(615e) Microwave Synthesis of Sapo-11: Aspects of Reactor Engineering
AIChE Annual Meeting
Thursday, November 20, 2008 - 10:10am to 10:35am
The effect of precursor volume, reaction temperature, reactor geometry, applicator type and frequency on the microwave synthesis of SAPO-11 were studied.
The nucleation time and crystallization rate were determined from crystallization curves for SAPO-11, for the various parameters investigated. Increasing volume of the reacting material decreases the reaction rate of SAPO-11 at 160˚C. In particular, the nucleation time increases with increase in the reaction volume. Increasing the reaction temperature increases the crystallization rate and decreases the nucleation time, however it also decreases the particle size. Nucleation of SAPO-11 under microwave heating is strongly dependant on the reaction temperature.
Reactor geometry is an important factor in microwave reactor engineering. Using wider geometry vessel (33 mm compared to 11 mm diameter) enhances the reaction rate, producing larger crystals in the same reaction time, even though the crystallization rate is decreased.
The crystallization rate is enhanced by applicator type in the following order CEM MARS®-5 oven > CEM Discover® ?focused? system > monomode waveguide at 2.45 GHz. The nucleation time is not effected by the choice of microwave applicator type for SAPO-11 synthesis.
The affect of microwave frequency on the nucleation and growth of SAPO-11 showed a dependence on the applicator type more than the specific frequency, for the frequency range 2.45?10.5 GHz. The difference between the crystallization rate observed at higher frequencies and that at 2.45 GHz maybe due to the multimode nature of the waveguide at frequencies above 2.45 GHz. The same circular S-band waveguide and reaction vessel were used at all frequencies. The multimode field distribution gives rise to enhanced crystallization rate. Sweeping the microwave frequency linearly between 8.7 and 10.5 GHz at rates of 10/s and 100/s showed an intermediate crystallization curve to that for fixed frequencies of 2.45 GHz and 5.8 - 10.5 GHz.
Keywords: SAPO-11, microwave synthesis, frequency, power delivery, reactor engineering.
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