The dissociation constants of protonated 2-amino-2-ethyl-1,3-propanediol, 2-amino-2-methyl-1-propanol, diethylmonoethanolamine, diisopropanolamine, dimethylmonoethanolamine, monoethanolamine, 1-amino-2-propanol, methylmonoethanolamine, triethanolamine, and the first and the second dissociation constants of piperazine and hydroxyethylpiperazine have been determined by electromotive force measurements from (293 to 353) K. The dissociation constants of protonated triethylamine have been determined with the same technique from (293 to 333) K. The experimental results and derived values of the standard state thermodynamic properties are reported and compared to available literature values.
IntroductionAqueous solutions of (alkanol)amines are frequently used for the removal of acid gases, such as CO 2 and H 2 S, from a variety of gas streams. The dissociation constant is one of the important factors in the selection of an (alkanol)amine solution for acid gas removal or in the interpretation of the kinetic mechanism of the absorption of the acid gas in the (alkanol)amine solution. 1 Dissociation constants can provide the following information:(1) a measure of the basic strength of the (alkanol)amine at a specific temperature and (2) a conventional acid gas removal plant is operated with an absorption/desorption cooling/heating cycle. In the absorber, the acid gas is (chemically) absorbed by the basic absorbent. At an elevated temperature in the desorber, the basic strength of the absorbent is reduced and the acid gas released. The basic strength is reduced as a result of less dissociation of the unprotonated absorbent at higher temperatures. Temperature-dependent dissociation constants provide the change in the reaction enthalpy which indicates the change of the basic strength of the absorbent within a given temperature range.The dissociation constants of protonated 2-amino-2-ethyl-1,3-propanediol (AEPD), 2-amino-2-methyl-1-propanol (AMP), diethylmonoethanolamine (DEMEA), diisopropanolamine (DIPA), dimethylmonoethanolamine (DMMEA), monoethanolamine (MEA), 1-amino-2-propanol (MIPA), methylmonoethanolamine (MMEA), triethanolamine (TEA), and the first and the second dissociation constants of piperazine (PZ) and hydroxyethylpiperazine (HEPZ) have been determined in this work by electromotive force measurements from (293 to 353) K. The dissociation constants of protonated triethylamine (TREA) have been determined with the same technique from (293 to 333) K. The results from the current work extend the temperature range of available literature values for the compounds investigated. For some of the compounds, no literature values were found, and the current work provides these values.
Theory and Experimental ProcedureThe theory and experimental procedure behind the measurements of dissociation constants of an (alkanol)amine have been given in detail elsewhere. 2 Measurements of the first and second dissociation constant of diamines are carried out in a similar manner. A protonated diamine dissociates according toThe equilibriu...