Prediction of productivity and specification of produced polyethylene in an industrial gas-phase Fluidized-bed reactor: heterogeneous modeling and process optimization

In this research is focused on modeling of the gas-phase ethylene copolymerization to linear low-density polyethylene reactor employing a heterogeneous approach and optimization of the process condition under steady-state condition. To establish a comprehensive mathematical framework, the bubble phase is represented as a plug-flow reactor, whereas the emulsion phase is modeled as a series of multi-stage stirred tank reactors. The moment method is integrated with the kinetic model to predict the molecular weight and chain length distribution of the produced polyethylene. The validity of the developed model is confirmed through a comparison of simulation results with available plant data. The simulation results demonstrate that approximately 38 % of the total polymer is generated within the bubble phase. Subsequently, to improve polymer productivity, a single-objective optimization problem is formulated, and the optimal operating condition of process are determined, considering polymer density and melt index as constraints. The optimization results indicate that applying the optimal conditions on the industrial reactor increases the production rate from 13.8 to 15.35 tons per hour.