Study On Molecular Design Of Extractants For Extractive Distillation

A computer-aided molecular design (CAMD) approach of extractants for extractive distillation was established for the systems of close boiling compounds or azeotropes. On the basis of group contribution methods, chain hydrocarbons and ring compounds were designed with genetic algorithm (GA), and monoaromatics with enumerate method. According to the requirements of the problem, the lasted Mod.UNIFAC groups were preselected and classified. A new group code scheme was introduced to fit the molecular design with GA. Besides modifying selection, crossover and mutation operators in simple genetic algorithm (SGA), two new kinds of operators which were inverting operator and mono-breeding operator were introduced. The method can resolve the problem how to combine the groups into the molecules and overcome the combinatorial explosion in molecular design. The monoaromatics were designed by the combinatorial rules of groups which were endued with the concepts of class and category.The molecular design program based on GA was written with C++ for its agility pointer function. The program of calculating the extractant indexes was written with Matlab for its strong numerical calculation function. At last the two parts were combined by interface files.The screening indexes of extractant include relative volatility, molecular weight, freezing point, boiling point, azeotrope judgement and molecule stability. The evaluating indexes of typical molecules include selectivity, heat capacity, enthalpy of vaporization, liquid viscosity, solvent power and performance index. The method was applied to acetone- methanol, butanol-butyl acetate and acetonitrile-water systems.A device of headspace gas chromatography was set up and adjusted for the study of extractant for extractive distillation. The vapor-liquid equilibrium of acetone-methanol system was measured with the extractants of water and glycol by the device. The results indicated that the molecular design method was reasonable and the program was reliable and practical.