Effects of Process Parameters on Carbon Deposition During Iron Catalyzed Fischer-Tropsch Synthesis Studied with a Tapered Element Oscillating Microbalance

Effects of Process Parameters on Carbon Deposition during Iron Catalyzed Fischer-Tropsch Synthesis studied with a Tapered Element Oscillating Microbalance

Ard C. J. Koeken,* Matthijs Ruitenbeek,^# Krijn P. de Jong*

* Inorganic Chemistry and Catalysis - Debye Institute for Nanomaterials Science - Utrecht University - Sorbonnelaan 16 - 3584 CA - Utrecht - The Netherlands

^# DOW Benelux BV, Hydrocarbons R&D, P.O. Box 48, NL-4530 AA Terneuzen - The Netherlands

Production of lower olefins from renewable feedstock or coal is of great interest to the chemical industry.[1] The Fischer-Tropsch synthesis (FTS) can be the key process to directly convert synthesis gas, a mixture of carbon monoxide and hydrogen gas produced from renewable feedstock or coal, into lower olefins. Iron catalysts have promising characteristics such as high olefin selectivity, high water-gas shift activity, and low cost.[2] Transformation of the catalytic phase, carbon deposition, sintering, and poisoning are the main causes for the deactivation of Fe catalysts during FTS.[2] In particular, at the high reaction temperatures required for a high lower olefin selectivity, carbon deposition is an issue as it may result in catalyst particle disintegration.[2] As the deposition of carbon on the catalytic surface increases the mass of the solid catalyst, measuring the mass in situ is a means to investigate the kinetics of carbon deposition. The Tapered Element Oscillating Microbalance (TEOM) allows for such a measurement at varying temperature and pressure under plug-flow conditions.[3]

            Here, the first TEOM study of carbon deposition during FT is presented for an a-Al₂O₃ supported Fe catalyst. The figure shows the influence of CO pressure on the carbon build-up and the weight-time yield (WTY). A clear increase in rate of carbon deposition with CO pressure is found.

Figure- A) Carbon build-up.

Figure- B) Product weight-time yields.

Conditions: 350 °C, 10 bar H₂, 50 mL/min H₂, 0.02 g catalyst (10wt% Fe).

In the full presentation we discuss extensively the effect of process parameters (e.g. P, T, H₂/CO ratio, GHSV) on carbon deposition. It is demonstrated that the TEOM is a powerful tool to investigate carbon deposition along with activity and selectivity under FTS conditions that are industrially relevant.

[1]        R. Diercks et al, Chem. Eng. Tech. 31 (2008) 631.

[2]        M. E. Dry, Appl. Catal A 138 (1996) 319-344

[3]        D. Chen et al, in Advances in Catalysis, Vol 51, Vol. 51, Elsevier Academic Press Inc, San Diego, 2007, pp. 351.

E-mail:   a.c.j.koeken@uu.nl

www:    http://www.anorg.chem.uu.nl/home/index.html