Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
1997-09-26
2001-05-08
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...
C526S144000
Reexamination Certificate
active
06228960
ABSTRACT:
The present invention relates to a process for the preparation of ethylene propylene (EP) and ethylene-propylene-diene (EPDM) elastomeric copolymers with a low content of residual chlorine.
More specifically the present invention relates to processes for the preparation of EP(D)M in liquid phase (solution or dispersion) preferably in liquid phase in a suspension of monomer.
EP(D)M elastomeric copolymers are at present produced in the presence of catalysts containing inorganic chlorine which at the end of the polymerization remains englobed in the polymer, causing problems of corrosivity of the polymer itself.
This problem is particularly felt in the case of polymerization with a slurry process (suspension of liquid monomer) in which the purification phase of the polymer is not very efficient.
The process in suspension on the other hand is preferable for other reasons such as high productivity, energy saving and reduced environmental impact.
The catalytic system used at present to produce EP(D)M elastomers essentially consists of a Vanadium salt, a chlorinated Aluminium alkyl and an activator.
The presence of chlorinated aluminium alkyl is the cause of most problems of corrosivity; in addition the acidity of the Aluminium compound can lead to undesired cationic reactions on the double bonds of the terpolymers with the consequent formation of cross-linked material and consequently of non-dispersed particles on the surface of the end-products.
Catalytic systems based on Vanadium are known however in which the aluminium compound is in the form of aluminium trialkyl and therefore not corrosive and with reduced Lewis acidity. These catalytic systems are satisfactorily used in the field of polyethylenes, but give EP(D)M with a wide molecular weight distribution.
For example Polymer, 1972, vol.13, July, pages 307-314, describes the reaction rate of VCl
3
+AlR
3
systems, without chlorinated activators, in relation to the various R (methyl, ethyl, isopropyl). From this study, it can be seen, in table 3, that TMA (trimethylaluminium) is slightly more active than TIBA (triisobutylaluminium) at 30° C., whereas at higher temperatures TMA has a considerably worse productivity than TIBA and TEA (triethylaluminium).
The catalytic system described in U.S. Pat. No. 4,514,514 essentially consists of a compound of Vanadium, a chlorinated activator and an Aluminium alkyl. Table VI of this document shows how TMA gives even lower yields (about half) than TIBA and TEA.
A process has now been found for the preparation of EP(D)M elastomeric copolymers which enables products with a low content of chlorine to be obtained.
In accordance with this, the present invention relates to a process for the preparation of ethylene-propylene (EPM) and ethylene-propylene-diene (EPDM) elastomeric copolymers in liquid phase, preferably in suspension of a liquid monomer, in the presence of a catalyst essentially consisting of a compound of Vanadium, a cocatalyst essentially consisting of an Aluminium trialkyl, and optionally an activator, preferably a chlorinated activator, characterized in that the Aluminium trialkyl is essentially Aluminium trimethyl and the Vanadium compound, as such or prepolymerized, is selected from:
(a) compounds having general formula (I) VO(L)
n
(X)
m
wherein n is an integer from 1 to 3 and m is from zero to 2, n+m being equal to 2 or 3;
(b) compounds having general formula (II) V(L)
p
(X)
q
wherein p is an integer from 1 to 4, q is from zero to 3, the sum of p+q being equal to 3 or 4; wherein L is a bidentate ligand deriving from a 1,3-diketone and X is a halogen, preferably Chlorine.
In other words the compound LH, from which the bidentate anion L
−
derives from the release of a hydrogen atom, has the general formula R
1
—CO—R
2
—CO—R
3
, wherein R
1
and R
3
are selected from —H and alkyl radicals, R
2
is an alkylene, or R
1
and R
2
jointly form a 5 or 6 term cycle.
Typical examples of Vanadium salts with bidentate ligands are acetylacetonate, 3-oxobutanalate (otherwise called 2-formylacetonate), 2-acetyl cyclopentanoate, 2-formyl cyclopentanoate (the latter two are described in Italian patent application IT-A-MI 96A 00294), preferably acetylacetonate.
In the preferred embodiment the Vanadium compound has general formula (II), wherein q is zero. Even more preferably the Vanadium compound is Vanadium acetylacetonate.
The above Vanadium compound can be used in the process of the present invention in the form of both solution and dispersion.
When the Vanadium is in the form of a dispersion, it is preferable for the above Vanadium compound to have a particle size of less than 200 microns, preferably less than 30 microns. Mixtures of Vanadium compounds can also be used.
The catalyst and cocatalyst can be fed separately to the polymerization environment, or, preferably, the Vanadium compound can be reacted with an organic compound of Aluminium before being introduced into the polymerization environment, according to the well-known preformation technique. The above organic compound of Aluminium has the general formula AlR
n
X
m
wherein R is a C
1
-C
20
alkyl group, X is halogen, preferably Chlorine, n+m=3. In the preferred embodiment the above organic compound of Aluminium is selected from diethylaluminium chloride (DEAC) and dimethylaluminium chloride.
According to this technique, the interaction between Vanadium compound and organic compound of aluminium is carried out in the presence of ethylene (or ethylene and alpha-olefins) producing a prepolymerized catalytic species insoluble in the practically hydrocarbon reaction environment. The molar ratio between organic compound of aluminium and Vanadium compound is between 1 and 20, preferably from 1.5 to 5.
The reaction time between Vanadium and Al-alkyl in an ethylene atmosphere, is between a few minutes and several hours, generally between 2 minutes and 2 hours, and is also selected in relation to the prepolymerization rate.
The prepolymerization is carried out in such a way that the ratio between grams of prepolymer and grams of Vanadium is between 2 and 150, preferably between 6 and 35, more preferably from 8 to 15. The above treatment can be carried out within a wide temperature range which can vary from −30° C. to 80° C., preferably from 15 to 30° C. The catalytic species thus obtained can be stored and used directly in the form of suspension, as obtained in the above process; alternatively it is possible to filtrate and dry the catalytic precipitate thus obtained, and in this case the catalytic Vanadium compound will be redispersed in the desired solvent. At the end of the prepolymerization process, granules of catalyst covered with a layer of homo or copolymer are obtained. The contact between organic compound of Aluminium and Vanadium compound can be carried out at essentially atmospheric pressure, or under ethylene pressure (or ethylene and alpha-olefin), generally less than 10 atmospheres, preferably at atmospheric pressure.
The process of the present invention comprises the use of TMA (Aluminium trimethyl) as cocatalyst. The molar ratio between the above cocatalyst and Vanadium (intended as compound having general formula (I) or (II) or as prepolymerized compound) is between 3 and 1000, preferably between 9 and 100, even more preferably between 15 and 50.
In the process of the present invention it is preferable to use an activator. These activators usually belong to the group of chlorinated organic compounds, for example ethyl trichloroacetate, n-butyl perchlorocrotonate, diethyl dichloromalonate, carbon tetrachloride, chloroform. The molar ratio between activator and Vanadium can vary from 0/1 to 1000/1, preferably from 0.5/1 to 40/1, even more preferably from 1/1 to 10/1.
The polymerization process of the present invention is carried out in liquid phase, preferably in a reaction medium in which the polymer is substantially insoluble. In the preferred embodiment the reaction medium prevalently consists of one of the comonomers, to which a saturated hydrocarbon, such as propane, butane, pe
Enichem S.p.A.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Rabago R.
Wu David W.
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