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I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
Vol. 17, No. 12
The Vacuum Assay Distillation Test' By A. G . Peterkin, Jr., and S. W. Ferris THEATLANTIC RETININQCo., PHILADELPHIA, PA.
HE most i m p o r t a n t within the system reaches 10 An assay distillation test under vacuum has been single operation in the mm. air will issue from the developed for petroleum products along the lines of the petroleum industry is tube into the system and suggestion contained in Bureau of Mines Bulletin 207. distillation, and probably the maintain the pressure a t that The apparatus and technic have been simplified and the most important phase of this point. To overcomesluggishmethod, as described, is suitable for routine control process a t the present time is ness of the mercury in falling work in the same way that the atmospheric assay disthe application of efficient through the capillary tube, tillation has been applied to light distillates. The fractionating equipment. about25mm.(linch) of 7-mm. test is of great value for distillation control. The value of the Enaler tubing is sealed a t the end of distillation test in still control the capillary. This tube is or in investigational work in the distillation of light fractions lipped to aid further in the issuance of the air a t the proper preshas long been recognized. The test is, however, only ap- sure. Two or three strings, leading from a point just above the plicable to products of low boiling range-naphthas, lamp lip almost to the surface of the mercury, overcome the tendency oils, etc.-and is manifestly incapable of application to the of the bubbles to enlarge during their ascent and disturb the heavier products, such as lubricating oils, etc. Where such mercury, since the strings, not being wetted, offer channels products are being distilled, the refiner has had to content through which the bubbles may rise without disturbance. himself with other tests. While in past operation, where no SPECIFICATIONS OF APPARATUS real fractionation has been obtained, these tests have served the purpose more or less satisfactorily, they are quite inadeBurner: Bunsen, adjusted t o give indistinct cone, with needlequate for controlling actual fractionation and for determining valve control of gas F1ask:a 250-cc. Claisen, Pyrex, insulated with '/4-inch asbestos the degree of separation attained. For example, the gravity of a very wide cut might be precisely the same as that of a rope and asbestos cement Over-all, vertical, 250 mm. very narrow cut, corresponding roughly to the middle fracBulb, diameter, 83 mm. tion of the wide cut. The same is true of viscosity. The First neck, 23 mm. 0.d. Second neck, 21 mm. 0. d. flash point may give some indication of the presence of light Second neck joined a t midpoint of first compounds, but only a very vague one, since a low flash may Distance between axes of necks, 77 mm. result from a small amount of exceedingly low boiling material, Outlet tube: or from a considerable amount of a much higher boiling maAngle with vertical, 48' Length, 135 mm. terial. Outside diameter, 8 mm. It was therefore attempted to develop an assay distillation, Condenser jacket: Metal, 280 mm. long similar to the Engler, but applicable to these heavier oils. Condenser tube: Pyrex, 460 mm. long The best method of accomplishing this seemed to be to emNeedle valves: '/4 inch Pressure-regulating tube: ploy a vacuum sufficiently high to make possible the exOver-all, length, 105 cm. amination of cuts over practically the whole range of crude Upper section, 25 cm., 35 mm. 0. d. petroleum. Lower section, 18 mm. 0.d. Dean, Hill, Smith, and Jacobs2 describe a vacuum distillaReceiver: 100-cc. graduated cylinder, without lip Stoppers: If exposed to heat, cork; if not, rubber tion a t a definite pressure (40 mm.), which they apply to Vacuum pump4 lubricating oils, in which temperature readings are recorded. Too little emphasis, however, seems to be laid upon it as a Procedure test comparable to the atmospheric assay, and too little notice taken of its possibilites. The apparatus, as described, One hundred cubic centimeters of the sample to be exis rather complicated and scarcely suited to routine work amined are charged into the flask and a clean receiver adin a testing room. justed. All stoppers are forced very strongly and a coat of The apparatus and method which were developed, and collodion applied. which are described below, have been successfully operated The pressure-regulating tube having been set to the apupon a routine basis for several months, with a degree of proximately correct immersion, as determined by the baroease and accuracy which compares very favorably with the metric reading, the needle valve is closed. After starting atmospheric assay. It has proved to be practically the only the pump, the needle valve is gradually opened and the pressatisfactory means of determining when the maximum yield sure allowed slowly to.drop until bubbles begin to issue. If of a product has been recovered. the pressure is not exactly correct, the tube is readjusted. If, however, this adjustment calls for decreasing the imMethod mersion, the pressure should first be allowed to rise slightly, Figure 1 presents the set-up. The only feature requiring since a sudden decrease in immersion will result in a n excomment is the pressure-regulation device. This consists of a cessive inrush of air. capillary tube, open to the air, and immersed to the proper The proper immersion having been made, the needle valve depth in mercury. For example, if it is desired to operate is so adjusted that the bubbles immerge a t a moderate rate. at 10 mm. absolute pressure, with the barometric pressure at A Bask conforming to the specifications below may be obtained from 763 mm., the tube is immersed 753 mm. When the pressure
T
Presented before Division of Petroleum Chemistry at the 69th Meeting of the American Chemical Society, Baltimore, Md., April 6 to 10, 1925. 2 Bur. of Mines, Bull. 207, 35 (1922). 1
A. H.Thomas Co , Philadelphia, Pa. 4 The vacuum pump used in this work and found thoroughly satisfactory is the Compound High Duty pump manufactured by the Beach-Russ Company.
INDUSTRIAL AND ENGINEERING CHEMISTRY
December, 1925
The only further attention necessary is an occasional inspection to see that the air rate remains normal. The heating is now started a t the side of the flask. The temperature is read when the first drop of distillate falls from the condenser tube, the rate adjusted to 5 cc. per minute, and the temperature read a t the 1, 3, 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, and 95 per cent points. The flame is gradually increased, and the burner pushed toward the center of the flask, maintaining the 5 cc. per minute rate up to the 95 per cent point. The flame is not increased after this point, and when the amount of material within the flask becomes practically constant, the vapor temperature is read as the end point. The most satisfactory pressure has been found to be 10 mm. A fairly accurate conversion may be obtained to figures a t 40 mm. (Bureau of Mines pressure) by adding 39" C. to the 10-mm. results. This factor has been repeatedly checked, and has been found to give satisfactory results. The distillation may, in all cases, be carried to 350" C. vapor temperature without serious cracking, and usually considerably higher.
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manner. For example, Table I presents the tests on three trade medium motor oils. None of these figures on the regular tests indicate the real difference in the oils, as shown by the assays (Figure 2). It will be noted, for example, that the oil having the lowest specific gravity and the lowest viscosity ( B ) , is really the heaviest as regards boiling range. The upper
part of curve B indicates further that this oil has been prepared by blending an overhead cut with a heavier oil, while A and C appear to be more nearly straight-run products. The curves show also that B has been prepared from a radically different crude than A and C. It will be seen that, with the proper amount of data from various crudes, a very shrewd guess as to the origin of these three oils could be made. Table I-Distillation Teste on Medium Motor Oil8 Sample A B C Specific gravity at 15.5' C. 0.9273 0.8910 0.9298 Saybol: viscosity at 100' F., sec. 328 302 315 Flash,o C. 177 216 177 Fire, C. 210 241 207 Disfiltafionof 10 mm.. C. Per cent Start 161 209 161 172 217 1 168 3
Figure 1-Apparatus
for Vacuum Aseay Distillation
Some samples, such as crudes, must be started a t atmospheric pressure, on account of the light materials present. In such caBes, the atmospheric distillation is carried to about 285' C . vapor. Immediately after making a temperature reading, the distillation is halted and the liquid allowed to cool until the vacuum may be applied without causing the liquid to boil. The flame is relighted, and the distillation carried on. Since 10 cc. are distilled before another temperature reading, the rate may be again adjusted, and the reading should be trustworthy. For samples containing a high percentage of wax, it has been found convenient to heat the water in the condenser jacket by means of a hand flame. Applications
While the principal usefulness of the vacuum assay distillation test is in the control of distillation and especially fractionation, it may also be usefully applied in an analytical
95 End Per cent at end
182 , 189 I99 214 227 237 248 258 268 284 306 321 336 98.5
223 226 232 243 253 260 268 277 288 316 381
176 182 192 206 215 227 236 246 258 274 288 323 330 98.5
The close agreement of the points to the curve will indicate the degree of accuracy of the method. Acknowledgment
Acknowledgment is due to J. Allen Alexander for work in perfecting the apparatus. New Invention for Italian Rayon Industry-The office of commercial attache, Rome, states that according to reports of the Agenzie delle Informazioni an Italian rayon company is negotiating the purchase of a Belgian patent for rayon production. This new process permits the production of a hollow, tubular rayon thread which will impart a greater softness and better draping qualities t o the finished production than have hitherto been attained. It is thus hoped t o overcome the stiffness of rayon fabrics, which has been one of the greatest drawbacks of this textile. Exports of rayon yarn and waste from Italy during the first seven months of 1925 amounted to 5,369,200 kilos, valued a t 317,686,722 lire (1 lira = $0.0395 a t current exchange), or nearly double the volume of exports during the like period of 1924.
