A method for removing VOCs, reducing odor grade in polyethylene or ethylene copolymer by micro-negative pressure

Abstract

The application provides a method for removing VOC in polyethylene and or ethylene copolymer and reducing odor grade, and particularly provides a device for removing gas phase impurities in polyethylene and ethylene copolymer, which comprises a micro-negative pressure steam stripping tower (2), a feed valve group (8) located upstream of the micro-negative pressure steam stripping tower, and a discharge valve group (9) located downstream of the micro-negative pressure steam stripping tower. The application also provides a method for removing VOC in polyethylene or ethylene copolymer resin and reducing odor grade by using the device.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of polymer production, and in particular, the present application provides a device for a process method for removing VOCs in polyethylene or ethylene copolymer, reducing odor grade, and a corresponding method. BACKGROUND

[0002] In recent years, the requirements for light weight of automobile products, environmental protection of household products and food contact materials are increasing. Because polyethylene and ethylene copolymer (LDPE, LLDPE, HDPE, POE, OBC, etc.) resins have excellent comprehensive properties such as non-toxicity, small density, easy processing, high impact strength, good corrosion resistance, high cost performance, and hygiene, they are widely used in automotive interior and exterior parts, household products, food packaging materials and medical packaging materials.

[0003] Due to the influence of multiple factors such as the purity of polymerized monomers, catalyst residues, polymerization process, decomposition of additives, and degradation of the resin itself, volatile organic compounds (VOCs) are still released in varying degrees in commercially available polyethylene and ethylene copolymer resins, polluting the environment and endangering people's health. With the increasing environmental awareness of the public and the increasing requirements of environmental protection laws and regulations, the VOC and odor problems in resins have attracted more and more attention from consumers and production enterprises. Most automobile manufacturers have begun to implement European standards (German Automotive Industry Association VDA277 standard) to strictly control the VOC of parts and require the total carbon volatile amount of interior materials to be <80 μg C / g. The newly revised national standard GB 4806.1-2016 "General Safety Requirements for Food Contact Materials and Products" clearly requires that food contact materials and products have no odor and touch. In addition, due to the high VOC content in existing polyethylene and ethylene copolymer resins, the resins produced need to be replaced multiple times after entering the packaging warehouse, which increases the difficulty of the packaging process and often results in excessive replacement gas emissions due to the introduction of new atmospheric emission laws and regulations. Therefore, the VOC release problem and odor problem in polyethylene and ethylene copolymer resins have become one of the problems to be solved.

[0004] In summary, there is still a lack of a method for efficiently removing VOCs in polyethylene and ethylene copolymer resins and reducing odor grade. SUMMARY

[0005] The purpose of the present application is to provide a method for removing gas phase impurities in polyethylene and ethylene copolymer resins.

[0006] In a first aspect of the present application, a device for removing gas phase impurities in polyethylene or ethylene copolymer is provided, characterized in that the device comprises:

[0007] a micro-negative pressure steam stripping tower (2);

[0008] a feed valve group (8) upstream of the micro-negative pressure steam stripping column, which is connected to the top feed port of the micro-negative pressure steam stripping column, for controlling the resin entering the micro-negative pressure steam stripping column;

[0009] a discharge valve group (9) downstream of the micro-negative pressure steam stripping column, which is used for controlling the resin flowing out of the micro-negative pressure steam stripping column.

[0010] In another preferred embodiment, the micro-negative pressure steam stripping column is a column with a dense phase moving bed structure.

[0011] In another preferred embodiment, the micro-negative pressure steam stripping column is a column with a built-in hot water generating device at the bottom.

[0012] In another preferred embodiment, in the micro-negative pressure steam stripping column, steam is introduced into the water accumulation tray at the bottom of the column, and the temperature of the water accumulation tray is controllable.

[0013] In another preferred embodiment, the device further comprises an external hot water inlet at the bottom of the column.

[0014] In another preferred embodiment, the external hot water inlet is used to add external hot water at a certain temperature to the bottom of the column through a pump.

[0015] In another preferred embodiment, the feed valve group is a rotary feed valve group.

[0016] In another preferred embodiment, the discharge valve group is a rotary discharge valve group.

[0017] In another preferred embodiment, the rotary feed valve group is a combination of two or more rotary discharge valves.

[0018] In another preferred embodiment, the rotary discharge valve group is a combination of two or more rotary discharge valves.

[0019] In another preferred embodiment, the rotary discharge valve is in the form of a gravity flap valve or a wing valve.

[0020] In another preferred embodiment, upstream refers to the upstream direction of resin flow, including the cut pellet system transported from the production device, and also including purchased commercial resins added to the device.

[0021] In another preferred embodiment, the micro-negative pressure steam stripping column further comprises a steam rising porous plate placed in the column body.

[0022] In another preferred embodiment, the micro-negative pressure steam stripping column further comprises a nitrogen inlet at the bottom of the column.

[0023] In another preferred embodiment, the device further comprises a pre-dehydration tower (1) located upstream of the feed valve group.

[0024] In another preferred embodiment, the pre-dehydration tower is a pre-dehydration tower of an existing structure of an original polyethylene and ethylene copolymer production device.

[0025] In another preferred embodiment, the pre-dehydration tower is a centrifugal dehydration tower.

[0026] In another preferred embodiment, the device further comprises a negative pressure blower, which is connected to the tail gas discharge port at the top of the micro-negative pressure steam stripping tower to control the vacuum degree in the tower.

[0027] In another preferred embodiment, the device further comprises a condenser (6), and the inlet of the condenser is connected to the outlet of the tail gas discharge negative pressure fan of the micro-negative pressure steam stripping tower.

[0028] In another preferred embodiment, the condensate at the condenser outlet is collected and sent to the plant sewage treatment system or returned to the underwater pelletizing system, and the non-condensable gas at the condenser outlet is sent to the tail gas treatment system.

[0029] In another preferred embodiment, the liquid phase outlet of the condenser is connected to a sewage treatment system.

[0030] In another preferred embodiment, the liquid phase outlet of the condenser is connected to an underwater pelletizing system.

[0031] In another preferred embodiment, the gas phase outlet end of the condenser is connected to an exhaust gas treatment system.

[0032] In another preferred embodiment, the device further comprises a circulating water cooling and conveying system, and the circulating water cooling and conveying system is used to rapidly cool down the resin discharged from the slightly negative pressure steam stripping tower.

[0033] In another preferred embodiment, the circulating water cooling and conveying device includes:

[0034] A heat exchanger (3) located downstream of the discharge valve group, the heat exchanger being connected to a circulating water tank via a delivery pump (4);

[0035] A venturi feeder (5), wherein the first inlet of the venturi feeder is connected to the discharge valve group, and the second inlet is connected to the heat exchanger.

[0036] In another preferred embodiment, the circulating water cooling and conveying system can also be replaced by the following method: the material coming out of the discharge valve group (9) first enters a buffer tank with stirring, and then the water and material mixture is conveyed to the downstream process by a conveying pump. Preferably, a Venturi cooling and conveying method is adopted.

[0037] In another preferred embodiment, the Venturi feeder (5) can be replaced by a stirred tank, and the delivery pump is located below the stirred tank to deliver the mixture of water and material after quenching to the downstream centrifugal dewatering process.

[0038] In another preferred embodiment, the circulating water cooling delivery system comprises:

[0039] a buffer tank;

[0040] a delivery pump connected to the buffer tank.

[0041] In another preferred embodiment, the material discharged from the discharge valve group (9) is delivered to a buffer tank with stirring, and then the mixture of water and material is delivered to the downstream process by the delivery pump.

[0042] In another preferred embodiment, the tail gas outlet of the micro-negative pressure steam stripping tower is connected to the condenser through a negative pressure fan (7).

[0043] In another preferred embodiment, the negative pressure fan is a centrifugal fan or a Roots fan.

[0044] In a second aspect of the present application, a method for removing gas phase impurities from polyethylene or ethylene copolymer is provided, characterized in that it comprises the steps of:

[0045] (i) feeding the polyethylene or ethylene copolymer into the feed valve group (8) to the top feed inlet of the micro-negative pressure steam stripping tower (2);

[0046] (ii) feeding steam into the water at the bottom of the micro-negative pressure steam stripping tower, controlling the temperature in the tower to generate water vapor and exchange heat with the polyethylene or ethylene copolymer, so that the temperature of the polyethylene or ethylene copolymer is maintained at 50-95°C to remove gas phase impurity molecules;

[0047] (iii) operating the rotary discharge valve group (9) to discharge the resin.

[0048] In another preferred embodiment, the temperature in the tower is the boiling point temperature of water corresponding to the operating pressure in the tower ± 5°C.

[0049] In another preferred embodiment, the steam is superheated steam (i.e., the temperature and pressure of the steam exceed the saturated steam pressure corresponding to the hot water temperature).

[0050] In another preferred embodiment, the hot water temperature is the corresponding saturated temperature under the required vacuum degree in the tower.

[0051] In another preferred embodiment, the hot water temperature is the corresponding non-saturated temperature under the required vacuum degree in the tower.

[0052] In another preferred embodiment, in step (2), the resin is heated to a temperature of 40-95°C, and the specific temperature is adjusted according to the softening temperature of the material, and generally is near the softening temperature of the resin.

[0053] In another preferred embodiment, in step (2), the resin is kept in the wet nitrogen stripping tower for 1-5h, preferably 1-3h.

[0054] In another preferred embodiment, the method further comprises step (iv): the resin is introduced into a Venturi feeder (5) to mix with condensed water, so as to cool the resin and then deliver it to the centrifugal dehydration process downstream.

[0055] In another preferred embodiment, the polyethylene or ethylene copolymer is introduced into the centrifugal dehydration process after being cooled.

[0056] In another preferred embodiment, the polyethylene or ethylene copolymer is introduced into a stirred tank with water to cool it, and the mixture of the cooled resin and water is delivered to the centrifugal dehydration process downstream by a pump.

[0057] In another preferred embodiment, the method further comprises step (iv): the resin is introduced into a stirred tank with water to mix with condensed water, so as to cool the resin and then deliver it to the centrifugal dehydration process downstream by a pump.

[0058] In another preferred embodiment, the condensed water is from a circulating water tank, is cooled by a heat exchanger (3), and is delivered into the Venturi feeder (5) or the stirred tank by a pump (4).

[0059] In another preferred embodiment, the material introduced into the tower from the top moves downward in the tower as a dense phase moving bed.

[0060] In another preferred embodiment, in step (4), the resin is cooled to below 60°C, preferably to below 50°C, and more preferably to below 40°C, in the Venturi feeder or the stirred tank.

[0061] In another preferred embodiment, step (iv) further comprises: the treated resin is first introduced into a bin for collection, and then is delivered to the subsequent process after being cooled by nitrogen.

[0062] In another preferred embodiment, step (iv) further comprises: the treated resin is further cooled by other cooling facilities.

[0063] In another preferred embodiment, the other cooling facilities are selected from the group consisting of a converter device with a cooling coil, or a stirred device to be cooled.

[0064] In another preferred embodiment, before the step (1), the method further comprises a step of: feeding the resin into the pre-dewatering tower (1) to perform a pre-dewatering step.

[0065] In another preferred embodiment, after the pre-dewatering step, the water content of the resin is 1-10 wt%, preferably 1-5 wt%.

[0066] In another preferred embodiment, the resin is a mixture of resin and water from the underwater pelletizing process of a polyethylene and ethylene copolymer plant.

[0067] In another preferred embodiment, after the pre-dewatering step, the removed water is returned to the underwater pelletizing process.

[0068] In another preferred embodiment, the method further comprises a step of: feeding the tail gas discharged from the top of the micro-negative pressure steam stripping tower into the negative pressure fan (7) to control the vacuum degree of the micro-negative pressure steam stripping tower.

[0069] In another preferred embodiment, the method further comprises a step of: condensing the tail gas discharged from the negative pressure fan (7) in the condenser (6).

[0070] In another preferred embodiment, after the condensing step, the condensed water is fed into the underwater pelletizing system or the sewage treatment system.

[0071] In another preferred embodiment, after the condensing step, the non-condensed gas is fed into the tail gas treatment system.

[0072] In another preferred embodiment, in the steps (1)-(3), the oxygen content of the gas phase component in the stripping tower is less than 1%, preferably less than 0.1%, and more preferably less than 100 ppm.

[0073] The device and method provided by the present application are suitable for polyethylene or ethylene copolymer, in particular LDPE, LLDPE, POE and OBC; and can achieve better results for low-melting-point LDPE, POE and OBC.

[0074] In another preferred embodiment, the polyethylene or ethylene copolymer is selected from the group consisting of LDPE, LLDPE, POE and OBC; more preferably LDPE, POE and OBC; and most preferably LDPE.

[0075] It should be understood that, within the scope of the present application, the above-mentioned technical features of the present application and the technical features specifically described below (such as in the examples) can be combined with each other to form new or preferred technical solutions. Due to the limited space, they will not be listed one by one here. BRIEF DESCRIPTION OF DRAWINGS

[0076] Figure 1It is a structure schematic diagram of the polyethylene VOC removal, odor grade reduction device of the present application.

[0077] 1-pre-dehydrator, 2-micro-negative pressure steam stripping tower, 3-heat exchanger, 4-conveying pump, 5-venturi feeder, 6-condenser, 7-negative pressure fan, 8-rotary feeding valve group, 9-rotary discharging valve group;

[0078] 21-underwater pellet cutting system, 22-underwater pellet cutting circulating water tank, 24-CWR (circulating cooling water return water), 25-conveying circulating water tank, 26-centrifugal dehydration process, 28-steam flow, 29-tail gas treatment system, 30-nitrogen flow, 31-CWS (circulating cooling water supply). DETAILED DESCRIPTION

[0079] The present application provides a device for removing VOC in polyethylene and olefin copolymer and reducing odor grade and a corresponding method thereof. The device removes the residual VOC in the resin by the process of gas diffusion migration under negative pressure environment and then steam removal.

[0080] Method for removing VOC in polyethylene and olefin copolymer and reducing odor grade

[0081] In order to overcome the deficiencies of the prior art, reduce the VOC content in the resin product of the existing polyethylene or ethylene copolymer production device, reduce the odor grade, improve the product quality, and reduce the VOC emission problem in the packaging process of the production device, the present application provides a process method for efficiently removing VOC in such resin and improving odor. The principle is to use the resin to keep a certain temperature and a certain negative pressure for a certain time, so that the low molecular VOC wrapped in the resin fully migrates and diffuses out, and then is removed by steam stripping. Under the condition that the resin does not melt and agglomerate, the higher the temperature, the better the removal effect. With the increase of temperature, the chain segment movement is more obvious, the small flake crystal region melts, the chain segments in the transition zone and amorphous region will move and rearrange and crystallize to form coarse flake crystals, which promotes the VOC small molecules wrapped in the resin to fully migrate and diffuse out. On the other hand, with the increase of temperature, the free volume of molecular chain expands, the diffusion coefficient and vapor pressure of VOC molecules wrapped in the resin also increase, so that VOC molecules are more likely to migrate from the inside of the resin to the surface of the material, and then be stripped by wet nitrogen, so that the VOC content in the resin product finally meets the requirements of VDA277 and GB 4806.1-2016.

[0082] The process adds a set of micro-negative pressure steam stripping equipment and auxiliary equipment between the underwater pelletizing process and the particle centrifugal dehydration process of the existing polyethylene and ethylene copolymer process device. The material is kept at a certain temperature, a certain vacuum degree and a certain residence time in this process, so that VOC is resolved from the resin and taken out by steam stripping. The mixed gas stripped out is condensed after being discharged, and the non-condensable gas and VOC are sent to the site tail gas treatment system, and the condensed water is returned to the underwater pelletizing system. The specific process is as follows:

[0083] ①The water and resin mixture transported from the upstream underwater pelletizing process first enters the newly added pre-dehydration equipment to dehydrate the resin to about 1% to 10% of water content. The pre-dehydrated PE resin is continuously fed from the top to the micro-negative pressure steam stripping tower through two-stage material transfer valves. The water from the pre-dehydration tower is returned to the upstream underwater pelletizing process by a pump.

[0084] ②After the PE resin enters the steam stripping tower, it forms a dense phase moving bed and slowly moves from top to bottom, ensuring a certain residence time. Due to the exhaust effect of the tower top negative pressure fan, the hot water at the bottom evaporates and rises along the uniformly distributed steam pipeline in contact with the material for heat exchange until the material is heated to a certain temperature range. At the same time, to prevent VOC accumulation in the system, a continuous discharge of mixed gas is required at the top of the tower. The mixed gas is condensed, and the non-condensable tail gas is sent to the site tail gas treatment system, and the condensate is collected and returned to the underwater pelletizing process or sent to the sewage treatment system.

[0085] ③The material from the bottom of the tower enters the Venturi feeder after passing through two-stage material transfer valves, mixes with cooling water, and is rapidly cooled before being transported to the downstream centrifugal dehydration process.

[0086] The equipment used to implement the above method includes:

[0087] 1-Pre-dehydration machine for removing a large amount of water in the resin transported from the upstream underwater pelletizing process.

[0088] 2-Micro-negative pressure steam stripping tower, the material is heated to a certain temperature in the tower, and stays for a certain time, while the vacuum degree in the tower is controlled, so that the VOC remaining in the resin is completely resolved and taken out with the steam by the negative pressure fan.

[0089] 3-Heat exchanger for cooling the water used to transport and cool the hot resin.

[0090] 4-Conveying pump for conveying water from the circulating water tank to the Venturi feeder.

[0091] 5-Venturi feeder that collects resin and mixes it with cooling water from the circulating water tank to rapidly cool the resin before being transported to the downstream centrifugal dehydration process.

[0092] 6-Condenser, used to cool the steam and VOC mixed gas out of the steaming column.

[0093] 7- Negative pressure fan, used to discharge the steam and VOC mixed gas and ensure a certain operating vacuum in the column.

[0094] 8- Rotating feeding valve group, controls the amount and speed of resin entering the steaming column, while preventing air leakage from the pre-dewatering column into the micro-negative pressure steam stripping column.

[0095] 9- Rotating discharge valve group, controls the discharge speed and amount of resin from the steaming column, while preventing water from being reversed into the micro-negative pressure steam stripping column.

[0096] The method and device can not only be used for VOC removal in newly produced polyethylene or ethylene copolymer resin, but also for VOC removal in existing commercially available polyethylene or ethylene copolymer resin. In addition, since the method and device of the present application have good stripping effect, they can also be used for removing some polar substances such as sulfur-containing and oxygen-containing small molecules, thereby reducing the odor grade of the resin product.

[0097] Features of the present application:

[0098] (1) The VOC in polyethylene or ethylene copolymer resin is removed by the device and method of the present application, and the VOC content in the final packaged resin is lower than that of untreated resin, which can be as low as 30 ppm or less (tested by VDA277), and the odor grade can be as low as grade 3 (tested by VW50180), which is much lower than the VOC content and odor grade of commercially available resins of the same grade.

[0099] (2) The method of the present application has a simple process, i.e. only a set of micro-negative pressure steam stripping column and auxiliary facilities are added between the original two processes, which has small layout and does not affect the operation and layout of the original device.

[0100] (3) The method of the present application uses steam for stripping, which has high heat transfer efficiency. By controlling the temperature range and negative pressure during the treatment process, the VOC molecules are quickly resolved, so the treatment efficiency is high, the steam consumption is low, and the resin quality is not affected, and there is no phenomenon of caking that affects the operation of the device.

[0101] (4) The device has low investment and operating cost, and can greatly improve the product quality.

[0102] In addition, the device and method provided by the present application are suitable for polyethylene or ethylene copolymer, especially LDPE, LLDPE, POE and OBC; and can achieve better results for low-melting-point LDPE, POE and OBC.

[0103] The device and method provided by the present application are suitable for polyethylene or ethylene copolymer, especially LDPE, LLDPE, POE and OBC; and can achieve better results for low-melting-point LDPE, POE and OBC. Figure 1The process flow of the method for efficiently removing VOCs from polyethylene or ethylene copolymer resin and reducing odor grade is described as follows:

[0104] Step 1) The mixture of resin and water from the underwater pelletizing system 21 of the production device enters the pre-dewatering tower 1 for dewatering treatment, and the removed water is returned to the underwater pelletizing circulating water tank 22 and then reused in the underwater pelletizing process.

[0105] Step 2) The wet resin after pre-dewatering treatment enters the top feeding port of the micro-negative pressure steam stripping tower 2 through the rotary feeding valve group 8.

[0106] Step 3) After the resin enters the micro-negative pressure steam stripping tower 2 provided with a steam rising porous plate, the resin exchanges heat with the steam (formed by evaporation of hot water at the bottom of the tower) rising from the tower bottom, and the temperature of the steam is controlled by controlling the temperature and pressure in the system, so that the resin is heated to 50-95°C, and a certain vacuum degree is maintained in the tower to allow the VOC molecules in the resin to be resolved. The material entering the tower from the top is a dense-phase moving bed moving from top to bottom in the tower.

[0107] Step 4) The resin after pre-dewatering treatment is discharged by the rotary discharge valve group 9.

[0108] Step 5) The resin after exiting the tower enters the Venturi feeder 5, where it is mixed with the water from the conveying circulating water tank 25 and cooled by the heat exchanger 3 (the heat exchanger 3 has a circulating cooling water supply device 31 and a circulating cooling water return device 24), and the water conveyed by the conveying pump 4 to cool the resin and then conveyed to the downstream centrifugal dewatering process 26.

[0109] Step 6) To prevent the enrichment of resolved VOCs in the system, the mixed gas discharged from the top of the micro-negative pressure steam stripping tower 2 by the negative pressure fan 7 is condensed by the condenser 6, and a portion of the non-condensed exhaust gas is discharged into the exhaust gas treatment system 30 on site, and the condensate is returned to the underwater pelletizing system or the sewage treatment system.

[0110] In order to verify the effect of the device, a device with a processing capacity of 1 Kg / h was processed, and experiments under the following conditions were carried out:

[0111] Example 1

[0112] The high pressure polyethylene pellets (LDPE, production plant packaging material VOC content: 120 ppm, odor rating 4.5 level) containing 1% water after underwater pelletizing and centrifugal dewatering treatment on the production device were loaded into the micro-negative pressure steam stripping column of the experimental device. The valve at the bottom was connected to the water tank, and the water was heated to 60°C by steam, the absolute pressure in the column was controlled to about 19930 Pa by the negative pressure fan at the top, the hot water evaporated into steam, and then rose to heat the polyethylene pellets in the column. After heating for 2 h, the material was rapidly cooled to 45°C with cold water. Then the material was discharged, and the polyethylene resin was treated according to the method of the industrial device, i.e. centrifugal dewatering and air drying.

[0113] VOC content (VDA 277): 28 ppm; odor rating: 3.5 level.

[0114] Example 2

[0115] The high density polyethylene pellets (HDPE, slurry method, production plant packaging material VOC content: 165 ppm, odor rating 4.5 level) containing 1% water after underwater pelletizing and centrifugal dewatering treatment on the production device were loaded into the micro-negative pressure steam stripping column of the experimental device. The valve at the bottom was connected to the water tank, and the water was heated to 75°C by steam, the absolute pressure in the column was controlled to about 38560 Pa by the negative pressure fan at the top, the hot water evaporated into steam, and then rose to heat the polyethylene pellets in the column. After heating for 2 h, the material was rapidly cooled to 45°C with cold water. Then the material was discharged, and the polyethylene resin was treated according to the method of the industrial device, i.e. centrifugal dewatering and air drying.

[0116] VOC content (VDA 277): 26 ppm; odor rating: 3.6 level.

[0117] Example 3

[0118] The high density polyethylene pellets (HDPE, gas phase method, production plant packaging material VOC content: 180 ppm, odor rating 4.8 level) containing 1% water after underwater pelletizing and centrifugal dewatering treatment on the production device were loaded into the micro-negative pressure stripping column of the experimental device. The valve at the bottom was connected to the water tank, and the water was heated to 75°C by steam, the absolute pressure in the column was controlled to about 38560 Pa by the negative pressure fan at the top, the hot water evaporated into steam, and then rose to heat the polyethylene pellets in the column. After heating for 2 h, the material was rapidly cooled to 45°C with cold water. Then the material was discharged, and the polyethylene resin was treated according to the method of the industrial device, i.e. centrifugal dewatering and air drying.

[0119] VOC content (VDA 277): 22 ppm; odor rating: 3.7 level.

[0120] Example 4

[0121] The commercial POE resin (VOC content: 160 ppm, odor rating 4.6) was charged into the micro-negative pressure stripping column of the experimental device. The valve at the bottom was connected to a water tank, the water was heated to 70°C by steam, the absolute pressure in the column was controlled to about 31180 Pa by the negative pressure fan at the top, the hot water evaporated into steam, which then rose to heat the POE granules in the column. After heating for 3 h, the material was rapidly cooled to 40°C by cold water. Then the POE resin was discharged and treated according to the method of the industrial device, i.e. centrifugal dewatering and air drying.

[0122] VOC content (VDA 277): 35 ppm; odor rating: 3.8.

[0123] Example 5

[0124] The commercial OBC resin (VOC content: 250 ppm, odor rating 4.5) was charged into the micro-negative pressure stripping column of the experimental device. The valve at the bottom was connected to a water tank, the water was heated to 80°C by steam, the absolute pressure in the column was controlled to about 47370 Pa by the negative pressure fan at the top, the hot water evaporated into steam, which then rose to heat the OBC granules in the column. After heating for 3 h, the material was rapidly cooled to 40°C by cold water. Then the OBC resin was discharged and treated according to the method of the industrial device, i.e. centrifugal dewatering and air drying.

[0125] VOC content (VDA 277): 40 ppm; odor rating: 3.6.

[0126] Example 6

[0127] The commercial LLDPE resin (VOC content: 185 ppm, odor rating 4.8) was charged into the micro-negative pressure stripping column of the experimental device. The valve at the bottom was connected to a water tank, the water was heated to 65°C by steam, the absolute pressure in the column was controlled to about 25020 Pa by the negative pressure fan at the top, the hot water evaporated into steam, which then rose to heat the LLDPE granules in the column. After heating for 3 h, the material was rapidly cooled to 40°C by cold water. Then the LLDPE resin was discharged and treated according to the method of the industrial device, i.e. centrifugal dewatering and air drying.

[0128] VOC content (VDA 277): 35 ppm; odor rating: 3.2.

[0129] All documents mentioned in the present application are incorporated herein by reference as if each document were individually incorporated by reference. In addition, it should be understood that various modifications and / or changes can be made to the present application by those skilled in the art, which modifications and / or changes are intended to be within the scope of the present application.

Claims

1. A method for removing gaseous impurities from polyethylene or ethylene copolymers, characterized in that: Including steps: (i) passing polyethylene or ethylene copolymer into a feed valve assembly (8) and into the top feed port of a slightly negative pressure steam stripping tower (2); (ii) introducing steam into the water at the bottom of the slightly negative pressure steam stripping tower, controlling the temperature in the tower to generate water vapor and exchange heat with the polyethylene or ethylene copolymer, maintaining the temperature of the polyethylene or ethylene copolymer at 50-95° C. to remove gas-phase impurity molecules; (iii) operating the rotary discharge valve assembly (9) to discharge the resin; The method is carried out in a device for removing gaseous impurities from polyethylene or ethylene copolymers, and the device comprises: Slightly negative pressure steam stripping tower (2); A feed valve group (8) located upstream of the slightly negative pressure steam stripping tower, the feed valve group being connected to the top feed port of the slightly negative pressure steam stripping tower and being used to control the resin from entering the slightly negative pressure steam stripping tower; a discharge valve group (9) located downstream of the slightly negative pressure steam stripping tower, the discharge valve group being used to control the resin to flow out of the slightly negative pressure steam stripping tower; The water temperature is the saturation temperature corresponding to the required vacuum condition in the tower; In the steps (i) to (iii), the oxygen content in the slightly negative pressure steam stripping tower is lower than 100 ppm.

2. The method according to claim 1, wherein The method further comprises the steps of: (iv) passing the polyethylene or ethylene copolymer into a venturi feeder (5) to mix it with circulating cooling water, thereby rapidly cooling the polyethylene or ethylene copolymer.

3. The method according to claim 1, wherein Before the step (i), the method further comprises the step of: placing the resin into a pre-dehydration tower (1) for a pre-dehydration step.

4. The method according to claim 1, wherein The method further comprises the step of passing the tail gas discharged from the top of the micro-negative pressure steam stripping tower into a negative pressure blower (7), thereby controlling the vacuum degree of the micro-negative pressure steam stripping tower.

5. The method according to claim 4, wherein The method further comprises the step of allowing the tail gas discharged through the negative pressure fan (7) to enter the condenser (6) for condensation.

6. The method according to claim 1, wherein The device further comprises a pre-dehydration tower (1) located upstream of the feed valve group.

7. The method according to claim 1, wherein The device also includes a negative pressure fan (7).

8. The method according to claim 1, wherein The device further comprises a condenser (6), the inlet of the condenser being connected to the outlet of the tail gas negative pressure blower (7) of the micro-negative pressure steam stripping tower, for separating water vapor and non-condensable gas in the tail gas of the micro-negative pressure steam stripping tower.

9. The method according to claim 1, wherein The device also includes a circulating water cooling and conveying system, which is used to rapidly cool the resin discharged from the micro-negative pressure steam stripping tower and convey the mixture of water and material to the downstream process.

10. The method according to claim 9, wherein The circulating water cooling and delivery system comprises: A heat exchanger (3) located downstream of the discharge valve group, the heat exchanger being connected to a circulating water tank via a delivery pump (4); A venturi feeder (5), wherein the first inlet of the venturi feeder is connected to the discharge valve group, and the second inlet is connected to the heat exchanger.

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