Formation of solids in ammonia-based CO2 capture processes — Identification of criticalities through thermodynamic analysis of the CO2–NH3–H2O system

Desorption of Ammonia Adsorbed on Prussian Blue Analogs by Washing with Saturated Ammonium Hydrogen Carbonate Solution

Prussian blue analogs (PBAs) have been reported as promising ammonia (NH₃) adsorbents with a high capacity compared to activated carbon, zeolite, and ion exchange resins. The adsorbed NH₃ was desorbed by heating and washing with water or acid. Recently, we demonstrated that desorption was also possible by washing with a saturated ammonium hydrogen carbonate solution (sat. NH₄HCO₃aq) and recovered NH₃ as an NH₄HCO₃ solid by introducing CO₂ into the washing liquid after desorption. However, this has only been proven for copper ferrocyanide and the relationship between the adsorption/desorption behavior and metal ions in PBAs has not been identified. In this study, we investigated the adsorption/desorption behavior of PBAs that are complexes of first row transition metals with hexacyanometalate anions. Six types of PBAs were tested in this study and copper ferricyanide exhibited the highest desorption/adsorption ratio. X-ray diffraction results revealed high structural stability for cobalt hexacyanocobaltate (CoHCC) and nickel ferricyanide (NiHCF). The Fourier transform infrared spectroscopy results showed that the NH₃ adsorbed on the vacancy sites tended to desorb compared to the NH₃ adsorbed on the interstitial sites as ammonium ions. Interestingly, the desorption/adsorption ratio exhibited the Irving-Williams order.

Changes in Synthetic Soda Ash Production and Its Consequences for the Environment

This publication presents a series of data of one of the most difficult chemical processes to implement in industrial conditions. Obtaining soda using the Solvay technique is a process with a world volume of about 28 Tg per year. The process is extremely physico-chemically complex and environmentally burdensome. The paper presents information on a multi-component system containing three phases with a chemical reaction. Calculations for such systems and their engineering are very complicated, but the authors show how the results of this work can be applied. This paper also describes modifications of the soda process to minimize the environmental burden and minimize the production input of Na2CO3. The modifications were beneficial in reducing CO2 emissions and increased the efficiency of the soda process, resulting in a measurable financial benefit. At the scale of the plant where the experiment was carried out, this reduction in CO2 emissions amounts to 7.93 Gg per year.

Ammonium salt production in NH3-CO2-H2O system using a highly selective adsorbent, copper hexacyanoferrate

Ammonia is a beneficial material that is widely used in agriculture, but its emission into the atmosphere causes air pollution. Recently, Prussian blue (PB) and its analogs (PBA) were found to be ammonia adsorbents with high selectivity and capacity. In this study, we utilized a highly potent PBA adsorbent, copper hexacyanoferrate (CuHCF), to desorb ammonia and turn it into a reusable form. Because the reported NH₃-CO₂-H₂O system phase diagram suggests the possibility of the recovery of solid NH₄HCO₃, we examined whether adsorbed ammonia desorbs into the saturated ammonium hydrogencarbonate solution (sat. NH₄HCO₃aq). We demonstrated that 40% of adsorbed ammonia desorbed into sat. NH₄HCO₃aq. After the desorption, CO₂ was blown into the washing liquid, and NH₄HCO₃ precipitated, which was confirmed by Fourier transform infrared spectroscopy. The molar amount of solid NH₄HCO₃ was almost equal to that of desorbed ammonia. Our findings pave the way for recovery of ammonia as a valuable product from waste gas.

Estimating speciation of aqueous ammonia solutions of ammonium bicarbonate: application of least squares methods to infrared spectra

The knowledge of the speciation and of the supersaturation of aqueous solutions of CO₂ and NH₃ is pivotal for the design and optimization of unit operations, e.g. absorption or crystallization, in the framework of ammonia-based CO₂ capture systems.

A low-energy chilled ammonia process exploiting controlled solid formation for post-combustion CO2capture

A new ammonia-based process for CO₂capture from flue gas has been developed, which utilizes the formation of solid ammonium bicarbonate to increase the CO₂concentration in the regeneration section of the process. Precipitation, separation, and dissolution of the solid phase are realized in a dedicated process section, while the packed absorption and desorption columns remain free of solids. Additionally, the CO₂wash section applies solid formation to enable a reduction of the wash water consumption. A rigorous performance assessment employing the SPECCA index (Specific Primary Energy Consumption for CO₂Avoided) has been implemented to allow for a comparison of the overall energy penalty between the new process and a standard ammonia-based capture process without solid formation. A thorough understanding of the relevant solid–solid–liquid–vapor phase equilibria and an accurate modeling of them have enabled the synthesis of the process, and have inspired the development of the optimization algorithm used to screen a wide range of operating conditions in equilibrium-based process simulations. Under the assumptions on which the analysis is based, the new process with controlled solid formation achieved a SPECCA of 2.43 MJ kg_CO2⁻¹, corresponding to a reduction of 17% compared to the process without solid formation (with a SPECCA of 2.93 MJ kg_CO2⁻¹). Ways forward to confirm this significant improvement, and to increase the accuracy of the optimization are also discussed.