Patent Description:
Processes for the polymerization of propylene are known which are carried out in the gas phase in fluidized or mechanically stirred bed reactors, in the presence of catalysts obtained from compounds of transition metals belonging to groups IV, V or VI of the Periodic Table of the Elements and aluminum alkyl compounds generating, in high yields, isotactic polypropylene being more than <NUM>%wt insoluble in xylene at <NUM>.

The polymer is obtained in the form of granules having a more or less regular morphology depending on the morphology of the catalyst; the dimension of the granules, which depends on the original dimension of the catalyst particles and on reaction conditions, is generally distributed around an average value.

In these types of processes the heat of reaction is removed by means of a heat exchanger placed inside the reactor or in the recycle line of the reaction gas.

A generally encountered problem in polymerization processes of this type results from the presence of very fine polymer particles which are produced either from already existing fine catalyst particles or from the breakage of the catalyst itself.

These fine particles tend to deposit onto, and electrostatically adhere to, the inner walls of the reactor and of the heat exchanger; as a result they grow in size by polymerization also causing an insulating effect and a lower heat transfer resulting in the formation of hot spots in the reactor.

These effects are enhanced when the gas-phase alpha-olefin polymerization process is carried out in the presence of highly active catalysts such as those comprising the reaction product of an aluminum alkyl with a titanium compound supported on a magnesium halide in active form.

As a consequence, a loss in fluidization efficiency and homogeneity generally occurs; for example catalyst feeding interruption may occur as well as clogging of the polymer discharge system; furthermore, excessive temperature can result in particles melting with the formation of layers of thin agglomerates which adhere to the reactor walls and in the formation of agglomerates which may clog the gas distribution plate.

These drawbacks lead to poor process reproducibility and can lead to a forced interruption of the run in order to remove deposits which have formed inside the reactor even after relatively short times.

In order to reduce the extent of catalyst fragmentation, the catalyst can be subject to a pre-polymerization step carried out under mild conditions which is believed to lower the tendency of the catalyst to break in the initial stages of the main polymerization process. For example, <CIT> discloses a prepolymerized catalyst component having average particle size equal to or lower than <NUM> comprising a solid catalyst component which comprises magnesium halide, a titanium compound having at least a Ti-halogen bond and at least two electron donor compounds one of which being selected from <NUM>,<NUM>-diethers and the other one being selected from esters of aromatic mono or dicarboxylic acids. In the final solid catalyst component, the amount of <NUM>,<NUM>-diether is relatively low.

Typically the pre-polymerization step is performed in a section of the plant immediately connected to the main polymerization section so that the prepolymer produced is directly fed to the main polymerization reactor (also called prepoly in-line) and is characterized by relatively high values of monomer conversion (<NUM>-<NUM> gpolymer/gcat). Alternatively, it can be carried out in a dedicated section and the prepolymer produced is stored for future use. In this latter case, even lower values of monomer conversion rates (<NUM>- <NUM> Polymer/gcat) are possible. In both cases however, while the pre-polymerization may reduce the extent of improper catalyst fragmentation, it has no effect in reducing the negative effects of the polymerization activity deriving from fine catalyst particles which are anyhow present either because already existing in the original catalyst or produced by the catalyst fragmentation.

The solutions proposed to avoid these drawbacks involve either trying to depress or kill the catalyst activity or reducing or eliminating the electrostatic voltage.

Patent Application <CIT> describes the introduction into the polymerization reactor of small amounts (generally smaller than <NUM> ppm with respect to the polymerization mixture) of a retarder selected from polymerization inhibitors or substances able to poison the catalyst, in order to reduce the olefin polymerization rate. However, as described in the same patent application, the use of larger quantities of the retarder adversely affects both the quality and properties of the polymer produced, such as the melt index, the melt flow ratio and/or the stereoregularity of the polymer, as well as reducing the efficiency of the process.

<CIT> describes the use of oxygen containing gaseous products and liquid or solid compounds containing active hydrogens to prevent the formation of agglomerates and reactor fouling in processes for preparing heterophasic propylene polymers. Among the compounds containing active hydrogens ethanol, methanol, ethylene glycol, propylene glycol and diethylene glycol are cited.

These compounds, known as polymerization inhibitors, must be used in an amount of a few ppm with respect to the polymer in order not to deactivate the catalyst; at such concentrations they are not effective as to a selective deactivation of the fine catalyst particles, whereas at higher concentrations the polymerization does not take place.

Several documents such as <CIT>, <CIT> propose carrying out the polymerization of propylene, either in slurry or gas-phase, in the presence of a mixed external electron donor system comprising a selectivity control agent (SCA) and a so called activity limiting agent (ALA). While the SCA can be an alkyl-alkoxy silane the ALA is typically selected among esters of mono or polycarboxylic fatty acids. The ALA should provide self-extinguishing properties which involve a strongly decrease of the catalyst activity as a consequence of the temperature increase above a threshold value. However, effective self-extinguishing properties are reached only when a substantial amount of ALA is used which leads to a total SCA+ALA/Ti ratio higher than that used when the SCA was the only donor. As a result, also the basic catalyst activity, i.e., the activity below the threshold value (about <NUM>), is depressed. On the other hand, lowering the amount of SCA to reach a total SCA+ALA/Ti ratio which ensures higher basic catalyst activity would involve production of polypropylene with a stereoregularity insufficient for many applications.

It is therefore felt the need of a gas-phase polymerization process carried out with a catalyst and/or conditions able to result in a polypropylene product having good morphological properties, high stereoregularity, and capable to show self-extinguishing properties such that the negative effects caused by the fine catalyst particle polymerization can be selectively solved or mitigated.

Accordingly, it is an object of the present disclosure a gas-phase process for the homo or copolymerization of propylene with other olefins, carried out in the presence of a catalyst system comprising:.

Preferably, the solid catalyst component has an average particle size ranging from <NUM> to <NUM> more preferably from <NUM> to <NUM>.

Among the <NUM>,<NUM>-diethers mentioned above, particularly preferred are the compounds of formula (I)
<CHM>
where R<NUM> and RII are the same or different and are hydrogen or linear or branched C<NUM>-C<NUM> hydrocarbon groups which can also form one or more cyclic structures; RIII groups, equal or different from each other, are hydrogen or C<NUM>-C<NUM> hydrocarbon groups; RIV groups equal or different from each other, have the same meaning of RIII except that they cannot be hydrogen; each of RI to RIV groups can contain heteroatoms selected from halogens, N, O, S and Si.

Preferably, RIV is a <NUM>-<NUM> carbon atom alkyl radical and more particularly a methyl while the RIII radicals are preferably hydrogen. Moreover, when RI is methyl, ethyl, propyl, or isopropyl, RII can be ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, isopentyl, <NUM>-ethylhexyl, cyclopentyl, cyclohexyl, methylcyclohexyl, phenyl or benzyl; when RI is hydrogen, RII can be ethyl, butyl, sec-butyl, tert-butyl, <NUM>-ethylhexyl, cyclohexylethyl, diphenylmethyl, p-chlorophenyl, <NUM>-naphthyl, <NUM>-decahydronaphthyl; R<NUM> and RII can also be the same and can be ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, neopentyl, phenyl, benzyl, cyclohexyl, cyclopentyl.

Specific examples of ethers that can be advantageously used include: <NUM>-(<NUM>-ethylhexyl)<NUM>,<NUM>-dimethoxypropane, <NUM>-isopropyl-<NUM>,<NUM>-dimethoxypropane, <NUM>-butyl-<NUM>,<NUM>-dimethoxypropane, <NUM>-sec-butyl-<NUM>,<NUM>-dimethoxypropane, <NUM>-cyclohexyl-<NUM>,<NUM>-dimethoxypropane, <NUM>-phenyl-<NUM>,<NUM>-dimethoxypropane, <NUM>-tert-butyl-<NUM>,<NUM>-dimethoxypropane, <NUM>-cumyl-<NUM>,<NUM>-dimethoxypropane, <NUM>-(<NUM>-phenylethyl)-<NUM>,<NUM>-dimethoxypropane, <NUM>-(<NUM>-cyclohexylethyl)-<NUM>,<NUM>-dimethoxypropane, <NUM>-(p-chlorophenyl)-<NUM>,<NUM>-dimethoxypropane, <NUM>-(diphenylmethyl)-<NUM>,<NUM>-dimethoxypropane, <NUM>(<NUM>-naphthyl)-<NUM>,<NUM>-dimethoxypropane, <NUM>(p-fluorophenyl)-<NUM>,<NUM>-dimethoxypropane, <NUM>(<NUM>-decahydronaphthyl)-<NUM>,<NUM>-dimethoxypropane, <NUM>(p-tert-butylphenyl)-<NUM>,<NUM>-dimethoxypropane, <NUM>,<NUM>-dicyclohexyl-<NUM>,<NUM>-dimethoxypropane, <NUM>,<NUM>-diethyl-<NUM>,<NUM>-dimethoxypropane, <NUM>,<NUM>-dipropyl-<NUM>,<NUM>-dimethoxypropane, <NUM>,<NUM>-dibutyl-<NUM>,<NUM>-dimethoxypropane, <NUM>,<NUM>-diethyl-<NUM>,<NUM>-diethoxypropane, <NUM>,<NUM>-dicyclopentyl-<NUM>,<NUM>-dimethoxypropane, <NUM>,<NUM>-dipropyl-<NUM>,<NUM>-diethoxypropane, <NUM>,<NUM>-dibutyl-<NUM>,<NUM>-diethoxypropane, <NUM>-methyl-<NUM>-ethyl-<NUM>,<NUM>-dimethoxypropane, <NUM>-methyl-<NUM>-propyl-<NUM>,<NUM>-dimethoxypropane, <NUM>-methyl-<NUM>-benzyl-<NUM>,<NUM>-dimethoxypropane, <NUM>-methyl-<NUM>-phenyl-<NUM>,<NUM>-dimethoxypropane, <NUM>-methyl-<NUM>-cyclohexyl-<NUM>,<NUM>-dimethoxypropane, <NUM>-methyl-<NUM>-methylcyclohexyl-<NUM>,<NUM>-dimethoxypropane, <NUM>,<NUM>-bis(p-chlorophenyl)-<NUM>,<NUM>-dimethoxypropane, <NUM>,<NUM>-bis(<NUM>-phenylethyl)-<NUM>,<NUM>-dimethoxypropane, <NUM>,<NUM>-bis(<NUM>-cyclohexylethyl)-<NUM>,<NUM>-dimethoxypropane, <NUM>-methyl-<NUM>-isobutyl-<NUM>,<NUM>-dimethoxypropane, <NUM>-methyl-<NUM>-(<NUM>-ethylhexyl)-<NUM>,<NUM>-dimethoxypropane, <NUM>,<NUM>-bis(<NUM>-ethylhexyl)-<NUM>,<NUM>-dimethoxypropane,<NUM>,<NUM>-bis(p-methylphenyl)-<NUM>,<NUM>-dimethoxypropane, <NUM>-methyl-<NUM>-isopropyl-<NUM>,<NUM>-dimethoxypropane, <NUM>,<NUM>-diisobutyl-<NUM>,<NUM>-dimethoxypropane, <NUM>,<NUM>-diphenyl-<NUM>,<NUM>-dimethoxypropane, <NUM>,<NUM>-dibenzyl-<NUM>,<NUM>-dimethoxypropane, <NUM>-isopropyl-<NUM>-cyclopentyl-<NUM>,<NUM>-dimethoxypropane, <NUM>,<NUM>-bis(cyclohexylmethyl)-<NUM>,<NUM>-dimethoxypropane, <NUM>,<NUM>-diisobutyl-<NUM>,<NUM>-diethoxypropane, <NUM>,<NUM>-diisobutyl-<NUM>,<NUM>-dibutoxypropane, <NUM>-isobutyl-<NUM>-isopropyl-<NUM>,<NUM>-dimetoxypropane, <NUM>,<NUM>-di-sec-butyl-<NUM>,<NUM>-dimetoxypropane, <NUM>,<NUM>-di-tert-butyl-<NUM>,<NUM>-dimethoxypropane, <NUM>,<NUM>-dineopentyl-<NUM>,<NUM>-dimethoxypropane, <NUM>-iso-propyl-<NUM>-isopentyl-<NUM>,<NUM>-dimethoxypropane, <NUM>-phenyl-<NUM>-benzyl-<NUM>,<NUM>-dimetoxypropane, <NUM>-cyclohexyl-<NUM>-cyclohexylmethyl-<NUM>,<NUM>-dimethoxypropane. Furthermore, particularly preferred are the <NUM>,<NUM>-diethers of formula (II)
<CHM>
where the radicals RIV have the same meaning defined in formula (I) and the radicals RIII and RV, equal or different to each other, are selected from the group consisting of hydrogen; halogens, preferably Cl and F; C<NUM>-C<NUM> alkyl radicals, linear or branched; C<NUM>-C<NUM> cycloalkyl, C<NUM>-C<NUM> aryl, C<NUM>-C<NUM> alkylaryl and C<NUM>-C<NUM> arylalkyl radicals and two or more of the RV radicals can be bonded to each other to form condensed cyclic structures, saturated or unsaturated, optionally substituted with RVI radicals selected from the group consisting of halogens, preferably Cl and F; C<NUM>-C<NUM> alkyl radicals, linear or branched; C<NUM>-C<NUM> cycloalkyl, C<NUM>-C<NUM> aryl, C<NUM>-C<NUM> alkaryl and C<NUM>-C<NUM> aralkyl radicals; said radicals RV and RVI optionally containing one or more heteroatoms as substitutes for carbon or hydrogen atoms, or both.

Preferably, in the <NUM>,<NUM>-diethers of formulae (I) and (II) all the RIII radicals are hydrogen, and all the RIV radicals are methyl. Moreover, are particularly preferred the <NUM>,<NUM>-diethers of formula (II) in which two or more of the RV radicals are bonded to each other to form one or more condensed cyclic structures, preferably benzene, optionally substituted by RVI radicals. Specially preferred are the compounds of formula (III):
<CHM>
where the RIII and RIV radicals have the same meaning defined in formula (I), RVI radicals equal or different are hydrogen; halogens, preferably Cl and F; C<NUM>-C<NUM> alkyl radicals, linear or branched; C<NUM>-C<NUM> cycloalkyl, C<NUM>-C<NUM> aryl, C<NUM>-C<NUM> alkylaryl and C<NUM>-C<NUM> aralkyl radicals, optionally containing one or more heteroatoms selected from the group consisting of N, O, S, P, Si and halogens, in particular Cl and F, as substitutes for carbon or hydrogen atoms, or both.

Specific examples of compounds comprised in formulae (II) and (III) are:.

Preferably, the <NUM>,<NUM>-diether/Mg molar ratio ranges from rom <NUM> to <NUM>. In a preferred embodiment, the Mg/Ti molar ratio ranges from <NUM> to <NUM> and more preferably from <NUM> to <NUM>.

Preferably, the olefin polymer part of the solid catalyst component (a) is selected from (co)polymers of olefins of formula CH<NUM>=CHR, in which R is hydrogen or a hydrocarbyl radical with <NUM>-<NUM> carbon atoms. More preferably the olefins are selected from ethylene, propylene or mixtures thereof. The use of ethylene or propylene alone is especially preferred.

The amount of olefin polymer in the solid catalyst component (a) preferably ranges from <NUM> to <NUM>%wt based on the total weight of solid catalyst component (a).

The solid catalyst component (a) is preferably a pre-polymerized solid catalyst component. It is obtainable by subjecting an original solid catalyst component containing Mg, Ti, halogen and an electron donor selected from <NUM>,<NUM>-diethers to pre-polymerization conditions in the presence of the olefin monomer and an Al-alkyl compound.

The pre-polymerized solid catalyst component comprises the original solid catalyst component containing Mg, Ti, halogen and an electron donor selected from <NUM>,<NUM>-diethers and an amount of polyolefin deriving from the polymerization of the original solid catalyst component with an olefin monomer, of equal to or lower than, <NUM> times the amount of the said original solid catalyst component.

The terms pre-polymerization conditions means the complex of conditions in terms of temperature, monomer concentration, temperature and amount of reagents suitable to prepare the pre-polymerized catalyst component as defined above.

It has been found particularly advantageous to carry out the pre-polymerization using low amounts of alkyl-Al compound. In particular, said amount could be such as to have an Al/catalyst weight ratio from ranging from <NUM> to <NUM>, preferably from <NUM> to <NUM> and more preferably from <NUM> to <NUM>. An external donor selected from silicon compounds, ethers, esters, amines, heterocyclic compounds, ketones and <NUM>,<NUM>-diethers of the general formula (I) previously reported can also be employed. However, use of an external donor in pre-polymerization is not strictly necessary.

The pre-polymerization can be carried out in liquid phase, (slurry or bulk) or in gas-phase at temperatures generally ranging from -<NUM> to <NUM> preferably from <NUM> to <NUM>. Preferably, it is carried out in a liquid diluent in particular selected from liquid light hydrocarbons. Among them, pentane, hexane and heptane are preferred. In an alternative embodiment the pre-polymerization can be carried out in a more viscous medium in particular having a kinematic viscosity ranging from <NUM> to <NUM> cSt at <NUM>. Such a medium can be either a pure substance or a homogeneous mixture of substances having different kinematic viscosity. Preferably, such a medium is an hydrocarbon medium and more preferably it has a kinematic viscosity ranging from <NUM> to <NUM> cSt at <NUM>.

The original catalyst component concentration in the liquid diluent preferably ranges from <NUM> to <NUM>/l, more preferably from <NUM> to <NUM>/l.

The pre-polymerization time can range from <NUM> to <NUM> hours, particularly from <NUM> to <NUM> hours and more specifically from <NUM> to <NUM> hours. The olefin monomer to be pre-polymerized can be fed in a predetermined amount and in one step in the reactor before the prepolymerization. In an alternative embodiment the olefin monomer is continuously supplied to the reactor during polymerization at the desired rate.

The original solid catalyst component not containing the olefin polymer is preferably characterized by a porosity, measured by the mercury method, due to pores with radius equal to or lower than <NUM>, ranging from <NUM><NUM>/g to <NUM><NUM>/g, preferably from <NUM><NUM>/g to <NUM><NUM>/g and more preferably from <NUM> to <NUM><NUM>/g.

The original solid catalyst component and the solid catalyst component (a) as well, comprises, in addition to the above mentioned electron donors, a titanium compound having at least a Ti-halogen bond and a Mg halide. The magnesium halide is preferably MgCl<NUM> in active form which is widely known from the patent literature as a support for Ziegler-Natta catalysts. Patents <CIT> and <CIT> were the first to describe the use of these compounds in Ziegler-Natta catalysis. It is known from these patents that the magnesium dihalides in active form used as support or co-support in components of catalysts for the polymerization of olefins are characterized by X-ray spectra in which the most intense diffraction line that appears in the spectrum of the non-active halide is diminished in intensity and is replaced by a halo whose maximum intensity is displaced towards lower angles relative to that of the more intense line.

The preferred titanium compounds used in the catalyst component of the present invention are TiCl<NUM> and TiCl<NUM>; furthermore, also Ti-haloalcoholates of formula Ti(OR)n-yXy can be used, where n is the valence of titanium, y is a number between <NUM> and n-<NUM> X is halogen and R is a hydrocarbon radical having from <NUM> to <NUM> carbon atoms.

Preferably, the original catalyst component (a) has an average particle size ranging from <NUM> to <NUM>.

The alkyl-Al compound (b), which can be the same used in the pre-polymerization, is preferably chosen among the trialkyl aluminum compounds such as for example triethylaluminum, tri-n-hexylaluminum, tri-n-octylaluminum. It is also possible to use mixtures of trialkylaluminum's with alkylaluminum halides, alkylaluminum hydrides or alkylaluminum sesquichlorides such as AlEt<NUM>Cl and Al<NUM>Et<NUM>Cl<NUM>.

Preferably, the aluminum alkyl compound (b) should be used in the gas-phase process in amount such that the Al/Ti molar ratio ranges from <NUM> to <NUM>, preferably from <NUM> to <NUM> and more preferably from <NUM> to <NUM>.

As mentioned the catalyst system includes external electron-donors (ED) selected from several classes. Among ethers, preferred are the <NUM>,<NUM> diethers also disclosed as internal donors in the solid catalyst component (a). Among esters, preferred are the esters of aliphatic saturated mono or dicarboxylic acids such as malonates, succinates and glutarates. Among heterocyclic compounds <NUM>,<NUM>,<NUM>,<NUM>-tetramethyl piperidine is particularly preferred. A specific class of preferred external donor compounds is that of silicon compounds having at least a Si-O-C bond. Preferably, said silicon compounds are of formula Ra<NUM>Rb<NUM>Si(OR<NUM>)c, where a and b are integer from <NUM> to <NUM>, c is an integer from <NUM> to <NUM> and the sum (a+b+c) is <NUM>; R<NUM>, R<NUM>, and R<NUM>, are alkyl, cycloalkyl or aryl radicals with <NUM>-<NUM> carbon atoms optionally containing heteroatoms selected from N, O, halogen and P. Particularly preferred are methylcyclohexyldimethoxysilane, diphenyldimethoxysilane, methyl-t-butyldimethoxysilane, dicyclopentyldimethoxysilane, <NUM>-ethylpiperidinyl-<NUM>-t-butyldimethoxysilane and <NUM>,<NUM>,<NUM>,trifluoropropyl-<NUM>-ethylpiperidinyl-dimethoxysilane and <NUM>,<NUM>,<NUM>,trifluoropropyl-metil-dimethoxysilane. The external electron donor compound used in the main polymerization process is employed used in such an amount to give a molar ratio between the organo-aluminum compound (b) used in the main polymerization process and said electron donor compound of from <NUM> to <NUM>, preferably from <NUM> to <NUM>, more preferably from <NUM> to <NUM> and especially from <NUM> to <NUM>.

The gas-phase process can be carried out with any gas-phase reactor or technology. Specifically, it can be carried out operating in one or more fluidized or mechanically agitated bed reactors. Typically, in the fluidized bed reactors the fluidization is obtained by a stream of inert fluidization gas the velocity of which is not higher than transport velocity. As a consequence the bed of fluidized particles can be found in a more or less confined zone of the reactor. In the mechanically agitated bed reactor the polymer bed is kept in place by the gas flow generated by the continuous blade movement the regulation of which also determine the height of the bed. The operating temperature is typically selected between <NUM> and <NUM>, preferably between <NUM> and <NUM>, while the operating pressure is generally set from <NUM> and <NUM> MPa, preferably between <NUM> and <NUM> MPa more preferably between <NUM> and <NUM> MPa. Inert fluidization gases are also useful to dissipate the heat generated by the polymerization reaction and are conveniently selected from nitrogen or preferably saturated light hydrocarbons such as propane, pentane, hexane or mixture thereof.

The polymer molecular weight can be controlled by using the proper amount of hydrogen or any other suitable molecular weight regulator such as ZnEt<NUM>. If hydrogen is used, the hydrogen/propylene molar ratio is generally comprised between <NUM> and <NUM>, the propylene monomer being comprised from <NUM>% to <NUM>% by volume, preferably from <NUM> to <NUM>% by volume, based on the total volume of the gases present in the reactor. The remaining portion of the feeding mixture is comprised of inert gases and one or more α-olefin comonomers, if any.

Another gas-phase technology usable according to the present disclosure comprises the use of gas-phase polymerization devices comprising at least two interconnected polymerization zones. The process is carried out in a first and in a second interconnected polymerization zone to which propylene and ethylene or propylene and alpha-olefins are fed in the presence of a catalyst system and from which the polymer produced is discharged. The growing polymer particles flow through the first of said polymerization zones (riser) under fast fluidization conditions, leave said first polymerization zone and enter the second of said polymerization zones (downcomer) through which they flow in a densified form under the action of gravity, leave said second polymerization zone and are reintroduced into said first polymerization zone, thus establishing a circulation of polymer between the two polymerization zones. Generally, the conditions of fast fluidization in the first polymerization zone is established by feeding the monomers gas mixture below the point of reintroduction of the growing polymer into said first polymerization zone. The velocity of the transport gas into the first polymerization zone is higher than the transport velocity under the operating conditions and is normally between <NUM> and <NUM>/s. In the second polymerization zone, where the polymer flows in densified form under the action of gravity, high values of density of the solid are reached which approach the bulk density of the polymer; a positive gain in pressure can thus be obtained along the direction of flow, so that it becomes possible to reintroduce the polymer into the first reaction zone without the help of mechanical means. In this way, a "loop" circulation is set up, which is defined by the balance of pressures between the two polymerization zones and by the head loss introduced into the system. Also in this case, one or more inert gases, such as nitrogen or an aliphatic hydrocarbon, are maintained in the polymerization zones, in such quantities that the sum of the partial pressures of the inert gases is preferably between <NUM> and <NUM>% of the total pressure of the gases. The operating temperature ranges from <NUM> and <NUM>, preferably between <NUM> and <NUM>, while the operating pressure ranges from <NUM> to <NUM> MPa, preferably between <NUM> and <NUM> MPa. Preferably, the catalyst components are fed to the first polymerization zone, at any point of said first polymerization zone. However, they can also be fed at any point of the second polymerization zone. The use of molecular weight regulator is carried out under the previously described conditions. By the use of the means described in <CIT> it is possible to totally or partially prevent that the gas mixture present in the riser enters the downcomer; in particular, this is preferably obtained by introducing in the downer a gas and/or liquid mixture having a composition different from the gas mixture present in the riser. According to a particularly advantageous embodiment of the present invention, the introduction into the downcomer of the said gas and/or liquid mixture having a composition different from the gas mixture present in the riser is effective in preventing the latter mixture from entering the downcomer. Therefore, it is possible to obtain two interconnected polymerization zones having different monomer compositions and thus able to produce polymers with different properties.

The pre-polymerization process for the preparation of the solid catalyst component (a) can be in principle carried out in a pre-polymerization section immediately upstream the gas-phase reactor. However, due to the relatively low degree of pre-polymerization it is preferred that said pre-polymerization process is carried out in a batch dedicated plant. The obtained catalyst component (a) can then be stored and fed to the polymerization plant when needed.

As explained, when in specific zones of the reactor the temperature reaches higher values due to undesired polymerization of fine particle, reactor operation problems can arise. The examples of the present application clearly show that when the catalyst system of the present disclosure is used the activity of the catalyst at temperature higher than <NUM> strongly decreases thereby showing self-extinguish properties that ensures for reduced or eliminate fouling problems. In connection with the present application, a satisfying level of self-extinguishing properties is present if the polymerization activity at temperature higher than <NUM> is <NUM>% or less, more preferably <NUM>% or less and especially <NUM>% or less, the value of the polymerization activity at <NUM>. It is therefore a further object of the present disclosure a method for carrying out a self-extinguishing gas-phase polymerization process for the polymerization of propylene comprising feeding into a gas-phase polymerization reactor propylene optionally in mixture with minor amounts of other olefins, and a catalyst system comprising:.

All the preferred and particular embodiments previously described also apply to the above described method.

It is worth noting that the catalyst of the present disclosure show, together with self-extinguishing properties, also the capability to polymerize at temperature lower than <NUM> giving simultaneously products in high yields, high steroregularity and valuable morphological properties expressed by bulk density values over <NUM><NUM>/g.

The following examples are given in order to better illustrate the invention without limiting it in any manner.

<NUM> of polymer were dissolved in <NUM> of o-xylene under stirring at <NUM> for <NUM> minutes, then the solution was cooled to <NUM> and after <NUM> minutes the insoluble polymer was filtered. The resulting solution was evaporated in nitrogen flow and the residue was dried and weighed to determine the percentage of soluble polymer and then, by difference, the X.

Determined by a method based on the principle of the optical diffraction of monochromatic laser light with the "Malvern Instr. <NUM>" apparatus. The average size is given as P50.

Determined according to ISO <NUM> (<NUM>, <NUM>).

The measure is carried out using a "Porosimeter <NUM> series" by Carlo Erba.

The porosity is determined by absorption of mercury under pressure. For this determination use is made of a calibrated dilatometer (diameter <NUM>) CD3 (Carlo Erba) connected to a reservoir of mercury and to a high-vacuum pump (<NUM>·<NUM>-<NUM> mbar). A weighed amount of sample is placed in the dilatometer. The apparatus is then placed under high vacuum (<<NUM> Hg) and is maintained in these conditions for <NUM> minutes. The dilatometer is then connected to the mercury reservoir and the mercury is allowed to flow slowly into it until it reaches the level marked on the dilatometer at a height of <NUM>. The valve that connects the dilatometer to the vacuum pump is closed and then the mercury pressure is gradually increased with nitrogen up to <NUM>/cm<NUM>. Under the effect of the pressure, the mercury enters the pores and the level goes down according to the porosity of the material.

The porosity (cm3/g), due to pores up to <NUM> for catalysts (<NUM> for polymers), the pore distribution curve, and the average pore size are directly calculated from the integral pore distribution curve which is function of the volume reduction of the mercury and applied pressure values (all these data are provided and elaborated by the porosimeter associated computer which is equipped with a "MILESTONE <NUM>/<NUM>" program by C.

An initial amount of microspheroidal MgCl<NUM>·<NUM>. 8C<NUM>H<NUM>OH was prepared according to the method described in Example <NUM> of <CIT> but operating at <NUM>,<NUM> rpm instead of <NUM>,<NUM>. The so obtained adduct having an average particle size of <NUM> was then subject to thermal dealcoholation at increasing temperatures from <NUM> to <NUM> operating in nitrogen current until the molar alcohol content per mol of Mg is <NUM>. The final particle size was determined to be P50= <NUM>.

Into a <NUM>-liter round bottom flask, equipped with mechanical stirrer, cooler and thermometer <NUM> of TiCl<NUM> were introduced at room temperature under nitrogen atmosphere. After cooling at -<NUM>, while stirring, <NUM> of microspheroidal MgCl<NUM>·<NUM>. 0C<NUM>H<NUM>OH were introduced. The temperature was then raised from -<NUM> up to <NUM> at a speed of <NUM>/min. When the temperature of <NUM> was reached, <NUM> of <NUM>,<NUM>-bis(methoxymethyl)fluorene, as internal donor, was introduced. At the end of the addition, the temperature was increased up to <NUM> at a speed of <NUM>/min and maintained fixed at this value for <NUM> minutes. Thereafter, stirring was stopped, the solid product was allowed to settle and the supernatant liquid was siphoned off maintaining the temperature at <NUM>. After the supernatant was removed, additional <NUM> of fresh TiCl<NUM> were added and the mixture was then heated at <NUM> and kept at this temperature for <NUM> minutes. Once again the stirring was interrupted; the solid product was allowed to settle and the supernatant liquid was siphoned off maintaining the temperature at <NUM>. A third aliquot of fresh TiCl<NUM> (<NUM>) was added, the mixture was maintained under agitation at <NUM> for <NUM> minutes and then the supernatant liquid was siphoned off. The solid was washed with anhydrous i-hexane five times (<NUM> x <NUM>) in temperature gradient up to <NUM> and one time (<NUM>) at room temperature. The solid was finally dried under vacuum and analyzed. Catalyst composition: Mg=<NUM> wt%; Ti=<NUM> wt%; I. =<NUM> wt%; P50= <NUM>.

A lab-scale fluidized bed reactor, equipped with recirculation gas compressor, heat exchanger, and automated temperature controller was used to polymerize propylene in gas phase. The fluidized bed reactor is set at the desired temperature, pressure and composition, such to reach the targets values after feeding the pre-polymerized catalyst into it. Target values for the polymerization are: total pressure <NUM> barg, composed of <NUM> %mol of propylene, <NUM> %mol of propane, and <NUM> %mol of hydrogen.

In a glass flask, <NUM> of triethyl aluminum, methyl-cyclohexyl dimethoxy silane (ED) when used, and about <NUM>-<NUM> of solid catalyst component (or prepolymerized catalyst) were charged in <NUM> of i-hexane. The catalyst is pre-contacted at room temperature for <NUM> minutes. Then, the content of the flask is fed into a <NUM> autoclave. The autoclave was closed, <NUM> grams of liquid propane (and from <NUM> to <NUM> grams of propylene only in comparative examples <NUM>-<NUM> where the in-line prepolymerization was performed) were added. The catalyst mixture was stirred at <NUM> for <NUM> (unless otherwise specified). Subsequently, the content of the autoclave was fed to the fluidized bed reactor that was set as described above. The polymerization was carried out for <NUM> hours, while the pressure of the reactor was kept constant by feeding continuously gaseous propylene, enough to make up for the reacted monomer. After <NUM> hours, the formed polymer bed is discharged, degassed and characterized.

Into a <NUM><NUM> glass-vessel/stainless steel autoclave with a mechanical anchor stirrer, at room temperature and under a nitrogen atmosphere, <NUM><NUM> of i-hexane containing <NUM> of tri-n-octyl aluminum (TNOA) and <NUM> of the spherical catalyst prepared as described above were introduced. The stirring was set at about <NUM> rpm, and the internal temperature was increased to <NUM> during a time of <NUM> minutes. Maintaining constant the temperature of the reactor, ethylene was carefully introduced with a constant flow for <NUM>. The polymerization was discontinued when a theoretical conversion of <NUM> of polymer per g of catalyst was deemed to be reached. The resulting pre-polymerized catalyst was dried under vacuum at room temperature and analyzed. It contained <NUM> of polyethylene per g of solid catalyst (<NUM>% polymer). Prepolymer composition: Mg=<NUM> wt%; Ti=<NUM> wt%; I. =<NUM> wt%; P50= <NUM>. The catalyst component was then used in a double run gas phase polymerization of propylene according to general procedure carried out at <NUM>° and <NUM> respectively.

Into a <NUM><NUM> glass-vessel/stainless steel autoclave with a mechanical anchor stirrer, at room temperature and under a nitrogen atmosphere, <NUM><NUM> of i-hexane containing <NUM> of tri-n-octyl aluminum (TNOA) and <NUM> of the spherical catalyst prepared as described above were introduced. The stirring was set at about <NUM> rpm, and the internal temperature was increased to <NUM> during a time of <NUM> minutes. Maintaining constant the temperature of the reactor, ethylene was carefully introduced with a constant flow for <NUM>. The polymerization was discontinued when a theoretical conversion of <NUM> of polymer per g of catalyst was deemed to be reached. The resulting pre-polymerized catalyst was dried under vacuum at room temperature and analyzed. It contained <NUM> of polyethylene per g of solid catalyst (<NUM>% of polymer). Pre-polymer composition: Mg=<NUM> wt%; Ti=<NUM> wt%; I. =<NUM> wt%; P50= <NUM>. The catalyst component was then used in a double run gas phase polymerization of propylene according to general procedure carried out at <NUM>° and <NUM> respectively.

Into a <NUM><NUM> glass-vessel/stainless steel autoclave with a mechanical anchor stirrer, at room temperature and under a nitrogen atmosphere, <NUM><NUM> of i-hexane containing <NUM> of tri-n-octyl aluminum (TNOA) and <NUM> of the spherical catalyst prepared as described above were introduced. The stirring was set at about <NUM> rpm, and the internal temperature was increased to <NUM> during a time of <NUM> minutes. Maintaining constant the temperature of the reactor, ethylene was carefully introduced with a constant flow for <NUM>. The polymerization was discontinued when a theoretical conversion of <NUM> of polymer per g of catalyst was deemed to be reached. The resulting pre-polymerized catalyst was dried under vacuum at room temperature and analyzed. It contained <NUM> of polyethylene per g of solid catalyst (<NUM>% polymer). Pre-polymer composition: Mg=<NUM> wt%; Ti=<NUM> wt%; I. =<NUM> wt%; P50= <NUM>. The catalyst component was then used in a double run gas phase polymerization of propylene according to general procedure carried out at <NUM>° and <NUM> respectively.

The catalyst component prepared according to the general procedure, without being subject to pre-polymerization, was used in a double run gas phase polymerization of propylene according to general procedure carried out at <NUM>° and <NUM> respectively.

The catalyst component prepared according to the general procedure, was used in the gas phase polymerization of propylene according to general procedure with the difference that an in-line pre-polymerization was carried out. In the first series of double run carried out at <NUM>° and <NUM> respectively (Comparative <NUM>) <NUM> of propylene were pre-polymerized for <NUM> minutes. In the second series (Comparative <NUM>) <NUM> of propylene were pre-polymerized for <NUM> minutes, and in the third series (Comparative <NUM>) <NUM> grams of propylene were pre-polymerized for <NUM> minutes. The polymer conversion was measured by weighting the pre-polymer produced in a parallel run carried out under identical conditions. Taking into account one gram of catalyst component the conversion in comparative <NUM> was <NUM> (<NUM>% polymer), in comparative <NUM> was <NUM> (<NUM>% polymer) and in comparative <NUM> was <NUM> (<NUM>% polymer).

Into a <NUM><NUM> glass-vessel/stainless steel autoclave with a mechanical anchor stirrer, at room temperature and under a nitrogen atmosphere, <NUM><NUM> of dried oil (Winog-<NUM>), <NUM><NUM> of i-hexane containing <NUM> of tri-n-octyl aluminum (TNOA) and <NUM> of the spherical catalyst prepared as described above were introduced. The stirring was set at about <NUM> rpm, and the internal temperature was increased to <NUM> during a time of <NUM> minutes. Maintaining constant the temperature of the reactor, <NUM> bar of hydrogen overpressure was introduced while ethylene was carefully fed with a constant flow for <NUM>. The polymerization was discontinued when a theoretical conversion of <NUM> of polymer per g of catalyst was deemed to be reached. The resulting pre-polymerized catalyst was maintained in oil/i-hexane slurry. <NUM><NUM> of slurry were diluted with i-hexane under stirring, the solvent siphoned off and the residual solid prepolymer washed <NUM> times with <NUM> of dried i-hexane, and analyzed. It contained <NUM> of polyethylene per g of solid catalyst. Prepolymer composition: Mg=<NUM> wt%; Ti=<NUM> wt%; I. 3wt%; P50= <NUM>. The catalyst component was then used in a double run gas phase polymerization of propylene according to general procedure carried out at <NUM>° and <NUM> respectively.

Into a <NUM><NUM> glass-vessel/stainless steel autoclave with a mechanical anchor stirrer, at room temperature and under a nitrogen atmosphere, <NUM><NUM> of dried oil (Winog-<NUM>), <NUM><NUM> of i-hexane containing <NUM> of tri-ethyl aluminum (TEA), <NUM> of the spherical catalyst prepared as described above and <NUM> of cyclo-hexyl-methyl dimethoxy silane (ED) were introduced. The stirring was set at about <NUM> rpm, and maintained, with continuous stirring at room temperature for <NUM> minutes and then the internal temperature was decreased to <NUM>. Maintaining constant the temperature of the reactor, propylene was carefully fed with a constant flow for <NUM>. The polymerization was discontinued when a theoretical conversion of <NUM> of polymer per g of catalyst was deemed to be reached. The resulting pre-polymerized catalyst was maintained in oil/i-hexane slurry. <NUM><NUM> of slurry was diluted with i-hexane under stirring, the solvent siphoned off and the residual solid prepolymer washed <NUM> times with <NUM> of dried i-hexane, and analyzed. It contained <NUM> of polypropylene per g of solid catalyst. Prepolymer composition: Mg=<NUM> wt%; Ti=<NUM> wt%; I. =<NUM> wt%; P50= <NUM>. The catalyst component was then used in a double run gas phase polymerization of propylene according to general procedure carried out at <NUM>° and <NUM> respectively.

Into a <NUM><NUM> glass-vessel/stainless steel autoclave with a mechanical anchor stirrer, at room temperature and under a nitrogen atmosphere, <NUM><NUM> of i-hexane containing <NUM> of tri-n-octyl aluminum (TNOA) and <NUM> of the spherical catalyst prepared as described above were introduced. The stirring was set at about <NUM> rpm, and the internal temperature was increased to <NUM> during a time of <NUM> minutes. Maintaining constant the temperature of the reactor, ethylene was carefully introduced with a constant flow for <NUM>. The polymerization was discontinued when a theoretical conversion of <NUM> of polymer per g of catalyst was deemed to be reached. The resulting pre-polymerized catalyst was dried under vacuum at room temperature and analyzed. It contained <NUM> of polyethylene per g of solid catalyst. Prepolymer composition: Mg=<NUM> wt%; Ti=<NUM> wt%; I. =<NUM> wt%; P50= <NUM>. The catalyst component was then used in a double run gas phase polymerization of propylene according to general procedure carried out at <NUM>° and <NUM> respectively.

The solid catalyst component was prepared according to the general procedure with the only difference that as internal donor (ID) <NUM>-i-propyl-<NUM>-i-butyl-<NUM>,<NUM>-dimetoxy propane was used instead of <NUM>,<NUM>-bis(methoxymethyl)fluorene. The catalyst composition was the following: Mg <NUM> wt%; Ti <NUM> wt%; ID <NUM> wt%; P50 <NUM>.

Into a <NUM><NUM> glass-vessel/stainless steel autoclave with a mechanical anchor stirrer, at room temperature and under a nitrogen atmosphere, <NUM><NUM> of i-hexane containing <NUM> of tri-n-octyl aluminum (TNOA) and <NUM> of the catalyst prepared as described above were introduced. The stirring was set at about <NUM> rpm, and the internal temperature was increased to <NUM> during a time of <NUM> minutes. Maintaining constant the temperature of the reactor, ethylene was carefully introduced with a constant flow for <NUM>. The polymerization was discontinued when a theoretical conversion of <NUM> of polymer per g of catalyst was deemed to be reached. The resulting pre-polymerized catalyst was dried under vacuum at room temperature and analyzed. It contained <NUM> of polyethylene per g of solid catalyst (<NUM> % polymer). Prepolymer composition: Mg <NUM>. 3wt%; Ti <NUM> wt%; ID <NUM>. 7wt%; at solvent zero; P50 <NUM>. The catalyst component was then used in a double run gas phase polymerization of propylene according to general procedure carried out at <NUM>° and <NUM> respectively.

Into a <NUM><NUM> glass-vessel/stainless steel autoclave with a mechanical anchor stirrer, at room temperature and under a nitrogen atmosphere, <NUM><NUM> of i-hexane containing <NUM> of tri-n-octyl aluminum (TNOA) and <NUM> of the spherical catalyst prepared as described in Example <NUM> were introduced. The stirring was set at about <NUM> rpm, and the internal temperature was increased to <NUM> during a time of <NUM> minutes. Maintaining constant the temperature of the reactor, ethylene was carefully introduced with a constant flow for <NUM>. The polymerization was discontinued when a theoretical conversion of <NUM> of polymer per g of catalyst was deemed to be reached. The resulting pre-polymerized catalyst was dried under vacuum at room temperature and analyzed. It contained <NUM> of polyethylene per g of solid catalyst (<NUM> % polymer). Prepolymer composition: Mg <NUM> wt%; Ti <NUM> wt%; at solvent zero; P50 <NUM>. The catalyst component was then used in a double run gas phase polymerization of propylene according to general procedure carried out at <NUM>° and <NUM> respectively.

Into a <NUM><NUM> glass-vessel/stainless steel autoclave with a mechanical anchor stirrer, at room temperature and under a nitrogen atmosphere, <NUM><NUM> of i-hexane containing <NUM> of tri-n-octyl aluminum (TNOA) and <NUM> of the spherical catalyst prepared as described above (Example <NUM>) and <NUM> of cyclo-hexyl-methyl dimethoxy silane (CHMMS) were introduced. The stirring was set at about <NUM> rpm, and maintained, with continuous stirring at room temperature for <NUM> minutes and then the internal temperature was decreased to <NUM>. Maintaining constant the temperature of the reactor, propylene was carefully fed with a constant flow for <NUM>. The polymerization was discontinued when a theoretical conversion of <NUM> of polymer per g of catalyst was deemed to be reached. The resulting pre-polymerized catalyst was dried under vacuum at room temperature and analyzed. It contained <NUM> of polypropylene per g of solid catalyst. Prepolymer composition: Mg <NUM> wt%; Ti <NUM> wt%; I. <NUM> wt%; P50 <NUM>. The catalyst component was then used in a double run gas phase polymerization of propylene according to general procedure carried out at <NUM>° and <NUM> respectively.

A catalyst component prepared according to the general procedure, without being subject to pre-polymerization, with the difference that <NUM>,<NUM>-dimethoxypropane (DMP) was used as ID. The catalyst composition was the following: Mg <NUM> wt%; Ti <NUM> wt%; ID <NUM> wt%; It was used in a single run gas phase polymerization of propylene according to general procedure carried out at <NUM>°.

Claim 1:
A gas-phase process for the homo or copolymerization of propylene with other olefins, carried out in the presence of a catalyst system comprising:
(a) a solid catalyst component comprising a titanium compound having at least a Ti-halogen bond, a Mg halide, an electron donor selected from <NUM>,<NUM>-diethers and an olefin polymer in an amount ranging from <NUM> to <NUM>% of the total weight of the solid catalyst component and in which the <NUM>,<NUM>-diether/Mg molar ratio ranges from <NUM> to <NUM>;
(b) an aluminum alkyl compound and
(c) an external electron donor (ED) compound selected from silicon compounds, ethers, esters, amines, heterocyclic compounds, ketones; said components (b) and (c) being employed in amounts such that the Al/(ED) molar ratio ranges from <NUM> to <NUM>.