【作者】 梅志坚；

【导师】 王文华；

【作者基本信息】 上海交通大学 ， 环境工程， 2008， 博士

【摘要】 汞作为一种对环境和人类健康有害的重金属元素,成为国内外极为关注的优先控制污染物。目前燃煤汞排放已经成为最大的人为汞污染排放源,中国是世界上少数能源消耗以煤为主的国家,控制燃煤汞排放是我国急需解决的环境问题。燃煤汞排放控制技术包括吸附法和等离子体法等多种,其中吸附法的研究比较多。但目前研究中使用的活性碳及其它改性吸附材料存在吸附容量小、稳定性差、速率低、成本过高和二次污染等问题,严重限制了其实际应用。本论文以氧化铝(AL)和活性碳(AC)为载体并辅以Co和Mn等具催化作用成分的复合吸附材料为研究对象,拟通过实验和理论计算筛选出吸附容量高且吸附速率快的烟气脱汞吸附材料,并对其进行再生试验研究,以降低运行成本和解决废弃材料的二次污染问题。论文首先研究了Co和Mn系列吸附剂的制备方法及条件、其它金属离子和非金属掺杂对吸附去除气态汞性能的影响。通过低温液氮吸脱附等温线(BET)、X射线粉末衍射(XRD)、X射线光电子能谱(XPS)、透射电镜(TEM)、热重分析(TGA)以及程序升温还原(TPR)等多种表征手段,探讨了各种制备因素对吸附材料的化学物理特性的影响,同时对构效关系及氧化还原反应活性位进行了深入的分析。研究表明,对氧化铝基吸附剂而言,Co3O4和MnO2都具有一定的去除汞的能力,但是易被SO2作用而失去活性。通过对Co3O4负载氧化铝吸附剂进行阳离子Cu和Mn的掺杂改性后发现:Cu离子掺杂产物Cu-Co-AL在活性没有太大提高的前提下,其抗SO2作用能力得到了很大增强。NH4Cl/NH4Br对Co-AL和Cu-Co-AL的改性提高了它们去除汞的能力,其中Cu-Co-AL掺杂NH4Cl/NH4Br后活性提高了45%。XPS和XRD表明掺杂NH4Cl/NH4Br后,N原子取代了金属氧化物表面的一部分晶格氧;BET和SEM表明掺杂后的吸附剂具有更大的比表面积。NH4Cl/NH4Br改性的Co-AL和Cu-Co-AL材料吸附汞饱和后,XPS表征显示其表面含有HgCl/HgBr。由此可见,掺杂改性对提高Co-AL和Cu-Co-AL去除汞能力的影响因素包括:比表面增大、N取代其晶体表面的氧以及阴离子的活化。同时,NH4Cl/NH4Br的掺杂提高了Cu-Co-AL材料的寿命,Cu-Co-Cl-AL和Cu-Co-Br-AL的寿命分别为158h和208h,远远高于Cu-Co-AL的26h。对活性炭基吸附剂而言,负载三种不同氯化物CoCl2、MgCl2和MnCl2后,CoCl2/AC表现出最高的去除汞能力,而MgCl2/AC最差,说明不同的阳离子对氯化物改性活性炭的活性产生了很大影响。氧化物MnO2、Co3O4和CuCo2O4在活性炭表面的负载能提高活性炭的高温去除汞的能力。用NH4Cl/NH4Br对Cu-Co-AC改性,所制备的吸附剂Cu-Co-Cl-AC和Cu-Co-Br-AC去除汞的能力得到了进一步的提高。当吸附温度从80℃上升到150℃时,Cu-Co-Cl-AC和Cu-Co-Br-AC去除汞的能力分别从91%和92.1%上升到92.5和100%。Cu-Co-Cl-AC和Cu-Co-Br-AC的寿命分别从Cu-Co-AC的24h上升到90h和105h。载体亦对负载的金属氧化物去除汞的活性有影响,对氧化铝基,Mn-AL表现出最大去除汞的能力;对活性炭基,Co-AC具有最大去除汞的能力。燃媒烟气试验结果表明:负载量为20wt%且300℃活化的CoCl2/AC在150℃时去除气态汞的效率可以达到99%以上,并且具有很好的抗SO2中毒能力; CoCl2/AC的饱和汞吸附容量为171mgHg/gAC,是未改性活性碳的826倍。论文还研究了吸附剂的再生方法。结果表明:Co-AL和Cu-Co-AL吸附剂达到饱和后能够加热再生,其中Co-AL的再生率在90%以上,而Cu-Co-AL的活性在再生过程中可以得到进一步提高。再生产生的高浓度元素汞可以回收利用而降低汞处理的成本,且不会对环境造成二次污染。论文最后利用DFT理论研究了N掺杂对提高Co-AL和Cu-Co-AL的汞吸附性能的原因。计算表明:N掺杂可显著降低汞在Co3O4(110)和CuCo2O4(110)表面化学吸附所需活化能Ea,氧空穴生成能OVFE与Ea之间存在很好的相关性。通过考察元素周期表中不同非金属元素掺杂对Co3O4(110)表面OVFE的影响,发现能提高Co3O4(110)晶格氧活性元素的顺序为:Si > N > Se > S > P > I > Te = C > B,而降低Co3O4(110)晶格氧活性的惰性剂为:Cl > F > Br;但是,Cl、F和Br更倾向于在吸附剂表面与汞结合,本实验中,XPS表征显示NH4Cl/NH4Br改性材料吸附汞后表面存在的HgCl和HgBr亦支持了上述结果。综上所述,本论文研制的氧化催化吸附剂不但可以快速去除烟气中的元素汞,而且材料可以再生,能够消除潜在的二次环境污染问题,该吸附剂在处理烟气脱汞技术中具有潜在的应用前景。更多还原

【Abstract】 Mercury is one of the most toxic pollutants and can easily be released into the atmosphere and severely threat human health and environment. Power plants are the largest mercury discharging resources. In China, coal is the major one-off energy and Hg pollution from combustion in air is severe environmental issue.Many technologies have been applied to control the mercury emission of coal-fired power plants, such as air pollution control devices (APCDs), sorbent injection (SI), electro-catalytic oxidation (ECO), photochemistry oxidation, oxidant injection, and catalytic oxidation, etc. Among them, SI is the most promising technology. However, there exist several problems with activated carbon and other sorbents such as low adsorption capacity, instability, low adsorption velocity, high operation costs and second pollution, which strictly confine SI application. In this paper, Co, Mn serial sorbents are selected as research object. High adsorption capacity and velocity materials for mercury are screened out, and the regeneration tests are processed to lower the operation costs and second pollution problem.Firstly, the preparation methods and qualification of Co, Mn serial sorbents, metal doping and non-metal doping effects on sorbent’s mercury removal ability are studied. How the preparation factors affect sorbents’chemical and physical property is investigated by BET、XRD、XPS、TEM、TGA and TPR. At the same time, the relationship between construction of sorbents and their mercury removal ability are analyzed.(一) Al2O3 carrier sorbentMnO2 and Co3O4 show some activity to remove the Hg from the simulated gas, but they lost activity when SO2 exist. The doping of Co3O4 by Cu can generate Cu-Co-AL which has similar Hgo removal ability to Co3O4 but better SO2 anti-poisoning ability. NH4Cl/NH4Br doping is beneficial to Co-AL and Cu-Co-AL’s Hgo removal ability, especially the dopant NH4Cl/NH4Br doped Cu-Co-AL whose Hg removal ability can increase 45%. The XPS and XRD results manifest that O atom of Co3O4 and CuCo2O4 surface has been replace by N atom, BET and SEM results manifest that NH4Cl/NH4Br doped Co-AL and Cu-Co-AL have higher specific surface area. Therefore, the Hgo removal ability improvement of NH4Cl/NH4Br doped sorbent can attribute to above phenomenon. Except that, the XPS results of spent NH4Cl/NH4Br doped Co3O4 or CuCoO4 manifest that anion Cl-/Br- participate the Hgo oxidation reaction. Cu-Co-Cl-AL and Cu-Co-Br-AL’s longevity reach 158 h and 208 h, respectively, which are far longer than Cu-Co-AL’s 26 h.(二) AC carrier sorbentAmong the three different chlorine-impregnated AC, CoCl2/AC shows the highest Hgo removal ability and MgCl2/AC show the lowest Hgo removal ability. The loading of metal oxides on AC can increase AC’s Hg removal ability. When oxides loaded on Al2O3, Mn-AL shows the highest Hgo removal ability. However, when oxides loaded on AC, Co-AC shows the highest Hgo removal ability. Cu-Co-Cl-AC and Cu-Co-Br-AC show higher Hgo removal ability than Cu-Co-AC. When adsorption temperature increases from 80℃to 150℃, Cu-Co-Cl-AC and Cu-Co-Br-AC’s Hgo removal ability increase from 91% and 92.1% to 92.5% and 100%, respectively. Cu-Co-Cl-AC and Cu-Co-Br-AC’s breakthrough time increase from Cu-Co-AC’s 24 h to 90 h and 105 h, respectively.(三) the experiments under actual flue gasThe experiment results show that when the loading value is 20 wt%, the mercury removal ability of CoCl2/AC activated at 300℃reach 99% at 150℃,and has perfect anti-SO2 ability. The mercury adsorption capacity of CoCl2/AC is 171mgHg/gAC,and 826 times as AC. CoCl2/AC was applied to the actual flue gas Hg adsorption. The combustion test was carried out on small-scale equipment in lab. The result showed that improved AC adsorbed 97% of the gaseous element Hg, compared with 3% of element Hg adsorbed by solution, which indicated that improved AC was feasible in the actual gas treatment. Secondly, spent sorbents can be regenerated by heating. Both Co-AL and Cu-Co-AL can be regenerated. The regeneration ratio of Co-AL is above 90%,and Cu-Co-AL’s activity can be improved during the process of regeneration. The regenerated element mercury can be collected by cold trap or react with other chemicals. The collected mercury can be sold to decrease the operation costs, and eliminate the second pollutions.DFT study show that N-doping can decrease the chemical adsorption activation energy (Ea) on Co3O4(110) and CuCo2O4(110) surface. There exist correlation between Ea and OVFE. Through investigating the OVFE variation of non-metal doped Co3O4(110), we find that the non-metal, which can increase the lattice oxygen activity of Co3O4(110) surface, include as follows: Si > N > Se > S > P > I > Te = C > B,and the non-metal, which can decrease the lattice oxygen activity of Co3O4(110), include as follows: Cl > F > Br。In conclusion, catalytic oxidation technique can not only remove element mercury pollutants effectively but also eradicate the potential second pollution. The technique might be practically applied in the field of flue gas mercury control.更多还原