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In this work, we investigate the stability of a continuous stirred tank reactor (CSTR) coupled to an isothermal, isobaric flash. The coupling is through the recycle of the reactant-rich stream from the downstream flash unit to the upstream reactor. We consider the first-order irreversible reaction A ? B occurring non-isothermally in the CSTR. The main focus of this work is to investigate the effect of delay arising as a result of transportation lag from the reactor to the separator on the system stability. In the absence of delay, it has been clearly shown that the coupled system exhibits static and dynamic instability. The effect of delay on the stability of the coupled system is studied for the two classical control strategies: (i) The fresh feed flow rate, F0, is flow controlled and the reactor effluent flow rate, F, is used to control the molar holdup in the reactor, MR. (ii) The flow rate, F, is flow controlled, and F0 is used to control MR. It is shown that delay induces new regions of dynamic instability. The system switches from instability to stability and vice versa for these two control strategies as the delay is increased. ? 2005 American Chemical Society.