Reactive distillation is a very broad topic and, although a wide range of issues are discussed in this thesis, the focus is exclusively on hybrid reactive distillation (i.e. reactive columns which include both reactive and non-reactive column sections) with application for the synthesis of fuel ethers. Specifically, the example of ETBE production is used to illustrate many of the salient points, and was the basis for much of the simulation study and the experimental work.
The thesis can be subdivided into three main topics: steady state simulation of reactive distillation and its implications for design (Chapters 3-6); dynamic simulation, including the study of dynamic effects such as multiplicity and hysteresis, and its application for control system design (Chapters 7-10); and experimental work on a reactive distillation pilot plant which has been constructed as part of this thesis (Chapters 11-12). Supplemental to this core are the literature review (Chapter 2), the conclusions and recommendations (Chapter 13) and the list of cited literature (Chapter 14).
The development of a satisfactory steady state model for reactive distillation requires attention to the fundamental behaviour of the system, including the reaction and phase behaviour, and this is discussed in Chapter 3 together with the principles behind the equilibrium stage model for distillation operations. The full reactive distillation column model is presented and then applied to the simulation of a MTBE column where experimental data was available and an ETBE column. Once the model is developed and validated, it can be used to study the behaviour of reactive distillation systems and to investigate attributes that differ from non-reactive distillation (Chapter 4). A steady state simulation model is also useful in formulating a design strategy for reactive distillation. Chapter 5 elaborates a design strategy and discusses the use of other tools for reactive column design, including reactive residue curves. It is important to integrate column design with global plant objectives to ensure that synergies are realised wherever possible and to maximise the profitability of the process equipment. This is discussed in Chapter 6 with reference to processing schemes, feed composition and process optimisation methods.
The extension of a steady state simulation model to the dynamic case is not trivial and the issues involved in this process are discussed in Chapter 7. The full dynamic model and examples of its application are also provided there. A dynamic simulation model is the ideal tool for control system design and invaluable in screening control configurations and examining transient process responses. Multiplicity is an inherently dynamic characteristic and Chapter 8 shows how the full dynamic capability of the simulation models was accessed to identify transitions between parallel steady states and investigate the implications for control. However, it was important to ensure that the observed simulation behaviour was physically realisable and the distinction between events with practical significance and situations that can only be realised via simulation was also discussed. Chapter 9 describes how dynamic simulations were applied to conceive an acceptable regulatory control system for the ETBE column described earlier. The benefits of reactive distillation are intimately linked to the effectiveness of the operating policy and advanced control was shown to be important to minimise the effects of process disturbances. Chapter 10 discusses a method for concurrently controlling both principal operating objectives (ether purity and isobutene conversion) and an integrated control scheme that is flexible enough to handle a wide range of operating policies and economic criteria.
Chapters 11 and 12 describe the experimental apparatus that was constructed in conjunction with the simulation studies. The design of the experimental equipment focussed on the catalyst support and the packing design, both of which were original, and the control system. The commissioning of the pilot plant and tests which were undertaken to assess the effectiveness of the design are discussed in Chapter 12. An optimisation of the pilot plant operation and the collection of pilot plant data which would permit further commercialisation of this technology were not undertaken as part of this thesis.
Program listings for the simulation models (Chapters 3-10), calculations for the pilot plant design (Chapter 11) and raw experimental data (Chapter 12) have not been included in the thesis in order to conserve space. These are available from the School of Chemical Engineering, Curtin University of Technology, on request.
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