ISDC‘STRIAL A N D ESGINEERISG C H E X I S T R Y
January 15, 1930
57
Moisture Content of Carbon Blacks’ William B. Plummer GEXERALATLAS C A R B O G
COMPANY,
60
X A L L ST., S E W YORK,
L-,1’.
Data on the determination of moisture in carbon that the observed Feight loss METHOD for the deblacks are given here. I t is concluded that essentially does not merely represent loss terminatioll of total moisture i n c a r b o n all of the total free moisture content of blacks is evolved of nloisture plus its “JTater blacks recently proposed ( 1 ) on Oven heating at 105-10” C., and that the higher gas” reaction with the carbon. involves mixing the sample results shown by one method are due to moisture It shows the original presence ( 5 grams) JTith 25 CC. of dry formation during the determination from the oil either of O2 its such, or of xvlene and 200 CC. of drv minmedium used and the oxygen adsorbed on the black. oxygen combined with carbon and hydrogen in comera1 oil, heating to 1 f 5 O C., passing dry nitrogen through the system until the xylene and pounds where the molecular H2 to O2 ratio is very much less water have been displaced from the carbon black-oil mixture, than 2.0. Because of these facts the xylene-oil method (1) was and continuing the nitrogen stream until all water has been displaced from the intermediate xylene receiver and absorbed studied further to determine possible causes of’ error. It has in the final CaClz tubes. By this method values of 3.54- been found that on bubbling ordinary commercial nitrogen 5.96 per cent total water are obtained for channel blacks, containing 0.3 per cent of oxygen through mineral oil a t whereas the same samples showed only 1.42-1.85 per cent 175” C. an apparent conversion of about 60 per cent by weight of the oxygen to water is obtained. With purified loss on ordinary drying for 6 hours a t 105” C. The moisture content of carbon blacks is an important “02-free” nitrogen bubbled through the oil only a small factor in many of their uses, so that the discrepancy be- blank is obtained. On the other hand, if thoroughly oventween this and the usual oven drying method becomes a dried carbon black be added to the oil and “02-free” nitrogen matter of practical importance as well as theoretical interest. passed through, the water evolved is equivalent to about 1 per cent, based on the black. Similarly, using black Hence it has been further investigated. Various types of blacks on heating in a 1-2 mm. vacuum previously heated in vacuum a t 1000” C., cooled in vacuum, show widely differing weight losses, as illustrated by the and saturated with dry O2 a t 25” C., the water evolved results in Table I. equals 1.45 per cent on the black.
A
Table I
Loss I N WEIGHTAT’
BLACK
0
450’ C. Per cent
High yield black 0.65 2.45 Channel black Roller black 3.59 Based on original material air dry only
7:O0 C. Per cenl 1.12 5.13 9.09
Experimental Work 950’ C. Per cent
1.61
7.23 15.94
Evidently it is necessary to go to 750” C. vacuum heating to obtain a loss with channel black equal to that shown by the xylene-oil method ( 1 ) a t 175” C., which is possible but would be surprising. Certain of Johnson’s (3) results bear directly on this question. .Johnson heated various samples of black a t 950” C. (atmospheric pressure) and analyzed the gases evolved. I n parallel determinations dry nitrogen was passed through the heating chamber and the HzO evolved was determined by absorption in CaCl2 tubes. I n Table I1 his moisture results are shown and the calculated total mols of C, H2, and 0 2 evolved in all gaseous forms are given. Table I1 FREE
COMBINED
GASIN DRYGAS GIVEN
&OAT OFF A T 960’ c. BLACK 105’C. 1 0 5 O C. C Hz Oa Per cenl Per cenf M o l s per 100 grams original black ChannelA 0.132 1.35 0.30 0.051 0.078 ChannelB 2.71 0.44 0.190 0.080 0.113 Roller D 2.92 0.44 0.276 0.111 0.174 Roller E 4.32 0.72 0.365 0.042 0.236 &OAT
M O LRATIO Hr:Oz I N DRY GAS AT 9500 c. 0.65 0.71 0.64 0.18
The Hz to 02 ratio is the most important result given in Table 11. The evolved gas was found by Johnson to contain C02, CO, H?, 02, CHI, CZHe, K2, and “illurninants.” A priori, it would not be impossible for such a gas to have been formed by synthetic reactions during the heating process, wit’h H20 and C as the only starting materials. If this were the case, however, the final HZt o 0 2 ratio, regardless of the actual components, would obviously be 2.0, which is far from being the case. This shows conclusively 1 Received December 7, 1929.
A train was set u p in which commercial tank nitrogen (0.3 per cent oxygen) was passed through two CaCl2 towers and bubbled through 500 cc. of ‘‘straw oil” held a t 175” C., through an oil trap (a cotton-filled U-tube held a t 100’ C.), through two CaClz absorption tubes, through a protective CaC12 U-tube, and through a standard “wet-test” gas meter (0.1 cubic foot dial). A total of 42 liters (1.5 cubic feet) of nitrogen was passed through the oil a t a rate of 17 liters (0.6 cubic foot) per hour. The oil flask was then by-passed and 28 liters (1.0 cubic foot) more passed through to sweep out the apparatus (Table 111). Following this a blank was run in which the nitrogen from the tank was passed through three bubbler bottles containing alkaline pyrogallol solution held a t 60-70” C. before passing through the CaC12 towers and the oil. Another duplicate run was then made, using the same volumes, with purified “02-free” nitrogen, but with 10 grams of thoroughly oven-dried channel carbon black mixed with the oil. The foregoing determinations of H20 absorbed are not exact, as, in order to maintain parallelism with the xyleneoil method, the CaCh tubes were not saturated with C 0 2 before the determination. The first run, therefore, was repeated, using unpurified nitrogen, but replacing one of the preliminary CaC12 towers with a soda lime tower and saturating the CaC12 absorption tubes with C02 before the test. Using the same quantities of nitrogen, etc., t,he H20 found mas about 10 per cent less than in the first run. This illustrates the magnitude of this error. Comparison of the present experiments with the xylene-oil method, however, should preferably be based on the similar condition of CaC12 tubes not saturated with C02. I n the final run purified nitrogen and saturated CaClz tubes were used, and 34 grams of channel black, treated as follows, were added to the oil. The black had been heated for 2 hours a t 1000” C and 1 mm. pressure, cooled
ASALYTICAL EDITION
58
in Tacuuni, saturated with dry oxygen at room temperature, and introduced into the oil flask without contact with air. Periodic weighings showed an initial rate of H,O evolution of about 0.200 gram per hour, falling regularly over a 6hour period to a constant value of 0.004 gram per hour, which corresponds with the blank obtained in the second run. I n all of these tests the oil was first dried by heating t o 250” C. while passing dry nitrogen through the flask during the heating and cooling period. Table I11 CaCh SATURATED RUN USED BLACK GEN WITH CO, TIME Grams Hours 1 None .. 0 . 3 7 0 0% N o 2.5 2 None Purified No 2.5 3 Oven-dried 10 Purified So 2.5 4 h’one , 0.37, 02 Yes 2.5 5 Degassed and saturated with 0 2 34 Purified Yes 6.5 a After deduction of corresponding blank. WEIGHT
BLACK
OF
h-ITRO-
..
.
APPARENT H20 Gram 7p . - of. blacka 0,1245 . 0.0115 0,0784 0:67 0.1122 .
.
.
0,5164
1.45
Discussion
The foregoing data show conclusively that oxygen in the nitrogen or adsorbed on the black may react with mineral oil under the test conditions. I n the description of the xylene-oil method the duration of the test and the purity and volume of the nitrogen used are not stated. It is understood, however,2 that the nitrogen was of high purity, that it passed over but not into the oil, and that all H?O mas evolved from the oil-black-xylene mixture in 10-30 minutes. This practically eliminates the nitrogen as a factor in the results, but the present data show the need for precautions on this point. It therefore seems probable that oxygen adsorbed on the black is the main factor. The rate of reaction observed in run 5, using 34 grams of black, might appear to be too low to account for the H20 evolved in 1030 minutes in the xylene-oil method using only a 5-gram sample. However, the kinetics of reactions in a liquidsolid-adsorbed gas system are so complex that it is difficult 2
Private communication from Carson.
Val. 2, h-0. 1
to predict the effect of the amount of solid present on the observed reaction velocity, while also this must depend largely on the particular character of the oil used. In the present case the oil was a refined paraffin wash oil (“straw” oil) and presumably more resistant to oxidation than the average petroleum fraction of like boiling range. Based on the apparent conversion of 0 2 to H20 observed in run 1, the 0.67 per cent H 2 0 evolved in run 3 would correspond t o 1.0 per cent oxygen adsorbed on the black, and the 1.45 per cent H 2 0 found in run 5 would correspond to 1.9 per cent oxygen. The work of Hulett and Cude (a) shows only about 0.14 per cent free O2 removable as such from channel blacks a t room temperature and 0.6-1.0 per cent removable as O?! C02, and CO a t 445” C., while their original analysis shows about 2.5 per cent total oxygen present. Johnson’s results (3) show about 3.0 per cent oxygen removable in all forms (except H20) a t 950” C. S o final conclusions can be drawn from these figures as to the original amount of adsorbed 0 2 , but from what is known of the niechanism of adsorption of 0 2 on carbon and other oxidizable surfaces, and of the mechanism of its subsequent removal (Langmuir’s general studies on oxygen films), it is probable that a large proportion of the total oxygen content is originally present as adsorbed 0 2 , regardless of the form in which it ultimately appears on heating and evacuating. All of the foregoing experimental observations and general facts are in agreement with the belief that the “additional moisture” shown by the xylene-oil method is mainly the product of the reaction of the mineral oil with the oxygen adsorbed on the black. Acknowledgment
These results are published with the permission of the Combustion Utilities Corporation, a t whose laboratories, at Linden, K. J., the work was carried out. Literature Cited (1) Carson, IKD.EKGCHEX.,Anal. Ed , 1, 225 (1929) (2) Hulett and Cude, Bur. Mines, Bull. 192, 76 (1922). (3) Johnson, IND.E N G CHEM, 20,904 (1928).
Anhydrous Magnesium Perchlorate as a Drying Agent’ Sam Lenher and Guy B. Taylor EXPERIMENTAL STATIOK. E . I.
DU
PONT
DE
T H E preparation of magnesium perchlorate and its use as a desiccating agent in the trihydrated and anhydrous forms have been described by Willard and Smith ( 2 ) . In a subsequent paper Smith, Brown, and Ross (I) advise the use of the trihydrate as a collector of water vapor in steel and organic combustion analysis, mainly because it can be more easily prepared in suitable physical condition. I n preparing the anhydrous salt, the trihydrate melts in its water of crystallization a t about 145” C. and passes slowly into the anhydrous form as the temperature is raised to 250” C. The result is a pasty mass, which is difficult to handle while being dehydrated and is not readily reduced to granules. We have found that if the trihydrate, “dehydrite,” is enclosed in a tube or bulb and a vacuum less than 0.1 mm. of mercury maintained while heating slowly to 250” C., the water of crystallization is removed so rapidly that the 1
Received November 5, 1929.
XEMOURS & COMPANY, W I L M I N G T O N , DEL.
salt does not fuse a t any stage of the operation. The reason for this is that the salt is partially dehydrated below its melting point, so that fusion cannot occur. The resulting material is in a better physical state for drying gases than the original “dehydrite.” Its capacity for water absorption is doubled, and its efficiency is greater where extremely low partial pressures of water vapor are significant. For evacuation during the dehydration a good oil-sealed pump of large capacity must be used to maintain the specified vacuum. A t a pressure of 10 mm. of mercury the salt melts on heating, just as it does in the open air. The dehydration of the trihydrate a t pressures below 0.1 mm. mercury a t temperatures of 140-250” C. is rapid. Our results indicate that under these conditions dehydration of a 10-gram sample is accomplished in 1 hour. Literature Cited (1) Smith, Brown, and Ross, IND. ENG.CHEM.,16, 20 (1924). (2) Willard and Smith, J . Am. Chem. SOC.,44, 2255 (1922).
