萘在选择性催化还原脱硝系统内的转化机制

Conversion mechanism of naphthalene in selective catalytic reduction DeNO system

萘是燃煤烟气中多环芳烃(PAHs)的主要成分,在经过选择性催化还原(SCR)脱硝系统时能被部分降解,但在脱硝烟气组分影响下难以彻底降解为CO_(x).不仅如此,部分萘会聚合生成高毒性PAHs.基于此,本文研究了脱硝烟气组分对V_(2)O_(5)-WO_(3)/TiO_(2)催化萘降解性能的影响.结果表明:不含烟气组分时,萘经过1,4-萘醌、邻苯二甲酸酐和马来酸酐等中间产物降解为CO_(x),其中酸酐(邻苯二甲酸酐和马来酸酐)是CO_(x)生成的重要中间体.除此之外,酸酐生成过程中不可避免的会生成乙炔基,该物质与萘结合生成更高分子量的菲和蒽,导致PAHs总选择性较高(0.24%).而在烟气(NO+NH_(3))条件下,NH_(3)会与萘作用生成含N副产物,极大抑制酸酐生成,使CO_(x)选择性从38.9%下降至22.5%.同时,伴随酸酐生成的乙炔基大幅降低,使PAHs总选择性从0.24%下降至0.03%.因此同步实现酸酐和乙炔基的彻底降解是萘高效去除的关键.

Naphthalene(Nap)is the majority component of polycyclic aromatic hydrocarbons(PAHs)in coal-fired flue gas,which can be partially degraded in the selective catalytic reduction(SCR)DeNO_(x) system.However,most of Nap cannot be degraded into COx affected by the flue gas components in the DeNO_(x) system.In addition,part of the Nap polymerizes to PAHs with higher toxicity.Based on this,this paper focuses on the effect of DeNO_(x) flue gas components on the conversion of Nap over DeNO_(x) catalyst(V_(2)O_(5)-WO_(3)/TiO_(2)).The results showed that,in the absence of DeNO_(x) flue gas components,Nap was degraded to CO_(x) through intermediates in the following order:1,4-naphthoquinone,phthalic anhydride,maleic anhydride,and then CO_(x).Acid anhydride(Phthalic anhydride and maleic anhydride)was found to be the key intermediate for CO_(x) production.Besides,the process of acid anhydride generation inevitably generated acetylene groups,which combine with Nap to form higher molecular weight phenanthrene and anthracene,resulting in higher total selectivity of PAHs(0.24%).With NO and NH_(3) existing,NH_(3) would interact with Nap to generate N-containing by-products,which greatly inhibited the generation of anhydride and reduced the CO_(x) selectivity from 38.9%to 22.5%.While the yield of ethynyl groups reduced accompanied by anhydride decreasing,the total PAHs selectivity decreased from 0.24%to 0.03%.Thus,the complete degradation of acid anhydride and ethynyl groups simultaneously was the key to the efficient abatement of Nap.