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변형된 ZSM-5 촉매상에서 n-헥산의 방향족화 반응에 관한 연구
Aromatization of n-Hexane over Modified HZSM-5 Catalysts-2. Aromatization over Ga/Hzsm-5
HWAHAK KONGHAK, April 1995, 33(2), 204-212(9), NONE
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Abstract
HZSM-5 촉매상에서 n-헥산의 방향족화 반응에 있어서 방향족 화합물의 선택도를 향상시키기 위하여 HZSM-5에 Ga를 함침시켜 변형한 다음 실험연구를 수행하였다. Ga 함침에 의하여 방향족 화합물의 선택도는 향상되었으며 Si/Al 비가 높은 경우에도 방향족 화합물의 생성이 관찰되었다. HZSM-5 촉매상에서는 ㅂ향족 화합물이 3차 생성물의 형태를 보였으나 Ga 함침촉매상에서는 2차 생성물로 판정되었다. 방향족 화합물의 생성추이에 있어서 Si/Al 비가 낮은 경우에는 툴루엔이 1차 및 최대 생성물이었으나 Si/Al 비가 높은 경우에는 벤젠이 1차 및 최대 생성물로 관찰되는데 이것은 프로필렌/C4의 비와 연관이 있는 것으로 확인되었다. 반응과정에서 생성되는 수소의 양을 측정한 결과, 방향족 화합물의 생성여부에 관계없이 Ga 함침에 의하여 수소의 생성이 크게 증가하였다. 이러한 Ga의 수소 제거작용에 의하여 크래킹 반응으로 생성된 저급 탄화수소 중에는 파라핀보다 올레핀의 생성이 증가되고 아울러 탈수소고리화 반응이 촉진되기 때문에 방향족 화합물에 대한 선택성이 향상되는 것으로 판단된다. 이로부터 수소전달과 관련하여 이원기능 촉매상에서 n-헥산의 방향족화 반응에 대한 반응경로를 유추하여 HZSM-5의 경우와 비교, 검토하였다.
HZSM-5 catalyst was synthesized and modified by impregnating Ga. The modified catalyst was then applied for the aromatization of n-hexane to give rise to a substantial improvement in the selectivity out to be the secondary product in contrast to their bing tertiary product over HZSM-5. With respect to the aromatics formation the primary and major product was found to be toluene over Ga/HZSM-5 of low Si/Al ratio whereas it was benzene over Ga/HZSM-5 of high Si/Al ratio. Evidently, this feature was related to the ratio of the amount of propylene to that of C4-hydrocarbons in the reaction mixture. The hydrogen production was significantly increased by the introduction of Ga regardless of the formation of aromatics. By virtue of the Ga’s role of hydrogen scavenger more olefins were formed by cracking reactions and the dehydrocyclization seemed to be promoted. Apparently, this gave rise to the enhancement of the aromatizing activity. From these results the reaction pathways were deduced for the n-hexane conversion over bifunctional Ga/HZSM-5 catalyst.
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