CN112933646A

CN112933646A - Method for removing VOC (volatile organic compounds) in polyethylene or ethylene copolymer and reducing odor grade under micro-negative pressure

Info

Publication number: CN112933646A
Application number: CN201911260253.1A
Authority: CN
Inventors: 周姣龙; 赵泽昊; 唐勇; 孙秀丽; 朱洁; 朱本虎; 李军方
Original assignee: Shanghai Institute of Organic Chemistry of CAS
Current assignee: Shanghai Institute of Organic Chemistry of CAS
Priority date: 2019-12-10
Filing date: 2019-12-10
Publication date: 2021-06-11

Abstract

The invention provides a method for removing VOC and reducing odor grade in polyethylene and ethylene copolymer by micro negative pressure, in particular to a device for removing gas-phase impurities in polyethylene and ethylene copolymer polyethylene or ethylene copolymer, which comprises the following steps: a micro-negative pressure steam stripping tower (2); a feed valve block (8) located upstream of the micro-negative pressure steam stripping column; a discharge valve group (9) is positioned at the downstream of the micro negative pressure steam stripping tower. The invention also provides a method for VOC removal and odor grade reduction in polyethylene or ethylene copolymer resins using the device.

Description

Method for removing VOC (volatile organic compounds) in polyethylene or ethylene copolymer and reducing odor grade under micro-negative pressure

Technical Field

The invention belongs to the field of polymer production, and particularly provides a device and a corresponding method for a process method for removing VOC (volatile organic compounds) in polyethylene or ethylene copolymer and reducing odor grade under micro-negative pressure.

Background

In recent years, the requirements for light weight of automobile products, environmental protection of household electrical appliances and food contact materials, and the like are increasing. Polyethylene and ethylene copolymer (LDPE, LLDPE, HDPE, POE, OBC and the like) resin have excellent comprehensive properties of no toxicity, small density, easy processing, high impact strength, good corrosion resistance, high cost performance, sanitation, no toxicity and the like, so the polyethylene and ethylene copolymer resin is widely applied to interior and exterior trims of automobiles, household appliances, food packaging materials and medical packaging materials.

Under the influence of multiple factors such as the purity of a polymerization monomer, catalyst residue, a polymerization process, decomposition of an auxiliary agent, degradation of resin and the like, the problems of releasing Volatile Organic Compounds (VOC) to different degrees, polluting the environment and harming the health of people still commonly exist in the polyethylene and ethylene copolymer resin sold in the market. With the increasing awareness of environmental protection and the increasing requirements of laws and regulations related to environmental protection, the problem of VOC and odor in resin is more and more emphasized by consumers and manufacturers, most automobile manufacturers begin to implement the european standard (VDA 277 standard of german automobile industry association) to strictly control VOC of parts and components, and the total carbon volatilization amount of interior materials is required to be less than 80 μ g C/g. The newly revised national standard GB 4806.1-2016 food contact material and product general safety requirement clearly requires that the food contact material and the product have no smell touch. In addition, because the VOC content in the existing polyethylene and ethylene copolymer resins is high, the produced resins need to be replaced repeatedly after entering a packaging bin, on one hand, the difficulty of the packaging process is increased, and on the other hand, the phenomenon that replacement gas is discharged beyond the standard often appears along with the release of new atmospheric emission laws and regulations, so that the VOC release problem and odor problem in the polyethylene and ethylene copolymer resins also become one of the problems to be solved urgently.

In view of the foregoing, there is still no method for effectively removing VOCs from polyethylene and ethylene copolymer resins and reducing odor levels in the art.

Disclosure of Invention

The invention aims to provide a method for removing gas phase impurities in polyethylene and ethylene copolymer resin.

In a first aspect of the present invention, there is provided an apparatus for removing gas phase impurities from polyethylene or ethylene copolymer, wherein the apparatus comprises:

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

the feeding valve group (8) is positioned at the upstream of the micro negative pressure steam stripping tower, is connected with a top feeding hole of the micro negative pressure steam stripping tower and is used for controlling resin to enter the micro negative pressure steam stripping tower;

and the discharge valve group (9) is positioned at the downstream of the micro negative pressure steam stripping tower and is used for controlling the resin to flow out of the micro negative pressure steam stripping tower.

In another preferred example, the slightly negative pressure steam stripping tower is a tower in which the material in the tower is stacked and flows in a dense phase moving bed structure.

In another preferred example, the micro negative pressure steam stripping tower is a tower with a hot water generating device arranged in the bottom.

In another preferred example, in the micro-negative pressure steam stripping tower, steam is introduced into a water accumulation disc at the bottom of the tower, and the temperature of the water accumulation disc is controllable.

In another preferred embodiment, the device further comprises an external hot water inlet positioned at the bottom of the tower.

In another preferred example, the external hot water inlet is used for adding external hot water with certain temperature to the bottom of the tower through a pump.

In another preferred example, the feeding valve group is a rotary feeding valve group.

In another preferred example, the discharge valve group is a rotary discharge valve group.

In another preferred example, the rotary feeding valve group is a combination of two or more rotary dischargers.

In another preferred example, the rotary discharging valve group is a combination of two or more rotary dischargers.

In another preferred embodiment, the rotary discharger is in the form of a gravity flap valve or a flap valve.

In another preferred embodiment, the upstream refers to the upstream of the resin flow direction, and comprises the commercial resin which is conveyed by a pelletizing system on a production device and is purchased from outside and is added into the device.

In another preferred embodiment, the micro-negative pressure steam stripping tower further comprises a steam rising perforated plate arranged in the tower body.

In another preferred embodiment, the micro-negative pressure steam stripping tower further comprises a nitrogen inlet positioned at the bottom of the tower.

In another preferred embodiment, the device further comprises a predehydration tower (1) located upstream of the inlet valve group.

In another preferred embodiment, the predehydration tower is a predehydration tower with the existing structure of the original polyethylene and ethylene copolymer production device.

In another preferred embodiment, the predehydration tower is a centrifugal dehydration tower.

In another preferred embodiment, the device further comprises a negative pressure fan, and the negative pressure fan is connected with a tail gas discharge port at the top of the micro-negative pressure steam stripping tower and used for controlling the vacuum degree in the tower.

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

In another preferred example, the condensate at the outlet of the condenser is collected and then sent to a whole plant sewage treatment system or returned to an underwater pelletizing system, and the non-condensable gas at the outlet of the condenser is sent to a tail gas treatment system.

In another preferred example, the liquid phase outlet end of the condenser is connected with a sewage treatment system.

In another preferred example, the liquid phase outlet end of the condenser is connected with an underwater pelletizing system.

In another preferred example, the gas phase outlet end of the condenser is connected with a tail gas treatment system.

In another preferred example, the device further comprises a circulating water cooling and conveying system, and the circulating water cooling and conveying system is used for rapidly cooling the resin discharged from the micro negative pressure steam stripping tower.

In another preferred embodiment, the circulating water cooling and conveying device comprises:

the heat exchanger (3) is positioned at the downstream of the discharge valve group and is connected with the circulating water tank through a delivery pump (4);

the venturi feeder (5), the first entry of venturi feeder links to each other with the valves of unloading, the second entry with the heat exchanger link to each other.

In another preferred example, the circulating water cooling delivery system can be replaced by the following modes: the material from the discharge valve group (9) firstly enters a buffer tank with stirring, and then the mixture of water and the material is conveyed to a downstream process by a conveying pump. Preferably by venturi cooling delivery.

In another preferred example, the Venturi feeder (5) can be replaced by a stirring tank, and a conveying pump is positioned below the stirring tank and used for conveying the mixture of the quenched water and the materials to a downstream centrifugal dehydration process.

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

a buffer tank;

and the delivery pump is connected with the buffer tank.

In another preferred example, the material from the discharge valve group (9) is conveyed into a buffer tank with stirring, and then the mixture of water and the material is conveyed to a downstream process by a conveying pump.

In another preferred example, the tail gas outlet of the micro-negative pressure steam stripping tower is connected with the condenser through a negative pressure fan (7).

In another preferred example, the negative pressure fan is a centrifugal fan or a roots fan.

In a second aspect of the present invention, there is provided a method for removing gas phase impurities from polyethylene or ethylene copolymer, comprising the steps of:

(i) introducing polyethylene or ethylene copolymer into a feeding valve group (8) and feeding the polyethylene or ethylene copolymer into a top feeding hole of a micro-negative pressure steam stripping tower (2);

(ii) introducing steam into water at the bottom of the micro-negative pressure steam stripping tower, controlling the temperature in the tower to generate steam, and exchanging heat with the polyethylene or ethylene copolymer to keep the temperature of the polyethylene or ethylene copolymer at 50-95 ℃ so as to remove gas-phase impurity molecules;

(iii) and operating the rotary discharge valve group (9) to discharge the resin.

In another preferred embodiment, the temperature in the column is within 5 ℃ of the boiling point of water at the operating pressure in the column.

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

In another preferred example, the temperature of the hot water is the corresponding saturation temperature under the condition of the required vacuum degree in the tower.

In another preferred example, the temperature of the hot water is the corresponding unsaturated temperature under the condition of the required vacuum degree in the tower.

In another preferred example, in the step (2), the resin is heated to 40 to 95 ℃, and the specific heating temperature is adjusted according to the softening temperature of the material, and generally corresponds to the vicinity of the softening temperature of the heated resin.

In another preferred example, in the step (2), the resin stays in the wet nitrogen stripping tower for 1 to 5 hours, preferably 1 to 3 hours.

In another preferred embodiment, the method further comprises the steps of: (iv) and introducing the resin into a Venturi feeder (5) to mix the resin with condensed water, so that the resin is subjected to quenching and cooling and then is conveyed to a downstream centrifugal dehydration process of the device.

In another preferred embodiment, the polyethylene or ethylene copolymer is subjected to rapid cooling and then subjected to a centrifugal dehydration step.

In another preferred example, the polyethylene or ethylene copolymer is put into a stirring tank with water to be quenched and cooled, and the mixture of the resin and the water after cooling is conveyed to a downstream centrifugal dehydration process by a conveying pump.

In another preferred embodiment, the method further comprises the steps of: (iv) and introducing the resin into a stirring tank with water, mixing the resin with condensed water, quenching the resin for cooling, and conveying the resin to a centrifugal dehydration process at the downstream of the device through a pump.

In another preferred example, the condensed water comes from a conveying circulating water tank, is cooled by a heat exchanger (3), and is conveyed by a conveying pump (4) to enter a Venturi feeder (5) or a stirring tank.

In another preferred embodiment, the material entering the tower from the top of the tower moves from top to bottom in the tower as a dense phase moving bed.

In another preferred example, in the step (4), the resin is quenched and cooled to below 60 ℃, preferably to below 50 ℃, and more preferably to below 40 ℃ in a venturi feeder or a stirring tank.

In another preferred example, the step (iv) further includes: the treated resin is firstly collected in a storage bin, and then is conveyed to the subsequent working procedures after being cooled by nitrogen.

In another preferred example, the step (iv) further includes: and further cooling the treated resin through other cooling facilities.

In another preferred embodiment, the further cooling means is selected from the group consisting of: converter equipment with a cooling coil cooler or stirring equipment to be cooled.

In another preferred example, before the step (1), the method further comprises the steps of: introducing the resin into a predehydration tower (1) to carry out a predehydration step.

In another preferred embodiment, after the pre-dehydration step, the water content of the resin is 1 to 10 wt%, preferably 1 to 5 wt%.

In another preferred embodiment, the resin is a mixture of resin and water from an underwater pelletizing process of polyethylene and ethylene copolymer equipment.

In another preferred example, after the pre-dehydration step is completed, the removed water is returned to the underwater pelletizing process.

In another preferred embodiment, the method further comprises the steps of: and introducing tail gas discharged from the top of the micro-negative pressure steam stripping tower into a negative pressure fan (7) so as to control the vacuum degree of the micro-negative pressure steam stripping tower.

In another preferred embodiment, the method further comprises the steps of: and leading the tail gas discharged by the negative pressure fan (7) to enter a condenser (6) for condensation.

In another preferred example, after the condensation step is finished, the condensed water is introduced into an underwater pelletizing system or a sewage treatment system.

In another preferred embodiment, after the condensation step is finished, the non-condensable gas is introduced into a tail gas treatment system.

In another preferred embodiment, in said steps (1) to (3), the oxygen content of the gas phase component in the stripper is lower than 1%, preferably lower than 0.1%, more preferably lower than 100 ppm.

The device and the method provided by the invention are applicable to polyethylene or ethylene copolymer, in particular LDPE, LLDPE, POE and OBC; the method has better effect on LDPE, POE and OBC with low melting point.

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; most preferred is LDPE.

It is to be understood that within the scope of the present invention, the above-described features of the present invention and those specifically described below (e.g., in the examples) may be combined with each other to form new or preferred embodiments. Not to be reiterated herein, but to the extent of space.

Drawings

Fig. 1 is a schematic diagram of the structure of the polyethylene VOC removal, odor-rating reducing device of the present invention.

The system comprises a pre-dehydrator 1, a micro negative pressure steam stripping tower 2, a heat exchanger 3, a delivery pump 4, a Venturi feeder 5, a condenser 6, a negative pressure fan 7, a rotary feeding valve bank 8 and a rotary discharging valve bank 9;

21-underwater pelletizing system, 22-underwater pelletizing circulating water tank, 24-CWR (circulating cooling water return), 25-conveying circulating water tank, 26-centrifugal dehydration process, 28-steam flow, 29-tail gas treatment system, 30-nitrogen flow and 31-CWS (circulating cooling water supply).

Detailed Description

The invention provides a device for removing VOC (volatile organic compounds) in polyethylene and olefin copolymer and reducing odor grade and a corresponding method thereof. The device can fully remove residual VOC in the resin through a steam removal process after gas diffusion and migration in a negative pressure environment.

Method for removing VOC (volatile organic compounds) in polyethylene and system copolymer and reducing odor grade

In order to overcome the defects of the prior art, reduce the VOC content in resin products in the prior polyethylene or ethylene copolymer production device, reduce the odor level, improve the product quality and reduce the VOC emission problem in the packaging process of the production device, the invention provides a process method for efficiently removing the VOC in the resin and improving the odor, which has the principle that the low molecular VOC wrapped in the resin is fully migrated and diffused out by keeping the resin for a certain time at a certain temperature under a certain negative pressure condition and then is removed by steam stripping, and the higher the temperature is under the condition that the resin is not melted and agglomerated, the better the removal effect is: with the increase of the temperature, the chain segment movement is more obvious, the small crystal regions melt, the chain segment movement of the transition region and the amorphous region is violent, and the chain segments of the regions move while being rearranged and crystallized to form coarse plate crystals, so that the VOC small molecules wrapped in the resin are promoted to be fully migrated and diffused; on the other hand, with the rise of temperature, the free volume of a molecular chain is enlarged, the diffusion coefficient and the vapor pressure of VOC molecules wrapped in the resin are also increased, so that the VOC molecules are easier to migrate from the inside of the resin and gather on the surface of the material, and then the VOC content in the resin product finally reaches the requirements of VDA277 and GB 4806.1-2016 through wet nitrogen stripping removal.

According to the process, a set of micro-negative pressure steam stripping equipment and auxiliary equipment are added between an underwater pelletizing process and a particle centrifugal dehydration process of the existing polyethylene and ethylene copolymer process device, materials are kept at a certain temperature, a certain vacuum degree and stay for a certain time in the process, so that VOC is resolved from resin and is taken out through steam stripping, mixed gas obtained by stripping is subjected to fixed-discharge and then condensed, wherein non-condensable gas and VOC are removed from a field tail gas treatment system, and condensed water returns to an underwater pelletizing system. The specific process is as follows:

firstly, the mixture of water and resin conveyed from the upstream underwater pelletizing process is firstly dehydrated to the water content of the resin of about 1 to 10 percent by adding newly added pre-dehydration equipment. And the pre-dehydrated PE resin is continuously fed into a micro negative pressure steam stripping tower from the top through a two-stage material transfer valve, and water from the pre-dehydration tower returns to an upstream underwater pelletizing process through a pump.

Secondly, after entering the steam steaming tower, the PE resin is piled up in a dense phase moving bed and moves slowly from top to bottom, and certain retention time is ensured. Due to the pumping and discharging function of the tower top negative pressure fan, hot water at the bottom of the tower is evaporated, rises along a steam pipeline which is uniformly distributed in the tower, and contacts with the material for heat exchange until the material is heated to a certain temperature range. Meanwhile, in order to prevent VOC from being enriched in the system, a continuously discharged mixed gas is required at the top of the tower, after the mixed gas is condensed, the uncondensed tail gas is sent to a field tail gas treatment system, and after the condensate is collected, the condensate returns to an underwater granulating process or a sewage treatment system.

Thirdly, the material from the tower bottom enters a Venturi feeder after passing through a two-stage material transferring valve, is mixed with cooling water and is rapidly cooled, and then is conveyed to a downstream centrifugal dehydration process.

The equipment for realizing the method comprises the following steps:

1-a pre-dehydrator used for removing a large amount of water in the resin conveyed from the upstream underwater pelletizing process.

2-little negative pressure steam strip tower, the material steam in the tower heats to the uniform temperature to dwell for the certain time, controls the vacuum in the tower simultaneously, lets the VOC who remains in the resin thoroughly resolve out to be taken out along with steam by negative pressure fan.

3-heat exchanger for cooling down the water conveying and cooling the hot resin.

And 4, a delivery pump for delivering water in the circulating water tank into the Venturi feeder.

And 5-a Venturi feeder, wherein the resin is collected and mixed with cooling water from a conveying circulating water tank to carry out quenching and cooling on the resin, and then the resin is conveyed to a downstream centrifugal dehydration process.

6-a condenser for cooling the mixture of steam and VOC coming out of the steaming tower.

And 7-a negative pressure fan used for discharging the mixed gas of the steam and the VOC and ensuring a certain operation vacuum degree in the tower.

And 8, rotating a feeding valve group to control the amount and speed of resin entering the steaming tower and prevent air in the pre-dehydration tower from leaking into the micro-negative pressure steam stripping tower.

And 9-rotating the discharging valve group to control the discharging speed and the discharging amount of the resin of the steaming tower and prevent water from reversely crossing the micro-negative pressure steam stripping tower.

The method and apparatus can be used not only for VOC removal of freshly made polyethylene or ethylene copolymer resins, but also for VOC removal of existing commercially available polyethylene or ethylene copolymer resins. In addition, the method and the device have good stripping effect, so that the method and the device can 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.

The invention is characterized in that:

(1) the VOC removal from polyethylene or ethylene copolymer resins using the apparatus and process of the present invention results in final output packaged resins having a lower VOC content than untreated resins, as low as 30ppm or less (as tested by VDA 277), and an odor rating as low as typically grade 3 (as tested by VW 50180), which is much lower than the VOC content and odor rating of commercially available resins of the same grade.

(2) The method has simple treatment process, namely only one set of micro-negative pressure steam stripping tower and auxiliary facilities are needed to be added between the two original working procedures, the layout is small, and the operation and the layout of the original device are not influenced.

(3) The method adopts steam for steam stripping, has high heat transfer efficiency, controls a proper temperature interval in the treatment process, has proper negative pressure, and quickly resolves VOC molecules, thereby having high treatment efficiency, less steam consumption, no influence on the quality of resin, no phenomenon of caking and the like which influence the operation of the device.

(4) The investment and the operation cost of the device are low, and the quality of the product is improved.

In addition, the device and the method provided by the invention are applicable to polyethylene or ethylene copolymers, in particular LDPE, LLDPE, POE and OBC; the method has better effect on LDPE, POE and OBC with low melting point.

The process flow of the method for effectively removing VOC from polyethylene or ethylene copolymer resin and reducing odor grade by combining the attached figure 1 is described as follows:

step 1) the mixture of resin and water from the underwater pelletizing system 21 of the production device enters a predehydration tower 1 for dehydration treatment, and the removed water returns to an underwater pelletizing circulating water tank 22 and is reused in the underwater pelletizing process.

And 2) the wet resin subjected to the pre-dehydration treatment in the step 2) enters a feed inlet at the top of the micro-negative pressure steam stripping tower 2 through a rotary feed valve group 8.

And 3) after entering a micro-negative pressure steam stripping tower 2 provided with a steam rising porous plate, exchanging heat with steam (formed by evaporation of hot water at the bottom of the tower) from a tower kettle, controlling the temperature and pressure in a system to control the temperature of the steam, heating the resin to 50-95 ℃, and maintaining a certain vacuum degree in the tower to resolve VOC molecules in the resin. The material entering the tower from the top of the tower moves from top to bottom in the tower in a dense phase moving bed.

And 4) controlling the discharging of the resin subjected to the pre-dehydration treatment by a rotary discharging valve group 9.

And 5) the resin discharged from the tower enters a Venturi feeder 5, and is cooled by a heat exchanger 3 (wherein the heat exchanger 3 is provided with a circulating cooling water supply device 31 and a circulating cooling water return device 24) from a conveying circulating water tank 25 in the Venturi feeder, and then the water conveyed by a conveying pump 4 is mixed, and the resin is subjected to quenching cooling and then conveyed to a centrifugal dehydration process 26 at the downstream of the device.

And 6) in order to prevent the analyzed VOC from being enriched in the system, after the mixed gas discharged by a negative pressure fan 7 at the top of the micro negative pressure steam stripping tower 2 is condensed by a condenser 6, one fixed row of noncondensable tail gas enters a tail gas treatment system 30 on the site of the device, and the condensate returns to an underwater pelletizing system or a decontamination water treatment system.

To verify the effectiveness of the device, a set of devices with a throughput of 1Kg/h was processed and subjected to the following tests:

example 1

The production apparatus was pelletized underwater, and then subjected to centrifugal dehydration treatment, and high-pressure polyethylene particles (LDPE, production apparatus packaging material VOC content: 120ppm, odor grade 4.5 grade) containing 1% of water were filled in a micro-negative pressure steam stripping tower of an experimental apparatus. The bottom of the tower is provided with a valve connected with a water accumulation tank, water is heated to 60 ℃ by steam, the top of the tower is controlled by a negative pressure fan to control the absolute pressure in the tower to be about 19930Pa, hot water is evaporated into steam, the steam rises to the tower to heat polyethylene granules, and after the steam is heated for 2 hours, the materials are quenched to 45 ℃ by cold water. Discharging, and carrying out centrifugal dehydration and air blow drying on the polyethylene resin according to the treatment method of an industrial device.

VOC content (VDA 277): 28 ppm; odor grade: and 3.5 grade.

Example 2

The production apparatus was pelletized underwater, and then subjected to centrifugal dehydration treatment, and high-density polyethylene particles (HDPE, slurry method, production apparatus packaging material VOC content: 165ppm, odor grade 4.5 grade) containing 1% of water were charged into a micro-negative pressure steam stripping tower of an experimental apparatus. The bottom of the tower is provided with a valve connected with a water accumulation tank, water is heated to 75 ℃ by steam, the top of the tower is controlled by a negative pressure fan, the absolute pressure in the tower is about 38560Pa, hot water is evaporated into steam, the steam rises to the tower to heat polyethylene granules, and after the steam is heated for 2 hours, the materials are quenched to 45 ℃ by cold water. Discharging, and carrying out centrifugal dehydration and air blow drying on the polyethylene resin according to the treatment method of an industrial device.

VOC content (VDA 277): 26 ppm; odor grade: and 3.6 levels.

Example 3

The production device is granulated under water and then is centrifugally dewatered, and high-density polyethylene particles (HDPE, gas phase method, production device packaging material VOC content: 180ppm, odor grade 4.8 grade) with 1% of water are filled into a micro-negative pressure stripping tower of an experimental device. The bottom of the tower is provided with a valve connected with a water accumulation tank, water is heated to 75 ℃ by steam, the top of the tower is controlled by a negative pressure fan, the absolute pressure in the tower is about 38560Pa, hot water is evaporated into steam, the steam rises to the tower to heat polyethylene granules, and after the steam is heated for 2 hours, the materials are quenched to 45 ℃ by cold water. Discharging, and carrying out centrifugal dehydration and air blow drying on the polyethylene resin according to the treatment method of an industrial device.

VOC content (VDA 277): 22 ppm; odor grade: and 3.7 stages.

Example 4

A commercial POE resin (VOC content: 160ppm, odor grade 4.6 grade) was charged to the slightly negative pressure stripper of the experimental set-up. The bottom of the tower is provided with a valve connected with a water accumulation tank, water is heated to 70 ℃ by steam, the absolute pressure in the tower is controlled to be about 31180Pa by a negative pressure fan at the top of the tower, hot water is evaporated into steam, the steam rises to the tower to heat POE granules, and the POE granules are heated for 3 hours and then cooled to 40 ℃ by cold water. Discharging, namely centrifugally dewatering the POE resin according to the treatment method of the industrial device, and then drying the POE resin by air.

VOC content (VDA 277): 35 ppm; odor grade: and 3.8 stages.

Example 5

A commercial OBC resin (VOC content: 250ppm, odor grade 4.5 grade) was loaded into the slightly negative pressure stripper of the experimental set-up. The bottom of the tower is provided with a valve connected with a water accumulation tank, water is heated to 80 ℃ by steam, the top of the tower is controlled by a negative pressure fan to control the absolute pressure in the tower to be about 47370Pa, hot water is evaporated to steam, the steam rises to the tower to heat OBC granules, and the OBC granules are heated for 3 hours and then quenched by cold water to 40 ℃. Discharging, and carrying out centrifugal dehydration and air blow drying on the OBC resin according to the treatment method of an industrial device.

VOC content (VDA 277): 40 ppm; odor grade: and 3.6 levels.

Example 6

A commercial LLDPE resin (VOC content: 185ppm, odor grade 4.8 grade) was loaded into the slightly negative pressure stripper of the experimental set-up. The bottom of the tower is provided with a valve connected with a water accumulation tank, water is heated to 65 ℃ by steam, the top of the tower is controlled by a negative pressure fan to control the absolute pressure in the tower to be about 25020Pa, hot water is evaporated to steam, the steam rises to the tower to heat LLDPE granules, and after the LLDPE granules are heated for 3 hours, the materials are quenched to 40 ℃ by cold water. Discharging, namely centrifugally dewatering the LLDPE resin according to the treatment method of an industrial device, and then drying the LLDPE resin by air blowing.

VOC content (VDA 277): 35 ppm; odor grade: and 3.2 stages.

All documents referred to herein are incorporated by reference into this application as if each were individually incorporated by reference. Furthermore, it should be understood that various changes and modifications of the present invention can be made by those skilled in the art after reading the above teachings of the present invention, and these equivalents also fall within the scope of the present invention as defined by the appended claims.

Claims

1. An apparatus for removing gas phase impurities from polyethylene or ethylene copolymers, said apparatus comprising:

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

2. The apparatus according to claim 1, characterized in that it further comprises a predehydration tower (1) upstream of the inlet valve group.

3. The device according to claim 1, characterized in that it further comprises a negative pressure fan (7).

4. The device according to claim 1, characterized in that the device further comprises a condenser (6), wherein an inlet of the condenser is connected with an outlet of a tail gas negative pressure fan (7) of the micro negative pressure steam stripping tower, and the condenser is used for separating water vapor and non-condensable gas in the tail gas of the micro negative pressure steam stripping tower.

5. The apparatus of claim 1, further comprising a circulating water cooling and conveying system for rapidly cooling the resin discharged from the micro-negative pressure steam stripping tower and conveying the mixture of water and material to a downstream process; preferably, the circulating water cooling system includes:

6. A method for removing gas-phase impurities from polyethylene or ethylene copolymer is characterized by comprising the following steps:

7. The method of claim 6, wherein said method further comprises the steps of:

(iv) introducing the polyethylene or ethylene copolymer into a Venturi feeder (5) to mix the polyethylene or ethylene copolymer with circulating cooling water, thereby carrying out quenching and cooling on the polyethylene or ethylene copolymer.

8. The method of claim 6, wherein prior to said step (1), further comprising the step of: the resin is fed into a predehydration tower (1) for predehydration.

9. The method of claim 6, wherein said method further comprises the steps of: introducing tail gas discharged from the top of the micro-negative pressure steam stripping tower into a negative pressure fan (7) so as to control the vacuum degree of the micro-negative pressure steam stripping tower; preferably, the method further comprises the steps of: and leading the tail gas discharged by the negative pressure fan (7) to enter a condenser (6) for condensation.

10. The method of claim 6, wherein in steps (1) to (3) the oxygen content in the slightly negative pressure steam stripper is less than 1%, preferably less than 0.1%, more preferably less than 100 ppm.