Clean Technology (청정기술)

The Korean Society of Clean Technology (한국청정기술학회)
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Effects of Cu and K Addition on Catalytic Activity for Fe-based Fischer-Tropsch Reaction

Fe계 Fischer-Tropsch 반응에서 촉매활성에 대한 Cu와 K의 첨가 효과

  • Lee, Chan Yong (Department of Chemical Engineering, University of Seoul) ;
  • Kim, Eui Yong (Department of Chemical Engineering, University of Seoul)
  • 이찬용 (서울시립대학교 화학공학과) ;
  • 김의용 (서울시립대학교 화학공학과)
  • Received : 2018.12.28
  • Accepted : 2019.03.01
  • Published : 2019.03.30
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Abstract

Effects of the Cu and K addition and the reduction condition of Fe-based catalysts for Fischer-Tropsch reaction are studied in a continuous flow reactor in this research. The catalysts for the reaction were prepared by homogeneous precipitation followed by incipient wetness impregnation. Physicochemical properties of the $Al_2O_3$ supported Fe-based catalysts are characterized by various methods including X-ray diffraction (XRD), temperature programmed reduction (TPR), and scanning electron microscopy (SEM). Catalytic activities and stabilities of the Fe/Cu/K catalyst are investigated in time-on-stream for an extended reaction time over 216 h. It is found that a reduction of the catalysts using a mixture of CO and $H_2$ can promote their catalytic activities, attributed to the iron carbides formed on the catalysts surface by X-ray diffraction analysis. The addition of Cu induces a fast stabilization of the reaction reducing the time to reach at the steady state by enhancement of catalytic reduction. The addition of K to the catalysts increases the CO conversion, while the physical stability of catalyst decreases with potassium loading up to 5%. The Fe/Cu (5%)/K (1%) catalyst shows an enhanced long term stability for the Fischer-Tropsch reaction under the practical reaction condition, displaying about 15% decrease in the CO conversion after 120 h of the operation.

본 연구에서는 Fischer-Tropsch 반응에서 Fe계 촉매의 환원조건과 Cu, K의 첨가에 대한 영향을 연속흐름 반응기를 통하여 살펴보았다. 반응을 위해 촉매는 균일상 침전에 의한 초기 습식함침법으로 제조하였으며 XRD, TPR, SEM 등의 기기를 통해 $Al_2O_3$에 담지 된 Fe 촉매에 대한 물리화학적 특성을 분석하였다. 216 h의 장시간 반응운전을 통해 Fe/Cu/K 촉매의 활성과 안정성에 대하여 조사하였다. $H_2$와 CO의 혼합물로 촉매를 환원시키면 촉매의 활성이 향상되었는데, 이는 촉매의 표면에 iron carbides가 형성되기 때문인 것으로 XRD 분석을 통해 확인되었다. 촉매에 Cu가 첨가되면 촉매의 환원성 향상으로 인하여 반응이 빠르게 안정되어 정상상태에 일찍 도달하였다. K를 첨가하게 되면 CO의 전화율은 향상되지만 함량을 5%까지 올리면 촉매의 물리적 안정성이 감소되었다. Fe/Cu (5%)/K (1%) 촉매로 Fischer-Tropsch 반응을 수행한 결과 120 h 이후에 약 15% 정도 CO의 전화율이 감소되었으나 장기간 안정된 반응을 수행할 수 있었다.

Keywords

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Figure 1. Schematic diagram of experimental apparatus for Fischer-Tropsch reaction.

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Figure 2. Changes of CO conversion with time of Fe catalysts after reduction with H2 only, and with CO/H2 during Fischer-Tropsch reaction.

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Figure 3. XRD patterns of Fe catalysts after reduction with H2 only (A), and with CO/H2 (B) at 375 ℃ for 12 h.

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Figure 4. Changes of CO conversion with time of Fe/Cu 1 wt%, 3 wt%, and 5 wt% catalysts during Fischer-Tropsch reaction.

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Figure 5. H2-Temperature programmed reduction profiles of Fe/Cu 1 wt%, 3 wt%, and 5 wt% catalysts.

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Figure 6. Changes of CO conversion with time of Fe/K 1 wt%, 3 wt%, and 5 wt% catalysts during Fischer-Tropsch reaction.

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Figure 7. Scanning electron microscopy images of Fe/K 5 wt% catalyst before (A) and after (B) Fischer-Tropsch reaction.

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Figure 8. Changes of CO conversion with time of Fe/Cu 5 wt%/K 1 wt% catalyst during Fischer-Tropsch reaction.

Table 1. Hydrocarbon selectivity of Fe/Cu and Fe/K catalysts (reaction period: 60 ~ 100 h)

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