Computerized design of solvents for extractive processes

[摘要] ENGLISH ABSTRACT:Separation processes are an integral part of chemical engineering. Thepurity of a chemical product is among the principal factors influencing itsvalue. Therefore, any method that can increase the purity of a product ordecrease the cost of purification will have a direct effect on theprofitability of the entire plant.An important class of separation processes is the solvent-basedseparations. This includes processes like extractive distillation, liquid-liquidextraction and chromatographic separation. Heterogeneous azeotropicdistillation is closely related to these processes. The most importantvariable in the design of a solvent-based separation process is the choiceof solvent.A genetic algorithm for the computer-aided molecular design of solventsfor extractive distillation had been previously developed by the author.This algorithm was improved and expanded to include liquid-liquidextraction, heterogeneous azeotropic distillation, gas-liquidchromatography and liquid-liquid (partition) chromatography. At the sametime the efficiency of the algorithm was improved, resulting in a speedincrease of up to 500% in certain cases. An automatic parameter tuningalgorithm was also implemented to ensure maximum efficiency of theunderlying genetic algorithm.In order to find suitable entrainers for heterogeneous azeotropic distillationa method is required to locate any ternary heterogeneous azeotropespresent in a system. A number of methods proposed in the literature wereevaluated and found to be computationally inefficient. Two new methodswere therefore developed for ternary systems. A methodology forapplying these methods to quaternary and higher systems was alsoproposed.Two algorithms to design blended solvents were also developed. Blendedsolvents allow the use of simpler and thus cheaper solvents by spreadingthe active functional groups over several molecular backbones. It wasobserved in a number of cases that the blended solvents performed betterthan their individual components. This was attributed to synergisticinteractions between these components. Experimental evidence for thiseffect was also found.The algorithm was applied to a number of industrially important separationproblems, including the extremely difficult final purification process ofalpha olefins. In each case solvents were found that are predicted toperform substantially better than those that are currently used in industry.A number of these predictions were tested by experiment and found tohold true.

[发布机构] Stellenbosch University