A control method for para-aramid solvent recovery
By mixing NMP replenishment solution with polymerization mother liquor and then performing distillation dehydration in PPTA fiber production, the contradiction between NMP replenishment and moisture control was resolved, thereby improving the stability of the polymerization solvent and the quality of the fiber, and reducing production costs.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- TAYHO ARAMID CO LTD NINGXIA
- Filing Date
- 2026-03-06
- Publication Date
- 2026-05-29
Smart Images
Figure SMS_1 
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Abstract
Description
Technical Field
[0001] This application belongs to the field of polymer production technology, and more specifically, relates to a method for controlling the recovery of para-aramid solvent. Background Technology
[0002] Para-aramid (PPTA) is a high-performance specialty fiber with excellent properties such as high strength, high modulus, and high temperature resistance. Its production process involves the polymerization of p-phenylenediamine (PPD) and terephthaloyl chloride (TPC) at low temperatures in a solvent system composed of N-methylpyrrolidone (NMP) and calcium chloride (CaCl2) to produce the PPTA polymer. This polymerization reaction is extremely sensitive to the moisture content of the solvent system, as moisture can undergo side reactions with the acyl chloride groups, leading to a decrease in the degree of polymerization and consequently affecting the mechanical properties of the fiber. Therefore, strictly controlling the moisture content in the polymerization solvent is crucial to ensuring the quality of PPTA fibers.
[0003] In the industrial continuous production of PPTA, the solvent after polymerization needs to be recycled to achieve the reuse of NMP. Since processes such as washing and drying continuously consume some NMP, pure NMP needs to be replenished periodically to maintain the material balance of the solvent system. However, NMP is highly hygroscopic, and the water content of commercially available NMP replenishment solutions is far higher than the moisture requirements of the polymerization solvent. In continuous production, if the NMP replenishment solution is directly mixed with CaCl2 solution to prepare the polymerization solvent, the moisture content of the polymerization solvent will increase, affecting the polymerization reaction and fiber quality. If it is added before the recycling process, an additional dehydration step is required, increasing energy consumption and cost.
[0004] Therefore, how to ensure the effective replenishment of NMP in the polymerization solvent and the effective control of moisture in the solvent system during continuous production is a technical problem that urgently needs to be solved in this field. Summary of the Invention
[0005] The technical effect to be achieved by this application is to provide a method for controlling the recovery of para-aramid solvent, which aims to solve the technical problem of how to simultaneously ensure the effective replenishment of NMP and the effective control of moisture in the solvent system during continuous production.
[0006] To achieve the above-mentioned technical effects, this application provides a method for controlling the recovery of para-aramid solvent, comprising the following steps:
[0007] The NMP supplement solution and the polymerization mother liquor are thoroughly mixed to obtain a mixture; the polymerization mother liquor is an aqueous solution obtained by washing PPTA resin after the polymerization reaction is completed.
[0008] The mixture was subjected to distillation and dehydration to obtain NMP feedstock;
[0009] The NMP raw material is mixed with a CaCl2 solution of 38-40% to prepare a polymerization solvent;
[0010] The polymerization solvent is returned to the polymerization reaction of the PPTA resin for continued use.
[0011] Furthermore, the water content of the NMP replenishing solution is higher than the water content requirement of the polymerization solvent; and / or, the water content of the polymerization solvent is less than 100 mg / kg.
[0012] As a preferred option, the NMP replenishing solution is thoroughly mixed with the polymerization mother liquor to obtain a mixture comprising:
[0013] The NMP replenishing solution and the polymerization mother liquor were thoroughly mixed at a volume ratio of 1:8-11 to obtain a mixture.
[0014] As a preferred option, the NMP replenishing solution is thoroughly mixed with the polymerization mother liquor to obtain a mixture comprising:
[0015] The NMP replenishing solution and the polymerization mother liquor were thoroughly mixed at a volume ratio of 1:10 to obtain a mixture.
[0016] As a preferred option, the NMP replenishing solution is added to the polymerization mother liquor in batches and thoroughly mixed.
[0017] Furthermore, the amount of NMP replenishing solution added in each batch is 5-10% of the total amount of NMP replenishing solution.
[0018] As a preferred option, the water content in the polymerization solvent is 47-95 mg / kg.
[0019] As a preferred option, the mixture is subjected to distillation and dehydration to obtain NMP feedstock, comprising:
[0020] The mixture was subjected to extraction, azeotropic distillation, deextracting and distillation in sequence to separate NMP raw material.
[0021] As a preferred option, the content of CaCl2 in the polymerization solvent is 8.0-8.5%.
[0022] The beneficial effects of this application are as follows:
[0023] 1. The solution provided in this application pre-injects NMP replenishment solution into the starting point of the recovery process of the polymerization mother liquor, and uses the refining process to remove the unstable moisture carried by the NMP replenishment solution along with the original moisture in the polymerization mother liquor. This avoids the problem of excessive moisture in the polymerization solvent caused by directly adding high-moisture NMP replenishment solution, and achieves effective replenishment of NMP and efficient control of moisture in the solvent system.
[0024] 2. The solvent recovery process of this application does not require additional dehydration equipment for NMP replenishment solution, making full use of the existing purification system. The process is simple, easy to operate, and reduces equipment investment and operating costs.
[0025] 3. The solution provided in this application is applicable to the industrial continuous production of PPTA, and can maintain the stability of the polymerization solvent quality during long-term continuous operation, thereby improving production efficiency and product quality consistency. Detailed Implementation
[0026] The embodiments of the technical solution of this application will be described in detail below. The following embodiments are only used to illustrate the technical solution of this application more clearly, and are therefore only examples, and should not be used to limit the scope of protection of this application.
[0027] The composition of the polymerization mother liquor used in the following examples is as follows: NMP 2%, water 76%, calcium chloride 4%, sodium chloride and other salts 17%, and a small amount of oligomers and monomer residues 1%.
[0028] Reference example
[0029] This reference example describes the application of the solvent recovery process of this application in a single batch production as a technical benchmark reference.
[0030] S10: PPTA polymer is prepared by continuous polymerization reaction. After polymerization, the mother liquor is obtained by multi-stage countercurrent water washing.
[0031] For details on how to perform this step, please refer to the preparation process in steps S4-S5 below.
[0032] S20: The polymerization mother liquor is purified to obtain NMP raw material;
[0033] This step includes the following sub-steps:
[0034] (1) Extraction treatment: Trichloromethane is used as the extractant. The maximum volume ratio of extractant to mother liquor is 1:1.1. Trichloromethane enters from the bottom of the extraction tower, and mother liquor enters from the top of the tower. They are in countercurrent contact. The extraction temperature is controlled below 50℃. The aqueous phase after extraction is treated as wastewater and enters the stripping tower. A small amount of trichloromethane in the aqueous phase is distilled and condensed for recovery.
[0035] (2) Azeotropic treatment: The extract phase is fed into the regeneration tower. The bottom temperature of the tower is 150°C and the top temperature is 60°C under normal pressure. NMP containing a small amount of water (about 15% water content) without chloroform is distilled out.
[0036] (3) De-extraction treatment: The crude NMP solution is fed into a vacuum distillation column, the pressure is controlled at about 80 mmHg, the bottom temperature is 120℃ and the top temperature is 130℃, to remove heavy components (calcium chloride, sodium chloride, powder, oligomers, diamine, acyl chloride, etc.) from the crude NMP.
[0037] (4) Distillation treatment: The crude NMP after deextracting is added to a calcium chloride solution with a mass fraction of 40% in proportion. After mixing, it is added to a dehydration tower (reduced pressure distillation tower). The bottom temperature of the tower is 152℃, the top temperature is about 30℃, the pressure is 40mmHg, and the bottom feed is continuous to obtain NMP feed with a water content of 76mg / kg.
[0038] S30: The NMP raw material is mixed with CaCl2 solution to obtain a polymerization solvent with a moisture content of less than 100 mg / kg.
[0039] Specifically, the CaCl2 solution used in this embodiment has a mass concentration of 38.98%, and the calcium chloride content of the polymerization solvent is 8.25%.
[0040] Example 1
[0041] S11: Mix the NMP replenishing solution and the polymerization mother liquor thoroughly at a volume ratio of 1:10 to obtain a mixture;
[0042] Specifically, the water content of the NMP replenishment solution was measured to be 241 mg / kg. The composition of the polymerization mother liquor was the same as that of the polymerization mother liquor in Reference Example S10 above, and will not be repeated here.
[0043] S21: The mixture is refined to obtain NMP raw material;
[0044] The only difference between this step and step S20 in the reference example is the object being processed: Comparative Example 1 processes pure polymerization mother liquor, while this example processes a mixture containing supplemented pure NMP. All other operating conditions are the same.
[0045] S31: The NMP raw material is mixed with CaCl2 solution to obtain a polymerization solvent with a moisture content of less than 100 mg / kg.
[0046] The process and operating conditions of this step are basically the same as those of step S30 in the reference example, and will not be repeated here.
[0047] Example 2
[0048] The only difference between this embodiment and Embodiment 1 is that in step S11, the NMP replenishing solution is mixed with the polymerization mother liquor in batches.
[0049] S12: Mix the NMP replenishing solution with the polymerization mother liquor in batches. Add 5% of the total amount for the first batch and stir for 30 minutes; add 5% of the total amount for the second batch and stir for 30 minutes; ...
[0050] The continuous production process involves constant replenishment of NMP to form a mixture.
[0051] The operating conditions of S22 and S32 are basically the same as those of S21 and S31 in Example 1, and will not be repeated here.
[0052] Comparative Example 1
[0053] The only difference between this comparative example and Example 1 is that in step S11, the NMP replenishment solution is not mixed with the polymerization mother liquor before solvent recovery treatment, but is directly mixed with the recovered NMP raw material after solvent recovery is completed.
[0054] S13: The polymerization mother liquor is purified to obtain NMP raw material;
[0055] The operating conditions for this step are basically the same as those for step S20 in the reference example, and will not be repeated here.
[0056] S23: Add the NMP replenishment solution directly to the recovered NMP raw material and mix thoroughly.
[0057] Specifically, the moisture content of the recovered NMP feedstock was 156 mg / kg. After thorough mixing, the moisture content of the NMP feedstock was 86 mg / kg.
[0058] S33: Mix the uniformly mixed NMP raw material with CaCl2 solution to prepare a polymerization solvent.
[0059] The process and operating conditions of this step are basically the same as those of step S30 in the reference example, and will not be repeated here.
[0060] PPTA polymers were prepared using the polymerization solvents prepared in steps S3 (S30, S31, S32, S33) of the above-mentioned reference examples, Examples 1-2, and comparative examples via a continuous polymerization process. The preparation process is as follows:
[0061] S4: PPD is dissolved in the polymerization solvent at a mass ratio of 1:17. PPD and phthaloyl chloride (TPC) are added to TPC in two steps at a molar ratio of 1:1. The polymerization reaction is carried out at low temperature (1-5℃). In the reactor, the liquid phase gradually turns into the solid phase to form an irregular solid polymer.
[0062] Specifically, in this step, 30-35% of the theoretical amount of TPC is added in the first step, and the reaction is carried out for 5 minutes; in the second step, the compensation amount is calculated based on the water content of the solvent, and the reaction is continued for 30 minutes.
[0063] S5: The reaction slurry after polymerization is washed in multiple countercurrent stages to form a mother liquor for the refining process. After drying, PPTA polymer is obtained.
[0064] Specifically, the multi-stage countercurrent washing process in this step is as follows: 12 washing stages. The first stage uses the return water from the second stage, and the water from the first stage is collected in the mother liquor tank. The second stage uses the return water from the third stage, and so on. The 12th stage uses 80℃ DW water for washing until the pH value reaches 6-7. The washed PPTA polymer slurry is then centrifuged for dehydration, fluidized bed drying (220℃, drying time 0.5 hours), and flash drying (150℃, drying time 0.5 hours) to obtain the PPTA polymer.
[0065] S6: PPTA polymer is dissolved in concentrated sulfuric acid, defoamed, filtered, dry-spun, wet-spun, washed, and dried to obtain para-aramid fiber.
[0066] Specifically, in this step, the PPTA polymer obtained in the previous step is dissolved in concentrated sulfuric acid with a mass fraction of 98%-102%, dissolved by twin-screw extrusion for 2 hours, degassed under vacuum, and filtered; then spun through a dry-jet wet spinning process, including spinning, multi-stage countercurrent water washing and alkali washing, steam roller drying, oiling, and winding to obtain para-aramid fibers.
[0067] Thirty batches were continuously produced for each of the reference example, Examples 1-2, and Comparative Example 1. The moisture content of the polymerization solvent prepared in steps S3 (S30, S31, S32, S33), the amount of secondary acyl chloride added in step S4, the intrinsic viscosity (IV value) of the PPTA polymer obtained in step S5, the change in the intrinsic viscosity (CV value), and the breaking strength of the para-aramid fiber obtained in step S6 were measured for each batch. The breaking strength test method was performed according to the FZ / T 54076-2014 standard for para-aramid (1414) filament. The data are summarized in Tables 1 to 4 below.
[0068] Table 1. Continuous Production Data (Reference Example)
[0069]
[0070] Table 2 Continuous Production Data of Example 1
[0071]
[0072] Table 3 Continuous Production Data of Example 2
[0073]
[0074] Table 4 Continuous Production Data for Comparative Example 1
[0075]
[0076] Experimental conclusion:
[0077] According to the data in Tables 1 to 4, the moisture content ranges of the polymerization solvent in the Reference Example, Example 1, and Example 2 were 36-95 mg / kg, 49-94 mg / kg, and 47-95 mg / kg, respectively. The moisture exceedance rate (greater than 100 mg / kg) was 0% in all 30 batches of continuous production. In Comparative Example 1, the moisture content range of the polymerization solvent was 100-675 mg / kg, with an average of approximately 310 mg / kg. All 30 batches showed severely excessive moisture content, with an exceedance rate as high as 100%, and the highest moisture content reached 675 mg / kg. The above data fully demonstrate that the method of this application can stably control the moisture content of the polymerization solvent below 100 mg / kg, while adding NMP supplemental solution after purification cannot effectively control the moisture content of the polymerization solvent.
[0078] The intrinsic viscosity (IV) values of the PPTA polymers in Reference Example, Example 1, and Example 2 ranged from 6.34 to 6.48 dL / g, 6.34 to 6.49 dL / g, and 6.33 to 6.45 dL / g, respectively, with standard deviations of 0.04, 0.04, and 0.03, and coefficients of variation (CV) of 0.60%, 0.63%, and 0.48%, respectively. In contrast, the intrinsic viscosity (IV) value of the PPTA polymer in Comparative Example 1 ranged from 5.91 to 7.12 dL / g, with a standard deviation of 0.31 and a CV as high as 4.40%, which is seven times higher than that of the method described in this application. This indicates that the PPTA polymer prepared in Comparative Example 1 had poor quality consistency, while the method described in this application stabilized the intrinsic viscosity of the PPTA polymer within a narrow range of 6.34 to 6.49 dL / g, demonstrating excellent quality stability.
[0079] The tensile strength ranges of the para-aramid fibers prepared by the reference example, Example 1, and Example 2 were 20.01-24.21 cN / dtex, 20.52-23.86 cN / dtex, and 22.38-24.11 cN / dtex, respectively, with fluctuation ranges of 4.20 cN / dtex, 3.34 cN / dtex, and 1.73 cN / dtex, respectively. The tensile strength range of the para-aramid fibers prepared by Comparative Example 1 was 13-23.5 cN / dtex, with a fluctuation range of 10.5 cN / dtex. The fibers prepared by the method of this application have a stable tensile strength in the high-performance range of 20-24 cN / dtex, while the lowest value of Comparative Example 1 is only 13 cN / dtex, which does not meet the requirements of the high-performance fiber standard, and the fluctuation range is 2.5-3 times that of the method of this application.
[0080] Example 2 uses a batch mixing method, with an average water content of 74 mg / kg for the polymerization solvent and an average amount of 0.46 kg / batch for the secondary acyl chloride. The PPTA polymer exhibits excellent IV value stability, and all indicators are basically equivalent to those in Example 1. This verifies the process flexibility and stability of the method in this application. The batch addition method can be selected and applied according to the actual production situation.
[0081] As can be seen from the above embodiments, reference examples, and comparative examples, the method for controlling the recovery of para-aramid solvent provided in this application achieves technical effects comparable to the ideal state under actual production conditions of NMP replenishment, resolving the contradiction between NMP replenishment and moisture control in continuous production, without requiring any new equipment. Furthermore, the beneficial effects of this application are significant.
[0082] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.
Claims
1. A method for controlling the recovery of para-aramid solvent, characterized in that, Includes the following steps: The NMP supplement solution and the polymerization mother liquor are thoroughly mixed to obtain a mixture; the polymerization mother liquor is an aqueous solution obtained by washing PPTA resin after the polymerization reaction is completed; the NMP supplement solution is added to the polymerization mother liquor in batches and thoroughly mixed. The mixture was subjected to extraction, azeotropic distillation, deextracting and distillation in sequence to separate and obtain NMP feedstock; The NMP raw material is mixed with a CaCl2 solution of 38-40% to prepare a polymerization solvent; The polymerization solvent is returned to the polymerization reaction of the PPTA resin for continued use.
2. The control method as described in claim 1, characterized in that, The NMP replenishment solution has a higher water content than the required water content of the polymerization solvent; and / or, the water content of the polymerization solvent is less than 100 mg / kg.
3. The control method as described in claim 1, characterized in that, The step of thoroughly mixing the NMP supplement solution with the polymerization mother liquor to obtain a mixture includes: The NMP replenishing solution and the polymerization mother liquor were thoroughly mixed at a volume ratio of 1:8-11 to obtain a mixture.
4. The control method as described in claim 1, characterized in that, The amount of NMP supplement solution added in each batch is 5-10% of the total amount of NMP supplement solution.
5. The control method as described in claim 1, characterized in that, The water content in the polymerization solvent is 47-95 mg / kg.
6. The control method as described in claim 1, characterized in that, The content of CaCl2 in the polymerization solvent is 8.0-8.5%.