Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2002-12-18
2004-04-06
Cheung, William (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S129000, C502S256000, C502S234000, C502S254000
Reexamination Certificate
active
06716938
ABSTRACT:
This invention relates to polymerization catalyst systems and polymerization processes.
Supported chromium oxide catalyst systems long have been used to prepare olefin polymers in hydrocarbon solution or slurry processes to give products having excellent characteristics from many standpoints. A number of supports have been broadly disclosed in the art for the support of chromium oxide catalyst systems including, silica, alumina, boria, zirconia, silica-alumina, and other refractory metals. In order to obtain a polymer product with easy processing characteristics, catalyst systems preferably have a low pore volume and high surface area. Generally, it is recognized that catalyst systems having a low pore volume and high surface area can result in a higher melt index and produce an olefin polymer that is easier to process. Unfortunately, it also has been found that decreasing the catalyst system pore volume usually corresponds to a decrease in the catalyst system surface area. These catalyst systems provide polymers with extraordinarily good properties which can only be achieved presently on the commercial scale by making bimodal polymers from two reactors. Thus the first benefit is one of economics. With the magnesia modified silica catalyst we get polymers with fabulous properties more cheaply than our competitors. For our HMW film it is necessary to add a fluoropolymer to process the resin when it is blown into film. So processing is not the real forte for this particular catalyst system. These characteristics are contrary to what is desired for polymer processability.
It is also known that catalyst systems need to be dry for best polymerization productivity and activity. Therefore, catalyst systems are heated and dried prior to use. Unfortunately, heating of catalyst systems can cause problems with catalyst system integrity. For example, if a catalyst system uses a silica-based inorganic oxide support, heat can cause the silica to melt, or sinter, and therefore decrease the surface area of the resultant catalyst system. If alumina is selected as a support material, heating of the alumina can cause the alumina to fracture and create uneven and rough catalyst system particulates which can result in a polymer product that is difficult to handle.
SUMMARY OF THE INVENTION
Therefore, it is an object of the invention to provide an improved silica-containing inorganic oxide catalyst system supports.
It is yet another object of this invention to provide a silica-containing inorganic oxides having a high surface area.
It is a further object of this invention to provide novel silica-containing inorganic oxides that either retain or increase surface area upon heating.
It is a further object of this invention to provide an improved chromium catalyst system.
It is yet another object of this invention to provide a catalyst system suitable for use in polymerization processes.
It is yet another object of this invention to provide a chromium catalyst system that can produce an olefin polymer having a decreased melt index.
In accordance with one embodiment of this invention a process is provided to prepare a magnesium treated silica-containing composition comprising contacting a silica-containing inorganic oxide with a magnesium-containing compound and converting said magnesium-containing compound to a magnesium oxide to produce a magnesium treated silica-containing composition.
In accordance with another embodiment of this invention a process is provided to contact said magnesium treated silica-containing composition with a chromium compound to produce a catalyst system composition.
In accordance with yet another embodiment of this invention a polymerization process is provided using a catalyst system comprising chromium supported on a magnesium treated silica-containing composition.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In accordance with the present invention, a predominately silica-containing compound is contacted with at least one magnesium compound convertible to the oxide form, and then calcined. The essence of this invention is either precipitating, or doping, magnesium within the pores of a silica-containing compound. Magnesium treatment of the silica-containing compound can be done in accordance with different embodiments of the invention, discussed in detail below. The resultant magnesium treated silica-containing compound can be used as a catalyst system support. As used in this disclosure, the term “support” refers to a carrier for another catalytic component. However, by no means, is a support necessarily an inert material; it is possible that a support can contribute to catalytic activity and selectivity.
Silica-containing compounds employed to prepare polymerization catalyst systems of the present invention must contain a major proportion of silica. Preferred silica-containing compounds contain a substantial proportion of silica, e.g., at least about 50% by weight of silica, preferably at least about 70%, and most preferably 90%, by weight of silica, although still larger proportions of silica can be used. The preferred predominantly silica-containing compounds of the present invention consist essentially of less than about 50% by weight of at least one additional metal oxide such as, for example, alumina, boria, magnesia, titania, zirconia and mixtures of any two or more thereof. Generally, the silica-containing compound employed has a surface area, prior to magnesium treatment, of at least about 10 square meters per gram (m
2
/g). Preferably, the initial surface area of the silica-containing compound, prior to treatment with a magnesium compound, can be at least 50 m
2
/g, and most preferably, any silica-containing compound employed is a high surface area silica, i.e., support, with a surface area in excess of about 100 m
2
/g.
In accordance with one embodiment of this invention, a magnesium salt can be used in a very concentrated aqueous solution and precipitated within the pores of a silica-containing compound. Exemplary magnesium salts include, but are not limited to, magnesium nitrate, magnesium chloride, magnesium acetate, and mixtures thereof. The concentrated aqueous solution of the magnesium salt is mixed with the silica-containing compound. Mixing can occur by spraying the aqueous solution containing the magnesium salt onto the silica-containing compound, or by slurrying the aforementioned components together. The concentration of the aqueous magnesium solution can be any amount sufficient to deposit enough magnesium into the pores of the silica-containing compound to increase the surface area of the silica-containing compound and yet, not significantly decrease the pore volume of the silica-containing compound. Usually, concentrations of about 125 millimoles of the magnesium salt per 100 g (mmol/100 g) of support are sufficient. Preferably, concentrations within a range of about 200 to about 700 mmol/100 g of support and most preferably, within a range of 250 to 400 mmol/100 g of support, are preferred. Higher or lower magnesium salt concentrations do not have significant, beneficial effects on surface area.
Contacting conditions of the silica-containing compound and the magnesium compound are not critical. Any temperature and any period of time can be suitable. For convenience, contacting generally is carried out at about room temperature, although higher or lower temperatures, within a range of about 40° F. to about 100° F., can be used. A time period sufficient to allow the support and magnesium compound to come into intimate contact is all that is necessary. Thus, the silica-containing compound and the magnesium salt solution can be brought into contact for as little time as a few seconds to several hours or more, such as, for example, about 5 seconds to about 24 hours, as convenient.
After sufficient contact time, any basic compound can be added to the magnesium/silica-containing compound slurry to precipitate the magnesium within the pores of the silica-containing compound. Exemplary basic compounds include, but are not limited to hydroxides, such as for ex
Benham Elizabeth A.
Collins Kathy S.
Eaton Anthony P.
Martin Shirley J.
McDaniel Max P.
Cheung William
Kilpatrick & Stockton LLP
Phillips Petroleum Company
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