AN OUTPUT MULTIPLICITY IN BINARY DISTILLATION - EXPERIMENTAL-VERIFICATION

Earlier it was believed that distillation multiplicity only could occu r as a result of separating a multicomponent mixture. It has, however, been proven theoretically using very simple distillation models that measuring process flows in units of mass or volume (as is always the c ase in practical applications) instead of moles may give rise to a bif urcation in the mapping between volumetric reflux flowrate and distill ate purity from the case of a single steady state to that of two stabl e and one unstable steady states being possible for a specific set of actuator settings. This paper verifies the existence of multiple stead y states on a semi-industrial scale distillation column separating a m ixture of methanol and isopropanol. Simulation studies show that the c olumn will exhibit multiplicity in central parts of the operating wind ow. An experiment is designed by which the unstable branch is mapped a nd the singular points identified under stable conditions. The results show that distillation column multiplicity is in fact a phenomenon of practical relevance which may lead to operational problems even for b inary distillation columns.