Patent ID: 8058366

Claim:
A method of polymerizing ethylene and 1-butene, 1-hexene, 1-octene, or combinations thereof in a polymerization reactor to form a bimodal polymer composition, the method comprising calculating a leading indicator target (LI T ) value in order to control the polymerization reactor and thereby to control the properties of a polymer product produced therein, wherein said properties comprise flow index (FI), as determined by ASTM D1238-01 Procedure B condition 190/21.6, the method of polymerization comprising: a) calculating a leading indicator target (LI T ) that corresponds to a target polymer product wherein said leading indicator target (LI T ) is defined as: LI T =( In ( FI T )âˆ’ A 1 âˆ’Câ€² 1 Ã—FI H )/ Câ€² 2 ; wherein FI T is the target flow index of the polymer that is to be produced after adjustment of reaction conditions to a new leading indicator (the flow index is determined by ASTM D1238-01 Procedure B at condition 190/21.6); wherein: A 1 =ln( Fl O )âˆ’ Câ€² 2 Ã—LI P âˆ’Câ€² 1 Ã—FI HO ; and wherein FI O is the measured flow index of polymer produced according to the previous leading indicator reactor conditions; wherein Câ€² 1 is a constant related to the catalyst system; wherein LI p is the leading indicator calculated by an exponentially weighted average technique from the previous time period for the time that the samples upon which FI O and FI HO were measured, LI p being an exponentially weighted moving average of the LI, calculated with a weighting factor, Î»=1-exp(âˆ’Î”t/(polymer residence time) based on the polymer residence time in the reactor, with the calculation being LI P =(Î»Ã—LI)+(1âˆ’Î»)Ã—LI p,Tâˆ’1 ; wherein FI HO is the flow index of the higher molecular weight polymer measured on polymer produced according to the previous leading indicator conditions, determined with the formula: FI HO =ln(âˆ’0.33759+0.516577*ln( I 21.6 )âˆ’0.01523*( I 21.6 /I 2.16 )); wherein FI H is the flow index of the higher molecular weight polymer produced by the catalyst system under current reactor parameters, estimated from models showing changes in FI H based on changes in reaction conditions; wherein Câ€² 2 is a constant related to the catalyst system; and b) changing at least one reactor parameter to adjust the leading indicator toward the leading indicator target value.