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Section 1(b)

(5) Ruhrchemie.

The long experience of RCH with cobalt catalyst operation led them to develop catalysts containing Fe precipitated on a carrier. Their objective shifted from time to time to Fe catalysts for olefine production, wax for production, or for catalysts to replace cobalt in existing FT units. RCH succeeded in developing a good Fe catalyst for wax production which would be operated exceptionally low temperatures, but the olefine producer did not get beyond laboratory stage.

During the regular FT meeting at Essen in September 1940, Dr. Roelen gave some information regarding the RCH work. Their findings are generally in good agreement with those of other laboratories. The main difference according to RCH of Fe versus Co is the lower hydrogenating capacity of Fe. This results in 3 important advantages.

1. There less CH₄ formed despite the fact that all Fe catalysts require higher temperatures than cobalt.
2. The products are more olefinic.
3. Fe can consume CO and H₂ over a much wider range. The first advantages allow a variation of operating conditions over a much wider range than cobalt with corresponding varying boiling ranges of the product, without lowering conversion or increasing methane.

The second is obvious as olefins are a very desirable product (for lube oils and Oxo-synthesis).

Third allows the use of straight watergas without shift.

RCH claim, they can start an Fe catalyst by different methods, such as H₂ reduction, watergas reduction or CO reduction. But it appears that here too the “forming” of the catalyst, the formation of the carbide must precede the actual synthesis.

In accord with KWI, it was found that addition of alkali (in very small concentrations) had a decided effect on the boiling range of the product. The following data were given:

While it is possible to vary the results with small changes in catalyst composition without any change in the operation, it is also possible to vary the operating conditions using the same catalyst and thus obtain varying results. For example, an increase in pressure raises the boiling range (same as over cobalt), all other conditions being equal:

For a proposed commercial operation to give maximum wax production, the following data were given by RCH. The catalyst is a ppt’d Fe cat:

This described catalyst was to be used for production of wax. If olefins were the main objective of the synthesis, the same catalyst with a higher Kieselguhr content was sued. As much as 10 m³ of the wax catalyst had been prepared in pilot plant operation. The following information was obtained regarding the preparation of this catalyst:

The iron is dissolved to give a solution of Fe (NO₃)₂ (non-ferric Ion), Cu is added as well as Ca (NO₃)₂ with Fe: Cu: Ca in the proportions 100-15-5. The metallic mitrates precipitated as carbonates by pouring the hot solution into a solution of hot soda. The endpoint of the recipitation is at 6.6-6.8 pH. At the end of the precipitation Kieselguhr is added and the batch is filtered. The cake is washed free of NO3 (0.4%, Na NO₃ on 100% Fe is maximum), is then slurried in a 20g/lit. KOH solution and again filtered, dried and formed.

The catalyst is next reduced with a mixture of H₂:N₂=3:1 using a space velocity of 3000 V/H/V in an analogous manner to cobalt catalyst. The reduction is carried out with hot gas (300° C). As soon as the catalyst has reached this temperature the reduction is complete (¾ hour).

The reduction occurs in steps from Fe (OH)₃ ---------Fe₂ O₃--------Fe₃O₄---------FeO--------Fe. With the stages overlapping, the several oxides are present in the final product. A good catalyst should, in fact, not contain more than 5-8% Fe based on the total iron present. The value of “total reduced Iron” (Reduktionswert”) was used to control the reduction. It should ;not exceed 65-75%. This value is determined by using 2% acetic acid. The catalyst is cooked 1½ hours in an excess of this acid. Fe and FeO dissolve, the remainder represents the unreduced iron oxide.

In starting a new batch, the catalyst is operated using watergas at minimum pressure at 130° C for ½ to 1 day. Following the “forming” the temperature and pressure are raised to operating level. The CO₂ usually added before shipment must be added very carefully to avoid overheating, since the heat of adsorption is very high.

The wax yield over this cycle depends largely on the proper KOH content (3.O%) of the fresh formed catalyst. The operating conditions for wax production are identical to those given under Lurgi Kreislauf operation and may be noted there.

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