THE DEHYDROGENATION OF BUTANE TO BUTYLENE.
Two (2) methods for the dehydrogenation of butane to produce feed for polymerization and alkylation plants were studied in Germany. One involved the direct release of hydrogen over a catalyst, and the other was via chlorination and HCl splitting. The catalytic dehydrogenation process was developed by I.G. and plants were built at three locations. The chlorination process was also developed by I.G. but no commercial installation was made or planned. for general information, however, there is attached a process flow diagram of a hypothetical plant employing the chlorination process.
The catalytic dehydrogenation process was carried out at 1020 to 1100 degrees Fahrenheit at practically atmospheric pressure, using a catalyst consisting of 2 percent weight K2O, 8 percent weight Cr2O3, and 90 percent weight Al2 O3. The conversion to olefins was ca. 18 percent per pass when a space velocity of 8 volumes of liquid butane per volume of catalyst per hour was used.
The catalyst was made by first precipitating alumina from an aluminum sulfate solution, then drying and grinding the precipitate. The ground alumina was then soaked in a chrome solution, pilled, dried, and put into the reactor. The finished catalyst had an apparent density of 1.0.
The reactor was a vertical bundle of 2½ inch tubes with flue gas circulated around the tubes. The tubes were made of 17 percent chrome, 17 percent nickel, “high” molybdenum content steel. The flue gas circulated around the tubes was at a temperature about 200 degrees Fahrenheit above that of the inside catalyst.
Catalyst was continually added at the top of the bundle and continually withdrawn at the bottom. The time required for the catalyst to pass through the tube was about 200 hours. Catalyst deactivation occurred primarily through carbon formation deposition. The spent catalyst contained 2.5 percent weight carbon and returned to the system. In the regeneration, care via taken that the temperature did not exceed the operating level of 1020 to 1100 degrees Fahrenheit.
The some space velocity and conversion were used for both normal and isobutene, but with normal butane the operating temperature was 1100 degrees Fahrenheit compared with 1020 degrees Fahrenheit for isobutene.
The exit stream from the dehydrogenation furnace was first cooled and then hydrogen, methane and other low boiling materials were separated. The butane-butylene mixture then was fed directly to alkylation. Acid life in alkylation was markedly influenced by the quality of dehydrogenation product. Small amounts of butadiene adversely affected acid life. Butadiene formation was minimized by carefully controlled dehydrogenation furnace operation, particularly avoiding tube plugging with resulting catalyst overheating.
In obtaining a product containing 18 percent olefins, a total weight loss of about 5 percent is incurred. That is, a 95 percent weight recovery of total C4 fraction is obtained. On this basis, an ultimate weight conversion of 78 percent butane to butylenes is realized. Losses through fractionation and alkylation plants will course reduce this figure.
Dehydrogenation under hydrogen pressure was studied, and the low pressure system was chosen in performance. (This decision was influenced by the difficulty of obtaining high pressure equipment in Europe during the war).
The following documents, transmitted to the Bureau of Ships, relate to this subjects:
XXIII. Dehydrierung
(I.G. - Leuna - report of Dr. Herbert)
XXIV. Materialfrngen in dur Dehydrierung.
(Politz - report of Dr. Huttner)
XXV. Mengenschema zur AT Anolage mit katalytischer Dehydrierung. I.”G.-Leuna- flow diagram and material balance of system including catalytic dehydrogenation of normal butane)
XXVI. Die Katalytische Dehydrierung von Propan zu propen. (I.G. - Leuna - report by Dr. Nowotny of 16 March 1944)
XXVII
THE MANUFACTURE OF NITRATION GRADE TOLUENE
The German supply of nitration grade toluene came from several sources. In addition coal tar fractionation and refining of DHD fractions, there were employed the Witol process, the Leutol process, and aromatization of heptanes.
The DHD process is fundamentally a device for producing aromatics and it was logically seen to be a parental source. Some nitration grade toluene was made directly from the normal DHD product by separation of a C7 fraction and application of methanol in an azcotropic distillation process. In another instance, a C7 fraction was separated from the DHD product and repassed again through the same process. The repassed product was then fractionated directly without the aid of added agents to produce toluene of nitration grade. In both cases, sulfuric acid treatment and redistillation were employed as a finishing operation.
The Witol process was a synthesis of toluene by the combination of methanol and benzene of four to one ratio of benzene to methanol was reacted, and the alkylated benzenes consisted of 70 percent toluene and 30 percent higher homologues.
To produce toluene from the poly-methylated benzenes, the Leutol process, which was quite similar to the Arobin process (discussed in this report), was employed. In the Leutol process, an aluminum silicate-molybdenum oxide catalyst is used, with a hydrogen pressure of ca. 200 atmospheres, to dealkylate the higher boiling compounds.
Perhaps of widest technical interest, however, is the heptane aromatizing process developed by Ruhrchemie. A plant was being built at Holten but it had not been completed by the end of the war.
The Ruhrchemie cyclizing process is specially designed for heptane-heptene fractions from the Fischer-Tropsch synthesis. These fractions would consist largely of normal heptane, with perhaps 10 percent of heptene-1 and 5 percent of other heptenes. This mixture was to be carefully fractionated from C6 and C8 components; i.e. to 99.5 percent purity. It was then to be passed over a chrome-alumina catalyst at atmospheric pressure and a temperature of 860 degrees Fahrenheit. The chrome-alumina catalyst was made as follows: (Al2O3 was precipitated, washed, dried, and ground in conventional manner, but careful washing was considered important. The ground alumina was then mixed with pure chromic nitrate salt with adequate water to make a viscous mixture. This mass was extruded into small cylinders, dried and finally roasted at a temperature of 1200 degrees Fahrenheit. Small amounts of cobalt, nickel, manganese, and thorium had been used individual tests as activators.) By using a liquid hourly space velocity of O.I. a 50 percent conversion to toluene was anticipated. By the recycle of unconsorted heptane, an ultimate yield of toluene equal to 78 percent weight of the feed was obtained in a pilot plant: this figure was expected to decrease to 70 percent in the commercial plant.
In the pilot plant in obtaining a 50 percent weight yield of toluene in one pass, the total loss to other materials was ca. 1.2 percent weight hydrogen, percent weight methane and other low boiling materials, and 3 to 4 percent weight of light gasoline, high boiling residues, etc.
The reaction cycle for this process was one-half (½) hour on production, about one-quarter hour oxidizing off carbon and one-quarter hour reducing the catalyst after oxidation. In the reduction step, hydrogen produced in the operation is used.
The toluene is separated from the reactor product liquid by simple fractionation, and after acid treating and redistillation it meets nitration grade specifications.
The use of a low pressure operation without hydrogen recycle is possible because of the absence of cyclopentanes in the feed. At low pressure cyclopentanes would decompose extensively to carbon and result in very rapid catalyst fouling.
Ruhrchemie was planning the application of this process to a wide boiling (190 to 390° F.) Fischer-Tropsch fraction to improve it as a motor gasoline component. Such a fraction could be reformed by this method to give a 93 percent weight yield of material of the same boiling range as the feed. With a 47 per cent volume aromatic content, the octane number of the product would be 68 compared with 18 for the feed.
The catalyst life was estimated to be about one year, which would be equivalent to a catalyst consumption of roughly one pound per barrel of liquid throughput. A general description of the process as announced by Ruhrchemie in 1943 was transmitted to the Bureau of Ships:
XXVIII. Die Aromatisierung von gradkettigen aliphatischen Kohlenwasserstoffen aus der Fischer-Tropsch - Synthese. (Ruhrchemie - report by Dr. Rottig in January 1943.)