INDUSTRIAL AND ENGINEERING CHEMISTRY
1152
TABLE11. VAPOR PRESSURE, SATURATED LIQUID, AND VAPORDENSITIESOF ISO-OCTANE Density, G./CC. Temp.,
c.
50 60 70 80 990 9.239 120 140 160 180 190 200 205 210 215 220 225 230 235 250 245 250 255 260 263 266 2269 70.676
Pressurea. Atm.
. . .. . .. . .. .. .. ..
0 1.736 2.783 4.253 67 .. 2 4 74 95 8,867 9.635 10.452 11 12 .. 32 23 08 13.214 14.249 15.342 16.500 17.724 19.022 20.406 21.873 22.793 23.746 2245..733058
Liquid Found
Vapor Lit.
0.6673 0 . 6 6 7 6 (6) 0.6586 0.6496 0.6498'(6) 0.6408 0 0.6303'(6) 0 .. 6 63 21 26 8 ..... 0.6027 ..,.. 0.5821 ..... 0.5602 ..... 0 . 5 3 6 0 0.5229 .. .. .. .. .. 0,5088 0 . 5 0 7 (8) 0,5011 ..... 0.4929 00 .. 44 87 46 70 ..... 0.4667 0.466'(8) 0.4570 0.4462 0.4350 ..... 0.4222 ,.... 0.4084 0 . 4 0 7 (8) 0.3920 ..... 0.3720 ..... 0.3575 ..... 0.3400 ..... 0 . 3 1 3 00 . 2 4 3
Found ..
Lit.
.. .. .. .. ..
..... ..... .....
....
.. .. .. ,. .. .....
.... ....
.....
.
I
.
.
0.0380 0.0418 0 .. 0 05 40 55 8 0 0.0555 0.0611 0.0676 0 0 .. 00 78 4278 0.0929 0.1049 0.1200 0.1321 0.1484 0.1749
..... 0.0479'(2)
.....
Vol. 43, No. 5
are in excellent agreement, while those of Beattie and Edwards are in good agreement only a t the higher temperatures. Using the equation and deviation curve, values of the vapor pressure in atmospheres a t even temperature intervals in degrees centigrade have been calculated and are given in Table 11. The saturated liquid and vapor densities are shown graphically in Figure 2 and listed in Table 11. The values reported in the table are smoothed values read from a large scale plot. Literature values are given for comparison. Smyth and Stoops (6) reported the density of liquid iso-octane up to 100" C. Their data agree well up to and including 80" C., but values a t 90" and 100" C. are at variance with those reported here. Beattie and Edwards ( 2 ) measured liquid densities, but estimated the vapor densities using the theorem of corresponding states and the density of n-heptane as a reference liquid. Their values for the liquid are in fair agreement, but the vapor densities a t the two comparable temperatures, 225" and 250" C., are approximately 14% smaller than those reported here.
0.0793'(0)
.....
..... .....
0 Calculated b means of equation log p &tm.) = 4.45144 - 1657.71/(t0 C . -t 273.160) and deviation ourve, Figure 1.
ACKNOWLEDGMENT
Grateful acknowledgment is made to the General Electric Co. for &anoia1 aid in the form of the Swope Fellowship to one of the authors (F.M.W.) and to t,he Phillips Petroleum Co. for furnishing the sample of iso-octane. LITERATURE CITED
point and dew point data were plotted and the curve was drawn midway between the two points. At the lower temperatures where the dew Doints were not obtained, the curve was located by assuming that the difference between the bubble and dew points was the same as a t higher temperatures. Because the difference was approximately constant and amounted to only 0.017 atmosphere, the error that might be introduced by such an assumption is relatively small. For the sake of comparison, the vapor pressure data reported by Smith ( 5 ) and by Beattie and Edwards ( d ) , expressed as a deviation from the smoothed values resulting from this investigation, are shown in Figure 1. As will be noted, the data of Smith
(1) Am. Petroleum Inst., "Selected Values of Properties of Hydrocarbons," API Research Project 44, National Bureau of Standards, Washington, D. C., Table 3a, June 30, 1945. ( 2 ) Beattie, J. A., and Edwards, D. G., J . Am. Chem. SOC.,70, 3382 (1948). (3) Kay, W. B.,
1x0. ENG.CHEM.,28, 1014 (1936). ~w.~B., ,J , Am. Chem. sot., 68, 1336 (1946). (5) Smith, E. R.. J. Research Natl. Bur. Standards. 24. 229 (1940). (6) Smyth, c. p., and Stoops, IV. N., J. Am. Chem.' S O C . , ' 1883 ~~, (4) K
(1928).
Swietoslawski, W'., "Ebulliometric Measurements," p. 57, New York, Reinhold Publishing Corp., 1945. (8) WilIingham, C. B., Taylor, W. J., Pignooco, J. M., and Rossini, F. D., J. Research N a t l . Bur. Standards, 35, 219 (1945). (7)
RECEIVED December 4, 1950.
artial Pressure of Acrylonitrile over Water J
C. E. FUNK, JR. Stamford Research Laboratories, American Cyanamid Co., Stamford, Conn. I n purifying acrylonitrile by distillation, losses are incurred through condenser vents, etc. Data on the partial pressure of acrylonitrileover water were required to permit the design of scrubbers to minimize these losses. Determinations were made at concentrations in which acrylonitrile is completely soluble in water, at both 25" and 40" C. Assuming Raoult's law to hold for the water, the acrylonitrile follows Henry's law over the range 0 to 3% acrylonitrile. The expressions: at 25' C., p = 14 c and at 40" C., p = 27 c , may be used for design purposes within this range. (p = partial pressure of acrylonitrile, millimeters of mercury; c = concentration, weight per cent.) The data presented should be of importance, not only to those interested in reducing distillation losses, but also to any large scale user of acrylonitrile in an aqueous sys-
tem. The latter will be able to predict to what extent losses may occur from his solutions, and to take steps to conserve this valuable reagent when necessary.
T
HE currently preferred methods of manufacturing acrylonitrile ( 6 ) ,an important chemical in the synthetic elastomers industry, require that it be separated from a mixture of by-products before being suitable for use or for sale. Separation is normally by distillation. Sound engineering practice dictates that the concomitant losses through condenser vents, etc., be held to a minimum. The solubility of acrylonitrile in water, although low, is still sufficient to make the use of water scrubbers attractive for this purpose. The determination of the partial pressure of acrylonitrile over water was undertaken specifically to permit the design of such
May 1951
INDUSTRIAL AND ENGINEERING CHEMISTRY
absorber units. The transpiration, or gas-saturation, procedure was employed, using two saturators in series. Determinations were made a t 25 and 40' C. O
EXPERIMENTAL
Commercial, amine-stabilized acrylonitrile (American Cyanamid Co.) was purified by agitation with 30% phosphoric acid and 30% sodium hydroxide, successively, then by steam distillation. It was not dried, as it was to be employed in an aqueous system. The purity of the acrylonitrile obtained in this manner is believed to be in the order of 99.9%on the moisture-free basis.
EO-
cubic foot per hour, and the total volume of air introduced between 0.05 and 0.1 cubic foot. The presaturator was a 1-liter Erlenmeyer flask containing about 800 ml. of solution. The h a 1 saturator was a 250-ml. gas-washin4 bottle with sealed-in disk, and contained about 200 ml. of solution. The large volume employed in the presaturator is further insurance that concentration changes in the final saturator will be negligible. The sulfuric acid absorbers, of which there were two in seriFs, were fabricated from Liebig condensers and were acked wlth perforated glass beads. The absorbent was heatef by passing steam through the jackets. On completing a run, the absorbent was drained and the column rinsed with fresh 90%acid, then with water. Frequent separate analyses of the two absorbent solutions indicated that substantially all the acrylonitrile was being removed in the f i s t absorber. The estimated accuracy of the several observations is: PESsure, *1 mm. of mercury; temperature, *0.1" C.; volume, *0.001 cubic foot. The calculations of partial pressure were made according t o the equation;
140-
5 1300
:z:120g 110-
P'
w-1100-
=
90-
32 80-
where p = partial pressure of acrylonitrile, mm. of mercury P'= absolute pressure over final saturator, mm. of mercury P = barometric ressure, mm. of mercury, corrected to 0" C. a n 8 also corrected for difference between vapor pressure of water at test temperature and its partial pressure over solution as determined by applying Raoult's law M = molecular weight of acrylonitrile = 53.06 a' = volume of air passed into system, corrected to test temperature, cubic feet g = weight of acrylonitrile evaporated, grams R = gas constant = 2.202 (cubic feet)(mm. mercury) (" K.) -1 (gram ; mole) T = test temperature, K.
U
o 70-
W
a
2 60W v)
50-I
2 40a
2 30-
The data obtained are presented in Table I and shown graphically in Figure 1. It will be seen that Henry's law is followed closely over the range 0 t o 3% acrylonitrile. Within this range the expressions:
ACRYLONITRILE CONCENTRATION, PER CENT BY WEIGHT
Figure 1. Partial Vapor Pressure of Acrylo; nitrile over Its Aqueous Solutions at 25 and 40' C.
At 25" C., p = 14c At 40" C., p = 27c
The principle of the transpiration methpd is adequate1 discussed in the standard textbooks on physlcal chemistry In the present determination, air saturated with water was passed into the system, and fritted-glass diffusion disks were employed in the saturators. A vacuum pump was used t o draw the air through the system, and both the barometric pressure and the differential pressure over the second saturator were observed. The acrylonitrile vapors were absorbed in a packed column containin hot 90% sulfuric acid, and the weight evaporated was determine! by Kjeldahl distillation of the absorbent. This procedure is a modification of a method developed by P. R. Averell and M. V. Norris based on the initial work of A. A. Lynch, all of these laboratories, for the determination of residual acrylonitrile in fumigated foodstuffs (7). A great advantage of the method is that the nitrile is sufficiently hydrolyzed in the absorber and subsequent Kjeldahl digestion is not required.
5, c).
*
*
Mv'P -
gRT -4-l
a c f
1153
The success of the transpiration method for determining vapor pressure depends largely on the use of a gas-flow rate sufficiently slow to ensure saturation and t o avoid the carry-over of mist. When working with a single substance, the apparatus may be tested in this respect by varying the gas rate while keeping other conditions constant. Saturation is then indicated by the obtaining of essentially identical results. In this case, where the test solution was divariant in composition, it was considered satisfactory that a variation of the gas rate in successive experiments did not interrupt the smoothness of the curve. The actual gas rate varied between 0.1 and 0.2
are valid for design purposes, where p is the partial pressure of acrylonitrile in millimeters of mercury and c is its concentration in per cent by weight. ANALYSIS
The concentration of acrylonitrile was found by analysis of a sample from the final saturator. To avoib loss of acrylonitrile
PRESSURE OF ACRYLONITRILE TABLEI. PARTIAL Detn.
Acrylonitrile ConcentraPartial tion, pressure, wt. % mm. Hg
Detn.
Acryioni trile ConcentraPartial tion, pressure, wt. % mm. Hg
Temperature = 2 j 0 C.
8 0
0.37 0.75 1.02 1.49 1.85 2.56 3.12 3.78 4.39
19 20 21 22 23
0.38 0.73 1.43 3.25 4.91
1
2 3 4 5 6
7
5.9 10.6 15.8 20.9 24.6 31.8 44.0 50.9 58.0
lo 11 12 13 14 15
17 18
4.89 5.60 5.70 5.85 6.05 6.55 6.85 7.05 7.25
63.3 71.0 74.4 73.7 83.7 80.4 80.6 84.8 86.3
6.33 6.77 7.24 7.63
132.3 140.2 146.0 138.1
Temperature = 40" C. 11.8 22 0 40.2 79.2 117.1
24 25 26 27
INDUSTRIAL AND ENGINEERING CHEMISTRY
1154
from the sample prior t o analysis, the following method was devised.
REAGENT.To 100 grams of dodecyl mercaptan (dodecanethiol) dissolved in 100 grams dioxane were added 100 ml. of 1 N alcoholic potassium hydroxide. PROCEDURE. Sufficient reagent (3.5 ml.) for 0.15 gram of acrylonitrile is pipetted into a Kjeldahl flask. A suitably sized sample is then pipetted into the reagent, inserting the pipet well into the flask. The mixture is swirled briefly, after which i t can be let stand until a convenient time to complete the determination. This is done by the usual Kjeldahl digestion and distillation. The quantity of organic material present makes the use of 50 ml. of concentrated sulfuric acid advisable. A blank must be run on the reagent. The results were calculated in terms of grams of acrylonitrile per milliliter of sample. T o convert t o per cent acrylonitrile by weight, the density of a saturated solution of acrylonitrile in water was determined at 25” and 40” C. These values were found to be 0.9890 gram per ml. a t 25” and 0.9817 gram per ml. a t 40”. Using the values of 7.4 and 7.9% acrylonitrile in the saturated solution at these temperatures ( 2 ) , intermediate values were obtained by linear interpolation. Handbook figures for the density of water at these temperatures were used-O.9971 a t 25 O and 0.9922 a t 40 (6). This analytical scheme is based on the use of alkaline mercaptan solutions as reagents in the analysis of acrylonitrile and other unsaturated compounds as reported by Beesing et nl. ( 1 ) . It offers some advantages over Beesing’s procedure, in that the effect, O
Vol. 43, No. 5
of side reactions, etc., affecting the mercaptan only, is minimized if not eliminated. The method as described here, however, is specific for compounds subject to Kjeldahl analysis, and thus is more limited in its scope than that of Beesing et al. ACKNOWLEDGMENT
The author is indebted to members of the Stamford Research Laboratories for helpful suggestions regarding the experimental and analytical procedures and in checking the calculations. LITERATURE CITED
(1) Beesing, D. W., Tyler, W. P., Kurtz, D. M., and Harrison, S.ti., Anal. Chem., 21, 1073 (1949). (2) Davis, H. S.,and Wiedeman, 0. F., IND. E m . CHEx., 37, 482-5
(1945).
(3) Getman, F. H., and Daniels, F., “Outlines of Physical Chemistry,” 7th ed., p. 153, New York, John Wiley & Sons, 1943. (4) Glasstone, S., “Textbook of Physical Chemistry,” 2nd ed., pp.
448, 630, New York, D. Van Nostrand Co., 1946. (5) Hodgman, C. D., ed., “Handbookof Chemistry and Physics,” 30th ed., p. 1695, Cleveland, Ohio, Chemical Rubber Publishing Co., 1946.
(6) Kirk, R. E., and Othmer, D. E., ed., “Encyclopedia of Chemical Technology,” Vol. 1, p. 184, New York, Interscience Pub-
lishers, 1947.
(7) Lynch, -4. A., Averell, P. R., and Norris, M. V., unpublished work. RECEIVED July 29, 1950
a NEWTON W. MCCREADY Philadelphia Quartz Co., Philadelphia, Pa. T h i s research was undertaken to obtain specific heal data on sodium silicate solutions over a wide range of composition and temperature. A stainless steel calorimeter was designed and used to measure the specific heats of sodium silicate solutions for mole ratios of silica to sodium oxide between 0.5 and 4.6 at various concentrations between about 15’ and 85” C. For most solutions the specific heat was a linear function of the temperature. The data were corrected for impurities and smoothed, using apparent molal heat capacities. The specific heat was found to decrease with increasing concentration and increasing silica-sodium oxide ratio. A few measurements were made on potassium silicate, whose specific heat is lower than that of sodium silicate at equivalent concentrations. These data are intended primarily to be of industrial importance, as in calculating heat requirements.
ESPITE the industrial importance of sodium silicate solutions, there are no published data on their specific heats. I n order to provide such data the following research was undertaken. The results are intended for practical use and no attempt wm made to obtain extreme precision or to derive conclusions of theoretical interest. Sodium silicate solutions may be considered to contain sodium oxide, slica, and water, and their composition is generally expressed in terms of these. This being a two-component system, the inclusion of temperature as a third variable requires that
numerous measurements be made to cover adequately the whole field and permit interpolation to any intermediate concentration. For the more alkaline solutions (ratio of less than about 2 silica per 1sodium oxide) the possible concentrations are limited by solubility (8, 13); with the more siliceous solutions very high viscosities limit the range. With a ratio of silica to sodium oxide much above 4 to 1 the solutions become unstable and precipitate silica. Sodium hydroxide may be considered as the limiting case of sodium silicate with no silica. As sodium hydroxide solutions have been studied by many investigators (1,5-5, 9, 10, I S ) no measurements were made upon them, except to calibrate the calorimeter. Specific heat as used here is the heat in defined calories (4.1840 absolute joules) ( 7 )to raise the temperature 1 C. There is some ambiguity in describing compositions of such solutions on a molal basis. Here the solutions will generally be listed by the mole ratio of silica to alkali (sodium oxide), and by the molality of the alkali as sodium oxide. APPARATUS
The calorimeter is shown in cross section in Figure 1. It is constructed mainly of stainless steel, and consists of an inner cylindrical vessel of about 850-cc. capacity, surrounded by a convection shield and an outer vessel, immersed in water. The inner and outer vessels were fitted with lids which bolt on and rubber gaskets to produce a tight fit. Four fiber tubes fitting over protuberances supported the inner vessel. The convection shield, with a tightly fitting lid, rested on small sections of cork.
