January, 1946
INDUSTRIAL AND ENGINEERING CHEMISTRY
". . .
I n the same paper the following statement appears: normally occurring amounts of moisture in carbon black are held so tightly that they do not effect cure." According t o the data presented here, this water does not affect cure, not because i t is held tightly by the carbon black, but because it is lcst t o the batch by evaporation. , EFFECT OF MOISTURE ON PHYSICAL PROPERTIES
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ingredients are in the batch. The probable explanation of this improvement is that water chills the Banbury batch and thereby reduces the heat deterioration of GR-S. Further, at the reduced temperature the stock would be less plastic, more work would be done on it, and physical properties would thus be enhanced. This effect is probably secondary to the reduction in heat deterioration. Since laboratory mill-mixed batches are much cooler than Banbury batches mixed in the factory, i t is not surprising that no improvement is noted in laboratory evaluations.
I n order t o evaluate the effect of moisture variation on physical properties, it is necessary t o pick equivalent rates of cure. As LITERATURE CITED a basis the point was chosen where the 300% modulus equals (1) Braendle, H. A., and Wiegand, W. G . , IND.ENQ.C H E ~ 36, ~ . ,724 1200 pounds per square inch ( M =~1200). ~ ~~ ~and elonga~ ~ i l ~ (1944). The results tion of various batches are compared at this point. (2) Cohrtn, L. H.. and Steinbery, M., IND. ENG.CEEM.,ANAL.E D , (Table 111) indicate no significant variation in physical properties 16, 15 (1944). (3) Macey, J. H., private communication, Nov. 27, 1944. with moisture content. (4)Poulos, T.,Vila, G. R., and Shepard, M. G., private communicaIt has been reported (3) that in factory operation the addition tion, Dee. 9, 1943. Qf water $0 Banbury batches results in improved Processing (5) Rupert, F. E., and Gage, F. W., IND.ENG.CHEM.,3 7 , 3 7 8 (1945). characteristics and physical properties. This improvement is pRnaENTsD before meeting of the Chemical Institute of Canada in Quebec, observed only when water is added after the compounding June 5, 1945.
Catalytic Conversion of Hydrocarbons Catalytic Promoting Effect of Antimony Tetroxide in the Aromatization of Hydrocarbons with a Chromia-Alumina Catalyst F. E. FISHER, H. C. WATTS, G. E. HARRIS, AND C. M. HOLLENBECK Skelly Oil Company, Puwhuska, Oklu. T h e activity of the catalyst in the catalytic aromatization of aliphatic hydrocarbons was improved to an appreciable extent by the addition of antimony tetroxide to the chromia-alumina catalyst. The aromatization reaction was carried out on three different types of charge stocks: a heptane fraction from a natural gasoline, a heavy straight-run gasoline, and a thermally cracked gasoline. Both the liquid and gaseous products were analyzed. The production of aromatics during any one reaction period increased through a maximum and then decreased. The yield of gaseous products paralleled the formation of aromatics until excessive cracking superseded the dehydrogenation-cyclization reaction.
I
N THE catalytic conversion of aliphatic hydrocarbons to
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aromatics, considerable effort has been focused on the oxides of the metals of Group VI of the periodic table as catalysts. Chromium and molybdenum oxides have received special attention as catalysts for the dehydrogenation cyclization of hydrocarbons. Mittasch et al. ( 6 ) patented a process in 1933 for the production of aromatic * hydrocarbons from low-boiling nonaromatic hydrocarbons using the oxides of the metals of the sixth group alone or in admixture with other materials. Moldavskil et aE. (7)published data in 1936, showing the aromatization of saturated and olefinic hydrocarbons when passed over chromium sesquioxide. Grosse (3)was issued two patents in 1938 on a process for converting aliphatic hydrocarbons of 6 t o 12 carbon atoms to aromatic hydrocarbons, using a catalyst comprising the oxides of the metals of Group VI deposited on an activated alumina ocarrier.
Considerable effort has also been spent in improving the activities and efficiencies of these catalysts in the conversion process (1). Various other materials have been mixed with the catalyst, especially various metallic oxides from other groups of the periodic table. However, attention has also been paid to improving catalytic activity by changing the structural nature of the catalyst particles either by the method of manufacture or by special treatments of the compounded catalyst. This paper deals with the activity improvement or promoting effect of antimony tetroxide upon a chromium sesquioxide catalyst. Although this combination of metallic oxides is the same as that described by Burk and Hughes (a), a n important difference is found in the method of preparation. The catalyst used in these experiments was made by depo.6 ting chromium trioxide and.antimony tetroxide on a n activau2- cilumina carrier instead of coprecipitating the three oxides as a gel, as Burk and Hughes did. CATALYSTANDAPPARATUS
Chromium trioxide was dissolved in water, and the resulting solution was mixed thoroughly with 8-14 mesh, Alorco grade A, activated alumina. The chromium trioxide was added in such proportions that the resulting dried, ignited catalyst contained 8% by weight CrzOa. The wet catalyst was dried slowly with constant stirring at 110" C. in a hot air oven until it appeared to be as dry as the original alumina. The dried catalyst was then moistened with acetone, and the calculated quantity of finely powdered antimony pentoxide was added so that 8 or 10% by weight of the dry, ignited catalyst was antimony tetroxide. The
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drying procedure was repeated, and a measured quantity of the dried catalyst was placed in the catalyst case, During the heating of the reactor to the reaction temperature, the excess water and acetone were driven out, the CrOa was converted to Cr203, and the SbZOBwas converted t o Sbz04. The decomposition of the oxides could be detected by the change in color of the catalyst from red t o green for the chromium oxides and yellow t o white for the antimony oxides. It was usually necessary to heat the freshly prepared catalyst about 5 to 6 hours in the catalyst case before the water and acetone were completely evaporated, the oxides were decomposed, and the temperature within the reactor attained reaction level.
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temperature a t various sections of the reactor, the volume of liquid charged, the volume of condensate, the volume of tail gas, and other reaction control functions. At the end of 4 hours i t was found that the yield of aromatic hydrocarbons had diminished due to the excessive carbon deposition on the catalyst. The operation was stopped a t the end of the 4-hour run by stopping the pump, shutting off all the heat, and purging the catalyst case with carbon dioxide which helped t o free the catalyst particles of adhering vapor. The catalyst mas then regenerated a t about 750" @. by the introduction of a mixture of carbon dioxide and air containing about 870 oxygen. The progress of the regeneration was followed by temperature readings, since the temperature a t any given level in the catalyst bed increased through a maximum and then decreased rapidly. The Cr203-A1203-Sb204 catalyst which was used in these experiments withstood about sixty-five regenerations with apparently little loss in activity. The methods of analysis used were as follows: DISTILLATIONS.A.S.T.M. Method D86-+O. UNSATURATION-BROXINE NUMBER.Universal Oil Products Method H-44-40. SPECIFICGRAVITY.Chainomatic specific gravity balance. GASANALYSIS. Burrell method and a conventional method of low-temperature fractionation. Analyses for unsaturated hydrocarbons in the normally gaseous fractions were carried out by a combination of fractionation and absorption. FRACTIONATION. A packed laboratory column of conventional type. DETERMINATION OF AROMATICS.Curve shown in Figure 2. Accuracy of this method compared t o a specific dispersion method was about "5%. INDUCTION PERIOD.A.S.T.X. Method D 5 2 5 42T. DETERMINATION OF Gull*. A.S.T.M. Method D381-42.
RECEIVER
AROMATPZATION
Figure 1.
Sketch of Apparatus
The reactor (Figure 1) consisted of a catalyst case of standard steel pipe; the main portion was 3-inch pipe about 30 inches long. This reactor held about 3875 ml. of the granular catalyst and was surrounded by an electrically heated furnace and insulated with Sil-0-Cel within a transite cylinder. Directly above the catalyst case and connected to it by a welded connection was a spiral heater coil made of about 7 feet of l/a-inch standard steel pipe. The heater was also electrically heated and insulated by Sil-0-Cel and transite. The heat supplied to the reactor and the preheaters was controlled by adjusting the amount of electrical current supplied to the furnaces. The temperature a t various positions mas determined by thermocouples incased within a well which extended along the vertical axis of the heater and reactor. The hydrocarbon charge was pumped into the preheater coil by means of a positive displacement, cone-valved pump. Accurate measurements were made of the liquid delivery of the pump before connecting it t o the preheater. A pressure gage in the charge line ensured the operation against continued pumping when the preheater or reactor was plugged. The hydrocarbon vapor was heated in t v o stages; the second stage was designated as the heater in these investigations. The effluent vapors passed through an ice-water-cooled metal condenser where the major portion of the products was condensed. The lighter gases were passed through a dry-ice-cooled condenser where the butanes and heavier were condensed and the lighter gases were passed through suitable metering and sampling devices and conveyed out of the laboratory. The reactor and preheaters were heated to the desired reaction temperature, and the pump was started. The reaction temperature was found to be almost self-sustaining, so the current t o the furnace was considerably diminished a t the beginning of the run. Readings were made a t half-hour intervals and included the
Several aromatization runs were carried out under a predetermined set of conditions using a chromia-alumina catalyst with and without Sb204: reaction temperature, 525-575' C.; space velocity, 0.15 t o 0.50 ml. per ml. per hour; and atmospheric pressure. These conditions were chosen as being easily attainable and suitable for catalytic conversion with the charge stocks and apparatus described. Three different charge stocks were selected: a commercial heptane fraction from natural gasoline, a heavy straight-run gasoline, and a thermally cracked gasoline or pressure distillate. The charge was pumped into the converter a t such a rate that the space velocity (milliliters of charge per milliliter of catalyst per hour) was within the range 0.17 to 0.24. The catalytic activities were indexed by comparing the yield of aromatic hydrocarbons in the liquid product from an on-stream period of 4 hours. A representative sample of the data obtained in these experiments is shown in Table I.
TABLEI. AROMATIZATION WITN .4m WITHOUT ANTIMONY TETROXIDE ReAroReaccovery, matics, tion Space Charge Temp., CataVelocity, Sp. Gr. %o?! Stock C. lyet Ml./Ml./Hr. ume d: ume n-€Ieptanea 550 Without 0.150 53.7 0.7920 40.0 With 0.210 48.1 0.8130 63.0 5.50 Without 0.180 47.3 0.8230 70.0 570 570 With 0.176 , 49.2 0,8460 86.0 530 Gtraight-run Without 0.219 51.7 0.8280 68.0 gasolineb 530 With 0.224 53.3 0.8390 65.0 540 Without 0.405 58.5 0.8164 44.0 Pressure 540 With 0.378 distillatee 47.7 0.8345 58.5 Commercial n-heptane: boiling range by A.S.T.M. distillation, 92' to9 6 O C.:d:: 0.7190. b Heavy straight-run gasoline; boiling range by A.S.T.M. distillation, 128O t o 209' C.:d% 0.7696. 0 Kettle bottoms"of thermally cracked gasoline fractionated t o remove lower-boiling constituents; boiling range by A.S.$.M. distillation, 62' t o 217' C.; d;: 0.7793.
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alumina. The presence of the induction period both before and after the addition of the SbnO4 in our experiments indicated t h a t our alumina catalyst carrier was probably a-Al20~.H2O in accordance with the findings of Archibald and Greensfelder. CONVERSION OF n-HEPTANE
The liquid recoveries and yield of aromatics in the conversion of the commercial n-heptane with the plain chromia-alumina catalyst were somewhat lower than those reported by previous investigators for the conversion of pure n-heptane. Grosse et al. (4) obtained a toluene yield of 65% by weight of the pure n-heptane charged under approximately the same conditions which, in these experiments, gave on the average only about 30% by weight SPECIFIC GRAVITY 2O0C/2O.C. yield. Differences in the nature of the charge Figure 2. Standard Curves for Conversion of Specific Gravity to stock, the lack of special activation of the catalyst Volume Per Cent Aromatics with hydrogen, and the longer duration of each run probably accounted for- the lower yields in these experiments compared to those of Grosse et al. The volume percentageb of aromatic hydrocarbons in the liquid The mechanism of this catalyst-promoting effect is not known. product were determined by the specific gravity curves of Figure The Sb20r probably affects the catalytic surface adsorption in a 2. These specific gravity curves were drawn from averaged values manner such that the velocity of the dehydrogenation-cyclizaof synthetic mixtures which were blended to approximate actual tion reaction is increased, However, the possibility exists also mixtures closely. Later in this work the values obtained by these that the presence of the Sbz04might inhibit the carbon deposition specific gravity curves were checked by a specific dispersion and thereby increase the over-all yield of aromatics. method (6). Upon the basis of theadata shown in Table I, the SbaO4 increased the yield of aromatics about 11 to 16%, based on the I I ! liquid product. However, upon the basis of the charge, in which calculations the liquid recovery influenced the results, the Sb204 increased the yield of aromatics by about 2 t o 10%. In the comparison of these yield values, it was assumed t h a t the small differences in space velocity were of negligible influence. 'This assumption was valid, since it was found that a space velocity difference of as much as 0.05 within the space velocity range of 0.17 to 0.24 affected the yield of aromatics in the liquid product about 3% and the yield on the basis of the charge only about 1%. The average increase in yield due t o a cerium-potassium oxide promoter used by Archibald and Greensfelder (1, page 359, 100 Figure 8) was about 10 to 15 mole % of the total liquid product taken from a 4-hour run period. These authors found that the 1 k cerium-potassium oxide promoter caused the reappearance of the induction period i n the conversion which was eliminated in conversions with a plain chromia-alumina catalyst by calcining the Figure 3. Production Rates for Liquid and Gaseous Product's during Aromatization of Heavy Straight-Run Gasoline TABLE 11. AROMATIZATION O F COMMERCIAL Ta-HEPTANE WITH 84% Al@1-8% Cr20a-8% Sb@4 CATALYST Table I1 gives a more complete compilation of the data of Operating temperature, C. 539 operation and analyses of the products from the conversion of the S ace velocity, ml./ml./hr. 0 255 &tal ml. charged during run 510 n-heptane fraction using the CrzOa-A120~-Sb04 catalyst. These Volume total liquid recovered 63.1 Volume o aromatics on product by sp. gr. 31.10 data represent a summary of a typical run sheet for the converSpecific gravity, dig 0.7658 sion process and are compiled for the purpose of evaluating the Bromine number 15.90 Liters of tail gas from run 177 yield of any one or all of the components of the various products: Gas composition % 6.6 The conversion of the commercial n-heptane from the product Unaatd. hydrobarbons Hydrogen 74.4 standpoint was comparatively simple. There were probably two Satd. hydrocarbons 18.9 Low temp. distillation, mol. % major competing reactions-i.e., fragmentation and cyclization H drogen 74.40 dthane 15.40 with both reactions including dehydrogenation. Assuming that the production of lower hydrocarbons was entirely a competing Ethene Ethane 0.12 3.43 Propane 2.68 reaction and was due to the cracking of the original heptane molePropene 1.39 cule, it was calculated t h a t about %yoof the heptane was lost Butanes 2.67 Total propane liquid, volume on oharge to the cyclization due t o fragmentation. The liquid product conTotal propene liquid volume on charge 3.27 1.64 Total butane liquid (volume on charge 3 90 sisted of the original charge with some higher- and lower-boiling Dry gas, mole % of'total gas Ca-free 93.36 nonaromatic compounds with about 31 % aromatic hydrocarbons, Mole % of dry gas Hydrogen 74.40 mainly toluene. Based on n-heptane, the yield of aromatics Methane 15.41 Ethane 3.43 was calculated t o be about 25.770 of the theoretical. About 10% Ethene 0 12 12.51 of the nonaromatic compounds in the liquid product were unLoss plus carbon, % by weight of total oharge saturated hydrocarbons, which indicated appreciable dehydro-
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saturated hydrocarbons correspondingly produced less hydrogen and more unsaturated gaseous hydrocarbons. Also, the pressure LATE AT 5550 c- .4xDATMoSPHERIC PREssVRE 84% distillate contained molecules with longer chains, and therefore 8% Cr.~0~-8% SbeOl CATALYST more of the heavier-than-methane hydrocarbons were produced in Space velocity ml./ml./hr. 0.344 the fragmentation reaction. ’% recovered oh ice-water-cooled condenser 50.2 Specific gravity, g z 0,8220 As a result of the formation and deposition of carbon on the Vol. % aromatics in product by sp. gr. 49.5 34.10 surface of the catalyst particles, aromatic hydrocarbon producBromine number Induction period, hours 0.5 tion attained a maximum and then decreased within a 4-hOUr A S T M. gum mg / l o 0 ml. 228.0 A:S:T:M. distiilatidn, C. period. The volume of tail gas produced per unit volume of Initial b.p. 59 charge paralleled this production of aromatics, However, the 10’3’ over 108 SO# over 140 carbon deposition favored the cracking reaction morc than the 104 90% over End point 274 aromatization reaction; therefore toward the end of the run, aromatization decreased whereas the gas production inTABLEIV. LIQUIDPRODUCTS FROM AROMATIZATION OF PRESSURE DISTILLATE creased. Figure 3 gives typical curves Volume Per Cent BfOType of Boiling prodAreA.S.T.M. ~ i ~ t0 c. ~ . , showing the rates of aromatization and Hydrocarbon Range, SP. Gr., Fraction Concentrate a C. di! Charge uct matics Number I.B.P. 50% E.P. gas production. The charge stock used A1 Mixed IBP-92 0 . 7 5 3 9 5.4 10.5 Trace 96.9 in the reaction illustrated in Figure 3 was A2 Mixed 92-100 0 . 7 5 9 3 1.4 2.7 7.8 heavy straight-run gasoline which was A3 Mixed 100-116 0 . 8 0 3 6 12.7 24.9 44.7 2?:7 A4 116-156 0 . 8 0 9 1 12.1 Mixed 23.8 49.3 17.4 charged at a space velocity of 0.126 and A5 Mixed 156-185 0 . 8 3 7 5 11.3 22.2 72.9 20.1 AG 185-EP Mixed 15.8 .... .. 8.1 .. a t a reaction temperature of 520” C. A3-A1 Nonaromatic 100-116 0 . 7 4 6 4 5.5 43.4 Trace 13.1 99 110 134. The parallelism between the rate of gas A4-A1 Nonaromatic 116-156 0 . 7 5 1 0 5.9 48.7 Trace 26.7 123 134 153 .45-A1 production and aromatization can be acNonaromatic 156-185 0 . 7 6 8 7 2.1 1 8 . 7 Trace 2.9 143 157 172 counted for by t h e dehydrogenation A3-A2 Aromatic 100-116 0 . 8 5 0 0 7.2 56.6 78.0 108 117 141 A4-A2 Aromatic 116-156 0 . 8 6 5 3 6.2 61.3 92.0 .... 133 139 151 which accompanied the cyclization; acA5-A2 Aromatic 156-171 0 . 8 5 2 1 6.0 52.9 78.0 158 163 170 A5-A3 Aromatic 171-178 0 . 8 6 5 9 2.4 23.3 92.0 .. 172 177 185 cording to the chemical equation for aro-. A5-A4 Aromatic 178-185 0 . 8 4 4 4 0.6 6.2 61.0 .* 182 188 195 matisation, for every mole of mononuclear aromatic hvdrocarbon Droduccd. 4 moles of hydrogen are produced. genation without cyclization. The gaseous products consisted However, a t the stage in the reaction when the aromatization largely of hydrogen and methane with various small percentages reaction started to diminish, the cracking and dehydrogenaof the higher-boiling hydrocarbon gases. About 12.5% of the tion without cyclization increased proportionately, and the result charge was lost due to carbon formation on the catalyst and in was an increase i n the rate of gas production. the handling and measuring of the products. It is postulated SWR-Ill ARY that a certain amount of polymerization takes place on the surface of the catalyst particles and the high-molecular-weight polyThe activity of the catalyst in the catalytic aromatization of aliphatic hydrocarbons was improved to an appreciable extent by mers are further decomposed into carbon. the addition of antimony tetroxide to the chromia-alumina catalyst. CONVERSION OF PRESSURE DISTILLATE An aromatization reaction using a commercial n-heptane Daction from a natural gaEoline witli the chromia-alumina-antimony Tables 111, IV,and V show summarized data for a typical contetroxide catalyst yielded about 25.7% of the theoretical amount version reaction on pressure distillate. Since the starting maof toluene. T h e gaseous products from this reaction were mainly hydrogen and methane. The presence of methane in these gaseterial was considerably more complex than the commercial nous products was good ovidence that the frap;mentation of the heptane charge, the products were correspondingly more numerheptane molecule %’asa major competing reaction in the process. ous and complex. The liquid product was fractionated and then The aromatization of a fraction of cracked gasoline yielded a each fraction was separated into a nonaromatic and an aromatic liquid product containing 49.57, aromatic hydrocarbons from which toluenc, xylenes, ethylbenzene, meqitylene, 1,3-dimethylhydrocarbon concentrate. Nonaromatic hydrocarbons were 4-ethylbenzene, and naphthalene were isolated. The gaseous separated from aromatics by azeotropic distillation with methanol. product consisted of hydrogen and methane with relatively The larger portion of the larger amounts of the gaseous hydrocarbons heavier than aromatics (Table IV) methane. The production of aromatic hydrocarbons during any one reacTABLE V. GASEOUSPRODUCTSwas in the toluene range tion period increased through a maximum and then decreased with the xylene and FROM AROMATIZATIONOF due to carbon formation on the surface of the catalyst. The PRESSURE DISTILLATE mesitylene fractions production of gaseous products paralleled the formation of Per cent in tail gas ranking next in quantity. aromatics until excessive ira-mentation superseded the aromatiza Hydrogen 34.37 tion reaction. 42.5 Besides toluene and the . Saturates Unsaturstes 23.14 three xylenes, such aroLITERATURE CITED Total liquid recovery, ’% on charge 89.30 matic hydrocarbons as Ct-free liquid recovery 77.50 (1) Archibald, R. C., and Greensfelder, B. S., IND. ENG.C H m f . , 37, Propane 3.75 ethylbenzene, mesity356-61 (1945). . , Propene 5.85 lene, 1,3-dimethyl-4Burk, R. E., and Hughes, E. C., U. S. P a t e n t 2,250,415 Butane 1.47 Butene 4.63 (July 22,1941). ethylbenBene a n d Pentane 1.03 Grosse, A. V., Zbid., 2,124,566 7 (July 26, 1938). Pentene 0.77 naphthalene were isoGrosso, A. V., Morroll, J. C., a n d Mattox, W. J., IND. ENG. Mole % of total gas lated from the aromatic Dry gas 92.43 CHEM., 32,528-31 (1940). Hydrogen 37.11 fractions. Grosse, A. V., and Wscklier, R. C., IND.ENC.CHEM.,ANAL.ED , Methane 35.20 11,614-24 (1939). Ethane 11.89 The gaseous products Ethene 4.48 (6) Mittasch, A., Pier, M., Wiotael, R., a n d Lanheinrich, H., U. S. (Table V) differ somePropane 4.24 P a t e n t s 1,913,940-1 (June 13, 1933). Propene 7.08 what from those of nLoss plur carbon, Yoby (7) Moldavskil, E. L., a n d K s m u s h e r , H., Compt. vend. acad. sci. wt. of total charge 7.80 heptane. The pressure U.R.S.S., 1, 356-9 (1936). Per Cent by wt. of dry distillate which origiga8 on total charge 22.40 P R E B ~ X Tbefore E D the 10th Annual I’etroleum Meeting of the Wichita Seonally contained more untion, AVCRICAN CHEXICAL SOCI.CTS
TABLE 111. SINOLE-PASS AROMATIZATION OF PRESSURE DISTIL-
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