Modeling of the molecular weight distribution and short chain branching distribution of linear low-density polyethylene from a pilot scale gas phase polymerization process

Abstract

Molecular weight distribution (MWD) and short chain branching distribution (SCBD) play a decisive role in the performance of linear low-density polyethylene (LLDPE). A model based on a non-standard polymerization reaction scheme is developed for ethylene/α-olefin gas phase copolymerization in a fluidized bed reactor. Experimental MWD and SCBD are simultaneously deconvoluted. The results obtained by this simultaneous deconvolution method are physically more relevant. Reduction of parameters and parameter estimability analysis are conducted to screen parameters to obtain a subset for reliable parameter estimation. The model based on the estimated parameters yields MWD and SCBD which are in good agreement with experimental ones for several LLDPE grades obtained from a pilot-scale gas phase polymerization process. The non-standard polymerization reaction scheme depicts well the “comonomer effect” - activation of dormant ethylene species.