L. L. HIRST – "THE HYDROGENATION OF COAL AND TAR-COAL AT WESSELING, GELSENBERG, SCHOLVEN, AND LEUNA; TAR AT BOTTROP, BÖHLEN, AND ZEITZ."

L. L. Hirst. Some hydrogenation plant operations in Germany have been summarized briefly in the following tables. There is a table each for hydrogenation of bituminous coal, brown coal and coal tar, also a table of vapor phase saturation and vapor phase splitting of liquid phase oils.

It will be recalled that in the Ruhr area two hydrogenation plants, Scholven and Gelsenberg, operated on bituminous coal and that one plant, Bottrop-Welheim, operated on bituminous coal tar pitch. The Wesseling plant which is also in Western Germany used Rhenish brown coal as raw material. In the Leipzig area there were several plants operating on either brown coal or brown coal tar. Leuna, which was the first coal hydrogenation plant to be built, operated mainly on brown coal. Brabag I at Böhlen and Brabag IV at Zeitz hydrogenated brown coal tar. The Winterschall A.G. plant at Lutzkendorf, which worked mainly on refining residues from petroleum, is not included in the tabulation. Table 1 summarizes the liquid phase bituminous coal hydrogenation information.

The Scholven plant was completed in 1936 and was designed to work at 300 atmospheres. Gelsenberg was a somewhat more modern plant built in 1939 to work at 700 atmospheres pressure in the liquid phase. The partial pressure of hydrogen at this total operating pressure was about 550 atmospheres. The liquid phase operating temperature at Scholven was about 460 to 475 degrees centigrade and the Gelsenberg operating temperature was a little higher. At Scholven the tin ammonium chloride combination was a little higher. At Scholven the tine ammonium chloride combination was used for catalyst pressure, it was possible to use iron sulfate and iron oxide residues from aluminum ore purification. At Gelsenberg, it was necessary to add sodium sulfide to neutralize the chlorine which was present in the coal charged. Hydrogen chloride if present as dilute solution in water is a serious corrosion agent for the alloy steels in converters, catchpots and pipes. At Scholven the percentage of coal in the paste was about 46. Initial operations at Gelsenberg started with 46% of coal in the past. However, very serious difficulties with the preheaters developed. The preheaters had been designed for the very high metal temperature of 560 degrees centigrade and so many tubes were ruptured that something had to be done to reduce the tube wall temperature. The solution adopted was to introduce a heat exchange between inbound paste and outcoming products. By accepting a rather high pressure drop through the system, it was possible to reduce the preheater tube wall temperature to 520 degrees centigrade, maximum, and subsequently operate with relatively few failures of preheaters. To secure effective heat exchange and hold the pressure drop within reason it was necessary t reduce the percentage of coal in the paste from 46% to 40%. It will be noticed that at Scholven about.59 kilogram of paste was pumped per hour per liter of liquid phase reaction space but that a similar figure for Gelsenberg was .97 to 1.15. When this figure was reduced to kilograms of coal per liter per hour, there is somewhat less spread, i.e., .271 for Scholven and .446 to .46 for Gelsenberg. The use of higher operating pressure at Gelsenberg permitted a material increase in the space velocity but when one compares the tons of steel in 300 and 700 atmosphere converters one finds that about 465# of steel are required per cubic foot of reaction space in the 300 atmosphere converter compared to 940# per cubic foot of 700 atmosphere converter reaction space. To get equal thru put of coal per ton of steel in the 700 atmosphere converters, it would be necessary to process.55 kilograms of coal or 1.35 liters of paste per hour per liter of reaction space. Possibly the low asphalt make at 700 atmospheres is a sufficient advantage to offset the unfavorable steel requirement for this operating pressure.

When one compares the amount of circulated gas per ton of paste, it is noted that a somewhat larger amount of gas was circulated at 300 atmospheres but that cooling gas is used in much greater quantities at Gelsenberg. The total circulated gas for Gelsenberg thus becomes 2,100 cubic meters per ton of paste as compared with 1,300 cubic meters per ton of paste at Scholven.

The paste preparation practice is essentially similar at both plants. However, at Gelsenberg the coal was dried prior to pasting. The sludge treatment was essentially the same in both plants although it was claimed by the Gelsenberg engineers that their kilns were able to handle a somewhat higher load for longer periods between shutdowns than was the case at Scholven.

In Table 2 are summarized the liquid phase brown coal practices for Leuna and Wesseling. At Leuna the inlet pressure was 230 atmospheres and at Wesseling 700 atmospheres. The temperatures were respectively 493 and 478 degrees centigrade. The temperatures were respectively 493 and 478 degrees centigrade. The temperatures given for Leuna represent those used under their best known operating conditions and the practice as it had evolved at the end of 1943. The Leuna catalyst was iron oxide residue from the purification of aluminum ore but at Wesseling 5% red iron ore and 1-1/2% sulfur, based on dry coal, was used as catalyst. You see a marked difference in the percentage of coal in the paste. It ran from 44% to 48% at Leuna and only 35.6% at Wesseling. The variation in coal content of Leuna paste came about through their hydrogenation at times of some excess brown coal tar from the Leipzig area. This excess tar became available after some of the tar hydrogenating plants were partially bombed out. The percentage of coal is very low in the Wesseling paste. However, the 5% of iron ore added as catalyst would reduce the coal that could be carried in suspension. The space velocity at Leuna is 1.15 volumes per hour per volume of reaction space and this is a little less than the average of 1.35 reported for Wesseling. The past space velocity for bituminous coal at Gelsenberg at 700 atmospheres was about the same as for brown coal at Leuna at 300 atmospheres. When these figures are revised to a basis of tons of ash-free coal per cubic meter of reaction space, they become .59 for Leuna and .49 for Wesseling. This higher rate is necessary because of the somewhat higher thru put of coal per volume of reaction space and because of higher temperatures of operation. The Leuna total circulating gas rate is about the same as for bituminous coal hydrogenation as practiced at Gelsenberg and somewhat greater than used at Scholven. Coal and paste preparation methods at Leuna and Wesseling were quite similar. In each case there is crushing, screening and pasting. At Wesseling the grinding of coal and mixing of vehicle were carried out simultaneously. At Leuna, two-thirds of the H.O.L.D. or Heavy Oil Let Down was centrifuged and the other one-third was added to the centrifuge residue for steam coking. At Wesseling, the H.O.L.D. was diluted with clean oil desanded and two-thirds centrifuged and the other one-third sent direct to paste making.

The liquid phase hydrogenation of coal tar is summarized in the third table which shows operation at Bottrop-Welheim, Böhlen and Zeitz. Pitch derived from numerous coal tar distilleries in the Ruhr area was treated at Welheim and brown coal tar derived from a number of distilleries in the Leipzig area was hydrogenated. The liquid phase operations on pitch at Welheim were started because the details of the Patt-Broche extraction process were not worked out by the time the hydrogenation part of the plant was ready to operate. The plant for hydrogenating this Patt-Broche extract had been designed and constructed in advance of the solution of the extraction plant difficulties so rather than let this equipment stand idle it was decided to treat high temperature pitch from carbonization of Ruhr bituminous coal. The refractory nature of the Patt-Broche extract had made it necessary to design the plant for the liquid phase treatment of the extract to phase hydrogenation of high temperature pitch and it will be noted that only 0.25% by weight of ferrous sulfate on grude was used as catalyst whereas at Böhlen which operated at only 300 atmospheres, on a considerably less refractory tar, .5% to 1.5% of a similar catalyst was used with a comparable thru put rate. The combined yield of gasoline and middle oil from the liquid phase operations at 480 degrees centigrade were 30% for Welheim and 45% for Böhlen. At Zeitz the liquid phase treatment was carried out on pelleted 5,058 (tungsten sulfide) catalyst. The variations, known as T.T.H. and M.T.H. operations were practiced. In the T.T.H. or very low temperature hydrogenation (operating range 350 to 356 degrees centigrade), the objective was to make lubricating oil and very pure wax. There was also a considerable yield of diesel oil but very little gasoline. In the M.T.H. or medium temperature hydrogenation (operating range 375 to 425 degrees centigrade), the product was 45% gasoline, 45% diesel oil and 10% of heavier material. It will be noted that the feed stock in both operations was very carefully filtered brown coal tar and that they were both once through operations with no recycle. As might be expected, thru-put rates were from one-half to one-third of those of the higher temperature operations. It is also significant that rather high gas circulation rates were used to maintain close temperature control. Conversion of tar to hydrocarbon gas (CH₄ and C₂H₆) was very low as would be expected from such low temperature operations. It was stated that the catalysts had relatively short life (40to 50 days) and that the position of a converter in a stall was progressively changed from #4 to #1. Catalyst was reclaimed by taking it from the converter and running it over a shaking screen. This operation chipped off the asphaltic, shellac-like deposit and restored the catalyst material. The lubricating oil produced was of machine and spindle oil grades and had a viscosity index of about 60. The wax produced was said to be sufficiently refined for use in manufacture of fatty acids for conversion to edible fats.

In Table 4 are presented summary of vapor phase saturation operations. This table shows for Wesseling, Scholven, Gelsenberg and Leuna the hydrogen partial pressure and the total pressure. The catalysts used for saturation were 5,058, 7,846 and 8,376, these latter two being war time substitutes developed as a result of tungsten shortage in Germany. 8,376 was found to have rather good phenol reducing qualities but to be less effective as a reducing agent for nitrogen compounds. In the German plants, the space velocity in kilograms per liter of catalyst space per hour feed rate ranged from .55 to 1.0. These feed rates are somewhat lower than attained under the best British practice. It seems odd that at a time when every effort was being strained by the Germans to produce gasoline for war purposes that they should have overlooked the possibility of increasing the output of their hydrogenation plant by proper design of the vapor phase converter.

In the 5^th table, we have the 300 atmospheres vapor phase splitting operations summarized for Leuna, Böhlen, Gelsenberg, Scholven and Wessling, and to this we have added the Welheim 700 atmosphere splitting operations. It is noted that at Leuna the total pressure used was as low as 230 atmospheres. The temperature ranged from 374 to 434 degrees centigrade on 6434 catalyst and from 480 to 502 degrees centigrade on Welheim catalyst. The feed rate varied from .63 to 1.1 for the 6,434 and from 1.7 to 1 on the Welheim operation. It is noted that three to four times as much cooling gas was required in the Welheim operation as for the 6434 operation. When reduced to cubic meters per ton of feed, we note that about 1,750 cubic meters are required for 6,434 splitting as compared with 2,500 or 2,600 for Welheim splitting.

The product produced in the Welheim type operation is high in aromatic constituents and according to the manager at Welheim his gasoline was the best aviation fuel available in Germany.

Table 1 shows a very high yield of liquid phase middle oil and gasoline per unit reaction volume for Leuna. I believe this figure was much higher than that obtained at Wesseling when hydrogenating Rhenish brown coal at somewhat higher pressures. Engineers at Leuna were questioned about what had been done to achieve these higher thru puts. They had made some progress in instrumenting the plant and this had resulted in much smoother operation which had in turn permitted them to operate the plant at considerably higher temperatures. This higher operating temperature, together with the discovery that a downward temperature gradient in the last converter, resulted in lower conversion to asphalt were in the main responsible for their achievement of higher output from Leuna without the addition of more converters and preheaters.