INDUSTRIAL AND ENGINEERING CHEMISTRY
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obtain high efficiencies. Fairly good efficiencies are obtained, however, by the simple diffusion process with beeswax and combinations of beeswax with other materials when 50 per cent solutions are used. The use of a more volatile solvent than Cellosolve is desirable in this process but, unfortunately, most of the highly volatile swelling solvents are poor solvents for the natural waxes, oils, and resins. If more highly moisture-resisting materials could be found that would dissolve in wood-swelling solvents, the amount that would have to be put into the wood to give good efficiencies might be materially reduced. Such a material is now being sought. The replacement process not only materially decreases the dimension changes but it also causes a retention of more nearly the green dimensions of wood than any other moistureexclusion treatment (Figure 1). The replacement process is thus of as great if not greater value in cutting down the degrade of wood due to the shrinkage occurring on initial seasoning as it is in maintaining uniform dimensions. The replacement process as here described is unquestionably too expensive for general use and in its present form is not applicable for treating large specimens. It should, however, be of value in seasoning and retaining the dimensions of small expensive articleq made from refractory woods. I n the case
VOL. 27, NO. 12
of woods, the seasoning degradation of which is small, the dry wood can be impregnated with a nonaqueous woodswelling solvent and the replacement carried on from this stage, thus avoiding the expense of replacing the water with Cellosolve. The simple process depending merely upon the diffusion of the solute from a wood-,welling solvent into the cell wall is not as yet in a state for recommendation. Because of it's simplicity further studies along this line are being made. Impregnations with synthetic resins under various conditions are also being studied and will form the material for another paper.
Literature Cited (1) Browne, F. L., IND.EKG.CHEM.,25, 835 (1933). (2) Dunlap, M. E., Ibid., 18, 1230 (1926). ( 3 ) Hunt, G. M., E. S. Dept. of Agr., Circ. 128 (1930). (4) MaoLean, J. D., unpublished F o r e s t Products Lab. rept. 8-4, M22W (1928). (5) Ytamm, A . J., IXD.ENG.CHmf., 27, 401 (1935). (6) Ytamm, A. *J., J . Agr. Research. 38, 23 (1929). (7) Stamm, A. J., J . Am. Chern. Soc., 56, 1195 (1934). (8) Stamni, A. J., and Loughborough, W. K., J . Phus. Chern., 39, 121 (1935).
RECEIVED M a y 29, 1935. Presented before the Division of Colloid Chemistry a t the 8 9 t h Meeting of t h e American Chemical Society, S e w York. N. Y.. April 22 t o 26, 1935.
Phase Equilibria in
Hydrocarbon J
B. H. SAGE
AND
W. N. L;ICEY
California Institute of Technology, Pasadena. Calif.
Systems IX.
Specific Heats
of n-Butane and Propane'
T
HE thermodynamic properties of indi-
vidual hydrocarbons and mixtures of hydrocarbons form the fundamental background u p o n i h i c h must be based the study of many of the perplexing problems of the petroleum technologist. Methods for determining the quantities ordinarily used in describing these properties have been discussed in earlier articles of this series. These methods (6, 7 ) , particularly adapted to studies within the ranges of pressure and temperature found in the recovery of petroleum and natural gas from underground sands, are capable of determining in certain cases sufficient facts to permit the construction of diagrams showing such thermodynamic properties as specific volume, heat content, and entropy in relation to pressure and temperature. They consist of pressure-volume-temperature studies accompanied by the determination of the specific heat at such a constant pressure 1 Parts I t o VIII appeared, respectively, 111 January, February, June, August, and Xovember. 1934, and in January, February, and June, 1935.
that the material remains completely condensed a t all temperatures studied. I n many naturally occurring hydrocarbon mixtures it is not possible to avoid the presence of a gas phase at some part of the temperature range from 60" to 220" F. a t pressures not exceeding 3000 pounds per square inch absolute. This necessitates additional methods of specific heat measurement which are satisfactory for use when the material under investigation either is entirely gaseous throughout the temperature range or consists of a mixture of gas and liquid phases.
Specific Heat Determinations S o t only is it desirable to have methods of specific heat determination which can be applied to hydrocarbon materials in both homogeneous and heterogeneous states, but it is also advantageous to be able to construct the thermodynamic diagram upon the basis of two or more sets of specific heat measurements made under widely different conditions. For example, if specific heat measurements are made only in the condensed region, the values for the thermodynamic diagram in the superheated region, calculated therefrom in conjunction with the P-V-T relations, are more uncertain than if specific heat measurements have been made for that region as well. The advantage of these additional specific heat measurements is great in establishing values of heat content and entropy a t low pressures where the calculations for one state carried across from a widely different state become uncertain.
DECEMBER, 1933
INDUSTRIAL AND ENGINEERING CHEMISTRY
148.5
B-
ill
TEMPERATURE
DEG.
F.
FIGURE2. SPECIFICHEAT AT CONSTANT PRESSURE OF THE LIQUID FOR n-BUTANE AND PROP.4NE
The p u r p o s e of the present paper is FIGURE1. APPARATUS EMPLOYINGto p r e s e n t specific ADIABATIC EXPANSION OF LIQUID h e a t results obtained bv methods applicable to gaseous and to two-phase systems, respectively. Results for nearly pure n-butane are compared with those obtained by the method for liquid systems described earlier (7). Observations, in limited number, upon propane are also presented. The results lie within the range of temperature from 70" to 220" F. The sample of butane used was obtained from the Philgas Company, who furnished the following special analysis: 99.21 per cent n-butane, 0.18 per cent isobutane, 0.61 per cent isopentane. The propane used was the same sample used in earlier work ( 7 ) and contained less than 0.01 per cent of impurity. Although the adiabatic expansion method of determining the specific heat a t constant pressure for a condensed material has been previously discussed in an earlier paper of the series (Y), several improvements in the apparatus have markedly increased the accuracy and are worthy of description. Briefly the method causes the liquid to expand adiabatically through a known pressure interval, the corresponding change in temperature being measured. The change in temperature per unit change in pressure can be used with the proper isobaric thermal expansion data to calculate the specific heat a t constant pressure from the following equation:
The revised apparatus is shown schematically in Figure 1. It consisted of a steel cell, C, within which the sample, E, was placed. The pressure was increased to a point well above the bubble-point pressure by addition of mercury, D. The sample was agitated until it had reached thermal equilibrium with the surrounding oil bath xhioh was carefully maintained within 0.02" F. of the desired temperature of operation. Difference of temperature between the sample and the oil bath \vas capahle of accurate measurement by means of the copper-constantan thermocouple junction, A , in the sample and the 3econd similar junction, B, cemented into a metal block submerged in the thermostat oil bath. This thermocouple was constructed of KO. 36 B and S gage wire and was held in place by support F . The initial pressure of t,he sample was maintained at a selected constant value by connecting the mercury line to a gas-filled chamber at the correct pressure. The change iri pressure was rapidly accomplished by closing off the first gas chamber and suddenly connecting the mercury line to a second one maintained at a somewhat lower pressure. Since the expansion of the liquid is not great, the time occupied in changing from one pressure to
the other was less than one s e c o n d . Both gas FIGURE3. APPARATUS EJIPLOYchambers were immersed ING ADIABATIC EXPANSION OF in a thermostat b a t h . GAS Pressures were measured with a fluid-pressure scale accurate to 1 pound per square inch. The pressure change utilized varied from 200 to 400 pounds per square inch, depending upon the hydrocarbon material, and a temperature change of the order of 1.5' F. resulted. A potentiometer, designed especially for measurement of thermocouple voltages and equipped to eliminate all parasitic potentials in the circuit, was used for measuring temperatures. This instrument permitted the measurement of temperatures to 0.002' F. with a single-junction copper-constantan couple. The use of a fixed and accurately reproducible pressure change made it possible, after one or two preliminary trials, to set the potentiometer in advance so that the changed temperature of the sample following the drop in pressure gave a null reading of the galvanometer. Since the adiabatic character of the expansion was dependent upon rapidity of operation compared to the rate at which heat could diffuse into the quiescent sample, it was necessary to make the final temperahre reading as promptly as possible. This was feasible within 1 second after the pressure change uccurred. This use of the galvanometer as a null instrument avoided the need of a string galvanometer. The length of time during which the changed temperature remained constant (before heat inflow from the oil bath reached the thermocouple junct,ion)varied from 10 or 12 seconds with viscous oils to 1 or 2 seconds for materials similar to propane near its critical state. In the case of heavy oils the limitation of accuracy of this method lies in the accuracy of determination of the relatively small thermal expansion rather than in the adiabatic expansion method itself. After a measurement of final temperature had been completed, agitation of the sample quickly brought it back t o thermal equilibrium, the pressures in t'he gas-filled chamber?, were readjusted, and the apparatus was ready for a repetition of the measurement. X series of measurements was thu:, made a t each temperature and the mean value used. The results of such series of measurements, using the sample of n-butane mentioned above, for a mean pressure of 500 pound:: per square inch absolute, are shown in Figure 2 as a solid line. The points indicated for this curve are in each case the average of at least six measurements. When good thermal expansion data are available, the results of this method are accurate to about 2 per cent. The measurement of the specific heat a t constant pressure for gases by use of the constant flow type of calorimeter is laborious and requires elaborate apparatus for good accuracy Eucken (d, 5) has used a method depending upon the same adiabatic expansion principle discussed above, obtaining good results for a number of gases. This method has, there-
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negligible. These variations probably resulted from differences in the rate of heat transfer from the suspended thermocouple in the different gases. The thermal expansions of the gases used, required in calculation of the specific heat, were obtained from their pressure-volume-temperature relations. Figure 4 shows results obtained by this method for nbutane and for propane in the gaseous state a t a n average pressure of 14.79 pounds per square inch absolute. The apparatus was found to be satisfactory both for pure substances and for mixed gases, giving results rapidly and with an accuracy within 2 per cent. The values given in Figure 4 are approximately 2.5 per cent lower than those obtained from the equation proposed by Lewis and McAdams (4).
Specific Heat at Constant Volume I
80
I
I00
I
120
140
T E MPERAT URE
160
180
200
J
DEG. F.
FIGURE4. SPECIFIC HEATAT CONSTANT PRESSURE OF THE GASFOR n-BUTANE AND PROPANE AT ATMOSPHERIC PRESSURE
fore, been adapted by the authors for studies of hydrocarbon gases at temperatures from 60" to 220" F. a nd a t pressures near atmospheric. The apparatus developed utilized a steel cell, A , shown in Figure 3. This heavy cell was not required for work at low pressures but was provided in order that the apparatus might be modified later for similar measu r e m e n t s at higher pressures. Within the cell, A , was suspended a t h i n - w a l l e d brass shield, B, w h i c h w a s perforated with a series of holes to permit rapid attainment of pressure equilibrium within the system. A fine (number 40 B and S gage) copper-constantan thermocouple junction, C, butt-joined with silver solder, was mounted within the b r a s s shield being held in place by the t w o c o p p e r supports, D. The o t h e r junction of this thermocouple was sealed within one of these supports and therefore remained a t the temperature of the cell, A , which was kept within 0.02' F. of any chosen temperature by immersion in a thermos t a t i c a 11y controlled oil bath. After a sample of gas had been placed in the cell, the pressure was raised to about 2 inches of merc u r y a b o v e atmospheric. The exact pressure was made reproducible by use of an electrical contact in a mercury manometer kept in an air thermostat. It was found by means of a cathetomeFIGURE5. BOMB FOR ter thaf the pressure thus conADIABATIC CALORIMETER trolled was reproducible to better than 0.001 inch. After the pressure in the cell had been adjusted and thermal equilibrium established, the pressure was dropped suddenly to atmospheric pressure by opening the outlets from the cell to the air. Since the suspended thermocouple junction followed the temperature of the gas rapidly while the sealed-in junction remained a t the bath and cell temperature, the dro in temperature of the gas upon the sudden expansion could &e measured with the potentiometer. An over-all calibration of the apparatus was made by using nitrogen gas as a standard material whose specific heat was well known throughout the temperature range involved in these studies. This over-all calibration included allowance for the effects of thermocouple lag, radiation, etc. To test the apparatus further, measurements of the specific heats a t constant pressure for hydrogen, carbon dioxide, methane, and ethane were made and compared to the values obtained by Eucken (8, 9) and coworkers. It was found that the calibration of the instrument differed by about 4 per cent between hydrogen and carbon dioxide but the variations with the gases other than hydrogen were
The determination of the specific heats of hydrocarbons existing as mixtures of liquid and gaseous phases cannot be carried out by either of the methods described above. For this case recourse was had to the use of an adiabatic calorimeter t o measure specific heat a t constant volume. Such a specific heat for a two-phase system involved some heat of vaporization or heat of solution, but this did not decrease the usefulness of the result for the thermodynamic calculations for which it was intended. The sample was placed in the bomb shown in Figure 5 . This bomb was machined from solid bar stock of alloy steel having a yield point of over 120,000 pounds per square inch. The two hemispherical ends, A and B, were threaded and sweated onto the cylindrical center section, C . Within the bomb was a heating coil, P, incased in a stainless steel tube, 0.030 inch in diameter, soldered through the walls of the bomb. A thermocouple well, E,was provided for the determination of temperature within the bomb. The working pressure of 500 pounds per square inch allowed a large factor of safety. The bomb, B, was suspended in a rin A (Figure G ) , by means of number 36 B and S gage wires. T%e ring in turn was supported upon trunnions D and H, within the jacket, E. The space between the bomb and the jacket was evacuated by an oil mm. of mercury. diffusion pump to a pressure of about To avoid heat transfer from the bomb by radiation, the jacket was submerged in an oil bath, F whose temperature was automatically maintained within 0.02' F. of that of the bomb. This control was accomplished by use of a photoelectric relay actuated by the light beam from the mirror of a high-sensitivity galvanometer connected in series with a thermocouple, one junction of which was on the inner surface of the jacket and the other on the outer surface of the bomb. Both of these surfaces were also highly polished to diminish radiation. In order to insure both thermal and phase equilibrium within the bomb, the latter was oscillated about the axis of the trunnions. To accomplish this movement without a stuffing box through the vacuum jacket wall, an iron bar was mounted on the shaft inside the jacket. This bar served to oscillate the bomb by following the movement of the electromagnet, G, outside the jacket. It was found that, when the apparatus was in operation and the bomb was at a tem-
L FIGURE 6.
ADIABATIC
CALORIMETER ASSE~~BLY
INDUSTRIAL .4ND ENGINEERING CHER'IISTRY
DECEMBER, 193.5
1487
perature of 160" F., Its temperature xouldchangele8i than0.03' F. per hour because of heat leakage to or from the jacket. I n making a determination with the calorimeter, a sample was placed in the bomb, the weights of materials added being ascertained by weighing the bomb. After assembling the apparatus and evacuating the jacket space, the temperature of the sample was determined to less than 0.003' E'. with the thermocouple, readings being repeated a t 5-minute intervals until found constant. Current was passed through the heater element inside the bomb for about 20 minutes; the bomb was oscillated slowly and frequent readings were taken of the current flowing and the voltage drop across the heater element. About 6 to 8 minutes after stopping the current in the heater, temperature readings were taken until a constant value was obtained. The process was repeated until the temperature of the sample had been gradually raised throughout the working range. The temperature readings were plotted against time and any rise or fall corrected for by the usual cooling curve method. These corrections were in all cases less than 0.3 per cent of the total rise. From each rise in temperature and the corresponding heat energy added, the heat capacity of the bomb and sample together was calculated. By subtracting the experimentally determined heat capacity of the bomb (containing hydrogen a t low pressure), that of the sample resulted. The heat capacity of the bomb amounted t o about 35 per cent of the whole for most cases in hydrocarbon studies. The amount of heat energy added as the result of agitation was found to be negligible, no rise in temperature being observed upon prolonged agitation with the heater current turned off. As a check upon the over-all accuracy of the calorimeter a determination was made upon water, the results being shown as experimental points in Figure 7 . The values given by the International Critical Tables for water, as saturated liquid, are shown in the form of the solid curve in Figure 7 for compaison. The experimentally determined values Tvere corrected for a small amount of vaporization in order t o make them directly comparable to the curve. This correction amounted to about 0.1 per cent of the total heat capacity. The results for water were not quite as consistent as those obtained for hydrocarbons, since the heating current required in this case was much greater than the apparatus was designed for. The larger variations in current thus encountered made it difficult t o integrate accurately to obtain the total energy input through the heater.
Experimental Results Figure 8 shows results obtained by this method for the samples of n-butane and propane described above. The quantity C. used as ordinate in Figure 8 is defined as the heat required to raise the temperature of the saturated liquid by 1O F. Correction for the heat utilized in vaporizing a portion of the liquid upon rise of temperature was calculated by the equation used by Osborne and Van Dusen (6) for ammonia: 1.02
I
I
DEG.
TEMPERATURE
F.
FIGURE 8. SPECIFIC HEATSOF
THE SATURATED LIQUIDFOR ~-BUT.AXE AND PROP.4NE
Correction mas also made for the heat capacity of the gas phase present. There are included in Figure 8 some data obtained by Dana and co-workers (1) for n-butane and propane. These data obtained from studies upon different samples are given for comparison. The experimental results of the present study shown in Figure 8 may be converted by calculation to values of specific heat at constant pressure for the saturated liquid. This cortversion makes use of the relation:
The resulting values for n-butane and for propane are shown in the form of the dashed-line curves of Figure 2. Although these curves are for saturated liquid while the solid-line curve obtained by the adiabatic expansion method is for a pressure of 500 pounds per square inch absolute, the isothermal change in specific heat from saturation t o 500 pounds per square inch is small (0.0002 B. t. u. per pound per O F.)2under these conditions, and the curves may be considered directly comparable. This isothermal change in specific heat would not be negligible in the region of the critical state or if the pressure difference were very large. The agreement between the two curves for n-butane is within the experimental error of the methods used. The necessary pressure-volume-temperature relations and values of heat of vaporization for n-butane used in the conversion calculations were determined by the present authors and will be published in a subsequent paper.
Acknowledgment
0"1.00
*
I
I
I
TEMPERATURE
DEG. F
FIGURE7. DETERMINATIONS OF SPECIFIC HEATOF WATER, AS SATURATED LIQUID,TO TESTAPPARATUS
This work was carried on under Research Project 37 of the American Petroleum Institute, and thanks are due the institute for financial assistance. H. S. Backus assisted materially in the adiabatic calorimeter measurements. J. E. Sherborne contributed to the construction and operation of the apparatus for determining specific heats of gases. 4
Calculated from the relation
-
(6P3 ) - J (63'23 D)T. T
VOL. 27, NO. 12
INDUSTRIAL AND ENGINEERING CHEMISTRY
1488
Nomenclature
Literature Cited
6? = heat added to system, B. t. u. M = mass of material in system, lb. u = sp. vol. of system, cu. ft./lb. 2' = abs. temp., Rankine p = abs. pressure, lb./sq. ft. C, = sp. heat at constant pressure, B. t. u./lb./" F. I = latent heat of vaporization, B. t. u./lb. x = quality of two-phase mixture, mass fraction in gas phase J = mechanical equivalent of heat, B. t. u./ft-lb. Subscripts: 1 = initial state 2 = final state s = condition of saturation
(1) Dana, L. I., Jenkins, A. C., Burdick, J. K., and Timm, R. C., Refrigerating. Eng., 12, 387 (1926). (2) Eucken, A, and von Lude, K., Z. phusik. Chen., B5, 413 (1929). (3) Eucken, A , and Parts, A, Ihid., B20, 184 (1933). (4) Lex-is, W.K., and Mcddams, W.H., C h e n . &: X e t . Eng., 36, 336 (1929). ( 5 ) Osborne, N.S.,and Van Dusen, M. S., Bur. Standards, Bull. 14, 397 (1918). (6) Sage, B. H., and Lacey, W. N., IND.ENG.CHEM.,26, 103 (1934). (7) Sage, B. H., Schaafsma, J. G., and Lscep, W. N.,Ibid., 26, 1218 (1934).
O
RECEIYED M a y 9, 1935.
New Method for Barium Chloride
B
ARIUhI compounds of commerce are ob-
tained either from witherite or barytes. Since the most plentiful barium mineral is b a r y t r t h i s ore is employed to a greater extent than the carbonate. The process used for the manufacture of soluble barium compounds is first to form barium sulfide by calcining the barytes with coke, leaching the sulfide with hot water, and then treating the solution with the proper chemical to obtain the desired barium salt. I n carrying out this procedure it is necessary to resort to different methods of purification in order to obtain a technically pure product. This is especially true in the manufacture of blanc fixe where such impurities as iron, sulfur compounds, etc., have a great tendency to lessen the value of the blanc fixe as a pigment. With these facts in mind i t seemed worth while to investigate the preparation of water-soluble compounds of barium from barytes without going through the intermediate stage of converting the barytes to barium sulfide.
Previous Work Different methods, in addition to the use of coke. have been used to decompose barium sulfate. Mosttowitsch (13) de1
Present address, Chemical and Pigment Company, Inc., Collinsville,
Ill.
Decomposition of Barium Sulfate by Calcium Chloride in Aqueous Solution R. NORRIS SHREVE
AND
W-ILLIAAI NELSON PRITCHARD, JR.1 Purdue University, Lafayette, Ind.
composed barium sulfate by heating it with silica a t 1000" C. Marcha1 (8) studied the dissociation pressure of barium sulfate a t 1800" C. and a mixture of barium sulfate and silica at 1250" C. Bundikov and Shilov ( 3 ) claimed to have obtained a 97.7 per cent decomposition of barium sulfate by heating it with silica in an electric furnace a t 1000" C. hl. Asselin reported to Arth (1) that he had prepared aqueous solutions of barium aluminate by heating barium sulfate with bauxite a t high temDeratures. Others who studied the reaction between barium sulfate and alumina in the presence of coke were Gaudin ( 5 ) , Martin (IO), Hershman (e),and hiorey (If). Booth and Ward ( 2 ) studied the reaction between barium sulfate and alumina between 100 and 1450' C. with satisfactory results. X'ewberry and Barret (Id) produced barium oxide by heating barium sulfate with magnesia a t 1500' C. Kharmandar'yan and Brodovich (8) claimed to have obtained a small yield of 99.6 per cent barium chloride by chlorinating barytes a t 600" C. for 2 hours in the presence of the catalysts alumina and carbon. Still (I;), while investigating, under the direction of the senior author, the chemistry of Farr's process (4) for the manufacture of finely divided barium sulfate by heating barytes with strong calcium chloride solutions, found that, under the conditions of high concentration of calcium chloride in aqueous solution and high temperature, the reaction
-
O
BaC12
CYLINDERS FIGURE 1. OVER'WITH ROTATI~VG
+ Cas04 = BaSOI + CaC12
might be reversed. I n order to study this reversion, it was necessary to remove the barium chloride formed from the
