A study of hydrocarbon production via Fischer-Tropsch synthesis from different model bio-syngases over un-promoted and rhenium-promoted alumina supported cobalt catalyst
Artikel i övriga tidskrifter, 2005
The model mixtures for biomass-derived-syngas consisted of H2 and CO of different molar H2/CO-ratios (2.1, 1.5 and 1.0) were applied for a fixed bed Fischer-Tropsch (FT) reactor over un-promoted and rhenium-promoted alumina-supported-cobalt-catalysts. The FT-reaction requires a H2/CO-molar-ratio of approximately 2.1 above the catalyst surface. For the ratios lower than 2.1, a water-gas-shift (WGS) activity is desired in order to increase the H2/CO-ratio. With lower H2/CO-ratios in the feed, the CO conversion and the CH4 selectivity (SCH4) decreased, while the C5+ selectivity (SC5+) and C3 (olefin/paraffin) ratio were slightly increased. However, the catalysts studied with dry feed had very low WGS activities (i.e. molar-usage-ratio). The addition of water slightly increased the molar-usage-ratio and resulted in an increase in SC5+ and a decrease in SCH4 for all types of bio-syngases and for both catalysts. Catalysts were deactivated by water. The Re-promoted was considerably more active and selective to longer hydrocarbons. The characterization of catalysts showed the positive effect of the rhenium in dispersion and reducibility of the catalysts.
In order to utilize the advantages of a bio-syngas with a low H2 content, the catalyst must possess a much higher WGS activity. It is suggested to add some iron (Fe) to enhance the WGS activity.