Dynamics of two specltic reactlon schemes mvolvmg selectivity behavior the consecutive-parallel reactlon, and the Van de Vusse reactIon, occumng m Isothermal CSTRs are exhaustively treated Analytic transient solutions are presented, and the precise reactor startup conditions that lead to umque transient maxunum or transient muumum m the yield of the desired product are rdentied These conslderatmns have direct apphcations m rational reactor design and operation For example, they imply that lpven a set of kmetlc and reactor parameters, the translent yield of the desved DrOdUct can be slzeably enhanced by simply choosing the reactor &rtup conditions appropiately INTRODUCTION A class of challengmg and practically unportant problems III reactor desrgn IS that mvolvmg reactlons with selectlvlty behavior (usually termed 'complex' reactlons) for m It, the rum IS to obtam a desued product dlstrrbutlon, typdied usually by the requirement that the yield of a spectic reaction product be maxumzed This class dtiers considerably from the one In which only the converslon of reactant(s) 1s of Import, because reactor destgn can be performed adequately-d uneconomlcaily-by over-design tn those cases Errors m product dlstnbutlon for complex reactlons cannot, however, be corrected merely by an overdeslgn Thus, general guldehnes are avadable m the reaction engmeenng literature (see Carberry [I] for a recent survey) which prescnbe whether a reactor with or wtthout nuxmg IS to be preferred m the steady state under diverse conditions mcludmg a variety of model reachon classes However, It appears that detied considerations of reactor dynamics have not been made m the hterature even for sunple sltuatlons of complex reactlons, although a plethora of pubhcatrons have dealt vvlth (largely the) non-isothermal reactor stab&y problems m the dynamic context We do so here for two specific reaction schemes Consecutive-Parallel kI kz A-B k3 -C,A-D Van de Vusse Network A -% BA C, A + A tP'D occurring m an isothermal CSTR In both schemes, B IS the desired product The reaction steps are all first order (hence hnear) for the first, and from the steady state design pomt of view, a reactor wlthout nuxmg-hence a tubular plug flow reactor (PFR)-1s preferred to maxrmaze yield of B For the Van de Vusse network[2], tTo whom correspondence should be addressed *Present address Department of Chemrcal Engmecrmg. Mlchlgan State University. East Lansing, MI 48823, U S A however, the general gmdehnes for steady state reactor selection do not apply, since a PFR IS to be preferred to mmlmlze degradation of desired product B, while a CSTR is desued to mmumze the effect of the second order side reactlon leading to undesved D We do not separately consider either the Consecutive kI A-B&C or the Parallel *1