5. Process synthesis and intensification of hybrid separations

Hybrid flowsheets are defined, in the context of process intensification, as alternatives suitable for replacing energy-intensive separation methods through the combination of more than one unit operation. Distillation is one of the first options considered for achieving a required separation; therefore, this chapter examines distillation-based hybrid alternatives. Due to the extent of the topic, this analysis is limited to the separation of bioalcohols utilizing pervaporation and liquid-liquid extraction as assisted distillation methods. For each case, different hybrid flowsheets are reported and commented on. The corresponding distillation-based processes are considered for comparison. Synthesis of the possible hybrid flowsheets appears to be important, especially when multicomponent mixtures are considered. This aspect is discussed for the combination of liquid-liquid extraction and distillation as applied to the separation of biobutanol from its fermentation broth. The synthesis of alternative hybrid flowsheets is reported, showing that one configuration can realize a 43% reduction in the total annual cost. Bioalcohol production by fermentation perfectly represents the case where distillation alone is penalized by the thermodynamics of the mixture, but its applicability can be extended using valid alternative hybrid flowsheets.