Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
2 0 7 /8 f; é3 5
F-6373-L(SGC)
--1--
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)
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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)
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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
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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)
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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)
--6--
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)
--7--
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)
--8--
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~
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_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)
--10--
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:
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F-6373-L(SCC)
--11--
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)
-12-
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~
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-13-
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)
-14-
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)
-15-
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
MFR 95
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)
--16--
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
IC5 45 9
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
MFR 105
20786~.~
F-6373-L(SGC)
-17-
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
IC5
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)
--18--
Pelleted
FI (g/10 min~6 . 5
Density (g/cc) o.948
MER 150
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.
