Patent ID: 7585923

Claim:
A method of polymerizing olefins in a polymerization reactor 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 =( ln ( FI T )− A 1 −C′ 1 ×FI H )/ C′ 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 as determined by ASTM D1238-01 Procedure B at condition 190/21.6); where: A 1 =ln ( FI O ) −C′ 2 ×LI P −C′ 1 ×FI HO ; wherein FI O is the measured flow index of polymer produced according to the previous leading indicator reactor conditions; wherein C′ 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 are measured, LI P being an exponentially weighted moving average of the LI, calculated with a weighting factor, λ=1−exp(−Δt/(polymer residence time) based on the polymer residence time in the reactor, with the calculation being LI P =(λ× LI )+(1−λ)× LI T−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 (−0.33759+0.516577 *ln ( I 21.6 )−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; C′ 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.