Laboratory Reactors for Determination of Kinetics

Continuously operated, fixed bed reactors are frequently used for kinetic measurements. Here the reactor is usually a cylindrical tube filled with catalyst particles. Feed of a known composition passes though the catalyst bed at a measured, constant flow rate. The temperature of the reactor wall is usually kept constant to facilitate an isothermal reactor operation. The main advantage of this reactor type is the wealth of experience with their operation and description. If heat and mass transfer resistances cannot be eliminated, they can usually be evaluated more accurately for packed bed reactors than for other reactor types. The reactor may be operated either at very low conversions as a differential reactor or at higher conversions as an integral reactor. 

In the differential flow reactor, the residence time is short so that the conversion remains small, usually a few per cent. This can be achieved in short beds and/or with high feed flow rates. Since the conversion is small all pellets operate approximately under the same conditions and variation of the volumetric flow rate can be neglected. The observed or apparent conversion rate follows directly from the measured inlet and outlet concentrations via a material balance over the bed  

The quantity (RA) can be further elaborated if interface mass and heat transfer coefficients are known, and with the theory of mass transfer with reaction inside porous catalysts as treated in Chapters 6 and 7  

Combining Equations 5.30 and 5.34 gives the equation for the determination of the reaction rate  

For an irreversible nth-order reaction, RA-kAC =kAC 0 (1-CA) holds and Equation 5.35 becomes  

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