INDUSTRIAL AND ENGINEERING CHEMISTRY
March 1953
with thin slabs. A standard deviation from the mean of 0.005 cm. (typical for these experiments) for a n individual thickness measurement, corresponds to only 2.7% of a 0.185-cm. slab, but 7.670 of a 0.066-cm. slab. The diffusion coefficients reported here ,were determined with thin sheets of dry rubber and, consequently, should be considered most pertinent to guayule in that form. Present evidence indicates that the findings enumerated above have a t least limited application t o resin extraction from rubber in other physical forms, such as worms. For example, it has been found that the solvents used in this work behave in worm deresination in a manner consistent with their diffusion rates reported here. Also, temperature changes have the same rather minor effect on the rate of worm extractions as on thin sheet extractions (a rise of nearly 50’ C. being required to double the rate with acetone). Temperature can have a decided effect on the completeness of the deresination, depending on the choice of solvent. A fuller knowledge of the role which the phenomenon of diffusion exerts in the mechanism of guayule deresination must await further detailed investigations. ACKNOWLEDGMENTS
The author is grateful to Eleanor C. Taylor, of the Bureau of Plant Industry, Soils, and Agricultural Engineering, for assist-
581
ance in preparation of the figures; and to Ruth V. Crook of this laboratory for the resin analyses. LITERATURE CITED (1) Am. Soc. Testing Materials, “Standards on Rubber Products,” Philadelphia, 1948. (2) Barrer, R. M., “Diffusion in and Through Solids,” Cambridge University Press, 1952. (3) Boucher, D. F., Brier, J. C., and Osburn, J. O., Trans. Am. Inst. Chem. Engrs., 3 8 , 9 6 7 (1942). (4)Clark, F. E., Banigan, T. F., Jr., Meeks, J. W., and Feustel, I. C., IND. ENQ.CKEM.,4 5 , 5 7 2 (1953). (5) Fan, H. P., Morris, J. C., and Wakeham, H., Ibid., 40, 195 (1948). ( 6 ) Hauser, E. A., and Le Beau, D. S., India Rubber World, 108, 37 (1943). (7) King, $3. O., Katz, D. L., and Brier, J. C., Trans. Am. Inst. Chem. Engrs., 40, 533 (1944).
( 8 ) Meeks, J. W., Banigan, T. F., Jr., and Planck, R. W., U. S. Patent 2,572,046 (Oct. 23, 1951).
(9) Nishimura, M. S., Hirosawa, F. N., and Emerson, R., IND. ENQ. CHEM.,39,1477 (1947). ( I O ) Osburn, J. O., and Katz, D. L., Trans. Am. Inst. Chem. Enars.. 40, 511 (1944). (11) Taylor, K. W., Econ. Botanu, 5, 255 (1951). Rubber Proiect. Jan. (12) Tint, H., Salinas Tech. File, Emergency ~. 18, 1945. (13) Walter, E. D., J. Am. Chem. SOC..66, 419 (1944). (14) Wood, J. W., and Fanning, R. J., Rubber A g e , 68, 195 (1950). RECEIVED for review June 30, 1952. ACCEPTED October 8, 1952.
Adsorption of Ammonia on Fuller’s Earth and Gas-Adsorbent Carbon G. L. BRIDGER AND R. D. SINNER1 Department of Chemical and Mining Engineering, Iowa State College, Ames, Iowa
T
H E adsorption of ammonia by various solids has been the subject of numerous invest&ations (1, 2). However, a literature search failed t o reveal data on the adsorption of ammonia a t constant pressure at temperatures just above its condensation point. The purpose of this paper is to present such data of sufficient accuracy for engineering design for the adsorp tion of ammonia on two adsorbents at atmospheric pressure and
a t temperatures near the condensation temperature of ammonia, -33.4”
c.
I n preliminary experiments, activated alumina, bauxite, bentonite, bone char, china clay, silica gel, zeolite, fuller’s earth, and gas-adsorbent carbon were tested for ammonia adsorption capacity at -5” and -30” C. The fuller’s earth and gasadsorbent carbon had the greatest adsorptive capacity and consequently were used in the more detailed studies. ADSORBENTS
*
The fuller’s earth used was Attaclay SF produced by the Attapulgus Clay Co., Philadelphia, Pa. The clay, originally in powder form, was compressed into tablets l / 4 inch in diameter and 1/16 inch in thickness. The bulk density of the tablets in a S/4-inch column was approximately 0.56 gram per cc. The gas-adsorbent carbon used was Columbia Grade 4SXW, 6 to 8 mesh, produced by Carbide and Carbon Chemicals Corp., New York, N. Y. In both cases the adsorbents were dried a t 120’ C. for 18 hours before using. APPARATUS AND PROCEDURE I 0.001 40
-
I
I
-20
I
I
0
TEMPERATURE,
I
I
20
I
I
40
I
I
60
*C.
Figure 1. Adsorption Isobars for Ammonia on GasAdsorbent Carbon and Fuller’s Earth at Atmospheric Pressure
The procedure used in determining adsorptive capacities was chosen t o give results of sufficient accuracy for design of commercial adsorbers. A drying tube of Drierite was used to remove water vapor from the inlet ammonia stream. An aluminum coil placed in a 1
Present address, The Ethyl C o w , Baton Rouge, La.
582
INDUSTRIAL AND ENGINEERING CHEMISTRY
cooling bath was used to cool the ammonia to the adsorption temperature. The gas then passed through the adsorbent which was placed in an &inch U-tube dipping into the cooling bath. Approximately 10 grams of adsorbent was used. A calcium chloride-ice mixture was used in the agitated bath. Additional cooling and temperature control was attained through the use of dry ice. During a run, ammonia gas was passed through the system at a rate sufficient to ensure a positive pressure of about 10 mm. of mercury above atmospheric pressure in the system. Adsorption a t the desired temperature was continued for 1 hour, which was considered sufficient for equilibrium since the maximum temperature rise of the adsorbent occurred in 10 minutes. Desorption was carried out by transferring the U-tube containing the adsorbent to a water bath and heating to 100” C. for 1 hour. The desorbed ammonia was absorbed in 2 N sulfuric acid. Back titration with standard sodium hydroxide solution was used to determine the amount of ammonia desorbed. An experimentally determined dead space correction was applied to account for the unadsorbed ammonia initially in the system. The adsorptive capacities thus determined are actually dif-
Vol. 45, No. 3
ferences in adsorptive capacities a t the specified temperature and 100” C., the temperature a t which desorption was carried out. The small amount of ammonia remaining on the adsorbent a t 100” C. is not considered significant for design of commercial adsorbers. RESULTS
The adsorption isobars are shown in Figure 1. Thc points were obtained in a random order. It is apparent that the two materials possess different adsorption characteristics. The fuller’s earth isobar increases sharply as condensation temperature is approached. The isobar for gas-adsorbent carbon indicates that the adsorptive capacity of the carbon approaches a constant value as the condensation temperature is approached. LITERATURE CITED (1) Deits, V. R . , “Bibliography of Solid Adsorbents,” U. S. Cane Sugar Refiners, Washington, D. C. (1944). (2) Emmett, P. H., Chem. Revs., 43,69-148 (1948). RECEIVED for review June 2 5 , 1952.
ACCEPTED Xovember 3, 1952.
Isomerization of ntanes and Hexanes NATURE AND CONTROL OF SIDE REACTIONS B. L. EVERING, E. L. D’OUVILLE, A. P. LIEN, AKD R. C. WAILTGH‘ Research Department, Standard Oil Co. (Zndiana), Whiting, Znd. NUMBER of publications have described the isomeriztttion of butanes, pentanes, and hexanes (5, 19). Butanes isomerize readily without side reactions under suitably controlled conditions, while pentanes and hexanes disproportionate and crack so readily that the isomerization reaction is secondary. With pentanes the lower boiling products are mainly the result of disproportionation between two molecules:
2CHa(CHz)&K --+ CJLo
+ CaH14
Although pentanes react primarily as shown above, small amounts of higher boiling products are formed because of cracking, and these lead to a hydrogen deficiency and gradual deactivation of the catalyst. The cracking (16)reaction is even more pronounced in the case of hexanes and results in more rapid catalyst deactivation. A number of materials have been investigated as inhibitors of the disproportionation and cracking reactions. Hydrogen ( 6 , 7 , 11, 15, 20, $6, 28), aromatics, naphthenes, and isobutane (2-methyl propane) (6, 16, 18) have been reported to inhibit the undesired side reactions in varying degrees. The present paper is concerned with a more detailed account of the inhibiting effect of hydrogen, aromatics, naphthenes, and isobutane and their effect on catalyst life. All these materials inhibit the disproportionation of pentanes and increase catalyst life during isomerization. Hexanes can be successfully isomerized only in the presence of hydrogen. Olefins nullify the effect of inhibitors and accelerate the disproportionation and cracking reactions. Additional information on the role of hydrogen chloride as a catalyst component is presented, supplementing that previously reported 1
Present address, Arapahoe Chemical Co , Boulder, Colo
(14). Finally a mechanism is proposed based on an intramolecular rearrangement while the hydrocarbon is associated with the ionized aluminum chloride-hgdrogen chloride complex. In this work single experiments are often found to be misleading because of changes in the physical condition of the catalyst during an experiment. Therefore the conclusions d r a m are based for the most part on life studies which are considered more reliable. These data are the outgrowth of the exploratory research which led to the development of the Indiana pentane and hexane isomerization processes. CATALYST AND REAGENTS
The aluminum chloride was obtained from the Hooker Electrochemical Co. In early experiments the aluminum chloride was resublimed under vacuum and stored in sealed glass ampoules. An ampoule was opened just prior to an experiment, weighed, and transferred as rapidly as possible to the reactor without other precautions to avoid contact with moisture in the air. The aluminum chloride as received gave substantially the same results under these circumstances as the resublimed material and therefore was used in all subsequent experiments. The ratio of chlorine t o aluminum corresponded closely to that found by Stevenson and Beeck (26) for their moist aluminum chloride. The authors’ catalyst presumably had the approximate empirical formula of Al~Cls.~(OH)0.6 that they reported. The hydrogen chloride was commercial anhydrous compressed gas from the Harshaw Chemical Go. Hydrogen was obtained from the National Cylinder Gas Co. and used as received. The n-butane, isobutane, n-pentane, and 2,3-dimethylbutane were Phillips Petroleum Co. technical grade hydrocarbons with purity better than 95% by volume; they were used without further purification. Pentanes and hexanes that were used in large quantities were narrow cuts fractionated from virgin midcontinent naphthas. The plant pentanes were 99+% C.;
