A two-part study is presented on a novel multistage distillation process for the recovery of diethanolamine from contaminated solutions. Such solutions, which pose serious problems in gas plants and oil refineries, cannot be easily purified because of the close volatilities of some of their constituents. The new process utilizes hexadecane as an inert carrier liquid to ensure proper fluid distribution in the distillation column, to avoid thermal degradation and fouling, and to facilitate separation of nonvolatile constituents. In part 1, the process is described together with new phase equilibrium data for mixtures of diethanolamine, bis(hydroxyethyl)piperazine, tris(hydroxyethyl)ethylene diamine, water, and hexadecane. The desired physical properties of the inert carrier are discussed and guidelines are presented for its selection, The nonrandom two liquid activity coefficient model was successfully used to represent the equilibrium data.