Vassileios Kanellopoulos

Dynamic evolution of the particle size distribution in multistage olefin polymerization reactors

Abstract A wide range of polyolefins are produced in catalytic particulate polymerization reactors (e.g., loop, continuous-stirred tank, horizontal stirred bed and fluidized-bed reactors). In each of these reactor configurations, the dynamic evolution of the particle size distribution (PSD) is a key variable that affects both the reactor operability and the end-use properties of the final product. In the present study, a comprehensive population balance model is developed to predict the evolution of particle size distribution in multistage olefin polymerization reactors. Specifically, the PSD is considered to evolve in time under the combined effect of particle aggregation and growth mechanisms. Two different numerical methods (i.e., the orthogonal collocation and the Galerkin on finite elements) are employed for solving the population balance equation. The performance of the two numerical methods is assessed in terms of accuracy, stability and computational efficiency of each method. It is shown that the dynamic evolution of PSD is highly affected by the operating conditions and the selected reactor configuration. Furthermore, it is shown that particle agglomeration can significantly affect the evolution of PSD in a multistage reactor configuration.

Dynamic evolution of the particle size distribution in gas-phase olefin polymerization fluidized bed reactors

In the present study, a comprehensive mathematical model is developed to predict the evolution of particle size distribution (PSD) in a gas-phase olefin polymerization fluidized bed reactor (FBR). To calculate the particle growth and the spatial monomer and temperature profiles in a particle, the random pore polymeric flow model (RPPFM) is employed. The RPPFM is solved together with a dynamic population balance model, accounting for both particle growth and agglomeration, to predict the PSD in the bed. To evaluate the extent of particle agglomeration in the bed, a new agglomeration kernel is developed in terms of the individual particle surface temperatures, the polymer softening temperature and a size dependent function, describing the mechanism of dual particle collisions. The effects of bulk polymerization temperature and propylene to ethylene molar ratio on the extent of particle agglomeration in an FBR are thoroughly analyzed.

Optimal Grade Transitions in an Industrial Slurry Phase Catalytic Olefin Polymerization Loop Reactor Series

Abstract Present market needs combined with the broad range of polyolefin applications have forced the polyolefin industry to operate under frequent grade transition policies. Consequently, under such market-driven operating schedules, the minimization of offspec polymer production and grade changeover time is prerequisite to any profitability analysis of the polyolefin production processes. In the present study, the optimal grade transition problem is examined in relation to an industrial Ziegler-Natta catalytic slurryphase ethylene-1-hexene polymerization loop-reactor series.

Modeling and Simulation of Particle Size Distribution in Slurry-Phase Olefin Catalytic Polymerization Industrial Loop Reactors

In the present study, a multi-scale, multi-phase, dynamic model is developed for the determination of the distributed properties (i.e., particle size distribution (PSD), molecular weight distribution (MWD)) of polyolefins produced in industrial catalytic gas and slurry phase olefin polymerization reactors (Scheme 1). The polymer MWD is determined by employing a generalized multi-site, Ziegler-Natta (Z-N) kinetic scheme (including site activation, propagation, site deactivation and site transfer reactions) in conjunction with the well-known method of moments. All the thermodynamic calculations are carried out using the Sanchez-Lacombe Equation of State (S-L EOS) (Kanellopoulos et al., 2006). A detailed population balance approach is employed to predict the PSD. The population balance model is combined with a single particle model and the comprehensive kinetic model to predict the properties of the final product in the reactors. Numerical simulations are carried out to investigate the effect of mass transfer limitations on the molecular and morphological properties of the produced polymer.

Dynamic Modeling and Optimization of Flash Separators for Highly-Viscous Polymerization Processes

In the present study, a multi-phase, multi-zone mathematical model is developed to describe the dynamic operation of industrial high-pressure separators (HPSs) for highlyviscous polymer systems. The proposed multi-phase, multi-zone description of the highpressure separator takes into account the complex gas carry-under and liquid droplets carryover phenomena. Moreover, the model takes into account the mass transfer rate from the liquid droplets to the gas phase as well as the bubble formation in the liquid zone. Extensive numerical simulations are carried out to determine the optimal operating conditions (i.e., temperature, pressure, feed composition and mass flowrate, etc.) on the dynamic performance and the separation efficiency of the HPS for highly-viscous fluids. It is shown that the proposed model is capable of simulating the dynamic operation of industrial-scale HPSs over a wide range of operating conditions (i.e., pressures 200-260 bar and temperatures 220-260 0C) and copolymers of different copolymer composition and viscoelastic properties (i.e., melt index in the range of 2-50 g/10min). Finally, it is shown that industrial HPSs do not operate near the thermodynamic equilibrium conditions. Therefore, their non-ideal behaviour should be taken into account when simulating their dynamic operation. Subsequently, model-based optimization and control studies are carried out to optimize the dynamic operation and performance of an industrial HPS.

DEVELOPMENT OF A DYNAMIC MULTI-COMPARTMENT MODEL FOR THE PREDICTION OF PARTICLE SIZE DISTRIBUTION AND MOLECULAR PROPERTIES IN A CATALYTIC OLEFIN POLYMERIZATION FBR

Abstract In the present study a comprehensive multi-compartment model is developed for the prediction of particle size distribution and particle segregation in a catalytic olefin polymerization FBR. To calculate the particle growth and the spatial monomer and temperature profiles in a particle, the random pore polymeric flow model (RPPFM) is utilized. The RPPFM is solved together with a dynamic discretized particle population balance model, to predict the particle size distribution (PSD) in each compartment. In addition, the polymer molecular properties are calculated, in each reactor compartment, by employing a generalized multi-site, Ziegler-Natta, kinetic scheme. The effects of various fluidized bed operating conditions on the morphological and molecular distributed polymer properties are thoroughly analyzed.