Kinetics Of Carbon Dioxide Absorption By Phase-change Absorbents

Carbon capture and sequestration?CCS?is an essential means of mitigating climate change and has received growing attention worldwide.Absorption with alkanolamine solutions is currently the most prevalent CO₂ capture technology.However,this technology cannot be applied cost-effectively on a large scale because it consumes considerable energy for CO₂ regeneration,causing CO₂ capture to account for more than 60% of the costs of an entire CCS process.Therefore,the development of low-cost,low-energy CO₂ capture technologies has been a prominent subject of academic discussion.A highly regarded alternative to alkanolamine absorption is phase-change absorption,during which the absorbent/absorbed product phase separation occurs and facilitates substantially reducing the energy consumption associated with regeneration.In this study,N,N-dimethylbutylamine?DMBA?and N,N-dimethylbutylamine?DEEA??Diethylenetriamine?DETA?and N,N-dimethylbutylamine?DEEA?were mixed to develop phase-change absorbents,and the reaction kinetics of CO₂ absorption in the absorbents were examined.A bubbling device was used to prepare phase-change absorbents with different CO₂ loading levels.The physico-chemical parameters of the absorbents under different conditions were specified,and the changes in the CO₂ loading of the upper and lower layers of the absorption solutions after a liquid–liquid separation were analyzed.A wetted-wall column was subsequently used to investigate the effects of temperature,CO₂ loading and gas flow rate on CO₂ absorption rate.The kinetic parameters such as mass transfer resistance,liquid film mass transfer resistance,total mass transfer resistance and enhancement factor of reaction were calculated by dynamic model.The experiment selected three kinds of new phase-change absorbents system: 4M DMBA + 2M DEEA mixed solution system,2M DMBA + 4M DEEA mixed solution system and 1M DETA + 4M DEEA mixed solution system.It was observed that after sufficient CO₂ was bubbled into the solutions,liquid–liquid phase separation occurred in the three mixed solutions.The CO₂ absorbed mainly concentrated in the lower layer of the solution,and the volume and CO₂ loading of the lower solution increased gradually with the amount of CO₂ bubbled,while the volume of the upper solution decreased and the CO₂ loading of the upper solution was small.The effects of different reaction conditions on CO₂ absorption rate were investigated in a wetted-wall column using 4M DMBA + 2M DEEA,2M DMBA + 4M DEEA and 1M DETA + 4M DEEA phase-change solvent as absorbers.This study determined that reaction temperature,CO₂ loading and the gas flow rate affected the CO₂ absorption rates to a certain extent.Overall,under the experimental conditions,the CO₂ absorption rate increased with increasing temperature and gas flow rate and decreased with increasing CO₂ loading,but the performance was different for different phase change solvents.The absorption characteristics of the three different phase-change absorbers were studied,the results showed that 4M DMBA + 2M DEEA had higher absorption capacity and reaction stability.A kinetics model also indicated that the CO₂ absorption of the phase-change absorbents used in this study was mainly affected by the liquid film mass transfer resistance.Expediting CO₂ absorption during a reaction caused changes in the concentration gradients of the products in the liquid film.This study contributes theoretically to the development of CO₂ absorption technologies.