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INDUSTRIAL A N D ENGINEERING CHEMISTRY
Vol. 23.
KO.2
Notes on the Carbon-Black Flame’ W. B. Wiegand BINKEY &
SMITH COMPANY,
41
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2 SI., ~ h -~E W
4
YORK,
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CARBON-BLACK T h e basic difference between carbon black and lampin the flame reactions. These factors are known to be capablack is defined in terms of the method of collection. flame may be defined ble of bringing about important as any self-luminous Possible causes of t h e unique properties of impingedifferences in quality. m e n t black are discussed. By reference t o two types hydrocarbon flame burning in s e c o n d a r y air which is SO of carbon-black flames-round a n d flat-the concepIn any event, and what“drafted” as to furnish optition of “combustion quotient” (s/Y) is developed a n d ever the governing cause, the mum yield of the d e s i r e d impingement process is the applied t o variations in flame size and shape, a n d t o grade of black, it being undrafting. only one thus far developed derstood that the black is which produces the unique The position of the impingement surface, t h e effect caught by impingement upon of flame, shape of gas flow, and of position of channel are combination of fineness of a surface placed within the briefly discussed in relation t o the quality and quansubdivision, brilliance and flame. From this same flame tity of black obtained. intensity of color, tinctorial Factors of importance in large-scale operations are and hiding power, and the there may be produced the totally d i f f e r e n t p i g m e n t mentioned“adhesion” or surface conknown as l a m p b l a c k , proditions which have led to vided only that the drafting be altered to induce the forma- the present wide and ever extending use of carbon black in tion of free soot. This soot, collected (by whatever means) the arts. extraneously to the flame, constitutes lampblack, in one or Two Types of Carbon-Black Flames other of its many forms. I n Figures 1 and 2 are shown, respectively, a round and With this distinction in mind it is readily understood why carbon black may be obtained from the flame of burning tar a flat flame capable of producing carbon black by the simple oils, even though not economically, and why lampblack may expedient of inserting a metal or other surface somewhere in be and is made from the flame of burning natural gas. Hence the luminous portion of the flames. These flames are very also the synonyms “impingement black” and “channel similar to the ordinary candle flame. They include the same black” for carbon black, the name “gas black” being less four major regions, (a) the dark region, (b) the yellow region, (c) the blue region, and ( d ) the faintly luminous envelope. It is suitable because ambiguous. The carbon-black flame is susceptible of almost infinite not proposed to review the prevailing ideas as to the genesis variations depending on the composition of the gas, the struc- and chemistry of these regions (see 1 , 4, 5, 7‘). On examining more closely these two types of flame, it is ture of the flame, the arrangement and motion of the collecting surface, size and shape of burning house, drafting, etc. Many seen that their essential difference is that in the latter case the of these factors, and by no means the least important ones, flame is flattened out with consequent increase in surface are exceedingly difficult to duplicate on a laboratory scale, area. This shape was developed in the days of gas illuminaa circumstance which has greatly impeded the systematic tion where the flat flame was found brighter, cleaner, and study of the various relationships. The present discussion steadier, and thus proved a more satisfactory illuminant (S), It will be useful to express the ratio of flame surface to will be restricted to some of the salient characteristics of the flame itself, as affecting the carbon black formed therefrom. flame volume by the quotient s/v. hlore broadly, s may be The question naturally arises, “Why does the collection, by defined as the total combustion surface or approximately impingement upon a surface within the flame, of the lumi- the sum of regions c and d (v. s.). By v will be understood nous carbon particles produce a black generically different the volume of gas contained within s. The expression s / u from that which results when the flame is caused t o smoke has been found convenient in the study of carbon-black flames, and the free soot collected?” No complete answer to this but having thus far not been worked out in mathematical important question seems to have been offered. The follow- detail it will a t this time be employed solely in a qualitative sense. ing possible factors are put forward as merely suggestive: The flat flame2clearly exhibits a greater s/zi than the round Early Fixation. By quick removal of the carbon particles from the flame there tends to be less opportunity for growth or flame. However, the flat flame is not uniformly flat. At both edges it swells, forming wings which approach a circle accretion, thus resulting in finer particle size. Electrical Repulsion. The luminous carbon particles emit in cross section. This thickening has been ascribed to an electrons, and as a result are positively charged ( 8 ) . This will overlapping effect ( 2 ) . For this reason the s/v is not unitend to keep them apart up to the point of collection. Gaseous Adsorption. The luminous particles of carbon are form a t all points in the flat flame, being greater between than in an active condition due to the heat released by their own a t the wings.3 This inequality may, however, largely disapcombustion, as also to that developed in the regions of gaseous pear in the case of multiple flames in close proximity under combustion. They are bathed in carbon monoxide, carbon the channel, as in the case of a carbon-black-burning house, dioxide, hydrogen, nitrogen, as well as some oxygen (6). As a result they carry with them, to the collecting plate or channel, and by control of drafting (11.i.) I n any case the round flame shows in general a lower and an adsorbed layer of gases which is known profoundly to affect their properties. These conditions are totally different in the more uniform s/v. case of free soot. 2 The type of flat flame here described is often called the “batwing.” Post-Impingement Conditions. Many layers of carbon are They are thus exposed The “fishtail” variety of flat flame is really totally distinct in structure. deposited on the channel in succession. to continued high temperaturesand to the various gases present The former issues from a narrow slot; the latter results from the impingement
A
cvlindrical iets. I n general t h e smaller the radius of curvature of similar bodies the greater s, v . In this case t h e central region of the flat flame is much thinner, so t h a t s ’ZIis greater despite the longer radius.
of
Received September 20, 1930. Presented before the Division of Rubber Chemistry a t t h e 80th Meeting of the American Chemical Society, Cincinnati, Ohio, September 8 to 1 2 , 1930. 1
two 3
I.VDc'STKI.4L A.VD ENGINEERING CHEMISTRY
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0.25-inch (6.3-nim.) round brass tips were employed with 2inch (&em.) spacing. I n the case of slotted tips three of 0.034-inch (0.86-mm.) opening were used spaced at 4 inches (10 em.) I n all cases the channel was scraped every 2 minutes. For convenience the gas used for these experiments was city as of the following composition: 9' Hydrogen
Carbon monoxide Methane.. . . Nitrogen. . . 11iuminants.. Carboa dioxide oxygen . . . . . . . . .
38 28 18 'I 7
o 4 4
4 2
a x O S
Tile later substitution of methane made no essential change in the relationships.
i ~ o l 23, . ?io. 2
exceedingly sensitive to slight changes in flow, whereas the latter i s relatively unaffected. This may be ascribed to the effectof gas pressure or flon on the heights of the free flames in the two cases. With the round burner tip increased flow results in incrwed height of free Artme. I n the case of the slotted bnrner tip, on the other hand, the flame expands laterally RS much as, or even more than, i t does vertically, so that in this case the position of the channel relative to the height of the free flame is influenced very little by alterations in pressure. The practical significance of this difference between the two tips is obvious. I n practice, on the large scale, it is difficult to keep the gas pressure absolutely uniform a t all time8 and in all regions of a carbon-black-burning house. The slotted tip has therefore the advantage over the round tip aa making possible a greater uniformity both as to yield and as to quality of product. A word of explanation should be made with regard to the apparently higher maximum yield figures for the round flame. Here again the absence of smothering has adversely affected the yields from the slotted tip. It is probable that the s / v ratio for the round flame when nndrafted is more nearly correct than that for the flat flame. The latter can, however, he improved as desired by careful control of smothering, thus bringing its s/u down to the proper value.
Figure 3-Implngement Viagrams Vbfsined With Round Flame
Yield vs. Channel Height I n Figure 4 are shown the comparative curves for yield of carbon black in the case of round and slotted tips as the channel height is varied but the rate of gas flow kept constant. It will be seen that in both cases the yield is sensitive to the position of the channel in relation to the height of the free flame. The flat flame is,however, more sensitive in this respect than the round. The dotted line indicates the course of the curves when R at each channel setting, to optithe flow of gas W ~ adjusted, mum yield. The marked upward extension of the curves, apparently indicating higher yields, must not, however, bc misinterpreted. It might, from this, be supposed that a lower channel height would constitute a marked improvement. I n practice this is not the case, because of the effect of drafting, which, as mentioned above, was not included in these experiments.a It must be repeated that these curves do not represent conditions in actual largescale operations; thcy are to be regarded only as a guide to certain general relationships.
7
- C H A N N E L HEIGHT
4
INCHES.
Figure 4-Yield
L (u
P
w. Channel Height at Conatant Gas Flow
1R~---
I
it'
s
10
GAS Figure 5-Yield
15
F L O W - CU.FT. oer Vd.
20 Hour.
Gas Flow at Fired Channel Height
Yield us. Flow at Fixed Channel Height Large-Scale Factors
In Figure 5 which shows the relation between flow of gas and yield of carbon black when channel height is k e d , there will be noted a striking difference between the behavior of the round flame and that of the flat flame. The former is 6 Drafting or smothering may be made t o coniroi the height of e name isruing at given ~ r e r s u i efrom a given orifice. Thus an increase in smothering miiy induce the same incraae in yield that would etherwise require a e h e r channel.
I n addition to the important matter of Artme structure there are of course other elements affecting quality and yield of carbon black. The size and shape of the burning house; total combustion of gas in relation to the size of house and in relation to the area of channel exposed; the spacing, width, and speed of channels; spacing, angle, and accuracy of orifice of the tips are factom of importance requiring proper adjust-
ISDUSTRIAL AND ENGINEERING CHEMISTRY
February, 1931
ment in relation to the quality of carbon black being made. Most of these factors can be determined only through largescale experimentation. The prime importance of channel height and rate of gas flow may be deduced from the experimental data already given. Finally there is the question of proper draft control which, as well as being of prime importance, is also most delicate and elusive. Many attempts have been made to regulate the draft by means of continuous analysis of the flue gases which escape through the top of the house. This method is found more cumbersome, as well as less sensitive, than the method of drafting based upon what is called the ‘[smoke blanket” of a burning house. This is a pall or cloud of smoke consisting, not of carbon black, but of sooty material which hangs a t about the general level of the channels and which rises or falls in a remarkably sensitive manner as the influx of air is varied. In addition to the ‘‘smoke blanket” the degree of luminosity of the flames (described as the “lightness” or “darkness” of the house) serves as an additional optical guide to the state of drafting. With any given set of conditions as to house construction, arrangement of flames, and channels, and with continuous
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control of the quality of black produced, the operative in charge of the plant is able to determine by the hourly output of carbon black the exact drafting conditions that will yield the best results. Proper adjustments are necessary as between winter and summer and as between night and day. Thus there rests a heavy load of responsibility on “Those Slaves of Fire who, morn and even,” and in a climate already semi-tropical, tend the ten million flames which yield the carbon black of commerce. Acknowledgment
It is desired gratefully to acknowledge the important assistance rendered by J. W. Snyder and H. A. Braendle. Literature Cited (1) Bone and Townend, “Flame and Combustion in Gases,” Chapts. 28 to 32. (2) Chamberlin and Thrun, IND. ENG.CHEM.,19, 764 (1927). (3) Luckiesh, “Artificial Light,” Chapt. V I . (4) Payman, Fuel Science Practice, 3, 403-6 (1924). (5) Smithells, J . Chem. Soc., 61, 217 (1892). (6) Smithells, Thorpe’s Dictionary of Applied Chemistry, p. 212 (1922). (7) Smithells and Ingle, J . Chem. SOC.,61, 204 (1892). (8) Thomson, “Conduction of Electricity through Gases,” Chapt. X.
Action of Alkali Hydroxides on Elementary Sulfur and Mercaptans Dissolved in Naphtha’ V. Vesselovsky2 and V. Kalichevskya
T
HIS investigation represents a qualitative and quantitative study of the effect of potassium and sodium hydroxides in various solvents on solutions of elementary sulfur and mercaptans in naphtha. The study of these reactions was undertaken with the purpose of determining the possibility of their utilization for sweetening and corrosion treatment of light petroleum distillates. Previous investigators working along similar lines reported that anhydrous potassium hydroxide reacts with elementary sulfur and mercaptans in gasoline (8). Potassium carbonate in alcoholic solution likewise reacts with sulfur, while in water the same reaction proceeds a t a much slower rate (3,4 ) . Partial removal of mercaptans by aqueous alkali hydroxides has been also investigated ( 2 ) . These publications present interesting possibilities for studying similar reactions in a variety of solvents and stimulated the present research. Materials
Sulfur purified by recrystallization from benzene. Ethyl, n-butyl, and n-heptyl mercaptans (Eastman Kodak Company reagents). Solvent naphtha of the following characteristics: Color. . . . . . . . . . . . . . . . . . . . . . . . . . . . .... Acidity, . . . . . . . . . . . . . . . . . . . . . . . . . .... Sulfur . . . . . . . . . . . . . . . . . . . . . . . . . . .... Specific gravity . . . . . . . . . . . . . . . . . .. . . . Engler distillation: Initial boiling point. . . . . . . . . . . . . . . . . 55 per cent off a t . , . . . . . . . . . . . . . . . . . End point.. .................... .... Sayholt thermal viscositg . . . . . . . . . . . . . . Copper strip test at 122 F. (50° C.) . . . . Doctor t e s t . . .....................
....
Anhydrous potassium and sodium hydroxides (c. P.). Absolute ether, absolute ethyl and isopropyl alcohols.
* Received October 13, 1930.
* Senior student in Chemical
Engineering, New York University, New York, N. Y. * 616 Livingston Road, Elizabeth, N . J.
Commercial 91 and 98 per cent isopropyl alcohols containing some butyl and amyl alcohols. Analytical Methods
DETERMINATION OF SuLFuR-Lamp method (check determinations agreed within 0.005 per cent). Though the lamp method for determining elementary sulfur in the oil usually gives low results, for purely comparative purposes observations made by this method should prove wholly satisfactory. For this reason the lamp method was used in favor of a more tedious analytical procedure. QUALITATIVE TEST FOR ELEMENTARY SULFUR-fiVe cubic centimeters of the sample were shaken with 1 cc. of 1 per cent naphtha solution of ethyl mercaptan in the presence of 5 cc. of doctor solution. Discoloration indicated the presence of elementary sulfur. The method permits detection of less than 0.0025 mg. of sulfur per cubic centimeter of naphtha solution, while the standard copper-strip corrosion test a t 122’ F, (50” C.) fails to discover less than 0.005 mg. of sulfur per 1 cc. QUALITATIVETEST FOR hbRCAPTANs-Standard doctor test. Reactions of Elementary Sulfur
On mixing a t room temperature a 0.227-0.315 per cent solution of elementary sulfur in naphtha with varying quantities of potassium and sodium hydroxide solutions or suspensions in various solvents, the following observations were made: On addition of the reagents to the naphtha solutions the oil develops an orange-yellow color and becomes turbid owing to separation of some minute particles of a white substance. A golden-yellow precipitate collects a t the bottom of the reaction vessel, but the oil remains turbid. On further standing the precipitate acquires a dark yellow-brown coloration and the white substance which is responsible for the turbidity of the oil precipitates out. On washing with
