INDUSTRIAL AND ENGINEERING CHEMISTRY
696
chemical plasticizers. A coating of the following formula, applied to a canvas or broadcloth surface, can be used either as a washable stiffening size of improved oil and flame resistance, or in heavier coatings to bring up gloss: High-viscosity highpropionate ester Alkyd balsam resin Tributyl phosphate
12 6 0
Ethyl acetate Butyl acetate Denatured alcohol Toluene
25
10 10 31
A great many variations of this formula, within the limitations of the compatibility and solubility characteristics of the mixed esters, will suggest themselves to those interested in special textile coatings.
Discussion Perhaps the outstanding point about the results described here is the superior resistance of the clear formulas to weathering. The reason for this is obviously the superior light resistance of these materials as compared with nitrocellulose, and their superior water resistance as compared with cellulose acetate. This water resistance is reflected in both permeability and absorption values in Table 11; as a matter of interest, the permeability values given there are set down against the dielectric constants of the various materials used : Material Cellulose nitrate (12% Na) Cellulose acetate-propionate or -butyrate Cellulose acetate (54-56% acetic acid)
C. (8)
5.0 3.0-3.1 4.1-4.3
from normal behavior on the part of the nitrocellulose which is responsible for the uncommonly good permeability shown by this material. One possible explanation is that the nitrate groups are present in the nitrocellulose in the ester form or “pseudo nitric” acid of Hantsch (1,4) which, being much less polar than the ionized or normal form, would give the low dielectric constant shown, and might account for the very low permeability because of environmental factors. The mixed esters bear a normal relation to cellulose acetate in this respect. As has been pointed out by Fordyce et al. @),it is not practical to go above cellulose butyrate in search of moisture resistance because of softness of the resulting esters; also since cellulose in itself has a rather polar unit cell, reasoring by Hildebrand’s rule leads to the conclusion that any cellulose ester must have a definitely greater permeability for moisture than a hydrocarbon such as paraffin.
Acknowledgment Samples of the acetate-propionate and higher butyryl acetate-butyrate esters tested in this program were kindly furnished by Malm and Farrow of the Eastman Kodak Company, as well as a description of the properties as they found them.
Literature Cited
Dielectric Constant a t 20’
VOL. 29, KO. 6
Kperm.
2.0 x 10-0 3.3-4.1 X 10-8 6 . 6 X 10-6
It would seem that the permeabilities shown here do not follow the suggestion of Hildebrand (6) who states that the dielectric constant of a solid is a rough measure of its permeability by polar gases. Although there are several fine examples of the truth of this rule (i. e., the moisture-proofing of Cellophane), it seems that there must be a certain deviation
(1) Farmer, J. SOC.Chem. I d . ,50, 75-9T (1931). (2) Fordyce, Salo, and Clarke, IND.ENG.CHEM.,28, 1310 (1936). (3) Hagedorn and Moeller, Cellulosechem., 12,29 (1931). (4) Hantsoh, Be?., 58,612,941 (1925); 60,1933 (1927). 28, 157 (1936). (5) Hercules Powder Co., IND.ENG.CHEM., (6) Hildebrand, “Solubility,” 1st ed., pp. 138-9,New York, Chemical
Catalog Co., 1922. (7) Kline, IND.ENG.CHEM.,27, 556 (1935). (8) Nowak, P.,A ~ Q ~Chem., w . 37, 584-7 (1933).
R E C E W ~April D 17, 1937. Presented before the Division of Paint and Varnish Chemistry at the 93rd Meeting of the American Chemical Society, Chapel Hill, N. C., April 12 to 16, 1937.
COKE-CARBON DIOXIDE RELATIONS KENNETH 0. SKINNER Northwest Experiment Station, U. S. Bureau of Mines, University Campus, Seattle, Wash.
EVERAL manufacturers prepare precipitated calcium
S
carbonate by passing carbon dioxide, produced by burning coke under a boiler, through a suspension of milk of lime. The solids contained in the gases are removed by some type of scrubber, and steam from the boiler is used for general heating purposes. I n this process, important factors are as follows: 1. What weight of coke must be burned with varying amounts of excess air (weight basis) t o produce V cubic feet of gas, and what weight of carbon dioxide is contained in the gases? 2. What is the total volume of gases, containing M per cent carbon dioxide by weight, required t o supply X pounds of carbon dioxide? 3. How many pounds of coke are required t o supply V cubic feet of gas containing N per cent carbon dioxide by volume?
Equations were derived to show the relations between the weights of coke and carbon dioxide and the total volume of gases produced. Complete combustion was assumed; that is, all the carbon was burned to carbon dioxide. Therefore, corrections would have to be made for coke lost in the ash or for other losses. The final equations were simplified by assuming the absence of sulfur. Coke used in the manufacture of precipitated calcium carbonate should contain less
than 1 per cent sulfur, unless the sulfur dioxide in the gas is removed. Figure 1 is drawn from the equation:
+ +
2350 (14.7 G)V (100 - A ) (100 Y ) (460 where W = coke required] Ib. V = gas, cu. f t . G = gage pressure, lb./sq. in. Y = excess air, yo A = ash in coke, weight ter cent t = temperature of gas, F. E
+ 6)
Equation 1 shows the pounds of coke required to deliver V cubic feet of gas a t t O F., G pounds gage pressure, using Y per cent excess air. The vertical line between the third and fo6rth quadrants indicates the weight of carbon dioxide contained in the gases. The weight of carbon dioxide was calculated from the expression, 0.0367 W (100 - A ) . The following equation,
where M
= carbon dioxide, per cent by weight X = carbon dioxide required, lb.
JUNE, 1937
INDUSTRIAL AND ENGINEERING CHEMISTRY
FIGURE 1. QUADRANTCHART SHOWING COKE-CARBON DIOXIDE RELATIONS BASEDUPON
shows the volume of gases at t O F., G pounds gage pressure, and containing M per cent carbon dioxide by weight required to deliver X pounds of carbon dioxide (item 2). The following equation, 1.125 (14.7 G ) N V W = (3) (460 1) (100 - A ) where N = carbon dioxide, per cent by volume
+
+
shows the pounds of coke required to deliver V cubic feet of gas containing N per cent carbon dioxide by volume (item 3). The pounds of carbon dioxide contained in the gases may be found from Figure 1. The dashed line in Figure 1 shows the method of using the chart and represents the graphical solution of Equation 1, from the following data: 500 cubic feet of flue gas were delivered at 200" E'. and a pressure of 25 pounds per square
697
THE
PERCENTEXCESS AIR
inch (gage). Sixty per cent excess air was used for combustion, and the coke was assumed to have 15 per cent ash. Under these conditions 5.2 pounds of coke would be required and there would be 16.2 pounds of carbon dioxide in the flue gases. The total volume of gases or the weight of carbon dioxide produced from burning the coke may be obtained by using the chart in the reverse order. If the weight of carbon dioxide is used as a starting point, the volume of gases and the weight of coke required may be determined. Grateful acknowledgment is made to B. W. Sidwell of the Universal Gypsum &. Lime Company for suggesting the calculations. RECEIVED January 22, 1937. Publislied by permission of the Director, U. S. Bureau of Mines. (Not subject t o copyright.) This report gives the results of work done under a cooperative agreement between the Northwest Experiment Station, U. S. Bureau of Mines. and the College of Mines, University of Washington, Seattle.
