Study On The Desulfurization Of The Alkaline Waste Liquid Containing S^2- With Fe₂O₃/MgO

In the process of ethylene production from high temperature cracking light diesel oil and other raw materials,it is inevitable to produce acid gas such as H₂S,which is mainly absorbed by sodium hydroxide solution,so as to achieve the purpose of removal.However,the alkali liquor after absorbing acid gas such as H₂S contains a large amount of sulfide,so it needs to be desulfurized first to meet the requirements of further purification treatment.Therefore,it is of great environmental significance and practical value to carry out efficient,economic and environmental protection desulfurization treatment of the waste alkali liquor containing S^2-produced in petrochemical or natural gas industry and realize the recycling of alkali liquor.In this paper,magnesium oxide with large specific surface area was prepared as carrier,and appropriate amount of iron oxide was loaded as Fe₂O₃/MgO desulfurizer.The waste alkali liquor containing S^2-was desulfurized by the absorption method used it.The alkali liquor after desulfurization can be recycled,and the desulfurizer after sulfur absorption can be recycled after regeneration.The specific process is as follows:Firstly,MgO carrier with alkali resistance was prepared by microwave method and precipitation method.By XRD and BET characterization,the MgO prepared by precipitation method has typical cubic phase of MgO and large specific surface area,and its grain size is12.2 nm,and the specific surface area can reach 289 m²/g.The optimum conditions for the preparation of MgO by the precipitation method were obtained.Magnesium oxalate was prepared from magnesium acetate and oxalic acid by aqueous solution precipitation method.Magnesium oxalate was heated to 450℃by 10℃/min in flowing air atmosphere and calcined at the constant temperature for 120 min to obtain MgO carrier with large specific surface area.Secondly,Fe₂O₃/MgO desulfurizer was prepared by equal volume impregnation method used the MgO with large specific surface area as carrier.The desulfurization performance of Fe₂O₃/MgO was investigated by using Na₂S solution as simulated waste alkali solution.The results show that the appropriate loading amount of Fe₂O₃ is about 12.5%.The amount of desulfurizer can be added according to the molar ratio of Fe in desulfurizer to S in waste alkali solution of 1.14:1.The suitable conditions for absorption reaction are as follows:temperature 25℃,time60 min.Although the alkalinity of the waste alkali solution decreased slightly,it still had strong alkalinity after desulfurization reaction.After adding appropriate amount of Na OH,the solution could still be used as the absorption solution of H₂S containing tail gas.Thirdly,the regeneration of Fe₂O₃/MgO after sulfur absorption was studied,and the suitable regeneration process was obtained.The results show that the desulfurizer still has good desulfurization performance after one-time regeneration,and the iron/sulfur molar ratio of saturated absorption can reach 1.49:1.After the tenth regeneration,the iron/sulfur molar ratio of the regenerated desulfurizer at absorption saturation can reach 1.82:1,which is about 79.02%of that of fresh desulfurizer.Finally,the transformation and distribution of S element in the process of the absorption desulfurization of the waste alkali liquor and the Fe₂O₃/MgO regeneration were investigated.The results showed that most of S^2-in the solution reacted with Fe³⁺on the absorbent to form iron sulfide and a small amount of S,and a small amount of S element existed in the solution as SO₄^2-.After liquid-phase air oxidation of the collected desulfurized precipitate,the iron sulfide on the desulfurized precipitate can be mostly converted into S,and a small amount of sulfide will be deeply oxidized to form SO₄^2-.After liquid-phase air oxidation,the desulfurized precipitate can be extracted with CS₂solvent to obtain elemental S product.The residual solid can be regenerated by calcining,and there will be a small amount of sulfate deposition in the regenerant.When a certain amount of sulfate deposition is accumulated,it can be removed by ammonia water replacement.