Luyben studied the simultaneous design of a simple gas-phase tubular reactor system with a single feed stream and independent reactor preheating and cooling for a reversible reaction. Reyes and Luyben studied an irreversible reaction system with a reactor feed preheating system (feed-effluent heat exchanger and furnace) but assumed equimolal concentrations of reactants in the recycle gas. A simple separation was assumed in both of these studies. Reyes and Luyben recently explored systems with more realistic separation systems (a distillation column) for gasphase tubular reactors with liquid recycle and with a dual recycle system. This paper extends this work for two cases: (1) the reversible reaction system is explored with a realistic feed preheating system and with two fresh feed streams, and (2) the irreversible reaction system is studied for nonequimolal reactant concentrations. The exothermic gas-phase reaction A + B <-> C occurs in an adiabatic tubular reactor. A gas recycle returns unconverted reactants from the separation section consisting of a simple separator in which product C is removed in the liquid phase and reactants A and B are recycled in the gas phase back to the reactor inlet. Optimum steady-state economic designs are shown to lead to poor dynamic responses. Slight modifications of the plant design lead to a much more easily controlled plant. In the reversible case, the additional furnace heat input leads to a better dynamic performance. In the irreversible case, a higher reactor inlet temperature improves dynamics.