Optimal synthesis, design and operation of hybrid separation processes
Hybrid separation systems have recently been hailed as one of the most promising alternatives to conventional capital and energy intensive separation processes. Hybrid separation systems are able to effectively separate mixtures commonly encountered in the fine chemical and pharmaceutical industries that are difficult or impossible to separate by conventional distillation processes due to azeotropic behaviour or low relative volatilities. In a hybrid process where a distillation column unit and a pervaporation unit are integrated into one process, the shortcomings of one method are outweighed by the benefits of the other. The addition of a pervaporation unit to the conventional distillation process, either before, after or fully integrated, adds complexity to the system but also more degrees of freedom which, if properly chosen, can result in capital and operating costs savings and can consequently increase the overall profitability of the system, particularly for difficult separations. The objective of this work was to study the optimal configuration, design and operation of hybrid distillation/ membrane processes taking into account the extra degrees of freedom afforded by these processes. This is achieved by firstly developing detailed mathematical models from first principles to accurately describe the distillation, membrane and their hybrid processes. Secondly, rigorous optimisation strategies were employed to study the hybrid systems and their constituents processes. The feasibility of the hybrid system was investigated through various studies. In the first study, the batch configuration, design and operation of the hybrid system was considered for the first time. The second study considers the optimal synthesis of continuous hybrid processes where more degree of freedoms have been explored than previously reported. The third study considered the novel multi-criteria optimisation of these systems. It was demonstrated in these studies that significant savings can be achieved when the optimal hybrid process is used instead of distillation or pervaporation alone.