Thomas Dederichs

Interfacial Properties of Emulsions Stabilized with Surfactant and Nonsurfactant Coated Boehmite Nanoparticles

The properties of emulsions stabilized with surface-modified boehmite particles of 26 and 8 nm in diameter have been investigated. The surface-modified particles were prepared by mixing aqueous dispersions of cationic boehmite particles with aqueous solutions of the surfactant p-dodecylbenzenesulfonic acid (DBSA) or the nonsurfactant p-toluenesulfonic acid (TSA). For the 26 nm particles, interfacial tension measurements indicate that p-dodecylbenzenesulfonic acid partitions between the particle surface and the oil-water interface, while p-toluenesulfonic acid remains on the particle surface. The partitioning of p-dodecylbenzenesulfonic acid supports the formation of emulsions, although in the absence of the particles the same surfactant concentration is not sufficient for emulsion stabilization. Due to the fast exchange kinetics, p-dodecylbenzenesulfonic acid is gradually replaced by particles. At equilibrium, the interfacial tension in the presence of the surface-modified particles is between the values for the pure particles and the pure surfactant solutions. However, the interfacial tension is independent of the surfactant concentration used in the preparation of the particles. Reducing the particle size to 8 nm leads to increased emulsion stability, and thus, the minimum particle concentration required to prepare stable emulsions was reduced to 0.1 g/L. However, above approximately 3.5 mmol/L of the sulfonic acids, the small particles dissolve slowly, and the emulsion stability is lost. This mechanism can be used to trigger the collapse of the emulsions.

Evaluating regulatory and market frameworks for energy storage deployment in electricity grids with high renewable energy penetration

Investment volumes in renewable energies in Germany are far ahead of the necessary infrastructure to integrate them into both the electricity market and the grid. For storages and other technologies offering flexibilities the current regulatory framework and the market design in Germany remain a barrier for upcoming investments. In this paper regulatory barriers for an economically efficient energy storage deployment are presented and evaluated using a generic optimization model for a multifunctional operation of storage technologies on electricity markets capable to consider different market and regulatory design changes. Due to the rising significance of grid restrictions for the integration of intermittent resources and upcoming new innovative storage technologies on distribution grid level, the electricity grid was integrated into the model. Such an approach enables a quantitative analysis of interaction between market operation and grid congestion. This is shown using a 110kV high-voltage grid in the North of Germany as a representative congested grid with ongoing curtailments due to high wind energy penetration. Storage technologies - and also other measures as demand-side and generation management - will need a flexible market and a sophisticated regulatory design in order to significantly add value to the future energy system.

Temperature-dependent colloidal stability of hydrophobic nanoparticles caused by surfactant adsorption/desorption and depletion flocculation.

Nanoparticles coated with self-assembled dodecyltrimethylammonium bromide shells are shown to undergo colloidal destabilization at higher temperatures. This is caused by two different mechanisms depending on the surfactant concentration. Up to a surfactant concentration of 55 mM, the surfactant micelles dissolve before the breakdown of the dispersion. In this case, the breakdown is triggered by desorption of surfactant molecules from the particle surface causing flocculation via hydrophobic interactions. Since the surfactant concentration influences the adsorption-desorption equilibrium, the breakdown temperature increases with increasing surfactant concentration from approximately 100 to 160 degrees C. Beyond 55 mM, surfactant micelles are still present when the dispersion breaks down and destabilization is caused by high temperature depletion flocculation. Since higher surfactant concentrations result in a larger number of micelles in solution, the breakdown temperature for concentrations above 55 mM decreases with increasing surfactant concentration.

Identification of environmentally relevant network hotspots

The EU research project IRENE-40 aims to construct a roadmap for the European and Pan-European transmission network up to 2050. In this context a holistic assessment of the grid development takes place. In particular, this includes an ecological assessment in which the power generation emission change that can be achieved by grid expansion measures is considered. The Optimal Power Flow (OPF) is used as the main tool for the studies. Each analysis is done with a quantification of the sensitivity of the results at changing CO2-price. Furthermore the OPF is extended with regard to an ecological approach: In an Ecological OPF a minimum-emission generation is simulated. That way grid development projects can be identified which lead to a positive economical impact but negative ecological impact and vice versa.