Experimental investigation of conventional control strategies for a heterogeneous azeotropic distillation column

In this work, a laboratory scale sieve plate distillation column was constructed to investigate the conventional control strategies of an isopropyl alcohol (IPA), cyclohexane (CyH) and water (H2O) heterogeneous azeotropic distillation column. Steady state process analysis showed that the optimal operation point should be located at a critical re¯ux, a transition point at which the dis- tillation path switches from a route that passes through IPA+H2O azeotrope to one that passes through IPA+CyH azeotrope. At this critical re¯ux, a high purity IPA product can be obtained with minimum energy consumption and maximum product recovery. However, the steady state is extremely sensitive to feed disturbances. A good control strategy must be able to maintain a steady column temperature pro®le that shows a plateau near 70 C to ensure passage around IPA+CyH azeotrope. In this study, an inverse double loop control strategy is recommended. Through experimental testing, the proposed control strategy was demon- strated to keep the product IPA purity at the desired high-purity level under all feed disturbance changes while other conventional control strategies fail.