The present work aims at investigating absorption of CO₂ into promoted and unpromoted aqueous K₂CO₃. For this we performed a series of lab experiments in a thermostated batch stirred tank gas-liquid reactor containing the solvent. The absorption of CO₂ was monitored by the decrease in the reactor pressure. To compare the different solvent blends, the experimental conditions, i.e., injection pressure, reactor temperature, stirring speed, and solvent volume were kept constant. For the interpretation of the experiments a simple absorption model is formulated based on which an apparent absorption rate is derived. Among the different rate promoters studied, we found that V₂O₅ results in a substantial increase of the absorption rate, while the use of B(OH)₃ in conjunction with V₂O₅ does not provide any tangible benefits. A semi-qualitative comparison with rate constants reported in the literature suggests that this hindering effect of B(OH)₃ is due to the lower pH of the solvent containing B(OH)₃. The solvent blends containing amine-promoters MEA and piperazine demonstrated rapid absorption. Comparison with the literature indicates that absorption in the presence of these promoters is mass transfer limited under the experimental conditions.

Absorption by aqueous potassium carbonate is gaining renewed interest as a post-combustion carbon capture technology due to its benign chemistry and low regeneration duty. In this work, we present new experimental data on the absorption rate of CO<inf>2</inf> into aqueous K<inf>2</inf>CO<inf>3</inf>. We performed absorption experiments on 25 wt% K<inf>2</inf>CO<inf>3</inf> at a temperature of 313–358 K and solvent loadings up to 70%, using a thermostatted, stirred batch reactor. A stagnant film model accounting for all reactive species was used to derive the second order rate constant (k<inf>2</inf>) for the reaction between CO<inf>2</inf> and OH⁻. The role of the reaction was found to diminish with increasing solvent loading due to a decrease in the hydroxide concentration, whereas the k<inf>2</inf> was instead found to increase with the solvent loading. To explain this behavior we developed an ion-contribution model that relates k<inf>2</inf> to the ionic composition of the solvent. The model describes the experiments over the whole range of data with good accuracy. The results of this work are relevant for industrial applications of aqueous K<inf>2</inf>CO<inf>3</inf> where the absorption process is operated at high solvent loading to minimize regeneration duties.

Aqueous potassium carbonate (K₂CO₃)-based absorption processes are among the first-generation carbon capture technologies ready for large-scale deployment. The high stability of aqueous K₂CO₃ and its low regeneration energy demand present clear advantages. However, the inherently slow CO₂ uptake by aqueous K₂CO₃ remains a key limitation. We present a comprehensive study on vanadium pentoxide (V₂O₅) as a rate promoter to enhance the absorption of CO₂ in aqueous K₂CO₃. The absorption rate of CO₂ was measured over a wide range of conditions, namely V₂O₅ concentrations up to 6 wt %, solvent loadings up to 60%, and temperatures between 313 and 358 K. The rate promoter was found to significantly enhance the absorption rate across all conditions, by up to a factor of 2–3 with respect to unpromoted K₂CO₃. Analysis of vanadium speciation indicated that this enhancement arises from the reaction between CO₂ and hydrogen monovanadate (HVO₄^2–), with a rate constant that increases exponentially with ionic strength. A kinetic model incorporating this relation accurately reproduced the observed absorption rates across the experimental range. The results of this work demonstrate V₂O₅ is an effective rate promoter under conditions typical of K₂CO₃-based processes, thus enabling reductions in compression duties and associated capital costs without major process changes.

This work investigates boric acid as an additive to potassium carbonate (K₂CO₃)-based solvents for CO₂ absorption.Boric acid increases the capacity for absorbing CO₂ by acting as a co-buffer. This effect was studied by absorption experiments in a stirred batch reactor using 25 wt% K₂CO₃, with boric acid concentrations up to 9 wt% and solvent loadings up to 70%. Our experiments show that while boric acid increases the vapor-liquid equilibrium pressures under rich solvent conditions, its presence results in a net increase in buffering capacity of aqueous K₂CO₃ by extending the lower limits of carbonate buffering.Boric acid was further shown to exhibit only a limited positive enhancement of CO₂ absorption rate, attributed to ionic effects on the reaction between CO₂ and hydroxide ions.Taken together, our results indicate that on its own, boric acid (or its salts) is unlikely to significantly improve column performance. However, under conditions of faster absorption, such as in the presence of a rate promoter, borates may serve as secondary additives by increasing CO₂ uptake through enhanced buffering capacity.