Microwave Synthesis of SAPO‐11 and AlPO‐11: Aspects of Reactor Engineering

Abstract

AlPO-11 and SAPO-11 are synthesized using microwave heating. The effects of precursor volume, reaction temperature, reactor geometry, stirring, applicator type and frequency on the microwave synthesis of SAPO-11 and AlPO-11 are studied. The nucleation time and crystallization rate are determined from crystallization curves for SAPO-11 (and/or AlPO-11), for the various parameters investigated. Increasing volume of the reacting material decreases the reaction rate of SAPO-11 at 160 degrees 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 decreases the particle size. Nucleation of SAPO-11 and AlPO-11 under microwave heating is strongly dependant on the reaction temperature. 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. Stirring the reacting solution during heating affects primarily the nucleation time. The effect of microwave frequency on the nucleation and growth of SAPO-11 shows 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. Sweeping the microwave frequency linearly between 8.7 and 10.5 GHz at rates of 10 min(-1) and 100 min(-1) shows an intermediate crystallization curve to that for fixed frequencies of 2.45 GHz and that for 5.8, 8.7 and 10.5 GHz.

High‐Throughput and Time‐Resolved Energy‐Dispersive X‐Ray Diffraction (EDXRD) Study of the Formation of CAU‐1‐(OH)2: Microwave and Conventional Heating

“…[51] There are only few studies that compare the influence of microwave-assisted and conventional heating on the crystallization rate, and the described data is not consistent. In ex situ quenching experiments on the crystallization of Fe-MIL-53 [45] and AlPO-11, [52] higher activation energies under MW conditions were reported. Nevertheless, MW heating led to an acceleration of the crystallization.…”

“…Possible explanations are the increase of the concentration of reaction sites (number of nuclei) and a higher mobility of the reactants in the microwave field that could lead to an increase of the collision frequency. [49,52,53] …”

Liquid-phase dehydration of sorbitol under microwave irradiation in the presence of acidic resin catalysts

“…However, accelerated MW-syntheses of Cu 2 O [16], molecular sieves like AlPO-11 and SAPO-11 [17] and metal-organic frameworks (MOFs) such as ironbenzenedicarboxylate [18] and copper-benzenetricarboxylate [19] are mainly due to a very large increase in pre-exponential factors (even with increased E a ). Very recently, Ahnfeldt et al [20] have shown the accelerated synthesis of a MOF (CAU-1-(OH) 2 ) with MWs is due to an increase of pre-exponential factor.…”

Microwave Reaction Enhancement: The Rapid Synthesis of SAPO-11 Molecular Sieves

“…6). Work submitted for publication [42], on the effect of reactor and synthesis parameters on the microwave synthesis of SAPO-11 will demonstrate the interaction of microwaves with the crystallization and nucleation rates.…”