Slurry Phase Iron Catalysts for Indirect Coal Liquefaction

This report covers the second six months of this three year grant under the University Coal Research program. During this period we have continued our work on understanding the attrition of precipitated iron catalysts and initiated work on synthesis of catalysts containing silica binders. As we show in this report, the use of a sedigraph particle size analyzer with an ultrasonic probe provides a simple method to test the strength of catalyst agglomerates. This approach allows us to compare the relative strength of a silica support and the hematite catalyst obtained from the Laporte run II. The silica support is considerably stronger than the hematite catalyst. In future work, we will use this approach to study the role of binders in influencing the strength of the precipitated catalysts. During this period, we have continued our study of Fel silica interactions to provide a fundamental understanding of the how silica binders influence the activity and attrition resistance of these catalysts. In our previous report we had shown how an irreducible silicate-like phase was observed when the Fe(N03)2 was co-precipitated with a tetraethylorthosilicate (TEOS) precursor. Based on the suggestion made by Dr. Tischer, the project manager, we used a colloidal silica precursor and added it to the calcined Fe20 3 catalyst. There was no detrimental effect on the reducibility of the hematite to a-Fe. We also studied a catalyst containing 30% Fe supported on silica and found that it does not reduce to a-Fe as quickly as an unsupported catalyst. But this is a kinetic effect and longer reduction periods allow complete reduction of the Fe20 3 to a-Fe. No silicate phase is seen to form at temperatures used in this study (723K). In future we will study the role of oxidation-reduction treatments on the Fe-silica interaction. The oxidation-reduction conditions will be similar to those encountered in a bubble column reactor during Fischer-Tropsch synthesis. In May of 1996, we received a set of samples from Dr. Burtron Davis from a FischerTropsch run lasting over 3000 hours. During this run, samples were obtained at various times. The samples are embedded in wax and therefore not subject to oxidation by the ambient atmosphere. A similar set of samples for a number of runs have also been received from Dr. Dragomir Bukur. Of these we have selected one run for in-depth study. These analyses should allow us to observe the phase evolution as a function of time on stream. Such analyses have previously been performed by Mossbauer spectroscopy at the University of Kentucky. Our objective here is to use a combination of X-ray diffraction and electron microscopy to map out the size distribution of the crystalline phases and the types of carbon present in these samples. The major difficulty in the use of x-ray diffraction is that the magnetite and carbide peaks overlap, making it difficult to properly assess the relative amounts of these phases. As we show in this report, we have developed an approach based on Reitveld refinement that allows us to separate the carbide and magnetite peaks. We will use this approach to complete the XRD analyses of these wax embedded samples.

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