Mechanism Study Of Sulfur,Carbon And Oxygen On The Removal Of Elemenal Mercury Over Activated Coke Loaded Iron-sulphide Adsorbent From Simulated Syngas

Coal is basic energy and important industrial raw materials in China,and advanced coal gasification technology is the cornerstone of the clean and efficient utilization of coal.However,the majority of mercury is released during the coal gasification process in the form of elemental mercury,which is too difficult to control.At present,the coal gas mercury removal adsorbent,represented by metal oxides,has defects such as sulfur poisoning,energy-extensive regeneration consumption,gasification product loss.Moreover,the influence mechanism of multiple components in syngas on mercury removal is still unclear.Therefore,exploratory study of the mechanism of elemental mercury removal from syngas under anaerobic assisted conditions and the interaction mechanism between multiple elements and mercury have important theoretical value and practical significance for the development of clean utilization of coal.This paper combines experiment and theory to systematically study the effect and mechanism of removing elemental mercury from gas by iron sulfur activated coke adsorbent（Fe S/AC）.A series of mercury adsorption experiments from single gas to comprehensive atmosphere were designed,and the influence of gas components（H₂S,CO,H₂,HCl,NH₃,CO₂,etc.）on the heterogeneous reaction of Fe S/AC mercury removal was studied in depth.Through X-ray photoelectron spectroscopy,Fourier transform infrared,programmed gradient heating and other characterization techniques,the physical and chemical properties of the adsorbent surface and the morphology of mercury-removed products were ascertained,and the reaction model of Hg on the surface of Fe S/AC was established by density functional theory,focusing on the sulfur,carbon,and oxygen elements from the atomic level to explain the interaction mechanism of mercury and multiple elements on the surface of Fe S（0 0 1）-S and the mechanism of mercury removal by Fe S,laying a solid foundation for the technology of metal sulfide to remove mercury from gas theoretical basis.Taking advantage of the characteristics that H₂S in gas can quickly sulfide on the surface of sulfur-poor iron sulfur compounds and assist in capturing gaseous Hg⁰,a new idea of Fe S combined with H₂S to efficiently remove mercury in gas under the condition of anaerobic assistance was proposed,and a liquid phase precipitation method was adopted.Fe S/AC was prepared at low temperature,and the influence of gas components on the mercury removal performance of active components and carriers was systematically analyzed.Fe S is dispersed on the surface of active coke as disordered microcrystals with high reactivity.Fe S/AC cooperates with H₂S to achieve efficient removal of elemental mercury in reducing atmosphere.Up to 80.73%～97.55%.The promotion of H₂S is less affected by other gas components;the promotion of HCl is strongly inhibited by NH₃;CO reduces the stability of activated coke mercury removal products,changes the physical and chemical properties of the Fe S/AC surface,and leads to carbon deposition on the adsorbent Poisoning;although the high concentration of H₂eliminates the negative impact of carbon deposition through the methanation reaction,it hinders the dissociation reaction of H₂S and weakens the mercury removal effect.TPD results show that the main mercury removal product of Fe S/AC in simulated gas is environmentally friendlyβ-Hg S,which requires low energy consumption for thermal regeneration and has good adsorption performance after regeneration,which reduces the disposal cost of deactivated adsorbents.In order to study the promotion effect of H₂S synergistically with Fe S on mercury removal and the sudden increase in the H2S on-off experiment,the first-principle method was used to calculate the mercury and sulfur species（crystals with S,H₂S,HS and Sexo）in the Fe S The stable adsorption configuration,thermodynamic parameters,electronic structure characteristics and catalytic reaction mechanism of（0 0 1）-S surface.The sulfur element of the mercury removal product comes from H2S.Since H2S,HS,and S will compete with Hg0 for adsorption sites,but cannot directly oxidize Hg0,the Fe S sorbent has a sulfur hysteresis effect,and the mercury removal efficiency temporarily increases after the sulfur source is interrupted.The process of combining S（ads）and Hg（ads）to form Hg S follows the Langmuir-Hinshelwood mechanism,and needs to overcome the activation energy barrier of 89.82 k J·mol^-1.The Fe S sorbent can better cope with the change of H₂S concentration in the reaction system than the metal oxide sorbent.Using the spin-polarized DFT-D2 method,the adsorption process of Hg was calculated on the carbon preadsorbed Fe S（0 0 1）surface and Fe S/graphene surface,in order to find out the influence mechanism of carbon poisoning on the demercuration of the adsorbent and the support.Mechanism of action of graphite microcrystals on Fe S loading.The adsorption process of elemental carbon produced by CO disproportionation on the Fe S surface is a strong chemisorption,which is beneficial to the adsorption process of Hg;but in the presence of H₂S,C tends to form CS formed by the combination of S,and stays on the surface in the form of-Fe-C-S.The interlayer interaction between Fe S and graphene contributes to the stability of Fe S loading.In order to simulate the microscopic surface of the real adsorbent,the reaction model of Hg on the sulfur defect and oxidized surface was constructed.The sulfur-deficient SV-site Fe has high reactivity,and the adsorption energy of reacting with Hg is-112.94k J·mol^-1.According to the thermodynamic parameters of the model,the introduction of O atoms to the Fe S surface has no obvious promoting or inhibiting effect on the trapping of Hg.Although the oxygen substitution doping will cause defect structures on the surface material,which can increase the surface reactivity,but the S produced by H2S dissociation is more likely to be adsorbed on the SV site,so the sulfur defect structure and Fe S oxidation have little effect on the adsorption of mercury in the gas atmosphere.This paper combines theoretical calculations with experimental results to deepen the understanding of the reaction mechanism for the removal of elemental mercury by metal sulfides in gas,establish the correlation between microscopic surface reactions and macroscopic adsorption characteristics,and accelerate the development of more economical and efficient Adsorbents for mercury removal from coal gas provide reliable theoretical support.This paper combines theoretical calculations with experimental results to deepen the understanding of the reaction mechanism for the removal of elemental mercury by metal sulfides in syngas,establish the correlation between microscopic surface reactions and macroscopic adsorption characteristics,and lay a solid foundation for the development of more economical and efficient adsorbents for capturing mercury from syngas.