Rotary dryers play a crucial role in catalyst manufacturing, where the drying step is essential for ensuring the final product meets precise standards. Though often overlooked, drying significantly influences key properties like uniformity, mechanical strength, and moisture content. This article explores the importance of the drying process, the reasons for using separate drying equipment, and how rotary dryers, with their customizable features, are ideally suited to meet the diverse needs of catalyst producers.
How is Drying Used in Catalyst Manufacturing?
A drying step is necessary after impregnating the catalyst substrate (support) with the active catalyst component. Drying removes the remaining solvent and helps to determine the metal distribution within the support.1
While impregnation was traditionally thought to be the most influential step on the metal profile in catalyst preparation, researchers have found in recent years that the conditions used in the drying step can also have a significant impact.2
Removal of the solvent causes the precursor or active catalytic component to increase in concentration, resulting in precipitation once it reaches supersaturation (precipitation may also occur as a result of dehydration, temperature, or a gas atmosphere). Precipitation can have important implications on the macroscopic distribution of the catalytic component on its substrate.3
What are the Stages of Drying in Catalyst Preparation?
The catalyst drying process is considered in three stages:4
Preheating
Preheating is the first stage of drying in which the support is initially heated. During this stage, drying rate and surface-level liquid vaporization both increase as the temperature rises.
Constant Rate
In the second stage of the drying process, the moisture transport occurring inside the support material keeps the surface saturated, allowing for vapor removal. The drying rate at this stage is dependent upon the rate of heat transfer to the evaporating surface, making surface temperature constant (referred to as the wet-bulb temperature).
Falling Rate
When the material reaches critical moisture content, in which the moisture transport occurring within the support can no longer keep the surface saturated, the drying rate begins to decline. This stage is known as the falling-rate period. During this stage, vaporization begins to occur within the solid.
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