929. FIELDNER, A. C., FISHER, P. L., AND BREWER, R. E. Ninth Annual Report of Research and Technologic Work on Coal in 1944. Synthesis of Liquid Fuels by Hydrogenation of Carbon Monoxide. Bureau of Mines Inf. Circ. 7322, 1945, pp. 75-79; Chem. Abs., vol. 40, 1946, p. 5897.
Critical discussion on the preparation and properties of metal carbides and the reaction mechanism between CO and Co or Fe or their oxides to form carbides was published. (See abs. 1434). The reaction is stated to be much too slow to account for the rate of synthesis of hydrocarbons by reduction of carbides with H2 when a mixture of CO and H2 is used. It is known that the presence of H2 with CO markedly accelerates the formation of C, which appears to proceed by way of the metal carbide. Since Co is a much more active catalyst than Fe for the water-gas reaction and because the most active Fe catalysts catalyze this reaction to only a slight degree at temperatures below 300°, it appears probable that H2O and CO2 are primary products on Co and Fe catalysts, respectively. Although metal carbides are formed on both Co and Fe, there is evidence that the mechanism of the synthesis on Co catalysts differs from that on Fe catalysts. An investigation has been made on the correlation of the physical properties, particularly X-ray diffraction pattern and ferromagnetism, of Fe catalysts with their mode of preparation and activity. An analysis of published data shows that the reaction rate in the Fischer-Tropsch synthesis is directly proportional to the partial pressure of the synthesis gas and inversely proportional to that of the products. The retardation of the rate by the products is large enough so that only little advantage is obtained, so far as space-time yield is concerned, by increasing the operating pressure from 5 to 20 atm. Under a total pressure of about 1 atm., dilution of the synthesis gas with N2 decreases the yield of liquid hydrocarbons per unit volume of gas but does not decrease the % conversion. In fact, such a dilution results in a conversion somewhat greater than would be calculated on the basis of a first-order-reaction. Photographs illustrate some of the development work being accomplished. The type of converter used in the Ruhrchemie plants to regulate the heat-transfer problem is illustrated. The catalyst is packed in narrow spaces between steel sheets through which cooling tubes are interlaced. Water under pressure is circulated through the tubes. The cost of such a converter is relatively high because of the large amounts of steel used per unit of oil produced. A promising method of removing the heat of reaction has been tested by the Bureau. It consists of flushing a cooling oil of proper boiling range over the catalyst particles, the heat of vaporization of this oil being supplied by the heat of the synthesis reaction. It has been found possible to maintain virtually complete adiabatic conditions in the converter, and precise temperature control has been readily obtained.