THE ANALYTICAL DISTILLATION OF GASOLINE HAROLD J. TORMEY, ST. BONAVENTURE COLLEGE, ST. BONAVENTURE, NEWYORK
The necessary equipment and the procedure for conductinf the analytical distillation of gasoline are described and a typical distillation curve is firesented. The procedure might well be made the subject of an interesting and informative laboratory exercise. The work might be extended i n certain courses i n other laboratories as it has i n this laboratory, to include a study of the factors affecting the analytical distillation of gasoline. Governmat specifications of motor and auiation gasoline are included.
. . . . . . The analytical distillation of gasoline is one of the most important determinations made in the evaluation of light petroleum fractions. Many large users of gasoline, including the United States government, purchase gasoline on specificationsand the data obtained by an analytical distillation along with the data obtained from the other determinations usually made indicate whether or not a particular sample meets all requirements. This deteimination can be made the subject of an interesting laboratory exercise and especially lends itself to a coijperative experiment with the sheet metal department since the distillation apparatus required could he constructed by that department. The specifications according to which the distillation apparatus represented in Figure 1 and in photograph on page 701 is constructed may be secured by a request for A. S. T. M. Distillation Apparatus Tentative Standard D-86-26-T addressed to the American Society for Testing Materials, 1315 Spruce St., Philadelphia, Penna. This apparatus may also be purchased from most of the larger supply houses. The specifications covering the construction of the Modified Bureau of Mines Distillation Apparatus as used by Cosden and Company are given in Figure 2. Apparatus In addition to the condenser and cabinet, the following apparatus is required: 1. Standard Engler Bask, 100 cc. 2. Standardized thermometer 3. Burner (gas, gasoline, alcohol, or electric heater) 4. Asbestos hoard 4" sq. with I'/," hole in center 5. Graduated cylinder, 100 cc. 6. Ring stand, rings, clamps
The specifications covering the flask and thermometer as adopted by Sub-committee XI of Committee D-I of the American Society for Testing Materials are as follows: Flask.-The flask used shall be the standard 100-cc. Engler flask described in the various textbooks on petroleum. Its dimensions are: 699
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Outside diameter of bulb.. . . . . . . . . . . . . . . . . . . . . . . . . . 6 . 5 cm. Outside diameter of neck.. . . . . . . . . . . . . . . . . . . . . . . . . . 1 . 6 Length of neck.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..15.0 Lengthofvaportube . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.0 Outside diameter of vapor tube.. . . . . . . . . . . . . . . . . . . . 0 . 6 Position of the vapor tube 9 cm. above the surface of the gasoline when the flask contains its charge of 100 cc. The tube is approximately in the middle of the neck. The observance of the prescribed dimensions is considered essential t o the attainment of uniformity of results. The flask shall be supported on a ring of asbestos having a circular opening, l'/," in diameter. Only this limited portion of the flask is t o be heated. Thermometer.-The thermometer shall be made of s e l e c t e d enamel-backed tubing having a diameter between 5.5 and 7 mm. The bulb shall be of Jena normal or Corning normal glass; its diameter shall be less than that of the stem and its length between 10 and 15mm. The total length of the thermometer shall be approximately 380 mm. The r a n g e s h a l l c o v e r O°C. (32°F.)to 270°C. (51X°F.), with the Length of the graduated portion between the limits of 210 t o 250 mm. The point marking 3 5 T shall not be less than 100 mm. or more than 120 mm. from the top of the bulb. The scale shall be graduated for total immersion with an accuracy within 0.5"C. Space above meniscus must be filled with inert gas.
Both the Engler flask and the standardized thermometer as described above are obtainable from most supply houses. Procedure and Details of Manipulation 1. The condenser box is filled with water containing a liberal portion of cracked ice. 2. The charge of gasoline (100 cc.) is measured into the clean dry Engler flask from a 100 cc. graduate. The graduate is used to receive the distillate without any drying. This procedure eliminates errors due to incorrect scaling of graduates and also avoids the creation of an apparent distilla-
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tion loss due to the impossibility of draining the gasoline entirely from the graduate. 3. The above-mentioned graduate is placed under the lower end of the
O P BUREAUOR MINESAPPARATUS FOR DISTILLATION FIGURE~.-MoD~~ICATION AS
USEDBY COSDEN AND COMPANY
condenser tube so that the latter extends downward below the top of the graduate a t least 1 inch. The condenser tube should be so shaped and bent that the tip can touch the wall of the graduate on the side adjacent to the condenser box. This detail permits distillates to run down the side
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of the graduate and avoids disturbance of the meniscus caused by the falling of the drops. The graduate is moved occasionally to permit the operator to ascertain that the speed of distillation is right, as indicated by the rate a t which drops fall. The proper rate is from 4 to 5 cc. per minute, which is approximately two drops a second. The top of the graduate is covered, preferably by several sheets of filter paper, the condenser tube passing through a snugly fitting opening. This minimizes evaporation losses due to circulation of air through the graduate and also excludes any water that may drip down the outside of the condenser tube on account of condensation on the ice-cooled condenser box. 4. A boiling stone (a bit of unglazed porcelain or a few grains of sand) is dropped into the gasoline in the Engler flask. The thermometer is equipped with a well-fitted cork and its bulb covered with a thin film of absorbent cotton (preferably the long-fibered variety sold for surgical dressing). The thermometer is fitted into the flask with the bulb just below the lower level of the side-neck opening and exactly in the center of the cross-section of the neck of the flask. The flask is connected with the condenser tube. 5. The source of heat in distilling gasoline may be a gas burner, an alcohol lamp, or an electric heater. Heat must be so applied that the first drop of gasoline falls from the end of the condenser tube in not less than five nor more than ten minutes. The initial boiling point or overpoint is the temperature shown by the thermometer when the first drop falls from the end of the condenser tube into the graduate. The operator should not allow himself to be deceived as sometimes (if the condenser tube is not dried from a previous run) a drop will be obtained and i t will be some time before a second one falls; in this case the first drop should be ignored. The amount of heat is then increased so that the distillation proceeds a t a rate of from 4 to 5 cc. per minute. The thermometer is read for each 5 cc. accumulating in the receiver. The end-point (also called dry point and maximum boiling point) is determined by continuing the heating after the flask bottom has boiled dry, until the column of mercury reaches a maximum and then starts to recede consistently. 6. Distillation loss is determined as follows: the condenser tube is allowed to drain for a t least five minutes after the heat is shut off, and a final reading is taken of the quantity of distillate collected in the receiving graduate. The distillation flask is removed from the condenser and thoroughly cooled as soon as i t can be handled. The condensed residue is poured into a small graduate or graduated test tube and its volume measured. The sum of its volume and the volume collected in the receiving graduate, subtracted from 100 cc., gives the figure for distillation loss. I t is convenient to have students work in groups of four. One student times the rate of distillation and advises a second student who controls
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the rate of heating as to whether the rate is satisfactory. If the rate of distillationis reported too slow or too fast the rate of heating is adjusted accordingly. A third student reads the temperature when a fourth student advises him of the overpoint and the accumulation of each five cc. of distillate. A second distil4 - . l a t i o n should be perf o r m e d on t h e same ... 3sample with a new group , of four students. The f results of the two distil--- ,!: --,.. lations should be approxi- a $, mately the same. - '- V , From the standpoint - " of volatility motor gaso$ k line may be looked upon B --- h as being composed of 1 : three portions: (1) a -low-boiling volatile por-.tion which is of value in -. o / L 1 2 0 J 4 4 0 M 6 0 m B C R I m starting., (2) an intermeU a / . - arc& diate and (3) the Fmune TYPICAL DIsTILLATIoN CURVEPOR GASOLINE power portion which is usually considered to be A composite of the distillation curves of fourteen differentsamples of gasoline. desirable in as large a percentage as can be completely vaporized by the carburetor. By the use of a fractionating column the relative proportions of the above-mentioned portions can be well brought out when the distillation curve is drawn. The United States government specifications for motor gasoline and aviation gasoline are given in the accompanying table.
.*
3
%
-:-
.,
U. S. Government Specifications MOTOR GASOLINE 122°F.( 50T.) 176°F. ( 80PC.) 284-F. (140DC.) 39Z°F. (200DC.) 437'F. (225'C.) 95%
Minimum
lo% Maximum 50% over, at or below 90y0over, at or below End-point not above Recovery (minimum) AVIATIONGASOLINE Distillation &nge Piphling Croda
Minimum 5% ~ a x i m u m
50°C. (l2ZaF.) 65T. (14Q°F.)
Domestic Cnade
5!1°C. (122'F.) 75°C. (167'F.)
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Minimum 50% Maximum
Minimum
705
..............
..............
9S°C. (2fl3"F.) .............. 125'C. (257°F.)
105'C. (221 OF.)
..............
Maximum Minimum Maximum
..............
..............
150 "C. (302 OF.)
1 7 5 T (347°F.)
End-Point Maximum
165°C. (329°F.)
1 9 0 T . (374'F.)
"'%
166°C. (311°F.)
A composite of the analytical distillation curves of 11 different samples of gasoline as obtained on the market is found in Figure 3.
