Polymerization process

Details Polymerization process Polymerization process

2000-10-30

2002-10-08

Wu, David W. (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S064000, C526S065000, C526S161000, C526S171000, C526S172000, C526S901000, C502S155000, C502S167000

Reexamination Certificate

active

06462152

ABSTRACT:

The present invention relates to a process for the polymerisation of 1-olefins.
The use of certain transition metal compounds to polymerise 1-olefins, for example, ethylene, is well established in the prior art. They include chromium-based catalysts, Ziegler-Natta catalysts and metallocene catalysts. WO98/27124 has recently disclosed 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.
Processes for the polymerisation of 1-olefins can be operated by polymerising the monomers in the gas phase, or in solution or in suspension in a liquid hydrocarbon diluent. 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.). Polymerisation of the monomers can alternatively 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.
It is known that, prior to its utilisation for polymerisation, the catalyst system may be converted into a prepolymer by an operation known as “prepolymerisation”, where the catalyst system is brought into contact with a 1-olefin. We have discovered that when the catalyst is a type such as those disclosed in WO 98/27124 above, prepolymerisation affords a number of process advantages.
Accordingly in a first aspect the present invention provides a process for the polymerisation of 1-olefins comprising the steps of:
a) preparing a prepolymer-based catalyst by contacting one or more 1-olefins with a catalyst system, and
b) contacting the prepolymer-based catalyst with one or more 1-olefins, wherein the catalyst system comprises
(1) a compound of 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 transition metal M; T is the oxidation state of the transition metal M and b is the valency of the atom or group X; R
1
, R
2
, R
3
, R
4
, R
5
, R
6
and R
7
are independently selected from hydrogen, halogen, hydrocarbyl, substituted hydrocarbyl, heterohydrocarbyl or substituted heterohydrocarbyl; and when any two or more of R
1
-R
7
are hydrocarbyl, substituted hydrocarbyl, heterohydrocarbyl or substituted heterohydrocarbyl, said two or more can be linked to form one or more cyclic substituents; optionally in the presence of (2) an activator.
We have found that performing a prepolymerisation step as defined above results in reduced activity in the main polymerisation, avoiding “hot spots” in the reactor. Other changes such as a reduction in the melt index potential are also observed.
Preferably in Formula I above M is Fe[II], Fe[III], Co[II] or Co[III]; X represents an atom or group covalently or ionically bonded to the transition metal M; T is the oxidation state of the transition metal M and b is the valency of the atom or group X; R
1
, R
2
, R
3
, R
4
, R
5
, R
6
and R
7
are independently selected from hydrogen, halogen, hydrocarbyl, substituted hydrocarbyl, heterohydrocarbyl or substituted heterohydrocarbyl; and when any two or more of R
1
-R
7
are hydrocarbyl, substituted hydrocarbyl, heterohydrocarbyl or substituted heterohydrocarbyl, said two or more can be linked to form one or more cyclic substituents.
As activator (2), the catalyst system may additionally include an alkylalumoxane which is normally 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). The alkylalumoxane, may be added either at the prepolymerisation stage (a) or before or during the main polymerisation stage (b).
Optionally the catalyst system may also comprise (3) a compound of the formula AlR
3
, where each R is independently C
1
-C
12
alkyl or halo, compound (3) being added either prior to prepolymerisation step (a) or before or during the main polymerisation step (b). The three substituents R in compound (3), which may be the same or different, are preferably hydrogen, methyl, ethyl, butyl or chloro. Preferred compounds (3) include trimethylaluminium (TMA), triethylaluminium (TEA), tri-isobutylaluminium (TIBA), tri-n-octylaluminium, ethylaluminium dichloride and diethylaluminium chloride. Most preferred are TMA and TIBA. However the preferred compound (3) may depend on the polymerisation conditions in which the catalyst is employed: for example, TMA is particularly effective at improving catalyst activity in gas phase and also the activity of unsupported catalysts in slurry phase, whilst TIBA is particularly effective in slurry phase polymerisation generally.
Regarding activator (2), 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 TIBA. Quantities of alkylalumoxane quoted herein include such trialkylalkylaluminium impurities, and accordingly component (3) in this invention is considered to comprise compounds of the formula AlR
3
additional to any AlR
3
compound incorporated within the alkylalumoxane (2), and quantities of component (3) quoted herein are calculated on that basis.
In the preparation of the catalyst systems of the present invention the quantity of activating compound (2) to be employed is easily determined by simple testing, for example, by the preparation of small test samples which can be used to polymerise small quantities of the monomer(s) and thus to determine the activity of the produced catalyst. It is generally found that the quantity employed is sufficient to provide 0.1 to 20,000 atoms, preferably 1 to 2000 atoms of aluminium per Fe, Co, Mn or Ru metal atom in the compound of Formula I. The amount of activator (2) required for optimum performance may also depend on the amount of alkylaluminium compound (3) present. For example, when compound (3) is trimethyl aluminium (TMA), and the amount of TMA in the catalyst is less than 500 molar equivalents relative to the metal atom of compound (1), the amount of alkylalumoxane (usually MAO) is preferably at least 1000 molar equivalents. However if more than 500 equivalents of TMA are present, the optimum amount of alkylalumoxane (usually MAO) is from 500 to 1000 equivalents.
Further compounds for use in the present invention include those comprising the skeletal unit depicted in Formula II:
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 transition metal M; T is the oxidation state of the transition metal M and b is the valency of the atom or group X; R
1
to R
4
, R
6
and R
19
to R
28
are independently selected from hydrogen, halogen, hydrocarbyl, substituted

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