is hexanediamine.

[0018] In some embodiments, the diamine in the first reactor is added in the form of pure liquid diamine or an aqueous solution of diamine; the mass fraction of diamine in the aqueous solution of diamine is 80-100%; in some embodiments, the mass fraction of diamine in the aqueous solution of diamine is 90-100%; the aqueous solution of diamine with low water content ensures that the product polyamide salt solution exists in a high concentration.

[0019] In some embodiments, the molar ratio of the dicarboxylic acid and the diamine continuously entering the first reactor is 0.99 to 1.01:1; in some embodiments, the molar ratio of the dicarboxylic acid and the diamine continuously entering the first reactor is 0.999 to 1.001:1.

[0020] In some embodiments, the reaction temperature in the first reactor is 55 to 85°C and is carried out under normal pressure; to ensure that the mixed liquid in the first reactor exists in the form of a uniform medium, the temperature in the first reactor is maintained at a certain temperature ±1°C, which depends on the concentration of the solute dissolved in the mixed solution in the first reactor. Preferably, the reaction temperature in the first reactor is 80°C. Since the reaction temperature in the first reactor is relatively low, no inert gas protection is required, and the reaction can be carried out under normal pressure. The temperature is less than the boiling point of the mixed liquid, and the reaction temperature is greater than the temperature of the saturated solution of the polyamide salt in the reactor to ensure that the polyamide salt solution exists in a uniform medium. The temperature is less than 90°C. Being in this temperature range is conducive to limiting the oxidation of diamines and ensuring that the quality of the polyamide salt solution meets the requirements for pre-polymerization production of polyamide.

[0021] In some embodiments, in step 1, the mass ratio of the first product returning to the first reactor and entering the second reactor is 0.1 to 3:1. The first product itself carries thermal energy, and a small amount of heat exchange through the first heat exchanger can reach the reaction temperature of the first reactor, forming a circulating stream returning to the first reactor, and adjusting the flow ratio of the circulating stream and the stream entering the second reactor, so that the first reactor is in the desired temperature range, greatly reducing the energy consumption of the entire reaction.

[0022] The mass ratio of the first product returning to the first reactor and entering the second reactor depends on the temperature of the first reactor. When the dicarboxylic acid feed amount of the first reactor accounts for the same amount of the total dicarboxylic acid feed amount, in order to reduce the temperature of the first reactor, the mass ratio of the first product returning to the first reactor is increased, so that the energy of the salt-forming system removed from the first reactor is increased. When the dicarboxylic acid feed amount of the first reactor accounts for more than 50% of the total dicarboxylic acid feed amount, the temperature rise in the first reactor is suppressed by increasing the mass ratio of the first product returning to the first reactor.

[0023] In some embodiments, the solute mass fraction in the first product is below 60%; in some embodiments, the solute mass fraction in the first product is 45-60%, and a heat exchange medium with low energy density can maintain the temperature of a saturated solution of the solute mass fraction.

[0024] In some embodiments, the molar ratio of the dicarboxylic acid and the diamine continuously entering the second reactor is 0.99 to 1.01:1; in some embodiments, the molar ratio of the two is 0.999 to 1.001:1. The closer the molar ratio of the two is to 1:1, the more favorable it is for the subsequent polycondensation process of the product polyamide salt solution. The ratio of the two is monitored by a pH detector to avoid fluctuations in the feed amount, especially the impact of fluctuations in the feed of solid dicarboxylic acid on this range.

[0025] In some embodiments, the second reactor and the salt preparation tank react under the protection of an inert gas; the inert gas includes any one of nitrogen, argon, and helium.

[0026] In some embodiments, the reaction temperature in the second reactor is 115-160°C and carried out under a pressure of 0.1-0.3Mpa; in order to avoid the crystallization and precipitation of high-concentration polyamide salt, clogging the pipeline and increasing the difficulty of equipment cleaning, the reaction temperature of the second reactor needs to be appropriately increased, but because the amine end groups of the diamine raw materials are prone to oxidation and deterioration at high temperatures, the second reactor and the salt preparation tank need to be carried out under the protection of inert gas, and the pressure in the second reactor should be appropriately increased to ensure that the water in the solution in the second reactor does not boil and evaporate, and to avoid the reduction of water in the solution causing the polyamide salt to precipitate in the form of a solid. The salt preparation tank maintains the same temperature and pressure as the second reactor. Preferably, the pressure in the second reactor is 0.12-0.3MPa;

[0027] In some embodiments, in step 2, the mass ratio of the second product returning to the second reactor and entering the salt preparation tank is 0.5 to 3:1. When the heat released by the reaction of the neutralization process of dicarboxylic acid and diamine in the second reactor is not enough to make up for the energy required for the temperature increase of the system, the second reactor as a whole presents an endothermic process, otherwise, the second reactor as a whole presents an exothermic process. The flow ratio of the circulating stream and the stream entering the salt preparation tank is adjusted to keep the second reactor in the desired temperature range. The mass ratio depends on the temperature of the second reactor. When the second reactor is an endothermic process and the temperature to be maintained in the second reactor increases, the energy transferred from the environment to the salt-forming system of the second reactor is increased by increasing the mass proportion returned to the second reactor to maintain the temperature of the second reactor; when the second reactor is an exothermic process and the temperature to be maintained in the second reactor increases, the energy transferred from the second reactor salt-forming system to the environment is reduced by reducing the mass proportion returned to the second reactor to maintain the temperature of the second reactor.

[0028] In some embodiments, the solute mass fraction in the second product is 65-85%; the polyamide salt solution prepared by the method of the present invention has a high mass concentration, and the entire reaction process does not require a water vapor evaporation process, thereby avoiding the latent heat of vaporization in the evaporation phase change process and saving energy consumption.

[0029] In some embodiments, the feed ratio of dicarboxylic acid and diamine in each reaction tank is adjusted so that the pH meter reading at the outlet of each reaction tank is 7.0-8.0. For example, when the pH is lower than 7.0, the amount of diamine added is increased, and when the pH is higher than 8.0, the amount of dicarboxylic acid added is increased.

[0030] In some embodiments, the pH meter reading at the outlet of each reaction tank is set to be 7.5-7.8.

[0031] In some embodiments, the dicarboxylic acid feed amount of the first reactor accounts for 20-80% of the total dicarboxylic acid feed amount of the first reactor and the second reactor. When the proportion of the dicarboxylic acid feed amount of the first reactor increases, the increase in the heat absorption of the solid dicarboxylic acid dissolution is less than the increase in the heat release of the neutralization reaction of the dicarboxylic acid and the diamine, resulting in an increase in the temperature in the first reactor. In order to maintain the temperature within a certain range, more energy needs to be removed through the first heat exchanger.

[0032] In some embodiments, when the dicarboxylic acid feed amount of the first reactor accounts for 20-50% of the total dicarboxylic acid feed amount of the first reactor and the second reactor, the first heat exchanger does not exist.

[0033] Preferably, in some embodiments, when the amount of dicarboxylic acid fed to the first reactor accounts for 35-50% of the total amount of dicarboxylic acid fed to the first reactor and the second reactor, the first heat exchanger does not exist. At this time, the energy generated by the reaction can freely allow the temperature in the first reactor to reach a corresponding value, which is between 55 and 85°C.

[0034] By adjusting and optimizing the salt formation ratio of the first reactor and the second reactor, the heat exchange between the high-concentration polyamide salt solution preparation process and the environment can be minimized, and the effect of completely eliminating the need for the first heat exchanger can be achieved, which can save process energy consumption to a greater extent and reduce production costs.

[0035] In some embodiments, the raw material of the salt preparation tank is supplementary dicarboxylic acid or diamine, and the temperature and pressure are the same as those of the second reactor. By adding a small amount of dicarboxylic acid or diamine, the error caused by feed fluctuations in the first reactor and the second reactor is further reduced.

[0036] The high-concentration polyamide salt solution prepared by the invention can be directly transported to a polyamide production line for use.

[0037] The present invention also provides a continuous production device for a two-component polyamide monomer solution, the continuous production device comprising a first reactor, a second reactor and a salt preparation tank;

[0038] The first reactor, the second reactor and the salt preparation tank are all provided with feed ports for dicarboxylic acid and diamine in the middle and upper parts, and discharge ports at the bottom; the feed port of each reaction tank is connected to the pH detector circuit of its discharge port, and the feed amount of dicarboxylic acid and diamine is adjusted according to the pH value of the discharge; the first reactor is also provided with a water feed port;

[0039] The bottom discharge port of the first reactor is connected to the first discharge pump, which sends part of the discharge to the first heat exchanger and returns to the first reactor, and sends part to the second reactor; the bottom discharge port of the second reactor is connected to the second discharge pump, which sends part of the discharge to the second heat exchanger and returns to the second reactor, and sends part to the salt preparation tank.

[0040] In some embodiments, the dicarboxylic acid is weighed by a loss-in-weight scale and then enters the first reactor and the second reactor respectively through a raw material conveyor; the raw material conveyor includes a screw conveyor and / or a scraper conveyor.

[0041] In some embodiments, the first reactor and the second reactor are stirred reactors.

[0042] In some embodiments, the bottom discharge port of the first reactor is connected to a first discharge pump to return part of the first product directly to the first reactor and send part of the first product to the second reactor.

[0043] A distributed computer control system is set up in a device for continuously producing a two-component polyamide monomer solution. The distributed computer control system can detect and regulate parameters such as temperature, pressure and flow rate in the production process through detection and display equipment, control valves, etc.

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] (1) The present invention provides a method for continuously producing a high-concentration two-component polyamide monomer solution. The high-concentration two-component polyamide monomer solution can be directly used as a raw material for producing polyamide without the need for evaporation and concentration to remove excess water, thereby reducing the equipment and energy consumption costs of the concentration process.

[0046] (2) The present invention performs energy exchange by heating or cooling the circulating stream, so that the temperature and concentration in the reactor are evenly distributed, and the crystallization of the two-component polyamide monomer is effectively controlled during the reaction.

[0047] (3) The present invention optimizes the reaction weight of the two-component polyamide monomers in different reactors, so that the endothermic effect and the exothermic effect of the entire process are mutually utilized to minimize the heat exchange amount with the environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 Schematic diagram of the continuous production device of the two-component polyamide monomer solution in Example 1.

[0049] Figure 2 This is a graph showing how the energy consumption of the first heat exchanger at different temperatures in the first reactor in Example 1 changes as the proportion of the dicarboxylic acid feed amount in the first reactor accounts for the total dicarboxylic acid feed amount.

[0050] Figure 3 It is the energy consumption of the second reactor when the first reactor 3 in Example 1 is at different reaction temperature energy balance points.

[0051] Figure 4 Schematic diagram of the continuous production device of the two-component polyamide monomer solution in Example 2.

[0052] Figure 5 This is a schematic diagram of the production and concentration process of the traditional two-component polyamide monomer solution in the prior art in Comparative Example 1.

[0053] Among them, there are a first loss-in-weight scale 1, a first screw conveyor 2, a first reactor 3, a first discharge pump 4, a first pH detector 5, a first heat exchanger 6, a first adipic acid feed control valve 7, a first hexamethylenediamine feed control valve 8, a second loss-in-weight scale 9, a second screw conveyor 10, a second reactor 11, a second discharge pump 12, a second pH detector 13, a second heat exchanger 14, a second adipic acid feed control valve 15, a second hexamethylenediamine feed control valve 16, a salt mixing tank 17, a third pH detector 18, a supplementary hexamethylenediamine control valve 19, a supplementary adipic acid control valve 20, a salt reaction tank 21, a heat exchanger 23 and a concentration tank 22. DETAILED DESCRIPTION

[0054] In order to make the purpose, technical scheme 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 can make modifications or equivalent substitutions based on the understanding of the technical scheme of the present invention without departing from the spirit and scope of the technical scheme of the present invention, and all should be included in the protection scope of the present invention.

[0055] Taking the preparation of nylon 66 salt solution as an example, the dicarboxylic acid is adipic acid, the diamine is hexamethylenediamine, the adipic acid is solid adipic acid in powder form, and the hexamethylenediamine is preferably an aqueous solution with a mass concentration of 98%. As an example of the embodiment of the present invention, the method and device can also be applied to other dicarboxylic acids and diamines to prepare a two-component polyamide salt solution.

[0056] Example 1

[0057] like Figure 1As shown, a continuous production device for a two-component polyamide monomer solution includes a first weight loss scale 1, a first screw conveyor 2, a first reactor 3, a first discharge pump 4, a first pH detector 5, a first heat exchanger 6, a first adipic acid feed control valve 7, a first hexamethylenediamine feed control valve 8, a second weight loss scale 9, a second screw conveyor 10, a second reactor 11, a second discharge pump 12, a second pH detector 13, a second heat exchanger 14, a second adipic acid feed control valve 15, a second hexamethylenediamine feed control valve 16, a salt preparation tank 17, a third pH detector 18, a supplementary hexamethylenediamine control valve 19, and a supplementary adipic acid control valve 20. The first reactor and the second reactor are stirred reactors, and the second reactor and the salt preparation tank are operated under nitrogen protection, and the nitrogen inlet is not shown in the figure.

[0058] The first adipic acid feed control valve 7, the first loss-in-weight scale 1, the first screw conveyor 2 and the adipic acid feed port in the upper part of the first reactor 3 are connected in sequence; the upper part of the first reactor 3 is also provided with an adipic acid feed port and a water feed port connected to the first hexamethylenediamine feed control valve 8; the bottom of the first reactor 3 is provided with a discharge port connected to the first discharge pump 4, and the first discharge pump 4 returns part of the first product to the first reactor 3 through the first heat exchanger 6, and part of it enters the second thermal reactor 11;

[0059] The second adipic acid feed control valve 15, the second loss-in-weight scale 9, the second screw conveyor 10 and the adipic acid feed port in the upper part of the second reactor 11 are connected in sequence; the second reactor 11 is also provided with an adipic acid feed port connected to the second hexamethylenediamine feed control valve 16 in the upper part, and the second reactor 11 is provided with a discharge port at the bottom connected to the second discharge pump 12. The second discharge pump 12 returns part of the second product to the second reactor 11 through the second heat exchanger 14, and part of the second product enters the salt preparation tank 17;

[0060] The salt preparation tank 17 is provided with a feed port connected to a control valve 19 for replenishing hexamethylenediamine and a control valve 20 for replenishing adipic acid at the top, and a discharge port at the bottom to obtain a nylon 66 salt solution product.

[0061] A first pH detector 5 is provided between the first discharge pump 4 and the first heat exchanger 6, and is connected to the first adipic acid feed control valve 7 and the first hexamethylenediamine feed control valve 8, and the input amount of ethylenediamine and adipic acid raw materials is appropriately adjusted by detecting the pH of the product;

[0062] Similarly, a second pH detector 13 is provided between the second discharge pump 12 and the second heat exchanger 14, which is connected to the second adipic acid feed control valve 15 and the second hexamethylenediamine feed control valve 16, and the input amount of ethylenediamine and adipic acid raw materials is appropriately adjusted by detecting the pH of the product;

[0063] The discharge port of the salt preparation tank 17 is provided with a third pH detector 18, which is connected to the lines of the hexamethylenediamine supplement control valve 19 and the adipic acid supplement control valve 20, and the input amount of ethylenediamine and adipic acid raw materials is appropriately adjusted by detecting the pH of the product.

[0064] Use Figure 1 The device shown is used to continuously produce a nylon 66 salt solution having a mass fraction of 70%, specifically comprising the steps of:

[0065] Step 1, a first weight loss scale 1 weighs 907 kg / h of solid adipic acid powder, accounting for 54% of the total solid adipic acid feed amount, and continuously enters the first reactor 3 through the first screw feeder 2, hexamethylenediamine enters the first reactor 3 at a constant rate of 736 kg / h, and water enters the first reactor 3 at a constant rate of 1264 kg / h, respectively, the molar ratio of adipic acid to hexamethylenediamine is 1:1, and the reaction temperature in the first reactor is 70°C; the mass fraction of the first product solute at the bottom discharge port of the first reactor 3 is 56%.

[0066] The first discharge pump 4 cools the first product (67.7% by mass) to 60°C through the first heat exchanger 6, and circulates back to the first reactor 3, and the remaining liquid enters the second reactor 11. The pH of the mixed liquid is monitored by the first pH detector 5 and maintained at 7.5-7.8.

[0067] Step 2, the second weight loss scale 9 weighs 780kg / h of solid adipic acid powder, which is continuously fed into the second reactor 11 through the second screw feeder 10, and hexamethylenediamine is fed into the second reactor 11 at a constant rate of 633kg / h, and the molar ratio of adipic acid to hexamethylenediamine is 1:1. The reaction temperature in the second reactor 11 is controlled to be 120°C, and the pressure is increased to 0.15MPa, and the reaction is carried out under a nitrogen atmosphere. The solute mass fraction of the second product at the bottom outlet of the second reactor is 70%, and the temperature of the second product is 70%.

[0068] The second discharge pump 12 heats the second product (62.5% by mass) to 135°C through the second heat exchanger 14 and circulates back to the second reactor 11, and the remaining liquid enters the salt preparation tank 17. The pH of the mixed liquid is monitored by the second pH detector 13 and maintained at 7.5-7.8.

[0069] Step 3, the external temperature of the salt preparation tank is kept at 120°C and the pressure is 0.15MPa. The pH of the nylon 66 salt solution discharged from the bottom of the salt preparation tank 17 is monitored by the third pH detection meter 18 to see whether it is between 7.6 and 7.7. The pH of the product is adjusted by adding adipic acid and hexamethylenediamine to produce a qualified 70% nylon 66 salt solution, which is directly used in the nylon 66 polycondensation process.

[0070] The first reactor 3 is controlled at different temperatures. As the proportion of the dicarboxylic acid feed amount of the first reactor to the total dicarboxylic acid feed amount changes, the energy consumption of the first heat exchanger 6 changes. Specifically, Figure 2 shown.

[0071] When the temperature of the first reactor 3 is the same, as the proportion of the dicarboxylic acid feed amount of the first reactor to the total dicarboxylic acid feed amount increases, the heat release of the neutralization reaction in the first reactor 3 increases, and the heat absorbed by the dissolution of solid adipic acid increases, but the exothermic effect of the neutralization reaction gradually increases and takes a dominant role. The energy consumption of the first heat exchanger 6 first decreases and then increases (first heating and then cooling). However, at the same temperature, there is an energy balance point between the heat release of the neutralization reaction and the heat absorption of the dissolution of solid adipic acid. At this salt formation ratio, the first heat exchanger 6 does not exchange any heat with the environment. When the first reactor 3 maintains different reaction temperatures and the energy consumption of the first heat exchanger 6 is 0, the proportion of adipic acid entering the first reaction to the total adipic acid consumption of the first reactor and the second reactor is specifically shown in Table 1.

[0072] Table 1 Proportion of adipic acid used in the first reactor when the energy consumption of the first heat exchanger is 0 at different reaction temperatures

[0073] The first reactor temperature / ℃ 60 65 70 75 80 85 Adipic acid proportion / wt% 26％ 30％ 35％ 39％ 44％ 50％

[0074] When the first reactor 3 is at different reaction temperature energy balance points, the energy consumption of the second reactor 11 is as follows: Figure 3 As shown. The temperature of the nylon 66 salt entering the second reactor 11 increases, and the specific gravity of the nylon 66 salt entering the second reactor 11 increases accordingly, the sensible heat in the second reactor 11 that rises to the final temperature of the product decreases, the amount of solid adipic acid dissolved in the second reactor 11 decreases, and the dissolution endothermic heat of solid adipic acid also decreases accordingly, and the exothermic heat of the reaction of adipic acid and hexamethylenediamine decreases at the same time. The temperature of the nylon 66 salt entering the second reactor 11 increases, and the endothermic reduction effect in the system is greater than the exothermic reduction effect, so the energy absorbed by the second heat exchanger from the environment decreases.

[0075] The higher the temperature of the first reactor 3, the more conducive it is to reducing the overall energy consumption of the high-concentration nylon 66 salt solution preparation process. However, when the temperature is higher than 80°C, the hexamethylenediamine end groups in the first reactor 3 undergo oxidation and deterioration, affecting the product quality of the nylon 66 salt solution. When the temperature is higher than 80°C, the first reactor 3 should be placed in an inert atmosphere, and when the temperature is lower than 80°C, no inert atmosphere is required. Based on this condition, the production of Example 2 was carried out.

[0076] Example 2

[0077] Schematic diagram of the continuous production device of two-component polyamide monomer solution Figure 4 As shown, the device is similar to that of Example 1. Figure 1Basically equivalent, but without the first heat exchanger 3, the continuous production of a nylon 66 salt solution with a mass fraction of 70% comprises the steps of:

[0078] Step 1, a first loss-in-weight scale 1 weighs 738 kg / h of solid adipic acid powder, accounting for 44% of the total solid adipic acid feed amount, and continuously enters the first reactor 3 through the first screw feeder 2, hexamethylenediamine enters the first reactor 3 at a constant rate of 598 kg / h, and water enters the first reactor 3 at a constant rate of 1264 kg / h, respectively. The molar ratio of adipic acid to hexamethylenediamine is 1:1, the reaction temperature in the first reactor is 80°C, and the mass fraction of the first product solute at the bottom discharge port of the first reactor 3 is 31%.

[0079] The first discharge pump 4 pumps 20 kg / h of liquid through the first pH detector 5 to monitor the pH of the mixed liquid to maintain it at 7.5-7.8, and the rest of the liquid enters the second reactor 11.

[0080] Step 2, the second weight loss scale 9 weighs 949 kg / h of solid adipic acid powder, which is continuously fed into the second reactor 11 through the second screw feeder 10, and hexamethylenediamine is fed into the second reactor 11 at a constant rate of 710 kg / h, and the molar ratio of adipic acid to hexamethylenediamine is 1:1. The reaction temperature in the second reactor 11 is controlled to be 120° C., and the pressure is increased to 0.15 MPa, and the reaction is carried out under a nitrogen atmosphere. The solute mass fraction of the second product at the bottom outlet of the second reactor is 70%.

[0081] The second discharge pump 12 heats the second product (41.7% by weight) to 130°C through the second heat exchanger 14 and circulates back to the second reactor 11, and the remaining liquid enters the salt preparation tank 17. The pH of the mixed liquid is monitored by the second pH detector 13 and maintained at 7.5-7.8.

[0082] Step 3, monitor whether the pH of the nylon 66 salt solution discharged from the bottom of the salt preparation tank 17 is between 7.6 and 7.7 through the third pH detection meter 18, adjust the product pH by adding adipic acid and hexamethylenediamine, and produce a qualified 70% nylon 66 salt solution, which is directly used in the nylon 66 polycondensation process.

[0083] Comparative Example 1

[0084] The schematic diagram of the conventional two-component polyamide monomer solution production and concentration process commonly used in the prior art is as follows: Figure 5 As shown, it usually includes a salt reaction tank 21, a heat exchanger 23 and a concentration tank 22. 1689 kg / h of pure adipic acid solid or adipic acid suspension and 1310 kg / h of hexamethylenediamine continuously enter the salt reaction tank 21 to react in the salt reaction tank 21, wherein the molar ratio of adipic acid to hexamethylenediamine is 1:1, the mass of solute in the mixed solution in the salt reaction tank 21 is about 50%, and the neutralization reaction is carried out at normal temperature and pressure.

[0085] The mixed liquid at the bottom outlet of the salt reaction tank 21 is heated to 90°C by the heat exchanger 23 and enters the concentration tank 22. The concentration tank 22 is equipped with a heating device, and the temperature is raised to 120°C and the pressure is raised to 0.13MPa. The mixed liquid boils and evaporates in the concentration tank 22, and the water vapor is discharged from the top of the concentration tank 22. The nylon 66 salt solution with a mass fraction of 70% is discharged from the bottom of the concentration tank 22 for subsequent nylon 66 polycondensation reaction.

[0086] Aspen Plus software was used for simulation calculation, and the overall energy consumption of Example 1, Example 2 and Comparative Example 1 was calculated according to the discharge flow rate of nylon 66 salt solution, as shown in Table 2.

[0087] Table 2 Comparison of product specifications and energy consumption of Examples 1 to 2 and Comparative Example 1

[0088]

[0089] * That is, the energy consumption of the first heat exchanger is 0kW

[0090] It can be clearly seen from Table 2 that the energy consumption of the present invention is greatly reduced compared with the preparation process in the prior art. Example 2 is a more preferred option, which does not require a first heat exchanger, has lower energy consumption for the overall reaction, and does not require evaporation and concentration to remove excess water, which greatly reduces the equipment and energy consumption costs of the concentration process.

Claims

1. A method for continuous production of a two-component polyamide monomer solution, characterized in that: Includes steps: Step 1, dicarboxylic acid, diamine and water are continuously introduced into a first reactor to react to obtain a first product; After the first product is discharged from the bottom, part of it passes through the first heat exchanger and returns to the first reactor through the first discharge pump, and part of it enters the second reactor; Step 2, adding dicarboxylic acid and diamine to the second reactor to further react with the product of the first reactor to obtain a second product; The second product is discharged from the bottom outlet through the second discharge pump, partially returns to the second reactor through the second heat exchanger, and partially enters the salt preparation tank; Step 3, adding dicarboxylic acid and diamine to the salt preparation tank, and continuously discharging from the bottom to obtain a two-component polyamide monomer solution; The discharge ports of the first reactor, the second reactor and the salt preparation tank are all provided with pH detectors, and the feed port of each reaction tank is connected to the pH detector circuit of its discharge port, and the feed amount of dicarboxylic acid and diamine is adjusted according to the pH value of the discharge; The molar ratio of the dicarboxylic acid and the diamine continuously entering the first reactor is 0.99-1.01:1; the reaction temperature in the first reactor is 55-85° C. and is carried out under normal pressure; the mass fraction of the solute in the first product is less than 60%; In step 1, the mass ratio of the first product returning to the first reactor and entering the second reactor is 0.1 to 3:1; The molar ratio of dicarboxylic acid and diamine continuously entering the second reactor is 0.99-1.01:1; the reaction temperature in the second reactor is 115-160° C. and the pressure is 0.1-0.3 MPa; In step 2, the mass ratio of the second product returning to the second reactor and entering the salt preparation tank is 0.5 to 3:1; The dicarboxylic acid feed amount of the first reactor accounts for 20 to 80% of the total dicarboxylic acid feed amount of the first reactor and the second reactor; When the dicarboxylic acid feed amount of the first reactor accounts for 20-50% of the total dicarboxylic acid feed amount of the first reactor and the second reactor, the first heat exchanger does not exist.

2. The method for continuous production of a two-component polyamide monomer solution according to claim 1, characterized in that: The dicarboxylic acid includes C6-C16 aliphatic or aromatic dicarboxylic acid; the diamine includes C4-C12 aliphatic diamine.

3. The method for continuous production of a two-component polyamide monomer solution according to claim 1, characterized in that: The diamine in the first reactor is added in the form of pure liquid diamine or diamine aqueous solution; the mass fraction of diamine in the diamine aqueous solution is 80-100%.

4. The method for continuous production of a two-component polyamide monomer solution according to claim 1, characterized in that: The second reactor and the salt preparation tank react under the protection of inert gas; The solute mass fraction in the second product is 65-85%.

5. The method for continuous production of a two-component polyamide monomer solution according to claim 1, characterized in that: The feed ratio of dicarboxylic acid to diamine in each reaction tank is adjusted so that the pH detector reading at the outlet of each reaction tank is 7.0-8.

0.

6. The method for continuous production of a two-component polyamide monomer solution according to claim 4, characterized in that: The inert gas includes any one of nitrogen, argon and helium.

Images