ISOMERIZATION OIL DEVELOPMENT COMPANY, LINDEN, N. 1.
Significant developments in the isomerization of paraffins, naphthenes, olefins, oxygencontaining compounds, and aromatics are included in this review of the literature of the past 2 years. Particularly interesting is the role of isomerization in several catalytic reforming processes which are being installed on a lerqe scale for imwovins the octane number of gasoline and for the production of aromatics from petroleum.
, T
HIS review covers the literature on isomerization for the past two years and supplements three previous annual reviews (31-3'3). Items of particular interest include the following: 1. The role of isomerization in several newly developed catalytic reforming processes being installed on a large scale, for improving the octane number of gasoline and for the production of aromatics from petroleum. 2. The commercial use of aluminum chloride-catalyzed isomerization on a narrow-cut petroleum fraction to convert methylcyclopentane to cyclohexane, for subsequent dehydrogenation to benzene. 3. Isomerization of olefins to improve the octane rating of gasoline produced in a commercial hydrocarbon synthesis plant in a treating step which also deoxygenates and stabilizes the product. ISOMERIZATION IN CATALYTIC REFORMING Several papers have emphasized the importance of isomerization in newly developed processes for naphtha reforming. These processes are given general coverage in a companion review (16) and only the part played by isomerization Gill be discussed here. Catalysts of the type heretofore used in conventional hydroforming have high dehydrogenation activity but only moderate isomerization activity. With these catalysts cyclohexanes are readily converted to aromatics with high selectivity, but alkylcyclopentanes, which are generally present in about equal amounts, do not contribute greatly to aromatics production. The development of new catalysts, which have high isomerization as well as dehydrogenation activity, allows alkylcyclopentanes to be converted to cyclohexanes. Although the equilibrium concentration of the cyclohexanes is low at reforming temperatures, their continuous removal by dehydrogenation to aromatics causes isomerization to continue in the desired direction. The isomerization of paraffins also occurs with the dual-function catalysts, but the contribution of this reaction to octane improvement is believed to be small because equilibrium is quite unfavorable to highly branched paraffins at reforming temperatures (11). The development of the Atlantic reforming process ( 7 , 1 1 ) started with the discovery that a catalyst composed of a hydrogenating component, such as nickel or platinum, deposited on a silica-alumina cracking catalyst would isomerize paraffins and napbthenes quite selectively under hydrogen pressure and in the temperature range 600' to 700" F. The isomerizing ability of this catalyst compares favoribly with that of aluminum chloride, except for the much higher temperature required. For example, normal heptane can be isomerized quite selectively by the new catalyst with up to 75% conversion, although in the presence of aluminum chloride catalyst, normal heptane and higher boiling paraffins tend to undergo chiefly side reactions. To make the new catalyst successful for reforming requiring higher temperature operation, i t was necessary t o reduce its
cracking activity. This was accomplished by high temperature steamin@:of the silica-alumina base, which reduced its surface area and raised the temperature for maximum selective isomerization up into the range of 850' t o 950' F., which is also suitable for the dehydrogenation of naphthenes. The reactions of pure compounds in Houdriforming, using a dual-function catalyst of undisclosed composition, was the subject of two papers (18, $9). Evidence was presented which strongly indicates that the isomerization of five- to six-membered rings occurs after partial dehydrogenation to cyclo-olefins. It is also postulated that isomerization and dehydrogenation take place a t different locations on the catalyst. The conversion of methylcyclopentane to benzene, therefore, would involve dehydrogenation to methylcyclopentene a t a dehydrogenation site, transfer to an isomerization site where isomerization to cyclohexene would take place, and transfer to a dehydrogenation site again for conversion t o benzene. The additional time required for these transfers to take place could account for the observation that more cracked products are formed from methylcyclopentane than from cyclohexane a t given conditions. It was also shown that the presence of benzene retards cracking with reforming catalysts, as previously reported with Friedel-Crafts catalyst. Commercial application of the Platforming process, discussed in the 1950 review, is now quite extensive. D a t a on t h e reactions (including isomerization) of pure compounds in Platforming have also been reported (14).
PARAFFINS An historical review of isomerization in the petroleum industry was presented as part of a symposium on Twenty-five Years of Progress in the Petroleum Industry a t the Diamond SOCIETY,September Jubilee Meeting of the AMERICAN CHEMICAL 1951 ( I S ) . Only a few of the wartime butane isomerization plants have been in operation the past few years, but undoubtedly more would be reactivated if any large increase in demand for high octane aviation gasoline should materialize. Details of a modified operating procedure now in use in one of the commercial vapor phase butane isomerization plants have been published (34). The larger part of each reactor tube is charged with activated bauxite with a physical mixture of the bauxite and aluminum chloride at the inlet end. The aluminum chloride is distributed on the bauxite by sublimation with butane feed to make an active catalyst. The inlet section of the bed mag be replaced several times before the remainder of the bed is spent. The few papers on paraffin isomerization published in the past 2 years have been mainly concerned with the mechanism of reaction. several isoparaffins isomerize almost instantaneously in the presence of alkyl fluoride and boron trifluoride (4.9). A carbonium ion mechanism is advanced. The effect of naphthenes in inhibiting undesired side reactions in paraffin isomerization has been investigated further (8). A study of the manner and rate of isomerization of several hexane isomers with aluminum chloride catalyst (10)and a study of isoparaffin rearrangements in the presence of strong sulfuric acid (%), which were published during the period of review, had been included in pre-
2037
2038
INDUSTRIAL AND ENGINEERING CHEMISTRY
vious reviews when available as preprints. Isomerization and hydrocracking reactions of normal paraffins up to Cli and of several napht,henes, in the presence of aluminum chloride-hydrogen chloride, was the subject of a German article (20). "Advances in Cat'alysis" (lb), contains a chapter on fundamental principles of catalytic activity by Seitz, in which cat.alyais is discussed in terms of atomic theory and the isomerization r e a d o n is used to illustrate general principles. Another chapter of this book, on hydrogen fluoride catalysis by Simons, includes a brief discussion of rearrangements catalyzed by hydrogen fluoride. An excellent review of the t,wo mechanisms-carbonium ion and free radical-Khich can explain substantially all reactions of aliphatic hydrocarbons, should also be listed ( 4 1 ) .
NAPHTHENES The importance of naphthcne isomerizat>ion in catalytic reforming processes \vas discussed in the first section of this revicw. The isomerization of naphthenes using an aluminum chloridearomatic coniples (Gustafson-type) catalyst v a s employed in t w o U. S.refineries during World War I1 t o convert, dimethylcyclopentane to methylcyclohexane, for subsequent dehydrogenation t o toluene (13). One of these plants is currently isomerizing methylcyclopentane to cyclohexane, which may be dehydrogenated t o benzene (63). The isomerization reaction is carried out a t about 200" 2'. in the presence of 0.1% hydrogen chloride based on feed, in a mechanically stirred reactor. The plant equipment for feed preparation, conversion, and product purification is said to be equally capable of producing bensene, toluene, xylenes, and niethylcyclohexane from petroleum. Additional papers in a series on the isomerization of saturated hydrocarbons have covered the promotional effect of oxygen and light upon the isomerization of methylcyclopentane with aluminum bromide catalyst, under rigidly controlled laboratory conditions (36, 36) and a study of the isomerizatioii of ethyl oyclopentane and dimethylcyclopentanes using the same catalyst (39). The rate, equilibrium, and mechanism of the isomerization of cyclohexane with aluminum chloride-hydrogen chloride catalyst have been studied, using commercial reagents so as to include any effect of trace moisture, oxygen, and other proton acceptors that might be present in a commercial iponierization plant ( 2 6 ) . The rate of isomerization is strongly dependent on the amounts of both aluminum chloride and hydrogen chloride in the system, and it is indicated that the rate-controlling reaction takes place on the surface of the catalyst.. It is theorized that the aluminum chloride and hydrogen chloride interact to form an ionized complex, which is the active catalyst, and that rearrangement, of the hydrocarbon molecule occurs when it is distorted by the simultaneous influence of a proton and an anion. It has now been show-n that aluminum chloride and hydrogen chloride interact stoichiometrically in the presence of proton acceptors although not otherwise (6) lending support, to the theory that the actual catalyst may be the ionized form of H41C1,. A detailed analysis of the products obtained by dist.illing methylcyclohexane from moist aluminum chloride has been reported (44).
Vol. 44, No. 9
works to particular advantage on the hydrocarbon synthesis product, ( I S ) . The isomerization of cycilohcuenes and methylcyclohexenes to substituted cyclopentenes using an alumina catalyst and the preparation of chemical derivatives of these compounds was the subject of a thesis (40). As mentioned earlier, ipomcrization of naphthenes under reforming conditions is indicated t o take place after dehydrogeiiatioii to cyclo-olefine The isomerization of olefins using hydrogen fluoride-activated alumina as catalyst was carried out experimentally in conjunction with rectification. By continuously recycling unconverted material and undesired isomers to the reaction zone, high ultimate yield8 of the desired, highly branched isomers were obtained ( 5 ) . Siniilar work was also done on other isomerization reactions (4). A German article discussed the practical significance of olefin isomerization and reviehTed t'he literature on hexene isomerization (21). A study of the isomerization of 1-hesene using several catalysts (previously reviewed as a preprint) has been published (30). Rearrangements involving 1-pentyne, 2-pentyne, and 1, 2-pentadiene, carried out in the presence of alcoholic pot,assium hydroxide, have been studied ( 2 9 ) . The isomerization of acetylenic hydrocarbons with metal oxide catalysts has been the subject of a series of Russian articles, of which the most recent one i,s listed (24). Isomerization reactions accompanying alkylation have been discussed in a number of interesting papers (17, 18, 63, 26, 37, 38).
OXYGEN-CONTAINING
COMPOUNDS
The isomerization of unsaturated fats from cis to trans position around the double bond is of practical interest' as a means of raising melting point and improving the resistance of fats to oxidation ( 3 ) . This can be accomplished by treatment with nitrous oxide or sulfur dioxide a t 100" t'o 120' C. or wit.h a trace of selenium a t 200' to 210' C. A thorough discussion of this cistrans isomerization and of the shifting of double bonds to form conjugated structures, 7%-hichmay be used to improve the drying properties of certain oils, v a s presented in one of a series of lectures on oil and fat chemistry (9). The isomerization of propylene oxide, carried out using a chromium oxide-tungstic oxide catalyst a t about 215' C., yieldctl primarily propionaldehyde, ITith allyl alcohol and dimethyldioxane as secondary products ( 8 7 ) . Catalysts varying in composition from 5-1 to 40-1 chromium-tungstic oxide ratio gave high yields of propionaldehyde, while higher and lower ratios increased the yields of allyl alcohol and dimethyldioxane. Result.: obtained with a chromium oxide catalyst had been report'ed previously (98).
AROMATICS
OLEFINS
The mechanism of the isomerization of p-xylene to m-xylene has been studied using aluminum bromide catalyst (2). The presence of hydrogen bromide was necessary for the reaction. Ternary combinat'ions of aromatics d h aluminurn bromide ant1 hydrogen bromide, in which the latter txyo were present in a 1 to 1 rat#io,were found. Similar behavior of aluminum chloride and hydrogen chloride (6) Tvas discussed earlier in this review, as supporting the theory that the actual catalyst is an ionized complex of the aluminum halide and hydrogen halide.
The hydrocarbon synt,hesis process for converting carbon monoxide plus hydrogen to liquid hydrocarbons, using an iron catalyst, produces a naphtha uhich is highly olefinic, containing primarily straight-chain hydrocarbons with a terminal double bond. In the first commercial U.S. plant using this process t,he raw gasoline produced is treated under mild cracking conditions (750' to 850' F.) with bauxite or other isomerization catalyst ( I ) , This treatment causes double bonds to migrate toward the center of the molecule, thereby raising octane number, and also converts any oxygen compounds present to hydrocarbons. It is st.at,edthat the octane number of the product is raised by as much as 20 units, This isomerization and treating step is not ney, but
Arnold, J . TI.,and Keith, P. C . , Advances in Chem. Serics, No. 5 (1951). ( 2 ) Baddeley, G., Holt, G., and Voss, D., J . Chem. SOC.,1952, 100. ( 3 ) Bailey, H. E., "Industrial Oil and Fat Products," 2nd ed., New Yoik, Interscience Publishing Co., Inc., 1951. (4) Berg, L., Hippely, P. R., and Reveal, W,S., Chem. Eng. ProgTess, 47, 283 (1951). (5) Berg, L., Saner, H. A, Gustafson, L. D., Luke, W.J., and Reveal, W.s.,paper presented before the Division of Petroleum CHEIIZ. . Soc., Milwaukee, \Vis., Chemistry, 121st Meeting, - 4 ~ March 30-April 3, 1952. ( 6 ) Brown, H. C., and Pearsall, H. TV., J . Am. Chem. SOC.,74, 191 (1952).
LITERATURE CITED (1)
September 1952
INDUSTRIAL AND ENGINEERING CHEMISTRY
(7) Ciapetta, F. G., paper presented before the Gordon Research Conference, New London, N. H., June 1951. (8) Condon, F. E., J . Am. Chem. Soc., 73, 3938 (1951). (9) Cowan, J. C., J . Am. Oil. Chemists’ SOC., 27,492 (1950). (10) Evering, B. L., and Waugh, R. C., IND. ENQ.CHEM.,43, 1820 (1951). (11) Fowle, M. J . , Bent, R. D., Ciapetta, F. G., Pitts, P. M., and Leum, L. N., Advances in Chem. Series, No. 5 (1951). (12) Frankenburg, W. G., Komarewsky, V. I., and Rideal, E. K.,
“Advances in Catalysts,” Val. 11, New York, Academic Press, Inc., 1950. (13) Gunness, R. C., Advances in Chem. Series, No. 5 (1951). (14) Haensel, V., and Donaldson, G. R., IND.ENG. CHEM.,43, 2102 (1951). (15) Haensel, V., and Sterba, M.J., Ihid., 44,2073 (1952). 116) Heinemann. H., Mills, G. A,, Hattman, J. B., and Kirsch, F. W.
paper presented before the Division of Petroleum Chemistry, 121st Meeting, AM. CHEM.SOC., Milwaukee, Wis., March
30-&4pril3,1952. (17) Ipatieff, V. N., Appell, H. R., and Pines, H., J . Am. Chem. Soc., 72, 4260 (1950). (18) Ipatieff, V. N., Meisinger, E. E., and Pines, H., Ihid., 72, 2772 (1950). (19) Jacobs, T. L., Akawie, R., and Cooper, R. G., Ihid., 73, 1273 (1951). (20) Koch, H., and Gilfert, W., OeZ u. Kohle, 49, 413 (December 1949). (21) Koch, H. and Van Raay, H., Ibid., 51, 161 (1951). (22) Komarewsky, V. I., and Ruther, W. E., J . Am. Chenc. Soc., 72,5501 (1950). (23) LaZerte, J. D., Ph.D. thesis, Northwestern University, 1948-9. (24) Levina, R. Ya., and Victorova, E. A., J . Gen. Chem. (U.S.S.R.), 20, No. 4, 677 (1950). (25) Lien, A. P., d’ouville, E. L., Evering, B. L., and Grubb, H. M., IND. ENG.CHEM.,44,351 (1952).
2039
(26) Linsk, J., J. Am. Chem. SOC.,72,4257 (1950). (27) Lundsted, L. G., Jackson, D. R., and McMahon, J. P., paper presented before the XIIth International Congress of Pure and Applied Chemistry, New York, Sept. 10-13, 1951. (28) Lundsted, L. G., Vaughn, T. H., Schwoegler, E. J., and Jacobs, E. C., IND. ENG.CHEM.,43,728 (1951). (29) Mills, G. A., Heinemann, H., Milliken, T. H. and Oblad, A. G., paper presented before the Division of Petroleum Chemistry, 121st Meeting, AM.CHEM.SOC., Milwaukee, Wis., March 30April 3, 1952. (30) Naragon, E. A., IND. ENG.CHEM.,42,2490 (1950). (31) Perry, S. F., Ihid., 40, 1624 (1948). (32) Ihid., 41, 1887 (1949). (33) Ibid., 42, 1715 (1950). (34) Persyn, C. L., Jr., Oil & Gas J.. 50, No. 40, 111 (1952). (35) Pines, H., Aristoff, E., and Ipatieff, V. N., J. Am. Chem. Soc., 72,4055 (1950). (36) Ibid., p. 4304. (37) Pines, H., Huntsman, J. D., and Ipatieff, V. N., Ibid., 73, 4343 (1951). (38) Pines, H., LaZerte, J. D., and Ipatieff, V. N., Ihid., 72, 2850 (1950). (39) Pines, H., Pavlik, F. J., and Ipatieff, V. N., Ibid., 73, 5378 (1951). (40) Roebuck, A. K., Ph.D. thesis, University of Wisconsin, 1948, Summaries of Doctoral Diss. 10,475 (1947-49). (41) Schmerling, Louis, J . Chem. Education, 28,562 (1951). (42) Schneider, A., and Kennedy, R. M., J . Am. Chem. Soc., 73, 5013 (1951). (43) Spaght, M. E., 0 2 1 Forum, 4 , 4 3 1 (November 1950). (44) Van Volkenburgh, R., and Greenlee, K. W., paper presented
before the Division of Organic Chemistry, 118th Meeting, AM.CHEM.SOC.,Chicago, Ill., Sept. 3-8, 1950.
RECEIVED for review July 30, 1952.
ACCIPTED July 30, 1952
NITRATION WILLARD
dec.
CRATER
HERCULES POWDER COMPANY, WILMINGTON, DEL.
T h e trend toward continuous nitration processes for the commercial manufacture of nitroglycerin is gradually spreading from Europe to the North American continent. The first such unit, in which the Biazzi process is used, was put in operation in North America in the spring of 1959, near Calgary, Alberta. Also, a similar unit is to be installed in an explosives factory to be built near Martinsburg, W. Va. A number of articles and patents have been published covering the production of nitro compounds such as the aromatic nitro compounds and nitroparaffins. The nitration of hexamethylenetetramine and other amines continues to b e of interest and several articles covering the various phases of ruch nitrations have appeared during the part year. Also, considerable work has been done on the mechanism and kinetics of nitration.
I
N K E E P I N G with the previous reviews of nitration processes and the mechanism of nitration, this 1952 review covere the treatment of organic compounds with nitric acid or its equivalent to produce both nitrates and nitro compounds. T h e data included are a resume of the articles and patents which have become available since the last review.
NITRIC ACID ESTERS CONTINUOUS NITRATION PROCESSES
T h e first commercial continuous nitration unit for the manufacture of nitroglycerin in North America was p u t in operation during t h e spring of 1952 b y Canadian Industries, Ltd., near Calgary, Alberta, Can. The Du P o n t Co. also plans t o install a similar unit in a n explosives factory t o be built near Martinsburg, W. Va. T h e Biazzi continuous nitration and washing process ( 1 7 ) for making nitroglycerin will be used b y Canadian Industries, Ltd., and D u Pont. This process has been in use in several countries in Europe for a number of years and i t was referred to in earlier reviews (18, 19).
It has bean pointed out ( 1 7 ) t h a t t h e main advantage of the Biazai process over the batch process is its safety factor, as only a relatively small quantity of explosive material is in process at a n y one time, In case of an accident, this reduces t o a minimum the possibility of the communication of explosion t o other buildings and the damage t o property. A comparison of nitroglycerin in process between the Biazzi unit (8) and the batch system is shown by the following figures expressed as percentages of the hourly production of nitroglycerin used for the manufacture of dynamite:
System Batch“ Biazzi
Max. Total Nitroglycerin in Nitrating House
200 36
Max. Separated Nitroglycerin in Nitrating House 200 ‘
4
Two charges of nitroglycerin in the building
T h e pictures showing the Biazzi continuous nitration units were furnished by courtesy of Mario Biazzi. T h e units shown are mounted in the shop on their regular panels and are set u p for testing. Two pictures show a unit for the manufacture of 2500 pounds per hour of nitroglycerin for use in dynamite. In Figure l A , the shell of the nitrator is lowered for internal inspection; in Figure l B , the shell is in operating position. Figure 2 shows in
