Novel Deep Eutectic Solvents For Carbon Dioxide Capture

Over the years,with the steady growth of carbon dioxide emissions,carbon dioxide capture is an important strategy to prevent global warming and climate change.Ionic liquids with negligible volatility and high thermal stability have become potential media for capturing CO₂.However,the shortcomings including high price,high toxicity,poor biodegradability and high demand for regeneration energy severely limit their applications in carbon dioxide capture.In this paper,new types of eutectic solvents were designed.The CO₂ absorption capacity were determined and the sensitivity of DES based on[MEAHCl][MEA]to water content and regeneration ability were further examined.The possibility of formation of DESs based on amino acid and MEA and their capacity of CO₂ absorption was explored.Furthermore,the interaction between amino acid and MEA and the interaction between amino acid-based DES and CO₂ were exploited based on molecular simulations.The main research contents and results are as follows:[MEAHCl][MEA]were prepared using a one-pot method by stirring a mixture of ammonium chloride（NH₄Cl）and ethanolamine（MEA）at 30 ℃ for 30 min.¹H NMR characterization shows that the DES prepared by the one-pot method is consistent with the system obtained by first preparing ethanolamine hydrochloride（MEAHCl）with hydrochloric acid and ethanolamine and then mixing with ethanolamine.The experimental results reveal that the novel DES exhibits a fast-initial dynamic CO₂absorption,about 22.5 wt%in 10 minutes.Nuclear magnetic（NMR）and infrared（FTIR）confirms that CO₂captures by[MEAHCl][MEA]is through the carbamate generation.The results from TGA,and combined TGA with FTIR indicate that[MEAHCl][MEA]has low thermal stability while it becomes more stable after CO₂absorption,not suitable for regeneration.To improve the regeneration ability,ethylene glycol/glycerol was introduced to[MEAHCl][MEA].The presence of EG/G leads to the increase in viscosity and improvement in thermal stability of the system,also confirmed by thermodynamics calculation.It is noted that the presence of EG/G does not result in significant decrease in CO₂ absorption capacity.Ethylene glycol/glycerin is not involved in the reaction with CO₂ TGA and TGA-FTIR analysis indicate the regeneration ability of[MEAHCl][MEA]with EG/G after CO₂ absorption.Furthermore,the CO₂capture from flue gas was investigated.The results show that the presence of water significantly improves the initial CO₂ absorption rate,and the amount of CO₂absorption increases slowly with increasing temperature.The possibility of formation of amino acid-based DES with MEA and their capacity of CO₂ absorption were examined.Hydrophilic amino acids with linear side chain are able to form DES with MEA while hydrophobic amino acids with looped side chain can form DES with MEA.It should be pointed out that hydrophobic amino acids with linear chain cannot form DES except for methionine.From the perspective of CO₂absorption capacity,the smaller the molecular weight,the stronger the ability of capturing CO₂ for the same type of DES.The molecular simulation results show that for the hydrophilic amino acid based MES the minimum energy of DES configuration decreases with the increase of molecular weight while the hydrophobic amino acid-based DES has the opposite trend.The simulation results from energy decomposition analysis based on force field reveal that the absolute value of the total interaction energy between DES and CO₂ is inversely proportional to the molecular weight.RDG analysis further indicates that the interaction between the DES and CO₂ is based on the van der Waals force.amino acids in the hydrophilic amino acid-based DES play a major role while ethanolamine in the hydrophobic amino acid-based DES has a leading effect.