The invention relates to a process for the preparation of an olefin polymerization catalyst component containing magnesium, titanium, halogen and an electron donor. The invention also relates to such a catalyst component and its use for the polymerization of xcex1-olefins such as propene.
Generally, so called Ziegler-Natta catalyst components of the above kind have been prepared by reacting a magnesium halide-alcohol complex with a titanium tetra-halide and an electron donor which usually is a phthalic acid diester. The preparation involves the use of large amounts of reagents and washing liquids, which are difficult to handle. Additionally, byproducts are formed, which cannot easily be regenerated or destroyed, but form an environmental problem.
For example, the preparation of a conventional polypropene catalyst component involves the reaction of a magnesium dichloride-alcohol complex with titanium tetrachloride to give reactive xcex2-magnesium dichloride as intermediate and hydrogen chloride and titanium alkoxy trichloride as byproducts. Then, the reactive xcex2-magnesium dichloride intermediate is activated with further titanium tetrachloride to give said catalyst component (the treatment with a titanium halide such as titanium tetrachloride is henceforth called titanation).
The titanium alkoxy trichloride byproduct formed in the titanation is a catalyst poison and must be carefully removed by extensive washing using large amounts of titanium tetrachloride. Further, the titanium alkoxy trichloride must be carefully separated from the titanium tetrachloride washing liquid, if the latter is to be reused e.g. for activating the reactive xcex2-magnesium dichloride. Finally, the titanium alkoxy trichloride is a problem waste, which is difficult to dispose of.
Thus, in a typical propene polymerization catalyst component preparation involving two titanations and three heptane washes, one mol of produced catalyst component (mol Mg) requires about 40 mol of titanium tetrachloride e.g. as washing liquid to be circulated (see Table 15 below), and produces as problem waste about three mol of titanium alkoxy trichloride as well as about three mol of hydrogen chloride.
Sumitomo, EP 0 748 820 A1 (hereinafter referred to as xe2x80x9cSumitomoxe2x80x9d), has prepared dialkoxy magnesium, reacted it with titanium tetrachloride to form an intermediate and then reacted the intermediate with phthalic acid dichloride to form a catalytically active propene polymerization catalyst component. The activity was raised by repeated titanations, as well as repeated washes with toluene and hexane. See page 10, lines 14 to 37, of said publication.
Said process of Sumitomo has avoided the reaction between the magnesium dichloride-alcohol complex and titanium tetrachloride, and thereby eliminated the formation of catalytically poisonous titanium alkoxy trichloride byproduct. However, as much as four titanations and hydrocarbon treatments are still needed to give satisfactory catalytic activity.
The purpose of the present invention is to provide a process which results in a catalyst component having satisfactory activity without producing harmful byproducts such as said titanium alkoxy trichloride or requiring the use of a large amounts of titanation reagent and/or washing liquid.
The problem described above has now been solved with a novel process for the preparation of a catalyst component of the above type, which is mainly characterized by the steps of:
(i) reacting a titaniumless magnesium compound (a) containing an alkoxy moiety, which titaniumless magnesium compound is selected from the group consisting of a compound or conplex containing halogen and alkoxide linked to magnesium, a complex containing a magnesium dihalide and an alcohol, and a non-complex magnesium dialkoxide, with a halogen compound (b) being capable of forming the electron donor by replacement of its halogen by said alkoxy moiety, to give an intermediate (ab); and
(ii) reacting said intermediate (ab) with a titanium halide (c), or
(i)xe2x80x2 reacting a titaniumless magnesium compound (a) containing an alkoxy moiety, which titaniumless magnesium compound is selected from the group consisting of a compound or complex containing halogen and alkoxide linked to magnesium, and a complex containing a magnesium dihalide and an alcohol, with a titanium halide (c), to give an intermediate (ac), and
(ii)xe2x80x2 reacting said intermediate (ac) with a halogen compound (b) being capable of forming the electron donor by replacement of its halogen by said alkoxy moiety.
It was found by the applicant, that the activity of a stoichiometric catalyst component, comprising a magnesium dihalide, a titanium tetrahalide and an electron donor, is the higher, the more magnesium dihalide it contains. Thus it is believed, that the purpose of the repeated toluene washes of e.g. Sumitomo has partly been to remove titanium tetrachloride and electron donor from the catalyst component precursor in order to raise the magnesium dichloride content and thus the catalytic activity, of the final catalyst component. The present invention solves the problem in another way. In the claimed process, magnesium dihalide is included or synthesized as part of the reacting material before any titanation takes place, and thus, the need for repeated cycles of titanation and washing is significantly reduced.
Preferably one, most preferably all of steps (i), (ii), (i)xe2x80x2 and (ii)xe2x80x2 are performed in solution. Then, the reaction product of step (ii) or (ii)xe2x80x2 is preferably recovered by precipitation.
According to one embodiment of the present invention, said compounds (a), (b) and (c) are in the claimed process contacted in essentially stoichiometric amounts. According to another embodiment, a stoichiometric excess, preferably a 5-20 fold excess, of said titanium halide (c) with respect to said magnesium compound (a), gives even better results.
Said halogen compound (b) used in the claimed process is an electron donor precursor, i.e. itself capable of forming the electron donor of the catalyst component by replacement of its halogen by an alkoxy group. By electron donor is in this connection meant an electron donor which forms a part of the titanous catalyst component produced by the claimed process and is in the art also called an internal electron donor. Such halogen compounds (b) are, e.g., C1-C20 alkyl halides, C7-C27 aralkyl halides and C2-C22 acyl halides, which react with alkoxy compounds to replace their halogen with the alkoxy group of the alkoxy compound and form e.g. the corresponding ethers and esters acting as internal electron donors.
Preferably, said halogen compound (b) is an organic acid halide having the formula Rxe2x80x3(COXxe2x80x2)n, wherein Rxe2x80x3 is an n-valent organic group having 1-20 carbon atoms, preferably an n-valent benzene ring, Xxe2x80x2 is a halogen, preferably chlorine; and n is the valence of Rxe2x80x3 and is an integer 1 to 6, preferably 1, 2, 3 or 4, more preferably 2. Most preferably, said halogen compound is phthalic acid dichloride Ph(COCl)2, wherein Ph is o-phenylene. Correspondingly, the electron donor formed therefrom is preferably an organic acid ester having the formula Rxe2x80x3(COOR)n, wherein R is an n-valent C1-C20 aliphatic group or an n-valent C7-C27 araliphatic group and Rxe2x80x3 and n are the same as above, and more preferably a phthalic acid diester Ph(COOR)2, wherein R is a C1-C20 alkyl or a C7-C27 aralkyl, more preferably a C1-C16 alkyl. Most preferably said electron donor is dioctyl phthalate.
The titanium halide (c) used in the claimed process is preferably a titanium halide of the formula (ORxe2x80x2)kTiX4-k, wherein Rxe2x80x2 is an alkyl group having 1 to 10 carbon atoms or an aralkyl group having 7 to 16 carbon atoms, X is a halogen and k is 0 to 3. More preferably, said titanium halide (c) is a titanium tetrahalide TiX4, wherein X is the same as above, most preferably titanium tetrachloride TiCl4.
It is preferable, if said titaniumless magnesium compound (a) is not a part of a solid magnesium halide, e.g. in the form of complex molecules on the surface of a solid magnesium halide carrier, but form a separate compound with an essentially stoichiometric composition. Often, said titaniumless magnesium compound is a complex. A complex is, according to Rxc3x6mpps Chernie-Lexicon, 7. Edition, Franckh""sche Verlagshandlung, W. Keller and Co., Stuttgart, 1973, page 1831, xe2x80x9ca derived name of compounds of higher order, which originate from the combination of molecules,xe2x80x94unlike compounds of first order, in the creation of which atoms participatexe2x80x9d.
According to one embodiment of the invention, the titaniumless magnesium compound (a) used in the claimed process is a titaniumless complex of the formula [MgX2]x.[K(OR)m]y, wherein X is a halogen, K is hydrogen, a metal of group 1, 2 or 13 of the Periodic Table, R is an alkyl having 1 to 20 carbon atoms, an aralkyl having 7 to 27 carbon atoms or an acyl having 2 to 22 carbon atoms, x is 0 to 20, m is the valence of K and is an integer from 1 to 6, and y is 1 to 20.
The magnesium dihalide MgX2 of said titaniumless complex (a) can be selected from magnesium chloride, magnesium bromide and magnesium iodide. Preferably, it is magnesium dichloride.
The alkoxy compound K(OR)m is in its most general form defined as a component of said titaniumless complex (a), which complex (a) is reacted further with said halogen compound (b) and said titanium halide (c) or said titanium halide (c) and said halogen compound (b). The alkoxy compound is, however, more closely defined in the following description of three main embodiments of the claimed process.
The gist of the invention is to choose the reactants and their order of reaction so that the magnesium dihalide is present when the titanium halide (c) is reacted.