Macromolecular Reaction Engineering最新文献

The information available in daily plant operation data is not fully exploited by polymer reaction engineers: what do the catalytic olefin polymerization plants tell? In this article, a method is proposed to increase catalyst and process know-how, based on experimentally acquired production rate results, coming from a continuous tandem reactor polymerization process. The polymer reaction engineering methodology is also discussed in detail for connecting the catalyst reaction performance to the expected activity profile and yield for batch operation, together with the residence time distribution effect for continuous operation. The potential of the proposed methodology is highlighted with a theoretical example and the effectiveness of the method is demonstrated with an applied example, accurately estimating deactivation parameter values for two catalysts based on plant information and, validated based on small-scale polymerization experiments.

This study addresses the challenges of time-delay and low accuracy in online gas-phase composition monitoring during olefin copolymerization processes. Three flowmeters based on different mechanisms are installed in series to measure the real-time exhaust gas flow rate from the reactor. For the same gas flow, the three flowmeters display different readings, which vary with the properties and composition of the gas mixture. Consequently, the composition of the mixed gas can be determined by analyzing the reading of the three flowmeters. Fitting equations and three machine learning models, namely decision trees, random forests, and extreme gradient boosting, are employed to calculate the gas composition. The results from cold-model experimental data demonstrate that the XGBoost model outperforms others in terms of accuracy and generalization capabilities. For the concentration of ethylene, propylene, and hydrogen, the determination coefficients (R²) were 0.9852, 0.9882, and 0.9518, respectively, with corresponding normalized root mean square error (NRMSE) values of 0.0352, 0.0312, and 0.0706. The effectiveness of the online monitoring device is further validated through gas phase copolymerization experiments involving ethylene and propylene. The yield and composition of the ethylene and propylene copolymers are successfully predicted using the online measurement data.

Methods for the evaluation of the Damkohler number for monomer transport during emulsion homopolymerization and copolymerization are extended to the analysis of gaseous monomers. Results indicate that the monomer transport limitation of gaseous monomers in both homo and copolymerization is strongly dependent on overall pressure through Henry's law relationship governing the concentration of monomer in the aqueous phase in equilibrium with monomer bubbles. At low pressures, most monomers studied exhibit monomer transport limitations; however, even at very high pressures, some gaseous monomers still exhibit monomer transport limitations.

Front Cover: In article number 2300031, Carlos Bruno Barreto Luna and co-workers develop reactive blends of polyamide 6 and acrylic acid-grafted polyethylene (PE-g-AA). The PE-g-AA carboxylic groups react with the amine terminal groups of polyamide 6, forming the amide group and interface stabilizing the PA6/PE-g-AA blend. This promote a refinement of the dispersed PE-g-AA particles in polyamide 6, generating high-performance in impact strength and elongation at break.

The mean-square radius of gyration of network polymers can be correlated with the graph diameter, and the fraction d of segments located in the diameter chain is used to investigate the dimensions of large-sized network polymers whose cycle rank is over 10³. A simplified Monte Carlo simulation model for the miniemulsion vinyl/divinyl copolymerization is used for the generation of large-sized network polymers, assuming the classical chemical kinetics are valid. Both conventional free-radical polymerization and living polymerization are considered, and the heterogeneity of network architecture is controlled by changing the reactivity ratio of double bond in divinyl monomer with respect to that in vinyl monomer. The network maturity index (NMI) which is the cycle rank per primary chain is used to represent the degree of development of the network architecture. As the NMI increases to be well-developed, the calibrated d, defined by d_c = d/f_d where f_d is a calibration constant that shows the degree of network heterogeneity, starts to follow the master curve. This characteristic behavior applies regardless of the polymerization mechanism and the heterogeneity of the formed network architecture. Detailed characteristics of the master curve and prospects for application to gel molecules are also discussed.

A multicomponent Flory-Huggins model is implemented and utilized to describe the liquid–liquid equilibrium phenomenon in mixtures of polypropylene and xylene, in the context of the well-known xylene solubles (XS) test. The XS experiment is a common procedure in many polymer laboratories, used to determine the percentage of xylene solubles in samples of polypropylene, which provides an approximate measure of the atactic and oligomeric chains. Despite the importance of the test, the literature lacks a thermodynamic perspective regarding the description of this extraction phenomenon. In the present study, the Flory-Huggins interaction parameter is adjusted in a multicomponent framework to ensure that equilibrium chain length distributions calculated with the proposed model best match experimental distributions. It is shown that the experimental data obtained from XS analyses can be accurately fitted by the proposed model and that the estimated Flory-Huggins interaction parameter is more sensitive to the polymer average molar mass than to the degree of tacticity, when a particular catalyst is considered.

Front Cover: In article number 2200057, Arash Alizadeh, Vasileios Touloupidis, and João B. P. Soares have developed a thermodynamic simulation package for the catalytic polymerization of olefins in autoclave slurry, loop slurry, gas-phase, and autoclave solution reactors. The simulator uses the Sanchez–Lacombe theory as one of the major thermodynamic models in the polymer industry. Simulations under industrial conditions show why thermodynamic effects must be included in olefin polymerization models.