3288.     ---------------.  [STORCH, H. H.]  Fischer-Tropsch and Related Syntheses.  Crucible, vol. 31, 1946, pp. 52, 54, 56, 58, 60.

        Paper given before the Physical Chemistry Division of the Pittsburgh Section of the American Chemical Society, which reviews German process development, followed by an analysis of kinetic data pertaining to the mechanism of the synthesis.  The prevailing operating process in Germany was that with a Co-Th-Mg-kieselguhr catalyst at 200°, 1-10 atm. pressure, and in 2-3 stages with yields of 150 gm. of product per cu. m. of 2 H₂+1 CO.  This method was improved by recycling 3 vol. of endgas from the 1^st stage, with condensation of product after each cycle and increase in yield of 30%.  By using H₂+1 CO instead of 2 H₂+1 CO, olefins were increased 20-55%.  A hot-gas recycle process was developed using a sintered Fe catalyst at 320°, 20 atm., and ¾ sec. contact time.  The space-time yield was 1 kg. per l. of catalyst per day.  A liquid phase operation with suspended Fe catalyst also was under development which yielded a better grade of gasoline of 90 octane number and more diesel fuel.  Two outstanding developments were the Synol and Oxo processes.  The former produces liquid hydrocarbons (50-65%) and alcohols (50-35%), boiling at 50°-350°, operates at 18-25 atm. and 200°-235°, with gas of 1 CO+0.8 H₂ composition, using as catalyst granules of fused Fe₃O₄; Al₂O₃:K₂=97:2.5:0.4.  The hydrocarbons are partly branched, the alcohols are normal.  The Oxo process consists in reacting a slurry of olefins with 3-5% of Co:ThO₂:MgO:kieselguhr=30:2:2:66 catalyst with 1 CO+1 H₂ gas at 200 atm. and 150°-170°.  The product (80% aldehydes and 20% alcohols) is hydrogenated at the same pressure and 180°-200° to produce the alcohol corresponding to the treated olefin with the addition of a C atom.  Important factors in the probable mechanism of the Fischer-Tropsch process are discussed.  The order of the reaction on Co, Ni, Fe, and Ru catalyst appears to be 0-1.  The life of the catalyst is increased markedly by operation of 7-20 atm.  Maximum conversion is obtained with Co catalysts at 5 atm. and space velocity of 150 vol. of gas per vol. of catalyst per hr.; with Ru more than 200 atm. is necessary.  The temperature coefficient on Co and Fe catalyst is about 1.6 per 10° in the range 190°-235°, corresponding to an activation energy of 20 kcal. per mol. of 2 H₂:1 CO.  The above catalysts form relatively unstable carbides with CO, which react with H₂ at temperatures below 350° to yield, quantitatively, CH₄ plus C₂H₆.  Above 350°, considerable decomposition to C occurs.  For maximum activity and life, Co catalysts should be inducted and reduced with H₂, and the initial synthesis should be prolonged at atmospheric pressure for several days before increasing the pressure to 10 atm.  Fe catalysts are preferably pretreated with CO at 0.1 atm. at the rate of 100 l. per 10 gm. of Fe, space velocity 4-25 l. of CO per hr., 325° before operation with synthesis gas at 10 atm.  Treatment with H₂ after the carbiding does not affect the activity of Fe catalysts, although the Fe carbide is converted to elemental Fe.  It is believed that the initial carbiding distorts the lattice structure enough that subsequent exposure to synthesis gas reforms the carbide.  Bureau of Mines tests show that the carbiding rate on Co catalysts is of the same order of magnitude as that of the synthesis.  The ratio of CH₄:C₂ hydrocarbons in the products from a Co catalyst is about 10, while that from an Fe-Cu catalyst is 0.5.  C₂H₄ plays an important role in the synthesis on Co but not on Fe-Cu catalysts.  The proportion of oxygenated organic compounds (chiefly alcohols) in the liquid products from Fe catalysts is greater than that from Co catalysts.  The chief oxygenated product from Co catalysts is H₂O and from Fe catalysts is CO₂, the ratio of H₂O:CO₂ in the products from the latter increasing with the pressure.  The reaction in the Fischer-Tropsch synthesis is relatively slow, 30 sec. of contact for a 60-70% conversion, as compared with 0.2 sec. for the reaction CO and steam over a Co-Cu catalyst at 325°.  This probably is due to the critical spacing of the metal atoms in the catalysts lattice.  A possible mechanism for the synthesis on Co and Fe catalysts is outlined in a series of equations depicting the reactions involved in the formation of normal a olefins, branched paraffins and oxygenated compounds.