Study Of Manganese-based Binary Metal Oxides And Their Capability For Gaseous Elemental Mercury Capture

Due to the high toxicity, persistence, transportability and bioaccumulation,mercury has attracted increasing attentions since Minamata Disease occured. In recentyears, more national or international treaties on mercury have been issued aiming toreduce mercury pollution including “Minamata Convention”. These treaties hasbrought huge pressure to China, which is the biggest mercury emission country in theworld. Coal is the most important energy source in the current and a near-futureenergy structure of China, therefore, coal-fired related mercury emission has becomethe key point for mercury control in China. Actually, China government has alreadytaken some measures to reduce mercury emission from coal-fired power plant,including revising “Emission Standard of Air Pollutant for Thermal Power Plants”(GB13223-2011). The maximum mercury emission concentration is capped in thisstandard. So far, the main technology for mercury emission control falls into thefollowing two groups:1. Oxidation technology. Firstly oxidize the flue gas elementalmercury catalytically or by injecting oxidant, and then remove the oxidized mercurythrough existing wet flue gas desulfurization system;2. Adsorption method. Removemercury by adsorbent, currently, activated carbon injection is the most testedadsorption technology, and halide is found very important for mercury adsorption.Since halide concentration in coal of China is usually relative low, removal efficiencyof activated carbon injection technology may depreciate if it is used in China.Additionally, oxidized technology only transfers mercury from flue gas intodesulfurization solution or gypsum and may cause the secondary pollution. In otherword, each technology has its own shortcomings and merits, but none has beenproved universal in all flue gas condition. Therefore, developing novel, high efficiency technology with independent intellectual property rights is of significance.In this work, a series of manganese-based binary metal oxides with high mercurycapacity and good regenerablity were prepared and characterized, the adsorption andoxidation mechanism of mercury on the sorbents surface was investigated, moreover,an process based on electro-filter precipitator for mercury removal was proposedbased on the good regenerability of the sorbents in order to reduce the operational costof the power plant. The main contents of this dissertation are listed below:Three kind of manganese oxides were prepared using different manganese salt asmanganese source. Based on the adsorption experiment and characterization results,the relationship between mercury adsorption performance and physiochemicalproperty was built. It was found that low temperature facilitated the mercuryadsorption on sorbent surface and manganese prepared using different manganese saltshowed different physiochemical property and different adsorption performance; highvalence manganese would benefit the adsorption and oxidation of mercury on sorbentsurface; simple heating treatment could release the adsorbed mercury from sorbentsurface and achieve a facile regeneration of the sorbent;A series of Zr-Mn binary metal oxides with different mercury content wereprepared, characterized and their capabilities for elemental mercury removal wereinvestigated. Based on the adsorption experiment and characterization results, therelationship between mercury adsorption performance and physiochemical propertywas built. It was found that manganese was the main component for mercuryadsorption and oxidation in Zr-Mn system, Zr could not only increase the BETspecific surface area of the sorbent but also enhance the reducibility of the sorbentwhich may benefit the mercury adsorption and oxidation on sorbent surface atrelatively low temperature; the adsorbed mercury on the sorbent surface could bereleased by heating treatment, however, the reusability was found not good enoughafter simple heating treatment; It was also found that most of the mercury capacity ofthe sorbent could be recovered by a simple washing treatment after heating, themechanism was discussed; A series of manganese-based Ce-Mn binary metal oxides with differentmanganese content were prepared, characterized and their capabilities for elementalmercury removal were investigated. Based on the adsorption experiment andcharacterization results, the relationship between mercury adsorption performance andphysiochemical property was built. It was found that manganese was the maincomponent for mercury adsorption and oxidation, as an important auxiliarycomponent, the doping of Ce, a rare earth element, could not only increase the BETspecific surface area of the sorbent but also enhance the reducibility of the sorbentwhich may benefit the mercury adsorption and oxidation on sorbent surface atrelatively low temperature; moreover, Ce-Mn binary metal oxides also showed goodregenerability through simple heating treatment; additionally, the regenerated sorbentalso demonstrated good reusability in adsorption-regeneration-adsorptionexperiments.A series of Sn-Mn binary metal oxides with different manganese content wereprepared, characterized and their capabilities for elemental mercury removal wereinvestigated. Based on the adsorption experiment and characterization results, therelationship between mercury adsorption performance and physiochemical propertywas built. It was found that manganese was also the main component for mercuryadsorption and oxidation in Sn-Mn system, Sn could not only increase the BETspecific surface area of the sorbent but also enhance the reducibility of the sorbent andimprove the acidity on sorbent surface, as a result, mercury adsorption capacity of thesorbent was increased; interestingly, the doping of Sn could expand the activetemperature window of the sorbent for mercury adsorption.Furthermore, a model for calculation of mercury desorption activation energy wasbuilt based on Hg-TPD experiments, aiming to quatify the regenerablity of thesorbent.