Devolatilization of Plastomer Pellets

Abstract

The devolatilization of plastomer pellets is carried out using nitrogen that is recycled in the process. Volatile hydrocarbons are removed from the nitrogen in a hydrocarbon extraction container (e.g., an adsorbent bed). In one embodiment, the recycled nitrogen contains less than 300 ppm of volatile hydrocarbons after treatment in the adsorbent bed.

Description

Devolatilization of Plastomer Pellets Field of Invention This invention relates to the devolatilization of alpha-ethylene plastomer pellets. Background of the Invention The term plastomer refers to ethylene-alpha olefin copolymers that have a low density (generally less than 0.905 g / cc, particularly since 0.865 to 0.905 g / cc, especially from 0.880 to 0.905 g / cc). Plastomers are typically manufactured in a solution polymerization process because they are sticky (and this stickiness makes them difficult to prepare in a suspension or gas-phase process). The stickiness also makes it difficult to remove hydrocarbon residues that remain in the copolymers from the devolatilization process. Several techniques are known for the disposal of hydrocarbon waste. For example, the following are known: 1) removal of comonomer that forms hydrocarbon solutions before recovery of the solid copolymer; 2) remove hydrocarbon residues from the solid copolymer particles (or powder) that have been recovered from the solution but have not yet been pelletized; 3) Use a devolatilization extruder to remove Ref. 320186 hydrocarbon residues during the pelletizing operation; and 4) removing the hydrocarbon residue from the copolymer pellets. (The present invention generally refers to this operation / process; but it may also include the optional use of techniques 1-3 above). In the past, the use of various disposal agents has been reported, including air, nitrogen, and gaseous hydrocarbons (such as propane). Now inventors have discovered that nitrogen can be used and then reused (recycled) for disposal in polymer pellets, especially when the recycled nitrogen has been treated to reduce the level of hydrocarbons in the recycled nitrogen to less than 300 ppm. Summary of the Invention In one embodiment, the invention provides: A process for the production of devolatilized alpha ethylene copolymer having a density from 0.865 to 0.905 g / cc and a melt index, I2, from 0.3 to 30 g / 10 minutes, measured by ASTM D1238 at a temperature of 190°C using a 2.16 kg charge, the process comprising: i) providing raw ethylene-alpha olefin copolymer pellets to a devolatilization vessel, wherein the raw pellets are characterized in that they contain a volatile hydrocarbon; ii) supply nitrogen gas to the devolatilization vessel; iii) unloading the devolatilized pellets from the devolatilization vessel, where the devolatilized pellets contain a lower level of volatile hydrocarbon than the unprocessed pellets; iv) recover the mixed waste gas comprising a mixture of nitrogen and hydrocarbon from the upper space of the devolatilization vessel; v) direct the mixed disposal gas towards a hydrocarbon extraction container; vi) recover the purified nitrogen from the hydrocarbon extraction container; and vii) recycle the purified nitrogen to the devolatilization container. In one embodiment, the invention provides: A process for the production of devolatilized alpha ethylene copolymer having a density from 0.865 to 0.905 g / cc and a melt index, I2, from 0.3 to 30 g / 10 minutes, measured by ASTM D1238 at a temperature of 190°C using a 2.16 kg charge, the process comprising: i) providing raw ethylene-alpha olefin copolymer pellets to the upper portion of a devolatilization vessel, wherein the raw pellets are characterized by containing a volatile hydrocarbon; ii) providing an upward flow of nitrogen gas to the lower portion of the devolatilization vessel, where the nitrogen is supplied at a temperature of 40 to 70 °C; iii) unloading the devolatilized pellets from the devolatilization vessel, wherein the devolatilized pellets contain a lower level of volatile hydrocarbon residue than the unprocessed pellets; iv) recovering mixed waste gas comprising a mixture of nitrogen and hydrocarbon from the upper space of the devolatilization vessel; v) direct the mixed disposal gas towards a hydrocarbon extraction container; vi) recover the purified nitrogen from the hydrocarbon extraction container; and vii) recycle the purified nitrogen to the bottom of the devolatilization vessel. The process of this invention is suitable for polyolefins having a density from approximately 0.865 to approximately 0.970 g / cc. It is particularly suitable for the lower end of this density range (where conventional steam removal is unsuitable due to the low VICAT softening temperature of lower-density plastomers and elastomers). Thus, in a commercial facility producing ethylene-alpha-olefin copolymers (and even homopolymers), the process of this invention can also be employed with higher-density polymers. Brief Description of the Figures Figure 1 provides a process flow diagram of one embodiment of the invention. In Figure 1, plastomer pellets are supplied to the devolatilization vessel 1 through pellet inlet line 2 (located near the top of the devolatilization vessel 1) and exit through pellet outlet line 3 (located near the bottom of the devolatilization vessel 1). In this mode, nitrogen enters the devolatilization vessel 1 through feed line 4. The nitrogen flow includes recycled nitrogen and some pure or feed nitrogen. In this mode, nitrogen exits through line 4a (and is supplied as an upward flow). The nitrogen is compressed using compressor 5 before entering the hydrocarbon extraction vessel 6, which, in this mode, is a vessel containing an alumina adsorbent and is operated on a temperature swing protocol. The recovered / purified nitrogen is directed to the heat exchanger 8 before being recycled back into the devolatilization vessel 1 through feed line 4. Additional nitrogen (also known as feed nitrogen) can be added through feed line 4 or through an optional additional feed line (not shown). Detailed Description of the Invention This invention relates to the treatment of polyolefin pellets (as opposed to non-pelletized polyolefin solids, typically referred to by those skilled in the art as granular or powdered polyolefin). A brief review of the typical operations for converting a polyolefin solution (in this case, where the solution is produced by a solution polymerization process) into polyolefin pellets. Solution Polymerization Process Descriptions of the typical solution polymerization process for the preparation of ethylene-alpha olefin copolymers are provided in U.S. Patents 9,512,282 (patent '282); 6,063,879; 6,878,658; and U.S. Application 20180350532 (Zhang et al.). Typical comonomers include 1-butene; 1-hexene; 1-octene (and mixtures thereof). The solvent is typically a mixture of Cg₆ to C₆O₅ alkanes and isoalkanes and may also include cyclic hydrocarbons (such as cyclopentane or cyclohexene). The description in patent '282 includes a review of some suitable / typical reactor configurations; catalyst deactivation systems; and polymer recovery systems that include one or more vapor / liquid (V / L) separators. The output of the final V / L separator includes a molten polymer stream containing the ethylene-alpha olefin copolymer along with residual hydrocarbons (especially residual solvent and alpha olefin comonomer). This molten polymer stream is typically directed through an extruder that has a die plate at the extruder outlet. The die plate is typically configured with a plurality of circular holes, thereby leading to the formation of spaghetti-like strands of the extrudate. These strands are continuously cut by one or more rotating die cutters (also referred to as blades by those skilled in the art) to form pellets.In some pelleting operations, a melt pump (also called a gear pump) can be placed between the extruder outlet and the die plate to generate additional pressure without causing overheating. Lower melt temperatures are generally preferred over higher melt temperatures to avoid polymer degradation. The die plate cutters can be water-cooled. Generally, due to the stickiness of plastomers, a lower die plate temperature is used for plastomers (compared to the die plate temperature used for higher-density ethylene copolymers). The pellets are conveyed away from the die plate using water, which can be either cooled or heated (as described below).Those skilled in the art know that higher water temperatures are typically used for higher density / higher crystallinity polymers (compared to the water temperature used for plastomers). The size and shape of plastomer pellets can be similar to the size and shape of pellets for higher density polyethylenes. Plastomer pellets can contain approximately 3 to 6% by weight of residual hydrocarbon. Additives can be incorporated into the cutting water to mitigate foaming and sticking problems, and the use of these additives is well known to those skilled in the art. The conventional water transport system described above (in this case, a pellet suspension in water transferred through pipes) is used to move the pellets to the devolatilization / finishing operations. This slurry water will be at a higher temperature than the water used to cool the die plate and can be used to heat the pellets. Heating the pellets to the devolatilization temperature using a gas stream would be time-consuming. It is preferable to preheat the pellets with the slurry water stream to a temperature close to the desired devolatilization temperature to facilitate the subsequent devolatilization step. In general, the temperature of the slurry water will depend on the softening temperature of the copolymer in the suspension. Rotating Hair Dryer Water can be removed from the suspension using a conventional rotary dryer. After spin drying, the pellets will typically contain approximately 0.05% water by weight. Air can be used to further reduce the water content. It is preferable to dry the pellets before the devolatilization stage to avoid the drop in pellet temperature resulting from water evaporation at the devolatilization temperature. In one embodiment, the suspended water will be used to heat (or alternatively, cool) the pellets to a temperature that is approximately 5°C lower than the VICAT softening temperature. In this way, the suspended water for a copolymer with a high VICAT temperature can be heated, while the suspended water for a copolymer with a low VICAT temperature may require cooling. The water removed in the rotary dryer can be returned to the die plate cutter for reuse / recycling. Transfer of Dry Pellets to Devolatilization Vessels The dried pellets are then directed to a holding vessel, which is preferably purged with nitrogen. Afterward, the pellets are conveyed to a devolatilization vessel. In one embodiment, this conveying is carried out using a nitrogen flow (and, in another embodiment, this nitrogen is recycled from the nitrogen purification system). The temperature of the nitrogen used for this transport must also be controlled (again, at a temperature no more than 5% lower than the VICAT softening temperature to mitigate stickiness problems). Devolatilization Vessels In one configuration, these containers will hold from approximately 150,000 to approximately 200,000 kilograms of plastomers and will have a retention time of approximately 12 to approximately 72 hours. Therefore, a typical global-scale plant will require multiple containers. In one embodiment, the containers have a conventional silo shape—in this case, a simple container with a circular cross-section. In one embodiment, the height-to-diameter ratio ranges from 3:1 to 8:1, particularly from 4:1 to 5:1. In one embodiment, a cone is placed at the bottom of the silo. The conical portion of the silo can be further divided into separate compartments to minimize the consolidation pressure experienced by the pellets in that area of ​​the silo. In one mode, the vessel is operated under vacuum to improve the rate of devolatilization. In an alternative mode, the vessel is operated under a small positive pressure to limit air ingress. In one configuration, the positive pressure ranges from 102 to 109 kPa. Operation at slightly above atmospheric pressure is preferred. Low-pressure tank operation can be costly due to vacuum requirements, and high-pressure tank operation requires a significant amount of removal agent to complete the devolatilization process to the same final VOC pellet content. Preferably, the containers are purged with nitrogen even when they are empty and when they are unloaded. These containers are filled by transporting nitrogen from the holding vessel. As previously stated, pellets typically contain approximately 3 to 5% by weight of residual hydrocarbon before the devolatilization process. In one configuration, the residual hydrocarbon (or volatile organic carbon, VOC) level will be reduced below 500 ppm, specifically below 300 ppm, and most notably below 150 ppm after devolatilization. Lower levels can be achieved (at a higher cost) by using longer residence times and / or increasing the temperature and / or nitrogen flow rate through the vessels. In one mode, the containers operate in batch mode; in this case, the containers are emptied / prepared for reuse once the target VOC level is reached. In one embodiment, the containers are insulated. In another embodiment, the containers are equipped with heat exchangers to compensate for heat loss in cold climates. In yet another embodiment, the exterior of the containers is equipped with a system for applying cooling water in warm climates—for example, a simple water spray can be applied to the exterior. Nitrogen Supply to Devolatilization Vessels Typically, nitrogen is heated to improve extraction / devolatilization efficiency. However, the maximum nitrogen temperature is influenced by the softening temperature of the plastomer being treated. The softening temperature can be measured using ASTM D1525, and the result is reported as the VICAT temperature (or VICAT softening temperature) in degrees Celsius. In one configuration, the maximum nitrogen temperature is 5°C lower than the VICAT softening temperature of the plastomer. In another configuration, the nitrogen flow rate per hour ranges from 2–10% by weight, specifically from 4–6% by weight, of the plastomer's weight in the vessel (for example, a vessel containing 200 tons of plastomer could be supplied with a nitrogen flow rate of 10 tons / hour to provide a nitrogen flow rate of 5% by weight / hour, based on the plastomer's weight). In one embodiment, nitrogen is added near the bottom of the vessel using a plurality of feed nozzles. In one embodiment, the nitrogen flow rate and velocity are not high enough to develop a fully fluidized bed; the advantages of avoiding a fully fluidized bed are known to those skilled in the art and are described in U.S. Patent 5,478,922 (Rhee, popr UCC). In one method, a small portion of the pellets is recirculated from the bottom to the top of the vessel. For lower-density resins devolatilized in large vessels, this step can be useful to prevent the pellets from clumping and blocking the devolatilization vessel. The pellets in the lower portion of the devolatilization vessel experience higher consolidation pressure and are more prone to clumping. Pellet recirculation can be achieved by directing some of the pellets through a valve at the bottom of the vessel into a collection chamber. The pellets in the collection chamber are then transferred with nitrogen to the top of the vessel. In one method, the amount of pellets transferred ranges from approximately 1 to 5% by weight per hour of the total pellet weight.It is preferred that the recirculation rate be kept at an optimum value to minimize the adverse impact of recirculation on the total devolatilization time. Nitrogen Purification System The fluid at the top of the vessels is a mixture of nitrogen and volatile hydrocarbon that has been removed from the pellets. This fluid can be referred to as mixed removal gas and is directed to a nitrogen purification system for hydrocarbon removal. The following types of technologies are generally suitable for the removal of volatile hydrocarbons (which may also be referred to as volatile organic hydrocarbons or VOCs by those skilled in the art) from mixed separation gas. 1. Adsorption A typical adsorption technology uses a bed packed with an adsorption medium (such as alumina, silica gel, a molecular sieve, zeolite, or activated carbon). The adsorption medium removes VOCs until the bed's adsorption limit is reached. At that point, the bed is regenerated to remove the VOCs. Typical examples of adsorption and regeneration operations include pressure swing adsorption (PSA), temperature swing adsorption (TSA), and vacuum swing adsorption (VSA). Each of these operations is well-known and commercially available. 2. Absorption The absorbent is usually a liquid (such as silicone oil) and the process can be conducted in a packed bed, a plate bed, or a spray tower that provides good contact between the mixed waste gas and the absorbent liquid. 3. Condensation A compressor and / or drill is used to condense the VOCs into a liquid. 4. Distillation (cryogenic) Cryogenic distillation can also be used to condense VOCs into a liquid. In cryogenic distillation, a cooling system is coupled with a condenser so that compounds with very low boiling points can be liquefied and recovered; in this case, volatile organic compounds. 5. Membrane Separation Membranes can be polymeric (such as silicone, polyvinylidene fluoride or poly(ether block amide)) or prepared from silica or zeolite. In one embodiment, the nitrogen purification system includes at least one bed of adsorption medium. In one embodiment, the overhead gas mixture is compressed before passing through the adsorption medium, specifically to a gauge pressure of 300–500 kilopascals (kPa). In one embodiment, a plurality of adsorption beds are employed; for example, 4–8 adsorption beds can be used in combination with 8–12 devolatilization vessels. This allows the adsorption beds to be regenerated without interrupting plastomer production. The adsorption beds can be regenerated using Temperature Oscillation or Pressure Oscillation protocols (both protocols are known to those skilled in the art). In one mode, the mixed waste gas is treated upstream of the compressor to remove solids (such as dust and grease) that could damage the compressor. As noted previously, the mixed waste gas can be compressed to 300–500 kPa. This can lead to the condensation of some VOCs, which can accumulate in a condensate drum. In one embodiment, the pressurized gas is then sent to an adsorption bed. Alumina is a suitable adsorbent because it contains sites that are active towards the VOC materials contained in a plastomer prepared by copolymerizing ethylene with alpha-definites in a solution polymerization process (such as C4a C10 hydrocarbons), and because alumina contains a relatively high number of active sites for a given unit volume. The particle size of the adsorbent particles is selected to optimize / balance the number of active sites available for a given volume (which favors small particle size) and the pressure drop in the bed (which favors large particle size) using techniques known to those skilled in the art. It should also be recognized that the bed height-to-diameter ratio and the gas flow rate will affect the pressure drop. The active sites become saturated with VOCs after a while, meaning the bed can no longer effectively remove VOCs from the mixed waste gas. The adsorbent bed is then regenerated (e.g., with steam or vacuum) to remove the VOCs from the adsorbent. In another modality, a membrane separation technology can be used as an alternative to (or in addition to) the adsorbent bed described above. Distillation and absorption techniques are also potentially suitable for VOC removal from mixed waste gas, but there is no preference for any of these techniques. VOC measurement Volatile organic compounds (VOCs) can be measured using techniques well-known to those skilled in the art. When precise VOC measurement is required, VOCs are measured according to ASTM D452612, Standard Practice for Determination of Volatiles in Polymers by Static Gas Chromatography. In practice, a VOC measuring device (e.g., a gas chromatograph) can be coupled to the devolatilization vessel to determine the amount of VOCs in the mixed removal gas. Mathematical models can then be used to calculate the ppm of VOCs in the devolatilized pellets from the amount of VOCs in the mixed separation gas. Effect of VICAT Softening Temperature Experts in the field know that linear ethylene homopolymers are quite crystalline and exhibit a high VICAT softening temperature. The crystallinity of copolymers decreases, so copolymers with higher amounts of comonomer become less crystalline and also exhibit a lower VICAT softening temperature. It is known to remove / devolatilize ethylene homopolymers and ethylene copolymers that still retain some crystallinity (and thus exhibit a relatively high VICAT softening point) with steam. However, at densities below approximately 0.905 g / cc, alpha-ethylene copolymers become sticky and have a VICAT softening temperature that makes steam removal difficult / ineffective. However, the inventors have observed that the reduced crystallinity of these copolymers is also associated with comparatively high diffusion rates of C6 to C8 VOC hydrocarbons from the pellets of these copolymers. Therefore, it is possible to use a lower temperature to remove these VOC hydrocarbons from the plastomer pellets. This is particularly effective for plastomers with a density range of approximately 0.880 to 0.905 g / cc. Antioxidants In one embodiment, the plastomer pellets contain a conventional antioxidant packing that includes a conventional primary antioxidant (e.g., a hindered phenol, such as those sold under the trademarks IRGANOX® 1010 or IRGNOX® 1076) and a conventional secondary antioxidant (e.g., a phosphite, such as that sold under the trademark IRGASTAB® 168). In one embodiment, the degradation of the antioxidant observed during the devolatilization process of this invention is less severe than the degradation observed with the use of a conventional steam removal process (and this can be quantified by measuring the amount of phosphite that is oxidized during each process). EXAMPLES Example 1: Batch Devolatilization 76.2 kilograms of ethylene-octene copolymer plastomer pellets having a density of 0.866 g / cc and a melt index, MI (or I2), of 0.58 g / 10 minutes (as determined by ASTM D1235 at a temperature of 190°C, using a 2.16 kg charge) were devolatilized in a column-shaped devolatilization vessel (or silo) using an upward flow of nitrogen gas provided at 40°C. Table 1 provides a summary of the other data from this experiment. The term pellet count describes the number of pellets contained in a 1-gram sample of the plastomer. The vessel was operated at a pressure of 106 kPa. The pellets had an initial temperature of 31°C. The nitrogen flow rate was 5 kg / hr, and the retention time was 4.6 hours. As shown in Table 1, the pellets initially contained volatile hydrocarbons (VOCs) at 4.98 wt%. After the 46-hour containment (or disposal) time, the pellets had a final VOC level of 80 parts per million (ppm). TABLE 1 Batch Elimination Experiment Resin Density g / cc 0.886 MI (I2) g / 10 min 0.58 Resin Mass kg 76.7 Pellet Count # / lg 41 Initial Resin VOC % by weight 4.98 Initial Pellet Temperature °C 31 Vessel Pressure kPa 106 Nitrogen Flow Rate Kg / h 5 Nitrogen Temperature °C 40 Containment Time h 46 Final Resin VOC ppm 80 Example 2: Batch Deletion In this example, 71.4 kg of the same type of plastomer pellets were treated in the same type of devolatilization vessel used in Example 1 under the conditions shown in Table 2. As summarized in Table 2, a nitrogen flow rate of 10 kg / hour at 47°C was observed to reduce the final VOC concentration in the pellets to 40 ppm. TABLE 2 Resin Density g / cc 0.886 MI g / 10 min 0.58 Resin Mass kg 71.4 Pellet Count # / lg 41 Initial Resin VOC % by weight 4.51 Pellets Initial Temperature °C 34.2 Vessel Pressure kPa 106 Nitrogen Flow Rate Kg / h 10 Nitrogen Temperature °C 47 Containment Time h 38 Final Resin VOC ppm 40 Example 3: Continuous Elimination In this example, 70.1 kg per hour of an ethylene-octene plastomer (density = 0.855 g / cc; melt index, MI or Is = 0.56 g / 10 mins) was fed into a silo-shaped devolatilization vessel. The continuous process provided a HUT of 17 hours. Nitrogen flow rates of 25 kg / h, 45 kg / hr, and 65 kg / hr at 57°C were supplied. As shown in Table 3, the flow rate of 25 kg / h produced pellets that have a final VOC concentration of 3200 ppm, while the flow rate of 65 kg / h reduced the VOC level to 140 ppm. TABLE 3 Continuous Elimination Resin density g / cc 0.885 MI g / 10 min 0.56 Resin Mass Flow Rate Kg / h 70.1 Pellet Count # / lg 40 Initial Resin VOC % by weight 4.65 Initial Pellet Temperature °C 57 Vessel Pressure kPa 104 Nitrogen Temperature °C 57 Containment Time h 17 Nitrogen Flow Rate Kg / h 25 45 65 Final Resin VOC ppm 3200 2500 140 Example 4: Sensitivity Analysis over Devolatilization Containment Time In this example, a sensitivity analysis is performed on the batch removal characteristics of plastomeric pellets with a bulk density of 0.880 g / cm³, a melting index (MI or I²) of 0.50 g / 10 min, and a VICAT softening point of 52.3°C in a silo-shaped devolatilization vessel. This sensitivity analysis was conducted using a mathematical model to determine the impact of each process variable on the total removal retention time. The model comprises a mathematical description of the pellet removal process as a multi-component, multi-phase heat and mass transfer process combined with thermodynamic and hydraulic considerations. This model was validated against extensive experimental data. Table 4 shows the process variables used for this sensitivity analysis as the base case scenario. TABLE 4 Model Inputs Used for the Base Case in Sensitivity Analysis Vessel Capacity kg 200 x 10³ Vessel Top Pressure kPa 10⁹ Vessel Diameter m 4.5 Pellet Filling Rate kg / h 53.4 x 10³ Pellet Recirculation Rate kg / h 1.67 x 10³ Initial Pellet Temperature °C VICAT - 5 Initial Pellet VOC % by weight 2.26 Pellet Size # Pellets / g 40 Bed Void Fraction - 0.35 Final Pellet VOC Content ppm 150 Nitrogen Removal Temperature °C VICAT - 5 Nitrogen Flow Rate kg / h 10 x 10³ Nitrogen Purity ppm of VOC 50 The data tabulated in Table 5 briefly illustrate how each independent process variable affects the overall containment time as a dependent variable. This results, in particular, in identifying the effect of the hydrocarbon level in the recycled nitrogen. As shown in Table 5, changing the purity level of the recycled nitrogen supplied to the devolatilization vessel, from 50 ppm in the base case to 100 ppm, increased the total containment time by less than 4%. This indicates that the load on the hydrocarbon extraction unit can be reduced while still achieving effective removal within a reasonable containment time. TABLE 5 Results of Sensitivity Analysis on a Resin of Plastomer of 0.880 g / cm3 and 0.5 MI with a Melting Point VICAT softening of 52.3°C Process Variables Baseline Deviation Containment Time (h) Baseline (process conditions equal to those described in Table 3) 50.5 Pellet Size 30 pellets / g 53.8 50 pellets / g 48.3 Initial Pellet VOCs 25% increase in initial VOCs from the baseline 54.0 Nitrogen Flow Rate 12*103 kg / h 44.8 8x103 kg / h 59.8 6x103 kg / h 76.4 Pellet Recirculation Rate 3.34 x 103 kg / h 56.4 Elimination Temperature / Nitrogen VICAT - 2°C 42.8 VICAT - 10°C 68.9 Initial Pellet Temperature VICAT - 7°C 56.6 Nitrogen Purity 100 ppm VOC 52.5 Top of Vessel Pressure 130 58.7 80 39.6 60 33.0 INDUSTRIAL APPLICABILITY A process for the devolatilization of plastomers. Plastomers have a wide variety of industrial uses and are particularly suitable for preparing a sealing layer in a multi-layer flexible packaging film. It is hereby stated that, as of this date, the best method known to the applicant for putting the aforementioned invention into practice is the one that is clear from the present description of the invention.

Claims

1. A process for the production of devolatilized alpha ethylene copolymer having a density from 0.865 to 0.905 g / cc and a melt index, I2, from 0.3 to 30 g / 10 minutes, measured by ASTM D1238 at a temperature of 190°C using a loading of 2.16 kg, characterized in that it comprises: i) supplying unprocessed pellets of the ethylene-alpha olefin copolymer to a devolatilization vessel, wherein the unprocessed pellets are characterized by containing a volatile hydrocarbon; ii) supplying nitrogen gas to the devolatilization vessel; iii) discharging the devolatilized pellets from the devolatilization vessel, wherein the devolatilized pellets contain a lower level of volatile hydrocarbons than the unprocessed pellets; iv) recovering mixed waste gas comprising a mixture of nitrogen and hydrocarbon from the upper space of the devolatilization vessel; v) directing the mixed waste gas to a hydrocarbon extraction container; vi) recovering purified nitrogen from the hydrocarbon extraction container; and vii) recycling the purified nitrogen to the devolatilization vessel.

2. A process for the production of devolatilized alpha-ethylene copolymer having a density from 0.865 to 0.905 g / cc and a melt index, I2, from 0.3 to 30 g / 10 minutes, as measured by ASTM D1238 at a temperature of 190°C using a 2.16 kg feed, characterized in that it comprises: i) providing unprocessed pellets of the alpha-ethylene copolymer to the upper portion of a devolatilization vessel, wherein the unprocessed pellets are characterized by containing a volatile hydrocarbon; ii) providing an upward flow of nitrogen gas to the lower portion of the devolatilization vessel, wherein the nitrogen is provided at a temperature from 40 to 70°C; iii) unloading the devolatilized pellets from the devolatilization vessel, wherein the devolatilized pellets contain a lower level of volatile hydrocarbon residue than the unprocessed pellets;iv) recovering the mixed waste gas comprising MA / a / ZUZ 1 a mixture of nitrogen and hydrocarbon from the upper space of the devolatilization vessel; v) directing the mixed waste gas to a hydrocarbon extraction container; vi) recovering the purified nitrogen from the hydrocarbon extraction container; and vii) recycling the purified nitrogen to the lower part of the devolatilization vessel.

3. The process according to claim 1 or 2, characterized in that the nitrogen gas comprises a combination of purified nitrogen and feed nitrogen and is provided as an upward flow.

4. The process according to claim 1 or 2, characterized in that the ethylene copolymer comprises ethylene and at least one alpha olefin selected from the group consisting of 1-butene; 1-hexene; and 1-octene.

5. The process according to claim 1 or 2, characterized in that it is completed as a batch process and wherein the pellets are not fluidized during the process.

6. The process according to claim 1 or 2, characterized in that the hydrocarbon extraction container is a temperature swing adsorption container.

7. The process according to claim 1 or 2, characterized in that the hydrocarbon extraction container is a pressure swing adsorption container.

8. The process according to claim 1, 5 characterized in that nitrogen is supplied to the devolatilization vessel at a temperature from 40 to 85°C.

9. The process according to claim 1 or 2, characterized in that the devolatilized pellets 10 contain less than 150 parts per million by weight of the volatile hydrocarbon.