A development by Farben [33-35] consisted of an oil circulation process in which cooling oil was passed simultaneously with syngas over iron catalyst particles (fused or sintered iron dually promoted with aluminum and potassium oxide or titanium, oxides of manganese and potassium ). Cooling is achieved by circulating oil heated by an exothermic reaction through an external heat exchanger. The process operates at a pressure of 20 to 25 atm (2.02-2.53 MPa) and a temperature of k2o compound name  260 to 300°C in the first stage, or 280 to 330°C if the second stage is used. Syngas production is controlled (H2/CO = 0.8 in this example) to produce about 0.5 kg of total product per liter of catalyst per day. The yield of C3+ hydrocarbons is about 150 grams per cubic meter of syngas (H2/CO = 1 in this example), with the following distribution: 16% C3 and C4 (85% olefins), 40% gasoline boiling up to 200°C (50% olefins), 20% gas oil (25% olefins), 20% paraffin and 4% alcohols, mainly methanol and ethanol. Naphtha has a research octane number of 62 to 65 and gas oil has a cetane number of 70+. Some of these patents have been assigned to the Standard Catalytic Company. The Standard Catalytic Company was formed by six U.S. oil companies to develop a synthetic fuel production process and entered into an agreement with Farben. After World War II, legal action splits the shares of Standard-Farben Corporation. Jersey acquired full title to 544 patents and ownership of the Standard Catalytic Company. Jersey retained half ownership of an additional 254 patents. Benson et al. [36] reported that, following preliminary work by F. Duftschmid et al., a pilot plant with a reactor diameter of 0.2 m and a height of 6 m (about 0.75 m3) was built during 1936 and 1937, as described above , and it operates first at 100 atm (10.1 MPa) and then at 15 to 20 atm (1.5 to 2.0 MPa). In 1938, a larger plant with a diameter of 0.5 meters and a height of 6 meters (4.7 cubic meters) went into operation. The recirculation rate is high, with 9-12 reactor volumes of catalyst/oil recirculated per hour [37]. At the end of the war they planned to build a 40,000 t/yr (860 bpd) plant for this process [37].
The Duftschmid process is considered to be different from the process developed by Ruhrchemie (described below) because the entire solid catalyst bed is submerged in oil [36]. However, Farben obtained a patent [38] in which the oil is sprayed onto the catalyst in a fixed bed. Liquids pass in the same direction as gases. They point out that while it is desirable to have a thin layer of liquid on the catalyst surface at all times, it may be advantageous to temporarily interrupt the trickle flow to induce a brief increase in catalyst temperature and, in effect, a catalyst regeneration step.
Early German liquid phase reactors consisted of a series of trays, each containing catalyst particles, contained in a cylindrical vertical reactor with a reflux condenser at the top and a reflux condenser at the bottom of the reactor. A device for liquid removal [35, 39]. The experiments were carried out in a 7-tray reactor with upward flow of reaction gas, 4.5 cm in diameter and 60 cm high.