Phase Equilibria in Hydrocarbon Systems

Phase Equilibria in Hydrocarbon Systems J

d

Volumetric and Phase Behavior of Methane-n-Pentane System' B. H. SAGE, H. H. REAMER, R . H. OLDS, AND W. N. LACEY California Institute of Technology, Pasadena, Calif.

The specific ~ o l u r n e of six mixtures of methane and n-pentane were determined for seven different temperatures between 100' and 466)" F., at pressures up to 5000 pounds per square inch. The composition of the dew-point g a s was experimentally established throughout the two-phase rcgion for temperatures above 160" F. The specific volume, bubble-point pressure, and dew-point pressure for each of the mixtures,

as well as the specific volumes and compositions of the coexisting phases for a number of temperatures, are recorded. The fugacity of each of the components in the coexisting phases is also included. The results are presented in graphical and tabular form.

LTHOUGH methane and n-pentane are important components of naturally occuri ing hydrocarbon mixtures, the properties of the methane-n-pentane system have not been extensively investigated. The measurements of Boomer, Johnson, and Piercey (I) upon the composition of the coexisting phases of the methane-pentane-nitrogen system furnished the first available data, and this work was later supplemented by Taylor and co-workers with measurements upon the methane-n-pentane system ( 1 6 ) , a t somewhat higher temperatures. However, the two individual components have been investigated in some detail. Kvalnes and Gaddy (6) and Michels and Nederbragt (6) have established the volumetric behavior of methane a t pressures up to 15,000 pounds per square inch 32" and and in the interval between 400"temperature F. These

A

--0 040

m _1

a W

a

+L 3

5

0035

9 v

k a w Wl

0 030

250

500

750

IO00

PRESSURE

1250

1500

1750

L B . P E R SQ IN

FIGURE 1. EXPERIRIEP~TAL RESULTSIN H h OF

data, together with values of the JouleThomson coefficient ( 2 ) a t low pressures, serve to establish the thermodynamic behavior of this hydrocarbon in the pure state. Young (JO> 17) studied the volumetric and phase behavior of pentane at relatively low pressures throughout the temperature interval between 104" and 460" F. Brown and co-workers (6, 9) established throttling curves for this hydrocarbon over a wide range of temperature and pressures. The gaseous isobaric heat capacity a t atmospheric pressure and the volumetric behavior in both the liquid and gas regions have also been investigated ( I S , 16). These data serve to establish the thermodynamic behavior of n-pentane with adequate accuracy for present purposes.

THE VICINITY OF BUBBLE POINT METH.4NE AND ?&PENTANE CONTAINING 0.03114 WEIQHT FRACTION METHANE

1108

Thls 18 the thirty-fifth paper in this series. Prearticles appeared during 1934-1940, inclusive, and in Jnne and July, 1942 1

VIOUS

September, 1942

INDUSTRIAL AND ENGINEERING CHEMISTRY

1109

buoyancy upon the stainless steel weights employed. It is believed that the specific weight of the gaseous mixture was determined with an uncertainty of not more than 0.1 per cent. Special care in conditioning the bulb was employed to avoid uncertainties resulting from adsorption of the heavier components on the surfaces of the glass or from solution in the lubricant employed on the stopcock. Apparently hydrocarbon mixtures a t atmospheric pressures are not ideal solutions ( 7 ) , and it is necessary to employ experimental measurements relating to their volumetric behavior to permit the calculation of the weight fraction of the component from the measured specific weight. The necessary volumetric data were obtained by extrapolation of the experimental results to low pressure in accordance with suitably adjusted equations of state. It is believed that this procedure reduced the uncertainty in the estimation of the composition from the measured specific weight to less than 0.002 in terms of weight fraction. For the most part, methods similar to those employed in connection with the study of the methane*-butane system were used (12). The study of the comRESULTS FOR A MIXTUREOF METHANE AND FIGURE 2. EXPERIIIENTAL position of the coexisting phases was carn - P E N T A K E C O N T A I N I K C 0.3857 W E I G H T FRACTION METHANE ried out with the apparatus utilized in the volumetric studies (14). The experimentally determined compositions of the dew-point gas included states from near the vapor presMethods sure of pure pentane to the maximum two-phase pressure for the system a t the temperature in question. Samples The total volumes of six different mixtures of methane and a-pentane were determined a t seven systematically chosen withdrawn a t the same pressure and temperature agreed within 0.0004 weight fraction n-pentane. This small uncertemperatures between 100" and 460" F. for pressures up to 5000 pounds per square inch. I n essence, the method involved the addition of known weights of methane and npentane t o a chamber whose effective volume could be varied by the addition or withdrawal of mercury. The temperature of measurement was controlled by immersing the chamber i n an agitated oil bath whose temperature was controlled automatically. Equilibrium between the phases was established by a magnetically driven mechanical agitator; the 0.06 pressure was measured by a pressure balance. The details -of the equipment employed for these volumetric measurem ments have been described (14). It is believed that the 6 weights of methane and n-pentane employed were estabc: lished with an uncertainty of not more than 0.08 per cent, while the temperature of the equilibrium chamber was known 3 0.05 within 0.05" F. relative to the international platinum scale. Y T h e pressures were determined within 0.3 pound per square inch a t pressures below 1000 pounds per square inch while 9 the uncertainty was as much as 2 pounds at pressures above L! 4000 pounds per square inch. The total volume of the 0.04 8 sample was established with an uncertainty of approximately a 0.1 per cent except a t the higher temperatures and pressures, where it may be as much as 0.18 per cent. The composition of the dew-point gas of the methane-npentane system was investigated by the withdrawal of a 0.03 portion of the gas phase from heterogeneous mixtures under isobaric, isothermal conditions. The composition of the I I I i i gas withdrawn was ascertained from its specific weight at a 0.I 0.2 0.3 pressure of approximately 10 pounds per square inch and a WEIGHT FRACTION METHANE temperature of 1000" F. The specific weight was determined by the change in weight of a glass bulb weighed against F I G U R E 3. S P E C I F I C V O L U M E - C O M P O S I T I O N DIAGR.4M FOR 280" F. an identical tare with appropriate corrections for the air

2

1110

I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY

Vol. 34, No. 9

lieved that the methane after purification contained less than 0.001 mole fraction of d impurities. 025 W The n-pentane employed was obtained e from the Philgas Department of the Phillips Petroleum Company, whose special analysis t 020 U indicated that it contained not more than W 0.007 mole fraction isopentane and a neg5 0.15 ligible quantity of other impurities. This 2 material was treated with several portions uk 010 of fuming sulfuric acid, carefully washed W with aqueous sodium carbonate and then n VI nith distilled water, and finally dried over 0.05 metallic sodium. The pentane was carefully fractionated in a glass column packed P W nith glass helices a t a reflux ratio of ap0 proximately 50 to 1. The first and last portions of the overhead material were discarded, while the intermediate fraction was -0.05 0 02 04 OB 08 collected for refractionation. The final WEIGHT FRACTION M E T H A N E product collected from the third fractionaFIQWRE 4. RESIDUAL SPECIFIC VOLUMES FOR THE R ~ E T HL\E-?L-PEXTAXE tion was condensed a t liquid air temperatures and a t a pressure of less than 10-6 SYSTEMAT 280" F. inch of mercury. It was then distilled a t reduced pressure into a steel weighing bomb. This container was stored a t a temperature to yield a vapor tainty was considered satisfactory under the conditions enpressure of the n-pentane in excess of the pressure of the countered in these measurements. atmosphere. The samples of n-pentane exhibited changes The specific volume of dew-point gas was ascertained from in vapor pressure from dew point to bubble point of apexperimental data relating to the volumetric behavior in the proximately 0.2 pound per square inch a t 280" F. heterogeneous region and measurements relating to the bubble-point liquid. The values of the specific volume were obtained by application of the following expression : Experimental Results ( n d - n") (V" - Va) A typical set of results relating to volumetric behavior Vd = (1) n" - nb for a state in the vicinity of the bubble point of a mixture The results obtained from this equation were in good agreement with values from the extrapolation of volumetric behavior in the gaseous region under isobaric, isothermal conditions t o compositions corresponding to dew point. Throughout all calculations associated with this work, a value of 10.73185 was taken for the universal gas constant when the pressure was expressed in pounds per square inch, the volume in cubic feet per pound mole, and the temperature in R. 2 ( " F. absolute). The temperature of the sl atmospheric ice point was taken to be a L W 491.69' R., and the molecular weights of ai methane and n-pentane were taken as 16.042 and 72.147, respectively. Throughw a 3 out all calculations, care was exercised to VI ensure that such a combination of analytiw a P cal and graphical procedures was employed that the accuracy of the primary data was not significantly impaired by any smoothing operations employed.

3

Materials The methane utilized was obtained from the Buttonwillow gas field in California. This natural material was freed of the traces of carbon dioxide and heavier hydrocarbons which it contained by passage through granular calcium chloride, sodium hydroxide, activated charcoal, ascarite, and magnesium perchlorate a t pressures in excess of 400 pounds per square inch. It is he-

0.2

0.4 WEIGHT

FIGURE5.

PRESSURE-COMPOSITION

0.6

0.8

1.0

FRACTION METHANE

DIAQRAMFOR

PENTANE SYSTEM

TEE

METHANE-n-

September, 1942


1111

with respect to pressure a t constant temperature a t the phase boundary is apparent a t several temperatures. Since experimental measurements were not conducted a t pressures below 200 pounds per square inch, the curves in the heterogeneous region for 100' and 160' F. were drawn with dashes a t the lower pressures. The points shown for these temperatures a t dew point were obtained by application of Equation 1 to the data for other mixtures where experimental results were carried to somewhat lower pressures than those shown in Figure 2. The location of the critical state has been indicated. The general type of behavior illustrated for this mixture on the compressibility factor-pressure plane is typical of that found for other mixtures containing a relatively high weight fraction of methane. The influence of composition upon the specific volume of the methane-n-pentane system at 280' F. is shown in Figure 3. The rapid increase in the specific volume with an increase in weight fraction of methane a t the lower pressures is clearly indicated. The linear relation of specific volume to the weight fraction of methane is shown. Although specific volume is not a particularly convenient variable to employ in the graphical representation of the behavior of gas phases, the residual specific volume which may be defined by the following expression is useful in this regard : =

WEIGHT

FRACTION

METHANE

FIQURE 6. COMPRESSIBILITY FACTOR FOR BUBBLE-POINT LIQUIDAND DEW-POINTGAS

b,T/P

-V

(2)

The variation in this quantity with the weight fraction of methane a t a temperature of 280" F. is portrayed in Figure 4. Consideration of this diagram indicates that a t low pressures the residual specific volume for the liquid phase is markedly in excess of the corresponding value for the gas phase. This results from the relatively small value of the specific volume of a liquid phase as compared to that of a gas phase at low pressures. Linear variation i n the residual specific volume with composition in the heterogeneous region also obtains.

containing 0.03114 weight fraction methane is depicted in Figure 1. The density of the experimental data shown in this diagram is typical of the number of m e as u r e m e n t s made upon other mixtures. The information for 460' F. has not been included in this diagram in order to allow the behavior a t the lower temperatures to be shown in 2000 greater detail. It may be seen that an increase in temperature results in an increase in bubble-point pressure z throughout the range of con1500 ditions depicted in Figure 1. K Redetermination of the volume n of a sample exposed to the 5 highest temperature used durw ing a series of measurements 3 gave no evidence of thermal 2w 1000 decomposition of the hydron a carbon. The experimental results obtained for a mixture containing 0.3857weight fraction methane 5 00 are portrayed in Figure 2. I n this instance the compressibility factor was employed instead of the specific volume in order to present the wide variations in specific volume with I50 200 250 300 350 reasonable accuracy. The disTEMPERATURE continuityin the first derivative DIAQRAM FOR THE M E T H A N E - / L - ~ E N T SYSTEM ANE of the compressibility factor FIGURE 7. PRESSURE-TEMPERATURE OF,


1112

Vol. 34, No. 9

The specific volumes of the six mixtures of methane and n-pentane investigated are recorded in Table I. It is believed that the 3000 uncertainty in these values is less than 0.3 per cent, except near the critical state. The specific volume and the pressure a t dew point and bubble point are recorded for each of the mixtures. The uncertainty in 1: 2 0 0 0 bubble-point pressure may be as much as 4 0 pounds per square inch a t the higher presLL sures. However, in most cases it is believed a w that the dew-point and bubble-point presm sures recorded in Table I do not involve un:1000 certainties greater than 2 pounds per square inch; a t the lower pressures this uncertainty is much smaller. The composition and specific volume of the coexisting phases are listed as a function of pressure and temperature in Table 11. These results were inter500 I000 I500 2000 polated graphically from the experimental PRESSURE L B P E R S O IN measurements already discussed. The comFIGURE8. EQCILIBRIUM COKSTAXTFOR METHANEAND n-PEzTazc position, pressure, and specific volume corresponding to the critical state for each of the temperatures investigated are included. The aressures. temDeratures. and specific volumes This may be sliowii by a combination of the following excorresponding tb the critical state, together k i t h the point pression with Equation 2 to yield Equation 4: of maximum pressure for existence of two phases and the nlbl f (1 ?%)be ba = nlbl n6b6 (3) cricondentherm are recorded for several compositions in Table 111. These results were obtained by graphical interE = (nlbl - nlb5 bs)T/P - V (4) polation of the volumetric and phase equilibrium data, and it Equation 4 may be differentiated a t constant temperature and is believed that they are consistent with the other results with pressure to yield : uncertainties in the temperature of 0.1 F., in the pressure of 3 ( ~ Z / ~ ~ I=) T(bi, P- b d ( T / P ) - @ V / ~ ~ I ) T , P ( 5 ) pounds per square inch, and in the specific volume of 1 per cent. Consideration of Equation 5 indicates that, as long as the rate of change of the specific volume with composition a t constant temperature and pressure is independent of comm position, the value of by/&^^)^,^ will also be independent E of the weight fraction of methane. The experimentally determined compositions of the dew&&E azo i point gas and the bubble-point liquid are shown graphically w in Figure 5. All of the bubble-point states and a few of the states in the vicinity of the maximum two-phase pressure a t each temperature were ascertained from discontinuities in the first derivative of the isothermal volume-pressure relation. For the most part the composition of the dew-point gas was established from the analyses of samples of the gas phase withdrawn from heterogeneous mixtures. The earlier measurements of Taylor and eo-workers (16) were employed to establish the behavior of the dew-point gas a t 100' and 160" F. I n addition, Dourson (4)made two isolated measurements of the composition of the dew-point gas a t 100" and 160" F. The latter data which were in good agreement with the earlier measurements of Taylor and eo-workers have been included in Figure 5. At temperatures above 160" F. the compositions of the dew-point gas are based almost entirely upon the analytical and volumetric results obtained in the course of this investigation. The loci of the cricondentherm (S), the critical state, and the maximum two-phase pressure are indicated. It is believed that with the exception of points in close proximity to the critical states, the composition of the dew-point gas was determined with an uncertainty of not more than 0.005 weight fraction methane. The information contained in Figure 5 has been employed to establish the dem-point pressure of several of the experimentally studied mixtures a t temperaWEIGHT FRACTION METHANE tures where the discontinuity in the first derivative of the isothermal volume-pressure relation was not sufficiently FIQKJRE 9. PROPERTIES OF THE METHAKE-~-PENTANE great to permit it. detection from the volumetric data. SYSTEM IK THE CRITICAL REGION

+

+


September, 1942

1113

TABLE I. SPECIFIC VOLUMES FOR MIXTURESOF METHANE AND ~ - P E X T A X E Pressure Lb./Sq. I n Absolute

7

0.03114

Weight Fraation Methane as follows: 0.08460 0,16119 0.3857 0.7783 Temperature,

D. P. B. P. 200 400 600 800 1000 1250 1500 1750 2000 2250 2500 2750 3000 3250 3500 3750 4000 4250 4500 4750 5000

(18)b 4.9115 (394.2) 0.02740 0.05886 0.02739 0.02729 0.02718 0.02708 0.02696 0.02684 0.02673 0.02661 0.02651 0.02641 0.02633 0.02624 0.02617 0.02609 0.02601 0.02594 0.02585 0.02577 0.02569 0.02560

(22.5) 4.5979 (952) 0.02927

.....

0,07606 0.04855 0.03532 0.02919 0.02903 0.02885 0.02869 0.02852 0.02838 0.02821 0.02811 0.02797 0.02787 0.02777 0.02767 0.02758 0.02748 0.02738 0.02729 0.02718

(30) 4.1729 (1592) 0.03244 0.31694 0.14835 0.09534 0.06954 0.05434 0.04243 0.03463 0.03223 0.03191 0.03164 0.03139 0.03115 0,03095 0.03075 0.03055 0.03038 0.03023 0.03008 0.02994 0.02984 0.02972

0,9248

--

0.03114

looo F.

(67) 2.8182 (2368) 0.04767

.....

0.35926 0.23061 0.16780 0.13068 0.10142 0.08219 0.06864 0.05856 0.05078 0.04652 0.04493 0.04378 0.04282 0,04204 0.04130 0.04068 0.04012 0.03961 0.03917 0.03872

(515) 0.55247 (1500) 0.16526 1.6016 0.72627 0.46724 0.33993 0.26481 0.20512 0.16528 0.13808 0.11893 0.10522 0.09496 0.08719 0.08111 0.07632 0,07248 0.06934 0.06668 0.06439 0.06244 0.06067 0.06903

... ..... 1.7220

0.84112 0.54800 0,40196 0.31484 0.24586 0.20080 0.16947 0.14668 0.12959 0.11661 0.10646 0,09845 0.09200 0.08674 0.08234 0.07870 0.07556 0.07285 0,07043 0.06832

(49) 1.9008 (465.8) 0.02926 0:035O1 0.02917 0.02899 0.02884 0.02864 0.02846 0.02830 0.02816 0.02802 0.02788 0.02775 0.02763 0.02749 0.02738 0.02726 0.02715 0.02705 0.02695 0.02683 0.02673

Weight Fraction Methane as follows: 0.08460 0.16119 0.3857 0.7783 Temperature, 160' F. (61.2) (82.4) (182) 2.8102 1.6112 1.1129 (1069) (1740) (2337) 0.03157 0.03587 0.05911 0.41333 ..... o:Oi)ii4 0.18094 0.43562 0.11486 0.27565 0.05963 0.08357 0.19992 0.04351 0.06544 0.03153 0.15565 0.05131 0,12112 0.03136 0.04209 0.09863 0.03105 0.03586 0.08269 0.03076 0.03524 0.03052 0.07091 0.03469 0.03029 0.06135 0.03422 0.03009 0.05644 0.02990 0.03383 0.05341 0.02973 0.03348 0.05116 0.03316 0 02955 0.04933 0.03285 0.02937 0.04784 0.02923 0.03260 0.04659 0.03237 0.02908 0.04563 0.02894 0.03216 0.04463 0.03193 0.04384 0.02880 0.02867 0.03173 0.04315 0.03154 0.02856 0.04251

Temperature, 220' F.

D. P. B. P. 200 400 600 800 1000 1250 1500 1750 2000 2250 2500 2750 3000 3250 3500 3750 4000 4250 4500 4750 5000

.....

B. P,

..... .....

200 400 600 800 1000 1250 1500 1750 2000 2250 2500 2750 3000 3250 3500 3750 4000 4250 4500 4750 5000

1.6801 0.82256 0.53705 0,39479 0.30998 0,24290 0.19905 0.16836 0.14594 0,12918 0.11637 0.10629 0.09821 0.09169 0.08634 0.08188 0.07815 0.07497 0.07221 0.06979 0.06765

..... 1:9227 0.94734 0.62268 0.46086 0.36420 0.28736 0.23674 0.20116 0.17494 0.15507 0.13956 0.12724 0.11728 0.10917 0.10251 0.09689 0.09217 0.08810 0.08455 0.08141 0.07859


0 .'04625 0.03169 0.03138 0.03110 0.03077 0.03047 0.03020 0.02996 0.02975 0.02955 0.02937 0.02919 0.02902 0.02884 0.02867 0.02852 0.02836 0.02821 0.02805 0,02791

D. P.

aoo

.....

(111) 0.86255 (542.6) 0.03177


400 600 800 1000 1250 1500 1750 2000 2250 2500 2750 3000 3250 3500 3750 4000 4250 4500 4750 500U

....

0.9248

0 :Ob264 0.04203 0.03972 0.03788 0.03676 0.03585 0.03512 0.03453 0.03402 0.03356 0.03316 0.03279 0.03246 0.03216 0.03189 0.03163 0.03137 0.03116 0.03090

.....

...... *... .....

0.07981 0.06001 0,05161 0,04728 0.04446 0.04248 0.04094 0.03977 0.03884 0.03808 0.03740 0.03679 0.03623 0.03570 0.03522 0,03477 0.03438

(625) 0.1504 (1025) 0.06605 0.68963 0.29820 0.16221 0.09549 0.06689 0.05256 0.04677 0.04373 0.04174 0.04025 0.03911 0.03818 0.03744 0.03677 0.03622 0.03572 0.03529 0.03489 0.03448 0.03418 0.03380 0 83246 0.38916 0.24094 0.16761 0.12485 0.09321 0.07531 0.06451 0.05781 0.06335 0.05016 0.04770 0 04588 0.04436 0.04310 0,04206 0.04116 0.04037 0.03968 0.03902 0.03845

..... 0 : Si6b4 0.40123 0.24612 0.16911 0.12472 0.09286 0.07478 0.06432 0.05755 0.05312 0.04993 0.04760 0.04578 0.04429 0.04308 0.04207 0.04121 0.04040 0.03971 0.03912 0.03859

..... ..... 1.3662

0.66715 0.43559 0.32006 0.25119 0.19668 0.16101 0.13632 0.11844 0.10524 0.09515 0.08728 0.08102 0.07597 0.07180 0.06832 0.06537 0.06285 0.06068 0.05879 0.05715

Temperature, 460' F. 1.0255 1.5892 0.49192 0.78614 0.31515 0.51884 0.22770 0.38556 0.17612 0.30597 0.13588 0.24269 0.11065 0.20096 0.09342 0.17151 0.08182 0.14976 0.07329 0.13326 0.06701 0.12036 0.06222 0.11011 0.05861 0.10179 0.05565 0.09493 0.05327 0.08921 0.05131 0.08434 0.04960 0.08020 0.04819 0,07662 0.04695 0.07352 0.04585 0.07078 0.04488 0.06838


.....

.....

2: 2033 1.0966 0.72773 0.54342 0.43305 0.34515 0.28695 0.24574 0.21497 0.19161 0.17298 0.15789 0.14548 0.13519 0.12654 0.11921 0.11281 0.10723 0.10234 0.09799 0.09418

2: b i b 3 1.2513 0,83202 0.62269 0.49788 0.39745 0.33117 0.28411 0.24904 0.22201 0.20063 0.18323 0.16895 0.15703 0.14698 0.13835 0.13086 0.12435 0.11864 0.11350 0.10902

2.6431 1.2703 0.84610 0.63426 0.60741 0.40617 0.33902 0.29126 0.25561 0.22809 0.20616 0.18836 0.17367 0.16134 0.15088 0.14191 0.13415 0.12733 0.12129 0.11588 0.11167

2.8958 1.4480 0.96567 0.72477 0.58045 0.46157 0.38874 0.33430 0.29365 0.26218 0.23720 0.21675 0.19991 0.18576 0.17375 0.16331 0.15433 0.14647 0.13954 0.13335 0.12784

..... .... ,... .... .....

0,07238 0.05278 0.04564 0.04247 0.04048 0.03902 0.03797 0.03709 0.03638 0.03577 0,03524 0.03474 0.03430 0.03391 0.03386 0.03324 0.03294 0.03264

..... 0.76568 0.34749 0.20573 0.13654 0.09759 0.07216 0.05953 0.05281 0.04879 0.04608 0.04410 0.04255 0.04134 0.04034 0.03947 0.03874 0.03808 0.03746 0.03687 0.03638 0.03593

.....

.....

.....

1.47827 ,....

0.94685 0.44793 0.28259 0.20087 0.15278 0.11606 0.09359 0.07913 0.06942 0.06293 0.05815 0,05460 0.04972 0.051?39 0.04796 0,04650 0,04523 0.04413 0.04320 0.04235 0.04161

0.72764 0.47793 0.35350 0.27925 0,22030 0.15430 0.18148 0.13447 0.11961 0.10812 0.09901 0.09162 0.08567 0.08059 0.07640 0.07283 0.06978 0.06711 0.06478 0.06275

.... 2: i737 1.1839 0.78733 0.58925 0.47064 0.37602 0.31325 0.26869 0.23549 0,20987 0.18965 0.17328 0.15974 0.14847 0.13894 0.13075 0.12361 0.11734 0.11182 0.10693 0,10260

0 Figures in parentheses are bubble-point or dew-point pressures expressed as pounds per square inch.

... 2: 7034 1.3501 0,89927 0.67416

0.53934 0.43175 0.36030 0.30932 0.27164 0.24236 0.21906 0.20015 0.18461 0.17154 0.16046 0.15093 0.14265 0.13546 0.12912 0.12385 0.11858


1114

OF COEXISTING LIQUIDAND GASPHASES IN TABLE 11. PROPERTIES PENTANE SYSTEM

Pressure Lb./Sq. 1;. Abs.

Compn., Wt. Fraotion Methane Liquid Gas

Sp Vol. Cu. F t . / d b . Liquid Gas Temperature,

15.6gn 20 40 GO 80 100 150 200 300 400 600 800 1000 1250 1500 1750 2000 2250 2455b

0.00000 0.00033 0.00191 0.00346 0.00499 0.00656 0.01056 0.01462 0.02300 0.03166 0.04990 0.06927 0.08993 0.11763 0,14822 0.18438 0.23402 0.31785 0.5094

0.0000 0.0555 0.2419 0.3592 0.4404 0.4995 0.5972 0.6522 0.7175 0.7538 0.7863 0.7957 0.7989 0.7957 0.7800 0.7560 0.7200 0.6600 0.5094

0.02634 0.02635 0.02639 0.02645 0.02650 0.02656 0.02669 0.02683 0.02711 0.02742 0.02804 0.02873 0.02947 0.03053 0.03184 0.03358 0.03640 0.04222 0.05985

42.48a 60 80 100 150 200 300 400 600 800 1000 1250 1500 1750 2000 2250 23386

0.00000 0,00120 0.00257 0.00396 0.00750 0.01109 0.01838 0.02596 0.04224 0.05940 0.07753 0.1020 0.1292 0.1631 0.2110 0.3066 0.4219

0.00000 0.07976 0,1542 0.2153 0.3304 0.4090 0.5009 0.5647 0.6165 0.6427 0.6516 0.6497 0.6368 0.6137 0.5689 0.4935 0.4219

0.02812 0.02816 0.02820 0.02825 0.02838 0.02851 0.02878 0.02907 0.02971 0.03043 0.03124 0.03242 0.03390 0.03600 0.03961 0.04950 0.06432

94.91" 100 150 200 300 400 600 800 1000 1250 1500 1750 2000 2081)

0.00000 0.00033 0.00358 0.00686 0.01368 0.02074 0.03592 0.05217 0.06932 0.09300 0.1207 0.1573 0.2247 0.3115

0.00000 0.01057 0.09887 0.1659 0.2611 0.3255 0.4087 0.4525 0.4678 0.4721 0.4615 0.4111 0.3900 0.3115

0.03027 0.03028 0.03043 0.03058 0.03091 0.03125 0.03204 0.03294 0.03396 0.03557 0.03766 0.04106 0.05008 0.06543

185.55" 200 300 400 600 800 1000 1250 1500 16105

0.00000 0.00096 0.00771 0.01456 0.02884 0.04439 0.06217 0.0896 0.1327 0.1948

0.00000 0.01345 0.08894 0.1431 0.2159 0.2608 0.2859 0.2851 0.2509 0.1948

0,03336 0.03341 0.03390 0.03440 0.03548 0.03676 0.03837 0.04132 0.04880 0.06572

329.160 400 600 800 1000 1025b

0.00000 0.00523 0.02031 0.03873 0.07140 0.08512

0.00000 0.02261 0.0794 0.1095 0.1013 0.08512

0.03891 0.2139 0.03962 0.1918 0.04190 0.1544 0.04536 0.1232 0.05806 0.08216 0.06620 0.06620

L%:ftr;;. Methane

Pentane

.

looo F.

6.079 4.764 3.703 3.024 2.553 2.207 1.648 1.305 0.9198 0.7080 0.4723 0.3478 0.2717 0.2097 0.1660 0.1340 0.1088 0.08611 0.05985

0 1.5 23 43 63 82 130 177 270 360 534 701 861 1052 1232 1400 1548 1677 1773

15.10 15.1 15.2 15.2 15.2 15.3 15.5 15.7 16.3 16.8 17.4 17.8 17.9 17.4 17.4 17.8 18.1 19.0 20.2

Temperature, 160' F. 1.973 1.798 1.633 1.495 1.236 1.048 0.7878 0.6275 0.4418 0.3333 0.2626 0.2031 0.1619 0.1305 0.1038 0.07838 0.06432

0 21 40 58 105 152 245 336 516 691 855 1053 1260 1430 1594 1757 1814

39.11 38.8 38.6 38.5 38.4 38.4 38.7 39.1 40.1 40.9 41.3 41.5 41.6 41.9 42.6 44.0 44.5

Temperature, 220° F. 0.8944 0.8820 0.7764 0.6918 0.5645 0.4734 0.3587 0.2822 0.2247 0.1739 0.1382 0.1106 0.08414 0.06543

0 6 52 99 191 282 462 636 808 1020 1212 1390 1564 1620

82.02 81.9 81.9 81.9 81.8 81.9 82.4 83.6 85.0 86.8 88.8 91.5 95.0 96.4

Temperature, 280' F. 0.4379 0.4285 0.3701 0.3231 0.2532 0.2051 0.1680 0.1276 0.09102 0.06572

0 12 104 194 375 550 720 914 1100 1182

148.0 148.0 148.3 148.5 149.0 149.3 149.8 152.0 155.6 157.6


a

0 55 208 358 506 622

238.68 238.1 236.6 236.2 236.8 236.9

Vapor pressure n-pentane.

b Critical state.

TABLE111. Wt . Fraction Methane 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

--

PROPERTIES O F METHANE-?%-PENTANE SYSTEM I N

-

Critical State Pressure Sp. vol. lb./sq. in'. cu. ft./ld. 387.4 494.2 0.0699 332.0 1115.0 0.0654 277.5 1635.0 0.0658 225.4 2043.0 0.0684 173.8 2300.0 0.0649 106.4 2445.0 0.0605

Temp.,

F.

...

...

... ...

... ...

Temp., F. 387.4 344.0 309.0 275.7 243.0 209.8 176.0 141.0

CricondenthermPressure Sp vol. lb./sq. in: cu.h./ld. 494.2 0.0699 862.0 0.1039 1042.0 0.1272 1127.0 0.1502 1160.0 0.1734 1152.0 0.1979 1114.0 0.2249 1074.0 0.2548

Vol. 34, No. 9

From the composition and specific volume of the coexisting phases the compressibility factor may be calculated. This variable is shorrn Equilibrium Constant for bubble-point liquid and denMethane Pentane point gas for a number of temperatures in Figure 6. The compressibility factor of the dew-point 1.0000 140 :84 0.7920 gas increases with an increase in the 70.58 0.4142 weight fraction of methane until 47.09 0.2884 35.38 0,2253 compositions approaching that of 28.34 0.1877 18.98 0.1367 the cricondentherm are reached. 14.30 0.1131 This increase in the compressibility 0.08901 9.603 0.07766 7.273 factor occurs even though the de0.07047 4.933 3.773 0.07204 crease in the weight fraction of pen0.07649 3.078 tane along the dew-point curve is 0,08638 2.524 2.143 0.1052 associated with a rapid increase 0.1350 1.851 0.1889 1.590 in pressure. The loci of the critical 1.325 0.3181 state, the cricondentherm, and the 1.0000 1.000 point of maximum pressure for tvio phases are included in Figure 6. 1.0000 The values for the compressibility 52 : 33 0.7234 39.26 0.5559 factor for pure pentane shown were 31.42 0.4556 taken from an earlier study (13). 0.3211 20.98 0.2555 15.76 The influence of pressure and 10.54 0.1967 7.928 0.1696 temperature upon the phase be0.1456 5.308 havior of the methane-n-pentane 0.1412 4.024 3.258 0.1465 system is portrayed in Figure 7. 2.641 0.1617 2.213 0.1900 The dew-point and bubble-point 0.2304 1.878 curves of four of the experimentally 1.567 0.3176 1.224 0.5552 studied mixtures, as well as the 1.0000 1.000 vapor pressure curve for n-pentane (IS), are shown. The loci of the 1.0000 critical state, the cricondentherm, 3i:j17 0.9555 and the point of maximum pressure 20.81 0.6804 15.65 0.5442 are included. Intersections of deu-10.45 0.4103 0.3455 7.870 point and bubble-point curves 5.272 0.2842 correspond to states a t which nia3.971 0.2645 3.181 0.2695 terials of the two compositions con2.538 0.2909 0.3333 2.080 cerned can coexist. 1.709 0.4044 From the compositions of the 1.311 0.5944 1.000 1.0000 coexisting phases the "gas-liquid equilibrium constant" was computed, and values are recorded in 1.0000 13:37 0.9463 Table 11. For graphical presenta9.036 0.7192 tion it is advantageous in the case 6.885 0.6089 4.695 0.5065 of the more volatile component to 3.550 0.4674 2.799 0.4636 employ the product of the equilib2.093 0.5165 rium constant and the pressure 1.474 0.6736 1.000 1.0000 as the dependent variable. The influence of pressure upon this quantity is indicated in Figure 8. 1.0000 4:66l 0.9276 The lower limit of the two-phase 3.268 0.7877 region a t each temperature corre2.322 0.7606 1.309 0.8931 sponds to the value of the vapor 1,000 1.0000 pressure of n-pentane while tile upper limit is the critical state. The data a t 340" F. were not established in sufficient detail to ascertain the THE CRITIC.4L REGION influence of pressure upon -hfax. Pressurethe equilibrium constant Temp., Pressure Sp vol e F. lb./sq. in: cu. it./ld: with great accuracy, aiid 387.4 494.2 0.0699 for this reason a portion 275.5 1338.0 0.0417 181.2 1965.0 0,0408 of the isotherm is sh0n.n 130.0 2240.0 0.0443 as a dashed line. The 100.0 2387.0 0,0487 ... ... ... general type of behavior ... ... ... ... ... found in Figure 8 corre... sponds to that encountered

THE

METHANE--~L-


September, 1942

TABLE Iv.

EKTHALPY

Pressure, Lb./Ss. In. Abs. 0 03114 I

0 200 400

600 800 1000 1250 1500 1750 2000 2250 2500 3000 3500 4000 4500 5000 0 200 400 600 800 1000 1250 1500 1750 2000 2250 2500 3000 3500 4000 4500 5000 0 200 400

600 800 1000 1250 1500 1750 2000 2250 2500 3000 3500 4000 4500 5000

0 60205 0.00215 0.80223 0.00230 0.00236 0.00241 0.00246 0.00250 0.00255 0.00258 0.00232 0.00271 0.00275 0.00279 0.00281

.....

..... o:o6iig

0.00152 0.00164 0.00177 0.00187 0.00195 0.00205 0.00212 0.00220 0.00231 0.00242 0.00261 0.00260 0.00268

..... ..... .....

-0.00409 -0.00300 -0.00192 -0.00105 0.00039 0.00011 0.00049 0.00077 0.00120 0.00152 0.00174 0.00186 0,00198

-

..... ..... ..... ..... ..... .....

.....

..... ..... .....

0.00173 0.00187 0.00200 0.00215 0.00229 0.00239 0.00253 0.00262 0.00270 0.00276 0.00275

..... ..... ..... ..... ..... ..... 0.00059

0.00095 0.00122 0.00145 0.00160 0.00170 0.00195 0.00214 0.00230 0 00242 0:002'50

9 0,00111 0.00139 0.00172 0.00199 0.00211 0.00229 0.00242

.....

.....

-0,00685 -0.00349 -0.00130 -0.00010 0.00065 0.00106

.

.

-0.00071 -0.00015 0.00029 0.00062 0.00111 0.00145 0.00173 0,00200 0.00213

-0.00092 0.00015 0.00076 0.00118 0.00150 0.00175

.....

-0.06009 -0.08170 -0,11772

.....

. .. ..

-0.02965 -0.01681 -0.01045 -0,00695 -0.00496 -0.00355 -0.00158 -0.00040 0.00035 0.00085 0.00125

Temperature, 340- F . -0,03819 -0.02590 -0.04195 -0.02615 -0,04650 -0.02629 -0,02625 -0.02601 -0.02555 - o ; O i i k -0.02452 -0.03030 -0.02301 -0.02269 -0.02113 -0,01729 -0.01903 -0.01295 -0.01690 -0.00969 -0,01486 -0.00545 -0,01136 -0.00309 -0.00840 -0.00161 -0,00620 -0.00065 -0.00445 -0.00300 -0.00002

..... . . . ..

-

-0.00016 0.00046 0.00100 0.00147

-0.00188 - 0.00077 0.00000 0.00060

0 . 0 0 0 8 ~ -0.00378 0.00136 -0.00215 0.00175 -0.00109

-0.02532 -0.02514 -0.02480 0.02486 -0.02374 -0.02304 -0.02202 -0.02085 0.01950 -0.01804 -0.01659 0.01518 0,01260 -0.01017 -0.00795 -0.00605 0.00445

-

-0.02023 - 0.02005 -0.01985 -0.01960 -0.01926 -0.01886 -0.01828 -0,01758 -0.01682 -0.01601 -0.01510 -0.01$13 -0.01205 0.00989 -0.00796 -0.00649 -0.00532

-0.03430 -0.03886 -0.04389 -0.04972 -0.05390 -0.05322 -0.04495 -0.03265 -0.02260 -0.02368 -0.01295 0.00857 -0.01705 0.00607 -0.01215 0.00441 0.00895 -0.00504 -0.00230 -0.00097 -0.00275 0.00003 -0.00145 0.00061 0.00068 0.00130 -0.00003

Temperature, 460' F. -0.02742 -0.01920 -0.02831 -0.01920 -0.02896 -0.01918 -0.02921 -0.01903 -0.01853 0.02899 -0.01883 0.02820 -0.02655 -0.01802 -0.02428 -0.01735 -0.02162 -0.01645 -0.01875 -0.01528 -0.01588 -0.01383 -0.01315 -0.01230 -0.W865 0.00965 -0.00543 -0.00761 -0.00339 -0.00698 -0.00210 -0.00468 -0.00112 -0.00350

Temperatui 'e, 280' F. 0.02875 -0.03002 -0,03135 ..... -0.03265 -0.03379 -0.03432 -0.03270 -0.02975 0.02595 o oiibz 0.02200 -0.01025 0.00738 -0.01862 -0.01670 -0.00527 -0.01105 -0.00269 -0.00770 -0.00119 0.00528 -0.00021 0,00353 0.00042 0.00095 -0.00228

-0.01805 0.01804 -0.01796 -0.01785 -0.01767 -0.01744 0.01703 -0.01649 0.01576 -0.01487 -0.01382 -0.01273 -0.01072 0,00897 -0.00729 -0.00572 -0.00435

-0.01597 -0.01686 -0.01571 -0.01551 -0.01525 0,01492 -0.01443 0.01385 -0.01319 -0.01247 -0.01174 -0.01096 -0.00948 0,00807 -0.00675 0.00555 0.00450

..... -0,01033

-0.00617 -0.00359 -0.00180 -0.00069 0.00001

.... .... .... .... .... ....

..... . --0.00305 0.00450 -0:oiiio -0.01433 -0.00200 0.00940 -0.00052 0.00029 - 0.00603

..... ..... ..,.. ..... ..... ..... ..... ..... - 0,00940 ..... -43.00635 -0.00419 0.00271 -0.00166 -

..... ..... f . . . .

.. , . .

-0,02965 -0.02801 -0.02597 -0,02342 -0 02050 -0.01489 -0.01022 -0.00717 -0.00512 -0.00365

.....

-0.01713 -0.01026 -0.00674 -0.00453 -0.00304 -0.00196 -0.00116 -0.00057 0.00024 0.00076 0.00112 0.00140 0.00165

-0.02696

-0.02303 -0,02214 -0.02110 -0.01990 -0.01859 -0.01777 -0.01714 -n...0139~ 0.01409 .-. .. -0.01058 -0.oiii5 - 0.00787 -0.00875 0.00580 0.00708 -0.00148 -0.00570

..... - 0.02539 - 0.02367 ..... ..... -0.02179 -0.01980

.

--0.00138 0.00210

-

-

-

-

--

-

-

-

-

..... .....

f . . . .

..... ..... .....

--

-

-

-

-

-

--

-

-0.01380 -0.01385 -0.01385 -0,01385 -0.01376 -0.01366 -0.01345 -0.01314 -0.01270 -0,01215 -0.01146 -0.01067 -0.00907 -0.00766 -0.00632 -0.00502 -0.00389

-0.01282 -0.01274 -0.01265 -0.01251 -0.01231 -0.01204 -0.01166 -0.01121 -0,01069 -0.01014 -0.00959 -0.00896 -0.00780 -0.00664 -0,00556 -0.00453 -0 00360

-0.01122 -0.01129

-0.01083 -0.01075

-0,01134 -0.01135 -0.01134 -0.01130 -0.01119 -0.01101 -0.01068 -0.01025 0.00970 - 0.00907 -0.00782 - 0.00664 - 0.00547 -0.00441 -0.00345

-

-0.00955 -0.00966 - 0.00974 -0.00979 - 0.00980 0.00977 0.00971 -0.00951 0.00927 0.00892 -0.00849 -0.00797 -0.00585 -0.00689

-

--0.00485 0.00392

-0.00307

-0.01062

-0.01031 0,01048 -0.01012 -0.00981

-n.. 00948 .. - -

-

0.00910 - 0.00866 -0.00818 -0.00667 -0.00770

-

0.00566 -0.00473 -0.00380 0,00289

-0.00947 -0.00942 -0.00931 -0.00917 - 0.00901 0.00880 0.00854 -0.00824 -0.00790 -0.00756 -0.00713 -0.00674 -0.00592 0.00500 0.00415 0.00326 - 0.00240

-

-

-

Enthalpy Enthalpy is an important thermodynamic function from an engineering standpoint, and i t is desirable to be able to predict such properties for multicomponent hydrocarbon systems. The volumetric data recorded in Table I permit the evaluation of the isothermal enthalpy-pressure derivative by the application of the following expression:

- T(bV/aT)p,n = T(dV/bT)p,n - TL

-0.04060 -0.03150 ..... ..... -0,04619 -0.03350 -0.05264 -0.03555 ..... -0.06043 -0.03735 ..... -0.06400 ..... -0.06330 -0.03880 ..... 0.03910 -0.01950 -0.04200 -0.03565 -0.01138 -0.02715 0.03035 -0.02475 - 0.00739 -0.01807 -0.01253 -0.00486 -0,01971 -0.01555 -0.00892 -0.00331 0.00228 - 0.00645 -0.01229 -0.00360 -0.00096 -0.00760

7

0.9248

-

in other binary hydrocarbon systems containing methane. The influence of composition upon the pressure, temperature, and specific volume corresponding to the critical state, the cricondentherm, and the point of maximum pressure is indicated in Figure 9.

(aH/aP)~,n= V

Weight Fraotion Methane as Follows: 0.08450 0.16119 0.3857 0.7783

-

-0.00168 -0.00098 -0.00039 0.00010 0.00081 0.00129 0.00166 0.00193 0.00219

.....

..... .

.

......

-0.03200 -0.03167 -0.03126 -0.03070 -0.03006 -0.02929 -0.02817 -0.02678 -0.02515 -0.02325 -0.02120 -0.01899 -0.01476 -0.01147 -0.00886 -0.00679 -0.00506

PER P O U N D / P O U N D PER

Temperature, 400' F. -0.02110 -0.02111 -0.02111 -0.02109 -0.02095 -0.02071 -0.02016 -0.01924 -0.01803 -0.01657 -0.01500 -0.01343 -0.01050 -0.00813 -0.00460 -0.00276 0.00621 -0.00152 -0.00468 -0.00069 0.00335

.....

.....

-0,03410 -0.03380 -0.03340

-0.03110 -0.02583 ..... -0.02556 ..... -0.03090 0.03055 -0.02524 ..... 0.03002 -0.02483 ..... -0.02926 -0.02435 ..... ..... -0.02832 -0.02381

.... .... .... .... .... .... .... .....

..... ..... .....

..... I

7

0.03114


Temperature, 22' F. -0,03075 -0.03565 -0.04779

..... .....

- 0,00030

0

200 400 600 800 1000 1250 1500 1750 2000 2250 2500 3000 3500 4000 4600 5000

..... .....

..... ..... ..... .....

.....

-

0.9248

TemDerature. 100' F.

..... .....

..... ..... 0.00000 0.00027 0.00060 0.00087 0.00112 0.00130 0.00149 0.00163 0.00185 0.00200 0.00217 0.00230 0.00235

PRESSURE COEFFICIENTS FOR MIXTURES OF METHANE+-PENTANE, I N B. T. u. SQUARE INCH

Weight Fraction Methane as Follows: 0.08450 0.16119 0.3857 0.7783

.....

1115

(6)

The values of the isothermal enthalpy-pressure derivative evaluated graphically from Equation 6 were smoothed with respect to pressure and temperature for each of the mixtures studied experimentally, and the results are recorded in Table IV. It is believed that the values given do not involve uncertainties greater than 5 per cent, except in the immediate vicinity of the critical state where the uncertainty is somewhat larger. The influence of pressure upon the isothermal enthalpy-pressure derivative of a mixture containing 0.9248 weight fraction methane is shown in Figure 10. The enthalpy of these mixtures may be estimated from the enthalpies of the components a t infinite attenuation (11, 13) and the data of Table IV, by application of the expression:


1116

Vol. 34, No. 9

has made possible the prosecution of this work. L. Fay Prescott, Louise 111.Reaney, and Betty R. Camomile assisted in the calculations necessary for the preparation of the data. Lee T. Carmichael assisted n-ith the laboratory measurements.

Nomenclature = specific gas constant = enthalpy, R t . u./lb. K = equilibrium constant 7~ = weight fraction of a component in the

b

H

system

P = pressure, lb.,/sq. in. abs. T = thermodynamic temperature, O R. T' = specific volume, cu. ft./lb. 6' = residual specific volume = b T / P - V ,

-

cu. ft./lb.

2 = compressibility factor

,

3000

2000

300

PRESSURE

IN

ISOTHERLIAL ~,S-rrI.~LPl--PRESSuREDERIVATIVE FOR A

FIGURE 10.

H

LE P E R S Q

4000

COXTAIXISG 0.9248 WEIGHT

=

H:ni

+ H:ni, + J p

FRACTIOK bIETH.4XE

(aH/dP)TdP

(7)

It should be realized that enthalpies obtained in this fwsliion are based upon the same datum states as are those of tile components which, for the sake of convenience, should both be taken as zero a t the same datum state. Fugacity

hf ISTCIZE

Superscripts " = two-phase region * = at infinite volume for the pure component Subscripts a = an average value b = bubble point d = dew point 1 = methane 5 = n-pentane

Literature Cited (1) Boomer, Johnson, and Piercey, Can. J . Research, B16, 319 (19381. (2) Budenholzer, Sage, and Laoey, ISD. ENG.CHEM.,31,369 (1939). (3) Cummings, Stones, and Volante, I b i d . , 25, 728 (1933). (4) Dourson, Sage, and Lacey, Am. Inst Mining Met. Enms., Tech.

sufficient care so that uncertainties in the fugacity of n-pentane greater than 1pound per square inch are unlikely, while the values for methane may be in error by as much as 1 per cent at the high pressures. The results of these calculations are recorded in Table 11. The ratio of the fugacity of methane to the pressure for the two-phase region of this system is portrayed as a function of pressure for several temperatures in Figure 11. These data are of the same general character as was found for the methane-n-butane system (1.9). The fugacity of n-pentane in the coexisting phase is shown as a function of pressure in Figure 12. It is of interest to note that the fugacity of this hydrocarbon in the heterogeneous region of the methanen-pentane system is approximately independent of pressure and primarily a function of temperature. This type of behavior is similar t o that found for n-butane in the heterogeneous region of the methane-n-butane system.

Acknowledgment This experimental program was carried out as a part of the activities of Research Project 37 of the American Petroleum Institute. The authors are indebted to the institute for financial support which

FIGURE 11.

FUGACITY O F METHANEIK THE COEXISTING LIQUID AND PHASES OF THE METHARE-?%-PENTANE SYSTEM

GAS

I N D U S T R I A L A N D ENGINEERING CHEMISTRY

September, 1942

1117

(8) Michels and Nederbragt, Physica, 3, 569 (1936). (9) Pattee and Brown, IND. ENQ.CHEM., 26,511 (1934). (10) Rose-Innes and Young, Phil. Mag.. [5]47, 353 (1899). (11) Sage, Budenholzer, and Lacey, IND.ENQ. C H ~ M32, . , 1262 (1940). (12) Sage, Hicks, and Lacey, Ibid., 32,1085(1940). (13) Sage and Lacey, Ihid., 34,730(1942). (14) Sage and Lacey, Trans. Am. Inst, Mining Met. Engrs., 136, 136 (1940). (15) Sage, Lacey, and Schaafsma, IND.ENO. CHEM.,27,48(1935). (16) Taylor, Wald, Sage, and Lacey, Oil Gas J., 38 (lo), 46 (1939). (17) Young, Sci. Proc. Roy. Dublin SOC.,12, 374 (1910).

500

IS00

1000

PRESSURE

LR PER

sa.

2000 IN.

FIGURIG 12. FUGACITY OF ?+PENTANE I N THE COEXISTINU LIQUID AND GAS PHASES OF TEE METHANE-WPENTANE SYSTEM

EFFECT OF LIGHT ON RIBOFLAVIN SOLUTIONS Effect of Sunlight on Reduced and Unreduced Solutions C . M. O’MALLEY

C. W, SIEVERT

..,.....,

Destruction by sunlight of riboflavin in two extracts of naturally occurring riboflavin and in one solution of the synthetic product were decreased from almost complete destruction to a comparatively small loss, by maintaining the riboflavin in the reduced state with sodium hydrosulfite during exposure to sunlight and reoxidation by air after exposure.

IBOFLAVIN has long been known t o be sensitive to light, and this sensitivity has always necessitated careful precautions in the assay for this vitamin. Connor and Straub (1) published data showing the destruction of riboflavin under various conditions. Every investigator has recognized the necessity for protecting riboflavin from light. However, to the authors’ knowledge the protective qualities of reduction have not been investigated. Data are presented in this paper showing that destruction by sunlight can be substantially prevented by converting the vitamin t o the reduced state. Two extracts of defatted milk solids and one solution of synthetic riboflavin were prepared in 2 per cent acetic acid and adjusted to a pH of 4.5 with sodium acetate. The solutions for the separate experiments were prepared by diluting

R

American Dry Milk Institute, lnc., Chicago, 111.

a suitable aliquot of the extract to 39 cc. I n the cases where the solutions were t o be reduced during exposure, they were made to 38 cc., and 0.5 cc. of hydrosulfite solution (9) was added. All final solutions had a concentration of approximately 0.1 microgram of riboflavin per cc. Of this, 13 CC. were used for the fluorometric readings. All readings were made on a Pfaltz & Bauer fluorophotometer by the procedure of Hodson and Norris (B). Exposure to sunlight was accomplished by placing the solutions in a flat-bottomed round Pyrex dish, 8 cm. in diameter and 4 cm. deep, covered by a Petri dish cover to prevent excessive evaporation. For 30 minutes these units were placed in the sunlight shining through a laboratory window. After exposure, the solutions in which the riboflavin had been reduced were vigorously shaken with access to air to reoxidize the riboflavin. Table I shows that reduced solutions of these extracts, not subjected to sunlight or other treatment and reoxidized by shaking in air, give values in agreement with those of the unreduced solutions. Table I also compares the values of the unreduced solutions before and after exposure to sunlight, and of the solutions before and after exposure where the riboflavin was in the reduced state during exposure. The percentage of the riboflavin remaining after exposure is shown for each case. Table I shows that about 90 per cent of the riboflavin in the unreduced solutions was destroyed by 30-minute exposure to sunlight, but that this destruction was cut to a comparatively small figure when the solutions were treated with hydrosulfite solution before exposure.

Phase Equilibria in Hydrocarbon Systems

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