U.S. patent application number 13/209218 was filed with the patent office on 2011-12-08 for system and process for production of polyethylene and polypropylene.
This patent application is currently assigned to H R D CORPORATION. Invention is credited to Rayford G. ANTHONY, Ebrahim BAGHERZADEH, Gregory BORSINGER, Abbas HASSAN, Aziz HASSAN.
Application Number | 20110300024 13/209218 |
Document ID | / |
Family ID | 40186253 |
Filed Date | 2011-12-08 |
United States Patent
Application |
20110300024 |
Kind Code |
A1 |
HASSAN; Abbas ; et
al. |
December 8, 2011 |
SYSTEM AND PROCESS FOR PRODUCTION OF POLYETHYLENE AND
POLYPROPYLENE
Abstract
A system for production of a polymer that may include a first
high shear mixing device configured for producing a nanodispersion
comprising particles or bubbles having a mean diameter less than 1
micron dispersed in a monomer-containing liquid or gaseous phase; a
pump configured for delivering a pressurized liquid stream
comprising the monomer to the first high shear mixing device; and a
vessel configured for receiving the nanodispersion and for
maintaining a predetermined pressure and temperature.
Inventors: |
HASSAN; Abbas; (Sugar Land,
TX) ; BAGHERZADEH; Ebrahim; (Sugar Land, TX) ;
ANTHONY; Rayford G.; (College Station, TX) ;
BORSINGER; Gregory; (Chatham, NJ) ; HASSAN; Aziz;
(Sugar Land, TX) |
Assignee: |
H R D CORPORATION
Houston
TX
|
Family ID: |
40186253 |
Appl. No.: |
13/209218 |
Filed: |
August 12, 2011 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
12141191 |
Jun 18, 2008 |
8022153 |
|
|
13209218 |
|
|
|
|
60946450 |
Jun 27, 2007 |
|
|
|
60946456 |
Jun 27, 2007 |
|
|
|
Current U.S.
Class: |
422/131 |
Current CPC
Class: |
Y10S 526/908 20130101;
B01F 13/1027 20130101; C08F 110/02 20130101; B01F 7/00766 20130101;
C08F 10/00 20130101; C08F 10/00 20130101; C08F 110/06 20130101;
B01F 2215/0481 20130101; C08F 110/02 20130101; C08F 2500/19
20130101; C08F 110/06 20130101; C08F 2/01 20130101; C08F 2500/24
20130101; C08F 2500/24 20130101; C08F 2500/19 20130101 |
Class at
Publication: |
422/131 |
International
Class: |
B01J 8/02 20060101
B01J008/02 |
Claims
1. A system for production of a polymer, the system comprising: a
first high shear mixing device configured for producing a
nanodispersion comprising particles or bubbles having a mean
diameter less than 1 micron dispersed in a monomer-containing
liquid or gaseous phase; a pump configured for delivering a
pressurized liquid stream comprising the monomer to the first high
shear mixing device; and a vessel configured for receiving the
nanodispersion and for maintaining a predetermined pressure and
temperature.
2. The system of claim 1, wherein the nanodispersion comprises
particles or bubbles having a mean diameter less than 400 nm.
3. The system of claim 1, wherein the first high shear mixing
device comprises a rotor-stator set having a rotor tip, and wherein
the mixing device is configured for operating at a flow rate of at
least 300 L/h and at a rotor tip speed of at least 22.9 m/sec.
4. The system of claim 3, wherein the rotor-stator set comprises a
shear gap having a gap width in the range from 0.025 mm to 10.0
mm.
5. The system of claim 3, wherein the first high shear mixing
device is capable of providing a shear rate of greater than 20,000
s.sup.-1.
6. The system of claim 3, wherein the first high shear mixing
device produces a local pressure of at least about 1034 MPa at the
rotor tip.
7. The system of claim 1, wherein the first high shear mixing
device is configured to provide an energy expenditure greater than
1000 W/m.sup.3.
8. The system of claim 1 wherein the vessel comprises a tower
reactor, a tubular reactor, a multi-tubular reactor, a tank reactor
or a fixed bed reactor.
9. The system of claim 1, wherein the vessel comprises a reaction
vessel configured to provide polymerization conditions in the range
of about 203 kPa to about 6080 kPa and in the range of about
20.degree. C. to about 230.degree. C.
10. The system of claim 9, wherein the nanodispersion comprises
ethylene and a polymerization catalyst dispersed in a solvent,
whereby at least a portion of ethylene is polymerized to form
polyethylene.
11. The system of claim 9, wherein the nanodispersion comprises
propylene and a polymerization catalyst dispersed in a solvent,
whereby at least a portion of proplyene is polymerized to form
polypropylene.
12. The system of claim 1, wherein the first high shear mixing
device comprises at least two rotors and at least two stators.
13. The system of claim 1 comprising a second high shear mixing
device in fluid communication with the first high shear mixing
device.
14. The system of claim 1, wherein the first high shear mixing
device comprises a flow pathway, and wherein the first high shear
mixing device is configured to provide varied shear force along the
flow pathway.
15. A system for production of a polymer, the system comprising: at
least one high shear mixing device configured for producing a
nanodispersion comprising particles or bubbles having a mean
diameter less than 1 micron, the at least one high shear mixing
device comprising at least one rotor and at least one stator
separated by a shear gap, and wherein the high shear mixing device
is configured to produce a tip speed at a tip of the at least one
rotor of greater than 22.9 m/s (4,500 ft/min); a pump configured
for delivering a pressurized liquid stream to the at least one high
shear mixing device; and a vessel configured for receiving the
nanodispersion from the at least one high shear mixing device.
16. The system of claim 15 wherein the shear gap is in the range of
about 0.02 mm to about 5 mm.
17. The system of claim 15, wherein the at least one high shear
mixing device produces a shear rate of greater than 20,000
s.sup.-1.
18. A system for production of a polymer, the system comprising: at
least one high shear mixing device comprising a rotor-stator set
having a rotor tip, wherein the device is configured for operating
at a flow rate of at least 300 L/h and at a tip speed of at least
22.9 m/sec, and wherein the device produces a nanodispersion
comprising particles or bubbles having a mean diameter less than 1
micron dispersed in a monomer-containing liquid or gaseous phase; a
pump configured for delivering a pressurized liquid stream
comprising the monomer to the high shear mixing device; and a
vessel configured for receiving the nanodispersion from the high
shear mixing device and for maintaining a predetermined pressure
and temperature.
19. The system of claim 18, wherein the at least one high shear
mixing device comprises at least two rotors and at least two
stators.
20. The system of claim 18, wherein the at least one high shear
mixing device produces a shear rate of greater than 20,000
s.sup.-1.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional application of U.S. Ser.
No. 12/141,191 filed on Jun. 18, 2008, which application claims the
benefit under 35 U.S.C. .sctn.119(e) of U.S. Provisional Patent
Application No. 60/946,450 filed Jun. 27, 2007, and U.S.
Provisional Patent Application No. 60/946,456 filed Jun. 27, 2007,
the disclosures of which are hereby incorporated herein by
reference.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] Not Applicable.
TECHNICAL FIELD
[0003] The present invention generally relates to the liquid phase
polymerization of ethylene or propylene monomer, in the presence of
a highly dispersed catalyst, to form polyethylene or polypropylene,
respectively. More particularly, the invention relates to
apparatus, systems, and methods for producing polyethylene or
polypropylene which employ high shear mixing of the reactants.
BACKGROUND
[0004] Polyethylene is a thermoplastic material that is created
through polymerization of ethylene monomer, and which is used in
the manufacture of a wide variety of consumer products, including
packaging, pipe extrusion, wire and cable sheathing and insulation,
and many other products. Because ethylene has no substituent groups
to influence the stability of the propagation head of the growing
polymer chain, polymers of varying degrees of branching can be
produced through radical polymerization, anionic addition
polymerization, ion coordination polymerization or cationic
addition polymerization. Today one of the most common methods of
preparing highly desirable linear (high density) polyethylene
involves contacting ethylene with a Ziegler-Natta catalyst system
that includes a transition metal catalyst such as TiCl.sub.4 and an
organo-compound of a non-transition metal of Groups IA to IIIA of
the Periodic Table of the Elements, particularly organo-aluminium
compounds.
[0005] Polypropylene is another thermoplastic polymer that is
widely used in the manufacturing of a variety of products,
including housings and parts for small and large appliances,
disposable containers, food packaging, ropes, textiles and plastic
automobile parts, and many more. It is chemically synthesized by
the catalyzed polymerization of propylene monomer. Polypropylene is
most often produced as a stereospecific polymer. Isotactic
polypropylene has all the pendant methyl groups oriented either
above or below the polymer chain. Any deviation or inversion in the
structure of the chain lowers the degree of isotacticity and
crystallinity of the polymer. Most commercially available
polypropylene is made with titanium chloride catalysts to produce
substantially isotactic polypropylene, which is highly desirable
for making a number of products that require a strong polymer.
[0006] Ziegler-Natta catalysts are stereospecific complexes that
limit incoming monomers to a specific orientation, only adding them
to the polymer chain if they are oriented in a specific direction,
to produce isotactic (unbranched) polymers. Because the
organo-compounds of transition metals are useful polymerization
catalysts only when supported, they are supported on a suitable
matrix material such as alumina, silica, or magnesia. Conventional
Ziegler-Natta catalysts are stereospecific complexes formed from a
halide of a transition metal, such as titanium, chromium or
vanadium with a metal hydride and/or metal alkyl, typically an
organoaluminum compound such as an alkylaluminum compound, for
example, triethylaluminum (TEAL), trimethyl aluminum (TMA) or
triisobutyl aluminum (TIBAL), as a co-catalyst. Both liquid phase
slurry (suspension) polymerization and gas phase polymerization
have been catalyzed using Ziegler-Natta catalysts. Although
polymerization rates increase with temperature, reaction
temperatures above 70-100.degree. C. seldom are employed because
high temperatures result in loss of stereospecificity as well as
lowered polymerization rates as a result of the decreased stability
of the initiator. In many polyolefin manufacturing processes today
metallocene based catalysts are replacing some Ziegler-Natta
catalysts.
[0007] Other transition metal catalysts that polymerize ethylene
are based on the oxides of chromium or molybdenum. Other transition
metal catalyst systems include the organo-compounds of transition
metals with n-allyl, cyclopentadienyl, norbornyl, benzyl, and arene
groups and also compounds including groups of the type exemplified
by the neopentyl and substituted silylmethyl compounds. Catalysts
that promote branching of the polymer are employed when a
low-density polyethylene is sought.
[0008] In a typical liquid phase slurry (suspension) polymerization
process ethylene or propylene monomer is dissolved in an organic
reaction medium and then contacted with a particulate catalyst. The
polyethylene or polypropylene that is formed is also dissolved in
the organic medium, which can become quite viscous. Although
polymerization rates increase with temperature, reaction
temperatures above 70-100.degree. C. seldom are employed because
high temperatures result in loss of stereospecificity as well as
lowered polymerization rates as a result of the decreased stability
of the catalyst.
[0009] At the present time, solution polymerization is generally
considered to be limited to production of low molecular weight
polyethylene and polypropylene. Existing processes and production
facilities for producing these polymers are typically subject to
various constraints including mass flow limitations, product yield,
plant size and energy consumption. Accordingly, there is continued
interest in the development of ways to improve the selectivity and
yield of polymers from catalyzed polymerization of ethylene and
propylene monomers.
SUMMARY
[0010] In accordance with certain embodiments of the invention, a
system for production of a polymer is provided that may include a
first high shear mixing device configured for producing a
nanodispersion having particles or bubbles having a mean diameter
less than 1 micron dispersed in a monomer-containing liquid or
gaseous phase; a pump configured for delivering a pressurized
liquid stream having the monomer to the first high shear mixing
device; and a vessel configured for receiving the nanodispersion
and for maintaining a predetermined pressure and temperature.
[0011] In accordance with certain embodiments of the invention, a
system for production of a polymer is provided that may include at
least one high shear mixing device configured for producing a
nanodispersion comprising particles or bubbles having a mean
diameter less than 1 micron, the at least one high shear mixing
device having at least one rotor and at least one stator separated
by a shear gap, and wherein the high shear mixing device is
configured to produce a tip speed at a tip of the at least one
rotor of greater than 22.9 m/s (4,500 ft/min); a pump configured
for delivering a pressurized liquid stream to the at least one high
shear mixing device; and a vessel configured for receiving the
nanodispersion from the at least one high shear mixing device.
[0012] In accordance with certain embodiments of the invention, a
system for production of a polymer is provided that may include at
least one high shear mixing device comprising a rotor-stator set
having a rotor tip, wherein the device is configured for operating
at a flow rate of at least 300 L/h and at a tip speed of at least
22.9 m/sec, and wherein the device produces a nanodispersion having
particles or bubbles having a mean diameter less than 1 micron
dispersed in a monomer-containing liquid or gaseous phase; a pump
configured for delivering a pressurized liquid stream comprising
the monomer to the high shear mixing device; and a vessel
configured for receiving the nanodispersion from the high shear
mixing device and for maintaining a predetermined pressure and
temperature.
[0013] In accordance with certain other embodiments of the
invention, a system for production of polyethylene or polypropylene
is provided which comprises at least one high shear mixing device
configured for producing a nanodispersion comprising
submicron-sized particles dispersed in a monomer-containing liquid
or gas phase. These and other embodiments and potential advantages
will be apparent in the following detailed description and
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a process flow diagram of a process for production
of either polyethylene or polypropylene, in accordance with an
embodiment of the present invention.
[0015] FIG. 2 is a longitudinal cross-section view of a multi-stage
high shear device, as employed in an embodiment of the system of
FIG. 1.
DETAILED DESCRIPTION
[0016] The present methods and systems for the production of
polyethylene and polypropylene, and their various copolymers, via
heterogeneous liquid-solid, liquid-gas-solid, or gas-solid phase
polymerization of the corresponding monomers and comonomers, in the
presence of a suitable catalyst or initiator, employ an external
high shear mechanical device to provide rapid contact and mixing of
chemical ingredients in a controlled environment in the high shear
mixer device, and a separate vessel or reactor. The high shear
device reduces the mass transfer limitations on the reaction and
thus increases the overall reaction rate.
[0017] Chemical reactions involving liquids, gases and solids rely
on the laws of kinetics that involve time, temperature, and
pressure to define the rate of reactions. In cases where it is
desirable to react two or more raw materials of different phases
(e.g. solid and liquid; liquid and gas; solid, liquid and gas), one
of the limiting factors in controlling the rate of reaction
involves the contact time of the reactants. In the case of
heterogeneously catalyzed reactions there is the additional rate
limiting factor of having the reacted products removed from the
surface of the catalyst to enable the catalyst to catalyze further
reactants. Contact time for the reactants and/or catalyst is often
controlled by mixing which provides contact with two or more
reactants involved in a chemical reaction. A reactor assembly that
comprises an external high shear device or mixer as described
herein makes possible decreased mass transfer limitations and
thereby allows the reaction to more closely approach kinetic
limitations. When reaction rates are accelerated, residence times
may be decreased, thereby increasing obtainable throughput. Product
yield may be increased as a result of the high shear system and
process. Alternatively, if the product yield of an existing process
is acceptable, decreasing the required residence time by
incorporation of suitable high shear may allow for the use of lower
temperatures and/or pressures than conventional processes. In some
cases, it may be possible to reduce the reactor size while
maintaining the same product yield.
System for Production of Polyethylene or Polypropylene
[0018] A high shear system will now be described in relation to
FIG. 1, which is a process flow diagram showing an embodiment of a
high shear system 1 for the production of polyethylene or
polypropylene by catalyzed polymerization of the corresponding
monomer. It should be understood that a similar method and system
is employed to prepare polyethylene and/or polypropylene copolymers
from the corresponding monomers and selected co-monomers. For
example, some suitable co-monomers for polymerization with ethylene
or propylene include short-chain alpha-olefins such as 1-butene,
1-hexene and 1-octene, vinyl acetate, and a various acrylates. The
basic components of the system include external high shear mixing
device (HSD) 40, vessel 10, and pump 5. As shown in FIG. 1, the
high shear device is located external to vessel/reactor 10. Each of
these components is further described in more detail below. Line 21
is connected to pump 5 for introducing a liquid stream containing
solvent and/or monomer. Line 13 connects pump 5 to HSD 40, and line
18 connects HSD 40 to vessel 10. Line 22 is connected to line 13
for introducing a slurry of finely divided catalyst suspended in a
suitable solvent. Line 17 is connected to vessel 10 for removal of
vent gas. Additional components or process steps may be
incorporated between vessel 10 and HSD 40, or ahead of pump 5 or
HSD 40, if desired. In an alternative configuration, line 22 is
instead configured for introducing a gaseous monomer stream into
HSD 40, to form a gas-solid dispersion, as further described below.
In still another alternative configuration, line 22 is configured
to provide a particulate catalyst stream and line 13 is configured
for carrying a solvent into HSD 40.
[0019] High Shear Mixing Device. Referring still to FIG. 1,
external high shear mixing device (HSD) 40, also sometimes referred
to as a high shear mixer, is configured for receiving an inlet
stream via line 13. Alternatively, system 1 may be configured with
more than one inlet line (not shown). For instance, HSD 40 may be
configured for receiving the monomer and catalyst streams via
separate inlet lines. Although only one high shear device is shown
in FIG. 1, it should be understood that some embodiments of the
system may have two or more high shear mixing devices arranged
either in series or parallel flow. HSD 40 is a mechanical device
that utilizes one or more generators comprising a rotor/stator
combination, each of which having a fixed gap between the stator
and rotor. HSD 40 is configured in such a way that it is capable of
producing a dispersion containing submicron--(i.e., less than one
micron in diameter) and micron-sized particles (e.g., catalyst
particles) dispersed in a gas or liquid medium flowing through the
mixer. For example, in some embodiments HSD 40 is capable of highly
dispersing a polymerization catalyst into a main liquid phase
comprising monomer and solvent, with which it would normally be
immiscible, at conditions such that at least a portion of the
monomer reacts to produce a polymerization product stream.
Alternatively, HSD 40 is configured to produce a dispersion
containing submicron- and micron-sized bubbles (e.g., gaseous
monomer) dispersed in a liquid medium comprising solvent. In
another alternative embodiment, HSD 40 is configured to produce a
dispersion containing micron- and submicron-sized monomer bubbles
and catalyst particles dispersed in a liquid solvent phase. For
carrying out certain gas-solid heterogeneous phase reactions, the
HSD 40 is configured for dispersing the catalyst particles into a
main gaseous monomer phase. In still another alternative
embodiment, HSD 40 is configured for dispersing catalyst and
gaseous monomer in a liquid solvent or in a solvent-monomer liquid
phase, for certain heterogeneous liquid-gas-solid phase
polymerization reactions. The high shear mixer comprises an
enclosure or housing so that the pressure and temperature of the
mixture may be controlled.
[0020] High shear mixing devices are generally divided into three
general classes, based upon their ability to mix fluids. Mixing is
the process of reducing the size of particles or inhomogeneous
species within the fluid. One metric for the degree or thoroughness
of mixing is the energy density per unit volume that the mixing
device generates to disrupt the fluid particles. The classes are
distinguished based on delivered energy densities. Three classes of
industrial mixers having sufficient energy density to consistently
produce mixtures or dispersions with particle sizes in the range of
submicron to 50 microns include homogenization valve systems,
colloid mills and high speed mixers. In the first class of high
energy devices, referred to as homogenization valve systems, fluid
to be processed is pumped under very high pressure through a
narrow-gap valve into a lower pressure environment. The pressure
gradients across the valve and the resulting turbulence and
cavitation act to break-up any particles in the fluid. These valve
systems are most commonly used in milk homogenization and can yield
average particle sizes in the 0-1 micron range.
[0021] At the opposite end of the energy density spectrum is the
third class of devices referred to as low energy devices. These
systems usually have paddles or fluid rotors that turn at high
speed in a reservoir of fluid to be processed, which in many of the
more common applications is a food product. These low energy
systems are customarily used when average particle sizes of greater
than 20 microns are acceptable in the processed fluid.
[0022] Between the low energy devices and homogenization valve
systems, in terms of the mixing energy density delivered to the
fluid, are colloid mills, which are classified as intermediate
energy devices. A typical colloid mill configuration includes a
conical or disk rotor that is separated from a complementary,
liquid-cooled stator by a closely-controlled rotor-stator gap,
which is commonly between 0.0254-10.16 mm (0.001-0.40 inch). Rotors
are usually driven by an electric motor through a direct drive or
belt mechanism. As the rotor rotates at high rates, it pumps fluid
between the outer surface of the rotor and the inner surface of the
stator, and shear forces generated in the gap process the fluid.
Many colloid mills with proper adjustment achieve average particle
sizes of 0.1-25 microns in the processed fluid. These capabilities
render colloid mills appropriate for a variety of applications
including colloid and oil/water-based emulsion processing such as
that required for cosmetics, mayonnaise, or silicone/silver amalgam
formation, to roofing-tar mixing.
[0023] An approximation of energy input into the fluid (kW/L/min)
can be estimated by measuring the motor energy (kW) and fluid
output (L/min). Tip speed is the circumferential distance traveled
by the tip of the rotor per unit of time. Tip speed is thus a
function of the rotor diameter and the rotational frequency. Tip
speed (in meters per minute, for example) may be calculated by
multiplying the circumferential distance transcribed by the rotor
tip, 2.pi.R, where R is the radius of the rotor (in meters, for
example) times the frequency of revolution (in revolutions per
minute). A colloid mill, for example, may have a tip speed in
excess of 22.9 msec (4500 ft/min) and may exceed 40 msec (7900
ft/min). For the purposes of this disclosure, the term "high shear"
refers to mechanical rotor stator devices (e.g., colloid mills or
rotor/stator mixers) that are capable of tip speeds in excess of
5.1 msec. (1000 ft/min) and require an external mechanically driven
power device to drive energy into the stream of materials to be
reacted. For example, in HSD 40, a tip speed in excess of 22.9 msec
(4500 ft/min) is achievable, and may exceed 40 msec (7900 ft/min).
In some embodiments, HSD 40 is capable of delivering at least 300
L/h with a power consumption of about 1.5 kW at a nominal tip speed
of at least 22.9 msec (4500 ft/min).
[0024] HSD 40 combines high tip speeds with a very small shear gap
to produce significant shear on the material being processed. The
amount of shear will be dependant on the viscosity of the fluid.
Accordingly, a local region of elevated pressure and temperature is
created at the tip of the rotor during operation of the high shear
device. In some cases the locally elevated pressure is about 1034.2
MPa (150,000 psi). In some cases the locally elevated temperature
is about 500.degree. C. In some cases these local pressure and
temperature elevations may persist for nano or pico seconds. In
some embodiments, the energy expenditure of the high shear mixer is
greater than 1000 W/m.sup.3. In embodiments, the energy expenditure
of HSD 40 is in the range of from about 3000 W/m.sup.3 to about
7500 W/m.sup.3. The shear rate is the tip speed divided by the
shear gap width (minimal clearance between the rotor and stator).
The shear rate generated in HSD 40 may be greater than 20,000
s.sup.-1. In some embodiments the shear rate is at least 1,600,000
s.sup.-1. In embodiments, the shear rate generated by HSD 40 is in
the range of from 20,000 s.sup.-1 to 100,000 s.sup.-1. For example,
in one application the rotor tip speed is about 40 msec (7900
ft/min) and the shear gap width is 0.0254 mm (0.001 inch),
producing a shear rate of 1,600,000s.sup.-1. In another application
the rotor tip speed is about 22.9 msec (4500 ft/min) and the shear
gap width is 0.0254 mm (0.001 inch), producing a shear rate of
about 902,000 s.sup.-1.
[0025] In some embodiments, HSD 40 comprises a colloid mill.
Suitable colloidal mills are manufactured by IKA.RTM. Works, Inc.
Wilmington, N.C. and APV North America, Inc. Wilmington, Mass., for
example. In some instances, HSD 40 comprises the Dispax
Reactor.RTM. of IKA.RTM. Works, Inc. Several models are available
having various inlet/outlet connections, horsepower, nominal tip
speeds, output rpm, and nominal flow rate. Selection of a
particular device will depend on specific throughput requirements
for the intended application, and on the desired particle size in
the outlet dispersion from the high shear mixer. In some
embodiments, selection of the appropriate mixing tools (generators)
within HSD 40 may allow for catalyst size reduction/increase in
catalyst surface area.
[0026] The high shear device comprises at least one revolving
element that creates the mechanical force applied to the reactants.
The high shear device comprises at least one stator and at least
one rotor separated by a clearance. For example, the rotors may be
conical or disk shaped and may be separated from a
complementary-shaped stator; both the rotor and stator may comprise
a plurality of circumferentially-spaced teeth. In some embodiments,
the stator(s) are adjustable to obtain the desired gap between the
rotor and the stator of each generator (rotor/stator set). Grooves
in the rotor and/or stator may change directions in alternate
stages for increased turbulence. Each generator may be driven by
any suitable drive system configured for providing the necessary
rotation.
[0027] In some embodiments, the minimum clearance between the
stator and the rotor is in the range of from about 0.0254 mm to
about 3.175 mm (about 0.001 inch to about 0.125 inch). In certain
embodiments, the minimum clearance between the stator and rotor is
about 1.524 mm (0.060 inch). In certain configurations, the minimum
clearance between the rotor and stator is at least 1.778 mm (0.07
inch). The shear rate produced by the high shear mixer may vary
with longitudinal position along the flow pathway. In some
embodiments, the rotor is set to rotate at a speed commensurate
with the diameter of the rotor and the desired tip speed. In some
embodiments, the colloidal mill has a fixed clearance between the
stator and rotor. Alternatively, the colloid mill has adjustable
clearance.
[0028] In some embodiments, HSD 40 comprises a single stage
dispersing chamber (i.e., a single rotor/stator combination, a
single generator). In some embodiments, high shear device 40 is a
multiple stage inline colloid mill and comprises a plurality of
generators. In certain embodiments, HSD 40 comprises at least two
generators. In other embodiments, high shear device 40 comprises at
least 3 high shear generators. In some embodiments, high shear
device 40 is a multistage mixer whereby the shear rate (which
varies proportionately with tip speed and inversely with
rotor/stator gap) varies with longitudinal position along the flow
pathway, as further described herein below.
[0029] In some embodiments, each stage of the external high shear
device has interchangeable mixing tools, offering flexibility. For
example, the DR 2000/4 Dispax Reactor.RTM. of IKA.RTM. Works, Inc.
Wilmington, N.C. and APV North America, Inc. Wilmington, Mass.,
comprises a three stage dispersing module. This module may comprise
up to three rotor/stator combinations (generators), with choice of
fine, medium, coarse, and super-fine for each stage. This allows
for creation of dispersions having a narrow distribution of the
desired particle size. In some embodiments, each of the stages is
operated with super-fine generator. In some embodiments, at least
one of the generator sets has a rotor/stator minimum clearance of
greater than about 5.08 mm (0.20 inch). In some embodiments, at
least one of the generator sets has a minimum rotor/stator
clearance of greater than about 1.778 mm (0.07 inch). In some
embodiments the rotors are 60 mm and the are stators 64 mm in
diameter, providing a clearance of about 4 mm.
[0030] Referring now to FIG. 2, there is presented a longitudinal
cross-section of a suitable high shear device 200. High shear
device 200 is a dispersing device comprising three stages or
rotor-stator combinations, 220, 230, and 240. Three rotor/stator
sets or generators 220, 230, and 240 are aligned in series along
drive input 250. The first generator 220 comprises rotor 222 and
stator 227. The second generator 230 comprises rotor 223, and
stator 228; the third generator 240 comprises rotor 224 and stator
229. For each generator the rotor is rotatably driven by input 250
and rotates, as indicated by arrow 265, about axis 260. Stator 227
is fixedly coupled to high shear device wall 255. Each generator
has a shear gap which is the distance between the rotor and the
stator. First generator 220, comprises a first shear gap 225;
second generator 230 comprises a second shear gap 235; and third
generator 240 comprises a third shear gap 245. In some embodiments,
shear gaps 225, 235, 245 are between about 0.025 mm and 10.0 mm
wide. In some embodiments, the process comprises utilization of a
high shear device 200 wherein the gaps 225, 235, 245 are between
about 0.5 mm and about 2.5 mm. In certain instances the gap is
maintained at about 1.5 mm. Alternatively, the gaps 225, 235, 245
are different for generators 220, 230, 240. In certain instances,
the gap 225 for the first generator 220 is greater than about the
gap 235 for the second generator 230, which is in turn greater than
about the gap 245 for the third generator. As mentioned above, the
generators of each stage may be interchangeable, offering
flexibility.
[0031] Generators 220, 230, and 240 may comprise a coarse, medium,
fine, and super-fine characterization. Rotors 222, 223, and 224 and
stators 227, 228, and 229 may be toothed designs. Each generator
may comprise two or more sets of rotor-stator teeth. Rotors 222,
223, and 224 may comprise a number of rotor teeth circumferentially
spaced about the circumference of each rotor. Stators 227, 228, and
229 may comprise a complementary number of stator teeth
circumferentially spaced about the circumference of each stator. In
some embodiments, the inner diameter of the rotor is about 11.8 cm.
In embodiments, the outer diameter of the stator is about 15.4 cm.
In certain embodiments, each of three stages is operated with a
super-fine generator, comprising a shear gap of between about 0.025
mm and about 3 mm. For applications in which solid particles are to
be sent through high shear device 200, shear gap width may be
selected for reduction in particle size and increase in particle
surface area. In some embodiments, the disperser is configured so
that the shear rate will increase stepwise longitudinally along the
direction of the flow. The IKA.RTM. model DR 2000/4, for example,
comprises a belt drive, 4M generator, PTFE sealing ring, inlet
flange 25.4 mm (1 inch) sanitary clamp, outlet flange 19 mm (3/4
inch) sanitary clamp, 2HP power, output speed of 7900 rpm, flow
capacity (water) approximately 300-700 L/h (depending on
generator), a tip speed of from 9.4-41 m/sec (1850 ft/min to 8070
ft/min).
[0032] Reactor/Vessel Vessel or reactor 10 is any type of vessel in
which a multiphase reaction can be propagated to carry out the
above-described conversion reaction(s). For instance, vessel 10 may
be a tower reactor, a tubular reactor or multi-tubular reactor, or
it may be a fixed bed reactor. In other embodiments, vessel 10 may
be a continuous or semi-continuous stirred tank reactor, or it may
comprise one or more batch reactors arranged in series or in
parallel. One or more line 15 may be connected to vessel 10 for
introducing the initial solvent and monomer, or for injecting
catalyst or other material.
[0033] Vessel 10 may include one or more of the following items:
stirring system, heating and/or cooling capabilities, pressure
measurement instrumentation, temperature measurement
instrumentation, one or more injection points, and level regulator
(not shown), as are known in the art of reaction vessel design. For
example, a stirring system may include a motor driven mixer. A
heating and/or cooling apparatus may comprise, for example, a heat
exchanger. Alternatively, as much of the polymerization reaction
may occur within HSD 40, in some embodiments, vessel 10 may serve
primarily as a storage vessel in some cases. Although generally
less desired, in some applications vessel 10 may be omitted,
particularly if multiple high shear mixers/reactors are employed in
series, as further described below. Line 16 is connected to vessel
10 for withdrawal or removal of the polyethylene, polypropylene or
copolymer product.
[0034] Heat Transfer Devices. In addition to the above-mentioned
heating/cooling capabilities of vessel 10, other external or
internal heat transfer devices for heating or cooling a process
stream are also contemplated in variations of the embodiments
illustrated in FIG. 1. Some suitable locations for one or more such
heat transfer devices are between pump 5 and HSD 40, between HSD 40
and vessel 10, and between vessel 10 and pump 5 when system 1 is
operated in multi-pass mode. Some non-limiting examples of such
heat transfer devices are shell, tube, plate, and coil heat
exchangers, as are known in the art.
[0035] Pumps. Pump 5 is configured for either continuous or
semi-continuous operation, and may be any suitable pumping device
that is capable of providing greater than 203 kPa (2 atm) pressure,
preferably greater than 3 atm pressure, to allow controlled flow
through HSD 40 and system 1. For example, a Roper Type 1 gear pump,
Roper Pump Company (Commerce Georgia) Dayton Pressure Booster Pump
Model 2P372E, Dayton Electric Co (Niles, Ill.) is one suitable
pump. Preferably, all contact parts of the pump comprise stainless
steel. If corrosive substances are to be pumped it may be desirable
to provide gold plated contact surfaces. In some embodiments of the
system, pump 5 is capable of pressures greater than about 2027 kPa
(20 atm). In addition to pump 5, one or more additional, high
pressure pump (not shown) may be included in the system illustrated
in FIG. 1. For example, a booster pump, which may be similar to
pump 5, may be included between HSD 40 and vessel 10 for boosting
the pressure into vessel 10. As another example, a supplemental
feed pump, which may be similar to pump 5, may be included in line
15 for introducing monomer, solvent, initiator or catalyst into
vessel 10. Line 24 connects vessel 10 to line 21 for introducing
the initial liquid stream into HSD 40 via pump 5 and line 13, or
for multi-pass operation, as further described herein below. As
still another example, a compressor type pump may be positioned
between line 17 and HSD 40 for recycling gas from vessel 10 to an
inlet of the high shear device.
Process for Production of Polyethylene or Polypropylene
[0036] In operation for the production of polymer by heterogeneous
liquid-solid or liquid-solid-gas phase catalyzed reaction of
ethylene and/or propylene, the monomer(s), any desired co-monomers,
and solvent are first combined in vessel 10. The monomers and/or
solvent may be initially introduced into vessel 10 via one or more
feed line 15. In some embodiments, the monomer solution contains
about 70% ethylene or propylene dissolved in a suitable organic
solvent, such as, for example, hexane, cyclohexane, butane or
pentane.
[0037] The process may be operated in either continuous or
semi-continuous flow mode, or it may be operated in batch mode. The
contents of vessel 10 are maintained at a specified bulk reaction
temperature using suitable heating and/or cooling capabilities
(e.g., cooling coils) and temperature measurement instrumentation.
Pressure in the vessel may be monitored using suitable pressure
measurement instrumentation, and the level of reactants in the
vessel may be controlled using a level regulator (not shown),
employing techniques that are known to those of skill in the art.
The contents are stirred or circulated continuously or
semi-continuously.
[0038] Pump 5 is operated to pump the liquid stream (e.g., solvent
or monomer-solvent solution) from reactor/vessel 10, via lines 24
and 21, and to build pressure and feed HSD 40, providing a
controlled flow through line 13 and high shear mixer (HSD) 40, and
throughout high shear system 1. In some embodiments, pump 5
increases the pressure of the liquid stream to greater than 203 kPa
(2 atm), preferably greater than about 304 kPa (3 atm). In some
applications, pressures greater than about 2027 kPa (20 atm) may be
used to accelerate reactions, with the limiting factor being the
pressure limitations of the selected pump 5 and high shear mixer
40. In some cases gaseous monomer may be introduced via a line
similar to line 22 into a liquid stream flowing through line 13. In
some embodiments, the monomer-containing stream in line 13
comprises ethylene and/or polyethylene monomer, plus any desired
co-monomers, dissolved in a suitable solvent, for the catalyzed
polymerization of the monomers to form polyethylene or
polypropylene, or a co-monomer thereof. In some embodiments, the
monomer-containing stream comprises solvent and gaseous monomer
bubbles, with or without catalyst particles or initiator.
[0039] Catalyst. A slurry of finely divided catalyst suspended in a
suitable solvent is combined with the monomer stream, or with a
solvent-monomer stream, in line 13, by introduction through line
22. In some embodiments, the catalyst slurry contains about 0.00001
to 0.1 percent Ziegler-Natta catalyst such as TiCl.sub.4/alkyl
aluminum chloride. In some embodiments, the catalyst is a
metallocene catalyst. Metallocene compounds consist of two
cyclopentadienyl anions (Cp) bound to a metal center in the
oxidation state II, generally corresponding to the general formula
(C.sub.5R.sub.5).sub.2M. Ziegler-Natta catalysts and metallocene
catalysts are well known in the field of olefin polymerization.
Alternatively, any other suitable olefin polymerization catalyst
may be employed in the present methods. In some embodiments, in
which a solid catalyst is sent through HSD 40, the selected mixing
tools (i.e., rotor/stator sets or generators) allow for catalyst
size reduction and/or increase in catalyst surface area.
[0040] The monomer-containing liquid stream is continuously pumped
into line 13 to form the high shear mixer feed stream. Additional
solvent may be introduced into line 13, and in some embodiments,
monomer and/or solvent is introduced independently into HSD 40. The
actual ratio of the raw materials used is determined based on the
desired selectivity and operating temperatures and pressures. In
some embodiments, the pressure is kept high enough throughout
system 1 to keep the monomer in solution. For the purposes of this
disclosure, the terms "superficial pressure" and "superficial
temperature" refer to the apparent, bulk, or measured pressure or
temperature, respectively, in a vessel, conduit or other apparatus
of the system. The actual temperatures and/or pressures at which
the reactants make contact and react in the microenvironment of a
transient cavity produced by the hydrodynamic forces of the high
shear mixer may be quite different, as further discussed elsewhere
herein.
[0041] After pumping, the catalyst and monomer liquid phase are
mixed within HSD 40, which serves to create a fine dispersion of
the catalyst in the monomer-containing liquid phase, which may also
include initiator. In some embodiments it creates a fine mixture,
emulsion or dispersion of the reactants, which may also include
catalyst. As used herein, the term "dispersion" refers to a
liquefied mixture that contains two distinguishable substances (or
phases) that will not readily mix and dissolve together. A
dispersion comprises a continuous phase (or matrix), which holds
therein discontinuous droplets, bubbles, and/or particles of the
other phase or substance. The term dispersion may thus refer to
foams comprising gas bubbles suspended in a liquid continuous
phase, emulsions in which droplets of a first liquid are dispersed
throughout a continuous phase comprising a second liquid with which
the first liquid is immiscible, and continuous liquid phases
throughout which solid particles are distributed. The term
"dispersion" encompasses continuous liquid phases throughout which
gas bubbles are distributed, continuous liquid phases throughout
which solid particles (e.g., solid catalyst) are distributed,
continuous phases of a first liquid throughout which droplets of a
second liquid that is substantially insoluble in the continuous
phase are distributed, and liquid phases throughout which any one
or a combination of solid particles, immiscible liquid droplets,
and gas bubbles are distributed. Hence, a dispersion can exist as a
homogeneous mixture in some cases (e.g., liquid/liquid phase), or
as a heterogeneous mixture (e.g., gas/liquid, solid/liquid, or
gas/solid/liquid), depending on the nature of the materials
selected for combination.
[0042] In HSD 40, the catalyst and monomer are highly dispersed
such that nanoparticles and microparticles of the catalyst are
formed for superior dissolution into solution and/or enhancement of
reactant mixing. For example, disperser IKA.RTM. model DR 2000/4, a
high shear, three stage dispersing device configured with three
rotors in combination with stators, aligned in series, is used to
create the dispersion of dispersible catalyst in liquid medium
comprising the monomers and any initiators (i.e., "the reactants").
The rotor/stator sets may be configured as illustrated in FIG. 2,
for example. For some applications, the direction of rotation of
the generators may be opposite that shown by arrow 265 (e.g.,
clockwise or counterclockwise about axis of rotation 260). The
combined reactants entering the high shear mixer via line 13
proceed to a first stage rotor/stator combination having
circumferentially spaced first stage shear openings. In some
applications, the direction of flow of the reactant stream entering
inlet 205 corresponds to the axis of rotation 260. The coarse
dispersion exiting the first stage enters the second rotor/stator
stage, having second stage shear openings. The reduced
particle-size dispersion emerging from the second stage enters the
third stage rotor/stator combination having third stage shear
openings. The dispersion exits the high shear mixer via line 18. In
some embodiments, the shear rate increases stepwise longitudinally
along the direction of the flow. For example, in some embodiments,
the shear rate in the first rotor/stator stage is greater than the
shear rate in subsequent stage(s). In other embodiments, the shear
rate is substantially constant along the direction of the flow,
with the stage or stages being the same. If the high shear mixer
includes a PTFE seal, for example, the seal may be cooled using any
suitable technique that is known in the art. For example, the
reactant stream flowing in line 13 may be used to cool the seal and
in so doing be preheated as desired prior to entering the high
shear mixer.
[0043] The rotor of HSD 40 is set to rotate at a speed commensurate
with the diameter of the rotor and the desired tip speed. As
described above, the high shear mixer (e.g., colloid mill) has
either a fixed clearance between the stator and rotor or has
adjustable clearance. HSD 40 serves to intimately mix the catalyst
and the liquid phase (i.e., monomer or solvent, or both). In some
embodiments of the process, the transport resistance of the
reactants is reduced by operation of the high shear mixer such that
the velocity of the reaction is increased by greater than a factor
of 5. In some embodiments, the velocity of the reaction is
increased by at least a factor of 10. In some embodiments, the
velocity is increased by a factor in the range of about 10 to about
100 fold. In some embodiments, HSD 40 delivers at least 300 L/h
with a power consumption of 1.5 kW at a nominal tip speed of at
least 22.9 msec (4500 ft/min), and which may exceed 40 msec (7900
ft/min). Although measurement of instantaneous temperature and
pressure at the tip of a rotating shear unit or revolving element
in HSD 40 is difficult, it is estimated that the localized
temperature seen by the intimately mixed reactants is in excess of
500.degree. C. and at pressures in excess of 5000 kPa (500
kg/cm.sup.2) under cavitation conditions. The high shear mixing
results in dispersion of the catalyst in micron or submicron-sized
particles (i.e., mean diameter less than one micron). In some
embodiments, the resultant dispersion has an average particle size
less than about 1.5 .mu.m. In some embodiments, the mean bubble
size is less than one micron in diameter. Accordingly, the
dispersion exiting HSD 40 via line 18 comprises micron and/or
submicron-sized particles. In some embodiments, the mean particle
size is in the range of about 0.4 .mu.m to about 1.5 .mu.m. In some
embodiments, the mean particle size is less than about 400 nm, in
the range of about 200 nm to about 400 nm, or is about 100 nm in
some cases. For the purposes of this disclosure, a nanodispersion
is a dispersion of heterogeneous solid-liquid phases in which the
sizes of the particles in the dispersed phase are less than 1000
nanometers (i.e., <1 micron in diameter). A nanodispersion is
sometimes also referred to herein as a "dispersion." In many
embodiments, the nanodispersion is able to remain dispersed at
atmospheric pressure for at least 15 minutes.
[0044] Once dispersed, the resulting nanodispersion exits HSD 40
via line 18 and feeds into vessel 10, as illustrated in FIG. 1,
wherein polymerization occurs or continues to take place. If
desired, the dispersion may be further processed prior to entering
vessel 10. For example, further mixing in one or more successive
high shear mixing devices, similar to HSD 40 with the same or
different generator configurations, may be performed, before the
process stream enters reactor/vessel 10. Although, in some
embodiments, the polymerization reaction may take place to at least
some extent without a catalyst or initiator, in most embodiments a
catalyst or initiator is included. Some suitable types of catalyst
are Ziegler-Natta catalysts and metallocene catalysts, as discussed
above. Alternatively, another suitable olefin polymerization
catalyst may be used. In some embodiments a chain transfer agent
(i.e., hydrogen) is added to terminate the polymerization process
and control the molecular weight of the polymer. Hydrogen may be
added at any point in the polymerization process where chain
termination is desired. One or more such additives may be injected
at line 13, line 18, or any other suitable point in the process, or
as illustrated in the flow diagram shown in FIG. 1. In some
embodiments, a heterogeneous reaction takes place in which the
intimately mixed monomer and finely divided catalyst are in the
form of a highly dispersed liquid. In some embodiments, as a result
of the intimate mixing of the reactants prior to entering reactor
10, a significant portion of the chemical reaction may take place
in HSD 40, with or without the presence of catalyst. Polymerization
of monomer to the corresponding polymer will occur whenever
suitable time, temperature and pressure conditions exist,
facilitated in some cases by the presence of the catalyst and/or
initiator. In this sense the polymerization of monomer may occur at
any point in the flow diagram of FIG. 1 if temperature and pressure
conditions are suitable. A discrete reactor is usually desirable,
however, to allow for increased residence time, agitation and
heating and/or cooling of the bulk reactants. Accordingly, in some
embodiments, reactor/vessel 10 may be used primarily for heating
and separation of volatile reaction products (i.e., vent gas) from
the polymerization product.
[0045] Alternatively, vessel 10 may serve as a primary reaction
vessel where most of the polymer is produced in some embodiments.
For example, the process may be operated as a single pass or "once
through" process in order to minimize subjecting the formed polymer
to shearing, in which case vessel 10 may serve as the primary
reaction vessel. Vessel/reactor 10 may be operated in either
continuous or semi-continuous flow mode, or it may be operated in
batch mode. The contents of vessel 10 may be maintained at a
specified reaction temperature using heating and/or cooling
capabilities (e.g., cooling coils) and temperature measurement
instrumentation. Pressure in the vessel may be monitored using
suitable pressure measurement instrumentation, and the level of
reactants in the vessel may be controlled using a level regulator
(not shown), employing techniques that are known to those of skill
in the art. The contents are stirred continuously or
semi-continuously.
[0046] The bulk or global operating temperature of the reactants is
desirably maintained below their flash points. In some embodiments,
the operating conditions of system 1 comprise a temperature in the
range of from about 20.degree. C. to about 230.degree. C. In some
embodiments, the temperature is less than about 200.degree. C. In
some embodiments, the temperature is in the range of from about
160.degree. C. to 180.degree. C. In specific embodiments, the
reaction temperature in vessel 10, in particular, is in the range
of from about 155.degree. C. to about 160.degree. C. In some
embodiments the process is operated at ambient temperature. In some
embodiments, the reaction pressure in vessel 10 is in the range of
from about 203 kPa (2 atm) to about 5573 kPa-6080 kPa (55-60 atm).
In some embodiments, reaction pressure is in the range of from
about 811 kPa to about 1520 kPa (about 8 to about 15 atm). In some
embodiments, the reaction pressure is less than 600 kPa (6 atm).
The superior dissolution and/or dispersion provided by the external
high shear mixing potentially allows a decrease in operating
pressure while maintaining or even increasing reaction rate.
Operating the polymerization process at decreased pressure
potentially decreases wear of the materials constituting the
reactors, the piping, and the mechanical parts of the plant, as
well as the ancillary devices, in some embodiments of the high
shear enhanced polymerization process.
[0047] The polymerization product may be produced either
continuously, semi-continuously or batch wise, as desired, and is
removed from system 1 via product line 16. In some embodiments, a
plurality of reactor product lines 16 are used to remove the
product. Vent gas, containing unconverted monomer vapor and any
volatile side reaction products, for example, exit reactor 10 via
line 17. In some instances, it may be desirable to use a compressor
type pump to recycle vent gases in line 17 back into HSD 40. The
vent gas may be further treated and vented, or its components may
be recycled, as desired, using known techniques. Reaction product
comprising polymer and dissolved, unconverted monomer exits reactor
10 by line 16. In some embodiments the product stream is further
processed. For example, the content of unconverted monomer in the
product stream may be reduced using suitable techniques as are
known. The polymer product may be used to manufacture any of a wide
variety of commercial products. For instance, it may serve as the
raw material for making packaging materials, vinyl flooring,
plumbing pipe, clothing, upholstery or building materials.
[0048] Multiple Pass Operation. Referring still to FIG. 1, the
system is configured for either single pass or multi-pass
operation, wherein, after the initial preparation of the
monomer-solvent solution in vessel 10 and commencement of the
process, the output from line 16 of vessel 10 goes directly to
recovery of the polymer product or to further processing. In some
embodiments it may be desirable to pass the contents of vessel 10,
or a portion thereof containing unreacted monomer, through HSD 40
during a second pass. In this case, the dispersion and the
initially formed polymer may be returned via lines 24 and 21, pump
5, and line 13, to HSD 40, for further dispersion and reaction.
Additional catalyst slurry may be injected via line 22 into line
13, or it may be added directly into the high shear mixer (not
shown), if needed. Additional solvent or monomer may be injected at
line 13, as needed.
[0049] In some embodiments, two or more high shear devices like HSD
40, or they may be configured differently, are aligned in series,
and are used to further enhance the reaction. Their operation may
be in either batch or continuous mode. In some instances in which a
single pass or "once through" process is desired, the use of
multiple high shear devices in series may also be advantageous. For
instance, in some applications, where low density product
containing shorter polymer chains is desired, the product may be
recycled via lines 24 and 21, to pump 5, and through high shear
mixer 40, before returning via line 18 to vessel 10. In some
embodiments where multiple high shear devices are operated in
series, vessel 10 may be omitted. When multiple high shear devices
40 are operated in series, additional reactant(s) may be injected
into the inlet feed stream of each device. In some embodiments,
multiple high shear devices 40 are operated in parallel, and the
outlet dispersions therefrom are introduced into one or more vessel
10.
[0050] In some alternative embodiments, the catalyst is not
circulated through HSD 40, but is instead retained in vessel 10,
where it is contacted by the premixed monomer(s) exiting HSD 40 via
line 18. For instance, in cases where very low molecular weight
and/or very low concentrations of high molecular weight polymer in
solvent are to be produced, a fixed bed reactor may be used as
vessel 10, provided that it is not allowed to become blocked by
polymer. In this case, solvent is pumped through line 21 and
gaseous monomer is injected via line 22 into the flowing stream in
line 13, which then flows into HSD 40 and is subjected to the high
shear mixing as described above, to form a gas-liquid dispersion.
For example, the injection could be propylene or ethylene gas
injected into a solvent medium like hexane and then polymerized
with the use of a catalyst. The gas-liquid dispersion then contacts
the catalyst in vessel 10, where polymerization occurs. Without
wishing to be limited by theory, it is believed that
submicron-sized bubbles dispersed in a liquid undergo movement
primarily through Brownian motion effects. The bubbles in the
product dispersion created by HSD 40 may have greater mobility
through boundary layers of catalyst particles in vessel 10, thereby
facilitating and accelerating the catalytic reaction through
enhanced transport of reactants.
[0051] In some variations of an above-described procedure, catalyst
is circulated through HSD 40 and gaseous monomer is introduced (via
line 22) into a flowing stream of solvent in line 13, which may
contain dissolved monomer. As a result of the high shear mixing, a
heterogeneous solid-gas-liquid reaction mixture exits HSD 40 via
line 18. The polymerization reaction may occur in HSD 40, line 18,
and/or vessel 10, or at any other point in system 1 where
temperature and pressure conditions are favorable.
[0052] In another variation of an above-described procedure, a
gas-solid heterogeneous phase polymerization reaction is carried
out in HSD 40. In this case, solvent or liquid monomer is not fed
into HSD 40, and instead a gaseous monomer stream flows through
line 13 and catalyst particles are introduced via line 22. A
dispersion of catalyst particles dispersed in gaseous monomer is
produced in the high shear mixing device. This variation may be
desired, for example, when is desirable for the gaseous monomers to
oligomerize in a gas-solid reaction with the catalyst.
[0053] In still another variation of an above-described procedure,
a liquid-liquid homogeneous phase mixture of dissolved monomer in a
suitable solvent (e.g., hexane) is introduced into HSD 40, with or
without catalyst, and is subjected to high shear mixing as
described above. The polymerization reaction may occur in HSD 40,
line 18, and/or vessel 10, or at any other point in system 1 where
catalyst is present and the temperature and pressure conditions are
favorable.
[0054] The application of enhanced mixing of the reactants by HSD
40 potentially causes greater polymerization of the monomer in some
embodiments of the process. In some embodiments, the enhanced
mixing potentiates an increase in throughput of the process stream.
In some embodiments, the high shear mixing device is incorporated
into an established process, thereby enabling an increase in
production (i.e., greater throughput). In contrast to some existing
methods that attempt to increase the degree of polymerization by
increasing reactor pressures, the superior dissolution and/or
dispersion provided by external high shear mixing may allow in many
cases a decrease in overall operating pressure while maintaining or
even increasing the polymerization rate. Without wishing to be
limited to a particular theory, it is believed that the level or
degree of high shear mixing is sufficient to increase rates of mass
transfer and may also produce localized non-ideal conditions that
enable reactions to occur that might not otherwise be expected to
occur based on Gibbs free energy predictions. Localized non ideal
conditions are believed to occur within the high shear device
resulting in increased temperatures and pressures with the most
significant increase believed to be in localized pressures. The
increase in pressures and temperatures within the high shear device
are instantaneous and localized and quickly revert back to bulk or
average system conditions once exiting the high shear device. In
some cases, the high shear mixing device induces cavitation of
sufficient intensity to dissociate one or more of the reactants
into free radicals, which may intensify a chemical reaction or
allow a reaction to take place at less stringent conditions than
might otherwise be required. Cavitation may also increase rates of
transport processes by producing local turbulence and liquid
micro-circulation (acoustic streaming). An overview of the
application of cavitation phenomenon in chemical/physical
processing applications is provided by Gogate et al., "Cavitation:
A technology on the horizon," Current Science 91 (No. 1): 35-46
(2006). The high shear mixing device of certain embodiments of the
present system and methods is operated under what is believed to be
cavitation conditions effective to dissociate the reactants into
free radicals which then form the polymer.
[0055] In some embodiments, use of an above-described high shear
process allows for greater catalyzed polymerization of monomer to
polymerization product and/or an increase in throughput of the
reactants. In some embodiments, an external high shear mixing
device is incorporated into an established process, thereby making
possible an increase in production compared to the process operated
without the high shear mixing of the reactants. In some
embodiments, a disclosed process or system makes possible the
design of a smaller and/or less capital intensive process than
previously possible without the incorporation of the external high
shear mixing device. In some embodiments, the application of a
disclosed method potentially reduces operating costs/increases
production from an existing process. In certain embodiments, the
use of a disclosed method may reduce capital costs for the design
of new polymerization processes. Still other potential benefits of
some embodiments of the system and method for the production of
polyethylene or polypropylene include, but are not limited to,
faster cycle times, increased throughput, higher monomer
conversion, reduced operating costs and/or reduced capital expense
due to the possibility of designing smaller reactors and/or
operating the polymerization process at lower temperature and/or
pressure. In some embodiments, a polymerization method is provided
for the production of polypropylene, polyethylene, or co-polymers
thereof, without the need for large volume reactors and without the
need to recover substantial amounts of unconverted monomer.
[0056] While preferred embodiments of the invention have been shown
and described, modifications thereof can be made by one skilled in
the art without departing from the spirit and teachings of the
invention. The embodiments described herein are exemplary only, and
are not intended to be limiting. Many variations and modifications
of the invention disclosed herein are possible and are within the
scope of the invention. Where numerical ranges or limitations are
expressly stated, such express ranges or limitations should be
understood to include iterative ranges or limitations of like
magnitude falling within the expressly stated ranges or limitations
(e.g., from about 1 to about 10 includes, 2, 3, 4, etc.; greater
than 0.10 includes 0.11, 0.12, 0.13, and so forth). Use of the term
"optionally" with respect to any element of a claim is intended to
mean that the subject element is required, or alternatively, is not
required. Both alternatives are intended to be within the scope of
the claim. Use of broader terms such as comprises, includes,
having, etc. should be understood to provide support for narrower
terms such as consisting of, consisting essentially of, comprised
substantially of, and the like.
[0057] Accordingly, the scope protection is not limited by the
description set out above but is only limited by the claims which
follow, that scope including all equivalents of the subject matter
of the claims. Each and every original claim is incorporated into
the specification as an embodiment of the present invention. Thus,
the claims are a further description and are an addition to the
preferred embodiments of the present invention. The disclosures of
all patents, patent applications, and publications cited herein are
hereby incorporated by reference, to the extent they provide
exemplary, procedural or other details supplementary to those set
forth herein.
* * * * *