Preparation device and preparation method of polyamide
Patent Information
- Application Number
- CN202311870516.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2023-12-29
- Publication Date
- 2025-07-01
Smart Images
Figure CN120227807A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to a preparation device and a preparation method for polyamide. Background Art
[0002] In industrial production, the salt solution polymerization method is mostly used for preparing diacid diamine type polyamide. In this method, the monomer diamine and diacid are first used to prepare a nylon salt solution with a certain concentration, and then the temperature and pressure are increased for the polymerization reaction. This method usually has the advantages of controllable polymerization temperature, avoiding local overheating, low system viscosity, and less gel content during polymerization. However, this method needs to be carried out under high-temperature and high-pressure process conditions; because a large amount of water is used as the reaction medium, a gas phase mainly composed of water vapor is formed inside the reaction system during the prepolymerization stage and the pre-polymerization stage of the raw materials for the polymerization reaction. This polymerization reaction usually uses a reaction kettle as the high-temperature and high-pressure reaction site, and the reaction kettle needs to be equipped with a sealing device to ensure its airtightness.
[0003] There are mainly two designs for the seal of the reaction kettle, a mechanical seal device and a magnetic seal device. A balance tank must be provided in the mechanical seal device; in the mechanical seal device, there are two non-connected cavities before and after the sealing ring. Generally, the sealing ring is a non-pressure-bearing component. The function of the balance tank is to balance the pressure in the cavities before and after the sealing ring to prevent the premature damage of the sealing ring; if a mechanical seal device is used to seal the reaction kettle, since the medium in the balance tank is usually a liquid, there is a risk that the liquid leaks into the reaction kettle and contaminates the materials in the kettle. Therefore, generally, the mechanical seal device is used in places with lower pressure and reaction systems with low requirements for material cleanliness.
[0004] In order to avoid contamination of the materials in the kettle and enable the reaction kettle to withstand a higher process pressure, a magnetic seal stirring device is usually installed on the reaction kettle. Generally, the conventional magnetic seal cavity is connected to the inside of the reaction kettle, and its sealing effect is achieved through a closed cavity, rather than the sealing ring in the mechanical seal device.
[0005] However, the reaction kettle equipped with a magnetic seal device has poor stability between product batches. In severe cases, it will cause the materials to solidify and damage the polymerization device, resulting in serious production accidents.
[0006] Therefore, there is an urgent need to provide a polyamide preparation device and method with high product stability and production safety. Summary of the Invention
[0007] In order to overcome the defects in the prior art that the reaction raw materials are easily contaminated, the stability of the products obtained when using a magnetic seal device is poor, and the production is unsafe, the present invention provides a polyamide preparation device and a preparation method. The present invention can effectively solve the problem of condensation reflux of gaseous water vapor in polyamide production, always maintain the uniformity of the materials in the kettle, thereby obtaining a product with stable performance and a polyamide product with high batch stability.
[0008] During the production process, the stability of the polyamide obtained from the reaction kettle equipped with a magnetic seal device is not good, and some batches cannot meet the required product performance requirements. During the process of studying the reasons for this result, the inventors found that since the magnetic seal cavity is connected to the reaction kettle, when the reaction kettle is heated and pressurized, water vapor in the reaction system will enter the magnetic seal cavity and condense to form condensed water, and then flow back to the reaction kettle, resulting in the problem that the temperature in the kettle cannot be accurately controlled, thereby causing fluctuations in other production process parameters. The fluctuations of these process parameters are the reasons for the poor stability between product batches. Seriously, the reflux of condensed water even causes the material to solidify and damage the polymerization device, resulting in very serious production accidents. The inventors solve the above technical problems through the following technical solutions:
[0009] The present invention provides a polyamide preparation device, which includes a magnetic seal element, a drive shaft and a reaction kettle. A cavity is formed inside the magnetic seal element, and the magnetic seal element is arranged on the top of the reaction kettle. One end of the drive shaft is arranged inside the reaction kettle, and the other end is arranged in the cavity;
[0010] The polyamide preparation device further includes a balance module, and the structure of the balance module is Structure One or Structure Two:
[0011] Structure One includes an intake pipe, a first exhaust pipe, and a pressure measuring element, a first signal processing element, and a first feedback element that are electrically connected in sequence. Both the first exhaust pipe and the intake pipe are communicated with the cavity. A first control valve and a second control valve are respectively arranged on the first exhaust pipe and the intake pipe. The pressure measuring element is arranged inside the reaction kettle and the cavity for respectively monitoring the internal pressures of the reaction kettle and the cavity. The first signal processing element is used to judge whether the pressure difference between the internal pressures of the reaction kettle and the cavity meets the set conditions. If it meets the set conditions, it is converted into a pressure control signal, or it is used to judge whether the internal pressure of the reaction kettle and / or the cavity reaches the rated pressure. If it does not reach the rated pressure, it is converted into a pressure control signal. The first feedback element is respectively connected to the first control valve and the second control valve, and is used to control the first control valve or the second control valve in real time according to the pressure control signal, so as to adjust the internal pressure of the cavity;
[0012] The second structure includes a second drainage pipe, a water content detection element, a second signal processing element, and a second feedback element that are electrically connected in sequence; the second drainage pipe communicates with the cavity, and a third control valve is provided on the second drainage pipe; the water content detection element is arranged inside the cavity and is used to detect the water content inside the cavity; the second signal processing element is used to judge whether the internal water content exceeds a threshold value and determine whether to send a water content control signal to the second feedback element; the second feedback element is connected to the third control valve and is used to control the opening and closing of the third control valve according to the water content control signal.
[0013] In the present invention, the pressure measuring element of the first structure can collect the internal pressures of the cavity in the magnetic seal element and the reactor, and judge whether the pressure difference between the two meets the set conditions through the signal processing element. If it meets the conditions, it is converted into a pressure control signal, and the opening and closing of the second control valve are controlled to adjust the intake volume of the protective gas to supplement the pressure of the cavity in the magnetic seal element to balance the pressures of the cavity in the magnetic seal element and the inside of the reactor; alternatively, the pressure measuring element of the first structure can also collect the internal pressures of the cavity in the magnetic seal element and the reactor, and judge whether the internal pressure of the reactor and / or the cavity reaches the rated pressure through the signal processing element. If it does not reach the rated pressure, it is converted into a pressure control signal, and the opening and closing of the second control valve are controlled to adjust the intake volume of the protective gas to supplement the pressure of the cavity in the magnetic seal element to make the reactor and / or the cavity reach the rated pressure.
[0014] In the present invention, the water content detection element of the second structure can collect the water content inside the cavity of the magnetic seal element and control the opening and closing of the first control valve to timely drain the condensed water in the cavity and prevent the condensed water from flowing back.
[0015] In the present invention, the magnetic seal element can be a magnetic cylinder in the art.
[0016] In some embodiments, the reactor is provided with a third exhaust pipe, and a fourth control valve is provided on the third exhaust pipe.
[0017] In a specific embodiment, the fourth control valve is connected to the first feedback element and is used to adjust the fourth control valve according to the pressure control signal, thereby controlling the internal pressure of the reactor to balance the internal pressure of the cavity and the internal pressure of the reactor.
[0018] In a specific embodiment, the fourth control valve is connected to the second feedback element and adjusts the fourth control valve according to the water content control signal, thereby controlling the internal pressure of the reactor.
[0019] The present invention provides a method for preparing polyamide, which comprises the following steps: successively concentrating, pre-polymerizing and post-polymerizing a polyamide salt solution, and the method for preparing polyamide adopts the polyamide preparation device as described above; and, the method for preparing polyamide further comprises one of the following Method 1 or Method 2:
[0020] Method 1: In the concentration step and the pre-polymerization step, monitor and compare the internal pressures of the reaction kettle and the cavity, and judge whether the difference between the internal pressures of the reaction kettle and the cavity meets the set conditions. If the set conditions are met, it is converted into a pressure control signal, or judge whether the internal pressure of the reaction kettle and / or the cavity reaches the rated pressure. If the rated pressure is not reached, it is converted into a pressure control signal; according to the pressure control signal, control the second control valve to adjust the flow rate of the protective gas entering the cavity to maintain the pressure balance between the cavity and the reaction kettle;
[0021] Method 2: In the concentration step and the pre-polymerization step, detect the internal water content of the cavity, judge whether the internal water content exceeds the threshold value, and determine whether a water content control signal needs to be sent to the second feedback element; according to the water content control signal, control the third control valve to discharge the liquid water in the cavity.
[0022] In the present invention, in Method 1, by controlling the pressure balance between the cavity and the reaction kettle, water vapor cannot enter the cavity and condense and flow back.
[0023] In the present invention, in Method 2, by timely discharging the water in the cavity, the condensation and reflux of water vapor are prevented.
[0024] In some embodiments, the set conditions include that the difference between the internal pressure of the reaction kettle and the internal pressure of the cavity is greater than or equal to 0.01 MPa.
[0025] In a specific embodiment, when the difference between the internal pressure of the reaction kettle and the internal pressure of the cavity is greater than or equal to 0.01 MPa, the comparison result of the pressure difference is converted into the control signal, and the first control valve or the second control valve is controlled.
[0026] In a specific embodiment, when the difference between the internal pressure of the reaction kettle and the internal pressure of the cavity is less than 0.01 MPa, no control signal is generated.
[0027] In some embodiments, when the liquid level inside the cavity is greater than or equal to a first preset liquid level, the water content signal is converted into the control signal, and the third control valve is controlled; preferably, the first preset liquid level is greater than or equal to 2%, where % is the percentage of the height of the first preset liquid level in the height of the cavity. For example, the first preset liquid level is greater than or equal to 3%, or greater than or equal to 5%.
[0028] In some embodiments, when the liquid level inside the cavity is less than a second preset liquid level, no control signal is generated; preferably, the second preset liquid level is less than 2%, where % is the percentage of the height of the second preset liquid level in the height of the cavity. For example, the second preset liquid level is less than 1%, or less than 0.5%.
[0029] In some embodiments, when the pressure in the cavity is less than the rated pressure, the second control valve is opened according to the pressure control signal, and the protective gas is introduced into the cavity to increase the pressure in the cavity to the pressure of the reaction kettle.
[0030] In some embodiments, when the water content in the cavity is greater than the threshold value, the third control valve is opened according to the control signal to discharge the liquid water in the cavity.
[0031] In some embodiments, the rated pressures of the cavity and the reaction kettle are set to 1.0 MPa. When the internal pressures of the cavity and the reaction kettle are lower than 1.0 MPa, the second control valve is automatically adjusted.
[0032] In some embodiments, the pressure relief rate of the fourth control valve on the third exhaust pipeline of the reaction kettle is 0.5 - 3.5 MPa / h, for example, 2.5 MPa / h.
[0033] In some embodiments, the polyamide salt solution is obtained by a salt formation reaction of diamine and diacid.
[0034] In a specific embodiment, the temperature of the salt formation reaction is 150°C or below.
[0035] In a specific embodiment, the molar ratio of the diamine monomer to the diacid monomer is (0.8 - 1.2):1, preferably (0.9 - 1.1):1.
[0036] In a specific embodiment, the diacid monomer is one or more of succinic acid, glutaric acid, adipic acid, suberic acid, sebacic acid, dodecanedioic acid, terephthalic acid, and isophthalic acid, preferably one or more of adipic acid, sebacic acid, or dodecanedioic acid.
[0037] In a specific embodiment, the diamine monomer is one or more of m-xylylenediamine, terephthalic acid, o-xylylenediamine, sebac diamine, cadaverine, dodecane diamine, hexamethylene diamine, and butanediamine.
[0038] In some embodiments, the concentration of the polyamide salt solution is 30-70 wt.%.
[0039] In some embodiments, the pH value of the polyamide salt solution is 5.8-9.2, preferably 7.0-8.5.
[0040] In the present invention, through the above salt formation method, not only is it convenient to control the molar ratio of diacid and diamine, but the polyamide salt solution is also in a homogeneous state with low viscosity, which is convenient for pipeline transportation of the salt solution, and the feeding is convenient and easy to operate.
[0041] In some embodiments, the concentration temperature is 150-210 °C, such as 160 °C or 180 °C.
[0042] In some embodiments, the concentration pressure is 0.3-1.0 MPa, such as 0.6 MPa or 0.8 MPa.
[0043] In some embodiments, the concentration of the polyamide salt solution after the concentration is 60-85 wt.%.
[0044] In the present invention, through the concentration, water in the system can be discharged at a lower temperature, reducing energy consumption and operation complexity, and can shorten the time for subsequent material heating and the drainage cycle, further improving the efficiency of the entire process.
[0045] In some embodiments, in Method 1, the protective gas includes nitrogen.
[0046] In some embodiments, in Method 2, the third control valve adopts an intermittent opening and closing mode; preferably, the intermittent time interval is 5 min.
[0047] In some embodiments, the pre-polymerization temperature is 210-260 °C, such as 230 °C or 255 °C.
[0048] In some embodiments, the pre-polymerization pressure is 0.5-3.5 MPa, such as 1.9 MPa or 2.8 MPa.
[0049] In some embodiments, the pre-polymerization time is 0.5-3 h, such as 1 h.
[0050] In some embodiments, the pre-polymerization includes depressurizing the reaction kettle.
[0051] In a specific embodiment, the pressure relief rate is 0.5 - 3.5 MPa / h, such as 2.0 MPa / h or 2.5 MPa / h.
[0052] In a specific embodiment, after the pressure relief, the pressure in the reactor is normal pressure.
[0053] In a specific embodiment, the temperature of the post-polymerization is 250 - 310 °C, such as 300 °C.
[0054] In the present invention, it is determined whether polymerization needs to be carried out under vacuum conditions according to the viscosity of the final product.
[0055] In a specific embodiment, the pressure of the post-polymerization is normal pressure; or, the pressure of the post-polymerization is -0.03 - -0.06 MPa.
[0056] In a specific embodiment, the time of the post-polymerization is 0.5 - 2 h, such as 0.5 h.
[0057] In the present invention, it is judged whether the viscosity of the post-polymerization product meets the requirements through a viscosity detection device; if it has reached, the pressure in the kettle is flushed to normal pressure or slightly positive pressure with an inert gas, the discharge valve at the bottom of the reactor is opened to discharge the material, and then the material is cast through a casting head, cooled and solidified in a cooling tank, sliced and granulated by a granulator, screened, dried and then packaged to complete the production.
[0058] In a specific embodiment, after the step of the post-polymerization is completed, the preparation method of the polyamide further sequentially includes: casting, cooling and pelletizing, screening, and drying.
[0059] In the present invention, those skilled in the art should know that polyamide can be called nylon, and resin is a general term for plastics and can refer to polyamide / nylon.
[0060] In the present invention, those skilled in the art should know that the magnetic seal element can be a magnetic cylinder.
[0061] On the basis of conforming to the common knowledge in the art, the above preferred conditions can be combined arbitrarily to obtain various preferred examples of the present invention.
[0062] The reagents and raw materials used in the present invention are all commercially available.
[0063] The positive and progressive effects of the present invention are as follows:
[0064] The present invention can effectively solve the problem of condensation and reflux of gaseous water vapor in the production of polyamide, always maintain the uniformity of the materials in the kettle, thereby obtaining a product with stable performance and a polyamide product with high batch stability. Description of the Drawings
[0065] Figure 1Schematic diagram of the polyamide preparation device in Embodiment 1 of this application.
[0066] Figure 2 Schematic diagram of the polyamide preparation device in Embodiment 2 of this application.
[0067] Figure 3 Schematic diagram of the polyamide preparation device in Comparative Example 1.
[0068] Explanation of reference numerals:
[0069] Magnetic seal element 1
[0070] Drive shaft 2
[0071] Reaction kettle 3
[0072] Cavity 4
[0073] Intake pipeline 1001
[0074] First exhaust pipeline 1002
[0075] Second exhaust pipeline 1003
[0076] Third exhaust pipeline 1004
[0077] Pressure measuring element 101
[0078] First signal processing element 102
[0079] First feedback element 103
[0080] First control valve 104
[0081] Second control valve 105
[0082] Third control valve 106
[0083] Fourth control valve 107
[0084] Water content detection element 108
[0085] Second signal processing unit 109
[0086] Second feedback element 110. Detailed implementation manners
[0087] The present invention will be further described below by way of examples, but the present invention is not limited to the scope of the described examples. For the experimental methods without specific conditions in the following examples, they are carried out according to conventional methods and conditions, or selected according to the product specifications.
[0088] Example 1
[0089] Figure 1The figure is a schematic structural view of the preparation device for the polyamide of this embodiment. The preparation device for the polyamide includes a magnetic seal element 1, a drive shaft 2, and a reaction kettle 3. A cavity 4 is formed inside the magnetic seal element 1, and the magnetic seal element 1 is arranged on the top of the reaction kettle 3. One end of the drive shaft 2 is arranged inside the reaction kettle 3, and the other end is arranged in the cavity 4;
[0090] The preparation device for the polyamide further includes a balance module, and the balance module is Structure One:
[0091] Structure One includes an intake pipeline 1001, a first exhaust pipeline 1002, and a pressure measuring element 101, a first signal processing element 102, and a first feedback element 103 that are electrically connected in sequence; both the first exhaust pipeline 1002 and the intake pipeline 1001 are communicated with the cavity 4, and a first control valve 104 and a second control valve 105 are respectively arranged on the first exhaust pipeline 1002 and the intake pipeline 1001; the pressure measuring element 101 is respectively arranged inside the reaction kettle 3 and the cavity 4 for respectively monitoring the internal pressures of the reaction kettle 3 and the cavity 4; the first signal processing element 102 is used to judge whether the difference between the internal pressures of the reaction kettle 3 and the cavity 4 meets the set condition, that is, is greater than or equal to 0.01 MPa. If the set condition is met, it is converted into a pressure control signal, or is used to judge whether the internal pressure of the reaction kettle 3 and / or the cavity 4 reaches the rated pressure. If the rated pressure is not reached, it is converted into a pressure control signal; the first feedback element 103 is respectively connected to the first control valve 104 and the second control valve 105, and is used to control the first control valve 104 or the second control valve 105 in real time according to the pressure control signal, so as to adjust the internal pressure of the cavity 4;
[0092] The reaction kettle 3 is provided with a third exhaust pipeline 1004, and a fourth control valve 107 is arranged on the third exhaust pipeline 1004; the fourth control valve 107 is connected to the first feedback element 103, and is used to adjust the fourth control valve 107 according to the pressure control signal, so as to control the internal pressure of the reaction kettle 3 and balance the internal pressure of the cavity 4 with the internal pressure of the reaction kettle 3.
[0093] Examples 2 - 6
[0094] Example 2 is a method for preparing polyamide. It uses the preparation device for polyamide in Example 1 to prepare PA6T / 66 resin, and includes the following steps:
[0095] S1. Salt formation
[0096] Under the condition of 120 °C, a PA6T / 66 salt solution with a concentration of 54 wt% is prepared (test condition: the pH value of the PA6T / 66 salt solution at 25 °C and a concentration of 10 wt% is 7.4), which is used to prepare PA6T / 66 resin;
[0097] S2. Concentration
[0098] After adding the PA6T / 66 salt solution into the reaction kettle 3, the temperature of the materials in the reaction kettle 3 is raised to 180°C through the heat medium in the jacket. During the heating process, along with the increase in the pressure in the reaction kettle 3, at this time, the pressure balance module starts to operate synchronously; its operation mode is to use the pressure sensor connected to the reaction kettle 3 as the pressure measuring element 101 to detect the pressure changes in the cavity 4 and the reaction kettle 3 in real time. When the difference between the internal pressure of the reaction kettle and the internal pressure of the cavity is greater than or equal to 0.01 MPa, an instruction is given to control the opening of the second control valve, nitrogen is filled into the cavity 4 of the magnetic cylinder, and the quantity is measured. At the same time, the internal pressure change of the magnetic cylinder is detected to make the pressure in the reaction kettle 3 and the pressure in the magnetic cylinder remain synchronized. During the process of raising the PA6T / 66 salt solution to 180°C, the pressure in the reaction kettle 3 gradually rises to 0.8 MPa. Under the adjustment of the balance module, the pressure in the magnetic cylinder also maintains the same rising rate as the pressure in the reaction kettle 3 and rises to 0.8 MPa, and the atmosphere in the magnetic cylinder is nitrogen and no condensed water is formed (as shown by the liquid water detection device);
[0099] Under the condition of constant pressure of 0.8 MPa, the salt solution concentration is increased from 54 wt% to 66 wt%, and the data shows that no condensed water is formed in the magnetic cylinder.
[0100] S3. Pre-polymerization
[0101] The temperature of the materials is raised to 230°C and kept constant for 1 h, the pressure in the kettle is controlled to be constant. When the difference between the internal pressure of the reaction kettle and the internal pressure of the cavity is greater than or equal to 0.01 MPa, an instruction is given to control the opening of the second control valve. Through the balance module, the pressure in the magnetic cylinder is the same as that in the kettle, both being 2.8 MPa. After the constant temperature and constant pressure are over, the temperature in the kettle is gradually raised to 295°C while keeping the pressure in the kettle constant. Under the action of the pressure balance module, the pressure in the magnetic cylinder remains synchronized, and it is proved by experiments that no condensed water is generated.
[0102] When the temperature in the kettle is raised to 295°C, the pressure in the kettle starts to be gradually reduced at a pressure relief rate of 2.5 MPa / h. Under the action of the balance module, the nitrogen in the magnetic cylinder is discharged through the exhaust pipeline, and the pressure in the magnetic cylinder is gradually reduced, and no condensed water is formed in the magnetic cylinder.
[0103] S4. Post-polymerization
[0104] When it is depressurized to atmospheric pressure, the temperature in the kettle is controlled to be steadily raised to 300°C, and no temperature fluctuation occurs during the process. After reacting for 30 min at this temperature and atmospheric pressure, the reaction ends. The molten materials are extruded from the casting head by nitrogen, granulated, screened, dried, and packaged through the cooling water tank to obtain the final PA6T / 66 product.
[0105] Examples 3-6 adopted the same process solutions (including preparation devices and preparation methods) as those in Example 2, which were repeated tests of Example 2.
[0106] Comparative Examples 1-5
[0107] Figure 3 It is a schematic structural diagram of the preparation device for the polyamide of Comparative Examples 1-5. The preparation device for this polyamide is a conventional reaction device in the art, which does not contain a pressure balance module, and other structures are the same as those in Example 3.
[0108] Comparative Example 1 is a preparation method for polyamide, which uses Figure 3 the preparation device for polyamide to prepare PA6T / 66 resin, including the following steps:
[0109] S1. Salt formation
[0110] Under the condition of 120 °C, a PA6T / 66 salt solution with a concentration of 54 wt% was prepared (test condition: the pH value of the PA6T / 66 salt solution at 25 °C and a concentration of 10 wt% was 7.4), which was used to prepare PA6T / 66 resin;
[0111] S2. Concentration
[0112] After adding the PA6T / 66 salt solution to the reaction kettle, the temperature of the materials in the reaction kettle was raised to 180 °C through the heat medium in the jacket. During the temperature increase process, as the pressure in the kettle gradually increased to 0.8 MPa, due to the absence of a balance module, the temperature vs time curve was more tortuous compared with that in the example during the temperature increase process, and there were occasional fluctuations in temperature rise and fall.
[0113] Under the condition of constant pressure at 0.8 MPa, the salt solution concentration was increased from 54 wt% to 66 wt%. Similarly, the temperature vs time curve was more tortuous compared with those in Examples 2-6, and there were occasional fluctuations in temperature rise and fall, and the fluctuation situation intensified, with an amplitude reaching ±5 °C.
[0114] S3. Pre-polymerization
[0115] The temperature of the materials was raised to 230 °C and kept at a constant temperature for 1 h, and the pressure in the kettle was controlled to be constant at 2.8 MPa. After the constant temperature and constant pressure ended, the temperature in the kettle was gradually raised to 295 °C, and the pressure in the kettle was kept constant at 2.8 MPa during the temperature increase process.
[0116] When the temperature in the kettle reached 295 °C, the pressure in the kettle was gradually reduced at a pressure relief rate of 2.5 MPa / h.
[0117] S4. Post-polymerization
[0118] When the pressure is released to atmospheric pressure, control the temperature in the kettle to steadily rise to 300 °C. After reacting for 30 minutes at this temperature and atmospheric pressure, end the reaction. Press the molten material out of the casting head through nitrogen to form a cast tape, and then granulate, screen, dry, and package it after cooling in a cooling water tank to obtain the final PA6T / 66 product.
[0119] Comparative Examples 2-5 adopt the same process scheme as Comparative Example 1 (including the preparation device and preparation method), which is a repeated test of Comparative Example 1.
[0120] Example 7
[0121] Figure 2 It is a schematic structural diagram of the preparation device of the polyamide in this example. The preparation device of the polyamide includes a magnetic seal element 1, a drive shaft 2, and a reaction kettle 3. A cavity 4 is provided inside the magnetic seal element 1, and the magnetic seal element 1 is arranged on the top of the reaction kettle 3. One end of the drive shaft 2 is arranged inside the reaction kettle 3, and the other end is arranged in the cavity 4;
[0122] The preparation device of the polyamide further includes a balance module, and the structure of the balance module is Structure Two:
[0123] Structure Two includes a second exhaust pipeline 1003, and a water content detection element 108, a second signal processing element, and a second feedback element that are electrically connected in sequence; the second drainage pipeline is communicated with the cavity 4, and a third control valve 106 is provided on the second exhaust pipeline 1003; the water content detection element 108 is arranged inside the cavity 4 for detecting the water content inside the cavity 4; the second signal processing element is used to judge whether the internal water content exceeds the threshold, that is, is greater than or equal to 2% (the percentage of the height of the first preset liquid level in the height of the cavity), and determine whether to send a water content control signal to the second feedback element; the second feedback element is connected to the third control valve 106 for controlling the opening and closing of the third control valve 106 according to the water content control signal.
[0124] The reaction kettle 3 is provided with a third exhaust pipeline 1004, and a fourth control valve 107 is provided on the third exhaust pipeline 1004; the fourth control valve 107 is connected to the second feedback element, and according to the water content control signal, the fourth control valve 107 is adjusted to control the internal pressure of the reaction kettle 3.
[0125] Examples 8-12
[0126] Example 8 is a preparation method of polyamide, which uses the preparation device of polyamide in Example 3 to prepare MXD6 resin, including the following steps:
[0127] S1. Salt formation
[0128] Under the condition of 90 °C, an MXD6 salt solution with a concentration of 51 wt% was prepared (test condition: the pH value of the MXD6 salt solution at 25 °C and a concentration of 10 wt% was 6.9), which was used to prepare MXD6 resin;
[0129] S2. Concentration
[0130] After adding the MXD6 salt solution to the reaction kettle 3, the temperature of the material in the reaction kettle 3 was raised to 160 °C through the heat medium in the jacket. During the heating process, the pressure in the reaction kettle 3 gradually increased to 0.6 MPa. During this process, the water content in the cavity 4 was measured. When the liquid level inside the cavity 4 was greater than or equal to the first preset liquid level, the water content signal was converted into the control signal, and the third control valve was controlled to intermittently drain the magnetic cylinder, with an interval of 5 min to drain the water in the magnetic cylinder; among them, the first preset liquid level was greater than or equal to 2%, and % was the percentage of the height of the first preset liquid level in the height of the cavity.
[0131] Under the condition of constant pressure at 0.6 MPa, the salt solution concentration was increased from 51 wt% to 70 wt%. The water content in the cavity 4 was measured. When the liquid level inside the cavity 4 was greater than or equal to the first preset liquid level, the water content signal was converted into the control signal, and the third control valve was controlled. This process was accompanied by intermittent exhaust operations of the magnetic cylinder, with an interval of 5 min to drain the water in the magnetic cylinder.
[0132] S3. Prepolymerization
[0133] The temperature of the material was raised to 210 °C and kept constant for 1 h, and the pressure in the kettle was controlled to be constant at 1.9 MPa. This process was accompanied by intermittent exhaust operations of the magnetic cylinder, with an interval of 5 min to drain the water in the magnetic cylinder. After the constant temperature and constant pressure ended, the temperature in the kettle was gradually raised to 255 °C while keeping the pressure in the kettle constant at 1.9 MPa; the water content in the cavity 4 was measured. When the liquid level inside the cavity 4 was greater than or equal to the first preset liquid level, i.e., 2% (where % was the percentage of the height of the first preset liquid level in the height of the cavity), the water content signal was converted into the control signal, and the third control valve was controlled. This process was accompanied by intermittent exhaust operations of the magnetic cylinder, with an interval of 5 min to drain the water in the magnetic cylinder.
[0134] When the temperature in the kettle was raised to 255 °C, the pressure in the kettle was gradually reduced at a pressure relief rate of 2.0 MPa / h. This process was accompanied by intermittent exhaust operations of the magnetic cylinder, with an interval of 5 min to drain the water in the magnetic cylinder.
[0135] S4. Post-polymerization
[0136] When it is depressurized to normal pressure, the temperature in the kettle is controlled to rise steadily to 260 °C, and there is no temperature fluctuation during the process. After reacting for 30 minutes at this temperature and normal pressure, the reaction is terminated. The molten material is extruded from the casting head as a cast tape by nitrogen, and after being cooled by a cooling water tank, it is pelletized, screened, dried, and packaged to obtain the final MXD6 product.
[0137] Examples 9-12 adopt the same process scheme as Example 8 above (including the preparation device and preparation method), and are repeated tests of Example 8.
[0138] Comparative Examples 6-10
[0139] Comparative Example 6 is a preparation method of polyamide, which uses the polyamide preparation device of Comparative Example 1 to prepare MXD6 resin, and includes the following steps:
[0140] S1. Salt formation
[0141] Under the condition of 90 °C, an MXD6 salt solution with a concentration of 51 wt% is prepared (test condition: the pH value of the MXD6 salt solution is 6.9 at 25 °C and a concentration of 10 wt%), which is used to prepare MXD6 resin;
[0142] S2. Concentration
[0143] After adding the MXD6 salt solution to the reaction kettle, the temperature of the material in the reaction kettle is raised to 160 °C through the heat medium in the jacket. During the heating process, the pressure in the kettle gradually rises to 0.6 MPa.
[0144] Under the condition of constant pressure of 0.6 MPa, the salt solution concentration is increased from 51 wt% to 70 wt%.
[0145] S3. Pre-polymerization
[0146] The material temperature is raised to 220 °C and kept constant for 1 h, and the pressure in the kettle is controlled to be constant at 1.9 MPa. After the constant temperature and constant pressure are completed, the temperature in the kettle is gradually raised to 255 °C, while keeping the pressure in the kettle constant at 1.9 MPa.
[0147] When the temperature in the kettle rises to 255 °C, the pressure in the kettle is gradually reduced at a pressure relief rate of 2.0 MPa / h.
[0148] S4. Post-polymerization
[0149] When it is depressurized to normal pressure, the temperature in the kettle is controlled to rise steadily to 260 °C. After reacting for 30 minutes at this temperature and normal pressure, the reaction is terminated. The molten material is extruded from the casting head as a cast tape by nitrogen, and after being cooled by a cooling water tank, it is pelletized, screened, dried, and packaged to obtain the final MXD6 product.
[0150] Effect Example 1
[0151] This performance example tests the performance of the polyamide products in Examples 2-6, 8-12 and Comparative Examples 1-5, 6-10.
[0152] The following are the test methods for various performance evaluations:
[0153] 1) Relative viscosity: The polymer is dissolved in concentrated sulfuric acid and tested in a constant temperature water bath at 25 °C according to standard ISO 307.
[0154] 2) Mn and PDI: Tested using a gel permeation chromatography (GPC) hexafluoroisopropanol system.
[0155] 3) Melting point Tm: Tested according to standard ISO11357. Specific steps: Differential scanning calorimeter (DSC) heating program: Heat at a rate of 10 °C / min to 350 °C, hold for 5 min, then cool at a rate of 10 °C / min to 25 °C, hold for 5 min, and then heat at a rate of 10 °C / min to 350 °C. The temperature corresponding to the endothermic peak of the second heating curve is the melting point Tm.
[0156] 4) Terminal amino or carboxyl groups: Quantitatively analyzed and measured by potentiometric titration. Specific steps: Use an automatic potentiometric titrator to titrate the content of terminal amino or carboxyl groups. Take 1 g of the polymer and dissolve it in a hexafluoroisopropanol solution. After the sample is completely dissolved, use a calibrated hydrochloric acid standard solution or KOH-ethanol solution to titrate and test the content of terminal amino or carboxyl groups.
[0157] 5) Chromaticity / YI: Tested according to standard HG / T 3862 Test Method for Yellow Index of Plastics.
[0158] 6) Tensile properties: Test tensile properties such as tensile strength, tensile modulus and elongation at break according to standard GB / T 1040.2 / 1A.
[0159] 7) Flexural properties: Test properties such as flexural strength and flexural modulus of the sample according to standard GB / T 9341.
[0160] 8) Yield rate: The product yield rate is obtained by comparing the actual obtained good products with the theoretically obtained good products.
[0161] The polyamides prepared in Examples 2-6, Examples 8-12 and Comparative Examples 1-5, 6-10 were tested respectively. The performance of the polyamide products in Examples 2-6 is shown in Table 1; the performance of the polyamide products in Comparative Examples 1-5 is shown in Table 2; the performance of the polyamide products in Examples 8-12 is shown in Table 3; the performance of the polyamide products in Comparative Examples 6-10 is shown in Table 4.
[0162] Table 1
[0163]
[0164] As can be seen from the data in Table 1, using the equipment and method, the qualified product rate of the PA6T / 66 products produced in Examples 2-6 is relatively high. The performances among the samples of 5 batches are very close, with small errors, and it has high stability between batches.
[0165] Table 2
[0166]
[0167] As can be seen from Table 2, there are large fluctuations in temperature, pressure and torque during the concentration stage, constant temperature and pressure stage and pressure relief stage. This results in large fluctuations in the qualified product rate, relative viscosity, terminal amino group, YI value and tensile strength of the products in Comparative Examples 1-5. The average qualified product rate is relatively low compared with that of the examples.
[0168] Table 3
[0169]
[0170] As can be seen from the data in Table 3, using the equipment and method, the qualified product rate of the MXD6 products produced in Examples 8-12 is relatively high. The performances among the samples of 5 batches are very close, with small errors, and it has high stability between batches.
[0171] Table 4
[0172]
[0173] As can be seen from Table 4, there are large fluctuations in temperature, pressure and torque during the concentration stage, constant temperature and pressure stage and pressure relief stage. This results in large fluctuations in the qualified product rate, relative viscosity, terminal amino group, YI value and tensile strength of the products in Comparative Examples 6-10. The average qualified product rate is relatively low compared with that of the examples.
Claims
1. A preparation device for polyamide, which comprises a magnetic seal element, a drive shaft and a reaction kettle. A cavity is formed inside the magnetic seal element, and the magnetic seal element is arranged on the top of the reaction kettle. One end of the drive shaft is arranged inside the reaction kettle, and the other end is arranged in the cavity; characterized in that: The preparation device for polyamide further comprises a balance module, and the structure of the balance module is Structure One or Structure Two: Structure One includes an intake pipeline, a first exhaust pipeline, and a pressure measuring element, a first signal processing element and a first feedback element that are electrically connected in sequence; both the first exhaust pipeline and the intake pipeline are communicated with the cavity, and a first control valve and a second control valve are respectively arranged on the first exhaust pipeline and the intake pipeline; the pressure measuring element is arranged inside the reaction kettle and the cavity for respectively monitoring the internal pressures of the reaction kettle and the cavity; the first signal processing element is used for judging whether the difference between the internal pressures of the reaction kettle and the cavity meets the set conditions. If the set conditions are met, it is converted into a pressure control signal, or for judging whether the internal pressure of the reaction kettle and / or the cavity reaches the rated pressure. If the rated pressure is not reached, it is converted into a pressure control signal; the first feedback element is respectively connected to the first control valve and the second control valve, and is used for controlling the first control valve or the second control valve in real time according to the pressure control signal, so as to adjust the internal pressure of the cavity; Structure Two includes a second drainage pipeline, and a water content detection element, a second signal processing element and a second feedback element that are electrically connected in sequence; the second drainage pipeline is communicated with the cavity, and a third control valve is arranged on the second drainage pipeline; the water content detection element is arranged inside the cavity for detecting the internal water content of the cavity; the second signal processing element is used for judging whether the internal water content exceeds the threshold value and determining whether to send a water content control signal to the second feedback element; the second feedback element is connected to the third control valve and is used for controlling the opening and closing of the third control valve according to the water content control signal.
2. The polyamide preparation apparatus according to claim 1, characterized in that, The reaction kettle is provided with a third exhaust pipeline, and a fourth control valve is arranged on the third exhaust pipeline; Preferably, the fourth control valve is connected to the first feedback element and is used for adjusting the fourth control valve according to the pressure control signal, so as to control the internal pressure of the reaction kettle and make the internal pressure of the cavity balance with the internal pressure of the reaction kettle; or, Preferably, the fourth control valve is connected to the second feedback element and adjusts the fourth control valve according to the water content control signal, so as to control the internal pressure of the reaction kettle.
3. A method for preparing a polyamide, which comprises the following steps: successively concentrating, pre-polymerizing and post-polymerizing a polyamide salt solution, characterized in that, The polyamide preparation method uses the polyamide preparation device as described in claim 1 or 2; and the polyamide preparation method further includes the following Method One or Method Two: Method 1: In the concentration step and the prepolymerization step, monitor and compare the internal pressures of the reaction kettle and the cavity, and determine whether the difference between the internal pressures of the reaction kettle and the cavity meets the set conditions. If the set conditions are met, convert it into a pressure control signal. Alternatively, determine whether the internal pressure of the reaction kettle and / or the cavity reaches the rated pressure. If the rated pressure is not reached, convert it into a pressure control signal; according to the pressure control signal, control the second control valve to adjust the flow rate of the protective gas entering the cavity to maintain the pressure balance between the cavity and the reaction kettle. Method 2: In the concentration step and the prepolymerization step, detect the internal water content of the cavity, determine whether the internal water content exceeds the threshold, and determine whether a water content control signal needs to be sent to the second feedback element; according to the water content control signal, control the third control valve to discharge the liquid water in the cavity.
4. The method for preparing a polyamide according to claim 3, characterized in that, The set conditions include that the difference between the internal pressure of the reaction kettle and the internal pressure of the cavity is greater than or equal to 0.01 MPa. Preferably, when the difference between the internal pressure of the reaction kettle and the internal pressure of the cavity is greater than or equal to 0.01 MPa, convert the comparison result of the pressure difference into the pressure control signal and control the second control valve. Preferably, when the difference between the internal pressure of the reaction kettle and the internal pressure of the cavity is less than 0.01 MPa, no pressure control signal is generated.
5. The method for preparing a polyamide according to claim 3, characterized in that, When the liquid level inside the cavity is greater than or equal to the first preset liquid level, convert the water content signal into the control signal and control the third control valve; preferably, the first preset liquid level is greater than or equal to 2%, where % is the percentage of the height of the first preset liquid level in the height of the cavity. For example, the first preset liquid level is greater than or equal to 3%, or greater than or equal to 5%. Or, when the liquid level inside the cavity is less than the second preset liquid level, no control signal is generated; preferably, the second preset liquid level is less than 2%, where % is the percentage of the height of the second preset liquid level in the height of the cavity. For example, the second preset liquid level is less than 1%, or less than 0.5%.
6. The method for preparing a polyamide according to claim 3, characterized in that, When the pressure of the cavity is less than the rated pressure, open the second control valve according to the pressure control signal to introduce the protective gas into the cavity to increase the pressure of the cavity to the pressure of the reaction kettle. Or, when the water content of the cavity is greater than the threshold, open the third control valve according to the control signal to discharge the liquid water in the cavity.
7. The method for preparing a polyamide according to claim 3, characterized in that, Set the rated pressures of the cavity and the reaction kettle to 1.0 MPa, and automatically adjust the second control valve when the internal pressures of the cavity and the reaction kettle are lower than 1.0 MPa. And / or, the pressure relief rate of the fourth control valve on the third exhaust pipeline of the reaction kettle is 0.5 - 3.5 MPa / h, for example, 2.5 MPa / h.
8. The method for preparing a polyamide according to claim 3, characterized in that, The polyamide salt solution is obtained by a salt-forming reaction of diamine and diacid and satisfies one or more of the following conditions: i. The molar ratio of the diamine monomer to the diacid monomer is (0.8 - 1.2):1, preferably (0.9 - 1.1):1; ii. The diacid monomer is one or more of succinic acid, glutaric acid, adipic acid, suberic acid, sebacic acid, dodecanedioic acid, terephthalic acid, and isophthalic acid, preferably one or more of adipic acid, sebacic acid, or dodecanedioic acid; iii. The diamine monomer is one or more of m - xylylenediamine, p - xylylenediamine, zero - xylylenediamine, decanediamine, pentanediamine, dodecanediamine, hexanediamine, and butanediamine; iv. The concentration of the polyamide salt solution is 30 - 70 wt.%; v. The pH value of the polyamide salt solution is 5.8 - 9.2, preferably 7.0 - 8.
5.
9. The method for preparing a polyamide according to claim 3, characterized in that, The process parameters of the concentration or the prepolymerization satisfy one or more of the following conditions: i. The temperature of the concentration is 150 - 210 °C, such as 160 °C or 180 °C; ii. The pressure of the concentration is 0.3 - 1.0 MPa, such as 0.6 MPa or 0.8 MPa; iii. The concentration of the polyamide salt solution after the concentration is 60 - 85 wt.%; iv. In Method 1, the protective gas includes nitrogen; v. In Method 2, the third control valve is opened and closed intermittently; preferably, the intermittent time interval is 5 min; vi. The temperature of the prepolymerization is 210 - 260 °C, such as 230 °C or 255 °C; vii. The pressure of the prepolymerization is 0.5 - 3.5 MPa, such as 1.9 MPa or 2.8 MPa; viii. The time of the prepolymerization is 0.5 - 3 h, such as 1 h; viiii. The prepolymerization includes depressurizing the reaction kettle; preferably, the depressurization rate is 0.5 - 3.5 MPa / h, such as 2.0 MPa / h or 2.5 MPa / h; preferably, after the depressurization, the pressure of the reaction kettle is normal pressure.
10. The method for preparing a polyamide according to claim 3, characterized in that, The process parameters of the post - polymerization satisfy one or more of the following conditions: i. The temperature of the post - polymerization is 250 - 310 °C, such as 300 °C; ii. The pressure of the post - polymerization is normal pressure; or, the pressure of the post - polymerization is - 0.03 - - 0.06 MPa; iii. The time of the post - polymerization is 0.5 - 2 h, such as 0.5 h; And / or, after completing the post - polymerization step, the method for preparing the polyamide further includes, in sequence: casting, cooling and pelletizing, screening, and drying.