Basic Research On The Capture Of Hydrogen Sulfide By Inoic Solvents

Hydrogen sulfide(H2S)is a kind of highly toxic and acidic gas that widely exists in industrial processes.It can not only corrode facilities and pipelines,deactivate the catalyst,but also pose potential threats to human health and environment.Utilizing alkanolamine solvents for the capture of H2S is the most used method in industry.But they often degrade resulting in solvent loss and bad desulfurization performance and their absorption rate for H2S is slow.Ionic solvents have shown enormous potential in the capture of acid gases because of their unique properties such as negligible vapor pressure,high thermal stability,and most importantly,they can be designed for specific application.Among them,ionic liquids have attracted considerable interests in the capture of H2S However,these ionic liquids for the capture of H2S are mostly cation-functionalized or anion-functionalized ionic liquids,with single active site.Their absorption capacity for H2S are still not ideal enough.To the best of our knowledge,studies on H2S absorption by anion and cation-functionalized ionic liquids are scarcely available in the literature,so designing an anion and cation-functionalized ionic liquids which can capture H2S efficiently is of great significance for decreasing production costs and reducing the harms of H2S to human health and environment.The detailed researches for the problems above are summarized as follows:The first part of this work is introducing multiple amine groups in the ionic liquid to increase the absorption capacity of H2S.Five multi-amine functionalized ionic liquids(MAILs)were synthesized by one-step method.They are[TETAH][Ac],[TETAH][Gly],[DETAH][Lys],[TETAH][Lys]and[TEPAH][Lys],respectively.The saturated absorption capacity of H2S in 30 wt%MAILs aqueous solutions were up to 1.33-2.80 mol/mol at room temperature and H2S partial pressure of 10 kPa,and they were in the sequence that[TEPAH][Lys]>[TETAH][Lys]>[DETAH][Lys]≈[TETAH][Gly]>[TETAH][Ac],which are higher than other functionalized ionic liquids reported in the literature.And the ratio of the number of amine groups in the ionic liquids to the saturated absorption capacity of H2S is close to 2:1.The strong basicity of the anion also has a promotion effect on the H2S absorption capacity.Then,[DETAH][Lys],[TETAH][Lys]and[TEPAH][Lys]tethered with amine groups on anions and cations are selected to determine the absorption capacity of H2S under the conditions with different temperatures and different ionic liquid concentrations.The results showed that the absorption capacity of H2S decreases with the increase of temperature.When the temperature rose to 40℃,their saturated absorption capacity for H2S decreased to 1.54 mol/mol,1.68mol/mol,2.18 mol/mol,respectively,which is higher than the highest value in the literature under the same conditions.But the viscosity of the MAILs synthesized in this work is high and needs to be improved.As the concentration of MAILs increased,the absorption capacity of H2S remained unchanged at first and then gradually decreased.When the concentration of MAILs reached 50 wt%,phase transition phenomenon occurred in the H2S absorption process.Therefore,the concentration of the MAILs should be less than 50 wt%.Finally,the MAILs after absorbing H2S were heated at 95℃ under N2 atmosphere to regenerate.After the absorption-desorption experiment was repeated five times,the regeneration ratio still remained above 80%,and the regeneration performance is excellent.Then[DETAH][Lys],[TETAH][Lys]and[TEPAH][Lys]were selected to investigate the effect of different MAILs,temperature and the concentration of MAILs on the H2S removal efficiency for low-concentration H2S(PH2S≈0.5 kPa).The results showed that the H2S removal efficiency of the three ionic liquids with a concentration of 30 wt%remained above 93%within 120 minutes at 25℃,while the H2S removal efficiency of the alcohol amine(MDEA)solutions under the same conditions quickly dropped below 75%within 120 minutes.Compared with MDEA,the desulfurization performance of the three ionic liquids are rather good.[TETAH][Lys]displayed an excellent desulfurization performance than others,and its H2S removal efficiency remained above 97%within 120 minutes.Low temperature and high concentration of ionic liquid are beneficial to enhance the desulfurization performance of ionic liquids.Finally,[DETAH][Lys],[TETAH][Lys]and[TEPAH][Lys]were mixed with MDEA according to certain proportion as MDEA activators.The effect of different MAILs,the addition ratio of MAILs,temperature and H2S concentrations in the feed gas on the desulfurization performance of MDEA were investigated.The results showed that after adding 5%[TETAH][Lys]to the MDEA aqueous solutions,the H2S removal efficiency remained about 90%in 120 minutes.[TETAH][Lys]significantly improves the desulfurization performance of MDEA.The H2S absorption capacity of[TETAH][Lys]-MDEA is about 0.6 mol/mol,which is 1.2 times that of MEA-MDEA,and the H2S removal efficiency is slightly higher than that of MEA-MDEA.In addition,[TETAH][Lys]has low vapor pressure,high thermal stability,and most importantly it can be completely regenerated at 100℃,while MEA is easy to degrade and volatilize,and its regeneration temperature nearly up to 125℃.Therefore,[TETAH][Lys]is more suitable as MDEA activators.