| Coal gasification is the basis of modern coal chemical industry,and is one of the most promising clean coal technologies,which has the advantages of high efficiency,wide application and so on.The pyrolysis is the necessary step of the coal gasification process,because the coal derived fuel gas is reducing atmosphere resulting in the release of elemental mercury is higher than that of the coal combustion process.Elemental mercuryhas serious harm to human health and ecological environment because of its neurotoxicity and bioaccumulation.But elemental mercuryhas properties of high volatile,slightly soluble in water and stable chemical,which resulting in it is the most difficult to be removed comparing with other forms of mercury.Therefore,the sorbents with high efficiency for mercury removal had very important practical significance.At the same time,in order to make the sorbents can be used in the industry,greatly reduce the cost of commercial operation,it is of great practical significance to study on the regeneration of the sorbentsfor mercury removal.In our preparatory work,the mercury removal performance of Pd-Fe bimetallic sorbents prepared by equal volume impregnation,coprecipitation and solvent heat method in the simulated medium was investigated,which proved the excellentmercury removal performance of Pd-Fe bimetallic sorbents.At the same time,the influence of the preparation conditions and the experimental conditions on the performance for mercury removal of the sorbents was further investigated.On this base,this paper chooses Beta molecular sieve,activated carbon and Al2O3 as the carrier,noble metal Pd and Fe2O3 as mercury removal active components,uses volume impregnation and coprecipitation method was used to prepare Pd-Fe bimetallic sorbents.The effects of three kinds of supports on sorbents for mercury removal and regenerations performance and the effect of the atmosphere on the mercury removal were investigated.Combined with XRD,FTIR,XPS,CO pulse adsorption,BET and Hg0-TPD characterization results,to explore the effects carriers.The main conclusions are as follows:?1?Carriers had the obvious influences on Pd-Fe bimetallic sorbents prepared by equal volume impregnation for mercury removal.The activity of Pd-Fe/AC was the best,and the mercury removal efficiency could be maintained above 95% in 400 min.Followed by the Pd-Fe/Beta,the mercury removal efficiency within 400 min could be maintained at more than 90%.The Pd-Fe/Al2O3 sorbent had the worst activity of mercury removal,and it was reduced from 98% to 75% within 400 min.The analysis results showed that the the surface content of active component Pd0 over Pd-Fe/AC is the highest,followed by Pd-Fe/Beta,and that of Pd-Fe/Al2O3 is the lowest.Aslo,the dispersion of Pd over Pd-Fe/AC is the best,and Pd-Fe/Al2O3 is the worst,those lead to the best activity of Pd-Fe/AC for mercury removal,and that of Pd-Fe/Al2O3 is the worst.?2?Carriers had the obvious influences on regeneration performance of Pd-Fe bimetallic sorbents prepared by equal volume impregnation.The regeneration efficiency of Pd-Fe/AC sorbent,the first mercury removal efficiency was above 95%.After 4 cycles of regeneration,the mercury removal efficiency was gradually reduced to about 80%.Followed by the Pd-Fe/Beta sorbent,the first mercury removal activity in 400 min to maintain more than 90%,after 4 cycles of regeneration,its mercury removal efficiency gradually decreased but remained at about 75%.The regeneration performance of Pd-Fe/Al2O3 sorbent was the worst,and the mercury removal efficiency was reduced to 25% after 4 cycles of regeneration.The reason is that the more PdS was generated over Pd-Fe/Al2O3 in the regeneration experiment,which resulted in the decrease of the content of active component Pd0,PdS can not be decomposed to produce Pd0 in the desorption experiment,so the mercury removal efficiency of Pd-Fe/Al2O3 sorbent decreases rapidly and the regeneration performance is poor.?3?Carriers had the small influences on regeneration performance of Pd-Fe bimetallic sorbents prepared by coprecipitation.The first mercury removal activity of Pd-Fe/AC sorbent remained above 95% in the 400 min,after the 4 cycles of regeneration,the mercury removal efficiency decreased gradually,but remained at about 80%.And the Pd-Fe/Beta and Pd-Fe/Al2O3 sorbents,the first mercury removal activity in the 400 min remained above 90%,after the 4 cycles of regeneration,the mercury removal efficiency decreased gradually but remained at about 75%.?4?H2S,H2 and CO atmosphere had the same effects on the Pd-Fe/AC?Pd-Fe/Beta and Pd-Fe/Al2O3 sorbents prepared by coprecipitation method.The H2 S atmosphere had an inhibitation effect on the sorbentsfor mercury removal.The reason might be that the addition of H2 S caused the poisoning of the active component Pd0 result in decrease of the mercury removal efficiency.H2 and CO atmosphere had a positive effect on the mercury removal activity of the sorbents.The possible reason was that the addition of H2 and CO would reduce the active component Pd0,and improved the mercury removal efficiency of the sorbents. |
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