701.    DEWEY, D. R.  Hydrocarbon Synthesis.  Wartime Work of the Kaiser Wilhelm Institut für Kohlenforschung. Ind. Chemist, vol. 21, 1945, pp. 681-683; Chim. et Ind., vol. 55, 1946, pp. 327-328; CIOS Rept. XXV/27, 1945; U.S. Naval Tech. Mission Rept. (in Europe), 110-45; TOM Reel 196; PB 289, 890, L 86,445; Chem. Abs., vol. 40, 1946, p. 7,557.

     Supplements the disclosures made by F. Fischer on his retirement as Director in 1943 (abs. 972).  Co remains the best catalyst for the normal-pressure synthesis; the Fe catalyst was found to be unsuitable.  In the medium-pressure synthesis, use of the Co catalyst gives a low yield of olefins and a high yield of paraffins, whereas the contrary is true with the Fe catalyst.  The Fe can be combined with 2-3% Cu and up to 1% of alkali; the higher the proportion of alkali, up to this limit, the higher the average molecular weight of the hydrocarbons made.  A pressure of 20 atm. gives the highest factor of conversion and the best yield of high-molecular compounds.  Below 10 atm. the life of the catalyst decreases rapidly and above 20 atm. the formation of O-containing compounds begins.  The best composition for the synthesis gas is 1 CO:1H₂.  Typical yields with Fe catalyst are as follows:  C₃-C₄ compounds containing 50% olefins; 20% gasoline fraction containing 50% olefins; 40% fraction boiling 200°-300°; 20% waxes m.p. above 15° 20%.  The temperature for the Co catalyst is about 190°, for the Fe 240°.  Evidently Fe was used in the commercial process to save the available Co for the Kogasin synthesis; Fe produces the waxes in satisfactory quantity, and that was the main point regardless of the nature of the lower products and the smaller yield of waxes than with Co.  The direct synthesis of iso-compounds dates only from 1940-41 and began with the production of C₃H₈-C₄H₁₀ mixtures with up to 90% of iso-C₄H₁₀ in the C₄ fraction.  It is thought that the formation of iso-compounds arises from the chain of reactions; water gas to higher alcohols; dehydration of alcohols to olefins; hydrogenation of olefins to isoparaffins.  Catalysts capable of promoting the simultaneous progress of these reactions include ThO₂, Th and Al oxides, Zn and Al oxides, Al₂O₃, and ZnO with Th, Ce, or Zr oxide.  The reaction is best carried out with a gas 1.2 CO:1 H₂ at 450° and 300 atm. With a ZnO-Al₂O₃ catalyst the composition of the products from C₄ upward is:  C₄H₁₀ (90% iso-C₄H₁₀), 60-70% by weight; C₅H₁₂ (96-98% iso-C₅H₁₂), 20-30% by weight; C₆, C₇, and C₈ small amounts.  Up to about 10% of alcohols, mostly isobutyl, is produced also.  The proportion of compounds with different numbers of C atoms in the molecule may be varied by altering the composition of the catalyst; if the ZnO is increased the proportion of higher compounds rises, and vice versa.  The ZnO-Al₂O₃ catalyst seems to be the best commercial proposition, because of its cheapness, but a catalyst of Al₂O₃ and ThO₂ (4:1) gives less alcohol and permits a faster gas rate.  Above 300 atm. (the best operating pressure) O-containing compounds are formed in increasing amounts.  At 400° the yield includes a high % of alcohols; at a slightly higher temperature dimethyl ether is produced; there is quite a narrow band around 450° where iso-C₄H₁₀ is produced; above this temperature the deposition of C becomes excessive.  The synthesis is generally insensitive to S.  Catalysts are known to be good for 6 months without any decrease in activity.  With the Ru catalyst, chiefly solid paraffins of high melting point are produced at over 100 atm. pressure.  It is now known that a catalyst life of 2 yr. or more can be expected at an operating pressure around 100 atm. and that increased pressure gives an increase in both yield and molecular weight of the paraffins produced.  The reaction has been operated at 1,000 atm. with complete success.  The catalyst is very sensitive to S; the concentration of S must be as low as 0.01 gm. per 100 m.³ to prevent rapid poisoning.  At 475°-500° and 30 atm. pressure with a catalyst of Cr oxide or Mo oxide, a gas 1 CO:1 H₂ yields aromatic compounds.  The factor of conversion is poor, and much CH₄ is formed; each m.³ of synthesis gas yields up to 10 gm. of liquid containing about 50% aromatics and 50% naphthenes.  The aromatics are chiefly xylene and toluene.  At the high temperatures, C deposition is troublesome; an improvement can be secured by adding 5-10% of K₂C O₃ to the catalyst, but this slows the reaction rate.  By means of methylation, with a catalyst of methyl chloride, Al chloride and Al metal, any lower paraffin may be converted into a more highly branched paraffin containing 1 more C atom.  Thus far, success has been achieved only with the conversion of iso-C₄H₁₀ during the reaction, thus again giving neopentane; but iso-C₅H₁₂ and the other butanes all yield neopentane again, being evidently decomposed into iso-C₄H₁₀.