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SECTION I(b)

(9) Comparative Tests with Fe Catalysts.

In the above sections, development work on Fe catalysts by different companies has been described. The reader may find it difficult to compare the results of this work, since each investigator is inclined to report in a different manner and also because the main objective of research may have been varied.

Apparently the German government felt the same way. Furthermore, it believed a decision regarding the use of Fe catalyst, at least in the three MP synthesis plants had to be made. To settle the argument, a set of tests in which each participant furnished his catalyst and operating personnel and using the same pressure and temperature was conducted by the government. The tests were carried out in the winter of 1943. 1944 at the Brabag plant in Ruhland. (See reference 1(b)/26 to I(b)/33 at end of this section.).

Appended to this report is a set of charts giving the operating data of each tests and the comparative yields. In addition, there is a copy of the report of each participant, after completing the test and comparing his own results with that of the others. Little work was carried out after completion of these tests and the results therefore represent the present state of German development of iron catalyst.

Note however that the range of operating conditions were not too wide and better results undoubtedly could have been obtained, if no limitations had been imposed. The arrangements for the tests were as follows:

Each reactor consisted of one double tube containing 4.8 liters of catalyst (O.D. 44 mm. I.D., 24 mm. Height 4½ m).

The fresh feedgas (identical for all units) had a CO:H₂ ratio 1:1.25 (watergas) and 12% inert. S content under 0.1 gm/100 m³.

The product recovery was conventional. The analytical methods are described in the attached report. The catalysts used by the participants are listed below. It was of importance to the Germans that the catalyst would be produced in one of the existing plants and did contain a minimum of critical material, such as copper (“Sparmetalle”).

COMPOSITION OF Fe-CATALYSTS FOR “R.A. VERSUCHE”

(All quantities based on 10 m3 Cat. Volume).

It may be seen that the composition does not vary greatly. Lurgi used a somewhat higher alkali content. At the same time the yield of oxygenated compounds was highest over this catalyst. The catalysts vary however in regard to their apparent density as shown below:

I.G.’s catalyst is fuzed, hence the high density. Brabag and K.W.I. use no carrier, while the three others use different type of carriers. Assuming that Fe is the only really active ingredient, it is of interest to note that the great variance in iron content had but little effect on the space velocity and specific output of the catalyst.

From the attached data sheet it can been see, that based on 10 m³ catalyst volume (standard FT reactor), a daily yield of 2.55 tons to 1.93 compares favorably with LP cobalt operation. The yield based on feed (88% CO+H₂) Watergas was from 99.5 to 87.4 g/m³. Oxygenated compounds are excluded in these yields. The operating pressure was identical (10 at) in all cases. The temperature and V/H/V were up to the individual operator. At the end of two weeks all units had reached around 220° C. The space velocities varied between 105 to 110 on the average. A summary of the results is listed below:

The products vary within a reasonable range: Lurgi+Brabag gave the most hard wax, one of the objects of this race. Rheinpreussen produced a very light product, which might be considered a failure. I.G. and KWI apparently produced the most olefins. The gasolines varied only little among themselves and also if compared with an LP cobalt gasoline. (See report of Analysis by KWI). The waxes were tested for their use as feed to oxidation plants. No definite conclusions were reached on the subject, but it was feared that the wax paraffins might be too highly branched.

Only three of the six catalysts operated 90 days with the first batch catalyst. The others ran into coke trouble and had to renew the charges repeatedly (4 times in the case of Rheinpreussen), before the required 90 days run could be completed. This was a serious drawback. If the catalyst could not be prepared with sufficient assurance that coke deposit would not occur, it could not be considered ready for commercial application. (Coking of an FT oven is serious problem requiring a shutdown of several weeks for cleanout).

The important fact about these tests is apparently that all participants obtained reasonably good results, under conditions similar to those used in MP cobalt operation with a set of greatly different Fe catalysts (great difference in Fe content). Another fact is the general use of copper and alkali to promote the catalyst.

Liquid Phase Operation

The idea of conducting the FT synthesis in liquid phase is not new as it had been attempted along time ago by Fischer. Today, it is considered as promising and research on the subject was carried out notably by I.G. Farben, Ruhrchemie, and Rheinpreussen. The easier control of the reaction temperature is the main incentive for the use of such a system. The main drawback, if any, is the probably loss in catalyst efficiency, a point which is not yet clear. Three types of operations were tried:

1. “Oel Kreislauf”: The use of a solid catalyst bed with the oil being circulated over the catalyst concurrently with gas.
2. “Schaumfahrweise” Suspension of the catalyst in the oil phase and dispersion of the catalyst by the gas using a ceramic disc or mechanical stirrer. The heat of reaction is removed by circulating the slurry through an eternal cooler.
3. Static liquid phase: Similar to (b), but the heat of the reaction is removed by a set of cooling tubes which are inserted in the liquid.

Systems (a) and (b) were used by I.G. Farben and system (c) by Rheinpreussen.

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