431142 Distribution Between C2 and C3 in the Low Temperature Fischer-Tropsch Synthesis over Cobalt and Iron Catalysts

Thursday, November 12, 2015: 12:30 PM
355D (Salt Palace Convention Center)
Xiaojun Lu, Xinying Liu, Diane Hildebrandt and David Glasser, MaPS Engineering, University of South Africa, Johannesburg, South Africa

Distribution between C2 and C3 in the low temperature Fischer-Tropsch Synthesis over cobalt and iron catalysts

Xiaojun Lu, Xinying Liu, Diane Hildebrandt and David Glasser


 Material and Process Synthesis Engineering, College of Science, engineering and Technology, University of South Africa, Johannesburg, South Africa. Email: lux@unisa.ac.za. Tel: +27 11 6709041

Keywords: Fischer-Tropsch Synthesis, cobalt catalyst, iron catalyst, product distribution.

Abstract

Deviation of C2 (including olefin and paraffin) in the ASF distribution in the Fischer-Tropsch Synthesis (FTS) has been observed consistently but relatively few studies have focused on this. Explanations for C2 deviation have been proposed by researchers and secondary reaction of ethene is suggested as the cause for the deviation.[1] However, the distribution between C2 and C3 has not been investigated as comprehensively as the C2+ products in the FTS reaction. This study mainly focuses on the distribution between C2 and C3 products in FTS over both a supported cobalt catalyst (10% Co/90% TiO2) and a precipitated iron catalyst (Fe/SiO2/K/Cu). The FTS experiments over the cobalt catalyst were conducted in a fixed bed reactor, a CSTR, and a batch reactor under wide range of operating conditions including varying the H2/CO ratio in the feed, the reaction temperature, and space velocity (SV) of the feed gas. The FTS experiments over the Fe catalyst were conducted in fixed bed reactors with H2, CO, and syngas as activation reagents respectively. The distributions between C2 and C3 were investigated both for olefins and paraffins. C3H6/C2H4 ratio was found to be a function of CO conversion only (as shown in Figure 1 below) regardless the reasons (such as temperature, SV, and H2/CO ratio in the feed) causing the change of conversion. The overall C3/C2 was found to be decided by reaction temperature mainly and space velocity has no effect on it. The unique distribution between C2 and C3 olefinic products suggests it is related to mechanism of FT reaction, as this phenomenon could not be explained by kinetics because such distribution is not affected by partial pressures of reactants and products. A model, based on competitive reactions between CO and olefins is being developed to describe the product distributions between C2 and C3 hydrocarbons.

Figure 1 distribution between C2 and C3 olefins as a function of CO conversion for Co/TiO2 (left) and precipitated Fe (right) catalysts

Reference:

[1]   Van der Laan, G P and Beenackers, A A C M. Catal. Rev.-Sci. Eng., 1999, 41, 255ĘC318.


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