(491m) Integrated Flowsheet and Molecular Design Using Molecular Signature Descriptors
Computer aided flowsheet design is a new technique for the design of process flowsheets according to a set of specified design targets. In this approach, a group contribution based methodology has been followed which considers the entire process as a collection of different process groups, analogous to the group contribution methods available for molecular design (d'Anterroches and Gani, 2004). However, some of the conventional compounds that meet the property constraints set during the flowsheet design may not be suitable for the actual process due to the environmental and safety constraints. This kind of situation will require identification of suitable molecule/molecules that meet the property targets of the flowsheet. This can be achieved through the integration of the flowsheet design with a molecular design problem. Here, the alternate molecular structures can be generated in place of the traditional compounds. The new flowsheet structures can then be generated according to the changes in the input molecules. In this work, we are introducing an algorithm that uses the concept of molecular signature descriptors for identifying the alternate molecular structures. The signature is a systematic coding system of atom types and the signature of a molecule can be obtained as a linear combination of its atomic signatures (Visco et al 2002). It has been proven that any of the topological indices of molecules can be represented in terms of molecular signatures and it is possible to correlate the topological indices to the actual properties and biological activities. Here, the new algorithm utilizes molecular property operators based on signatures for solving the reverse problem of obtaining the molecular structures that satisfy the property targets estimated in the process design step. A new set of equations will be employed to ensure that the molecule meets the safety and environmental constraints as well. The principles in graph theory are incorporated to avoid the generation of infeasible structures. Since the molecular operators are formed based on molecular signatures, the property models based on different topological indices can be represented on the same property platform. Since different properties are described using different topological indices, the height of molecular signature required to describe those topological indices will be different. However, techniques have been developed to describe all topological indices with a single signature height. The final solution will be obtained as a set of the biggest signature height used to describe the topological indices. Therefore, the accuracy of prediction will not be compromised because off this transformation. The property models required to describe the target properties may be based on QSPR/QSAR (quantitative structure-property/activity relationship) models or in the form of group contribution methods. In the developed algorithm, the group contribution models can also be represented using the signatures which allow for the simultaneous consideration of all property targets irrespective of whether the targets are based on process design or other constraints. Once the suitable alternative is found according to the target properties, the new flowsheet can be generated. This contribution will illustrate the developed methods and highlight their use through a case study.