April 1955
INDUSTRIAL AND ENGINEERING CHEMISTRY
space velocity is thus an approximation of the actual situation. At the end of run the reactor was purged with nitrogen a t the temperature of the run until no more liquid product condensed. The time of the purge thus varied from run to run, The variable flow rates together with the variation of time and temperature of the nitrogen purge probably account for the anomalous coke yields obtained in a few of the runs. After all the hydrocarbon had been removed, the coke was burned off in 2% oxygen a t 500" C. The combustion gases were passed over cupric oxide a t 750" C. t o ensure complete conversion to carbon dioxide. The carbon dioxide was converted to barium carbonate for determination of carbon yield and for radioactivity measurements ( 4 ) . An end-window Geiger tube having a window thickness of 1.8 mg. per square cm. was used. T o determine the radioactivity of the feed, samples were converted t o carbon dioxide by combustion in oxygen over cupric oxide a t 750' C. Barium carbonate mounts prepared from samples of the same radiocarbon dioxide showed a =t2% variation due t o statistical errors in counting and to variations in the character of the surface of the mount. RESULTS AND DISCUSSION
Table I1 summarizes the results. Within experimental error, the radioactivity of the coke is the same as that of the labeled hydrocarbon from which i t was formed. The fact that the average value of activity of coke/activity of feed is 0.98 and not 1.00 may be significant. If so, it probably reflects changes occurring during the nitrogen purge. I n any case the valid conclusion can be drawn that, under the conditions of the experiments, all the carbon atoms of the n-heptane, n-octane, or 1-octene molecule appear to be equally involved in coke formation. These results suggest the following picture for coke formation in catalytic cracking. The first step is adsorption of reactant molecules on the surface of the catalyst. A few remain on the catalyst surface and, through a series of chemical changes, become coke. Most of the molecules either desorb unchanged or undergo cracking followed by .desorption of all fragments as product. A process in which some fragments desorb while others remain as coke seems most unlikely. The proposal of Thomas
Table 11.
845
Catalytic Cracking on Labeled Hydrocarbons
Tpp., C.
Space Velocity0
Feed/ Catalyst, G. n-Heptane-4C14
,550 575
0.5
0.7
0.88 0.96
510
510
520 530 545 545 545 570 570
0
Carbon on Catalyst,
%
Activity Coke/ Activity Feed
0.26 0.31
0.97 0.96
n-Octane-1 C 1 4 1 .08 0.72 0.76 1.38 0.53 ' 0.77 0.66 0.73 2.28
2.0 1.3 1.2 1.0 1.6
1.4 1.2 1.2 1.3
1-Octene-1C" 335 2.3 0.65 1.2 335 3.0 1.43 1.2 350 1.7 0.66 1.6 Volumes of feed per volume of catalyst per hour.
1.00
0.97 0.99
that coke forms through dehydrogenation and polymerization appears reasonable. ACKNOWLEDGMENT
Thanks are due to A. A. Hruby and G. Kandalic for assistance with the experimental work, LITERATURE CITED
(1) Blue, R. W., and Engle, C. J., IND.ENG.CHEM.,49, 494 (1951). (2) Greensfelder, B. S., Voge, H. H., and Good, G. M., Ibid., 41,2573 (1949). (3) Hansford, R. C . , Ibid., 39, 849 (1947). (4) Roberts, J. D., Bennett, W., Holroyd, E. W., and Fugitt, C. H., Anal. Chem.. 20. 904 (1948). ( 5 ) Roberts, J. D.; A/lhAbhon, R. E., and Hine, J. S., J . Am. Chem. Soc., 72, 4237 (1950). (6) T h o m a s , C . L., IND. ENC.CHEM.,41, 2564 (1949). (7) T h o m a s , C . L., J . Am. Chem. Soc.. 66. 1586 (1944). (8) Van Pelt, A. J., and Wibaut, J. P..'Rev. trav. chim., 57, 1055 (1938); 60, 55 (1941). (9) Whitmore, F. C., and Rothrock, H. S., J . Am. Chem. Soc., 55, 1106 (1933). ACCEPTED December 9, 1954. RECEIVED for review June 30, 1954.
Comparative Cleaning by Diphase Cleaners and Alkaline Salts LLOYD OSIPOW, HERBERT PINE, CORNELIA T. SNELL, AND FOSTER DEE SNELL Foster D . Snell, Inc., 29 West 15th S t . , New York 11, N. Y .
A
PREVIOUS report compared a diphase cleaner ( 1 ) with emulsion cleaners, using radioactive contaminants ( 2 ) . Earlier work showed many of the factors involved in metal cleaning ( 3 ) . I n the current work, the detergent efficiency of alkaline salts was compared with that of a diphase cleaner for removing greasy soil of known composition from steel. EXPERIMENTAL METHOD
The experimental soils were baRed on a mixture of mineral oil and petrolatum, with a small proportion of carbon black present as solid soil. Variations were made by adding different amounts of a fatty acid to the soil base. The composition of the seven soils used is given in Table I. The letters at the tops of the columns indicate specific soils.
Table I. Petrolatum Kaydol mineral oil Excelsior black Stearic acid XXX Oleic acid Lauric acid
Soil Compositions A 45 50 5
.. .. ..
B 40 50 5 5
.. ..
Parts C 35 50 5 10
.. ..
by Weight D E 40 35 50 50 5 5
.. 5 ..
i6 ..
F 40 50 5
1:
5
G 35 50 5
::
10
T h e alkaline salts were all sodium salts, used alone and in mixtures as follows : sodium metasilicate pentahydrate, trisodium phosphate dodecahydrate, anhydrous sodium carbonate, sodium sesquicarbonate dihydrate, equal parts by weight of the
INDUSTRIAL AND ENGINEERING CHEMISTRY
846
3
I
ot
I
I
I
I
I
I
I
I
4
5
6
7
8
9
IO
II
SOllS
'
3
I
of 75°C.
I
I
I
4
5
6
NUMBER
of
- I 7
1
I
I
I
8
9
IO
II
REVOLUTIONS per
SECOND
Figure 1. Viscosity curves for six soils a t 50" and 75' C.
metasilicate with anhydrous sodium tripolyphosphate, and equal parts of sodium carbonate with anhydrous sodium tripolyphosphate. These salts are all commonly used in cleaning operations. T o minimize the variables, no surfactant was added to the alkaline salts, but as soon as any reaction occurred with the fatty acid of the soil soap was present. To permit this to have its maximum effect, all runs were made with distilled water. The solvent part of the diphase cleaner had the following composition : Parts by Weight 67.0 22.5 5.4 3.6 1.5
Mineral spirits Pine oil Oleic acid Triethanolamine Butyl Cellosolve
Addition of water t o t h e nonaqueous solution produced the diphase cleaner. However, in the discussion and tables, statements concerning the percentage of detergent refer to the amount of nonaqueous solution or alkaline salt added to the water. Steel panels, SAE 1010, 1 X 2 inches, were precleaned by scrubbing with steel wool and perchloroethylene, followed by rinsing in perchloroethylene. The panels were then coated on one side with the appropriate soil by brushing, using 150 mg. of soil applied to 1 x 1.5 inches of panel surface. The panels were cleaned by mechanical dipping at the rate of 36 cycles per minute. Weights of the panels before and after washing gave the amount of soil removed. The concentrations selected for study were somewhat lower than those initially present in commercial operation. I n use such a cleaning bath is applied until exhaustion is reached. The concentrations, therefore, represent partial exhaustion but without the contaminants present a t that stage. Times were so selected that cleaning would not ordinarily be complete. Therefore, the comparison is of rate of cleaning, for all the compositions can remove the soil to practically 100% under some conditions of time, temperature, and concentration. RESULTS
Results presented in Table I1 show that a t 25" C . the alkaline cleaners are ineffective in the removal of any of the soils in 3
Vol. 47,No. 4
minutes. All of the soils are removed to a substantial extent by the diphase cleaner. Thus Table I1 demonstrates that for cold cleaning, a popular concept in some areas, the presence of solvent is an essential. Data for detergency a t 50" C. in 1 minute are shown in Table 111. There was no significant difference in cleaning effectiveness for the different alkaline cleaners, but the soils differed substantially in ease of removal. Soil without fatty acids was the most difficult to remove, by both the diphase cleaner and the alkaline salts. Soils containing oleic acid were more readily removed by the alkaline salts than those containing stearic acid. The diphase cleaner appeared to remove with equal ease soils containing either fatty acid. With all soil combinations, the diphase cleaner was far more effective than any of the alkaline salts used a t this temperature and time. Detergency test data a t 75" C. and 0.5 minute are presented in Table IV. Results again showed notably greater detergency by the diphase cleaner than by any of the alkaline salts or combinations used. Soils containing oleic acid were most readily removed, the soil without free fatty acids was most difficult to remove, and soils containing lauric and stearic acids were intermediate in ease of removal. The temperature in this case is not unlike many cleaning operations, and comparison of Tables 111 and IV stresses the significance of temperature, particularly when time is taken into account. Cleaning baths are commonly used until clean work can no longer be obtained. Therefore, cleaning tests were conducted a t 75" C. for 0.5 minute with detergent concentrations reduced to 0.5%, with results as shown in Table V. The reduction in concentration resulted in a very thin nonaqueous layer for the diphase cleaner and reduced its effectiveness to a greater extent than that of the alkaline salts. However, the diphase cleaner
Table 11.
Soil Removal a t 25" C., 3-Minute Cleaning Time, 2.0% Detergent Concentration (Triplicate runs) Soil Removal, % A B C D 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 73.7 81.3 74.9 82.7
Detergent Sodium metasilicate Trisodium phosphate Sodium carbonate Sodium sesquicarbonate Diphase cleaner
E 0 0 0 0 87.5
Table 111. Soil Removal a t 5OoC., 1-Minute Cleaning Time, 2.0% Detergent Concentration (Triplicate runs) Soil Removal, A B C 22.8 21.5 36.1 43.9 51.6 2.5 44.3 28.3 22.5 37.8 52.4 15.6 95.4 100.0 78.4
Detergent Sodium metasilicate Trisodium phosphate Sodium carbonate Sodium sesquicarbonate Diphase cleaner
% E
D 61.9 63.0 61.8 57.6 100.0
74.2 75.5 68.1 69.1 100.0 x
Table IV.
Soil Removal a t 75" C., 0.5-Minute Cleaning Time, 2.0y0Detergent Concentration A
Detergent Sodium metasilicate Trisodium phosphate Sodium carbonate Sodium sesquicarbonate Diphase cleaner 1 : 1 Sodium metasiljcate and sodium tripolyphosphate 1 : 1 Sodium carbonate and sodium tripolyphosphate
(Single run) B Soil C Removal, D 3'% E
F
G
72.0 67.8 53.6 67.8 5 6 . 7 68.8
63.0 74.3 72.4
76.8 88.8 70.0
82.2 80.0 72.5
64.6 70.7 89.3 97.2
75 0 100.0
100.0
80.0
76.0 100.0
62.5 64.5
62.0
81.3
76.7
80.0 62.0
60.7
62.0
89.6
72.5
70.0
68.8
67.8 64.3 58.7 79.3 93.2 60.8 64.3 100.0
58.7 89.3
76.8
April 1955 Table V.
INDUSTRIAL AND ENGINEERING CHEMISTRY Soil Removal at 75’ C., 0.5-AVinute Cleaning Time, 0.5% Detergent Concentration
Detergent Sodium metasilicate Trisodium phosphate Sodium carbonate Sodium sesquicarbonate Diphase cleaner 1 : 1 Sodium metasilicate and sodium tripolyphosphate 1 : 1 Sodium carbonate and sodium tripolyphosphate
(Duplicate runs) Soil Removal. % A B C D E F 45.8 5 5 . 0 7 1 . 3 6 6 . 3 7 9 . 0 6 6 . 4 56.6 7 7 . 8 6 4 . 6 8 2 . 3 7 3 . 1 7 3 . 0 4 4 . 4 6 6 . 5 69.8 6 8 . 3 7 9 . 7 5 6 . 5 52.5 68.5 8 0 . 4 7 5 . 2 8 2 . 0 66.4 77.5 80.1 86.0 86.6 77.3 87.9
G 75.8 72.2 74.2 77.2 82.9
55.4
60.1
71.4
68.3
81.4
70.9
71.1
56.6
550
73.3
72.0
81.0
72.8
77.3
841
the alkaline cleaners rose rapidly with an increase in temperature, while the diphase cleaner maintained a high level of cleaning efficiency regardless of temperature. The p H values for the alkaline cleaners a t 2% concentration ranged from 9.1 for sodium sesquicarbonate to 11.7 for sodium metasilicate pentahydrate. This difference in p H had no effect on cleaning effectiveness. Tor alkaline salts soils containing oleic acid were more readily removed than those containing saturated fatty acids. The latter soils were more readily removed than those that did not contain fatty acids. The viscosity of the soil was not a factor, for a t a given temperature all soils had the same viscosity. Results using the Stormer viscometer are plotted in Figure 1. Undoubtedly the polarity of the double bond in oleic acid is a factor promoting the ease of removal of soils containing it. ACKKOWLEDGMENT
still appeared substantially more effective than the alkaline salts, which did not differ greatly from each other in performance. The soil without free fatty acids continued to be most difficult to remove, while the two containing oleic acid were removed most readily. DISCUSSION
Soils containing high levels of fatty acids would be expected to be most readily removed by alkaline salts because of soap formation. Nonetheless, the diphase cleaner was most effective in the removal of soil under all test conditions. The effectiveness of
The investigation described herein was supported by Solventol Chemical Products, Inc., Detroit, Mich. LITERATURE CITED
(1) Campbell, C. A , , U. S. Patent 2,399,205 (1946); 2,583,165 (1952). (2) Osipow, Lloyd, Begura, Gonaalo, Jr., Snell, C. T., and Snell, F. D., IND. ESG.CHEM.,45, 2779-82 (1953). (3) Reich, Irving, a n d Snell, F. D., Ibid., 40, 1233-7, 2233-7 (1948).
ACCEPTEDOctober 30, 1954. Presented before the Divlaion of Colloid Chemistry a t the 126th Meeting of the A a f E R I C A N C H E Y I C d L S O C I E T Y , x e w York, 9.Y . , 1954. RECEIVED for review August 24, 1954.
Process Development Data
Heat of Combustion of Some
Organosilicon Compounds K. B. GOLDBLUM AND L. S. MOODY Chemical Development Department, Chemical and Metallurgical Division, General Electric Co., Pittsjield, MQSS.
T
HE paucity of data on the heat of combustion of organosilicon compounds has proved frustrating to workers in need of these data for thermodynamic calculations. This work was undertaken principally to determine the heat of combustion of octamethylcyclotetrasiloxane, as part of the evaluation of a proposed industrial method for the preparation of this valuable silicone intermediate. A search of the literature failed to reveal any information on the heat of formation or combustion of this compound or of analogous compounds from which these values might have been calculated. The thermal stability and oxidation resistance of the silicones, in general, are well established. I n initial experiments, it was found exceedingly difficult to oxidize the selected compounds completely in an oxygen bomb calorimeter. The error arising from incomplete combustion in this equipment has been emphasized ( l a , IS). Special precautions and techniques had to be used by these workers to give reliable results. Because of the necessity for special precautions and techniques, i t was decided to investigate sodium peroxide fusion as a means of obtaining complete oxidation of the selected organosilicon compounds. The use of the Parr sodium peroxide bomb calorimeter (manufactured by The Parr Instrument Co., Moline, Ill., hereafter called the calorimeter), was suggested by the successful use of sodium compounds t o determine silicon quantitatively in the
General Electric Research Laboratory, in this laboratory, and in other laboratories (1, 2, 4, 5, 10, 14, 16). The use of the calorimeter was complicated by the fact that this instrument is semiempiric?l and has a narrow range of accuracy for certain types of carbon- and hydrogen-containing compounds, mainly coal samples (6, 8, 9 ) . It is assumed in the instructions for the use of this instrument (6) that 73% of the heat liberated is due to heat of combustion and the remaining 27% is due to the reaction of the oxidation products, carbon dioxide and water, with the sodium peroxide melt. Further, the manufacturers state ( 7 ) that there are “difficulties involved in attempting precise calorimetric tests in a peroxide bomb calorimeter because of the numerous side reactions involved, some of which may not go to completion and for which heats of reaction may not be well established.” Despite these limitations and complications, it was decided t o use this equipment in view of the excellent record of the sodium peroxide fusion method for the quantitative estimation of silica in organosilicon compounds. Nine pure compounds containing only carbon, hydrogen, and oxygen, whose heats of conibustion are given in the literature, were oxidized. From a statistical analysis method of least squares, values attributable to the heats of reaction of carbon dioxide and of water with the sodium peroxide melt and the energy equivalent of the calorimeter system were determined for
