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1. <I>Reaction-separation interactions</I>: A<I> waste minimisation approach</I> to process design that promotes opportunistic recycling and includes a systematic technique for designing a recycle network in the context of an overall process. 2. <I>Azeotropic separation systems</I>: (a) A novel geometric approach for synthesis of cleaner and cost effective distillation sequences for homogeneous azeotropic mixtures with and without boundary crossing. Important insights include: • a geometric approach for synthesizing and screening the alternative separation sequences which results in a catalogue pairing the RCMs of the ternary systems with their most promising separation sequences: • a novel procedure for entrainer minimisation for azeotropic distillation sequences, and • new evidences linking the <I>type of separation sequence, the azeotropic column feedstage location</I> and<I> the volatility of an entrainer </I>with the separability of homogeneous azeotropic mixtures. These findings conclusively explain the peculiar dependencies of the separability of homogeneous azeotropic mixtures on the reflux ratio and the number of stages. (b) A geometric approach for synthesis of cost effective distillation sequences for heterogeneous azeotropic mixtures which enables the graphical prediction of the <I>absolute minimum number of units, the region and the point of desirable entrainer flowrate, the optimum decanter tie line position, and the distillate composition for the entrainer recovery column</I>. (c) Guidelines for exploiting feed composition flexibility to improve azeotropic separation based on a novel geometric approach. Important insights include: • the significance of the binary, ternary and desirable ternary feed compositions, and a procedure to achieve the desirable ternary feed composition. • the development of a selection catalogue for feed preconcentration based on a novel geometric approach. • the use of mixing and recycling for grassroot design and retrofit.

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In ths work, new multicomponent feasibility, column design and column sequencing tools are proposed. These tools are particularly useful in the synthesis of distillation columns and column sequences that separate azeotropic mixtures, where they provide accurate design parameters as well as good estimates of product compositions for use in commercial simulators. Recent work on ternary mixtures has led to the development of a new criterion for establishing staged column feasibility. This new criterion provides a necessary and sufficient condition for staged-column feasibility, and a column design method is developed based on this criterion for the design of simple and complex columns. The column design method can be extended to describe non-ideal column operation as well as packed columns. The column design method is particularly useful in the design of columns that separate azeotropic mixtures as it provides accurate column specifications where conventional shortcut methods fail. A retrofit method for increasing throughput is also developed using the new feasibility criterion. A new feasibility test for product compositions from columns separating multicomponent mixtures is introduced. Unlike present methods, the new feasibility test requires only the specification of the principal mole fractions in both products. Visualisation is not required as feasibility is established numerically. The feasibility test is therefore applicable to mixtures with any number of components. The feasibility test is extended to identify feasible and potentially feasible classes of splits, which are defined by product regions instead of product compositions. Various classes of splits are then grouped according to type. A column design method for columns separating multicomponent azeotropic mixtures is developed. Based on a new criterion developed for application in ternary mixtures, the new column design method requires the specification of the principal mole fractions in both products. The design method is developed for two cases - columns that produce pure components and columns that perform general splits. In both cases a matrix of feasible operating parameters can be constructed, which can be used to identify favorouble operating parameters. The feasibility and column design methods are used to develop an algorithmic column sequence synthesis procedure for multi component azeotropic mixtures. Given a feed composition and product requirements, the synthesis procedure makes use of the feasibility test for classes of splits to generate a number of potentially feasible column sequences, each of which has an associated recycle superstructure. Feasible column sequences are then identified and the multi component column design methods are employed for every column in the sequence.

This thesis concerns the automated synthesis of separation processes. A single multi- component stream is to processed to give one or more pure component product streams. A list of units are available for the task and the aim is to find the optimal flowsheet structure in terms of cost. Implicit enumeration (IE) has been used to tackle the synthesis problem. The main advantage of this approach is that IE does not require the development of a superstructure. A disadvantage of using IE is that it is necessary to discretise the values of unit operating conditions in order for there to be a finite search space (Fraga et al., 2000). The user may not have any idea of the effect of the discretisations on the quality of the solution. In addition, the optimal solution may be missed between the discrete values chosen. The purpose of this work is to address these issues. Interval analysis is used to bound the effects of this discretisation. This allows the cost of each particular flowsheet to be bounded based on the level of discretisation used. The technique is demonstrated by bounding the effect of discretisation on the synthesis of distillation flowsheets. The use of runs with progressively finer uniform discretisation lead to the isolation of the optimal structure. This result leads to the development of an adaptive algorithm that changes the discreti sation profile in response to bounding information from downstream in the search. The algorithm operates recursively and isolates the optimal process structure for each stream encountered. This builds up to the isolation of the overall optimal process structure for the feed process stream. The effectiveness and performance of the new algorithm are evalu ated using two very different separation problems. The first is a distillation sequence and the second a separation of a protein from a biological stream.

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