Tuesday, May 3, 2011
Process synthesis for ethanol production, from lignocellulosic material, has been performed chiefly throughout the application of mass and energy balances and design heuristics. The resulting configurations have been economically evaluated. This work proposes a process synthesis methodology, based on the optimal selection of a specific configuration from a starting superstructure, defined in six stages, namely pretreatment, pretreated material hydrolysis, detoxification, fermentation, recuperation and dehydration. In each stage a number of technological alternatives were identified as suitable for the purpose. They were characterized by an index, defined by items such as, the potential to generate commercial products, technological availability, installation and operational costs, environmental impact and safety and operational issues. The value to each item in the index, was assigned considering literature information and estimations and their contribution depends linearly from the key process variables, e.g. composition of raw materials, or inhibitors concentration. A linear optimization problem was formulated in order to minimize a performance index, defined by the weighed sum of each stage index, constrained to a minimal ethanol yield. The resulting process considered lignin solvent extraction pretreatment from wood, simultaneous saccharification and fermentation of cellulose, pentoses fermentation, distillation and molecular sieves dehydration. This process was rigorously evaluated both technical and economically in order to improve estimations and recalculate indexes. Results show little variation in the process, between estimations and recalculated indexes results, showing in this way this could be used as a robust tool for process synthesis and integration in complex scenarios.