Method for dehydration of raw material in production of polyphenylene sulfide and method for production of polyphenylene sulfide
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- ZHEJIANG NHU SPECIAL MATERIALS CO LTD
- Filing Date
- 2023-08-15
- Publication Date
- 2026-07-21
AI Technical Summary
The dehydration reaction in the current production of polyphenylene sulfide is inefficient and easily forms a large number of bubbles, which increases the foaming height, affects the filling degree of the reaction device, causes raw material loss and imbalance of proportion, and thus reduces yield and quality.
The method of first heating and then depressurizing is adopted to control the filling degree of the reaction device to 80%-85%. The filling degree is maintained at 80%-86% by adding a second polar solvent with a surface tension less than that of water to break the bubbles. The dehydration temperature is reduced by depressurization, which shortens the dehydration time.
It improves dehydration efficiency, reduces raw material loss, ensures the balance of raw material ratio, and enhances the yield and quality of polyphenylene sulfide.
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Figure BDA0004403860980000151
Abstract
Description
Technical Field
[0001] This invention relates to the field of polyphenylene sulfide (PPS) technology, and in particular to a method for dehydrating raw materials and a method for producing PPS. Background Technology
[0002] Currently, the most commonly used synthetic route for the commercial production of polyphenylene sulfide (PPS) is the sodium sulfide method. The sodium sulfide method involves a dehydration reaction. This dehydration process typically uses sodium hydrosulfide (NaHS) solution, liquid alkali (NaOH), and N-methylpyrrolidone (NMP) in an inert gas atmosphere at atmospheric pressure or a combination of initial pressure control and subsequent atmospheric pressure. The dehydration endpoint temperature is generally controlled above 200°C until the water content in the system is within a specified range for the next polymerization reaction.
[0003] Typically, the system consists of two phases at the beginning of the dehydration reaction: NMP phase / Na2S phase. Under alkaline conditions, as the dehydration reaction temperature rises, NMP hydrolyzes in large quantities into sodium N-methyl-4-aminobutyrate (SMAB), forming a SMAB-NaSH complex. This substance not only directly leads to a large loss of NMP solvent, greatly increasing the overall production cost, but also results in high volatility and low thermal stability of the PPS resin synthesized by reacting with p-dichlorobenzene (PDCB) during the polymerization stage, thus hindering the application of PPS resin in the preparation of fibers, films, monofilaments, etc.
[0004] Meanwhile, dehydration methods using atmospheric pressure or a combination of pressure retardation and atmospheric pressure often lead to increased sulfur loss during the dehydration reaction and large fluctuations in the system's water content, directly affecting the polymerization reaction. Furthermore, these methods are carried out at high temperatures and strong alkalis, causing severe corrosion to the reaction equipment, and the resulting metallic rust directly impacts product quality. Additionally, in the preparation of polyphenylene sulfide (PPS), dehydration operations using atmospheric pressure or a combination of pressure retardation and atmospheric pressure typically involve a dehydration reaction time of 3-5 hours and a polymerization time of 6-24 hours, resulting in low reaction efficiency. Therefore, to improve the continuity of dehydration polymerization and increase the utilization efficiency of the dehydration polymerization reactor, one dehydration reactor is usually used in conjunction with multiple polymerization reactors.
[0005] With the improvement of polymerization process and the use of high-efficiency additives, the polymerization speed has been greatly increased, that is, the polymerization efficiency has been improved. However, the dehydration efficiency has not been improved enough, becoming the bottleneck for the overall yield improvement.
[0006] To improve dehydration reaction efficiency, the dehydration reaction rate and the single-batch dehydration filling density can be increased. One common method to accelerate the dehydration reaction is vacuum dehydration, where the evaporation of water in the solution is facilitated by the formation and collapse of bubbles, thus speeding up the dehydration process. However, vacuum dehydration easily leads to the formation of a large number of bubbles or violent boiling, especially since bubble formation increases the foaming height, necessitating a reduction in the liquid filling volume of the dehydration vessel. Simultaneously, during vacuum dehydration, the raw materials in the solution are carried away from the reaction vessel along with the evaporating water vapor in the bubbles. This not only increases the load on the dehydration distillation column but also causes raw material loss and imbalance in the proportions, ultimately resulting in a decrease in the yield and quality of polyphenylene sulfide (PPS). Summary of the Invention
[0007] Therefore, it is necessary to provide a method for dehydrating raw materials in the production of polyphenylene sulfide (PPS) and a method for producing PPS, which can effectively avoid increasing the foaming height of the dehydration liquid, make full use of the volume of the reaction device, improve dehydration efficiency, reduce raw material loss, ensure the balance of raw material ratio, and thus improve the yield and quality of PPS.
[0008] A method for dehydrating raw materials in the production of polyphenylene sulfide, comprising:
[0009] Sodium hydrosulfide aqueous solution, alkaline aqueous solution and first polar solvent are placed in the reaction device to make the filling degree of the reaction device 80%-85%, and then heated to obtain a dehydrated liquid system. Then, the pressure inside the reaction device is reduced and maintained at 30kPa-50kPa.
[0010] The dehydration liquid system is heated and dehydrated. When the dehydration reaches the predetermined water content condition, the dehydration is stopped. When foam appears on the surface of the dehydration liquid, a second polar solvent is added to the dehydration liquid system. The surface tension of the second polar solvent is less than that of water. The filling degree of the reaction device is controlled to be maintained at 80%-86%.
[0011] In one embodiment, the molar ratio of the first polar solvent to the sodium hydrosulfide aqueous solution is 1.6:1 to 1.8:1;
[0012] And / or, the molar ratio of the alkaline aqueous solution to the sodium hydrosulfide aqueous solution is 1.01:1-1.03:1.
[0013] In one embodiment, the mass ratio of the first polar solvent to the second polar solvent is 0.9:1 to 1.1:1;
[0014] And / or, the surface tension difference between the second polar solvent and the water is 30mN / m-40mN / m.
[0015] In one embodiment, the first polar solvent and the second polar solvent are the same.
[0016] In one embodiment, the decompression rate is 1.8 kPa / min to 2.4 kPa / min during the process of reducing pressure and maintaining the pressure of the dehydrated liquid system at 30 kPa-50 kPa.
[0017] In one embodiment, in the step of heating the dehydration liquid system for dehydration, the heating rate is 0.8℃ / min-1.1℃ / min;
[0018] And / or, in the step of heating the dehydrated liquid system for dehydration, the heating temperature is 140℃-160℃.
[0019] In one embodiment, during the heating process, the temperature is raised to 90°C-110°C for 0.4h-0.6h.
[0020] In one embodiment, both the first polar solvent and the second polar solvent are selected from organic solvents, wherein the organic solvent is selected from at least one of N-methylpyrrolidone, tetramethylurea, and hexamethylphosphoric triamine;
[0021] And / or, the alkaline aqueous solution is selected from sodium hydroxide aqueous solution and / or potassium hydroxide aqueous solution.
[0022] In one embodiment, the second polar solvent is added to the dehydration liquid system by spraying.
[0023] A method for producing polyphenylene sulfide (PPS) involves dehydrating the raw materials using the dehydration method described above for PPS production.
[0024] In the dehydration method of raw materials in the production of polyphenylene sulfide (PPS) of the present invention, a first polar solvent is first mixed with an aqueous solution of sodium hydrosulfide and an alkaline aqueous solution in a reaction device to generate sodium sulfide. Then, under heating conditions, the sodium sulfide completely dissolves in water and the first polar solvent to form a dehydration liquid system. Simultaneously, by reducing the pressure and maintaining the pressure of the reaction device at 30 kPa-50 kPa, compared with atmospheric pressure, this setting can lower the final temperature of dehydration, shorten the dehydration time, and thus improve the dehydration efficiency. In addition, by heating the dehydration liquid system for dehydration, a second polar solvent is added during this process. Utilizing the characteristic that the surface tension of the second polar solvent is much lower than that of water, the bubbles generated during the dehydration process come into contact with the second polar solvent and rupture, avoiding an increase in foaming height caused by a large number of bubbles. This maintains the filling degree of the entire reaction device at 80%-86%, thereby fully utilizing the volume of the reaction device while improving dehydration efficiency, reducing raw material loss, ensuring the balance of raw material ratio, and thus improving the yield and quality of PPS. Detailed Implementation
[0025] To facilitate understanding of the present invention, it will be described in more detail below. However, it should be understood that the present invention can be implemented in many different forms and is not limited to the embodiments or examples described herein. Rather, these embodiments or examples are provided to make the disclosure of the present invention more thorough and complete.
[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments or examples only and is not intended to be limiting of the invention.
[0027] The present invention provides a method for dehydrating raw materials in the production of polyphenylene sulfide, comprising:
[0028] Sodium hydrosulfide aqueous solution, alkaline aqueous solution and first polar solvent are placed in the reaction apparatus to make the filling degree of the reaction apparatus 80%-85%, and then heated to obtain a dehydrated liquid system. Then, the pressure inside the reaction apparatus is reduced and maintained at 30kPa-50kPa. Specifically, an aqueous solution of sodium hydrosulfide, an alkaline aqueous solution, and a first polar solvent are placed in a reaction apparatus, with the apparatus filled to 80%-85%. At this point, the alkaline substance (e.g., alkaline hydroxide) and sodium hydrosulfide undergo a neutralization reaction to produce sodium sulfide and water. Since sodium sulfide is readily soluble in water, a saturated sodium sulfide aqueous solution is formed, with some sodium sulfide still precipitating out as solid. Simultaneously, some sodium sulfide also hydrolyzes to produce hydrogen sulfide gas and sodium hydroxide, making the system alkaline. As the temperature rises, some of the first polar solvent (e.g., NMP) hydrolyzes under alkaline conditions to form sodium N-methyl-4-aminobutyrate. This sodium N-methyl-4-aminobutyrate forms a complex with sodium sulfide in the presence of water, thereby completely dissolving the sodium sulfide in the mixed solvent of water and the first polar solvent, thus obtaining a dehydrated liquid system. Simultaneously, by reducing the pressure inside the reaction apparatus from atmospheric pressure to 30-50 kPa and maintaining this pressure, the final dehydration temperature is lowered compared to atmospheric pressure, the dehydration time is shortened, and thus the dehydration efficiency is improved. Furthermore, because the dehydrated liquid system is first obtained through heating, and then subjected to pressure reduction, this setup avoids excessive foaming and boiling over.
[0029] Optionally, the molar ratio of the first polar solvent to the sodium hydrosulfide aqueous solution is 1.6:1-1.8:1, preferably 1.75, and the molar ratio of the alkaline aqueous solution to the sodium hydrosulfide aqueous solution is 1:1-1.05:1, preferably 1.01:1-1.03:1, and more preferably 1.015. This configuration further ensures that the filling degree of the reaction apparatus is 80%-85%, while simultaneously facilitating the reaction of sodium hydrosulfide and the alkaline substance to generate sufficient sodium sulfide, and allowing sodium sulfide to dissolve better in water and the polar solvent to form a stable dehydration liquid system.
[0030] Optionally, the alkaline aqueous solution is selected from sodium hydroxide aqueous solution and / or potassium hydroxide aqueous solution, preferably sodium hydroxide aqueous solution.
[0031] Optionally, the mass fraction of the solute in the alkaline aqueous solution is 40%-48%; and the mass fraction of sodium hydrosulfide in the sodium hydrosulfide aqueous solution is 38%-45%.
[0032] In one embodiment, the reaction apparatus is subjected to reduced pressure while stirring. This arrangement further prevents bumping.
[0033] In one embodiment, the reaction apparatus can be a reaction vessel or a vacuum distillation column.
[0034] Optionally, during the process of reducing pressure and maintaining the dehydration liquid system pressure at 30kPa-50kPa, the decompression rate is 1.8kPa / min-2.4kPa / min. This setting helps to lower the boiling point of water and improve the subsequent dehydration efficiency, while also preventing the primary polar solvent or the subsequent secondary polar solvent from being extracted in large quantities, which could lead to an imbalance in the raw material and solvent ratio, thereby affecting the yield and quality of polyphenylene sulfide.
[0035] Optionally, during the heating process, the temperature is raised to 90℃-110℃ for 0.4h-0.6h. This setting allows the sodium sulfide generated in the reaction to fully dissolve in the mixed solvent of water and the first polar solvent, reducing the amount of hydrogen sulfide gas generated from the hydrolysis of sodium sulfide being carried away by water vapor during dehydration. This helps reduce the loss of total sulfur in the system, ensures the balance of raw material proportions, and thus improves dehydration efficiency and the yield of polyphenylene sulfide.
[0036] The dehydration method for raw materials in the production of polyphenylene sulfide of the present invention involves heating and dehydrating the above-obtained dehydration liquid system under pressure. When the dehydration reaches a predetermined water content, the dehydration is stopped. When foam appears on the surface of the dehydration liquid, a second polar solvent is added to the dehydration liquid system. The surface tension of the second polar solvent is less than that of water. The filling degree of the reaction device is controlled to be maintained at 80%-86%.
[0037] Specifically, when foam appears on the surface of the dehydration liquid, a second polar solvent is added. Utilizing the fact that the surface tension of the second polar solvent is much lower than that of water, the bubbles generated during the dehydration process come into contact with the second polar solvent and burst. This avoids an increase in foam height caused by a large number of bubbles, maintaining the filling degree of the entire reaction device at 80%-86%. Thus, the volume of the reaction device can be fully utilized while improving dehydration efficiency, reducing raw material loss, ensuring a balanced raw material ratio, and ultimately improving the yield and quality of polyphenylene sulfide.
[0038] Optionally, the mass ratio of the first polar solvent to the second polar solvent is 0.8:1-1.2:1, preferably 0.9:1-1.1:1, and more preferably 1.0; both the first and second polar solvents are selected from organic solvents, and the organic solvents are selected from at least one of N-methylpyrrolidone, tetramethylurea, and hexamethylphosphoric triamine, preferably N-methylpyrrolidone. This configuration better avoids an increase in the foaming height on the surface of the dehydration liquid, further controls the filling degree of the reaction device to be maintained at 80%-86%, thereby fully utilizing the volume of the reaction device, further improving the dehydration rate, and reducing raw material loss.
[0039] Optionally, the surface tension difference between the second polar solvent and the water is 30 mN / m-40 mN / m, preferably 32 mN / m-38 mN / m. This setting helps to accelerate the bursting speed of bubbles in the dehydration liquid, further improving the dehydration efficiency.
[0040] It should be noted that the first polar solvent and the second polar solvent may be the same or different. Preferably, in this invention, the first polar solvent and the second polar solvent are the same. This arrangement facilitates the recovery of the polar solvent.
[0041] By reducing pressure, the boiling point of water can be lowered, thereby reducing the required dehydration temperature for the entire dehydration system. Optionally, in the step of heating the dehydration system, the heating temperature is 140℃-160℃, preferably 150℃. This setting can further improve the dehydration rate while reducing energy consumption.
[0042] Furthermore, in the step of heating the dehydration liquid system for dehydration, the heating rate is 0.8℃ / min-1.1℃ / min, preferably 1.0℃ / min. This setting further makes the temperature of the entire dehydration liquid system more uniform, which is beneficial to further improve the dehydration rate.
[0043] Optionally, the second polar solvent can be added to the dehydration liquid system by spraying. This arrangement allows the second polar solvent to absorb some of the volatilized sulfur-containing substances (e.g., hydrogen sulfide gas) and bring them back into the dehydration liquid system, thereby further reducing the loss of sulfur-containing substances (e.g., hydrogen sulfide) and thus reducing the sulfur loss rate.
[0044] In one embodiment, dehydration to a predetermined water content condition refers to a molar ratio of water to total sulfur in the dehydration liquid system of 1.1:1 to 1.25:1, preferably 1.15:1. This setting is beneficial for the subsequent polymerization reaction, thereby improving the yield and quality of polyphenylene ether resin. Understandably, based on 1 mol of total sulfur, the molar amount of water is 1.1-1.25; simultaneously, the molar amount of total sulfur refers to the total molar amount of all sulfur in the entire dehydration liquid system. In one embodiment, during the heating and dehydration process, the water content in the dehydration liquid system is detected by sampling or by rapid detection using a moisture titrator.
[0045] In one embodiment, a radiation level gauge or a radar level gauge is used to detect foam on the surface of the dehydration liquid.
[0046] It should be noted that in this invention, the reaction device is connected to the dehydration distillation column, so that a small amount of the first polar solvent or the second polar solvent volatilized in the dehydration liquid system can be separated by the dehydration distillation column and then recycled back to the reaction device.
[0047] Meanwhile, this invention also provides a method for producing polyphenylene sulfide (PPS), which employs the dehydration method for raw materials described above in PPS production to dehydrate the raw materials. This PPS production method effectively avoids the increase in foaming height caused by a large number of bubbles, maintaining the filling degree of the entire reaction device at 80%-86%. Therefore, it can fully utilize the volume of the reaction device while improving dehydration efficiency, reducing raw material loss, ensuring the balance of the raw material ratio, and thus improving the yield and quality of PPS.
[0048] The following specific embodiments will further illustrate the dehydration method of raw materials and the production method of polyphenylene sulfide.
[0049] It should also be noted that the raw materials and reagents involved in the embodiments and comparative examples of this invention can all be purchased from the market.
[0050] Example 1
[0051] 35.7 kg (360 mol) of the first polar solvent (N-methylpyrrolidone), 28.0 kg (200 mol) of sodium hydrosulfide aqueous solution (mass fraction 40%) and 19.2 kg (202 mol) of sodium hydroxide aqueous solution (mass fraction 42%) were mixed in a reactor. At this time, the filling degree of the reactor was 83.0%, and the reactor was connected to a dehydration distillation column. Under stirring, the mixture was heated to 95 °C for 0.5 h. At this time, the sodium sulfide in the reactor was completely dissolved in the mixed solvent composed of water and the first polar solvent, that is, the dehydration liquid system was obtained.
[0052] Then, the pressure inside the reactor is reduced and maintained at 40 kPa, with a decompression rate of 2.0 kPa / min. Under this pressure, the temperature is increased to 150°C to dehydrate the dehydration liquid system, with a heating rate of 0.9°C / min. During this process, when foam appears on the surface of the dehydration liquid, 32.6 kg of a second polar solvent (N-methylpyrrolidone) is added to the dehydration liquid by spraying. It should be noted that during the entire dehydration process, a small amount of the first or second polar solvent that evaporates is refluxed back to the reactor through a dehydration distillation column, and water vapor is discharged from the top of the dehydration distillation column.
[0053] When the molar ratio of water to total sulfur in the dehydrated liquid in the reactor was detected to be approximately 1.2, dehydration was stopped, and the remaining dehydrated liquid was obtained. At this point, the reactor filling degree was 84.9%, and the total dehydration time was 2.0 hours. Calculations showed that 30.7 kg of solution was removed, of which the water content was 98.88 wt%, the molar ratio of water to total sulfur was 1.18, and 1.4 mol of hydrogen sulfide gas was lost during dehydration.
[0054] Example 2
[0055] 33.7 kg (340 mol) of the first polar solvent (N-methylpyrrolidone), 28.0 kg (200 mol) of sodium hydrosulfide aqueous solution (mass fraction 40%) and 19.6 kg (206 mol) of sodium hydroxide aqueous solution (mass fraction 42%) were mixed in a reactor. At this point, the reactor was 81.4% filled and connected to a dehydration distillation column. The mixture was heated to 95 °C for 0.5 h under stirring. At this point, the sodium sulfide in the reactor was completely dissolved in the mixed solvent composed of water and the first polar solvent, thus obtaining the dehydration liquid system.
[0056] Then, the pressure inside the reactor is reduced and maintained at 30 kPa, with a decompression rate of 1.8 kPa / min. Under this pressure, the temperature is raised to 140°C to dehydrate the liquid, with a heating rate of 0.8°C / min. During this process, when foam appears on the surface of the dehydrated liquid, 35.4 kg of a second polar solvent (N-methylpyrrolidone) is added to the dehydrated liquid by spraying. It should be noted that during the entire dehydration process, a small amount of the first or second polar solvent that evaporates is refluxed back to the reactor through a dehydration distillation column, and water vapor is discharged from the top of the dehydration distillation column.
[0057] When the molar ratio of water to total sulfur in the dehydrated solution in the reactor was detected to be approximately 1.2, dehydration was stopped, and the remaining dehydrated solution was obtained. At this point, the reactor filling degree was 86.0%, and the total dehydration time was 2.1 hours. Calculations showed that a total of 30.9 kg of solution was removed, of which the water content was 98.32 wt%, the molar ratio of water to total sulfur was 1.25, and 1.5 mol of hydrogen sulfide gas was lost during dehydration.
[0058] Example 3
[0059] 28.3 kg (323 mol) of the first polar solvent (N-methylpyrrolidone), 28.3 kg (202 mol) of sodium hydrosulfide aqueous solution (mass fraction 40%), and 19.6 kg (206 mol) of sodium hydroxide aqueous solution (mass fraction 42%) were mixed in a reactor. At this point, the reactor was filled to 80.0% and connected to a dehydration distillation column. The mixture was heated to 110 °C for 0.6 h under stirring. At this point, the sodium sulfide in the reactor was completely dissolved in the mixed solvent composed of water and the first polar solvent, thus obtaining the dehydration liquid system.
[0060] Then, the pressure inside the reactor is reduced and maintained at 50 kPa, with a decompression rate of 2.4 kPa / min. Under this pressure, the temperature is increased to 160°C to dehydrate the liquid, with a heating rate of 1.0°C / min. During this process, when foam appears on the surface of the dehydrated liquid, 31.2 kg of a second polar solvent (N-methylpyrrolidone) is added to the dehydrated liquid by spraying. It should be noted that during the entire dehydration process, a small amount of the first or second polar solvent that evaporates is refluxed back to the reactor through a dehydration distillation column, and water vapor is discharged from the top of the dehydration distillation column.
[0061] When the molar ratio of water to total sulfur in the dehydrated liquid in the reactor was detected to be approximately 1.2, dehydration was stopped, and the remaining dehydrated liquid was obtained. At this point, the reactor filling degree was 80.1%, and the total dehydration time was 1.9 hours. Calculations showed that a total of 31.1 kg of solution was removed, of which the water content was 99.22 wt%, the molar ratio of water to total sulfur was 1.14, and 1.3 mol of hydrogen sulfide gas was lost during dehydration.
[0062] Example 4
[0063] The only difference between Example 4 and Example 1 is that the first polar solvent is N-methylpyrrolidone and the second polar solvent is tetramethylurea; all other conditions are the same.
[0064] After dehydration in this embodiment, the filling degree of the reactor was 84.5%, and the total dehydration time was 2.5 hours. Calculations showed that a total of 31.1 kg of solution was removed, of which the water content was 96.8 wt%, the molar ratio of water to total sulfur was 1.25, and 1.6 mol of hydrogen sulfide gas was lost during dehydration.
[0065] Example 5
[0066] The only difference between Example 5 and Example 1 is that a second polar solvent (N-methylpyrrolidone) is added directly to the dehydration liquid system via a pump; all other conditions are the same.
[0067] After dehydration in this embodiment, the filling degree of the reactor was 84.1%, and the total dehydration time was 2.7 hours. Calculations showed that a total of 31.5 kg of solution was removed, of which the water content was 97.2 wt%, the molar ratio of water to total sulfur was 1.1, and 2.4 mol of hydrogen sulfide gas was lost during dehydration.
[0068] Example 6
[0069] The only difference between Example 6 and Example 1 is that both the first polar solvent and the second polar solvent are hexamethylphosphoric acid triamine, while all other conditions are the same.
[0070] After dehydration in this embodiment, the filling degree of the reactor was 82.3%, and the total dehydration time was 2.4 hours. Calculations showed that a total of 30.5 kg of solution was removed, of which the water content was 98.9 wt%, the molar ratio of water to total sulfur was 1.24, and 1.6 mol of hydrogen sulfide gas was lost during dehydration.
[0071] Comparative Example 1
[0072] The only difference between Comparative Example 1 and Example 1 is that the mass of the first polar solvent (N-methylpyrrolidone) is 35.7 kg (360 mol), and the mass of the second polar solvent (N-methylpyrrolidone) is zero, that is, no second polar solvent (N-methylpyrrolidone) is added, and all other conditions are the same.
[0073] In this comparative example, the temperature needs to be raised to 180℃ for dehydration, and the entire dehydration time needs to be 3.6 hours to achieve a water-to-total-sulfur molar ratio of approximately 1.2 in the dehydrated solution within the reactor, and to achieve a reactor filling degree of 51.6% after dehydration. Simultaneously, calculations show that a total of 31.4 kg of solution was dehydrated, of which the water content was 96.4 wt%, the water-to-total-sulfur molar ratio was 1.23, and 4.5 mol of hydrogen sulfide gas was lost during dehydration.
[0074] Comparative Example 2
[0075] 27.3 kg (275.6 mol) of the first polar solvent (N-methylpyrrolidone), 21.4 kg (152.7 mol) of sodium hydrosulfide aqueous solution (mass fraction 40%), and 14.7 kg (154.3 mol) of sodium hydroxide aqueous solution (mass fraction 42%) were mixed in a reactor. At this point, the reactor was 63.4% full and connected to a dehydration distillation column. Under stirring, the mixture was heated to 95°C for 0.5 h. At this point, the sodium sulfide in the reactor was completely dissolved in the mixed solvent composed of water and the first polar solvent, thus obtaining the dehydration liquid system. During the heating process to 95°C for 0.5 h, 19.6 kg of the second polar solvent (N-methylpyrrolidone) was added to the dehydration liquid by spraying.
[0076] Then, the pressure inside the reactor is reduced and maintained at 40 kPa, with a decompression rate of 2.0 kPa / min. Under this pressure, the temperature is increased to 150°C to dehydrate the dehydration liquid system, with a heating rate of 0.9°C / min. It should be noted that during the entire dehydration process, a small amount of the first or second polar solvent that evaporates is refluxed back to the reactor through the dehydration distillation column, and water vapor is discharged from the top of the dehydration distillation column.
[0077] In this comparative example, the temperature needs to be raised to 175℃ for dehydration, and the entire dehydration time needs to be 3.4 hours to achieve a water-to-total sulfur molar ratio of approximately 1.2 in the dehydrated solution within the reactor, and to achieve a reactor filling degree of 63.4% after dehydration. Simultaneously, calculations show that a total of 24.4 kg of solution was dehydrated, of which the water content was 97.8 wt%, the water-to-total sulfur molar ratio was 1.20, and 1.8 mol of hydrogen sulfide gas was lost during dehydration.
[0078] Comparative Example 3
[0079] The only difference between Comparative Example 3 and Example 1 is that 7.1 kg (71.7 mol) of a second polar solvent was added during the heating process to 95°C for 0.5 h under stirring. At this time, the filling degree of the reactor was 90%, and all other conditions were the same.
[0080] In this comparative example, the temperature needs to be raised to 178℃ for dehydration, and the entire dehydration time needs to be 3.6 hours to achieve a water-to-total sulfur molar ratio of approximately 1.2 in the dehydrated solution within the reactor, and to achieve a reactor filling degree of 59.5% after dehydration. Simultaneously, calculations show that a total of 30.6 kg of solution was dehydrated, of which the water content was 98.6 wt%, the water-to-total sulfur molar ratio was 1.25, and 4.2 mol of hydrogen sulfide gas was lost during dehydration.
[0081] Comparative Example 4
[0082] The only difference between Comparative Example 4 and Example 1 is that the pressure inside the reactor was reduced and maintained at 20 kPa, while all other conditions were the same.
[0083] In this comparative example, dehydration only required heating to 120℃, with a total dehydration time of 2.2 hours. This resulted in a water-to-total-sulfur molar ratio of approximately 1.2 in the dehydrated solution within the reactor. After dehydration, the reactor's filling degree was 78.5%. Simultaneously, calculations showed that a total of 31.1 kg of solution was dehydrated, containing 98.5 wt% water with a water-to-total-sulfur molar ratio of 1.13. Additionally, 5.2 mol of hydrogen sulfide gas was lost during dehydration.
[0084] Comparative Example 5
[0085] The only difference between Comparative Example 5 and Example 1 is that the pressure inside the reactor was reduced and maintained at 70 kPa, while all other conditions were the same.
[0086] In this comparative example, the temperature needs to be raised to 175℃ for dehydration, and the entire dehydration time is 3.2 hours to achieve a water-to-total sulfur molar ratio of approximately 1.2 in the dehydrated solution within the reactor, with the reactor filling degree reaching 85.1% after dehydration. Simultaneously, calculations show that a total of 30.87 kg of solution was dehydrated, of which the water content was 99.21 wt%, the water-to-total sulfur molar ratio was 1.11, and 1.3 mol of hydrogen sulfide gas was lost during dehydration.
[0087] Comparative Example 6
[0088] The only difference between Comparative Example 6 and Example 1 is that the second polar solvent is water, while all other conditions are the same.
[0089] In this comparative example, the temperature needs to be raised to 185℃ for dehydration, and the entire dehydration time needs to be 4.7 hours to achieve a water-to-total sulfur molar ratio of approximately 1.2 in the dehydrated solution within the reactor, and to achieve a reactor filling degree of 52.1% after dehydration. Simultaneously, calculations show that a total of 60.8 kg of solution was dehydrated, of which the water content was 98.5 wt%, the water-to-total sulfur molar ratio was 1.15, and 1.6 mol of hydrogen sulfide gas was lost during dehydration.
[0090] The remaining dehydrated liquids obtained in Examples 1-6 and Comparative Examples 1-6 were used for subsequent polymerization reactions to prepare polyphenylene sulfide. The specific preparation method is as follows: the corresponding remaining dehydrated liquids were placed from the reaction vessel into the polymerization vessel, and then p-dichlorobenzene was added to the polymerization vessel, wherein the molar ratio of p-dichlorobenzene to the total sulfur in the remaining dehydrated liquid was 1.01:1; then the temperature was raised to 225°C, and the reaction was maintained at this temperature for 2 hours, and then water was added, wherein the molar ratio of the added water to the total sulfur in the remaining dehydrated liquid was 0.8:1. The temperature was increased to 260℃ at a rate of 0.5℃ / min and maintained for 2 hours. After the reaction was completed, the temperature was slowly decreased to 100℃ at a rate of 1.2℃ / min to obtain a reactant containing polyphenylene sulfide. The reactant containing polyphenylene sulfide was filtered through a 120-mesh sieve, then washed sequentially with NMP, 0.1% dilute hydrochloric acid, and water, and finally dried to obtain the corresponding polyphenylene sulfide. The yield, thermal stability, and nitrogen content of the corresponding polyphenylene sulfide were calculated and tested. The specific calculation results are shown in Table 1.
[0091] Table 1
[0092]
[0093] As shown in Table 1, the dehydration method of raw materials in the production of polyphenylene sulfide of the present invention can avoid the increase in foaming height caused by a large number of bubbles, so that the filling degree of the entire reaction device is maintained at 80%-86%. Thus, the volume of the reaction device can be fully utilized while improving dehydration efficiency, reducing raw material loss, ensuring the balance of raw material ratio, and thereby improving the production efficiency and quality of polyphenylene sulfide.
[0094] 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.
[0095] 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 invention 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 invention patent should be determined by the appended claims.
Claims
1. A method for dehydrating raw materials in the production of polyphenylene sulfide, characterized in that, include: Sodium hydrosulfide aqueous solution, alkaline aqueous solution and first polar solvent are placed in the reaction device to make the filling degree of the reaction device 80%-85%, and then heated to obtain a dehydrated liquid system. Then, the pressure inside the reaction device is reduced and maintained at 30kPa-50kPa. The dehydration liquid system is heated and dehydrated. When the dehydration reaches a predetermined water content, the dehydration is stopped. When foam appears on the surface of the dehydration liquid, a second polar solvent is added to the dehydration liquid system. The surface tension of the second polar solvent is less than that of water. The filling degree of the reaction device is controlled to be maintained at 80%-86%. Both the first polar solvent and the second polar solvent are selected from organic solvents.
2. The method for dehydrating raw materials in the production of polyphenylene sulfide according to claim 1, characterized in that, The molar ratio of the first polar solvent to the sodium hydrosulfide aqueous solution is 1.6:1 to 1.8:1; And / or, the molar ratio of the alkaline aqueous solution to the sodium hydrosulfide aqueous solution is 1.01:1-1.03:
1.
3. The method for dehydrating raw materials in the production of polyphenylene sulfide according to claim 1, characterized in that, The mass ratio of the first polar solvent to the second polar solvent is 0.9:1 to 1.1:1; And / or, the surface tension difference between the second polar solvent and the water is 30mN / m-40mN / m.
4. The method for dehydrating raw materials in the production of polyphenylene sulfide according to claim 1, characterized in that, The first polar solvent and the second polar solvent are the same.
5. The method for dehydrating raw materials in the production of polyphenylene sulfide according to claim 1, characterized in that, During the process of reducing pressure and maintaining the pressure of the dehydrated liquid system at 30kPa-50kPa, the decompression rate is 1.8kPa / min-2.4kPa / min.
6. The method for dehydrating raw materials in the production of polyphenylene sulfide according to claim 1, characterized in that, In the step of heating and dehydrating the dehydrated liquid system, the heating rate is 0.8℃ / min-1.1℃ / min; And / or, in the step of heating and dehydrating the dehydrated liquid system, the dehydration temperature is 140℃-160℃.
7. The method for dehydrating raw materials in the production of polyphenylene sulfide according to claim 1, characterized in that, During the heating process, the temperature is raised to 90℃-110℃ for 0.4h-0.6h.
8. The method for dehydrating raw materials in the production of polyphenylene sulfide according to claim 1, characterized in that, The organic solvent is selected from at least one of N-methylpyrrolidone, tetramethylurea, and hexamethylphosphoric triamine; And / or, the alkaline aqueous solution is selected from sodium hydroxide aqueous solution and / or potassium hydroxide aqueous solution.
9. The method for dehydrating raw materials in the production of polyphenylene sulfide according to claim 1, characterized in that, The second polar solvent is added to the dehydration liquid system by spraying.
10. A method for producing polyphenylene sulfide, characterized in that, The raw materials are dehydrated using the dehydration method for the production of polyphenylene sulfide as described in any one of claims 1-9.