MXPA06004683A - Separation of polymer particles and vaporized diluent in a cyclone - Google Patents

Abstract

An olefin polymerization process wherein monomer, diluent and catalyst are circulated in a continuous loop reactor and product slurry is withdrawn and passed through a heated conduit to a cyclone. The cyclone allows better separation of vaporized diluent. In a preferred embodiment, the slurry is heated in a flashline heater so that a high percentage of the withdrawn diluent is vaporized. The vaporized diluent and concentrated intermediate product are passed to a cyclone where a majority of the vaporized diluent is separated and thereafter condensed by heat exchange, without compression, and recycled to the reactor. Also an apparatus for separating vaporized diluent and polymer particles using a cyclone.

Description

SEPARATION OF POLYMERIC PARTICLES AND DILUZENTE VAPORIZADO IN A CYCLONE Field of the Invention This invention relates to the polymerization of olefin monomers in a liquid medium Background of the Invention Addition polymerizations can be carried out in a liquid which is a solvent for the resulting polymer. When high density (linear) ethylene polymers became commercially available in 1950, this was the method used. It was soon discovered that a more efficient way to produce such polymers was to carry out the polymerization under suspension conditions. More specifically, the polymerization technique of choice, polymerization was made by continuous suspension in a pipe loop reactor with the product being taken through settling columns, which operate at the beginning of a batch to recover the product. This technique has enjoyed international successes with millions of pounds (kilograms) of ethylene polymers thus produced annually. With this success has come the desirability, under certain circumstances, of building a smaller number of large reactors opposed to a larger number of small reactors for a given plant capacity. The product can be taken continuously as well. However, the product is taken, the diluent is separated from the solid polymer particles, so that the solid polymer particles can be recovered. Various separation arrangements and / or used to separate the diluent have been proposed. In general, it is desirable to separate the diluent in such a way that it can be easily and economically recycled to the loop reactor.

SUMMARY OF THE INVENTION In accordance with one aspect of this invention, a process for producing solid polymer particles is provided. The process includes polymerizing, in a loop reaction zone, at least one monomer to produce a fluid suspension comprising solid polymer particles in a liquid medium (e.g., a liquid diluent). A portion of the suspension is withdrawn as an intermediate product of the process. The withdrawal may be in a batch form, such as using sedimentation columns, or it may be continuous, such as using an elongated hollow annex. The removed portion (the intermediate product) is passed through a heated conduit, producing a concentrated intermediate product and vaporized diluent. The concentrated intermediate product and the vaporized diluent are separated by centrifugal force in a cyclone, and the concentrated intermediate product is passed to a reception zone. In the present process, at least approximately 75% of the vaporized diluent (or other vaporized medium), can be separated from the intermediate product concentrated in the cyclone. Alternatively, at least about 90% of the vaporized diluent (or other vaporized medium) can be separated from the concentrated intermediate product in the cyclone. Alternatively, at least about 95% of the vaporized diluent (or other vaporized medium) can be separated from the concentrated intermediate product in the cyclone. Alternatively, at least about 99% of the vaporized diluent (or other vaporized medium) can be separated from the concentrated intermediate product in the cyclone. Alternatively, at least about 99.9% of the vaporized diluent (or other vaporized medium) can be separated from the concentrated intermediate product in the cyclone. Rather than characterizing the efficiency of the cyclone based on the separation of the diluent, the efficiency of the cyclone can be characterized based on the separation of solids from the gas stream. In the current process, at least about 90% of the polymer solids can be separated from the liquid medium in a cyclone. Alternatively, at least about 95% of the polymer solids can be separated from the liquid medium in the cyclone. Alternatively, at least about 99% of the polymer solids can be separated from the liquid medium in a cyclone. Alternatively, at least about 99.9% of the polymer solids can be separated from the liquid medium in a cyclone. The separation efficiency of solids can be very high (99.99% or higher, for example, 99.999%), but the efficiency depends in part on the particle size distribution. The process may also include passing the separated vaporized diluent (or other vaporized medium) from the cyclone to a filter and filtering the fine polymer particles from the separated vaporized diluent. The separated vaporized diluent (or other vaporized medium) leaving the cyclone before it reaches the filter can contain less than about 95% by weight of the polymer particles, alternatively less than about 99% by weight of fine polymer particles, alternatively less of about 99.9% by weight of fine polymer particles, alternatively less than about 99.99% by weight of fine polymer particles, alternatively less than 99.999% by weight of fine polymer particles. In accordance with another aspect of the invention, a loop reactor apparatus is provided. The apparatus includes a pipe loop reactor adapted to conduct an olefin polymerization process comprising polymerizing at least one olefin monomer to produce a fluid suspension comprising solid polymeric olefin particles in a liquid medium (eg, a liquid diluent). The apparatus may also include at least one elongated hollow fitting (e.g., a 2 inch (2.54 cm) pipe) in direct fluid communication with the pipe loop reactor. The elongated hollow attachment is adapted for removal of a portion of the fluid suspension from the pipe loop reactor. The apparatus may also include a separation line in fluid communication with the elongated hollow annex. The separation line is surrounded by a duct adapted for indirect heating. The apparatus may also include a cyclone in fluid communication with the separation line. The loop reactor apparatus may also include a first chamber in fluid communication with the cyclone, a second chamber in fluid communication with the first chamber, a first valve disposed between the first chamber and the second chamber, a purge column in fluid communication with the lint chamber, a second valve disposed between the second chamber and the purge column, and a controller for operating the first valve and the second chamber valve, so that the valves do not open at the same time. The cyclone may have a vapor outlet and a solids outlet. The loop reactor apparatus may also include a fine polymer particle filter fluidly connected to the cyclone. The loop reactor apparatus may also include a funnel (piece of transition pipe) between the separation line and the cyclone.

Brief Description of the Figures Figure 1 is a view of a loop reactor and polymer recovery system; Figure 2 is a cross section along line 2-2 of Figure 1, showing a continuous take-up annex; Figure 3 is a cross-section along the line 3-3 of Figure 2, showing a pressure valve arrangement in the continuous intake assembly; Figure 4 is a cross-section of a tangential location for the continuous intake assembly; Figure 5 is a side view of a loop reactor elbow showing both a settler and a continuous take-up assembly; Figures 6a and 6b is a cross section through line 6-6 of Figure 5, showing the orientation of two of the continuous take-up assemblies; Figure 7 is a side view showing another orientation of the continuous take-up assembly; Figure 8 is a cross-sectional view of the drive mechanism; Figure 9 is a view showing another configuration for the loops where the upper segments 14a are half-circles of 180 degrees and where the vertical segments are at least twice as long as the horizontal segments and Figure 10 is a view that shows the longest axes arranged horizontally. Figure 11 is a view of a downstream recovery system. Figures 12a and 12b are top and side views respectively, of a cyclone separator.

Detailed Description of the Invention Surprisingly, it has been found that the suspension of the continuous intake product in an olefin polymerization reaction, carried out in a loop reactor in the presence of an inert diluent allows operation of the reactor at a concentration of solids very superior. The commercial production predominantly of ethylene polymers in isobutane diluent, has been generally limited (in the past), to a maximum concentration of solids in the reactor of 37-40 weight percent. However, it was found that the continuous intake allows significant increases in the concentration of solids. In addition, the continuous intake itself, carries some additional increase in solids content, compared to the content in the reactor from which the product is taken due to the placement of the continuous intake annex, which selectively removes, a suspension of a stratum where solids are more concentrated. Therefore, concentrations greater than 40 weight percent are possible in accordance with this invention. Through this application, the weight of the catalyst is inconsiderate, since the productivity, particularly with chromium oxide in silica, is extremely high. Also surprisingly, it has been found that higher solids circulate more aggressively (Higher circulation speeds with high concentration of accompanying solids) are not accompanying, but it may be possible to use high circulation speeds. However, in more aggressive circulation in combination with continuous intake, solids concentrations greater than 50 percent by weight can be removed from the reactor by continuous intake. For example, continuous intake can easily allow to operate at higher points of 5-6 percent, that is, the reactor can be adjusted to easily originate solids by 10%; and more aggressive circulation can easily add another 7-9 percentage points, which puts the reactor above 50 percent. But, because the continuous intake is positioned to take the suspension of a stratum in the stream which has an average concentration higher than the solids, the product currently recovered has approximately a concentration higher than 3 percentage points (or greater) than the average of the reactor suspension. In this way, the operation can proceed to an effective suspension concentration of 55 percent or more, that is, an average of 52 percent in the reactor and the removal of a component which is currently above 55 percent (it is say, 3 percentage points). It should be emphasized that in commercial operation, as soon as a percentage point increases in the concentration of solids, it is significant. Therefore, going from 37-40 percent in average concentration of solids in the reactor to 41, is important; In this way going to more than 50 is truly remarkable.

The present invention is applicable to any polymerization of olefin in a loop reactor, producing a suspension of unreacted polymer product and monomer (in the case of polypropylene) or diluent (unreacted monomer and diluents in the case of polyethylene). In the case of polypropylene, a diluent is not used. Suitable olefin monomers are 1-olefins having up to 8 carbon atoms per molecule and do not branch closer to the double bond than position 4. The invention is particularly suitable for the homopolymerization of ethylene and copolymerization of ethylene and a 1- higher olefin such as butene, 1-pentene, 1-hexene, 1-octene or 1-decene. Especially preferred is ethylene and 0.01 to 10 weight percent, alternatively 0.01 to 5 weight percent, alternatively 0.1 to 4 weight percent of higher olefin, based on the total weight of the ethylene and comonomer. An alternately sufficient comonomer may be used to give the amounts described above for incorporation of comonomer into the polymer. The present invention is applicable to any suspension polymerization in a liquid medium. The invention is particularly applicable to olefin polymerizations in a liquid diluent in which the resulting polymer is largely insoluble under polymerization conditions. More particularly, the invention is applicable to any polymerization of olefin in a loop reactor using a diluent, to produce a suspension of solid polymers and liquid diluent. Suitable diluents (as opposed to solvents or monomers) are well known in the art and include hydrocarbons which are inert and liquid under reaction conditions. Suitable hydrocarbons include isobutane, propane, n-pentane, i-pentane, neopentane and n-hexane, with isobutane being especially preferred. Additionally, current techniques can be employed where unreacted monomer is the liquid medium for polymerization. For example, current techniques can be used for polypropylene polymerization wherein propylene is the liquid medium and the inert diluent is not present in any substantial amount. A diluent can still be used by the catalyst. For illustration, but not as a limitation, the present invention will be described in conjunction with a polyethylene process using an inert diluent as the liquid medium, but it is understood that the present invention may also be employed wherein the monomer is used as the liquid medium and could take the place of the diluent in the following descriptions.

Suitable catalysts are well known in the art. Particularly suitable is chromium oxide in a support such as silica as is widely described for example, in US Patent No. 2,825,721, which is incorporated by reference. Reference herein to silica supports also means encompassing any known support containing silica such as, for example, silica-alumina, silica-titania and silica-alumina-titania. Any other known support, such as aluminum phosphate, can also be used. The invention is also applicable to polymerizations using organometallic catalysts including those frequently referred to in the art as Ziegler catalysts (or Ziegler-Natta catalysts) and metallocene catalysts. Referring now to the figures, Figure 1 shows a loop reactor 10 having vertical segments 12, upper horizontal segments 14 and lower horizontal segments 16. These upper and lower horizontal segments define upper and lower horizontal flow zones. The reactor is cooled by means of two pipe heat exchangers formed by a pipe 12 and jacket 18. Each segment is connected to the next segment by a light curve or elbow 20, thus providing a continuous flow path substantially free of internal obstructions. The polymerization mixture is circulated by means of propellants 22 (shown in Figure 8), driven by an engine 24. The monomer, comonomer, if any, and make the diluent, lines are introduced lines 26 and 28, respectively, which can enter the reactor directly to one or plurality of locations or can be combined with the Condensed diluent recycling line 30 as shown. The catalyst is introduced via introduction means 32, which provide a zone (location) for introduction of the catalyst. The elongated hollow attachment for continuously taking a suspension of intermediate product, is broadly designated by the reference character 34. The continuous tap mechanism 34 is located at or adjacent to one end of the downstream of one of the loop sections of the reactor horizontal bottom 16 and adjacent or in a connection elbow 20. Alternatively, the polymer suspension can be removed from the loop to a settler, as illustrated in US Patent No. 4,424,341, which is incorporated herein by reference. The withdrawn suspension can pass from the settler to the separation line and into the cyclone. The separation line conduit has an indirect heat exchange medium, such as a separation line heater. The continuous take-up annex is shown at the downstream end of a lower horizontal segment of the loop reactor which is the preferred location. The location may be in an area near the last point in the loop where the flow is turned upwards before the point of introduction of the catalyst to allow the fresh catalyst, the maximum possible time in the reactor before it first passes a point of taking. However, the continuous intake annex can be located in any segment or any elbow. Also, the segment of the reactor to which the continuous intake annex is attached, can be of a longer diameter to decrease the flow and therefore, also allow stratification of the flow, so that the output product can have an even higher concentration of solids. The suspension of the continuously withdrawn intermediary product is passed via conduit 36 into a first chamber, for example, a high pressure separation chamber 38. The conduit 36 includes a surrounding circuit 40 which is provided with a hot fluid, which provides indirect heating to the suspension material in the separation line conduit 36. The vaporized diluent leaves the separation chamber 38 via the conduit 42 for further processing which includes condensation by simple heat exchange using the recycle condenser 50, and returning to the system, without the need for compression, via the recycle thinner line 30. The recycle condenser 50 can utilize any suitable heat exchanger fluid known in the art, under any of the conditions known in the art. However, preferably, a fluid is used at a temperature that can be economically provided. A suitable temperature range for this fluid is from about 32 ° F (0 ° C) to about 200 ° F (93.33 ° C), alternatively from approximately 70 ° F (21.10 ° C) to approximately 100 ° F (37.7 ° C). (Cooling tower water temperature in ° F is preferred, but other temperatures are possible so that the range should be expanded). The polymer particles are removed from the high pressure separation chamber 38 via line 44 for further processing using techniques known in the art. Preferably, they are passed to a low pressure separation chamber 46 and subsequently recovered as the polymer product via line 48. The separated diluent is passed through a compressor 47 to line 42. This high pressure separation design is widely described in Hanson and Sherk, U.S. Patent No. 4,424,341. In U.S. Patent No. 4,424,341, a method is provided for recovering polymer solids from a polymerization effluent comprising a suspension of the polymer solids in a liquid diluent. The method comprises heating the effluent and vaporizing the diluent in the heated effluent by exposing the heated effluent to a pressure drop in a first separation step. The pressure and temperature of the effluent heated in the first separation step are such that a major amount of the diluent will be evaporated and the vapor can be condensed without compression by heat exchange with a fluid having a temperature in the range of about 40 ° F. (4.4 ° C) to approximately 130 ° F (54.4 ° C). The diluent vapor is separated from the polymer solids and then condensed if compression by heat exchange with a fluid having a temperature in the range of about 40 ° F. (4.4 ° C) to approximately 130 ° F (54.4 ° C). The polymeric solids of the first separation stage are then subjected to a lower pressure separation step to vaporize the remaining remaining diluent if any, and the diluent vapor and the solid polymers are separated. Surprisingly, it has been found that the continuous intake not only allows higher concentration of solids upstream in the reactor, but also allows better operation of the high separation pressure, thus allowing the majority of the removed diluent to be separated and recycled without compression. . However, 70 to 90 percent of the diluent can be recovered in general in this manner. Preferably, 90 to 95% or more, alternatively 90 to 99 percent or more, alternatively 90 to 99.9 percent or more, of the diluent, are reserved in this form. Because the flow is continuous rather than intermittent, the separation line heaters work well. Also, the separation lines can be designated with an appropriate amount of pressure drop to give high velocities and high heat transfer coefficients and limit the maximum flow. In such designs, the outlet pressure of CTO will be higher than it could be otherwise. The pressure drop after the continuous intake valve (which regulates the continuous flow rate outside the reactor), is not drastic, as the pressure drops after the adjustment key of a sedimentation column. With the sedimentation columns, the suspension temperature in the separation line is higher, and less heat is transferred in the suspension, making the separation line heater less efficient.

Alternatively, the separating line heater can be discharged into a cyclone separating vaporized diluent from polymeric solids. The cyclone may be connected to a separation tank or lint receiver as shown in Figure 11, which is described in more detail below. Figure 2 shows the elbow 20 with a continuous take-up mechanism 34 in greater detail. The continuous take-up mechanism comprises a take-up cylinder 52, a suspension take-off line 54, an emergency quick-closing valve 55, a proportional motor valve 58 for regulating the flow and a flow line 60. The reactor runs completely "liquid". Because the monomer dissolves, the liquid has a slight compressive capacity, thus allowing pressure control of the entire liquid system with a valve. The diluent inlet is maintained generally constant, the proportional motor valve 58 is used to control the continuous removal rate to maintain the total reactor pressure within the designated set points. Figure 3, which is taken along the line section 3-3 of Figure 2, shows the light curve or elbow 20 associated with it, the continuous take-up mechanism 34 in greater detail, the elbow 20 This is an elbow that carries an annex. As shown, the mechanism comprises a take-up cylinder 52 attached, in this case, at a right angle to a tangent to the external surface of the elbow. On exiting the cylinder 52 is the suspension removal line 54. Arranged within the intake cylinder 52 is a pressure valve 62 which serves two purposes. First, it provides a simple and reliable cleaning mechanism for the intake cylinder if it should still get stuck with the polymer. Second, it can serve as a quick-closing valve for complete continuous jack assembly. Figure 4 shows a preferred attached orientation for the take-up cylinder 52, where it is tangentially fixed to the bend of the elbow 20 and at a point only prior to the flow of the upwardly rotating suspension. This opening is elliptical inside the surface. The lengthening is also done to improve the intake of solids. Figure 5 shows four things. First, it shows an angled orientation of the take-up cylinder 52. The take-up cylinder is shown at an alpha angle, in a plane that is (1) perpendicular to the center line of the horizontal segment 16 and (2) located at the downstream end of the horizontal segment 16. The angle with this plane is taken in the downstream direction of the plane. The vertex for the angle is the center point of the radius of the elbow as shown in Figure 5. The plane can be described as the horizontal segment through the sectional plane. Here, the demonstrated angle is approximately 24 degrees. Second, it shows a plurality of continuous take-up annexes 34 and 34a. Third, it shows an annex 34, oriented in a vertical centerline plane of the lower segment 16, and the other, 34a, located at an angle to such a plane as will be shown in more detail in Figure 6. Finally, it shows the combination of Annexes of continuous intake 34 and a conventional sedimentation column 64 for batch removal if desired. In another embodiment of this invention, a polymerization process is provided. The process comprises: 1) polymerizing, in a loop reaction zone, at least one olefin monomer in a liquid diluent to produce a fluid suspension, wherein the fluid suspension comprises a liquid diluent and the polymer solid polymer particles of olefin; 2) removing the fluid suspension comprising removing the liquid diluent and removing solid polymer particles by alternately carrying out the following steps: a) allowing the suspension of fluid to settle in at least one settling zone and subsequently removing a set of the suspension thus sedimented from the sedimentation zone as an intermediate product of the process, subsequently quickly closing the valve in the lower part of the sedimentation zone; and b) subsequently continuously removing the fluid suspension comprising removing dilute liquid and removing solid polymer particles as an intermediate product of the process. In step b), the reactor conditions can be adjusted during the start to produce solids in the reactor by at least 10%. As can be seen from the relative sizes, the continuous intake cylinders are much smaller than the conventional sedimentation columns. Still, three annexes of continuous taking of 2 inches (5.08 centimeters) of ID, as much suspension of the product as 14 columns of sedimentation of 8 inches (20.32 centimeters) can be removed. This is significant because with current large commercial loop reactors of 15,000-18,000 gallons (56,850-68,220 liters), 68-inch sedimentation columns (172.72 cms) are used. It is not desirable to increase the size of the sedimentation columns due to the difficulty in making reliable valves for larger diameters. As previously noted, by doubling the diameter of the pipe, the volume is increased four times and there simply is not enough space so that four times as many sedimentation columns are easily placed. Also, numerous larger sedimentation columns are more expensive and require a more complicated control scheme than the continuous take-up device. Therefore, the invention makes feasible the operation of more efficient, larger reactors. Reactors of 20,000 gallons (75,800 liters) or greater, and even 30,000 gallons (113,700 liters) or greater, are made possible by this invention. In general, the continuous take cylinders will have a nominal internal diameter within the range of 1 inch (2.54 centimeters) to less than 8 inches (20.32 centimeters). Preferably, they will be approximately 2-3 inches (5.08-7.62 centimeters) in internal diameter. Also, smaller continuous take cylinders are generally less risky than larger and larger diameter settling columns. This is because if casing failure should occur, a smaller line and therefore shorter oil spill speed are involved. Also, continuous take cylinders have a lower tendency to clog and therefore, involve hazardous maintenance procedures. Figure 6 is taken along the line section 6-6 of Figure 5 and the take-off cylinder 34a is shown attached at a location that is oriented at a beta angle to a vertical plane containing the reactor centerline . This plane can be referred to as the vertical center plane of the reactor. This angle can be taken from any of the sides of the plane or from both sides if it is not zero. The vertex of the angle is located in the center line of the reactor. The angle is contained in the plane perpendicular to the reactor line as shown in Figure 6. It is noted that there are three concepts of orientation in this document. First, there is the union orientation, that is, tangential as in Figure 4 and perpendicular as in Figure 2 or 7 or any angle between these two limits from 0 to 90 degrees. Second, there is the orientation regarding how far away the as-to-union curve is as represented by the alpha angle (Figure 5). This may be any of from 0 to 60 degrees, but is preferably from 0 to 40 degrees, more preferably from 0 to 20 degrees. Third, the beta angle is from the center of the plane of the longitudinal segment (Figure 6). This angle can be from 0 to 60 degrees, preferably 0 to 45 degrees, more preferably 0-20 degrees. Figure 7 shows an embodiment in which the continuous take cylinder 52 has an attached orientation of an alpha orientation, perpendicular to 0 (inherent since it is at the end, but still in the straight section), and a beta orientation of 0, is say, it is straight to the plane of the vertical centerline of the lower horizontal segment 16. Figure 8 shows in detail, propelling means 22 for continuously moving the suspension along its flow path. As can be seen in this embodiment, the propeller is in a slightly elongated section of pipe, which serves as the propulsion zone for the circulation reagents. Preferably, the system is operated to generate a differential pressure of at least 18 psig (12,654 kg / m2), preferably at least 20 psig (14,060 kg / m2), more preferably at least 22 psig (15,466 kg / m2) between the ends upstream and downstream of the propulsion zone in a reactor of nominal diameter of two feet (0.6069 meters) with a total flow path length of approximately 959 feet (289.56 meters) using isobutane 'to predominantly make ethylene polymers. It is possible as much as 50 psig (35,150 kg / m2) or more. This can be done by controlling the speed of rotation of the propeller, reducing the space between the propeller and the inner wall of the housing pump or using a more aggressive propeller design as is known in the art. This differential high pressure can be produced by the use of at least one additional pump. In general, the system is operated to generate a differential pressure, expressed as a pressure loss per unit length of the reactor, of at least 0.07 feet (0.0213 meters), generally 0.07 to 0.15 feet (0.0213 to 0.0457 meters). of pressure drop per foot (centimeters) of reactor length for a reactor of nominal diameter of 24 inches (0.6095 meters) 1. Preferably, this pressure drop per unit length is 0.09 to 0.11 inches (0.022 to 0.27 centimeters) per 24 inches (60.95 centimeters) in diameter of the reactor. For larger diameters, a higher suspension speed and a higher pressure drop per unit length of the reactor are needed. This assumes the density of the suspension which is generally about 0.5-0.6. Figure 9 shows the upper segments as semi-circles of 180 degrees, which are the preferred configuration. The vertical segments are at least twice the length, generally about seven to eight times the length of the horizontal segments. For example, the vertical flow path can be 190-226 feet (57.91-68.58 meters) and horizontal segments of 25-30 feet (7.62-9.14 meters), along the length of the flow path. Any number of loops can be employed in addition to the four described here and the eight represented in FIGURE 1, but generally, four or eight are used. The reference to nominal diameter of two feet (0.6095 meters) means an internal diameter of approximately 2 inches (5.08 centimeters). The flow length is generally greater than 500 feet (152.4 meters), generally greater than 900 feet (274.32 meters), with approximately 940 to 2000 feet (286.512 to 60.9.6 meters) being truly satisfactory. Figure 10 shows a horizontal loop reactor 11 that includes horizontal segments and vertical straight and curved segments. The vertical segments define vertical flow zones. The reactor is cooled by means of two heat exchange pipes formed by pipe 12 and jacket 18. As shown, each straight vertical segment is connected to two horizontal segments by a light curve or elbow 20, thus providing a flow path continuous substantially free of internal obstructions. As shown, the curved vertical segments are half-circles of 180 degrees that extend between the adjacent horizontal segments, which are another desired configuration. Alternatively, the vertical segments can all be straight pipe circuits or any desirable combination, as long as the vertical segments are connected to the horizontal segments. In Figure 10, the horizontal segments are at least twice the length, generally, approximately seven to eight times the length of the vertical segments. For example, horizontal segments can be 190-225 feet (59.912-68.58 meters) in the length of the flow path and vertical segments can be 25-30 feet (7.62-9.144 meters) in path length. Any number of loops can be used in addition to the four described in this document, but in general, four to eight are used. The reference to a nominal diameter of two feet (0.6096 meters) means an internal diameter of approximately 21.9 inches (0.5562 meters). The length of the flow is generally greater than 500 feet (152.4 meters), generally greater than 900 feet (274.32 meters), with approximately 940 to 2000 feet (286.512 to 609.6 meters) being really satisfactory. The continuous take-up annex 34 is shown at the downstream end of a horizontal segment of the loop reactor. The location may be in the area near the last point in the loop, where the flow is turned upward before the catalyst inuction point to allow fresh catalyst in the maximum possible time in the reactor before its first step at the point of taking. However, the continuous intake annex can be located in any segment or any elbow.

The horizontal loop reactor of Figure 10 can be used as an alternative to the vertical loop reactor 10 of Figures 1 and 9 and in combination with any of the other features of the present invention. Figure 11 shows an alternative arrangement for the upstream recovery system for separating solid polymer particles from the diluent in the suspension of the intermediate product separated from the polymerization reactor. After the suspension of the intermediate product is removed from the reactor, it passes through one or more conduits 36. The conduits 36 typically include surrounding conduits 40 which are provided with a heated fluid, thereby forming separating line heaters to provide indirect heating to the suspension traveling through the separation line 36. This separation line heater, heats the reactor effluent, or at least prevents excessive cooling of the effluent. The surrounding duct 40 can be essentially the same length as the separation line 36. In some systems using a separation line heater, some or all of the diluents will be separated in the separation line 36 prior to introduction to the chamber Separation 28. However, the terms "separation chamber" and "separation tank" are still frequently used for the tank that follows the separation line, where the vaporized diluent is separated from the polymer solids. The "separation tank" or "separation chamber" is still used even though there is little or no separation in the separation tank if all or substantially all of the diluent is vaporized in the separation line. In some designs which have separation lines that are discharged at high pressures and without downstream drying devices, separation lines are designed if there is little or no pressure drop at the tank inlet which follows, other than that associated with the flow in the line at high speeds and the one that changes this flow as it enters the tank. It is also contemplated that all or substantially all of the diluents are vaporized by the time the removed material reaches the tank after the separation line. The conduit 36 may be surrounded by several sections of the surrounding conduit 40 to provide greater control over the heating of the separation line. For example, a separation line heater can have 20 or more sections of the surrounding duct, every 20 or more feet (6,096 meters) in length. The heater sections of the separation line can carry a steam controller, to perform temperature controls, or they can have individual steam controllers. As described in U.S. Patent No. 4,424,341, the surrounding duct 40 should be provided with low pressure steam to prevent the melting of solid polymer particles traveling through the line of the separation line 36. The suspension of the intermediate product passes. via conduit 36 to the downstream separation equipment. For example, the separation lines 36 can be discharged to a high pressure separation chamber 38, as shown in FIGURE 1. As another example, the separation line heater can be discharged to a "funnel" 66 and / or a Cyclone 68 as shown in FIGURE 11. Funnel 66 provides a zone where the material within a plurality of separation line 36 can be combined to form a single stream comprising diluent and solid polymeric particles. As such, this funnel does not need to have an opening in the tip that is larger than the opening of the bottom (like a funnel used in the home), but rather it can be of any shape or size that facilitates the fusion of one or more streams individual at the entrance or a combined stream at the exit. This funnel can be used to form the stream in the input dimensions of standard cyclones described below. As well, since the speeds in the separation lines are sometimes very high, the funnel or transition piece can be used to slowly decrease the suspension at speeds acceptable for use in a cyclone. Additionally, the funnel can be designed so that there is more than one entry to the cyclones or so that more than one cyclone can be used. From the funnel 66, the single stream can be fed to a cyclone 68 in which the diluent is vaporized and other vapor components are separated from the solid polymeric particles. A cyclone 68 separates vapor and solids by centrifugal force. Cyclones are widely used to collect dust as well as a wide variety of other applications. (See Perry's Chemical Engineer's Handbook, Seventh Edition, pp. 17-27, which is incorporated herein by reference). The illustrations in Perry 's do not represent the high efficiency cyclone to be used in this service. A gas charged with particles enters a cylindrical or conical chamber, tangentially at one or more points and exits through a central opening. The particles, by virtue of their inertia, will tend to move towards the outlet separating wall, which is left in a receiver. A cyclone is similar to a sedimentation chamber, except that the gravitational acceleration is at least partially replaced by centrifugal acceleration. In a cyclone, the path of the gas involves a double vertex, with the gas that rotates downwards in the outlet and upwards in the inlet. The gas exits in an upper portion of the cyclone, and the solids exit in a lower portion of the cyclone. The cyclone 68 can be operated at a pressure and temperature similar to that used by high pressure separation chambers described above. By means of additional examples, cyclone 68 can be operated at the pressure and temperatures typically employed for an intermediate pressure separation chamber, for example, the intermediate pressure separation chamber of a two-stage separation system as shown in FIG. Hanson et al. U.S. Patent No. 4,424,342, which has been incorporated herein by reference. Preferably, the cyclone or cyclone zone can be operated at a pressure within the range of 100-1500 psig (7-105 kg / cm2), alternatively 125-275 psig (8.8-19 kg / cm2), alternatively 150 -250 psig (10.5-17-6 kg / cm2), alternatively 140-190 psig (9.8-13.4 kg / cm2), alternatively approximately 170 psig (11.9 kg / cm2). The cyclone or cyclone zone can be operated at a temperature within the range of 100-250 ° F (37.8-121 ° C), preferably 130-230 ° F (54. -110 ° C), more preferably 150-210 ° F. (65.6-98-9 ° C) or 170-200 ° F (76.6-93.3 ° C). The narrowest ranges are particularly suitable for polymerizations using l-hexene comonomer and isobutane diluent, with the widest ranges being suitable for higher 1-olefin comonomers and hydrocarbon diluents in general. By directing the separation line (s) to the cyclone, the best separation efficiency can be achieved and substantially all solids can be prepared from the superheated steam stream. The complete vapor separation of the hydrocarbon takes place in the purge column. The cyclone may be connected to a separation tank or a lint receiver 70 as shown in FIGURE 11. Because most of the vapor is separated by cyclone 68, the lint receiver 70 may be smaller than the lint chambers. Separation or separation gas separators that have been used in the past. For example, the volume of an exemplary lint receiver (the receiving area) may be in the range of 33.675 gal. (127,628 liters) (13'X28 'more cone) while the lint receiver may be approximately 13,500 gal (51,165 liters) (with approximate dimensions of 10'X20' plus cone), and both may have a maintained design of approximately 44,000 pounds (19958.4 kilograms) of the intermediate polymer product discharged from the reaction zone and processed in the recovery system. This is for a lint receiver system for a loop reactor that has a volume of 35,500 gallons (134381.7 liters). The lint receiver 70 may be smaller because the small space or none is used to separate the gas from the lint. Another disadvantage is that a line running down the cyclone is not generally required. The vaporized diluent exits in cyclone 68 via conduit 72 for further processing which may include passing through a separation gas filter 74 where the fines are separated from the separation gas. The fines are passed from the filter 74 using cycle repeating valves 76a and 76b. The separation gas leaves the top of the filter 74. The separation gas can be condensed by indirect heat exchange or by compression and recycling for the polymerization reactor or related systems. The polymeric particles are separated from the fluff receiver 70 and pass into a fluff chamber 78. The fluff chamber 78 is located after the fluff receiver 70, or more particularly after the control valve 80 which controls the flux receiver output. fluff. The control valve 80 can be a cycle repeating ball placed upstream of the lint chamber 78, and a second cycle repeating ball valve 82 can be placed downstream of the lint chamber 78. The lint chamber 78 can act as a downward chamber, to lower the pressure of the material to be transferred to the lint receiver 70. The cycle repeating valves operate in such a way that the upper valve opens while the bottom valve closes. During this period, the lint chamber 78 is filled with polymeric solids from the lint receiver 70, at a desired level or amount of an amount of polymer solids, which does not exceed the maximum available capacity. Preferably, the lint chamber is completely filled. The proportion in which the valve cycle repeats is varied to control the level of lint in the lint receiver 70. When the desired level or quantity is reached, the upper valve 89 closes and the bottom valve 82 opens , and the polymer solids are transferred to a relatively low pressure vessel, such as a purge column. These stages are repeated as needed to transfer the -lubber receiver material 70 to the purge column.

A controller can be connected to the first valve and the second valve, and the controller can be adapted to alternate the opening of each of the valves. Preferably, the cycle repeater valve controller can be used to maintain a constant level of the polymer of the intermediate product at the bottom of the separation chamber. This gives the diluent in the polymer product time to diffuse into the particle to the surface and vaporize. Also, by maintaining a level in the separation chamber, the cycle repeating valves can be given a "polymer seal", so that if the valve base is used or it does not perfectly seal the gas in the zone of high pressure (but still holds most of the polymer back) from the low pressure zone, any high pressure gas that escapes from the high pressure zone to the low pressure zone, has to pass through the tortuous path of empty space between the particles. This lowers the leakage of high pressure gas to the low pressure zone. Both of these points contribute to improving the efficiency of the recovery of high pressure separation gas by means of condensation without compression. Other suitable means can be used for opening the first and second valves, so that the valves are not open at the same time. The cycle repeating valves can be configured and operated in such a way that the residence time of the polymeric solids is maintained at a desired level. The residence time of polymer solids is preferably maintained at substantially zero to 2 minutes. Alternatively, the residence time of polymer solids is preferably maintained in the range of about 10 seconds to 30 minutes. Alternatively, the residence time of polymer solids is preferably maintained in the intervals of 30 to 90 minutes or 30 to 120 minutes. By maintaining a desired level of solid polymeric olefin particles in an intermediate pressure zone, the residence time of polymer solids, which is the average amount of waste time of polymer particles in the intermediate pressure zone, can be controlled. An increase in polymeric solids residence time that allows the separation and / or separation of more diluents, includes more diluents that enter from the polymer solids, thereby increasing the purity and processability of the polymer leaving the zone. In addition, by maintaining a desired level of polymer solids in the intermediate pressure zone, a pressure seal can be created between the zone and the downstream equipment. In addition, operation and maintenance costs are reduced by providing a pressure seal between the intermediate pressure zone and the purge zone that does not require the use of on / off valves. Additionally, the need for a separate lint chamber can be eliminated. The pressure seal can count at the level of polymer solids to restrict the flow of liquid or gaseous diluent (if any is present) outside the intermediate pressure zone. The polymeric solids particles can substantially close most of the flow path (cross-sectional area) available for the diluent. However, it is contemplated that a small amount of the flow path may be available through small openings between adjacent particles. This small continuous flow can reduce the final recovery efficiency of the diluent in the intermediate pressure zone. Another way to allow solids to descend from the high pressure separation tank to the low pressure separation tank or purge column is to use a restriction valve; preferably a Vee notched ball valve. The Vee notched ball valve simply restricts the flow of gas and solids by means of a variable aperture area and is capable of being adjusted to sustain a constant solid level in the high pressure separation tank. This single valve can replace the two cycle repeating valves, the lint chamber 78, and is small to be less expensive than two cycle repeating valves. Since it moves less than the cycle repeating valves, the valve usage ratio is much lower than in the cycle repeating valves, and its maintenance is reduced. Also the pressure reduces the safe turning operation in the downstream material, so that it can be operated more consistently and without reacting the valves constantly at a changing upstream pressure. The simple Vee notched or other suitable ball valve (such as a rotary valve with a ball valve added for insulation purposes), uses the above-described principle of polymer seal so that the valve does not have to handle the full drop of pressure between the low and high pressure zones. The length and diameter of the line between the two pressure zones change to be selected to control the proportion of gas spillage passing the valve, the pressure observed in the valve, and the distance separating the two valves. From the lint chamber 78, the polymer particles can pass into a low pressure separation chamber or a purge column. It has been found that continued recovery not only allows high concentrations of solids upstream in the reactor, but also allows the best operation of the separation line heaters in the cyclone, thereby allowing substantially all of the removed diluent to be vaporized. in the separation line and separated in the cyclone.

Figures 12 (a) and 12 (b) show a top and bottom view, respectively, of a cyclone for use in the present process and apparatus. The cyclone for the present process may be configured a little differently than that shown in Figure 12 (a) and 12 (b). For example, the top view does not need to be concentric circles for a very high efficiency cyclone. As another example, the bottom of the cyclone can be large or short to provide a very large bottom outlet. The cyclone receives a fluid stream from the loop reactor through an inlet of the cyclone 84. The inlet of the cyclone 84 can be any shape but is often rectangular, and its size such that it is larger in the vertical direction than the horizontal The inlet of cyclone 84 discharges the fluid stream in the upper portion 86 of the cyclone. By discharging the fluid stream tangentially in a tank, the improved separation originates, even if the tank is not, strictly speaking, a cyclone tank, and such discharge is generally superior to the discharge in a perpendicular manner. The fluid travels downward at a vertex to a lower position 88 of the cyclone. The solids are separated from the vapor by centrifugal force. The separated solids leave a solids outlet 90, and the separated vapor leaves a vapor outlet 92, which may extend a distance in the cyclone. In Figure 12, Dc is the diameter of the upper portion of the cyclone. Bc is the amplitude of the entrance, while Hc is the height of the entrance. Lc is the length of the upper portion of the cyclone, and Zc is the length of the reduced, lower portion of the cyclone. Relative sizes for the cyclone in Figure 12 are optional. The often selected option vendor is Fisher-Losterman for high efficiency cyclones and their literature can be consulted for configurations.

Table 1 shows the estimated performance of a typical separation chamber with the separation line entering tangentially. The amount of solids and the particle size distribution are given by the lint in the upper feed of the cyclone. Table 1 Table 2 shows the estimated performance of a cyclone and a lint receiver arrangement. The particle size distribution for the solids fed to the Separation Gas Filter is shown.

Table 2 EXAMPLES A fourth vertical column polymerization reactor was used using a 26 inch (66.04 cm) D51795 / 81-281 pump jet from Lawrance Pumps on deck M51879 / FAB to polymerize ethylene and hexene-1. This pump was compared to a 24 inch pump (60.96 centimeters, which gave less aggressive circulation (0.66 feet (0.20 meters) of pressure drop to 0.98 (0.29 meters).) This was then compared to the same more aggressive circulation and a continuous take-up assembly of the type shown by the reference character 34 of Figure 5. These results are shown below.

Table 3 While this invention has been described in detail by illustrative purposes, it is not constructed as a limitation thereof, but is intended to cover all changes within the scope and scope of the invention.

Claims (22)

NOVELTY OF THE INVENTION Having described the present is considered as a novelty, and therefore, it is claimed as property contained in the following: CLAIMS

1. A process for producing solid polymer particles, characterized in that the process comprises: polymerizing, in a loop reaction zone, at least one monomer to produce a fluid suspension comprising solid polymer particles in a liquid medium; continuously removing a portion of the suspension, which comprises removing liquid medium and removing solid polymer particles, as an intermediate product of the process; passing the intermediate product through a heated duct, producing a concentrated intermediate product and a vapor; separating the vapor of the concentrated intermediate product by centrifugal force in a cyclone.

2. The process according to claim 1, characterized in that at least about 90% of the vapor is separated from the concentrated intermediate product in the cyclone and passed to a filter zone.

3. The process according to claim 1, characterized in that it further comprises: passing the steam separated from the cyclone to a filter; and filter fine polymer particles of steam separated via the filter.

4. The process according to claim 1, characterized in that at least about 90% of the polymer solids in the intermediate product are separated from the medium withdrawn in the cyclone. The process according to claim 1, characterized in that it comprises the step of maintaining a concentration of solid polymer particles in the suspension in the area of more than 40 weight percent. The process according to claim 1, characterized in that the vaporized diluent separated from the cyclone, is condensed without compression by heat exchange with a fluid having a temperature within the range of about 32 ° F (0 ° C) to approximately 200 ° F (93.3 ° C). The process according to claim 1, characterized in that it comprises passing the concentrated intermediate product to a receiving zone, wherein the volume of the receiving zone is in the range from about 1000 to about 2,000 cubic feet (28.3 to about 566 cubic meters). 8. The process according to claim 1, characterized in that it further comprises the step of maintaining the polymer solids in the receiving zone for a residence time of polymer solids sufficient to remove substantially all of the diluent without entering. 9. A process according to claim 8, characterized in that the residence time of polymer solids is from about 10 seconds to about 30 minutes. 10. A process according to claim 8, characterized in that the residence time of polymer solids is from about 30 to about 120 minutes. 11. A loop reactor apparatus, characterized in that it comprises: a pipe loop reactor adapted to conduct an olefin polymerization process comprising polymerizing at least one olefin monomer, to produce a fluid suspension comprising solid polymer particles of olfain in a liquid medium; and at least one elongated hollow fitting in fluid communication with the pipe loop reactor, adapted for removal of a portion of the fluid suspension from a pipe loop reactor; a separation line in fluid communication with at least one elongated hollow annex, wherein the separation line is surrounded by a conduit adapted to indirectly heat; and a cyclone in fluid communication with the separation line. 12. The loop reactor apparatus according to claim 11, characterized in that it further comprises: a first chamber in fluid communication with the cyclone; a second chamber in fluid communication with the cyclone; a first valve disposed between the first chamber and the second chamber; a purge column in fluid communication with the second chamber; a second valve disposed between the second chamber and the purge column; and a controller for operating the first valve and the valve of the second chamber so that the valves do not open at the same time. The loop reactor apparatus according to claim 12, characterized in that the volume of the pipe loop reactor is in the range of 30,000 gallons (113,700 liters) to 60,000 gallons (227,400 liters). 14. The loop reactor apparatus according to claim 11, characterized in that the cyclone comprises a vapor outlet and a solids outlet, and the loop reactor apparatus further comprises a filter of fine polymer particles, fluidly connected to the outlet of the reactor. cyclone vapor. 1

5. The loop reactor apparatus according to claim 11, characterized in that it further comprises a funnel fluidly connected and disposed between the separation line and the cyclone. 1

6. The loop reactor apparatus according to claim 11, characterized in that it comprises a level sensor in contact with the first chamber for sensing the level of polymer solids in the first chamber, wherein the level sensor is connected to the first chamber. valve and is adapted to maintain a desired level of polymer solids in the first chamber. 1

7. The loop reactor apparatus according to claim 11, characterized in that it further comprises a chronometer connected to the first valve, wherein the chronometer determines the opening and closing of the first valve, so that the polymer solids are kept in the first camera for a desired time. 1

8. A process, characterized in that it comprises: polymerizing at least one monomer in a reactor to produce a suspension comprising solid polymer particles and a liquid; substantially continuously removing via a valve, a discharge suspension from the reactor, the discharge suspension comprises removing solid polymer particles and removing liquid, wherein the discharge suspension has a solids concentration greater than the solids concentration of the suspension in the reactor; modulating the valve to adjust the flow rate of the discharge suspension to facilitate the control of a pressure in the reactor; passing the discharge suspension of the reactor through a main duct to vaporize at least a majority of the liquid in the discharge suspension; separating the steam from the heated discharge suspension via centrifugal forces in a cyclone; discharge the vapor separated from an upper portion of the cyclone; and discharging a polymer stream comprising said solid polymer particles and residual hydrocarbon from a lower portion of the cyclone. 1

9. The process according to claim 18, characterized in that it comprises passing the polymer stream from the lower portion of the cyclone to a purge column. The process according to claim 18, characterized in that it comprises passing the polymer stream from the lower portion of the cyclone to a lower pressure separation tank. 21. The process according to claim 18, characterized in that it comprises passing the polymer stream from the lower portion of the cyclone to a lint chamber. 22. The process according to claim 21, characterized in that it comprises passing the polymer stream from the lint chamber to a purge column.