Synthesis and Design of Ternary Heterogeneous Azeotropic Distillation Processes Including Advanced Complex Column Configurations

This thesis presents a novel methodology for synthesis of sequences separating ternary heterogeneous azeotropic mixtures employing distillation columns and decanters. Column design methods developed for assessing feasibility of proposed separations and for identifying economically attractive designs of columns in sequences. Design methods for advanced and complex configurations of heterogeneous azeotropic columns exploit the boundary value method. The methods can be used for establishing product feasibility in a column and evaluating a column design on a basis of cost. A new design method is developed for columns with integrated decanters, in which the existence of two liquid phases is not limited to the decanter. For a column with multiple heterogeneous stages, multiple feasible designs can be generated, corresponding to different numbers of heterogeneous stages and various ratios of two liquid phases on the heterogeneous stages. The resulting feasible designs have different total numbers of stages and feed locations for a given set of product specifications and reflux ratio. The new design method is extended further for double-feed columns and columns with intermediate decanters.A systematic approach for synthesising separation sequences for ternary heterogeneous azeotropic mixtures is developed. The synthesis procedure of Tao et al. (2003) and Vanage (2005), which considers only simple single-feed columns, decanters, and columns with integrated decanters, is extended to include more industrially relevant and novel options. The approach systematically assesses opportunities to employ doublefeed columns and columns with intermediate decanters. The option of introducing a heterogeneous liquid stream directly to a column is also systematically considered. With these advanced column configurations included in the synthesis method, a wider range of sequences may be considered, allowing sequences that are more attractive than conventional designs to be identified. The feasibility of a separation proposed for anindividual column in a sequence may be assessed using the new column design method. As the column design method allows a column to be evaluated in terms of cost,separation sequences can be evaluated and the most economic sequences can be identified.Case studies are presented to demonstrate the applicability of the sequence synthesis approach and column design methods. The case studies indicate that the presence of heterogeneous liquid in columns considerably improves the economic performance in some cases. The economic performance is also affected by the number of heterogeneous stages. The number of heterogeneous stages that leads to near-optimal designs can be determined using the new column design methods. For some mixtures, employing complex column configurations makes the separation feasible and provides significant cost savings. For other mixtures, the complex columns may not be as attractive as single-feed columns with integrated decanters. Column design details and other results from the column design methods are used successfully to initialise rigorous simulationsand to facilitate simulation convergence.