(223a) Experimental and Numerical Investigation of Flame-Spray-Assisted TiO2 Synthesis From Titanium Tetraisopropoxide

sebastian.hardt@uni-due.de

Titania nanoparticles (TiO₂) are of major interest for catalytical and electronic applications, especially as a major material for photocatalysis and dye-sensitized solar cells. It is accessible via processing of either TiCl₄ or titanium tetraisopropoxide (TTIP). Up to now, industrial processes producing TiO₂ are based on the combustion of TiCl₄ leading to particles in a size regime between a few ten and a few hundred nanometers. With respect to high activity based on a high surface area, more dilute reaction systems must be applied for the formation of very small titania nanoparticles. A promising route also enabling for large-scale synthesis is flame-assisted spray pyrolysis of a flammable organic solvent containing the titania precursor.

In our approach, a mixture of isopropanol and TTIP is used as the precursor material. An oxygen jet around a hollow injector needle atomizes the liquid and forms a spray. Isopropanol as a solvent allows for the formation of dilute mixtures within a wide range and also suppresses the premature decomposition of TTIP inside the supply system. To enable operation points between 200 and 2000 mbar the burner is assembled in a pressure-controlled stainless steel housing.

Our work focuses on the investigation of the synthesis route within a wide pressure regime, the characterization of the synthesized nanoparticles and the numerical simulation of the spray flame reactor. Therefore, ex-situ particle-diagnostic techniques such as nitrogen adsorption (BET), transmission electron microscopy (TEM), x-ray diffraction (XRD) and UV-VIS spectroscopy are applied. Spray formation and droplet evaporation is modeled in an Euler-Lagrange formulation. The mechanisms for TTIP combustion and TiO₂ formation described by Tsantilis et al. are used to calculate the particulate species [1]. The highly turbulent spray flame is simulated in 3D using simplified reaction kinetics. The population balance equations, that describe the particle dynamics, are solved using a monodisperse approach. Our experimental setup enables the formation of crystalline titania nanoparticles at sizes of 10 nm and below depending on pressure and precursor concentration. It is found that the materials exhibit a narrow particle-size distribution and that they mostly consist of the anatase phase. The simulation of the spray flame reactor shows the temperature distribution, the particle number concentration as well as particle diameters.

[1]   S.Tsantilis, H.K.. Kammler, S.E.Pratsinis, Population Balance modeling of flame synthesis of titania nanoparticles, Chem. Eng. Sci. 57 (2002)