Semicontinuous Distillation of Quaternary Mixtures Using One Distillation Column and Two Integrated Middle Vessels

A novel semicontinuous system for the separation of quaternary liquid mixtures is presented in this work. This semicontinuous system is a process intensification technique that uses one distillation column and two integrated middle vessels to achieve a separation which would traditionally be carried out using three continuous distillation columns. The system is a theoretical extension of the conventional ternary semicontinuous process, which has been repeatedly demonstrated to be profitable at intermediate flow rates when compared to continuous systems. Dynamic simulation results are used to demonstrate feasibility and performance of the system for three examples: a mixture of n-hexane, n-heptane, n-octane, and n-nonane, a mixture of benzene, toluene, ethyl-benzene, and o-xylene, and a mixture of six alcohols and water. The results show that this new technique can achieve separation objectives while staying within safe operating limits. The semicontinuous system for the first example is compared to a conventional continuous system and is shown to be more profitable for low to intermediate production rates.