Removal of Diluted NO Using Activated Carbon Fibers

Abstract

Effective adsorption of dilute nitrogen oxides (N0x) is one of the most important processes for purifying the polluted air, for i nstance in t unnels or on busy roads. Activated carbon fibers (ACF, Tab le 1) were examined on their usefulness as adsorbents for the removal of dilute NO, where NO is a main component of NOx.
Adsorption t ests were carried out at room temperature with an NO measuring apparatus in w hich a controlled potential electrolysis sensor was used (Figs.1 and 2). ACFs in an “as received” state i. e. without pretreatment were found to adsorb a considerable amount of N O at 5 p pm concentration dilut ed with air o r N2( Fig.4). T he test gas was t hen to b e dried with s ilica gel. O n t he other h and, the AC Fs preheated at 423 K for 24 h in air showed very low capacities of NO adsorption except for PAN-ACF, even though preheating adsorbent is a usual treatment and a matter of course.
Each of the 4 kinds of ACF showed its particular characteristics of NO adsorption (Fig.6, Tables 2and 3). P AN-ACF's NO adsorption capacity reached 0.071 mmolig. The ACF samples' weight reduced by 7-25% during NO adsorption tests, which corresponds presumably to the removal of ad sorbed water on t he ACFs (Fig.7). T here were limited scopes for h eating ACFs without damaging thei r NO adsorption capacity and for recovering it after NO desorption (Figs.8 and 9). When heated at 473 K, a PAN-ACF sample having fully a dsorbed NO evolved to a maximum NO concentration of 3 80 ppm and maximum NO2 o f 3.6 ppm in a very short time ( Fig.10).