1048
INDUSTRIAL A N D ENGINEERING CHEMISTRY
dry in the air, a t room temperature, for 24 to 72 hours, depending upon the moisture in the air of the room. In winter, if no steam vapor is present, 24 hours are generally suffioient. No heating or drying in desiccators is permitted, as then some of the crystal water is lost. The high molecular weight of this salt will practically eliminate the effect of errors due to slight inaccuracy in weighing, or small impurities still present. Five grams of borax
Vol. 15, No. 1 0
correspond to 26.2 cc. of normal acid; 19,109 grams to 1/10 normal, and 6.825 grams to 1/28 normal acid. Methyl orange is generally recommended as an indicator for borax solution, but it is somewhat lacking in sharpness, especially in dilute solution. This difficulty has now been overcome by the use of dimethylamidoazobenzene. This indicator is prepared by dissolving 1 gram of the salt in 1 liter of alcohol. The end point is very sharp.
High-speed Stirring as an Aid t o Chemical Action' By C. H.Milligan and E. Emmet Reid JOHNS HOPKINS UNIVERSITY, BALTIMORE, MD.
C
ONTACT is conceded For the literature relative The relation of speed of stirring to velocity of reaction has been studied in the ethylation of benzene and i n the hydrogenation of to the ethylation of benzene to be essential to chemical action, and by ethylene and for details cottonseed oil i n presence of nickel. I n both C ~ S C Sthe reaction rates as to the products obtained, it is Usual to shake O r stir are nearly proportional to speed of stirring. reference may be made to mixtures to facilitate reaca previous article.2 tions, but quantitative data Rapid stirring appears to aid the chlorination of toluene connecting the violence of the agitation with the rates of reactions are lacking. Such data are desirable for the de- and of acetic acid, but quantitative comparisons have not sign of equipment. Of course, conclusions drawn from small- been made. scale laboratory experiments are not to be applied recklessly THESTIRRER(FIG.2 ) to plant apparatus. The speed of the motor was 1700 r. p. m., which was multiWhere we have two consecutive reactions, one of which is extremely rapid and the other slow, the over-all velocity plied about eight times by an arrangement of pulleys carried depends on the slow reaction and is related to the circum- on a steel frame. Ball bearings were provided for the stirrer stances that favor or hinder it. If we consider the mutual shaft and for the upper end of the countershaft. The speed solution of the reactants as the first of the two reactions of the motor was controlled by a variable resistance. The followed by a chemical change, we come to the conclusion speed of the stirrer was measured by a speed counter, the end that if the desired reaction is rapid but the rate of solution of which carried a toothed wheel which meshed with a thread is slow, the reaction rate will be related to the rate of stir2 J . A m . Chem. Soc., 44, 206 (1922). ring, while if the solubility is great and the reaction comparatively slow, stirring will be of little importance. The present investigation is a preliminary study of the relation between speed of stirring and reaction rate in several nonhomogeneous systems. I n the action of sulfur dioxide on benzene in the presence of aluminium chloride, stirring has little influence, since the gas dissolves readily anyway and the reaction rate is probably slow, but the absorption of ethylene by benzene in presence of aluminium chloride and the hydrogenation of cottonseed oil using nickel as catalyst are enormously accelerated by intensive stirring. With the apparatus used by the authors and over the range covered by their experiments, the rates of these two reactions are roughly linear functions of the speed of stirring, and may be approximately expressed by v = a br, in which v is rate of gas absorption and r is speed of stirring. The rate when the gas is only bubbled through is a, and b is a constant for a particular stirrer. In the ethylation of benzene, a has a considerable positive value since the gas is moderately soluble in the liquid, while in the hydrogenation experiments a is negligible. Here the absorption of hydrogen increases faster than the rate of stirring for low speeds, the relation becoming linear at higher speeds. I n Fig. 1 the absorptions in cubic centimeters per minute are plotted against speeds of stirring in thousands of revolutions per minute. At 13,000r. p. m. 1volume of benzene was reacting with 6.5 volumes of ethylene, and 1 volume of c6ttonseed oil in presence of 0.12 per cent nickel was taking up 2.3 volumes of hydrogen, 1000 3 p m whereby its iodine number was being lowered 2.6 per minute. FIG.1-VAKIATIONOF ABSORPTION OB HYDROGEN AND ETRYLENE WITH
+
1
Received May 10, 1923.
SPEEDOF STIRRING
INDUSTRIAL A N D ENGl 'NEERING CHEMISTRY
October, 1923
cut in the top end-of the stirrer shaft. The speed counter was mounted on a swivel joint so that it could be snapped in and out of gear in taking the readings. The reaction vessel was a glasP bottle which was heated in a water or oil bath. The stirrer head was a disk, 37 mm. in diameter, carrying a bell-shaped projection a t the bottom. Into the central cavity were drilled eight 2-mm. radial holes. The delivery tube for the gas terminated just beneath the bell. The stirrer shaft was surrounded by a tube which was carried by the frame above and passed tightly through the
1049
HYDROGENATIOX-AS the rate of hydrogenation varies with the proportion absorbed, the aim was to adjust gas flow and speed of stirring so that approximately 80 per cent of the hydrogen would be used up. The entering and emerging gas streams passed through two flowmeters placed side by side. The capillaries for these were cut from the same piece of tuba ing, the one on the exit side being just five times as long as the other, so that when the two read the same the absorption was just 80 per cent. The flowmeters were calibrated separately, The results are not so satisfactory as those on ethylation on account of the greater number of variables, but they show the same trend. Two runs were made with different preparations of catalyst, both nickel suspended on infusorial earth. The data from the first run are plotted in Fig. 1 and the results of both are given in Tables I1 and 111. As in the ethylation experiments, the readings were made within a short period of time so as to mimimize the effect of changes due to progressive hydrogenation. The three determinations in which the hydrogen was entirely absorbed are marked by (*). In these the amounts taken up are much smaller than in corresponding experiments with excess of hydrogen. TABLE 11-HYDROGENATION (011,250 grams, catalyst, 1.5 grams; 20 per cent nickel) ----Hydrogen, Cc Cc per R. p. M. In Absorbed Per cent 1000 R. p. M. A t 180' C . 1670 50 25 50 15 2200 50 41 82 19 3300 95 81 86 25 7800 350 298 85 38 10,700 665 475 84 44 13,500 755 633 84 47 13,500 433 433 100 32* A t 185" C. 5900 433 361 83 61 6800 488 407 83 60 7600 515 425 83 56 7500 242 242 100 32* ?
FIG 2-THE
STIRRER
stopper, thus making a liquid seal for the stirrer shaft. To prevent swirling of the liquid large baffles were provided. These were carried by round rods passing through the stopper. By meane of pliers applied to the projecting squared upper ends of these rods the baffles could be turned in so as to pass through the neck of the bottle.
BENZENE-A mixture of 250 grams of benzene and 50 grams of anhydrous aluminium chloride was kept a t 80" C. and ethylene passed in, the speed of the stirrer being adjusted so that only an occasional bubble of gas escaped absorption. The rates of stirring and of gas flow were read and then the gas rate was changed. In a run in which constant conditions of stirring, etc., are maintained, the reaction velocity increases for a time and then remains fairly constant for a considerable period, changing gradually as the ethylation proceeds, The measurements made here were all from a single run. Sufficient time was allowed for the reaction to get well under. way before starting readings and then the adjustments were made a s quickly as possible and the readings taken with the passage of a minimum amount of gas so as to avoid great changes in the composition of the mixture. T o produce monoethylbenzene 77 liters of ethylene would have been required, which is several times the volume necessary for the readings. The ethylene was passed through a meter and the time given is for 0.01 cubic foot or 283 cc. The results are given in Table I, the last column of which shows the roughly constant values of b. ETHYLATION OF
TABLE I-ABSORPTIONO F ETHYLENE R. p. M. 0 1000 1000 3000 3000 6000 6000 7600 8000 10,000 10,000 13,000
Seconds per 283 Cc.
..
84 87 30 37 I9
21 16 15 12.5 13 9.5
Cc. per Minute 80 202 196 565 457 896 810 1065 1135 1360 1300 1790 ~~
~
Increase Due t o Stirring
... 122
116 485 377 816 730 985 1055 1260 1220 1720
TABLE 111-HYDROGENATION (Oil, 250 grams; catalyst, 3 grams; 10 per cent nickel) ----Hydrogen, Cc Cc. per R. p. M. In Absorbed Per cent 1000 R. p. M. A t 180' C. 80 1580 33.5 27 18 1800 42 75 56 23 2240 36 80 45 16 126 80 36 3400 158 7800 272 75 35 362 9000 272 75 30 362 355 75 10,200 34 473 413 517 12,850 80 32* A t 190' C. 4600 247 198 80 43 7200 427 360 84 50
----.
EXPERIMENTAL
b
...
122 116 162 126 136 122 129 132 126 122 132
The following experiments were made on the chlorination of toluene and acetic acid: Into 400 grams of toluene at 100" C. chlorine was passed while stirring with a silver stirrer at 6000 r. p. m. There was practically total absorption at 1100 cc. per minute, the chief product being benzyl chloride. I n the presence of a trace of ferric chloride the gas was absorbed as rapidly as it could be admitted. Under the same conditions, 6000 r. p. m. and 100" C., 475 grams acetic acid, containing 17.5 grams of red phosphorus which had been rubbed to a paste with a part of the acid, absorbed chlorine as rapidly as it could be conveniently passed in, averaging about 1470 cc. per minute. During the second hour the rate averaged only 715 cc. per minute. At the end of about an hour all the phosphorus had dissolved. A. P. Strietmann, president of The Biscuit and Cracker Manufacturers' Association, has founded a Research Fellowship a t the University of iMinnesota on fermentation problems arising in the industry of which he is the head. This research will be conducted in the Department of Biochemistry under the direction of C. H. Bailey. A. H. Johnson has been selected t o carry on the work under this fellowship.
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