Study of the mechanism of microwave heating of zeolite A and the easily heatable composition

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We studied what factors are important in the microwave heating of zeolite A and how the microwave heating proceeds.It was easy to heat hydrated 4A and 3A zeolites to a glowing (melting) temperature by microwave radiation from room temperature but was different to heated by microwaves. 3A zeolite was not heated by microwaves under the above condition used for 4A zeolite. 5A zeolite could not be heated at all. The easiness of microwaves heating was in the order of 4A>3A>>5A. There are differences in the cation distribution among these zeolites, i. e., 5A zeolite has no cations on the 4-membered oxygen ring sites but the other two have. It was expected from dielectric properties that the cation on 4-ring site can absorb microwave at >450℃ with a higher efficiency but cations in other locations are ineffective for absorption. The following mechanism for the microwave heating was proposed : In the initial period, the hydrated zeolite absorbs the microwaves through its absorbed water and its temperature rises. The absorbed water completes desorption by ca. 400-470℃. In this temperature range the zeolite begins to absorb microwaves and absorption efficiency becomes high with increasing temperature. When zeolite reaches 450-500℃ thermal runaway starts. 5A zeolite cannot reach thermal runaway conditions because of absence of caution on 4-ring site. The absorbed water plays the role of preheating agent in the initial period of microwave heating.The easiness of heating of zeolite with NaィイD1+ィエD1, KィイD1+ィエD1 or AgィイD1+ィエD1 ion on the 4-ring site was studied. It was in the order of NaィイD1+ィエD1>AgィイD1+ィエD1>KィイD1+ィエD1. From this result, it was found that zeolite with the smaller cation on the 4-ring site can be easily heated by microwaves.