Computer-Aided Molecular Design Of Environmental Friendly Solvents For Separation Process

Extractive distillation and liquid-liquid extraction are effective separation processes to deal with the separation of close boiling compounds or azeotropes systems. The selection of appropriate solvents is the key. As global environment problem increasing severely, the selection of environmental friendly solvents is the trend. A new multi-objective optimization approch, based on simulated annealing algorithms and fuzzy comprehensive evaluation method, is presented and applied to the computer-aided molecular design of environmentally benign solvents for separation processes.Firstly, based on the characteristic of fuzziness and involvement of multiple factors in selection of solvents, the fuzzy comprehensive evaluation method is used to evaluate the design solvents, the membership functions are established according to the separation and environmental performance.Secondly, the modified simulated annealing approach for multi-objective optimization problem is proposed,which can record the optimal solution in the process of annealing, improving the quality of solution; evaluating the solution by the synthetical value of target functions, the algorithm can obtain a set of Pareto optimum by running the algorithm multiple times.Based on Modfied UNIFAC method, classifying and pre-selection the functional groups systematically are described according to some rules. The functional groups are coded according to the real-coded technique. The solvent molecules are represented by a matrix, including a group vector and a composition vector.The multi-objective optimization model of CAMD for separation process is formulated, and the multi-objective optimization approach combined simulated annealing approach and fuzzy comprehensive evaluation is applied to CAMD. The steps and flowsheet of multi-objective optimization approach are addressed, the parmeters are suitably designed. The new molecules can be generated by addition, deletion, replacement and restoration, which can ensure the molecular structures satisfy the construction and chemical feasible criteria.Finally, the CAMD multi-objective optimization approach is illustrated with four extractive distillation examples and four liquid-liquid extraction examples, the program is programmed using Matlab language, the design results are examined by the process simulation software PROII, confirm the validity of the proposed multi-objective optimization method. The solvents not only satisfy the requirement of the separation process, furthermore, but satisfy the requirement of environment.