Numerical Analysis of Industrial Styrene Polymerization in Nonideal Tower Reactors

An integrated model combining computational fluid dynamics (CFD) with polymerization kinetics was developed to investigate the industrial styrene thermal polymerization process. The comprehensive kinetic model was coupled with the CFD model by user-defined function (UDF) codes based on the method of moments. Meanwhile, a simulation based on the ideal reactor model was conducted. The results predicted by CFD, including the monomer conversion, molecular weight, and molecular weight distribution described by Flory’s distribution, compared satisfactorily with the plant data and exhibited higher accuracy than those of the ideal reactor model. A higher reaction temperature and a lower volume flow rate result in a higher monomer conversion and a wider molecular weight distribution. The increase of rotational speed of helical ribbon impellers improves the mixing efficiency and uniformity of species concentration in the stirred sections. The CFD model could provide valuable guidance for the optimization of operation conditions and the design of nonideal reactors

Ethylene–Propylene Segmented Copolymer as an in Situ Compatibilizer for Impact Polypropylene Copolymer: An Assessment of Rheology and Morphology

This work aims to probe the roles of ethylene–propylene segmented copolymer (EPS) in impact polypropylene copolymers (IPCs) by rheological and morphological investigations. A series of IPCs with different EPS contents and molecular structures are prepared by an atmosphere-switching polymerization process (ASPP). The Palierne emulsion model is used to describe the relationship between the rheological response to small amplitude oscillatory deformation and the morphology of IPC. It is found that this model describes well the linear viscoelastic responses of IPC, if the role of EPS is taken into account. An increase in the content of EPS and the length of its PP segments leads to a decrease in the size of the ethylene–propylene random copolymer (EPR) phase domains and the interfacial tension. These results strongly confirm the role of the EPS as a compatibilizer in the IPC system. The adhesion between the PP matrix and the EPR phase domains is enhanced by the presence of the EPS that is produced in situ during the ASPP. For this reason, ASPP is capable of making IPC with an excellent rigidity–toughness balance

In Situ Raman Spectroscopy Real-Time Monitoring of a Polyester Polymerization Process for Subsequent Process Optimization and Control

Here, in situ Raman spectroscopy is used to develop a method for determining in real time the percentage of esterification denoted as Ester%, a key quality index of polymerization processes in polyester industries. Specifically, Raman spectra of the polymerization (esterification and polyesterification) of terephthalic acid (PTA) and 1,4-butanediol (BDO) to obtain poly(butylene terephthalate) (PBT) are monitored as a function of reaction time. They are processed through a background subtraction algorithm to yield Raman spectra, which allows for the identification and quantification of Raman bands corresponding to the ester and carboxylic groups. The Ester% is calculated by the ratio between the ester and carboxylic groups in terms of the characteristic peak intensities or areas. The ratio based on the Raman peak areas yields more satisfactory results, namely, the calculated values of the Ester% are less noisy and agree better with those obtained by titration. The established in situ Raman spectroscopy method allows for real-time monitoring and quantification of the Ester% during the polymerization process. It will be adopted for process optimization and control at a pilot scale and ultimately at an industrial production scale

Homogeneous Fluidization of Geldart D Particles in a Gas–Solid Fluidized Bed with a Frame Impeller

The influence of agitation of a frame impeller on the fluidization performance of Geldart D particles is experimentally and numerically studied in a gas–solid stirred fluidized bed, using a three-dimensional (3D) unsteady computational fluid dynamics (CFD) simulation. The bed pressure drops obtained from simulations are in reasonable agreement with those measured with pressure transducers, which validates the CFD models. The experimental results of the pressure fluctuation and the simulated ones of the solid volume fraction distribution show that Geldart D particles can perform homogeneous fluidization in the presence of the impeller. The homogeneous fluidization regime expands as the minimum bubbling velocity increases with the agitation speed while the minimum fluidizing velocity remains unaffected. In addition, the uniformity of particle velocities that are distributed in the entire fluidized bed is also improved by the agitation of the frame impeller

Kinetic Parameter Estimation for Linear Low-Density Polyethylene Gas-Phase Process from Molecular Weight Distribution and Short-Chain Branching Distribution Measurements

Kinetic parameter estimation for a complex copolymerization process has always been a challenge in the modeling procedure. This study aims at the kinetic parameter estimation for a linear low-density polyethylene (LLDPE) gas-phase process from molecular weight distribution (MWD) and short-chain branching distribution (SCBD) measurements. First, experimental MWD and SCBD are simultaneously deconvoluted to obtain intermediate model parameters as output variables. Then, appropriate nominal values of the kinetic parameters are provided by solving an optimization problem. This procedure plays a significant role in narrowing down the range of the nominal values. The determined output variables and nominal parameter values are used to form a sensitivity matrix for parameter estimability analysis. After that, a new parameter ranking strategy is proposed using hierarchical clustering. Based on the determined nominal values, the ranking results obtained using the proposed strategy in a robustness test are more robust than those obtained under random nominal values. Lastly, the hierarchical clustering is combined with Wu’s mean squared error-based method to determine an estimable parameter subset, during which the selected kinetic parameters are estimated by matching the intermediate model parameters. The gas-phase copolymerization process model based on the estimated parameter values is further validated with different MWD and SCBD measurements. Model predictions show good agreement with experimental data