J Jan Meuldijk

Vesicle‐Directed Growth of Silica

Silica-coated vesicles have been produced by the deposition of silica onto unilamellar vesicles from aqueous solution for the first time. The quaternary ammonium surface of the surfactant vesicles is receptive to silica and facilitates deposition of up to 5-10 nm of it. The petrified vesicles are stable to dehydration and can be visualized by conventional TEM (see Figure) without additional staining agents.

Highly sustainable catalytic dehydrogenation of alcohols with evolution of hydrogen gas

The catalytic dehydrogenation of alcohols into aldehydes and ketones in the absence of H-acceptors was studied with several transition metal catalysts in order to develop a large-scale procedure. Applying Ru(OCOCF3)2(CO)(PPh3)2, the so called Robinson catalyst, several secondary alcohols could be dehydrogenated with high selectivity into the corresponding ketones in relatively short reaction times. Highly effective atom utilization could be realized avoiding solvents and giving hydrogen gas as the sole by-product. However, in contrast to Robinsons work the catalytic dehydrogenation of primary alcohols appeared to be problematic due to decarbonylation with concomitant catalyst deactivation and aldol condensation under the strong acid or basic conditions applied.

A model for the coagulation of polyvinyl acetate particles in emulsion

In the present work we develop a mathematical model for the coagulation of polymer particles in emulsion polymerization systems. The model considers a Brownian coagulation kernel and assumes that interactions between particles can be described through the DLVO theory, where the presence of a Stern layer is accounted for. The model is then compared with experimental data for the coagulation of monomer swollen polyvinyl acetate particles, carried on with three different seeds at various operating conditions, showing in all cases a satisfactory agreement.

Seeded emulsion polymerization of styrene: influence of acrylic acid on the particle growth process

The seeded batch emulsion copolymerization of styrene and acrylic acid was studied. The polymerization rate was investigated with pH as the main parameter. Some attempts were made to evaluate the average number of growing chains per particle during Stage II of the emulsion polymerization process. The final latex products were characterized by means of conductometric aqueous titration and potentiometric titration in an organic solvent mixture. The distribution of the acid groups over the aqueous phase, the particle surface, and the interior of the particles together with the kinetic results provided insight into important features governing the incorporation of acrylic acid. The results indicate that pH is the dominating parameter for the incorporation process. An optimal incorporation on the surface of the particles is observed for a low value of pH. In that case, all the acid groups are protonated.

Seeded emulsion polymerization of styrene : incorporation of acrylic acid in latex products

Seeded batch emulsion polymerization of styrene and acrylic acid was studied. The influence of pH and acrylic acid content on the polymerization rate and the amount of carboxylic acid groups incorporated in the final latex products was investigated. The distribution of the functional groups over the aqueous phase, the latex particle surface, and the interior of the latex particle was determined using aqueous conductometric titration and nonaqueous potentiometric titration at intermediate and complete overall conversions. Combined with kinetic results, the carboxylic acid group distribution history provided valuable information about the process of incorporation of acrylic acid in latex products. Two-step processes in which a shot of acrylic acid was performed in the last stage of the emulsion polymerization reaction were investigated as a strategy to increase the surface incorporation efficiency.

The mechanism of the oxidation of benzyl alcohol by iron(III)nitrate: Conventional versus microwave heating

The mechanism of the oxidation of benzyl alcohol with iron(III)nitrate nonahydrate under conventional and under microwave heating conditions has been investigated and the reaction conditions have been optimized. A series of redox reactions leads to the formation of benzaldehyde and other products. Direct comparison between conventional and microwave heating revealed identical conversions profiles. Mastering the microwave induced heat, absence of a real microwave effect and byproduct formation are the major factors to advise a traditional batch-wise way of process development to a larger scale.

Aspects of coagulation during emulsion polymerization of styrene and vinyl acetate

The influence of recipe and process conditions on the coagulation behavior of polystyrene (PS) and polyvinyl acetate (PVAc) latices has been studied. Seeded batch experiments reveal a significant influence of electrolyte concentration on the coagulation behavior of both PS and PVAc latices. Within the experimental error, no dependency of the coagulation behavior on process conditions, in terms of energy dissipation, reactor scale, impeller type, and impeller diameter, has been observed for the reactor scales investigated. These results indicate that intrinsic chemical influences such as electrolyte concentration dominate the coagulation behavior during emulsion polymerization and also in the absence of polymerization over the process conditions.

Production of copolymers with a predefined intermolecular chemical composition distribution by emulsion polymerisation in a continuously operated reactor

The influence of residence time distribution on the intermolecular chemical composition distribution (CCD) for the emulsion copolymerisation of styrene and methyl acrylate has been investigated. A special tubular reactor, the pulsed packed column (PPC), has been used. The PPC combines intensive radial mixing with limited axial mixing, thus providing good heat transfer to the reactor wall and proper emulsification for low net flow rates. A simple backmixing model was developed for feed stream mixing in the PPC. A combination of this backmixing model with a simple mechanistic model for emulsion copolymerisation was used to calculate the CCD of the PPC product. Experimental and calculated results are in good agreement. Production of copolymer having a bimodal CCD in the PPC is compared to the performance of a semi-batch process. The two processes are similar in terms of conversion; however, the CCD of the PPC product shows a characteristic difference. In the PPC some copolymer with an intermediate chemical composition is formed through backmixing of side feed streams. This work demonstrates that the PPC is a promising alternative for semi-batch processes, although some product characteristics will be slightly different.

Dynamic modeling of limited particle coagulation in emulsion polymerization

In emulsion polymerization, a limited degree of particle coagulation may occur. Particle coagulation is caused by a loss of colloidal stabilization when the surface coverage of emulsifier on the particles drops below a critical value. It has been demonstrated experimentally in a previous article that the time scale for particle coagulation is small compared to the time scale for particle growth by polymerization and absorption of monomer. This indicates that the coagulation process can probably be described by von Smoluchowski kinetics. Based on this result, a comprehensive dynamic model for the simulation of limited particle coagulation in emulsion polymerization has been developed. It has been shown that there is a reasonable agreement between simulations with the dynamic model and experimental data (e.g., conversion time history, particle number, and particle size distribution).

A novel reactor for continuous emulsion polymerisation

Abstract It has been demonstrated earlier that a Pulsed Packed Column is a suitable reactor for continuous emulsion polymerization of styrene. The emulsion polymerization of vinyl acetate follows a different mechanism, which renders the process more liable to instabilities when carried out in a continuous flow reactor. It was demonstrated that emulsion polymerization of vinyl acetate in a Pulsed Packed Column can be carried out in a stable manner, and with a sufficient reaction rate, provided the rate of backmixing is limited.