INDUSTRIAL AND ENGINEERING CHEMISTRY
72
mony. The potential readings were taken at the end of five minutes as specified by Parks and Beard (5). The butter serum was prepared according to the method of Nissen (4). The results for the different electrometric methods are given in Tables I and 11. DISCUSSION The hydrogen-ion concentration of dairy products may be determined by the glass electrode, the quinhydrone electrode, or the hydrogen electrode with an accuracy which is within experimental error. A decided drift occurs when platinum electrodes are used with quinhydrone, and is especially noticeable with ice cream mix and butter serum. This drift, however, may be eliminated by the use of gold electrodes. The stick antimony electrode determinations were from 0,307 to 0.646 pH units higher than those of the glass electrode. The errors appear to increase with high concentration of serum solids and with the lactic acid content. The effects upon the stick antimony electrode of solutions containing citric acid, lactic acid, and lactose are emphasized in the following experiments. A solution containing 0.235 gram of citric acid per 150 ml. was neutralized with sodium hydroxide to a pH of 3.72 as meas-
Vol. 7, No. 1
ured by the glass electrode. This solution showed a pH of 4.26 by the stick antimony electrode. Another solution containing 2 ml. of c. P. lactic acid per 150 ml. was neutralized with sodium hydroxide to a pH of 3.68 as measured by the glass electrode. This solution by the antimony electrode gave a pH of 4.45. A solution of 5 grams of lactose in 150 ml. showed a pH of 5.86 by both the glass and antimony electrodes. These results indicate that the errors of the antimony electrode in dairy products are due t o citrates and lactates. Since citrate and lactate ions form complexes with antimony in solution, it seems probable that a similar complex formation takes place a t the surface of the antimony electrode. As a result the electrode does not measure the true hydrogen-ion concentration of the solution. LITERATUR~ CITED (1) Bailey, C. H., J.A m . Chena. Soc., 42, 45 (1920). Duncombe, J. Dairy Sci., 7, 86 (1924). Leeds & Northrup Co., Notebook 3.18 (1930). Nissen, B. H., IND. ENQ.CHEM.,Anal. Ed., 3,374 (1931). Parks and Beard, J. Am. Chem. Soc., 54, 856 (1932). Popoff, Kuna, and Snow, J. Phys. Chem., 32, 1059 (1928). Robertson, G. R., IND. ENQ.CHEW,Anal. Ed., 3, 5 (1931). Rosebury, F., Ibid., 4, 398 (1932).
(2) (3) (4) (5) (6) (7) (8)
RECBIVED May 28, 1934.
Routine High-Vacuum Distillation of Oils An Apparatus and Conversion Chart K. M. WATSONAND CHARLESWIRTH, 111, Universal Oil Products Company, Riverside, Ill.
A
GENERALLY standardized method for evaluating apparatus are the adequate size of the vapor delivery tube the boiling points of heavy oils is badly needed for the and the method of connecting the McLeod gage direct to the extension of both the practical and scientific aspects flask to avoid errors due to pressure drop in the delivery tube. of petroleum technology. In addition to the importance of However, in using an apparatus similar to that of Davis and the boiling range as an indication of volatility, it has been Hornberg, it was found impossible to avoid errors due to found (6) that most of the difficultly measurable physical diffusion of small amounts of condensable vapors into the properties of petroleum fractions are better correlated on the McLeod gage. As a result the pressures read were appreciably basis of boiling point than any other easily determined prop- too low, even though the amount of condensate formed was so small as to be invisible. Errors as great as 26.7' C. (80' F.) erty. Various types of equipment have been proposed for opera- were encountered in the boiling points of pure compounds as tion a t pressures ranging from a few hundredths of a milli- determined in this way. Errors due to condensation in the McLeod gage can be meter up to 10 or 20 mm. of mercury. The low pressures have the advantage of permitting the distillation of heavier minimized by careful manipulation, although this procedure stocks without decomposition. On the other hand, operation is both difficult and uncertain. A trap cooled with liquid air a t low pressures increases the difficulty of manipulation and or solid carbon dioxide and placed in the line connecting the uncertainty of converting the observed temperatures to the flask to the McLeod gage was found to eliminate all condensation in the gage. The amount of condensate collected normal boiling points a t atmospheric pressure. The apparatus here described was developed to permit in the trap never exceeds a few tenths of a cubic centimeter operation a t pressures of approximately 0.1 mm. of mercury. and introduces a negligible error in the distillation if suitable As compared to previously proposed methods, it has the precautions are taken. The most important of these is flushadvantage of satisfactory accuracy of pressure measurements, ing the entire McLeod gage and connecting lines with air due to the elimination of condensable vapors in the McLeod before evacuating. The distilling flask is evacuated while the gage, It is also unique in general design through the exten- gage is filled with air a t atmospheric pressure. The air in the sive use of ground-glass connections, which allows a minimum gage is then slowly released into the flask before heat is of difficulty in manipulation and cleaning. A new nomo- applied, sweeping out all vapor and filling the connecting lines graph has also been devised for accurately converting ob- with air. Care is also taken to maintain a constant or diserved temperatures to normal boiling points. As a result of minishing pressure throughout the distillation. the improved convenience of both the chart and apparatus, APPARATUS the method is satisfactory as a routine inspection and has The apparatus finally adopted is shown in Figure 1. been used as such for the past several months with gratifying Special attention was given to obtaining an arrangement easy consistency. Davis and Hornberg (4) recently developed a vacuum to clean and reassemble. For this reason ground-glass joints distillation apparatus using a McLeod gage for accurate were extensively used to minimize the difficulty of keeping the measurement of pressure. Outstanding features of this system vacuum-tight.
January 15, 1935
ANALYTICAL EDITION
The distilling flask, A , is an ordinary round-bottomed flask of 300 cc. capacity to which is sealed the female portion of a 25-mm. interchangeable ground-glass joint. Several of these flasks ma be prepared and used interchangeably. In the inside of the flasg is a row of four sharp points directed downward toward the center, as shown. These points are made by heating a spot on the wall of the flask to redness and indenting it deeply with a
73
A good oil-sealed rotary pump is a satisfactory source of vacuum for work with oils boiling up to 537' C. (lOOOo F.). For operation of the McLeod gage an auxiliary vacuum pump of some type is necessary. A good water-jet filter pump will suffice. Dry air is admitted to the McLeod gage chamber through a calcium chloride drying tube, M. A special compound manufactured by the Merco Nordstrom Valve Company (No. 650 for hot oils, gases, asphalt, and steam) was found satisfactory for lubricating the large ground-glass joint at the top of the flask. It is supplied in small sticks but tends to crumble to a powder. In applying it the joint is coated with a thin layer of ordinary high-vacuum stopcock grease and the powdered lubricant spread on this sticky surface.
MANIPULATION Samples with low initial boiling points are topped in a preliminary distillation a t atmospheric pressure to remove all material boiling below 260' C. (500" F.). I n this procedure a charge of 200 cc. is weighed into a 250-cc. Engler distilling flask and distilled until the vapor temperature reaches 260" C. (500' F.). The amount of bottoms left in the flask is weighed and its specific gravity determined. The percentage bottoms by weight and by volume are calculated. The charge to the vacuum flask is then weighed out from the bottoms to correspond to exactly 100 cc. of the original sample. The vacuum distillation is recorded in volume units, adding the percentage volume overhead in the topping operation to the volumes of distillate recovered. If the sample has no extremely lowboiling material present and shows no noncondensable loss in SCALd L' f ? f f 7 INCHES the topping operation, the calculations may be simplified by FIGURE1. HIGH-VACUUM ENGLERDISTILLATION APPARATUS topping out exactly a round figure volume percentage-for example, 10 or 20 per cent as indicated by the distillate small iile. Although the flask is more difficult to clean, the points are of considerable value in puncturing the large liquid collected. I n starting a distillation the McLeod gage is flashed with air films that tend to rise up into the neck of the flask under many conditions of operation. With this arrangement it is ordinarily and shut off from the rest of the system. The apparatus is not necessary t o use boiling chips or clay to prevent bumping then assembled and evacuated. If the sample contains lowand foaming. The male section of the interchangeable ground-glass joint is boiling materials, trap L is cooled during the evacuation, sealed to the vapor delivery tube, B, the McLeod gage connec- When the pressure indicated by the manometer is less than 1 tion, C, and the thermometer tube, D. The thermometer tube mm., stopcock N is opened, allowing the air in the McLeod terminates in the male section of a ground-glass joint, E. The gage to sweep out the connecting lines. Distillation is female section of the joint is sealed shut to form a cap and the thermometer suspended from a small glass hook sealed to the started when the pressure has reached a fairly steady value in the neighborhood of 0.1 to 0.3 mm. of mercury. center. The cooled condensate trap, F,is joined into the McLeod gage con n e c t i o n by two ground-glass joints. The trap itself is formed to fit loosely into a wide-mouth vacuum bottle of 450 cc. (1 pint) VAPOR PRESSURES capacity. When distilling oils that contain no OF materials boiling below 205' to 260' C. (400" to HYDROCARSONS 500" F.), this trap is satisfactorily cooled with LOW RANGE acetone and solid carbon dioxide. The vapor delivery tube is surrounded by a glass jacket, G, through which water is circulated, and which is sealed directly to the vapor tube. The end of the vapor delivery tube is curved downward, terminating in the male section of a groundglass joint. The female section of this joint issealed to a 100-cc. graduate, H . If desired, a dropping tip, J , may be sealed into the vapor tube above the graduate. This tip makes observation of the initial boiling point easy but complicates cleaning. The vacuum pump line is connected to the vapor delivery tube by means of a short rubber tube connection, K . This one rubber tube connection is used to provide a certain amount of flexibility for assembly. The pump line is joined to the McLeod gage and to a manometer, as indicated. The pump is protected by a cooled trap, L, to condense any light materials which may pass through the condenser a t the beginning of the run. This trap is ordinarily cooled with solid carbon dioxide and acetone only during the initial stages of evacuation. It is then bypassed by means of the two three-way stopcocks. It is not necessary to use this trap when running samples with initial boiling points above 232' C. (450" F.) if the water in the condenser is 15.6' C. (60" F.) or lower. FIGURE2. BOILINGPOINTCONVERSION CHART
74
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 7 , No. 1
of the Brown and Coats chart. This gives a scale which is not logarithmic but gives considerable curvature when pressure is plotted against scale distance on semi-log paper. The deviation from logarithmic of the pressure scale derived in this way changes when different constant-temperature lines on the Brown and Coats chart are used as its basis. For this reason it is impossible to duplicate the entire Brown and Coats chart in nomographic or rectangular coordinates. The temperature scale was derived by laying out a rectangular chart similar to that of Cox but using the empirical pressure scale described above. The temperature divisions were established by drawing a straight line on this chart at a 45" angle and desigj r o 0 m nating it as representing the vapor pressure of the hydrocarbon boiling at 343.3' C. (650" F.). The temperature scale was then marked off from the Brown and Coats chart data for this boiling point. This resulted in a chart similar in appearance to the Cox chart but different in that both pressure and temperature scales are empirically derived. Figure 2 was prepared by laying off the temperature and pressure scales directly from the rectangular coordinate chart described above. The boiling point scale was then established graphically, using the data of the Brown and Coats chart. The nomograph is in good agreement with this chart over the range of conditions encountered in ordinary vacuum distillations. Slight errors are introduced for extremely high- or low-boiling materials, but these errors are probably not greater than the error of the extrapolation to high temperatures in the original chart.
It has been found most satisfactory to operate a t a distillation rate of 2 cc. per minute. Readings of temperature and pressure are recorded corresponding to each 5 cc. of distillate. Fortunately the distillation under high vacuum does not seem to be as sensitive to variations in operating conditions as the ordinary Engler distillation a t atmospheric pressure.
RESULTS
% D/sriLLec
FIGURE3. HIGH-VACUUM AND ATMOSPHERIC ENGLER DISTILLATION CURVES Wide variation in distillation rate and size of Aask caused little change in the results obtained. When operating in the range near 0.1 mm., pressure has no appreciable effect on the final results as long as cracking does not occur. Cracking is indicated by a sudden rise in pressure.
In order to obtain the entire boiling range of a material having an initial boiling point below 260" C. (500" F.), it is necessary to run an ordinary 100-cc. Engler distillation a t atmospheric pressure in conjunction with the vacuum distillation. The distillation is conducted in a 200-cc. Aask using the A. S. T. M. condenser and burner shield, maintaining the distillation rate a t 4 to 5 cc. per minute. The atmospheric pressure distillation is taken as correct for the lower part of the boiling range and the vacuum for the upper. The results given in Table I are typical. TABLEI. RESULTSOF DISTILLATION TOPPIKQ OPERATION
The value of a high-vacuum distillation depends largely on the accuracy of the chart used for converting the observed temperatures to normal boiling points. Various equations and semi-empirical vapor-pressure charts have been proposed, most of which are unsatisfactory except over narrow ranges. The Cox chart (3) is one of the most extensively used, but its accuracy is not satisfactory where large pressure changes are involved. The vapor-pressure lines on the Cox chart are actually curved to a considerable degree, especially for highboiling materials if the chart is laid out from the data on hexane. Coats and Brown (1, 8) have developed a method of correIating and extrapolating vapor-pressure data which, it is believed, is the most logical and reliable now available. Large-scale charts can be obtained from G. G. Brown a t the University of Michigan, covering temperatures from -212 O to 704" C. (-350" to +1300"F.) and pressures fromO.O1 mm. of mercury to 5000 pounds per square inch. Where wide ranges of conditions are involved, it is recommended that this chart be used in preference to any of the other schemes which have been proposed. The only disadvantage of the Brown and Coats chart is that it is somewhat difficult t o read because of the wide range covered and the curvature of the pressure lines. For this reason the nomographic chart shown in Figure 2 was derived from the Brown and Coats chart to expedite routine conversions. The pressure scale of Figure 2 was laid off proportional to the pressure intercepts on the 287.8' C. (550" F.) temperature line
S p . nr. 0.9365 0.9446
Charge Bottoms Distillate
TEMPERATURE CONVERSION
Grams
cc.
187.3 151
200 160 40 00
...
....
Loss
V A C U U J l DISTILLATION-CHARGE,
DIETILLATE
PERCENT OVER
cc. 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75
NORMAL TEMPERATURE PRESSUREB O I L I N Q POINT F. O c. Mm. a c. 150 154 164 174 184 194 204 2 14 225 240 252 277 310 346 390 426
20 25 30 36 40 45 50 55 60 65 70 75 80 85 90 95
76.6 GRAMS
65.6 67.8 73.3 78.9 84.4 90.0 95.6 101.1 107.2 115.6 122.2 136.1 154.4 174.4 198.9 218.9
0.35 0.31 0.28 0.265 0.240 0,220 0.180 0.155 0.135 0.105 0,085 0.084 0.105 0.095 0.120 0.160
251.7 257.2 268.3 276.1 285.0 294.4 304.4 314.4 323.9 338.9 350.0 363.3 387.8 412.8 437.8 457.8
ATMOSPHERIC P R E S S U R E , 100-CC. E N G L E R DISTILLATION
DISTILLATl
cc. 0 5 10 15
20 25 30 35 40
45
TEMPERATURE
' F.
c. 190.0 233.9 243.9 251.1 257.2 262.8 267.8 274.4 281.7 290.6
DISTILLATE
TEMPERATURE F. O c.
cc.
O
50 55 60 65 70 75 80 85 90 95
573 591 612 636 662 686 699 711 719 736
300.6 310.6 322.2 335.6 350.0 363.3 370.6 377.2 381.7 391.1
The two distillation curves are plotted in Figure 3. It will be noted that the lower portion of the vacuum distillation curve is in good agreement with that portion of the atmospheric pressure curve below cracking temperatures. This
January 15, 1935
ANALYTICAL EDITION
close agreement is typical of the results on many different types of stocks and indicates that the method and conversion chart have a satisfactory degree of accuracy in this range. The final distillation curve is plotted by accepting the atmospheric pressure results in the low range and the vacuum in the high range. The time required for a complete vacuum distillation, including assembling and cleaning the apparatus, ranges from 75 to 90 minutes. Additional time is required for the atmospheric pressure distillation and the topping operation if the sample contains light material.
ACKNO WLLE D GME NT The authors are indebted to R.A. Weppner and the analytical staff of the Universal Oil Products Company, particu-
73
larly M. J. Stross, W. K. Simpson, and W. W. Johnstone, for valuable suggestions and assistance. LITERATURE CITED (1) Brown, G. G., Proo. Seventh Annual Convention, Natl. Gasoline Assoo. of America, pp. 59-72 (1928). (2) Coats, H. B., and Brown, a. G., Dept. of Engr. Research, Univ. Mioh., Circ. Series No. 2 (December, 1928). (3) Cox, E. R., IND. ENQ.CHEM.,15, 592 (1923). (4) Davis, A. L., and Hornberg, C. V., Natl. Petroleum News, 25, No. 38, 65 (1933). (5) Watson, K. M., and Nelson, E. E”., IND.ENQ.CHEM.,25, 880 ( 1933). R~CEIVH August ~ D 27, 1934. Presented before the Division of Petroleum Chemistry at the 88th Meeting of the American Chemicd Society, Cleveland, Ohio, September 10 to 14,1934.
Apparatus for Extraction of Solids by Upward Flow of Solvent F. E. HOLMES, St. Bernard, Ohio
I
thus preventing the reduction of hydrostatic pressure on this small experimental animals, a larger apparatus than the side which might otherwise result from boiling of the solvent. A surprisingly low head of liquid is required for upward usual Soxhlet extractor was required. Several difficulties that were encountered when this extraction was attempted flow of solvent. It is considered desirable to stir the meal occasionally durin the apparatus ordinarily available were overcome by the ing extraction to break up any channeling that might have use of the extractor illustrated in Figure 1. It was found that when solvent was made to pass down occurred. This was accomplished more easily in the cylinthrough cottonseed meal, the meal tended to pack so that the drical vessel than in a flask-shaped vessel. flow of liquid through it almost stopped. Holvever, when the CONSTRUCTION OF APPARATUS flow of liquid was reversed, so that it was upward through the meal, the flow continued a t a satisfactory rate indefinitely. The body of the extractor is constructed of Pyrex glass tubing. Even with an upward flow of solvent, the meal caked enough Since it is entirely separate, the inner cylinder may be conto make its removal from the sides of a round vessel through a structed of either Pyrex or ordinary soda-lime tubing. The dimensions of the outside cylinder of the largest extractor used narrow aperture a tedious procedure. This objection was were approximately 6.25 X 55 cm. (2.5 X 22 inches). The overcome in the present apparatus by making the walls center tube had an inside diameter of about 10 mm. The straight from bottom to top with the opening a t the top the limits of the size of this tube are determined on the one hand by the undesirability of sacrificing full width of the cylinders. more space than necessary, and The inner cylinder containon the other hand by the reing the meal could be easily quirement that the tube allow OUTER CYLINDER free passage of vapor and exr e m o v e d , a n d since t h e tract in opposite d ir ec t ions. c y l i n d r i c a l form and wide INNER CYLINDER The space between the inside top offered no obstruction, and outside cylinders was about. the cake could be shaken out or CONDENSER 2 mm. Provision for connection with the boiling flask may in one mass. be by a plain tube and cork or An o u t s i d e t u b e t o conby a standard-taper glass joint. duct s o l v e n t from the conThe condenser is made of thin denser to t h e e x t r a c t i o n v O U T E R CYLINDER copper sheet,ing by soldering a FRESH SOLVENT plain cone t o one end of a short c h a m b e r h a s t h e double of EXTRACTOR SOLVENT VAPOR cylinder a n d a disk t o the disadvantage of being fragile other. The diameter at the and of cooling t h e s o l v e n t base of the cone is such that a MATERIAL BEING too much before it r e a c h e s clearance of about 0.5 mm. is ’IdNER C Y L I N D f R left between the edge of the t h e meal. T h e present OF EXTRACTOR cone and the inside wall of t8he apparatus was designed to ONE O f INDPNTAouter glass cylinder. The avoid fragile projecting parts TION5 TO C E N T E R function of the projecting edge and to maintain a high temof the cone is t o direct solvent against this wall so that it flows perature in t h e solvent into the space between the where it is in contact with the inner and outer cylinders. The meal. The wide space bedisk which forms the top of the tween the inner and o u t e r condenser is made large enough to extend well over the top cylinders for solvent returning edge of the extractor. Copper from the condenser permits FIGURE 1. DIAGRAM OF APPARATUS inlet and outlet tubes for coolthe free escape of gas bubbles, Glaris Condenser a t right ing water are soldered in place.
N PREPARING cottonseed meal for fat-free diets for
