Preparation And Properties Of Phase Change Solvents Based On Amino Acid Ionic Liquids

Phase change solvent was a novel liquid material for carbon caprure,which can separate into two immiscible phases during the CO₂ capturing procedure under a certain temperature.The solvent system can significantly decrease the energy consumption since the solvent can be regenerated by only heating the rich-CO₂ phase.The research progress of CO₂ capture liquid materials was summarized in this paper.A series of phase change absorbents based on amino acid ionic liquids?AAILs?were synthesized.The effects of molecular structure and concentration of absorbents on CO₂ capacity,phase change performance and regeneration properties were studied.The phase change mechanism was also investigated.Firstly,small molecular AAILs were synthesized,the effects of molecular structure and concentration of AAILs on CO₂ capacity and phase change performance were investigated,the mechanism of phase change during CO₂ capture process were discussed,and the regeneration properties were tested.Then,in order to improve phase change performance and better thermal stability,polymeric amino acid ionic liquids?PAAILs?were synthesized,the effects of chemical structure and concentration of PAAILs on CO₂ capacity and phase change performance were studied,the mechanism of phase change after capturing CO₂ were discussed,and the regeneration properties were tested.Finally,to achieve efficient and rapid separation of the solid phase and liquid phase,polymeric amino acid ionic liquids-magnetic nanoparticles?PAAILs-Fe₃O₄?composite solvents were prepared and the effects of Fe₃O₄ on CO₂absorption capacity,phase change and regeneration were studied.Firstly,AAILs were synthesized through ion change and subsequent neutralization reactions using quaternary ammonium salts?e.g.TMA,VBTAC,TMOA,CH?as cations and amino acids?e.g.Gly,His,Asp,Arg,Trp?as anions.Chemical structure and thermal stability were characterized by nuclear magnetic resonance?¹H-NMR?,Fourier transform infrared spectroscopy?FT-IR?and thermogravimetric analysis?TG?.The effects of molecular structure and concentration of AAILs on CO₂ capacity and phase change performance were studied.The mechanism of phase change on CO₂ capture process was further investigated,as well as the regeneration properties were tested.CO₂ capacity was varied by the molecular structures.Highest CO₂ capacity was endowed on[TMBA][Gly]among the Glycine based AAILs,which was up to 0.69 mol CO₂/mol AAILs.The CO₂ capacity of[TMA][Arg]was 1.41 mol CO₂/mol AAILs,which presented highest capacity among the AAILs using TMA⁺as cation.Compared to glycine with simpler chemical structure,tryptophan is more complex with double amine groups.[TMA][Trp]solvents demonstrated better phase change efficiency than the TMA][Gly],due to the trend of the complex formation with‘cross-linked'network structure while reacting with CO₂.The regeneration and recycle experiments showed that the regeneration rate of the whole[TMA][Trp]absorbent was 93%,while the regeneration rate was 71%,which CO₂ was stripped by only heating solid rich-CO₂ phase.Secondly,PAAILs were synthesized through free-radical polymerization of DADMAC,ion change and then reacted with Gly,His,Trp or Asp,respectively.The effects of chemical structure and concentration of PAAILs on CO₂ capacity and phase change performance were studied.The mechanism of phase change on CO₂ capture process was further explored via nuclear magnetic resonance-¹H-NMR and¹³C-NMR.Then,the regeneration properties were tested by different desorption methods.Of all the PAAILs synthesized,P[DADMAC][His]achieved the highest CO₂ capacity of 0.85 mol CO₂/mol AAILs.Temperature had significant effect on CO₂ take in.With the increase of the temperature,the amount of CO₂ captured in the saturated solution decreased from 0.58 mol CO₂/mol AAILs to 0.33 mol CO₂/mol AAILs.The phenomenon of phase change occurred in both P[DADMAC][Gly]and P[DADMAC][Trp]solvents during CO₂-absorpting procedure.The higher the concentration was,the more solid CO₂-rich phase was.The regeneration and recycle experiments showed that the regeneration rate of the whole P[DADMAC][Trp]absorbent was 93%,while the regeneration rate got79%,which CO₂ was stripped by heating solid rich-CO₂ phase.Thirdly,by the electrostatic interaction between PAAILs and carboxyl groups modified Fe₃O₄nanoparticles,compositeabsorbentsofP[DADMAC][Gly]-Fe₃O₄and P[DADMAC][Trp]-Fe₃O₄ were succussefully prepared.The effects of the amount of magnetic nanoparticles on CO₂ absorption capacity,phase change and regeneration were investigated.The particle size and zeta potential of the composite solvents were characterized by dynamic light scattering?DLS?.The presence of Fe₃O₄ played a positive role in the phase separation efficiency.The amount of the magnetic nanoparticles increased,the phase separation efficiency accelerated.The regeneration and recycle experiments of the composite solvents showed the regeneration rate was 56%,which CO₂ was stripped by heating solid rich-CO₂phase.In this paper,we synthesized a series of phase change absorbents based on AAILs and PAAILs-Fe₃O₄ composite absorbents,with easier access to raw materials,high CO₂ capacity and efficiency,low energy consumption,easy operation and other advantages.The products indeed have the prospect of application in industrial carbon capture.