Phase Separation Behavior Of CO₂ Phase Change Absorbent Developed Based On Salting-out Effect

The ever-increasing greenhouse effect has become a pressing problem that humankind needs to solve.As a representative substance of greenhouse gases,the reduction of CO2 emission cannot be delayed.CCS technology is a promising approach for reducing the emission of CO2 directly into the atmosphere and thus slowing down the greenhouse effect.In CCS,one of the mature methods is the chemical absorption process.However,the wide application is limited due to the excessively high regenerative energy consumption.Analysis of energy consumption for revealed that the energy consumption of desorption process for absorbing temperature and water evaporation accounts for 40 to 50%of the total desorption energy consumption.And this part can be significantly reduced by the improvement of the absorbent.Phase change absorbent was considered as a promising absorbent to save the energy consumption due to the reduced amount of regenerated liquid volume.In the previous study,our group has proposed a method to develop the CO2 phase change absorbents based on the salting-out effect.And a series of MEA phase-change absorbents successfully developed.However,the research on the phase separation mechanism of salting-out effect still needs to be improved.Based on this,the turbid point method was used to study the effect of the chemical structure of the amine on its phase separation behavior.Then,the amine with strong phase separation capability was selected to form the phase change absorbents with various organic solvents.Finally,a phase change absorbent with excellent CO2 capture performance was developed,which could be the foundation for the industrial application of phase change absorbents.The results showed that the phase separation ability increased as the amino groups increased and the carbon chain length decreased.The stronger the steric hindrance effect of the amine was enhanced,the phase separation ability of the amine was weakened.The number of active hydrogen of the amine and the cyclic amine structure of the amine had no obvious effect on the phase separation ability.In combination with the phase separation ability and absorption-desorption properties of amines,diethylenetriamine(DETA)was selected for organic solvent screening.The results showed that the phase change absorbent of DETA-solvent A-H2O system exhibits the best overall performance.When the mass ratio of DETA-solvent A-H2O was 2:5:3,the absorbent exhibited the maximum CO2 cyclic loading of lower phase,which was 3.16 mol/kg,the volume ratio was reduced by 66%.Five absorption-desorption experiments cycles showed that the DETA-solvent A-H2O system had good cyclic stability.Finally,chemical structure of the solid product of DETA phase change absorbent was determined by NMR analysis.