Designing Of New Deep Eutectic Solvents For Ammonia And Sulfur Dioxide Capture

In recent years,industrial sources have emitted a large amount of waste gas containing ammonia(NH3)and sulfur dioxide(SO2),which poses a serious threat to the ecological environment and human health.On the other hand,NH3 and SO2 can both be used as important chemical raw material in the chemical production process,which has extremely huge environmental and economic benefits for its efficient capture and recycling of NH3 and SO2.At present,the most widely adopted methods to capture NH3 and SO2 from industrial tail gas are wet scrubbing.However,these methods are associated with some shortcomings such as the industrial waste water generation and high energy consumption.To address these defects,ionic liquids(ILs)provide a new strategy for NH3 elimination and recycling due to their wide liquid range,extremely low volatility and tunable chemical structure.However,most ILs have high cost due to the high viscosity and/or the expensive price of feedstocks,which significantly limits their large-scale application in the industry.Therefore,deep eutectic solvents(DESs),which have similar physiochemical properties as ILs and simpler synthesis steps and lower cost than ILs,have started to be considered as a new and green type of candidates to achieve highly efficient,reversible,and selective absorption of NH3 and SO2.Moreover,improving the gas absorption capacity,selectivity and regeneration to a greater extent is also the key to DESs as NH3 and SO2 absorbents.Based on this,the paper designs a new type of DESs,which can achieve efficient and reversible selective capture of NH3 and SO2 by precisely regulating the types and ratios of hydrogen bond donors and hydrogen bond acceptors.The details are as follows:Firstly,a class of natural DESs based on sugars was designed and synthesized.This type of DESs is composed of a mixture of choline chloride(Ch Cl)and sugars.The sugars selected for DESs preparation are D-(+)-xylose,D-(-)-ribose and D-(-)-fructose.Due to sugars containing abundant hydroxyl groups that enable strong hydrogen-bond interaction with NH3 in DESs,sugars are regarded as the key components of NH3 absorption.The experimental results show that this type of DESs exhibit the ability to effectively capture NH3 at elevated temperatures and reduced pressures(e.g.,1.745 mol/kg at 343.2 K and 14.0 k Pa).The DESs also display good reversibility and excellent NH3/CO2 selectivity for NH3 absorption.Moreover,the enthalpy change was validated by quantum chemistry calculations,further verifying that this type of DESs is a kind of low-energy,high-efficiency and green NH3 absorbent with great potential.Secondly,a new class of weak acidic binary DESs based on heterocyclic weak acids(HWAs)was designed and synthesized,consisting of N-methylacetamide(MAA)as the hydrogen bond acceptor and HWAs as the hydrogen bond donor.Among them,HWAs include imidazole,1,2,4-triazole and tetrazole;HWAs have strong hydrogen bond donor ability and can form strong hydrogen with NH3,which is the key component of NH3 absorption.The results suggested that this new type of DESs has super NH3 absorption capacity and NH3 absorption rate,and also exhibit high NH3/CO2selectivity and excellent NH3 recycling performance.Since tetrazole is more acidic than the latter two HWAs,the solubilities of NH3 in MAA+tetrazole DESs are much higher than those in MAA+imidazole and MAA+triazole DESs;while NH3 capacity in MAA+tetrazole DESs is better than previously reported ILs and DESs-possessing the highest NH3 absorption at low pressure.In addition,the mechanism of NH3 absorption was analyzed by spectroscopic characterizations(~1H-NMR),quantum chemical calculation,AIM calculation and ETS-NOCV calculation.Thirdly,a new class of DESs composed of 1-ethyl-3-methylimidazolium chloride([emim]Cl)and imidazole was designed and synthesized for SO2 capture.considering the strong electron-donating ability of Cl~-in[emim]Cl and the weak basicity of tertiary N in imidazole,both components should exhibit strong interaction with SO2,which is electron-deficient and Lewis acidic.The research results show that the charge transfer interaction between Cl~-and SO2 in[emim]Cl plays a more critical role in SO2absorption than acid-base interaction between the basic N and SO2 in imidazole.Meanwhile,The SO2 absorption capacities of[emim]Cl+imidazole(1:0.5)reach as high as 19.15 mol/kg at 101.3 k Pa and 5.73 mol/kg at 2.0 k Pa,exceeding most other solvents reported in the literature.The DESs also display good reversibility and excellent selectivity for SO2 absorption,which is rather important for practical SO2capture applications.Moreover,the mechanism of SO2 absorption was analyzed by quantum chemistry calculations and spectroscopic characterizations.In summary,this paper has successfully constructed a series of new DESs through a green and simple synthesis method,and achieved efficient and reversible selective capture of NH3 and SO2,which has a good industrial application prospect.