NH_4Cl改性活性炭脱除气态Hg~0的特性分析
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摘要
制备了原始活性炭与NH_4Cl改性活性炭,对其进行了物化特性表征,在固定床汞吸附实验台上考察了N2气氛下颗粒粒径、NH_4Cl溶液浓度、SO_2、CO_2等因素对活性炭脱除Hg~0性能的影响。研究结果表明:NH_4Cl浸渍改性没有造成活性炭孔隙结构的明显变化,但使得Cl元素成功担载到活性炭表面;随着颗粒粒径增大,活性炭吸附Hg~0的外部传质速率、内部扩散速率均降低,较小的颗粒粒径有利于活性炭脱汞;由NH_4Cl改性在活性炭表面所产生的卤素官能团(AC-Cl)能够有效地氧化烟气中的Hg~0,增强了活性炭对于Hg~0的氧化吸附作用;SO_2能有限地促进原始活性炭的脱汞性能,对NH_4Cl改性活性炭脱汞性能则表现出先促进后抑制并主要体现抑制作用的现象,并且抑制作用随SO_2浓度的增大而增加;CO_2由于能在活性炭表面极化,且能与氨基官能团反应生成有利于吸附汞的羰基,促进了活性炭的脱汞性能。
A raw activated carbon and NH_4Cl modified activated carbon were prepared and characterized. Gas-phase Hg~0 removal performance of the sorbent samples were evaluated in a fixed-bed reactor under N2 atmosphere. Effect of sorbent size, NH_4Cl solution concentration, SO_2, and CO_2 on mercury removal was explored. The results showed that the porous structure of raw activated carbon does not change during NH_4Cl modification process, but some Cl-containing group remains on activated carbon surface. With the increase of sorbent size, the external mass transfer coefficient and the internal diffusion rate decreases, which indicate that smaller particle size is beneficial to improve mercury removal performance of activated carbon. Due to the generated Cl-containing functional groups can oxidize gaseous Hg~0 effectively, the oxidation adsorption capability of NH_4Cl-impregnated activated carbon is enhanced. SO_2 in flue gas promotes mercury removal of raw activated carbon, but for NH_4Cl modified activated carbon, SO_2 first promotes mercury removal then inhibits. The inhibition on mercury removal by SO_2 was increased with the concentration of SO_2. Due to the polarization on the surface of activated carbon and the reaction with amino functional groups to form carbonyl groups, CO_2 in flue gas improves mercury removal capability of activated carbon.
A raw activated carbon and NH_4Cl modified activated carbon were prepared and characterized. Gas-phase Hg~0 removal performance of the sorbent samples were evaluated in a fixed-bed reactor under N2 atmosphere. Effect of sorbent size, NH_4Cl solution concentration, SO_2, and CO_2 on mercury removal was explored. The results showed that the porous structure of raw activated carbon does not change during NH_4Cl modification process, but some Cl-containing group remains on activated carbon surface. With the increase of sorbent size, the external mass transfer coefficient and the internal diffusion rate decreases, which indicate that smaller particle size is beneficial to improve mercury removal performance of activated carbon. Due to the generated Cl-containing functional groups can oxidize gaseous Hg~0 effectively, the oxidation adsorption capability of NH_4Cl-impregnated activated carbon is enhanced. SO_2 in flue gas promotes mercury removal of raw activated carbon, but for NH_4Cl modified activated carbon, SO_2 first promotes mercury removal then inhibits. The inhibition on mercury removal by SO_2 was increased with the concentration of SO_2. Due to the polarization on the surface of activated carbon and the reaction with amino functional groups to form carbonyl groups, CO_2 in flue gas improves mercury removal capability of activated carbon.
引文
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[3]孙青柯,黄亚继,王靓,等.磁性Fe3O4-Ag复合纳米颗粒吸附剂脱汞性能实验研究[J].化工进展, 2017, 36(3):1101-1106.SUNQK,HUANGYJ,WANGL,etal.Experimentalstudyon mercuryremovalefficienciesofmagneticFe3O4-Agcomposite nanoparticles[J]. Chemical Industry and Engineering Progress, 2017,36(3):1101-1106.
[4]尹建军,段钰锋,王运军,等.生物质焦的表征及其吸附烟气中汞的研究[J].燃料化学学报, 2012, 40(4):390-396.YIN J J, DUAN Y F, WANG Y J, et al. Characterization of biomass charanditsmercuryadsorptionperformance[J].JournalofFuel Chemistry and Technology, 2012, 40(4):390-396.
[5]LEESS,LEEJY,KEENERTC.Bench-scalestudiesofin-duct Mercurycaptureusingcupricchloride-impregnatedcarbons[J].Environ.Sci.Technol., 2009, 43(8):2957-2962.
[6]任建莉,周劲松,骆仲泱,等.活性炭吸附烟气中气态汞的实验研究[J].中国电机工程学报, 2004, 24(2):171-175.RENJL,ZHOUJS,LUOZY,etal.Anexperimentalstudyon activatedcarbonsorbentforgas-phasemercuryremovalfromflue gas[J]. Proceedings of the CSEE, 2004, 24(2):171-175.
[7]LUJ,CHENEYMA,WUF,etal.Effectsofchemicalfunctional groups on elemental mercury adsorption on carbonaceous surfaces[J].Journal of Hazardous Materials, 2011, 186:108-113.
[8]杨宏旻,张斌,侯文慧,等.负载Cu O/Cl活性炭的气态汞脱除特性[J].南京航空航天大学学报, 2009, 41(6):814-818.YANG H M, ZHANG B, HOU W H, et al. Removal Characteristics ofvapour-phaseelementalmercurythroughactivecarbon-supported CuO/Cl[J].JournalofNanjingUniversityofAeronautics&Astronautics, 2009, 41(6):814-818.
[9]DIAMANTOPOULOU I, SKODRAS G, SAKELLAROPOULOUS G P.Sorptionofmercurybyactivatedcarboninthepresenceoffluegas components[J]. Fuel Processing Technology, 2010, 91(2):158-163.
[10]MILLER S J, DUNHAM G E, OLSON E S, et al. Flue gas effects on a carbon-based mercury sorbent[J]. Fuel Processing Technology, 2000,65(66):343-363.
[11]YANG H, XU Z, FAN M, et al. Adsorbents for capturing mercury in coal-firedboilerfluegas[J].JournalofHazardousMaterials,2007,146(1):1-11.
[12]ZENG H C, JIN F, GUO J. Removal of elemental mercury from coal combustionfluegasbychloride-impregnatedactivatedcarbon[J].Fuel, 2004, 83:143-146.
[13]徐欢,沈伯雄,张笑,等.化铵改性竹炭对单质汞吸附性能的影响[J].环境工程学报, 2017, 11(6):3647-3652.XUH,SHENBX,ZHANGX,etal. Effects onelementalmercury adsorptioncharacteristicsofbamboocharcoalmodifiedby ammonium halide[J]. Chinese Journal of Environmental Engineering,2017, 11(6):3647-3652.
[14]梅志坚.控制烟气汞排放的钴锰系列吸附剂研究[D].上海:上海交通大学, 2008.MEIZJ.ThestudyofCo、Mnseriessorbentfortheremovalof elementmercuryfromsimulatedfluegas[D].Shanghai:Shanghai Jiaotong University, 2008.
[15]ZHOU Q, DUAN Y F, ZHAO S L, et al. Modeling and experimental studies of in-duct mercury capture by activated carbon injection in an entrained flow reactor[J]. Fuel Processing Technology, 2015, 140(21):304-311.
[16]SKODRASG,DIAMANTOPOULOUI,etal.Kineticstudiesof elemental mercury adsorption in activated carbon fixed bed reactor[J].Journal of Hazardous Materials, 2008, 158(1):1-13.
[17]谢菲.球形活性炭对CO2吸附行为研究[D].上海:华东理工大学,2011.XIEF.AdsorptionperformanceofCO2onsphericalactivated carbon[D].Shanghai:EastChinaUniversityofScienceand Technology, 2011.
[18]LI Y H, LEE C W, GULLETT B K. Importance of activated carbon’s oxygen surface functional groups on elemental mercury adsorption[J].Fuel, 2003, 82:451-457.