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Pitch계 활성탄소섬유를 이용한 NO2 흡착

NO2 Adsorption using Pitch-based Activated Carbon Fiber

문승현^† 전상구 신대현 김광호 오창섭¹

Seung-Hyun Moon^† Sang-Goo Jeon Dae-Hyun Shin Kwang-Ho Kim Chang-Sup Oh¹

한국에너지기술연구원, 대전 305-343 ¹호서대학교 화학공학과, 아산 336-795

Waste Utilization Laboratory, Korea Institute of Energy Research, Daejeon 305-343, Korea ¹Department of Chemical Engineering, Hoseo University, Asan 336-795, Korea

shmoon@kier.re.kr

HWAHAK KONGHAK, April 2002, 40(2), 133-138(6), NONE

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Abstract

핏치계 활성탄소섬유(ACF)를 1,100 ℃에서 열처리하거나 원료 그대로 사용하여 NO2 250-1,000ppm, O2 0-10%, 반응온도 30-70 ℃의 조건에서 NO2의 흡착 및 환원 특성을 고찰하였다. TPD 실험과 DRIFTS 분석으로 NO2 흡착종을 분석하였다. ACF상에서 NO2는 빠른 속도로 환원과 흡착이 이루어졌고, 반응온도가 상승할수록 흡착파과점의 출현이 빨라졌으며 정상상태에서 NO2흡착/환원 비가 증가하였다. NO2유입농도가 증가하면 흡착속도와 환원속도 모두 빨라져 파과점 역시 짧은 시간에 나타나고, ACF가 지니고 있는 활성점의 양이 일정함을 알 수 있었다. 산소농도 증가는 NO2의 흡착속도 증가 및 환원속도 감소로 나타났는데 파과점의 출현은 흡착과 관계가 있음을 나타내었다. NO2흡착 후의 TPD 실험에서 발생하는 가스의 O/N 몰비는 흡착시간이 길수록 감소하였으며 일정한 값에 수렴하여 ACF에 흡착된 NO2는 흡착시간이 길수록(흡착량이 증가할수록) 높은 산화상태에서 낮은 산화상태로 변화됨을 알 수 있었다. 이러한 사실은 DRIFTS 측정에서도 확인되었다. NO2의 흡착과 환원반응에 관계하는 활성점을 파악하기 위하여 여러 가지 전처리로 ACF표면의 산소관능기 종류와 양을 조절하였고, 이들 시료에서 NO2의 흡착실험을 한 결과 NO2의 흡착점은 C=O이고 환원활성점은 vacant carbon이라는 것을 확인하였다.

Adsorption and reduction of NO2 over pitch based ACFs as received and calcined at 1,100 ℃ were studied in the ranges of concentrations (NO2: 250-1,000 ppm, O2: 0-10%) and temperatures (30-70 ℃). Temperature-programmed-desorption (TPD) and Diffuse reflectance spectroscopy (DRIFTS) were also applied to analyze adsorbed NO2 species. Pitch based ACFs showed rapid NO2 reduction and adsorption. A higher reaction temperature of 70 ℃ decreased the ratio of NO2 adsorption to reduction in the stationary state and shortened the time to the breakthrough. Higher NO2 concentration increased the rates of both adsorption and reduction to shorten breakthrough time, whereas oxygen changed NO2 profiles, by enhancing NO2 adsorption rate and decreasing both reduction rate and capacity. The mole ratio of O/N evolved from TPD decreased and converged to a constant value according to NO2 adsorption time, showing that NOx species adsorbed on the ACF changed its oxidation state from higher to lower one along with the time of NO2 adsorption. Such a trend was confirmed by the DRIFTS spectra of the adsorbed NO2 over the ACF. To investigate active sites for NO2 adsorption and reduction, the amount and types of oxygen functional groups were controlled by various pre-treatment. NO2 adsorption on these pre-treated ACF showed that NO2 adsorption site was C=O and NO2 reduction site was vacant carbon.

Keywords

NO2 ACF Reducton Adsorption Oxidation

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