本文關鍵詞：銀改性復合氧化物催化氧化煙氣中零價汞的研究　出處：《上海交通大學》2015年博士論文　論文類型：學位論文

  更多相關文章： 零價汞 催化氧化 銀摻雜 活性氯

【摘要】：燃煤過程所造成的汞排放及污染問題,近年來已引起國際社會的廣泛關注。為此,我國修訂了《火電廠大氣污染物排放標準》(GB13223-2011),并對燃煤電廠的汞排放提出了具體限制要求。將煙氣中的零價汞(Hg~0)氧化為二價汞(Hg2+),繼而通過現(xiàn)有的空氣污染控制裝置進行聯(lián)合去除,是目前去除Hg~0的較好的方法。針對我國燃煤氯含量普遍較低及傳統(tǒng)催化劑較窄的活性溫度窗口等問題,開發(fā)高效及寬活性溫度窗口的催化劑具有重要意義。本文通過摻雜銀(Ag)作為改性組分,旨在研制能對Hg~0高效轉(zhuǎn)化的催化劑,通過氧化實驗對其去除Hg~0的性能進行評價,并考察了溫度及煙氣組分對催化劑性能的影響,同時通過物理化學表征以及汞和氯的活性分析,進而探討催化劑在不同溫度區(qū)間氧化Hg~0的機制,為催化劑的實際應用提供理論依據(jù)。論文主要得到了以下結(jié)論:1.采用Ag改性V2O5-TiO2(V-Ti)催化劑來提高催化劑氧化Hg~0的性能,并通過添加分散劑來獲得均勻分散的銀納米顆粒以進一步提高催化劑的氧化能力。研究發(fā)現(xiàn)在催化劑制備過程中,添加聚乙烯吡咯烷酮(PVP)可以進一步提高銀納米顆粒的分散度,且制備的銀納米顆粒尺寸更小,更有利于Ag,V和Ti元素的協(xié)同作用而具有最高的催化效率,而當添加離子液體([bmim][BF4])后,則產(chǎn)生較大的銀納米顆粒,導致催化劑的比表面積變小,催化氧化Hg~0性能比Ag-V-Ti稍差些;銀物種主要以金屬銀的形態(tài)存在,其本身的氧化性能不高,主要作為助催化劑來提高活性組分釩的氧化能力。2.采用銀改性一系列選擇性催化還原(SCR)催化劑,并考察了復合催化劑的氧化Hg~0性能。結(jié)合表征結(jié)果及氧化實驗,發(fā)現(xiàn)V2O5-MoO3-TiO2(V-Mo-Ti)氧化的效率比V2O5-WO3-TiO2(V-W-Ti)高,元素鉬具有抗硫的特性,加銀能進一步增強V-Mo-Ti的性能,5ppmv(1)HCl時,摻雜0.5%Ag可以達到90%的氧化Hg~0效率,催化效率提高20-40%左右,活性溫度窗口也得到拓寬(150-450℃);Ag和Mo增強了催化劑吸附Hg~0的能力;Ag-Mo/V-Ti在只有氧氣(O2)和氮氣(N2)存在時也具有一定的氧化能力,且低溫性能更好,HCl是反應的主要催化組分;Ag-Mo/V-Ti氧化Hg~0在低溫時發(fā)生Semi-Deacon反應,而高溫時發(fā)生Full-Deacon反應,此外,吸附的氧氣和活性氧也可以氧化Hg~0生成氧化汞,繼續(xù)和氯化氫反應生成氯化汞。3.采用銀改性MoO3-TiO2(Mo-Ti)催化劑,并考察了復合催化劑的氧化Hg~0性能。當結(jié)合銀和鉬后,Ag(2%)-Mo-Ti在各個溫度區(qū)間氧化Hg~0的性能都有顯著的提高,然而催化劑在低溫時性能更高,更適合在低溫下操作。組分分析表明,HCl是主要的催化組分,催化劑在O2不存在時也有很高的催化效果,此外,催化劑有很好的抗硫能力;低溫時,吸附的活性氯和吸附的Hg~0通過LangmuirHinshelwood機制發(fā)生反應;而且,銀和鉬結(jié)合生成鉬酸銀,有利于晶格氧轉(zhuǎn)為化學吸附氧進而參與反應,也提高了催化劑的氧化性能。4.采用銀改性CeO2-TiO2(Ce-Ti)催化劑,并考察了復合催化劑的氧化Hg~0性能。結(jié)合表征結(jié)果及氧化實驗,發(fā)現(xiàn)銀納米顆粒負載在載體二氧化鈦表面,且銀主要是以金屬銀的形式存在,它能使元素鈰保持更多的高價態(tài)Ce(IV),提高了催化劑的氧化能力并降低催化劑的氧化還原溫度;Ag-Ce-Ti在高溫時有更強的氧化能力,且HCl是主要的催化組分,HCl在低溫時以活性氯的形式參與反應,400℃左右才有氯氣產(chǎn)生并參與反應;催化劑在低溫時抗硫性能較好,高溫時SO2極大的抑制Hg~0的氧化;結(jié)合Ag、Mo和Ce,催化劑在各個溫度區(qū)間氧化Hg~0的效率都很高,且抗硫性能良好。5.引入AgI-TiO2來去除煙氣中的Hg~0,并通過摻雜Ag進一步提高催化劑的性能及穩(wěn)定性。AgI-TiO2具有很高的氧化Hg~0效率,在350℃時通入5ppmvHCl效率達到100%,強于KI-Ti;摻雜Ag能顯著延長AgI-TiO2催化劑高性能的時間,2%的Ag含量較合適,氧化Hg~0的效率在10h后仍能達到90%以上;HCl是反應的主要組分,且O2是必要的;通入氯化氫時,銀對氯化氫有催化作用,導致活性氯的產(chǎn)生,然后氧化碘離子為活性碘,活性碘和Hg~0形成中間體Hg-I*進而加速Hg~0的氧化,然后,氯轉(zhuǎn)化中間體為最終產(chǎn)物HgCl2,活性碘和銀又生成碘化銀,保持Ag(2%)-AgI-Ti中的碘含量;此外,Ag(2%)-AgI-Ti具有很好的熱穩(wěn)定性以及化學穩(wěn)定性。6.對催化劑的NH3氧化及脫硝性能進行了分析,發(fā)現(xiàn)Ag(5%)-Ti在各個溫度下都具有很高的NH3氧化能力,且不同的溫度時氧化NH3的機理不同,低溫時N2O產(chǎn)量較多,而高溫時NO產(chǎn)量較多;催化劑的脫硝性能隨溫度呈先升高后降低的趨勢,在250℃時的脫硝效率最高,高溫時對脫硝會產(chǎn)生不利的影響,總體來說Ag適用于逃逸NH3的去除。同樣,摻雜Ag能提高V-Mo-Ti、Mo(5%)-Ti和Ce(5%)-Ti的NH3氧化能力,且在高溫時提高Mo(5%)-Ti和Ce(5%)-Ti催化劑氧化NH3的選擇性能;摻雜Ag后,低溫時V-Mo-Ti催化劑的脫硝性能提高,而高于300℃時,催化劑的脫硝性能又降低;在Mo(5%)-Ti和Ce(5%)-Ti上摻雜Ag后,不利于催化劑脫硝反應的進行;Ag(2%)-AgI-Ti氧化NH3的能力隨溫度的升高而增強,催化劑氧化NH3主要轉(zhuǎn)化為NO,而兩者之間幾乎不發(fā)生反應,不適合用于脫硝反應中。本文制備的催化劑在低含量HCl時都具有較高的氧化Hg~0能力,且活性溫度窗口都較寬,具有較強的實際應用前景。
[Abstract]:Mercury emission and pollution problems caused by coal combustion, in recent years has caused widespread concern in the international community. Therefore, China revised the "thermal power plant air pollutant emission standards" (GB13223-2011), and put forward specific requirements to limit mercury emissions from coal-fired power plants. The flue gas in Hg0 oxidation (Hg~0) two mercury (Hg2+), and then through the existing air pollution control device for combined removal, is a good method of the removal of Hg~0. According to China's coal chlorine content is generally low and narrow the traditional catalyst active temperature window and other issues, has important significance to the catalyst efficiency and hair wide active temperature window. This paper the silver doped (Ag) as a modified component, aimed at the development of catalyst for Hg~0 energy efficient conversion, the performance was evaluated by the removal of Hg~0 on the oxidation experiment, and the effects of temperature and smoke components on the catalyst performance At the same time, through physical and chemical characterization and activity of mercury and chlorine analysis, and to explore the mechanism of oxidation of Hg~0 catalysts in different temperature range, to provide a theoretical basis for the practical application of catalyst. The main results are as follows: 1. using Ag modified V2O5-TiO2 (V-Ti) catalyst to improve the performance of catalytic oxidation of Hg~0, and by adding dispersant to obtain silver nanoparticles dispersed in order to further improve the oxidation ability of the catalyst. The study found that in the preparation process of the catalyst, adding polyvinylpyrrolidone (PVP) can improve the dispersion of silver nanoparticles and silver nanoparticles, smaller size preparation, more conducive to the synergistic effect of V and Ti Ag. The element has the highest catalytic efficiency, and when adding ionic liquid ([bmim][BF4]), produces larger silver nanoparticles, resulting in the surface area of the catalyst decreases, catalytic oxidation Hg~0 performance is slightly worse than Ag-V-Ti; silver species existed mainly in the form of metallic silver oxide, its performance is not high, mainly as a catalyst to improve active component vanadium oxidation ability of.2. by modification of a series of selective catalytic reduction (SCR) catalyst was studied and the oxidation performance of Hg~0 composite catalyst. According to the characterization results and oxidation experiments, found that V2O5-MoO3-TiO2 (V-Mo-Ti) oxidation efficiency of V2O5-WO3-TiO2 (V-W-Ti), has the characteristics of sulfur element molybdenum, silver can further enhance the performance of V-Mo-Ti, 5ppmv (1) HCl, doped 0.5%Ag can reach 90% Hg~0 oxidation efficiency, improve the efficiency of catalytic activity about 20-40%. The temperature window has been widening (150-450 C); Ag and Mo enhanced the ability of adsorption of Hg~0 catalyst; Ag-Mo/V-Ti (O2) only in oxygen and nitrogen (N2) is also an oxidant, low temperature and better performance, HCl Is the main component of the catalytic oxidation of Hg~0; Ag-Mo/V-Ti Semi-Deacon reaction at low temperature, and high temperature Full-Deacon reaction, in addition, the adsorption of oxygen and active oxygen can also Hg~0 oxidation reaction to mercuric oxide, and hydrogen chloride generated by mercuric chloride.3. Silver Modified MoO3-TiO2 (Mo-Ti) catalyst, and the effects of the oxidation performance of Hg~0 composite catalyst. When combined with silver and molybdenum, Ag (2%) can significantly improve -Mo-Ti performance in each temperature range of Hg~0 oxidation catalysts, but at low temperature is higher, more suitable for low temperature operation. Group analysis showed that HCl is the main constituent of catalyst, catalyst has catalytic effect very high, when there is no O2 in the catalyst has good anti sulfur ability; when the temperature is low, the adsorption of chlorine and the adsorption of Hg~0 by LangmuirHinshelwood reaction mechanism; moreover, silver and molybdenum combine to form molybdenum Acid silver, in favor of lattice oxygen into the chemical adsorption oxygen and then participate in the reaction, but also improve the oxidation performance of.4. catalysts modified by silver catalyst CeO2-TiO2 (Ce-Ti), and the effects of the oxidation performance of Hg~0 composite catalyst. According to the characterization results and oxidation experiments revealed that silver nanoparticles loaded on the carrier surface of titanium dioxide and silver mainly is there the silver form, it can keep high valence cerium more Ce (IV), improve the oxidation ability of catalyst and reduce the oxidation of the catalyst reduction temperature; Ag-Ce-Ti has stronger oxidation ability in high temperature, and HCl is the main catalytic group, HCl at low temperature with active chlorine in the form of reaction at the temperature of 400 DEG C to produce chlorine and sulfur resistance reaction; good catalyst at low temperature, the oxidation inhibition of Hg~0 SO2 greatly at high temperature; combined with Ag, Mo and Ce, the catalyst at different temperature range The efficiency of Hg~0 is very high, and the sulfur resistance of good.5. AgI-TiO2 is used to remove the Hg~0 in the flue gas, and by doping Ag to further improve the performance and stability of.AgI-TiO2 catalyst with Hg~0 oxidation efficiency is very high, at 350 degrees C in 5ppmvHCl efficiency reached 100%, stronger than the KI-Ti doped Ag can significantly prolong the time; AgI-TiO2 catalysts with high performance, the content of Ag 2% is appropriate, the efficiency of oxidation of Hg~0 can reach more than 90% after 10h; HCl is the main component of the reaction points, and O2 is necessary; the hydrogen chloride, silver has catalytic effect on hydrogen chloride, resulting in active chlorine, iodine and oxidation ion is the active iodine, then oxidized active iodine and the formation of Hg~0 intermediates Hg-I* and accelerated Hg~0, the conversion of chlorine intermediates to the final product HgCl2, the activity of iodine and silver and silver iodide generated, Ag (2%) iodine content in -AgI-Ti; in addition, Ag (2%) -AgI-Ti has very good 鐑ǔ瀹氭，

本文編號：1413687