Systematic design of biorefinery downstream processes

Downstream processing of biofuels and bio-based chemicals often represents the bottleneck for the economic sustainable development of new processes. It is also a challenging problem for process synthesis and optimization, due to the intrinsic nonideal thermodynamics of the liquid mixtures derived from the (bio)chemical conversion of biomass. In this Chapter, it is outlined a recent mathematical framework for the structural and parameter optimization of process flowsheets with rigorous and detailed models. The optimization problem is formulated within the Generalized Disjunctive Programming (GDP) framework and the solution of the reformulated MINLP problem is approached with a decomposition strategy based on the Outer-Approximation algorithm. At first, the mathematical formulation and the numerical implementation are outlined. In the second portion of the Chapter, several validation examples in the field of biorefineries are proposed spanning from the economic optimization of single distillation columns, the dewatering task of diluted bio-mixtures, up to the distillation sequencing with simultaneous mixed-integer design of each distillation column for a quaternary mixture in the presence of azeotropes.