A method and system for continuous production of long carbon chain polyamides

Abstract

This invention discloses a method and system for the continuous production of long-chain polyamides. The method includes: (1) feeding a diacid and a diamine into a prepolymerization reactor for a prepolymerization reaction, wherein the prepolymerization reactor is a horizontal screw reactor; (2) evaporating and dehydrating the product of the prepolymerization reaction; and (3) the output from step (2) entering a final polymerization reactor for continuous final polycondensation. The long-chain polyamides prepared by this method and system have a narrow molecular weight distribution, low viscosity, and stable performance. In particular, compared with batch methods, the process has a high degree of automation and high production efficiency.

Description

Technical Field

[0001] This invention belongs to the field of preparation technology of long carbon chain polyamides, and particularly relates to a method and system for one-step continuous production of long carbon chain polyamides. Background Technology

[0002] Polyamide, also known as nylon, refers to polyamides with ten or more methylene groups in their chain segments. As the number of methylene carbon chains increases, the concentration of amide groups decreases, and the properties of the polyamide change. Therefore, long-chain polyamides possess most of the general properties of ordinary polyamides, such as good mechanical properties, wear resistance, lubricity, solvent resistance, and ease of molding and processing, while also exhibiting unique advantages such as low water absorption, good dimensional stability, and excellent dielectric properties. Due to their superior properties compared to short-chain polyamides, they are a key research area both domestically and internationally.

[0003] Because the polymerization process of long-chain polyamides is extremely complex and involves multiple operating conditions, all reported polymerization processes are batch processes. Furthermore, as the number of carbon chains increases, the solubility of diacids and diamines in water gradually decreases, requiring heating for complete dissolution. Therefore, most disclosed long-chain polyamide production processes require dissolving diacids and diamines in organic solvents, then mixing them batch-wise to produce long-chain polyamide salts. The resulting salts then require further post-processing before becoming raw materials for the polymerization reaction. Compared to short-chain polyamides, the production process is extremely lengthy.

[0004] CN110066393B discloses a long-chain polyamide resin and its preparation method. The raw materials for producing the long-chain polyamide resin include 1,5-pentanediamine and a long-chain dicarboxylic acid. The preparation process is as follows: a polyamide salt aqueous solution is prepared under nitrogen or inert gas protection; the pH value is adjusted to 6.60-7.49 with a small amount of pentanediamine or a long-chain dicarboxylic acid; one or more additives are added as needed to obtain a polyamide salt aqueous solution; and then high-temperature polycondensation is carried out. This invention uses a two-step method to produce polyamide, but the disadvantages are that the steps are lengthy and complex, resulting in high energy consumption and large emissions of waste, which does not conform to the current trend of energy conservation and emission reduction.

[0005] CN115947937A provides a batch process for producing high-viscosity long-chain nylon, comprising the following steps: Step S1, placing a diacid, a diamine, deionized water, and an antioxidant in a reactor, maintaining the reactor pressure by venting steam during the reaction; Step S2, transferring the long-chain nylon from the reactor to a first thickener for polymerization, and holding it for 30-90 minutes; Step S3, transferring the long-chain nylon from the first thickener to a second thickener for further polymerization, obtaining high-viscosity long-chain nylon particles. Although this invention omits the salt-forming step, the entire production process remains batch-based. In fact, omitting the salt-forming step can significantly reduce the batch-to-batch product quality stability. Furthermore, batch-based operation consumes a large amount of manpower, increasing production costs. Summary of the Invention

[0006] To overcome the problems existing in the prior art, this invention provides a one-step continuous production method and system for long-chain polyamides. This method and system simplify the production process of long-chain polyamides and optimize the manufacturing process. Not only is the process simple, but the continuous process also improves the batch-to-batch product quality stability. The long-chain polyamides prepared by this method and system have a narrow molecular weight distribution and exhibit low and stable viscosity when the molecular weight difference is small. In particular, compared to batch methods, the process has a high degree of automation and high production efficiency.

[0007] One of the objectives of this invention is to provide a method for continuous production of long-chain polyamides, comprising: (1) feeding a diacid and a diamine into a prepolymerization reactor for a prepolymerization reaction, wherein the prepolymerization reactor is a horizontal screw reactor; (2) evaporating and removing water from the product of the prepolymerization reaction; and (3) the discharge from step (2) entering a final polymerization reactor for continuous final polycondensation.

[0008] Preferably, the dicarboxylic acid fed into the prepolymer reactor is a dicarboxylic acid melt, and the diamine fed into the prepolymer reactor is a diamine melt.

[0009] In a preferred embodiment, step (1) includes: (1.1) mixing a diacid with water and heating to melt it to obtain a diacid melt, and heating a diamine to melt it to obtain a diamine melt; (1.2) feeding the diacid melt and the diamine melt into the horizontal screw reactor for a prepolymerization reaction.

[0010] In step (1.1), the purity ranges of the diacid and the diamine are 95.00% to 99.99% and 97.00% to 99.99%, respectively. More preferably, the purity ranges of the diacid and the diamine are 97.50% to 99.99% and 98.80% to 99.99%, respectively.

[0011] In a further preferred embodiment, the weight ratio of the dicarboxylic acid to water in step (1.1) is 1:0.5 to 1:1.5, preferably 1:0.7 to 1:1.2, for example 1:0.5, 1:0.6, 1:0.8, 1:1, 1:1.2, 1:1.4 or 1:1.5.

[0012] For heating dicarboxylic acids: there are no particular restrictions on the temperature, as long as it can be heated to a melt, it can be 90 to 150°C; the heating medium can be any one of heat transfer oil, low-pressure steam or medium-pressure steam, preferably low-pressure steam; stirring can be used during heating, there are no particular restrictions on the stirring speed, it can be 60 to 350 r / min; there are no particular restrictions on the melting or heating time, it can be 5 to 30 minutes.

[0013] For heating diamines: there are no particular restrictions on the temperature, as long as it can be heated to a melt, it can be 70-100℃; the heating medium can be any one of hot water, heat transfer oil, low-pressure steam or medium-pressure steam, preferably hot water; stirring can be used during heating, and there are no particular restrictions on the stirring speed, it can be 60-320 r / min; there are no particular restrictions on the melting or heating time, it can be 5-30 minutes.

[0014] In a further preferred embodiment, a protective gas is used for purging before step (1.1), the protective gas being selected from any one or more of carbon dioxide, nitrogen, and inert gases, the inert gas being selected from helium and / or argon.

[0015] In a preferred embodiment, the temperature inside the horizontal screw reactor is controlled to be 150–300°C, preferably 180–250°C, for example 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C or 250°C.

[0016] The horizontal screw reactor is equipped with a jacket for heat dissipation, and the refrigerant is either heat transfer oil or molten salt.

[0017] In a further preferred embodiment, the pressure inside the horizontal screw reactor is controlled to be 1.1–2.5 MPa, preferably 1.23–1.81 MPa, for example 1.1 MPa, 1.2 MPa, 1.3 MPa, 1.4 MPa, 1.5 MPa, 1.6 MPa, 1.7 MPa, 1.8 MPa, 2.0 MPa, 2.2 MPa or 2.5 MPa.

[0018] In a further preferred embodiment, the residence time of the material in the horizontal screw reactor is 20 to 150 minutes, preferably 30 to 110 minutes, for example 20 minutes, 40 minutes, 60 minutes, 80 minutes, 100 minutes, 120 minutes, 140 minutes or 150 minutes.

[0019] In a preferred embodiment, taking the horizontal screw reactor along the material flow direction as 0-100%, a feed inlet one is provided at the front end or at a position of 0-10% of the horizontal screw reactor, and a feed inlet two is provided at a position of 15-50%.

[0020] For example, the horizontal screw reactor has a feed inlet one at the front end or at a position of 0% (i.e., the very front), 2%, 4%, 6%, 8%, or 10%, and a feed inlet two at a position of 15%, 18%, 20%, 22%, 25%, 28%, 30%, 32%, 35%, 38%, 40%, 42%, 45%, 48%, or 50%.

[0021] In a further preferred embodiment, in step (1), the diamine is divided into two streams. The dicarboxylic acid is mixed with the first stream of diamine and fed into the feed inlet one of the horizontal screw reactor, and the second stream of diamine is fed into the feed inlet two of the horizontal screw reactor.

[0022] In a further preferred embodiment, the molar ratio of the dicarboxylic acid to all diamines is 0.995 to 0.909, preferably 0.995 to 0.975; and / or, the first diamine accounts for 90% to 100% (molar percentage or mass flow rate percentage) of all diamines, preferably 92% to 100%, and preferably does not contain 100%, for example, 90%, 92%, 94%, 96%, 98% or 99%.

[0023] In a preferred embodiment, the dicarboxylic acid and the first diamine are fed into the horizontal screw reactor by a feed pump.

[0024] In a further preferred embodiment, the outlet pressure of the first feed pump is 1.1 to 2.5 MPa, preferably 1.23 to 1.81 MPa, for example 1.1 MPa, 1.3 MPa, 1.5 MPa, 1.8 MPa, 20 MPa, 2.3 MPa or 2.5 MPa.

[0025] In a further preferred embodiment, the feed pump and the material pipeline involved are preferably both heat-traced, with a heat tracing temperature of 110-250°C, and the heat tracing method is any one of electric heat tracing, steam heat tracing, or heat transfer oil heat tracing.

[0026] In a preferred embodiment, taking the horizontal screw reactor along the material flow direction as 0-100%, an online pH meter is installed at a position of 15% to 50% (e.g., 15%, 20%, 25%, 30%, 35%, 40%, 45%, or 50%) of the horizontal screw reactor to detect the pH value of the material in the reactor.

[0027] In a further preferred embodiment, the flow rate of the second diamine is controlled to control the pH value in the horizontal screw reactor at a set value, which is between 7 and 7.5.

[0028] In a further preferred embodiment, the flow rate of the second diamine is controlled according to the following formula (1):

[0029]

[0030] Where, q m Q represents the mass flow rate of the second diamine, in g / s; V The total material volume (L, Mr) within the screw reactor is represented. 二胺 Indicates the molecular weight of the diamine; B = 10 2ΔpH ΔpH=pH 定 -pH 测 C is the temperature compensation parameter for pH value, and C is 0 to 4.62 (e.g., 0, 1, 2, 3, 4 or 4.62); kb1 represents the first dissociation constant of the diamine in water; τ represents the feeding time compensation, s, and τ is 0.5 to 1.4 (e.g., 0.5, 0.6, 0.8, 1, 1.2 or 1.4).

[0031] In a preferred embodiment, step (2) is performed inside a falling film evaporator.

[0032] In a further preferred embodiment, the temperature of the falling film evaporator is controlled to be 150-250°C, for example, 150°C, 160°C, 200°C, 220°C, 240°C or 250°C.

[0033] The material pipelines involved in the falling film evaporator all require heat tracing, with a heat tracing temperature of 150-250°C, and the heat tracing method can be any one of electric heat tracing, steam heat tracing, or thermal oil heat tracing.

[0034] In a further preferred embodiment, the refrigerant discharged from the horizontal screw reactor is reused as the heat medium for the falling film evaporator, saving energy consumption. At the same time, the falling film evaporator is preferably equipped with a heat insulation layer.

[0035] In a preferred embodiment, the pressure of the material entering the final polymerization reactor is controlled between atmospheric pressure and 0.4 MPaG.

[0036] In a preferred embodiment, the pressure of the final polymerization reactor is controlled to be 10 kPaA to 0.2 MPaG.

[0037] The final polymerization reactor maintains a certain pressure and exhausts steam. Its gas phase outlet is equipped with a pressure regulating valve to control the pressure inside the reactor. A condenser and a vacuum system are installed after the gas phase outlet.

[0038] In a further preferred embodiment, the temperature inside the final polymerization reactor is controlled to be 170–250°C, for example, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, or 250°C.

[0039] The final polymerization reactor is equipped with jacket heating as a supplement to the external circulation heating, and the heat medium is any one of heat transfer oil, high-pressure steam or molten salt.

[0040] In a preferred embodiment, in step (3), a portion of the discharge from the final polymerization reactor is recycled externally and then fed back into the final polymerization reactor, while a portion of the discharge is collected externally as a product.

[0041] In a further preferred embodiment, a portion of the material discharged from the external circulation is heated and then fed into the final polymerization reactor.

[0042] An external circulation heat exchanger is installed on the external circulation pipeline to heat part of the material discharged from the external circulation. Preferably, the outlet temperature of the external circulation heat exchanger is 172–257°C (preferably higher than the temperature inside the final polymerization reactor). The heat transfer medium is any one of heat transfer oil, high-pressure steam, or molten salt. The external circulation is carried out by a pump, and both the pump and the material pipelines involved in the final polymerization reactor require heat tracing. The heat tracing temperature is 170–250°C, and the heat tracing method is any one of electric heat tracing, steam heat tracing, or heat transfer oil heat tracing.

[0043] In a further preferred embodiment, the external circulation volume of the final polymerization reactor is 0.5 to 2 times the volume of the material inside the final polymerization reactor, and / or the external extraction volume of the final polymerization reactor is 0.02 to 0.2 times the volume of the material inside the final polymerization reactor.

[0044] For example, the external circulation volume of the final polymerization reactor is 0.5, 0.6, 0.8, 1, 1.2, 1.2, 1.4, 1.6, 1.8, or 2 times the volume of the material inside the final polymerization reactor, and / or the external extraction volume of the final polymerization reactor is 0.02, 0.04, 0.06, 0.08, 0.1, 0.12, 0.14, 0.16, 0.18, or 0.2 times the volume of the material inside the final polymerization reactor.

[0045] A second objective of this invention is to provide a system for the continuous production of long-chain polyamides, for carrying out the method described in one objective of this invention. The system includes a prepolymerization reactor, a falling film evaporator, and a final polymerization reactor connected in sequence, wherein the prepolymerization reactor is a horizontal screw reactor.

[0046] The horizontal screw reactor is equipped with a jacket for heat dissipation, and the refrigerant is either heat transfer oil or molten salt.

[0047] In a preferred embodiment, taking the horizontal screw reactor along the material flow direction as 0-100%, a feed inlet one is provided at the front end or at a position of 0-10% of the horizontal screw reactor, and a feed inlet two is provided at a position of 15-50%.

[0048] In a further preferred embodiment, a main feed pipeline for the diacid-diamine mixture is provided at one of the feed inlets for conveying the diacid melt and the first stream of diamine melt into the horizontal screw reactor; a diamine bypass feed pipeline is provided at the second feed inlet for conveying the second stream of diamine melt into the horizontal screw reactor.

[0049] In a further preferred embodiment, a feed pump is provided on the main feed line of the dicarboxylic acid-diamine mixture, and / or a flow meter is provided on the diamine bypass feed line.

[0050] In a preferred embodiment, taking the horizontal screw reactor along the material flow direction as 0-100%, an online pH meter is installed at a position of 15% to 50% (e.g., 15%, 20%, 25%, 30%, 35%, 40%, 45%, or 50%) of the horizontal screw reactor to detect the pH value of the material in the reactor.

[0051] In a preferred embodiment, the online pH meter is electrically connected to the flow meter and is used to adjust the flow rate of diamine on the diamine bypass feed line according to the pH value fed back by the online pH meter (preferably using formula (1)).

[0052] In a preferred embodiment, the system may further optionally include a dicarboxylic acid mixing vessel and a diamine mixing vessel.

[0053] In a further preferred embodiment, the discharge end of the dicarboxylic acid mixing vessel is connected to the main feed pipeline of the dicarboxylic acid-diamine mixture, and the discharge end of the diamine mixing vessel is connected to both the main feed pipeline of the dicarboxylic acid-diamine mixture and the diamine bypass feed pipeline.

[0054] In a preferred embodiment, a pressure regulating module is provided on the pipeline between the falling film evaporator and the final polymerization reactor for regulating the pressure of the material entering the final polymerization reactor.

[0055] In a preferred embodiment, an exhaust port and an exhaust pipeline are provided at the top or upper part of the final polymerization reactor. Preferably, a condenser is provided on the exhaust pipeline. More preferably, the other end of the exhaust pipeline is connected to a vacuum system.

[0056] In a further preferred embodiment, the final polymerization reactor is equipped with a jacket for heating, and the heat transfer medium is any one of heat transfer oil, high-pressure steam or molten salt.

[0057] In a preferred embodiment, an external circulation pipeline is provided between the discharge end (or bottom / lower part) of the final polymerization reactor and the top or upper part of the final polymerization reactor, so that some material is fed into the final polymerization reactor as feed after external circulation.

[0058] In a further preferred embodiment, an external circulation heat exchanger is provided on the external circulation pipeline for heating a portion of the externally circulated material; and / or, an external circulation pump is further provided on the external circulation pipeline.

[0059] In a further preferred embodiment, an external sampling pipeline is provided at the discharge end (or bottom / lower part) of the final polymerization reactor, or an external sampling bypass is provided on the external circulation pipeline for sampling out the product.

[0060] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values; these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. In the following, various technical solutions can, in principle, be combined with each other to obtain new technical solutions, which should also be considered as specifically disclosed herein.

[0061] Compared with the prior art, the present invention has the following beneficial effects:

[0062] The method and system simplify the production process of long-chain polyamides and optimize the production process. Not only is the process simple, but the continuous process also improves the stability of product quality between batches and reduces the product quality deviation between batches.

[0063] The method and system described above produce long-chain polyamides with a narrow molecular weight distribution, low viscosity, and stable batch-to-batch quality. In particular, compared to batch methods, the process offers a high degree of automation and high production efficiency. Attached Figure Description

[0064] Figure 1 A schematic diagram of the system described in this invention is shown.

[0065] exist Figure 1 The components are: 1. Dicarboxylic acid mixing vessel; 2. Diamine mixing vessel; 3. Prepolymerization vessel; 4. Final polycondensation vessel; 5. Falling film evaporator; 6. External circulation heat exchanger; 7. Pressure regulating module. Detailed Implementation

[0066] The present invention will now be described in detail with reference to specific embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention are still within the scope of protection of the present invention.

[0067] It should also be noted that the various specific technical features described in the following embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the various possible combinations will not be described separately in this invention.

[0068] Furthermore, various embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention. The resulting technical solutions are part of the original disclosure of this specification and also fall within the protection scope of the present invention.

[0069] Unless otherwise specified, the raw materials used in the examples and comparative examples are all disclosed in the prior art, such as those that can be directly purchased or prepared according to the preparation methods disclosed in the prior art.

[0070] In the embodiment, the method employs Figure 1 The system shown is used, and the system further includes a diacid mixing tank and a diamine mixing tank; the discharge end of the diacid mixing tank is connected to the main feed pipeline of the diacid-diamine mixture, and the discharge end of the diamine mixing tank is connected to the main feed pipeline of the diacid-diamine mixture and the diamine bypass feed pipeline, respectively.

[0071] The system further includes a prepolymerization reactor, a falling film evaporator, and a final polymerization reactor connected in sequence, wherein the prepolymerization reactor is a horizontal screw reactor. Taking the horizontal screw reactor as a flow rate of 0-100% along the material flow direction, a first inlet is provided at the front end or at a position of 0-10% of the flow rate, and a second inlet is provided at a position of 15-50% of the flow rate. A main feed pipeline for the diacid-diamine mixture is provided at the first inlet for conveying the diacid melt and a first stream of diamine melt into the horizontal screw reactor; a diamine bypass feed pipeline is provided at the second inlet for conveying a second stream of diamine melt into the horizontal screw reactor. A feed pump is provided on the main feed pipeline for the diacid-diamine mixture, and a flow meter is provided on the diamine bypass feed pipeline. Taking the horizontal screw reactor along the material flow direction as 0-100%, an online pH meter is installed at a position of 15-50% in the horizontal screw reactor to detect the pH value of the material in the reactor. The online pH meter is electrically connected to the flow meter and is used to adjust the flow rate of diamine on the diamine bypass feed line according to the pH value fed back by the online pH meter in combination with formula (1).

[0072] An external circulation pipeline is installed between the discharge end and the top of the final polymerization reactor, allowing a portion of the discharged material to be circulated externally before being fed back into the final polymerization reactor. An external circulation heat exchanger is installed on the external circulation pipeline to heat the portion of the discharged material. An external circulation pump is further installed on the external circulation pipeline. An external sampling pipeline, or an external sampling bypass, is installed at the discharge end of the final polymerization reactor for product sampling.

[0073] The method includes:

[0074] A dicarboxylic acid and water are mixed in a dicarboxylic acid mixing vessel and heated to melt, resulting in a dicarboxylic acid melt. A diamine is heated in a diamine mixing vessel and melted to obtain a diamine melt. The diamine melt is divided into two streams. The dicarboxylic acid melt is mixed with the first stream of diamine melt and fed into the feed inlet one of the horizontal screw reactor. The second stream of diamine melt is fed into the feed inlet two of the horizontal screw reactor.

[0075] The dicarboxylic acid and diamine undergo a prepolymerization reaction in a horizontal screw reactor. The prepolymerization product enters a falling film evaporator for evaporation and water removal. The effluent from the falling film evaporator enters a final polymerization reactor for continuous final polycondensation.

[0076] Part of the material in the final polymerization reactor is heated by an external circulation heat exchanger before being fed into the final polymerization reactor, and part of the material is sourced externally as a product; part of the material in the external circulation is heated before being fed into the final polymerization reactor.

[0077]

Example 1

[0078] Example 1 uses sebacic acid and decanoic acid to produce long-chain nylon. The purity of the raw materials is 99.0% and 98.5%, respectively, and the weight ratio of dicacic acid to water is 1:1.

[0079] use Figure 1 The system shown has a horizontal screw reactor with a temperature controlled at 180℃ and a pressure controlled at 1.3 MPaG. The residence time of the material in the horizontal screw reactor is controlled at 70 minutes. Feed inlet one is located at the front end of the reactor (0%), and feed inlet two is located at 15% of the reactor. The molar ratio of dicarboxylic acid to all diamines is 0.995, and the first diamine has a mass percentage of 98.6% of the total diamines. A pH meter is installed at 25% of the horizontal screw reactor to monitor the pH value in the reactor. The flow rate of the diamine branch is adjusted according to equation (1) to control the pH value in the reactor at 7.3. In equation (1), pH 定 The value is 7.3, C is 2.12, and Mr is 7.3. 二胺 The concentration is 172.312 g / mol, and kb1 is 3.76 × 10⁻⁶. -7 τ is 0.99. The temperature of the falling film evaporator is controlled at 185℃. The pressure of the material entering the final polymerization reactor is controlled at 0.2 MPaG, the temperature of the final polymerization kettle is controlled at 210℃, and the pressure is controlled at 0.15 MPaG. The outlet temperature of the external circulation heat exchanger is 230℃, the external circulation volume of the final polymerization reactor is twice the volume of the material inside the final polymerization reactor, and the external intake volume is 0.5 times the volume of the material inside the final polymerization reactor.

[0080] After 168 hours of operation, the number-average molecular weight of the long-chain polyamide product was 1.34 × 10⁻⁶. 4 The weight-average molecular weight is 1.97*10. 4 The PDI is 1.47 and the rheological viscosity is 920 Pa·s (240℃).

[0081] Samples were taken at 8h, 24h and 168h of operation to analyze product stability. The relative average deviations of number-average molecular weight, weight-average molecular weight, PDI, and rheological viscosity were ±1.07%, ±1.50%, ±2.55%, and ±1.09%, respectively, indicating good product quality stability.

[0082] This embodiment enables continuous production with no batch gaps, resulting in very stable product quality.

[0083]

Example 2

[0084] Example 2 uses decanediamine and dodecanoic acid to produce long-chain nylon with raw material purities of 99.0% and 97%, respectively, and the feed weight ratio of diacid and water is 1:1.02.

[0085] use Figure 1 The system shown has a horizontal screw reactor with a temperature controlled at 190℃ and a pressure controlled at 1.33 MPaG. The residence time of the material in the horizontal screw reactor is controlled at 100 minutes. Feed inlet one is located at the front end of the reactor (0%), and feed inlet two is located at 15% of the reactor. The molar ratio of dicarboxylic acid to all diamines is 0.992, and the first diamine has a mass percentage of 99.1% of the total diamines. A pH meter is installed at 25% of the horizontal screw reactor to monitor the pH value in the reactor. The flow rate of the diamine branch is adjusted according to equation (1) to control the pH value in the reactor at 7.4. In equation (1), pH 定 The value is 7.4, C is 1.42, and Mr... 二胺 The concentration is 172.312 g / mol, and kb1 is 3.76 × 10⁻⁶. -7 τ is 1.00. The temperature of the falling film evaporator is controlled at 195℃. The pressure of the material entering the final polymerization reactor is controlled at 0.15 MPaG, the temperature of the final polymerization kettle is controlled at 220℃, and the pressure is controlled at 0.12 MPaG. The outlet temperature of the external circulation heat exchanger is 240℃, the external circulation volume of the final polymerization reactor is 2.3 times the volume of the material inside the final polymerization reactor, and the external intake volume is 0.4 times the volume of the material inside the final polymerization reactor.

[0086] After 96 hours of operation, the number-average molecular weight of the long-chain polyamide product was 1.41 × 10⁻⁶. 4 The weight-average molecular weight is 2.31*10. 4 The PDI is 1.64 and the rheological viscosity is 1374 Pa·s (240℃).

[0087] Samples were taken at 8h, 24h and 96h of operation to analyze product stability. The number average molecular weight deviation was ±1.50%, the weight average molecular weight deviation was ±2.14%, the PDI deviation was ±3.22%, and the rheological viscosity deviation was ±2.56%, indicating that the product quality stability was good.

[0088] This embodiment enables continuous production with no batch gaps, resulting in very stable product quality.

[0089]

Example 3

[0090] Example 3 uses dodecanoic acid and dodecanoic acid to produce long carbon chain nylon. The purity of the raw materials is 96.5% and 97%, respectively, and the weight ratio of diacid to water is 1:1.05.

[0091] use Figure 1The system shown has a horizontal screw reactor with a temperature controlled at 195℃ and a pressure controlled at 1.38 MPaG. The residence time of the material in the horizontal screw reactor is controlled at 150 minutes. Feed inlet one is located at the front end of the reactor (0%), and feed inlet two is located at 15% of the reactor. The molar ratio of dicarboxylic acid to all diamines is 0.99, and the first diamine has a mass percentage of 99.7% of the total diamines. A pH meter is installed at 25% of the horizontal screw reactor to monitor the pH value in the reactor. The flow rate of the diamine branch is adjusted according to equation (1) to control the pH value in the reactor at 7.43. In equation (1), pH 定 The value is 7.43, C is 2.71, and Mr... 二胺 It is 200.36 g / mol, and kn1 is 7.98*10. -8 τ is 1.03. The temperature of the falling film evaporator is controlled at 205℃. The pressure of the material entering the final polymerization reactor is controlled at 0.12 MPaG, the temperature of the final polymerization kettle is controlled at 225℃, and the pressure is controlled at 0.10 MPaG. The outlet temperature of the external circulation heat exchanger is 245℃, the external circulation rate of the final polymerization reactor is 2.8 times the volume of the material inside the final polymerization reactor, and the external intake rate is 0.25 times the volume of the material inside the final polymerization reactor.

[0092] After 96 hours of operation, the number-average molecular weight of the long-chain polyamide product was 1.73 × 10⁻⁶. 4 The weight-average molecular weight is 2.97*10. 4 The PDI is 1.72, and the rheological viscosity is 3518 Pa·s (240℃).

[0093] Samples were taken at 8h, 24h and 96h of operation to analyze product stability. The number average molecular weight deviation was ±1.81%, the weight average molecular weight deviation was ±2.93%, the PDI deviation was ±4.19%, and the rheological viscosity deviation was ±3.66%, indicating that the product quality stability was good.

[0094] This embodiment enables continuous production with no batch gaps, resulting in very stable product quality.

[0095]

Example 4

[0096] Comparative Example 1 uses sebacic acid and decanoic acid to produce long-chain nylon with raw material purities of 99.0% and 98.5%, respectively, and the weight ratio of dicacic acid to water is 1:1.

[0097] use Figure 1The system shown features a horizontal screw reactor with a temperature controlled at 180°C and a pressure controlled at 1.3 MPaG, and a residence time of 70 minutes. The horizontal screw reactor has only one feed inlet at the front end. The molar ratio of diacid to diamine is 0.995. The falling film evaporator temperature is controlled at 200°C. The pressure of the material entering the final polymerization reactor is controlled at 0.2 MPaG, and the temperature of the final polymerization kettle is controlled at 210°C and the pressure at 0.15 MPaG. The outlet temperature of the external circulation heat exchanger is 230°C. The external circulation volume of the final polymerization reactor is twice the volume of the material inside the reactor, and the external intake volume is 0.5 times the volume of the material inside the reactor.

[0098] After 168 hours of operation, the number-average molecular weight of the long-chain polyamide product was 1.44E*10. 4 The weight-average molecular weight is 2.75*10. 4 The PDI is 1.91, and the rheological viscosity is 2496 Pa·s (240℃).

[0099] It can be seen that the product obtained in Comparative Example 1 has a significantly higher rheological viscosity despite similar molecular weight differences, making it difficult to process in later applications. The molecular weight distribution of the product obtained in Comparative Example 1 is significantly wider than that in Example 1, indicating that the degree of polymerization of the product is not as uniform as that in Example 1, resulting in quality differences. Moreover, for nylon, a wide molecular weight distribution means poor mechanical strength.

[0100]

Example 5

[0101] Comparative Example 2 uses decanediamine and dodecanoic acid to produce long-chain nylon with raw material purities of 99.0% and 97%, respectively, and the feed weight ratio of diacid to water is 1:1.02.

[0102] use Figure 1 The system shown has a horizontal screw reactor with a temperature controlled at 190°C and a pressure controlled at 1.33 MPaG. The residence time of the material in the horizontal screw reactor is controlled at 100 minutes. Feed inlet one is located at the front end of the reactor (0%), and feed inlet two is located at 15% of the reactor. The molar ratio of dicarboxylic acid to all diamines is 0.992, and the first diamine has a mass percentage of 99.1% of all diamines. A pH meter is installed at 25% of the horizontal screw reactor to monitor the pH value in the reactor. The flow rate of the diamine branch is adjusted according to formula (1) to control the pH value in the reactor at 7.4. The parameters in formula (1) are the same as in Example 2. The temperature of the falling film evaporator is controlled at 195°C. The pressure of the material entering the final polymerization reactor is controlled at 0.15 MPa, the temperature of the final polymerization reactor is controlled at 220°C, and the pressure is controlled at 0.12 MPaG. The final polymerization reactor has no external circulation; it relies entirely on jacket heating to maintain the internal temperature. The external heating volume is 0.4 times the volume of the material inside the final polymerization reactor.

[0103] After 96 hours of operation, the number-average molecular weight of the long-chain polyamide product was 7.1 × 10⁻⁶. 3 The weight-average molecular weight is 1.84*10. 4 The PDI is 2.59.

[0104] It can be seen that the product obtained in Comparative Example 2 not only has a significantly lower molecular weight than that in Example 2, but also a significantly wider molecular weight distribution. The wider molecular weight distribution compared to Example 2 indicates that the degree of polymerization of the product is not as uniform as in Example 2, resulting in a quality difference. Furthermore, for nylon, a wider molecular weight distribution implies lower mechanical strength.

[0105] The present invention has been described in detail above with reference to specific embodiments and exemplary examples; however, these descriptions should not be construed as limiting the present invention. Those skilled in the art will understand that various equivalent substitutions, modifications, or improvements can be made to the technical solutions and embodiments of the present invention without departing from the spirit and scope of the invention, and all such modifications and improvements fall within the scope of the present invention. The scope of protection of the present invention is defined by the appended claims.

Claims

1. A method for continuous production of long-chain polyamide, comprising: (1) The dicarboxylic acid and diamine are fed into the prepolymerization reactor for prepolymerization reaction. The prepolymerization reactor is a horizontal screw reactor. (2) The product of the prepolymerization reaction is evaporated to remove water. (3) The output of step (2) enters the final polymerization reactor for continuous final polycondensation.

2. The method according to claim 1, characterized in that, Step (1) includes: (1.1) mixing a diacid with water and heating to melt it to obtain a diacid melt, and heating a diamine to melt it to obtain a diamine melt; (1.2) feeding the diacid melt and the diamine melt into the horizontal screw reactor for a prepolymerization reaction; Preferably, in step (1.1), the weight ratio of the dicarboxylic acid to water is 1:0.5 to 1:1.5, and more preferably 1:0.7 to 1:1.2; More preferably, a protective gas is used for purging before step (1.1), the protective gas being selected from any one or more of carbon dioxide, nitrogen, and inert gases, the inert gas being selected from helium and / or argon.

3. The method according to claim 1, characterized in that, The temperature inside the horizontal screw reactor is controlled to be 150–300°C, preferably 180–250°C; and / or, The pressure inside the horizontal screw reactor is controlled to be 1.1–2.5 MPa, preferably 1.23–1.81 MPa; and / or, The residence time of the material in the horizontal screw reactor is 20 to 150 minutes, preferably 30 to 110 minutes.

4. The method according to claim 1, characterized in that, Taking the horizontal screw reactor along the material flow direction as 0-100%, a feed inlet one is provided at the front end or at a position of 0-10% of the horizontal screw reactor, and a feed inlet two is provided at a position of 15-50% of the horizontal screw reactor; Preferably, in step (1), the diamine is divided into two streams, and the dicarboxylic acid is mixed with the first stream of diamine and fed into the feed inlet one of the horizontal screw reactor, while the second stream of diamine is fed into the feed inlet two of the horizontal screw reactor. More preferably, the molar ratio of the dicarboxylic acid to all the diamines is 0.995 to 0.909, preferably 0.995 to 0.975; and / or, the first diamine accounts for 90% to 100% of all the diamines, preferably 92% to 100%.

5. The method according to claim 4, characterized in that, Taking the horizontal screw reactor along the material flow direction as 0-100%, an online pH meter is installed at a position of 15%-50% of the horizontal screw reactor to detect the pH value of the material in the reactor; preferably, the flow rate of the second diamine is controlled to maintain the pH value in the reactor at a set value, which is between 7 and 7.

5.

6. The method according to claim 1, characterized in that, Step (2) is performed in a falling film evaporator; preferably, the temperature of the falling film evaporator is controlled at 150–250°C; and / or, The pressure in the final polymerization reactor is controlled to be 10 kPaA to 0.2 MPaG; and / or, The temperature inside the final polymerization reactor is controlled at 170–250°C.

7. The method according to any one of claims 1 to 6, characterized in that, In step (3), part of the discharge from the final polymerization reactor is recycled externally and then fed back into the final polymerization reactor, while part of the discharge is collected externally as a product. Preferably, a portion of the material discharged from the external circulation is heated before being fed into the final polymerization reactor; More preferably, the external circulation volume of the final polymerization reactor is 0.5 to 2 times the volume of the material inside the final polymerization reactor, and / or the external extraction volume of the final polymerization reactor is 0.02 to 0.2 times the volume of the material inside the final polymerization reactor.

8. A system for continuous production of long-chain polyamides, for carrying out the method according to any one of claims 1 to 7, the system comprising a prepolymerization reactor, a falling film evaporator, and a final polymerization reactor connected in sequence, wherein, The prepolymer reactor is a horizontal screw reactor.

9. The system according to claim 8, characterized in that, Taking the horizontal screw reactor along the material flow direction as 0-100%, a feed inlet one is provided at the front end or at a position of 0-10% of the horizontal screw reactor, and a feed inlet two is provided at a position of 15-50% of the horizontal screw reactor; Preferably, a main feed pipeline for the diacid-diamine mixture is provided at one of the feed inlets for conveying the diacid melt and the first stream of diamine melt into the horizontal screw reactor; a diamine bypass feed pipeline is provided at the second feed inlet for conveying the second stream of diamine melt into the horizontal screw reactor. More preferably, a feed pump is provided on the main feed line of the dicarboxylic acid-diamine mixture, and / or a flow meter is provided on the diamine bypass feed line.

10. The system according to claim 9, characterized in that, Taking the horizontal screw reactor along the material flow direction as 0-100%, an online pH meter is installed at a position of 15%-50% of the horizontal screw reactor to detect the pH value of the material in the reactor; Preferably, the online pH meter is electrically connected to the flow meter and is used to adjust the flow rate of diamine on the diamine bypass feed line according to the pH value fed back by the online pH meter.

11. The system according to claim 9, characterized in that, The system may further optionally include a diacid mixing vessel and a diamine mixing vessel; preferably, the discharge end of the diacid mixing vessel is connected to the main feed pipeline of the diacid-diamine mixture, and the discharge end of the diamine mixing vessel is connected to the main feed pipeline of the diacid-diamine mixture and the diamine bypass feed pipeline, respectively.

12. The system according to any one of claims 8 to 11, characterized in that, An external circulation pipeline is provided between the discharge end of the final polymerization reactor and the top or upper part of the final polymerization reactor, so that some materials are fed into the final polymerization reactor after external circulation. Preferably, an external circulation heat exchanger is provided on the external circulation pipeline for heating part of the external circulation discharge; and / or, an external circulation pump is further provided on the external circulation pipeline; More preferably, an external sampling pipeline is provided at the discharge end of the final polymerization reactor, or an external sampling bypass is provided on the external circulation pipeline for sampling out the product.

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