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METHODS OF DELIVERING CATALYST
SYSTEMS FOR PROPYLENE
CROSS REFERENCE TO RELATED 5
This application claims the benefit of Provisional Application No. 60/417,254 filed Oct. 9, 2002, the disclosure of which are incorporated by reference. 10
FIELD OF INVENTION
Embodiments of the present invention generally relate to catalyst delivery for olefin polymerization. 15
Methods for forming polypropylene can include passing a stream having propylene monomers to a polymerization 20 reactor to contact a catalyst and form polypropylene. However, problems may arise that reduce the catalyst efficiency. For example, high efficiency catalysts may experience a reduced efficiency when exposed to poisons that may be present in polymerization reactors. Conventional catalyst 25 carriers, such as hexane, generally do not protect high activity catalyst systems from a reduction in efficiency when exposed to poisons. Therefore, it is desirable to provide a transport medium capable of maintaining catalyst efficiency in the presence of poisons. 30
SUMMARY OF THE INVENTION
In certain embodiments, a polymerization process includes providing a catalyst slurry having a metallocene 35 catalyst and a first oil, providing a transport medium including a second oil and combining the transport medium and the catalyst slurry to form a catalyst mixture. The process may further include introducing the catalyst mixture to a polymerization reactor and contacting olefin monomers with the 40 catalyst mixture to polymerize the olefin monomers and form polyolefins.
In certain embodiments, providing the catalyst slurry includes mixing the catalyst slurry in a first vessel to ^ maintain the metallocene catalyst suspended in the first oil.
In certain embodiments, providing the catalyst slurry includes passing the catalyst slurry from a first vessel to a second vessel prior to combining the transport medium and the catalyst slurry, the second vessel having a substantially 50 conical portion and a volume that is smaller than the volume of the first vessel. The process may further include passing the catalyst mixture through at least one meter configured to measure a catalyst addition rate. In yet other embodiments, providing the catalyst slurry includes monitoring the catalyst 55 addition rate by disposing the catalyst slurry in a second vessel having a catalyst slurry inlet and a catalyst slurry outlet and measuring the change of level of catalyst slurry within the second vessel.
In certain embodiments, the catalyst slurry includes 25 wt go % or less of the catalyst solids mixed with the first oil. In certain embodiments, the second oil flow rate is between 10 wt % and 100 wt % of the catalyst slurry flow rate.
In certain embodiments, combining the second oil and the catalyst slurry forms a catalyst mixture to provide a mixture 65 with a lower viscosity than the viscosity of the catalyst slurry.
In certain embodiments, the metallocene catalyst has an activity of 500 gPP/(gcat*hr) or more.
In certain embodiments, the metallocene catalyst is supported.
In certain embodiments, the first oil and the second oil include mineral oil. In yet other embodiments, the first oil and the second oil each have a kinematic viscosity of from 0.63 centistokes to 200 centistokes at 40° C.
In other embodiments, the polymerization process includes providing a catalyst slurry including a metallocene catalyst and a first mineral oil having a kinematic viscosity of from about 0.63 centistokes to 200 centistokes at 40° C, providing a transport medium including a second mineral oil, combining the transport medium and the catalyst slurry to form a catalyst mixture, introducing the catalyst mixture to a polymerization reactor and contacting propylene monomers with the catalyst mixture to polymerize the propylene monomers and form polypropylene.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 illustrates a system that may be employed for providing a catalyst slurry to a polymerization reactor.
FIG. 2 illustrates an enlarged view of a specific example of a molecular sieve unit.
FIG. 3 illustrates a polymerization process wherein the recycle stream is mixed with an essentially pure, "fresh" feed stream to form an input stream prior to purification.
FIG. 4 illustrates an example of a system operably connected to a polymerization vessel to deliver catalyst to the polymerization vessel.
Various specific embodiments, versions and examples of the invention will now be described, including preferred embodiments and definitions that are adopted herein for purposes of understanding the claimed invention. It is understood, however, that for determining infringement, the scope of the "invention" will refer to any one or more of the appended claims, including their equivalents, and elements or limitations that are equivalent to those that are recited. References to specific "embodiments" are intended to correspond to claims covering those embodiments, but not necessarily to claims that cover more than those embodiments.
Embodiments of the invention include a polymerization process. The polymerization process includes passing a feed stream having olefin monomers through a polymerization reactor to polymerize the olefin monomers and form a polyolefin. The feed stream preferably includes olefin monomers, either alone or in combination, e.g., mixtures, having from 2 carbon atoms up to 16 carbon atoms per molecule. For example, the feed stream may include ethylene, propylene, butene, pentene, hexane, septene and/or octene. More preferably, the feed stream includes propylene monomers. In certain embodiments, the feed stream includes propylene monomers in an amount of from 85 wt % to 90 wt %. In other embodiments, the feed stream includes propylene monomers in an amount of 95 wt % or more.
The polymerization process may be carried out in any type of polymerization system including, but not limited to, a solution, gas phase or slurry process, or combinations thereof. Typically, in a gas phase polymerization process, a continuous cycle is employed wherein one part of the cycle of a reactor system, a cycling gas stream, otherwise known as a recycle stream or fluidizing medium, is heated in the
reactor by the heat of polymerization. This heat is removed from the recycle composition in another part of the cycle by a cooling system external to the reactor. The gaseous stream containing one or more monomers may be continuously cycled through a fluidized bed in the presence of a catalyst 5 under reactive conditions. The gaseous stream is withdrawn from the fluidized bed and recycled back into the reactor. Simultaneously, polymer product is withdrawn from the reactor and fresh monomer is added to replace the polymerized monomer. Alternatively, other types of gas phase poly- 10 merization processes can also be used.
Slurry polymerization typically involves forming a suspension of solid, particulate polymer in a liquid polymerization medium, to which monomers and optionally hydrogen, along with catalyst, are added. The suspension (which 15 may include diluent) can be intermittently or continuously removed from the reactor where the volatile components can be separated from the polymer and recycled, optionally after a distillation, to the reactor.
In a specific embodiment, a slurry process may be carried 20 out continuously in one or more loop reactors. The catalyst as a slurry or as a dry free flowing powder can be injected regularly to the reactor loop, which can itself be filled with circulating slurry of growing polymer particles in a diluent. Hydrogen, optionally, may be added as a molecular weight 25 control. The reactor may be maintained at a pressure of from 27 bar to 45 bar, or preferably from 36 bar to 43 bar and at a temperature in the range of from 38° C. to 121° C, or preferably from 60° C. to 105° C. Reaction heat can be removed through the loop wall since much of the reactor is 30 in the form of a double-jacketed pipe. The slurry may exit the reactor at regular intervals or continuously to a heated low pressure flash vessel, rotary dryer and a nitrogen purge column in sequence for removal of the diluent and all unreacted monomer and comonomers. The resulted hydro- 35 carbon free powder can then be compounded for use in various applications. Alternatively, other types of slurry polymerization processes can be used.
In any of the types of polymerization processes described above, a catalyst is used to promote polymerization. Any 40 catalyst capable of polymerizing polyolefins in a polymerization reactor is contemplated. For example, high activity metallocene catalyst systems, e.g., catalyst systems having an efficiency of 500 gPP/(gcat*hr) or more, may be utilized. Preferably, the catalyst has an efficiency of 2500 gPP/ 45 (gcat*hr) or more. Even more preferably, the catalyst has an efficiency of 3500 gPP/(gcat*hr) or more, and alternatively, 5000 gPP/(gcat*hr) or more. Useful catalysts are described in detail in U.S. Pat. No. 6,368,999, which catalyst descriptions are hereby incorporated by reference. In processes 50 described herein, the amount of active metallocene is preferably 1.5 wt % or less and the amount of metal alkyl scavenger is 12 wt % or less of the metallocene catalyst. A catalyst having a low amount of active metallocene in combination with a low amount of metal alkyl scavenger, or 55 no metal alkyl scavenger, has been discovered to have a high sensitivity to poisons, resulting in lower catalyst efficiencies, and therefore lower polyolefin product yield. Certain aspects described herein include providing increased catalyst efficiency. 60
Certain polymerization processes may employ ZieglerNatta catalysts for a period of time, which may be followed by the use of metallocene catalysts for additional polymerizations. For example, the process may include contacting propylene monomers with a Ziegler-Natta catalyst system to 65 form polyolefins. Contacting the propylene monomers with a Ziegler-Natta catalyst system may generate poisons in the
product mixture. At least a portion of the product mixture may be recycled and combined with the propylene monomers to contact the Ziegler-Natta catalyst system. The process may further include stopping the introduction of Ziegler-Natta catalyst to the polymerization reactor to cease the polymerization. A metallocene catalyst system may then be passed to the polymerization reactor to polymerize the propylene monomers. In doing so, the metallocene catalyst efficiency may be reduced due to the poisons generated by the Ziegler-Natta polymerization process. For example, the activity of metallocene catalysts exposed to those poisons may be 50 gPP/(gcat*hr) or less. Although the specific poisons and poison levels can vary widely, the term "poisons", as used herein, refers to substances which reduce the catalyst efficiency, and specifically includes alcohols (e.g., methanol, isopropanol and ethanol) and halogen moeties (e.g., fluorides and organohalides such as methyl chloride).
In one or more embodiments, a polymerization process is provided that includes providing a catalyst slurry to a polymerization reactor, the catalyst slurry including a metallocene catalyst and a first oil. Suitable metallocene catalysts are represented by the formula:
wherein: M is a metal of Group 4, 5, or 6 of the Periodic Table preferably, zirconium, hafnium and titanium, most preferably zirconium;
R1 and R2 are identical or different, preferably identical, and are one of a hydrogen atom, a C^C^ alkyl group, preferably a C^^ alkyl group, a C^C^ alkoxy group, preferably a C^^ alkoxy group, a C6-C10 aryl group, preferably a C6-C8 aryl group, a C6-C10 aryloxy group, preferably a C6-C8 aryloxy group, a C2-C10 alkenyl group, preferably a C2-C4 alkenyl group, a C7-C40 arylalkyl group, preferably a C7-C10 arylalkyl group, a C7-C40 alkylaryl group, preferably a C7-C12 alkylaryl group, a C8-C40 arylalkenyl group, preferably a C8-C12 arylalkenyl group, or a halogen atom, preferably chlorine; or a conjugated diene which is optionally substituted with one or more hydrocarbyl, tri(hydrocarbyl)silyl groups or hydrocarbyl, tri(hydrocarbyl)silylhydrocarbyl groups, said diene having up to 30 atoms not counting hydrogen;
R5 and R6 are identical or different, preferably identical, are one of a hydrogen atom, a halogen atom, preferably a fluorine, chlorine or bromine atom, a C^C^ alkyl group, preferably a C^-C,^ alkyl group, which may be halogenated, a C6-C10 aryl group, which may be halogenated, preferably a C6-C8 aryl group, a C2-C10 alkenyl group, preferably a C2-C4 alkenyl group, a C7-C40 arylalkyl group, preferably a C7-C10 arylalkyl group, a C7-C40
-Sn—, —O—, — S—, X)—, —P(R14)—, or
—B(R14)—, —A1(R14)—, — Ge—SO—, —S02—, —N(R14)—, —P(0)(R14)—;
wherein: R14, R15 and R16 are identical or different and are a hydrogen atom, a halogen atom, a Q-C^ branched or linear alkyl group, a C1-C20 fluoroalkyl or silaalkyl group, a C6-C30 aryl group, a C6-C30 fluoroaryl group, a C^-cjo alkoxy group, a C2-C20 alkenyl group, a C7-C40 arylalkyl group, a C8-C40 arylalkenyl group, a C7-C40 alkylaryl group, or R14 and R15, together with the atoms binding them, form a cyclic ring; preferably, R14, R15 and R16 are identical and are a hydrogen atom, a halogen atom, a C^-C^ alkyl group, a CF3 group, a C6-C8 aryl group, a C6-C10 fluoroaryl group, more preferably a pentafluorophenyl group, a C^-C^ alkoxy group, in particular a methoxy group, a C2-C4 alkenyl group, a C7-C10 arylalkyl group, a C8-C12 arylalkenyl group, or a C7-C14 alkylaryl group;
or, R7 is represented by the formula:
wherein: R17 to R24 are as defined for R1 and R2, or two or more adjacent radicals R17 to R24, including R20 and R21, together with the atoms connecting them form one or more rings; preferably, R17 to R24 are hydrogen;
M2 is carbon, silicon, germanium or tin;
the radicals R3, R4, and R10 are identical or different and have the meanings stated for R5 and R6, or two adjacent R10 radicals are joined together to form a ring, preferably a ring containing from about 4-6 carbon atoms. Preferably, the metallocene catalyst is one of the high
efficiency metallocene catalysts described above. The cata
lyst slurry preferably includes 75 wt % or more of the first oil and 25 wt % or less of the metallocene catalyst. More preferably, the catalyst slurry includes from 90 wt % to 60 wt % first oil and from 10 wt % to 40 wt % metallocene catalyst. The first oil may be or include a mineral oil having a kinematic viscosity of from 0.63 centistokes (cSt) to 200 cSt at 40° C. Preferably, the mineral oil has a kinematic viscosity of from 50 cSt to 100 cSt, or from 45 cSt to 65 cSt, or from 25 cSt to 85 cSt. Preferably the first oil is or includes paraffinic mineral oil, such as Kaydol white oil commercially available from Witco Corporation The first oil may include mineral oil in amount greater than 95 wt %. More preferably the first oil includes 100 wt % mineral oil, i.e., the first oil is "pure" mineral oil. A schematic diagram that illustrates an example of the process is shown in FIG. 1.
The polymerization process preferably further includes providing a transport medium that includes a second oil. It has been discovered that providing the transport medium reduces catalyst particle attrition in process pumps. The second oil preferably has the same composition as the first oil, i.e., mineral oil. More preferably, the second oil has a viscosity that is lower than the viscosity of the catalyst slurry. For example, the second oil preferably has a kinematic viscosity of from 0.63 cSt to 200 cSt at 40° C. One purpose of the transport medium is to protect catalyst efficiency, e.g., to maintain the catalyst efficiency in comparison to catalyst systems not encountering poisons. The barrier properties of the transport medium preferably reduce the high activity catalyst system's sensitivity to poisons produced in the polymerization process.
FIG. 1 illustrates a system that may be employed for providing a catalyst slurry to a polymerization reactor 100. In order to maintain a homogeneous catalyst slurry, the catalyst slurry may be introduced to a first vessel 102 to maintain the metallocene catalyst suspended in the first oil. The first vessel 102 includes a mixer (not shown) configured to maintain uniform suspension of the metallocene catalyst particles in the first oil. Preferably, upon transfer from the first vessel 102 to another vessel or reactor, the catalyst slurry maintains the same solids concentration as upon introduction to the first vessel 102. For example, the first vessel 102 may include an anchor type mixer, e.g., a member shaped in the form of an anchor having a base proximate the base of the first vessel 102.
The first vessel 102 may include a catalyst slurry inlet 104, a catalyst slurry outlet 106 and a housing 108 having an upper portion and a lower portion. The lower portion may be disposed proximate the catalyst slurry outlet 106 and have a proximal end nearest the catalyst slurry inlet 104 and a distal end nearest the catalyst slurry outlet 106. The process may include passing a different catalyst to the polymerization reactor 100 at different times. Therefore, the first vessel 102 should be designed for complete displacement of the catalyst solids, e.g., flushing. The lower portion of the first vessel 102 should have a surface that is angled to encourage the catalyst to collect in a particular area. As used herein, "angled" is a plane greater than 0° and less than 90° from horizontal. In at least one embodiment, the surface is substantially conical. One way to flush the first vessel 102 is by passing a fluid, such as the first oil, through the first vessel 102, to remove any remaining catalyst slurry prior to filling the first vessel 102 with a different catalyst slurry. Accordingly, the proximal end preferably has a circumference that is greater than the circumference of the distal end, thereby facilitating cleaning of the first vessel 102 between polymerizations. The first vessel 102 may be sized based on individual system requirements. Mixing the catalyst slurry in the first vessel
102 operates to minimize catalyst particle attrition and provide for a higher catalyst solids concentration than systems not employing a catalyst slurry including a first oil.
The first vessel 102 may also have a first oil inlet 110 to receive additional amounts of the first oil to flush the first 5 vessel 102. The first vessel 102 may be flushed in between polymerization runs. Alternatively, the first vessel 102 may be flushed prior to changing the catalyst to be disposed in the first vessel 102. As a result of the angled surface, e.g., the substantially conical portion, flushing the first vessel 102 10 results in improved removal of the catalyst slurry from the first vessel 102 in comparison to vessels not having a conical portion.
The process may further include passing the catalyst slurry from a first vessel 102 to a second vessel 112 prior to 15 introducing the catalyst slurry into the polymerization vessel 100. The second vessel 112 may have a catalyst slurry inlet 114 and a catalyst slurry outlet 116 respectively configured to receive and discharge the catalyst slurry. Furthermore, the second vessel 112 may have a angled lower surface, e.g., a 20 substantially conical portion, and a volume that is smaller than the volume of the first vessel 102. The second vessel 112 may be used to meter, e.g., measure, the catalyst addition rate into the polymerization vessel 100. As a result, the second vessel 112 volume need only be large enough to 25 adequately meter the catalyst slurry and provide a sufficient volume of catalyst slurry to the polymerization vessel 100. Alternatively, metering may occur in the first vessel 102. When metering in the first vessel 102, the volume of the first vessel 102 should be small enough to adequately determine 30 a fluid level in the first vessel 102. The metering may include passing the catalyst slurry through at least one flow monitoring device (not shown) configured to measure a catalyst addition rate. Alternatively, the catalyst addition rate may be monitored via one or more gear pumps 125 disposed in the 35 conduit operably connected to the catalyst slurry outlet 116. The catalyst slurry exiting the second vessel 112 generally has a low pressure. Therefore, the pressure of the catalyst mixture may be increased by passing the catalyst mixture through the one or more gear pumps 125. A second oil may 40 be introduced into the one or more gear pumps 125 to prevent catalyst particle damage from the gear pumps 125. A preferred "flow monitoring device" can be what is commonly recognized or referred to in the polymerization reactor industry as a "meter" including a member configured to 45 measure the rate of the catalyst slurry flowing therethrough.
The transport medium 118 and the catalyst slurry are combined in the one or more gear pumps 125 to form a catalyst mixture 120, which is subsequently introduced to the polymerization vessel 100. Preferably, the catalyst mix- 50 ture 120 includes from 25 wt % to 75 wt % catalyst slurry and from 25 wt % to 75 wt % transport medium. The catalyst mixture 120 is then introduced to the polymerization reactor 100 so that the propylene monomers are contacted with the catalyst mixture 120 to polymerize the propylene monomers 55 and form polypropylene. Polymerization occurs in polymerization vessel 100 as described above.
Feed Stream Purification
In one or more embodiments, a polymerization process is 60 provided that includes contacting olefin monomers with a supported metallocene catalyst to polymerize the monomers and form a product mixture that includes macromers and/or polymers, unreacted or partially reacted monomers, and poisons. Preferably, the olefin monomers have from two to 65 sixteen carbon atoms. More preferably, the olefin monomers include propylene, ethylene, or combinations thereof. The
product mixture may include poisons in an amount of 2.5 ppm or more. Preferably, the supported metallocene catalyst system is a high efficiency metallocene catalyst system as described above.
The polymerization process may occur in a system utilizing a specific catalyst system for a polymerization run, such as a Ziegler-Natta catalyst system, and subsequently using a different catalyst system for another polymerization run, such as a metallocene catalyst system. For example, the process may include contacting propylene monomers with a Ziegler-Natta catalyst system to form polypropylene, thereby generating poisons in the product mixture. At least a portion of the product mixture may be recycled and combined with monomers to contact the Ziegler-Natta catalyst system. The process may further include stopping the flow of Ziegler-Natta catalyst to the polymerization reactor to cease the polymerization based on that particular catalyst system. A metallocene catalyst system may then be introduced to the polymerization reactor to polymerize the monomers. However, "poisons", such as organohalides and alcohols produced by the Ziegler-Natta catalysts are still present and may reduce the efficiency of the metallocene catalyst system. The product mixture including poisons may then be combined with the "fresh" propylene monomers to pass through the polymerization reactor and contact the metallocene catalyst system. The fresh propylene feed stream may include a small amount of impurities, which may also function as poisons. High efficiency, and therefore high yield, polymerization catalysts are particularly sensitive to poisons as a result of a low amount of metal alkyl scavenger present in the catalyst. Therefore, the poison level should be reduced prior to passing monomers through a polymerization process. Additionally, the process may further include removing a portion of the product mixture and passing it through a removal device including zeolite particles supported by a mesh screen, the zeolite particles having a pore size of from 6 A to 16 A, thereby preventing the passage of molecules having a size of greater than 16 A therethrough. In doing so, at least a portion of poisons from the product mixture are transferred to the zeolite particles providing a purified monomer stream having poisons in an amount of 1 ppm or less. More preferably, the purified monomer stream has poisons in an amount of 0.5 ppm or less.
Preferably, the removal device (discussed in further detail below) includes molecular sieve particles having an average pore size of from 6 A to 16 A. As used herein, the term "molecular sieve" means a structure having a high surface area to prevent the passage of specified molecules therethrough, such as molecules having a critical diameter of up to 10 A. For example, the molecular sieve unit may include an X type molecular sieve. A type X structured zeolite is characterized by Formula I below:
(0.9+-0.2)M2/KO:Al2O3(2.5+-0.5)SiO2.yH2O Formula I
where M represents at least one cation having a valence of not more than 3, n represents the valence of M and y is a value up to 8 depending upon the identity of M and the degree of hydration of the crystal. The cation M may be one or more of a number of cations such as a hydrogen cation, an alkali metal cation, or an alkaline earth cation or other selected cations and is generally referred to as an exchangeable site. The type X zeolite can be present in the base material in concentrations generally ranging from 75 wt % to 90 wt % of the base material based on a volatile free composition. The remaining material in the base material