| The mercury pollution by the emission of coal-fire is a serious challenge,globally.The activated carbon injection has considered one of the most widely used method,whereas activated carbon developed porous structure has proven to capture the mercury.However,there are some drawbacks that are included but not limited to high cost and low mechanical strength.The activated coke is considered as potential candidate as adsorbent for pollutant removal in industry to replace activated carbon because of its range of sources,abundance,low cost,and easy access.Besides,the activated coke is one of the most widely used adsorbent for the environment protection.In this paper,Zhundong lignite was used as material to to prepare powdery activated coke rapidly and directionally by one-dimensional settling furnace,and further studies the adsorption performance and mechanism of elemental mercury by Zhundong coal-based activated coke.The pores and surface active sites of activated coke can take up mercury,resulting in a loss of activity,and spent activated coke is usually sent to landfill and stack.However,disposal in landfill and stack not only are a waste of resources but also readily produce secondary pollution.Improving reusability of activated coke are two approaches to achieving cost savings.Therefore,the regeneration performance and activated in situ of the spent activated coke were studied in the regeneration process.Exploring different regenertion methods and mechanism,with the purpose of impoving the re-adsorption performance of the activated coke.The elemental mercury and its compounds have important applications in many fields.Hence,it is of great significance to recover and synthesize high additional value mercury-containing compounds from the desorbed mercury.Through present research,screening of activated coke with excellent adsorption performance to the adsorption performance mercury by activated coke to the regeneration performance of the spent activated coke,and finally the recovery and desorption of elemental mercury,the industrial applications can be completed.Which can provide theoretical support for the application of activated coke to control mercury in coal-burning flue gas.Some main conclusions were obtained as follow:The porous structure and functional groups of activated coke were affected by the coal quality through,preparation method and the preparation process.It is found by comparison with other kinds of coal that the Zhundong lignite is abundant raw material,high volatiles,high water content and low price,hence the Zhundong lignite was considered as raw materials that suitable for the preparation of activated coke.In this paper,the Zhundong lignite was used to prepare activated coke with excellent physical and chemical properties in a drop-tube reactor with one-step method.The pore structure is mainly micropores and amount of mesoporous.According to the adsorption theory,mesoporous can provide an adsorption channel for the adsorbent,while micropore can provide the adsorption sites for the adsorbent.Besides,the Zhundong coal-based activated coke with rich functional groups which are conducive to the adsorption of mercury.Hence,the activated coke with advantageous performance which was prepared by the Zhundong lignite.The Hgo-adsorption mechanism of the Zhundong coal-based activated coke was evaluated using a fixed-bed adsorption system,and the effects mechanism of different atmosphere conditions on Hg0 adsorption have been researched systematicly.The enhanced adsorption mechanism by activated coke was explored by optimizing process parameters.The results showed that the active site and pore structure of activated coke was occupiede by SO2 and H2O,resulting in inhibiting effect on Hgo adsorption.Nevertheless,O2,O2+SO2 and O2+H2O+SO2 promoted Hgo removal over the activated coke,respectively.The O2 is considered enhance reactive oxygen(O*)on the surface of activated coke,which can promote the formation of HgO.Under the condition of O2+SO2,the O*and SO2(ads)to form SO3(ads),and then the SO3(ads)reacted with O*,Hg0 to form HgSO3(ads),the reaction might occur spontaneously according to the Gibbs,the is unstable,and finally,HgSO3(ads)reacted with with the O2 to formed HgSO4(ads).Two reaction paths were considered under O2+SO2+H2O condition,the one pathes is the O2 and SO2 adsorbed on the activated coke to form O2(ads)and SO2(ads),and then the O2(ads)further formed O*.Subsequent oxidation and hydration of SO2(ads)and H2O(ads)formed H2SO4(ads)nH2O,and finally,the H2SO4(ads)·nH2O reacted with O*,Hg0 to form HgSO4·nH2O(ads).Another path was the O2(ads)reacted with SO2(ads)to form H2SO3(ads),subsequent reacted with Hgo to from HgSO4(ads).In order to increase the adsorption performance of active coke on Hg0 adsorption,the optimum atmosphere that 6%O2+8%H2O+800ppmSO2,at 70℃ was determined.According to the calculation results of adsorption kinetics,the maximum adsorption capacity is 13.72ug/g.The activated coke after absorbing Hg0 was explored.Firstly,the desorption rules of Hgo and the effects on the activated coke were investigated using microwave and thermal methods,respectively.In the thermal methods under N2 atmosphere the desorption rate,carbon consumption and decomposition amount of functional groups increases with increasing temperature,and the carbon consumption was 0.23%.On the desorption curve,two peaks emerged during the desorption process at 130℃ and 390℃,indicating that there were two kinds of adsorption states on the surface of the activated coke.At 130℃,the peaks on the curve represent the physical adsorption of Hg0 on the activated coke,while the main peaks at 390℃ show decomposition of the peak HgO.In the 5 min,desorption completely of the spent activated coke by microwave method,and the carbon consumption was 0.12%.The re-adsorption performance after regenerations were subsequently investigated,the Hgo removal efficiency of activated coke that desorption by microwave method is higher than that of thermal method.The results indicate that microwave can promote the increase microporous structure,besides inhibit the decomposition of functional groups.The activated coke after enhanced adsorption was desorbed by microwave,and the physical and chemical properties of the activated coke after desorbing were systematically studied.In the microwave desorption process,irradiation inducing HgSO4 to react with carbon to form elemental sulfur and the decomposition of HgO-(C)and HgSO4·nH2O,while the CO and CO2 were formed by the reaction of carbon with sulfate and functional group pyrolysis.Finally,researching on the activation in situ during desorption of mercury on actived coke by heating method,the desorption rule and activation mechanism were explored under different atmosphere conditions.The method exhibited a shorter desorption time(10s)to achieve complete regeneration,and the desorption temperature is 950℃.The results indicate that the re-adsorption performance of activated coke that was desorbed under N2 and O2 had a significantly rduced.HoWever,the physical and che1ical properties which promote Hgo removal over the activated coke were increase,under the desorption atmosphere of H2O,CO2 and SFG,respectively.In order to prevents waste of resources and secondary pollution,the Hg0 that desorbed form the spent activated coke was recovered by condensation or converted into high value-added mercury-containing compounds.An ice-water mixture was used as the condensing agent,the effects of the condensing temperature and carrier gas on recovery efficiency was investigated.The condensation efficiency at 200 mL/min,500 mL/min,800 mL/min,1000 mL/min and 1200 mL/min were 72.36%,86.2%,68.45%,49.61%and 26.32%,respectively.Besides,the recovery efficiency of Hg0 increased with the decrease of the condensation temperature,and the recovery efficiency at 5,0 and-5℃ was 65.24%,86.52%and 97.85%respectively.Due to Hg0 has a saturation vapor pressure under the low temperatures,which makes the mercury vapor unable to achieve complete condensation.In addition,high value-added mercury sulfide and mercury selenide are synthesized at different temperatures.According to thermodynamic calculation,the ΔG of reaction between Hg and S/Se at room temperature is less than zero,S and Hg0 can react at low temperature,and the reaction speed is fast.Although Se and Hg0 can be spontaneously processed,their reaction speed is slowly,so they need to be synthesized at high temperature.O2 has a weak promoting effect on the synthesis of HgS and HgSe,and SO2 and H2O(g)greatly inhibited the synthesis of compounds.Therefore,the desorbed Hg0 should be separated from SO2 and H2O(g)by condensation to obtain high purity Hg0,and then further solidification... |
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