Macromolecular Reaction Engineering最新文献

The iron-containing imidazolium-based ionic liquids (ILs) 1-n-butyl-3-methylimidazolium heptachlorodiferrate (BMI.Fe₂Cl₇) and 1-n-butyl-3-methylimidazolium tetrachloroferrate (BMI.FeCl₄) are applied as catalysts in the homogeneous polymerization of n-butyl vinyl ether. Both solventless conditions as well as using different organic solvents, catalyst concentrations, temperatures, and reaction times are tested to assess the polymerization conditions that lead to the highest molecular weights of poly(n-butyl vinyl ether). The Lewis acidic IL BMI.Fe₂Cl₇ proves to be highly efficient, even at low catalyst concentrations. In bulk polymerization, polymers with 142 kg mol⁻¹ are obtained using a 1:10000 molar ratio of catalyst to monomer. In solution polymerization, the monomer consumption is also rapid and the molecular weight of the polymer is related to the catalyst concentration used. These results indicate the potential of this catalyst for industrial applications. In contrast with the acidic IL, the neutral iron-containing imidazolium-based IL BMI.FeCl₄ does not show any catalytic activity.

A detailed mathematical model of the propylene-1-hexene copolymerization based on the two-dimensional probability generation function technique is developed. It calculates the joint molecular weight-copolymer composition distribution (MWD-CCD) of the copolymer, as well as the average copolymer composition distribution, the molecular weight distribution (MWD), the copolymer composition distribution (CCD), average molecular weights and composition, and yield. The parallelized execution of the model code allows for obtaining the different copolymer microstructure distributions efficiently. The model allows for reaching a thorough understanding of the copolymer microstructure under different operating conditions of a semibatch reactor. It also has the potential to become a powerful tool for selecting operating conditions to obtain a material with target molecular properties.

Front Cover: Microreactor parts made of stainless steel are modified by a chemically inert ultra-thin sol-gel film which combines ultra-low surface energy with a smoothening of the surface by preferential coating accumulation in surface rifts. The applied films lead to a significant inhibition of polymer deposit formation as well as to an extended operating time of microreactors employed during aqueous polymerization of poly(vinylpyrrolidone). This is reported by Guido Grundmeier and co-workers in article number 2200043.

In the present paper, a dynamic optimization problem regarding grade transitions in bulk poly(propylene) polymerization processes is formulated and solved for the first time. Initially, a detailed dynamic process model is presented and implemented, comprising mass and energy balances, some of the polymer properties (such as the melting flow index and the xylene solubles) and regulatory control loops. Additionally, the effects of cocatalyst and electron donor on the propagation rate constant are taken into account. Then, the dynamic optimization problem is formulated and an evolutionary algorithm is used to solve the resulting nonlinear programming problem. It is shown that there is significant coupling among the manipulated variables and the controlled performance and polymer property variables, which adds complexity to the grade transition problem and demands the simultaneous manipulation of multiple variables during transitions. Despite the inherent open-loop unstable nature of the analyzed process, it is shown that smooth grade transition trajectories can be accomplished through proper adjustment of the objective function weights. Finally, it is shown that the obtained optimum trajectories can significantly diminish the transition time, which can be of paramount importance for the plant economics.

To predict the polymer properties produced by free-radical polymerization of N-vinylpyrrolidone (NVP) in aqueous solution a detailed kinetic model has been developed. The kinetic model allows to calculate the chain length distribution, the number of branching points, and the number of terminal double bonds (TDB). The latter is accounted for since TDBs are a precondition for branching. While monomer conversion can be predicted sufficiently using independently determined rate constants for propagation and termination, here the predictions of structural properties by a newly developed extended kinetic model to experimental findings are compared. Polymer produced in a continuous stirred tank reactor is analyzed by gel permeation chromatography (GPC), field flow fractionation (FFF), and high-pressure liquid chromatography (HPLC).

In this work, polymeric microspheres based on glycidyl methacrylate and divinylbenzene with magnetic properties are synthesized by the suspension polymerization technique. To obtain magnetic properties, magnetite particles modified by oleic acid are synthesized in the laboratory. The effects of stirring speed, concentration of magnetite added, and concentration of stabilizer on the particles’ properties are studied. The magnetic microspheres are characterized according their morphology, magnetite incorporation, and magnetic and thermal properties. The incorporation of iron particles is mainly affected by stirring speed during synthesis and the amount of added magnetic material. The saturation magnetization of the microspheres is affected by the content of incorporated magnetic material. The modification with oleic acid is important for incorporation of the magnetic material in the copolymer matrix. Polymeric particles with superparamagnetic behavior are obtained with spherical morphology and saturation magnetization of 7.11 (emu g⁻¹) when employing a monomer molar ratio of 50/50, 1% poly(vinyl alcohol), 20% magnetite particles modified by oleic acid, and stirring speed of 500 rpm.

In this work, the synthesis of magnetic microspheres of poly(glycidyl methacrylate-co-divinylbenzene) via suspension polymerization is reported. The concentrations of divinylbenzeneand benzoyl peroxide in the microspheres synthesis are studied. The microspheres, characterized by thermal analysis , scanning electron microscopy, vibrating sample magnetometry , and light scattering detection , show good morphological control and thermal stability. This material presents a narrow size range and an appreciable fraction of superparamagnetic particles. The increase in divinylbenzene concentration can cause a decrease in the mean diameter of the microspheres. On the other hand, the increase in benzoyl peroxide concentration causes an increase in the mean diameter of the microspheres.

Models are developed for gas-phase ethylene/1-hexene copolymerization using a 3-site hafnocene catalyst. The models accurately predict joint molecular weight distribution and copolymer composition data for 15 semibatch lab-scale copolymerization runs and 6 steady-state pilot-plant copolymerization runs, respectively. Kinetic rate constants and activation energies, which are common to both models, are estimated for the three types of active sites for each reaction in the kinetic scheme. Using parameter subset selection and estimation techniques, it is found that 34 of the 61 parameters should be estimated from the data. Incorporating the pilot-plant data allow for estimation of two parameters, a deactivation rate constant and a β-hydride elimination activation energy, that are not estimable using the lab-scale data alone. At the 95% confidence level, 25 of the 34 parameters are significantly different than zero, which is more than the 19 significant parameter estimates obtained from the lab-scale data alone. Good fits to the data are obtained, as are reliable predictions for a validation run not used in parameter estimation.

The present work aims to produce  functionalized polymer networks to target the bioactive molecule trans-resveratrol found in winemaking residues, specifically at grape stems. The synergistic choice of photoinitiation, polymerization composition, and molecular imprinting approach allows the functionalization of these materials. Experimental design is applied to methodically perform the syntheses. The amount of crosslinker, the total monomer's concentration, and the ratio of trans-resveratrol to the functional monomer 4-vinylpyridine (4VP) are the factors selected for this experimental design. The binding capacities and the selectivity of the synthesized materials are assessed through sorption experiments in acetonitrile and hydroalcoholic media. Consequently, a multivariate linear regression analysis leads to describe the uptake of trans-resveratrol by the materials in both media. The crosslinker content and the ratio of trans-resveratrol to 4VP are found to be impactful parameters while designing such materials. These studies allow the identification of working conditions for sorption/desorption processes combining a high retention capability of the adsorbents with selectivity. Furthermore, four materials are selected to enrich trans-resveratrol from grape stems extracts in a continuous process of solid-phase extraction. The results show that the functionalized materials are able to enrich 12-fold the content of trans-resveratrol in some fractions demonstrating the interest of such polymers.