MXPA97006175A - Procedure of polimerizac - Google Patents

Abstract

The invention relates to the continuous polymerization of olefins in fluidized bed with gas, especially ethylene, propylene or mixtures of these with other alpha-olefins, in which the recirculation gas containing the monomer used to fluidize the bed is passed through a separator. The separator is charged with, and kept at least partially filled with, liquid. The entrained catalyst and / or polymer particles are separated from the recirculating gas in the separator and these separated particles are kept in suspension in the separator liquid. The recirculation stream can be cooled to condense at least part of the liquid hydrocarbons, the condensed liquid, which may be a monomer or an inert liquid, is separated from the recirculating gas in the separator and fed directly to the bed to produce cooling by the latent heat of vaporization. the processing reduces fouling in the separated

Description

POLYMERIZATION PROCEDURE Field of the Invention The present invention relates to a continuous process for the gas phase polymerization of olefins in a fluidized bed reactor. Background of the Invention Procedures for the homopolymerization and copolymerization of olefins in the gas phase are well known in the art. Such processes can be carried out for example, by introducing the gaseous monomer into a stirred and / or fluidized bed comprising the polyolefin and a polymerization catalyst. In the polymerization of fluidized bed olefins, the polymerization is carried out in a fluidized bed reactor in which a bed of polymer particles is maintained in a fluidized state by means of a rising gas stream composed of the gaseous reaction monomer .

The initiation of said polymerization generally employs a bed of polymer particles similar to the polymer to be manufactured. During the course of the polymerization, new polymer is generated by the catalytic polymerization of the monomer, and the product polymer is extracted to maintain the bed at approximately constant volume. An industrially favored process employs a fluidization grid to distribute the fluidizing gas to the bed and, which acts as a support for the bed when the gas supply is cut off. The polymer produced is generally removed from the reactor through a discharge conduit disposed in the lower part of the reactor, close to the fluidization grid. The fluidized bed comprises a bed of growing polymer particles. This bed is maintained in a fluidized state by means of the continuous upward flow from the base of the fluidizing gas reactor. The polymerization of olefins is an exothermic reaction and, therefore, it is necessary to provide means to cool the bed and remove the polymerization heat. In the absence of such cooling, the bed would increase in temperature and, for example, the catalyst would become inactive or the bed would start to melt. In the polymerization of fluidized bed olefins, the preferred process for the removal of the polymerization heat is to supply to the polymerization reactor a gas, the fluidizing gas, which is at a temperature lower than the desired polymerization temperature, by passing the gas through through the fluidized bed to remove the polymerization heat, extracting the gas from the reactor and cooling it by means of a passage through an external heat exchanger and recirculating it to the bed. The temperature of the recirculating gas can be adjusted in the heat exchanger to maintain the fluidized bed at the desired polymerization temperature. In this alpha-olefin polymerization process, the recirculating gas generally comprises a monomeric olefin, optionally with, for example, an inert diluent gas such as nitrogen or a gaseous chain transfer agent such as hydrogen. Thus, the recirculation gas serves to supply the monomer to the bed, fluidize the bed and maintain the bed at the desired temperature. The monomers consumed by the polymerization reaction are usually replaced by adding replacement gas to the recirculation gas stream. It is well known that the production rate (i.e., the hourly yield in terms of polymer weight produced per unit volume of reactor space per unit time) in commercial gas fluidized bed reactors of the above-mentioned type is limited by the maximum heat flow that can be extracted from the reactor. The removed heat flow can be increased, for example, by increasing the recirculation gas velocity and / or by reducing the recirculation gas temperature and / or by changing the heat capacity of the recirculation gas. However, there is a limit as to the recirculation gas velocity that can be used in commercial practice. Above this limit, the bed can become unstable or even escape from the reactor in the gaseous stream, leading to a blockage of the recirculation duct and to a damage of the recirculating or blower gas compressor. There is also a limit to the degree to which recirculation gas can be cooled in practice. This is determined mainly by economic considerations and, in practice, is usually determined by the temperature of the industrial cooling water available in the plant. If desired, cooling may be employed, but this increases production costs. The prior art suggests a series of methods for increasing the heat removal capacity of the recirculation stream, for example by introducing a volatile liquid. EP 89691 relates to a method for increasing the hourly efficiency in continuous gas fluidized bed processes for the polymerization of fluid monomers, the process comprising cooling part or all of the unreacted fluids to form a two-phase gas mixture and liquid entrained below the dew point and introduce said biphasic mixture back into the reactor. The specification of EP 89691 states that a primary limitation on the degree to which the recirculation gas stream can be cooled below the dew point lies in the requirement that the gas to liquid ratio be maintained at a level sufficient to maintaining the liquid phase of the biphasic fluid mixture in a entrained or suspended state until the liquid evaporates and further asserts that the amount of liquid in the gas phase will not exceed about 20 weight percent, and preferably will not exceed about 10 weight percent; percent by weight, provided that the velocity of the biphasic recirculation stream is high enough to maintain the liquid phase in suspension in the gas and to maintain the fluidized bed within the reactor. EP 89691 further discloses that it is possible to form a biphasic fluid stream within the reactor at the point of injection by separately injecting gas and liquid under conditions that produce a biphasic current, but that there is a small disadvantage in this mode of operation due to the added and unnecessary cost of the separation of the gas and liquid phases after cooling. EP 173261 relates to a particular means for the introduction of a recirculation current in fluidized-bed reactors and, in particular, to a means for the introduction of a recirculation stream composed of a two-phase mixture of gas and liquid entrained as it is described in EP 89691 (supra). WO 94/25495 describes a fluidized bed polymerization process comprising passing a gaseous stream composed of monomer through a fluidized bed reactor in the presence of a catalyst under reaction conditions, to produce polymer product and a composite stream by unreacted monomer gases, compression and cooling of said stream, mixing said stream with the components of the feed stream and recirculating a gas and a liquid phase to the reactor, a method for determining stable operating conditions comprising: (a) observe the changes in the density per unit volume of fluidization in the reactor associated with changes in the composition of the fluidizing medium; and (b) increasing the cooling capacity of the recirculation stream by changing the composition without exceeding the level at which a reduction in density per unit volume of fluidized bed or a parameter indicating it can be irreversible. US 5,436,304 relates to a process for the polymerization of alpha-olefins in a gas-phase reactor provided with a fluidized bed and a fluidizing medium, in which the fluidizing medium serves to control the cooling capacity of the reactor and wherein the function (Z) of the density per unit volume is maintained at a value equal to or greater than the calculated limit of the density function per unit volume. WO 94/28032, which is incorporated herein by reference, refers to a continuous gas-fluidized bed process, in which the recirculating gas stream is cooled to a temperature sufficient to form a liquid and a gas . By separating the liquid from the gas and then feeding the liquid directly to the fluidized bed at or above the point at which the gaseous current passing through the fluidized bed has substantially reached the temperature of the gaseous stream extracted from the reactor, the total amount can be increased of liquid that can be reintroduced in the fluidized bed polymerization reactor in order to cool the bed by evaporation of liquid, improving the cooling level to obtain the highest productivity. During the operation of the process described in WO 94/28032, the entrainment of catalyst and / or polymer particles (fines) in the gaseous recirculation stream can lead to fouling or blocking of the separator used to separate the liquid from the gas. Scale incrustations may also occur when the process operates without cooling the gaseous recirculation stream to a temperature at which the liquid condenses, for example, during the start of the process of WO 94/28032. SUMMARY OF THE INVENTION It has now been discovered that this problem can be overcome or at least alleviated by charging the separator with liquid. Thus, in accordance with the present invention, a continuous gas fluidized bed process is provided for the polymerization of olefin monomers selected from (a) ethylene, (b) propylene, (c) mixtures of ethylene and propylene, and ( d) one or more other alpha-olefins mixed with (a), (b) or (c), in a fluidized bed reactor by the continuous recirculation of a gas stream composed of at least part of the ethylene and / or propylene through of a fluidized bed in said reactor in the presence of a polymerization catalyst under reaction conditions, passing at least part of said gaseous stream extracted from said reactor through a separator, characterized in that: (a) the separator is charged with liquid; (b) the separator is kept at least partially filled with liquid; (c) the gaseous stream fed to the separator entrains catalyst and / or polymer particles; (d) substantially, all entrained catalyst and / or polymer particles are separated from the gas stream in the separator and held in suspension in the separator liquid; and (e) optionally, the liquid from the separator is introduced directly into the fluidized bed. Preferably, at least part of the gaseous stream withdrawn from the reactor is cooled to a temperature at which the liquid condenses, and at least part of the condensed liquid is separated from the gas stream in the separator. Preferably, the liquid from the separator is introduced directly into the fluidized bed above the upper limit of the temperature gradient between the incoming fluidizing gas (the gaseous stream fed to the reactor) and the bed rest. The present invention solves, or at least alleviates, the problem defined above, keeping the catalyst and / or polymer particles in suspension in the separator liquid. The liquid that is charged to the separator can be composed of condensable comonomers, for example, butene, hexene, 4-methylpent-l-ene and octene or inert condensable liquids, for example, pentane, isopentane, butane or hexane. The recirculation gaseous stream drawn from the reactor is composed of unreacted gaseous monomers and optionally, inert hydrocarbons, inert gases such as nitrogen, reaction promoters or moderators such as hydrogen, as well as entrained catalyst and / or polymer particles. The gaseous recirculation stream fed to the reactor additionally comprises replacement monomers sufficient to replace the monomers polymerized in the reactor. The process according to the present invention is suitable for the manufacture of polyolefins in the gas phase by the polymerization of one or more olefins, at least one of which is ethylene or propylene. The preferred alpha-olefins used in combination with ethylene and / or propylene in the process of the present invention are those with 3 to 8 carbon atoms. However, if desired, small amounts of alpha-olefins with more than 8 carbon atoms, for example 9 to 18 carbon atoms, may be employed. In this way, it is possible to produce ethylene or propylene homopolymers or copolymers of ethylene and / or propylene with one or more C3-C8 alpha olefins. Preferred alpha-olefins are but-1-ene, pent-1-ene, hex-1-ene, 4-methylpent-l-ene, oct-1-ene and butadiene. Examples of higher olefins which can be copolymerized with the primary ethylene and / or propylene monomers, or as partial replacement of the C3-C8 alpha-olefin comonomer are dec-1-ene and ethylidene norbornene. When the process for the copolymerization of ethylene or propylene with alpha-olefins is used, ethylene or propylene are present as major components of the copolymer, and preferably, they are present in an amount of at least 70%, more preferably at least 80% of monomers / total comonomers. The process according to the present invention can be used to prepare a wide range of polymer products, for example, linear low density polyethylene (LLDPE) based on copolymers of ethylene with butene, 4-methylpent-1-ene or hexene and polyethylene high density (HDPE) which may, for example, be homopolyethylene or ethylene copolymers with a small proportion of higher alpha-olefin comonomer, for example, butene, pent-1-ene, hex-1-ene or 4-methylpent -log. The condensing liquid of the recirculating gaseous stream may be a condensable monomer, for example, butene, hexene or octene used as a comonomer for the production of LLDPE or it may be an inert condensable liquid, for example butane, pentane or hexane. In the present specification, the term "condensable" means that the dew point of the gaseous composition comprising the condensable material is above the lower temperature of the recirculation circuit. It is important that the liquid evaporate within the bed under the polymerization conditions that are employed so that the desired cooling effect is obtained and the substantial accumulation of liquid in the bed is prevented. The process is particularly suitable for the polymerization of olefins at an absolute pressure of 0.5 to 6 MPa and at a temperature of 30 ° C to 130 ° C. For example, for the production of LLDPE, the temperature will suitably vary in the range of 75-90 ° C and for HDPE the temperature will vary from 80-105 ° C depending on the activity of the catalyst used. The polymerization reaction can be carried out in the presence of a catalyst system of the Ziegler-Natta type, consisting of a solid catalyst formed essentially by a transition metal compound and a complementary catalyst formed by an organic compound of a metal ( that is to say, an organometallic compound, for example an alkylaluminum compound). High activity catalyst systems have been known for years and are capable of producing large amounts of polymer in a relatively short time, thus making it possible to avoid the step of removing catalyst residues from the polymer. These high activity catalyst systems generally comprise a solid catalyst essentially based on transition metal, magnesium and halogen atoms. It is also possible to use a high activity catalyst, essentially composed of chromium oxide activated by a heat treatment and associated with a granular support based on a refractory oxide. The process is also suitable for use with metallocene catalysts and Ziegler catalysts supported on silica. The catalyst can suitably be used in the form of a prepolymer powder prepared previously during a prepolymerization step with the aid of a catalyst as described above. The prepolymerization can be carried out by any suitable method, for example, polymerization in a liquid hydrocarbon diluent or in the gas phase using a batch process, a semi-continuous process or a continuous process. Preferably, substantially all of the gaseous recirculation stream drawn from the reactor is cooled and the condensed liquid is separated and substantially all of the separated liquid is directly introduced into the fluidized bed. The recirculating gaseous stream is suitably cooled by means of an exchanger or heat exchangers to a temperature such that the liquid condenses in the recirculating gaseous stream. Suitable heat exchangers are known in the art. The recirculating gas stream leaving the head of the reactor carries a quantity of catalyst and / or polymer particles and most of these can be separated from the recirculating gas stream by means of a cyclonic separator. A small proportion of these particles are entrained in the gas stream of - - recirculation and separates, together with the condensed liquid, the gaseous recirculation current in the gas / liquid separator. Alternatively, the cyclone separator can be removed and substantially all entrained catalyst and / or polymer particles are separated from the recirculating gas stream in the gas / liquid separator. The separated fines can be introduced back into the fluidized bed together with the liquid stream of the gas / liquid separator. Preferably, the fines are reintroduced into the fluidized bed suspended in the liquid stream of the gas / liquid separator. Suitably, these particles can be kept suspended and thus avoid incrustations of the gas / liquid separator by, for example, agitation of the liquid in the gas / liquid separator (mechanical agitation), by bubbling a gaseous stream through the liquid or keeping it in circulation the liquid is continued by means of an external circuit, that is, the separator liquid is continuously withdrawn and returned to the separator. Preferably, a portion of the liquid in the separator is circulated continuously by means of a pump. Suitably enough liquid is circulated for the pump to run continuously. A portion of the circulating liquid can be introduced directly into the fluidized bed through a valve that opens to allow the entry of - liquid to a fluidized bed feed line. Preferably, the valve is actuated by a liquid level controller that controls and maintains the liquid level in the separator between the setpoint limits. The recirculating gaseous stream may also comprise inert hydrocarbons used for catalyst injection, activators or reaction moderators in the reactor. Replenishing monomers, for example ethylene or propylene, to replace the monomers consumed by the polymerization reaction can be added to the recirculating gas stream in any suitable position. The condensable replenishing comonomers, eg, butene, hexene, 4-methylpent-1-ene and octene, which replace the condensable comonomers consumed by the polymerization reaction can be introduced in liquid form and added to the recirculating gas stream in any position adequate Suitable separators are, for example, cyclone separators, large vessels that reduce the velocity of the gaseous stream to effect the separation of the condensed liquid and the fines (drum dehydrator), gas-liquid fog separators and liquid washers, for example, dust washer with Venturi constriction. Such separators are well known in the art.

The use of a mist-type gas-liquid separator is particularly advantageous in the process of the present invention. An additional advantage of the use of a mist-type separator is that the pressure loss in the separator may be less than in other types of separators, thereby improving the efficiency of the overall process. A fog separator particularly suitable for use in the process of the present invention is a commercially available vertical gas separator known as "Peerless" (Type DPV P8X). This type of separator uses the coalescence of liquid droplets on a separating device to separate the liquid from the gas. A large liquid reservoir is provided at the bottom of the separator for collecting the liquid and in which the condensable liquid is charged before the cooling of the recirculating gas stream begins to a temperature at which the liquid condenses. The liquid reservoir allows the liquid to be stored therein, providing control over the introduction of liquid from the separator to the fluidized bed. This type of separator is very effective and provides a 100% separation of condensed liquid from the gas stream. The separated liquid washes the fines of the separating device thus avoiding fouling on the deflectors. The separator liquid, together with any fines, is suitably introduced into the fluidized bed above the upper limit of the temperature gradient between the incoming fluidizing gas and the bed rest. The introduction of liquid from the separator can be carried out at a plurality of points in the fluidized-bed region and these can be at different heights in this region. The point or points of introduction of liquid are arranged so that the local concentration of liquid does not adversely affect the fluidization of the bed or the quality of the product, and allows the rapid dispersion of the liquid from each point and the evaporation in the bed to remove the polymerization heat from the exothermic reaction. In this way, the amount of liquid introduced for cooling purposes can be much closer to the maximum load that can be tolerated without altering the fluidization characteristics of the bed and, therefore, offers the opportunity to obtain better levels of reactor productivity. The liquid can, if desired, be introduced into the fluidized bed at different heights within the bed. Said technique can facilitate an improved control over the incorporation of comonomers. The controlled dosing of fluid to the fluidized bed provides additional control over the temperature profile of the bed and, in case the liquid contains comonomer, provides useful control over the incorporation of comonomer into the copolymer.

The liquid is preferably introduced into the lower part of the fluidized bed region above the limit of the temperature gradient between the incoming fluidizing gas and the bed rest. Commercial processes for the polymerization of gas-fluidized-bed olefins are generally carried out under substantially isothermal steady-state conditions. However, although almost the entire fluidized bed is maintained at the desired substantially isothermal polymerization temperature, there is usually a temperature gradient in the region of the bed immediately above the point of introduction of the recirculated gaseous stream cooled in the bed. The lower temperature limit of this region in which the temperature gradient exists is the temperature of the cold inlet gas stream, and the upper limit is the substantially isothermal bed temperature. In commercial reactors of the type employing a fluidisation grid, typically 10 to 15 m in height, this temperature gradient normally exists in an area of approximately 15 to 30 cm (6 to 12 inches) above the grid. In order to obtain the maximum benefit of the cooling of the separator liquid, it is important that the liquid is introduced into the bed above the region in which the temperature gradient exists, ie the part of the bed that has substantially reached the temperature of the recirculating gaseous stream leaving the reactor. The point or points of introduction of liquid into the fluidized bed can be, for example, 50 to 200 cm, preferably 50 to 70 cm, above the fluidization grid. In practice, the temperature profile within the fluidized bed can be determined in principle during the polymerization using, for example, thermocouples disposed in or on the walls of the reactor. The point or points of introduction of the liquid are arranged to ensure that the liquid enters the bed region in which the return gas stream has substantially reached the temperature of the recirculating gas stream which is withdrawn from the reactor. It is important to ensure that the temperature inside the fluidized bed is maintained at a level that is below the sintering temperature of the polyolefin that forms the bed. The gas from the separator is recirculated to the bed, usually in the lower part of the reactor. If a fluidization grid is used, said recirculation is usually carried out below the grid, and the grid facilitates even distribution of the gas to fluidize the bed. The use of fluidization grid is preferred.

The process of the present invention operates with a gas velocity in the fluidized bed that must be greater than or equal to that required to achieve a bubbling bed. The minimum gas velocity is generally about 6 cm / sec, although the process of the present invention is preferably carried out using a gas velocity in the range of 30 to 100, more preferably 50 to 70 cm / sec. . In the process according to the present invention, the catalyst or prepolymer can, if desired, be introduced into the fluidized bed directly with the liquid stream of the separator. This technique can lead to improved dispersion of the catalyst or prepolymer in the bed. If desired, liquid or liquid soluble additives, for example, activators, complementary catalysts and the like can be introduced into the bed along with the liquid stream of the separator. In the event that the process of the present invention is used to make ethylene homo- or copolymers, replacement ethylene can be advantageously introduced, for example, to replace the ethylene consumed during the polymerization, in a separate gaseous stream before its reintroduction into the bed (for example, below the fluidization grid if it is used). Adding the replacement ethylene to the separate gas stream, instead of in the recirculating gas stream before separation, the amount of liquid that can be recovered from the separator can be increased and productivity improved. The liquid stream from the separator can be subjected to additional cooling (for example, using cooling techniques) before being introduced into the fluidized bed. Preferably, the liquid stream is subjected to additional cooling while being circulated externally, as described above, including and cooler in the external circuit. This allows an even greater cooling effect in the bed than that provided by the evaporation effect of the liquid (latent heat of vaporization) only, thus providing a potential increase in the productivity of the process. The cooling of the liquid stream of the separator can be achieved by the use of suitable cooling means, for example, a simple heat exchanger or cooler located between the separator and the reactor, or between the point where the liquid is extracted and which is reintroduced to the separator. A further advantage of this particular aspect of the present invention is that, by cooling the liquid prior to its introduction into the fluidized bed, any tendency of the catalyst or prepolymer that may be contained in the liquid stream to be polymerized prior to introduction into the fluidized bed will be reduced. the bed. The liquid can be introduced into the fluidized bed by injection means suitably arranged. A single injection means may be used or a plurality of injection means may be arranged in the fluidized bed. A preferred arrangement is to arrange a plurality of liquid injection means substantially equally spaced in the fluidized bed in the region of liquid introduction. The number of liquid injection means used is that which is required to provide sufficient penetration and dispersion of the liquid in each liquid injection means to obtain a good liquid dispersion in the bed. A preferred number of liquid injection means is four. Each liquid injection means may, if desired, be fed with the liquid from the separator by means of a common conduit suitably disposed within the reactor. This can be provided, for example, by means of a conduit passing through the center of the reactor. The liquid injection means are preferably arranged so that they protrude substantially vertically in the fluidized bed, although they may be arranged so that they protrude from the walls of the reactor in a substantially horizontal direction. The rate at which the liquid can be introduced into the bed depends mainly on the degree of cooling desired in the bed, and this in turn depends on the desired production rate of the bed. The production rates that can be obtained from commercial fluidized bed polymerization processes for the polymerization of olefins depend, inter alia, on the activity of the catalysts employed, and on the kinetics of said catalysts. Thus, for example, when catalysts having very high activity are used, and high production rates are desired, the rate of liquid addition will be high. Typical liquid introduction rates may vary, for example, in the range of 0.25 to 4.9, preferably, 0.3 to 4.9 cubic meters of liquid per cubic meter of bedding material per hour, or even superiors For conventional Ziegler type catalysts of "superactive" type (ie, those based on transition metals, magnesium halides and organometallic complementary catalysts, the liquid addition rate may vary, for example, in the range of 0.5 to 1. , 5 cubic meters of liquid per cubic meter of bed material per hour In the process of the present invention, the ratio by weight of liquid: total gas that can be introduced into the bed can vary, for example, in the range of 1: 100 to 2: 1, preferably in the range of 5: 100 to 85: 100, more preferably in the interval from 6: 100 to 25: 100. The gas that is returned to the reactor is indicated by total gas to fluidize the bed together with the gas used to assist in the operation of the liquid injection medium, for example, spray gas. The spray gas may suitably be an inert gas, for example, nitrogen, although preferably it is replacement ethylene. By injecting the liquid in the fluidized bed in this way, any catalyst that is present in the liquid can benefit from the localized cooling effect of the liquid penetration surrounding each liquid injection medium, which can avoid hot spots and the consequent agglomeration . Any other suitable injection means can be used as long as the penetration and dispersion of liquid in the bed from such means is sufficient to obtain a good dispersion of liquid in the bed. The preferred injection means is a nozzle or a plurality of nozzles that include gas-induced spray nozzles in which a gas is used to assist in the injection of liquid or spray-only nozzles with liquid. According to another aspect of the present invention, a continuous gas fluidized bed process is provided for the polymerization of olefin monomer selected from (a) ethylene, (b) propylene, (c) mixtures of ethylene and propylene and (d) one or more other alpha-olefins mixed with (a), (b) or (c), in a fluidized bed reactor, continuously recirculating a composite gas stream, at least on the part of ethylene and / or propylene, through a fluidized bed in said reactor in the presence of a polymerization catalyst under reaction conditions, cooling at least part of said gaseous stream withdrawn from the reactor to a temperature at which liquid condense, separating at least part of the condensed liquid from the gas stream in a separator, characterized in that: (a) the separator is charged with liquid; (b) the separator is kept at least partially full of liquid; (c) the gaseous stream fed to the separator entrains catalyst and / or polymer particles, - (d) substantially, all entrained catalyst and / or polymer particles are separated from the gas stream in the separator and are kept in suspension in the separator liquid; and (e) is directly introduced into the liquid fluidized bed of the separator by means of one or more liquid nozzles or gas induced spray nozzles.

The injection means are suitably nozzles projecting into the bed through the reactor wall (or through a reactor support grid), provided with one or more jet outlets that disperse the liquid in the bed. It is important in the process of the present invention to obtain a good dispersion and penetration of the liquid in the bed. The factors that are important for obtaining a good penetration and dispersion are the amount of movement and the direction of the liquid entering the bed, the number of points of introduction of the liquid per unit of bed cross section and the spatial arrangement of the liquid introduction points. The liquid from the separator can be introduced into the reactor in the form of one or more jets of liquid only, or one or more jets of liquid and gas, from one or more jet outlets, each jet having a flow of horizontal momentum in the case of liquid jets of at least 100 x 103 Kg s "1 m" 2 xms "1 and, in the case of gas / liquid jets of 200 x 103 Kg s" 1 m "2 xms" 1, in the that the flow rate of horizontal movement is defined as the liquid mass flow rate (kilograms per second) in the horizontal direction per unit cross section (square meters) of jet outlet from which it leaves, multiplied by the horizontal component of the speed (meters per second) of the jet. Preferably, the momentum flow of each of the liquid or gas / liquid jets is at least 250 x 103, and more preferably at least 300 x 103 kg "1 m ~ 2 x m s" 1. Particularly preferred is the use of a horizontal momentum flux in the range of 300 x 103 to 500 x 103 Kg s "1 m" 2 xms "1. In the event that the liquid jet leaves a jet outlet in a direction that is not horizontal, the horizontal component of the jet velocity is calculated from Cosine Q ° x actual velocity of the jet, where Q ° is the angle of the jet with the horizontal.The direction of movement of one or more jets of liquid or liquid / gas in the bed is preferably substantially horizontal.In the event that one or more of the outlets of the jet disperse the liquid or liquid / gas jet in a non-horizontal direction, preferably they will be directed to a angle not greater than 45 °, more preferably not more than 20 ° with the horizontal In the WO 94/28032 gas-induced spray nozzles and nozzles are described with suitable liquid only. With the use of the process according to the present invention, the gas phase fluidized bed polymerization can be initiated by charging the bed with particulate polymer particles, charging the separator with liquid and then initiating gas flow through the bed. BRIEF DESCRIPTION OF THE DRAWINGS In the following, procedures according to the present invention will be illustrated with reference to the accompanying drawing. The Figure shows schematically a method according to the present invention. Detailed Description of the Drawings The Figure illustrates a gas phase fluidized bed reactor essentially comprising a reactor body 1 which is generally a vertical cylinder provided with a fluidizing grid 2 disposed at its base. The reactor body comprises a fluidized bed 3 and a velocity reduction zone 4 which generally has an increased cross section relative to the fluidized bed. The gaseous reaction mixture leaving the upper part of the fluidized bed reactor constitutes a gaseous recirculation stream and is passed through the conduit 5 to a cyclonic separator 6 for the separation of most of the fines. The separated fines can be suitably recirculated to the fluidized bed. The recirculating gas stream leaving the cyclone separator is passed through a first heat exchanger 7., a compressor 8 and a second heat exchanger 9. The heat exchanger or heat exchangers may be disposed well upstream or downstream of the compressor 8, preferably as shown, one on each side of the compressor. After cooling to a temperature at which condensate is formed, the resulting gas-liquid mixture is passed to the separator 10, where it separates the liquid. Before cooling the gaseous recirculation stream to a temperature at which the liquid condenses, liquid is charged into the separator. The level of liquid in the separator is controlled by a liquid level controller 11. The gas leaving the separator is recirculated through the conduit 19 to the lower part of the reactor 1. The gas is passed through the fluidization grid 2 to the bed 3, thus ensuring that the bed is maintained in a fluidized state. The liquid from the separator 10 is circulated through the conduits 12 and 13 and, by means of a pump 14 located in the conduit 12. A portion of liquid in circulation is passed through the valve 15 to the reactor 1 through the conduit 16. The valve 15 is controlled by means of a liquid level controller 11. The catalysts or prepolymer can be fed into the reactor via line 17 in the liquid stream of the separator. The product polymer particles can be suitably removed from the reactor via conduit 18. The arrangement shown in the Figure is particularly suitable for use when upgrading existing gas phase polymerization reactors using fluidized bed processes.

Claims (10)

1. NOVELTY OF THE INVENTION Having described the present invention, the content of the following Claims is considered a novelty and, therefore, claimed as property: 1. A fluidized bed process with continuous gas for the polymerization of olefin monomers selected from among (a) ethylene, (b) propylene, (c) mixtures of ethylene and propylene, and (d) one or more other alpha-olefins mixed with (a), (b) or (c), in a fluidized bed reactor by continuously recirculating a gaseous stream composed at least of the ethylene and / or propylene through a fluidized bed in said reactor in the presence of a polymerization catalyst under reaction conditions, passing at least part of said gas stream extracted from said reactor through a separator, characterized in that: (a) the separator is charged with liquid; (b) the separator is kept at least partially full of liquid; (c) the gaseous stream fed to the separator entrains catalyst and / or polymer particles; (d) substantially, all entrained catalyst and / or polymer particles are separated from the gas stream in the separator and held in suspension in the separator liquid; and (e) optionally, the liquid from the separator is introduced directly into the fluidized bed.
2. 2. A process according to claim 1, wherein at least part of the gas stream withdrawn from the reactor is cooled to a temperature at which liquid condenses and at least part of the condensed liquid is separated from the gas stream in the separator.
3. 3. A process according to claim 1 or claim 2, wherein most of the catalyst and / or polymer particles entrained in the gas stream withdrawn from the reactor are separated from the gas stream by means of a cyclone separator.
4. A method according to any one of the preceding claims, wherein the particles are kept in suspension by stirring the liquid in the separator or by circulating the liquid continuously by means of an external circuit.
5. A process according to any one of the preceding claims, wherein the entrained catalyst and / or polymer particles that are separated from the gas stream in the separator are reintroduced into the fluidized bed along with the liquid stream of the separator.
6. 6. A process according to any one of the preceding claims, wherein the liquid is introduced directly into the fluidized bed with a flow rate in the range of 0.25 to 4.9 cubic meters of liquid per cubic meter of bed material per hour.
7. 7. A process according to any one of the preceding claims, wherein the ratio by liquid weight: total gas that is introduced into the bed varies in the range of 1: 100 to 2: 1.
8. 8. A continuous gas fluidized bed process for the polymerization of olefin monomer selected from (a) ethylene, (b) propylene, (c) mixtures of ethylene and propylene and (d) one or more other alpha-olefins mixed with (a), (b) or (c), in a fluidized bed reactor, continuously recirculating a composite gas stream, at least on the part of ethylene and / or propylene, through a fluidized bed in said reactor, in the presence of a polymerization catalyst under reaction conditions, cooling at least part of said gaseous stream extracted from said reactor to a temperature at which liquid condenses, separating at least part of the condensed liquid from the gas stream in a separator, characterized in that: ) the separator is charged with liquid; (b) the separator is kept at least partially filled with liquid; (c) the gaseous stream fed to the separator entrains catalyst and / or polymer particles; (d) substantially, all entrained catalyst and / or polymer particles are separated from the gas stream in the separator and kept in suspension in the separator liquid; and (e) is directly introduced into the liquid fluidized bed of the separator by means of one or more liquid nozzles or gas induced spray nozzles.
9. A method according to claim 8, wherein the liquid is introduced into the reactor in the form of one or more jets of liquid, or one or more jets of liquid and gas, from one or more jet outlets, each jet having a flow of horizontal movement in the case of liquid jets of at least 100 x 103 Kg s "1 m" 2 xms "1 and, in the case of gas / liquid jets of 200 x 103 Kg s" 1 m '2 xms
10. 10. A method according to claim 9, in which the jet or the liquid or liquid / gas jets are directed substantially horizontally in the bed.