CA2078655A1 - Production of bimodal ethylene polymers in tandem reactors - Google Patents

Production of bimodal ethylene polymers in tandem reactors

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Publication number
CA2078655A1
CA2078655A1 CA 2078655 CA2078655A CA2078655A1 CA 2078655 A1 CA2078655 A1 CA 2078655A1 CA 2078655 CA2078655 CA 2078655 CA 2078655 A CA2078655 A CA 2078655A CA 2078655 A1 CA2078655 A1 CA 2078655A1
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reaction zone
ethylene
catalyst
polymer
reactor
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French (fr)
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Ahmed Hussein Ali
Robert Olds Hagerty
Shimay Christine Ong
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ExxonMobil Oil Corp
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Abstract

F-6373-L(SGC) ABSTRACT

A process is provided for producing a bimodal ethylene polymer blend comprising contacting in a first gas phase, fluidized bed reaction zone under polymerization conditions, a gaseous monomeric composition comprising a major proportion of ethylene and, optionally, hydrogen, with a non-prereduced supported titanium/magnesium precursor catalyst as primary catalyst component in combination with a hydrocarbyl aluminum reducing co-catalyst, the hydrogen/ethylene molar ratio (H2/C2 ratio) being no higher than about 0.3 and the ethylene partial pressure being no higher than about 100 psia, to produce a relatively high molecular weight (HMW) polymer associated with catalyst particles, transferring the HMW/catalyst particles to a second gas phase, fluidized bed reaction zone into which is also fed hydrogen and a gaseous monomeric composition comprising a major proportion of ethylene, under polymerization conditions including an H2/C2 ratio of at least about 0.9 and at least about 8.0 times that in the first reaction zone, and an ethylene partial pressure of at least 1.7 times that in said first reaction zone, to produce a low molecular weight (LMW) polymer deposited on and within the voids of the HMW
polymer/catalyst particles, the resulting bimodal polymer blend obtained from the second reaction zone having a fraction of HMW
polymer of at least about 0.35.

Description

2 0 7 /8 f; é3 5 F-6373-L(SGC) PRCDUCTION OF BIMODAL ETffYLENE POLYMERS

The invention relates to a process for produc mg ethylene polymers of high settled buIk density comprising a mixture of relatively high and low moleclllar weight polymers, by gas-phase, fluidized bed polymerization in tandem reactors.

In accordance with this invention, bimcdal ethylene polymer blends having a desirable combination of processability and mechanical properties and high ættled buIk density are produced by a process including the ~teps of polymerizing gaæous monomeric compositions comprising a major proportion of ethylene in at least two gas phase, fluidized bed reactors operating in the tandem mode under the following conditions. In the first reactor, a gas comprising monomeric composition and, optionally, a small amount of hydrogen, is contacted under polymerization conditions with a supported, non-preredu~ed titani~m/magnesium complex catalyst precursor as hereinafter defined in combination with a hydrocarbyl alumi~um reducing co-catalyst, at a hydrogen/ethylene molar ratio of no higher than about 0.3 and an ethylene partial pressure no higher than about 100 psia such as to produce a relatively high molecular weight (HMW) polymer powder wherein the polymer is deposited on the catalyst particles. m e HMW polymer powder containing the catalyst is then transferred to a second reactor with, optionally, additional co-catalyst which may be the same or different from the co-catalyst utilized in the first reactor but with no additional transition metal catalyst component, tcgether with a gaseous mixture ccmprising hydrogen and monomeric composition wherein additional polymerization is carried out at a hydrogen/ethylene molar ratio of at least about 0.9, the ratio being sufficiently high such that it is at least about 8.0 times that in the first reactor, and an ethylene partial pressure at least about 1.7 times that in the first reactor, to produce a relatively low molecular weight (LMW) polymer much of which is 207~3~

F-6373-L(SGC) deposited on and within the HMW polymer/catalyst particles from the first reactor, such that the fraction of HMW polymer in the bimodal polymer leaving the second reactor is at least ab~ut 0.35.

The foregoing conditions provide for a process wherein the production of fines tending to fcul compressors and other equipment is kept to a relatively low level. Moreover, such conditions provide for an inhibited level of productivity in the first reactor with a resulting increased level of productivity in the second reactor to produoe a bimodal polymer blend having a favorable melt flow ratio (MER, an indication of molecular weight distribution) and a high degree of homogeneity (indicated by low level of gels and low heterogeneity index) caused by a substantial degree of blending of HMW and LMW
polymer in each final p~lymer particle inherently resulting from the process operation. Related to the foregoing effects is the fact that the process is capable of producing bim~dal polymers of relatively high settled bulk density (~), e.g., of at least 21 lb/ft3. m is iB surprising since the supporbed magnesium-titanium complex catalyst precursor utilized in the pro oess generally cannot be used to produ oe polymers of such high fiBD's when used in prior processes, including single stage gas phase fluidized bed processes, unless it is prereduced before use, e.g., with an aluminum alkyl.

me bimodal blend is capable of being processed without undue diffi~llty into films having a superior combination of mechanical properties.

The drawing is a schematic diagram of a process illustrating the invention.

me gaseous monomer entering both reactors may consist wholly of ethylene or may c~mprise a preponderance of ethylene and a minor amount of a comonomer such as a 1-olefin containing 3 to ab~ut 10 carbon atoms. Comonomeric 1-olefins which may be employed æ e, for example, l-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 2 (~ 7 ~3 ~i e5 $
F-6373-L(SGC) l-octene, l-decene, and mixtures thereof. The ccmon~mer may be present in the moncmeric compositions entering either or both reactors.

In many cases, the monomer composition will not be the same in both reactors. For example, in making resin intended for high density film, it is preferred that the monomer enterLng the first reactor contain a minor amount of comonomer such as 1-hexene so that the HMW ccmponent of the bimDdal product is a copolymer, whereas the monomer fed to the second reactor consists essentially of ethylene so that the LMW component of the product is sub6tantially an ethylene homopolymer. When a oomonomer is employed so as to obtain a desired copolymer in either or both reactors, the molar ratio of comonomer to ethylene may be in the range, for example, of about 0.005 to 0.7, preferably about 0.04 to 0.6.

Hydrogen may or may not be used to modulate the molecular weight of the HMW polymer made in the first re~ctor. mus, hydrogen may be fed to the first reactor such that the molar ratio of hydrogen to ethylene (H2/C2 ratio~ is, for example, up to about 0.3, preferab~ly about 0.005 to 0.2. In the second reactor it is necssmary to produce a LMW polymer with a low encugh molecular weight and in sufficient quantity so as to produce a bimodal resin which can be formed, with a minimum of processLng difficulties, into end use products such as films and bottles havLng a superior ocmbination of mechanical properties. For ~his purpose, hydrogen is fed to the second reactor with the ethylene oDntaining monomer such that the hydrogen to ethylene mole ratio in the gas phase is at least about 0.9, preferably in the range of ab wt 0.9 to 5.0 and most preferably in the range of ab~ut 1.0 to 3.5. Moreover, to provide a sufficient difference between the molecular weights of the polymers in the first and second reactor so as to obtain a bimDdal resin product having a wide enough molecular weight distribution nmcmmmary for the desired levels of prooessability and me,chanical properties, the hydrogen to 2Q78~a F-6373-L(SGC) ethylene m~le ratios in the two reactors should be such that the ratio in the second reactor is at least about 8.0 times the ratio in the first reactor, for example in the range 8.0 to 10,000 tLmes such ratio, and preferably 10 to 200 times the ratio in the first reactor.

Utilizing the hydrogen to ethylene ratios set out previously to obtain the desired molecular weights of the HMW and IMW polymers produced in the first and second reactors respectively tends to result in relatively high polymer productivity in the first reactor and relatively low productivity in the second rea~tor.
m is tends to result in turn in a bimodal polymer product containing too little LMW polymer to maintain satisfactory processability. A significant part of this invention lies in the discovery that this effect can be largely overccme by employing ethylene partial pressures in the two reactors so as to reduoe the polymer productivity in the first reactor and raise such productivity in the second reactor. For this purpose, the ethylene partial pressure employed in the first reactor is no higher than about 100 psia, for example in the range of about 15 to 100 psia, preferably in the range of ab~ut 20 to 80 psia, preferably 20 to 50 psia, and the ethylene partial pressure in the second reactor is, for example in the range of akout 26 to 170 psia, preferably about 70 to 120 psia, with the ethylene partial pressures in any specific process being such that the ratio of ethylene partial pressure in the second to that in the first reactor is at least akout 1.7, preferably about 1.7 to 7.0, and more preferably akout 2.0 to 4Ø

In some instanccs, it may be advantageous to add an aIkane, e.g., of abcut 5 to 8 carbon atoms, to the first (HMW) reactor for the purpose of reducing or eliminating static charge which often forms under the conditions employed in this reactor. Such charge, if not removed or reduced, has a tendency to cause catalyst and resin fines to migrate to the wall of the reactor where they may foul pressure taps causing erroneous readings for the bed level.

2~786~1~

F-6373-L~SGC) Preferred aIkanes for this purpose are isopentane which may be used, for example, at a partial pressure in the first reactor of at least akout 40 psi, e.g., 40-50 psi, and n-hexane which may be used, for example, at a partial pressure of at least about 10 psi, e.g., 10-12 psi.

If desired for any purpose, e.g., to control superficial gas velocity or to absorb heat of reaction, an inert gas such as nitrogen may also ke present in one or koth reactors in addition to the mon~mer and hydrogen. mus the total pressure in koth reactors may be in the range, for example, of akout lOo to 600 psig, preferakly about 200 to 350 psig.

The temperature of polymerization in the first reactor may be in the range, for example, of about 60 to 130C, preferably about 60 to 90C, while the temperature in the second reactor may be in the range, for example, of about 80 to 130C, preferably about 90 to 120C. For the purpose of controlling molecular weight and productivity in both reactors, it is preferred that the temperature in the second reactor be at least about 10C higher, preferably akcut 30 to 60C higher than that in the first reactor.

m e residence time of the catalyst in each reactor is controlled so that the pro~uctivity is suppressed in the first reactor and enhanced in the second reactor, consistent with the desired properties of the bimodal polymer product. mus, the residence time may be, for example, a~out 0.5 to 6.0 hours, preferably akout 1.0 to 3.0 hours in the first reactor, and, for example, abcut 1 to 12 h s, preferably abcut 2.5 to 5.0 hours in the second reactor, with the ratio of residence time in the second reactor to that in the first reactor being in the range, for example, of about 5.0 to 0.7, preferably about 2 to 1.

The su~erficial gas velocity throuyh both reactors is sufficiently high to disperse effectively the heat of reaction so as to prevent 207$6~;~
F-6373-L(SGC) the temperature from rising to levels which could partially melt the polymer and shut the reactor down, and high enough to mainta m the integrity of the fluidized beds. Such gas velocitv is in the range, for example, of about 40 to 120, preferably about 50 to 90 cm/sec.

The productivity of the pr~rccc in the first reactor in terms of grams of polymer per gram atom of transition metal in the catalyst multiplied by 106, may be in the range, for example, of about 1.6 to 16.0, preferably about 3.2 to 9.6; in the second reactor, the productivity may be in the range, for example, of about 0.6 to 9.6, preferably about 1.6 to 3.5, and in the overall process, the productivity is m the range, for example, of about 2.2 to 25.6, preferably about 4.8 to 16Ø m e foregoing ranges are basel on analysis of residual catalyst metals in the resin product.

m e polymer produced in the first reactor has a flow index (FI or I21, measured at l90~C in aocordance with ASDM D-1238, Condition F), for example, of about 0.05 to 5, preferably about 0.1 to 3 grams/10 min. and a density in the range, for example, of akout 0.890 to 0.960, preferably about 0.900 to 0.940 grams/cc.

m e polymer produced in the second reactor has a melt index (MI
or I2, measured at 190C in aocordance with ASTM D-1238, Condition E) in the range, for example, of about 10 to 4000, preferably about 15 to 2000 grams/10 min. and a density in the range, far example, of about 0.890 to 0.976, preferably about 0.930 to 0.976 grams/oc. m ese values are calculated based on a single reactor process model using steady state process data.

m e final granular bimodal polymer from the second reactor has a weight fraction of HMW polymer of at least about 0.35, preferably in the range of about 0.35 to 0.75, more preferably about 0.45 to 0.65, a flow index in the range, for exa-mple, of about 3 to 200, preferably about 6 to 100 grams/10 min., a melt flaw ratio (MER, calculated as the ratio of flow index to melt index) in the range, for example, of about 60 to 250, preferably about 80 to 150, a density in the range, for example, of about 0.89 to 0.965, preferably 2 ~ 7 ~ 6 A~ ~

F--6373-LtSGC) about 0.910 to 0.960, an average particle size (APS) in the range, for example, of about 127 to 1270, preferably about 380 to 1100 microns, an~ a fines content (defined as particles which pass through a 120 mesh screen) of less than about 10 weight percent, preferably less than about 6 weight percent. With regard to fines content, it has been found that a very low amount of fines are produced in the first (HM~ reactor and that the percentage of fines changes very little across the second reactor. mis is surprising since a relatively large amount of fines are produced when a single gas phase, fluidized bed system is used to produce a relatively lcw molecular weight (L~W) polymer as defined herein. A probable explanation for this is that in the prooess of this invention, the L~W polymer formed in the second reactor deposits primarily within the void structure of the HMW polymer particles produced in the first reactor, minimizing the formation of L~W fines. miS is indicated by an increase in settled kulk density (SBD) across the second reactor while the APS stays fairly constant.

When pellets are formed from granular resin which was stabilized and ccmpour~ed with two passes on a Brabender extruder to ensure uniform blending, such pellets have a flow index in the range, for example, of about 3 to 200, preferably about 6 to 100 grams/10 min., a melt flow ratio in the range, for example, of about 60 to 250, preferably abaut 80 to 150, and a heterogeneity index (HI, the ratio of the FI's of the granular to the pelle~ed resin) in the range for example of about 1.0 to 1.5, preferably abcut 1.0 to 1.3. HI indicates the relative degree of inter-particle heterogeneity of the granNlar resin.

The catalyst used in the polymerization is a type of Ziegler-Natta catalyst, also referred to in the literature as a coordination catalyst, which comprises:
(i) a catalyst precursor complex or mixture of ccmplexes consisting essentially of magnesium, titanium, a halogen, and an electron donor, as hereinafter defined, supported on an inorganic porous carrier; and (ii) at least one hydrocarbyl aluminum co-catalyst.

2078B~

F-6373-L(SGC) The titanium based ccmplex or mixture of complexes is exemplified by an empirical formwla MgaTi(OR)bXc(ED)d wherein R is an aliphatic or aromatic hydrocarbon radical having 1 to 14 carbon atoms or ooR~
wherein R' is an aliphatic or aromatic hydrocarbon radical having 1 to 14 carbon atoms; each OR group is alike or different; X is Cl, Br, or I, or mixtures thereof; ED is an electron donor, which is a liquid Lewis base in which the precursors of the titanium based complex æe soluble; a is 0.5 to 56; b is O, 1, or 2; c is 1 to 116, particularly 2 to 116; and d is 2 to 85. me complex is formed by reacting appropriate titanium and magnesium compounds in the presence of the electron donor.

A titanium compound which can be Il~P~ in the above pre~arations has the formula Ti(OR)aXb wherein R and X are as defined for component (i) above; a is O, 1 or 2; b is 1 to 4; and a+b is 3 or 4. Suitable ccmpcLnds are TiC13, TiC14, Ti(oC6H5)C13, Ti(OoOCH3)C13 and Ti(OCOC6H5)C13.

A maqnesium compound which may be reacted with the foregoing titanium compound in the presence of an electron donor to form the complex has the formula MgX2 wherein X is as defined for c=rponent (i) above. Suitable examples are MgC12, MgBr2, and MgI2. Anhydrous MgC12 is a preferred CQmpaUnd. Abcut 0.5 to 56, and preferably about 1 to 10, moles of the magnRsium compound are used per mole of titanium oompcund.

The electron donor present in the catalyst composition is an organic compound, liquid at temperatures in the range of about 0C to about 200C. It is also known as a Lewis base. The titanium and magnesium oompourds are b~th soluble in the electron donor.

The electron donors may be selected from the group oonsisting of aIkyl esters of aliphatic and aromatic carboxylic acids, aliphatic ketones, aliphatic amunes, aliphatic alcohols, aIkyl and cycloalkyl ethers, and mixtures thereof, each electron donor 207~65~

F-6373-L(SGC) _g_ having 2 to 20 carbon atams. Among these electron donors, the preferred are alkyl and cycloalkyl ethers having 2 to 20 carbon atams; dialkyl, diaryl, and alkyaryl ketones having 3 to 20 carbon atams; and aIkyl, alkoxy, and alkylaIkoxy esters of aIkyl and aryl carboxylic acids having 2 to 20 carbon atams. The m~st preferred electron donor is tetrahydrofuran. Okher examples of suitable electron donors are methyl formate, ethyl aoetate, butyl a oe tate, ethyl e~hpr~ dioxane, di-n-propyl ether, dibutyl ether, ethyl formate, methyl a oetate, ethyl anisate, ethylene carb~nate, tetrahydropyran, and ethyl propionate.

The co-catalyst may, for example, have the formula AlR"eX' ~g wherein X' is Cl or OR"; R" and R" are saturated aliphatic hydrocarbon radicals having 1 to 14 carbon atams and are alike or different; f is 0 to 1.5; g is 0 or 1; and e + f + g = 3. Examples of suitable R, R', R", and R" radicals are: methyl, ethyl, propyl, iscpropyl, butyl, isobutyl, tert-butyl, pentyl, neopentyl, hexyl, 2-methy1pentyl, heFt~yl, octyl, isooctyl, 2-ethyhexyl, 5,5-dircthyIheKyl, nonyl, isodbcyl, undecyl, dodbcyl, cyclohexyl, c~cloheptyl, and cyclooctyl. Examples of suitable R and R' radicals are pbenyl, phenethyl, methyloxypbenyl, benzyl, tolyl, xylyl, naphthal, and methylnaphthyl. Some examples of useful co-catalysts are triisobutylaluminum, trihexyaluminum, di-isobutylalumLnum, hydride, dihexylal hydride, di-isobutylhexylaluminum, trimethylaluminum, triethylaluminum, diethylalummum chloride, 12(C2H5)3C13, and Al(C2H5)2(OC2H5).
The preferred support for the titanium/magnesium precursor comple~ is silica. Other suitable inorganic oxide suF~crts are aluminum phosphate, alumina, silica/alumina mixtures, silica pretreated with an organoaluminNm ccmpaund such as triethyaluminum, and silica mcdified with diethylzinc, suKh modifier being used in a quantity sufficient to react with the hydroxyl groups on the support which okherwise tend to react with and deactivate part of the titanium in the catalyst, but not in ~fficient quantity to function as a cc-catalyst. A typical support is a solid, particulate material essentially inert to the polymerization. It is used as a dry powder having an average ': - - ' . .

207~6~5 F-6373-L(SGC) particle size of about 10 to 250 microns and preferably about 30 to about 100 microns; a surface area of at least about 3 s~yare meters per gram and preferably at least about 50 square meters per gram; and a pore size of at least about 80 Angstroms and preferably at least about 100 Angstroms. Gene-rally, the amount of support used is that which will p-rovide about 0.01 to about 0.5, and preferably about 0.2 to about 0~35 millimole of transition metal per gram of support. Impregnation of the above-mentioned catalyst precursor into, for example, silica is accomplished by mixing the complex and silica gel in the electron donor solvent followed by solvent removal under reduced pressure and/or elevated temperature.

In most inst~noas, it is preferred that the titanium/magnesium precursor complex not be physically cambined with the hydrocarbyl aluminum co-catalyst prior to being fed to ~he first reactor, but that these components be fed to such reactor separately, and that an additional quantity of the hydrocarbyl aluminum co-catalyst be fed to the second reactor in an amount sufficient to increase catalyst activity in the second reactor. In any case, it is not ncae~ry in the process of this invention to prereduce or activate the titanium/magnesium precursor complex with an amcunt of co-catalyst prior to feeding the complex to the first reactor, i.e., the titanium/magnesium precursor complex is in its original oxidation state as prepared when added to the reactor. If the precursor complex is physically combined with some co-catalyst prior to being fed to the first reactor, it is ~evertheless often advantageous to feed additional quantities of co-catalyst to each reactor to maintain the level of activity of or fully activate the catalyst. The co-catalyst is fed to each reactor neat or as a solution in an inert solvent such as isopentane.

Broad, exemplary ranges and preferred ranges of molar ratios of various components of the foregoing catalyst systems utilizing titanium/magnesium complexes are as follows:

207~

F-6373-L(SCC) Table I
Brcad Exemplary Preferred CatalystccmponentsRanqe Ranae 1. Mg:Ti0.5:1 to 56:1 1.5:1 to 5:1 2. Mg:X0.005:1 to 28:1 0.075:1 to 1:1 3. Ti:X0.01:1 to 0.5:1 0.05:1 to 0.2:1 4. Mg:ED0.005:1 to 28:1 0.15:1 to 1.25:1 5. Ti:ED0.01:1 to 0.5:1 0.1:1 to 0.25:1 6.Total Cb-catalyst:Ti 0.6:1 to 250:1 11:1 to 105:1 7. ED:Al0.05:1 to 25:1 0.2:1 to 5:1 Specific examples of the described catalysts cc~prising a titanium/magnesium ccmplex, and methods for their preparation are disclosed, for example, in U.S. Patent Nos. 3.989,881; 4,124,532, 4,174,429; 4,349,648; 4,379,759; 4,719,193; and 4,888,318; and European Patent application Publication Nos. 0 012 14~; 0 091 135; 0 120 503; and 0 369 436; and the entire disclosures of these patents and publications pertaining to catalysts are inccrpor~ted herein by reference.

Ihe amount of hydrocarbyl alumi~um co-catalyst added to the first reactor is generally in the range, for example, of abaut 2 to 100 gram atoms of co-catalyst metal, e.g., aluminum, per gram atom of transition metal, e.g., titanium, preferably abaut 5 to 50 gram atoms of co-catalyst metal per gram atom of transition metal.
Any amount of co-catalyst added to the second reactor is not included in the foregoing ranges. However, it is preferred that additional co-catalyst be fed to the second reactor to increase catalyst activity.

Referring ncw to the drawing, the titanium/magnesium pre sor complex is fed into first reactor 1 through line 2. Ethylene, ccmoncmer, e.g., 1-hexene, if used, hydrogen, if used, aIkane, e.g., " 2078~
F-6373-L(SGC) isopentane, if used, inert gas such as nitrogen, if used, and co-catalyst, e.g. triethylalumunum (TEAL), æ e fed through line 3 into recycle line 4 where they are combined with recycle gas and fed into the bottom of reactor 1. m e gas velocity is high enough and the size and density of the particles in reactor 1 are such as to form a fluidized or dense bed 5 comprising catalyst particles associated with polymer formed by the polymerization of ethylene and, if present, camonomer within reactor 1. The conditions Ln reactor 1, e.g. partial pressure of ethylene, hydrogen/ethylene molæ ratio, temperature, etc. are controlled such that the polymer which forms is of relatively high molecular weight (HMW). Recycle gas leaving the tcp of reactor 1 through line 4 is recompressed in compressor 6, cooled in heat exchanger 7 after passing through valve 8 and are fed to the bottom of reactor 1 after beLng ccmbined with make-up gases and co-catalyst fram line 3 as described.

Periodically, when sufficient H~W polymer has formed in reactor 1, the polymer and catalyst 1 are transferred to discharge tank 9 by opemng valve 10 while valves 11, 12 and 13 remain closed.
When an amount of the HMW polymer and catalyst from reactor 1 which is desired to be transferred has been fed to discharge tank 9, the transfer system to second reactor 14 is activated by opem ng valve 13 to force the HMW polymer and catalyst into transfer hose 15. Valve 13 is then closed to isolate transfer hose 15 from discharge tank 9 and valve 11 is opened, ensuring that any gases leaking through valve 13 are vented and do not back-leak across valve 10 into reactor 1.
Transfer hose 15 is then pressurized with reactor-cycle gas from reactor 14 by opening valve 16. To minimize upsets in reactor 14, surge vessel 17 is used to store gas for pressuring transfer hose 15.
With valve 16 still in the open position, valve 18 is opened to oonvey HMW polymer and catalyst into reactor 14. Both valves 16 and 18 are left open for a period to sweep transfer hose 15. Valves 18 and 16 are then closed se~uentially. Transfer hose 15 is then vented by opening valve 13, valve 11 having remained open dMring the transfer operation. Discharge tank 9 is then purged with purified nitrogen through line 18A by opening valve 12.

207~

F-6373-L(SGC) During the transfer, cycle gas camprising hydrocarbons and hydrogen leaves reactor 14 thraugh line 19, is campressed by compressor 20, flaws through valve 21 in line 24 and thraugh surge tank 17, valve 16 and pressurized transfer hose 15 as described, thus effect mg the transfer of HMW polymer and catalyst to reactor 14.

After the transfer to reactor 14 is effected, the flaw of gas fram reactor 14 to transfer hose 15 is stapped by closing valves 21 and 16. Ethylene, hydrogen, camonamer, e.g., n-hexene, if used, inert gas such as nitrogen, if used, and co-catalyst or catalyst component, if used, e.g., TEAL, are fed to reactor 14 thraugh line 25 after being combined with unreacted cycle gas leaving the top of reactor 14 through line 19 which is oampressed in campressor 20, cooled in heat exchanger 26 and en~rs the bottom of reactor 14 thrcugh line 27.
The gas velocity and size and density of the particles in reactor 14 are such as to form fluidized or dense bed 28 of bimcdal polymer particles associated with the catalyst, including the transition metal primary catalyst camponent added to reactor 1. The conditions in reactor 14, e.g., partial pressure of ethylene, hydrogen/ethylene ratio and temperature, are controlled such that a relatively law molecular weight (LMW) polymer forms primarily within the voids of the HMW polymer/catalyst particles transferred fram reactor 1. After a sufficient amount of LMW polymer has farmed resulting in a bimodal polymer having a desirable molecular weight distribution and ather prcperties, the polymer is transferred to discharge tank 29 by cpening valve 30 while keeping valve 31 closed. After substantially all the polymer has been transferred to discharge tank 29, it is collected by closing valve 30 and apening valve 31, resulti~g in the pre~sure discharge of the final polymer pro~uct thrcugh line 32.
he follawing examples further illustrate the invention.
Example 1 A catalyst was prepared by reacting MgC12, tetrahydrofuran (THF) and TiCl3Ø33 AlCl3, adding the resulting complex to dehydrated silica treated with sufficien~ triethylaluminum to react with the OH graups in the silica but not enaugh to function significantly as partial ---`` 2078~S

F--6373--LISGC) activator or co-catalyst, and drying the resulting silica supported catalyst precursor. m e prooe dure used to prepare the catalyst was substantially that of Example 4 of U.S. Patent No. 4,888,318 exoept that the partial activation of the supported titanium/magnesium precursor ccmplex with tri-n-hexyalumlnum and diethylaluminNm chloride, as shown Ln the patent, was omitted. m e free flowLng catalyst powder contained the following weight percentages of components: Ti, 1.13; Mg, 1.95; Cl, 8.22; THF, 15.4; and Al, 1.41.

Using the foregoing non-prereduoe d catalyst, a gas phase, fluidized bed polymerization prooess was carried out using two reactors operating in the tandem mode as shown in the drawing. m e process included the feeding of 1-butene as ccmonomer and triethylaluminum (TEAL) as co-catalyst to both reactors and isoFentane to the first reactor. Nitrogen was used to control the total pressure in both reactors at about 300 psig. Averages of other conditions in both reactors, which were controlled to produ oe a bimcdal polymer suitable for being formed into high density films, are shown in Table II, wherein IIPC2=~ is the partial pressure of the ethylene, "H2/C2" is the molar ratio of hydrogen to ethylene, "C4/C2" is the molar ratio of 1-butene to ethylene in the gas phase, and "IC5" is the partial pressure of isopentane.

Table II
Reactor 1 (HMW)Reactor 14 (~MW) Temp. (C) 74 110 PC~ (psi) 43 - 84 + 3 7~2 ratiO0.018 2.1 C4/C2 ratio0.085 0.008 IC5 (psi) 43 9 TE~L (PPMW) 510 94 m rcughput (Ib/hr) 24 44 Resid. Time (hrs) 3.0 2.7 2~7~

F-6373-L~SGC) m e HMW polymer leaving reactor 1 was found b,v direct nYasurement to have a flow index (FI or I21) of 0.5 g/10 min. and a density of 0.928 g/cc while the LMW polymer produced m reactor 14 was calclllated from a single reactor process model to have a melt index (MI or I2) of 1000 g/10 min. and a density of 0.975 g/cc.

Prcperties of the bimodal polymer obtained from reactor 14 in granular or pelleted form æ e shown in Table III, where m "SBD"
is the ættled buIk density and "APS" is the average particle size.

Table III
Granular SBD (lb/ft ) 21 Fines (wt.%) 4 APS (inch) 0.019 Productivity (lb/Ib solid cat) 2500 HMW Fraction 0.5~

Pelleted FI (g/10 min) 7.9 Density (g/cc)0.947 Exam~le 2 This example was similar to EXample 1 except that th~ conditions were controlled to produoe a LMW ccmponent of high MI to improve processability. m e process conditions employed in the two reactors are shown in Table IV.

2 0 7 ~ r; ~; r~

F--6373--L(SGC) Table IV
Reactor 1 ~HMW) Reactor 14 (LMW) Temp. (C) 74 llo PC (psi)29 +- 3 70 + 3 H2/2C2 ratio 0.015 2.4 C4/C2 ratio0.050 0.005 TEAL (PPMW)380 94 m roughput (lb/hr) 24 40 Resid. Time (hrs) 3.0 3.0 The HMW polymer leaving reactor 1 was found by direct measurement to have a flow index (FI or I21) of 0.5 g/10 min. and a density of 0.929 g/cc while the LMW polymer produoed in reactor 14 was calculated frcm a single reactor process mcdel to have a melt index (MI or I2) of 1400 g/10 min. and a density of 0.975 g/cc.

Prc~erties of the bimodal polymer obtained from LMW reactor 14 in granular or pelleted form are shcwn in Table V.

ble V
Granular SBD (lb/ft3) 21 Fines (wt.%) 5 APS (inch)0.018 Productivity (Ib/Ib solid cat) 2800 HMW Fraction 0.60 Pelleted FI (g/10 min) 9.0 Density (g/cc) 0.948 20786~.~

F-6373-L(SGC) Example 3 This example was similar to Examples 1 and 2 except that conditions were controlled to test the effect of a higher catalyst bed temperat~re in HMW reactor l. Pr~r~cs conditions employed in each reactor are shown in Table VI.

Table VI
Reactor 1 (HMW~ Reactor 14 (LMW) Ten p. ( C) 100 110 PC (psi)45 ~_ 3 103 ~ 3 H2~C2 ratio0.000 1.8 C4/C2 ratiO0.048 0.026 TE~L (PPMW) 510 94 m roughput (lb/hr) 24 45 Resid. Time (hrs) 3.0 2.6 m e HMW polymer leaving reactor 1 was found by direct measuremrnt to have a flow index (FI or I21) of 0.3 g/10 min. and a densitv of 0.928 g/cc while the IMW polymer produced in reactor 14 was calculated from a single reactor process mcdel to have a melt index (MI or I2) of 600 g/10 min. and a densitv of 0.970 g/cc.

Properties of the bimcdal polymer obtained frc~ IMW reactor 14 are shnwn in Table VII.

Table VII
Granular SBD (lb/ft3) 21 Fines (wt.~) 6 APS (inch) 0.018 Productivit,v (lb/lb solid cat) 1800 HMW Fraction 0.53 ,, 2 0 7 8 6 ~ rtj F--6373--L(SGC) Pelleted FI (g/10 min~6 . 5 Density (g/cc) o.948 Surprisingly, it was found that the non-preredu~sd catalyst of this example yielded a granular bimodal resin having a ccmmercially acceptable settled bulk density (SBD) of 24 Ib/ft3 when used in the tandem mode process of this in~ention, whereas prereduction of the silica-supported TilMg ccmplex has been found to be neclsslry to obtain this level of SBD when the catalyst is used in a single stage gas phase fluldized bed process.

Claims (11)

1. A process for producing a bimodal ethylene polymer blend, which process comprises :
contacting in a first gas phase, fluidized bed reaction zone under polymerization conditions, a gaseous monomeric composition comprising a major proportion of ethylene and, optionally, hydrogen, with a supported titanium/magnesium complex catalyst precursor, as hereinafter defined, as primary catalyst component in combination with a hydrocarbyl aluminum as reducing co-catalyst, the hydrogen/ethylene molar ratio (H2/C2 ratio) being no higher than about 0.3 and the ethylene partial pressure being no higher than about 100 psia, to produce a relatively high molecular weight (HMW) polymer associated with catalyst particles;
transferring the HMW/catalyst particles to a second gas phase, fluidized bed reaction zone into which is also fed hydrogen and a gaseous monomeric composition comprising a major proportion of ethylene, but no additional transition metal component of said catalyst, under polymerization conditions including a H2/C2 ratio of at least 0.9 and at least 8.0 times that in the first reaction zone, and an ethylene partial pressure of at least 1.7 times that in the first reaction zone, to produce a relatively low molecular weight (LMW) polymer deposited on and within the voids of the HMW
polymer/catalyst particles, the resulting bimodal polymer blend obtained from the second reaction zone having a fraction of HMW
polymer of at least about 0.35;
the titanium/magnesium complex being supported on an inorganic porous carrier and having the empirical formula MgaTi(OR)bXc(ED)d wherein R is an aliphatic or aromatic hydrocarbon radical having 1 to 14 carbon atoms or COR' wherein R' is an aliphatic or aromatic hydrocarbon radical having 1 to 14 carbon atoms; each OR group is alike or different; X is Cl, Br, or I, or a mixture thereof; ED is an electron donor, which is a liquid Lewis base in which the precursors of the titanium-based complex are soluble; a is 0.5 to 56; b is 0, 1, or 2; c is 1 to 116; and d is 2 to 85, the complex being added to F-6373-L(SGC) the first reaction zone in its initial oxidation state after it is formed by reacting a compound having the formula Ti(OR)aXb wherein R
and X are as defined for the formula of the complex, a is 0, 1 or 2;
b is 1 to 4; and a+b is 3 or 4, with a compound having the formula MgX2 wherein X is as defined for the formula of said complex, in the presence of the electron donor ED.
2. A process according to claim 1 wherein the monomeric composition fed to either or both reaction zones comprises a minor amount of a 1-olefin containing 3 to 10 carbon atoms as comonomer.
3. A process according to claim 2 wherein the 1-olefin is 1-hexene.
4. A process according to claim 2 or 3 wherein the monomeric composition entering the first reaction zone comprises ethylene and the comonomer, the molar ratio of comonomer to ethylene being from 0.04 to 0.7, and the monomeric composition entering the second reaction zone consists essentially of ethylene.
5. A process according to any preceding claim wherein the H2/C2 ratio in the first reaction zone is from 0.005 to 0.3 and the H2/C2 ratio in the second reaction zone is from 0.9 to 5Ø
6. A process according to any preceding claim wherein the H2/C2 ratio in the second reaction zone is from 1.0 to 3.5, and is from 10 to 200 times the H2/C2 ratio in the first reaction zone.
7. A process according to any preceding claim wherein the ethylene partial pressure in the first reaction zone is from 15 to 100 psia, the ethylene partial pressure in the second reaction zone is from 25 to 170 psia, and the ratio of ethylene partial pressure in the second reaction zone to that in the first reaction zone is from 1.7 to 7Ø

F-6373-L(SGC)
8. A process according to any preceding claim wherein the fraction of HMW polymer in the product obtained from the second reaction zone is from 0.35 to 0.75.
9. A process according to any preceding claim wherein the temperature in the second reaction is at least about 10°C higher than that in the first reaction zone.
10. A process according to any preceding claim wherein the composition in the first reaction zone includes a gaseous alkane having from 5 to 8 carbon atoms in an amount sufficient to reduce or eliminate static charge in the fluidized bed and the resulting tendency of catalyst and resin fines to migrate to the walls of the reaction zone.
11. A process according to claim 10 wherein said alkane is isopentone and/or n-hexane.
CA 2078655 1991-09-20 1992-09-18 Production of bimodal ethylene polymers in tandem reactors Abandoned CA2078655A1 (en)

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Applications Claiming Priority (2)

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CA 2078655 CA2078655A1 (en) 1991-09-20 1992-09-18 Production of bimodal ethylene polymers in tandem reactors

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