Chemical Modeling of the TMA–CO2–H2O System: A Draw Solution in Forward Osmosis for Process Water Recovery

• Published in: Journal of chemical and engineering data 2017-04, Vol.62 (4), p.1214-1222
• Main Authors: Kolliopoulos, Georgios, Carlos, Michael, Clark, Timothy J, Holland, Amy M, Peng, Ding-Yu, Papangelakis, Vladimiros G
• Format: Article
• Language: English
• ISSN: 0021-9568; 1520-5134
• DOI: 10.1021/acs.jced.6b00780

Forward osmosis (FO) is an innovative membrane-based process that requires limited external energy input to recover water as it relies on the spontaneous osmotic pressure gradient between a process water stream and a more concentrated solution; the latter is termed a “draw solution”. A suitable draw solution should have properties that allow its solute to be separated into recoverable products that can, in turn, be used to regenerate the initial draw solution with minimum energy requirements. These properties are crucial for the economics of the FO process because the basic energy requirement in FO arises from the separation and regeneration of the draw solution. Recently, it was proposed that such a draw solution can be an aqueous carbonated trimethylamine solution (TMAH:HCO3). In this project, the properties, i.e., composition, pH, and vapor–liquid equilibria (VLE), of the binary TMA–H2O and the ternary TMA–CO2–H2O systems were studied to generate thermodynamic data required to enable accurate speciation calculations by means of OLI-MSE software. Necessary analytical methods to measure accurately total dissolved TMA and total dissolved CO2 (within 4% error) in aqueous TMAH:HCO3 solutions were developed. Both VLE data at 50 and 60 °C and pH–composition data at 4 and 25 °C for the ternary TMA–CO2–H2O system were used to regress the missing binary interaction parameters and improve the model performance. Our resulting databank estimates total pressure (P Total), partial pressure of TMA (P TMA), partial pressure of CO2 (P CO2), and pH, with 8, 15, 10, and 1% average absolute relative deviations (AARD), respectively.