Effect of Atmosphere on Desulfurization of Coal during Carbonization T. A. MANGELSDORF AKD F. P. BROUGHTON Department of Fuel and Gas Engineering, Massachusetts Institute of Technology, Cambridge, Mass.
A
R E C E N T paper b y The results of an investigation on the desulc h l o r i d e s o l u t i o n to remove furization of coal during carbonization are any hydrogen sulfide which it Snow'rePorts the results of an extended investigamight contain. presented and compared with those recently tion of the effect of various atThe coal used in these experimospheres on the elimination of reported by Snow. Since the eXPerimental merits was r u n - o f - m i n e from sulfur from coal during carbonimethods of the two invesligations were similar Indiana Seam NO. 5 and consation. During the early part and the results differ considerably, it is contained 3.9 per cent sulfur. After eluded lhat the type of coal treated is an imb e i n g c r u s h e d to pass an 8of 1928 Some work on the. same problem was carried out in this mesh screen, it was treated on a portant factor in determining the most effective laboratory. The r e s u l t s were Wilfley table to removeas desulfurizing agent, (2nd the extent of desulfurizanot Dublished a t that time bemuch pyrites as possible. The tion. caus;! it was intended to study sample reserved for the subsethe problem further. This has quent treatment amounted to 50 not been possible, however, and although the data are admit- per cent of that passed over the table and contained 2.26 per tedly incomplete, it seems best to present them a t this time to cent sulfur. It fused a t a temperature of about 475" C. and supplement the work of Snow and to point out the fact that had the following proximate analysis: the various atmospheres may have decidedly different effects % % on different coals. Moisture 2.01 Fixed oarbon 50.67 Volatile oombustible matter
EXPERIMENTAL PROCEDURE
42.00
Ash
5.32
Portions of the coal containing 2.26 per cent sulfur were The experimental work on this problem was carried out by charged into the electric furnace and heated a t 600" C. R. A. Jack and G. A. K. Stachelhaus, using a method similar The size of the charge varied from 20 to 30 grams, and the heating rate was such that the final temperature was reached to that reported by Snow. The desulfurization was accomplished by heating the coal in just one hour after heating began. The first runs were a t 600" C. in a stream of gas, its progress being followed by made to determine the effect of heat alone, when the only analyzing for the amount of hydrogen sulfide carried out in gases in contact with the coal, other than any residual air in the tube, were those resulting from its own decomposition. the gas. Heating was done in a These tests were followed with runs in which various gases were nichrome-wound v e r tic a 1- passed through the coal during the entire heating period. The tube electric furnace. The gas flow was kept constant a t 3 cubic feet (0.08 cubic meter) tube was of g l a z e d porce- per hour. The effect of five gases-carbon monoxide, hydrogen, blue lain, 0.75 inch (0.9 cm.) in water gas, illuminating gas, and steam-was investigated. diameter and 20 inches (50.8 em.) long. The charge was The progress of the sulfur elimination during the heating supported midway between period, as indicated by the hydrogen sulfide content of the gas the ends by a metallic screen stream, is shown in Figure 1. The following is a summary of which had been forced into the results obtained giving as maximum sulfur elimination position. An asbestos plug the values obtained after 7 hours of heating; the elimination COAL TEMPERATURE W C . ORICINAL SULFUR a t the bottom end contained after several hours was exceedingly slow: the delivery tube for the gas S ELIMINATEDLoss I N WBIGFIT R ~ T I O % S TO GAS USED A 0 HzS O F COAL TOTAL Loss introduced into the furnace, % % and through a similar plug a t Heat alone 33.5 28.5 1.18 the top a protected thermo- Carbon monoxide 3% 5 32.0 1.20 Illuminating 42.5 29.0 1.48 couple was i n s e r t e d to the Steam 45.0 40.4 1.13 ' 0 2 4 6 8 Hydrogen 5 2 . 5 3 4 . 2 1 .56 center of the charge; a glass Blue water TIME-HOURS 66.0 32.5 2.09 tube carried the gases from FIGURE1. PROGRESSOF S U L F U RE L I M I N A T I O Nthe furnace. The values reported are for single runs with the exception DURING HEATING PERIOD The furnace gases passed of those for heat alone and for illuminating gas. For these through a traD to remove tar two cases the reported values are averages of two runs made and then bubbled through a train of wish botiles containing 2 for check purposes. It was indicated by these check runs per cent sodium hydroxide solution to absorb the hydrogen that the curves were reproducible within a 5 per cent range sulfide. Two trains were available so that the gas could be of sulfur removal. sent to one by the turn of a three-way cock, while the other could be removed for titration with standard iodine and DISCUSSION OF RESULTS renewal of the solution. When illuminating gas was used as a The results show that all the gases were effective in removdesulfurizing agent, it was first passed through cadmium ing sulfur as hydrogen sulfide. The exact extent of desulfuri1 IND.ENQ. CHEM.,24, 903 (1932) zation was greater than that indicated, owing to some elimi1136
October, 1932
INDUSTRIAL AND ENGINEERING CHEMISTRY
nated sulfur which went into tar and liquors, and to organic sulfur in the gas. Sulfur balances reported in the literature by others indicate that the sulfur appearing in these two products is usually less than 10 per cent of the total. Hence it is probable that the total elimination was not over 10 per cent greater than that appearing as hydrogen sulfide. Although the sulfur in the tar and as organic sulfur undoubtedly varied somewhat with the various atmospheres, it is doubtful whether these variations were sufficient to alter greatly the conclusions based on the hydrogen sulfide in the gas regarding the efficiency of the several gases as desulfurizing agents. The results of this investigation and those reported by Snow are not entirely comparable since the experimental procedures differed in several respects. The coal used by Snow was of a smaller size and the rate of gas flow was less than in the present work. These two differences should counterbalance t o some extent. Snow reports the total sulfur elimination after 4 hours of treatment based on the sulfur remaining in the coke; this investigation shows the progressive elimination over the entire heating period based on the hydrogen sulfide in the gas. Although Snow states that sulfur elimination was substantially complete in his 4-hour heating period,
1137
in this investigation sulfur continued to come off, in some cases even after 7 hours of treatment. However, some general comparisons of the results may be made. The most striking difference is in the effect of water gas. Snow found the percentage sulfur elimination by a mixture of carbon monoxide and hydrogen to be intermediate between that produced by the two gases used separately. The present work shows a greater elimination with the mixture than with either of the separate constituents. Since the differences in both investigations are greater than the possibility of experimental error, it must be concluded that the different gases react differently with different coals. Snow’s results show a generally higher percentage elimination. This is due partly to the sulfur in the tar and the organic sulfur which are not included in the present results, and it may be to some extent a result of the smaller size coal which he used; however, it is probably due in part to the different coals used. It is evident from the results of these two investigations that conclusions made from work on one coal cannot be applied with safety to a coal of different chemical composition. RECEIVED May 3, 1932.
Preferential Wetting of Solids by Liquids NOAHS. DAVIS,JR., Roessler and Hasslacher Chemical Co., Niagara Falls, N. Y., Vacuum Oil Co., Inc., Paulsboro, N. J.
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HEX two immiscible liquids are brought into contact with a solid, it usually happens that one
of the liquids wets the surface of the solid to the exclusion of the other liquid. This phenomenon of preferential wetting is encountered in many industrial processesfor example, in the flotation of ores, in the Trent process of cleaning coal, in the making of white lead by the Dutch process, etc. Preferential wetting determines to a considerable extent the behavior of solid particles a t the interface of two immiscible liquids, and the ability of certain solids to emulsify pairs of liquids. There has been a considerable amount of experimental work and a number of theoretical studies on interfacial surface tensions, spreading of liquids, behavior of solid particles a t liquid interfaces, and other phases of the phenomenon of preferential wetting, etc., carried out by Biiicke (d), Nuttall (8), Haskins (G), Des Courdes (cited by lihumbler, I O ) , Hofman (6), Stark ( I I ) , Rhumbler ( I O ) , Rheinders (Q), Finkle, Draper, and Hillebrand (S), Freundlich ( d ) , McMillen ( 7 ) , and others. Bartell and his associates (1) have made many measurements of what is termed the “adhesion tension” between a liquid and a solid, a quantity which is involved directly in the phenomenon of preferential wetting, as will be shown. QU.4LITATIVE STUDY O F PREFERENTIAL WETTING The displacement of one liquid by another from the surfaces of a powdered solid may be observed readily by the following procedure: Work 20 rams of the solid and either of the liquids together to form a s o 8 putty; add the second liquid a few drops at a time, working it into the putty after each addition. If the solid R i preferentially wet by the first liquid, it will be found that very little of the second liquid can be worked into the putty. If, however, the solid is preferentially wet by the second liquid, successive additions are readily worked into the putty. Presently the putty becomes somewhat crumbly and has about the same consistency as cottage cheese. Further additions of the second liquid then liberate relatively large amounts of the first
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HARRYA. CURTIS,
liquid, until eventually practically all of the first liquid has been removed from the putty. Lesser quantities of the solid and of the liquids may be used if necessary, and, with a little experience, single drops of the liquids and corresponding1 small amounts of the solid will suffice for observations whici will determine which of two liquids preferentially wets a given solid. The displacement of one liquid by another was observed in the manner indicated for twenty-five pairs of liquids, using in each case water as one of the liquids, and trying each pair of liquids on fifteen different solids. The results are given in Table I. QUANTITATIVE ASPECTSOF PREFERENTIAL WETTING I n the ordinary capillary tube method of determining surface tension of a liquid, y=---
zr COS e h5g
(1)
wherer
radius of tube surface tension of liquid against air density of liquid rise of liquid in tube g = gravity constant 8 = angle of contact between tube and liquid = y = s = h =
It is obvious that. if a liquid for which the liquid-solid angle of contact is zero be used, the radius of the capillary tube may be determined from known or measured values of y, h, s, and 8. Having thus found r, the angle of contact for a second liquid may be determined from known values of r and g, and the known or measured values of y, h, and s for the second liquid. It is evident, then, that the angle of contact between the wall of a tube of any solid and the surface of any liquid may be determined, provided there may be found one liquid for which the liquid-solid angle of contact is zero. If the radius of the capillary tube can be determined by direct measurement, the necessity of finding a liquid of zero angle of liquidsolid contact is, of course, avoided.
