In the catalysts of chemical reactions there are various reaction protocols which may be employed in the course of bringing a catalyst into contact with the reactants involved in such chemical reactions. In one type of procedure in which the catalyst system may be used and then regenerated for further use, a stream of one or more reactants is passed through a bed of the catalyst with the reaction taking place in the catalyst bed and perhaps carried to conclusion after the chemical stream passes from the catalyst bed into a post-reaction system. An alternative system in which the catalyst is "used up" involves introducing the catalyst, either continuously or intermittently, into a reaction zone where it catalyzes the chemical reaction involved and ultimately is withdrawn from the reaction zone as a minute portion of the desired product. One example of this type of operation is in reactor injection molding (RIM) in which molded articles are formed of products such as polyurethane and the like. Here, the catalyst system is actually introduced into the mold along with the polymer precursor and at the conclusion of the polymerization step the mold is opened and the molded article then withdrawn.
Another and more widely used industrial process involving the introduction of catalyst into reaction zones is in the polymerization of unsaturated hydrocarbons over catalyst systems which are generally referred to as Ziegler-Natta or simply Ziegler catalysts. Such Ziegler-type catalyst systems and their use in the polymerization of unsaturated hydrocarbons are well known in the art. The hydrocarbons involved in such polymerizations normally take the form of short chain alpha olefins such as ethylene, propylene and butylene, including substituted alpha olefins such as substituted vinyl compounds, for example, vinyl chloride or vinyl toluene. However, such unsaturated hydrocarbons can also include di-olefins such as 1-3-butadiene or 1-4-hexadiene or acetylenically unsaturated compounds such as methyl acetylene or 2-butyne.
Ziegler-type catalysts incorporate a transition metal, usually titanium, zirconium or hafnium, although other transition metals found in Groups 4, 5 and 6 of the Periodic Table of Elements may be employed, which function to provide sites .for the insertion of monomer units into growing polymer chains. One type of such polymerization catalysts are the so-called homogeneous catalyst systems in which the transition metal compound is a metallocene comprising one or more substituted or unsubstituted cyclopentadienyl groups coordinated with the transition metal atom forming the situs for polymer growth. Such metallocene-based catalyst systems are the subject of European Patent Application EP 129,368 and U.S. Pat. Nos. 4,794,096 to Ewen and 4,892,851 to Ewen et al., the latter two patents disclosing catalysts useful in the polymerization of propylene to form isotactic or syndiotactic polypropylene.
The more widely used transition metal catalysts are the so-called heterogeneous catalyst systems in which a transition metal halide, usually zirconium, hafnium or titanium, di-, tri-, or tetra-halides, are incorporated with a support structure, principally based upon magnesium or zinc halides, ethoxides or the like. For example, U.S. Pat. No. 4,476,289 to Mayr et al. discloses so-called "activated" titanium tetrahalides, more specifically, titanium tetrachloride, supported on anhydrous magnesium or zinc halides, principally magnesium chloride or magnesium bromide. The transition metal component is used in conjunction with a second component, commonly referred to as a co-catalyst, which as described in the Mayr et al. patent, is a hydride or organometallic compound based primarily upon aluminum, although lithium or magnesium based compounds are also disclosed. A supported catalyst containing yet another component is disclosed in U.S. Pat. No. 4,636,486 to Mayr et al. Here, the titanium compound, which may be a halide, an oxyhalide or an alcoholate in either the di-, tri-, or tetravalent form, is composited with the magnesium support, together with an electron donor compound. Such electron donors, commonly referred to as internal electron donors because they are incorporated as part of the transition metal catalyst component, can be selected from a broad class of compounds including amines, amides, phosphines, ethers, thioethers, alcohol esters, aldehydes, and ketones. As in the case of the aforementioned U.S. Pat. No. 4,476,289 to Mayr, the catalyst system here also includes a co-catalyst such as triethylaluminum, commonly referred to as TEAL.
Yet a third component often employed in Ziegler-type catalyst systems is a so-called external electron donor. The external electron donors function similarly as the internal electron donors and in a complimentary or supplementary manner to regulate monomer insertion into the polymer chain growing on the transition metal active sites. Thus, the electron donors can have an impact upon catalyst activity, polymer molecular weight, and polymer morphology as reflected in stereospecificity and physical parameters such as melting point. For example, in the polymerization of propylene, the addition of electron donors under controlled conditions can result in dramatic increases in activity (the amount of polymer produced per unit of catalyst) and in stereoregularity, e.g., an increase in isotactic structure with a corresponding decrease in atactic structure. The most widely used external electron donors are organosilicon compounds such as organosilanes and organosiloxanes including silyl ethers and esters such as alkyl or arylalkyl alkoxysilanes.
U.S. Pat. No. 4,287,328 to Kikuta et al., is directed to the polymerization of alpha olefins in the presence of multi-component catalyst systems involving a "solid product" combined with an organoaluminum compound including, for example, C.sub.1 -C.sub.10 trialkylaluminum, triethylaluminum, alkyl alkyoxyaluminums, and alkylaluminum halides, and an electron donor including various organic acids, alcohols, ethers, aldehydes, ketones, amines, alkenol amines, esters, phosphines, phosphites, thioethers, thioalcohols, silanes, and siloxanes. The "solid product" catalyst component is formed by reacting a trivalent metal halide such as aluminum trichloride, aluminum tribromide or ferric trichloride with a rivalent metal compound such as magnesium, calcium, or zinc hydroxide or oxide or carbonate with titanium tetrachloride, characterized as an electron acceptor. Numerous orders of additions and conditions of mixing for the various components are described in Kikula et al., especially in columns 6 through 9. The mixing of the various components can be carried out over periods of several minutes to several hours.
U.S. Pat. No. 4,567,155 to Tovrog et al., discloses multi-component catalyst systems useful in the gas phase polymerization of alpha olefins. In Tovrog et al., the catalyst systems comprise two base catalyst components, each containing subcomponents. The first component, identified as component "A" comprises a titanium component supported on a hydrocarbon insoluble magnesium component in combination with an electron compound. The second major component is a co-catalyst component, characterized as component "B" comprising a trialkylaluminum, an aromatic acid ester and an unhindered secondary amine. Tovrog discloses that catalyst components may be pre-polymerized or otherwise pretreated before being added to the reactor for periods ranging from minutes to hours. In the Tovrog procedure, catalyst components can be added together or separately through one or more valve controlled ports in the reactor vessel. In a procedure specifically described in Tovrog, aluminum alkyl, co-catalyst, and titanium catalyst component were combined in a dry box under nitrogen and flushed into a 2 liter reactor in propylene. Additional propylene and hydrogen were then charged to the reactor.
The pre-polymerization of Ziegler-type catalysts prior to the catalyst being supplied to the polymerization reactor is a well -known expedient. The pre-polymerization step is typically accomplished in a relatively small pre-polymerization reactor prior to introduction of the catalyst into the main polymerization reactor.
U.S. Pat. No. 4,767,735 to Ewen et al. discloses a pre-polymerization process carried out in an elongated tubular reactor for a period of less than a minute and usually ten seconds or less prior to introduction of the catalyst system to a loop-type reactor. Operation may be continuous or intermittent. In the Ewen et al. procedure, an organic solvent stream such as hexane or heptane is established in a pre-mixing line. To this stream are added sequentially a co-catalyst, an external electron donor and a supported catalyst component to form a catalyst system which is then pre-polymerized by contact with propylene for a few seconds in the small diameter tubular reactor. An alternative mode of operation involves adding the electron donor to the carrier stream after the addition of the catalyst component, but still before the addition of the propylene. Ewen et al. disclose that the co-catalyst should be present when the electron donor and the transition metal catalyst component contact one another in order to avoid poisoning of the titanium catalyst.
High efficiency catalyst systems employing external electron donors which may be characterized generally as sec or tert alkyl or cycloalkyl, alkyl dialkoxy silanes in combination with titanium tetrachloride supported on magnesium based supports derived from dialkoxy magnesium compounds are disclosed in U.S. Pat. No. 4,927,797 to Ewen. By way of example, the supported catalyst may be formulated through the reaction of diethoxy magnesium, titanium tetrachloride and n-butyl phthalate under appropriate conditions as specified in the patent. A suitable external electron donor here is methylcyclohexyl dimethoxysilane which is compared with diphenyldimethoxysilane as disclosed in the aforementioned Ewen et al. patent.