Medium pressure synthesis with iron

Medium-Pressure Synthesis with Iron Catalysts. 284... 

I.G. Farbenindustrie, Rheinpreussen, and Others—Modification of Medium-Pressure Synthesis with Iron Catalysts (hot gas recycle,... 

Medium-pressure synthesis with iron catalysts. Up to January, 1935, the maximum yields of C5+ hydrocarbons obtained with iron catalysts at atmospheric pressure were 30-40 g./m.3 synthesis gas. The decline of catalyst activity amounted to 20% within 8 days (19). Fischer and Meyer (20) improved the yields of the normal-pressure synthesis with iron catalysts (in 1934-1936) to 50-60 g./m.3 synthesis gas and the lifetime of the catalyst from 8 days to about 30 days. These results were obtained with iron-copper precipitation catalysts (1 atm., 230-240°C.). The decline of catalyst activity was closely connected with changes of the composition of the reaction products. The color of the synthetic products changed from white to yellow and formation of fatty acids and organic iron salts was detected. Increased carbon monoxide content of the synthesis gas and increased alkali content of the catalyst accelerated this phenomenon. 

Fischer reported these results in the fall of 1937 to the German industry, and Pichler gave detailed data in a talk on Medium-Pressure Synthesis with Iron Catalysts on September 10, 1940 (22). 

Recycle operation is also advantageous for the medium-pressure synthesis with iron catalysts. The advantages of the gas recycle are not the same as with cobalt catalysts due to the fact that iron catalysts have a greater tendency to form carbon dioxide in addition to hydrocarbons (instead of water) and to produce highly unsaturated hydrocarbons also in single pass operation. In the case of iron catalysts the gas recycle increases the tendency to produce water and changes the consumption ratio of hydrogen-carbon monoxide, and has a favorable influence on the... 

Schwarzheide—experiments with iron catalysts (comparison of different precipitation catalysts with a Nil 3 type fused iron catalyst). In view of the favorable results obtained by the Coal Research Institute in Miilheim (Fischer Pichler, 1937), industrial companies started experiments on medium-pressure synthesis with iron catalysts. 

In 1943 it seemed preferable to replace the cobalt catalysts of the medium-pressure synthesis with iron catalysts without changing the converters. Comparative experiments were carried out by different groups in order to find out the status of the development work. The experiments were performed on the basis of the following rules ... 

I.G. Farbeninduslrie, Rheinpreussen, and others—modification of medium-pressure synthesis with iron catalysts (hot-gas recycle, oil slurry, oil recycle). Hot gas recycle. As already discussed, recycle operations (with removal of liquid reaction products after each step) with a ratio of recycle gas to fresh feed of 1 1 tconsumption ratio of hydrogen to carbon monoxide, increase in some cases the olefin content of the products and the total yields, and result in a smoother operation which can be important for the lifetime of the catalysts. 

Under the title Synol Process Wenzel (46) published experiments in the field of the medium-pressure synthesis with iron catalysts. The following conditions were mentioned as promoting the formation of alcohol (a) low synthesis temperature (preferably below 200°C.), (b) high pressure (e.g., 20 atm.), (c) operation in several stages, preferably with recycling of gas, minimum conversion in each stage, and removal of carbon dioxide between the stages. 

In connection with their work on medium-pressure synthesis with cobalt catalysts, Fischer and Pichler began (1936-1937) some research work with iron catalysts too. The first positive results, comparable with results obtained with cobalt catalysts were achieved when an iron precipitation catalyst that had been in use at atmospheric pressure for several weeks was switched to operation at a synthesis gas pressure of 15 atm. The initial pretreatment of the catalyst at 1 atm. proved to be necessary for the successful use of the catalyst at higher pressure. The combination of proper pretreatment (reduction and carbonization) followed by synthesis at elevated pressures increased the yields of Cs+ hydrocarbons to more than double and the lifetime of the catalyst was... 

Pichler and Merkel (24) investigated the composition of iron catalysts at various stages of pretreatment and synthesis by chemical and thermo-magnetic analysis. Copper-free iron catalysts, carburized at 325°C. before medium-pressure synthesis, were virtually completely transformed to a ferromagnetic higher iron carbide with a Curie point of 265°C., whose formula corresponded to approximately Fe2C. 

D. Iron catalysts for medium-pressure require pretreatment with reducing gases. A very cautious reduction of fused iron catalysts with pure dry hydrogen was necessary while active catalysts could be pretreated with synthesis gas only. 

The synthesis of formamides was discovered by W. Reppe in the 40s using iron, nickel or cobalt catalysts under high pressure. Use of bases (NaOH, NaOMe, etc.) in alcohohc medium has recently allowed much milder conditions hence dimethylformamide can, for example, be prepared at room temperature under only 5 to 10 bar with excellent yields (Table IX). 

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