Efficient, energy-saving and continuous polyvinyl chloride polymerization production process

Abstract

According to the efficient, energy-saving and continuous polyvinyl chloride polymerization production process disclosed by the invention, a set of auger type continuous polymerization reactor is additionally arranged below a feed port of a main reaction kettle, and 2-4 small reaction kettles are additionally arranged behind the main reaction kettle, so that the main reaction kettle becomes a solid-liquid separation and polymerization reaction multifunctional integrated kettle; the volume of each solid-liquid separation and polymerization reaction multifunctional integrated kettle is 1 / 4 of that of the main reaction kettle, a solid substance high-position sensor and a low-speed stirrer are arranged in each solid-liquid separation and polymerization reaction multifunctional integrated kettle, a clear liquid circulating pump is arranged outside each solid-liquid separation and polymerization reaction multifunctional integrated kettle, and a PVC suspension tangential inlet is formed in each solid-liquid separation and polymerization reaction multifunctional integrated kettle; the upper and lower parts of the clear liquid heat exchanger are respectively connected with a cold water and high-temperature hot water outlet and a cold water and high-temperature steam inlet; the clear liquid heat exchanger converts conventional heat exchange between water and a gaseous monomer into heat exchange between water and a liquid material, so that the heat exchange efficiency is improved by dozens of times, forced circulation flow can enhance the heat exchange efficiency, PVC scaling can be prevented, the quality problem is avoided, continuous reaction materials enter the main reaction kettle, and the heat exchange efficiency is improved by dozens of times. Meanwhile, the reaction product polyvinyl chloride particles are discharged, so that a continuous polymerization process is formed, and the polymerization efficiency is greatly improved.

Description

Technical Field

[0001] The present invention relates to an efficient, energy-saving and continuous polyvinyl chloride polymerization production process, belonging to the technical field of polyvinyl chloride production in chemical raw materials. Background Art

[0002] Polyvinyl chloride resin (abbreviated as PVC) is one of the world's four major plastic products and has a wide range of uses. In the production of polyvinyl chloride, in order to save labor and reduce costs, people have continuously increased the volume of the polymerization kettle; however, since the heat exchange of the polymerization kettle mainly relies on the surface jacket for heat exchange, the larger the volume of the polymerization kettle, the smaller the relative specific surface area, and it is very difficult to improve the production efficiency; during production, since the heat cannot be dissipated in time, in order to prevent the temperature and pressure from rising sharply, it is necessary to reduce the speed of the polymerization chemical reaction, which will inevitably lead to insufficient production capacity of large polymerization kettles; at the same time, in order to dissipate the heat generated by the reaction in time, it is necessary to increase the stirring speed. High-speed stirring can not only accelerate the heat exchange speed, but also prevent solid polyvinyl chloride particles from adhering to the wall of the reaction kettle to ensure product quality. However, the problem is that the generated polyvinyl chloride is solid particles, and the solid particles will settle at the bottom of the reaction kettle, which brings a very large resistance to high-speed stirring, will cause the power consumption to increase exponentially, and seriously may burn out the motor.

[0003] In the polymerization production process of PVC, first, vinyl chloride monomer (abbreviated as VCM) is mixed with water, then heated, and additives such as initiators are added. Polymerization reaction will occur under certain temperature and pressure conditions. A large amount of heat will be released during the reaction process. Only by dissipating this heat in time can the polymerization reaction proceed stably and the polymerization kettle will not be damaged by high pressure. Therefore, it is necessary to continuously cool with water. Since the polymerized PVC is solid powder, these solid powders deposit at the bottom of the polymerization kettle (or reaction kettle), which not only hinders heat transfer, but also causes a huge resistance to the stirrer in the polymerization kettle, resulting in a sharp increase in the temperature and pressure in the polymerization kettle; in order to ensure the safety of the polymerization kettle, people have to slow down the reaction speed, reducing the production efficiency; moreover, the power consumption of the stirrer is still increasing because the fluidity of solids is much lower than that of liquids. The more PVC is generated, the greater the resistance to the stirring shaft. At the same time, because the thermal conductivity of solid powder PVC is very small, the heat in the polymerization kettle cannot be transferred out in time, which not only reduces the production efficiency, but also the overheated PVC will re-polymerize into super-large molecules, reducing the purity of the polymerized product; and some polymers adhere to the wall of the polymerization kettle, forming small PVC pieces, and the colors of these small pieces will be different from other colors, thus forming many small dots of different colors, mostly black or red, and some form fish-eye-shaped polymers, affecting the product quality.

[0004] In order to improve production efficiency and product quality, the stirring speed needs to be increased. However, due to the limitation of the heat transfer area, even if the stirring speed is increased, the heat still cannot be dissipated in time. Moreover, it is not suitable to increase the stirring speed for solid particles because stirring solid particles is quite laborious, which will multiply the power of the motor. This not only increases the investment in the motor by many times but also increases the energy consumption.

[0005] A large amount of heat is released during the polymerization reaction. This heat will increase the pressure inside the polymerization kettle, posing a safety hazard. Since it is a reversible reaction, a large amount of heat energy will affect the forward progress of the polymerization reaction, that is, it will proceed in the direction of the decomposition reaction. Also, due to the very poor thermal conductivity of polyvinyl chloride solid particles, the heat cannot be dissipated in time, thus reducing the polymerization efficiency. Another important problem is that the generated polyvinyl chloride solid particles will adhere to the surface of the polymerization kettle. Over time, excessive polymerization will occur, and the color will also become darker, thus affecting the product quality. To improve the heat exchange efficiency, people have developed a method of adding a reflux condenser outside the main reaction kettle to solve the problem of insufficient heat exchange area. This indeed improves the heat exchange efficiency. Specifically, a condenser is added to the top of the polymerization kettle to increase the cooling area, which has a certain effect on improving productivity. However, this method can only cool the gas inside the polymerization kettle. However, the heat transfer coefficient of the gas is much lower than that of the liquid, so the improvement of the heat transfer efficiency is not significant. Moreover, there are always a small amount of inert gases in the polymerization kettle, such as N2, CO2, etc. These inert non-condensable gases will accumulate on the tube wall of the condenser to form a gas film, thus hindering heat exchange. Additionally, an important point is that the gas inside the top condenser is static, and inevitably, some polymers will adhere to the condenser wall, forming PVC small patches. These small patches not only affect heat exchange but also have a different color from normal PVC. After the small patches fall off, they form spots of different colors, mostly black and red, further affecting the product quality. Summary of the Invention

[0006] In order to overcome the problems in the prior art that solid particles will precipitate at the bottom of the reaction kettle, which brings very great resistance to high-speed stirring, to solve the problem that heat cannot be dissipated in time, and to solve the quality problem of polyvinyl chloride products, the present invention provides a brand-new high-efficiency, energy-saving and continuous polyvinyl chloride polymerization production process, which can greatly improve the production efficiency. The technical solution adopted is to transform the conventional polymerization kettle, that is, to add a set of auger-type continuous polymerization reactor under the feed inlet of the main reaction kettle, aiming to make the polymerization reaction proceed stably and at the same time enable the raw materials (deionized water and vinyl chloride monomer) to be fully mixed, so that the reaction kettle becomes the main reaction kettle for continuous polymerization reaction; 2-4 small reaction kettles are added behind the main reaction kettle. The small reaction kettle can not only carry out polymerization reaction, but also carry out solid-liquid separation, making it a multi-functional kettle for solid-liquid separation and polymerization reaction. The volume of each multi-functional kettle for solid-liquid separation and polymerization reaction is 1 / 4 of that of the main reaction kettle. It is internally provided with a high-level sensor for solids and a low-speed stirrer, externally provided with a clear liquid circulation pump, and provided with a tangential inlet for PVC suspension on the top, and the tangential inlet for PVC suspension is connected to the PVC suspension discharge port of the main reaction kettle. Above the clear liquid circulation pump is a clear liquid heat exchanger. The lower end of the clear liquid heat exchanger is connected to the outlet of the clear liquid circulation pump, the upper end is connected to a circulation liquid valve, and then connected to the main reaction kettle through a circulation liquid pipe. The upper and lower parts of the clear liquid heat exchanger are respectively connected to the cold water and high-temperature hot water outlets and the cold water and high-temperature steam inlets; in this way, the clear liquid heat exchanger converts the heat exchange between conventional water and gaseous monomer into the heat exchange between water and liquid materials, increasing the heat exchange efficiency by more than ten times. This is because the density of the liquid is dozens of times greater than that of the gas, and at the same time the thermal conductivity of the liquid is also much greater than that of the gas. Forced circulation can enhance the heat exchange efficiency and prevent the formation of PVC scale, thus avoiding quality problems.

[0007] During operation: Vinyl chloride monomer and deionized water enter the feed buffer from the monomer inlet and water inlet respectively, and then enter the screw-type continuous polymerization reactor in the main reaction kettle for mixing and polymerization reactions. At the same time, start the high-speed stirrer, and open the cold water and high-temperature steam inlets and the cold water and high-temperature hot water outlets respectively. First, introduce hot steam for heating. At this time, the screw-type continuous polymerization reactor and the main reaction kettle carry out polymerization reactions. Since the polymerization reaction is exothermic, the temperature in the reaction kettle rises rapidly. When the temperature rises to a certain level, stop inputting hot steam and change to introducing cooling water for cooling; the generated polyvinyl chloride is concentrated at the bottom of the main reaction kettle, then passes through the PVC suspension discharge port, and then enters the PVC suspension tangential inlet through the control valve, and enters the solid-liquid separation and polymerization reaction multi-functional kettle in a rotating manner. At the same time, start the low-speed stirrer, and the rotation direction of the low-speed stirrer is the same as the rotation direction of the suspension, which can accelerate the solid-liquid separation. In the solid-liquid separation and polymerization reaction multi-functional kettle, the unreacted vinyl chloride continues to react to form polyvinyl chloride. The low-speed stirrer makes the solid and liquid separate by themselves. The supernatant (water and unreacted monomer) is on the top, and the reaction product polyvinyl chloride thick slurry is on the bottom. The supernatant enters the clear liquid circulating pump through the circulating pump suction pipe, and then is transported to the clear liquid heat exchanger for forced circulation cooling, and finally enters the main reaction kettle to complete a cycle. When the polyvinyl chloride thick slurry of the reaction product reaches the upper solid high-level sensor, automatically close the control valve, then manually close the circulating liquid valve, and finally close the clear liquid circulating pump. At this time, a gas space is formed in the clear liquid heat exchanger, and the gas is vinyl chloride monomer. Then open the exhaust valve, discharge the small amount of unreacted vinyl chloride to the vinyl chloride gas holder through the gas holder connecting pipe, and finally discharge the product polyvinyl chloride thick slurry through the polyvinyl chloride thick slurry outlet and enter the next process for dehydration treatment. In this way, there is a continuous supply of reaction materials into the main reaction kettle, and at the same time, the reaction product polyvinyl chloride particles are discharged, forming a continuous polymerization process, which greatly improves the polymerization efficiency; in the main reaction kettle, since there are no large amounts of solid particles, the power consumption is very low, and it is more than ten times more energy-saving than a conventional reaction kettle with solid substances.

[0008] Beneficial effects: The solid particles in the main reaction kettle are timely sent into the solid-liquid separation and polymerization reaction multi-functional kettle, which improves the heat transfer efficiency and has low power consumption. It solves the problem that the solid particles in the prior art will precipitate at the bottom of the reaction kettle, thus bringing a very large resistance to the high-speed stirrer, and it is more than ten times more energy-saving than a conventional reaction kettle with solid substances; since the heat is timely dissipated, the pressure in the main reaction kettle will not increase sharply, eliminating the unsafe hidden danger of high pressure. At the same time, the polymerization efficiency is improved, and over-polymerization is avoided, which can ensure the product quality; replace the top condenser added outside the reaction kettle with a clear liquid heat exchanger. At this time, it becomes forced circulation liquid heat exchange, which further increases the heat exchange efficiency, eliminates the generation of polyvinyl chloride patches, and ensures the product quality. Description of the Drawings

[0009] Figure 1 It is a schematic diagram of the working principle of one main reactor with two multi-functional integrated reactors for solid-liquid separation and polymerization reaction.

[0010] Figure 1 Among them: 1. Feed buffer, 2. Monomer inlet, 3. Water inlet, 4. Main reactor, 5. Screw-type continuous polymerization reactor, 6. Cold water and high-temperature steam inlet, 7. High-speed stirrer, 8. PVC suspension discharge port, 9. Control valve, 10. Multi-functional integrated reactor for solid-liquid separation and polymerization reaction, 11. Tangential inlet of PVC suspension, 12. High-level sensor for solid matter, 13. Low-speed stirrer, 14. Outlet of concentrated PVC slurry, 15. Suction pipe of circulation pump, 16. Circulation pump for clear liquid, 17. Heat exchanger for clear liquid, 18. Outlet of cold water and high-temperature hot water, 19. Gas holder connecting pipe, 20. Exhaust valve, 21. Circulation liquid valve, 22. Circulation liquid pipe. Specific implementation mode

[0011] Add a set of screw-type continuous polymerization reactor below the feed inlet of the main reactor, and add 2 multi-functional integrated reactors for solid-liquid separation and polymerization reaction behind the main reactor. The volume of each multi-functional integrated reactor for solid-liquid separation and polymerization reaction is 1 / 4 of that of the main reactor, which is equipped with a high-level sensor for solid matter and a low-speed stirrer inside, a circulation pump for clear liquid outside, and a tangential inlet of PVC suspension on the top. The tangential inlet of PVC suspension is connected to the PVC suspension discharge port of the main reactor; a heat exchanger for clear liquid is arranged above the circulation pump for clear liquid, the lower end is connected to the outlet of the circulation pump for clear liquid, the upper end is connected to the circulation liquid valve, and then connected to the main reactor through the circulation liquid pipe; the upper and lower parts of the heat exchanger for clear liquid are respectively connected to the outlet of cold water and high-temperature hot water and the inlet of cold water and high-temperature steam; during operation: vinyl chloride monomer and deionized water enter the feed buffer from the monomer inlet and water inlet respectively, and then enter the screw-type continuous polymerization reactor in the main reactor for mixing and polymerization reaction. At the same time, start the high-speed stirrer, open the cold water and high-temperature steam inlet and the cold water and high-temperature hot water outlet respectively, first introduce hot steam for heating. At this time, the screw-type continuous polymerization reactor and the main reactor carry out polymerization reaction. When the temperature rises to a certain degree, stop inputting hot steam and change to input cooling water; the generated PVC particles are concentrated at the bottom of the main reactor, and then pass through the PVC suspension discharge port, then through the control valve into the tangential inlet of PVC suspension, and then into the multi-functional integrated reactor for solid-liquid separation and polymerization reaction. Start the low-speed stirrer, and the supernatant is transported by the circulation pump for clear liquid into the heat exchanger for clear liquid for forced circulation cooling, and then enters the main reactor to complete a cycle; when the reaction product, concentrated PVC slurry, reaches the high-level sensor for solid matter at the upper part, automatically close the control valve, then manually close the circulation liquid valve and the circulation pump for clear liquid, open the exhaust valve, discharge the small amount of unreacted vinyl chloride into the vinyl chloride gas holder, and finally discharge the product, concentrated PVC slurry, through the outlet of concentrated PVC slurry and enter the next process for dehydration treatment.

Claims

1. An efficient, energy-saving and continuous polyvinyl chloride polymerization production process, characterized in that: Add a set of screw-type continuous polymerization reactor (5) below the feed inlet of the main reactor (4), and add 2 - 4 small reactors behind the main reactor (4) to form a multi-functional integrated reactor for solid-liquid separation and polymerization reaction (10). The volume of each multi-functional integrated reactor for solid-liquid separation and polymerization reaction (10) is 1 / 4 of that of the main reactor (4). It is equipped with a high-level sensor for solids (12) and a low-speed stirrer (13) inside, a clear liquid circulation pump (16) outside, and a tangential inlet for PVC suspension (11) on the top. The tangential inlet for PVC suspension (11) is connected to the PVC suspension discharge port (8) of the main reactor (4). There is a clear liquid heat exchanger (17) above the clear liquid circulation pump (16). The lower end of the clear liquid heat exchanger (17) is connected to the outlet of the clear liquid circulation pump (16), and the upper end is connected to a circulation liquid valve (21), and then connected to the main reactor (4) through a circulation liquid pipe (22). The upper and lower parts of the clear liquid heat exchanger (17) are respectively connected to the cold water and high-temperature hot water inlet (3) and the cold water and high-temperature steam outlet; During operation: Vinyl chloride monomer and deionized water enter the feed buffer (1) from the monomer inlet (2) and water inlet (3) respectively, and then enter the screw-type continuous polymerization reactor (5) in the main reactor (4) for mixing and polymerization reaction. At the same time, start the high-speed stirrer (7), and open the cold water and high-temperature steam inlet (6) and the cold water and high-temperature hot water outlet (18) respectively. First, introduce hot steam for heating. At this time, the screw-type continuous polymerization reactor (5) and the main reactor (4) carry out polymerization reaction. Since the polymerization reaction is exothermic, the temperature in the reactor rises rapidly. When the temperature rises to a certain level, stop inputting hot steam and change to input cooling water for cooling; The generated polyvinyl chloride accumulates at the bottom of the main reactor (4), then passes through the PVC suspension discharge port (8), and then enters the tangential inlet for PVC suspension (11) through the control valve (9), and enters the multi-functional integrated reactor for solid-liquid separation and polymerization reaction (10) in a rotating manner. At the same time, start the low-speed stirrer (13), and the rotating direction of the low-speed stirrer (13) is the same as the rotating direction of the suspension; In the multi-functional integrated reactor for solid-liquid separation and polymerization reaction (10), the unreacted vinyl chloride continues to react to form polyvinyl chloride. The low-speed stirrer (13) enables the solid and liquid to separate automatically. The supernatant is on the top, and the reaction product polyvinyl chloride thick slurry is on the bottom. The supernatant enters the clear liquid circulation pump (16) through the circulation pump suction pipe (15), and then is transported into the clear liquid heat exchanger (17) for forced circulation cooling, and finally enters the main reactor (4) to complete a cycle; When the polyvinyl chloride thick slurry of the reaction product reaches the high-level sensor for solids (12) at the upper part, automatically close the control valve (9), then manually close the circulation liquid valve (21), and finally close the clear liquid circulation pump (16). Then open the exhaust valve (20) to discharge the small amount of unreacted vinyl chloride to the vinyl chloride gas holder through the gas holder connecting pipe (19). Finally, discharge the product polyvinyl chloride thick slurry through the polyvinyl chloride thick slurry outlet (14) and enter the next process for dehydration treatment;In the main reactor (4), continuous reaction materials enter, and at the same time, reaction product polyvinyl chloride particles are discharged, forming a continuous polymerization process.

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