(801e) Solubility of Carbon Dioxide in Aqueous Solutions of Potassium Carbonate (“Activated Hot Potassium Carbonate Process”)

In the Hot Potassium Carbonate Process carbon dioxide is removed from gaseous streams by chemical absorption in an aqueous solution of potassium carbonate. It is common to "activate" the solvent by adding so-called “promoters”, like borates and vanadates, the role of which is, however, not fully understood. In the present inves­ti­gation we studied the influence of borates and vanadates on the equilibrium solubility of carbon dioxide in aqueous solutions of potassium carbonate in three steps. In the first step the complex reaction network in these solutions was studied by ⁵¹V-NMR-spectroscopy. The investigations reveal that besides the various complexes that are described in the literature, carbonato-vanadate complexes exist. Based on these experimental results and on literature data, the reaction network was modeled quantitatively [1]. In the second step, the solubility of carbon dioxide in four different activated aqueous solutions of K₂CO₃ was determined experimentally at two tempe­ratures that are typical for carbon dioxide absorption (343 K) and solvent regene­ration (383 K) in the Hot Potassium Carbonate Process. The mass fraction of K₂CO₃ in the solvent was 0.26 g/g, the mass fractions of boron (vanadium) was varied between 0.006 and 0.013 g/g (0.01 and 0.02 g/g). Two set-ups were used for the experiments: A headspace gas chromatographic technique was applied to determine the solubility of CO₂ at partial pressures of carbon dioxide between (1 and 140) kPa and the synthetic gas solubility technique was applied for total pressures between (0.4 and 10) MPa. The new experimental results are compared to predictions from a physico-chemical model for the solubility of CO₂ in aqueous solutions of K₂CO₃ [2]. The results reveal that both the borate and the vanadate reduce the solubility of CO₂ in such solutions. In the third step, the model was extended to describe that "salting-out" phenomenon quantitatively, taking into account not only the new gas solubility data but also the new data on the chemical reactions [1]. The new model provides an excellent basis for simulations of the Hot Potassium Carbonate Process.

[1] McCann N., Wagner M., Hasse H.; Dalton Trans., 2013, 42, 2622-2628

[2] Pérez-Salado Kamps, Á., Meyer E., Rumpf B., Maurer, G.; J. Chem. Eng. Data, 2007, 52, 817-832