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新型Fe3O4@EDTA-Fe复合材料去除烟气中NO并同步回收N2O的效能及机制
Alternative TitleA Novel Fe3O4@EDTA-Fe Composite Based Technology for Removing NO from Flue Gas with N2O Recovery
HAFIZ MUHAMMAD ADEEL SHARIF
Subtype博士
Thesis Advisor王爱杰
2019-06
Degree Grantor中国科学院生态环境研究中心
Place of Conferral北京
Degree Name理学博士
Degree Discipline环境科学
KeywordNo去除,N2o回收,磁性吸附剂,选择性,烟气,容量损失,再生与修复 No Removal, N2o Recovery, Magnetic Adsorbents, Selectivity, Flue Gas, Capacity Lost, Regeneration And Reconstruction
Abstract

    燃烧过程中氮氧化物(NOx)的排放导致的大气污染是目前重要的环境问题之一。烟气中氮氧化物的传统处理技术通常将烟气中的氮转化为无害的氮气(N2)排放,而将这些氮化合物进行转换进行资源回收的从而进行回研究工作则相对较少。在本研究中,我们开发了一种新型纳米磁性吸附材料Fe3O4@EDTA-Fe(II)用于去除烟气中的一氧化氮(NO),并以亚硫酸盐(烟气脱硫产物)作为还原剂,对Fe3O4@EDTA-Fe(II)吸附的NO进行选择性转化,得到具有工业应用价值的一氧化二氮(N2O)。
    首先在单纯NO体系中研究了Fe3O4@EDTA-Fe(II)对NO的吸附行为及机制。通过FTIR、XPS和XRD等手段分析,表明NO的去除主要通过化学吸附作用与Fe3O4@EDTA-Fe(II)形成Fe3O4@EDTA-Fe(II)-NO配合物。研究中发现pH对NO吸附去除效率及N2O的生成效率有显著影响,NO吸附最佳pH条件为7.5,此时Fe3O4@EDTA-Fe(II)对NO吸附容量可以达到0.303±0.037 mmol·g−1。N2O生成的最佳pH条件为8.0,此时超过90%的NO可以转换为N2O。另外, Fe3O4@EDTA-Fe(II)表现出良好的稳定性,在连续5次循环后的NO吸收效率和N2O回收能力可以保持在95%以上。
    由于氧气(O2)是实际烟气中的重要组成成分,因此为了尽量模拟实际烟气条件,本研究进一步考察了O2存在时,Fe3O4@EDTA-Fe(II)体系对NO的处理效果。O2的存在会将Fe3O4@EDTA-Fe(II)中的-Fe(II)转化为-Fe(Ⅲ),从而降低其对NO的吸收能力。NO去除效率取决于吸收剂中-Fe(II)的含量,而O2的存在会降低-Fe(II)的含量。如果不把氧化形成的-Fe(Ⅲ)还原为-Fe(II),Fe3O4@EDTA-Fe(II)则不具有可再生利用的能力。在NO与O2比例为80:20时,NO的去除效果最差,去除率降低了19.6±2.74%。此外,-Fe(II)转化为-Fe(Ⅲ)是非自发反应,在-Fe(II)没有再生时,系统不能进一步去除和还原NO。本研究中,针对Fe3O4@EDTA-Fe(II)吸附剂的再生,我们开发了中性红作为电子中介体的电化学再生方法。在NO与O2比例为80:20条件下,连续5个运行周期后,NO的吸附容量和N2O回收容量相较于第1周期均可保持在95%以上。
    进一步增加循环周期数, 发现即使在吸附剂再生条件下NO的吸附容量和N2O回收容量均有明显下降(相较于第1周期,第7周期后此两项指标数值分别下降16%和 20%)。通过高分辨透射电镜,观察到此时吸附剂上的EDTA-Fe功能层明显损失。进一步通过TGA分析,发现功能层损失对应的理论NO吸附容量损失接近于实验数值,证实了EDTA-Fe功能层损失是NO吸附容量降低的原因。针对这一问题,建立了EDTA-Fe(II)功能层修复的方法,即将受损吸附材料顺序置于EDTA溶液和Fe(II)溶液中浸泡。修复后,吸附材料对NO的吸附容量几乎可完全恢复到受损前状态。
    总体上,本研究结果表明, Fe3O4@EDTA-Fe(II)新型磁性吸附剂用于去除烟气中NO具有低物耗、低能耗、同步回收有价资源(N2O)等优势,在烟气脱硝方面具有较好的应用潜力。

Other Abstract

    The chemical absorption and chemical reduction (CACR) technique is one of the promising approach for nitrogen oxides (NOx) reduction from flus gas using Fe-EDTA solution system. However, this traditional technology for NOx treatment from flue gas commonly entail the formation of harmless nitrogen gas (N2), while less effort has been made to recover the N-containing chemicals produced. One reason for this, the separation of N2O from the system not easy presumably under same condition. To rectify this issue, we developed a novel nano-magnetic adsorbent, i.e., Fe3O4 coated by EDTA-Fe(II) for NO binding with terminal Fe(II). The NO adsorbed by Fe3O4@EDTA-Fe(II) was then selectively converted to N2O, a valuable compound in many industries, by using sulfite (a product from desulfurization in flue gas treatment) as the reductant for the regeneration of Fe3O4@EDTA@Fe(II).
    The experiment was firstly carried out by using pure NO to explore its adsorption behavior and mechanism on Fe3O4@EDTA-Fe(II). According to the analysis by various characterization approaches, such as FTIR, XPS and XRD, the removal of NO was confirmed as a result of the formation of Fe3O4@EDTA-Fe(II)-NO complex. Additionally, pH was found to significantly influent the efficiencies of NO adsorption and N2O production. At the optimal pH (7.5 and 8.0 for NO adsorption and N2O recovery, respectively), the maximum NO adsorption capacity of Fe3O4@EDTA-Fe(II) was measured as 0.303 ± 0.037 mmol·g−1, over 90% of which was converted to N2O during the recovery process. Moreover, Fe3O4@EDTA-Fe(II) exhibited good stability, retaining over 95% of both its adsorption and N2O recovery capabilities after 5 consecutive cycles. The oxygen (O2) is complimentary part of flue gas, so that to intimate these conditions the mixture of NO and O2 gas has been prepared and employed to the Fe3O4@EDTA-Fe(II) system. The presence of O2 declines the NO absorption ability of Fe3O4@EDTA-Fe(II) by the transformation of –Fe(II) into –Fe(III) and subsequently NO absorption lost. The NO removal efficiency depends upon the concentration of –Fe(II) but O2 contents decrease this concentration. However, the reusability of Fe3O4@EDTA-Fe is also not possible without restoration of –Fe(II) for NO absorption. The maximum decrease ~19.6±2.74% was seen against 80:20 for NO:O2 ration of mix gas, which was the highest concentration used for NO and O2 mixture. In addition, the transformation of –Fe(II) into –Fe(III) is not spontaneous, hence, the removal and reduction of NO is inevitable without the restoration of –Fe(II). In this study, we developed a electrochemical method with neutral red as the electron mediator for the regeneration of Fe3O4@EDTA-Fe(II). With the presence of 20% of O2 in the NO-O2 mixed gas, this regeneration strategy enabled over 95% retaining of the NO adsorption capacity and N2O recovery capacity after five cycles operation. When further increasing the operation cycles, the capacities of NO adsorption and N2O recovery were found to be decreased obviously (decrease of 16% and 20%, respectively, after 7th cycle compared to the 1st cycle). Through HR-TEM, we observed some loss of the EDTA-Fe(II) function layer here, which was then quantified by the TGA analysis. Subsequently, the theoretical capacity loss of NO adsorption was calculated accordingly, which was closed to the observed value in the experiment, confirming the decline of NO adsorption capacity is owing to the detachment of EDTA-Fe(II) function layer. In order to resolve this problem, we further established a method by simply mixing the ruined Fe3O4@EDTA-Fe(II) particles with the EDTA and Fe(II) solutions to repair the function layer. By this method, the recovery of the NO adsorption capacity and N2O recovery capacity was then verified.
    Overall, The findings from this study indicate Fe3O4@EDTA-Fe(II) may hold great potential for application to NO removal from flue gas with the benefits of resource recovery (N2O), decreased chemical use and low energy consumption.
 

Pages122
Language英语
Document Type学位论文
Identifierhttp://ir.rcees.ac.cn/handle/311016/42176
Collection中国科学院环境生物技术重点实验室
Recommended Citation
GB/T 7714
HAFIZ MUHAMMAD ADEEL SHARIF. 新型Fe3O4@EDTA-Fe复合材料去除烟气中NO并同步回收N2O的效能及机制[D]. 北京. 中国科学院生态环境研究中心,2019.
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