- Title
- The effect of piperazine (PZ) on CO₂ absorption kinetics into aqueous ammonia solutions at 25.0°C
- Creator
- Li, Lichun; Conway, William; Puxty, Graeme; Burns, Robert; Clifford, Sarah; Maeder, Marcel; Yu, Hai
- Relation
- International Journal of Greenhouse Gas Control Vol. 36, Issue May 2015, p. 135-143
- Publisher Link
- http://dx.doi.org/10.1016/j.ijggc.2015.02.015
- Publisher
- Elsevier
- Resource Type
- journal article
- Date
- 2015
- Description
- Piperazine (PZ) has been reported as an effective rate promoter in the aqueous ammonia-based solvent process for the post combustion capture (PCC) of CO₂. However, the detailed promotion effect of PZ on CO₂ absorption into partially loaded ammonia solutions and the mechanism of this process are still unclear. In an effort to determine the detailed promotion effect of PZ in aqueous ammonia-based solvents, overall mass transfer coefficients (KG) describing the absorption of CO₂ into aqueous PZ/NH₃ solutions were determined using a wetted-wall column apparatus at 25°C. The effect of added PZ (from 0 to 0.5M) on the mass transfer of CO₂ into 3.0M NH₃ solutions over a range of pre-loaded CO₂ concentrations of 0.9M at 25°C are reported in this work. The fast kinetic reactions of CO₂(aq) with blended solutions containing PZ/NH₃ were investigated using stopped-flow spectrophotometry at 25.0°C. Analysis of the kinetic measurements using a chemical model which incorporates the complete reaction sets of the individual amines with CO₂ (i.e., NH₃₋CO₂₋H₂O and PZ₋CO₂₋H₂O) resulted in good agreement with the experimental data. The contribution distribution from each reactive species was calculated based on the proposed reaction scheme of the PZ₋NH₃₋CO₂₋H₂O system. Results show that both the PZ/PZH⁺ and PZCO₂̅/PZCO₂H pathways make contributions to the promotion of CO₂ absorption into PZ promoted aqueous NH3 solutions. Importantly, the reactive piperazine mono-carbamate species, PZCO₂̅/PZCO₂H, which is present in the CO₂₋loaded mixtures of PZ/NH₃, plays an important role in the promotion of CO₂ absorption into CO₂₋loaded aqueous NH₃ solutions. The mass transfer simulation results reveal that there are additional reactions occurring in the gas-liquid interface and gas phase due to the volatility of NH₃, which requires further improvement on the simulation model.
- Subject
- CO₂ capture; aqueous ammonia solutions; piperazine; promotion mechanisma
- Identifier
- http://hdl.handle.net/1959.13/1336969
- Identifier
- uon:27740
- Identifier
- ISSN:1750-5836
- Language
- eng
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