Macromolecular Reaction Engineering最新文献

In the present work, the catalyst performances of USY and REY zeolites and MgO, ZnO, and Mg_xAlO_y oxides are investigated in the pyrolysis of virgin high-density polyethylene (HDPE) and of post-consumer polyolefin waste. The influence of operation parameters and catalyst deactivation resistance over four reaction cycles are evaluated. The results indicate that basic oxides do not show relevant cracking activity, so that the only identified effect for these catalysts is the production of liquid products with higher contents of paraffins when compared to thermal pyrolysis. Among the evaluated oxides, Mg_xAlO_y is the most active and resistant to deactivation. The zeolites promote cracking and secondary reactions of isomerization, cyclization, and aromatization. Particularly, USY promotes the production of higher-quality oils and shows higher deactivation resistance, when compared to REY. Additionally, a significant loss of catalyst activity is identified in reactions conducted with post-consumer polyolefin wastes. However, increase in rates of coke formation and the presence of contaminants (such as halogens and metals) are not detected in the catalysts after the reactions.

Liquid carbon dioxide (LCO₂) or supercritical carbon dioxide (ScCO₂) can be used as an important solvent medium for preparing polymer particles through dispersion polymerization. However, based on the weak solvent characteristics of CO₂, the development of stabilizers used in dispersion polymerization has always been an important challenge. These stabilizers are progressing toward the low-cost, pollution-free, and simple synthesis routes, et al. In this research, pentaerythritol tetra (3-mercaptopropionate) (PTMP) is used to control the homopolymerization or copolymerization of vinyl acetate (VAc)/vinyl propionate (VPr), the homopolymers or copolymers with thiol group are synthesized by the one-pot method. These homopolymers or copolymers are used as the stabilizers to stabilize the dispersion polymerization of N-vinyl-2-pyrrolidone (NVP) in ScCO₂. The results show that the structural unit proportion of the stabilizers, the concentration of stabilizers or 2, 2´-azobis(isobutyronitrile) (AIBN), and the time interval for dispersion polymerization have significant impacts on the conversion percentage of NVP and the molecular weight of polymers. The maximum conversion percentage of NVP can get to 95%, and the molecular weight of poly(N-vinyl-2-pyrrolidone)(PNVP) can reach 22.3 kPa. SEM analysis indicates that the PNVP obtained has regular spherical characteristics.

The impact of different agitator configurations used during the emulsion polymerization of vinylidene fluoride (VDF) is studied with the goal of achieving a solids content of 55 wt% while minimizing particle coagulation and maintaining low levels of surfactant. The design and number of impellers, their spacing and the agitation speed are shown to have a strong influence on the transfer of gaseous monomer to the aqueous phase, and thus the rate of polymerization. Increasing the number of impellers on the central shaft, and decreasing the spacing of the impellers close to the latex surface has a strong influence on the ability to incorporate gaseous monomer, so the solids content and the latex level in the reactor increased. Furthermore, it is found that changes in the agitation rate during the reaction is necessary at high solids content to avoid destabilizing the particles in view of the low surfactant concentrations used.

Development of accurate and robust dynamic models for the description of emulsion copolymerization processes is fundamental for the implementation of monitoring, advanced control, and optimization strategies. There are several studies on the dynamic modeling of styrene/1,3-butadiene rubber (SBR) emulsion copolymerization, but most of them focus on hot conditions or only one semi-batch reactor, as in the case of cold conditions. For this reason, the present study focuses on the dynamic modeling of SBR cold emulsion copolymerization processes considering a train of 15 continuous stirred tank reactors, as in many real industrial sites. The developed dynamic model is implemented by using the digital twin (DT) concept, which involves the online reading of process variables and an adaptive strategy for online tuning of some of the model parameters, being also sensitive to the effect of real-time changes on the number of reactors in the train, a subject that has been overlooked previously, but which is important at the plant site. The practical application of the DT for monitoring a real industrial process illustrates the robustness and accuracy of the developed tool, making it useful for opportune detection of process anomalies and opening the way for future advanced control strategies.

Anionic polyelectrolytes can be used for a variety of applications, including flocculation and enhanced oil recovery. While it is widely recognized that polyelectrolyte synthesis is impacted by the pre-polymer formulation and polymerization conditions, the specific relationships between these factors and the subsequent polymer properties are not well understood. Therefore, the current work intends to improve understanding of ionic strength (IS) effects during the copolymerization of 2-acrylamido-2-methylpropane sulfonic acid (AMPS) and acrylamide (AAm). The aims of the study are i) to use in situ H¹ NMR to study copolymerization kinetics, and ii) to determine how increasing IS impacts copolymerization kinetics (and, by extension copolymer microstructure). It is found that altering IS prior to copolymerization has significant impacts on the reactivity ratios, and therefore impacts the microstructure through multiple mechanisms. Increasing IS causes a crowding effect, where the propagating chain develops a random coil conformation and causes steric hindrance of the large AMPS monomer, decreasing the likelihood of AMPS propagation. When the IS is increased further, the ionic shielding effect is more impactful, increasing the likelihood of AMPS propagation. Ultimately, this work will make it possible to manipulate IS to synthesize AMPS/AAm copolymers with specific desirable properties for target applications.

The deposition process during emulsion polymerization can be classified as both particulate and reaction fouling, but a deeper understanding of the deposition mechanism, especially in combination with the polymerization process, is lacking. Here, a more in-depth understanding of the deposition mechanism is sought by investigating the fouling formation of a Vinyl acetate and Versa 10 copolymer on a heated stainless steel surface during emulsion polymerization. Its deposition behavior is also compared with the behavior of an already reacted polymer. All possible influencing factors are investigated separately, and the fouling is quantified by the mass based fouling resistance and the fouling layer composition. The fouling rates of both experimental approaches (ongoing reaction versus already reacted polymer) are used to determine the fraction of reaction fouling along the reaction pathway. The solids content and the driving temperature difference are identified as the main factors influencing fouling formation. The deposited material is composed of latex particles and emulsifier with particle size and number depending on the respective equilibrium composition of the fluid phase. The reaction fouling rate is correlated with the proportion of free initiator radicals and the amount of dissolved monomer in the aqueous phase.

Heat seal and mechanical properties of 1-octene grafted low density polyethylene films containing various concentrations of Dicumyl peroxide as the initiator and 1-octene grafting agent is investigated through using experimental measurements. The results of differential scanning calorimeter (DSC) measurements revealed that the melting temperature shifts to higher values and the peak of the DSC curve becomes wider with the increase of 1-octene concentrations. Thermogravimetric analysis (TGA) revealed a higher thermal stability up to 20 °C for 1-octene grafted PE compared with neat LDPE alloy. The results of stress–strain measurements revealed that the 1-octene grafted PE alloys has higher tensile strength in comparison with neat PE alloy and samples containing only DCP initiator. The results of heat seal analysis indicated that both DCP initiator and 1-octene tended to offer a moderate increase peel strength of PE alloy. DMTA measurements for various grafted PE alloys show a higher damping factor in comparison with neat LDPE alloy. Rheological measurements indicated a higher storage modulus up to 25% and higher complex viscosity for grafted PE samples containing 1-octene comonomer.

Online near-infrared spectroscopy technique is employed to investigate the kinetics of the anionic polymerization of butadiene with n-butyllithium initiator in the presence of the microstructure modifier 1,2-diethoxypropane (DEP) in cyclohexane solvent. A phenomenological kinetic model is developed to describe the anionic polymerization process in the presence of DEP, and its influence on the microstructure of polybutadiene under different conditions is determined.