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저온 플라즈마-촉매 공정을 이용한 탄소산화물의 메탄화 반응 연구

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Alternative Title
Nonthermal plasma-catalytic methanation of carbon oxides
Abstract
This work dealt with plasma-assisted catalytic hydrogenation of carbon oxides (COX) to produce methane, a main component of synthesis natural gas (SNG). Conventionally, the conversion of chemically stable COX (CO and CO2) into CH4 is performed in the presence of catalysts (of group Ⅷ elements such as Ni, Ru and Co) at relatively high temperatures in the range of 300∼400℃. From the practical application point of view, the operating temperature of the catalytic process should be as low as possible so that the process consumes the least amount of energy for heating up the gas and the formation of coke is relieved. As an alternative process, this work proposed the combination of nonthermal plasma with catalysis. While plasma-catalytic reforming of hydrocarbons has been extensively studied elsewhere, the application of plasma-catalysis to the production of methane is scarce in the literature.
A coaxial dielectric barrier discharge (DBD) reactor packed with different catalysts was employed for the production of methane. The reactor was energized by alternating current (AC) voltage (frequency: 1 kHz) in the range of 0∼10.3 kV. The molar ratio was fixed at 3.0 (H2/CO) for CO methanation and at 4.0 (H2/CO2) for CO2 methanation, respectively. The characteristics of several heterogeneous catalysts such as Ni/α-alumina, Ni/TiO2/α-alumina and Ni/β-zeolite were comparatively examined with and without the plasma. The relevant components in the effluent gas (COX, CH4 and H2) were analyzed by a gas chromatograph. The DBD plasma was found to help improve the catalytic conversion of carbon oxides in to methane particularly at low temperatures and nickel contents. On the other hand, with bare alumina or zeolite, there was no catalytic conversion of COX at 180∼300℃, even with the application of nonthermal plasma, which suggests that the plasma itself hardly converts COx into methane, even though it can assist the catalytic reactions.
The CO methanation can be explained by the so-called carbide mechanism, which states that CO is adsorbed on the catalyst surface and immediately dissociated into C and O when the temperature is high enough to overcome the activation barrier for this process. Subsequently, the hydrogenations of the adsorbed C and O take place, leading to the formation of methane. Presumably, the rate-determining step (RDS) is the dissociation of the absorbed CO into C and O. The acceleration of the RDS by the plasma is quite probable, because energetic species like electrons and excited molecules can take part in the dissociation of the adsorbed CO, which may partly explain why the conversion of carbon oxides increases under the plasma discharge condition. The methanation of CO2 is known to proceed via the same route as that of CO, once CO2 is dissociated into CO and O. Overall, the rate of CO2 methanation was some what lower than that of CO methanation, which is obviously because CO2 has two C-O bonds to break, i.e., CO2 methanation requires one more step to go. Apart from the change in the catalytic activity due to the plasma discharge, an X-ray diffraction analysis showed that the particle size of Ni got smaller and Ni was more uniformly dispersed on the support when the catalyst was exposed to the discharge. As a result, the increased effective reaction sites must have improved the catalytic methanation rate, more or less. Other plasma actions like local heating can also affect the catalytic activity. Further study is needed to identify which plasma action has a dominant influence on the catalytic methanation.
Author(s)
좌은진
Issued Date
2011
Awarded Date
2012. 2
Type
Dissertation
URI
http://dcoll.jejunu.ac.kr/jsp/common/DcLoOrgPer.jsp?sItemId=000000005823
Alternative Author(s)
Jwa, Eun jin
Affiliation
제주대학교
Department
대학원 에너지응용시스템학부 에너지화학공학전공
Advisor
목영선
Table Of Contents
SUMMARY ⅰ
목 차 ⅲ
LIST OF TABLES ⅵ
LIST OF FIGURES ⅶ
Ⅰ. 서론 1
Ⅱ. 이론적 배경 및 선행연구 4
1. 개질 반응 및 메탄화 반응 4
1) 촉매 및 담지의 특성 6
(1) β-zeolite의 특성 6
(2) 촉매 제조 방법 8
2) 메탄화 반응 선행연구 8
3) 메탄화 반응기구 11
2. 플라즈마의 소개 13
1) 플라즈마의 분류 14
2) 플라즈마의 종류 16
(1) 코로나 방전 17
(2) 글로우 방전 16
(3) 글라이딩 아크 방전 17
(4) 대기압 제트 플라즈마 18
(5) 유전체 배리어 방전 18
3) 플라즈마 전력 측정 19
3. 플라즈마-촉매 상호작용 21
1) The packed-bed reactor 23
2) Plasma-catalyst configurations 23
4. 탄소 산화물(COX) 메탄화 반응에 필요한 계산 26
1) 물질 수지를 통한 전환율 및 선택도 계산 26
2) 열역학적 평형상수의 결정 26
3) 열역학적 평형전환율의 계산 30
(1) CO 메탄화 반응에서의 평형전환율 결정 30
(2) CO2 메탄화 반응에서의 평형전환율 결정 30
5. 분석 장비 33
1) 가스 크로마토그래피(Gas chromatography, GC) 33
(1) 열전도성 검출기(Thermal conductivity detector, TCD) 35
2) 퓨리에 변환 적외선 분광기(Fourier-transform infra-red spectroscopy, FTIR) 36
3) 주사 전자 현미경(Field emission scanning electron microscopy, FE-SEM) 36
4) 투과 전자 현미경(Transmission electron microscope, TEM) 38
5) 엑스선 회절기(X-ray diffraction analyzer, XRD) 38
Ⅲ. 연구 방법 40
1. 촉매준비 40
2. 실험 방법 40
Ⅳ. 연구 결과 43
1. DBD 플라즈마를 이용한 촉매적 COX 메탄화 특성 43
1) COX의 메탄 전환 효율 변화 43
2) COX의 선택도 48
3) 담지 종류 (Al2O3, zeolite)가 메탄화에 미치는 영향 48
4) 니켈 함량이 메탄화에 미치는 영향 52
5) TiO2가 메탄화에 미치는 영향 58
2. 방전전압과 온도가 전환효율에 미치는 영향 62
3. 온도에 따른 방전전력 비교 62
4. DBD 플라즈마 촉매적 메탄화 반응에 따른 니켈 입자 변화 65
1) TEM 분석결과 65
2) XRD 분석결과 65
Ⅴ. 결 론 69
참고문헌 69
Degree
Master
Publisher
제주대학교 대학원
Citation
좌은진. (2011). 저온 플라즈마-촉매 공정을 이용한 탄소산화물의 메탄화 반응 연구
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