Study On The Reaction Mechanic Between Vanadium Substances And Sulfur Compounds In Tannin Desulfurization System

Tannin desulfurization technology is an important method of wet catalytic oxidation to remove H₂S.The technology is widely used in coking,fertilizer and other industries.However,like other catalytic oxidation desulfurization methods,the tannin desulfurization technology also enrich certain amounts of thiosulfate,sulfate,thiosulfur and other sulfur-containing by-products during the conversion of gas phase H₂S to stable elemental sulfur.The accumulation of these secondary salts had a negative impact on industrial operations,so reducing or inhibiting the formation of by-products has become one of the issues that companies are currently facing.Based on the previous research results,it is inferred that the conversion of HS^-to elemental sulfur is not a simple reaction step but is divided into two steps.That is,the reaction between HS^-and the oxidized pentavalent vanadium V?V?immediately generates the polysulfide ion S_x^2-,and then S_x^2-is slowly converted into the stable elemental sulfur S₈.Due to the active nature of S_x^2-,it is easily oxidized by the oxidizing substances in the solution to produce oxygen-containing sulfur by-products.Obviously,accelerating the conversion of S_x^2-to S₈ plays a crucial role in reducing or inhibiting the occurrence of side reactions.Therefore,ultraviolet spectrophotometry and electrochemical method were used to study the mechanism of action between vanadium and sulphur compounds in tannin extract desulfurization system,aiming to provide theoretical ideas for reducing the occurrence of side reactions.Through the study of this paper,the main conclusions are as follows:?1?It was found that the absorption wavelength of sodium sulfide and sodium metavanadate in the carbonate buffer was before 300 nm by UV-Vis spectroscopy,and there was a strong absorption can be seen at 360 nm,which was caused by the generating polysulfide ion.Therefore,polysulfide ions were generated preferentially in the reaction between V?V?and HS^-.Meanwhile 360nm can be used as the optimal absorption wavelength for studying this reaction.At the same time,the experiment also shows that at this wavelength,the absorbance value of the polysulfide solution has a good relationship with its concentration and UV-Vis spectra can be used as a method for detecting polysulfide ions.In addition,the experimental results show that when the concentration ratio of sodium sulfide and sodium metavanadate is 50:1,the generated polysulfide ion concentration is the highest.Since then,the concentration of S_x^2-has gradually decreased with the increase of the HS^-concentration,which indicates hydrogen concentration should not be too high,otherwise it will increase the possibility of formation of by-products in process of V?V?reacted with HS^-.The study also found that the reaction temperature has no significant effect on the reaction between V?V?and HS^-,but the reaction time has a greater impact on the experiment:in the experiment,within 5 min,the concentration of S_x^2-decreased by 63.3%;After 80 minutes,the concentration of S_x^2-no longer changed,and 85.9%S_x^2-has transform into other by-product but not elemental sulfur.?2?Cyclic voltammetry using a glassy carbon electrode as a working electrode was chosen to study the migration of sulfur.The results show that the scanning speed 500 mV/s and 5000 mV/s are conducive to research experiments,the optimal concentration of electrolyte KCl is 0.5 mol/L,the experiment in the case of multi-cycle scanning,analysising the second ring dates can more objectively reflect the experimental results.And the formation of S_x^2-is unavoidable during the desulfurization process.And that the existing form of S_x^2-is mainly S₂^2-and S₃^2-.With the increase of HS^-concentration,the concentration of S_x^2-increases and a new product S₄^2-is generated.Based on these conclusions,the reaction mechanism between sulfur-containning substance and V?V?was given:2HS^-+HV₂O₇^3-?S₂^2-+HV₂O₅^-+2OH^-S₂^2-+HS^-+OH^-?S₃^2-+H₂O+2e S₃^2-+HS^-+OH^-?S₄^2-+H₂O+2e2S₄^2-?S₈In addition,the study also found that if the desulfurization system is in highly alkaline or acidic,it is not conducive to sodium vanadate to play its oxidation capacity.The best pH value is about 8.4.?3?In the experiment,the complexation of tetravalent vanadium and S_x^2-was studied.The results showed that there was no complexation in an alkaline environment,instead produced a brown-black substance VO?OH?₂,which is not the widely considered VOS substance in industry.It was found that VO²⁺was generated in the environment of OH^-,S^2-,and S_x^2-solutions,and that VO?OH?₂was formed only can exist in the p H range of 5¹1.At 18°C,the solubility product constant of VO?OH?₂ is 1.63×10^-11.Therefore,vanadium is not a factor that hinders the rapid conversion of polysulfide ions into elemental sulfur.