INDUSTRIAL AND ENGINEERING CHEMISTRY
January, 1926
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High-Precision Fractional Distillation in the Laboratory',' By W. A. Peters, Jr., and Theodore Baker E. I.
DU PONT DE
NEYOURS & (20.. EXPERIMENTAL STATION, HENRYCLAY,WILMINGTON. DEL.
N T H E separation of liquids by fractional distillation, the plant has been hitherto far ahead of the laboratory. Indeed, components could be isolated in the plant which could not even be discovered by distillation of laboratory samples. After consideration of the most effective laboratory fractionating apparatus in common use-for example, the Norton & Otto, the Le Bel-Henninger, and the customary Hempel columns-it was concluded that the Hempel type had the greatest possibilities for development. One difficulty with the ordinary Hempel is the excessive hold-up of liquid in the column. No matter how tall a column is, it cannot give sharp cuts if the amount of liquid held up in the column itself is too great compared to the size of the cuts desired. Other defects, also commonly found in the other types of column mentioned, are the restriction of the opening a t the base, which prevents the free return of the liquid and the free entrance of the vapors into the column, and the lack of control of the reflux, which usually depends entirely on wall cooling. Owing to the uncontrolled loss of heat from the walls, these columns cannot usually be made high enough to be really efficient.
I
Apparatus for Low-Boiling Liquids With these defects in mind, the apparatus shown in Figure 1 was developed for ordinary separations such as the analysis of mixtures of water and the lower alcohols. The column is a glass tube 12.5 mm. inside diameter a t the base and may be slightly less at the top. All glass used in the apparatus, except the filling, should be Pyrex. The filling is of glass rings made by cutting soft glass tubing 5 mm. outside diameter into pieces 5 mm. long. Lessing rings have also been used with success. A convenient length for the column is 1.5 meters, for the jacket 1.08 meters, and for the dephlegmator 20 cm. It will be noted that there is no constriction at the bottom or top of the column, the rings being supported a t the bottom by a wire put through two small holes in the wall of the column. On this wire an openwork ball of wire may be placed, if necessary, to keep the rings from slipping through. The column itself is jacketed with a single glass tube, which serves to cut down the radiation loss somewhat, but especially to diminish the effects of draft. At the top is a dephlegmator by means of which a definite controlled amount of reflux is furnished to the column. This dephlegmator is arranged so that a regulated amount of cooling water can be admitted and also so that the level of this cooling water can be adjusted. The dephlegmator is made as small as will conveniently give the necessary reflux, and the connections between it and the condenser are as short as possible to cut down unnecessary hold-up to a minimum. The water supply must be susceptible of very delicate regulation as by the use of a needle valve. The dephlegmator may conveniently be made as the upper part of the column. During the preliminary experiments the plan was tried of using only a condenser and no dephlegmator, afterwards dividing the distillate between the reflux and take-off. Inferior results as regards sharpness of cuts were obtained this way, however, 1 2
Received November 23, 1925. Contribution No. 2 from the du Pont Experimental Station.
and for two apparent reasons. There is in the partitioning device an appreciable hold-up of the distillate, which can hardly be made less than 1 cc. Moreover, by such an arrangement the fractionating effects of the dephlegmator are lost, whereas with the present design the enrichment due to the dephlegmator becomes surprisingly great at the critical points when the speed of take-off is decreased in proportion to the reflux, as happens when reaching the point where the last of a certain component is being distilled off. A thermometer reading to fifths or tenths of a degree should be placed as shown in the vapor space above the dephlegmator. The condenser also should be small, to avoid unnecessary hold-up of condensate. The one shown is 1 cm. outside diameter by 12 cm. long. The heat supplied to the flask must be constant in amount and easily controlled. A gas burner can be used if the gas pressure does not vary and the flame is protected from drafts. An electric heater is preferable, but must have means for delicate adjustment. An internal electric heater has been used with success where the charge is a nonconductor. The diameter of the ring filling is a matter requiring some consideration. If too small rings are used, there will result undue obstruction both of the upward flow of the vapor and of the downward flow of the reflux, and there will consequently be an excessive hold-up and a tendency to load which will limit the speed of operation. If, on the other hand, the rings are too large, the scrubbing effect for a given height Z 5 M M IM becomes i n a d e q u a t e . For 12 to 12.5 mm. diameter columns 5 mm. 500 C C TO external diameter glass I-LITEL? tubing gives a convenient filling which works well and gives r e a s o n a b l e speed. If a column of appreciably less than 12 mm. diameter with the same size filling is used, I it is difficult to obtain FLooP LcvfL7 as the Figure I-Simplest Type Column, for uniform Low-Boiling Liquids filling is liable to wedge a t various points, leaving empty spaces; and if the column is very much smaller yet, only one piece of the filling can be allowed per layer. The writers did not get quite such sharp cuts or such good speed with 4-mm. filling as with 5-mm., and the control was more difficult. A 10-mm. column has been operated with 5-mm. filling, but the operation was slow and the
u n
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INDUSTRIAL A N D ENGINEERING CHEMISTRY I
Cftrmumdrr
Figure 2-Precision Column for Higher Temperatures
,odccF/o,k
control somewhat difKcult. This arrangement is advised only where extra small samples have to be analyzed. Recently, in order to run samples of 2 or 3 liters a t speeds of 10 or 12 cc. per minute distillate, a column of about 38 mm. diameter has been used, about 240 cm. high, jacketed, and electrically heated. The filling is 6-mm. tubing and the dephlegmator is of 25-mm. brass tubing, 40 cm. maximum wetted height. This is giving satisfaction for the purpose for which it was designed, but, of course, would not be suitable for the analysis of 100- to 200-cc. samples because of the large hold-up of liquid in the column, with consequent loss of sharpness in the cuts.
Vol. 18, No. 1
The hold-up of liquid in a column 12.8 mm. in diameter with 1.22 meters (4 feet) depth of 5-mm. filling was found to be about 15 cc. during working, which is a minimum for effective operation. Other columns, such as that of D ~ f t o n have , ~ less hold-up, but Dufton's column was found impractical for ordinary laboratory use because it has to be operated a t an extremely low rate to give sharp separations. As regards the rate of distillation and method of operation, it is generally best to start with total reflux and to regulate the rate of boiling so that the column just fails to load u p
with condensate, then to allow the dephlegmator to warm up to the exact point where the desired amount of distillate passes, which will generally be 0.5 to 2.5 cc. per minute, according to conditions and the kind of separation being: made. just sufficient water or air is supplfied to the dephlegmator to stabilize conditions. Working in this way with petroleum, the reflux will be approximately 15 cc. per minute and the distillate 1 cc. per minute, giving a reflux ratio of 15 to 1. Apparatus for High-Boiling Liquids The simple form of column is good for materials boiling below 100' C. For accurate work above this temperature the apparatus shown in Figure 2, developed primarily for analyzing samples of petroleum', should be used. For somewhat less accurate work a t temperatures between 100" and 200' C., the apparatus shown in Figure 1 is satisfactory if provided with a winding of 0.016 inch nichrome resistance wire spaced three or four turns to the inch around the column jacket and a rheostat to adjust the heat input to the radiation loss. It is desirable also to lag the jacket-e. g., with as-
* J . SOC.Chcm. Ind., 88,
45T (1919).
January, 1926
INDUSTRIAL A N D ENGINEERING CHEMISTRY
bestos twine. For finer adjustment of the reflux a t higher temperatures, the water is drained from the dephlegmator and a regulated amount of air is blown in for cooling. The operation of the complete apparatus shown in Figure 2 is nearly the same as that of the simpler apparatus, except that the temperature of the outside jacket is carefully adjusted by regulating the amount of heat put into the heating elements of the jacket itself and the amount and temperature of air blown through the jacket. With these three factors under control, the temperature of the jacket a t both the bottom and top can easily be kept about the same as that of the vapors in the column a t the corresponding heights. With this column the accuracy of separation is practically the same a t temperatures around 250" C. as at temperatures below 100" C. The only limit to the temperature is imposed by the connections. Rubber stoppers cannot be used for high temperatures and cork begins to char at 300' C. Mercury seals were used with fair success for the analysis of naphthalene, but mercury begins to vaporize rapidly a t temperatures above 300" C. and is objectionable because poisonous. Fusible metal seals. were tried, but none could be found which did not expand and break the glass on solidifying. The stopper in the neck of the distilling flask gives the most trouble. If a small depression is made in the bottom of the flask and the residue after each distillation is blown or pulled out through a glass tube inserted through the side opening, the larger stopper may be left in place for a number of runs. Stoppers coated with glue have lasted 10 hours with temperatures in the flask going up to 350' C. a t the end of the run. Of course, the small stopper in the side opening can easily be changed every two or three runs. The heaters shown are of the following capacity: under
IO I5 20 25 30 35 40 45 VOLUME OF DISTILLATE IN C.C. Figure 3-Analysis of Synthetic Mixture, Acetone-Ethyl AlcoholWater-n-Butyl Alcohol 0
5
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flask 1 kilowatt, jacket heater 900 watts, air heater 500 watts. The heat input was regulated by using Central Scientific Company's water-cooled rheostats N o . 49698 on the flask and air heaters and S o . 4969B on the jacket heater. The arrangement of the heaters for the flask and air is obvious from the figure. The jacket heater is made by running four straight pieces of resistance wire through the annular space between the outer and intermediate jacket walls. These wires come in the open top and out through four small holes pierced through the wall of the outer jacket a t the base. The bottom of one wire is connected in series to the top of the next by an insulated copper wire run up outside the column. These vertical heater wires expand on heating, and to prevent short circuiting one or more may be strung with small pieces of glass tubing. The jacket tubes at the top are most conveniently spaced with three small wedges of wood or other material. The size of sample is determined by the accuracy desired and the amount of material which is to be distilled. Usually 25 t o 50 cc. of distillate should be collected. For more accurate work 100 cc. of distillate are desirable, and for the most accurate work much larger samples should be used. For isolating pure compounds from complex mixtures, it is necessary to make preliminary cuts on large samples, either in this or in larger apparatus, and then re-run twice or more with this column. Results
In Figure 3 are shown the results obtained with the simpler type of apparatus in the analysis of a synthetic mixture of water, acetone, and ethyl and n-butyl alcohols, made up according to the following composition: acetone 30, ethyl
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INDUSTRIAL A N D ENGINEERING CHEMISTRY
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alcohol 3, water 5, and n-butyl alcohol 67 cc. The results of the analysis are indicated ,on the graph. The binary mixture of n-butyl alcohol and water boiling at approximately 93' C. contains 37 per cent water, and this figure is used in calcuiating the amount of water given off at that temperature. Figure 4 shows the result of a distillation of a mixture containing 30 CC. acetone, no ethyl alcohol, 5 cc. water, and 65 cc. n-butyl alcohol. If, although the curve shows no break, it were assumed that ethyl alcohol were present in this mixture, and the amount were calculated in the same manner as for the previous case, the ethyl alcohol would be estimated as 0.3 cc. If this correction is applied to the other curve, it brings the ethyl alcohol down to 3.2 per cent, which is very close to the true value. It will be seen that amounts of ethyl alcohol as low as 3 or 4 per cent can be determined with a fair degree of accuracy, and concentrations as small as 1 per cent can be detected with considerable certainty in a single distillation. Application to Organic Isomers For an instance of the application of this type column to the separation of organic isomers, we are indebted to Dr. M. L. Cline, working with Professor Reid of Johns Hopkins University. At his request one of the writers designed a column for the separation of 0- and pethylnitrobenzenes. The column was 12.5 mm. bore and was packed with glass rings for a length of 150 cm. The column was jacketed and was heated with the vapors from a flask of boiling xylene, the condensed xylene being returned to the flask. The distillation of the isomers was carried out under reduced pressure, so controlled as to bring the boiling point of the lower-boiling isomer a few degrees below the jacket temperature. The ortho compound distilled over at constant temperature and finally distillation ceased. The pressure was then lowered in steps and the distillation continued until the temperature remained constant while 30 cc. of the less volatile isomer distilled o?er. The original sample weighed 760 grams. The pure ortho compound distilled off weighed 384 grams (50 per cent). The intermediate mixed product weighed 60 grams (8 per cent), leaving in the flask 317 grams (42 per cent) of the pure para compound. By way of comparison, it may be noted that to separate these same isomers Beilstein and Kuhlberg4 fractionated twenty times while Schultz and Flackslanders fractionated eighty times in %degree cuts to get two fractions 220-30" C. and 245-50' C. with a small middle portion. They fractionated one hundred more times to obtain constant boiling fractions 223-4' C. and 241-2' C. The saving of time effected by the use of an efficient column can readily be appreciated, A number of these columns have been in use in the laboratories of this company for over a year and have proved themselves practicable and efficient in the distillation of a variety of materials. 4 1
Ann., 156, 206 (1870). J . firakt. Chern., [2]66, 162 (1902).
Future Policy of British Dyestuffs Corporation Lord Ashfield, the chairman of the British Dyestuffs Corporation, has stated that under the management of the present board of directors the corporation will not be permitted t o become a mere distributing agency for dyestuffs, and that no matter what arrangements are made they will not be inimical t o t h e interests of their customers, the color users, but will be made for the purpose of securing the widest measure of freedom for them in the conduct of their business and for the purchase of their colors at the world's prices. The corporation will continue t o be a large manufacturing company, whose aim will be t o meet, so far as its resources will permit and upon an ever-widening scale, the needs of English color users. A large staff of skilled chemists will be employed.
Effect of Sulfur upon Nitrogen Content of Legumes' By J. R. Neller STATEAGRICULTURAL EXPERIM~NT STATION, PULLMAN,WASH.
OTWITHSTANDING the rapid advances in methods for the chemical fixation of elemental nitrogen, it is still recognized that the natural or bacterial processes of fixation continue to supply by far the greater amount of fixed nitrogen needed for plants and animals. As a consequence the discovery that sulfur, or a sulfate salt such as gypsum, will in some cases increase the nitrogen content of legumes is worthy of considerable attention. Early in the history of the United States it was found that under certain conditions, gypsum would cause a marked increase in the growth of clover. More recently it was found that elemental sulfur functioned in a manner similar to gypsum. Experiments have shown that sulfur undergoes s comparatively rapid oxidation after mixing with a warm, moist, arable soil. This oxidation goes completely to the trioxide stage. Moreover, it is known that the oxidation is caused by microorganisms, as very little takes place in a sterilized soil. The bacteria which thus have the ability to convert sulfur into sulfuric acid have recently been studied and described by Lipman2 and his associates. Table I shows the percentage of sulfur recovered as watersoluble sulfate sulfur from two types of eastern Washington soils after periods ranging from 15 to 105 days. It may be noted that the rate of oxidation gradually decreased, probably owing to the initial oxidation of the more available portion of the flowers of sulfur used. The sulfur was added a t the rate of 1 part to 2000 parts of soil, or approximately 1000 pounds per acre. A large amount of the sulfuric acid produced by the bacterial oxidation is neutralized by basic compounds in the soil, but as shown in a previous papera the pH of the soil solution may also be decreased.
N
Table I-Progressive
Palouse silt loam Ritzville silt loam
Oxidation of Sulfur Added t o Eastern Washington Soils -PBR CENT oXIDIzSD-------. 15 30 45 75 105 days days days days days 72.1 85.5 33.7 53.9 63.9 29.8 43.1 51.4 66.3 82.9
The nitrogen contents of yields of alfalfa given in Table I1 were obtained under plant-house conditions with a Ritzville loam brought in from the semiarid east central part of Washington. These results are indicative of field crops that may be obtained under irrigated conditions in that region. As shown in this table, sulfur and gypsum gave similar results, the yield increases ranging from 49.3 to 81.1 per cent. Table 11-Yield and Nitrogen and Sulfur Contents of First Cuttlng Alfalfa on Sulfured and Unsulfured Ritzville and Palouse
Loam
SULPUR AND GYPSUMAPPLICATIONS LBS.PBR ACRE 1000 159 500 200 cas04 Check Sulfur Sulfur Cas04 61.7 47.5 53.4 Yield, grams 31.8 57.6 2.38 2.37 2.18 Nitrogen, per cent 1.65 2.27 Sulfur, per cent 0.120 0.237 0.321 Yield increase, per cent 81.1 94.0 49.3 68.0 Nitroaen increase, per cent 37.6 44.2 43.6 32.7 Sulfur increase, per cent 97.5 175.8
The point of particular interest in this table is that in every case the use of sulfur caused an increase in the nitrogen I Presented under the title "Sulfur and the Utilization of the Other Chemical Elements by Legumes," as a part of the Symposium on Chemistry and Plant Life before the joint sessions ,of the Divisions of Agricultural and Food Chemistry and Biological Chemistry at the 70th Meeting of the American Chemical Society, Los Angeles, Calif., August 3 to 8, 1925. I Soil Scicncd, 12, 475 (1921). a J . Am. SOC.Agron., 17, 26 (1925).
