Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Plural component system comprising a - group i to iv metal...
Reexamination Certificate
2000-01-21
2002-09-17
Wu, David W. (Department: 1713)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Plural component system comprising a - group i to iv metal...
C502S117000, C526S129000, C526S160000, C526S907000, C526S943000
Reexamination Certificate
active
06451725
ABSTRACT:
The invention relates to a method for preparing catalyst components. Particularly the invention relates to a method for making catalysts comprising metallocenes of transition metals. Further the invention relates to a process for homo or copolymerization of alphaolefins in the presence of the catalysts made by the method.
Recent developments in the field of olefin polymerization catalysts include metallocene catalysts, which comprise metallocene compounds of transition metals together with alumoxane compounds. These catalysts have been suggested to be used as a homogenous system or deposited onto carrier, for example inorganic oxide carriers. Thus these catalysts typically comprise as a procatalyst component a metallocene compound, for example bis(cyclopentadienyl)titanium dialkyl or bis(cyclopentadienyl)zirconium alkonyl or chlorides thereof, and an activator component, which typically is alumoxane or an ionic activator.
One known problem related to the use of metallocene catalysts is the poor morphology of the resulting polymer particles, which can be seen as a low bulk density and as inhomogenous polymer. Because of the so-called replication phenomena the forming polymer particles assume similar morphology as the catalyts particles used to polymerize monomers, the problems related to poor morphology of polymer can be decreased by improving the morphology of the catalysts used for polymerization.
Supported metallocene catalysts are typically prepared by impregnating methylalumoxane and metallocene compound onto a support or carrier material. Such methods are usually slurry or solution methods, in which the first step is the formation of a solution of the metallocene compound and alumoxane. This solution is added into a porous carrier material, after which the solvent is removed by evaporation. Most often the solvent is used in rather big amounts, even so that the carrier material is added to a solution of metallocene and alumoxane compounds. This kind of method necessitates an efficient evaporating, in which the components rather tend to deposit on the surface of the carrier than to impregnate evenly into the pores of the carrier material. Thus the method leads normally to catalysts having a bad morphology, uneven metallocene distribution on the carrier and thus to a bad quality of polymer particles and to an unnecessarily low catalyst activity.
The use of high amounts of solvents in the preparation of the catalysts is, as such, a disadvantage. There are also methods known in which the amount of the solvent used is limited. Thus for example, in W094/21691 there is disclosed a method in which the support comprises porous silica, which is contacted with a volume of a mixture comprising a metallocene and an alumoxane, wherein the volume of the mixture is no greater than the total pore volume of the silica. After evaporation of the solvent an active catalyst is achieved, which results in lower fouling of the reactor and improved polymer morphology in the polymerization of alphaolefins.
All methods based on the impregnation of metallocene/alumoxane solutions onto carriers have certain disadvantages. After the evaporation of the solvent the catalysts are in active form and therefore they are very sensitive for poisoning. During a prolonged storage this can lead to a deactivation of the catalyst. This problem can be avoided by preparing the catalysts just before use. However the catalyst preparation itself requires a considerable amount of time involving one or more solvent evaporation steps and so on. Most often the site of the catalyst preparation and the site of polymerization are very far from each other and the transport of the catalyst takes time.
Another disadvantage of the known metallocene catalyst preparation methods is that the solubility of most metallocenes is very poor even in aromatic solvents. A further disadvantage of the known methods in which solutions of metallocene compounds and alumoxane compounds are used is that the stability of these complex solutions is very poor. Yet another disadvantage for some applications is the low molecular weight of the polymerized product. For example, Inoue et al. disclose a method which produces a syndiotactic polypropylene wax having an intrinsic viscosity in a range of 0.01-0.4 dl/g as measured at 135° C. in a tetralin solution, corresponding to a molecular mass of 70-14,000. Thus, there is a need for improved methods for making metallocene catalysts without the disadvantages described above.
The present invention relates to a method for preparing metallocene catalysts for olefin polymerization while avoiding the disadvantages described above. Thus, one object of the invention is a method for making metallocene catalyst components, where the disadvantages related to catalyst poisoning, poor solubility of metallocenes and poor stability of metallocene/alumoxane complexes can be avoided. A further object of the invention is a method in which metallocenes having good morphology and hence a good morphology of the polymer is achieved. Thereby polymers having a very small amount of fines can be produced. Yet another object of the invention is to manufacture a polymer with a narrow molecular weight distribution measured with GPC.
According to the invention it has been surprisingly found that it is possible to add metallocenes onto catalyst carriers without any solvents in a temperature which is, however, below the boiling point of the metallocene compound. Thus the elimination of this step characteristic to all methods in prior art makes possible to avoid the disadvantages of the known methods and to achieve the goals of the invention.
Thus one embodiment of the invention relates to a method for preparing catalyst components for ethylene homo or copolymerization, which catalyst component comprises at least one metallocene compound on porous carrier or support material. The catalyst component is prepared by mixing a metallocene compound, as a pure compound, with a carrier, in the absence of solvents, at a temperature which is at least 50° C., but below the vapourization temperature of the metallocene compound in reactor conditions for a sufficient time so as to obtain the catalyst component with metallocene evenly distributed onto the carrier particles.
By mixing the carrier material with said metallocene in the absence of any solvents a so-called “dry mixing method” having several advantages is achieved. The poor solubility of most metallone compounds into typical solvents and the extra step of removing these solvents are no longer problems. The catalyst according to the method has good morphology properties and no tendency towards fouling in the polymerization. The polymers produced by using the catalysts of the invention have good morphology properties, narrow molecular weight distribution and composition distribution.
The essential feature of the invention is that the metallocene compound is mixed with the carrier particles in dry state. This means that no solvents are used. The metallocene is physically mixed with the carrier material at an elevated temperature for a sufficient time to achieve an even distribution of the metallocene onto carrier particles. The mixing is carried out in the temperature which is at least 50° C. but below the vapourization temperature of the metallocene compound in reaction conditions.
Different metallocene compounds have different melting and boiling points and therefore, different mixing temperatures for each metallocene compound can be used. The upper limit for the highest temperature applicable is the temperature where the metallocene compound vaporizes. Therefore, it is possible to use temperatures, in which the metallocene compound is flowing or even melted. However, in some cases the temperature can be below the melting point of the metallocene compound. The reasons why in such temperatures an even distribution of the metallocene compound can be achieved, is not exactly known, but it is possible that the contact of carrier particles with the metallocene compound at an elevated temperature inc
Hokkanen Harri
Knuuttila Hilkka
Salo Eija
Birch & Stewart Kolasch & Birch, LLP
Borealis Technology Oy
Rabago R.
Wu David W.
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