High-Temperature Pyrolysis of Hydrocarbons. I.Methane to Acetylene A. Holmen,' 0. A. Rokstad, and A. Solbakken SINTEF, The Norwegian Institute of Technology, University of Trondheim, N-7034 Trondheim-NTH,
Norway
Pyrolysis of methane has been studied in an electrically heated tubular reactor in the temperature region 15002000 OC. High yields of acetylene were obtained at short residence times. Hydrogen dilution and reduced pressure were used to prevent carbon formation during the pyrolysis. The methane decomposition showed autoacceleration at low conversion, and this is explained mainly as an effect of heat transfer from reactor wall to gas. A possible explanation is given for the lower activation energies found in high temperature flow reactors compared to shock tubes.
Introduction Our interest in high-temperature pyrolysis of hydrocarbons was based upon the need to find processes for cheap production of acetylene from petroleum feedstocks to replace expensive acetylene from carbide. Many processes for acetylene production have been developed and even operated commercially with some success. (A comprehensive survey of processes has been published by Miller, 1965.) These include the use of an electric arc (Huels, DuPont), regenerative techniques (Wulff process), flame techniques, incomplete combustion with 0 2 (BASF, SBA, Tsutsumi), admixture with hot combustion gases (Hoechst HTP), etc. Recent developments which have not yet reached the commercial stage are the use of plasma torches, shock tubes, and isothermal techniques (Happel and Kramer, 1967; Othmer, 1965). Common for all acetylene processes are high temperatures, short reaction times, and rapid quenching, or in short very high heat-fluxes. For theoretical reasons such conditions would be characteristic for an acetylene process. Thermodynamically acetylene is unstable relative to most other hydrocarbons a t lower temperatures. A relation between standard free energy of formation of hydrocarbons and temperature shows that most hydrocarbons become more unstable when temperature is increased. Acetylene, however, becomes less unstable when temperature is increased (Miller, 1965), and a t temperature higher than about 1500 K acetylene is more stable than most other hydrocarbons. Acetylene is still unstable relative to the elements carbon and hydrogen, and rapid quenching is necessary to prevent its decomposition. The experimental system used by us is in principle the one used by Happel and Kramer (1967), although several modifications are made. Compared t o other processes, the electrically heated reaction tube makes it easier to control the temperature profile in the reactor and thus makes it possible to obtain high yields of acetylene and a relatively pure product gas. One of the main objectives of this work was to find correlations a n d data meaningful to the construction of larger reactors. A reactor with 50 times higher capacity has been built and is shown to give the same high yield of acetylene, showing that the basic information for such a scaleup was sufficient. Experimental Section A schematic diagram of the experimental apparatus is shown in Figure 1. Methane and hydrogen were metered from storage cylinders to an electrically heated graphite reactor. The methane used was obtained from G. L. Loos and Co.
(99.0% minimum purity). Power input to the furnace was controlled manually with a variable transformer (13.2 kVA) connected to a 220-V supply. T h e resistance element was designed to use high amperage, low voltage current. Four windows in the outer, watercooled reactor shell allow an optical pyrometer (Leeds & Northrup) to be used for determination of the temperature profile on the outside of the reactor tube and the maximum temperature inside the reactor. The hot effluent gas was rapidly quenched using either indirect water cooling (the cold-finger method as described below) or injection of water directly into the hot gas stream. Samples of the product gas were analyzed by means of gas chromatography. Before entering the sampling valve the gas passed through a filter to remove any entrained solid or liquid particles. The gas sampling valve used is described elsewhere (Solbakken and Emmett, 1969). The reactor design shown in Figure 2 allows experiments to be made a t temperatures up to about 2300 "C. The reactor tube (CGW graphite from Union Carbide) which also serves as the heating element, is 600 mm long with 20 mm 0.d. Two different inside diameters have been used, 7 mm and 10 mm. The reactor tube is threaded into a water-cooled copper plate a t the top (reactor inlet) and into the stainless steel quench zone a t the bottom. Due to the thermal expansion of the graphite tube (about 5 mm from 20 "C to 2000 "C) the electrical connection to the contact plate a t the reactor inlet consists of YlG-in. watercooled copper tubes coiled as spirals. Part of the feed tube, as indicated in Figure 2, consists of a flexible copper tube. This arrangement, therefore, allows free expansion in the length direction for the graphite element. At 2000 "C under vacuum the radiation effect from the graphite element would be about 55 kW. T o keep the power consumption a t a reasonable level the element was insulated by means of two graphite tubes (type AGR from Union Carbide) placed concentrically about the heating element, each 540 mm long and with outside/inside diameter of 36/30 and 70/64. Two layers of graphite felt were placed between these two tubes. The shell of the reactor (constructed of copper) was vacuum tight since leakage of air into the system would cause serious damage t o the insulation and the graphite element. The quench zone consists of a water-cooled tube made of stainless steel. This cooler consists of two parts separated from each other by electrical insulation. The upper part of this tube, shown in Figure 2 , is directly connected to the graphite tube thus constituting the second electrical connection. Water was injected into the hot product gas a t the bottom of the conical part of the quench zone. The cold-finger system consists of Ind. Eng. Chem., Process Des. Dev., Vol. 15, No. 3, 1976
439
1'' 220
QUARTZ WINDOWS
AR
I
QUARTZ
NiNDOW
v
IRANSFORMERS
H2 C H q
I! WATER PUMP
1
Figure 1. Experimental apparatus.
F E E D T,'OE
an additional cooler placed inside the other, thus forming a narrow annulus. The distance between the reactor outlet and the top of the cold finger (conical shaped) is about 5 mm. Mercury manometers attached to the reactor inlet and outlet, the rotameters, and the gas sampling valve provided the necessary pressure measurements. Gas analysis was accomplished with a Perkin-Elmer F-11 gas chromatograph (F.I.D.). The column used was a 12 f t X 1b in. stainless steel column packed with 3% 2-ethylhexyl sebacate on silica gel (80-100 mesh). The chromatograph was operated isothermally a t 110 "C and the gas sampling valve permitted the introduction of a constant volume into the carrier gas.
Interpretation of Data The data obtained from the experimental runs consist of temperature, pressure, and flow rate measurements and of chromatographic analysis. To obtain conversion and yield data vs. residence time a t specified temperatures the following calculation procedures are used. It is assumed that hydrogen, ethylene, acetylene, and carbon are the only reaction products. The amount of e remaining components such as ethane, tars, diacetylene. !nd other highly unsaturated products are generally very small and will have practically no influence on the material balance calculations. The conversion of methane is defined as
I
f .
?CHI
=
NOCHI
- NCH4
N'cH~
The yield of acetylene (based on methane in feed)
and the selectivity of acetylene (based on methane reacted)
(3) In all experimental work of this kind one of the main problems is to establish a method which gives the true temperature of the reacting gases. Several possibilities have been considered including thermocouple measurements, the use of an optical pyrometer on thin filaments in the gas stream, spectroscopic methods etc. However, as far as the true gas temperature is concerned, no direct method is available. In accordance with other investigations a t high temperature (Happel and Kramer, 1967; Jampolskie e t al., 1968) the temperature wa. neasured by means of an optical pyrometer. This metho ves wall temperatures and not gas temperatures. Obvio , v, the difference between the wall and the gas temperaturl $11be heavily influenced by the feed rate. At 440
Ind. Eng
'
,>em.,Process Des. Dev.,Vol.
15, No. 3, 1976
Figure 2. Design of the reaction furnace.
1400 " C Kunugi et al. (1961),by equilibrium considerations, estimated the true gas temperature to be about 70-100 "C lower than indicated by thermocouple measurements (wall temperatures) a t maximum yield of acetylene. The optical pyrometer was used to measure wall temperatures over the visible section of the reactor tube during each run. Examples of measured temperature profiles are shown in Figure 3. The conversion and yield data (Figures 4-7) are correlated with the maximum reactor temperature. Another possibility to characterize each run which has been considered is the concept of an equivalent isothermal temperature (Eisenberg and Bliss, 1967). This temperature is defined as the temperature at which an isothermal reactor would give the same conversions as the nonisothermal reactor. Thus with first-order kinetics (4)
Common for all experimental work of this kipd is the lack of knowledge of the gas temperature. We have used eq 4 in the discussion given below about the activation energy for methane pyrolysis. The rate constant hl for the methane decomposition is calculated from the plug-flow reactor equation
1800 ---o
1600
? - 1400 W
2
22
n
1200
K
1000
L
800
i-
600
-
400
-
200
F E E D RATE = 3 0 L i M l N I C H b * H 2 I
0 008
0004
1
0012 0.01 6 RESIDENCE TIME I S E C )
0020
F i g u r e 5. Yield of acetylene from methane a t different tempera. tures. Same conditions as in Figure 4. 10
20
30
50
40
50
REACTOR LENGTH I C M I
F i g u r e 3. Temperature profiles of reaction tube a t two different feed rates. z W 30 loo
I
-
> c
25 0
20
2 15 yi w
10
5
0004
L
b
L
I
0 DO4
-
-
8
0 008
,
,
1
,
0012 0016 RESIDEUCE T I M E I S E C I
0020
F i g u r e 4. Methane conversion a t different temperatures. Feed composition, CHd:H2 = 1:l;total pressure after reactor 100 mmHg; -, reactor tube i.d. = 7 mm; cold finger quench; - - - -, reactor tube i.d. = 10 mm; water quench. rCH4 X
d V = -dNcH,
0012 0016 RESIDENCE T I M E I S E C I
0020
F i g u r e 6. Selectivity of ethylene from methane at different temperatures. Feed composition, CH4:Hz = 1:1,total pressure after reactor 100 mmHg; reactor tube i.d. = 7 mm; cold finger quench.
-
s z 8 5
LO -
30
A
-
(5)
which was integrated over the whole reactor. With first-order kinetics the reaction rate rCH4 becomes
The pressure, temperature, and gas composition continuously change throughout the reactor tube and it follows that the true residence time must be determined by a stepwise calculation. This is done by using the measured temperature profile and assuming first-order kinetics for the methane decomposition (2CH4 C2H2 3&), no side reactions, and a linear pressure drop.
-
aoo8
+
Results and Discussion The experimental arrangement described above was used to obtain conversion and yield data for the pyrolysis of methane-hydrogen mixtures in the temperature region 1500-2000 "C. Characteristic data are presented in Figures 4-7. As seen in Figure 4, the conversion curves take an S-form including an induction period. Similar behavior has been reported by others (Jampolskie et al., 1968;Eisenberg and Bliss,
0004
5
0008
,
L-----
0004
,
a008
0012 0015 RESIDENCE T I M E I SEC I
0020
---1---i--_
0012 0016 RESIDENCE T I M E I S E C I
0020
F i g u r e 7. Yield of carbon formed during pyrolysis of methane a t different temperatures. Same conditions as in Figure 4: A, reactor tube i.d. = 10 mm; water quench; B, reactor tube i.d. = 7 mm; cold finger quench.
1967; Palmer et al., 1968). This autoacceleration of the reaction at lower conversions is discussed below. A comparison between the conversion curves for 10- and 7-mm tube diameter (Figure 4) indicates that the conversion in the 10-mm tube is less at comparable wail temperatures. Ind. Eng. Chem., Process Des. Dev., Vol. 15, No. 3, 1976
441
Table I. Product Gas Composition from Pyrolysis of Methane-Hydrogen Product gas composition, mole %
Conversion methane, %
Residence time, s
Max. inside temp, “C
C H4
C2H6
C2H4
47.3 98.6 99.6 11.9 53.7 81.7
0.0031 0.0118 0.0176 0.0032 0.0078 0.0144
1757 1766 1765 1640 1632 1629
21.71 0.49 0.12 41.67 18.46 6.60
0.03
0.48 0.04 0.04 0.69 0.42 0.11
-
-
0.13 0.02 -
C2H2 7.60 14.13 11.30
0.88 7.54 11.00
Mole ratio CH4:H2 = 1:l; Reaction pressure, 100 mmHg.
50
55
Figure 8. Arrhenius plot of first-order rate constant for the decomposition of methane. As described in the Experimental Section, the gas temperature may be much lower than the measured wall temperature. Because of the smaller surface to cross-section ratio in the 10-mm tube it is reasonable that the gas temperature is lower in this tube than in the 7-mm tube a t the same wall temperature and flow rate. Practical acetylene yields of 85-90% are obtainable from methane, and with a high purity as shown in Table 1.The reaction intermediates are of particular interest in the discussion of the mechanism which is done below. Figure 6 shows, for instance, the selectivity of ethylene formation as a function of residence time and temperature, and at short residence time we even find small amounts of ethane as shown in Table I. Of special interest is the carbon formed during the reaction, as shown in Figure 7 . I t is important to note the difference of about 10% between the carbon formation in the 7- and 10-mm tube. This is probably not a wall effect, but rather is due to different quenching techniques. With the 10-mm tube we used a highly effective water quenching, and the carbon formed on the shorter contact time side of the maximum yield in Figure 5 is rather small. With the 7-mm tube mostly the “coldfinger” quenching was used, which obviously was not effective, especially after some time, leading to a higher scattering of the results. Some carbon is formed throughout the reaction tube even a t smaller conversions. Part of this settles on the wall and must be removed a t intervals. Two types of carbon deposits were observed on the reactor wall. The carbon formed a t low conversion of methane is more compact than the carbon formed in zones of higher conversion. 442
Ind. Eng. Chem., Process Des. Dev.. Vol. 15,No. 3, 1976
This suggests different modes of carbon formation. Some of the carbon may be formed by dehydrogenation of methane giving a graphite-like deposit on the reactor surface. At higher conversion of methane to acetylene the carbon is formed from acetylene giving a soot-like deposit on the wall of the reactor and in the subsequent quench zone. The carbon formed on the high contact-time side of the maximum yield is almost proportional to the decrease in acetylene yield, and therefore suggests a splitting of acetylene. I t will be shown in part 2 of this series that this reaction is very sensitive to the partial pressure of acetylene. At higher partial pressures of acetylene the system became unstable and sudden rapid carbon formation could be observed. To obtain a stable situation one had to lower reaction pressure. This instability zone is treated in more detail in part 2 of this series. It is important for the stability of larger reactors. Happel and Kramer (1973) seem to have found a method to stabilize the gases, making it possible to work a t higher pressures. The overall methane decomposition is generally accepted to be of first order (Khan and Crynes, 1970), although Eisenberg and Bliss (1967) reported that the reaction is not first order. The Arrhenius parameters for the first-order rate constant were determined from the plot in Figure 8. The activation energy of 88 700 cal/mol is in accordance with most other published values for flow reactors (Happel and Kramer, 1967; Jampolskie et al., 1968; Palmer et al., 1968; Murgulescu and Schneider, 1960, 1961; Shantarowich and Pavlov, 1962). Shock-tube studies generally give a higher overall activation energy than nonshock-tube studies (Khan and Crynes, 1970). The high activation energy suggests that methane dehydrogenation is the rate-determining step (Skinner and Ruehrwein, 1959). CH,+CH,+H The lower activation energy for methane pyrolysis found in flow reactors has been explained as an effect of surface on the reaction (Jampolskie et al., 1968). Surface effects are not expected in shock-tube experiments, and the observed activation energy should then be close to the dissociation energy of the C-H bond. Surprisingly Eisenberg and Bliss (1967) and Palmer et al. (1968) did not find any effect of increasing the surface-tovolume ratio of the flow reactor. As suggested by Happel and Kramer (1967) and later shown experimentally by Palmer et al. (1968),carbon nuclei formed in the gas phase present active surfaces for heterogenous decomposition. Such carbon nuclei should, however, be active in shock tubes as well as in flow reactors if they are important for the decomposition of methane. The difference in observed activation energy for the methane decomposition in shock tubes and flow reactors is therefore not explained by carbon nuclei in the gas phase. At high temperatures the true gas temperature in flow re-
pressure dependent. Strong dilution with an inert gas should anyhow make the unimolecular rate constant almost independent of the methane concentration. If we consider the pyrolysis of methane at low conversion the termination reactions may be neglected and we get the following rate expression
actors is generally unknown. The temperature difference between the reactor wall and the bulk of the gas increases with increasing flow rate. The activation energy is usually determined by measuring the first-order rate constant a t different temperatures in the same range of conversion. The gas flow rate used must therefore be higher at higher temperature, and consequently the temperature difference between reactor wall and gas bulk becomes much higher a t higher temperature. This idea may be illustrated in the following way, considering a homogenous gas reaction. The activation energy E is determined by measuring the rate constant k (7') a t two different temperatures.
rCH4 =
(7) '
Suppose the more correct activation energy is E' = 101 000 cal/mol as found by Skinner (1959) in shock tube studies. Assuming T I = 1700 K, Tz = 2000 K, E = 88 700 cal/mol (our experimental value based on wall temperatures), this gives A2 = 42 K. Such an increase in temperature difference between wall and gas in flow reactors a t high temperature may thus explain the lower activation energy found in these reactors compared to shock tubes. The gas phase decomposition of methane involves free radicals. Ethane is probably an intermediate product in the formation of ethylene and acetylene from methane. Ethane may be formed by the primary reactions: CH4
-+
CH3 + H
+ H CH3 + Hz CH:j + CH3 C2H6
CH4
---*
-+
(1) (11)
(111)
Experimentally the concentration of ethane in the hightemperature pyrolysis of methane was found to be very low. A low concentration may be explained by a high value of the rate constant for reaction IV CzH6
+H
+
CzHs
+ Hz
(IV)
Based on the expression of Baldwin and Melvin (1964) we estimate this rate constant at 2000 K to be in the range 1013 to 1014cm3 mol-l s-l. Assuming ( H )to be in the range to mol cm-3 and (CzH6) = mol ~ m - we ~ ,estimate a rate of mol cm-3 s-I which is of the same order of magnitude as half of the experimental rate of methane decomposition at 2000 K and 0.1 atm of methane pressure. Ethane may thus be a reactive intermediate in the pyrolysis of methane a t high temperature. The stability of the radicals formed in the initiation reaction (I) increases strongly with temperature relative to the elements HZand C. This indicates the thermodynamic possibility of an increased concentration of these radicals during pyrolysis a t high temperature. The rate constant for the unimolecular reaction (I) may be
= k1(CH4) - ~ I I ( C H ~ ) ( H )
(11)
This may be integrated from zero to small values o f t and (H) considering (CH4) as essentially constant. Substituting the result into the expression for methane decomposition we get rCH4
= kI(CH4)(2 - e - - k ~ ~ ( C H 4 ) t )
(12)
This equation predicts an autoacceleration of the methane pyrolysis at low conversion. If we use the expression for h11 given by Walker (1968)
kII Combining the two expressions gives
(10)
The concentration of H atoms at such low conversions is given by the differential equation dt
Since the true gas temperature is unknown, T Iand T Zare the measured wall temperatures of the reactor. Assume that the lowest temperature T I approximately gives the gas temperature (at low feed rate) and that the other gas temperature is A2 lower than the wall temperature Tz (at high feed rate). A more correct expression for determining the activation energy would then be
kr(CH4) + ~ I I ( C H ~ ( H )
= 1.26 X 10" exp
(- 'x","") 1. mol-l s-l
(13)
a t a temperature of 2000 K and a partial pressure of methane of 0.1 atm we find that the period of autoacceleration is less s. This time is too short to explain our experimental than autoacceleration. Therefore we believe that the S-form of our experimental curves must be explained as an effect of gas flow rate on the temperature profile and on the heat transfer from the reactor wall to the gas. At lower temperatures Schneider (1963) and Eisenberg and Bliss (1967) showed that addition of ethane accelerated the decomposition of methane. As a consequence of this the normal autoacceleration disappeared (Schneider, 1963). The effect of ethane decreased with increasing temperature and was not observed above 1500 "C. This suggests that radicals formed from ethane were important at lower temperatures, while at higher temperatures the radical concentration was so high that the ethane contribution was not significant. Simplified Reaction Model Prior to the experimental work we studied a simplified reaction model which it may be of interest to compare with our experimental results. The overall course of the pyrolysis of methane may be described as occurring stepwise
All these products are found in the product mixture from the pyrolysis of methane. At high temperature ethane and ethylene are short-lived. If the reaction time is too long the acetylene formed is decomposed to carbon and hydrogen. A lower activation energy for the last step compared to the first makes it possible to obtain high yields of acetylene from methane at high temperatures. Making some reasonable assumptions as to the reaction orders and the magnitude of the rate constant it is possible to use the step model to calculate the gas composition during the pyrolysis as a function of time. Thus, we considered an isothermal reactor and assumed, as did Guljaev and Polak (1965), the three first steps to be irreversible reactions of first order with rate constants k l , ha, and k3, respectively. The last reaction was assumed to be irreversible of second order according to the results of several investigations of the homogeneous decomposition of acetylene (Miller, 1965; Holmen and Rokstad, 1973). It is reasonable to assume that hz >> k l which means that the concentration of ethane during the pyrolysis is very low. Ind. Eng. Chern.,
Process Des. Dev.. Vol. 15, No. 3,
1976
443
I
-
ACETYLENE
I
L
10-5
10-5
10-4 10-3 REACTION TIME i S E C 1
10-2
10-1
Figure 9. Isothermal pyrolysis o f methane a t 2100 K simulated by t h e simplified model. P u r e methane a t start. Curves for acetylene a n d carbon depend o n t o t a l pressure.
Then the system is described by the following differential equations. dnCH4
dt
- klnCH4
-dnC2H4 - -1k l n C H 4 - k dt 2
3
n
~
~
~
~
The reaction volume is given by the expression
where n, is the total number of moles, ~ O C H . , is the number of moles of methane at the start, and P is total pressure. The differential equations have been integrated by a stepwise procedure on a Univac 1107 computer. The initial conditions n o n ~ 2=~n o4H 2 = 0. The following expressions were n o ~ 2= ~ were used for the rate constants
k3
91 000
(- RT 40 000 = 2.58 X lo8 exp - ( RT )
k l = 4.5 X
lOI3
exp
(18)
Acknowledgment The authors wish to thank Professor Ketil Motzfeld for construction of the reaction furnace. Support of this work by the Royal Norwegian Council for Scientific and Industrial Research is gratefully acknowledged. Nomenclature (CHI) = concentration of methane, etc. E = activation energy i.d. = internal diameter k = rate constant L = lengthof reactor N C H =~ flow rate of methane at conversion ~ c H mol/s ~ , NOCH, = feed rate of methane, mol/s ni = moles of species i at time t nio = moles of species i at time 0 nt = total number of moles P = total pressure R = gasconstant T C H ~= rate of methane decomposition T = temperature, K T,, = equivalent isothermal temperature, K t = time, s V = reactionvolume A = temperature difference ~ C = H conversion ~ of methane @ c ~ H=~ yield of acetylene (based on methane feed) O C ~ H= ~ selectivity of acetylene (based on methane reacted) Literature Cited Baldwin, R. R., Melvin, A,, J. Chem. SOC., 1785 (1964). Eisenberg. B., Bliss, H., Chem. Eng. Progr., Symp. Ser., 63 (72),3 (1967). Gay, I. D., Kistiakowsky, G. 6.. Michael, J. V., Niki, H.. J. Chem. Phys., 43, 1720
(1965).
(19)
k l and k 3 are given by Kozlow and Knorre (1962) and k 4 is given by Gay et al. (1965). Figure 9 shows an example of simulation of isothermal pyrolysis of methane at constant pressure using the described model. The model gives a picture of the product formation which is very similar to our experimental results a t low pressure. The importance of a low hydrocarbon pressure for obtaining high yield of acetylene is clearly demonstrated in Figure 9. We were not able to measure the maximum of ethylene shown in Figure 9 because the reaction time was too short at such high temperatures. Figure 6 shows that ethylene becomes a more important product at lower residence time, indicating the existence of such an ethylene maximum. Our model studies have shown that the position of the
444
acetylene maximum is sensitive to the gas temperature. Thus, changing the temperature from 2100 to 1800 K increases the time for maximum acetylene by an order of magnitude. Below about 2200 K at a pressure of 0.132 atm the model predicts that the maximum yield of acetylene increases with increasing temperature. A t 2100 K and 0.132 atm the model gives a maximum yield of 90%, which is in good agreement with experimental values.
Ind. Eng. Chem., Process Des. Dev., Vol. 15, No. 3, 1976
Guljaev, G. W., Polak, L. S., Kinet. Catal. (Engl. Trans/.), 3, 399 (1965). Happel, J., Kramer. L.. Ind. Eng. Chem., 59,(l),39 (1967). Happel, J., Kramer, L., German Patent 2 307 300 (1973); US. Patent 3 843 744
(1974). Holmen, A,, Rokstad, 0. A,, "Carbon Formation during Pyrolysis of Acetylene," (in Norwegian): Report to the Royal Norwegian Council for Scientific and Industrial Research, 1973. Jampolskie, Yu. P., Gordon. M. D., Lawovskie, K. P.,Neffekhimiya, 8,198 (1968). Khan, M. S..Crynes, B. L., Ind. Eng. Chem., 62 (lo),54 (1970). Koziov, G. I., Knorre, V. G.. Combust. flame, 6, 253 (1962). Kunugi, T., Tamura. T., Naito. T., Chem. Eng. Prog., 57 (ll),43 (1961). Miller, S.A,, "Acetylene. Its Properties, Manufacture and Uses," Vol. I, Ernest Benn. London, 1965. Murgulescu, I. G., Schneider, I. A,, Acad. Rep. fop. Rom., Stud. Cercet. Chim.,
8,367 (1960). Murgulescu, I. G., Schneider, I. A., Z.Phys. Chem. (Leipzig), 218, 338 (1961). Othmer, D.F., Hydcarbon froc., 44 (3),145 (1965). Palmer, H. E., Lahaye. J., Hou, K. C., J. Phys. Chem., 72, 348 (1968). Schneider, I. A,, 2. Phys. Chem., 223, 234 (1963). Shantarowich, P. S., Pavlov. B. V., lnt. Chem. Eng., 2, 415 (1962). Skinner, G. E., Ruehrwein, R. A,, J. Phys. Chem., 63, 1736 (1959). Solbakken, A,, Emmett, P. H., J. Am, Chem. Soc., 91, 31 (1969). Walker, R. W., J. Chem. SOC.A, 2391 (1968).
Received for review December 26, 1974 Accepted M a r c h 6,1976
