INDUSTRIAL A N D ENGINEERING CHEMISTRY
May, 1926
Conclusions
T a b l e 111-Atmospheric Corrosion of Chromium Iron: L a b o r a t o r y
Tests Chromium Per cent 16.02 13.00 9.23 8.29
-Corrosion Run I 0.00005 0.00007 0 . 00007 0.00005 0.0032 0,0023 0.0117 0 0061
Rates, Cm,/Year-Run I11 0.00015 0.00005 0,00012 0.00013 0.0026 0,0022 0.0076 0.0076
Average 0.00008
0.00009 0.0026
0.0082
535
The rapid test of corrosion resistance on bare steel described in this paper has given results within a few days comparing favorably with the results of long-time service tests on the same steels by the A. S. T. M. It is believed that the essential features which make such close comparison possible are the proper preparation of the samples by previous corrosion and the use of moisture as the sole accelerating agent.
Influence of Rate of Stirring on Reaction Velocity',? By F. C. Huber and E. Emmet Reid THE J O H N S HOPKISSUNIVERSITY,
BALTIXORE,
LID.
I n consecutive reactions we may have a slow reacThe influence of speed of stirring on the ratio of a tion followed by an exnumber of reactions has been studied. Three classes Historical tremely rapid one, or the have been found, those in which the rate is approxireverse. I n either case the It is, of course, impossible mately a linear function of the speed of stirring, those to mention all In which o v e r - a l l rate depends on stirring has been used t o acin which this relation becomes linear only after a certhat of the slow reaction. celerate chemical reactions, tain speed is attained, and those in which the rate is We may regard the reaction but a few are listed in which independent of the speed of stirring. To Class 1 of a gas with a liquid as the effect of s t i r r i n g w a s belong the ethylation of benzene by ethylene, the oxidastudied quantitatively. two consecutive reactions, Marc3 studied the rate of tion of sodium arsenite by oxygen, the oxidation of p of which the first is the crystallization. H e f o u n d nitrotoluene by chromate mixture, and the reduction of solution of the gas in the that at a c e r t a i n nitrobenzene by iron and dilute acid; to Class 2 the speed for any given temperaliquid and the second the turefurther increases in speed catalytic hydrogenation of cottonseed oil and of a hyreaction between the disdrocarbon; and to Class 3 the saponification of ethyl had no influence on the rate. solved gas and the liquid, H e also found salts whose benzoate at 60" C. and the reaction of benzyl chloride The rate of solution may be Of crysta11ization were with dilute aqueous solutions of sodium acetate and independent of the speed of slow and the reaction of the at 2oo c. stirring. Brunner4 s h o w e d dissolved gas rapid, in which t h a t the rate of solution was - case the observed rate of reDroDortional t o the 2/. Dower action must depend on the of {he stirring speed: Later, Van Name and Edgar6 showed that the rate of reaction of iodine rate of solution which is dependent on stirring. I n case a gas with metals is proportional t o the 4/; power of the speed. Zeng- dissolves quickly but reacts slowly after it is in solution, heliss found t h a t if a gas is passed through a parchment capsule stirring may be expected to have little effect. the rate of reaction between the gas and the solution is increased. The reactions studied group themselves into three classes : Friend and Bennet' studied the rate of solution of pure iron in dilute sulfuric acid a t speeds ranging from 145 to 4000 r. p. m. (I) those in which the rate of reaction is approximately a They found t h a t the rate of solution is proportional t o the speed linear function of the speed of stirring, (2) those in which of stirring. Tzentnershvers found t h a t the rotation of a magnesium cylinder in dilute hydrochloric acid hastened its solution. the relation becomes linear only after a certain speed is reached, and (3) those that are but slightly affected by Danniensg noticed that the absorption of ethylene in sulfuric acid was increased 20 t o 27 times by stirring a t 200 r. p. m. Re- changes in the rate of stirring. cently, a n article from this laboratory, by Milligan and Reid,'o For Class 1 we have the relation described the influence of high-speed stirring on several systems. of stirring, from none up to 12,000 r. p. m.
1 Presented under the title "The Relation of-Reaction Velocity to Rate of Stirring in Various Systems" before the Division of Organic Chemistry at the 69th Meeting of the American Chemical Society, Baltimore, Md., April 6 to 10, 1925. Received November 7, 1925. From Ph.D. dissertation of B. C. Huber, 1925. Z . physik. C h e m . , 61, 385 (1908); 79, 71 (1912); Z. Lileklrochem., 15, 679 (1909). 4 Z . p h r s i k . Chem., 47, 56 (1904). 4 [bid., 73, 97 (1910). C o m p t . vend., 170, 583; 171, 167 (1920). 7 J . Chem. SOC.( L o n d o n ) , 121, 41 (1922). 8 Rec. lruu. chim., 42, 579 (1923). 0 Comfit. rend., 175, 585 (1922). loTHIS JOURNAL, 15, 1048 (1923).
*
a=a+br
in which v is the reaction velocity, r the rate of stirring in thousands r. p. m., a the velocity when there is no stirring, and b a constant. The curves all cut the axis above the origin. I n the second class the reaction is very slow with no stirring, the rate increases a t first more rapidly than the speed of stirring, and later the relation becomes linear. The straight part of the curve is represented by 2,
= b(r
- r')
in which r' is the rate of stirring a t which the linear part of the curve would cut the axis if it were prolonged. It is
INDUSTRIAL AND EN(XNEERING CHEMISTRY
536
somewhat less than the speed a t which the relation becomes linear. T o the first class belongs the ethylation of benzene by ethylene in presence of aluminum chloride (Figure 1). The numerical values given are for the writers' apparatus under certain conditions and would be entirely different for another stirrer and for other experimental conditions. If u is the volume of ethylene absorbed by 1 mol of benzene per minute, we have for the first run: v = 44 13.5r I n the oxidation of sodium arsenite by gaseous oxygen, v is cubic centimeters of oxygen absorbed in 20 minutes by 250 cc. of 0.2 M solution. v = 8 200r When p-nitrotoluene is oxidized by alkaline permanganate, v is grams of p-nitrobenzoic acid per hour v = 2.5 0 . 4 5 ~ The reduction of nitrobenzene by an iron disk in 0.1 N hydrochloric acid is also in this class. To the second class belong the hydrogenation of cottonseed oil with a nickel catalyst (Figure 2), and of Solvenol with a platinum oxide catalyst. For these we have v = 40(r - 5.3) v = 125(r - 6.3) and respectively, in which v is the volume of hydrogen absorbed by 100 grams of the oil per minute. I n both cases the relation becomes linear a t 7000 to 8000 r. p. m. with this particular stirrer. The solution of iron from a 50-mm. disk in 0.1 N sulfuric acid follows the equation
+
+
+
v = 4.qr
- 0.8)
in which v is milligrams of iron dissolved in 30 minutes. I n this the relation is linear throughout the range of speeds covered, hut for lower speeds the curve would probably be similar to those for the hydrogenations. I n hydrogenation a gas, a liquid, and a heavy metal powder must be brought together. With slow stirring the catalyst is probably not kept in uniform distribution and only R part of it is effective. At a certain speed all of it is brought into action, and from there on the rate depends on bringing the gas into contact with the liquid and the relation becomes 1'inear. The saponification of ethyl benzoate by dilute aqueous caustic soda and the hydrolysis of benzyl chloride by the same were found to belong to the third class; that is, the rates were not considerably affected by changes in the rate of stirring. Apparatus
The stirring machine used has been previously described by Milligan and Reid'" and by Berry.ll I n this investigation two types of reaction vessels were used. The first was the gas-tight vessel previously described. The second was not gas tight and was designed for liquid-liquid and liquidsolid systems. This vessel consisted of a copper can provided with a copper water jacket. Eight baffle plates, also of copper, fitted tightly into the can. The baffles were attached to a circular copper cover, through a hole in the center of which the stirrer shaft entered. This apparatus provides very efficient baffling. Two arms, riveted to the jacket of the vessel, were bolted to two heavy brackets fastened to the frame, The arms were provided with slots so that the vessel could readily be centered with reference to the stirrer shaft. The stirrer head was of a new type, it consisted merely of a disk of metal, 37 mm. in diameter, grooved radially on the bottom. Stirrer shafts and heads of iron, bronze, and monel metal were employed. 11
Dhsnfolion. Johns Kopkins University, 1923.
Vol. 18, No. 5
As copper was found unsuitable for some purposes, a monel metal can was made which fitted inside the copper vessel. A set of monel baffles was also provided. Ethylation of Benzene by Ethylene
This reaction has been previously described by Milligan and Reid and improved by Berry. The charge was 460 grams of benzene and 45 grams of aluminum chloride which was heated to 80" C. and dry, purified ethylene admitted. When a fresh charge was used an incubation period of 30 minutes to 1 hour was required before the reaction
P 'S
F
6
220
200
i 180
E
160
4 140 120
e
IO0
E th y /a tion
60
o Run A Run x Run
I
'
/
'
2
I
3
I
4
I
I
I
I
I
I
5 6 7 8 9 10 Thousands R P M
I
I!
o f Benz e m I D
LU
1
/2
I
I
1314
I
15
I
started. When the reaction was going well the stirrer was set a t any desired speed and the flow of ethylene and the time in seconds taken for the absorption of 0.01 cubic foot (283 cc.) of ethylene. The stirrer speed was changed, the flow of ethylene again adjusted, and another reading taken. The adjustments and readings were made in a short time to avoid great changes in the composition of the reaction mixture. I n all cases the rate of admission of ethylene was so adjusted that i t was totally adsorbed, not more than one bubble a minute being allowed to escape from the trap a t the end of the train. The data obtained confirm the results of Milligan and Reid. Table I-Ethylation Run
I
R. p. m. r 3600 4480 6240 7200 8000 8640 9120 11050 12000 3510 4880 6240 7200 8400 8732 9120 11050 11910 3680 4480 5120 5920 6720 7520 8000 8640 9120 10560 11 520
Seconds for 283 cc. 30 26.4 22 21 20 18 17 15 14
28 24 21 20 17 16.5 15 14 13 28 25 24 22 21 19 18 17 16.5 15 14
of Benzene
cc.
CaHa(mol./ mln. 94.3 107 129 138 151 158 166 189 202
101 118 136 151 166 170 189 202 218 101 113 118 129 138 148 157 165 170 188 202
a
v-a
44
50.3 63 85 94 107 114 122 145 158
52
49 66 84 99 114 118 137 150 166 53 65 70 81 90 100 109 117 122 140 154
48
b 14.0 14.1 13.6 13.1 13.4 13.2 13.4 13.1 13.2 Av. 15.5 14.0 13.5 13.5 13.7 13.6 13.5 15.0 13.6 13.9 14.4 14.5 13.7 13.7 13.4 13.3 13.6 13.5 13.4 13.3 13.4
The volume per mol per minute is plotted against rate of stirring in thousands r. p. m. in Figure 1. By drawing a line through the points so obtained and extending this to the
INDUSTRIAL A N D ENGINEERING CHEMISTRY
May, 1926
axis the values 44, 52, and 48 are obtained for a of the formula. I n the three runs different values were obtained on account of variations in the catalyst and in operating conditions. The data for three experiments are given in Table I. Oxidation of Sodium Arsenite
According to Dhar,I2 "It is well known that a solution of sodium arsenite is not oxidized by atmospheric oxygen under ordinary conditions." However, under the conditions of the present writers' experiments sodium arsenite is oxidized by oxygen. The iron stirrer may have been the necessary catalyst. -4stock solution of arsenic trioxide in sodium hydroxide was made up in the proportion 1Asz03to 6NaOH. This solution was molar with respect to arsenic trioxide, 198 grams per liter. For each run 50 cc. of this solution were diluted to 250 cc., heated to 65' C., and a 10-cc. sample taken for the zero titration. The solution was transferred to the gas-tight stirring vessel and oxygen admitted a t the rate of 50 cc. per minute for 20 minutes. At the end of this time a 10-cc. portion was taken, added to an excess of standard iodine solution, and back-titrated with sodium thiosulfate solution. A fresh portion was taken for each speed. A 3-hour run was made a t 8000 r. p. m. to see how far the reaction would go. Samples were withdrawn every 20 minutes. By the end of this time there was 70 per cent oxidation and the reaction had slowed down greatly. The value of a was obtained directly. The full data are in Table 11.
Reduction of Nitrobenzene
The nitrobenzene was reduced by iron and hydrochloric acid, the iron being a 50-mm. disk attached to the monel metal shaft in place of the usual stirrer head. The solution was 500 cc. of 0.1 N hydrochloric acid at 20' C. with 10 cc. of nitrobenzene for each run, the time being one hour. The resulting mixture was analyzed for aniline as follows: The solution was made alkaline and steam-distilled for one hour. The distillate was then strongly acidified and the volume of nitrobenzene recovered was measured. A blank showed that 9.9 cc. of nitrobenzene were recovered by this method.
Run
I
R. p. m. r 0 3200 6300 8000 9600
Oxidation Per cent 0.76 6.35 12.0 15.7 18.5
3520 5760 9600
7. 6 10.9 18.3
84 120 201
I1
a 8
v
-a
Table IV-Reduction R. p. m. Per cent r reduced 0 9 15 3680 6720 20 9600 26 0 7 7200 24 10560 30
Run
I
I1
of Nitrobenzene a
b
v-a
...
..
9
6 11 17
1.63 1.64 1.77
17 23
2.36 2.18
..
I
...
Hydrogenation of Cottonseed Oil
This reaction has been previously studied by Milligan and Reid, whose methods were followed. The hydrogen was purified by being passed through pyrogallol and soda lime, through the meter and flowmeter, and then dried. The reaction mixture consisted of 450 grams of cottonseed oil kept a t a temperature of 165" C. and 5 grams of a nickel catalyst prepared by Dr. Milligan. 1
Table 11-Oxidation of Sodium Arsenite Oxygen absorbed Cc. 8 70 134 173 204
537
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
b
...
0 62 126 165 196
19.4 19.7 20.6 20.5
76 112 193
21.6 19.4 20.1
Oxidation of #-Nitrotoluene
p-Nitrotoluene is readily oxidized to p-nitrobenzoic acid. The product of the reaction is an insoluble solid and can be conveniently determined. The oxidizing solution contained 58 grams of potassium permanganate and 10 grams of sodium hydroxide per liter; 450 cc. of this solution were used for each run. The runs were made in the monel apparatus. The oxidizing solution was first heated to 70" C. The stirrer speed was then adjusted as desired, and finally 10 grams of p-nitrotoluene were added. After one hour the alkaline solution was cooled to about 10" C. and filtered by suction through asbestos. This removed most of the manganese dioxide formed. The filtrate was then acidified to precipitate the p-nitrobenzoic acid, allowed to settle, and filtered through asbestos. The precipitate was then dissolved in hot, dilute sodium hydroxidereprecipitated, cooled, and filtered through a small filter paper in a Buchner funnel, dried, and weighed. An allow, ance of 0.37 gram was made for loss due to solubility in the volume of water used. Table 111-Oxidation of @-Nitrotoluene R. p. m. 1
0 4000 6400 8000 9600 12
Nitrobenzoic acid Grams 2.5 4.2 5.5 6.3 6.8
J . phys. chcm.. !28,'948 (1924).
a 2.5
v-a
0 1.7 3.0 3.8 4.3
Table V-Hydrogenation Run
I
I1
I11 b
0:42 0.47 0.47 0.45
R. p. m. I
r'
5440 7040 8240 8800 9500 10080 10980 12000 12640 5440 6400 7040 8240 8640 9500 9920 10640 11600 4480 6240 7040 8240 8640 9280 9920 10640 10980 11600 12480
5300
I -r'
2940 3500 4200 4780 5680 6700 7340 4400
... 2640 3840 4240 5100 5520 6240 7200
4500
. ..
...
2540 3740 4140 4780 5420 6140 6480 7100 7980
of Cottonseed Oil Seconds For 283 cc. 72 38 25 23 18 16 13
11 9.5 38 27 20 15 13 11 10 9 8 72 38 30 21 19 17 15 13 12
11 9.5
Cc./lOO gram/ min. 42 79 121 131 168 189 233 275 318 79 112 149 207 233 275 303 335 378 42 79 101 144 159 180 201 233 251 275 318
b
... I..
41.1 37.4 40.0 39.5 41.0 41.0 43.3
... ...
66.4 53.9 55.0 53.9 54.9 53.6 52.5
... ...
39.4 38.5 38.4 37.9 37.1 37.9 38.7 38.7 39.8
INDUSTRIAL AND ENGINEERING CHEMISTRY
538
Two flowmeters were used, one on the entering gas and the other on the gas coming through. The capillaries of these were of the same bore, but one five times as long as the other so adjusted that just 80 per cent of the gas was being absorbed when the readings on the two flowmeters were identical. For any given speed the flow of hydrogen was adjusted till the readings were the same and the time taken for the admission of 283 cc. The volume of hydrogen entering was multiplied by 0.8 and divided by 4.5 to obtain the volume gas absorbed per minute by 100 grams of the oil. As 1 efore, the adjustments and readings were made as quickly as possible so that the composition of the oil would not change greatly during the measurements. -4t the maximum speed of stirring the oil could be hardened i o an iodine number of 4 in less than 4 hours. The rate of hydrogenation fell off markedly after half of the calculated amount of hydrogen was taken up. The results were plotted (Figure 2) and the value of T' of the formula obtained by laying a ruler on the straight part of the curve and seeing where it cut the axis. The values of r' so obtained were 5300, 4400, and 4500, which were used in calculating b.
was attached to the monel shaft by small nuts, also monel, rubber washers being used to prevent contact between the iron and the monel shaft. A standard solution of 1 N sulfuric acid was made up, 50 cc. of which, diluted to 500 cc., were used for each run. The temperature was 20" C. and the duration of each was 30 minutes, a t the end of which the entire solution was titrated with standard potassium permanganate solution. Table VII-Solution
( \ '
Hydrogenation of Solvenol
The Solvenol used was a commercial solvent said to be chiefly dipentene. The catalyst was prepared by adding a solution of 5 grams sodium carbonate and 20 grams sodium nitrate to a boiling solution containing 1 gram of platinum as chloride. The oxide came down as a light orange flocculent precipitate, which was easily filtered and washed. The apparatus used was the same as with cottonseed oil. An attempt was made to hydrogenate without adding any solvent, but the water formed caused the separation of the catalyst. Hence alcohol was added. The charge was 1.50 grams Solvenol and 1.50 grams alcohol. I n Runs I and II,0.2 gram of catalyst was used and 0.3 gram in Run 111. The temperature was 60" C. and the hydrogen was passed in a t such a rate, for any giren speed, that just 80 per cent was absorbed. The values of r' were found, as before, and were 6300, 6300, and 6100. Table VI-Hydrogenation R . p. m. Run I
I1
r
5760 7040 8320 8800 9280 9920 10560 11040 11840 12640 5760 7040 8320 8800 9280 9920 10560 11040 11840 12640
r' 6300
r-r'
...
2626 2500 2980 3620 4260 4740 5540 6340 6300
... ...
2020 2500 2980 3620 4260 4740 5540 6340 6100
... ...
2220 2700 3180 3820 4460 4940 5740 6540
of Solvenol Seconds t o admit 283 cc. 50 44 36 30 25 19 16 15 13 11
Cc./min./ 100 grams So1v en o1 181 206 251 301 363 477 567 603 700 820
125 121 122 132 133 12s 126 130
50 44 37 29 24 19 16.5 15 13 11
181 206 244 312 377 477 550 603 700 820
121 125 126 132 130 127 126 130
44 37 30 24 21 16.5 15 13
206 244 301 377 431 550 603 700 820 901
11 10
b . . I
...
... . ..
... iik
140 135 144 135 141 141 139
Solution of Iron i n Dilute Sulfuric Acid
The vessel used in this work was the monel metal can provided with monel baffle plates. A disk 50 mm. in diameter of commercial sheet steel provided the iron. The disk
Vol. 18, No. 5
of Iron in Dilute Acid
R. p. m. ' I
Y
3040 4000 5760 6720 8160 9280 10000 11360
7-1'
2240 3200 4960 5920 7360 8480 9200 10560
800
Iron dissolved ME. 10 14 22 26 33 38 42 48 ~I
b 4.4 4.4 4.4 4.4 4.5 4.5 4.6 4.5
Saponification of Ethyl Benzoate
The runs were carried out a t 20" C. using two concentrations of sodium hydroxide, and were of 5 and 30 minutes' duration. The procedure used was to introduce the alkali solution, 500 cc. in volume, into the copper reaction vessel, bring it to the desired temperature, adjust the machine to the desired speed, and then add 10 grams of ethyl benzoate. At the end of the run the entire solution was titrated with standard acid, using phenolphthalein as indicator. Table VIII-Saponification Run
R. D. m.
Time Minutes
4000 11360
of Ethyl Benzoate NaOH normality
Saponification Per cent
0.172
9.31 9.70 24.88 25.27 24.25 25.12 25.28
4000 9600
Reactions of Benzyl Chloride
The reactions of benzyl chloride with sodium acetate, 0.1 N and 0.2 AT,with sodium hydroxide, 0.174 N , were carried out in the monel metal vessel in a solution volume of 500 ce. a t 20" C. The solutions were put in the reaction vessel, the desired temperature attained, the machine adjusted for the desired speed, and, finally, 10 grams of benzyl chloride added. S t the end of the run, 30 minutes or one hour, the entire solution was titrated with standard silver nitrate solution, 1 cc. of which equaled 0.01 gram benzyl chloride, using Mohr's method. The alkaline solutions were first neutralized with sulfuric acid. It was thought that the presence of a large amount of an inorganic salt in the water solution might cut down the solubility and make the effect of stirring more evident, but such was not the case. Table IX-Reaction
Rates of Benzyl Chloride with Sodium Acetate and Hydroxide
Sodium acetate
Normality 0.1
Sodium acetate
0.2
Sodium hydroxide
0.174
Sodium hydroxide Saturated with sodium sulfate
0.174
SoLUrroN
R. p. m. 2560 6720 9600 2560 6720 9600 2880 6400 9600 3200 6400 9600 3200 9600
Time Minutes 30
60
Per cent reaction 0.35 0.38 0.40 0.36 0.39 0.38 0.52 0.50 0.53 0.66 0.68 0.68 1.00
1.01
