| Sewage sludge is one of the main by-products in the process of sewage treatment.The sludge contains certain harmful substances,such as heavy metals,organic pollutants,plastics and etc.,if it is disposed improperly,it will result in serious environmental and ecological harm.In addition,the sludge is also a kind of resource,if it is utilized rationally,it can turn waste into treasure,in which pyrolysis is an effective method.The sludge activated carbon was a kind of loose porous carbon material,which was prepared through pyrolysis and activation process.The activated carbon prepared shows excellent physical and chemical properties,such as larger specific surface area,diverse species of surface functional groups,and rich pore structure.These excellent properties provide a broad application space and prospect for it.In this study,the method of microwave one-step pyrolysis/physical activation was adopted to prepare activated sludge char（ASC）,and its adsorption characteristics of hydrogen sulfide were studied.In order to further improve the saturated H2S adsorption capacity of sludge char samples,N was added to the samples modify ASC to prepare Nitrogen-doped sludge char（NSC）.In this paper,the possibility of one-step microwave pyrolysis/physical activation was explored.Through orthogonal experiment,four factors including pyrolysis temperature,activation agent type/flow rate,residence time in the constant temperature level and sludge moisture content were taken into account on the adsorption effect of hydrogen sulfide through ASC samples,and the influence of different adsorption conditions on the adsorption of hydrogen sulfide by ASC was also conducted.The internal adsorption mechanism of hydrogen sulfide by ASC samples was explored,and the adsorption effect of hydrogen sulfide through NSC samples was also studied.Through the experimental research,the following conclusions are drawn:（1）The orthogonal experiment results showed that the most significant factors affecting the H2S saturated adsorption capacity of steam-ASC and CO2-ASC samples were the residence time and the flow rate of activation agent,respectively.The results of H2S adsorption kinetics showed that the H2S saturated adsorption capacity of steam-ASC（3.507-9.149 mg/g）showed significantly higher than that of CO2-ASC（1.594-3.451 mg/g）at the pyrolysis/physical activation temperature range of 500-700℃.2)FTIR analysis showed that the functional groups of different ASCs were similar,and steam/CO2 activation could remove the acid methylene functional groups,making the alkaline characteristics of the sample surface more obvious and more beneficial for the H2S adsorption,and physical adsorption played a dominant role in the adsorption process.At the same time,the XPS results showed that the formation of sulfate,sulfone and sulfide on ASC further proved that there was a small amount of chemical adsorption in the adsorption process of H2S by ASC.（3）Nitrogen doped process has a significant impact on improving the H2S adsorption performance of sludge char.The H2S saturated adsorption capacity of the optimal N-doped sludge char（NSC-7）was 1.04 times that of the ASC sample（steam-ASC（No.5））.The results showed that nitrogen doped was an important method for the modification of H2S adsorbents.（4）The results of N2 adsorption/desorption isotherms and XPS analysis results showed that the BET surface area of the sample（NSC-7）decreased by 33.4%（from 169.9m2/g to 113.1m2/g）compared with that of steam-ASC（No.5）,which may reduce the physical adsorption of the sample to some extent.However,Nitrogen addition can enhance the chemical adsorption on the sample surface.The XPS results also indirectly proved this point.According to the XPS spectra of S2p of the used NSC sample,only three S functional groups of sulfate,sulfone and sulfoxide were found,and no sulfide functional groups existed,indicating that H2S reacted more fully on the surface of NSC,and the sulfide was further oxidized into a higher sulfur state.（5）Thermal regeneration was carried out on the adsorbed saturated ASC（experiment subject:steam-ASC（No.5）and CO2-ASC（No.6’））,and the experimental conditions of the regeneration experiment were as follows:N2 atmosphere,residence time of 60 minutes,heating temperature of500℃.After the first regeneration,the H2S saturated adsorption capacity could reach 86%of the initial adsorption capacity,and after the third regeneration,the H2S saturated adsorption capacity could still reach 64%of the initial adsorption capacity.It showed that the sludge char has excellent regeneration performance. |
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