1524
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
Vol. 45, No. 7
perature more than 2' or 3' above the recent maximum amtemperature curve into the future by the methods eeiggested in bient, or a rapid rise in temperature (0.5" C. or more per hour), this report, it is well to bear in mind the several approximations should serve as a warning. made in these calculations. Most of these approximations overPROCEDURES FOR DEALIKG WITH SELF-HEATING HYDROGEX estimate the hazard and underestimate the time before eruption. PEROXIDE TANKS.As shown in Figures 5 and 6, long delays will However, a t least two factors may operate in the opposite direcusually occur between the inception of rapid decomposition and tion-possible breakdown of stabilizers a8 the reaction proceeds the attainment of excessive temperatures. This delay allows time and the formation of a blanket of gas bubbles on the interior surfor extended efforts to control the reaction. faces, which might reduce heat transfer. In the early stages of elf-heating, the decomposition can be curbed by the addition of stabilizers or by cooling with water. It LITERATURE CITED is advisable t o stock packages of e6ergency stabilizers a t large (1) Satterfield, C . N.,K a m n a g h , G. AI., and Resuick, H., ISD. ESQ. storage locations. External cooling with water sprays may dissiCHEX.,43,2507 (1951). pate heat a t least ten times as fast as air convection, with obvious (2) Schumb, W C., Ibid., 41,992 (1949). advantages in bringing a self-heating tank under control. In(3) Shanley, E. S., and Greenspan, F. P., Ibid.. 39, 1536 (1947). ternal cooling n-ith clean water, thus diluting the peroxide, is also (4) Stoever, H. J., "Xpplied Heat Transmission," K e x York, &ICGraw-Hill Book Co.. 1941. a very effective means of control. ( 5 ) Williams, G. C., Satterfieid, C . N., and Isbin, E. S., J . Am. Rocket While attempting to control a self-heating tank, a careful timeSoc., 22, No. 2, 7 0 (1952). temperature record should be kept to provide a running record of RECEIVED f o r review December 20, 1952. the effectiveness of the control means. I n projecting the timeA C C E P T E D April 15, 1953.
Granular Adsorbents for Sugar
Refining SOME PHYSICAL PROPERTIES OF BONE CHAR AND SYNTHAD ELLIOTT P. BA4RRETT Baugh and Sons Co., Philadelphia, Pa., and Mellon I n s t i t u t e , Pittsburgh, P a .
AIRIISON JONNARD1 AND J. H. RIESSMER Mellon Institute, Pittsburgh, P a .
T
HE increasingly general use of Synthad (a synthetic adsorbent manufactured by Baugh and Sons Co.. Philadelphia, Pa.) as a granular adsorbent in sugar refining, makes it desirable to report results of comparisons between three of its important physical properties and those of bone char, to which no reference has been made in earlier publications ( 1 , 2). The heat of wetting is important because it causes a rise in temperature when the sugar liquors come in contact with freshly regenerated adsorbents. Thermal conductivity and specific heat arc of obvious importance in connection with the thermal regeneration of the products. Because Synthad is used in the same way as bone char and in the same equipment, obtaining strictly comparable results for the two adsorbents, rather than absolute accuracy, was stressed in making the measurements. HEAT OF WETTING
The calorimeter was a cylindrical Dewar flask of 66O-ml capacity, A Beckman thermometer, which could be read to f0.002' C., was so placed, in the center of the flask, that its bulb was near the bottom. A small Nichrome wire coil, of measured resistance, was located a t one side of the thermometer, This was utilized to measure the heat capacity of the svstem bv applying a measured voltage for a measured time. Diametrically opposite the resistance coil was a wire-mesh basket suspended from a thread attached t o a motor-driven reciprocating mechanism. This served both as a stirrer to accelerate the attainment of thermal equilibrium within the system, and as a receptacle for the adsorbent, when introduced into the calorimeter. I n each measurement, 350 ml. of water were introduced into the flask, stirring was begun, and temperature readings were made a t predetermined time intervals until the time-temperature curve
could be accurately extrapolated to the time a t which a wcighed amount of the adsorbent, 60 to 80 grams. was dumped into the basket. After addition of the adsorbent to the calorimeter, temperature readings weie continued until a steadr state was reached, following which a known amount of heat was liberated electrically within the system, and the resultant rise in temperature, corrected for heat losses, waq used as the measure of the heat capacity of the system. The magnitude of the heat of wetting is dependent on the dryness of the surface of the adsorbent as determined by the pretreatment of the material. Table I compares the results obtained when new adsorbents a e r e maintained a t 72" F. and 61% relative humidity for several days n i t h results for the same adsorbents maintained a t 220' F. for 5 days, and with those obtained when the adeoi bents aere heated to 1100' F. for 156 t o 157 minutes, in the absence of air, prior to wetting. Evidently, once the superficial moisture has been removed, the heat of wetting of Synthad C-38 is only about 58 to 60% that of bone char.
TABLE I. HEATSOF WETTING OF BOXE CHARAND SYNTHAD C-38 Sdsorbent Bone char EH-1 Synthad C-38 Bone char EH-1 Synthad (2-38 Bone char EH-1 Synthad C-38 0
1
Present addreaa, Shell Chemical Corp., New York, N. Y.
Pretreatment 72' F 61% R.H 72' F:: 61% R.H: 220' F., 5 days 220' F., 5 days l l O O o F., 157 min. 11OO0 F., 166 min.
Heat of Wetting, Ratio, Cal./G. Synthad/ a t i 2 O F. Bone Char 1 . 8 0 rt. 0,07= 1.066 1 . 9 0 -+: 0.07 9.45 i .0 . 0 6 0.600 5 . 6 6 -+: 0 . 0 i 1 5 . 9 rt. 0 . 9 0.584 9 . 3 =t0 . 4
Limits average deviations from mean of 5 observations.
INDUSTRIAL AND ENGINEERING CHEMISTRY
July 1953
THERMAL CONDUCTIVITY
The apparatus consisted of a flat brass plate which could be maintained a t about 211” F. by steam condensing on its bottom surface. This was surmounted by a hollow cylinder of 80% magnesia pipe insulation 5.5 inches in internal diameter. A layer of adsorbent was packed into the hollow space t o a depth of 1 inch and a metal can closely fitting the inside of the insulation was placed on top of the adsorbent and pressed firmly down upon it. A known weight of water at about 85’ F. was put into the can and a n insulating cover carrying a thermometer and stirrer was placed on its top. The quantity of heat transferred in unit time was determined by measuring the temperature of the water in the can at predetermined time intervals. CONDUCTIVITIES O F BONECHAR Table 11. THERMAL
1525
in quartz spheres of 70-ml. capacity together with a sufficient quantity of copper slugs t o ensure that the sphere would sink in water. The spheres were evacuated a t 450” F. and were then sealed off. I n making a measurement, the quartz sphere was suspended in a tube furnace and maintained a t the desired temperature for several hours. Then the layers of insulation covering the bottom of the furnace and the top of the calorimeter were slid aside momentarily while the bulb was quickly lowered into 1250 ml. of water in the calorimeter. The resultant rise in temperature
AND
SYKTHAD
Bone char into cycle 1 Bone char into cycle 10 Bone char into cycle 15 Bone char into cycle 20 Av. Synthad into cycle 1 Synthad into cycle 10 Synthad into cycle 15 Synthad into cycle 20 Ax-.
38.6 42.8 44.9 46.4 43.2 40.4 45.2 45.5 47.0 44.5
43.7 49.4 53.5 51.4 49.5 45.9 53.5 52.0 54.2 51.4
0.1030 0.0965 0.1048 0.0975 0.1005 0.1032 0.1022 0.0995 0.1007 0.1014
The method is subject to three disadvantages: (1) The temperature of measurement is far below t h a t a t which adsorbents are regenerated in a reburning kiln. (2) The adsorbents are not dry. (Under the conditions of measurement the moisture contents would be 2 to 40/,.) (3) The degree of packing is greater than the normal “loose packing” which, presumably, prevails in reburning kilns. Measurements were made on adsorbents into cycles 1, 10, 15, and 20 of the comparison of bone char and Synthad made a t the Revere Sugar Refinery ( 1 ) . Results are shown in Table I1 which also compares the “loose-packed” bulk densities of the adsorbents with their densities as packed into the apparatus. I n spite of t h e disadvantages of the method of measurement, it is evident that there is no significant difference between the thermal conductivities of the two adsorbents. For comparison, the data of Robinson are quoted in Table 111 (6).
Sample i n Quorfz Bulb
/
Thermocouple
Polenfiomefer
Ammeter
\
F/osk
CONDUCTIVITIES OF SEVERAL BONECHARS TABLE 111. THERMAL Char h-o. 66 service char
No. 32 service char No. 36 service char Fraction on No. 30 screen Fraction through No. 30 screen Original mixture No. 34 discard char
Mean Density. Temp., Lb./Cu. Ft. F. 57.0 129 54.5 621 54.5 698 65.0 129 69.4 594 69.4 622 69.4 685 73 4 73 4 83.9 83.9 75.4 78.2 78.2 86.6 88.2
610 680 610 682 129 608
709
129 572 624 707
Therm. Cond., B.t.u./ Hr. Sq. Ft. (” F./Ft.) 0.072 0,092 0.099 0.072 0.094 0.095 0.099 0.108 0.114 0.112 0.118 0.092 0.109 0.117 0.103 0.129 0.132 0.136
SPECIFIC HEAT
Specific heats were measured with the apparatus shown schematically in Figure 1. Samples of Synthad and bone char representing adsorbents into cycle 1 of the Revere Sugar Refinery comparison ( 1 ) were ground to pass 60-mesh. They were placed
Figure 1. Apparatus
was noted and, when a steady state had been reached, a known amount of heat was liberated electrically via t h e resistance coil, so t h a t the heat capacity of the system was directly measured incidentally t o each determination. Specific heat of the adsorbent was computed from the rise in temperature of the calorimeter, corrections being made for the heat capacity of the quartz and the copper. Measurements were made at progressively higher temperatures until the quartz spheres shattered from thermal shock upon being lowered into the calorimeter. There was no observable reaction between the copper slugs and their environment, and the copper remained bright and shiny throughout the measurements. Results are given in Table IV. Deitz and Robinson (3) report an average specific heat of 0.21 B.t.u. per pound per degree Fahrenheit for bone char over the range 05 temperatures commonly used in reburning. T h e average values of Table IV are a little less than 5 % higher. It is apparent that the average specific heat increases .with temperature by about 0.01 l3.t.u. per pound per degree Fahrenheit every
INDUSTRIAL AND ENGINEERING CHEMISTRY
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S'ol. 45, No. 7
DISCUSSION OF RESULTS
TABLEIv.
HEATSO F BONE CHAR
Table V summarizes the results for the two adsorbente. The absolute values, when the relatively small number of observations Temperatures of Adsorbent, F. ~ Measurement Initial Final and~the lpossibility of systematic errors are taken into account, are No. (in furnace) (in calorimeter) probably accurate within 3= 10%. The ratios, however, involving Bone Char the same syst,ematic errors for both adsorbents, are probably 1 482 82 0.195 reliable to within 2%. 2 568 88 0.206 Evidently there is no significant difference between t.he ad85 0.214 3 651 45 732 85 0.221 sorbents with respect to specific heat and thermal conductivity, 88 0.239 813 6 887 88 0.246 but, the heat of wett,ing of Synthad is much smaller than t.hat of Av. 0.219 bone char. It has been suggested by de Whalley and Dickinson Synthad (4)that, the heats of wetting of bone chars with similar histories 1 504 83 00.218 .195 might be used as measures of their relative areas. It is, however, 2 545 82 3 544 83 0.213 not surprising that this concept does not appear t o be applicable 4 63 1 82 0.215 t o the Synthad and bone char used for these measurements be5 795 87 0.215 6 865 85 0.242 cause, in spite of their very similar properties, they are not 7 967 87 0.244 Av. 0,220 chemically identical. The area - of the Synthad was approximately 90 square meters per gram TABLE v. PHYSICAL PROPERTIES O F SYXTHAD C-38 4 S D B O X E CHAR and that of the bone char Temp. Ratio of about 120, indicating, on the Range of ddsorbents Results Results, Property and Neasurements, Used for Bone Synthad Synthad/Bone de Whalley and Dickinson hyGnits Reported F. Measurement char C-38 Char pothesis, a ratio of heats of wet70-72 Heat of wetting, calories/ New adsorbents heated 15.9 9.3 0.58 ting of about 0.75, the actual t o 1100O F.and cooled gram in d r y atmosphere ratio was about 0.6. 90-210 Thermal conductivity. Average of samples into 0.100 0.101 1.01 SPECIFIC
O
SYKTH.4D Av. Specific Heat from 1 ~ i ~ to i ~~ 1 i Temp., B.t.u./Lb. F. -4XD
O
B.t.u./ft. hr.
F.
Specific heat, B.t.u./lb. 0 P.
80-900
cycles 1, 10, 15, 20 of refinery test New adsorbents dried pulverized, and evacdated in quartz bulb
ACKNOWLEDGRZENT 0.24
0.24
1.00
The authors Fish to thank Baurrh and Sons Co. and Mellon Institute for permiseion to publish this material. I
100' F. over the range from 500" to 900' F. A t the Revere Sugar Refinery, where char is reburned in thin-tube alloy steel char temperature in reburning is cusretorts, the tomarily between 850" and 900" F. If this is taken as representative of maximum temperatures for refineries in general, it Seems that a specific heat of 0.24 may approximate more closely to working conditions than one of 0.21.
LITERATURE CITED
(1) B a r r e t t , B r o w n , and Oleck, I X D . ENG.C H E W , 4 3 , 6 3 9 (1961). (2) B a r r e t t , Joyner, a n d H a l e n d a , Ibid., 44, 1827 (1952). ( 3 ) ~~i~~ a n d ~ ~ b Ibid., i 40, ~ 1073 ~ (1948,, ~ ~ , (4) de W h a l l e y a n d D i c k i n s o n , Intern. Sugar. J . , 48, 7 3 (1946). ( 5 ) R o b i n s o n , Proc. Tech. Session Bone Char, 1949, 300. RECEIVED for review Xovember 14, 1952.
ACCEPTEDMarch 2 2 , 1953.
tobenzothiazole Vulcanization Using Sulfur-35 IRVING AUERBACH The Goodyear Tire and Rubber Co., Akron 16, Ohio
S
INCE the discovery of the accelerating properties of mercapto-
benzothiazole (MBT), a number of mechanisms have been suggested to account for its role ( 3 , 5 , 6, 8). The formulation of these mechanisms was hampered from the very beginning, because the process of vulcanization itself was not well understood. Furthermore, intermediates were suggested whose presence was not assured. I n the light of newer information on the mechanism of vulcanization and because of the possibilities opened up by tracer techniques, a re-examination of this problem was undertaken. EXPERIMENTAL WORK
B y using either radioactive elementary sulfur or mercaptobenzothiazole in which the mercapto group was tagged, the analytical procedures were greatly simplified and very rapidly performed. Thus, it was possible t o extract vulcanized samples
containing tagged mercaptobenzothiazole with alcohol, determine consumed mercaptobenzothiazole, and then re-extract the same samples with chloroform to determine mercaptobenzothiaaole combined as the zinc mercaptide. Similarly, combined sulfur was determined by using radioactive sulfur in the vulcanization formula. Extracting with acetone and determining the residual activity in the vulcanizate gave the total combined sulfur. By re-extracting with an alcohol-ether solution of hydrochloric acid, zinc sulfide was removed. The residual activities of the samples then indicated organically combined sulfur, The term "consumed mercaptobenzothiazole" refers to mercaptobenzothiazole products not soluble in alcohol and combined sulfur includes rubber-sulfur compounds and zinc sulfide. The test specimens were prepared in the following manner. GR-S, containing 4.78% fatty acid, or unextracted pale crepe
