Note: Descriptions are shown in the official language in which they were submitted.
9587-1
~0696~t3
BACKGROUND OF THE INVENTION
1. Fie ld of the Invention
.
The invention relates to the catalytic copoly-
merization of ethylene with other copolymerizable monomers
in a fluid bed reactor to produce low (0.900 to 0.925) and
medium (0.926 to 0.940) density ethylene copolymers.
2. Description of the Prior Art
The commercialization of low and medium density
ethylene polymers is much more significant in the United
States, and in the rest of the world, than is the
commercialiæation of high density (> 0.940) ethylene
polymers. The low density polymers are usually made
commercially by homopolymerizing ethylene with ree
radical catalysts under very high pressures (> 15,000 psi)
in tubular and stirred reactors, in the absence of solvents.
The medium density polymers can also be made commercially
by the high pressure process, or by blending high pressure
polyethylene with high density polyethylene made in a low
pressure process with transition metal based catalysts.
The preparation of ethylene polymers in the
absence of solvents under low pressures (~ 40-350 psi)
in a fluid bed reactor, using various supported chromium
containing catalysts, is disclosed in U.S. 3,023,203;
U.S. 3,687,920; U.S. 3,704,287; U.S. 3,709,853, Belgium
Patent 773,050 and Netherlands Patent Application
2.
~ ~ .
, ~
9587-1
~0696~8
72-10881. These publications also disclose that the
ethylene polymers produced may be ethylene homopolymers
or copolymers of ethylene and one or more other alpha
olefins.
The disclosures in these patent publications are
primarily concerned with the preparation of high density
ethylene polymers. Furthermore, because of the technical
difficulties involved, it has not been possible, prior to
the present invention, to provide a commercially useful
process for the production of low and medium density
ethylene polymers in a low pressure fluid bed process.
In order to provide such a useful process, the catalyst
employed must be one which can, simultaneously, copoly-
merize ethylene with other alpha olefins so as to provide
the desired density range in the copolymer product, provide
a polymer product having a particle size which is
conducive to being readily fluidized in a fluid bed
reactor; provide such a high degree of productivity that
the catalyst residues in the polymer product are so small
as to allow them to remain therein, and thus avoid the
need for catalyst removal steps; provide a polymer product
which can be readily molded in a variety of molding
applications, i.e., provide a polymer product having a
relatively wide melt index range; provide a polymer
product which has a relatively small low molecular weight
fraction content so as to ellow the product to meet
3.
. ~
.. . . .
` ~CH69648 9587-1
Federal Food and Drug Administration standards for
extractables (C 5.5 weight percent at 50C. in n-hexane)
for food contact applications; and be used in solid form
to provide such copolymer products under the operating
conditions which can be readily achieved in a commercial
sized fluid bed reactor.
Thus, attempts to use various prior art catalysts,
for the purposes of attempting to make low to medium density
ethylene polymers in a commercially useful fluid bed
process have not been successful to date, since such
catalysts do not provide the desired combination of
features noted above. For example, certain Ziegler
catalysts provide products which have a very narrow melt
~ntex range (0.0 to ~ < 0.2), and are readily subject to
catalyst poisoning and have a relatively low productivity ~`
as evidenced by a catalyst residue content of greater
~; than about ten parts per million of transition metal.
The Ziegler polymers thus usually have to undergo a
catalyst resitue removal operation.
The supported bis(cyclopen~adienyl)chromium
[II] catalysts disclosed in U.S. 3,687,920; U.S. 3,709,853
and Belgian Patent 773,050 do not readily allow for the
copolymerization of enough of the suitable comonomers with
e~thylene~to provide copolymers having densities below
.,
about 0.945.
Although the family of supported silyl chromate
catalysts disclosed in U.S. 3,324,095, U.S. 3,324,101 and
~ 4.
:' - :'
1o~9648 9587 -1
U.S. 3,704,287 will provide ethylene cop~lymers of
relatively low density, some of thecatalysts in the family
will provide polymer products which have a high content
of small particle sizes which cannot be readily fluidized,
and/or which have a narrow melt index range (0.0 to~
0.2), and/or which have a relatively high n-hexane
extractables content,
The supported chromium oxide catalysts disclosed
in U.S. 2,825,721 and 3,023,203 can be used to provide
low and medium density ethylene copolymers provided that
relatively high ratios of comonomer to ethylene are
employed in the monomer feed stream. However, the copoly-
mers produced have a relatively narrow melt index range
(0,0 to ~ < 0.2), The supported titanated chromium oxide
catalysts disclosed in U.S. 3,622,521 provide copolymers
which havé a significantly higher melt ~ndex range,
Netherlands Patent Application 72-10881 discloses the
use of a supported fluorided and titanated chromium
ox~de catalyst-~or ethylene polymerization purposes.
However U.S. 3,622,521 and Netherlaffds Patent Application
72-10881 do no~ disclose a practical method for making
low to medium density ethylene copolymer~ in a commercially
useful fluid bed process,
lCH6g 6 4 8 9587 -l . .
Thus, based on the technology known prior to
the present invention, it was not possible to make low
to medium density ethylene polymers having a relatively
high melt index of > 0.0 to about 2.0, a relatively low
n-hexane soluble fraction and a relatively low residual .
catalyst content at relatively low temperatures and
pressures in the absence of solvent in a commercially
useful fluid bed process.
SUMMARY OF THE INVENTION
It has now been unexpectedly found that ethylene
copolymers having a density of about 0.900 to 0.940 and
a melt index of > 0.0 to at least about 2.0 which have a
relatively low n-hexane extractables content and residual
catalyst content can be produced at relatively high
productivities for commercial purposes in a fluid bed
process if the ethylene is polymerized in the process of
the present in~ention with one or more C3 to C6 alpha
olefins in the presence of a supported catalyst which
has a speci1c particle size and which contains specific
amounts of chromium, titanium and optionally fluorine.
An object of the present invention is to provide
a process: for producing, with relatively high productivities
and in a low pressure fluid bed process, ethylene copoly-
mers~which have a density of about 0.900 to 0.940, a :
melt index of ~ 0.0 to at least about 2.0, a relatively
6.
.
~..................... . . . : . .
~CU69648 9587-1
low n-hexane extractables content, and a relatively low
residual catalyst content.
BRIEF DESCRIPTION OF THE DRAWINGS
The drawing shows a fluid bed reactor system in
which the catalyst system of the present in~ention may be
employed.
DESCRIPTION OF THE PREFERRED EMBODIMENT
It has now been found that the desired low to
medium density ethylene copolymers may be readily produced
with relatively high productivities in a low pressure fluid
bed reaction process, if the comonomers are copolymerized
under a specific set of operating conditions, as detailed
below, and in the presence of a particulate activated
supported catalyst which contains specific amounts of
chromium, titanium, and optio~ally, fluarine as is also
detailed below.
The Copolymers
The copolymers which may be prepared in the
process of the present invention are copolymers of a
ma~or mol percent ( ~ 85 %) of ethylene, and a minor
mol percent (< 15 %) of one or more C3 to C6 alpha
olefins. These alpha olefins are preferably propylene,
butene-l, pentene-l and hexene-l.
The copolymers have a density of about 0.90Q
to 0.925 for low density polymers and of about 0.926 to
0.940 for medium density polymers. The density of the
polymer, at a given melt index level for the pol~mer, is
7.
.~ .
1CP69648 9S87 -1
primarily regulated by the amount of the C3 to C6
comonomer which is copolymerized with the ethylene. In
the absence of the comonomer, the ethylene would homo-
polymerize with the catalyst of the present invention to
provide homopolymers having a density of about > 0.95.
Thus, the addition of progressively larger amounts of the
comonomers to the polymers results in a progressive
lowering, in approximately a linear fashion, of the dens~ty
of thé polymer. ~he amount of each of the various C3 to
C6 comonomers needed to achieve the same result will vary
from monomer to monomer, under the same reaction conditions.
Thus, to achieve the same results, in terms of
a given density, at a given melt index level, larger molar
amounts of the comonomers would be needed in the order
of C3~ C4 ~ C5 ~ C6-
The melt index of a polymer is a reflection ofits molecular weight. Polymers having a relatively high
molecular weight, have a relati~ely low melt index.
Ultra-high molecular weight ethylene polymers have a
high load (HLMI) melt index of about 0.0 and very high
molecular weight polymers have a high load melt index
i
(HLMI) of about 0.0 to about 1Ø Such high molecular
we~ght polymers are difficult, if not impossi~le, to
mold in conventional injection molding equipment. The
copolymers made in the process of the present invention,
on the other hand, can be readily molded, in such
equipment. They ha~e a standard or normal load melt
.
9587-1
1069~i48
index of ~ 0.0 to at least about 2.0, and preferably of
about 0.1 to 1.5, and a high load melt index (HLMI) of
about 1 to about 100. The melt index of the polymers which
are made in the process of the present invention is a
function of a combination of the ~olymerization temperature
of the reaction, the density of the polymer and the titanium
content of the catalyst. Thus, the melt index is raised
by increasing the polymer~zation temperature and/or by
decreasing the density o the polymer (by increasing the
comonomer/ethylene ratio) and/or by increasing the
titanium content of the catalyst.
The copolymers made in the process of the present
invention have a n-hexane extractables content (at 50C.)
of less than about 12 percent, and preferably of less
than about 5.5 percent. Increasing the fluorine content
of the catalyst improves the rate of incorporation of
the C3 to C6 comonomer in the copolymer. An increase
in 1uorine content, however, also tends to lower the
melt index of the polymers.
The copolymers made in the process of the
present invention ha~e a residual catalyst content, in
terms of parts per million of chromium metal, of the
order of less than about ten parts per million, and
; . preferably of the order of less than about three parts
per million. This catalyst residue content is primarily
~ :
9587-1 ~
~06964~
a function of the productivity of the catalyst. The
productivity of the catalyst is primarily a function of
the chromium content thereof.
The copolymers of the present invention have
an average particle size of the order of about 0.005 to
about 0.06 inches, and preferably of about 0.01 to
about 0.05 inches, in diameter. The particle size is
important for the purposes of readily fluidizing the
polymer particles in the fluid bed reactor, as described
below.
Activated SuPPorted CatalYst
:.
The catalyst used in the process of the present
invention is a chromium oxide (CrO3) based catalyst which
is formed, in general, by depositing a suitable chromium
compound, titanium compound and fluorine compound on a
dried support, and then activating the resulting composite
composition by heating it in air or oxygen at a temperature
of about 300 to about 900C., and preferably at about
700 to 850C., for at least two hours, and preferably
for about 5 to 15 hours. The chromium compound and
titanium compound are usually deposited on the support
from solutions thereof, and the fluorine compound is
usually dry blended with the supported titanium and
chromium compounds, and in such quantities as to
~; .
~ provide, after the activation step, the desired
:,
:
~ ~ 10.
,
'~ :
.. ..
,
1069648 9587-l
levels of Cr, Ti and F in the catalyst. After the com-
pounds are placed on the support and it is activated,
there results a powdery, free-flowing particulate
material. About ~,005 to 1 weight percent of the compasite
catalyst is employed per pound of polymer produced.
The order of the addition of the chromium com-
pound, titanium compound and fluorine compound to the
support is not critical provided that all of the com-
pounds are added before the activation of the composite
catalyst and the support is dried before the titanium
compound is added thereto.
After the activation of the suppGrted catalyst
it contains, based on the combined weight of the support
and the chromium, titanium and fluorine therein,
about 0.05 to 3.0, and preferably about 0.2
to 1.0, weight percent of chromium (calculated as Cr),
about 1.5 to 9.0, and preferably about 4.0
to 7.0 , weight percent of titanium (calculated as Ti),
and
~0.0 to about Z.5, and preferably about 0.1
to 1.0, weight percent of fluorine (calculated as
F)-
The chromium compounds which may be used include
; CrO3, or any compound of chromium which is ignitable to
CrO3 under the activation conditions employed. At least
a portion of the chromium in the supported, activated
catalyst must be in the hexavalent state. Chromium
9587-1
1069648
compounds other than CrO3 which may be used are disclosed
in U.S. 2,825,721 and 3,622,521 and include chromic
acetyl acetonate, chromic nitrate, chromic acetate,
chromic chloride, chromic sulfate, and ammonium
chromate.
Water soluble compounds of chromium, such as
CrO3, are the preferred compounds for use in depositing
the chromium compound on the support from a solution of
the compound. Organic solvent soluble chromium compounds
may also be used.
The titanium compounds which may be used include
all those which are ignitable to TiO2 under the activation
. conditions employed, and include those disclosed in U.S.
3,622,521 and Netherlands Patent Application 72-10881.
These compounds include those having the structures
(R')nTi(OR')m and
(RO)mTi(OR )n
where m is 1, 2, 3 or 4; n is 0, 1, 2 or 3 and
m + n - 4, and,
:20 TiX4
where R is a Cl to C12 alkyl, aryl or cyclo-
alkyl group, and combinations thereof, such as aralkyl,
alkaryl, and the like;
.
12.
':~
~ -~
i. . : . .
9587-1
~0696419
R' is R, cyclopentadienyl, and C2 to C12 alkenyl
groups, such as ethenyl, propenyl, isopropenyl, butenyl
and the like; and
X is chlorine, bromine, fluorine or iodine.
The titanium compounds would thus include
titanium tetrachloride, titanium tetraisopropoxide and
titanium tetrabutoxide. The titanium compounds are more
conveniently deposited on the support from a hydrocarbon
solvent solution thereof.
The titanium (as Ti) is present in the catalyst,
with respect to the Cr (as Cr), in a mol ratio of about
0.5 to 180, and preferably of about 4 to 35.
The fluorine compounds which may be used include
HF, or any compound of fluorine which will yield HF under
the activation conditions employed. Fluorine compounds
other than HF which may be used are disclosed in
Netherlands patent application 72-10881. These compounds -
lnclude ammonium hexafluorosilicate, ammonium tetra-
fluoroborate, and ammonium hexafluorotitanate. The
fluorine compounds are conveniently deposited on the
. support from an aqueous solution thereof, or by dry
. ,~
~lending the solid fluorine compounds with the other -
components of the catalyst prior to activation.
The inorganic oxide materials which may be used
as a support in the eatalyst compositions of the present
invention are porous materials having a high surface area,
that is, a surface area in the range of about 50 to about
1000 square meters per gram, and a particle size of about
. .
~ CH6964~ 9587-1
50 to 200 microns. The inorganic oxides which may be used
include silica, alumina, thoria, zirconia and other
comparable inorganic oxides, as well as mixtures of such
oxides.
The catalyst support which may have the chromium
and/or fluorine compound deposited thereon should be dried
before it is brought into contact with the titanium
compound. This is normally done by simply heating or pre-
drying the catalyst support with a dry inert gas or dry
air prior to use. It has been found that the temperature
of drying has an appreciable effect on the molecular
weight distribution and the melt index of the polymer
produced. The preferred drying temperature is 100 to
300C.
Activation of the supported catalyst can be
accomplishet at nearly any temperature up to about its
sintering temperature. The passage of a stream of dry-
air or oxygen through the supported catalyst during
the activation aids in the displacement of the water -
from the support. Activation temperatures of from
about 300C to 900C for a short period of about
: : :
8i x hours or so should be sufficient if well dried
air or oxygen is used, and the temperature is not
permltted to get so high as to cause sintering of
the~eupport.
14.
,:~ ~ . ;
~C~9648 9587-1
Any grade of support can be used but micro-
spheroidal intermediate density (MSID) silica having a
surface area of 300 square meters per gram, and a pore
diameter of about 200 A, and an average particle size of -
about 70 microns (~v0.0028 inches) (W R. Grace's G-952
~rade), and intermediate density (ID) silica having a
surface area of about 300 m2/gr, a pore diameter of about
160 A and an average particle size of about 103 microns
(^~0.0040 inches) (W R. Grace's G-56 grade) are preferred.
When incorpora~ed in a porous support of high
surface area, as described herein, the chromium forms
active sites on the surface and in the pores of the
support. Although the actual mechanism of the process is
not entirely understood, it is believed that the polymers
begin to grow at the surface as well as in the pores of
the supported catalyst. When a pore grown polymer becomes
large enough in the fluidized bed, it ruptures the support
thereby exposing fresh catalyst sites in the inner pores
of the support. The supported catalyst may thus subdivide
many times during its lifetime in the fluidized bed and
~ ~ thereby enhance the production of low catalyst residue
;~ polymars, thereby eliminating the need for recovering
the catalyst from the polymer particles. If the support
is too large, it may resist rupture thereby preventing
subdivision which would result in catalyst waste. In
addition, a large support may act as a heat sink and cause
: ~
-~ ~ "hot spots" to form.
15^.
. ~ ~
,': ' .
1,~ , . . . . . .
.. .. ...
1069648 9587-1
The Polymerization Reaction
After the activated catalyst has been formed,
the copolymerization reaction is conducted by contacting
a stream of the comonomers, in a fluid bed reactor as
described below, and substantially in the absence of
catalyst poisons such as moisture, oxygen, carbon
monoxide and acetylene, with a catalytically effective
amount of the catalyst at a temperature and at a
pressure sufficient to initiate the polymerization
reaction. The catalyst of the present invention can be
used in the presence of up to about 200 parts per million
of C02.
In order to achieve the desired density ranges
in the copolymers it is necessary to copolymerize enough
; of the 2 C3 comonomers with ethylene to achieve a level
of 1.0 to 15 mol percent of the C3 to C6 comonomer in the
- copolymer. The amount of comonomer needed to achieve this
result will depend on the particular comonomer(s) being
employed and on the fluoride content of the catalyst.
Some increased fluoride content of the catalyst improves
the comonomer incorporation. Further, the various intended
comonomers have different reactivity rates, relative to
the reactivity rate of ethylene, with respect to the
copolymerization thereof with the catalysts of the present
invention. ~Therefore, the amount of comonomer used in the
stream of monomers fed to the reactor will also vary -
depending on the reactivity of the comonomer.
~ 16.
.~ '
loN~g 6 4 8 9587-1
There is provided below a listing of the amounts,
in mols, of various comonomers that must be copolymerized
with ethylene in order to provide polymers having the
desired density range at any given melt index. The
listing also indicates the concentration, in mol %, of
such comonomers which must be present in the gas stream
of monomers which is fed to the reactor.
mol % needed mol % needed
Comonomer in copolymer in gas stream
propylene 3.0 to 15 6 to 30
butene-l 2.5 to 12 6 to 25
pentene-l 2.0 to 9.0 4 ~o 18
hexene-l 1.0 to 7.5 3 to 15
A fluidized bed reaction system which can be
used in the practice of the process of the present inven-
tion is illustrated in Figure 1. With reference thereto
the reactor 10 consists of a reaction zone 12 and a
velocity reduction zone 14.
The reaction zone 12 comprises a bed of growing
polymer particles, formed polymer particles and a minor
amount of catalyst fluidized by the continuous flow of
polymerizable and modifying gaseous components in the form
of make-up feed and recycle gas through the reaction zone.
To maintain a viable fluidized bed, mass gas flow through
the bed must be above the minimum flow required for
fluidization, preferably from about 1.5 to about 10 times
;
17.
11~69648 9587-1
Gmf and more preferably from about 3 to about 6 times Gmf. Gmf
is used in the accepted form as the abbreviation for the
minimum mass gas flow required to achieve fluidization,
C. Y. Wen and Y. H. Yu, "Mechanics of Fluidization'~,
Chemical Engineering Progress Symposium Series, Vol. 62,
p. 100~111 (1966).
It is essential that the bed always contains
particles to prevent the formation of localized "hot
spots" and to entrap and distribute the powdery catalyst
throughout the reaction zone. On start up, the reaction
zone is usually charged with a base of particulate polymer
particles before gas flow is initiated. Such particles
may be identical in nature to the polymer to be fonmed
or different therefrom. When different, they are with-
drawn with the desired formed polymer particles as the
first product. Eventually, a fluidized bed of the desired
particles supplants the start-up bed.
The supported catalyst used in the fluidized bed
..
is preferably stored for service in a reservoir 32 under
a nitrogen blanket.
Fluidization is achieved by a high rate of gas
recycle to and through the bed, typically in the order of
about 50 times the rate of feed of make-up gas. The
fluidized bed has the general appearance of a dense mass
. ~
~ of viable particles in possibly free-vortex flow as created
. ~ .
18.
`, ;
.:
~CH~9 6 4 8 9587-1
by the percolati~n of gas through the bed. The pressure
drop through the bed is equal to or slightly greater than
the mass of the ~ed divided by the cross-sectional area.
It is thus dependent on the geometry of the reactor.
Make-up gas is fed to the bed at a rate equal to
the rate at which particulate polymer product is withdrawn.
The composition of the make-up gas is determined by a gas
analy~er 16 positioned above the bed. The gas analyzer
determines component deficiency in the gas being recycled
and the composition of the make-up gas is adjusted accord-
ingly to maintain an essentially steady state gaseous
composition within the reaction zone.
To insure complete fluidization, the recycle gas
and, where desired, part of the make-up gas are returned to
the reactor at point 18 below the bed. There exists a gas
distribution plate 20 above the point of return to aid
fluidizing the bed.
The portion of the gas stream which does not react
in the bed constitutes the recycle gas which is removed from
the polymerization zone, preferably by passing it into a
velocity reduction zone 14 above the bed where entrained
particles are given an opportunity to drop back into the
bed. Particle return may be aided by a cyclone 22 which
may be part of the velocity reduction zone or exterior
thereto. Where desired, the recycle gas may then be passed
through a filter 24 designed to remove small particles at
high gas flow rates to prevent dus~ from contacting heat
transfer surfaces and compressor blades.
19 .
;
1069648 9587-1
The recycle gas is then passed through a heat
exchanger 26 wherein it is stripped of heat of reactio~
before it is returned to the bed. By constantly removing
heat of reaction, no noticeable temperature gradient
appears to exist within the upper portion of the bed. A
temperature gradient will exist in the bottom 6 to 12 inches
- of the bed, between the temperature of the inlet gas and the
temperature of the remainder of the bed. Thus it has been
observed that the bed acts to almost immediately adjust
the temperature of the recycle gas above this lower 6 to
12 inch bed zone to make it conform to the temperature of
the bed thereby maintaining itself at an essentially
constant temperature under steady state conditions. The
recycle is then compressed in a compressor 28 and returned
to the reactor at its base 18 and to the fluidized bed
through distribution plate 20. The compressor 28 can also
be placed upstream of the heat exchanger 26.
The distribution plate 20 plays an important
role in the operation of the reactor. The fluidized bed
contains growing and formed particulate polymer particles
as well as catalyst particles. As the polymer particles
are hot and possibly active, they must be prevented from
settling, for if a quiescent mass is allowed to exist, any
active catal~st contained therein may continue to react
~nd cause fusion. Diffusing recycle gas through the bed
at a rate sufficient to maintain fluidization at the base
of the bed is, therefore, important. The distribution
plate 20 ser~es this purpose and may be a screen, slotted
20.
106964B
9587-l
plate, perforated plate, a plate of the bubble cap type and
the like. The elements of the plate may all be stationary,
or the plate may be of the mobile type disclosed in U.S.
3,298,792. Whatever its design, it must diffuse the recycle
gas through the particles at the base of the bed to keep
them in a fluidized condition, and also serve to support a
quiescent bed of resin particles when the reactor is not
in operation. The mobile elements of the plate may be used
to dislodge any polymer particles entrapped in or on the plate.
Hydrogen may be used as a chain transfer agent in
the polymerization reaction of the present invention in
amounts varying between about 0.001 to about lO moles of
hydrogen per mole of ethylene and comonomer.
Also, if desired for temperature control of the
system, any gas inert to the catalyst and reactants can
also be present in the gas stream.
It is essential to operate the fluid bed reactor
at a temperature below the sintering temperature of the
. polymer particles. To insure that sintering will not
occur, operating temperatures below the sintering temper-
ature are desired. For the production of the ethylene
copolymers in the process of the present invention an
operating temperature of about 30 to 105C. is preferred,
and a temperature of about 75 to 95C. is most preferred.
Temperatures of about 75 to 9SC. are used to pr~pare
products having a density of about 0.900 to 0.920, and
temperatures of about 85 to 100C. are used to prepare
1CN~648 9587-1
products having a density of about 0.921 to 0.940.
~ he fluid bed reactor is operated at pressures
of up to about 1000 psi, and is preferably operated at a
pressure of from about 150 to 350 psi, with operation
at the higher pressures in such ranges favoring heat
transfer since an increase in pressure increases the
unit volume heat capacity of the gas.
The catalyst is injected into the bed at a
rate equal to its consumption at a point 30 which is
above the distribution plate 20. Preferably, the
catalyst is injected at a point located about 1/4 to
3/4 up the side of the bed. Injecting the catalyst
at a point above the distribution plate is an
important feature of this invention. Since the
catalysts used in the practice of the invention are
highly active, injection into the area below the
distribution plate may cause polymerization to begin
there and eventually cause plugging of the distribution
plate. Injection into the viable bed, instead, aids
in distributing the catalyst throughout the bed and
tends to preclude the formation of localized spots
of high catalyst concentration which may result in
the formation of "hot spots".
Inert gas such as nitrogen is used to carry
the Gatalyst into the bed.
22.
.
1C~69648 9587-1
- The production rate of the bed is solely
controlled by the rate of catalyst injection. The
productivity of the bed may be increased by simply
increasing the rate of catalyst injection and decreased
by reducing the rate of catalyst injection.
Since any change in the rate of catalyst
injection will change the rate of generation of the
heat of reaction, the temperature of the recycle gas
is adjusted upwards or downwards to accommodate the
change in rate of heat generation. This insures
the maintenance of an essentially constant temperature
in the bed. Complete instrumentation of both the
fluidized bed and the recycle gas cooling system, is,
of course, necessary to detect any temperature change
in the bed so as to enable the operator to make a
8uitable adjustment in the temperature of the recycle
gas.
.
Under a given set of operating conditions, the
fluidized bed is maintained at essentially a constant
.height by withdrawing a portion of the bed as product
at a rate equal to the rate of formation of the
particulate polymer product. Since the rate of heat
i ; generation is directly rela~ed to product formation,
a measurement of the temperature rise of the gas across
23,
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~ ~ '
- ,, ,. , - . ~ . :
~9648 9587-1
the reactor (the difference between inlet gas temperature
and exit gas temperature) is detçrminat~ve of the rate of
particulate polymer formation at a constant gas velocity.
The particulate polymer product is preferably
continuously withdrawn at a point 34 at or close to the
distribution piate 20 and in suspension with a portion of
the gas stream which is vented before the particles settle
to preclude further polymerization and sintering when
the particles reach their ultimate collection zone. The
suspending gas may also be used, as mentioned above, to
drive the product of one reactor to anather reactor.
The particulate polymer product is conveniently
and preferably withdrawn through the sequential operation
of a pair of timed valves 36 and 38 defining a segregation
zone 40. While valve 38 is closed, valve 36 is opened to
emit a plug of gas and product to the zone 40 between it
and valve 36 which is then closed. Valve 38 is then
opened to deliver the product to an external recovery
zone. Valve 38 is then closed to wait the next product
recovery operation.
.: ~
Finally, the fluidized bed reactor is equipped
with an aequate venting system to allow venting the bed
dur;ng start up and shut down. The reactor does not
require~the use~of stirring means and/or wall scrapping
means.
24.
~: :
; ''~
1~69648 9587-1
The supported catalyst system of this invention
appears to yield a fluid bed product having an average
particle size between about 0.005 to about 0.06 inches
and preferably about 0.01 to about 0.05 inches wherein
supported catalyst residue is unusually low.
The feed stream of gaseous monomer, with or
without inert gaseous diluents, is fed into the reactor
at a space time yield of about 2 to 10 pounds/hour/cubic
foot of bed volume.
The following Examples are designed to illustrate
the process of the present invention and are not intended
as a limitation upon the scope thereof.
The properties of the polymers produced in the
Examples were determined by the following test methods:
Density ASTM D-1505 - Plaque is
conditioned for one hour at
100C. to approach equilibrium
crystallinity.
Melt Index (MI) ASTM D-1238 - Condition E -
Measured at 190C. - reported
. . ~ .
as grams per 10 minutes.
Flow Rate (HLMI) ASTM D-1238 - Condition F -
Measured at 10 times the
1.
weight used in the melt -~
index te~t above.
Fiow Rate Ratio (FRR) = Flow Rate
Melt Index
25.
; '
. . . . . . ..
..
~- ~C~9648 9587-1
productivity a sample of the resin product
is ashed, and the weight %
of ash is determined; since
the ash is essentially
composed of the supported
catalyst, the productivity
is thus the pounds of
polymer produced p~r pound
of total catalyst consumed.
n-hexane extractables a sample of resin is
lightly pressed into film
samples and extracted with
n-hexane at 50C. for four
hours.
EXAMPLES 1 to 21
A.~ CatalYst Preparation: The catalysts used in Examples 1-21
were prepared as follows:
To a solution of the desired amount of CrO3 in
thre~e liters of distilled water there was added 500 grams
20 ~ of a porous silica support having a particle size of about
70 microns and a surface area of about 300 square meters
per gram. The mixture of the support, water and CrO3 was
stirred~and~allowed to stand for about 15 minutes. It
was then filtered to remove about 2200-2300 ml of solution.
1:
26.
,`~, ~; '
~ : : .
': : . . . . . . . . .. .
~069648
9587-1
The CrO3 loaded silica was then dried under a stream of
nitrogen for about four hours at 200C.
About 400 grams of the supported CrO3 was then
slurried in about 2000 ml of dry isopentane, and then a
desired amount of tetraisopropyl titanate was added to
the slurry. The system was then mixed thoroughly and
then the isopentane was dried by heating the reaction
vessel.
The dried material was then transferred to an
activator (heating vessel) and a desired quantity of
(NH4)2SiF6 was added and admixed. The composition was
then heated under N2 at 50C. for about one hour and
then at 150C. for about one hour to insure that all the
i80pentane was rem~ved and to slowly remove organic
residues from the tetraisopropyl titanate so as to avoid
any danger of a fire. The N2 stream was then replaced
with a stream~of dry air and the catalyst composition ~as
:
activated at 300C. for about two hours and then at 750C.
, ~ :
or 825C. for about eight hours. The activated catalyst
was then cooled with dry air (at ambient temperatures) to
about 150C. and further cooled from 150C. to room
temperature with N2 (at ambient temperature).
The amounts of the chromium, titanium and
fluorine c~ompounds which were added to provide the
desired levels of these elements in the activated
catalyst are as follows:
~ 27.
.. '
1069648
9587-1
Weight % of Weight % of
compound element in
added to the activated
support catalyst
- CrO3 Cr (as Cr)
0.8 0 4
0.6 0.3
0.53 0.26
0.33 0.17
0.13 0.07
Ti(isopropyl)4 Ti (as Ti)
5.6
28 4.5
4.1
(NH4)2siF6 F (as F)
1.5 0.7
0.6 0.3
B: Use of Catalysts in Examples 1 to 21
- A series of 21 experiments were conducted in which
ethylene was copolymerized with butene-l. Each of the
reactLons was conducted for 2 to 4 hours, after equilibrium
was reached, in one or the other of two fluid bed reactor
systems. One system, Reactor A, was as described in the
drawing. It has a lower section 10 feet high and l3 1/2 inches
in (i~ner) diameter, and an upper section which was 16 feet
high and 23 1/2 inches in (inner) diameter. The other
system, Reactor B, had the flared upper section of Reactor A
replaced by a straight sided section which was 16 1/2 feet
; 28.
10696~8 9587-1
high and 13 1/2 inches in (inner) diameter. The lower
section of Reactor B had the same dimensions as those of
the lower section of Reactor A.
EXAMPLES 1 to 8
~ .
Examples 1 to 8 were run in Reactor B under a gas
veloclty of 4 times Gmf and a pressure of 30~ psig. The cata-
lysts ~sed in-thes~ Examples were prepared as disclosed above.
After activation, at 825C., each of the supported
catalysts contained 0.4 weight 7O Cr, 4.5 weight % Ti,
and 0.3 weight % of F. The other reaction conditions
for Examples 1-8 were as shown in Table I below:
TABLE I
C4Hg/ H2/ Space
C2H4 C2H4 Time Yield,
Temp. mol mol lbs/hr/ft3
Example C. ratio Ratio of bed space
1 90 0.07 0.04 5.2
2 89 0.10 -- 8.7
3 90 0.10 -- 5.2
4 90 0.09 -- 6.3
0.11 -- 6.8
6 95 0.085 -- 7.2
7 95 0.07 -- 6.3
~ 8 95 0.07 -- 7.2
: : The copolymers produced in Examples 1-8 had the properties
shown in Table II below:
29.
: .
9587_1
1069648
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` 9587-1
1069648
EXAMPLES 9 to 17
Examples 9 to 15 were run in Reactor B, and
Examples 16 and 17 were'run in Reactor A, under a gas
velocity of 4 times Gmf. The catalysts used in these
examples were prepared as disclosed above. After
activation, at 825C., the supported catalysts contained
4.1 or 5.6 weight 7O of Ti, 0.6 or 1.5 weight % of F and
0.4, 0.26, 0.17 and 0.07 weight % of Cr. The variations
in these catalysts, and the other reaction conditions
for Examples 9 to 17 were as shown in Table III below:
.~ .
, ~ .
,:
31.
.
9587-1
~06964~
_~ ~ ~
.,,
P~
Q~ O ~ U) oo oO 0
~o u~ ~ ~ ~ ~ ~ ~ u~
I x
J O
~ O ~d
~ ~ e ~ o o o o O O o o O
o U~
00 ~ ~rl 00 ~o X 00 0~ 00 X C~ o~
o o o o o o o o o
C`~ o. ~
" C~ e ~ O O O O O O O O O
H
H
~ . ~ .
~4 O O O O O O O O O ''
~1a~ ~rl O O O O O O O O O : ~
.~
~ o I~ ~ r_ I~ ~ I~ I~ 1~ h'~
E~ oo oo oo o~ X co ~o ~o oo
. . . . . . . . .
O O O O O O O O O
O C`l C~ l O ~ ~
o o o o o o o o o
E c~ o ,
32 .
10696~8
9-587-1
The copolymers produced in Examples 9 to 17 had the
properties shown below in Table IV.
o o o o o o o o o
a~ ~Al N t.~
¢ ~ ~ ~ O O O O O O O O O
I .
X ~ ~ ~ ~ ~ ~ ~ U~
3 ~
o o o o o o o o o ''
o a~ o~ o o o o o u~
~1 0
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~ ¢ O O O O O O O O O
~ o o o o o o o o o
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10696~8
9587-1
EXAMPLES 18 to 21
Examples 18 to 21 were run in Reactor B under a
pressure of 300 psig and a gas velocity of 4 times Gmf.
The catalysts used in these examples were prepared as
disclosed above. After activation, at 825C., each of
the supported catalysts contained 0.4 weight %, Cr, 4.5
weight % of Ti and 0.3 weigh~ ~/O of F. The other reaction
conditions for Examples 18 to 21 were as shown in Table
V below: ,
TABLE V
Space
. C4Hg/ Time Yield
Temp, C2H4 lbs/hr/ft3
Example C. mol Ratio of bed space
18 86 0,07 3,7
19 89 0.06 3,7
0.085 4.3
21 95 0.04 3.6
The copolymers produced in Examples 18 to 21 had the :
properties shown In TabLe ~I below:
'
~ 34,
~069648 9587-1 .
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aJ a~.~
c~ ~ ~ ~
td~rl' ~` O O O O
a)
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o~ o ~ o
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U~ _, oo
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o o o o
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35.
.. . . .
~ . .
9587-1
~069648
EXAMPLES 22 to 39
.
A. Catalyst Preparation: The catalysts used in
Examples 22 to 39 were prepared as were the catalysts for
Examples 1 to 21. The source of chromium was Cr~3, the
source of titanium was tetraisopropyl titanate and the
source of F, when used, was (NH4)2SiF6. In some cases,
however, no source of fluorine was used in making the
catalyst.
The supports used for all the catalysts was a
porous silica support having a particLe size of about
70 microns and a surface area of about 300 square meters
per gram.
The catalysts of Examples 22 to 31 were
activated by being heated at 750C. in dry air for about
eight hours, and the catalysts of Examples 32 to 39 were
activated by being heated at 900C. in dry air for about
; eight hours. After activation, the catalysts contained
various amounts of Cr, Ti, and, optionally, F, and these
amounts are listed below in Table VII.
B. Use of Catalysts in Examples 22 to 39
The catalysts were used in each experiment to
copolymerize butene-l with e~hylene at 91C. in Reactor A
under a pressure of 300 psig and at a gas velocity of about
4 times Gmf. The reactions were conducted using a mol ratio
of C4Hg/C2H4 of 0.080 ~ O.002 and a space time yield of
3.9 to 4.8 lbs/hr/ft3 of bed space. The exact values are
shown below in Table VII. Table VII also discloses the
productivity of the catalyst in each experiment, and
various properties of the polymers that were produced.
36;
9587-1
1069648
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