Practice of Kinetics (Comprehensive Chemical Kinetics, Volume 1)

232 EXPERIMENTAL METHODS FOR HETEROGENEOUS REACTIONSV5 X, 6 X.Fig. 28. Principle of the recycle reactor for kinetic measurements in flow systems.where X, and Xi are the mole fractions of product. The average overall rate basedon the feed and product isA mass balance across the reactor shows thatGXe+FXo = (G+F)XiDifferential conversion is achieved when Xi -P X,, which occurs when G >> I;.Thus a net conversion level, X,-Xo, is obtained whilst the conversion per cycleis differential. This type of reactor is not subject to the analytical errors of thedifferential reactor except at low overall conversions. A second advantage is thatheat transfer is improved, due to the large recycle gas volume, and isothermaloperation is more easily achieved. Much of the work associated with developingthis type of reactor has been concerned with the kinetics of simple reactions.However, recent work has shown the effects of more complex kinetics involvingconsecutive and simultaneous reactionsz0’. One of the major difficulties with therecirculation reactor is the design of a suitable recycle pump, especially for hightemperatures and pressures. Various designs are discussed by Melville and Gowenlockzoo.The thermal syphon principlezo4 and reciprocating flow with a singlepistonZo3 have been used by Russian workers. LandZo8 has described a diaphragmtype pump which operates uiu the vibration of a loudspeaker coil. Boudart et d209have constructed a glass pump with a teflon coated piston, actuated by alternatelyenergising a pair of solenoids. The latter two pumps work at subatmosphericpressures and have pumping rates of about one liter per minute. If all the exit gas