Converting syngas to gasoline is an attractive proposition, given the significant increase in oil prices ($126/barrel and rising) coupled with the ever-increasing demand for gasoline. Syngas is obtained from non-renewable sources by steam reforming of petroleum hydrocarbons and by coal gasification and from renewable sources by biomass gasification.1 Syngas can be converted directly to hydrocarbon fuels by Fischer-Tropsch (FT) chemistry using Co or Fe catalysts.2,3 Most of the Fischer-Tropsch studies on Fe catalyst to date have involved precipitated or fused iron catalyst. Iron catalysts are known to give products high in olefinic content. One approach for obtaining gasoline with high aromatic content (higher octane rating) would be to support Fe on ZSM-5 catalyst, which would convert the olefins produced from Fe catalyst to aromatics over ZSM-5. There have been a few studies involving FT reactions over Fe/ZSM-5 catalysts prepared by various methods.4,5 Most of these catalysts were prepared by mixing the ZSM-5 catalyst with the precipitated Fe catalyst

In this work, Fe/ZSM-5 catalyst was prepared using the incipient wetness impregnation technique with subsequent testing of the catalyst in a packed bed reactor. Operating conditions including temperature, pressure, space velocity as well as pre-treatment conditions were varied to determine their individual and combined effects on CO conversion and individual selectivity towards methane, towards carbon dioxide and towards gasoline. Catalyst lifetime studies and various regeneration techniques were also investigated.

Significant findings from this work include:

1. Increased pressure and/or temperature gives rise to increased gasoline yield.

2. Coking of the catalyst increases significantly at temperatures above 360 °C.

3. Preliminary examination of catalyst regeneration by flowing air at 500 oC indicates that almost complete recovery of catalyst activity may be achieved.

4. Regeneration of the catalyst by flowing steam at 500 °C leads to dealumination of the zeolite structure, possibly leading to permanent loss in catalyst activity.

References:

1. Lv, P., Yuan, Z., Wu, C., Ma L., Chen Y. and Tsubaki, N., Energy Conversion and Management, 48, 1132-1139, (2007).

2. Kolasinski Kurt W., Surface Science-Foundations of Catalysis and Nanotechnology, John Wiley & Sons, Ltd. (2002).

3. Anderson, Robert B., The Fischer-Tropsch Synthesis, Academic Press (1984)

4. Yoneyama, Y., He, Y., Morii, Y., Azuma, S. and Tsubaki, N., Catalysis Today, 104, 37-40, (2005).

5. Pour, A., Zamani, Y., Tavasoli, A., Shahri, S., Taheri, S., Fuel, 87, 2004-2012 (2008).