7. Medium Pressure Fischer-Tropsch Units.
(a) General. The medium pressure units were expected to give more higher boiling materials, particularly wax and also to have a longer catalyst life. However, they had the disadvantage of giving a very paraffinic gasoline (still the most important product) with a lower octane number.
In the meantime processes had been developed which used Fischer olefins as feedstock, and it became necessary to revise operations to produce a maximum of olefins. The Germans succeeded in these attempts. The development was carried through by Ruhrchemie, Hoesch, and Lurgi. By the end of 1944 the RCH and Hoesch plants had substantially completed the construction of equipment to produce a maximum of olefins on their MP-FT units.
The process used consisted in a combination of staging and gas recycle (“Kreislauf”), the operating temperature being substantially unchanged. Plants could still use the original reactors and the standard cobalt catalyst as furnished by Ruhrchemie.