U.S. patent application number 15/502376 was filed with the patent office on 2017-08-17 for process for ethylene polymerization with improved ethylene feed system.
This patent application is currently assigned to Basell Polyolefine GmbH. The applicant listed for this patent is BASELL POLYOLEFINE GMBH. Invention is credited to Rodrigo CARVAJAL, Elke DAMM, Reinhard KUEHL, Harald PRANG, Phil PYMAN.
Application Number | 20170233505 15/502376 |
Document ID | / |
Family ID | 51298584 |
Filed Date | 2017-08-17 |
United States Patent
Application |
20170233505 |
Kind Code |
A1 |
KUEHL; Reinhard ; et
al. |
August 17, 2017 |
PROCESS FOR ETHYLENE POLYMERIZATION WITH IMPROVED ETHYLENE FEED
SYSTEM
Abstract
The present disclosure relates to a process for the preparation
of polyethylene by polymerizing in a slurry ethylene and optionally
one or more C.sub.3 to C.sub.10 alpha-olefins. In some embodiments,
the polymerization is carried out in a cylindrical polymerization
reactor equipped with an agitator for mixing the contents of the
reactor and inducing a flow of the slurry, the ethylene is fed into
the reactor by an ethylene injection system comprising one or more
injection nozzles which project through the bottom reactor head or
through the reactor wall and extend from 0.02-0.5 times the inner
diameter D into the reactor, and the ethylene exits the injection
nozzle with an exit velocity from 10-200 m/s.
Inventors: |
KUEHL; Reinhard; (Bornheim,
DE) ; PRANG; Harald; (Erftstadt, DE) ;
CARVAJAL; Rodrigo; (Bonn, DE) ; DAMM; Elke;
(Bad Vilbel, DE) ; PYMAN; Phil; (Bad Soden,
DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
BASELL POLYOLEFINE GMBH |
Wesseling |
|
DE |
|
|
Assignee: |
Basell Polyolefine GmbH
Wesseling
DE
|
Family ID: |
51298584 |
Appl. No.: |
15/502376 |
Filed: |
August 6, 2015 |
PCT Filed: |
August 6, 2015 |
PCT NO: |
PCT/EP2015/068171 |
371 Date: |
February 7, 2017 |
Current U.S.
Class: |
526/64 |
Current CPC
Class: |
B01F 2215/0481 20130101;
B01F 3/04531 20130101; B01J 8/224 20130101; B01F 7/22 20130101;
C08F 10/02 20130101; B01F 7/00633 20130101; B01J 4/002 20130101;
B01J 8/226 20130101; B01J 19/1875 20130101; C08F 10/02 20130101;
B01F 2215/0431 20130101; B01J 19/0066 20130101; B01J 2208/00902
20130101; C08F 10/02 20130101; B01F 2215/0422 20130101; B01J 19/18
20130101; C08F 2/18 20130101; C08F 2/01 20130101 |
International
Class: |
C08F 10/02 20060101
C08F010/02; B01J 8/22 20060101 B01J008/22 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 7, 2014 |
EP |
14180180.3 |
Claims
1. A process for the preparation of polyethylene by polymerizing in
a slurry ethylene and optionally one or more C.sub.3 to C.sub.10
alpha-olefins at a temperature from 60-95.degree. C. and a pressure
from 0.15-3 MPa; wherein the polymerization is carried out in a
cylindrical polymerization reactor having a cylindrical reactor
wall, a bottom reactor head and a top reactor head and the reactor
has an inner diameter D and is equipped with an agitator for mixing
the contents of the reactor and inducing a flow of the slurry;
wherein the ethylene is fed into the reactor by an ethylene
injection system comprising one or more injection nozzles which
project through the bottom reactor head or through the reactor wall
and extend from 0.02-0.5 times the inner diameter D into the
reactor and wherein the ethylene exits the injection nozzle with an
exit velocity from 10-200 m/s.
2. The process of claim 1, wherein the injection nozzles projecting
through the bottom reactor head or through the reactor wall have a
direction into the reactor, a sloped ethylene outlet with an outlet
tip and an outlet base, and an angle between the direction of the
injection nozzle and the line connecting the outlet tip and the
outer base of from 20-80.degree., and the slope of the ethylene
outlet is oriented with respect to the flow of the slurry such that
the outlet tip is in an upstream position and the outlet base is in
a downstream position with respect to the flow of the slurry.
3. The process of claim 1, wherein the agitator comprises a motor,
a vertical rotating shaft centrally located in the reactor, and one
or more stages of agitator blades attached to the rotating shaft;
and wherein the agitator induces primarily a vertical flow of the
slurry in a circular cross-section around the agitator shaft.
4. The process of claim 1, wherein the vertical flow of the slurry
in the circular cross-section is a downward flow.
5. The process of claim 1, wherein the one or more injection
nozzles project through the bottom reactor head and extend
vertically from 0-0.2 times the inner diameter D into the reactor,
and the horizontal distance from the center of the reactor to the
outlet of the injection nozzles is from 0.1-0.45 times the inner
diameter D.
6. The process of claim 5, wherein the ethylene injection system
comprises at least two injection nozzles, and all injection nozzles
are arranged on a circular line around the reactor center.
7. The process of claim 6, wherein the injection nozzles are
uniformly distributed on the circular line.
8. The process of claim 1, wherein the one or more injection
nozzles project through the cylindrical reactor wall at a wall
passing point positioned in the lower two thirds of the reactor,
and extend from 0.02-0.48 times the inner diameter D into the
reactor.
9. The process of claim 8, wherein the injection nozzles are
inclined downward.
10. The process of claim 9, wherein the horizontal angle between
the direction of the injection nozzle and the horizontal is of from
5-60.degree..
11. The process of claim 8, wherein the flow of the slurry in the
polymerization reactor has a circular component, and the injection
nozzles are inclined towards the downstream direction of the
circular flow.
12. The process of claim 11, wherein the radial angle between the
direction of the injection nozzle and a line running from the wall
passing point to the center of the reactor is from
5-60.degree..
13. The process of claim 8, wherein the outlets of the injection
nozzles are located at a position below the agitator.
14. The process of claim 8, wherein the wall passing points are
arranged at the same height of the reactor and uniformly
distributed around the reactor.
15. The process of claim 1, wherein the reactor is in a
multi-reactor polymerization system.
16. A process for the preparation of polyethylene by polymerizing
in a slurry ethylene and optionally one or more C.sub.3 to C.sub.10
alpha-olefins at a temperature from 60-95.degree. C. and a pressure
from 0.15-3 MPa; wherein the polymerization is carried out in a
cylindrical polymerization reactor having a cylindrical reactor
wall, a bottom reactor head and a top reactor head, the reactor has
an inner diameter D and is equipped with an agitator for mixing the
contents of the reactor and inducing a flow of the slurry; wherein
the ethylene is fed into the reactor by an ethylene injection
system comprising one or more injection nozzles which project
through the cylindrical reactor wall at a wall passing point
positioned in the lower two thirds of the reactor and extend from
0.02-0.48 times the inner diameter D into the reactor; and wherein
the ethylene exits the injection nozzle with an exit velocity from
10-200 m/s.
17. The process of claim 16, wherein the injection nozzles are
inclined downward and the horizontal angle between the direction of
the injection nozzle and the horizontal is from 5-60.degree..
18. The process of claim 16, wherein the flow of the slurry in the
polymerization reactor has a circular component, the injection
nozzles are inclined towards the downstream direction of the
circular flow, and the radial angle between the direction of the
injection nozzle and a line running from the wall passing point to
the center of the reactor is from 5-60.degree..
19. The process of claim 17, wherein the outlets of the injection
nozzles are located at a position below the agitator.
20. A process for the preparation of polyethylene by polymerizing
in a slurry ethylene and optionally one or more C.sub.3 to C.sub.10
alpha-olefins at a temperature from 60-95.degree. C. and a pressure
from 0.15-3 MPa; wherein the polymerization is carried out in a
multi-reactor system comprising a cylindrical polymerization
reactor having a cylindrical reactor wall, a bottom reactor head
and a top reactor head, wherein the reactor has an inner diameter D
and is equipped with an agitator for mixing the contents of the
reactor and inducing a flow of the slurry; wherein the ethylene is
fed into the reactor by an ethylene injection system comprising one
or more injection nozzles which project through the bottom reactor
head or through the reactor wall and extend from 0.02-0.5 times the
inner diameter D into the reactor and wherein the ethylene exits
the injection nozzle with an exit velocity from 10-200 m/s.
Description
FIELD OF THE INVENTION
[0001] The present disclosure relates to a process for ethylene
polymerization. In some embodiments, the present disclosure relates
to an ethylene slurry polymerization process having reduced fouling
through an improved ethylene feed system.
BACKGROUND OF THE INVENTION
[0002] Various processes can be used to produce polyethylene,
including gas phase processes, solution processes, and slurry
processes. In ethylene slurry polymerization processes, diluents
such as hexane or isobutane may be used to dissolve the ethylene
monomer, comonomers and hydrogen, and the monomer(s) are
polymerized with a catalyst. Following polymerization, the polymer
product formed is present as a slurry of polyethylene particles
suspended in the liquid medium.
[0003] In typical multi-reactor cascade processes, shown e.g., in
WO 2005/077992 A1 and WO 2012/028591 A1, the reactors can be
operated in parallel or in series, and the types and amounts of
monomer and conditions can be varied in each reactor to produce a
variety of polyethylene materials, including unimodal or multimodal
polyethylene material. Such multimodal compositions are used in a
variety of applications; e.g., WO 2012/069400 A1 discloses trimodal
polyethylene compositions for blow moldings.
[0004] A potential challenge encountered using continuous stirred
tank reactors in ethylene slurry polymerization systems is the
fouling that can occur on the reactor internals. For instance,
ethylene monomer is introduced into the reactor in gaseous form and
dissolves in the diluent. The solid catalyst component is dosed
into the reactor and is suspended in the diluent. When the
dissolved ethylene comes into contact with the catalyst particles,
polyethylene is formed. The reaction occurs throughout the reactor,
including near the interior reactor surfaces and reactor internals,
and the area around the ethylene inlet nozzles since the local
concentration of ethylene is at its highest at the discharge of the
inlet nozzle. The ethylene feed, in many such reactions, would
immediately dissolve and be mixed so as to form a uniform
concentration in the diluent in contact with uniformly distributed
catalyst particles. However, if dissolution of the ethylene and
mixing of the reactor contents is not adequate, solid polyethylene
can deleteriously adhere to interior reactor surfaces and reactor
internals. If such adhesion is ongoing, the accumulated material
can form solid lumps and interfere with reactor performance.
Ultimately, if not remedied, this process of fouling may lead to a
unit shutdown for cleaning.
[0005] Conventional systems have fed the ethylene through a nozzle
without a length of pipe in the bottom of the reactor. The ethylene
entered the reactor directly at the reactor wall, which led to
fouling around this nozzle due to the very high concentration of
ethylene and in the suspension. Fouling also occurred inside the
nozzle itself. Due to low velocities of ethylene at the exit of the
nozzle, catalyst-containing suspension would migrate into the
nozzle and react with the ethylene to form polyethylene particles.
To prevent total plugging of the nozzle, the nozzle would have to
be cleaned frequently.
[0006] Therefore, a continuing need exists for ethylene slurry
polymerization processes having improved performance through more
efficient ethylene dissolution and mixing, resulting in reduced
internal reactor fouling.
SUMMARY OF THE INVENTION
[0007] The present disclosure provides processes for ethylene
slurry polymerization using an ethylene distribution system.
[0008] The disclosure provides processes for the preparation of
polyethylene by polymerizing in a slurry ethylene and optionally
one or more C.sub.3 to C.sub.10 alpha-olefins at a temperature from
60-95.degree. C. and a pressure from 0.15-3 MPa, where the
polymerization is carried out in a cylindrical polymerization
reactor having a cylindrical reactor wall, a bottom reactor head
and a top reactor head, where the reactor has an inner diameter D
and is equipped with an agitator for mixing the contents of the
reactor and inducing a flow of the slurry. In some embodiments, the
ethylene is fed into the reactor by an ethylene injection system
comprising one or more injection nozzles which project through the
bottom reactor head or through the reactor wall and extend from
0.02-0.5 times the inner diameter D into the reactor and wherein
the ethylene exits the injection nozzle with an exit velocity from
10-200 m/s.
[0009] In some embodiments, the injection nozzles projecting
through the bottom reactor head or through the reactor wall have a
direction into the reactor, a sloped ethylene outlet with an outlet
tip and an outlet base, and an angle between the direction of the
injection nozzle and the line connecting the outlet tip and the
outer base of from 20-80.degree.. In certain embodiments, the slope
of the ethylene outlet is oriented in a way with respect to the
flow of the slurry that the outlet tip is in an upstream position
and the outlet base is in a downstream position with respect to the
flow of the slurry.
[0010] In some embodiments, the agitator comprises a motor, a
vertical rotating shaft, which may be centrally located in the
reactor, and one or more stages of agitator blades attached to the
rotating shaft; and wherein the agitator induces primarily a
vertical flow of the slurry in a circular cross-section around the
agitator shaft.
[0011] In some embodiments, the vertical flow of the slurry in the
circular cross-section is a downward flow.
[0012] In some embodiments, the one or more injection nozzles
project through the bottom reactor head and extend vertically from
0.04-0.2 times the inner diameter D into the reactor, and the
horizontal distance from the center of the reactor to the outlet of
the injection nozzles is from 0.1-0.45 times the inner diameter
D.
[0013] In some embodiments, the ethylene injection system comprises
at least two injection nozzles, and all injection nozzles are
arranged on a circular line around the reactor center.
[0014] In some embodiments, the injection nozzles are uniformly
distributed on the circular line.
[0015] In some embodiments, the one or more injection nozzles
project through the cylindrical reactor wall at a wall passing
point positioned in the lower two thirds of the reactor and extend
from 0.02-0.48 times the inner diameter D into the reactor.
[0016] In some embodiments, the injection nozzles are inclined
downward.
[0017] In some embodiments, the horizontal angle between the
direction of the injection nozzle and the horizontal is of from
5-60.degree..
[0018] In some embodiments, the flow of the slurry in the
polymerization reactor has a circular component, and the injection
nozzles are inclined towards the downstream direction of the
circular flow.
[0019] In some embodiments, the radial angle between the direction
of the injection nozzle and a line running from the wall passing
point to the center of the reactor is from 5-60.degree..
[0020] In some embodiments, the outlets of the injection nozzles
are located at a position below the agitator.
[0021] In some embodiments, the wall passing points are arranged at
the same height of the reactor and uniformly distributed around the
reactor.
[0022] In some embodiments, the reactor is one of a multi-reactor
polymerization system.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 depicts a side view of an ethylene feed injection
nozzle.
[0024] FIG. 2 depicts a side view of an ethylene slurry
polymerization reactor with a bottom feed ethylene injection
system.
[0025] FIG. 3 depicts a top view of an ethylene slurry
polymerization reactor with a bottom feed ethylene injection
system.
[0026] FIG. 4 depicts a side view of an ethylene slurry
polymerization reactor with a side feed ethylene injection
system.
[0027] FIG. 5 depicts a top view of an ethylene slurry
polymerization reactor with a side feed ethylene injection
system.
DETAILED DESCRIPTION OF THE INVENTION
Polyethylene Slurry Production Process
[0028] In some embodiments, the process of the present disclosure
for producing polyethylene includes the slurry polymerization of
ethylene and optionally one or more C.sub.3 to C.sub.10
alpha-olefins as comonomers in the presence of an ethylene
polymerization catalyst, a diluent, such as hexane or isobutane,
and optionally hydrogen. The polymerization may proceed in a
suspension of particulate polyethylene in a suspension medium
comprising the diluent, unreacted ethylene and optionally one or
more comonomers. Polyethylene polymers obtained by the process
described in the present disclosure can be ethylene homopolymers or
copolymers of ethylene containing up to 40 wt. %, and from 0.1 to
10 wt. % of recurring units derived from
C.sub.3-C.sub.10-1-alkenes. The comonomers may be chosen from
propylene, 1-butene, 1-pentene, 1-hexene, 1-octene and mixtures
thereof. The slurry polymerization may occur at reactor
temperatures from 60-95.degree. C., from 65-90.degree. C., and from
70-85.degree. C., and at reactor pressures from 0.15-3 MPa, from
0.2-2 MPa, and from 0.25-1.5 MPa.
[0029] The polyethylene polymers produced by the polymerization
process may be high density polyethylene (HDPE) resins having a
density in a range from 0.935-0.970 g/cm.sup.3. Alternatively, the
density is in a range from 0.940-0.970 g/cm.sup.3 and from
0.945-0.965 g/cm.sup.3. The density is measured according to DIN EN
ISO 1183-1:2004, Method A (Immersion) with compression molded
plaques of 2 mm thickness prepared with a defined thermal history:
pressed at 180.degree. C., 20 MPa for 8 min with subsequent
crystallization in boiling water for 30 min.
[0030] The polyethylene polymers produced by the polymerization
process may have a melt index (MI.sub.21.6) from 1-300 dg/min, from
1.5-50 dg/min, or and from 2 dg/min to 35 dg/min. The MI.sub.21.6
is measured according to DIN EN ISO 1133:2005, condition G at a
temperature of 190.degree. C. under a load of 21.6 kg.
Catalyst
[0031] The polymerization can be carried out using customary
ethylene polymerization catalysts, e.g., the polymerization can be
carried out using Phillips catalysts based on chromium oxide, using
titanium-based Ziegler-type catalysts, i.e., Ziegler-catalysts or
Ziegler-Natta-catalysts, or using single-site catalysts. For the
purposes of the present disclosure, single-site catalysts are
catalysts based on chemically uniform transition metal coordination
compounds. The single-site catalysts may be those comprising bulky
sigma- or pi-bonded organic ligands, e.g. catalysts based on
mono-Cp complexes, catalysts based on bis-Cp complexes, which may
be designated as metallocene catalysts, or catalysts based on late
transition metal complexes, including iron-bis(imine) complexes.
Furthermore, it is also possible to use mixtures of two or more of
these catalysts for the polymerization of olefins. Such mixed
catalysts are often designated as hybrid catalysts.
[0032] The catalysts may be of the Ziegler type and may comprise a
compound of titanium or vanadium, a compound of magnesium and
optionally a particulate inorganic oxide as a support.
[0033] The titanium compounds may be selected from the halides or
alkoxides of trivalent or tetravalent titanium, with titanium
alkoxy halogen compounds or mixtures of various titanium compounds.
Examples of titanium compounds are TiBr.sub.3, TiBr.sub.4,
TiCl.sub.3, TiCl.sub.4, Ti(OCH.sub.3)Cl.sub.3,
Ti(OC.sub.2H.sub.5)Cl.sub.3, Ti(O-i-C.sub.3H.sub.7)Cl.sub.3,
Ti(O-n-C.sub.4H.sub.9)Cl.sub.3, Ti(OC.sub.2H.sub.5)Br.sub.3,
Ti(O-n-C.sub.4H.sub.9)Br.sub.3, Ti(OCH.sub.3).sub.2Cl.sub.2,
Ti(OC.sub.2H.sub.5).sub.2Cl.sub.2,
Ti(O-n-C.sub.4H.sub.9).sub.2Cl.sub.2,
Ti(OC.sub.2H.sub.5).sub.2Br.sub.2, Ti(OCH.sub.3).sub.3Cl,
Ti(OC.sub.2H.sub.5).sub.3Cl, Ti(O-n-C.sub.4H.sub.9).sub.3Cl,
Ti(OC.sub.2H.sub.5).sub.3Br, Ti(OCH.sub.3).sub.4,
Ti(OC.sub.2H.sub.5).sub.4 and Ti(O-n-C.sub.4H.sub.9).sub.4. In an
embodiment of the preset disclosure, the titanium compounds may
comprise chlorine as the halogen. In an embodiment, the titanium
halides may comprise only halogen in addition to titanium or may be
titanium chlorides or may be titanium tetrachloride. The vanadium
compounds may be vanadium halides, vanadium oxyhalides, vanadium
alkoxides or vanadium acetylacetonates. In an embodiment, the
vanadium compounds are in the oxidation states 3 to 5.
[0034] In the production of the solid component, at least one
compound of magnesium may be used. These compounds may be
halogen-comprising magnesium compounds such as magnesium halides
including chlorides or bromides, and magnesium compounds from which
the magnesium halides can be obtained in a customary way, e.g., by
reaction with halogenating agents. In an embodiment of the preset
disclosure, the halogens are selected from chlorine, bromine,
iodine and fluorine, as well as mixtures of two or more of these
halogens.
[0035] Possible halogen-containing magnesium compounds are
magnesium chlorides or magnesium bromides. Magnesium compounds from
which the halides can be obtained are, for example, magnesium
alkyls, magnesium aryls, magnesium alkoxy compounds, magnesium
aryloxy compounds and Grignard compounds. The halogenating agents
may be, for example, halogens, hydrogen halides, SiCl.sub.4 and
CCl.sub.4. In an embodiment, chlorine or hydrogen chloride is the
halogenating agent.
[0036] Examples of, halogen-free compounds of magnesium are
diethylmagnesium, di-n-propylmagnesium, diisopropylmagnesium,
di-n-butylmagnesium, di-sec-butylmagnesium, di-tert-butylmagnesium,
diamylmagnesium, n-butylethylmagnesium, n-butyl-sec-butylmagnesium,
n-butyloctylmagnesium, diphenylmagnesium, diethoxymagnesium,
di-n-propyloxymagnesium, diisopropyloxymagnesium,
di-n-butyloxymagnesium, di-sec-butyloxymagnesium,
di-tert-butyloxymagnesium, diamyloxymagnesium,
n-butyloxyethoxymagnesium, n-butyloxy-sec-butyloxymagnesium,
n-butyloxyoctyloxymagnesium and diphenoxymagnesium.
[0037] Examples of Grignard compounds are methylmagnesium chloride,
ethylmagnesium chloride, ethylmagnesium bromide, ethylmagnesium
iodide, n-propylmagnesium chloride, n-propylmagnesium bromide,
n-butylmagnesium chloride, n-butylmagnesium bromide,
sec-butylmagnesium chloride, sec-butylmagnesium bromide,
tert-butylmagnesium chloride, tert-butylmagnesium bromide,
hexylmagnesium chloride, octylmagnesium chloride, amylmagnesium
chloride, isoamylmagnesium chloride, phenylmagnesium chloride and
phenylmagnesium bromide.
[0038] The magnesium compounds for producing the particulate solids
may be, apart from magnesium dichloride and magnesium dibromide,
the di(C.sub.i-C.sub.10-alkyl)magnesium compounds. In one
embodiment, the Ziegler-type catalyst comprises a transition metal
selected from titanium, zirconium, vanadium, and chromium.
[0039] The Ziegler-type catalyst may be added to the slurry reactor
by first mixing the catalyst with the diluent, such as hexane, in a
mixing tank to form a slurry which may be subsequently pumped. A
positive displacement pump, such as a membrane pump may be used to
transfer the catalyst slurry to the slurry polymerization
reactor.
[0040] Catalysts of the Ziegler type may be used for polymerization
in the presence of a cocatalyst. Accordingly, the slurry
polymerization of the present disclosure may be carried out in the
presence of a cocatalyst. In an embodiment, cocatalysts are
organometallic compounds of metals of Groups 1, 2, 12, 13 or 14 of
the Periodic Table of Elements, such as organometallic compounds of
metals of Group 13 and organoaluminum compounds. The organoaluminum
compounds may be selected from aluminum alkyls such as
trialkylaluminum compounds, trimethylaluminum (TMA),
triethylaluminum (TEAL), tri-isobutylaluminum (TIBAL), and
tri-n-hexylaluminum (TNHAL). In an embodiment of the present
disclosure, the aluminum alkyl is TEAL. The cocatalyst(s) may be
miscible with the diluent and comprised in the suspension
medium.
[0041] The cocatalyst can be added to the slurry reactor. In an
embodiment, the cocatalyst is added by first mixing the cocatalyst
with the diluent, such as hexane or isobutane, in a mixing tank. A
positive displacement pump, such as a membrane pump may be used to
transfer the cocatalyst to the slurry polymerization reactor.
[0042] The process of the present disclosure is carried out in at
least one polymerization reactor. It may include a polymerization
in a stand-alone polymerization reactor or it may include a
polymerization in one polymerization reactor of a multi-reactor
system. Such multi-reactor systems may be operated in parallel or
in series. It is possible to operate two, three or more
polymerization reactors in parallel. In an embodiment, the
polymerization reactors of the multi-reactor system are operated in
series; i.e. the reactors are arranged as a cascade. Such a series
may include two or three reactors operating in series.
[0043] The process of the present disclosure is carried out in a
cylindrical polymerization reactor which comprises a cylindrical
reactor wall, a bottom reactor head connected to the cylindrical
reactor wall at a bottom tangent and a top reactor head connected
to the cylindrical reactor wall at a top tangent. The cylindrical
polymerization reactor has an inner diameter D which corresponds to
the inner diameter of the cylindrical reactor wall and a height H
which is the distance from the bottom tangent to the top tangent
measured along the central axis of the cylindrical polymerization
reactor. The reactor may have a height/diameter ratio (H/D) of from
1.5-4 and a height/diameter ratio (H/D) of from 2.5-3.5.
[0044] The reactor is equipped with an agitator for mixing the
contents of the reactor and inducing a flow of the slurry. In an
embodiment of the present disclosure, the agitator is arranged
centrally in the reactor and may comprise a motor located on the
top reactor head, a rotating shaft extending along the reactor's
central axis and one or more stages of agitator blades. There may
be 2-6 stages of agitator blades attached to the rotating shaft
including 4-5 stages of agitator blades. A stage of agitator blades
may comprise several agitator blades such as 2-4 blades.
[0045] In an embodiment, the motor rotates the agitator shaft and
the attached agitator blades. The rotation of the blades induces
primarily a vertical flow of the slurry in a circular cross-section
around the agitator shaft. This vertical flow of the slurry may be
a downward flow. At the bottom head, this flow changes direction,
and flows first outward toward the reactor wall and then back
upward to the top, changes direction again and then back to the
center of the polymerization reactor. The rotation of the agitator
also results in a secondary flow pattern of slurry in the reactor.
This secondary flow is a circular flow in the direction of rotation
of the agitator. To control this circular flow, the polymerization
reactor may be equipped with one or more baffles.
[0046] According to the process of the present disclosure, the
ethylene is fed into the polymerization reactor by an ethylene
injection system comprising one or more injection nozzles, which
project through the bottom reactor head or through the reactor wall
and extend from 0.02-0.5 times the inner diameter D into the
reactor. The length by which the injection nozzles extend into the
reactor is the distance from the point where the injection nozzle
center line exits the injection nozzle at its ethylene outlet to
the point where the injection nozzle center line passes the inner
surface of the reactor wall or the inner surface of the bottom
reactor head.
[0047] The ethylene is provided to the injection nozzles from the
outside of the reactor, passes the reactor wall at the wall passing
points of the injection nozzles and exits the injection nozzles
through the outlets of the injection nozzles arranged within the
polymerization reactors. The injection nozzles may be straight
pipes of an inner diameter D.sub.N and have a defined direction
into the reactor. The direction of the injection nozzles
corresponds to the direction of the injection nozzle center lines.
According to the present disclosure, the ethylene is fed to the
reactor with an ethylene exit velocity of from 10-200 m/s,
including from 25-150 m/s. The desired ethylene exit velocity is
achieved by designing diameter D.sub.N of the one or more injection
nozzles in an appropriate way so that the targeted ethylene flow
rate to the slurry polymerization results in the desired ethylene
exit velocity. The relatively high exit velocity provides high
differential speed with respect to the circulating reactor
contents, and higher turbulence, which provides improved
mixing.
[0048] In an embodiment of the present disclosure, the end of the
injection nozzle as arranged within the polymerization reactor,
i.e. the ethylene outlet of the injection nozzle, is sloped and has
an outlet tip and an outlet base. The slope may be arranged such
that the angle between the direction of the injection nozzle and
the line connecting the outlet tip and the outlet base, i.e. the
angle between the injection nozzle center line and the line
connecting the outlet tip and the outlet base, is from about
20-80.degree., including from about 30.degree. to 60.degree.. The
slope of the ethylene outlet may be oriented in such a way with
respect to the flow of the slurry that the outlet tip is in an
upstream position and the outlet base is in a downstream position
with respect to the flow of the slurry. Orientation of the nozzle
in this manner minimizes migration of slurry into the nozzle to
reduce or prevent fouling. For injection nozzles having a sloped
ethylene outlet, the point where the injection nozzle center line
exits the injection nozzle is the point where the center line meets
the line connecting the outlet tip and the outlet base.
[0049] FIG. 1 illustrates an embodiment of an injection nozzle of
the present disclosure. Injection nozzle 110 projects through
reactor wall 101, which can be either the wall of the reactor
bottom head or the cylindrical side wall of the reactor, and has an
outlet 111 which has an outlet tip 112 and an outlet base 113.
Angle a is the angle between line 114 connecting outlet tip 112 and
outlet base 113 and center line 115 of injection nozzle 110. Angle
a may be from 20-80.degree.. Distance 116 is the extension of
injection nozzle 110 into the polymerization reactor.
[0050] For injection nozzle 110 shown in FIG. 1, ethylene is
provided from below and exits the injection nozzle through outlet
111. The slurry flows in direction 130 corresponding to a flow from
an upstream point 131 to a downstream point 132. According to the
embodiment shown in FIG. 1, the slope of the ethylene outlet 111 as
defined by line 114 is oriented in a way with respect to the flow
of the slurry that the outlet tip 112 is in an upstream position
and the outlet base 113 is in a downstream position with respect to
direction 130 of the flow of slurry.
[0051] In an embodiment of the present disclosure, the one or more
injection nozzles project through the bottom reactor head. In this
embodiment the injection nozzles extend vertically from 0.04-0.2
times the inner diameter D into the reactor, including from
0.07-0.15 times the inner diameter D into the reactor, and the
horizontal distance from the center of the reactor to the outlet of
the injection nozzles is from 0.1-0.45 times the inner diameter D,
or from 0.2-0.4 times the inner diameter D. Consequently, the
outlets of the injection nozzles are located below the agitator at
positions where the downward flow of the slurry induced by the
agitator has changed direction and flows primarily outward towards
the reactor wall. Accordingly, the outlets of sloped injection
nozzles are oriented in a way that the outlet tips are positioned
in the direction of the reactor center and the outlet bases are
positioned in the direction of the reactor walls. When the ethylene
injection system comprises two or more injection nozzles, all
injection nozzles may be arranged on a circular line around the
reactor center. The injection nozzles may be uniformly distributed
on the circular line and have uniform spacing, so that with two
nozzles there is 180 degrees of spacing between the nozzles; when
there are three nozzles, there is 120 degrees of spacing between
the nozzles; and when there are four nozzles, there is 90 degrees
of spacing between the nozzles.
[0052] FIGS. 2 and 3 illustrate an embodiment in which two
injection nozzles project through the bottom reactor head.
[0053] Reactor 100, as shown in FIG. 2, includes a cylindrical
reactor wall 102 that extends from a bottom tangent 103 to a top
tangent 104; a bottom reactor head 105 connected to the cylindrical
reactor wall 102 at the bottom tangent 103; a top reactor head 106
connected to the cylindrical reactor wall 104 at the top tangent
104; and an agitator 120 for mixing the contents of the reactor
100. The agitator 120 has a motor 121, a rotating shaft 122 which
is centrally located in the reactor 100, extending along the
reactor's central axis and is driven by motor 121 in a direction of
rotation 123, and three stages of agitator blades 124 attached to
the rotating shaft 122. The reactor has a height, H, measured along
its central axis from the bottom tangent 103 to the top tangent
104, and an inner diameter D.
[0054] The blades of agitator stages 124 convey the contents of the
reactor 100 in a primary flow pattern 133 with a flow vector 133a
initially oriented downward along the central axis of the reactor
100 to the bottom head 105, where it changes direction and flows
first outward toward the reactor wall 102 and then back upward to
the top head 106, changes direction again and then back to the
impeller(s) 103. The rotation of the blades of stages 124 also
result in a secondary flow pattern 134 in the reactor. The
secondary flow 134 is a circular motion in the direction of
rotation 123 of the rotating shaft 122.
[0055] The reactor 100 also contains an ethylene injection system
for feeding ethylene into the reactor 100. An embodiment shown in
FIG. 2 has two injection nozzles 110 that project inward through
the bottom reactor head 105. The injection nozzles 110 have sloped
ethylene outlets 111 which are oriented in a way that the outlet
tips are positioned in a direction toward the reactor center and
the outlet bases are positioned in a direction toward the reactor
wall. In some embodiments, the diameter of injection nozzles 110 is
adapted to maintain an ethylene exit velocity from 10-200 m/s.
[0056] FIG. 3 is a top view of reactor 100 shown in FIG. 2. The
depicted agitator stage 124 has four agitator blades attached to
rotating shaft 122. The rotation of the agitator blades of stages
124 defines a circular cross-section 125. The two ethylene outlets
111 of the two injection nozzles used in the embodiment shown in
FIG. 3 have the same distance from the center of the reactor and
thus also from rotating shaft 122 and are accordingly positioned on
circle 117.
[0057] In another embodiment of the present disclosure, the one or
more injection nozzles project through the cylindrical reactor
wall. In this embodiment, the injection nozzles extend from
0.02-0.48 times the inner diameter D into the reactor, such as from
0.1-0.4 times the inner diameter D into the reactor, and the
injection nozzles project through the wall at a wall passing point
positioned in the lower two third of the reactor; i.e., a point
with a distance of not more than H*2/3 from the bottom tangent
which connects the cylindrical reactor wall and the bottom tangent.
In some embodiments, the wall passing point, at which the injection
nozzles projects through the cylindrical reactor wall, is
positioned at a point in the lower half of the reactor, i.e. at a
point with a distance of not more than H/2 from the bottom tangent,
alternatively the wall passing point is positioned in the lower
third of the reactor, i.e., a point with a distance of not more
than H/3 from the bottom tangent.
[0058] The injection nozzles projecting through the cylindrical
reactor wall may incline downward. For inclining injection nozzles,
the horizontal angle between the direction of the injection nozzle
and the horizontal, i.e. the angle between the center line of the
injection nozzle and the horizontal, ma be from 5-60.degree., from
7.5-45.degree., and from 10-30.degree.. The injection nozzles
projecting through the cylindrical reactor wall may also have a
radial deviation such that the center line of the injection nozzles
is not passing through the reactor center. This deviation may be
towards the downstream direction of the circular flow of the slurry
which can be induced as a secondary flow pattern by the rotation of
the agitator. Injection nozzles not directed to the reactor center
may have a radial angle between the direction of the injection
nozzle, i.e. the center line of the injection nozzle, and a line
running from the wall passing point to the center of the reactor,
of from 5-60.degree., from 7.5-45.degree., and from 10-30.degree..
The outlets of the injection nozzles may be arranged at a height
which differs from the height of a stage of agitator blades
attached to the agitator shaft. The outlets of the injection
nozzles may be arranged below at least one stage of the agitator
blades, and the outlets of the injection nozzles may be located at
a position below the agitator, i.e. below all stages of the
agitator blades. Consequently, the outlets of the injection nozzles
may be located at positions where the primary flow pattern is a
downward flow of the slurry with an additional, smaller, circular
flow. Accordingly, the outlets of sloped injection nozzles may be
arranged in a way that the outlet tip is in upstream position with
respect to the primary flow pattern.
[0059] The injection nozzles projecting through the cylindrical
reactor wall may be positioned in a way that all wall-passing
points are arranged at the same height of the reactor. In an
embodiment, the injection nozzles are uniformly distributed around
the reactor and have uniform spacing, so that with two nozzles
there is a 180 degree spacing between the nozzles; when there are
three nozzles, there is a 120 degree spacing between the nozzles;
and when there are four nozzles, there is a 90 degree spacing
between the nozzles. Orienting the nozzles in this way prevents
solids from entering the nozzles if solids settle in the reactor,
as well as maximizing the number of nozzles that can be installed
relative to an installation on the bottom of the reactor. Higher
numbers of nozzles provide even more improved mixing and
distribution of the ethylene.
[0060] FIGS. 4 and 5 illustrate an embodiment in which two
injection nozzles project through the cylindrical reactor wall. The
reactor shown in FIGS. 4 and 5 is identical to that depicted in
FIGS. 2 and 3 and is agitated in the same manner.
[0061] The ethylene injection system for feeding ethylene into the
reactor 100 shown in FIG. 4 has two injection nozzles 110 that
project inward through the cylindrical reactor wall 102 at wall
passing points 118 positioned at the same height in the lower third
of the reactor. The injection nozzles 110 may incline downward with
a horizontal angle .beta. between the center lines 115 and the
horizontal 135. When injection nozzles 110 incline downward, angle
.beta. may be from about 5-60.degree.. The ethylene outlets 111 of
the injection nozzles 110 are located at a position below the
agitator 120, i.e. below all stages of agitator blades 124.
Distances 119 are the horizontal distances of the outlets of the
injection nozzles to the center of the reactor. The injection
nozzles 110 have sloped ethylene outlets 111 which are oriented in
a way that the outlet tips are positioned in an upward position
corresponding to the primarily downward flow in the circular
cross-section defined by the rotation of the agitator blades. The
diameter of injection nozzles 110 is adapted to maintain an
ethylene exit velocity from about 10-200 m/s.
[0062] FIG. 5 is a top view of reactor 100 shown in FIG. 4. The two
injection nozzles 110 may have a tangential deviation towards the
downstream direction of the circular flow of the slurry 134 for
which the tangential deviation has a radial angle .gamma. between
the center lines 115 of the injection nozzle 110 and a line 136
running from the wall passing point 118 to the center of the
reactor thus to rotating shaft 122. When injection nozzles 110 have
a tangential deviation, angle .gamma. may be from 5-60.degree..
[0063] While multiple embodiments are disclosed, still other
embodiments will become apparent to those skilled in the art from
the following detailed description. As will be apparent, certain
embodiments, as disclosed herein, are capable of modifications in
various obvious aspects, all without departing from the spirit and
scope of the claims as presented herein. Accordingly, the drawings
and detailed description are to be regarded as illustrative in
nature and not restrictive.
* * * * *