Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Organic compound containing
Reexamination Certificate
2001-04-24
2004-01-13
Harlan, Robert (Department: 1713)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Organic compound containing
C502S157000, C526S064000, C526S065000, C526S161000, C526S127000, C526S154000, C526S172000, C526S901000, C526S905000
Reexamination Certificate
active
06677267
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to transition metal compounds and to polymerisation catalyst systems employing them.
The use of certain transition metal compounds to polymerise 1-olefins, for example, ethylene, is well established in the prior art. The use of Ziegler-Natta catalysts, for example, those catalysts produced by activating titanium halides with organometallic compounds such as triethylaluminium, is fundamental to many commercial processes for manufacturing polyolefins. Over the last twenty or thirty years, advances in the technology have led to the development of Ziegler-Natta catalysts which have such high activities that that olefin polymers and copolymers containing very low concentrations of residual catalyst can be produced directly in commercial polymerisation processes. The quantities of residual catalyst remaining in the produced polymer are so small as to render unnecessary their separation and removal for most commercial applications. Such processes can be operated by polymerising the monomers in the gas phase, or in solution or in suspension in a liquid hydrocarbon diluent. Polymerisation of the monomers can be carried out in the gas phase (the “gas phase process”), for example by fluidising under polymerisation conditions a bed comprising the target polyolefin powder and particles of the desired catalyst using a fluidising gas stream comprising the gaseous monomer. In the so-called “solution process” the (co)polymerisation is conducted by introducing the monomer into a solution or suspension of the catalyst in a liquid hydrocarbon diluent under conditions of temperature and pressure such that the produced polyolefin forms as a solution in the hydrocarbon diluent. In the “slurry process” the temperature, pressure and choice of diluent are such that the produced polymer forms as a suspension in the liquid hydrocarbon diluent. These processes are generally operated at relatively low pressures (for example 10-50 bar) and low temperature (for example 50 to 150° C.).
Commodity polyethylenes are commercially produced in a variety of different types and grades. Homopolymerisation of ethylene with transition metal based catalysts leads to the production of so-called “high density” grades of polyethylene. These polymers have relatively high stiffness and are useful for making articles where inherent rigidity is required. Copolymerisation of ethylene with higher 1-olefins (eg butene, hexene or octene) is employed commercially to provide a wide variety of copolymers differing in density and in other important physical properties. Particularly important copolymers made by copolymerising ethylene with higher 1-olefins using transition metal based catalysts are the copolymers having a density in the range of 0.91 to 0.93. These copolymers which are generally referred to in the art as “linear low density polyethylene” are in many respects similar to the so called “low density” polyethylene produced by the high pressure free radical catalysed polymerisation of ethylene. Such polymers and copolymers are used extensively in the manufacture of flexible blown film.
An important feature of the microstructure of the copolymers of ethylene and higher 1-olefins is the manner in which polymerised comonomer units are distributed along the “backbone” chain of polymerised ethylene units. The conventional Ziegler-Natta catalysts have tended to produce copolymers wherein the polymerised comonomer units are clumped together along the chain. To achieve especially desirable film properties from such copolymers the comonomer units in each copolymer molecule are preferably not clumped together, but are well spaced along the length of each linear polyethylene chain. In recent years the use of certain metallocene catalysts (for example biscyclopentadienylzirconium dichloride activated with alumoxane) has provided catalysts with potentially high activity and capable of providing an improved distribution of the comonomer units. However, metallocene catalysts of this type suffer from a number of disadvantages, for example, high sensitivity to impurities when used with commercially available monomers, diluents and process gas streams, the need to use large quantities of expensive alumoxanes to achieve high activity, and difficulties in putting the catalyst on to a suitable support.
WO98127124 discloses that ethylene may be polymerised by contacting it with certain iron or cobalt complexes of selected 2,6-pyridinecarboxaldehydebis (imines) and 2,6-diacylpyridinebis(imines). These complexes are disclosed as being suitable for preparing homopolymers of ethylene. It is disclosed that in polymerisation processes, the complexes may be used in association with a neutral Lewis acid such as methylaluminoxane (MAO). Ratios of aluminium in the MAO to Fe or Co in the complex exemplified are in the range from 31:1 to 2485:1.
We have developed novel catalysts utilising complexes similar to the above which are disclosed in our copending application WO GB98/2638. This discloses polymerisation of ethylene using a catalyst which comprises a transition metal salt of a 2,6-diacylpyridinebis(imine) supported on silica, with an MAO cocatalyst. Ratios of aluminium in the MAO to transition metal in the complex are stated to range from 0.1-20000:1, preferably 1-2000:1, and typically at least 500:1. Ratios in the examples range from 31:1 upwards.
SUMMARY OF INVENTION
We have now surprisingly discovered that the activity of catalysts comprising the above compounds and MAO in polymerisation of 1-olefins can be maintained or even improved by reducing the ratio of aluminium in the MAO to transition metal. Accordingly in a first aspect the invention provides a catalyst for the polymerisation of olefins comprising
(1) a complex having the formula (I)
wherein M is Fe[II], Fe[III], Co[I], Co[II], Co[III], Mn[I], Mn[II], Mn[III], Mn[IV], Ru[II], Ru[III] or Ru[IV]; X represents an atom or group covalently or ionically bonded to the metal M; T is the oxidation state of the metal; b is the valency of the atom or group X; and R
1
to R
7
are each independently selected from hydrogen, halogen, hydrocarbyl, substituted hydrocarbyl, heterohydrocarbyl, substituted heterohydrocarbyl or SiR′
3
where each R′ is independently selected from hydrogen, halogen, hydrocarbyl, substituted hydrocarbyl, heterohydrocarbyl, substituted heterohydrocarbyl; and when any two or more of R
1
to R
7
are hydrocarbyl, substituted hydrocarbyl, heterohydrocarbyl or substituted heterohydrocarbyl, said two or more can be linked to form one or more cyclic substituents;
(2) an activator which is an alkylalumoxane; and
(3) a support material,
wherein the atomic ratio of aluminium in the alkylalumoxane (2) to transition metal M in (1) is from 6:1 to 25:1.
DETAILED DESCRIPTION OF THE INVENTION
As alkylalumoxanes are added to catalysts in order to enhance their activity, the invention is particularly surprising. Alkylalumoxanes are relatively expensive and also undesirable from a safety point of view, so the ability to use smaller quantities whilst maintaining or enhancing polymerisation activity is especially advantageous. It is preferred that the atomic ratio of aluminium to transition metal M is from 8:1 to 22:1, and more preferably from 12:1 to 18:1.
The activator (2) is preferably a (C
1
-C
4
) alkylalumoxane, the alkyl group generally being methyl, ethyl, propyl or isobutyl. Preferred is methylalumoxane (also known as methylaluminoxane or MAO) or modified methylalumoxane (MMAO), which additionally contains isobutylalumoxane. The term “alkylalumoxane” as used in this specification includes alkylalumoxanes available commercially which may contain a proportion, typically about 10 wt %, but optionally up to 50 wt %, of the corresponding trialkylaluminium; for instance, commercial MAO usually contains approximately 10% trimethylaluminium (TMA), whilst commercial MMAO contains both TMA and triisobutylalumini
Berardi Alain
Speakman John Gabriel
BP Chemicals Limited
Finnegan, Henderson Farabow, Garrett and Dunner L.L.P.
Harlan Robert
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