November, 1930
INDUSTRIAL AND ENGINEERING CHEMISTRY
1209
Production of Carbon Black from Propane’ W. B. Plummer and T. P. Keller GESERALATLASCARBONCOMPANY, 60 WALLSI.,h7Ew YORK,h-. Y .
The effect of various factors on the production of gas manifolds each carrying ORE than 200 million carbon black from propane in an apparatus similar to five vertical “1/8-inch pipe” pounds of c a r b o n that of the commercial channel process has been risers 20 cm. high. The air black are made yearly studied. These factors include height of channels pipes were covered with a by the channel process, but above the flames, per cent combustion, and temperalayer of broken brick in order practically no d a t a are ture of channels. Complete data are presented showto insure uniform flow u p available in the l i t e r a t u r e ing the properties of the various blacks in rubber test wards. The burner tips, of relative to its operating charcompounds. Results show the possibility of producs t a n d a r d commercial type acteristics and governing faction of good grades of channel-process carbon black w i t h 0.48-mm. (0.019-inch) tors. The most complete disfrom the higher gaseous hydrocarbons, and cast conslots, were placed in suitable cussion of the subject is given siderable light on the factors governing that process. sockets a t the top of the risers. by Neal and Perrott (2), but The complex character of the factors involved is shown, The channels used were of they deal mainly with the and it is hoped that they may stimulate further cons t a n d a r d “6 X 2 inch” mechanical features of plant sideration and study of the matter. size. were a d i u s t a b l e for construction and the DroDerties of the product. IChBmheight, and were so mounted berlin and Rose (1) have reported on a laboratory study of as to slide out of the apparatus readily to permit scraping. the operating factors of this process, but most of their results Temperatures were read on several thermocouples inserted in were obtained on a very small apparatus using only one the body of the chamber, and on two thermocouples made of burner. Several factors were not under close control, and the fine wire with flexible leads and peened into small holes in the upper side of the channels. Air and gas were supplied under results are in general inconclusive. A knowledge of the general mechanism of formation of positive pressure and metered by calibrated orifice flowcarbon blacks in flames is much to be desired, since as yet meters. I n the first tests the apparatus was not provided with in the commercial production of carbon blacks by the com- heat insulation, but later the walls and hood were covered bustion of natural gas it has only been possible (1) in the with a 12-cm. layer of Sil-0-Cel brick thoroughly cemented ordinary channel process, to produce blacks of certain defi- and held tightly in place. nite typical properties but in low yields, and (2) in special Commercial liquefied Pyrofax gas (approximately 83 per processes, operating a t higher combustion chamber tempera- cent propane) was used in all tests a t a standard rate of 0.05 tures and without impingement of the flames on collecting cu. m. (1.8 cu. ft.) per tip per hour, the air being proporsurfaces, to produce blacks in considerably higher yields but tioned to give the desired per cent combustion on the basis having modified properties. The causes for these differences of an air-gas ratio of 23.9 for 100 per cent combustion. are not known, and it has not yet been possible to control Since flue analyses from commercial channel-process plant the variations in yields and properties, both in the desired indicate an air-gas ratio four times that for 100 per cent direction, simultaneously. combustion, this ratio was used as standard except where Cnfortunately, however, it has not been possible to derive otherwise noted. I n test operations the product was removed from the present data any simple and clear-cut conclusions from the channels by hand scraping a t 10-minute intervals as to the mechanism of formation of blacks in flames or the throughout the test, the channels remaining stationary bebasic causes for the variation of their properties under various tween scrapings. I n the commercial process the channels are production conditions. It is nevertheless hoped that these in constant reciprocating movement, so that some black is results may be stimulating to other workers in this field. removed by the scrapers almost as soon as formed while part Although the gas used (propane) differs appreciably from may remain in the flames for as much as 15 minutes. The the natural gas (methane-ethane mixtures) used in the chan- scraping cycle of 10 minutes used in the present tests was nel process, the general mechanism of the flame reactions of intended to represent an average time of exposure of black to adjacent homologous hydrocarbons should be identical, al- the flames after its deposition. though the existing differences in ignition temperature, rate Physical Tests Made of flame propagation, and critical temperature of thermal decomposition might produce differences in the position and For color value the reference standard was prepared by magnitude of maxima, etc. mixing with a spatula on a glass plate 0.05 gram of standard The results indicate that the higher hydrocarbon gases give commercial channel carbon black with 5 grams of zinc oxide channel blacks having slightly improved modulus and tensile using 40 drops of raw linseed oil as a vehicle. Color deterproperties in rubber. This improvement would, however, minations were made by mixing the given black with varying seldom be economic owing to the higher value and inter- quantities of zinc oxide until approximate identity with the mittent supply of such gases a t refineries or in the fields. standard was obtained. Oil adsorption was determined by adding raw linseed oil Description and Operation of Apparatus from a buret to 5 grams of black while mixing vigorously on a The standard test unit consisted essentially of a sheet-iron glass plate, and determining the minimum amount required box approximately 50 X 90 cm. in cross section and 64 cm. to give complete adhesion of the material in a coherent ball. deep, provided with a suitable hood for removing the smoke. Iodine adsorptions were obtained by wetting 1 gram of black Three air-distributing pipes and two gas manifolds were lo- with 10 cc. of glacial acetic acid, adding 25 cc. of approxicated lengthwise at the bottom of the box, the air pipes being mately 0.015 N iodine solution, shaking mechanically for slotted on the bottom to give uniform distribution, and the 3 hours, centrifuging, and titrating the residual iodine in an aliquot with thiosulfate solution. I Received March 1, 1930.
M
INDUSTRIAL AND ENGI NEERING CHEMISTRY
1210
Acetone-extractable matter was determined by treating 3 grams of black in an alundum thimble in an extraction apparatus of the usual type, the extraction being continued over night. All rubber tests were made on a compound having the following formula: Smoked sheets Zinc oxide Sulfur Stearic acid Diphenylguanidine Black
Parts b y weight 100 5 4 1 1 25
The first two series of tests were made by varying the channel height in the uninsulated and insulated units. Both sets of results were similar, and only those for the insulated unit are shown in Table I. Chamberlin (1) has indicated that maximum yield with methane is obtained when the channel height is equal to that of the free-burning flame. This is confirmed as regards both yields and properties by the present results, since the free-burning height of the flames was 70 mm. using Pyrofax at 0.05 cubic meter per hour, this being approximately the maximum amount of this gas that could be burned without some tendency to blow the flame away from the tips. It will be observed that all properties except the adsorptivities pass through a maximum at this (70 mm.) optimum channel height. Data are also shown for a commercial channel black made from natural gas and for a commercial high-yield carbon black as prepared by a special process, details of which cannot be made available at present, this black having modified properties as defined in Table I. Apparently the quality of black made from propane (Pyrofax) is slightly higher than that made from natural gas, but not sufficiently so to justify the much greater raw material cost, since the yield is only twice as great, of C h a n n e l H e i g h t (Insulated U n i t ) STD. COMCOM- MERCIAL HIGHNo. CHANNELYIELD 1503 BLACK BLACK MERCIAL
No. 1504
em.
No. 1501
No. 1502
...
... .. .. .
45 70 95 120 400 400 400 400 517 516 515 515 1.67 3.00 1.38 0.65 80 90 85 90 100
50
155
80
.. .. ...
26.7 0
110 20.0 0
112 20.8 0
of C h a n n e l T e m p e r a t u r e
No. 14950
Results
MISCELLANEOUS DATA: Channel height, mm. Combustion, per cent Channel temperature,'C. Yield Ibs. p e r M c u . ft. Color'value, percent std. Oil adsorption, cc. per 100 grams Iodine adsorption, mg.per gram Acetone extract, per cent PROPERTIESIN RUBBER: Max. modulus 500 per cent elongation, kg. per sq. cm. Ultimate tensile at mas. modulus: Kg. per sq. cm. Per cent Max. tensile, kg. per sq.
optimum. On the other hand, when the channels were superheated to 650" C. the yields dropped off very sharply and the desirable properties are again lower. The temperature of 516" C., giving the optimum results, is approximately that existing on the channels of the commercial process under the conditions of combustion and heat loss existing therein. This shows the close parallelism of optinium results for methane and propane. T a b l e 11-Effect
All cures were made in bolted 2-cavity molds heated in a paraffin bath a t 140' C. and tested in the usual manner. Abrasion tests were made on the Grasselli abrasion machine using Garalan abrasion paper and determining ratios to a standard test block on each piece of paper.
Table I-Effect
Vol. 22, No. 11
115 20.4 0
135 30.8 0.3
. e .
12.9 0.2
190
214
191
190
169
218
268 570
281 570
267 570
281 610
266 620
251 540
288
304
288
292
282
265
Cure. t o max. modulus, 120 120 120 105 105 min. at 140.' C. Abrasion resistance, per 101.5 103.5 102.0 102.0 100 cent std.
90 85.5
Table I1 shows the effect of channel temperature. The first represents the non-insulated unit, the second with insulation around the chamber, and the third with insulation and with electric heating applied to the channels by suitable coils placed on their upper surface. Although the yield is somewhat greater at the lowest channel temperature, most of the desirable properties are distinctly lower t,han at the
MISCELLANEOUS DATA: Channel height. mm. 70 Combustion, per ceiit 400 Channel tempprature, C. 410 I-ield, Ibs. per M cu. f t . 3.46 Color value. per cent std. 90 Oil adsorption. cc. per 100 grams 135 Iodine adsorption, mg. per gram 26.2 Acetone extract, per cent 1.6 PROPERTIES IN R ~ J B B R R : Max. modulus 500 per cent elongation, kg. per sq. cm. 200 Ultimate tensile at max. modulus, kg. per sq. crn. 270 Ultimate elongation a t max. modulus, per 580 cent Max, tensile kg. per sq. cm. 299 Cure to max: modulus, min. a t 140' C. 120 Abrasion resistance. per cent std. 107.0 a Unit not insulated. b Unit insulated. C Ur.3 insulated, channels electrically heated. d Approximate value.
No. 1501b 70 400 516 3.00 90 110 20.0 0
No. l608C
70 400 650
0.47 OOd 190 25.8 4.0
214
179
281
267
570 304 105 103.5
560 267 105 99.3
It is not possible to vary the percentage combustion very considerably without producing large changes in the channel temperature. Since the latter has been shown (Table 11) to be an important variable, it becomes necessary to compare results as in Table 111. At 400 per cent combustion the chan nels were electrically heated to give the same temperature (650" C.) as was'developed when the air supply was reduced to 70 per cent. Both as to yields and properties these results will be seen to be considerably below the optimum, but surprisingly little difference which is attributable directly to the combustion ratio is to be observed. T a b l e 111-Effect
of P e r c eTner m a epeeC r aotrunrbeu) s t i o n ( C o n s t a n t C h a n n e l
No. No. 1507" 1508b MISCELLANEOUS DATA: Channel height, mm. Combustion, per cent Channel temperature, * C. Yield, lbs. per M cu. ft. Color value, per cent standard Oil adsorption, cc. per 100 gram9 Iodine adsorption, mg. per gram Acetone extract. Der cent PROPERTIES IN RUBBER: 179 Max. modulus 500 per cent elongation, kg. per sq. cm. 181 Ultimate tensile at max. modulus. kg. per sq. cm. 256 560 267 560 Ultimate elongation a t max. modulus, per cent 284 267 Maximum tensile, kg. per sq. cm. 120 105 Cure t o max modulus. min. at 140' C. 96.3 99 3 Abrasion resistance, per cent std. a Unit insulated. b Unit insulated, channels electrically heated. c Approximate value. d Rubber properties determined after extraction with acetone.
The data given in Table IV, showing the effect of complete removal of the channels, might be regarded as a continuation of Table I in which the height of the channels has become infinite. Viewed from this standpoint there is an apparent discontinuity in the yield figures, but it should be observed that the data of Table I do not show the total black formed, but only that collected on the channels, whereas in Table IV No. 1505 represents the total black formed. A continuous deterioration in properties will be observed as the channel height is increased infinitely. It must be emphasized that this observed decrease in yield on removal of the channels applies only to the given temperature and combustion conditions-i. e., to low chamber temperature and a large excess of air. At higher temperatures, obtained with lower excess air and heat-insulated chambers, higher yields may be observed in the absence of channels.
November, 1930
I N D U S T R I A L A N D ENGINEERING CHEMIXTRY
121 1
It will be obvious that in this test, since no channels mere used, it was necessary to connect the fume hood tightly with the top of the unit, and to arrange suitable bag filters and exhausters to collect the black made.
channels is that of a cooling agent, and it has been known that this has a lower limit of desirability, but the present results show this effect more clearly. On complete removal of the channels the yields and properties (Table IV) are not so much diminished as might have T a b l e IV--Effect of Presence of C h a n n e l s been expected from other considerations. Although an enNo. 1501 No. 1505 tirely different type of black might have been expected in this MISCELLANEOUS DATA: case, that which was actually produced must apparently be Channel height, mm. 70 NO channels regarded merely as an inferior grade of channel black. In Combustion, per cent 400 400 Channel temperature, C. 520 413a other words, while the presence and cooling action of the chanYield. Ibs. ner M cu. ft. 3.00 1.65 nels do cont,rol the yield and quality of the black the limit Color valui, per cent std. 90 90b Oil adsorption, cc. per 100 grams 110 105 of variation of properties is such (compared with the properIodine adsorption, my. per gram 20.0 15.0 Acetone extract, per cent 0 0.7 ties of blacks made by other processes) that it cannot be PROPERTIES I N RUWJEK: definitely said to control the type of black made. FurtherMax. modulus 500 per cent elongation, kg. per sq. cm. 214 179 281 Ultimate tensile at max. modulus, kg. per sq. cm. 274 more, from the data presented it does not appear that the 670 610 Ultimate elongation at max. modulus, per cent type of the black is appreciably affected by the atmosphere Max tensile kg. per sq. cm. 304 295 Cure’ to max: modulus, min. at 140’ C. 105 105 surrounding the flames-i. e., the per cent excess air-for Abrasion resistance, per cent std. 103.5 92.0 similar temperature conditions. It must therefore be cona This is the temperature in the burner house, and corresponds t o 405’ C. in the corresponding test with channels. cluded that the type of the black is determined by conditions 6 Approximate value. within the flame itself-i. e., such factors as size, shape, temDiscussion perature of the gaseous layers, temperature of the luminous One of the facts shown most directly by the present results carbon particles, etc. Certain of these factors are not suscep is at carbon black equal in quality to that made from tible to direct investigation. Certain of the others have been methane may be made from hydrocarbons as high as propane, the subject of special studies, which have not, however, made although this presumably cemes to be true with the higher possible general conclusions as to exact cause of difference in liquid hydrocarbons. The close agreement between various the type of black produced by various luminous flames. maxima observed for propane with the operating conditions Acknowledgment of the commercial channel process using methane shows the The authors wish to express their appreciation to the Genessential identity of the basic flame reactions of the two gases. The function of the channels is clearly shown to be mainly eral Atlas Carbon Company for permission to publish these a cooling effect by the very large change in yields and proper- results and to C. ,J, Wright, vice president of this company, ties observed when the channels are superheated to G50° C. whose interest and support have made it possible to carry on (Table 11). The fart that with further cooling to tempera- this work. Literature Cited tures below the optimum the yield is not much greater, while the properties are lower in general, is not easily interpreted. (1) Chamberlin and Rose, Am. Inst. Chem. Eng., Preprint (June 19, 1999). I t has always been generally assumed that the function of the (2) Neal and Perrott, Bur. Mines, Bull. 192 (1922).
The Slacking of Coal and Its Proper Interpretation’ S. W. Parr and D. R. Mitchell fiNIVERSITY OF
ILLINOIS, URBANA,ILL.
LACKING tests on coal are carried out by bringing the coal into moisture equilibrium with the air, drying for 23 hours, submerging in water for 1 hour, drying, and &merging again-repeating thus the routine through eight cycles ( I ) . After each drying the amount passing through a l/rinch (G-mm.) sieve is weighed and the cumulative percentage after eight cycles is taken as the slacking index. It has been proposed to use this factor as an indication of rank, beginning with the lignites and extending up through the sub-bituminous into the true bituminous, supposedly giving a measure of lignitic character to any coal having slacking proclivities. This interpretation of the phenomenon of “slacking” is altogether misleading and erroneous. If slacking were a fixed and definite function, the case would be different, but it is not.
S
Slacking of Lignite
For example, if a lignite is thoroughly dried and then thoroughly soaked with water, it thoroughly disintegrates. The explanation is comparatively simple. The lignites are peculiar in that they not only have a high moisture conReceived July 31. 1930. Presented before the Division of Gas and Fuel Chemistry a t the 80th Meeting of the American Chemical Society, Cincinnati, Ohio, September 8 to 12, 1930. 1
tent, but this free moisture is distributed uniformly throughout the texture of the material, so that in discharging this moisture there remains a considerable volume of capillary space corresponding to the high percentage content of water normally present in the freshly mined material. This is, moreover, consistent with the facts developed by Porter and Ralston ( S ) , who maintain that the “heat of wetting is probably to be explained by assuming that each particle of the dried coal acts as a sponge of a tissue permeated with microscopic pores.‘’ The suggestion is further made (2, p. 27) that the heat may be produced by two processes: (1)the mere penetration of the liquid into minute capillaries,” or ( 2 ) “the formation of a colloidal condition.’’ I n any event, upon the accession of water energy is developed and no argument is needed to show that either capillary or colloidal forces are ample to bring about the rupture and disintegration of the substances when water is added to the dried material. The slacking of a lignite, therefore, is due to the wetting and not to the drying process, and the disintegration is substantially 100 per cent after one complete cycle. Characteristics of Coals Having Slacking Tendencies
Let us turn now t o certain bituminous coals that are said to show slacking tendencies after storage in the open for
