Selectivity effects on series reactions by reactant storage and PSA operation

This work evaluates adsorptive reactors used to improve the operation of a sequential reaction scheme, A +D/--> B +D/--> C, for the total removal of A from a stream with an excess of B. In the adsorptive-reactor concept, the reactor is filled with a physical mixture of catalyst and an adsorbent, the latter being thermodynamically selective toward primary reactant A. In thi s case, the sorbent is periodically regenerated using the principles of pre ssure swing adsorption and purged with secondary reactant D. This concept i s restricted to low temperatures to have sufficient adsorption capacity. Im proved reaction selectivity arises from the accumulation of A in the unit. The reaction of A maximizes the driving force for regeneration and thus acc elerates the regeneration half-cycle. The adsorptive reactor is compared to a conventional plug-flow reactor (PFR) and to PSA and PFR units in series. Reaction selectivity improved and pure B recovered over these alternative reactors under realistic conditions. The volume-based productivity is lower than that of PFR, but higher than that of PSA. The purge-gas flow rate can be manipulated to balance the sorption flux and reaction rate, thereby max imizing the conversion of A. The influence of differences in sorption kinet ics is discussed and the required sorbent characteristics are identified.