254
INDUSTRIAL Ait‘D ENGliVEERING G’HEMIS1’RY
1701*23, KO.3
The Thermodynamic Properties of Dichlorodifluoromethane, a New Refrigerant I-The Equation of State of Superheated Vapor“* Ralph M . Buffington and W. IC. Gilkey FRICIDAIRECORPORATION, DAYTOX,O m o
T HAS become increasThe constants of a Beattie-Bridgeman equation of been t o determine experistate for superheated dichlorodifluoromethane vapor m e n t a l l y the pressure-volingly evident during the past few yeam that there were determined from measurements of isometrics ume-temperature re1 a t ions between volumes of 1.4 and 4.2 liters per mol. In this over the high pressure range, is a real need for a refrigerant which combines f a v o r a b l e region the isometrics are straight. The final equation and from these to evaluate the constants of a suitable engineering properties w i t h is p = RT(V + B)/Vz - A/Vz equation of state. non-inflammabilitv and nonwhereA=23.7 (1 - 0.305/V)and B = 0.59 (1 - 0.622/V). toxicity to a greater extent Procedure and Apparatus The units are atmospheres, degrees Centigradeabsolute, than any hitherto available. and liters per gram-mol. The equation has been shown It n-as decided to measure At the ktlanta meeting of the A M E R I C A N CHEMICAL so- to fit the observed data with an average error of 0.5 isometrics, thisbeinga simple per cent. and direct method of obtainCIETY Midgley and Heiine (3) ing the required data in a pointed out the unique advantages of fluorochloro derivatives, especially dichloro- form particularly adapted to the determination of the equadifluoromethane, as refrigerants, and described a conimercial tion of state. process for the manufacture of this hitherto little known A quantity of dichlorodifluoromethane was weighed into a steel cylinder of known volume. A pressure gage was atcompound. Early in the course of the development of dichlorodifluoro- tached to the cylinder, which was then immersed in a conmethane by Frigidaire Corporation, it was realized that stant-temperature bath. When the pressure became conits practical application as a refrigerant would require the stant the pressure and temperature were read, establishing determination of its thermodynamic properties, and the con- one point on an isometric. Other points on the same isostruction of usable tables therefrom. This program was metric were then obtained by raising the temperature of the undertaken and preliminary results on the essential Table I-Pressure-Volume-Temperature Data properties were quoted by Midgley and Henne. p(obsd.) - P(calcd.) Biobsd.) - RT/I’ This work has been continued and since the formaV 1 p (calcd .) P(0hsd.) p (obsd,) RT/V p(ohsd.) tion of the Kinetic Chemical Company to handle Liters/nruiii ‘ll#l. A1m. C. x 100 Alm. x 100 m o l manufacture and sale, the Jackson Laboratory of 14.8> 14.93 0.7 19.4: fi.j.1 1 . 4 2 6 -30.0 E. I. du Pont de Nemours and Company has 19.6 15.88 16.10 1.4 20.32 -26.2 93.4 16.86 17.09 1.3 21.12 -23.6 cooperated in certain phases of the work. 104.6 17.65 17.88 1.2 21.76 -21.7 I n laying out the program, the aim was to pro18.63 115.6 18.43 1.1 22.39 -20.2 vide data for the construction of tables for refrig13.98 13.93 67.2 -0.5 17..58 -26.2 1,387 14.05 68.3 13.99 -0.4 17.63 -26.0 eration use, characterized by (1) completeness in 83.3 15.00 1 4 . 9 8 -0.1 18.41 -22.7 both saturated and superheated regions, (2) ther98.9 15.99 16.00 0. I 19.24 -20.2 109.5 16.66 16.69 0.2 19.81 -18.7 modynamic consistency, and ( 3 ) moderately high 1 2 8 2 1 2 . 9 4 0 . 0 1 6 . 2 0 5 7 . 8 1.667 27.0 accuracy. Experimental methods were chosen ac74.1 13.92 13.86 -23.2 -0.4 17.08 cordingly, no attempts being made to secure the 14.32 82.3 14.41 -0.7 17.48 -22.0 14.91 14.86 -0.3 17.92 90.6 -20.6 highest attainable precision. The required con15.69 15.61 -0.5 18.56 103.5 -18.9 16.43 16.37 115.9 -0.4 19.15 -17.0 sistency was secured by making full use of thermo17.05 16.99 -0.4 19.64 126.1 -15.6 dynamic relationships in criticizing and correlat11.17 11.21 55 0 . 4 13.45 2.002 -20.0 ing the measurements of the various properties. 13.44 100 13.39 0.4 15.29 -13.7 A knowledge of the pressure-volume-temperature 54 10.10 10.15 0.5 11.86 2.262 -16.8 relations of a refrigerant vapor is necessary for a 12.09 12.09 0.0 13.53 -11.9 100 very large part of both the engineering and thermo8.76 8.79 0.3 10.00 -13.8 53 2.676 10 4 1 99 10.45 0.4 11.41 - 9.6 dynamic calculations-for example, those of heat 7.51 content, entropy, piston displacement, and work of 53 7.50 -0.1 8.37 -13.2 3.197 99 8.87 8.86 -0.1 9.55 - 7.8 compression. For this work it is convenient to 30 5.40 5.41 0 . 2 5.94 4.183 - 9.8 represent the pressure-volume-temperature rela34 5.49 5.50 0.2 6.02 - 9.5 tions of the vapor by means of an equation of 6.93 54 5.95 0.3 6.43 - 7.9 99 6 92 6.95 0.4 7.30 - 5.0 state. Any equation which reduces to the perfcct gas law a t low pressures, and which satisfactorily represents these relations a t high pressures, over bath by stages and observiiig the corresponding pressurcs. Other isometrics were obtained by repeating the procedure R considerable temperature range, may be extrapolated to lower pressures. The general plan of attack has, therefore, with different amounts of dichlorodifluoromethane in tlic cylinder. 1 Received December 29, 1930. The essential parts of the apparatus are shown schemati* Other papers, t o follow shortly, h i l l report the vapor pressure, the cally in Figure 1. The container A was a section of orthobaric densities and critical data; the latent and specific heats of the inch (1.6-mm.) steel tubing, 5 inches (12.7 cm.) in diameter liquid; and finally the heat contents and entropies of liquid, saturated vapor, and superheated vapor. and 12 inches (30.5cm.) long, t o which were welded bumped
I
March, 1931
INDUSTRIAL AND EiYGI9EERI.YG CHEMISTRY
255
RT A heads of the same thiclmess. The exterior surface was p = (V B) - V2 V2 chromium-plated and polished t o prevent rusting and facilitate drying. The upper head was fitted with a small needle where A and B are functions of volume only. valve, threaded for a standard flare connection. The total weight was 2.2 kg. and the volume 3.84 liters. The pressure A = Ao(1 gage D mas a Bourdon-tube test gage, with 6-inch 1;15.2-cm.) dial, graduated in 2-pound (0.14-atm.) divisions from 0 B = Ba(l to 300 pounds (0 to 20 atm.) and calibrated before and after the messurements against a standard dead-weight gage. The pressure was communicated to the gage through the Differentiating Equation 1 a t constant volume,
+
); +)
According to Equations 1 t o 4 each isometric IS a straight line whose (extrapolated) intercept a t T = 0 is - A / P and B)/Tr2,-4and B being, in turn, linear whose slope is R(V functions of l/T-. Formally, therefore, two isometrics are sufficient to determine the equation of state. The data were plotted as pressures against temperatures on a large scale and the isometrics drawn in as the best straight lines through the points for each volume. The slope of each isometric was then used in determining a value of B for that volume from Equation 4. Then, instead of determiiing A at once from the intercept, a somewhat different method was used. The values of B were plotted against 1 / V (Figure 2 ) and the best straight line drawn through the points, thus determining the constants of Equation 3. Then the smootlied values of B from this equation were used to calculate values
+
C
Figure 1-Schematic Representation of Vapor D e n s i t y Apparatus
steel U-tube, C, half filled with mercury. ;ibove the mercury level at c, everything, including the Bourdon tube, was filled with oil. The trap was immersed in the bath alongside the cylinder, thus holding the entire vapor volume at constant temperature; and the vapor was at the same time prevented from coming in contact with the oil in the gage. The volume between a and b, amounting to 30 cc., was added to the volume of the cylinder as a correction. Two other corrections to the volume of the cylinder are t o be considered-the change in volume due to thermal expansion of the cylinder, and the change in volume of the cylinder and Bourdon tube with pressure. Calculation showed that these could be neglected. The cylinder and contents were weighed on a torsion balance of 4.5 kg. capacity, using a duplicate cylinder as a counterpoise. Under these conditions the balance was sensitive to 0.2 gram, but small changes in position of the cylinder on the balance pan introduced errors of the order of 0.5 gram. Equation of State
I t nas found that the data could he well represented by a n equation of state of the Keyes type (Z), and the preliminary data were reported in this way by LIidgley and Henne (*?). The Beattie-Bridgeman ( I ) type of equation was found to represent the data equally well, and is used here because it simplifies the calculation of the various thermodynamic quantities for which a n equation of state is required. Beattie and Bridgeman have designed this equation to represent data in the region where the isometrics are curved, but in the range covered by these measurements the isometrics are straight and the equation is considerably simplified. I t takes the following form:
Figure 2-Graphical
D e t e r m i n a t i o n of E q u a t i o n s 5 and 6
The dotted lines represent the probable error of individual points
of A for each volume, through Equation 1, using simultaneous values of pressure and temperature rend from the isometric near the middle of the experimental range. The ~ a l u e of s -1 thus obtained were plotted against l / V and the best straight line drawn through the points (Figure 2 ) , thus determining the constants of Equation 2. The final equation of state thus obtained is:
p
=
RT vz (V + B ) -
A V2
INDUSTRIAL AND ENGINEERIA-‘G CHEMISTRY
256 A = 23.7(1
- ”””>
B = 0.59 1 where p
(
“3
pressure in absolute atmospheres absolute Centigrade temperature (” C. 273.1) volume in liters per gram mol (molecular weight = 120.9) R = 0.08207
T V
= = =
+
Table I gives the pressure-volume-temperature data and compares the observed pressures with those calculated from Equations 1, 5, and 6, and also with those calculated from the perfect gas law. It will be seen that the equation reproduces the observed pressures within an average error of 0.5 per cent, and without any systematic drifts while the deviations from the perfect gas law amount to as much 11s 30 per cent of the observed pressures.
Vol. 23, No. 3
The corresponding probable errors in A and B are shown by the dotted lines in Figure 2. Consideration of the probable errors, and also of the deviations of the observed data from the equation of state, indicates that the over-all error of this equation a t 15 atmospheres is about 1 per cent, and is less than that at all lower pressures. As a check on the accuracy of the equation of state at low pressures, there are available three determinations3 of the vapor density at atmospheric pressure which were made using a glass bulb of 230 cc. capacity and weighing on an analytical balance. (Table 11) Table 11-Comparison of Low-Pressure Density D e t e r m i n a t i o n s w i t h Equation of S t a t e a n d Perfect Gas Law p(obsd.) -p(calcd.) P(obsd.) R T / V V t g(obsd.) p(calcd.) p(obsd.) p(obsd.) RTIV X 100 x 100 Atm. C. A f m . Atm. -1.4 0.1 0.984 25.17 28.5 0.970 0.969 1.001 -2.0 24.49 2 5 . 6 0.9S1 0.986 -0.5 -2.4 -0.3 1.004 22.32 0 . 0 0.980 0.983
-
Errors Literature Cited
The following estimates are placed on the probable errors of the experimental quantities.Volume of apparatus.. . . . . . . . . . . . Negligible Weight of vapor.. . . . . . . . . . . . . . . . 1 gram Temperature. . . . . . . . . . . . . . . . . . . 10 0 . 0 3 3 atm. (0.5 lbd per sq. in.) Pressure. . . . . . . . . . . . . . . . . . . . . . . dp/dT ......................... 0.00033 atm. per C .
c.
(1) Beattie and Bridgeman, J . A m . Chem. Soc., SO, 3133 (1928); Proc. A m . Acad. Arts Sci., 63, 229 (1928). (2) Keyes and Felsing, J . A m . Chcm. Soc., 41, 589 (1919). (3) Midgley and Henne, IND. ENG.CHEM.,22, 542 (1930). 8 The authors are indebted to F. W. Gerard, of this laboratory. for these measurements.
Solid Carbon Dioxide from Mexico‘ James Welford Martin 233 BROADWAY, NEWYORK,N. Y.
BOUT fifteen years ago an oil company; in drilling just south of Tampico, Mexico, in the State of Vera Cruz on the Hacienda of Quebrache, was surprisedand disgusted-to bring in a well of non-inflammable gas under high pressure but containing practically no oil. Subsequent wells brought in commercial amounts of oil, but in all the wells large quantities of carbon dioxide had to be continuously blown 08 in order to obtain satisfactory oil production. With a rapidly developing market for solid carbon dioxide both in this-country and abroad, the value of this gas that has been blowing away became apparent, particularly since the total open flow of the present wells was found to be capable of producing more than 900 tons of solid carbon dioxide daily.
A
Character of Gas
The gas issues from the wells along with some crude oil, but on passing through very simple separators, gas analyzing 95 per cent carbon dioxide and 5 per cent combustible gases is obtained. Among these combustible gases are ordinary gasoline, some methane, and ethane, and a fraction of a per cent of sulfur compounds. The pressure on the flowing well is about 1000 pounds per square inch, well above the liquefying pressure of carbon dioxide at ordinary atmospheric temperatures, and the temperature of the issuing gas is about 100’ F. It is the unique combination of high pressure and high quality, coupled with proximity to water transportation, that has made this source of carbon dioxide commercially attractive. 1 Received
December 29, 1930.
Stability of the Field
.
Oil production in the Quebrache field diminishes from year to year, as is usual in all oil fields, but the flow of gas appears to be without limit. The best indication of the possible life of the field as to gas production is found in its past history. The production at Quebrache is now more than fourteen years old and the rock pressure has not diminished. I n fact, one of the wells “blew wild” from 1916 to 1927, discharging probably 1000 tons of carbon dioxide per day, yet there was no apparent diminution in flow on this well or drop in pressure on adjacent wells. Preliminary Work
With this potential source of large supply of carbon dioxide, the ownersZabout a year ago set out to determine if it was commercially feasible to produce solid carbon dioxide in Mexico and market this product in New York. There were several problems that confronted them before any commercial developments could be undertaken. Among these was the lack of knowledge as to whether the gas could be purified without a sacrifice of pressure and whether it could be sufficiently purified to produce ice of commercial quality. Furthermore, there was little to guide them in determining the cost of plant and the cost of production and transportation, or in regard to the losses to expect between the plant and Xew York. To obtain this basic information samples of the gas were sent to the laboratory of a New York consultanta and a 2
bono, 8
Carbonic Products Corp., New York City (Cia. Industrial de CarA,). Ralph H . McKee, Columbia University.
s.
