Explosive Properties of Dioxan-Air Mixtures G. W. JONES, H. SEAMAN,AND R. E. KENNEDY Pittsburgh Experiment Station, U. S. Bureau of Mines, Pittsburgh, Pa.
U
K T I L recently tetramet hylene 1,4oxide, CHzOCH&H2OCHz,
produce higher concentrations in the bomb caused some of the dioxan to condense out in L J the copper tube leading into the bomb. a l s o called "dioxan," The upper limit was t h e d i s c o v e r y of determined in a n apwhich was announced by Lourenzo ( I S ) in paratus which permit1863, has r e m a i n e d ted the entire apparatus to be heated suffia chemical c u r i o s i t y . ciently to prevent The recent d e v e l 0 pdioxan vapor from conm e n t of methods for its production in comdensing out. This apparatus consisted of a mercial q u a n t i t y has 2.5-inch (6.4-cm.) cyled to a n i n v e s t i g a lindrical glass tube 3 tion of its properties, feet (91.4 cm.) long, so which disclosed it to be a solvent for cellulose FIGURE 1. APPARATUS FOR DETERMIXING IGNITIONTEMPERATURE^ OF constructed that the COWRUSTIBLE GASESAYD VAPORS p r e p a r e d d i o xan-air acetate, cellulose esters, mixtures were i n t r o and a variety of resins, oils, and waxes. It is already in use in cellulose acetate solu- duced at the bottom of this upright glass tube and discharged tions, in the manufacture of plastics, and as a solvent in at the top. Ignition of the prepared mixture was effected by various preparations. Since dioxan is a combustible liquid electric sparks across a spark gap situated near the bottom yielding inflammable vapors, i t is desirable, in order t o of the tube. This apparatus has been described in a previous safeguard those who make use of it, t o determine its limit publication ( I O ) . The temperature of the explosion tube and of inflammability and the pressures which mixtures of its connections leading from the vaporizer mas maintained at 100' to 110' C. The upper limit for dioxan in air (dried by vapors with air may produce on explosion. calcium chloride) at 100' C. and at laboratory pressures was LIMITSO F INFLAMMABILITY AND PRESSURES DEVELOPED found to be 22.25 per centby volume. The dioxan was supplied by t h e Carbide and Carbon IGNITION TEMPERATURE Chemicals Corporation of New York. The material received was fractionally distilled, and tests described in this paper The ignition temperature of dioxan-air mixtures was were made with the fraction boiling between 100.5' and determined by the static method, using a quartz bulb of 102O c. 88 cc. capacity. A drawing of the ignition temperature The lower limit of inflammability was determined in the apparatus is given in Figure 1. limits of inflammability bomb (9). The lower inflammable The quartz bulb, A , was mounted in the electric furnace, C, limit found for dioxan-air mixtures in this closed bomb and whose temperature could be controlled by altering the current by the pressures developed when the mixtures were ignited are means of rheostat T. The temperature was measured by means of a thermocouple, D, located inside the electric furnace between given in Table I. copper shield B and bulb A. The copper shield was used to give TABLEI. LOWERINFLAMMABLE LIMITAND PRESSURES nearly uniform temperature inside the furnace over the area ocDEVELOPED cupied by the quartz bulb. The temperatures were measured with a potentiometer. The mixtures were prepared in the 19Initial temperature, 24O t o 26O C.; initial pressure, 721-41 mm. mercury) PRESSURE DEVELOPED PROPAQATED liter bottle, Y , as follows: The bottle was first thoroughly cleaned and filled with normal air; then a measured volume of the liquid TEST DIOXAN ABOVE ATMOSPHERIC FLAMB dioxan was added to the bottle from a 5-cc. buret; stopper M % b y vol. Lb./sg. in. ( K g . / s q . om.) and manifold, which connected the bottle t o the quartz bulb, 1.88 .. .. 9 No 1.92 .. .. No 13 were connected with the bottle, and the liquid dioxan in the 1.96 .. .. No 12 bottle was vaporized by rotating the bottle. Four 0.5-inch (1.3.. 11 1.96 NO em.) glass marbles were placed in the bottle before the dioxan (2:ii) 10 30 1.98 Yes 36 7 (2.53) ~. 2.04 Yea was added. This assisted in vaporizing the dioxan when the (2.74) 2.05 39 Yes bottle was rotated. The vaporization of the liquid developed (3.02) 43 2.13 Yes a pressure inside the bottle, which pressure was registered by the (2.95) 42 2.22 Yes 45 (3.16) 2.34 Yes manometer, N . The manifold leading from the bottle to the 3.24 69 (4.85) Yes quartz bulb consisted of glass and copper tubing, a copper shot 1 80 (5.62) 3.54 Yes flash-back arrester,. E,. and a rubber connection to the three-way The lower inflammable limit in air (dried by calcium chlo- s t ? f ~ ~ $ o ~ d u rine making tests follows: Cock was closed ride) was 1.97 Per cent by volume at laboratory temperatures cock H opened. A high-vacuum pump was then started, and and messures. the auartz bulb and connections were comoletelv evacuated. A Towtentlomet
and
of dioxan was pr&ent. ~ i ~ hof dioxan ~ per in air could not be obtained at laboratory temperatures. Saturation was reached at this point, and attempts made t o
After the bulb was evacuated, stopcock H was then turned to con~nect the bulb with the prepared dioxan-air mixture in bottle Y . ~k~operation caused the dioxan-air mixture to rush into the quartz bulb, where it was heated t o a predetermined temperature.
1283
IN DUSTR IAL AND EN GINEERIN G CHEM ISTRY
1284
The time required for the gas mixture to enter the bulb and reach atmospheric pressures (or slightly higher) was only a small fraction of a second. In practice it was necessary only t o turn cock H momentarily to connect with the bottle and then close it again. At the instant that cock H was closed, cock X was opened to connect with the water reservoir, F , and a stop watch was started. The bulb was put into communication with the reservoir so that, when the mixture in the bulb was ignited, the pressure developed was released into the reservoir, thus preventing the breaking of the quartz bulb. Ignition of the mixture was shown by a flame, the forcing of water from the reservoir, and usually a sharp report. The percentage of dioxan in the test mixture was determined by calculation. Knowing the molecular weight and density of the material, the temperature, pressure, and volume of the air in bottle Y , the cubic centimeters of dioxan necessary to be added to give a desired concentration were calculated in advance. The apparatus described is similar to that used by Mason and Wheeler (16) with the addition of certain modifications such that combustible liquids could also be tested in it. Before the ignition temperature apparatus was used for determining the ignition temperatures of various combustible gases and vapors it was calibrated against a combustible gas whose ignition temperature was known. The values obtained for the ignition temperature of methane-air mixtures by Mason and Wheeler using a n 85-00. quartz bulb were as follows: METHANE IQNITION METH.ANE IQNITIONMETHANE IQNITION TEMP. IN MIXTURE TEMP. I N MIXTURE TEMP. % c. % a. c. % c. 2.45 690 8.00 692 11.40 711 4 05 684 10.15 703 12.80 720 6.00 685
I N MIXTURE
Values found by Dixon and Coward (j), using the concentric tubes device in which the methane and air were brought together in motion in a tube heated to a definite temperature, varied from 650' t o 750' C. depending on the concentration of methane in the mixture. Taffanel and Le Floch (22) using a bomb found a minimum ignition temperature of 675' C. The values for methane-air mixtures in the apparatus described here gave the following results : METHANEIQNITION TEMP % c. 3.75 648 5.25 645
METHAVE IQNITION TEVP
% 7.30 9.75
c.
even if the mixture is raised to the ignition point. If this is true, then such combustible-air mixtures, which in the quartz bulb tests show a decrease in ignition temperature with increased concentrations of the combustible, should be tested by a method whereby increased concentrations of the vapor may be produced and a t the same time the vapor surrounded by an ample supply of oxygen. The ideal method for use under these circumstances would then appear to be that of allowing a drop of the combustible liquid to fall on a rather extensive heated surface whereby the droplet could move about freely in contact with air. If this were done, there would be concentrations of pure vapor immediately surrounding the liquid droplet, and, as the distance from the droplet increased, the concentration of vapor would rapidly decrease, finally ending with normal air a t a short distance. This idea was first tested out by preparing a bath consisting of 55 per cent potassium nitrate and 45 per cent sodium nitrate, which has a melting point of 227' C. This mixture was melted in a 4-inch (10.2-em.) metal container, provided with a stirrer and thermocouple for registering the temperature of the bath. When a droplet of liquid amylene was placed on the surface of the bath, i t moved about on the surface for some time and then suddenly ignited a t a much lower temperature than the lowest temperature, 381 ' C., given by the quartz bulb. Eventually it was found that a temperature of only 273" C. would cause ignition of the amylene on the surface of the bath. At this temperature t h e lags were 10 or more seconds, and close inspection of the droplet as i t moved about on the surface showed that ignition usually took place a t the instant the droplet disappeared (became completely vaporized). Also, as the droplet diminished in size and became very small, the liquid turned dark in color. Apparently the amylene, owing to the continued heat, decomposed, and perhaps decomposition products caused the ignition. TABLE 11. IGNITIOX TEMPERATURES IN AIR OF COMBUSTIBLE GASESAND VAPORS USING 88-CC. QUARTZ BULB COMBUSTIBLE
CO\fRUSTIBLE Required for complete In combustion mixture
% Methane (CH4)
9.45
660
Manufactured
gas"
18.40
Acetone (C3HeO)
4.95
Methyl formate (CZHIOP)
9.45
Propylene dichloride (C3HeCIz)
4.95
IGNITION TEMPER&C
TURE.
% b y vol. 3.75 i 2.5
648
The ignition temperatures of methane-air mixtures given by the present apparatus are slightly lower than those found by Mason and Wheeler; this may be explained by the fact that this quartz bulb is slightly larger than the bulb used by them and that the air-free methane used contained 1.3 per cent of ethane. Ethane has a lower ignition temperature than methane. The values obtained are also lower than those of Taffanel and Le Floch or Dixon and Coward. The ignition temperature apparatus (Figure 1) has been used in this laboratory on a number of gases and vapors, a few of the results of which are listed in Table 11. The results show that for some gases and vapors the concentration of the combustible present in the mixture does not greatly affect the ignition temperature-for example, methane, manufactured gas, acetone, methyl formate, and propylene dichloride. On the contrary, P-N-amylene and dioxan each show a marked drop in the ignition temperatures with increased concentration. For such mixtures the question arises as to whether the quartz bulb method is the proper one to give the minimum temperature a t which such mixtures might become ignited when used industrially. If the concentration of a combustible such as amylene in air is increased, a point will be reached where the oxygen supply in the mixture is so lorn (above the upper inflammable. limit) that i t is impossible to propagate flame through the bulb
Vol. 25, No. 11
7.30 9.75 8.10 13.15 18.40 20.00 3.50 6.70 9.90 6.20 9.80 13.50 17.35 3.30 3.90 4.05 4.60 5.15
648
R45 - ._
648 660 572 567 577 579 579 565 56 1 531 517 500 498 566 570 560 557 560
8-N-amylene (CsHlo)
2.15 476 2.92 455 4.03 438 a Composed of Cot, 2.2 per cent; illurninants, 4.1; 09, 2.0; Hz, 45.0; CO, 10.7; CHI, 23.3; CzHe, 1.4; N2,11.3. Dioxan (ChHaOz)
4.00
These preliminary tests showed that amylene, under certain conditions, might become ignited a t much lower temperatures than that given by the quartz bulb method, and therefore a method should be used to give these lower ignition temperatures for liquids of this nature. A knowledge of the minimum ignition temperatures is desirable so that such liquids may be safely used in industry.
Soyemher, 1933
I N D U S T R I A L -4N D E N G I N E E R I N G C I3 E M I S T R Y
It was thought t h a t perhaps the heated nitrate bath, owing to the presence of nitrates, was the cause of the greatly lowered ignition temperature. However, a review of the literature showed that Lewis (11) obtained a value of 270' C. for the ignition temperature of amylene in air, using the drop method. Test tubes, crucibles, and small beakers were then tried as containers, and tests were made by partially submerging them in the heated bath. TABLE111. MINIMUMIGNITION TEMPERATURE OF COMBUSTIBLE-AIR MIXTURES COYBCCTIHLE
'1
6
FORMUL~
MIX. IGNITION TEMP. Quartz Drop bulb method
CIH60 Crotonaldehyde CsHuCl N-amyl chloride C~HSOJ Dioxan Amylene CsHia Acetaldehyde Divinyl ether Butylene Propylene Ethyl alcohol (abs.) Methvl formate Pentinone Butanone Hexanone Propylene dichloride Acetone Manufactured gas Methane Test made in 88-cc. quartz bulb. Test made in 3/r-inch (1.9-cm.) Pvrex test tube
c.
c.
36ga
2321 258b
...
438~ 381~
266d
,..
275d 399d
...
380c
443a
45v 485b 498"
such as propylene dichloride and methyl formate, gave ignition temperature values by the drop method equally as high as the quartz bulb method. For example (Table 111), methyl formate when tested by the drop method using a Pyrex test tube of inch diameter and 6 inch length could not be ignited a t a temperature of 482' C., the temperature a t which the nitrate bath began to vaporize. I n Table I11 there are listed the minimum ignition temperatures of several combustible-air mixtures for comparison with dioxan-air mixtures. Some have been determined both by the quartz bulb and drop methods. The values reported for the drop method are the lowest obtained when various heated surfaces and containers were used. The particular size and kind of container which gave the minimum ignition temperature is so designated in the table.
2138. ZlbI .
.
CO~YCLUSIOSS
I
...
Above 4820
514a
... ...
645''
..
505a
1285
533" ... 557a .\bore 5630 561. ... 5137~ ...
With a tebt tube, 5 / s inch (1.6 cm.) inside diameter and 6 inches (15.2 em.) long, it was found t h a t ignitions could not be obtained for amylene a t any temperature. This was thought to be due t o the fact that one drop of amylene gave so rich a mixture with air in this small test tube that the mixture was above the upper explosive limit and therefore incapable of propagating flame. When a porcelain crucible, open a t the top so t h a t there was free access of air as the droplet moved about and vaporized on the bottom of the crucible, was substituted, a minimum ignition temperature of 276" C. was obtained. However, reproducible results could not be obtained unless the porcelain crucible was thoroughly cleaned before each determination. Tests were made with containers, such as various-sized crucibles of porcelain, nickel, iron, and copper, and with beakers and test tubes of various sizes. S o definite procedure has been found as yet which will give minimum ignition temperatures for different combustible liquids. The drop method of determining the ignition temperature has been used by a number of investigators (11-26) but a compilation of the reiults obtained 011 the same combustible shows wide variations. These variations for combustible-air mixtures are in many cases probably due to the fact that some of the apparatus used were not designed to produce mixtures having the proper oxygen concentration surrounding the heated vapor. The preliminary tests made show that in the case of some liquids, such as amylene and dioxan, the ignition temperature may, under certain conditions, be much lower than the ignition temperatures as found for its vapor mixed only with air in a container such as a quartz bulb. For example (Table 111), the lowest temperature of ignition of dioxan-air mixtures in the quartz bulb tests was found to be 438', while by the drop method using a 50-cc. Pyrex beaker, the liquid dioxan ignited a t 266" C. Combustibles which by the quartz bulb method gave rather constant or increased ignition temperatures as the concentration of the combustible in the mixture increased,
The lower inflammable limit of dioxan vapor in air (dried with calcium chloride) a t laboratory temperatures and pressures is 1.97 per cent by volume. The upper inflammable limit in dry air (dried with calcium chloride) a t laboratory pressures and 100" to 110' C. is 22.25 per cent by volume. The ignition temperatures of dioxan-air mixtures when determined in an 88-cc. quartz bulb varied with the concentration of the dioxan present. A mixture containing 2.15 per cent dioxan in air gave 476" C., and, as the concentration of dioxan was increased until 4.03 per cent was present, the ignition temperature was lowered to 438' C. Because the ignition temperature of dioxan-air mixtures in the quartz bulb tests decreased with increased concentration of dioxan, tests were supplemented by the drop method of determining ignition temperatures. This method gave a minimum ignition temperature of 266' C. Ignition temperature tests that have been made on acetone, methyl formate,. propylene dichloride, amylene, and dioxan by both the static method using a quartz bulb and the drop method in which drops of the liquid are dropped on heated metal, glass, porcelain, or liquid (molten) surfaces, have shown that, if by the quartz bulb method the ignition temperature is markedly reduced with increase in concentration of the combustible, then under the right conditions the drop method will give ignition temperatures lower than those found by the quartz bulb method. If, on the other hand, the ignition temperatures found by the quartz bulb method show rather constant or increasing ignition temperatures with increase in concentration, then values obtained by the drop method will be equal t o or higher than by the quartz bulb method. Tests made t o determine the pressures developed when dioxan-air mixtures are ignited in a closed bomb showed that the pressures developed may reach 80 pounds per square inch (j.62 kg. per sq. cm.) above atmospheric pressure. LITERATURE CITED (1) Anschuta and Broeker, Be?., 59B,2844 (1926). (2) Bridgeman and Marvin, IAD.ENG.CHEM.,20,1219 (1928). (3) Clarke, J. Chem. SOC.,101,1789 (1912). (4) Davidson, IND.EXQ.CHEM.,18,669 (1926). (5) Dixon and Coward, J . Chem. SOC.,95,514 (1909). (6) Faworski, J. Russ. Phus. Chem. SOC.,38, 741 (1906). (7) Ghosh, J . Chem. Soc., 107,1589 (1935). (8) Holm, Z. angew. Chem.. 26,273 (1913). (9) Jones, Harris, and Miller, Bur. Mines, Tech. Paper 544 (1932). (10) Jones, Miller, and Seaman, IND. Eso. CHEW., 25,771 (1933). (11) Lewis, J. Chem. SOC.,1931,2456. (12) Lewis, Nierenstein, and Rich, J. A m . Chem. Soc., 47, l i 2 b (1925). (13) Lourenao, Ann. chim., 3, 67, 288 (1863). (14) Macheth, J. Chem. SOC.,107,1824 (1915).
1N D U S T R I A L A N D
1286
E N G I N E E R I N G C H E 21. I S T R Y
Makowwiecki, J. Russ. P h y s . Chem. Soc., 40,752 (1908). Mason a n d Wheeler, J . C h e h . SOC.,121, 2079 (1922). Masson a n d Hamilton, IND.E m . C H E M . ,19, 1336 (1927). Ibid., 20, 813 (1928). Moore, J. SOC.Chem. Ind.,36, 109 (1917). Paterno and Spallino, Atti mad. Lincei, [ 5 ] 16, I 87 (1906). ESG.C H E M . 21, , 695 (1929). Reid and Hoffman, IND.
(15) (16) (17) (18) (19) (20) (21)
Vol. 25, No. 11
(22) Taffanel and Le Floch, Compt. rend., 157, 469 (1913). (23) T a n a k a and S a g a i , Proc. I m p . Acad. (Tokyo), 2, 219 (1926). (24) T a n a k a and Sagai, J. SOC.Chem. Znd. Jagon, 29, 266 (1926). (25) Thompson, IND. ENG.C H E M . ,21, 134 (1929). (26) Wurtz, Ann. chim., [3] 69, 323 (1863). R E C E I V EM D a y 23, 1933. Published by permission of the Director, U. S Bureau of Mines. (Not subject to copyright.)
Catalytic Oxidation of Ethylbenzene in the Liquid Phase ~
AND J. J. STUBBS, Bureau of Chemistry and Soils, Washington, D. C. C. E. SENSEMAN
N A PREVIOUS article (4)
I
The catalytic action of manganese dioxide in ber, which was then placed in the authors presented data a glycerol b a t h p r e v i o u s l y the liquid-phase oxidation of ethylbenzene has on the liquid-phase oxidaheated to approximately the been studied, with particular emphasis on the tion of p-cymene in which a desired temperature, and the formation of acetophenone. Phenylmethylcarfinely divided manganese dioxflow of oxygen w a s s t a r t e d . binol is found as a reaction product in almost ide prepared by reducing potasAfter the oxidizing period, the sium permanganate with formalweight of the material in t h e constant quantities after oxidation periods of dehyde was used as a catalyst. reaction chamber was obtained, 5.75 hours or more. An explanation is adIt was shown that this oxide as well as that of the products vanced f o r this constancy of yield. Reaction had a decidedly accelerating which had distilled off during products identijied were: wafer, carbon dioxide, effect upon the reaction. the course of the run and had formaldehyde, phenylmefhylcarbinol, acetopheAfter that investigation it was been condensed and collected decided t o make a similar in a flask immersed in an ice none, and benzoic acid. study of the catalytic value of bath. this same oxide in the oxidation ANALYSIS O F P R O D U C T S . of ethylbenzene, looking particularly toward the production Oxidation products detected qualitatively were: of acetophenone, an organic chemical of increasing imporIDENTIFICATION METHOD tance. I n studying the mechanism of the oxidation reactions Phenylmethylcarbinol M. p. of the acid phthalic ester, 108-108.5° C. neutralization equivalent of thla ester, (cor.) ; of a number of hydrocarbons, Stephens (5) found that aceto267 M. p. of the phenylhydrazone 102-103' C. (cor.) phenone is produced in considerable quantity when oxygen Acetophenone M. p., 121.20 C. (cor.); nedtralization equivais passed through ethylbenzene over a long period of time and Benzoic acid lent. 123 Formaldehyde R&g&oitest no catalyst is used. King, Swann, and Keyes (3) found that Carbon dioxide Barium hydroxide teat Cupric sulfate teat manganese acetate catalyzed this reaction to the extent that Water 20.6 per cent of the ketone, based upon the initial material, The phenylmethylcarbinol, acetophenone, and benzoic was formed during a period of 24 hours, the reaction being carried out a t a temperature of 102' to 104' C. Keither of acid were determined quantitatively as follows: these investigations showed the formation of the alcohol, The solution of these three in ethylbenzene as taken from the phenylmethylcarbinol, or the further oxidation of aceto- reaction chamber was thoroughly extracted with aqueous sodium phenone t o benzoic acid. Binapfl and Krey (1) claim that, bicarbonate solution which reacted with any uncombined acid. The aqueous solution was then treated with dilute sulfuric acid after passing oxygen through ethylbenzene for 7 hours a t a and the liberated organic acid extracted with ether. After washtemperature of 130" to 140' C., using as an oxygen carrier ing the ether solution free of all sulfuric acid, it was made up to a manganous hydroxide precipitated on marble powder, 59 definite volume, an aliquot was removed, the ether was evapoper cent of the ethylbenzene is recovered and a residue rated, alcohol and water were added, and the acid was titrated with 0.1 N sodium hydroxide solution, phenolphthalein being (quantity not stated) is obtained consisting of 80 per cent used as an indicator. From this titration result, the total quanacetophenone and 20 per cent phenylmethylcarbinol. tity of acid was calculated. From the material insoluble in the bicarbonate solution, ethylEXPERIMENTAL PROCEDURE benzene was removed by distilling at atmospheric pressure from a distilling flask, after which the residue was distilled A technical grade of ethylbenzene was distilled, and the long-neck under reduced pressure to avoid possible decomposition of the fraction boiling a t 135' to 137" C. was used. The catalyst, alcohol. The alcohol fraction contained also the acetophenone. manganese dioxide, was prepared according t o the method The weights of both fractions were obtained. To a one-gram described in a former article (4). Except for the changes sample of the mixture of ketone and alcohol, acetic acid was added. The acetophenone was precipitated as the phenylhydranoted, the apparatus was also the same as described therein. zone, which was filtered off, washed with 50 per cent alcohol, For greater convenience in operation, a n accurately Cali- dried, and weighed. From this weight the total acetophenone brated flowmeter was substituted for the mechanical dry was calculated. The alcohol in the mixture was determined by meter, and a sintered disk made of powdered Pyrex glass was the acetylation method of Gildemeister and Hoffmann (9). sealed into the bottom of the reaction chamber as a substitute DISCUSSION OF RESULTS for t h e alundum disk. This glass disk gave better dispersion Table I has been compiled primarily to show the effect of of the oxygen gas, resulting in better contact of gas, liquid, the temperature variable. B y the inclusion of the first and and catalyst, and better agitation. I n conducting t h e experiments, 50 grams of ethylbenzene last runs given, comparison is also made between results oband 0.5 gram of catalyst were poured into the reaction cham- tained when using no oxide, a finely divided commercial man-
,/
-'
