Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymerizing in tubular or loop reactor
Reexamination Certificate
1995-02-27
2001-03-06
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymerizing in tubular or loop reactor
C526S118000, C526S119000, C526S124200, C526S129000, C526S153000, C526S348200, C526S348400, C526S348500, C526S352000, C526S904000
Reexamination Certificate
active
06197899
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the polymerization of olefins. In one aspect the present invention relates to slurry or particle form polymerization. In another aspect the present invention relates to olefin polymerization using a continuous loop-type reactor. In still another aspect the present invention relates to novel catalyst systems for use in the polymerization of olefins.
BACKGROUND OF THE INVENTION
One of the more common techniques employed for the polymerization of olefins involves carrying the polymerization out in a liquid diluent under conditions such that the polymer is formed in the forms of solid particles such that the reaction product is a slurry of particulate polymer solids suspended in a liquid medium. Such reaction techniques have been referred to as slurry or particle form polymerizations. A particularly desirable method for carrying out such particle form polymerization involves the use of continuous loop-type reactors. Examples of such reactor systems are disclosed in U.S. Pat. No. 3,152,872 and U.S. Pat. No. 4,424,341, the disclosures of which are incorporated herein by reference.
In the past, many of the commercial particle form polymerization processes have used chromium based catalysts. Such processes have, however, also been carried out using titanium based catalyst and organometallic cocatalysts.
When using low levels of cocatalyst in the particle form polymerization the applicants have noted some problems in using a titanium based catalyst. Even though the levels of cocatalysts are high enough to ensure sufficient productivity, it has been observed that with a titanium-containing catalyst system when the level of cocatalyst drops below a certain level there is a tendency for a skin of some type to form within the reactor walls inhibiting heat transfer. On bench scale units where the polymerization is only an hour or so long and where heat transfer is usually not critical the phenomena is usually not observed. However, in commercial scale polymerizations, particularly in loop reactors the phenomena has been observed.
The exact nature of this skin formation is not understood at this time. It has been theorized by the applicants that it may be due to the formation of soluble polymer or soluble catalyst. One theory of the applicants is that it may actually be due to the bleeding off of hydrocarbon soluble species from the catalyst.
An object of the present invention is to provide a method for the particle form polymerization of olefins using a titanium containing catalyst system with a reduced tendency to cause the formation of a skin during the polymerization.
Another object of the present invention is to provide a process for the particle form polymerization of olefins using a titanium based catalyst which can be employed satisfactorily with low cocatalyst levels.
Another object of the present invention is to provide a titanium catalyst which can be used in a commercial scale particle form polymerization without the employment of high levels of cocatalyst.
Other aspects, objects, and advantages of the present invention will be apparent to those skilled in the art having the benefit of the following disclosure.
SUMMARY OF THE INVENTION
In accordance with the present invention there is provided a method for the polymerization of olefins which comprises contacting an olefin with a titanium-containing catalyst under particle form polymerization conditions in a polymerization zone wherein said catalyst is prepared by contacting a particulate titanium-containing catalyst having hydrocarbon soluble titanium components with an organometallic reducing agent prior to the introduction of the catalyst into the polymerization zone.
In accordance with another aspect of the present invention there is provided a catalyst for the polymerization of olefins. The catalyst is prepared by contacting a particulate titanium-containing catalyst having hydrocarbon soluble titanium components with an organometallic reducing agent prior to the introduction of the catalyst into the polymerization zone.
In accordance with a particularly preferred embodiment the titanium-containing catalyst is prepared by contacting a titanium alkoxide and a magnesium dihalide in a suitable liquid to produce a solution, the solution is contacted with a suitable precipitating agent to obtain a solid, the solid after possibly being contacting with olefin to form prepolymer is contacted with titanium tetrachloride, and then the resulting solid is contacted with a hydrocarbyl aluminum compound prior to the introduction of the solid into a polymerization vessel.
DETAILED DESCRIPTION OF THE INVENTION
It is considered that this invention would have application for any particle form polymerization when the catalyst is a titanium-containing catalyst which contains hydrocarbon soluble titanium components. A wide range of such titanium-containing catalysts are known. Some examples of such catalysts include those disclosed in U.S. Pat. Nos. 4,477,586; 4,394,291; 4,325,837; 4,326,988; 4,363,746; 4,329,253; 4,618,661; 4,626,519; 4,555,496; 4,384,982; 4,406,818; and 4,384,982; the disclosures of which are incorporated herein by reference. For the purpose of this disclosure a catalyst is deemed to be a catalyst containing hydrocarbon soluble titanium components if the titanium components are soluble when the catalyst is placed in a C
4
to C
8
hydrocarbon at a temperature in the range of 0° C. to 110° C.
The organometallic reducing agent that is contacted with the titanium-containing solid catalyst can be selected from generally any of those type of organometallic reducing agents that have in the past been used as cocatalysts with such titanium-containing catalysts. Examples include organometallic compounds such as hydrocarbyl aluminum compounds, hydrocarbyl boron compounds, and hydrocarbyl alkali or alkaline earth metal compounds. Some specific examples of such reducing agents include triethylboron, diethylmagnesium, diethylzinc, n-butyl lithium, and the like. The currently preferred organometallic reducing agent is selected from compounds of the formula R
m
AlZ
3-m
wherein R is a hydrocarbyl group having 1 to 8 carbons, Z is a halogen, hydrogen, or hydrocarbyl group having 1 to 8 carbons, and m is a number in the range of 1 to 3. The currently most preferred organometallic reducing agents are selected from trialkylaluminum compounds, especially triethylaluminum.
The amount of reducing agent employed in pretreating the titanium-containing catalyst can vary over a wide range. The optimum amount needed for the best overall improvement in the particle form polymerization can be determined by routine experimentation. Generally, excess organometallic reducing agent can be used; however, in such cases it is desirable to subject the resulting product to a number of washes with a hydrocarbon solvent to assure that soluble organometallic reducing agent is removed from the catalyst prior to the introduction of the catalyst into the polymerization process.
The invention is particularly useful when applied to a titanium-containing catalyst containing olefin prepolymer of the type disclosed in U.S. Pat. No. 4,325,837. Such catalysts are prepared by reacting a titanium alkoxide with a magnesium dihalide in a suitable liquid to form a solution. The resulting solution is then contacted with a suitable precipitating agent and the resulting solid is contacted with titanium tetrachloride either before or after prepolymer of an olefin is added to the solid.
Examples of the titanium alkoxides include the titanium tetraalkoxides in which the alkyl groups contain 1 to about 10 carbon atoms each. Some specific examples include titanium tetramethoxide, titanium dimethoxide diethoxide, titanium tetraethoxide, titanium tetra-n-butoxide, titanium tetrahexyloxide, titanium tetradecyloxide, titanium tetraisopropoxide, and titanium cyclohexyloxide.
The magnesium halide is preferably selected from magnesium chlorides.
The titanium alkoxide and the magnesium dihalide can be combined in any suitable liquid. Examples
Benham Elizabeth A.
Cone Grover W.
McDaniel Max P.
Mitchell Kent E.
Welch M. Bruce
Bowman Edward L.
Phillips Petroleum Company
Wu David W.
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