MXPA99000503A - Polim recovery - Google Patents

Abstract

Methods have been invented to devolatilize polymer solutions which include, in certain aspects, dissolving a viscous polymer in a solvent, forming a polymer-solvent solution, introducing the polymer-solvent solution in a thermal dryer, heating or cooling the solution polymer-solvent in the thermal dryer forming a polymer product with solvent removed and separate solvent (which can include other residues), vaporizing the solvent separated with other waste, if present, in the thermal dryer forming a vapor, remove the steam from the thermal dryer, and discharge the product polymer from the thermal dryer

Description

POLYMER RECOVERY This invention is directed to devolatilization and recovery of polymer and, in certain aspects, to the production of a polymer product with a residual level of less than one hundred parts per million (ppm), the polymer product being produced from a initial polymer solution having a residual level of up to fifty percent by weight, based on the weight of the polymer. A particular method according to this invention is directed to the devolatilization of ethylene propylene diene monomer terpolymer (EPDM). The prior art describes a wide variety of systems and methods of devolatilization and polymer recovery. Certain prior art methods have one or more disadvantages: a multi-stage process including a finishing stage; required extraction of contaminants, residual solvent and monomers; use of an immiscible fluid mixed with a polymer flowing to maintain the heat transfer coefficient, increase in conductive diffusion force, or lower partial pressure; polymer entrainment in upper vent systems, known as "snow", and polymer product flowing in vent systems, known as "vent vent"; production of polymer product with inconsistent properties, such as varying viscosity, or production of gels or degraded product polymer; and additional unit operations of process to remove the immiscible gas or liquid.

The need for a simple, efficient, effective stage method to devolatilize viscous polymers has existed for a long time. There has long been a need for such a method, which is relatively less expensive than existing methods and requires deployment of reduced capital compared to existing methods. There has long been a need for such a method, which produces a quality product with consistent properties without unacceptable viscosity variation, and without product degradation. There has long been a need for such a method, which does not require additional extraction, an additional finishing step, or use of an immiscible fluid to maintain heat transfer. The need for such a method has existed for a long time, in which the snow and the vent of the vent are significantly reduced, thereby improving the quality of the product. The present invention describes systems and methods for the devolatilization of polymer. Devolatilization is the removal of an unreacted monomer polymer product, solvent, oligomers, and volatile condensation products, collectively referred to herein as "waste." In one aspect, the present invention is directed to a method characterized by: (A) introducing a polymer-solvent solution in a thermal dryer, (B) treating the polymer-solvent solution in the thermal dryer forming a product polymer and solvent separated, the solvent separated with residues therein that are vaporized in the thermal dryer forming a vapor containing solvent and residues, (C) removing the steam from the thermal dryer, and (D) discharging the polymer product having a level of solvent of not more than 0.5 percent by weight of solvent and other residues of the thermal dryer. In another aspect, a method according to the present invention includes: transporting a viscous polymer in solution with a solvent in a treatment vessel of a thermal dryer for devolatilization; apply a reduced pressure or vacuum inside the treatment vessel; removing at least a portion of the residues contained in the viscous polymer solution by means of the vacuum inside the treatment vessel; and flowing the polymer product from the treatment vessel for further processing, such as pelletizing. In another aspect, the method includes a step of cooling or heating the viscous polymer solution in the treatment vessel to maintain the polymer at the desired temperature to achieve low residue with acceptable product quality. In one aspect, such method is free of oxygen. The methods according to this invention can be either batch or continuous, and can be used to recover any known viscous polymer. The methods according to this invention can be aqueous or anhydrous (ie, in the absence of water), and an optional volatile extraction agent can be used. The use of an immiscible heat transfer fluid is optional.

In certain embodiments, the viscous polymer solution is produced using a dissolver extruder that is fed with pelletized polymer by a volumetric feeder. The solvent is injected into the dissolver extruder under high pressure (for example 13.8 MPa) by means of a high pressure injection system. With such a system, the solvent under pressure is injected into an area filled with polymer in the dissolving extruder. In another embodiment, the viscous polymer solution is produced in one or more solution polymerization reactors, operated either in parallel or in series. One such system is described in commonly owned US Patent 3,914,342 (Mitchell). Preferably, the viscous polymer solution is transported from the reactor or reactors to the thermal dryer via single or multiple flash evaporation vessels to reduce the solvent content. A useful method for simulating this polymer recovery process is a dissolver extruder having six barrel sections through which the polymer flows. Five of the six sections of barrel are heated by a fluid medium, for example, pumping system, hot oil. In certain preferred embodiments, the first of the six barrel sections is cooled, for example to approximately 30 degrees centigrade (° C), to prevent the polymer from binding to a polymer inlet of the dissolver extruder. A cooled glycol system provides sufficient cooling. An electrical, pneumatic or hydraulic power system is used, in certain embodiments, to drive a rotary arrow in the dryer treatment vessel to facilitate drying and movement of the polymer through the container. In that aspect, the arrow is driven directly by an electric motor with a gear reducer. The arrow is conveniently sealed from the outside environment with a double mechanical seal with an inert damping fluid (such as an oil damper). In a further aspect, a discharge end of the arrow also penetrates an outer shell and is sealed with a double mechanical seal with an inert shock absorber (such as an oil damper) and is supported by one or more external supports. A vacuum system useful with methods according to the present invention has a vacuum pump sealed with oil and a condenser (such as a tube and shell heat exchanger) disposed between the pump and a vent outlet of the treatment vessel. In one aspect, dual vapor collection traps are used alternatively. Appropriate calibrators indicate vacuum levels at desired points in the system. In one embodiment, a single screw discharge device is used to transport polymer from the thermal dryer to the downstream processing equipment. Twin gear or gear pump discharge devices are also suitable. Further processing of the devolatilized polymer product flowing from the treatment vessel may include cooling, drying and packing. One method includes running the polymer product through a water bath and then pelletizing it in a pelletizing machine (such as a machine commercially available from Cumberland Strand Chopper Co.). The methods according to this invention, as shown by the data presented below, produce substantially improved and unexpected results, as compared to several methods of the prior art. In certain embodiments, the present invention describes a method for devolatilizing a polymer-solvent solution, including the method of transporting the polymer-solvent solution in a thermal dryer or forming the solution therein by introducing the polymer and solvent into the thermal dryer. , treat the polymer-solvent solution in the thermal dryer to separate the polymer product from the solvent and residues, vaporize at least a portion of the solvent (or solvent with residues therein) in the thermal dryer, thereby forming a vapor containing solvent (or solvent and other waste), removing steam from the thermal dryer, and discharging the polymer product having at most 0.5 percent total waste (including solvent) by weight of the thermal dryer. The polymer product has a solvent level that is conveniently less than 2000 ppm, preferably less than 1600 ppm, more preferably less than 1000 ppm. The polymer product also has a residual thermonomer content (such as a diene) in the polymer product of less than 100 ppm, preferably less than 50 ppm, and especially less than 10 ppm. The discharged polymer product is suitable for processing by a pelletizing machine. The method thus includes feeding the polymer product to a pelletizing machine, and producing the pelletized polymer product. The polymer has a Mooney viscosity that is conveniently greater than 20, preferably greater than 50, more preferably 70 or greater and can generally be as high as 250, preferably as high as 120.; or a melt index (12) (ASTM D-1238 Condition 190 / 2.16) of less than 1 g / 10 minutes to as low as 0.001 g / 10 minutes. The polymer is conveniently selected from the group consisting of ethylene / propylene / diene terpolymers (EPDM), heterogeneous polyethylene, homogeneous polyethylene, linear polyethylene, low density polyethylene, polypropylene, polyurethane, ethylene propylene rubbers, and polystyrene. The residence time of the polymer-solvent solution in the thermal dryer is conveniently less than 50 minutes, preferably less than 30 minutes and especially 15 minutes or less; the residues initially present in the polymer-solvent solution are normally at a level of between 5 percent and 80 percent by weight, and are reduced by this method to a level in the polymer product of less than 0.5 percent by weight; preferably less than 0.2 percent by weight. The residues initially present in the polymer-solvent solution at a level of 10 percent to 50 percent by weight are preferably reduced to a level of less than 1000 ppm, or when the residues are initially present at a level of 2-25 percent. they are reduced to a level of 500 ppm or less, in the polymer product. The solvent is usually a Cs or heavier hydrocarbon, usually up to a C14 hydrocarbon, or a mixture of such hydrocarbons.

The method can also be performed without the addition of oxygen, water or both. The method includes a variation wherein the polymer and solvent are fed continuously to the thermal dryer and the polymer product is continuously produced by and transported from the thermal dryer. The method can be a batch method. The polymer product discharged from the thermal dryer is conveniently received by a discharge apparatus, which transports the polymer product from the thermal dryer. The discharge apparatus is conveniently a discharge system with a housing, a single screw conveyor rotatably mounted therein, and a direct driver motor for rotating the single screw conveyor. The single screw conveyor is preferably mounted on supports and sealed at its conductive end with double mechanical seals to isolate the housing components from external influences, such as atmospheric gases, particularly oxygen. The housing has an inlet and an outlet, and the system conveniently runs under vacuum, for example 10-200 mmHg (1 .3-26.7 kPa), preferably about 25 mmHg (3.3 kPa). The method also includes heating or cooling the poiimer-solvent solution in the thermal dryer, using dryer temperatures maintained between 50 ° C and 290 ° C, preferably between 125 ° C and 290 ° C, more preferably between 150 ° C and 220 ° C. The method can also remove residual steam by a vacuum system that is in fluid communication with the thermal dryer. The method includes since then condensing and collecting solvent from the steam removed from the vacuum system. The method further comprises injecting nitrogen into the thermal dryer ("nitrogen sweep"). The polymer product conveniently has a viscosity that is substantially the same as that of the polymer used to form the polymer-solvent solution. Therefore, it is an object of at least certain preferred embodiments of the present invention to provide: New, useful, unique, efficient, non-obvious methods and systems for devolatilizing polymers; Such methods, which reduce the residues in a polymer from an initial content of 5 percent to 80 percent by weight to less than 0.5 percent, especially less than 0.2 percent by weight; and such methods, which preferably reduce residues in a polymer from an initial content of 10 percent to 50 percent by weight to less than 1000 ppm; and such methods, which most preferably reduce residues in a polymer from an initial solvent content of 5-25 percent by weight to less than 500 ppm. Such methods, which achieve an acceptable polymer residue level in a single stage device; Such methods, which do not require extraction or immiscible fluids to maintain the speed of diffusion and heat transfer; Such methods, in which the snowfall and the venting of the vent are reduced and, preferably, substantially reduced; and Such methods in which the quality of the polymer product is consistent, and such method in which a variety of variant molecular weight solvents can be used (e.g., isobutane, cyclohexane, or ISOPARM® E (a trademark of and made by Exxon Chemical, which is usually a mixture of C8-C10 hydrocarbons.) Certain embodiments of this invention are not limited to any particular individual feature described herein, but include combinations of them distinguished from the prior art in their structures and functions. characteristics of the invention have been amply described, so that the detailed descriptions that follow can be better understood, and in order that the contributions of this invention are better appreciated There are, of course, additional aspects of the invention described below and which may be included in the subject matter of the claims of this invention. s experts in the technique, who have the benefit of this invention, its teachings and suggestions, will appreciate that the conceptions of this invention can be used as a creative basis to design other structures, methods and systems for realizing and practicing the present invention. The claims of this invention to be read include any legally equivalent device or method, which do not depart from the spirit and scope of the present invention. The present invention recognizes and addresses the aforementioned problems and long-felt needs, and provides a solution to those problems and a satisfactory fulfillment of those needs in their various possible and equivalent modalities thereof. For an expert in this technique, who has the benefit of the embodiments, teachings, descriptions and suggestions of this invention, other purposes and advantages will be appreciated from the following description of the preferred embodiments, given for the purpose of description, when They take in conjunction with the accompanying drawings. The detail in these descriptions is not intended to obstruct this patent objective of claiming this invention no matter how others may subsequently disguise it by way of variations in form or additions of further improvements. Additionally, the term "solution," as used herein, may include a paste. A more particular description of the embodiments of the invention briefly summarized above, may be had by reference to the modalities, which are shown in the drawings, which form a part of this specification. These drawings illustrate certain preferred embodiments and are not to be used to inappropriately limit the scope of the invention, which may have other equally effective or legally equivalent modalities. Fig. 1 is a schematic view of a system useful for studying the methods according to the present invention without the need to use a polymer reaction process as a feed stream. Fig. 2 is a partial schematic cross-sectional view of the dissolver extruder of the system of Fig. 1. Fig. 3 is a schematic view of part of the system of Fig. 1. Fig. 4 is a schematic side view of the thermal dryer of the system of Fig. 1.

Fig. 5A is a schematic view of a thermal dryer and associated apparatus useful in methods according to the present invention. Fig. 5B is a side view of a conveyor shown in Fig. 5A. Fig. 6 is a schematic view of a second system useful in methods according to the present invention. Figs. 7-16 present data for methods according to the present invention. Referring now to Fig. 1, a system 10 according to the present invention has a volumetric feeder 12 for feeding pelletized polymer to an inlet funnel 15 of a dissolving extruder. 14; a thermal dryer 50; a solvent tank 16; and a vacuum system 66. The solvent is pumped from solvent tank 16 via lines 18 and 22 via a pump 20 to a pump 30. Pump 30 pumps the solvent through line 24 to an injector system 26. The injector system 26 injects the solvent into a third zone or barrel 25 of a dissolving extruder 14. As shown in Figs. 2 and 3, the arrow 35 of the dissolver extruder 14 is rotated by a conductive system 31 which includes an electric motor 41, a conductive strip 43, a high torque slip clutch 45, a driving pulley 47 and a gear system 49 that is interconnected with the arrow 35. A valve 51 controls the flow in line 19. A valve 53 controls the flow in line 22. A valve 55 controls the flow in line 24. A gauge 57 indicates the pressure in line 24 An adjustable release valve 59 provides the release protection for the pump 30 and is in communication with the valve 55 via the lines 63 and 65. As shown in Fig. 3, the valve 67 controls the flow of the solution of polymer-solvent in the sample line 69. The hot oil from a hot oil source 81 flows via line 83 to the barrel sections 23, 25, 27, 28 and 29 of the dissolver 14 extruder. The hot oil comes out of these sections I saw to lines 85, each with its own control valve 87, and outlet line 89. The dissolver extruder 14 produces a solution flowing from a viscous solvent polymer, which is fed via line 32 to thermal dryer 50 ( Fig 1). The valve 34 controls the delivery of the polymer solution to the dryer 50. The thermal dryer 50 (see Figs 1 and 4) has a shell 52 and an apparatus thereon for heating the flowing solution of polymer and solvent and for moving it from the entrance 36 to the exit 38. Normally, a rotating hollow arrow 56 with mixing and transport elements 54 and 58 working in combination with counter hooks 59 inside the shell 52 kneads and moves the polymer-solvent solution inside. of the shell 52. The shell, rotary arrow, counter hooks, movement elements, and mixing elements can all serve as the heat transfer members for heating or cooling the polymer-solvent solution. The heat transfer means (such as steam or hot oil) can be pumped through a channel or channels in each of these members. As shown in Fig. 4, a hot oil system 90 is used in a mode for flowing the heat transfer medium through the arrow 56 and related members. A conductor system 60 is interconnected with and the arrow 56 rotates (Figs 1 and 4). A source of hydraulic fluid under pressure (not shown) provides the conductive fluid for driving the system 60. Certain debris released from the polymer-solvent solution (e.g., vaporized volatiles, vaporized solvent, unreacted monomers, oligomers) rises within of the container 52 and flowing through an upper outlet 62. In one embodiment, these residues flow in a vent dome 64 (Figs 1 and 4). A vacuum system 66 evacuates the debris from the shell 52 via lines 71, 72, 73, 74 and 75. The debris is condensed in a condenser 68 and collected in a trap 76 or trap 77. The remaining waste is removed via line 75. The polymer product leaves the shell 52 of the thermal dryer 50 and moves through the cooling means 84 via line 86 in a cutting apparatus 82 to the packing equipment (not shown) (Fig. 1). Fig. 5A illustrates one embodiment of a thermal dryer 100 (like the dryer 50) and associates apparatuses and connections. The dryer 100 has a hollow housing 102 with an arrow 104 extending lengthwise to agitate and move a polymer-solvent solution flowing into the housing 102 through an inlet 1 16 (such as the inlet 36)., Fig. 1) to the housing 102. The arrow 104 is rotated by a direct driver motor 106 interconnected with a gear case 108. The external push supports 110 and external radial supports 1 12 facilitate the rotation of the arrow 104. No there is direct exposure of the supports with the thermal support 110 or the radial supports 1 12 to a flowing heating medium or to the polymer flowing at the conducting end (left end of Fig. 5A). Preferably, the interior of the system is sealed and under high vacuum (normally to withstand a pressure operating range of 2.4 kPa at a negative pressure of 750 mmHg (100 kPa) of absolute vacuum). At each housing end 102, an arrow-housing interface area with double mechanical seals 1 14 is sealed. The polymer product flows through an outlet 1 18 via the conduit 1 19 to a discharge device 130 (as the apparatus of the invention). discharge 39, Fig. 4), which moves the polymer product from the thermal dryer 100 for further processing. The coupling 120 allows the injection of heat transfer means, such as hot oil, into the rotating main shaft 104 of the thermal dryer 100. A channel in the arrow 104 extends only to the inlet 1 16 so that the heating medium it does not heat the apparatus beyond the inlet 116. As with the system of Fig. 1, it can be used in the vacuum system with thermal dryer 100 to remove debris. Thermal dryers are commercially available from Krauss-Maffei Verfahrenstechnik GmbH and List AG. A simple screw discharge device 130 (Fig. 5A), as shown in Fig. 5B, is used to transport the polymer product from the thermal dryer 100 to the downstream equipment. The simple screw device 130 comprises a housing 134, a direct driver motor 131, brackets 132 (usually including a back-push bracket and a roller stand) to support a simple screw 135 and to absorb the thrust of the screw, a seal double mechanical 133 to isolate components disposed within the housing 134 from atmospheric pollution and to prevent the intrusion of atmospheric oxygen. The polymer product entering the device 130 via the inlet 136, (connected to the outlet 1 18 of Figure 5a via the conduit 119), is transported by the screw 135 to the discharge 137, and flows through the flange of discharge 138. The advantages of using the single screw device 130 or similar device, include less mechanical conductive complexity; true screw integrity that provides good sealing capability (ie, less leakage and ability to use a double mechanical seal); less cutting that allows better polymer product quality (less cutting-induced degradation); more efficient pumping of the polymer from the inlet to the outlet (less loss of transmission force); and better temperature control for downstream handling (such as pelletizing).

Polymers useful in this invention include, but are not limited to, EPDM, heterogeneous polyethylene, for example, polymerized LLDPE as described in US Patent 4,076,698.

(Andersen et al); homogeneous polyethylene, as described in U.S. Patent 3,645,992 (Elston); substantially linear polyethylene as described in US Patent 5,272,236 or 5,278,272 (Lai et al.); low density polyethylene (LDPE), and other thermoplastics, such as polypropylene, including those thermoplastics made in high pressure polymerization, paste or solution processes. Other polymers and copolymers include SIS and SBS type polymers, PELLATHANE R polyurethane (a trademark of The Dow Chemical Company), ethylene-polypropylene (EPR s) gums, and polystyrene. The novel methods described and claimed herein are surprisingly useful for high viscosity, high molecular weight elastomeric polymers. Fig. 6 shows a system 200 useful in a continuous process according to the present invention. The polymer solution enters a devolatilization vessel 202 via line 210 and the solvent evaporates instantaneously through an outlet 220. The polymer solution is deposited towards a gear pump inlet 208 and flows therefrom to a thermal dryer system 206 (such as that of Figs 1 -5B) and additional solvent is removed as described above. One or more additional devolatilization reactors can be used between the reactor 202 and the thermal dryer 206. In one aspect, the polymer-solvent solution is 50 percent to 70 percent by weight of polymer and, therefore, is 50 percent to 30 percent in weight of waste.

EXAMPLES In certain methods according to the present invention, pellets of ethylene propylene diene monomer ("EPDM") are fed as follows to the dissolver extruder. The NordelMR material contains lrganoxMR 1076 (an obstructed phenolic antioxidant made by Ciba Geigy) in varying concentrations ranging between 100 ppm and 200 ppm. * 0.3 cm pellet size Nordel ™ is a registered trademark of DuPont Dow Elastomers L.L.C.

The dissolver extruder is an extruder Werner and Pfleiderer Co. Model ZSK-30, co-rotating, completely interengranado, double screw, 30 millimeters (mm) with a length-to-diameter ratio (L / D) of 21: 1 in the extruder configuration with the screws being just over 20: 1 . The extruder is equipped with a high pressure injector from Werner and Pfleiderer Co. Located in the third section of barrel downstream and is powered by an AC motor of 3600 revolutions per minute, 15 horsepower, class one, division two , controlled by a digital speed controller. The extruder is fed little by little with resin by a double-bore volumetric feeder K-Tron, (with one of the two holes removed). The feeder tank in the feeder is loaded by hand and has a capacity of 3.7-7.5 kg). With one of the screws removed, the feeder has a feed speed of 0-45 kg / h. In the examples described below, the solvent used is solvent lsopar RE (made by Exxon Chemical) and in one aspect the solvent lsoparMR E was mixed with n-nonane, a hydrocarbon of C9, at a level of two percent by weight (for simulate the residual diene since it has a higher boiling point than the solvent lsoparMR E). The thermal dryer used to process the three types of EPDM has a horizontal shell and a rotary arrow as shown in Fig. 1. The heat transfer medium is pumped through the armor, arrow and disc elements. The discs have mixing bars at their tips to clear the inner surfaces of the shell from the product accumulation. Stationary counter hooks (see hooks 59, Fig. 4) are secured to the interior of the shell and have the shape to interact with the parts rotating, producing a mixing and kneading action. The discs are placed on the arrow at an angle for forward momentum proportion and consistent product discharge. The dryer has a total volume of approximately 17 liters. A dryer discharge apparatus 39 is a double screw extruder (having a length-to-diameter ratio of 7) energized by a hydraulic conductor. The discharge section of the shell is attached to the middle section to give the double discharge screw a horizontal position. As the polymer is pushed forward by the disks in the arrow, this is picked up by the double screw and extruded through the holes of the die located in an end flange. Heat is supplied to the dryer through an external hot oil system of 40 watts. The hot oil system has its own pump and temperature controller providing hot oil to the thermal dryer at a desired temperature setting point (for example 150-220 ° C). The hot oil is piped through a rotary union to the arrow (a hollow tube) and disc elements. The thermal dryer is made of three sections that are bolted together. Each of the three sections is chamfered and heat is provided by hot oil on the chamfered side of each of these sections. The vent dome (attached to the top of the unit by a flange connection) is grooved and hot oil flows through these channels to keep the dome warm. The hydraulic drive system comprises two separate hydraulic units. One unit energizes the main conductor of the dryer, which rotates the arrow and the other unit energizes the small double screw conductor. Both units have a reservoir of oil enclosed in a rectangular shape with high pressure oil pumps powered by alternating current motors mounted in the upper parts of the reserves. The maximum pressure of the units is adjustable with an internal release valve. The hydraulic oil is discharged from the pump through a manual adjustable flow valve. The high pressure hydraulic lines are linked to the power conductors and units using hydraulic quick disconnect lines. The hydraulic lines return from the conductors again to the oil reserves. The pressure gauges in the hydraulic conductive units are used to estimate the torque in the double screw extruder and agitator. By adjusting the position of the discharge valve in a unit, the flow velocity and thus the speed of the conductor to which it is connected, are adjustable. The maximum pressures of the stirring shaft are 15 MPa.

A vacuum pump sealed with oil is used for the vacuum system. A tube and shell heat exchanger is used as a condenser between the vent dome and the vacuum system, with glycol cooled on the shell side at 1 -5 ° C. The condensed vapors are collected in one of two condensate traps (38 I stainless steel containers) placed on weight scales to measure speed. When one trap is full, the other trap is opened with valve while the first trap is emptied into a solvent drum when filling the trap with nitrogen. The vacuum level in the dryer unit and in the vacuum lines is measured via a connection in the valve with a mercury-filled manometer. The traps are equipped with gauges to measure the level of vacuum. Initially, a flange with three holes approximately 0.3 cm in diameter is used with a hole connected as a die for the double screw in the dryer. Subsequently, the hole is enlarged to 0.5 cm and the other two are connected. The melt is extruded in a 3.7 m long water bath, and then it is pelleted with a Cumberland Strand Chopper.

BATCH METHOD In a batch method according to the present invention, the conductive system, the vacuum system and the heating system are as described above. The dryer is also used, but is shortened by approximately fifty percent in length (only one section is used) and the discharge extruder is replaced with a terminal plate.

The samples are prepared for this test by placing approximately 1 kg of lsoparMR E solvent in a bag together with approximately 1 kg of polymer. The polymer then absorbs the solvent and equilibrates. Samples vary from a gelatinous consistency of 25 Mooney viscosity to a semi-solid material of about 70 Mooney viscosity. The dryer is loaded with the contents of such bags and the material is processed as described above. These data and batch method results are shown in Table I. The data show substantially improved, unexpected results. Some material is devolatilized from a solvent content of 50 percent by weight to less than 0.2 percent by weight. In Table I, products No. 1470 and 2522 are Nordel ™ materials; "Oil temperature C" is the temperature of the heat transfer medium in the thermal dryer; "RPM of the agitator" is the speed of the arrow in the thermal dryer; "Vacuum (mm Hg (kPa))" is the level of vacuum in the system; "Lot time" is the residence time in minutes) in the thermal dryer; "N2 sweep" is the amount of nitrogen injected into the thermal dryer in standard cubic meters per hour); "Temp. ° C of Prod." is the temperature of the exit polymer in degrees Celsius; "Mooney viscosity" is the viscosity of the exit polymer; and "volatile ppm" is the level of volatiles (residues) of the exit polymer.

CONTINUOUS METHOD Table II presents the running conditions of the dissolving extruder for 24 samples in a continuous method according to the present invention. Because the screw feed volume area in the feed throat of the 30 mm twin screw extruder, only the 0.3 cm pellet EPDM samples were used. At the start of the dissolver extruder, low feed rates were used to the low Mooney viscosity EPDM extruder (7.5 kg / h) of NordelMR 2722), to form an initial melt seal within the extruder before starting any solvent feed to the extruder. The dissolver extruder is run at low speeds without solvent until the polymer flow is established in the thermal dryer. High extruder discharge pressures (eg greater than 7 MPa) are necessary to clean the line (1.3 cm internal diameter) between the discharge of the dissolver extruder and the dryer. The solvent is injected into the barrel of zone three (barrel section 25, Fig. 1), through a high pressure injector with a back pressure of 4.1 -5.5 MPa. The solvent-to-EPDM percentage by weight is kept low initially (10-20 percent). When the solvent is being fed to the extruder, a detector is used in the feed throat to check that the solvent does not evaporate instantaneously back to the feed tank. After establishing the solvent to the extrusion without problems, the percentage ratio of solvent to EPDM is increased to a level of 50 weight percent over a three or four stage process. As the percentage ratio of solvent EPDM members, the total motor torque decreases, allowing much higher throughput speeds than dry EPDM materials (that is, they do not contain solvent). The desired speeds are achieved by increasing polymer addition rates first and then increasing the flow velocities of the solvent. The maximum solvent addition is limited to 9.3 - 10 kg / h due to limitations of the pump (pump 30, Fig. 1). Samples 1-8 and 22-24 are NordelMR 5892 material. Samples 9-15 are NordelMR 2722 material. Samples 16-21 are NordelMR 3681 material. In Table II, "Mooney polymer" is the viscosity of the input polymer; "Polymer feed" is the input polymer feed speed to the thermal dryer in kg / h; "Solvent feed" is the rate of solvent feed to the thermal dryer in kg / h; "Residence time in min" is the residence time (calculated average) in minutes of the polymer-solvent solution in the thermal dryer; "Torque pressure" is the driver motor torque measured in MPa; other column headings have the same meaning as in Table I. The temperature of the 50 percent EPDM stream is 180 to 220 ° C. To control the discharge temperature of the dissolver extruder to around 200 ° C, the screw speed is adjusted up or down within a limited range. The maximum screw speed of the dissolving extruder is 600 revolutions per minute, while the lower limit is set by the conductive torque and / or high percentage filling of the screws. Partially closing the valve in the polymer line going to the thermal dryer (that is, increasing the discharge pressure of the extruder) also increases the discharge temperature. The screw speed, discharge pressure, and control of extruder barrel zone temperatures (barrel zones 23, 25, 27, 28, 29), are all used, so that the polymer supply to the thermal dryer remains in the target temperature range. The dissolving extruder runs at stable amp loads and stable discharge pressures, all indicative of good solvent incorporation. Samples of the solution are taken periodically manually via the discharge line 69 (Fig. 3) and inspected physically to ensure that a uniform solution is being generated. Table II presents the running conditions of the 24 samples. The dryer is preheated to 150 ° C with the hot oil system before being fed with a polymer stream. When the polymer stream is introduced to the unit, the hydraulic arrow conductor is started and the speed of the arrow is adjusted to the desired number of revolutions per minute. When the solvent is added to the polymer stream, the vacuum is conducted by valve to the thermal dryer and adjusted to desired vacuum levels. Using view glasses on top of the dryer, the polymer level in the dryer is monitored. When the desired level is reached, the double screw hydraulic drive unit is started. By adjusting the speed of the double screw, the amount of polymer being discharged from the unit can be matched to the amount of polymer entering, and in this way, the level of the thermal dryer remains relatively constant.

The consistency of the product is characterized by Mooney viscosities. Fig. 7 shows the Mooney viscosity for the 24 samples on the left vertical axis and the sample number on the horizontal axis. The three solid horizontal lines represent the initial Mooney viscosities for the EPDM materials. In all cases, little or no Mooney fall is experienced unexpectedly. Polymer residence times in the dryer are as long as 41 minutes, with discharge melt temperatures as high as 287 ° C. Arrow speeds in the dryer are evaluated as high as 70 revolutions per minute, and torque loads as high as 13.9 MPa (as measured in the hydraulic conductive unit) are observed. None of these conditions produces any significant polymer degradation. NordelM EPDM products contain standard anti-oxidizing packages (eg, 1500 ppm lrganox R 1076 (a clogged phenolic antioxidant made by Ciba-Geigy Corporation). The devolatilization performance is measured by gas chromatography in the upper space of the final products This is accomplished by sampling the top space of a sealed sample vial containing the final product of the thermal dryer within a few seconds (ie, within less than 15 seconds) of discharge For each sample, a known quantity of product ( approximately 0.5 grams) is placed in a sealed septum bottle.The sample bottle is placed in an automated top analyzer connected to a gas chromatograph.The contents of the sample bottle are then analyzed using a superior space extraction procedure quantitative multiple The concentration of the residual solvent in the sample bottle is determined from the analy quantitative isis of known solvent standards analyzed under identical multiple upper space extraction conditions. Fig. 8 shows the residual levels (vertical axis indicates parts per million (ppm) of solvent lsoparMR E) for the 24 samples (the sample number is indicated on the horizontal axis). Only one sample is above 2,000 ppm and was run with a vacuum level of 200 mmHG (27 kPa). Within the ranges of temperature, vacuum level, residence time and other variables, 19 samples unexpectedly dropped below 1, 000 ppm residual solvent. Normally the devolatilization of EPDM materials with prior art extrusion equipment results in vent clogging due to snowing. EPDM rubbers with higher viscosities usually have a bigger problem. In the breather dome of the dryer, only a small amount of snow occurs in the lower portion or section of the dome. Accumulation over several hours of run time is less. This represents an unexpected result of the present invention. Fig. 9 shows the relationship of vacuum level, residence time and devolatilized EPDM residue levels (NordelMR 2722). The vacuum level in absolute mmHg (with value in kPa being indicated in parentheses) is exposed on the left vertical axis, and is indicated as the first bar in each pair of bars for each example. The residence time in minutes is also displayed on the left vertical axis (values that are not enclosed in parentheses, for example, 50, 45, etc.), and is indicated as the second bar in each pair of bars for each sample . The solvent residues in parts per million are exposed on the right vertical axis, and are indicated by the small graphically connected boxes. The number of the sample is indicated on the horizontal axis. For Fig. 9, the polymer contains 25 to 50 percent solvent entering the dryer, and the dryer is filled to 40 percent. As shown in Fig. 9, as the vacuum level increases or residence time decreases, the level of residual solvent in the polymer increases. A sample, the sample number 15, is not included in the data that supports Fig. 9 because its percentage level of start solvent in EPDM is low (10 percent). Figs. 10 and 11 also show the same relationship as fig. 9 (with the axis and the bars being defined as described above with respect to Fig. 9), but with the other EPDM materials (NordeI 3681 and NordelMR 5892). Also, for Fig. 10, the polymer contains from 40 to 50 percent solvent upon entering the dryer and the dryer is filled to 25 to 40 percent, while for Fig. 1 1, the polymer contains from 40 to 50 percent of solvent and the dryer is filled at 40 to 50 percent. The same trends can be seen for these two EPDMs as for that of Fig. 9. In Fig. 11, a sample is left out again (sample number 7) due to a low level of starting solvent (12 percent). Table II I presents information with respect to certain examples referenced in Figs. 9, 10 and 1 1. Certain variables are varied for these samples, including how to fill the thermal dryer is ("Percentage of filling"); if nitrogen is present and, if so, how much, ("N2 m3 / h"); rotational speed of the thermal dryer arrow ("RPM"); the amount of material being fed to the thermal dryer, more solvent polymer in kg / h ("kg / h of total power"); the temperature of the heat transfer medium as it is fed to the thermal dryer, 150 ° C. P any indication that it is not used ("Oil Temp (° C)"); and the amount of solvent as a percentage by weight of the total thermal dryer feed ("percentage of solvent"). Samples 7 and 15 in Table il have starting solvent levels in the range of 10 percent by weight. The two samples are run under different conditions, but the final devolatilized EPDM product unexpectedly has residue levels of less than 100 ppm. Two thirds of the samples are run with a nitrogen sweep of the dryer at a level of 0.06 to 0.14 m3 / h. The rest of the samples are run without nitrogen. Table II presents three pairs of samples, one from each of the three different EPDM materials, with and without nitrogen scavenging. These sample pairs are run under the same conditions except for nitrogen. The data indicate lower solvent residue levels for NordelMR 3681 and NordeIMR 5892 with nitrogen. The NordeIMR 2722 samples show statistically the same level of residues. Some of the samples are collected after adding approximately 2 percent by weight of n-nonane to the solvent lsopar R E.

The samples are tested for n-nonane residues and the data are presented in Fig. 12. (The right vertical axis of Fig. 12 shows the percentage by weight of n-nonane in the total residues). N-nonane is present in the total residues in a range of 3-6.5 percent by weight). Three different temperature profiles are used for the samples described above. First, the hot oil system runs at 200 ° C and the chapped side of the shell in the three sections of the dryer and the vent dome are valve driven. The hot oil temperatures of the hot oil system have an average 5 ° C change (inlet to outlet). Polymer temperatures vary from 21 1 ° C-233 ° C in the second section of the dryer. The second condition runs the hot oil system at 150 ° C with the chapped side of the shell in the three dryer sections and the valve-driven vent dome. The hot oil temperatures inlet and outlet of the hot oil system have a change of 3 ° C. Polymer temperatures vary from 167-187 ° C at the same point. The third condition runs the hot oil system at 150 ° C with the valve-driven vent dome and all three sections of the unit are driven by valve out after the dryer is running. Polymer temperatures vary from 1 15-205 ° C. Fig. 13 presents data for the three different materials of NordelMR EpDM run at the same level of dryer filling (40 percent), rotary speed of the dryer shaft (50 rpm), and approximately the same residence time of the dryer (26 minutes) Both the temperature of the EPDM materials in the dryer and the peak recorded hydraulic pressure required to rotate the shaft at 50 RPM's are shown. The vertical axis shows the measured torque MPa. The vertical axis also shows the polymer temperature of the dryer in CC (the value on the vertical axis, which is not in parentheses, this is 250, 200, 150, etc.). These data, unexpectedly, show no significant difference in torque requirements between the EPDM materials of 27 Mooney, 50 Mooney and 65 Mooney. One possible reason for the similarity in torque requirements for the three different EPDM materials is a change in the condition of the polymer melt at varying temperatures (from a continuous melt to a discontinuous melt, that is, crumbs). Average temperatures are: material of 27 Mooney viscosity = 180 ° C, material of 50 Mooney viscosity = 190 ° C, and material of 65 Mooney viscosity = 215 ° C. If these temperatures are reached through a mechanical means, there would have been higher torque requirements for the larger Mooney EPDM materials. The data regarding thermal dryer run conditions, presented in Fig. 14-16, shows sample differences and torque requirement similarities. In each of Fig. 14-16, the vertical axis shows the torque requirement in MPa. In each of Fig. 14-16, the vertical axis also shows the disc temperature in ° C (the value on the vertical axis, which is not in parentheses, this is 240, 220, etc.).

In conclusion, therefore, it is seen that the present invention and the embodiments described herein and those covered by the appended claims are well adapted to accomplish the objectives and obtain the stated purposes. Certain changes can be made in the matter in question without departing from the spirit and scope of this invention. It is considered that changes within the scope of this invention are possible and it is further intended that each element or step declared in any of the following claims be understood as referring to all equivalent elements or steps.

Two separate trial results reported here; ** CND = could not be determined Table II Table IV * Total residues in the diet were 650-680 grams Table V

Claims (20)

1. CLAIMS 1 . A method for devolatilizing a polymer-solvent solution, characterized by an iteration of the following sequential steps: (A) introducing a polymer-solvent solution having a solvent content plus residues of less than 80 percent by weight in a thermal dryer , (B) treat the polymer-solvent solution in the thermal dryer to form the polymer product and separate solvent, the solvent separated with residues therein vaporizing in the thermal dryer to form a vapor containing solvent and residues, (C) ) removing the vapor containing solvent and residues from the thermal dryer, and (D) discharging the polymer product from the thermal dryer that has no more than 0.5 percent by weight of solvent and residues.
2. 2. The method of claim 1, wherein the polymer-solvent solution is fed continuously to the thermal dryer and the polymer product is continuously produced by and transported from the thermal dryer.
3. The method of claim 1, wherein the product polymer discharged from the thermal dryer is received by a discharge apparatus, which transports the polymer product from the thermal dryer, wherein the discharge device system is characterized by : a single or double screw conveyor rotatably mounted in a housing, the housing having an interior towards which the polymer product flows through a housing inlet, a direct conductor motor at a conductive end of the housing connected to the screw conveyor single or double to rotate it, dual mechanical seals at the conductive end of the housing to seal an interfacial area of the single or double screw conveyor and housing, supports at the conductive end to facilitate the rotation of the single or double screw conveyor, and a outlet for the polymer product to flow from the housing.
4. The method of any of claims 1 - 3 further comprising at least one of the following: heating the polymer-solvent solution in the thermal dryer at a temperature from 50 ° C to 290 ° C, stirring the polymer solution solvent in the thermal dryer, or inject an inert extraction agent in the thermal dryer to facilitate the separation of waste.
5. The method of any of the preceding claims further characterized by: (E) feeding an initial polymer-solvent solution with a residue level of 70 percent by weight or greater to a devolatilization reactor, (F) devolatilizing the initial solution polymer-solvent in the devolatilization reactor producing a feed polymer with a residue level of 30 percent to 50 percent by weight, and (G) feed the polymer feed solution-solve the thermal dryer to produce the polymer solution -solvent.
6. The method of any of the preceding claims, wherein the vapor is removed by a vacuum system in fluid communication with the thermal dryer.
7. The method of claim 6, wherein a vacuum from 10 mmHg to 200 mmHg (1 .3 to 27 kPa) is maintained within the thermal dryer by the vacuum system.
8. The method of any of the preceding claims further characterized by: (E) condensing and collecting solvent from the steam removed by the vacuum system.
9. The method of any of the preceding claims, wherein the product polymer is suitable for processing by a pelletizing machine and the method is further characterized by: (E) feeding the product polymer to a pelletizing machine, and ( F) produce a polymer of pelleted product with the peying machine.
10. The method of any of the preceding claims, wherein the level of solvent in the polymer product is less than 2000 parts per million. eleven .
11. The method of claim 1, wherein the polymer is selected from the group consisting of EPDM, heterogeneous polyethylene, homogeneous polyethylene, linear polyethylene, low density polyethylene, polypropylene, ethylene propylene rubber, and polystyrene.
12. The method of any of the preceding claims, wherein the polymer is a terpolymer of ethylene, an alpha-olefin, and a diene, and wherein the level of residual diene in the polymer product is less than 100 ppm.
13. The method of any of the preceding claims, wherein the polymer has a Mooney viscosity greater than 20.
14. The method of any of the preceding claims, wherein the polymer has a melt index of less than 1 g / 10. minutes 15.
15. The method of any one of the preceding claims, wherein the polymer-solvent solution has a residence time in the thermal dryer of less than 50 minutes.
16. The method of claim 1, wherein the residues are initially present in the polymer-solvent solution at a level of between 5 percent and 80 percent by weight, and where the level of residues in the polymer product is lower that 0.2 percent by weight.
17. 17. The method of claim 1, wherein the method is performed in the absence of at least one of oxygen or water.
18. 18. The method of any of the preceding claims, wherein the devolatilization of the polymer-solvent solution does not cause any significant polymer degradation.
19. 19. A method for devolatilizing a polymer having a Mooney viscosity greater than 50, the method being characterized by: (A) introducing a polymer-solvent solution in a thermal dryer, (B) treating the polymer-solvent solution in the dryer thermally forming a separate polymer and solvent product, with the product polymer having at most 0.5 percent by weight of solvent, and other residues, the solvent separated with residues therein vaporizing in the thermal dryer, forming a vapor containing solvent and residues , where the polymer-solvent solution has a residence time of less than 50 minutes in said dryer, (C) removing the steam from the thermal dryer using a vacuum in fluid communication with said dryer from 10 mmHg to 200 mmHg (1.3 a 27 kPa), and (D) discharge polymer product with solvent removed from the thermal dryer.
20. 20. A discharge system for use with a thermal dryer for drying a polymer product comprising: a single or double screw conveyor rotatably mounted in a housing, the housing having an interior toward which the product polymer flows through the housing inlet, a direct driver motor at a conducting end of the housing connected to the single or double screw conveyor to rotate it, dual mechanical seals at the conductive end of the housing to seal an interfacial area of the single or double screw conveyor and the housing, supports at the conductive end to facilitate the rotation of the single or double screw conveyor, and an outlet for the product polymer to flow from the housing.