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1. Object of Investigation

The Ruhrchemie works at Holten has previously been visited by more than one party of investigators. Reports on the Fischer-Tropsch plant of Ruhrchemie A.G. (30/XXVII-69)* and a supplementary report on Ruhrchemie A.G. (30/XXXII-96) are already available. In addition Prof. Martin, president of the directors and Dr.Roelen, chief chemist, have been interrogated in London. A large number of documents which were evacuated from Holten during the war were discovered at Reelkirchen, nr.Detmold, and the most important of these were taken to London.

It was desired to ascertain the whereabouts of the remaining documents which had been left at Reelkirchen. Arising from the discussions with Prof. Martin and Dr. Roelen, further details were required concerning the process for methanisation of coal gas and about Ruchrchemie’s experiences on manufacture and grading of catalysts in general, and cn the removal of organic sulphur compounds from gases. It was also desired to obtain information on the stage of development reached in processes for the production of acetylene from methane or natural gas and of hydrogen cyanide from mixtures of methane or natural gas with ammonia. It was known that Ruhrchemie A.G. held patent rights for a method of carrying out these reactions.

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2. Personnel Interrogated

The following were interrogated at Sterkrade-Holten on March 7th and 8th, 1946:

Director Schrieber
Director Tramm
Dr.Rohe (Legal adviser)
Dr.Heckel (Research chemist, catalyst preparation)
Dr.Hanisch (Research chemist, assistant to Dr.Roelen)
Dr.Gehrke (Chemist in charge of catalyst manufacture)
Dr.Herbke (Chemical engineer, catalyst reduction)
Dr.Kolling (Research chemist, production of acetylene and cyanides))

* These reports are CIOS Final Reports, and the reference numbers should be quoted as follows:- CIOSXXVII-69, Item and CIOSXXXIII-96 Item 30>

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3. Return of Evacuated Documents.

Dr.Röhe stated that all remaining documents at Reelkirchen were brought back to Holten with the permission of the military authorities, between June and September 1945. They have been classified and distributed to the appropriate departments of Ruhrchemie. Since the documents required by us were produced, it was not thought necessary to examine all those brought back from Reelkirchen.

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4. Catalysts made by Ruhrchemie

Besides making cobalt Fischer catalyst for their own and other synthesis plants in the Rhur, Ruhrchemie have made iron Fischer catalyst, iron oxide-sodium carbonate “Feinreinigungsmasse” from synthesis gas, nickel catalyst for methane synthesis, and chrome-alumina dehydrogenation catalyst.

Contrary to the information obtained by a previous team, however, it was denied that carbon monoxide conversion catalyst was made on these works. A sample produced was said to be the standard product sold by I.G.

Full details of the preparation of the nickel catalyst were obtained and the plant, which is not seriously damaged, was inspected. As the process of coal gas methanisation is primarily associated with Rhur-gas A.G. information obtained is fully reported in connection with the latter target.

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5. Pelleting and Grading of Catalysts

It is generally necessary that any catalyst for a gaseous reaction shall be in the form of pellets or granules between certain limits of size. Ruhrchemie have carried out experiments on the granulation of catalyst over a number of years, mainly confining their attention to precipitated catalyst supported on kieselguhr.

The simple procedure of breaking up and screening the dried filter-cake gives an excessive proportion of fines and dust to unable product, and is not employed on the technical scale. Four improved methods have been either used or investigated by Ruhrchemie.

(a) The standard process for making cobalt Fischer Catalyst

In this process the wet filter cake is pressed into threads, which are dried, forced through a screen, and finally graded on a vibrating screen. This method has been fully described in the report on the Sterkrade-Holten Fischer-Tropsch plant. 30/XXVI-69.

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(b) The so-called “Kornmuhle” Process

In this method the precipitation, filtering and washing stages were similar to those in the standard process. The machine for for extrusion of the moist cake, which was also like that for the cobalt catalyst, but slightly smaller, was a wedge-shaped trough, about 3 ft. long, 2 ft. 6 in. deep, and 2 ft. wide at the top. About half-way down were two impellers, resembling those of a Rootes blower, and occupying the whole length of the trough. Below these, a third axle was geared to rotate at about the same speed as the impellers. This was understood to be some form of agitator, to avoid separation of water from the paste before extrusion. In the bottom of the trough were two rows of holes, some 3/16in. in diameter and about ½ in. apart.

The threads passing from the extruder were caught on a moving belt, and carried through a drying cabinet, about 6 yds. long. In this, the belt was heated from below by a series of burners. Thus in this process, as opposed to the other method used for cobalt catalyst, the threads were carefully kept apart during the drying stage. Finally, the dried threads, which came off the belt in lengths of up to several inches, are passed through the “Kornmuhle”, a vertical cylinder about 5 ft. high and 1 ft. diameter. This contains a vertical axle rotating at fairly high speed, and carrying four platforms with radial ribs on each. By means of a series of truncated cones attached to the outer casing, the catalyst is fed to the center of each rotating platform, and thrown centrifugally against the outer casing where it is redirected towards the center by the next cone and so on. It was said that the threads are broken into lengths roughly equal to their diameter; fines amounted to only 10% of the product, compared with 40% standard process. The plant, which had been used for making nickel catalyst, had an output of ½ cu.m.per day.

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(c) Buttner Drum or “Schiffchen” Process.

In this process the catalyst paste was pressed into depressions in the outer surface of a steel drum, heated internally, and rotated at such a speed that the catalyst was dry after about ¾ of a revolution. The process had only been used on a experimental scale, but a full-sized drum, capable of producing 5 cu.m. of finished catalyst in 24 hours, was in course of construction in co-operation with the firm of Buttner, of Krefeld. This model was inspected. It consisted of a steel cylinder, 6 ft. in diameter and 4 ft. long mounted to rotate on a horizontal axis; grooves about ⅛in. wide, 1/16 in. deep, at 4 grooves per inch, were machined on the outer surface, into these grooves, steel strips 1/8 in. wide, ¼ in. deep with 1/8 in. teeth cut on one edge, were bent into position, and it was proposed to weld the ends of these strips together to make complete rings. Finally, plain strips ⅛ in. x 3/16 in. were to be placed between the toothed strips to bring the surface of the completed drum flush with the tops of the teeth. The pieces of catalyst produced would thus be of approximately half cylinder shape, and were referred to as “Schiffchen”.

The paste was to be fed by three feed screws into a box about 4 ft. x 6 in whose open side was to be pressed side. The drum would rotate at 20-25 revs. per hour, and most of the dried particles would fall out after completing ¾ revolution, as the result of shrinkage. The removal of the dried particles would be assisted by tapping the drum.

The surface of the drum was finally to be cleaned by means of a brush fixed below the feed box.

Dr. Heckel spoke highly of this plant in so far as its performance could be judged from the smaller-scale work. It was said to give only 5% fines and dust in the total product.

On the other hand, Dr. Roelen, who had been interviewed in London some months earlier, appeared to have little confidence in this process and stated that work on it had been discontinued during the war. Judging from the condition of the drum under construction, this latter statement appears improbable.

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(d) Dry pressing of catalyst.

Ruhrchemie have experimented from time to time with compressed or tableted catalysts, but do not recommend them. To obtain a coherent tablet, pressures in excess of 500 atm. are required which results in insufficient porosity. This agrees with Dr. Roelen’s statement that, for a given porosity, the hardness and particularly the abrasion resistance of a catalyst obtained by drying a paste or filter cake will be higher than that of one obtained by dry pressing.

It does not appear that any large-scale dry pressing plant was ever used, but there was a tableting press by Killian in the laboratory. This was a plunger type not differing in any essential respect from similar machines of British design. It was stated that a small ring-press made by Koppern of Hattingen had been tried, but failed entirely and was scrapped.

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6. Organic Sulphur Removal

Ruhrchemie have carried out extensive researches on the removal of organic sulphur compounds both from synthesis gas or coal gas. As regards the former there little to add to the information obtained by teams investigating the Fischer-Tropsch process. The iron oxide-sodium carbonate Feinreinigungsmasse was invariable used. A superior form of material with an unusually high porosity was stated to be made by Brabag for use in synthesis plants in Eastern Germany. Its iron oxide constituent was Lautermasse, somewhat similar to Luxmasse. Part of this was pasted with the sodium carbonate and the remainder added subsequently to the hot paste, prior to forming it into suitable-sized pellets. For high porosity, it was important that the mass, before forming, should not be at all fluid. The product so obtained could be used at rather lower temperatures, and achieved a better removal of organic sulphur than other forms of Feinreinigungsmasse was unsuccessful with coke-oven gas. When fresh it reduced the total sulphur to about 1gm/100 cu.m. but it quickly became fouled. The sulphided nickel-magnesiakieselguhr contact ultimately developed for the Ruhrgas process of coke-oven gas methanisation was claimed to reduce the organic sulphur of oil washed gas to as low as 0.2 gm/100 cu.m. The preliminary oil-washing used 1.6kg/cu.m of oil at 25°C., and left in the gas 100-150 gm benzole and 15-25gm organic sulphur per 100 cu.m.gas.

A copper sulphide contact was also experimented with and gave promising results. The nickel sulphide catalyst was preferred, however, largely because it could so readily be made from the spent methanisation catalyst.

The performance claimed for the nickel sulphide contact was not fully substantiated by the actual test figures obtained at the Altenessen plant, which showed an average organic sulphur after the Luxmasse catch box of about 0.8 gm/100 cu.m. It was explained that the Altenessen figures were averages over fairly long periods, and included occasions when the purity of the original coke-oven gas was far below standard, owing to effects of air attacks on the coke oven plants.

Methods of determining organic sulphur compounds in gas were discussed. Apart from the ordinary combustion method in which the sulphur is eventually determined as sulphuric acid, Ruhrchemie have used a method in which the sulphur in the organic compounds is reduced to H₂S over silica at 700°C., the H₂S being absorbed in cadmium acetate solution and determined in the ordinary way.

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7. The production of Acetylene and Cyanides from Methane and Natural Gas.

(a) Summary

Ruhrchemie A.G. developed a process for the production of acetylene from methane during the years 1929-1938, and successfully operated a semi-industrial scale plant converting 30 cu.m. of methane per hour. This plant was inspected and found to have been almost completely destroyed by bombing. A full scale plant was designed during the war, but was not constructed. The process was intermittent, and consisted of alternate reaction and heating periods in a furnace packed with special refractory materials maintained at 1400-1500°C. During the reaction periods methane was passed through the furnace at reduced pressure (70-80 mm. Hg), and was thereby converted to acetylene, diacetylene, hydrogen and carbon. During the heating periods, which were carried out at atmospheric pressure, the heat lost in the reaction periods was restored by burning a further quantity of methane with air in the furnace. The carbon deposited during the reaction periods was also burnt during the heating periods. The gaseous products of the reaction were separated by scrubbing with water in several stages carried out at different pressures.

Laboratory-scale experiments on the production of cyanides and ethylene from methane and ethane had been carried out.

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(b) General

The process was developed on a laboratory and semi-industrial scale by Ruhrchemie A.G. in the period 1929-1938. It was based on researches carried out at the Kaiser Wilhelm Institut by Fischer and collaborators on synthesizing benzene. It was found that methane cracked to acetylene when heated to a sufficiently high temperature, and that some benzene was also formed. The yields of benzene, however, were always small, and the acetylene largely decomposed to carbon and hydrogen during cooling.

The best yields of acetylene were obtained when methane was heated to 1400-1500°C. at a low pressure. The optimum pressure found for the reaction was 76 mm. Hg. No catalyst was necessary for the reaction, but it was always found that the yield of acetylene improved with time because a film of hard carbon was deposited on the surfaces of the reaction vessel and its presence inhibited secondary decomposition.

A small-scale plant was developed in 1936, in which the process gas, after passing through a high temperature zone at low pressure, was shock-cooled by means of a water spray. The reaction products were then separated by a fractional scrubbing process with water. The problems which had to be overcome were:

1. to find a suitable method of maintaining the reaction temperature at 1400-1500°C. and supplying the endothermic heat of reaction.
2. to minimize the formation of undesired byproducts, the chief of which were carbon and diacetylene.
3. to recover the acetylene formed with a high degree of purity, free from diactylene. The latter is explosive and also forms resins with the acetone used in the storage bottles.

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(c) High Temperature stage.

The process was operated intermittently in a “regeneratively” heated furnace. In the experimental plant this was a tower 4m. high and 29m. internal diameter, with double steel walls. The central 3m. was occupied by a column of packing consisting of 2m. of firebrick surmounted by 1m. of alumina plates of special construction.

The temperature was maintained by running alternate one-minute heating and reaction periods. During the heating period, heating gas and air were burnt at atmospheric pressure at burners in the head of the furnace, after being preheated by passage through the double wall. The waste gases passed downwards through the packing. The temperature at the top of the column rose from 1450° to 1500° during this period. the heating gas and air supplies were then shut off, and the pressure was reduced to 70-80mm.Hg. The change-over valves were located in cool parts of the gas circuits..

In the reaction period, the process gas (containing99 per cent of methane) was passed upwards at 60 cu.m. per hour. Decomposition of methane to acetylene, diacetylene, hydrogen and carbon occurred in the section of the column which was packed with alumina plates, where the temperature was 1150-1500°C. The lower 2m. of the column preheated the process gas.

72 per cent of the methane was decomposed, half to acetylene and diacetylene and half to carbon. The carbon formed was deposited on the alumina plates in a reactive form and was burnt off in the following heating period. The gaseous products were stated to be completely free from suspended carbon. The composition of the gas leaving the reaction zone was:-

H₂ 70.7, CH₄ 15.7, C₂H₂ 90.8, C₄H₂ 0.3, N₂ 3.5 per cent.

The proportion of diacetylene formed was stated to be smaller than in the I.G. plant at Hüls (arc process).

The shock-cooling of the gas leaving the furnace reduced its temperature to about 40°C.

The alumina plates which occupied the reaction zone of the furnace where 15 x 10cm. and 7 mm. thick, and were arranged in layers set edgewise, with consecutive layers at right angles to each other. They were made of pure alumina prepared by Siemens from bauxite, and their manufacture had been developed by the Koppers company. Their manufacture was expensive (about 10,000 RM per ton pre-war) because they tended to distort during cooling after their initial firing at about 2000°C. This was minimized by very rapid cooling through the 1700-1600°C an improved method of making the plates had been developed by a Hungarian firm (Budapester Glaswerke) who added 0.3 per cent. of chromium oxide to the alumina and obtained a product which was free from the tendency to distort. This reduced the cost to 500RM per ton.

Berylluim oxide was a possible alternative to alumina, but was still more expensive.

It was essential that the plates should be completely free from porosity in order to avoid disintegration.

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(d) Separation of acetylene

The effluent gas was compressed to 10 atm., and acetylene was separated by scrubbing with water in four counter-current towers, and a vacuum vessel, as follows:-

1. The gas was washed in the first tower with sufficient water to remove the whole of the diacetylene present. This also removed 25 per cent. of the acetylene.
2. The water leaving the first tower was expanded to atmospheric pressure in a second tower, and part of the hydrogen-methane mixture left at the outlet end of the scrubbing system was passed through it. This removed the acetylene from the water but left the diacetylene in solution. the gas leaving this tower was returned to the compressor and recirculated through the scrubber system.
3. The gas leaving the first tower was washed with water at 10atm. in the third tower to remove all its acetylene.
4. The water from the third tower was expanded to 2atm. and freed from methane and hydrogen in a fourth tower by passing through it gas from the final vacuum vessel. The gas leaving the fourth tower contained some acetylene, and was returned to the compressor and recirculated through the scrubber system.
5. The acetylene was released from the water leaving the fourth tower by means of a vacuum vessel.

A flow diagram of the scrubbing process is shown in Fig. 1.

The scrubbing towers were packed with Raschig rings, but the most effective packing had been found to be a type of plate known as “Kittelboden” which had been developed by the Bamag firm before the war. They had been used successfully at the Ruhrchemie works for removal of carbon dioxide by water scrubbing (in the ammonia plant).

The “Kittelboden” referred to were circular grids made of sectors of “expanded” metal plate, arranged so that the gas and water passing through the slots in them were given a rotary motion. The passage of the gas produced a spray at the edges of the slots.

It was stated that these plates were very cheap and permitted high gas and water throughputs without priming, with a low pressure drop. The maximum efficiency of a “Kittelboden”

It was stated that these plates were very cheap and permitted high gas and water throughputs without priming, Kittelboden” plate was 0.3 theoretical plate. Their maximum efficiency was spread over a wider range of gas and water rates than that of Raschig rings, but this range was narrower than that for bubble-cap plates.

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(e) Power and Material Requirements for Large Plant.

A full-scale plant was designed in 1943 for the Hungarian firm Nitrochemie A.G. This plant was to produce 7000kg. of acetylene per day from natural gas containing 99 per cent. of methane. It was to be constructed by the coke-oven manufacturing firm Carl Still, of Recklinhausen, Westphalia, but construction does not appear to have been started.

The following estimates were given for the material and power requirements:

Power.

Materials:

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(f) Production of cyanides.

Laboratory scale work has been done o the production of hydrocyanic acid from a mixture of methane and ammonia. The mixture was passed through heated tubes under conditions similar to those used for the production of acetylene. No hydrogen cyanide was formed in clean tubes, but some was obtained after a layer of carbon had formed on the walls of the tube. There had been no development of the process to a larger scale.

8. Production of Ethylene from Ethane

Ruhrchemie A.G. had succeeded in converting ethane (residue from coke oven gas separation) to ethylene by a process similar to that used for the production of acetylene from methane.

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