October, 1928
ISDUSTRIAL AA-D ESGIIYEERISG CHEIIfISTRY
chloride was less than that obtained by hledvedev, . a condition which probably is explained by the additional contact catalysts employed by hledvedev. Methyl Nitrite as Catalyst
.
Methyl nitrite in amounts of 1.0 to 2.0 per cent by volume were also shown to exert a promoting action less vigorous than that of nitrogen dioxide but more pronounced than that of other catalysts investigated under approximately similar operating conditions. The action of methyl nitrite was probably based on ii s spontaneous decomposition a t elevated temperatures into nitrogen dioxide or nitric oxide and a carbon-hydrogen-oxygen residue, the former acting as the catalyst. Explanation of Promoting Action of Nitrogen Dioxide and Methyl Nitrite
In order to obtain data on the character of oxygenated deiivatives formed in these reactions, experiments on a larger scale were necessary, utilizing a semi-continuous apparatus as mentioned previously. In a typical series of experiments, using pure methane as the hydrocarbon source, four passes of the gas through the system, adding oxygen before each pass in order, to maintain a constant oxygen-hydrocarbon ratio, resulted in a yield of oxygenated derivatives amounting to 25 mg. methanol, 205 mg. formaldehyde, and 76 mg. formic acid per liter (standard conditions) of methane decomposed. This was equivalent to 0.0093 atom carbon per liter of methane decomposed. Of the original amount of methane present. 80.3 per cent was decomposed in four passes, while 27.1 per cent appeared as oxygenated derivatives. Calculations indicated that 0.0151 atom of carbon per liter of methane decomposed should have been obtained, whereas only 0.0093 atom, or 61.5 per cent, was experimentally determined to have been present. The actual yield of oxygenated derivatives was probably decreased by decomposition reactions which took place in the condensate and scrubber during the run, since nitric acid was continuously present on account of the partial solution of nitrogen dioxide in water. I n fact, if the condensate temperature was allowed to rise to room temperature, it was observed
1055
that an ebullition occurred within the liquid, iridicatirig a decomposition reaction which resulted in the formation of a gas. Among these oxidations may have been those of formaldehyde and methanol to formic acid, as well. It is improbable that the pronounced action of small amounts of nitrogen dioxide in accelerating the partial oxidation of gaseous hydrocarbon-oxygen mixtures was a result of the formation of unstable intermediates by chemical reaction of the hydrocarbon and nitrogen dioxide. A more satisfactory explanation n-as sought in the readiness with which nitrogen in its oxides changes its valence, thus giving an opportunity for the accomplishment of adsorption phenomena of some character. In any case, the action of nitrogen dioxide appeared to be an additional example of homogeneous catalysis in the gaseous phase, for changing the composition of the chamber in which the catalysis occurred had apparently no effect on the nature of the reaction. hloreover. the rate of oxidation obtained in the small single-pass unit agreed closely with rates and degrees of oxidation obtained in the larger semi-continuous apparatus. For the purposes of this investigation it suffices to indicate that the promoting action of small amounts of nitrogen dioxide in partial oxidation of hydrocarbon-oxygen mixtures is far superior to that of the other solid and gaseous catalysts which were investigated. hloreover, the yields of oxygenated derivatives obtained were about double the amounts which the best5 of previous investigations on the basis of singlepass oxidation was able to indicate, and were many times larger than the yields secured by Wheeler and Blair4 in a circulation apparatus. Tabulated Results
Tables I to I11 show representative results obtained with variable gas-oxygen mixtures a t different temperatures under the influence of different catalysts. One hundred and fourteen tests were made in all. These results are most easily considered by noting the changes in percentages of carbon monoxide, the contraction in volume, tile “n-factor,” and the percentage of total hydrocarbons con\-erted to oxygenated derivatives under the varying conditions.
Relative Rates of Reaction of Olefins in Combustion with Oxygen and in Oxidation with Aqueous Potassium Permanganate’” Harold S. Davis3 LIASSACHUSETTS
ISSTITUTEOF TECHNOLOGY, CAMBRIDGE, hfASS.
With a view to investigating the relative rates of combustion of the olefins, known mixtures of ethylene and propene and of ethylene and isobutene were exploded with oxygen, and the proportion of each olefin remaining unburned was found by analysis of the products. One slow combustion was also made of a mixture of ethylene and isobutene. In every case propene or isobutene burned faster than ethylene. To test their relative ease of oxidation by potassium 1 Contribution No. 34 from the Research Laboratory of Organic Chemistry, Massachusetts Institute of Technology. 2 This paper contains results obtained in an investigation o n the “Relative Rates of Reaction of the Olefins” listed as Project No. 19 of American Petroleum Institute Research. Financial assistance in this work has been received from a research fund of the American Petroleum Institute donated by John D. Rockefeller. This fund is being administered by the Institute with the cooperation of the Central Petroleum Committee of the National Research Council. Director and research associate, Project N o . 19.
permanganate, known mixtures of ethylene and isobutene were dissolved in water and oxidized by a deficiency of permanganate. Then the proportion of each olefin unoxidized was found by boiling out the gases and analyzing them. Here again isobutene reacted faster than ethylene. Calculations of the relative rates of reaction based on a formula developed by Francis, Hill, and Johnston are given. Relative Rates of Combustion with Oxygen
A
PPARATUS-Fifty cubic centimeter samples of the gas mixtures were exploded over lmter in upright thick’ walled Carius tubes (or similar ones of Pyrex glass). The upper end of the tube mas closed by a rubber stopper (wired in) through which passed two glass tubes carrying platinum or tungsten electrodes and an exit tube with a glass stopper. The inner surface of rubber exposed was small and was
INDUSTRIAL A N D ENGINEERING CHEMISTRY
1056
Table I-Inflammation
I
Mixture
(1) C2H4 2 0 . 6 C3Ha 1 7 . 8 Oz 53.6
Original mixture, per cent by vol.
Appearance of combustion
Flash, no carbon
(3)
(4)
20.6 17.8 53.6
21.7 21.8 50.5
9.9 29.9 5s
0.9
1.07
l
CZH4 73 CsHs 89 7s
0 2
Flash, no carbon
86 100
..
1
I
(21
1.1
Percentage consumed
or S l o w C o m b u s t i o n of Olefin-Oxygen M i x t u r e s
Ethylene, Propene, Oxygen
Experiment
Vol. 20, No. 10
Deep purple flame, carbon deposit
Gentle flash, carbon deposit
69 100 97
52 72 79
1
CzH, 10 CaH8 27 0 2 60 0.9
(6)
(7)
23.0 15.8 50.0
24.3 23.5 45.6
0.8
0.5
Lurid Light flash at flame, car- top only of bon detube posit
I
+
Ethylene, Isobutene, Oxygen
(5)
CzH4 36 C4Hs 86 0 2 97
..
No explosion but slow combtistion, no carbon
2s
-02 37
53 62
Mixtures contain proportions of oxygen corresponding with CnHn 202,yield on explosion mainly carbon monoxide and hydrogen, without separation 2 of carbon or material steam formation. Bone and Townend, 09. cit., p. 394. a
always wet with water before the explosion. It showed no signs of oxidation. The lower end of the tube was connected with a water-leveling bulb. I n the experiments recorded here the combustions were always incomplete, both olefins and oxygen being found in the products. The passage of the flame through the tube was clearly marked and the detonations very mild. It was hoped that these conditions would favor differential combustion of the olefins.4 The apparatus used in experiment 7 for the slow combustion of a non-explosive mixture of ethylene and isobutene is shown in Figure 1. MaTERrALs-Commercial “refined” ethylene in a steel cylinder from a well-known firm was used. It dissolved only very slowly in 86 per cent sulfuric acid and was 99.5 per cent soluble in bromine water. Propene was prepared by adding phosphorus pentoxide slowly to well-cooled and well-stirred c. P. isopropanol and heating the product.
The only data essential for the problem under investigation were the volumes of the two olefins and of the oxygen in the gas mixture before and after combustion. However, the other measurements mere useful to check the conclusions. Table I, which summarizes the experiments, shows that in every case propene or isobutene burned faster than ethylene with oxygen. It is known that olefins undergo thermal decomposition in flames and any acetylene thus produced would be counted as ethylene in the method of analysis employed. However, except possibly in the case of highly endothermic ones such as acetylene, which decompose explosively a t high temperatures or under shock, the rate a t which hydrocarbons combine with oxygen far exceeds that a t which they decompose in flames. The data in Table I1 indicate that thermal decomposition of the olefins played only a minor part in these experiments. Practically all the carbon from the olefins used up was to be found in oxygenated products (Con, CO, and CH20). T a b l e I1 (gas) used up, as shown by analysis before and after combustion. in CO and COz of gaseous products. necessary to unite with all the C in olefins used up, to give the CO? found and CO (or formaldehyde). EXPERIMENT A B C
A-02 B--02 C-Oz actually f/ame Jpreader
1 3 4 5 7
CC.
CC.
cc.
41.8 49.0 46.0 5s.2 27.8
41.8 46.1 41.1 49.4 18.2
44.0 48.8
41.3 55.4 32.8
Relative Rates of Reaction with Aqueous Potassium Permanganate F i g u r e 1-Apparatus Used in Experime?t 7 for C o m b u s t i o n of a Non-Explosive Mixture of E t h y l e n e a n d I s o b u t e n e
Isobutene was made from tertiary butanol (m. p. 16” C. and miscible with water without any cloud) by dehydration with oxalic acid a t about 95” C. Commercial oxygen made from liquid air was used. All the gases were well washed with water. PROCEDURE FOR ANALYSIS-carbon dioxide was determined by absorption in caustic alkali in the usual manner. Propene and isobutene were measured by absorption with 86 per cent sulfuric acid to constant volume. The separation from ethylene, which remains undissolved, is very sharp in the case of isobutene, but is less satisfactory for propene. The ethylene residue in the gas was measured by absorption into saturated bromine water, then oxygen by pyrogallol, and carbon monoxide by acid cuprous chloride. 4 Differential combustion of hydrocarbons and hydrogen has already been proved. Bone and Townend, “Flame and Combustion in Gases,” p. 405 (1927).
PROCEDURE-TO prepare a water solution containing known quantities of ethylene and isobutene, 100 cc. of an analyzed mixture of the two gases were forced into the reaction chamber A (Figure 2) full of water. The displaced water rose up into D. After vigorous stirring the residual gas was withdrawn and the quantities of ethylene and isobutene in it were determined by analysis. The volumes of olefins dissolved by the water were calculated. This water in the flask was then rapidly stirred and a solution of potassium permanganate slowly added, the total quantity being insufficient to oxidize all the dissolved olefins. At the rate used (about 1 cc. of nearly saturated solution per minute) the permanganate color penetrated into the rapidly moving water only about 3 cm. from the inlet. It was noticed, however, that if the rate was increased the violet permanganate color mould permeate almost the entire solution, disappearing like a flash when the feed was cut off. It was therefore concluded: (1) that the stirring was good, although difficult in a vessel completely full, and that for the 5
Bone and Townend, 09. cit., p. 380.
ISDUflTRIAL A S D ENGINEERISG CHEMISTRY
October, 1928
most part the permanganate was in contact with an excess of dissolved olefins, so that the latter must have really competed for the oxidizing agent; (2) that the reactions, although rapid, were by no means instantaneous, since the color could be made to permeate the whole solution. After oxidation, the water in the reaction chamber was boiled out directly from the flask without venting to the air and the evolved gases were collected over mercury. A considerable quantity of water was also displaced partly by exA-1000-cc. flask completely filled with a water solution of olefins B-Stirrer system provided with a gastight stuffing box a t the top. The glass stirrer tube is cemented to the propeller shaft a t m and the glass tube extends up around the shaft bearing. Any gas leakage must first pass down the narrow space between these tubes and can therefore be seen a t once
1057
The results are summarized in Table 111. In every case a greater proportion of isobutene than of ethylene was oxidized. CaLcuLaTron-s-Values of the ratios of the reaction coefficients, assuming the reactions to be of the second order, show fair agreement. The following calculations of the relative rates of reaction of the olefins in the two series of tests were made for those experiments in which each of the two olefins competing for the reagent was incompletely oxidized. They are based on the formula developed by Francis, Hill, and Johnston6 for the case where two substances compete (in irreversible reactions of the second order) for a third substance: where
= fractions of olefins A and B which react Y A and Y B K A and K B = velocity constants of oxidation reactions
of the two olefins
The values for the separate experiments and the average values are summarized in Table IV. R a t e s of R e a c t i o n of Olefins OXIDATION WITH AQUEOUSPERMANGANATE K propene K isobutene K isobutene Eupt. K ethylene Expt. K ethylene Expt. K ethylene 8 1.32 9 1.67 11 2.03 Average 1 71 2.8 1.64 RATIOSO F RELATIVE RATES Combustion with Oxidation by Oxygen Aqueous Permanganate 1 Ethylene 1 ... Propene 1.7 1.6 Isobutene 2.8 T a b l e IV-Relative
C-Inlet tube for delivering gases, or permanagate solution directly under stirrer blades D-Water overflow system designed to prevent escape of gases
CO&rBUSTION WITH
OXYGEN
I
E-Exit
tube for gases
F i g u r e 2-Apparatus f o r C o m p e t i tive O x i d a t i o n s of Olefins b y Perm a n g a n a t e in Aqueous.Solution
-
pnnsion and partly by priming. In the last three experiments this water was collected in an evacuated flask placed between the reaction chamber and the gas buret. After the reaction chamber had been thoroughly boiled out, it was shut off and the intermediate flask also boiled out so that all the gases, including some air, were collected over a minimum of water. The volumes of ethylene and isobutene in these gases were found by analysis. The reaction chamber was not placed in a constant-temperature bath. Room temperature was about 23-24’ C.
NO.
8 9
10 11
T a b l e 111-Oxidation in W a t e r S o l u t i o n b y P e r m a n g a n a t e : E t h y l e n e os. I s o b u t e n e BEFORE AFTER OXIDATION OXIDATION OXIDIZED CC. cc. cc. Per cent Ethylene 35.7 19 4 16.3 45.6 Isobutene 34.9 15.6 19 3 55.3 Ethylene 38.2 20.9 17.3 45.3 Isobutene 40.1 15.5 20.6 61.4 Ethylene 33.1 0.16 32.9 99.4 Isobutene 32.3 0.0 32.3 100 Ethylene 27.8 6 3 21.5 77.3 lsobutene 28 5 1.4 27.1 95.1
.
Comparison of Reactions w i t h Oxygen a n d w i t h B r o m i n e
There are certain striking analogies between the reactions of olefins with oxygen and with bromine: (a) Ethylene reacts more slowly than propene or isobutene in the following cases: (A) bromination in carbon tetrachloride solution;7 (R) combustion with oxygen; (C) oxidation with aqueous permanganate. ( b ) I n bromination of the olefins the main action is bromine addition to the unsaturated carbon atoms. I n combustion there is good evidence that the primary reactions are the addition of one or two atoms of oxygen t o the olefin.8 ( c ) The rates of combustiong and of bromination’ of olefins can both be decreased by intensive drying.
These analogies perhaps justify the suggestion that the natures of the groups attached to unsaturated carbon atom affect, through the same mechanism, the number of the molecules in the olefins which become active in unit time both for bromination and oxidation. The nature of that mechanism which concerns the atoms in the olefin molecules remains to be shown. 6
7
J . Am. Chem. Soc., 47, 2222 (1925). Results by the author, as yet unpublished. and Townend, Op. cit., p. 380. I b i d . , Chap. XXIV.
1 Bone 9
Soft Drink Business Uses Much Sugar and Fruit J. W. Sale, of the United States Department of Agriculture, estimates that more than 11,000,000,COO bottles of soft drinks and non-alcoholic beverages are consumed in the United States each year. They play a n important role in providing a market for many farm products. It is estimated that into these 11,000,000,000 bottles go 250,000 tons of sugar, 5,000,000 pounds of fruit acid, 50,000 pounds of artificial color, 1,000,000 gallons of flavoring extract, and 400,000,000 gallons of carbonated water. There are all kinds of soft drinks. Some are pure fruit juices. Others belong to the “ade” class and contain from 15 to 20 per
cent of juice, often with other ingredients added. There are also the non-alcoholic cordials, cereal beverages, and the bottled sodas, the latter accounting for the bulk of the business. Most soft drinks now are free from harmful substances, but some are found to contain unwholesome or injurious acids, arsenical dyes, metallic salts, uncertified coal-tar dyes, or soap bark. Popular belief holds that artificial colors are harmful, but this is a mistake, provided they are the right kinds of colors. Careful tests have established that many of the coal-tar dyes are entirely harmless, and these are permitted for use in beverages.
