Study On The Phase Change Of Organic Super Alkali/organic Solvent System To Capture Hydrogen Sulfide

Natural gas is a clean source of energy with better quality than coal and oil.However,the highly toxic and corrosive hydrogen sulfide?H₂S?gases are widely present in natural gas fields,which seriously affect the transportation,storage and the safty utilization of natural gas.On the other hand,H₂S is also an important sulfur resource,which could be use to produce sulfuric acid and other sulfur-containing compounds.However,the traditional desulfurization methods often have drawbacks such as low absorption capacity and high energy consumption for regeneration.There are still many challenges in the field of natural gas desulfurization.Therefore,the development of cost-effective H₂S capture and sulfur resource conversion technology is of important significance for improving the industrial upgrading of natural gas.In recent years,the concept of phase-change capture technology for acid gas CO₂ was put forward and has attracted extensive attention.Different from traditional desulfurization technology,the CO₂ phase-change capture technology could effectively reduce energy consumption of regeneration process because only CO₂-rich needs to to be heated for regeneration.Based on this,this paper focuses on the development of H₂S phase-change capture technology to reduce the energy consumption of absorbent regeneration and increase the absorption capacity of H₂S as well as improve the utilization of sulfur resources.The specific research content includes the following aspects:First and foremost,the organic superbase 1,5-diazabicyclo[4.3.0]non-5-ene?DBN?was used as absorbent,low viscosity and high boiling point organic solvents hexadecane and hexanol were used as solvents.The liquid-liquid phase-change was achieved after bubbling into H₂S gas.The absorption product was confirmed to be[DBNH]⁺[SH]^-salt via nuclear magnetic resonance spectroscopy?¹H NMR?and Fourier transform infrared?FTIR?spectroscopy.UV-visible absorption spectroscopy?UV-vis?shows that the phase-change phenomenon was attributed to the polarity difference between the upper and lower phases after absorption of H₂S.In addition,considering that only the lower phase needs to be heated for regeneration,the gravimetric absorption capacity is calculated to be 0.205g H₂S/g lower phase at 1 bar and 293.15 K,which is the highest absorption capacity of H₂S obtained so far.Furthermore,DBN,hexanol and H₂S were mainly concentrated in the lower phase,while hexadecane was mainly concentrated in the upper phase when the absorption reached equilibrium.This DBN-hexadecane-hexanol system has excellent desulfurization performance,and the highest desulfurization rate was higher than 99%.The absorbed H₂S can be desorbed by bubbling into N₂ at 80 C.Five cycles of absorption and desorption experiments show that the absorption capacity of each cycle remains basically unchanged.The ¹H NMR analysis of the lower phase absorbent after each desorption shows that its chemical shift was consistent with that of the mixture of DBN and hexanol before H₂S absorption,which indicats that the absorption system has excellent chemcial stability.Besides,the organic superbase 1,8-diazabicyclo[5.4.0]undec-7-ene?DBU?was used as absorbent,and the organic solvent with distinguished physical as well as chemical properties was used as solvent.The system with the blends of DBU-triethylene glycol dimethyl ether?TEGDME?-H₂O was selected and it could achieve liquid-liquid phase-change H₂S after absorption.¹H NMR and FTIR spectroscopy analysis indicated that the absorption product was[DBUH]⁺[SH]^-salt.The results of UV-vis spectroscopy indicated that the formation of the two phases was due to the salting-out effect of the resulted product[DBUH]⁺[SH]^-salt,which separated the low-polarity TEGDME from the highly polar H₂O solution.In addition,the effects of different absorption conditions such as component concentration,temperature and H₂S partial pressure on the absorption property were also investigated.The effect of water content in the system on the distribution of DBU and TEGDME in the upper and lower phases was quantitatively analyzed by gas chromatography?GC?.The results showed that the water content has no effect on the mass percentage of DBU and TEGDME in the upper phase while the mass percentage of DBU increases with the decrease of H₂O content in the lower phase.Fourthermore,the mass percentage of TEGDME decreases with the decrease of water content.Only the solvent TEGDME was stay in the upper phase.However,H₂S,H₂O,DBU and a small amount of TEGDME were concentrated in the lower phase after the absorption reached equilibrium.Finally,the liquid phase Claus reaction was used as the chemical regeneration method of the absorbent to realize the reversible trapping of H₂S and convert the harmful H₂S gas into sulfur element.Finally,Aimed at converting the absorption products of H₂S-rich into high value-added sulfur-containing organic chemicals.The organic superbase tetramethylguanidine?TMG?was used as an absorbent and the organic solvent N-methylpyrrolidone?NMP?with low saturated vapor pressure and viscosity was used as solvent,which could achieve the liquid-solid phase-change after absorbing H₂S.The results of powder X-ray diffraction?XRD?and FTIR showed that different organic solvents had no effect on the structure of the absorbed products,but could not directly prove the structure and composition of the absorbed products.The single crystal was obtained by recrystallization of the absorbed product.The single crystal X-ray diffraction analysis showed that the crystal was 1,1-dimethylthiourea.In summary,the concept of H₂S phase-change absorption was proposed for the first time in this paper,and the phase-change capture of H₂S in three different superbases systems were studied.Compared with the traditional H₂S liquid absorbent,the absorption system in this paper has low volatility and viscosity as well as high H₂S absorption loading.The research results of this study provide an important reference information for reducing the energy consumption of H₂S capture and improving the utilization value of sulfur resources.