(615b) Temperature Distribution within Zeolite Precursor Solutions In the Presence of Microwaves

enhanced reaction rates achieved for many processes, including organic synthesis[1], inorganic synthesis[2] and polymerization[3]. With over an order in magnitude time saving for many reactions, there is a huge potential for energy savings[4] and rapid processing, including continuous processing[5-7].

Rapid microwave heating is not solely and/or clearly proven to be the main factor contributed to this synthesis enhancement by microwaves[8]. Nevertheless, temperature distribution or temperature gradients within the heated media may occur resulting in ?hot spots?. The severity of this temperature gradient depends on the dielectric properties and thus, the penetration depth of the heated media. This temperature distribution may contribute to the rate enhancement since the rate is exponentially dependent on the temperature. Conner et al.[9] showed that non-uniformity of the field distribution, which is dependent on the dielectric properties and temperature, gave rise to enhancement of silicalite synthesis in a 33 mm diameter reactor compared to a 11 mm reactor.

Herrmann et al.[10] measured the temperature inside a reactor vessel at two points; near the wall and in the center for three different zeolite precursors; MFI, VFI. and LTA. They showed that the smaller the skin depth of the solution the greater the temperature variation between the wall and the center. However, these workers did not test the hypothesis that overheating can lead to rate enhancement. We will investigate this temperature distribution inside the reactor vessel at different heights and radial distances from the wall for water, NaY, silicalite, and SAPO-11 precursor solutions. Since NaY precursor solution has the smallest penetration depth (2.5 mm at room temperature and 2.45 GHz), it is expected to exhibit the greatest temperature variations. Thus, we investigated the effect of overheating on the rate of enhancement for this zeolite synthesis

Keywords: Microwave, over heating, temperature distribution, zeolite synthesis.

References

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[10].Herrmann, R.; Scharf, O.; Schwieger, W.; Studies in Surface Science and Catalysis 2004, 154A, 155.