ERNEST COTTON Ė "HYDROFORMING AND D H D"
E. Cotton. In the time allotted, I didnít feel I could into very much detail on the DHD hydroforming. There have been two papers issued which apparently were the preliminary writeups of these processes. I understand that there is probably a more complete story in the Leuna report. I was looking through that yesterday and I noticed there seems to be a little bit more information there; Iím not sure of how much though.
I thought it might be of interest here to show a little bit of the difference between the U.S. and the German hydroforming process, because although the hydroforming process was invented by the Germans, it actually was developed in this country before the Germans got around to using it. In this country, what we would call the standard hydroforming process uses a molybdenia on alumina catalyst containing from 8-1/2 percent to 9 percent of molybdenia. The charge which is normally used here for making toluene is a heart cut from straight run gasoline. Total straight run gasoline and naphtha can be charged for motor gasoline production. The charge is first preheated to around 1,015oF. Recycle gas which is 50-60 percent hydrogen, is mixed with the charge using about 2,500 cu. ft. per barrel. Temperature of the recycle gas is 1,150oF and is heated in a separate furnace. The mixture passes down through the first reactor under about 225 lb pressure and comes out of that reactor at about 925oF. It is reheated to about 1,035oF, passes through the tail reactor, and comes out of there around 935oF. The material is cooled, the gas separated and recycled back through a furnace into the inlet of the first reactor. Most of the plants are provided with what we would call a hydrogen enrichment and recycled back through a furnace into the inlet of the first reactor. Most of the plants are provided with what we call a hydrogen enrichment tower, where a part of the hydrocarbons are absorbed to increase, the percentage of hydrogen in the recycle gas. The cycles on these plants generally run about 4-1/2 hours on reaction and about 3 hours on regeneration, with 1-1/2 hours for purging and valve-switching, etc. or a total of 9 hours. The space velocity, expressed as volume of oil per volume of catalyst per hour, is about 0.45. The yields that I have here are from some early claims on the process for making motor gasoline. If you make 85 percent yield on an East Texas gasoline, you get a 75 ASTM octane number product, containing about 35 percent aromatics and 15 percent olefins. If you run for 80 octane material, you get about 82 percent yield. If you run for 80 octane material, you get about 82 percent yield, the aromatics are up to 45 percent and the olefins down to about 12.
The German hydroforming process is essentially the same as the American. One of the differences in the processes is that the Germans use three reactors in a series instead of two. The feed coming in is mixed with recycle gas using 3,350 to 5,600 cu. ft. per barrel. The mixture is heated together in a furnace, instead of separately as in the American system, up to around 968oF, and enters the first reactor at 220 lb per sq. in. It passes down through the reactor and out of the bottom at 896oF., is reheated in a separate furnace to 986oF, which is slightly higher than the inlet to the first reactor, passes down through the second reactor, comes out at 923oF, is reheated to 986oF, again, and comes out of the third reactor at around 950oF. The cycle on reaction is from 6 to 12 hours and the cycle on regeneration is also 6 to 12 hours. It is reported that the space velocity on this process is 0.8 as compared to 0.45 for U.S. work. The yields, based on straight run gasoline, were 72 to 73 percent of 80 ASTM octane number product, containing 50 percent aromatics. In fact, they operated the plant to produce material containing 50 percent aromatics and that was the control point for length of cycle, etc. The olefins were only 1.5% as compared to 12-15 percent on American hydroformer operation. Another difference between these two processes is the catalyst bed arrangement. In the American plants, the catalyst is dumped into each reactor in a solid bed. The Germans had some idea that they should distribute the activity, if you want to call it that, of the catalyst through these reactors in order to get a more uniform reaction and coke deposition. In the first reactor the catalyst was divided into three beds. The upper bed, which sees the carhe first, was a catalyst containing 5 percent of molybdenum oxide with a particle size of 10-15mm. The center section catalyst was also 10-15 mm particles, but contained 10 percent molybdenum oxide. The lower bed contained 10 percent molybdenum oxide but the size was 6-10 mm. In the second reactor there were two beds, the upper bed containing 10 percent molybdenum oxide with the larger size (10-15mm) and the lower bed containing 10 percent molybdenum oxide with 6-10 mm particles. In the third reactor, there was one bed of 10 percent molybdenum oxide with 6-10mm size. It is quite possible that the comparison of yields and octane numbers is not very good because of the charge stock. I would suspect that if the same feed stock was used you would come out with very close to the same result. The only thin that looks somewhat out of line is the low olefin content and it is quite possible that the lower temperature at the inlet of the first reactor might have something to do with the olefins. Iím not sure about that. The pressures were, in sense, the same.
The DHD process was strictly a German development; it was tried out originally in a hydrogenation plant stall. The Germans tended to use as high a pressure as they could. This seemed to be the starting point instead of starting from atmospheric. The DHD process was used principally on hydro-gasoline. I donít know what it would do on straight run gasoline, but I assume that it would be quite different from hydroformer. In the DHD, the charge is normally an over to 365oF hydro-gasoline. The charge is fractionated to take off a 185oF end point front end cut, because it was not considered necessary to hydroform or DHD this gasoline. The bottoms from the splitter is preheated by heat exchange and in a furnace using convection heat only, no radiant heating, up to 932oF. Under 617 p.s.i.g. pressure, the feed passed down through the first reactor coming out at 842oF. This was reheated to around 950oF., passed through the second reactor, coming out at 914oF, reheated again to 968oF passed through the third reactor, coming out at 950oF, reheated again to 986oF, passed through the fourth reactor at 986oF. You see there is a decreasing temperature spread or drop through the reactors. The pressure dropped from 617 p.s.i.g. at the outlet of the feed pump to around 441p.s.i.g. at the inlet of the fourth reactor. At the outlet of the fourth reactor the material is cooled by heat exchange to around 572oF and passed through the fifth reactor containing the same catalyst for the hydrogenation of olefins. This is something quite different from anything that is done here. The effluent from the fifth reactor is cooled, the gas separated and the recycle gas sent back in with the reactor charge, using about 3000 feet per barrel, which is more or less in line.
The product is first fractionated to remove some heavy bottoms and is then mixed with the overhead from the charge and stabilized to remove the light material. The reaction cycle on the hydro-gasoline is 120 to 240 hours, with about 24 hours on regeneration. The Germans stated that if they were using hydro-gasoline in the hydroforming plants, the cycle on the hydroformer would be somewhere near 100 hours, so I donít think the long cycle here is designed to the pressure but more to the hydro-gasoline. Although they designed the plant for a space velocity of 0.5 V/H/V, they were only able to get up to .33 to .43. The yield from the case charge itself was 74 to 77 percent. I do not have an octane number on the product, but the aromatics were 50-52 percent, which was again the point of control. The DHD catalyst contains 8 to 10 percent molybdenum oxide on alumina and is prepared in 8-10 mm cubes instead of the granular type of catalyst which we know as the regular hydroformer catalyst. I donít think it is advisable to go into any more details at this time, since more details are given in the report. I might be able to answer a few questions if anyone has them.
W. C. Schroeder. Thank you, Mr. Cotton. Would you let us have copies of those drawings?
D. W. Gould. Mr. Cotton, were these hydroformer plants identical in construction and similar in operational feed in making toluene in Germany? I presume all this was for aviation fuel.
E. Cotton. Apparently, as far as I know. Someone else might know whether or not they were making toluene by the method we were using in this country.
W. C. Schroeder. Mr. Kuhne, what is your understanding, Dr. Haensel?
V. Haensel. I think there is another point there. The double DHD process, or better known as the HHD, is primarily designed to making toluene, and I think Dr. Horne has some information on this.
W. A. Horne. In the interrogation of Dr. Piere, it was learned that they had numerous sketches made up for making toluene by use of the double DHD process, whereby they retreated their product from the first stage. They also had a process worked up for solvent extraction of the DHD gasoline. Those were the only two proposed methods which they had, other than methanol alkylation of benzenes. There was a plant in operation at Altenburg producing 5,000 bbls. a month by alkylation of methanol and benzene, and I believe that was the only source of toluene, other than coal distillation.
V. Haensel. As far as I can remember, the documents contained some data or some flow diagrams on the 20,000 ton double DHD unit, but I donít know where it was going to be constructed. It was for 20,000 tons of final toluene, presumably not nitration grade. Another toluene plant was going to be constructed at Ruhrchemie for direct aromitization of the C-17 cut, presumably from the FT process, but that plant was only started. It was started away back, but discontinued and then started again, but they were pretty well bombed out soon after the second start on construction.
_____________. Isnít it true that the Kellogg people put up the German Hydroforming plants?
W. C. Schroeder. Dr. Weir, do you know the answer to that?
H. M. Weir. Iím not sure about that, but the ones that I saw were wartime constructed, and I donít know if anyone saw a plant that was built before the war.
E. Cotton. The ones that I saw were quite different in design from the American hydroformers and didnít look to me like a Kellogg job. Some of the plants were still under construction.
H. M. Weir. If there was one, there was only one, about 1938.
W. C. Schroeder. That was a very good picture of those processes, Mr. Cotton.
J. G. Allen. I notice we did not get this talk of Mr. Bays on "aviation fuel quality". I mentioned that their best aviation gasoline contained about 20 percent alkylate, the other 80 percent was DHD gasoline. That was the main use of this product.
W. C. Schroeder. Mr. Bays, as you know, isnít here, but I think we will find time this afternoon to ask Dr. Horne to cover the subject for us. Can you do that?
W. A. Horne. Iíll give you a few words on it.
W. C. Schroeder. We will take that up as soon as we finish this program this afternoon.
The next discussion will be on the "OXO Process," by Horace M. Weir.