Polyamide salt dissolving and concentrating system and method and application

Abstract

The invention discloses a polyamide salt dissolving and concentrating system, a polyamide salt dissolving and concentrating method and application. The polyamide salt dissolving and concentrating system comprises a dissolving kettle and an evaporator; the polyamide salt slurry outlet of the dissolving kettle is connected with the polyamide salt slurry inlet of the evaporator through a pipeline; and the dissolving kettle is a powder dissolving kettle with a Venturi tube ejector. According to the invention, the powder dissolving kettle with the Venturi tube ejector is adopted, so that the water quantity required for dissolving polyamide salt can be effectively reduced, and the material consumption is reduced; in addition, steam discharged by the evaporator is returned to the powder dissolving kettle with the Venturi tube ejector for reuse, waste heat recovery can be achieved, heat is saved, and waste water discharge is greatly reduced.

Description

Technical Field

[0001] This invention relates to the field of polyamide preparation technology, specifically to a polyamide salt dissolution and concentration system, method, and application. Background Technology

[0002] Polyamide resins are an important class of polymer materials with excellent mechanical properties and chemical resistance, and are widely used in aerospace, electronics, automotive, and other fields. Nylon production processes consist of two main parts: salt formation and polymerization. Current large-scale industrial polyamide salt (i.e., nylon salt) production mainly uses the aqueous phase salt formation method, where the polyamide salt remains in an aqueous solution throughout the process, eliminating the need for polyamide salt powder. However, for long-chain polyamide salts, due to the low purity and water insolubility of biologically derived long-chain diacid raw materials, solvent salt formation is often used to obtain polyamide salt products with higher purity. Solvent salt formation differs from aqueous phase salt formation in that it adds a process of polyamide salt precipitation and re-dissolution. The resulting polyamide salt product is a powder, which needs to be prepared into an aqueous solution before polymerization. Therefore, the dissolution and concentration of the polyamide salt are crucial steps in this process. Current technology uses conventional batch stirred tanks to mix water and polyamide salts. Polyamide salts have low solubility in water; the more water added, the faster the dissolution rate. However, this increases the energy consumption in the concentration stage and generates large amounts of continuous wastewater. Furthermore, polyamide salts are highly caking, easily forming clumps and adhering to the walls during mixing with water, leading to uneven mixing. Additionally, most existing nylon production facilities operate on a batch basis, with manual feeding and batching, which not only compromises product stability but also poses a risk of dust exposure and injury to personnel.

[0003] In view of the above, there is an urgent need for a high-efficiency, low-energy-consumption method for the continuous dissolution and concentration of polyamide salts. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides a polyamide salt dissolution and concentration system, method, and application. This invention utilizes a specially designed powder dissolution kettle with a venturi injector, which improves dissolution efficiency, reduces energy consumption, thereby reducing production costs and achieving environmental protection. Furthermore, the polyamide salt feeding unit ensures accurate addition of raw materials, improving the quality stability of the final product. Through a rationally designed process and control method, continuous production is achieved, increasing production efficiency and reducing the error rate of manual operation. Additionally, the polyamide salt feeding unit of this invention fully considers dust prevention and closed-loop collection; waste gas during the feeding process is collected in a closed loop and sent to a waste gas treatment system, ensuring operator safety and reducing environmental pollution.

[0005] One objective of this invention is to provide a polyamide salt dissolution and concentration system, comprising a dissolution vessel and an evaporator; the polyamide salt slurry outlet of the dissolution vessel is connected to the polyamide salt slurry inlet of the evaporator via a pipeline; the dissolution vessel is a powder dissolution vessel equipped with a Venturi tube injector.

[0006] In a preferred embodiment of the present invention,

[0007] The powder dissolving vessel with a Venturi injector is selected from the powder dissolving vessel with a Venturi injector in Chinese patent application CN202411642933.0, the full text of which is incorporated herein by reference: The dissolving vessel is a powder dissolving vessel with a Venturi injector; the powder dissolving vessel with a Venturi injector includes a dissolving vessel body, a Venturi injector, and a top saturated steam injector; the Venturi injector is connected to the side wall of the dissolving vessel body, and the axis of the Venturi injector is parallel to the horizontal plane; the Venturi injector includes a first saturated steam inlet end and a powder inlet end located outside the dissolving vessel body, and a mixed material outlet end connected to the side wall of the dissolving vessel body; the top saturated steam injector is located at the top of the dissolving vessel body.

[0008] In a preferred embodiment of the present invention, the top saturated steam injector includes:

[0009] The top saturated steam injection body is located inside the top of the dissolving vessel body and above the outlet end of the mixture.

[0010] The second saturated steam inlet is located outside the dissolving vessel body and connected to the top surface of the top saturated steam injection component body; and,

[0011] A top saturated steam nozzle assembly is disposed on the bottom surface of the top saturated steam injector body;

[0012] The top saturated steam nozzle assembly is connected to the second saturated steam inlet end;

[0013] Preferably,

[0014] The top saturated steam nozzle assembly includes multiple top saturated steam nozzles;

[0015] More preferably,

[0016] The top saturated steam injector body is in the shape of an annular tube; and / or,

[0017] The top saturated steam injection component is coaxially arranged with the dissolving vessel body; and / or

[0018] The distance between two adjacent top saturated steam nozzles is the same; and / or,

[0019] The outlet end of each of the top saturated steam nozzles is set vertically downward;

[0020] Most preferably,

[0021] The number of top saturated steam nozzles in the top saturated steam nozzle group is at least four.

[0022] In a preferred embodiment of the present invention

[0023] The Venturi injector is connected to the upper side wall of the dissolving vessel body; and / or,

[0024] The venturi injector has a reduced diameter section, and the powder inlet end is connected to this reduced diameter section; and / or,

[0025] The axis of the outlet end of the mixture is tangent to the side wall of the dissolving vessel body.

[0026] In a preferred embodiment of the present invention

[0027] The first saturated steam inlet is connected to a saturated steam inlet pipeline, and the powder inlet is connected to a powder inlet pipeline; and / or,

[0028] The second saturated steam inlet is connected to the saturated steam inlet pipeline;

[0029] More preferably,

[0030] The axis of the first saturated steam inlet is parallel to the horizontal plane; and / or,

[0031] The axis of the powder inlet is perpendicular to the horizontal plane.

[0032] In a preferred embodiment of the present invention

[0033] The dissolving vessel body is provided with a plurality of central saturated steam injection elements, which are located below the Venturi tube injector; each of the central saturated steam injection elements is connected to the dissolving vessel body;

[0034] Preferably,

[0035] Multiple central saturated steam jets are arranged parallel to each other and sequentially from top to bottom; and / or,

[0036] The distance between two adjacent central saturated steam injectors is the same;

[0037] More preferably,

[0038] Each of the aforementioned central saturated steam injectors is horizontally arranged;

[0039] Preferably, each of the central saturated steam injectors is connected to the side wall of the dissolving vessel body.

[0040] In a preferred embodiment of the present invention, each of the central saturated steam injectors includes:

[0041] The central saturated steam injection component body is located within the melting vessel body;

[0042] The central saturated steam inlet end: is located outside the melting vessel body and connected to the outer surface of the central saturated steam injector body; and

[0043] A central saturated steam nozzle assembly is disposed on the inner side of the central saturated steam injector body;

[0044] The central saturated steam nozzle assembly is connected to the central saturated steam inlet end;

[0045] Preferably,

[0046] The central saturated steam injector body is in the shape of an annular tube; and / or,

[0047] The central saturated steam jet body is coaxially arranged with the melting vessel body.

[0048] In a preferred embodiment of the present invention

[0049] Each of the aforementioned central saturated steam nozzle groups includes multiple pairs of central saturated steam nozzles. Each pair of central saturated steam nozzles includes an upper central saturated steam nozzle and a lower central saturated steam nozzle. The upper central saturated steam nozzle is inclined upward, and the lower central saturated steam nozzle is inclined downward.

[0050] Preferably,

[0051] The angle between the upper central saturated steam nozzle and the horizontal plane is 20–70°, more preferably 30–60°; and, or,

[0052] The angle between the lower central saturated steam nozzle and the horizontal plane is 20-70°, more preferably 30-60°;

[0053] More preferably,

[0054] The distance between any two adjacent pairs of central saturated steam nozzles is the same;

[0055] Most preferably,

[0056] Each of the aforementioned central saturated steam nozzle groups comprises at least four pairs of central saturated steam nozzles.

[0057] In a preferred embodiment of the present invention

[0058] The inner wall of the dissolving vessel body is polished or coated with PTFE; and / or,

[0059] The inner wall of the venturi injector is polished or coated with PTFE; and / or...

[0060] The outer wall of the top saturated steam jet component is polished or has a PTFE coating; and / or...

[0061] The outer wall of the central saturated steam jet component is polished or has a PTFE coating.

[0062] In a preferred embodiment of the present invention

[0063] The melting vessel body is equipped with a heat tracing jacket, which is connected to the heat tracing medium inlet pipeline and the heat tracing medium outlet pipeline respectively;

[0064] Preferably, the dissolving vessel body comprises, from top to bottom, a connected upper end cap, a cylindrical body, and a lower cone; the bottom end of the lower cone is provided with a mixed powder outlet (i.e., the polyamide salt slurry outlet of the dissolving vessel); the cylindrical body and the lower cone in the dissolving vessel body are provided with heat tracing jackets;

[0065] More preferably, the heat tracing jacket is provided with a heat medium guide plate.

[0066] In a preferred embodiment of the present invention,

[0067] The dissolving vessel is also connected to a polyamide salt feeding unit, which includes a polyamide salt silo, a loss-in-weight scale, and a rotary feed valve. The bottom outlet of the polyamide salt silo is sequentially connected to the pipelines of the loss-in-weight scale and the rotary feed valve. The rotary feed valve is connected to the powder inlet via a pipeline. The loss-in-weight scale and rotary feed valve are conventional loss-in-weight scales and rotary feed valves used in the chemical industry, and no special restrictions are imposed in this invention. Preferably...

[0068] The polyamide salt silo is further connected to a salt-forming section; the salt-forming section is a salt-forming section using conventional solvent salt-forming methods in the art, and no special limitations are imposed in this invention; and / or,

[0069] The rotary feed valve is optionally provided with a flushing port on the pipeline connecting it to the powder inlet; and / or,

[0070] The top of the polyamide salt silo is provided with an outlet, and a dust filter and a fan are connected in sequence to the top outlet; more preferably,

[0071] The fan is connected to an exhaust gas treatment system, which includes conventional exhaust gas treatment equipment in the art, and is not specifically limited in this invention.

[0072] In a preferred embodiment of the present invention,

[0073] The evaporator is followed by a polymerization section; the polymerization section is a conventional polyamide salt polymerization process for preparing polyamide in the art, and no special limitations are imposed in this invention; and / or,

[0074] The evaporator can be a conventionally used evaporator in the prior art for evaporating and concentrating the polyamide salt slurry; the evaporator is also provided with a steam outlet, which is optionally connected via pipeline to the top saturated steam jet, the middle saturated steam jet, and the first saturated steam inlet of the powder dissolving vessel with a Venturi tube ejector; and / or,

[0075] A feed tank is also provided on the pipeline connecting the polyamide slurry outlet of the dissolving vessel and the polyamide slurry inlet of the evaporator; preferably,

[0076] A jet mixer is provided on the side wall of the feed tank; a bypass is provided on the polyamide salt slurry discharge pipeline connected to the bottom of the feed tank, which is connected to the jet mixer pipeline on the side wall of the feed tank, so that part of the discharged polyamide salt slurry can be returned to the feed tank through the jet mixer. The jet mixer is a conventional jet mixer in the art, which achieves a high-speed mixing effect. Since the solubility of polyamide salt in water is not high, the jet mixer can prevent the precipitation or sedimentation of polyamide salt. No special limitations are made in this invention; and / or,

[0077] A polyamide salt transfer pump is also provided after the feed tank; and / or,

[0078] A polyamide salt feed pump is also installed on the pipeline connecting the evaporator and the polymerization section.

[0079] In a preferred embodiment of the present invention,

[0080] An additive feed line is also connected to the pipeline connecting the polyamide slurry outlet of the dissolving vessel to the polyamide slurry inlet of the evaporator; preferably,

[0081] A jacketed multi-way plunger device is installed at the connection point between the additive feed line and the polyamide slurry outlet of the dissolving vessel and the polyamide slurry inlet of the evaporator. This jacketed multi-way plunger device is selected from the jacketed multi-way plunger device described in Chinese patent application CN202311422249.7, which is hereby incorporated in its entirety:

[0082] The jacketed multi-way plunger device includes a first plunger valve and a second plunger valve. A first pipeline is vertically connected to the end of the first plunger valve, and a second pipeline is obliquely connected to the first plunger valve. A third pipeline is vertically connected to the end of the second plunger valve, and the first pipeline is obliquely connected to the second plunger valve. By integrating the first and second plunger valves into one unit through the arrangement of the pipelines, the device achieves pipeline shut-off and flow functions, while simultaneously enabling continuous material feeding.

[0083] The angle between the central axis of the first plunger valve and the central axis of the second pipeline is 20-40°.

[0084] The angle between the central axis of the second plunger valve and the central axis of the first pipeline is 30-60°.

[0085] One end of the first pipeline is the first material inlet, and the first plunger valve is perpendicularly connected to the side wall of the first pipeline near the first material inlet.

[0086] The other end of the first pipeline is a beveled cut, which is used to connect to the second plunger valve at an angle.

[0087] One end of the second pipeline is the second material inlet, and the other end is a beveled cut for oblique connection with the first plunger valve.

[0088] The second pipeline has a necking structure at one end located at the second material inlet, which can control the flow rate of the material (catalyst) entering through the second material inlet and prevent local sedimentation and blockage of the pipeline.

[0089] The second pipeline is also provided with a dispersion component inside the necking structure, which is used to perform secondary dispersion on the material (catalyst) entering the second pipeline through the second material inlet, reduce the possibility of local agglomeration, and enable it to enter the polymer melt uniformly.

[0090] The dispersion component includes a groove or protrusion structure disposed on the inner wall of the second pipeline. The groove or protrusion structure is disposed along the axial direction on the inner wall of the second pipeline, and multiple grooves or protrusion structures are uniformly disposed along the circumference.

[0091] One end of the third pipeline is the third material inlet, and the other end is the mixed material outlet. The side wall of the third pipeline is perpendicularly connected to the second plunger valve.

[0092] The jacketed multi-way plunger device is externally equipped with a jacket for introducing hot oil to heat the polymer melt inside the device. The heating temperature is required to be 250-270℃, which can ensure that the material can be continuously fed and avoid clogging the pipeline.

[0093] The jacket is provided with at least one partition to divide the interior of the jacket cavity into at least two heat medium cavities, and each heat medium cavity has a heat medium inlet and a heat medium outlet on the corresponding jacket side wall.

[0094] The second objective of this invention is to provide a method for dissolving and concentrating polyamide salts, comprising the step of dissolving polyamide salts with saturated steam in a dissolving vessel to obtain a polyamide salt slurry, which is then sent to an evaporator for concentration to obtain a concentrated polyamide salt solution.

[0095] In a preferred embodiment of the present invention,

[0096] The ratio of the mass flow rate of the polyamide salt to the total mass flow rate of the saturated steam is (3-9):1, preferably (3-6):1; and / or,

[0097] The polyamide salt (nylon salt) is a polyamide salt prepared by conventional solvent salting methods in the art, and no special limitations are imposed in this invention, such as nylon 612 salt, nylon 1018 salt, nylon 1211 salt, nylon 1212 salt, etc.; and / or,

[0098] The temperature of the heating medium introduced into the heating jacket of the dissolving vessel is 100–200°C, preferably 150–190°C; and / or, the inlet temperature of the saturated steam is 100–200°C, preferably 140–180°C; and / or, the inlet pressure of the saturated steam is 0.1–1.5 MPaG, preferably 0.3–0.6 MPaG; and / or,

[0099] The operating conditions of the evaporator include: a temperature of 130–240°C, preferably 130–180°C, and / or a pressure of 0.3–2.5 MPaG, preferably 0.3–1 MPaG; and / or,

[0100] The water content of the polyamide salt concentrate is 5-30 wt%, preferably 5-10 wt%; preferably...

[0101] The resulting polyamide salt concentrate is sent to the subsequent polymerization stage; and / or,

[0102] The steam obtained in the evaporator can optionally be recycled back to the dissolving vessel for reuse.

[0103] In a preferred embodiment of the present invention,

[0104] The polyamide salt slurry is mixed with the polymerization additive and then fed into the evaporator; preferably,

[0105] The polymer additive includes at least one of antioxidants, chain extenders, and molecular weight regulators; and / or,

[0106] Based on 100 wt% of the polyamide salt, the amount of the polymer additive is 0.1 to 1.0 wt%, preferably 0.1 to 0.5 wt%.

[0107] More preferably,

[0108] The antioxidant is selected from at least one of hindered phenolic antioxidants and phosphite antioxidants, preferably from at least one of antioxidants 1098, 1010, 1076, 168, and 264; and / or,

[0109] The chain extender is selected from at least one of epoxy-functionalized chain extenders, oximidazolium chain extenders, and carbonate-functionalized chain extenders, preferably from at least one of ECO-1120, PBO, and isophthaloyl biscaprolactam (IBC); and / or,

[0110] The molecular weight regulator is selected from at least one of benzoic acid, acetic acid, aliphatic thiols, polyphenols, and amines, preferably from at least one of benzoic acid and acetic acid.

[0111] The present invention can adopt the following specific technical solutions:

[0112] a) Continuous feeding of polyamide salts: Polyamide salt powder is conveyed from the salt-forming section to the polyamide salt silo, where it is precisely metered using a loss-in-weight weighing system and a rotary feed valve, and added to the dissolving vessel at a controlled flow rate. Simultaneously, fresh saturated steam from the pipeline network is mixed with optional recycled steam and introduced into the dissolving vessel. This invention, through the aforementioned feeding unit, achieves precise metering and automated continuous feeding of polyamide salts. The accompanying dust removal system enables the closed-loop collection of exhaust gases, reducing dust inhalation and explosion hazards. The pipeline between the rotary feed valve and the dissolving vessel is preferably equipped with a flushing / purging port to ensure no powder residue. This process can be performed manually or using a remote shut-off valve, achieving fully automated control through an automatic control system.

[0113] b) Polyamide Salt Dissolution: The polyamide salt is fed from the polyamide salt feeding unit into a powder dissolution vessel equipped with a venturi injector, where it is thoroughly dissolved by mixing with saturated steam. This invention utilizes a powder dissolution vessel with a venturi injector, where saturated steam is directly mixed with the polyamide salt at a relatively high temperature. This eliminates the need for a stirrer, reducing equipment investment and facilitating scale-up of the equipment. During this process, the polyamide salt and saturated steam are thoroughly mixed to form a polyamide salt slurry, simultaneously achieving a preheating effect.

[0114] c) Evaporation and Concentration: The homogeneous polyamide salt slurry flows by gravity into the feed tank and is then pumped to the evaporator via a polyamide salt transfer pump. Optionally, the feed tank uses a jet mixer to further mix the polyamide salt slurry, ensuring uniformity and preventing sedimentation. Optional polymerizing additives are mixed with the polyamide salt slurry and fed to the evaporator; the flow rate of the polymerizing additives is controlled proportionally to the flow rate of the polyamide salt slurry. Optionally, a specially designed jacketed multi-pump device is used at the polymerizing additive injection point. The evaporator is precisely designed according to the material characteristics and adopts a relatively advanced tube-and-shell structure in the nylon industry. The polyamide salt slurry enters from the bottom and forms a gas-liquid two-phase structure under the action of the heat medium, with an enlarged gas phase space at the top. Compared to traditional stirred tanks heated by a jacket, the tube-and-shell structure has a large contact area, eliminates the need for a stirrer, has high heat exchange efficiency, and a small equipment size, saving on equipment investment. The pressure at the top of the evaporator is determined by the gas-liquid phase equilibrium characteristics of the material at a specified concentration. Under the action of a heat transfer medium, the solution is concentrated to a specified concentration. The vapor phase is discharged through the top and optionally reused in the dissolution vessel. The polyamide salt concentrate is then pumped to the downstream polymerization stage via a polyamide salt feed pump.

[0115] A third objective of this invention is to provide an application of a system for one objective of this invention or a method for another objective of this invention in the field of polyamide preparation.

[0116] The beneficial effects of this invention are:

[0117] This invention achieves continuous feeding and precise metering of polyamide salts, ensuring the stability of subsequent continuous polymerization, and boasts a high degree of automation, improving production efficiency. This invention develops equipment and control processes that combine a powder dissolving vessel with a Venturi injector and a tubular evaporator, meeting the requirements of continuous production. The specially designed dissolving vessel reduces the amount of water required to dissolve the polyamide salt, thus reducing material consumption. Existing technologies do not reuse evaporator exhaust, resulting in large continuous wastewater discharges. This invention returns the steam discharged from the evaporator to the dissolving vessel for reuse, achieving waste heat recovery, saving heat, reducing wastewater discharge, and lowering operating costs. The system of this invention can be extended to any other production plant that includes dissolution and concentration processes. Attached Figure Description

[0118] Figure 1 This is a simplified process flow diagram of the polyamide salt dissolution and concentration method of the present invention.

[0119] Figure 1 In the diagram, 1 is a polyamide salt silo, 2 is a dust filter, 3 is a fan, 4 is a loss-in-weight scale, 5 is a rotary feed valve, 6 is a dissolving kettle, 7 is a feed tank, 8 is a jet mixer, 9 is a polyamide salt transfer pump, 10 is an evaporator, 11 is a polyamide salt feed pump, and 12 is a jacketed multi-way plunger device.

[0120] A is the salt formation section, B is the polymerization section, and C is the waste gas treatment system;

[0121] S1 is polyamide salt, S2 is protective gas, S3 is additive, S4 is the heat tracing medium introduced into the heat tracing jacket of the dissolving vessel, S5 is the heat medium of the evaporator, S6 is polyamide salt slurry, S7 is polyamide salt concentrate, S8 is evaporator exhaust steam, S9 is saturated steam, and S10 is fresh saturated steam.

[0122] Figure 2 This is a front view of the powder dissolving vessel with a Venturi injector according to the present invention.

[0123] Figure 2 In the diagram, 6-1 is the dissolving vessel body; 6-2 is the Venturi tube ejector; 6-21 is the first saturated steam inlet; 6-22 is the powder inlet; 6-23 is the mixed material outlet; 6-3 is the top saturated steam ejector; 6-31 is the second saturated steam inlet; 6-41 is the first middle saturated steam ejector; 6-42 is the second middle saturated steam ejector; 6-5 is the heat tracing jacket; 6-51 is the heat tracing medium inlet pipeline; and 6-52 is the heat tracing medium outlet pipeline. Detailed Implementation

[0124] The present invention will now be described in detail with reference to specific embodiments and accompanying drawings. 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.

[0125] Unless otherwise specified, the raw materials used in the embodiments and comparative examples of this invention 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.

[0126] Example 1

[0127] like Figure 1 As shown, the polyamide salt dissolution and concentration system includes a dissolution vessel 6 and an evaporator 10; the polyamide salt slurry outlet of the dissolution vessel 6 is connected to the polyamide salt slurry inlet of the evaporator 10 via a pipeline; the dissolution vessel 6 is a powder dissolution vessel with a Venturi tube ejector (i.e., the powder dissolution vessel with a Venturi tube ejector of Example 1 in Chinese Patent Application CN202411642933.0), and the polyamide salt slurry outlet of the dissolution vessel 6 is the mixed powder outlet of the powder dissolution vessel with the Venturi tube ejector;

[0128] The dissolving vessel 6 is also connected to a polyamide salt feeding unit, which includes a polyamide salt silo 1, a loss-in-weight scale 4, and a rotary feeding valve 5. The bottom outlet of the polyamide salt silo 1 is connected in sequence to the loss-in-weight scale 4 and the rotary feeding valve 5. The rotary feeding valve 5 is connected in a pipeline to the powder inlet 6-22 of the powder dissolving vessel with a Venturi injector. A salt forming section A is connected before the polyamide salt silo 1. An outlet is provided at the top of the polyamide salt silo 1, and a dust filter 2 and a fan 3 are connected in sequence to the top outlet. An exhaust gas treatment system C is connected after the fan 3.

[0129] The evaporator 10 is connected to the polymerization section B; the evaporator 10 is provided with a steam outlet; the steam outlet is connected to the top saturated steam injector, the middle saturated steam injector and the first saturated steam inlet of the powder dissolving kettle with a venturi tube injector through a pipeline.

[0130] A feed tank 7 is also provided on the pipeline connecting the polyamide salt slurry outlet of the dissolving vessel 6 to the polyamide salt slurry inlet of the evaporator 10; a jet mixer 8 is provided on the side wall of the feed tank 7; a polyamide salt delivery pump 9 is also provided after the feed tank 7; a polyamide salt feed pump 11 is also provided on the pipeline connecting the evaporator 10 and the polymerization section B; a branch line connecting the polyamide salt feed pump 11 to the polymerization section B is also optionally provided; an additive feed pipeline is also connected to the pipeline connecting the polyamide salt slurry outlet of the dissolving vessel 6 to the polyamide salt slurry inlet of the evaporator 10; a jacketed multi-way plunger device 12 is provided at the connection between the additive feed pipeline and the pipeline connecting the polyamide salt slurry outlet of the dissolving vessel 6 to the polyamide salt slurry inlet of the evaporator 10, and the jacketed multi-way plunger device 12 is selected from Chinese patent application CN202311422249.7. Figure 2 A jacketed multi-way plunger device, wherein the angle between the central axis of the first plunger valve and the central axis of the second pipeline is 30°, and the angle between the central axis of the second plunger valve and the central axis of the first pipeline is 45°.

[0131] Example 2

[0132] A method for dissolving and concentrating long-chain nylon 1018 salt using the system of Example 1 includes the following steps:

[0133] a) Continuous feeding of polyamide salt: Powdered nylon 1018 salt S1 is transported to the polyamide salt silo 1 through the self-forming salt section A. It is precisely measured by the loss-in-weight scale 4 and the rotary feed valve 5 and continuously fed into the powder inlet end of the Venturi injector of the dissolving vessel 6 at a flow rate of 250 kg / h. At the same time, saturated steam (the inlet temperature of saturated steam is 152℃, the inlet pressure of saturated steam is 0.40 MPaG, and the flow rate is 12.5 kg / h) is introduced into the Venturi injector. The saturated steam forms a high-speed airflow in the narrowing section of the Venturi injector and draws in the powdered nylon 1018 salt. The powdered nylon 1018 salt is quickly dispersed in the saturated steam and moves towards the mixed material outlet end of the Venturi injector, and finally enters the body of the dissolving vessel 6. Low-pressure steam is introduced into the heating jacket of the dissolving vessel 6 for heating. The temperature of the low-pressure steam is 150℃.

[0134] b) Polyamide salt dissolution: Saturated steam (inlet temperature 152℃, inlet pressure 0.40 MPaG, flow rate 12.5 kg / h) is introduced into the top saturated steam injector of dissolving vessel 6. Under the action of the top saturated steam, nylon 1018 salt is uniformly dispersed on the cross-section of the dissolving vessel 6 and moves downward. Saturated steam is introduced into the three middle saturated steam injectors (inlet temperature 155℃, inlet pressure 0.40 MPaG, flow rate 12.5 kg / h for each middle saturated steam injector). Under the action of multiple saturated steam injectors, nylon 1018 salt is fully mixed with saturated steam and transferred out from the polyamide salt slurry outlet of dissolving vessel 6.

[0135] c) Evaporation and Concentration: The polyamide salt slurry S6 obtained in step b) flows by gravity into the feed tank 7, and is then sent to the evaporator 10 via the polyamide salt transfer pump 9. The feed tank 7 is further mixed using a jet mixer 8 to ensure slurry uniformity and prevent sedimentation. The additive benzoic acid S3 is mixed with the polyamide salt slurry S6 through the additive feed line and sent to the evaporator 10. The amount of benzoic acid added is 0.35 wt% of the polyamide salt. The mixture is evaporated and concentrated in the evaporator 10. The operating pressure of the evaporator 10 is 0.40 MPaG, and the temperature is 152°C. Steam is used as the heat source on the shell side of the evaporator. The concentrated polyamide salt solution S7 obtained from the evaporation and concentration has a concentration of 90 wt%. All the steam S8 discharged during the concentration process is recycled to the dissolving tank 6. The concentrated polyamide salt solution S7 is pumped to the downstream polymerization section for nylon polymerization. A portion of the polyamide salt concentrate S7 is optionally circulated back to the evaporator 10 to increase the flow rate and concentration of the concentrate, thereby improving flow, reducing the residence time in the tubes, and preventing scaling.

[0136] Comparative Example 1

[0137] Comparative Example 1 uses a traditional vertical stirred tank dissolution process for the polymerization pretreatment of nylon 1018 salt:

[0138] 250 kg / h of powdered nylon 1018 salt was intermittently added to a conventional vertical stirred tank for dissolution, using water instead of saturated steam as the solvent. The mass flow ratio of water to polyamide salt was 4:6. The polyamide salt dissolved in the water under the action of the stirrer, resulting in a polyamide salt slurry. The dissolution tank temperature was 80℃, the pressure was 0 MPaG, and the jacket of the dissolution tank was heated by low-pressure steam.

[0139] The polyamide salt slurry obtained from the vertical stirred tank flows by gravity into the feed tank, and is then pumped to the evaporator via a polyamide salt transfer pump. The feed tank uses a jet mixer for further mixing to ensure slurry homogeneity and prevent sedimentation. Benzoic acid, an additive, is mixed with the polyamide salt slurry through an additive feed line and sent to the evaporator at a concentration of 0.35 wt% of the polyamide salt. The mixture is concentrated in the evaporator at an operating pressure of 0.40 MPaG and a temperature of 142°C, using steam as the heat source on the evaporator shell side. The concentrated polyamide salt solution has a concentration of 90 wt%, and the steam flow rate during concentration is 139 kg / h, which is discharged to the waste gas treatment system. After cooling, it generates a continuous wastewater flow rate of 139 kg / h. The concentrated polyamide salt solution is then pumped to the downstream polymerization section for nylon polymerization.

[0140] Comparative Example 1 involves no heat recovery throughout the entire process, generating 139 kg / h of wastewater. Compared to Comparative Example 1, Example 2 utilizes the powder dissolving kettle with a Venturi injector of this invention, reducing the water addition ratio required for polyamide salt dissolution from 6:4 (mass of salt:mass of water) to 8:2. Furthermore, Example 2 incorporates steam recycling, significantly reducing fresh steam consumption. Overall, the amount of fresh water (steam) replenished is reduced by 83%, resulting in an annual water saving of 1110 tons for a 2000-ton scale plant, and an annual heat recovery saving of 7.61 x 10⁻⁶ tons. 5 MJ reduced wastewater discharge by 1,110 tons.

[0141] As can be seen from Examples 1-2, this invention has developed an equipment and control process that combines a powder dissolving kettle with a Venturi injector and a tubular evaporator for polyamide salts, meeting the requirements of continuous production. The powder dissolving kettle with a Venturi injector effectively reduces the amount of water required to dissolve polyamide salts, thus reducing material consumption. Furthermore, this invention returns the steam discharged from the evaporator to the powder dissolving kettle with the Venturi injector for reuse, achieving waste heat recovery, saving heat, and significantly reducing wastewater discharge.

[0142] It should be noted that the embodiments described above are only for explaining the present invention and do not constitute any limitation on the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory terms, not limiting terms. Modifications can be made to the present invention within the scope of the claims, and revisions can be made to the present invention without departing from the scope and spirit of the present invention. Although the present invention described herein relates to specific methods, materials, and embodiments, it does not mean that the present invention is limited to the specific examples disclosed herein; on the contrary, the present invention can be extended to all other methods and applications with the same function.

[0143] All publications, patent applications, patents, and other references mentioned in this specification are incorporated herein by reference. Unless otherwise defined, all technical and scientific terms used in this specification have the meanings commonly understood by those skilled in the art. In case of conflict, the definitions in this specification shall prevail.

[0144] When this specification uses the prefixes “known to those skilled in the art,” “prior art,” or similar terms to derive materials, substances, methods, steps, apparatus, or components, the objects derived from such prefixes cover those commonly used in the art at the time of this application, but also include those that are not currently commonly used but will become generally recognized in the art as suitable for similar purposes.

[0145] The endpoints and any values ​​of the ranges disclosed in this application are not limited to the precise ranges or values; such ranges or values ​​should be understood to include values ​​close to them. 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 principle, various technical solutions can be combined with each other to obtain new technical solutions, which should also be considered as specifically disclosed herein.

[0146] In the context of this specification, except where expressly stated otherwise, any matters or issues not mentioned shall apply directly to those known in the art without any modification.

[0147] Furthermore, any implementation described herein can be freely combined with one or more other implementations described herein, and the resulting technical solutions or technical ideas shall be regarded as part of the original disclosure or original record of the present invention, and should not be regarded as new content not disclosed or anticipated herein, unless those skilled in the art consider the combination to be obviously unreasonable.

Claims

1. A polyamide salt dissolution and concentration system, comprising a dissolution vessel and an evaporator; the polyamide salt slurry outlet of the dissolution vessel is connected to the polyamide salt slurry inlet of the evaporator via a pipeline; the dissolution vessel is a powder dissolution vessel equipped with a Venturi tube injector.

2. The system as described in claim 1, characterized in that: The powder dissolving vessel with a Venturi injector includes a dissolving vessel body, a Venturi injector, and a top saturated steam injector; the Venturi injector is connected to the side wall of the dissolving vessel body, and the axis of the Venturi injector is parallel to the horizontal plane; the Venturi injector includes a first saturated steam inlet end and a powder inlet end located outside the dissolving vessel body, and a mixture outlet end connected to the side wall of the dissolving vessel body; the top saturated steam injector is located at the top of the dissolving vessel body; preferably, The top saturated steam injector includes: a top saturated steam injector body disposed inside the top of the dissolving vessel body and above the outlet end of the mixture; a second saturated steam inlet end disposed outside the dissolving vessel body and connected to the top surface of the top saturated steam injector body; and a top saturated steam nozzle assembly disposed on the bottom surface of the top saturated steam injector body; wherein the top saturated steam nozzle assembly is connected to the second saturated steam inlet end.

3. The system as described in claim 2, characterized in that: The dissolving vessel body is equipped with multiple central saturated steam injectors, which are located below the Venturi tube injector; each of the central saturated steam injectors is connected to the dissolving vessel body; preferably... Multiple central saturated steam jets are arranged parallel to each other and sequentially from top to bottom; and / or, The distance between two adjacent central saturated steam injectors is the same; more preferably, Each of the central saturated steam jets is horizontally positioned.

4. The system as described in claim 2, characterized in that: The dissolving vessel is also connected to a polyamide salt feeding unit, which includes a polyamide salt silo, a loss-in-weight scale, and a rotary feed valve. The bottom outlet of the polyamide salt silo is sequentially connected to the pipelines of the loss-in-weight scale and the rotary feed valve. The rotary feed valve is connected to the powder inlet end via a pipeline. Preferably, The polyamide salt silo is also connected to a salt-forming section; and / or, The rotary feed valve is optionally provided with a flushing port on the pipeline connecting it to the powder inlet; and / or, The top of the polyamide salt silo is provided with an outlet, and a dust filter and a fan are connected in sequence to the top outlet; more preferably, The fan is also connected to an exhaust gas treatment system.

5. The system as described in claim 1, characterized in that: The evaporator is further connected to a polymerization section; and / or, The evaporator is also provided with a steam outlet; and / or, A feed tank is also provided on the pipeline connecting the polyamide slurry outlet of the dissolving vessel and the polyamide slurry inlet of the evaporator; preferably, The feed tank sidewall is equipped with a jet mixer; and / or A polyamide salt transfer pump is also provided after the feed tank; and / or, A polyamide salt feed pump is also installed on the pipeline connecting the evaporator and the polymerization section.

6. The system as described in any one of claims 1-5, characterized in that: An additive feed line is also connected to the pipeline connecting the polyamide slurry outlet of the dissolving vessel to the polyamide slurry inlet of the evaporator; preferably, A jacketed multi-way plunger device is provided at the connection point between the additive feed pipeline and the pipeline connecting the polyamide slurry outlet of the dissolving vessel and the polyamide slurry inlet of the evaporator; more preferably, The jacketed multi-way plunger device includes a first plunger valve and a second plunger valve; the end of the first plunger valve is vertically connected to a first pipeline, and the first plunger valve is obliquely connected to a second pipeline; the end of the second plunger valve is vertically connected to a third pipeline, and the first pipeline is obliquely connected to the second plunger valve; more preferably, the angle between the central axis of the first plunger valve and the central axis of the second pipeline is 20-40°; and / or, the angle between the central axis of the second plunger valve and the central axis of the first pipeline is 30-60°.

7. A method for dissolving and concentrating polyamide salt, preferably using the system described in any one of claims 1-6, comprising the step of dissolving polyamide salt with saturated steam in a dissolving vessel to obtain a polyamide salt slurry, which is then concentrated in an evaporator to obtain a concentrated polyamide salt solution.

8. The method as described in claim 7, characterized in that: The ratio of the mass flow rate of the polyamide salt to the total mass flow rate of the saturated steam is (3-9):1, preferably (3-6):1; and / or, The polyamide salt is a polyamide salt prepared by solvent salt formation; and / or, The inlet temperature of the saturated steam is 100–200°C, preferably 140–180°C; and / or the inlet pressure of the saturated steam is 0.1–1.5 MPaG, preferably 0.3–0.6 MPaG; And / or, The operating conditions of the evaporator include: a temperature of 130–240°C, preferably 130–180°C, and / or a pressure of 0.3–2.5 MPaG, preferably 0.3–1 MPaG; and / or, The water content of the polyamide salt concentrate is 5-30 wt%, preferably 5-10 wt%; preferably... The resulting polyamide salt concentrate is sent to the subsequent polymerization stage; and / or, The steam obtained in the evaporator can optionally be recycled back to the dissolving vessel for reuse.

9. The method as described in any one of claims 7-8, characterized in that: The polyamide salt slurry is mixed with the polymerization additive and then fed into the evaporator; preferably, The polymer additive includes at least one of antioxidants, chain extenders, and molecular weight regulators; and / or, Based on 100 wt% of the polyamide salt, the amount of the polymer additive is 0.1 to 1.0 wt%, preferably 0.1 to 0.5 wt%.

10. The application of the system as described in any one of claims 1-6 or the method as described in any one of claims 7-9 in the field of polyamide preparation.

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