Methods for improving gas phase polymerization

Abstract

Processes disclosed herein allow increased gas phase reactor production rates by reducing monomer and comonomer partial pressure and increasing induced condensing agent (ICA) composition partial pressure in the reaction zone. Monomer and comonomer are reduced at a constant molar ratio of ethylene to comonomer to maintain density and increases in ICA composition partial pressure offset decreases in comonomer partial pressure such that the stickiness limit temperature of polymer particles in the reaction zone remains constant. The increased ICA composition partial pressure provides for additional heat removal from the reaction zone and a corresponding increase in polymer production.

Description

METHODS FOR IMPROVING GAS PHASE POLYMERIZATION CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to and the benefit of U.S. Provisional Application number 63 / 653,434, filed May 30, 2024, the disclosure of which is incorporated herein by reference in its entirety. FIELD OF THE INVENTION

[0002] The present disclosure relates to systems and methods for operating a polyolefin polymerization reactor with improved production rates. BACKGROUND OF THE INVENTION

[0003] Polyolefins may be produced using gas phase polymerization processes. If the process is a gas-phase fluidized bed polymerization process, the process may include a gas stream including one or more monomers continuously passed through a fluidized bed of catalyst and growing polymer particles. As polymerization occurs, a portion of the monomers are consumed, and the gas stream is heated in the reactor by the heat of polymerization. A portion of the gas stream exits the reactor and may be recycled back to the reactor with additional monomers and additives. The recycle stream may be cooled, so as to maintain the temperature of the resin and gas stream inside the reactor below the stickiness limit temperature. The melt initiation temperature is the temperature at which the reaction mixture including polymer particles begins to stick together forming agglomerates. Particle agglomerations may lead to the formation of chunks and / or sheets of polymer that cannot be removed from the reactor as product and which may fall onto the reactor distributor plate impairing fluidization of the bed or causing reactor failure. Additionally, since the polymerization reaction is exothermic, the amount of polymer produced in a fluidized bed polymerization process may be correlated to the amount of heat that can be withdrawn from the reaction zone.

[0004] There may be advantages to cooling the recycle stream below its dew point resulting in condensing a portion of the gaseous recycle stream outside of the reactor. The dew point of the recycle stream is the temperature at which liquid condensate first begins to form in the gaseous recycle stream. The dew point can be calculated knowing the gas composition and is thermodynamically defined using an equation of state. The process of purposefully condensing a portion of the recycle stream is referred to in the industry as “condensed mode” operation. When a recycle stream temperature is lowered to a point below its dew point in condensed modeoperation, an increase in polymer production may be possible.

[0005] Cooling of the recycle stream to a temperature below the dew point temperature produces a two-phase gas / liquid mixture that may have entrained solids contained in both phases. The liquid phase of the two-phase gas / liquid mixture in condensed mode operation is generally entrained in the gas phase of the mixture. Vaporization of the liquid occurs when heat is added or pressure is reduced. Generally, the vaporization occurs when the two-phase mixture enters the fluidized bed, with the heat of polymerization providing the heat of vaporization. The vaporization thus provides an additional means of extracting heat of reaction from the fluidized bed.

[0006] The cooling capacity of the recycle gas may be increased further while at a given reaction temperature and a given temperature of the cooling heat transfer medium by adding non- polymerizing, non-reactive materials to the reactor, which are condensable at the temperatures encountered in the process heat exchanger (cooler). The non-reactive condensable materials are collectively referred to as condensing agents, sometimes referred to as induced condensing agents (ICAs) because of the added cooling they induce. Increasing concentrations of ICAs in the reactor causes corresponding increases in the dew point temperature of the reactor gas, which promotes higher levels of condensing, higher heat transfer (better cooling), and improved production rates from the reactor. However, the use of an ICA is governed by its solubility in the polymer, where the ICA acts to depress the polymer melting point. Attempts to operate polymerization reactors with excessive ICA concentrations have led to the polymer particles suspended in the fluid bed to soften and become cohesive or “sticky” and, in some cases, to solidification of the fluid bed in the form of large chunks or sheets. While the use of an ICA may improve polymer production, there remains a challenge in balancing the increased cooling capacity against polymer softening and stickiness.

[0007] Fluidization of the solid particles in a gas phase reactor bed is maintained by a “recycle gas” loop. Gas phase material comprising nitrogen, ICA, unreacted monomer, and optionally hydrogen is withdrawn from the reactor through an overhead line into a compressor. Higher pressure recycle gas, from the compressor discharge is routed through a heat exchanger where it is cooled before being reinjected into the bottom of the reactor. After entering the reactor, the recycle gas flows through a distributor plate at the base of the fluidized bed to distribute the flow of recycle gas more uniformly over the horizontal cross-section of the bed to maintain fluidization. The aforementioned recycle gas heat exchanger is where the heat of polymerization is removed from the process.

[0008] This heat removal is generally calculated by the heat exchange equation, Q=mCpΔT, where Q is the total heat removed, m is the mass flow rate of the recycle gas, Cp is the specific heat capacity of the recycle gas, and ΔT is the temperature reduction of the recycle gas. Mass flow of recycle gas is limited by solids entrainment. Specific heat capacity comprises components of sensible heat and latent heat of vaporization but is generally assumed to be a constant for a selected ICA composition. The temperature of the cooled recycle gas is also generally assumed to be a constant as limited by cooling water temperature. Therefore, maximizing reactor production rates have generally been maximized by maximizing the reaction zone temperature to approach the melt initiation temperature of the polymer particles—i.e., Q is maximized by maximizing ΔT.

[0009] US 2022 / 0098332 discloses a method for increasing Q by increasing Cpthrough mixing ICAs. It was discovered that individual ICAs had different combinations of heat capacity and propensity to solubilize in specific polymers, such that mixing ICAs in specific ratios permitted a higher volume of the mixed ICA composition resulting in a higher heat capacity at a fixed stickiness limit.

[0010] Operating within the currently understood boundary conditions on recycle gas mass flow rate and reaction zone temperature as limited by existing equipment design and / or configuration, it would be advantageous to develop other methods for increasing heat removal from a gas phase reactor by increasing the specific heat capacity of the recycle gas.

[0011] Even within the constraints of safe operation, real-time control of gas phase polymerization reactors is complex. The complexity of reactor control adds further to the difficulty and uncertainty of experimentation if one wishes to alter operating conditions to achieve higher production rates. Large-scale gas phase plants are expensive and highly productive. Risks associated with experimentation in such plants are high because downtime (such as that caused by passing the melt initiation temperature) is costly. Therefore, exploring design and operating boundaries experimentally is difficult in view of the costs and risks.

[0012] There is a remaining need for methods of determining stable operating conditions for gas fluidized bed polymerization with condensing agents, to facilitate design of the plant and the determination of suitable process conditions for suitable or maximum production rates in a given plant design. Furthermore, because reactor conditions vary with time there is a need for processes in the production of polyolefins in a gas phase reactor which allow real-time calculation and control of process parameters to maximize production rates.SUMMARY OF THE INVENTION

[0013] This disclosure provides processes for polymerizing olefins at increased production rates by controlling process parameters to improve heat removal from the process. In at least one embodiment, a process to polymerize olefins in a gas phase polymerization reactor comprises contacting ethylene, an alpha-olefin comonomer, a polymerization catalyst, and an induced condensing agent (ICA) composition, in a reaction zone of the gas phase polymerization reactor under first polymerization conditions comprising a temperature (TRZ), a molar ratio of ethylene to the alpha-olefin comonomer (ECR), a first ethylene partial pressure (EPP1), and a first ICA partial pressure (IPP1) to form first polymer particles. The process further comprises implementing second polymerization conditions in the reaction zone, comprising TRZ, ECR, a second ethylene partial pressure (EPP2), and a second ICA composition partial pressure (IPP2) to form second polymer particles. The process is further characterized by the first polymer particles and the second polymer particles having the same stickiness limit temperature (TSL), wherein TSLminus TRZ is greater than or equal to a threshold value.

[0014] In some embodiments, IPP1 and IPP2 are points on a curve defined by IPPi= f1(EPPi, CPPi) and corresponding to TSL. wherein: IPPiis a partial pressure of the ICA composition in the reaction zone at which polymer particles have the stickiness limit temperature (TSL), corresponding to ethylene partial pressure (EPP1); CPPiis a partial pressure of the alpha olefin comonomer in the reaction zone (EPP1 / ECR); f is a function determined by thermodynamic estimation of hydrocarbon solubility, laboratory melt initiation temperature tests, or a combination thereof; and all other process parameters in the reaction zone are assumed to be constant.

[0015] In some embodiments, wherein EPP2 is less than EPP1, IPP2 is greater than IPP1, or a combination thereof.

[0016] The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter, which form the subject matter of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiments disclosed may be readily utilized as a basis for modifying or designing other catalyst compositions and / or processes for carrying outthe same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. The novel features which are believed to be characteristic of the invention, both as to its compositions and methods, together with further objects and advantages will be better understood from the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The claimed subject matter may be understood by reference to the following description taken in conjunction with the accompanying drawings, in which like reference numerals identify like elements, and in which:

[0018] FIG.1 is a schematic diagram of a gas phase polymerization system, according to one embodiment;

[0019] FIG. 2 is a diagram of a control system for controlling a gas phase polymerization process, according to one embodiment;

[0020] FIG.3 shows overlaid graphs of monomer partial pressure vs. ICA partial pressure in reactor gas at constant temperature and corresponding heat transfer, according to embodiments of the disclosure; and

[0021] FIG.4 shows demonstrated polymerization conditions within model limits of TSL-TRZ, according to embodiments of the disclosure.

[0022] While the disclosed process and system are susceptible to various modifications and alternative forms, the drawings illustrate specific embodiments and / or aspects herein described in detail by way of example. It should be understood, however, that the description herein of a specific embodiment is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims. DETAILED DESCRIPTION OF THE INVENTION

[0023] Illustrative embodiments of the subject matter claimed below will now be disclosed. In the interest of clarity, some features of some actual implementations may not be described in this specification. It will be appreciated that in the development of any such actual embodiments, numerous implementation-specific decisions must be made to achieve the developer’s specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a developmenteffort, even if complex and time-consuming, would be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.

[0024] The words and phrases used herein should be understood and interpreted to have a meaning consistent with the understanding of those words and phrases by those skilled in the relevant art. No special definition of a term or phrase, i.e., a definition that is different from the ordinary and customary meaning as understood by those skilled in the art, is intended to be implied by consistent usage of the term or phrase herein. To the extent that a term or phrase is intended to have a special meaning, i.e., a meaning other than the broadest meaning understood by skilled artisans, such a special or clarifying definition will be expressly set forth in the specification in a definitional manner that provides the special or clarifying definition for the term or phrase.

[0025] For example, the following discussion contains a non-exhaustive list of definitions of several specific terms used in this disclosure (other terms may be defined or clarified in a definitional manner elsewhere herein). These definitions are intended to clarify the meanings of the terms used herein. It is believed that the terms are used in a manner consistent with their ordinary meaning, but the definitions are nonetheless specified here for clarity. Definitions

[0026] As used herein, “iC4” and “isobutane” refer to 2-methylpropane.

[0027] As used herein, “nC4” and “n-butane” refer to normal-butane.

[0028] As used herein, “iC5” and “isopentane” refer to 2-methylbutane.

[0029] As used herein, “nC5” and “n-pentane” refer to normal-pentane.

[0030] As used herein, “neoC5” and “neo-pentane” refer to 2,2-dimethylpropane.

[0031] As used herein, “nC6” and “n-hexane” refer to normal-hexane.

[0032] As used herein, “C6inerts” refers to various hexane isomers that are inert to reaction conditions and may include nC6, 2-methylpentane, 3-methylpentane, 2,2-dimethyl butane, 2,3- dimethylbutane, 2-hexene, and / or 3-hexene.

[0033] As used herein, “comprising” is to be interpreted as specifying the presence of the stated features, integers, steps, or components as referred to, but does not preclude the presence or addition of one or more features, integers, steps, or components, or groups thereof. Moreover, each of the terms “by”, “comprising,” “comprises”, “comprised of” “including,” “includes,” “included,” “involving,” “involves,” “involved,” and “such as” are used in their open, non-limiting sense and may be used interchangeably. Further, the term “comprising” is intended to include examples and aspects encompassed by the terms “consisting essentially of” and “consisting of.”Similarly, the term “consisting essentially of” is intended to include examples encompassed by the term “consisting of.”

[0034] As used herein, “ICA” refers to a condensing agent. “ICAs” refers to condensing agents. “ICA composition” refers to the total condensing agent in the reactor and encompasses compositions with two or more condensing agents. ICAs suitable for use in methods of the present disclosure may include C3-C6hydrocarbons or combinations thereof. For example, ICAs suitable for use may include n-butane, isobutane, n-pentane, isopentane, neo-pentane, hexane, isohexane, and other hydrocarbon compounds that are similarly non-reactive in the polymerization process. A “binary ICA composition” is an ICA composition that includes two ICAs, and a “ternary ICA composition” is an ICA composition that includes three ICAs.

[0035] As used herein, “linear low density polyethylene” (LLDPE) refers to polyethylene having a density in the range of from 0.900 g / cm3to 0.945 g / cm3, from 0.901 g / cm3to 0.940 g / cm3, from 0.902 g / cm3to 0.935 g / cm3, from 0.903 g / cm3to 0.930 g / cm3, from 0.904 g / cm3to 0.925, or from 0.905 g / cm3to 0.920 g / cm3. In some embodiments, LLDPE herein can be produced with one or more Ziegler-Natta catalysts, one or more single-site transition metal catalysts, such as, but not limited to, metallocene catalysts, or a combination thereof. In some embodiments, LLDPE herein can be produced in one or more gas phase reactors.

[0036] As used herein, “melt index” refers to a measure of the use of flow of the melt of the thermoplastic polymer. Melt index may be measured according to ASTM D1238-13 at suitable weight and temperature. Generally, the melt index of polyolefins is measured at 2.16 kg at 190°C, 5 kg at 190°C, or 21.6 kg at 190°C.

[0037] As used herein, “polyethylene” denotes a polymer of ethylene and optionally one or more C3-C18alpha-olefins, while the term “polyolefin” denotes a polymer of one or more C2-C18alpha-olefins and optionally one or more comonomers. An “olefin” is an unsaturated hydrocarbon that contains at least one carbon-carbon double bond. An alpha-olefin is a hydrocarbon that contains at least one carbon-carbon double bond at one end of a carbon chain (e.g., 1-butene, vinyl- cyclohexane). For the purposes of this disclosure, ethylene shall be considered an α-olefin.

[0038] As used herein, “real-time” means data processed, and systems adjusted, without intentional delay, given the processing limitations of the system and the time to accurately measure the data.

[0039] As used herein, Mn is number average molecular weight, Mw is weight average molecular weight, and Mzis z average molecular weight, wt % is weight percent, and mol % ismole percent. Molecular weight distribution (MWD), also referred to as polydispersity index (PDI), is defined to be Mw divided by Mn. Unless otherwise noted, all molecular weights (e.g., Mw, Mn, Mz) are reported in units of g / mol.

[0040] With reference to a product being produced by a continuous reaction, the expression “instantaneous” value of a property of the product denotes the value of the property of the most recently produced quantity of the product. The most recently produced quantity typically undergoes mixing with previously produced quantities of the product before a mixture of the recently and previously produced product exits the reactor. In contrast, with reference to a product being produced by a continuous reaction, “average” (or “bed average”) value (at a time “T”) of a property denotes the value of the property of the product that exits the reactor at time T. Gas phase polymerization

[0041] The present disclosure relates to processes for production of polyolefins in a gas phase reactor at increased rates by reducing temperature and increasing the concentration of an ICA composition in the reaction zone of the gas phase reactor. Changes to the reaction zone temperature and ICA concentration are implemented while keeping the reactor temperature at least a threshold value below the stickiness limit of the polymer particles in the fluidized bed of the gas phase reactor. The use of condensed phase cooling allows for increased production rates as compared to cooling the recycle gas without condensing a portion of the gas to a liquid because the heat of vaporization of the liquid portion of the recycle stream increases cooling capacity.

[0042] The production rate of a gas phase reactor is commonly limited by the ability to remove the heat of the exothermic polymerization reaction from the reaction zone. Polymer production rates can be increased by higher mass flow rate in the recycle gas loop, higher specific heat capacity in the recycle gas, or higher reactor temperature. However, recycle gas mass flow is limited by entrainment of solids that may cause plugging of and / or damage to mechanical equipment in the recycle gas loop. Specific heat capacity of the recycle gas can be increased by an increased concentration of ICA. However, increasing ICA concentration in the recycle gas leads to more ICA being absorbed into the polymer particles, thereby approaching a stickiness limitation. Higher reactor temperatures lead to a higher ΔT across the one or more heat exchangers in the recycle gas loop and hence more heat removal. However, increased reaction zone temperature moves the polymer particles closer to their melting point, thereby approaching a stickiness limitation.

[0043] Surprisingly, it has been discovered that reaction zone temperature can be reduced and ICA concentration can be increased to produce increased heat removal from the reactor whileproducing polymer particles at a temperature that is at least a threshold value below the stickiness limit for such polymer particles, as described in more detail below. Polymerization Reactor

[0044] The methods described may be used in pilot plant or commercial size reactors including a variety of designs. For example, the model can be used in commercial-scale reactions, such as gas-phase fluidized-bed polymerization reactions, that can be monitored and optionally also controlled. Some such reactions can occur in a reactor having the geometry of the fluidized bed reactor 101 discussed with respect to FIG. 1. In other embodiments, a reactor is monitored and optionally also controlled while operating to perform polymerization using any of a variety of different processes (e.g., slurry or gas phase processes).

[0045] Generally, in a gas-phase fluidized-bed process used for producing polymers, a gaseous stream containing one or more monomers is continuously cycled through a fluidized bed in the presence of a catalyst 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. (See, for example, U.S. Pat. Nos. 4,543,399; 4,588,790; 5,028,670; 5,317,036; 5,352,749; 5,405,922; 5,436,304; 5,453,471; 5,462,999; 5,616,661; and 5,668,228; all of which are incorporated by reference.)

[0046] FIG.1 is a schematic diagram of a polymerization system 100 that can be monitored and controlled in accordance with embodiments described. The polymerization system 100 includes a fluidized bed reactor 101. The fluidized bed reactor 101 has a bottom end 103, a straight section 105, a top expanded section 107, and a distributor plate 109 within the straight section 105. A fluidized bed 111 of granular polymer (once formed) and catalyst particles is contained within the straight section 105 and may optionally extend slightly into the top expanded section 107. The bed is fluidized by the steady flow of recycle gas through the distributor plate 109. The recycle gas enters fluidized bed reactor through line 113, additional reaction and inert gases (including ICAs) may be added in adjustable ratios through line 115. Aluminum alkyl (optional) may be added through line 117. The flow rate of the recycle gas is regulated to maintain circulation of fluidized bed 111. In some embodiments, a recycle gas velocity of from about 1 ft / sec to about 3 ft / sec, such as from about 2 ft / sec to about 3 ft / sec, or from about 2.4 ft / sec to about 2.8 ft / sec is used to maintain a fluidized bed 111 in the reactor 101 while operating the reactor 101 at a totalpressure of about 4200 kPa or less, about 700 kPa to about 4200 kPa, about 1300 kPa to about 2800 kPa, or about 1700 kPa to about 2500 kPa.

[0047] The polymerization system 100 has one or more catalyst lines 119 for controlling the addition of polymerization catalyst to a reaction zone (not shown) within fluidized bed 111, and generally within straight section 105. Within the reaction zone, the catalyst particles react with reaction gases including an olefin monomer (e.g., ethylene) and optionally a comonomer and other reaction gases (e.g., hydrogen) to produce the granular polymer particles. As new polymer particles are produced, other polymer particles are continually withdrawn from the fluidized bed 111 through a product discharge line 121 to product recovery system 123. The fluidized bed 111 may be maintained at a constant height by withdrawing a portion of the fluidized bed 111 at a rate equal to the rate of formation of particulate product. The product may be removed continuously or nearly continuously via a series of valves (not shown) into a fixed volume chamber (not shown), which is simultaneously vented back to the reactor. The fixed volume chamber and venting back to the reactor allows for highly efficient removal of the product, while recycling a large portion of the unreacted gases back to the reactor.

[0048] Unreacted olefins and ICA composition within the product recovery system may be removed via line 125, compressed in compressor 127, and travel via line 129 to heat exchanger 131 to be cooled before being recycled (e.g., via line 133) to line 113. The particles within product recovery system 123 may be degassed (or “purged”) with a flow of inert gas such as nitrogen through line 135 to remove substantially all of the dissolved hydrocarbon materials. In some instances, the polymer granules may be treated with a small stream of humidified nitrogen to deactivate trace quantities of residual catalyst. The purge gas may be removed via line 137 to be vented to flare or recycled with further processing.

[0049] The polymerization system 100 also has a cooling loop which includes a first recycle gas line 139, compressor 141, a second recycle gas line 143, and cooling system 145 (such as a circulating gas cooler), coupled with the fluidized bed reactor 101. Cooling system 145 may accept cooling water via line 147 and expel heated water via line 149. Cooling of the recycle gas is a method used to cool polymerization system 100 to reduce or eliminate issues that may arise from exothermic polyolefin production. During operation, the cooled circulating gas from cooling system 145 flows via line 113 through inlet 151 into the fluidized bed reactor 101, then propagates upward through fluidized bed 111 and out from the fluidized bed reactor 102 via outlet 153.

[0050] The top expanded section 107 may also be known as a “velocity reduction zone,” and is designed to reduce the quantities of particle entrainment in the recycle gas line from the fluidized bed. The diameter of the top expanded section 107 generally increases with the distance from straight section 105. The increased diameter causes a reduction in the speed of the gas stream, which allows most of the entrained particles to settle back into the fluidized bed 111, thereby minimizing the quantities of solid particles that are “carried over” from the fluidized bed 111 through the recycle gas line 139. In some instances, a screen (not shown) may be included upstream of the compressor 141 to remove larger material.

[0051] To maintain a reactor temperature, the temperature of the recycle gas may be continuously adjusted up or down to accommodate changes in the rate of heat generation due to the polymerization reaction. One or more temperature sensors 155 may be located in the fluidized bed and used with a control system and the cooling loop to control the temperature of the fluidized bed 111 near the process set-point. Heated reactor gas, which carries heat energy from the fluidized bed reactor 101, is withdrawn from the outlet 153 and is pumped by the compressor 141 via line 143 to cooling system 145 where the temperature of the heated reactor gas is reduced and at least a portion of the ICA composition present is condensed to a liquid. The recycle gas from the cooling system 145, including condensed liquids, flows via line 113 to the reactor inlet 151 to cool the fluidized bed 111. Temperature sensors (not shown) near the inlet and outlet of the cooling system 145 may provide feedback to a control system (not shown) to regulate the amount by which cooling system 145 reduces the temperature of the recycle gas entering the fluidized bed reactor 101.

[0052] The fluidized bed reactor 101 may also include skin temperature sensors 157, mounted in positions along a wall of the straight section 105 of the fluidized bed reactor 101 so as to protrude into the bed from the reactor wall by a small amount (e.g., about one eighth to one quarter of an inch (3-6 mm)). The skin temperature sensors 157 may be configured and positioned to sense the temperature of the resin near the wall of the fluidized bed reactor 101 during operation.

[0053] The temperature sensors 155 in the fluidized bed 111 can include a resistance temperature sensor positioned and configured to sense bed temperature during reactor operation at a location within the fluidized bed reactor 101 away from the reactor wall. The resistance temperature sensor can be mounted so as to protrude into the bed more deeply than the skin temperature sensors 157 (e.g., about 8 to 18 inches (20-46 cm) away from the reactor wall).

[0054] Other sensors and other apparatuses may be employed to measure other reaction parameters during a polymerization reaction. The reaction parameters may include instantaneous and bed-averaged resin product properties (e.g., melt index and density of the polymer resin product being produced by the polymerization system 100 during a polymerization reaction). Resin product properties may be measured by periodically sampling the resin when exiting the reactor (e.g., about once per hour), and performing the appropriate tests in a quality control laboratory.

[0055] Other measured reaction parameters may include reactor gas composition (e.g., concentrations and partial pressures of reactant gases, ICA, and other inert gases, such as nitrogen, inert hydrocarbon, and the like). The reactor gas composition may be measured by removal of gas from upper portion 107 via line 159 to a gas chromatograph (“GC”) system 161. GC system 161 may also be connected by lines (not shown) other than line 159 to other parts of polymerization system 100, such as recycle gas line 139, compressor 141, line 143 or any combination thereof.

[0056] The process control variables may be controlled to obtain the desired productivity for the polymerization system 100 and properties for the resin. For example, the parameters used to control gas phase composition within the fluidized bed reactor 101 can include the concentration (partial pressure) and composition of the ICA composition and comonomer, the partial pressure of monomer, the type and properties of catalysts, and the temperature of the reaction process. For example, a polymerization reaction during a transition from production of a certain grade of polyolefin to a different grade may be controlled by controlling process control variables to ensure that the product (e.g., the granular resin) has properties compliant with an initial specification set at the start of the transition, the product produced during the transition ceases to comply with the initial specification set at a first time, and the product has properties compliant with a final specification set at the end of the transition. In the processes described herein, stickiness of the resin during the reaction may be controlled by a control system adjusting (or regulating) the temperature in the reaction zone and / or the concentration (partial pressure) of the ICA composition used in the reaction.

[0057] FIG. 2 is a block diagram of a control system 200 that can be used to control the polymerization system 100. The control system 200 may be a distributed control system (DCS), a direct digital controller (DDC), a programmable logic controller (PLC), or other suitable systems or combination of systems. The control system 200 has a processor 201 that implements machine readable instructions from a storage system 203. Illustrative processors may include a single coreprocessor, a multiple core processor, a virtual processor, a virtual processor in a cloud implementation, an application specific integrated circuit (ASIC), or a combination of these systems. Illustrative storage systems 203 can include random access memory (RAM), read only memory (ROM), hard drives, virtual hard drives, RAM drives, cloud storage systems, optical storage systems, physically encoded instructions (for example, in an ASIC), or a combination of these systems.

[0058] Adjustments to control settings may be determined based on the input of data from temperature sensors 155 and 157, the GC 161, and lab data 205, among others. After determining new control settings, the control system 200 may make in real time, or recommend, adjustments, for example, to the process cooling systems 207, the ICA addition and recycling systems 209, flow control systems 211, and termination systems 213, among others.

[0059] The reactor and associated methods may be an element of a staged reactor employing two or more reactors in series, where one reactor may produce, for example, a high molecular weight polyolefin and another reactor may produce a low molecular weight polyolefin. Polyolefin Production

[0060] Polyolefin polymerization may be performed by contacting in a reactor (such as the fluidized bed reactor 101 of FIG.1) an olefin monomer (optionally with a comonomer) with one or more catalysts (supported or not) in the presence of ICA composition and optionally hydrogen. The individual flow rates of olefin monomer, optional comonomer, optional hydrogen, and ICA composition (or individual components thereof) may be controlled to maintain fixed gas composition targets. The concentration of all gases may be measured with a chromatograph. A solid catalyst, a catalyst slurry, or liquid solution of the catalyst(s) may be injected directly into the reactor using a carrier gas (e.g., purified nitrogen), where the feed rate of catalyst(s) may be adjusted to change or maintain the catalyst inventory in the reactor.

[0061] In some embodiments, the polymerization reaction may be performed at a reactor pressure of about 4,200 kPa or less, about 700 kPa to about 4,200 kPa, about 1,300 kPa to about 2,800 kPa, or about 1,700 kPa to about 2,500 kPa.

[0062] Generally, the olefin monomer concentration is controlled and monitored by the olefin monomer partial pressure. In some embodiments, the olefin partial pressure may be at about 4200 kPa or less, such as about 500 kPa to about 2,000 kPa, about 1,000 kPa to about 1,800 kPa, about 1,200 kPa to about 1,700 kPa, or about 1,400 kPa to about 1,600 kPa.

[0063] The comonomer concentration may be controlled and monitored by a comonomer to olefin monomer mole ratio (or alternatively, the flow rates of comonomer and olefin monomer are held at a fixed ratio). When present, the comonomer may be at a relative concentration to the olefin monomer that will achieve the desired weight percent incorporation of the comonomer into the finished polyolefin. In some embodiments, the comonomer may be present with the olefin monomer in a mole ratio in the gas phase of from about 0.0001 to about 50 (comonomer to olefin monomer), from about 0.0001 to about 5, from about 0.0005 to about 1.0, or from about 0.001 to about 0.5.

[0064] The olefin monomer or comonomers, for example, may be a C2-C18alpha-olefin. In some embodiments, the olefin monomer is ethylene, and a comonomer is a C3-C12alpha olefin. In some embodiments, the olefin monomer may be ethylene or propylene, and a comonomer may include C4-C10 alpha-olefins. For example, C2-C18 alpha-olefins that may be utilized as a comonomer in embodiments described may include: ethylene, propylene, 1-butene, 1-pentene, 1- hexene, 1-heptene, 1-octene, 4-methylpent-1-ene, 1-decene, 1-dodecene, 1-hexadecene, and the like, and a combination thereof. Additionally, a polyene may be used as a comonomer according to some embodiments described. For example, polyenes may include: 1,3-hexadiene, 1,4- hexadiene, cyclopentadiene, dicyclopentadiene, 4-vinylcyclohex-1-ene, methyloctadiene, 1- methyl-1,6-octadiene, 7-methyl-1,6-octadiene, 1,5-cyclooctadiene, norbornadiene, ethylidene norbornene, 5-vinylidene-2-norbornene, 5-vinyl-2-norbornene, and olefins formed in situ in the polymerization medium. When olefins are formed in situ in the polymerization medium, the formation of polyolefins containing long chain branching may occur. Additional examples of comonomers may include isoprene, styrene, butadiene, isobutylene, chloroprene, acrylonitrile, and cyclic olefins. Combinations of the foregoing may be utilized in the methods described.

[0065] Examples of polymers that can be produced in accordance with the method described may include the following: homopolymers and copolymers of C2-C18 alpha olefins; polyvinyl chlorides, ethylene propylene rubbers (EPRs); ethylene-propylene diene rubbers (EPDMs); polyisoprene; polystyrene; polybutadiene; polymers of butadiene copolymerized with styrene; polymers of butadiene copolymerized with isoprene; polymers of butadiene with acrylonitrile; polymers of isobutylene copolymerized with isoprene; ethylene butene rubbers and ethylene butene diene rubbers; polychloroprene; norbornene homopolymers and copolymers with one or more C2-C18 alpha olefin; and terpolymers of one or more C2-C18 alpha olefins with a diene. In some embodiments, the polyolefin produced by the method described may include olefinhomopolymers (e.g., homopolymers of ethylene or propylene). In some instances, the polyolefin produced may be copolymers, terpolymers, and the like of the olefin monomer and the comonomer.

[0066] In some embodiments, the polyolefin produced may be a polyethylene or a polypropylene. Exemplary polyethylenes produced by the methods described may be homopolymers of ethylene or copolymers of ethylene (or terpolymers of ethylene) having at least one alpha-olefin (comonomer) where the ethylene content may be at least about 50% by weight of the total monomers involved. Exemplary polypropylenes produced by the methods described may be homopolymers of propylene or interpolymers of propylene and at least one alpha-olefin (comonomer) where the propylene content may be at least about 50% by weight of the total monomers involved.

[0067] Hydrogen gas is often used in olefin polymerization to control the final properties of the polyolefin. For some types of catalyst systems, increasing concentrations (or partial pressures) of hydrogen may alter the molecular weight or melt index of the polyolefin generated. The melt index can thus be influenced by the hydrogen concentration. Generally, the amount of hydrogen in the polymerization is expressed as a mole ratio relative to the total polymerizable monomer (e.g., relative to ethylene or relative to a blend of ethylene and hexene or propylene). The amount of hydrogen used in some polymerization processes is an amount necessary to achieve the desired melt index (or molecular weight) of the final polyolefin resin. In some embodiments, the mole ratio in the gas phase of hydrogen to total polymerizable monomer (H2to monomer) may be about 0.00001 or greater, about 0.0005 or greater, about 0.001 or greater, about 10 or less, about 5 or less, about 3 or less, or about 0.10 or less, where a range may include a combination of an upper mole ratio with a lower mole ratio described. Catalyst

[0068] Exemplary catalysts suitable for use in the embodiments described may include: Ziegler Natta catalysts, chromium based catalysts, vanadium based catalysts (e.g., vanadium oxychloride and vanadium acetylacetonate), metallocene catalysts and other single-site or single- site-like catalysts, cationic forms of metal halides (e.g., aluminum trihalides), anionic initiators (e.g., butyl lithiums), cobalt catalysts and mixtures thereof, nickel catalysts and mixtures thereof, rare earth metal catalysts (i.e., those containing a metal having an atomic number in the Periodic Table of 57 to 103), such as compounds of cerium, lanthanum, praseodymium, gadolinium and neodymium. A single catalyst may be used, or a mixture of catalysts may be employed, if desired.The catalyst may be soluble or insoluble, supported or unsupported. Further, the catalyst may be a prepolymer, spray dried with or without a filler, a liquid, or a solution, slurry / suspension, or dispersion.

[0069] Traditional Ziegler-Natta catalysts are transitional metal catalysts that are well known in the art. Examples of transition metal catalysts are discussed in U.S. Pat. Nos. 4,115,639, 4,077,904, 4,482,687, 4,564,605, 4,721,763, 4,879,359 and 4,960,741, the disclosures of which are hereby fully incorporated herein by reference. The transition metal catalyst compounds that may be used in the present invention include transition metal compounds from Groups 3 to 17, preferably 4 to 12, more preferably 4 to 6 of the Periodic Table of Elements.

[0070] Transition metal catalyst compounds based on magnesium / titanium electron-donor complexes that are useful in the invention are described in, for example, U.S. Pat. Nos.4,302,565 and 4,302,566, the disclosures of which are hereby fully incorporated herein by reference.

[0071] British Patent Application No.2,105,355 and U.S. Pat. No.5,317,036, the disclosures of which are hereby incorporated herein by reference, describe various vanadium catalyst compounds.

[0072] Still other transition metal catalyst compounds and catalyst systems suitable for use in the present invention are disclosed in U.S. Pat. Nos.4,124,532, 4,302,565, 4,302,566, 4,376,062, 4,379,758, 5,066,737, 5,763,723, 5,849,655, 5,852,144, 5,854,164 and 5,869,585 and published EP-A20416815 A2 and EP-A10420436, the disclosures of which are hereby fully incorporated herein by reference.

[0073] Other catalysts may include cationic catalysts such as AlCl 3, and other cobalt, iron, nickel and palladium catalysts well known in the art. See for example U.S. Pat. Nos.3,487,112, 4,472,559, 4,182,814 and 4,689,437, the disclosures of which are hereby fully incorporated herein by reference.

[0074] For more details on Ziegler-Natta catalysts, see for example, U.S. Pat. Nos.3,687,920, 4,086,408, 4,376,191, 5,019,633, 4,482,687, 4,101,445, 4,560,671, 4,719,193, 4,755,495, 5,070,055, the disclosures of which are hereby incorporated herein by reference.

[0075] Also, or instead, a catalyst compound of the present disclosure can be a chromium or chromium-based catalyst. Such catalysts and polymerization processes have been described, for example, in U.S. Patent Application Publication No.2011 / 0010938 and U.S. Pat. Nos.7,915,357, 8,129,484, 7,202,313, 6,833,417, 6,841,630, 6,989,344, 7,504,463, 7,563,851, 8,420,754, and 8,101,691.

[0076] In some embodiments processes disclosed herein utilize single-site transition metal catalysts. Exemplary -site transition metal catalysts suitable for use in the embodiments described may include metallocene catalysts and other single-site or single-site-like catalysts. A single catalyst may be used, or a mixture of catalysts may be employed, if desired. The catalyst may be soluble or insoluble, supported or unsupported. Further, the catalyst may be a prepolymer, spray dried with or without a filler, a liquid, or a solution, slurry / suspension, or dispersion.

[0077] Metallocenes may include “half sandwich” and “full sandwich” compounds having one or more pi-bonded ligands (e.g., cyclopentadienyl and ligands isolobal to cyclopentadienyl) bound to at least one Group 3 to Group 12 metal atom (Including the Lanthanide series and Actinide series elements), and one or more leaving groups bound to the at least one metal atom. The metallocene may be supported on a support material and may be supported with or without another catalyst component.

[0078] The structure of the metallocene catalyst compound may take on many forms, such as those disclosed in, for example, U.S. Pat. Nos.5,026,798, 5,703,187, and 5,747,406, including a dimer or oligomeric structure, such as disclosed in, for example, U.S. Pat. Nos. 5,026,798 and 6,069,213. Others include those catalysts described in U.S. Patent Application Publication Nos. US2005 / 0124487A1, US2005 / 0164875A1, and US2005 / 0148744. In some embodiments, the metallocene may be formed with a hafnium metal atom (e.g., bis(n-propylcyclopentadienyl) hafnium Xn, bis(n-butylcyclopentadienyl) hafnium Xn, or bis(n-pentylcyclopentadienyl) hafnium Xn, where X is one of chloride or fluoride and n is 2), such as is described in U.S. Pat. Nos. 6,242,545 and 7,157,531.

[0079] A catalyst compound of the present disclosure can be a chromium or chromium-based catalyst. Chromium-based catalysts include chromium oxide (CrO3) and silylchromate catalysts. Chromium catalysts have been the subject of much development in the area of continuous fluidized-bed gas-phase polymerization for the production of polyethylene polymers. Such catalysts and polymerization processes have been described, for example, in U.S. Patent Application Publication No. 2011 / 0010938 and U.S. Pat. Nos. 7,915,357, 8,129,484, 7,202,313, 6,833,417, 6,841,630, 6,989,344, 7,504,463, 7,563,851, 8,420,754, and 8,101,691.

[0080] Other catalysts for use in processes of the present disclosure include “non-metallocene complexes” that are defined to be transition metal complexes that do not feature a cyclopentadienyl anion or substituted cyclopentadienyl anion donors (e.g., cyclopentadienyl, fluorenyl, indenyl, methylcyclopentadienyl). Examples of families of non-metallocene complexes that may besuitable can include late transition metal pyridylbisimines (e.g., U.S. Pat. No.7,087,686), group 4 pyridyldiamidos (e.g., U.S. Pat. No. 7,973,116), quinolinyldiamidos (e.g., U.S. Pub. No. 2018 / 0002352 A1), pyridylamidos (e.g., U.S. Pat. No.7,087,690), phenoxyimines (e.g., Accounts of Chemical Research 2009, 42, 1532-1544), and bridged bi-aromatic complexes (e.g., U.S. Pat. No.7,091,292), the substance of which are fully incorporated herein by reference. Control of reaction zone monomer and ICA concentration

[0081] In some instances, during operation of a gas phased polymerization reactor, the feed rate of ethylene and alpha-olefin comonomer are reduced to control or limit productivity of the catalyst. The reduction of ethylene partial pressure (EPP) and alpha-olefin comonomer partial pressure (CPP) is performed at a set mol ratio of ethylene to alpha-olefin comonomer (ECR) when it is desired to maintain a constant density of the ethylene copolymer product irrespective of monomer feed rate. The partial pressure of the ICA (IPP) composition can be increased to produce polymer particles in the reaction zone having the same stickiness as polymer particles prior to reduction of the monomer feed.

[0082] It has been unexpectedly discovered that reducing monomer feed partial pressure and backfilling with an increase in ICA composition partial pressure to maintain a constant stickiness of polymer particles produced in the reaction zone results in an increased capacity to remove heat (Q) from the polymerization process and a corresponding increase in polymer production in the reaction zone. It has further been unexpectedly discovered that reduction in monomer feed partial pressure and offsetting increase in ICA composition partial pressure to maintain a constant stickiness of polymer particles also improves purging performance during product recovery. Without wishing to be bound by any particular theory, it is believed that polymer particles so produced contain a lower level of absorbed alpha-olefin comonomer and an increased amount of absorbed ICA composition such that the average molecular weight. The average molecular weight of the absorbed components is reduced thereby reducing the amount of inert purge gas needed to reduce the volatile organic content (VOC) of the polymer particles to levels acceptable for storage.

[0083] FIG. 3 illustrates an embodiment of the processes disclosed herein by way of a dimensionless graph. Dimensionless axes are used since absolute values of the various process parameters will vary based on the catalyst type, the target polymer properties, and the specific ICA composition. The magnitude of the parameter changes (e.g., EPP, CPP, IPP, ECR, Q) may vary based on the thermodynamics of a particular polymerization system (e.g., catalyst type, ICA composition, polymer grade), but the direction of the changes will be consistent. EPP1and IPP1in FIG.3 represent stable reactor operation where polymer production rates have been maximized by maximizing the ICA partial pressure at EPP1 to achieve heat removal Q1 and a polymer production rate corresponding to Q1. With respect to heat exchange equation, Q=mCpΔT, Cpand ΔT are assumed to be constants, such that the only way to increase Q is to increase m. The lower end of ΔT is set by cooling water temperature and the upper end of ΔT is TRZ, and TRZ was limited to no higher than a minimum threshold below the stickiness limit temperature TSL.

[0084] The processes disclosed herein hold the stickiness temperature constant by reducing comonomer partial pressure to CPP2 and increasing the ICA composition to IPP2. ICA partial pressure IPP is increased an amount sufficient to offset the drop in comonomer partial pressure CPP to maintain a constant stickiness limit temperature TSLfor particle of the polymer product--i.e., first polymer particles produced at first polymerization conditions comprising a temperature (TRZ), a molar ratio of ethylene to the alpha-olefin comonomer (ECR), a first ethylene partial pressure (EPP1), and a first ICA partial pressure (IPP1) have a stickiness limit temperature TSL, and the second polymer particles produced at second polymerization conditions comprising TRZ, ECR, a second ethylene partial pressure (EPP2), and a second ICA composition partial pressure (IPP2) have the same stickiness limit temperature TSL. IPP2is greater than IPP1resulting in an increase in m in the heat exchange equation. TSLminus TRZis greater than or equal to a threshold value to avoid sheeting and / or chunking in the reaction zone.

[0085] Referring to FIG.3, in some embodiments of the process, IPP1and IPP2are points on a curve defined by IPPi= f1(EPPi, CPPi), wherein f is a function determined by thermodynamic estimation of hydrocarbon solubility in particles of polymer product in the reaction zone. All points on the curve IPPi= f1(EPPi, CPPi) correspond to stickiness limit temperature TSL. Reaction zone operating temperature TRZis selected to be at least a threshold value below TSLto avoid sheeting and / or chunking in the reaction zone. The numerical value of the threshold value can vary based on catalyst type, polyethylene grade, reactor configuration, or a combination thereof. IPPiis a partial pressure of the ICA composition in the reaction zone at which polymer particles have the stickiness limit temperature (TSL), corresponding to ethylene partial pressure (EPP1). To maintain constant density of the polymer product, is a partial pressure of the alpha olefin comonomer CPPiin the reaction zone is reduced along with EPP1to maintain a ratio of EPP to CPP of ECR, the ethylene to alpha-olefin comonomer molar ratio. All other process parameters in the reaction zone are assumed to be constant or substantially constant between first polymerization conditions and second polymerization conditions.

[0086] In some embodiments, ethylene partial pressure EPP1 is reduced to a lower ethylene partial pressure EPP2 as shown in FIG. 3 in order to reduce and / or control catalyst activity. Correspondingly, alpha-olefin comonomer partial pressure is reduced to from CPP1to CPP2, such that EPP1 / CPP1 and EPP2 / CPP2 are both equal to the ethylene to alpha-olefin comonomer molar ratio corresponding to the desired density of the polymer product.

[0087] In some embodiments, ICA composition partial pressure IPP1is increased to a higher ICA composition partial pressure EPP2as shown in FIG.3 in order to offset the reduction in alpha- olefin comonomer partial pressure CPP, such that first polymer particles produced under first polymerization conditions comprise a first weight percent of absorbed ICA composition and a second weight percent of absorbed alpha-olefin comonomer, and second polymer particles produced under second polymerization conditions comprise a third weight percent of absorbed ICA composition and a fourth weight percent of absorbed alpha-olefin comonomer. The third weight percent of the ICA composition is greater than the first weight percent of the ICA composition. The fourth weight percent of alpha-olefin comonomer is less than the second weight percent of condensed alpha-olefin comonomer. First polymer particles and second polymer particles both have the same or substantially the same stickiness limit temperature TSLwherein, TSL=f2(first polymerization conditions)=f2(second polymerization conditions).

[0088] In some embodiments, the molecular weight of the alpha-olefin comonomer is greater than the molecular weight of the ICA composition. Without wishing to be bound by any particular theory, it is believed that the average molecular weight of the combined absorbed ICA composition and absorbed alpha-olefin comonomer in the first polymer particles is greater than the average molecular weight of the combined absorbed ICA composition and absorbed alpha-olefin comonomer in the first polymer particles. It is further believed that a first amount of purge gas and / or a first amount of venting is required in the product recovery section of the gas phase polymerization facility in order for first polymer particles to be processed to form a first polymer product having a volatile organic compound (VOC) content suitable for storage of the first polymer product. It is further believed that a second amount of purge gas and / or a second amount of venting is required in the product recovery section of the gas phase polymerization facility in order for second polymer particles to be processed to form a second polymer product having a VOC content suitable for storage of the second polymer product. It is further believed that the second amount of purge gas and / or second amount of venting is less than the first amount of purge gas and / or firstamount of venting for product a first polymer product and a second polymer product that have the same or substantially the same VOC content.

[0089] In some embodiments, the process under first polymerization conditions, a first gas phase composition is withdrawn from the reaction zone, wherein the first gas phase composition comprises a first mol fraction of the ICA composition and a second mol fraction of the alpha-olefin comonomer. The process under first polymerization conditions further comprises condensing a first portion of the withdrawn first gas phase composition yielding a first condensed stream. The process under first polymerization conditions further comprises recycling at least a portion of the first condensed stream to the reaction zone.

[0090] In some embodiments, the process under second polymerization conditions, a second gas phase composition is withdrawn from the reaction zone, wherein the second gas phase composition comprises a third mol fraction of the ICA composition and a fourth mol fraction of the alpha-olefin comonomer. The process under second polymerization conditions further comprises condensing a second portion of the withdrawn second gas phase composition yielding a second condensed stream. The process under second polymerization conditions further comprises recycling at least a portion of the second condensed stream to the reaction zone.

[0091] In some embodiments, in comparing the first polymerization conditions and the second polymerization conditions, as described above, the third mol fraction of the ICA composition is greater than the first mol fraction of the ICA composition, and the fourth mol fraction of the alpha- olefin comonomer is less than the second mol fraction of the alpha-olefin comonomer.

[0092] In some embodiments, in comparing the first polymerization conditions and the second polymerization conditions, as described above, the first condensed stream comprises a first amount of a condensed ICA composition and a first amount of condensed alpha-olefin comonomer, and the second condensed stream comprises a second amount of a condensed ICA composition and a second amount of condensed alpha-olefin comonomer. The second amount of condensed ICA composition is greater than the first amount of condensed ICA composition. The second amount of condensed alpha-olefin comonomer is less than the first amount of condensed alpha-olefin comonomer.

[0093] In some embodiments, in comparing the first polymerization conditions and the second polymerization conditions, as described above, the first condensed stream has a first latent heat of vaporization, the second condensed stream has a second latent heat of vaporization, and the second latent heat of vaporization is greater than the first latent heat of vaporization.

[0094] In some embodiments, a first polyolefin product is withdrawn from the reaction zone at a first mass flow rate under first polymerization conditions, and a second polyolefin product is withdrawn from the reaction zone under second polymerization conditions at a second mass flow rate. As shown in FIG. 3, ICA partial pressure IPP2 in the second polymerization conditions is greater than ICA partial pressure IPP1 in the first polymerization conditions. Correspondingly, heat transfer or heat removal capacity Q2 is greater than Q1, and hence, the second mass flow of the second polymer product is greater than the first mass flow of the first polymer product.

[0095] In some embodiments, the first polyolefin product and the second polyolefin product as described above have the same density, have a density in the range of from 0.900 g / cm3to 0.945 g / cm3, or a combination thereof.

[0096] In some embodiments, the process under first polymerization conditions further comprises stripping the first polyolefin product with a first amount of an inert gas to remove a portion of the ICA composition and a portion of the alpha-olefin comonomer to produce a first finished polyolefin product, and the process under second polymerization conditions further comprises stripping the second polyolefin product with a second amount of an inert gas to remove a portion of the ICA composition and a portion of the alpha-olefin comonomer to produce a second finished polyolefin product. The first amount of inert gas and the second amount of inert gas are sufficient to produce the first finished polyolefin product and the second finished polyolefin product, respectively, wherein the first finished polyolefin product and the second finished polyolefin product have the same volatile organic compound (VOC) content, and the second amount of inert gas is less than the first amount of inert gas.

[0097] In some embodiments, the first polymer particles comprise a first weight percent of the ICA composition and a second weight percent of the alpha-olefin comonomer, the second polymer particles comprise a third weight percent of the ICA composition and a fourth weight percent of the alpha-olefin comonomer, wherein the third weight percent of the ICA composition is greater than the first weight percent of the ICA composition, and the fourth weight percent of alpha-olefin comonomer is less than the second weight percent of alpha-olefin comonomer.

[0098] In some embodiments of the process, alpha-olefin comonomers is selected from propylene, 1-butene, 1-hexene, or 1-octene, or a combination thereof.

[0099] In some embodiments of the process, the ICA composition comprises one or more C3-C6 hydrocarbons. In some embodiments, the ICA composition comprises a first ICA and a second ICA. In some embodiments, the first ICA and the second ICA, respectively, are selectedfrom isopentane and isobutane, isobutane and n-butane, n-hexane and iso-pentane, isobutane and propane, isopentane and neo-pentane, and neo-pentane and isobutane. In some embodiments, the ICA composition is substantially free of C3-C6hydrocarbons other than the first ICA and the second ICA. In some embodiments, the gas phase composition is substantially free of C3-C6 aliphatic hydrocarbons other than the first ICA and / or the second ICA.

[0100] In some embodiments of the process, one or more aspects of the process are implemented by a control system. Such one or more aspects include, but are not limited to, changing the ethylene partial pressure from EPP1 to EPP2, changing the ICA partial pressure from ICA1to ICA2, maintaining the temperature (TRZ), maintaining the stickiness limit of polymer particles, maintaining the molar ratio of ethylene to the alpha-olefin comonomer (ECR), or a combination thereof is implemented by a control system. In some embodiments of the process, the control system comprises a distributed control system (DCS), a direct digital controller (DDC), a programmable logic controller (PLC), or a combination thereof. Total Allowable Condensing Agent Composition

[0101] A fluidized bed process is performed where the velocity of the gaseous recycle stream is sufficient to maintain the reaction zone in a fluidized state. In a fluidized bed polymerization process, the amount of fluid circulated to remove the heat of polymerization may be greater than the amount of fluid needed for support of the fluidized bed and for adequate mixing of the solids in the fluidized bed. The excess velocity provides additional gas flow to (and through) the fluid bed for additional cooling capacity and more intensive mixing of the reactor bed. However, to prevent excessive entrainment of solids in a gaseous stream withdrawn from the fluidized bed, the velocity of the gaseous stream may be regulated.

[0102] A fluidized bed within a gas phase reactor may include reactive components, other reagents (anti-slip, anti-static), and inert components including inert gas and ICAs. The combination of all these components can make up 100% of the flow (e.g., of volume or mass balance) of gas in and through a gas phase reactor. The total allowable ICA composition (Z) is the amount of the combination of ICAs that is subject to the concentration of other components in the fluidized bed.

[0103] Therefore, in order to increase Z, a portion of another component of the gas stream may be decreased. An increase in Z may allow for greater cooling of the reactor and therefore increased production rates but is limited by reactor volume and venting. Substantially all (e.g., 100%) of the components entering the reactor leave the reactor either in the product stream or the recycle stream.Z is increased by decreasing another component. For example, an increase in Z may be accomplished by lower quantities of other inert compounds including nitrogen. Alternatively, Z may be increased by using monomer and comonomer feeds with fewer inert impurities, a higher purity feed may allow for increased addition of ICA composition.

[0104] The ratio of inert components can be varied but may be limited by reactor venting. In order to maintain the mass balance for a given inert gas concentration, the inert gas flow into the reactor must equal the inert gas vented from the reactor. Reducing the concentration of inert gas in the reactor may result in more total vent flow. An increased vent flow may result in greater material loss and may also be limited by reactor design. For a given reactor producing a particular grade of polyolefin, the minimum inert gas can be ascertained based on a cost analysis balancing the reactor design including limits on vent flow and raw material loss associated with increased production rates related to improved cooling from a greater quantity of ICA composition. Because the reactive components and other components that aid in product formation may be specific to one embodiment of a desired product, they may be kept constant. Alternatively, Z may be increased by lowering the concentration of monomers or comonomers. Without being limited by theory, reduction of pressures of monomer and comonomer may decrease the catalyst activity, but it is possible that the cost associated with a decrease in catalyst activity is overcome by the improved production rates that accompany increased cooling from additional Z.

[0105] Furthermore, Z may be increased by increasing the overall reactor pressure. For example, if the individual components are at a specific partial pressure increasing the total pressure in the reactor would therefore increase pressure available to an ICA composition. An increase in pressure of the reactor may be limited by reactor design, feedstock pressures and compression costs, changes in the solubility and stickiness of the products and reactants. Therefore, the total allowable ICA composition may be a cost benefit analysis of individual options for increasing Z including, but not limited to removal of portions of other components or reactor pressurization. The cost analysis may take into account many factors including the catalyst activity, feedstock purity and availability, reactor design (in pressure, volume, and venting), product grades, and flow rates sufficient to fluidize the bed. The cost of any of these factors may be balanced by increased production rate resulting from improved cooling due to additional volume (or pressure) allotted to ICA composition.

[0106] In some embodiments, the total allowable amount of ICA composition is increased through use of a mixture of ICAs, such as, but not limited to, isopentane and isobutane, isobutaneand n-butane, n-hexane and iso-pentane, isobutane and propane, isopentane and neo-pentane, or neo-pentane and isobutane. Methods for optimizing mixtures of ICAs are disclosed in US 2022 / 0098332, the substance of which is fully incorporated by reference herein. Stickiness limit temperature

[0107] As discussed above, there may be limits to the concentrations of condensable gases, whether ICAs, comonomers or combinations thereof, that can be tolerated in the reaction system. Above certain limiting concentrations, the condensable gases can cause a sudden loss of fluidization in the reactor, and a consequent loss in ability to control the temperature in the fluidized bed. The loss of fluidization is indicative of the stickiness limit. Stickiness limits in general are the limitations of given reactor conditions (e.g., ICA amount; temperature; etc.) in a gas phase reactor, past which polymer particles become excessively sticky, negatively impacting operations. For example, as used herein, stickiness limit temperature (TSL) defines a trade-off between ethylene partial pressure EPP, alpha-olefin comonomer partial pressure CPP, and ICA composition partial pressure IPP. Also as used herein, the Stickiness Limit Temperature (TSL) is the temperature above which operations risk causing excessive stickiness of the growing polymer particles, risking sheeting, fouling, and / or loss of fluidization, and ultimately requiring reactor shutdown.

[0108] In conjunction with a calculated stickiness limit temperature TSL, a TSL for a given polymerization system (catalyst, polymer grade, reactor configuration, etc.) has a corresponding reaction zone temperature TRZ. The TRZis at least a threshold value below TSL, such that TSLminus TRZ is greater than or equal to a threshold value.

[0109] In some embodiments, a TSLand a corresponding threshold value between TSLand TRZis calculated by Method A, which entails determining TSLempirically through modeling reactor conditions against sheeting and / or loss of fluidization observations (at which point it is assumed that reactor temperature reached a value at which polymer became excessively sticky, thereby causing such sheeting and / or loss of fluidization). For example, a suitable laboratory method for determining stickiness limit is described in U.S. Pat. No. 10,029,226, incorporated by reference. The method estimates stickiness limit by measuring stirrer rotations per minute in an autoclave as the temperature is increased. As the mixture becomes overly sticky the stirrer stops at a certain temperature. The test can be performed at varying levels of the condensing agent and the stickiness temperature correlated to the SL as a linear function. The stick limit of a particular grade of polyolefin is therefore calculated as a linear function of multiple laboratory tests determiningstickiness temperature. Another suitable laboratory method for determining stickiness and SL is described in U.S. Pat. No.8,273,834, incorporated by reference. The method describes the use of melting point depression to determine stickiness, using differential scanning calorimetry and a prediction of reaction mixture solubility in polyethylene. Another example of a general computational method for stickiness limit temperature can be defined in terms of ICA composition concentrations (that is, TSL= f(IPP)). Optionally, other gas components, and particularly other heavy gas components (e.g., C4+ hydrocarbon gases, meaning those having 4 or more carbons; optionally C3+ hydrocarbon gases), can be included in the function; thus, gas components in the example of polymerization of ethylene and one or more α-olefin comonomers (e.g., 1-butene or 1- hexene) can include any one or more of isobutane, n-butane, isobutylene, cis-2-butene, isopentane, 1-hexene, 1-butene, n-pentane, n-hexane, and / or cyclohexane. In general, this relationship looks as follows: TSL = HPPActual / MAHPP, where HPPActual is the actual partial pressure of the “heavy” gas components, and MAHPP is the modeled maximum allowable heavies partial pressure as a function of reactor temperature, determined empirically by correlating observed performance of a reactor vs. reactor and polymer product conditions that affect stickiness (polymer density, melt index, and reactor temperature), where the observed performance includes the threshold operating temperature beyond which operations incur an unacceptable risk of stickiness (that is, the observed performance can incorporate conservative assumptions to avoid any sheeting or fouling in the reactor). With this guidance, the skilled artisan can apply such principles to a given polymerization reaction to model stickiness temperature based upon observed performance as a function of at least ICA amounts (ICAPP).

[0110] An example of this development follows, starting from E1, in which the Stickiness Limit is taken as Stickiness Limit Temperature (TSL), and thus temperature is incorporated into the empirical correlation for MAHPP. T^౨౮∙∑^ ^సభ^^^∙େ^^ୗ^ൌ∙ 100 E1TSL is the stickiness limit temperature; P୰^is reactor pressure in psia; x୧is the component mole fraction in the reactor gas; C୧ୀ^…୬are the specific component coefficients (e.g., 0.137, 0.193, 0.17, 0.17, 0.42, 1, 0.17, 0.137, 1.15, 1.15), determined throughempirical modeling to fit this model to observed temperature vs. partial pressure data; and i=1…n are references to the specific “heavy” gas components, including ICAs (e.g., isobutane, n-butane, isobutylene, cis-2-butene, isopentane, 1-hexene, 1-butene, n-pentane, n-hexane, cyclohexane, respectively).

[0111] Taking this further, MAHPP is determined empirically by modeling reactor temperature against the conditions (reactor pressure, heavy component concentrations or partial pressures, and product density and MI), determining relevant constant factors for each condition to determine MAHPP for a given reactor of interest. Continuing the example, MAHPP can be determined in this manner, resulting in the relationship as shown in equation E2 for production of a given resin (preferably a polyethylene resin such as a copolymer of at least 80wt% ethylene- derived units and 20wt% or less of units derived from one or more α-olefin comonomers): T^౨౮∙∑^ ^సభ^^^∙େ^^ୗ^ൌଷସ^∙^ି^.ଽ^ ∙୪୭^భబ ^୍ି^.ସଷ^∙^^^ିଶ^^ ∙ 100 E2TSL, Prx, xi,ci, and i are as in Equation E1 above Tୖ ଡ଼ is the reactor temperature in °C;^ is the resin density in g / cm3; MI is the resin melt index in g / 10 min. (2.16 kg at 190°C);

[0112] It is possible to use simulations of the process at various reactor conditions to identify suitable TSLvalues for given conditions, and therefore determine operating TRXthat is a desired amount below the stickiness limit TSL (that is, the threshold value difference between TSL and TRX). For example, suitable process simulations may be accomplished using commercial modelling software, such as PRO / II produced by SimSci™ or Aspen Plus produced by Aspentech.

[0113] Alternatively, , a TSL and a corresponding threshold value between TSL and TRZ for suitably safe reactor operation (safe in terms of avoiding excessive polymer stickiness) is calculated by Method B, the method described in U.S. Pat. No.7,683,140, the contents of which are fully incorporated herein by reference.

[0114] In yet further embodiments, a TSL and a corresponding threshold value between TSL and TRZis calculated by Method C, the computational method described in U.S. Pub. App. No.2022 / 0098332, and especially in paragraphs

[0138] –

[0157] therein, the contents of which are fully incorporated herein by reference. Polyolefin Products

[0115] Polymer products herein include copolymers of C2 to C40 olefins, preferably C2 to C20 olefins, preferably a copolymer of an alpha-olefin and another olefin or alpha-olefin (ethylene is defined to be an alpha-olefin for purposes of this invention). Preferably, the polymers are or include ethylene copolymerized with one or more of propylene, butene or hexene, and optional dienes. Preferred examples include thermoplastic polymers such as ultra low density polyethylene, very low density polyethylene (“VLDPE”), linear low density polyethylene (“LLDPE”), low density polyethylene (“LDPE”), medium density polyethylene (“MDPE”), and high density polyethylene (“HDPE”).

[0116] Polyethylene polymers produced in a gas phase polymerization process are characterized by a number of parameters, including, but not limited to, density, melt index (I2), high load melt index (I21 or HLMI), melt index ratio (MIR), number average molecular weight (Mn), weight average molecular weight (Mw), Z-average molecular weight (Mz), molecular weight distribution (Mw / Mnor MWD), the ratio of the Z-average molecular weight to the weight average molecular weight (Mz / Mw), composition distribution melt index, and branching index (g′). These parameters are related to physical characteristics of polymer chains, including, but not limited to, lengths of polymer chains, distribution of lengths of polymer chains, comonomer distribution among and along polymer chains, and length and number of branches on polymer chains. These physical characteristics of polymer chains lead to different mechanical properties that make different polyethylene polymers suitable for a broad range of end-use applications. Certain Embodiments

[0117] Disclosed herein is a process to polymerize olefins in a gas phase polymerization reactor, wherein the process is transitioned from first polymerization conditions to second polymerization conditions. The second polymerization conditions provide for increased heat removal from the reaction zone of the reactor as compared to the first polymerization conditions.

[0118] In a first group of embodiments, in addition to the forgoing limitations, the process comprises contacting ethylene, an alpha-olefin comonomer, a polymerization catalyst, and an induced condensing agent (ICA) composition, in a reaction zone of the gas phase polymerization reactor under first polymerization conditions comprising a temperature (TRZ), a molar ratio ofethylene to the alpha-olefin comonomer (ECR), a first ethylene partial pressure (EPP1), and a first ICA partial pressure (IPP1) to form first polymer particles. The process further comprises implementing second polymerization conditions in the reaction zone, comprising TRZ, ECR, a second ethylene partial pressure (EPP2), and a second ICA composition partial pressure (IPP2) to form second polymer particles. The first polymer particles and the second polymer particles have a stickiness limit temperature (TSL), and TSLminus TRZis greater than or equal to a threshold value.

[0119] In a second group of embodiments, in addition to the limitations of each embodiment of the first group of embodiments, each such embodiment of the process is further characterized by one of more of the following: a) IPP1and IPP2are points on a curve defined by IPPi=f1(EPPi, CPPi) and corresponding to TSL, wherein: i) IPPi is a partial pressure of the ICA composition in the reaction zone at which polymer particles have the stickiness limit temperature (TSL), corresponding to ethylene partial pressure (EPP1); ii) CPPi is a partial pressure of the alpha olefin comonomer in the reaction zone (EPP1 / ECR); iii) f1is a function determined by thermodynamic estimation of hydrocarbon solubility, laboratory melt initiation temperature tests, or a combination thereof; and iv) all other process parameters in the reaction zone are assumed to be constant; b) EPP2 is less than EPP1; c) IPP2is greater than IPP1; d) the molecular weight of the alpha-olefin comonomer is greater than the molecular weight of the ICA composition; and

[0120] In a third group of embodiments, in addition to the limitations of each embodiment of the first and second groups of embodiments, each such embodiment of the process is further comprises: a) under first polymerization conditions: i) withdrawing a first gas phase composition from the reaction zone, wherein the first gas phase composition comprises a first mol fraction of the ICA composition and a second mol fraction of the alpha-olefin comonomer;ii) condensing a first portion of the first gas phase composition yielding a first condensed stream; and ii) recycling at least a portion of the first condensed stream to the reaction zone; and b) under second polymerization conditions: i) withdrawing a second gas phase composition from the reaction zone, wherein the second gas phase composition comprises a third mol fraction of the ICA composition and a fourth mol fraction of the alpha-olefin comonomer; ii) condensing a second portion of the second gas phase composition yielding a second condensed stream; and iii) recycling at least a portion of the second condensed stream to the reaction zone; wherein the third mol fraction of the ICA composition is greater than the first mol fraction of the ICA composition; and the fourth mol fraction of the alpha-olefin comonomer is less than the second mol fraction of the alpha-olefin comonomer.

[0121] In a fourth group of embodiments, in addition to the limitations of each embodiment of the third group of embodiments, each such embodiment of the process is further characterized by one of more of the following: a) the first condensed stream comprises a first amount of a condensed ICA composition and a first amount of condensed alpha-olefin comonomer; and the second condensed stream comprises a second amount of a condensed ICA composition and a second amount of condensed alpha-olefin comonomer; wherein the second amount of condensed ICA composition is greater than the first amount of condensed ICA composition, and the second amount of condensed alpha-olefin comonomer is less than the first amount of condensed alpha-olefin comonomer; b) the first condensed stream has a first latent heat of vaporization; the second condensed stream has a second latent heat of vaporization; and the second latent heat of vaporization is greater than the first latent heat of vaporization; and c) the first and second gas phase compositions are substantially free of C3-C6aliphatic hydrocarbons other than the first ICA, the second ICA.

[0122] In a fifth group of embodiments, in addition to the limitations of each embodiment of the first through fourth groups of embodiments, each such embodiment of the process further comprises: a) under first polymerization conditions, withdrawing a first polyolefin product from the reaction zone at a first mass flow rate; and b) under second polymerization conditions, withdrawing a second polyolefin product from the reaction zone at a second mass flow rate; wherein the second mass flow rate is greater than the first mass flow rate.

[0123] In a sixth group of embodiments, in addition to the limitations of each embodiment of the fifth group of embodiments, the process further characterized by one or more of the following: a) the first polyolefin product and the second polyolefin product have a density in the range of from 0.900 g / cm3to 0.945 g / cm3, such as from a low of any one of 0.901, 0.902, 0.903, 0.905, 0.906, 0.907, 0.908, 0.909, or 0.910 g / cm3to a high of any one of 0.912, 0.915, 0.920, 0.925, 0.930, 0.935, 0.940, or 0.945 g / cm3, with ranges from any foregoing low end to any foregoing high end contemplated (e.g., 0.908 to 0.920 g / cm3or 0.910 to 0.935 g / cm3); b) the first polyolefin product comprises a first weight percent of the ICA composition and a second weight percent of the alpha-olefin comonomer; and the second polyolefin product comprises a third weight percent of the ICA composition and a fourth weight percent of the alpha-olefin comonomer; wherein: the third weight percent of the ICA composition is greater than the first weight percent of the ICA composition; and the fourth weight percent of alpha-olefin comonomer is less than the second weight percent of alpha-olefin comonomer; and c) stripping the first polyolefin product with a first amount of an inert gas to remove a portion of the ICA composition and a portion of the alpha-olefin comonomer to produce a first finished polyolefin product; and stripping the second polyolefin product with a second amount of an inert gas to remove a portion of the ICA composition and a portion of the alpha-olefin comonomer to produce a second finished polyolefin product; wherein: the first finished polyolefin product and the second finished polyolefin product have the same volatile organic compound content; and the second amount of inert gas is less than the first amount of inert gas.

[0124] In a seventh group of embodiments, in addition to the limitations of each embodiment of the first through the sixth groups of embodiments, each such embodiment of the process is further characterized by one or more of the following: a) the alpha-olefin comonomer is selected from propylene, 1-butene, 1-hexene, or 1- octene, or a combination thereof; b) the ICA composition comprises one or more C3-C6hydrocarbons; and c) the ICA composition comprises a first ICA and a second ICA; wherein in further embodiments: i) first ICA and the second ICA, respectively, are selected from: isopentane and isobutane; isobutane and n-butane; n-hexane and iso-pentane; isobutane and propane; isopentane and neo-pentane; and neo-pentane and isobutane; and ii) the ICA composition is substantially free of C3-C6 hydrocarbons other than the first ICA and the second ICA.

[0125] In some embodiments, in addition to the limitations of any one of the foregoing embodiments, in each such embodiment: changing the ethylene partial pressure from EPP1 to EPP2; changing the ICA partial pressure from ICA1to ICA2; maintaining the temperature (TRZ); maintaining the stickiness limit of polymer particles; maintaining the molar ratio of ethylene to the alpha-olefin comonomer (ECR); or a combination thereof is implemented by a control system. In further embodiments, the control system comprises a distributed control system (DCS), a direct digital controller (DDC), a programmable logic controller (PLC), or a combination thereof. Test Methods / Polymer Characterization

[0126] Density (g / cm3): Density measurements were made following ASTM D-1505.

[0127] Gel permeation chromatography (“GPC”) 4D Methodology: a) Unless otherwise indicated, the distribution and the moments of molecular weight (Mw, Mn, Mz, Mw / Mn, etc.), the comonomer content (C2, C3, C6, etc.), the branching index (gʹ), and CCDI (Mw-specific, 5-95, and Mn-Mz) are determined by using a high temperature Gel Permeation Chromatography (Polymer Char GPC-IR) equipped with a multiple-channel band- filter based Infrared detector IR5, an 18-angle light scattering detector and a viscometer. Three Agilent PLgel 10-μm Mixed-B LS columns are used to provide polymer separation. Aldrich reagent grade 1,2,4- trichlorobenzene (“TCB”) with 300 ppm antioxidant butylated hydroxytoluene (“BHT”) is used as the mobile phase. The TCB mixture is filtered through a 0.1-μm Teflon filter and degassed with an online degasser before entering the GPC instrument.The nominal flow rate is 1.0 ml / min. and the nominal injection volume is 200 μl. The whole system including transfer lines, columns, and detectors are contained in an oven maintained at 145°C. Given amount of polymer sample is weighed and sealed in a standard vial with 80-μl flow marker (heptane) added to it. After loading the vial in the autosampler, polymer is automatically dissolved in the instrument with 8 ml added TCB solvent. The polymer is dissolved at l60°C with continuous shaking for about 1 hour for most polyethylene samples or 2 hours for polypropylene samples. The TCB densities used in concentration calculation are 1.463 g / ml at room temperature and 1.284 g / ml at l45°C. The sample solution concentration is from 0.2 to 2.0 mg / ml, with lower concentrations being used for higher molecular weight samples. The concentration (c), at each point in the chromatogram is calculated from the baseline-subtracted IR5 broadband signal intensity (I), using the following equation: c = βI, where β is the mass constant. The mass recovery is calculated from the ratio of the integrated area of the concentration chromatography over elution volume and the injection mass which is equal to the pre-determined concentration multiplied by injection loop volume. The conventional molecular weight (IR MW) is determined by combining universal calibration relationship with the column calibration which is performed with a series of monodispersed polystyrene (PS) standards ranging from 700 to 10M g / mole. The MW at each elution volume is calculated with following equation: where the variables withwhile those without a subscript are for the test samples. In this method, αPS=0.67 and KPS=0.000175, while α and K for other materials are as calculated and published in literature (Sun, T. et al. Macromolecules 2001, 34, 6812), except that for purposes of this invention and claims thereto, α=0.695 and K=0.000579 for linear ethylene polymers, α=0.705 and K=0.0002288 for linear propylene polymers, α=0.695 and K=0.000181 for linear butene polymers, α is 0.695 and K is 0.000579 x (1 - 0.0087 x w2b + 0.0000l8 x (w2b)2) for ethylene-butene copolymer where w2b is a bulk weight percent of butene comonomer, α is 0.695 and K is 0.000579 x (l - 0.0075 x w2b) for ethylene- hexene copolymer where w2b is a bulk weight percent of hexene comonomer, and α is 0.695 and K is 0.000579 x (l - 0.0077 x w2b) for ethylene-octene copolymer where w2b is a bulk weight percent of octene comonomer. Concentrations are expressed in g / cm3, molecularweight is expressed in g / mole, and intrinsic viscosity (hence K in the Mark-Houwink equation) is expressed in dl / g unless otherwise noted. b) The comonomer composition is determined by the ratio of the IR5 detector intensity corresponding to CH2 and CH3 channel calibrated with a series of PE and PP homo / copolymer standards whose nominal value are predetermined by NMR or FTIR. In particular, this provides the methyls per 1000 total carbons (“CH3 / 1000TC”) as a function of molecular weight. The short-chain branch (“SCB”) content per 1000TC (“SCB / 1000TC”) is then computed as a function of molecular weight by applying a chain-end correction to the CH3 / 1000TC function, assuming each chain to be linear and terminated by a methyl group at each end. The weight % comonomer is then obtained from the following expression in which f is 0.3, 0.4, 0.6, 0.8, and so on for C3, C4, C6, C8, and so on co-monomers, respectively: c) The bulk composition of the polymer from the GPC-IR and GPC-4D analyses is obtained by considering the entire signals of the CH3and CH2channels between the integration limits of the concentration chromatogram. First, the following ratio is obtained d) Then the samementioned previously in obtaining the CH3 / 1000TC as a function of molecular weight, is applied to obtain the bulk CH3 / 1000TC. A bulk methyl chain ends per 1000TC (“bulk CH3end / l000TC”) is obtained by weight- averaging the chain-end correction over the molecular-weight range. Then and bulk SCB / 1000TC is converted to bulk w2 in the same manner as described above. e) The LS detector is the 18-angle Wyatt Technology High Temperature DAWN HELEOSII. The LS molecular weight (M) at each point in the chromatogram is determined by analyzing the LS output using the Zimm model for static light scattering (Light Scattering from Polymer Solutions, Huglin, M. B., Ed.; Academic Press, 1972.): Here, ΔR(θ) is the measuredintensity at scattering angle θ, c is the polymer concentration determined from the IR5 analysis, A2 is the second virial coefficient,P(θ) is the form factor for a monodisperse random coil, and K0 is the optical constant for the system: where NAis Avogadro’s number, the refractive index increment for the system.The refractive index, n=1.500 for and λ = 665 nm. For analyzing polyethylene homopolymers, ethylene-hexene copolymers, and ethylene-octene copolymers, dn / dc=0.1048 ml / mg and A2=0.0015; for analyzing ethylene-butene copolymers, dn / dc=0.1048*(l-0.00126*w2) ml / mg and A2= 0.0015 where w2 is weight percent butene comonomer. f) A high temperature Agilent (or Viscotek Corporation) viscometer, which has four capillaries arranged in a Wheatstone bridge configuration with two pressure transducers, is used to determine specific viscosity. One transducer measures the total pressure drop across the detector, and the other, positioned between the two sides of the bridge, measures a differential pressure. The specific viscosity, ηs, for the solution flowing through the viscometer is calculated from their outputs. The intrinsic viscosity, ηs, at each point in the chromatogram is calculated from the equation [η]= ηs / c, where c is concentration and is determined from the IR5 broadband channel output. The viscosity MW at each point is calculated as M = KPSMaps+1 / [η], where αpsis 0.67 and Kpsis 0.000175. g) The branching index (gʹvis) is calculated using the output of the GPC-IR5-LS-VIS method as follows. The average intrinsic viscosity, [η]avg, of the sample is calculated by: where the summations are over theslices, i, between the integration limits. h) The branching index gʹvjsis defined as gʹvjs= ([η]avg) / (KMvα), where Mvis the viscosity- average molecular weight based on molecular weights determined by LS analysis and the K and a are for the reference linear polymer, which are, for purposes of this invention and claims thereto, α = 0.695 and K = 0.000579 for linear ethylene polymers, α = 0.705 and K=0.0002288 for linear propylene polymers, α = 0.695 and K=0.000181 for linear butene polymers, α = 0.695 and K is 0.000579 x ( l- 0.0087 w2b + 0.0000l8 x (w2b)2) for ethylene-butene copolymer where w2b is a bulk weight percent of butene comonomer, α is 0.695 and K is 0.000579*(1 - 0.0075 x w2b) for ethylene-hexene copolymer where w2b is a bulk weight percent of hexenecomonomer, and α is 0.695 and K is 0.000579*(1 - 0.0077 x w2b) for ethylene-octene copolymer where w2b is a bulk weight percent of octene comonomer. Concentrations are expressed in g / cm3, molecular weight is expressed in g / mole, and intrinsic viscosity (hence K in the Mark- Houwink equation) is expressed in dl / g unless otherwise noted. Calculation of the w2b values is as discussed above.

[0128] Melt index (g / 10 min. or dg / min.): MI, also referred to as I2or I2.16in recognition of the 2.16 kg loading used in the test, was measured according to ASTM D-1238, 190°C, 2.16 kg. EXAMPLES

[0129] The following examples are included to demonstrate some embodiments of the invention. It should be appreciated by those of skill in the art that the techniques disclosed in the examples which follow represent techniques discovered by the inventor to function well in the practice of the invention, and thus can be considered to constitute preferred modes for its practice. However, those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments which are disclosed and still obtain a like or similar result without departing from the spirit and scope of the invention.

[0130] The unexpected increase in productivity was observed in a commercial sized gas phase polymerization reactor while producing an ethylene-hexene copolymer having an I2(melt index, 2.16 kg @ 190°C) of 5 dg / min. and a density of 0.908 g / cm3. Ethylene partial pressure was reduced to lower the catalyst productivity due to a catalyst feeder rate limitation external to the gas phase polymerization reactor. This resulted in a reduced concentration of 1-hexene in the reactor in order to maintain the molar ratio or ethylene to comonomer (ECR) as required to keep the density of the polymer product constant.

[0131] The density of the polyethylene product made in a gas phase polymerization reactor is primarily driven by the comonomer to ethylene molar ratio (ECR). Lower density polyethylene products require a higher concentration of comonomer (partial pressure) to make the target density. Lower density products have higher solubility which increases the stickiness of the product at a given temperature, or alternatively, decreases the stickiness limit temperature (TSL). This limits the amount of ICA that can be added to the reaction zone of the reactor to increase the polymer production rate without encountering operational issues such as sheeting.

[0132] When ethylene partial pressure EPP was reduced to control catalyst productivity, comonomer partial pressure CPP was reduced to maintain a constant molar ratio of ethylene and 1-hexene and constant density of the polymer product of 0.908 g / cm3. The reduced concentrationof 1-hexene in the reactor results in the amount of comonomer absorbed into the polyethylene particles in the reaction zone being reduced. Without other changes, this would result in an increase in the stickiness limit temperature TSLof polymer particles in the reaction zone. In order to maximize production of polymer product, ICA partial pressure IPP was increased such that the calculated TSL was moved back to its original value prior to reduction of the ethylene partial pressure. The added increment of ICA partial pressure resulted in an increase in capacity to remove heat (i.e., increase Q as previously defined), thereby increasing the polymer production rate.

[0133] Examples 1-5 are shown in Table 1 below. The reaction zone temperature (TRZ) in Examples 1-5 was 170°F / 76.7°C. The polymer product P1 in all of Examples 1-5 was an ethylene- hexene copolymer made with a metallocene catalyst and isopentane as the ICA composition having a density of 0.908 g / cm3and an I2 of 5.0 dg / min. Examples 1 and 3-5 show calculated values for EPP, hexene mol%, and iC5mol%, which show the allowable amount of iC5increasing as hexene content is decreased (at a constant ratio of ethylene to hexene) while maintaining a constant value of TSL-TRZ. In Example 2, P1 was produced with the same polymerization conditions as in Example 1 except that the IC5was not maximized to the stickiness limit of the polymer particles produced. TABLE 1 T EPP ECR 1-hex TSL-TRZTSL-TRZEx.RZene iC5(°F / °C) (psi / kPa) (EPP / CPP) (mol%) (mol%) Method B Method C 6 4 6 6 6Method B (as described above)

[0134] Method B requires that the polymerization conditions for P1 are such that the value of TSL-TRZ is greater than or equal to -8.6°F (-4.8°C). Example 2 has the same hexene content as Example 3 but a lower amount of iC5 and a value of TSL-TRZ of -8.0°F (-4.4°C), which is greater than the lower limit of -8.6°F (-4.8°C) for P1. is less than or equal to -8.6°F (-4.8°C). Therefore, stable operations were demonstrated with the comonomer and ICA amounts within the limits defined by Method B.Method C (as described above)

[0135] Method C requires that the polymerization conditions for P1 are such that the value of TSL-TRZis greater than or equal to 24.5°F (13.6°C). Example 2 has the same hexene content as Example 3 but a lower amount of iC5 and a value of TSL-TRZ of 25.9°F (14.4°C), which is greater than the lower limit of -24.5°F (13.6°C) is less than or equal to -8.6°F (-4.8°C). Therefore, stable operations were demonstrated with the comonomer and ICA amounts within the limits defined by Method C.

[0136] FIG. 4 illustrates the TSL-TRZ limit for P1, wherein ICA content=f(comonomer content), and the region below the TSL-TRZlimit defines combinations of ICA content and comonomer content TSL-TRZis greater than or equal to the TSL-TRZlimit.

[0137] For the sake of brevity, only certain ranges are explicitly disclosed herein. However, in addition to recited ranges, any lower limit may be combined with any upper limit to recite a range not explicitly recited, as well as ranges from any lower limit may be combined with any other lower limit to recite a range not explicitly recited, in the same way, ranges from any upper limit may be combined with any other upper limit to recite a range not explicitly recited. Additionally, within a range includes every point or individual value between its end points even though not explicitly recited. Thus, every point or individual value may serve as its own lower or upper limit combined with any other point or individual value or any other lower or upper limit, to recite a range not explicitly recited.

[0138] Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the processes, machines, means, processes, and / or steps described in the specification. As one of the ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, means, processes, and / or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein, may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, means, processes, and / or steps.

Claims

CLAIMS What is claimed is:

1. A process to polymerize olefins in a gas phase polymerization reactor, the process comprising: a) contacting ethylene, an alpha-olefin comonomer, a polymerization catalyst, and an induced condensing agent (ICA) composition, in a reaction zone of the gas phase polymerization reactor under first polymerization conditions comprising a temperature (TRZ), a molar ratio of ethylene to the alpha-olefin comonomer (ECR), a first ethylene partial pressure (EPP1), and a first ICA partial pressure (IPP1) to form first polymer particles; and b) implementing second polymerization conditions in the reaction zone, comprising TRZ, ECR, a second ethylene partial pressure (EPP2), and a second ICA composition partial pressure (IPP2) to form second polymer particles; wherein: i) the first polymer particles and the second polymer particles have a stickiness limit temperature (TSL); and ii) TSLminus TRZis greater than or equal to a threshold value.

2. The process of claim 0, wherein IPP1 and IPP2 are points on a curve defined by IPPi=f1(EPPi, CPPi) and corresponding to TSL; wherein: IPPi is a partial pressure of the ICA composition in the reaction zone at which polymer particles have the stickiness limit temperature (TSL), corresponding to ethylene partial pressure (EPPi); CPPi is a partial pressure of the alpha olefin comonomer in the reaction zone (EPPi / ECR); f1is a function determined by thermodynamic estimation of hydrocarbon solubility, laboratory melt initiation temperature tests, or a combination thereof; and all other process parameters in the reaction zone are assumed to be constant.

3. The process of claim 0 or claim 2, wherein EPP2is less than EPP1.

4. The process of claim 0 or any one of claims 2-3, wherein IPP2 is greater than IPP1.

5. The process of claim 0 or any one of claims 2-4, wherein the molecular weight of the alpha-olefin comonomer is greater than the molecular weight of the ICA composition.

6. The process of claim 0 or any one of claims 2-5, further comprising: a) under the first polymerization conditions: i) withdrawing a first gas phase composition from the reaction zone, wherein the first gas phase composition comprises a first mol fraction of the ICA composition and a second mol fraction of the alpha-olefin comonomer; ii) condensing at least a portion of the first gas phase composition, yielding a first condensed stream; and iii) recycling at least a portion of the first condensed stream to the reaction zone; and b) under the second polymerization conditions: i) withdrawing a second gas phase composition from the reaction zone, wherein the second gas phase composition comprises a third mol fraction of the ICA composition and a fourth mol fraction of the alpha-olefin comonomer; ii) condensing at least a portion of the second gas phase composition, yielding a second condensed stream; and iii) recycling at least a portion of the second condensed stream to the reaction zone; wherein the third mol fraction of the ICA composition is greater than the first mol fraction of the ICA composition; and the fourth mol fraction of the alpha-olefin comonomer is less than the second mol fraction of the alpha-olefin comonomer.

7. The process of claim 0, wherein: a) the first condensed stream comprises a first amount of a condensed ICA composition and a first amount of condensed alpha-olefin comonomer; and b) the second condensed stream comprises a second amount of a condensed ICA composition and a second amount of condensed alpha-olefin comonomer;wherein the second amount of condensed ICA composition is greater than the first amount of condensed ICA composition; and the second amount of condensed alpha-olefin comonomer is less than the first amount of condensed alpha-olefin comonomer.

8. The process of claim 0 or claim 7, wherein: a) the first condensed stream has a first latent heat of vaporization; b) the second condensed stream has a second latent heat of vaporization; and c) the second latent heat of vaporization is greater than the first latent heat of vaporization.

9. The process of claim 0 or any one of claims 7-8, wherein the first and second gas phase compositions are substantially free of C3-C6 aliphatic hydrocarbons other than the ICA composition.

10. The process of claim 0 or any one of claims 2-9, further comprising: a) under first polymerization conditions, withdrawing a first polyolefin product from the reaction zone at a first mass flow rate; and b) under second polymerization conditions, withdrawing a second polyolefin product from the reaction zone at a second mass flow rate; wherein the second mass flow rate is greater than the first mass flow rate.

11. The process of claim 0, wherein the first polyolefin product and the second polyolefin product each have a density in the range of from 0.900 g / cm3to 0.945 g / cm3.

12. The process of claim 0 or claim 11, wherein: a) the first polyolefin product comprises a first weight percent of the ICA composition and a second weight percent of the alpha-olefin comonomer; and b) the second polyolefin product comprises a third weight percent of the ICA composition and a fourth weight percent of the alpha-olefin comonomer; wherein:the third weight percent of the ICA composition is greater than the first weight percent of the ICA composition; and the fourth weight percent of alpha-olefin comonomer is less than the second weight percent of alpha-olefin comonomer.

13. The process of claim 0 or any one of claims 11-12, further comprising: a) stripping the first polyolefin product with a first amount of an inert gas to remove a portion of the ICA composition and a portion of the alpha-olefin comonomer to produce a first finished polyolefin product; and b) stripping the second polyolefin product with a second amount of an inert gas to remove a portion of the ICA composition and a portion of the alpha-olefin comonomer to produce a second finished polyolefin product; wherein the first finished polyolefin product and the second finished polyolefin product have the same volatile organic compound content; and the second amount of inert gas is less than the first amount of inert gas.

14. The process of claim 0 or any one of claims 2-13, wherein the alpha-olefin comonomer is selected from propylene, 1-butene, 1-hexene, or 1-octene, or a combination thereof.

15. The process of claim 0 or any one of claims 2-14, wherein the ICA composition comprises one or more C3-C6hydrocarbons.

16. The process of claim 0 or any one of claims 2-15, wherein the ICA composition comprises a first ICA and a second ICA.

17. The process of claim 0, wherein the first ICA and the second ICA, respectively, are selected from: a) isopentane and isobutane; b) isobutane and n-butane; c) n-hexane and iso-pentane; d) isobutane and propane;e) isopentane and neo-pentane; and f) neo-pentane and isobutane.

18. The process of claim 0, wherein the ICA composition is substantially free of C3-C6hydrocarbons other than the first ICA and the second ICA.

19. The process of claim 0 or any one of claims 2-18, wherein a control system implements one or more of the following: changing the ethylene partial pressure from EPP1to EPP2; changing the ICA partial pressure from ICA1 to ICA2; maintaining the temperature (TRZ); maintaining the stickiness limit of polymer particles; and maintaining the molar ratio of ethylene to the alpha-olefin comonomer (ECR).

20. The process of claim 0, wherein the control system comprises a distributed control system (DCS), a direct digital controller (DDC), a programmable logic controller (PLC), or a combination thereof.

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