Experimental investigation of a regenerative catalytic reactor

A pilot plant is developed to investigate the Regenerative Cyclic Reactor (RCR) system. The proposed RCR system utilizes the inherent characteristics of the thermal regenerator to provide control over the temperature profiles along the reactor in order to enhance the reactant conversion. The RCR system is a transient adiabatic reactor which avoids the radial temperature gradients set up in tubular reactors. The reaction being investigated, the dehydrogenation of ethylbenzene to styrene, uses steam as a diluent. The steam is also used as the temperature regeneration medium.

The pilot plant design accommodates a steady state adiabatic reactor (SSAR) arrangement (one and two stage processes) as well as a one bed RCR system. Thus it is possible to compare the transient and steady state reactors.
With only electrical heating available, radiative electrical firebar heaters are used to generate the high system temperatures. Mathematical models are used to aid the heater design and to predict the temperatures for steady state operation. Other models are used to help in assessing the power load step up and step down rates.
The small flowrates, long pipe lengths, and the high temperature levels pose considerable problems in heat loss compensation over the system. Models are developed to assess the transfer resistances limiting the operational temperatures on ceramic bead insulated resistance wires. Heat shields utilizing these wires and a copper plate covering are successfully commissioned. Mathematical descriptions of these shields are also developed. A combination of these shields and heat tracing tapes enables reactor temperatures within the industrial operation range to be attained.

A series of transient runs of varying duration for the RCR, as well as steady state runs are carried out. Comparisons show that much higher

conversions are obtained for the RCR than the SSAR. A significant increase in conversion and the time taken to achieve steady state conversion occurs as the catalyst is regenerated by the steam. Steady state conversions for the early runs show some agreement with model predictions based on steady state kinetics. The transient runs and the later steady state runs show conversions much higher than those predicted by mathematical models.