June. 1932
INDUSTRIAL AND ENGINEERING CHEMISTRY LITERATURE CITED
Booth, H. S., J . Chcm. Education, 7 , 1250 (1930). Booth, H . S., Ibzd., 7, 1269 (1930). Booth and McIntyre, ISD. EKQ.CHmr., Anal. Ed., 2, 12 (1930). Booth, Mong, and Burchfield, ISD. ENG.CHEM.,24, 328 (1932). Chablay, E., Snn. cham., I, 469 (1914). ChabriB, Bull. SOC. chim.,[3] 7 , 24 (1892). Germann and Booth, J . Phys. Chem., 30, 371 (1926). Meslans, Compt. r e n d , 110,717 (1890). Midgley and Henne, 1x1). EKQ.CHEM., 22, 542 (19:30).
641
(10) Sayers, Yant, Chornyak, and Shoaf, Bur. Mines, Rept. Investigations 3013 (1930). (11) Swarts, F., Bull. sci. acad. roy. Belo., [31 24, 474 (1892). (12) Swarts, F., Chem. Zentr., 1903, I, 13. (13) Swarts, F., Bull. sci. acad. roy. Belg., 1911,563. (14) Wourtzel, J . chim. phys., 11, 57 (1913). RECEIVED March 17, 1932. E. M. Bixby was the holder of a n Ohio Chemical and hlanufactriring Company Fellowship for pure science research in anesthetic gases, 1929-1931.
Decomposition of Dichlorodifluoromethane by Flames THOMAS 3 l I D G L E Y , JR., b N D
hLBERT
L. HENNE
Department of Chemistry a t the Ohio State University, Columbus, Ohio
/(2.
The cubical content of the ICHLORODIFLUOROA method is presented iuhich makes it possible ?*IETHAKE(CC1zFz), lo calculate at a n y given time the acid concentra(4) The variation of the acid the t r a d e n a m e s of tion generated in a n y g h e n room by the decom~ ~ ~ d which a r e F-12 a n d K i n e t i c position of a known quantity of dichlorod$luorocentration in the air supporting N ~ 12, . is a nontoxic, noninmethane by a flame. It is demonstrated that ecen flammable g a s , condensing a t TO obtain the concentration -28" C . ( - 18.4" F.) a n d under the worst possible circumstances life is not of flue gas in a given kitchen, ideally adapted. by virtue of its endangered. it is necessary only to sample stability and inertness, for use the air, analyze i t for oxygen, as a refrigerant. I n common with all other organic materials, it decomposes on passage and compare i t with a sample of fresh air. The results of through a flame. Recently tests were carried out by the such analyses are listed in Table I. Kinetic Chemicals Corporation showing the concentration of hydrogen chloride and hydrogen fluoride that would be TABLE r. ANALYSESOF FLUE; GASES dM0UXT obtained in a hermetically sealed room, as a method of comGEX N.4TrjP.E OF KITCHEX O F COOKISO paring the relative stabilities and other properties of various KITCHEX O X YR, refrigerants, but the results naturally bear no relation t o .A 19 8 Food class Heavy B 20.6 Main kitchen of hospital Heavy those obtainable under working conditions. A tightly C 19.6 Corridor of hospital None (very defective venticlosed room containing a flame is, obviously, inherently a lation) lethal chamber, regardless of the presence or absence of other D 20.6 Serving kitchen of hospital ward Light E 20.6 Blank ..... materials. The following experimental work was carried Restaurant F 20.1 Heavy out t o complete the earlier work by showing what concentraG 20.1 Restaurant Heavy tions of the combustion products of F-12 could be obtained Apartment H 19.5 Heavy I 19.5 Apartment Heavy under the conditions existing in a kitchen, taking as a ventilaJ 20.6 Blank ..... tion standard the vorst conditions that would be tolerated Ii 20.2 Cafeteria Heavy in such a 17-orkingspace. L 19.5 Apartment Heavy 3f 19.6 House Heavy Obviously the discussion should hinge upon the worst 20.2 House Moderate 20.6 Blank ..... conditions actually tolerated by people in rooms containing open flames and not upon what can be obtained within P 20.0 House Heavy 20.0 House Heavy hermetically sealed containers. 26 20.6 Large house Moderate 20.6 Large house Moderate It would appear that the simplest method of learning what T 20.6 Blank ..... occurs would have been to visit a large number of kitchens u 20 6 Largehouse Light while in use, introduce yarious quantities of dichlorodiKitchenette Y 20 5 Light Kitchenette TT. 20 5 Moderate fluoromethane, and note the resulting effects upon the occus 20 6 Kitchenette Light pants. Such a procedure would have amounted to human 120 6 Blank ..... Z LO. 6 Large house Moderate experimentation; therefore, preference was g k e n to an indirect method of securing the required information. The T a B L E 11. C a R B O N DIOXIDE I N KITCHEN details are reported hereafter.
D
2
PROCEDURE To calculate the acid concentration vs. time curve for a given kitchen when it is under operating conditions, and when a n assumed amount of F-12 has been released in it, the following information is needed: (1) The prevailing concentration of flue gas. (2) The ventilation rate.
TIME Minutes
CO2
0
6.9
6
3.1 1.8
9 12 18
1 2 3
70 4.5
TIME Manutea
CO2
% 1.1 1.1
0.7 0.5
The ventilation rate for one of the most heavily contaminated kitchens (kitchen L, Table I) was obtained as follows: The adjustment of the burners for preparing a
~
I N D U S T R I A L A N D E 3 G I ?1‘ E E R I N G C H E h.l: I S T R Y
642
Vol. 24, No. 6
TABLE111. DECOMPOSITION OF DICHLORODIFLUOROMETHANE AT VARIOUS COKCENTRATIOSS TOTALVOLUMETRIC RATIO,AIR:FUEL
CClzFz DECOMPOSED
70b y UOZ.
%
15:l
0.1
20:l
CChFp DECOMPOSED 10:1 A1R:FUEL RATIO ACID:AIR % % by uol.
FOR
63.8
FUELGas: AIR^
% ay voi.
ACID:FLUEGAS
9% by uol.
96.0
0.26
66.6
0.39
0.1
94.4
0.19
50.0
0.38
0.51
15:l
0.2
63.1
0.34
66.6
20:l
0.3
28.0
0.li
50.0
0.34
20:l
0.6
12.2
0.14
50.0
0.28
1.0
10.1
0.20
50.0
0.40
3.0
8.2
0.48
50.0
0.96
20:l 5.0 6.5 1.65 Calculated on basis of complete combustion which requires volumetric ratio of &:fuel of 10:1.
50.0
1.30
E:1 20:l
0
CChF? I N AIR
certain meal and the position of the windows and doors chosen by the occupants for bearable operating conditions were noted; subsequently, when the kitchen was not in use, the same conditions were duplicated. A given quantity of carbon dioxide was then admitted, and the atmosphere in the room was sampled at noted time intervals for 30 minutes; the samples were later analyzed for carbon dioxide. The results are given in Table 11 and plotted on Figure 1.
Heating T’entilating Engrs., 18, 362 (1912) ] indicates that twenty changes of air per hour is a proper requirement for kitchens. I t is thus made clear that, in the case of the kitchen used in the present experiments, the ventilation was one-third worse than what is considered normal. The cubical content of the room vias obtained by nieasurement. The rate of decomposition of dichlorodifluoromethane a t various concentrations was measured in the laboratory. Figure 2 diagrammatically presents the arrangement of the apparatus which was used as follows:
FIGURE 1. VENTILATION CURVEFOR KITCHEN L
Natural gas was fed at a known rate to the burner. Simultaneously, a known mixture of air and dichlorodifluoromethane &-as delivered partially through the flame and partially around the flame; the air-adjusting valve was operated in such a way that as much air as poqsible passed through the flame. 4 blue flame TWS obtained, and combustion of the fuel was complete. The flue gases were drawn by suction through the absorption train and measured; the suction was so adjusted that ver little outside air was sucked in through the vent. After eacg run, the amount of acid absorbed by the potassium hydroxide was titrated with phenolphthalein as indicator. The results are listed in Table 111 and plotted on Figure 3.
Weather conditions were selected so that no winds would give abnormally rapid ventilation. Since the admission of carbon dioxide increased the density of the atmosphere in the kitchen, a compensating temperature rise was obtained before releasing the carbon dioxide. Under these conditions the presence of the carbon dioxide tended t o counteract the normally generated convection currents, thus reducing the ventilation rate to something less than that prevailing under regular operating conditions. The Irentilation curve thus determined shows that one-half of the air in the room was changed every 2 minutes. John D. Small [Trans. Am. SOC.
It is to be noted that the curve of Figure 3 presents a very distinct maximum a t about 0.2 per cent. This is due to the fact that the presence of a small amount of dichlorodifluoromethane does not affect the combustion very much, while larger amounts disturb i t considerably. When air containing more than 0.3 per cent of dichlorodifluoromethane is used as the combustion supporting agent, the flame flickers considerably, acquires a livid color, and is easily put out. rlt the same time, the water generated by the oxidation of the fuel condenses partially around the flame instead of being eliminated with the flue gases.
4
a fiINU?fS
l6
20
WATEQ-ADJUS TING V 4 LVC
&
ILLUMINATIN.
‘04s
OF APPARATUS FOR MEASURING RATEOF DECOMPOSITION OF DICHLORODIFLUOROMETHANE FIGURE 2. DIAGRAM
June, 1932
I N D U S T R I A L A l\J D E N G I N E E R I N G C H E M I S T R Y C ALCULATIOXS
The dimensions of the kitchen under investigation were 8.5 X 7 X 13 feet (773.5 cubic feet). The normal oxygen content of the outside air was 20.6 per cent. In the investigated kitchen i t was 19.5 per cent-a reduction of 1.1 per cent, indicating a 5.3 per cent contamination by flue gas.
tity of acid actually present in the room a t any giyen time, i t is necessary to construct curve I11 (the acid lost) and measure the area between it and curve 11. TABLE IV.
0
PERCENTAGE O F ACID I Y FLUEGAS AT V 4 R I OUS CONCENTRATIOhS OF DICHLORODIFLUOROMETHANE
DATAFOR CONSTRUCTION OF CGRVE11, FIGURE 4
TIME Mznutes
CC1,Fx %
0 0.5 1 2 3 4 5
5 3.6 2.8 1.8 1.35 1.05 0.80 0.65 0.50 0.40 0.30
6 k
FIGURE 3.
643
9 10 11 12 13 14
0.25 0.18 0.12 0.10 0.0;
.$CID I S
FLUEGAS %
ACID PER SIINUTE
cu. it. 0.14 0.117 0.0976 0.063 0.051
1 3 1 os 0 89 0 5s 0 47 0 40 0 36 0 34 0 34 0 33 0 34 0 34 0 46 0 40 0 38 0 27
0.043 0,039 0.037 0.037 0.036 0.037 0.03i 0.050 0.043 0.041
0.029
A certain rate of flue gas production is needed to maintain this 5.3 per cent contamination. This rate is calculated as follows: Every 2 minutes, one-half of 773.5 cubic feet of air enters the room. During t h a t time a sufficient amount of flue gas must be produced so that the degree of contamination a t the end of the '-minute period will still be 5.3 per cent. This is represented by the equation: 386.75 - 100 - 5.3 386.75; 100 where .z = cu. ft. of flue gas produced in 2 minutes
FIGURE 4. D ~ ~ T F OA R
C.4SE
I
The area beneath curve I11 represents the arid 1o.t by ventilation up to the time point a t which curve I11 ends. The construction of curve I11 rests on the observed fact that half the air in the room discharges every 2 minutes. Hence, only half of the acid formed 2 minutes prior to the time point being determined remains in the room. Thus curve I11 is caonstructed to intersect a point half~vaybetween curve I1 and zero, 2 minutes prior to the end point of curve I11 and a point only one-quarter of the distance down from curve I1 4 minutes prior to the end of curve 111, etc. Theoretically it should be possible to compute the OF ACID AT ANY G I ~ E Y TIME( C 4 s E 1) FIGURE i. COYCEYTR~TION acid concentrations by integration, but actually the niathematical function aos2 foregoing data the acid of curve I1 is too comconcentration r w ~ l t i n g k &Z% plev to render the calfrom any rate or type culus practical. The csgraphical m e t h o d of of leak a t any subsequent time may be cal82 measuring the area beculatrd, and the acid tween curves I1 and I11 I I I I4I-! ! 16 l 8 20 4, Q concentration 2's. time YIMP u has the advantage of curve niay he conFIGCRE 6 . D 4 T 4 FOR C 4 S E 11 being more simple and structed. direct. CASEI. A 3 per cent concentration of dichlorodifluoromethane is obtained by releasing 16.8 pounds of the gas instantly in the kitchen. Curve I, Figure 4, concentration of dichlorodifluoromethane os. time is constructed from the ventilation data; curve I1 is constructed by reading the dichlorodifluoromethane concentration on curve I a t any given time, referring t o Figure 3 to obtain acid per cent in flue gas corresponding to this concentration, and multiplying this by 10.88 (flue gas produced per minute). The result expresses the rate of acid production in cubic feet per minute. The data used to construct curve I1 are tabulated in Table IV. The area beneath curve I1 a t any time represents the total acid produced u p to that time; but owing to ventilation some of this acid has been lost. Hence, t o obtain the quan-
Solving for L gives 21.76 cubic feet. Hence the rate of flue gas production is 10.88 cubic feet per minute. From the
&-
s i
E*'
;
''
OOzls
INDUSTRIAL AND ENGINEERING CHEMISTRY
644
refrigerant gas into the room; curve I1 represents the accumulated percentage of the gas in the kitchen; curve I11 represents the rate of acid formation. Figure 9 represents the concentration of acid' a t any given time, and is similar to Figures 5 and 7 . In a manner similar to the above three cases, any combination of rates and concentrations may be calculated and the results evaluated by comparing with the established toxicity measurements. For purposes of comparison, Figure 10, representing sulfur dioxide in similar weight quantities and leak conditions as cases I and I1 of dichlorodifluoromethane, is appended.
4
3
120
%
to80
3
$ a4o
a
4
2
6
8
N
/2
/O
Mtn u t e s
/6
/8
FIGURE8. DATAFOR C.4SE 111 I
I
I
I
I
I
I
Vol. 24, No. 6
1
I
I
I
I
I
1
I
DISCUSSIOX OF CALCULATIOXS I
FIGURE 9. CONCENTRATION OF ACIDA T ANY GIVENTIhlE (C.4SE 111)
By constructing a family of curves similar in nature t o curve I11 and measuring the resulting areas, the data in Table V are obtained. The values in the third column are obtained by dividing those in the second column by 7 3 . 5 , the cubical content of the room. These results are plotted and compared with tosicity measurements of the acids in Figure 5 . CASE 11. Twenty pounds of dichlorodifluoromethane are admitted into the room in 10 minutes. Curre I, Figure 6, represents the rate of admission of dichlorodifluoromethane (2 pounds per minute = 4.6 cubic feet per minute = 0.59 per cent per minute). Curve I1 is obtained by a process similar to that of Figure 4. It represents the accumulated percentage of the refrigerant in the kitchen. Curve I11 represents the rate of acid formation. It is obtained from curve I1 and Figure 3, as iyas curve I1 (Figure 4) of case I. T.4BLE
TIVE
1 ' .
ACIDCONCENTRATIONS
ACID C O E C E S T R ~ T I O NTIME .kclo C O S C E Y T R ~ T I O S .lfInutes C u .ft 70
The results indicate that, in the worst ventilated kitchens, the air contains only about 19.5 per cent oxygen as against a normal of 20.6, corresponding to a 5.3 per cent contamination of flue gas. Under these conditions, with a n initial concentration of 5 per cent F-12, the maximum concentration of acids obtainable is 0.018 per cent; under more nearly normal conditions, admitting 20 pounds or 5.9 per cent F-12 in 10 minutes, the maximum concentration of acids is 0.014 per cent. I n either case the result would be 10 to 15 minutes of discomfort, due to the irritating characteristics of the halogen acids, but the concentration would a t no time approach a dangerous one. With sulfur dioxide, on the other hand, taken as representing a typical noncombustible
FIGURE 10. CONCENTRATIOS OF SULFURDIOXIDEAT A n GIVEN TIXEIiY 'i73-CUBIC FOOTROOM
refrigerant, the concentration of noxious material nould reach a maximum of 7 . 5 per cent when admitted rapidly, and 2 per cent when admitted a t the rate of 20 pounds in 10 minutes. Either of these concentrations is well above the Figure 7 is derived from curve 111, Figure 6, in the same highest that can be tolerated. It would appear from these data that, because of the manner as the latter was derived from curve I1 (Figure 4) of case I. Table VI gives the acid concentrations for case necessity of the renewal of the atmosphere to support life in the presence of a flame, the refrigerants of this type present 11. no hazard due to the toxic nature of the combustion products. The ventilation necessary to keep the room habitable will TABLET'I. ACID COSCENTRATIOSS also keep the combustion products below the dangerous TIXE ACIDCONCEXTRATION TIME ACIDCONCEKTRLTIONS point, Any members of the halogenated hydrocarbon cu. i t . Minul es Minutes cu. / t . % % 12 0.11 0 . 0 1 3 class, which possess no other harmful property than yielding 2 0.004 0.03 14 0.09 0.011 0.010 4 0.0s halogen acids on combustion, must be considered entirely 0.013 16 0.10 0.013 6 0.10 18 0.10 0.013 0.014 0.11 S safe for use around human habitation of any kind. 20 0.009 0.07 0.013 10 0.11 CASE 111. Four pounds of dichlorodifluoromethane are admitted in 4 minutes, plus 21 pounds in 10 minutes. This case corresponds to what happens when the liquid line of a household refrigerator leaks. Four pounds are rapidly discharged, and it takes then about 10 minutes to liberate the remaining 2 pounds into the room. Curve I, Figure 8, represents the rate of admission of the
ACTUAL TESTS I n order to ascertain whether the present method of calculation was correct, it was deemed advisable to check the computed results by means of actual tests. Moreover, the 1 Experiments conducted b y R. A . Kehoe, a t t h e University of Cincinnati, demonstrate t h a t hydrogen fluoride is not more toxic t h a n hydrogen chloride, and hence t h a t these t u o m a y be considered together.
