1563
V O L U M E 2 4 , NO. 10, O C T O B E R 1 9 5 2
cate the extent of these losses and enable an equivalence factor (F)to be applied. Sugar Loqt Lb./Lb. of Original Adsorbent Maximum Average
330 !Or
Mauimum
Bone char W a s h water to sewer Char t o kiln
4 x 0
z o t
Poxdered carbon
0 00042 0 00035 0 00077
0.116
0 00091 0 00064 0 00153 1.07
0 00064 0 9 0 00113 0.522
Using any of the equivalence factors obtained above for destrose chars with the niaxinium loss figures for bone char and the minimum losses for poir-dered carbon, the advantage is with the bone char systems.
:
4CKhOW LEDG%IENT
THRU ZOO I
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1
0"
0"
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Figure 6.
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c.l
m
*
1
H 0"ss;gs u,%
o w * PARTICLE SIZE MICRONS N
1
g 0 g n
Effect of Mesh Size on Decolorizing Efficiency of Bone Char
A question always raised in a discussion of the relative merits of a bone char versus powdered carbon system is the loss of sugar.
I n a char system this loss is the total of sugar in thtl water seirered in the final washing of the char and the sugar contained in char sent to the kilns. With a powdered carbon system the loss is confined to the spent carbon thrown away. Since no equivalrnce factor ( F ) has brcn available, no clear-cut comparison hap been poesihle. Starch hydrolyzates from the neutralization step and subsequent filtration contain a variable amount of fats and Poaps, depending upon the completeness and effectiveness of the processing. These fats and soaps are readily adsorbed on the char or potrdered rarhon and hinder the removal of sugar in the subsrquent sweetening off process. Data collected over a period of 6 months indi-
The virgin bone char samples, B and C, given in Table I, were supplied by Diright Gillette of Refined Syrups and Sugars, Inc., and were obtained by passing virgin bone char over a Sutton, Steele, and Steele clits-ifier. Thr samples represent the lightest and heaviest discards. LITERATURE CITED
(1) Bahcock, -1.B.. Proc. Tech. Sessiou Bone C h n r . Bone ('liar Research Project. Inc.. 19-30 (1949). (2) B a u s , Reni.. Irid. Erig. Chrin., 19, 1296 (1927). (3) Bone Char Research Project. I n c . , Proc. Second Tech. Sessiori Bone Char. 1 5 ~ - 1 3 111951). (4) Cleland, J. E.. and Fetzw, W R., Isn.ENG.CHEM... ~ - . I I . , ED., 13,558 (1941). ( 5 ) Kuowles. H. I., P r o c . T t c i i . S e s n i o i i Bone Char. Bone Char Research Project. Inc., 9-17 (1949). (6) Spencer-SIesde. "Cane Sugar Handbook,'' p. 350, Sew York. John TYiley d Ponu, 1945, (7) Wayne, T. B.. Iiid. Eng. Cherri.. 20, 933--940 (1923). RECEITED for rel-ien. February 29, 1952, Accepted .illgrist 6, 1952. Prcsented in part hrfort, tlir Sugar Indriitry Technicians a t t h e annual meeting
M a s 1950.
Sensitive Method for Determination of Vapor Composition KENNETH AI. SkNCIER', Departnient of Chemistry, T h e Johns Hopkins 1-nirersity, Baltimore, \Id. A sensitive method for determination of the tapor composition of binary mixtures has been developed in order to study vapor-liquid equilibria. The method is illustrated by application to the methanol-carbon tetrachloride system. The greatest sensiti\ it? is obtainable in the dilute range where, for a 1-liter sample at a pressure of 25 m m . of mercurj, as little as 0.0002 mole fraction of methanol in carbon tetra-
THE
present method of analysis of vapor coniposition has been developed primarily t o study solution-vapor equilibria of interacting components in dilute solution ranges hitherto inaccessible. For example, in nonpolar solvents containing less than 0.005 mole fraction of alcohol the est,ent of intermolecaular hydrogen bonding becomes small, but in this concentration region tlw usual physical-chemical analytical procedures begin to fail. Refractive index ( 2 ) has been used to study the methanol-carhon tetrachloride solution-vapor equilibria, but the analJ.sis of the vapor composition has been limited to Concentrations gre:xter 1
Present address. Rroolihaven Xational Laboratory. L-iitun, L. I
,
S
Y.
chloride can be detected with *lo% accuracj; at concentrations greater than 0.002 mole fraction of methanol an accuracy within + l q ~is obtainable. The method is principally intended to investigate association in dilute solution ranges hitherto inaccessible such as hydrogen bonding of alcohols at concentrations hitherto not accessible where intramolecular association becomes small.
than 0.01 mole fraction of methanol. The vapor analysis ?:in OP made by infrared absorption using long cell paths, but suitahle equipment is frequently unavailable. The method of analysis described here is capable of much greater sensitivity than that of density or refractive index, eqircially for systems of interacting components where the deviations are frequently larger for the vapor-liquid equilibria-that is, the slope of the relation of X 2's. concentration for interacting binary systems, where X can be, for example, refractive index, density, or total pressure of the condensed vapor, is frequently much larger for the total pressure relation and especially so in the dilute
1564
ANALYTICAL CHEMISTRY
ranges (Figure 1). Under favorable conditions the present method can analyze a vapor mixture of 0.0002 mole fraction of methanol in carbon tetrachloride within an accuracy of f10%; for 0.001 mole fraction of methanol an accuracy of better than =k1% is attainable. A reproducibility of analysis of about f1% methanol was obtained by analyzing four different vapor mixtures five or six times.
that the slope of the curve aP,/AS,, and therefore the sensitivity of the analysis, is indeed greatest for the most dilute solutions. For this binary mixture higher temperatures provide better discrimination for analysis. I t is also apparent that the accuracy in the range of the broad maximum of the total pressure is less than in the dilute ranges, and more suitable methods may be required for comparable accuracy in this range. There will be ambiguity in the determination of vapor concentration for systems with positive or negative deviations-that is, there exist two concentrations with the same Pi. This difficulty is surmounted in the projected application because the approximate vapor composition is known. APPARATUS
The detailed design of the analysis manometer is illustrated in Figure 2 and its function in the apparatus is shown in Figure 3.
,
0 0
.2 .01
.6 .02 (E) .03
.4 (A)
.8 04
1.0 .05
Na
Figure 1. Calibration Curve for Analysis Manometer for Vapor Mixtures of Tvlethanol and Carbon Tetrachloride A . 0 to 1.0 mole fraction methanol E . 0 to 0.05 mole fraction methanol
The method depends upon obtaining a calibration of the total pressure-concentration relation for the condensed vapor sample in equilibrium with its vapor a t a temperature for which the slope of the total pressure-liquid composition function is large. Synthetic vapor mixtures of accurately known composition are condensed into a specially designed manometer, and the total pressure over the condensed vapor sample is measured as a function of concentration. A vapor sample of unknown concentration is analyzed by repeating the process; the measured total pressure of this condensed vapor sample leads to its composition by means of the calibration. The method is one of substitution, so that systematic errors cancel, and the accuracy is limited principally by errors in pressure measurement, temperature control, and preparation of the synthetic vapor mixtures. As an application of the principle and procedure of the method, the methanolcarbon tetrachloride system has been studied. The calibration thus obtained has been used for estensive studies on this system (1).
The calibration data consist of: the mole fraction of methanol, AT,, in the synthetic vapor mixtures with carbon tetrachloride, and the total pressure, P,, in millimeters of mercury above the condensed vapor samples, which has been measured a t 49.340' C. I n Figure 1 these data are plotted in two ranges; on the abscissa range A is 0 to 1.0 and range B is 0 to 0.05 mole fraction of methanol in carbon tetrachloride vapor. Although there is approximately 100-mm. difference in the vapor pressure of pure methanol and pure carbon tetrachloride a t 49" C., because of the large positive deviations of this system, the total pressure change is actually 250 mm. upon addition of only 0.1 mole fraction of methanol. And it can be seen from Figure 1
The analysis manometer is essentially a temperature-controlled closed-end manometer with the condensed vapor sample confined in the lower leg in contact with its equilibrium vapor and a vacuum a plied above the other leg. Provision is made to lower or raise t t e mercury column in order to adjust its height, to evacuate the manometer, or to admit a vapor sample. The inner diameter of both legs of the manometer tubin is large, 1.1 em., to minimize capillary effects, and the height of &e lower leg above the cutoff is about 5 em. The temperature of the entire manometer is controlled to fO.OO1 O C. by circulating temperaturecontrolled water from a bath through a glass jacket that fits around the entire manometer. The constant temperature bath consistp of an insulated 5-gallon jar with a powerful stirrer, two heaters, a Beckman thermometer (calibrated against a Kational Bureau of Standards platinum resistance thermometer), and a toluene-mercury regulator operating a thyratron relay. A Central Scientific pump (catalog numher 17955) operated a t maximum speed is used to circulatethe bathwater. Thisarrangement provides a control of fO.O0loC. a t 49.340" C. The temperature of the circulated water is measured in the bath and not in the jacket, but the difference that may exist is small because of the large diameter of the water hose, its short length, and the high flow rate; any small temperature difference, however, is unimportant because both synthetic and unknown vapor samples are compared under identical conditions. If significant change in the ambient temperature is expected, it is essential for highest accuracy that the jacket temperature beknownandheldconstant. Acathetometer with reproducibility of a single reading of 1 0 . 0 1 mm. is used to read pressure by comparing heights of the mercury menisci with a standard Invar meter stick. The calibration section of the analysis apparatus is used to provide synthetic vapor mixtures. PROCEDURE
The mercury column of the manometer is lowered (stopcocks 11 and 13) and the manometer is evacuated. By flaming the small trap (Figure 2) mercury can be "bumped" out. A 1-liter vapor sample a t a pressure of 25 mm. of mercury for calibration (from 5 ) or for analysis (from 10) is introduced into the analysis section, filling the 1-liter volume to 25 mm. Liquid nitrogen is used to freeze the vapor in the manometer trap. When the pressure is reduced to about 1 micron-pumping (1 and 5 ) is sometimes necessary to remove residual air-the mercury column of the manometer is raised in order to isolate the sample in the lower manometer leg. The glass jacket is lowered in place and rubber stoppers, threaded on the manometer, are fastened a t its ends. The water from the constant temperature, bath, A , is then circulated up through the jacket and back to the bath. \17hen the sample is isolated above the lower manometer leg and a vacuum is applied to the other manometer leg, the pressure can be measured as soon as temperature equilibrium is attained. For this measurement the vapor and liquid space above the lower manometer leg must be the same for all determinations, because the composition of the liquid and the vapor in equilibrium and therefore its equilibrium pressure ill change as material is exchanged between the liquid and vapor phases by changes in vapor volume. This consideration is especially important when the vapor and liquid compositions are very different and when the amount of material in the vapor phase is large compared to t h a t in the liquid phase. In order to reproduce this vapor volume, the
V O L U M E 2 4 , NO. 10, O C T O B E R 1 9 5 2 mercury column was adjusted ( I 1 and 13) so that the mercury meniscus was always a t ho (Figure 2) as determined by the cathetometer. This adjustment can usually be made t o within 10.05 mm., and an interpolation from several neighboring heights can be made. CALCULATION
From the cathetometer readings hot h,, and h2 are calculated ( h ? - ho), the difference in the heights of the mercury menisci, and ( h , - ho), the height of the liquefied vapor sample whose density is p . The desired pressure, Pt, is obtained from the expression :
Pt = (h,
- ho) -
(hi
1565 methanol and carbon tetrachloride are about 100 mm. of mercury, a 2-liter flask would contain about 0.01 mole of each vapor before condensation would occur or 0.32 gram of methanol and 1.6 grams of carbon tetrachloride. The flask is now returned to the manifold, which is then evacuated, and a portion of the va or mixture is admitted t o the analysis section ( 5 ) and condensefin the small trap of the analysis manometer according to the procedure previously described. The methanol and carbon tetrachloride were thoroughly dried over calcium oxide by refluxing, and the middle half was collected by distillation with a boiling point constant to f0.05' C.
- ho) P/PHg
where P H ~is the density of mercury a t the temperature of the manometer. The second term is a small correction; the value of p is calculated from the knowledge of the pressure (hz - ho) and the corresponding liquid composition taken from the calibration. I n a series of analyses less than 30 minutes is required for one vapor analysis.
' i'
'\,J
CALIBRATION
The calibration section (Figure 3) provides means of preparing synthetic vapor samples. In the receivers below 7 and 8 are stored purified and deaerated methanol and carbon tetrachloride. A weighed soft-glass ampoule is fastened in place below 6 by means of a short rubber tube, and when the manifold and ampoule are evacuated either liquid can be condensed into the ampoule using an ice-water coolant. The ampoule is sealed off and both parts are weighed to determine the weight increase. In this manner a series of am oules is prepared containing accurately known amounts of met anol or earbon tetrachloride from which appropriate mole ratios can be selected. The ampoules are weighed to 10.0001 gram and corrections are applied for the buoyancy effect on the ampoule and the brass weights. The two ampoules that will give the desired mole ratio are placed in the 2-liter flask, which is then evacuated to less than 1 micron. The flask is removed from the manifold by first closing 4 and then breaking taper B. The ampoules are broken by shaking the flask, and mixing of the vapors is hastened by shaking the glass splinters or using a heat lam . The quantity of liquid in each ampoule is adjusted so that t f e partial pressure of the substance in the 2-liter flask a t room temperature is less than its vapor pressure. At about 20' C. where the vapor pressures of
IR
t o v a c u u m or vapor sample
I
I
CH'oH
1
4tr
Rough P"m0
c c 1 4.- - .
.. . . .- . . .. .
I
1
Both
4
'I
Figure 3. Schematic Diagram of Analysis and Calibration Sections of Apparatus for Vapor Analysis
It is of considerable importance to exclude air during an analysis. The presence of air in the vapor to be analyzed causes several undesirable effects: The condensation rate of the vapor is low; after thermal equilibrium is attained the rate of presbure equilibrium is low.; and whatever noncondensable gases are present will be compressed in the lower manometer leg and give a corresponding error, The first two items are sensitive indicators of the presence of air. SUMMARY
- removable Figure 2.
jacket
Detail of Analysis Manometer
The sensitivity of this method of the analysis of vapor composition for a particular system depends primarily upon a large slope of the total pressure-composition function, APtlAN,. Many systems exist that are more favorable for study in this connection than methanol-carbon tetrachloride. Some systems of components apparently with small values of the slope due to small differences in their pure vapor pressuies are adaptable to this method 01' analysis because of large interactions usually due to hydrogen bonding as in the present system. The selection of the proper temperature of the analysis is important in order to obtain the greatest APt/ALV,. For particular systems and conditions, the accuracy obtainable depends primarily upon the quality of temperature control, the pressure measurements, and the calibration. Because the analysis depends upon a graphical calibration, some error is introduced by the interpolations. The calibration curve obtained from synthetic vapor samples does not represent the total pressure above solutions of these compositions, because the liquid phase changes composition when the vapor space above it is filled, unless large amounts of material are used. However, this consideration has no bearing upon the value of a method of analysis which depends upon substitution. The method may also be applied to determine total pressure
1566
ANALYTICAL CHEMISTRY
.-
ahove solutions, provihd that large liquid volumes are used. It criticism of Donald H. .4ndrews of The Johns Hopkins University should then be possible to obtain accurate total pressure-compoand the fellowship award of the Standard Oi' "- -' I' sition data, and such information i8 especially significant because LITERATURE CITED i t is possible to predict vapor-li %I (1) Smeier. K. M., to be published. pressure data. (2) Scatchard, G., Wood, S. E., and Mochel, J. N.. J . An. Cham. Soe. 68, 1957 (1946). ACKNOU
Theauthor wishes to ackuowleuge m z VUUBUIB
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RECEIV for ~ review ~ February 29, 1952. Accepted July 7 , 1952. Based on The Johns Hopkins University. October 1949. in partial fulallmentof the requirementsof P ~ . D degree. .
a thesis submitted to
Manometric Gas Analysis Apparatus - _ JAIlES N. PITTS, JR., DONALD D. DEFORD, ARID GERALD W. RECKTENWALD Department of Chemistry, Northwestern Unieersity, Eoanston, I l l .
,
Although great strides have been made i n recent years i n the development of new and improved methods of gas analysis, most of these methods have the disadvantage of requiring expensive and elaborate equipment and sliilled operators or of being restricted to the determination of a particular gas i n a narrow oonocntration range. The work reported i n this paper was undertaken to develop an inexpensive, aocurate, and versatile gas analysis apparatus which could be operated with a minimum of training and effort. An apparatus which requires only 2 to 6 m l . of sample and employs "bead" reagents for selective removal of the various components i n the sample has heen developed. Expensive burets are eliminated by measurementof pressure changes rather than volume changes. The precision and aecuraoy are of the order of +0.2% absolute for oxygen and oarbon dioxide. Despite its simplicity, the apparatus promises to be very useful for accurate analyses of a wide variety of gaseous samples.
I
N TWO comprehensive review articles (6, 7) Nash has sum-
manzed the extensive literature dealing hith recent analytical methods far the quantitative analysis of gases. Much of the ourrent work is concerned with specific instrumental methods based an physical properties suoh as density, thermal conduetivity, and magnetism, and less attention has been devoted to the development of new apparatus employing volumetric or manometric techniques. The instrumental methods have achieved considerable SuccesE in the analysis of two- or threecomponent systems, hut, in general, these methods do not permit a complete analysis of a multicomponent gas sample. Although great progress has heen made in the application of mass spectrometric and infrared techniques to the analysis of multicomponent systems, the high cost of commercial instruments precludes their use in many leborat,ories. A t the present time volumetric procedures based on the removal of the various components by selective ohemieal reactions seem best suited for the analysis of gaseous mixtures with inespensive apparatus. The fundamental design and operntion of macrovolumetric apparatus of the Orsat type (8) is well known, and this type of equipment has been widely used. Recently, Brooks et ai. (8) and many others have devoted considerable attention to refinements in the Orset method. These improvements increase the versatility, accuracy, and precision of the method, but in many cases the speed and simplicity of the hasir Omat unit. hsa been sacrificed. Several excellent microvolumetric analyzers 81%available (1. 5. 9). The constant orensure &vI)aratusof Blacet, and Leigh-
tremely useful under circumstanoes in which only small quantities of gas (0.1 to 0.5 ml.) are available. The B-L method utilizes solid "bead" reagents for the most part, thus eliminating error8 due to undesired absorption of gases in reagent solutions or confining liquids. In the hands of a trained analvst this method is capable of excellent accuracy and precision. However, to obtain results of high accuracy with this apparatus, the operator must he well trained, and i t is us1idly necessary to exercise considerable citie in making the analy:i s . In D rdei to overcome the difficulties inherent in the Orsat-type tus, snd to avoid working appara ~. in the micro range, the authors have developed B simple, versatile, acourate, and inexpensive gas analysis apparatus of the manometric type. Osygen and carbon dioxide may be determined with this instrument, s h a m in Figures 1, 2 and 3, with an average accuracy and precision of the order of 0.2% absolute. A minimum expenditure of time and'effort on the part of t,he analyst is necessary to carry oat the determinations. DESCRIPTION OF .4PPARATUS
The apparatus consists principally of pipet, manometer, and syringe units, each of which is descrihed in detail. Pipet Unit. The essential features of this unit are a reaotion Figure 1. Assembled cup, R, a three-way T Stopcock, Apparatus S. with 1-mm. cavillaw arms. a'water-jacketed pa; pipet, P,of approlrimately 5-ml. volume, and spherical expansion chamber, E, about 3.5 em. in diameter. , ,,, .~~., .L.-.L ..... > / ! ~ ~ , r n e volumes 0 1 m e pipcb aiiu snpauawn c i i i t i i ~ v ~&IC: r noz ormca.~. A small beaker containing mercury is placed beneath the reaction cup; the height of the mercury level in the beaker is adjusted so that. the lower edge of the cup is immersed to a depth of 1to 2 em. The reaction cup is butt-joined to one arm of the stnpoock with Tygon tubing, so that the cup can be replaced reaflily. Components R, S,P, and E are joined with I-mm. borosihate glass capillary tubing. The confining volume of the pipet is indicated by two fiducial marks, Mx and M2, inscribed on the capillary tubing in the positions indicated. The expansion chamber is sealed directly to a 12/3 ball joint, so that the entire pipet Bystem can be removed for cleaning or replaced by another pipet unit. In order to avoid trapping small amounts of sample, it is imnortant that the hore of the plug of stopcock S be sdl aligned with the cspil-
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