Computer Aided Molecular Design Of Solvents For Separation Processes

Special distillation and liquid-liquid extraction are important ways to deal with liquid mixtures which are difficult to be separated. Selection of solvents is the key issue. This paper is focus on the selection of solvents. A novel general method of Computer aided molecular design based on improved MGASA hybrid algorithm, combined with Mod. UNIFAC Group Contribution method is put forward, and used to select solvents for extraction distillation, azeotropic distillation and liquid-liquid extraction.CAMD of chemical separation solvents is generally based on group contribution method. Some groups with certain structure are selected firstly, and then combined with one another to form a molecule according to certain rules. The one of the two difficult issues is mathematic optimization method, designed to deal with the problem of'combination explosion'. The other is the method of molecular compounding, which has to be thought to avoid production of rubbish molecules.On the issue of mathematic optimization, though some optimization algorithm, such as Genetic algorithm, Taboo algorithm and simulated annealing algorithm are adopted in current CAMD, some disadvantages exist and the results relies on the running parameters firmly. Improved MGASA hybrid algorithm is put forward in this paper, which combined with the advantages of GA and SA, avoiding their disadvantages. Some operations in GA and SA are improved according to the need of molecular design.Firstly, operations including crossover, mutation and new state producing which are based knowledge is founded. Secondly, recover operation is added to MGASA to reduce the amount of illegal molecule which produced in general MGASA operations. Thirdly memory operation is added to avoid the optimization result lost and reduce the degree reling on convergence.This paper puts forward a novel code strategy, which coding the number of groups compounding a legal molecule in binary system.Here called group number binary cluster for short. This coding strategy has several advantages.Molecule can be coded simply. Including and decoding operations can be carried out easily. Paraffin, cycloparaffin and aromatic groups are coded together and searched synchronously in this coding strategy.This strategy guarantee the complete search for solves because of getting rid of the limits on the number of each kind of groups and the category of groups. Constracting with former strategies, this strategy extend the searching field.While it saves computing cost with omitting the redundancy.On the issue of molecule compounding, legal molecule should satisfy the demand of molecular integrality and chemical stability. About molecular integrality, Yangzhensheng has put forward a theorem. This paper amends the theorem and recovers the illegal molecule according to the amended theory. Chemical stability is put in fitness function.This reduces the complexity of recovering illegal molecule according to molecular integrality and chemical stability synchronously. Computing cost is saved at the same time.MGASA method is applied for separation solvents of extraction distillation, azeotropic distillation and liquid liquid extraction. Rules for adaptable solvents and fitness functions are amended. Matlab programs for searching solvents for the above three kinds of processes are compiled. And the results of application on practical systems show excellent searching ability. Some useful solvents are founded besides those mentioned in literature. In a word, the CAMD method put forward in this paper has high level of rightness and can be used in practical chemical processes.