Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
1997-05-06
2003-04-08
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...
C526S352000, C526S124300, C526S158000, C526S124800, C502S103000, C502S115000, C502S125000
Reexamination Certificate
active
06545106
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process for the polymerization of olefins, more precisely to a polymerization process in the presence of a catalytic system comprising a solid catalytic complex based on magnesium, on transition metal and on halogen, and an organometallic compound (cocatalyst).
TECHNOLOGY REVIEW
British Patent GB 1,464,909 discloses catalytic systems comprising a solid based on magnesium, on transition metal and on halogen, and a cocatalyst. In Example 1 of that patent, ethylene is polymerized in the presence of triisobutylaluminium (cocatalyst) and a catalytic solid obtained by mixing magnesium ethoxide with tetrabenzyltitanium and by adding ethylaluminium dichloride thereto until a solid precipitate is obtained.
The polyethylene obtained in the presence of this known catalytic solid has a high content of oligomers (low molecular weight polymers comprising not more than 15 monomer units) which are responsible, during subsequent use of the polyethylene, for example in a bottle-blowing process, for the emission of fumes. Moreover, the oligomers degrade the mechanical and rheological properties of the polyolefins.
SUMMARY OF THE INVENTION
The invention is directed towards overcoming this drawback by providing a novel process for the manufacture of polyolefins which have in particular a low content of oligomers and improved mechanical and rheological properties.
DETAILED DESCRIPTION OF THE INVENTION
To this end, the invention relates to a process for the polymerization of olefins, according to which at least one olefin is placed in contact with a catalytic system comprising:
a) a solid catalytic complex based on magnesium, on transition metal and on halogen, the said catalytic complex being prepared by reacting, in a first step, at least one magnesium compound chosen from oxygen-containing organomagnesium compounds and halogen-containing magnesium compounds with at least one compound of a transition metal from group IVB or VB of the Periodic Table chosen from oxygen-containing organic compounds and halogen-containing compounds of a transition metal, until a liquid complex is obtained, and, in a subsequent step, by precipitating the said liquid complex using a halogen-containing organoaluminium compound of general formula AlR
n
X
3-n
in which R is a hydrocarbon radical, X is a halogen and n is less than 3, in order to collect a solid catalytic complex, and
b) an organometallic compound of a metal from groups IA, IIA, IIB, IIIA and IVA of the Periodic Table;
according to the invention, the solid catalytic system also comprises:
c) at least one electron donor used after the first step in the preparation of the solid catalytic complex leading to the production of a liquid complex.
One of the essential features of the invention lies in the use of an electron donor in a step subsequent to the first step in the preparation of the solid catalytic complex leading to the production of a liquid complex. The Applicant has, indeed, observed that the use of an electron donor during the first step in the preparation of a liquid complex leads to catalysts which produce polymers of low apparent density, which is reflected in a low production efficiency. The electron donor may thus be used either during the preparation of the solid catalytic complex (at the same time as the subsequent step or in an additional step) or at the polymerization stage at the same time as the solid catalytic complex and the organometallic compound.
The solid catalytic complex used in the process according to the invention is preferably not prepolymerized.
In a first variant of the process according to the invention, the electron donor is used during the preparation of the solid catalytic complex immediately after the first step, that is to say after formation of the liquid complex, and before the precipitation step. The treatment using the electron donor may be carried out by any suitable known means. The electron donor may be added in the pure state to the liquid complex or in the form of a solution in a solvent such as liquid aliphatic, cycloaliphatic and aromatic hydrocarbons. The preferred solvents are hydrocarbons containing up to 20 carbon atoms, and in particular linear alkanes (such as n-butane, n-hexane and n-heptane) or branched alkanes (such as isobutane, isopentane and isooctane) or cycloalkanes (such as cyclopentane and cyclohexane). Good results are obtained with linear alkanes. Hexane is preferred.
The temperature at which the treatment using the electron donor is carried out in the first variant is generally below the decomposition temperatures of the electron donor and of the liquid complex. It is in particular at least −20° C., more precisely at least 0° C., values of at least 20° C. being more common. The temperature is usually not more than 150° C., more particularly not more than 120° C., temperatures of not more than 100° C. being recommended, for example not more than 70° C.
The duration of the treatment using the electron donor in the first variant is commonly from 0.5 minute to 5 hours, preferably from 1 minute to 2 hours, for example from 5 minutes to 1 hour. The pressure at which the treatment is performed is not critical; the process is preferably performed at atmospheric pressure.
The amount of electron donor used in the first variant is usually at least 0.01 mol per mole of transition metal used, more precisely at least 0.02 mol, values of at least 0.05 mol being the most advantageous. The amount of electron donor used usually does not exceed 50 mol per mole of transition metal used, and preferably does not exceed 30 mol, values of not more than 20 mol being the most recommended. Amounts from 0.2 to 12 mol are particularly suitable.
The first variant makes it possible not only to reduce the content of oligomers in the polyolefins obtained, but also to increase the activity of the solid catalytic complex towards polymerization, and to increase the apparent density of the polyolefins obtained. In addition, the solid catalytic complex obtained according to the first variant is more sensitive to regulators of the molecular weight of the polyolefins, such that it requires less molecular weight regulator (for example hydrogen) in order to obtain a given molecular weight. The first variant also makes it possible to modify the morphology of the solid catalytic complex and consequently the morphology of the polyolefins obtained with this solid catalytic complex. This variant makes it possible in particular to decrease the particle size distribution width of the solid catalytic complex.
In a second variant of the process according to the invention, the electron donor is used during the preparation of the solid catalytic complex after the step of precipitation of the liquid complex, and preferably after possible intermediate steps of maturation and washing of the precipitate (which are described later), but before placing the solid catalytic complex in contact with the olefin in order to polymerize it. To this end, the electron donor may be added, in the pure state or in the form of a solution in a solvent as described above, to a suspension of the solid catalytic complex in an inert diluent. This inert diluent may be chosen, for example, from aliphatic and cycloaliphatic hydrocarbons. Cycloalkanes or linear or branched alkanes containing up to 20 carbon atoms are suitable for use. Hexane is particularly suitable.
The temperature, the duration, the pressure and the amount of electron donor used in the treatment using the electron donor according to the second variant are in accordance with those of the first variant which are described above.
The second variant makes it possible not only to reduce the content of oligomers in the polyolefins obtained, but also makes it possible to modify the response of the solid catalytic complex to the polyolefin molecular weight regulators (for example hydrogen) by variation in the amount of electron donor used. Indeed, it has been observed that the more the amount of electron donor used is increased, the more pronounc
Choi Ling-Siu
Schneller Marina V.
Solvay ( Societe Anonyme)
Venable
Wu David W.
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