Process synthesis procedures can be significantly enhanced using process sim­ulation packages as shown in previous case studies. Simulation packages are essential for evaluating the amount of studied alternative process flowsheets. The described approach corresponds to knowledge-based process synthesis (see Chapter 2). In this regard, the task of process synthesis for the biotechnological production of fuel ethanol has mostly been undertaken using the approach based on the present knowledge. The other main approach is the optimization-based process synthesis that relies on the use of optimization for identifying the best configuration. For this, the definition of a superstructure, which considers a sig­nificant amount of variations in the topology of technological configurations of a given process, is required. The evaluation and definition of the best technological flowsheet are carried out through tools such as mixed-integer nonlinear program­ming (MINLP). The advantages and drawbacks of this strategy were disclosed in Chapter 2, Section 2.3.

Several cost-effective flowsheet configurations for the production of fuel etha­nol from renewable resources like biomass have been reported in the literature. Most of the proposed flowsheets have been defined using different heuristic rules and knowledge-based rules, and have involved the use of such tools as commercial process simulators. However, a cost-effective flowsheet for bioethanol production utilizing an optimization-based approach has not been found in the literature. In the following case study, an optimization-based strategy was implemented in order to preliminarily synthesize several technological schemas for ethanol production from lignocellulosic biomass employing a net revenue function as a comparison criterion.