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Journal of the Korean Chemical Society (JKCS)

ISSN 1017-2548(Print)
ISSN 2234-8530(Online)
Volume 33, Number 1
JKCSEZ 33(1)
February 20, 1989 

Effect of SiO2/Al2O3 Ratio of HZSM-5 Catalyst on the Synthesis of Methyl tert-butylether

Methyl tert-Butylether 합성에 미치는 HZSM-5 촉매의 SiO2/Al2O3 비의 영향
Geon-Joong Kim, Wha-Seung Ahn, Byung-Rin Cho, Lee-Mook Kwon

김건중, 안화승, 조병린, 권이묵
HZSM-5를 촉매로 하여 메탄올과 이소부틸렌으로부터 Methyl tertiary butyl ether(MTBE)의 기상합성실험을 하였으며, zeolite 촉매의 SiO2/Al2O3 비 및 반응조건의 영향을 연구하였다. 각 촉매들은 pyridine을 흡착시켜 temperature programmed desorption(TPD) 및 IR법으로 산점의 세기와 특성을 조사하였으며, 승온탈착실험을 통하여 각 반응물 및 생성물의 흡착특성을 검토하였다. HZSM-5의 SiO2/Al2O3비가 증가할수록 강한 산점의 수는 감소하여 메탄올의 탈수반응은 억제되고 MTBE에 대한 선택도가 증가하였다. MTBE에 대한 전환율과 선택도는 i-C4H8의 세공내 확산저항에 의하여 큰 영향을 받음을 알 수 있었다. MTBE합성반응은 발열적이어서, 전반적으로 80℃의 반응온도가 합성에 적합하였다. 한편 각 촉매상에 생성된 coke의 특성을 TG, DTA 및 IR spectrum으로 측정하였다. 침착된 coke의 양은 HY > H-Mordenite > HZSM-5순이었으며, H-Mordenite에 있어서는 누적된 coke의 양이 HZSM-5보다 현저하지는 않았으나, 세공의 배향이 1방향성이므로 반응시간이 길어짐에 따라 심한 활성감퇴가 일어났다. HY는 큰 세콩을 가지고 있어 i-C4H8의 중합이 쉽게 일어났으며, HZSM-5에 비하여 많은 coke의 참착과 빠른 활성감퇴를 나타내었다.

Methyl tert-butyl ether(MTBE) was synthesized from vapor phase reaction of methanol with iso-butylene over HZSM-5 catalysts, and effects of SiO2/Al2O3 ratio in the HZSM-5 catalysts and reaction conditions on products distribution have been examined. Acid strength and acid type of each catalyst with different SiO2/Al2O3 ratio were measured using pyridine adsorption followed by temperature programmed desorption(TPD) and IR analysis. Reactants and products adsorption characteristics on different acid sites have also been examined. As the SiO2/Al2O3 ratio of HZSM-5 catalyst was increased, selectivity to MTBE was improved as a result of decrease in dimethylether(DME) formation at the strong acid sites. Conversion and selectivity to MTBE were also greatly enhanced as i-C4H8/CH3OH reactant ratio was increased, and overall about 80℃ was adequate for the MTBE synthesis. The properties of deposited coke on spent catalysts were examined by TG, DTA and IR spectrum analysis, indicating the amount of the coke deposit in the order of HY > H-Mordenite > HZSM-5. Even if the coke deposited on H-Mordenite was little more in amount than to that on HZSM-5, the former deactivated quickly due to its non-interconnected channel structure. For HY, owing to its lange pore size, significant i-C4H8 polymerization was occured, and rapid deactivation and severe coke formation has resulted within few hours.

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