CA2583013C - Rapid termination of gas phase polymerization - Google Patents

Abstract

A gas phase polymerization may be rapidly terminated by injecting a "kill" gas at number of locations including in the polymer disengagement zone and to the gas recycle loop while the compressor winds down.

Description

RAPID TERMINATION OF GAS PHASE POLYMERIZATION
FIELD OF THE INVENTION
The present invention relates to one or more processes to rapidly terminate ("kill") a gas phase polymerization of one or more olefin monomers. In a gas phase polymerization the reaction is exothermic and if there is an emergency shutdown then the reaction has to be "killed" quickly.
If the termination is slow the temperature of the reactor bed may rise and the polymer particles in the bed may stick (sinter) together. To prevent this the operators of gas phase reactors, and particularly polyethylene reactors tend to run the reactors at a lower temperature than optimum so that if there is an emergency shutdown the temperature difference between the reaction temperature in the bed and the sintering temperature is sufficient to minimize the likelihood of sintering the bed.
BACKGROUND OF THE INVENTION
When an event occurs that suggest an emergency shut down of a fluidized bed gas phase reactor there is some delay in injecting kill gas into the reactor. Typically the "kill gas" may not be injected for several seconds (typically 10 to 15 seconds) after the alarm and subsequently depending on the type of shutdown the top valve may be opened. This delay gives the operators time to ensure the event is "real" and not a false reading. The delay is not a large concern provided there is a sufficient temperature differential between the polymer bed and the polymer sticking temperature.
One type of catalyst deactivation process is to open the vent gas valve at the top of the reactor (top of the disengagement zone) and subsequently inject a deactivator ("kill gas") into the base of the reactor below the distributor plate and to pull the kill gas up through the bed.
Concurrently the recycle line is closed. This teaches away from the present invention U.S. 4,547,555 issued Oct 15, 1985 to Cook et al. assigned to Mobil Oil Corporation teaches emergency "killing" a gas phase reactor by injecting a kill gas (CO) into the recycle line with the recycle system open and the vent closed. The patent does not disclose or suggest injecting a kill gas into the top of the reactor. The patent teaches against the present invention.
U.S. patent 5,270,408 issued Dec. 14, 1993 to Union Carbide Chemicals & Plastics Corporation teaches a method of terminating a gas phase polymerization reaction by introducing a kill gas into the reactor while routing the reaction gas from the reactor through an expander (and thence to a flare) to also drive a compressor which is used to inject a kill gas into the reactor below the diffuser plate. This reduces "surge" on the compressor. The process does not suggest to inject the kill gas in the polymer disengagement zone.
U.S. 6,013,741 issued Jan 11,2000, to Ohtani et al., assigned to Mitsui Chemicals, Inc. discloses injecting a kill gas into the reactor through at least two ports at locations from -0.3D to 0.3 D and 0.3D to 2D from the distributor plate where D is the diameter in cm of the fluidized bed. The patent teaches away from injecting the deactivator into the polymer disengagement zone.
U.S. 4,786,695 issued Nov. 22, 1988 to Cook et al. assigned to Mobil Oil Corporation teaches using a carrier gas in conjunction with a "kill

2 gas" (CO2) to improve the rate of penetration of the kill gas into the reaction medium. The patent doesn't suggest injecting the kill gas into the polymer disengagement zone.
SUMMARY OF THE INVENTION
The present invention provides a process for the termination of a fluidized gas phase polymerization reaction of one or more C2-8 olefin monomers, typically gaseous but some may be condensed or partially condensed, in a reactor system comprising a reactor, having an inlet in its lower portion below a diffuser plate, a polymer disengagement zone, and a vent in its upper portion leading to a flare stack, a reactor gas recycle loop including a compressor, so that the temperature rise of the bed of polymer in the reactor does not rise above the sticking temperature of the polymer comprising recapturing energy from the reaction while maintaining the reactor gas cycle loop open and injecting a gaseous mixture comprising from 0 up to 90 mole % of one or more inert gases and from 100 to 10 mole % of one or more gaseous catalyst deactivators in an amount sufficient to deactivate the catalyst in the reactor system into at least the polymer disengagement zone and the reactor gas cycle loop to disperse said gas mixture thoroughly through the bed of polymer..
BRIEF DESCRIPTION OF THE DRAWING
Figure 1 is a schematic diagram of a fluidized bed gas phase reactor.
BEST MODE
As used in this specification recapturing energy from the reaction includes venting reactor gas through a turbo expander, the use of a

3 flywheel on the compressor, and the use of capacitors or batteries, or both as an electrical equivalent of the flywheel.
The fluidized bed gas phase process for the polymerization of alpha olefins, and particularly polyethylene has been practiced since at least as early as the mid 1970's for linear low density polyethylene (LLDPE ) and high density polyethylene (HDPE).
A fluidized gas phase reactor will be described in conjunction with figure 1.
A fluidized bed gas phase reactor generally comprises a reactor 1.
Monomers or make up monomers are fed through a feed line 2 optionally entering a recycle loop 3 downstream from a compressor 4 and a heat exchanger 5. Make up monomer or part of it may be a high pressure liquefied monomer such as ethylene to reduce the load on the heat exchanger. The make up monomers and recycle gas stream enter the reactor 1 at 6 below the distributor plate 7. Above distributor plate 7 is a fluidized bed of growing polymer particles 8. Catalyst and optionally co catalysts are fed through separate lines (not shown) into the fluidized bed 8 of growing particles. The velocity of the make up monomers and recycle gas is sufficiently high to keep the bed of growing polymer particles 8 fluidized. At the upper end of the reactor is a disengagement zone 9.
Polymer is withdrawn from the fluidized bed of polymer particles 8 by a line (not shown) and is fed to degassers and to a pelletizer (not shown) typically by the use of ball or rotary valves and a timing mechanism. The gas leaves the disengagement zone through the recycle gas valve 10 which communicates with the recycle line 3 so that the recycle gas passes

4 through the compressor 4 and the heat exchanger 5 and make up monomer is added to the recycle gas line 3. In an emergency shutdown (e.g. a power failure etc.) the reactor may be vented through valve 11 and line 12 to a suitable vent means such as a flare stack. In accordance with one embodiment of the present invention the reactor is not vented to the flare stack until the reaction has been essentially killed ( e.g. more than 80, preferably more than 95 c/o of the catalyst has been deactivated) A kill gas source 13 such as one or more cylinders is fed to kill gas line 14 which enters the gas recycle line 3 at 20 which is at or proximate to the recycle gas valve 10. Additionally kill gas line 14 also vents into the disengagement zone of the reactor at 16. The kill gas line may vent into a number of additional locations including into the reactor at 17 below the distributor plate 7, into the lowest 10% of the polymer bed (bed of growing particles 8) above the distributor plate 7, and at the inlet of the compressor and the heat exchanger (not shown).
As noted above there may be a significant difference between the temperature of the bed of polymer and the sintering temperature of the polymer. This may be on the order of 10 C to 15 C. However, as productivity increases are required (e.g. as a result of the use of more active single site type catalysts) this temperature difference may be reduced. Preferably, the rise of the bed temperature after a "kill" is commenced should be less than about 10 C, preferably less than 5 C most preferably less than 3 C.
There are a number of methods to recover energy from the reaction.
The reaction gasses under pressure may be cycled through an

5 external turbo-expander to drive the compressor in the recycle line (e.g.
concurrent venting and operation of the recycle line).
A different approach is proposed herein whereby the momentum (moment of inertia) of the compressor in the recycle line is increased. The moment of inertia of the electric motor driving the compressor or the compressor itself ( e.g. the shaft and blades etc.) or both could be increased. A simple mechanical method to increase the moment of inertia of the compressor would be to attach a flywheel to the compressor shaft.
There are several advantages to increasing the moment of inertia of the compressor. This tends to smooth out operation, reduces the risk of surge during operation and shutdown. Typically the shutdown time is in the range from about 5 to 30 seconds after the introduction of the kill gas is commenced. The wind down time is proportional to the moment of inertia of the compressor (all else being equal, e.g. at steady state entering a shutdown this should apply). One of ordinary skill in the art should be able to determine the mass and shape of the flywheel required to provide the required increase in "wind down time" of the compressor. Typically the kill procedure should be as short as practical, generally within about 5 to 35 seconds, preferably from about 10 to 25 seconds, most preferably from about 10 to 20 seconds.
The electrical equivalent of a flywheel could be one or more capacitors or one or more batteries or a combination thereof. The capacitors or batteries or both need only store enough energy to drive the compressor for the required wind down time as noted above.

6 It should also be noted that towards the end of the shutdown the fluidized bed will collapse, that is it is no longer fluidized. This event will also help to thoroughly distribute the kill gas through out the bed. During the shut down the kill gas may achieve two results. It deactivates the catalyst and terminates the reaction and consequently the generation of heat (and corresponding rise in bed temperature) and it also initially dilutes and eventually displaces the reactive monomers initially reducing the rate of reaction until the catalyst is deactivated.
In contrast to the prior procedures the steps of injecting the "kill gas"
and venting through the recycle line should be taken promptly (within 5, preferably less than 3 seconds) after the shut down proceed is commenced. At the commencement of the shutdown vent valve 11 at the top of the reactor may remain closed until the reaction is essentially killed.

Valve 15 is opened and deactivator (kill) gas enters line 14 and flows to the bottom of the reactor through vent 17, the top of the reactor through vent 16 and into the recycle line through 20 (e.g. injected at least one location selected from below the distributor plate and the polymer bed above the distributor plate, preferably within the lowest 10% of the bed above the distributor plate, and at least one location selected from the polymer disengagement zone, the inlet to the gas recycle system, the inlet to the heat exchanger, and the inlet to the compressor).
Valve 10 to the recycle line remains open during the shut down at least until the compressor has wound down. After the reaction is substantially terminated (killed) valve 11 may be opened to vent the reactor of the kill gas and any residual reactants and inert gases. Also at

7 that time valve 10 on the recycle line may be closed. As the kill gas is drawn from the polymer disengagement zone through the gas recycle loop and compressor of a gas phase reactor system it reduces the formation of fines in the recycle line and particularly in the compressor and the heat exchanger.
The monomers used in a gas phase reactor typically comprise one or more C2-6 olefins such as ethylene, propylene, 1-butene and 1-hexene.
Typically, the monomers comprise at least about 80 mole % of ethylene and the balance from 0 to 20 mole % of one or more comonomers. The reaction gas typically comprises a chain transfer agent such as hydrogen and one or more inert ballast gases such as nitrogen and possibly ethane.
The reactor gas may also comprise a liquid (condensed gas below its dew point such as pentane or isopentane or possibly a monomer) which evaporates in the reactor bed to remove heat as disclosed in U.S. patents 4,532,311 and 4,588,790 issued Sept 24, 1985 and May 13, 1986 respectively to Jenkins III, assigned to Union Carbide Corporation ; U.S.
patents 5,462,999 and 5,436,304 issued Oct. 31,1995 and July 25,1995 respectively to Griffin et al. assigned to Exxon Chemical Patent Inc. and U.S. patents 5,405,922 and 5,352,749 issued April 11, 1995 and Oct.
4,1993 to DeChellis et at. assigned to Exxon Chemicals Patent Inc.
The catalysts used in fluidized bed gas phase polymerization are typically a supported catalyst. The support may be an inorganic or refractory support, including for example alumina, silica, clays or modified clays; or an organic support (including polymeric support such as polystyrene or cross-linked polystyrene). Some refractories include silica

8 and alumina which may be treated to reduce the number of surface hydroxyl groups. The support or carrier may be a spray-dried silica.
Generally the support will have an average particle size from about 0.1 to about 1,000, preferably from about 10 to 150 microns. The support typically will have a surface area of at least about 10 m2/g, preferably from about 150 to 1,500 m2/g. The pore volume of the support should be at least 0.2, preferably from about 0.3 to 5.0 ml/g.
Generally the refractory or inorganic support may be heated at a temperature of at least 200 C for up to 24 hours, typically at a temperature from 500 C to 800 C for about 2 to 20 hours, preferably 4 to 10 hours. The resulting support will be essentially free of adsorbed water (e.g. less than about 1 weight %) and may have a surface hydroxyl content from about 0.1 to 5 mmol/g of support, preferably from 0.5 to 3 mmol/g.
A silica suitable to prepare the component polymers of the present invention has a high surface area and is amorphous. For example, commercially available silicas are marketed under the trademark of Sylopol 958 and 955 by the Davison Catalysts, a Division of W.R. Grace and Company and ES-70W by lneos Silica.
While heating is the most preferred means of removing OH groups inherently present in many carriers, such as silica, the OH groups may also be removed by other removal means, such as chemical means. For example, a desired proportion of OH groups may be reacted with a suitable chemical agent, such as a hydroxyl reactive aluminum compound (e.g.
triethyl aluminum) or a silane compound. This method of treatment has

9 been disclosed in the literature and two relevant examples are: U.S. Patent 4,719,193 to Levine in 1988 and by Noshay A. and Karol F.J. in Transition Metal Catalyzed Polymerizations, Ed. R. Quirk, 396, 1989. For example the support may be treated with an aluminum compound of the formula Al((0)aR1)bX3..b wherein a is either 0 or 1, b is an integer from 0 to 3, R1 is a C1_8 alkyl radical, and X is a chlorine atom. The amount of aluminum compound is such that the amount of aluminum on the support prior to adding the remaining catalyst components will be from about 0 to 2.5 weight %, preferably from 0 to 2.0 weight % based on the weight of the support.
The clay type supports are also preferably treated to reduce adsorbed water and surface hydroxyl groups. The clays may be further subjected to an ion exchange process which may tend to increase the separation or distance between the adjacent layers of the clay structure.
The polymeric support may be cross linked polystyrene containing up to about 50 weight %, preferably not more than 25 weight %, most preferably less than 10 weight % of a cross linking agent such as divinyl benzene.
The catalyst may be a single site type catalyst or a more conventional Ziegler Natta catalyst or a chrome catalyst.
Single site catalysts tend to be bulky ligand single site catalyst of the formula II:
(14n ¨ M (Y)p wherein M is selected from the group consisting of Ti, Zr, and Hf; L is a monoanionic ligand independently selected from the group consisting of cyclopentadienyl-type ligands, and a bulky heteroatom ligand containing not less than five atoms in total (typically of which at least 20%, preferably at least 25% numerically are carbon atoms) and further containing at least one heteroatom selected from the group consisting of boron, nitrogen, oxygen, phosphorus, sulfur and silicon, said bulky heteroatom ligand being sigma or pi-bonded to M, Y is independently selected for the group consisting of activatable ligands; n may be from 1 to 3; and p may be from 1 to 3, provided that the sum of n+p equals the valence state of M, and further provided that two L ligands may be bridged.
Non-limiting examples of bridging group include bridging groups containing at least one Group 13 to 16 atom, often referred to a divalent moiety such as but not limited to at least one of a carbon, oxygen, nitrogen, silicon, boron, germanium and tin atom or a combination thereof. Preferably the bridging group contains a carbon, silicon or germanium atom, most preferably at least one silicon atom or at least one carbon atom. The bridging group may also contain substituent radicals as defined above including halogens.
Some bridging groups include but are not limited to a di C1-6 alkyl radical (e.g. alkylene radical for example an ethylene bridge), di C6_10 aryl radical (e.g. a benzyl radical having two bonding positions available), silicon or germanium radicals substituted by one or more radicals selected from the group consisting of C16 alkyl, C6_10 aryl, phosphine or amine radical which are unsubstituted or up to fully substituted by one or more C1_ 6 alkyl or C6-10 aryl radicals, or a hydrocarbyl radical such as a C1-6 alkyl radical or a C6_10 arylene (e.g. divalent aryl radicals); divalent C1_8 alkoxide radicals (e.g. -CH2CHOHCH2-) and the like.
Exemplary of the silyl species of bridging groups are dimethylsilyl, methylphenylsilyl, diethylsilyl, ethylphenylsilyl or diphenylsilyl compounds.
Most preferred of the bridged species are dimethylsilyl, diethylsilyl and methylphenylsilyl bridged compounds.
Exemplary hydrocarbyl radicals for bridging groups include methylene, ethylene, propylene, butylene, phenylene and the like, with methylene being preferred.
Exemplary bridging amides include dimethylamide, diethylamide, methylethylamide, di-t-butylamide, diisoproylamide and the like.
The term "cyclopentadienyl" refers to a 5-member carbon ring having delocalized bonding within the ring and typically being bound to the active catalyst site, generally a group 4 metal (M) throughii5 - bonds. The cyclopentadienyl ligand may be unsubstituted or up to fully substituted with one or more substituents selected from the group consisting of C1-10 hydrocarbyl radicals in which hydrocarbyl substituents are unsubstituted or further substituted by one or more substituents selected from the group consisting of a halogen atom and a C1-4 alkyl radical; a halogen atom; a Ci-8 alkoxy radical; a C6_10 aryl or aryloxy radical; an amido radical which is unsubstituted or substituted by up to two C1-8 alkyl radicals; a phosphido radical which is unsubstituted or substituted by up to two C1_8 alkyl radicals;
silyl radicals of the formula ¨Si¨(R)3 wherein each R is independently selected from the group consisting of hydrogen, a C1-8 alkyl or alkoxy radical, and C6_10 aryl or aryloxy radicals; and germanyl radicals of the formula Ge¨(R)3 wherein R is as defined above.
Typically the cyclopentadienyl-type ligand is selected from the group consisting of a cyclopentadienyl radical, an indenyl radical and a fluorenyl radical where the radicals are unsubstituted or up to fully substituted by one or more substituents selected from the group consisting of a fluorine atom, a chlorine atom; C1.4 alkyl radicals; and a phenyl or benzyl radical which is unsubstituted or substituted by one or more fluorine atoms.
In the above formula for the single site catalysts if none of the L
ligands is bulky heteroatom ligand then the catalyst could be a bis Cp catalyst (a traditional metallocene) or a bridged constrained geometry type catalyst or tris Cp catalyst.
If the catalyst contains one or more bulky heteroatom ligands the catalyst would have the formula:
(D)m (L)p ¨ M ¨ (Y)p wherein M is a transition metal selected from the group consisting of Ti, Hf and Zr; D is independently a bulky heteroatom ligand (as described below);
L is a monoanionic ligand selected from the group consisting of cyclopentadienyl-type ligands; Y is independently selected from the group consisting of activatable ligands; m is 1 or 2; n is 0, 1 or 2 and p is an integer and the sum of m+n-Fp equals the valence state of M, provided that when m is 2, D may be the same or different bulky heteroatom ligands.
For example, the catalyst may be a bis (phosphinimine), or a mixed phosphinimine ketimide dichloride complex of titanium, zirconium or hafnium. Alternately, the catalyst could contain one phosphinimine ligand or one ketimide ligand, one "L" ligand (which is most preferably a cyclopentadienyl-type ligand) and two "Y" ligands (which are preferably both chloride).
The preferred metals (M) are from Group 4 (especially titanium, hafnium or zirconium) with titanium being most preferred. In one embodiment the catalysts are group 4 metal complexes in the highest oxidation state.
The bulky heteroatom ligands (D) include but are not limited to phosphinimine ligands (PI) and ketimide (ketimine) ligands. The phosphinimine ligand (PI) is defined by the formula:

R21 p = N _ wherein each R21 is independently selected from the group consisting of a hydrogen atom; a halogen atom; C1-20, preferably C1_10 hydrocarbyl radicals which are unsubstituted by or further substituted by a halogen atom; a C1-8 alkoxy radical; a C6_10 aryl or aryloxy radical; an amido radical; a silyl radical of the formula:
¨Si¨(R22)3 wherein each R22 is independently selected from the group consisting of hydrogen, a C1_8 alkyl or alkoxy radical, and C6-10 aryl or aryloxy radicals;
and a germanyl radical of the formula:
_Ge_(R22)3 wherein R22 is as defined above.

, The preferred phosphinimines are those in which each R21 is a hydrocarbyl radical, preferably a C1-6 hydrocarbyl radical.
Suitable phosphinimine catalysts are Group 4 organometallic complexes which contain one phosphinimine ligand (as described above) and one ligand L which is either a cyclopentadienyl-type ligand or a heteroatom ligand.
As used herein, the term "ketimide ligand" refers to a ligand which:
(a) is bonded to the transition metal via a metal¨nitrogen atom bond;
(b) has a single substituent on the nitrogen atom (where this single substituent is a carbon atom which is doubly bonded to the N atom);
and (c) has two substituents Sub 1 and Sub 2 (described below) which are bonded to the carbon atom.
Conditions a, b and c are illustrated below:
Sub 1 Sub 2 X /
C
II
N
I
metal The substituents "Sub 1" and "Sub 2" may be the same or different and may be further bonded together through a bridging group to form a ring. Exemplary substituents include hydrocarbyls having from 1 to 20, preferably from 3 to 6, carbon atoms, silyl groups (as described below), amido groups (as described below) and phosphido groups (as described below). For reasons of cost and convenience it is preferred that these substituents both be hydrocarbyls, especially simple alkyls and most preferably tertiary butyl.
Suitable ketimide catalysts for the second polymer used in the blends of the present invention are Group 4 organometallic complexes which contain one ketimide ligand (as described above) and one ligand L
which is either a cyclopentadienyl-type ligand or a heteroatom ligand.
The term bulky heteroatom ligand (D) is not limited to phosphinimine or ketimide ligands and includes ligands that contain at least one heteroatom selected from the group consisting of boron, nitrogen, oxygen, phosphorus, sulfur and silicon. The heteroatom ligand may be sigma or pi-bonded to the metal. Exemplary heteroatom ligands include silicon-containing heteroatom ligands, amido ligands, alkoxy ligands, boron heterocyclic ligands and phosphole ligands, as all described below.
Silicon containing heteroatom ligands are defined by the formula:
¨ (Y)SiRxRyRz wherein the ¨ denotes a bond to the transition metal and Y is sulfur or oxygen.
The substituents on the Si atom, namely Rx, Ry and Rz are required in order to satisfy the bonding orbital of the Si atom. The use of any particular substituent Rx, Ry or Rz is not especially important to the success of this invention. It is preferred that each of Rx, Ry and Rz is a C1-2 hydrocarbyl group (i.e. methyl or ethyl) simply because such materials are readily synthesized from commercially available materials.
The term "amido" is meant to convey its broad, conventional meaning. Thus, these ligands are characterized by (a) a metal-nitrogen bond; and (b) the presence of two substituents (which are typically simple alkyl or silyl groups) on the nitrogen atom.
The terms "alkoxy" and "aryloxy" is also intended to convey its conventional meaning. Thus, these ligands are characterized by (a) a metal oxygen bond; and (b) the presence of a hydrocarbyl group bonded to the oxygen atom. The hydrocarbyl group may be a C1_10 straight chained, branched or cyclic alkyl radical or a C6_13 aromatic radical which radicals are unsubstituted or further substituted by one or more C1_4 alkyl radicals (e.g. 2,6 di-tertiary butyl phenoxy).
Boron heterocyclic ligands are characterized by the presence of a boron atom in a closed ring ligand. This definition includes heterocyclic ligands which also contain a nitrogen atom in the ring. These ligands are well known to those skilled in the art of olefin polymerization and are fully described in the literature (see, for example, U.S. Patent's 5,637,659;
5,554,775; and the references cited therein).
The term "phosphole" is also meant to convey its conventional meaning. "Phospholes" are cyclic dienyl structures having four carbon atoms and one phosphorus atom in the closed ring. The simplest phosphole is C4PH4 (which is analogous to cyclopentadiene with one carbon in the ring being replaced by phosphorus). The phosphole ligands may be substituted with, for example, C1_20 hydrocarbyl radicals (which may, optionally, contain halogen substituents); phosphido radicals; amido radicals; or silyl or alkoxy radicals. Phosphole ligands are also well known to those skilled in the art of olefin polymerization and are described as such in U.S. Patent 5,434,116 (Sone, to Tosoh).

The single site type catalysts may be activated with an activator selected from the group consisting of:
(i) a complex aluminum compound of the formula R122A10(R12A10)mAIR122 wherein each R12 is independently selected from the group consisting of C1_20 hydrocarbyl radicals and m is from 3 to 50, and optionally a hindered phenol to provide a molar ratio of Al:hindered phenol from 2:1 to 5:1 if the hindered phenol is present;
(ii) ionic activators selected from the group consisting of:
(A) compounds of the formula [R13] [B(R14)4]- wherein B is a boron atom, R13 is a cyclic C5_7 aromatic cation or a triphenyl methyl cation and each R14 is independently selected from the group consisting of phenyl radicals which are unsubstituted or substituted with a hydroxyl group or 3 to 5 substituents selected from the group consisting of a fluorine atom, a C1_4 alkyl or alkoxy radical which is unsubstituted or substituted by a fluorine atom; and a silyl radical of the formula -Si-(R15)3; wherein each R15 is independently selected from the group consisting of a hydrogen atom and a C1_4 alkyl radical; and (B) compounds of the formula [(R18)t ZH][B(R14)41-wherein B is a boron atom, H is a hydrogen atom, Z is a nitrogen atom or phosphorus atom, t is 2 or 3 and R18 is independently selected from the group consisting of C1-15 alkyl radicals, a phenyl radical which is unsubstituted or substituted by up to three C1_4 alkyl radicals, or one R18 taken together with the nitrogen atom may form an anilinium radical and R14 is as defined above; and (C) compounds of the formula B(R14)3 wherein R14 is as defined above; and (iii) mixtures of (i) and (ii).
Preferably the activator is a complex aluminum compound of the formula R122A10(R12A10)mAIR122 wherein each R12 is independently selected from the group consisting of C14 hydrocarbyl radicals and m is from 3 to 50, and optionally a hindered phenol to provide a molar ratio of Al:hindered phenol from 2:1 to 5:1 if the hindered phenol is present. In the aluminum compound, preferably R12 is methyl radical and m is from 10 to 40. The preferred molar ratio of Al:hindered phenol, if it is present, is from 3.25:1 to 4.50:1. Preferably the phenol is substituted in the 2, 4 and 6 position by a C2-6 alkyl radical. Desirably the hindered phenol is 2,6-di-tert-buty1-4-ethyl-phenol.
The aluminum compounds (alumoxanes and optionally hindered phenol) are typically used as activators in substantial molar excess compared to the amount of the transition metal in the catalyst.
Aluminum:transition metal molar ratios of from 10:1 to 10,000:1 are preferred, most preferably 10:1 to 500:1 especially from 10:1 to 120:1.
Ionic activators are well known to those skilled in the art. The "ionic activator" may abstract one activatable ligand so as to ionize the catalyst center into a cation, but not to covalently bond with the catalyst and to provide sufficient distance between the catalyst and the ionizing activator to permit a polymerizable olefin to enter the resulting active site.
Examples of ionic activators include:
triethylammonium tetra(phenyl)boron, tripropylammonium tetra(phenyl)boron, tri(n-butyl)ammonium tetra(phenyl)boron, trimethylammonium tetra(p-tolyl)boron, trimethylammonium tetra(o-tolyl)boron, tributylammonium tetra(pentafluorophenyl)boron, tripropylammonium tetra(o,p-dimethylphenyl)boron, tributylammonium tetra(m,m-dimethylphenyl)boron, tributylammonium tetra(p-trifluoromethylphenyl)boron, tributylammonium tetra(pentafluorophenyl)boron, tri(n-butyl)ammonium tetra(o-tolyl)boron, N,N-dimethylanilinium tetra(phenyl)boron, N,N-diethylanilinium tetra(phenyl)boron, N,N-diethylanilinium tetra(phenyl)n-butylboron, di-(isopropyl)ammonium tetra(pentafluorophenyl)boron, dicyclohexylammonium tetra(phenyl)boron, triphenylphosphonium tetra(phenyl)boron, tri(methylphenyl)phosphonium tetra(phenyl)boron, tri(dimethylphenyl)phosphonium tetra(phenyl)boron, tropillium tetrakispentafluorophenyl borate, triphenylmethylium tetrakispentafluorophenyl borate, tropillium phenyltrispentafluorophenyl borate, triphenylmethylium phenyltrispentafluorophenyl borate, benzene (diazonium) phenyltrispentafluorophenyl borate, tropillium tetrakis (2,3,5,6-tetrafluorophenyl) borate, triphenylmethylium tetrakis (2,3,5,6-tetrafluorophenyl) borate, tropillium tetrakis (3,4,5-trifluorophenyl) borate, benzene (diazonium) tetrakis (3,4,5-trifluorophenyl) borate, tropillium tetrakis (1,2,2-trifluoroethenyl) borate, triphenylmethylium tetrakis (1,2,2-trifluoroethenyl) borate, tropillium tetrakis (2,3,4,5-tetrafluorophenyl) borate, and triphenylmethylium tetrakis (2,3,4,5-tetrafluorophenyl) borate.
Readily commercially available ionic activators include:
N,N-dimethylaniliniumtetrakispentafluorophenyl borate;
triphenylmethylium tetrakispentafluorophenyl borate (tritylborate); and trispentafluorophenyl borane.
Ionic activators may also have an anion containing at least one group comprising an active hydrogen or at least one of any substituent able to react with the support. As a result of these reactive substituents, the ionic portion of these ionic activators may become bonded to the support under suitable conditions. One non-limiting example includes ionic activators with tris (pentafluorophenyl) (4-hydroxyphenyl) borate as the anion. These tethered ionic activators are more fully described in U.S.
Patents 5,834,393; 5,783,512; and 6,087,293.
The ionic activators may be used in amounts to provide a molar ratio of transition metal to boron from 1:1 to 1:6, preferably from 1:1 to 1:2.
There are a number of strategies to combine the components of a Ziegler Natta catalyst system. For example a number of patents assigned to Union Carbide Corporation, represented by U.S. Patent 4,302,566 to Karol et al., and U.S. Patent 4,302,565 to Goeke et al. both issued November 24, 1981, teach forming a catalyst or catalyst precursor composition from the titanium compound, the magnesium compound, and the electron donor compound and then impregnating the support with the precursor composition and then contacting the impregnated support, typically in the reactor, with the co-catalyst compound in one or more steps.
The catalyst or catalyst precursor composition is formed by dissolving the titanium compound and the magnesium compound in the electron donor compound at a temperature of about 20 C up to the boiling point of the electron donor compound. The titanium compound can be added to the electron donor compound before or after the addition of the magnesium compound, or concurrent therewith. The dissolution of the titanium compound and the magnesium compound can be facilitated by stirring, and in some instances by refluxing these two compounds in the electron donor. After the titanium compound and the magnesium compound are dissolved, the catalyst or catalyst precursor may be isolated by crystallization or by precipitation with a C5_8 aliphatic or aromatic hydrocarbon such as hexane, isopentane or benzene.
The crystallized or precipitated catalyst or catalyst precursor may be isolated, in the form of fine, free flowing particles. The catalyst or catalyst precursor may be recovered and then dissolved in a solvent or may be directly used without recovery to impregnate a suitable support as discussed above.
When made as disclosed above the catalyst or catalyst precursor composition has the formula:
Mgm Ili (OR) n Xp [ED]q wherein ED is the electron donor compound, m is from 0.5 to 56, and preferably from 1.5 to 5, n is 0, 1 or 2, p is from 2 to 116, and preferably from 6 to 14, q is from 2 to 85, and preferably from 4 to 11, R may be a C1-14 aliphatic or aromatic hydrocarbon radical, or COR' wherein R' may be a C1-14 aliphatic or aromatic hydrocarbon radical and, X
is selected from the group consisting of Cl, Br, I or mixtures thereof, preferably Cl. The subscript for the element titanium (Ti) is the Arabic numeral one. In the above formula the letters m, n, p and q define the molar ratios of the components.
The longevity of this approach is illustrated by above noted WO
01/05845.
Another approach is to impregnate the support with a soluble magnesium compound such as a dialkyl magnesium compound (i.e.
MgR2). The Mg is then precipitated with a halogen donating compound.
Then the impregnated support is reacted with a titanium compound, and optionally an electron donor and an aluminum compound. These types of approaches are illustrated by ICI's U.S. Patent 4,252,670 issued February 24, 1981 to Gaunt et al.; U.S. Patent 5,633,419 issued April 1997 to Spencer et al. assigned to the Dow Chemical Company; EP 0 595 574 issued January 1, 1997 in the name of Berardi, assigned to BP Chemicals Ltd.; and U.S. Patent 6,140,264 issued October 31, 2000 to Kelly et al., assigned to NOVA Chemicals Ltd.
Typically the Ziegler-Natta catalyst made by the preceding approach will comprise an aluminum compound of the formula Al((0)aR1)bX3-b wherein a is either 0 or 1, b is an integer from 1 to 3, R1 is a C1_10 alkyl radical and X is a chlorine atom, a titanium compound of the formula Ti(OR2)Xd_c wherein R2 is selected from the group consisting of a C1.4 alkyl radical, a C6_10 aromatic radical, and a radical of the formula ¨COR3 wherein R3 is selected from the group consisting of a C1-4 alkyl radical and a C6_10 aromatic radical, X is selected from the group consisting of a chlorine atom and a bromine atom, c is 0 or an integer up to 4 and d is an integer up to 4 and the sum of c+d is the valence of the Ti atom; a magnesium compound of the formula (R5)eMg X2-e wherein each R5 is independently a C1_4 alkyl radical and e is 0, 1 or 2; an alkyl halide selected from the group consisting of CCI4 or a C3_6 secondary or tertiary alkyl halide and optionally an electron donor, a molar ratio of Al toll from 1:1 to 15:1; a molar ratio of Mg:Ti from 1:1 to 20:1; a molar ratio of halide from the alkyl halide to Mg from 1:1 to 8:1; and a molar ratio of electron donor to Ti from 0:1 to 15:1.
Typically the catalyst components are reacted in an organic medium such as an inert C6_10 hydrocarbon which may be unsubstituted or is substituted by a C1_4 alkyl radical. Some solvents include pentane, hexane, heptane, octane, cyclohexane, methyl cyclohexane, hydrogenated naphtha and ISOPAR E (a solvent available from Exxon Chemical Company) and mixtures thereof.
Typically the aluminum compounds useful in the formation of the catalyst or catalyst precursor in accordance with the present invention have the formula Al((0)eR1)bX3_b wherein a is either 0 or 1, preferably 0, b is an integer from 1 to 3, preferably 3, R1 is a C1-10, preferably a C1-8 alkyl radical and X is a halogen atom preferably a chlorine or bromine atom. Suitable aluminum compounds include, trimethyl aluminum, triethyl aluminum (TEAL), tri-isobutyl aluminum (TiBAL), diethyl aluminum chloride (DEAC), tri-n-hexyl aluminum (TnHAI), tri-n-octyl aluminum (Tn0A1), and mixtures thereof. The aluminum compounds containing a halide may be an aluminum sesqui-halide. Preferably, in the aluminum compound a is 0 and R1 is a C1.8 alkyl radical.
The magnesium compound may be a compound of the formula (R6)eMg X2.e wherein each R6 is independently a C1-4 alkyl radical and e is 0, 1 or 2. Some commercially available magnesium compounds include magnesium chloride, dibutyl magnesium and butyl ethyl magnesium. If the magnesium compound is soluble in the organic solvent it may be used in conjunction with a halogenating agent to form magnesium halide (i.e. MgX2 where X is a halogen preferably chlorine or bromine, most preferably chlorine) which precipitates from the solution (potentially forming a substrate for the Ti compound). Some halogenating agents include CCI4 or a secondary or tertiary halide of the formula R6CI wherein R6 is selected from the group consisting of secondary and tertiary C3-6 alkyl radicals.
Suitable chlorides include sec-butyl chloride, t-butyl chloride and sec-propyl chloride. The halide is added to the catalyst in a quantity of from 5 to 40 weight %, preferably from 10 to 30 weight % based on the weight of silica.
The CI:Mg molar ratio should be from 1:1 to 8:1, preferably from 1.5:1 to 6:1, most preferably from 1.5:1 to 3:1.
The titanium compound in the catalyst has the formula Ti(OR2),)(d..6 wherein R2 is selected from the group consisting of a C1.4 alkyl radical, a C6-10 aromatic radical, and a radical of the formula ¨COR3 wherein R3 is selected from the group consisting of a C14 alkyl radical and a C6-i0 aromatic radical, X is selected from the group consisting of a chlorine atom and a bromine atom, c is 0 or an integer up to 4 and d is an integer up to 4 and the sum of c+d is the valence of the Ti atom. The titanium compound may be selected from the group consisting of T1CI3, TiC14, Ti(0C4H6)C13, Ti(OCOCH3)C13 and Ti(OCOC6H5)C13. Most preferably the titanium compound is selected from the group consisting of TiCI3 and TiCI4.
Generally the titanium in the catalyst or catalyst precursor is present in an amount from 0.25 to 1.25, preferably from 0.25 to 0.70, most preferably from 0.35 to 0.65 weight % based on the final weight of the catalyst (inclusive of the support). As noted above an electron donor may be and in fact is preferably used in the catalysts or catalysts precursor used in accordance with the present invention. The electron donor is selected from the group consisting of C3_18 linear or cyclic aliphatic or aromatic ethers, ketones, esters, aldehydes, amides, nitriles, amines, phosphines or siloxanes. Preferably, the electron donor is selected from the group consisting of diethyl ether, dipropyl ether, dibutyl ether, tetrahydrofuran, acetone, ethyl benzoate, and diphenyl ether and mixtures thereof. The electron donor may be used in a molar ratio to the titanium from 0:1 to 15:1 preferably in a molar ratio to Ti from 3:1 to 12:1, most preferably from 3:1 to

10:1.
In the catalyst or catalyst precursor the molar ratio of Mg:Ti may be from 0.5:1 to 50:1, preferably from 1:1 to 20:1, most preferably from 2:1 to 10:1. The molar ratio of aluminum to titanium in the catalyst may be from , 1:1 to 15:1, preferably from 2:1 to 12:1, most preferably from 3:1 to 10:1.
Optionally all, generally from 0 to not more than about 60 weight %, preferably from 10 to 50 weight %, of the aluminum (compound in the catalyst) may be used to treat the support. The remaining aluminum compound in the catalyst may be added sometime after the titanium addition step preferably after the electron donor step. The molar ratio of halide (from the alkyl halide or CCI4) to Mg may be from 1:1 to 8:1 preferably from 1.5:1 to 6:1, most preferably from 1.5:1 to 3:1. The molar ratio of electron donor, if present, to Ti may be from 3:1 to 12:1, most preferably from 3:1 to 10:1. The molar ratio of Mg:Al in the catalyst or catalyst precursor may be from 0.1:1 to 3:1, preferably from 0.4:1 to 3:1.
The co-catalyst or activators for Ziegler Natta catalysts may be selected from the group consisting of tri C2_6 alkyl aluminums, alkyl aluminum chlorides, and mixtures thereof. This includes triethyl aluminum, tri propyl aluminum, tributyl aluminum, tri isobutyl aluminum, tri n-hexyl aluminum, diethyl aluminum chloride, dibutyl aluminum chloride, and mixtures thereof. A preferred co-catalyst is triethyl aluminum. While the aluminum halides might be useful in accordance with the present invention they increase the amount of halide in the polymer resulting in increased consumption of additives to neutralize and stabilize the resulting polymer.
The co-catalyst may be fed to the reactor to provide from 10 to 50, preferably 10 to 40, more preferably from 17 to 30, most preferably from 20 to 26 ppm of aluminum (Al ppm) based on the polymer production rate.
In accordance with the present invention the molar ratio of total Al The active catalyst species in the chrome catalyst is hexavalent chromium. Typically a chromium compound which is convertible to hexavalent chromium (e.g. Cr03) is dissolved or dispersed in a liquid medium and the support is impregnated with the compound. Exemplary of such chromium compounds are tert-butyl chromate, chromium acetylacetonate and the like. The chromium compound may also include a silyl chromate of the formula (R10)3Si-0-Cr02-0-Si(R10)3 wherein R1 is selected from the group consisting of C1_10, preferably C1_6, most preferably C1-4 alkyl groups.
Typically the chromium compound is dissolved or suspended in an organic medium such as an inert C5_10 hydrocarbon which may be unsubstituted or is substituted by a C1_4 alkyl radical. Some solvents include pentane, hexane, heptane, octane, cyclohexane, methyl cyclohexane, hydrogenated naphtha and ISOPAR E (a solvent available from Exxon Chemical Company) and mixtures thereof.
After impregnation of the support the catalyst may be calcined.
Calcination can take place by heating in the presence of molecular oxygen at a temperature within the range of 700 to 2000 F (371 to 1093 C), preferably 900 to 1700 F (482 to 927 C) for about 1/2 hour to 50 hours, more preferably 2-10 hours. At least a substantial portion of the chromium in low valence stage is converted to the hexavalent form.
Gas phase polymerization of olefins and particularly alpha olefins has been known for at least about 30 years. Generally a gaseous mixture comprising from 0 to 15 mole % of hydrogen, from 0 to 30 mole % of one or more C2_8 alpha olefins, from 15 to 100 mole % of ethylene, and from 0 to , 75 mole % of nitrogen and/or a non-polymerizable hydrocarbon at a temperature from 50 C to 120 C, preferably from 60 C to 120 C, most preferably from 75 C to about 110 C, and at pressures typically not exceeding 3,500 KPa (about 500 psi), preferably not greater than 2,400 KPa (about 350 psi) are polymerized in the presence of a supported catalyst system in a single reactor.
One of the advantages of the present invention is an improved "kill"
time for a reaction. This may arise when for example there is a power outage or the cycle gas compressor fails and the reaction needs to be stopped ("killed") quickly. As noted above generally gas phase polymerizations are operated below the sintering temperature of the resulting polymer. However, the faster the "kill" system the closer one can operate to the sintering temperature. The practical result is the operation of the reactor at a higher temperature and a greater output. This is important for conventional Ziegler Natta catalysts and chrome based catalyst.
However, for single site catalyst which has a higher reactivity/throughput than Ziegler Natta and chrome catalyst the issue is more important.
The present invention is also useful with a mixed catalyst system where either two or more catalysts (which may or may not be of the same type ¨ e.g. single site-single site or single site ¨Ziegler Natta) are in the same reactor or two or more catalyst are on the same support ( e.g. spray dried together).
The kill gas may be any polar gas or a gas containing one or more polar component such as air, CO, CO2, water vapor, air, pure oxygen, C1-6 alcohols, Ci.6 ketones, and C1_6 aldehydes.. Preferably the kill gas is CO, CO2 or a mixture thereof, optionally together with one or more inert carrier gasses such as N2 to speed its penetration into the fluidized bed of reacting polymer.
The present invention will now be illustrated by the following non limiting examples.
EXAMPLES
Example 1 Applicant's plant at Joffre Alberta is designed for a open vent rapid kill using CO. Applicants use a sophisticated computer control process to operate the plant and the control process is well modeled to permit simulations of plant operation.
When an open vent rapid kill using CO as the kill gas is simulated on computer models the kill time is in the order of 90 seconds.
When the kill procedure of the present invention with kill gas injected at the gas cycle valve, below the distributor plate, in the lower portion of the polymer disengagement section of the reactor and at the inlet to the compressor and the heat exchanger with the compressor still rotating ( without power) and the reactor vent closed the kill time was on the order of 30 seconds and the rise in the temperature of the reactor bed was to a temperature less than the sticking (fusion) temperature of the polymer.

Claims (7)

The embodiments of the invention in which an exclusive privilege or right is claimed are defined as follows:

1. A process for the termination of a fluidized gas phase polymerization reaction of one or more C2-8 olefin monomers in a reactor system, comprising;
a reactor having:, a) an inlet in its lower portion below a diffuser plate;
b) a polymer disengagement zone; and c) a vent in its upper portion leading to a flare stack;
and a reactor gas recycle loop including a compressor and heat exchanger, so that the temperature rise of the bed of polymer in the reactor does not exceed the sticking temperature of the polymer comprising;
recapturing energy from the reaction to increase the moment of inertia of the compressor to provide a wind down time from 5 to 35 seconds for the compressor after commencement of the termination procedure using one of:
a) a turbo expander within the gas recycle loop;
b) a fly wheel on the compressor shaft;
c) batteries;
d) a capacitor; or e) batteries and a capacitor;
while maintaining the reactor gas cycle loop open and injecting a gaseous mixture comprising from 0 up to 90 mole % of one or more inert gases and from 100 to 10 mole % of one or more gaseous catalyst deactivators in an amount sufficient to deactivate catalyst in the reactor system into at least the polymer disengagement zone and the reactor gas cycle loop to disperse said gas mixture thoroughly through the bed of polymer.

2. The process according to claim 1, wherein the inert gas is nitrogen.

3. The process according to claim 2, wherein the gaseous catalyst deactivator is selected from the group consisting of CO2, CO, air, pure oxygen, water vapor, C1-6 alcohols, C1-6 ketones, and C1-6 aldehydes.

4. The process according to claim 3, wherein said one or more C2-8 olefin monomers are selected from the group consisting of ethylene, propylene, 1-butene, and 1-hexene.

5. The process according to claim 4, wherein the gaseous mixture comprising from 0 up to 90 mole % of one or more inert gases and from 100 to 10 mole % of one or more gaseous catalyst deactivators is injected into at least one location selected from below the diffuser plate and within the lowest 10% of the polymer bed above the diffuser plate and into the polymer disengagement zone, the inlet to the gas recycle loop, the inlet to the heat exchanger, and the inlet to the compressor.

6. The process according to claim 5, wherein a portion of the catalyst deactivator is injected into the upper portion of the polymer disengagement zone.

7. The process according to claim 6, wherein the temperature rise of the polymer bed is less than 5° C below the sintering temperature of the polymer in the bed.