Design And Control Of A New Pressure Swing Distillation With Heat Integration For Separating Maximum Boiling Azeotropes

Phenol is mainly obtained by the three-step Hock process with acetone asco-product. In recent years, demand for acetone has decreased in contrast to theincreasing need for phenol. To seek an alternative for phenol production, a one-potsynthesis from cyclohexylbenzene has been reported with cyclohexanone asbyproduct and it is very promising in the future. However, phenol and cyclohexanoneform a pressure insensitive maximum boiling azeotrope and cannot be separatedcompletely by a simple distillation process.In this work, the conventional pressure swing distillation process is extended toseparate the pressure-insensitive binary azeotropes by using suitable entrainers. Withthe help of residue curve maps and distillation experiments, acetophenone was provedto be a suitable pressure swing entrainer and a new pressure swing distillation processwas implemented in Aspen Plus. Rigorous simulations were run for both fully andpartially heat-integrated processes and a comparison based on total annual cost (TAC)was made between these two configurations. The results reveal that the partiallyheat-integrated one is much more competitive and an optimum process was obtained.Then, two temperature control structures and one composition/temperature cascadecontrol scheme were proposed to stabilize this optimized new pressure swingdistillation process. The effectiveness of the control structures was tested with thefeed flow rate and feed composition disturbances. It is indicated that the columnoperating at higher pressure (HPC) cannot be perfectly controlled by the temperaturecontrol schemes. The reason for the drawback of the temperature control structures isthe existence of an extremely small amount of intermediate non-key component. Thus,a composition/temperature cascade control structure is proposed to cope with thiscontrol problem and a robust control w achieved. The result of this work reveals thatthis new pressure-swing distillation process with adding a suitable pressure swingentrainer is worth considering during the conceptual design stage of the distillationprocesses for separating pressure insensitive maximum boiling azeotropes.