Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2002-04-18
2003-10-07
Choi, Ling-Siu (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S351000, C526S125300, C526S123100, C526S124100, C502S103000, C502S115000, C502S132000
Reexamination Certificate
active
06630544
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a polymerization process for propylene. In particular, the invention relates to premixing a magnesium halide-supported Ziegler-Natta catalyst with a portion of an organoaluminum cocatalyst prior to polymerization.
BACKGROUND OF THE INVENTION
Ziegler-Natta catalysts, by which we mean a transition metal compound that incorporates a Group 4-8 transition metal, preferably a Group 4-6 transition metal, and one or more ligands that satisfy the valence of the metal are known to effectively promote the high yield polymerization of olefins possessing commercially desirable characteristics. However, the use of conventional Ziegler-Natta catalysts is subject to important limitations. Thus, new and improved catalysts are continually being sought and developed.
It is known that Ziegler-Natta catalysts can be supported on magnesium halides. U.S. Pat. No. 4,124,532 discloses the polymerization of ethylene and propylene with high activity catalysts. These catalysts comprise complexes which may contain magnesium and titanium. These complexes are prepared by reacting the halide MX
2
(where M may be Mg) with a compound M'Y (where M' may be Ti and Y is one or more halogens or an organic radicals) in an electron donor compound. These complexes are then isolated by either crystallization, by evaporation of the solvent or by precipitation. Polymerization is carried out with these complexes and an alkyl aluminum compound.
U.S. Pat. No. 4,173,547 to Graff discloses contacting a carrier with an organoaluminum halide and a dialkylmagnesium compound and then contacting the treated carrier with an organotitanium compound.
U.S. Pat. No. 4,302,565 to Goeke et al. and U.S. Pat. No. 4,302,566 to Karol et al. disclose catalyst systems for producing ethylene copolymers provided by a “precursor composition” which is the solid reaction product of magnesium chloride and titanium tetrachloride. This “precursor composition” is activated with an organoaluminum compound. They set forth a continuous process for ethylene copolymer production employing a gas phase fluidized bed vertical tubular reactor. A catalyst system is provided by a “precursor composition” which is the solid reaction product of magnesium chloride and titanium tetrachloride. This “precursor composition” is activated with an organoaluminum compound. Two methods are disclosed. One is by dry blending which has the disadvantage of handling a pyrophoric solid. The other activates in a hydrocarbon slurry, the hydrocarbon solvent is removed by drying and the partially activated precursor composition is fed to the polymerization reactor where the activation is completed with additional activator compound which can be the same or a different compound. In both methods, a catalyst preparation procedure separate from the polymerization is needed. This results in extra cost and complexity.
U.S. Pat. No. 4,732,882 to Allen et al. teaches a supported organomagnesium compound which is contacted with a transition metal compound and then with trimethylaluminum. Allen teaches that trimethylaluminum is superior to other alkyl aluminum compounds, but does not recognize the benefit of premixing a portion of the alkyl aluminum. In fact, Allen teaches that the method of combining trimethylaluminum with the catalyst precursor is not critical.
U.S. Pat. No. 4,833,111 to Nowlin contacts an alcohol with a slurry of a dialkylmagnesium compound and a support and then treats the resultant slurry with a transition metal compound. This resultant slurry is contacted with a halogenated alkylaluminum compound and then that product is activated with trimethylaluminum. While Nowlin teaches improved activity due to the pretreatment with the halogenated alkyl aluminum compound he does this by first reacting the slurry of the transition metal compound with solvent, then removing the solvent under reduced pressure and then treating the catalyst precursor with trimethylaluminum. Nowlin's process is complicated, involves several steps, and requires specific and different aluminum compounds.
U.S. Pat. No. 6,187,866 provides for the in-situ blending of polymers by contacting ethylene and one or more comonomers in two or more fluidized bed reactors connected in series under polymerization conditions with a catalyst system. The catalyst system is based upon a magnesium/titanium based precursor containing an electron donor which is treated with a precursor activator to influence the melt flow ratio of the polymer blend and then with a hydrocarbyl aluminum cocatalyst to complete the activation. By this process, they control the melt flow ratio of the blend or the bulk density of the blend. To activate the catalyst slurry, they treat with a first alkyl aluminum compound for 1-4 hours and then with a second alkyl aluminum compound for another 1-4 hours followed by complete activation in the polymerization reactor. The process is complicated and limited to the in situ blending of polymers.
Despite the importance of olefin polymerizations and the considerable research that has been done on various catalyst systems, there remains a need to improve the activity of the catalyst. This can be important from a cost view since the catalyst is typically one of the more costly ingredients. Similarly, the equipment for catalyst handling can add to the cost. Any improvement in catalyst activity decreases these costs. However, even more important is that the residual metal in the polymer is reduced. High levels of residual metal can have a deleterious effect on polymer properties such as color and aging. It is therefore important to keep the residual metals as low as possible. Any improvement in catalyst activity lowers the residual metals in the polymer.
SUMMARY OF THE INVENTION
The invention is a process for making polypropylene. A magnesium halide-supported Ziegler-Natta catalyst is premixed with 1 to 10% of an organoaluminum cocatalyst. This premix is then added to a heated mixture containing propylene and 90 to 99% of the organoaluminum cocatalyst. Temperature is maintained for the reaction mixture to produce polypropylene.
The process of the invention is easy to practice and affords enhanced catalyst activity. Since the catalyst is not removed from the final polymer, an increase in activity results in a polymer with lower residual metals. The process is robust and gives an improvement in activity for copolymers of propylene as well as the homopolymer. It is effective in the presence of molecular weight regulators and modifiers which can be used in propylene polymerizations.
DETAILED DESCRIPTION OF THE INVENTION
In the first step of the process of the invention, propylene is mixed with from about 90 to 99% of the organoaluminum cocatalyst.
The organoaluminum cocatalyst is an alkyl aluminum or an alkyl aluminum halide. Preferred alkyl aluminums include trialkyl or triaryl aluminum compounds, which preferably have the formula AIR
3
where each R is a C
1
-C
30
hydrocarbyl. Particularly preferred alkyl aluminums are trimethylaluminum, triethylaluminum, tri-n-propylaluminum triisopropyl-aluminum, tri-n-butylaluminum, triisobutylaluminum, and tri-n-hexyl-aluminum. Suitable alkyl aluminum halides include dialkyl aluminum halide and alkyl aluminum dihalide compounds, which preferably have the formula AIR
2
X or AIRX
2
where X is Cl, Br, or I.
Exemplary alkyl aluminum halides are dimethylaluminum chloride, methylaluminum dichloride, diethylaluminum chloride, ethylaluminum dichloride, diisobutylaluminum chloride, isobutylaluminum dichloride, methylaluminum sesquichloride, ethylaluminum sesquichloride, and isobutylaluminum sesquichloride.
Preferably, organosilane modifiers are used in the polymerization. These help to maintain and control the stereoregularity of the polymer. They can also offer certain improvements such as an improved sensitivity to hydrogen as a means of controlling molecular weight. Preferred organosilane modifiers are alkyl alkoxysilanes which have the formula R
y
Si(OR)
4−y
where R is as previously described and y is an integ
Kist Edward D.
Klendworth Douglas D.
Meyer Karen E.
Reinking Mark K.
Choi Ling-Siu
Schuchardt Jonathan L.
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