| Sulfur dioxide(SO2),one of the most prevalent atmospheric pollutants,is mainly emitted from fossil fuels combustion,which seriously threatens the health of human beings and the safety of environment.However,SO2 is an important raw material of producing sulfur and sulfuric acid,and the direct emission causes the waste of resources.Ionic liquids(ILs),which typically consist of ions and are generally liquid at room temperature,have great advantages in the field of gas separation.Among them,normal ILs can absorb a large amount of SO2 only by physical interaction at a high concentration of SO2.But for capturing low-concentration SO2(such as 0.2 vol%)in flue gas,functional ILs with some special groups are more effective.The strong chemical interactions between functional ILs and SO2 cause high absorption enthalpy.Up to now,the effective way to regenerate SO2-absorbed ILs is high-temperature treatment by steam sweeping,yielding a mixture of SO2 and steam,which is hard to separate.Besides,the high temperature also needs the high stability of ILs.To solve the problems of high-energy consumption,this thesis aims at finding a mild regeneration method to convert the absorbed SO2 to an easily separable product and regenerate the ILs.In this work,we used the liquid-phase Claus reaction to regenerate SO2-absorbed functional ILs.Binary systems consisting of function ILs and solvents(ethylene glycol or H2O)were used as absorbents of SO2 and liquid media for Claus reaction.The effect of various factors on the conversion of Claus reaction was studied,and the reaction mechanism was invesitigated.The main results and conclusions are shown as follows(1)Functional ILs(monoethanolaminium lactate-[MEA]L,1,1,3,3-tetramethylguanidinium lactate-[TMG]L,tetraethyl ammonium lactate-[N2222]L)mixed with ethylene glycol(EG)were used to absorb SO2 with a concentration of 2 vol%,and then H2S was added to regenerate the absorbents via the liquid-phase Claus reaction.It was found that the reaction of H2S with SO2 in the absorbents proceeded fast under mild conditions without the addition of any catalysts.Among them,[MEA]L+EG has the greatest conversion of absorbed SO2 as high as 96.4%.The conversion of absorbed SO2 decreases with the increase of temperature,and the most suitable temperature is 40℃.The initial H2S pressure and mass fractions of EG have no obvious influence on the conversion.The XDR spectra of sulfur products are very consistent with the standard spectrum of rhombic sulfur(S8).The structure of the IL before and after regeneration were analyzed by 1H NMR and it was not changed.We also confirmed the recyclability of the absorption-regeneration process for 3 cycles,indicating that the Claus reaction has the potential for regeneration of functional ILs.Beyond that,we studied the reason of dissolved sulfur in functional ILs,and put up solutions.(2)The above three functional ILs were mixed with water instead of EG to yield three absorbents of[MEA]L+H2O,[TMG]L+H2O,[N2222]L+H2O,and the Claus reaction in three absorbents was studied.The result shows that adding water can reduce the conversion of absorbed SO2,and the conversion rate increases with the increasing the acidity of absorbents.To explain this phenomenon,we studied the Claus reaction in H2SO3,NaHSO3 and Na2SO3 aqueous solutions.It turns out that the conversion of Claus reaction is related to the forms of S(Ⅳ),the oxidability:H2SO3>HSO3->SO32-,and their proportions dependent on the pH of solutions.Based on the absorption mechanism of SO2 in functional ILs aqueous solution,H2S reacts with HSO3-and SO32-with weaker oxidability,resulting in the lower conversion rate. |
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