Weak Electrolyte Vapor-Liquid Equilibria

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Research Summary: An equation of state model which successfully correlates vapor liquid equilibria behavior of weak electrolyte systems containing ammonia, hydrogen sulfide, and carbon dioxide has recently been developed by the principal investigators. This earlier work was focused primarily on the vapor phase, so that the vapor phase behavior for a given overall liquid phase composition was successfully characterized. In this project, work will focus on the liquid phase. Specifically, several proposed modifications to the existing model will be examined so that concentrations of individual species in the liquid phase will be successfully characterized. In addition, the feasibility of replacing the perturbed hard chain equation, which is presently in the model, with a cubic equation of state, will be examined. Finally, an experimental program will be undertaken whereby total pressure, temperature, and the density and conductivity of both phases will be measured in situ. These results, along with the theoretical model, will then be used to calculate phase compositions. The program will eliminate the two features which have given traditional methods so much trouble--overly complex theoretical models and removing and analyzing samples from equilibrium cells. Innovation: The proposed work will lead to two scientific innovations. First, it will continue to develop the application of equations of state to weak electrolyte systems. The equation of state development will lead to a model which will be simpler than those models currently used to represent weak electrolyte behavior. The proposed methods will possess the many advantages which have made equations of state so popular for representing non-electrolyte vapor liquid equilibria. The second innovation is that an experimental technique will be developed which will eliminate the need to remove and analyze samples from the equilibrium cell. With current techniques, this is the most difficult step, so its elimination will indeed be a major development in the methods used to study these systems. Significance: The proposed research will have considerable practical impact in the area of sour water processing, water purification, natural gas processing, and heavy oil refining. The reason this work is applicable in so many areas is that techniques for the CO2-NH3-H2O and H2S-NH3-H2O systems can be easily extended to systems in which the ammonia is replaced by amines, glycols, or alcohols. Thus, much industrial interest results because of the importance of H2S removal from natural gas by amine treating. At this point, the problems associated with weak electrolyte VLE have not been solved satisfactorily. The proposed techniques couple new approaches in the experimental procedure with new approaches to modelling the behavior in a manner that may solve the problem.