Low-pressure separator and separation method of olefin polymerization product

Abstract

The invention relates to the field of high-pressure free radical polymerization, and discloses a low-pressure separator and a separation method of olefin polymerization products, the low-pressure separator comprises a cylinder, and a feed pipe, a light component discharge pipe and an external heating system which are arranged on the cylinder; wherein the upper half part of the feeding pipe is a spiral pipe, the lower half part of the feeding pipe is a straight pipe, and the lower half part of the feeding pipe extends into the cylinder body. According to the low-pressure separator, the entrainment amount of polymers in light-component materials at a top outlet can be reduced, the scaling and crosslinking risks caused by too large difference between the wall surface temperature and the melt temperature can be effectively reduced, and the number of crystal points of film blowing of products is reduced.

Description

Technical Field

[0001] The invention relates to the field of high-pressure free radical polymerization, and in particular to a low-pressure separator and a method for separating olefin polymerization products. Background Art

[0002] High-pressure free radical polymerization is an important method for producing low-density polyethylene, ethylene-vinyl acetate copolymer and ethylene-acrylate copolymer. At present, tubular high-pressure free radical polymerization and kettle high-pressure free radical polymerization are two main types of devices for producing these products. There are also processes that use a combination of tubular reactors and kettle reactors. However, no matter what kind of high-pressure free radical polymerization device, the content of polymer in the material at the reactor outlet is usually below 40wt%. In the case of producing general grades, the content of polymer in the material at the reactor outlet is between 20wt% and 30wt%. Therefore, it is necessary to separate a large amount of unreacted monomers from the polymer.

[0003] In the existing high-pressure free radical polymerization system, if the unreacted monomers and impurities and other light components, such as ethylene, vinyl acetate, initiator solvents and other materials are to be separated from the polymer melt, the separation pressure needs to be reduced to below 1MPa. As we all know, the lower the pressure, the lower the content of light components in the polymer, but the energy consumption of the compression unit increases. It is particularly important to note that if the operation is unstable, during the separation process of the polyolefin melt and the light components, the gas phase material formed by the light components will entrain more polymer melts, resulting in a series of problems such as blockage of pipelines and equipment in the low-pressure circulation loop, decreased heat exchange efficiency, and high ethylene unit consumption. Therefore, how to improve the efficiency of the separator and reduce polymer entrainment is an important basis for ensuring the efficient and stable operation of the high-pressure free radical polymerization device and improving the economy of the device.

[0004] Chinese patent CN107074991B discloses a low-pressure separator, which controls the structural parameters such as the height-to-diameter ratio of the low-pressure separator, the ratio of the inner diameter of the feed pipe to the inner diameter of the low-pressure separator, the position of the feed pipe outlet, and the surface roughness of the low-pressure separator, so as to reduce surface dirt. In addition, the feed pipe of the patent is a pipe that widens from the top to the bottom, and the widened portion of the feed pipe has a cone with a total cone angle of 5°-40°. However, the patent requires a special manhole flange that is disconnected at the top of the container to install and disassemble the feed pipe, which undoubtedly increases the difficulty of equipment maintenance.

[0005] Therefore, a low-pressure separator and a method for separating olefin polymerization products are needed to separate polymers and light components under low pressure, reduce the amount of polymer entrainment in the light components, reduce wall adhesion and scaling on the inner wall of the separation device, and ensure long-term stable operation of the polymerization device. Summary of the invention

[0006] The purpose of the present invention is to overcome the problem that in the existing high-pressure olefin polymerization process, when separating the polymer and light components such as unreacted monomers and impurities in the mixed material generated by the polymerization reaction, the gas phase material formed by the light components will entrain more polymer melts, and the polymer melts will adhere to the inner wall of the separation device, posing the risk of scaling and cross-linking. A low-pressure separator and a method for separating olefin polymerization products are provided. The low-pressure separator can reduce the entrainment of polymers in the light component materials at the top outlet, and can effectively reduce the scaling and cross-linking risks caused by the excessive difference between the wall temperature and the melt temperature, and reduce the number of crystal points of the product blown film.

[0007] In order to achieve the above object, the present invention provides a low-pressure separator in a first aspect, wherein the low-pressure separator comprises:

[0008] A cylinder, and a feed pipe, a light component discharge pipe and an external heating system arranged on the cylinder;

[0009] Wherein, the upper half of the feed pipe is a spiral pipe, and the lower half is a straight pipe, and the lower half extends to the inside of the cylinder.

[0010] Preferably, the inner diameter of the spiral tube of the feed pipe is 0.05-0.6 m, preferably 0.1-0.3 m; the spiral angle is 1-360°, preferably 5-180°, more preferably 10-90°.

[0011] Preferably, the height ratio between the upper half and the lower half of the feed pipe is 0.01-1.5:1, preferably 0.05-0.5:1.

[0012] A second aspect of the present invention provides a method for separating an olefin polymerization product, wherein the separation method is carried out in the aforementioned low-pressure separator, and the method comprises the following steps:

[0013] S1, feeding the mixture containing polymer and light component into the low-pressure separator through a feed pipe for separation to obtain polymer and light component;

[0014] S2. The separated polymer is discharged from the bottom outlet of the low-pressure separator, and the light component is discharged from the light component discharge pipe;

[0015] In S1, the temperature of the external heating medium is controlled by the external heating system to be 2-80°C higher than the internal temperature of the low-pressure separator.

[0016] Preferably, in S1, the mixed material in the feed pipe has a velocity of 0.05-25 m / s in the horizontal direction at the outlet of the spiral pipe, preferably a velocity of 1-15 m / s in the horizontal direction.

[0017] Through the above technical solution, the beneficial technical effects achieved by the present invention are as follows:

[0018] (1) The low-pressure separator provided by the present invention has a special feed pipe structure. The upper part of the feed pipe is a spiral pipe, and the lower part is a straight pipe. When the material enters the cylinder through the feed pipe, it not only has a vertical speed, but also has a certain speed in the horizontal direction, thereby increasing the polymerization speed of the polymer melt and significantly reducing the entrainment of the light component material to the polymer in the light component discharge pipe;

[0019] (2) In the present invention, preferably, by controlling the difference between the temperature of the external heating system in the low-pressure separator and the temperature of the polymer melt, on the one hand, the melt fluidity can be improved, thereby reducing the adhesion of the polymer melt on the wall surface and reducing the number of crystal points in the product blown film; on the other hand, the degradation of the polymer melt caused by excessively high temperature can be avoided. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a schematic diagram of a low-pressure separator;

[0021] Figure 2 It is a top view schematic diagram of the spiral tube of the low-pressure separator feed pipe.

[0022] Description of Reference Numerals

[0023] 1. The head of the cylinder 2. The straight section of the cylinder 3. The bottom feeding section of the cylinder

[0024] 4. Discharge valve 5. Spiral tube of feed pipe 6. Straight tube of feed pipe

[0025] 7. Bottom outlet 8. Light component discharge pipe DETAILED DESCRIPTION

[0026] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0027] A first aspect of the present invention provides a low-pressure separator, wherein the low-pressure separator comprises:

[0028] A cylinder, and a feed pipe, a light component discharge pipe and an external heating system arranged on the cylinder;

[0029] Wherein, the upper half of the feed pipe is a spiral pipe, and the lower half is a straight pipe, and the lower half extends to the inside of the cylinder.

[0030] In the present invention, the upper part of the feed pipe is designed to be spiral, and the centrifugal separation effect generated by the spiral pipe allows the mixed material to have a vertical speed as well as a horizontal speed, thereby extending the residence time of the mixed material, further increasing the aggregation speed of the polymer melt in the mixed material, and reducing the entrainment amount of the polymer in the light component in the light component discharge pipe.

[0031] According to the present invention, preferably, the inner diameter of the spiral tube of the feed pipe is 0.05-0.6 m, preferably 0.1-0.3 m.

[0032] According to the present invention, preferably, the helix angle of the spiral tube of the feed tube is 1-360°, preferably 5-180°, and more preferably 10-90°. The helix angle is the angle formed by the two ends of the spiral tube with the spiral tube as a part of the arc of a circle. The top view of the spiral tube is as shown in Figure 2 As shown, Figure 2 α is the helix angle. When the two ends of the spiral tube form a circle, the helix angle is 360°.

[0033] Figure 2 (a) is a schematic diagram when the spiral angle α is less than 90°. The material enters from one end of the spiral tube, is discharged from the other end of the spiral tube, and then enters the straight section of the feed pipe. After this process, the material has a horizontal velocity at the outlet of the spiral tube, i.e., the inlet of the straight section, so it is in the form of a swirl in the straight tube. Figure 2 (b) is a schematic diagram when the helix angle α>90°. As the helix angle increases, the material can develop more fully in the spiral tube, thereby regulating the initial liquid state of the straight tube section entering the feed pipe.

[0034] According to the present invention, preferably, the inner diameter of the straight tube of the feed pipe is 0.1-2 m, preferably 0.2-1 m.

[0035] In the present invention, preferably, the spiral tube and the straight tube of the feed tube have different inner diameters. Setting different inner diameters for the feed tubes can reduce the flow rate of the material entering the straight tube, which is conducive to the liquids agglomerating to form larger droplets.

[0036] In the present invention, the above-mentioned preferred technical solution is adopted to limit the inner diameter and the helical angle of the spiral tube and the straight tube of the feed pipe, so as to control the horizontal speed of the mixed material in the feed pipe and further improve the separation effect of the separator.

[0037] According to the present invention, preferably, the height ratio of the spiral tube to the straight tube of the feed pipe is 0.01-1.5:1, preferably 0.05-0.5:1.

[0038] According to the present invention, preferably, the low-pressure separator further comprises a bottom outlet arranged below the cylinder and a discharge valve connected to the bottom outlet.

[0039] According to the present invention, preferably, the external heating system is arranged outside the cylinder, and the external heating system is a jacket or a coil.

[0040] According to the present invention, preferably, the cylinder comprises a head, a straight cylinder section and a bottom discharge section of a truncated cone structure, and the opening on the top of the head is connected to the corresponding light component discharge pipe.

[0041] According to the present invention, preferably, the inner diameter of the light component discharge pipe is 0.1-1.5 m, preferably 0.15-0.9 m.

[0042] According to the present invention, preferably, the number of the light component discharge pipes is 1-4, preferably 1-2. When the number of the light component discharge pipes is greater than 1, the light component discharge pipes are evenly distributed circumferentially to the central axis of the cylinder head. Preferably, when the number of the light component discharge pipes is greater than 1 and is an even number, the distances from the light component discharge pipes to the central axis of the cylinder head are equal and symmetrically distributed.

[0043] In the present invention, preferably, the ratio of the distance from the central axis of the light component discharge pipe to the central axis of the cylinder head to the inner diameter of the straight section of the cylinder is 0.1-0.8:1, preferably 0.2-0.7:1. By adopting the above-mentioned preferred technical scheme, the light component discharge pipe is evenly distributed with the central axis of the head, so that the gas material of the light component can be evenly discharged, avoiding excessive polymer entrainment in a part of the light component.

[0044] According to the present invention, preferably, the height ratio of the head of the cylinder to the straight section is 0.025-0.5:1, preferably 0.125-0.25:1. In the present invention, the total height of the cylinder is not particularly limited, and those skilled in the art can make an adaptive selection according to needs. Preferably, the total height of the cylinder is determined according to the residence time of the material and the superficial gas velocity of the gas material in the straight section.

[0045] In the present invention, preferably, the cone angle of the bottom material section is 30-120°, preferably 45-100°, and the height of the bottom material section can be calculated by the cone angle of the bottom material section.

[0046] According to the present invention, preferably, the ratio of the height of the straight tube of the feed pipe to the height of the cylinder is 0.2-0.8:1, preferably 0.3-0.6:1, so that the gas material has a sufficient residence time in the low-pressure separator, while reducing the impact of the feed on the liquid level of the polymer melt. In the present invention, preferably, the straight tube of the feed pipe extends entirely into the cylinder.

[0047] According to the present invention, preferably, the ratio of the inner diameter of the straight tube of the feed pipe to the inner diameter of the straight section of the barrel is 0.1-0.5:1, preferably 0.15-0.4:1.

[0048] In the present invention, there is no particular restriction on the inner diameter of the bottom outlet. Preferably, the ratio of the inner diameter of the bottom outlet to the inner diameter of the straight section of the cylinder is 0.05-0.4:1, preferably 0.1-0.3:1.

[0049] In the present invention, Figure 1 As shown, as a preferred embodiment of the present invention, the low-pressure separator includes a head 1 of the cylinder, a straight cylinder section 2 of the cylinder, a bottom discharge section 3 of the cylinder, a spiral tube 5 and a straight tube 6 of the feed pipe arranged on the cylinder, a bottom outlet 7 arranged below the cylinder, a discharge valve 4 connected to the bottom outlet, and a light component discharge pipe 8.

[0050] A second aspect of the present invention provides a method for separating an olefin polymerization product, wherein the separation method is carried out in the aforementioned low-pressure separator, and the method comprises the following steps:

[0051] S1, feeding the mixture containing polymer and light component into the low-pressure separator through a feed pipe for separation to obtain polymer and light component;

[0052] S2. The separated polymer is discharged from the bottom outlet of the low-pressure separator, and the light component is discharged from the light component discharge pipe;

[0053] In S1, the temperature of the external heating medium is controlled by the external heating system to be 2-80°C higher than the internal temperature of the low-pressure separator.

[0054] In the present invention, the internal temperature of the low-pressure separator is the temperature of the polymer measured in the cylinder of the low-pressure separator.

[0055] In the present invention, by controlling the temperature difference between the external heating system of the low-pressure separator and the internal temperature of the low-pressure separator, on the one hand, the fluidity of the polymer melt can be improved, the adhesion of the polymer melt on the wall surface can be reduced, and the number of crystal points of the product film blowing can be reduced; on the other hand, the degradation of the polymer melt caused by excessively high temperature can be avoided.

[0056] In the present invention, the low-pressure separator is used to separate high-pressure olefin free radical polymerization products. Usually, the outlet material of the high-pressure free radical polymerization reactor passes through at least two separators with different pressure levels, so that the unreacted monomers are basically separated completely. The low-pressure separator described in the present invention is the last-stage separator.

[0057] In the present invention, the mixed material containing polymer and light components comes from the previous separator, and the polymer is a product of olefin free radical polymerization. There is a wide range of selection for the type of the polymer, which can be a copolymer or a homopolymer, and is preferably one of polyethylene and / or ethylene-vinyl acetate copolymer.

[0058] In the present invention, the light component includes olefins and may also include at least one of residual initiator from the polymerization reaction, unreacted telogen and unreacted comonomer.

[0059] In the present invention, the external heating system of the low-pressure separator adopts a conventional heating method in the art, preferably steam and / or pressurized hot water heating.

[0060] According to the present invention, preferably, in S1, the temperature of the external heating medium is 5-50°C higher than the internal temperature of the low-pressure separator, for example, 5°C, 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, and any value in the range consisting of any two values.

[0061] According to the present invention, preferably, in S1, the internal temperature of the low-pressure separator is at least 50° C. higher than the melting point of the polymer, preferably 50-150° C. The above preferred technical solution can further reduce the adhesion of the polymer melt on the wall surface and reduce the degradation of the polymer melt caused by excessive temperature.

[0062] According to the present invention, preferably, the pressure of the low-pressure separator in S1 is 0.1-0.7 MPa, preferably 0.1-0.5 MPa, and the internal temperature of the low-pressure separator is 150-280°C, preferably 160-250°C.

[0063] In the present invention, preferably, during the operation of the low-pressure separator, the material level of the polymer in the low-pressure separator is controlled to be higher than the bottom unloading section to ensure that the separation of the polymer and the light component is continuously carried out.

[0064] According to the present invention, preferably, the mass flow rate ratio of the polymer to the light component in the low-pressure separator is 0-10: 1, for example, 0: 1, 1: 1, 2: 1, 3: 1, 4: 1, 5: 1, 6: 1, 7: 1, 8: 1, 9: 1, 10: 1, and any value in the range consisting of any two values, preferably 1-5: 1. When the mass flow rate ratio of the polymer to the light component in the low-pressure separator is 0: 1, it is the initial stage of the polymerization reaction, and there is no polymer in the low-pressure separator.

[0065] In the present invention, there is no particular limitation on the flow rate of the mixed material, and those skilled in the art can make adaptive adjustments as needed. Preferably, the flow rate of the mixed material is 5-30 t / h.

[0066] In the present invention, preferably, the material level signal of the polymer in the low-pressure separator is monitored in real time to control the discharge valve connected to the outlet of the low-pressure separator to keep the volume ratio of the polymer to the light component in the low-pressure separator stable.

[0067] According to the present invention, preferably, the content of light components in the polymer discharged from the bottom outlet of the low-pressure separator is less than 1wt%, preferably less than 0.5wt%, and more preferably not more than 0.1wt%, based on the total weight of the discharged polymer.

[0068] In the present invention, the temperature and pressure in the low-pressure separator are adjusted to control the content of light components in the polymer discharged from the bottom outlet of the low-pressure separator to be less than 1 wt % based on the total weight of the discharged polymer.

[0069] According to the present invention, in S1, the mixed material in the feed pipe has a speed of 0.05-25 m / s in the horizontal direction of the spiral pipeline outlet, for example, 0.05 m / s, 0.1 m / s, 0.2 m / s, 0.5 m / s, 1 m / s, 1.5 m / s, 2 m / s, 3 m / s, 4 m / s, 5 m / s, 6 m / s, 7 m / s, 8 m / s, 9 m / s, 10 m / s, 15 m / s, 20 m / s, 25 m / s, and any value in the range composed of any two numerical values, preferably has a speed of 1-15 m / s in the horizontal direction.

[0070] In the present invention, preferably, the flow rate of the mixed material in the feed pipe in S1 is 0.5-25 m / s, for example, 0.5 m / s, 1 m / s, 2 m / s, 3 m / s, 4 m / s, 5 m / s, 6 m / s, 7 m / s, 8 m / s, 9 m / s, 10 m / s, 11 m / s, 12 m / s, 13 m / s, 14 m / s, 15 m / s, 16 m / s, 17 m / s, 18 m / s, 19 m / s, 20 m / s, 25 m / s, and any value in the range composed of any two values, preferably 1-15 m / s.

[0071] In the present invention, the above preferred technical solution is adopted to control the inner diameter and the helical angle of the low-pressure separator, thereby controlling the horizontal speed of the mixed material in the feed pipe, prolonging the residence time of the mixed material in the cylinder, and improving the separation efficiency.

[0072] According to the present invention, preferably, the average residence time of the mixed material in the cylinder of the low-pressure separator is 5-600 s, preferably 10-100 s.

[0073] According to the present invention, preferably, the polymer discharged from the bottom outlet of the low-pressure separator is sent to the extrusion granulator through a discharge valve, and the distance from the discharge valve to the outlet of the extrusion granulator is less than 2 m, preferably less than 1 m.

[0074] In the present invention, since the polymer itself has high viscosity, the distance from the discharge valve of the low-pressure separator to the outlet of the extrusion granulator is controlled so that the polymer flows into the granulator under the action of gravity, thereby reducing the resistance of the polymer.

[0075] In the present invention, preferably, use Figure 1 The process of separating polymer and light components in mixed materials by low-pressure separator includes:

[0076] S1. The mixed material from the upper separator is introduced into the straight section 2 of the cylinder of the low-pressure separator through the spiral tube 5 and the straight tube 6 of the feed pipe connected to the head 1 of the cylinder in turn, ensuring that the mixed material has a horizontal velocity.

[0077] The low-pressure separator uses an external heating system to heat the cylinder, and controls the temperature of the external heating medium to be 2-80°C higher than the internal temperature of the low-pressure separator to separate the polymer and light components in the mixed material.

[0078] S2. The separated polymer is discharged from the bottom outlet 7 of the low-pressure separator at the bottom discharge section 3 of the cylinder, and the light component is discharged from the light component discharge pipe 8. The discharged polymer is sent to the extrusion granulator through the discharge valve 4 to obtain a polymer product.

[0079] According to a particularly preferred embodiment of the present invention, a method for separating an olefin polymerization product, wherein the separation method is carried out in the aforementioned low-pressure separator, the method comprising the following steps:

[0080] S1. Introduce the mixed material into the cylinder of the low-pressure separator through a feed pipe, wherein the mass flow rate ratio of the polymer to the light component in the mixed material is 1-5:1, the mixed material in the spiral tube of the feed pipe has a speed of 0.05-25 m / s in the horizontal direction, preferably has a speed of 1-15 m / s in the horizontal direction, and the average residence time of the mixed material in the cylinder of the low-pressure separator is 10-100 s.

[0081] The low-pressure separator is heated by jacketed medium-pressure steam, the temperature of the external heating medium is 5-30°C higher than the internal temperature of the low-pressure separator, the pressure of the low-pressure separator is 0.1-0.5MPa, the internal temperature of the low-pressure separator is 160-250°C, and the internal temperature of the low-pressure separator is 50-150°C higher than the melting point of the polymer.

[0082] S2. The separated polymer is discharged from the bottom outlet of the low-pressure separator, and the light component is discharged from the light component discharge pipe. The discharged polymer is sent to an extrusion granulator through a discharge valve, and the light component content in the obtained polymer product is not higher than 0.1wt%.

[0083] The present invention will be described in detail below through examples and comparative examples. In the following examples and comparative examples,

[0084] The melting point of the polymer is measured by DSC differential scanning calorimetry test, and the test temperature is 10-200°C;

[0085] The light component content in the polymer derived from the bottom outlet of the low-pressure separator was obtained by sampling and performing headspace gas chromatography at a temperature of 90°C.

[0086] The reagents or instruments used without indicating the manufacturer are all conventional products that can be obtained through commercial channels.

[0087] Example 1

[0088] exist Figure 1 The polymer and light components in the mixed material are separated in the low pressure separator shown.

[0089] The inner diameter of the spiral tube of the feed pipe of the low-pressure separator is 0.12m, the helix angle is 30°, the inner diameter of the straight tube is 0.45m, the height of the straight tube is 1.85m, and the height ratio of the spiral tube to the straight tube of the feed pipe is 0.2:1;

[0090] The inner diameter of the light component discharge pipe is 0.175m, there are two light component discharge pipes, and the ratio of the distance from the center axis of the light component discharge pipe to the center axis of the cylinder head to the inner diameter of the straight cylinder section of the cylinder is 0.4:1;

[0091] The total height of the cylinder is 6.03m, the height of the cylinder head is 0.5m, the height of the straight section of the cylinder is 3.8m, the inner diameter of the straight section of the cylinder is 2.0m, the cone angle of the bottom discharge section is 60°, and the inner diameter of the bottom outlet is 0.6m.

[0092] S1. Introduce the mixed material into the cylinder of the low-pressure separator through the feed pipe. The flow rate of polyethylene in the mixed material is 15 t / h, and the flow rate of light components is 4.6 t / h (including unreacted ethylene, residual initiator and unreacted telogen). The mixed material in the spiral tube of the feed pipe has a speed of 10 m / s in the horizontal direction, the flow rate of the mixed material at the inlet of the feed pipe is 87 m / s, and the average residence time of the mixed material in the cylinder of the low-pressure separator is 20 s.

[0093] The low-pressure separator is heated by jacketed medium-pressure steam, the temperature of the external heating system is 220°C, the pressure of the low-pressure separator is 0.12MPa, the internal temperature of the low-pressure separator is 210°C, and the DSC test shows that the melting point of polyethylene is 110°C.

[0094] S2. The separated polyethylene is discharged from the bottom outlet of the low-pressure separator, and the light component is discharged from the light component discharge pipe. The discharged polyethylene is sent to the extrusion granulator through the discharge valve. The distance from the discharge valve to the outlet of the extrusion granulator is 1m, and the light component content in the obtained polymer product is 0.1wt%.

[0095] Example 2

[0096] The low-pressure separator of Example 1 is used to separate the polymer and light components in the mixed material, which is different from Example 1 in that:

[0097] S1. Introduce the mixed material into the cylinder of the low-pressure separator through the feed pipe. The flow rate of polyethylene in the mixed material is 14.2 t / h, and the flow rate of light components is 4.5 t / h (including unreacted ethylene, residual initiator and unreacted polymerization agent). The mixed material in the spiral tube of the feed pipe has a speed of 10 m / s in the horizontal direction, the flow rate of the mixed material at the inlet of the feed pipe is 87 m / s, and the average residence time of the mixed material in the cylinder of the low-pressure separator is 18 s.

[0098] The low-pressure separator is heated by jacketed medium-pressure steam, the temperature of the external heating system is 210°C, the pressure of the low-pressure separator is 0.11 MPa, the internal temperature is 200°C, and the DSC test shows that the melting point of polyethylene is 110°C.

[0099] S2. The separated polyethylene is discharged from the bottom outlet of the low-pressure separator, and the light component is discharged from the light component discharge pipe. The discharged polyethylene is sent to the extrusion granulator through the discharge valve to obtain a polyethylene product with a light component content of 0.1wt%.

[0100] Example 3

[0101] The low-pressure separator of Example 1 is used to separate the polymer and light components in the mixed material, which is different from Example 1 in that:

[0102] S1. Introduce the mixed material into the cylinder of the low-pressure separator through the feed pipe, the flow rate of ethylene-vinyl acetate copolymer in the mixed material is 11.6 t / h, the flow rate of light components is 4.1 t / h (the light components include unreacted ethylene and vinyl acetate, residual initiator and unreacted polycondensing agent), the mixed material in the spiral tube of the feed pipe has a speed of 10 m / s in the horizontal direction, the flow rate of the mixed material in the feed pipe is 87 m / s, and the average residence time of the mixed material in the cylinder of the low-pressure separator is 30 s.

[0103] The low-pressure separator is heated by jacketed medium-pressure steam, the temperature of the external heating system is 195°C, the pressure of the low-pressure separator is 0.11 MPa, the internal temperature is 190°C, and the DSC test shows that the melting point of ethylene-vinyl acetate copolymer is 88°C.

[0104] S2. The separated ethylene-vinyl acetate copolymer is discharged from the bottom outlet of the low-pressure separator, and the light component is discharged from the light component discharge pipe. The discharged ethylene-vinyl acetate copolymer is sent to an extrusion granulator through a discharge valve to obtain a polyethylene product with a light component content of 0.09wt%.

[0105] Example 4

[0106] The low-pressure separator of Example 1 is used to separate the polymer and light components in the mixed material, which is different from Example 1 in that:

[0107] S1. The mixed material is introduced into the cylinder of the low-pressure separator through the feed pipe. The low-pressure separator is heated by jacketed medium-pressure steam. The temperature of the external heating system is 200°C, the pressure of the low-pressure separator is 0.11MPa, the internal temperature is 200°C, and the DSC test shows that the melting point of polyethylene is 110°C.

[0108] S2. The separated polyethylene is discharged from the bottom outlet of the low-pressure separator, and the light component is discharged from the light component discharge pipe. The discharged polyethylene is sent to the extrusion granulator through the discharge valve to obtain a polyethylene product with a light component content of 0.12wt%.

[0109] Example 5

[0110] exist Figure 1 The polymer and light components in the mixed material are separated in the low pressure separator shown.

[0111] The difference from Example 1 is that the inner diameter of the spiral tube of the feed pipe of the low-pressure separator is 0.12m, the helix angle is 150°, the inner diameter of the straight tube is 0.4m, the height of the straight tube is 1.85, and the height ratio of the spiral tube to the straight tube of the feed pipe is 0.3:1;

[0112] The inner diameter of the light component discharge pipe is 0.175m, there are two light component discharge pipes, and the ratio of the distance from the center axis of the light component discharge pipe to the center axis of the cylinder head to the inner diameter of the straight cylinder section of the cylinder is 0.4:1;

[0113] The total height of the cylinder is 6.03m, the height of the cylinder head is 0.5m, the height of the straight section of the cylinder is 3.8m, the inner diameter of the straight section of the cylinder is 2.0m, the cone angle of the bottom discharge section is 60°, and the inner diameter of the bottom outlet is 0.6m.

[0114] S1. Introduce the mixed material into the cylinder of the low-pressure separator through the feed pipe. The flow rate of polyethylene in the mixed material is 15 t / h, and the flow rate of light components is 4.6 t / h (including unreacted ethylene, residual initiator and unreacted polymerization agent). The mixed material in the spiral tube of the feed pipe has a speed of 18 m / s in the horizontal direction, the flow rate of the mixed material in the feed pipe is 87 m / s, and the average residence time of the mixed material in the cylinder of the low-pressure separator is 20 s.

[0115] The low-pressure separator is heated by jacketed medium-pressure steam, the temperature of the external heating system is 220°C, the pressure of the low-pressure separator is 0.12MPa, the internal temperature is 210°C, and the DSC test shows that the melting point of polyethylene is 110°C.

[0116] S2. The separated polyethylene is discharged from the bottom outlet of the low-pressure separator, and the light component is discharged from the light component discharge pipe. The discharged polyethylene is sent to the extrusion granulator through the discharge valve. The distance from the discharge valve to the outlet of the extrusion granulator is 1.0m, and the light component content in the obtained polymer product is 0.1wt%.

[0117] Comparative Example 1

[0118] The low-pressure separator of Example 1 is used to separate the polymer and light components in the mixed material. The difference from Example 1 is that the feed pipe is not provided with a spiral pipe 5, and the mixed material is directly introduced from the straight pipe of the feed pipe.

[0119] S1. The jacket of the external heating system of the low-pressure separator is heated by low-pressure steam, the temperature of the external heating system is 180°C, the pressure of the low-pressure separator is 0.12MPa, and the internal temperature of the low-pressure separator is 210°C. The horizontal velocity of the mixed material in the feed pipe of the low-pressure separator is lower than 0.05m / s, the flow rate of the mixed material in the feed pipe is 87m / s, the average residence time of the mixed material in the cylinder of the low-pressure separator is 20s, and the DSC test shows that the melting point of polyethylene is 109°C.

[0120] S2. The separated polyethylene is discharged from the bottom outlet of the low-pressure separator, and the light component is discharged from the light component discharge pipe. The discharged polyethylene is sent to the extrusion granulator through the discharge valve to obtain a polyethylene product with a light component content of 0.1wt%.

[0121] Comparative Example 2

[0122] The low-pressure separator of Comparative Example 1 is used to separate the polymer and light components in the mixed material, which is different from Comparative Example 1 in that:

[0123] S1. The horizontal velocity of the mixed material in the feed pipe of the low-pressure separator is lower than 0.05 m / s, the flow velocity of the mixed material in the feed pipe is 87 m / s, the average residence time of the mixed material in the cylinder of the low-pressure separator is 20 s, the heating temperature of the external heating system of the low-pressure separator is 175°C, the pressure of the low-pressure separator is 0.11 MPa, the internal temperature of the low-pressure separator is 210°C, and the DSC test shows that the melting point of polyethylene is 111°C.

[0124] S2. The separated polyethylene is discharged from the bottom outlet of the low-pressure separator, and the light component is discharged from the light component discharge pipe. The discharged polyethylene is sent to the extrusion granulator through the discharge valve to obtain a polyethylene product with a light component content of 0.1wt%.

[0125] Test Example 1

[0126] The number of crystal points of the polymer product and the mass of polymer entrained by the top light component were determined. The results are shown in Table 1.

[0127] The mass of polymer carried by the light component in the light component discharge pipe is obtained by cooling and separating the polymer and performing material balance calculation on the system;

[0128] The number of crystal points of the separated polymer product was measured by ASTM D3351 method.

[0129] Table 1

[0130]

[0131] It can be seen from the results in Table 1 that the comparison between Example 1 and Example 2 and Comparative Example 1 and Comparative Example 2 shows that the low-pressure separator of the present invention has better performance in the working conditions of separating polyethylene and separating ethylene-vinyl acetate copolymer. Specifically, the wall scaling degree of the inner wall surface of the low-pressure separator of the present invention is lighter, and the polymer entrainment amount at the outlet of the light component discharge pipe is less, the product quality is more stable, and the optical performance is good, so it has better economic efficiency.

[0132] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A low pressure separator, characterized in that: The low pressure separator comprises: A cylinder, and a feed pipe, a light component discharge pipe and an external heating system arranged on the cylinder; The upper part of the feed pipe is a spiral pipe, and the lower part is a straight pipe, and the lower part extends to the inside of the cylinder.

2. The low-pressure separator according to claim 1, wherein: The inner diameter of the spiral tube of the feed pipe is 0.05-0.6 m, preferably 0.1-0.3 m; the helix angle is 1-360°, preferably 5-180°, more preferably 10-90°; Preferably, the inner diameter of the straight tube of the feed pipe is 0.1-2 m, preferably 0.2-1 m; Preferably, the height ratio of the spiral tube to the straight tube of the feed pipe is 0.01-1.5:1, preferably 0.05-0.5:

1.

3. The low-pressure separator according to claim 1, wherein: The low-pressure separator also includes a bottom outlet arranged below the cylinder and a discharge valve connected to the bottom outlet; Preferably, the external heating system is arranged outside the cylinder, and the external heating system is a jacket or a coil.

4. The low-pressure separator according to claim 1, wherein: The cylinder body comprises a head, a straight cylinder section and a bottom discharge section of a truncated cone structure, and the opening on the top of the head is connected to the corresponding light component discharge pipe; Preferably, the inner diameter of the light component discharge pipe is 0.1-1.5 m, preferably 0.15-0.9 m; Preferably, the number of the light component discharge pipes is 1-4, preferably 1-2; Preferably, when the number of the light component discharge pipes is greater than 1, the light component discharge pipes are evenly distributed in the circumferential direction from the central axis of the cylinder head; Preferably, when the number of the light component discharge pipes is greater than 1 and is an even number, the distances from the light component discharge pipes to the central axis of the cylinder head are equal and symmetrically distributed.

5. The low-pressure separator according to claim 4, wherein: The height ratio of the head and the straight section of the cylinder is 0.025-0.5:1, preferably 0.125-0.25:1; Preferably, the straight tube section is connected to the bottom blanking section, and the taper angle of the bottom blanking section is 30-120°, preferably 45-100°; Preferably, the ratio of the height of the straight tube of the feed pipe to the height of the cylinder is 0.2-0.8:1, preferably 0.3-0.6:

1.

6. A method for separating olefin polymerization products, characterized in that: The separation method is carried out in a low-pressure separator according to any one of claims 1 to 5, and the method comprises the following steps: S1, feeding the mixture containing the polymer and the light component into the low-pressure separator through a feed pipe for separation to obtain the polymer and the light component; S2. The separated polymer is discharged from the bottom outlet of the low-pressure separator, and the light component is discharged from the light component discharge pipe; In S1, the temperature of the external heating medium is controlled by the external heating system to be 2-80°C higher than the internal temperature of the low-pressure separator.

7. The separation method according to claim 6, wherein: In S1, the temperature of the external heating medium is 5-50°C higher than the internal temperature of the low-pressure separator; Preferably, in S1, the internal temperature of the low-pressure separator is at least 50°C higher than the melting point of the polymer, preferably 50-150°C; Preferably, the pressure of the low-pressure separator in S1 is 0.1-0.7 MPa, preferably 0.1-0.5 MPa, and the internal temperature of the low-pressure separator is 150-280°C, preferably 160-250°C.

8. The separation method according to claim 6 or 7, wherein: The polymer in the mixed material is an olefin free radical polymerization product, and the light component includes olefins and may also include at least one of residual initiator, unreacted telogen and unreacted comonomer; Preferably, the mass flow ratio of polymer to light component in the low-pressure separator is 0-10:1, preferably 2-5:1; Preferably, the content of light components in the polymer discharged from the bottom outlet of the low-pressure separator is less than 1 wt%, preferably less than 0.5 wt%, and more preferably not more than 0.1 wt%, based on the total weight of the discharged polymer.

9. The separation method according to any one of claims 6 to 8, wherein: In S1, the mixed material in the feed pipe has a velocity of 0.05-25 m / s in the horizontal direction at the outlet of the spiral pipe, preferably a velocity of 1-15 m / s in the horizontal direction; Preferably, the average residence time of the mixed material in the cylinder of the low-pressure separator is 5-600 s, preferably 10-100 s.

10. The separation method according to any one of claims 6 to 9, wherein: The polymer discharged from the bottom outlet of the low-pressure separator is sent to the extrusion granulator through the discharge valve. The distance from the discharge valve to the outlet of the extrusion granulator is less than 2 m, preferably less than 1 m.

Images