INITIATION AND PROPAGATION OF EXPLOSIVE REACTIONS IN CHLORINE-ETHANE MIXTURES W .
W .
LAWRENCE
A N D
Ethyl Corp., Baton Rouge, La.
5 .
E .
COOK
70821
The injection of liquid chlorine into ethane a t 150 p.s.i.g. and 80’ C. or above results in a violent reaction with rapid pressure rise; presence of small percentages
of ethylene leads to extremely violent reaction a t 70’ C. Vapor-phase mixtures of ethane with 15 to 70% chlorine burn a t modest velocities. Vigorous reaction occurs as a result of autoignition a t 205’ to 224’C.; the presence of ethylene moderates the effect due to premature reaction.
THEpurposes of this study were to determine the speed of propagation of the chlorine-ethane vapor-phase reaction in pipes a t different chlorine-ethane ratios, the initiation temperature of this reaction in a closed vessel, and the effect of injecting liquid chlorine into gaseous ethane at different temperatures. The high-temperature chlorination of paraffin hydrocarbons was studied in detail by Vaughn and Rust (1940). They studied the chlorinations of ethane, ethylene, and ethyl chloride and included effects of added oxygen or variation of the vessel wall, and concluded that “chlorination reactions take place in a diversity of ways, such as by chain mechanisms involving atoms and radicals, bimolecular metatheses, and association processes involving a third body.” The high-temperature nonphotochemical (thermal) reaction of ethane and chlorine in the presence of oxygen was found to have a mechanism leading to the rate equation:
d[HCl] dt
-
h[Clp]’ ‘[CpHs]’ ’ [021
The chlorination of ethane was highly dependent on the surface, which acted both to produce chlorine atoms and to terminate reaction chains. Chlorination of ethaneethylene mixtures was also studied. It was shown that ethane is more reactive than ethylene. Above 293*, substitution is the only process, since addition is reduced to zero. Ethane is almost exclusively the reactive component in such a mixture. Thus it was found possible to chlorinate the paraffin of either an ethane-ethylene or ethane-ethyl chloride mixture to the practical exclusion of the olefin or monohalide. I n a study on the structure of chlorine flames by Simmons and Wolfhard (1957) the most striking feature was the large quantity of soot formed. This carbon led to very high heat losses through radiation, which in turn affected not only the temperature but also the propagation of the flame. Limits of flammability were evaluated for ethane-air-chlorine a t 380 mm. of Hg pressure and 50°C. The burning velocities were determined. Reaction of chlorine-ethane mixtures gave a burning rate range of 5 to 10 cm. per second. I n studies on the ignition limits of ethane-chlorine mixtures, Labadze and Kokochashvili (1959, 1962) found that the lower limit of self-ignition a t various concentraInd. Eng. Chem. Process Des. Develop., Vol. 9, No. 1, January 1970
tions of ethane-chlorine is difficult to determine because it depends on the composition and the state of the surface of the container used. Upper and lower limits of flammability of ethane in chlorine were investigated by Bartkowiak and Zabetakis (1960). They found the upper limit at 75 volume % ethane and the lower limit a t 1.0 volume % when using 100 p.s.i.g. and 100°C. Other conditions were also tested and reported. Experimental
The experiments covered three distinct situations. I n the first, mixtures of ethane and chlorine were prepared in a 5-gallon vessel equipped with an agitator in order to obtain a homogeneous mixture. These were introduced to a reactor, which consisted of a 6-foot length of “double extra strong” steel 2-inch pipe. This pipe was fitted horizonally through a large valve to a 5-gallon, nitrogenfilled tank, used to absorb gas expansion during the course of reaction. Thus pressure increases could be kept small. Automobile taillight bulbs loaded with Thermite starter powder were used to ignite the mixture. Thermal elements were mounted along the pipe to follow the reaction. Sensitive thermocouples started and stopped an elapsed time meter, which could be read to 0.01 second. The apparatus was designed to allow measurements of the propagation of a flame front in pipe at essentially constant pressure conditions to simulate propagation in long runs of pipe to vessels of relatively large capacity. I n the second phase of the work the same chlorineethane mixtures were charged to a 250-ml. Magnedash assembly, equipped with an exposed, sensitive thermocouple in the gas to record temperature changes accurately
VACUUM PUMP START TIMER
STOP TIMER
VENT
1
THERMITE BUL (TO I 2 V B A T T E R Y
C2H6-CI*
NZ
M I X
Figure 1. Apparatus for study of burning velocities
47
and a strain gage to record pressure changes accurately. In the final part of the study a modification of this apparatus allowed sudden introduction of liquid chlorine to a heated charge of ethane, leading to estimation of explosive threshold temperatures for this system.
Table I. Reaction of Chlorine-Ethane Mixtures
2-inch pipe (double extra strong) Composition, 5; Ethane Chlorine
Preig n zt zo n Condzt zo n.s Pressure. p.s.i.g. Temp., C. 200
85.2 85.2 70.7 69.9 69.9 69.9 69.9 68.6 68.6 68.6 68.6 68.6 60.4 60.4 60.4 60.4 60.4 54 54 52.7 52.7 52.7 31 31 47 47
14.8 14.8 29.35 30.1 30.1 30.1 30.1 31.4 31.4 31.4 31.4 31.4 39.6 39.6 39.6 39.6 39.6 46 46 47.3 47.3 47.3 69 69 .53 53
27 28
200 200 200 200 200
200 200 200 200 190 180 105 105 160 155 155 100 100 136 130 120 100 100 100 188
Discussion of Results
Propagation@
More than eight different mixtures ranging from 15 to 70% chlorine were prepared and tested in the 2-inch flame propagation apparatus. Attempts were made to follow the rate of travel of the reaction after initiation by thermite charges. The results (Table I ) were difficult to evaluate. Compositions below 30% chlorine did not appear to fire. The others reacted but with low energy release such that identification of flame travel could be timed in only a few cases. Even then wide variations were recorded. Generally, these rates averaged about 1 t o 3 feet per second at 103°C. Composition between 40 to 7 0 5 chlorine did not seem to have much effect and pressure variation from 100 to 155 p.s.i.g. did not result in any change. I n almost all cases the reactor contained a yellow oily to gummy deposit whether propagation was recorded on the elapsed time meter or not. This material could not be washed out with kerosine but was readily flushed out with water. After this treatment the internal surfaces were clean and bright. The HC1 produced by reaction probably was responsible. I n general, it was concluded that the burning velocities of the mixtures tested were relatively low. Equal molar gas mixtures of ethane in chlorine, which were heated in a closed 250-cc. bomb, gave vigorous but not violent reaction between 205" and 224" C. (Table 11). Maximum pressures of about 450 p.s.i.g. were recorded
None Kone None None None None None None None None None None 6 inches 8 inches Some 1 ft./sec. 1 ft./sec. 2 ft./swb 3 ft./sec. 20 ft./sec.
26 52
52 52 52 75 75 100 100 100 105 105 103 103 103 103
103 103 103 103 103 103
...
None
103
1 ft./sec. 1 ft./sec.
103
None
"Propagation as recorded on elasped time meter or evidenced by carbon deposit I n most cases a n oily deposit was found in apparatus, uhich is not recorded as propagation. 'Large valve closed during this firing, leauing reactor isolated from ballast.
Table II. Autoignition of Ethane-Chlorine Mixtures
Autoignition Chlorine, S 49 49 49 49 36.6d 32.1d 24.jd
Temp,, C.
Pressure, p .s .i.g .
205 218 None'
...
224 210
...
-. . .
150
340
450
200 None
310
430
...
Rate of Pressure Rise, P . S . I . See. I
...
336 350
... ...
Konee None'
Maximum" Pressure, Temp., C. p.s.ig.
-. -
...
400
150 150 130 115 135 175 200
940
None 1400
1250 None Kone
...
... ...
Charged Pressureb, P.S.I.G.
...
" M a x i m u m temperature probably not real, since recorder reaction is slow. b A t ambient cond. ' N o ignition; reaction products observed in wssel. Mixed with commercial ethane containing 2 to 5% ethylene, all others cylinder ethane (CP). 'Heated to 300" C., no indication of ignition. 'Heated to 300° C., no indication of ignition; vent gas analyzed for C12,none found. Table 111. Reactivity of Ethane with liquid Chlorine
250-cc vessel
Temp., C. 29 65 75
85 100 22 60 70
75-80 a
48
Initial Pressure, P.S.I.G. 150 150 150 150 150 150 150 150 150
Rate,
Chlorine, G. 66 65 73 75 76
70.8 76.0 71.5
78.0
P.SI.iSec. ...
... ...
-...
125,000 50,000
...
Ethylene, 9 0
0 0 0 0 5.3 1.9 1.9 5.3
Results N o reaction KOreaction N o reaction 17-second delay Violent reaction N o reaction N o reaction Extremely violent Extremely violent
Not measurable.
Ind. Eng. Chem. Process Des. Develop., Vol. 9, No. 1, January 1970
with pressure rises of 1000 to 1500 p s i . per second. Three runs were made in which ethane, containing about 5'; ethylene, was used. In two of these no ignition was recorded, but reaction had obviously taken place. The vent gas of one was analyzed and no chlorine remained. Presumably, the presence of ethylene initiated some chain reaction, which used up the chlorine. I n the third case (where ignition was observed) this premature reaction did not have time to consume the chlorine; autoignition occurred at 210" C. The above experiments all involved the use of gaseous mixtures, prepared a t ambient temperature (25-28" C.). The apparatus, which had been used in the second series of tests above, was modified such that about 70 grams of liquid chlorine could be injected rapidly after the ethane was heated to the desired temperature. This temperature was measured by a sensing thermocouple in the gas; a strain gage recorded pressure rise. The experimental data show that below about 80'C. no reaction occurred, but above this temperature a violent explosion took place, yielding pressure rises in the order of 100,000 p.s.i. per second (Table 111). When ethane containing 2% ethylene was used, this lower temperature
limit dropped to about 65°C. and the violence of the reaction increased such that strain gages were destroyed; no rate of pressure rise could be obtained. I n general, it is concluded that introduction of liquid chlorine to pipes or vessels containing ethane should be avoided because of the potentially explosive nature of the system. Literature Cited
Bartkowiak, A., Zabetakis, M. G., Bur. Mines Rept. Invest. 5610 (1960). Labadze, K., Kokochashvili, V., T r . Thilissk Gos. Unit. 74, 875-82 (1959); C A 57, 8791a. Labadze, K., Kokochashvili, V., T r . Thilissk Gos. Uniu. 1961 80, 287-95 (pub. 1962); C A 60, 15675a. Simmons, R . F., Wolfhard, G. G., A R S Journal 27, 44-8 (1957). Vaughn, W. E., Rust, F. F., J . Org Chem. 5 , 449 (1940).
RECEIVED for review October 31,1968 ACCEPTED October 10,1969
RHEOLOGICAL INTERPRETATION OF BRABENDER PLASTI-CORDER (EXTRUDER HEAD) DATA M . G .
ROGERS
Research and Development Laboratory, Dow Chemical of Canada, Ltd., Sarnia, Ontario, Canada
A method has been developed for relating Brabender Plasti-Corder extrusion data to more fundamental rheological units. Torque-screw speed measurements provided information for constructing flow curves up to a shear rate of 100 sec. , while pressure-output values, measured simultaneously at the die, were utilized for completing the curve. Correlation of experimental results for high density polyethylenes and polystyrenes with lnstron capillary rheometer data validated the theoretical approach. -1
THEBrabender Plasti-Corder is a torque rheometer widely
Theory
used for many years to study the rheological behavior of polymer melts under various processing conditions (Blake, 1958; Schmitz, 1966). Two publications (Blyler and Daane, 1967; Goodrich and Porter, 1967) have shown ways of converting torque-rheometer data obtained on the roller-type measuring head attachment into fundamental rheological units. Using a similar approach it is now possible to convert torque measurements obtained with the extruder head attachment into rheological units consistent with those found with an Instron capillary rheometer.
Torque-Screw Speed Measurements. The basis in the development of the theory relating torque-screw speed data to shear stress-shear rate data is the experimental fact that the measured torque is a function of the screw speed and is independent of the die dimensions used in the experiments. Torque, of course, is dependent on the polymer and temperature. I n its simplest form the Brabender extruder may be regarded as two coaxial cylinders composed of an inner cylinder (screw) of radius rl cm, and length z cm, where
Ind. Eng. Chem. Process Des. Develop., Vol. 9, No. 1, January 1970
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