Melt devolatilization reactor, polyamide 12 production apparatus, and production method

Abstract

The present application relates to a melt devolatilization reactor, a polyamide 12 preparation device and a preparation method. The melt devolatilization reactor comprises a reaction cavity, which is provided with a melt feeding port, a vacuum exhaust port and a melt discharging port; a feeding flow guide plate is arranged in the reaction cavity, which divides the inner cavity of the reaction cavity into a flow guide sub-cavity and a devolatilization sub-cavity, the melt feeding port is communicated with the flow guide sub-cavity, the melt discharging port is communicated with the devolatilization sub-cavity, there is a material passing gap between the edge of the feeding flow guide plate and the side wall of the reaction cavity, the flow guide sub-cavity is communicated with the devolatilization sub-cavity through the material passing gap, and a plurality of protrusions are arranged on the side wall of the devolatilization sub-cavity. The melt can flow to the material passing gap along the feeding flow guide plate, enter the devolatilization sub-cavity, and the melt film flowing down the side wall is repeatedly spread, torn and recombined when flowing through the plurality of protrusions, so that the melt surface is constantly updated, and the gas-liquid contact area is increased. In this way, the deep devolatilization is completed in the process of melt flow.

Description

Technical Field

[0001] This invention relates to the field of resin preparation technology, and in particular to a melt devolatilization reactor, a polyamide 12 preparation apparatus, and a preparation method. Background Technology

[0002] Polyamide 12 (PA12) is a long-chain polyamide obtained by ring-opening hydrolysis polymerization of dodecyl lactam. Polyamide 12 has the characteristics of low water absorption, good oil resistance, hydrolysis resistance, good flexibility and excellent low-temperature toughness, and is widely used in automotive fluid pipelines, pneumatic hoses, hydrogen energy transmission pipelines, medical interventional catheters and 3D printing consumables.

[0003] Polyamide 12 is typically prepared using dodecyl lactam as a monomer. First, it undergoes hydrolysis and ring-opening under high temperature and pressure to generate a prepolymer, followed by polycondensation under reduced pressure to remove free water. Traditional polymerization processes generally result in polyamide 12 with a high residual monomer content, leading to a strong odor. To reduce the residual monomer content, the traditional approach is to perform post-processing such as hot water extraction or solid-phase extraction on the polyamide 12 granules after polymerization and granulation. However, these post-processing methods require additional equipment for extraction, washing, and drying, resulting in high equipment investment, long process flows, and high energy consumption. Summary of the Invention

[0004] Therefore, it is necessary to provide a melt devolatilization reactor, a polyamide 12 preparation apparatus and preparation method to solve the problem that polyamide 12 prepared by traditional polymerization processes generally has a high residual monomer content.

[0005] The first aspect of the present invention provides a melt devolatilization reactor, the scheme of which is as follows:

[0006] A melt devolatilization reactor includes a reaction chamber, which has a melt inlet, a vacuum outlet, and a melt outlet. A feed guide plate is disposed within the reaction chamber, dividing the inner cavity of the reaction chamber into a guide sub-cavity and a devolatilization sub-cavity. The melt inlet communicates with the guide sub-cavity, and the melt outlet communicates with the devolatilization sub-cavity. A material passage gap is formed between the edge of the feed guide plate and the sidewall of the reaction chamber, allowing the melt to pass through. The guide sub-cavity communicates with the devolatilization sub-cavity through the material passage gap. Multiple protrusions are distributed on the sidewall of the devolatilization sub-cavity.

[0007] Preferably, the protrusion has a spherical crown structure.

[0008] Preferably, the height of the protrusion is 30mm to 70mm.

[0009] Preferably, the width of the material passage gap is 30mm to 80mm.

[0010] Preferably, the height of the protrusion is not less than the width of the material passage gap.

[0011] Preferably, the protrusion is hemispherical.

[0012] Preferably, the projection of the feed guide plate on the horizontal plane is circular and is coaxially arranged with the melt feed port.

[0013] Preferably, the feed guide plate is inclined downward from its center to its edge on the side facing the melt feed inlet.

[0014] Preferably, the plurality of protrusions are arranged in multiple rows along the circumferential sidewall of the devolatilization cavity, with each row spaced apart along the circumferential sidewall of the devolatilization cavity, and the protrusions in adjacent rows are staggered in the vertical direction.

[0015] Preferably, the vertical spacing between two adjacent protrusions in the same column is 50mm to 150mm.

[0016] A second aspect of the present invention provides a polyamide 12 preparation apparatus, the scheme of which is as follows:

[0017] A polyamide 12 preparation apparatus includes a monomer melting vessel, a prepolymer ring-opening vessel, a prepolymerization vessel, a postpolymerization vessel, and the melt devolatilization reactor;

[0018] The outlet of the monomer melting reactor is connected to the inlet of the prepolymer open-ring reactor, the outlet of the prepolymer open-ring reactor is connected to the inlet of the prepolymer reactor, the outlet of the prepolymer reactor is connected to the inlet of the postpolymer reactor, and the outlet of the postpolymer reactor is connected to the melt inlet of the melt devolatilization reactor.

[0019] Preferably, the polyamide 12 preparation apparatus further includes a melt pump, and the outlet of the post-polymerization reactor is connected to the melt inlet of the melt devolatilization reactor through the melt pump.

[0020] A third aspect of the present invention provides a method for preparing polyamide 12, the scheme of which is as follows:

[0021] A method for preparing polyamide 12, using the aforementioned polyamide 12 preparation apparatus, the preparation method comprising the following steps:

[0022] Dodecyl lactam, end-capping agent, catalyst and water are added to the monomer melting vessel and heated to melt, thereby obtaining molten raw material;

[0023] The molten raw material is transferred to the prepolymer ring-opening reactor for hydrolysis and ring-opening to obtain polyamide 12 prepolymer;

[0024] The polyamide 12 prepolymer is transferred to the prepolymerization reactor, where some moisture is removed and preliminary polycondensation is performed under the conditions of introducing protective gas or negative pressure to obtain the first polyamide 12 melt.

[0025] The first polyamide 12 melt is transferred to the post-polymerization reactor and polycondensation and thickening are continued under vacuum conditions to obtain the second polyamide 12 melt.

[0026] The second polyamide 12 melt is fed into the melt devolatilization reactor, where residual dodecyl lactam and volatile components are removed under vacuum conditions to obtain the third polyamide 12 melt.

[0027] Preferably, the operating vacuum levels of the prepolymerization reactor, the postpolymerization reactor, and the melt devolatilization reactor are increased progressively.

[0028] Preferably, the temperature inside the melt devolatilization reactor is 190℃~250℃, and the absolute pressure is 1kPa~10kPa.

[0029] Preferably, the mass ratio of the dodecyl lactam, the capping agent, the catalyst, and water is 100:(0.1~0.8):(0.05~0.1):(8~15).

[0030] Preferably, the capping agent includes at least one of adipic acid and terephthalic acid.

[0031] Preferably, the catalyst comprises at least one of phosphoric acid and sodium hypophosphite.

[0032] Preferably, the temperature inside the prepolymer open-ring reactor is 210℃~250℃, the holding pressure is 2.5MPa~3MPa, and the holding time is 2h~4h.

[0033] Preferably, the temperature inside the prepolymer reactor is 190~240℃, and the reaction time is 0.5h~3h.

[0034] Preferably, the temperature inside the post-polymerization reactor is 190~240℃, and the reaction time is 0.5h~3h.

[0035] The present invention has the following beneficial effects:

[0036] The aforementioned melt devolatilization reactor is equipped with a feed guide plate and protrusions within the reaction chamber. During operation, the melt enters the guide chamber through the melt inlet, falls onto the feed guide plate, flows along its edge, and enters the devolatilization chamber through the material passage gap between the edge of the feed guide plate and the sidewall. The melt then forms a film and flows down the sidewall of the devolatilization chamber. As the melt film flows down the sidewall, it is repeatedly spread, torn, and recombine as it passes through multiple protrusions, thus continuously renewing the melt surface. Residual dodecyl lactam, oligomers, moisture, and volatile organic compounds inside the melt escape from the renewed gas-liquid interface under vacuum conditions and are extracted through the vacuum evacuation port. The devolatilized melt then collects at the bottom of the reaction chamber and is led out through the melt outlet. In this way, deep devolatilization is completed as the melt flows downwards. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the structure of a melt devolatilization reactor according to one embodiment;

[0038] Figure 2 For containing Figure 1 A schematic diagram showing the arrangement of protrusions in a melt devolatilization reactor;

[0039] Figure 3 As one embodiment includes Figure 1 The diagram shows a schematic of the polyamide 12 preparation apparatus in a melt devolatilization reactor.

[0040] Explanation of reference numerals in the attached figures:

[0041] 100. Melt devolatilization reactor; 110. Reaction chamber; 111. Melt inlet; 112. Vacuum evacuation port; 113. Melt outlet; 120. Feed guide plate; 121. Guide surface; 114. Inner cavity; 1142. Guide sub-cavity; 1144. Devolatilization sub-cavity; 1146. Material passage gap; 130. Protrusion; 10. Polyamide 12 preparation device; 200. Monomer melting vessel; 300. Prepolymerization ring-opening vessel; 400. Prepolymerization vessel; 500. Postpolymerization vessel. Detailed Implementation

[0042] To facilitate understanding of the present invention, a more complete description will be given below with reference to the accompanying drawings. Preferred embodiments of the invention are shown in the drawings. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein; these embodiments are provided to provide a thorough and complete understanding of the disclosure of the invention.

[0043] Please refer to Figure 1As shown, a melt devolatilization reactor 100 according to an embodiment of the present invention includes a reaction chamber 110. The reaction chamber 110 is provided with a melt inlet 111, a vacuum extraction port 112, and a melt outlet 113. A feed guide plate 120 is provided inside the reaction chamber 110. The feed guide plate 120 divides the inner cavity 114 of the reaction chamber 110 into a guide sub-cavity 1142 and a devolatilization sub-cavity 1144. The melt inlet 111 communicates with the guide sub-cavity 1142. The melt outlet 113 communicates with the devolatilization sub-cavity 1144. A material passage gap 1146 for melt to pass through is provided between the edge of the feed guide plate 120 and the side wall of the reaction chamber 110. The guide sub-cavity 1142 communicates with the devolatilization sub-cavity 1144 through the material passage gap 1146. A plurality of protrusions 130 are distributed on the side wall of the devolatilization sub-cavity 1144.

[0044] When the melt devolatilization reactor 100 is operating, the melt enters the flow guide chamber 1142 through the melt inlet 111, falls onto the feed guide plate 120, flows along the feed guide plate 120 to its edge, and enters the devolatilization chamber 1144 through the material passage gap 1146 between the edge of the feed guide plate 120 and the sidewall. The melt then forms a film and flows down the sidewall of the devolatilization chamber 1144. As the melt film flows down the sidewall, it is repeatedly spread, torn, and recombined as it passes through multiple protrusions 130, thus continuously renewing the melt surface. Residual dodecyl lactam, oligomers, moisture, and volatile organic compounds inside the melt escape from the renewed gas-liquid interface under vacuum conditions and are extracted through the vacuum evacuation port 112. The devolatilized melt then collects at the bottom of the reaction chamber 110 and is led out through the melt outlet 113. In this way, deep devolatilization is completed as the melt flows downwards.

[0045] In some examples, the melt inlet 111 is located at the top of the reaction chamber 110. In some examples, the vacuum evacuation port is located at the top of the reaction chamber 110. In some examples, the melt outlet 113 is located at the top of the reaction chamber 110.

[0046] It is understood that the feed guide plate 120 can be connected to the inner wall of the reaction chamber 110 via a connector, such as a connecting rod. The connector can be attached to the edge of the feed guide plate 120 or to the guide surface 121 of the feed guide plate 120. The guide surface 121 is the side surface of the feed guide plate 120 facing the melt inlet 111.

[0047] The orthographic projection of the feed guide plate 120 on the horizontal plane covers the drop range of the melt inlet 111, so that the melt falling from the melt inlet 111 can fall onto the feed guide plate 120 and enter the degassing chamber 1144 from the material passage gap 1146 through the guide plate 120.

[0048] In some examples, the projection of the feed guide plate 120 on the horizontal plane is circular and is coaxial with the melt feed port 111.

[0049] In some examples, the guide surface 121 gradually slopes downward from its center to the edge, that is, the guide surface 121 is a curved surface that is high in the middle and low at the edge. The melt falling into the middle of the guide surface 121 can be distributed to the surrounding areas along the guide surface 121 and flow evenly through the material passage gaps 1146 at various circumferential locations to the sidewall of the devolatilization chamber 1144, which helps to form a melt film of relatively uniform thickness on the sidewall.

[0050] In some examples, the feed gap 1146 is an annular gap extending circumferentially along the reaction chamber 110. Further, the annular gap has a uniform width at all points, allowing the melt to enter the devolatilization chamber 1144 uniformly circumferentially. In some examples, the width of the feed gap 1146 is 30-80 mm, specifically, for example, 30 mm, 40 mm, 50 mm, 60 mm, 70 mm, 80 mm, etc. Further, the width of the feed gap 1146 is 45-55 mm. Further, the width of the feed gap 1146 is 50 mm. When the feed gap 1146 is within the above-mentioned width range, the melt can flow down the sidewall in a relatively uniform film formation. The width of the feed gap 1146 is the shortest distance between the edge of the feed gap 1146 and the inner sidewall of the reaction chamber 110.

[0051] like Figure 2 As shown, in some examples, multiple protrusions 130 are arranged in multiple rows along the axial direction of the devolatilization chamber 1144 (the axial direction is vertical when the melt devolatilization reactor 100 is operating). In some examples, the protrusions 130 in adjacent rows are staggered in the axial direction of the devolatilization chamber 1144, that is, the protrusions 130 in adjacent rows are not aligned in the melt flow direction and are arranged in a staggered manner. In this way, when the melt flows down the sidewall, it will encounter the protrusions 130 in sequence regardless of which path it flows along. The melt film is repeatedly separated and rejoined by the protrusions 130, which helps to continuously and fully renew the melt surface.

[0052] In some examples, the spacing l between two adjacent protrusions 130 in the same row is 50~150mm, such as 50mm, 80mm, 100mm, 120mm, 150mm, etc. Here, the spacing l between two protrusions 130 refers to the shortest distance between the edge of one protrusion 130 and the edge of another protrusion 130.

[0053] In some examples, the angle α between the geometric center of each protrusion 130 and the line connecting the geometric centers of the two nearest protrusions 130 in an adjacent row is 60° to 120°, specifically 60°, 75°, 90°, 105°, 120°, etc. When the protrusions 130 are arranged in staggered rows with the above spacing and angle, a staggered array with appropriate density can be formed on the sidewall, taking into account both the tearing effect of the melt film and the need for smooth flow of the melt.

[0054] The protrusion 130 has a convex surface on the side facing away from the sidewall of the degassing cavity 1144. In some examples, the protrusion 130 has a spherical cap structure. In other words, the convex surface of the protrusion 130 is a spherical cap surface. This facilitates the smooth distribution and convergence of the melt film along the convex surface. In some examples, the protrusion 130 is hemispherical. In some examples, the diameter of the hemispherical protrusion 130 is 10~50mm, specifically, for example, 10mm, 20mm, 30mm, 40mm, 50mm, etc.

[0055] In some examples, the number density of protrusions 130 on the sidewall of the dewaxing cavity 1144 is 0.05~2 per cm. 2 For example, 0.05 per cm 2 0.2 pieces / cm 2 0.5 pieces / cm 2 1 piece / cm 2 1.5 pieces / cm 2 2 per cm 2 wait.

[0056] In some examples, the height of the protrusion 130 is 30-70 mm, specifically 30 mm, 40 mm, 50 mm, 60 mm, 70 mm, etc. Further, the height of the protrusion 130 is 45-55 mm. Further still, the height of the protrusion 130 is 50 mm. When the protrusion 130 is within the above height range, it can effectively tear the melt film flowing down the wall, renew the melt surface, remove residual monomers and moisture, and at the same time maintain the smooth flow of the melt.

[0057] The height range of the aforementioned protrusion 130 is also adapted to the width of the aforementioned material passage 1146. In some examples, the height of the protrusion 130 is not less than the width of the material passage 1146, preventing the melt from falling directly to the bottom of the reaction chamber 110 after passing through the material passage 1146. In some examples, the height of the protrusion 130 is equal to the width of the material passage 1146. In some examples, the height of the protrusion 130 is greater than the width of the material passage 1146. Further, the height of the protrusion 130 is 1 to 10 mm greater than the width of the material passage 1146, specifically, for example, 1 mm, 3 mm, 6 mm, 8 mm, 10 mm, etc.

[0058] In some examples, the melt devolatilization reactor 100 has a jacket structure to insulate the reaction chamber 110 during devolatilization, keeping the melt at a suitable temperature for flow and devolatilization. In some examples, the heating medium within the jacket includes at least one of biphenyl and diphenyl ether, offering the advantage of precise temperature control.

[0059] Furthermore, the present invention also provides a polyamide 12 preparation apparatus 10.

[0060] Please refer to Figure 3 As shown, a polyamide 12 preparation apparatus 10 of an embodiment of the present invention includes a monomer melting vessel 200, a prepolymer ring-opening vessel 300, a prepolymerization vessel 400, a postpolymerization vessel 500, and a melt devolatilization reactor 100 of any of the above examples, which are connected in sequence.

[0061] More specifically, the outlet of the monomer melting reactor 200 is connected to the inlet of the prepolymerization open-ring reactor 300. The outlet of the prepolymerization open-ring reactor 300 is connected to the inlet of the prepolymerization reactor 400. The outlet of the prepolymerization reactor 400 is connected to the inlet of the postpolymerization reactor 500. The outlet of the postpolymerization reactor 500 is connected to the melt inlet 111 of the melt devolatilization reactor 100.

[0062] Monomer melting reactor 200 is used to melt raw materials such as dodecyl lactam. Prepolymer ring-opening reactor 300 is used to hydrolyze and open the ring of dodecyl lactam to obtain polyamide 12 prepolymer. Prepolymerization reactor 400 is used to initially polycondense the polyamide 12 prepolymer to obtain the first polyamide 12 melt. Postpolymerization reactor 500 is used to further polycondense and thicken the first polyamide 12 melt to obtain the second polyamide 12 melt. Melt devolatilization reactor 100 is used to remove residual dodecyl lactam and volatile components under vacuum conditions to obtain the third polyamide 12 melt.

[0063] In some examples, the monomer melting vessel 200 is a pressure-resistant reactor. In some examples, the prepolymer ring-opening vessel 300 is a pressure-resistant reactor. Pressure-resistant reactors can withstand high temperatures and pressures, meeting the requirements for monomer melting and high-temperature, high-pressure closed-loop opening.

[0064] In some examples, the prepolymerization reactor 400 is a negative pressure reactor. In some examples, the postpolymerization reactor 500 is a negative pressure reactor. In some examples, the melt devolatilization reactor 100 is a negative pressure reactor. Negative pressure reactors can operate under negative pressure or even vacuum conditions to facilitate moisture removal, polycondensation thickening, or deep devolatilization.

[0065] In some examples, at least one of the monomer melting vessel 200, prepolymer open-ring vessel 300, prepolymerization vessel 400, and postpolymerization vessel 500 is equipped with a stirrer. Further, all of the monomer melting vessel 200, prepolymer open-ring vessel 300, prepolymerization vessel 400, and postpolymerization vessel 500 are equipped with stirrers.

[0066] In some examples, at least one of the monomer melting vessel 200, the prepolymerization ring-opening vessel 300, the prepolymerization vessel 400, and the postpolymerization vessel 500 is a vertical reactor. Further, the monomer melting vessel 200, the prepolymerization ring-opening vessel 300, the prepolymerization vessel 400, and the postpolymerization vessel 500 are all vertical reactors.

[0067] In some examples, at least one of the monomer melting vessel 200, prepolymerization ring-opening vessel 300, prepolymerization vessel 400, and postpolymerization vessel 500 employs a jacketed structure. Further, all of the monomer melting vessel 200, prepolymerization ring-opening vessel 300, prepolymerization vessel 400, and postpolymerization vessel 500 employ a jacketed structure. In some examples, the heating medium within the jacket includes at least one of biphenyl and diphenyl ether, offering the advantage of precise temperature control.

[0068] In some examples, the polyamide 12 preparation apparatus 10 also includes a melt pump (not shown in the figure), and the outlet of the post-polymerization reactor 500 is connected to the melt inlet 111 of the melt devolatilization reactor 100 via the melt pump.

[0069] In some examples, the polyamide 12 preparation apparatus 10 also includes a strip-forming and pelletizing mechanism (not shown in the figure), through which the discharge from the melt devolatilization reactor 100 is stripped and pelletized.

[0070] The above-mentioned polyamide 12 preparation device 10 does not require additional hot water extraction or solid phase extraction post-processing steps, and can effectively reduce the residual monomer content and TVOC content in the product, reduce the odor of the product, and help reduce equipment investment and production energy consumption.

[0071] Furthermore, the present invention also provides a method for preparing polyamide 12.

[0072] One embodiment of the polyamide 12 preparation method uses the polyamide 12 preparation apparatus 10 of any of the above examples, and the preparation method includes the following steps:

[0073] S1: Add dodecyl lactam, capping agent, catalyst and water to monomer melting vessel 200 and heat to melt to obtain molten raw material.

[0074] S2: Transfer the molten raw material to the prepolymer ring-opening reactor 300 for hydrolysis and ring-opening to obtain polyamide 12 prepolymer.

[0075] S3: The polyamide 12 prepolymer is transferred to the prepolymer reactor 400, where some moisture is removed and preliminary polycondensation is carried out under the conditions of introducing protective gas or negative pressure to obtain the first polyamide 12 melt.

[0076] S4: The first polyamide 12 melt is transferred to the post-polymerization reactor 500 and polycondensation and thickening are continued under vacuum conditions to obtain the second polyamide 12 melt.

[0077] S5: The second polyamide 12 melt is fed into the melt devolatilization reactor 100, where residual dodecyl lactam and volatile components are removed under vacuum conditions to obtain the third polyamide 12 melt.

[0078] In some examples, in step S1, before adding the raw materials, the air in the monomer melting vessel 200 is replaced with nitrogen, and then the temperature is raised to 130~170°C under nitrogen protection to melt the dodecyl lactam, so that the dodecyl lactam is fully melted and mixed evenly.

[0079] In some examples, in step S1, heating and melting are performed under a protective atmosphere.

[0080] In some examples, in step S1, the mass ratio of dodecyl lactam, capping agent, catalyst and water is 100:(0.1~0.8):(0.05~0.1):(8~15).

[0081] In some examples, in step S1, the capping agent includes at least one of adipic acid and terephthalic acid. The catalyst includes at least one of phosphoric acid and sodium hypophosphite.

[0082] In some examples, in step S2, the temperature inside the prepolymer ring-opening reactor 300 is 210~250℃, the holding pressure is 2.5~3.0MPa, and the holding time is 2~4h. This allows the dodecyl lactam to fully hydrolyze and open the ring, forming an oligomer prepolymer.

[0083] In some examples, in step S2, after the reaction is complete, the pressure is slowly released to atmospheric pressure at a rate of 0.5~2 kPa / s, and then the prepolymer is transferred to the prepolymer reactor 400. Slow pressure release helps to maintain the stability of the material state.

[0084] In some examples, in step S3, a protective gas is introduced or the reaction is carried out under a slight negative pressure condition. The absolute pressure of the slight negative pressure condition is, for example, 80~95 kPa.

[0085] In some examples, in step S3, the temperature inside the prepolymer reactor 400 is 190~240℃, and the reaction time is 0.5~3h.

[0086] In some examples, in step S4, the absolute pressure of the vacuum in the post-polymerization reactor 500 is no greater than 10 kPa. In some examples, in step S4, the temperature in the post-polymerization reactor 500 is 190~240℃, and the reaction time is 0.5~3h.

[0087] In some examples, stirring is initiated during polymerization in step S4. In other examples, the melt viscosity is monitored by the current value of the stirring motor, and stirring is stopped when the current reaches a target value.

[0088] In some examples, in step S5, the absolute vacuum pressure inside the reaction chamber 110 is 1~10 kPa. The temperature inside the reaction chamber 110 is 190~250℃. The melt residence time is 5~30 min. The melt residence time can be adjusted by the frequency of the melt pump.

[0089] In some examples, the operating vacuum levels of the prepolymer reactor 400, postpolymer reactor 500, and melt devolatilization reactor 100 are progressively increased along the material conveying direction. For example, the prepolymer reactor 400 is under slight negative pressure, the postpolymer reactor 500 is under high vacuum, and the melt devolatilization reactor 100 is under deep vacuum, thus forming a progressively increasing vacuum gradient that allows moisture and volatile components to be gradually removed.

[0090] The following specific embodiments further illustrate the present invention. These specific embodiments are provided to better understand the present invention, but are not intended to limit the scope of the invention and do not constitute a limitation on its content or protection.

[0091] Example 1

[0092] The polyamide 12 polymerization apparatus of this embodiment includes a monomer melting kettle 200, a prepolymer ring-opening kettle 300, a prepolymerization kettle 400, a postpolymerization kettle 500, a melt pump, a melt devolatilization reactor 100, and a strip pelletizing mechanism connected in sequence.

[0093] The outlet of the monomer melting reactor 200 is connected to the inlet of the prepolymer open-ring reactor 300. The outlet of the prepolymer open-ring reactor 300 is connected to the inlet of the prepolymer reactor 400. The outlet of the prepolymer reactor 400 is connected to the inlet of the postpolymer reactor 500. The outlet of the postpolymer reactor 500 is connected to the melt inlet 111 of the melt devolatilization reactor 100 via a melt pump.

[0094] Both the monomer melting reactor 200 and the prepolymer ring-opening reactor 300 are vertical jacketed pressure-resistant reactors. The prepolymerization reactor 400, the postpolymerization reactor 500, and the melt devolatilization reactor 100 are all vertical jacketed negative pressure reactors. A heating medium is introduced into the jacket; in this embodiment, the heating medium is biphenyl.

[0095] The melt devolatilization reactor 100 includes a vertical reaction chamber 110. The top of the reaction chamber 110 has a melt inlet 111 and a vacuum extraction port 112, while the bottom of the reaction chamber 110 has a melt outlet 113. The vacuum extraction port 112 is connected to a vacuum system. The melt inlet 111 is connected to the outlet of the post-polymerization reactor 500 via a melt pump. The melt discharged from the melt outlet 113 is drawn and granulated by a pelletizing mechanism. A feed guide plate 120 is installed inside the reaction chamber 110 and below the melt inlet 111. The feed guide plate 120 is coaxially arranged with the melt inlet 111 and located directly below it. The orthographic projection of the feed guide plate 120 on the horizontal plane covers the discharge range of the melt inlet 111. The feed guide plate 120 divides the inner cavity 114 of the reaction chamber 110 into a flow guide sub-cavity 1142 and a devolatilization sub-cavity 1144. The feed guide plate 120 slopes downward from its center to its edge on the side facing the melt inlet 111. There is an annular material passage gap 1146 extending circumferentially along the reaction chamber 110 and of equal width at all points between the edge of the feed guide plate 120 and the side wall of the reaction chamber 110. The flow guide sub-cavity 1142 communicates with the devolatilization sub-cavity 1144 through the annular material passage gap 1146. In this embodiment, the width of the annular material passage gap 1146 is 50 mm.

[0096] Multiple hemispherical protrusions 130 are distributed on the sidewall of the devolatilization cavity 1144. The height of each protrusion 130 is 50 mm. The protrusions 130 are arranged in multiple rows along the axial direction of the devolatilization cavity 1144, and the distance l between two adjacent protrusions 130 in the same row is 100 mm. The protrusions 130 in two adjacent rows are staggered from each other along the axial direction of the devolatilization cavity 1144, and the angle α between the geometric center of each protrusion 130 and the line connecting the geometric centers of the two nearest protrusions 130 in the adjacent row is 120°.

[0097] The preparation method of polyamide 12 in this embodiment uses the above-mentioned polyamide 12 polymerization apparatus and includes the following steps:

[0098] Step 1: Add 400 kg of dodecyl lactam, 3.2 kg of adipic acid as a capping agent, 0.2 kg of phosphoric acid as a catalyst, and 40 kg of deionized water sequentially to a monomer melting reactor 200. After closing the reactor lid, replace the air inside the reactor three times with nitrogen. Under nitrogen protection, raise the temperature to 130°C and hold for 1.5 hours to allow the dodecyl lactam to fully melt.

[0099] Step 2: Transfer the molten dodecyl lactam to a prepolymer ring-opening reactor 300, heat to 220°C, maintain pressure at 2.5 MPa, and maintain the temperature and pressure for 3 hours to allow the dodecyl lactam to fully open the ring and obtain polyamide 12 prepolymer.

[0100] Step 3: After the ring-opening reaction is completed, the pressure is slowly released to atmospheric pressure at a rate of 1 kPa / s, and the polyamide 12 prepolymer is transferred to the prepolymer reactor 400. Nitrogen gas is introduced into the prepolymer reactor 400, and the reaction is carried out under slight positive pressure at 210°C with stirring for 0.5 h to obtain the first polyamide 12 melt with low molecular weight.

[0101] Step 4: Transfer the first polyamide 12 melt to the post-polymerization reactor 500, start stirring, gradually establish a high vacuum environment with an absolute pressure not exceeding 10 kPa, a polymerization temperature of 210℃, and a residence time of 1 h. The molecular weight of the melt gradually increases. Monitor the melt viscosity by the current value of the stirring motor. Stop stirring when the current reaches the target value to obtain a high molecular weight second polyamide 12 melt.

[0102] Step 5: The second polyamide 12 melt is pumped to the melt devolatilization reactor 100 by the melt pump. The temperature of the melt devolatilization reactor 100 is 220°C. The melt is guided to the side wall of the devolatilization chamber 1144 by the feed guide plate 120 and flows down the wall. The hemispherical protrusions 130 on the side wall tear the melt and increase the gas-liquid contact area. Under vacuum conditions, the residual monomers and moisture inside the melt are removed. The residence time of the melt is adjusted by the frequency of the melt pump.

[0103] Step 6: After devolatilization, the melt is sequentially drawn into strips, water-cooled and pelletized, and dried to obtain polyamide 12 resin particles.

[0104] Example 2

[0105] The polyamide 12 polymerization apparatus in this embodiment is the same as in Embodiment 1.

[0106] The preparation method of polyamide 12 in this embodiment includes the following steps:

[0107] Step 1: Add 400 kg of dodecyl lactam, 1.6 kg of terephthalic acid as a capping agent, 0.2 kg of sodium hypophosphite as a catalyst, and 40 kg of deionized water sequentially to a monomer melting reactor 200. After closing the reactor lid, replace the air inside the reactor three times with nitrogen. Under nitrogen protection, raise the temperature to 140°C and hold for 1.5 hours to allow the dodecyl lactam to fully melt.

[0108] Step 2: Transfer the molten dodecyl lactam to a prepolymer ring-opening reactor 300, heat to 230°C, maintain pressure at 3.0 MPa, and maintain the temperature and pressure for 3 hours to allow the dodecyl lactam to fully open the ring and obtain polyamide 12 prepolymer.

[0109] Step 3: After the ring-opening reaction is completed, the pressure is slowly released to atmospheric pressure at a rate of 2 kPa / s, and the polyamide 12 prepolymer is transferred to the prepolymer reactor 400. Stirring is started in the prepolymer reactor 400, and the reaction is carried out at 230°C for 0.5 h under slight negative pressure and absolute pressure of 80 kPa to obtain the first polyamide 12 melt with low molecular weight.

[0110] Step 4: Transfer the first polyamide 12 melt to the post-polymerization reactor 500, start stirring, gradually establish a high vacuum environment with an absolute pressure not exceeding 5 kPa, a polymerization temperature of 230℃, and a residence time of 0.8 h. The molecular weight of the melt gradually increases. Monitor the melt viscosity by the current value of the stirring motor. Stop stirring when the current reaches the target value to obtain a high molecular weight second polyamide 12 melt.

[0111] Step 5: The second polyamide 12 melt is pumped to the melt devolatilization reactor 100 by the melt pump. The temperature of the melt devolatilization reactor 100 is 250°C. The melt is guided to the side wall of the devolatilization chamber 1144 by the feed guide plate 120 and flows down the wall. The hemispherical protrusions 130 on the side wall tear the melt and increase the gas-liquid contact area. Under vacuum conditions, the residual monomers and moisture inside the melt are removed. The residence time of the melt is adjusted by the frequency of the melt pump.

[0112] Step 6: After devolatilization, the melt is sequentially drawn into strips, water-cooled and pelletized, and dried to obtain polyamide 12 resin particles.

[0113] Example 3

[0114] The polyamide 12 polymerization apparatus in this embodiment is the same as in Embodiment 1.

[0115] The preparation method of polyamide 12 in this embodiment includes the following steps:

[0116] Step 1: Add 400 kg of dodecyl lactam, 0.4 kg of adipic acid as a capping agent, 0.2 kg of phosphoric acid as a catalyst, and 40 kg of deionized water sequentially to a monomer melting reactor 200. After closing the reactor lid, replace the air inside the reactor three times with nitrogen. Under nitrogen protection, raise the temperature to 130°C and hold for 1.5 hours to allow the dodecyl lactam to fully melt.

[0117] Step 2: Transfer the molten dodecyl lactam to a prepolymer ring-opening reactor 300, heat to 240°C, maintain pressure at 3.5 MPa, and maintain the temperature and pressure for 3 hours to allow the dodecyl lactam to fully open the ring and obtain polyamide 12 prepolymer.

[0118] Step 3: After the ring-opening reaction is completed, slowly release the pressure to atmospheric pressure and transfer the polyamide 12 prepolymer to the prepolymer reactor 400. Nitrogen gas is introduced into the prepolymer reactor 400, and the reaction is carried out under slight positive pressure at 240°C with stirring for 0.3 hours to obtain the first polyamide 12 melt with low molecular weight.

[0119] Step 4: Transfer the first polyamide 12 melt to the post-polymerization reactor 500, start stirring, gradually establish a high vacuum environment with an absolute pressure not exceeding 10 kPa, a polymerization temperature of 250℃, and a residence time of 1 h. The molecular weight of the melt gradually increases. Monitor the melt viscosity by the current value of the stirring motor. Stop stirring when the current reaches the target value to obtain a high molecular weight second polyamide 12 melt.

[0120] Step 5: The second polyamide 12 melt is pumped to the melt devolatilization reactor 100 by the melt pump. The temperature of the melt devolatilization reactor 100 is 270°C. The melt is guided to the side wall of the devolatilization chamber 1144 by the feed guide plate 120 and flows down the wall. The hemispherical protrusions 130 on the side wall tear the melt and increase the gas-liquid contact area. Under vacuum conditions, the residual monomers and moisture inside the melt are removed. The residence time of the melt is adjusted by the frequency of the melt pump.

[0121] Step 6: After devolatilization, the melt is sequentially drawn into strips, water-cooled and pelletized, and dried to obtain polyamide 12 resin particles.

[0122] Comparative Example 1

[0123] The polyamide 12 polymerization apparatus used in this comparative example differs from that in Example 1 in that it does not include a melt devolatilization reactor.

[0124] The preparation method of polyamide 12 in this comparative example includes the following steps:

[0125] Steps 1-4 are the same as steps 1-4 in Example 1.

[0126] Step 5: The melt is sequentially drawn into strips, water-cooled and pelletized, and dried to obtain polyamide 12 resin particles.

[0127] Comparative Example 2

[0128] The polyamide 12 prepared in this comparative example was obtained using a hot water extraction post-treatment process. Specifically, the preparation method of polyamide 12 includes the following steps:

[0129] Step 1: Prepare polyamide 12 resin particles according to the method of Comparative Example 1.

[0130] Step 2: Extract the polyamide 12 resin particles in boiling water for 6 hours.

[0131] Step 3: Wash and dry the extracted polyamide 12 resin particles.

[0132] Five batches of polyamide 12 products prepared in Examples 1-3 and Comparative Examples 1-2 were subjected to residual monomer content (residual monomer) testing, total volatile organic compound (TVOC) testing, and odor rating assessment. The residual monomer test was used to determine the weight percentage of residual dodecyl lactam in the resin, and the test method was in accordance with standard GB / T 41489-2022. The TVOC test was used to determine the content of total volatile components in the resin, and the test method was in accordance with standard GB / T 47192-2026. The odor rating was used to assess the intensity of the odor when the resin is heated, and the test method was in accordance with standard VDA270:2022. The test results are shown in Table 1.

[0133] Table 1

[0134]

[0135] As shown in Table 1, compared with Comparative Example 1, Examples 1 to 3, by setting up a melt devolatilization reactor at the end of the polymerization unit for deep melt devolatilization, reduced the residual dodecylamide content of the resulting resin from 0.2-0.25 wt% to no more than 0.01 wt%, TVOC from 150-300 ppm to no more than 30 ppm, and odor level from 2-4 to 1. Compared with Comparative Example 2, Examples 1 to 3 achieved lower residual monomer content, TVOC content, and odor level without additional hot water extraction or solid-phase extraction post-treatment processes, which helps to reduce equipment investment and production energy consumption. The low-residual-monomer, low-odor polyamide 12 resin prepared in the above examples can meet the usage standards of high-requirement fields such as automotive piping, medical interventional catheters, and 3D printing consumables.

[0136] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0137] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this patent should be determined by the appended claims.

Claims

1. A melt devolatilization reactor, characterized in that, The device includes a reaction chamber, which has a melt inlet, a vacuum outlet, and a melt outlet. A feed guide plate is installed inside the reaction chamber, dividing the inner cavity of the reaction chamber into a guide sub-cavity and a devolatilization sub-cavity. The melt inlet communicates with the guide sub-cavity, and the melt outlet communicates with the devolatilization sub-cavity. A material passage gap is formed between the edge of the feed guide plate and the side wall of the reaction chamber, allowing the melt to pass through. The guide sub-cavity communicates with the devolatilization sub-cavity through the material passage gap. Multiple protrusions are distributed on the side wall of the devolatilization sub-cavity.

2. The melt devolatilization reactor as described in claim 1, characterized in that, The protrusion has a spherical crown structure.

3. The melt devolatilization reactor as described in claim 1, characterized in that, At least one of the following conditions (1) to (4) must be met: (1) The height of the protrusion is 30mm~70mm; (2) The width of the material passage gap is 30mm~80mm; (3) The height of the protrusion is not less than the width of the material passage gap; (4) The protrusion is hemispherical.

4. The melt devolatilization reactor as described in claim 1, characterized in that, At least one of the following conditions (1) to (2) must be met: (1) The projection of the feed guide plate on the horizontal plane is circular and is coaxially arranged with the melt feed port; (2) The feed guide plate is inclined downward from its center to its edge on the side facing the melt feed port.

5. The melt devolatilization reactor according to any one of claims 1 to 4, characterized in that, The protrusions are arranged in multiple rows along the axial direction of the devolatilization cavity, and the protrusions in adjacent rows are staggered from each other in the axial direction of the devolatilization cavity.

6. The melt devolatilization reactor as described in claim 5, characterized in that, At least one of the following conditions (1) to (2) must be met: (1) The distance between two adjacent protrusions in the same column is 50~150mm; (2) The angle between the geometric center of each of the protrusions and the line connecting the geometric centers of the two nearest protrusions in the adjacent row is 60°~120°.

7. A polyamide 12 preparation apparatus, characterized in that, Includes monomer melting reactor, prepolymer ring-opening reactor, prepolymerization reactor, postpolymerization reactor, and melt devolatilization reactor as described in any one of claims 1 to 6; The outlet of the monomer melting reactor is connected to the inlet of the prepolymer open-ring reactor, the outlet of the prepolymer open-ring reactor is connected to the inlet of the prepolymer reactor, the outlet of the prepolymer reactor is connected to the inlet of the postpolymer reactor, and the outlet of the postpolymer reactor is connected to the melt inlet of the melt devolatilization reactor.

8. The polyamide 12 preparation apparatus according to claim 7, characterized in that, The polyamide 12 preparation apparatus also includes a melt pump, and the outlet of the post-polymerization reactor is connected to the melt inlet of the melt devolatilization reactor through the melt pump.

9. A method for preparing polyamide 12, characterized in that, Using the polyamide 12 preparation apparatus according to claim 7 or 8, the preparation method includes the following steps: Dodecyl lactam, end-capping agent, catalyst and water are added to the monomer melting vessel and heated to melt, thereby obtaining molten raw material; The molten raw material is transferred to the prepolymer ring-opening reactor for hydrolysis and ring-opening to obtain polyamide 12 prepolymer; The polyamide 12 prepolymer is transferred to the prepolymerization reactor, where some moisture is removed and preliminary polycondensation is performed under the conditions of introducing protective gas or negative pressure to obtain the first polyamide 12 melt. The first polyamide 12 melt is transferred to the post-polymerization reactor and polycondensation and thickening are continued under vacuum conditions to obtain the second polyamide 12 melt. The second polyamide 12 melt is fed into the melt devolatilization reactor, where residual dodecyl lactam and volatile components are removed under vacuum conditions to obtain the third polyamide 12 melt.

10. The method for preparing polyamide 12 as described in claim 9, characterized in that, At least one of the following conditions (1) to (8) must be met: (1) The operating vacuum levels of the prepolymerization reactor, the postpolymerization reactor, and the melt devolatilization reactor are increased step by step; (2) The temperature inside the melt devolatilization reactor is 190℃~250℃ and the absolute pressure is 1kPa~10kPa; (3) The mass ratio of the dodecyl lactam, the capping agent, the catalyst and water is 100:(0.1~0.8):(0.05~0.1):(8~15); (4) The capping agent includes at least one of adipic acid and terephthalic acid; (5) The catalyst includes at least one of phosphoric acid and sodium hypophosphite; (6) The temperature inside the prepolymer open-ring reactor is 210℃~250℃, the holding pressure is 2.5MPa~3MPa, and the holding time is 2h~4h. (7) The temperature inside the prepolymer reactor is 190℃~240℃, and the reaction time is 0.5h~3h; (8) The temperature inside the post-polymerization reactor is 190℃~240℃ and the reaction time is 0.5h~3h.

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