硝酸改性活性炭上氧/氮官能团对脱汞性能的促进作用

采用硝酸氧化手段对活性炭进行了表面处理,并在固定床反应器上测试了其脱除单质汞的性能.研究表明,在模拟烟气中硝酸改性活性炭能有效脱除单质汞.采用元素分析、Brunauer-Emmett-Teller(BET)比表面积、扫描电子显微镜(SEM)、拉曼(Raman)光谱、Boehm滴定、程序升温脱附(TPD)和X射线光电子能谱(XPS)等手段研究了活性炭表面官能团对其脱汞性能的影响.结果表明:硝酸氧化处理能同时增加活性炭表面含氧官能团和含氮官能团的含量.与改性活性炭的物理性质相比,其化学性质对脱汞性能的影响更大,单质汞主要被改性活性炭氧化为Hg O而去除.在脱汞反应中,羰基、酯基和酸酐等含氧官能团可能是活性吸附位点,反应后这些官能团被还原为羟基或者醚基;而吡咯等含氮官能团可能是活性催化位点.此外,基于上述表征结果提出了硝酸改性活性炭表面官能团的脱汞机制.

Enhanced Effect of O/N Groups on the Hg0 Removal Efficiency over the HNO3-Modified Activated Carbon

HNO₃-modified activated carbon (AC) was prepared to determine its mercury removal ability on a fixed-bed reactor. In this study, the HNO₃-modified AC was found to be effective for mercury removal in simulated flue gas. The original sample, the HNO₃-modified sample and the production sample were characterized by elemental analysis, Brunauer-Emmett-Teller (BET) specific surface area measurements, scanning electron microscopy (SEM), Raman spectra, Boehm titrations, temperature programmed desorption (TPD) technique, and X-ray photoelectron spectroscopy (XPS). The results show that HNO₃ treatment increases the content of oxygen and nitrogen on the AC. Compared with the physical characteristics of HNO₃-modified AC, the effects of its chemical characteristics on mercury removal are more significant. The Hg⁰ is mainly oxidized to HgO by the HNO₃-modified AC. The oxygen functional groups, possibly carbonyls, esters or anhydrides were found to be the adsorption sites for mercury removal, and these groups were reduced to hydroxyl groups or ether groups. The N-functional groups, possibly pyrrolic tautomers, were found to be the active catalytic sites. The mechanism for Hg⁰ removal by HNO₃-modified activated carbon is proposed based on the characterization results.