Reactor for Microactivity Test

The microactivity test uses small quantities of catalyst, only 4 grams, and a feed of 1.33 g in 75 seconds, so it is a very fast test, but the test s empirical usefulness is strictly limited to one well-known technology, for an endothermic reaction and one very limited type of catalyst. 

The standardized conversion is obtained from the measured conversion and the correlation between ASTM reference catalysts and their measured conversions.  

Then the standard emphasizes that all operations such as catalyst pretreatment and analytical techniques must be done as standardized to obtain meaningful relative results. 

The tube is much longer than needed for the catalyst volume to provide a surface for preheating and to minimize temperature losses at the discharge end. The tube can be bent into a U shape and immersed in a fluidized sand bath, or it can be straight and placed inside a tubular furnace in a temperature-equalizing bronze block. Thermocouples are usually inserted 

Good heat transfer on the outside of the reactor tube is essential but not sufficient because the heat transfer is limited at low flow rates at the inside film coefficient in the reacting stream. The same holds between catalyst particles and the streaming fluid, as in the case between the fluid and inside tube wall. This is why these reactors frequently exhibit ignition-extinction phenomena and non-reproducibility of results. Laboratory research workers untrained in the field of reactor thermal stability usually observe that the rate is not a continuous function of the temperature, as the Arrhenius relationship predicts, but that a definite minimum temperature is required to start the reaction. This is not a property of the reaction but a characteristic of the given system consisting of a reaction and a particular reactor. 

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