U.S. patent application number 11/190481 was filed with the patent office on 2007-02-01 for blow molding polyethylene resins.
Invention is credited to Maria A. Apecetche, Kevin Joseph Cann, Ronald S. Eisinger, Mark Gregory Goode, Stephen P. Jaker, John H. Moorehouse, Cliff R. Mure.
Application Number | 20070027276 11/190481 |
Document ID | / |
Family ID | 37335458 |
Filed Date | 2007-02-01 |
United States Patent
Application |
20070027276 |
Kind Code |
A1 |
Cann; Kevin Joseph ; et
al. |
February 1, 2007 |
Blow molding polyethylene resins
Abstract
Disclosed herein are various processes, including continuous
fluidized-bed gas-phase polymerization processes for making a high
strength, high density polyethylene copolymer, comprising
(including): contacting monomers that include ethylene and
optionally at least one non-ethylene monomer with fluidized
catalyst particles in a gas phase in the presence of hydrogen gas
at an ethylene partial pressure of 100 psi or more and a
polymerization temperature of 105.degree. C. or less to produce a
polyethylene copolymer having a density of 0.945 g/cc or more and
an ESCR Index of 1.0 or more wherein the catalyst particles are
prepared at an activation temperature of 700.degree. C. or less,
and include silica, chromium, and titanium.
Inventors: |
Cann; Kevin Joseph; (Rocky
Hill, NJ) ; Eisinger; Ronald S.; (Charleston, WV)
; Goode; Mark Gregory; (Hurricane, WV) ;
Moorehouse; John H.; (Kendall Park, NJ) ; Mure; Cliff
R.; (Hillsborough, NJ) ; Jaker; Stephen P.;
(Woodbridge, NJ) ; Apecetche; Maria A.;
(Bridgewater, NJ) |
Correspondence
Address: |
Univation Technologies, LLC
Suite 1950
5555 San Felipe
Houston
TX
77056
US
|
Family ID: |
37335458 |
Appl. No.: |
11/190481 |
Filed: |
July 27, 2005 |
Current U.S.
Class: |
526/95 ; 526/104;
526/129; 526/352; 526/901; 526/905 |
Current CPC
Class: |
C08F 210/08 20130101;
C08F 2500/14 20130101; C08F 2500/12 20130101; C08F 2500/13
20130101; C08F 2500/14 20130101; C08F 210/14 20130101; C08F 2500/12
20130101; C08F 2500/04 20130101; C08F 2/34 20130101; C08F 2500/13
20130101; C08F 210/16 20130101; C08F 210/16 20130101; C08F 2500/04
20130101; C08F 210/16 20130101; C08F 210/16 20130101; C08F 210/16
20130101; C08F 4/24 20130101 |
Class at
Publication: |
526/095 ;
526/901; 526/905; 526/104; 526/352; 526/129 |
International
Class: |
C08F 4/06 20060101
C08F004/06 |
Claims
1. A continuous fluidized-bed gas-phase polymerization process for
making a high strength, high density polyethylene copolymer,
comprising: contacting monomers that include ethylene and
optionally at least one non-ethylene monomer with fluidized
catalyst particles in a gas phase in the presence of hydrogen gas
at an ethylene partial pressure of 100 psi or more, to produce a
polyethylene copolymer having a density of 0.945 g/cc or more and
an ESCR Index of 1.0 or more wherein the catalyst particles are
prepared at an activation temperature of 700.degree. C. or less,
and said catalyst consists essentially of silica, chromium, and
titanium.
2. A continuous fluidized-bed gas-phase polymerization process for
making a high strength, high density polyethylene copolymer,
comprising: contacting monomers that include ethylene and
optionally at least one non-ethylene monomer with fluidized
catalyst particles in a gas phase in the presence of hydrogen gas
at an ethylene partial pressure of 100 psi or more, to produce a
polyethylene copolymer having a density of 0.945 g/cc or more, an
ESCR Index of 1.0 or more, and a Die Swell of from 80% to 100%,
wherein the catalyst particles are prepared at an activation
temperature of 650.degree. C. or less, and said catalyst consists
essentially of silica, chromium, and titanium.
3. A continuous gas-phase polymerization process for making a high
strength, high density polyethylene copolymer, comprising:
contacting monomers that include ethylene and optionally at least
one non-ethylene olefin with fluidized catalyst particles in a
gas-phase fluidized-bed reactor in the presence of hydrogen gas at
an ethylene partial pressure of 100 psi or more, to produce a
polyethylene copolymer having a density of from 0.945 to 0.960 g/cc
and an ESCR Index of 1.0 or more, wherein: (a) the catalyst
particles include a silica support that is porous and has a surface
area of less than 400 square meters per gram; (b) the catalyst
particles have been prepared by contacting the silica support with
a combination consisting of a chromium compound and a titanium
compound in a vessel; raising the internal temperature of the
vessel containing the dried particles and dry air to a final
activation temperature of 650.degree. C. or below; to form
activated catalyst particles; lowering the internal temperature of
the vessel containing the activated catalyst particles; removing
air from the vessel using dry nitrogen; and (c) the polyethylene
resin is formed with a bulk density of 20 lb/ft3 or more; (d) the
polyethylene resin has an ESCR Index of 1.0 or more; (e) the
polyethylene resin has a density of from 0.945 to 0.960 g/cc; (f)
the polyethylene resin has a Molecular Weight Distribution of from
15 to 30.
4. The process of claim 1 wherein the ESCR Index is 1.2 or
greater.
5. The process of claim 3 wherein the ESCR Index is 1.2 or
greater.
6. The process of claim 1 wherein the density of the polyethylene
copolymer is from 0.950 to 0.965 and the ESCR Index is 1.2 or
greater.
7. The process of claim 1 wherein the ESCR Index is 1.3 or
greater.
8. The process of claim 3 wherein raising the internal temperature
of the vessel containing the dried particles to a final activation
temperature of 650.degree. C. or below includes raising the
internal temperature of the vessel containing the dried particles
and dry air at a rate of from 25 to 55.degree. C. per hour to the
final activation temperature and the polyethylene resin is formed
at a polymerization temperature of 100.degree. C. or less.
9. The process of claim 3 wherein rising the internal temperature
of the vessel containing the dried particles to a final activation
temperature of 650.degree. C. or below includes raising the
internal temperature of the vessel containing the dried particles
and dry air at a rate of from 25 to 55.degree. C. per hour to the
final activation temperature and the polyethylene resin is formed
at a polymerization temperature of 100.degree. C. or less.
10. The process of claim 1 wherein the polyethylene resin has a
Percent Die Swell of 80% or more.
11. The process of claim 3 wherein the polyethylene resin has a
Percent Die Swell of 80% or more.
12. The process of claim 1 wherein the supported catalyst particles
are prepared using an activation temperature of 650.degree. C. or
less, than 600.degree. C. or less, or 550.degree. C. or less.
13. The process of claim 1 wherein the ESCR Index is 1.4 or
more
14. The process of claim 1 wherein the chromium is present in the
amount of less than 1.0 wt %.
15. The process of claim 1 wherein the non ethylene monomer is
1-butene, 1-hexene, or 1-octene, or mixtures thereof.
16. The process of claim 1 wherein the ethylene partial pressure is
100 psi or greater.
17. The process of claim 1 wherein the catalyst productivity is
4000 lb/lb or more.
18. The process of claim 1 wherein the catalyst productivity is
4000 lb/lb or more with a residence time of 2 hours or more.
19. The process of claim 1 wherein the H2/C2 molar ratio in the
cycle gas is 0.01 or more.
20. The process of claim 1 wherein the monomers arm directed
through a reactor that includes at least a first section having a
first diameter and a second section having a second diameter,
wherein the second diameter is larger than the first diameter.
21. The process of claim 1 wherein oxygen is present in the range
of about 10 to 500 ppbv based on the ethylene feed rate.
22. The process of claim 1 wherein the surface area of the catalyst
support is less than 400 square meters per gram.
23. The process of claim 1 wherein the polyethylene resin is formed
with a bulk density of 20 lb/ft.sup.3 or more.
24. The process of claims 1, 2 or 3 wherein the polymerization is
conducted in the presence of triethyl aluminum.
25. A continuous fluidized-bed gas-phase polymerization process for
making a high strength, high density polyethylene copolymer,
comprising: contacting monomers that include ethylene and
optionally at least one non-ethylene monomer with fluidized
catalyst particles in a gas phase in the presence of hydrogen gas
at an ethylene partial pressure of 100 psi or more to produce a
polyethylene copolymer having a density of 0.945 g/cc or more and
an ESCR Index of 1.5 or more wherein the catalyst particles are
prepared at an activation temperature of 700.degree. C. or less,
and said catalyst consists essentially of silica, chromium, and
titanium.
26. The continuous fluidized-bed gas phase polymerization process
of claim 25, wherein said activation temperature is one of less
than 650.degree. C., or less than 600.degree. C. or less than
550.degree. C.
Description
BACKGROUND
[0001] 1. Field of Inventions
[0002] This patent is related to polyethylene resins and continuous
fluidized-bed gas-phase polymerization processes for making
polyethylene resins.
[0003] 2. Description of Related Art
[0004] As evidenced by the many earlier patents in the field of
fluidized-bed gas phase polymerization, which include some of the
patents listed on the face of this patent, the manufacture of
polyethylene resins in a fluidized-bed gas phase process has been
the subject of a great deal of development effort and expense.
[0005] One of the problems in using a fluidized-bed gas phase
process to form polyethylene resins is making a resin with
desirable properties, particularly properties appropriate for blow
molding purposes, while still having a high productivity and
avoiding production problems, e.g., sheeting and the like.
Therefore, it would be desirable to obtain a resin product with
desirable properties, e.g., sufficiently high Environmental Stress
Crack Resistance (ESCR) and proper die swell, while also achieving
high catalyst productivities, using a fluidized-bed gas phase
process.
[0006] U.S. Pat. No. 5,166,279 refers to processes for the gas
phase co-polymerization of ethylene, in which polyethylene resins
are formed. However, the processes disclosed in that patent are
said to provide products with reduced die swell, in contrast with
the processes herein, which provide polyethylene resins with
increased die swell. Also, the disclosed ESCR levels are low in
relation to the densities of the resins. That is, the ESCR Index
(described below) is below 1.0. Further still, the disclosed
catalyst productivities for low reactor temperatures are low.
[0007] Processes for gas phase polymerization of ethylene are
disclosed in WO 01/77191 but neither ESCR nor die swell is
discussed. Further, the processes involve low productivities.
SUMMARY
[0008] Disclosed herein are various processes, including continuous
fluidized-bed gas-phase polymerization processes for making a high
strength, high density polyethylene copolymer, comprising
(including): contacting monomers that include ethylene and
optionally at least one non-ethylene monomer with fluidized
catalyst particles in a gas phase in the presence of hydrogen gas
at an ethylene partial pressure of 100 psi or more and a
polymerization temperature of 105.degree. C. or less to produce a
polyethylene copolymer having a density of 0.945 g/cc or more and
an ESCR Index of 1.0 or more wherein the catalyst particles are
prepared at an activation temperature of 700.degree. C. or less,
and include silica, chromium, and titanium.
[0009] Also disclosed herein are continuous fluidized-bed gas-phase
polymerization processes for making a high strength, high density
polyethylene copolymer, comprising: contacting monomers that
include ethylene and optionally at least one non-ethylene monomer
with fluidized catalyst particles in a gas phase in the presence of
hydrogen gas at an ethylene partial pressure of 100 psi or more and
a polymerization temperature of 105.degree. C. or less to produce a
polyethylene copolymer having a density of 0.945 g/cc or more, an
ESCR of 45 hours (10% Igepal) or more, and a Die Swell of from 80%
to 100%, wherein the catalyst particles are prepared at an
activation temperature of 700.degree. C. or less, and include
silica, chromium, and titanium.
[0010] Also disclosed is a continuous gas-phase polymerization
process for making a high strength, high density polyethylene
copolymer, comprising: contacting monomers that include ethylene
and optionally at least one non-ethylene olefin with fluidized
catalyst particles in a gas-phase fluidized-bed reactor in the
presence of hydrogen gas at an ethylene partial pressure of 100 psi
or more and a polymerization temperature of 105.degree. C. or less
to produce a polyethylene copolymer having a density of from 0.945
to 0.960 g/cc and an ESCR Index of 1.0 or more, wherein:
[0011] (a) the catalyst particles include a silica support that is
porous and has a surface area of less than 400 square meters per
gram;
[0012] (b) the catalyst particles have been prepared by contacting
the silica support with a chromium compound in a vessel; raising
the internal temperature of the vessel containing the dried
particles and dry air to a final activation temperature of
650.degree. C. or below; maintaining the activation temperature for
a period of from 4 to 8 hours to form activated catalyst particles;
lowering the internal temperature of the vessel containing the
activated catalyst particles; removing air from the vessel using
dry nitrogen; and
[0013] (c) the polyethylene resin is formed at a polymerization
temperature of 105.degree. C. or less;
[0014] (d) the polyethylene resin is formed with a bulk density of
20 lb/ft3 or more;
[0015] (e) the polyethylene resin has an ESCR Index of 1.0 or
more;
[0016] (f) the polyethylene resin has a density of from 0.945 to
0.960 g/cc;
[0017] (g) the polyethylene resin has a Molecular Weight
Distribution of from 15 to 30.
BRIEF DESCRIPTION OF DRAWINGS
[0018] FIG. 1 is a flow diagram of a process for making
polyethylene resin.
DETAILED DESCRIPTION
[0019] A detailed description now follows, for purposes of enabling
a person having ordinary skill in the art of making polyethylene to
make and use the claimed invention, without undue experimentation.
Various terms as used herein are defined below. To the extent a
term used in a claim is not defined below, or elsewhere herein, it
is given the broadest definition persons in the pertinent art have
given that term based on any definition or usage of the term in one
or more printed publications or issued patents, including any
dictionary definitions.
[0020] In specific embodiments, some of which are described below,
polyethylene resins are obtained by particular polymerization
processes in which specific ingredients and processing conditions
are used. For example, a polyethylene resin having improved
properties (e.g., high Environmental Stress Crack Resistance (ESCR)
and desirable Die Swell) can be obtained by directly contacting
monomers that include ethylene and other comonomers (e.g., hexene)
in a fluidized bed reactor, in the presence of oxygen and hydrogen,
at a high ethylene partial pressure (e.g., 100 psi and preferably
higher) using a low polymerization temperature (e.g., less than
105.degree. C. and preferably less than 100.degree. C.) with a
particular catalyst that (a) includes titanium together with a low
amount of chromium (less than 1.0 wt% and preferably 0.50 wt % or
lower), (b) is supported by a porous support particle that consists
essentially of silica, (c) has a low surface area (less than 400
square meters per gram) and (d) is activated in a specific way that
includes careful control of activation temperature, which includes
using an activation temperature within a particular range, e.g.,
greater than 450.degree. C. but less than 700.degree. C. or
650.degree. C. and preferably a narrower range, as specified below.
A polyethylene resin can be produced having superior properties,
particularly a polyethylene useful for blow molding purposes. At
least one of the superior properties is an ESCR Index that is
substantially higher than when certain elements are not utilized,
as demonstrated in the examples below. Furthermore, the
polyethylene resin is produced at high productivities, e.g., 5000
lb/lb and greater (i.e., pounds of polymer per pound of
catalyst).
[0021] At least one of the enhancements offered by the processes
described herein is providing a polyethylene having a superior ESCR
at given density, preferably a density within any of the ranges
specified herein. It is generally recognized that ESCR tends to be
inversely proportional (albeit not a straight line relationship) to
density, so that ESCR tends to generally be higher as resin density
decreases. With the processes herein, however, high ESCR is
achieved even where the density of the polyethylene resin is
relatively high. That is, forming higher density resins results in
less of a decrease in ESCR. This improvement in ESCR performance
can be characterized herein by the ESCR Index, a parameter defined
below. Also, with the processes herein, the resulting polyethylene
resins have superior Die Swell levels. For example, increasing ESCR
can tend to lower Die Swell. In other processes, a polyethylene
resin Die Swell often suffers at certain ESCR levels. But with the
processes herein, a Die Swell of 80% and even higher is obtainable,
e.g., 80% and above, or 85% and above, or 90% and above, or 95% and
above, where the desirable upper limit for Die Swell is 100%.
[0022] One of the key features to successful operation of the
process is utilizing a combination of low activation temperature
for the catalyst and low polymerization temperature. It is
important, for example, that the process use a catalyst prepared
with a particular activation temperature. It has been discovered,
for example, that using an activation temperature higher than a
certain level, e.g., about 700.degree. C. or 750.degree. C., can
lead to catalysts having a detrimental effect on the polymer
produced in the gas phase process, e.g., leading to a polymer with
narrower molecular weight distributions than desired, along with
lower-than-desirable ESCR values. On the other hand, an activation
temperature that is too low, e.g., lower than 500.degree. C.,
particularly lower than about 450.degree. C., can lead to catalysts
with low productivities. But controlling catalyst activation
temperature is not necessarily enough, as demonstrated by the
experimental results below, and other factors are desirably be
implemented, including providing certain process conditions,
preferably high ethylene partial pressures and low polymerization
temperatures. As demonstrated by the Examples, it is the right
combination of the various factors that leads to the best
results.
[0023] In order to minimize the process steps and complexity, it is
advantageous that the final product (i.e., the polyethylene having
the desired properties) be produced as a result of directly
contacting the monomers with the catalyst particles described
herein, e.g., in a single vertical reactor vessel as shown in FIG.
1, as opposed to first contacting the monomers with catalyst
particles in one reactor vessel to form a prepolymer, then
transferring that prepolymer to a different reactor to form the
final polymer. Also, the material that enters the vertical reactor
vessel preferably experiences a decrease in velocity when it passes
from the section with low cross-sectional area to the section with
high cross-sectional area. The catalyst, which is supported on
porous silica, includes both titanium and chromium, and the
catalyst has low amounts of chromium, e.g., lower than 1.0 wt %, or
.ltoreq.0.7 wt %, or .ltoreq.0.5 wt %, or .ltoreq.0.30 wt %.
Preferably, the amount of chromium is less than 1.0 wt %. When
combined with other factors, the polymerization described herein
may be less likely to experience agglomeration and sheeting when
the catalyst particles that are making direct contact with the
monomers are loaded with such low levels of chromium, particularly
less than 1.0 wt %, or less than 0.50 wt %, or even lower.
[0024] In one embodiment, the catalyst is prepared, not only using
low activation temperature, but also according to a controlled
procedure, exemplified by the following. A suitable chromium
compound can be deposited on a suitable support, usually in aqueous
solution. The support can be dried to reduce or eliminate water
before the support, a suitable titanium compound and a suitable
liquid are mixed together. The support can be dried to remove the
liquid and deposit the titanium compound on the support. Then, the
support containing chromium and titanium compounds can be heated in
a suitable heated vessel, first in nitrogen at lower temperatures,
then in an oxygen containing material (e.g. air or pure oxygen) at
a suitable higher temperature for a suitable time.
[0025] Also, it is preferred that the polymerization be conducted
at a high ethylene partial pressure, e.g., at ethylene partial
pressure of .ltoreq.100 psi, or .ltoreq.150 psi; or .ltoreq.200
psi, or .ltoreq.250 psi, or .ltoreq.300 psi. Furthermore,
productivities .ltoreq.4000 lb/lb, or .ltoreq.4500 lb/lb,
.ltoreq.5000 lb/lb, or .ltoreq.5500 lb/lb, or .ltoreq.6000 lb/lb,
or .ltoreq.6500 lb/lb, or .ltoreq.7000 lb/lb, are a preferred
aspect of the process described herein in gas-phase polymerization
fluid bed systems, preferably having a residence time of .ltoreq.2
hours, or .ltoreq.2.5 hours, or .ltoreq.3 hours, or .ltoreq.3.5
hours, at the above-mentioned ethylene partial pressures.
[0026] Furthermore, to achieve a polyethylene with a satisfactory
ESCR, when comonomer is used, the preferred comonomers are
1-butene, 1-hexene, or 1-octene, or mixtures thereof.
Specific Embodiments:
[0027] Different specific embodiments of the processes, some of
which are set forth in certain claims, include (but are not limited
to) the following:
[0028] In one or more of the processes disclosed herein, the ESCR
Index of the polyethylene resin can be at various levels above 1.0,
e.g., 1.1 or above; or 1.2 or above; or 1.3 or above; or 1.4 or
above; or 1.5 or above; or 1.6 or above; or 1.7 or above; or 1.8 or
above; or 1.9 or above; or 2.0 or above; or 2.5 or above; or 2.8 or
above, and such ESCR Index levels can be combined with any of the
measured ESCR levels and densities disclosed herein.
[0029] In at least one specific embodiment, the density of the
polyethylene copolymer ranges from 0.950 to 0.965 g/cc.
[0030] In one or more of the processes described herein, the
raising of the internal temperature of the vessel containing the
dried particles to a final activation temperature, e.g, of
650.degree. C. (of any of the other activation temperatures
identified herein) includes raising the internal temperature of the
vessel containing the dried particles and dry air at a rate of from
25 to 55.degree. C. per hour to the final activation temperature
and the polyethylene resin is formed at any of the polymerization
temperatures described herein, e.g., 100.degree. C. or less.
[0031] In one or more of the processes described above or elsewhere
herein, the Percent Die Swell (Die Swell) of the polyethylene resin
can range from 80% to 100%, such as 80% or more; or 85% or more; or
90% or more; or 95% or more, all with a preferred upper limit of
100%. Examples of Die Swell ranges are 81% and above; or 83% and
above; or 85% and above
[0032] In one or more of the processes described above or elsewhere
herein, the supported catalyst particles are prepared using an
activation temperature of 650.degree. C. or less; or less than
650.degree. C.; or 600.degree. C. or less; or 550.degree. C. or
less; or 500.degree. C. or less.
[0033] In one or more of the processes described above or elsewhere
herein, the ESCR of the polyethylene resin (10% Igepal) is 47 hours
or more; or .ltoreq.48 hours; or .ltoreq.50 hours; or .ltoreq.52
hours; or .ltoreq.54 hours; or .ltoreq.56 hours; or .ltoreq.58
hours; or .ltoreq.70 hours; or .ltoreq.80 hours; or .ltoreq.100
hours.
[0034] In one or more of the processes described above or elsewhere
herein, the chromium in the catalyst is present in the amount of
less than 1.0 wt %; or .ltoreq.0.7 wt %; or .ltoreq.0.5 wt %; or
.ltoreq.0.3 wt %.
[0035] In one or more of the processes described above or elsewhere
herein, the non-ethylene monomer is 1-butene, 1-hexene, or
1-octene, or mixtures thereof.
[0036] In one or more of the processes described above or elsewhere
herein, the ethylene partial pressure is 100 psi ethylene or
greater; or 125 psi ethylene or greater; or 150 psi ethylene or
greater; or 175 psi ethylene or greater; or 200 psi ethylene or
greater; or 250 psi ethylene or greater; or 300 psi ethylene or
greater.
[0037] In one or more of the processes described above or elsewhere
herein, the catalyst productivity is 4000 lb/lb or more; or
.gtoreq.4500 lb/lb; or .gtoreq.5000 lb/lb; or .gtoreq.5500 lb/lb;
or .gtoreq.6000 lb/lb; or .gtoreq.6500 lb/lb.
[0038] In one or more of the processes described above or elsewhere
herein, the catalyst productivity is 4000 lb/lb or more (or any of
the productivities identified above) with a residence time of 2
hours or more; or .gtoreq.2.5 hours; or .gtoreq.3 hours; or
.gtoreq.3.5 hours; or .gtoreq.4 hours.
[0039] In one or more of the processes described above or elsewhere
herein, the H2/C2 molar ratio in the cycle gas is 0.01 or more; or
.gtoreq.0.015; or .gtoreq.0.02; or .gtoreq.0.03; or .gtoreq.0.05;
or .gtoreq.0.10; or .gtoreq.0.15; or .gtoreq.0.20.
[0040] In one or more of the processes described above or elsewhere
herein, the monomers are directed through one or more reactors that
include at least a first section having a first diameter and a
second section having a second diameter, wherein the second
diameter is larger than the first diameter.
[0041] In one or more of the processes described above or elsewhere
herein, oxygen is present in the range of about 10 to 500 ppbv
based on the ethylene feed rate.
[0042] In one or more of the processes described above or elsewhere
herein, the surface area of the catalyst support is less than 400
square meters per gram, or .ltoreq.380 square meters per gram; or
.ltoreq.360 square meters per gram.
[0043] In one or more of the processes described above or elsewhere
herein, the polyethylene resin is formed with a bulk density of 20
lb/ft.sup.3 or more; or .gtoreq.23 lb/ft.sup.3; or .gtoreq.25
lb/ft.sup.3; or .gtoreq.27 lb/ft.sup.3.
[0044] In one or more of the processes described above or elsewhere
herein, the polymerization is conducted in the presence of triethyl
aluminum (TEAl).
Catalyst Preparation
[0045] Certain claims refer to a catalyst that includes chromium
and titanium. Catalysts containing chromium and titanium, useful
for making the polyethylene resins herein, are exemplified by the
catalysts described in U.S. Pat. No. 4,011,382, except that
fluoride is not used in certain embodiments herein. The text of
that patent referring to catalysts and gas phase polymerization is
hereby incorporated by reference except that for the catalysts
described herein fluoride is not required.
[0046] A preferred catalyst for the invention herein is a chromium
oxide (CrO.sub.3) based catalyst which can be formed, in general,
by depositing a suitable chromium compound and a suitable titanium
compound on a support, and then activating the resulting
composition by heating it in an oxygen containing material (e.g.,
air or pure oxygen) at a suitable temperature for a suitable time
(described below).
[0047] The chromium compound and titanium compound can be deposited
on the support from solutions thereof and in such quantities as to
provide, after the activation step, the desired levels of Cr and Ti
in the catalyst. After the compounds are placed on the support and
it is activated, there results a powdery, free-flowing particulate
material.
[0048] The order of the addition of the chromium compound and the
titanium compound to the support is not critical but it is
preferred that all the components are added before the activation
of the composite catalyst, and also that the support is dried to
reduce or eliminate water before the titanium compound is added
thereto.
[0049] After activation, the supported catalyst preferably
contains, based on the combined weight of the support and the
chromium and titanium therein, (a) about 0.1 to 1.5, and preferably
about 0.2 to 1.0, and most preferably 0.3 to 0.7 weight percent of
Cr; and (b) about 1.5 to 9.0, and preferably about 3.0 to 5.0,
weight percent of titanium.
[0050] Chromium compounds. A suitable chromium compound includes
CrO.sub.3, or any compound of chromium which is ignitable to
CrO.sub.3 under the activation conditions employed. At least a
portion of the chromium in the supported, activated catalyst must
be in the hexavalent state. Chromium compounds other than CrO.sub.3
are disclosed in U.S. Pat. Nos. 2,825,721 and 3,622,521 (the
disclosures of which patents are hereby incorporated for reference)
and include chromic acetyl acetonate, chromic nitrate, chromic
acetate, chromic chloride, chromic sulfate, and ammonium chromate.
Water soluble compounds of chromium, such as CrO.sub.3 and chromic
acetate, are the preferred compounds for use in depositing the
chromium compound on the support from a solution of the compound.
Chromium compounds soluble in organic solvents may also be
used.
[0051] Titanium compounds. Any suitable titanium compound can be
used, including particularly those that are ignitable to TiO.sub.2
under the activation conditions employed, and include those
disclosed in U.S. Pat. No. 3,622,521 (hereby incorporated by
reference) and Netherlands Patent Application 72-10881. These
compounds include those having the structures
(R').sub.nTi(OR').sub.m and (RO).sub.mTi(OR').sub.n where m is 1,
2, 3 or 4; n is 0, 1, 2 or 3 and m+n=4, and where R is a C.sub.1 to
C.sub.12 alkyl, aryl or cycloaryl group, and combinations thereof,
and the like, wherein: R' is R, cyclopentadienyl, and C.sub.2 to
C.sub.12 alkenyl groups. These compounds also include those having
the structures TiX.sub.4 wherein X is chlorine, bromine, fluorine
or iodine. Accordingly, suitable titanium compounds 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 mole ratio of about 1 to 100, and
preferably of about 4 to 18.
[0052] Silica supports. An inorganic oxide support is used as a
catalyst support, preferably silica. The inorganic oxides are
necessarily porous materials, e.g., those with a surface area that
is less than 400 square meters per gram, or less than 380, or less
than 360 square meters per gram. The inorganic oxides have a
particle size ranging from about 10 to 200 microns in one
embodiment, and preferably from about 10 to 90 microns. Although
silica is the preferred inorganic oxide, it is contemplated that in
certain situations, the inorganic oxides may also be (or include)
alumina, thoria, zirconia and other comparable inorganic oxides, as
well as mixtures of such oxides.
[0053] Although any grade of support can be used for use with
chromium, one of the preferred silicas is W. R. Grace's 955 grade,
or any other silica having a surface area of about 300 square
meters per gram, a pore volume of about 1.75 cc per gram, and an
average particle size of about 40 microns. A suitable
chromium-containing silica has about 0.5 weight percent chromium
with a surface area of about 300 square meters per gram, a pore
volume of about 1.45 cc per gram, and an average particle size of
about 40 microns (e.g. W. R. Grace's 957HS grade).
[0054] When using 955 or 957 HS grade supports, activation
temperatures higher than a certain level, e.g., about 700.degree.
C., can lead to catalysts that produce polymer with narrower
molecular weight distributions, along with low ESCR values.
[0055] Drying. The catalyst support having the chromium deposited
thereon are preferably dried to reduce or eliminate water before it
is brought into contact with the titanium compound. This can be
done by applying heat in a conventional manner, or otherwise drying
the catalyst support with a dry, inert gas (e.g., nitrogen) or dry
air prior to use. In general, the preferred drying temperature is
140 to 300.degree. C., and a preferred drying time is about 2 to 4
hours, where drying can be conducted by passing a stream of
nitrogen through the catalyst support.
[0056] Activation. The catalyst activation temperature can be
700.degree. C. or below, but for superior performance are
preferably within a range having an upper limit of (i.e., less than
or equal to) about 650.degree. C., or 600.degree. C., or
550.degree. C., or 500.degree. C., with a lower limit of (i.e.,
greater than or equal to) about 350.degree. C., or 400.degree. C.,
or 450.degree. C., where the range can be selected using any of the
combinations of those upper and lower limits. The catalyst
activation time at or near the activation temperature is within a
range having an upper limit of 10 hours, or 8 hours, or 7 hours, or
6 hours, with a lower limit of 1 hour, or 2 hours, or 3 hours or 4
hours. Additional requirements for activation times are set forth
below. However, it has been discovered that, surprisingly, a
polyethylene having superior properties can be obtained when a
particular range of catalyst activation temperature is used in
combination with a particular range of polymerization temperature,
in a gas phase environment, e.g., below 750.degree. C., or
700.degree. C., or 650.degree. C., or 600.degree. C. The
combination of about 600.degree. C. activation temperature
(+/-100.degree. C.) and about 6 hours activation time (+/-30
minutes) is most preferred, although similar combinations based on
the temperatures and times above are also beneficial.
Gas Phase Polymerization
[0057] Referring to FIG. 1, an illustrative polymerization section
150 can include a reactor 160 in fluid communication with one or
more discharge tanks 175 (only one shown), surge tanks 180 (only
one shown), and recycle compressors 190 (only one shown). The
polymerization section 150 can also include more than one reactor
160 arranged in series, parallel, or configured independent from
the other reactors, each reactor having its own associated tanks
175, 180 and compressors 190 or alternatively, sharing any one or
more of the associated tanks 175, 180 and compressors 190. For
simplicity and ease of description, embodiments of the invention
will be further described in the context of a single reactor
train.
[0058] In one or more embodiments, the reactor 160 can include a
reaction zone 162 in fluid communication with a velocity reduction
zone 164. The reaction zone 162 can include a bed of growing
polymer particles, formed polymer particles and catalyst particles
fluidized by the continuous flow of polymerizable and modifying
gaseous components in the form of make-up feed and recycle fluid
through the reaction zone 162.
[0059] Referring now to FIG. 1, a feedstream 105 can be directed to
enter the cycle line before the blower but may also be at any point
in the polymerization system including to the reactor fluid bed,
the expanded section or to the cycle line before or after the
cooler as depicted with alternative feedstream location 147. The
term "feed stream" as used herein refers to a raw material, either
gas phase or liquid phase, used in a polymerization process to
produce a polymer product. For example, a feed stream may be any
olefin monomer including substituted and unsubstituted alkenes
having two to 12 carbon atoms, such as ethylene, propylene,
1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene,
1-decene, 1-dodecene, styrene, and derivatives thereof. The feed
stream also includes non-olefinic gas such as nitrogen and
hydrogen. The feeds may enter the reactor at multiple and different
locations. For example, monomers can be introduced into the
polymerization zone in various ways including direct injection
through a nozzle (not shown in the drawing) into the bed. The feed
stream may further include one or more non-reactive alkanes that
may be condensable in the polymerization process for removing the
heat of reaction. Illustrative non-reactive alkanes include, but
are not limited to, propane, butane, isobutane, pentane,
isopentane, hexane, isomers thereof and derivatives thereof.
[0060] For the purpose of polymerization with chromium oxide type
catalysts, the gas mole ratio of hydrogen to ethylene in the
reactor is typically in the range of about 0 to 0.5, more typically
in the range of 0.01 to 0.4 and most typically in the range of 0.03
to 0.3. A preferred embodiment includes the addition of hydrogen
gas. The use of hydrogen affects the polymer molecular weight and
distribution, and ultimately influences the polymer properties.
[0061] The fluidized bed has the general appearance of a dense mass
of individually moving particles as created by the percolation of
gas through the bed. The pressure drop through the bed is equal to
or slightly greater than the weight of the bed divided by the
cross-sectional area. It is thus dependent on the geometry of the
reactor. To maintain a viable fluidized bed in the reaction zone
162, the superficial gas velocity through the bed must exceed the
minimum flow required for fluidization. Preferably, the superficial
gas velocity is at least two times the minimum flow velocity.
Ordinarily, the superficial gas velocity does not exceed 5.0 ft/sec
and usually no more than 2.5 ft/sec is sufficient.
[0062] In general, the height to diameter ratio of the reaction
zone 162 can vary in the range of from about 2:1 to about 5:1. The
range, of course, can vary to larger or smaller ratios and depends
upon the desired production capacity. The cross-sectional area of
the velocity reduction zone 164 is typically within the range of
about 2 to about 3 multiplied by the cross-sectional area of the
reaction zone 162.
[0063] The velocity reduction zone 164 has a larger inner diameter
than the reaction zone 162. As the name suggests, the velocity
reduction zone 164 slows the velocity of the gas due to the
increased cross sectional area. This reduction in gas velocity
drops the entrained particles into the bed, allowing primarily only
gas to flow from the reactor 160. That gas exiting the overhead of
the reactor 160 is the recycle gas stream 149.
[0064] The recycle stream 149 is compressed in a compressor 190 and
then passed through a heat exchange zone where heat is removed
before it is returned to the bed. The heat exchange zone is
typically a heat exchanger 192 which can be of the horizontal or
vertical type. If desired, several heat exchangers can be employed
to lower the temperature of the cycle gas stream in stages. It is
also possible to locate the compressor downstream from the heat
exchanger or at an intermediate point between several heat
exchangers. After cooling, the recycle stream is returned to the
reactor 160. The cooled recycle stream absorbs the heat of reaction
generated by the polymerization reaction.
[0065] Preferably, the recycle stream is returned to the reactor
160 and to the fluidized bed through a gas distributor plate 195. A
gas deflector 196 is preferably installed at the inlet to the
reactor to prevent contained polymer particles from settling out
and agglomerating into a solid mass and to prevent liquid
accumulation at the bottom of the reactor as well to facilitate
easy transitions between processes which contain liquid in the
cycle gas stream and those which do not and vice versa. An
illustrative deflector suitable for this purpose is described in
U.S. Pat. No. 4,933,149 and 6,627, 713.
[0066] An activated precursor composition with or without an
aluminum alkyl modifier (hereinafter collectively referred to as
catalyst) is preferably stored for service in a catalyst reservoir
155 under a blanket of a gas which is inert to the stored material,
such as nitrogen or argon. Preferably, the catalyst reservoir 155
is equipped with a feeder suitable to continuously feed the
catalyst into the reactor 160. An illustrative catalyst reservoir
is shown and described in U.S. Pat. No. 3,779,712, for example. A
gas that is inert to the catalyst, such as nitrogen or argon, is
preferably used to carry the catalyst into the bed. Preferably, the
carrier gas is the same as the blanket gas used for storing the
catalysts in the catalyst reservoir 155. In one embodiment the
catalyst is a dry powder and the catalyst feeder comprises a
rotating metering disk. In another embodiment the catalyst is
provided as a slurry in mineral oil or liquid hydrocarbon or
mixture such as for example propane, butane, isopentane, hexane,
heptane or octane. An illustrative catalyst reservoir is shown and
described in WO 2004094489. The catalyst slurry may be delivered to
the reactor with a carrier fluid, such as, for example, nitrogen or
argon or a liquid such as for example isopentane or other C3 to C8
alkane. It is possible to modify the catalyst during delivery to
the reactor along the feed addition line with the aluminum alkyl
modifiers, which are described elsewhere herein.
[0067] The catalyst is injected at a point into the bed where good
mixing with polymer particles occurs. For example, the catalyst is
injected into the bed at a point above the distributor plate 195.
Injecting the catalyst at a point above the distribution plate 195
provides satisfactory operation of a fluidized-bed polymerization
reactor. Injection of the catalyst into the area below the
distributor plate 195 could cause polymerization to begin there and
eventually cause plugging of the distributor plate 195. Injection
directly into the fluidized bed aids in distributing the catalyst
uniformly throughout the bed and tends to avoid the formation of
localized spots of high catalyst concentration which can cause "hot
spots" to form. Injection of the catalyst into the reactor 160
above the bed can result in excessive catalyst carryover into the
recycle line 149 where polymerization could occur leading to
plugging of the line 149 and heat exchanger 192.
[0068] The modifier compound (e.g., an aluminum alkyl compound, a
non-limiting illustrative example of which is triethyl aluminum),
can be added to the reaction system either directly into the
fluidized bed or downstream of the heat exchanger 192, in which
case the modifier is fed into the recycle system from a dispenser
156. The amount of modifier added to the polymerization reactor
when using the chromium oxide catalyst and particularly the
titanated chromium oxide based catalyst can be, broadly speaking,
in the range of about 0.005 to about 10 modifier to chromium on a
molar basis, or more narrowly in the range of about 0.01 to 5 and
even more narrowly in the range of about 0.03 to 3 and most
narrowly in the range of 0.05 to 2.
[0069] The polymerization reaction is conducted substantially in
the absence of catalyst poisons such as moisture, oxygen, carbon
monoxide and acetylene. However, oxygen can be added back to the
reactor at very low concentrations to alter the polymer structure
and its product performance characteristics. Oxygen may be added at
a concentration relative to the ethylene feed rate to the reactor
of about 10 to 600 ppbv, and more preferably about 10 to 500
ppbv.
[0070] In order to achieve the desired density ranges in the
copolymers it is necessary to copolymerize enough of the comonomers
with ethylene to achieve a level of about 0 to anywhere from 5 to
10 weight percent of the comonomer in the copolymer. The amount of
comonomer needed to achieve this result will depend on the
particular comonomer(s) being employed, the activation temperature
of the catalyst and its formulation. The ratio of the comonomer to
ethylene is controlled to obtain the desired resin density of
copolymer product.
[0071] A gas analyzer 151 can be used to determine the composition
of the recycle stream and the composition of the make-up feedstream
stream 105 and 147 can be adjusted accordingly to maintain an
essentially steady state gaseous composition within the reaction
zone 162. The gas analyzer 151 can be a conventional gas analyzer
that determines the recycle stream composition to maintain the
ratios of feed stream components. Such equipment is commercially
available from a wide variety of sources. The gas analyzer 151 may
be positioned to receive gas from a sampling point located between
the velocity reduction zone 164 and heat exchanger 192.
[0072] The rate of polymer production in the bed depends on the
rate of catalyst injection and the concentration of monomer(s) in
the reaction zone. The production rate is conveniently controlled
by adjusting the rate of catalyst injection. Since any change in
the rate of catalyst injection will change the reaction rate and
thus the rate at which heat is generated in the bed, the
temperature of the recycle stream entering the reactor is adjusted
to accommodate any change in the rate of heat generation. This
ensures the maintenance of an essentially constant temperature in
the bed. Complete instrumentation of both the fluidized bed and the
recycle stream cooling system is, of course, useful to detect any
temperature change in the bed so as to enable either the operator
or a conventional automatic control system to make a suitable
adjustment in the temperature of the recycle stream.
[0073] 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 the rate of formation of the
particulate polymer product. Since the rate of heat generation is
directly related to the rate of product formation, a measurement of
the temperature rise of the fluid across the reactor (the
difference between inlet fluid temperature and exit fluid
temperature) is indicative of the rate of particulate polymer
formation at a constant fluid velocity if no or negligible
vaporizable liquid is present in the inlet fluid.
[0074] On discharge of particulate polymer product from reactor
160, it is desirable and preferable to separate fluid from the
product and to return the fluid to the recycle line 149. There are
numerous ways known to the art to accomplish this separation. In
one or more embodiments, fluid and product leave the reactor 160
and enter the product discharge tanks 175 (one is shown) through
valve 177, which may be a ball valve designed to have minimum
restriction to flow when opened. Positioned above and below the
product discharge tank 175 are conventional valves 178, 179. The
valve 179 allows passage of product into the product surge tanks
180 (only one is shown).
[0075] In a typical mode of operation, valve 177 is open and valves
178,179 are in a closed position. Product and fluid enter the
product discharge tank 175. Valve 177 closes and the product is
allowed to settle in the product discharge tank 175. Valve 178 is
then opened permitting fluid to flow from the product discharge
tank 175 to the reactor 162. Valve 178 is then closed and valve 179
is opened and any product in the product discharge tank 175 flows
into the product surge tank 180. Valve 179 is then closed. Product
is then discharged from the product surge tank 180 through valve
184. The product can be further purged to remove residual
hydrocarbons and conveyed to storage or compounding. The particular
timing sequence of the valves 177, 178, 179, 184 is accomplished by
the use of conventional programmable controllers which are well
known in the art.
[0076] Another preferred product discharge system which may be
alternatively employed is that disclosed and claimed in U.S. Pat.
No. 4,621,952. Such a system employs at least one (parallel) pair
of tanks comprising a settling tank and a transfer tank arranged in
series and having the separated gas phase returned from the top of
the settling tank to a point in the reactor near the top of the
fluidized bed.
[0077] The fluidized-bed reactor is equipped with an adequate
venting system (not shown) to allow venting the bed during start up
and shut down. The reactor does not require the use of stirring
and/or wall scraping. The recycle line 149 and the elements therein
(compressor 190, heat exchanger 192) is desirably smooth surfaced
and devoid of unnecessary obstructions so as not to impede the flow
of recycle fluid or entrained particles.
[0078] Various techniques for preventing fouling of the reactor and
polymer agglomeration can be used. Illustrative of these techniques
are the introduction of finely divided particulate matter to
prevent agglomeration, as described in U.S. Pat. Nos. 4,994,534 and
5,200,477; the addition of negative charge generating chemicals to
balance positive voltages or the addition of positive charge
generating chemicals to neutralize negative voltage potentials as
described in U.S. Pat. No. 4,803,251. Antistatic substances may
also be added, either continuously or intermittently to prevent or
neutralize electrostatic charge generation. Condensing mode
operation such as disclosed in U.S. Pat. Nos. 4,543,399 and
4,588,790 can also be used to assist in heat removal from the fluid
bed polymerization reactor.
[0079] The conditions for polymerizations vary depending upon the
monomers, catalysts and equipment availability. The specific
conditions are known or readily derivable by those skilled in the
art. For example, the temperatures are within the range of from
about -10.degree. C. to about 120.degree. C., often about
15.degree. C. to about 110.degree. C. Pressures are within the
range of from about 0.1 bar to about 100 bar, such as about 5 bar
to about 50 bar, for example. Additional details of polymerization
can be found in U.S. Pat. No. 6,627,713, which is incorporated by
reference at least to the extent it discloses polymerization
details.
Test Methods
[0080] The following test methods should be utilized to obtain the
numerical values for certain properties and features as set forth
in the claims, e.g. ESCR, density, productivity, chromium content,
or melt indices, although it is understood that those values also
refer to any results obtained by other testing or measuring methods
that might not necessarily be disclosed herein, provided such other
testing or measuring methods are published, e.g., in at least one
patent, patent application, or scientific publication. Also, it is
understood that the values set forth in the claims may have some
degree of error associated with their measurement, whether
experimental, equipment, or operator error; and that any value in
the claim is approximate only, and encompasses values that are plus
or minus (+/-) 10% or even 20% from the measured value.
[0081] ESCR values are based on ASTM D1693, condition B. The
reagent used is either 10% Igepal CO-630 in water or 100% Igepal
CO-630 unless otherwise specified.
[0082] As noted above, the ESCR of any polyethylene resin formed by
any of the claimed processes herein is higher than the ESCR of
polyethylene resins formed by other processes, particularly the gas
phase processes disclosed in U.S. Pat. No. 5,166,279 that are
carried out in a fluidized bed, provided the two resins being
compared for ESCR have the same densities. Generally, for any
polyethylene, ESCR tends to be higher for lower density materials.
Accordingly, for example, a polyethylene formed with a density of
0.950 g/cc will tend to have a higher ESCR than a polyethylene
formed with a density of 0.960. g/cc. Therefore, to make a proper
comparison the ESCR needs to be adjusted to accommodate any density
difference. That comparison can be achieved using a parameter
referred to herein as the "ESCR Index," an empirically derived
value that combines measured ESCR of a polyethylene resin with its
density. The ESCR Index is defined herein as the measured ESCR (10%
Igepal) divided by the product of 0.0481 and
(Density).sup.-142.
[0083] Density values are based on ASTM D1505.
[0084] Flow Index (I.sub.21) values are based on ASTM D1238, run at
190.degree. C., with 21.6 kg weight; the standard designation for
that measurement is 190/21.60.
[0085] Melt Index (I.sub.2) values are based on ASTM D1238, run at
190.degree. C., with 2.16 kg weight; the standard designation for
that measurement is 190/2.16.
[0086] SEC measurements are provided in accordance with the
following procedure, using Polymer Laboratories instrument; Model
HT-GPC-220, Columns Shodex, Run Temp: 140.degree. C., Calibration
Standard: traceable to NIST, Solvent: 1,2,4 Trichlorobenzene.
[0087] The Die Swell ratio S.sub.r is defined as the extrudate
diameter divided by the die diameter, D.sub.e/D.sub.0, where
D.sub.e and D.sub.0 are the diameters of the extrudate and die,
respectively. The percent die swell (%DS) of the polyethylene
compositions was calculated using the following procedure. The
compositions were extruded at 190.degree. C. and a shear rate of
997.2 s.sup.-1. The cylinder of the rheometer used in this
experiment has a bore diameter of 9.5504 mm. The piston speed was
maintained at 82 mm/min. The polymer was passed at a constant rate
through a capillary die 20 mm in length and 1 mm in diameter. The
time (t) in seconds to extrude a rod 15.24 cm in length was
measured. The swell ratio S.sub.r is calculated as follows:
S.sub.r=0.9044 {square root over (t)}
[0088] where t=time to extrude a 15.24 cm rod
The percent die swell (%DS) is defined as
(D.sub.e/D.sub.0-1)*100.
EXAMPLES
[0089] Polyethylene resin samples were prepared using catalysts
made using different activation temperatures, and also using
different polymerization conditions, as noted in Tables 1 and 2
below. All the examples are blow-molding products produced in a
gas-phase, fluidized-bed polymerization pilot reactor. These
examples illustrate the improvement in ESCR of a polyethylene resin
when using certain catalyst specifications and reaction process
conditions.
[0090] Catalysts employed in the Examples were prepared as follows.
About 500 grams of a porous silica support containing 2.5 weight
percent chromium acetate, which amounts to 0.5% Cr content (Grade
957HS chromium on silica, produced by Davison Catalyst division of
W. R. Grace and Co) having a particle size of about 40 microns and
a surface area of about 300 square meters per gram were dried by
passing a stream of nitrogen through it for about 4 hours at about
150.degree. C. About 400 grams of the dried supported chromium
compound were then slurried in about 2330 ml of dry isopentane, and
then 96 grams of tetraisopropyl titanate were added to the slurry.
The system was mixed thoroughly and then isopentane was removed by
heating the reaction vessel. The dried material was then
transferred to a heating vessel where it was heated under dry
nitrogen at 325.degree. C. for about 2 to 4 hours to ensure that
all the isopentane was removed and to slowly remove any organic
residues from the tetraisopropyl titanate so as to avoid any danger
of an explosive mixture within the vessel in the next step. The
nitrogen stream was then replaced with a stream of dry air and the
catalyst composition was heated slowly at a rate of about
50.degree. C. per hour or 100.degree. C. per hour to the specified
"Activation Temperature" (see below) where it was activated for
about 6 hours. The activated catalyst was then cooled with dry air
(at ambient temperature) to about 300.degree. C. and further cooled
from 300.degree. C. to room temperature with dry nitrogen (at
ambient temperature). Activation temperature set points of either
600.degree. C. or 825.degree. C. were employed. Catalysts made
using this procedure and employed in the examples had a composition
of about 0.5 wt % chromium and about 3.8 wt % titanium.
[0091] The nominal specifications for the product in Examples 1-15
and 17-20 of Tables 1 and 2 were: resin density=0.954 g/cm.sup.3,
Flow Index I.sub.21=24. In Example 16 the resin density was raised
to 0.957 g/cm.sup.3. Product was made continuously in the
fluidized-bed reactor. Cycle gas was circulated through the reactor
and heat of reaction was removed in a heat exchanger. Catalyst
powder was continuously introduced into the fluidized bed.
Monomers, hydrogen and oxygen were fed into the cycle gas piping.
Product was transferred intermittently into a product chamber,
depressurized, degassed briefly, and then discharged into a drum.
The drum contained butylated hydroxytoluene, an antioxidant
stabilizer, as a temporary storage stabilizer, and was treated with
a stream of moist nitrogen. Certain conditions in the fluidized-bed
reactor were maintained at a constant value or in a narrow range.
Ethylene partial pressure was about 200 psi except for Example 18
in which it was increased to 250 psi. The H.sub.2/C.sub.2 molar gas
ratio in the cycle gas was maintained at about 0.05. Total reactor
pressure was 340-394 psig. Superficial gas velocity within the
fluidized bed was 1.3-1.8 ft/s. Average residence time of resin in
the reactor ranged from 2.5 to 5 hours. Except for Example 20,
triethyl aluminum, diluted in isopentane, was fed continuously into
the fluidized bed in the range from 0.17 to 2.8 moles aluminum per
mole chromium. Parameters that were changed in the experiments are
summarized in Tables 1 and 2.
[0092] In Examples 1-8 the catalyst that was used had been
activated at 825.degree. C. set point. In those examples, the
reactor temperature was maintained at from 105.degree. C. to
106.degree. C. The ESCR of the polymer product, measured in 10 wt %
Igepal, had a median failure time F.sub.50 ranging from 24 to 42
hours and averaging 33 hours. The breadth of the molecular weight
distribution was characterized by the dispersity index, defined as
the ratio of the weight average molecular weight Mw and the number
average molecular weight Mn (Mw/Mn), and the dispersity index for
these comparative examples ranged from 9.7 to 11.1. Virtually all
of those resin samples had an ESCR Index of less than 1.0.
[0093] In Examples 12-17, 19 and 20 the catalyst used had been
activated at 600.degree. C. set point. The reactor temperature was
between 98.degree. C. and 102.degree. C. The ESCR had a median
failure rate ranging from 48 to 80 hours and averaging 55 hours.
Note that the resin density in Example 16 was relatively high at
0.957 g/cm.sup.3. Surprisingly, ESCR was high, even though ESCR was
expected to decrease in conjunction with an increase in resin
density. These examples employing low activation temperature
catalyst together with lower reactor temperature demonstrated an
improvement in ESCR despite being at higher density than other
similar products. The dispersity index, Mw/Mn, increased to a range
from 17.3 to 26.0 which provided better polymer processability. All
of those resin samples had an ESCR Index of 1.0 or more.
[0094] In Example 11, the catalyst that was used had been activated
at 600.degree. C. set point. However, in that example, the
polymerization was carried out at a temperature of 106.degree. C.
Oxygen was fed to the reactor during this test to make product with
the desired specifications, but the precise amount of added oxygen
was not measured. The ESCR median failure time of polymer produced
was 30 hours. This example demonstrated that high reactor
temperature with a particular catalyst did not give the desired
improved ESCR performance, and that something more was required. A
combination of a certain type of catalyst and process conditions
was needed to achieve the improved product properties.
[0095] In Examples 9 and 10, catalyst activated at 825.degree. C.
was used at polymerization reaction temperatures of 101 and
100.degree. C., respectively. The F.sub.50 10 wt % Igepal ESCR
ranged from 28 to 39 hours as the polymerization temperature was
decreased. Examples 9 and 10 exhibited a broadened polymer
molecular weight distribution relative to Example 8. This
broadening of the MWD was evidenced by the dispersity index, Mw/Mn,
of 15.4 and 14.8 for Examples 9 and 10, respectively but was not as
extensive as found in the other examples. These results showed that
high ESCR products were not obtained when the certain process
conditions were used with catalysts activated at unduly high
temperatures.
[0096] Further improvements to the ESCR were demonstrated in
Examples 13 and 17 with catalyst activated at 600.degree. C.
setpoint. At a 101.degree. C. polymerization temperature, the
F.sub.50 100 wt % Igepal ESCR was 99 hrs, which increased to 123
hrs at a polymerization temperature of 98.degree. C. The
corresponding catalyst productivities at 200 psi ethylene partial
pressures and about 3.0 hr residence times in the reactor were
greater than 6300 lb/lb. The reactor operated well with no
instances of resin agglomeration or disruption to the
polymerization process.
[0097] In Example 18 with catalyst activated at 600.degree. C.
setpoint, the catalyst productivity was increased from 6350 to 8670
lb/lb compared to Example 17 by increasing the ethylene partial
pressure from 200 to 250 psi with no decrease in the F.sub.50 10 wt
% Igepal ESCR. The F.sub.50 100 wt % Igepal ESCR increased from 123
to 175 hr. The reactor continued to operate well at the higher
ethylene partial pressure.
[0098] In Example 19, an approximate tripling of the TEAl feed to
the reactor compared with Example 17 corresponded to an F.sub.50 10
wt % Igepal ESCR of 66 hr compared with 48 hr. Example 19 exhibited
relatively broad molecular weight distribution with Mw/Mn=31.5. In
this example it was demonstrated that molecular weight distribution
of the polymer could be increased by the addition of TEAl
modifier.
[0099] In Example 20 the TEAl addition was discontinued, and the
F.sub.50 10 wt % Igepal ESCR was 47 hrs, essentially the same as
that of Example 17 for which TEAl was present at a 0.22 TEAl/Cr
mole ratio. This result demonstrated that the TEAl modifier was not
needed to achieve the results obtained using a combination of
catalyst activated at lower temperatures with lower reaction
temperatures, which provided a polymer with high ESCR values and a
broadened molecular weight distribution.
[0100] These examples illustrate, among other things, the
surprising effect on ESCR of using a particular combination of
catalyst activation temperature and polymerization temperature at
high ethylene partial pressures in a fluidized-bed gas phase
polymerization process, for polyethylene copolymers, which included
ethylene units as well as other monomeric units. The high ESCR
values were obtained using low activation temperature set points,
e.g., 600.degree. C., together with low polymerization reactor
temperatures, e.g., 98.degree. C. to 102.degree. C. Consistent with
that, intermediate ESCR values were obtained if the polymerization
temperature was increased from its lowest value.
[0101] In examples 8 through 10 which employed catalysts activated
at high temperatures and run at both high and low reaction
temperatures, the polymers produced had percent die swell values
ranging from 75.8 to 78.4. In examples 17 through 20 which employed
catalysts activated at lower reaction temperatures and in which the
processes were run at low reaction temperatures (both with and
without aluminum alkyl present), the polymers produced had
significantly higher percent die swell values ranging between 86.2
and 91.2. Moreover, higher ESCR values were obtained for the
polymers produced in examples 17 through 20 when compared to ESCR
values found in examples 8 through 10. This shows that polymers
with improved ESCR performance can be obtained while at the same
time increasing the percent die swell. TABLE-US-00001 TABLE 1
Example 1 2 3 4 5 Activation temperature, .degree. C. 825 825 825
825 825 TEAl/Cr, mol/mol 0.8 0.7 2.8 2.4 0.6 Ethylene partial
pressure, psi 200 200 200 200 220 H.sub.2/C.sub.2 gas mole ratio
0.05 0.05 0.05 0.05 0.30 C.sub.6/C.sub.2 gas mole ratio 0.0015
0.0019 0.0016 0.0015 0.0013 Oxygen addition, ppbv 297 270 270 400
190 Reactor temperature, .degree. C. 106 106 106 106 105 Residence
time, hr 4.0 3.7 3.3 4.0 2.5 Catalyst productivity, lb/lb 11,100
10,400 12,800 10,600 7,600 Resin settled bulk density, lb/ft.sup.3
21 21 22 20 23 Resin average particle size, in 0.023 0.022 0.029
0.023 0.022 Resin fines, wt % 2.6 3.1 1.4 2.3 2.3 Polymer density,
g/cc 0.9542 0.9528 0.9521 0.9529 0.9553 FI I.sub.21, dg/min 28.7
33.7 18.9 23.7 35.6 MI I.sub.2, dg/min 0.29 0.36 0.16 0.21 0.44 MFR
I.sub.21/I.sub.2 99.0 94.9 121.2 110.7 80.9 Mn 11,400 11,900 14,800
13,400 na Mw 121,800 125,900 149,600 130,400 na Mw/Mn 10.7 10.6
10.1 9.7 na ESCR, 10% Igepal F50, hr 38 39 34 32 28 ESCR Index 1.01
0.85 0.66 0.70 0.88 ESCR, 100% Igepal F50 (hr-ml/g) na na na na na
Percent Die Swell Na Na Na Na Na Example 1 2 3 4 5 Example 6 7 8 9
10 Activation temperature, .degree. C. 825 825 825 825 825 TEAl/Cr,
mol/mol 1.1 2.0 0.26 0.22 0.17 Ethylene partial pressure, psi 220
220 200 200 200 H.sub.2/C.sub.2 gas mole ratio 0.30 0.30 0.050
0.050 0.057 C.sub.6/C.sub.2 gas mole ratio 0.0012 0.0010 0.00085
0.00093 0.00095 Oxygen addition, ppbv 190 290 90 400 383 Reactor
temperature, .degree. C. 105 105 105 101 100 Residence time, hr 2.4
2.5 3.0 2.8 2.7 Catalyst productivity, lb/lb 9,400 8,600 11,060
5,640 5,000 Resin settled bulk density, lb/ft.sup.3 23 22 25 23.1
23.4 Resin average particle size, in 0.025 0.023 0.034 0.024 0.026
Resin fines, wt % 1.4 1.7 0.6 1.3 0.9 Polymer density, g/cc 0.9533
0.9547 0.9538 0.9536 0.9537 FI I.sub.21, dg/min 22.0 21.1 21.8 21.1
21.7 MI I.sub.2, dg/min 0.22 0.18 0.21 0.18 0.19 MFR
I.sub.21/I.sub.2 100.0 117.2 103.5 116.7 117.0 Mn na na 15,023
10,167 9,799 Mw na na 167,504 156,349 145,161 Mw/Mn na na 11.1 15.4
14.8 ESCR, 10% Igepal F50, hr 42 24 24 39 28 ESCR Index 0.98 0.69
0.60 0.95 0.69 ESCR, 100% Igepal F50 (hr-ml/g) na na 42 54 58
Percent Die Swell Na Na 78.4 77.2 75.8 Example 6 7 8 9 10 na = data
not available
[0102] TABLE-US-00002 TABLE 2 Example 11 12 13 14 15 Activation
temperature, .degree. C. 600 600 600 600 600 TEAl/Cr, mol/mol 0.3
0.3 0.30 0.4 0.24 Ethylene partial pressure, psi 200 200 200 200
200 H.sub.2/C.sub.2 gas mole ratio 0.05 0.045 0.051 0.05 0.05
C.sub.6/C.sub.2 gas mole ratio 0.0011 0.0017 0.00103 0.0016 0.0019
Oxygen addition, ppbv Not Meas. 140 240 330 187 Reactor
temperature, .degree. C. 106 102 101 98 98 Residence time, hr 2.5
4.6 2.7 2.5 2.6 Catalyst productivity, lb/lb 8,800 8,900 7,800
5,400 7,200 Resin settled bulk density, lb/ft.sup.3 27 27 22.0 23
24 Resin average particle size, in 0.020 0.022 0.027 0.021 0.026
Resin fines, wt % 5.5 4.7 1.9 4.3 3.0 Polymer density, g/cc 0.9546
0.9552 0.9551 0.9554 0.9553 FI I.sub.21, dg/min 24.7 22.5 25.3 25.4
24.9 MI I.sub.2, dg/min 0.24 0.20 0.23 0.21 0.23 MFR
I.sub.21/I.sub.2 102.9 113.6 110.8 121.0 109.6 Mn Na 9,271 7,912
9,676 7,418 Mw Na 229,627 185,953 167,682 187,414 Mw/Mn Na 24.8
23.5 17.3 25.3 ESCR, 10% Igepal F.sub.50, hr 30 48 50 48 80 ESCR
Index 0.85 1.49 1.53 1.53 2.52 ESCR, 100% Igepal F.sub.50, hr na
157 99 129 215 Percent Die Swell na na 86.4 na na Example 11 12 13
14 15 Example 16 17 18 19 20 Activation temperature, 600 600 600
600 600 .degree. C. TEAl/Cr, mol/mol 0.2 0.22 0.30 0.69 0 Ethylene
partial pressure, 200 200 250 199 200 psi H.sub.2/C.sub.2 gas mole
ratio 0.05 0.052 0.053 0.054 0.050 C.sub.6/C.sub.2 gas mole ratio
0.0007 0.00125 0.00129 0.00128 0.00127 Oxygen addition, ppbv 233
222 190 370 221 Reactor temperature, .degree. C. 98 98 98 98 98
Residence time, hr 2.5 2.8 3.0 2.9 2.8 Catalyst productivity, lb/lb
6,500 6,350 8,670 6,330 5,570 Resin settled bulk density, 23 23.4
23.4 22.6 24.9 lb/ft.sup.3 Resin average particle 0.026 0.026 0.030
0.025 0.024 size, in Resin fines, wt % 3.1 1.8 0.6 1.6 2.3 Polymer
density, g/cc 0.9570 0.9541 0.9547 0.9541 0.9534 FI I.sub.21,
dg/min 23.8 23.4 22.2 21.3 22.2 MI I.sub.2, dg/min 0.21 0.20 0.18
0.15 0.19 MFR I.sub.21/I.sub.2 113.2 119.3 125.9 142.0 117.6 Mn
7,863 7,367 7,391 5,559 8,213 Mw 204,613 176,827 181,258 175,367
157,650 Mw/Mn 26.0 24.0 24.5 31.5 19.2 ESCR, 10% Igepal F.sub.50,
hr 53 48 52 66 47 ESCR Index 2.15 1.26 1.5 1.74 1.11 ESCR, 100%
Igepal F.sub.50, hr 107 123 175 206 123 Percent Die Swell na 87.1
89.3 91.2 86.2 Example 16 17 18 19 20 na = data not available
* * * * *