7NDUSTRIAL A N D ENGINEERING CHEMISTRY
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Vol. 23, No. 6
The Flame-Pressure Process for Carbon Black',' A. W. Francis3 ARTHURD. LITTLE,INC., CAMBRIDGE, MASS.
c
The best grades of carbon black are made by burning ARBON black suitable combustion in the luminous hydrocarbon gases with a continuous flame. The for printer's ink and zone. T h e s e a r e u s u a l l y yields are seldom over 3 per cent because the upper other pigments as well burned c o m p l e t e l y before inflammability limits of the hydrocarbons are so low as r u b b e r compounding is leaving the flame. The pale that an excess of oxygen is always present to consume usually made by deposition blue zone in a methane flame most of the carbon. Stifling the flames is futile. upon a metal plate from a is wide because the temperaSince an increase in pressure raises the upper incontinuous luminous flame of ture of thermal decomposition flammability limits, much higher yields of carbon n a t u r a l gas burning in the is high and more time is reblack can be obtained by burning hydrocarbons conopen air. The yield by this quired to reach i t ; but with tinuously in an atmosphere of compressed air. Yields method has always been low, higher hydrocarbons, which of high-grade carbon black have been trebled at 100 however, seldom exceeding 3 are more easily decomposed, pounds pressure in small-scale equipment, and comper cent (9). this zone may become vanishputations have been made indicating that this can be Thermal decomposition of ingly thin. Its inner border increased much more. The process also permits utilih y d r o c a r b o n gases can be in all cases is defined by the zation of the heat of combustion of the gas. made to give 30 or 40 Der cent locus of mixtures correspondyields of ;arbon, but 'because ing to the upper inflammaof the high temperature (1200-1300" C.) required for a reason- bility limit of the gas (with trivial corrections for preheatable reaction rate, the product is inferior in tinctorial power, ing and rate of flow of gas). The great theoretical and pracand therefore unfit for use in printer's ink. I n rubber com- tical significance of the upper inflammability limit upon yield pounding it has only limited use, principally in side walls of carbon has been neglected heretofore. of tires rather than the tread. Mechanism of Combustion of Methane Because of the higher quality of carbon black deposited from a continuous flame, numerous attempts have been made I n the following discussion the figures and equations for to increase the yield. Control of draft and improvement in methane will be used, but the principles apply equally to burner tips have effected only trivial increases. The design other hydrocarbons. The upper inflammability limit of methof the deposition plates has distinguished various processes, ane in air is about 14 per cent. Such a mixture contains such as the channel, disk, plate, and cylinder processes, but 18 per cent of oxygen, or more than enough to gasify all the these distinctions are only superficial. carbon according to the equation Since carbon is an incomplete combustion product of hydroCHI + 02 +CO Hz HzO (a) carbons, it is a common fallacy to suppose that its production could be increased by stifling the flame in some way. The low yield usually obtained is therefofe due to the fact This has been the subject of several patents (7, 11). At that in every part of the flame proper there is an excess of least one of them ('7) recommends a mixture which is com- oxygen for Equation a. A small amount of carbon is formed by the side reaction pletely non-inflammable. The idea can be disproved easily CHa 0 2 ---f C 2Hz0 (b) by experiment, since any attempt to stifle a hydrocarbon flame by mixing carbon dioxide or nitrogen with the gas or the air The relative amounts oxidized according to (a) and ( h ) are supply, or by limiting the supply of air, makes the flame non- governed by the relative excess of oxygen a t some critical luminous. The effect of even traces of carbon dioxide in point in the flame, and by the equilibrium decreasing the luminosity of flame is well known. The candleC + Hz0 =* CO 4- H2 (C) power of a flame is decreased 3.4 per cent by 0.1 per cent carbon dioxide in the atmosphere ( I O ) . The reason for this ap- between their products. This equilibrium adjusts itself readily a t the temperature of the luminous portion of the parent anomaly will appear presently. flame.
+ +
+
Parts of Hydrocarbon Flame
For the present purposes luminous hydrocarbon flames may be considered as divided into four parts: the inner dark portion consisting of gas-air mixtures too rich to burn (really not part of the flame a t all); the intermediate pale blue zone of preliminary combustion and rising temperature; the bright yellow portion where the temperature is high enough to decompose some of the unburned hydrocarbon to free carbon, which is usually burned in the same zone unless a cooler solid is interposed; and the outer blue envelope (top, sides, and bottom) containing little or no hydrocarbon, but considerable hydrogen and carbon monoxide from incomplete I Received March 17,1931. Presented before the Division of Petroleum Chemistry at the Slst Meeting of the American Chemical Society, Indianapolis, Ind., March 30 to April 3, 1931. 2 From a thesis submitted in 1920 to the Worcester Polytechnic Institute in partial fulfilment of the requirements for the degree of chemical engineer. 8 Present address, Vacuum Oil Co.,Paulsboro, N. J.
+
Attempts to Increase Carbon Yield
To effect an appreciable increase in yield of carbon, therefore, we must change conditions so as to diminish the excess of oxygen in the flame by raising the upper inflammability limit of the hydrocarbon, or to shift the equilibrium (c) toward the left. ADDITIONOF INERT GASES-Let us consider the effect of added nitrogen or carbon dioxide upon the upper inflammability limit of methane in air as shown in Table I. Inflammability Limits of Methane in Air w i t h Added Nitrogen or Carbon Dioxide (6) ADDEDNITROGEN ADDEDCARBONDIOXIDE N2 CH4 0 2 COz CH, Oz
Table I-Upper
% % % % % % 14.0 18.0 14.0 18.0 0 0 12.0 16.6 8.9 11.5 16.6 8.8 9.9 l5,l 13.5 10.2 16.0 18.0 7.9 13.5 17.8 9.0 15.3 27.7 6.1 12.1 23.0a 7.3 14.6 35.95 a Further increase of inert gas renders all mixtures non-intlammable,
INDUSTRIAL AND ENGINEERING CHEMISTRY
June, 1931
I n the last case for each added gas the limit mixture contains 2 volumes of oxygen for 1 of methane, or enough for complete combustion to carbon dioxide and steam: CHI
+ 202 +COn + 2H20
I n principle this relation might have been predicted without Table I, since when combustion of a mixture is almost inhibited by stifling, only stoichiometric proportions of reactants would be likely to react a t all. Recalling the fact that this upper limit defines the inside border of the combustion
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INCREASE OF PRESSERE-hother factor, not previously changed, can be modified so as greatly to improve the yield of carbon during flame combustion. This is the pressure of the atmosphere surrounding the flame. With increased pressure we should expect increased luminosity and an increased deposition of carbon upon a suitable surface because of the very pronounced increase in the upper inflammability limit of methane in air, as shown in Table I11 and Figure 1. of Pressure upon Upper Inflammability Limit in Air ( I ) Pressure, atm. 1 10 50 125 Methane, r0 13.5 17.0 29.5 45.4
Table 111-Effect
At 50 atmospheres, for example, the limit mixture contains only 14.75 per cent oxygen, or half the amount required for Equation a, instead of 1.3 times as much as is the case a t atmospheric pressure. The amount of carbon oxidized is necessarily reduced. The effect of this increase in inflammability limit upon yield of carbon is automatic, since the flame itself finds the richer mixture. The pressure also affects the equilibrium of Equation c by mass action so as to give more carbon. This is due to the fact that there are 2 volumes of gas on the right side of the equation and only 1 on the left. An increase in pressure, therefore, shifts the equilibrium toward the left. Increase in Luminosity
These predictions have been verified experimentally. The increase in luminosity with pressure was demonstrated simply in an apparatus consisting of a 2-liter filter flask supported upside down (Figure 2 ) with a two-hole rubber stopper and glass tubes wired in. Compressed air entered the side arm and was exhausted through the long glass tube, the pressure in the flask being controlled by the screw pinch clamp on the exhaust.
Pressureh Atmospheres Figure 1-Pressure
a n d Inflammability Limits for Methane in Air
zone of a flame, we see that in effect the addition of an inert gas to the atmosphere would actually provide for the methane in the flame a greater proportion of oxygen rather than less; and we should expect more nearly complete combustion of the hydrocarbon, in agreement with the facts. The futility of partial stifling of the flame is apparent. A mixture containing 1.3 mols of oxygen to 1 of methane, which if burned would give a little carbon, is now non-inflammable and, being well within the dark zone (really not part of the flame a t all), could not possibly give any carbon. ATMOSPHERE ENRICHED I N OYYGEN-ASmight be expected, the inflammability limits of methane are wider in an atmosphere of oxygen or one enriched with oxygen. These are shown in Table I1 (1): Table 11-Effect
of Oxygen in Atmosphere o n Inflammability Limits of Methane
“atmosphere” CH4in upper limit mixture 01 in
%
%
21 13.3
33 25.1
% ,50
38.8
% 66 47.5
% 100 59.2
From the reasoning in the last paragraph it would be supposed that in such atmospheres greater amounts of carbon would be produced; but another factor, higher flame temperature, is involved, and this affects equilibrium ( e ) unfavorably as to yield of carbon. Methane burns in oxygen with a very brilliant flame resembling that of acetylene in air; but little carbon could be collected from it. I n balancing the two factors, flame temperature and inflammability limit, there should be some ideal “atmosphere” of nitrogen and oxygen for maximum yield of carbon, and the chances are against its being identical with ordinary air. Experiment indicates that it would be close to it, possibly slightly enriched with oxygen, but economy precludes the practical use of enriched atmospheres.
Apparatus for Determining Effects of Increased Pressure o n Luminosity of Flame
Methane under pressure controlled by a needle valve entered through the short glass tube. The gas was ignited before lowering the filter flask over it, and the stopper was wired in while continuing a gentle air stream with the exhaust wide open to avoid smothering the flame. Then the pinch clamp on the exhaust was screwed up gradually, the pressure of air and gas being increased a t the same time. This requires some dexterity to avoid extinguishing the flame. Flames of burning liquids were tested in the same apparatus, using a one-hole rubber stopper and substituting for the short glass tube an ampule of the liquid, which was supported by the long glass tube by means of a wire. The wick consisted, not of cotton or asbestos, which might introduce complications in the flame, but of about six capillary glass tubes such as are used for melting points. These tubes were cut carefully the same length, and just projected from the neck of the ampule.
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At all pressures above 2 atmospheres a methane flame becomes narrow and sharply pointed (unless it impinges upon a plate). The whole flame becomes bright orange and almost smoky, whereas a t atmospheric pressure it is only feebly luminous. Flames of other carbonaceous materials, such as gaseous, liquid, and solid hydrocarbons, alcohols (except methanol), and even wood, are affected similarly by pressure. The distinction between methanol and ethanol in this respect is significant. At 6 atmospheres the ethanol gives a flame which is almost smoky, while the methanol shows no appreciable luminosity. This difference is probably due to the fact that all the carbon of methanol is already combined with oxygen, whereas in the case of ethanol this is true of only half the carbon. Carbon atoms thus partly oxidized are probably reduced to elementary form with much greater difficulty.
n
fiGUR.5
panded to reduced to Frankland flame with
Vol. 23, No. 6
a spherical shape. Under pressure the flame is a ‘kpike.” By means of a platinum thermometer could detect no variation in temperature of the pressure. Determination of Yields
I n order to determine the yields of carbon from hydrocarbon flames under pressure, a 1.5-liter bomb was designed (Figure 3) with air and gas inlets, exhaust, a sight glass, and a deposition plate which could be rotated by an external crank. This apparatus was operated in the same manner as the iilter flask. The flame was kindled, the cover was bolted on with exhaust and air supply open; then pressure was controlled by the exhaust valve, and the size of the flame by the gas inlet. After opening the bomb, the carbon produced was scraped off from the deposition plate, dried, and weighed. Estimation of Gas Consumption
3
Apparatus for Determining Yields of Carbon from Hydrocarbon Flames under Pressure
Source of Carbon in Hydrocarbon Flames
These observations make it extremely improbable that the carbon found in hydrocarbon flames could arise from decomposition of nascent methanol, as claimed by Bone and Townend (a), although they admit (3) that no carbon is deposited by thermal decomposition of methanol. This view is supported further by the practical non-luminosity of flames of glycerol, all of whose carbon is already combined with oxygen, as compared with those of propane, its parent hydrocarbon, or with those of other organic compounds of similar viscosity or volatility. Frankland (5) in 1862 made similar observations upon the candlepower of flames of liquids and solid fuels in air of absolute pressures from 0.3 to 4 atmospheres. The candlepower of wax candle flames varied almost linearly with the pressure, falling off 5.1 per cent for each inch (25.4 mm.) of mercury below atmospheric, and becoming zero at the lower pressure mentioned. With pressures above atmospheric the same relation continued until the flame became too smoky. Even ethyl alcohol burned with a brightly luminous flame which was almost smoky a t 4 atmospheres. He made similar observations for the candlepower of hydrocarbon gas flames over the moderate barometric range of pressures available. Rosa, Crittenden, and Taylor (IO) made similar observations but found a smaller variation in candlepower, 0.6 per cent per centimeter of mercury for gas flames. Frankland draws the surprising, but undoubtedly accurate, conclusion that “compression of the atmosphere renders combustion less perfect and rarefaction makes it more complete.” He accounts for this by supposing that at low pressures the oxygen molecules are less impeded and so can penetrate the flame more readily; and also that under reduced pressure more surface is offered by the flame, which is ex-
The estimation of the amount of gas consumed was less convenient. At first the exhaust gases were bubbled through sodium hydroxide solution, and the carbonate was estimated gravimetrically by diluting an aliquot sample and adding barium chloride. The assumption was made that all the carbon of the gas was either deposited or oxidized to carbon dioxide, so that determination of both would show the amount of gas consumed. This method was found unsatisfactory because the exhaust was so rapid that the removal of carbon dioxide from it was by no means quantitative. The method finally used to measure the gas supplied was to employ an auxiliary bomb of 1600 cc. capacity and a pressure gage. Before the experiment this bomb was Wed from the cylinder to a pressure substantially above that desired for the combustion. During the run the gas was drawn from this bomb alone, so that its volume multiplied by the difference between the initial and final pressures, ’in atmospheres, gave the volume of gas used. It was usual to continue the run until the pressure in the auxiliary bomb and combustion bomb were equal, as evidenced by the extinguishing of the flame. Cause and Prevention of Flickering
The principal difficulty in the study of continuous flames under pressure is their excessive flickering. This is due partly to drafts from the air supply and to irregularities in pressure; but even when these factors are corrected, the former by suitable baffles, there is frequently a rhythmic “jumping” of the flame, about 100 beats per minute. A similar observation was made by Chamberlain and Rose (4) in flames a t atmospheric pressure, but the frequency was much greater, about 600 per minute. They showed the regularity of the beats and analyzed the various shapes of the flame, but did not account for the phenomenon. At one time in the present investigation it was thought to be due to the strokes of the air compressor, but this cause was eliminated by drawing from a tank of compressed air. The flame could always be rendered perfectly steady by turning it down to a height of 1 em., but such small flames were not efficient in depositing carbon because of their relatively large surface causing excessive combustion of the carbon. It was finally concluded that this rhythmic flickering was due to the fact that the rate of propagation of the flame downwards exceeds the linear velocity of the gas upwards, so that intermittently the flame front advances into the burner tip, where that portion is extinguished by the richness of the mixture. This tendency is much greater in a pressure atmosphere than in the open air, because the luminous zone occupies practically the whole flame, so that the flame front
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
June, 1931
or inner border of the combustion zone is normally close to the burner tip, instead of having a wide dark zone as a margin of adjustment. The obvious remedy is to make the opening in the burner tip narrower in order to increase the linear speed of the gas through it. This proved successful in eliminating flickering, but the adjustment of size of opening is difficult because, if it is too narrow, the flame tends to blow out, and the slightest irregularities in width of slot make the flame very uneven. Various forms of burner tips were tried to prevent flickering. No particular shape showed any advantage, the only requirement being proper width of slot for the size of flame desired. The following general conclusions were drawn : An ordinary slot lava tip, such as is used in carbon-black factories and old-fashioned open gas jets, does not give a flat flame in a pressure atmosphere. The flame becomes narrow and cylindrical in shape, and is not the most efficient in depositing carbon. The same is true of the tip with two impinging jets often used with acetylene for illuminating purposes, giving a flat flame in the open air. A long, flat flame seemed essential for best results, and this was attainable only by using a narrow slot as long as the desired flame. I n the laboratory apparatus the most convenient and efficient tip for this purpose was the common “wing tip” or “flame spreader,” squeezed together to an inside width of about 0.8 mm., although other forms of slot tips were used. Typical runs are recorded in Table IV. The yield seems to bear no relation to rate of gas flow. Its relation to pressure is partly obscured because of the greater difficulty in obtaining steady conditions under higher pressures. Nos. 7 , 8, and 9 show the relation somewhat exaggerated because the yield a t atmospheric pressure (0.17 per cent) is much less than that obtained commercially (nearly 3 per cent), since the flame was necessarily much too small in the size of bomb available. T a b l e IV-Yields
of C a r b o n D e p o s i t e d f r o m Continuous F l a m e s of M e t h a n e in Air u n d e r P r e s s u r e
MEAN RATE OF No. PRESSURE GAS Atm. Lilcrs/hour 53 13.8 68 59 38 30 20 8.3 120 13.6 67 55 12.1 52 54 78 39 6.7 89 21 8.2 104 9.3 2s 50 51 27
11.6 10.7
43 47 7 8 9 5
71 28 100
YIELD^
TYPE
grades of carbon black now on the market. The quality and tinctorial power of the products were tested by making pastes with linseed oil and rubbing on a microscope slide in comparison with some premium commercial carbon blacks; and also similar pastes with zinc oxide containing 1 per cent of the blacks. The slides gave true blacks and grays, respectively, which matched those of the standard blacks in color and shade. The quality of black seemed to be the same whether it was made from methane, propane, gasoline, or even paraffi, in the flame-pressure process.
F i g u r e 4-Theoretical Yield of C a r b o n f r o m M e t h a n e in Air u n d e r Pressure a n d a t 437’ C.
Calculation of Yields at Various Pressures
OF n p
% ’ 8.75 8.50 8.12 7.22 7.08 6.97 6.62 6.53
615
Flame spreader Cu tube squeezed to slot, S X 0.25 mm. Flame spreader Flame spreader Flame spreader Machined slot Flame spreader 76-mm. Cu tube with 1-mm. slot i n side
6.48 6.36 6.28
Flam; spreader Flame spreader 9.9 76-mm. Fe tube with 1-mm. slot in side 5.13 118 5.85 Machinedslot 8.8 51 5.64 Commercial lava tip 33 4.67 Conical tapering hole 9.7 Conical tapering hole 6.6 39 4.10 32 0.17 Conical tapering hole 1.0 3% yield = 1 pound per 1000 cubic feet of methane.
I n all experiments in Table IV except Nos. 59, 47, 7 , 8, and 9 long slots (at least 5 cm.) were used. In general, the long slot had an advantage in yield of 2 to 3 per cent over any small tip. This is the reason that the yield in No. 59 did not quite equal No. 53, in spite of the much higher pressure. No. 59 was made in a much smaller bomb, which permitted higher pressures but not so large a flame. From all these considerations it seems probable that, with a large bomb, suitable tips, and properly controlled gas and air supply, i t should be possible to increase the yields considerably above those obtained-to perhaps 20 per cent when operated a t 20 atmospheres (280 pounds gage). Quality of Carbon Produced
The carbon produced in these experiments is equal in tinctorial power to, and apparently identical with, the best
I n order to estimate the probable theoretical limiting yields of carbon from methane a t various pressures, the yields have been computed on the basis of certain assumptions. Even if these assumptions are not accurate, the tendencies and general conclusions will probably be valid. It is assumed, (!)$ That the various possible flame reactions are in complete equilibrium at some single temperature, which is that of the carbon upon the deposition plate, and is close to that of the plate itself. (2) That this temperature is the minimum one a t which the reactions will proceed a t appreciable speed. This is reasonable because the flame temperature is much higher than this, but as the carbon cools by radiation, its amount increases continually until the reactions are no longer fluid and the equilibria are “frozen.” (3) ,That this temperature is the same a t all pressures. This is implied in (2) and is supported by Frankland‘s observation. (4) That this temperature can be found by computing the single temperature for all equilibria a t which the yield of carbon from methane should be equal to the best actually obtained at atmospheric pressure-namely, 3 per cent. (5) That the proportions of methane and air reacting correspond with the upper inflammability limit a t the given pressure as shown in Table 111. This assumption is merely tentative, but is more reasonable than any other in regard to relative amounts of reactants, and some such assumption is necessary.
The flame equilibria are as follows:
+ 2H2 C- CHd HP + COPC- HzO + CO C + HzO HP + CO C
c + co, e 2 c o
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+++
+++
COz CH4 2H2 2CO (5) CO 3Hz C= Hz0 CH, (6) COz 4Hz e 2Hz0 CH4 (7) but only three of these are independent. We can take almost any three, but for convenience we will choose the first three. The equilibrium constants of these equations can be calculated from free-energy equations as functions of temperature as given by Lewis and Randall (8), with slight modifications for more recent work. At 710" K. (437" C.), which was found by trial computations to be the temperature gi+ng results most closely in agreement with observed yields (this is in fair agreement with the observation (9) that the plates must be kept somewhat below red heat for best yields), the values of these equilibrium constants are as follows:
Ki
=
6.68
KP = 0.00029
K3 = 0.136
carbon continuously and removing it intermittently through an air lock without releasing the pressure; and also a mechanism for controlling the gas and air pressures with a small, adjustable but not fluctuating, difference between them in order to maintain the flames a t constant height. There should be a means of kindling the flame while the autoclave is under pressure. A simple spark gap is unsuitable for this purpose, because in order to kindle a flame it must be in an inflammable mixture; and when a combustible gas issues into air, such a mixture exists only in a narrow zone around the sides of the jet. Furthermore, a spark plug might distort the flame, and might be short-circuited by carbon. A suitable device for kindling the flame might be a temporary pilot jet of hydrogen impinging upon platinum black, or a jet of electrolytic gas past a spark gap protected from carbon deposition by a recess.
The over-all reaction in a methane flame up to and including the deposition of carbon upon a plate is as follows: nNz
+ 0.263nOz + uCH4 nNz + hHz + wHpO + xCO + yCOz + mCH4 + CC --f
in:which the literal coefficients (except the last) indicate the partial pressures in atmospheres. The number 0.263 is the ratio of oxygen to nitrogen by volume in air. I n order to find the eight unknowns, we have the following eight equations:
+ + + + + + + + + + x + y + m + c = u (to balance carbon)
'Oou 1.263% u = L (inflammability limit) h w x y m = P (pressure, atm.) w 2m = 2%(to balance hydrogen) w x 2y = 0.526%(to balance oxygen)
n h
(4)
(5)
(6) (7)
(8)
These simultaneous equations can be solved best by trial. This is a very tedious task since in order to have the results comparable, the equations must hold with much greater accuracy than the values of the constants seem to warrant. The solutions a t various pressures are given in Table V. Table V-Calculated INFLAMMA-
N2 Afm. 0.663 1.326 3.29 6.47 12.59 17.94 20.0 23.0 31.9 54.0
Economics of the Process
From an economic standpoint the most serious difficulty in the flame-pressure process for carbon black is the cost of installation of the equipment for compressing the large amounts of air required. The cost of power is negligible, because there is an excess of power available from the hot compressed exhaust gases. Indeed, the possibility of conserving the heat of combustion is an important advantage of this process over others. I n the laboratory bomb the minimum ratio of volume of air to that of gas was 22. This could not be decreased much further without partially stifling the flame, which has been shown to be intolerable for the production of carbon. The theoretical minimum air ratio is 8.6, assuming 20 per cent yield of carbon from methane according to the equation: 5CH4
+ 902 + 34Nz +C + 4COs + 10HzO + 34Nz
It is possible that on a large scale, with sufficient baffles to allow very little of the air to pass the flame without going through it, the air ratio might be cut down to 15 or possibly 12; but even this would require large air-compressing equipment. With natural gas a t its present low price in the carbonblack fields, the yield of carbon black is not economically important. It is cheaper to burn five times as much gas to
Partial Pressures a n d Yields of Carbon i n Equilibrium a t 437' C. in a Methane Flame
BILITY
PRESSURE LIMIT Afm. % 1 13.5 2 14.1 5 15.3 10 17.0 20 20.5 30 23.5 34 24.R 40 26.5 60 32.0 126.3 45.4 5 Per gram mol of gas.
Vol. 23, No. 6
H2
Atm. 0.0605 0.0966 0.177 0.286 0 478 0.705 0.79 0.91 1.32 2.55
Hi0 Alm. 0.151 0.328 0.904 1.96 4.19 6.64 7.6 9.0 13.5 25.3
The calculated percentage yield of carbon in the last column is plotted in Figure 4 against the pressure in the first column. This indicates that the yield should increase rapidly with the pressure up to about 34 atmospheres and then decrease gradually, The decrease is due to the increasing amounts of methane which are prevented from decomposition by the effect of high pressures upon equilibrium (1). Requirements of Commercial Plant
I n addition to the features of the laboratory equipment, a commercial plant would require a means of scraping off the
co Afm. 0.0053 0.0073 0,0109 0.0145 0.0187 0.0201 0.0205 0.021 0.022 0.021
COP Atm 0.0964 0.181 0,408 0.723 1,205 1.39 1.45 1.55 1.64 1.55
CHI Atm. 0.0244 0.0624 0.210 0.545 1,522 3.31 4.14 5.55 11.6 42.9
C Molsa
0.004 0.024 0.121 0.385 1.112 2.25 2.72 3.38 5.75 12.3
CARBON YIELD
% 2.93 8.75 16.15 23.1 28.8
32.3 32.7 32.2 30.2 21.6
produce a given output than to install a process such as is here described. As the supply of gas begins to diminish, however, and as the network of pipe lines to cities becomes more extensive, the price of natural gas will rise considerably, and increased yields will become more important. This process will economize on gas still further in that, by using the hot compressed exhaust gases in an expansion engine, an excess of industrial power is made available, which otherwise would require the direct combustion of the gas in gas engines or under boilers. I n other words, the heat of combustion of the gas in a carbon-black plant can be utilized.
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Literature Cited (1) Bone and Townend, "Flame and Combustion in Gases," pp. 98 and 101, Longmans, 1927. (2) Bone and Townend, I b i d . , pp. 387 and 413. (3) Bone and Townend, I b i d . . p. 381. (4) Chamberlain and Rose, IND.ENG.CHEM., 20, 1013 (1928). (5) Frankland, J . Chem. Soc., 16, 137 (1862). ( 6 ) Jones, Bur. Mines, Tech. Paper 450, 15 (1929).
617
(7) Lewis, U. S. Patent 1,418,811(1922). (8) Lewis and Randall, "Thermodynamics," pp. 572-5, McGraw-Hill, 1923. (9) Neal and Perrott, Bur. Mines, Bull. 192, 12 (1922). (10 :Rosa, Crittenden, and Taylor, Trens. Illurn. Eng. SOC.,10, 843 (19151. (11) U. S.Patents: Rumbarger, 1,401,737(1921);Matlock, 1,438,542(1922); Darrah, 1,448,655 (1923); Matlock, 1,458,351(1923); Matlock, 1,508,367(1924); Bonnington, 1,515,333(1924); Messenger, 1,577,481 (1926).
Characteristics of a Vanadium Catalyst and a New Catalyst for Sulfuric Acid' W. W. Scott and E. B. Layfield UNIVERSITY OB SOUTHERN CALIFORNIA, Los ANGELES, CALIF.
The calcium-vanadium catalyst of Holmes and Elder bility of l e a k s to a negliHE i n t e r e s t of t h e has been studied under different conditions of operagible value. The sample of senior contributor in t h i s p r o b l e m was tion, and its characteristics determined by using differi n l e t g a s was t a k e n off brought about by his work ent amounts of catalyst, and different rates of gas flow. through the three-way stopon v a n a d i u m catalysts in A catalyst has been prepared along the Same lines, cock and drawn into a stand1917, and in patents on this using as a Promoter barium, which exhibits higher ard Orsat apparatus for gas s u b j e c t . This work was conversive ability, particularly at high rates of gas flow. a n a l y s i s , in which chromic done with pure vanadium Its characteristics have been determined and plotted, oxide solution was used as c a t a l y s t s on a semi-plant and it has been found to operate very well at 450" C., the a b s o r b i n g liquid and scale, making 200 pounds of giving as high as 98.8 per cent conversion. mercury was used in the levelacid per day. Since then the ing bulb. subject of promoters has arisen and the problem has been An electric tube furnace about 32 cm. long with a fused handed over to the junior author. silica tube 30 mm. inside diameter served as the converter. The apparatus for determining the conversive ability of Inside of the silica tube, extending from the middle of the catalysts had been set up and was in working order when furnace out on the inlet side, was a Pyrex tube of 20 mm. Holmes and Elder (1) announced a vanadium catalyst pro- diameter with the catalyst supported in the furnace end moted with calcium giving 98 per cent conversion a t 500" C. (Figure 2). A thermocouple and an exit tube for the gases using a flow of 12 liters per hour over 75 cc. of contact mass. came in from the other end of the silica tube and reached It was therefore decided to prepare this catalyst and de- nearly to the middle of the furnace. termine its characteristics by using different contact masses Leaving the converter, the gases passed 'through an oband different rates of flow, and to try different elements as servation bottle, where some of the sulfur trioxide condensed, promoters. The unique feature of this type of catalyst is a three-way stopcock for removal of a sample, an equalizing that the vanadium, promoter, and carrier are all precipitated bottle, and into a suction pump. as one mass. Procedure
T
Apparatus
The air and sulfur dioxide were turned on and adjusted to about 8 per cent sulfur dioxide in the mixture, and sent into the converter. The catalyst under study was mounted in the furnace. After the s u c t i o n p u m p was started, the p r e s s u r e and suction were adjusted so that the pressure inside the apparatus was the same as that on the outside. The f u r n a c e was heated to 500" C. and the apparatus allowed to run for a while to reach e q u i l i b r i u m . The percentage of sulfur dioxide in the inlet gases was then measured with an Orsat gas analysis apparatus, as described by Scott ( 2 ) , the buret being read to 0.1 per cent. If this value was outside the Used in Study of Vanadium Catalysts for Converting Sulfur r a n g e 7.4 to 8.4 per Dioxide to Sulfur Trioxide
The apparatus (Figure 1) used was similar to that employed by Holmes and Elder and in previous catalytic inv e s t i g a t i o n s by the senior author (1). Air prcrrurc ryrtem, reduced Fa* A and sulfur dioxide from Airi ofrom derked rrluu. Line regulated pressure supS Q t r r m y l i n d r r o f liquid, plies were passed rrJuccd t o d e s i r e d WdueJ. through gages and into a mixing bottle to inREICH'J METHOD FOR sure constant gas composition. A three-way s t o p c o c k in the line from the mixing bottle permitted removal of a s a m p l e of i n l e t gas while the a p p a r a t u s was in operation. -4 water U-gage between the line and the atmosphere permitted maintenance of atmospheric pressure inside the setup, reducing the possi1 Received
1931.
February 28,
Figure 1-Apparatus
