경질올레핀을 제조하기 위한 n-옥탄의 접촉분해반응에서 H-ZSM-5 촉매의 소성 및 스팀 처리 영향을 550~750 ℃ 범위에서 조사하였다. 소성 및 스팀 처리 온도를 높이면 H-ZSM-5 촉매의 비표면적, 기공부피 및 강산점이 줄어들었다. 650 ℃ 이상에서 스팀 처리는 제올라이트 구조 내 알루미늄의 탈알루미늄화 및 미세기공의 붕괴로 강산점이 소멸되어, 미세 기공부피가 줄어들며 입자 간 결합에 의한 중기공이 형성되었다. 27Al 및 29Si MAS NMR 스펙트럼으로부터 스팀 처리로 발생하는 탈알루미늄의 과정을 검토하였다. 제올라이트 격자의 알루미늄이 사면체 배위구조 알루미늄 → 5개 배위구조 알루미늄 → 팔면체 배위구조 알루미늄으로 변화과정을 거침을 알 수 있었다. n-옥탄 접촉 분해반응의 전환율, 경질올레핀 수율 및 에틸렌/프로필렌 비가 H-ZSM-5의 소성 및 스팀 처리 온도가 증가함에 따라 감소하는 경향을 나타내었으며, 스팀 처리는 소성 처리보다 활성저하 정도가 더욱 심하여 750 ℃에서 24시간 스팀 처리 후에는 H-ZSM-5가 촉매로서의 기능을 상실하여 열분해반응에 근접하는 전환율, 경질올레핀 수율 및 에틸렌/프로필렌 비의 결과를 나타내었다.

Catalytic cracking of n-octane was carried out over H-ZSM-5 zeolite catalysts after calcination with air and steaming with 100% steam in the temperature range of 550-750 ℃ for 24 h and compared with the results of thermal cracking. The increase of calcination and steaming temperature resulted in the decrease of surface area, pore volume, and strong acid sites, which was mainly caused by the dealumination of H-ZSM-5 framework. It was found by 27Al and 29Si MAS NMR that the dealumination was proceeded through the transformation process of tetrahedral framework Al→penta-cordinated Al→octahedral framework Al and the phenomena was much more severe in steaming conditions than that of calcination. In the catalytic cracking of n-octane, as the temperatures of calcination and steaming were increased, the conversion of n-octane, the selectivity of light olefins and ethylene to propylene ratio were decreased due to the dealumination of framework aluminum resulting the loss of acidic strengths. The conversion, selectivity of light olefins and ethylene to propylene ratio reached almost to the level of thermal cracking after steaming at 750 ℃ for 24 h.

Catalytic Cracking n-Octane Dealumination Steam Treatment H-ZSM-5

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