Study On The Performance Of Green Systems For Hydrogen Sulfide Removal Based On Heteropoly Compounds

Hydrogen sulfide(H2S)is a toxic and harmful gas widely existed in natural gas,refinery waste gas,coke oven gas and syngas.Not only will it pose a threat to human health,it will also cause corrosion of production equipment and pipelines and poisoning of catalysts.When it is discharged into the atmosphere,it will form acid rain,cause greenhouse effect and destroy the ozone layer.Hence,it must be removed and transformed.Liquid redox sulfur recovery process(LRSR)is one of the most potential desulfurization processes because of its high desulfurization load,high desulfurization efficiency and sulfur recovery.Heteropoly compounds are ideal redox mediators for LRSR process due to their excellent structural stability and redox properties.Based on these,a new water solution system and an ionic liquid system have been developed.The factors affecting desulfurization and regeneration performance were investigated in detail.Desulfurization products were separated and determined.The principles of desulphurization and regeneration were discussed.The main contents are as follows:1)A series of lacunary-type rare earth heteropoly compounds(NH4)11[Ln(PMo11O39)2](Ln=Sm,Ce,Dy and Gd)were prepared and proved to be successfully synthesis by Fourier transform infrared(FT-IR)and Raman spectrum.The obtained heteropoly compounds were dissolved in a certain volume of deionized water and used for desulfurization experiments.The effects of rare earth elements,reaction temperature,concentration of heteropoly compounds,hydrogen sulfide concentration and pH on desulfurization performance were investigated.The results showed that the(NH4)11[Sm(PMo11O39)2]exhibited the best desulfurization performance.The optimum absorption temperature was 25?.The higher concentration of heteropoly compounds and the lower hydrogen sulfide concentration were beneficial to the removal of hydrogen sulfide.The optimum solution pH was 5.The dissolution of hydrogen sulfide and the structure of heteropoly compounds in aqueous solution were significantly affected by solution pH,the structural changes of heteropoly compounds under different pH conditions were discussed by characterization of FT-IR spectra,UV-vis spectra and Cyclic voltammetry(CV).The results showed that when the pH of the solution was 1,the anion of heteropoly compounds existed in the Keggin type structure of PMo12O403-.When the pH of solution was 3,heteropoly anions mainly existed in two forms:Keggin-type PMo12O403-and lacunary-type PMo11O397-.When the pH of solution was 5,PMo11O397-was the main species.Further increasing the pH of the solution will lead to the decomposition of heteropoly anions.When the solution pH was 5,the heteropoly anions were stable in the form of lacunary Keggin-type PMo11O397-and the desulfurization efficiency was the best.Hence,pH 5 was selected as the optimal pH for the experiment.Regeneration of desulfurization solutions was through electrochemical method.The desulfurization performance before and after regeneration under different pH conditions were compared.The effects of current intensity,regeneration time and cycle times on regeneration performance were investigated.The results of regeneration experiments show that electrochemical technology is an excellent method for regeneration of heteropoly compounds.The desulfurization performance of the desulfurization solution after regeneration was better than that of the desulfurization solution in the studied pH range.When the pH of the solution was 5,the desulfurization solution exhibited the best regeneration performance.The optimal current intensity was 0.015A and the optimal regeneration time was 12 h.After four cycles,the desulfurization efficiency was still higher than 90%within 10 h.The X ray diffraction(XRD)was used to characterize the desulphurization products.The results showed that the product was elemental sulfur and the characteristic peak of 23.04°,25.8° and 27.7° showed that the sulfur was rhombic sulfur.In order to investigate the stability and mechanism of desulfurization and regeneration,the samples were characterized by FT-IR and X ray photoelectron spectroscopy(XPS).FT-IR results show that heteropoly compounds can still maintain the basic Keggin structure after hydrogen sulfide absorption and regeneration.Desulphurization mechanism:[Sm(PMo(?)11O39)2]-11+22H2S ?[Sm(PMo(?)11O39)2]-55 + 22S? 44H+Regeneration mechanism:Anode:[Sm(PMo(?)11O39)2]-55-44e'?[Sm(PMo(?)11O39)2]-11 Cathode:44H+ + 44e-? 22H2?The reaction mechanism of the whole absorption-regeneration process:H2S(g)?S??H2?2)The heteropoly compounds(n-Bu4N)3XMo12O40(X=P,Si,V)with different central atoms and two ionic liquids([Bmim]HCO3,[Bmim]Mes)were prepared.The obtained heteropoly compounds were dissolved in the corresponding ionic liquids for the removal of hydrogen sulfide at high temperature.The heteropoly compounds were proved to be successfully synthesized through characterization of FT-IR and XRD.The thermal stability of(n-Bu4N)3VMo12O40 and[Bmim]OAc was analyzed by TGA-DSC.The results show that the thermal stability of heteropoly compounds and ionic liquids is good enough to meet the experimental requirements.The effects of central atom species,ionic liquid type,heteropoly compound concentration,hydrogen sulfide concentration and reaction temperature on desulfurization performance were investigated.The experimental results showed that the central atoms have a great influence on the desulphurization performance of heteropoly compounds.The desulfurization performance of heteropoly compounds were as follows:VMo12O403->-PMo12O403->SiMo12O404-.The desulfurization performance of(n-Bu4N)3VMo12O40 in different ionic liquids were as follows:[Bmin]OAc>[Bmim]Mes>[Bmim]HCO3>[Bmim]Cl.The higher concentration of heteropoly compounds and the lower hydrogen sulfide concentration were beneficial to the removal of hydrogen sulfide.The optimum absorption temperature was 150?.The regeneration of desulfurization solution was achieved by bubbling air into the solution.The effects of regeneration temperature and recycling on regeneration performance were investigated.The regeneration results showed that the regeneration temperature had little effect on the regeneration performance,and the desulfurization efficiency of the desulfurization solution could be restored to 98.4%under 60?.The filtered desulfurization product was characterized by XRD.The results showed that the desulfurization product was rhombic sulfur.The samples were characterized by FT-IR and XPS.The results showed that both the central atom V and the coordination atom Mo were involved in the oxidation of hydrogen sulfide.?(?)turned to ?(?)and Mo(?)turned to Mo(?)after oxidation of H2S.The regeneration mechanism is that the oxygen in the air oxidize ?(?)and Mo(?)to ?(?)and Mo(?)respectively.The products after desulfurization were characterized by XPS.The results showed that the desulfurization products were elemental sulfur and sulfate.