remains one of the most difficult and least understood mixing problems, in contempt of its major significance for optimization of suspension polymerization. The first step of the process, the liquid-liquid mixing and even more the medium conversion stage with increased dispersed phase viscosity and sticky polymer-monomer particles already determines the size of the final particle size distribution.Xie et al. are introducing this major challenge and give a meaningful introduction about suspension polymerization. [1] It has been widely used to produce poly-(vinyl chloride), poly-(vinylidene chloride) copolymers, polystyrene, poly-(methyl methacrylate), and high value-added polymer particulate products (e.g., chromatographic separation media, ion exchange resins, and enzyme immobilization supports). During the suspension polymerization process, a monomer (or monomers) that is immiscible or slightly soluble in water is first dispersed to form monomer droplets by stirring in the aqueous phase containing a dispersant-the liquid-liquid mixing process.Recent studies have revealed unexpected developments in drop size by only small changes in the geometrical constraints of batch vessels used for suspension polymerization. The effect of the dispersed phase fraction, surfactant concentration, as well as baffle length on the evolving drop size distribution in different low viscous liquid-liquid systems is investigated. The analysis is focused on the drop-dominated systems by hindering the coalescence by polyvinyl alcohol (PVA) concentrations up to three times higher than the critical micelle concentration. The influence of PVA on drop size in breakage-dominated systems is well reproduced with population balance equation simulations. The drops are measured using a photo-optical system with automated image analysis. The measured drop sizes increase with increasing dispersed phase fraction. As coalescence is completely hindered, all observed coalescence effects are connected to phase inversion, a catastrophic phenomenon during suspension polymerization for industrial production processes. Phase inversion can be reproduced for all studied solvents with and without the use of surfactants. In particular, the influence of the baffles can be reproduced. The system is adapted and trained to detect phase inversion as a warning system to make the suspension polymerization process more stable and robust.
Core-shell pore structures are materials where in a single particle a porous core is surrounded by a shell of another pore size distribution. These could be either a microporous shell on a mesoporous support or the opposite structure. An approach to synthesize those materials based on carbide-derived carbons is presented [1, 2]. The synthesis was carried out in two steps: shell structure and core structure synthesis. In the shell preparation, carbide or NiCl 2 -impregnated carbide were converted partially with chlorine at a set temperature. In the second step, the remaining carbide core or impregnated remaining carbide core was further extracted with chlorine at a different temperature. The partially prepared and fully converted materials were characterized by N 2 and CO 2 sorption, XRD, Raman spectroscopy, and TEM. The characterization showed porous carbon shells covering an unreacted carbide core proving the successful partial conversion. The final core-shell powder exhibits a pore size distribution which is a bimodal mixture of the core and the shell materials. The results also indicate that the catalyst and catalyst loading has a strong influence both for pore structure and carbon structure of the resulting core-shell materials.[
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