Continuous polymerization production process of high-purity PA6

Abstract

The invention belongs to the technical field of high polymer material synthesis, and particularly relates to a high-purity PA6 continuous polymerization production process which comprises the following specific steps: S1, uniformly mixing a caprolactam solution, a modifier and a delustering agent in a storage tank to form a raw material solution, preheating the raw material solution to 140 DEG C by using medium-temperature hot coal, forming low-temperature hot coal after the medium-temperature hot coal releases heat, and cooling the low-temperature hot coal to the room temperature; the preheated raw material solution is pumped into a pre-polymerization pipe for a pre-polymerization reaction, a stirrer continuously operates in the pre-polymerization reaction, and a low polymer is prepared after a pre-polymerization reaction product is dried; s2, pumping the oligomer into a post-polymerization pipe for post-polymerization reaction, removing impurities from the formed melt through a continuous filter, and feeding the melt into a pelletizing system to prepare slices; s3, performing three-stage extraction on the slices in three tower sections; and S4, drying and cooling the extracted slices to obtain the high-purity PA6. The whole condensation polymerization time is greatly shortened, and the method is suitable for industrial production.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of high polymer material synthesis, and particularly relates to a high-purity PA6 continuous polymerization production process. BACKGROUND

[0002] Polyamide 6 (PA6), also known as nylon 6, is a high molecular compound polymerized from caprolactam monomer, has a translucent milky white crystalline form, has excellent mechanical properties and outstanding wear resistance, has a low friction coefficient, is suitable for making high wear-resistant parts such as bearings and gears, and can be used continuously at a temperature of 80-120 DEG C. PA6 is widely used in the fields of fibers, engineering plastics, film packaging materials, electronic and electrical precision components and industrial machinery accessories, and has the characteristics of thermoplasticity, chemical resistance, high toughness, self-lubricating property and modifiability.

[0003] As one of the largest engineering plastics in the world, PA6 is mainly produced by the ring-opening continuous polymerization process of caprolactam (CPL). Although the traditional process has realized large-scale production, it has significant defects. In the polymerization link, the conventional technology adopts normal pressure or low pressure operation of the pre-polymerization pipe without a stirring device, which causes uneven mixing of the reaction materials, easily causes local overheating or incomplete reaction, causes wide molecular weight distribution and increased gel particles, and finally the residual monomer content of the product is generally higher than 1.0%, which is difficult to meet the needs of high-end applications; in addition, the conventional extraction process mostly uses single-stage or simple extraction tower structure, the mass transfer efficiency is low, the chips are not fully contacted with hot water, the residual monomer removal rate is not high, and the extraction time needs to be prolonged or the water consumption needs to be increased, which in turn increases the energy consumption.

[0004] Therefore, a new PA6 polymerization production process is needed to solve the problems existing in the prior art. SUMMARY

[0005] The purpose of the present application is to provide a high-purity PA6 continuous polymerization production process to solve the problems raised in the background art.

[0006] A high-purity PA6 continuous polymerization production process, the specific steps are as follows: S1, uniformly mix caprolactam solution, modifier and matting agent in a storage tank to form a raw material liquid, the raw material liquid is preheated to 140 DEG C using medium-temperature hot coal, the medium-temperature hot coal is formed into low-temperature hot coal after heat release, and the preheated raw material liquid is pumped into a pre-polymerization pipe for pre-polymerization reaction, and a stirrer continuously operates in the pre-polymerization reaction, and the pre-polymerization reaction material is dried to obtain an oligomer; S2, the oligomer is pumped into a post-polymerization tube for post-polymerization reaction, the low-temperature hot coal is used to cool the post-polymerization tube during the reaction, the low-temperature hot coal is formed into high-temperature hot coal after absorbing heat, the high-temperature hot coal is formed into medium-temperature hot coal after water cooling and then enters S1 for circulation, and the melt formed by post-polymerization reaction enters a pelletizing system after impurity removal by a continuous filter to obtain the chip; S3, the chip is transported into the top of an extraction tower in a sugar-cane structure, the chip falls from the top of the extraction tower under the action of gravity, hot water flows from the bottom to the top of the extraction tower, and the extraction tower comprises three tower sections with different sizes which are connected in series to realize different flow rates of the hot water in the three tower sections for three-stage extraction. S4, the chip after extraction is dried and cooled to obtain high-purity PA6.

[0007] As a preferred embodiment of the above technical solution, the raw material solution is prepared by uniformly mixing 90-95wt% caprolactam solution, 1-2wt% modifier and 3-9wt% matting agent.

[0008] As a preferred embodiment of the above technical solution, the caprolactam solution is a caprolactam aqueous solution with a mass fraction of 30%-40%.

[0009] As a preferred embodiment of the above technical solution, the modifier is prepared by mixing PTA (terephthalic acid), SEED (seed agent) and benzylamine according to a mass ratio of 1:1-3:1-2, the SEED is a low-molecular-weight polymer formed by preliminary polymerization of caprolactam monomers, acts as a crystal seed for polymerization reaction, reduces the activation energy of caprolactam ring-opening polymerization, accelerates the polymerization reaction process and improves the reaction efficiency.

[0010] As a preferred embodiment of the above technical solution, the matting agent is titanium dioxide particles with a particle size of ≤5μm.

[0011] As a preferred embodiment of the above technical solution, the reaction conditions of the pre-polymerization reaction in the pre-polymerization tube are as follows: the operating pressure in the pre-polymerization tube is 0.30-0.40MPa, the temperature is 190-200℃, the stirrer continuously operates at a stirring speed of 60-80rpm, and the residence time is 40-50min.

[0012] As a preferred embodiment of the above technical solution, the reaction conditions of the post-polymerization reaction in the post-polymerization tube are as follows: the operating pressure in the post-polymerization tube is 0.02-0.05MPa, the temperature is 260-270℃, and the residence time is 40-50min.

[0013] As a preferred embodiment of the above technical solution, the temperature of the low-temperature hot coal is 200-210℃, the temperature of the medium-temperature hot coal is 230-240℃, and the temperature of the high-temperature hot coal is 260-270℃.

[0014] As the preferred technical scheme of the above, the extraction tower comprises three towers with different sizes connected in series, and the sizes of the three towers from bottom to top are: Φ1.4m*H2.4m, Φ0.9m*H2.0m and Φ1.4m*H2.4m, so that the flow rates of the hot water in the three towers are 0.4m / s, 1.0m / s and 0.4m / s respectively, and the extraction times in the three towers are 6s, 2s and 6s respectively.

[0015] As the preferred technical scheme of the above, the hot coal is liquid phase biphenyl.

[0016] Compared with the prior art, the present application has the following beneficial effects: 1. The raw material liquid is preheated by the method, so that the overall polycondensation reaction time is greatly reduced, and the oligomer content reaches a peak when the reaction time is 40-50min. If the raw material liquid is not preheated, the oligomer content is still increasing after 70min of reaction time, which means that the polycondensation reaction is still continuing. The long reaction time leads to low economic benefit and is not suitable for industrial production.

[0017] 2. In the method, stirring is carried out in the pre-polymerization reaction, so that the reactants are fully contacted. The oligomer content of caprolactam ring-opening polymerization is an exothermic reaction. In the process without stirring, the reaction heat is easy to accumulate in the system to form a hot spot area, which leads to the degradation of PA6 molecular chain. The temperature of the area far away from the hot spot is low, and the reaction rate is slow, which leads to the maximum value of the oligomer content being 67.2%, which is much lower than the peak value of 86.3% of the oligomer content in the present application. In addition, caprolactam polymerization is a reversible reaction, and the by-product water will inhibit the forward progress of polymerization. Insufficient contact of raw materials and too long reaction time will further reduce the efficiency of the pre-polymerization reaction.

[0018] 3. The three-stage extraction process with different flow rates in the method can prolong the contact time of the extraction hot water and the chips in the first stage of slow extraction, so as to realize the pre-removal of deep impurities. The second stage of fast extraction can quickly remove the dissolved impurities, so as to avoid the enrichment of impurities affecting the mass transfer driving force. The third stage of slow extraction can remove trace residual impurities and protect the chip morphology. Through experiments, the impurity removal effect of the three-stage extraction process with different flow rates in the method is obviously better than that of the three-stage extraction process with a single flow rate. DETAILED DESCRIPTION

[0019] The technical scheme of the present application will be described clearly and completely in combination with the embodiments of the present application.

[0020] Embodiment 1 A continuous PA6 polymerization production process with high purity, and the specific steps are as follows: S1, 900 kg of a 30% by mass caprolactam aqueous solution, 10 kg of a modifier, and 90 kg of a matting agent are mixed to form 1000 kg of a raw material solution, the raw material solution is preheated to 140°C using liquid phase biphenyl at 230°C, the liquid phase biphenyl is cooled to 200°C, then the raw material solution at 140°C is pumped into a pre-polymerization tube, and a pre-polymerization reaction is carried out under the following reaction conditions: an operating pressure of 0.30 MPa in the pre-polymerization tube, a temperature of 190°C, a continuous operation of a stirrer in the pre-polymerization tube, a stirring speed of 60 rpm, a residence time of 40 min, and the pre-polymerization reaction product is dried to form an oligomer; The modifier is prepared by mixing PTA (terephthalic acid), SEED (a seed agent), and benzhydrylamine at a mass ratio of 1:1:1; and the matting agent is titanium dioxide particles with a particle size of ≤5 μm.

[0021] S2, the oligomer is placed in a post-polymerization tube to carry out a post-polymerization reaction, the post-polymerization reaction in the post-polymerization tube is carried out under the following reaction conditions: an operating pressure of 0.02 MPa in the post-polymerization tube, a temperature of 260°C, and a residence time of 40 min; during the reaction, the post-polymerization tube is cooled using liquid phase biphenyl at 200°C in S1, the liquid phase biphenyl is heated to 260°C after absorbing heat, and then cooled to 230°C by water cooling to enter the circulation in S1, and the melt formed by the post-polymerization reaction is filtered by a continuous filter to enter a pelletizing system to form a chip.

[0022] S3, the chip is transported to the top of an extraction tower in a sugar-cane structure, the chip falls from the top of the extraction tower under the action of gravity, hot water flows from the bottom to the top of the extraction tower to realize different flow rates of the hot water in three sections of the tower, the extraction tower includes three sections of different sizes connected in series, the sizes of the three sections from bottom to top are Φ1.4 m×H2.4 m, Φ0.9 m×H2.0 m, and Φ1.4 m×H2.4 m, the flow rates of the hot water in the three sections are 0.4 m / s, 1.0 m / s, and 0.4 m / s, and the extraction times in the three sections are 6 s, 2 s, and 6 s, respectively.

[0023] S4, the chip after extraction is dried and cooled to form high-purity PA6.

[0024] Example 2 A continuous polymerization production process for high-purity PA6 is provided, and the specific steps are as follows: S1, 925 kg of a 35% by mass caprolactam aqueous solution, 15 kg of a modifier, and 60 kg of a matting agent are mixed to form 1000 kg of a raw material solution, the raw material solution is preheated to 140°C using liquid phase biphenyl at 235°C, the liquid phase biphenyl is cooled to 205°C, then the raw material solution at 140°C is pumped into a pre-polymerization tube, and a pre-polymerization reaction is carried out under the following reaction conditions: the operating pressure in the pre-polymerization tube is 0.35 MPa, the temperature is 195°C, the stirrer in the pre-polymerization tube is continuously operated at a stirring speed of 70 rpm, the residence time is 45 min, and the pre-polymerization reaction product is dried to form an oligomer; The modifier is prepared by mixing PTA (terephthalic acid), SEED (a seed agent), and benzhydrylamine at a mass ratio of 1:2:1; and the matting agent is titanium dioxide particles with a particle size of ≤5 μm.

[0025] S2, the oligomer is placed in a post-polymerization tube to carry out a post-polymerization reaction, the reaction conditions of the post-polymerization reaction in the post-polymerization tube are as follows: the operating pressure in the post-polymerization tube is 0.03 MPa, the temperature is 265°C, and the residence time is 45 min; during the reaction, the post-polymerization tube is cooled using liquid phase biphenyl at 205°C in S1, the liquid phase biphenyl is heated to 265°C after absorbing heat, and then cooled to 235°C by water cooling to enter the circulation in S1, and the melt formed by the post-polymerization reaction is filtered by a continuous filter to enter a pelletizing system to form a pellet.

[0026] S3, the pellet is transported to the top of an extraction tower in a sugar cane structure, the pellet falls from the top of the extraction tower under the action of gravity, hot water flows from the bottom to the top of the extraction tower, and the flow rates of the hot water in the three sections of the tower are different in the three-stage extraction; the extraction tower includes three sections of different sizes connected in series, the sizes of the three sections from bottom to top are Φ1.4 m×H2.4 m, Φ0.9 m×H2.0 m, and Φ1.4 m×H2.4 m, the flow rates of the hot water in the three sections are 0.4 m / s, 1.0 m / s, and 0.4 m / s, and the extraction times in the three sections are 6 s, 2 s, and 6 s, respectively.

[0027] S4, the pellet after extraction is dried and cooled to form high-purity PA6.

[0028] Example 3 A continuous polymerization production process for high-purity PA6 is provided, and the specific steps are as follows: S1, 950 kg of a 40% by mass aqueous caprolactam solution, 20 kg of a modifier and 30 kg of a matting agent are mixed to form 1000 kg of a raw material solution, the raw material solution is preheated to 140°C using liquid phase biphenyl at 240°C, the liquid phase biphenyl is cooled to 210°C, then the raw material solution at 140°C is pumped into a pre-polymerization tube, and pre-polymerization is carried out under the following reaction conditions: the operating pressure in the pre-polymerization tube is 0.40 MPa, the temperature is 200°C, the stirrer in the pre-polymerization tube is continuously operated at a stirring speed of 80 rpm, the residence time is 50 min, and the pre-polymerization reactant is dried to form an oligomer; The modifier is prepared by mixing PTA (terephthalic acid), SEED (a seed agent) and benzhydrylamine at a mass ratio of 1:3:2; and the matting agent is titanium dioxide particles with a particle size of ≤5 μm.

[0029] S2, the oligomer is placed in a post-polymerization tube to carry out post-polymerization, the post-polymerization in the post-polymerization tube is carried out under the following reaction conditions: the operating pressure in the post-polymerization tube is 0.05 MPa, the temperature is 270°C, and the residence time is 50 min; during the reaction, the post-polymerization tube is cooled using liquid phase biphenyl at 210°C in S1, the liquid phase biphenyl is heated to 270°C after absorbing heat, and then cooled to 240°C by water cooling to enter the circulation in S1, and the melt formed by the post-polymerization is filtered by a continuous filter to remove impurities, and then enters a pelletizing system to form a chip.

[0030] S3, the chip is fed into the top of an extraction tower in a sugar-cane structure, the chip falls from the top of the extraction tower under the action of gravity, hot water flows from the bottom to the top of the extraction tower, and the flow rate of the hot water is different in the three sections of the tower; the extraction tower comprises three sections of towers connected in series and having different sizes, the sizes of the three sections of towers from bottom to top are Φ1.4 m×H2.4 m, Φ0.9 m×H2.0 m and Φ1.4 m×H2.4 m, the flow rates of the hot water in the three sections of towers are 0.4 m / s, 1.0 m / s and 0.4 m / s, and the extraction times in the three sections of towers are 6 s, 2 s and 6 s, respectively.

[0031] S4, the chip after extraction is dried and cooled to form a high-purity PA6.

[0032] Comparative Example 1 Comparative Example 1 is different from Example 1 only in that the raw material solution in S1 is not preheated to 140°C, and the other steps are the same as in Example 1.

[0033] Comparative Example 2 Comparative Example 2 is different from Example 1 only in that the pre-polymerization in S1 is not adjusted to include the continuous operation of the stirrer at 60 rpm during the reaction, and the other steps are the same as in Example 1.

[0034] 10g of the reaction product of different reaction time of the pre-polymerization in Example 1-Example 3 and Comparative Example 1-Comparative Example 2 was sampled respectively, and the proportion of oligomers in the reaction product was determined, and the results are shown in Table 1 below: From Table 1 above, it can be seen that, in Comparative Example 1, since the raw material liquid is not preheated, the overall polycondensation reaction time is greatly prolonged, and in Example 1-Example 3, the oligomer proportion reaches a peak when the reaction time is 40-50 min, while in Comparative Example 1, the oligomer proportion is still increasing after 70 min of reaction time, which shows that the polycondensation reaction is still continuing, and the long reaction time leads to low economic efficiency, which is not suitable for industrial production.

[0035] In Comparative Example 2, since no stirring is performed in the pre-polymerization, the reactants cannot fully contact, and the oligomer proportion caprolactam ring-opening polymerization is an exothermic reaction, in the process without stirring, the reaction heat is easy to accumulate inside the system, forming a hot spot area, leading to degradation of PA6 molecular chain; while the temperature in the area away from the hot spot is low, the reaction rate is slow, leading to the maximum value of the oligomer proportion to stay at 67.2%, which is much lower than the peak value of 86.3% of the oligomer proportion in Example 1-Example 3.

[0036] In addition, caprolactam polymerization is a reversible reaction, and the byproduct water will inhibit the forward progress of polymerization, and insufficient contact of raw materials and too long reaction time will further reduce the efficiency of the pre-polymerization in Comparative Example 1 and Comparative Example 2.

[0037] Comparative Example 3 The differences between this comparative example 3 and Example 1 are as follows: S3, the slices are transported into the top of the extraction tower with a sugar gourd structure, the slices fall from the top of the extraction tower under the action of gravity, and the hot water flows from the bottom of the extraction tower to the top of the extraction tower, the extraction tower includes three tower segments with the same size in series, the size of the three tower segments is: Φ1.4m×H2.4m, and the flow rate of the hot water in the three tower segments is 0.4m / s.

[0038] The other method steps are the same as those of Example 1.

[0039] Comparative Example 4 The differences between this comparative example 4 and Example 1 are as follows: S3, the slices are transported into the top of the extraction tower with a sugar gourd structure, the slices fall from the top of the extraction tower under the action of gravity, and the hot water flows from the bottom of the extraction tower to the top of the extraction tower, the extraction tower includes three tower segments with the same size in series, the size of the three tower segments is: Φ0.9m×H2.0m, and the flow rate of the hot water in the three tower segments is 1.0m / s.

[0040] Other method steps are the same as Example 1.

[0041] Residue detection was performed on the three extracted slices provided in Example 1, Comparative Example 3 and Comparative Example 4, respectively, and the caprolactam content and oligomer content in the extracted slices were measured as shown in Table 2 below: As can be seen from Table 2 above, using the first-stage slow extraction hot water flow rate in Example 1 can extend the contact time between the extraction hot water and the slices, achieving pre-removal of deep impurities; the second-stage fast extraction hot water flow rate can quickly take away the dissolved impurities, avoiding the enrichment of impurities affecting the mass transfer driving force; and the third-stage slow extraction hot water flow rate can remove trace residual impurities while protecting the slice morphology.

[0042] In Comparative Example 3 and Comparative Example 4, single flow rate extraction was used, and the impurity removal effect was significantly inferior to the scheme in Example 1.

[0043] Although embodiments of the present application have been shown and described, it is to be understood that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the present application, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A continuous polymerization process for producing high-purity PA6, characterized in that, The specific steps are as follows: S1. The caprolactam solution, modifier and matting agent are uniformly mixed in the storage tank to form a raw material liquid. The raw material liquid is first preheated to 140°C using medium-temperature hot coal. After the medium-temperature hot coal releases heat, it becomes low-temperature hot coal. The preheated raw material liquid is pumped into the prepolymerization tube to carry out the prepolymerization reaction. The stirrer runs continuously during the prepolymerization reaction. After the prepolymerization product is dried, an oligomer is obtained. S2. The oligomer is pumped into the post-polymerization tube for post-polymerization reaction. During the reaction, the low-temperature hot coal is used to cool the post-polymerization tube. After the low-temperature hot coal absorbs heat, it becomes high-temperature hot coal. The high-temperature hot coal is cooled by water to form medium-temperature hot coal and then enters S1 for circulation. The melt formed by the post-polymerization reaction is filtered through a continuous filter to remove impurities and then enters the pelletizing system to obtain chips. S3. The slice is fed into the top of the extraction tower of the candied hawthorn structure. The slice falls from the top of the extraction tower under the action of gravity. The hot water for extraction flows from the bottom to the top of the extraction tower. The extraction tower includes three tower sections of different sizes connected in series, so that the hot water for extraction can be extracted at different rates in the three tower sections. S4. After the extracted slices are dried and cooled, high-purity PA6 is obtained.

2. The continuous polymerization production process for high-purity PA6 according to claim 1, characterized in that: The raw material solution is prepared by uniformly mixing 90-95 wt% caprolactam solution, 1-2 wt% modifier and 3-9 wt% matting agent.

3. The continuous polymerization production process for high-purity PA6 according to claim 2, characterized in that: The caprolactam solution is an aqueous solution of caprolactam with a mass fraction of 30%-40%.

4. The continuous polymerization production process for high-purity PA6 according to claim 2, characterized in that: The modifier is prepared by mixing PTA, SEED and benzylamine in a mass ratio of 1:1-3:1-2.

5. The continuous polymerization production process for high-purity PA6 according to claim 2, characterized in that: The matting agent is titanium dioxide particles with a particle size ≤ 5 μm.

6. The continuous polymerization production process for high-purity PA6 according to claim 1, characterized in that: The reaction conditions for the prepolymerization reaction carried out in the prepolymerization tube are as follows: the operating pressure in the prepolymerization tube is 0.30-0.40 MPa, the temperature is 190-200℃, the stirrer runs continuously, the stirring speed is 60-80 rpm, and the residence time is 40-50 min.

7. The continuous polymerization production process for high-purity PA6 according to claim 1, characterized in that: The reaction conditions for the post-polymerization reaction carried out in the post-polymerization tube are as follows: operating pressure in the post-polymerization tube is 0.02-0.05 MPa, temperature is 260-270℃, and residence time is 40-50 min.

8. The continuous polymerization production process for high-purity PA6 according to claim 1, characterized in that: The low-temperature hot coal temperature is 200-210℃, the medium-temperature hot coal temperature is 230-240℃, and the high-temperature hot coal temperature is 260-270℃.

9. The continuous polymerization production process for high-purity PA6 according to claim 1, characterized in that: The extraction column comprises three columns of different sizes connected in series. The dimensions of the three columns from bottom to top are Φ1.4m×H2.4m, Φ0.9m×H2.0m, and Φ1.4m×H2.4m, respectively. The flow velocities of the extraction hot water in the three columns are 0.4m / s, 1.0m / s, and 0.4m / s, respectively, and the extraction times in the three columns are 6s, 2s, and 6s, respectively.

10. A continuous polymerization production process for high-purity PA6 according to any one of claims 1-9, characterized in that: The thermal coal is liquid-phase biphenyl.

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