Low pressure separator and method for separating olefin polymerization products

Abstract

The application relates to the field of high-pressure radical polymerization, and discloses a low-pressure separator and a separation method of an olefin polymerization product. The low-pressure separator comprises a barrel, a feeding pipe, a light component discharge pipe and an external heating system arranged on the barrel; the upper half of the feeding pipe is a spiral pipe, the lower half is a straight pipe, and the lower half extends to the inside of the barrel. The low-pressure separator can reduce the amount of polymer entrained in the light component material at the top outlet, effectively reduce the risk of fouling and crosslinking caused by too large temperature difference between the wall surface and the melt, and reduce the number of crystal points in the product film.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of high-pressure radical polymerization, in particular to a low-pressure separator and a method for separating an olefin polymerization product. BACKGROUND

[0002] High-pressure radical polymerization device is an important method for producing low-density polyethylene, ethylene-vinyl acetate copolymer and ethylene-acrylate copolymer. At present, tubular high-pressure radical polymerization device and kettle-type high-pressure radical polymerization device are two main types of devices for producing the above-mentioned products, and there is also a process combining tubular reactor and kettle-type reactor. However, no matter what kind of high-pressure radical polymerization device, the content of polymer in the material at the outlet of the reactor is usually below 40wt%, and in the case of producing general grades, the content of polymer in the material at the outlet of the reactor is between 20wt% and 30wt%. Therefore, a large amount of unreacted monomer needs to be separated from the polymer.

[0003] In the existing high-pressure radical polymerization system, if the unreacted monomer and impurities such as light components, such as ethylene, vinyl acetate, initiator solvent and other materials, are to be separated from the polymer melt, the separation pressure needs to be reduced to below 1MPa. It is well known that 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 not stable, during the separation of polyolefin melt and light components, the gas phase material formed by the light components will entrain a large amount of polymer melt, resulting in a series of problems such as blockage of pipelines and equipment in the low-pressure circulation loop, reduction of heat exchange efficiency, and high consumption of ethylene. Therefore, how to improve the efficiency of the separator and reduce the entrainment of polymer is an important basis for ensuring the efficient and stable operation of the high-pressure radical polymerization device and improving the economic efficiency of the device.

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

[0005] Therefore, there is a need for a low-pressure separator and a method for separating an olefin polymerization product, which can separate the polymer and the light components at a low pressure, reduce the amount of polymer entrained in the light components, reduce the wall sticking and fouling of the inner wall of the separation device, and ensure the long-term stable operation of the polymerization device. SUMMARY

[0006] The purpose of the present application is to overcome the problem that in the existing high-pressure olefin polymerization process, when separating the mixture of polymer and unreacted monomer and light components such as impurities generated by the polymerization reaction, the gas phase material formed by the light components entrains a large amount of polymer melt, and the polymer melt adheres to the inner wall of the separation device, which has the risk of fouling and crosslinking. The present application provides a low-pressure separator and a method for separating olefin polymerization products, which can reduce the amount of polymer entrained in the light component material at the top outlet, effectively reduce the risk of fouling and crosslinking caused by too large temperature difference between the wall surface and the melt, and reduce the number of crystal points in the film blowing product.

[0007] To achieve the above-mentioned purpose, the present application provides a low-pressure separator, 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 into the interior of the cylinder.

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

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

[0012] The present application provides a method for separating olefin polymerization products, 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 components into the low-pressure separator through the feed pipe for separation to obtain polymer and light components;

[0014] S2, discharging the obtained polymer from the bottom outlet of the low-pressure separator, and discharging the light components 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 higher than the internal temperature of the low-pressure separator by 2-80℃.

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

[0017] Through the above technical solution, the present application has the following beneficial technical effects:

[0018] (1) The low pressure separator provided by the application has a special feed pipe structure, the upper half of the feed pipe is a spiral pipe, and the lower half is a straight pipe, so that the material has not only a vertical speed but also a certain speed in the horizontal direction when entering the cylinder through the feed pipe, thereby improving the coalescence speed of the polymer melt and significantly reducing the entrainment of light component material in the light component discharge pipe to the polymer;

[0019] (2) In the application, 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 of the product blown film; on the other hand, the degradation of the polymer melt caused by excessively high temperature is avoided. BRIEF DESCRIPTION OF DRAWINGS

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

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

[0022] REFERENCE SIGNS

[0023] 1, head of the cylinder 2, straight cylinder section of the cylinder 3, bottom discharge section of the cylinder

[0024] 4, discharge valve 5, spiral pipe of the feed pipe 6, straight pipe of the feed pipe

[0025] 7, bottom outlet 8, light component discharge pipe DETAILED DESCRIPTION

[0026] The endpoints of the ranges and any values disclosed herein are not limited to the precise values recited as the exact dimensions are not critical to the application. Any numeric range recited is intended to include all values from the lower value to the upper value. For values that are less than one, one unit in the low value is considered to be 0.000... (one less than the number of nines representing the horns of the decade). For values that are greater than one, one unit in the high value is considered to be 2.000... (one more than the number of nines representing the horns of the decade). Numeric ranges include endpoints unless otherwise indicated. Numeric ranges include integers within the range unless otherwise indicated. Numeric ranges include both endpoints and all the values between them unless otherwise indicated.

[0027] The first aspect of the application 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 application, the upper half of the feeding pipe is designed as a spiral shape, and the centrifugal separation effect generated by the spiral pipe enables the mixture to have a horizontal velocity in addition to a vertical velocity, thus prolonging the residence time of the mixture and further improving the coalescence speed of the polymer melt in the mixture, and reducing the entrainment amount of the polymer in the light components in the light component outlet pipe.

[0031] According to the application, preferably, the inner diameter of the spiral pipe of the feeding pipe is 0.05-0.6m, preferably 0.1-0.3m.

[0032] According to the application, preferably, the spiral angle of the spiral pipe of the feeding pipe is 1-360°, preferably 5-180°, more preferably 10-90°, the spiral angle being the included angle formed by the spiral pipe as a part of a circular arc, and the spiral pipe having a top view as shown in Figure 2 , Figure 2 wherein a is the spiral angle, and when the spiral pipe forms a circle at both ends, the spiral angle is 360°.

[0033] Figure 2 (a) is a schematic view when the spiral angle a is less than 90°, the material enters from one end of the spiral pipe, and is discharged from the other end of the spiral pipe and then enters the straight pipe section of the feeding pipe, and after this process, the material has a horizontal velocity at the outlet of the spiral pipe, i.e. the inlet of the straight pipe section, so that it is in the form of a vortex in the straight pipe, Figure 2 (b) is a schematic view when the spiral angle a is greater than 90°, and as the spiral angle increases, the material can develop more fully in the spiral pipe, so that the initial liquid state entering the straight pipe section of the feeding pipe can be controlled.

[0034] According to the application, preferably, the inner diameter of the straight pipe of the feeding pipe is 0.1-2m, preferably 0.2-1m.

[0035] In the application, preferably, the inner diameters of the spiral pipe and the straight pipe of the feeding pipe are different, and the feeding pipe is provided with different inner diameters, so that the flow rate of the material entering the straight pipe can be reduced, which is beneficial to the mutual aggregation of liquids to form larger droplets.

[0036] In the application, by using the above preferred technical solutions, the inner diameters of the spiral pipe and the straight pipe of the feeding pipe and the spiral angle are limited, so that the horizontal velocity of the mixture in the feeding pipe can be controlled, and the separation effect of the separator can be further improved.

[0037] According to the application, preferably, the height ratio of the spiral pipe to the straight pipe of the feeding pipe is 0.01-1.5:1, preferably 0.05-0.5:1.

[0038] According to the application, 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 application, 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 application, preferably, the cylinder comprises a head, a straight cylinder segment and a bottom discharge segment of a circular truncated cone structure, and the head is provided with an opening at the top and connected to a corresponding light component discharge pipe.

[0041] According to the application, preferably, the light component discharge pipe has an inner diameter of 0.1-1.5m, preferably 0.15-0.9m.

[0042] According to the application, preferably, the number of light component discharge pipes is 1-4, preferably 1-2. When the number of light component discharge pipes is greater than 1, the light component discharge pipes are evenly distributed in the circumferential direction to the central axis of the cylinder head. Preferably, when the number of light component discharge pipes is greater than 1 and even, the distance from the light component discharge pipes to the central axis of the cylinder head is equal and symmetrically distributed.

[0043] In the application, 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 cylinder segment is 0.1-0.8:1, preferably 0.2-0.7:1. By adopting the above preferred technical solution, the light component discharge pipes are evenly distributed around the central axis of the head, which can uniformly guide the light component gas material out and avoid excessive polymer entrainment in part of the light component.

[0044] According to the application, preferably, the height ratio of the head to the straight cylinder segment of the cylinder is 0.025-0.5:1, preferably 0.125-0.25:1. In the application, the total height of the cylinder is not particularly limited, and those skilled in the art can adaptively select according to the need, 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 cylinder segment.

[0045] In the application, preferably, the cone angle of the bottom discharge segment is 30-120°, preferably 45-100°, and the height of the bottom discharge segment can be calculated by the cone angle of the bottom discharge segment.

[0046] According to the application, preferably, the ratio of the height of the straight pipe of the feed pipe to the height of the cylinder is 0.2-0.8:1, preferably 0.3-0.6:1, which can make the gas material have sufficient residence time in the low-pressure separator, while reducing the influence of the feed on the polymer melt liquid level. In the application, preferably, the straight pipe of the feed pipe extends into the cylinder.

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

[0048] In the present application, the inner diameter of the bottom outlet is not particularly limited, and preferably, the ratio of the inner diameter of the bottom outlet to the inner diameter of the straight cylinder section of the cylinder is 0.05-0.4:1, preferably 0.1-0.3:1.

[0049] In the present application, as shown in the preferred embodiment of the present application, the low-pressure separator comprises a head 1 of a cylinder, a straight cylinder section 2 of the cylinder, a bottom discharge section 3 of the cylinder, a helical pipe 5 of a feed pipe and a straight pipe 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. Figure 1

[0050] The second aspect of the present application 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 a mixture containing a polymer and a light component into the low-pressure separator through the feed pipe for separation to obtain the polymer and the light component;

[0052] S2, discharging the obtained polymer from the bottom outlet of the low-pressure separator, and discharging the light component 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 higher than the internal temperature of the low-pressure separator by 2-80℃.

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

[0055] In the present application, by controlling the 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 flowability 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 in the blown film product 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 application, the low-pressure separator is used for separating high-pressure olefin radical polymerization products, and the outlet material of the high-pressure radical polymerization reactor is usually passed through at least two separators with different pressure levels, so that the unreacted monomers are substantially completely separated, and the low-pressure separator of the present application is the last stage separator.

[0057] ​In the present application, the mixture containing polymer and light components is from the upper separator, and the polymer is the product of olefin radical polymerization, and the type of the polymer has a wide selection range, which can be a copolymer or a homopolymer, and preferably one of polyethylene and / or ethylene-vinyl acetate copolymer.

[0058] In the present application, the light components include at least one of olefins, initiators remaining from polymerization, telogens and unreacted comonomers.

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

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

[0061] According to the present application, preferably, in S1, the internal temperature of the low-pressure separator is at least 50℃ higher than the melting point of the polymer, and preferably 50-150℃. By using the above preferred technical solution, the adhesion of the polymer melt to the wall surface can be further reduced, and the degradation of the polymer melt caused by excessively high temperature can be reduced.

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

[0063] In the present application, preferably, during the operation of the low-pressure separator, the level of the polymer in the low-pressure separator is controlled to be higher than the bottom discharge section, so as to ensure the continuous separation of the polymer and the light components.

[0064] According to the present application, preferably, the mass flow ratio of the polymer and the light components 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 between any two numerical values, and preferably 1-5:1. When the mass flow ratio of the polymer and the light components in the low-pressure separator is 0:1, it is the starting stage of the polymerization reaction, and the low-pressure separator does not contain the polymer.

[0065] In the present application, the flow rate of the mixture is not particularly limited, and those skilled in the art can make adaptive adjustment according to the needs, and preferably the flow rate of the mixture is 5-30t / h.

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

[0067] According to the present application, preferably, the content of the 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 application, by adjusting the temperature and pressure in the low-pressure separator, the content of the light components in the polymer discharged from the bottom outlet of the low-pressure separator is controlled to be less than 1wt% based on the total weight of the discharged polymer.

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

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

[0071] In the present application, by using the above preferred technical solutions, the horizontal direction speed of the mixture in the feed pipe is controlled by controlling the inner diameter and spiral angle of the low-pressure separator, the residence time of the mixture in the cylinder is prolonged, and the separation efficiency is improved.

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

[0073] According to the present application, preferably, the polymer discharged from the bottom outlet of the low-pressure separator is sent to an extrusion granulator through a 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.

[0074] In the present application, 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 application, preferably, the low-pressure separator used in the process for separating the polymer and light components from the mixed material comprises Figure 1

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

[0077] The low-pressure separator uses an external heating system to heat the cylinder, and the temperature of the external heating medium is controlled to be 2-80℃ higher than the internal temperature of the low-pressure separator, so as to separate the polymer and light components from the mixed material.

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

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

[0080] S1, the mixed material is introduced into the cylinder of the low-pressure separator through the feed pipe, the mass flow ratio of the polymer and the light components in the mixed material is 1-5:1, the mixed material has a horizontal velocity of 0.05-25 m / s in the spiral pipe of the feed pipe, preferably a horizontal velocity of 1-15 m / s, 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℃ higher than the internal temperature of the low-pressure separator, the pressure of the low-pressure separator is 0.1-0.5 MPa, the internal temperature of the low-pressure separator is 160-250℃, and the internal temperature of the low-pressure separator is 50-150℃ higher than the melting point of the polymer.

[0082] ​S2, the polymer separated is guided out from the bottom outlet of the low pressure separator, the light components are guided out from the light component outlet pipe, the guided polymer is sent to an extrusion granulator through an outlet valve to obtain a polymer product with a light component content of not more than 0.1 wt%.

[0083] The application 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℃;

[0085] The light component content in the polymer guided out from the bottom outlet of the low pressure separator is sampled and measured by a headspace gas chromatography method, and the temperature is 90℃;

[0086] The reagents or instruments used are not marked with the manufacturer, and are all conventional products that can be obtained through market purchase.

[0087] Example 1

[0088] In Figure 1 The mixture is separated in the low pressure separator shown.

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

[0090] The inner diameter of the light component outlet pipe is 0.175m, there are 2 light component outlet pipes, and the ratio of the distance from the central axis of the light component outlet pipe to the central 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 head of the cylinder is 0.5m, the height of the straight cylinder section of the cylinder is 3.8m, the inner diameter of the straight cylinder section of the cylinder is 2.0m, the taper angle of the bottom discharge section is 60°, and the inner diameter of the bottom outlet is 0.6m.

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

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

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

[0095] Example 2

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

[0097] S1, the mixed material is introduced into the cylinder of the low pressure separator through the feed pipe, the flow rate of the polyethylene in the mixed material is 14.2 t / h, and the flow rate of the light components is 4.5 t / h (including unreacted ethylene, residual initiator and unreacted telogen), the mixed material in the spiral pipe of the feed pipe has a horizontal velocity of 10 m / s, 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 jacketed and heated by 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 of the low pressure separator is 200°C, and the melting point of the polyethylene is 110°C as determined by DSC.

[0099] S2, the separated polyethylene is discharged from the bottom outlet of the low pressure separator, and the light components are discharged from the light component outlet pipe, the discharged polyethylene is sent to an extrusion granulator through a discharge valve, the distance from the discharge valve to the outlet of the extrusion granulator is 1 m, and the content of the light components in the polymer product is 0.1 wt%.

[0100] Example 3

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

[0102] S1, the mixed material is introduced into the cylinder of the low pressure separator through the feed pipe, the flow rate of the polyethylene in the mixed material is 14.2 t / h, and the flow rate of the light components is 4.5 t / h (including unreacted ethylene, residual initiator and unreacted telogen), the mixed material in the spiral pipe of the feed pipe has a horizontal velocity of 10 m / s, 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.

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

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

[0105] Example 4

[0106] The low pressure separator of Example 1 is used to separate the polymer and the light components in the mixed material, and the difference from Example 1 is 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℃, the pressure of the low pressure separator is 0.11MPa, the internal temperature is 200℃, and the melting point of the polyethylene is 110℃ by DSC test.

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

[0109] Example 5

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

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

[0112] The inner diameter of the light component outlet pipe is 0.175m, there are 2 light component outlet pipes, and the ratio of the distance from the central axis of the light component outlet pipe to the central 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 head of the cylinder is 0.5m, the height of the straight cylinder section of the cylinder is 3.8m, the inner diameter of the straight cylinder section of the cylinder is 2.0m, the taper angle of the bottom discharge section is 60°, and the inner diameter of the bottom outlet is 0.6m.

[0114] S1, the mixture is introduced into the cylinder of the low pressure separator through the feed pipe, the flow rate of the polyethylene in the mixture is 15 t / h, the flow rate of the light components is 4.6 t / h (including unreacted ethylene, residual initiator and unreacted telogen), the mixture has a horizontal velocity of 18 m / s in the spiral pipe of the feed pipe, the flow rate of the mixture in the feed pipe is 87 m / s, and the average residence time of the mixture 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 0.12 MPa, the internal temperature is 210 °C, and the melting point of the polyethylene is 110 °C as determined by DSC.

[0116] S2, the separated polyethylene is discharged from the bottom outlet of the low pressure separator, and the light components are 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 1.0 m, and the content of the light components in the polymer product is 0.1 wt%.

[0117] Comparative Example 1

[0118] The low pressure separator of Example 1 is used to separate the polymer and light components in the mixture, and the difference from Example 1 is that the spiral pipe 5 is not provided in the feed pipe, and the mixture 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 0.12 MPa, and the internal temperature of the low pressure separator is 210 °C. The velocity of the mixture in the feed pipe of the low pressure separator in the horizontal direction is less than 0.05 m / s, the flow rate of the mixture in the feed pipe is 87 m / s, the average residence time of the mixture in the cylinder of the low pressure separator is 20 s, and the melting point of the polyethylene is 109 °C as determined by DSC.

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

[0121] Comparative Example 2

[0122] The low pressure separator of Comparative Example 1 is used to separate the polymer and light components in the mixture, and the difference from Comparative Example 1 is that:

[0123] S1, the velocity of the mixture in the feed pipe of the low pressure separator is less than 0.05 m / s in the horizontal direction, the flow rate of the mixture in the feed pipe is 87 m / s, the average residence time of the mixture in the low pressure separator cylinder is 20 s, the heating temperature of the external heating system of the low pressure separator is 175 ℃, the pressure of the low pressure separator is 0.11 MPa, the internal temperature of the low pressure separator is 210 ℃, and the melting point of the polyethylene obtained by DSC test is 111 ℃.

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

[0125] Test Example 1

[0126] The number of crystal points of the polymer product and the amount of polymer entrained by the light components at the top were measured, and the results are shown in Table 1.

[0127] The amount of polymer entrained by the light components in the light component discharge pipe was obtained by cooling and separating the polymer, and calculating the material balance of the system;

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

[0129] Table 1

[0130]

[0131] As can be seen from the results in Table 1, the comparison of Example 1, Example 2 and Comparative Example 1, Comparative Example 2 shows that the low pressure separator of the present application has better performance in the working conditions of separating polyethylene and separating ethylene-vinyl acetate copolymer. Specifically, the low pressure separator of the present application has less wall sticking and scaling on the inner wall surface, and the amount of polymer entrained 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 above describes the preferred embodiments of the present application, but the present application is not limited thereto. Within the technical concept of the present application, various simple modifications can be made to the technical solutions of the present application, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be considered as disclosed by the present application, and all fall within the protection scope of the present application.

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; 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 into the cylinder, so that the mixture has both vertical and horizontal velocities.

2. The low pressure separator of claim 1, wherein, The inner diameter of the spiral pipe of the feed pipe is 0.05-0.6m; and the spiral angle is 1-360°.

3. The low pressure separator of claim 2, wherein, The inner diameter of the spiral pipe of the feed pipe is 0.1-0.3m; and the spiral angle is 5-180°.

4. The low pressure separator of claim 3, wherein, The spiral angle of the spiral pipe of the feed pipe is 10-90°.

5. The low pressure separator of claim 1, wherein, The inner diameter of the straight pipe of the feed pipe is 0.1-2m.

6. The low pressure separator of claim 5, wherein, The inner diameter of the straight pipe of the feed pipe is 0.2-1m.

7. The low pressure separator of claim 1, wherein, The height ratio of the spiral pipe to the straight pipe of the feed pipe is 0.01-1.5:

1.

8. The low pressure separator of claim 7, wherein, The height ratio of the spiral pipe to the straight pipe of the feed pipe is 0.05-0.5:

1.

9. The low pressure separator of claim 1, wherein, The low-pressure separator further comprises a bottom outlet arranged below the cylinder and a discharge valve connected to the bottom outlet.

10. The low pressure separator of claim 1, wherein, The external heating system is arranged outside the cylinder, and the external heating system is a jacket or a coil.

11. The low pressure separator of claim 1, wherein, The cylinder comprises a head, a straight cylinder segment and a bottom discharge segment of a circular truncated cone structure, and a hole is opened on the top of the head and connected to a corresponding light component discharge pipe.

12. The low pressure separator of claim 1, wherein, The inner diameter of the light component discharge pipe is 0.1-1.5m.

13. The low pressure separator of claim 12, wherein, The inner diameter of the light component discharge pipe is 0.15-0.9m.

14. The low pressure separator of claim 1, wherein, The light component discharge pipe is 1-4.

15. The low pressure separator of claim 14, wherein, The light component discharge pipe is 1-2.

16. The low pressure separator of claim 1, wherein, 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 to the central axis of the head of the cylinder.

17. The low pressure separator of claim 16, wherein, When the number of the light component discharge pipes is greater than 1 and is even, the light component discharge pipes are symmetrically distributed and have equal distances to the central axis of the head of the cylinder.

18. The low pressure separator of claim 11, wherein, The height ratio of the head to the straight cylinder segment of the cylinder is 0.025-0.5:

1.

19. The low pressure separator of claim 18, wherein, The height ratio of the head to the straight cylinder segment of the cylinder is 0.125-0.25:

1.

20. The low pressure separator of claim 11, wherein, The straight cylinder segment is connected to the bottom discharge segment, and the taper angle of the bottom discharge segment is 30-120°.

21. The low pressure separator of claim 20, wherein, The taper angle of the bottom discharge segment is 45-100°.

22. The low pressure separator of claim 11, wherein, The ratio of the height of the straight pipe of the feed pipe to the height of the cylinder is 0.2-0.8:

1.

23. The low pressure separator of claim 22, wherein, The ratio of the height of the straight pipe of the feed pipe to the height of the cylinder is 0.3-0.6:

1.

24. A method for separating an olefin polymerization product, characterized by, The separation method is carried out in the low-pressure separator of any one of claims 1-23, and the method comprises the following steps: S1, feeding a mixture containing a polymer and a light component into the low-pressure separator through a feed pipe for separation to obtain a polymer and a light component; S2, discharging the obtained polymer from the bottom outlet of the low-pressure separator, and discharging the light component from the light component discharge pipe; In S1, the temperature of the external heating medium is controlled by the external heating system to be higher than the internal temperature of the low-pressure separator by 2-80℃.

25. The separation method of claim 24, wherein, In S1, the temperature of the external heating medium is higher than the internal temperature of the low-pressure separator by 5-50℃.

26. The separation method of claim 24, wherein, In S1, the internal temperature of the low-pressure separator is at least 50℃ higher than the melting point of the polymer.

27. The separation method of claim 26, wherein, The internal temperature of the low-pressure separator in S1 is 50-150℃ higher than the melting point of the polymer.

28. The separation method of claim 24, wherein, The pressure of the low-pressure separator in S1 is 0.1-0.7MPa, and the internal temperature of the low-pressure separator is 150-280℃.

29. The separation method of claim 28, wherein, The pressure of the low-pressure separator in S1 is 0.1-0.5MPa, and the internal temperature of the low-pressure separator is 160-250℃.

30. The separation method of claim 24, wherein, The polymer in the mixture is an olefin radical polymerization product, and the light component includes olefin, and possibly at least one of residual initiator, unreacted telogen and unreacted comonomer.

31. The separation method of claim 24, wherein, The mass flow ratio of the polymer and the light component in the low-pressure separator is 0-10:

1.

32. The separation method of claim 31, wherein, The mass flow ratio of the polymer and the light component in the low-pressure separator is 2-5:

1.

33. The separation method of claim 24, wherein, The content of the light component in the polymer discharged from the bottom outlet of the low-pressure separator is less than 1wt% based on the total weight of the discharged polymer.

34. The separation method of claim 33, wherein, The content of the light component in the polymer discharged from the bottom outlet of the low-pressure separator is less than 0.5wt% based on the total weight of the discharged polymer.

35. The separation method of claim 34, wherein, The content of the light component in the polymer discharged from the bottom outlet of the low-pressure separator is not higher than 0.1wt% based on the total weight of the discharged polymer.

36. The separation method of claim 24, wherein, The mixture in the feed pipe in S1 has a velocity of 0.05-25m / s in the horizontal direction at the outlet of the spiral pipe.

37. The separation method of claim 36, wherein, The mixture in the feed pipe in S1 has a velocity of 1-15m / s in the horizontal direction at the outlet of the spiral pipe.

38. The separation method of claim 24, wherein, The average residence time of the mixture in the low-pressure separator cylinder is 5-600s.

39. The separation method of claim 38, wherein, The average residence time of the mixture in the low-pressure separator cylinder is 10-100s.

40. The separation method of claim 24, wherein, 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 2m.

41. The separation method of claim 40, wherein, 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 1m.

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