(60e) Utilization and Benefits of a Nanoparticle Extraction Process in a Drop Column for Production of High Quality Organosols

The establishing of high quality organosols requires the production of stable colloidal and functionalized particles with a minimum amount of stabilizing surfactants (fatty acids) in a liquid organic medium. The magnetite nanoparticles used have special magnetic properties and therefore, they have a great technological application potential. Thus, they are very interesting for a broad range of research areas for example in the field of magnetic fluids and functional materials. Furthermore, possible areas of application are coatings and composite materials used in chemical reactors as magnetically separable catalyst material as well as in the biomedical sector. Particularly in combination with polymers it is necessary, that the magnetite nanoparticles are available as stabilized colloids in the organic phase. But on an industrial scale the nanoparticles are synthesized mainly in the aqueous phase. The transfer of the particles into the organic phase is conventionally done by strategies based on filtration with subsequent drying and redispersion steps. But the properties of magnetite nanoparticles are limited, because they tend to oxidation and agglomeration due to their increased surface area/volume ratio.

Hence, a new type of particle extraction process is of great importance, which includes the transfer of the magnetite nanoparticles from the aqueous phase into an immiscible organic phase directly through the liquid-liquid phase boundary. The engineering concept is a miniplant, where the continuous phase transfer can be realized using a drop column. Based on the individual process steps the enrichment of surfactant molecules at the liquid-liquid droplet interface leads to an adsorption on the particle surface and the particles become chemically grafted [1]. Subsequently, the magnetite nanoparticles are functionalized and hydrophobized, whereby the extraction of the particles into the organic phase is reached. Both steps are elementary for the phase transfer mechanism.

Previous investigations using a lab centrifuge as transfer device have evaluated the chemical absorption of different surfactants on the magnetite particle surface regarding to the ability to disintegrate the agglomerates in primary particles [2].

The liquid-liquid particle extraction process in the drop column is used in a partial recirculation operation as well as in a continuous process with a closed circuit of both phases. In the first case the aqueous phase is stationary and the organic phase is in recirculation. The necessary experimental setup, materials and relevant parameters for a stable process behavior are presented. The process behavior within the drop column is characterized by a particle-free phase transfer, whereby the measured total organic carbon is only dependent on the used surfactant. Based on the modeling of the system the transfer behavior can be characterized, if the transfer fluxes of the surfactant are evaluated. Furthermore, the mass flows and the yield of transferred magnetite are determined by ICP-OES measurements. The additional determination of interfacial tensions using the pendant-drop method provides conclusions regarding to the impact of interaction of the elementary processes and procedures at the phase boundary. Moreover, the transfer kinetics is specified and compared with calculated theoretical values resulting from a kinetic approach. As a consequence of this, the colloidal stability of the resulting organosols is estimated and compared with the results of the transfer device as mentioned before, a lab centrifuge. In both devices different forces affect the phase transfer so different organic solvents are applied. The differences in colloidal stability are characterized by a dispersion analyzer (Lumisizer) as well as theoretically with the use of solubility distances by Hansen.

[1] Rudolph, M., Erler, J., Peuker, U.A., 2012. A TGA-FTIR perspective of fatty acid adsorbed on magnetite nanoparticles – decomposition steps and magnetite reduction. Colloid and Surfaces A: Physicochemical and Engineering Aspects 397, 16-23.

[2] Erler, J., Machunsky, S., Grimm, P., Schmid, H.-J., Peuker, U.A., 2013. Liquid-liquid phase transfer of magnetite nanoparticles – evaluation of surfactants. Powder Technology 247, 265-269.