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Electrostatic Method for Determining Fusain in Bituminous Coal'sz J. D. Davis3 and J. A. Younkinsd PITTSBURGH EXPERIMEST STATION, U. S . BUREAUOF M I A ~ SAND , CARSEGIE INSTITUTE OF TECHSOLOGY, PITTSBURGH, PA.
A method for the direct determination of fusain in LTHOUGH fusain has Apparatus and Method 60-mesh air-dried coal is presented. This method inbeen separated from volves preliminary separation of all the fusain in an coal by gravity methA 0.5-gram sample of the impure state by gravity and subsequent purification coal is shaken with a mixods and studied, notably by in a current of inert gas by an electrostatic field. The ture of gasoline and carbon British investigators (d,S, 4, purity of fusain finally recovered is conveniently 5,7'),* no direct method for its tetrachloride of 1.40 to 1.45 checked by the microscope. Results of analyses of specific gravity in a 10-cc. quantitative determination synthetic mixtures of coal and fusain together with c e n t r i f u g e t u b e . This is has been evolved as far as analyses of actual coal samples show the precision of s p u n 10 m i n u t e s o n t h e the writers are aware. the method. c e n t r i f u g e shown in FigSinnatt (6) analyzes for fusain ure 2. This treatment floats in coal by determining the volatile matter in the coal sample, having previously found most of the coal and packs the fusain mixed with bone coal the volatile-matter content of fusain-free coal and of pure in the bottom of the tube. Most of the coal is now removed fusain. As fusain always contains considerably less vola- with a small spoon and the liquid poured out. Particles tile than coal, mixtures of the two will show lower vola- of coal still adhering to the tube are wiped out with a piece tile than pure coal by an amount proportional to the fusain of filter paper on a glass rod. The fusain mixed with bone present. It seemed highly desirable to the writers, however, coal and mineral matter is now transferred to a weighed to have a direct method for separation and determination of 2-inch (5-em.) watch glass by washing with benzene. The fusain as such. A further desideratum was that the method benzene is evaporated on a water bath and the residue be applicable to 60-mesh air-dried coal such as is used in weighed. This is next brushed into the weighed tray of the standard methods for the analysis of coal ( I ) . The method de- electrostatic separator shown in Figure 3. Here the fusain scribed herein is proposed as accomplishing this purpose. It is removed by the electric field; the mineral matter and bone has not yet been tested on a wide variety of coals and fusains, coal remain and can be weighed. Since the original sample but there seems to be nothing against its general application; it is presented a t this time, therefore, with the hope that others interested in fusain will try it.
A
Properties of Fusain
Fusain is very similar to charcoal. It is usually soft enough to crumble in the fingers, but sometimes it is rendered hard by adsorbed inorganic salts, calcite for example. The soft variety, which is low in ash, will have a true specific gravity of around 1.47; that for hard fusain may be as high as 1.77, depending on the amount and character of inorganic salts adsorbed. It has a black streak, whereas that of the coal (bituminous) is brown. Under the microscope powdered fusain has the very characteristic structure shown in Figure I-B. Figure I-A is a sample of coal for comparison. It will be noted that fusain appears to consist of fibers or bundles of fibers. ThiA is important, because it offers a ready means of determining whether or not fusain separated in the course of analysis is pure. A binocular microscope of 70 diameters magnification serves admirably for checking the purity of 60-mesh fusain. The electrical resistance of this size per cubic centimeter is about 5000 ohms, as compared with 50 megohms for bituminous coal. However, this is a variable property and difficult to measure accurately. Its electrostatic capacity is fairly high when compared with coal and the impurities of coal, and this is the property on which the following method is based. 1 Received April 11, 1929. Presented before the Division of Gas and Fuel Chemistry at the 77th Meeting of the American Chemicdl Society, Columbus, Ohio, April 29 t o May 3, 1929. * Published by permission of the Director, U. S. Bureau of Mines, and of the Carnegie Institute of Technology, and the Mining Advisory Board. (Not subject t o copyright.) 8 Fuels chemist, Pittsburgh Experiment Station, U. S. Bureau of Mines. 4 Research Fellow, U. S. Bureau of Mines and Carnegie Institute of Technology. Italic numbers in parenthesis refer to literature cited at end of article.
*
Figure l-(A)
(B) Coal and (B) Fusain, 60-Mesh and Finer.
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was weighed in the air-dried state, in order to be consistent the fusain and bone coal a t this point should be allowed to come to moisture equilibrium with the atmosphere before weighing. However, the amount of moisture so taken up is usually so small that this procedure may be neglected without serious error. As the weight of fusain plus mineral m a t t e r plus bone coal is known, the amount of the former can be determined by difference. If desired, the fusain recovered can be brushed out of the forward end of the separator and weighed directly. In either case both the residue and recovered fusain must be examined under the microscope to make sure that the separation has been complete. If one treatment does not remove all the fusain, it be n e c e s s a r y t o Figure 2-Centrifuge for Rough Separation of Fusain from Coal shake the residue on the tray and again apply the electric field. This operation is repeated until the residue is free from fusain. If the recovered fusain is found to contain foreign matter, the tray is brushed out and charged with the impure fusain, which is again treated under an electric field of less intensity than the first one. By working in this way and checking with the microscope, practically complete separation is obtained.
its positive charge and receives a negative one, driving it back to the tray. The motion of the particles is rapid and if a current of'gas is simultaneously passed between the electrodes all the fusain is quickly removed from the field. Referring again to Figure 3, the electric field is produced by the output of a high-tension transformer of about 500-watt capacity connected to 110-volt supply, the secondary winding giving about 20,000 volts. The output is rectified in the usual manner by a General Electric Kenotron tube. One terminal of the transformer is grounded, as also is the tray of the separator, and the top electrode of the separator is connected to the Kenotron. The separator consists of a glass box 23/4 inches (7.0 em.) in width by 1 inch (2.5 cm.) in depth by 71/2 inches (1.66 cm.) in length made by gluing together strips cut from window glass. The top electrode is a piece of lead foil glued to the inside surface; the terminal is a short wire passed through a hole in the glass and sealed in with DeKhotinsky wax. The tray serves as a bottom electrode. This is a sheet of l/lb-inch (0.16-em.) aluminum with wood sides glued on. A tubulated plug of wood with a rubber gasket closes one end of the box and admits a slow stream of dry natural or other non-oxidizing gas. The box is held by rubber bands on the sliding wood member shown, and can be given a reciprocating motion by the eccentric device which is driven by a variable-speed motor. The whole apparatus is mounted on a board fitted with leveling screws so that on shaking the sample on the tray the tendency is to keep it uniformly and thinly distributed, which is important. Fusain covered deeply by foreign matter will not be lifted by the field; if it is lifted,.probably some of the foreign matter will be carried along with it, making retreatment necessary. Regulation of the field intensity with the arrangement just described is best effected by adjustment of the filament current to the Kenotron. With 20,000 volts high-tension supply and electrodes 3/4 inch (2.0 cm.) apart, the writers found a filament current of 4.5 amperes adequate.
1
I
L-
Figure 3-Electrostatic
VOl. I, x o . 3
4
I d
Outfit for Separation of Fusain from Coal
Fusain has higher electrical conductivity and higher electrostatic capacity than the coal and mineral matter, and will take on an electric charge sufficient to cause it t o be repelled from the charged (positive) tray while the foreign matter remains, unless a very strong electric field is used, The fusain, on reaching the top or negative electrode, delivers
Results of Trials
To test the method, a SUPdY of pure fusain was obtained from partings in the Pittsburgh coal bed and synthetic mixtures of this with the pure coal were made up and analyzed as follows:
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I N D U S T R I A L A N D ENGNIEERING CHEMIX T RY
Determination of Fusain i n Synthetic Mixtures of Coal and Fusain (60-Mesh, Air-Dried) PRESENT FOUND P R E S E ~ T FOUND PRESENT FOUND Per cent Per cent Per cent Per cenl Per cent Per renl 10 11 24 15 15 34 5 5 50 67 67 57 70 67 00) 98 5 39
5 4 5 5 5 (6 (150-mesh) 4
Average
9 86 9 36 9 9s 9 48 11 85 Sverage 10 29
15 07 16 03
Average 15 48
It will be noted that these results have a tendency t o be slightly high, probably due to mineral matter being carried over with the fusain; in fact, in several samples some calcite was detected in recovered fusain by the microscope. The fusain was selected for freedom from extraneous ash and was therefore lower in ash than a true sample from the mine would be. To be representative of the fusain of the mine, which undoubtedly carries a certain proportion of the extraneous ash of the bed, the fusain recovered should also contain some extraneous mineral matter. The results are probably about what they would be if the fusain had contained its natural amount of extraneous mineral matter. They are therefore better than they appear. Tests with fusains containing large amounts of absorbed mineral matter (inherent ash) show that this is carried over with recovered fusain in the separator. The following series of duplicate determinations selected a t random from results on coal samples (not synthetic mixtures) mill give an idea of how closely a chemist may expect
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to check his results. Two determinations only were made in each of these cases. Duplicate Determinations of Fusain in Coal Samples SAMPLE SAMPLE Per cent Per cent (a) (b) (a) (b)
Advantage of Method
An important advantage of the method is that the completeness of separation of coal and fusain electrostatically can be checked veiy closely by the microscope. One can actually see the separation in progress and adjust conditionsfield strength, shaking, etc.-so that good results may be obtained with samples of varying character. It should be observed that small quantities of fusain (say less than 4 per cent) are not readily detected in coal by the microscope. On the other hand, very small amounts of coal in fusain are easily seen. Literature Cited (1) Am SOC.Testing Materials, 1927, Pt. 11, p. 535. (2) Beet, Fuel, 7, 487 (1928). ( 3 ) Cooper, Proc. R o y Soc. Edznburgh, 44, 88 (1924). (4) Hickling, Trans I n s f . Mtnrng Eng. (London), 53, 137 (1916). ( 5 ) Lessing, J . SOL. Chem. I n d , 44, 2771‘ (1925). (6) Sinnatt, Trans Inst. Mznzng En& (London), 62, 156 (1921). (7) Sinnatt, Stern, and Bayley, C o d Age, 18, 384 (1920).
Determination of Sulfur in Petroleum Oils’ R. C. Griffin ARTHURD. LITTLE,I N C . , CAMBRIDGE, MASS.
T IS well known that under some conditions and with some types of organic sulfur compounds, such as mercaptans, both the bomb and lamp methods for determining total sulfur in petroleum products give low results. An investigation of both procedures has been made in this laboratory and methods devised for overcoming some of the difficulties encountered. Further work on this subject is contemplated, but the results available are presented now with the thought that they will be of interest. Unless otherwise noted, the standard lamp method (A. S. T. hf. Method D90-26T, Sulfur in Kaphthas and Illuminating Oils) and the standard bomb method (A. S. T. 11.Method D129-27, Sulfur in Petroleum Oils Heavier than Illuminating Oil) have been used throughout. An Emerson monel metal bomb with gold linings was used. It was found advisable to remove the lower lining after each determination, as there is a tendency for some of the liquids t o creep in back of the lining.
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Experimental
EXPERIMEKT I-Five determinations made in the bomb on pure elementary sulfur without any organic solvent present showed an average recovery of sulfur of 87.45 per cent with a minimum of 86.95 per cent and a maximum of 91.80 per cent. In the latter case 3 per cent of the sulfur was found between the bomb lining and the bomb itself and may have been an accumulation from previous determinations. 1 Received April 16, 1929. Presented before the Division of Petroleum Chemistry a t the 77th Meeting of the American Chemical Society,‘ Columbus, Ohio, April 29 to May 3, 1929.
EXPERIMENT 11-Varying amounts of elementary sulfur were dissolved in c. P. benzene (S = 0.057 per cent) and oleum-treated gas oil (S = 0.099 per cent) was added until the calculated sulfur contents of the mixtures were 0.40, 1.18, and 1.74 per cent, respectively. These were tested in the bomb by chemist “R,” with the following recoveries of sulfur-65, 67, and 57 per cent. EXPERIMENT 111-A similar series was made up of the same materials by chemist “P” and the bomb determinations carried out by other analysts, with the following results: SAYPLP:6
SAMPLE 7
SAMPLC 8
0.433
Average 0 : 285 0.512 0 : 78s Percentage of calculated sulfur recovered 71 56 62 a Potassium iodide solution was used after the combustion instead of bromine water under the assumption t h a t persulfates might be formed and these reduced to sulfates b y the potassium iodide. Although iodine was liberated and a higher result obtained, we are inclined to believe t h a t this result is abnormal.
EXPERIhlENT IV-cetyl sulfide made in this laboratory and which, from the melting point and acetyI value, was considered t o be very nearly c. P., was dissolved in c. P. benzene. Bomb determinations showed a recovery of 50 and 77 per cent sulfur. EXPERIMENT V-A comparison of the two methods was made on gas oils, with the following results:
