Title : Thermodynamic modeling for the carbonate system na k hco3 co3 in alkanolamines solutions: An extended application for CO2 scrubbing
Abstract:
CO2 is considered as the major contributor to the Earth’s global warming. Though the cause of emission is driven by regional dynamics, the growth of CO2 concentration in atmosphere has been around 40% since the beginning of the 21st century. In recognition that coal-fired power plant is a single large source of CO2 emission makes the post-combustion capturing (PCC) an optimal solution. Furthermore, the presence of acidic gas tends to result in equipment corrosion and pipeline clogging, so that ensuring the security of adsorption process must be in focus. Over the past decades, scientists and researchers are on the lookout for techniques to fasten the CO2 adsorption process; many have found that amine additives such as monoethanolamine (MEA), diethanolamine (DEA) as well as other blended amine solutions are capable of improving the adsorption efficiency. It is well-known that potassium carbonate (K2CO3), aka. hot potash solutions, are among the most prevalent solid sorbents particularly effective to improve the overall performance of CO2 stripping process. Here the biggest challenge presents is the low in the rate of reaction, thus resulting in poor CO2 mass transfer if the solution is used alone. By the addition of amine promotors such as MEA or DEA, the rate of adsorption can be greatly enhanced. For example, a study had concluded that when K2CO3 aqueous solution is promoted by DEA (20 wt.%), the absorption performance could reach equilibrium enhanced by a factor of 5. Due to its physical nature, K2CO3 presents thermal stability, thus capable of serving as an inert, solid sorbent even when temperature exceeds 373 K.
CO2 absorption technology involves in-depth analysis of chemical equilibrium for all three phases. As such, the aim of this study is to develop a comprehensive thermodynamic model which can be used to forecast the solid-liquid-gas (SLV) equilibrium system that contains Na-K-HCO3-CO3 in alkanolamines solutions, so that this model can be further applied for the calculation of partial pressure of CO2 under different temperature, loading of solid sorbents, and/or contents of solvent composition. We consider a model reliable for the direct calculation of CO2 solubility in the promoted, hot potash solution only if both SLE and VLE parameters are accurate. As for preliminary study, we have found an ample of references that reports on the vapor-liquid equilibrium (VLE) data for both systems: MEA-CO2-H2O and DEA-CO2-H2O. However, we can hardly find any relevant data pertaining to the SLE system that reports on the solubility of K2CO3, KHCO3 in alkanolamine solutions. As such, another objective of this work is to conduct solubility experiments for the proposed, solid-liquid system: K2CO3-KHCO3-MEA-H2O, K2CO3-KHCO3-DEA-H2O, from the temperature range of 283 – 353 K at atmospheric pressure; this was achieved by adjusting the solubility parameters using the Mixed-Solvent Electrolyte model. All these should aid in the effort for the development of a comprehensive model, which can be applied to forecast the CO2 solubility in the promoted, potash
