CROSS-REFERENCE TO RELATED APPLICATIONS

None.

TECHNICAL FIELD OF THE DISCLOSURE

This application relates to systems and methods for improved reactor control, in particular systems and methods for improved control of polyolefin reactors.

BACKGROUND

Polyolefin properties depend on a number of factors, such as reactor temperature, reaction time, average residence time, olefin concentration, α-olefin comonomer concentration, hydrogen concentration, catalyst type, catalyst concentration, co-catalyst concentration, activator concentration, reactor configuration, reactor volume, and the like. Determining the necessary conditions to produce a polyolefin having desired properties typically requires time and cost-intensive repeated testing to determine whether any particular combination of properties will yield the desired polyolefin properties.

As the complexity of the resins produced and the complexity of the processes to manufacture them have increased, there is an parallel need for a more advanced systematic method of process control. Determining the key process parameters to monitor and control becomes increasingly difficult when the desired polyolefin is a bimodal polyolefin, and when more than one reactor is being used. Bimodal polyolefins with reverse comonomer composition distribution (CCD) have excellent mechanical properties, but are often particular difficult to determine manufacturing.

Accordingly, improved systems and methods for reactor control are needed.

SUMMARY

This summary is provided to introduce various concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify required or essential features of the claimed subject matter nor is the summary intended to limit the scope of the claimed subject matter.

This summary and the following detailed description provide examples and are explanatory only of the invention. Accordingly, the foregoing summary and the following detailed description should not be considered to be restrictive. Additional features or variations thereof can be provided in addition to those set forth herein, such as for example, various feature combinations and sub-combinations of these described in the detailed description.

In an aspect, the disclosed processes are applicable to bimodal resins produced in a single reactor utilizing a dual catalyst system, in which the production of two distinct polymers in one reactor renders the characterization of each individual polymer extremely difficult. While simple systems can use melt flow and density to control a polymerization process to the targeted molecular weight distribution, the current disclosure provides methods based upon process sample GPC (gel permeation chromatography), SCB (short chain branching) analysis and dynamic rheology.

In one aspect, this disclosure provides methods based on dynamic rheology and rapid GPC to determine what process conditions to adjust to produce the targeted molecular weight distribution for dual catalyst systems in a single reactor, for example, a dual metallocene catalyst system in a single reactor. The methods were developed to input a target rheology-frequency scan and/or a rapid GPC of the desired polymer. The rheology and MWD obtained from a current process sample was input into the disclosed method at regular intervals. The method would then correlate a designed experimental model, for example a model obtained using previously collected pilot plant data, with the current reaction process conditions. Any minor corrections or offsets can be added to match the current process to the current sample. The method would then compare the current rheology and MWD to the target, calculate a trajectory, translate that trajectory to a change in reactor control parameters. In an aspect, for example, the method could provide a suggestion for new control set points in reactor conditions. These steps would be repeated until the process sample rheology and MWD matched the target polymer rheology and MWD.

In one aspect, for the single reactor dual catalyst system, while some key reactor conditions can be held constant, the H2(hydrogen pressure), temperature, and co-monomer (for example, hexane) can be varied using the disclosed method to obtain a target resin. The same basis methodology is applicable in other resin processes, for example, the Advanced Dual Loop (ADL) process, although a different combination of key and manipulated parameters can be used. Therefore, this model development entails using data collected in a systematic fashion along with mathematical modeling on the systems to be controlled.

According to an aspect, this disclosure provides a method of controlling an olefin polymerization reactor system, the method including: a) selecting n input variables I1, I2, I3, . . . In, each input variable corresponding to a process condition for an olefin polymerization process; b) identifying m response variables, R1, R2, R3, . . . Rm, each response variable corresponding to a measurable polymer property, wherein two of the m response variables are molecular weight distribution (MWD) and short chain branching (SCB); c) adjusting one of more of the n input variables I1to Inin a plurality of polymerization reactions using the olefin polymerization reactor system, to provide a plurality of olefin polymers and measuring each of the m response variables R1to Rmas a function of the input variables for each olefin polymer; d) analyzing the change in each of the response variables R1to Rmas a function of the input variables I1to Into determine the coefficients according to the following general equation for each response variable R1to Rm:
R1-m=C0+Σu=1u=nCu(Iu)
e) calculating a Response Surface Model (RSM) using general equations for each response variable R1to Rm(R1-m) determined in step d) to correlate any combination of the n input variables I1to Inwith one or more of m response variables R1to Rm; f) applying n selected input variables Is1, Is2, Is3, . . . Isnto the calculated Response Surface Model (RSM) to predict one or more of m target response variables, Rt1, Rt2, Rt3, . . . Rtm, each target response variable corresponding to a measurable polymer property; and g) using the n selected input variables Is1to Isnto operate the olefin polymerization reactor system and provide a polyolefin product.

According to some aspects, the general equation for each response variable R1to Rmis

R1-m=C0+∑u=1u=n⁢Cu⁡(Iu)+∑v=1v′⁢Cv⁡(product⁢⁢of⁢⁢a⁢⁢unique⁢⁢⁢combination⁢⁢of⁢⁢2⁢⁢of⁢⁢I1⁢⁢to⁢⁢In,independently⁢⁢selected)
wherein v′ is the total number of unique combinations of any 2 of I1to In, independently selected.

According to some aspects, the general equation for each response variable R1to Rmis

R1-m=C0+∑u=1u=n⁢Cu⁡(Iu)+∑v=1v′⁢Cv⁡(product⁢⁢of⁢⁢a⁢⁢unique⁢⁢combination⁢⁢of⁢⁢2⁢⁢of⁢⁢I1⁢⁢to⁢⁢In,independently⁢⁢selected)+∑w=1w′⁢Cw⁡(product⁢⁢of⁢⁢a⁢⁢unique⁢⁢combination⁢⁢of⁢⁢3⁢⁢of⁢⁢I1⁢⁢to⁢⁢In,independently⁢⁢selected)
wherein v′ is the total number of unique combinations of any 2 of I1to In, independently selected; and w′ is the total number of unique combinations of any 3 of I1to In, independently selected.

According to some aspects, the general equation for each response variable R1to Rmis

R1-m=C0+∑u=1u=n⁢Cu⁡(Iu)+∑v=1v′⁢Cv⁡(product⁢⁢of⁢⁢a⁢⁢unique⁢⁢combination⁢⁢of⁢⁢2⁢⁢of⁢⁢I1⁢⁢to⁢⁢In,independently⁢⁢selected)+∑w=1w′⁢Cw⁡(product⁢⁢of⁢⁢a⁢⁢unique⁢⁢combination⁢⁢of⁢⁢3⁢⁢of⁢⁢I1⁢⁢to⁢⁢In,independently⁢⁢selected)+∑x=1x′⁢Cx⁡(product⁢⁢of⁢⁢a⁢⁢unique⁢⁢combination⁢⁢of⁢⁢4⁢⁢of⁢⁢I1⁢⁢to⁢⁢In,independently⁢⁢selected)
wherein v′ is the total number of unique combinations of any 2 of I1to In, independently selected; w′ is the total number of unique combinations of any 3 of I1to In, independently selected; and x′ is the total number of unique combinations of any 4 of I1to In, independently selected.

According to another aspect, this disclosure provides a method of controlling an olefin polymerization reactor system, the method comprising: a) selecting one or more of m target response variables, Rt1, Rt2, Rt3, . . . Rtm, each target response variable corresponding to a measurable polymer property; b) calculating n selected input variables Is1, Is2, Is3, . . . Isnusing the Response Surface Model (RSM) of claim1, to achieve the one or more of m target response variables, Rt1, Rt2, Rt3, . . . Rtm; c) using the n selected input variables Is1to Isnto operate the olefin polymerization reactor system and provide a polyolefin product; d) measuring one or more properties of the polyolefin product corresponding to m measured response variables, Rm1, Rm2, Rm3, . . . Rmm; and e) repeating steps a) through d) to reduce the difference between the target response variables Rt1to Rtmand the measured response variables Rm1to Rmm.

These and other aspects and embodiments according to this disclosure are provided in the drawings, detailed description and claims.

