Macromolecular Reaction Engineering最新文献

The impact of common process catalyst poisons on the performance of a 6th generation Ziegler–Natta catalysts during the gas phase polymerization of propylene are examined using two approaches: introducing propylene without purification, or with one or two sets of purification columns, and by introducing carbon dioxide (CO₂), oxygen (O₂), water (H₂O), methanol (CH₃OH), ethyl acetate (C₄H₈O₂) and dimethyl sulfoxide (C₂H₆SO) during the polymerization. As expected, purification columns increases the catalyst activity significantly, slightly reduce catalyst decay. Injecting TiBA during the reaction leads to an activity increase. The addition of two full sets of columns substantially increased the repeatability of polymerization reactions. The power of deactivation of poisons injected during the polymerization reaction is: O₂ > CO₂ > CH₃OH > C₂H₆SO > C₄H₈O₂ > H₂O. Adding CO₂, O₂, and CH₃OH resulted in a progressive decrease in molecular weight while almost no effect is observed with H₂O. However, C₄H₈O₂, and C₂H₆SO resulted in a mild increase in molecular weight. Additionally, the effects on crystallinity and stereoregularity are similar where CO₂, O₂, H₂O and CH₃OH caused a progressive decrease while C₄H₈O₂ and C₂H₆SO resulted in a mild increase, indicating some isotacticity control by these two poisons.

The present work presents phenomenological models to describe the coordination polymerization of β-myrcene using the Ziegler–Natta catalyst system composed by neodymium versatate (NdV₃), diisobutylaluminum hydride (DIBAH), and dimethyldichlorosilane. The kinetic parameters required to simulate the reactions are estimated, and the amount of DIBAH used as a chain transfer agent (CTA) is obtained by a data reconciliation strategy since it can participate in side reactions. Several experiments are performed at different conditions to evaluate the impact of key operation variables on the control of monomer conversion and average molar masses. It is shown that the initial NdV₃, β-myrcene, and DIBAH concentrations exert strong influences on the course of the polymerization. The kinetic mechanism of Coordinative Chain Transfer Polymerization (CCTP) fits well with the data of final average molar masses and monomer conversion, while the dynamic trajectories of these variables are fitted better by kinetic mechanisms of more conventional coordination polymerizations, considering site deactivation and termination by chain transfer. In all cases, the proposed models are able to predict the experimental data well after successful parameter estimation and reconciliation of CTA concentrations, indicating that the kinetic mechanism can be characterized by different kinetic regimes.

Front Cover: In article number 2200038, Miguel Rosales-Guzmán and co-workers investigate the effect of reaction temperature and carbon dioxide pressure on the simultaneous copolymerization of 1-octene and glycidyl methacrylate (GMA) in the absence of solvents or stabilizers. Emphasis is given to the molar composition of the obtained copolymers although other features are investigated such as the morphology and the post-polymerization hydrolysis of the epoxy moiety in GMA.

The current work describes the synthesis of a new polyHIPE-like sulfonated poly(styrene-co-n-acylglycerol) and its use as an efficient heterogeneous catalyst to convert oleic acid into methyl oleate in esterification reactions. This new environmentally friendly polymer incorporates n-acylglycerol macromonomer as a versatile strategy for glycerol valorization. Macroporous micrometric polymer particles are synthesized through suspension polymerization process without using porogenic agents. polyHIPE-like copolymers formed with different feed compositions of styrene and n-acylglycerol are chemically modified via sulfonation reactions to form a highly efficient catalyst for esterification of oleic acid to methyl oleate, exhibiting conversions lying in the interval from 52% to 96%, depending mainly on the amount of n-acylglycerol macromonomer into the copolymer chains. The experimental results indicate the great potential of this new heterogeneous catalyst based on modified poly(styrene-co-n-acylglycerol) to be successfully employed in esterification reactions of vegetable oils intended for the production of long chain alkyl esters of carboxylic acids, widely used as biofuels.

Deposit formation and fouling in reactors for polymer production and processing especially in microreactors is a well-known phenomenon. Despite the flow and pressure loss optimized static mixers, fouling occurs on the surfaces of the mixer elements. To improve the performance of such parts even further, stainless steel substrates are coated with ultra-thin films which have low surface energy, good adhesion, and high durability. Perfluorinated organosilane (FOTS) films deposited via chemical vapor deposition (CVD) are compared with FOTS containing zirconium oxide sol-gel films regarding the prevention of deposit formation and fouling during polymerization processes in microreactors. Both film structures led to anti-adhesive properties of microreactor component surfaces during aqueous poly(vinylpyrrolidone) (PVP) synthesis. To determine the morphology and surface chemistry of the coatings, different characterization methods such as X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy as well as microscopic methods such as field-emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM) are applied. The surface free energy and wetting properties are analyzed by means of contact angle measurements. The application of thin film-coated mixing elements in a microreactor demonstrates a significant lowering in pressure increase caused by a reduced deposit formation.

One approach used in the industry to improve the properties of polyethylene is to use multi-reactor with a single catalyst or multiple catalysts in a single reactor. In the latter case, two catalysts with distinct kinetics are selected to achieve the desired product properties. Such mixed catalyst systems enable tailored and advantageous properties at the cost of more challenging process control, because the ratio of the two catalysts serves as an additional manipulated variable. A fast method to estimate the ratio of active catalysts using headspace gas chromatography measurements is proposed here. In this method, a small perturbation in the feed rate is introduced to induce transient responses in the gas phase concentration. Ideally, with known responses from each individual catalyst, the active catalyst ratio can be estimated. To demonstrate this concept, a process model is developed in Aspen Plus. A set of dynamic simulation is performed to understand the responses of each catalyst and the mixed catalyst system, to changes in feed comonomer concentration. The results demonstrate that this method has significantly faster responses compared to feedback from bulk polymer properties and induces minimal process upset or product off-spec due to small perturbations in a short period of time.

The sustainability of consumer materials, such as plastics, belongs to the most important aspect of eco-efficiency analyses. Besides mechanical recycling, chemical recycling represents an interesting waste management pathway. In theory, this technique does not rely on single-grade feedstock to maintain product quality. However, cross-contamination of feedstocks potentially leads to above-specification impurities in obtained pyrolysis oils. This study investigates the potential downstream poisoning of a fourth-generation Ziegler-Natta catalyst, using selected model poisons at high (worst-case) concentrations. With experimental and computational analysis, economic feasibility factors such as catalyst activity and microstructural properties are evaluated during the synthesis of high-density polyethylene (HDPE) and linear low-density polyethylene (LLDPE). Noticeable effects on the catalyst activity can be observed when the poison interacts with the co-catalyst, whereas a lower impact is observed for interactions with the activated catalyst-co-catalyst complex. Molecular weight distribution (MWD) and comonomer composition distribution (CCD) modeling highlighted marginal to no polymer property changes caused by contaminants. Combined with the applicability of pyrolysis post-treatments, these observations show that chemical recycling can be a promising technique for post-consumer plastic waste treatment.

This paper builds on the theoretical framework of the previous articles on the solubility of vapors in semicrystalline polyethylenes produced in the gas phase process. The present article clarifies the theoretical basis for an activity coefficient approach, which results from a constraint on the amorphous phase within semicrystalline polymers. This concept is coupled to an advanced equation of state for use in polyolefin reaction engineering, and presented in a modular way the procedure for computing the requisite thermodynamic quantities. A temperature dependence on polymer crystallinity is also introduced. In the interest of developing a more predictive model for solubility, the model using single pure gas isotherms are parameterized. The results demonstrate the ability to predict single and mixed gas absorption, including new data published herein. The validity of the model is further demonstrated through comparisons with literature studies on batch scale ethylene polymerization. Finally, how a simple correlation to standard polymer characteristics yields accurate predictions in the absence of measured data for parametrization is demonstrated.

Front Cover: The development of the macromolecular configuration in 3D space follows a stochastic pattern. The exact position of each next carbon atom is always constrained by physics but can still have infinite options. The Monte Carlo methodology followed in the presented work, replicates this process and manages to predict the developed radius of gyration value. This is reported by Vasileios Touloupidis and Andreas Albrecht in article number 2200002.