In practice, chemical process synthesis-design involves identification of the processing route to reach a desired product from a specified set of raw materials, design of the operations involved in the processing route, the calculations of utility requirements, the calculations of waste and emission to the surrounding and many more. In terms of approaches to solve the synthesis-design problem three major lines of attack have emerged: (a) the knowledge based approach  which relies on engineering knowledge & problem insights, (b) the optimization approach  which relies on the use of mathematical programming techniques, (c) hybrid approach which combine two or more approaches. D’Anterroches  proposed a group contribution based hybrid approach to solve the synthesis-design problem where, chemical process flowsheets could be synthesized in the same way as atoms or groups of atoms are synthesized to form molecules in computer-aided molecular design (CAMD) techniques . The main idea here was to apply the principle of group-contribution approach from chemical property estimation to the synthesis and design of chemical process flowsheets. That is, use process-groups representing different unit operations (reactor, distillation, flash, crystallization, etc.), bonds representing streams and/or recycles, rules for chemical feasibility also representing process flowsheet feasibility and sum of group contributions representing the performance of the flowsheet. In the next stage, the design parameters for the operations of the high ranked flowsheets are established through reverse engineering approaches based on driving forces available for each operation. In the final stage, rigorous simulation is performed to validate the synthesis-design. Note that since the flowsheet is synthesized and the operations in the flowsheet designed to match a set of design targets, there are no iterations involved as the final flowsheet is among the best, if not the best.
In this work, the flowsheet synthesis-design framework is expanded to include process-groups representing the unit operations from biochemical processes and new flowsheet property models to predict the environmental impact, process safety, product recovery and purity, which are employed to screen the generated alternatives. The extended framework implemented in the form of a computer- aided tool , ProCAFD will be highlighted through two case studies, one involving the synthesis of a chemical process flowsheet (the well-known Hydrodealkylation of toluene process) and another for a biochemical process (production of Bio-ethanol). In both cases, various process alternatives were generated quickly using the ProCAFD tool. The framework was able to generate not only the reported designs, but also various innovative designs, due to predictive nature of the methods used. The application-examples also focus on the use of SFILES notation system, developed specially for the process-group based synthesis-design method, to store and/or visualize the structural information of any process flowsheet represented by process-groups. As an extension, the SFILES notation is extended to store the process information through which representation of flowsheet alternatives for rigorous process simulation (for example, with an external process simulator) would be possible.
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