Patent Description:
Polypropylene can be prepared by polymerization of propylene in one or more reactors in which feed materials such as monomer, comonomer, catalyst, activator, chain transfer agent, and catalyst diluent are introduced. The polymerization reaction within the reactor yields polypropylene as part of a polymerization product. The propylene can be recovered, and remaining portions of the polymerization product (e.g., unreacted propylene, unreacted comonomer, and catalyst diluent) can be further processed, typically downstream from the reactor in monomer recovery systems. The polypropylene can be a homopolymer, random copolymer, or block copolymer.

In some cases, catalysts used in propylene polymerization can be mixed with a carrier fluid for transport to a polymerization reactor. Also, propylene can be pre-polymerized to produce polypropylene particles that are then fed to a polymerization reactor. The carrier fluid for the catalyst that is fed to the reactor and that is fed to a pre-polymerization system is a cost in propylene polymerization. Moreover, as the size of commercial polypropylene manufacturing plants increases to meet global demand, so does the demand for these carrier fluids, and alternative carrier fluid sources are desirable for various reasons including to obtain stable supply, to reduce operating cost, and to simplify plant design.

Disclosed is a process for pre-polymerizing propylene that includes adding a catalyst and a hydrocarbon to a first mixer; mixing the catalyst and the hydrocarbon in the first mixer to form a first catalyst suspension comprising the catalyst and the hydrocarbon; flowing the first catalyst suspension from the first mixer to a second mixer; adding a co-catalyst and an optional electron donor agent to the first catalyst suspension in or upstream of the second mixer; pre-polymerizing propylene in the second mixer to form a second catalyst suspension comprising the hydrocarbon and catalyst particles coated with polypropylene; and flowing the second catalyst suspension to a polymerization reactor or to a storage tank.

Also disclosed herein a pre-polymerization system that includes a first feed line comprising a catalyst; a first mixer having a first inlet connected to the first feed line; a first transfer line containing a first catalyst suspension and having an end connected to an outlet of the first mixer; a second mixer having an inlet connected to an opposite end of the first transfer line, wherein the second mixer is configured to pre-polymerize propylene in a presence of the catalyst to produce a coating of polypropylene on catalyst particles received from the first transfer line; a second feed line comprising a co-catalyst, wherein the second feed line is connected to the first transfer line or to a second inlet of the second mixer; an optional third feed line comprising an electron donor agent, wherein the optional third feed line is connected to the first transfer line or to a third inlet of the second mixer; a second transfer line having an end connected to an outlet of the second mixer; and a polymerization reactor coupled to an opposite end of the second transfer line, wherein the polymerization reactor is configured to polymerize propylene in a presence of the catalyst particles having the coating of polypropylene to produce a product polypropylene.

The following figures form part of the present specification and are included to further demonstrate certain aspects of the present invention. The invention may be better understood by reference to one or more of these figures in combination with the detailed description of specific embodiments presented herein.

While the inventions disclosed herein are susceptible to various modifications and alternative forms, only a few specific embodiments have been shown by way of example in the drawings and are described in detail below. The figures and detailed descriptions of these specific embodiments are not intended to limit the breadth or scope of the inventive concepts or the appended claims in any manner. Rather, the figures and detailed written descriptions are provided to illustrate the inventive concepts to a person of ordinary skill in the art and to enable such person to make and use the inventive concepts.

The figures described above and the written description of specific structures and functions below are not presented to limit the scope of what Applicant has invented or the scope of the appended claims. Rather, the figures and written description are provided to teach any person skilled in the art to make and use the inventions for which patent protection is sought. Those skilled in the art will appreciate that not all features of a commercial embodiment of the inventions are described or shown for the sake of clarity and understanding. Persons of skill in this art will also appreciate that the development of an actual commercial embodiment incorporating aspects of the present inventions will require numerous implementation-specific decisions to achieve the developer's ultimate goal for the commercial embodiment. Such implementation-specific decisions may include, and likely are not limited to, compliance with system-related, business-related, government-related, and other constraints, which may vary by specific implementation, location, and time. While a developer's efforts might be complex and time-consuming in an absolute sense, such efforts would be, nevertheless, a routine undertaking for those of skill in this art having benefit of this disclosure. It must be understood that the inventions disclosed and taught herein are susceptible to numerous and various modifications and alternative forms. Lastly, the use of a singular term, such as, but not limited to, "a," is not intended as limiting of the number of items. Also, the use of relational terms, such as, but not limited to, "top," "bottom," "left," "right," "upper," "lower," "up," "down," "side," and the like are used in the written description for clarity in specific reference to the figures and are not intended to limit the scope of the invention or the appended claims.

The terms "configured to", "configured for use", "adapted for use", and similar language is used herein to reflect that the particular recited structure or procedure is used in a disclosed system or process. For example, unless otherwise specified, a particular structure "configured for use" means it is "configured for use in an olefin polymerization system" and therefore is designed, shaped, arranged, constructed, and/or tailored to effect an olefin polymerization, as would have been understood by the skilled person.

The terms "conduit" and "line" are interchangeable, and as used herein, refer to a physical structure configured for the flow of materials therethrough, such as pipe or tubing. The materials that flow in the "conduit" or "line" can be in the gas phase, the liquid phase, the solid phase, or a combination of these phases.

The term "stream" as used herein refers to a physical composition of materials that flow through a "conduit" or "line".

The terms "pre-polymerization" and "pre-polymerizing" as used herein refer to conditions of polymerization that are performed to achieve a lower reaction rate and monomer conversion, as compared with the reaction rate and monomer conversion achieved under normal polymerization conditions. The purpose of pre-polymerization is to affect the bulk properties and improve reactor operability. Bulk properties include average particle size, fines, and bulk density. Reaction rate can be lowered by adjusting the reactor temperature, concentration of comonomer, and alkyl concentration.

The term "mixed butanes" as used herein refers to a mixture of n-butane and isobutane. An exemplary stream of "mixed butanes" includes at least about <NUM> vol% n-butane and less than about <NUM> vol% isobutane.

Disclosed herein are systems and processes for pre-polymerizing a catalyst for use in the polymerization of propylene. The systems and processes involve using propylene, propane, n-butane, mixed butanes, or a combination thereof as a catalyst carrier and as a diluent during pre-polymerization of the catalyst. The disclosed system and process may be performed on a batch or continuous basis. The pre-polymerized catalyst can then be introduced into a reactor configured for the polymerization of propylene. Use of propylene as the catalyst carrier and pre-polymerization diluent simplifies the hydrocarbon separations after recovery from the polymerization product (recovered from the polymerization reactor) because propylene used as diluent can be isolated under the same conditions that unreacted propylene is isolated. Use of propane, n-butane, mixed butanes, or combinations thereof as the catalyst carrier and pre-polymerization diluent i) provides an option for propylene polymerization systems and processes that have a limited availability of isobutane or would like to reduce the cost of the carrier diluent since n-butane and mixed butanes have a lower cost than isobutane, ii) reduce the size of or eliminate the need for equipment related to isobutane feed, treatment, storage, and recovery, and iii) improves monomer efficiency since less propylene will be lost in the hydrocarbon separations due to the higher boiling point for the n-butane (as compared to isobutane).

Turning now to the figures, <FIG> illustrate process flow diagrams of embodiments of pre-polymerization systems <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>. Aspects and embodiments of each system <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> are described below.

<FIG> (not according to the invention) illustrates a process flow diagram of an embodiment of a pre-polymerization system <NUM>. The system <NUM> in <FIG> utilizes propylene as the diluent for the catalyst. Two mixing vessels are utilized, a first mixer <NUM> and a second mixer <NUM> coupled to one another by the various lines that are configured to transport the catalyst suspension and introduce co-catalyst and an optional electron donor agent for pre-polymerization of propylene in the second mixer <NUM>.

In the system <NUM> of <FIG>, propylene is fed to the first mixer <NUM> via feed line <NUM>. The feed line <NUM> has an end connected to the inlet <NUM> of the first mixer <NUM>. A control valve <NUM> can be included in feed line <NUM> and configured to control the amount of propylene that is introduced into the first mixer <NUM> via the inlet <NUM>. In some embodiments, the control valve <NUM> can be an actuator valve that opens and closes to allow and disallow a flow of propylene in feed line <NUM>. In other embodiments, the control valve <NUM> can be a throttling valve that can control the size of the orifice that is open for flow of propylene through the valve <NUM>. The control valve <NUM> can be controlled by any controller known in the art with the aid of this disclosure. The propylene in feed line <NUM> can be in liquid phase and comprise greater than <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM> wt% of the contents of the feed line <NUM> based on a total weight of contents in the feed line <NUM>, with the remainder of components in the feed line <NUM> being liquid hydrocarbons other than propylene. In an embodiment, the feed line <NUM> can contain about <NUM> wt% propylene based on a total weight of the contents in the feed line <NUM>.

A catalyst hopper <NUM> contains catalyst particles that are introduced into the first mixer <NUM> via feed line <NUM>. The feed line <NUM> has an end connected to an outlet <NUM> of the catalyst hopper <NUM> and an opposite end connected to the inlet <NUM> of the first mixer <NUM>. The catalyst particles are solid particles of the catalyst used for polymerization of propylene. The catalyst particles can include solid particles of Ziegler-Natta catalyst, metallocene catalyst, or a combination of Ziegler-Natta and metallocene catalysts, for example. In some aspects, the solid catalyst particles may include the catalyst(s) associated with a support material (e.g., silica, alumina, titania, MgCl<NUM>, or combinations thereof). A control valve <NUM> can be included in feed line <NUM> to regulate the flow of catalyst particles from the catalyst hopper <NUM> into the first mixer <NUM>. In some embodiments, the control valve <NUM> can be a cycling valve that meters the amount of catalyst particles that flow in feed line <NUM> to the first mixer <NUM>. In other embodiments, the control valve <NUM> can be an actuator valve that opens and closes to allow and disallow a flow of catalyst particles in feed line <NUM>. In yet other embodiments, the control valve <NUM> can be a throttling valve that can control the size of the orifice that is open for flow of catalyst particles through the valve <NUM>. The control valve <NUM> can be controlled by any controller known in the art with the aid of this disclosure.

In some aspects, the inlets <NUM> and <NUM> can be embodied as a single inlet for the first mixer <NUM>, and feed lines <NUM> and <NUM> can be configured to combine into a single feed line which is connected to the single inlet for the first mixer <NUM>.

The first mixer <NUM> is configured to mix propylene and solid catalyst particles to form a catalyst suspension for transport in the pre-polymerization system <NUM>. The first mixer <NUM> can be embodied as any vessel that is suitable for mixing catalyst suspensions, and particularly, for mixing catalyst suspensions that are used for the polymerization of propylene, e.g., for introduction to a loop slurry reactor or a gas phase reactor. The vessel can generally be cylindrical in shape. The top and bottom of the vessel can be flat or can have a contour that is appropriate for holding pressurized contents, e.g., at a pressure suitable for coupling with a polymerization reactor. In some embodiments, the first mixer <NUM> can have a stirrer extending within the vessel such that the first mixer <NUM> is a continuous stirred tank. In some aspects, the height of the first mixer <NUM> can be <NUM>-<NUM> feet; alternatively, or <NUM>-<NUM> feet; or alternatively, <NUM>-<NUM> feet as measured tangent to tangent. In some aspects, the diameter of the first mixer <NUM> can be <NUM>-<NUM> feet; alternatively, <NUM>-<NUM> feet; alternatively, <NUM>-<NUM> feet; alternatively, <NUM>-<NUM> feet; or alternatively, <NUM>-<NUM> feet.

The temperature of the first mixer <NUM> can be controlled by heat exchange jackets <NUM> on the walls of the first mixer <NUM> that circulate coolant or refrigerant therethrough (e.g., via coolant/refrigerant input and output lines <NUM> and <NUM>) to control the temperature of the contents of the first mixer <NUM> to a temperature in the range of from about <NUM> to about <NUM>; alternatively, from about <NUM> to about <NUM>; alternatively, from about <NUM> to about <NUM>; alternatively, about <NUM>. In alternative embodiments, the temperature of the first mixer <NUM> can be controlled by an external heat exchange circulation loop coupled to the first mixer <NUM> that removes a portion of the catalyst suspension and cools the suspension in a heat exchanger before passing the cooled suspension back to the first mixer <NUM>, or by any other heat exchange mechanism known in the art with the aid of this disclosure.

A transfer line <NUM> has an end connected to an outlet <NUM> of the first mixer <NUM> and an opposite end connected to an inlet <NUM> of the second mixer <NUM>. The transfer line <NUM> is configured to transport the catalyst suspension from the first mixer <NUM> to the second mixer <NUM>. Limited polymerization of propylene may occur in line <NUM> because of the low temperature controlled in the first mixer <NUM> and because the co-catalyst and optional electron donor agent are not present in line <NUM>. A control valve <NUM> can be included in transfer line <NUM> to regulate the flow of catalyst suspension from the first mixer <NUM> to the second mixer <NUM>. In some embodiments, the control valve <NUM> can be an actuator valve that opens and closes to allow and disallow a flow of catalyst suspension in transfer line <NUM>. In other embodiments, the control valve <NUM> can be a throttling valve that can control the size of the orifice that is open for flow of catalyst suspension through the valve <NUM>. The control valve <NUM> can be controlled by any controller known in the art with the aid of this disclosure.

In aspects of the system <NUM> of <FIG>, co-catalyst can be fed to the second mixer <NUM> via feed line <NUM>. It is recognized that in some aspects, the co-catalyst may not be needed in order to affect pre-polymerization of propylene in the system <NUM>, while in other aspects, co-catalyst is required to affect pre-polymerization of propylene to a level that is adequate for propylene to be considered pre-polymerized within the disclosed of this disclosure. In aspects where co-catalyst is required for pre-polymerization to adequate levels, the feed line <NUM> can have an end connected to a co-catalyst source <NUM> and an opposite end connected to an inlet <NUM> of the second mixer <NUM>. Suitable co-catalyst include, but are not limited to, aluminoxane compounds, organoboron or organoborate compounds, ionizing ionic compounds, organoaluminum compounds, organozinc compounds, organomagnesium compounds, organolithium compounds, or combinations thereof. Examples of organoaluminum compounds include trialkylaluminum, trialkyloxyaluminum, alkylaluminum dihalide, and dialkylaluminum halide in which the halogen component is provided by chlorine, bromine, or iodine. An example of trialkylaluminum compound is triethylaluminum. A control valve <NUM> can be included in feed line <NUM> to regulate the flow of co-catalyst from the co-catalyst source <NUM> to the second mixer <NUM>. In some embodiments, the control valve <NUM> can be an actuator valve that opens and closes to allow and disallow a flow of co-catalyst in feed line <NUM>. In other embodiments, the control valve <NUM> can be a throttling valve that can control the size of the orifice that is open for flow of co-catalyst through the valve <NUM>. The control valve <NUM> can be controlled by any controller known in the art with the aid of this disclosure.

In some aspects of the system <NUM> of <FIG>, an electron donor agent optionally can be fed to the second mixer <NUM> via feed line <NUM>. When electron donor agent is utilized in the system <NUM>, the feed line <NUM> can have an end connected to the electron donor agent source <NUM> and an opposite end connected to an inlet <NUM> of the second mixer <NUM>. Electron donors can include amines, amides, ethers, ketones, nitriles, phosphines, stibines, arsines, phosphoramides, thioethers, thioesters, aldehydes, alcoholates, amides, silanes, and salts of organic acids. Examples of suitable esters include esters of carboxylic, alkoxy or amino acids, and esters of aromatic acids. An example of a silane compound is diphenyl dimethoxy silane. A control valve <NUM> can be included in feed line <NUM> to regulate the flow of electron donor agent from the electron donor agent source <NUM> to the second mixer <NUM>. In some embodiments, the control valve <NUM> can be an actuator valve that opens and closes to allow and disallow a flow of electron donor agent in feed line <NUM>. In other embodiments, the control valve <NUM> can be a throttling valve that can control the size of the orifice that is open for flow of electron donor agent through the valve <NUM>. The control valve <NUM> can be controlled by any controller known in the art with the aid of this disclosure.

In aspects of the disclosure, the electron donor agent and be introduced in the pre-polymerization system <NUM> upstream of the polymerization reactor <NUM>; alternatively, the electron donor agent can be introduced to the polymerization reactor <NUM>; or alternatively, the electron donor agent can be introduced into both the pre-polymerization system <NUM> upstream of the polymerization reactor <NUM> and to the polymerization reactor <NUM>.

In some aspects, the inlets <NUM>, <NUM>, and <NUM> can be embodied as two inlets or a single inlet for the second mixer <NUM>. For example, the second mixer <NUM> may include only inlets <NUM> and <NUM>. In such embodiments, feed lines <NUM> and <NUM> can be configured to combine into a combined feed line that is connected to inlet <NUM>, while the transfer line <NUM> is connected to the inlet <NUM>. In other embodiments, the transfer line <NUM> and feed lines <NUM> and <NUM> can be configured to combine into a combined feed line that is connected to a single inlet for the second mixer, e.g., inlet <NUM>.

The second mixer <NUM> is configured to operate under conditions that pre-polymerize propylene in the presence of the catalyst contained in/on the catalyst particles such that a coating of polypropylene is produced on the solid catalyst particles. The reaction conditions (e.g., one or more of pressure, temperature, residence time, catalyst particle concentration in the propylene, co-catalyst concentration in the propylene, and electron donor agent concentration in the propylene) of the catalyst suspension within the second mixer <NUM> may be controlled to have a lower temperature and/or lower polymerization rate, as compared to a polymerization reactor <NUM>, to allow the pre-polymer particles to form without exceeding a pre-polymer particle size that would foul any downstream lines (e.g., line <NUM>) and/or downstream equipment (e.g., pump <NUM>, valve <NUM>, inlet <NUM>). In some aspects, the reaction conditions that are controlled in the second mixer <NUM> for pre-polymerization of propylene are co-catalyst concentration in the propylene, electron donor agent concentration in the propylene, temperature, and residence time of the catalyst suspension in the second mixer <NUM>. The pressure in the second mixer <NUM> can be controlled by a supply of inert gas or other pressure control mechanism known in the art with the aid of this disclosure.

The pre-polymerization reaction is an exothermic reaction, so temperature control generally involves the removal of the heat of reaction to maintain the temperature of the catalyst suspension in the second mixer <NUM>. The temperature of the second mixer <NUM> can be controlled by heat exchange jackets <NUM> on the walls of the second mixer <NUM> that circulate coolant therethrough (e.g., via coolant/refrigerant input and output lines <NUM> and <NUM>) to control the temperature of the contents of the second mixer <NUM> to a temperature in the range of from about <NUM> to about <NUM>; alternatively, from about <NUM> to about <NUM>; alternatively, from about <NUM> to about <NUM>; alternatively, about <NUM>. In alternative embodiments, the temperature of the second mixer <NUM> can be controlled by an external heat exchange circulation loop coupled to the second mixer <NUM> that removes a portion of the catalyst suspension and cools the suspension in a heat exchanger before passing the cooled suspension back to the second mixer <NUM>, or by any other heat exchange mechanism known in the art with the aid of this disclosure. In some aspects, the amount of propylene can be in excess of the other reactants in an amount such that any heat of pre-polymerization reaction is absorbed by the bulk amount of propylene in the second mixer <NUM>, also referred to herein as adiabatic operation, such that temperature in the second mixer <NUM> can be controlled by the amount of reactants instead of with heat exchange mechanisms. The residence time of the catalyst suspension in the second mixer <NUM> can be controlled by the flow rate of the catalyst suspension into and out of the second mixer <NUM> (e.g., via valve <NUM> and valve <NUM>), the volume of the second mixer <NUM>, or both. The catalyst particle concentration in the propylene can be controlled by the valve <NUM> in line <NUM>. The co-catalyst concentration can be controlled by the valve <NUM> in line <NUM>. The electron donor agent concentration in the propylene can be controlled by the valve <NUM> in line <NUM>.

The second mixer <NUM> can be embodied as any vessel that is suitable for pre-polymerization of propylene onto the catalyst particles prior to introduction of the pre-polymerized catalyst particles to a polymerization reactor. In some embodiments, the second mixer <NUM> can have a stirrer extending within the vessel such that the second mixer <NUM> is a continuous stirred tank. The vessel can generally be cylindrical in shape. The top and bottom of the vessel can be flat or can have a contour that is appropriate for holding pressurized contents, e.g., at a pressure suitable for coupling with a polymerization reactor. In some aspects, the height of the second mixer <NUM> can be <NUM>-<NUM> feet; alternatively, or <NUM>-<NUM> feet; or alternatively, <NUM>-<NUM> feet as measured tangent to tangent. In some aspects, the diameter of the second mixer <NUM> can be <NUM>-<NUM> feet; alternatively, <NUM>-<NUM> feet; alternatively, <NUM>-<NUM> feet; alternatively, <NUM>-<NUM> feet; or alternatively, <NUM>-<NUM> feet.

A transfer line <NUM> has an end connected to an outlet <NUM> of the second mixer <NUM> and an opposite end connected to a polymerization reactor <NUM>. The transfer line <NUM> is configured to transport the pre-polymerized catalyst suspension from the second mixer <NUM> to the polymerization reactor <NUM>. A control valve <NUM> and pump <NUM> can be included in transfer line <NUM> to regulate the flow of pre-polymerized catalyst suspension from the second mixer <NUM> to the polymerization reactor <NUM>. In some embodiments, the control valve <NUM> can be an actuator valve that opens and closes to allow and disallow a flow of pre-polymerized catalyst suspension in transfer line <NUM>. In other embodiments, the control valve <NUM> can be a throttling valve that can control the size of the orifice that is open for flow of pre-polymerized catalyst suspension through the valve <NUM>. The control valve <NUM> can be controlled by any controller known in the art with the aid of this disclosure. The pump <NUM> can be embodied as any pump suitable for pumping a slurry of a solid suspended in a liquid (e.g., the pre-polymerized catalyst suspension containing solid catalyst particles coated with polypropylene and mixed in liquid propylene) at a head pressure suitable for feeding the pre-polymerized catalyst suspension to the polymerization reactor <NUM>. Suitable pressures for the pre-polymerized catalyst suspension in transfer line <NUM> include any pressure that is higher than the pressure in the polymerization reactor <NUM>.

In some embodiments, pre-polymerization can continue in transfer line <NUM> as the pre-polymerized catalyst suspension flows from the outlet <NUM> of the second mixer <NUM> to the inlet <NUM> of the polymerization reactor <NUM>.

The polymerization reactor <NUM> is configured to polymerize propylene in the presence of the pre-polymerized catalyst particles (the catalyst particles having the coating of polypropylene) to produce product polypropylene. In aspects, polymerization of propylene is performed under bulk polymerization conditions, where propylene is included as a liquid in the polymerization reactor <NUM> in an amount of at least <NUM>, <NUM>, or <NUM> wt% based on the liquids in the polymerization reactor <NUM>. The polymerization reactor <NUM> can be embodied as one or more polymerization reactors, e.g., one or more loop slurry reactors in series or parallel. The polymerization reactor <NUM> can also be embodied as one or more loop reactors and one or more gas phase reactors connected in series. For example, in some aspects the polymerization reactor <NUM> can be two loop reactors. Configurations for these types of polymerization reactors are known, each capable of producing a polypropylene by contacting an olefin monomer with a pre-polymerized catalyst suspension that is introduced via the disclosed system <NUM>. In aspects where the polymerization reactor <NUM> is more than one reactor, the reactors can be configured to operate in parallel or in series. The polymerization reactor <NUM> generally has an inlet <NUM> for the second catalyst suspension and a polymerization product discharge outlet <NUM>. One or more other inlets may be included on polymerization reactor <NUM> for other reaction components, such as inlets for propylene, comonomer, catalyst, co-catalyst, electron donor agent, or any combination thereof. For clarity, these inlets are not shown on the polymerization reactor <NUM>. Polymerization product containing the polypropylene can flow from the polymerization reactor <NUM> via polymerization product discharge outlet <NUM> to a product separation system, which can be of any configuration known in the art.

<FIG> illustrates a process flow diagram of another embodiment of a pre-polymerization system <NUM>. The system <NUM> in <FIG> utilizes propylene as the diluent for the catalyst. Two mixing vessels are utilized, a first mixer <NUM> and a second mixer <NUM> coupled to one another by the various lines that are configured to transport the catalyst suspension and introduce co-catalyst and an optional electron donor agent for pre-polymerization of propylene in and/or upstream of the second mixer <NUM>. Like parts in <FIG> with respect to <FIG> are labeled with the same numerals, and the previous description of the like parts applies to the system <NUM> unless otherwise stated. Different than the system <NUM> in <FIG>, the second mixer <NUM> in system <NUM> in <FIG> is embodied as a static mixer, and the co-catalyst and electron donor agent are combined with the catalyst suspension in transfer lines between the first mixer <NUM> and the second mixer <NUM>.

In the system <NUM> of <FIG>, the catalyst suspension is prepared in the first mixer <NUM> in the same manner as described for the system <NUM> in <FIG>. The first mixer <NUM> in system <NUM> can have temperature control (e.g., jackets <NUM>) as described for the first mixer <NUM> in <FIG>.

A transfer line <NUM> has an end connected to an outlet <NUM> of the first mixer <NUM> and an opposite end connected to the suction inlet of a pump <NUM>. The transfer line <NUM> is configured to transport the catalyst suspension from the first mixer <NUM> to the pump <NUM>. No polymerization of propylene occurs in line <NUM> because the co-catalyst and optional electron donor agent are not present in line <NUM>. A control valve <NUM> can be included in transfer line <NUM> to regulate the flow of catalyst suspension from the pump <NUM> to the second mixer <NUM>. In some embodiments, the control valve <NUM> can be an actuator valve that opens and closes to allow and disallow a flow of catalyst suspension in transfer line <NUM>. In other embodiments, the control valve <NUM> can be a throttling valve that can control the size of the orifice that is open for flow of catalyst suspension through the valve <NUM>. The control valve <NUM> can be controlled by any controller known in the art with the aid of this disclosure.

The pump <NUM> can be embodied as any pump suitable for pumping a slurry of a solid suspended in a liquid (e.g., the catalyst suspension in line <NUM>, which transforms to the pre-polymerized catalyst suspension containing solid catalyst particles coated with polypropylene and mixed in liquid propylene) at a head pressure suitable for feeding the pre-polymerized catalyst suspension to the polymerization reactor <NUM>. Suitable pressures for the catalyst suspension and pre-polymerized catalyst suspension in transfer lines <NUM>, <NUM>, <NUM>, and <NUM> include any pressure that is higher than the pressure in the polymerization reactor <NUM>. The pumped catalyst suspension exits the pump <NUM> in line <NUM>. No polymerization of propylene occurs in line <NUM> because the co-catalyst and optional electron donor agent are not present in line <NUM>.

The co-catalyst in line <NUM> can combine with the catalyst suspension in line <NUM> such that the first catalyst suspension in line <NUM> contains propylene, catalyst particles, and the co-catalyst. In some embodiments, line <NUM> can have an end connected to the second mixer <NUM>. In these embodiments, it is contemplated that reaction conditions (e.g., one or more of pressure, temperature, catalyst particle concentration in the propylene, and co-catalyst concentration in the propylene) of the catalyst suspension in line <NUM> can be controlled such that a controlled amount of polymerization of propylene occurs on the surface of the catalyst particles in a manner that is consistent with pre-polymerization; alternatively, any combination of these conditions in line <NUM>, in addition to residence time in line <NUM>, are such that no significant amount of pre-polymerization can occur in line <NUM> (e.g., for catalyst systems that require electron donor agent to initiate pre-polymerization, as discussed below).

In optional embodiments, the electron donor agent in line <NUM> can combine with the first catalyst suspension in line <NUM> such that the first catalyst suspension in line <NUM> contains propylene, catalyst particles, the co-catalyst, and the electron donor agent. Line <NUM> can have an end connected to the inlet <NUM> of the second mixer <NUM>. Reaction conditions (e.g., one or more of pressure, temperature, catalyst particle concentration in the propylene, co-catalyst concentration in the propylene, and electron donor agent concentration in the propylene) of the catalyst suspension in line <NUM> can be controlled such that a controlled amount of polymerization of propylene occurs on the surface of the catalyst particles in a manner that is consistent with pre-polymerization; alternatively, any combination of conditions in line <NUM>, in addition to residence time in line <NUM>, are such that no significant amount of pre-polymerization occurs in line <NUM>.

The first catalyst suspension can flow into the inlet <NUM> of the second mixer <NUM>. The second mixer <NUM> is configured to polymerize propylene in the presence of the catalyst to produce a coating of polypropylene on the catalyst particles that are received from the transfer line <NUM> or <NUM>. As discussed above, the second mixer <NUM> can be embodied as a static mixer. In some aspects, the static mixer can have fixed baffles <NUM> (e.g., in a helical arrangement, or any other baffle arrangement) placed within a housing <NUM>, where the baffles <NUM> continuously blend the components of the first catalyst suspension. The housing <NUM> can have a length in the range of from about <NUM> ft to about <NUM> ft (<NUM> to <NUM>); alternatively, from about <NUM> ft to about <NUM> ft (<NUM> to <NUM>). The housing <NUM> can have a diameter in the range of about <NUM> in to about <NUM> in (<NUM> to <NUM>); alternatively, from about <NUM> in to about <NUM> in (<NUM> to <NUM>).

Reaction conditions (e.g., one or more of pressure, temperature, residence time, catalyst particle concentration in the propylene, co-catalyst concentration in the propylene, and electron donor concentration in the propylene) of the catalyst suspension in the second mixer <NUM> can be controlled such that a controlled amount of polymerization of propylene can occur on the surface of the catalyst particles in a manner that is consistent with pre-polymerization. In some aspects, the reaction conditions that are controlled in the second mixer <NUM> for pre-polymerization of propylene are co-catalyst concentration in the propylene, electron donor agent concentration in the propylene, temperature, and residence time of the catalyst suspension in the second mixer <NUM>. The reaction conditions within the second mixer <NUM> may be controlled to have a lower temperature and/or lower polymerization rate, as compared to a polymerization reactor <NUM>, to allow the pre-polymer particles to form without exceeding a pre-polymer particle size that would foul any downstream lines (e.g., line <NUM>) and/or downstream equipment (e.g., inlet <NUM>).

The pressure in the second mixer <NUM> can be controlled by the pressure of line <NUM>. The temperature of the second mixer <NUM> can be controlled by heat exchange jackets <NUM> on the walls of the second mixer <NUM> that circulate coolant therethrough (e.g., via coolant/refrigerant input and output lines <NUM> and <NUM>) to control the temperature of the contents of the second mixer <NUM> to a temperature in the range of from about <NUM> to about <NUM>; alternatively, from about <NUM> to about <NUM>; alternatively, from about <NUM> to about <NUM>; alternatively, about <NUM>. In alternative embodiments, the temperature of the second mixer <NUM> can be controlled by any other heat exchange mechanism known in the art with the aid of this disclosure. In some aspects, the amount of propylene can be in excess of the other reactants in an amount such that any heat of pre-polymerization reaction is absorbed by the bulk amount of propylene in the second mixer <NUM>, also referred to herein as adiabatic operation, such that temperature in the second mixer <NUM> can be controlled by the amount of reactants instead of with heat exchange mechanisms. The residence time of the catalyst suspension in the second mixer <NUM> can be controlled by the flow rate of the catalyst suspension into and out of the second mixer <NUM> (e.g., via pump <NUM>), the volume of the housing <NUM> of the second mixer <NUM>, or both. The catalyst particle concentration in the propylene can be controlled by the valve <NUM> in line <NUM>. The co-catalyst concentration can be controlled by the valve <NUM> in line <NUM>. The electron donor agent concentration in the propylene can be controlled by the valve <NUM> in line <NUM>.

Line <NUM> has an end connected to the outlet <NUM> of the second mixer <NUM> and an opposite end connected to the inlet <NUM> of the polymerization reactor <NUM>. The pre-polymerized catalyst suspension can flow from the outlet <NUM> of the second mixer <NUM> to the inlet <NUM> of the polymerization reactor <NUM> via transfer line <NUM>. In some embodiments, pre-polymerization can continue in transfer line <NUM> as the pre-polymerized catalyst suspension flows from the outlet <NUM> of the second mixer <NUM> to the inlet <NUM> of the polymerization reactor <NUM>.

It is contemplated that any combination of transfer lines <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> can be collectively referred to as a transfer line in system <NUM>. For example, transfer lines <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> can be referred to a single transfer line in which the control valve <NUM>, pump <NUM>, and second mixer <NUM> are placed.

Once introduced into the polymerization reactor <NUM>, the pre-polymerized catalyst particles contact propylene monomer under polymerization conditions to form bulk polypropylene as a polymerization product. As described above for the system <NUM> in <FIG>, the polymerization product containing polypropylene is recovered from the polymerization reactor <NUM> via polymerization product discharge outlet <NUM>.

<FIG> illustrates a process flow diagram of another embodiment of a pre-polymerization system <NUM>. Like parts with respect to <FIG> and/or <FIG> are labeled with the same numerals, and the previous description of the like parts applies to the system <NUM> unless otherwise stated. The system <NUM> in <FIG> utilizes a saturated hydrocarbon as the diluent for the catalyst. The saturated hydrocarbon can be any C<NUM> to C<NUM> saturated hydrocarbon. In some aspects, the hydrocarbon used as diluent can include propane, n-butane, mixed butanes, or a combination thereof.

Similar to the system <NUM> in <FIG> and the system <NUM> in <FIG>, system <NUM> in <FIG> includes the first mixer <NUM>. Similar to the system <NUM> in <FIG>, the system <NUM> includes the second mixer <NUM> embodied as a static mixer. However, different from both system <NUM> in <FIG> and system <NUM> in <FIG>, in the system <NUM> of <FIG>, the feed line <NUM> through which propylene is introduced into the system <NUM> is placed upstream of the second mixer <NUM> at a location that is downstream of the locations where the catalyst, co-catalyst, and optional electron donor agent are introduced (e.g., downstream of the location where the feed line <NUM> connects with transfer line <NUM>, downstream of the location where the feed line <NUM> connects with transfer line <NUM>, or both). The saturated hydrocarbon that is used to make catalyst suspensions is introduced via feed line 301a or 301b in combination with feed line <NUM>, i.e., in two locations in the system <NUM> of <FIG>.

In one aspect, a first amount of the saturated hydrocarbon, in liquid phase, is introduced to the catalyst hopper <NUM> via feed line 301a. The saturated hydrocarbon mixes with the catalyst particles in the catalyst hopper <NUM>, and a slurry of the catalyst particles in the liquid saturated hydrocarbon flows from the catalyst hopper <NUM> to the first mixer <NUM> via feed line <NUM>. The catalyst particles are solid particles of the catalyst as described for <FIG>. The feed line <NUM> has an end connected to an outlet <NUM> of the catalyst hopper <NUM> and an opposite end connected to the inlet <NUM> of the first mixer <NUM>. A control valve <NUM> can be included in feed line <NUM> to regulate the flow of the slurry from the catalyst hopper <NUM> into the first mixer <NUM>. In some embodiments, the control valve <NUM> can be a cycling valve that meters the amount of the catalyst slurry that flows in feed line <NUM> to the first mixer <NUM>. In other embodiments, the control valve <NUM> can be an actuator valve that opens and closes to allow and disallow a flow of the catalyst slurry in feed line <NUM>. In yet other embodiments, the control valve <NUM> can be a throttling valve that can control the size of the orifice that is open for flow of the catalyst slurry through the valve <NUM>. The control valve <NUM> can be controlled by any controller known in the art with the aid of this disclosure.

In another aspect, the first amount of saturated hydrocarbon, in liquid phase, is introduced to the first mixer <NUM> via feed line 301b, while dry catalyst is fed to the first mixer <NUM> from the catalyst hopper <NUM> via line <NUM> and valve <NUM>. In such an aspect, the valve <NUM> is configured to meter or actuate solid catalyst particles into the first mixer <NUM>, where the solid catalyst particles mix with the saturated hydrocarbon in the first mixer <NUM>.

The first mixer <NUM> is configured to mix the catalyst particles and saturated hydrocarbon to form the first catalyst suspension. Similar to the first mixer <NUM> in <FIG> and <FIG>, the first mixer <NUM> in the system <NUM> of <FIG> can be embodied as any vessel that is suitable for mixing catalyst suspensions, and particularly, for mixing catalyst suspensions that are used for the polymerization of propylene, e.g., for introduction to a loop slurry reactor or a gas phase reactor. The vessel can generally be cylindrical in shape. The top and bottom of the vessel can be flat or can have a contour that is appropriate for holding pressurized contents, e.g., at a pressure suitable for coupling with a polymerization reactor. In some embodiments, the first mixer <NUM> can have a stirrer extending within the vessel such that the first mixer <NUM> is a continuous stirred tank. The first mixer <NUM> in system <NUM> can have temperature control (e.g., jackets <NUM>) as described for the first mixer <NUM> in <FIG>; alternatively, since a saturated hydrocarbon is used to dilute the catalyst in the first mixer <NUM>, cooling jackets <NUM> may not be needed for the first mixer <NUM>. The dimensions of the first mixer <NUM> in system <NUM> can be those described for the first mixer <NUM> in the system <NUM> in <FIG>. The mixed first catalyst suspension can flow from the outlet <NUM> of the first mixer <NUM> via transfer line <NUM>, which has an end connected to the outlet <NUM> of the first mixer <NUM>.

A second amount of the saturated hydrocarbon flows in feed line <NUM>. The feed line <NUM> can be connected to the transfer line <NUM> downstream of the outlet <NUM> of the first mixer <NUM> and upstream of the location where the feed line <NUM> connects to transfer line <NUM>. A control valve <NUM> can be included in feed line <NUM> to regulate the flow of the second amount of saturated hydrocarbon in feed line <NUM>. In some embodiments, the control valve <NUM> can be an actuator valve that opens and closes to allow and disallow a flow of the saturated hydrocarbon in feed line <NUM>. In other embodiments, the control valve <NUM> can be a throttling valve that can control the size of the orifice that is open for flow of the saturated hydrocarbon through the valve <NUM>. The control valve <NUM> can be controlled by any controller known in the art with the aid of this disclosure.

The feed line <NUM> and the transfer line <NUM> are configured to combine to form transfer line <NUM> that contains the first catalyst suspension having a third amount of the liquid saturated hydrocarbon and the catalyst particles. The third amount of the saturated hydrocarbon in line <NUM> is the sum of the amount of saturated hydrocarbon contained in the transfer line <NUM> and the amount of saturated hydrocarbon contained in the feed line <NUM>. The transfer line <NUM> has an end connected to the suction inlet of the pump <NUM>. No polymerization of propylene occurs in line <NUM> because propylene is not present in line <NUM>. A control valve <NUM> can be included in feed line <NUM> to regulate the flow of the first catalyst suspension in transfer line <NUM>. In some embodiments, the control valve <NUM> can be an actuator valve that opens and closes to allow and disallow a flow of the catalyst suspension in transfer line <NUM>. In other embodiments, the control valve <NUM> can be a throttling valve that can control the size of the orifice that is open for flow of the catalyst suspension through the valve <NUM>. The control valve <NUM> can be controlled by any controller known in the art with the aid of this disclosure.

The pump <NUM> can be similarly configured as previously described, and the first catalyst suspension can flow from the pump <NUM> via transfer line <NUM>. No polymerization of propylene occurs in line <NUM> because propylene is not present in line <NUM>.

The co-catalyst in line <NUM> can combine with the first catalyst suspension in line <NUM> such that the first catalyst suspension in line <NUM> contains the saturated hydrocarbon, catalyst particles, and the co-catalyst in line <NUM>.

In some embodiments, line <NUM> can have an end that combines with the feed line <NUM> (containing propylene) such that the first catalyst suspension combines with propylene such that the first catalyst suspension in line <NUM> contains the saturated hydrocarbon, propylene, catalyst particles, and the co-catalyst. The end of the line <NUM> can connect with the inlet <NUM> of the second mixer <NUM>. In other embodiments such as that shown in the system <NUM> of <FIG>, line <NUM> can have an end that can combine with feed line <NUM> (containing the electron donor agent) such that the first catalyst suspension in line <NUM> contains the saturated hydrocarbon, catalyst particles, the co-catalyst, and the electron donor agent. Line <NUM> can have an end that combines with feed line <NUM> (containing propylene) such that the first catalyst suspension in line <NUM> contains the saturated hydrocarbon, propylene, catalyst particles, the co-catalyst, and the electron donor agent.

Reaction conditions (e.g., one or more of pressure, temperature, residence time, propylene concentration in the saturated hydrocarbon, catalyst particle concentration in the saturated hydrocarbon, co-catalyst concentration in the saturated hydrocarbon, and the optional electron donor agent concentration in the saturated hydrocarbon) of the catalyst suspension in line <NUM> can be controlled such that a controlled amount of polymerization of propylene occurs on the surface of the catalyst particles in a manner that is consistent with pre-polymerization. Alternatively, any combination of conditions in line <NUM> are such that no significant amount of pre-polymerization occurs in line <NUM>.

The first catalyst suspension can flow into the inlet <NUM> of the second mixer <NUM>. The second mixer <NUM> is configured to polymerize propylene in the presence of the catalyst to produce a coating of polypropylene on the catalyst particles that are received from the transfer line <NUM>. As discussed above, the second mixer <NUM> can be embodied as a static mixer. In some aspects, the static mixer can have fixed baffles <NUM> (e.g., in a helical arrangement, or any other baffle arrangement) placed within a housing <NUM>, where the baffles <NUM> continuously blend the components of the first catalyst suspension. Reaction conditions (e.g., one or more of pressure, temperature, residence time, catalyst particle concentration in the propylene, co-catalyst concentration in the propylene, and electron donor concentration in the propylene) of the catalyst suspension in the second mixer <NUM> of <FIG> can be controlled such that a controlled amount of polymerization of propylene can occur on the surface of the catalyst particles in a manner that is consistent with pre-polymerization. In some aspects, the reaction conditions that are controlled in the second mixer <NUM> for pre-polymerization of propylene are concentration in the saturated hydrocarbon, co-catalyst concentration in the saturated hydrocarbon, electron donor agent concentration in the saturated hydrocarbon, temperature, and residence time of the catalyst suspension in the second mixer <NUM> in the system <NUM> of <FIG>. The reaction conditions within the second mixer <NUM> may be controlled to have a lower temperature and/or lower polymerization rate, as compared to a polymerization reactor <NUM>, to allow the pre-polymer particles to form without exceeding a pre-polymer particle size that would foul any downstream lines (e.g., line <NUM>) and/or downstream equipment (e.g., inlet <NUM>).

The pressure in the second mixer <NUM> can be controlled by the pressure of line <NUM>. The temperature of the second mixer <NUM> can be controlled by the techniques described for the second mixer <NUM> in <FIG>. In some aspects, the amount of saturated hydrocarbon can be in excess of the reactants in an amount such that any heat of pre-polymerization reaction is absorbed by the bulk amount of saturated hydrocarbon in the second mixer <NUM>, also referred to herein as adiabatic operation, such that temperature in the second mixer <NUM> can be controlled by the amount of saturated hydrocarbon relative to the amount of reactants instead of with heat exchange mechanisms. The residence time of the catalyst suspension in the second mixer <NUM> can be controlled by the flow rate of the catalyst suspension into and out of the second mixer <NUM> (e.g., via pump <NUM>), the volume of the housing <NUM> of the second mixer <NUM>, or both. The propylene concentration in the saturated hydrocarbon can be controlled by the valve <NUM> in feed line <NUM>. The catalyst particle concentration in the saturated hydrocarbon can be controlled by the valve <NUM> in line <NUM>. The co-catalyst concentration can be controlled by the valve <NUM> in line <NUM>. The electron donor agent concentration in the propylene can be controlled by the valve <NUM> in line <NUM>.

It is contemplated that any combination of transfer lines <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> can be collectively referred to as a transfer line in system <NUM>. For example, transfer lines <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> can be referred to a single transfer line in which the control valve <NUM>, pump <NUM>, and second mixer <NUM> are placed.

Once introduced into the polymerization reactor <NUM>, the pre-polymerized catalyst particles contact propylene monomer under polymerization conditions to form bulk polypropylene as a polymerization product. As described above for the system <NUM> in <FIG> and the system <NUM> in <FIG>, the polymerization product containing polypropylene is recovered from the polymerization reactor <NUM> via polymerization product discharge outlet <NUM>.

<FIG> (not according to the invention) illustrates a process flow diagram of an embodiment of a continuous pre-polymerization system <NUM>. Like parts with respect to <FIG> are labeled with the same numerals, and the previous description of the like parts applies to the system <NUM> unless otherwise stated.

Similar to the system <NUM> in <FIG>, the system <NUM> in <FIG> utilizes a saturated hydrocarbon as the diluent for the catalyst. The saturated hydrocarbon can be any C<NUM> to C<NUM> saturated hydrocarbon. In some aspects, the saturated hydrocarbon used as diluent can include propane, n-butane, mixed butanes, or a combination thereof. Similar to the system <NUM> in <FIG>, the system <NUM> in <FIG>, and the system <NUM> in <FIG>, the system <NUM> in <FIG> includes the first mixer <NUM>. The first mixer <NUM> in system <NUM> can have temperature control (e.g., jackets <NUM>) as described for the first mixer <NUM> in <FIG>; alternatively, since a saturated hydrocarbon is used to dilute the catalyst in the first mixer <NUM>, cooling jackets <NUM> may not be needed for the first mixer <NUM>. Similar to the system <NUM> in <FIG>, the system <NUM> includes the second mixer <NUM> embodied as a continuous stirred-tank.

The saturated hydrocarbon that is used to make catalyst suspensions is introduced via feed lines <NUM> and <NUM>, i.e., in two locations in the system <NUM> of <FIG>. Transfer line <NUM> contains the first catalyst suspension that is prepared in the manner described for the system <NUM> in <FIG>. The first catalyst suspension can flow in transfer line <NUM> to combine with feed line <NUM> that contains propylene to form line <NUM> such that the first catalyst suspension contains the saturated hydrocarbon, the catalyst particles, and propylene. Transfer line <NUM> can have an end connected to the inlet <NUM> of the second mixer <NUM>. No polymerization of propylene occurs in line <NUM> because the co-catalyst and optional electron donor agent are not present in line <NUM>. Alternatively, transfer line <NUM> can be connected to the inlet <NUM> of the second mixer <NUM>, and the feed line <NUM> can combine with feed line <NUM> or feed line <NUM>, or feed line <NUM> can be connected to another inlet of the second mixer <NUM> (see dashed feed line <NUM> in <FIG>). In such embodiments, line <NUM> has an opposite end connected with the inlet <NUM> of the second mixer <NUM>.

The reaction conditions (e.g., one or more of pressure, temperature, residence time, propylene concentration in the saturated hydrocarbon, catalyst particle concentration in the saturated hydrocarbon, co-catalyst concentration in the saturated hydrocarbon, and electron donor agent concentration in the saturated hydrocarbon) of the catalyst suspension within the second mixer <NUM> may be controlled to have a lower temperature and/or lower polymerization rate, as compared to a polymerization reactor <NUM>, to allow the pre-polymer particles to form without exceeding a pre-polymer particle size that would foul any downstream lines (e.g., line <NUM>) and/or downstream equipment (e.g., pump <NUM>, valve <NUM>, inlet <NUM>). In some aspects, the reaction conditions that are controlled in the second mixer <NUM> for pre-polymerization of propylene are propylene concentration in the saturated hydrocarbon, co-catalyst concentration in the saturated hydrocarbon, electron donor agent concentration in the saturated hydrocarbon, temperature, and residence time of the catalyst suspension in the second mixer <NUM>. The pressure in the second mixer <NUM> can be controlled by a supply of inert gas or other pressure control mechanism known in the art with the aid of this disclosure. The temperature of the second mixer <NUM> can be controlled by heat exchange jackets <NUM> on the walls of the second mixer <NUM> that circulate coolant therethrough (e.g., via coolant/refrigerant input and output lines <NUM> and <NUM>) to control the temperature of the contents of the second mixer <NUM> to a temperature in the range of from about <NUM> to about <NUM>; alternatively, from about <NUM> to about <NUM>; alternatively, from about <NUM> to about <NUM>; alternatively, about <NUM>. In alternative embodiments, the temperature of the second mixer <NUM> can be controlled by an external heat exchange circulation loop coupled to the second mixer <NUM> that removes a portion of the catalyst suspension and cools the suspension in a heat exchanger before passing the cooled suspension back to the second mixer <NUM>, or by any other heat exchange mechanism known in the art with the aid of this disclosure. In some aspects, the amount of saturated hydrocarbon can be in excess of the reactants in an amount such that any heat of pre-polymerization reaction is absorbed by the bulk amount of saturated hydrocarbon in the second mixer <NUM>, also referred to herein as adiabatic operation, such that temperature in the second mixer <NUM> can be controlled by the amount of saturated hydrocarbon relative to the reactants instead of with heat exchange mechanisms. The residence time of the catalyst suspension in the second mixer <NUM> can be controlled by the flow rate of the catalyst suspension into and out of the second mixer <NUM> (e.g., via valve <NUM> and valve <NUM>), the volume of the second mixer <NUM>, or both. The catalyst particle concentration in the propylene can be controlled by the valve <NUM> in line <NUM>. The co-catalyst concentration can be controlled by the valve <NUM> in line <NUM>. The electron donor agent concentration in the propylene can be controlled by the valve <NUM> in line <NUM>.

Line <NUM> has an end connected to an outlet <NUM> of the second mixer <NUM> and an opposite end connected to the inlet <NUM> of the polymerization reactor <NUM>. The flow of the pre-polymerized catalyst suspension from the second mixer <NUM> via line <NUM> to the polymerization reactor <NUM> is the same as described for the system <NUM> in <FIG>.

<FIG> illustrate process flow diagrams of pre-polymerization systems that utilize a storage tank <NUM>. Like parts in <FIG> with respect to <FIG> are labeled with the same numerals, and the previous description of the like parts applies unless otherwise stated.

<FIG> (not according to the invention) illustrates a process flow diagram of an embodiment of a batch pre-polymerization system <NUM>. The system <NUM> in <FIG> is similar to the system <NUM> of <FIG>, except the pre-polymerized catalyst suspension flows via line <NUM> to a storage tank <NUM> before flowing to the polymerization reactor <NUM> via line <NUM>. Line <NUM> is connected to the outlet <NUM> of the second mixer <NUM> and to an inlet <NUM> of the storage tank <NUM>. Line <NUM> is connected to the outlet <NUM> of the storage tank <NUM> and to the inlet <NUM> of the polymerization reactor <NUM>.

<FIG> illustrates a process flow diagram of another embodiment of a batch pre-polymerization system <NUM>. The system <NUM> in <FIG> is similar to the system <NUM> of <FIG>, except the pre-polymerized catalyst suspension flows via line <NUM> to a storage tank <NUM> before flowing to the polymerization reactor <NUM> via line <NUM>. Line <NUM> is connected to the outlet <NUM> of the second mixer <NUM> and to an inlet <NUM> of the storage tank <NUM>. Line <NUM> is connected to the outlet <NUM> of the storage tank <NUM> and to the inlet <NUM> of the polymerization reactor <NUM>.

<FIG> (not according to the invention) illustrates a process flow diagram of another embodiment of a batch pre-polymerization system <NUM>. The system <NUM> in <FIG> is similar to the system <NUM> of <FIG>, except the pre-polymerized catalyst suspension flows via line <NUM> to a storage tank <NUM> before flowing to the polymerization reactor <NUM> via line <NUM>. Line <NUM> is connected to the outlet <NUM> of the second mixer <NUM> and to an inlet <NUM> of the storage tank <NUM>. Line <NUM> is connected to the outlet <NUM> of the storage tank <NUM> and to the inlet <NUM> of the polymerization reactor <NUM>.

In each of the systems <NUM>, <NUM>, <NUM>, and <NUM> described hereinabove, the storage tank <NUM> can be embodied as any vessel that is suitable for storing pre-polymerized catalyst suspensions, e.g., for introduction to a polymerization reactor <NUM>. The vessel can generally be cylindrical in shape. The top and bottom of the vessel can be flat or can have a contour that is appropriate for holding pressurized contents, e.g., at a pressure suitable for coupling with a polymerization reactor. In some embodiments, the storage tank <NUM> can have a stirrer extending within the vessel such that the storage tank <NUM> is a continuous stirred tank. In some aspects, the height of the storage tank <NUM> can be <NUM>-<NUM> feet; alternatively, or <NUM>-<NUM> feet; or alternatively, <NUM>-<NUM> feet as measured tangent to tangent. In some aspects, the diameter of the storage tank <NUM> can be <NUM>-<NUM> feet; alternatively, <NUM>-<NUM> feet; alternatively, <NUM>-<NUM> feet; alternatively, <NUM>-<NUM> feet; or alternatively, <NUM>-<NUM> feet. In some aspects, the storage tank <NUM> can have a volume that is larger than a volume of the first mixer <NUM>, the second mixer <NUM>/<NUM>, or both the first mixer <NUM> and the second mixer <NUM>/<NUM>.

The storage tank <NUM> enables an operator to make pre-polymerized catalyst suspensions at production rates that exceed the rate of consumption of the pre-polymerized catalyst suspension by the polymerization reactor <NUM>. The size of the storage tank <NUM> can be designed to provide a residence time for the catalyst suspension such that pre-polymer particles sizes are not too large to flow in the lines and equipment upstream of the polymerization reactor <NUM>. Additionally, or alternatively, the storage tank <NUM> can have a cooling system (a cooling circuit, a cooling jacket, or internally placed cooling elements) that cools the pre-polymerized catalyst suspension to lower the polymerization rate or stop pre-polymerization of propylene until the pre-polymerized catalyst suspension is introduced to the polymerization reactor <NUM>.

It is contemplated that the appropriate flow devices for introducing the pre-polymerized catalyst suspension into the polymerization reactor <NUM> can be included in line <NUM> of <FIG> and <FIG>, line <NUM> of <FIG>, and line <NUM> of <FIG>.

The coolant/refrigerant that is utilized to control the temperature of the first mixer <NUM> and the coolant/refrigerant that is utilized to control the temperature of the second mixer <NUM>/<NUM> can be part of the same coolant/refrigerant circuit or be separate coolant/refrigerant circuits. Coolants/refrigerants suitable for controlling the first mixer <NUM> and second mixer <NUM>/<NUM> to the temperatures disclosed herein can include water, methane, ethane, propane, propylene, mixed butanes, or combinations thereof. In some aspects, the coolant/refrigerant is a coolant such as cooling water; in other aspects, the coolant/refrigerant is a refrigerant selected from methane, ethane, propane, propylene, mixed butanes, or combinations thereof.

In aspects, any combination of the lines/conduits described in <FIG> can include insulation wrapped therearound so as to prevent heat exchange of the conduit contents with the surrounding environment.

Pre-polymerization conditions in the second mixer <NUM>/<NUM> and any lines downstream thereof include the weight ratio of propylene to catalyst, the weight ratio of co-catalyst to catalyst, the weight ratio of electron donor agent to catalyst, temperature, and residence time. Suitable values for the weight ratio of propylene to catalyst include values in the range of from <NUM> to <NUM> propylene/g catalyst; alternatively, from <NUM> to <NUM> propylene/g catalyst; alternatively, from <NUM> to <NUM> propylene/g catalyst; alternatively, from <NUM> to <NUM> propylene/g catalyst; alternatively, from <NUM> to <NUM> propylene/g catalyst; alternatively, about from <NUM> to <NUM> propylene/g catalyst. Suitable values for the weight ratio of co-catalyst to catalyst include values in the range of from <NUM> to <NUM> co-catalyst/g catalyst; alternatively, from <NUM> to <NUM> co-catalyst/g catalyst; alternatively, from <NUM> to <NUM> co-catalyst/g catalyst; alternatively, from <NUM> to <NUM> co-catalyst/g catalyst; alternatively, about <NUM> co-catalyst. Suitable values for the weight ratio of electron donor agent to catalyst include values in the range of from <NUM> to <NUM> donor agent/g catalyst; alternatively, <NUM> to <NUM> donor agent/g catalyst; alternatively, about <NUM> donor agent/g catalyst. Suitable temperatures for pre-polymerization in values in the range of from about <NUM> to about <NUM>; alternatively, from about <NUM> to about <NUM>; alternatively, from about <NUM> to about <NUM>; alternatively, about <NUM> to about <NUM>; alternatively, from about <NUM> to about <NUM>. Suitable values for the residence time in the second mixer <NUM> include values in the range of <NUM> to <NUM> minutes; alternatively, from <NUM> to <NUM> minutes; alternatively, from <NUM> to <NUM> minutes; alternatively, from <NUM> to <NUM> minutes. Suitable values for the residence time in the second mixer <NUM> include values in the range of <NUM> to <NUM> minutes; alternatively, from <NUM> to <NUM> minutes; alternatively, from <NUM> to <NUM> minutes.

Also disclosed herein are processes for pre-polymerizing propylene.

One process for pre-polymerizing propylene can include adding a catalyst and a hydrocarbon (e.g., propylene or the saturated hydrocarbon described herein) to the first mixer <NUM>; mixing the catalyst and the hydrocarbon in the first mixer <NUM> to form a first catalyst suspension comprising the catalyst and the hydrocarbon; flowing the first catalyst suspension from the first mixer <NUM> to a second mixer <NUM> or <NUM>; adding a co-catalyst and optionally an electron donor agent to the first catalyst suspension in or upstream of the second mixer <NUM> or <NUM>; pre-polymerizing propylene in the second mixer <NUM> or <NUM> to form a second catalyst suspension comprising the hydrocarbon and catalyst particles coated with polypropylene; and feeding the second catalyst suspension to a polymerization reactor <NUM> or to a storage tank <NUM>. In aspects where the second catalyst suspension is fed to the storage tank <NUM>, the process can further include flowing the second catalyst suspension from the storage tank <NUM> to the polymerization reactor <NUM>. In aspects of the process where the hydrocarbon is propylene, the second mixer can be the second mixer <NUM> embodied as a stirred tank or the second mixer <NUM> embodied as a static mixer. In aspects of the process where the hydrocarbon comprises propane, n-butane, mixed butanes (a mixture of isobutane with other butanes), or a combination thereof, the second mixer can be the second mixer <NUM> embodied as a stirred tank or the second mixer <NUM> embodied as a static mixer. The process can be performed on a continuous basis or a batch basis.

Another process is a continuous pre-polymerization process with reference to <FIG>. The process can include adding a catalyst and propylene to the first mixer <NUM>, mixing the catalyst and the hydrocarbon in the first mixer <NUM> to form a first catalyst suspension comprising the catalyst and propylene; flowing the first catalyst suspension from the first mixer <NUM> to a second mixer <NUM>, wherein the second mixer <NUM> is a stirred tank; adding a co-catalyst and optionally an electron donor agent to the first catalyst suspension in the second mixer <NUM>; pre-polymerizing propylene in the second mixer <NUM> to form a second catalyst suspension comprising propylene, catalyst particles coated with polypropylene, co-catalyst, and optionally the electron donor agent; and feeding the second catalyst suspension to a polymerization reactor <NUM>. In aspects, the catalyst particles in propylene, the co-catalyst, and the optional electron donor agent are each added via separate inlets <NUM>, <NUM>, and <NUM> of the second mixer <NUM>; alternatively, any of the lines containing the catalyst particles in propylene, the co-catalyst, and the optional electron donor agent can be combined prior to being introduced to the second mixer <NUM>, and the combined line can be connected to the respective inlet.

Another process is a continuous pre-polymerization process with reference to <FIG>. The process can include adding a catalyst and propylene to the first mixer <NUM>; mixing the catalyst and propylene in the first mixer <NUM> to form a first catalyst suspension comprising the catalyst and propylene; flowing the first catalyst suspension from the first mixer <NUM> to a second mixer <NUM>, wherein the second mixer <NUM> is a static mixer; adding a co-catalyst and optionally an electron donor agent to the first catalyst suspension upstream of the second mixer <NUM>; pre-polymerizing propylene in the second mixer <NUM> to form a second catalyst suspension (e.g., a pre-polymerized catalyst suspension) comprising propylene, catalyst particles coated with polypropylene, co-catalyst, and optionally the electron donor agent; and feeding the second catalyst suspension to a polymerization reactor <NUM>. In aspects, only the co-catalyst is added to the first catalyst suspension; alternatively, both the co-catalyst and the electron donor agent are added to the first catalyst suspension. In one aspect, the co-catalyst is added to the first catalyst suspension at a location in a transfer line that is upstream of the location where the electron donor agent is added. In another aspect, the electron donor agent is added to the first catalyst suspension at a location in a transfer line that is upstream of the location where the co-catalyst is added.

Another process is a continuous pre-polymerization process with reference to <FIG>. The process can include adding a catalyst and a first amount of a saturated hydrocarbon to the first mixer <NUM>; mixing the catalyst and the first amount of the saturated hydrocarbon in the first mixer <NUM> to form a first catalyst suspension comprising the catalyst and the hydrocarbon; flowing the first catalyst suspension from the first mixer <NUM> to a second mixer <NUM>, wherein the second mixer <NUM> is a static mixer; adding a co-catalyst, propylene, and optionally an electron donor agent to the first catalyst suspension upstream of the second mixer <NUM>; pre-polymerizing propylene in the second mixer <NUM> to form a second catalyst suspension (e.g., a pre-polymerized catalyst suspension) comprising propylene, the saturated hydrocarbon catalyst particles coated with polypropylene, co-catalyst, and optionally the electron donor agent; and feeding the second catalyst suspension to a polymerization reactor <NUM>. In aspects, a second amount of the saturated hydrocarbon is combined with the first catalyst suspension downstream of the outlet <NUM> of the first mixer <NUM> and upstream of the location where additional components are added to the first catalyst suspension. In aspects, only the co-catalyst and propylene are added to the first catalyst suspension; alternatively, the co-catalyst, propylene, and the electron donor agent are added to the first catalyst suspension. In one aspect, the co-catalyst is added to the first catalyst suspension at a location in a transfer line that is upstream of the location where the electron donor agent is added and where the propylene is added. In another aspect, the electron donor agent is added to the first catalyst suspension at a location in a transfer line that is upstream of the location where the co-catalyst is added and where the propylene is added.

Another process is a continuous pre-polymerization process with reference to <FIG>. The process can include adding a catalyst and a first amount of a saturated hydrocarbon to the first mixer <NUM>; mixing the catalyst and the first amount of the saturated hydrocarbon in the first mixer <NUM> to form a first catalyst suspension comprising the catalyst and the hydrocarbon; flowing the first catalyst suspension from the first mixer <NUM> to a second mixer <NUM>, wherein the second mixer <NUM> is a stirred tank; adding propylene to the first catalyst suspension; adding a co-catalyst and optionally the electron donor agent to the first catalyst suspension in the second mixer <NUM>; pre-polymerizing propylene in the second mixer <NUM> to form a second catalyst suspension comprising propylene, the saturated hydrocarbon, catalyst particles coated with polypropylene, co-catalyst, and optionally the electron donor agent; and feeding the second catalyst suspension to a polymerization reactor <NUM>. In aspects, the catalyst particles in the saturated hydrocarbon, the co-catalyst, and the optional electron donor agent are each added via separate inlets <NUM>, <NUM>, and <NUM> of the second mixer <NUM>; alternatively, any of the lines containing the catalyst particles in the saturated hydrocarbon, the co-catalyst, and the optional electron donor agent can be combined prior to being introduced to the second mixer <NUM>, and the combined line can be connected to the respective inlet. In aspects, propylene can be added to the first catalyst suspension in a transfer line upstream of the second mixer <NUM>, via a feed line for the co-catalyst, via a feed line for the optional electron donor agent, or via an additional inlet of the second mixer <NUM> (dashed lines in <FIG>).

Another process is a batch pre-polymerization process with reference to <FIG>. The process can include adding a catalyst and propylene to the first mixer <NUM>, mixing the catalyst and the hydrocarbon in the first mixer <NUM> to form a first catalyst suspension comprising the catalyst and propylene; flowing the first catalyst suspension from the first mixer <NUM> to a second mixer <NUM>, wherein the second mixer <NUM> is a stirred tank; adding a co-catalyst and optionally an electron donor agent to the first catalyst suspension in the second mixer <NUM>; pre-polymerizing propylene in the second mixer <NUM> to form a second catalyst suspension comprising propylene, catalyst particles coated with polypropylene, co-catalyst, and optionally the electron donor agent; and flowing the second catalyst suspension to a storage tank <NUM>. In some aspects, the process can additionally include flowing the second catalyst suspension from the storage tank <NUM> to a polymerization reactor <NUM>. In aspects, the catalyst particles in propylene, the co-catalyst, and the optional electron donor agent are each added to the second mixer <NUM> via separate inlets <NUM>, <NUM>, and <NUM>; alternatively, any of the lines containing the catalyst particles in propylene, the co-catalyst, and the optional electron donor agent can be combined prior to being introduced to the second mixer <NUM>, and the combined line can be connected to the respective inlet.

Another process is a batch pre-polymerization process with reference to <FIG>. The process can include adding a catalyst and propylene to the first mixer <NUM>; mixing the catalyst and propylene in the first mixer <NUM> to form a first catalyst suspension comprising the catalyst and the propylene; flowing the first catalyst suspension from the first mixer <NUM> to a second mixer <NUM>, wherein the second mixer <NUM> is a static mixer; adding a co-catalyst and optionally an electron donor agent to the first catalyst suspension upstream of the second mixer <NUM>; pre-polymerizing propylene in the second mixer <NUM> to form a second catalyst suspension (e.g., a pre-polymerized catalyst suspension) comprising propylene, catalyst particles coated with polypropylene, co-catalyst, and optionally the electron donor agent; and flowing the second catalyst suspension to a storage tank <NUM>. In some aspects, the process can additionally include flowing the second catalyst suspension from the storage tank <NUM> to a polymerization reactor <NUM>. In aspects, only the co-catalyst is added to the first catalyst suspension; alternatively, both the co-catalyst and the electron donor agent are added to the first catalyst suspension. In one aspect, the co-catalyst is added to the first catalyst suspension at a location in a transfer line that is upstream of the location where the electron donor agent is added. In another aspect, the electron donor agent is added to the first catalyst suspension at a location in a transfer line that is upstream of the location where the co-catalyst is added.

Another process is a batch pre-polymerization process with reference to <FIG>. The process can include adding a catalyst and a first amount of a saturated hydrocarbon to the first mixer <NUM>; mixing the catalyst and the first amount of the saturated hydrocarbon in the first mixer <NUM> to form a first catalyst suspension comprising the catalyst and the hydrocarbon; flowing the first catalyst suspension from the first mixer <NUM> to a second mixer <NUM>, wherein the second mixer <NUM> is a static mixer; adding a co-catalyst, propylene, and optionally an electron donor agent to the first catalyst suspension upstream of the second mixer <NUM>; pre-polymerizing propylene in the second mixer <NUM> to form a second catalyst suspension (e.g., a pre-polymerized catalyst suspension) comprising propylene, the saturated hydrocarbon catalyst particles coated with polypropylene, co-catalyst, and optionally the electron donor agent; flowing the second catalyst suspension to a storage tank <NUM>. In some aspects, the process can additionally include flowing the second catalyst suspension from the storage tank <NUM> to a polymerization reactor <NUM>. In aspects, a second amount of the saturated hydrocarbon is combined with the first catalyst suspension downstream of the outlet <NUM> of the first mixer <NUM> and upstream of the location where additional components are added to the first catalyst suspension. In aspects, only the co-catalyst and propylene are added to the first catalyst suspension; alternatively, the co-catalyst, propylene, and the electron donor agent are added to the first catalyst suspension. In one aspect, the co-catalyst is added to the first catalyst suspension at a location in a transfer line that is upstream of the location where the electron donor agent is added and where the propylene is added. In another aspect, the electron donor agent is added to the first catalyst suspension at a location in a transfer line that is upstream of the location where the co-catalyst is added and where the propylene is added.

Another process is a batch pre-polymerization process with reference to <FIG>. The process can include adding a catalyst and a first amount of a saturated hydrocarbon to the first mixer <NUM>; mixing the catalyst and the first amount of the saturated hydrocarbon in the first mixer <NUM> to form a first catalyst suspension comprising the catalyst and the hydrocarbon; flowing the first catalyst suspension from the first mixer <NUM> to a second mixer <NUM>, wherein the second mixer <NUM> is a stirred tank; adding propylene to the first catalyst suspension; adding a co-catalyst and optionally the electron donor agent to the first catalyst suspension in the second mixer <NUM>; pre-polymerizing propylene in the second mixer <NUM> to form a second catalyst suspension comprising propylene, the saturated hydrocarbon, catalyst particles coated with polypropylene, co-catalyst, and optionally the electron donor agent; and flowing the second catalyst suspension to a storage tank <NUM>. In some aspects, the process can additionally include flowing the second catalyst suspension from the storage tank <NUM> to a polymerization reactor <NUM>. In aspects, the catalyst particles in the saturated hydrocarbon, the co-catalyst, and the optional electron donor agent are each added via separate inlets <NUM>, <NUM>, and <NUM> of the second mixer <NUM>; alternatively, any of the lines containing the catalyst particles in the saturated hydrocarbon, the co-catalyst, and the optional electron donor agent can be combined prior to being introduced to the second mixer <NUM>, and the combined line can be connected to the respective inlet. In aspects, propylene can be added to the first catalyst suspension in a transfer line upstream of the second mixer <NUM>, via a feed line for the co-catalyst, via a feed line for the optional electron donor agent, or via an additional inlet of the second mixer <NUM>.

Aspects of the invention is further illustrated by the following examples, which are not to be construed in any way as imposing limitations to the scope of this invention. Various other aspects, modifications, and equivalents thereof which, after reading the description herein, may suggest themselves to one of ordinary skill in the art without departing from the spirit of the present invention or the scope of the appended claims.

Example <NUM> is a pre-polymerization performed with the system <NUM> illustrated in <FIG>. For Example, <NUM>, dry catalyst was introduced from the hopper <NUM> into the first mixer <NUM> via line <NUM> at a rate of <NUM> lb/hr (<NUM>/hr). Propane used as the saturated hydrocarbon was introduced via line 301b into the first mixer <NUM> at a rate of <NUM> lb/hr (<NUM>/hr), such that the concentration of catalyst particles in the first mixer <NUM> was <NUM> wt% based on a weight of propane in the first mixer <NUM> (i.e., the concentration of catalyst particles in the first catalyst suspension was <NUM> wt% based on the weight of propane in the first catalyst suspension). The catalyst suspension was mixed in the first mixer <NUM>, which was controlled at a temperature of <NUM>.

The first catalyst suspension was removed from the first mixer <NUM> via line <NUM> and mixed with propane from line <NUM>. Propane flow in line <NUM> was <NUM>,<NUM> lb/hr (<NUM>/hr). The total flow of propane in line <NUM> was thus <NUM>,<NUM> lb/hr (<NUM>/hr) propane, and the total flow of catalyst particles in line <NUM> was <NUM> lb/hr (<NUM>/hr) catalyst. Triethylaluminum was fed into the first catalyst suspension as the co-catalyst via line <NUM> at a rate of <NUM> lb/hr (<NUM>/hr). Proprietary electron donor agent was fed into the first catalyst suspension via line <NUM> at a rate of <NUM> lb/hr (<NUM>/hr). Propylene was fed into the first catalyst suspension via line <NUM> at a rate of <NUM> lb/hr (<NUM>/<NUM>/hr).

The first catalyst suspension containing propane, catalyst particles, triethylaluminum, proprietary electron donor, and propylene was introduced to static mixer <NUM>. The static mixer <NUM> was controlled to a temperature of <NUM> using refrigerant in cooling jackets <NUM>.

The pre-polymerized catalyst suspension flowed from the static mixer <NUM> in line <NUM> to a polymerization reactor <NUM>, where polypropylene was produced at polymerization conditions that included a productivity of <NUM>,<NUM> lb polypropylene/lb catalyst, and the liquid in the reaction medium in the reactor contained <NUM> wt% propane and <NUM> wt% propylene. The polymerization reactor <NUM> had a volume of <NUM>,<NUM> gallons (<NUM><NUM>), with <NUM>,<NUM> lb (<NUM>,<NUM>) propylene circulating therein.

Lines <NUM>, <NUM>, <NUM>, and <NUM> (the transfer line in Example <NUM>) had a diameter of <NUM> in (<NUM>).

Aspect <NUM> is a pre-polymerization system comprising a first feed line comprising propylene, a second feed line comprising a catalyst, a first mixer having a first inlet connected to the first feed line and a second inlet connected to the second feed line, a first transfer line containing a first catalyst suspension and having an end connected to an outlet of the first mixer, a second mixer having a first inlet connected to an opposite end of the first transfer line, wherein the second mixer is configured to pre-polymerize propylene in the presence of the catalyst to produce a coating of polypropylene on catalyst particles received from the first transfer line, a third feed line comprising a co-catalyst, wherein the third feed line is connected to the first transfer line or to a second inlet of the second mixer, a second transfer line having an end connected to an outlet of the second mixer, and a polymerization reactor coupled to an opposite end of the second transfer line, wherein the polymerization reactor is configured to polymerize propylene in the presence of the catalyst particles having the coating of polypropylene to produce a product polypropylene.

Aspect <NUM> is the pre-polymerization system of Aspect <NUM>, wherein the second mixer is a stirred tank.

Aspect <NUM> is the pre-polymerization system of any of Aspects <NUM> to <NUM>, wherein the second mixer is a static mixer.

Aspect <NUM> is the pre-polymerization system of any of Aspects <NUM> to <NUM>, further comprising a storage tank having an inlet connected to the opposite end of the second transfer line and an outlet connected to an inlet of the polymerization reactor.

Claim 1:
A process for pre-polymerizing propylene comprising:
adding a catalyst and a hydrocarbon to a first mixer;
mixing the catalyst and the hydrocarbon in the first mixer to form a first catalyst suspension comprising the catalyst and the hydrocarbon;
flowing the first catalyst suspension from the first mixer to a second mixer;
adding a co-catalyst and an optional electron donor agent to the first catalyst suspension in transfer lines between the first mixer and the second mixer;
pre-polymerizing propylene in the second mixer to form a second catalyst suspension comprising the hydrocarbon and catalyst particles coated with polypropylene; and
flowing the second catalyst suspension to a polymerization reactor or to a storage tank;
wherein the hydrocarbon is propylene and wherein the second mixer is a static mixer.