00797387 THE CONVERSION OF NATURAL GAS TO ACETYLENE: FACTORS IN THE DESIGN OF DISCHARGE TUBES THIS IS AN ORIGINAL MANUSCRIPT IT may not be copied without THE AUTHOR’S PERMISSION Approved: Approved: Dean of the Graduate School THE CONVERSION OF NATURAL GAS TO ACETYLENE: FACTORS IN THE DESIGN OF DISCHARGE TUBES THESIS Presented to the Faculty of the Graduate School of The University of Texas in Partial Fulfillment of the Requirements For the Degree of DOCTOR OF PHILOSOPHY By Gray Thompson Hamblen, B. S., M. S., (Austin, Texas) Austin, Texas June, 1937 PREFACE Under the direction of Dr. E. P. Schoch, work has been in progress since 1931 on the chemical effect of various types of electric discharges on natural gas of high methane content. The goal is the utilization of the vast quantities of natural gas wasted in the oil fields of Texas. W. B. Franklin, T. T. Covey, and H. D. McAfee repeated the most promising work done in Germany by Franz Fischer and his cbworkers. An alternating current discharge, partly silent and partly of the arcing type, was used. R. S. Sullins investigated the action of the pure glow discharge. F. V. L. Patten and A. A. Draeger studied the effect of high frequency current produced by an oscillator built by Judson Swearingen and Otto Gerbes. W. B. Franklin, J. L. Franklin, C. R. Hocott, and C. F. Jones discovered the advantage of direct current over alternating current. The principle products synthesized by all these discharges were acetylene and ethylene. This dissertation presents part of the work done with direct current at higher power made available by the purchase of a thyratron rectifier. Two groups of workers were at work at the same time. C. R. Hocott and C. F. Jones worked with a tube in which the gas was blown perpendicular to the discharge. Joe C. Krejci, Jack Steele, and the writer worked with tubes thru which the gas was blown longitudinally from cathode to anode. Krejci’s dissertation presents the results of a systematic study pf the action of the discharge in a 5.2 cm. tube. Steele’s thesis gives the procedure and the analytical methods. In the writer’s paper, the results obtained with three tubes of different dimensions are compared with the object of arriving at the best tube design. The results of a study of the characteristics of the discharge are also given. For a complete presentation of the results obtained by the group of workers including the writer, reference must be made to the thesis of Jack Steele 1 and the dissertation of Joe 0. Krejci. 2 The writer wishes to express his appreciation to Dr* E. P. Schoch for the privilege of working on this important problem and for his assistance and kind encouragement. The writer also wishes to acknowledge his gratitude to his co-workers, Mr. Joe C. Krejci and Mr. Jack Steele. Thanks are also due Mr. Charles Jones and Mr. Claude Hocott for their valuable advice and for overcoming the difficulties encountered in the installation of the rectifier. The writer also wishes to thank Mr. W. L. Benson and his assistant, Mr. Joe Me Gee, for their aid in the construction of the apparatus. 1 Steele, Jack: Thesis, The University of Texas, June, 1937 2 Krejci, Joe C. : Dissertation, The University of Texas, June, 1937. TABLE OF CONTENTS PAGE Preface . .......... iv Statement of the Problem ...... 1 Part I. THE TYPE OF DISCHARGE AND THE DISCHARGE CHARACTERISTICS ........ 4 The type of discharge ............... 5 The influence of pressure ............. 9 The influence of the rate of gas passage ..... 13 The effect of current .... 14 The minimum resistance required for stability of the discharge . 16 The effect of tube size .18 Part 11. FACTORS IN DISCHARGE TUBE DESIGN 19 The tube materials ................ 19 The working pressure . . ...... 21 The relative proportions of power and methane . . . 24 The time of contact 33 The electrode distance ....... 40 The tube diameter ............ 43 The current • . • . . . • • . . 43 The electrode size 45 A number of small tubes versus one large tube ... 45 The growth of on the electrodes 46 PAGE Part III. EXPERIMENTAL DATA 47 Summary 50 Bibliography ...» 52 STATEMENT OF THE PROBLEM According to experimental conditions, acetylene, ethylene, benzene, and liquid and solid polymers can be made by means of the electric discharge. Ethylene was obtained as the principle product by Brewer and Kueck 3 in experiments at liquidair temperatures and at very low power input. Benzene in small Quantities has been made by Fischer, 4 who used a combination of heat and electrical effects. Liquid and solid polymers were obtained by Lind and by passing methane at a very low flow rate through a semi-corona discharge. Franklin 6 made mixtures of acetylene and ethylene at low power input, but, when the power was increased to two KW, the ethylene became negligible and acetylene predominated. Since the production of anything but acetylene requires very carefully controlled or impractical conditions, the utilization of natural gas for acetylene production is the most promising possibility. This is not unfortunate, since acetylene can be used as an intermediate in many chemical syntheses. In the design of an electric discharge tube commercially applicable for the conversion of natural gas to acetylene, one is confronted with the following questions: 1. What type of discharge should be used? 2. What should be the ratio of power to gas fed to the tube? 3. Should the power be at low voltage and high current or at high voltage and low current? 4. How long should the gas be subjected to the discharge, and what should the pressure be? 5. Should the gas be handled in one large tube or in a number of small units? With the exception of the work of Fischer and his co- and that of W. B. and J. L. and Hocott and Jones,little of the work on the electrical conversion of methane to acetylene has been directed toward commercial application* A large amount of progress has been made by these workers in answering the above questions of design, but all of the investigations have been hampered by the lack of high power at conditions suitable for the discharge. Hocott and Jones found that the direct current discharge was more efficient and more easily controlled than the alternating current discharge. In order to make possible the investigation of the direct current discharge at higher power input, a thyratron rectifier capable of supplying any amount of power up to 60 KW was purchased by the Chemistry Department from the General Electric Company. The work of Hocott and Jones was necessarily confined to inputs of less than 1 KW. The work reported in this paper is part of the work extending the investigation to higher power. The object was to study the discharge characteristics and to answer on the basis of the new work and work already done on the questions of design listed above. 3 Brewer, A. K. and Kueck, P. D.: J. Phys. Chern., 35, 1923 (1931) 4 Fischer, Franz; Brenn.- Chem., 9, 309, (1928) 3 Lind, S. C. and Glockler, George J.: J. Am. Chem. Soc., 51, 2811 (1929) 6 Franklin, W. B.: Thesis, The University of Texas, Aug 1931. 7 Fischer, Franz, end Peters, Kurt: Brenn.-Chem., 10, 108 (1929). 8 Peters, Kurt, and Pranschke, Alex: Brenn.-Chem., 11. 239 (1930). — * 9 1 0 Franklin, W. 8., Franklin, J. L.: Dissertations, The University of Texas, June, 1934. — Hocott, C. R., Jones, C. F.: Theses, The University of Texas, June, 1934. PART I: THE TYPE OF DISCHARGE AND THE DISCHARGE CHARACTERISTICS 1 2 Acetylene can be made by the glow discharge in methane, but the glow discharge is characteristic of low pressures and low current densities, both of which are undesirable from the standpoint of commercial application. Low current density involves little power, and the maintenance of low pressure is costly. Acetylene can also be made in the electric arc at atmospheric pressure, but operation is greatly hindered by carbon formation. The most favorable type of discharge is that which takes place from small electrodes at pressures of from 20 to 100 mm. of mercury. In order to study the effects of tube design, this type discharge was tried in three different tubes: (1) a large pyrex bulb 30 cm. in diameter, provided with small carbon electrodes placed 8 and 12 cm. apart; (2) a 5.2 cm. silica tube, 40 cm. long, with electrodes 4,8, and 12 cm. apart; (3) a 2.2 cm. silica tube with electrodes 8 cm. apart. In all cases, the gas flow was from cathode to anode. The electrodes were small carbon cylinders, 2 mm. to 10 mm. in diameter and from 4to 30 mm. long. They were attached to rods of coldrolled steel. The discharge with alternating and direct currents up to one ampere has been studied by Franklin 13 at electrode distances of 1 to 50 cm. in a tube 5.2 cm. in diameter. Franklin referred to the discharge as a typical arc, and further evidence that this is the case is given in the following pages. A study of the Influence of the pressure, rate of gas passage, current, and the tube size on the characteristics of the arc is also given, since such a study is necessary in the design of a discharge tube. 12 Sullins, R. S. : Thesis, The University of Texas, August, 1932. The type of discharge. Darrow 14 defines the glow discharge as one for which the voltage is of the order of hundreds of volts and the current is in milli-amperes. In the case of the arc he states that the voltage is of the order of tens of volts and the current is from 10 to 100 amperes. He has in mind the glow discharge at low pressure and the arc at atmospheric pressure. The discharge used in this work took place at pressures between 20 and 100 cm. of mercury. The field strength was from 100 to 500 volts per cm., and the current was from 0.5 to 5.0 amperes. In the light of the above definition, the discharge seemed to be an intermediate case. Darrow quotes Compton: "An arc is a discharge which has a falling or sensibly horizontal characteristic, and at the cathode a voltage drop of the order of the minimum ionizing or minimum exciting potential of the vapor.” By ’’characteristic” is meant the voltage versus current curve. Such a curve for the discharge used is shown by the curves of Fig. I , and they show that the characteristic does fall. The cathode fall is the voltage drop across an indiscernable, thin sheaf before the cathode. No attempt was made to measure this voltage. Nottingham^ s showed that, except for extremely short dis tances in front of the electrodes, the voltage drop per cm. across the distance between the electrodes supporting an arc is constant. That the field was constant for the discharge used in this work was shown by comparison of the voltages per cm., at constant pressure and rate of gas passage, when the electrodes were 4,8, and 12 cm. apart in the 5.2 cm. tube. Table I gives the data arranged for comparison. The inconsistencies in the data are the results of several causes. The voltage would vary from day to day, probably because of changes in the composition of the gas. Carbon deposited rapidly on the electrodes, causing the distance between them to shrink at about the rate of 3.5 mm. per minute. Also, because the tube had to be dismantled for cleaning after each trial and reassembled for the next trial, there were probably small variations in the electrode distance. The falling characteristic and the constant field strength furnish the basis for defining the discharge as an arc, particularly since doubling the distance between the electrodes of a glow discharge does not double the voltage. This is because most of the voltage drop of a glow discharge is in front of the cathode. Further evidence that the discharge was an arc and not a glow was shown by its behavior on electrodes of different sizes. For a given pressure and electrode temperature, the glow discharge will change to an arc when the current density on the cathode is raised above a certain critical value in the order of 0.1 ampere per square cm. At the point of change, the discharge abandons most of the area of the cathode and concentrates on one spot. The current density is increased greatly, and thus for a given electrode size, much more power can be delivered to an arc than to a glow discharge. When the cathode was a centimeter in diameter, the discharge emerged from a very small spot on the electrode. A glow discharge would have covered the entire face of the cathode. A small cathode, 2 mm. in diameter was substituted, and no change in the discharge was noted. Hence the cathode area had little to do with the discharge. 13 Franklin, W. B. : Dissert at ion, The University of Texas, June, 1934. 14 Barrow, K. K.: Electrical Phenomena in Gases, The Williams and Wilkins Company, Baltimore (1932 J Nottingham: Journal of the Franklin Institute, 206, 43 (1928), 207, 299 (19297 FIG. I Current: 1 ampere < . Rate of flow: 850 liters per hour Electrode distance: 4 cm. # Electrode distance: 8 cm. Pres., Voltage, Volts * Pre s., Voltage, Volts mm. of Volts per ~x mm of Volts per Hg cm. *x* Hg cm. 20 425 106 * 20 850 106 40 575 144 * 40 975 122 50 650 163 -x- 50 1125 141 60 700 175 * 60 1350 169 Current: 0.5 ampere 5. Rate of flow: 3400 liters per hour Electrode distance: 8 cm. 'X- Electrode distance: 12 cm. 90 2050 253 -x- 90 3300 275 110 2150 269 * no 3500 291 Current;: 1 ampere. Rate of flow: 3400 liters per hour Electrode distance: 8 cm. -x- Electrode distance: 12 cm. 80 1600 200 -x- 80 2000 167 100 1750 219 ’X- 100 2900 241 110 1850 231 ’X- no 3070 256 TABLE I 5.2 cm. tube The Influence of pressure. The gas in the discharge tube was broken down at about 20 mm. of mercury pressure, and the current was raised to a predetermined value by supplying more power to the series circuit consisting of the tube and the ballast resistance. When the pressure was increased, the current fell, and it was necessary to supply more power in order to raise the current to the desired value. The influence of the pressure at constant current and rate of gas passage is shown by the curves of Fig. 2, which indicate that the voltage was a linear function of the pressure to about 120 mm. At this point, the curves begin to flatten. This may have been the result of very rapid shrinkage of the electrode distance at the higher pressures where the rate of carbon deposition on the electrodes was great. However, correction was made for this shrinkage from a measurement of the length of the carbon deposits. A description of the discharge over the pressure range of the curves of Fig. 2 will now be given. The 2.2 cm. tube was used, and the current and flow rate were held constant at 0.5 amperes and 1700 liters per hour. At 21 mm. the discharge was blue and attenuated, at 60 mm. the blue discharge was squeezed to a smaller volume; at 80 mm. carbon began forming in the tube, and slight, yellow streaks appeared near the electrodes. At the first appearance of the yellow color, the voltage and the current fluctuated slightly. At 100 mm., all of the discharge was yellow, and the current and the voltage were steady. Raising the temperature further increased the intensity of the yellow and the rate of carbon formation. At 274 mm., the carbon growth on the electrodes was so rapid that the duration of the experiment was limited to one or two minutes. The behavior of the discharge with 0.5 amperes and at 3400 liters per hour was much like that at 1700 liters per hour. The yellow color appeared at about the same pressure. At 200 mm., a second, more violently unstable condition of the voltage and the current was encountered. The tendency was for the current to decrease and the voltage to increase in a transition to another of discharge. This discharge was bluestreaked and very unsteady. It finally went out. The pressure at which the very unsteady condition of the discharge occurred was smaller at the higher currents. With the 5.2 cm. tube, at currents of 2 amperes and above, this condition was encountered at about 100 mm. pressure. By using a larger ballast resistance, the discharge could be maintained through the pressure range of unsteadiness (about 10 mm.), and a steady discharge could be maintained at higher pressures. The voltage here was less than it had been at the steady condition at lower pressures. The voltage across the tube was greater on some days than it was on others. When it was greater, the pressures at which the unsteady conditions of the discharge were encountered were lower. From this, it appears that the unsteadiness was a result of critical voltages and not pressures. For the 2.2 cm. tube, the pressure-voltage characteristic was different for 1.5 amperes than it was for 0.5 amperes. At pressures below 44 mm., the discharge was blue and attenuated, just as it was at 0.5 amperes. At 44 mm., the discharge changed to the yellow color. Up to this point, the characteristics had been similar to those at 0.5 amperes, with the exception that the yellow color appeared at a lower pressure. At 68 mm., a light blue streak appeared in the center of the discharge. Further increase of the pressure intensified the blue, and the unstable condition was found near 100 mm., while at 0.5 amperes, it was found at 200 mm. The curves of Fig. 3 show that at the appearance of the streak, the voltage reached a maximum after which it decreased with increasing pressure. For the rising part of the characteristic, it was necessary to apply more power as the pressure was raised in order to maintain a constant current. Over the pressure range where the voltage fell with the pressure, the power had to be decreased to keep the current constant. The appearance of the streak did not in all cases herald a decrease in the voltage with rising pressure, but in all cases of the streaked discharge, the voltage did not increase so rapidly with pressure as it did with the unstreaked discharge. FIG. II The Influence of the rate of gas passage. The curves for two rates of gas passage, shown by Fig. 2, indicate that the voltage increased with the rate of gas flow. The two curves are parallel. That this increase in voltage was not so marked at the higher currents is shown by the curves of Fig. 3, which represent the conditions at 1.5 amperes in the 2.2 cm. tube. An Increase in the velocity of the gas would also cause a change from the yellow discharge to the streaked type. For the 2.2 cm. tube, the discharge was yellow with 1700 liters of gas flowing per hour, but when the rate was changed to 3400 liters per hour, the discharge was streaked for the pressure range of 40 to 100 mm. of mercury. A possible explanation for the increase in voltage with the gas velocity is the retardation of the positive ions bearing current to the cathode. It is reasonable to suggest that the current of the streaked discharge, which was characteristic of the higher currents and the higher gas velocities was born more by electrons than by ions. The intense, central blue streak suggested a beam of electrons. This would account for the lessening of the effect of the gas velocity at the higher currents, where a smaller number of gas molecules per electron would be available for the production of ions, and thus the burden of bearing the current would be shifted more to the electrons. At the higher gas velocities, more ions would be blown backward from the cathode, and this again would shift the current to the electrons. FIG. III FIG. IV The effect of the current. Some of the effects of the current on the characteristics of the discharge have already been mentioned. The voltage-current characteristics for three pressures and a constant rate of gas passage are given by Fig. 1. These curves, which are for the 5.2 cm. tube with the electrodes 8 cm. apart, show that the voltage decreased as the current was increased. Mrs. Hertha has shown that the relation between the current and the voltage for an arc is given by the equation: V = A-FB i where V is th voltage drop between the electrodes, A and B are constants, and i is the current. This is the equation of a parabola, and inspection of the curves of Fig. 1 reveals that the current range included two curves of parabolic shape, one from 0.5 amperes to 2.5 amperes and another from 2.5 to 4.5 amperes. It has already been mentioned that the arc at the higher currents had a central, blue streak, while no such streak was visible at the lower currents. This indicates that the parabola for the lower currents is characteristic of the unstreaked arc, while the curve for the higher currents is the characteristic of the streaked discharge. The minimum resistance required for stability of the discharge. According to Kaufmann’s criterion l7 a discharge is self-sustaining only when de-|- R > 0 di where de is the rate of change of voltage with current, di R is the minimum resistance required for stability A discharge having a falling characteristic will always need a series resistance in order to be self-sustaining, since de/di, the slope of the characteristic, is negative. A tangent drawn to the curve for 70 mm. pressure gives 883 ohms as the minimum resistance for a self-sustaining arc at 0.5 amperes. This resistance was found to be sufficient for the discharge at these conditions. The tangent at 1 ampere, gives 257 ohms as minimum resistance. Tangents at higher values of the current show that less resistance is required for stable arcs at higher currents. A tangent at 4 amperes gives 70 ohms as the minimum resistance. Although this small resistance was not tried, it is believed that it would not be sufficient for a stable discharge. The smallest resistance tried at 4 amperes was 333 ohms, which was found to be sufficient. It was necessary to add more series resistance at the higher rates of gas passage. A resistance of 800 ohms was sufficient at 0.5 amperes for 1700 liters per hour, but for 4910 liters per hour, 1500 ohms was found to be too small. The discharge at this gas velocity was unsteady even with 3000 ohms This data was for the 5.2 cm. tube. This implies that the higher gas velocities obtained at the same volumetric flow rate through the 2.2 cm. tube would make higher resistances necessary. This was not found to be the case. Mien power amounting to slightly more than half of that used in the discharge was dissipated in the series resistance, the discharge was usually stable. This was a good working rule for determining the necessary resistance. 16 Ayrton, Mrs. Hertha: The Electric Arc, ”The Electrician” Printing and Publishing Company, Limited, London. Kaufmann, W. : Ann* d. Physik (4) 2, 158 (1900) The effect of the Tube size. No matter how small the tube, the discharge could never be made to fill it entirely. This was probably due to the fact that the walls of the tube became negatively charged and repelled the electrons flowing in the arc. But the cross-sectional area of the discharge, and therefore the current density, was proportional to the size of the confining tube. An arc carrying 3 amperes in the 30 cm. bulb had a diameter of about 6 cm. In the 5.2 cm. tube, the diameter was about 3.5 cm., while in the 2.2 cm. tube, the discharge had a diameter of about 1.5 cm. It has already been shown that Increasing the gas velocity increased the voltage, particularly at the lower currents. Therefore, for a given volumetric flow rate the voltage across the electrodes of the 2.2 cm. was greater than the voltage for the 5.2 cm. tube. In order to determine if the increased velocity were the only factor involved in increasing the voltage, tests were made at 0.5 amperes in the 2.2 and 5.2 cm. tubes with volumetric flow rates such that the mass velocity was the same. The curves of Fig. V show the results of these tests. The voltages for the larger tube were higher. The difference between the voltages for the two tubes decreased with pressure. The greater voltage for the larger tube can be explained by the smaller current density in the larger tube, since it has been shown that for a given tube, the voltage decreased with current, or current density. For the same current in tubes of different sizes, the current density would be greater in the smaller tube, hence the lower voltage for the smaller tube. The streaked discharge was characteristic of the higher currents. The streak appeared in the 2.2 cm. tube at about 1.5 amperes, while in the 5.2 cm. tube, the streak did not appear until the current was about 2.5 amperes. This can also be explained on the basis of higher current densities in the smaller tube. However, the streak appeared in the 30 cm. bulb at the same current that it appeared in the 5.2 cm. tube. PART II: FACTORS IN DISCHARGE TUBE DESIGN The tube materials. In order to prevent short circuiting, it was necessary to make the tubes of a non conducting materials Pyrex tubes were tried, but at the higher power inputs, they were softened by the heat and were pushed in by the atmosphere. Pyrex also had the disadvantage of catalizing carbon deposition. Silica tubes were tried, and it was found that they not only resisted the heat but were inactive catalytically for carbon deposition. The electrodes were made from carbon obtained from drycell cathodes or arc light electrodes. It was found that coldrolled steel melted when used as the anode. Steel cathodes were pitted by the action of the discharge. Both steel and carbon electrodes catalized carbon growths. Carbon was selected as the electrode material because it was a better refractory. FIG. V The working pressure. At currents below 2 amperes, the pressure could be raised to one ot two hundred mm. without encountering a violently unstable discharge. It has been stated that with currents of 2 amperes and above, the discharge would become unstable and finally go out between 100 and 120 mm. pressure. Stable discharges at higher pressures could be obtained by adding a greater series resistance, but the added resistance would cause unnecessary waste of power. Also, the number of OH necessary to produce a cubic meter of acetylene at the higher pressures was higher. This is shown by the following data. At the lower currents, the discharge was of the yellow, stable type up to pressures over 270 mm. But the formation of carbon made operation at higher pressures troublesome. The curve of Fig. VI shows the relationship between carbon formation and pressure. Though the amount of methane converted to carbon barely reached 10 per cent, the growth of carbon deposits on the electrodes and fouling of the tube made operation at the higher pressures impractical. On the basis of these results, it was concluded that operation above 100 mm. was undesirable for the production of acetylene. At pressures below 100 mm., at constant current and rate of gas passage, the voltage and hence the power input varied almost linearly with the pressure, and the acetylene varied almost linearly with the power. Therefore, if the per cent of acetylene is plotted against the pressure, a curve having the same trend as the voltage-versus-pressure curve should be the result. The curves of Fig. VII show the per cent of acetylene plotted against the power and pressure and this result is indicated. The data, which correspond to curve lof Fig. 2, was taken under the following experimental conditions: tube size, 2.2 cm.; electrode distance, 8 cm.; current, 0.5 amperes; rate of gas passage, 1700 liters per hour. A comparison of the curves shows that the acetylene-versus-pressure curve has the same trend as the voltage-versus-pressure curve. If the per cent acetylene varied linearly with the power, the value of the KWH per cubic meter of acetylene should be constant. Actually this value was somewhat higher for the lower pressures. FIG. VI FIG. VII Pres., Voltage Per cent M per mm. of Hg acetylene cubic meter of acetylene 90 1460 13.1 12.1 100 Unsteady discharge 110 740 5.8 16.6 Tube size: 5.2 cm. Electrode distance: 8 cm. Rate of gas flow: 1700 liters per hour. Current: 2.5 amperes The relative proportions of power and methane. The endothermic reaction 2CH4 = C2H 2 + 3H 2 - 95.6 Kg. cal. gives the theoretical energy that must be added to methane to convert it to acetylene and hydrogen. Converted to electrical units, this energy consumption is at the rate of 4.63 KWH per cubic meter of acetylene formed at 20 degrees C. and 760 mm. pressure. The quantitative conversion would yield a mixture of hydrogen and acetylene in the ratio of 3:1, or a mixture containing 25 per cent of acetylene. If the electrical power added were used 100 per cent in the formation of acetylene and hydrogen, a kilowatt applied to a tube would require a methane flow rate of 432 liters per hour. But in addition to the energy used for the above reaction, energy was used in heating the gas, in heating the parts of the tube, in the radiation of energy, and in the formation of carbon from methane. Under the most favorable conditions from the standpoint of efficiency alone, eight times the theoretical amount of methane were used for the applied energy, or more specifically, the proportions used were 2800 liters per hour per kilowatt. Here 95 per cent of the energy was used in the formation of acetylene, but the concentration of the acetylene in the end gas was necessarily small (5.8%) due to the large excess of methane. To increase the amount of acetylene, it was necessary to increase the ratio of energy to methane. This could be accomplished at a constant rate of gas passage by raising the current, by increasing the electrode distance, or by increasing the pressure. It could also be done by reducing the rate of gas flow. The quantitative relationships of such changes are given in the section on discharge characteristics. If the power input was raised, more power was diverted to channels other than that of the formation of acetylene, namely, carbon formation and the generation of heat and radiant energy. Curve 2of Fig. 8 shows the decrease in efficiency (a rise in the value of the KWH per cubic meter of acetylene) as the power was Increased at a constant pressure and rate of gas flow through the 5.2 cm. tube. Also, the curves of Fig. 10a show the same result for Increasing the power-to-methane ratio. N o t only did this loss of power lower the efficiency, but it contributed in many cases to the mechanical failure of the tube by the formation of carbon on the walls and subsequent short circuiting to this carbon. It is the purpose of this section to discuss tube failures brought on by the use of too much power, and to arrive at a practical figure for the ratio of methane to energy added to the tube. When carbon formed on the walls of the tube, there was danger of an arc jumping from the cathode to the conductive carbon. Such an arc almost Invariably cracked the tube. Also, the carbon coating shut in the radiant energy, and thus contributed to overheating. That this energy was considerable was shown by the fact that the light striking the wooden table under the discharge tube often caused the wood to smoke. The presence of carbon on the walls did not necessarily mean that the discharge would jump to the walls. It was only when the heat was excessive through the use of too much power that arcing would occur. At lower power input, the discharge would behave with the walls completely covered with carbon. Some of the trials in which arcing occurred because of the use of too much power are given by Table 11. All of the experiments except the last were made with the 5.2 cm. tube. It was 40 cm. long and had a cubic capacity of 850 cubic centimeters. The last experiment was made with the 2.2 cm. tube. When the arc travelled down the side of the tube, its path was marked by a deposit of hard carbon which was very difficult to remove. Even after careful cleaning, the portion of the tube contacted by the arc acted catalytically as a surface for the condensation of carbon. The path would be marked again by a deposit of carbon, but this deposit could be removed by wiping with a cloth. Arcing was more probable in a tube that had been subjected to several arcs. The tubes which had been cracked by the arcs could be used again, because the cracks were vacuum tight. However, after several cracks had been made close together, the tube would break. Table u shows that the use of power near that theoretically required for the conversion of methane to acetylene would often cause the discharge to arc to the tube wall. Accordingly, 18 for the systematic study of the discharge made by Krejci, changes in the methane-power ratio were made within limits such that the power seldom exceeded the theoretical power required for the conversion of all of the methane to acetylene and hydrogen. The power input ranged between 0.3 and 4.0 KW, and the rates of gas passage were from 850 to 3400 liters per hour. Very few trials succeeded where the power input was greater than the theoretical power. Nov/ that it has been decided that the theoretical power is the practical limit for the power applied to the tube, it remains to be decided what fraction of this power should be used to obtain the best results, that is, results where not only the acetylene content of the gas is high but the energy efficiency is good. Certainly the use of 50 per cent of the theoretical power would not endanger the tube. The curves of Fig. 8 show plots of the per cent theoretical power against the per cent of acetylene in the end gas and the per cent theoretical power against the number of OH necessary to make a cubic meter of acetylene. At 50 per cent of the theoretical power, there was 9.5 per cent of acetylene in the end gas and energy was used at the rate of 9.5 KWH per cubic meter of acetylene produced. These curves represent a good average of the conditions imposed. They were for 80 mm. pressure, a gas flow rate of 1700 liters per hour, and at an electrode distance of 8 cm. Since an energy efficiency of 4.65 KWH per cubic meter of acetylene represents the use of 100 per cent of the power in making acetylene and hydrogen, a value of 9.5 represents the use of about half of the energy applied for this purpose. In the section covering discharge characteristics, it was stated that about half of the power spent in the tube had to be used in an external resistance in order to maintain a stable discharge. This placed the overall energy consumption at 14.3 OH per cubic meter of acetylene. This value is near that of the calcium carbide process which requires 13 KWH. The curves of Fig. 8 were plotted for a constant rate of gas passage and variable power. In order to show that at constant power and variable rate of gas flow the efficiency dropped as the ratio of power to methane was increased, the curves of Fig. 9 were plotted for approximately 2 KW at varying gas flow rates. The curves show that at 50 per cent of the theoretical power, 11 per cent of acetylene was obtained at B*2 KWH per cubic meter. In order to show that in general it was a good policy to use power inputs of about half of the theoretical power, Tables Illa, Illb, and Ilic are given. Table Illa shows that power inputs of from 40 to 60 per cent of the theoretical power gave fair amounts of acetylene at good efficiencies. Comparison with Table lIIb, for power inputs of 80 to 100 per cent of the theoretical, shows that very little more acetylene could be produced by the application of more power and that the efficiency values were not so good as those of Table Illa. Table Ilic shows that the per cent of acetylene held up well at even the lower power inputs of from. 20 to 40 per cent of the theoretical power and that the efficiencies were very good. The question arises: would it he possible to design a tube to take care of a large amount of excess power and thus convert all of the methane to acetylene, even at the sacrifice of efficiency. Ben the discharge tube is large in proportion to the power applied, the generalization that the tube cannot be operated with an excess of power does not hold. This is due to the fact that the small amount of power is not sufficient to cause overheating. worked with such a tube with alternating current and obtained the following results: Diameter of tube: 5.2 cm. Electrode distance: 50 cm. Volume of tube: 1700 c.c. Rate of gas flow: 215 1/h Pressure: 55 mm. of Hg Power: 1.574 KW Per cent of theoretical power: 317 Per cent of acetylene: 15.28 KWH per cubic meter: 27.30 Per cent hydrogen: 71.3 Per cent of methane: 9.0 Per cent of CH. converted to C 2 H 2 : 47.7 4 Per cent of CH/ converted to C: 8.1 The data show that the use of 300 per cent of the theoretical power did not produce much more acetylene than the use of the 88 per cent of the theoretical power (see the first line of Table Illb) where 14 per cent of acetylene was produced. The results of Peters and Pransehke, 20 who worked with a similar tube, show that very little more acetylene can be produced by the addition of a large excess of power. Table IV gives their results. It is also to be noted that the best efficiencies were obtained where the power input was about 50 per cent of the theoretical power. 18 Krejci, Joe C. : Op. cit. Franklin, W. B.: The sis, The University of Texas, June, 1931. FIG. VIII FIG. IX Pres. Elec- Rate Current Volts Power Per mm. of trode of Amperes KW cent of Hg dis- gas theoretical tance flow power cm. 1/h 82 27 2250 2.0 3500 7.00 118.7 80 26 1700 1.0 4250 4.25 108.2 -• 26 2550 1.0 5200 5.20 88.1 — 20 1700 1.0 3700 3.70 94.1 65 10 1700 2.0 1600 3.20 81.4 85 12 1700 2.0 2300 4.60 117.1 90 8 1700 4.5 930 4.20 106.9 80 8 850 1.5 1350 2.03 103.1 80 8 1700 4.0 850 3.40 86.5 TABLE II Elec- Rate Pres., Volt- Cur- W Per Per KWH trode of mm. of age rent cent cent per Dis- Gas Hg -Amp. of Cu- tance, Flow Theor. bic cm. 1/h Power Meter 4 850 70 800 0.5 0.80 40.6 8.2 9.6 4- 850 100 800 0.5 0.80 40.6 7.8 10.3 8 850 80 1300 1.0 1.30 60.6 10.4 11.7 8 1700 80 1580 1.0 1.58 40.2 9.2 8.2 8 1700 80 1450 1.5 2.40 61.1 12.5 8.5 8 2550 90 1600 1.5 2.40 40.6 9.8 7.8 12 3400 120 3100 1.0 3.10 39.5 8.4 9.3 TABLE IIIa 5.2 cm. tube 40 to 60 per cent of the theoretical power 8 1700 80 1390 2.5 3.48 88.7 14.0 10.1 8 1700 90 1130 3.0 3.39 86.3 12.0 12.6 8 1700 90 990 3.5 3.47 88.3 9.5 17.3 8 1700 80 920 4.5 4.16 106.0 11.1 17.1 8 850 80 1630 1.0 1.63 83.2 11.8 12.4 8 850 80 1350 1.5 2.03 103.0 11.4 16.1 TABLE IIIb 80 to 100 per cent of the theoretical power 8 850 40 575 0.5 0.58 29.2 6.6 8.9 8 1700 80 1800 0.5 0.90 22.9 6.3 7.5 8 2550 90 1700 1.5 1.70 28.8 8.1 6.1 8 5400 80 1600 1.0 1.60 20.3 7.1 5.7 8 3400 90 1630 1.5 2.45 31.2 9.2 6.4 12 2550 48 1775 1.0 . 1.78 30.1 7.9 7.9 TABLE IIIc 20 to 40 per cent of the theoretical power The time of contact. A comparison of the results obtained with the same volumetric rates of gas passage through the 2.2 cm. tube and the 5.2 cm. tube shows that the shorter time of contact in the smaller tube had little to do with the acetylene yield or the efficiency. The data in Table V are arranged for comparison. The higher gas velocity through the smaller tube caused the voltage to be higher and the per cent of acetylene ■k From Peters and Pranschke: Brenn. Chem. 11, 239 (1930) to be higher in proportion. At 0.5 ampere, 1700 liters of gas per hour, and an electrode distance of 8 cm.; and also at 1 ampere, 3400 1/h, and 8 cm., the values for the OH per cubic meter of acetylene were higher for the smaller tube. In the first case, an explanation for the lower efficiency of the smaller tube may be found in the fact that, for the higher gas velocities, some of the methane molecules passed through the tube without having a chance to plunge through the discharge. At the higher flow rate of the second case, the discharge was the blue streaked type, and this type was found to be less efficient than the yellow type. However, where the type of discharge was the same for both tubes, the change in efficiency was small in proportion to the change in gas velocity (the velocity in the smaller tube was 5.6 times that in the larger tube), and it was concluded that the reaction time was so short that no provision needed to be made for holding the gas in the discharge to allow time for reaction. The curves of Fig. 10a show that an increase in the efficiency (a decrease in the value for the KWH per cubic meter of acetylene) was the result of increasing the flow of gas through the discharge. An increase in the gas flow increased the probabi lity of an electron hitting a fresh methane molecule, and the increase in efficiency indicated that this was a prime factor in the production of acetylene, since at the slower rates of gas flow, there was a greater chance for an electron to hit an acetylene molecule or a hydrogen molecule and thus have its energy absorbed without contributing to the acetylene yield. Peters and Wagner 2l showed that the efficiency for acetylene formation was less for mixtures of hydrogen and methane than it was for pure methane. The detention of the gases too long in the discharge had the effect of diluting the methane with the hydrogen formed in the formation of the acetylene or carbon. A comparison of the results obtained with the 2.2 cm. tube and the 30 cm. bulb show the result of leaving the gas too long in the discharge. The data is arranged in Table VI for comparison. The table shows that the carbon formation was greater at the slower rate of gas passage. In order to determine whether the increased decomposition of methane to carbon were the only factor lowering the efficiency, the energy necessary to form the additional carbon was taken into account, and the KWH per cubic meter of acetylene was recalculated as follows: The energy required to make gaseous carbon and hydrogen from methane is given by the equation CH 4 (g) = 2H 2 (g) + C (g) - 178.9 Kg.- cal. It would therefore require 14.45 KWH to convert the 1700 liters of methane to carbon and hydrogen. At 27 mm., 6.5 per cent of the methane was converted to carbon in the small tube, while in the bulb, this conversion was 8.8 per cent. The energy for the additional conversion was 0.33 KWH. Allowance for this energy changes the value of the KWH per cubic meter of acetylene from 13.65 to 11.8. Since the value for the smaller tube was 8.27, the additional carbon formed in the bulb does not account for the loss in efficiency. Therefore, some of the electron energy must have been lost in bombarding the hydrogen molecules. 20 Peters, Kurt, and Pranschke, Alex.: Op. cit 21 Peters, Kurt and Wagner, 0. H. , Zeit. f. Phys. Chern A. 153, 161 (1931). FIG. Xa FIG. Xb Rate of gas passage l/h Pres, mm. of Hg Theo- retical power W Power O Per cent of theo- retical power Per cent acetylene IM per cubic meter of c 2 h 2 15 17 0.04 0.79 1975 16.0 131.0 58 20 0.13 0.72 554 8.2 110.0 750 -60 1.74 2.40 138 12.4 14.0 1060 65 2.45 1.72 70 8.0 11.6 1080 60 2.50 1.40 56 6.9 12.3 1580 80 3.19 1.60 50 5.3 11.8 TABLE IV* Electrode distance: 8 cm. Rate of gas passage: Current: 1700 1/h 1 ampere 5.2 cm. tube 2.2 cm. tube Pres. Volts Per KWH Pres. Volts Per KWH cent per cent per CgHg cubic C2H2 cubic meter meter 60 1400 9.4 7.1 Z 57 1630 9.4 8.1 70 1520 9.3 7.8 -x- 66 1900 10.8 7.7 80 1580 9.2 8.2 * 87 1900 10.4 8.1 90 1620 9.0 8.7 % 100 1975 10.8 7.9 100 1560 8.2 9.4 w Electrode distance: 8 cm. Current: 0.5 ampere Rate of gas passage: 1700 1/h 50 1630 5.8 7.4 * 40 1100 2.8 10.8 60 1700 6.1 7.2 * 60 1500 4.8 9.1 70 1820 6.4 7.3 * 80 1880 5.8 8.3 80 1800 6.3 7.5 * 100 2300 8.0 7.1 90 1800 6.1 7.6 * 125 2900 10.4 6.1 100 1750 5.9 7.7 *X" Electrode distance: 8 cm. Current: 1 ampere Rate of gas passage: 3400 1/h 80 1600 7.1 5.7 * 61 2100 0 • 03 to 90 1700 7.5 5.6 * 81 2200 6.6 8.3 100 1775 7.1 6.3 * 101 1650 5.0 8.5 TABLE V Pres. mm. of Hg Volts Per cent Frac. dec. Frac. dec. to c 9 h 2 Frac. dec. to 0 KW KWH per c .m. of °2 H 2 >2.2 cm. tube 27 1370 13.4 Si. 454 0.389 0.065 2.74 8.27 47 1300 11.6 0.397 0.325 0.072 2.60 9.42 67 1220 13.5 0.442 0.389 0.53 2.44 7.37 30 cm. bulb 27 1220 7.85 0.291 0.203 0.088 2.44 1365 75 1350 6.64 0.258 0.167 0.091 2.70 TABLE VI Electrode distance: 8 cm. Current: 2 amperes Rate of gas passage: 1700 liters per hour The electrode distance. The data in Table VII show the effect of increasing the electrode distance from 4 to 8 cm. and from Bto 12 cm. It appears that the efficiency was decreased, but the results are not directly comparable, because an increase in the electrode distance at a constant rate of gas passage increased the power-to-methane ratio. The results were obtained at power inputs of from Ito 3 KM. A glance at the efficiency curve of Fig. 9 for approximately 2 KW (electrode distance: 8 cm.) shows that in most cases the increase in power-to-methane ratio could account for the decrease in efficiency. It was therefore concluded that the changes made in the electrode distance made little difference in the efficiency. But the tube was difficult to operate when the electrode distance was greater than 8 cm. For a given ballast resistance, the discharge was more likely to go out when the electrodes were farther apart. More power was associated with the longer electrode distance, and higher rates of gas flow had to be employed to satisfy the condition that 50 per cent of the theoretical power be employed. The discharge was more difficult to control at the higher flow rates; it blew about and was more likely to short circuit to the tube wall. With electrodes far apart, the anode and the tube walls surrounding it became very hot. In some of the trials with electrodes 10 to 20 cm. apart, the iron rod supporting the anode melted. This was remedied by shielding the iron with carbon, but the accumulation of heat at the anode end of the tube was conducive to short circuiting to the wall. On the basis of the operating difficulties at electrode distances greater than 8 cm., it was decided that longer distances were impractical. Current: 1 ampere Rate of gas passage: 850 1/h Electrode distance: 4 cm. « Electrode distance : 8 cm. Pres . Volts Per MH Per * Pres. Volts Per KWH Per mm. cent per cent * mm. cent per cent of 02% c.m. theor * Of c 2 h 2 c.m. theor Hg power « Hg power 20 425 5.2 8.6 21.6 * 20 850 7.8 10.9 43.1 40 575 6.6 8.9 29.2 -x- 40 975 9.2 10.2 49.5 60 700 7.7 9.6 35.3 * 60 1350 12.0 10.2 68.5 'Current: 0.5 ampere. Rate of gas passage: 3400 1/h Electrode distance: 8 cm. * Electrode distance : 12 cm. 90 2050 5.5 4.9 13.4 -x- 90 3300 6.9 6.1 21.0 110 2150 5.8 4.9 13.7 * 110 3500 6.5 6.9 22.3 Current: 1 ampere. Rate of gas passage: 3400 1/h Electrode distance: 8 cm. * Electrode distance 12 cm. 100 1775 7.1 6.3 22.6 -x 100 2900 8.8 8.1 36.9 110 1800 7.6 6.3 22.9 -x- 110 3070 8.7 8.9 39.0 120 1875 6.8 7.0 23.9 * 120 3100 8.4 9.3 39.5 TABLE VII 5.2 cm. tube The tube diameter. The trials made with the 30 cm. bulb showed the disadvantage of holding the gas too long in the discharge. Also, at a short electrode distance, a tube of wide diameter would allow some of the gas to by-pass without coming in contact with the discharge. At the beginning of the work, it was thought that the 2.2 cm. tube could be operated at higher pressures, because the shorter time of contact would reduce carbon formation. It was found that the fraction of the methane converted to carbon in the 2.2 cm. tube was about the same as it was in the 5.2 cm. tube, and hence the higher pressures were not possible with the smaller tube. The yield and efficiency were about the same in both tubes, and it was concluded that there was no advantage in using the smaller tube. Also, there was more danger of short circuiting to the walls with the smaller tube, and the current changed to the less efficient blue, streaked discharge at lower currents. Accordingly, it was decided that the 5.2 cm. tube was the better tube. The current. The blue, streaked discharge characteristic of the higher currents has been described. The data of Table VIII show that the efficiency decreased as the current was increased. It is true that the power increased with the current and was probably the controlling factor in decreasing the efficiency. But extremely wide differences, for example, the difference between the efficiency at 4.0 amperes and that at 4.5 amperes suggested some specific effect of the current. However, the higher currents were undesirable for another reason. The cathode spot and the anode were hotter at the higher currents. This caused the carbon deposits on the electrodes to be longer, and more difficult to remove. No method of removing these deposits during operation of the tube was developed in this work. By blowing the gas perpendicularly across the electrodes, Hocott and Jones 22 were successful in combating these growths. Their theory of the formation of the deposits was that fluffy carbon black melted on the electrodes, solidified, and built up the ’’trees 0 . By blowing the gas across the electrodes, carbon black was removed before it melted and solidified. At the higher currents, the hotter electrodes would probably make this method less effective. 22 Hocott, 0. R. and Jones: Dissertation, The University of Texas, June, 1937. Electrode distance 8 cm. • 5.2 cm. tube Rate of gas flow; 1700 1/h Pressure: 90 mm. of Hg Current, .Amperes Volts Per cent 02% KW KWH per c .m. Per cent of theor. power 2.0 1550 15.1 5.06 10.2 78.0 2.5 1460 15.1 5.65 12.1 95.0 5.0 1150 12.0 5.59 12.6 86.5 5.5 990 9.5 5.47 17.5 88.5 4.0 950 10.5 5.80 16.8 96.7 4.5 950 10.5 4.19 19.0 107.0 TABLE VIII The electrode size. The electrode size had nothing to do with the type of discharge or the amount of decomposition. Since the smaller electrodes became hotter than the larger ones, the carbon deposits were longer on the smaller electrodes. A number of small tubes versus one large tube. On the basis of the results obtained, it appears that conversion of large amounts of gas would require the use of a number of small tubes consuming from 1 to 3 KW each rather than the use of one large tube with high power input. It has been shown that the working pressure was from 70 to 100 mm. of Hg. The average field strength in this range was from 150 to 200 volts per cm. Then at an electrode distance of 8 cm. and a current of 2 amperes, about 3KM were dissipated in the tube. On the basis of the results discussed in the section on the effect of current, it was deemed inadvisable to use currents in excess of three amperes. Therefore, increasing the power by increasing the current was not advisable and also, since the voltage decreased with the current, not much additional power could be added by increasing the current. Since pressures above 100 mm. were not feasible, increasing the field strength by increasing the pressure was limited, and, to increase the power per tube, the distance between the electrodes had to be increased The disadvantages of working at long electrode distances have been discussed. Hence it appears that the use of a number of small tubes rather than one large one is more favorable. The growth of "trees" on the electrodes. The greatest obstacle to the practical use of the electric discharge for the production of acetylene from methane is the growth of T, trees” on the electrodes. At pressures near 100 mm. , the trees did not grow as rapidly as they did at higher pressures. The method of Hocott and Jones for preventing growths by keeping the carbon blown off of the electrodes has been described. Similar methods were tried for the longitudinal gas flow. The electrodes were steam-lined to direct the gas over the ends of the electrodes and thus keep the carbon off. Also, the gas was introduced at high velocity by means of a baffle arrangement around the cathode in order to keep the carbon blown off of this electrode. But none of the methods prevented the growth of the trees at the rate of about 3.5 mm. per minute. A single tree would grow from the cathode, and a number of them would form on the anode, because the discharge played about on this electrode. PART III: EXPERIMENTAL DATA The data taken with the 5.2 tube is given in the dissertation of Joe C. Krejci.The complete data for the 2.2 cm. tuhe and the 30 cm. bulb are given below. 23 Krejci, Joe 0. : Ojo. cit. Pres, mrn. of Volts Per cent °2H 2 Frac, dec. Frac, dec. to G2H 2 Frac, dec. to C KW Per cent of theor. power WH per c.m. of C2H 2 21 650 2.01 0.0416 0.0416 0.0 0.325 8.3 9.15 40 1100 2.79 0.0698 0.0596 0.0102 0.55 14.0 10.83 60 1500 4.76 0.1183 0.1065 0.0118 0.75 19.1 9.13 80 1880 5.75 0.159 0.133 0.026 0.94 23.9 8.3 100 2388 7.96 0.2385 0.1972 0.0413 1.195 30.2 7.13 125 2900 10.42 0.3465 0.2805 0.066 1.45 36.9 6,08 150 3300 10.98 0.316 0.2885 0.0275 1.65 42.0 6.73 175 3540 11.83 0.419 0.335 0.084 1.77 45.0 6.2 200 3750 11.63 0.399 0.325 0.074 1.875 47.7 6.8 2.2 cm. tube. Electrode distance: 8 cm. Rate of gas passage: 1700 1/h Current: 0.5 ampere zn 1400 2.61 0.0551 0.0551 0.0 0.70 8.9 7.49 60 1850 3.31 0.0709 0.0709 0.0 0.925 11.8 7.68 93 2500 5.67 0.1282 0.1282 0.0 1.25 15.9 5.76 100 2690 5.9 0.1338 0.134 0.0 1.345 17.1 5.92 125 3120 6.53 0.144 0.1495 0.0 1.56 19.9 6.14 150 3290 6.36 0.1635 0.148 0.0155 1.645 20.9 6.53 202 4050 8.0 0.1753 0.188 0.0 2.05 26.1 6.35 2.2 cm. tube. Electrode distance: 8 cm. Rate of gas passage: 3400 1/h Current: 0.5 ampere Pres, mm. of Hg Volts Per cent C2H 2 Frac, dec. Frac, dec. to C 2 H 2 Frac, dec. to C W Per cent of theor. power KW per c.m. of 26 1840 10.15 0.314 0.267 0.047 1.84 46.8 8.13 46 1800 9.54 0.317 0.251 0.066 1.8 45.8 8.43 57 1630 9.35 0.2695 0.237 0.0325 1.63 41.5 8.10 66 1900 10.8 0.351 0.292 0.059 1.9 48.4 7.65 87 1900 10.38 0.323 0.276 0.047 1.9 48.4 8.12 100 1975 10.76 0.359 0.2925 0.066 1.975 50.2 7.94 2.2 cm. tube. Electrode distance: 8 cm. Rate of gas passage; 1700 1/h Current: 1 a mpere 41 2470 8.07 0.2195 0.1965 0.043 2.47 31.4 7.39 61 2100 6.44 0.1646 0.1503 0.0143 2.10 26.9 8.23 81 2200 6.63 0.1766 0.1562 0.0104 2.2 28.0 8.29 101 1650 5.04 0.1363 0.1145 0.0218 1.65 21.0 8.49 2.2 cm. tube. Electrode distance: 8 cm. Rate of gas passage: 3400 1/h Current: 1 ampere 50 1520 11.59 0.331 0.2895 0.0415 2.28 58.0 9.21 68 1770 13.5 — — — 2.66 67.5 8.93 75 1700 13.5 0.408 0.366 0.042 2.55 64.9 8.25 100 1750 12.48 0.3545 0.3185 0.036 2.63 66.7 9.48 2.2 cm. tube. Electrode distance: 8 cm. Rate of gas passage: 1700 1/h Current: 1.5 amperes Pres. mm. of Hg Volts Per cent c 2 h 2 Frac. dec. Frac, dec to C 2 H 2 Frac, dec to 0 KW Per cent of theor. power KWH per c.m. of c 2 h 2 44 1530 7.44 0.1668 0.1713 0.0 2.29 29.2 7.75 56 1700 9.55 0.2035 0.2165 0.0 2.55 32.4 6.2 68 1800 9.75 0.231 0.2265 0.0045 2.70 34.3 6.92 :so 1760 9.48 0.205 0.217 0.0 2.64 33.6 6.72 100 1620 9.02 0.183 0.186 0.0 2.43 30.9 6.67 2.2 cm. tube. Electrode distance: 8 cm. Rate of gas passage: 3400 1/h Current: 1.5 amperes 27 1370 13.4 0.454 0.389 0.065 2.74 69.6 8.27 47 1300 11.63 0.397 0.325 0.072 2.60 66.0 9.42 67 1220 13.5 0.442 0.389 0.053 2.44 62.0 7.37 2.2. cm. tube. Electrode distance: 8 cm. Rate of gas passage: 1700 1/h Current: 2 amperes 25 800 9.65 0.395 0.269 0.026 3.2 81.4 16.68 2.2 cm. tube. Electrode distance: 8 cm. Rate of gas passage: 1700 1/h Current: 4 amperes 80 750 8.11 0.263 0.216 0.053 3.0 76.2 17.25 2.2 cm. tube. Electrode distance: 8 cm. Rate of gas passage: 1700 1/h Current? 4 amperes 27 1220 7.85 0.291 0.203 0.088 2.44 62.1 13.65 75 1350 6.64 0.258 0.1672 0.0908 2.70 68.6 17.58 20 cm. bulb Electrode distance"? 8 cm. Rate of gas passage: 1700 1/h Current: 2 amperes SUMMARY Part I: THE TYPE OF DISCHARGE AND THE DISCHARGE CHARACTERISTICS 1. The discharge was a typical arc. 2. In general, the voltage Increased linearly with the pressure. Deviations from this rule were discussed, and the pressures at which the discharge was unstable were noted. 3. The voltage increased with the rate of gas passage. The effect was greater at the lower currents. 4. The voltage decreased with the current. Two voltage current characteristics were noted in the current range from 0.5 to 5.0 amperes. 5. The series resistance required to maintain a stable discharge was the resistance which dissipated slightly more than one half of the power used in the discharge. Kaufmann’s criterion was discussed in connection with the voltage-current characteristics. The cross-sectional area of the discharge was propor tional to the size of the discharge tube, but it would never fill the tube. The characteristics of the arc in three tubes were compared. Part II: FACTORS IN DISCHARGE TUBE DESIGN 1. Silica was better than pyrex as a tube material, because it would withstand the heat at higher power input and because it would not catalyze carbon deposition. Carbon was the most refractory electrode material. 2. Carbon deposition or unstable discharges hindered operation at pressures in excess of 100 mm. 3. The limit to the amount of power that could be applied to a tube without mechanical difficulties was found to be the power theoretically required to convert all of the methane flowing through the tube to acetylene. 4. Operation at 40 to 50 per cent of the theoreti cal power was found to lead to a good compromise between the acetylene yield and the efficiency. 5. The time of contact required for reaction was found to be very short. Long time of contact in the biggest tube was found to be undesirable. The results with the 2.2 cm. tube and the 5.2 cm. tube were compared, and it was found that the acetylene yield and the efficiency were about the same for both tubes, but the shorter time of contact in the smaller tube gained no advantage. 6. Operation was difficult at electrode distances greater than 8 cm. Changes in the electrode distance made little difference in the efficiency. 7. The discharge characteristics and the acetylene yield were independent of the size of the electrodes. 8. Operation at currents in excess of 3 amperes was found to be undesirable, because the efficiency was lowered and the carbon deposition on the electrodes was troublesome. The formation of ’’trees” which bridged between the electrodes was discussed. BIBLIOGRAPHY Ayrton, Mrs. Hertha: The Electric Arc, ’’The Electrician” Printing and Publishing Company, Limited, London. Brewer, A. K. and Kueck, P. D.: J. Phys. Chem., 35, 1293 (1931) Darrovir, K. K. : Electrical Phenomena in Gases, The Williams and and Wilkins Company, Baltimore 71932) Fischer, Franz; Brenn.-Chem., 9, 309 (1928) Franz and Peters, Kurt; Brenn.-Chem., 10, 108 (1929) Franklin, J. L.: Dissertation, The University of Texas, June, Franklin, W. B.: Thesis, The University of Texas, August, 1934. : Dissertation, The University of Texas, June, 1934 Hocott, C. R. : Thesis, The University of Texas, June, 1934. * Dissertation, The University of- Texas.:, June, 1937. Junes, C. F.: Thesis, The University of Texas, June, 1934. ; Dissertation, The University of Texas, June 1937. Kaufmann, W. : Ann, d. Phys Ik, (4), 2, 158 (1900) Krejci, J. C.: Dissertaion, The University of Texas, June, 1937 Lind, 5. C. and Glockler, George: J. Am,. Chem. Soc., 41, 2811 (1929) Nottingham: Journal of the Franklin Institute, 206, 43 (1928) Ibid., 207, 299 (19297 ’ Peters, Kurt and Pranschke, Alex: Brenn.-Chem., 11, 239 (1930) Peters, Kurt and Wagner, 0. H. : Zeit. f. Phys* Chem., A, 153, 161 (1931) ~ ~ Steele, Jack: Thesis, The University of Texas, June, 1937. Sullins, R. S. : Thesis, The University of Texas, August, 1932.