A simple chemical model to represent CO2-amine-H2O vapour-liquid-equilibria

Vapour-liquid-equilibria (VLE) models of CO2-amine-H2O systems are critical to understand the behaviour of these systems as a function of composition and temperature. Such models are a crucial component of any process simulation and the prediction of process performance. VLE models consist of chemical reactions and an activity model to describe non-ideal chemical behaviour at high ionic strength. For CO2-amine-H2O systems complex and highly dimensional activity models are used such as Pitzer, UNIQUAC and eNRTL equations. These require many tens of parameters to be known or determined, and in many cases this leads to over-fitting. The resulting parameter values then have little physical meaning and extrapolation to different conditions is unreliable. In this work a much simpler activity model, specific ion interaction theory (SIT), has been used and its performance assessed using published VLE data of CO2 absorption in aqueous MEA, AMP, PZ and mixtures of AMP and PZ. This simple activity model, which requires the determination of few if any parameters, coupled to an appropriate chemical model, was found to yield results as good as or better than that found for the more complex models. Extrapolation using this simpler model will be much more reliable than a complex model that contains many ill-defined parameter values and its inclusion in process simulation is much more straightforward.