Process for a gas phase olefin polymerization

The present invention relates to a process for introducing a solid catalyst into a gas-phase olefin polymerization reactor. It comprises in particular storing the catalyst in the form of a dry powder in a hopper, withdrawing from the hopper a measured amount of the said catalyst, introducing the said amount of the catalyst and a liquid hydrocarbon into a mixing chamber, mixing the said catalyst with the said liquid hydrocarbon so as to form in the said chamber a suspension of the entrained catalyst with the said liquid hydrocarbon, and introducing the said suspension into the said reactor. In a preferred form, the liquid hydrocarbon is continuously introduced into the chamber and forms a continuous stream to which is added the measured amount of the catalyst and which flows into the reactor.

BACKGROUND OF THE INVENTION 
The present invention relates to a process for the introduction of a 
catalyst into a gas-phase olefin polymerization reactor, in particular 
into a fluidized bed reactor. 
The catalysts used in gas-phase olefin polymerizations are often provided 
in the solid state. The solid catalysts can be kept either in the form of 
a suspension in a liquid hydrocarbon or in the form of a dry powder. Now, 
it has been observed that some solid catalysts which are particularly 
active in polymerization have properties which deteriorate when they are 
kept in suspension. There therefore appears a need to keep solid catalysts 
in the form of a dry powder. Moreover, many catalysts are now manufactured 
and delivered in this form because they can be transported and handled 
more easily. 
It is known that solid catalysts used in the form of a dry powder are 
generally introduced in this form into gas-phase olefin polymerization 
reactors using in particular a gaseous fluid such as a carrier gas, for 
example nitrogen, hydrogen, a gaseous olefin or a mixture of these gases. 
This method of introduction, carried out entirely in the absence of 
liquid, is, for example, described in French Patent Application 
FR-2,705,252-A. However, it has been observed that this method of 
introduction can cause one or a number of problems characterized in 
particular by the use of large volumes of gaseous fluids introduced with 
the catalyst into the reactor, an insufficiently homogeneous dispersion of 
the catalyst in the reactor, an excessive entrainment of the catalyst out 
of the fluidized bed, and the appearance of hot spots, both in the 
fluidized bed and above the bed. These problems can arise separately or 
simultaneously, depending on the type of catalyst used, in particular 
depending on the composition or the size of the catalyst. 
Patent Application of Luxembourg LU-A-79915 discloses a process for 
introducing a solid catalyst into a liquid phase polymerization reactor. 
The catalyst in the form of a dry powder is contacted with a liquid in two 
successive settling zones wherein the catalyst falls by gravity under the 
protection of the liquid. Contacting the catalyst in the form of a dry 
powder with the liquid neither produces any mixing of entrained catalyst 
with the said liquid, nor forms a suspension of the catalyst in the said 
liquid. In such a contacting step, the liquid is used as a screen for 
protecting the catalyst, and not as a carrier for suspending and 
transporting the catalyst into the polymerization reactor. Once the 
catalyst falls by gravity through the settling zones under the protection 
of the liquid, it is then entrained into the polymerization reactor with 
the help of a liquid stream. The process thus involves relatively large 
amounts of liquid which may affect the catalyst activity. 
A process has now been found which makes it possible to very substantially 
reduce or even to completely avoid the above-mentioned problems. The 
process has the advantage of being able to make use of catalysts which are 
different both in their composition and in their size and providing a more 
universal process which makes it possible to use different catalysts in 
the same reactor. 
SUMMARY OF THE INVENTION 
More particularly, the present invention relates to a process for 
introducing a solid catalyst into a gas-phase olefin polymerization 
reactor through which passes a gaseous reaction mixture containing at 
least one olefin to be polymerized, which process is characterized in that 
it comprises: 
storing under an inert atmosphere the solid catalyst in the form of a dry 
powder in a hopper, 
withdrawing under an inert atmosphere from the hopper a measured amount of 
the catalyst in the form of a dry powder, 
introducing the measured amount of the catalyst in the form of a dry powder 
and a liquid hydrocarbon into a mixing chamber, 
mixing the said catalyst with the said liquid hydrocarbon in the mixing 
chamber so as to form in the said chamber a suspension of the entrained 
catalyst with the said liquid hydrocarbon, and 
introducing the said suspension into the gas-phase olefin polymerization 
reactor.

DETAILED DESCRIPTION OF THE INVENTION 
The solid catalyst can be a catalyst containing a transition metal 
belonging to group IV, V or VI of the Periodic Classification of the 
elements, such as titanium, vanadium, chromium, zirconium or hafnium. It 
can be in particular a catalyst of Ziegler-Natta type containing one or a 
number of transition metals, especially those mentioned above, in the 
halogenated compound form. The catalyst of Ziegler-Natta type may 
preferably be a catalyst comprising a halogenated compound of at least one 
of these transition metals, combined with a magnesium compound and 
optionally a porous support, such as silica. 
The solid catalyst can also be a high-activity catalyst of metallocene 
type, which can be, for example, represented by the general formula 
EQU (Cp).sub.m MR.sub.x R.sup.1.sub.y 
in which Cp represents a substituted or unsubstituted cyclopentadienyl 
ring, M represents a transition metal from group IV, V or VI of the 
Periodic Classification of the elements, such as zirconium, titanium or 
hafnium, R and R.sup.1, being identical or different, represent a 
hydrocarbon radical containing from 1 to 20 carbon atoms, a halogen atom 
or another monovalent ligand, m=1 to 3, x=0 to 3 and y=0 to 3, provided 
that the sum of m, x and y is equal to the oxidation state of M. 
Metallocene-type catalyst examples are found in EP-0,129,368, U.S. Pat. 
No. 5,324,800 and EP-0,206,794. 
The solid catalyst can also be a high-activity catalyst, represented by a 
compound containing a monocyclopentadienyl heteroatom. Such a catalyst is, 
for example, disclosed in EP-0,416,815 and EP-0,420,436. 
The catalysts of Ziegler-Natta type, in particular the high-activity 
catalysts and in particular the catalysts of metallocene type, are 
preferably used on a porous support, such as a refractory oxide, for 
example silica or alumina. 
These high-activity catalysts are generally used in the presence of a 
cocatalyst such as an alkylaluminium, in particular an aluminoxane. Other 
cocatalysts can also be trialkylaluminium compounds, ionic activators or 
compounds which ionize the catalysts, for example boranes. 
The solid catalyst can also be a high-activity catalyst based on a chromium 
oxide supported on a refractory oxide, such as silica, and activated by a 
heat treatment. 
The solid catalyst used in the present invention can also have been brought 
beforehand into contact with at least one olefin, such as ethylene or 
propylene, under conditions where the olefin partially or completely 
polymerizes. The catalyst in this case can be used in the form of a 
prepolymer, i.e. a catalyst prepolymerized using olefin containing, for 
example, from 0.01 to 200, preferably from 0.1 to 100, g of polyolefin per 
millimole of transition metal. 
The process comprises the storage of the solid catalyst in the form of a 
dry powder, that is to say a powder which is substantially free from 
liquid, containing, for example, less than 30% and preferably less than 
20% or 10% by weight of liquid. The catalyst particles can have a mean 
diameter by mass of 20 to 250, preferably of 20 to 200 and more especially 
of 30 to 150 .mu.m. 
The catalyst powder is stored in a hopper under an inert atmosphere, such 
as nitrogen. The pressure, P1, of the hopper is preferably greater than 
the pressure, P2, prevailing in the polymerization reactor. 
The process comprises the withdrawal from the hopper of a measured amount 
of the catalyst in the form of a dry powder, under an inert atmosphere. 
The measured amount can range, for each withdrawal, from 1 to 2,000 g of 
catalyst, in particular from 1 to 500 and preferably from 20 to 200 g of 
catalyst, when it concerns a non-prepolymerized catalyst, or alternatively 
from 20 to 2,000 and preferably from 50 to 1,500 g of catalyst, when it 
concerns a prepolymerized catalyst as described above. 
The withdrawal can be carried out by transfer under an inert atmosphere of 
the catalyst in the form of a dry powder from the storage hopper to a zone 
connected to the said hopper, either by a pressure difference between the 
hopper and the zone or by gravity or by both means simultaneously, and by 
isolation in the zone of the measured amount of the catalyst in the form 
of a dry powder. The zone can be essentially composed of a chamber 
isolated by inlet and outlet valves, the inlet valve being in 
communication with the storage hopper, in particular the bottom of the 
hopper, and the outlet valve with a mixing chamber as described below. The 
zone used for withdrawing the measured amount of catalyst can also be 
essentially composed of a cavity hollowed out in a cylindrical, 
frustoconical or preferably spherical plug of a valve alternately bringing 
(a) the storage hopper into communication with the cavity, in order to 
fill the latter with the catalyst powder, and (b) the cavity thus filled 
with catalyst into communication with a mixing chamber as described below, 
in order to empty the cavity and to introduce the measured amount of 
catalyst into the said mixing chamber. 
The process also comprises the introduction of the measured amount of the 
catalyst in the form of a dry powder into a mixing chamber. The 
introduction of the catalyst can be carried out either by gravity, the 
catalyst charge being allowed to fall into the mixing chamber, or by a 
pressure difference or both means simultaneously, for example using a 
pressurized fluid which drives the catalyst from the space where the 
catalyst has been withdrawn and which pushes the catalyst charge into the 
mixing chamber. However, preference is given to introduction by simple 
gravity, in particular when the catalyst powder is capable of flowing 
freely. The mixing chamber has a volume which can be markedly greater than 
the volume of the measured amount of catalyst at rest and which can, for 
example, be from 2 to 100 times, preferably from 5 to 50 times, the volume 
of the measured amount of catalyst at rest. 
The process comprises the introduction of a liquid hydrocarbon into the 
mixing chamber. It also comprises mixing in the chamber the catalyst in 
the form of a dry powder with the liquid hydrocarbon so as to form in the 
said chamber a suspension of the entrained catalyst with the said liquid 
hydrocarbon. The main function of the introduction of the liquid is 
preferably to produce a mixing of the catalyst with the liquid 
hydrocarbon, to form a suspension of the entrained catalyst with the 
liquid hydrocarbon, to entrain and to introduce the suspension thus formed 
into the polymerization reactor and to improve the introduction of the 
catalyst into the reactor. The introduction of the liquid hydrocarbon and 
the mixing of the catalyst with the liquid hydrocarbon are preferably 
carried out so as to keep the catalyst in suspension in the chamber and to 
keep the catalyst entrained with the liquid hydrocarbon when it is 
introduced into the reactor. In particular, the liquid hydrocarbon can be 
introduced into the chamber so as to create a liquid stream, preferably a 
vortical or cyclonic stream, suitable in particular to mix the catalyst 
with the liquid hydrocarbon, to form a suspension of the entrained 
catalyst with the liquid hydrocarbon, to keep the catalyst in, suspension 
and to entrain it with the liquid hydrocarbon into the reactor. Such a 
process has the advantage of not making use of mechanical stirring for 
forming the suspension. Thus, the agitation created by the liquid stream 
can be sufficient to form the suspension and to entrain the catalyst with 
the liquid hydrocarbon into the reactor. 
The liquid hydrocarbon can be introduced into the chamber non-continuously 
or, preferably, continuously. 
In particular, the non-continuous introduction of liquid can generally be 
carried out for a period of time at least equal to, or preferably greater 
than, the period of time for introduction of the catalyst charge, for 
example a period of time from 1.5 to 20 times, preferably from 2 to 10 
times, greater than the period of time for introduction of the measured 
amount of catalyst. 
The non-continuous introduction of liquid and that of the measured amount 
of catalyst can be carried out in various ways, for example according to 
the histograms of FIGS. 1A, B and C in which represent, periodically with 
time (over a period of 3 successive cycles, by way of example), the 
introduction of liquid and of catalyst into the chamber, the abscissa t 
representing the time and the ordinate Q the flow rates for introduction 
of liquid and of catalyst. Each cycle comprises the discharge of the 
suspension from the chamber and its introduction into the reactor (not 
represented in the histograms). Thus, the introduction of catalyst into 
the chamber can be carried out before, after or during the introduction of 
liquid, for example according to the histograms FIGS. 1A, B and C 
respectively in However, it is preferable to carry out the introduction of 
catalyst after, or more particularly during, the introduction of liquid. 
According to one of the preferred methods, the introduction of the 
measured amount of catalyst into the chamber can be carried out 
simultaneously with introduction of the liquid into the said chamber, or 
preferably during part of the period of time for introduction of the 
liquid, in particular after the beginning of the introduction of the 
liquid. 
Thus, according to one of the preferred methods, the process can comprise: 
storing under an inert atmosphere the solid catalyst in the form of a dry 
powder in a hopper, 
withdrawing under an inert atmosphere from the said hopper a measured 
amount of the catalyst in the form of a dry powder, 
introducing a liquid hydrocarbon into a mixing chamber, 
adding the measured amount of the catalyst in the form of a dry powder to 
the liquid hydrocarbon in the mixing chamber, 
mixing the said catalyst with the said liquid hydrocarbon in the mixing 
chamber as to form in the said chamber a suspension of the entrained 
catalyst with the said liquid hydrocarbon, and 
introducing the said suspension into the gas-phase olefin polymerization 
reactor. 
In this case, the storage of the catalyst, the withdrawal of the measured 
amount of catalyst, the introduction of the liquid into the chamber and 
the mixing of the catalyst with the liquid are carried out in a way 
identical to that which has been described above. It is in particular 
preferable that the period of time for introduction of the liquid should 
be at least equal to, or preferably greater than, that for the addition of 
the catalyst to the liquid, for example according to periods of time which 
are identical to those described above for the introductions of catalyst 
and of liquid into the chamber. Moreover, it is preferable to carry out 
the addition of the measured amount of catalyst to the liquid 
simultaneously with introduction of the liquid into the chamber or 
preferably during part of the period of time for introduction of the 
liquid into the chamber, in particular after the beginning of the 
introduction of the liquid. 
It is preferable to introduce the liquid continuously into the chamber and 
thus to add the measured amount of catalyst to the liquid introduced 
continuously into the chamber. 
Thus, according to another preferred alternative form, the process can 
comprise: 
storing under an inert atmosphere the solid catalyst in the form of a dry 
powder in a hopper, 
withdrawing under an inert atmosphere from the hopper a measured amount of 
the catalyst in the form of a dry powder, 
continuously introducing a liquid hydrocarbon into a mixing chamber so as 
to form a continuous stream of the liquid hydrocarbon passing through the 
chamber and flowing into the polymerization reactor, 
adding the measured amount of the catalyst in the form of a dry powder to 
the continuous stream of the liquid hydrocarbon in the mixing chamber so 
as to mix the said catalyst with the said liquid hydrocarbon and to form 
in the said chamber a suspension of the said catalyst with the said liquid 
hydrocarbon, and 
introducing the said suspension entrained by the continuous stream of the 
liquid hydrocarbon into the gas-phase olefin polymerization reactor. 
In this case, the storage of the catalyst, the withdrawal of the measured 
amount of catalyst and the introduction of the liquid into the chamber, 
apart from the continuous way of introducing it, are carried out in a way 
identical to that which has been described above. In particular, it is 
preferable to introduce, into the chamber, a continuous vortical or 
cyclonic stream of liquid to which is intermittently added, for example 
periodically, the measured amount of the catalyst in the form of a dry 
powder. The addition of the catalyst to the liquid is non-continuous, 
preferably periodic, but each addition can be brought sufficiently close 
to the previous one with time, so that a catalyst suspension in the 
chamber is produced semi-continuously or substantially continuously and so 
that the catalyst is thus introduced substantially continuously into the 
reactor. The histograms of FIGS. 2A and B represent a continuous 
introduction of liquid and a non-continuous and periodic introduction of 
catalyst into the chamber (over a period, by way of example, of 3 
successive cycles), that is to say a non-continuous and periodic addition 
of catalyst to the liquid introduced continuously into the chamber, the 
abscissa t representing the time and the ordinate Q the flow rates for 
introduction into or for addition to the chamber of the liquid and of the 
catalyst. The histogram of FIG. 2B shows a preferred alternative form with 
respect to FIG. 2A in which each catalyst addition can be brought closer 
with time to the previous one with the aim of producing a substantially 
continuous introduction of the catalyst into the reactor. 
The liquid hydrocarbon is advantageously a relatively volatile liquid under 
the polymerization conditions in the gas-phase reactor, in particular in a 
fluidized bed. The liquid hydrocarbon is in particular chosen so that it 
can instantaneously or very quickly evaporate as soon as it enters into 
the fluidized bed, in particular into the region of the bed where the 
temperature is substantially constant and highest. 
The liquid hydrocarbon can be a liquid which is inert with respect to the 
catalyst, for example at least one saturated hydrocarbon, in particular a 
C.sub.2 to C.sub.8 hydrocarbon, such as one or a number of alkanes or 
cycloalkanes, in particular a C.sub.2 to C.sub.8 alkane, preferably a 
C.sub.3 to C.sub.7 alkane, for example n-pentane and/or isopentane. The 
liquid hydrocarbon can also be at least one unsaturated hydrocarbon, for 
example a C.sub.2 to C.sub.10 hydrocarbon, such as at least one liquid, in 
particular C.sub.2 to C.sub.10, preferably C.sub.3 to C.sub.8, olefin or 
non-conjugated diene, for example propylene, 1-butene, 1-hexene, 
4-methyl-1-pentene, 1-octene, ethylidenenorbornene, 
4-methyl-1,4-hexadiene, 2-methyl-1,5-hexadiene or 1,4-hexadiene, or 
alternatively a mixture of one or a number of olefins or dienes, in 
particular C.sub.2 to C.sub.10 olefins or dienes, with at least one inert 
liquid hydrocarbon, such as at least the saturated C.sub.2 to C.sub.8 
hydrocarbon. 
The liquid hydrocarbon can preferably be at least a portion of a liquid 
obtained by cooling and condensation of at least a part of the gaseous 
reaction mixture which passes through the gas-phase olefin polymerization 
reactor and is returned to the said reactor, and which contains in 
particular the olefinic monomer or monomers to be polymerized, such as the 
olefins and the non-conjugated dienes mentioned above, and optionally one 
or a number of saturated hydrocarbons, such as the alkanes or cycloalkanes 
mentioned above, and by separation of the cooled gaseous reaction mixture, 
which is recycled to the said reactor. The liquid hydrocarbon can in 
particular be that obtained by cooling, condensation and separation of the 
recycled gaseous reaction mixture, such as described in Patent Application 
PCT No. WO 94/28032, published on Dec. 8, 1994. Part of this liquid can be 
used as liquid hydrocarbon in the present invention and can advantageously 
be introduced continuously into the mixing chamber as described above. 
The amount of liquid hydrocarbon introduced into the chamber is sufficient 
to suspend the catalyst i.e. to form a suspension of the catalyst in the 
liquid hydrocarbon and preferably to entrain the suspension as far as into 
the polymerization reactor. The chamber and the device connecting the 
chamber to the reactor can be rinsed using the liquid hydrocarbon at the 
end of each non-continuous introduction of liquid. Generally, the total 
amount of liquid hydrocarbon used per gram of catalyst (prepolymerized or 
non-prepolymerized) to be introduced with the catalyst into the reactor 
can be from 5 to 100 and preferably from 10 to 50 cm.sup.3. 
The liquid hydrocarbon is introduced into the chamber under a pressure P3 
greater than the pressure P2 existing in the polymerization reactor and 
preferably equal to or less than the pressure P1 existing in the storage 
hopper. By way of example, P3 can be from 1.02 to 2 times, preferably from 
1.03 to 1.5 times and in particular from 1.04 to 1.1 times greater than 
P2. P1 can be from 1.0 to 2.0 times and preferably from 1.02 to 1.2 times 
greater than P3. 
The process of the invention also comprises the introduction of the 
suspension into the reactor. Generally, the catalyst suspension can be 
introduced using a pipe connecting the chamber to the reactor. During its 
introduction, the catalyst is generally kept entrained with the liquid in 
order to avoid it settling out between the chamber and the reactor. In 
particular, it has been observed that the vortical or cyclonic effect 
produced by the introduction of the liquid into the chamber can be 
sufficient to keep the catalyst entrained with the liquid. In addition, 
the suspension can be introduced into the reactor by gravity or preferably 
by a pressure difference between the chamber and the reactor or 
alternatively by both means at the same time. The pressure P2 in the 
reactor is generally greater than atmospheric pressure: it can range in 
particular from 0.2 MPa to 6 MPa and preferably from 1 to 4 MPa (in 
absolute pressure). In the case of an introduction by a pressure 
difference, the pressure in the chamber is greater than the pressure P2 of 
the reactor: it can be in particular from 1.01 to 2 times and preferably 
from 1.05 to 1.5 times greater than P2. The total period of time for 
producing the catalyst suspension in the liquid and for carrying out the 
transfer of the suspension from the chamber into the reactor is generally 
very short, of the order of a few seconds, for example from 0.5 to 10 and 
preferably from 0.5 to 5 seconds. 
A gas-phase polymerization reactor generally contains an agitated and/or 
preferably fluidized bed, the bed being composed essentially of particles 
of catalyst and of polymer in the course of formation. The catalyst 
suspension is preferably introduced directly into the bed. In the 
preferred case of a fluidized bed reactor which generally comprises a 
vertical cylinder equipped at its base with a fluidization grid, the 
catalyst suspension is directly introduced into the fluidized bed, that is 
to say at a point located above the fluidization grid and below the top of 
the bed. It is preferable to introduce the suspension into the region of 
the bed where the temperature is substantially constant and highest and in 
particular into the lower half of the bed, for example into the region 
beginning at 0.7 m and preferably at 1 m above the fluidization grid and 
extending up to half the height of the bed. 
The catalyst suspension can be introduced using a pipe connecting the 
chamber to the reactor. The pipe can emerge on the internal wall of the 
reactor or even enter inside the reactor, that is to say preferably inside 
the bed. At the place where the pipe emerges or enters into the reactor, 
it can be directed downwards and form with a vertical plane and in 
particular with the vertical wall of the reactor an angle of 10 to 
80.degree. and preferably of 20 to 70.degree.. The pipe can have an 
internal diameter ranging from 5 to 30 and preferably from 10 to 25 mm. 
The pipe can be equipped with at least one valve located close to the 
reactor in order to isolate the chamber from the reactor, in particular 
for reasons of safety and to avoid material rising up from the bed inside 
the pipe during the non-continuous steps where the suspension is not 
introduced into the reactor. 
The pipe can also be equipped with a valve located close to the outlet of 
the chamber, in particular when the liquid is introduced non-continuously 
into the chamber. In this case, this valve can be opened before or after 
or even simultaneously with the beginning of the introduction of the 
liquid hydrocarbon into the chamber, so as to bring the chamber into 
communication with the reactor, and can be closed before or after or even 
simultaneously with the end of the introduction of the liquid hydrocarbon 
into the chamber, so as to isolate the chamber from the reactor. An 
alternative form can consist in opening the valve simultaneously with the 
beginning of the introduction of the liquid hydrocarbon into the chamber 
and in closing it simultaneously with the end of this introduction. An 
alternative form which is preferred can consist in opening the valve after 
the beginning of the introduction of the liquid hydrocarbon, so that at 
least the bottom of the chamber is filled with liquid and so that the 
catalyst is easily suspended therein, and then in closing the valve before 
the end of the introduction of liquid, so as to keep a liquid heel in the 
chamber for the following cycle. Another alternative form which is also 
preferred can consist in opening the valve before the beginning of the 
introduction of the liquid hydrocarbon and in closing it before the end of 
this introduction. In the case of a continuous introduction of the liquid 
hydrocarbon into the chamber, the valve is not necessary or can be left 
constantly open. In this case, a continuous stream of the liquid 
hydrocarbon passes through the chamber and flows into the reactor, while 
the measured amounts of catalyst are intermittently or semi-continuously 
added to the continuous stream passing into the chamber. 
It was observed that, by thus making use of the process of the present 
invention, the problems posed by the introduction of solid catalyst in the 
form of a dry powder in the absence of liquid were solved. In particular, 
it was observed that the catalyst could be easily suspended in the liquid 
hydrocarbon and introduced into the reactor and that carrying out both of 
these operations in the same process did not prejudice the good dispersion 
of the catalyst in the reactor and in particular in the bed where the 
polymerization takes place. It was thus observed that this process did not 
require making use of a large amount of liquid. 
FIG. 3 diagrammatically represents a device which can be made use of in the 
process of the invention. It shows a storage hopper (1) for the solid 
catalyst in the form of a dry powder, which hopper is supplied with solid 
catalyst via a line (2) equipped with a valve (3) and with an inert gas, 
such as nitrogen, via a line (4) equipped with a valve (5). The base of 
the hopper (1) is in communication with a zone (6) composed of a cavity 
hollowed out in a spherical plug of a valve, which cavity makes it 
possible to withdraw a predetermined volume of catalyst stored in the 
hopper (1), to isolate this volume of catalyst from the hopper (1) and to 
deliver it into a mixing chamber (7) via a line (8). The chamber (7) is 
composed essentially of a vertical cylindrical part closed at its top, 
where the line (8) emerges, and terminated by a conical bottom (9), the 
lower end of which is in communication with a gas-phase polymerization 
reactor (10) via a pipe (11). The pipe (11) is equipped with a valve (12) 
close to the bottom (9) of the chamber and with a pair of valves (13) 
close to the reactor (10). A line (14) for introduction of a liquid 
hydrocarbon, equipped with a valve (15), emerges in the upper part of the 
chamber (7). 
FIG. 4 diagrammatically represents the a cross section taken along lines 
4-4 of the chamber (7) shown in FIGS. 3 and 5. The line (14) emerges 
tangentially to the vertical wall of the chamber (7), so as to create a 
vortical or cyclonic stream capable of suspending the solid catalyst in 
the liquid hydrocarbon. 
FIG. 5 diagrammatically represents another device which can be made use of 
in the process of the invention. It shows the same components with the 
same references as those described in FIG. 3, except for the fact that the 
pipe (11) does not have a valve (12) but has an elbow which forms an angle 
of 90.degree. and which has a small radius. This device can in particular 
be used when the liquid hydrocarbon is introduced continuously into the 
chamber (7) via the line (14). 
FIG. 6 diagrammatically represents a gas-phase olefin polymerization 
installation which uses a fluidized bed reactor (10) and the device for 
introduction of catalyst represented in FIG. 3 with the same components 
and the same references. The reactor (10) is composed essentially of a 
vertical cylinder containing a fluidization grid (17) at its base and of a 
hemispherical bottom (18) and, in its upper part, of a tranquillization 
zone (19) terminated by a hemispherical top (20). The reactor (10) 
contains a fluidized bed (21). A line (22) for recycling the gaseous 
reaction mixture passing through the bed (21) leaves via the top (20) of 
the reactor in order to return to the bottom (18) of the reactor. The line 
(22) successively contains, in the direction of flow of the recycled 
gaseous reaction mixture, a cyclone (23) which makes it possible to stop 
the fine particles entrained with the gaseous reaction mixture out of the 
bed (21), a first heat exchanger (24), a compressor (25) and a second heat 
exchanger (26). The balance of fresh gas constituting the gaseous reaction 
mixture is introduced via the line (27) emerging into the line (22). A 
line (28) makes it possible to discharge the polymer manufactured in the 
reactor (10). 
FIG. 7 diagrammatically represents another gas-phase olefin polymerization 
installation which uses the device for introduction of catalyst as 
represented in FIG. 3 with the same components and the same references. 
The polymerization installation is identical to that represented in FIG. 6 
with the same references, except for the fact that the line (22) for 
recycling the gaseous reaction mixture comprises, after the second heat 
exchanger (26), a gas/liquid separator (29), such as that described in 
Patent Application PCT No. WO 94/28032, containing, in the upper part, the 
start of a line (30) which makes it possible to recycle the gaseous 
reaction mixture directly to the bottom (18) of the reactor under the 
fluidization grid (17) and, in the lower part, the start of a line (31) 
equipped with a pump (32) which makes it possible for the liquid separated 
from the gaseous reaction mixture to be conveyed directly into the bed 
(21), in particular into the region of the bed where the temperature is 
substantially constant and highest. A line (14) equipped with a valve (33) 
leaves from the portion of the line (31) located after the pump (32), 
which line (14) makes it possible to withdraw a part of the liquid which 
is conveyed into the chamber (7) of the device for introduction of the 
catalyst. This installation is particularly advantageous when it operates 
according to the process described in WO 94/28032, that is to say when the 
gaseous reaction mixture is cooled in the heat exchanger (26) below its 
dew point, so as to form a mixture of gas and of liquid, and when the gas 
is separated from the liquid in the separator (29). This installation is 
in addition particularly useful when it is used in combination with the 
process for introduction of catalyst according to the present invention, 
operating in particular with a portion of the liquid separated from the 
gas in the separator (29). This portion of the liquid is introduced 
continuously into the mixing chamber (7), so as to form a continuous 
stream passing through the chamber (7) as far as into the reactor (10) via 
the pipe (11) and so as to add measured amounts of catalyst to this stream 
in the chamber in order to form a catalyst suspension entrained with the 
stream into the reactor (10) via the pipe (11). 
FIG. 8 diagrammatically represents an alternative form of the 
polymerization installation as represented in FIG. 7 with the same 
components and the same references but arranged differently. The line (22) 
for recycling the to gaseous reaction mixture comprises, after the first 
heat exchanger (24), the second exchanger (26) and then, subsequently, the 
gas/liquid separator (29). A line (30) equipped with the compressor (25) 
leaves via the top of the separator (29), which line (30) recycles the 
gaseous reaction mixture separated from the liquid directly to the bottom 
(18) of the reactor under the fluidization grid (17). A line (31) equipped 
with a pump (32) leaves from the bottom of the separator (29), which line 
(31) conveys the liquid separated from the gas directly into the bed (21), 
in particular into the region of the bed where the temperature is 
substantially constant and highest. A line (14) equipped with a valve (33) 
leaves from the portion of the line (31) located after the pump (32), 
which line (14) makes it possible to withdraw a part of the liquid which 
is conveyed into the chamber (7) of the device for introduction of the 
catalyst. This installation is particularly advantageous when it operates 
according to the process described in WO 94/28032, in particular as 
described above for FIG. 7. This installation is also particularly useful 
when it is used in combination with the process for introduction of 
catalyst according to the present invention, in particular as described 
above for FIG. 7. 
FIG. 9 diagrammatically represents another alternative form of the 
polymerization installation as represented in FIG. 7 with the same 
components and the same references but arranged differently. The line (22) 
for recycling the gaseous reaction mixture comprises, after the first heat 
exchanger (24), the gas/liquid separator (29). A line (30) equipped with 
the compressor (25) and then with the second heat exchanger (26) leaves 
via the top of the separator (29), which line recycles the gaseous 
reaction mixture separated from the liquid directly to the bottom (18) of 
the reactor under the fluidization grid (17). A line (31) equipped with a 
pump (32) leaves from the bottom of the separator (29), which line (31) 
conveys the liquid separated from the gas directly into the bed (21), in 
particular into the region of the bed where the temperature is 
substantially constant and highest. A line (14) equipped with a valve (33) 
leaves from the portion of the line (31) located after the pump (32), 
which line (14) makes it possible to withdraw a part of the liquid which 
is conveyed into the chamber (7) of the device for introduction of the 
catalyst. This installation is particularly advantageous when it operates 
according to the process described in WO 94/28032, in particular as 
described above for FIG. 7, except for the fact that the first exchanger 
(24) cools the gaseous reaction mixture below its dew point. This 
installation is also particularly useful when it is used in combination 
with the process for introduction of catalyst according to the present 
invention, in particular as described above for FIG. 7. 
The process for introduction of catalyst according to the present invention 
is very particularly suitable for the continuous gas-phase polymerization 
of one or a number of olefins, optionally as a mixture with a diene, in 
particular in a fluidized bed reactor, under an (absolute) pressure P2 
ranging from 0.2 to 6 MPa and preferably from 1 to 4 MPa. The 
polymerization temperature and in particular the temperature of the 
fluidized bed can be kept at a value ranging from 30 to 130.degree. C. and 
preferably from 50 to 110.degree. C. A gaseous reaction mixture passes 
through the reactor with an ascending velocity which can range from 0.3 to 
0.9 m/s and preferably from 0.4 to 0.8 m/s. The gaseous reaction mixture 
can contain one or a number of olefins, in particular C.sub.2 to C.sub.10 
and preferably C.sub.2 to C.sub.8 olefins, optionally with a 
non-conjugated diene, for example ethylene or propylene, or a mixture of 
ethylene with at least one C.sub.3 to C.sub.10 and preferably C.sub.3 to 
C.sub.8 olefin, for example propylene, 1-butene, 1-hexene, 
4-methyl-1-pentene or 1-octene, and/or alternatively with at least one 
diene, for example a non-conjugated diene such as ethylidenenorbornene, 
4-methyl-1,4-hexadiene, 2-methyl-1,5-hexadiene or 1,4-hexadiene. It can 
also contain hydrogen and/or at least one inert gas such as nitrogen or an 
alkane or cycloalkane, for example a C.sub.2 to C.sub.8 alkane or 
cycloalkane. The polymerization process can in particular be carried out 
according to the process described in Patent Application PCT No. WO 
94/28032. 
The polymerization process which uses the process for introduction of 
catalyst according to the invention is very particularly suitable for 
manufacturing polyolefins in the powder form, in particular linear low 
density or high density polyethylene, with a density ranging for example 
from 0.87 to 0.97, or polypropylene, or copolymers of propylene with 
ethylene and/or C.sub.4 to C.sub.8 olefins, or elastomeric copolymers of 
propylene with ethylene and optionally at least one non-conjugated diene 
with a density ranging, for example, from 0.85 to 0.87. 
The following example illustrates the present invention. 
EXAMPLE 1 
The process is carried out with an installation such as that represented in 
FIG. 6, in which ethylene is copolymerized with 1-butene in the gas phase. 
The gaseous reaction mixture moving in the reactor (10) contains ethylene, 
1-butene, hydrogen, nitrogen, ethane, n-pentane and isopentane under a 
total pressure of 2 MPa and at an ascending velocity of 0.55 m/s. The 
polymerization temperature in the fluidized bed is 93.degree. C. A 
catalyst based on titanium, magnesium and chlorine is used, as described 
in Example 1 of Patent Application FR-2,706,467. The catalyst is stored in 
the hopper (1) in the form of a dry powder composed of particles having a 
mean diameter by mass of 45 .mu.m and kept under a nitrogen atmosphere 
under a pressure of 2.7 MPa. The pair of valves (13) remains constantly 
open. At the start of the cycle of operations for introducing the catalyst 
into the reactor, the valves (12) and (15) are closed. The valve (12) is 
first of all opened and then the valve (15) is opened immediately 
afterwards, allowing a 0.8 liter liquid mixture of n-pentane and of 
isopentane to enter into the chamber (7) under a pressure of 2.5 MPa. 
Immediately after opening the valve (15), 40 g of the catalyst, withdrawn 
from the hopper (1), are introduced via the measuring zone (6), are 
suspended in the liquid mixture and are entrained in the form of a 
suspension via the pipe (11) with an internal diameter of 14 mm. 
The valve (12) and then the valve (15) are then closed. The total period of 
time for suspending the catalyst and for introducing it into the reactor 
is 2 seconds. The cycle of the operations for introduction of the catalyst 
is completed and a new cycle is ready to be carried out. Under these 
conditions, it is observed that the entrainment of the fine particles out 
of the fluidized bed is low and that the polymerization takes place 
satisfactorily.