Supported polymerization catalysts

Details Supported polymerization catalysts Supported polymerization catalysts

2001-04-09

2003-12-16

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...

C526S348000, C526S943000, C502S152000, C502S087000

Reexamination Certificate

active

06664352

ABSTRACT:

This invention relates to supported polymerization catalysts.
In the preparation of polymers, e.g. polyolefins and in particular polypropylenes and polyethylenes, it is conventional practice to use catalysts such as Ziegler Natta or metallocene catalysts. These, in particular the metallocene catalysts, may particularly effectively be used in supported form, i.e. where the catalyst has been impregnated into a porous, particulate inorganic or organic support material, e.g. an inorganic oxide such as silica, alumina, silica-alumina, or zirconia, an inorganic halide such as a magnesium chloride, or an organic polymer such as an acrylate or a styrene-divinylbenzene. The use of a support for the catalyst improves the handling characteristics of the polymer product and gives better control of reaction rates.
Such supported catalysts may be prepared by mixing the support (optionally after a heat treatment step) and a liquid containing the catalyst, using quantities of the liquid which are comparable to the pore volume of the support material such that catalyst waste is avoided. Using such small volumes of liquid, the formation of a mud or a slurry is avoided and in effect the mixing process is a dry-mixing process. While slurry mixing provides uniformity of loading of catalyst onto support which is superior to that achieved in conventional dry mixing, the volume of solvent used is significantly higher and this is environmentally undesirable. Moreover, with slurry mixing, the supported catalyst often has to be washed in order to avoid fouling in the polymerization reactor.
In general, the support and the catalysts are stirred during the impregnation step, e.g. using a magnetic stirrer or a helical stirrer.
The preparation of supported polymerization catalysts is described for example in NO-C-171858 (Neste), U.S. Pat. No. 5,559,071 (Hoechst), U.S. Pat. No. 5,625,015 (Exxon) WO95/11263 (Mobil), WO95/15216 (Borealis), WO95/12622 (Borealis), WO94/14855 (Mobil) and WO96/16093 (Exxon).
We have now found that the properties of such supported catalysts are improved if the mixing of catalyst and support is effected using mixing apparatus which creates a mechanically fluidized bed of the particulate support material in which catalyst impregnation may take place.
Many fluid bed devices are known—indeed at its simplest a fluid bed of a solid particulate material can be created by passing a continuous flow of gas through the particulate material. However by use of a mechanically created fluidized bed the loss of solvent during impregnation is avoided and gas generated fluid beds provide little if any mixing effect. By mechanically fluidized it is meant that bed fluidization is achieved at least partly through the use of agitation of the particles caused by a mechanical, ie. solid, apparatus, preferably a mixing apparatus, rather than solely by passage of a gas through the bed. Gas passage may be used in addition to mechanical agitation but, as mentioned above, this may be undesirable due to solvent loss.
Thus viewed from one aspect the invention provides a process for the preparation of a supported polymerization catalyst, e.g. a catalyst for the polymerization of C
2-10
&agr;-olefins, in particular propylene and ethylene, said process comprising impregnating a porous particulate support in a mechanically fluidized state with at least one catalyst material or component thereof.
Viewed from a further aspect the invention provides the use of a supported catalyst prepared according to the process of the invention as a polymerization catalyst.
Viewed from a yet still further aspect the invention provides a method for the preparation of a polymer, said method comprising impregnating a mechanically fluidized porous particulate support material with a catalyst or two or more components thereof and polymerizing a monomer or monomer mixture in the presence of the catalyst-impregnated support material.
Mixing methods may be characterized by their Froude number (Fr) which is given by the equation
Fr
=
R
⁢
 
⁢
ω
2
g
i.e. the ratio of centrifugal force to gravity. Mixers generally fall into the categories:
1. Froude number below 1 (e.g. thrust mixers and free fall mixers)
2. Froude number above 1 (e.g. fluid bed mixers)
3. Froude number considerably above 1 (e.g. centrifugal and intensive mixers).
The mixers used according to the present invention will generally have a Froude number of 1.005 to 2.8, more preferably 1.05 to 2.2.
More particularly, the mixers used according to the invention will preferably put at least 30% wt, more preferably at least 50% wt of the support material into a “weightless” condition when in operation (see for example Forberg, Mixing-powder handling and processing 4: 318 (September 1992)).
The support material used according to the invention is conveniently an inorganic or organic material, e.g. an inorganic oxide such as silica, alumina, silica-alumina, zirconia, magnesia or titania, talc or an inorganic halide such as magnesium chloride, or a polymer such as an acrylate, methacrylate or styrene-divinylbenzene. Silica, alumina or titania or combinations thereof loaded with chromium compounds e.g. chromium oxides, may also advantageously be used as support materials.
Preferably the support material, if inorganic, is subjected to a heat treatment (calcination) before catalyst impregnation, e.g. by a period of heat treatment in a dry, non-reducing (e.g. oxygen containing) atmosphere such as air at a temperature of at least 200° C., preferably at least 400° C. and especially preferably at least 600° C., for a period of 0.5 to 50 hours, e.g. 2 to 30 hours, preferably 10 to 20 hours. The support material before calcination conveniently has a surface area of 20 to 1000 m
2
/g (BET method), e.g. 100 to 400 m
2
/g, a porosity of up to 5 mL/g, e.g. 0.2 to 3.5 mL/g and a mean particle size of 3 to 250 &mgr;m, especially 5 to 200 &mgr;m, preferably 5 to 100 &mgr;m, e.g. 5 to 50 &mgr;m, in particular 10 to 40 &mgr;m. The average pore diameter in the support is preferably 10 to 1000 Å, e.g. 50 to 900 Å, more preferably 40 to 350 Å. Examples of suitable support materials include Sylopol 2109 (a silica available from Grace Davison with an average particle size of 20 &mgr;m and a pore volume of 1.5-2.0 mL/g), ES70F (a silica available from Crosfield with an average particle size of 14 &mgr;m and a surface area of 281 m
2
/g) and MD 747JR (a silica available from Crosfield with an average particle size of 20 &mgr;m). SP9-275, Davison 955, Davison 948, XP02408, SP9-10150, SP9-10156 Sylopol 5550, XP02403, Sylopol 55SJ, SP9-10180, and Sylopol 2104 silicas from Grace Davison, ES70 and ES70X silicas from Crosfield, and CS2133, CS2040, MS3040, MS3040F, SP2-7877, MS3040A and MS1733 silicas from PQ Corporation may also be used. Examples of suitable polymer supports include porous polypropylene and polyethylene available from Accurel or Akzo Nobel, and monodisperse polymethacrylates and polystyrenes available from Dyno Speciality Polymers, Lillestrøm, Norway.
Alternatively, the support material may be dehydrated chemically by reaction of surface hydroxyl groups with chemical agents such as for example chlorosilanes and aluminium alkyls. By way of example see EP-A-507876, EP-A-670336, EP-A-670325 and “The Chemistry of Silica”, Chapter 6, R. K. Iler, Wiley, 1979.
The catalyst with which the support material is impregnated may be any polymerization catalyst or combination of two or more catalysts, optionally together with one or more co-catalysts or catalyst activators. Where two or more components, e.g. catalysts and co-catalysts, are used, these can be loaded onto the support sequentially or simultaneously. Preferably the catalyst is a Ziegler Natta catalyst (i.e. the combination of a transition metal (e.g. Ti, V or Cr) compound and an aluminium compound), a pyrazolyl catalyst (e.g. as described in WO97/17379, U.S. Pat. No. 4,808,680, EP-A-482934, U.S. Pat. No. 5,312,394 or EP-A-617052) or an &eegr;-liganded metal catalyst, e.g. a metallocene catalyst. Such catalysts will ge

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