920. FIELDNER, A. C., AND BREWER, R. E. Tenth Annual Report of Research and Technologic Work on Coal for the Fiscal Year 1945. Electron-Microscope Studies of Fischer-Tropsch Catalyst. Bureau of Mines Inf. Circ. 7352, 1946, pp. 15-18; Chem. Abs., vol. 40, 1946, p. 5898.
Fischer-Tropsch catalyst consisting of Co-ThO2-MgO-kieselguhr was studied by the electron microscope. Co oxide and several types of kieselguhr also were studied. A micrograph of the mixed catalyst shows the characteristic open structure of kieselguhr. Its effectiveness as a carrier is probably the result of this open structure, which permits the reacting gases to penetrate freely to the active components. The particles and aggregates are seen on the micrograph range in size from several microns down to 0.01 micron. Calculations from the effective surface area of this catalyst measured by an N2-absorption method indicate that, if the material were composed of nonporous particles, their average diameter would be 0.015 micron. Apparently the larger particles are either aggregates of these very small ones or are porous enough so that gases can readily penetrate them. Since calculations of surface area from electron micrographs depend on the visually apparent particle size, such measurements obviously would not show the area effective in catalyzing the Fischer-Tropsch synthesis. Measurements made on a number of micrographs of the Co oxide gave an area of 4 m.2 per gm., compared to 62 m.2 per gm. obtained by the N2 absorption method. For use in a proposed small-scale Fischer-Tropsch experimental plant, a CO generator was developed utilizing pitch coke or petroleum coke as fuel and having an O2 blast. The raw gas leaving the generator contains approximately 97% CO, 1.6% N2, 1% H2 and 0.5% CO2 and O2. Most of the ash in the fuel is volatilized and is present in the gas as smoke necessitating electric precipitation methods for cleaning. Although the experimental unit had a capacity of 25,000 cu. ft. per day of CO, extension of the same principle to larger units seems warranted.