Purification of partially degraded diethanolamine solutions

Alkanolamine solutions are widely used in the gas processing industries for the removal of acid gases (e.g. C0₂and H₂S). These solutions frequently become contaminated with amine degradation products, heat stable salts, heavy hydrocarbons and particulates. The contaminants pose serious problems to the sound performance of gas processing plants. Although distillation is the most promising method to separate the contaminants, conventional single-effect flash reclaimers suffer from several problems such as incomplete recovery of amine and low product purity due to the close volatility of amines and certain degradation products. It is shown that these problems can be alleviated by using a novel multi-stage distillation process in which a special inert carrier liquid is employed. The inert liquid ensures proper fluid flows in the distillation column and increases the amine recovery. The desired physical properties of the inert liquid were identified and the liquid was selected accordingly. The vapour-liquid and liquid-liquid equilibrium data for mixtures of diethanolamine, its principal degradation products, water and the inert liquid were investigated. These data are essential to design and simulate the process under various operating conditions. The appropriate thermodynamic models required to represent the equilibrium data were determined and a number of design options, including the conventional singlestage flash process, were evaluated by means of the ASPEN process simulator. Advantages of the new process developed in this study include high amine recoveries and good amine purity. Thermal degradation of amines and potential fouling of heat transfer tubes in conventional amine reclaimers is avoided since the amine mixtures are not passed through the heat exchanger.Applied Science, Faculty ofChemical and Biological Engineering, Department ofGraduat