Supported polyolefin catalyst for the (Co-)polymerization of ethylene in gas phase

The present invention relates to a catalyst and a process for preparing a catalyst suitable for polymerization of olefins. The process is carried out in a hydrocarbon liquid medium and comprises successively contacting a refractory oxide support with (a) a dialkylmagnesium optionally with a trialkylaluminium, (b) a particular monochloro organic compound, (c) a titanium and/or vanadium compound(s), and then (d) with ethylene optionally mixed with a C.sub.3 -C.sub.8 alpha-olefin in the presence of an organo-aluminium or organozinc compound to form a prepolymerized catalyst. The catalyst has a high activity, particularly in a gas phase polymerization of ethylene, and has a great ability of copolymerizing alpha-olefins with ethylene.

The present invention relates to a solid catalyst of Ziegler-Natta type, 
suitable for the polymerization or copolymerization of olefins, and to a 
process for the preparation of the said catalyst. 
It is known that olefin polymerization catalyst systems of Ziegler-Natta 
type consist of a solid catalyst comprising at least one compound of a 
transition metal belonging to group IV, V or VI of the Periodic 
Classification of the Elements and of a cocatalyst comprising at least one 
organometallic compound of a metal belonging to group II or III of this 
Classification. A high-activity solid catalyst is preferably employed, 
which comprises at least one compound of a transition metal such as 
titanium, and a magnesium compound, such as magnesium chloride. The 
cocatalyst is usually chosen from organoaluminium or organozinc compounds. 
European Patent Application EP-A-0 133 383 discloses a supported polyolefin 
catalyst for the polymerization of ethylene at temperatures greater than 
150.degree. C., such as in a solution process or a high pressure process. 
The catalyst is obtained by treating a dehydrated particulate support 
material with (a) a dihydrocarbyl magnesium, (b) a transition metal 
compound and (c) ethyl aluminium dichloride. The catalyst thus obtained 
may be prepolymerized with at least one alpha-olefin having from 4 to 18 
carbon atoms. 
Furthermore, a method for the preparation of a solid catalyst is known 
according to European Patent Application EP-A-0,014,523, which consists in 
reacting an organomagnesium compound in a liquid hydrocarbon medium with a 
support based on an inorganic oxide, a "halogenating agent" and a compound 
of a transition metal, in the presence of a Lewis base. The "halogenating 
agent" is chosen from a very wide variety of products comprising hydrogen 
halides, silicon halides, carboxylic acid halides, phosphorus 
pentachloride, thionyl chloride, sulphuryl chloride, phosgene, nitrosyl 
chloride, halides of mineral acids, chlorine, bromine, chlorinated 
polysiloxanes, hydrocarbyl aluminium halides, aluminium chloride, ammonium 
hexafluorosilicate and hydrocarbyl halides, such as carbon tetrachloride, 
chloroform, ethyl chloride, ethylene dichloride, or 1,1,1-trichloroethane. 
It has been found, however, that when such halogenating agents are 
employed, the solid catalysts generally exhibit a mediocre activity in 
olefin polymerization. It has also been observed that certain halogenating 
agents such as hydrogen halides are extremely corrosive towards metals and 
require the use of special and costly equipment. Furthermore, it has been 
found that during the catalyst preparation the liquid hydrocarbon medium 
can be contaminated by the halogenating agent employed, either because the 
latter is not consumed completely during the reaction, or because it 
results in the formation of new chlorine-containing compounds which are 
soluble in this medium and are difficult to separate from the latter. It 
then becomes necessary to apply a specific treatment to purify the liquid 
hydrocarbon medium at each catalyst preparation. 
The catalysts of EP-A-0,014,523 are described for use in a gas phase olefin 
polymerization process, e.g. by means of a fluidized-bed reactor in which 
the polymer particles being formed are kept in the fluidized state by 
means of a reaction gas mixture containing the olefin(s) to be polymerized 
and travelling as an upward stream at a velocity which is sufficiently 
high to effectively remove the heat of polymerization and to maintain the 
bed in the fluidized state. However, it has been observed that when 
olefins are polymerized, these catalysts produce polymer particles which, 
above a certain size, or above a certain degree of progress of 
polymerization, tend to break up, yielding particles of undesirable shape 
and size, and of relatively low bulk density. It has also been found that 
this phenomenon is still more pronounced when ethylene is copolymerized in 
gas phase with an alpha-olefin containing, for example, from 3 to 8 carbon 
atoms. 
Another major disadvantage of the process of EP-A-0,014,523 stems from the 
fact that in the conditions for gas phase copolymerization of ethylene 
with an alpha-olefin containing from 3 to 8 carbon atoms these catalysts 
require a relatively high partial pressure of the said alpha-olefin in the 
reaction gas mixture for a given quantity of alpha-olefin to be fixed in 
the copolymer. A high pressure of this alpha-olefin in the reaction gas 
mixture increases the losses in particular of this costly raw material 
when the copolymer powder is recovered and degassed outside the 
polymerization reactor. 
There has now been found a process for the preparation of a solid catalyst 
of Ziegler-Natta type, supported on a refractory oxide, which exhibits a 
very high activity in olefin polymerization. Furthermore, this catalyst is 
prepared in such conditions that the above-mentioned catalyst production 
disadvantages can be reduced. In particular, the catalyst can be prepared 
by means of common equipment and in the presence of a liquid hydrocarbon 
medium which does not require a purification treatment after each catalyst 
preparation. Moreover, the catalyst has a structure such that the gas 
phase polymerization of ethylene can be conducted up to a high conversion 
with reduced risks of bursting the polymer particles and lowering the bulk 
density of the polymer powder. Furthermore, in the conditions of a gas 
phase copolymerization of ethylene with at least one alpha-olefin 
containing from 3 to 8 carbon atoms to produce an ethylene copolymer of a 
given content of the alpha-olefin(s), the use of this solid catalyst makes 
it possible, when compared with the catalysts known previously, to reduce 
in a remarkable manner the partial pressure of the said alpha-olefin(s) in 
the reaction gas mixture. This advantage not only makes it possible to 
improve the industrial operating conditions of a gas phase 
copolymerization process, but also to produce ethylene copolymers which 
have a density which is markedly reduced for a given proportion of 
alpha-olefin(s) to ethylene in the reaction gas mixture, compared to that 
for catalysts known previously. 
The subject of the present invention is a process for the preparation of a 
solid catalyst capable of being employed for the polymerization or 
copolymerization of olefins especially ethylene, said catalyst comprising 
atoms of magnesium, chlorine, titanium and/or vanadium, and a solid 
support based on a refractory oxide, which process is characterized in 
that it comprises: 
a) in a first stage, bringing a solid support based on a refractory oxide 
containing hydroxyl groups, into contact with a dialkylmagnesium 
optionally mixed or complexed with a trialkylaluminium, 
b) in a second stage, bringing the product resulting from the first stage 
into contact with a monochloro organic compound selected amongst secondary 
or tertiary alkyl or cycloalkyl monochlorides containing 3 to 19 carbon 
atoms and amongst compounds of general formula R.sup.9 R.sup.10 R.sup.11 
CCl, in which R.sup.9 is an aryl radical containing from 6 to 16 carbon 
atoms, and R.sup.10 and R.sup.11 are identical or different radicals 
chosen from hydrogen, alkyl radicals containing from 1 to 6 carbon atoms 
and aryl radicals containing from 6 to 16 carbon atoms, which are 
identical to or different from R.sup.9, 
c) in a third stage, bringing the product resulting from the second stage 
into contact with at least one tetravalent titanium or vanadium compound 
or a trivalent vanadyl compound, and 
d) in a fourth stage, bringing the product resulting from the third stage 
into contact with ethylene or ethylene mixed with an alpha-olefin 
containing from 3 to 8 carbon atoms, in the presence of at least one 
activating agent selected amongst the organoaluminium and organozinc 
compounds, in such quantities to obtain the solid catalyst in the form of 
a prepolymer containing from 1 to 200 g preferably from 10 to 200 g of 
(co-)polymer of ethylene per milliatom of titanium, or vanadium, or 
titanium plus vanadium and that the molar ratio of the quantity of the 
metal(s) (Al and/or Zn) of the activating agent to the quantity of 
titanium, or vanadium, or titanium plus vanadium is from 0.3 to 10, each 
of the four stages being performed in a hydrocarbon liquid medium. 
The first three stages produce a particular catalytically active 
intermediate solid product especially comprising a magnesium chloride 
compound obtained from a particular chlorine source and also at least one 
compound of titanium or vanadium at its maximum valency of 4 or vanadium 
at its maximum valency 5 in vanadyl group, these elements being fixed on a 
solid support based on a refractory oxide. However, this intermediate 
solid product exhibits disadvantages of catalysts supported on a 
refractory oxide such as giving in a gas phase polymerisation process low 
bulk density (co-)polymers of ethylene. The fourth stage of the process of 
the present invention consists in converting the disadvantageous 
intermediate solid product into a particular ethylene prepolymerized 
catalyst, having substantial improvements in a gas phase ethylene 
(co-)polymerisation, in particular in copolymerising more easily 
alpha-olefins containing 3 to 8 carbon atoms with ethylene. 
The solid support based on refractory oxide contains hydroxyl functional 
groups and may have a specific surface area (BET) of 50 to 1,000 m.sup.2 
/g e.g. 100 to 600 m.sup.2 /g and a pore volume of 0.5 to 5 ml/g e.g. 1 to 
3 ml/g. 
The quantity of hydroxyl groups in the support depends on the support 
employed, on its specific surface area, on the physicochemical treatment 
and on the drying to which it may have been subjected beforehand. A 
support which is ready for use generally contains from 0.1 to 5, 
preferably from 0.5 to 3 millimoles of hydroxyl group per gram. The 
support which may be granular, is preferably devoid of free water at the 
time of its use in the catalyst preparation. For this purpose, it can be 
preferably rid of free water by means which are known per se, such as a 
heat treatment ranging from 100.degree. C. to 950.degree. C. e.g. 
150.degree. C. to 700.degree. C. The support may be chosen, in particular, 
from a silica, an alumina, a silica-alumina, or a mixture of these oxides, 
and may consist of particles which have a mass-mean diameter ranging from 
20 to 250 microns, preferably 30 to 200 microns, especially 50 to 150 
microns. The use of a silica is preferred, especially ones sold by 
Crosfield Company (Great Britain) under the commercial reference "SD 490" 
or by W.R. Grace Company (USA) under the commercial reference "SG 332" or 
a microspheroidal silica sold by W.R. Grace Company (USA) under the 
commercial reference "SD 3217". 
The first stage of the preparation of the solid catalyst consists in 
brin8in8 the solid support into contact with a dialkylmagnesium of general 
formula 
EQU Mg R.sup.1 R.sup.2 
optionally mixed or complexed with a trialkylaluminium of general formula 
EQU Al R.sup.3 R.sup.4 R.sup.5 
in which formulae R.sup.1, R.sup.2, R.sup.3, R.sup.4 and R.sup.5 are 
identical or different alkyl radicals containing from 1 to 12 carbon 
atoms, preferably from 2 to 8 carbon atoms, the quantity of 
trialkylaluminium used preferably not exceeding a molar ratio of 1/1 
relative to the dialkylmagnesium in particular the molar ratio being 
0.01/1 to 1/1, e.g. 0.1/1 to 0.5/1. Dibutylmagnesium, dihexylmagnesium, 
butylethylmagnesium, ethylhexylmagnesium or butyloctylmagnesium is 
preferably employed. 
When the dialkylmagnesium is employed with a trialkylaluminium, an addition 
compound of general formula 
EQU MgR.sup.1 R.sup.2.x AlR.sup.3 R.sup.4 R.sup.5 
can be prepared beforehand, in which formula R.sup.1, R.sup.2, R.sup.3, 
R.sup.4 and R.sup.5 are defined as above and x is a number equal to or 
lower than 1 in particular from 0.01 to 1, e.g. from 0.01 to 0.5. The 
addition compound is prepared according to known methods, such as heating 
a mixture of dialkylmagnesium and trialkylaluminium in solution in a 
liquid hydrocarbon medium to a temperature ranging, preferably, from 30 to 
100.degree. C. A compound of addition of dibutylmagnesium with 
triethylaluminium, or else dihexylmagnesium with triethylaluminium. or 
else butyloctylmagnesium with triethylaluminium, is preferably employed. 
In all cases the dialkylmagnesium, and, if present, the trialkylaluminium 
or the addition compound is preferably added in the first stage in the 
form of a solution in a liquid hydrocarbon e.g. alkane or cycloalkane, 
such as n-hexane or n-heptane. 
The first stage, like the other three stages of the catalyst preparation, 
is carried out in a hydrocarbon liquid medium consisting of at least one 
liquid saturated hydrocarbon e.g. alkane or cycloalkane, having from 4 to 
12 carbon atoms, e.g. 4 to 8 carbon atoms, such as n-butane, n-pentane, 
isopentane, n-hexane n-heptane or cyclohexane, this hydrocarbon being 
inert towards the various compounds involved in the preparation of the 
solid catalyst. The hydrocarbon liquid medium may be the same or different 
in each stage of the catalyst preparation. 
During the first stage, the dialkylmagnesium and the trialkylaluminium, if 
employed, will be fixed on the solid support. This fixing may result 
simultaneously from a reaction between the hydroxyl groups of the solid 
support and the organometallic compounds, and from a physicochemical 
absorption, probably partly due to the organometallic compounds being 
complexed by some oxygen atoms of the refractory oxide. These 
organometallic compounds can themselves become fixed on the support in a 
complexed form, in particular in dimeric or trimeric form. A support can 
be generally evaluated using its overall capacity for fixing a 
dialkylmagnesium and optionally a trialkylaluminium. Its maximum fixing 
capacity depends on the nature of the support, on its specific surface 
area, on the physicochemical treatment and on the drying to which the 
support may have been subjected beforehand. The maximum fixing capacity of 
a support can be generally from 1 to 5, preferably from 1 to 3 millimoles 
of dialkylmagnesium e.g. dibutylmagnesium or trialkylaluminium per gram of 
support. 
The molar quantity of dialkylmagnesium and optionally of trialkylaluminium 
to be used can be less than, identical to, or in an excess relative to the 
number of moles of hydroxyl groups present in the support. However, in 
order to avoid using an excessive quantity of dialkylmagnesium and 
optionally trialkylaluminium, the quantity of these compounds is generally 
slightly higher than the maximum quantity capable of being fixed on the 
solid support. Thus, in the first stage of the process it is preferred to 
contact each gram of support with a quantity of the dialkylmagnesium, or 
dialkylmagnesium plus trialkylaluminium corresponding to 0.1 to 7.5 
millimoles, preferably from 0.5 to 4.5 millimoles and more particularly 
from 1 to 3.5 millimoles. 
The first stage can be carried out in various ways. It is possible, for 
example, to add the dialkylmagnesium and optionally the trialkylaluminium 
to the solid support which has preferably been suspended beforehand in the 
hydrocarbon liquid medium. This addition can be carried out slowly, for 
example over a period of 10 to 300 e.g. 30 to 120 minutes, with agitation 
e.g. stirring and at a temperature of 0.degree. C. to 80.degree. C., e.g. 
10 to 60.degree. C. When a dialkylmagnesium and a trialkylaluminium are 
both employed, their contact with the solid support can be brought about 
either by successive addition of the two organometallic compounds in any 
order or by addition of the mixture or complex formed beforehand by these 
two organometallic compounds, to the hydrocarbon liquid medium containing 
the solid support. 
Any significant excess of organometallic compound which is not fixed in the 
support can be removed by filtration and/or by one or more washings with a 
hydrocarbon liquid. It has been found, however, that it is possible to use 
a molar quantity of dialkylmagnesium and optionally of trialkylaluminium 
which can go up to 1.5 times the quantity of organometallic compounds 
corresponding to the maximum fixing capacity of the support, without it 
being subsequently necessary to remove by washings the excess of 
organometallic compounds which are not fixed in the support. It has 
surprisingly been found that in these conditions the possible small excess 
quantity of organometallic compounds which are not fixed in the support 
does not in any way interfere with the catalyst preparation and that 
substantially no fine particles can be formed during the subsequent 
stages. 
The second stage of the preparation of the solid catalyst consists in 
bringing the solid product resulting from the first stage into contact 
with a monochloro organic compound. This compound may be a secondary or 
preferably tertiary alkyl monochloride containing 3 to 19, preferably 3 to 
13 carbon atoms and having the general formula 
EQU R.sup.6 R.sup.7 R.sup.8 C Cl 
in which R.sup.6 and R.sup.7 are identical or different alkyl radicals 
containing from 1 to 6 e.g. 1 to 4 carbon atoms such as methyl, ethyl or 
n-propyl and R.sup.8 is a hydrogen atom or, preferably, an alkyl radical 
containing from 1 to 6 e.g. 1 to 4 carbon atoms, identical to or different 
from R.sup.6 and R.sup.7, such as methyl, ethyl or n-propyl. Secondary 
propyl chloride, secondary butyl chloride, but especially tert-butyl 
chloride are preferred. 
The monochloro organic compound may also be a secondary or preferably 
tertiary cycloalkyl monochloride of general formula 
##STR1## 
in which R.sup.8 is a hydrogen atom or, preferably, an alkyl radical 
containing from 1 to 6, e.g. 1 to 4 carbon atoms such as methyl or ethyl 
and n is a number from 4 to 8, e.g. 5 to 8, especially 5, such as 
cyclohexyl chloride or 1-methyl-1 chlorocyclohexane. 
The monochloro organic compound can also be a compound containing at least 
one aryl radical, of general formula: R.sup.9 R.sup.10 R.sup.11 CCl, in 
which R.sup.9 is an aryl radical containing from 6 to 16 e.g. 6 to 10 
carbon atoms and R.sup.10 and R.sup.11 are identical or different radicals 
chosen from hydrogen, alkyl radicals containing from 1 to 6 e.g. 1 to 4 
carbon atoms such as methyl, ethyl or n-propyl, and aryl radicals 
containing from 6 to 16 e.g. 6 to 10 carbon atoms, identical to or 
different from R.sup.9. The aryl radicals for R.sup.9, R.sup.10 and/or 
R.sup.11 are usually aromatic hydrocarbyl groups such as phenyl, totyl or 
naphthyl. Benzyl chloride and 1-phenyl-1-chloroethane may be preferred. 
It has surprisingly been found that the chlorination of the organometallic 
compounds fixed in the solid support is considerably improved by the use 
of secondary or tertiary alkyl or cycloalkyl monochlorides or the use of 
monochloro organic compounds containing at least one aryl radical compared 
to the use of hydrocarbyl polychlorides in particular carbon 
tetrachloride. 
By virtue of its unexpected behaviour, the monochloro organic compound can 
be used during this stage is a relatively low quantity, nevertheless 
making it possible to form a solid product substantially free from basic 
functional groups which are capable of subsequently reducing a compound of 
a transition metal such as tetravalent titanium employed during the third 
stage. The proportion of residual reductive basic functional groups is 
such that less than 10 %, preferably less than 5 % of the transition metal 
of the intermediate solid product resulting from the third stage is in the 
reduced state. 
The product resulting from the first stage may be contacted with the 
monochloro organic compound in a quantity such that the molar ratio of the 
quantity of monochloro organic compound to the quantity of the magnesium, 
or magnesium plus aluminium contained in the product resulting from the 
first stage is from 1 to 3.5, preferably 1.5 to 3.0. 
It has surprisingly been found that when this particular quantity of 
monochloro organic compound is used, the product resulting from the second 
stage can contain reduced amounts of basic functional groups capable of 
reducing a compound of a transition metal at its maximum valency or even 
hardly any or especially none compared to the use of corresponding amounts 
of hydrocarbyl polychlorides. The residual quantity (if any) of monochloro 
organic compound at the end of this stage is generally practically nil or 
negligible and usually does not exceed approximately 1,000 parts per 
million by weight (ppm) in the liquid hydrocarbon medium. It is thus 
therefore no longer necessary to wash the solid product resulting from the 
second stage and to purify the liquid hydrocarbon medium after each 
catalyst preparation. 
The second stage is carried out in the hydrocarbon liquid medium by 
bringing the monochloro organic compound into contact with the product 
resulting from the first stage, at a temperature ranging from 0.degree. C. 
to 90.degree. C., preferably from 20.degree. C. to 60.degree. C. The 
operation can be carried out in various ways, for example by adding the 
monochloro organic compound to the product resulting from the first stage 
in suspension in the hydrocarbon liquid medium. This addition is carried 
out, preferably slowly, for example, over a period of 10 to 600 minutes 
e.g. 20 to 300 minutes and with agitation e.g. stirring. 
The third stage of the preparation of the solid catalyst consists in 
bringing the product resulting from the second stage into contact with at 
least one compound of titanium or vanadium at the maximum valency of 4, or 
with a vanadyl compound with vanadium at the valency of 5. These titanium 
or vanadium compounds are preferably soluble in the hydrocarbon liquid 
medium in which the catalyst is prepared. It is possible to choose, in 
particular, a tetravalent titanium compound of general formula 
EQU Ti (OR).sub.m X.sub.4-m 
a tetravalent vanadium compound of general formula 
EQU V (OR.sub.m X.sub.4-m 
or a vanadyl compound of general formula 
EQU VO (OR).sub.m X.sub.4-m 
in which formulae R is an alkyl radical containing from 1 to 6, e.g. 2 to 6 
such as 2 to 4 carbon atoms e.g. methyl, ethyl, propyl. isopropyl or 
butyl, X is a chlorine or bromine atom, m is a whole or fractional number 
equal to or greater than 0 and smaller than 4 e.g. 0 to 3, and n is a 
whole or fractional number equal to or greater than 0 and smaller than 3, 
e.g. 0 to 2. 
The use of titanium tetrachloride is preferred. 
The contact is brought about in the liquid hydrocarbon medium, so that a 
maximum quantity of titanium and/or vanadium compounds can be fixed by 
impregnation in the support, preferably while avoiding any reduction of 
these transition metals, as this generally leads to reduce activity of the 
catalyst in ethylene (co-)polymerization. For this reason the product 
resulting from the second stage is preferably substantially free from any 
basic functional group capable of reducing a titanium and/or vanadium 
compound. It has been surprisingly found, furthermore, that the product 
obtained under the particular circumstances of chlorination during the 
second stage is particularly capable of fixing a large amount of titanium 
and/or vanadium compounds. This makes it possible to contact the product 
resulting from the second stage with the titanium and/or vanadium 
compound(s) in a quantity which is substantially lower than that employed 
during the impregnation stage described in EP-A-0,014,523, in particular a 
quantity such that the atomic ratio of the quantity of titanium, or 
vanadium, or titanium plus vanadium to the quantity of the magnesium, or 
magnesium plus aluminium contained in the product resulting from the 
second stage is from 0.1 to 0.9, preferably 0.2 to 0.7. As a result of 
this, most, if not all, of the quantity of titanium and/or vanadium 
compound(s) used is found to be fixed in the support preferably with an 
unchanged valency state. It is found that at the end of this stage the 
quantity of titanium and/or vanadium compound(s) remaining in the free 
state in the liquid hydrocarbon medium can be relatively low or 
negligible. Advantageously, in certain cases it appears to be no longer 
necessary to wash the solid product resulting from the third stage. 
The third stage is generally carried out at a temperature ranging from 0 to 
150.degree. C., preferably from 20 to 120.degree. C. In practice the 
operation can be carried out in various ways. For example, the titanium 
and/or vanadium compound(s) can be added to the product resulting from the 
second stage in suspension in the hydrocarbon liquid medium. This addition 
is preferably performed slowly, for example over a period of 10 to 300 
minutes e.g. 20 to 200 minutes, and with agitation e.g. stirring. 
According to a preferred embodiment, the third stage can be carried out in 
a way which advantageously makes it possible to yield a solid catalyst 
having a particularly high activity in ethylene polymerization or 
copolymerization and which produces ethylene (co-)polymers with a narrow 
molecular weight distribution. It consists especially in bringing the 
product resulting from the second stage into contact first of all with at 
least one halogen-rich titanium or vanadium compound, and then with at 
least one titanium or vanadium compound containing little or no halogen 
preferably at least one alkoxide-rich titanium or vanadium compound. The 
halogen-rich titanium or vanadium compound is chosen in particular from a 
tetravalent titanium compound of general formula 
EQU Ti (OR).sub.p X.sub.4-p 
a tetravalent vanadium compound of general formula 
EQU VO (OR).sub.p X.sub.4-p 
and a vanadyl compound of general formula 
EQU VO (OR).sub.q X.sub.3-q 
in which formulae R and X have definitions identical to those above, p is a 
whole or fractional number equal to or greater than 0 and smaller than 2 
e.g. 0 to 1.5, or 0 to 1 and q is a whole or fractional number equal to or 
greater than 0 and smaller than 1.5 e.g. 0 to 1 or 0 to 0.5. The 
halogen-rich titanium or vanadium compound is preferably titanium 
tetrachloride, vanadium tetrachloride or vanadyl trichloride. The use of 
titanium tetrachloride is preferred. 
The alkoxide-rich titanium or vanadium compound containing little or no 
halogen is chosen in particular from a tetravalent titanium compound of 
general formula 
EQU Ti (OR).sub.r X.sub.4-r 
a tetravalent vanadium compound of general formula 
EQU V (OR).sub.r X.sub.4-r 
and a vanadyl compound of general formula 
EQU VO (OR).sub.s X.sub.b 3-s 
in which formulae R and X have definitions identical to those above, r is a 
whole or fractional number equal to or greater than 2 and smaller than or 
equal to 4 e.g. 2.5 to 4, or 3 to 4 and s is a whole or fractional number 
equal to or greater than 1.5 and smaller than or equal to 3 e.g. 2 to 3, 
or 2.5 to 3. In particular, the alkoxide-rich compound containing little 
or no halogen is preferably a titanium tetraalkoxide, a vanadium 
tetraalkoxide and a vanadyl trialkoxide, especially titanium or vanadium 
tetraisopropoxide, titanium or vanadium tetra-n-propoxide, titanium or 
vanadium tetrabutoxide, titanium or vanadium tetraethoxide, vanadyl 
tri-n-propoxide, vanadyl tributoxide and vanadyl triethoxide. 
The proportion of alkoxide-rich titanium or vanadium compounds containing 
little or no halogen relative to the halogen-rich ones which is used 
during this stage can be such that the molar ratio of the former to the 
latter is from 0.1 to 3, preferably 0.2 to 2. 
The conditions in which the two successive contacts are brought about 
correspond to those defined above for a single contact. In particular the 
total quantity of titanium and/or vanadium compounds is such that the 
atomic ratio of the total quantity of titanium, or vanadium, or titanium 
plus vanadium to the quantity of the magnesium, or magnesium plus 
aluminium contained in the product resulting from the second stage is from 
0.1 to 0.9, preferably 0.2 to 0.7. 
The solid product resulting from the third stage comprises a support based 
on a refractory oxide containing halogenated compounds of magnesium, 
tetravalent titanium and/or vanadium and/or trivalent vanadyl. The atomic 
ratio between the quantity of magnesium and the quantity of titanium 
and/or vanadium in the solid product may be generally from 2 to 8, 
preferably from 2.5 to 5. 
The fourth stage of the preparation of the solid catalyst consists in 
bringing the solid product resulting from the third stage, also called 
intermediate solid product, into contact with ethylene or ethylene mixed 
with an alpha-olefin containing from 3 to 8 carbon atoms, in the presence 
of at least one organoaluminium or organozinc compound. The contact may be 
carried out in a batchwise or continuously and is preferably brought about 
by adding to the solid product resulting from the third stage, in 
suspension in the hydrocarbon liquid medium, ethylene and optionally an 
alpha-olefin containing 3 to 8 carbon atoms, e.g. propylene, butene-1, 
hexene-1, methyl-4-pentene-1 or octene-1, preferably at a steady slow flow 
rate and over a period such that the solid catalyst obtained is in the 
form of a prepolymer containing from 1 to 200 g, preferably from 10 to 200 
g, e.g. 20 to 100 g of polymer per milliatom of titanium, or vanadium, or 
titanium plus vanadium. The alpha-olefin optionally employed mixed with 
the ethylene is used in a minor quantity compared to ethylene, preferably 
such that the proportion of copolymerized alpha-olefin in the prepolymer 
is not higher than 10 % by weight and preferably from 0.1 to 7 % by weight 
relative to the ethylene. The ethylene prepolymerised catalyst thus 
obtained at the end of the fourth stage comprises a (co-)polymer of 
ethylene having a relatively high crystallinity and a low solubility in 
liquid hydrocarbon and presents a particular high capability of 
incorporating C.sub.3 to C.sub.8 alpha-olefins in an ethylene copolymer 
during a copolymerisation. The contact in the fourth stage can be 
generally brought about with agitation, e.g. stirring, at a temperature 
which is generally between 10.degree. C. and 100.degree. C., preferably 
between 40.degree. C. and 90.degree. C., and at a pressure which is 
generally higher than atmospheric pressure and lower than 2 MPa e.g. 0.2 
to 1 MPa. The duration of this contact can be of 10 to 900 minutes, e.g. 
30 to 600 minutes. 
This contact may be advantageously brought about in the presence of 
hydrogen, which may be added to the reaction mixture once at the beginning 
of the contact, or else a number of times, or also slowly at a steady flow 
rate while the contact is brought about. The quantity of hydrogen used 
during this stage is such that the partial pressure of hydrogen may be 
from 0.01 to 1 MPa e.g. 0.05 to 0.5 MPa. The presence of hydrogen during 
this stage, even in a very small quantity, makes it possible subsequently 
to manufacture ethylene polymers or copolymers with a perfectly 
homogeneous composition, in particular ones free from gels. 
The contact in the fourth stage is brought about in the presence of an 
activating agent chosen from organoaluminium compounds such as 
trialkylaluminium or alkylaluminium hydrides, chlorides and alcoholates, 
or organozinc compounds such as diethylzinc. The activating agent may be 
added to the liquid hydrocarbon medium either once at the beginning of the 
contact or a number of times distributed between the beginning and the end 
while the contact is brought about. The quantity of activating agent used 
during this stage is such that the atomic ratio between the quantity of 
the metal(s) (Al and/or Zn) of the activating agent and the quantity of 
titanium, or vanadium, or titanium plus vanadium is from 0.3 to 10, 
preferably 0.7 to 5, e.g. 0.8 to 3. 
An electron-donor compound such as a Lewis base can be employed during any 
one of the four stages, but is not essential. On the contrary, it is 
better not to employ a compound of this type because its presence rapidly 
decreases the activity of the solid catalyst in ethylene 
(co-)polymerization. Preferably the electron-donor compound is 
substantially absent. The quantity of electron-donor compound added, if it 
is used, in the preparation of the solid catalyst may be limited to a very 
small proportion, in particular such that the molar ratio of the quantity 
of electron-donor compound to the quantity of titanium, or vanadium, or 
titanium plus vanadium is lower than 1/5 e.g. from 0 to 0.2, preferably 
than 1/10 e.g. from 0 to 0.1, and that the molar ratio of the quantity of 
electron-donor compound to the quantity of the magnesium, or magnesium 
plus aluminium is lower than 1/10 e.g. from 0 to 0.1, preferably lower 
than 1/20 e.g. from 0 to 0.05. The electron-donor compound may be an 
organic electron-donor compound free from labile hydrogen, e.g. selected 
amongst ether, thioether, amine, amide, phosphine, sulfoxide, 
phosphoramide, silane, or ester. 
The catalyst obtained after this last stage is a solid ethylene 
prepolymerised catalyst of Ziegler-Natta type based on titanium and/or 
vanadium, capable of being employed for the polymerization or 
copolymerization of olefins. It comprises the essential elements already 
existing in the intermediate solid product obtained at the end of the 
third stage in similar proportions, in particular a refractory oxide and 
atoms of chlorine, magnesium, titanium and/or vanadium, and additionally 
comprises an organoaluminium compound and/or an organozinc compound. More 
precisely, this catalyst comprises, per milliatom of titanium, or 
vanadium, or titanium plus vanadium, from 1 to 200 g, preferably from 10 
to 200 g of polyethylene or of a copolymer of ethylene with a minor amount 
of an alpha-olefin containing 3 to 8 carbon atoms, from 0.2 to 15 g, 
preferably from 0.3 to 10 g of a refractory oxide, from 1 to 10, 
preferably from 1.4 to 5 milliatoms of magnesium, from 0.1 to 20, 
preferably from 0.3 to 10 milliatoms of aluminium, or zinc, or aluminium 
plus zinc, and from 0 to a value less than 0.2, preferably from 0 to 0.1 
e.g. 0.001 to 0.08 millimole of an electron-donor compound. This solid 
catalyst is in the form of non-sticky particles which may have a mass-mean 
diameter of 50 to 500 microns, preferably 80 to 400 microns, e.g. 100 to 
300 microns and a bulk density ranging from 0.25 to 0.60 preferably from 
0.3 to 0.5, e.g. 0.4 to 0.5 g/cm.sup.3. 
The solid catalyst obtained at the end of the fourth stage may be 
advantageously washed one or more times with a liquid hydrocarbon e.g. an 
alkane such as n-hexane, and can be employed as such. directly in a gas 
phase ethylene polymerization or copolymerization, in particular in a 
fluidized-bed reactor. It can be isolated, if desired, from the 
hydrocarbon liquid medium in which it was prepared or with which it was 
washed, for example by evaporating the latter at a temperature which can 
range up to 100.degree. C. e.g. 10 to 80.degree. C. and optionally under a 
partial vacuum. 
The solid catalyst prepared according to the present invention is 
particularly suitable for the gas phase polymerization of ethylene and 
especially for the gas phase copolymerization of ethylene with at least 
one alpha-olefin containing from 3 to 8 carbon atoms e.g. propylene, 
butene-1, hexene-1, methyl-4-pentene-1, or octene-1, in particular high 
density polyethylene (density: 0.94 to 0.97 g/cm.sup.3), and linear low 
density polyethylene or very low density polyethylene (density: 0.88 to 
0.94 g/cm.sup.3) having from 3 to 30% e.g. 5 to 25% by weight of C.sub.3 
to C.sub.8 alpha-olefins, for example by means of a fluidized-bed reactor, 
at a temperature of 20.degree. C. to 110.degree. C., preferably 40 and 
100.degree. C., under a total pressure which can vary from 0.5 to 5 MPa, 
the ratio of the partial pressure of the alpha-olefin(s) to that of 
ethylene being of 0.01 to 0.5. preferably 0.02 to 0.45 e.g. 0.03 to 0.43. 
The solid catalyst is preferably employed conjointly with a cocatalyst. 
The latter may be chosen from organoaluminium and organozinc compounds 
identical &o or different from the activating agent used during the fourth 
stage of the preparation of the catalyst. It may be introduced into the 
polymerization medium simultaneously with or separately from the solid 
catalyst in an amount such that the atomic ratio of the metal(s) (Al 
and/or Zn) of the cocatalyst to titanium, or vanadium, or titanium plus 
vanadium is from 0.1 to 10, preferably 0.2 to 5. The gas phase ethylene 
polymerization or copolymerization carried out in the presence of the 
solid catalyst prepared according to the present invention has the 
advantage of progressing to a high conversion without a substantial drop 
of the bulk density (0.32 to 0.45 g/cm.sup.3) of the polymer or copolymer 
powder produced which may have a Ti and/or V content from 1 to 15 ppm, 
preferably 2 to 10 ppm. 
Furthermore, for manufacturing an ethylene copolymer of a given 
alpha-olefin content, the solid catalyst prepared according to the present 
invention requires a relatively low proportion of alpha-olefin relative to 
ethylene in the reaction gas mixture employed for the gas phase 
copolymerization. The solid catalyst of the present invention has the 
specific property of incorporating a particularly high content of a 
C.sub.3 to C.sub.8 alpha-olefin, e.g. butene-1 or methyl-4 pentene-1, in 
an ethylene copolymer during a gas phase copolymerisation under a total 
pressure of 1.5 MPa, the said property being expressed by at least one of 
the following equations: 
EQU A=a x (pC4/pC2) (1) 
wherein A is the butene-1 content by weight of an ethylene/butene-1 
copolymer prepared at 95.degree. C. in a gas phase copolymerisation 
carried out with the catalyst of the present invention in the presence of 
a reaction gas mixture containing ethylene and butene-1, (pC4/pC2) is the 
ratio of the partial pressure of butene-1 to that of ethylene in the said 
reaction gas mixture ranging from 0 to 0.43, preferably from 0.01 to 0.36 
e.g. 0.01 to 0.1, and a is a number from 50 to 70, preferably 60 to 70; 
EQU B=b x (pC6/pC2) (2) 
wherein B is the methyl-4-pentene-1 content by weight of an 
ethylene/methyl-4 pentene-1 copolymer prepared at 70.degree. C. in a gas 
phase copolymerisation carried out with the catalyst of the present 
invention in the presence of a reaction gas mixture containing ethylene 
and methyl-4 pentene-1, (pC6/pC2) is the ratio of the partial pressure of 
methyl-4 pentene-1 to that of ethylene in the said reaction gas mixture 
ranging from 0 to 0.3, preferably from 0.01 to 0.25 e.g. 0.01 to 0.1, and 
b is a number from 80 to 100, preferably 90 to 100. 
The following nonlimiting examples illustrate the present 
invention. In the Tables 1, 2 and 3, the productivity is expressed in grams 
of (co-)polymer per milliatom of Ti or V; MI2.16 is the melt index of 
(co-)polymer measured according to the standard method ASTM-D-1238, 
condition E; BD is the bulk density of (co-)polymer powder at rest; 
pC4/pC2 is the ratio of the partial pressure of butene-1 to that of 
ethylene in the reaction gas mixture.

EXAMPLE 1 
Preparation of a Catalyst 
A support was employed, consisting of an "SD 490" Registered Trademark 
silica powder sold by Crosfield Company (Great Britain) which had a 
specific surface area (BET) of 300 m.sup.2 /g and a pore volume of 1.7 
ml/g. It consisted of particles having a mass-mean diameter of 100 
microns. It was dried for 5 hours at 500.degree. C., in an air atmosphere, 
to obtain a silica powder rid of free water and containing 1 millimole of 
hydroxyl group per gram. All the subsequent operations were carried out 
under an inert nitrogen atmosphere. 
600 ml of n-hexane and 60 g of the dried silica were introduced into a 
stainless steel 1-litre reactor fitted with a stirrer rotating at 250 
revolutions per minute, followed slowly over 1 hour by 190 millimoles of 
dibutylmagnesium, at a temperature of 20.degree. C. The mixture thus 
obtained was stirred at 20.degree. C. for 1 hour. The solid product (A) 
thus obtained was washed three times, each with 600 ml of n-hexane at 
20.degree. C. and after these washings it contained 1.7 milliatoms of 
magnesium per gram of silica. 
The reactor containing the solid product (A) in suspension in 600 ml of 
n-hexane was then heated to 50.degree. C. 204 millimoles of tert-butyl 
chloride were introduced into the reactor slowly over 1 hour with 
stirring. At the end of this time the mixture was stirred at 50.degree. C. 
for 1 hour and was then cooled to room temperature (20.C). The solid 
product (B) obtained was washed three times, each with 600 ml of n-hexane 
at 20.degree. C. After these washings it contained 1.7 milliatoms of 
magnesium and 2.7 milliatons of chlorine per gram of silica, and 
substantially no basic functional group reductive towards titanium 
tetrachloride. 
The reactor containing a quantity of the solid product (B) containing 30 g 
of silica in suspension in 600 ml of n-hexane was then heated to 
25.degree. C. 15.3 millimoles of titanium tetrachloride were introduced 
into the reactor slowly over 1 hour with stirring. The mixture obtained 
was stirred at 25.degree. C. for 1 hour. 15.3 millimoles of titanium 
tetraisopropoxide were then introduced slowly over 1 hour with stirring 
into the reactor, which was kept at 25.degree. C. The mixture obtained was 
then stirred at 25.degree. C. for 1 hour and was then cooled to room 
temperature (20.C). The solid product (C) obtained was washed three times, 
each time with 600 ml of n-hexane at 20.degree. C. After these washings, 
it contained 1.7 milliatoms of magnesium, 3.9 milliatoms of chlorine and 
0.45 milliatoms of tetravalent titanium per gram of silica, and 
substantially no trivalent titanium. 
2 litres of n-hexane, 10.8 millimoles of tri-n-octylaluminium and a 
quantity of solid product (C) containing 6 milliatoms of titanium were 
introduced into a stainless steel 5-litre reactor fitted with a stirrer 
rotating at 750 revolutions per minute and heated to 70.degree. C. A 
volume of 280 ml of hydrogen, measured under normal conditions, was then 
introduced therein, followed by ethylene at a steady rate of 160g/h for 3 
hours. At the end of this time the reactor was degassed and its content 
was transferred to a rotary evaporator where the n-hexane was evaporated 
off at 60.degree. C. under a partial vacuum. The solid catalyst (D) which 
was ready for use was thus obtained in the form of a prepolymer powder 
consisting of particles which had a mass-mean diameter of 250 microns and 
contained 80 g of polyethylene per milliatom of titanium. 
EXAMPLE 2 
Preparation of a Catalyst 
The operation was carried out exactly as in Example 1 for the preparation 
of solid products (A) and (B). Next, 600 ml of n-hexane and a quantity of 
the solid product (B) containing 30 g of silica were introduced into a 
stainless steel 1-litre reactor fitted with a stirrer system rotating at 
250 revolutions per minute and heated to 50.degree. C., followed slowly by 
25.5 millimoles of titanium tetrachloride over 1 hour. The mixture 
obtained was then stirred at 50.degree. C. for 1 hour and was then cooled 
to room temperature (20.C). The solid product (E) obtained was washed 
three times, each time with 600 ml of n-hexane at 20.degree. C. After 
these washings, it contained 1.7 milliatoms of magnesium, 4.8 milliatoms 
of chlorine and 0.54 milliatoms of tetravalent titanium per gram of 
silica, and substantially no trivalent titanium. 
2 litres of n-hexane, 18 millimoles of tri-n-octylaluminium and a quantity 
of solid product (E) containing 6 milliatoms of titanium were introduced 
into a stainless steel 5-litre reactor fitted with a stirrer device 
rotating at 750 revolutions per minute and heated to 70.degree. C. A 
volume of 400 ml of hydrogen, measured under normal conditions, was then 
introduced therein, followed by ethylene at a steady rate of 100 g/h for 3 
hours. At the end of this time the reactor was degassed and its content 
was transferred to a rotary evaporator where the n-hexane was evaporated 
off at 60.degree. C. under a partial vacuum. The solid catalyst (F) which 
was ready for use was thus obtained in the form of a prepolymer powder 
consisting of particles with a mass-mean diameter of 220 microns and 
containing 50 g of polyethylene per milliatom of titanium. 
EXAMPLE 3 
Preparation of a Catalyst 
The operation was carried out exactly as in Example 2 for the preparation 
of the solid products (A), (B) and (E). 
Next, 2 litres of n-hexane, 10.8 millimoles of tri-n-octylaluminium and a 
quantity of solid product (E) containing 6 milliatoms of titanium were 
introduced into a stainless steel 5-litre reactor fitted with a stirrer 
device rotating at 750 revolutions per minute and heated to 70.degree. C. 
A volume of 400 ml of hydrogen, measured under normal conditions, was then 
introduced therein, followed by ethylene at a steady rate of 160 g/h for 3 
hours. At the end of this time 7.2 millimoles of tri-n-octylaluminium were 
added to the mixture and the reactor was then degassed and its content was 
transferred to a rotary evaporator, where the n-hexane was evaporated off 
at 60.degree. C. under a partial vacuum. The solid catalyst (G) which was 
ready for use was thus obtained in the form of a powder consisting of 
particles which had a mass-mean diameter of 260 microns and contained 80 g 
of polyethylene per milliatom of titanium. 
EXAMPLE 4 
Preparation of a Catalyst 
The operation was carried out exactly as in Example 1 for the preparation 
of the solid product (A). 
Next, 600 ml of n-hexane and a quantity of the solid product (A) containing 
60 g of silica were introduced into a stainless steel 1-litre reactor 
fitted with a stirrer rotating at 250 revolutions per minute and heated to 
50.degree. C., followed slowly over 1 hour by 306 millimoles of tert-butyl 
chloride. At the end of this time the mixture was stirred at 50.degree. C. 
for 1 hour and was then cooled to room temperature (20.C). The solid 
product (H) obtained was washed three times, each time with 600 ml of 
n-hexane at 20.degree. C. After these washings it contained 1.6 milliatoms 
of magnesium and 3.2 milliatoms of chlorine per gram of silica, and 
substantially no functional group reductive towards titanium 
tetrachloride. 
The reactor containing a quantity of the solid product (H) containing 30 g 
of silica, in suspension in 600 ml of n-hexane, was then heated to 
50.degree. C. 24 millimoles of titanium tetrachloride were introduced into 
the reactor slowly over 1 hour with stirring. At the end of this time the 
mixture was stirred at 50.degree. C. for 1 hour and was then cooled to 
room temperature (20.C). The solid product (I) obtained was washed three 
times, each time with 600 ml of n-hexane at 20.degree. C. After these 
washings it contained 1.6 milliatoms of magnesium, 4.25 milliatoms of 
chlorine and 0.49 milliatoms of tetravalent titanium per gram of silica, 
and substantially no trivalent titanium. 
Two litres of n-hexane, 9.6 millimoles of tri-n-octylaluminium and a 
quantity of the solid product (I) containing 6 milliatoms of titanium were 
introduced into a stainless steel 5-litre reactor fitted with a stirrer 
rotating at 750 revolutions per minute and heated to 70.degree. C. A 
volume of 400 ml of hydrogen, measured under normal conditions, was then 
introduced therein, followed by ethylene at a steady rate of 160 g/h for 3 
hours. At the end of this time the reactor was degassed and its content 
was transferred to a rotary evaporator, where the n-hexane was evaporated 
off at 60.degree. C. under a partial vacuum. The solid catalyst (J) which 
was ready for use was thus obtained in the form of a prepolymer powder 
consisting of particles with a mass-mean diameter of 250 microns and 
containing 80 g of polyethylene per milliatom of titanium. 
EXAMPLE 5 
600 ml of n-hexane and 60 g of a dry silica identical to that employed in 
Example 1 were introduced into a stainless steel 1-litre reactor fitted 
with a stirrer device rotating at 250 revolutions per minute, followed 
slowly over 1 hour by a mixture of 80 millimoles of dibutylmagnesium and 
40 millimoles of triethylaluminium at a temperature of 20.degree. C. At 
the end of this time the mixture was stirred at 20.degree. C. for 1 hour. 
The solid product (K) thus obtained was washed three times, each time with 
600ml of n-hexane at 20.degree. C., and contained 1.1 milliatoms of 
magnesium and 0.68 milliatoms of aluminium per gram of silica. 
The reactor containing the solid product (K) in suspension in 600 ml of 
n-hexane was then heated to 50.degree. C. 254 millimoles of tert-butyl 
chloride were introduced into the reactor slowly over 1 hour with 
stirring. At the end of this time the mixture was stirred at 50.degree. C. 
for 1 hour and was then cooled to room temperature (20.C). The solid 
product (L) obtained was washed three times, each time with 600 ml of 
n-hexane at 20.degree. C. and contained 1.1 milliatoms of magnesium, 0.4 
milliatoms of aluminium and 2 milliatoms of chlorine per gram of silica, 
and substantially no basic functional group reductive towards titanium 
tetrachloride. 
The reactor containing a quantity of the solid product (L) containing 30 g 
of silica in suspension in 600 ml of n-hexane was then heated to 
50.degree. C. 30 millimoles of titanium tetrachloride were introduced into 
the reactor slowly over 1 hour with stirring. At the end of this time the 
mixture was stirred at 50.degree. C. for 1 hour and was then cooled to 
room temperature (20.C). The solid product (M) obtained was washed three 
times, each time with 600 ml of n-hexane at 20.degree. C. and contained 
1.1 milliatoms of magnesium, 0.4 milliatoms of aluminium, 3.1 milliatoms 
of chlorine and 0.4 milliatoms of tetravalent titanium per gram of silica, 
and substantially no trivalent titanium. 
2 litres of n-hexane, 10.8 millimoles of tri-n-octylaluminium and a 
quantity of the solid product (M) containing 6 milliatoms of titanium were 
introduced into a stainless steel 5-litre reactor fitted with a stirrer 
device rotating at 750 revolutions per minute and heated to 70.degree. C. 
A volume of 400 ml of hydrogen, measured under normal conditions, was then 
introduced therein, followed by ethylene at a steady rate of 160 g/h for 3 
hours. At the end of this time the reactor was degassed and its content 
was transferred to a rotary evaporator where n-hexane was evaporated off 
at 60.degree. C. under a partial vacuum. The catalyst (N) which was ready 
for use was thus obtained in the form of a prepolymer powder consisting of 
particles which had a mass-mean diameter of 250 microns and contained 80 g 
of polyethylene per milliatom of titanium. 
EXAMPLE 6 
Preparation of a Catalyst 
A support was employed, consisting of an "SG 332" Registered Trademark 
silica powder sold by W.R. Grace Company (United States of America), which 
had a specific surface area (BET) of 300 m.sup.2 /g and a pore volume of 
1.7 ml/g. It consisted of particles which had a mass-mean diameter of 80 
microns. It was dried for 8 hours at 200.C under an air atmosphere and a 
silica powder rid of free water and containing approximately 2 millimoles 
of hydroxyl groups per gram was obtained. All the subsequent operations 
were carried out under an inert nitrogen atmosphere. 
600 ml of n-hexane and 60 g of dried silica were introduced into a 
stainless steel 1-litre reactor fitted with a stirrer rotating at 250 
revolutions per minute, followed slowly over 1 hour by 60 millimoles of 
dibutylmagnesium at a temperature of 20.degree. C. 
The reactor was then heated to 50.degree. C. and 120 millimoles of 
tert-butyl chloride were introduced therein slowly over 1 hour with 
stirring. While the temperature continued to be maintained at 50.C, 30 
millimoles of titanium tetrachloride were introduced. At the end of this 
introduction the reactor was then heated to 80.degree. C. and was kept 
stirred at this temperature for 2 hours. At the end of this time the 
reactor was cooled and a solid (0) was obtained, containing 0.5 milliatoms 
of titanium per gram of silica, in suspension in hexane containing less 
than 100 ppm (parts by weight per million) of titanium. 
2 litres of n-hexane, 7.2 millimoles of tri-n-octylaluminium and a quantity 
of the solid product (0) containing 6 milliatoms of titanium were 
introduced into a stainless steel 5-litre reactor fitted with a stirrer 
rotating at 750 revolutions per minute and heated to 70.degree. C. A 
volume of 280 ml of hydrogen, measured under normal conditions, was then 
introduced therein, followed by ethylene at a steady rate of 60 g/h for 4 
hours. At the end of this time the reactor was degassed and its content 
was transferred to a rotary evaporator, where the n-hexane was evaporated 
off at 60.degree. C. under a partial vacuum. The solid catalyst (P) which 
was ready for use was thus obtained in the form of a powder consisting of 
particles which had a mass-mean diameter of 250 microns and contained 40 g 
of polyethylene per milliatom of titanium. 
EXAMPLE 7 
Preparation of a Catalyst 
A support was employed consisting of an "SG 332" Registered Trademark 
silica powder sold by W.R. Grace Company (United States of 35 America), 
which had a specific surface area (BET) of 300 m.sup.2 /g and a pore 
volume of 1.7 ml/g. It consisted of particles which had a mass-mean 
diameter of 80 microns. It was dried for 8 hours at 200.C and a silica 
powder rid of free water and containing approximately 2 millimoles of 
hydroxyl group per gram was obtained. All the subsequent operations were 
carried out under an inert nitrogen atmosphere. 
600 ml of n-hexane and 60 g of dried silica were introduced into a 
stainless steel 1-litre reactor fitted with a stirrer rotating at 250 
revolutions per minute, followed slowly over 1 hour by 138.6 millimoles of 
dibutylmagnesium at a temperature of 20.degree. C. The mixture thus 
obtained was stirred for 1 hour at 20.degree. C. and a solid product (Q) 
was obtained. 
The reactor was then heated to 50.degree. C. and 277.2 millimoles of 
tert-butyl chloride were introduced therein slowly for 1 hour with 
stirring. At the end of this time the mixture continued to be stirred for 
1 hour at 50.degree. C. and was then cooled to room temperature (20.C). A 
solid product (R) was obtained in suspension in n-hexane, containing 
chlorine and magnesium in a Cl/Mg atomic ratio equal to 1.69 and 
containing no functional group reductive towards titanium tetrachloride. 
The liquid phase of this suspension contained 500 ppm of tert-butyl 
chloride. 
The reactor containing the suspension of the solid product (R) in n-hexane 
was then heated to 50.degree. C. 69.3 millimoles of titanium tetrachloride 
were introduced therein slowly over 2 hours with stirring. The mixture 
thus obtained was kept stirred for 1 hour at 50.degree. C. and was then 
cooled to room temperature. A solid (S) was thus obtained in suspension in 
n-hexane which, after three washings, each time with 600 ml of n-hexane, 
contained 2.18 milliatoms of magnesium, 5.7 milliatoms of chlorine and 
0.65 milliatoms of tetravalent titanium per gram of silica, and 
substantially no trivalent titanium. 
2 litres of n-hexane, 9.6 millimoles of tri-n-octylaluminium and a quantity 
of the solid product (S) containing 6 milliatoms of titanium were 
introduced into a stainless steel 5-litre reactor fitted with a stirrer 
rotating at 750 revolutions per minute and heated to 70.degree. C. A 
volume of 280 ml of hydrogen, measured under normal conditions, was then 
introduced therein, followed by ethylene at a steady rate of 120 g/h for 4 
hours. At the end of this time the reactor was degassed and its content 
was transferred to a rotary evaporator, where the n-hexane was evaporated 
off at 60.degree. C. under a partial vacuum. The solid catalyst (T) which 
was ready for use was thus obtained in the form of a prepolymer powder 
consisting of particles which had a mass-mean diameter of 250 microns and 
contained 80 g of polyethylene per milliatom of titanium. 
EXAMPLE 8 
Preparation of a Catalyst 
The procedure was exactly as in Example 7, apart from the fact that 277.2 
millimoles of sec-butyl chloride were introduced into the reactor instead 
of tert-butyl chloride, and that solid products (Rl) and (Sl) were 
obtained and used instead of the solid products (R) and (S) respectively 
for preparing a solid catalyst (Tl). 
The solid product (Rl) was obtained in suspension in n-hexane, containing 
chlorine and magnesium in a Cl/Mg atomic ratio equal to 1.57 and 
containing substantially no functional group reductive towards titanium 
tetrachloride. The liquid phase of this suspension contained 900 ppm of 
sec-butyl chloride. 
The solid product (Sl) contained 2.05 milliatoms of magnesium, 5.2 
milliatoms of chlorine and 0.58 milliatoms of tetravalent titanium per 
gram of silica, and substantially no trivalent titanium. 
The solid catalysts (Tl) was obtained in the form of a prepolymer powder 
consisting of particles which had a mass-mean diameter of 250 microns and 
contained 80 g of polyethylene per milliatom of titanium. 
EXAMPLE 9 
Preparation of a Catalyst 
The procedure was exactly as in Example 7, apart from the fact that 69.3 
millimoles of vanadyl trichloride were introduced into the reactor instead 
of titanium tetrachloride. A solid product (S2) was thus obtained in 
suspension in n-hexane which, after three washings each with 600 ml of 
n-hexane, contained 2.1 milliatoms of pentavalent vanadium per gram of 
silica, and substantially no tetravalent vanadium. 
2 litres of n-hexane, 9.6 millimoles of tri-n-octylaluminium and a quantity 
of the solid product (S2) containing 6 milliatoms of vanadium were 
introduced into a stainless steel 5-litre reactor fitted with a stirrer 
rotating at 750 revolutions per minute and heated to 70.degree. C. A 
volume of 280 ml of hydrogen, measured under normal conditions, was then 
introduced therein, followed by ethylene at a steady rate of 120 g/h for 4 
hours. At the end of this time the reactor was degassed and its content 
was transferred to a rotary evaporator, where the n-hexane was evaporated 
off at 60.degree. C. under a partial vacuum. The solid catalysts (T2) 
which was ready for use was thus obtained in the form of prepolymer powder 
consisting of particles which had a mass-mean diameter of 250 microns and 
contained 80 g of polyethylene per milliatom of vanadium. 
EXAMPLE 10 (COMATIVE ) 
Preparation of a Catalyst 
The mixture prepared in Example 7, which contained the solid product (Q) 
was employed. 
The reactor containing the solid product (Q) was heated to 50.C and 277.2 
millimoles of normal-butyl chloride were introduced therein slowly with 
stirring over 1 hour. At the end of this time the mixture thus obtained 
continued to be stirred at 50.degree. C. for 1 hour and was then cooled to 
room temperature. The liquid phase of the suspension thus obtained 
contained approximately 50,000 ppm of normal-butyl chloride. The solid 
product (U) contained chlorine and magnesium in a Cl/Mg atomic ratio of 
approximately 0.2, as well as some basic functional groups capable of 
reducing titanium tetrachloride. 
The reactor containing the suspension of the solid product (U) in n-hexane 
was heated to 50.degree. C. 69.3 millimoles of titanium tetrachloride were 
introduced therein slowly over 2 hours with stirring. The mixture thus 
obtained was kept stirred for 1 hour at 50.degree. C. and was then cooled 
to room temperature. A solid (V) was obtained as a suspension in hexane, 
and was washed three times, each time with 600 ml of n-hexane at 
20.degree. C. After these washings the solid (V) contained 2.0 milliatoms 
of magnesium, 5.1 milliatoms of chlorine, 0.41 milliatoms of tetravalent 
titanium and 0.39 milliatoms of trivalent titanium per gram of silica. 
2 litres of n-hexane, 9.6 millimoles of tri-n-octylaluminium and a quantity 
of the solid product (V) containing 6 milliatoms of titanium were 
introduced into a stainless steel 5-litre reactor fitted with a stirrer 
rotating at 750 revolutions per minute and heated to 70.degree. C. A 
volume of 280 ml of hydrogen, measured under normal conditions, was then 
introduced therein, followed by ethylene at a steady rate of 120 g/h for 4 
hours. At the end of this time the reactor was degassed and its content 
was transferred to a rotary evaporator, where the n-hexane was evaporated 
off at 60.degree. C. under a partial vacuum. The solid catalyst (W) which 
was ready for use was thus obtained in the form of a prepolymer powder 
consisting of particles which had a mass-mean diameter of 250 microns and 
contained 80 g of polyethylene per milliatom of titanium. 
EXAMPLE 11 
Gas Phase Polymerization of Ethylene in a Fluidized-Bed Reactor 
800 g of an anhydrous and deaerated polyethylene powder were introduced as 
a powder charge into a fluidized-bed reactor of 20 cm diameter. This 
powder was fluidized with the aid of an upward gas stream propelled at a 
velocity of 15 cm/s and consisting of a mixture of ethylene and hydrogen 
at a total pressure of 1.5 MPa. 8 millimoles of tri-n-octylaluminium were 
introduced into the reactor, followed by a quantity of a solid catalyst 
prepared according to the present invention, equivalent to 0.8 milliatoms 
of titanium. Only for the solid catalyst (P), 8 millimoles of 
triethylaluminium were used instead of tri-n-octylaluminium. The total 
pressure in the reactor was kept constant and equal to 1.5 MPa by ethylene 
addition and the polymerization reaction spent between 3 and 5 hours. 
Table 1 shows, according to the catalysts used, the operating conditions of 
the ethylene polymerization and the characteristics of the polyethylene 
powders obtained. By way of comparison, instead of introducing the 
catalyst (F) prepared according to the present invention, the intermediate 
solid product (E) was introduced in a quantity which was equivalent in 
milliatoms of titanium and it was noted especially that the polyethylene 
powder obtained with the solid catalyst (F) exhibited a bulk density which 
was clearly higher than that of the polyethylene obtained with the 
intermediate solid product (E). 
EXAMPLE 12 
Gas Phase Copolymerization of Ethylene With 1-Butene in a Fluidized-Bed 
Reactor 
800 g of an anhydrous and deaerated powder of a copolymer of ethylene and 
1-butene were introduced as a powder charge into a fluidized-bed reactor 
of 20 cm diameter. This powder was fluidized with the aid of an upward gas 
stream propelled at a velocity of 15 cm/s and consisting of a mixture of 
ethylene, 1-butene and hydrogen at a total pressure of 1.5 MPa. 8 
millimoles of tri-n-octylaluminium were introduced into the reactor, 
followed by a quantity of a solid catalyst prepared according to the 
present invention, equivalent to 0.8 milliatoms of titanium. For the solid 
catalysts (T), (Tl), (T2) and (W), 8 millimoles of triethylaluminium were 
used instead of tri-n-octylaluminium. 
By way of comparison, instead of introducing the solid catalyst (G) 
prepared according to the present invention, the intermediate solid 
product (E) was introduced in a quantity which was equivalent in 
milliatoms of titanium. Also by way of comparison, instead of introducing 
the solid catalyst (T) prepared according to the present invention, the 
solid catalyst (W) of Comparative Example 10 prepared with the aid of a 
primary alkyl monochloride was introduced. 
Table 2 shows the operating conditions of the copolymerizations of ethylene 
with 1-butene and the characteristics of the copolymer powders obtained. 
It was noted especially that the copolymer powder obtained with the solid 
catalyst (G) exhibited a bulk density which was markedly higher than that 
of the copolymer obtained with the intermediate solid product (E). 
Furthermore, it was noted that to obtain a copolymer of a given density, 
the ratio of the partial pressure of 1-butene to that of ethylene was 
markedly lower in the case of a solid catalyst prepared according to the 
present invention than in the case of an intermediate solid product 
prepared according to a process not comprising the fourth stage. It was 
also observed that the productivity in copolymer was markedly greater with 
the catalyst (T) according to the present invention than with the catalyst 
(W). 
EXAMPLE 13 
Preparation of a Catalyst 
The "SG 332" Registered Trademark silica powder sold by W.R. Grace Company 
(United States of America) was dried for 8 hours at 200.degree. C. under 
an air atmosphere to obtain a silica which was rid of free water and 
approximately contained 2 millimoles of hydroxyl group per gram. All the 
subsequent operations were carried out under an inert nitrogen atmosphere. 
600 ml of n-hexane and 60 g of the dried silica were introduced into a 
stainless steel 1-litre reactor fitted with a stirrer rotating at 250 
revolutions per minute, followed slowly over 1 hour by 190 millimoles of 
dibutylmagnesium at a temperature of 20.degree. C. The mixture thus 
obtained was stirred for 1 hour at 20.degree. C. and a solid product was 
obtained containing 1.55 milliatoms of magnesium per gram of silica. The 
reactor was then heated to 50.degree. C. and 186 millimoles of tert-butyl 
chloride were introduced therein slowly for 1 hour with stirring. At the 
end of this time, the mixture continued to be stirred for 1 hour at 
50.degree. C. and was then cooled to room temperature (20.C). A solid 
product (X) was obtained in suspension in n-hexane, containing chlorine 
and magnesium in a Cl/Mg atomic ratio equal to 1.6 and containing 
substantially no functional group reductive towards titanium 
tetrachrloride. The liquid phase of this suspension contained 600 ppm of 
tert-butyl chloride. 
The reactor containing the suspension of the solid product (X) in n-hexane 
was then heated to 50.degree. C. 48 millimoles of titanium tetrachloride 
were introduced therein slowly over 2 hours with stirring. The mixture 
thus obtained was kept stirred from 1 hour at 50.degree. C. and was then 
cooled to room temperature. A solid product (Y) was thus obtained in 
suspension in n-hexane which, after three washings, each time with 600 ml 
of n-hexane, contained 1.63 milliatoms of magnesium, 5 milliatoms of 
chlorine and 0.53 milliatoms of tetravalent titanium per gram of silica, 
and substantially no trivalent titanium. 
2 litres of n-hexane, 9.6 millimoles of tri-n-octylaluminium and a quantity 
of the solid product (Y) containing 6 milliatoms of titanium were 
introduced into a stainless steel 5-litre reactor fitted with a stirrer 
rotating at 750 revolutions per minute and heated to 70.degree. C. A 
volume of 280 ml of hydrogen, measured under normal conditions, was then 
introduced therein, followed by ethylene at a steady rate of 120 g/h for 4 
hours. At the end of this time the reactor was degassed and its content 
was transferred to a rotary evaporator where the n-hexane was evaporated 
off at 60.degree. C. under a partial vacuum. The solid catalyst (Z) which 
was ready for use was thus obtained in the form of a prepolymer powder 
consisting of particles which had a mass-mean diameter of 250 microns and 
contained 80 g of polyethylene per milliatom of titanium. 
EXAMPLE 14 (COMATIVE) 
Preparation of a Catalyst 
The procedure was exactly as in Example 13, apart from the fact that the 
186 millimoles of carbon tetrachloride were introduced into the reactor 
instead of tert-butyl chloride, and that solid products (Xl) and (Yl) were 
obtained and used for preparing a solid catalyst (Zl) instead of the solid 
products (X) and (Y) respectively. 
The solid product (Xl) was obtained in suspension in n-hexane, containing 
chlorine and magnesium in a Cl/Mg atomic ratio equal to 0.97 and 
containing functional groups reductive towards titanium tetrachloride. The 
liquid phase of this suspension contained a lot of chlorine-containing 
organic compounds. 
The solid product (Yl) contained 1.72 milliatoms of magnesium, 3.4 
milliatoms of chlorine, 0.45 milliatoms of tetravalent titanium and 0.1 
milliatoms of trivalent titanium per gram of silica. 
The solid catalyst (Zl) was obtained in the form of a prepolymer powder 
consisting of particles which had a mass-mean diameter of 250 microns and 
contained 80 g of polyethylene per milliatom of titanium. 
EXAMPLE 15 
Gas Phase Polymerization of Ethylene in a Fluidized-Bed Reactor. 
The procedure was exactly as in Example 12, apart from the use of the solid 
catalyst (Z). By way of comparison, instead of using the solid catalyst 
(Z) prepared according to the present invention, the solid catalyst (Zl) 
was used. 
Table 3 shows the operating conditions of the ethylene polymerization and 
the characteristics of the polyethylene powders obtained. It was noted 
especially that the productivity of the solid catalyst (Zl) was markedly 
lower than that of the solid catalyst (Z). 
EXAMPLE 16 
Gas Phase Copolymerisation of Ethylene with Butene-1 in a Fluidized-Bed 
Reactor. 
The procedure was exactly as in Example 12, apart from the use of the solid 
catalyst (P) in a quantity equivalent to 0.8 milliatom of titanium, the 
use of 8 millimoles of tri-n-octylaluminium, at a temperature of 
95.degree. C., with a mixture of ethylene, butene-1 and hydrogen, 
containing 10% (by volume) of hydrogen, the ratio (pC.sub.4 /pC.sub.2) of 
the partial pressure of butene-1 to that of ethylene being of 0.03. 
In these conditions, a copolymer of ethylene with 2% by weight of butene-1 
was obtained in the form of a powder of a bulk density of 0.43 g/cm.sup.3. 
EXAMPLE 17 
Gas Phase Copolymerisation of Ethylene with Butene-1 in a Fluidized-Bed 
Reactor. 
The procedure was exactly as in Example 16, apart from the ratio (pC.sub.4 
/pC.sub.2) of 0.05. 
In these conditions, a copolymer of ethylene with 3.3% by weight of 
butene-1 was obtained in the form of a powder of a bulk density of 0.42 
g/cm.sup.3. 
EXAMPLE 18 
Gas Phase Copolymerisation of Ethylene with Methyl-4-Pentene-1 in a 
Fluidized-Bed Reactor. 
The procedure was exactly as in Example 12, apart from the use of the solid 
catalyst (P) in a quantity equivalent to 0.8 milliatom of titanium, the 
use of 8 millimoles of tri-n-octylaluminium, at a temperature of 
70.degree. C., with a mixture of ethylene, methyl-4-pentene-1 and 
hydrogen, containing 10% (by volume) of hydrogen, the ratio (pC.sub.6 
/pC.sub.2) of the partial pressure of methyl-4-pentene-1 to that of 
ethylene being of 0.05. 
In these conditions, a copolymer of ethylene with 4.8% by weight of 
methyl-4-pentene-1 was obtained in the form of a powder of a bulk density 
of 0.41 g/cm.sup.3. 
EXAMPLE 19 
Gas Phase Copolymerisation of Ethylene with Methyl-4-Pentene-1 in a 
Fluidized-Bed Reactor. 
The procedure was exactly as in the Example 18, apart from the ratio 
(pC.sub.6 /pC.sub.2) of 0.1. 
In these conditions, a copolymer of ethylene with 9.5% by weight of 
methyl-4-pentene-1 was obtained in the form of a powder of a bulk density 
of 0.38 g/cm.sup.3. 
TABLE 1 
__________________________________________________________________________ 
Polymerization of ethylene 
Solid catalyst 
Tempera- 
% H2 (in 
Produc- 
MI.sub. 2.multidot.16 
Density 
BD 
or solid product 
ture (.degree.C.) 
volume) 
tivity 
g/10 min 
(g/cm.sup.3) 
(g/cm.sup.3) 
__________________________________________________________________________ 
(D) 100 26 3300 1.9 0.96 0.42 
(F) 90 39 3100 2.5 0.97 0.40 
(E) 90 39 3200 2.4 0.97 0.30 
(comparative) 
(J) 90 40 3600 1 0.96 0.38 
(P) 90 40 3050 1.1 0.96 0.36 
__________________________________________________________________________ 
TABLE 2 
__________________________________________________________________________ 
Copolymerization of ethylene with 1-butene 
% C.sub.4 by 
Solid catalyst 
Tempera- 
% H.sub.2 in 
Produc- 
MI.sub. 2.multidot.16 
Density 
weight in 
BD 
or solid product 
ture (.degree.C.) 
(volume) 
pC.sub.4 /pC.sub.2 
tivity 
g/10 min 
(g/cm.sup.3) 
the copolymer 
(g/cm.sup.3) 
__________________________________________________________________________ 
(G) 85 20 0.07 4560 1.8 0.943 
3.6 0.41 
(E) 85 20 0.08 4000 1.0 0.948 
2.7 0.28 
(comparative) 
(G) 85 24 0.04 4230 1.8 0.947 
2.8 0.39 
(G) 80 9 0.30 5800 1.3 0.921 
7.6 0.43 
(G) 80 9 0.32 7150 1.8 0.914 
9.4 0.38 
(T) 85 29 0.053 
3841 5.04 
0.945 
3.3 0.32 
(T1) 85 25 0.045 
3950 4.1 0.945 
3.2 0.34 
(T2) 85 25 0.045 
3120 3.3 0.944 
3.0 0.35 
(W) 85 25 0.044 
1960 1.9 0.944 
2.1 0.37 
(comparative) 
__________________________________________________________________________ 
TABLE 3 
______________________________________ 
POLYMERIZATION OF ETHYLENE 
Solid Tempera- % H.sub.2 (in 
Produc- BD 
catalyst 
ture (.degree.C.) 
volume) tivity MI.sub. 2.multidot.16 
(g/cm.sup.3) 
______________________________________ 
(Z) 90 39 3050 1 0.39 
(Z1) 90 39 2090 3 0.35 
Compar- 
ative 
______________________________________