(474b) Dynamic Control of a Column / Side-Reactor Process

If the temperature range suitable for reasonable chemical reaction kinetics does not match the temperature range suitable for vapor-liquid equilibrium, reactive columns are not economically attractive. One way to overcome this temperature mismatch is use a flowsheet that features a distillation column with multiple side reactors. The column operates at a pressure that gives temperatures favorable for separation, while the reactors operate at temperatures (and pressures) favorable for reaction kinetics. This paper discusses the controllability of a column/side-reactor process based on the steady-state design studied by Kaymak and Luyben (Ind. Eng. Chem. Res., 2007). The effectiveness of two different control structures is explored. The first uses two temperature controllers, one with direct action and the other with reverse action. The second control structure uses an internal composition analyzer. One of the main conclusions is that the opposite actions of controllers in the two-temperature control structure result in a breakthrough that moves the column to a different operating condition. The composition and temperature controllers in the second structure have the same action and provide reasonably effective control.