MXPA97002418A - Process for polymerizing monomers in lechosfluidiza - Google Patents

Abstract

The present invention relates to a process for polymerizing alpha-olefin (s) in a gas phase reactor having a fluidized bed and a fluidization medium comprising a gas phase to produce polymer product where the fluidization medium includes condensable hydrocarbon fluids. saturated or unsaturated and serves to control the cooling capacity of said reactor, the process comprising employing in the fluidization medium a level of liquid entering the reactor which is between 18 and 50% by weight based on the total weight of the medium. fluidization and maintain the bulk density function (Z), at a value equal to or greater than the calculated limit of the bulk density function in Table A, where X and Y in Table A are calculated in accordance with the following equations: where Pbf is the fluidized bulk density, Pbs is the bulk density settled, Pg is the density of the gas, and Ps is the solid density (resin) and where dp is the density etro of average heavy particle, g is the acceleration of gravity (9.805 m / sec2), Uo is the superficial velocity of the gas, yæ is the viscosity of the g

Description

PROCESS FOR POLYMERIZING MONO EROS IN FLUIDIZATION BEDS Field of the Invention The present invention relates to a process for polymerization of gas phase olefins, in fluidized bed reactors. The present invention achieves substantial savings in both energy and capital costs by considerably increasing the polymer production rate capacity of a given sized reactor. Background of the Invention The discovery of the process for the production of polymers in fluidized beds has provided means for the production of a diverse set of polymers. Using a gas fluidized bed polymerization process substantially reduces energy requirements compared to other processes and, most importantly, reduces the capital investment required to run such a process to produce polymers. Fluidized gas bed polymerization plants generally employ a continuous cycle. In a part of the cycle, in a reactor, a cycle gas stream is heated by the polymerization heat. This heat is removed in another part of the cycle by means of a cooling system external to the reactor.

Generally, in a gas fluidized bed process for producing polymers from alpha-olefin monomers, a gaseous stream containing one or more monomers is continuously passed through a fluidized bed under reactive conditions, in the presence of a catalyst. This gaseous stream is removed from the fluidized bed and recycled back to the reactor. Simultaneously, the polymer product is removed from the reactor and new monomer is added to replace the unreacted monomer. It is important to remove the heat generated by the reaction in order to maintain the temperature of the gaseous stream within the reactor at a level below the degradation temperatures of the polymer and the catalyst. In addition, it is important to prevent agglomeration or the formation of pieces of polymer that can not be removed as a product. This is achieved by controlling the temperature of the gaseous stream in the reaction bed at a temperature below the melting or sticking temperature of the polymer particles produced during the polymerization reaction. In this way, it is understood that the amount of polymer produced in a fluidized bed polymerization process is related to the amount of heat that can be removed from a reaction zone in a fluidized bed within the reactor. Conventionally, heat has been removed from the recycle gas stream by cooling the stream outside the reactor. A requirement of a fluidized bed process is that the velocity of the recycle gas stream is sufficient to maintain the fluidized bed in a fluidized state. In a conventional fluidized bed reactor, the amount of fluid circulated to remove the polymerization heat is greater than the amount of fluid required to support the fluidized bed and for adequate mixing of the solids in the fluidized bed. However, to prevent excessive entrapment of solids in a gaseous stream removed from the fluidized bed, the velocity of the gas stream must be regulated. Also, in a steady state fluidized bed polymerization process, where the heat generated by the polymerization reaction is substantially proportional to the rate of polymer production, the heat generated is equal to the heat absorbed by the gas stream and lost by other gases. means, such that the temperature of the bed remains constant. For a time, it was thought that the temperature of the gaseous stream external to the reactor, otherwise known as the temperature of the recycle stream, could not be reduced below the dew point of the recycle stream. The dew point of the recycle stream is that temperature at which the liquid condensate begins to form in the gaseous recycle stream. It is believed that introducing a liquid into a gaseous phase recycle stream in a fluidized bed polymerization process would invariably result in clogging of the recycle stream lines., the heat exchanger, the area under the fluidized bed, or the gas distributor plate. As a consequence of operating at a temperature above the dew point of the recycle stream to avoid the problems associated with the liquid that is in the recycle gas stream, the production rates in commercial reactors can not be increased significantly without enlarging the diameters of the reactor. In the past, there was concern that excessive amounts of liquid in the recycle stream would disturb the fluidization process to such an extent that the fluidized bed collapsed, resulting in the sintering of the solid polymer particles into a solid mass, causing the shutdown of the reactor. This widespread belief in the sense of avoiding liquid in the recycle stream can be seen in the following documents: United States Patents Nos. 3,922,322; 4,035,560; 4,359,561; and 5,028,670, and European Patent Applications Nos. 0 050 477 and 0 100 879. Contrary to this belief, it has been demonstrated, as disclosed by Jenkins, III and co-workers in U.S. Patent No. 4,543,399 and the U.S. Patent No. 4,588,790 related, that a recycle stream can be cooled to a temperature below the dew point in a fluidized bed polymerization process, resulting in the condensation of a portion of the recycle stream. The disclosures of these two Jenkins patents, III are incorporated herein by reference. The resulting stream containing trapped liquid is then returned to the reactor without the aforementioned phenomena of agglomeration and / or plugging which are believed to occur when a liquid is introduced into a fluidized bed polymerization process. This process of intentionally introducing a liquid into a recycle stream or reactor is known in the industry as "condensed mode" operation of a gas phase polymerization process. The aforementioned US patents of Jenkins, III et al. Disclose that, when the recycle stream temperature is lowered to a point below its dew point in a "condensed mode" operation, an increase in polymer production, compared to production in a non-condensed mode, due to the increased cooling capacity. Likewise, Jenkins, III and colleagues found that a substantial increase in spacetime yield, the amount of polymer production in a given volume of the reactor, can be achieved by operating in "condensed mode" with little or no change in the properties of the polymer. product The liquid phase of the mixture of the gas / liquid recycle stream of two phases in "condensed mode" remains trapped or suspended in the gas phase of the mixture. Cooling the recycle stream to produce this two-phase mixture results in a liquid / vapor equilibrium. Vaporization of the liquid occurs only when heat is added or the pressure is reduced. The increase in the yields in space time achieved by Jenkins, III and collaborators is the result of this increased cooling capacity of the recycle stream, which, in turn, is due to the greater temperature differential between the incoming recycle stream and the temperature of the fluidized bed, as well as the vaporization of the condensed liquid trapped in the recycle stream. Jenkins, III et al. Illustrate the difficulty and complexity of control in general and of trying to extend the stable operating zone to optimize the performance in space time in a gas phase reactor. In Jenkins, III et al., The recycle gas is cooled and added to the reactor at a temperature below the dew point, so that the condensed fluids evaporate into the reactor. The cooling capacity of the recycle gas can be further increased while being at a given temperature of the cooling heat transfer medium. One option described is to add materials that do not polymerize (isopentane) to increase the dew point. Due to the greater cooling, more heat can be removed and therefore it is said that greater yields are possible in space time. Jenkins, III and collaborators recommend not to exceed 20% by weight, preferably 2 to 12% by weight, of liquid condensed in the recycle gas. Some of the potential hazards described include the formation of "mud", maintaining a sufficiently high velocity of the recycle gas, or preventing the accumulation of liquid in a distributor plate. Jenkins, III and collaborators do not comment on where the upper limits lie for polymerizable or non-polymerizable condensable materials, nor the question of how to optimize performance in space time using condensed mode. A gaseous fluidized bed reactor can be controlled to give the desired melt index and density for the polymer at an optimum production. Generally, great care is taken to avoid conditions that may lead to the formation of pieces or sheets or, in the worst case, an unstable fluidized bed that collapses, or causes the polymer particles to melt together. The control of a fluidized bed therefore has to be exerted to reduce the formation of pieces and the rolling and to prevent the collapse of the bed or the need to terminate the reaction and stop the reactor. This is the reason why commercial scale reactors are designed to operate well within proven stable operation zones, and by which reactors are used in a carefully circumscribed manner. Even within the constraints of safe, conventional operation, control is complex, increasing the difficulty and uncertainty of experimentation if new and improved operating conditions are to be found. There are target values, determined by the polymer and the catalyst, by the operating temperature, the ratio of co-monomer (s) to monomer, and the ratio of hydrogen to monomer. The reactor and the cooling system are contained within pressure vessels. Its content is supervised, without interfering unduly with fluidization, measuring, among other parameters (1) the pressure at the top; (2) the pressure differential at various heights along the bed; (3) the temperature upstream of the bed; (4) the temperature in the fluidized bed and the temperature downstream of the bed; as well as (5) the composition of the gases; and (6) the gas flow rate. These measurements are used to control the addition of the catalyst, the monomer partial pressure, and the velocity of the recycle gas, among others. The removal of the polymer is constrained in some cases by settled (non-fluidized) bulk density or fluidized bulk density, depending on the design of the plant, and these parameters must also be monitored, as well as the level of ash in the polymer. The plant is a closed system. In operation, changes in the process of one or more of the measured values lead to consequent changes in the other points. In the design of the plant, the optimization of the capacity depends on the most restrictive element in the overall design. There is no generally accepted view on what causes piece formation or lamination. Obviously, some fusion of the polymer particles is involved, possibly due to insufficient heat transfer caused by inadequate fluidization in the fluidized bed. However, no clear correlations have yet been found between individual readings and measurements and the occurrence of lump formation and lamination. All of the measured values and controls are therefore conventionally used to remain within safe, known operating areas for a given plant design. Large-scale gas-phase plants are expensive and highly productive. The risks associated with the experiment in such plants are high, because the stoppage time is expensive. Therefore, it is difficult to explore the design and operation limits experimentally in view of the costs and risks. It will be desirable to provide a method of determining a stable operating condition for gas fluidized bed polymerization, to facilitate the optimum design of the plant and the determination of desirable process conditions in a given plant design. It would also be desirable to provide a gaseous fluidized bed polymerization process that provides maximum reactor productivity.

It is therefore within the objects of the invention to help determine zones of stable operation for a gaseous fluidized bed process and a plant design of this type, to find criteria for running a process safely with low risk of failure and same time high reactor productivities, and / or to avoid any restriction in the overall capacity of the plant due to reactor productivity. SUMMARY OF THE INVENTION This invention relates to a process for polymerizing alpha-olefins in a gas phase reactor at considerably higher production rates than hitherto contemplated. The invention is directed to a process for polymerizing alpha-olefins in a gas phase reactor having a fluidized bed and a fluidization medium, wherein the fluid level in the fluidization medium is greater than 15, preferably greater than 20% in weight, based on the total weight of the fluidization medium. The invention is also directed to a process for polymerizing alpha-olefins in a gas phase reactor having a fluidized bed and a fluidization medium such that the enthalpy change of the fluidization medium leaving and entering the reactor is greater than 40 Btu / lb (22 cal / g), preferably greater than 50 Btu / lb (27 cal / g). The invention further provides a process for polymerizing alpha-olefins in a gas phase reactor at a production rate of greater than about 500 lb / hr-ft2 (2.441 kg / hr-m2). This invention, in another embodiment, relates to a method for determining stable operating conditions of a gas phase fluidized bed polymerization reactor, identifying a property useful for determining the stability of a fluidized bed and controlling the composition of the fluidized bed. a fluidization medium or recycle stream to establish a range of values for the property, to maintain the stable operation condition. The invention, in another embodiment, is also directed to a process for controlling a gas-phase fluidized-bed polymerization reactor, monitoring a reactor condition indicative of the occurrence of a failure condition and controlling the composition of a medium. fluidization or recycle stream in response to the occurrence, to avoid the occurrence of the failure condition. In a preferred embodiment, a bulk density function is monitored. This function is maintained equal to or preferably over a value that depends on temperature, pressure, particle variables such as size, solid density and settled bulk density, and gas variables such as composition and velocity, as defined below. in this patent description. The invention still further provides, in another embodiment, a method of determining stable operating conditions of a gas fluidized bed polymerization reactor operating in condensed mode, which comprises observing changes in fluidized bulk density in the reactor , associated with changes in the composition of the fluidization medium; and increasing the cooling capacity of the recycle stream without exceeding the level at which a reduction in fluidized bulk density is irreversible. As a general rule, a reduction in the bulk density function to less than the minimum or limit value, as defined later in this patent description, may involve the risk of disruption of the fluidized bed, and should be avoided. In another embodiment of the invention, a gaseous fluidized bed polymerization process is provided for the polymerization of a polymer by passing a gaseous stream comprising monomer through a fluidized bed reactor in the presence of a catalyst under reactive conditions, to produce polymer product and a stream comprising unreacted monomer gases, by compressing and cooling said stream, mixing said stream with feed components and returning a gaseous phase and a liquid phase to said reactor, the improvement comprising cooling said stream such that the liquid phase is greater than 15%, preferably greater than 20% by weight of the total weight of the returned stream, and the composition of the stream is such that the bulk density function is maintained about a limit value, such as this is described later in this patent description. In one embodiment, a process is provided for polymerizing alpha-olefin (s) in the presence of a metallocene catalyst in a gas phase reactor having a fluidized bed and a fluidization medium having a gas phase and a liquid phase which enter the reactor, said process comprising: a) controlling the cooling capacity of said fluidization means by controlling the ratio of said gas phase to said liquid phase; b) calculate a limit of the bulk density function; c) maintain or supervise a bulk density function (Z); and d) adjust the bulk density function (Z) to maintain the bulk density function (Z) at a value greater than or equal to the calculated limit of the bulk density function. In one embodiment of the invention, a continuous process for polymerizing alpha-olefin (s) in the presence of a metallocene catalyst in a gas phase reactor having a fluidized bed and a fluidization medium having a phase is provided. gaseous and a liquid phase entering the reactor, said process comprising: a) controlling the cooling capacity of said fluidization means controlling the relation of said gaseous phase to said liquid phase; and b) maintain a bulk density (Z) function at a value greater than or equal to the calculated limit of the bulk density function.

In still another embodiment of the invention, there is provided a continuous process for increasing the productivity of a gas phase polymerization reactor having a fluidization medium and a fluidized bed, said process comprising passing a gas stream comprising monomer to through a reaction zone in the presence of a metallocene catalyst to produce a polymer product, remove said polymer product, remove said fluidization medium comprising unreacted monomer from said reaction zone, mix said fluidization medium with hydrocarbon and monomer ( s) polymerizable (s) to form a liquid and a gas phase, and recycle said fluidization medium to said reactor, the process comprising: a) introducing said hydrocarbon into said fluidization medium to allow an increase in the cooling capacity of the medium of fluidization over at least 40 Btu / lb; b) increase the withdrawal rate of the polymer product to more than at least 500 lb / hr-ft2; c) calculate a bulk density function limit; and d) maintaining a bulk density function value (Z) greater than or equal to the calculated limit of the bulk density function. BRIEF DESCRIPTION OF THE DRAWINGS The above objects, aspects and advantages of this invention will become clearer and will be more fully understood upon reading the following detailed description in conjunction with the accompanying drawings, in which: Figure 1 is a schematic illustration of the preferred embodiment of the reactor used in the practice of the improved gaseous fluidized bed polymerization process for the production of polymers of this invention. Figure 2 is a graph of the isopentane molar percentage and the fluidized bulk density of Table 1. Figure 3 is a graph of the isopentane molar percentage and the fluidized bulk density of Table 2. Detailed Description of the Invention In the following description, similar parts are indicated throughout the description and drawings with the same reference numerals, respectively. The drawing is not necessarily to scale, and certain parts have been exaggerated to better illustrate the improved process of this invention. This invention is not limited to any particular type or class of polymerization reaction, but is particularly suitable for polymerization reactions involving the polymerization of one or more monomers, for example olefin monomers of ethylene, propylene, butene-1, pentene -1, 4-methylpente-no-1, hexene-1, octene-1, and styrene. Other monomers may include polar vinyl, conjugated and non-conjugated dienes, acetylene and aldehyde monomers. The catalysts employed in the improved process may include coordinate anionic catalysts, cationic catalysts, free radical catalysts, anionic catalysts, and include a transition metal component or metallocene component that includes single or multiple cyclopentadienyl components reacted with one component either alkyl or metal alkoxy, or a component of an ionic compound. These catalyst may include partially and fully activated precursor compositions, those catalysts modified by pre-polymerization or encapsulation, and those supported catalysts in a carrier. Although, as previously mentioned, the present invention is not limited to any specific type of polymerization reaction, the following discussion of the operation of the improved process is directed to the gas phase polymerization of olefin-type monomers, for example polyethylene, where has found that the present invention is particularly advantageous. A significant increase in reactor productivity is possible without an adverse effect on the quality or properties of the product. To achieve greater cooling capacities, and therefore higher reactor productivity, it may be desirable to raise the dew point of the recycle stream to allow a greater increase in heat by being removed from the fluidized bed. For the purposes of this application, the terms "recycle stream" and "fluidization medium" are interchangeable. The dew point of the recycle stream can be increased by increasing the operating pressure of the reaction / recycle stream and / or increasing the percentage of condensable fluids and reducing the percentage of non-condensable gases in the recycle stream, in the manner described by Jenkins, III et al., U.S. Patent Nos. 4,588,790 and 4,543,399. The condensable fluid can be inert to the catalyst, the reactants and the polymer product produced; it may also include co-monomers. The condensable fluid can be introduced into the reaction / recycle system at any point in the system, as will be illustrated below from Figure 1. For the purposes of this patent description, the term "condensable fluids" includes saturated or unsaturated hydrocarbons. unsaturated Examples of suitable inert condensable fluids are readily volatile liquid hydrocarbons, which may be selected from saturated hydrocarbons containing from 2 to 8 carbon atoms. Some suitable saturated hydrocarbons are propane, n-butane, isobutane, n-pentane, isopentane, neopentane, n-hexane, isohexane or other saturated C6 hydrocarbons, n-heptane, n-octane and other saturated C7 and C8 hydrocarbons, or mixtures thereof . The preferred inert, condensable hydrocarbons are C5 and C6 saturated hydrocarbons. The condensable fluids may also include condensable, polymerizable co-monomers such as olefins, alpha-olefins, diolefins, diolefins containing at least one alpha-olefin, or mixtures thereof, including some of the aforementioned monomers which may be incorporated in whole or in part in the polymer product.

In practicing the invention, the amount of gas in the recycle stream and the velocity of the recycle stream must be maintained at levels sufficient to maintain the liquid phase of the mixture suspended in the gas phase until the recycle stream enters the recycle stream. the fluidized bed, so that the liquid does not accumulate in the lower head of the reactor below the distributor plate. The velocity of the recycle stream must also be high enough to support and mix the fluidized bed within the reactor. It is also desirable that the liquid entering the fluidized bed be dispersed and vaporized rapidly. Controlling the composition, temperature, pressure and surface velocity of the gas in relation to the composition and physical characteristics of the polymer is important to maintain a viable fluidized bed. A viable fluidized bed or a stable operating condition is defined as a fluidized bed of particles that are suspended and well mixed in a stable stage under reaction conditions without the formation of significant amounts of agglomerates (chips or sheets), which would disturb the reactor or the operations of the downstream process. In a preferred embodiment, more than 15% by weight, preferably more than 20% by weight of the recycle stream can be condensed, or be in the liquid phase without encountering disruption of the fluidization process, with the proviso that the limits of Safe operation of the stable operation zones determined with the help of bulk density measurements of the fluidized bed are not exceeded. During the polymerization process, a smaller portion (typically less than about 10%) of the gas stream flowing up through the fluidized bed reacts. The portion of the current that does not react, that is, the larger portion, passes into a region on the fluidized bed called the free boarding zone, which may be a rate reduction zone. In the free boarding zone, the larger solid polymer particles that are projected above the bed by the eruption of gas bubbles through the surface or trapped in the gas stream, are allowed to fall back into the fluidized bed. The smallest solid polymeric particles, known in the industry as "fine particles", are removed together with the recycle stream because their terminal settlement rates are less than the velocity of the recycle stream in the free boarding zone. The operating temperature of the process is set or adjusted to a temperature lower than the melting or sticking temperature of the polymer particles produced. It is important to maintain this temperature to prevent plugging of the reactor by pieces of polymer that develop rapidly if the temperature reaches high levels. These pieces of polymer can become too large to be removed from the reactor as a polymer product and cause process and reactor failure. Also, the pieces that enter the process of handling downstream of the polymeric product can disturb, for example, transfer systems, drying units, or extruders. The walls of the reactor can be treated according to U.S. Patent No. 4,876,320, incorporated herein by reference. In a preferred embodiment of this invention, the point of entry for the recycle stream is preferably below the bottom point of the fluidized bed in order to provide uniform flow of the recycle stream through the entire reactor to In order to maintain the fluidized bed in a suspended condition and ensure uniformity of the recycle stream passing upwards through the entire fluidized bed. In another embodiment of the present invention, the recycle stream can be divided into two or more separate streams, one or more of which may be introduced directly into the fluidized bed, with the proviso that the gas velocity below and through the entire fluidized bed is sufficient to maintain the bed suspended. For example, the recycle stream can be divided into a liquid and a gas stream which can then be introduced separately into the reactor. In the practice of the improved process of this invention, the recycle stream comprising a mixture of a gas phase and a liquid phase within the reactor below the distributor plate can be formed by separately injecting a liquid and a recycle gas under conditions that they will produce a current comprising both phases. The advantages of this invention are not limited to the production of polyolefins. In this way, this invention can be practiced in relation to any exothermic reaction carried out in a gaseous fluidized bed. The advantages of a process operating in condensed mode over other processes generally increase directly with the proximity of the dew point temperature of the recycle stream to the reaction temperature within the interior of the fluidized bed. For a given dew point, the advantages of the process can be increased directly with the percentage of liquid in the recycle stream returned to the reactor. The invention allows high percentages of liquid to be used in the process. A gaseous fluidized bed reactor which is particularly suitable for the production of polymers by the processes of the present invention is best illustrated in the accompanying drawing, generally designated in Figure 1 by reference number 10. It should be noted that the system of the reaction sketched in Figure 1 is intended to be merely exemplary. The present invention is suitable for any conventional fluidized bed reaction systems. Referring now to Figure 1, the reactor 10 comprises a reaction zone 12 and a free boarding area which in this case is also a speed reduction zone 14. The height-to-diameter ratio of the reaction zone 12 can vary, depending on the production capacity and the desired residence time. The reaction zone 12 includes a fluidized bed comprising polymer particles in development, existing formed polymer particles, and small amounts of catalyst. The fluidized bed in the reaction zone 12 is supported by a recycle stream or fluidization means 16, generally constituted by feed and recycle fluids. The recycle stream enters the reactor through a distributor plate 18 in the lower section of the reactor, which aids in the uniform fluidization and support of the fluidized bed in the reaction zone 12. In order to maintain the fluidized bed of the Reaction zone 12 in a suspended and viable state, the gas surface velocity of the gas flow through the reactor generally exceeds the minimum flow required for fluidization. The polymer particles in the reaction zone 12 help to prevent the formation of localized "hot spots" and trap and distribute the catalyst particles throughout the fluidized bed. Upon starting, the reactor 10 is charged with a polymeric particle base before the flow of the recycle stream 16 is introduced. These polymer particles are preferably equal to the new polymer particles to be produced.; however, if they are different, they are removed with the first newly formed product after the start of the recycle and catalyst flows and the establishment of the reaction. This mixture is generally segregated from the subsequent essentially new production for alternate arrangement. The catalysts used in the improved process of this invention are usually oxygen sensitive; therefore, the catalyst is preferably stored in a catalyst tank 20 under a blanket of a gas, inert to the stored catalyst, such as but not limited to nitrogen or argon. The fluidization of the fluidized bed in the reaction zone 12 is achieved by the high rate at which the recycle stream 16 flows to and through the reactor 10. Typically in operation, the rate of the recycle stream 16 is approximately 10 to 50. times the rate at which the feed is introduced into the recycle stream 16. This high rate of recycle stream 16 provides the surface gas velocity needed to suspend and mix the fluidized bed in the reaction zone 12 in a fluidized state . The fluidized bed has an appearance generally similar to that of a vigorously boiling liquid, with a dense mass of individually moving particles caused by percolation and bubbling of gas through the fluidized bed. As the recycle stream 16 passes through the fluidized bed in the reaction zone 12, there is a pressure drop. This pressure drop is equal to or slightly greater than the weight of the fluidized bed in the reaction zone 12, divided by the cross-sectional area of the reaction zone 12, thus making the pressure drop dependent on the geometry of the reactor . Referring again to Figure 1, the feed enters the recycle stream 16 in, but not limited to, a point 22. The gas analyzer 24 receives gas samples from the recycle stream 16 and monitors the composition of the recycle stream 16. the recycle stream 16 passing through it. The gas analyzer 24 is also adapted to regulate the composition of the recycle stream line 16 and the feed to maintain a stable state in the composition of the recycle stream 16 in the reaction zone 12. The gas analyzer 24 usually analyzes samples taken from the recycle stream line 16 at a point between the free approach zone 14 and a heat exchanger 26, preferably between a compressor 28 and the heat exchanger 26. The recycle stream 16 passes upwards to through the reaction zone 12, adsorbing heat generated by this polymerization process. That portion of the recycle stream 16 that does not react in the reaction zone 12 leaves the reaction zone 12 and passes through the free boarding or speed reduction zone 14. As previously described, in this region, the speed reduction zone 14, a larger portion of the trapped polymer falls back into the fluidized bed in the reaction zone 12, thereby reducing the amount of solid polymer particles that are carried to the recycle stream line 16. The flow of recycle 16, once removed from the reactor on the free boarding zone 14, is then compressed in the compressor 28 and passes through the heat exchanger 26, where the heat generated by the polymerization reaction and the gas compression is removed from the the recycle stream 16 before returning the recycle stream 16 back to the reaction zone 12 in the reactor 10. The heat exchanger 26 is of conventional type and can be placed in of the recycle stream line 16 either in a vertical or horizontal position. In an alternative embodiment of this invention, more than one heat exchange zone or compression zone may be included within the recycle stream line 16. Referring back to Figure 1, the recycle stream 16, coming out of the heat exchanger 26 returns to the bottom of the reactor 10. Preferably, a fluid flow deflector 30 prevents polymer from settling in a solid mass and keeps the entrapment of liquid particles and polymeric within the recycle stream 16 below the distributor plate 18. The preferred type of fluid flow deflector plate is in the form of an annular disk, for example of the type described in United States Patent No. 4,933,149. Using an annular type disk provides both upward central flow and external peripheral flow. The central flow upwards helps in the entrapment of droplets of liquid in the lower head and the external peripheral flow helps to minimize the accumulation of polymer particles in the lower head. The distributor plate 18 diffuses the recycle stream 16 to prevent the current from entering the reaction zone 12 in a centrally arranged upwardly moving stream or jet, which would break fluidization of the fluidized bed in the reaction zone 12. The temperature of the fluidized bed is fixed in a manner dependent on the point of particle bonding, but basically it depends on three factors: (1) the activity of the catalyst and the rate of catalyst injection that controls the rate of polymerization and the consequent rate of generation of heat, (2) the temperature, pressure and composition of the recycle and feed streams introduced into the reactor, and (3) the volume of the recycle stream passing through the fluidized bed. The amount of liquid introduced into the bed, either with the recycle stream or by separate introduction, as previously described, especially affects the temperature because the liquid vaporizes in the reactor and serves to reduce the temperature of the fluidized bed. Usually, the rate of catalyst addition is used to control the rate of polymer production. The temperature of the fluidized bed in the reaction zone 12 in the preferred embodiment remains constant in a stable state by continuously withdrawing the heat of reaction. A stable state of the reaction zone 12 occurs when the amount of heat generated in the process is balanced with the amount of heat removed. Consequently, the temprature, pressure and composition at any given point in the process are constant over time. There is no significant temperature gradient in the lower part of the fluidized bed in the reaction zone 12 in the region on the gas distributor plate 18. This gradient results from the difference between the temperature of the recycle stream 16 entering through of the distributor plate 18 in the lower part of the reactor 10 and the temperature of the fluidized bed in the reaction zone 12. The efficient operation of the reactor 10 requires good distribution of the recycle stream 16. If the developing particles were allowed to settle or formed of polymer and catalyst outside the fluidized bed, fusion of the polymer could occur. In an extreme case, this can result in the formation of a solid mass throughout the reactor. A commercial-sized reactor contains thousands of pounds or kilograms of polymer solids at any given time. The removal of a solid mass of polymer of this magnitude would imply great difficulty, requiring a substantial effort and a prolonged time of unemployment. Determining the stable operating conditions with the aid of improved polymerization processes with bulk density measurement can be carried out, in cases where the fluidization and the fluidized bed support in the reaction zone 12 inside the reactor 10 are maintained. In the preferred embodiment, variations in fluidized bulk density for a given degree of polymer and / or catalyst composition are used to optimize process conditions and plant design. The fluidized bulk density is the ratio of the pressure drop measured upwards through a centrally fixed portion of the reactor to the height of this fixed portion. It is a mean value, which may be greater or less than the bulk density located at any point in the fixed reactor portion. It should be understood that under certain conditions known to those skilled in the art, an average value can be measured, which is greater or less than the bulk density of the localized bed. The inventors have discovered that as the concentration of the condensable component in the gas stream flowing through the bed increases, an identifiable point can be reached beyond which there is a danger of process failure if the concentration is further increased. This point is characterized by an irreversible reduction in the fluidized bulk density with an increase in the concentration of condensable fluid in the gas. The liquid content of the recycle stream entering the reactor may not be directly relevant. The reduction in fluidized bulk density generally occurs without corresponding change in the settled bulk density of the granules of the final product. In this way, the change in fluidization behavior reflected by the reduction in fluidized bulk density apparently does not imply any permanent change in the characteristics of the polymer particles. The concentrations of gaseous condensable fluid at which reductions in fluidized bulk density occur depend on the type of polymer being produced and other process conditions. They can be identified by monitoring the fluidized bulk density with increasing concentrations of condensable fluid in the gas for a given type of polymer and other process conditions. The fluidized bulk density (FBD) depends on other variables in addition to the concentration of condensable fluid in the gas, including, for example, the surface velocity of the gas flowing through the reactor, and the particle characteristics such as size, density and settled bulk density (SBD), as well as gas density, viscosity, temperature and pressure. Thus, in tests to determine changes in fluidized bulk density attributable to changes in the concentration of gaseous condensable fluid, significant changes in other conditions must be avoided. Therefore, it is within the scope of this invention to monitor these other variables from which the fluidized bulk density can be determined, which affect bed instabilities. For purposes of this application, monitoring or maintaining the fluidized bulk density includes monitoring or maintaining those variables described above that affect the fluidized bulk density or are used to determine the fluidized bulk density. Although some modest fall in fluidized bulk density can be accommodated, without loss of control, additional changes in gas composition or other variables, which also increase the dew point temperature, can be accompanied by an irreversible reduction in density at fluidized bulk, the development of "hot spots" in the reactor bed, the formation of molten agglomerates, and eventual reactor shutdown. Other practical consequences directly related to the reduction of the fluidized bulk density include a reduced polymeric capacity of a fixed volume reactor discharge system and a reduced residence time in polymer / catalyst reactor at a constant rate of production of polymer. The latter can, for a given catalyst, reduce the catalyst productivity and increase the level of catalyst residues in the polymer product. In a preferred embodiment, it is desirable to minimize the concentration of condensable fluid in the gas for a given target reactor production rate and the associated cooling requirements. By using such variations in fluidized bulk density, stable operating conditions can be defined. Once an appropriate composition has been identified, the composition can be used to achieve much higher cooling capacities for the recycle stream (without encountering bed instabilities) by cooling that composition to a greater extent. Non-polymerizable, condensable materials may be added in appropriate amounts so that a particular degree achieves high reactor productivity while maintaining good conditions in the fluidized bed while remaining within the stable operating zone thus determined. High reactor productivity can be achieved in a process or, in terms of plant design, a large capacity plant can be designed with a relatively small reactor diameter or existing reactors can be modified to provide increased capacity without changing the reactor size . At higher productivities of the reactor, it has been found that, remaining within the limits defined by the acceptable changes in fluidized bulk density, condensed liquid levels can be accommodated well above typically more than about 15, 18, 20, 22 , 25, 27, 30 or even 35%, while avoiding significant levels of chip formation or lamination that are a result of the fluidized bed disruption. The condensed liquid levels based on the total weight of the recycle stream or the fluidization medium are in the range of between 15 and 50% by weight, preferably more than 20 to 20% by weight, and even with greater preference of 20 to about 40% by weight, and most preferably from about 25 to about 40% by weight. Preferably, the fluidized bulk density is observed using a pressure difference measurement from a part of the fluidized bed not susceptible to disturbances on the distributor plate. Meanwhile, conventionally, variations in the fluidized bulk density in the lower part of the bed can be taken as indicative of the bed disruption on the distributor plate, while the higher fluidized bulk density measured away from the distributor plate is used as a In a stable reference, it has now surprisingly been found that changes in the higher fluidized bulk density correlate with changes in the composition of the stream and can be used to find and define zones of stable operation. The bulk density function (Z), as defined herein, is Z = [(Pbf - Pg) / Ph3 / (Ps - Pg) / Ps] where Pb £ is the fluidized bulk density, Pbs is the bulk density settled, Pg is the density of gas, and Ps is the solid density (resin). The bulk density function (Z) can be calculated from process and product measurements. In one embodiment, the bulk density function (Z) is defined as Z less than or equal to 0.59-Pg / Pbs / 1-Pg / Ps where Pbf is the fluidized bulk density, Pbs is the bulk density settled , Pg is the density of gas, and Ps is the solid density (resin). In the present invention, disruption of fluidization is prevented by keeping the value of the bulk density function (Z) around about the minimum or limit values shown in the following Tables A and B based on the values calculated for X and Y For the purposes of this patent description and the appended claims, X and Y are defined according to the following equations: X = LOG [dpPgU0 / μ] Y = LOG [gdp3Pbs (Ps-Pg) / Psμ2l where dp is the average heavy particle diameter, g is the acceleration of gravity (9.805 m / sec2), U0 is the superficial velocity of gas, and μ is the viscosity of gas. For the purposes of this patent disclosure and the appended claims, the calculated limit of the bulk density function is based on the values for the function X and Y calculated using the above formulas. The calculated limit is the determined number of Tables A and / or B using the calculated values for X and Y. Table A shows the values for the calculated limit of the bulk density function for the X and Y ranges. Table B shows the values for the calculated limit of the bulk density function for the preferred ranges of X and Y. Although Tables A and / or B represent only point values selected for X and Y, a person skilled in the art will recognize that it will generally be necessary to interpolate the values of X and Y to obtain a corresponding limit Z-value. In a preferred embodiment, the bulk density function (Z) is maintained at a value greater than or equal to, more preferably greater than, the value provided in Tables A and / or B using the values for X and Y In still another embodiment, the bulk density function (Z) is maintained at a level greater than 1% over the value limit of the bulk density function determined from Tables A and B and with greater preference greater than 2%, even with greater preference greater than 4%, and with greater preference greater than 5%. In yet another embodiment, the bulk density function (Z) is in the range of about 0.2 to 0.7, preferably in the range of about 0.3 to about 0.6, with greater preference greater than about 0.4 to around 0.6. The particle diameter (dp) can be in the range of 100 to 3,000 microns, preferably of about 500 to 2,500 microns, more preferably of about 500 to 2,000 microns, most preferably 500 to 1,500 microns. The gas viscosity (μ) may be in the range of about 0.01 to about 0.02 centipoise (cp), preferably 0.01 to 0.18 cp, and most preferably 0.011 to about 0.015 cp. The settled bulk density (SBD or Pbs) can be in the range of about 10 to 35 lb / ft3 (160.2 to 561 kg / m3), preferably around 12 to 35 lb / ft3 (193 to 561 kg / m3), more preferably from about 14 to 32 lb / ft3 (224.3 to 513 kg / m3) and most preferably from about 15 to 30 lb / ft3 (240.3 to 481 kg / m3). The gas density (Pg) can be in the range of about 0.5 to about 4.8 lb / ft3 (8 to 77 kg / m3), preferably about 1 to 4 lb / ft3 (16 to 64.1 kg / m3) ), more preferably from about 1.1 to about 4 lb / ft3 (17.6 to 64.1 kg / m3), and most preferably from about 1.2 to about 3.6 lb / ft3 (19.3 to 57.9 kg / m3). The resin solid density (Ps) may be in the range of 0.86 to about 0.97 g / cc, preferably in the range of 0.87 to about 0.97 g / cc, more preferably in the range of 0.875 to about 0.970. g / cc, and most preferably in the range of 0.88 to about 0.97 g / cc. The temperature of the reactor can be between 60 and 120 ° C, preferably 60 to 115 ° C, and most preferably in the range of 70 to 110 ° C. The reactor pressure can be 100 to 1,000 psig (689.5 to 6,895 kPag), preferably around 150 to 600 psig (1,034 to 4,137 kPag), more preferably 200 to about 500 psig (1,379 to 3,448 kPag), and with the greatest preference between 250 to 400 psig (1,724 to 2,758 kPag).

TABLE A Limit Bulk Density Function TABLE B Bulk Density Function Preferred Rank Limit Advantageously, the recycle stream is cooled and passes at a rate through the reactor such that the cooling capacity is sufficient for a reactor productivity expressed in pounds (lbs) of polymer per hr / ft 2 of cross-sectional area of the reactor exceeding of 500 lb / hr-ft2 (2,441 kg / hr-m2), especially 600 lb / hr-ft2 (2,929 kg / hr-m2), involving a change of enthalpy of the recycle stream of the reactor inlet conditions with the reactor outlet conditions of at least 40 Btu / lb (22 cal / g), preferably 50 Btu / lb (27 cal / g). Preferably, the liquid and gaseous components of the stream are added in a mixture below the distributor plate of the reactor. This reactor productivity is equal to the yield in space time multiplied by the height of the fluidized bed. In the preferred embodiment of the present invention, the liquid introduced into the reactor 10 is vaporized in order to achieve the benefits of the increased cooling capacity of the reactor of this polymerization process. High levels of liquid in the bed can promote the formation of agglomerates that can not be broken by mechanical forces present in the bed, thus potentially leading to defluidization, bed collapse and reactor shutdown. In addition, the presence of liquids can influence the local temperatures of the bed and affect the ability of the process to produce polymer having consistent properties, since this requires an essentially constant temperature throughout the bed. For these reasons, the amount of liquid introduced into the fluidized bed under a given set of conditions should not materially exceed the amount that will vaporize in the lower region of the fluidized bed, where the mechanical forces associated with the inlet of the recycle stream through the The distributor plate are sufficient to break up the agglomerates formed by the interaction of liquid and particles. It has been discovered in this invention that, for a given composition and physical characteristics of the product particles in the fluidized bed and reactor and recycle conditions related or otherwise given, defining boundary conditions related to the composition of the flowing gas Through the bed, a viable fluidized bed can be maintained at high cooling levels. While not wishing to be bound by any theory, the inventors suggest that the observed reduction in fluidized bulk density may reflect an expansion of the dense particulate phase and changes in the behavior of bubbles within the fluidized bed. Referring back to Figure 1, a catalyst activator, if required, depending on the catalyst used, it is generally added downstream of the heat exchanger 26. The catalyst activator can be introduced from a dispenser 32 into the recycle stream 16. However, the improved process of the present invention is not limited to the location of the insertion of the catalyst activator or any other required components such as catalyst promoters. The catalyst of the catalyst tank can be injected either intermittently or continuously into the fluidized bed reaction zone 12 at a preferred rate at a point 34 that is on the gas distributor plate 18. In the preferred embodiment, as described above, the catalyst is injected at a point where mixing with polymer particles within the fluidized bed 12 is best achieved. Because some catalysts are highly active, the preferred injection in the reactor 10 must be on the gas distributor plate 18, not below it. The injection of catalyst into the area below the gas distributor plate 18 can result in polymerization of the product in this area, which would eventually result in plugging of the gas distributor plate 18. Also, introducing the catalyst onto the plate Gas distributor 18 assists in the uniform distribution of catalyst throughout the fluidized bed 12 and, therefore, helps prevent the formation of "hot spots" resulting from high local concentrations of catalyst. The injection is preferably in the lower portion of the fluidized bed in the reaction zone 12 to provide uniform distribution and to minimize the transport of catalyst to the recycle line where the polymerization may lead to eventual clogging of the recycle line and the exchanger of heat. A variety of techniques for catalyst injection can be used in the improved process of the present invention, for example the technique described in U.S. Patent No. 3,779,712, the disclosure of which is incorporated herein by reference. An inert gas such as nitrogen, or an inert liquid that volatilises easily under reactor conditions, is preferably used to bring the catalyst to the reaction zone 12 of the fluidized bed. The catalyst injection rate and monomer concentration in the recycle stream 16 determine the rate of polymer production in the reaction zone 12 of the fluidized bed. It is possible to control the production rate of the polymer produced by simply adjusting the catalyst injection rate. In the preferred mode of operation of the reactor 10 using the improved process of the present invention, the height of the fluidized bed in the reaction zone 12 is maintained by the removal of a portion of the polymer product at a rate consistent with the formation of the polymeric product . Instrumentation is useful to detect any change in temperature or pressure throughout the reactor 10 and the recycle stream 16 to monitor changes in the condition of the fluidized bed in the reaction zone 12. Likewise, this instrumentation allows the adjustment either manual or automatic of the catalyst injection rate and / or the temperature of the recycle stream. In operation of the reactor 10, the product is removed from the reactor by means of a discharge system 36. The discharge of the polymer product is preferably followed by the separation of fluids from the polymer product. These fluids can be returned to the recycle stream line 16 as a gas at point 38 and / or as a condensed liquid at point 40. The polymer product is routed to downstream processing at point 42. The discharge of the product Polymeric is not limited to the method shown in Figure 1, which illustrates only one particular discharge method. Other discharge systems can be used, for example those described and claimed in U.S. Patent Nos. 4,543,399 and 4,588,790, to Jenkins, III et al. According to the present invention, a process for increasing reactor productivity in polymer production in a fluidized bed reactor using an exothermic polymerization reactor is provided by cooling the recycle stream to less than its dew point and returning the current of resulting recycle to the reactor. The recycle stream containing more than 15, preferably more than 20% by weight of liquid can be recycled to the reactor to maintain the fluidized bed at a desired temperature.

In the process of the invention, the cooling capacity of the recycle stream or the fluidization medium can be significantly increased both by the vaporization of the condensed liquids trapped in the recycle stream and as a result of the greater temperature differential between the incoming recycle stream and the temperature of the fluidized bed. In one embodiment, the polymer product produced by the process of the invention has a density in the range of about 0.90 to about 0.939 g / cc. In the preferred embodiment, the polymers, homopolymers or copolymers produced are selected from a film grade resin having an MI of 0.01 to 5.0, preferably 0.5 to 5.0, and a density of 0.900 to 0.930; or a molding grade resin having an MI of 0.10 to 150.0, preferably 4.0 to 150.0, and a density of 0.920 to 0.939; or a high density resin having an MI of 0.01 to 70.0, preferably 2.0 to 70.0, and a density of 0.940 to 0.970; all units of density being in g / cm3 and the melt index (MI) being in g / 10 min, as determined according to method ASTM-1238, condition E. Depending on the target resin, different conditions can be adopted of recycling, providing levels of reactor productivity not previously contemplated. First of all, for example, a film-grade resin in which the recycle stream has a butene / ethylene molar ratio of 0.001 to 0.60, preferably 0.30 to 0.50 or a molar ratio of 4-methyl can be produced. -pentene-1 / ethylene from 0.001 to 0.50, preferably 0.08 to 0.33, or a mole ratio of hexene / ethylene from 0.001 to 0.30, preferably 0.05 to 0.20; or a mole ratio of octene-1 / ethylene from 0.001 to 0.10, preferably 0.02 to 0.07; a hydrogen / ethylene molar ratio of 0.00 to 0.4, preferably 0.1 to 0.3; and an isopentane level of 3 to 20 mol% or an isohexane level of 1.5 to 10 mol%, and wherein the cooling capacity of the recycle stream is at least 40 Btu / lb, preferably at least 50 Btu / lb, or the percent by weight condensate is at least 15, preferably more than 20. Second, the process can be used to yield a molding-grade resin in which the recycle stream has a molar ratio of butene-1 / ethylene from 0.001 to 0.60, preferably from 0.10 to 0.50, or a molar ratio of 4-methyl-pentene-1 / ethylene from 0.001 to 0.30, preferably 0.05 to 0.12, or a mole ratio of octene-1 / ethylene from 0.001 to 0.10, preferably 0.02 to 0.04; a hydrogen / ethylene molar ratio of 0.00 to 1.6, preferably 0.3 to 1.4; and an isopentane level of 3 to 30 mol%, or an isohexane level of 1.5 to 15 mol%, and where the cooling capacity of the recycle stream is at least 40 Btu / lb, preferably at least 50 Btu / lb, or the percentage by weight of condensate is at least 15, preferably more than 20. Also, resins with high density grades can be made by a process in which the recycle stream has a butene / ethylene molar ratio of 0.001 to 0.30, preferably 0.001 to 0.15, or a molar ratio of 4-methyl-pentene-1 / ethylene from 0.001 to 0.25, preferably 0.001 to 0.12, or a mole ratio of hexene / ethylene from 0.001 to 0.15, preferably 0.001 to 0.07, or a molar ratio of octene-l / ethylene from 0.001 to 0.05, preferably 0.001 to 0.02; a molar ratio of hydrogen to ethylene from 0.00 to 1.5, preferably 0.3 to 1.0; and an isopentane level of 10 to 40 mol%, or an isohexane level of 5 to 20 mol%, and where the cooling capacity of the recycle stream is at least 60 Btu / lb, preferably more than 75 Btu / lb, and most preferably more than at least 75 Btu / lb, or the percent by weight condensate is at least 12, preferably greater than 20. In plums In order to provide a better understanding of the present invention, including advantages and representative limitations of it, the following examples are offered in relation to the actual tests carried out in the practice of this invention. Example 1 A fluidized gas phase reactor was operated to produce a copolymer containing ethylene and butene. The catalyst used is a complex of tetrahydrofuran, magnesium chloride and titanium chloride, reduced with diethyl aluminum chloride (molar ratio of diethyl aluminum chloride to tetrahydrofuran of 0.30), impregnated on silicon dioxide treated with triethyl aluminum. The activator is triethyl aluminum (TEAL). The data in Table 1 and illustrated in Figure 2 show the parameters of the reactor as the level of isopentane gradually increases to achieve the additional cooling required to obtain higher reactor productivity. This example shows that excessive amounts of isopentane lead to changes in the fluidized bed and finally to its disruption in the formation of hot spots and agglomerates that need to stop the reactor. As the concentration of isopentane increases, the fluidized bulk density decreases, indicating a change in fluidization of the bed which also results in an increase in the bed height. The catalyst rate was reduced in an attempt to reverse the change in the fluidized bed. However, at this point, although the bed height returned to normal, the disruption accompanied by hot spots and agglomerations in the bed was irreversible and the reactor was stopped. Further, from the data in Table 1, it can be seen that the operation of the reactor was stable while the value of the bulk density function (Z) remained at a level above the calculated limit (based on the values for the X and Y functions and Tables A and B). Once the value of the bulk density function (Z) fell below the calculated limit value, the operation of the reactor became unstable and had to be stopped.

TABLE 1 * Based on the values for the X and Y functions, Tables A and B were used to determine the limits. In addition, in a second run, Table 2 and Figure 3 show that as the concentration of isopentane increases gradually, the fluidized bulk density is reduced, as expected from Table 1. However, this time the fluidized bulk density increased gradually as a result of reducing the isopentane concentration. Thus, in this case, the change in fluidization of the bed was recoverable and reversible. The data in Table 2 show that keeping the value of the bulk density function (Z) equal to or greater than the calculated limit value (determined from the values for the X and Y function and Tables A and B), the change in fluidization of the bed remained stable.

TABLE 2 * Based on the values for the X and Y functions; Tables A and B were used to determine the limits.

The bulk density function shown in Tables 1 and 2 clearly illustrates a point at which changes in fluidization of the bed are not reversible, due to the excessive use of a condensable fluid. This point is defined to be where the bulk density (Z) function becomes smaller than the limit value calculated for the bulk density function. In "amp 2" The following examples were carried out essentially in the same manner as in Example 1, using the same type of catalyst and activator to produce ethylene / butene homopolymers and copolymers of various density ranges and melt index.

TABLE 3 * Based on the values for the X and Y functions; Tables A and B were used to determine the limits.

These runs demonstrate the advantages of achieving higher reactor productivities at condensed liquid levels exceeding 20% by weight, while maintaining the bulk density function (Z) above the limit values calculated for the bulk density function, such as It was defined earlier. Due to the downstream handling processes, for example, product discharge systems, extruders and the like, certain reactor conditions had to be manipulated in order not to exceed the overall capacity of the plant. Therefore, the full advantages of this invention can not be fully appreciated by the examples shown in Table 3. For example, in Run 1 of Table 3, the gas surface velocity was kept low at about 1.69 ft / sec ( 0.52 m / sec) and, therefore, the performance in the reflected time space is much smaller than what would otherwise be the case. If the speed were maintained at around 2.4 ft / sec (0.74 m / sec), the estimated space time performance would be more than 15.3 lb / hr-ft3 (244.8 kg / hr-m3). Runs 2 and 3 of Table 3 show the effect of operating a reactor at a high gas surface velocity and a condensed weight percentage well above 20%. The achieved space time yields were around 14.3 and 13.0 lb / hr-ft3 (228.8 and 208 kg / hr-m3), demonstrating a significant increase in the production rate. Such high STY or high production rates are neither taught nor suggested by Jenkins, III and collaborators. Similar to run 1, Run 4 of Table 3 shows a gas surface velocity of 1.74 ft / sec (0.53 m / sec) to 21.8% by weight of condensed liquid. If the speed in run 4 is increased to 3.0 ft / sec (0.92 m / sec), the STY that could be achieved would increase from 7.7 to 13.3 lb / hr-ft3 (123.2 to 212.8 kg / hr-m3). If the speed in run 5 is increased to 3.0 ft / sec (0.92 m / sec), the space time performance that could be achieved would increase from 9.8 to 17.0 lb / hr-ft3 (156.8 to 272 kg / hr-m3) ). For all runs 1-5, the fluidized bulk density function (Z) was maintained on the limit value for the bulk density function, as defined above. Example 3 The data shown for the cases of Example 3, Table 4, were prepared by extrapolating information from real operations using thermodynamic equations well known in the art to project the objective conditions. These data in Table 4 illustrate the advantages of this invention if limitations of the auxiliary equipment of the reactor are removed.

TABLE 4 * Based on the values for the X and Y functions; Tables A and B were used to determine the limits.

In run 1, the surface gas velocity is increasing from 1.69 ft / sec to 2.40 ft / sec (0.52 m / sec to 0.74 m / sec), which gives an STY greater than 15.3 lb / hr-ft3 (244.8 kg / hr-m3) compared to the initial value of 10.8 lb / hr-ft3 (172.8 kg / hr-m3). In an additional step, the recycle inlet stream is cooled to 40 ° C from 46.2 ° C. This cooling increases the level of recycle condensate to 34.4% by weight and allows additional improvement in the STY at 18.1 lb / hr-ft3 (289.6 kg / hr-3). In the last step, the composition of the gas is changed by increasing the concentration of the condensable inert, isopentane, thereby improving the cooling capacity. Thanks to these means, the level of recycle condensate increases further to 44.2% by weight and the STY reaches 23.3 lb / hr-ft3 (372.8 kg / hr-m3). Globally, the steps in increments provide a 116% increase in the production capacity of the reactor system. In run 2, the recycle inlet temperature is cooled to 37.8 ° C from 42.1 ° C. This cooling increases the recycle condensate from 25.4 to 27.1% by weight, and an increase in STY from 14.3 to 15.6 lb / hr-ft3 (228.8 to 249.6 kg / hr-m3). In a further step, the concentration of C6 hydrocarbons is increased from 7 to 10 mol%. This improvement in cooling capacity allows an increase in STY to 17.8 lb / hr-ft3 (284.8 kg / hr-m3). As a final step to demonstrate the value of this improvement, the recycle inlet temperature is again reduced to 29.4 ° C. This additional cooling allows an STY of 19.8 lb / hr-ft3 (316.8 kg / hr-m3) upon reaching the condensate level of the recycle stream of 38.6% by weight. Globally, incremental steps provide a 39% increase in the production capacity of the reactor system. Although the present invention has been described and illustrated with reference to particular embodiments thereof, those skilled in the art will appreciate that the invention lends itself to variations not necessarily illustrated herein. For example, it is within the scope of this invention to use an increased activity catalyst to increase the production rate or reduce the temperature of a recycle stream using refrigeration units. For this reason, then, references should be made only to the appended claims for the purposes of determining the true scope of the present invention.

Claims (14)

1. CLAIMS 1. A process for polymerizing alpha-olefin (s) in a gas phase reactor having a fluidized bed and a fluidization medium having a gas phase and a liquid phase entering the reactor, said process comprising: a) controlling the cooling capacity of said fluidization means controlling the ratio of said gas phase to said liquid phase; b) calculate a bulk density function limit (as defined herein); c) maintain or supervise a bulk density function; and d) adjusting the bulk density function to maintain the bulk density function at a value greater than or equal to the calculated limit of the bulk density function.
2. 2. A continuous process for polymerizing alpha-olefin (s) in a gas phase reactor having a fluidized bed and a fluidization medium having a gas phase and a liquid phase entering the reactor, said process comprising: a) controlling the cooling capacity of said fluidization means by controlling the ratio of said gas phase to said liquid phase; and b) maintain a bulk density function at a value greater than or equal to a calculated limit of the bulk density function (as defined herein).
3. 3. A continuous process for increasing the reactor productivity of a gas phase polymerization reactor having a fluidization medium and a fluidized bed, said process comprising passing a gaseous stream comprising monomer through a reaction zone in the presence of a catalyst for producing a polymer product, removing said polymer product, removing said fluidization medium comprising unreacted monomer from said reaction zone, mixing said fluidization medium with hydrocarbon and polymerizable monomer (s) to form a liquid and a gaseous phase, and recycling said fluidization medium to said reactor, the process comprising: a) introducing said hydrocarbon into said fluidization means to allow an increase in the cooling capacity of the fluidization medium over at least 40 Btu / lb ( 22 cal / g); b) increase the withdrawal rate of the polymer product above at least 500 lb / hr-ft2 (2,441 kg / hr-m2); c) calculate a bulk density function limit (as defined herein); and d) maintaining a value of the bulk density function greater than or equal to the calculated limit of the bulk density function.
4. 4. A process for polymerizing alpha-olefin (s) in a gas phase reactor having a fluidized bed and a fluidization medium comprising a gas phase to produce a polymeric product, wherein the fluidization medium serves to control the capacity of the fluid. cooling of said reactor, the process comprising employing in the fluidization medium a liquid level entering the reactor that is greater than 15% by weight based on the total weight of the fluidization medium and calculating a limit of the density function a bulk (as defined herein), where the bulk density function is maintained at a value greater than or equal to the calculated limit of the bulk density function. The process according to claim 3, wherein the liquid level is in the range of 15 to 50% by weight, preferably in the range of 20 to 40% by weight based on the total weight of the fluidization medium . The process according to any of the preceding claims 3 to 5, wherein the liquid level is greater than 20% by weight, preferably greater than 22% by weight, more preferably greater than 25% by weight of liquid, based on the total weight of the fluidization medium. The process according to any of the preceding claims 3 to 6, wherein the polymer product is removed at a rate greater than 500 lb / hr-ft2 (2,441 kg / hr-m2), preferably greater than 600 lb / hr -ft2 (2.929 kg / hr-m2). 8. The process according to any of the preceding claims, where the bulk density function is greater than the calculated limit of the bulk density function. 9. The process according to any of the preceding claims, wherein the calculated limit is in the range of 0.2 to 0.7, preferably 0.3 to 0.6, more preferably 0.4 to 0.6. The process according to any of the preceding claims, wherein the bulk density function is greater than 1%, preferably 2%, over the calculated limit of the bulk density function. The process according to any of the preceding claims, wherein said fluidizing means comprises: i) butene-1 and ethylene at a molar ratio of 0.001 to 0.60 or 4-methyl-pentene-1 and ethylene at a molar ratio of 0.001 to 0.50, or hexene-1 and ethylene at a molar ratio of 0.001 to

   0. 30, or octene-1 and ethylene at a molar ratio of 0.001 to 0.10; ii) a condensable fluid comprising from 1.5 to 20 mol% of the fluidization medium, or i) butene-1 and ethylene at a molar ratio of 0.001 to

   0. 60, or 4-methyl-pentene-1 and ethylene at a molar ratio of

   0. 001 to 0.50, or hexene-1 and ethylene at a molar ratio of 0.001 to 0.30, or octene-1 and ethylene at a molar ratio of 0.001 to

   0. 10; ii) a condensable fluid comprising from 1.5 to 30 mol% of the fluidization medium, or i) butene-1 and ethylene at a molar ratio of 0.001 to

   0. 30, or 4-methyl-pentene-1 and ethylene at a molar ratio of

   0. 001 to 0.25, or hexene-1 and ethylene at a molar ratio of 0.001 to 0.15, or octene-1 and ethylene at a molar ratio of 0.001 to

   0. 05; ii) a condensable fluid comprising 5 to 40 mol% of the fluidization medium. The process according to any of the preceding claims, wherein the gas phase enters the reactor separately and apart from the liquid phase and / or where the liquid phase enters the reactor below the distributor plate. 13. The process according to any of the preceding claims 3 to 12, wherein the ratio of the fluidized bulk density to the settled bulk density is less than 0.59. The process according to any of the preceding claims, wherein the bulk density function is greater than or equal to (0.59-Pg / Pbs) / (1-Pg / Ps), where Pbf is the fluidized bulk density, Pbs is the settled bulk density, Pg is the gas density, and Ps is the solid density (resin).