2673.     ---------------.  [PICHLER, H.]  Lecture and Discussion on Iron Catalysts for the Middle-Pressure Synthesis, Sept. 9, 1940.  TOM Reel 101; Transl. on TOM Reel 244, 21 pp.

                    In general, it has been found that the best catalysts are those prepared by precipitation of ferric nitrate solutions with Na₂CO₃ or NH₃; they are designated normal Fe catalysts.  They must be inducted before use, and the best method, therefore, appears to be that of passing pure CO at lower pressures and higher temperatures than are used in the following synthesis and at a high gas velocity, for example:  1/10 atm., 255°-325°, and 400 l. of CO gas/kg. Fe/hr.  The induction period is terminated when the formation of CO₂ has passed through a maximum and has reached a more or less constant minimum value, generally in about 25 hr.  With a catalyst thus inducted, a synthesis pressure of 15 atm., a temperature of 235°, and a synthesis gas composition of 3 CO:2 H₂, maximum yields of 130-160 gm./N m.³ of gas can be obtained.  An Fe catalyst made and operated as above had a life of 1 ½ yr. without regeneration at a temperature of 260°; it still gave a yield of 140 gm./N m.³  The ideal synthesis gas was produced by passing CO₂ and steam over hot coke according to the equation 5 C+4 H₂+CO₂=6 CO+4 H₂.  The CO₂ for the conversion is obtained by scrubbing the end gases from the synthesis process.  Addition of small amounts of alkali (0.5-5% K₂CO₃) to the Fe catalyst has no important effect on the total yield of products but does change their quality, an increase in the paraffins and oxygenated products and a decrease in the liquid and gasol hydrocarbons with increasing alkali contents.  The lifetime of the catalyst also is longer at a low alkali content (1% K₂CO₃ or other alkaline salt) than it is at a higher content.  It was found that treatment of the catalyst with H₂ either before induction with CO or between the induction period and the synthesis proper offers no improvement in the activity of the catalyst.  Some increase in the activity and a better stability of the catalyst does, however, result by interrupting the synthesis and treating with H₂; this must be done before the catalyst has deteriorated to a great extent.  The use of kieselguhr as carrier in the Fe catalyst is detrimental to its activity unless added after alkalization.  As regards mechanism of the induction process, it is assumed that the primary reaction is the reduction of the ferric oxide into ferromagnetic Fe₃O₄, which, at the low temperature and pressure of the induction, is converted directly into carbide by action of the CO without going through the Fe phase.  In presence of 100% CO induction gas and at the low pressures and high CO velocities used during the induction, the CO₂ is rapidly removed from the catalyst and the carbide remains stable without oxidation.  The action of CO on the Fe catalyst is 3-fold:  the reduction process differs from the H₂ reduction, the CO deposits free C on the catalyst thus loosening the crystal lattice and making more surface available for the reaction, and carbides are formed.  With a CO+H₂ mixture, liquid and solid hydrocarbons are forming on the catalyst surface and preventing the activating gases from coming in contact with the catalyst.  Some description is given of the products of the middle-pressure synthesis.  The Fe catalysts are not only superior to the Co catalysts because of their cheapness, but also for the cheaper apparatus required and the more stable lifetime that they exhibit.  The antiknock properties of the benzine made with the Fe catalyst are better than those made with the Co catalyst, and the unsaturated gasol hydrocarbons can be used to greater advantage for production of high-quality benzine3.  Fe catalysts have the disadvantage of working at higher temperatures, hence greater steam pressure, if cooling is done with H₂O.  Furthermore, they have a greater tendency to form C than do the Co catalysts.  This report includes the only published data on induction methods for Fe catalysts.  The documents translated are:  PG-21559-NID; PG-21574-NID (lecture by Dr. Pichler); PG-21581-NID (recent investigations); and PG-21577-NID (behavior of Fe catalysts where operated with H₂-rich synthesis gas.)