The Experimental Research And Mechanism On Composite Sorbent For H₂S Removal From Coal Gas

Coal gasification technology is the one of important technologies for efficient coal utilization,but H₂S in coal gas can corrode the downstream device and cause serious environment pollution.High efficiency H₂S removal from coal gas is one of the key issues to realize high efficiency coal clean utilization.At present,the mid-and high-temperature for H₂S removal technology using solid sorbent is the research focus on coal gas purification.However,the researches on the vairous prepare conditions and active components on sorbent are imperfect,and it lack in-depth and systematic study on the durability of desulfurization performance and the evolution of chemical and physical structure of sorbent.The intensive study on the prepare conditions,active component,the evolution of chemical and physical structure during desulfurization process and reaction kinetic has important theoretical and practical significance for further improving the desulfurization performance and intensive study on the reaction mechanism of high temperature H₂S removal from coal gas.The paper firstly prepared the Mn_xO_y/Al₂O₃ sorbent with good desulfurization performance,and then investigated the effect of calcination conditions（calcination temperature,calcination time,calcination atmosphere）on the desulfurization performance of Mn_xO_y/Al₂O_3,indicating the influence mechanism of evolution of physical and chemical structure on the desulfurization performance of Mn_xO_y/Al₂O₃.The result shows that the calcination temperature and calcination time have slight effect on breakthrough sulfur capacity（BSC）of fresh sorbent.The BSC of Mn_xO_y/Al₂O₃ calcined in H₂ and N₂ are higher than BSC of Mn_xO_y/Al₂O₃ calcined in air.The phase transformation of Al₂O₃,the mutual transformation between Al₂O₃ and Mn Al₂O₄,and the disappearance of some micropores during desulfurization-regeneration cycles could lead Mn_xO_y to be covered by Al₂O₃,which cause the loss of active component.It leads the BSC decreasing during several desulfurization-regeneration cycles.When the calcination temperature of sorbent is 900°C and the calcination time is above 6 h,the tissue structure of sorbent is more stable,which is beneficial for the BSC durability during several desulfurization-regeneration cycles.In order to improve the durability of desulfurization performance of sorbent during desulfurization-regeneration cycles,the paper studied the effect of loading sequence and prepared conditions on the variation of desulfurization performance and physical-chemical structure of Mn based sorbent modified with La during desulfurization-regeneration cycles,which can reveal the effect mechanism of La modification on the sorbent for high temperature H₂S removal.The results show that the La loading methods,La amount and preparation conditions have effect on the desulfurization performance of sorbent.Compared the sorbent with co-impregnation of Mn and La and the sorbent with La loading on the surface of Mn_xO_y/Al₂O₃,Mn_xO_y/Al₂O₃-La with Mn loading on the Al₂O₃ modified with La has better BSC durability.The extent of BSC decreasing of Mn_xO_y/Al₂O₃-La during desulfurization-regeneration cycles decreases with the increasing of La amount while the BSC of fresh sorbents decrease.The formation of La Al O₃ in sorbent modified with La can improve the thermal stability of tissue structure of sorbent,it can inhibit Mn_xO_y being covered with Al₂O₃,leading better BSC durability during desulfurization-regeneration cycles.The Ce modified the sorbent with different loading sequences,aiming to further improve the desulfurization performance of sorbent.The results show that the Ce loading can decrease the binding energy of Mn ion and improve the H₂S adsorption capability of regenerated sorbent,which can significantly increase H₂S removal efficiency of regenerated sorbent during desulfurization-regeneration cycles.The Ce loading sequence has effect on the desulfurization performance of sorbent modified with Ce.The BSC and BSC durability of Ce/Mn_xO_y/Al₂O₃-La with Ce loading on Mn_xO_y/Al₂O₃-4.83La-9 are worse than that of Mn_xO_y/Al₂O₃-4.83La-9,because that the Ce oxides agglomerate on the surface of Ce/Mn_xO_y/Al₂O₃-La would lead the pore blocking.So,the BSC of Ce/Mn_xO_y/Al₂O₃-La is low.The stability of pore structure is poor,which leads less BSC durability of Ce/Mn_xO_y/Al₂O₃-La during desulfurization-regeneration cycles.The Ce⁴⁺in the Ce-Mn_xO_y/Al₂O₃-La with co-impregnation of Mn and Ce based oxides can improve the electron cloud density of Mn ion,which is beneficial for H₂S adsorption,so Ce-Mn_xO_y/Al₂O₃-La has higher BSC than other sorbents.The physico-chemical structure of Ce-Mn_xO_y/Al₂O₃-La is much stable,which leading better BSC durability during desulfurization-regeneration cycles.The paper studied the effect of the reaction temperature,space velocity and gas component in desulfurization process on the desulfurization performance of sorbent to reveal the effect of critical factor on the desulfurization performance of sorbent.H₂ and CO in coal gas almost has no effect on the desulfurization performance of Mn_xO_y/Al₂O₃-900and Ce-Mn_xO_y/Al₂O₃-La.The desulfurization performance of Ce-Mn_xO_y/Al₂O₃-La has slight differences with the various H₂S concentrations,and higher H₂S concentration is harmful for the desulfurization performance of Mn_xO_y/Al₂O₃-4.83La-9.The existence of H₂O or CO₂ is adverse for H₂S removal efficiency and BSC of Mn_xO_y/Al₂O₃-900 and Ce-Mn_xO_y/Al₂O₃-La,but H₂S removal efficiency of Ce-Mn_xO_y/Al₂O₃-La is higher than that of Mn_xO_y/Al₂O₃-900.The BSC of Mn_xO_y/Al₂O₃-900 and Ce-Mn_xO_y/Al₂O₃-La increase with the rising of reaction temperature when the reaction temperature is lower than 850°C.However,when the reaction temperature is above 850°C,the BSC of Mn_xO_y/Al₂O₃-900decreases,while the BSC of Ce-Mn_xO_y/Al₂O₃-La slightly changes with the rising of reaction temperature.The lower weight hourly space velocity（WHSV）has little effect on the BSC of sorbent,but the BSC of Mn_xO_y/Al₂O₃-900 and Ce-Mn_xO_y/Al₂O₃-La decrease with higher WHSV,the extent of BSC decreasing of Mn_xO_y/Al₂O₃-900 is higher than that of Ce-Mn_xO_y/Al₂O₃-La,indicating that Ce-Mn_xO_y/Al₂O₃-La can be applied for high temperature H₂S removal with larger WHSV range.In order to reveal the regeneration characterization of sorbent,the paper systematic analyzed the evolution law of physicochemical structure and regeneration capacity in regeneration process according to the study on the various regeneration atmosphere and regeneration conditions.The results show that the reaction rat with O₂ regeneration is higher than that of regeneration process using SO₂,and the BSC of regenerated sorbent with O₂ regeneration is higher than that of sorbent with SO₂regeneration.The pore structure of regenerated sorbent is destroyed seriously in the regeneration process with excessively high O₂ concentration,leading the lower BSC of regenerated sorbent.The BSC of regenerated sorbent is highest when the regeneration temperature is 850°C.Too high WHSV in regeneration process is unfavorable for the BSC of regenerated sorbent.