PL148569B1 - Method of limiting the production of molten polymer deposite layers during polymerization of alpha-olefines - Google Patents

Description

The present invention relates to a method of limiting the formation of molten polymer layers during the polymerization of oC-olefins. conventional low-density polyethylene was previously obtained by polymerization in thick-walled autoclaves or tubular reactors at pressures as high as 3.44 bar and at temperatures up to 300 ° C or more. The molecular structure of high pressure low density polyethylene (HP-LDPE) is highly complex. The rearrangements of the arrangement of its individual components are basically unlimited. HP-LDPE polyethylenes are characterized by the intricate architecture of long-chain branched molecules. These long-chain branches drastically affect the melting rheology of this type of resins. HP-LDPE polyethylenes also show a spectrum of short chain branches, generally from 1 to 6 carbon atoms in length. This short chain branching disrupts crystal formation and reduces the density of the resin. A technology has been developed whereby low density polyethylene can be produced by a fluidized bed method at low pressure and low temperature by copolymerizing ethylene with a variety of o-olefins. These low pressure LDPE (LP-LDPE) resins generally contain only a small amount, if any, of long chain branches and are sometimes referred to as linear LDPE resins. They contain short-chain branching, the length of the side chains and the frequency of their occurrence are regulated by the type and amount of comonomer used during the polymerization. It is known that low-pressure polyethylene of high or low density can be conveniently produced by the fluid bed method, using different types of catalysts. as a result of 148 5692 148 569 which are obtained products of low and high density in the full range * The correct choice of catalysts * until use in this process depends, in part, on the type of end products desired, i.e. products such as high density resins, Low density resins, extrusion resins, film resins, and other criteria. The various catalysts that can be used to make polyethylenes in fluidization reactors can be divided into the following types: flow I. Silylchromate type catalysts disclosed in US Patent No. Baker and Carrick Americas No. 3,324,101 and United States Patent Specification Carrick, Karapinka, and Turbet No. 3,324,095. Silylochromate catalysts are characterized by the presence of groups of the formula Si - 0 - Cr and 1L in them. wherein R is a hydrocarbyl group of 1-14 carbon atoms. Preferred silylchromate catalysts are bis (triarylsilyl) chromates and a more preferred catalyst is bis (trafenylsilyl) chromate. This type of catalyst is used on a carrier such as silicon dioxide, alumina, thorium dioxide, zirconium dioxide, etc. Other carriers may also be used. such as carbon black, microcrystalline cellulose, unsulfonated ion exchange resins, etc. Ty II. The bis (cyclopentadienyl) chromium (II) compounds disclosed in U.S. Patent No. 3,879,368. These types of bis (cyclopentadienyl) chromium (II) compounds have the formula 1, wherein R 'and R "may be the same or different and represent hydrocarbon radicals with 1 - 20 (inclusive) carbon atoms, and an 'in "can represent the same or different integers from 0 to 5 (inclusive). Hydrocarbon radicals with the symbols R "and r", which may be saturated or unsaturated, may include aliphatic, alicyclic and aromatic radicals, such as methyl, ethyl, propyl, butyl, pentyl, cyclopentyl, cyclohexyl, allyl, phenyl radicals and naphthyl These catalysts are used on a carrier as described above. Type III. Catalysts as described in U.S. Patent 4,011,382. Such catalysts include chromium and titanium in the form of oxides and, optionally, fluorine and a carrier. The catalysts contain, based on the total weight of the carrier and chromium, titanium and fluorine, about 0.05 - 3%, preferably about 0.2 - 1.0% by weight of chromium (as Cr), about 1.5 - 9 0.0%, preferably about 4.0-7.0% by weight of titanium (calculated as Ti) and 0.0-2.5, preferably 0.1-1.0% by weight of fluorine (calculated as F). Chromium compounds that can be used with type III catalysts include CrO, or any chromium compound oxidizable to CrO under the activation conditions used. At least some of the chromium in the supported, activated catalyst must be hexavalent chromium. Chromium compounds other than CrO which may be used herein are disclosed in U.S. Patent Nos. 2,825,721 and 3,622,521 and include chromium acetylacetonate, chromium nitrate, chromium acetate, chromium chloride, chromium sulfate, and ammonium chromate. The titanium compounds that may be used here include all those compounds that are oxidizable to TiOp under the activation conditions used, and include those compounds that are disclosed in US Patent 3,622,521 and Dutch Patent Application No. 72-10881. which may be used here are HF or any fluorine compound that will provide HF under the activation conditions used. Fluorine compounds other than HF that can be used are disclosed in Dutch Patent Application No. 72-10881.148 569.3 Inorganic oxide materials that can be used as a carrier in a catalytic composition are porous materials with a large surface, i.e. from about 50 to about 1000 m / g with an average particle size of about 20 - 200 millimeters. The inorganic oxides that can be used include silicon dioxide, alumina, thorium dioxide, zirconium dioxide, and other comparable inorganic oxides, as well as mixtures of these oxides. Type IV. Catalysts as described in United States Patent Application Serial No. 892,325 filed on March 31, 1978 in the name of *. J. Karola et al. And entitled "Production of ethylene copolymers in a fluidized bed reactor." Catalysts of this type contain at least one titanium compound, at least one magnesium compound, at least one electron donor compound, at least one activator compound, and at least one inert carrier. The titanium compound has a structure represented by the formula Ti (OR) aX4, where R is an aliphatic or aromatic hydrocarbon radical with 1-14 carbon atoms, or a group of the formula COR # where R 'is aliphatic or an aromatic hydrocarbon radical of 1-14 carbon atoms, X is Cl, Br or J, a is 0 or 1, b is 2-4 inclusive, aa + b - 3 or 4. For titanium compounds that can be used singly or in combination , include: TiCl-, TiCl4, Ti (OCH5) Cl3, Ti (OC6H5) Cl3, Ti (OCCH3) Cl3 and Ti (OCC6H5) Cl3. The structure of the magnesium compound is Mgl? where X is Cl, Br or J These types of compounds may be used singly or in combination their: MgClp, MgBrp and MgJ2. The preferred compound is anhydrous MgCl2. The titanium compound and the magnesium compound are generally used in a form that will facilitate their dissolution in the electron donor compound. The electron donor compound is a liquid organic compound. at a temperature of 25 ° C, in which the titanium compound and the magnesium compound are partially or completely soluble. Compounds - electron donors are known by this name or by the name of Lewis bases. Compounds that are electron donors include compounds such as alkyl esters of aliphatic and aromatic carboxylic acids, aliphatic ethers, cyclic ethers and aliphatic ketones. The catalyst can be modified using a boron halide of the formula BR.X%. In which R is an aliphatic or aromatic hydrocarbon radical of 1-14 carbon atoms, or a group of the formula OR ", in which R 'also represents an aliphatic or aromatic hydrocarbyl containing 1-14 14 carbon atoms. X 'represents a substituent selected from the group consisting of Cl and Br or a mixture thereof, and c is 0 or 1 when R is an aromatic or aliphatic hydrocarbon and 0, 1 or 2 when when R is OR'. Boron halide compounds may be used singly or in combination. These include: BC13, BBr3, B (C2H5) C12, B (OC2H5) C12, B (OC2H5) 2C1, B (C6H5) C12, B ( OC6H5) C12, B (C6H13) C12, BfOCglL-JClg and B (OCGH5) 2Cl. boron trichloride is not preferred. The activating compound is represented by the formula Al (R ") cX'dH, where X 'is Cl or OR ^ R1 and R *" are the same or different and represent saturated hydrocarbon radicals of 1 - 14 carbon atoms, d is 0 - 1.5 »e is 1 or 0, and c + d + e« 3 »This type of activator compounds can be used individually or as combinations thereof. For carriers that are solids particulate materials include inorganic substances, such as silicon dioxide and alumina, and molecular sieves, as well as organic substances, such as olefinic polymers, e.g. polyethylene. In general, the above catalysts are introduced together with the substances to be polymerized. to a reactor having flared sections at the top and sections with straight sides. The recycle gas reaches the bottom of the reactor and goes up through the distribution plate to the fluidized bed in the straight-sided section. The gas expansion plate-4 148 569 serves to ensure proper gas distribution and to support the resin bed when the gas flow is stopped. The gas leaving the fluidized bed lifts the resin particles with it. Most of these particles are released as the gas passes through the expanded section of the reactor where the gas flow rate is reduced. The operational difficulties associated with the use of Type I - III catalysts in the above-described reactors are substantially eliminated, resulting in a cost-effective production. and efficient low pressure polyethylene resins, low or high density polyethylene resins with a wide variety of applications. A type IV catalyst is used to meet the requirements of certain end-use ethylene resins such as film making, injection molding or rotational molding. However, efforts to make certain ethylene resins using type IV catalysts on a porous silica support in certain fluidized bed reactors have proved unsatisfactory from an industrial practice point of view. In the first place, this is due to the formation of layers of molten polymer deposits in the reactor after a short operation time has elapsed. The deposits vary considerably in dimensions, but are similar in most respects. Typically, they are about 6.35 mm to 12.7 mm thick and about 30.48 cm to 152.4 cm long, with some specimens even longer. Their width is about 7.62 cm. cm to over 45t72 cm. These layers have a longitudinally oriented molten polymer core and their surface is covered with a granular resin fused to the core. The edges look hairy with molten polymer threads. After a relatively short period of time during polymerization, scum layers begin to appear in the reactor and clog the product discharge system, forcing the reactor to shut down. Accordingly, there is now a need to improve the polymerization methods needed to make polyolefin products using catalysts on Thus, the subject of the present invention is a method of substantially reducing or eliminating the formation of molten polymer layers during low pressure polymerization in a fluidized bed oC-olefins using titanium compounds as catalysts. in the production of polyolefins by polymerization of 06-olefins with the use of titanium-based polymerization catalysts, consisting in the neutralization of the electric charge, according to the invention it consists in contacting the surfaces of the reaction vessel in which there is a polymerization with a chromium-containing compound such as bis (cyclopentadienyl) chromium in an amount reducing the size of the scale formation formed during the polymerization to at least 3.5 x 453 x 10 "7 g moles of chromium / 0.0929 m2. the chromium containing is used in an inert solvent, especially toluene. More particularly, the inert solvent is introduced into the reaction vessel under an inert atmosphere. With reference to the lower part of the figure, a typical fluidized bed reaction system for the polymerization of oC-olefins includes a reactor 10 having a reaction zone 12 and a rate reduction zone. 14. The reaction zone 12 contains a deposit of increasing polymer particles, formed polymer particles and smaller amounts of catalyst particles in the fluid phase due to the constant flow of polymerized and changing gas components, in the form of ready feed 1 of the recycle gas through the reaction zone. In order to maintain the viability of the fluidized bed, the mass flow rate of the gas through the bed is usually kept above the minimum flow necessary to maintain fluidization. Preferably it is about 1.5 to about 10 x G G, and more preferably from about 3 to about 6 x G G. The symbol G ^ is used as it is to abbreviate the minimum gas flow required to effect fluidization. See: CY Wen and TH Tu, "Mechanice of Pluidization", Chemical Progress Symposlum Series, Vol. 62, pp. 100-111 (1966). It is highly desirable that the deposit always contain particles in order to prevent the formation of local "hot spots"; and the entrainment and distribution of the fine-grained catalyst throughout the reaction zone. Typically, prior to the commencement of the process, the reactor is charged with the base-forming fine-grained polymer particles before the gas flow is even started. Such particles may be essentially identical to or different from the polymer to be produced. In the latter case, they are removed with the particles of the formed polymer as the first product. Ultimately, the fluidized bed of the target polymer particles displaces the starting bed. The relevant catalyst used in the fluidized bed process is preferably kept for use in a tank 16 under a blanket of an inert gas such as nitrogen or argon. gas circulation rate, back and forth through the bed, normally at a row rate of 50 x the finished gas feed rate. The fluidized bed generally looks like a dense mass of viable particles in a freely swirling flow created by the percolation of gas through the bed. The pressure drop across the bed is equal to or slightly greater than the mass of the bed divided by the cross-sectional areas. It therefore depends on the geometry of the reactor. Finished gas is introduced into the bed at a rate equal to the rate at which the produced fine-grained polymer is removed. The composition of the finished gas is determined in a gas analyzer 18 located above the bed. The gas analyzer determines the composition of the recycle gas, and the composition of the finished gas is adjusted accordingly to maintain a substantially steady state of the composition of the gases within the reaction zone. To ensure complete fluidization, the recycle gas and, if required, Part or all of the finished gas is returned to the reactor at the base 20 below the bed. A gas distribution plate 22 located above the return point ensures proper gas distribution and also serves to support the resin bed when the gas flow is stopped. The portion of the gas stream that does not react with the bed is recycle gas, removed from the polymerization zone, preferably by directing it to the rate reduction zone 14 above the bed. There, just the entrained particles have the possibility of falling back into the bed. The circulating gas is then compressed in the 24t compressor and then passed through the heat exchanger 26, which takes away its heat of reaction before returning the gas back to the bed. Due to the constant removal of the heat of reaction, no more significant a temperature gradient at the top of the bed. In contrast, a temperature gradient will exist at the bottom of the bed, in a layer with a thickness of about 15.24-30.48 cm, between the inlet gas temperature and the temperature of the rest of the bed. It is also observed that the bed almost immediately equalizes the temperature of the recycle gas above the bottom layer of the bed zone with the temperature of the rest of the bed, and thus maintains its essentially constant temperature under predetermined conditions. The recycle gas is then returned to the reactor at the base 20 and through the distribution plate to the fluidized bed. The compressor 24 may also be located downstream of the heat exchanger 26. For typical polymerization reactions of the type contemplated herein, hydrogen may be used as the primary transfer medium. If ethylene is used as the monomer, the assumed hydrogen / ethylene ratio will vary from about 0 to about 2.0 moles hydrogen per mole of monomer in the gas stream. Any gas inert to the gas stream may also be present in the gas stream. talcum 1 of reactants. The cocatalyst is added to the recycle gas stream upstream of its feed to the reactor, for example, from feeder 28 via line 30. As is well known, it is important to operate the fluidized bed reactor at a temperature below the sintering temperature of the polymer particles. Thus, in order to ensure that such sintering does not occur, an operating temperature lower than the sintering temperature is desirable. For the production of ethylene polymers, an operating temperature of about 90 to 100 ° C is preferably used, resulting in products with a density of about 0.94-0.97, while when using temperatures of about 75-95 ° C, preferably products with a density of about 0.91-0.94 "are obtained. Typically, the fluidized bed reactor is operated at a pressure of not more than about 6.88" 10 Pa, preferably at a pressure of about 10.32 "10" Pa to 20.48 "10" Pa. The operation carried out at a higher pressure in this range favors the heat transfer since the increase in pressure increases the heat capacity per unit volume of gas. The catalyst is injected into the bed at point 32 above the distributor plate 22 at a rate corresponding to its wear. A gas that is inert to the catalyst, such as nitrogen or argon, is used to transfer the catalyst to the bed. The injection of the catalyst at the point above the spreading plate 22 is an important and essential feature. Since the catalysts normally used are highly active, injection into the space below the spreading plate could cause polymerization to begin there and eventually clog the plate. On the other hand, injection into the bed helps to distribute the catalyst throughout the bed space and excludes the formation of local places with high catalyst concentration, which could lead to the formation of "hot spots". In a given set of process conditions, the fluidized bed is basically maintained at a constant height by discharging part of the bed as a product at a rate corresponding to the formation rate of the given polymer product. Since the rate of heat release is directly related to the formation of the product, measuring the temperature rise of the gas across the reactor (the difference between the inlet gas temperature and the outlet gas temperature) is an indicator of the rate of formation of a given polymer at a constant gas velocity. The fine-grained polymer produced preferably drains away. at point 34, on or near the distribution plate. The fine-grained polymer formed is conveniently and preferably discharged using the sequential operation of a pair of synchronized valves 36 and 38 defining the separation zone 40. When valve 38 is closed, valve 36 is opened to discharge the gas plug and product into zone 40, which is between this valve and the valve 36, which is then closed. The valve 38 then opens to discharge the product into the outer recovery zone, and after this discharge, the valve 38 closes awaiting the next product recovery operation. The fluidizing reactor is provided with a suitable venting system to allow the bed to be vented during initiation and shutdown. The reactor does not require the use of mixing and / or wall scraping devices. The reactor vessel is constructed typically of carbon steel and is designed to operate under the operating conditions indicated above. Refer again to the figure for a better explanation of the problems associated with the use of Type IV catalysts. A titanium-based catalyst (type IV) is introduced into reactor 10 at point 32. In a typical operation with certain resins, after a short period of time, i.e. a period of about 36-72 hours, deposits begin to form in reactor 10. , at the location of the reactor closest to its wall and approximately half the diameter of the reactor upstream of the base of the fluidized gold. Molten resin layers begin to appear in the separation zone 40, the moths clog the system and necessitate shutdown of the reactor. More significantly, herb formation starts after the product has been produced in an amount equivalent to 6-10 times the weight of the resin in reactor 10. A number of possible causes have been investigated to eliminate the phenomenon of molten polymer scale formation. During the test, thermocouples were installed inside the walls of the reactor at levels 1/4 and 1/2 the diameter of the reactor above the gas distribution plate. For conventional operations, the "skin" thermocouples indicate a temperature equal to that of the fluidized bed. However, in the event that screed formation occurs, these thermocouples indicate temperature variations up to 20 ° C. above the fluidized bed temperature, thus providing a reliable indication of the occurrence of screed phenomena. In addition, an electrostatic voltmeter was used to measure the voltage on a 12.7 mm spherical electrode placed in the fluidized bed at a depth of 25.4 mm radially from the reactor wall and 1/2 the reactor diameter above the gas distribution plate. This type of electrode location was chosen because the initiation of layer formation was observed in the band contained in the area defined by the distance of 1/4 - 3/4 of the diameter of the reactor upwards above the base of the fluidized bed. As is well known for deeply fluidized beds, this corresponds to the region of lowest mixing intensity close to the wall, that is to say the null zone, in which the movement of the particle close to the wall varies from generally upwards to generally downwards. Possible causes investigated included factors influencing fluidized bed mixing, reactor operating conditions, catalyst and resin particle sizes, particle size distribution, and other causes. Correlation was found between the formation of deposits and the build-up of static electric charge on the resin particles closest to the reactor wall. In the event that the level of static stress of the resin particles at the individual points closest to the wall of the fluidized bed reactor is low, the reactor operates normally and no deposits are formed. In the event that the static voltage level exceeds a critical level at these points, plaque formation occurs in an uncontrolled manner and the reactor must be shut down. Surprisingly, plaque formation did not occur to any significant degree with any resin using Type IV catalysts. in reactors previously used type II catalysts or in reactors previously used type I-III catalysts. It was subsequently found that bedding formation could be substantially reduced, and in some cases completely eliminated, by keeping the static tension in the fluidized bed at the point closest to the walls of the reactor below the critical level for film formation. The critical level is not a constant, but is a complex function dependent on the variables, including sintering temperature of the resin, operating temperature, fluidized bed drag forces, resin particle size distribution, and recycle gas composition. Critical voltage level Vc for formation The first order is the sintering temperature of the resin, the bed temperature in the reactor and the concentration of hydrogen in the recycle gas. This relationship can be presented as follows: Vc = -8000 - 50 Ts + 90 T ^ l + 150 To, in which the formula Vc denotes the voltage (in volts), below which no layer formation takes place8 H8 569, Ts is the sintering temperature of the resin ( in ° C) in the reactor operating conditions, It means the temperature of the reactor (in ° C) and D * ?! stands for% mole of hydrogen in the recycle gas. The sintering temperature of the resin under the operating conditions of the reactor is the temperature at which the deposited resin bed in contact with a gas of the same composition as the recycle gas used in the production of the resin sinter and forms agglomerates with a re-fluidization aid after allowing the bed to settle for 15 minutes. The sintering temperature decreases with lowering the resin density, with increasing the melt number and with increasing the amount of dissolved monomers. The constants in the above equation were determined on the basis of data collected during the operation of the reactor, when the reactor was just beginning to show signs of deposit formation through variations in the measured temperature " skin "thermocouple over bed temperature." The voltage indicated on the voltage probe described above varies with time as a result of the random nature of the fluidized bed. Thus, the critical voltage Vc is expressed as a time average. The voltage measurements are difficult to interpret because an additional static electric charge is created when the bed layer, formed due to the static charge, separates from the reactor wall. In addition, the film formation phenomenon may start in a very confined location and then spread further, thus obscuring the interpretation of voltage readings. Although the mechanism of film formation is not fully understood, it is assumed that the static electricity generated in the liquid bed loads resin particles. When the particle count reaches a level at which the electrostatic forces trying to keep the charged particle close to the reactor wall outweigh the drag forces in the bed, trying to move the particle away from the wall, the layer of catalyst-containing polymerizable resin particles is formed by the non-fluidic layer of the reactor. The removal of heat from this layer is insufficient to remove the polymerization heat, since the non-fluidized layer close to the wall has less contact with the fluidizing gas than the particles found in the fluidized portions of the bed. The heat of polymerization causes the temperature of the non-fluidized layer near the reactor wall to increase until the particles melt and sinter. At this point, other particles from the fluidized bed adhere to the molten layer and as a result it grows in size until its contact with the reactor wall loosens. As it is known, the separation of the dielectric from the conductor (in this case the bed layer from the reactor wall) causes the production of additional static electricity, as a result of which further deposit formation is accelerated. The current state of knowledge indicates various methods of limiting or even eliminating static stress. . These include: 1) reducing the rate of charge formation, 2) increasing the speed of electrical charge removal, and 3) neutralizing the electrical charge. Some of the methods that can be used with the fluidized bed are: 1) the use of an additive to increase the conductivity of the particles thereby creating a discharge path; 2) the installation of grounding devices in the fluidized bed to provide additional surface area to discharge charges to the ground, 3) ionizing a gas or particles by means of an electric discharge to form ions to neutralize electrostatic charges on the particles, and 4) using radioactive sources to create ions to neutralize electrostatic charges on the particles The application of these methods to an industrial fluidized bed polymerization reactor may not be feasible or realistic. The additive used must not act as a poison to the polymerization catalyst and must not adversely affect the quality of the product produced. For example, water, which is the most widely used additive for reducing electrostaticity on particles, cannot be used as it is a serious catalyst poison. The installation of grounding devices can, in fact, lead to additional electrostatic charge, as rubbing of the resin particles against the metal surfaces creates an electrostatic charge on the resin particles. The use of ion generators and radioactive sources poses serious problems related to the scale of production. The ions generated by electrical discharge or radiation will be attracted to the walls of the reactor and other grounded bodies and will only travel a limited distance before contacting a grounded site. Hence, the ions cannot travel from their place of production long enough to discharge the region of the bed in which bedding formation takes place. The generation of ions within the fluidized bed is severely limited by the quenching effect of the cloud of charged particles that is formed around the ion generator. Thus, the necessary number of ion-generating sources may prove to be high, in addition to the complicated and dangerous use of radioactive sources or electric discharge generators in or near a pressurized, hydrocarbon-containing reactor. During these studies, it was found that an effective method was treating the walls of the reactor to reduce the generation of electrostatic charge includes the use of the reactor for short-term operation, such as, for example, 2 weeks, using a catalyst containing chromium (type I - IH) for at least part of the The residence time in the reactor is divalent or trivalent chromium. However, it was also unexpectedly found that when the reactor walls were treated with a chromium-containing compound prior to the commencement of polymerization, the chromium present in the reactor was divalent or trivalent chromium, then the formation of deposits remain essentially in the course of polymerization Limited, and in some cases completely eliminated. The chromium-containing compounds contemplated for use in the process of the invention are those where the chromium contained in the reactor is divalent or trivalent chromium. For the sake of illustration only, the following compounds may be given as suitable for use in the process according to the invention: Chromium bis (cyclopentadienyl) compounds of formula I, in which R 'and R "may be the same or different and represent radicals hydrocarbons with 1 to 20 (inclusive) carbon atoms and 'in' can represent the same or different integers from 0 to 5 inclusive. Hydrocarbon radicals which may be saturated or unsaturated include aliphatic, alicyclic and aromatic radicals such as methyl, ethyl, propyl, butyl, pentyl, cyclopentyl, cyclohexyl, allyl, phenyl and naphthyl radicals. Other specific compounds suitable for this application include chromium acetylacetonate, chromium nitrate, chromous or chromium acetate, chromous or chromium chloride, chromous or chromium bromide, chromous or chromium fluoride, chromous or chromium sulfate, and polymerization catalysts made of chromium compounds. , containing divalent or trivalent chromium. The preferred chromium containing compound is bis (cyclopentadienyl) chromium (chromocene) because it produces excellent results. In general, the chromium-containing compound is introduced into the reactor prior to polymerization. It can be introduced into the reactor. in any manner such as to bring it into contact with the wall surfaces of the reactor. In a preferred embodiment, the chromium compound is dissolved in a suitable solvent and introduced into the reactor under an inert or non-reactive atmosphere. A resin may be used to help distribute the chromium compound throughout the reactor. Suitable solvents for this application include benzene, toluene, isopentane, hexane, and water, although suitable solvents are not limited to the above-mentioned. The choice and manner of using the solvent depends on the form of the chromium containing compound and the chosen method of application. The function of the solvent is to transfer and help the chromium containing compound to disperse. Suitable inert or non-reactive gases include nitrogen, carbon dioxide, methane, ethane, and air, although the respective gases are not limited to those listed above. The amount of chromium compound used in the process should be sufficient to cause the outside effect and the amount generally also the person skilled in the art will define. However, in general, it is preferred to use a chromium compound in an amount of at least 3 * 5 x 453 x - x 10 moles of chromium / 0.0929 m2 of treated surface, preferably} from 1.0 x 453 x 10 to about 5 x 453 x 10.5 moles of chromium / 0.0929 m2 of treated surface The polymers to which the method of the invention first relates and which have the above-mentioned problems of deposit formation in the presence of titanium catalysts are linear ethylene homopolymers or linear ethylene copolymers (greater mole%, ≥90%) with one or more than one oC-olefin compound with 3-8 carbon atoms (lower mole%, ≥10%). The 8 carbon atoms should not contain any branching on any carbon atoms closer than 4. Preferred C-olefins with 3 to 8 carbon atoms are: propylene, butene-1, pentene-1, hexene-1, 4-methylpentene-1 , heptene-1 and octene-1. The present description is not intended to exclude its use in the process According to the invention, it is an oC-olefinic homopolymer, as well as copolymeric resins in which the monomer is not ethylene. The homopolymers and copolymers have a density ranging from about 0.97 to 0.91. The density of the copolymer, at a given level of melt index, is primarily governed by the amount of comonomer of 3-8 carbon atoms that is copolymerized with ethylene. Thus, the gradual addition of more and more comonomers to the copolymers tends to gradually decrease the density of the copolymer. The amount of each of the different C, -Cr comonomers necessary to obtain the same result will vary from monomer to monomer under the same reaction conditions. In the absence of a comonomer, ethylene will homopolymerize. The melt number of the homopolymer and copolymer is a reflection of its molecular weight. Polymers with relatively high molecular weight exhibit a relatively high viscosity and a low melt number. In a typical embodiment of the method according to the invention, the melt polymer matrix formation is limited, as shown in Fig. 1, susceptible to the problems of film formation during polymerization of the above-described materials using Type IV catalysts, a partial granular polyethylene resin is filled, which is purged with a non-reactive gas such as nitrogen and fluidized with by circulating said unreactive gas through the reactor at a rate greater than the lowest fluidization rate (Gmf) of the granulated polyethylene, preferably at 3-5 Gmf. It should be understood that the use of a fluidized resin bed is only an convenience in the process mentioned and is not essential to it. While circulating the unreactive gas, a chromium-containing compound such as bis (cyclopentadienyl) chromium is introduced into the reactor, either alone or preferably as a solution in an inert solvent such as toluene. The concentration of the chromium-containing chemical in the inert solvent is not critical to the process, but may be chosen by one skilled in the art to ensure complete dissolution of the chromium-containing chemical in the solvent. In a preferred case, typically a toluene solution with a content of 6 - 8% by weight of bis (cyclopentadienyl) chromium is used. Approximately 4 × 453 × 10 "moles of a chromium-containing compound are injected into the reactor for each 0.0929 m2 of surface to be treated. The circulating unreactive gas brings the chromium-containing chemical into contact with the metal surfaces in the system. The reactor preparation is carried out by long enough to achieve the desired result, usually over a number of hours or even days. In another embodiment, the treatment method is that a chemical solution is applied to metal surfaces by painting, spraying or Other application methods are well known to a person skilled in the art. After such treatment, the reactor is ready to begin polymerization in the usual manner. The Summary of the Invention is explained in general terms. The following examples will explain some specific methods. its use, however, it should be understood that the scope of the invention is not limited to Various modifications are made to the process of the present invention. Examples 1-8 give a description of the fluidized bed reactor process as shown in FIG. 1. A titanium-based Ziegler catalyst was used, deposited on a porous silica carrier, prepared by the method described above under Type IV. Triethylaluminum was used as the cocatalyst. The products obtained in the examples were ethylene-1-butene copolymers. Hydrogen was used as the chain conveyor to control the melt index of the polymer. The reactors in Examples I and II were not used to produce polyethylene with any other catalyst except those catalysts of the type described above as type IV. Example I Fluidized bed reactor began to operate under the operating conditions for producing the copolymer. low-density ethylene film, 0.918, melt index 1r0 and sticking temperature 104 ° C. The reaction begins with the introduction of the catalyst into the reactor, previously loaded with a bed of granulated resin similar to that intended for the production of the product. The catalyst is a mixture of 5 »5 parts of titanium tetrachloride, 8.5 parts of magnesium chloride and 14 parts of tetrahydrofuran, applied to 100 parts of silica (Davison, grade 952). Before applying the catalyst, these silica is dehydrated at 800 ° C and mixed with 4 parts of triethylaluminum, and after application it is activated with 35 parts of tri-n-hexylaluminum. Before starting the catalyst feed, the reactor and resin bed are brought to an operating temperature of 85 ° C and the contaminants are blown out by circulating nitrogen through the resin bed. The ethylene, butene, and hydrogen concentrations are set to 53% 924 # and 11 #, respectively. The catalyst is introduced at a rate of 0.3 parts triethylaluminum / part catalyst. The reactor starts up as normal. After 29 hours of product production, equivalent to 6 to 1/2 times the weight of the fluidized bed, the temperature deviation from the temperature of the thermocouple placed inside the reactor wall at a height of 1/2 of the diameter of the reactor above the gas distribution plate is determined by using a thermocouple placed inside the reactor wall. 1 to 2 ° C above bed temperature. Experience previously accumulated has shown that this type of temperature variation is indicative of the formation of resin sheets in the fluidized bed. Simultaneously, the voltage of the bed, measured with an electrostatic voltmeter connected to a 12.7 mm diameter spherical electrode, placed 25.4 mm from the reactor wall at a height of 1/2 the reactor diameter above the gas distribution plate, rises from reading about +1,500 to +2000 for reading above +5,000 volts, then, within 3 minutes, it drops back to +2000 volts. Variations in temperature and voltage last approximately 12 hours and increase both in frequency and in magnitude. At this time, a layer of molten polyethylene resin begins to appear in the resin produced. The signs of film formation are becoming more and more severe, that is, the temperature varies up to 20 ° C above the bed temperature and remains high for extended periods of time. Voltage variations are also becoming more and more frequent. The reactor is shut down due to excessive deposit formation. 12 148 569 Example II. The fluidized bed reactor used in Example 1 is started and the process of producing a linear low density copolymer suitable for extrusion or rotomoulding, having a density of 0.934f, an alloy number of 5 and a sticking temperature of 118 ° C. The reactions begin with the introduction of a catalyst similar to for the catalyst used in example I, with the difference that 28 parts of tri-n-hexylaluminum are used for activation. The reactor was previously loaded with a bed of granulated resin similar to the overflow to make the product. Before starting the catalyst feed, the reactor and resin bed were brought to an operating temperature of 85 ° C and the impurities were purged with nitrogen. Ethylene, butene and hydrogen are introduced into the reactor at a concentration of 52%, 14 * and 21 £, respectively. Eocatalyst is introduced in an amount of 0.3 parts of triethylaluminum part of the catalyst. The reactor is operated continuously for 48 hours and during this time resins are produced in an amount equivalent to 9 times the amount of resin contained in the deposit. After 48 hours of running smoothly, they begin to emerge from the reactor, along with the normal granular product, also the molten resin layer. At that time, the voltage measured at a distance of 1/2 the diameter of the reactor above the distribution plate averaged 4-2000 and ranges from 0 to +10,000 volts, while the "skin" thermocouples at the same height show variations of 15 ° C above bed temperature. After 2 hours of noticing the first layers of deposits in the product withdrawn from the reactor, it is necessary to stop the feed of catalyst and cocatalyst to the reactor in order to reduce the rate of resin production as the layers clog the resin discharge system. After another hour, the catalyst and cocatalyst charge begin again. Layering continues and after 2 hours the feed of the catalyst and cocatalyst is stopped again, and the reactions are terminated by injection of carbon monoxide. The voltage during this time is? +12,000 volts, and thermocouple variations continue until injection. poisons. Overall, the reactor was run for 53 hours, during this time period, producing resins at 10-1 / 2 of the volume of the bed before the reaction was terminated due to the formation of plaque layers. Example III. The reactor used in Examples I and II was treated as follows. This involves loading the bed of granulated resin into the reactor and purging and drying the bed with high purity nitrogen until the water vapor concentration is below 10 ppm (vol). The bed is then fluidized by circulating nitrogen. A toluene solution of chromocene bis (cyclopentadienyl) chromium is injected into the bed. • 4.3 x 453 x 10 -5 moles of chromocene are added to each 0.0929 m of steel surface of the system. The bed was heated to 92 ° C and nitrogen was circulated for 24 hours. After the treatment is completed, the bed is cooled to a temperature of 40 ° C, and then about 566 liters of air are injected into each 453 g of chromocene contained in the system, in order to oxidize the chromocene before removing the resin from the reactor. The reactor prepared in this way is then charged with a resin bed similar to that described in example I. The bed temperature is brought to 85 ° C, blown in, and the concentration of ethylene, butene, hydrogen and cocatalyst is adjusted to the same level as in example I, and then injection is performed the same as in example of catalyst I. The reactor is operated under the operating conditions for producing a low density polyethylene copolymer for film production having a density of 0.918, a melt index of 1.0, and a sintering temperature of 104 ° C, as in Example 1. Within 90 hours. When the reactor is operated, approximately 3 times more product is obtained than in Example I. After this time, the reactor is shut down and subjected to periodic inspection and maintenance. No temperature deviation and no resin layering are observed. At the end of gray, the voltage measured near the wall at 1/2148 569 13 in diameter of the reactor above the gas distribution plate is stabilized at around -100 volts and will not be seen during the gray period, at any time any major voltage deviation. . The reactor used in Example III is then loaded with a bed of resin similar to that described in Example II above. The bed is heated to 90 ° C, purged and the concentration of ethylene, butene and hydrogen, respectively 51%, 13% and 18%, as well as the cocatalyst (0.3 parts per part of the catalyst) is established before the injection of the catalyst. The reaction begins in an even manner and produces a linear low density polyethylene resin with a density of 0.934, a foot number of 5 and a sintering temperature of 118 ° C. The reactor is operated continuously for 80 hours and during this time a vitality is obtained. in an amount equivalent to 20 times the weight of the resin deposit (before it is converted into a different quality product). Thermocouples placed close to the surface of the reactor wall, 1/4 and 1/2 the diameter of the reactor above the distribution plate, showed several short, one minute temperature variations. The voltage measured near the reactor wall at 1/2 the diameter of the reactor above the gas distribution plate was on average +1200 volts. The voltage fluctuates from 0 up to +8000 volts. Some pieces of resin, typically 6.35 x 25f4 x 25.4 mm in size, having the appearance of a sintered fine particle can be seen in the product discharge tank. They constitute 0.01% of the resin produced. They do not reduce the production rate in the reaction system, nor do they adversely affect the quality of the resin produced. As it turns out from the above description, the following data corresponds to the formula for Vc presented in the previous section of this description: Vc «-8000 -50 ( sintering temperature) + 90 (hydrogen concentration) + 150 (operating temperature) «-8000 -0.50 (118 ° 0) +90 (18 #) +150 (90 ° C) -« +1 220 volts. Examples V - VIII. In order to determine the critical voltage, four grays are made using a reactor and using the method of Examples I and II above. Each gray used a variety of ethylene-butene-1 copolymers and / or ethylene homopolymers as shown in the table below. Critical Voltage Vc is the voltage level measured near the wall of the reactor at 1/2 the diameter of the reactor above the distribution plate when the reactor shows signs of initiation of plaque formation (normally the "skin" thermocouple then exhibits slight temperature variations above the bed temperature). The gluing temperature Bie is determined from tests in which, after the reaction is complete, the bed is allowed to settle for 15 minutes and then refluidized. The results obtained are presented in the table below: Table Example 1 V VI VII VIII H2% mol 2 11 14 30 21 Ethylene concentration% mol 3 • 53 51 50 65 Butene concentration% mol 4 24 23 7 0 Catalyst of example 5 II II II14 148 569 Table - cd Example Y VI VII VIII Resin melt index 1.0 2.0 12.0 7.5 Resin density 0.918 0.918 0.926 0.965 Sintering temperature 104 102 108 125+ Operating temperature ° C 85 85 85 110 Vc volts + 200 to +1000 +200 to +1000 +2100 +4100 From the results given in the table, for example V it can be seen that the formation of molten polymer deposits starts at a voltage above +1000 volts. In addition, the table shows that the critical stress depends on the sintering temperature of the resin, the working temperature and the concentration of hydrogen in the recycle gas. Claims 1. Method to reduce the formation of molten polymer deposits during the production of polyolefins by polymerization of α-olefins with the use of catalysts titanium-based polymerization, consisting in the neutralization of the electric charge, which is characterized by the contacting of the surfaces of the reaction vessel in which the polymerization takes place with a chromium-containing compound, such as bis (cyclopentadienyl) - chromium in an amount reducing the size of the formation of deposits formed during polymerization of at least 3 »5 x 453 x 10" "g moles of chromium / 0.0929 m. 2. The method according to claim The process of claim 1, which comprises chromium in an inert solvent. 3. The method according to claim 2, characterized in that the solvent is toluene. 4. The method according to p. The process of claim 2, wherein the inert solvent is introduced into the reaction vessel under an inert atmosphere. that the relationship is used as a neutral solution-148 569 5-n * (R ") n. (H) 5-n * FORMULA 1 28- * I PL

Claims (5)

Claims 1. A method of limiting the formation of layers of molten polymer deposits during the production of polyolefins by polymerization of α-olefins with the use of titanium-based polymerization catalysts, involving the neutralization of the electric charge, characterized by contacting the surfaces of the reaction vessel in which polymerization with a chromium-containing compound such as bis (cyclopentadienyl) -chromium in an amount reducing the size of the scale formation formed during polymerization of at least 3 "5 x 453 x 10" "g moles of chromium / 0.0929 m is important. 2. The method according to claim The process of claim 1, which comprises chromium in an inert solvent. 3. The method according to claim 2, characterized in that the solvent is toluene. 4. The method according to p. The process of claim 2, wherein the inert solvent is introduced into the reaction vessel under an inert atmosphere. in that it is used as an indifferent solution-148 569 5. -n * (R ") n. (H) 5-n * FORMULA 1 28- * I PL