Role of the Precipitation Device on the Properties of Al2O3-TiO2 Mixed Oxides
Advancing the chemical engineering fundamentals
Chemical Reaction Engineering: Practical Applications (T2-2c)
Keywords: Al2O3-TiO2 mixed oxides, impinging jets, rotating disc reactor
Recent works [1-3] have proved that Al2O3-TiO2 mixed oxides could be excellent catalysts for many important industrial processes. Among different possible ways to produce these oxides, we have chosen a cost-effective route based on the neutralization reaction generated by rapid mixing of two reacting aqueous solutions containing sodium aluminate and titanyl sulphate, respectively. Precipitation takes place at pH = 9 and at a temperature value of 70°C. The concentrations of both solutions are chosen in such a way that the final suspension at the outlet of the precipitator contain 60 g.L-1 of solid phase. Two kinds of Al2O3-TiO2 catalysts are produced: the first one is composed of 10 % of TiO2 and 90 % of Al2O3, while the second one contains 30 % of TiO2 and 70 % of Al2O3.
Earlier, it was shown [4] that the properties of agglomerate particles strongly depend on the type of precipitation device used for producing them, so the aim of this work is to study the role of the type of precipitation reactor on the quality of Al2O3-TiO2 mixed oxides in order to obtain a catalyst with controlled end-use properties. In this context, three types of precipitation reactors are used. The first one is a standard reactor of a diameter of 15 cm (2.5 litres stirred tank) equipped with a Rushton turbine having a diameter of 5 cm and a rotating speed of 1000 min-1. This reactor, which is normally used to produce these kinds of materials, is considered as the reference device. Two new rapid mixing devices are also used to produce the above mentioned mixed oxides. The first rapid mixer is composed of two opposite impinging jets submerged in the standard reactor described above [5], while the second rapid mixer is a rotating disc reactor named sliding disc mixing device [6]. The properties of the products obtained by these new devices are compared with the properties of the products obtained by the standard reactor.
In all cases, very porous agglomerates are obtained. The particle size distribution and fractal dimension of agglomerates are measured with a Malvern Mastersizer S particle analyzer. Specific surface area and porosity are determined from sorption isotherms, while the homogeneity of TiO2 distribution into Al2O3 matrix is checked by X-ray microanalysis in a scanning electron microscope.
Experiments reveal that the type of the precipitation device and operating conditions play a major role on the properties of Al2O3-TiO2 mixed oxides [7]. Best results are obtained by the combination of the impinging jets mixing device with the standard stirred tank: specific surface area and the mesoporosity are higher than ones obtained by using other devices.
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[2] Segawa K., Takahashi K., Satoh S., Catalysis Today, 2000, 63, 123 – 131.
[3] Macleod N., Cropley R., Keel J.M., Lambert R.M., J. of Catalysis, 2004, 221, 20 – 31.
[4] Rousseaux J.M., Muhr H., Plasari E., Can. J. Chem. Eng., 2000, 78, 650 – 662.
[5] Bénet N., Muhr H., Plasari E., Rousseaux J.M., Powder Technology, 2002, 128, 93 – 98.
[6] Rousseaux J.M., Falk L., Muhr H., Plasari E., AIChEJ, 1999, 45, 2203 – 2213.
[7] Mouret G., MS, Institut National Polytechnique de Lorraine, 2005.
See the full pdf manuscript of the abstract.
Presented Tuesday 18, 16:20 to 16:40, in session Chemical Reaction Engineering: Practical Applications (T2-2c).
